bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent advances in controlling the internal and external properties of self-assembling cyclic peptide nanotubes and dimers
Authors: Rodríguez-Vázquez N. , Amorín M. , Granja J. R.
Published: March 2017

Tuning the internal and external properties of self-assembling cyclic peptide nanotubes.
Polyurethane based organic macromolecular contrast agents (PU-ORCAs) for magnetic resonance imaging
Authors: Garmendia Sofiem , Mantione Daniele , Alonso-de Castro Silvia , Jehanno Coralie , Lezama Luis , Hedrick James L. , Mecerreyes David , Salassa Luca , Sardon Haritz
Published: March 2017

Combination of its convenience for non-invasive application and high spatial resolution make Magnetic Resonance Imaging (MRI) one of the leading imaging modalities.
Palladium-catalyzed coupling of azoles with 1-aryltriazenes via C–H/C–N cleavage
Authors: Dai Wei-Can , Wang Zhong-Xia
Published: March 2017

Arylation of azoles was performed via C–H functionalization with 1-aryltriazenes in the presence of PdCl2, dppe, CuCl and ButOLi.
Two pairs of Zn(ii) coordination polymer enantiomers based on chiral aromatic polycarboxylate ligands: synthesis, crystal structures and properties
Authors: Huang Ji-Han , Hou Guang-Feng , Ma Dong-Sheng , Yu Ying-Hui , Jiang Wen-Hong , Huang Qi , Gao Jin-Sheng
Published: March 2017

Two pairs of Zn-based chiral coordination polymers were synthesized under hydrothermal conditions, exhibiting medium second-harmonic generation (SHG) activities and luminescent behavior.
An investigation of mass transfer-reaction kinetics of NO absorption by wet scrubbing using an electrolyzed seawater solution
Authors: Han Zhitao , Yang Shaolong , Zhao Dongsheng , Liu Bojun , Pan Xinxiang , Yan Zhijun
Published: March 2017

The mass transfer-reaction kinetics of NO absorption by wet scrubbing using electrolyzed seawater was studied in a bench-scale bubbling reactor.
Electrospun poly-ε-caprolactone scaffold modified with catalytic nitric oxide generation and heparin for small-diameter vascular graft
Authors: Gao Jingchen , Wang Yaping , Chen Siyuan , Tang Di , Jiang Li , Kong Deling , Wang Shufang
Published: March 2017

Vascular grafts are significantly needed in peripheral vascular surgery; however, small diameter grafts are not always available, and synthetic grafts perform poorly because of acute thrombosis and neointimal proliferation after implantation.
Comparison of Li, Na, Mg and Al-ion insertion in vanadium pentoxides and vanadium dioxides
Authors: Kulish Vadym V. , Manzhos Sergei
Published: March 2017

We investigate and compare main vanadium oxide phases for Li, Na, Mg and Al-ion batteries.
Reversible mechanical protection: building a 3D “suit” around a T-shaped benzimidazole axle
Authors: Zhu Kelong , Baggi Giorgio , Vukotic V. Nicholas , Loeb Stephen J.
Published: March 2017

A benzimidazole molecule can be protected from deprotonation with strong base by converting into a suit[1]ane – a type of 3D mechanically interlocked molecule. Utilising a combination of ring-closing and ring-opening metathesis, the wearing of the protective “suit” can be made reversible.
Multifunctional CaSc2O4:Yb3+/Er3+ one-dimensional nanofibers: electrospinning synthesis and concentration-modulated upconversion luminescent properties
Authors: Liu Meihong , Gu Ming , Tian Yue , Huang Ping , Wang Lei , Shi Qiufeng , Cui Cai’e
Published: March 2017

In this paper, an electrospinning technique was developed to prepare CaSc2O4:Yb3+/Er3+ one dimensional (1D) nanofibers for the first time.
Polypyrrole prepared in the presence of methyl orange and ethyl orange: nanotubes versus globules in conductivity enhancement
Authors: Li Yu , Bober Patrycja , Trchová Miroslava , Stejskal Jaroslav
Published: March 2017

The preparation of highly conducting polymer nanostructures with defined and uniform nanoscale morphologies represents a research challenge.
Evolution of CaGd2ZnO5:Eu3+nanostructures for rapid visualization of latent fingerprints
Authors: Seeta Rama Raju G. , Park Jin Young , Nagaraju Ganji Purnachandra , Pavitra E. , Yang Hyun Kyoung , Moon Byung Kee , Yu Jae Su , Huh Yun Suk , Jeong Jung Hyun
Published: March 2017

CaGd2ZnO5:Eu3+fluorescent nanostructures provide three levels of identification with high-quality imaging on various hydrophilic and hydrophobic substrates.
Controllable III–V nanowire growth via catalyst epitaxy
Authors: Han Ning , Wang Ying , Yang Zai-xing , Yip SenPo , Wang Zhou , Li Dapan , Hung Tak Fu , Wang Fengyun , Chen Yunfa , Ho Johnny C.
Published: March 2017

In this III–V nanowire growth study, small catalyst nanoparticles have higher solubility of the group III precursors, which not only enable the faster nanowire growth rate, but also yields epitaxial growth accounting for the better crystallinity.
Estimation of EMI‐induced phase noise and jitter on oscillator/clock signals
Authors: Mehri M. , Masoumi N.
Published: March 2017

An analytic approach is proposed for estimation of electromagnetic interference (EMI)‐induced phase noise and jitter. The radiated susceptibility of an oscillator implemented on the PCB is defined based on its fundamental specification. Closed‐form expressions are derived for EMI‐added phase noise and jitter on the oscillator output signal. A simple oscillator board is designed and implemented to verify the derivations. The measurement results confirm the accuracy of the proposed method.
Improving the performance of cellular uplinks via power overbooking
Authors: Lau Katrina , Goodwin Graham C. , Wigren Torbjörn , Brus Linda
Published: March 2017

The problem of uplink grant under‐utilisation, which impacts third generation cellular system performance, is now also emerging in fourth and fifth generation systems, with the introduction of fast uplink access. This study addresses the problem of grant under‐utilisation in third generation systems, where these effects are known to be highly significant. Such under‐utilisation occurs since mobiles are allowed to use only parts of their granted power resources according to the standard. The inevitable uncertainty introduced by grant under‐utilisation is modelled by a grant utilisation probability. This study then proposes the use of statistical overbooking of grants, subject to a pre‐specified risk of overload, to mitigate the problem. Two generic overbooking strategies based on this approach are then investigated and it is shown that significant gains in throughput can be achieved. Based on the analysis, a practical overbooking algorithm is described, together with laboratory and field test results. It is shown that very significant performance improvements are obtained, both in terms of throughput and latency.
Adaptive α‐plane line differential protection
Authors: Sarangi Saumendra , Pradhan Ashok Kumar
Published: March 2017

Alpha plane (α ‐plane)‐based differential relay protecting a transmission line uses the ratio of the current phasors of both ends and has numerous advantages. Such an approach either uses phase or sequence components of currents. For a normal operating condition and external fault, the ratio remains within restraining region in the α ‐plane. During high resistance internal fault, the computed ratio at times lies inside the restraining region resulting misoperation of the technique. The scheme which uses sequence components of the currents has limited performance for single pole tripping and line impedance unbalance conditions. In this study, two features: phase angle between voltage and current and magnitude of change in currents of both ends of the line supplement the relay in identifying an internal fault. This improves the performance of phase current‐based α ‐plane relay. The proposed method is tested for Western Electricity Coordinating Council (WSCC) 9‐bus and two source equivalent system and results for various cases show improved performance.
Microsecond‐scale fast fusing and cutout characteristics of high current fuse
Authors: Zhang Yu , Su Jiancang , Zheng Lei , Li Rui , Yu Binxiong , Qiu Xudong , Zeng Bo , Cheng Jie , Xu Xiudong
Published: March 2017

As to the problem that common high current fuses have a long cutout time at ms scale to protect the DC power source, an effective way for fast arc extinction and cutout of fuse is put forward in this study, based on the burst high‐pulse current discharge from a parallelly connected filter capacitor. Through increasing the discharge current from the filter capacitor, the total cutout time of fuse can be reduced from ms to 40 μs after the load of the DC800 V power source was shorted in experiment. The method for designing the crucial parameters of the short‐circuit fault protection in DC power source is also presented. Experimental results showed that the DC1500V/32A fuse with a single fuse body and solidified filling quartz sand can reduce the time before arc forms (Tf) and total cutout time (Te) to 30 and 44 μs, respectively. The effects of the shorted load impedance on the DC power source protection are also studied. It showed that the dynamic short‐load impedances formed by the breakdown semiconductor parts in short‐circuit faults were <25 mΩ, and the corresponding Te of fuse was compressed in the range between 50 and 90 μs.
Strong dynamic interactions between multi‐terminal DC network and AC power systems caused by open‐loop modal coupling
Authors: Du Wenjuan , Fu Qiang , Wang Haifeng
Published: March 2017

This study examines the AC/DC dynamic interactions in an AC power system with an integrated multi‐terminal DC network (MTDC) based on a closed‐loop interconnected model of the MTDC/AC power system, wherein, the MTDC and the AC system are modelled as two interconnected open‐loop subsystems. Analysis in this study indicates that when a complex pole of the open‐loop MTDC subsystem is close to an electromechanical oscillation mode (EOM) of concern in the open‐loop AC subsystem on the complex plane, this open‐loop modal coupling may cause strong dynamic interactions between the MTDC and the AC system. It is very likely that when the open‐loop modal coupling occurs, the small‐signal stability of the MTDC/AC power system may considerably degrade. In this study, New England test system integrated with an MTDC for wind power transmission is used to demonstrate and validate analysis and conclusions made. Both the master–slave control and the DC voltage droop control for the MTDC are examined. Study cases show that the open‐loop modal coupling caused considerable damping degradation of EOM of concern, imposing serious threat to power system small‐signal stability.
Distorted reflector antennas: fast and accurate estimation of the surface distortion profile using a new formula
Authors: Haddadi Abolfazl , Ghorbani Ayaz , Taghikhani Parastoo
Published: March 2017

The high‐frequency applicability of reflector antennas is limited by the distortions and the errors on the reflector surface. Different techniques can be used to compensate the degradation of the radiation characteristics if the surface distortion profile is known. Here, a fast and accurate iterative method has been proposed to determine the surface distortion profile which is based on a newly developed variational formula. The surface fitting has been done in the general form of B‐splines, which is suitable for both local and global distortions. Different types of the distortions have been studied to check the accuracy of the method. It has been shown that for distortion amplitudes lower than half of wavelength, the proposed algorithm converges with a high accuracy. In comparison with the previous works, the proposed algorithm has higher accuracy and faster convergence and it needs a lower number of far‐field measurements. Despite the microwave holography, in the proposed method there is no need to compute the aperture fields.
The XXL Survey
Authors: Mantz A. B. , Abdulla Z. , Allen S. W. , Carlstrom J. E. , Logan C. H. A. , Marrone D. P. , Maughan B. J. , Willis J. , Pacaud F. , Pierre M.
Published: March 2017

We present results from a 100 ks XMM-Newton observation of galaxy cluster XLSSC 122, the first massive cluster discovered through its X-ray emission at z ≈ 2. The data provide the first precise constraints on the bulk thermodynamic properties of such a distant cluster, as well as an X-ray spectroscopic confirmation of its redshift. We measure an average temperature of kT = 5.0 ± 0.7 keV; a metallicity with respect to solar of Z/Z⊙ = 0.33−0.17+0.19, consistent with lower-redshift clusters; and a redshift of
z = 1.99+0.07-0.06
, consistent with the earlier photo-z estimate. The measured gas density profile leads to a mass estimate at r500 of M500 = (6.3 ± 1.5) × 1013 M⊙. From CARMA 30 GHz data, we measure the spherically integrated Compton parameter within r500 to be Y 500 = (3.6 ± 0.4) × 10−12. We compare the measured properties of XLSSC 122 to lower-redshift cluster samples, and find good agreement when assuming the simplest (self-similar) form for the evolution of cluster scaling relations. While a single cluster provides limited information, this result suggests that the evolution of the intracluster medium in the most massive, well-developed clusters is remarkably simple, even out to the highest redshifts where they have been found. At the same time, our data reaffirm the previously reported spatial offset between the centres of the X-ray and SZ signals for XLSSC 122, suggesting a disturbed configuration. Higher spatial resolution data could thus provide greater insights into the internal dynamics of this system.
Imaging and Intervention of Biliary Leaks and Bilomas
Authors: Arellano Ronald , Vadvala Harshna
Published: March 2017

Biliary leaks and bilomas develop due to hepatobiliary surgery, trauma, or locoregional therapy for hepatic malignancies. Though uncommon, they can be a source of abdominal pain, hyperbilirubinemia, and sepsis. A variety of diagnostic tools and interventional techniques are available to diagnose and manage biliary leaks and bilomas. Successful management often requires a multidisciplinary approach between the radiologist, surgeon, and endoscopist.
Estimation of Relative Load From Bar Velocity in the Full Back Squat Exercise
Authors: Sánchez-Medina Luis , Pallarés Jesús , Pérez Carlos , Morán-Navarro Ricardo , González-Badillo Juan
Published: March 2017

The use of bar velocity to estimate relative load in the back squat exercise was examined. 80 strength-trained men performed a progressive loading test to determine their one-repetition maximum (1RM) and load-velocity relationship. Mean (MV), mean propulsive (MPV) and peak (PV) velocity measures of the concentric phase were analyzed. Both MV and MPV showed a very close relationship to %1RM (R2=0.96), whereas a weaker association (R2=0.79) and larger SEE (0.14 vs. 0.06 m·s−1) were found for PV. Prediction equations to estimate load from velocity were obtained. When dividing the sample into 3 groups of different relative strength (1RM/body mass), no differences were found between groups for the MPV attained against each %1RM. MV attained with the 1RM was 0.32±0.03 m·s−1. The propulsive phase accounted for ~82% of concentric duration at 40% 1RM, and progressively increased until reaching 100% at 1RM. Provided that repetitions are performed at maximal intended velocity, a good estimation of load (%1RM) can be obtained from mean velocity as soon as the first repetition is completed. This finding provides an alternative to the often demanding, time-consuming and interfering 1RM or nRM tests and allows implementing a velocity-based resistance training approach.
Electron-silane scattering cross section for plasma assisted processes
Authors: Verma Pankaj , Kaur Jaspreet , Antony Bobby
Published: March 2017

Silane is an important molecule with numerous applications to natural and technological plasmas. In such environments, where plasma assisted processes are vital, electron induced reactions play a major role in its chemistry. In view of this, electron induced scattering of molecules such as silane finds significance. This article reports a comprehensive study of electron impact cross sections for silane over a wide energy range. In particular, the emphasis is given in providing a complete dataset for various electron scattering events possible with silane. Such dataset is the need for the plasma modeling community. Moreover, literature survey shows that the cross section database for silane is fragmentary. To fill this void, we have computed the differential elastic, total, rotational excitation, and momentum transfer cross sections. Two formalisms that are reliable in their energy domain are employed to accomplish the task: the R-matrix method through QUANTEMOL-N at low incident energies and the spherical complex optical potential formalism at intermediate to high energies. Interestingly, the comparison of the present cross section exhibits a good concurrence with the previous data, wherever available.
Characterization of chemical contaminants and their spectral properties from an atmospheric pressure ns-pulsed microdischarge in neon
Authors: Sillerud Colin H. , Schwindt Peter D. D. , Moorman Mathew , Yee B. T. , Anderson John , Pfeifer Nathaniel B. , Hedberg E. L. , Manginell Ronald P.
Published: March 2017

Portable applications of microdischarges, such as the remediation of gaseous wastes or the destruction of volatile organic compounds, will mandate operation in the presence of contaminant species. This paper examines the temporal evolution of microdischarge optical and ultraviolet emissions during pulsed operation by experimental methods. By varying the pulse length of a microdischarge initiated in a 4-hole silicon microcavity array operating in a 655 Torr ambient primarily composed of Ne, we were able to measure the emission growth rates for different contaminant species native to the discharge environment as a function of pulse length. It was found that emission from hydrogen and oxygen impurities demonstrated similar rates of change, while emissions from molecular and atomic nitrogen, measured at 337.1 and 120 nm, respectively, exhibited the lowest rate of change. We conclude that it is likely that O2 undergoes the same resonant energy transfer process between rare gas excimers that has been shown for H2. Further, efficient resonant processes were found to be favored during ignition and extinction phases of the pulse, while emission at the 337.1 nm line from N2 was favored during the intermediate stage of the plasma. In addition to the experimental results, a zero-dimensional analysis is also presented to further understand the nature of the microdischarge.
Beatification: Flattening the Poisson bracket for two-dimensional fluid and plasma theories
Authors: Viscondi Thiago F. , Caldas Iberê L. , Morrison Philip J.
Published: March 2017

A perturbative method called beatification is presented for a class of two-dimensional fluid and plasma theories. The Hamiltonian systems considered, namely, the Euler, Vlasov-Poisson, Hasegawa-Mima, and modified Hasegawa-Mima equations, are naturally described in terms of noncanonical variables. The beatification procedure amounts to finding the correct transformation that removes the explicit variable dependence from a noncanonical Poisson bracket and replaces it with a fixed dependence on a chosen state in the phase space. As such, beatification is a major step toward casting the Hamiltonian system in its canonical form, thus enabling or facilitating the use of analytical and numerical techniques that require or favor a representation in terms of canonical, or beatified, Hamiltonian variables.
Parasitic momentum flux in the tokamak core
Authors: Stoltzfus-Dueck T.
Published: March 2017

A geometrical correction to the E×B drift causes an outward flux of co-current momentum whenever electrostatic potential energy is transferred to ion parallel flows. The robust, fully nonlinear symmetry breaking follows from the free-energy flow in phase space and does not depend on any assumed linear eigenmode structure. The resulting rotation peaking is counter-current and scales as temperature over plasma current. This peaking mechanism can only act when fluctuations are low-frequency enough to excite ion parallel flows, which may explain some recent experimental observations related to rotation reversals.
Magnetic field profile analysis for gyrotron experimental investigation
Authors: Pagonakis Ioannis Gr. , Avramidis Konstantinos A. , Gantenbein Gerd , Rzesnicki Tomasz , Samartsev Andrey , Jelonnek John
Published: March 2017

The external applied magnetic field plays a main role on the gyrotron operation. Even if the gyrotron design is optimized for the nominal magnetic profile, it is possible the performance to be better for an alternative one. This unexpected result can happen for several reasons, such as the manufacturing imperfections, the misalignment issues, and several unknown factors in gyrotron theory and design. The systematic experimental investigation of the gyrotron in different magnetic profiles is very important for the optimization of the gyrotron operation and for the better understanding of the gyrotron behavior. In this sense, an analytical approach for the definition of the appropriate magnetic profiles based on the beam characteristics instead of the coil currents definition is proposed for a systematic experimental study. Using this technique, operational maps in the space of the important magnetic profile parameters are developed, which are very useful for the characterization of the gyrotron performance. For the demonstration of this idea, the operational maps of the short-pulse prototype of the 170 GHz, 1 MW European ITER gyrotron project are presented.
Nonlinear evolution of electron shear flow instabilities in the presence of an external guide magnetic field
Authors: Jain Neeraj , Büchner Jörg , Muñoz Patricio A.
Published: March 2017

The dissipation mechanism by which the magnetic field reconnects in the presence of an external (guide) magnetic field in the direction of the main current is not well understood. In thin electron current sheets (half thickness close to an electron inertial length) formed in a quasi-steady state of collisionless magnetic reconnection, electron shear flow instabilities are potential candidates for providing an anomalous dissipation mechanism which can break the frozen-in condition of the magnetic field affecting the structure and rate of reconnection. We present the results of investigations of the evolution of electron shear flow instabilities, from linear to nonlinear state, in guide field magnetic reconnection. The properties of the plasma turbulence resulting from the growth of instability and their dependence on the strength of the guide field are studied. For this sake, we utilize the three dimensional electron-magnetohydrodynamic simulations of electron current sheets. We show that, unlike the case of current sheets self-consistently embedded in anti-parallel magnetic fields, the evolution of thin electron current sheets in the presence of a finite external guide field (equal to the asymptotic value of the reconnecting magnetic field or larger) is dominated by high wave number non-tearing mode instabilities. The latter causes the development of, first, a wavy structure of the current sheet. The turbulence, developed later, consists of current filaments and electron flow vortices. As a result of the nonlinear evolution of instability, the current sheet broadens simultaneously with its flattening in the central region mimicking a viscous-like turbulent dissipation. Later, the flattened current sheet bifurcates. During the time of bifurcation, the rate of the change of mean electron flow velocity is proportional to the magnitude of the flow velocity, suggesting a resistive-like dissipation. The turbulence energy cascades to shorter wavelengths preferentially in the direction perpendicular to the guide magnetic field. The degree of anisotropy of the turbulence was found to increase with the increasing strength of the guide field.
Numerical characterization of magnetized capacitively coupled argon plasmas driven by combined dc/rf sources
Authors: Yang Shali , Zhang Ya , Wang Hong-Yu , Wang Shuai , Jiang Wei
Published: March 2017

The characteristics of magnetized capacitively coupled plasmas (CCPs) driven by combined dc/rf sources in argon have been investigated by a one-dimensional implicit Particle-in-cell/Monte Carlo collision model. Discharges operating at 13.56 MHz with a fixed rf voltage of 300 V are simulated at the pressure of 50 mTorr in argon. Four cases, i.e., CCP driven by rf source, rf + dc sources, rf source with magnetic field, and rf + dc sources with magnetic field, are presented and compared at the Vdc = −100 V, B = 50 Gs, and γi = 0.2. It is found that, with the influence of dc voltage and magnetic field, the plasma density has been greatly enhanced by over one order of magnitude over the rf-only case. This is due to the fact that the mean free path of electrons decreases by the cyclotron motion and the energetic secondary electrons are trapped by the magnetic field, leading to a significant increase in heating and ionization rates. Moreover, transition of the stochastic to Ohmic electron heating mechanism takes place as the magnetic field increases because electron kinetics can be strongly affected by the magnetic field. In general, we have demonstrated that such a configuration will enhance the discharge and thus enable CCPs work under extremely high energy density stably that can never be operated by any other configurations. We expect that such a configuration can promote many related applications, like etching, sputtering, and deposition.
A continuous-wave clinotron at 0.26 THz with sheet electron beam
Authors: Xi Hongzhu , He Zhaochang , Wang Jianguo , Li Rong , Zhu Gang , Chen Zaigao , liu Jinsong , Liu Luwei , Wang Hao
Published: March 2017

A high performance continuous-wave (CW) clinotron with a sheet electron beam at 0.26 THz is presented in this paper. The mode selection is discussed by studying the dispersion curve of the high frequency structure, distribution of the electric field, coupling impedance, and particle-in-cell simulation result, showing that the designed clinotron operates in the fundamental mode TM10. The planar comb gratings are fabricated by using the wire electrical discharge machining technology with the processing error less than 0.005 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with a maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed clinotron can operate at the fundamental mode TM10 and generate an output power of 820 mW at a frequency of 0.26 THz with a large frequency tuning range from 0.25 THz to 0.262 THz.
Discontinuities and nonlinear shear Alfvén waves by the mixed Eulerian-Lagrangian kinematic description
Authors: Liu Hai-Feng , Zhu Li-Min
Published: March 2017

In the frame of mixed Eulerian–Lagrangian description, a large-perturbation magnetohydrodynamic (MHD) equilibrium system is developed to describe the propagation of nonlinear Alfvén waves in an ideal magnetofluid. The system is only dependent on the reference flow variables and the displacement vector of the fluid particles. Some interesting results are obtained: nonlinear MHD wave speeds are obtained; fixing the equilibrium magnetic field, a large-negative gradient of displacement can generate directional discontinuities; a large-positive pressure perturbation or magnetic perturbation can bring about a high velocity nonlinear Alfvén wave while a large-negative pressure perturbation or magnetic perturbation can bring about a low velocity nonlinear Alfvén wave; a great-negative magnetic perturbation may give birth to counter-propagating Alfvén waves. Our results have a high relevance to such issues as discontinuities, counter-propagating nonlinear Alfvén waves, and ultra-speed Alfvén waves in interplanetary space.
Towards realistic characterization of the solar wind suprathermal populations and their effects
Authors: Lazar M.
Published: March 2017

This Brief Communication presents a straightforward analytical method for estimating the effects of suprathermal particle populations present in space plasmas, based on a refined Kappa modelling of the velocity distributions which enables comparison with the thermal (core) component. If the observed distribution with suprathermal tails can be reproduced by a Kappa power-law, the core is extracted as a particular Maxwellian limit which needs to be cooler and contain a less number of particles. This approach enables study of the kinetic instabilities driven by anisotropic bi-Kappa distributions, among other applications. Thus, the electromagnetic electron cyclotron instability is found to be stimulated by the suprathermal electrons, confirming the existence of an additional free energy in these populations. Limiting to a standard Maxwellian modelling, as was and still is customary for the analysis of distributions observed in the solar wind, may therefore lead to misleading interpretations of these instabilities and other kinetic effects involving suprathermal populations.
Crystallization of a three-dimensional complex plasma under laboratory conditions
Authors: Steinmüller B. , Dietz C. , Kretschmer M. , Thoma M. H.
Published: March 2017

The influence of neutral gas pressure for crystallization of cylindrical complex plasmas under laboratory conditions is investigated. For the analysis of the complex plasma structure, different methods are adopted: First, the pair correlation and a criterion based on the shape of the Voronoi cells are applied. Besides this, a new implementation, which connects the Minkowski structure metric with the benefits from the scalar product of the local bond order parameter, is presented. In addition, the bcc sensitive Minkowski structure metric is used to identify the crystalline structures. All criteria display the same behavior: Decreasing the neutral pressure leads to crystallization. This is the opposite behavior to that observed in former ground based experiments.
Energy conversion mechanism for electron perpendicular energy in high guide-field reconnection
Authors: Guo X. , Horiuchi R. , Cheng C. Z. , Kaminou Y. , Ono Y.
Published: March 2017

The energy conversion mechanism for electron perpendicular energy, both the thermal and the kinetic energies, is investigated by means of two-dimensional, full-particle simulations in an open system. It is shown that electron perpendicular heating is mainly due to the breaking of magnetic moment conservation in separatrix region because the charge separation generates intense variation of electric field within the several electron Larmor radii. Meanwhile, electron perpendicular acceleration takes place mainly due to the polarization drift term as well as the curvature drift term of E·u⊥ in the downstream near the X-point. The enhanced electric field due to the charge separation there results in a significant effect of the polarization drift term on the dissipation of magnetic energy within the ion inertia length in the downstream.
Zonal flow generation in inertial confinement fusion implosions
Authors: Peterson J. L. , Humbird K. D. , Field J. E. , Brandon S. T. , Langer S. H. , Nora R. C. , Spears B. K. , Springer P. T.
Published: March 2017

A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. This new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.
Generation of two-dimensional binary mixtures in complex plasmas
Authors: Wieben Frank , Schablinski Jan , Block Dietmar
Published: March 2017

Towards the investigation of polydisperse complex plasmas, the generation of binary mixtures is a first and important step. In this paper, the requirements for the generation of two-dimensional binary mixtures are discussed and first experiments are presented. In particular, the material dependent mass loss of the particles is taken into account by monitoring the charge-to-mass ratio of both species using a resonance method. The charge ratio q1/q2 of the species is determined and the spacial properties of the two-component crystals are examined and compared to numerical simulations.
Chaos emerging in soil failure patterns observed during tillage: Normalized deterministic nonlinear prediction (NDNP) and its application
Authors: Sakai Kenshi , Upadhyaya Shrinivasa K. , Andrade-Sanchez Pedro , Sviridova Nina V.
Published: March 2017

Real-world processes are often combinations of deterministic and stochastic processes. Soil failure observed during farm tillage is one example of this phenomenon. In this paper, we investigated the nonlinear features of soil failure patterns in a farm tillage process. We demonstrate emerging determinism in soil failure patterns from stochastic processes under specific soil conditions. We normalized the deterministic nonlinear prediction considering autocorrelation and propose it as a robust way of extracting a nonlinear dynamical system from noise contaminated motion. Soil is a typical granular material. The results obtained here are expected to be applicable to granular materials in general. From a global scale to nano scale, the granular material is featured in seismology, geotechnology, soil mechanics, and particle technology. The results and discussions presented here are applicable in these wide research areas. The proposed method and our findings are useful with respect to the application of nonlinear dynamics to investigate complex motions generated from granular materials.
Linear theory and measurements of electron oscillations in an inertial Alfvén wave
Authors: Schroeder J. W. R. , Skiff F. , Howes G. G. , Kletzing C. A. , Carter T. A. , Dorfman S.
Published: March 2017

The physics of the aurora is one of the foremost unsolved problems of space physics. The mechanisms responsible for accelerating electrons that precipitate onto the ionosphere are not fully understood. For more than three decades, particle interactions with inertial Alfvén waves have been proposed as a possible means for accelerating electrons and generating auroras. Inertial Alfvén waves have an electric field aligned with the background magnetic field that is expected to cause electron oscillations as well as electron acceleration. Due to the limitations of spacecraft conjunction studies and other multi-spacecraft approaches, it is unlikely that it will ever be possible, through spacecraft observations alone, to confirm definitively these fundamental properties of the inertial Alfvén wave by making simultaneous measurements of both the perturbed electron distribution function and the Alfvén wave responsible for the perturbations. In this laboratory experiment, the suprathermal tails of the reduced electron distribution function parallel to the mean magnetic field are measured with high precision as inertial Alfvén waves simultaneously propagate through the plasma. The results of this experiment identify, for the first time, the oscillations of suprathermal electrons associated with an inertial Alfvén wave. Despite complications due to boundary conditions and the finite size of the experiment, a linear model is produced that replicates the measured response of the electron distribution function. These results verify one of the fundamental properties of the inertial Alfvén wave, and they are also a prerequisite for future attempts to measure the acceleration of electrons by inertial Alfvén waves.
On the nonlinear trapping nature of undamped, coherent structures in collisionless plasmas and its impact on stability
Authors: Schamel Hans , Mandal Debraj , Sharma Devendra
Published: March 2017

An outstanding notion for collisionless plasmas is the essential nonlinear character of their coherent structures, which in the stationary, weak amplitude limit are described by a continuum of cnoidal electron and ion hole modes governed by a multiparametric nonlinear dispersion relation. The well-known discrete structure of undamped linear plasma modes is seamlessly embedded in this nonlinear continuum as the microscopic texture of plasma begins to reveal itself in the high temperature collisionless plasma limit. This transforms the linear-threshold-based operating mechanism of plasma turbulence into a fundamental nonlinear, multifaceted one. Based on a comprehensive three-level description of increasing profundity, a proof of this novel dictum is presented, which makes use of the joint properties of such structures, their coherency and stationarity, and uses in succession a fluid, linear Vlasov and a full Vlasov description. It unifies discrete and continuum limits by resolving the inevitable resonant region and shows that coherent electrostatic equilibria are generally controlled by kinetic particle trapping and are hence fundamentally nonlinear. By forging a link between damped and growing wave solutions, these modes render plasma stability complex and difficult to evaluate due to the entangled pattern of the stability boundary in function and parameter space, respectively. A direct consequence is the existence of negative energy modes of arbitrarily small amplitudes in the subcritical region of the two-stream instability as well as the failure of linear Landau (Vlasov, van Kampen) theory, whenever resonant particles are involved, in addressing the onset of instability in a current-carrying plasma. Responsible for this subtle phase space behavior is hence the thresholdless omnipresence of the trapping nonlinearity originating from coherency. A high resolution, exact-mass-ratio, multispecies, and collisionless plasma simulation is employed to illustrate exemplarily how tiny seed fluctuations in phase-space can act as a triggering agent for a subcritical plasma excitation verifying an access to these modes in the noisy, collisionless plasma limit.
The different evolution of plasma density voids and blobs in the edge region of a simply magnetized toroidal plasma
Authors: Barni R. , Caldirola S. , Fattorini L. , Riccardi C.
Published: March 2017

The analysis of the anomalous transport in magnetised plasmas has pointed out the substantial contribution of intermittent burst events corresponding to positive density fluctuations propagating outwards to the edges of the devices. Much less attention was paid to negative density fluctuation structures, which could be named depletions or voids, whose propagation could contribute to the global anomalous transport, in particular, when a non-negligible diffuse plasma background is present in magnetized plasma device edges. Here, we discuss the results of an experimental investigation aimed to study the spatio-temporal evolution of density depletion structures propagating inwards in a magnetized plasma column simply magnetized toroidal device. Evidence of this behavior was gathered by a conditional sampling analysis applied to time series of plasma fluctuations. We observe that a significant fraction of void structures, after being ejected outside the main plasma column, gets pulled inwards and disappears by merging at the column edge. On the other hand, a smaller fraction as well as most of the positive density structures, after ejection, ends up advected towards the edges of the device and gets lost from the main plasma column. These behaviors testify the richness and complexity of density structure evolution in magnetized plasma turbulence.
Elastic moduli of δ-Pu239 reveal aging in real time
Authors: Maiorov Boris , Betts Jonathan B. , Söderlind Per , Landa Alexander , Hernandez Sarah C. , Saleh Tarik A. , Freibert Franz J. , Migliori Albert
Published: March 2017

We study the time evolution (aging) of the elastic moduli of an eight-year-old polycrystalline δ-Pu 2.0 at. % Ga alloy (δ-Pu:Ga) at different fixed temperatures from 295 K to nearly 500 K in real time using Resonant Ultrasound Spectroscopy. After 8 years of aging at 295 K, the bulk and shear moduli increase at a normalized rate of 0.2%/year and 0.6%/year, respectively. As the temperature is raised, two time dependences are observed, an exponential one of about a week, followed by a linear one (constant rate). The linear rate is thermally activated with an activation energy of 0.33 + 0.06 eV. Above 420 K a qualitative change in the time evolution is observed; the bulk modulus decreases with time while the shear modulus continues to stiffen. No change in the behavior of the time evolution is observed as the α−β transition temperature is crossed as would be expected if a decomposition of δ-Pu:Ga to α-Pu and Pu3Ga occurred over the temperature range studied. Our results indicate that the main mechanism of aging is creation of defects that are partially annealed starting at T = 420 K.
Observation of ion-ion counter streaming instability in presheath-sheath region of a mesh grid immersed in low temperature plasma
Authors: Prasad Kella Vara , Ghosh J. , Chattopadhyay P. K. , Sharma D. , Saxena Y. C.
Published: March 2017

Instabilities in the sheath-presheath region formed in plasma-boundary layers are known to modify the particle flow velocities and their distribution functions, hence influencing the particle transport in this region significantly. In this paper, experimental observations of the ion-ion counter streaming instability excited in the sheath-presheath region of Argon (Ar), Helium (He), and Ar + He plasmas have been reported. These instabilities are excited in the vicinity of a stainless steel mesh grid placed inside the plasma. Floating potential (FP) fluctuations from the grid and from a movable Langmuir probe placed in the sheath-presheath region are measured. The frequency spectra of FP fluctuations in an argon plasma show a dominant broad peak in the range of 10–20 kHz centering around 15 kHz, which is identified as due to the ion-ion counter streaming instability. This frequency peak exists only in the sheath-presheath region and ceases to exist when the mesh grid is covered with a thin metal foil from one side, which restricts the counter streaming of the ions. The measured wave number, k, of the wave matches quite well with the calculated one from the dispersion relation of ion-ion counter streaming instability. The experiments are repeated to study the instability in He and Ar + He (two ion species) plasmas in similar experimental conditions. The neutral pressure threshold for sustenance of this instability has also been observed.
Kinetic instabilities in a mirror-confined plasma sustained by high-power microwave radiation
Authors: Shalashov A. G. , Viktorov M. E. , Mansfeld D. A. , Golubev S. V.
Published: March 2017

This paper summarizes the studies of plasma kinetic instabilities in the electron cyclotron frequency range carried out over the last decade at the Institute of Applied Physics in Nizhny Novgorod. We investigate the nonequilibrium plasma created and sustained by high-power microwave radiation of a gyrotron under the electron cyclotron resonance condition. Resonant plasma heating results in the formation of at least two electron components, one of which, more dense and cold, determines the dispersion properties of the high-frequency waves, and the other, a small group of energetic electrons with a highly anisotropic velocity distribution, is responsible for the excitation of unstable waves. Dynamic spectra and the intensity of stimulated electromagnetic emission are studied with high temporal resolution. Interpretation of observed data is based on the cyclotron maser paradigm; in this context, a laboratory modeling of non-stationary wave-particle interaction processes has much in common with similar processes occurring in the magnetosphere of Earth, planets, and solar coronal loops.
Accurate modeling of plasma acceleration with arbitrary order pseudo-spectral particle-in-cell methods
Authors: Jalas S. , Dornmair I. , Lehe R. , Vincenti H. , Vay J.-L. , Kirchen M. , Maier A. R.
Published: March 2017

Particle in Cell (PIC) simulations are a widely used tool for the investigation of both laser- and beam-driven plasma acceleration. It is a known issue that the beam quality can be artificially degraded by numerical Cherenkov radiation (NCR) resulting primarily from an incorrectly modeled dispersion relation. Pseudo-spectral solvers featuring infinite order stencils can strongly reduce NCR—or even suppress it—and are therefore well suited to correctly model the beam properties. For efficient parallelization of the PIC algorithm, however, localized solvers are inevitable. Arbitrary order pseudo-spectral methods provide this needed locality. Yet, these methods can again be prone to NCR. Here, we show that acceptably low solver orders are sufficient to correctly model the physics of interest, while allowing for parallel computation by domain decomposition.
Kinetic energy partition method applied to ground state helium-like atoms
Authors: Chen Yu-Hsin , Chao Sheng D.
Published: March 2017

We have used the recently developed kinetic energy partition (KEP) method to solve the quantum eigenvalue problems for helium-like atoms and obtain precise ground state energies and wave-functions. The key to treating properly the electron-electron (repulsive) Coulomb potential energies for the KEP method to be applied is to introduce a “negative mass” term into the partitioned kinetic energy. A Hartree-like product wave-function from the subsystem wave-functions is used to form the initial trial function, and the variational search for the optimized adiabatic parameters leads to a precise ground state energy. This new approach sheds new light on the all-important problem of solving many-electron Schrödinger equations and hopefully opens a new way to predictive quantum chemistry. The results presented here give very promising evidence that an effective one-electron model can be used to represent a many-electron system, in the spirit of density functional theory.
Characterizing gas flow from aerosol particle injectors
Authors: Horke Daniel A. , Roth Nils , Worbs Lena , Küpper Jochen
Published: March 2017

A novel methodology for measuring gas flow from small orifices or nozzles into vacuum is presented. It utilizes a high-intensity femtosecond laser pulse to create a plasma within the gas plume produced by the nozzle, which is imaged by a microscope. Calibration of the imaging system allows for the extraction of absolute number densities. We show detection down to helium densities of 4×1016 cm−3 with a spatial resolution of a few micrometers. The technique is used to characterize the gas flow from a convergent-nozzle aerosol injector [Kirian et al., Struct. Dyn. 2, 041717 (2015)] as used in single-particle diffractive imaging experiments at free-electron laser sources. Based on the measured gas-density profile, we estimate the scattering background signal under typical operating conditions of single-particle imaging experiments and estimate that fewer than 50 photons per shot can be expected on the detector.