bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear and non-linear infrared response of one-dimensional vibrational Holstein polarons in the anti-adiabatic limit: Optical and acoustical phonon models
Authors: Falvo Cyril
Published: February 2018

The theory of linear and non-linear infrared response of vibrational Holstein polarons in one-dimensional lattices is presented in order to identify the spectral signatures of self-trapping phenomena. Using a canonical transformation, the optical response is computed from the small polaron point of view which is valid in the anti-adiabatic limit. Two types of phonon baths are considered: optical phonons and acoustical phonons, and simple expressions are derived for the infrared response. It is shown that for the case of optical phonons, the linear response can directly probe the polaron density of states. The model is used to interpret the experimental spectrum of crystalline acetanilide in the C=O range. For the case of acoustical phonons, it is shown that two bound states can be observed in the two-dimensional infrared spectrum at low temperature. At high temperature, analysis of the time-dependence of the two-dimensional infrared spectrum indicates that bath mediated correlations slow down spectral diffusion. The model is used to interpret the experimental linear-spectroscopy of model α-helix and β-sheet polypeptides. This work shows that the Davydov Hamiltonian cannot explain the observations in the NH stretching range.
Biomass energy utilization and soil carbon sequestration in rural China: A case study based on circular agriculture
Authors: Wu Guanglei , Cheng Da , Li Lijun , Li Caihong , Jiang Gaoming , Zheng Yanhai
Published: February 2018

Biogas projects have been promoted by the Chinese government in rural areas for several decades. However, these projects have proceeded slowly under the lack of biogas production technology. A circular agricultural experiment in combination with a local biogas promotion project was carried out in Jiangjiazhuang, a typical agricultural village in China, from 2008 to 2015. Agricultural production proceeded in an agricultural loop: “Crops → Grains/crop residues → Human/cattle → Human/cattle excreta → Biogas digester → Biogas/biogas residues → Domestic fuels/organic fertilizers → Crops.” The abundant crop residues were used as cattle forage to turn the biomass energy into human-edible food. Human/cattle dejecta was used as the substrate to produce biogas for livelihood energy. Biogas digester residues were used as organic fertilizers after composting to improve soil quality and crop yield. The results showed that the proportion of crop residues used for cattle forage increased from 1.3% in 2008 to 86.2% in 2015, while cattle population increased from 3 to 198. The proportion of biogas in total household energy increased from 1.1% in 2008 to 62.3% in 2015. Soil organic carbon increased under organic fertilizer application from 83.8 Mg C hm−2 to 213.5 Mg C hm−2. Our findings demonstrate that the promotion of circular agriculture may effectively enhance the utilization rate of biomass energy (crop residues) and reduce the consumption potential of fossil energy over 50%. Circular agriculture is a sustainable agricultural system that could improve the environmental conditions in rural areas.
Turbulent stress measurements of fibre suspensions in a straight pipe
Authors: MacKenzie Jordan , Söderberg Daniel , Swerin Agne , Lundell Fredrik
Published: February 2018

The focus of the present work is an experimental study of the behaviour of semi-dilute, opaque fibre suspensions in fully developed cylindrical pipe flows. Measurements of the normal and turbulent shear stress components and the mean flow were acquired using phase-contrast magnetic resonance velocimetry. Two fibre types, namely, pulp fibre and nylon fibre, were considered in this work and are known to differ in elastic modulus. In total, three different mass concentrations and seven Reynolds numbers were tested to investigate the effects of fibre interactions during the transition from the plug flow to fully turbulent flow. It was found that in fully turbulent flows of nylon fibres, the normal, ⟨uzuz⟩+, and shear, ⟨uzur⟩+ (note that ⟨·⟩ is the temporal average, u is the fluctuating velocity, z is the axial or streamwise component, and r is the radial direction), turbulent stresses increased with Reynolds number regardless of the crowding number (a concentration measure). For pulp fibre, the turbulent stresses increased with Reynolds number when a fibre plug was present in the flow and were spatially similar in magnitude when no fibre plug was present. Pressure spectra revealed that the stiff, nylon fibre reduced the energy in the inertial-subrange with an increasing Reynolds and crowding number, whereas the less stiff pulp fibre effectively cuts the energy cascade prematurely when the network was fully dispersed.
Observation of electron driven quasi-coherent modes and their connection with core intrinsic rotation in KSTAR ECH and ohmic L-mode plasmas
Authors: Lee J. A. , Lee W. , Kwon J. M. , Ko S. H. , Leem J. , Yun G. S. , Park H. K. , Park Y. S. , Kim K. W. , Luhmann N. C. ,   KSTAR Team
Published: February 2018

Quasi-coherent (QC) modes, known as a type of the trapped electron mode (TEM) turbulence, have been measured in the outboard core region of low-density electron cyclotron resonant heating (ECH) injected and ohmically heated L-mode plasmas on the Korea Superconducting Tokamak Advanced Research (KSTAR) device. It appears that QC modes of 20–60 kHz occur or strengthen with an increase of the electron temperature to ion temperature ratio, but weaken or are fully suppressed by increased density/collisionality. Toroidal rotation shear, which is strongly related to the density/collisionality, also seems to stabilize the QC modes. Linear gyrokinetic simulations indicate that TEM is the most unstable mode at low densities where the QC modes are observed for both the ECH and ohmic plasmas. At high densities where the QC modes are suppressed, the most unstable mode is the ion temperature gradient (ITG) mode for the ECH plasmas but still TEM for the ohmic plasmas. In the ECH plasmas, it is found that the direction of the core toroidal intrinsic rotation is gradually reversed from the co-current to counter-current direction and the QC mode is suppressed as the line-averaged density increases, which can be explained by the transition of dominant micro-turbulence (TEM to ITG). However, in the ohmically heated plasmas, the acceleration of the core toroidal rotation is not fully explained by the TEM-ITG transition since the direction of the core toroidal rotation is counter-current direction when the QC mode is observed. Furthermore, the core toroidal rotation is accelerated to the counter-current direction even the line-averaged density decreases.
Theoretical analysis and Vsim simulation of a low-voltage high-efficiency 250 GHz gyrotron
Authors: An Chenxiang , Zhang Dian , Zhang Jun , Zhong Huihuang
Published: February 2018

Low-voltage, high-frequency gyrotrons with hundreds of watts of power are useful in radar, magnetic resonance spectroscopy and plasma diagnostic applications. In this paper, a 10 kV, 478 W, 250 GHz gyrotron with an efficiency of nearly 40% and a pitch ratio of 1.5 was designed through linear and nonlinear numerical analyses and Vsim particle-in-cell (PIC) simulation. Vsim is a highly efficient parallel PIC code, but it has seldom been used to carry out electron beam wave interaction simulations of gyro-devices. The setting up of the parameters required for the Vsim simulations of the gyrotron is presented. The results of Vsim simulations agree well with that of nonlinear numerical calculation. The commercial software Vsim7.2 completed the 3D gyrotron simulation in 80 h using a 20 core, 2.2 GHz personal computer with 256 GBytes of memory.
Experimental investigation on the repetitively nanosecond pulsed dielectric barrier discharge with the parallel magnetic field
Authors: Liu Yidi , Yan Huijie , Guo Hongfei , Fan Zhihui , Wang Yuying , Ren Chunsheng
Published: February 2018

The effects of a parallel magnetic field on the unipolar positive nanosecond pulsed dielectric barrier discharge are experimentally investigated through electrical and spectral measurements. The discharge is produced between two parallel-plate electrodes in the ambient air with a parallel magnetic field of 1.4 T. Experimental results show that both the discharge intensity and uniformity are improved in the discharge with the parallel magnetic field. The intensity ratio of the spectrum at 371.1 nm and 380.5 nm, which describes the average electron density, is increased by the parallel magnetic field. Meanwhile, the intensity ratio of the spectrum at 391.4 nm and 337.1 nm, which describes the electron temperature, is also increased. It is speculated that both the average electron density and the electron temperature are increased by the parallel magnetic field. The aforementioned phenomena have been explained by the confinement effect of the parallel magnetic field on the electrons.
Transfer and patterning of chemical vapor deposited graphene by a multifunctional polymer film
Authors: Kaplas Tommi , Bera Arijit , Matikainen Antti , Pääkkönen Pertti , Lipsanen Harri
Published: February 2018

Graphene is seeking pathways towards applications, but there are still plenty of unresolved problems on the way. Many of those obstacles are related to synthesis and processing of graphene. Chemical vapor deposition (CVD) of graphene is currently one of the most promising techniques that enable scalable synthesis of high quality graphene on a copper substrate. From the transient metal substrate, the CVD graphene film is transferred to the desired dielectric substrate. Most often, the transfer process is done by using a supporting poly(methyl methacrylate) (PMMA) film, which is also a widely used electron beam resist. Conventionally, after graphene is transferred to the substrate, the supporting PMMA film is removed by organic solvents. Hence, the potential of using the same PMMA layer as a resist mask remains unexplored. Since PMMA is an electron beam resist, the same polymer film can be useful both for transferring and for patterning of graphene. In this work, we demonstrate simultaneous transfer and patterning of graphene by using the same PMMA film. With our demonstrated method, we are able to receive sub-micron resolution very easily. The graphene transfer and its subsequent patterning with the same resist layer may help developing device applications based on graphene and other 2D materials in the near future.
Adaptive frozen orbital treatment for the fragment molecular orbital method combined with density-functional tight-binding
Authors: Nishimoto Yoshio , Fedorov Dmitri G.
Published: February 2018

The exactly analytic gradient is derived and implemented for the fragment molecular orbital (FMO) method combined with density-functional tight-binding (DFTB) using adaptive frozen orbitals. The response contributions which arise from freezing detached molecular orbitals on the border between fragments are computed by solving Z-vector equations. The accuracy of the energy, its gradient, and optimized structures is verified on a set of representative inorganic materials and polypeptides. FMO-DFTB is applied to optimize the structure of a silicon nano-wire, and the results are compared to those of density functional theory and experiment. FMO accelerates the DFTB calculation of a boron nitride nano-ring with 7872 atoms by a factor of 406. Molecular dynamics simulations using FMO-DFTB applied to a 10.7 μm chain of boron nitride nano-rings, consisting of about 1.2 × 106 atoms, reveal the rippling and twisting of nano-rings at room temperature.
Mixtures of glyme and aprotic-protic ionic liquids as electrolytes for energy storage devices
Authors: Stettner T. , Huang P. , Goktas M. , Adelhelm P. , Balducci A.
Published: February 2018

Ionic liquids (ILs) have been proven to be promising electrolytes for electrochemical energy storage devices such as supercapacitors and lithium ion batteries. In the last years, due to deficiency in storage of lithium on earth, innovative systems, such as sodium-based devices, attracted considerable attention. IL-based electrolytes have been proposed also as electrolytes for these devices. Nevertheless, in the case of these systems, the advantages and limits of IL-based electrolytes need to be further investigated. In this work we report an investigation about the chemical-physical properties of mixtures containing bis(2-methoxyethyl)ether diglyme (2G), which is presently considered as one of the most interesting solvents for sodium-based devices, and the ionic liquids 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and 1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrH4TFSI). The conductivities, viscosities, and densities of several mixtures of 2G and these ILs have been investigated. Furthermore, their impact on the electrochemical behaviour of activated carbon composite electrodes has been considered. The results of this investigation indicate that these mixtures are promising electrolytes for the realization of advanced sodium-based devices.
Temperature dependence of dissociative electron attachment to bromo-chlorotoluene isomers: Competition between detachment of Cl− and Br−
Authors: Mahmoodi-Darian Masoomeh , Huber Stefan E. , Mauracher Andreas , Probst Michael , Denifl Stephan , Scheier Paul , Märk Tilmann D.
Published: February 2018

Dissociative electron attachment to three isomers of bromo-chlorotoluene was investigated in the electron energy range from 0 to 2 eV for gas temperatures in the range of 392-520 K using a crossed electron-molecular beam apparatus with a temperature regulated effusive molecular beam source. For all three molecules, both Cl− and Br− are formed. The ion yields of both halogenides show a pronounced temperature effect. In the case of Cl− and Br−, the influence of the gas temperature can be observed at the threshold peak close to 0 eV. The population of molecules that have some of their out-of-plane modes excited varies strongly in the temperature range investigated, indicating that such vibrations might play a role in the energy transfer towards bond breaking. Potential energy curves for the abstraction of Cl− and Br− were calculated and extrapolated into the metastable domain. The barriers in the diabatic curves approximated in this way agree well with the ones derived from the temperature dependence observed in the experiments.
Composite pulses in N-level systems with SU(2) symmetry and their geometrical representation on the Majorana sphere
Authors: Greener H. , Suchowski H.
Published: February 2018

High fidelity and robustness in population inversion is very desirable for many quantum control applications. We expand composite pulse schemes developed for two-level dynamics and present an analytic solution for the coherent evolution of an N-level quantum system with SU(2) symmetry, for achieving high fidelity and robust population inversion. Our approach offers a platform for accurate steering of the population transfer in physical multi-level systems, which is crucial for fidelity in quantum computation and achieving fundamental excitations in nuclear magnetic resonances and atomic physics. We also introduce and discuss the geometrical trajectories of these dynamics on the Majorana sphere as an interpretation, allowing us to gain physical insight on the dynamics of many-body or high-dimensional quantum systems.
Applying neutron transmission physics and 3D statistical full-field model to understand 2D Bragg-edge imaging
Authors: Xie Q. , Song G. , Gorti S. , Stoica A. D. , Radhakrishnan B. , Bilheux J. C. , Kirka M. , Dehoff R. , Bilheux H. Z. , An K.
Published: February 2018

Bragg-edge imaging, which is also known as neutron radiography, has recently emerged as a novel crystalline characterization technique. Modelling of this novel technique by incorporating various features of the underlying microstructure (including the crystallographic texture, the morphological texture, and the grain size) of the material remains a subject of considerable research and development. In this paper, Inconel 718 samples made by additive manufacturing were investigated by neutron diffraction and neutron radiography techniques. The specimen features strong morphological and crystallographic textures and a highly heterogeneous microstructure. A 3D statistical full-field model is introduced by taking details of the microstructure into account to understand the experimental neutron radiography results. The Bragg-edge imaging and the total cross section were calculated based on the neutron transmission physics. A good match was obtained between the model predictions and experimental results at different incident beam angles with respect to the sample build direction. The current theoretical approach has the ability to incorporate 3D spatially resolved microstructural heterogeneity information and shows promise in understanding the 2D neutron radiography of bulk samples. With further development to incorporate the heterogeneity in lattice strain in the model, it can be used as a powerful tool in the future to better understand the neutron radiography data.
Driving reconnection in sheared magnetic configurations with forced fluctuations
Authors: Pongkitiwanichakul Peera , Makwana Kirit D. , Ruffolo David
Published: February 2018

We investigate reconnection of magnetic field lines in sheared magnetic field configurations due to fluctuations driven by random forcing by means of numerical simulations. The simulations are performed with an incompressible, pseudo-spectral magnetohydrodynamics code in 2D where we take thick, resistively decaying, current-sheet like sheared magnetic configurations which do not reconnect spontaneously. We describe and test the forcing that is introduced in the momentum equation to drive fluctuations. It is found that the forcing does not change the rate of decay; however, it adds and removes energy faster in the presence of the magnetic shear structure compared to when it has decayed away. We observe that such a forcing can induce magnetic reconnection due to field line wandering leading to the formation of magnetic islands and O-points. These reconnecting field lines spread out as the current sheet decays with time. A semi-empirical formula is derived which reasonably explains the formation and spread of O-points. We find that reconnection spreads faster with stronger forcing and longer correlation time of forcing, while the wavenumber of forcing does not have a significant effect. When the field line wandering becomes large enough, the neighboring current sheets with opposite polarity start interacting, and then the magnetic field is rapidly annihilated. This work is useful to understand how forced fluctuations can drive reconnection in large scale current structures in space and astrophysical plasmas that are not susceptible to reconnection.
Remarks on the chemical Fokker-Planck and Langevin equations: Nonphysical currents at equilibrium
Authors: Ceccato Alessandro , Frezzato Diego
Published: February 2018

The chemical Langevin equation and the associated chemical Fokker-Planck equation are well-known continuous approximations of the discrete stochastic evolution of reaction networks. In this work, we show that these approximations suffer from a physical inconsistency, namely, the presence of nonphysical probability currents at the thermal equilibrium even for closed and fully detailed-balanced kinetic schemes. An illustration is given for a model case.
Optimization of long range potential interaction parameters in ion mobility spectrometry
Authors: Wu Tianyang , Derrick Joseph , Nahin Minal , Chen Xi , Larriba-Andaluz Carlos
Published: February 2018

The problem of optimizing Lennard-Jones (L-J) potential parameters to perform collision cross section (CCS) calculations in ion mobility spectrometry has been undertaken. The experimental CCS of 16 small organic molecules containing carbon, hydrogen, oxygen, nitrogen, and fluoride in N2 was compared to numerical calculations using Density Functional Theory (DFT). CCS calculations were performed using the momentum transfer algorithm IMoS and a 4-6-12 potential without incorporating the ion-quadrupole potential. A ceteris paribus optimization method was used to optimize the intercept σ and potential well-depth ϵ for the given atoms. This method yields important information that otherwise would remain concealed. Results show that the optimized L-J parameters are not necessarily unique with intercept and well-depth following an exponential relation at an existing line of minimums. Similarly, the method shows that some molecules containing atoms of interest may be ill-conditioned candidates to perform optimizations of the L-J parameters. The final calculated CCSs for the chosen parameters differ 1% on average from their experimental counterparts. This result conveys the notion that DFT calculations can indeed be used as potential candidates for CCS calculations and that effects, such as the ion-quadrupole potential or diffuse scattering, can be embedded into the L-J parameters without loss of accuracy but with a large increase in computational efficiency.
Employing general fit-bases for construction of potential energy surfaces with an adaptive density-guided approach
Authors: Klinting Emil Lund , Thomsen Bo , Godtliebsen Ian Heide , Christiansen Ove
Published: February 2018

We present an approach to treat sets of general fit-basis functions in a single uniform framework, where the functional form is supplied on input, i.e., the use of different functions does not require new code to be written. The fit-basis functions can be used to carry out linear fits to the grid of single points, which are generated with an adaptive density-guided approach (ADGA). A non-linear conjugate gradient method is used to optimize non-linear parameters if such are present in the fit-basis functions. This means that a set of fit-basis functions with the same inherent shape as the potential cuts can be requested and no other choices with regards to the fit-basis functions need to be taken. The general fit-basis framework is explored in relation to anharmonic potentials for model systems, diatomic molecules, water, and imidazole. The behaviour and performance of Morse and double-well fit-basis functions are compared to that of polynomial fit-basis functions for unsymmetrical single-minimum and symmetrical double-well potentials. Furthermore, calculations for water and imidazole were carried out using both normal coordinates and hybrid optimized and localized coordinates (HOLCs). Our results suggest that choosing a suitable set of fit-basis functions can improve the stability of the fitting routine and the overall efficiency of potential construction by lowering the number of single point calculations required for the ADGA. It is possible to reduce the number of terms in the potential by choosing the Morse and double-well fit-basis functions. These effects are substantial for normal coordinates but become even more pronounced if HOLCs are used.
Hamiltonian structure of the guiding center plasma model
Authors: Burby J. W. , Sengupta W.
Published: February 2018

The guiding center plasma model (also known as kinetic MHD) is a rigorous sub-cyclotron-frequency closure of the Vlasov-Maxwell system. While the model has been known for decades and it plays a fundamental role in describing the physics of strongly magnetized collisionless plasmas, its Hamiltonian structure has never been found. We provide explicit expressions for the model's Poisson bracket and Hamiltonian and thereby prove that the model is an infinite-dimensional Hamiltonian system. The bracket is derived in a manner which ensures that it satisfies the Jacobi identity. We also report on several previously unknown circulation theorems satisfied by the guiding center plasma model. Without knowledge of the Hamiltonian structure, these circulation theorems would be difficult to guess.
Short-time dynamics of lysozyme solutions with competing short-range attraction and long-range repulsion: Experiment and theory
Authors: Riest Jonas , Nägele Gerhard , Liu Yun , Wagner Norman J. , Godfrin P. Douglas
Published: February 2018

Recently, atypical static features of microstructural ordering in low-salinity lysozyme protein solutions have been extensively explored experimentally and explained theoretically based on a short-range attractive plus long-range repulsive (SALR) interaction potential. However, the protein dynamics and the relationship to the atypical SALR structure remain to be demonstrated. Here, the applicability of semi-analytic theoretical methods predicting diffusion properties and viscosity in isotropic particle suspensions to low-salinity lysozyme protein solutions is tested. Using the interaction potential parameters previously obtained from static structure factor measurements, our results of Monte Carlo simulations representing seven experimental lysoyzme samples indicate that they exist either in dispersed fluid or random percolated states. The self-consistent Zerah-Hansen scheme is used to describe the static structure factor, S(q), which is the input to our calculation schemes for the short-time hydrodynamic function, H(q), and the zero-frequency viscosity η. The schemes account for hydrodynamic interactions included on an approximate level. Theoretical predictions for H(q) as a function of the wavenumber q quantitatively agree with experimental results at small protein concentrations obtained using neutron spin echo measurements. At higher concentrations, qualitative agreement is preserved although the calculated hydrodynamic functions are overestimated. We attribute the differences for higher concentrations and lower temperatures to translational-rotational diffusion coupling induced by the shape and interaction anisotropy of particles and clusters, patchiness of the lysozyme particle surfaces, and the intra-cluster dynamics, features not included in our simple globular particle model. The theoretical results for the solution viscosity, η, are in qualitative agreement with our experimental data even at higher concentrations. We demonstrate that semi-quantitative predictions of diffusion properties and viscosity of solutions of globular proteins are possible given only the equilibrium structure factor of proteins. Furthermore, we explore the effects of changing the attraction strength on H(q) and η.
Micro-cones on a liquid interface in high electric field: Ionization effects
Authors: Subbotin Andrey V. , Semenov Alexander N.
Published: February 2018

We formulate and explore electrohydrodynamic equations for conductive liquids taking dissociation/recombination processes into account and discover a novel type of liquid cones which carry both surface and net bulk charge and can be formed on a liquid interface in an electric field. The bulk charge is generated by the corona discharge due to a high electric field at the cone apex. We establish correlation between the cone angle and physical parameters of the liquid on the one hand and the electric current passing through the cone on the other hand. It is shown that the current strongly increases when the cone angle tends to a critical value which is a function of the dielectric permittivity of the liquid. The cone stability with respect to axially symmetric perturbations is analyzed. It is shown that the cones with apex angles close to the critical angle are likely to be stable. The effect of the imposed flow on the cone apex stability is also discussed.
Electron reflection in thermionic energy converters
Authors: Lim Ian T. , Lambert Scott A. , Vay Jean-Luc , Schwede Jared W.
Published: February 2018

We investigate the impact of electron reflection on space charge in thermionic energy converters. Using the particle-in-cell code Warp3D, we simulate electron reflection and discover that specular and diffuse reflection produce fundamentally distinct behavior. Our simulations suggest that the effects of reflection may have been misidentified in experiments as anomalously large gap sizes. As a result, electron reflection may significantly alter the analysis and optimization of real-world converters.
Plasma density injection and flow during coaxial helicity injection in a tokamak
Authors: Hooper E. B.
Published: February 2018

Whole device, resistive MHD simulations of spheromaks and tokamaks have used a large diffusion coefficient that maintains a nearly constant density throughout the device. In the present work, helicity and plasma are coinjected into a low-density plasma in a tokamak with a small diffusion coefficient. As in previous simulations [Hooper et al., Phys. Plasmas 20, 092510 (2013)], a flux bubble is formed, which expands to fill the tokamak volume. The injected plasma is non-uniform inside the bubble. The flow pattern is analyzed; when the simulation is not axisymmetric, an n = 1 mode on the surface of the bubble generates leakage of plasma into the low-density volume. Closed flux is generated following injection, as in experiments and previous simulations. The result provides a more detailed physics analysis of the injection, including density non-uniformities in the plasma that may affect its use as a startup plasma [Raman et al., Phys. Rev. Lett. 97, 175002 (2006)].
Analytical models of transmission probabilities for electron sources
Authors: Jensen Kevin L. , Finkenstadt Daniel , Shiffler Donald A. , Shabaev Andrew , Lambrakos Samuel G. , Moody Nathan A. , Petillo John J.
Published: February 2018

Electron emission from coated surfaces as a result of thermal, field, and photoemission effects is often described theoretically using models dependent on the Kemble approximation for the transmission probability D(k). The validity of the approximation for the simple potential profiles (rectangular, triangular, and parabolic) is examined, and generalizations with respect to the exponential of the Gamow tunneling factor and the coefficients of D(k), which are generally ignored, are examined and extended to when the barriers become wells. As a result, unity transmission probabilities (D(k)→1) with regard to both resonant tunneling barrier and reflectionless well behavior are contrasted. The adaptation of the findings to a general thermal-field-photoemission equation is considered. Consequences for the usage of general emission equations in beam optics code [e.g., Particle-in-Cell (PIC)] such as MICHELLE are discussed.
Demonstration of laser-produced neutron diagnostic by radiative capture gamma-rays
Authors: Zhang Xiaopeng , Wei Wenqing , Fu Changbo , Yuan Xiaohui , An Honghai , Deng Yanqing , Fang Yuan , Gao Jian , Ge Xulei , Guo Bing , He Chuangye , Hu Peng , Hua Neng , Jiang Weiman , Li Liang , Li Mengting , Li Yifei , Li Yutong , Liao Guoqian , Liu Feng , Liu Longxiang , Wang Hongwei , Yang Pengqian , Yang Su , Yang Tao , Zhang Guoqiang , Zhang Yue , Zhu Baoqiang , Xi Xiaofeng , Zhu Jianqiang , Sheng Zhengming , Zhang Jie
Published: February 2018

We report a new scenario of the time-of-flight technique in which fast neutrons and delayed gamma-ray signals were both recorded in a millisecond time window in harsh environments induced by high-intensity lasers. The delayed gamma signals, arriving far later than the original fast neutron and often being ignored previously, were identified to be the results of radiative captures of thermalized neutrons. The linear correlation between the gamma photon number and the fast neutron yield shows that these delayed gamma events can be employed for neutron diagnosis. This method can reduce the detecting efficiency dropping problem caused by prompt high-flux gamma radiation and provides a new way for neutron diagnosing in high-intensity laser-target interaction experiments.
Enhancing the x-ray output of a single-wire explosion with a gas-puff based plasma opening switch
Authors: Engelbrecht Joseph T. , Ouart Nicholas D. , Qi Niansheng , de Grouchy Philip W. , Shelkovenko Tatiana A. , Pikuz Sergey A. , Banasek Jacob T. , Potter William M. , Rocco Sophia V. , Hammer David A. , Kusse Bruce R. , Giuliani John L.
Published: February 2018

We present experiments performed on the 1 MA COBRA generator using a low density, annular, gas-puff z-pinch implosion as an opening switch to rapidly transfer a current pulse into a single metal wire on axis. This gas-puff on axial wire configuration was studied for its promise as an opening switch and as a means of enhancing the x-ray output of the wire. We demonstrate that current can be switched from the gas-puff plasma into the wire, and that the timing of the switch can be controlled by the gas-puff plenum backing pressure. X-ray detector measurements indicate that for low plenum pressure Kr or Xe shots with a copper wire, this configuration can offer a significant enhancement in the peak intensity and temporal distribution of radiation in the 1–10 keV range.
Novel circuit design for high-impedance and non-local electrical measurements of two-dimensional materials
Authors: De Sanctis Adolfo , Mehew Jake D. , Alkhalifa Saad , Tate Callum P. , White Ashley , Woodgate Adam R. , Craciun Monica F. , Russo Saverio
Published: February 2018

Two-dimensional materials offer a novel platform for the development of future quantum technologies. However, the electrical characterisation of topological insulating states, non-local resistance, and bandgap tuning in atomically thin materials can be strongly affected by spurious signals arising from the measuring electronics. Common-mode voltages, dielectric leakage in the coaxial cables, and the limited input impedance of alternate-current amplifiers can mask the true nature of such high-impedance states. Here, we present an optical isolator circuit which grants access to such states by electrically decoupling the current-injection from the voltage-sensing circuitry. We benchmark our apparatus against two state-of-the-art measurements: the non-local resistance of a graphene Hall bar and the transfer characteristic of a WS2 field-effect transistor. Our system allows the quick characterisation of novel insulating states in two-dimensional materials with potential applications in future quantum technologies.
Collisionless kinetic theory of oblique tearing instabilities
Authors: Baalrud S. D. , Bhattacharjee A. , Daughton W.
Published: February 2018

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. We find that this stabilization is associated with the density-gradient-driven diamagnetic drift. The analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. A simple analytic estimate for the stability criterion is provided.
General connected and reconnected fields in plasmas
Authors: Mahajan Swadesh M. , Asenjo Felipe A.
Published: February 2018

For plasma dynamics, more encompassing than the magnetohydrodynamical (MHD) approximation, the foundational concepts of “magnetic reconnection” may require deep revisions because, in the larger dynamics, magnetic field is no longer connected to the fluid lines; it is replaced by more general fields (one for each plasma specie) that are weighted combination of the electromagnetic and the thermal-vortical fields. We study the two-fluid plasma dynamics plasma expressed in two different sets of variables: the two-fluid (2F) description in terms of individual fluid velocities, and the one-fluid (1F) variables comprising the plasma bulk motion and plasma current. In the 2F description, a Connection Theorem is readily established; we show that, for each specie, there exists a Generalized (Magnetofluid/Electro-Vortic) field that is frozen-in the fluid and consequently remains, forever, connected to the flow. This field is an expression of the unification of the electromagnetic, and fluid forces (kinematic and thermal) for each specie. Since the magnetic field, by itself, is not connected in the first place, its reconnection is never forbidden and does not require any external agency (like resistivity). In fact, a magnetic field reconnection (local destruction) must be interpreted simply as a consequence of the preservation of the dynamical structure of the unified field. In the 1F plasma description, however, it is shown that there is no exact physically meaningful Connection Theorem; a general and exact field does not exist, which remains connected to the bulk plasma flow. It is also shown that the helicity conservation and the existence of a Connected field follow from the same dynamical structure; the dynamics must be expressible as an ideal Ohm's law with a physical velocity. This new perspective, emerging from the analysis of the post MHD physics, must force us to reexamine the meaning as well as our understanding of magnetic reconnection.
Detailed balance as a quantum-group symmetry of Kraus operators
Authors: Andersson Andreas
Published: February 2018

A unital completely positive map governing the time evolution of a quantum system is usually called a quantum channel, and it can be represented by a tuple of operators which are then referred to as the Kraus operators of the channel. We look at states of the system whose correlations with respect to the channel have a certain symmetry. Then we show that detailed balance holds if the Kraus operators satisfy a very interesting algebraic relation which plays an important role in the representation theory of any compact quantum group.
Fabry-Perot optical cavity inspires new surface acoustic wave resonator
Authors: Kim Meeri
Published: February 2018

A new study borrows principles of design from optical resonators to create a high-quality factor Fabry-Perot acoustic resonator.
Transition metal complex-mediated chemistry of 1,3,5-cycloheptatrienes
Authors: Dyakonov Vladimir A. , Kadikova Gulnara N. , Dzhemilev Usein M.
Published: February 2018

The current review summarizes the published data on transition metal complex-mediated chemistry of 1,3,5-cycloheptatrienes. It addresses homodimerization of cycloheptatrienes and cyclocodimerization of the latter with alkenes, dienes and alkynes in the presence of transition metal complexes that occur via [2π + 2π], [3π + 2π], [6π + 2π], [6π + 4π] and [6π + 2π + 2π] cycloadditions. Special attention is given to the application of these reactions in the synthesis of valuable strained bi-, tri- and polycyclic compounds and for the development of methods of stereoselective synthesis of natural products.

The bibliography includes 91 references.
Rodent management issues in South Pacific islands: a review with case studies from Papua New Guinea and Vanuatu
Authors: Brown Peter R. , Aplin Ken P. , Hinds Lyn A. , Jacob Jens , Thomas Sarah E. , Ritchie Barbara J.
Published: February 2018

Rodents are a key pest to agricultural and rural island communities of the South Pacific, but there is limited information of their impact on the crops and livelihoods of small-scale farmers. The rodent pest community is known, but the type and scales of damage to different crops on different islands are unknown. Knowledge about rodent pest management in other geographical regions may not be directly transferable to the Pacific region. Many studies on islands have largely focussed on the eradication of rodents from uninhabited islands for conservation benefits. These broadscale eradication efforts are unlikely to translate to inhabited islands because of complex social and agricultural issues. The livelihoods, culture and customs of poor small-scale farmers in the South Pacific have a large bearing on the current management of rodents. The aim of the present review was to describe the rodent problems, impacts and management of rodents on South Pacific islands, and identify gaps for further research. We compared and contrasted two case studies. The situation in Papua New Guinea is emergent as several introduced rodent species are actively invading new areas with wide-ranging implications for human livelihoods and conservation. In Vanuatu, we show how rodent damage on cocoa plantations can be reduced by good orchard hygiene through pruning and weeding, which also has benefits for the management of black pod disease. We conclude that (1) damage levels are unknown and unreported, (2) the impacts on human health are unknown, (3) the relationships between the pest species and their food sources, breeding and movements are not known, and (4) the situation in Papua New Guinea may represent an emergent crisis that warrants further investigation. In addition, there is a need for greater understanding of the invasive history of pest rodents, so as to integrate biological information with management strategies. Ecologically based rodent management can be achieved on Pacific Islands, but only after significant well funded large-scale projects are established and rodent ecologists are trained. We can learn from experiences from other locations such as Southeast Asia to guide the way.
Between corpus-based and corpus-driven approaches to textual recurrence
Authors: Goźdź-Roszkowski Stanisław
Published: February 2018

The article investigates the link between lexical and meaning patterns in the specialized discourse of judicial opinions. It presents an analysis of the N that pattern in a corpus of US Supreme Court opinions. The analysis looks at the distribution of a selection of nouns found in the pattern across different discourse functions. It is shown that judicial opinions use a range of status-indicating nouns in the N that pattern to perform five main functions: evaluation, cause, result, confirmation and existence. Yet, evaluation plays a central role in judicial writing and most status-indicating nouns are used to signal sites of contentions, i.e. challenged propositions are likely to be labelled as arguments, assumptions, notions or suggestions. By drawing on the concept of semantic sequence (Hunston 2008), the analysis illustrates how corpus-based and corpus-driven approaches can complement one another to build a picture of common epistemological practices in the corpus of legal texts.
Lexical bundles in Early Modern and Present-day English Acts of Parliament
Authors: Lehto Anu
Published: February 2018

This chapter analyses three-word sequences in Early Modern and Present-day English legal writing by defining their grammatical and functional distribution in Acts of Parliament. The method follows a corpus-driven approach: the lexical bundles are retrieved automatically from the corpus using frequency as the criterion. The study indicates that lexical bundles in acts extend to the textual level and reveals consistent word combinations on the level of the lexis. The study illustrates that the acts are established as a genre, and the overall distribution of both grammatical types and functions of bundles is rather similar in all the analysed periods. Nevertheless, textual organisation is more important in contemporary acts and textual links further become more specific, although early modern bundles already show textual patterning. Noun phrase and prepositional phrases also increase in contemporary acts, indicating a change to nominal writing conventions.
Let's just say we’d like to avoid any great power entanglements: desecuritization in post-Mao Chinese foreign policy towards major powers
Authors: Vuori Juha A.
Published: February 2018

Previous studies on securitization in China have shown how security discourses can have various domestic political functions, how even security issues can be contested, and how China engages with the securitization moves of neighbouring states. Despite this growing literature, there is however no general view of desecuritization as a part of Chinese foreign policy towards the major powers. To fill this gap, the present article examines desecuritization in the foreign policy of post-Mao China. This discussion begins with the desecuritization of the Cold War, and then views how China has sought to prevent the securitization of China's rise in the US. This discussion contributes to the study of Chinese foreign policy maxims by providing it with insights seen through the lens of desecuritization.
Existential threats and regulating life: securitization in the contemporary Middle East
Authors: Mabon Simon
Published: February 2018

This article applies the concept of securitization to the Middle East with a focus upon the securitization of the Shi’a other. Such processes occur across time and space and are not restricted to state borders, escaping the Westphalian straitjacket. As a consequence, one must consider the construction of space and political structures across the region in order to understand the traction that such moves can find. It appears then, that in seeking to maintain short-term survival, regimes have sacrificed long-term stability, but the impacts of such moves transcend the typically linear constructed audiences within securitization moves. A key contribution of this article is to consider the extent to which audiences within the Middle East, both intended and unintended, transcend the linear audiences found within conventional processes of securitization. The article uses two case studies as a means of exploring the extent to which securitization can be applied to the Middle East. Such an approach helps us to identify the logics that are involved within the process of securitization, with consideration of the idea that we can populate a broad framework about the universal application of securitization to context specific cases.
SNAREing an ARP requires a LIR
Authors: Tooze Sharon A.
Published: February 2018

The fusion of autophagosomes with lysosomes is an obligatory step in the self-eating process of autophagy. In this issue, Kumar et al. (2018. J. Cell Biol. https://doi.org/10.1083/jcb.201708039) identify a protein complex, the autophagosome recognition particle (ARP), that chaperones a key SNARE, syntaxin 17, to the autophagosome membrane. Intriguingly, this protein complex coordinates both delivery and membrane insertion as a prelude to fusion.
How mitotic spindles point to the exit
Authors: Short Ben
Published: February 2018

Study reveals that an interaction between myosin-10 and Wee1 may link spindle positioning to mitotic progression.
ZEB1, ZEB2, and the miR-200 family form a counterregulatory network to regulate CD8+ T cell fates
Authors: Guan Tianxia , Dominguez Claudia X. , Amezquita Robert A. , Laidlaw Brian J. , Cheng Jijun , Henao-Mejia Jorge , Williams Adam , Flavell Richard A. , Lu Jun , Kaech Susan M.
Published: February 2018

Long-term immunity depends partly on the establishment of memory CD8+ T cells. We identified a counterregulatory network between the homologous transcription factors ZEB1 and ZEB2 and the miR-200 microRNA family, which modulates effector CD8+ T cell fates. Unexpectedly, Zeb1 and Zeb2 had reciprocal expression patterns and were functionally uncoupled in CD8+ T cells. ZEB2 promoted terminal differentiation, whereas ZEB1 was critical for memory T cell survival and function. Interestingly, the transforming growth factor β (TGF-β) and miR-200 family members, which counterregulate the coordinated expression of Zeb1 and Zeb2 during the epithelial-to-mesenchymal transition, inversely regulated Zeb1 and Zeb2 expression in CD8+ T cells. TGF-β induced and sustained Zeb1 expression in maturing memory CD8+ T cells. Meanwhile, both TGF-β and miR-200 family members selectively inhibited Zeb2. Additionally, the miR-200 family was necessary for optimal memory CD8+ T cell formation. These data outline a previously unknown genetic pathway in CD8+ T cells that controls effector and memory cell fate decisions.