bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐profile omnidirectional dual‐polarised antenna for 2.4 GHz WLAN applications
Authors: Liu Ying , Xue Jin , Wang Hui , Gong Shuxi
Published: June 2014

A low‐profile omnidirectional dual‐polarised antenna for 2.4 GHz wireless local area network (WLAN) applications is proposed. The vertically/horizontally dual‐polarised radiation patterns are achieved by combining a modified monopole antenna with a printed arc dipole array. The overall volume of the presented antenna is less than 0.63λ0 × 0.63λ0 × 0.057λ0 (λ0 is the free‐space wavelength at central frequency). To verify the design, a prototype antenna is fabricated and tested. The measured results show that the −10 dB impedance bandwidths for vertical polarisation (VP) and horizontal polarisation (HP) have both covered the required band of 2.4–2.48 GHz and the isolation, in the operating band, is more than 24 dB. The measured cross‐polarisation levels within the working plane for VP and HP are lower than −18 dB. Stable antenna gains are greater than 0.46 and 0.44 dBi for VP and HP over the operating frequency band, respectively.
Fractional normalised filtered‐error least mean squares algorithm for application in active noise control systems
Authors: Shah S.M. , Samar R. , Raja M.A.Z. , Chambers J.A.
Published: June 2014

A novel fractional normalised filtered‐error least mean squares (FN‐FeLMS) algorithm is designed for secondary path modelling in active noise control systems. The update is formed as a combination of the conventional LMS and a fractional update derived from the Riemann–Liouville differintegral operator. The algorithm is considered for (machine) noise reduction for a primary path with zero‐mean binary or Gaussian sources as inputs. An anti‐noise signal is generated to alleviate the effect of noise and to minimise the filtered error by improved secondary path modelling. The proposed arrangement is evaluated for a number of different scenarios by varying the step size and fractional orders. Simulation results show that the proposed technique is more robust to step size variation; it outperforms the traditional FeLMS approach in terms of convergence, model accuracy and steady‐state performance for a given signal‐to‐noise ratio.
Effects of periodic trench structure on cathodo‐luminescence in InGaN/GaN multi‐quantum wells
Authors: Kim G. , Kim S.W. , Kim J.H. , Park E. , Park B.‐G.
Published: June 2014

To reduce strain and the quantum‐confined Stark effect (QCSE), periodic trenches in an InGaN/GaN multi‐quantum well (MQW) are patterned by electron‐beam (e‐beam) lithography and the inductively‐coupled plasma (ICP) dry etching process. The effects of the fabricated structure are investigated by measuring cathodo‐luminescence (CL) spectra and comparing it with the data of an as‐grown sample without trench patterns. The peak wavelength of the prepared samples is clearly blue‐shifted, and it is confirmed that the strain and the QCSE are reduced by the effects of the trench structures. It is also confirm that the peak intensity of CL spectra shows a maximum when 90% of the active region is remaining, because the trench patterns reduce the light emitting area as well as the strain and the QCSE.
Proximity estimation for location‐based services with round‐trip time
Authors: Zobenko A. , Scherrer T. , Kim Soo‐Yong
Published: June 2014

A proximity estimation algorithm is proposed to measure distances between a transceiver and a receiver for location‐based services in indoor environments. To improve the measurement accuracy, proximity is estimated using the propagation delay caused by the round‐trip travel of the signal. Moreover, to reduce power consumption, frequency downconversion with a mixer is adopted to use frequencies below the gigahertz range. Being a low‐power design, the proposed architecture is suitable for mobile devices such as wearable and internet‐of‐things products. In addition, the implementation of this algorithm on Wi‐Fi‐equipped devices does not need development of special schematics, since it is based on the IEEE 802.11 standard, it could be made with usual Wi‐Fi quadrature amplitude modulation (QAM)‐modulators. The accuracy enhancement of the proposed estimation was verified in comparison with the conventional algorithms by means of simulation.
Reduced memory decoding schemes for turbo decoding based on storing the index of the state metric
Authors: Zhan Ming , Wu Jun , Wen Hong
Published: June 2014

In the implementation of turbo‐like decoder, the size of state metrics cache (SMC) has a predominant impact on the core area and the overall power dissipation. Different from previous reported decoding schemes, in the proposed decoding schemes, a compressing module and a regeneration module are added to the decoder. The compressing module sorts the forward state metrics from the minimum to the maximum, by which an index sequence and the corresponding increase metrics are calculated, and subsequently are stored in the SMC. In the regeneration module, the forward state metrics are estimated with the index sequence and the increase metrics that accessed from the SMC. With the cost of dummy calculation that is performed by the compressing and the regeneration modules, two decoding schemes are proposed. For an eight‐state turbo codes, the linear and the nonlinear estimation based decoding schemes reduce the SMC size by 62.5% and 57.5%, respectively. The bit error rate (BER) simulation is performed for both binary turbo code and duo binary convolutional turbo code, and shows BER of the linear estimation‐based scheme is superior to that of the enhanced max‐log‐MAP (the maximum a posteriori probability) algorithm, whereas BER of the non‐linear estimation‐based decoding scheme is very close to that of the near optimal decoding scheme.
Design and comparison of interior permanent magnet synchronous motors with non‐uniform airgap and conventional rotor for electric vehicle applications
Authors: Carraro Enrico , Bianchi Nicola
Published: June 2014

In recent years, electric mobility is becoming a growing reality because of the increase of the oil demand and cost as well as the environmental effect of the conventional internal combustion engines. Since about a decade, in the USA, a public–private cooperative research initiative, called FreedomCAR (US Drive by mid 2012) has been working for developing high efficiency and cost competitive technologies for the electrification of private transport. This research presents the design and the comparison of two high performance, radial magnetisation, interior permanent magnets and synchronous motors, according to the FreedomCAR targets, equipped with different rotor shape geometries. The first is characterised by a non‐uniform airgap, whereas the second presents a conventional rotor shape. Both the machines are equipped with the same stator and a fractional slot concentrated winding. This paper highlights the benefits for using a non‐uniform airgap rotor design, especially concerning the efficiency, that represents the most difficult target to be satisfied.
Rethinking the Boundaries: Towards a Butlerian Ethics of Vulnerability in Sex Trafficking Debates
Authors: Szörényi Anna
Published: June 2014

Feminist debates on sex trafficking have become entrenched and polarised, with abolitionists producing images of helpless abused victims, while sex worker advocates work hard to achieve some recognition of the agency of migrant sex workers. This article explores constructions of embodiment, subjectivity and agency in the debate, showing how abolitionist views, in spite of their efforts to challenge liberal pro-sex perspectives, rely on a familiar vision of the body as a singular, bounded and sovereign entity whose borders must be secured against invasion. The result is a vision in which victimisation is taken to epistemically compromise the subjectivities of sex workers, forcing them and their advocates to argue for recognition of their agency according to familiar liberal models of consent in order to be able to enter the debate. Drawing on the recent work of Judith Butler on consent and vulnerability, this article argues that what is needed is a rethinking of bodily ontology so that the vulnerability of sex workers is not opposed to their agency, but rather seen as an inevitable aspect of embodied sociality, constituting a call to ethical engagement and a recognition of the inequitable global distributions of precarity that produce sex trafficking as part of contemporary geopolitics. From this perspective, the alignment between radical feminist efforts to secure women's bodily borders and global efforts to secure national borders no longer appears as coincidence.
My Body is My Manifesto! SlutWalk, FEMEN and Femmenist Protest
Authors: O'Keefe Theresa
Published: June 2014

This paper uses an intersectional analysis to look at contemporary forms of women's popular protest in the hopes of raising questions about the explicit use of the gendered body in struggles for women's emancipation. Specifically, it explores the protests of SlutWalk and FEMEN to suggest that such body protests exemplify a problematic interface between third-wave and postfeminism. This interface or junction is most noticeable and problematic in relation to uncontested auto-sexualisation or ‘femmenism’. I argue that any subversive potential these recent mobilisations might offer is limited through their reproduction of patriarchal, hegemonic norms. This piece is theoretical in the main, though it does include some preliminary qualitative research by way of drawing on websites, news reports, Twitter feeds, Facebook pages, and other online content produced by or about SlutWalk and FEMEN. The hope is to raise questions about the value of this increasingly pervasive use of sexualised, gender protest for feminist organising, not merely as an academic exercise but for its utility in practice.
Theoretical spectroscopic investigations of HNSq and HSNq (q = 0, +1, −1) in the gas phase
Authors: Ben Yaghlane S. , Jaidane N.-E. , Cotton C. E. , Francisco J. S. , Al Mogren M. M. , Linguerri R. , Hochlaf M.
Published: June 2014

We performed accurate ab initio investigations of the geometric parameters and the vibrational structure of neutral HNS/HSN triatomics and their singly charged anions and cations. We used standard and explicitly correlated coupled cluster approaches in connection with large basis sets. At the highest levels of description, we show that results nicely approach those obtained at the complete basis set limit. Moreover, we generated the three-dimensional potential energy surfaces (3D PESs) for these molecular entities at the coupled cluster level with singles and doubles and a perturbative treatment of triple excitations, along with a basis set of augmented quintuple-zeta quality (aug-cc-pV5Z). A full set of spectroscopic constants are deduced from these potentials by applying perturbation theory. In addition, these 3D PESs are incorporated into variational treatment of the nuclear motions. The pattern of the lowest vibrational levels and corresponding wavefunctions, up to around 4000 cm−1 above the corresponding potential energy minimum, is presented for the first time.
Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths
Authors: Isegawa Miho , Liu Fengyi , Maeda Satoshi , Morokuma Keiji
Published: June 2014

Photodissociation pathways of nitromethane following π → π* electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH3 and NO2 (2B2) is formed by direct dissociation from the S1 state. Important pathways involving S1 and S0 states for production of various dissociation products CH3NO + O (1D), CH3O(X2E) + NO (X2Π), CH2NO + OH, and CH2O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH3NO2, the OH radical roaming in OH dissociation from CH2N(O)(OH), and the NO roaming in NO dissociation from CH3ONO.
Self-compensated standing wave probe for characterization of radio-frequency plasmas
Authors: Sung Ta-Lun , Matsumura Shosaku , Teii Kungen , Teii Shinriki
Published: June 2014

A simple self-compensated Langmuir probe using the character of a standing wave is developed for characterization of radio-frequency (RF) discharge plasmas. This probe is based on a concept that the interference of RF field is eliminated at the node of a standing wave which exists ideally at one-fourth of the RF wavelength (λ/4) away from the probe tip in the plasma. The fluctuation of plasma space potential is suppressed as confirmed by comparison with a non-compensated probe and a self-compensated probe using an inductor-capacitor (LC) resonant circuit. The plasma parameters obtained with the standing wave probe are in agreement with those with the LC resonant probe within discrepancy of 15% indicating high reliability of the results.
Relativistic Fermi-Ulam map: Application to WEGA stellarator lower hybrid power operation
Authors: Fuchs V. , Laqua H. P. , Seidl J. , Krlín L. , Pánek R. , Preinhaelter J. , Urban J.
Published: June 2014

Analytical and numerical support is here provided in support of the explanation [Laqua et al., Plasma Phys. Controlled Fusion 56, 075022 (2014)] for the observation of ∼MeV electrons during Lower Hybrid (LH) operation in EC pre-heated plasma at the WEGA stellarator [Otte et al., Nukleonika, 57, 171 (2012)]. In the quoted experiments, LH power from the WEGA TE11 circular waveguide, 9 cm diameter, un-phased, 2.45 GHz antenna, is radiated into a B ≅ 0.5 T, n¯e ≅ 5 × 1017 1/m3 plasma at Te ≅ 10 eV bulk temperature with an EC-generated 50 keV population of electrons. In response, the fast electrons travel around flux or drift surfaces essentially without collisions, repeatedly interacting with the rf field close to the antenna mouth, and gaining energy in the process. Our WEGA antenna calculations indicate a predominantly standing electric field pattern at the antenna mouth. From a simple approximation of the corresponding Hamiltonian equations of motion, we derive here a relativistic generalization of the simplified area-preserving Fermi-Ulam (F-U) map [M. A. Lieberman and A. J. Lichtenberg, Phys. Rev. A 5, 1852 (1972), Lichtenberg et al., Physica D 1, 291 (1980)], allowing phase-space global stochasticity analysis. At typical WEGA plasma and antenna conditions, and with correlated phases between electron–antenna electric field interaction events, the F-U map and supporting numerical simulations predict an absolute energy barrier in the range of 300 keV. In contrast, with random phases intervening between interaction events, the electron energy can reach ∼MeV values, compatible with the measurements on WEGA [Laqua et al., Plasma Phys. Controlled Fusion 56, 075022 (2014)].
A note on the Landauer principle in quantum statistical mechanics
Authors: Jakšić Vojkan , Pillet Claude-Alain
Published: June 2014

The Landauer principle asserts that the energy cost of erasure of one bit of information by the action of a thermal reservoir in equilibrium at temperature T is never less than kBT log 2. We discuss Landauer's principle for quantum statistical models describing a finite level quantum system \documentclass[12pt]{minimal}\begin{document}${\cal S}$\end{document}S coupled to an infinitely extended thermal reservoir \documentclass[12pt]{minimal}\begin{document}${\cal R}$\end{document}R. Using Araki's perturbation theory of KMS states and the Avron-Elgart adiabatic theorem we prove, under a natural ergodicity assumption on the joint system \documentclass[12pt]{minimal}\begin{document}${\cal S}+{\cal R}$\end{document}S+R, that Landauer's bound saturates for adiabatically switched interactions. The recent work [Reeb, D. and Wolf M. M., “(Im-)proving Landauer's principle,” preprint arXiv:1306.4352v2 (2013)] on the subject is discussed and compared.
KOALA: A program for the processing and decomposition of transient spectra
Authors: Grubb Michael P. , Orr-Ewing Andrew J. , Ashfold Michael N. R.
Published: June 2014

Extracting meaningful kinetic traces from time-resolved absorption spectra is a non-trivial task, particularly for solution phase spectra where solvent interactions can substantially broaden and shift the transition frequencies. Typically, each spectrum is composed of signal from a number of molecular species (e.g., excited states, intermediate complexes, product species) with overlapping spectral features. Additionally, the profiles of these spectral features may evolve in time (i.e., signal nonlinearity), further complicating the decomposition process. Here, we present a new program for decomposing mixed transient spectra into their individual component spectra and extracting the corresponding kinetic traces: KOALA (Kinetics Observed After Light Absorption). The software combines spectral target analysis with brute-force linear least squares fitting, which is computationally efficient because of the small nonlinear parameter space of most spectral features. Within, we demonstrate the application of KOALA to two sets of experimental transient absorption spectra with multiple mixed spectral components. Although designed for decomposing solution-phase transient absorption data, KOALA may in principle be applied to any time-evolving spectra with multiple components.
Correlation functions for fully or partially state-resolved reactive scattering calculations
Authors: Manthe Uwe , Welsch Ralph
Published: June 2014

Flux correlation functions and the quantum transition state concept are important tools for the accurate description of polyatomic reaction processes. Combined with the multi-configurational time-dependent Hartree approach, they facilitate rigorous full-dimensional calculations of cumulative and initial-state selected reaction probabilities for six atom reactions. In recent work [R. Welsch, F. Huarte-Larrañaga, and U. Manthe, J. Chem. Phys. 136, 064117 (2012)], an approach which allows one to calculate also state-to-state reaction probabilities within the quantum transition state concept has been introduced. This article presents further developments. Alternative generalized flux correlation functions are introduced and discussed. Equations for the calculation of fully state-resolved differential cross section using arbitrary definitions of the body fixed frame are derived. An approach for the efficient calculation of partially state-resolved observables as a function of the collision energy is introduced. Finally, numerical test studying the D + H2 reaction illustrate important aspects of the formalism.
On-the-fly ab initio semiclassical dynamics: Identifying degrees of freedom essential for emission spectra of oligothiophenes
Authors: Wehrle Marius , Šulc Miroslav , Vaníček Jiří
Published: June 2014

Vibrationally resolved spectra provide a stringent test of the accuracy of theoretical calculations. We combine the thawed Gaussian approximation (TGA) with an on-the-fly ab initio (OTF-AI) scheme to calculate the vibrationally resolved emission spectra of oligothiophenes with up to five rings. The efficiency of the OTF-AI-TGA permits treating all vibrational degrees of freedom on an equal footing even in pentathiophene with 105 vibrational degrees of freedom, thus obviating the need for the global harmonic approximation, popular for large systems. Besides reproducing almost perfectly the experimental emission spectra, in order to provide a deeper insight into the associated physical and chemical processes, we also develop a novel systematic approach to assess the importance and coupling between individual vibrational degrees of freedom during the dynamics. This allows us to explain how the vibrational line shapes of the oligothiophenes change with increasing number of rings. Furthermore, we observe the dynamical interplay between the quinoid and aromatic characters of individual rings in the oligothiophene chain during the dynamics and confirm that the quinoid character prevails in the center of the chain.
Control scheme of nonadiabatic transitions with the dynamical shift of potential curve crossing
Authors: Scheit Simona , Arasaki Yasuki , Takatsuka Kazuo
Published: June 2014

We investigate how the nuclear dynamics at an avoided crossing is affected and can be controlled by the introduction of a laser field whose cycle is comparable to the time-scale of the nuclear dynamics. By introducing the concepts of light-induced effective potential energy curves and dynamical avoided crossing, we describe the laser controlled nuclear dynamics and present basic control scenarios, giving a detailed explanation of the underlying dynamical mechanisms. The scenarios presented allow for examples to understand from a different perspective the results of dynamic Stark control experiments. The proposed interpretation is applied to the laser-controlled nonadiabatic dynamics between the two lowest 1Σ+ states of LiF, where the usefulness of the concepts developed is elucidated.
Measurements of gas hydrate formation probability distributions on a quasi-free water droplet
Authors: Maeda Nobuo
Published: June 2014

A High Pressure Automated Lag Time Apparatus (HP-ALTA) can measure gas hydrate formation probability distributions from water in a glass sample cell. In an HP-ALTA gas hydrate formation originates near the edges of the sample cell and gas hydrate films subsequently grow across the water–guest gas interface. It would ideally be desirable to be able to measure gas hydrate formation probability distributions of a single water droplet or mist that is freely levitating in a guest gas, but this is technically challenging. The next best option is to let a water droplet sit on top of a denser, immiscible, inert, and wall-wetting hydrophobic liquid to avoid contact of a water droplet with the solid walls. Here we report the development of a second generation HP-ALTA which can measure gas hydrate formation probability distributions of a water droplet which sits on a perfluorocarbon oil in a container that is coated with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane. It was found that the gas hydrate formation probability distributions of such a quasi-free water droplet were significantly lower than those of water in a glass sample cell.
Kinetics of phase separation in polymer mixtures: A molecular dynamics study
Authors: Singh Awaneesh , Puri Sanjay , Dasgupta Chandan
Published: June 2014

We present detailed results from a molecular dynamics (MD) simulation of phase-separation kinetics in polymer mixtures. Our MD simulations naturally incorporate hydrodynamic effects. We find that polymeric phase separation (with dynamically symmetric components) is in the same universality class as segregation of simple fluids: the degree of polymerization only slows down the segregation kinetics. For d = 2 polymeric fluids, the domain growth law is L(t) ∼ tϕ with ϕ showing a crossover from 1/3 → 1/2 → 2/3. For d = 3 polymeric fluids, we see the crossover ϕ = 1/3 → 1. Our MD simulations do not yet access the inertial hydrodynamic regime (with L ∼ t2/3) of phase separation in 3-d fluids.
Statistical dynamics of classical systems: A self-consistent field approach
Authors: Grzetic Douglas J. , Wickham Robert A. , Shi An-Chang
Published: June 2014

We develop a self-consistent field theory for particle dynamics by extremizing the functional integral representation of a microscopic Langevin equation with respect to the collective fields. Although our approach is general, here we formulate it in the context of polymer dynamics to highlight satisfying formal analogies with equilibrium self-consistent field theory. An exact treatment of the dynamics of a single chain in a mean force field emerges naturally via a functional Smoluchowski equation, while the time-dependent monomer density and mean force field are determined self-consistently. As a simple initial demonstration of the theory, leaving an application to polymer dynamics for future work, we examine the dynamics of trapped interacting Brownian particles. For binary particle mixtures, we observe the kinetics of phase separation.
Symmetry effects on elastic wedge waves at anisotropic edges
Authors: Pupyrev Pavel D. , Lomonosov Alexey M. , Hess Peter , Mayer Andreas P.
Published: June 2014

A laser-operated, angle-tunable transducer was employed to excite selectively elastic waves guided along the apex of a solid wedge. The propagation of wedge waves at anisotropic monocrystalline silicon edges with different symmetry properties was studied by optical detection. The reduced symmetry in crystals, as compared to isotropic media, causes a number of new features, such as the existence of supersonic leaky wedge waves, tilted spatial pulse profiles, and other peculiarities of their localization. Experimental and theoretical results are presented for three different types of symmetry configurations: the wedge symmetric about its midplane, the wedge symmetric about the plane normal to its apex line, and the wedge symmetric about one of its faces. The experiments include accurate measurements of the phase velocity and the wave field distribution, providing information on localization and coupling of wedge waves with other waves. Theoretically, the wedge waves were treated by the Laguerre function method, extended to modes that are not localized at the tip of the wedge. This approach allowed an accurate description of the observed localized and leaky wedge waves in anisotropic wedges.
Fluid breakup during simultaneous two-phase flow through a three-dimensional porous medium
Authors: Datta Sujit S. , Dupin Jean-Baptiste , Weitz David A.
Published: June 2014

We use confocal microscopy to directly visualize the simultaneous flow of both a wetting and a non-wetting fluid through a model three-dimensional (3D) porous medium. We find that, for small flow rates, both fluids flow through unchanging, distinct, connected 3D pathways; in stark contrast, at sufficiently large flow rates, the non-wetting fluid is broken up into discrete ganglia. By performing experiments over a range of flow rates, using fluids of different viscosities, and with porous media having different geometries, we show that this transition can be characterized by a state diagram that depends on the capillary numbers of both fluids, suggesting that it is controlled by the competition between the viscous forces exerted on the flowing oil and the capillary forces at the pore scale. Our results thus help elucidate the diverse range of behaviors that arise in two-phase flow through a 3D porous medium.
Critical interparticle distance for the remarkably enhanced dielectric constant of BaTiO3-Ag hybrids filled polyvinylidene fluoride composites
Authors: Luo Suibin , Yu Shuhui , Fang Fang , Lai Maobai , Sun Rong , Wong Ching-Ping
Published: June 2014

Discrete nano Ag-deposited BaTiO3 (BT-Ag) hybrids with varied Ag content were synthesized, and the hybrids filled polyvinylidene fluoride (PVDF) composites were prepared. The effect of Ag content on the dielectric properties of the composites were analyzed based on the diffused electrical double layer theory. Results showed that with a higher Ag content in BT-Ag hybrids, the dielectric constant of BT-Ag/PVDF composites increases fast with the filler loading, while the dielectric loss and conductivity showed a suppressed and moderate increase. The dielectric constant of BT-0.61Ag/PVDF (61 wt. % of Ag in BT-Ag hybrid) composites reached 613, with the dielectric loss of 0.29 at 1 kHz. It was deduced that remarkably enhanced dielectric constant appeared when the interparticle distance decreased to a critical value of about 20 nm.
A remotely accessible solar tracker system design
Authors: Çinar Said M. , Hocaoğlu Fatih O. , Orhun Murat
Published: June 2014

In this paper, a new solar tracking system designed and constructed at Afyon Kocatepe University to maximize the efficiencies of different photovoltaic (PV) panels is proposed. The system is composed of two main parts: first is the mechanical part, whereas the second is the control part. The mechanical part of the system has the ability to move both in vertical and in horizontal axes. Servo engines are selected and used at this part. On the other hand, control part is designed as to be achieved via remote access. The control strategy of the system should easily be altered when desired. This enabled us to test different control algorithms. Moreover, different PV panels produced by different technologies are tested on the system. Electricity generation outputs of PV panels obtained from the tracking system are compared with outputs of fixed ones. Finally comparison results of different control strategies are presented and discussed.
Synthesis, transport properties, and electronic structure of Cu2CdSnTe4
Authors: Dong Yongkwan , Khabibullin Artem R. , Wei Kaya , Ge Zhen-Hua , Martin Joshua , Salvador James R. , Woods Lilia M. , Nolas George S.
Published: June 2014

A new stannite phase was synthesized and its temperature dependent transport properties were investigated. Cu2CdSnTe4 possesses strong p-type conduction, while the temperature dependence of the thermal conductivity exhibits typical dielectric behavior. Electronic structure calculations allowed for a description of the transport characteristics in terms the energy band structure, density of states, and Fermi surface. The potential for thermoelectric applications is also discussed.
Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles
Authors: Tsakiris N. , Anoop K. K. , Ausanio G. , Gill-Comeau M. , Bruzzese R. , Amoruso S. , Lewis L. J.
Published: June 2014

We address the role of laser pulse fluence on expansion dynamics and size distribution of the nanoparticles produced by irradiating a metallic target with an ultrashort laser pulse in a vacuum, an issue for which contrasting indications are present in the literature. To this end, we have carried out a combined theoretical and experimental analysis of laser ablation of a bulk copper target with ≈50 fs, 800 nm pulses, in an interval of laser fluencies going from few to several times the ablation threshold. On one side, molecular dynamics simulations, with two-temperature model, describe the decomposition of the material through the analysis of the evolution of thermodynamic trajectories in the material phase diagram, and allow estimating the size distribution of the generated nano-aggregates. On the other side, atomic force microscopy of less than one layer nanoparticles deposits on witness plates, and fast imaging of the nanoparticles broadband optical emission provide the corresponding experimental characterization. Both experimental and numerical findings agree on a size distribution characterized by a significant fraction (≈90%) of small nanoparticles, and a residual part (≈10%) spanning over a rather large size interval, evidencing a weak dependence of the nanoparticles sizes on the laser pulse fluence. Numerical and experimental findings show a good degree of consistency, thus suggesting that modeling can realistically support the search for experimental methods leading to an improved control over the generation of nanoparticles by ultrashort laser ablation.
A theoretical study on the performances of thermoelectric heat engine and refrigerator with two-dimensional electron reservoirs
Authors: Luo Xiaoguang , He Jizhou , Long Kailin , Wang Jun , Liu Nian , Qiu Teng
Published: June 2014

Theoretical thermoelectric nanophysics models of low-dimensional electronic heat engine and refrigerator devices, comprising two-dimensional hot and cold reservoirs and an interconnecting filtered electron transport mechanism have been established. The models were used to numerically simulate and evaluate the thermoelectric performance and energy conversion efficiencies of these low-dimensional devices, based on three different types of electron transport momentum-dependent filters, referred to herein as kx, ky, and kr filters. Assuming the Fermi-Dirac distribution of electrons, expressions for key thermoelectric performance parameters were derived for the resonant transport processes, in which the transmission of electrons has been approximated as a Lorentzian resonance function. Optimizations were carried out and the corresponding optimized design parameters have been determined, including but not limited to the universal theoretical upper bound of the efficiency at maximum power for heat engines, and the maximum coefficient of performance for refrigerators. From the results, it was determined that kr filter delivers the best thermoelectric performance, followed by the kx filter, and then the ky filter. For refrigerators with any one of three filters, an optimum range for the full width at half maximum of the transport resonance was found to be <2kBT.
Effects of neutral interactions on velocity-shear-driven plasma waves
Authors: Enloe C. L. , Tejero E. M. , Amatucci W. E. , Crabtree C. , Ganguli G. , Sotnikov V.
Published: June 2014

In a laboratory experiment, we demonstrate the substantial effects that collisions between charged and neutral particles have on low-frequency (Ωi ≪ ω ≪ Ωe) shear-driven electrostatic lower hybrid waves in a plasma. We establish a strong (up to 2.5 kV/m) highly localized electric field with a length scale shorter than the ion gyroradius, so that the ions in the plasma, unlike the electrons, do not develop the full E × B drift velocity. The resulting shear in the particle velocities initiates the electron-ion hybrid (EIH) instability, and we observe the formation of strong waves in the vicinity of the shear with variations in plasma densities of 10% or greater. Our experimental configuration allows us to vary the neutral background density by more than a factor of two while holding the charged particle density effectively constant. Not surprisingly, increasing the neutral density decreases the growth rate/saturation amplitude of the waves and increases the threshold electric field necessary for wave formation, but the presence of neutrals affects the dominant wave frequency as well. We show that a 50% increase in the neutral density decreases the wave frequency by 20% while also suppressing the electric field dependence of the frequency that is observed when fewer neutrals are present. The majority of these effects, as well as the values of the frequencies we observe, closely match the predictions of previously developed linear EIH instability theory, for which we present the results of a numerical solution.
The properties of the extraordinary mode and surface plasmon modes in the three-dimensional magnetized plasma photonic crystals based on the magneto-optical Voigt effects
Authors: Zhang Hai-Feng , Liu Shao-Bin , Tang Yi-Jun
Published: June 2014

In this paper, the properties of the extraordinary mode and surface plasmon modes in the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with face-centered-cubic lattices that are composed of the core tellurium (Te) spheres with surrounded by the homogeneous magnetized plasma shells inserted in the air, are theoretically investigated in detail by the plane wave expansion method, as the magneto-optical Voigt effects of magnetized plasma are considered (the incidence electromagnetic wave vector is perpendicular to the external magnetic field at any time). The optical switching or wavelength division multiplexer can be realized by the proposed 3D MPPCs. Our analyses demonstrate that the complete photonic band gaps (PBGs) and two flatbands regions for the extraordinary mode can be observed obviously. PBGs can be tuned by the radius of core Te sphere, the plasma density and the external magnetic field. The flatbands regions are determined by the existence of surface plasmon modes. Numerical simulations also show that if the thickness of magnetized plasma shell is larger than a threshold value, the band structures of the extraordinary mode will be similar to those obtained from the same structure containing the pure magnetized plasma spheres. In this case, the band structures also will not be affected by the inserted core spheres. It is also provided that the upper edges of two flatbands regions will not depend on the topology of lattice. However, the frequencies of lower edges of two flatbands regions will be convergent to the different constants for different lattices, as the thickness of magnetized plasma shell is close to zero.
Octupolar out-of-plane magnetic field structure generation during collisionless magnetic reconnection in a stressed X-point collapse
Authors: von der Pahlen J. Graf , Tsiklauri D.
Published: June 2014

The out-of-plane magnetic field, generated by fast magnetic reconnection, during collisionless, stressed X-point collapse, was studied with a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code, using both closed (flux conserving) and open boundary conditions on a square grid. It was discovered that the well known quadrupolar structure in the out-of-plane magnetic field gains four additional regions of opposite magnetic polarity, emerging near the corners of the simulation box, moving towards the X-point. The emerging, outer, magnetic field structure has opposite polarity to the inner quadrupolar structure, leading to an overall octupolar structure. Using Ampere's law and integrating electron and ion currents, defined at grid cells, over the simulation domain, contributions to the out-of-plane magnetic field from electron and ion currents were determined. The emerging regions of opposite magnetic polarity were shown to be the result of ion currents. Magnetic octupolar structure is found to be a signature of X-point collapse, rather than tearing mode, and factors relating to potential discoveries in experimental scenarios or space-craft observations are discussed.
Vertical cavity surface emitting lasing from cyano-substituted thiophene/phenylene co-oligomer single crystals
Authors: Yamashita Kenichi , Nakahata Takuya , Hayakawa Takashi , Sakurai Yusaku , Yamao Takeshi , Yanagi Hisao , Hotta Shu
Published: June 2014

We have achieved to observe vertical cavity surface emitting lasing (VCSEL) from an optically pumped organic single crystal. A vapor-grown thiophene/phenylene co-oligomer (TPCO) single crystal with in-plane polarization component was used as the gain medium in an optical microcavity. Since the top and bottom surfaces of the TPCO crystal serve as high-quality resonators, well-defined Fabry-Pérot resonance is achieved. Furthermore, by using high reflectivity distributed Bragg reflector as the cavity resonator, we have observed lasing emissions with a line width of 0.9 nm and a threshold of ∼3 mJ/cm2. The VCSEL-type optical feedback configuration demonstrated in this study is expected to be one of the available means to realize the electrically pumped organic laser device.
Pulsed direct current field induced phase transformation in graphene nanoplatelets
Authors: Zhang F. , Eisenhut F. , Burkel E.
Published: June 2014

Graphene nanoplatelets were consolidated at various conditions using spark plasma sintering utilizing ON-OFF DC pulse energizing. The phase transformation from graphene nanoplatelets to diamond can occur at pressure of 80 MPa and at temperatures of 1100 °C to 1500 °C without any catalysts being involved. However, no diamond formation could be observed in sintering experiments at the same pressure-temperature conditions with steady AC heating. Our results indicate that the phase formation of diamond induced by the pulsed DC field was determined by the presence of plasmas in areas of locally increased densities of stacking faults in the layered graphene nanoplatelets under sintering-pressures.
Electron- and photon-induced plasmonic excitations in two-dimensional silver nanostructures
Authors: Hoang C. V. , Rana M. , Nagao T.
Published: June 2014

Plasmons are the quasi particles of collective oscillations of electrons and form the basis of plasmonics and optical metamaterials. We combined electron spectroscopy and optical spectroscopy techniques to study plasmons in atomically smooth Ag films and in epitaxial Ag nanodisks to map the momentum-energy dispersion curves of the two-dimensional (2D) sheet plasmon and the quasi-2D plasmons to clarify the essential differences between them. Our experimental results combined with the results of numerical electromagnetic simulations showed that the bulk-like nature of the silver plasmon starts in layers that are only two atoms thick.
Observation of spontaneous ferroelectric polarization reversal in multiferroic Mn1−xNixWO4 (x ≈ 0.16)
Authors: Song Young-Sang , Chung Jae-Ho , Woo Shin Kwang , Hoon Kim Kee , Hwan Oh In
Published: June 2014

In this Letter, we report the effect of replacing Mn2+ ions with Ni2+ on the ferroelectricity of multiferroic MnWO4 single crystals. When the amount of substitution was close to 16%, the sign of ferroelectric polarization spontaneously became negative with respect to initial dc poling field at a few degrees below TC. Neutron diffraction intensities revealed a sudden change in the underlying spiral spin ordering that occurred coincidentally with the observed sign reversal. This unusual behavior in zero magnetic fields suggests that strong competitions between the two different magnetic ions may provide an efficient route to manipulation of existing multiferroics.
Infrared near-field imaging and spectroscopy based on thermal or synchrotron radiation
Authors: Peragut Florian , Brubach Jean-Blaise , Roy Pascale , De Wilde Yannick
Published: June 2014

We demonstrate the coupling of a scattering near-field scanning optical microscope combined with a Fourier transform infrared spectrometer. The set-up operates using either the near-field thermal emission from the sample itself, which is proportional to the electromagnetic local density of states, or with an external infrared synchrotron source, which is broadband and highly brilliant. We perform imaging and spectroscopy measurements with sub-wavelength spatial resolution in the mid-infrared range on surfaces made of silicon carbide and gold and demonstrate the capabilities of the two configurations for super-resolved near-field mid-infrared hyperspectral imaging and that the simple use of a properly chosen bandpass filter on the detector allows one to image the spatial distribution of materials with sub-wavelength resolution by studying the contrast in the near-field images.
Spatiotemporally separating electron and phonon thermal transport in L1 FePt films for heat assisted magnetic recording
Authors: Xu D. B. , Sun C. J. , Brewe D. L. , Han S.-W. , Ho P. , Chen J. S. , Heald S. M. , Zhang X. Y. , Chow G. M.
Published: June 2014

We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L10 FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated.
Investigation of dominant spin wave modes by domain walls collision
Authors: Ramu M. , Purnama I. , Goolaup S. , Chandra Sekhar M. , Lew W. S.
Published: June 2014

Spin wave emission due to field-driven domain wall (DW) collision has been investigated numerically and analytically in permalloy nanowires. The spin wave modes generated are diagonally symmetric with respect to the collision point. The non-propagating mode has the highest amplitude along the middle of the width. The frequency of this mode is strongly correlated to the nanowire geometrical dimensions and is independent of the strength of applied field within the range of 0.1 mT to 1 mT. For nanowire with film thickness below 5 nm, a second spin wave harmonic mode is observed. The decay coefficient of the spin wave power suggests that the DWs in a memory device should be at least 300 nm apart for them to be free of interference from the spin waves.
Characteristics of stress-induced defects under positive bias in high-k/InGaAs stacks
Authors: Palumbo F. , Winter R. , Krylov I. , Eizenberg M.
Published: June 2014

The introduction of InGaAs as a channel material for complementary metal-oxide-semiconductor technology presents major challenges in terms of the characterization of the various defects that affect the performance and reliability. Understanding the generation of defects by constant voltage stresses is crucial in terms of their concentration profiles and energy levels. In particular, we want to understand the real nature of the defects responsible for the dispersion of C-V in strong accumulation. Here, we show that the degradation under positive bias of metal/Al2O3/n-InGaAs capacitors reveals two contributions depending on the temperature that affects the C-V curves in a different way. Based on features of stressed C-V curves, it is possible to estimate the onset point of the distribution of border traps near the midgap condition. The results suggest that these defects are strongly related to the characteristics of the InGaAs substrate.
Tunable radio-frequency negative permittivity in nickel-alumina “natural” meta-composites
Authors: Shi Zhi-cheng , Chen Shou-gang , Sun Kai , Wang Xin , Fan Run-hua , Wang Xu-ai
Published: June 2014

“Natural” metamaterials with intrinsic negative permittivity and permeability have attracted significant attention because of their wide promising applications and facile preparation processes. In order to match the negative permeability band which is usually located in the radio-frequency range, radio-frequency negative permittivity is desired. Moreover, the negative permittivity should be tunable to satisfy different application circumstances. Herein, nickel/alumina composites consisting of nickel particles homogeneously dispersed in alumina were prepared using a facile wet chemical process. A percolation phenomenon appears, and expected radio-frequency negative permittivity is obtained. Furthermore, the dependences of negative permittivity on the composites' compositions and microstructures are investigated in detail. It is shown that higher nickel content results in higher negative permittivity magnitude and lower negative permittivity frequency. Besides, the addition of alumina particles leads to decreasing negative permittivity magnitude and higher negative permittivity frequency band owing to the deteriorated interconnectivity between nickel particles. The present work will greatly facilitate the fabrication and application of “natural” metamaterials with tailored properties.
A nitrogen doped low-dislocation density free-standing single crystal diamond plate fabricated by a lift-off process
Authors: Mokuno Yoshiaki , Kato Yukako , Tsubouchi Nobuteru , Chayahara Akiyoshi , Yamada Hideaki , Shikata Shinichi
Published: June 2014

A nitrogen-doped single crystal diamond plate with a low dislocation density is fabricated by chemical vapor deposition (CVD) from a high pressure high temperature synthetic type IIa seed substrate by ion implantation and lift-off processes. To avoid sub-surface damage, the seed surface was subjected to deep ion beam etching. In addition, we introduced a nitrogen flow during the CVD step to grow low-strain diamond at a relatively high growth rate. This resulted in a plate with low birefringence and a dislocation density as low as 400 cm−2, which is the lowest reported value for a lift-off plate. Reproducing this lift-off process may allow mass-production of single crystal CVD diamond plates with low dislocation density and consistent quality.