News / Highlights / Colloquium
- 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 31 July 2014
A new theoretical study elucidates mechanisms that could help in producing coherent radiations, and could ultimately help to achieve high-contrast images of biological samples
Ever heard of the water window? It consists of radiations in the 3.3 to 4.4 nanometre range, which are not absorbed by the water in biological tissues. New theoretical findings predict a novel way of achieving coherent radiations within the water window. These could be the basis of an optimal technique to obtain a high-contrast image of the biological samples or to be used in high-precision spectroscopy. Now, a new theoretical study identifies the physical mechanism needed to efficiently generate the harmonic radiations - which are multiples of an incoming laser’s frequency - at high laser intensities that occur beyond the saturation threshold of atoms and molecules. These findings, aimed at improving conventional methods of coherent radiation production to reach the water window, were recently published in the EPJ D by José Pérez-Hernández from the Centre for Pulsated Laser, CLPU, in Salamanca, Spain, and colleagues.
- Published on 21 July 2014
The seminal 1914 experiment of James Franck and Gustav Hertz provided a graphic demonstration of the quantisation properties of atoms, and thereby laid the foundations of modern atomic physics. This EPJ D colloquium revisits the experiment on the occasion of its Centenary and compares the traditional and modern interpretations, as well as highlighting the link between microscopic processes, which are governed by the laws of quantum mechanics, and macroscopic phenomena, as observed in the laboratory.
- Published on 17 July 2014
In this EPJ D topical review, the authors present a systematic study of gas breakdown potentials. An analysis of the key elementary processes involved in low-current low-pressure discharges is given, with the aim of illustrating how such discharges are used to determine swarm parameters and how such data may be applied to the modeling of discharges.
- Published on 30 June 2014
New study provides proof of the validity of a filtering device for ultra-cold neutral atoms based on tunnelling
Techniques for controlling ultra-cold atoms travelling in ring traps currently represent an important research area in physics. A new study published in EPJ D gives a proof of principle, confirmed by numerical simulations, of the applicability to ultra-cold atoms of a very efficient and robust transport technique called spatial adiabatic passage (SAP). Yu Loiko from the University of Barcelona, Spain, and colleagues have, for the first time, applied SAP to inject, extract, and filter the velocity of neutral atoms from and into a ring trap. Such traps are key to improving our understanding of phenomena involving ultra-cold atoms, which are relevant to high-precision applications such as atom optics, quantum metrology, quantum computation, and quantum simulation.
- Published on 30 June 2014
A new study relevant for cancer radiation therapy shows that DNA building blocks are susceptible to fragmentation on contact with the full range of ions from alkaline element species
Scientists now have a better understanding of how short DNA strands decompose in microseconds. A European team found new fragmentation pathways that occur universally when DNA strands are exposed to metal ions from a family of alkaline and alkaline earth elements. These ions tend to replace protons in the DNA backbone and at the same time induce a reactive conformation leading more readily to fragmentation. These finding have been published by Andreas Piekarczyk, from the University of Iceland, and colleagues in a study in EPJ D. They could contribute to optimising cancerous tumour therapy through a greater understanding of how radiation and its by-products, reactive intermediate particles, interact with complex DNA structures.
- Published on 19 June 2014
Physicists have published a new theoretical foundation explaining the mechanism of protein folding and unfolding in water
Investigating the structure and dynamics of so-called Meso-Bio-Nano (MBN) systems—micron-sized biological or nanotechnology entities—is a rapidly expanding field of science. Now, scientists Alexander Yakubovich and Andrey Solov'yov from MBN Research Centre in Frankfurt, Germany, have produced a new theoretical study of a protein macromolecules changing from a coil structural conformation to a globular one. Their statistic mechanics model, just published in EPJ D, describes the thermodynamic properties of real proteins in an aqueous environment, using a minimal number of free physical parameters.
- Published on 11 March 2014
Inducing biological tissue damage with an atmospheric pressure plasma source could open the door to many applications in medicine
Plasma medicine is a new and rapidly developing area of medical technology. Specifically, understanding the interaction of so-called atmospheric pressure plasma jets with biological tissues could help use them in medical practice. Under the supervision of Sylwia Ptasinska from the University of Notre Dame, in Indiana, USA, Xu Han and colleagues conducted a quantitative and qualitative study of the different types of DNA damage induced by atmospheric pressure plasma exposure, in a paper published in EPJ D as part of a special issue on nanoscale insights into Ion Beam Cancer Therapy. This approach, they hope, could ultimately lead to devising alternative tools for cancer therapy as well as applications in hospital hygiene, dental care, skin diseases, antifungal care, chronic wounds and cosmetics treatments.
- Published on 26 February 2014
The effect of spatial ordering of molecules on surfaces is commonly utilised to deposit ultra-thin films, where the film thickness is only a few nanometres. In this EPJ D review paper, several methods are discussed that are distinguished from other thin film deposition processes by exactly these effects, leading to self-assembling and self-limiting layer growth and, eventually, to coatings with unique and fascinating properties, and applications in micro-electronics, optics, chemistry, and biology.
- Published on 26 February 2014
A new study represents a step forward in our understanding of the nature of exchange interactions between identical particles, which only occur at the quantum level
Two-particle interference has been the focus of many studies, specifically in quantum optics with photons. However, interference between two massive, identical particles is not so well understood. In a study published in EPJ D, Pedro Sancho from the CLPU—Centre for Pulsed Lasers—in Salamanca, Spain, uncovers a counterintuitive result whereby particles called bosons do not behave as expected—they are overlapping, and not interfering—due to the combination of interference and so-called exchange interaction. The latter is a quantum mechanical effect that alters their symmetry when identical particles are exchanged.