The 2015 Dissertation Prize of the Global Neutrino Network has been awarded to three former graduate students, amongst others Tri Astraatmadja, who was part of the Leiden/Nikhef ANTARES group during More info
his PhD research. Astraatmadja receives the award for his thesis 'Starlight between the waves: In search of TeV photon emission from Gamma-Ray Bursts with the ANTARES Neutrino Telescope'.
This is the first year that the GNN Dissertation Prize is awarded. It recognises young postdoctoral candidates who have written an outstanding thesis and contributed significantly to the project. Primary criteria of the selection are the scientific quality, the didactics and the form of the thesis.
Astraamadja has focused on the ANTARES telescope, which operated as a gamma-ray telescope. This is possible by searching for down-going muons produced in interactions of gamma-rays in the Earth’s atmosphere. He looked at the short time windows when satellite experiments had announced a Gamma Ray Burst (GRB). The sophisticated tools developed by Astraatmadja will make it possible for the much bigger KM3NeT detector to detect gamma-rays from a GRB with a significance of three standard deviations.
The Netherlands eScience Center has announced to fund a new Path-Finding Project led by professor Dorothea Samtleben from the Leiden Institute of Physics (LION). This project aims to make the More info
processing of detection signals more efficient for the KM3NeT neutrino telescope, which is currently under construction in the Mediterranean Sea. High processing efficiency is vital for finding lower-energy neutrinos and the ability to alert other observatories in case of a special astronomical event.
Neutrinos are almost massless particles that have extremely little interaction with anything, so they undisturbedly speed through the Universe, even permeating stars. So when they are produced inside a star, they smoothly travel outwards and eventually reach Earth with all information still intact about their creation. Also, neutrinos have zero charge, so they are not deflected by any magnetic field and point directly to their origin. This makes these tiny particles a valuable source of information for astrophysicists, to study the spectacular events that produce them.
Unfortunately, their properties also make neutrinos incredibly hard to detect. Scientists need large volumes of material to hunt them down, like for example the water of the Mediterranean Sea where the KM3NeT neutrino telescope is under construction. Once in a while, one out of billions of neutrinos interacts with the water in the vicinity of the detector, and produces a light signal, which gets recorded. The trick is to process these signals and deduce the incoming particle’s characteristics as efficient as possible. When this happens fast enough, even real-time observation is possible. In that scenario the computers at KM3NeT can immediately alert their counterparts at optical observatories about a special astronomical event, so they’re able to photograph it. And they can extract online accurate information on the neutrino event candidates, to improve their selection efficiencies also for lower-energy neutrinos.
‘For real-time observation we need professional computing expertise to efficiently address the filtering of our huge data volume,’ says Samtleben. ‘The actual value of this grant is an eScience engineer to work with us for a full year. But mostly we’re establishing this first connection with the eScience center, to build a fruitful collaboration where their expertise and tools will enhance the science potential of the KM3NeT neutrino telescope. And they get a great playground to explore their tools and expertise. This could lead to a long-lasting partnership.’
Researchers at FOM-institute AMOLF and the Leiden Institute of Physics (LION) have developed a rubber rod with strange bending behaviours. Beyond a certain point, it bends more under decreasing pressure. More info
This behaviour doesn’t fit our expectations and does not conform to secular laws that predict the bending process. The rod is made out of metamaterial – material with special properties that are not found in nature. By providing the rod with a carefully selected pattern of small holes, the researchers managed to induce the strange behaviour. They published their work, a collaboration with Harvard University, in Physical Review Letters on July 21.
The metamaterial makes up a rubber rod of about twenty centimeter containing a pattern of elliptically shaped holes. These holes give the metarod its special property. The physicists noticed that a self-amplifying effect occurs at a turning point under a certain pressure level: the rod keeps bending further, while the pressure decreases. Group leader Martin van Hecke: ‘Imagine pushing a car forward. You expect to make the car go faster by pushing harder, but in this case the car speeds up if you push less.’
The researchers started looking for a mechanism that could explain this counter-intuitive effect. They discovered that you can easily squeeze together the metamaterial with a slight push, but it strongly resists stretching when you pull. Regular materials without holes show no significant difference between pushing and pulling, unless extremely high pressures are at play. This sensitivity to the difference between pulling and pushing causes the strange effect during bending of the metamaterial rod. The shape and place of the holes precisely determine the moment this effect occurs. So by changing the hole pattern, the scientists can custom-make materials with specific properties.
Ancient building principles
The development of the metamaterial rod challenges century-old building principles. The relationship between bending and pressure was established 250 years ago by Leonhard Euler, in his universal law of elastic instability of rods. Since then, his theory has formed the basis for building houses and bridges. Euler assumed that materials only show a distinction between pushing and pulling under extreme pressure. The new metamaterial rod displays a different behaviour, opening doors for new developments. ‘Building bridges with our metamaterial rod is never going to happen,’ says van Hecke. ‘But I can imagine a robot arm that is able to bent in a clever way thanks to mechanical switches that are based on this new material.’
Johannes Jobst - researcher at the Leiden Institute of Physics (LION) – has been awarded a Veni grant from the Netherlands Organisation for Scientific Research (NWO). Veni grants are handed More info
out to very talented researchers who have recently obtained a PhD. Jobst receives the maximum amount of 250,000 euro and will use the money to study how electric switching affects free-flying electrons in graphene transistors.
Graphene is made up of just a single layer of carbon atoms, and has shown great promise for a wide range of applications since its discovery in 2004. The material even earned a Physics Nobel Prize in 2010, awarded to Kostya Novoselov and Dutchman Andre Geim. One of the amazing properties of graphene is its incredible conductivity; electrons travel large distances without changing direction. Compared to conventional semiconductors, that are commonly used in electric devices, this promises great performance improvements.
The key to improving computers is the computer chip – a series of many tiny electric switches, or transistors. Simply put: the faster transistors switch, the faster computers are. And more of them means a more powerful computer. We cannot make traditional silicon transistors any faster, and for the past years the main effort has been put into making them smaller in order to squeeze more on a chip. However, we’ll soon reach a minimum size beyond which this transistor faces limitations, putting technology progress to a halt.
The solution may lie in graphene transistors. They switch faster than silicon and therefore increase computers speeds. ‘In theory they are a thousand times faster,’ says Jobst. ‘So instead of three gigahertz computers, we'd have clock rates of three terahertz. And because electrons fly freely in graphene without scattering, they produce much less waste heat, meaning a lot less power consumption.’
But computers should also work in practise, not just in theory. What will happen when we actually use graphene in electric switches? How will the electric field, used to switch such transistors, affect the free-flying electrons? By using a novel technique, based on low-energy electron microscopy (LEEM), Jobst is going to find out what happens. The Veni grant enables him to perform his research at LION and Columbia University, New York for three more years as senior postdoctoral researcher.
M.P. Bakker, T. Ruytenberg, W. Loffler, A. Barve, L. Coldren, M.P. van Exter, D. Bouwmeester (2015) Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory, Phys. Rev. B., 91, 24, 241305-5. [DOI][pdf]
J.J. Renema, Q. Wang, R. Gaudio, I. Komen, K. op ’t Hoog, D. Sahin, A. Schilling,
M.P. van Exter, A. Fiore, A. Engel, M.J.A. de Dood (2015) Position-Dependent Local Detection Efficiency in a Nanowire
Superconducting Single-Photon Detector, Nano Lett., 15, 7, 4541-4545. [DOI][pdf]
28 Aug, 13:15, De Sitterzaal
Van Marum Colloquium Prof. Miquel Salmeron (Lawrence Berkeley Natiional Laboratory): New era of surface science: the solid-gas and solid-liquid interfaces
8 Sept, 16:15, Academy building, Rapenburg
Thesis Defense Mathias Diez - IL: On electronic signatures of topological
superconductivity Promotor: Prof.dr. C.W.J. Beenakker