- Published on 14 October 2014
In this EPJ D colloquium paper, the authors review a cross-section of recent results relating to low-energy positron scattering from atomic targets, and present a comparison of the latest measurements and calculations for positron collisions with the noble gases, together with a brief update on the newest studies addressing other atomic targets. In particular, they provide an overview of the work that has been done in examining elastic scattering, positronium formation, direct and total ionisation, as well as total scattering, at typical energies ranging from 0.1 eV to a few hundred eV.
- Published on 08 October 2014
How does an electric (or magnetic) dipole behave in an electromagnetic field, when its velocity becomes comparable with the speed of light?
This problem has been solved for the first time in a paper recently published in EPJ Plus, where novel relativistic effects were found. In particular, it has been shown that the concept of “hidden” momentum of magnetic dipoles in an electric field, being disputable up to date, is strongly required to derive relativistically adequate solutions. Moreover, a novel concept of “latent” momentum of electric dipole should be also involved into the description of dipoles.
- Published on 02 October 2014
Simulating the cost of generating a combination of electricity sources while accounting for the fluctuating nature of energy production and demand provides tools to optimise such energy mix
Increasing reliance on renewable energies is the way to achieve greater CO2 emission sustainability and energy independence. Yet, because such energies are only available intermittently and energy cannot be stored easily, most countries aim to combine several energy sources. Now, in a new study in EPJ Plus, French scientists have come up with an open source simulation method to calculate the actual cost of relying on a combination of electricity sources. Bernard Bonin from the Atomic Energy Research Centre CEA Saclay, France, and colleagues demonstrate that cost is not directly proportional to the demand level. Although recognised as crude by its creator, this method can be tailored to account for the public’s interest—and not solely economic performance—when optimising the energy mix.
- Published on 29 September 2014
Improved theoretical model of photoabsorption of nitrous oxide matters because its by-product, nitric oxide, is involved in the catalytic destruction of stratospheric ozone
New theoretical physics models could help us better grasp the atmospheric chemistry of ozone depletion. Indeed, understanding photoabsorption of nitrous oxide (N2O)-- a process which involves the transfer of the energy of a photo to the molecule--matters because a small fraction of N2O reacts with oxygen atoms in the stratosphere to produce, among other things, nitric oxide (NO). The latter participates to the catalytic destruction of ozone (O3). Now, new theoretical work unveils the actual dynamic of the photoabsorption of nitrous oxide (N2O) molecules. These findings by Mohammad Noh Daud from the University of Malaya, Kuala Lumpur in Malaysia, have just been published in EPJ D. The work has led to new calculations of the probability of an absorption process taking place, also referred to as absorption cross section, which confirm experimental results.
- Published on 29 September 2014
Bohmian mechanics provides an explanation of quantum phenomena in terms of point particles guided by wave functions. This EPJ D review focuses on the formalism of non-relativistic Bohmian mechanics, rather than its interpretation, and although the Bohmian and standard quantum mechanical theories have different formalisms, they both yield exactly the same predictions for all phenomena.
- Published on 25 September 2014
Over the past 15 years, the density matrix renormalisation group (DMRG) has become increasingly important for ab initio quantum chemistry. Its underlying wavefunction ansatz, the matrix product state (MPS), is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS, viz. the rank of the decomposition, controls the size of the corner of the many-body Hilbert space that can be reached with the ansatz, and can be systematically increased until numerical convergence is reached. The MPS ansatz naturally captures exponentially decaying correlation functions, and the DMRG therefore works extremely well for noncritical one-dimensional systems.
- Published on 23 September 2014
New theoretical model of the effect of triangular defects in graphene provides numerical estimates of the resulting current rectification with potential applications in security screening.
Electronic transport in graphene contributes to its characteristics. Now, a Russian scientist is proposing a new theoretical approach to describe graphene with defects—in the form of artificial triangular holes—resulting in the rectification of the electric current within the material. Specifically, the study provides an analytical and numerical theory of the so-called ratchet effect —which results in a direct current under the action of an oscillating electric field, due to the skew scattering of electronic carriers by coherently oriented defects in the material. These findings are published in EPJ B by Sergei Koniakhin from the Ioffe Physical-Technical Institute and the Academic University - Nanotechnology Research and Education Centre, both affiliated with the Russian Academy of Sciences in St. Petersburg.
- Published on 08 August 2014
Nuclear systems ranging from light nuclei to massive neutron stars can be well described by nucleons interacting through two-body and three-body forces. From electrostatics we know that two identical uniformly charged spheres repel at any distance but the repulsion disappears when the spheres completely overlap. Similarly, in some modern expressions of nuclear three-body force it is assumed that the nuclear repulsion between the three nucleons is zero when they occupy the same position in space.
- Published on 31 July 2014
A new theoretical model outlines the conditions under which a novel nanostructure, such as the nano-pea pod, can exhibit localised electrons for electronics applications
Periodic chain-like nanostructures are widely used in nanoelectronics. Typically, chain elements include the likes of quantum rings, quantum dots, or quantum graphs. Such a structure enables electrons to move along the chain, in theory, indefinitely. The trouble is that some applications require localised electrons - these are no longer in a continuous energy spectrum but in a discrete energy spectrum, instead. Now, a new study by Russian scientists identifies ways of disturbing the periodicity of a model nanostructure to obtain the desired discrete spectrum with localised electrons. These findings have been published in EPJ B by Dr. Eremin from the Mordovian State University, in Saransk, Russia and colleagues.