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Christian R Scullard, Susana Serna, Lorin X Benedict, C Leland Ellison, Frank R Graziani
In this work, we elucidate the mathematical structure of the integral that arises when computing the electron-ion temperature equilibration time for a homogeneous weakly coupled plasma from the Lenard-Balescu equation. With some minor approximations, we derive an analytic formula, requiring no input Coulomb logarithm, for the equilibration rate that is valid for moderate electron-ion temperature ratios and arbitrary electron degeneracy. For large temperature ratios, we derive the necessary correction to account for the coupled-mode effect, which can be evaluated very efficiently using ordinary Gaussian quadrature...
January 2018: Physical Review. E
Miguel A Sierra, David Sánchez, Alvar R Garrigues, Enrique Del Barco, Lejia Wang, Christian A Nijhuis
Recent experiments demonstrate a temperature control of the electric conduction through a ferrocene-based molecular junction. Here we examine the results in view of determining means to distinguish between transport through single-particle molecular levels or via transport channels split by Coulomb repulsion. Both transport mechanisms are similar in molecular junctions given the similarities between molecular intralevel energies and the charging energy. We propose an experimentally testable way to identify the main transport process...
February 9, 2018: Nanoscale
Tohid Farajollahpour, Shirin Khamouei, Shabnam Safari Shateri, Arash Phirouznia
Friedel oscillations of the graphene-like materials are investigated theoretically for low and intermediate Fermi energies. Numerical calculations have been performed within the random phase approximation. It was demonstrated that for intra-valley transitions the contribution of the different Dirac points in the wave-number dependent quantities is determined by the orientation of the wave-number in k-space. Therefore, identical contribution of the different Dirac points is not automatically guaranteed by the degeneracy of the Hamiltonian at these points...
February 8, 2018: Scientific Reports
Hanyu Zhu, Jun Yi, Ming-Yang Li, Jun Xiao, Lifa Zhang, Chih-Wen Yang, Robert A Kaindl, Lain-Jong Li, Yuan Wang, Xiang Zhang
Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation...
February 2, 2018: Science
Carlo R Laing
We consider finite and infinite all-to-all coupled networks of identical theta neurons. Two types of synaptic interactions are investigated: instantaneous and delayed (via first-order synaptic processing). Extensive use is made of the Watanabe/Strogatz (WS) ansatz for reducing the dimension of networks of identical sinusoidally-coupled oscillators. As well as the degeneracy associated with the constants of motion of the WS ansatz, we also find continuous families of solutions for instantaneously coupled neurons, resulting from the reversibility of the reduced model and the form of the synaptic input...
February 5, 2018: Journal of Mathematical Neuroscience
Hao Shu, Yongmei Shi, Gang Chen, Zan Wang, Duan Liu, Chunxian Yue, B Douglas Ward, Wenjun Li, Zhan Xu, Guangyu Chen, Qi-Hao Guo, Jun Xu, Shi-Jiang Li, Zhijun Zhang
The apolipoprotein E (APOE) ε4 and ε2 alleles are acknowledged genetic factors modulating Alzheimer's disease (AD) risk and episodic memory (EM) deterioration in an opposite manner. Mounting neuroimaging studies describe EM-related brain activity differences among APOE alleles but remain limited in elucidating the underlying mechanism. Here, we hypothesized that the APOE ε2, ε3, and ε4 alleles have distinct EM neural substrates, as a manifestation of degeneracy, underlying their modulations on EM-related brain activity and AD susceptibility...
February 2, 2018: Brain Imaging and Behavior
Wenbo Gu, Daniel O'Connor, Dan Nguyen, Victoria Y Yu, Dan Ruan, Lei Dong, Ke Sheng
PURPOSE: Intensity Modulated Proton Therapy (IMPT) is the state-of-the-art method of delivering proton radiotherapy. Previous research has been mainly focused on optimization of scanning spots with manually selected beam angles. Due to the computational complexity, the potential benefit of simultaneously optimizing beam orientations and spot pattern could not be realized. In this study, we developed a novel integrated beam orientation optimization (BOO) and scanning-spot optimization algorithm for intensity modulated proton therapy (IMPT)...
February 2, 2018: Medical Physics
Vincent P Mauro
Biotherapeutics are increasingly becoming the mainstay in the treatment of a variety of human conditions, particularly in oncology and hematology. The production of therapeutic antibodies, cytokines, and fusion proteins have markedly accelerated these fields over the past decade and are probably the major contributor to improved patient outcomes. Today, most protein therapeutics are expressed as recombinant proteins in mammalian cell lines. An expression technology commonly used to increase protein levels involves codon optimization...
February 1, 2018: BioDrugs: Clinical Immunotherapeutics, Biopharmaceuticals and Gene Therapy
Yilmaz Gul, Stuart N Holmes, Maksym Myronov, Sanjeev Kumar, Michael Pepper
We have investigated hole transport in quantum wires formed by electrostatic confinement in strained germanium two-dimensional layers. The ballistic conductance characteristics show the regular staircase of quantum levels with plateaux at n2e2/h, where n is an integer, e is the fundamental unit of charge and h is Planck's constant. However as the carrier concentration is reduced, the quantised levels show a behaviour that is indicative of the formation of a zig-zag structure and new quantised plateaux appear at low temperatures...
January 30, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Daewoo Pak, Nan Du, Yunsoo Kim, Yanni Sun, Zachary F Burton
We advocate for a tRNA- rather than an mRNA-centric model for evolution of the genetic code. The mechanism for evolution of cloverleaf tRNA provides a root sequence for radiation of tRNAs and suggests a simplified understanding of code evolution. To analyze code sectoring, rooted tRNAomes were compared for several archaeal and one bacterial species. Rooting of tRNAome trees reveals conserved structures, indicating how the code was shaped during evolution and suggesting a model for evolution of a LUCA tRNAome tree...
January 26, 2018: Transcription
Scott A Robson, Koh Takeuchi, Andras Boeszoermenyi, Paul W Coote, Abhinav Dubey, Sven Hyberts, Gerhard Wagner, Haribabu Arthanari
Backbone resonance assignment is a critical first step in the investigation of proteins by NMR. This is traditionally achieved with a standard set of experiments, most of which are not optimal for large proteins. Of these, HNCA is the most sensitive experiment that provides sequential correlations. However, this experiment suffers from chemical shift degeneracy problems during the assignment procedure. We present a strategy that increases the effective resolution of HNCA and enables near-complete resonance assignment using this single HNCA experiment...
January 24, 2018: Nature Communications
Angelo Giussani, Irene Conti, Artur Nenov, Marco Garavelli
The UVB-induced photomechanism leading the carbonyl group of a thymine nucleobase to react with the carbon-carbon double bond of a consecutive thymine nucleobase in a DNA strand to form the thymine-thymine (6-4) photodamage adduct remains poorly understood. Key questions remain unanswered, concerning both the intrinsic features of the photoreaction (such as the contribution (or not) of triplet states, the nature of the involved states and the time-scale of the photoprocess) and the role played by the non-reactive surroundings of the two reactive pyrimidine nucleobases (such as the nature of the flanked nucleobases and the flexibility of the whole DNA molecule)...
January 23, 2018: Faraday Discussions
Daniele De Martino
In this work maximum entropy distributions in the space of steady states of metabolic networks are considered upon constraining the first and second moments of the growth rate. Coexistence of fast and slow phenotypes, with bimodal flux distributions, emerges upon considering control on the average growth (optimization) and its fluctuations (heterogeneity). This is applied to the carbon catabolic core of Escherichia coli where it quantifies the metabolic activity of slow growing phenotypes and it provides a quantitative map with metabolic fluxes, opening the possibility to detect coexistence from flux data...
December 2017: Physical Review. E
Jeffrey R Haack, Cory D Hauck, Michael S Murillo
We have extended a recently developed multispecies, multitemperature Bhatnagar-Gross-Krook model [Haack et al., J. Stat. Phys. 168, 822 (2017)JSTPBS0022-471510.1007/s10955-017-1824-9], to include multiphysics capabilities that enable modeling of a wider range of physical conditions. In terms of geometry, we have extended from the spatially homogeneous setting to one spatial dimension. In terms of the physics, we have included an atomic ionization model, accurate collision physics across coupling regimes, self-consistent electric fields, and degeneracy in the electronic screening...
December 2017: Physical Review. E
Venu Mehta, Ramandeep S Johal
We consider a quasistatic quantum Otto cycle using two effectively two-level systems with degeneracy in the excited state. The systems are coupled through isotropic exchange interaction of strength J>0, in the presence of an external magnetic field B which is varied during the cycle. We prove the positive work condition and show that level degeneracy can act as a thermodynamic resource, so that a larger amount of work can be extracted than in the nondegenerate case, both with and without coupling. We also derive an upper bound for the efficiency of the cycle...
September 2017: Physical Review. E
Gregory A Babbitt, Erin E Coppola, Jamie S Mortensen, Patrick X Ekeren, Cosmo Viola, Dallan Goldblatt, André O Hudson
Since the elucidation of the genetic code almost 50 years ago, many nonrandom aspects of its codon organization remain only partly resolved. Here, we investigate the recent hypothesis of 'dual-use' codons which proposes that in addition to allowing adjustment of codon optimization to tRNA abundance, the degeneracy in the triplet-based genetic code also multiplexes information regarding DNA's helical shape and protein-binding dynamics while avoiding interference with other protein-level characteristics determined by amino acid properties...
January 17, 2018: Journal of Molecular Evolution
A I Smirnov, T A Soldatov, O A Petrenko, A Takata, T Kida, M Hagiwara, A Ya Shapiro, M E Zhitomirsky
We observe a disappearance of the 1/3 magnetization plateau and a striking change of the magnetic configuration under a moderate doping of the model triangular antiferromagnet RbFe(MoO_{4})_{2}. The reason is an effective lifting of degeneracy of mean-field ground states by a random potential of impurities, which compensates, in the low-temperature limit, the fluctuation contribution to free energy. These results provide a direct experimental confirmation of the fluctuation origin of the ground state in a real frustrated system...
July 28, 2017: Physical Review Letters
Lena C Jake, Thomas M Henderson, Gustavo E Scuseria
We study the behavior of Hartree-Fock (HF) solutions in the vicinity of conical intersections. These are here understood as regions of a molecular potential energy surface characterized by degenerate or nearly degenerate eigenfunctions with identical quantum numbers (point group, spin, and electron numbers). Accidental degeneracies between states with different quantum numbers are known to induce symmetry breaking in HF. The most common closed-shell restricted HF instability is related to singlet-triplet spin degeneracies that lead to collinear unrestricted HF solutions...
January 14, 2018: Journal of Chemical Physics
Yasuhiro Shimizu, Takuya Takahashi, Syunpei Yamada, Ayako Shimokata, Takaaki Jin-No, Masayuki Itoh
Spin-state crossover beyond a conventional ligand-field theory has been a fundamental issue in condensed matter physics. Here, we report microscopic observations of spin states and low-energy dynamics through orbital-resolved NMR spectroscopy in the prototype compound LaCoO_{3}. The ^{59}Co NMR spectrum shows the preserved crystal symmetry across the crossover, inconsistent with d orbital ordering due to the Jahn-Teller distortion. The orbital degeneracy results in a pseudospin (J[over ˜]=1) excited state with an orbital moment observed as ^{59}Co hyperfine coupling tensors...
December 29, 2017: Physical Review Letters
Leonard Pomeranz, John McCarthy, Randy Day, Kevin Zawilski, Peter Schunemann
We report on first demonstrations of CdSiP2-based optical parametric oscillators that are pumped by eye-safe Q-switched nanosecond laser sources operating at 1.57 μm. One device reached 40% optical conversion efficiency generating 10 mJ of energy near degeneracy in the 3 μm region. Angle tuning of a similar device through the middle infrared was demonstrated with the signal and idler waves being tuned from 2.28 μm to 5.05 μm.
January 1, 2018: Optics Letters
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