“We’ve discovered a way to change the three-dimensional structure of a well-established semiconductor material to enable new optical properties while maintaining its very attractive electrical properties,” said Paul Braun, a professor of materials science and engineering and of chemistry who led the research effort.
The team published its advance in the journal Nature Materials.
Photonic crystals are materials that can control or manipulate light in unexpected ways thanks to their unique physical structures. Photonic crystals can induce unusual phenomena and affect photon behavior in ways that traditional optical materials and devices can’t. They are popular materials of study for applications in lasers, solar energy, LEDs, metamaterials and more.
Using an epitaxial approach, researchers developed a 3-D photonic crystal LED, the first such optoelectronic device. | Graphic by Eric Nelson
However, previous attempts at making 3-D photonic crystals have resulted in devices that are only optically active – that is, they can direct light – but not electronically active, so they can’t turn electricity to light or vice versa.
To create a 3-D photonic crystal that is both electronically and optically active, the researchers started with a template of tiny spheres packed together. Then, they deposit gallium arsenide (GaAs), a widely used semiconductor, through the template, filling in the gaps between the spheres.
The GaAs grows as a single crystal from the bottom up, a process called epitaxy. Epitaxy is common in industry to create flat, two-dimensional films of single-crystal semiconductors, but Braun’s group developed a way to apply it to an intricate three-dimensional structure.
“The key discovery here was that we grew single-crystal semiconductor through this complex template,” said Braun, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Laboratory at Illinois. “Gallium arsenide wants to grow as a film on the substrate from the bottom up, but it runs into the template and goes around it. It’s almost as though the template is filling up with water. As long as you keep growing GaAs, it keeps filling the template from the bottom up until you reach the top surface.”
The Illinois team’s photonic crystal has both properties.
“With our approach to fabricating photonic crystals, there’s a lot of potential to optimize electronic and optical properties simultaneously,” said Erik Nelson, a former graduate student in Braun’s lab who now is a postdoctoral researcher at Harvard University. “It gives you the opportunity to control light in ways that are very unique –to control the way it’s emitted and absorbed or how it propagates.”
To create a 3-D photonic crystal that is both electronically and optically active, the researchers started with a template of tiny spheres packed together. Then, they deposit gallium arsenide (GaAs), a widely used semiconductor, through the template, filling in the gaps between the spheres.
The GaAs grows as a single crystal from the bottom up, a process called epitaxy. Epitaxy is common in industry to create flat, two-dimensional films of single-crystal semiconductors, but Braun’s group developed a way to apply it to an intricate three-dimensional structure.
“The key discovery here was that we grew single-crystal semiconductor through this complex template,” said Braun, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Laboratory at Illinois. “Gallium arsenide wants to grow as a film on the substrate from the bottom up, but it runs into the template and goes around it. It’s almost as though the template is filling up with water. As long as you keep growing GaAs, it keeps filling the template from the bottom up until you reach the top surface.”
The epitaxial approach eliminates many of the defects introduced by top-down fabrication methods, a popular pathway for creating 3-D photonic structures. Another advantage is the ease of creating layered heterostructures. For example, a quantum well layer could be introduced into the photonic crystal by partially filling the template with GaAs and then briefly switching the vapor stream to another material.
Once the template is full, the researchers remove the spheres, leaving a complex, porous 3-D structure of single-crystal semiconductor. Then they coat the entire structure with a very thin layer of a semiconductor with a wider bandgap to improve performance and prevent surface recombination.
To test their technique, the group built a 3-D photonic crystal LED – the first such working device.
Now, Braun’s group is working to optimize the structure for specific applications. The LED demonstrates that the concept produces functional devices, but by tweaking the structure or using other semiconductor materials, researchers can improve solar collection or target specific wavelengths for metamaterials applications or low-threshold lasers.
“From this point on, it’s a matter of changing the device geometry to achieve whatever properties you want,” Nelson said. “It really opens up a whole new area of research into extremely efficient or novel energy devices.”
The U.S. Department of Energy and the Army Research Office supported this work. Other Illinois faculty involved in the project are electrical and computer engineering professors James Coleman and Xiuling Li, and materials science and engineering professor John Rogers.
Sam Harris is an American author, and neuroscientist, as well as the co-founder and current CEO of Project Reason. He received a Bachelor of Arts in philosophy from Stanford University, before receiving a Ph.D. in neuroscience from UCLA (2009). He is a proponent of scientific skepticism and is the author of The End of Faith (2004), which won the 2005 PEN/Martha Albrand Award, Letter to a Christian Nation (2006), a rejoinder to criticism of his first book, The Moral Landscape (2010), and Lying (2011).
He is a well-known contemporary critic of religion and a member of the New Atheism movement. Harris calls for separation of church and state, civil rights for the non-religious as well as freedom to criticize religion. Harris has also written numerous articles in Huffington Post, Los Angeles Times, The Washington Post, The New York Times, Newsweek as well as in scientific journals such as Nature. He has written articles on Islam, Christianity, and religion in general.
In his 2010 book, The Moral Landscape, he posits that science can shed light on questions regarding moral values and facilitate human well-being. After the release of his books, he continued to give numerous talks at institutions such as University of Oxford, Harvard, Cambridge, Caltech, UCSD, Stanford University, Tufts University as well as TED, where he proposed an expansion of the scientific method and the possible implications of its contribution to human morality. Harris has also made an appearance in the 2005 film The God Who Wasn't There, as well as numerous television appearances for Bill Maher and Bill O'Reilly.
Although always interested in religion, Harris grew up in a secular home with parents who rarely discussed God. Harris was married in 2004. His wife, Annaka Harris, is Co-Founder of Project Reason and an editor of scientific, nonfiction books.
Harris attended Stanford University as an English major, but dropped out of school. Harris has admitted experimenting with the drug ecstasy as a student and the powerful insights he felt it gave him into spirituality and psychology. Harris found himself interested in spiritual and philosophical questions when he was at Stanford and the notion that he might be able to achieve spiritual insights without the help of drugs. After leaving Stanford, he traveled to Asia, where he studied meditation with Hindu and Buddhist teachers. Eleven years later, he returned to Stanford and completed a B.A. degree in philosophy. In 2009 he earned a Ph.D. degree in neuroscience at University of California, Los Angeles, using functional magnetic resonance imaging to conduct research into the neural basis of belief, disbelief, and uncertainty.
Un tuffo nel vuoto, il paracadute sulle spalle, davanti a sé un paesaggio da mozzare il fiato. Se i voli estremi dei base jumpers si consumano in pochi secondi, a catturarne gli attimi più suggestivi ci pensa questo video diffuso da una piattaforma video australiana dedicata ai filmati di argomento sportivo.
Sullo sfondo di spettacolari salti nel vuoto vi sono le cime di Norvegia, Svizzera e Francia, dove i temerari del volo hanno affrontato cadute libere di 1800 metri e oltre. Basta vederli lanciarsi in slow motion, per avere l'impressone che, in volo, l'adrenalina lasci spazio ad attimi di grande pace e silenzio.
Ma non tutti i lanci vanno a lieto fine. Guarda anche il video della disavventura di Christopher Brewer, un base jumper americano a cui non si è aperto il paracadute. Un sabato Brewer si è lanciato da un'altezza di 270 metri, da un ponte sospeso su un fiume della West Virginia. Il suo paracadute non si è aperto e il 27enne è precipitato in acqua a una velocità di 120 km all'ora. Fortunatamente la tuta alare che indossava ha frenato la caduta e il ragazzo è sopravvissuto. (Immagini sconsigliate a un pubblico sensibile).
Guma de mestecat fara zahar, dulciurile si bauturile racoritoare, comercializate drept alternative sanatoase la produsele zaharoase, pot deteriora dintii si cauza probleme gastrice.
De asemenea, este foarte putin probabil ca aceste alimente sa favorizeze scaderea în greutate, spun cercetatorii.
Dezvaluirea a ceea cercetatorii au numit "riscul ascuns al produselor fara zahar" ar putea afecta vânzarile acestora, mai ales datorita faptului ca oamenii le considera sanatoase si au încredere în ele.
Studiul, intitulat "Sunt produsele fara zahar cu adevarat benefice sanatatii dentare?" a analizat rolul substantelor folosite în unele produse pentru a reduce riscul aparitiei cariilor. Rezultatele sale au indicat ca în timp ce substantele numite alcooli de zahar sau polioli reduc riscul aparitiei cariilor, ele pot provoca o aciditate în gura care duce la eroziunea smaltului dintilor.
Substantele în cauza includ xilitolul, care este utilizat pe scara larga în multe produse din Uniunea Europeana, el fiind proclamat drept "benefic pentru dantura".
Ca urmare a rezultatelor, cercetatorii de la Universitatile din Boston, Helsinki si Nevada sustin ca publicul ar trebui sa fie informat cu privire la continutul de sorbitol si xilitol al unor produse, având în vedere ca acestea indica un risc ascuns de eroziune. Mai mult, acesti aditivi acizi sunt responsabili si de aparitia unor cazuri de tulburari gastrice si chiar diaree osmotica.
The device automatically produces classifications similar to those of a sommelier and can be useful in detecting defects during the elaboration of these wines.
Cava varies in type according to the amount of sugar added with the expedition liqueur after secondary fermentation (which produces carbonic gas). Therefore it is useful to know the exact amount of sugar added, since this is what determines the type of cava which will be produced. The resulting classifications are: Brut Nature (<3 g/L, no sugar added), Extra Brut (<6 g/L), Brut (<12 g/L), Extra Dry (12-17 g/L), Dry (17-35 g/L), Medium-Dry (33-50 g/L) and Sweet (>50 g/L).
In order to design the electronic tongue, researchers from the UAB Group of Sensors and Biosensors, led by professor Manel del Valle, identified different cava samples using voltammetric measurements. Thanks to a combination of chemical measurement systems and advanced mathematical procedures -- principal component analysis (PCA), discrete wavelet transform (DWT), and artificial neural network (ANN) -- researchers achieved to copy the human taste system and distinguish between different types of cava, thus obtaining a classification similar to that of a sommelier. Through the use of the second order standard addition method (SOSAM) it was possible to quantify the amount of sugar added in the cava production process, demonstrating the efficiency of these processing tools.
The electronic tongue currently can identify three types of cava: Brut, Brut Nature and Medium-Dry. However, with proper training it will be able to identify all types available on the market.
Researchers of the UAB Group of Sensors and Biosensors, considered one of the world's leading groups in its sector, has spent years working on the development of electronic tongues. It currently is working on perfecting the device through the incorporation of biosensors.
Electronic tongues are bio-inspired systems created with the aim of reproducing human perception senses. The device contains a sensor matrix (with differentiated, broad and complementary response) to obtain chemical information from samples as are obtained by the human senses. Next, the perception of taste is based on the generation of sensory patterns of the nerves activated by the brain and nerve print recognition; this last step is achieved with the use of computerised systems which interpret data obtained by the sensor matrix. As in biological mechanisms, a learning and training process is needed so that the electronic tongue can be capable of recognising the properties that must be identified.
Penn Fraser Jillette (born March 5, 1955) is an American magician, comedian, illusionist, juggler, bassist and a best-selling author known for his work with fellow illusionist Teller in the team Penn & Teller, and advocacy of atheism, libertarian philosophy, free-market economics, and scientific skepticism.
Jillette was born in Greenfield, Massachusetts. His mother, Valda R. Jillette (née Parks) (November 8, 1909—January 1, 2000), was a secretary, and his father, Samuel H. Jillette (March 14, 1912—February 14, 1999), worked at Greenfield's Franklin County Jail. Jillette became disenchanted with traditional illusionist acts that presented the craft as authentic magic, such as The Amazing Kreskin on The Tonight Show Starring Johnny Carson. At age eighteen, he saw a show by illusionist James Randi, and became enamored of his approach to magic that openly acknowledged deception as entertainment rather than a mysterious supernatural power. Jillette regularly acknowledges Randi as the one person on the planet he loves the most besides members of his family.
Jillette worked with high school classmate Michael Moschen in developing and performing a juggling act during the years immediately following their 1973 graduation. In 1974, Jillette graduated from Ringling Brothers and Barnum & Bailey Clown College. That same year, he was introduced to Teller by Weir Chrisimer, a mutual friend. The three then formed a three-person act called Asparagus Valley Cultural Society which played in Amherst, Massachusetts and San Francisco, California. In 1981, he and Teller teamed up as Penn & Teller, and went on to do a successful on- and Off Broadway show called "Penn & Teller" that toured nationally.
Uno degli indicatori più usati per valutare la crisi italiana è lo “spread con i bund tedeschi”. Lo spread è considerato infatti un indicatore della capacità di un paese di restituire i prestiti.
Lo stato italiano, per esempio, ha moltissimi debiti, costituiti sostanzialmente da tutti i titoli di stato (Bot, btp ecc) emessi in cambio di soldi presi in prestito da cittadini, banche , altri paesi. Ma oggi l’italia è da questo punto di vista meno credibile (è stata recentemente degradata da due agenzie che valutano le capacità dei debitori di rendere i soldi) e per far acquistare i suoi bot deve offrire interessi sempre più alti.
E siccome lo spread è la differenza o “allargamento” (spread in inglese) di rendimento tra i titoli di Stato (come i btp) italiani e quelli tedeschi (“bund”), meno l’Italia è credibile, più alti sono gli interessi che deve pagare per avere prestiti e più aumenta lo spread con i titoli tedeschi, giudicati molto affidabili.
Pagare alti interessi può infine avere come conseguenza l'impossibilità di ridurre i debiti, il che farebbe di nuovo crollare l'affidabilità del paese, in una spirale sempre più inarrestabile.
Conform cercetarilor, creierul uman prefera gândurile pozitive, optimiste si vestile bune cu privire la viitor, în detrimentul gândurilor si emotiilor negative.
Cercetatorii din cadrul University College din Londra, declara ca aproximativ 80% din oameni sunt optimisti, chiar daca o buna parte din ei nu se recunosc sub aceasta etichetare.
În decursul experimentelor, oamenii de stiinta au testat nivelul optimismului a 14 persoane, ale caror creiere au fost scanate în acest scop.
Când noutatile au fost pozitive, s-a înregistrat mai multa activitate în cadrul lobilor frontali ai creierului, care sunt asociati si cu procesarea erorilor.
În cazul expunerilor la stiri sau evenimente negative, cele mai optimiste persoane înregistrau o activitate minima în lobii frontali, în timp ce subiectii predominant pesimisti prezentau activitate maxima în aceiasi lobi frontali, ca si cum creierul ar fi ales respingerea gândurilor si trairilor negative.
"Spre exemplu, anunturile conform carora fumatul ucide nu sunt eficiente asupra oamenilor care cred ca nu sunt supusi riscului de a face cancer. Rata divorturilor este de aproximativ 50%, dar oamenii nu cred ca vor ajunge vreodata în pragul despartirii. Creierul alege întotdeauna viziuni optimiste. Cu toate ca retelele neuronale sunt exterem de sofisticate, este cumva reconfortant sa vezi cum creierul alege raspunsuri gresite dar optimiste, în ciuda evidentei reale", declara dr. Chris Chambers si dr. Tali Sharot, cercetatorii care au supervizat experiementul.
They are a daily essential for millions of Britons hoping to ward off ill-health. But despite the millions of pounds spent on vitamin pills, they do nothing for our health, according to a major study.
Researchers spent more than six years following 8,000 people and found that those taking supplements were just as likely to have developed cancer or heart disease as those who took an identical-looking dummy pill.
And when they were questioned on how healthy they felt, there was hardly any difference between the two groups.
Experts said the study – one of the most extensive carried out into vitamin pills – suggested that millions of consumers may be wasting their money on supplements. Many users fall into the category of the ‘worried well’ – healthy adults who believe the pills will insure them against deadly illnesses – according to Catherine Collins, chief dietician at St George’s Hospital in London.
She said: ‘It’s the worried well who are taking these pills to try and protect themselves against Alzheimer’s disease, heart attacks and strokes.
‘But they are wasting their money. This was a large study following people up for a long period of time assessing everything from their mobility and blood pressure to whether they were happy or felt pain.’
Multi-vitamin supplements have become increasingly popular as a quick and easy way of topping up the body’s nutrient levels. But a series of studies have indicated that, for some people, they could actually be harmful.
Two studies published last year suggested supplements could raise the risk of cancer.
One found pills containing vitamin E, ascorbic acid, beta-carotene, selenium and zinc increased the risk of malignant melanoma, the deadliest form of skin cancer, four-fold.
The other discovered women on a daily multi-vitamin pill increased their risk of breast cancer by up to 20 per cent.
While the evidence that vitamins can do harm is still limited, the latest study seems to confirm that many people are at the very least taking them unnecessarily.
A team of French researchers, led by experts at Nancy University, tracked 8,112 volunteers who took either a placebo capsule, or one containing vitamin C, vitamin E, beta-carotene, selenium and zinc, every day for just over six years.
They assessed the state of their health at the beginning and end of the trial, taking a quality of life survey designed to measure everything from mobility and pain to vitality and mental health.
When researchers analysed how many in each group had gone on to develop serious illnesses over the years, they found little difference.
In the supplement group, 30.5 per cent of patients had suffered a major health ‘event’, such as cancer or heart disease.
In the placebo group, the rate was 30.4 per cent.
There were 120 cases of cancer in those taking vitamins, compared to 139 in the placebo group, and 65 heart disease cases, against 57 among the dummy pill users.
In a report on their findings, published in the International Journal of Epidemiology, the researchers said: ‘The perception that supplementation improves general well-being is not supported by this trial.’
Miss Collins said the results of the study ‘reinforce the idea that if you’re worried about your health and start taking multi-vitamins, you will still be worried about it six years later’.
But the Health Supplements Information Service, which is funded by supplements manufacturers, said the finding that vitamins had no impact on how people perceived their health was ‘to be expected’.
Spokeswoman Dr Carrie Ruxton said: ‘The role of vitamin supplements is to prevent deficiencies and make sure people are receiving their recommended levels.
‘They won’t have a measurable impact on how you feel on a day-to-day basis but what they are doing is topping up your recommended levels to the right amount. They are not meant to be a magic bullet.’
The team just unveiled a new photovoltaic energy conversion system that can be powered by heat, the sun’s rays, a hydrocarbon fuel, or a decaying radioisotope. The button-sized power generator that can also run three times longer than a lithium-ion battery of the same weight.
The science behind the device is not necessarily groundbreaking, as engineers have long used the surface of a material to convert heat into precisely tuned wavelengths of light. However MIT’s method to convert light and heat into electricity is much more efficient than previous versions.
Described in the journal Physical Review A, MIT’s breakthrough was enabled by a material with billions of nanoscale pits etched on its surface. When this pitted material absorbs heat, it radiates energy at precisely chosen wavelengths depending on the size of the pits. It is hoped that the technology may one day be used to generate power for spacecraft on long term missions where sunlight may not be available.
“Being able to convert heat from various sources into electricity without moving parts would bring huge benefits,” says Ivan Celanovic, research engineer in MIT’s Institute for Soldier Nanotechnologies (ISN), “especially if we could do it efficiently, relatively inexpensively and on a small scale.” Celanovic went on to say that he believes his team could triple the efficiency of their prototype, adding that “It’s a neat example of how fundamental research in materials can result in new performance that enables a whole spectrum of applications for efficient energy conversion.”
Considering that space firms are looking for new ways to power spacecraft efficiently now that the shuttle fleet has been retired, we imagine NASA will be among the many companies interested in this technology.
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