Making Strong Fibers

Written by Science Knowledge on 11:01 PM

Structure of various fibersSchematic structures of various fibers. With decreasing disorder and defect density, the fiber strength increases (left to right). (Left) Typical commodity textile fiber contains amorphous and crystalline regions as well as voids and foreign particles; tensile strength, ~0.5 GPa. (Middle) High-performance polymer fibers contain chain ends, entanglements, voids, and defects; tensile strength, ~5 GPa. The structure of currently produced carbon nanotube fibers resembles this structure. In addition, carbon nanotube fibers often contain foreign particles in the form of catalysts. (Right) On the basis of predicted strain to failure (15), ideal carbon nanotube fibers without defects or entanglements will have a specific tensile strength of 70 N/tex; for a single-wall carbon nanotube fiber a diameter of 2 nm, this would translate to a tensile strength of 70 GPa.

Today’s polymeric and carbon fibers are up to 10 times as strong as that available half a century ago (see the figure, left and middle panels). High-performance polymeric fibers find applications in textiles such as firefighter clothing, bulletproof vests, and cables requiring stiffness and strength in tension; high-performance carbon fibers find applications in structural composites, for example, in airplanes, satellites, and tennis rackets. Even stronger fibers can be made using carbon nanotubes. These fibers will be lighter than existing fibers and may increase the performance of airplanes, space vehicles, and many sports and leisure goods.

In applications such as advanced textiles and structural composites, high-performance polymeric and carbon fibers have two key advantages over high-strength bulk materials such as steel. First, as a result of their low density, the specific strength (strength divided by density) of polymeric and carbon fibers is 5 to 10 times that of high-strength bulk materials. Second, fibers can be more easily processed into complex shapes.

One reason that fibers can have higher strength than bulk materials is that they can be processed with small diameters, which minimizes defects. The diameters of current commercial high-performance polymeric fibers range from 10 to 15 μm, and those of carbon fibers range from 5 to 10 μm; making fibers with even smaller diameters will further increase the strength.

Innovations in polymer synthesis and fiber processing have been critical for making high-performance fibers. The first high performance fiber, Kevlar was developed in the 1960s at DuPont, a company with a long history in fiber synthesis. In the 1980s, polyethylene, first synthesized in the 1930s, was processed into a high-performance commercial fiber (with the trade names Spectra and Dyneema), based on gel-spinning technology invented at DSM in the Netherlands. The high-strength polymeric fiber Zylon, based on rigid-rod polymer research that began in the 1970s at the U.S. Air Force Research Laboratory, was commercialized in 1998 by Toyobo in Japan. High-strength polyacrylonitrile-based carbon fibers were developed by optimizing parameters such as the polyacrylonitrile-copolymer composition, fiber spinning, and polyacrylonitrile stabilization and carbonization. Other high-strength fibers include silicon carbide, alumina, glass, and alumina borosilicate fibers; however, these fibers have relatively high densities.

Kevlar, Zylon, Spectra, Dyneema, and the carbon-fiber precursor polyacrylonitrile are all processed from solutions typically containing 5 to 20 weight percent (wt %) of polymer (1, 5). The rest of the mass is the solvent. Solvent removal disrupts the structure and worsens tensile properties. Entanglements, chain ends, voids, and foreign particles act as stress concentration points, lowering strength (see the figure, middle panel). Conversion of polyacrylonitrile to carbon involves heat treatment under tension in air and then in an inert environment. During this process,
~40% of the mass is lost in the form of gases. Gas diffusion, particularly at high temperature, also disrupts and degrades the structure and lowers strength.

Carbon nanotube fibers can also be processed from liquid media. Alternatively, they may be pulled from nanotube “forests” or drawn as an aerogel fiber from the gas phase in a reactor. The latter process appears to be particularly promising. The resulting fiber consists mostly of flattened double-walled nanotubes with diameters of 5 to 10 nm and a length of about
1 mm. The specific strength of this fiber is up to 2.5 times that of the strongest commercial fiber today.

The method used to make this fiber eliminates two problems encountered in the formation of high-strength polymeric and polyacrylonitrile-based carbon fibers: the solvent and gas removal. However, some key challenges need to be ironed out. The catalyst particles must be eliminated from the fiber; drawing conditions must be optimized to eliminate entanglements between carbon nanotubes; and conditions must be tuned so that the growth of a given carbon nanotube is not terminated and that the fiber is pulled at the rate at which nanotubes are growing.

The structure of carbon nanotube fibers is similar to that of high-strength polymeric fibers (see the figure, middle panel). Both types of fibers are strong and stiff along the fiber axis in tension, but relatively weak in axial compression and transverse to the fiber axis. However, carbon nanotube fibers are electrically and thermally conducting, whereas current high-strength polymeric fibers are insulators of both heat and electricity. Potential applications of carbon nanotube fibers will thus be those requiring high strength and stiffness in tension, high energy absorption, and electrical and thermal conductivity. The low density of these fibers would provide further weight savings.

Carbon nanotubes can also act as a nucleating agent for polymer crystallization and as a template for polymer orientation. No other nucleating agents are as narrow and long as a single-wall carbon nanotube. The tensile strength of a poly (vinyl alcohol) film tripled with the addition of 1 wt % of single-wall carbon nanotubes. Similarly, incorporation of 1 wt % of carbon nanotubes in polyacrylonitrile increased the tensile strength and modulus of the resulting carbon fiber by 64% and 49%, respectively. Polyacrylonitrile/carbon nanotube composites have good tensile and compressive properties. Next-generation carbon fibers used for structural composites will thus likely be processed not from polyacrylonitrile alone but from its composites with carbon nanotubes.

If processing conditions can be developed such that all carbon nanotube ends, catalyst particles, voids, and entanglements are eliminated, this would result in a continuous fiber with perfect structure, low density, and tensile strength close to the theoretical value. Such a carbon nanotube fiber could have 10 times the specific strength of the strongest commercial fiber available today. However, many challenges have to be overcome to achieve this goal.

*.* Source of Information : 15th February 2008 Science

DNA’s Self-Regard

Written by Science Knowledge on 11:29 PM

Recognition of double-stranded (ds) DNA sequences is usually thought to require some unwinding of the double helix to expose the bases for interactions with singlestranded nucleic acid sequences or with proteins. Thus, it would be reasonable to assume that recognition between dsDNA sequences

in solution would require processes involving single stranded DNA, such as triplehelix formation. Baldwin et al. examined a binary mixture of two different dsDNA sequences of identical length (294 base pairs) and GC base proportion (50%) in electrolytic solution under minor osmotic stress. Under conditions of low fluorescent labeling to avoid quenching, liquid- crystalline spherulites form, and the two DNAs within these structures prefer to self-associate rather than mix. The authors suggest, based on their recent theoretical work, that association between identical DNAs is favored as this arrangement maintains registry of the phosphate backbone and surrounding counterions; different sequences result in small changes in pitch that can disrupt these interactions and extract an energetic penalty. Other mechanisms may also operate, but dsDNA recognition occurs in the presence of intervening solution.

*.* Source of Information : 15th February 2008 Science

What’s It All Good For?

Written by Science Knowledge on 11:25 PM

Enzyme kinetics is a subject dreaded by all but hard-core biochemists. Purifying proteins and measuring product generated or substrate consumed at varying concentrations of enzyme and substrate—not to mention the characterization of competitive and noncompetitive inhibitors— and then integrating these data within a mechanistic scheme that spits out rate constants… well, this is not the stuff that dreams are made of, and neither is reading someone else’s enzyme kinetics papers.

Umejiego et al. have applied this kind of information (a random order of substrate binding and a rate-limiting hydrolysis of the covalent enzyme intermediate) in designing a small-molecule screen for inhibitors of the enzyme inosine- 5’-monophosphate dehydrogenase (IMPDH). Why should we care? Because IMPDH salvages purines in order to supply guanine in the human pathogen Cryptosporidium parvum, and because the C. parvum enzyme differs enough from human IMPDH to serve as a drug target. By screening under kinetically defined conditions where the conserved IMP site was occupied, whereas the less conserved NAD site was empty, they managed to fish out 10 candidates from a starting pool of 44,000 compounds. Four of these were more potent inhibitors of C. parvum growth than the standard drug paromomycin in a cell culture assay.

*.* Source of Information : 15th February 2008 Science

The More the Merrier

Written by Science Knowledge on 11:03 PM

The relationship between the number of species in an ecological community and the functional aspects of the ecosystem is usually studied experimentally by observing the effects of random changes in diversity. However, a study of rocky intertidal pools reveals that the nonrandom variation in species diversity that is characteristic of natural habitats yields better predictions of functional effects than experiments in which the species composition is altered randomly. Bracken et al. quantified the effects of both kinds of variation in seaweed diversity on nutrient dynamics (nitrogen uptake) in a set of tide pools in which the number of species increased as disturbance (caused by heavy surf) decreased. The effects of natural realistic variation were compared with the effects of artificial diversity gradients established by random groupings of species. Increased diversity in the “real-world” pools was associated with higher rates of nutrient acquisition by the plants, whereas the artificial communities showed no relationship. These results present new challenges for experimental ecologists studying the consequences of biodiversity loss in ecosystems.


*.* Source of Information : 15th February 2008 Science

Living off the Air

Written by Science Knowledge on 10:51 PM

Aeroponics—cultivating plants without soil or water—started to take off in 1983 when Rick Stonerof Agrillouse, a company in Berthoud, Colorado, patented a water-conserving, pesticide-free way to grow crops. NASA chipped in funding for application to potential future space colonies. The colonies are still beyond the horizon, but commercial production of air-grown veggies is becoming a reality. Optometrist La, Forrest of Frederick, Colorado, has expanded his aeroponic greenhouse to about 150 square meters, which may make him the world's largest aeroponicfarmer. His company, Crow Anywhere Air-Foods, grows tiny seedlings of mesclun and other greensfor restaurants; misting their roots with a nitrogen and calcium rich spray every 20 minutes. Forrest's equipment involves several thousand nozzles, pipes, and other parts. But he says he is working on a simpler, cheaper 500-part system to sell to like-minded growers.

This is the first I've seen someone else trying to make a go of it, says (Award Harwood, who patented an aeroponic system with a cloth conveyer belt but couldn't make it pay. As far as the U.S. growers know, the technique hasn't caught on anywhere else in the world. But Stoner sees a big potential: The technology can be set up anywhere, including Iceland or Antarctica, he says.

*.* Source of Information : 4th April 2008 Science


Third Party Parasitism

Written by Science Knowledge on 9:34 PM

For more than 50 million years, Agaonidae wasps have laid their eggs in the ovules of the enclosed flowers, or syconia, of fig trees. The grubs stimulate the formation of a small gall and feed on the plant, tissue. The payback for the loss of reproductive power to the fig tree occurs when the young wasps emerge and carry their host's pollen to other trees. Fortunately for the trees, wasps don, Lay eggs in every ovule in a syconium, even though in evolutionary terms this might seem a good strategy for the wasp; rather than being deterred by the tree itself, the fig wasps are in fact preyed on by another wasp. The parasitoid's ovipositor is just long enough to penetrate the wall of the fig and reaches only the outer most ovules. Dunn et al. show that thanks to the packing architecture of the ovules within the syconium, the fig wasps predominantly use inner ovules that are out of range of the parasitoid, allowing the other ovules to mature into fig seeds and thereby stabilizing this mutualism.

*.* Source of Information : 4th April 2008 Science

Imaging Satellite - The Best View Yet from Space

Written by Science Knowledge on 9:51 PM

When the GeoEye-1 surveillance satellite comes online this spring, its advanced optics will produce more-detailed images than any commercial satellite, capturing objects as small as home plate on a baseball diamond and filling in the fuzzy spots on Google Earth.

How to Capture Images from 425 miles up

1. GET INTO ORBIT
The 4,400-pound GeoEye-1 will travel 425 miles into space on the back of a Delta 2 rocket from Vandenberg Air Force Base near Lompoc, California. Over the satellite’s planned seven-year life, it will be able to adjust its orbital altitude by 60 miles, which it will need to do to maintain a consistent view of Earth: Atmospheric drag and pressure from solar winds will gradually push the satellite down.

2. RECEIVE COMMANDS
GeoEye operators send instructions on what and when to photograph from one of four ground stations in Alaska, Virginia, Norway and Antarctica. Even though the satellite will be used commercially, all transmissions are encrypted under the licensing terms of the National Oceanic and Atmospheric Administration.

3. GET IN POSITION
GeoEye-1 is the fi rst non-military satellite to use military-grade GPS units, highly accurate devices that tell the satellite exactly where it is in the sky. Two star trackers calibrate the camera’s location and angle based on known star coordinates. Combined, these systems can pinpoint an object’s position on the ground within nine feet, 1.5 times as accurate as previous satellites.

4. ALIGN THE CAMERA
Once the satellite is over the target a New York City block or a miles-wide patch of rainforest in Brazil—reaction wheels spin to orient it. As it nears the proper position, the wheels spin in reverse to halt the satellite’s rotation and train the camera on the target.

5. CHECK THE LIGHTING
Ground control calculates the sun’s and the satellite’s angle to Earth to determine exposure time. Because the satellite’s 16-inch resolution depends critically on the precise shape and spacing of the optics, they are sealed in a tube and kept at around 72°F to prevent them from warping in the widely varying temperatures of space. The tube’s door opens only when the camera is ready to take an image.

6. TAKE THE SHOT
The camera scans the target in 20,000 37,500-by-1-pixel strips every two seconds, allowing it to easily create a 90-billion-pixel image (about 6,000 square miles) in two minutes. A data-processing unit compresses the image files and stores them on a one-terabyte solid-state drive.

7. BEAM IT DOWN
The sat can capture an area the size of Texas every day. It downloads encrypted images to the ground stations 40 times a day over radio waves. Once GeoEye combines the strips into full images, they are sent to buyers including Google Earth and countries with limited or no surveillance satellites, as well as the government’s National Geospatial-Intelligence Agency, which is Geo-Eye’s primary customer.

*.* Source of Information : April 2008 Popular Science

Edible Antifreeze

Written by Science Knowledge on 11:42 PM

Borrowing a trick from the Arctic snow fl ea could banish freezer burn.

Putting food back in the freezer after it thaws causes ice crystals to grow, imparting the unwelcome crunchy texture and mildew-like taste of freezer burn. Now food chemist Srinivasan Damodaran of the University of Wisconsin–Madison has derived edible antifreeze from papaya enzymes and gelatin. His concoction, which stunts ice-crystal growth, promises always-creamy ice cream and juicier T-bones, even after their third trip between icebox and table. While studying gelatin, Damodaran realized that its protein is similar to the one that keeps the lowly snow flea from freezing in Arctic temperatures. To isolate the molecule involved, he mixed the gelatin with papaya enzymes, which are excellent at freeing proteins from other cellular material, and separated all the protein chunks by size. Then he mixed each batch with ice cream. The final step was to subject the dessert to a series of temperature changes until he found the one that remained ice-crystal-free. Damodaran still wants to better understand how the proteins work, but a patent for the process is in the works. In a few years, ice cream with a beard of frost should be a relic.

*.* Source of Information : May 2008 Popular Science

Surrogate Goats

Written by Science Knowledge on 10:00 PM

For mothers who have trouble breastfeeding or risk passing on HIV to their children, fortified goat milk could soon be the best alternative. Scientists at the Russian Academy of Sciences have genetically engineered goats that carry the human gene for the protein lactoferrin, normally found only in high concentrations in breast milk. The protein, which is absent in baby formula, is critical because it protects infants from bacteria and viruses while their immune systems are still maturing. In the next few years, scientists aim to stock a farm with engineered goats that would make fortified milk for rural villages, helping to lower infection babies.

*.* Source of Information : May 2008 Popular Science

Inside The Tsunami Factory

Written by Science Knowledge on 9:30 PM

Tsunami
What causes a monster wave? Scientists are drilling seismic hot zones to find out.

Over the past 1,300 years, the Nankai Trough, the 500-mile-long boundary between two tectonic plates off the southwestern coast of Japan, has been one of the world’s most active tsunami hotspots. Now an international team of scientists has embarked on a multiyear project to drill four miles down into the heart of this subterranean wave machine. The Nankai Trough Seismogenic Zone
Experiment, called Nantroseize, will be the first attempt to penetrate a tsunami generating hotspot and could help scientists understand the source of the huge swells. “We can monitor the ocean all we want, but we’ll never understand why some earthquakes produce tsunamis and why others do not until we understand how faults work,” says geophysicist Nathan Bangs of the University of Texas.

Last year, prior to drilling, researchers aboard captured 3-D seismic images of the fault zone where one plate slips beneath the other. The images helped the scientists pick the best spots to drill, but they also revealed new, steeper faults in the rock. Bangs says these near-vertical faults could explain why the Nankai Trough produces roughly one monster earthquake (8+ on the Richter scale) every 150 years.

More answers should come in the next four years, as researchers drop a drill down to the ocean floor and send it churning into as much as 20,000 feet of rock. By dropping seismometers and other instruments into the holes, they will be able to monitor the fault zone in real time. Although most scientists doubt that they will ever truly be able to predict tsunamis, the information could help identify other potential tsunami hotspots around the globe.

*.* Source of Information : May 2008 Popular Science

Why do some people dream?

Written by Science Knowledge on 12:05 AM

Why do some people dream more than others? Unless you’re a character in A Nightmare on Elm Street, you probably dream the same amount as everyone else: upward of two hours a night, according to the National Institutes of Health. The brain’s sleep cycle, however, makes it extremely difficult to remember dreams. “During sleep, our memory systems are completely shut down, and we’re basically living on a self-erasing tape,” explains neurologist Mark Mahowald, director of the Minnesota Regional Sleep Disorders Center. It’s like the “record” button in your brain has been switched off.

So why is it that some people regularly recall the intricate plots of their bizarre dreams? “The primary determinant of whether you’re going to remember a dream is if you awaken during it,” Mahowald says. Waking up snaps your memory into action, and it absorbs the bits of a dream that might otherwise fade into your subconscious. Frequent wakers are more likely to remember their dreams than deep sleepers, he adds. The content of your dreams might also play a role in retrieving your somnolent synapses. Bad dreams typically jolt you awake, so people who suffer from frequent nightmares may also be more likely to remember what they dream.

Research on dreaming has shown that it’s possible to train yourself to better recall whatever you were dreaming about just prior to waking up, says Alan Manevitz, a psychiatrist at Weill Cornell Medical Center in New York.

*.* Source of Information : May 2008 Popular Science

WHY IS YAWNING CONTAGIOUS?

Written by Science Knowledge on 11:37 PM

Go ahead; admit it—you’re yawning right now. That’s OK, we forgive you. We know it’s not because you’re bored. It’s just that seeing other people yawn, reading about yawning, or even just thinking about it can make you yawn. And it’s a good thing, too: Passing yawns around a campfi re might have kept our ancestors alive.

Picking up another person’s yawn may be an empathetic refl ex, says evolutionary psychologist Gordon Gallup of the State University of New York at Albany. When you see someone yawn, neurons in your brain fi re and cause you to “feel” what that person is experiencing, commanding you to perform the action even if you don’t actually feel the need.

Scientists have yet to figure out why we yawn at all, though. Some say it signals boredom, whereas others have suggested that it balances carbon dioxide and oxygen levels in the blood. Most recently, Gallup theorized in a study last year that yawns cool our brains so that they run effi ciently, similar to running a fan in a computer. He found that, contrary to common perception, cooling the brain with a yawn keeps people from nodding off.

Alternatively, E.O. Smith, an emeritus professor of anthropology at Emory University, contends that yawning may have encouraged our ancestors to go to bed early. “Contagious yawning didn’t arise in a vacuum on a Saturday afternoon,” Smith says. Spreading a case of the yawns around a bonfi re, he posits, may have prompted night owls to climb up into their comfy tree beds with their sleepier brethren, out of danger from stealthy predators.

*.* Source of Information : May 2008 Popular Science


About Me

In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.


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