bluuebunny/crossref_metadata_2025 huggingface dataset:
Distributed space‐time coding with decode‐and‐forward–amplify‐and‐forward selection relaying protocol in cooperative wireless sensor networks
Authors: Zhang Tian
Published: June 2013

Distributed space‐time coding (DSTC) with an efficient relaying protocol, referred to as amplify‐and‐forward and decode‐and‐forward (DF–AF) selection relaying, has not received much attention yet. In the DF–AF selection relaying‐aided DSTC transmissions, each relay could adaptively process the received signal according to its decoding state to improve the performance. In this study, the authors analyse the pairwise error probability (PEP) performance, the diversity order and the union bound on the error probability of the DSTC with DF–AF selection relaying in cooperative wireless sensor networks. More specifically, by introducing a random variable vector to denote the decoding state of the relays, the upper bounds of PEP are derived first for the DSTC with DF–AF selection relaying based on the Chernoff bound. Then, the diversity order and the union bound on the error probability are obtained based on the upper bounds of PEP. Finally, simulation results verify the theoretical analysis and demonstrate that the DSTC with DF–AF selection relaying has better error performance than the DSTC with DF protocol and the DSTC based on AF protocol.
Ultra‐high frequency near‐ground short‐range propagation measurements in forest and plantation environments for wireless sensor networks
Authors: Rao Thipparaju Rama , Balachander Dhanavanthan , Tiwari Nishesh , MVSN Prasad
Published: June 2013

The growing interest in applications of wireless sensor networks (WSNs) in vegetation environment has made it important to understand and predict the impact of vegetation on coverage and signal quality. As most of the proposed vegetation attenuation models are mainly based on measurements in temperate climate their prediction accuracy needs to be tested in tropical climate. With the presence of high humidity and high temperature in the tropical climate the attenuation because of vegetation is bound to increase. Very few researches have been reported about the attenuation because of vegetation related to WSN applications in scrub forest and plantation environments from the regions having tropical climate in Indian subcontinent. This study focuses on short‐range, near to ground received signal strength measurements at 915 and 2400 MHz to evaluate vegetation attenuation models for planning and deployment of wireless sensor communications/networks in tropical climate for precision agriculture and plantation management applications. The measurements have been done in scrub forest, mango and guava plantation environment. It is found that International Telecommunication Union (ITU) Recommendation (ITU‐R) and Weissberger models under predict vegetation because of attenuation, whereas the Cost 235 model has high prediction accuracy in the scrub forest and plantation environments in tropical climate.
Queuing analysis of distributed and receiver‐oriented sensor networks: distributed DS‐CDMA‐based medium access control protocol for wireless sensor networks
Authors: Nagendrappa Thippeswamy Muddenahalli , Takawira Fambirai
Published: June 2013

The DRMACSN (distributed and receiver‐oriented sensor networks) MAC (medium access control) protocol is a receiver‐oriented protocol, which employs channel load sensing scheme to reduce the delay and the energy consumption in the network. This study presents the queuing analysis of the DRMACSN protocol for DS‐CDMA‐based wireless sensor networks. In this study, a discrete‐time Geom/G /1 and M /G /1 multiple vacation queuing models that are used to model the behaviour of the DRMACSN MAC protocol are discussed. The study provides the results for the packet delay of the DRMACSN MAC protocol through simulations and the analysis. The results show that a reduced delay performance can be achieved by implementing the channel load blocking technique.
Energy‐efficient two‐hop extension protocol for wireless body area networks
Authors: Lin Chih‐Shin , Chuang Po‐Jen
Published: June 2013

Recent technological advances in integrated circuits, wireless communications and physiological sensing have allowed ultra‐low power, intelligent‐monitoring tiny devices to settle around the human body, forming a wireless body area network (WBAN) to collect information for a particular purpose. As these tiny devices are low‐weighted and energy‐restricted, ‘energy efficiency’ becomes a key issue. Built in 2012 to facilitate the development of WBAN, the ‘IEEE 802.15.6’ standard operates with one‐hop star and two‐hop restricted tree topologies. Its two‐hop extension protocol has relaying nodes (working as a microhub), process node joining and schedule two‐hop transmissions, thus reducing their lifetime. To reduce the energy consumption and overhead for relaying nodes, the authors introduce a new two‐hop extension protocol which lets the generally better resource‐equipped hub directly transmit packets to the downlink relayed nodes. Analytical and experimental evaluations show that when advancing ‘IEEE 802.15.6’ in extending the lifetime of relaying nodes with less energy consumption and overhead, the authors’ new protocol also retains its advantages, including longer lifetime for relayed nodes and lower bit error rates.
Image‐sensing enabled augmented reality for perceived exertion and cardiorespiratory endurance
Authors: Hsiao Kuei‐Fang , Rashvand Habib F. , Su Jui‐Yuan
Published: June 2013

The global problem of students’ health deterioration has been identified worldwide and the condition is becoming seriously dangerous in many industrial nations where students are under huge pressure for performance. One practical solution to this menacing problem is to enhance the classes by injecting extra movements into the existing lectures by making a better use of computer technology in the form of integrating the augmented reality (AR) through an image‐sensing system to engage the students’ dynamics. The authors’ tests provide extensive measurement results, but here they present those related to the use of the new technology mainly in connection with studying the impact of AR on user perception, namely perceived exertion (PRE), and the physical fitness indicator, cardiorespiratory endurance (CRE). In this study, using the computer technology in the form of AR interacting with images, the authors study the impact of AR and report their experimental measurement results for PRE and CRE as two main factors of students’ physical fitness. In connection with the PRE statistical data, the CRE results for over 364 students show significant improvements in some exercises more than others.
Evaluation of Temporomandibular Joint Total Replacement with Alloplastic Prosthesis: Observational Study of 27 Patients
Authors: Briceño Fernando , Ayala Ronmell , Delgado Karlina , Piñango Sabrina
Published: June 2013

Background

Temporomandibular joint (TMJ) total replacement with alloplastic prostheses has been performed since 1960s. Research in these last two decades has achieved important improvement in the development of biomaterials, design, adaptation, and fixation of the prosthesis components.

Objective

To evaluate total TMJ replacement with alloplastic prostheses.

Methods

We studied 27 patients, between 19 and 73 years old, who had total TMJ uni- or bilateral replacement surgery with custom-made alloplastic prostheses manufactured by TMJ Concepts, Inc. (Ventura, CA) between 1996 and 2011. The general data and preoperative measurements were taken from medical records. Subjective data related to pain, diet consistency, and current quality of life were collected with a questionnaire answered by the patients; measures of maximum interincisal opening and lateral mandibular movements were obtained from direct examination.

Results

We found significant difference ( p < 0.05) comparing pre- to postoperative results about improvement in mouth opening, pain relief, and satisfaction with the surgery and diet consistency.

Conclusion

The results of this study show that total alloplastic TMJ prostheses are an efficient, safe, and stable long-term solution for patients who need TMJ total replacement.
The Role of Investment Management Systems in Regulatory Compliance: A Post-Financial Crisis Study of Displacement Mechanisms
Authors: Gozman Daniel , Currie Wendy
Published: June 2013

The financial crisis of 2007-2009 and the resultant pressures exerted on policymakers to prevent future crises have precipitated coordinated regulatory responses globally. A key focus of the new wave of regulation is to ensure the removal of practices now deemed problematic with new controls for conducting transactions and maintaining holdings. There is increasing pressure on organizations to retire manual processes and adopt core systems, such as Investment Management Systems (IMS). These systems facilitate trading and ensure transactions are compliant by transcribing regulatory requirements into automated rules and applying them to trades. The motivation of this study is to explore the extent to which such systems may enable the alteration of previously embedded practices. We researched implementations of an IMS at eight global financial organizations and found that overall the IMS encourages responsible trading through surveillance, monitoring and the automation of regulatory rules and that such systems are likely to become further embedded within financial organizations. We found evidence that some older practices persisted. Our study suggests that the institutionalization of technology-induced compliant behaviour is still uncertain.
Identifiability and inference of pathway motifs by epistasis analysis
Authors: Phenix Hilary , Perkins Theodore , Kærn Mads
Published: June 2013

The accuracy of genetic network inference is limited by the assumptions used to determine if one hypothetical model is better than another in explaining experimental observations. Most previous work on epistasis analysis—in which one attempts to infer pathway relationships by determining equivalences among traits following mutations—has been based on Boolean or linear models. Here, we delineate the ultimate limits of epistasis-based inference by systematically surveying all two-gene network motifs and use symbolic algebra with arbitrary regulation functions to examine trait equivalences. Our analysis divides the motifs into equivalence classes, where different genetic perturbations result in indistinguishable experimental outcomes. We demonstrate that this partitioning can reveal important information about network architecture, and show, using simulated data, that it greatly improves the accuracy of genetic network inference methods. Because of the minimal assumptions involved, equivalence partitioning has broad applicability for gene network inference.
Self-assembly of binary nanoparticles on soft elastic shells
Authors: Jiang Yangwei , Zhang Dong , Jin Yankang , Zhang Linxi
Published: June 2013

The self-assembly behaviors and phase transitions of binary nanoparticles (NPs) adsorbed on a soft elastic shell are investigated through molecular dynamics simulation. The conformations of adsorbed binary NPs depend on the bending energy Kb of elastic shell and the binding energy D0 between the NPs and the elastic shell. The ordered structures of binary NPs are observed at the moderate adhesive strength and bending energy, in which the small NPs are located near the vertices of regular pentagons as well as the large NPs are distributed along the sides of the regular pentagons. The shape of soft elastic shell can be adjusted by adding the adsorbed binary NPs, and this investigation can provide an effective way to regulate and reshape surfaces or membranes with the sizes in the micrometer range or smaller.
Four-wave mixing in a quantum cascade laser amplifier
Authors: Friedli Peter , Sigg Hans , Hinkov Borislav , Hugi Andreas , Riedi Sabine , Beck Mattias , Faist Jérôme
Published: June 2013

We present the direct observation of four-wave mixing over a detuning range of more than 3 THz in an InGaAs/AlInAs strain-compensated quantum cascade laser (QCL) amplifier emitting at 4.3 μm by simultaneous injection of a single mode QCL and a broadly tunable source. From its intensity, we determine a χ(3) of 0.9 × 10−15 m2 V−2, in good agreement with transport model simulations based on the density matrix approach. This four-wave-mixing mechanism is an important driving factor in mode proliferation occurring in connection with the recent demonstration of comb generation in broadband QCLs.
Positioning dielectric sheets on an electrostatic induction sheet conveyor using a built-in displacement sensor
Authors: Modabberifar M.
Published: June 2013

The present paper proposes a method for positioning and control of dielectric sheet displacement using a novel built-in position sensor for an electrostatic induction sheet conveyor (EISC) which is used for dielectric sheet conveying. The actuator utilizes electrostatic actuation technology based on induced charges and can be used in automated systems for conveying dielectric sheets. The proposed sensing system superimposes a high-frequency sensors signal onto a low-frequency driving signal and uses the actuator's electrodes for position sensing. The operational principle of the built-in sensor is similar to typical capacitance-type linear encoder. In this paper, details of the built-in position sensor based on the exact model of the actuator and feedback position control are reported. The experimental results confirmed that the sensor can work successfully by sharing the same electrodes with the driving operation.
Causal structure of oscillations in gene regulatory networks: Boolean analysis of ordinary differential equation attractors
Authors: Sun Mengyang , Cheng Xianrui , Socolar Joshua E. S.
Published: June 2013

A common approach to the modeling of gene regulatory networks is to represent activating or repressing interactions using ordinary differential equations for target gene concentrations that include Hill function dependences on regulator gene concentrations. An alternative formulation represents the same interactions using Boolean logic with time delays associated with each network link. We consider the attractors that emerge from the two types of models in the case of a simple but nontrivial network: a figure-8 network with one positive and one negative feedback loop. We show that the different modeling approaches give rise to the same qualitative set of attractors with the exception of a possible fixed point in the ordinary differential equation model in which concentrations sit at intermediate values. The properties of the attractors are most easily understood from the Boolean perspective, suggesting that time-delay Boolean modeling is a useful tool for understanding the logic of regulatory networks.
Wetting in electrolyte solutions
Authors: Ibagon Ingrid , Bier Markus , Dietrich S.
Published: June 2013

Wetting of a charged substrate by an electrolyte solution is investigated by means of classical density functional theory applied to a lattice model. Within the present model the pure, i.e., salt-free solvent, for which all interactions are of the nearest-neighbor type only, exhibits a second-order wetting transition for all strengths of the substrate-particle and the particle-particle interactions for which the wetting transition temperature is nonzero. The influences of the substrate charge density and of the ionic strength on the wetting transition temperature and on the order of the wetting transition are studied. If the substrate is neutral, the addition of salt to the solvent changes neither the order nor the transition temperature of the wetting transition of the system. If the surface charge is nonzero, upon adding salt this continuous wetting transition changes to first-order within the wide range of substrate surface charge densities and ionic strengths studied here. As the substrate surface charge density is increased, at fixed ionic strength, the wetting transition temperature decreases and the prewetting line associated with the first-order wetting transition becomes longer. This decrease of the wetting transition temperature upon increasing the surface charge density becomes more pronounced by decreasing the ionic strength.
System of laser pump and synchrotron radiation probe microdiffraction to investigate optical recording process
Authors: Yasuda Nobuhiro , Fukuyama Yoshimitsu , Kimura Shigeru , Ito Kiminori , Tanaka Yoshihito , Osawa Hitoshi , Matsunaga Toshiyuki , Kojima Rie , Hisada Kazuya , Tsuchino Akio , Birukawa Masahiro , Yamada Noboru , Sekiguchi Koji , Fujiie Kazuhiko , Kawakubo Osamu , Takata Masaki
Published: June 2013

We have developed a system of laser-pump and synchrotron radiation probe microdiffraction to investigate the phase-change process on a nanosecond time scale of Ge2Sb2Te5 film embedded in multi-layer structures, which corresponds to real optical recording media. The measurements were achieved by combining (i) the pump-laser system with a pulse width of 300 ps, (ii) a highly brilliant focused microbeam with wide peak-energy width (ΔE/E ∼ 2%) made by focusing helical undulator radiation without monochromatization, and (iii) a precise sample rotation stage to make repetitive measurements. We successfully detected a very weak time-resolved diffraction signal by using this system from 100-nm-thick Ge2Sb2Te5 phase-change layers. This enabled us to find the dependence of the crystal-amorphous phase change process of the Ge2Sb2Te5 layers on laser power.
Understanding tandem organic photovoltaic cell performance
Authors: Lassiter Brian E. , Kyle Renshaw C. , Forrest Stephen R.
Published: June 2013

We develop a framework to understand the performance of tandem organic photovoltaic (OPV) cells consisting of a series-connected stack of an arbitrary number of sub-cells. The power conversion efficiency penalty, Δη, is defined as the loss incurred when the tandem cell is at its maximum power point (MPP) but one or more sub-cells are not operating at their individual MPPs. To minimize Δη, the current at the MPP for each sub-cell must be equal. We also develop a method to calculate the tandem cell spectral mismatch factor and fill factor, showing that they are related to both the fill factors and short circuit currents of all the constituent sub-cells. By including the current generated in the dark, exciton dissociation at the donor-acceptor heterojunction, and photoconductivity, along with current losses due to polaron-pair and bimolecular recombination, we simulate the operation of small molecule bilayer and mixed-layer sub-cells used in the tandem, and from these results derive the behavior of the integrated device. This analysis is used to understand and optimize tandem OPV cell performance.
The canonical work function-strain relationship of the platinum metal: A first-principles approach to metal-gate transistor optimization
Authors: Wang X. F. , He L. , Halas S. , Pieńkos T. , Lin J. G. , Durakiewicz T.
Published: June 2013

Work function Φ is a crucial factor in improving the high-k/metal gate stack. Here we present a systematic study of the strain-dependent work function on the Pt metal gate (100) surface using the first-principles calculation. We find that the compressive strain increases Φ, while the tensile strain decreases its value, with the biaxial strain leading to the maximum change of Φ. We identify the mechanism of Φ modification by analyzing the effect of strain on the bulk electronic structure and surface dipole. Finally, we propose a canonical strain-Φ relationship, which provides a design principle for the work function tuning with strain.
Dynamics study of the OH + NH3 hydrogen abstraction reaction using QCT calculations based on an analytical potential energy surface
Authors: Monge-Palacios M. , Corchado J. C. , Espinosa-Garcia J.
Published: June 2013

To understand the reactivity and mechanism of the OH + NH3 → H2O + NH2 gas-phase reaction, which evolves through wells in the entrance and exit channels, a detailed dynamics study was carried out using quasi-classical trajectory calculations. The calculations were performed on an analytical potential energy surface (PES) recently developed by our group, PES-2012 [Monge-Palacios et al. J. Chem. Phys. 138, 084305 (2013)]10.1063/1.4792719. Most of the available energy appeared as H2O product vibrational energy (54%), reproducing the only experimental evidence, while only the 21% of this energy appeared as NH2 co-product vibrational energy. Both products appeared with cold and broad rotational distributions. The excitation function (constant collision energy in the range 1.0–14.0 kcal mol−1) increases smoothly with energy, contrasting with the only theoretical information (reduced-dimensional quantum scattering calculations based on a simplified PES), which presented a peak at low collision energies, related to quantized states. Analysis of the individual reactive trajectories showed that different mechanisms operate depending on the collision energy. Thus, while at high energies (Ecoll ≥ 6 kcal mol−1) all trajectories are direct, at low energies about 20%–30% of trajectories are indirect, i.e., with the mediation of a trapping complex, mainly in the product well. Finally, the effect of the zero-point energy constraint on the dynamics properties was analyzed.
Acoustic detection and ranging using solvable chaos
Authors: Corron Ned J. , Stahl Mark T. , Chase Harrison R. , Blakely Jonathan N.
Published: June 2013

Acoustic experiments demonstrate a novel approach to ranging and detection that exploits the properties of a solvable chaotic oscillator. This nonlinear oscillator includes an ordinary differential equation and a discrete switching condition. The chaotic waveform generated by this hybrid system is used as the transmitted waveform. The oscillator admits an exact analytic solution that can be written as the linear convolution of binary symbols and a single basis function. This linear representation enables coherent reception using a simple analog matched filter and without need for digital sampling or signal processing. An audio frequency implementation of the transmitter and receiver is described. Successful acoustic ranging measurements in the presence of noise and interference from a second chaotic emitter are presented to demonstrate the viability of the approach.
Ultrathin InAlN/GaN heterostructures on sapphire for high on/off current ratio high electron mobility transistors
Authors: Lugani Lorenzo , Carlin Jean-François , Py Marcel A. , Martin Denis , Rossi Francesca , Salviati Giancarlo , Herfurth Patrick , Kohn Erhard , Bläsing Jürgen , Krost Alois , Grandjean Nicolas
Published: June 2013

We report on InAlN/GaN high electron mobility transistors (HEMTs) grown by metal organic vapor phase epitaxy on sapphire with ultrathin buffers. Two dimensional electron gas (2DEG) exhibiting high mobility (1100 cm2/V s) and low sheet resistivity (356 Ω/□) is achieved at room temperature for a buffer thickness as low as ∼0.1 μm. It is shown that despite a huge dislocation density imposed by this thin buffer, surface roughness is the main factor which affects the transport properties. In addition, sapphire surface nitridation is found to drastically affect the properties of the InAlN/GaN 2DEG. Eventually, HEMTs are processed from these heterostructures. Maximum current densities of 0.35 A/mm and current on-off ratios higher than 109 are measured, which make them suitable for high performance GaN based sensing in harsh environments.
Improved iron gettering of contaminated multicrystalline silicon by high-temperature phosphorus diffusion
Authors: Fenning D. P. , Zuschlag A. S. , Bertoni M. I. , Lai B. , Hahn G. , Buonassisi T.
Published: June 2013

The efficacy of higher-temperature gettering processes in reducing precipitated iron concentrations is assessed by synchrotron-based micro-X-ray fluorescence. By measuring the same grain boundary before and after phosphorus diffusion in a set of wafers from adjacent ingot heights, the reduction in size of individual precipitates is measured as a function of gettering temperature in samples from the top of an ingot intentionally contaminated with iron in the melt. Compared to a baseline 820 °C phosphorus diffusion, 870 °C and 920 °C diffusions result in a larger reduction in iron-silicide precipitate size. Minority carrier lifetimes measured on wafers from the same ingot heights processed with the same treatments show that the greater reduction in precipitated metals is associated with a strong increase in lifetime. In a sample contaminated with both copper and iron in the melt, significant iron gettering and complete dissolution of detectable copper precipitates is observed despite the higher total metal concentration. Finally, a homogenization pre-anneal in N2 at 920 °C followed by an 820 °C phosphorus diffusion produces precipitate size reductions and lifetimes similar to an 870 °C phosphorus diffusion without lowering the emitter sheet resistance.
Large reversible entropy change at the inverse magnetocaloric effect in Ni-Co-Mn-Ga-In magnetic shape memory alloys
Authors: Emre Baris , Yüce Süheyla , Stern-Taulats Enric , Planes Antoni , Fabbrici Simone , Albertini Franca , Mañosa Lluís
Published: June 2013

Calorimetry under magnetic field has been used to study the inverse magnetocaloric effect in Ni-Co-Mn-Ga-In magnetic shape memory alloys. It is shown that the energy dissipated during a complete transformation loop only represents a small fraction (5% to 7%) of the latent heat of the martensitic transition. It is found that the entropy values obtained from isofield temperature scans agree well with those obtained from isothermal magnetic field scans. The reproducibility of the magnetocaloric effect has been studied from isothermal measurements. Reproducible entropy values under field cycling have been found within a temperature interval bounded by the start temperature of the forward transition at zero field and the start temperature of the reverse transition under applied field. Large reversible entropy changes around 11 J/kg K have been found for fields up to 6 T.
Two-dimensional reconfigurable gradient index memory metasurface
Authors: Goldflam M. D. , Driscoll T. , Barnas D. , Khatib O. , Royal M. , Marie Jokerst N. , Smith D. R. , Kim Bong-Jun , Seo Giwan , Kim Hyun-Tak , Basov D. N.
Published: June 2013

Creation and control of spatial gradients in electromagnetic properties is a central theme underlying optical device design. In this work, we demonstrate that through modification of the spatial and temporal distribution of current, we can obtain increased control over the shape of these gradients. We are able to write spatially sharp gradients with ∼50% change in the index of refraction over length scales of only a few wavelengths as observed through diffraction limited terahertz spectroscopy. Furthermore, we assess the potentials for such gradients for beam-steering applications.
Performance limits for field effect transistors as terahertz detectors
Authors: Kachorovskii V. Yu. , Rumyantsev S. L. , Knap W. , Shur M.
Published: June 2013

We present estimates of the performance limits of terahertz detectors based on the field effect transistors (FETs) operating in the regime of broadband detection. The maximal responsivity is predicted for short-channel FETs in the subthreshold regime. The conversion efficiency of the device, Q (defined as the ratio of the power dissipated by radiation-induced dc current to the THz dissipated power) has an absolute maximum as a function of two variables: the power and the frequency of the incoming radiation. The maximal value of Q is on the order of 10%.
Sensing H+ with conventional neural probes
Authors: Trantidou T. , Prodromakis T. , Tsiligkiridis V. , Chang Y.-C. , Toumazou C.
Published: June 2013

In this paper, we demonstrate a technique for transforming commercially available neural probes used for electrical recordings, into chemical sensing devices for detection of ionic concentrations in electrolytes, with particular emphasis to pH. This transformation requires a single post-processing step to incorporate a thin indium tin oxide membrane for sensing H+. Measured results indicate a chemical sensitivity of 28 mV/pH, and relatively low leakage currents (2–10 nA) and drifts (1–10 mV/h). The proposed sensing device demonstrates the possibility of a low-cost implementation that can be reusable and thus versatile, with potential applications in real-time extracellular but mainly intracellular chemical monitoring.
Mobility enhancement in amorphous InGaZnO thin-film transistors by Ar plasma treatment
Authors: Kang Jung Han , Namkyu Cho Edward , Eun Kim Chang , Lee Min-Jung , Jeong Lee Su , Myoung Jae-Min , Yun Ilgu
Published: June 2013

The effects of Ar plasma treatment on the back-channel of amorphous InGaZnO (a-IGZO) thin-film transistors are investigated. A decrease in metallic ion-oxygen bonding in the Ar plasma-treated a-IGZO channel layer was observed by X-ray photoelectron spectroscopy (XPS) depth profile analysis. An increase in the channel charge carrier concentration is estimated from the increased oxygen vacancy atomic ratio using XPS curve decomposition analysis. The plasma-treated area of the a-IGZO back-channel is varied with a photoresist screening layer with a varied open window length (Lp). From the Lp-dependent channel resistance analysis, a carrier concentration-dependent field-effect mobility enhancement is observed.
Carrier density dependence of polarization switching characteristics of light emission in deep-ultraviolet AlGaN/AlN quantum well structures
Authors: Park Seoung-Hwan , Shim Jong-In
Published: June 2013

The carrier density dependence of the polarization switching characteristics of the light emission in deep-ultraviolet AlGaN/AlN quantum well structures was investigated using the multiband effective-mass theory and non-Markovian model. The critical Al composition from transverse electric (TE) to transverse-magnetic (TM) polarization decreases gradually with increasing carrier density. This can be explained by the fact that matrix elements for TM-polarization above the band-edge (k||=0) is much larger than those for TE-polarization. That is, the light emission for TM-polarization becomes larger than that for TE-polarization at higher carrier density because carriers will occupy higher states above k||=0 in the conduction and valence bands. As a result, the critical Al composition is reduced with increasing carrier density. Also, the critical Al composition is observed to decrease with increasing well width.
Budget gains for physical sciences will be uncertain at best
Authors: Kramer David
Published: June 2013

The administration’s spending blueprint for 2014 finds room for a new space mission and increases for the physical sciences, but R&D budget decreases are looming.
Going with the Flow: Sustainable Water Management as Ontological Cleaving
Authors: Lavau Stephanie
Published: June 2013

In this paper, I consider what it might be to do sustainable management through a case study of the Goulburn River in southeastern Australia. Rather than evaluating sustainable development as more or less successful techniques, or as competing discourses of integrating resource use and environmental protection, I attend to sustainable management as ontological work. Engaging with work on relational materiality, I tell of irrigation water and environmental water as emergent in particular gatherings of practices, technologies, and stories of river management and rural life. I argue that sustainable management of the Goulburn's flow performs ontological cleaving: ontological multiplicity is both drawn together and held apart. Through processes of translation and segregation, irrigation water and environmental water are made to intermingle, whilst sustaining ontological difference. This paper contributes to the consideration of how ontological difference is managed and extends recent work on the materialities of water. In doing so, it engages with concerns about the politics of water management and confronts social science critiques about the ambiguity of sustainable development.
Global Colour Model of QCD and Its Relationship to the NJL Model, Chiral Perturbation Theory and Other Models
Authors: Cahill Reginald T. , Gunner Susan M.
Published: June 2013

The Global Colour Model (GCM) of QCD is a very successful model. Not only is
it formally derivable from QCD but under various conditions it reduces to the
NJL model and also to Chiral Perturbation Theory, and to other models. Results
presented include the effective gluon propagator, the difference between
constituent and exact quark propagators, various meson and nucleon
observables, a new form for the mass formula for the Nambu–Goldstone
mesons of QCD, and the change in the MIT bag constant in nuclei.
Quark Triangle Diagrams and Radiative Meson Decays
Authors: Jones N. R. , Liu Dongsheng
Published: June 2013

The radiative meson decays V→
Pγ and P →γγ are
analysed using the quark triangle diagram. Experimental data yield well
determined estimates of the universal quark–antiquark–meson
couplings
gvqq′
and
gpqq′
for the light meson sector. Also predictions for the ratios of neutral to
charged heavy meson decay coupling constants are given and await experimental
confirmation.
Hadron-Nucleon Scattering Lengths from QCD Sum Rules
Authors: Kondo Y. , Morimatsu O. , Nishino Y.
Published: June 2013

Hadron–nucleon scattering lengths are studied by the QCD sum rule. First
we explain our motivation and present the formulation for calculating
hadron-nucleon scattering lengths by the QCD sum rule, where the relation
between the hadron mass in the nuclear medium and the hadron–nucleon
scattering length is also clarified. Secondly we discuss two applications, the
pion–nucleon scattering lengths and the nucleon-nucleon scattering
lengths. In the case of the pion–nucleon scattering length we show that
the results of the QCD sum rule are consistent with the low-energy theorem. In
the case of the nucleon–nucleon scattering lengths we show that the
results of the QCD sum rule are in qualitative agreement with experiment.
Higher Twist Structure Functions
Authors: Signal A. I.
Published: June 2013

I discuss the importance of some of the higher twist structure functions, and
then calculate the twist-two, three and four parton distribution functions
involving two quark unpolarized correlations using the wavefunction of the MIT
bag model.
Quarks in Finite Nuclei
Authors: Guichon P. A. M. , Saito K. , Thomas A. W.
Published: June 2013

We describe the development of a theoretical description of the structure of
finite nuclei based on a relativistic quark model of the structure of the
bound nucleons which interact through the (self-consistent) exchange of scalar
and vector mesons.
Solving the Bethe - Salpeter Equation in Minkowski Space: Scalar Theories and Beyond
Authors: Kusaka K. , Williams A. G. , Simpson K. M.
Published: June 2013

The Bethe–Salpeter equation (BSE) for bound states in scalar theories is
reformulated and solved in terms of a generalized spectral representation
directly in Minkowski space. This differs from the conventional approach,
where the BSE is solved in Euclidean space after a Wick rotation. For all but
the lowest-order (i.e. ladder) approximation to the scattering kernel, the
naive Wick rotation is invalid. Our approach generates
the vertex function and Bethe–Salpeter amplitude for the entire allowed
range of momenta, whereas these cannot be directly obtained from the Euclidean
space solution. Our method is quite general and can be applied even in cases
where the Wick rotation is not possible.
Diffusion of Excited Neutral Particles: Basic Studies and Potential Applications
Authors: Haydon S. C. , Fewell M. P.
Published: June 2013

Recent experiments, carried out in highly pure samples of molecular nitrogen,
have demonstrated the strong influence exerted by neutral, excited metastable
states. The influence of the electronically excited, metastable
N2(A) state on the ionisation growth is demonstrated
through observation of the diffusion phenomena associated with the spatial and
temporal growth of ionisation. Evidence has also emerged demonstrating the
existence of a second metastable particle influence. The diffusion time
observed, however, is not consistent with it being due entirely to an
electronically excited state such as the metastable
N2(a′) state. Rather the observations suggest the
possibility that intersystem crossings between the
N2(a′), the highly vibrationally excited
N2(X) states and the N2(A) state
may be responsible for the increased diffusion time and large molecular size.
The possible relevance of these findings to applications such as plasma
nitriding is canvassed.
Solid State and Magnetic Properties of Pure, Intercalated and Superconducting Fullerenes
Authors: Buntar V. , Sauerzopf F. M. , Weber H. W.
Published: June 2013

A review of some of the solid state and the magnetic properties of fullerenes
is presented. We summarise and discuss experimental results on magnetism of
pure C60, C70 and higher
fullerenes. The main features of the structure and the magnetic properties of
intercalated fullerenes, such as metallofullerenes,
TDAE-C60 and polymeric
A1C60, are presented. Attention is
also paid to the mixed state properties of fullerene superconductors,
especially to the evaluation of the critical fields and the characteristic
lengths of these materials. Some new experimental results on this subject are
also presented.
Polarised Electron Study of Angular Momentum Coupling in the Neon 3p States
Authors: Yu D. H. , Hayes P. A. , Williams J. F. , Furst J. E.
Published: June 2013

The excitation of the 2p5
3p[]3 and 2p5
3p′[½]1 states in the neon 3p
manifold by transversally polarised electrons is studied in the electron
energy region near threshold and beyond. The spin-orbit and exchange
interactions during the excitation are explored by the measurement of
integrated Stokes parameters P2
and P3 for the decay radiation
from these states. Experimental evidence is given for the breakdown of LS
coupling for the neon 3p (J = 1) state and the
important role of spin–orbit and exchange interactions of the atomic
electrons for the excitation of the state. Negative ion resonances strongly
influence the polarisations of the decay radiations.
Atomistic Simulation of Interfaces in Materials: Theory and Applications
Authors: Yarovsky Irene
Published: June 2013

The theoretical background, methodology and some applications of atomistic
simulation of interfaces in materials are described in this paper. Interfaces
between crystalline solids and polymers as well as between two polymers can be
simulated using the methods described. Applications include various interfaces
in a multilayered coated metal system. The methodology enables such properties
as the work of adhesion, interfacial stability, degree of curing in polymers
and permeability to small molecules to be predicted. In addition, interfacial
structure and molecular mechanisms of adhesion and barrier performance of
coatings can be revealed.
Ab Initio Theory of Magnetic Correlations in Itinerant Magnets
Authors: Ling Michael F.
Published: June 2013

One of the challenging problems in modern magnetism is the description of the
paramagnetic state because at finite temperatures the effect of spin
fluctuation plays a fundamental role in altering the electronic structure. In
magnetic metals, the magnetic properties are linked to the underlying
spin-polarised electronic structure in a highly complex manner. In recent
years, first-principles electronic structure theories
based on the spin density functional (SDF) theory have been able to provide a
quantitative account of many ground-state magnetic properties. In this
article, the effect of spin fluctuation on the spin-polarised electronic
structure and thus the magnetic properties will be discussed and its
incorporation into ab initio calculations explained. If the magnetic and
compositional ordering energies of magnetic metallic alloys are close, the
compositional and magnetic correlations can profoundly influence each other. A
theoretical formalism for treating these correlations within the framework of
a first-principles electronic structure theory will be
elaborated and the application to a number of magnetic alloys discussed and
compared with experiments.
Experimental and Theoretical Investigations of Electron Dynamics in a Semiconductor Sinai Billiard
Authors: Micolich A. P. , Taylor R. P. , Newbury R. , Dettmann C. P. , Fromhold T. M.
Published: June 2013

We describe a surface gate-defined mesoscopic semiconductor billiard with a
square geometry which we can evolve continuously to a Sinai geometry by
adjusting the bias on a circular gate located at the centre of the square. We
concentrate on clusters of magneto-conductance structure formed on two
magnetic field scales, which emerge during the transition from the square to
the Sinai geometry. This change in shape is accompanied by a transition from
non-chaotic to chaotic electron dynamics, which has been a topic of
considerable interest for many years. The observed structure is due to quantum
chaotic processes induced by the presence of the circle. Our experimental
results agree with classical dynamics simulations which suggest the two field
scales are determined by two families of electron trajectories which sample
the full geometry and corner sub-geometry. Finally, we report the observation
of striking similarities in the structures observed on the two different field
scales. This indicates the emergence of self-similarity with the introduction
of the circle to the Sinai billiard geometry.
Higher Dimensional Exact Solutions of Einstein’s Field Equations for a Massive Point Particle with Scalar Point Charge
Authors: Joshi M. P. , Khadekar G. S.
Published: June 2013

The exact spherically symmetric static solution of Einstein’s field
equations in higher dimensions for a massive point particle with a scalar
point charge as the source of a massless scalar field is derived in
Schwarzschild coordinates. There exists no Schwarzschild horizon. This result
is an extension in higher dimensions of a similar one obtained by Hardell and
Dehnen (1993) earlier for 4D space-time.
Evaluation of Exchange and Anisotropy Constants of Molecular Species from High Field Mössbauer Spectra
Authors: Cashion J. D. , Shannon S. R.
Published: June 2013

The molecular field equations for the allowed spin directions for dimer and
trimer molecular species have been solved numerically for a range of values of
the exchange and anisotropy interactions and of the applied magnetic field.
The results may be used for the evaluation of the exchange and anisotropy
constants from high field Mössbauer spectra or for selecting the best
conditions for proposed experiments in order to determine these parameters.
Hyperfine Field and Induced Moment of 181Ta in the Rare Earth - Iron Laves Compounds
Authors: Komissarova B. A. , Ryasny G. K. , Shpinkova L. G. , Sorokin A. A. , Tsvyashchenko A. V. , Fomicheva L. N. , Denisova A. S.
Published: June 2013

The hyperfine magnetic fields and their temperature dependence for
181Ta in ErFe2 and
TmFe2 have been measured by the TDPAC method.
Respectively, the following values were obtained at T
≈ 80 K: 16·3(2) T and 17·6(2) T. These data complete those
for other RFe2 Laves phases (except
CeFe2) obtained earlier and are discussed in common in
the framework of the model predicting the induction of the localised 5d moment
at Ta ions due to 5d-3d band hybridisation enhanced by the 4f-5d interaction.
Nuclear Spin-lattice Relaxation Rates of Ni and Ru in Fe
Authors: Beck E. , Brewer W. D. , Funk T. , Klein E.
Published: June 2013

We have determined the nuclear spin-lattice relaxation (SLR) rates of Ni and
Ru as dilute impurities in iron using the method of thermal cycling on
oriented nuclei. The samples were prepared by recoil implantation from the
heavy ion reactions used to produce the radioactive Ni and Ru isotopes
employed in the measurements. In the 3d impurity series, only Sc, Ti, and Cu
remain to complete the systematics of the SLR in iron host; in the 4d series,
values for Zr and Pd are still missing and the datum for Rh has a large
experimental uncertainty. We discuss the comparison with theory and with other
experimental results.
Neutron Magnetic Tomography: A Feasibility Study
Authors: Leeb H. , Hochhold M. , Badurek G. , Buchelt R. J. , Schricker A.
Published: June 2013

Neutron magnetic tomography, the recently proposed extension of the neutron
depolarisation technique, is considered. The available numerical methods for
the analysis of the data are reviewed and the possibility of visualising the
magnetic structure within bulk materials is demonstrated by specific examples.
Various ways to implement the method experimentally are presented. Estimates
of the feasibility in terms of required measuring time indicate that
visualisation is within experimental reach with modern neutron optical
devices.
Recent Developments in Electron Momentum Spectroscopy of Solids
Authors: Vos Maarten
Published: June 2013

With the advent of two-dimensional electron detection, electron momentum
spectroscopy of solids evolved from a spectroscopy in its infancy to a new,
viable technique, looking for its place in solid state physics. Here I give an
overview of the first sets of experiments, the evolution of the interpretation
of these experiments and possible future directions.
One-dimensional Self-organised Structures in Dusty Plasmas
Authors: Tsytovich V. N.
Published: June 2013

A dusty plasma is an open system in which the formation of structures is a
natural phenomenon. The first part of the present review is devoted to an
introduction to dusty plasma physics and a formulation of the new theoretical
kinetic and new hydrodynamic approaches used in subsequent parts. In the new
hydrodynamic approach only dust–plasma particle collisions are taken
into account and the usual binary plasma collisions are neglected. This
description takes into account the possibility of plasma absorption on dust
particles and is appropriate for open systems. The second part of the review
contains a description of one-dimensional plasma–dust self-organised
structures where the energy source corresponds to the plasma fluxes towards
the dust regions from the plasma regions where the dust is absent. The fluxes
are created by the structures in a self-consistent manner to increase the ion
density and decrease the electron density, drift velocity and electrostatic
potential inside the structure. The third part contains the theory of shock
waves in dusty plasmas, modification of the Gugoniot relation and analyses of
the possibility of an increase of dust density behind the shock front. All
parts are based on the modern point of view of the physics of dusty plasmas
and mainly new material is presented. The review is written in the form of
lectures and therefore the references to the existing literature are given in
the text, with more details in the last section devoted to some historical
comment. The references to general reviews are given separately as
[A]-[D].
Studies of the Electron-impact Double-ionisation Process in Magnesium using Coincidence Techniques
Authors: Ford M. J.
Published: June 2013

This article will review recent measurements of the electron-impact
double-ionisation of atomic magnesium. Results for the resonant Auger
double-ionisation process with coincident detection of all three outgoing
electrons, the (e, 3e) experiment, and for the direct double-ionisation
process where only two outgoing electrons are detected, the (e, (3 –
1)e) experiment, will be discussed. The results are analysed with reference to
ionisation mechanisms and comparisons are made with calculated
double-ionisation cross sections.
Future Directions in Electron Momentum Spectroscopy of Matter
Authors: Weigold Erich
Published: June 2013

The development of coincidence spectrometers with multivariable detection
techniques, higher energy kinematics, monochromated and spin-polarised
electron sources, will usher in a new generation of electron momentum
spectroscopy revealing new electronic phenomena in atoms, molecules and
solids. This will be enhanced by developments in target preparation, such as
spin polarised, oriented and aligned atoms and molecules, radicals, surfaces
and strongly correlated systems in condensed matter.