bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron temporal diagnostic for high-yield deuterium–tritium cryogenic implosions on OMEGA
Authors: Stoeckl C. , Boni R. , Ehrne F. , Forrest C. J. , Glebov V. Yu. , Katz J. , Lonobile D. J. , Magoon J. , Regan S. P. , Shoup M. J. , Sorce A. , Sorce C. , Sangster T. C. , Weiner D.
Published: May 2016

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic deuterium–tritium (DT) implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments—a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ∼16 m to a streak camera in a well-shielded location. An ∼200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ∼40 ± 10 ps was measured in a dedicated experiment using hard x-rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. The measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.
Automatic outdoor monitoring system for photovoltaic panels
Authors: Stefancich Marco , Simpson Lin , Chiesa Matteo
Published: May 2016

Long-term acquisition of solar panel performance parameters, for panels operated at maximum power point in their real environment, is of critical importance in the photovoltaic research sector. However, few options exist for the characterization of non-standard panels such as concentrated photovoltaic systems, heavily soiled or shaded panels or those operating under non-standard spectral illumination; certainly, it is difficult to find such a measurement system that is flexible and affordable enough to be adopted by the smaller research institutes or universities. We present here an instrument aiming to fill this gap, autonomously tracking and maintaining any solar panel at maximum power point while continuously monitoring its operational parameters and dissipating the produced energy without connection to the power grid. The instrument allows periodic acquisition of current-voltage curves to verify the employed maximum power point tracking approach. At the same time, with hardware schematics and software code being provided, it provides a flexible open development environment for the monitoring of non-standard generators like concentrator photovoltaic systems and to test novel power tracking approaches. The key issues, and the corresponding solutions, encountered in the design are analyzed in detail and the relevant schematics presented.
Three-dimensional tomographic imaging for dynamic radiation behavior study using infrared imaging video bolometers in large helical device plasma
Authors: Sano Ryuichi , Peterson Byron J. , Teranishi Masaru , Iwama Naofumi , Kobayashi Masahiro , Mukai Kiyofumi , Pandya Shwetang N.
Published: May 2016

A three-dimensional (3D) tomography system using four InfraRed imaging Video Bolometers (IRVBs) has been designed with a helical periodicity assumption for the purpose of plasma radiation measurement in the large helical device. For the spatial inversion of large sized arrays, the system has been numerically and experimentally examined using the Tikhonov regularization with the criterion of minimum generalized cross validation, which is the standard solver of inverse problems. The 3D transport code EMC3-EIRENE for impurity behavior and related radiation has been used to produce phantoms for numerical tests, and the relative calibration of the IRVB images has been carried out with a simple function model of the decaying plasma in a radiation collapse. The tomography system can respond to temporal changes in the plasma profile and identify the 3D dynamic behavior of radiation, such as the radiation enhancement that starts from the inboard side of the torus, during the radiation collapse. The reconstruction results are also consistent with the output signals of a resistive bolometer. These results indicate that the designed 3D tomography system is available for the 3D imaging of radiation. The first 3D direct tomographic measurement of a magnetically confined plasma has been achieved.
Influence of residual plasma drift velocity on the post-arc sheath expansion of vacuum circuit breakers
Authors: Mo Yongpeng , Shi Zongqian , Bai Zhibin , Jia Shenli , Wang Lijun
Published: May 2016

The residual plasma in the inter-contact region of a vacuum circuit breaker moves towards the post-arc cathode at current zero, because the residual plasma mainly comes from the cathode spots during the arc burning process. In the most previous theoretical researches on the post-arc sheath expansion process of vacuum circuit breakers, only the thermal motion of residual plasma was taken into consideration. Alternately, the residual plasma was even assumed to be static at the moment of current zero in some simplified models. However, the influence of residual plasma drift velocity at current zero on the post-arc sheath expansion process was rarely investigated. In this paper, this effect is investigated by a one-dimensional particle-in-cell model. Simulation results indicate that the sheath expands slower with higher residual plasma drift velocity in the initial sheath expansion stage. However, with the increase of residual plasma drift velocity, the overall plasma density in the inter-contact region decreases faster, and the sheath expansion velocity increases earlier. Consequently, as a whole, it needs shorter time to expel the residual plasma from the inter-contact region. Furthermore, if the residual plasma drift velocity is high enough, the sheath expansion process ceases before it develops to the post-arc anode. Besides, the influence of the collisions between charges and neutrals is investigated as well in terms of the density of metal vapor. It shows that the residual plasma drift velocity takes remarkable effect only if the density of the metal vapor is relatively low, which corresponds to the circumstance of low-current interruptions.
Analysis of acoustic and entropy disturbances in a hypersonic wind tunnel
Authors: Schilden Thomas , Schröder Wolfgang , Ali Syed Raza Christopher , Schreyer Anne-Marie , Wu Jie , Radespiel Rolf
Published: May 2016

The tunnel noise in a Mach 5.9 Ludwieg tube is determined by two methods, a newly developed cone-probe-DNS method and a reliable hot-wire-Pitot-probe method. The new method combines pressure and heat flux measurements using a cone probe and direct numerical simulation (DNS). The modal analysis is based on transfer functions obtained by the DNS to link the measured quantities to the tunnel noise. The measurements are performed for several unit-Reynolds numbers in the range of 5 ⋅ 106 ≤ Re/m ≤ 16 ⋅ 106 and probe positions to identify the sensitivities of tunnel noise. The DNS solutions show similar response mechanisms of the cone probe to incident acoustic and entropy waves which leads to high condition numbers of the transfer matrix such that a unique relationship between response and source mechanism can be only determined by neglecting the contribution of the non-acoustic modes to the pressure and heat flux fluctuations. The results of the cone-probe-DNS method are compared to a modal analysis based on the hot-wire-Pitot-probe method which provides reliable results in the frequency range less than 50 kHz. In this low frequency range the findings of the two different mode analyses agree well. At higher frequencies, the newly developed cone-probe-DNS method is still valid. The tunnel noise is dominated by the acoustic mode, since the entropy mode is lower by one order of magnitude and the vorticity mode can be neglected. The acoustic mode is approximately 0.5% at 30 kHz and the cone-probe-DNS data illustrate the acoustic mode to decrease and to asymptotically approach 0.2%.
Excitation of dust kinetic Alfven waves by semi-relativistic ion beams
Authors: Rubab N. , Jaffer G.
Published: May 2016

The growth rates for dust kinetic Alfvén wave (DKAW) based on semi-relativistic Maxwellian distribution function are investigated in a hot and magnetized plasma. The dispersion relation of DKAW is obtained on a dust acoustic velocity branch, and the kinetic instability due to cross-field semi-relativistic ion flow is examined by the effect of dust parameters. Analytical expressions are derived for various modes as a natural consequence of the form of the solution, and is shown through graphical representation that the presence of dust particles and the cross-field semi-relativistic ions sensibly modify the dispersion characteristics of low-frequency DKAW. The results are valid for a frequency regime well below the dust cyclotron frequency. We suggest that semi-relativistic particles are an important factor in the growth/damping of DKAWs. It is also found that relativistic effects appear with the dust lower hybrid frequency are more effective for dust kinetic Alfvén waves in the perpendicular component as compared to the parallel one. In particular, the relativistic effects associated with electrons suppress the instability while ions enhance the growth rates. The growth rates are significantly modified with dust parameters and streaming velocity of cross-field ions.
The effects of electron thermal radiation on laser ablative shock waves from aluminum plasma into ambient air
Authors: Sai Shiva S. , Leela Ch. , Prem Kiran P. , Sijoy C. D. , Chaturvedi S.
Published: May 2016

The effect of electron thermal radiation on 7 ns laser ablative shock waves from aluminum (Al) plasma into an ambient atmospheric air has been numerically investigated using a one-dimensional, three-temperature (electron, ion, and radiation) radiation hydrodynamic code MULTI. The governing equations in Lagrangian form are solved using an implicit scheme for planar, cylindrical, and spherical geometries. The shockwave velocities (Vsw) obtained numerically are compared with our experimental values obtained over the intensity range of 2.0 × 1010 to 1.4 × 1011 W/cm2. It is observed that the numerically obtained Vsw is significantly influenced by the thermal radiation effects which are found to be dominant in the initial stage up to 2 μs depending on the input laser energy. Also, the results are found to be sensitive to the co-ordinate geometry used in the simulation (planar, cylindrical, and spherical). Moreover, it is revealed that shock wave undergoes geometrical transitions from planar to cylindrical nature and from cylindrical to spherical nature with time during its propagation into an ambient atmospheric air. It is also observed that the spatio-temporal evolution of plasma electron and ion parameters such as temperature, specific energy, pressure, electron number density, and mass density were found to be modified significantly due to the effects of electron thermal radiation.
Nonlinear dynamics of circularly polarized laser pulse propagating in a magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons distributions
Authors: Etemadpour R. , Sepehri Javan N. , Dorranian D.
Published: May 2016

The nonlinear dynamics of a circularly polarized laser pulse propagating in the magnetized plasmas whose constituents are superthermal ions and mixed nonthermal high-energy tail electrons is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude is obtained using a relativistic two-fluid model. Based on this nonlinear equation and taking into account some nonlinear phenomena such as modulational instability, self-focusing and soliton formation are investigated. Effect of the magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons on these phenomena is considered. It is shown that the nonthermality and superthermality of particles can substantially change the nonlinearity of medium.
Generalized quantum master equations in and out of equilibrium: When can one win?
Authors: Kelly Aaron , Montoya-Castillo Andrés , Wang Lu , Markland Thomas E.
Published: May 2016

Generalized quantum master equations (GQMEs) are an important tool in modeling chemical and physical processes. For a large number of problems, it has been shown that exact and approximate quantum dynamics methods can be made dramatically more efficient, and in the latter case more accurate, by proceeding via the GQME formalism. However, there are many situations where utilizing the GQME approach with an approximate method has been observed to return the same dynamics as using that method directly. Here, for systems both in and out of equilibrium, we provide a more detailed understanding of the conditions under which using an approximate method can yield benefits when combined with the GQME formalism. In particular, we demonstrate the necessary manipulations, which are satisfied by exact quantum dynamics, that are required to recast the memory kernel in a form that can be analytically shown to yield the same result as a direct application of the dynamics regardless of the approximation used. By considering the connections between these forms of the kernel, we derive the conditions that approximate methods must satisfy if they are to offer different results when used in conjunction with the GQME formalism. These analytical results thus provide new insights as to when proceeding via the GQME approach can be used to improve the accuracy of simulations.
Accurate bulk density determination of irregularly shaped translucent and opaque aerogels
Authors: Petkov M. P. , Jones S. M.
Published: May 2016

We present a volumetric method for accurate determination of bulk density of aerogels, calculated from extrapolated weight of the dry pure solid and volume estimates based on the Archimedes' principle of volume displacement, using packed 100 μm-sized monodispersed glass spheres as a “quasi-fluid” media. Hard particle packing theory is invoked to demonstrate the reproducibility of the apparent density of the quasi-fluid. Accuracy rivaling that of the refractive index method is demonstrated for both translucent and opaque aerogels with different absorptive properties, as well as for aerogels with regular and irregular shapes.
Novel high-pressure phases of AlP from first principles
Authors: Liu Chao , Hu Meng , Luo Kun , Yu Dongli , Zhao Zhisheng , He Julong
Published: May 2016

By utilizing a crystal structure prediction software via particle swarm optimization, this study proposes three new high-pressure phases of aluminum phosphide (AlP) with high density and high hardness, in addition to previously proposed phases (wz-, zb-, rs-, NiAs-, β-Sn-, CsCl-, and Cmcm-AlP). These new phases are as follows: (1) an I4¯3d symmetric structure (cI24-AlP) at 55.2 GPa, (2) an R3¯m symmetric structure (hR18-AlP) at 9.9 GPa, and (3) a C222 symmetric structure (oC12-AlP) at 20.6 GPa. Based on first-principle calculations, these phases have higher energetic advantage than CsCl- and β-Sn-AlP at ambient pressure. The independent elastic constants and phonon dispersion spectra are calculated to check the mechanical and dynamic stabilities of these phases. According to mechanical property studies, these new AlP phases have higher hardness than NiAs-AlP, and oC12-AlP has the highest hardness of 7.9 GPa. Electronic band structure calculations indicate that NiAs- and hR18-AlP have electrical conductivity. Additionally, wz-, zb-, and oC12-AlP possess semiconductive properties with indirect bandgaps, and cI24-AlP has a semiconductive property with a direct bandgap.
Solvent organization around the perfluoro group of coumarin 153 governs its photophysical properties: An experimental and simulation study of coumarin dyes in ethanol as well as fluorinated ethanol solvents
Authors: Mondal Saptarsi , Halder Ritaban , Biswas Biswajit , Jana Biman , Singh Prashant Chandra
Published: May 2016

The self-aggregation property of the perfluoro group containing molecules makes it important in the research fields of biology and polymer and organic synthesis. In the quest of understanding the role of the perfluoro group on the photophysical properties of perfluoro-containing molecules in biologically important fluoroethanol solvents, we have applied photophysical as well as molecular dynamics simulation techniques to explore the properties of perfluoro groups containing molecule coumarin-153 (C153) in ethanol (ETH), monofluoroethanol (MFE), difluoroethanol (DFE), and trifluoroethanol (TFE) and compared them with the molecules without perfluoro moiety, namely coumarin-6H (C6H) and coumarin-480 (C480). In contrast to C6H and C480, the excited state lifetime of C153 in fluorinated ETHs is not monotonic. The excited state lifetime of C153 decreases in MFE and DFE as compared to ETH, whereas in TFE, it increases as compared to MFE and DFE. Molecular dynamics simulation reveals that the carbon terminal away from the OH group of fluorinated ETHs has a preferential orientation near the perfluoro (CF3) group of C153. In MFE and DFE, the CF3 group of C153 prefers to have a CF2—F⋯H —(CHF) type of electrostatic interaction over CF2—F⋯F —(CH2) kind of dispersion interaction which increases the rate of nonradiative decay, probably due to the electrostatic nature of the CF2—F⋯H —(CHF) hydrogen bond. On the other hand, in TFE, C—F⋯ F—C type of dispersion interaction, also known as fluorous interaction, takes place between the CF3 groups of C153 and TFE which decreases the rate of nonradiative rate as compared to MFE and DFE, leading to the increased lifetime of C153 in TFE. Photophysical and MD simulation studies clearly depict that the structural organization of solvents and their interaction with the fluorocarbon group are crucial factors for the photophysical behavior of the fluorocarbon containing molecules.
The effect of electron beams on cyclotron maser emission excited by lower-energy cutoffs
Authors: Zhao G. Q. , Feng H. Q. , Wu D. J.
Published: May 2016

Electron-cyclotron maser (ECM) is one of the most important emission mechanisms in astrophysics and can be excited efficiently by lower-energy cutoffs of power-law electrons. These non-thermal electrons probably propagate as a directed collimated beam along ambient magnetic fields. This paper investigates the ECM, in which the effect of electron beams is emphasized. Results show the dependence of emission properties of the ECM on the beam feature. The maximum growth rate of the extraordinary mode (X2) rapidly decreases as the beam momentum increases, while the growth rate of the ordinary mode (O1) changes slightly. In particular, the ordinary mode can overcome the extraordinary mode and becomes the fastest growth mode once the beam momentum is large enough. This research presents an extension of the conventional studies on ECM driven by lower-energy cutoffs and may be helpful to understand better the emission process of solar type I radio bursts, which are dominated by the ordinary mode emission.
Transfer of energy between a pair of molecules near a plasmonic core-shell nanoparticle: Tunability and sensing
Authors: Daneshfar Nader , Yavari Asghar
Published: May 2016

Our model is applied to the calculation of interaction energy between a pair of dipolar molecules (point dipoles) in the vicinity of a nanoshell monomer with core-shell structure, based on the dipole quasi-electrostatic theory of classical electrodynamics and using the Drude and Maxwell-Garnett model. In other words, this work discusses the intermolecular energy transfer from a donor molecule to an acceptor molecule near a spherical nanoparticle that is important for practical applications like sensing. It is shown that the proximity of plasmonic nanoparticles can have a strong effect on the energy transfer between molecules. In addition to the influence of the size, composition, embedding medium, and the filling fraction of doped particles on the interaction energy, the contribution of the dipolar, quadrupolar, octupolar, hexadecapolar, triakontadipolar, and higher order multipole interactions is presented and analyzed. Briefly, we will show that it is possible to achieve enhanced energy transfer by manipulation of different parameters as mentioned above.
Understanding the dynamics and energetics of magnetic reconnection in a laboratory plasma: Review of recent progress on selected fronts
Authors: Yamada Masaaki , Yoo Jongsoo , Myers Clayton E.
Published: May 2016

Magnetic reconnection is a fundamental process at work in laboratory, space, and astrophysical plasmas, in which magnetic field lines change their topology and convert magnetic energy to plasma particles by acceleration and heating. One of the most important problems in reconnection research has been to understand why reconnection occurs so much faster than predicted by magnetohydrodynamics theory. Following the recent pedagogical review of this subject [Yamada et al., Rev. Mod. Phys. 82, 603 (2010)], this paper presents a review of more recent discoveries and findings in the research of fast magnetic reconnection in laboratory, space, and astrophysical plasmas. In spite of the huge difference in physical scales, we find remarkable commonality between the characteristics of the magnetic reconnection in laboratory and space plasmas. In this paper, we will focus especially on the energy flow, a key feature of the reconnection process. In particular, the experimental results on the energy conversion and partitioning in a laboratory reconnection layer [Yamada et al., Nat. Commun. 5, 4474 (2014)] are discussed and compared with quantitative estimates based on two-fluid analysis. In the Magnetic Reconnection Experiment, we find that energy deposition to electrons is localized near the X-point and is mostly from the electric field component perpendicular to the magnetic field. The mechanisms of ion acceleration and heating are also identified, and a systematic and quantitative study on the inventory of converted energy within a reconnection layer with a well-defined but variable boundary. The measured energy partition in a reconnection region of similar effective size (L ≈ 3 ion skin depths) of the Earth's magneto-tail [Eastwood et al., Phys. Rev. Lett. 110, 225001 (2013)] is notably consistent with our laboratory results. Finally, to study the global aspects of magnetic reconnection, we have carried out a laboratory experiment on the stability criteria for solar flare eruptions, including “storage and release” mechanisms of magnetic energy. We show that toroidal magnetic flux generated by magnetic relaxation (reconnection) processes generates a new stabilizing force which prevents plasma eruption. This result has led us to discover a new stabilizing force for solar flares [Myers et al., Nature 528, 526 (2015)].
A multi-GHz chaotic optoelectronic oscillator based on laser terminal voltage
Authors: Chang C. Y. , Choi Daeyoung , Locquet A. , Wishon Michael J. , Merghem K. , Ramdane Abderrahim , Lelarge François , Martinez A. , Citrin D. S.
Published: May 2016

A multi-GHz chaotic optoelectronic oscillator based on an external cavity semiconductor laser (ECL) is demonstrated. Unlike the standard optoelectronic oscillators for microwave applications, we do not employ the dynamic light output incident on a photodiode to generate the microwave signal, but instead generate the microwave signal directly by measuring the terminal voltage V(t) of the laser diode of the ECL under constant-current operation, thus obviating the photodiode entirely.
Scaled experiments of explosions in cavities
Authors: Grun J. , Cranch G. A. , Lunsford R. , Compton S. , Walton O. R. , Weaver J. , Dunlop W. , Fournier K. B.
Published: May 2016

Consequences of an explosion inside an air-filled cavity under the earth's surface are partly duplicated in a laboratory experiment on spatial scales 1000 smaller. The experiment measures shock pressures coupled into a block of material by an explosion inside a gas-filled cavity therein. The explosion is generated by suddenly heating a thin foil that is located near the cavity center with a short laser pulse, which turns the foil into expanding plasma, most of whose energy drives a blast wave in the cavity gas. Variables in the experiment are the cavity radius and explosion energy. Measurements and GEODYN code simulations show that shock pressures measured in the block exhibit a weak dependence on scaled cavity radius up to ∼25 m/kt1/3, above which they decrease rapidly. Possible mechanisms giving rise to this behavior are described. The applicability of this work to validating codes used to simulate full-scale cavity explosions is discussed.
Intensity-dependent nonlinearity of the lateral photoconductivity in InGaAs/GaAs dot-chain structures
Authors: Golovynskyi S. L. , Dacenko O. I. , Kondratenko S. V. , Lavoryk S. R. , Mazur Yu. I. , Wang Zh. M. , Ware M. E. , Tarasov G. G. , Salamo G. J.
Published: May 2016

Photoelectric properties of laterally correlated multilayer InGaAs/GaAs quantum dots (QDs) heterostructures are studied. The response of the photocurrent to increasing excitation intensity is found to be nonlinear and varying with excitation energy. The structures are photosensitive in a wide range of photon energies above 0.6 eV. The spectral dependence of the photoconductivity (PC) is caused by strong interaction between the bulk GaAs and the lower energy states of the wetting layer, the QDs, as well as the defect states in the GaAs band gap. In particular, a mechanism for the participation of deep electron trap levels in the photocurrent is clarified. These structures also demonstrate a high sensitivity of up to 10 A/W at low excitation intensities. However, at higher excitation intensities, the sensitivity reduces exhibiting a strong spectral dependence at the same time. The observed sublinear PC dependence on excitation power results from a direct electron-hole recombination both in the QDs and in GaAs host. The solution of rate equations included the contributions of QD ground and exited states, bulk GaAs states and the states of defects within the GaAs bandgap describes well the experimental data.
Three-dimensional direct observation of Gouy phase shift in a terajet produced by a dielectric cuboid
Authors: Nguyen Pham Hai Huy , Hisatake Shintaro , Minin I. V. , Minin O. V. , Nagatsuma Tadao
Published: May 2016

The generation of the terajet at the terahertz (THz) frequency with the capability of subwavelength beam-compression has been attracting increasing research interest, as did the generation of the nanojet at the optical frequency. In particular, a terajet generated from a dielectric cuboid was not previously studied experimentally in the THz region. We here experimentally demonstrate three-dimensional visualizations and characterization of a terajet generated from a dielectric cuboid with a refractive index of n = 1.46 at 125 GHz. The subwavelength compressed beam and the Gouy phase shift phenomena of the terajet are directly observed. It is also found out that a calculation model of Gouy phase shift based on focused Gaussian beam by a lens cannot explain the Gouy phase shift of compressed beam by the terajet. The intensity enhancement of about 7.4 dB and full width at half maximum of 0.6λ are obtained at the distance 0.5λ from the cuboid.
Heterogeneity and nearest-neighbor coupling can explain small-worldness and wave properties in pancreatic islets
Authors: Cappon Giacomo , Pedersen Morten Gram
Published: May 2016

Many multicellular systems consist of coupled cells that work as a syncytium. The pancreatic islet of Langerhans is a well-studied example of such a microorgan. The islets are responsible for secretion of glucose-regulating hormones, mainly glucagon and insulin, which are released in distinct pulses. In order to observe pulsatile insulin secretion from the β-cells within the islets, the cellular responses must be synchronized. It is now well established that gap junctions provide the electrical nearest-neighbor coupling that allows excitation waves to spread across islets to synchronize the β-cell population. Surprisingly, functional coupling analysis of calcium responses in β-cells shows small-world properties, i.e., a high degree of local coupling with a few long-range “short-cut” connections that reduce the average path-length greatly. Here, we investigate how such long-range functional coupling can appear as a result of heterogeneity, nearest-neighbor coupling, and wave propagation. Heterogeneity is also able to explain a set of experimentally observed synchronization and wave properties without introducing all-or-none cell coupling and percolation theory. Our theoretical results highlight how local biological coupling can give rise to functional small-world properties via heterogeneity and wave propagation.
Current-driven nanowire formation on surfaces of crystalline conducting substrates
Authors: Kumar Ashish , Dasgupta Dwaipayan , Dimitrakopoulos Christos , Maroudas Dimitrios
Published: May 2016

The formation and precise manipulation of nanoscale features by controlling macroscopic forces is essential to advancing nanotechnology. Toward this end, we report here a theoretical study on formation of nanowires with precisely controlled widths, starting from single-layer conducting islands on crystalline conducting substrates under the controlled action of macroscopic forcing provided by an externally applied electric field that drives island edge electromigration. Numerical simulations based on an experimentally validated model and supported by linear stability theory show that large-size islands undergo a current-induced fingering instability, leading to nanowire formation after finger growth. Depending on the substrate surface crystallographic orientation, necking instabilities after fingering lead to the formation of multiple parallel nanowires per island. In all cases, the axis of the formed nanowires is aligned with the direction of the externally applied electric field. The nanowires have constant widths, on the order of 10 nm, which can be tuned by controlling the externally applied electric field strength. Our findings have important implications for developing future lithography-free nanofabrication and nanoelectronic patterning techniques.
Fast continuous tuning of terahertz quantum-cascade lasers by rear-facet illumination
Authors: Hempel Martin , Röben Benjamin , Schrottke Lutz , Hübers Heinz-Wilhelm , Grahn Holger T.
Published: May 2016

GaAs-based terahertz quantum-cascade lasers (QCLs) are continuously tuned in their emission frequency by illuminating the rear facet with a near-infrared, high-power diode laser. For QCLs emitting around 3.1 THz, the maximum tuning range amounts to 2.8 GHz for continuous-wave operation at a heat sink temperature of 55 K, while in pulsed mode 9.1 and 8.0 GHz are achieved at 35 and 55 K, respectively.
High density of (pseudo) periodic twin-grain boundaries in molecular beam epitaxy-grown van der Waals heterostructure: MoTe2/MoS2
Authors: Diaz Horacio Coy , Ma Yujing , Chaghi Redhouane , Batzill Matthias
Published: May 2016

Growth of transition metal dichalcogenide heterostructures by molecular beam epitaxy (MBE) promises synthesis of artificial van der Waals materials with controllable layer compositions and separations. Here, we show that MBE growth of 2H-MoTe2 monolayers on MoS2 substrates results in a high density of mirror-twins within the films. The grain boundaries are tellurium deficient, suggesting that Te-deficiency during growth causes their formation. Scanning tunneling microscopy and spectroscopy reveal that the grain boundaries arrange in a pseudo periodic “wagon wheel” pattern with only ∼2.6 nm repetition length. Defect states from these domain boundaries fill the band gap and thus give the monolayer an almost metallic property. The band gap states pin the Fermi-level in MoTe2 and thus determine the band-alignment in the MoTe2/MoS2 interface.
Propagation of phase modulation signals in time-varying plasma
Authors: Yang Min , Li Xiaoping , Wang Di , Liu Yanming , He Pan
Published: May 2016

The effects of time-varying plasma to the propagation of phase modulation signals are investigated in this paper. Through theoretical analysis, the mechanism of the interaction between the time-varying plasma and the phase modulation signal is given. A time-varying plasma generator which could produce arbitrary time-varying plasma is built by adjusting the discharge power. A comparison of results from experiment and simulation prove that the time-varying plasma could cause the special rotation of QPSK (Quadrature Phase Shift Keying) constellation, and the mechanism of constellation point’s rotation is analyzed. Additionally, the experimental results of the QPSK signals’ EVM (Error Vector Magnitude) after time-varying and time-invariant plasma with different ωp/ω are given. This research could be used to improve the TT&C (Tracking Telemeter and Command) system of re-entry vehicles.
Phosphite-induced reactive oxygen species production and ethylene and ABA biosynthesis, mediate the control of Phytophthora capsici in pepper (Capsicum annuum)
Authors: Liu Peiqing , Li Benjin , Lin Ming , Chen Guoliang , Ding Xueling , Weng Qiyong , Chen Qinghe
Published: May 2016

Phytophthora capsici is an oomycete pathogen with a broad host range that inflicts significant damage in vegetables. Phosphite (Phi) is used to control oomycete diseases, but the molecular mechanisms underlying Phi-induced resistance to P. capsici are unknown. Thus, Phi-inhibited mycelial growth on strain LT1534 and primed host defence were analysed. We demonstrated that Phi (>5 µg mL–1) had a direct antibiotic effect on mycelial growth and zoospore production, and that mortality and DNA content were significantly reduced by pre-treatment with Phi. In addition, elevated hydrogen peroxide (H2O2) promoted callose deposition and increased the levels of soluble proteins and Capsicum annuum L. pathogenesis-related 1 (CaPR1) expression. Furthermore, Phi (1 g L–1) significantly increased the transcription of the antioxidant enzyme genes, and the genes involved in ethylene (ET) and abscisic acid (ABA) biosynthesis, as well as mitogen-activated protein kinase (MAPK) cascades. However, pre-treatment with reactive oxygen species (ROS), ABA and ET biosynthesis inhibitors decreased Phi-induced resistance and reduced the expression of ABA-responsive 1 (CaABR1) and lipoxygenase 1 (CaLOX1). In addition, the decreased ROS and ABA inhibited Phi-induced expression of CaMPK17–1. We propose that Phi-induced ROS production, ET and ABA biosynthesis mediate the control of P. capsici, and that ABA functions through CaMPK17–1-mediated MAPK signalling.
The formation of charcoal reflectance and its potential use in post-fire assessments
Authors: Belcher Claire M. , Hudspith Victoria A.
Published: May 2016

Charcoal has an exceptional ability to reflect light when viewed using reflectance microscopy. The amount of light reflected is variable depending on the differential ordering of graphite-like phases within the charcoal itself. It has been suggested that this relates to the temperature of formation, whereby higher formation temperatures result in high charcoal reflectance. However, this explanation is derived from oven-based chars that do not well represent the natural combustion process. Here, we have experimentally created charcoals using a cone calorimeter, in order to explore the development of charcoal reflectance during pre-ignition heating and peak heat-release rate, through to the end of flaming and the transition to char oxidation. We find that maximum charcoal reflectance is reached at the transition between pyrolysis and char oxidation, before its conversion to mineral ash, and indicates that our existing understanding of reflectance is in error. We suggest that charcoal reflectance warrants additional study as it may provide a useful quantitative addition to ground-based fire severity surveys, because it may allow exploration of surface heating after the main fire front has passed and the fire transitions to smouldering phases.
A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle
Authors: Mackinder Luke C. M. , Meyer Moritz T. , Mettler-Altmann Tabea , Chen Vivian K. , Mitchell Madeline C. , Caspari Oliver , Freeman Rosenzweig Elizabeth S. , Pallesen Leif , Reeves Gregory , Itakura Alan , Roth Robyn , Sommer Frederik , Geimer Stefan , Mühlhaus Timo , Schroda Michael , Goodenough Ursula , Stitt Mark , Griffiths Howard , Jonikas Martin C.
Published: May 2016

Significance

Eukaryotic algae, which play a fundamental role in global CO
2
fixation, enhance the performance of the carbon-fixing enzyme Rubisco by placing it into an organelle called the pyrenoid. Despite the ubiquitous presence and biogeochemical importance of this organelle, how Rubisco assembles to form the pyrenoid remains a long-standing mystery. Our discovery of an abundant repeat protein that binds Rubisco in the pyrenoid represents a critical advance in our understanding of pyrenoid biogenesis. The repeat sequence of this protein suggests elegant models to explain the structural arrangement of Rubisco enzymes in the pyrenoid. Beyond advances in basic understanding, our findings open doors to the engineering of algal pyrenoids into crops to enhance yields.
High-speed atomic force microscopy reveals structural dynamics of amyloid β
1–42
aggregates
Authors: Watanabe-Nakayama Takahiro , Ono Kenjiro , Itami Masahiro , Takahashi Ryoichi , Teplow David B. , Yamada Masahito
Published: May 2016

Significance

Amyloid fibril formation underlies the pathogenesis of a large number of diseases. Among the neurodegenerative diseases, the process is prominent in Alzheimer’s disease. Fibril elongation has been thought to be a nucleation-dependent process that faithfully duplicates nucleus structure as each monomer adds to the fibril end. Polymorphism in fibril structure thus has been postulated to depend on initial nucleus structure. However, there is little direct observation of growing amyloid fibril structure. Here, using high-speed atomic force microscopy, we observed that Aβ
1–42
fibril formation produced two distinct morphomers, “straight” and “spiral.” Surprisingly, we observed switching between these structures after the initiation of fibril elongation. Our results provide previously unidentified insights into the process of nucleation-dependent Aβ
1–42
fibril formation.
Mutant cycle analysis with modified saxitoxins reveals specific interactions critical to attaining high-affinity inhibition of hNa
V
1.7
Authors: Thomas-Tran Rhiannon , Du Bois J.
Published: May 2016

Significance

Chronic pain plagues at least 50 million Americans and has an estimated annual cost in excess of $200 billion. Consequently, there exists significant interest in developing effective, nonnarcotic analgesics. Drugs that target individual voltage-gated sodium channel (Na
V
) subtypes have appreciable therapeutic potential as pain medicines. Our work uses small-molecule design and protein mutagenesis to gain insight into the molecular architecture of the ion conduction pore of Na
V
. These studies have revealed structural differences in the outer mouth of the channel that potentiate the binding of guanidinium toxins. Such findings are helping advance the preparation of isoform-selective Na
V
antagonists.
Primer release is the rate-limiting event in lagging-strand synthesis mediated by the T7 replisome
Authors: Hernandez Alfredo J. , Lee Seung-Joo , Richardson Charles C.
Published: May 2016

Significance

Lagging-strand DNA is replicated in multiple segments called Okazaki fragments, whose formation involves a complex molecular cycle mediated by DNA primase, polymerase, and other replisome components. In addition, synthesis of the lagging strand must occur in lockstep with the leading strand. Using the simple replication system of bacteriophage T7, we found that primer release from the DNA primase domain of T7 primase helicase is a critical regulatory event in the initiation of Okazaki fragments and that the T7 single-stranded binding protein, gp2.5, regulates initiation timing.
USP6 oncogene promotes Wnt signaling by deubiquitylating Frizzleds
Authors: Madan Babita , Walker Matthew P. , Young Robert , Quick Laura , Orgel Kelly A. , Ryan Meagan , Gupta Priti , Henrich Ian C. , Ferrer Marc , Marine Shane , Roberts Brian S. , Arthur William T. , Berndt Jason D. , Oliveira Andre M. , Moon Randall T. , Virshup David M. , Chou Margaret M. , Major Michael B.
Published: May 2016

Significance

Ubiquitin-specific protease 6 (USP6) is a deubiquitylase that is overexpressed by chromosome translocation in two human neoplasms, aneurysmal bone cyst and nodular fasciitis. The relevant substrates of this ubiquitin-specific protease are not clear. Here, we identify the Wnt receptor Frizzled (Fzd) as a key target of the USP6 oncogene. Increased expression of USP6 increases the membrane abundance of Fzd, and hence increases cellular sensitivity to Wnts. USP6 opposes the activity of the ubiquitin ligase and tumor suppressor ring finger protein 43 (RNF43). This study identifies a new mechanism for pathological Wnt pathway activation in human disease and suggests a new approach to regulate Wnt activity therapeutically.
mir-276a strengthens
Drosophila
circadian rhythms by regulating
timeless
expression
Authors: Chen Xiao , Rosbash Michael
Published: May 2016

Significance

The circadian clock regulates biochemical, physiological, endocrine, and behavioral features of higher organisms. Although the timekeeping mechanism and many of the functions it governs rely on transcriptional regulation, posttranscriptional regulation also plays an important role. We show here that levels of the abundant
Drosophila
microRNA mir-276a oscillate under 24-h light–dark cycles and are regulated by the transcription factor Chorion factor 2. mir-276a is important for robust rhythmicity and binds to a single site in the 3' UTR of the important clock gene
timeless
(
tim
). We used clustered, regularly interspaced, short palindromic repeats to generate fly strains missing this mir-276a–binding site. Because these strains have elevated TIM levels and enhanced arrhythmicity, the data indicate that mir-276a helps maintain proper TIM levels, which are important for robust rhythmicity.
Research on individual differences in executive functions
Authors: Friedman Naomi P.
Published: May 2016

Executive functions (EFs), such as response inhibition, interference control, and set shifting, are general-purpose control mechanisms that enable individuals to regulate their thoughts and behaviors. Because bilingual individuals use EF-like processes during language control, researchers have become interested in the hypothesis that this use might train EFs, resulting in better performance on non-linguistic EF tasks. Although this bilingual advantage hypothesis seems straightforward to test, it involves a number of important decisions in terms of how to assess bilingualism and EFs. In this article, I focus on the complexity of measuring EFs, drawing on individual differences research (conducted with participants not selected for bilingualism). Specifically, I discuss issues related to (1) the measurement of EFs (particularly the effects of task impurity and unreliability) and (2) the multicomponent nature of EFs. Within each of these topics, I elaborate on consequences for research on bilingual advantages and provide some recommendations.
Coliform Bacteria Monitoring in Fish Systems: Current Practices in Public Aquaria
Authors: Culpepper Erin E. , Clayton Leigh A. , Hadfield Catherine A. , Arnold Jill E. , Bourbon Holly M.
Published: May 2016

Public aquaria evaluate coliform indicator bacteria levels in fish systems, but the purpose of testing, testing methods, and management responses are not standardized, unlike with the coliform bacteria testing for marine mammal enclosures required by the U.S. Department of Agriculture. An online survey was sent to selected aquaria to document current testing and management practices in fish systems without marine mammals. The information collected included indicator bacteria species, the size and type of systems monitored, the primary purpose of testing, sampling frequency, test methods, the criteria for interpreting results, corrective actions, and management changes to limit human exposure. Of the 25 institutions to which surveys were sent, 19 (76%) responded. Fourteen reported testing for fecal indicator bacteria in fish systems. The most commonly tested indicator species were total (86%) and fecal (79%) coliform bacteria, which were detected by means of the membrane filtration method (64%). Multiple types and sizes of systems were tested, and the guidelines for testing and corrective actions were highly variable. Only three institutions performed additional tests to confirm the identification of indicator organisms. The results from this study can be used to compare bacterial monitoring practices and protocols in fish systems, as an aid to discussions relating to the accuracy and reliability of test results, and to help implement appropriate management responses.

Received August 23, 2015; accepted December 29, 2015
In–out asymmetry of divertor particle flux in H-mode with edge localized modes on EAST
Authors: Liu J.B. , Guo H.Y. , Wang L. , Xu G.S. , Xia T.Y. , Liu S.C. , Xu X.Q. , Li Jie , Chen L. , Yan N. , Wang H.Q. , Xu J.C. , Feng W. , Shao L.M. , Deng G.Z. , Liu H.
Published: May 2016

The in–out divertor asymmetry in the Experimental Advanced Superconducting Tokamak (EAST), as manifested by particle fluxes measured by the divertor triple Langmuir probe arrays, is significantly enhanced during type-I edge localized modes (ELMs), favoring the inner divertor in lower single null (LSN) for the normal toroidal field (B
t) direction, i.e. with the ion B  ×  

∇

B direction towards the lower X-point, while the in–out asymmetry is reversed when the ion B  ×  

∇

B is directed away from the lower X-point. The plasma flow measured by the Mach probe at the outer midplane is in the ion Pfirsch–Schlüter (PS) flow direction, opposite to both B  ×  

∇

B and E  ×  B drifts, i.e. towards the inner divertor for normal B
t, and the outer divertor for reverse B
t, consistent with the observed in–out divertor asymmetry in particle fluxes. Since the particle source from an ELM event is predominantly located near the outer midplane, this new finding suggests a critical role of the PS flow in driving the in–out divertor asymmetry. The divertor asymmetry during type-III ELMs exhibits a similar trend to that during type-I ELMs. Strong in–out divertor asymmetry is also present during inter-ELM and ELM-free phases for the normal field direction, i.e. with more particle flux to the lower inner divertor target, but the peak particle flux merely becomes more symmetric, or slightly reversed, for reverse B
t, i.e. reversed B  ×  

∇

B drift direction.
Affine cellularity of affine 𝑞-Schur algebras
Authors: Cui Weideng
Published: May 2016

We first present an axiomatic approach to proving that an algebra with a cell theory in Lusztig’s sense is affine cellular in the sense of Koenig and Xi; then we will show that the affine

q
q

-Schur algebra

U

r
,
n
,
n

\mathfrak {U}_{r,n,n}

is affine cellular. We also show that

U

r
,
n
,
n

\mathfrak {U}_{r,n,n}

is of finite global dimension and its derived module category admits a stratification when the parameter

v
∈

C

∗

v\in \mathbb {C}^{*}

is not a root of unity.
The complement of the figure-eight knot geometrically bounds
Authors: Slavich Leone
Published: May 2016

We show that some hyperbolic

3
3

-manifolds which are tessellated by copies of the regular ideal hyperbolic tetrahedron are geodesically embedded in a complete, finite volume, hyperbolic

4
4

-manifold. This allows us to prove that the complement of the figure-eight knot geometrically bounds a complete, finite volume hyperbolic

4
4

-manifold. This is the first example of geometrically bounding hyperbolic knot complements and, amongst known examples of geometrically bounding manifolds, the one with the smallest volume.