#Calculations find best phosphors for better LEDS University of California Santa barbara rightoriginal Studyposted by Sonia Fernandez-UCSB on November 12 2013new research makes it possible to optimize phosphorsâ##a key component in white
LED lightingâ##allowing for brighter more efficient lights. hese guidelines should permit the discovery of new and improved phosphors in a rational rather than trial-and-error mannersays Ram Seshadri a professor in the department of materials at University of California
Santa barbara as well as in the department of chemistry and biochemistry of the findings. The results of this research performed jointly with materials professor Steven Denbaars
and postdoctoral associate researcher Jakoah Brgoch appear in The Journal of Physical chemistry C. LED (light-emitting diode) lighting has been a major topic of research due to the many benefits it offers over traditional incandescent or fluorescent lighting.
LEDS use less energy emit less heat last longer and are less hazardous to the environment than traditional lighting.
Already utilized in devices such as street lighting and televisions LED TECHNOLOGY is becoming more popular as it becomes more versatile and brighter.
According to Seshadri all of the recent advances in solid-state lighting have come from devices based on gallium nitride LEDS a technology that is largely credited to UC Santa barbara materials professor Shuji Nakamura who invented the first high-brightness
blue LED. In solid-state white lighting technology phosphors are applied to the LED chip in such a way that the photons from the blue gallium nitride LED pass through the phosphor
which converts and mixes the blue light into the green-yellow-orange range of light. When combined evenly with the blue the green-yellow-orange light yields white light.
The notion of multiple colors creating white may seem counterintuitive. With reflective pigments mixing blue and yellow yields green;
however with emissive light mixing such complementary colors yields white. Until recently the preparation of phosphor materials was more an art than a science based on finding crystal structures that act as hosts to activator ions
which convert the higher energy blue light to lower energy yellow/orange light. o far there has been no complete understanding of
what make some phosphors efficient and others notseshadri says. n the wrong hosts some of the photons are wasted as heat
and an important question is: How do we select the right hosts? s LEDS become brighter for example as they are used in vehicle front lights they also tend to get warmer
and inevitably this impacts phosphor properties adversely. ery few phosphor materials retain their efficiency at elevated temperaturesbrgoch says. here is little understanding of how to choose the host structure for a given activator ion such that the phosphor is efficient and such that
the phosphor efficiency is retained at elevated temperatures. owever using calculations based on density functional theory the researchers have determined that the rigidity of the crystalline host structure is a key factor in the efficiency of phosphors:
The better phosphors possess a highly rigid structure. Furthermore indicators of structural rigidity can be computed using density functional theory allowing materials to be screened before they are prepared and tested.
This breakthrough puts efforts for high-efficiency high-brightness solid-state lighting on a fast track.
Lower-efficiency incandescent and fluorescent bulbsâ##which use relatively more energy to produce lightâ##could become antiquated fixtures of the past. ur target is to get to 90 percent efficiency
or 300 lumens per wattsays Denbaars who also is a professor of electrical and computer engineering and co-director of the Solid State Lighting & Energy Center.
#Photon detector is quantum leap from semiconductors A new superconducting detector array can measure the energy of individual photons.
The design and construction of an instrument based on these arrays as well as an analysis of its commissioning data appear in the Publications of the Astronomical Society of the Pacific. hat we have made is essentially a hyperspectral video camera with no intrinsic noisesays Ben Mazin assistant professor
of physics at University of California Santa barbara. n a pixel-per-pixel basis it s a quantum leap from semiconductor detectors;
it s as big a leap going from film to semiconductors as it is going from semiconductors to these superconductors.
through near-IR using Microwave Kinetic Inductance Detectors (MKIDS. An MKID is a type of superconducting photon detector;
microwave refers to the readout frequency rather than the frequency at which the detectors operate.
MKIDS were developed first a decade ago by Mazin his Ph d. adviser Jonas Zmuidzinas professor of physics at the California Institute of technology and Henry Leduc at NASA s Jet propulsion laboratory.
MKIDS are used in astronomy for taking measurements across the electromagnetic spectrum. In his lab at UC Santa barbara Mazin has adapted these detectors for the ultraviolet optical and near-IR parts of the spectrum.
Superconductivity is a quantum phenomenon that occurs as certain materials are cooled to near absolute zero thereby eliminating all electrical resistance and magnetic fields.
MKIDS which operate at cryogenic temperatures (typically 0. 1 Kelvin) allow astronomers to determine the energy
and arrival time of individual photons. orty years ago we were doing optical astronomy with photographic plates
which use light to change a chemical emulsionmazin explains. hen we switched from photographic plates to the charge couple devices (CCDS) contained in today s electronics per-pixel performance of the detectors went up by a factor of 20. n the last decade CCDS
and other semiconductor-based detectors for the optical and near-IR have started to hit fundamental limits in their per-pixel performancemazin adds. hey ve gotten about as good as they can get in a given pixel.
The way they continue to improve is by making huge pixel mosaics which is appropriate for many
which enable thousands of devices to be read out over a single microwave feed line.
The size of the arrays is limited by the microwave readout which uses very similar technology to a cellphone base station.
This means the number of MKIDS that can be read out for a given price is increasing according to Moore s Lawâ##overall processing power for computers doubles every two yearsâ
##which should enable megapixel arrays within a decade. Mazin and his team lens-coupled a 2024-pixel array to the Palomar 200-inch and the Lick 120-inch telescopes in Southern California and Northern California respectively.
ARCONS was on these telescopes for 24 observing nights during which data was collected on optical pulsars compact binaries high redshift galaxies and planetary transits.
RCONS is very sensitive but it s been coupled with 5-meter telescopesmazin says. he 8-to 10-meter telescopes such as Keck are at better sites with four times the collecting area. e hope to deploy MKID instruments in the next several
years at Keck and other telescopes to make fascinating new observations including using MKIDS coupled to a coronagraph to directly discover
and take spectra of planets around nearby stars. Source: UC Santa Barbar
#Wireless device grabs lost energy from Wi-fi Using inexpensive materials configured and tuned to capture microwave signals researchers have designed a power harvesting device with efficiency similar to that of modern solar panels.
The device wirelessly converts the microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device according to a report appearing in Applied Physics Letters.
It operates on a similar principle to solar panels which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources including satellite signals sound signals
or Wi-fi signals the researchers say. The key to the power harvester lies in its application of metamaterials engineered structures that can capture various forms of wave energy and tune them for useful applications.
Undergraduate engineering student Allen Hawkes working with graduate student Alexander Katko and lead investigator Steven Cummer professor of electrical and computer engineering designed an electrical circuit capable of harvesting microwaves.
They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7. 3v of electrical energy.
By comparison Universal serial bus (USB) chargers for small electronic devices provide about 5v of power. e were aiming for the highest energy efficiency we could achievesays Hawkes. e had been getting energy efficiency around 6 to 10 percent
but with this design we were able to dramatically improve energy conversion to 37 percent which is comparable to
what is achieved in solar cells.?It s possible to use this design for a lot of different frequencies
and types of energy including vibration and sound energy harvestingkatko says. ntil now a lot of work with metamaterials has been theoretical.
We are showing that with a little work these materials can be useful for consumer applications
. or instance a metamaterial coating could be applied to the ceiling of a room to redirect and recover a Wi-fi signal that would
otherwise be lost Katko says. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use. he properties of metamaterials allow for design flexibility not possible with ordinary devices like antennassays Katko. hen traditional antennas are close to each other in space they talk to each other
and interfere with each other s operation. The design process used to create our metamaterial array takes these effects into account allowing the cells to work together. ith additional modifications the researchers say the power harvesting metamaterial could potentially be built into a cell phone allowing the phone to recharge wirelessly while not in use.
This feature could in principle allow people living in locations without ready access to a conventional power outlet to harvest energy from a nearby cell phone tower
instead. ur work demonstrates a simple and inexpensive approach to electromagnetic power harvestingsays Cummer. he beauty of the design is that the basic building blocks are self-contained and additive.
One can simply assemble more blocks to increase the scavenged power . or example a series of power harvesting blocks could be assembled to capture the signal from a known set of satellites passing overhead the researchers explain.
The small amount of energy generated from these signals might power a sensor network in a remote location such as a mountaintop
or desert allowing data collection for a long-term study that takes infrequent measurements. The Army Research Office supported the research.
Source: Duke university You are free to share this article under the Creative Commons Attribution-Noderivs 3. 0 Unported license
#ouble-play motion keeps critters stable and agile Animals that push forward and back at the same time aren t wasting effort.
They are maximizing both stability and maneuverability simultaneously a new study shows. The finding while it could lead to more agile robots serves primarily to shed light on a question that has baffled biologists:
why do animals exert force in ways that don t move them toward their destination? A robot designer would likely avoid the side-to-side sashaying of a running lizard
or cockroach movements that seem inefficient. So why do the animals behave this way? A research team led by Johns hopkins university engineers says that the extra exertion isn t necessarily wasteful after all.
It allows at least some animals to accomplish a double-play often described as impossible in engineering textbooks. ne of the things they teach you in engineering is that you can't have both stability
and maneuverability at the same timesays Noah Cowan the associate professor of mechanical engineering who supervised the research. he Wright Brothers figured this out
when they built their early airplanes. They made their planes a little unstable to get the maneuverability they needed. hen an animal
or vehicle is stable it resists unwanted changes in direction. On the other hand if it is maneuverable it has the ability to quickly change course when desired.
Generally engineers have assumed that a system can rely on one property or the other but not both.
Not so. nimals are a lot more clever with their mechanics than we often realizecowan says. y using just a little extra energy to control the opposing forces they create during those small shifts in direction animals seem to increase both stability
and other shelters where they avoid being eaten by predators in their Amazon basin habitat. In a lab the team filmed the fish at 100 frames per second to study how they used their fins to stay in one place in these tubes even
while the other region pushes the water backwardsays Eric Fortune a professor of biological sciences at the New jersey Institute of technology who was a co-author of the paper. his arrangement is rather counter-intuitive like two propellers fighting against each other. f the fish wants to move forward
This biomimetic robot was developed in the lab of Malcolm Maciver associate professor of mechanical and biomedical engineering at Northwestern University and a co-author. e are far from duplicating the agility of animals with our most advanced robotsmaciver says. ne exciting implication of this work is that we might be held back in making more agile machines by our assumption that it s wasteful
or useless to have forces in directions other than the one we are trying to move in.
and maneuverable can also be found in the hovering behavior of hummingbirds and bees says senior author Cowan who directs the Locomotion in Mechanical and Biological Systems Lab at Johns Hopkins Whiting School of engineering. s an engineer
I think about animals as incredible living robotssays lead author Shahin Sefati a doctoral student advised by Cowan. t has taken several years of exciting multidisciplinary research during my Phd studies to understand these robots better. he National Science Foundation
and Office of Naval Research funded the study d
#Dendrites are like minicomputers in your brain University of North carolina at Chapel hill rightoriginal Studyposted by Mark Derewicz-UNC on October 30 2013the branch-like projections of neurons called dendrites are not just passive wiring
but act more like tiny computers multiplying the brain s processing power. uddenly it s
as if the processing power of the brain is much greater than we had originally thoughtsays Spencer Smith an assistant professor in the University of North carolina at Chapel hill s School of medicine.
His team s findings published in the journal Nature could change the way scientists think about longstanding scientific models of how neural circuitry functions in the brain
what you thought was simple wiring turns out to be transistors that compute informationsmith says. hat s what this finding is like.
Dendrites effectively act as mini-neural computers actively processing neuronal input signals themselves. Directly demonstrating this required a series of intricate experiments that took years
and Ikuko Smith set up their own lab at the University of North carolina. They used patch-clamp electrophysiology to attach a microscopic glass pipette electrode filled with a physiological solution to a neuronal dendrite in the brain of a mouse.
The idea was to directly istenin on the electrical signaling process. ttaching the pipette to a dendrite is tremendously technically challengingsmith says. ou can t approach the dendrite from any direction.
As the mice viewed visual stimuli on a computer screen the researchers saw an unusual pattern of electrical signalsâ##bursts of spikesâ##in the dendrite.
and found that known mechanisms could support the dendritic spiking recorded electrically further validating the interpretation of the data. ll pointed the data to the same conclusionsmith says. he dendrites are not passive integrators of sensory-driven input;
they seem to be a computational unit as well. is team plans to explore what this newly discovered dendritic role may play in brain circuitry and particularly in conditions like Timothy syndrome in
start with strange chemistry Stanford university University of California Davis rightoriginal Studyposted by Andy Fell-UC Davis on October 30 2013bacteria have been making hydrogen for billions of years
In a study published in the journal Science chemists describe a key step in assembling a hydrogen-generating catalyst. t s pretty interesting that bacteria can do thissays David Britt professor of chemistry at University of California Davis
and co-author on the paper. e want to know how nature builds these catalystsâ##from a chemist s perspective these are really strange things. he bacterial catalysts are organized based on precisely clusters of iron and sulfur atoms with side groups of cyanide and carbon monoxide.
Those molecules are highly toxic unless properly controlled Britt notes. The cyanide and carbon monoxide groups were known to come from the amino acid tyrosine Britt says.
That work will be published separately. ogether these results show how to make this interesting two-cluster enzymebritt says. his is unique new chemistry. ames Swartz professor of chemical engineering
and bioengineering at Stanford university contribute to the work which was supported by grants from the US Department of energy.
#How food can build better lithium batteries Cornell University rightoriginal Studyposted by Anne Ju-Cornell on October 29 2013a component of corn starch
and the yolk-shell structure of eggs can improve the durability and performance of lithium-sulfur battery cathodes report researchers.
Lithium-sulfur batteries are a promising alternative to today s lithium-ion batteries. here is currently a great need for high-energy long-life
and low-cost energy storage materials and lithium sulfur batteries are one of the most promising candidatessays Weidong Zhou a former postdoctoral researcher in Professor Hector Abruã a s lab at Cornell
University and first author of two papers which are published in ACS Nano and the Journal of the American Chemical Society. rom electric vehicles to solar and wind power applications for better lithium-based battery technologies are countless.?
Lithium-sulfur batteries could potentially offer about five times the energy density of today s typically used lithium-ion batteriessays Yingchao Yu a Phd student with Abruã a
and co-first author on the JACS publication. ut a lithium-sulfur battery is not a stable system as its capacity tends to fade over a short period of time. fter about 50 charge cycles the energy density of a lithium-sulfur
battery decreases rapidly due to a phenomenon called the polysulfide shuttling effect which is when the polysulfide chains in the battery s cathode (positive end) dissolve in the electrolyte the ionizing liquid that allows electrons to flow.
To combat this problem and stabilize the sulfur the researchers used amylopectin a polysaccharide that s a main component of corn starch. he corn starch can effectively wrap the graphene oxide-sulfide composite through the hydrogen bonding to confine the polysulfide among the carbon layerssays Hao Chen
co-first author of the ACS Nano publication and a former Phd student in the lab of Francis Disalvo paper co-author
and professor of chemistry and chemical biology. s an additive it greatly improves the cycling stability of the battery. n another approach to improving lithium-sulfur battery durability the researchers also report a new way
to make lithium-sulfur cathodes by synthesizing a nanocomposite consisting of sulfur coated with a common inexpensive conductive polymer called polyaniline and
modeled after the way an egg is encased in a shell but has room to move around inside.
Similar sulfur-polyaniline composites have previously been synthesized in a ore-shellstructure but the new method provides an internal void within the polymer shell called a olk-shellstructure. hen the lithium-sulfur battery was discharged fully the volume of the sulfur expanded dramatically to 200 percent.
If you think about the beauty of an egg yolk there is some empty space inside with space for the yolk to expandyu says.
The polyaniline coating which chemically is a benzene ring with ammonium and strung into cross-linked chains is also soft and flexible
and can protect against the hellcracking during long cycling. Provisional patents for these innovations have been filed through the Cornell Center for Technology Commercialization and Enterprise.
The Department of energy and the Energy Materials Center at Cornell an Energy Frontier Research center funded by the US DOE funded the papers.
#Dolphin-like radar finds hidden explosives University of Southampton rightoriginal Studyposted by Andrew Duff-Southampton on October 25 2013inspired by the way dolphins hunt scientists have developed a new type of radar that can
The twin inverted pulse radar (TWIPR) is able to distinguish true argetssuch as electronic circuits that can be used in explosive
The new system is based on a sonar concept called twin inverted pulse sonar (TWIPS) developed by Tim Leighton professor from the University of Southamptonâ#Institute of Sound and Vibration research.
The dolphinsâ##sonar wouldnâ##t work if they couldnâ##t distinguish the fish from the bubbles.
while simultaneously suppressing nonlinear scattering from oceanic bubbles. Leightonâ#team proposed that the TWIPS method could be applied to electromagnetic waves
To test the proposal they applied TWIPR radar pulses to a arget dipole antenna with a diode across its feedpointâ##to distinguish it from lutterepresented by an aluminium plate and a rusty bench clamp.
The antenna is typical of circuitry in devices associated with covert communications espionage or explosives.
or instance certain electronic components can scatter radar signals nonlinearly if driven by a sufficiently strong radar signal in contrast to naturally occurring objects
which tend to scatter linearly. iven that the diode target measures 6 cm in length weighs 2. 8 g costs less than one Euro
and requires no batteries it could allow the manufacture of small lightweight and inexpensive location and identification tags for animals infrastructure (pipelines conduits for example)
It can carry the bandwidth to search for mobile phone resonances to locate victims from their mobile phones even
when the phones are turned off or the batteries have no charge remaining. n addition to the applications discussed above such technology could be extended to other radiations such as magnetic resonance imaging (MRI) and light detection and ranging (LIDAR)
which for example scatters nonlinearly from combustion products offering the possibility of early fire detection systems. esearchers from University college London contributed to the study.
University of Southamptonyou are free to share this article under the Creative Commons Attribution-Noderivs 3. 0 Unported license c
#First supercapacitor on a silicon chip could power phones Vanderbilt University rightoriginal Studyposted by David Salisbury-VU on October 24 2013engineers have constructed the first supercapacitor made out of silicon.
These power cells could allow mobile devices that recharge in seconds and stay charged for weeks.
In fact it should be possible to construct these power cells out of the excess silicon that exists in the current generation of solar cells sensors mobile phones
and a variety of other electromechanical devices providing a considerable cost savings. f you ask experts about making a supercapacitor out of silicon they will tell you it is a crazy ideasays Cary Pint an assistant professor of mechanical engineering at Vanderbilt University who headed the development
. ut we ve found an easy way to do it. nstead of storing energy in chemical reactions the way batteries do upercapsstore electricity by assembling ions on the surface of a porous material.
and operate for a few million cycles instead of a few thousand cycles like batteries. These properties have allowed commercial supercapacitors
which are made out of activated carbon to capture a few niche markets such as storing energy captured by regenerative braking systems on buses
and electric vehicles and to provide the bursts of power required to adjust of the blades of giant wind turbines to changing wind conditions.
Supercapacitors still lag behind the electrical energy storage capability of lithium-ion batteries so they are too bulky to power most consumer devices.
However they have been catching up rapidly. he big challenge for this approach is assembling the materialssays Pint. onstructing high-performance functional devices out of nanoscale building blocks with any level of control has proven to be quite challenging
and when it is achieved it is difficult to repeat. o Pint and his research team decided to take a radically different approach:
they used porous silicon a material with a controllable and well-defined nanostructure made by electrochemically etching the surface of a silicon wafer.
This allowed them to create surfaces with optimal nanostructures for supercapacitor electrodes but it left them with a major problem.
Silicon is considered generally unsuitable for use in supercapacitors because it reacts readily with some of chemicals in the electrolytes that provide the ions that store the electrical charge.
With experience in growing carbon nanostructures Pint s group decided to try to coat the porous silicon surface with carbon. e had no idea
what would happensays Pint. ypically researchers grow graphene from silicon-carbide materials at temperatures in excess of 1400 degrees Celsius.
Inspection under a powerful scanning electron microscope showed it looked nearly identical to the original material
but it was coated by a layer of graphene a few nanometers thick. They tested the coated material
And when they used it to make supercapacitors they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated porous silicon and significantly better than commercial supercapacitors.
The novel supercapacitor design is described in a paper published in the journal Scientific Reports. The graphene layer acts as an atomically thin protective coating.
Pint and his group argue that this approach isn t limited to graphene. he ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storagehe
since it is very expensive and wasteful to produce thin silicon wafers. int s group is currently using this approach to develop energy storage that can be formed in the excess materials or on the unused backsides of solar cells and sensors.
The supercapacitors would store excess electricity that the cells generate at midday and release it when the demand peaks in the afternoon. ll the things that define us in a modern environment require electricitysays Pint. he more that we can integrate power storage into existing materials
and devices the more compact and efficient they will become. he National Science Foundation and the Army Research Office funded the study i
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