Posts by Jai Ganesh

Jai Ganesh · Science HQ

Covalent Bond

Gist

A covalent bond is a chemical bond where atoms share a pair of electrons to achieve a more stable configuration. This sharing creates an attractive force between the nuclei of the atoms and the shared electrons, holding the atoms together in a molecule. Covalent bonds typically form between nonmetals, and the result is either a small molecule with low melting and boiling points or a giant covalent structure with high melting and boiling points.

A covalent bond is a chemical bond formed when two atoms share a pair of electrons to achieve stability. This sharing allows atoms to fill their outer electron shells, and the bond is the force of attraction between the nuclei of both atoms and the shared electrons. Covalent bonds typically form between two nonmetal atoms.

Summary

A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full valence shell, corresponding to a stable electronic configuration. In organic chemistry, covalent bonding is much more common than ionic bonding.

Covalent bonding also includes many kinds of interactions, including σ-bonding, π-bonding, metal-to-metal bonding, agostic interactions, bent bonds, three-center two-electron bonds and three-center four-electron bonds. The term "covalence" was introduced by Irving Langmuir in 1919, with Nevil Sidgwick using "co-valent link" in the 1920s. Merriam-Webster dates the specific phrase covalent bond to 1939, recognizing its first known use. The prefix co- (jointly, partnered) indicates that "co-valent" bonds involve shared "valence", as detailed in valence bond theory.

In the molecule H2, the hydrogen atoms share the two electrons via covalent bonding. Covalency is greatest between atoms that have similar electronegativities, regardless of whether the elements are the same as each other. Covalent bonding that entails the sharing of electrons over more than two atoms is said to be delocalized.

Details

A covalent bond, in chemistry, is the interatomic linkage that results from the sharing of an electron pair between two atoms. The binding arises from the electrostatic attraction of their nuclei for the same electrons. A covalent bond forms when the bonded atoms have a lower total energy than that of widely separated atoms.

A brief treatment of covalent bonds follows. For full treatment, see chemical bonding: Covalent bonds.

Molecules that have covalent linkages include the inorganic substances hydrogen, nitrogen, chlorine, water, and ammonia (H2, N2, Cl2, H2O, NH3) together with all organic compounds.

A single line indicates a bond between two atoms (i.e., involving one electron pair), double lines (=) indicate a double bond between two atoms (i.e., involving two electron pairs), and triple lines (≡) represent a triple bond, as found, for example, in carbon monoxide (C≡O). Single bonds consist of one sigma (σ) bond, double bonds have one σ and one pi (π) bond, and triple bonds have one σ and two π bonds.

Covalent bonds are directional, meaning that atoms so bonded prefer specific orientations relative to one another; this in turn gives molecules definite shapes, as in the angular (bent) structure of the H2O molecule. Covalent bonds between identical atoms (as in H2) are nonpolar—i.e., electrically uniform—while those between unlike atoms are polar—i.e., one atom is slightly negatively charged and the other is slightly positively charged. This partial ionic character of covalent bonds increases with the difference in the electronegativities of the two atoms. See also ionic bond.

When none of the elements in a compound is a metal, no atoms in the compound have an ionization energy low enough for electron loss to be likely. In such a case, covalence prevails. As a general rule, covalent bonds are formed between elements lying toward the right in the periodic table (i.e., the nonmetals). Molecules of identical atoms, such as H2 and buckminsterfullerene (C60), are also held together by covalent bonds.

Lewis formulation of a covalent bond

The idea that two electrons can be shared between two atoms and serve as the link between them was first introduced in 1916 by the American chemist G.N. Lewis, who described the formation of such bonds as resulting from the tendencies of certain atoms to combine with one another in order for both to have the electronic structure of a corresponding noble-gas atom.

In Lewis terms a covalent bond is a shared electron pair.

In a Lewis structure of a covalent compound, the shared electron pair between the hydrogen and chlorine ions is represented by a line. The electron pair is called a bonding pair; the three other pairs of electrons on the chlorine atom are called lone pairs and play no direct role in holding the two atoms together.

Each atom in the hydrogen chloride molecule attains a closed-shell octet of electrons by sharing and hence achieves a maximum lowering of energy. In general, an incomplete shell means that some attracting power of a nucleus may be wasted, and adding electrons beyond a closed shell would entail the energetic disadvantage of beginning the next shell of the atom concerned. Lewis’s octet rule is again applicable and is seen to represent the extreme means of achieving lower energy rather than being a goal in itself.

A covalent bond forms if the bonded atoms have a lower total energy than the widely separated atoms. The simplest interpretation of the decrease in energy that occurs when electrons are shared is that both electrons lie between two attracting centres (the nuclei of the two atoms linked by the bond) and hence lie lower in energy than when they experience the attraction of a single centre.

Lewis structures of more complex molecules can be constructed quite simply by extending the process that has been described for hydrogen chloride.

In some older formulations of Lewis structures, a distinction was made between bonds formed by electrons that have been supplied by both atoms (as in H―Cl, where one shared electron can be regarded as supplied by the hydrogen atom and the other by the chlorine atom) and covalent bonds formed when both electrons can be regarded as supplied by one atom, as in the formation of OH− from O2− and H+. Such a bond was called a coordinate covalent bond or a dative bond and symbolized O → H−. However, the difficulties encountered in the attempt to keep track of the origin of bonding electrons and the suggestion that a coordinate covalent bond differs somehow from a covalent bond (it does not) have led to this usage falling into disfavour.

Resonance

The blending together of these structures is actually a quantum mechanical phenomenon called resonance. At this stage, resonance can be regarded as a blending process that spreads double-bond character evenly over the atoms that participate in it. In ozone, for instance, each oxygen-oxygen bond is rendered equivalent by resonance, and each one has a mixture of single-bond and double-bond character (as indicated by its length and strength).

Hypervalence

Lewis structures and the octet rule jointly offer a succinct indication of the type of bonding that occurs in molecules and show the pattern of single and multiple bonds between the atoms. There are many compounds, however, that do not conform to the octet rule. The most common exceptions to the octet rule are the so-called hypervalent compounds. These are species in which there are more atoms attached to a central atom than can be accommodated by an octet of electrons.

In Lewis terms, hypervalence requires the expansion of the octet to 10, 12, and even in some cases 16 electrons. Hypervalent compounds are very common and in general are no less stable than compounds that conform to the octet rule.

The existence of hypervalent compounds would appear to deal a severe blow to the validity of the octet rule and Lewis’s approach to covalent bonding if the expansion of the octet could not be rationalized or its occurrence predicted. Fortunately, it can be rationalized, and the occurrence of hypervalence can be anticipated. In simple terms, experience has shown that hypervalence is rare in periods 1 and 2 of the periodic table (through neon) but is common in and after period 3. Thus, the octet rule can be used with confidence for carbon, nitrogen, oxygen, and fluorine, but hypervalence must be anticipated thereafter. The conventional explanation of this distinction takes note of the fact that in period-3 elements the valence shell has n = 3, and this is the first shell in which d orbitals are available. (These orbitals are occupied after the 4s orbitals have been filled and account for the occurrence of the transition metals in period 4.) It is therefore argued that atoms of this and subsequent periods can use the empty d orbitals to accommodate electrons beyond an octet and hence permit the formation of hypervalent species.

In chemistry, however, it is important not to allow mere correlations to masquerade as explanations. Although it is true that d orbitals are energetically accessible in elements that display hypervalence, it does not follow that they are responsible for it. Indeed, quantum mechanical theories of the chemical bond do not need to invoke d-orbital involvement. These theories suggest that hypervalence is probably no more than a consequence of the greater radii of the atoms of period-3 elements compared with those of period 2, with the result that a central atom can pack more atoms around itself. Thus, hypervalence is more a steric (geometric) problem than an outcome of d-orbital availability.

Additional Information:

Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability. Nonmetals will readily form covalent bonds with other nonmetals in order to obtain stability, and can form anywhere between one to three covalent bonds with other nonmetals depending on how many valence electrons they posses. Although it is said that atoms share electrons when they form covalent bonds, they do not usually share the electrons equally.

Introduction

Only when two atoms of the same element form a covalent bond are the shared electrons actually shared equally between the atoms. When atoms of different elements share electrons through covalent bonding, the electron will be drawn more toward the atom with the higher electronegativity resulting in a polar covalent bond. When compared to ionic compounds, covalent compounds usually have a lower melting and boiling point, and have less of a tendency to dissolve in water. Covalent compounds can be in a gas, liquid, or solid state and do not conduct electricity or heat well. The types of covalent bonds can be distinguished by looking at the Lewis dot structure of the molecule. For each molecule, there are different names for pairs of electrons, depending if it is shared or not. A pair of electrons that is shared between two atoms is called a bond pair. A pair of electrons that is not shared between two atoms is called a lone pair.

Octet Rule

The Octet Rule requires all atoms in a molecule to have 8 valence electrons--either by sharing, losing or gaining electrons--to become stable. For Covalent bonds, atoms tend to share their electrons with each other to satisfy the Octet Rule. It requires 8 electrons because that is the amount of electrons needed to fill a s- and p- orbital (electron configuration); also known as a noble gas configuration. Each atom wants to become as stable as the noble gases that have their outer valence shell filled because noble gases have a charge of 0. Although it is important to remember the "magic number", 8, note that there are many Octet rule exceptions.

Single Bonds

A single bond is when two electrons--one pair of electrons--are shared between two atoms. It is depicted by a single line between the two atoms. Although this form of bond is weaker and has a smaller density than a double bond and a triple bond, it is the most stable because it has a lower level of reactivity meaning less vulnerability in losing electrons to atoms that want to steal electrons.

Double Bonds

A Double bond is when two atoms share two pairs of electrons with each other. It is depicted by two horizontal lines between two atoms in a molecule. This type of bond is much stronger than a single bond, but less stable; this is due to its greater amount of reactivity compared to a single bond.

Triple Bond

A Triple bond is when three pairs of electrons are shared between two atoms in a molecule. It is the least stable out of the three general types of covalent bonds. It is very vulnerable to electron thieves!

Jai Ganesh · Dark Discussions at Cafe Infinity

2396) François Jacob

Gist:

Work

The biochemical processes that take place within an organism's cells are controlled by the genes found inside DNA molecules. François Jacob and Jacques Monod proved how the genetic information is converted during the formation of proteins by means of a messenger, which proved to the substance we now know as RNA. Different cells work in different ways at different times, however. This too is regulated by genes. In the early 1960s Monod and Jacob mapped the intricate processes that determine how genes are expressed or suppressed in a self-regulating process.

Summary

François Jacob (born June 17, 1920, Nancy, France—died April 19, 2013, Paris) was a French biologist who, together with André Lwoff and Jacques Monod, was awarded the 1965 Nobel Prize for Physiology or Medicine for discoveries concerning regulatory activities in bacteria.

Jacob received an M.D. degree (1947) and a doctorate in science (1954) from the University of Paris. Most of the work of Jacob, Lwoff, and Monod was carried out at the Pasteur Institute (Paris), which Jacob joined in 1950 as a research assistant. In 1960 he became head of the department of cellular genetics at the institute, and from 1965 he was also professor of cellular genetics at the Collège de France. In 1977 he became a member of the Academy of Sciences.

With a coworker at the Pasteur Institute, Jacob discovered that the genes of a bacterium are arranged linearly in a ring and that the ring can be broken at almost any point. In 1958 Monod and Jacob began to collaborate on studies of the regulation of bacterial enzyme synthesis. One of their first major contributions was the discovery of regulator genes (operons), so called because they control the activities of structural genes. The latter, in turn, not only transmit hereditary characteristics but also serve in the production of enzymes, other proteins, and ribonucleic acid (RNA).

Jacob and Monod also proposed the existence of an RNA messenger, a partial copy of the gene substance deoxyribonucleic acid (DNA), that carries genetic information to other parts of the cell. They also found that in a normal cell the balance between regulator and structural genes enables the cell to adapt to varying conditions. An interruption in this balance, however, can stimulate the production of new enzymes that can prove either beneficial or destructive to the cell. In addition to his research activities, Jacob wrote important books on the history and philosophy of the life sciences, including La Logique du vivant: une histoire de l’hérédité (1970; The Logic of Life: A History of Heredity).

Details

François Jacob (17 June 1920 – 19 April 2013) was a French biologist who, together with Jacques Monod, originated the idea that control of enzyme levels in all cells occurs through regulation of transcription. He shared the 1965 Nobel Prize in Medicine with Jacques Monod and André Lwoff.

Early years

Jacob was born the only child of Simon, a merchant, and Thérèse (Franck) Jacob, in Nancy, France. An inquisitive child, he learned to read at a young age. Albert Franck, Jacob's maternal grandfather, a four-star general, was Jacob's childhood role model. At seven he entered the Lycée Carnot, where he was schooled for the next ten years; in his autobiography, he describes his impression of it: "a cage". He was antagonized by rightist youth at the Lycée Carnot around 1934. He describes his father as a "conformist in religion", while his mother and other family members important in his childhood were secular Jews; shortly after his bar mitzvah, he became an atheist.

Though interested (and talented) in physics and mathematics, Jacob was horrified at the prospect of spending two additional years in "an even more draconian regime" to prepare for higher study at the Polytechnique. Instead, after observing a surgical operation that cemented his "slight interest" in medicine, he entered medical school.

During the German occupation of France—and on the heels of his mother's death—Jacob left France for Great Britain to join the war effort. Jacob, who had only completed his second year of medical studies, joined the medical company of the French 2nd Armored Division in 1940. He was injured in a German air attack in 1944 and returned to now-liberated Paris on 1 August 1944. For his wartime service, he was awarded France's WWII highest decoration for valor, the Cross of Liberation, as well as Légion d'honneur and croix de guerre.

After his recovery, Jacob returned to medical school and began researching tyrothricin and learning the methods of bacteriology in the process. He completed a thesis he described as "replicating American work" on the effectiveness of the antibiotic against local infections, and became a medical doctor in 1947. Though attracted to research as a career, he was discouraged by his own perceived ignorance after attending a microbiology congress that summer. Instead, he took a position at the Cabanel Center, where he had done his thesis research; his new work entailed the manufacture of an antibiotic, tyrothricin. Later, the center was contracted to convert gunpowder factories for penicillin production (though this proved impossible).

Also in this period, he met and began courting his future wife, Lise Bloch. Jacob remarried in 1999 to Geneviève Barrier.

Research

In 1961 Jacob and Monod explored the idea that the control of enzyme expression levels in cells is a result of regulation of transcription of DNA sequences. Their experiments and ideas gave impetus to the emerging field of molecular developmental biology, and of transcriptional regulation in particular.

For many years it had been known that bacterial and other cells could respond to external conditions by regulating levels of their key metabolic enzymes, and/or the activity of these enzymes. For instance, if a bacterium finds itself in a broth containing lactose, rather than the simpler sugar glucose, it must adapt itself to the need to 1) import lactose, 2) cleave lactose to its constituents glucose and galactose, and 3) convert the galactose to glucose. It was known that cells ramp up their production of the enzymes that do these steps when exposed to lactose, rather than wastefully producing these enzymes all the time. Studies of enzyme activity control were progressing through theories of the (allosteric) action of small molecules on the enzyme molecule itself (switching it on or off), but the method of controlling the enzyme production was not well understood at the time.

With the earlier determination of the structure and central importance of DNA, it became clear that all proteins were being produced in some way from its genetic code, and that this step might form a key control point. Jacob and Monod made key experimental and theoretical discoveries that demonstrated that in the case of the lactose system outlined above (in the bacterium E. coli), there are specific proteins that are devoted to repressing the transcription of the DNA to its product (RNA, which in turn is decoded into protein).

This repressor (the lac repressor) is made in all cells, binding directly to DNA at the genes it controls, and physically preventing the transcription apparatus from gaining access to the DNA. In the presence of lactose, some of the lactose is converted to allolactose, which binds to the repressor making it no longer able to bind to DNA, and the transcriptional repression is lifted. In this way, a robust feedback loop is constructed that allows the set of lactose-digesting protein products to be made only when they are needed.

Jacob and Monod extended this repressor model to all genes in all organisms in their initial exuberance. The regulation of gene activity has developed into a very large sub-discipline of molecular biology, and in truth exhibits enormous variety in mechanism and many levels of complexity. Current researchers find regulatory events at every conceivable level of the processes that express genetic information. In the relatively simple genome of baker's yeast, (Saccharomyces cerevisiae), 405 of its 6,419 protein-encoding genes are directly involved in transcriptional control, compared to 1,938 that are enzymes.

Jai Ganesh · This is Cool

2448) Invertor

Gist

An inverter is an electronic device that converts direct current (DC) to alternating current (AC). This conversion is necessary to power standard household appliances and electronics, which run on AC power, from DC sources like solar panels or car batteries. Inverters are essential for applications like backup power systems, off-grid solar setups, and electric vehicles.

An inverter's primary function is to convert direct current (DC) to alternating current (AC). This conversion is crucial for running standard household appliances, which require AC power, from DC sources like car batteries, solar panels, or an inverter's own battery during a power outage. Inverters are essential for making DC power usable for AC systems.

Details

A power inverter, inverter, or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.

The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.

A power inverter can be entirely electronic or a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry.

Static inverters do not use moving parts in the conversion process.

Power inverters are primarily used in electrical power applications where high currents and voltages are present; circuits that perform the same function for electronic signals, which usually have very low currents and voltages, are called oscillators.

Input and output:

Input voltage

A typical power inverter device or circuit requires a stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. Examples include:

* 12 V DC, for smaller consumer and commercial inverters that typically run from a rechargeable 12 V lead acid battery or automotive electrical outlet.
* 24, 36, and 48 V DC, which are common standards for home energy systems.
* 200 to 400 V DC, when power is from photovoltaic solar panels.
* 300 to 450 V DC, when power is from electric vehicle battery packs in vehicle-to-grid systems.
* Hundreds of thousands of volts, where the inverter is part of a high-voltage direct current power transmission system.

Output waveform

An inverter may produce a square wave, sine wave, modified sine wave, pulsed sine wave, or near-sine pulse-width modulated wave (PWM) depending on circuit design. Common types of inverters produce square waves or quasi-square waves. One measure of the purity of a sine wave is the total harmonic distortion (THD). Technical standards for commercial power distribution grids require less than 3% THD in the wave shape at the customer's point of connection. IEEE Standard 519 recommends less than 5% THD for systems connecting to a power grid.

There are two basic designs for producing household plug-in voltage from a lower-voltage DC source, the first of which uses a switching boost converter to produce a higher-voltage DC and then converts to AC. The second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage.

Square wave

A 50% duty cycle square wave is one of the simplest waveforms an inverter design can produce, but adds ~48.3% THD to its fundamental sine wave. Thus, a square wave output can produce undesired "humming" noises when connected to audio equipment and is better suited to low-sensitivity applications such as lighting and heating.

Sine wave

A power inverter device that produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter. To more clearly distinguish the inverters with outputs of much less distortion than the modified sine wave (three-step) inverter designs, the manufacturers often use the phrase pure sine wave inverter. Almost all consumer grade inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave output at all, just a less choppy output than the square wave (two-step) and modified sine wave (three-step) inverters. However, this is not critical for most electronics as they deal with the output quite well.

Where power inverter devices substitute for standard line power, a sine wave output is desirable because many electrical products are engineered to work best with a sine wave AC power source. The standard electric utility provides a sine wave, typically with minor imperfections but sometimes with significant distortion.

Sine wave inverters with more than three steps in the wave output are more complex and have significantly higher cost than a modified sine wave, with only three steps, or square wave (one step) types of the same power handling. Switched-mode power supply (SMPS) devices, such as personal computers or DVD players, function on modified sine wave power. AC motors directly operated on non-sinusoidal power may produce extra heat, may have different speed-torque characteristics, or may produce more audible noise than when running on sinusoidal power.

Modified sine wave

The modified sine wave is the sum of two square waves, one of which is delayed one-quarter of the period with respect to the other. The result is a repeated voltage step sequence of zero, peak positive, zero, peak negative, and again zero. The resultant voltage waveform better approximates the shape of a sinusoidal voltage waveform than a single square wave. Most inexpensive consumer power inverters produce a modified sine wave rather than a pure sine wave.

If the waveform is chosen to have its peak voltage values for half of the cycle time, the peak voltage to RMS voltage ratio is the same as for a sine wave. The DC bus voltage may be actively regulated, or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variations. By changing the pulse width, the harmonic spectrum can be changed. The lowest THD for a three-step modified sine wave is 30% when the pulses are at 130 degrees width of each electrical cycle. This is slightly lower than for a square wave.

The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called pulse-width modulation (PWM). The generated gate pulses are given to each switch in accordance with the developed pattern to obtain the desired output. The harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. It can be shown that the minimum distortion of a three-level waveform is reached when the pulses extend over 130 degrees of the waveform, but the resulting voltage will still have about 30% THD, higher than commercial standards for grid-connected power sources. When operating induction motors, voltage harmonics are usually not of concern; however, harmonic distortion in the current waveform introduces additional heating and can produce pulsating torques.

Numerous items of electric equipment will operate quite well on modified sine wave power inverter devices, especially loads that are resistive in nature such as traditional incandescent light bulbs. Items with a switched-mode power supply operate almost entirely without problems, but if the item has a mains transformer, this can overheat depending on how marginally it is rated.

However, the load may operate less efficiently owing to the harmonics associated with a modified sine wave and produce a humming noise during operation. This also affects the efficiency of the system as a whole, since the manufacturer's nominal conversion efficiency does not account for harmonics. Therefore, pure sine wave inverters may provide significantly higher efficiency than modified sine wave inverters.

Most AC motors will run on MSW inverters with an efficiency reduction of about 20% owing to the harmonic content. However, they may be quite noisy. A series LC filter tuned to the fundamental frequency may help.

A common modified sine wave inverter topology found in consumer power inverters is as follows: An onboard microcontroller rapidly switches on and off power MOSFETs at high frequency like ~50 kHz. The MOSFETs directly pull from a low voltage DC source (such as a battery). This signal then goes through step-up transformers (generally many smaller transformers are placed in parallel to reduce the overall size of the inverter) to produce a higher voltage signal. The output of the step-up transformers then gets filtered by capacitors to produce a high voltage DC supply. Finally, this DC supply is pulsed with additional power MOSFETs by the microcontroller to produce the final modified sine wave signal.

More complex inverters use more than two voltages to form a multiple-stepped approximation to a sine wave. These can further reduce voltage and current harmonics and THD compared to an inverter using only alternating positive and negative pulses; but such inverters require additional switching components, increasing cost.

Near sine wave PWM

An example of PWM voltage modulated as a series of pulses ■. Low pass filtering with series inductors and shunt capacitors is required to suppress the switching frequency. Once filtered, this results in a near sinusoidal waveform ■. The filtering components are smaller and more convenient than those required to smooth a modified sine wave to an equivalent harmonic purity.
Some inverters use PWM to create a waveform that can be low pass filtered to re-create the sine wave. These only require one DC supply, in the manner of the MSN designs, but the switching takes place at a far faster rate, typically many kHz, so that the varying width of the pulses can be smoothed to create the sine wave. If a microprocessor is used to generate the switching timing, the harmonic content and efficiency can be closely controlled.

Output frequency

The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz. The exception is in designs for motor driving, where a variable frequency results in a variable speed control.

Also, if the output of the device or circuit is to be further conditioned (for example stepped up) then the frequency may be much higher for good transformer efficiency.

Output voltage

The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 120 or 240 VAC at the distribution level, even when there are changes in the load that the inverter is driving. This allows the inverter to power numerous devices designed for standard line power.

Some inverters also allow selectable or continuously variable output voltages.

Output power

A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 watts.

Not all inverter applications are solely or primarily concerned with power delivery; in some cases the frequency and or waveform properties are used by the follow-on circuit or device.

Additional Information:

What is an inverter?

An inverter is an electronic device that converts direct current (DC) into alternating current (AC). It is commonly used to power household appliances and electronic devices that require AC power when only DC power sources are available, such as in solar power systems or car batteries. Inverters are essential for ensuring compatibility and efficient operation of a wide range of electrical equipment in different settings.

How does an inverter work?

An inverter converts DC power into AC power using electronic circuits. It typically involves switching and modulation techniques to create an AC waveform from a DC input. These circuits can include transistors, transformers, and control systems to manage the conversion process efficiently.

What are the different types of inverters?

There are several types of inverters, including pure sine wave inverters, modified sine wave inverters, and square wave inverters. Pure sine wave inverters produce high-quality AC power, suitable for sensitive electronics. Modified sine wave inverters are more cost-effective and suitable for less sensitive devices, while square wave inverters are the least expensive but may not work with all devices.

What is the difference between an inverter and a generator?

An inverter and a generator are both used to provide power, but they operate in fundamentally different ways and serve distinct purposes. An inverter converts direct current (DC) from sources like batteries or solar panels into alternating current (AC), which is used to power household appliances and electronic devices. It relies on stored or generated DC power and is often used in renewable energy systems or as a backup power solution in conjunction with batteries. In contrast, a generator produces AC power directly by converting mechanical energy into electrical energy through the combustion of fuels such as gasoline, diesel, or natural gas. Generators are typically used for providing power during outages, in remote locations without access to the grid, or for powering heavy-duty equipment. While inverters are quiet, environmentally friendly, and efficient for small to medium loads, generators can provide higher power output and are suitable for more demanding applications but can be noisy and produce emissions.

Can an inverter be used with solar panels?

Yes, inverters are commonly used in solar power systems to convert the DC electricity generated by solar panels into AC power for use in homes and businesses. This conversion is crucial for integrating solar energy into the existing electrical grid and for powering standard household appliances.

What is the efficiency of an inverter?

The efficiency of an inverter varies depending on its design and quality. High-quality inverters can have efficiencies of 90% or higher, meaning they lose only a small percentage of energy during the conversion process. Efficiency is a critical factor, as it affects the overall performance and energy savings of the system.

How do I choose the right inverter for your needs?

To choose the right inverter, consider factors such as the total wattage of the devices you plan to power, the type of waveform required (pure sine wave or modified sine wave), and the inverter's input and output voltage compatibility. Additionally, assess the inverter's capacity, ensuring it can handle peak loads and future expansion.

Can an inverter run continuously?

Yes, many inverters are designed for continuous operation. However, it’s important to ensure that the inverter is properly rated for the load it will be handling and that it has adequate cooling to prevent overheating. Continuous operation also depends on the availability of a reliable power source, such as a well-maintained battery or solar panel array.

What safety features should an inverter have?

Important safety features for inverters include overload protection, short circuit protection, over-voltage and under-voltage protection, and thermal protection to prevent overheating. These features help protect both the inverter and connected devices from damage due to electrical faults or excessive load.

How do I maintain an inverter?

Regular maintenance of an inverter includes keeping it clean and dust-free, ensuring adequate ventilation, checking connections and wiring for wear and tear, and periodically testing the inverter’s performance. Proper maintenance extends the inverter's lifespan and ensures reliable operation.

Can an inverter be used in vehicles?

Yes, inverters are often used in vehicles to power AC devices using the vehicle’s DC battery. This is useful for camping, road trips, or running equipment that requires AC power while on the move. Vehicle inverters come in various sizes and capacities, suitable for different applications.

Can an inverter be used with a battery backup system?

Yes, an inverter can be integrated with a battery backup system to provide power during outages. The battery stores DC power, and the inverter converts it to AC power to run household appliances and electronic devices. This setup ensures continuous operation even when the main power supply is unavailable, making it ideal for critical applications and areas prone to power interruptions.

What size inverter do I need for my home?

The size of the inverter you need depends on the total wattage of the appliances and devices you plan to power. Calculate the combined wattage of all devices and choose an inverter with a capacity slightly higher than the total wattage to ensure efficient operation and to accommodate any additional load. This approach prevents overloading and extends the inverter's lifespan.

How long can an inverter run on battery power?

The runtime of an inverter on battery power depends on the capacity of the battery and the power consumption of the connected devices. Larger batteries with higher amp-hour (Ah) ratings can provide power for a longer duration. Additionally, using energy-efficient devices can help extend the runtime, allowing for more extended periods of use during power outages or off-grid scenarios.

Are there any noise concerns with using an inverter?

Most modern inverters are designed to operate quietly, but some may produce a low-level humming sound due to the internal cooling fans and electronic components. The noise level is usually minimal and should not be disruptive in a typical home environment. For those sensitive to noise, it's advisable to choose inverters specifically marketed as silent or low-noise models. These models ensure a quieter operation, suitable for use in bedrooms, offices, or other noise-sensitive areas.

When should I consider upgrading my inverter?

You might consider upgrading your inverter if you plan to power more demanding devices or multiple devices simultaneously. Additionally, if you experience issues like power fluctuations or insufficient capacity, upgrading to a more powerful or higher-quality inverter could resolve these issues.

Luminous-1.5KVA-Inverter-with-Battery.png

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - III

1. Without perestroika, the cold war simply would not have ended. But the world could not continue developing as it had, with the stark menace of nuclear war ever present. - Mikhail Gorbachev

2. If I read a book and it makes my whole body so cold no fire can ever warm me, I know that is poetry. - Emily Dickinson

3. Love keeps the cold out better than a cloak. - Henry Wadsworth Longfellow

4. My childhood landscape was not land but the end of the land - the cold, salt, running hills of the Atlantic. I sometimes think my vision of the sea is the clearest thing I own. - Sylvia Plath

5. Our sympathy is cold to the relation of distant misery. - Edward Gibbon

6. Living indoors without fresh air quickly poisons the blood and makes people feel tired and seedy when they don't know why. For myself, I sleep out of doors in winter as well as summer. I only feel tired or seedy when I have been indoors a lot. I only catch cold when I sleep in a room. Robert Baden-Powell

7. I saw the gooseflesh on my skin. I did not know what made it. I was not cold. Had a ghost passed over? No, it was the poetry. - Sylvia Plath

8. Do not hide behind utopian logic which says that until we have the perfect security environment, nuclear disarmament cannot proceed. This is old-think. This is the mentality of the Cold War era. We must face the realities of the 21st century. The Conference on Disarmament can be a driving force for building a safer world and a better future. - Ban Ki-moon.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10671. What does the term in Biology Endocrine system mean?

#10672. What does the term in Biology Endocytosis mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6302.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9808.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5467. What does the noun modus operandi mean?

#5468. What does the noun modus vivendi mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2528. Where is the Sphenoid bone situated?

Jai Ganesh · Jokes

Q: Why is Fast Food increasing illegal immigration?
A: "Fast" food slows you down when it hits your stomach, parks there, and lets the fat have time to get off and apply for citizenship.
* * *
Q: Where do they hold prizefights in Fastfoodland?
A: In an onion ring!
* * *
Q: Why do hamburgers go to the gym?
A: To get better buns.
* * *
Q: Why did the man climb to the roof of the fast food restaurant?
A: The told him the meal was on the house!
* * *
Q: Where are the best tacos served?
A: In the Gulp of Mexico!
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9807.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6302.

Jai Ganesh · Exercises

Hi,

2653.

Jai Ganesh · This is Cool

Hydroelectric power

Gist

Hydroelectric power is electricity generated by harnessing the energy of flowing or falling water, which spins turbines connected to generators. It is a renewable energy source that converts the kinetic and potential energy of water into electricity, which is then transmitted to the grid. While it is efficient and reliable, its construction can be expensive and have significant environmental impacts.

Hydroelectricity is power generated by harnessing the energy of flowing or falling water, which spins turbines connected to generators to produce electricity. This process converts the potential energy of water stored at a height into kinetic energy as it flows downhill, which then turns turbines to create electricity. It is a form of renewable energy, as it uses the natural water cycle without depleting water resources, and is a reliable source with zero greenhouse gas emissions from power generation itself.

Summary

Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power. Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel-powered energy plants. However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.

Construction of a hydroelectric complex can have significant environmental impact, principally in loss of arable land and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding, dam failure can be catastrophic.

In 2021, global installed hydropower electrical capacity reached almost 1,400 GW, the highest among all renewable energy technologies. Hydroelectricity plays a leading role in countries like Brazil, Norway and China. but there are geographical limits and environmental issues. Tidal power can be used in coastal regions.

China added 24 GW in 2022, accounting for nearly three-quarters of global hydropower capacity additions. Europe added 2 GW, the largest amount for the region since 1990. Meanwhile, globally, hydropower generation increased by 70 TWh (up 2%) in 2022 and remains the largest renewable energy source, surpassing all other technologies combined.

Details

Hydroelectric power is electricity produced from generators driven by turbines that convert the potential energy of falling or fast-flowing water into mechanical energy. In the early 21st century, hydroelectric power was the most widely utilized form of renewable energy; in 2019 it accounted for more than 18 percent of the world’s total power generation capacity.

In the generation of hydroelectric power, water is collected or stored at a higher elevation and led downward through large pipes or tunnels (penstocks) to a lower elevation; the difference in these two elevations is known as the head. At the end of its passage down the pipes, the falling water causes turbines to rotate. The turbines in turn drive generators, which convert the turbines’ mechanical energy into electricity. Transformers are then used to convert the alternating voltage suitable for the generators to a higher voltage suitable for long-distance transmission. The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the powerhouse.

Hydroelectric power plants are usually located in dams that impound rivers, thereby raising the level of the water behind the dam and creating as high a head as is feasible. The potential power that can be derived from a volume of water is directly proportional to the working head, so that a high-head installation requires a smaller volume of water than a low-head installation to produce an equal amount of power. In some dams, the powerhouse is constructed on one flank of the dam, part of the dam being used as a spillway over which excess water is discharged in times of flood. Where the river flows in a narrow steep gorge, the powerhouse may be located within the dam itself.

In most communities the demand for electric power varies considerably at different times of the day. To even the load on the generators, pumped-storage hydroelectric stations are occasionally built. During off-peak periods, some of the extra power available is supplied to the generator operating as a motor, driving the turbine to pump water into an elevated reservoir. Then, during periods of peak demand, the water is allowed to flow down again through the turbine to generate electrical energy. Pumped-storage systems are efficient and provide an economical way to meet peak loads.

In certain coastal areas, such as the Rance River estuary in Brittany, France, hydroelectric power plants have been constructed to take advantage of the rise and fall of tides. When the tide comes in, water is impounded in one or more reservoirs. At low tide, the water in these reservoirs is released to drive hydraulic turbines and their coupled electric generators (see tidal power).

Falling water is one of the three principal sources of energy used to generate electric power, the other two being fossil fuels and nuclear fuels. Hydroelectric power has certain advantages over these other sources. It is continually renewable owing to the recurring nature of the hydrologic cycle. It does not produce thermal pollution. (However, some dams can produce methane from the decomposition of vegetation under water.) Hydroelectric power is a preferred energy source in areas with heavy rainfall and with hilly or mountainous regions that are in reasonably close proximity to the main load centers. Some large hydro sites that are remote from load centers may be sufficiently attractive to justify the long high-voltage transmission lines. Small local hydro sites may also be economical, particularly if they combine storage of water during light loads with electricity production during peaks. Many of the negative environmental impacts of hydroelectric power come from the associated dams, which can interrupt the migrations of spawning fish, such as salmon, and permanently submerge or displace ecological and human communities as the reservoirs fill. In addition, hydroelectric dams are vulnerable to water scarcity. In August 2021 Oroville Dam, one of the largest hydroelectric power plants in California, was forced to shut down due to historic drought conditions in the region.

Additional Information

Water can be a powerful force in nature. Its power can be seen in floods that uproot trees or heard in the roar of a waterfall. That power, called waterpower or hydropower, can be used as an alternative energy source. Unlike fossil fuels, it cannot be used up. When waterpower is harnessed, it can be used to create electricity, or hydroelectricity.

Hydroelectric power plants are usually located in dams that are built across rivers. In a dam water is collected at a higher elevation and is then led downward through large pipes to a lower elevation. The falling water causes wheels called water turbines to rotate. The rotating turbines run machines called generators, which produce electricity.

Oceans can also be used to create hydroelectricity. Those waterpower sources are known as tidal power and wave power. Tidal power is created during the tide, when the water level along the oceanic coast changes. Wave power is harnessed by the up-and-down motion of waves.

Waterpower has been in use for thousands of years. The waterwheel was probably invented in the 1st century bce. Ancient Romans used it to grind grain. It was widely used throughout the Middle Ages and into modern times. Water turbines were first introduced in 1827. They were used originally for irrigation. Today, water turbines are used almost exclusively to generate electric power.

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Jai Ganesh · Dark Discussions at Cafe Infinity

2395) Robert Burns Woodward

Gist:

Work

Nature is full of organic substances—a large and highly diverse array of chemical compounds that contain the basic element carbon. Building, or synthesizing, organic substances using chemical methods is important in both scientific and industrial contexts. Synthesis often entails complicated, multistep processes. Robert Woodward mastered these processes and, in the 1950s and 1960s, successfully synthesized a large number of substances: quinine, cholesterol, cortisone, several antibiotic substances, and chlorophyll, the substance that gives leaves their green color.

Summary:

Robert Burns Woodward (born April 10, 1917, Boston, Mass., U.S.—died July 8, 1979, Cambridge, Mass.) was an American chemist best known for his syntheses of complex organic substances, including cholesterol and cortisone (1951), strychnine (1954), and vitamin B12 (1971). He was awarded the Nobel Prize for Chemistry in 1965, “for his outstanding achievements in the art of organic chemistry.”

Early life and education

Woodward’s early years are often told as the story of a boy-genius. He was an autodidact who, even as a child, had a passion for chemistry. At age 14, Woodward bought a copy of Ludwig Gattermann’s Practical Methods of Organic Chemistry and requested issues of chemistry journals from Verlag Chemie of Berlin. Later in life he did nothing to discourage a persistent legend that he had performed all the experiments in Gattermann’s book.

Woodward entered the Massachusetts Institute of Technology in 1933, then lost interest in, and patience with, the undergraduate routine and dropped out. Not wishing to lose such a gifted student, James Flack Norris, an organic chemistry professor, tracked down Woodward in the food technology department. Norris interceded, and Woodward was allowed to fulfill his course requirements by examination. In just four years Woodward obtained both bachelor’s and doctoral degrees. Upon graduation, he spent the summer of 1937 at the University of Illinois, leaving in the fall to join the chemistry department at Harvard University, where he remained until his death in 1979. Woodward was married in 1938 to Irja Pullman and in 1946 to Eudoxia Muller; he had two daughters from the first marriage and a daughter and son from the second.

Scientific career

The chemistry of natural products was Woodward’s base for a broad engagement in organic chemistry. During World War II, Woodward worked on the structural elucidation of penicillin, and he and William Doering sought synthetic routes to quinine. In 1948 Woodward published the structure of strychnine, beating English chemist Robert Robinson in the competition to solve this difficult chemical puzzle. During the 1950s, Woodward collaborated with the pharmaceutical company Pfizer, Inc., on the structural analysis of a new series of antibiotics: terramycin, aureomycin, and magnamycin.

Woodward was known among his colleagues for his aggressive use of the latest analytic tools. He strongly believed in the utility of instruments such as spectrophotometers in organic synthesis. Such instruments could routinely assist the chemist in the characterization of compounds, and they suggested new generalizations about the relationship of structure to physical properties. Indeed, Woodward’s early theoretical pursuits centred on the use of two types of physical data—ultraviolet absorption (1941–42) and optical rotatory dispersion (1961). Both of these generalizations about spectra and structure created new utility for routine spectroscopic measurements. These instrumental techniques altered the traditional, complementary relationship between synthesis and structural determination and reduced the latter to a relatively commonplace procedure.

Nevertheless, Woodward’s achievements in the field of structure determination remain milestones in organic chemistry: penicillin (1945), patulin (1948), strychnine (1947), ferrocene (1952), cevine (1954), gliotoxin (1958), ellipticine (1959), calycanthine (1960), oleandomycin (1960), streptonigrin (1963), and tetrodotoxin (1964). With the American biochemist Konrad Bloch, he also first proposed the correct biosynthetic pathway to the steroid hormones in living organisms.

Woodward undertook and completed one of the first total syntheses of the steroids cholesterol and cortisone (1951) and then the related terpene lanosterol (1954). In 1954 syntheses of strychnine and lysergic acid were announced, followed in 1956 by a synthesis of reserpine that has become a model of elegant technique and has been used for the commercial production of this tranquilizer. Subsequent achievements included the synthesis of chlorophyll (1960), tetracycline (1962), colchicine (1963), and cephalosporin C (1965). In a large-scale collaboration with Albert Eschenmoser of the Federal Institute of Technology in Zürich, Woodward completed in 1971 the synthesis of the complicated coenzyme vitamin B12 (cyanocobalamin) by a sequence of more than 100 reactions. The work on vitamin B12 led to the recognition and formulation, with the American chemist Roald Hoffmann, of the concept of conservation of orbital symmetry, explicating a broad group of fundamental reactions. These Woodward-Hoffman rules were probably the most important theoretical advance of the 1960s in organic chemistry. At the time of his death, Woodward was working on the synthesis of erythromycin.

Woodward lived between the worlds of academy and industry. During his career, he held consultancies with Eli Lilly and Company, Merck & Co., Inc., Mallinckrodt Pharmaceuticals, Monsanto Company, Polaroid Corporation, and Pfizer. In 1963 Ciba (later Ciba-Geigy Ltd., now Novartis International AG), a Swiss pharmaceutical firm, set up the Woodward Research Institute in Basel. He then held dual appointments as director of the institute and as Donner Professor of Science at Harvard. Between Basel and Cambridge, more than 400 graduate and postdoctoral students trained in Woodward’s laboratories.

The Woodward style

Woodward’s talks and lectures on organic chemistry were fastidious, well prepared, and long. Careful precision was the hallmark of his chemical work as well. Woodward was known for his innovative thinking on the theory of organic chemistry. Throughout his career, he demonstrated that the understanding of chemical reaction mechanisms made possible the planning and successful execution of extended sequences of reactions to build up complex compounds. The requisite intellectual discipline, largely initiated by Woodward, did indeed become a major endeavour in organic chemistry.

Woodward’s genius lay not in the creation of new reagents—that is, new synthetic methods—but in his power to marshal all the available facts and solve even the most intricate of puzzles. He had an enormous capacity for information and superb mental organization. Given the set of data on a structure or the planning of a synthesis, Woodward brought to bear a most remarkable ability to see the entire problem at once and to solve it systematically. His brilliance lay in the quality and depth of his thought, his painstaking preparations, and his chemical intuition. Woodward’s work was central to the chemical thought of the times, and his influence on other organic chemists was arguably greater than that of any other in his era.

Details

Robert Burns Woodward (April 10, 1917 – July 8, 1979) was an American organic chemist. He is considered by many to be the preeminent synthetic organic chemist of the twentieth century, having made many key contributions to the subject, especially in the synthesis of complex natural products and the determination of their molecular structure. He worked closely with Roald Hoffmann on theoretical studies of chemical reactions. He was awarded the Nobel Prize in Chemistry in 1965.

Early life and education

Woodward was born in Boston, Massachusetts, on April 10, 1917. He was the son of Margaret Burns (an immigrant from Scotland who claimed to be a descendant of the poet, Robert Burns) and her husband, Arthur Chester Woodward, himself the son of Roxbury apothecary, Harlow Elliot Woodward.

His father was one of the many victims of the 1918 influenza pandemic.

From a very early age, Woodward was attracted to and engaged in private study of chemistry while he attended a public primary school, and then Quincy High School, in Quincy, Massachusetts. By the time he entered high school, he had already managed to perform most of the experiments in Ludwig Gattermann's then widely used textbook of experimental organic chemistry. In 1928, Woodward contacted the Consul-General of the German consulate in Boston (Baron von Tippelskirch), and through him, managed to obtain copies of a few original papers published in German journals. Later, in his Cope lecture, he recalled how he had been fascinated when, among these papers, he chanced upon Diels and Alder's original communication about the Diels–Alder reaction. Throughout his career, Woodward was to repeatedly and powerfully use and investigate this reaction, both in theoretical and experimental ways. In 1933, he entered the Massachusetts Institute of Technology (MIT), but neglected his formal studies badly enough to be excluded at the end of the 1934 fall term. MIT readmitted him in the 1935 fall term, and by 1936 he had received the Bachelor of Science degree. Only one year later, MIT awarded him the doctorate, when his classmates were still graduating with their bachelor's degrees. Woodward's doctoral work involved investigations related to the synthesis of the female sex hormone estrone. MIT required that graduate students have research advisors. Woodward's advisors were James Flack Norris and Avery Adrian Morton, although it is not clear whether he actually took any of their advice. After a short postdoctoral stint at the University of Illinois, he took a Junior Fellowship at Harvard University from 1937 to 1938, and remained at Harvard in various capacities for the rest of his life. In the 1960s, Woodward was named Donner Professor of Science, a title that freed him from teaching formal courses so that he could devote his entire time to research.

Research and career:

Early work

The first major contribution of Woodward's career in the early 1940s was a series of papers describing the application of ultraviolet spectroscopy in the elucidation of the structure of natural products. Woodward collected together a large amount of empirical data, and then devised a series of rules later called the Woodward's rules, which could be applied to finding out the structures of new natural substances, as well as non-natural synthesized molecules. The expedient use of newly developed instrumental techniques was a characteristic Woodward exemplified throughout his career, and it marked a radical change from the extremely tedious and long chemical methods of structural elucidation that had been used until then.

In 1944, with his post doctoral researcher, William von Eggers Doering, Woodward reported the synthesis of the alkaloid quinine, used to treat malaria. Although the synthesis was publicized as a breakthrough in procuring the hard to get medicinal compound from Japanese occupied southeast Asia, in reality it was too long and tedious to adopt on a practical scale. Nevertheless, it was a landmark for chemical synthesis. Woodward's particular insight in this synthesis was to realize that the German chemist Paul Rabe had converted a precursor of quinine called quinotoxine to quinine in 1905. Hence, a synthesis of quinotoxine (which Woodward actually synthesized) would establish a route to synthesizing quinine. When Woodward accomplished this feat, organic synthesis was still largely a matter of trial and error, and nobody thought that such complex structures could actually be constructed. Woodward showed that organic synthesis could be made into a rational science, and that synthesis could be aided by well-established principles of reactivity and structure. This synthesis was the first one in a series of exceedingly complicated and elegant syntheses that he would undertake.

Later work and its impact

Culminating in the 1930s, the British chemists Christopher Ingold and Robert Robinson among others had investigated the mechanisms of organic reactions, and had come up with empirical rules which could predict reactivity of organic molecules. Woodward was perhaps the first synthetic organic chemist who used these ideas as a predictive framework in synthesis. Woodward's style was the inspiration for the work of hundreds of successive synthetic chemists who synthesized medicinally important and structurally complex natural products.

Jai Ganesh · This is Cool

2447) Laughing Gas

Gist

Laughing gas is the common name for nitrous oxide (N2O), a colorless gas with a slightly sweet odor and taste that is used medically as an anesthetic and pain reliever, particularly in dentistry and surgery. It is also used as a propellant in whipped cream, as an oxidizer in rocket engines, and has recreational uses for its euphoric effects. In the environment, it is a powerful greenhouse gas and a major contributor to ozone depletion.

N2O is called laughing gas because inhaling it produces euphoric, giggling effects due to its anesthetic properties. This colloquial name was given by Humphry Davy, and the gas's ability to cause a brief "high" is why it's used recreationally.

Summary

Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an oxide of nitrogen with the formula N2O. At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen.

Nitrous oxide has significant medical uses, especially in surgery and dentistry, for its anaesthetic and pain-reducing effects, and it is on the World Health Organization's List of Essential Medicines. Its colloquial name, "laughing gas", coined by Humphry Davy, describes the euphoric effects upon inhaling it, which cause it to be used as a recreational drug inducing a brief "high". When abused chronically, it may cause neurological damage through inactivation of vitamin B12. It is also used as an oxidiser in rocket propellants and motor racing fuels, and as a frothing gas for whipped cream.

Nitrous oxide is also an atmospheric pollutant, with a concentration of 333 parts per billion (ppb) in 2020, increasing at 1 ppb annually. It is a major scavenger of stratospheric ozone, with an impact comparable to that of CFCs. About 40% of human-caused emissions are from agriculture, as nitrogen fertilisers are digested into nitrous oxide by soil micro-organisms. As the third most important greenhouse gas, nitrous oxide substantially contributes to global warming. Reduction of emissions is an important goal in the politics of climate change.

(CFC: Chlorofluorocarbons).

Details:

Nitrous oxide (laughing gas) is a sedative healthcare providers use to keep you comfortable during procedures. It’s a colorless, faintly sweet-smelling gas that you breathe in through a nosepiece. Unlike other sedation options, you can drive shortly after receiving nitrous oxide.

What is nitrous oxide (laughing gas)?

Nitrous oxide (N20) — commonly known as laughing gas — is a type of short-acting sedative. It’s a colorless, slightly sweet-smelling gas that you breathe in through a mask or nosepiece.

Physicians and dentists have been using nitrous oxide since the mid-19th century — and it’s still one of the most common inhaled sedatives used today. It’s fast-acting and it wears off quickly, making it an ideal sedation option for short or minor procedures.

What does laughing gas do?

Nitrous oxide slows down your nervous system and induces a sense of calm and euphoria. It reduces anxiety and helps you stay comfortable during medical or dental procedures. It doesn’t fully put you to sleep, so you’ll still be able to respond to your provider’s questions or instructions.

Despite its name, laughing gas might not make you laugh. (But then again, it could.) Everyone responds a little differently.

Nitrous oxide takes effect quickly. Within three to five minutes, you might feel:

* Calm.
* Relaxed.
* Happy.
* Giggly.
* Mildly euphoric.
* Light-headed.
* Tingling in your arms and legs.
* Heaviness, like you’re sinking deeper into the exam chair or table.

Who shouldn’t use nitrous oxide sedation?

Laughing gas is a safe medical and dental sedation option for most people, from children to adults. But it might not be right for kids under the age of 2 and those with:

* Certain respiratory conditions, like chronic obstructive pulmonary disease (COPD).
* Stuffy nose (nasal congestion).
* Vitamin B12 deficiency.
* Severe psychiatric conditions.

Ask your healthcare provider whether you’re a candidate for nitrous oxide sedation.

Treatment Details:

What should I expect if I’m getting laughing gas?

Your healthcare provider will talk with you and answer any questions before your procedure. They’ll ask you to sign a consent form so you can receive nitrous oxide.

When it’s time for your procedure, your provider will:

* Place a mask over your nose and mouth. (If you’re getting laughing gas at your dentist’s office, they’ll give you a smaller mask that only covers your nose.)
* Open a tank valve to allow nitrous oxide and oxygen to flow into your mask. (They’ll start with a very low dose to see how you respond.)
* Adjust the dosage until you feel the desired effects.
* Do your procedure. (In many cases, your provider will also give you local anesthesia before beginning. This is because nitrous oxide reduces pain but won’t totally eliminate it. So, it’s common to combine it with other forms of anesthesia.)
* Stop the flow of laughing gas once your procedure is over.
* Ask you to breathe in pure oxygen through your mask until you feel alert again.
* Remove the mask from your face.
* Monitor you for a few minutes before releasing you to go home.

It’s normal to feel a little nervous if you’ve never had laughing gas before. The good news is that you’ll be able to tell your provider if you develop undesirable side effects. If you start to feel dizzy or nauseous, your provider can simply adjust the dosage until it feels comfortable to you.

How long does laughing gas last?

The effects of nitrous oxide last until your provider turns off the gas flow. Once this happens, it takes about 5 to 10 minutes for the sedative to leave your system and for your headspace to return to normal. Due to the short-acting nature of nitrous oxide, you can drive shortly after your procedure.

Additional Information

Nitrous oxide (N2O), one of several oxides of nitrogen, is a colourless gas with pleasant, sweetish odour and taste, which when inhaled produces insensibility to pain preceded by mild hysteria, sometimes laughter. (Because inhalation of small amounts provides a brief euphoric effect and nitrous oxide is not illegal to possess, the substance has been used as a recreational drug.) Nitrous oxide was discovered by the English chemist Joseph Priestley in 1772; another English chemist, Humphry Davy, later named it and showed its physiological effect. A principal use of nitrous oxide is as an anesthetic in surgical operations of short duration; prolonged inhalation causes death. The gas is also used as a propellant in food aerosols. In automobile racing, nitrous oxide is injected into an engine’s air intake; the extra oxygen allows the engine to burn more fuel per stroke. It is prepared by the action of zinc on dilute nitric acid, by the action of hydroxylamine hydrochloride (NH2OH·HCl) on sodium nitrite (NaNO2), and, most commonly, by the decomposition of ammonium nitrate (NH4NO3).

nitrous-oxide-molecule-529553256-58a3b96b3df78c47588cbca7.jpg

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - II

1. Good is positive. Evil is merely privative, not absolute: it is like cold, which is the privation of heat. All evil is so much death or nonentity. Benevolence is absolute and real. So much benevolence as a man hath, so much life hath he. - Ralph Waldo Emerson

2. Continuous eloquence wearies. Grandeur must be abandoned to be appreciated. Continuity in everything is unpleasant. Cold is agreeable, that we may get warm. - Blaise Pascal

3. What is absurd and monstrous about war is that men who have no personal quarrel should be trained to murder one another in cold blood. - Aldous Huxley

4. When I was in the White House, I was confronted with the challenge of the Cold War. Both the Soviet Union and I had 30,000 nuclear weapons that could destroy the entire earth and I had to maintain the peace. - Jimmy Carter

5. As love without esteem is capricious and volatile; esteem without love is languid and cold. - Jonathan Swift

6. We are not interested in the fact that the brain has the consistency of cold porridge. - Alan Turing

7. If you take a reasonable amount of vitamin C regularly, the incidence of the common cold goes down. If you get a cold and start immediately, as soon as you start sneezing and sniffling, the cold just doesn't get going. - Linus Pauling

8. When I am working on a book or a story, I write every morning as soon after first light as possible. There is no one to disturb you, and it is cool or cold, and you come to your work and warm as you write. - Ernest Hemingway.

Jai Ganesh · Science HQ

Sublimation

Gist

Sublimation is the process where a substance transitions directly from a solid to a gas without becoming a liquid first. It is an endothermic process, meaning it requires energy, and can be seen in everyday examples like the disappearance of dry ice (CO2) and the evaporation of snow on a cold, dry day without melting. The opposite process, where a gas turns directly into a solid, is called deposition.

Sublimation is the process where a solid turns directly into a gas without becoming a liquid first. Common examples include dry ice (solid carbon dioxide), which turns into gas at room temperature, and mothballs (naphthalene), which slowly release a gas that repels moths.

Summary

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. The verb form of sublimation is sublime, or less preferably, sublimate. Sublimate also refers to the product obtained by sublimation. The point at which sublimation occurs rapidly (for further details, see below) is called critical sublimation point, or simply sublimation point. Notable examples include sublimation of dry ice at room temperature and atmospheric pressure, and that of solid iodine with heating.

The reverse process of sublimation is deposition (also called desublimation), in which a substance passes directly from a gas to a solid phase, without passing through the liquid state.

Technically, all solids may sublime, though most sublime at extremely low rates that are hardly detectable under usual conditions. At normal pressures, most chemical compounds and elements possess three different states at different temperatures. In these cases, the transition from the solid to the gas state requires an intermediate liquid state. The pressure referred to is the partial pressure of the substance, not the total (e.g. atmospheric) pressure of the entire system. Thus, any solid can sublime if its vapour pressure is higher than the surrounding partial pressure of the same substance, and in some cases, sublimation occurs at an appreciable rate (e.g. water ice just below 0 °C).

For some substances, such as carbon and math, sublimation from solid state is much more achievable than evaporation from liquid state and it is difficult to obtain them as liquids. This is because the pressure of their triple point in its phase diagram (which corresponds to the lowest pressure at which the substance can exist as a liquid) is very high.

Sublimation is caused by the absorption of heat which provides enough energy for some molecules to overcome the attractive forces of their neighbors and escape into the vapor phase. Since the process requires additional energy, sublimation is an endothermic change. The enthalpy of sublimation (also called heat of sublimation) can be calculated by adding the enthalpy of fusion and the enthalpy of vaporization.

Details:

Definition of Sublimation

Sublimation is the process in which a solid directly changes into a gas without passing through the liquid phase. This process occurs when the temperature and pressure of the solid are raised to a point where the molecules have enough energy to break free from the intermolecular forces holding them in place and escape into the gas phase.

Sublimation Point

The sublimation point is the temperature and pressure at which the solid and gas phases of a substance are in equilibrium. At this point, the vapor pressure of the solid is equal to the pressure of the gas. The sublimation point is typically higher than the melting point of a substance.

Working Principle of Sublimation

Sublimation is the process in which a solid directly changes into a gas without passing through the liquid phase. This process occurs when the temperature and pressure of the solid are raised to a point where the molecules of the solid have enough energy to break free from the intermolecular forces holding them together and escape into the gas phase.

Sublimation is a process that occurs when a solid directly changes into a gas without passing through the liquid phase. This process has a number of applications, including freeze drying, desalination, purification, and 3D printing.

Characteristics of Sublimation

Sublimation is the process by which a solid directly changes into a gas without passing through the liquid phase. This process is the opposite of deposition, in which a gas directly changes into a solid. Sublimation is a physical change, meaning that the chemical composition of the substance does not change.

The following are some of the characteristics of sublimation:

* It occurs at a temperature and pressure below the triple point of the substance. The triple point is the temperature and pressure at which the three phases of a substance (solid, liquid, and gas) can coexist in equilibrium.
* It is a relatively slow process. This is because the molecules of a solid are more tightly packed together than the molecules of a gas, and it takes more energy to break these bonds.
* It is more common for substances with a high vapor pressure. Vapor pressure is the pressure exerted by the vapor of a substance when it is in equilibrium with its liquid or solid phase. Substances with a high vapor pressure are more likely to sublime because their molecules are more likely to escape from the solid or liquid phase.
* It can be used to purify substances. Sublimation can be used to separate a solid from impurities that have a lower vapor pressure. The solid is heated until it sublimes, and the impurities are left behind.
* It is used in a variety of applications. Sublimation is used in a variety of applications, including:

** Freeze-drying: Sublimation is used to remove water from food and other products.
** Dye sublimation printing: Sublimation is used to print images on fabrics and other materials.
** Vacuum coating: Sublimation is used to coat surfaces with a thin layer of metal or other material.

Examples of Sublimation

Some common examples of sublimation include:

* Dry ice (solid carbon dioxide) sublimes at atmospheric pressure. This is why dry ice “smokes” when it is exposed to air.
* Iodine sublimes at a temperature of 114°C (237°F). This is why iodine crystals disappear when they are heated.
* Naphthalene (mothballs) sublimes at a temperature of 80°C (176°F). This is why mothballs slowly disappear over time.

Sublimation is a unique and interesting physical change that has a variety of applications. By understanding the characteristics of sublimation, we can use this process to our advantage in a variety of ways.

Applications of Sublimation

Sublimation is the process of a solid turning directly into a gas without passing through the liquid phase. This process is used in a variety of applications, including:

Dye Sublimation Printing

Dye sublimation printing is a digital printing technology that uses heat to transfer dye onto materials such as paper, fabric, and plastic. This process is often used for creating high-quality prints on t-shirts, mugs, and other promotional items.

3D Printing

Sublimation is used in 3D printing to create objects from a digital file. In this process, a filament of plastic is heated until it melts and is then deposited layer by layer to create a three-dimensional object.

Food Processing

Sublimation is used in the food processing industry to remove moisture from food products. This process helps to preserve food and extend its shelf life.

Pharmaceuticals

Sublimation is used in the pharmaceutical industry to create drugs and other pharmaceutical products. This process allows for the precise control of the drug’s dosage and purity.

Electronics

Sublimation is used in the electronics industry to create thin films of metal and other materials. These films are used in a variety of electronic devices, such as transistors and capacitors.

Textile Printing

Sublimation printing is a digital printing technology that uses heat to transfer dye onto fabrics. This process is often used for creating high-quality prints on t-shirts, sportswear, and other textiles.

Other Applications

Sublimation is also used in a variety of other applications, including:

* Cosmetics: Sublimation is used to create makeup and other cosmetic products.
* Art: Sublimation is used to create prints on canvas, paper, and other materials.
* Industrial: Sublimation is used to create labels, decals, and other industrial products.

Sublimation is a versatile process that has a wide range of applications. It is a powerful tool that can be used to create high-quality products in a variety of industries.

Additional Information

Sublimation, in physics, is the conversion of a substance from the solid to the gaseous state without its becoming liquid. An example is the vaporization of frozen carbon dioxide (dry ice) at ordinary atmospheric pressure and temperature. The phenomenon is the result of vapour pressure and temperature relationships. Freeze-drying of food to preserve it involves sublimation of water from the food in a frozen state under high vacuum.

Sublimation is the process of changing a solid into a gas without passing through the liquid phase. To sublime a substance, a certain energy must be transferred to the substance via heat (q) or work (w). The energy needed to sublime a substance is particular to the substance's identity and temperature and must be sufficient to do all of the following:

* Excite the solid substance so that it reaches its maximum heat (energy) capacity (q) in the solid state.
* Sever all the intermolecular interactions holding the solid substance together
* Excite the unbonded atoms of the substance so that it reaches its minimum heat capacity in the gaseous state

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