bluuebunny/crossref_metadata_2025 huggingface dataset:
On classifiers for blind feature‐based automatic modulation classification over multiple‐input–multiple‐output channels
Authors: Kharbech Sofiane , Dayoub Iyad , Zwingelstein‐Colin Marie , Simon Eric Pierre
Published: February 2016

Modulation recognition is crucial for a good environmental awareness required by cognitive radio systems. In this study, the authors design and compare models of four among the most commonly used classifiers for feature‐based automatic modulation classification (FB‐AMC) algorithms. Classifiers whose models will be designed are classification tree, K‐nearest neighbours, artificial neural networks (ANNs), and support vector machines. In this study, they apply some statistical pattern recognition techniques in the context of blind FB‐AMC over multiple‐input–multiple‐output channels. Comparison criteria are classification accuracy and computational complexity. To improve the impartiality of this comparison, each classifier is optimally deployed by selecting its optimal model with respect to their context. Model selection for the classifiers is done using the ‘k‐fold cross‐validation’ model validation technique. The comparison study, within the considered context, shows that ANN classifiers have the best performance/complexity tradeoff.
Scalable macromodelling methodology for the efficient design of microwave filters
Authors: Caenepeel Matthias , Chemmangat Krishnan , Ferranti Francesco , Rolain Yves , Dhaene Tom , Knockaert Luc
Published: February 2016

The complexity of the design of microwave filters increases steadily over the years. General design techniques available in literature yield relatively good initial designs, but electromagnetic (EM) optimisation is often needed to meet the specifications. Although interesting optimisation strategies exist, they depend on computationally expensive EM simulations. This makes the optimisation process time consuming. Moreover, brute force optimisation does not provide physical insights into the design and it is only applicable to one set of specifications. If the specifications change, the design and optimisation process must be redone. The authors propose a scalable macromodel‐based design approach to overcome this. Scalable macromodels can be generated in an automated way. So far the inclusion of scalable macromodels in the design cycle of microwave filters has not been studied. In this study, it is shown that scalable macromodels can be included in the design cycle of microwave filters and re‐used in multiple design scenarios at low computational cost. Guidelines to properly generate and use scalable macromodels in a filter design context are given. The approach is illustrated on a state‐of‐the‐art microstrip dual‐band bandpass filter with closely spaced pass bands and a complex geometrical structure. The results confirm that scalable macromodels are proper design tools and a valuable alternative to a computationally expensive EM simulator‐based design flow.
Radiation characteristics of circular waveguide antenna loaded with ferrite rod
Authors: Sheikh Sharif Iqbal Mitu , Algarni A.M. , Ragheb Hassan
Published: February 2016

High power waveguide antennas are widely used for military and commercial application. In this study, a magnetised ferrite rod loaded circular waveguide antenna (CWA) is presented, where the main beam is steered by varying the external magnetising field (H0). To predict the limitations of this multimode antenna, the modes supported by the structure and the lossy ferrimagnetic resonance region needs to be calculated. An analytical technique, based on boundary values, is used to derive six characteristic equations for the partially ferrite loaded CWA. The non‐trivial solution of the equations is used to plot the mode chart and identify the low‐loss operating region. Using HFSS simulator, the coaxially excited ferrite loaded CWA is optimised to demonstrate a beam scan up to ±30° for H0 = ±142 KA/m. Experimental results are used to verify the simulated scan characteristics of the antenna.
Symmetrical series‐fed dual‐polarised microstrip antenna lattice with odd number of radiating elements
Authors: Slomian Izabela , Gruszczynski Slawomir , Wincza Krzysztof
Published: February 2016

A concept of symmetrical microstrip antenna lattice having an odd number of radiating elements has been proposed. In the presented antenna array, all radiating elements are connected in series along both X and Y axes, which allows for generation of dual polarisation and for reduction of dissipation losses in the feeding network. The proposed approach extends the idea of the previously developed antenna lattice, in which an even number of radiating elements has been considered. This study presents the design procedure for the proposed concept, which is confirmed by simulations and measurements of the developed 5 × 5 antenna lattice operating at 5.4 GHz.
Higher‐mode textile patch antenna with embroidered vias for on‐body communication
Authors: Paraskevopoulos Anastasios , Fonseca Duarte de Sousa , Seager Rob D. , Whittow William G. , Vardaxoglou John Costas , Alexandridis Antonis A.
Published: February 2016

This study presents a wearable textile higher‐mode microstrip patch antenna (HMMPA) that has been designed to radiate omni‐directionally at 2.4 GHz Industrial Scientific and Medical (ISM) band. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that plays an important role in generating the optimal mode for on‐body radiation. The embroidery technique enabled a side‐fed low‐profile antenna which could be placed directly against the body. The proposed textile HMMPA antenna performance is compared with a probe‐fed HMMPA antenna fabricated with rigid copper radiating parts, for both free space and on‐body conditions. The on‐body antenna performance has been tested by performing near‐field measurements of the antenna on a full‐body specific anthropomorphic mannequin phantom in an anechoic chamber. Results show that the proposed textile HMMPA antenna with vias made from conductive thread can radiate on‐body with good efficiency while minimising the radiation in the broadside direction.
When Aesthetics, Surgery, and Psychology Meet: Aesthetic Nasal Proportions in Patients Having Rhinoplasty and Normal Adults
Authors: Naraghi Mohsen , Atari Mohammad , Asadollahi Hossein
Published: February 2016

The aesthetic nasal proportions have played a significant role in rhinoplasty practice. On the other hand, psychological variables also play a crucial role in rhinoplasty. It is of paramount importance for facial plastic surgeons to consider both sides to achieve a more satisfactory outcome. The present study aimed to compare aesthetic nasal proportions between primary rhinoplasty candidates and a demographically matched control group to determine whether patients having rhinoplasty have different aesthetic nasal proportions compared with healthy adults who are not interested in rhinoplasty. Sixty patients having rhinoplasty were selected consecutively from a surgical clinic. A control group (n = 60) with the same demographic characteristics was selected. Photographs were taken using a digital camera on a fixed zoom setting. All images were captured at a distance of 1.5 m. Frontal and right lateral views were used to compare nasolabial angle, nasofrontal angle, nasofacial angle, alar width, intercanthal distance, nasal length, and width-to-length ratio. Independent t tests were used for comparisons. Independent t tests verified that nasofrontal angle, nasal length, and width-to-length ratio were significantly different between the two groups (p < 0.01). Effect sizes ranged between 0.11 and 0.69. Aesthetic proportions were not significantly different in four factors. Nasolabial angle, nasofacial angle, alar width, and intercanthal distance were not different (p > 0.05). Four major aesthetic nasal proportions were statistically similar in a group of patients having rhinoplasty and a control group with no interest in rhinoplasty. Surprisingly, the patients having rhinoplasty showed a mean width-to-length ratio closer to aesthetic ideal. Therefore, applying for rhinoplasty may have strong psychological reasons (e.g., body dysmorphic symptoms) compared with realistic aesthetic appraisals.
Thermodynamics analysis of aluminum plasma transition induced by hypervelocity impact
Authors: Liu Zhixiang , Zhang Qingming , Ju Yuanyuan
Published: February 2016

The production of plasmas during hypervelocity meteoroid and space debris impact has been proposed to explain the presence of paleomagnetic fields on the lunar surface, and also the electromagnetic damage to spacecraft electronic devices. Based on Gibbs' ensemble theory, we deduce Saha equation of state and figure out the ionization degree; further, by using the derivation of Clausius-Clapeyron equation, we obtain the entropy increase and latent heat of plasma transition after vaporization; finally, we analyze the conversion efficiency of kinetic energy into internal energy, present two key contradictions, and revise them with the entropy increase, latent heat, and conversion efficiency. We analyze the aluminum plasma transition from multiple perspectives of the equation of state, latent heat of phase transition, and conversion efficiency and propose the internal energy and impact velocity criterion, based on the laws of thermodynamics.
Perspective: 4D ultrafast electron microscopy—Evolutions and revolutions
Authors: Shorokhov Dmitry , Zewail Ahmed H.
Published: February 2016

In this Perspective, the evolutionary and revolutionary developments of ultrafast electron imaging are overviewed with focus on the “single-electron concept” for probing methodology. From the first electron microscope of Knoll and Ruska [Z. Phys. 78, 318 (1932)], constructed in the 1930s, to aberration-corrected instruments and on, to four-dimensional ultrafast electron microscopy (4D UEM), the developments over eight decades have transformed humans’ scope of visualization. The changes in the length and time scales involved are unimaginable, beginning with the micrometer and second domains, and now reaching the space and time dimensions of atoms in matter. With these advances, it has become possible to follow the elementary structural dynamics as it unfolds in real time and to provide the means for visualizing materials behavior and biological functions. The aim is to understand emergent phenomena in complex systems, and 4D UEM is now central for the visualization of elementary processes involved, as illustrated here with examples from past achievements and future outlook.
An online debris sensor system with vibration resistance for lubrication analysis
Authors: Ding Yongbin , Wang Yanxue , Xiang Jiawei
Published: February 2016

The health condition of the lubricated systems can be directly indicated by the concentration and material type of the abrasive particles, which may provide very early warnings of faults/failures and benefit the condition based maintenance. Oil debris particle detecting techniques are thus important for machinery condition monitoring and fault diagnosis. This work proposes a new structure of online debris sensor (ODS), which applies the radial magnetic field, different from the traditional axial magnetic field. The designed ODS can effectively reduce the interferences of the background noise and the vibration of the machine in operation. Moreover, in order to optimally determine the number of turns of an inductive coil and the current of the drive coils, two methods are developed respectively in this work which can ensure sensitivity and anti-vibration features of the ODS. The instrumentation circuit system for detecting debris particles and sensing signals has been also designed to extract and to record the signatures of particles. The designed ODS device is then applied to analyze micro debris particles in the lubricating system on a test rig. Experimental results have demonstrated that ODS can successfully detect the 120 μm(H) ferrous particles and 500 μm(H) non-ferrous particles under vibration conditions.
Molecular finite-size effects in stochastic models of equilibrium chemical systems
Authors: Cianci Claudia , Smith Stephen , Grima Ramon
Published: February 2016

The reaction-diffusion master equation (RDME) is a standard modelling approach for understanding stochastic and spatial chemical kinetics. An inherent assumption is that molecules are point-like. Here, we introduce the excluded volume reaction-diffusion master equation (vRDME) which takes into account volume exclusion effects on stochastic kinetics due to a finite molecular radius. We obtain an exact closed form solution of the RDME and of the vRDME for a general chemical system in equilibrium conditions. The difference between the two solutions increases with the ratio of molecular diameter to the compartment length scale. We show that an increase in the fraction of excluded space can (i) lead to deviations from the classical inverse square root law for the noise-strength, (ii) flip the skewness of the probability distribution from right to left-skewed, (iii) shift the equilibrium of bimolecular reactions so that more product molecules are formed, and (iv) strongly modulate the Fano factors and coefficients of variation. These volume exclusion effects are found to be particularly pronounced for chemical species not involved in chemical conservation laws. Finally, we show that statistics obtained using the vRDME are in good agreement with those obtained from Brownian dynamics with excluded volume interactions.
The Bardeen–Cooper–Schrieffer functional of superconductivity and its mathematical properties
Authors: Hainzl C. , Seiringer R.
Published: February 2016

We review recent results concerning the mathematical properties of the Bardeen–Cooper–Schrieffer (BCS) functional of superconductivity, which were obtained in a series of papers, partly in collaboration with R. Frank, E. Hamza, S. Naboko, and J. P. Solovej. Our discussion includes, in particular, an investigation of the critical temperature for a general class of interaction potentials, as well as a study of its dependence on external fields. We shall explain how the Ginzburg–Landau model can be derived from the BCS theory in a suitable parameter regime.
A noninvasive high frequency oscillation ventilator: Achieved by utilizing a blower and a valve
Authors: Yuan YueYang , Sun JianGuo , Wang Baicun , Feng Pei , Yang ChongChang
Published: February 2016

After the High Frequency Oscillatory Ventilation (HFOV) has been applied in the invasive ventilator, the new technique of noninvasive High Frequency Oscillatory Ventilation (nHFOV) which does not require opening the patient’s airway has attracted much attention from the field. This paper proposes the design of an experimental positive pressure-controlled nHFOV ventilator which utilizes a blower and a special valve and has three ventilation modes: spontaneous controlled ventilation combining HFOV, time-cycled ventilation combining HFOV (T-HFOV), and continuous positive airway pressure ventilation combining HFOV. Experiments on respiratory model are conducted and demonstrated the feasibility of using nHFOV through the control of fan and valve. The experimental ventilator is able to produce an air flow with small tidal volume (VT) and a large minute ventilation volume (MV) using regular breath tubes and nasal mask (e.g., under T-HFOV mode, with a maximum tidal volume of 100 ml, the minute ventilation volume reached 14 400 ml). In the process of transmission, there is only a minor loss of oscillation pressure. (Under experimental condition and with an oscillation frequency of 2-10 Hz, peak pressure loss was around 0%-50% when it reaches the mask.)
Geometrical and total efficiencies of CdZnTe rectangular parallelepiped detector using arbitrary positioned point, plane, and volumetric sources
Authors: Hamzawy A. , Badawi Mohamed S. , Thabet Abouzeid A. , Gouda Mona M. , El-Khatib Ahmed M. , Abbas Mahmoud I.
Published: February 2016

Gamma-ray detectors are widely used in many fields like environmental measurements, medicine, space science, and industry, where the detector geometrical, total, photopeak efficiencies and peak-to-total ratio could be required. The calculation of the detector efficiency depends mainly on the value of the geometrical efficiency, which depends on the solid angle subtended by the source-detector system. The present work introduces a direct analytical method to calculate the geometrical and total efficiencies of CdZnTe gamma-ray detector using off-axis isotropic radiating γ-ray [point, disk, and cylindrical] sources. To test the validity of the present work, the results are compared with some published data and also to prove how much it is important to determine the efficiency of difficult gamma-ray detection arrangement.
On the connection between dissipative particle dynamics and the Itô-Stratonovich dilemma
Authors: Farago Oded , Grønbech-Jensen Niels
Published: February 2016

Dissipative Particle Dynamics (DPD) is a popular simulation model for investigating hydrodynamic behavior of systems with non-negligible equilibrium thermal fluctuations. DPD employs soft core repulsive interactions between the system particles, thus allowing them to overlap. This supposedly permits relatively large integration time steps, which is an important feature for simulations on large temporal scales. In practice, however, an increase in the integration time step leads to increasingly larger systematic errors in the sampling statistics. Here, we demonstrate that the prime origin of these systematic errors is the multiplicative nature of the thermal noise term in Langevin’s equation, i.e., the fact that it depends on the instantaneous coordinates of the particles. This lead to an ambiguity in the interpretation of the stochastic differential Langevin equation, known as the Itô-Stratonovich dilemma. Based on insights from previous studies of the dilemma, we propose a novel algorithm for DPD simulations exhibiting almost an order of magnitude improvement in accuracy, and nearly twice the efficiency of commonly used DPD Langevin thermostats.
A compact lithium pellet injector for tokamak pedestal studies in ASDEX Upgrade
Authors: Arredondo Parra R. , Moreno Quicios R. , Ploeckl B. , Birkenmeier G. , Herrmann A. , Kocsis G. , Laggner F. M. , Lang P. T. , Lunt T. , Macian-Juan R. , Rohde V. , Sellmair G. , Szepesi T. , Wolfrum E. , Zeidner W. , Neu R. ,   ASDEX Upgrade Team
Published: February 2016

Experiments have been performed at ASDEX Upgrade, aiming to investigate the impact of lithium in an all-metal-wall tokamak and attempting to enhance the pedestal operational space. For this purpose, a lithium pellet injector has been developed, capable of injecting pellets carrying a particle content ranging from 1.82 × 1019 atoms (0.21 mg) to 1.64 × 1020 atoms (1.89 mg). The maximum repetition rate is about 2 Hz. Free flight launch from the torus outboard side without a guiding tube was realized. In such a configuration, angular dispersion and speed scatter are low, and a transfer efficiency exceeding 90% was achieved in the test bed. Pellets are accelerated in a gas gun; hence special care was taken to avoid deleterious effects by the propellant gas pulse. Therefore, the main plasma gas species was applied as propellant gas, leading to speeds ranging from 420 m/s to 700 m/s. In order to minimize the residual amount of gas to be introduced into the plasma vessel, a large expansion volume equipped with a cryopump was added into the flight path. In view of the experiments, an optimal propellant gas pressure of 50 bars was chosen for operation, since at this pressure maximum efficiency and low propellant gas flux coincide. This led to pellet speeds of 585 m/s ± 32 m/s. Lithium injection has been achieved at ASDEX Upgrade, showing deep pellet penetration into the plasma, though pedestal broadening has not been observed yet.
Impact of structure symmetry on light trapping properties of periodic nanostructures: A systematic discussion and quantification
Authors: Wang Puqun , Peters Ian Marius
Published: February 2016

Submicron periodic nanostructures have great potential for light trapping in ultra-thin silicon solar cells. In addition to period, aspect ratio, and structure geometry, the symmetry of the periodic nanostructures also has an impact on their light trapping properties. It has been generally agreed that breaking of symmetry in such structures can enhance light trapping. However, the quantitative relation of asymmetry and light trapping is still an open question. In this work, we suggest a method to quantify the impact of structure symmetry using periodic inverted nanopyramids (PiNPs) as a case study. Different degree of asymmetry is introduced into the structure by changing the cross section of the baseline PiNPs into hexagon, octagon, or circle and by skewing the PiNPs to different degree. We then present a systematic discussion of the impact of broken symmetry on absorption in the context of ultra-thin silicon solar cells. The results demonstrate that the light trapping effects of periodic nanostructures increase with the degree of asymmetry. For the investigated configurations, breaking of symmetry could improve the absorbed photocurrent density by up to 3 mA/cm2. We also propose explanations for the enhanced absorption due to breaking of symmetry from the perspective of diffraction and near-field enhancement.
Quantum anomalous Hall effect in stable dumbbell stanene
Authors: Zhang Huisheng , Zhang Jiayong , Zhao Bao , Zhou Tong , Yang Zhongqin
Published: February 2016

Topological property of the dumbbell (DB) stanene, more stable than the stanene with a honeycomb lattice, is investigated by using ab initio methods. The magnetic DB stanene demonstrates an exotic quantum anomalous Hall (QAH) effect due to inversion of the Sn spin-up px,y and spin-down pz states. The QAH gap is found to be opened at Γ point rather than the usual K and K′ points, beneficial to observe the effect in experiments. When a 3% tensile strain is applied, a large nontrivial gap (∼50 meV) is achieved. Our results provide another lighthouse for realizing QAH effects in two-dimensional systems.
Coexistence of impurity-induced quasi-one-dimensional electronic structure and topological surface states of Bi2Se3
Authors: Shokri R.
Published: February 2016

Using scanning tunneling spectroscopy (microscopy) (STS, STM) in combination with angle-resolved photoelectron spectroscopy (ARPES), we report on the coexistence of the topological surface state with a long range periodic modulation of the electronic structure on the surface of Bi2Se3 at room temperature. The electronic modulation manifests itself as a two-dimensional commensurate superlattice characterized by stripes running parallel to the surface lattice vectors when the near-surface region of samples are doped with trace amounts of iron or cesium. In both cases, the electronic signature is observed in STM only at energies within the valence band more than 130 meV blow the Dirac point energy (ED). ARPES experiments show the presence of intact Dirac cone, indicating that the electronic stripes do not influence the Dirac surface states. We suggest that the stripe states are the bulk properties of Bi2Se3 induced by trace amounts of cesium and iron impurities residing in bismuth and selenium substitutional sites and/or in the van-der-Waals gap.
Compressive and rarefactive dressed solitons in plasma with nonthermal electrons and positrons
Authors: Abdelwahed H. G. , El-Shewy E. K. , Zahran M. A. , Elwakil S. A.
Published: February 2016

The study of dressed solitary ion waves in a collisionless unmagnetized plasma composed warm fluid of ion, nonthermal distributed positrons and electrons are discussed. Concerning nonlinear ion acoustic waves, a reductive perturbation method is applied to obtain the KdV equation in terms of first order potential. Our results exemplify that, if soliton amplitude enlarged, the shape of the wave sidetrack from KdV equation. In order to improve the soliton shape, the perturbed KdV equation is suggest. In particular, the effects of nonthermal positrons and ionic temperature on the electrostatic dressed rarefactive and compressive soliton structures are discussed.
Dielectric relaxation in monoclinic hydroxyapatite: Observation of hydroxide ion dipoles
Authors: Horiuchi N. , Wada N. , Nozaki K. , Nakamura M. , Nagai A. , Yamashita K.
Published: February 2016

We prepared monoclinic hydroxyapatite (HAp) ceramics and measured their dielectric properties. The dielectric dispersion that was observed in the monoclinic HAp consisted of two different relaxations and could be expressed by a summation of two Debye-like relaxations. One relaxation was ascribed to the reorientational motions of OH− ions. The temperature dependence of the relaxation time obeyed the Arrhenius equation. The relaxation time decreased with temperature but decreased discontinuously at 483 K, the monoclinic-hexagonal phase transition temperature of HAp. Correspondingly, the activation energy changed from 0.74 eV for the monoclinic phase to 0.43 eV for the hexagonal phase. The results suggest that the mobility of the OH− ions increases discontinuously with the phase transition to hexagonal HAp. However, critical phenomena, such as critical slowing down, were not observed.
Developing of an environmental cell TEM holder for dynamic in situ observation
Authors: Bataineh Khaled M.
Published: February 2016

This paper deals with the subject of “in situ” development of environmental-transmission electron microscope (E-TEM) holder assemblies. In E-TEM, the sample is continuously subjected to gases as opposed to conventional TEM where the sample is under high vacuum. E-TEM offers the possibility of achieving a new level of material analysis. E-TEM allows obtaining information about chemical information during the reaction at atomic level. Rarefied gas dynamics analysis is used to assess the proposed design. The analysis is focused on determining the molecular distribution inside the vacuum chamber and calculating the impingement rate on the target surface of the specimen. Simulations are performed to predict the molecular interaction with the specimen at given pressures to determine the proper position of a specimen within a vacuum chamber to optimize and predict reaction characteristics. Results of direct simulation Monte Carlo show that the two sides of the sample operate at different temperatures due to the gas flow and experience different molecular distributions.
Observation of 20–400 kHz fluctuations in the U-3M torsatron
Authors: Dreval M. B. , Yakovenko Yu. V. , Sorokovoy E. L. , Slavnyj A. S. , Pavlichenko R. O. , Kulaga A. E. , Zamanov N. V. , Hirose A.
Published: February 2016

First observations of quasi-coherent fluctuations in the frequency range of 20–400 kHz in Alfvén-wave-heated plasmas of the U-3M torsatron are presented. The excitation conditions of these modes depend on the radio frequency antenna type and the plasma density, the appearance of the modes correlating with the presence of both suprathermal electrons and high-energy ions in the plasma, which supports our opinion that the modes are excited by energetic particles. Complicated evolution of the mode frequencies with abrupt changes at the instants of plasma confinement transitions is observed at the initial stage of each discharge. The frequencies become stable at the stage of the plasma current flattop. Raw estimates show that toroidicity-induced Alfvén eigenmodes could be responsible for the 150–400 kHz fluctuations. Low-frequency 20–70 kHz bursts are observed during plasma confinement transitions. The poloidal mode number of one of these bursts with the frequency of 20 kHz burst was determined to be m = 2. This mode rotated in the electron diamagnetic rotation direction with a frequency lower than the geodesic acoustic mode frequency and can be identified as a drift-sound-type mode.
Simple laser stabilization to the strontium 88Sr transition at 707 nm
Authors: Norcia Matthew A. , Thompson James K.
Published: February 2016

We describe frequency stabilization of a laser at 707 nm wavelength using FM spectroscopy in a hollow cathode lamp. The laser is stabilized to the 88Sr metastable 3P2 to 3S1 optical transition. The stabilized laser is utilized for laser-cooling and trapping of strontium atoms. We also briefly describe how the same hollow cathode lamp is used to simultaneously derive a polarization spectroscopy signal for stabilizing the blue-MOT laser at 461 nm.
Influence of matching field on critical current density and irreversibility temperature in YBa2Cu3O7 films with BaMO3 (M = Zr, Sn, Hf) nanorods
Authors: Horide Tomoya , Taguchi Kenta , Matsumoto Kaname , Matsukida Naoki , Ishimaru Manabu , Mele Paolo , Kita Ryusuke
Published: February 2016

The influence of the matching field (BΦ) on critical current density (Jc) and irreversibility temperature (Tirr) in YBa2Cu3O7 films containing BaMO3 (M = Zr, Sn, Hf) nanorods was investigated. It was revealed that the irreversibility temperature normalized by the critical temperature (Tirr/Tc) was influenced by BΦ, for B > BΦ, but Tirr/Tc did not depend on which BaMO3 material was used for B < BΦ, i.e., there was no dependence on nanorod density, diameter, interface sharpness, or Tc in the case of ideal nanorods. However, Jc/Jc(0 T) was found to decrease with increasing BΦ at low magnetic field strengths and to improve at high magnetic field strengths. In addition to Jc being dependent on BΦ, the Tc term in Tirr and Jc(0 T) were also found to have an effect on Jc.
Experimental and theoretical cross sections for positron scattering from the pentane isomers
Authors: Chiari L. , Zecca A. , Blanco F. , García G. , Brunger M. J.
Published: February 2016

Isomerism is ubiquitous in chemistry, physics, and biology. In atomic and molecular physics, in particular, isomer effects are well known in electron-impact phenomena; however, very little is known for positron collisions. Here we report on a set of experimental and theoretical cross sections for low-energy positron scattering from the three structural isomers of pentane: normal-pentane, isopentane, and neopentane. Total cross sections for positron scattering from normal-pentane and isopentane were measured at the University of Trento at incident energies between 0.1 and 50 eV. Calculations of the total cross sections, integral cross sections for elastic scattering, positronium formation, and electronic excitations plus direct ionization, as well as elastic differential cross sections were computed for all three isomers between 1 and 1000 eV using the independent atom model with screening corrected additivity rule. No definitive evidence of a significant isomer effect in positron scattering from the pentane isomers appears to be present.
An opto-mechanical coupled-ring reflector driven by optical force for lasing wavelength control
Authors: Ren M. , Cai H. , Chin L. K. , Huang J. G. , Gu Y. D. , Radhakrishnan K. , Ser W. , Liu A. Q.
Published: February 2016

In this paper, an opto-mechanical coupled-ring reflector driven by optical gradient force is applied in an external-cavity tunable laser. A pair of mutually coupled ring resonators with a free-standing arc serves as a movable reflector. It obtains a 13.3-nm wavelength tuning range based on an opto-mechanical lasing-wavelength tuning coefficient of 127 GHz/nm. The potential applications include optical network, on-chip optical trapping, sensing, and biology detection.
Temperature evolution of defects and atomic ordering in Si1−xGex islands on Si(001)
Authors: Richard M.-I. , Malachias A. , Stoffel M. , Merdzhanova T. , Schmidt O. G. , Renaud G. , Metzger T. H. , Schülli T. U.
Published: February 2016

The observation of atomic ordering and signatures of defects in self-assembled Ge islands using x-ray diffraction techniques have been previously treated as unrelated subjects. However, mutual understanding can be achieved when both subjects are studied in a common frame. Here, we report on measurements and analysis of both defects and atomic ordering in Si1−xGex islands epitaxially grown on Si(001) substrates as a function of growth temperature. By using x-ray diffraction and mapping around a bulk forbidden reflection, defect sizes, and in-plane spacing between nearby dislocations are extracted and related to the composition of the islands. The results fit well with an independent determination using selective wet chemical etching and atomic force microscopy measurements. Moreover, the temperature dependence of the ordered domain size is discussed. Although both atomic ordering and defect formation take place independently in the system, it is found that the relaxation provided by the onset of defects does not affect the formation of ordered domains, recently pointed out to be stabilized by strain and surface equilibrium on islands facets.
Two superconducting domes separated by a possible Lifshitz transition in LaFeAs1−xPxO
Authors: Shen Chenyi , Si Bingqi , Cao Chao , Yang Xiaojun , Bao Jinke , Tao Qian , Li Yuke , Cao Guanghan , Xu Zhu-An
Published: February 2016

Two distinct superconducting (SC) domes were discovered in the phase diagram of P-doped iron pnictide superconductors LaFeAs1−xPxO with x ranging from 0 to 1. The first SC dome is centered around x = 0.3 and then disappears as P content increases to x = 0.5. For x > 0.5, a second SC dome appears, and Tc reaches another maximum at x = 0.7. Although the maximum of Tc in the two domes is close to each other, the estimated upper critical field (Hc2) is much larger in the first SC dome, implying a difference in the nature between the two SC domes. Further band calculations and thermopower measurements suggest that there could be a Lifshitz transition in the electronic structure between the two SC domes.
Finite-element heat-transfer computations for parallel surfaces with uniform or non-uniform emitting
Authors: Ivanova S. M. , Muneer T.
Published: February 2016

Radiation heat transfer has very many applications in building physics. In such studies, one has to deal with radiant energy exchanges between surfaces of different orientation and aspects. Two principal cases that may be cited here are exchanges between (i) surfaces that share a common edge and are at an angle to each other, and (ii) surfaces that are parallel to each other. Examples that may be cited here are walls of buildings and also ceiling and floor areas. In a previous work, the authors presented a generalised, numerical-oriented solution for analysing radiant exchange that belongs to case (i) cited above. In the present article, a generalised treatment for case (ii) is presented. A software tool is also provided for analysing the radiant exchange for surfaces that are parallel to each other and have uniform or non-uniform reflectivity, incident irradiation and/or emission. As a demonstration of the applicability of the present work, calculation of incident reflected irradiation on the walls of urban street canyons with varied orientation and non-uniform reflectivity is presented. Finally, the application of the presently developed tools for enhancing building design has been highlighted.
Power fluctuation minimization in grid connected photovoltaic using supercapacitor energy storage system
Authors: Worku Muhammed Y. , Abido M. A. , Iravani R.
Published: February 2016

In this paper, an efficient control is proposed and implemented to minimize the power fluctuation of grid connected photovoltaic (PV) with supercapacitor energy storage system (SCESS). The SCESS is used to minimize the power fluctuation caused by changes in temperature and irradiation. The optimal size of the SCESS and its control strategy are developed for continuously charging and discharging SCESS to achieve its objectives. Adaptive Neuro-fuzzy Inference System is developed in real time using dSPACE to generate the maximum power from the PV system. The SCESS is integrated with the system through a bi-directional buck boost converter. The system model and the control strategy have been developed in Real Time Digital Simulator (RTDS) that consists of PV array, buck converter, buck-boost converter, and voltage source converter (VSC). To transfer the available DC power to the grid, an independent P-Q control is proposed and implemented for the VSC. The proposed controller is examined through hardware in the loop setup using RTDS and dSPACE 1104 controller. Furthermore, the superiority of the proposed approach has been confirmed by comparing the results with those reported in the literature.
Photoluminescence limiting of colloidal PbS quantum dots
Authors: Ullrich B. , Xi H. , Wang J. S.
Published: February 2016

The exposure of colloidal 2 nm PbS quantum dots to growing continuous wave laser excitation at 532 nm increases the photoluminescence intensity with the square root of the optical stimulus. The results herein in conjunction with previous findings [B. Ullrich and H. Xi, Opt. Lett. 38, 4698 (2013)] advocate the square root trend to be the general limiting function for photo-carrier transport and emission of optically excited nano-sized materials. We further show that the excitation of one electron-hole pair per quantum dot defines the saturation threshold for photoluminescence intensity and dynamic band filling.
Reversible control of magnetism in La0.67Sr0.33MnO3 through chemically-induced oxygen migration
Authors: Grutter A. J. , Gilbert D. A. , Alaan U. S. , Arenholz E. , Maranville B. B. , Borchers J. A. , Suzuki Y. , Liu Kai , Kirby B. J.
Published: February 2016

We demonstrate reversible control of magnetization and anisotropy in La0.67Sr0.33MnO3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La0.67Sr0.33MnO3 leach oxygen from the film through a solid-state redox reaction to form porous Gd2O3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped La0.67Sr0.33MnO3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd2O3 layer and the magnetization of the La0.67Sr0.33MnO3 returns to the uncapped value. These findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.
Nanopillar array band-edge laser cavities on silicon-on-insulator for monolithic integrated light sources
Authors: Lee Wook-Jae , Kim Hyunseok , Farrell Alan C. , Senanayake Pradeep , Huffaker Diana L.
Published: February 2016

A simple and unique laser scheme comprised of a finite-size nanopillar array on a silicon-on-insulator grating layer is introduced for realizing an on-chip monolithically integrated light source. A photonic band-edge mode, confined by the grating substrate in the vertical direction, shows a quality factor as high as 4000. We show that the proposed laser cavity allows direct coupling into a waveguide, which is essential for monolithic integration. In addition, III-V semiconductor nanopillars are grown on a silicon-on-insulator grating substrate in order to demonstrate the feasibility of epitaxy on 3D surfaces. These results provide a practical solution for on-chip integration of a monolithic light source.
Efficient thermal conductance in organometallic perovskite CH3NH3PbI3 films
Authors: Chen Qi , Zhang Chunfeng , Zhu Mengya , Liu Shenghua , Siemens Mark E. , Gu Shuai , Zhu Jia , Shen Jiancang , Wu Xinglong , Liao Chen , Zhang Jiayu , Wang Xiaoyong , Xiao Min
Published: February 2016

Perovskite-based optoelectronic devices have shown great promise for solar conversion and other optoelectronic applications, but their long-term performance instability is regarded as a major obstacle to their widespread deployment. Previous works have shown that the ultralow thermal conductivity and inefficient heat spreading might put an intrinsic limit on the lifetime of perovskite devices. Here, we report the observation of a remarkably efficient thermal conductance, with a conductivity of 11.2 ± 0.8 W m−1 K−1 at room temperature, in densely packed perovskite CH3NH3PbI3 films, via noncontact time-domain thermal reflectance measurements. The temperature-dependent experiments suggest the important roles of organic cations and structural phase transitions, which are further confirmed by temperature-dependent Raman spectra. The thermal conductivity at room temperature observed here is over one order of magnitude larger than that in the early report, suggesting that perovskite device performance will not be limited by thermal conductance.
One electron-controlled multiple-valued dynamic random-access-memory
Authors: Kye H. W. , Song B. N. , Lee S. E. , Kim J. S. , Shin S. J. , Choi J. B. , Yu Y.-S. , Takahashi Y.
Published: February 2016

We propose a new architecture for a dynamic random-access-memory (DRAM) capable of storing multiple values by using a single-electron transistor (SET). The gate of a SET is designed to be connected to a plurality of DRAM unit cells that are arrayed at intersections of word lines and bitlines. In this SET-DRAM hybrid scheme, the multiple switching characteristics of SET enables multiple value data stored in a DRAM unit cell, and this increases the storage functionality of the device. Moreover, since refreshing data requires only a small amount of SET driving current, this enables device operating with low standby power consumption.
Tunable multimode electromagnetically induced absorption transmission in metal-insulator-metal resonators
Authors: Liu Dongdong , Pan Yue-Wu , Sun Yan , Xia Xiushan , Wang Jicheng , Lu Jian
Published: February 2016

The tunable multimode electromagnetically induced absorption (EIA)-like transmission was investigated in a two-ring system. In this system, by introducing asymmetry factor δi = λr - λr′, we provided several ways to modulate the EIA-like transmission spectra. An off-to-on EIA-like response could be realized by changing the radius or the refractive index of the rings. During the off-to-on process, we found the red shift and blue shift effects in the spectra are appeared and the widths of EIA-like dips are broadened. Numerical simulation by finite element method was conducted to verify our discussion. We believe all these would provide guidelines to design the useful EIA-like devices.
Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers
Authors: Bac Seul-Ki , Lee Hakjoon , Lee Sangyeop , Choi Seonghoon , Yoo Taehee , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: February 2016

Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.
Magnetic hyperthermia heating of cobalt ferrite nanoparticles prepared by low temperature ferrous sulfate based method
Authors: Yadavalli Tejabhiram , Jain Hardik , Chandrasekharan Gopalakrishnan , Chennakesavulu Ramasamy
Published: February 2016

A facile low temperature co-precipitation method for the synthesis of crystalline cobalt ferrite nanostructures using ferrous sulfate salt as the precursor has been discussed. The prepared samples were compared with nanoparticles prepared by conventional co-precipitation and hydrothermal methods using ferric nitrate as the precursor. X-ray diffraction studies confirmed the formation of cubic spinel cobalt ferrites when dried at 110 °C as opposed to conventional methods which required higher temperatures/pressure for the formation of the same. Field emission scanning electron microscope studies of these powders revealed the formation of nearly spherical nanostructures in the size range of 20-30 nm which were comparable to those prepared by conventional methods. Magnetic measurements confirmed the ferromagnetic nature of the cobalt ferrites with low magnetic remanance. Further magnetic hyperthermia studies of nanostructures prepared by low temperature method showed a rise in temperature to 50 °C in 600 s.
A novel magnetic field-assisted polishing method using magnetic compound slurry and its performance in mirror surface finishing of miniature V-grooves
Authors: Wang Youliang , Wu Yongbo , Mitsuyoshi Nomura
Published: February 2016

A novel magnetic field-assisted polishing technique was proposed for finishing 3D structured surface using a magnetic compound (MC) slurry. The MC slurry was prepared by blending carbonyl-iron-particles, abrasive grains and α-cellulose into a magnetic fluid which contains nano-scale magnetite particles. An experimental setup was constructed firstly by installing an oscillation worktable and a unit onto a polishing machine. Then, experimental investigations were conducted on oxygen-free copper workpiece with parallel distributed linear V-grooves to clarify the influence of the polishing time and abrasive impact angle on the grooves surface qualities. It was found that (1) the groove form accuracy, i.e. the form retention rate η varied with the polishing locations. Although the form retention rate η deteriorated during the polishing process, the final η was greater than 99.4%; (2) the effective impact angle θm affected the material removal and form accuracy seriously. An increase of the absolute value θm resulted with an increase of material removal rate and a decrease of the form accuracy; (3) the work-surface roughness decreased more than 6 times compared with the original surface after MC slurry polishing. These results confirmed the performance of the proposed new magnetic field-assisted polishing method in the finishing of 3D-structured surface.
Magnetic microstructure in a stress-annealed Fe73.5Si15.5B7Nb3Cu1 soft magnetic alloy observed using off-axis electron holography and Lorentz microscopy
Authors: Kovács A. , Pradeep K. G. , Herzer G. , Raabe D. , Dunin-Borkowski R. E.
Published: February 2016

Fe-Si-B-Nb-Cu alloys are attractive for high frequency applications due to their low coercivity and high saturation magnetization. Here, we study the effect of stress annealing on magnetic microstructure in Fe73.5Si15.5B7Nb3Cu1 using off-axis electron holography and the Fresnel mode of Lorentz transmission electron microscopy. A stress of 50 MPa was applied to selected samples during rapid annealing for 4 s, resulting in uniaxial anisotropy perpendicular to the stress direction. The examination of focused ion beam milled lamellae prepared from each sample revealed a random magnetic domain pattern in the sample that had been rapidly annealed in the absence of stress, whereas a highly regular domain pattern was observed in the stress-annealed sample. We also measured a decrease in domain wall width from ∼ 94 nm in the sample annealed without stress to ∼ 80 nm in the stress-annealed sample.