Posts Tagged ‘Technology’

Defining electrical units of measurement in terms of universal constants allows precise standards to be established. Both the unit of volt and ohm can be defined from the elementary charge e and the Planck constant by exploiting the Josephson effect and the quantum Hall effect, respectively.

However, an equivalent, robust standard for the ampere is still lacking. One proposal is to use single-electron pumps i.e. quantum devices that shuffle electrons one at a time with a certain frequency f , so that the standard of current can be defined from the product of the elementary charge and the frequency (ef).The drawback is that these devices operate in the tunnelling regime, whose stochastic nature results in fluctuations of the measured current from the value ef.

Scientists at the Physikalisch-Technische Bundesanstalt Institute have now experimentally demonstrated a device configuration that can overcome this problem. They have implemented a series of three single-electron pumps and two charge detectors, which monitor the flow of electrons across the pumps. Single electrons are shuffled across by applying voltage pulses to each pump in a certain sequence. Then, subsequent pulses allow the detection of pumping errors, that is, of events in which a pump fails to shuffle an electron. The knowledge of these errors allows, in turn, the current fluctuations to be determined from ef, and eventually to achieve a tenfold improvement in accuracy compared with the case of individual electron pumps.

Single Electron Source

Figure: SEM image of the device. The semiconductor part between source and drain (green) consists of three pumps and two charge nodes (blue, red). Each pump is
defined by three metallic top gates (yellow) forming a QD in the semiconductor.


Article @ DOI: 10.1103/PhysRevLett.112.226803

Edited and Extracted from Reliable single-electron source by Elisa De Ranieri


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At the start of 2013, the European Union awarded one of the two Future and Emerging Technology ‘flagship’ initiatives to the Human Brain Project (the other one going to a project focused on graphene). Almost simultaneously, President Barack Obama announced the BRAIN (Brain Research through Advancing Innovative Neurotechnologies) Initiative in the US.

As one of the flagships initiatives, the Human Brain Project is due to receive a staggering €1 billion over 10 years, half of which will come from the European Union and other half from the funding agencies of the individual countries involved. It is a large collaboration involving over 100 partners, and €72 million (~US$98 million) will be awarded during the first 30 months alone. The principal goals of the project are to simulate the activity of a human brain using supercomputers and to use the knowledge obtained to improve the way computers work.

The BRAIN initiative originated from a call from a large number of scientists to launch a collaborative effort, which was named the Brain Activity Map project, to record and analyse the activity of large sets of neurons in the brain. This call was answered by the White House who backed it with the promise of several hundred million dollars of public funding over the next few years and called for support from private investors. So far, about US$110 million have been committed by the Defense Advanced Research Projects Agency, National Institutes of Health and National Science Foundation for the first year, and private investors have promised around US$130 million for each of the next few years.

The initiatives originate from two simple facts. First, that our current understanding of how the brain works is very poor, which hampers the discovery of effective cures for mental health diseases. Second, that the neuron network in the human brain is extremely vast and complex. Understanding the way in which signals are transmitted and how these transmissions translate into thoughts and sensations can only be achieved through large collaborations, which are able to produce and analyse huge sets of data. It is, therefore, no coincidence that the BRAIN initiative has been compared with endeavors such as the Human Genome Project and even the Apollo project that landed a man on the Moon.

 Extracted from doi:10.1038/nnano.2014.23

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Scientists have developed a hot-gas lens that possesses improved optical capabilities and damage threshold (estimated to be vastly superior) to that of conventional glass optics. Once optimized, such lenses may be useful for focusing ultra-intense laser beams such as those used in X-ray lasers, laser-driven accelerators and laser fusion experiments.

The lens is capable of transmitting beams whose intensities are two orders of magnitude higher than the maximum intensity that solid-state lenses can transmit without sustaining damage. In case of breakdown, the lens repairs instantaneously, unlike solid-state optics, which are either permanently impaired or must be left to cool for hours.

The idea of using a hot metal tube to create a temperature gradient and thus a lens-like refractive index profile in a gas has been around for some time. Bell Laboratories in the USA investigated the idea in the 1960s not long after the development of the first lasers. Early designs were plagued by severe limitations in terms of their large size, high complexity and weak focusing. Their apertures were small (of the order of 7 mm), their focal lengths were very long (2.5 m to 10 m) and they required complicated ancillary apparatus. These were of the order of a meter in length, and were thus long and bulky.

To address these issues, the scientists designed a composite gas lens that consists of two parts. The first stage is a 50-mm-long metal-tube gas lens with a 10-mm-diameter aperture that is heated from below and refracts the outer rays of a light beam. The second stage is a shorter tube, 25 mm in length; it contains a spiral flame that mainly acts on the inner rays. The stainless-steel tubes of both lenses are heated to around 400 °C so that they become red hot. The result is a flame lens, which brings light to a sharp focus and is more compact and has a focusing power that is four times stronger per unit length than earlier gas-lens designs.

A prototype flame lens with a focal length of about 2 m in proof-of-principle experiments that include focusing of high-intensity light, imaging of highly chromatic sources and drilling plastic with high-energy pulses. Scientists are now using aerodynamic theory to optimize the lens structure and further improve its performance.

Articles taken and edited from : Graydon, Oliver. “Optics: The flame lens.” Nature Photonics 7.8 (2013): 592-592.

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