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Trees are source for high-capacity, soft batteries

A closeup of the soft battery, created with wood pulp nanocellulose. Credit: Courtesy of Max Hamedi and Wallenberg Wood Science Center
A closeup of the soft battery, created with wood pulp nanocellulose.
Credit: Courtesy of Max Hamedi and Wallenberg Wood Science Center

A method for making elastic high-capacity batteries from wood pulp was unveiled by researchers in Sweden and the US. Using nanocellulose broken down from tree fibres, a team from KTH Royal Institute of Technology and Stanford University produced an elastic, foam-like battery material that can withstand shock and stress.

“It is possible to make incredible materials from trees and cellulose,” says Max Hamedi, who is a researcher at KTH and Harvard University. One benefit of the new wood-based aerogel material is that it can be used for three-dimensional structures.

“There are limits to how thin a battery can be, but that becomes less relevant in 3D, ” Hamedi says. “We are no longer restricted to two dimensions. We can build in three dimensions, enabling us to fit more electronics in a smaller space.”

A 3D structure enables storage of significantly more power in less space than is possible with conventional batteries, he says.

“Three-dimensional, porous materials have been regarded as an obstacle to building electrodes. But we have proven that this is not a problem. In fact, this type of structure and material architecture allows flexibility and freedom in the design of batteries,” Hamedi says.

The process for creating the material begins with breaking down tree fibres, making them roughly one million times thinner. The nanocellulose is dissolved, frozen and then freeze-dried so that the moisture evaporates without passing through a liquid state.

Then the material goes through a process in which the molecules are stabilised so that the material does not collapse.

“The result is a material that is both strong, light and soft,” Hamedi says. “The material resembles foam in a mattress, though it is a little harder, lighter and more porous. You can touch it without it breaking.”

The finished aerogel can then be treated with electronic properties. “We use a very precise technique, verging on the atomic level, which adds ink that conducts electricity within the aerogel. You can coat the entire surface within.”

In terms of surface area, Hamedi compares the material to a pair of human lungs, which if unfurled could be spread over a football field. Similarly, a single cubic decimeter of the battery material would cover most of a football pitch, he says.

“You can press it as much as you want. While flexible and stretchable electronics already exist, the insensitivity to shock and impact are somewhat new.”

Hamedi says the aerogel batteries could be used in electric car bodies, as well as in clothing, providing the garment has a lining.

The research has been carried out at the Wallenberg Wood Science Center at KTH. KTH Professor Lars Wågberg also has been involved, and his work on aerogels is in the basis for the invention of soft electronics. Another partner is leading battery researcher, Professor Yi Cui from Stanford University.


Story Source:

The above story is based on materials provided by KTH The Royal Institute of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Gustav Nyström, Andrew Marais, Erdem Karabulut, Lars Wågberg, Yi Cui & Mahiar M. Hamedi. Self-Assembled Three-Dimensional And Compressible Interdigitated Thin Film Supercapacitors And Batteries. Nature Communications, May 29, 2015 DOI:10.1038/ncomms8259

What Is a Power Supply?

Solar panels are a type of power supply.
Solar panels are a type of power supply.

A power supply is a device that takes an incoming electrical current and amplifies it to levels required by various devices. In many instances, this type of device is also implemented to take the incoming electricity and deliver it across many other electronic devices, often at different preset levels. This device allows manufacturers to create electronics and machinery that can handle many different tasks from a single source of power, without the need for various adapters and additional hardware. Within other devices, a power supply is used to transform various types of power into a compatible format to be stored, like solar energy to electrical energy.

Perhaps the most common use of this type of device is within computer systems. As electricity enters the power supply, it is momentarily stored and then distributed to numerous functions throughout the system, allowing the motherboard, hard drive, and other various devices to receive electricity in order to function. Each one of these items requires a separate voltage, and it is delivered through specialized connectors that attach in a certain manner. For example, motherboards require either a 20-pin or a 24-pin power supply, and they are not interchangeable without the purchase of an additional adapter.

Modern vehicles also require a type of power supply in order to function, and it is referred to as an alternator. Although the wiring and design may be different, it essentially works in the exact same manner by taking incoming power and delivering it throughout the vehicle at the necessary levels. Alternators can be found on everything from lawn mowers to sea craft and industrial equipment, and without them, the devices would be rendered useless.

automobile alternator - Winged Post 0419515
An automobile engine’s alternator essentially serves as an electric generator.

Another common type of power supply can be found on windmills and solar panels, and its primary function is to convert various types of energy into electricity so that it can be stored and distributed across a grid. This is referred to as a generator, and it is often a free-standing object that is installed between the power source and the storage unit. Home and commercial generators, used during power outages, also work off of this same premise by transforming petroleum products into electrical energy by means of an engine. Many types of industrial tools also implement a type of generator. Other common types of power supplies are used within circuit breakers, battery-powered items and transformers.

 

Source / Courtesy : WiseGeek

Synthetic spider silk strong enough for a superhero

Spider silk web Winged Post

Spider silk of fantastical, superhero strength is finally speeding toward commercial reality — at least a synthetic version of it is. The material, which is five times stronger than steel, could be used in products from bulletproof vests to medical implants, according to an article in Chemical & Engineering News(C&EN).

Alex Scott, a senior editor at C&EN, notes that spider silk’s impressive strength has been studied for years, and scientists have been trying to make a synthetic version of the super-strong protein in the lab. For other simpler proteins, scientists have been able to insert relevant genes into bacterial DNA, essentially turning the microorganisms into protein factories. But spider silk has not been so easy to churn out. In fact, the challenge has caused big name companies including DuPont and BASF to bow out after several years of investment.

Now, small firms just might have found the right genetic tricks, the article states. They are coaxing not just genetically engineered bacteria but also goats, transgenic silkworms and even alfalfa to produce multiple different versions of synthetic spider and spider-silkworm silks. One company has even taken their iteration to the market — though theirs is a non-fiber kind of spider silk for use in cosmetics. So far, commercialization has been on a modest scale. But the research pipeline for synthetic spider silk is very active, and scientists expect that production is right on the verge of scaling up.


Story Source:

The above story is based on materials provided by American Chemical Society. Note: Materials may be edited for content and length.


Journal Reference:

  1. Alex Scott. Spider Silk Poised For Commercial Entry. Chemical & Engineering News, 2014; 92 (9): 24-27 [link]

Sports: ‘Performance enhancing’ drugs decrease performance

Comparisons were made between pre-1932 records (when steroids became available) and post, and it was found that the times, distances and other results did not improve as expected in the doping era. Credit: © berc / Fotolia
Comparisons were made between pre-1932 records (when steroids became available) and post, and it was found that the times, distances and other results did not improve as expected in the doping era.
Credit: © berc / Fotolia

Doping is damaging the image of sport without benefiting athletes’ results, according to University of Adelaide research.

Researchers from the University’s School of Medical Sciences collated sporting records (including Olympic and world records) of male and female athletes across 26 sports, between 1886 and 2012. Comparisons were made between pre-1932 records (when steroids became available) and post, and it was found that the times, distances and other results did not improve as expected in the doping era.

The findings were published in the Journal of Human Sport and Exercise.

“The effects of doping in modern sports are far and widespread, encompassing not only the athletes and sporting teams involved, but also sponsors and fans,” says Dr Aaron Hermann, lead author on the paper.

“This research looked at 26 of the most controlled and some of the most popular sports, including various track and field events like 100m sprints, hurdles, high jump, long jump and shot-put, as well as some winter sports like speed skating and ski jumping.

“The average best life records for ‘doped’ top athletes did not differ significantly from those considered not to have doped. Even assuming that not all cases of doping were discovered during this time, the practice of doping did not improve sporting results as commonly believed,” he says.

Dr Hermann says these results not only demonstrate the negative impact of doping on sports results but may also show that doping is more widespread than initially thought.

“The 2000 Olympics gold medal result for the women’s 100m sprint was even poorer than the gold medal obtained in the 1968 Olympics, the first year of doping testing in the Olympics,” Dr Hermann says.

“This research demonstrates that doping practices are not improving results and in fact, may be harming them — seemingly indicating that ‘natural’ human abilities would outperform the potentially doping ‘enhanced’ athletes — and that in some sports, doping may be highly prevalent,” he says.

Dr Hermann hopes these findings will change elite athletes’ and junior sports participants’ perceptions on doping.

“The success rate of doping tests may be as little as 4% and some anti-doping initiatives to date have been very ineffective,” says Dr Hermann.

“Doping may produce a minor improvement in one aspect of performance but in other areas, it may have a detrimental effect, which outweighs the positive.

“In many sports, there are perceptions that an athlete needs to dope in order to remain competitive and I hope these findings will confront those ill-informed views, and help stamp out doping in sport,” he says.


Story Source:

The above story is based on materials provided by University of Adelaide.Note: Materials may be edited for content and length.


Journal Reference:

  1. Aaron Hermann, Maciej Henneberg. Long term effects of doping in sporting records: 1886-2012. Journal of Human Sport and Exercise, 2014; 9 (3): 727 DOI: 10.14198/jhse.2014.93.05

Just like humans, dolphins have complex social networks

Through intensive photo-ID surveys conducted along the Indian River Lagoon, which were carried out over a six- and-a-half year period, researchers from Harbor Branch Oceanographic Institute at Florida Atlantic University were able to learn about the association patterns as well as movement behavior and habitat preferences of some 200 individual dolphins.

They may not be on Facebook or Twitter, but dolphins do, in fact, form highly complex and dynamic networks of friends, according to a recent study by scientists at Harbor Branch Oceanographic Institute (HBOI) at Florida Atlantic University. Dolphins are known for being highly social animals, and a team of researchers at HBOI took a closer look at the interactions between bottlenose dolphins in the Indian River Lagoon (IRL) and discovered how they mingle and with whom they spend their time.

Through intensive photo-ID surveys conducted along the IRL, which were carried out over a six- and-a-half year period, the researchers were able to learn about the association patterns as well as movement behavior and habitat preferences of some 200 individual dolphins.

In a paper recently published in the journal Marine Mammal Science, the team found that individual dolphins exhibited both preference and avoidance behavior — so just like humans, they have dolphins they like and associate with and ones they avoid. The study also found that IRL dolphins clustered into groups of associated animals, or “communities,” that tended to occupy discrete core areas along the north-south axis of the lagoon system.

“One of the more unique aspects of our study was the discovery that the physical dimensions of the habitat, the long, narrow lagoon system itself, influenced the spatial and temporal dynamics of dolphin association patterns,” said Elizabeth Murdoch Titcomb, research biologist at HBOI who worked on the study with Greg O’Corry-Crowe, Ph.D., associate research professor at HBOI; Marilyn Mazzoil, senior research associate at HBOI, and Elizabeth Hartel. “For example, communities that occupy the narrowest stretches of the Indian River Lagoon have the most compact social networks, similar to humans who live in small towns and have fewer people with whom to interact.”

In addition to providing a unique glimpse into dolphin societies, this novel study provides important insight and knowledge on how dolphins organize themselves, who they interact with and who they avoid, as well as when and where. It also gives scientists and resource managers the roadmap needed to understand how dolphin populations perceive and use their environment, and how social networks will influence information transfer and potentially breeding behavior and disease transmission.

The IRL is a 156-mile long estuary located on Florida’s east coast. The lagoon is long and narrow and composed of three distinct water bodies; Mosquito Lagoon, Banana River, and the Indian River. There are five inlets and one lock (Cape Canaveral lock) connecting the IRL to the Atlantic Ocean. The estuary ranges in width from a few meters to 9 kilometers and averages in depth at approximately 1.5 meters with maximum depths at around 4 meters. In 1990, the United States Environmental Protection Agency designated the IRL as an “Estuary of National Significance” to help preserve one of the most biodiverse estuaries in North America. Researchers from HBOI have been conducting photo identification studies of IRL bottlenose dolphins since 1996, identifying more than 1,700 individual dolphins. Among the findings enabled by this data is identification of a distinct IRL stock now breeding its third generation since the study began, and insights into breeding and social behavior.


Story Source:

The above story is based on materials provided by Florida Atlantic University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Elizabeth Murdoch Titcomb, Greg O’Corry-Crowe, Elizabeth F. Hartel, Marilyn S. Mazzoil. Social communities and spatiotemporal dynamics of association patterns in estuarine bottlenose dolphins. Marine Mammal Science, 2015; DOI: 10.1111/mms.12222

Academic Achievement Vs. Family Income

 

In middle-schoolers, neuroscientists find differences in brain structures where knowledge is stored. Credit: Illustration: Jose-Luis Olivares/MIT
In middle-schoolers, neuroscientists find differences in brain structures where knowledge is stored.
Credit: Illustration: Jose-Luis Olivares/MIT

 

Many years of research have shown that for students from lower-income families, standardized test scores and other measures of academic success tend to lag behind those of wealthier students.

A new study led by researchers at MIT and Harvard University offers another dimension to this so-called “achievement gap”: After imaging the brains of high- and low-income students, they found that the higher-income students had thicker brain cortex in areas associated with visual perception and knowledge accumulation. Furthermore, these differences also correlated with one measure of academic achievement — performance on standardized tests.

“Just as you would expect, there’s a real cost to not living in a supportive environment. We can see it not only in test scores, in educational attainment, but within the brains of these children,” says MIT’s John Gabrieli, the Grover M. Hermann Professor in Health Sciences and Technology, professor of brain and cognitive sciences, and one of the study’s authors. “To me, it’s a call to action. You want to boost the opportunities for those for whom it doesn’t come easily in their environment.”

This study did not explore possible reasons for these differences in brain anatomy. However, previous studies have shown that lower-income students are more likely to suffer from stress in early childhood, have more limited access to educational resources, and receive less exposure to spoken language early in life. These factors have all been linked to lower academic achievement.

In recent years, the achievement gap in the United States between high- and low-income students has widened, even as gaps along lines of race and ethnicity have narrowed, says Martin West, an associate professor of education at the Harvard Graduate School of Education and an author of the new study.

“The gap in student achievement, as measured by test scores between low-income and high-income students, is a pervasive and longstanding phenomenon in American education, and indeed in education systems around the world,” he says. “There’s a lot of interest among educators and policymakers in trying to understand the sources of those achievement gaps, but even more interest in possible strategies to address them.”

Allyson Mackey, a postdoc at MIT’s McGovern Institute for Brain Research, is the lead author of the paper, which appears the journal Psychological Science. Other authors are postdoc Amy Finn; graduate student Julia Leonard; Drew Jacoby-Senghor, a postdoc at Columbia Business School; and Christopher Gabrieli, chair of the nonprofit Transforming Education.

Explaining the gap

The study included 58 students — 23 from lower-income families and 35 from higher-income families, all aged 12 or 13. Low-income students were defined as those who qualify for a free or reduced-price school lunch.

The researchers compared students’ scores on the Massachusetts Comprehensive Assessment System (MCAS) with brain scans of a region known as the cortex, which is key to functions such as thought, language, sensory perception, and motor command.

Using magnetic resonance imaging (MRI), they discovered differences in the thickness of parts of the cortex in the temporal and occipital lobes, whose primary roles are in vision and storing knowledge. Those differences correlated to differences in both test scores and family income. In fact, differences in cortical thickness in these brain regions could explain as much as 44 percent of the income achievement gap found in this study.

Previous studies have also shown brain anatomy differences associated with income, but did not link those differences to academic achievement.

In most other measures of brain anatomy, the researchers found no significant differences. The amount of white matter — the bundles of axons that connect different parts of the brain — did not differ, nor did the overall surface area of the brain cortex.

The researchers point out that the structural differences they did find are not necessarily permanent. “There’s so much strong evidence that brains are highly plastic,” says Gabrieli, who is also a member of the McGovern Institute. “Our findings don’t mean that further educational support, home support, all those things, couldn’t make big differences.”

In a follow-up study, the researchers hope to learn more about what types of educational programs might help to close the achievement gap, and if possible, investigate whether these interventions also influence brain anatomy.

“Over the past decade we’ve been able to identify a growing number of educational interventions that have managed to have notable impacts on students’ academic achievement as measured by standardized tests,” West says. “What we don’t know anything about is the extent to which those interventions — whether it be attending a very high-performing charter school, or being assigned to a particularly effective teacher, or being exposed to a high-quality curricular program — improves test scores by altering some of the differences in brain structure that we’ve documented, or whether they had those effects by other means.”


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Anne Trafton. Note: Materials may be edited for content and length.

What Is Diode Voltage Drop?

Diodes

 

A diode is a common semiconductor device used in many different types of electronic circuits. When an electrical signal passes through a diode, the diode consumes a small amount of the signal’s voltage in its operation. The difference between the voltage of the signal entering the diode and the voltage of the signal exiting the diode is the diode voltage drop. Although a diode voltage drop can refer to either the diode’s forward or reverse voltage drop, it typically describes the forward voltage drop.

The construction of a diode involves joining an anode and a cathode, two pieces of material with different electrical charges. The anode is positively charged and the cathode is negatively charged. At the point where these two different materials meet, called the junction, the two different opposing charges effectively cancel each other out. This area without a charge is the diode’s depletion layer, which forms an insulating layer within the diode between the anode and cathode.

When an electrical signal enters a diode’s cathode, the additional negative force increases the width of the depletion layer as it reacts with the positively charged anode. The wider depletion layer will block the signal from passing through the diode and consume all of the voltage in the process. For example, if 5 volts enter the diode, the diode voltage drop will also be 5 volts. A diode in this state is reverse biased, and the voltage drop is the diode’s reverse voltage drop.

An electrical signal entering a diode’s anode creates a different set of conditions within the diode. The negatively charged signal will bridge across the anode, meet the cathode, and pass through the diode, continuing on to the rest of the circuit. In the process, a relatively small amount of thevoltage is lost overcoming the anode’s positive charge. For a typical silicon diode, the voltage lost is approximately 0.7 volts. A diode in this state is forward biased, and the voltage drop is the diode’s forward voltage drop.

The difference between the forward and reverse states in a diode permits them to block a signal in one direction by dropping 100% of the voltage but allowing it to pass in the other by only dropping a small amount. As most diodes have a reverse voltage drop of 100%, the assumption is that the term “diode voltage drop” refers to the forward voltage drop; however, this is not always the case.

Specialty diodes exist that do not drop 100% of the reverse voltage, such as varicap or varactor diodes. In these diodes, the charges of the cathodes and anodes are not even across their widths. As a result, these diodes can allow part of the signal entering the cathode to pass through the diodes even though they are in a reverse biased state. When describing the voltage drop in these types of diodes, it is important to differentiate between the forward and reverse voltage drops.

 

Source / Courtesy : WiseGeek

What Is Voltage Drop?

 

A multimeter can be used to measure voltage drop.
A multimeter can be used to measure voltage drop.

Voltage drop is a term used to describe any reduction in the supply voltage in a complete electrical circuit. The term may be used to describe a voltage loss across a specific component in the circuit, the voltage loss measured across the entire circuit, or as a broad description of the phenomenon of voltage loss in a circuit in general. All electrical circuits, no matter how simple, present a certain amount of resistance to the flow of electrical current through them. This resistance effectively makes the electrical current work harder, and thus absorbs energy. This expenditure of energy is what causes the reduction in voltage described by the term voltage drop.

For example, a simple circuit can be made up of a 9-volt battery attached to a simple flash light bulb with a small switch. If one were to measure the voltage across the batteries terminals with the switch open, the multimeter reading would be approximately 9 volts. If one were to close the switch and illuminate the bulb, that reading would drop by approximately 1.5 volts. That reduction in voltage is what is known as a voltage drop, and it comes about as the result of the work the battery has to do to illuminate the bulb. Each and every component in a circuit, including the wiring, offers a certain amount of resistance to the flow of electrical current and will cause an associated voltage drop.

In applications that are extremely supply voltage sensitive, such as electronic devices, these voltage losses have to be carefully calculated and the supply voltage adjusted to make provision for them. A 12 volt direct current (DC) power supply, for instance, will typically produce an output of 13.8 volts to accommodate this voltage drop phenomenon. In applications that require very long cable runs, it is common practice to uses fairly heavy cables that present less resistance to the flow of electric current in an attempt to minimize the effects of voltage losses. The total potential loss of voltage in any circuit thus needs to be carefully calculated during the design and specification phase of a project to ensure that the final result meets all requirements.

Any voltage loss in a circuit can, fortunately, be calculated with great accuracy using a voltage drop formula. This makes it possible to achieve consistent and predictable results at the end of an installation. These calculations will differ according to the type of circuit, voltage supply, and components involved and can be extremely complex, often requiring the use of a voltage drop calculator. They do, however, take the guess work of accurately adjusting power supply specifications to accommodate circuit resistance.

 

Source / Courtesy : WiseGeek

What Is Electrical Energy?

On a diesel-electric locomotive, a diesel engine provides power to an electric traction motor that turns the unit's wheels.
On a diesel-electric locomotive, a diesel engine provides power to an electric traction motor that turns the unit’s wheels.

Electrical energy results from the movement of an electrical charge, and is commonly referred to as simply “electricity.” Ultimately, it has its origin in the electromagnetic force: one of the four fundamental forces of nature and the one that is responsible for the behavior of electrically charged objects. Electrical energy is the result of the interaction of subatomic particles with this force. Electricity manifests itself in natural phenomena such as lightning and is essential to life at a fundamental level. The ability of humans to generate, transmit and store electricity is crucial to modern industry, technology and, in most countries, domestic life.

The Origin of Electrical Energy

There are two types of electrical charge, called positive and negative. If two electrically charged objects are brought close to one another, they will experience a force. If the charges are the same — both positive or both negative — the force will act to push the objects away from one another. If they have different charges, they will attract one another. This repulsion or attraction is known as the electromagnetic force, and it can be harnessed to create a flow of electrical energy.

Atoms consist of a nucleus containing positively charged protons, with negatively charged electrons orbiting around it. Protons normally stay put in the nucleus, but electrons can move from atom to atom, allowing them to flow through materials, such as metals, that conduct electricity. A place with an excess of electrons over protons will have a negative charge; a place with a deficit will have a positive charge. Since opposite charges attract one another, electrons will flow from a negatively charged area to a positively charged one if allowed to do so, creating an electric current.

Using Electrical Energy

Electricity is useful both in itself and as a means of transferring energy over long distances. It is essential to various industrial processes, telecommunications and the Internet, computers, televisions and many other devices in common use. It can also be converted into other forms of energy for use in a variety of other applications.

When an electric current flows through a conductor, it generates a certain amount of heat. The amount generated depends on how well the material conducts electricity. A good conductor, such as copper, produces very little. For this reason, copper wires and cables are commonly used to transmit electricity: when heat is produced, energy is lost, so a good conductor minimizes energy loss. Materials that conduct electricity less well produce more heat, so they tend to be used in electric heaters, cookers and ovens, for example.

Electrical energy can also be converted into light. Early arc lights depended on an electrical discharge across a small gap to heat the air to the point where it glows — the same principle as lightning. Later, the filament light bulb was introduced: this relies on the current causing a thin, coiled wire to glow white-hot. Modern, energy-saving light bulbs pass a high voltage current through a thin gas, causing it to emit ultraviolet light, which strikes a fluorescent coating to produce visible light.

When a conducting material, such as a copper wire, is moved in a magnetic field, a current is generated. Conversely, a current flowing through a wire will, if it experiences a magnetic field, produce movement. This is the principle behind an electric motor. These devices consist of an arrangement of magnets and coils of copper wire such that when a current flows through the wire, a turning motion is produced. Electric motors are widely used in industry and in the home, for example in washing machines and DVD players.

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Measuring Electrical Energy

Energy is measured in joules, a term named after the physicist James Prescott Joule. One joule is roughly the amount of energy required to lift a one pound (0.45 kilogram) weight a vertical distance of nine inches (22.9 cm). It is, however, usually more convenient to think of electricity in terms of power, which is energy divided by time, or the rate at which it flows. This gives the possibly more familiar unit of the watt, named after the scientist James Watt. One watt is equivalent to one joule per second.

There are a number of other units that relate to electricity. The coulomb is the unit of electrical charge. It can be regarded as a quantity of electrons — 1.6 x 1019 — since all electrons have the same, very small, charge. The ampere, usually abbreviated to “amp”, is the unit of electric current, or the number of electrons that flow in a given amount of time. One amp is equivalent to one coulomb per second.

The volt is the unit of electromotive force, or the amount of energy that is transferred per unit of charge, or coulomb. One volt is equivalent to one joule of energy being transferred for each coulomb of charge. Power, in watts, is equivalent to volts multiplied by amps, so a five amp current at 100 volts would be equivalent to 500 watts.

Generating Electrical Energy

Most electricity is generated by devices that convert rotational motion into electrical energy, using the same principle as an electric motor, but in reverse. The movement of coils of wire within a magnetic field produces an electric current. Commonly, heat, often generated by the burning offossil fuels, is used to produce steam that powers a turbine to provide the rotational motion. In a nuclear power plant, nuclear energy provides the heat. Hydroelectric power uses the movement of water under gravity to drive the turbine.

The electricity generated at power plants is generally in the form of alternating current (AC). This means that the current is constantly reversing its direction, many times per second. For most purposes, AC works well, and this is how electricity reaches the home. Some industrial processes, however, require direct current (DC), which flows in one direction only. For example, the manufacture of certain chemicals uses electrolysis: the splitting of compounds into elements or simpler compounds using electricity. This requires direct current, so these industries will either require AC to DC conversion or will have their own DC supply.

It is more efficient to transmit electricity through power lines at higher voltages. For this reason, generating plants use devices called transformers to increase the voltage for transmission. This does not increase the energy or power: when the voltage is raised, the current is reduced and vice versa. Long distance transmission of electricity takes place at many thousands of volts; however, it cannot be used in homes at these voltages. Local transformers reduce the voltage to around 110 volts in the USA, and 220-240 volts in Europe, for domestic supplies.

Electricity for small, low power devices is often supplied by batteries. These use chemical energy to generate a relatively small electric current. They always generate a direct current, and therefore have a negative and a positive terminal. Electrons flow from the negative to the positive terminal when a circuit is completed.

 

Source / Courtesy : WiseGeek

ActiveGuard mattress liners reduce bed bugs

This is a bed bug, Cimex lectularius. Ohio State University entomologists found that ActiveGuard mattress liners reduce feeding and egg laying, even in bed bug populations that are resistant to pyrethroids. Credit: Gary Alpert, Harvard University, Bugwood.org, CC BY-NC 3.0 US
This is a bed bug, Cimex lectularius. Ohio State University entomologists found that ActiveGuard mattress liners reduce feeding and egg laying, even in bed bug populations that are resistant to pyrethroids.
Credit: Gary Alpert, Harvard University, Bugwood.org, CC BY-NC 3.0 US

 

Products that claim to control bed bugs have been on the market for years. Some work, and some don’t.

Dr. Susan Jones, a professor of entomology at Ohio State University, knows this as well as anyone, after having tested many such products for years. While there have been some flops in the past, she and her colleagues have found one that looks promising as a new tool for bed bug control programs. The results of their research are published in an article in the Journal of Medical Entomology.

Mattress liners sold under the trade name ActiveGuard are impregnated with an insecticide called permethrin, which is considered safe for humans and other mammals. Permethrin — which belongs to a class of pesticides called pyrethroids — is found in medical creams to treat scabies, shampoos for head lice, and it’s the active ingredient in some flea-control products for dogs and cats.

In recent years, however, some bed bug populations have developed resistance to some pyrethroids and related pesticides, making them less lethal. But for Jones and her team, killing bed bugs is only one part in the effort to control them.

“Death doesn’t have to be the end-point that we measure in studies,” Dr. Jones said. “Physical or behavioral changes can significantly affect the impact of bed bugs before death even occurs.”

One of these things is fecundity — the bed bugs’ ability to lay eggs and reproduce. In order to lay eggs, female bed bugs must first have a bloodmeal, so the Ohio researchers set out to test ActiveGuard’s effects on bed bug feeding.

“Feeding in bed bugs and fecundity are very tightly coupled,” Jones said. “If a female bed bug doesn’t feed, then she is unlikely to lay eggs, and if she doesn’t lay eggs, then the life cycle is interrupted.”

Surprisingly, they found the ActiveGuard fabric to be extremely effective, even in bed bug populations that were resistant to pyrethroids. Bed bugs that were exposed to the fabric for ten minutes were significantly less likely to even attempt feeding compared to those on untreated fabric, and the majority were unable to feed successfully. Even when they were successful, their bloodmeals were only half the size of bed bugs that were not exposed to the fabric.

Even more surprising, out of 52 females tested, only one laid a single egg.

“We were totally shocked, and we were also shocked by how quickly we started seeing these sublethal effects,” Jones said. “After just one minute of being on the fabric, their probing behavior was reduced, and by ten minutes they just weren’t feeding much. If a female bed bug doesn’t feed, she doesn’t lay eggs.”

The researchers do not yet know how or why the ActiveGuard fabric affects female bed bug feeding and fecundity — it may disorient or irritate them, but at this point that is only speculation.

“We are still trying to figure out what is going on,” Jones said. “That will be a future paper.”

Previous research by Dr. Jones showed that ActiveGuard was very effective at killing some bed bug populations, but was less so with ones that were resistant to pyrethroids. The results of this study suggest that even sublethal exposure can have far-reaching consequences.


Story Source:

The above story is based on materials provided by Entomological Society of America. Note: Materials may be edited for content and length.


Journal Reference:

  1. Susan C. Jones , Joshua L. Bryant , Frances S. Sivakoff. Sublethal Effects of ActiveGuard Exposure on Feeding Behavior and Fecundity of the Bed Bug (Hemiptera: Cimicidae). Journal of Medical Entomology, March 2015 DOI:10.1093/jme/tjv008