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Ribeiro de Almeida R.R.,Kent State University | Ribeiro de Almeida R.R.,State University of Maringa | Zhang C.,Kent State University | Parri O.,University of Southampton | And 3 more authors.
Liquid Crystals | Year: 2014

We present freeze-fracture transmission electron microscopy (FF-TEM), dielectric spectroscopy and electro-optic measurements on a dimeric liquid crystal mixture, which previously was proposed to form the twist-bend nematic (Ntb) phase. Our FF-TEM studies provide a direct image of a 10.5 nm periodic structure, consistent with the expected nanoscale, heliconical twist-bend modulation of the molecular orientation. Dielectric measurements in the 100 Hz to 10 MHz range reveal three nearly Debye-type dispersion processes in the nematic and the twist-bend phase. Low frequency 8 V/µm electric fields applied on planar cells cause the optical-scale stripe texture (another characteristic feature of the Ntb phase) to disappear. Higher (>16 V/µm) fields gradually realign the heliconical axis along the electric field; it relaxes back after the field removal. © 2014, © 2014 Taylor & Francis. Source

Zhang C.,Kent State University | Lavrentovich O.D.,Kent State University | Jakli A.,Kent State University | Jakli A.,Wigner Research Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Recent cryo-TEM studies in the helical nanofilament (HNF) phase of several bent-core liquid crystal materials having blue structural color showed that in subsequent layers the nanofilaments twist with respect to each other by about 37 angle, leading to a secondary helical structure that can explain their opal appearance. In this paper, after summarizing these observations, we show additional features that help understanding why the same bent-core homologs P-n-O-PIMB with n ≥?9 do not show structural color. © 2014 SPIE. Source

Boguslawski K.,ETH Zurich | Marti K.H.,ETH Zurich | Legeza O.,Wigner Research Center | Reiher M.,ETH Zurich
Journal of Chemical Theory and Computation | Year: 2012

We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740]. © 2012 American Chemical Society. Source

News Article
Site: http://phys.org/physics-news/

"EuPRAXIA will define the missing step towards a new generation of plasma accelerators with the potential for dramatically reduced size and cost," said EuPRAXIA coordinator Ralph Assmann from DESY. "It will ensure that Europe is kept at the forefront of accelerator-based science and applications." The EuPRAXIA consortium includes 16 laboratories and universities from five EU member states. In addition, it includes 18 associated partners from eight countries, involving leading institutes in the EU, Japan, China and the United States. Particle accelerators have evolved over the last 90 years into powerful and versatile machines for discoveries and applications. Today some 30,000 accelerators are operated around the world, among those some of the largest machines built by human mankind. A new technology for particle acceleration has emerged and has demonstrated accelerating fields a thousand times beyond those presently used: Plasma acceleration uses electrically charged plasmas, generated by strong lasers, instead of the usual radio frequency used in conventional accelerators, to boost particles like electrons to high energies. By the end of 2019, EuPRAXIA will produce a conceptual design report for the worldwide first five Giga-Electronvolts plasma-based accelerator with industrial beam quality and dedicated user areas. EuPRAXIA is the required intermediate step between proof-of-principle experiments and versatile ultra-compact accelerators for industry, medicine or science, e.g. at the energy frontier of particle physics as a plasma linear collider. The study will design accelerator technology, laser systems and feedbacks for improving the quality of plasma-accelerated electron beams. Two user areas will be developed for a novel free-electron laser, high-energy physics and other applications. An implementation model will be proposed, including a comparative study of possible sites in Europe, a cost estimate and a model for distributed construction but installation at one central site. As a new large research infrastructure, EuPRAXIA would place Europe at the forefront of the development of novel accelerators driven by the world's most powerful lasers from European industry in the 2020's. The EuPRAXIA consortium has the following participants: Centre National de la Recherche Scientifique (CNRS), Commissariat à l'Énergie Atomique et aux énergies alternatives (CEA) and Synchrotron SOLEIL from France, DESY and the University of Hamburg from Germany, Istituto Nazionale di Fisica Nucleare (INFN), Consiglio Nazionale delle Ricerche (CNR), Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenible (ENEA) and Sapienza Universita di Roma from Italy and Instituto Superior Técnico (IST) from Portugal, Science & Technology Facilities Council (STFC), University of Manchester, University of Liverpool, University of Oxford, University of Strathclyde and Imperial College London from the UK. Associated partners are: Jiaotong University Shanghai and Tsingua University Beijing from China, Extreme Light Infrastructures - Beams (ELI-B) in Czech Republic, University of Lille in France, High Energy Accelerator Research Organization (KEK), Kansai Photon Science Institute, Japan Atomic Energy Agency, Osaka University and RIKEN Spring-8 Center from Japan, Helmholtz-Institut Jena, Helmholtz-Zentrum Dresden-Rossendorf and Ludwig-Maximillians-Universität München from Germany, Wigner Research Center of the Hungarian Academy of Science in Hungary, University of Lund in Sweden, European Organization for Nuclear Research (CERN) in Switzerland, Center for Accelerator Science and Education at Stony Brook University & Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL), SLAC National Accelerator Laboratory and University of California at Los Angeles (UCLA) in the U.S.

Antchev G.,Bulgarian Academy of Science | Aspell P.,CERN | Atanassov I.,Bulgarian Academy of Science | Atanassov I.,CERN | And 88 more authors.
Physical Review Letters | Year: 2013

The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of √s=7 TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to |η|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section σDD=(116±25) μb for events where both diffractive systems have 4.7<|η|minâ¡<6.5. © 2013 CERN. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Source

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