Wednesday, May 02, 2007

Fusion Weapons

Fission weapons discussed above are ultimately limited in their destructive capability by the sheer size a subcritical mass can assume -- and be imploded quickly enough by high explosives to form a supercritical assembly. The largest known pure fission weapon tested had a 500 kiloton yield. This is some thirty-eight times the release which destroyed Hiroshima in 1945. Not satisfied that this was powerful enough, designers developed thermonuclear (fusion) weapons.

Fusion exploits the energy released in the fusing of two atoms to form a new element; e.g. deuterium atoms fusing to form helium, 2H + 2H = 4He2 , as occurs on the sun. For atoms to fuse, very high temperatures and pressures are required. Only fusion of the lightest element, hydrogen, has proven practical. And only the heavy isotopes of hydrogen, 2H (deuterium) and 3H (tritium), have a low enough threshold for fusion to have been used in weapons successfully thus far.

The first method tried (boosting) involved simply placing 3H in a void within the center of a fission weapon, where tremendous temperatures and high pressures were attendant to the fission explosion. This worked; contributing energy to the overall explosion, and boosting the efficiency of the Pu fissioning as well (fusion reactions also release neutrons, but with much higher energy).

Because 3H is a gas at room temperature, it can be easily 'bled' into the central cavity from a storage bottle prior to an explosion, and impact the final yield of the device. This is still used today, and allows for what is termed 'dial-a-yield' capability on many stockpiled weapons.

Multistage thermonuclear weapons -- the main component of today's strategic nuclear forces -- are more complex. These employ a 'primary' fission weapon to serve merely as a trigger. As mentioned above, the fission weapon is characterized by a tremendous energy release in a small space over a short period of time. As a result, a very large fraction of the initial energy release is in the form of thermal X-rays.

These X-rays are channeled to a 'secondary' fusion package. The X-rays travel into a cavity within a b28.jpg (8660 bytes)cylindrical radiation container.

The radiation pressure from these X-rays either directly, or through an intermediate material often cited as a polystyrene foam, ablates a cylindrical enclosure containing thermonuclear fuel (shown in blue at left); this can be Li2H (lithium deuteride).

Running along the central axis of this fuel is a rod of fissile material, termed a 'sparkplug'.

The contracting fuel package becomes denser, the sparkplug begins to fission, neutrons from this transmute the Li2H into 3H that can readily fuse with 2H (the fusion reaction 3H + 2H has a very high cross-section, or probability, in typical secondary designs), heat increases greatly, and fusion continues through the fuel mass.

A final 'tertiary' stage can be added to this in the form of an exterior blanket of 238U, wrapping the outer surface of the radiation case or the fuel package. 238U is not fissionable by the slower neutrons which dominate the fission weapon environment, but fusion releases copious high energy neutrons and this can fast fission the ordinary uranium.

This is a cheap (and radiologically very dirty) way to greatly increase yield. The largest weapon ever detonated -- the Soviet Union's 'super bomb', was some 60 MT in yield, and would have been nearer 100MT had this technique been used in its tertiary. Again, to control the yield precisely, 3H may be bled from a separate tank into the core of the primary, as shown in the hypothetical diagram on the left of a modern thermonuclear weapon.

This primary/secondary/tertiary or multistage arrangement can be increased -- unlike the fission weapon -- to provide insane governments with any arbitrarily large yield.

Fusion, or thermonuclear weapons, are not simple to design nor are they likely targets of construction for would-be terrorists today.

Many aspects of the relevant radiation transport, X-ray opacities, and ultra-high T and D equations-of-state (EOS) for relevant materials are still classified to this day (though increasing dissemination of weapons-adaptable information from the inertially-confined fusion (ICF) area may change this in time). Keeping such information classified makes good sense.


Monday, April 23, 2007

Nuclear Weapons - Fission Wreapons

Nuclear weapons exploit two principle physical, or more specifically nuclear, properties of certain substances: fission and fusion.

Fission is possible in a number of heavy elements, but in weapons it is principally confined to what is termed slow neutron fission in just two particular isotopes: 235U and 239Pu. These are termed fissile, and are the source of energy in atomic weapons. An explosive chain reaction can be started with relatively slight energy input (so-called slow neutrons) in such material.

Isotopes are 'varieties' of an element which differ only in their number of neutrons. For example, hydrogen exists as 1H 2H and 3H -- different isotopes of the same chemical element, with no, one, and two neutrons respectively. All the chemical properties, and most of the physical properties, are the same between isotopes. Nuclear properties may differ significantly, however.

The fission, or 'splitting' of an atom, releases a very large amount of energy per unit volume -- but a single atom is very small indeed. The key to an uncontrolled or explosive release of this energy in a mass of fissile material large enough to constitute a weapon is the establishment of a chain reaction with a short time period and high growth rate. This is surprisingly easy to do.

Fission of 235U (uranium) or 239Pu (plutonium) starts in most weapons with an incident source of neutrons. These strike atoms of the fissile material, which (in most cases) fissions, and each atom in so doing releases, on average, somewhat more than 2 neutrons. These then strike other atoms in the mass of material, and so on.

If the mass is too small, or has too large a surface area, too many neutrons escape and a chain reaction is not possible; such a mass is termed subcritical. If the neutrons generated exactly equal the number consumed in subsequent fissions, the mass is said to be critical. If the mass is in excess of this, it is termed supercritical.

Fission (atomic) weapons are simply based on assembling a supercritical mass of fissile material quickly enough to counter disassembly forces.

The majority of the energy release is nearly instantaneous, the mean time from neutron release to fission can be of the order of 10 nanoseconds, and the chain reaction builds exponentially. The result is that greater than 99% of the very considerable energy released in an atomic explosion is generated in the last few (typically 4-5) generations of fission -- less than a tenth of a millisecond.

This tremendous energy release in a small space over fantastically short periods of time creates some unusual phenomena -- physical conditions that have no equal on earth, no matter how much TNT is stacked up.

Plutonium (239Pu) is the principal fissile material used in today's nuclear weapons. The actual amount of this fissile material required for a nuclear weapon is shockingly small.

In the Fat Man (Nagasaki) weapon design an excess of Pu was provided. Most of the remaining bulk of the weapon was comprised of two concentric shells of high explosives. Each of these was carefully fashioned from two types of explosives with differing burn rates. These, when detonated symmetrically on the outermost layer, caused an implosion or inward-moving explosion.

The two explosive types were shaped to create a roughly spherical convergent shockwave which, when it reached the Pu 'pit' in the center of the device, caused it to collapse.

The Pu pit became denser, underwent a phase change, and became supercritical.

A small neutron source, the initiator, placed in the very center of this Pu pit, provided an initial burst of neutrons -- final generations of which, less than a microsecond later, saw the destruction of an entire city and more than 30,000 people..

Nearly all the design information for weapons such as these is now in the public domain; in fact, considering the fact that fission weapons exploit such a simple and fundamental physical (nuclear) property, it is no surprise that this is so. It is more surprising that so much stayed secret for so long, at least from the general public.

A neutron reflector, often made of beryllium, is placed outside the central pit to reflect neutrons back into the pit. A tamper, often made of depleted uranium or 238U helps control premature disassembly. Modern fission devices use a technique called 'boosting' , to control and enhance the yield of the device.

Today's nuclear threat lies mostly in preventing this fissile special nuclear material (often referred to as SNM) from falling into the wrong hands: once there, it is a very short step to construct a working weapon.

source : simplethinking

Low-salt diet prevents heart attacks and strokes

Eating less salt can reduce the risk of cardiovascular disease by 25% and cut the risk of death from all causes by a fifth, according to a new study.

The 15-year study of 2400 people demonstrates for the first time that cutting back on salt can reduce the risk of diseases such as stroke and heart attack, in addition to lowering blood pressure.

Volunteers in the study who were assigned to a low-salt regime had a 20% lower risk of death from all causes over the course of the study than their control counterparts. The findings should compel governments to take more action to reduce the salt content of processed foods, says Nancy Cook at the Brigham and Women's Hospital in Boston, Massachusetts, US, who led the study.

Numerous studies have documented how consuming foods high in salt can lead to high blood pressure. This happens because the salt draws more water into the blood, and the increase in fluid volume exerts more pressure on vessel walls. High blood pressure is known to contribute to heart disease, but few studies have shown a direct link between salty foods and the condition.

Salt snapshot

In the late-1980s and early-1990s Cook and colleagues collected urine samples from more than 3000 people with above-normal blood pressure. Analysing the urine samples collected over the course of a 24-hour-period gave the researchers a snapshot of the subjects' salt intake. On average, they were consuming 10 grams of salt per day.

Cook's team then randomly assigned half of these participants to attend weekly workshops that taught how to cook low-salt meals and read nutrition labels on packaged foods.

After approximately three months of this nutrition counselling, urine sampling revealed that the subjects reduced their daily salt intake by about 3 grams per day on average – the equivalent of about half a teaspoon.

Fifteen years later Cook's team was able to obtain follow-up health information about 2415 of the participants from medical records and telephone interviews.

Healthy choices

Phone interviews indicated that those who had received training on how to reduce their salt intake many years ago continued to consume less of it than their control counterparts. For example, 47% of those who received this intervention said they looked for reduced-salt foods in the supermarket, compared with 29% of the control group.

Of the 200 people who had developed cardiovascular disease – including heart attacks and stroke – in the past 15 years, 112 had received no dietary recommendations and 88 were in the group taught to reduce their salt intake.

After controlling for factors such as weight and age, the researchers calculated that reducing one's salt intake by 30% could decrease the risk of cardiovascular disease by 25%.

Cook says that the results of the study should encourage governments to "work with the food industry to come up with lower sodium foods", and notes that salt content is highest in processed and fast-foods. "People generally consume much more salt than what is biologically needed."

In 2006, the American Medical Association urged the US Food and Drug Administration to revoke the "generally recognised as safe" (GRAS) status of salt and to adopt stricter salt guidelines.

Current US dietary guidelines recommend that people consume less than one teaspoon of salt per day.

Journal reference: BMJ (DOI: 10.1136/bmj.39147.604896.55)

Genes versus heat – a reptile sex trigger

High temperatures can make an Australian lizard that is genetically male develop into a female. The finding throws new light on how sex is determined in reptiles.

For most reptiles, a gene on a sex chromosome triggers an embryo to develop as either a male or a female. In some species, males have an X and a Y chromosome, while females are XX, as in mammals. In other species of lizards, males are ZZ while females are ZW, as in birds.

But for a third group of reptiles, which includes all crocodiles, alligators and marine turtles, temperature, rather than a gene on a sex chromosome, triggers either male or female differentiation. Extreme low or high temperatures generally lead to more females.

Now a team led by Alex Quinn at Canberra University in Australia has found that the central bearded dragon (Pogona vitticeps) is susceptible to both types of sex trigger, and that temperature can override its genetic gender.

Transitional form

When the team incubated eggs at relatively high temperatures – between 34°C and 37°C – the majority of embryos that had ZZ sex chromosomes (genetically male), hatched as females. The team thinks the bearded dragon represents a transitional form, in evolutionary terms, between the two main methods of sexual determination.

The research shows that, for the bearded dragon at least, the W chromosome is not necessary in producing a female. The team suspects that a double dose of a particular gene on the Z chromosome is instead crucial for maleness, and that this gene is inactivated by high temperatures.

“The possibility that there is a male-determining, dosage-dependent gene on the Z chromosome of bearded dragons is an important insight,” says Quinn, “because to date, scientists have discovered the master sex-determining gene only in mammals and a single species of fish.”

The team plans to hunt for that master gene in the bearded dragon. They also want to investigate how widespread the phenomenon of temperature sex reversal really is in reptiles.

If many other reptiles with sex chromosomes are also susceptible to temperature, this would broaden the number of species that could be vulnerable to climate change.

“The concern is that the current rate of climate warming could be too rapid for these species to adapt to, and this could potentially result in heavily skewed sex ratios, and even population crashes in some cases,” Quinn says.

Journal reference: Science (vol 316, p 411)

Regular aspirin use may protect cancer

Regular aspirin use may protect more than just your heart - it could also reduce your risk of getting cancer.

Aditya Bardia and colleagues at the Mayo Clinic College of Medicine in Rochester, Minnesota, analysed the cancer history of more than 22,000 post-menopausal women over 12 years. Those who reported taking aspirin regularly at the start of the study were 16 per cent less likely to develop cancer and 13 per cent less likely to die from it during that time. The only lifestyle factor that influenced the results was smoking, which reduced the protective effect slightly.

Bardia says aspirin's anti-inflammatory action is probably responsible, although a similar effect
was not seen with other anti-inflammatories, such as ibuprofen. The findings were presented at a meeting of the American Association for Cancer Research in Los Angeles this week.

From issue 2600 of New Scientist magazine, 23 April 2007, page 16

Saturday, April 07, 2007

Fule Cells ?????????

You’ve probably heard about fuel cells. In 2003, President Bush announced a program called the Hydrogen Fuel Initiative (HFI) during his State of the Union Address. This initiative, supported by legislation in the Energy Policy Act of 2005 (EPACT 2005) and the Advanced Energy Initiative of 2006, aims to develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020. The United States has dedicated more than one billion dollars to fuel cell research and development so far.

So what exactly is a fuel cell, anyway? Why are governments, private businesses and academic institutions collaborating to develop and produce them? Fuel cells generate electrical power quietly and efficiently, without pollution. Unlike power sources that use fossil fuels, the by-products from an operating fuel cell are heat and water. But how does it do this?

If you want to be technical about it, a fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.

The other electrochemical device that we are all familiar with is the battery. A battery has all of its chemicals stored inside, and it converts those chemicals into electricity too. This means that a battery eventually "goes dead" and you either throw it away or recharge it.

With a fuel cell, chemicals constantly flow into the cell so it never goes dead -- as long as there is a flow of chemicals into the cell, the electricity flows out of the cell. Most fuel cells in use today use hydrogen and oxygen as the chemicals.

Sir William Grove invented the first fuel cell in 1839. Grove knew that water could be split into hydrogen and oxygen by sending an electric current through it (a process called electrolysis). He hypothesized that by reversing the procedure you could produce electricity and water. He created a primitive fuel cell and called it a gas voltaic battery. After experimenting with his new invention, Grove proved his hypothesis. Fifty years later, scientists Ludwig Mond and Charles Langer coined the term fuel cell while attempting to build a practical model to produce electricity.

There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by their operating temperature and the type of electrolyte they use. Some types of fuel cells work well for use in stationary power generation plants. Others may be useful for small portable applications or for powering cars. The main types of fuel cells include:

Polymer exchange membrane fuel cell (PEMFC)
The Department of Energy (DOE) is focusing on the PEMFC as the most likely candidate for transportation applications. The PEMFC has a high power density and a relatively low operating temperature (ranging from 60 to 80 degrees Celsius, or 140 to 176 degrees Fahrenheit). The low operating temperature means that it doesn't take very long for the fuel cell to warm up and begin generating electricity.

Solid oxide fuel cell (SOFC)
These fuel cells are best suited for large-scale stationary power generators that could provide electricity for factories or towns. This type of fuel cell operates at very high temperatures (between 700 and 1,000 degrees Celsius). This high temperature makes reliability a problem, because parts of the fuel cell can break down after cycling on and off repeatedly. However, solid oxide fuel cells are very stable when in continuous use. In fact, the SOFC has demonstrated the longest operating life of any fuel cell under certain operating conditions. The high temperature also has an advantage: the steam produced by the fuel cell can be channeled into turbines to generate more electricity. This process is called co-generation of heat and power (CHP) and it improves the overall efficiency of the system.

Alkaline fuel cell (AFC)
This is one of the oldest designs for fuel cells; the United States space program has used them since the 1960s. The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.

Molten-carbonate fuel cell (MCFC)
Like the SOFC, these fuel cells are also best suited for large stationary power generators. They operate at 600 degrees Celsius, so they can generate steam that can be used to generate more power. They have a lower operating temperature than solid oxide fuel cells, which means they don't need such exotic materials. This makes the design a little less expensive.

Phosphoric-acid fuel cell (PAFC)
The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at a higher temperature than polymer exchange membrane fuel cells, so it has a longer warm-up time. This makes it unsuitable for use in cars.

Direct-methanol fuel cell (DMFC)
Methanol fuel cells are comparable to a PEMFC in regards to operating temperature, but are not as efficient. Also, the DMFC requires a relatively large amount of platinum to act as a catalyst, which makes these fuel cells expensive.

Source : How Stuff Works , Wikipedia

Friday, April 06, 2007

A Hydrogen Fule Cell In Ten Minutes

A fuel cell is a device that converts a fuel such as hydrogen, alcohol, gasoline, or methane into electricity directly. A hydrogen fuel cell produces electricity without any pollution, since pure water is the only byproduct.

Hydrogen fuel cells are used in spacecraft and other high-tech applications where a clean, efficient power source is needed.

You can make a hydrogen fuel cell in your kitchen in about 10 minutes, and demonstrate how hydrogen and oxygen can combine to produce clean electrical power.

To make the fuel cell, we need the following:
>One foot of platinum coated nickel wire, or pure platinum wire.
>A popsickle stick or similar small piece of wood or plastic.
>A 9 volt battery clip.
>A 9 volt battery.
>Some transparent sticky tape.
>A glass of water.
>A volt meter.

The first step is to cut the platinum coated wire into two six inch long pieces, and wind each piece into a little coiled spring that will be the electrodes in our fuel cell. Next, we cut the leads of the battery clip in half and strip the insulation off of the cut ends. Then we twist the bare wires onto the ends of the platinum coated electrodes, as shown in the photo. The battery clip will be attached to the electrodes, and two wires will also be attached to the electrodes, and will later be used to connect to the volt meter.

The electrodes are then taped securely to the popsickle stick. Lastly, the popsickle stick is taped securely to the glass of water, so that the electrodes dangle in the water for nearly their entire length. The twisted wire connections must stay out of the water, so only the platinum coated electrodes are in the water.
Now connect the red wire to the positive terminal of the volt meter, and the black wire to the negative (or "common") terminal of the volt meter. The volt meter should read 0 volts at this point, although a tiny amount of voltage may show up, such as 0.01 volts.

Your fuel cell is now complete.

To operate the fuel cell, we need to cause bubbles of hydrogen to cling to one electrode, and bubbles of oxygen to cling to the other. There is a very simple way to do this.

We touch the 9 volt battery to the battery clip (we don't need to actually clip it on, since it will only be needed for a second or two).

Touching the battery to the clip causes the water at the electrodes to split into hydrogen and oxygen, a process called electrolysis. You can see the bubbles form at the electrodes while the battery is attached.

Now we remove the battery. If we were not using platinum coated wire, we would expect to see the volt meter read zero volts again, since there is no battery connected.

The platinum acts as a catalyst, allowing the hydrogen and oxygen to recombine.

The hydrolysis reaction reverses. Instead of putting electricity into the cell to split the water, hydrogen and oxygen combine to make water again, and produce electricity.

We initially get a little over two volts from the fuel cell. As the bubbles pop, dissolve in the water, or get used up by the reaction, the voltage drops, quickly at first, then more slowly.

After a minute or so, the voltage declines much more slowly, as most of the decline is now due only to the gasses being used up in the reaction that produces the electricity.

Notice that we are storing the energy from the 9 volt battery as hydrogen and oxygen bubbles.

We could instead bubble hydrogen and oxygen from some other source over the electrodes, and still get electricity. Or we could produce hydrogen and oxygen during the day from solar power, and store the gasses, then use them in the fuel cell at night. We could also store the gasses in high pressure tanks in an electric car, and generate the electricity the car needs from a fuel cell.

OK the fun part again :

The electrode connected to the negative side of the battery has electrons that are being pushed by the battery. Four of the electrons in that electrode combine with four water molecules. The four water molecules each give up a hydrogen atom, to form two molecules of hydrogen (H2), leaving four negatively charged ions of OH-.

The hydrogen gas bubbles up from the electrode, and the negatively charged migrate away from the negatively charged electrode.

At the other electrode, the positive side of the battery pulls electrons from the water molecules. The water molecules split into positively charged hydrogen atoms (single protons), and oxygen molecules. The oxygen molecules bubble up, and the protons migrate away from the positively charged electrode.

The protons eventually combine with the OH- ions from the negative electrode, and form water molecules again.

When we remove the battery, the hydrogen molecules that are clinging as bubbles to the electrode, break up due to the catalytic action of the platinum, forming positively charged hydrogen ions (H+, or protons), and electrons

At the other electrode, the oxygen molecules stuck in bubbles on the platinum surface draw electrons from the metal, and then combine with the hydrogen ions in the water (from the reaction at the other electrode) to form water.

The oxygen electrode has lost two electrons to each oxygen molecule. The hydrogen electrode has gained two electrons from each hydrogen molecule. The electrons at the hydrogen electrode are attracted to the positively charged oxygen electrode. Electrons travel more easily in metal than in water, so the current flows in the wire, instead of the water. In the wire, the current can do work, such as lighting a bulb, or moving a meter.

source : sci-toys

Tuesday, April 03, 2007

Make a solar cell in your kitchen

A solar cell is a device for converting energy from the sun into electricity.The high-efficiency solar cells ,are made from highly processed silicon, and require huge factories, high temperatures, vacuum equipment, and lots of money.

If we are willing to sacrifice efficiency for the ability to make our own solar cells in the kitchen out of materials from the neighborhood hardware store, we can demonstrate a working solar cell in about an hour.

Our solar cell is made from cuprous oxide instead of silicon. Cuprous oxide is one of the first materials known to display the photoelectric effect, in which light causes electricity to flow in a material.

Thinking about how to explain the photoelectric effect is what led Albert Einstein to the Nobel prize for physics, and to the theory of relativity.

Materials you will need:

The solar cell is made from these materials:

>A sheet of copper flashing from the hardware store. We will need about half a square foot.

>Two alligator clip leads.

>Low voltage bulb

>An electric stove. The gas stove wont work . The little 700 watt burners probably won't work -- mine is 1100 watts, so the burner gets red hot.

>A large clear plastic bottle off of which you can cut the top. A large mouth glass jar will also work.

>Table salt. We will want a couple tablespoons of salt.

>Tap water.

>Sand paper or a wire brush on an electric drill.

>Sheet metal shears for cutting the copper sheet.

How to build the solar cell:

The first step is to cut a piece of the copper sheeting that is about the size of the burner on the stove. Wash your hands so they don't have any grease or oil on them. Then wash the copper sheet with soap or cleanser to get any oil or grease off of it. Use the sandpaper or wire brush to thoroughly clean the copper sheeting, so that any sulphide or other light corrosion is removed.

Next, place the cleaned and dried copper sheet on the burner and turn the burner to its highest setting.

As the copper starts to heat up, you will see beautiful oxidation patterns begin to form. Oranges, purples, and reds will cover the copper.

As the copper gets hotter, the colors are replaced with a black coating of cupric oxide. This is not the oxide we want, but it will flake off later, showing the reds, oranges, pinks, and purples of the cuprous oxide layer underneath.

When the burner is glowing red-hot, the sheet of copper will be coated with a black cupric oxide coat. Let it cook for a half an hour, so the black coating will be thick. This is important, since a thick coating will flake off nicely, while a thin coat will stay stuck to the copper.

After the half hour of cooking, turn off the burner. Leave the hot copper on the burner to cool slowly. If you cool it too quickly, the black oxide will stay stuck to the copper.

As the copper cools, it shrinks. The black cupric oxide also shrinks. But they shrink at different rates, which makes the black cupric oxide flake off.

The little black flakes pop off the copper with enough force to make them fly a few inches. This means a little more cleaning effort around the stove, but it is fun to watch.

When the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will be gone. A light scrubbing with your hands under running water will remove most of the small bits. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This might damage the delicate red cuprous oxide layer we need to make to solar cell work.

Cut another sheet of copper about the same size as the first one. Bend both pieces gently, so they will fit into the plastic bottle or jar without touching one another. The cuprous oxide coating that was facing up on the burner is usually the best side to face outwards in the jar, because it has the smoothest, cleanest surface.

Attach the two alligator clip leads, one to the new copper plate, and one to the cuprous oxide coated plate. Connect the lead from the clean copper plate to the positive terminal of the meter. Connect the lead from the cuprous oxide plate to the negative terminal of the meter.

Now mix a couple tablespoons of salt into some hot tap water. Stir the saltwater until all the salt is dissolved. Then carefully pour the saltwater into the jar, being careful not to get the clip leads wet. The saltwater should not completely cover the plates -- you should leave about an inch of plate above the water, so you can move the solar cell around without getting the clip leads wet.

The chemistry behind it :

Cuprous oxide is a type of material called a semiconductor. A semiconductor is in between a conductor, where electricity can flow freely, and an insulator, where electrons are bound tightly to their atoms and do not flow freely.

In a semiconductor, there is a gap, called a bandgap between the electrons that are bound tightly to the atom, and the electrons that are farther from the atom, which can move freely and conduct electricity.

Electrons cannot stay inside the bandgap. An electron cannot gain just a little bit of energy and move away from the atom's nucleus into the bandgap. An electron must gain enough energy to move farther away from the nucleus, outside of the bandgap.

Similarly, an electron outside the bandgap cannot lose a little bit of energy and fall just a little bit closer to the nucleus. It must lose enough energy to fall past the bandgap into the area where electrons are allowed.

When sunlight hits the electrons in the cuprous oxide, some of the electrons gain enough energy from the sunlight to jump past the bandgap and become free to conduct electricity.

The free electrons move into the saltwater, then into the clean copper plate, into the wire, through the meter, and back to the cuprous oxide plate.

*Note:The cell produces 50 microamps at 0.25 volts.
This is 0.0000125 watts (12.5 microwatts).
Don't expect to light light bulbs or charge batteries with this device. It would take acres of them to power your house.

Source : SciToys

Saturday, March 24, 2007

Free Beer For Geeks (Free As In Freedom)

Vores Øl (Danish for Our Beer) is presented as the first open source beer. Today also known as Free Beer. The recipe is published under a Creative Commons license. The beer was created by students at the IT-University in Copenhagen together with Superflex, a Copenhagen-based artist collective, to illustrate how open source concepts might be applied outside the digital world. The students brewed the first 100 litre batch, titled 'version 1.0', of the dark heavy beer in the school cafeteria, and created label designs and a website to promote the beer and publish the recipe.


The following recipe is as shown on the official website (As of September 2005), although other variants may exist due to the freedom given to modify the recipe.

Recipe for approximately 85 l (approximately 6% alcohol by volume).

Malt extract

Four types of malted barley are used:
6 kg pilsner malt
4 kg münsner malt
1 kg caramel malt
1 kg lager malt

The malt is crushed and put in 55–60 °C hot water for 1–2 hours.

The mash is filtered and the liquid now contains about 10 kg malt extract.

Taste and sugar

50 g Hallertauer (Northern Brewer) hops
60 g Tettnang hops
300 g guarana beans (Guarana beans can typically be bought at health food stores).
4 kg sugar

The malt extract is brought to a boil in a large pot with Hallertauer NB hops and approximately 70 l (18.5 gal) of water.

After half an hour, the guarana beans and sugar are added.

The mixture simmers for about an hour, the heat is turned off, and the Tettnang hops are added and left to sit for 10 minutes. The mixture is then filtered and cooled in a sealed container.


Yeast is added and the beer is fermented at room temperature for approximately 2 weeks.

When the beer is fully fermented, it is transferred to bottles. First 4 g sugar is added per liter and some yeast from the bottom of the fermentation tanks for priming.

The beer is then left in the bottles at room temperature for 8-10 days for carbonation.

source :

Friday, March 23, 2007

Molecular Nanobot in Various Uses

In Japan photo-reactive nanocrystals are being developed for more efficient solar cell production. Rice University is developing methods that use the reactivity of nanoparticles to clean contaminants, especially biological contaminants from water. In agriculture, nano-sensors will be sprinkled on crops or soil to monitor temperature, water, salinity, nitrogen and disease. Robert Freitas is developing an artificial red blood cell able to deliver 236 times more oxygen to tissues than natural red blood cells. Freitas predicts his device will be used to treat anaemia and lung disorders, but also will enhance human performance in sport and warfare. Researchers at the Florida University have created a nanocapsule gel to deliver drugs into the eyes through soft contact lenses.

The importance of nanotechnology to the future of mankind cannot be overstated. Nanotech’s promise is clean industries, cures for disease, nearly unlimited energy supplies, a continuance of Moore’s Law, the end of hunger, and the elmination of aging. Welcome to Molecular Nanobots.

There is so much to explore once you start exploring within nanotechnology - you'll quickly find that the all aspects of the very small - end up being very, very large

source :-

Tuesday, March 20, 2007

Virtual Lab From ChemCollective

The Virtual Laboratory from the ChemCollective is a new personal favorite. The online version is a java applet, but they now have a downloadable version that will run on any Windows desktop computer. The software allows a student or instructor to simulate many lab activities. Acid base titration, buffer chemistry, limiting reactant stoichiometry and solution equilibria are but a few of the simulations that are possible with this software. There is also an Authoring Program that allows instructors to design their own lab activities and add their own reagents.

If you have java virtual machine installed than download the 1 MBversion or else download the 12 MB version

Download 12 MB With Java Plugin

Download 1 MB (Without JAVA)