Prague, 28 June 2017
- Published on Thursday, 20 October 2016 07:38
Exact simulation lifts the 80-year-old mystery of the degree to which atoms can be dressed with photons
In 1937, US physicist Isidor Rabi introduced a simple model to describe how atoms emit and absorb particles of light. Until now, this model had still not been completely explained. In a recent paper, physicists have for the first time used an exact numerical technique: the quantum Monte Carlo technique, which was designed to explain the photon absorption and emission phenomenon. These findings were recently published in EPJ D by Dr Flottat from the Nice –Sophia Antipolis Non Linear Institute (INLN) in France and colleagues. They confirm previous results obtained with approximate simulation methods.
- Published on Wednesday, 12 October 2016 11:04
New method to make permanent magnets more stable over time
For physicists, loss of magnetisation in permanent magnets can be a real concern. In response, the Japanese company Sumitomo created the strongest available magnet—one offering ten times more magnetic energy than previous versions—in 1983. These magnets are a combination of materials including rare-earth metal and so-called transition metals, and are accordingly referred to as RE-TM-B magnets. A Russian team has now been pushing the boundaries of magnet design, as published in a recent study in EPJ Plus. They have developed methods to counter the spontaneous loss of magnetisation, based on their understanding of the underlying physical phenomenon. Roman Morgunov from the Institute of Problems of Chemical Physics at the Russian Academy of Sciences and colleagues have now developed a simple additive-based method for ensuring the stability of permanent magnets over time, with no loss to their main magnetic characteristics.
- Published on Wednesday, 12 October 2016 10:30
Pursuing a detective's approach to carbon atom breakup yields clues relevant to fusion reactions and astrophysics phenomena
Regardless of the scenario, breaking up is dramatic. Take for example the case of carbon (12C) splitting into three nuclei of helium. Until now, due to the poor quality of data and limited detection capabilities, physicists did not know whether the helium fragments were the object of a direct breakup in multiple fragments up front or were formed in a sequence of successive fragmentations. The question has been puzzling physicists for some time. Now, scientists from Denmark's Aarhus University have used a state-of-the-art detector capable of measuring, for the first time, the precise disintegration of the 12C into three helium nuclei. Their findings, released in a study published in EPJ A, reveal a sequence of fragmentations, relevant to developing a specific kind of fusion reactions and in astrophysics.
- Published on Wednesday, 12 October 2016 10:12
History shows experiments to be just as key as theory in gravity physics
In the 1950s and earlier, the gravity theory of Einstein's general relativity was largely a theoretical science. In a new paper published in EPJ H, Jim Peebles, a physicist and theoretical cosmologist who is currently the Albert Einstein Professor Emeritus of Science at Princeton University, New Jersey, USA, shares a historical account of how the experimental study of gravity evolved.
- Published on Monday, 03 October 2016 14:54
The self-consistent field theory (FCFT) is a convenient theoretical tool to describe the ordered structures of copolymer melts. It supports the current understanding of many polymeric systems. In a new EPJ E Colloquium Ying Jiang and colleagues showcase the versatility and power of the wormlike-chain formalism for calculating the microphase-separated crystallographic structures of multi-component wormlike polymers.
- Published on Monday, 19 September 2016 16:36
Physicists elucidate reactions underlying positive ion beams hitting molecular targets relevant in proton therapy
Ion-molecule reactions are ubiquitous. They are important in the emergence of primordial life as solar wind falls onto chemicals turning them into the prebiotic building blocks of life. Ion-molecule reactions are also the basic process underlying the proton-biomolecule collisions relevant in proton therapies in cancer. To better understand these mechanisms, a new study provides novel data on low-energy proton collisions with furan and its derivative molecules, which are models for the deoxyribose sugar unit found in biological processes. These findings have been published in EPJ D by Tomasz Wasowicz from Gdansk University of Technology, Poland, and colleagues, as part of the topical issue “Low-Energy Interactions related to Atmospheric and Extreme Conditions.”
- Published on Tuesday, 09 August 2016 17:19
Stabilising materials with transient magnetic characteristics makes it easier to study them
Magnetic materials displaying what is referred to as itinerant ferromagnetism are in an elusive physical state that is not yet fully understood. They behave like a magnets under very specific conditions, such as at ultracold temperatures near absolute zero. Physicists normally have no other choice than to study this very unique state of matter in a controlled fashion, using ultracold atomic gases. Now, a team based at ETH Zurich, Switzerland has introduced two new theoretical approaches to stabilise the ferromagnetic state in quantum gases to help study the characteristics of itinerant ferromagnetic materials. These results were recently published in EPJ B by Ilia Zintchenko and colleagues.
- Published on Monday, 08 August 2016 15:00
Crystallization, a typical self-organization process during which a disordered state spontaneously transforms into an ordered one, a crystal, usually proceeds by nucleation and growth. In the initial stages of the transformation, a localized nucleus of the new phase forms due to a random fluctuation. Most of these small nuclei disappear after a short time, but in some rare cases a crystalline embryo may reach a critical size, after which further growth becomes thermodynamically favorable and the entire system is converted into the new phase.
In this EPJ E review paper, Jungblut and Dellago discuss several theoretical concepts and computational methods to better understand crystallization. More specifically, they address the rare event problem arising in the simulation of nucleation processes, and explain how to calculate nucleation rates accurately. Particular emphasis is placed on discussing statistical tools to analyze crystallization trajectories and identify the transition mechanism.
- Published on Monday, 25 July 2016 12:50
Testing liquid metals as target material bombarded by high-energy particles
There is a growing interest in the scientific community in a type of high-power neutron source that is created via a process referred to as spallation. This process involves accelerating high-energy protons towards a liquid metal target made of material with a heavy nucleus. The issue here is that scientists do not always understand the mechanism of residue nuclei production, which can only be identified using spectrometry methods to detect their radioactive emissions. In a new study examining the radionuclide content of Lead-Bismuth-eutectic (LBE) targets, scientists at the Paul Scherrer Institute Villigen (PSI) found that some of the radionuclides do not necessarily remain dissolved in the irradiated targets. Instead, they can be depleted in the bulk LBE material and accumulate on the target's internal surfaces. These findings have recently been published in EPJ Plus by Bernadette Hammer-Rotzler affiliated with the PSI and the University of Bern, Switzerland, and colleagues from Switzerland, France and Sweden. The results improve our understanding of nuclear data related to the radionuclides stemming from high-power targets in spallation neutron sources. They contribute to improving the risk assessment of future high-power spallation neutron beam facilities --including, among others, the risk of erroneous evaluation of radiation dose rates.
- Published on Friday, 22 July 2016 14:42
New theoretical models that better describe the interaction between dark matter and ordinary particles advance the quest for dark matter
In the quest for dark matter, physicists rely on particle colliders such as the LHC in CERN, located near Geneva, Switzerland. The trouble is: physicists still don't exactly know what dark matter is. Indeed, they can only see its effect in the form of gravity. Until now, theoretical physicists have used models based on a simple, abstract description of the interaction between dark matter and ordinary particles, such as the Effective Field Theories (EFTs). However, until we observe dark matter, it is impossible to know whether or not these models neglect some key signals. Now, the high energy physics community has come together to develop a set of simplified models, which retain the elegance of EFT-style models yet provide a better description of the signals of dark matter, at the LHC. These developments are described in a review published in EPJ C by Andrea De Simone and Thomas Jacques from the International School for Advanced Studies SISSA, in Trieste, Italy.