bluuebunny/crossref_metadata_2025 huggingface dataset:
Glimpsing Speech in the Presence of Nonsimultaneous Amplitude Modulations From a Competing Talker: Effect of Modulation Rate, Age, and Hearing Loss
Authors: Fogerty Daniel , Ahlstrom Jayne B. , Bologna William J. , Dubno Judy R.
Published: September 2016

Purpose

This study investigated how listeners process acoustic cues preserved during sentences interrupted by nonsimultaneous noise that was amplitude modulated by a competing talker.

Method

Younger adults with normal hearing and older adults with normal or impaired hearing listened to sentences with consonants or vowels replaced with noise amplitude modulated by a competing talker. Sentences were spectrally shaped according to individual audiograms or to the mean audiogram from the listeners with hearing impairment for a younger spectrally shaped control group. The modulation spectrum of the noise was low-pass filtered at different modulation cutoff frequencies. The effect of noise level was also examined.

Results

Performance declined when nonsimultaneous masker modulation included faster rates and was maximized when masker modulation matched the preserved primary speech modulation. Vowels resulted in better performance compared with consonants at slower modulation cutoff rates, likely due to suprasegmental features. Poorer overall performance was observed with increased age or hearing loss, and for listeners who received spectrally shaped speech.

Conclusions

Nonsimultaneous amplitude modulations from a competing talker significantly interacted with the preserved speech segment, and additional listener factors were observed for age and hearing loss. Importantly, listeners may obtain benefit from nonsimultaneous competing modulations when they match the preserved modulations of the sentence.
GaSb‐based 2.0 μm SDL with 17 W output power at 20°C
Authors: Holl P. , Rattunde M. , Adler S. , Bächle A. , Diwo‐Emmer E. , Aidam R. , Wagner J.
Published: September 2016

A gallium antimonide‐based semiconductor disk laser (SDL) emitting 17 W of continuous wave output power at a heat sink temperature of 20°C and an emission wavelength of 2.02 μm are presented. This high‐output power is achieved by optimising the thermal management and reducing the quantum deficit of the SDL structure.
Record 34.2% efficient mm‐wave N‐polar AlGaN/GaN MISHEMT at 87 GHz
Authors: Romanczyk B. , Guidry M. , Wienecke S. , Li H. , Ahmadi E. , Zheng X. , Keller S. , Mishra U.K.
Published: September 2016

A novel device technology has been developed to enable the fabrication of high performance mm‐wave GaN high electron mobility transistors (HEMTs) for solid‐state power amplifiers operating in W‐band. By utilising the reverse polarisation of N‐polar GaN, an in‐situ GaN cap layer added in the device access regions acts to improve the channel conductivity and reduces the impact of surface states on device performance. A low dispersion HEMT with 149 GHz peak fT and 285 GHz peak fmax demonstrated simultaneous high efficiency and output power density with 34.2% peak power‐added efficiency and an associated 2.5 W/mm output power at 87 GHz.
Phase bias estimation for multi‐channel HRWS SAR based on Doppler spectrum optimisation
Authors: Wang Zhibin , Liu Yanyang , Li Zhenfang , Xu Gang , Chen Junli
Published: September 2016

By applying digital beam‐forming (DBF) technique, the along‐track multi‐channel synthetic aperture radar (SAR) system can simultaneously achieve high‐resolution and wide‐swath (HRWS) imaging. However, the presence of unavoidable phase biases tends to degrade the DBF performance. To address this issue, a novel phase bias estimation algorithm based on Doppler spectrum optimisation is proposed. By exploiting the fact that phase bias would cause Doppler spectrum broadened, the phase biases can be successfully estimated by maximising a sharpness optimisation of the Doppler spectrum. The effectiveness of the algorithm is validated by experimental result carried out on the SAR data collected by an air‐borne multi‐channel system.
ICT services for active ageing and independent living: identification and assessment
Authors: Christophorou Christophoros , Kleanthous Styliani , Georgiadis Dimosthenis , Cereghetti Donato M. , Andreou Panayiotis , Wings Cindy , Christodoulou Eleni , Samaras George
Published: September 2016

Based on the demographic changes and the rapid increase of older population in Europe, major challenges are expected to rise, both in the economy as well as the society, whether the dominant care model for supporting elderly in living independently at home continues to rely on informal and formal caregivers’ assistance. To respond to the above challenges, assistive technologies are called to develop Information and Communication Technology (ICT) services for supporting seniors to remain active and independent, for as long as possible, in their chosen home environment. The work described in this Letter is based on the Miraculous‐Life project and it emphasises the identification and assessment of a set of services that an ICT system for Ageing Well should support, in an actual end‐users setting. The outcome of this work may inform fellow researchers and other projects in the area of Ageing Well in: (i) understanding which ICT services can be the most valuable for end‐users’ Quality of Life, (ii) prioritising the development of related ICT services and (iii) facilitating better recourse allocation in order to reduce any risks associated to implementation failures of these services within their respective projects. A final trial phase is planned, aiming to validate the Miraculous Life prototype longitudinally in a naturalistic environment with a larger sample size. During this trial, it will be investigated if perceived usefulness, satisfaction and motivation could be predicted by sociodemographic variables and personality.
Static corrective control for asynchronous sequential machines and its application to on‐board computers
Authors: Yang Jung–Min , Woo Kwak Seong
Published: September 2016

Corrective controllers can modify the stable‐state behaviour of asynchronous sequential machines in a desirable way. This study addresses a static corrective control scheme formulated as a static feedback law. As no internal states are needed, the use of static corrective controllers greatly reduces the implementation cost. The existence condition for static corrective controllers is found to be more restrictive than that of dynamic controllers. Based on the existence condition, the output of the static corrective controller is assigned so as to match the closed‐loop system to a reference model. The proposed static controller is applied to the model matching problem of on‐board computer error counters implemented on field‐programmable gate array systems.
Decentralised intelligent transport system with distributed intelligence based on classification techniques
Authors: Osaba Eneko , Onieva Enrique , Moreno Asier , Lopez‐Garcia Pedro , Perallos Asier , Bringas Pablo G.
Published: September 2016

This study is focused on a decentralised intelligent transportation systems with distributed intelligence based on classification techniques. The rationale behind this architecture is to offer a fully distributed, flexible and scalable system. The architecture encompasses the entire process of capture and management of available road data, enabling the generation of services to promote transportation efficiency. Besides that, thanks to the embedded classification techniques, the system is capable of predicting and reacting to certain events, facing them in an appropriate way. The aim of this work is to demonstrate how the system works in two different real‐world use cases. To achieve this objective, how the architecture acts to deal with some incidences is proven. In addition, both use cases serve to show the effective communication between the different components of the system. Besides this, this work demonstrates the fundamental role played by the artificial intelligence techniques working in the system. The well‐known C4.5 algorithm has been used for the accurate prediction of traffic congestion and pollution level. The authors explain in this work the reasons for using this classification technique, and the previous experiments performed.
Spatio‐temporal probabilistic query generation model and sink attributes for energy‐efficient wireless sensor networks
Authors: Kumar Pramod , Chaturvedi Ashvini
Published: September 2016

Proliferation in Micro‐Electro‐Mechanical‐Systems (MEMS) technology along with advancement in distributed computing infrastructure has facilitated the versatile usage and deployment of wireless sensors networks (WSNs) in last one and half decades. WSNs support large number of applications from the civilian and military regimes. Irrespective of these regimes; owing to difficulty associated with battery replenishment, proper energy usage has been at centre stage in WSNs operations. The lifetime of WSNs typically depends upon sensor's energy dissipation pattern, which is non‐homogeneous with respect to spatial distribution over any short epochs. The genesis behind this non‐homogeneity is random generation of queries, which owes to application specific spatio‐temporal parameters. Importance of spatio‐temporal parameters is ubiquitous in WSNs paradigm and uncertainties are inevitable with these parameters, although the degree of uncertainties varies in accordance to applications served. Thus, from network design perspectives, precision involved with spatio‐temporal aspects must be given due priority to obtain a mathematical model that maintains a good rapport with realistic query generation process. With these motivations, the study explores: (i) uses of energy‐efficient clustering schemes, (ii) incorporation of spatio‐temporal parameters uncertainties into probabilistic model of query generation using fuzzy‐intervals bound, and (iii) sink attributes to enhance network lifetime. For various network surveillance scenarios; the performance measures average residual energy status and service‐time‐duration are estimated and analysed.
PIAPF for manoeuvring target tracking in the presence of multiplicative noise
Authors: Keshavarz‐Mohammadiyan Atiyeh , Khaloozadeh Hamid
Published: September 2016

In this study, a prediction‐interval‐based adaptive particle filter (PIAPF) is developed to track a manoeuvring target in the presence of multiplicative measurement noise. In PIAPF, input augmentation technique is utilised to estimate the state variables of target and unknown inputs (manoeuvres) simultaneously. To cope with unknown sudden changes of system state variables (caused by manoeuvres), the covariance matrix of the importance density function is adaptively adjusted based on the prediction interval of the output estimation. In addition, a theorem is developed which confirms that the output estimation error is upper bounded by a given probability. The likelihood function of the non‐stationary state‐dependent error of sensors, which is modelled as multiplicative noise, is then obtained for weight calculation of PIAPF. The proposed PIAPF is then used to track a manoeuvring target in a wireless sensor network with distance‐measuring sensor nodes. Simulation results demonstrate the effectiveness of the proposed PIAPF in terms of tracking accuracy and computational load.
Phase noise coherence of two continuous wave radio frequency signals of different frequency
Authors: Rönnow Daniel , Amin Shoaib , Alizadeh Mahmoud , Zenteno Efrain
Published: September 2016

A method is proposed for determining the correlated and uncorrelated parts of phase noise spectra (PNS) of two continuous wave radio signals of different frequencies, ω1 and ω2. The PNS of the two signals and of mixed signals are measured. The PNS are modelled as having a correlated part that is the same for both signals, except for a multiplicative factor, and uncorrelated parts, that are different for the two signals. A property of the model that the PNS of some mixing products are linear combinations of the PNS of the signals at ω1, ω2, and ω1 − ω2 is experimentally verified. The difference of the PNS at ω1 + ω2 and ω1 − ω2 is proportional to the correlated part of the PNS and is a part of auxiliary functions that are used for finding the multiplicative factor and the correlated, partly correlated, and uncorrelated phase noise at different offset frequencies. A conventional spectrum analyser was used to characterise two signal generators, a phase‐coherent and a non‐phase‐coherent one. For the phase‐coherent generator the phase noise of two signals was found to be correlated for offset frequencies below 10 Hz, partly correlated for 10 Hz–1 kHz and uncorrelated above 1 kHz.
Modelling of wire resistance effect in PCM‐based nanocrossbar memory
Authors: El‐Hassan Nemat H. , Kumar Nandha Thulasiraman , Almurib Haider Abbas F.
Published: September 2016

At nanoscale grain boundaries and surface scattering effects lead to an increase of connecting wires electrical resistivity with decreasing wire dimensions. This increase of resistivity leads to significant power loss across connecting wires in nanocrossbars. In this study, the resistance of connecting wire as a function of material properties and feature size is calculated. Then the effect of the connecting wires resistance in phase change memory (PCM) performance in PCM‐based passive nanocrossbar was evaluated. The performance metrics tested are: programmed resistance levels, programming duration, and energy consumption. Based on the simulation results, it was found that the power consumed in connecting wires decreases the power supplied to PCM cells. This reduction in power results in higher programmed low resistive state (R ON). The effect of connecting wire resistance on PCM performance is studied as a function of the wire size, cell position on the nanocrossbar, and nanocrossbar size. Simulation results showed that the programmed R ON is inversely proportional to feature size. Moreover, it increases up to almost 40%, with decreasing feature size to 40 nm. Moreover, programmed R ON increases proportionally with increasing nanocrossbar size. Moreover, R OFF /R ON ratio drops almost 90% of targeted ratio at 1 kbit nanocrossbars. Furthermore, cells closer to supply sources are the least affected by wire resistance, while cells furthest from supply are the most affected. Finally, at the end of this study two methods are suggested to resolve the programmed R ON reliability issue caused by energy drop across connecting wires.
Mechanisms of Lung Injury and Bronchopulmonary Dysplasia
Authors: Jobe Alan
Published: September 2016

Although bronchopulmonary dysplasia (BPD) is the most frequent adverse outcome for infants born at < 30 weeks gestational age, there remain major gaps in understanding the pathophysiology, and thus there are few effective targeted therapies to prevent and treat BPD. This review will focus on the substantial problems and knowledge gaps for the clinician and investigator when considering lung injury and BPD. The epidemiology of BPD is clear: BPD is a lung injury syndrome predominantly in extremely low-birth-weight infants with an incidence that increases as gestation/birth weight decrease, with growth restriction, in males and with fetal exposures and with injury from postdelivery respiratory care. However, we do not have a good definition of BPD that identifies the infants that die of respiratory disease before 36 weeks or that predicts long-term outcomes as well. The injury resulting in BPD likely begins as altered lung development before delivery in many infants (small for gestational age, chorioamnionitis, tobacco exposure), can be initiated by resuscitating at birth, and then amplified by postnatal exposures (oxygen, mechanical ventilation, infection). Conceptually the events leading to BPD are the continued interplay of lung development that is altered progressively by injury and repair to result in poorly defined phenotypes of BPD. The injury pathways prominently cause inflammation, and as a proof of principle, corticosteroids can decrease the incidence and severity of BPD, as demonstrated by three recent trials of the early use of steroids. There are likely “adaptation” and “tolerance” responses that modulate the injury and repair to increase or decrease the damage, interactions that are not understood. BPD is a more complex disease.
Newborn Critical Congenital Heart Disease Screening Using Pulse Oximetry: Nursing Aspects
Authors: Hom Lisa , Martin Gerard
Published: September 2016

Congenital heart disease (CCHD) is the most common birth defect. Screening for the most critical forms (CCHD) using pulse oximetry was added to the Recommended Uniform Screening Panel in the United States in 2011. Since then, CCHD screening has become nearly universal in the United States. Nurses are ideally situated to contribute to the development of best practices for implementation and provide education to families on CCHD screening. Much of the standardization, advocacy, and development of national recommendations occurred with key input from nurses. Nurses often have responsibility for educating parents, performing the screening, interpreting the screening algorithm, and the documentation of results. The nurse role often includes implementing follow-up quality improvement initiatives to ensure that systematic and accurate screening occurs. Smooth implementation can be achieved by identifying champions early, obtaining input from a multidisciplinary team including both physician and nursing leaders, and identifying ways to integrate screening into already existing workflow. By knowing the basics of why screening is important, how to screen, current recommendations on the follow-up for positive screens and the limitations of CCHD screening, nurses can advocate for their patients and positively impact outcomes for infants born with CCHD through early identification before discharge.
EFSUMB Recommendations and Guidelines for Gastrointestinal Ultrasound - Part 1: Examination Techniques and Normal Findings (Short version)
Authors: Nylund Kim , Maconi Giovanni , Hollerweger Alois , Ripolles Tomas , Pallotta Nadia , Higginson Antony , Serra Carla , Dietrich Christoph , Sporea Ioan , Saftoiu Adrian , Dirks Klaus , Hausken Trygve , Calabrese Emma , Romanini Laura , Maaser Christian , Nuernberg Dieter , Gilja Odd
Published: September 2016

In October 2014 the European Federation of Societies for Ultrasound in Medicine and Biology formed a Gastrointestinal Ultrasound (GIUS) task force group to promote the use of GIUS in a clinical setting. One of the main objectives of the task force group was to develop clinical recommendations and guidelines for the use of GIUS under the auspices of EFSUMB. The first part, gives an overview of the examination techniques for GIUS recommended by experts in the field. It also presents the current evidence for the interpretation of normal sonoanatomical and physiological features as examined with different ultrasound modalities.
Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators
Authors: Joshi G. , Miller R. , Ogden L. , Kavand M. , Jamali S. , Ambal K. , Venkatesh S. , Schurig D. , Malissa H. , Lupton J. M. , Boehme C.
Published: September 2016

Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators, we cover almost five octaves in resonance frequency within a single setup. The measurements with a common π-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.
Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes
Authors: Jeong Junseok , Choi Ji Eun , Kim Yong-Jin , Hwang Sunyong , Kim Sung Kyu , Kim Jong Kyu , Jeong Hu Young , Hong Young Joon
Published: September 2016

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p–n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunneling probability determined by wire/film junction geometry and size.
Combined effects of vertical and lateral confinement on the magnetic properties of MnAs micro and nano-ribbons
Authors: Steren L. B. , Tortarolo M. , Fernandez Baldis F. , Sirena M. , Sacchi M. , Etgens V. H. , Eddrief M. , Santos B. , Mentes T. O. , Locatelli A.
Published: September 2016

The micromagnetic domain structure of MnAs films gave place to an intense research activity in the last few years due to its potential application in magneto-electronic devices such as domain-wall track memories and logic circuits. These applications require a full knowledge of miniaturization effects on the magnetic properties of the material. In this work, X-ray photoemission electron microscopy has been used for imaging magnetic domains in lithographically fabricated MnAs ribbons, addressing the dependence of the domain configuration on film thickness and ribbon width. Our experiments show a transition from head-on to regular stripe domains below a critical width/thickness ratio wc ≈ 6. Micromagnetic simulations suggest that this transition is correlated to the magnetic structure of the surface plane. Depending on the ribbon width and thickness, the magnetic configuration is shown to evolve from flux-closure domain structure to a state of almost homogeneous magnetization, observed for narrower ribbons. The evolution of the domain structure, magnetic fraction, and magnetization with temperature has been studied across the ferromagnetic/paramagnetic transition. Our experiments show that the magnetic configuration in ribbons exhibits higher stability to temperature variations than in as-cast films.
Motif analysis for small-number effects in chemical reaction dynamics
Authors: Saito Nen , Sughiyama Yuki , Kaneko Kunihiko
Published: September 2016

The number of molecules involved in a cell or subcellular structure is sometimes rather small. In this situation, ordinary macroscopic-level fluctuations can be overwhelmed by non-negligible large fluctuations, which results in drastic changes in chemical-reaction dynamics and statistics compared to those observed under a macroscopic system (i.e., with a large number of molecules). In order to understand how salient changes emerge from fluctuations in molecular number, we here quantitatively define small-number effect by focusing on a “mesoscopic” level, in which the concentration distribution is distinguishable both from micro- and macroscopic ones and propose a criterion for determining whether or not such an effect can emerge in a given chemical reaction network. Using the proposed criterion, we systematically derive a list of motifs of chemical reaction networks that can show small-number effects, which includes motifs showing emergence of the power law and the bimodal distribution observable in a mesoscopic regime with respect to molecule number. The list of motifs provided herein is helpful in the search for candidates of biochemical reactions with a small-number effect for possible biological functions, as well as for designing a reaction system whose behavior can change drastically depending on molecule number, rather than concentration.
Existence regimes for the formation of nonlinear dissipative structures in inhomogeneous magnetoplasmas with non-Maxwellian electrons
Authors: Masood W. , Zahoor Sara , Gul-e-Ali  , Ahmad Ali
Published: September 2016

Nonlinear dissipative structures are studied in one and two dimensions in nonuniform magnetized plasmas with non-Maxwellian electrons. The dissipation is incorporated in the system through ion-neutral collisions. Employing the drift approximation, nonlinear drift waves are derived in 1D, whereas coupled drift-ion acoustic waves are derived in 2D in the weak nonlinearity limit. It is found that the ratio of the diamagnetic drift velocity to the velocity of nonlinear structure determines the nature (compressive or rarefactive) of the shock structure. The upper and lower bounds for velocity of the nonlinear shock structures are also found. It is noticed that the existence regimes for the drift shock waves in one and two dimensions for Cairns distributed electrons are very distinct from those with kappa distributed electrons. Interestingly, it is found that both compressive and rarefactive shock structures could be obtained for the one dimensional drift waves with kappa distributed electrons.
Three axis vector atomic magnetometer utilizing polarimetric technique
Authors: Pradhan Swarupananda
Published: September 2016

The three axis vector magnetic field measurement based on the interaction of a single elliptically polarized light beam with an atomic system is described. The magnetic field direction dependent atomic responses are extracted by the polarimetric detection in combination with laser frequency modulation and magnetic field modulation techniques. The magnetometer geometry offers additional critical requirements like compact size and large dynamic range for space application. Further, the three axis magnetic field is measured using only the reflected signal (one polarization component) from the polarimeter and thus can be easily expanded to make spatial array of detectors and/or high sensitivity field gradient measurement as required for biomedical application.
Development and calibration of an air-floating six-axis force measurement platform using self-calibration
Authors: Huang Bin , Wang Xiaomeng , Li Chengwei , Yi Jiajing , Lu Rongsheng , Tao Jiayue
Published: September 2016

This paper describes the design, working principle, as well as calibration of an air-floating six-axis force measurement platform, where the floating plate and nozzles were connected without contact, preventing inter-dimensional coupling and increasing precision significantly. The measurement repeatability error of the force size in the platform is less than 0.2% full scale (FS), which is significantly better than the precision of 1% FS in the six-axis force sensors on the current market. We overcame the difficulties of weight loading device in high-precision calibration by proposing a self-calibration method based on the floating plate gravity and met the calibration precision requirement of 0.02% FS. This study has general implications for the development and calibration of high-precision multi-axis force sensors. In particular, the air-floating six-axis force measurement platform could be applied to the calibration of some special sensors such as flexible tactile sensors and may be used as a micro-nano mechanical assembly platform for real-time assembly force testing.
Wave propagation in spatially modulated tubes
Authors: Ziepke A. , Martens S. , Engel H.
Published: September 2016

We investigate wave propagation in rotationally symmetric tubes with a periodic spatial modulation of cross section. Using an asymptotic perturbation analysis, the governing quasi-two-dimensional reaction-diffusion equation can be reduced into a one-dimensional reaction-diffusion-advection equation. Assuming a weak perturbation by the advection term and using projection method, in a second step, an equation of motion for traveling waves within such tubes can be derived. Both methods predict properly the nonlinear dependence of the propagation velocity on the ratio of the modulation period of the geometry to the intrinsic width of the front, or pulse. As a main feature, we observe finite intervals of propagation failure of waves induced by the tube’s modulation and derive an analytically tractable condition for their occurrence. For the highly diffusive limit, using the Fick-Jacobs approach, we show that wave velocities within modulated tubes are governed by an effective diffusion coefficient. Furthermore, we discuss the effects of a single bottleneck on the period of pulse trains. We observe period changes by integer fractions dependent on the bottleneck width and the period of the entering pulse train.
Computing dispersive, polarizable, and electrostatic shifts of excitation energy in supramolecular systems: PTCDI crystal
Authors: Megow Jörg
Published: September 2016

The gas-to-crystal-shift denotes the shift of electronic excitation energies, i.e., the difference between ground and excited state energies, for a molecule transferred from the gas to the bulk phase. The contributions to the gas-to-crystal-shift comprise electrostatic as well as inductive polarization and dispersive energy shifts of the molecular excitation energies due to interaction with environmental molecules. For the example of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI) bulk, the contributions to the gas-to-crystal shift are investigated. In the present work, electrostatic interaction is calculated via Coulomb interaction of partial charges while inductive and dispersive interactions are obtained using respective sum over states expressions. The coupling of higher transition densities for the first 4500 excited states of PTCDI was computed using transition partial charges based on an atomistic model of PTCDI bulk obtained from molecular dynamics simulations. As a result it is concluded that for the investigated model system of a PTCDI crystal, the gas to crystal shift is dominated by dispersive interaction.
Reverse Mössbauer effect as a possible source of “hot” molecules absorbed in crystalline solids at low temperature
Authors: Demontis Pierfranco , Suffritti Giuseppe B.
Published: September 2016

As an attempt to explain some of the many anomalies and unresolved problems which have been reported about the dynamic behavior of particles and molecules absorbed in crystalline solids, the “reverse Mössbauer effect” (RME) is proposed. RME theory posits that a particle in non-equilibrium state with respect to a crystal (colliding with the crystal or absorbed in it, but set out of thermal equilibrium by some external cause) is scattered by the whole crystal with a momentum proportional to a vector representing a reciprocal lattice point. The scattering is expected to occur with a well-defined probability and the momentum transferable to the particle is expected to follow a predictable distribution. The RME theory, in practice, is an extension of the Bragg–von Laue scattering law to high-energy colliding particles, in general, and can be applied to any particle or molecule colliding with the surface of a crystalline solid or absorbed in it, but not in thermal equilibrium with the crystal lattice. We verified the RME theory by considering a well-defined unresolved problem. In an experimental study about methane adsorbed in the zeolite Na-ZSM-5 [H. Jobic, Chem. Phys. Lett. 170, 217 (1990)] reporting neutron inelastic-scattering spectra (recoiled bands) at 10 K, the translational kinetic energy of methane resulted to be much higher than equilibrium expected value, namely, about 85 K (or 7.3 meV). The author concluded that “the interpretation of this unusual behavior has yet to be found.” In the present study, on the basis of the RME, an explanation of this behavior is put forward.
Optical smoothing of laser imprinting in planar-target experiments on OMEGA EP using multi-FM 1-D smoothing by spectral dispersion
Authors: Hohenberger M. , Shvydky A. , Marozas J. A. , Fiksel G. , Bonino M. J. , Canning D. , Collins T. J. B. , Dorrer C. , Kessler T. J. , Kruschwitz B. E. , McKenty P. W. , Meyerhofer D. D. , Regan S. P. , Sangster T. C. , Zuegel J. D.
Published: September 2016

Direct-drive ignition on the National Ignition Facility (NIF) requires single-beam smoothing to minimize imprinting of laser nonuniformities that can negatively affect implosion performance. One-dimensional, multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required smoothing [Marozas et al., Bull. Am. Phys. Soc. 55, 294 (2010)]. A prototype multi-FM SSD system has been integrated into the NIF-like beamline of the OMEGA EP Laser System. Experiments have been performed to verify the smoothing performance by measuring Rayleigh–Taylor growth rates in planar targets of laser-imprinted and preimposed surface modulations. Multi-FM 1-D SSD has been observed to reduce imprint levels by ∼50% compared to the nominal OMEGA EP SSD system. The experimental results are in agreement with 2-D DRACO simulations using realistic, time-dependent far-field spot-intensity calculations that emulate the effect of SSD.
Charge neutrality breakdown in confined aqueous electrolytes: Theory and simulation
Authors: Colla Thiago , Girotto Matheus , dos Santos Alexandre P. , Levin Yan
Published: September 2016

We study, using Density Functional theory (DFT) and Monte Carlo simulations, aqueous electrolyte solutions between charged infinite planar surfaces, in contact with a bulk salt reservoir. In agreement with recent experimental observations [Z. Luo et al., Nat. Commun. 6, 6358 (2015)], we find that the confined electrolyte lacks local charge neutrality. We show that a DFT based on a bulk-HNC expansion properly accounts for strong electrostatic correlations and allows us to accurately calculate the ionic density profiles between the charged surfaces, even for electrolytes containing trivalent counterions. The DFT allows us to explore the degree of local charge neutrality violation, as a function of plate separation and bulk electrolyte concentration, and to accurately calculate the interaction force between the charged surfaces.
Modification of the phonon spectrum of bulk Si through surface nanostructuring
Authors: Iskandar A. , Gwiazda A. , Huang Y. , Kazan M. , Bruyant A. , Tabbal M. , Lerondel G.
Published: September 2016

In this paper, we present experimental evidence on the change of the phonon spectrum and vibrational properties of a bulk material through phonon hybridization mechanisms. The phonon spectrum in a finite material is strongly affected by the presence of free surfaces, which is the addition of a contribution from an essentially two-dimensional crystal. The phonon spectrum of a bulk material can hence be altered by a hybridization mechanism between confined phonon modes in nanostructures introduced on the surface of a bulk material and the underlying bulk phonon modes. We measured the heat capacities of bare and surface-structured silicon substrates originating from the same silicon wafer. Then, we deduced important features of the phonon spectra of the samples investigated through a rigorous analysis of the measured heat capacity curves. The results show that the shape and size of the nanostructures made on the surface of the bulk substrate have a strong effect on the phonon spectrum of the bulk material.
Structural analysis, optical and dielectric function of [Ba0.9Ca0.1](Ti0.9Zr0.1)O3 nanocrystals
Authors: Herrera-Pérez G. , Morales D. , Paraguay-Delgado F. , Borja-Urby R. , Reyes-Rojas A. , Fuentes-Cobas L. E.
Published: September 2016

This work presents the identification of inter-band transitions in the imaginary part of the dielectric function (ε2) derived from the Kramers–Kronig analysis for [Ba0.9Ca0.1](Ti0.9Zr0.1)O3 (BCZT) nanocrystals synthesized by the modified Pechini method. The analysis started with the chemical identification of the atoms that conform BCZT in the valence loss energy region of a high energy-resolution of electron energy loss spectroscopy. The indirect band energy (Eg) was determined in the dielectric response function. This result is in agreement with the UV-Vis technique, and it obtained an optical band gap of 3.16 eV. The surface and volume plasmon peaks were observed at 13.1 eV and 26.2 eV, respectively. The X-ray diffraction pattern and the Rietveld refinement data of powders heat treated at 700 °C for 1 h suggest a tetragonal structure with a space group (P4 mm) with the average crystal size of 35 nm. The average particle size was determined by transmission electron microscopy.
Electronic bandstructure and optical gain of lattice matched III-V dilute nitride bismide quantum wells for 1.55 μm optical communication systems
Authors: Fan W. J. , Bose Sumanta , Zhang D. H.
Published: September 2016

Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near- and mid-infrared applications, particularly in 1.55 μm optical communication systems. Incorporating dilute amounts of bismuth (Bi) into GaAs reduces the effective bandgap rapidly, while significantly increasing the spin-orbit-splitting energy. Additional incorporation of dilute amounts of nitrogen (N) helps to attain lattice matching with GaAs, while providing a route for flexible bandgap tuning. Here we present a study of the electronic bandstructure and optical gain of the lattice matched GaNxBiyAs1−x−y/GaAs quaternary alloy quantum well (QW) based on the 16-band k·p model. We have taken into consideration the interactions between the N and Bi impurity states with the host material based on the band anticrossing and valence band anticrossing model. The optical gain calculation is based on the density matrix theory. We have considered different lattice matched GaNBiAs QW cases and studied their energy dispersion curves, optical gain spectrum, maximum optical gain, and differential gain and compared their performances based on these factors. The thickness and composition of these QWs were varied in order to keep the emission peak fixed at 1.55 μm. The well thickness has an effect on the spectral width of the gain curves. On the other hand, a variation in the injection carrier density has different effects on the maximum gain and differential gain of QWs of varying thicknesses. Among the cases studied, we found that the 6.3 nm thick GaN3Bi5.17As91.83 lattice matched QW was most suited for 1.55 μm (0.8 eV) GaAs-based photonic applications.
Magneto transport in crossed electric and magnetic fields in compensated bulk GaN
Authors: Syngayivska G. I. , Korotyeyev V. V. , Kochelap V. A. , Varani L.
Published: September 2016

Low-temperature high-field electron transport is studied for compensated bulk GaN subjected to crossed electric and magnetic fields. The electron kinetics, distribution function, and field dependencies of the magneto transport characteristics are analyzed by using the Monte-Carlo method. At zero magnetic field, for an ionized impurity concentration of 1016 cm−3 and an electron concentration of 1015 cm−3, it is shown that dissipative streaming transport with a strong anisotropic electron distribution in the momentum space is realized at electric fields in the range 3−10 kV/cm and for a lattice temperature of 30 K. The magnetic field destroys the dissipative streaming transport. Indeed, for a magnetic field greater than 4 T, the electrons are predominantly confined in a region of the momentum space where their energy is smaller than the optical phonon energy and the strong inelastic scattering by optical phonons is practically eliminated. A quasi-ballistic electron transport occurs in the form of a vortex-like motion in the momentum space. The axis of rotation of this vortex coincides with the average electron momentum. A general analysis of the distribution function suitable for any configuration of the Hall circuit is presented. The main magneto transport characteristics (dissipative current, Hall current, and Hall electric field) are studied for the short and open Hall circuits. We show that the magneto transport measurements can provide valuable information on the main features of the electron distribution function and electron dynamics in GaN. Finally, we suggest that the strong dependency of the dissipative current on the parameters of the Hall circuit can be used for current modulation and current switching.
High pressure and time resolved studies of optical properties of n-type doped GaN/AlN multi-quantum wells: Experimental and theoretical analysis
Authors: Kaminska A. , Jankowski D. , Strak P. , Korona K. P. , Beeler M. , Sakowski K. , Grzanka E. , Borysiuk J. , Sobczak K. , Monroy E. , Krukowski S.
Published: September 2016

High-pressure and time-resolved studies of the optical emission from n-type doped GaN/AlN multi-quantum-wells (MQWs) with various well thicknesses are analysed in comparison with ab initio calculations of the electronic (band structure, density of states) and optical (emission energies and their pressure derivatives, oscillator strength) properties. The optical properties of GaN/AlN MQWs are strongly affected by quantum confinement and polarization-induced electric fields. Thus, the photoluminescence (PL) peak energy decreases by over 1 eV with quantum well (QW) thicknesses increasing from 1 to 6 nm. Furthermore, the respective PL decay times increased from about 1 ns up to 10 μs, due to the strong built-in electric field. It was also shown that the band gap pressure coefficients are significantly reduced in MQWs as compared to bulk AlN and GaN crystals. Such coefficients are strongly dependent on the geometric factors such as the thickness of the wells and barriers. The transition energies, their oscillator strength, and pressure dependence are modeled for tetragonally strained structures of the same geometry using a full tensorial representation of the strain in the MQWs under external pressure. These MQWs were simulated directly using density functional theory calculations, taking into account two different systems: the semi-insulating QWs and the n-doped QWs with the same charge density as in the experimental samples. Such an approach allowed an assessment of the impact of n-type doping on optical properties of GaN/AlN MQWs. We find a good agreement between these two approaches and between theory and experimental results. We can therefore confirm that the nonlinear effects induced by the tetragonal strain related to the lattice mismatch between the substrates and the polar MQWs are responsible for the drastic decrease of the pressure coefficients observed experimentally.
Temperature and doping dependent changes in surface recombination during UV illumination of (Al)GaN bulk layers
Authors: Netzel Carsten , Jeschke Jörg , Brunner Frank , Knauer Arne , Weyers Markus
Published: September 2016

We have studied the effect of continuous illumination with above band gap energy on the emission intensity of polar (Al)GaN bulk layers during the photoluminescence experiments. A temporal change in emission intensity on time scales from seconds to hours is based on the modification of the semiconductor surface states and the surface recombination by the incident light. The temporal behavior of the photoluminescence intensity varies with the parameters such as ambient atmosphere, pretreatment of the surface, doping density, threading dislocation density, excitation power density, and sample temperature. By means of temperature-dependent photoluminescence measurements, we observed that at least two different processes at the semiconductor surface affect the non-radiative surface recombination during illumination. The first process leads to an irreversible decrease in photoluminescence intensity and is dominant around room temperature, and the second process leads to a delayed increase in intensity and becomes dominant around T = 150–200 K. Both processes become slower when the sample temperature decreases from room temperature. They cease for T < 150 K. Stable photoluminescence intensity at arbitrary sample temperature was obtained by passivating the analyzed layer with an epitaxially grown AlN cap layer.
Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas
Authors: Morrison C. , Casteleiro C. , Leadley D. R. , Myronov M.
Published: September 2016

The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.
Enhanced ionic conductivity with Li7O2Br3 phase in Li3OBr anti-perovskite solid electrolyte
Authors: Zhu Jinlong , Li Shuai , Zhang Yi , Howard John W. , Lü Xujie , Li Yutao , Wang Yonggang , Kumar Ravhi S. , Wang Liping , Zhao Yusheng
Published: September 2016

Cubic anti-perovskites with general formula Li3OX (X = Cl, Br, I) were recently reported as superionic conductors with the potential for use as solid electrolytes in all-solid-state lithium ion batteries. These electrolytes are nonflammable, low-cost, and suitable for thermoplastic processing. However, the primary obstacle of its practical implementation is the relatively low ionic conductivity at room temperature. In this work, we synthesized a composite material consisting of two anti-perovskite phases, namely, cubic Li3OBr and layered Li7O2Br3, by solid state reaction routes. The results indicate that with the phase fraction of Li7O2Br3 increasing to 44 wt. %, the ionic conductivity increased by more than one order of magnitude compared with pure phase Li3OBr. Formation energy calculations revealed the meta-stable nature of Li7O2Br3, which supports the great difficulty in producing phase-pure Li7O2Br3 at ambient pressure. Methods of obtaining phase-pure Li7O2Br3 will continue to be explored, including both high pressure and metathesis techniques.
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
Authors: Hong Fang , Yue Binbin , Wang Jianli , Studer Andrew , Fang Chunsheng , Wang Xiaolin , Dou Shixue , Cheng Zhenxiang
Published: September 2016

We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35 K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well.