bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalisation of genetic algorithm and fast Fourier transform for synthesising unequally spaced linear array shaped pattern including coupling effects
Authors: You Pengfei , Liu Yanhui , Xu Kaida , Zhu Chunhui , Liu Qing Huo
Published: December 2016

Antenna arrays with shaped patterns have drawn significant attention for their wide applications in radar, sonar and communication systems. The combination of genetic algorithm (GA) and fast Fourier transform (FFT) has been used to synthesise shaped pattern of antenna array's factor without considering coupling effects. In this work, the GA‐FFT method is generalised by integrating with a new virtual active element pattern (AEP) expansion method which approximates each AEP as the radiation pattern by exciting several equally spaced virtual elements surrounding the real element position. The generalised GA‐FFT can be applied for the shaped pattern synthesis of unequally spaced linear arrays including mutual coupling and platform effect. Several synthesis examples with different pattern shapes and different antenna structures are given to demonstrate the effectiveness, accuracy and robustness of the proposed method.
Origin of CH+ in diffuse molecular clouds
Authors: Valdivia Valeska , Godard Benjamin , Hennebelle Patrick , Gerin Maryvonne , Lesaffre Pierre , Le Bourlot Jacques
Published: December 2016

Context. Molecular clouds are known to be magnetised and to display a turbulent and complex structure where warm and cold phases are interwoven. The turbulent motions within molecular clouds transport molecules, and the presence of magnetic fields induces a relative velocity between neutrals and ions known as the ion-neutral drift (vd). These effects all together can influence the chemical evolution of the clouds.

Aims. This paper assesses the roles of two physical phenomena which have previously been invoked to boost the production of CH+ under realistic physical conditions: the presence of warm H2 and the increased formation rate due to the ion-neutral drift.

Methods. We performed ideal magnetohydrodynamical (MHD) simulations that include the heating and cooling of the multiphase interstellar medium (ISM), and where we treat dynamically the formation of the H2 molecule. In a post-processing step we compute the abundances of species at chemical equilibrium using a solver that we developed. The solver uses the physical conditions of the gas as input parameters, and can also prescribe the H2 fraction if needed. We validate our approach by showing that the H2 molecule generally has a much longer chemical evolution timescale compared to the other species.

Results. We show that CH+ is efficiently formed at the edge of clumps, in regions where the H2 fraction is low (0.3−30%) but nevertheless higher than its equilibrium value, and where the gas temperature is high (≳ 300 K). We show that warm and out of equilibrium H2 increases the integrated column densities of CH+ by one order of magnitude up to values still ~ 3−10 times lower than those observed in the diffuse ISM. We balance the Lorentz force with the ion-neutral drag to estimate the ion-drift velocities from our ideal MHD simulations. We find that the ion-neutral drift velocity distribution peaks around ~ 0.04 km s-1, and that high drift velocities are too rare to have a significant statistical impact on the abundances of CH+. Compared to previous works, our multiphase simulations reduce the spread in vd, and our self-consistent treatment of the ionisation leads to much reduced vd. Nevertheless, our resolution study shows that this velocity distribution is not converged: the ion-neutral drift has a higher impact on CH+ at higher resolution. On the other hand, our ideal MHD simulations do not include ambipolar diffusion, which would yield lower drift velocities.

Conclusions. Within these limitations, we conclude that warm H2 is a key ingredient in the efficient formation of CH+ and that the ambipolar diffusion has very little influence on the abundance of CH+, mainly due to the small drift velocities obtained. However, we point out that small-scale processes and other non-thermal processes not included in our MHD simulation may be of crucial importance, and higher resolution studies with better controlled dissipation processes are needed.
Perception of Noise Pollution in a Youth and Adults School in Curitiba-PR
Authors: Borges Filho Orlando , Ribas Angela , Gonçalves Claudia , Lacerda Adriana , Riesemberg Renato , Klagenberg Karlin
Published: December 2016

Introduction Nowadays noise remains the third largest cause of environmental pollution on Earth. It appears that despite the existing noise control legislation the issue deserves further supervision by the public authorities so that the ceilings established for the various activities are observed. People exposed to noise are more likely to develop numerous auditory and non-auditory problems directly impacting persona family and working life.

Objectives The objective of this study is to research and consequently understand how the population of students of a youth and adult school in Curitiba perceives noise pollution as well as look into the actions that the school adopts in order to guide the students on the topic.

Method We applied a structured questionnaire to 120 individuals and assessed the following variables: characterization of the place of residence occupation leisure health and perception of soundscapes. We also applied a closed questionnaire about educational actions for noise pollution to the school's geography teacher.

Results Questionnaire responses show that people perceive noise in the most diverse environments they frequent and are able to identify the source of the noise but this perception proved fragile as the majority does not take measures to prevent or mitigate these noises. At school there are no actions aimed at environmental education on the subject studied.

Conclusion The studied group does not perceive the noise as a harmful agent and does not prevent themselves from it and the school not work contents related to noise pollution leaving a significant gap in the awareness process of this population.
Exome Sequencing Identifying Dual Mutations in Calcium Signaling Genes GNAO1 and ATP2B3 in a Patient with Early Infantile Epileptic Encephalopathy
Authors: Serajee Fatema , Huq Ahm , Ueda Keisuke
Published: December 2016

Early infantile epileptic encephalopathy (EIEE) is an age-dependent epileptic encephalopathy. It occurs early in life with various types of seizures, especially tonic spasms and its overall prognosis is poor. We report a 5-year-old boy with EIEE, severe developmental delay, intractable epilepsy, and congenital cerebellar ataxia. His infantile spasms were treated successfully with ACTH, but he later developed intractable focal seizures. Whole exome sequencing revealed a maternally inherited missense mutation in the ATP2B3 gene (c.3338C > T/p.T1113M) and a de novo missense mutation in the GNAO1 gene (c.133G > C/p.G45R). Both genes are associated with calcium signaling pathways. The ATP2B3 gene is associated with intracellular calcium clearance, resulting in abnormal calcium homeostasis and X-linked spinocerebellar ataxia-1. The GNAO1 gene is associated with G protein signaling, affecting calcium signaling, and EIEE. Both mutations are related to maintain cellular calcium homeostasis, but the phenotype was not significantly more severe than those which have been reported.
Sonographic Cervical Shortening after Labor Induction is a Predictor of Vaginal Delivery
Authors: Indraccolo Ugo , Scutiero Gennaro , Greco Pantaleo
Published: December 2016

Objective Analyzing if the sonographic evaluation of the cervix (cervical shortening) is a prognostic marker for vaginal delivery.

Methods Women who underwent labor induction by using dinoprostone were enrolled. Before the induction and three hours after it, the cervical length was measured by ultrasonography to obtain the cervical shortening. The cervical shortening was introduced in logistic regression models among independent variables and for calculating receiver operating characteristic (ROC) curves.

Results Each centimeter in the cervical shortening increases the odds of vaginal delivery in 24.4% within 6 hours; in 16.1% within 24 hours; and in 10.5% within 48 hours. The best predictions for vaginal delivery are achieved for births within 6 and 24 hours, while the cervical shortening poorly predicts vaginal delivery within 48 hours.

Conclusion The greater the cervical shortening 3 hours after labor induction, the higher the likelihood of vaginal delivery within 6, 24 and 48 hours.
Note: Reconstruction of fluid flows in porous media using geometric a priori information
Authors: Maisl Michael , Scholl Hagen , Schorr Christian , Seemann Ralf
Published: December 2016

X-ray tomography typically suffers from insufficient temporal resolution when imaging dynamic processes. Using the example of multiphase flow in solid porous media, we adapt an iterative algorithm to compute 3d tomograms from 2d projections, which allows for a significant reduction of scan time while maintaining a high level of reconstruction quality. To this end, a priori knowledge about the porous medium is incorporated into the reconstruction algorithm. This algorithm is universal when monitoring dynamic changes in any static matrix and allows for an at least five times decreased imaging time with respect to standard reconstruction algorithms.
Bias voltage-controlled ferromagnetism switching in undoped zinc oxide thin film memory device
Authors: Li S. S. , Chuang Ricky W. , Su Y. K. , Hu Y. M.
Published: December 2016

The bipolar resistive switching properties of Pt/ZnO/Pt multilayer film structure were investigated in this study. The M-H curves corresponding to the Pt/ZnO/Pt bipolar resistive switching device maintained at initial, high resistance, and low resistance states were individually obtained; all of which were ferromagnetic in nature. The strength of saturation magnetization of the device separately set at low resistance state, and the initial state was found to be strongest and weakest, respectively. Photoluminescence and X-ray photoelectron results indicate the presence of oxygen vacancies in the ZnO thin film. This resistive switching behavior accompanied with ferromagnetism could be attributed to the intrinsic defects. The results clearly demonstrate that the ferromagnetic switching capability of Pt/ZnO/Pt device is critically dependent on the bias voltage administered, which potentially allows this device to have magneto-electrical device applications.
Stability of ideal MHD configurations. I. Realizing the generality of the G operator
Authors: Keppens R. , Demaerel T.
Published: December 2016

A field theoretical approach, applied to the time-reversible system described by the ideal magnetohydrodynamic (MHD) equations, exposes the full generality of MHD spectral theory. MHD spectral theory, which classified waves and instabilities of static or stationary, usually axisymmetric or translationally symmetric configurations, actually governs the stability of flowing, (self-)gravitating, single fluid descriptions of nonlinear, time-dependent idealized plasmas, and this at any time during their nonlinear evolution. At the core of this theory is a self-adjoint operator G, discovered by Frieman and Rotenberg [Rev. Mod. Phys. 32, 898 (1960)] in its application to stationary (i.e., time-independent) plasma states. This Frieman-Rotenberg operator dictates the acceleration identified by a Lagrangian displacement field ξ, which connects two ideal MHD states in four-dimensional space-time that share initial conditions for density, entropy, and magnetic field. The governing equation reads d2ξdt2=G[ξ], as first noted by Cotsaftis and Newcomb [Nucl. Fusion, Suppl. Part 2, 447 and 451 (1962)]. The time derivatives at left are to be taken in the Lagrangian way, i.e., moving with the flow v. Physically realizable displacements must have finite energy, corresponding to being square integrable in the Hilbert space of displacements equipped with an inner product rule, for which the G operator is self-adjoint. The acceleration in the left-hand side features the Doppler-Coriolis operator v·∇, which is known to become an antisymmetric operator when restricting attention to stationary equilibria. Here, we present all derivations needed to get to these insights and connect results throughout the literature. A first illustration elucidates what can happen when self-gravity is incorporated and presents aspects that have been overlooked even in simple uniform media. Ideal MHD flows, as well as Euler flows, have essentially 6 + 1 wave types, where the 6 wave modes are organized through the essential spectrum of the G operator. These 6 modes are actually three pairs of modes, in which the Alfvén pair (a shear wave pair in hydro) sits comfortably at the middle. Each pair of modes consists of a leftgoing wave and a rightgoing wave, or equivalently stated, with one type traveling from past to future (forward) and the other type that goes from future to past (backward). The Alfvén pair is special, in its left-right categorization, while there is full degeneracy for the slow and fast pairs when reversing time and mirroring space. The Alfvén pair group speed diagram leads to the familiar Elsässer variables.
Electric-double-layer doping of WSe2 field-effect transistors using polyethylene-oxide cesium perchlorate
Authors: Fathipour Sara , Pandey Pratyush , Fullerton-Shirey Susan , Seabaugh Alan
Published: December 2016

Electric double layers (EDLs) formed between polyethylene oxide cesium perchlorate and multilayer WSe2 field-effect transistors (FETs) are explored as a means for contact and access region doping. In this application, the electric double layer is formed using a top field plate or a side gate and then locked into place by cooling of the device below the glass transition temperature of the polymer. A dual work-function Ti/Pd contact is used to form the Schottky contacts with Ti as the n-contact and Pd as the p-contact and these are evaporated in a single evaporation. Using the EDL doping technique, sheet carrier density and current density are as high as (4.9 ± 1.9) × 1013 cm−2 and 58 μA/μm for n-doping and (3.5 ± 1.9) × 1013 cm−2 and 50 μA/μm for p-doping for the highest channel conductivities. The weak temperature dependence of the transfer characteristics at high doping levels reveals that the current in the Schottky contacts is dominated by tunneling with a contact resistance of 1 kΩ μm for the p-branch and 3.4 kΩ μm for the n-branch, comparable to the best WSe2 FET reports. At the highest carrier densities, the temperature coefficient of the conductance becomes negative as the mobility of the channel controls the temperature dependence. Using EDL doping, n-FET and p-FET configurations are demonstrated.
Electrical contacts to nanocrystalline diamond films studied at high temperatures
Authors: Shimoda Naotaka , Kato Yoshimine , Teii Kungen
Published: December 2016

Electrical contacts of Ni, NiSi, Cu, Au, Al, and Ti electrodes to an n-type nanocrystalline diamond film are studied at temperatures between room temperature and 500 °C in a vacuum by the transmission line measurement. Direct current-voltage characteristics measured between pairs of electrodes on the film show almost straight lines, typical of ohmic contacts, for all kinds of electrode materials. The measured series resistance is divided into resistance of the film, resistance of the electrode, and the contact resistance between the electrode and film. The Ni electrode has the lowest contact resistance, which decreases from about 380 to 200 mΩ cm2 with temperature. The contact resistance accounts for a large portion of the total resistance at low temperatures. The results confirm that the contact resistance has a close relation with the work function of electrodes such that the larger the work function, the lower the contact resistance.
Compact nanosecond laser system for the ignition of aeronautic combustion engines
Authors: Amiard-Hudebine G. , Tison G. , Freysz E.
Published: December 2016

We have studied and developed a compact nanosecond laser system dedicated to the ignition of aeronautic combustion engines. This system is based on a nanosecond microchip laser delivering 6 μJ nanosecond pulses, which are amplified in two successive stages. The first stage is based on an Ytterbium doped fiber amplifier (YDFA) working in a quasi-continuous-wave (QCW) regime. Pumped at 1 kHz repetition rate, it delivers TEM00 and linearly polarized nanosecond pulses centered at 1064 nm with energies up to 350 μJ. These results are in very good agreement with the model we specially designed for a pulsed QCW pump regime. The second amplification stage is based on a compact Nd:YAG double-pass amplifier pumped by a 400 W peak power QCW diode centered at λ = 808 nm and coupled to a 800 μm core multimode fiber. At 10 Hz repetition rate, this system amplifies the pulse delivered by the YDFA up to 11 mJ while preserving its beam profile, polarization ratio, and pulse duration. Finally, we demonstrate that this compact nanosecond system can ignite an experimental combustion chamber.
Novel electric thermophoretic sampling device with highly repeatable characteristics
Authors: Altenhoff Michael , Teige Christian , Storch Michael , Will Stefan
Published: December 2016

A novel thermophoretic sampling device for probing nanoparticle aggregates in all types of flames as well as in particle-laden gases and aerosols is presented. For the motion of the sampling probe, a tubular electric linear motor is utilized, and its design and operation are described in detail. The spatial and temporal performance is determined from oscilloscope measurements and high-speed recordings of one motion profile featuring three different resident times. Motion sequences offering a minimum residence time of 3 ms and a maximum velocity of 4.1 m s−1 simultaneously providing smooth probe movement and minimal vibrations are feasible. For a stroke length of 100 mm, maximum deviations between sampling and setpoint positions of 0.14 mm in axial, 0.02 mm in horizontal, and 0.36 mm in vertical direction are determined, respectively. The evaluation of standard deviations among individual motion sequences for every time step shows high precision in all directions of movement. The influence of probe invasion on a laminar premixed flame produced using a McKenna burner is characterized employing high-speed recordings. Soot radiance intensities are temporally evaluated in four regions of interest near the sampling probe where maximum changes in the order of 20% are observed. Thermophoretic sampling was performed on the flame at 17 mm height above burner using ethene and ethyne as fuels with an equal equivalence ratio of 2.7. Morphological soot aggregate properties are derived from comprehensive transmission electron microscopy analysis and show satisfying results.
Hydrogen-induced atomic structure evolution of the oxygen-chemisorbed Cu(110) surface
Authors: Shan Weitao , Liu Qianqian , Li Jonathan , Cai Na , Saidi Wissam A. , Zhou Guangwen
Published: December 2016

Using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) modeling, we determine the mechanism of the atomic structural evolution of the oxygenated Cu(110) surface induced by the reaction of adsorbed hydrogen with chemisorbed oxygen in the Cu(110)-c(6 × 2)-O structure. Our STM observations show that the reconstructed Cu(110)-c(6 × 2)-O surface undergoes a phase transition to the (2 × 1)-O reconstruction in the course of oxygen loss induced by the reaction with H2 gas. Using DFT modeling, we find that the surface phase transition is initiated via the adsorption of molecular hydrogen on the chemisorbed oxygen, which results in the formation of H2O molecules that desorb spontaneously from the surface. The loss of chemisorbed oxygen induces the c(6 × 2) → (2 × 1) transition that involves the diffusion of Cu―O―Cu chains along the ⟨1¯10⟩ direction.
Maximum available flux of charged particles from the laser ablation plasma
Authors: Sakai Yasuo , Itagaki Tomonobu , Horioka Kazuhiko
Published: December 2016

The laser ablation plasma was characterized for high-flux sources of ion and electron beams. An ablation plasma was biased to a positive or a negative high voltage, and the fluxes of charged particles through a pair of extraction electrodes were measured as a function of the laser intensity IL. Maximum available fluxes and the ratios of electron and ion beam currents Je/Ji were evaluated as a function of the laser irradiance. The ion and the electron fluxes increased with a laser intensity and the current ratio was around 40 at IL = 1.3 × 108 W/cm2 which monotonically decreased with an increase of the laser intensity. The current ratios Je/Ji were correlated to the parameters of ablation plasma measured by the electrostatic probes. The results showed that the ion fluxes are basically enhanced by super-sonically drifting ions in the plasma and the electron fluxes are also enhanced by the drift motion together with a reduction of the sheath potential due to the enhanced ion flux to the surrounding wall.
Study on the creation and destruction of transport barriers via the effective safety factors for energetic particles
Authors: Ogawa Shun , Leoncini Xavier , Dif-Pradalier Guilhem , Garbet Xavier
Published: December 2016

Charged particles with low kinetic energy move along the magnetic field lines, but so do not the energetic particles. We investigate the topological structure changes in the phase space of energetic particles with respect to the magnetic one. For this study, cylindrical magnetic fields with non-monotonic safety factors that induce the magnetic internal transport barrier are considered. We show that the topological structure of the magnetic field line and of the particle trajectories can be quite different. We explain this difference using the concept of an effective particle q-profile. Using this notion, we can investigate the location and existence of resonances for particle orbits that are different from the magnetic ones. These are examined both numerically by integrating an equation of motion and theoretically by the use of Alfvén's guiding center theory and by the use of an effective reduced Hamiltonian for the integrable unperturbed system. It is clarified that, for the energetic particles, the grad B drift effect shifts the resonances and the drift induced by curvature of the magnetic field line leads to the vanishing of the resonances. As a result, we give two different mechanisms that lead to the creation of transport barriers for energetic particles in the region where the magnetic field line is chaotic.
Processes setting the structure of the electron distribution function within the exhausts of anti-parallel reconnection
Authors: Egedal J. , Wetherton B. , Daughton W. , Le A.
Published: December 2016

In situ spacecraft observations within the exhausts of magnetic reconnection document a large variation in the velocity space structure of the electron distribution function. Multiple mechanisms help govern the underlying electron dynamics, yielding a range of signatures for collisionless reconnection. These signatures include passing beams of electrons separated by well-defined boundaries from betatron heated/cooled trapped electrons. The present study emphasizes how localized regions of non-adiabatic electron dynamics can mix electrons across the trapped/passing boundaries and impact the form of the electron distributions in the full width of the exhaust. While our study is based on 2D simulations, the described principles shaping the velocity space distributions also apply to 3D geometries making our findings relevant to spacecraft observation of reconnection in the Earth's magnetosphere.
The effect of a negatively chirped laser pulse on the evolution of bubble structure in nonlinear bubble regime
Authors: Vosoughian H. , Riazi Z. , Afarideh H. , Sarri G.
Published: December 2016

In the nonlinear bubble regime, due to localized depletion at the front of the pulse during its propagation through the plasma, the phase shift between carrier waves and pulse envelope plays an important role in plasma response. The Carrier-Envelope Phase (CEP) breaks down the symmetric transverse ponderomotive force of the laser pulse that makes the bubble structure unstable. Our studies using a series of two-dimensional particle-in-cell simulations show that the utilization of a negatively chirped laser pulse is more effective in controlling the pulse depletion rate, and consequently, the effect of the CEP in the bubble regime. The results indicate that the pulse depletion rate diminishes during the propagation of the pulse in plasma that leads to postponing the effect of Carrier-Envelope Phase (CEP) in plasma response, and therefore, maintaining the stability of the bubble shape for a longer time than the un-chirped laser pulse. As a result, a localized electron bunch with higher maximum energy is produced during the acceleration process.
Dielectric coats effect on the third harmonic generation by a metallic nanoparticle lattice exposed to intense laser radiation
Authors: Sepehri Javan N. , Amjadi N. , Mohammadzadeh H.
Published: December 2016

In this work, we theoretically study the effect of coating of metallic nanoparticles on the third harmonic generation in a periodic three-dimensional lattice. Taking into account the effects of dielectric shell of nanoparticles and microscopic electromagnetic fields on the nonlinear dynamics of electrons, equations describing the laser–nanoparticle interaction are derived in the non-relativistic approximation. We pay special attention on the effects of the thickness and the kind of shell of nanoparticles upon the third harmonic efficiency. It is found that in some frequency areas, existence of shell can amplify the microscopic fields in the place of conduction electrons, which can lead to the improvement of harmonic generation. This amplification could be essential if the frequency region related to the shell effect improvement coincides with that of the plasmon resonance.
Suppression of vortex-induced vibration of a circular cylinder using thermal effects
Authors: Wan Hui , Patnaik Soumya S.
Published: December 2016

Transverse vortex-induced vibration (VIV) of a cylinder with various body-to-fluid density ratio and stiffness is studied. The cylinder is elastically mounted and heated, and the flow direction is aligned with the direction of the thermal induced buoyancy force. Amplitude of VIV can be reduced as the thermal control parameter Richardson number (Ri) increases, or even be fully suppressed when Ri is above a critical value. This critical Richardson number depends on both body-to-fluid density and structural stiffness. A higher critical Richardson is required to fully suppress the VIV of a structure with smaller density ratio. With the same density or mass, a structure with intermediate stiffness vibrating in lock-in regime needs higher critical Ri to suppress VIV than either rigid or flexible structures. Drag experienced by the body is also studied. It is found that for a flexible body, drag gradually increases with the Richardson number. For a body with intermediate stiffness, both drag and amplitude of VIV can be reduced until the Richardson number reaches the critical value, after which drag builds up if the Richardson number is further increased. A drag reduction of 30%–40% can be obtained at the critical Richardson number.
On the effectiveness of the thermoelectric energy filtering mechanism in low-dimensional superlattices and nano-composites
Authors: Thesberg Mischa , Kosina Hans , Neophytou Neophytos
Published: December 2016

Electron energy filtering has been suggested as a promising way to improve the power factor and enhance the ZT figure of merit of thermoelectric materials. In this work, we explore the effect that reduced dimensionality has on the success of the energy-filtering mechanism for power factor enhancement. We use the quantum mechanical non-equilibrium Green's function method for electron transport including electron-phonon scattering to explore 1D and 2D superlattice/nanocomposite systems. We find that, given identical material parameters, 1D channels utilize energy filtering more effectively than 2D as they: (i) allow one to achieve the maximal power factor for smaller well sizes/smaller grains which are needed to maximize the phonon scattering, (ii) take better advantage of a lower thermal conductivity in the barrier/boundary materials compared to the well/grain materials in both: enhancing the Seebeck coefficient; and in producing a system which is robust against detrimental random deviations from the optimal barrier design. In certain cases, we find that the relative advantage can be as high as a factor of 3. We determine that energy-filtering is most effective when the average energy of carrier flow varies the most between the wells and the barriers along the channel, an event which occurs when the energy of the carrier flow in the host material is low, and when the energy relaxation mean-free-path of carriers is short. Although the ultimate reason for these aspects, which cause a 1D system to see greater relative improvement than a 2D, is the 1D system's van Hove singularity in the density-of-states, the insights obtained are general and inform energy-filtering design beyond dimensional considerations.
Nuclei-selected atomic-orbital response-theory formulation for the calculation of NMR shielding tensors using density-fitting
Authors: Kumar Chandan , Kjærgaard Thomas , Helgaker Trygve , Fliegl Heike
Published: December 2016

An atomic orbital density matrix based response formulation of the nuclei-selected approach of Beer, Kussmann, and Ochsenfeld [J. Chem. Phys. 134, 074102 (2011)] to calculate nuclear magnetic resonance (NMR) shielding tensors has been developed and implemented into LSDalton allowing for a simultaneous solution of the response equations, which significantly improves the performance. The response formulation to calculate nuclei-selected NMR shielding tensors can be used together with the density-fitting approximation that allows efficient calculation of Coulomb integrals. It is shown that using density-fitting does not lead to a significant loss in accuracy for both the nuclei-selected and the conventional ways to calculate NMR shielding constants and should thus be used for applications with LSDalton.
Topos quantum theory reduced by context-selection functors
Authors: Nakayama Kunji
Published: December 2016

In this paper we deal with quantum theories on presheaves and sheaves on context categories consisting of commutative von Neumann algebras of bounded operators on a Hilbert space. Our aim is first to reduce presheaf-based topos quantum theory via sheafification and then to import quantum probabilities to the reduced sheaf quantum theory. The first is done by means of a functor that selects some expedient contexts. Note that since the functor defines a Grothendieck topology on the category consisting of all contexts, it induces a sheaf topos on which we construct a downsized quantum theory. We also show that the sheaf quantum theory can be replaced by a more manageable presheaf quantum theory. Quantum probabilities are imported by means of a Grothendieck topology that is defined on a category consisting of probabilities and that enables to regard them as intuitionistic truth-values. From these topologies, we construct another Grothendieck topology that is defined on the product of the context category and the probability category. It reflects the selection of contexts and the identification of probabilities with truth-values. We construct a quantum theory equipped with quantum probabilities as truth-values on the sheaf topos induced by the Grothendieck topology.
“Embedded Emitters”: Direct bandgap Ge nanodots within SiO2
Authors: Kuo M. H. , Chou S. K. , Pan Y. W. , Lin S. D. , George T. , Li P. W.
Published: December 2016

Microdisk-arrays of vertically stacked 30–70 nm Ge nanodots embedded within SiO2 were fabricated using thermal oxidation of Si0.75Ge0.25 abacus-shaped pillars and followed by post-annealing in oxygen-deficient conditions. The Ge nanodots are subjected to increasing quantum-confinement and tensile-strain by reducing dot size. We show that considerable quantum-confinement and tensile-strain can be generated within 30 nm Ge nanodots embedded in SiO2, as evidenced by large Raman red shifts for the Ge-Ge phonon lines in comparison to that for bulk Ge. These large quantum-confinement and tensile-strain facilitate direct-bandgap photoluminescence experimentally observed for the Ge nanodots, and are consistent with the strain-split photoluminescence transitions to the light-hole (LH) and heavy-hole (HH) valence bands at 0.83 eV and 0.88 eV, respectively. Time-resolved photoluminescence measurements conducted from 10–100 K show temperature-insensitive carrier lifetimes of 2.7 ns and 5 ns for the HH and LH valence-band transitions, respectively, providing additional strong evidence of direct bandgap photoluminescence for tensile-strained Ge nanodots.
Visible-blind ultraviolet photodetector based on p-Cu2CdSnS4/n-ZnS heterojunction with a type-I band alignment
Authors: Meng Lei , Li Yongfeng , Yao Bin , Ding Zhanhui , Yang Gang , Liu Ruijian , Deng Rui , Liu Lei
Published: December 2016

A visible-blind ultraviolet photodetector based on a p-Cu2CdSnS4/n-ZnS (CCTS/ZnS) heterojunction was fabricated by the radio frequency magnetron sputtering technique. Mo and In metals were used as p-type and n-type contact electrodes, respectively. Current−voltage measurement of the CCTS/ZnS heterojunction photodetector showed a good rectifying behavior. The photodetector showed a peak photocurrent at 330 nm and a sharp photocurrent edge at about 380 nm, suggesting a typical visible-blind characteristic. X-ray photoelectron spectroscopy measurements and first-principles calculations indicate that the CCTS/ZnS heterojunction has a type-I band alignment. The conduction-band offset leads to the barrier that inhibits the drifting of photo-generated electrons from p-CCTS to n-ZnS layer, well interpreting the spectral response characteristics of the device.
On the flow structures and hysteresis of laminar swirling jets
Authors: Ogus G. , Baelmans M. , Vanierschot M.
Published: December 2016

In this paper different flow patterns of an annular jet with a stepped-conical nozzle as well as the transition between these patterns are numerically investigated as a function of the swirl number S which is the ratio of tangential momentum flux to axial momentum flux. The Reynolds number of the jet based on the axial velocity and the nozzle hydraulic diameter is 180. The 3D Navier Stokes equations are solved using the direct numerical simulation. Four different flow patterns are identified and their associated flow structures are discussed. Starting from an annular jet at zero swirl, spinning vortices around the central axis originate with increasing swirl. As the swirl is further increased, the onset of vortex breakdown occurs, followed by jet attachment to the nozzle. Decreasing the swirl number back from this flow pattern, the Coanda effect near the nozzle outlet creates a wall jet. This wall jet remains till the decreasing swirl number equals to zero, showing hysteresis in flow patterns between an increase and a subsequent decrease in swirl. The determined flow states are experimentally validated. Potential applications related to these flow patterns and their hysteretic behavior are also briefly discussed.
A stress-controlled shear cell for small-angle light scattering and microscopy
Authors: Aime S. , Ramos L. , Fromental J. M. , Prévot G. , Jelinek R. , Cipelletti L.
Published: December 2016

We develop and test a stress-controlled, parallel plates shear cell that can be coupled to an optical microscope or a small angle light scattering setup, for simultaneous investigation of the rheological response and the microscopic structure of soft materials under an imposed shear stress. In order to minimize friction, the cell is based on an air bearing linear stage, the stress is applied through a contactless magnetic actuator, and the strain is measured through optical sensors. We discuss the contributions of inertia and of the small residual friction to the measured signal and demonstrate the performance of our device in both oscillating and step stress experiments on a variety of viscoelastic materials.
Carrier emission of n-type gallium nitride illuminated by femtosecond laser pulses
Authors: Li Runze , Zhu Pengfei , Chen Jie , Cao Jianming , Rentzepis Peter M. , Zhang Jie
Published: December 2016

The carrier emission efficiency of light emitting diodes is of fundamental importance for many technological applications, including the performance of GaN and other semiconductor photocathodes. We have measured the evolution of the emitted carriers and the associated transient electric field after femtosecond laser excitation of n-type GaN single crystals. These processes were studied using sub-picosecond, ultrashort, electron pulses and explained by means of a “three-layer” analytical model. We find that for pump laser intensities on the order of 1011 W/cm2, the electrons that escaped from the crystal surface have a charge of ∼2.7 pC and a velocity of ∼1.8 μm/ps. The associated transient electrical field evolves at intervals ranging from picoseconds to nanoseconds. These results provide a dynamic perspective on the photoemission properties of semiconductor photocathodes.
Fractional Schrödinger equation with Riesz-Feller derivative for delta potentials
Authors: Jarosz Stefânia , Vaz Jayme
Published: December 2016

The fractional Schrödinger equation with the Riesz-Feller derivative is discussed and solved when the potential involves delta functions. Some results in the literature are generalized.
Mirror-field confined compact plasma source using permanent magnet for plasma processings
Authors: Goto Tetsuya , Sato Kei-ichiro , Yabuta Yuki , Sugawa Shigetoshi
Published: December 2016

A mirror-field confined compact electron cyclotron resonance (ECR) plasma source using permanent magnets was developed, aiming for the realization of high-quality plasma processings where high-density reactive species are supplied to a substrate with minimizing the ion bombardment damages. The ECR position was located between a microwave transmissive window and a quartz limiter, and plasmas were transported from the ECR position to a midplane of the magnetic mirror field through the quartz limiter. Thus, a radius of core plasma could be determined by the limiter, which was 15 mm in this study. Plasma parameters were investigated by the Langmuir probe measurement. High-density plasma larger than 1011 cm−3 could be produced by applying 5.85-GHz microwave power of 10 W or more. For the outside region of the core plasma where a wafer for plasma processings will be set at, the ion current density was decreased dramatically with distance from the core plasma and became smaller by approximately two orders of magnitude that in the core plasma region for the radial position of 40 mm, suggesting the realization of reduction in ion bombardment damages.
Half-metallicity obtained in silicene nanosheet by nitrogenation engineering
Authors: Qian Yan , Wu Haiping , Kan Erjun , Lu Ruifeng , Deng Kaiming
Published: December 2016

Based on the facts that most components and devices are based on silicon and modern industry is transferring to atomic scale era, engineering half-metallicity in low-dimensional silicon-based materials has vast importance in spintronic field, since such half-metals can perfectly match with the previous silicon-based components. Hence, we investigated the possibility of achieving half-metallic silicene nanosheet by using first-principles calculations, and expectedly observed that silicene could be transferred to half-metal when it is fully nitrogenated on one Si sublattice. Notably, it possesses a half-metallic gap of ∼0.25 eV, and the estimated Curie temperature is of ∼374 K. This is very significant for the stability of half-metallicity and practical applications at high temperature. The other two types of nitrogenated silicene were also studied, and the results show that both compounds behave as of metallic nature. This work indicates that nitrogenation, which can be experimentally realized by generating silicene on the surface of some nitrides, maybe is an open way to search for silicon-based low-dimensional half-metals.
Measurements of the sound velocity of shock-compressed liquid silica to 1100 GPa
Authors: McCoy C. A. , Gregor M. C. , Polsin D. N. , Fratanduono D. E. , Celliers P. M. , Boehly T. R. , Meyerhofer D. D.
Published: December 2016

The sound velocity in a shocked material provides information about its off-Hugoniot behavior of a material at high pressures. This information can be used to extend the knowledge gained in Hugoniot experiments and to model the re-shock and release behavior. Silica is one of the most important materials for equation of state studies because of its prevalence in the earth's interior and the well-defined properties of α-quartz. This article presents the sound velocity measurements of amorphous fused silica over the range 200 to 1100 GPa using laser-driven shocks and an α-quartz standard. These measurements demonstrate the technique proposed by Fratanduono et al. [J. Appl. Phys. 116, 033517 (2014)] to determine the sound velocity from the arrival of acoustic perturbations. The results compare favorably to the SESAME 7386 equation-of-state table. The Grüneisen parameter was calculated from the sound velocity data and found to be Γ=0.66±0.05 at densities above 6 g/cm3, an increase in precision by a factor of two over previous measurements.
Focal overlap gating in velocity map imaging to achieve high signal-to-noise ratio in photo-ion pump-probe experiments
Authors: Shivaram Niranjan , Champenois Elio G. , Cryan James P. , Wright Travis , Wingard Taylor , Belkacem Ali
Published: December 2016

We demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments. This significantly enhances signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams. This enhancement is achieved by tilting the laser beams with respect to the surface of the VMI electrodes which creates a gradient in flight time for particles born at different points along the beam. By suitably pulsing our microchannel plate detector, we can select particles born only where the laser beams overlap. This spatial gating in velocity map imaging can benefit nearly all photo-ion pump-probe VMI experiments especially when extreme-ultraviolet light or X-rays are involved which produce large background signals on their own.
Toward the III–V/Si co-integration by controlling the biatomic steps on hydrogenated Si(001)
Authors: Martin M. , Caliste D. , Cipro R. , Alcotte R. , Moeyaert J. , David S. , Bassani F. , Cerba T. , Bogumilowicz Y. , Sanchez E. , Ye Z. , Bao X. Y. , Pin J. B. , Baron T. , Pochet P.
Published: December 2016

The integration of III-V on silicon is still a hot topic as it will open up a way to co-integrate Si CMOS logic with photonic devices. To reach this aim, several hurdles should be solved, and more particularly the generation of antiphase boundaries (APBs) at the III-V/Si(001) interface. Density functional theory (DFT) has been used to demonstrate the existence of a double-layer steps on nominal Si(001) which is formed during annealing under proper hydrogen chemical potential. This phenomenon could be explained by the formation of dimer vacancy lines which could be responsible for the preferential and selective etching of one type of step leading to the double step surface creation. To check this hypothesis, different experiments have been carried in an industrial 300 mm metalorganic chemical vapor deposition where the total pressure during the annealing step of Si(001) surface has been varied. Under optimized conditions, an APBs-free GaAs layer was grown on a nominal Si(001) surface paving the way for III–V integration on silicon industrial platform.
The effect of illumination power density on carbon defect configuration in silicon doped GaN
Authors: Kaess Felix , Reddy Pramod , Alden Dorian , Klump Andrew , Hernandez-Balderrama Luis H. , Franke Alexander , Kirste Ronny , Hoffmann Axel , Collazo Ramón , Sitar Zlatko
Published: December 2016

A study of efficacy of point defect reduction via Fermi level control during growth of GaN:Si as a function of above bandgap illumination power density and hence excess minority carrier density is presented. Electrical characterization revealed an almost two-fold increase in carrier concentration and a three-fold increase in mobility by increasing the illumination power density from 0 to 1 W cm−2, corroborating a decrease in compensation and ionic impurity scattering. The effect was further supported by the photoluminescence studies, which showed a monotonic decrease in yellow luminescence (attributed to CN) as a function of illumination power density. Secondary ion mass spectroscopy studies showed no effect of illumination on the total incorporation of Si or C. Thus, it is concluded that Fermi level management changed the configuration of the C impurity as the CN−1 configuration became energetically less favorable due to excess minority carriers.
Optical study of local strain related disordering in CVD-grown MoSe2 monolayers
Authors: Krustok J. , Raadik T. , Jaaniso R. , Kiisk V. , Sildos I. , Marandi M. , Komsa H.-P. , Li B. , Zhang X. , Gong Y. , Ajayan P. M.
Published: December 2016

We present temperature dependent micro-photoluminescence and room temperature photoreflectance spectroscopy studies on aged MoSe2 monolayers with high surface roughness. A0 and B0 exciton bands were detected at 1.512 eV and 1.72 eV, respectively, which are 50–70 meV lower than those commonly reported for high-quality samples. It is shown that the difference can be accounted for using a model of localized excitons for disordered MoSe2 monolayers where the optical band gap energy fluctuations could be caused by random distribution of local tensile strain due to surface roughness. The density of localized exciton states is found to follow the Lorentzian shape, where the peak of this distribution is about 70 meV from the energy of delocalized states.
Self-biased microwave ferromagnetic performance of patterned Ni80Fe20 thin films
Authors: Yang Ru , Liu Xiaomin , Du Honglei , Sun Nian X. , Lin Hwaider , Li Shandong
Published: December 2016

Patterned Ni80Fe20 permalloy films with strip length of 5 mm, strip distance of 40μm and various ferromagnetic (FM) strip widths from 20 to 40μm were prepared by pulse laser deposition and photolithography for study the microwave performance of permalloy films. Comparing with the continuous magnetically isotropic permalloy film, the anisotropy fields HK increase with the decrease of the FM strips’ width. As a result, the ferromagnetic resonance frequency fr is enhanced from 1.71 GHz of continuous film to 2.1 GHz of patterned film with FM strip width of 20μm. The comparison between fr and HK demonstrates that the enhancement of fr can be attributed to the increase of HK due to the shape anisotropy of permalloy strips.
Identification of the low-energy excitations in a quantum critical system
Authors: Heitmann Tom , Lamsal Jagat , Watson Shannon , Erwin Ross , Chen Wangchun , Zhao Yang , Montfrooij Wouter
Published: December 2016

We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.24)2Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R) (2006)].