bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling and analysis of heterogeneous cellular networks using a matern cluster process
Authors: Wang Ying , Zhu Qi
Published: October 2017

Heterogeneous cellular networks (HCNs) are usually modelled as a Poisson point process (PPP) due to mathematical tractability. However, in urban areas, small cells are more likely to cluster around hotspots rather than be uniformly distributed. Meanwhile, in reality, small cell locations are not completely independent of the macro base station (MBS) locations. To capture both features, the authors propose a new modelling method considering inter‐tier dependence for a two‐tier HCN, where MBSs follow a PPP, small cells follow a Matern cluster process and are not allowed to be deployed inside the MBS exclusion regions (i.e. within a prescribed distance from each MBS). Approximate expressions of the average coverage probability and the area spectral efficiency (ASE) are obtained, respectively. Simulation results confirm the accuracy of the derivations. It is observed that the model can achieve a good tradeoff between coverage and ASE, and if the small cell density in this model is kept identical to the HCN without inter‐tier dependence, both coverage and ASE can benefit from involving the inter‐tier dependence in the HCN.
Gittins index based control policy for a class of pursuit‐evasion problems
Authors: Tan Cheng , Xu Changbao , Yang Lin , Wong Wing Shing
Published: October 2017

In this study, the authors develop a novel approach to a class of pursuit‐evasion problems modelled in the form of discrete time feedback control systems, where the opposing parties have asymmetric capability. The authors assume the control policy of the evader, described as a random variable, is unknown to the pursuer. This pursuit‐evasion problem is formulated as a quadratic optimisation problem from the perspective of the pursuer. Due to the curse of dimensionality, this pursuit‐evasion problem cannot be practically solved by dynamic programming. In this study, the authors reformulate it as a multi‐armed bandit problem. A heuristic policy based on the Gittins index is proposed to solve this problem, which can be computed based on a forward induction. Simulation results show the proposed policy outperforms a random decision policy.
Simplified fuzzy ‐Padé controller for attitude control of quadrotor helicopters
Authors: Abdollahi Taleb , Salehfard Sepideh , Xiong Cai‐Hua , Ying Jiang‐Feng
Published: October 2017

In this study, a simplified fuzzy‐Padé controller (FPC) for attitude control of quadrotor helicopters is proposed, which is non‐linear, fractional, and model independent. To determine some of the unknown coefficients of the Padé approximant, a proportional–derivative‐type fuzzy logic controller (FLC) is first designed. The responses of the simplified FPC due to step set‐point manoeuvres are compared with those of the FLC in terms of several performance indices such as rise time, settling time, percentage overshoot, integral absolute error, integral of time multiplied by AE, central processing unit time, and energy consumption. Simulation results demonstrate that in each case the proposed FPC presents an improved performance over the FLC. The asymptotic stability of the simplified FPC is proved with Lyapunov stability theory and La Salle's invariant set theorem. Unlike the FLC, the proposed FPC is simple enough to be implemented on the on‐board electronics of the quadrotor. Flight experiments in hovering conditions are given to demonstrate the effectiveness of the simplified FPC.
On certain topological indices of octahedral and icosahedral networks
Authors: Arockiaraj Micheal , Kavitha S. Ruth Julie , Balasubramanian Krishnan , Liu Jia‐Bao
Published: October 2017

The authors have computed topological indices of two metal–organic frameworks of considerable interest in reticular chemistry, namely octahedral and icosahedral networks. The topological indices of these metal–organic frameworks are extremely useful not only in the characterisation of these complex networks but also in obtaining correlation relationships of a number of their properties. In this study, they have obtained exact analytical expressions for a large number of topological indices such as the Randić index, Zagreb index, harmonic index, sum–connectivity index, atom–bond connectivity index, geometric–arithmetic index and their corresponding variants for the two newly constructed networks. Furthermore, they have used the recently introduced partition method by the transitive closure of Djoković–Winkler relation to obtain the Wiener indices for the chain and even cyclic octahedral and icosahedral frameworks with an observation that this method is not successful in computing the Wiener index of these two networks and they pose an open problem for the same.
Common mode voltage reduction technique in a three‐to‐three phase indirect matrix converter
Authors: Rahman Khaliqur , Al‐Emadi Nasser , Iqbal Atif , Rahman Syed
Published: October 2017

In this study, common mode voltage (CMV) reduction using space vector pulse‐width modulation (SVPWM) technique is proposed for a three‐phase induction motor drive fed by a three‐to‐three phase indirect matrix converter (MC). The proposed SVPWM effectively reduces the peak of the CMV without affecting the output voltage gain. By adopting the proposed SVPWM there is no change in the dv/dt of CMV at the terminal of the machine when compared to the existing method. The proposed control is possible by proper placement of zero vectors in the rectifier stage and discarding zero voltage vectors in the inverter stage of the indirect MC. The control technique is implemented in MATLAB/Simulink environment. Hardware setup is developed and control algorithm is implemented using dSPACE working in conjunction with the FPGA interface board. The results of the proposed SVPWM are compared with the existing method of CMV elimination and the improvement is established. The simulation results obtained are verified with the experimental results. The obtained results confirm a reduction of CMV by 48% (peak) and validate the viability of the proposed scheme in a three‐phase induction motor drive system.
Clustering‐based chance‐constrained transmission expansion planning using an improved benders decomposition algorithm
Authors: Li Yunhao , Wang Jianxue , Ding Tao
Published: October 2017

This study presents a chance‐constrained transmission expansion planning (TEP) approach considering the uncertainty of renewable generation and load. On the basis of the underlying idea of density‐based clustering techniques, a novel scenario generation method is presented to characterise the uncertainty sources in the form of representative scenarios. Then, the chance constraints imposed on the sampling scenarios are incorporated into the TEP model to avoid uneconomical transmission investment. The authors further develop an improved Benders decomposition (BD) algorithm with specialised Benders cuts to solve the chance‐constrained TEP problem. Numerical examples are given to verify the validity of the proposed TEP approach in simulating uncertainties and providing reasonable planning schemes. Their results on two test systems also demonstrate that the proposed BD algorithm is computationally efficient in solving this kind of chance‐constrained TEP problem.
Fuzzy enhanced image fusion using pixel intensity control
Authors: Nandal Amita , Bhaskar Vidhyacharan
Published: October 2017

This study is based on improving the visual quality of the images captured under different illumination conditions, i.e. overexposed and underexposed. This study presents a fuzzy image enhancement process based on a finite fuzzy set which is defined to optimise entropy, noise, intensity and edge information. In the proposed fuzzy approach, the overexposed and underexposed images are mapped to form a fuzzy set using membership functions. In the fuzzification process, the degree of belonging of each input to an appropriate fuzzy membership is calculated with respect to intensity, entropy, edge information and background noise. Therefore, the proposed method preserves the details of the image. Indeed, the fuzzy systems are well suited to model the uncertainty that occurs when conflicting operations are performed. Some effective approaches can enhance the image data without increasing noise. However, their ability to reduce the noise during the sharpening process is limited. The proposed method enhances the image by controlling sharpness parameter which affects the visual quality of the image. Both qualitative and quantitative assessments are performed to evaluate the performance of the proposed algorithm.
Side lobe level reduction and gain enhancement of a pyramidal horn antenna in the presence of metasurfaces
Authors: Moradi Anis , Mohajeri Farzad
Published: October 2017

In this study, the design method and experimental presentation of low‐refractive‐index metasurfaces have been reported. These metasurfaces are employed in the interior E‐plane walls of a pyramidal horn antenna. The target is a linearly polarised horn antenna with low side lobe levels (SLLs) and symmetric radiation patterns in the Ku band (13–18 GHz) for satellite communications. Particle swarm optimisation algorithm has been applied to the design procedure to achieve low‐loss dispersion‐engineered metasurfaces with desirable surface impedance characteristics. The metasurfaces were fabricated using precise low‐cost printed‐circuit board technique. There was perfect agreement between the measurement and simulation results. The fabricated horn showed low SLLs and an increase in the gain across the entire bandwidth. The SLLs are reduced by 14–29 dB in the E‐planes and the gain is improved by 1.2–2.3 dB compared with a corresponding conventional horn. The far field radiation patterns of the metahorn verify the metasurface design approach. Furthermore, this method assures a lighter horn with an easier manufacturing technique in comparison with the other conventional horns, such as corrugated horns.
Compact pseudoanalytic formulations of coaxial coil antennas in a cylindrically multilayered medium for well‐logging applications
Authors: Hong Decheng , Yu Yang , Ren Yi , Huang Wei‐Feng , Liu Qing Huo
Published: October 2017

In this study, the authors present a set of compact and no‐overflow formulations to calculate the response of logging tools with coaxial coil antennas in a concentric cylindrically multilayered formation. It can be applied to fast forward computation and the inverse problem for electromagnetic well‐logging. The tool mandrel can be cylindrically multilayered, and the electrical parameters of each layer are arbitrary. In contrast with previous formulations, they adopt the novel reflection and transmission coefficients in the authors’ formulations so that the notorious overflow problem for numerical computation can be obviated. Numerical results in comparison with those from other approaches have demonstrated the validity and stability of their new formulations.
Combining heuristic and exact approaches for solving the routing and spectrum assignment problem
Authors: Hai Dao Thanh , Morvan Michel , Gravey Philippe
Published: October 2017

Efficient algorithms for solving the routing and spectrum assignment (RSA) problem in flex‐grid optical networks are of paramount importance to leverage network efficiency. Exact approaches based on integer linear programming (ILP) models are known to be computationally hard and hence, difficult to solve for realistic models while heuristics have inherent downsize of local optimal trapping. In addressing those issues, this paper firstly presents a novel and efficient heuristic based on the genetic algorithm (GA) to provide (near‐) optimal solutions to the RSA problem. The effectiveness of the GA‐based algorithm is benchmarked against typically used reference heuristics for a set of network scenarios and it is shown that in addition to the better performance than conventional heuristics in the literature, the proposed GA technique indeed could achieve optimal solutions in most cases while the running time is still manageable. Secondly, we propose to make use of efficient solutions from the heuristic approaches to set the upper‐bound and warm‐start point for ILP formulation. This combination has been shown very productive in enhancing running time performance and increasing the capability of achieving an optimal solution and/or improving the solution quality in a given time span compared with traditional ways for solving ILP models.
Approach to dynamic voltage stability analysis for DFIG wind parks integration
Authors: Baa Wafaa Majid , Dessaint Louis‐A
Published: October 2017

In this study, an improved voltage stability index that can evaluate the unstable behaviour of the power system with doubly‐fed induction generator (DFIG) wind parks integration is presented. Accordingly, voltage stability constrained optimal power flow (VSC‐OPF) is studied including an improved impedance‐based (IB) index. In particular, this study has two main contributions. First, it proposes an IB index with consideration of DFIG capability curve limits and on‐load tap changer (OLTC) behaviour. The proposed voltage stability index can detect precisely the voltage collapse, especially after the occurrence of a given contingency due to the dynamic elements of the system. In this study, a model is proposed for DFIG capability curve limits that can be integrated to the internal circuit of the generator. In particular, the proposed model can be appended to impedance matching theory. Furthermore, the OLTC model is added to this index. The index uses the concept of the coupled single‐port circuit. The second contribution proposes a VSCOPF with an improved IB index that is also compared with three existing VSC‐OPF methods in stressed and single line outage conditions. These approaches are tested and validated on modified WSCC test system, IEEE 39‐bus, IEEE 57‐bus and Polish 2746‐bus systems.
Optimisation and optimal geometry design for thermal energy storages in high temperature concentrating solar power
Authors: Berrhazi Samir , Ahmed Ouammi , Benchrifa Rachid
Published: October 2017

This study presents a comprehensive decision support model formulated as a finite‐horizon‐constrained optimisation problem to optimally design the geometry variables that maximise the net present value (NPV) associated to the thermal energy storage (TES) investment over a given time horizon. This study faces one of the main problems in a TES, which is to react to the unpredictable production/demand processes, by determining a high‐level optimal size of the TES maximising the NPV that captures the storage benefits as well as detailed fixed and variable costs over a chosen time horizon. The storage benefits are defined, so that they model the costs of the expected discharged thermal energy over a year. Moreover, the authors account for various costs model regarding the total costs of the heat transfer tube material, the storage material, and the insulation material. The proposed decision model can be considered as practical framework that can support engineers and decision makers in the process of design and planning of future. They investigate performance and efficiency of the proposed decision support system framework through representative case studies. Numerical studies demonstrate the usefulness and efficacy of the proposed decision model.
Quick and oscillation free peak power estimation using SEHC algorithm for single‐sensor‐based PV‐fed battery charging
Authors: Kumar Nishant , Hussain Ikhlaq , Singh Bhim , Panigrahi Bijaya Ketan
Published: October 2017

This study deals with a new version of hill‐climbing (HC) algorithm for maximum power peak estimation of the solar photovoltaic (PV) panel, which has self‐estimation (SEn) and decision‐taking ability. Moreover, it is based on a single sensor, which is applicable for the PV array‐fed battery charging. The working principle of Self‐Estimated HC (SEHC) algorithm is based on three consecutive operating points on the power‐current characteristic. By using perpendicular line analogy (PLA), these points decide direction, and an optimised operating position for next iteration, which is responsible for quick maximum power point tracking as well as improved dynamic performance. Moreover, in every new iteration, the step size is reduced by 90% from the previous step size, which provides an oscillation‐free steady‐state performance. Owing to a single sensor, the computational burden, as well as calculation complexity of the SEHC algorithm is less, so it can be simply implemented on a cheaper microcontroller. The effectiveness of the proposed technique is validated by MATLAB simulation as well as tested on the experimental prototype. Moreover, the performance of SEHC algorithm is compared with recent state‐of‐the‐art techniques. The highly suitable and satisfactory results of SEHC algorithm show the superiority over the state‐of‐the‐art methods.
Stokes parameters and DOA estimation of polarised sources with unknown number of sources
Authors: Chang Wenxiu , Ru Jingpei , Deng Lifei
Published: October 2017

In this study, the problem of Stokes parameters and direction‐of‐arrival estimation of polarised sources is addressed based on the block‐sparsity reconstruction, in case of an unknown number of sources. Since Stokes parameters have four components, the block‐sparsity model of polarised sources is introduced by employing the difference coarray of the coprime array with cross‐dipole sensors. In case of an unknown number of sources, a novel estimate approach is proposed by combining the block orthogonal matching pursuit (BOMP) algorithm with the deterministic maximum likelihood (DML). In the proposed approach, the DML test step and refining grid step are added in each iteration of BOMP to identify the number of sources and to reduce the estimation error incurred by the grid mismatch. This approach has low computational complexity and is suitable for both the completely polarised and partially polarised sources. Simulations are used to verify the performance of the proposed approach.
Numerical simulation of electromagnetic coupling in explicitly meshed wiring looms and bundles
Authors: Meng Xuesong , Sewell Phillip , Vukovic Ana , Zhang Zhewen , Benson Trevor M. , Jones Chris , Earl Simeon , Walton Rebecca , South Geoff
Published: October 2017

In this study, the unstructured transmission line modelling (UTLM) method based on a tetrahedral mesh is applied to model the electromagnetic coupling into wire looms and bundles with multiple cores that are typical of an aircraft system, when they are exposed to plane wave illuminations. The impact on the electromagnetic coupling into wires of both bundle configuration and the positioning of the bundle relative to simple structures are investigated using the UTLM method with explicit meshing of the wires. The work not only confirms that UTLM method as a powerful tool for dealing with wire looms and bundles but provides invaluable information on the margins to be expected in key experimental waveform parameters such as peak amplitude and frequency response.
The diffuse molecular component in the nuclear bulge of the Milky Way
Authors: Riquelme D. , Bronfman L. , Mauersberger R. , Finger R. , Henkel C. , Wilson T. L. , Cortés-Zuleta P.
Published: October 2017

Context. The bulk of the molecular gas in the central molecular zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from >20 K in the coldest and densest regions (n ~ 104-5 cm-3) up to more than 100 K for densities of about n ~ 103 cm-3. Recently, a more diffuse, hotter (n ~ 100 cm-3, T ~ 250 K) gas component was discovered through absorption observations of H3+. This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy.

Aim. We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption.

Methods. Using the Atacama Large (sub)Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located toward the Galactic bulge region at (l, b) = (−2°.13, −1°.0), but outside the main molecular complexes.

Results. ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components at ~0, −153, and −192 km s−1. The component at ~0 km s−1 could represent gas in the Galactic disk while the velocity components at −153, and −192 km s−1 likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.
An Efficient Fe/H2O Medium in situ Reduction and Cyclization Reaction for the Synthesis of Pyrazolo[3,4-a]acridin-10-one and Pyrazolo[4,3-a]acridin-10-one Derivatives
Authors: Rong Liangce , Xu Hui , Li Lei , Lin Cong , Kou Wang , Ling Zhi , Xu Zhongyun
Published: October 2017

An efficient and simple method for the synthesis of pyrazolo[3,4-a]acridine and pyrazolo[4,3-a]acridine derivatives directly form nitro compounds by in situ reduction and cyclization reaction under Fe/H2O medium is reported. Compared to amino compounds, nitro compounds are more stable and easier to obtain. In addition, because iron is a nontoxic, inexpensive, and environmentally friendly reductant, this method is especially suitable for organic synthesis. The other advantages of this process are cheap raw materials, less pollution, and wide substrate range.
Cervical Intramedullary Schwannoma with Syrinx: Case Report and Review of the Literature
Authors: AlQarni Abdulaziz , AlArifi A. , Alassiri Ali , Kouli Amjed , Abbas M.
Published: October 2017

Schwannoma is a nerve sheath tumor originating from the Schwann cell. It is benign in nature and it arises from anywhere where Schwann cells can be found. It is rarely found in the parenchyma of the spinal cord. Intramedullary schwannomas (or neurilemmomas) without evidence of neurofibromatosis are rare spinal cord tumors. Intramedullary schwannoma was first reported in 1932 by Penfield. Our patient presented with neck pain, gradually worsening, weakness in the right upper and lower limbs, numbness in both shoulders, and a decrease in the grasping strength of both hands over a 4-year period. A magnetic resonance imaging of the spine showed a heterogeneously enhancing mass in the cervical spinal cord extending from the C2 to T1 levels with associated hemorrhagic changes. Histologically, the tumor was found to be composed of bland spindle cells with blunt-ended and sometimes wavy nuclei admixed with hyalinized vasculature. Surrounding reactive spinal cord parenchyma with frequent Rosenthal fibers was also observed. Focal Verocay bodies were evident, and with immunohistochemistry, there was diffuse and strong positivity for S100, which is confirmatory for the diagnosis of schwannoma. We report a case of cervical intramedullary schwannoma presented with syringobulbia in a young adult.
Validation of a Patient-Completed Caprini Risk Score for Venous Thromboembolism Risk Assessment
Authors: Fuentes H. , Paz L. , Al-Ogaili A. , Andrade X. , Oramas D. , Salazar-Adum J. , Diaz-Quintero L. , Acob C. , Tafur A. , Caprini J.
Published: October 2017

Introduction Individualized risk assessment for venous thromboembolism (VTE) using the Caprini risk score (CRS), coupled with targeted prophylaxis based on the score, is effective in reducing postoperative VTE. Critics contend that using this tool is time consuming for health care providers. We decided to create a patient-completed CRS and conducted a prospective study to compare the scores calculated by a patient with those calculated by a blinded physician for the same patient.

Methods In phase 1, we interviewed patients in our deep vein thrombosis (DVT) support group who had a history of thrombosis and included their family members to determine areas of misunderstanding in the original CRS. We created a patient-completed form based on these interviews. In phase 2, we further optimized the questions after a CRS-trained, blinded physician scored 20 hospitalized patients during the pilot study. In the final (third) phase, we measured the agreement level between the new form filled out by the trained physicians and those filled out by the patients. The study was approved by our local institutional review board. Using PASS version 11, we determined that a sample size of 37 individuals achieves a power of 80%, to detect a 0.1 difference between the null hypothesis correlation of 0.5 and the alternative hypothesis correlation of 0.7 using a two-sided hypothesis test with a significance level of 0.05. We tabulated the individuals' answers and categorized the scores by using SPSS version 23 to estimate the kappa value, linear correlation, and the Bland–Altman test. A kappa value greater than 0.8 indicated an “almost perfect agreement.”

Results We tested the first patient-completed CRS version (phase 2) in a 20-patient pilot study. A poor agreement was observed with the body mass index (BMI) responses in multiple iterations, and so we excluded the BMI calculation from the final patient-completed CRS form. We recruited 42 patients with an average age of 55, mostly female (45%), who completed less than college education (62%) to fill out the updated CRS form (phase 3). An almost perfect agreement was found for both the individual questions and the overall score comparing physician and patient answers, resulting in a high correlation (r = 0.95). In Bland–Altman, we did not find any trend for extreme values.

Conclusion We created and validated a patient-completed CRS form that has an excellent agreement level with the physician-completed form. From the results, the physician only needs to calculate the BMI. The average time for a patient to complete the form was 5 minutes. The average time for the physician to finalize the score was approximately 6 minutes. Implementation studies are needed to assess the correlation of the aggregated score, derived from this form, with the occurrence of perioperative VTE.
Vorsicht Brandgefahr
Authors: Schwab Gisela
Published: October 2017

Checkliste Die Gefahr, dass es im OP zu Verbrennungen am Patienten oder zu
einer Explosion am Tisch kommt, wird häufig unterschätzt. Wir stellen Ihnen die
häufigsten Gefahrenquellen vor und geben Tipps, wie sich Brände oder
Verbrennungen vermeiden lassen.
HIV und Malaria: Auswirkungen und Interaktionen zwischen Antimalariamedikamenten und antiretroviraler Therapie
Authors: Brehm Thomas , Schmiedel Stefan
Published: October 2017

HIV und Malaria sind weltweit 2 der wichtigsten Infektionskrankheiten und gemeinsam für über 2 Mio. Todesfälle pro Jahr verantwortlich. Koinfektionen treten insbesondere in Subsahara-Afrika häufig auf. Die Infektionen scheinen sich gegenseitig zu begünstigen und den jeweiligen Krankheitsverlauf auf vielfältige Weise negativ zu beeinflussen. HIV-positive Reisende in Malariaendemiegebiete sind keinem allgemein erhöhten Malariarisiko ausgesetzt, jedoch müssen bei Chemoprophylaxe oder notfallmäßigen Selbstbehandlung vielfältige Wechselwirkungen zwischen Antimalariamedikamenten und antiretroviraler Therapie beachtet werden.
Weitere Untersuchungen und Surveillance bei Risikogruppen notwendig
Authors: Burchard Gerd
Published: October 2017

Migranten und Asylbewerber aus Hochinzidenzländern der Tuberkulose (TB) haben ein erhöhtes Risiko, bereits bei der Einreise in andere Länder mit niedriger TB-Inzidenz aktiv an einer TB erkrankt oder latent mit M. tuberculosis infiziert zu sein. Eine andere Frage ist jedoch, wie hoch die TB-Inzidenz bei denjenigen Migranten aus Hochinzidenzländern ist, bei denen sich im Screening zunächst keine aktive TB nachweisen ließ. Hierzu gibt es bisher kaum Daten.
Mediated populism, culture and media form
Authors: Higgins Michael
Published: October 2017

This comment seeks to identify some key concerns in the study of mediated populism. The paper highlights the relationship between populism and political conditions, noting that the weak party structures and non-conventional party-media relations that characterise populist actors applies across the political left and right, who engage strategically according to media conditions. In setting out the terms in which mediated populism operates, the paper stresses the turn to emotionality in media, with a particular prominence on the expression of aggressiveness. It links with the rise of participatory media, with an attendant shift in the style and form of language to characterise political discussion and influences on legitimate political speech. The paper then looks at the use of “fake news” as a means of positioning media within the discredited elite, warranting the easy dismissal of hostile content. While showing how the political and media environment provides fertile grounds for populism, and the extent to which populism is encouraged by media affordances, the article concludes by recommending the purposeful cultivation by media of alternative and proactive forms of inclusion and emotional engagement.
Experimental characterization of the transition to coherence collapse in a semiconductor laser with optical feedback
Authors: Panozzo M. , Quintero-Quiroz C. , Tiana-Alsina J. , Torrent M. C. , Masoller C.
Published: October 2017

Semiconductor lasers with time-delayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity time-traces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of low-frequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the inter-dropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the well-known time-delayed Lang–Kobayashi model are in good qualitative agreement with the observations.
Optoelectronics of inverted type-I CdS/CdSe core/crown quantum ring
Authors: Bose Sumanta , Fan Weijun , Zhang Dao Hua
Published: October 2017

Inverted type-I heterostructure core/crown quantum rings (QRs) are quantum-efficient luminophores, whose spectral characteristics are highly tunable. Here, we study the optoelectronic properties of type-I core/crown CdS/CdSe QRs in the zincblende phase—over contrasting lateral size and crown width. For this, we inspect their strain profiles, transition energies, transition matrix elements, spatial charge densities, electronic bandstructures, band-mixing probabilities, optical gain spectra, maximum optical gains, and differential optical gains. Our framework uses an effective-mass envelope function theory based on the 8-band k ⋅ p method employing the valence force field model for calculating the atomic strain distributions. The gain calculations are based on the density-matrix equation and take into consideration the excitonic effects with intraband scattering. Variations in the QR lateral size and relative widths of core and crown (ergo the composition) affect their energy levels, band-mixing probabilities, optical transition matrix elements, emission wavelengths/intensities, etc. The optical gain of QRs is also strongly dimension and composition dependent with further dependency on the injection carrier density causing the band-filling effect. They also affect the maximum and differential gain at varying dimensions and compositions.
Generation of underwater discharges inside gas bubbles using a 30-needles-to-plate electrode
Authors: Chen Zhiqiang , Krasik Yakov E. , Cousens Samuel , Ambujakshan Arun T. , Corr Cormac , Dai Xiujuan J.
Published: October 2017

Underwater discharges inside helium (He) gas bubbles were generated using a 30-needles-to-plate electrode system with the gas flowing through the needles. The set-up allows continuous treatment of flowing water. The plasma electron temperature and density determined from spectral line intensities and profiles of the Hα and Hβ hydrogen lines were found to be 1.1 ± 0.6 eV and ∼5 × 1016 cm−3, respectively. These parameters are comparable with those of plasmas generated by other underwater gas bubble discharges for the production of OH radicals. The two main long-lived species, hydrogen peroxide (H2O2) and nitrate ions (NO3−), produced in plasma treated water were measured. It was found that without a continuous water flow, the energy yield of H2O2 was comparable with other underwater discharges, while with a continuous flow, the production of H2O2 appeared to be somewhat reduced by nitrites from dissolved air.
Real and financial market interactions in a multiplier-accelerator model: Nonlinear dynamics, multistability and stylized facts
Authors: Cavalli F. , Naimzada A. , Pecora N.
Published: October 2017

In the present paper, we investigate the dynamics of a model in which the real part of the economy, described within a multiplier-accelerator framework, interacts with a financial market with heterogeneous speculators, in order to study the channels through which the two sectors influence each other. Employing analytical and numerical tools, we investigate stability conditions as well as bifurcations and possible periodic, quasi-periodic, and chaotic dynamics, enlightening how the degree of market interaction, together with the accelerator parameter and the intervention of the fiscal authority, may affect the business cycle and the course of the financial market. In particular, we show that even if the steady state is locally stable, multistability phenomena can occur, with several and complex dynamic structures coexisting with the steady state. Finally, simulations reveal that the proposed model is able to explain several statistical properties and stylized facts observed in real financial markets, including persistent high volatility, fat-tailed return distributions, volatility clustering, and positive autocorrelation of absolute returns.
Cluster decomposition of full configuration interaction wave functions: A tool for chemical interpretation of systems with strong correlation
Authors: Lehtola Susi , Tubman Norm M. , Whaley K. Birgitta , Head-Gordon Martin
Published: October 2017

Approximate full configuration interaction (FCI) calculations have recently become tractable for systems of unforeseen size, thanks to stochastic and adaptive approximations to the exponentially scaling FCI problem. The result of an FCI calculation is a weighted set of electronic configurations, which can also be expressed in terms of excitations from a reference configuration. The excitation amplitudes contain information on the complexity of the electronic wave function, but this information is contaminated by contributions from disconnected excitations, i.e., those excitations that are just products of independent lower-level excitations. The unwanted contributions can be removed via a cluster decomposition procedure, making it possible to examine the importance of connected excitations in complicated multireference molecules which are outside the reach of conventional algorithms. We present an implementation of the cluster decomposition analysis and apply it to both true FCI wave functions, as well as wave functions generated from the adaptive sampling CI algorithm. The cluster decomposition is useful for interpreting calculations in chemical studies, as a diagnostic for the convergence of various excitation manifolds, as well as as a guidepost for polynomially scaling electronic structure models. Applications are presented for (i) the double dissociation of water, (ii) the carbon dimer, (iii) the π space of polyacenes, and (iv) the chromium dimer. While the cluster amplitudes exhibit rapid decay with an increasing rank for the first three systems, even connected octuple excitations still appear important in Cr2, suggesting that spin-restricted single-reference coupled-cluster approaches may not be tractable for some problems in transition metal chemistry.
Density functional theory formulation for fluid adsorption on correlated random surfaces
Authors: Aslyamov Timur , Khlyupin Aleksey
Published: October 2017

We provide novel random surface density functional theory (RSDFT) formulation in the case of geometric heterogeneous surfaces of solid media which is essential for the description of thermodynamic properties of confined fluids. The major difference of our theoretical approach from the existing ones is a stochastic model of solid surfaces which takes into account the correlation properties of geometry. The main building blocks are effective fluid-solid potentials developed in the work of Khlyupin and Aslyamov [J. Stat. Phys. 167, 1519 (2017)] and geometry-based modification of the Helmholtz free energy for Lennard-Jones fluids. The efficiency of RSDFT is demonstrated in the calculation of argon and nitrogen low temperature adsorption on real heterogeneous surfaces (BP280 carbon black). These results are in good agreement with experimental data published in the literature. Also several models of corrugated materials are developed in the framework of RSDFT. Numerical analysis demonstrates a strong influence of surface roughness characteristics on adsorption isotherms. Thus the developed formalism provides a connection between a rigorous description of the stochastic surface and confined fluid thermodynamics.
Potential energy surfaces for O + O2 collisions
Authors: Varga Zoltan , Paukku Yuliya , Truhlar Donald G.
Published: October 2017

We present global potential energy surfaces for nine adiabatic electronic states of O3, namely, 1 1A′, 2 1A′, 1 1A″, 1 3A′, 2 3A′, 1 3A″, 1 5A′, 2 5A′, and 1 5A″. These are the states of O3 that are accessed in electronically adiabatic collisions of a ground-state triplet O2 molecule with a ground-state triplet O atom. The surfaces are based on XMS-CASPT2 electronic structure calculations with dynamically scaled external correlation. The active space has 12 active electrons distributed in the nine 2p orbitals. The adiabatic surfaces are fitted to analytic functions using a many-body expansion where the pairwise additive term is fitted to an accurate diatomic potential including a damped dispersion term, and the many-body part, without disconnected terms, is fitted with permutationally invariant polynomials in mixed exponential-Gaussians to the electronic structure data points. The selection and weighting of points for the fits are designed to produce surfaces suitable for describing energy transfer and dissociation in high-energy collisions.
Atomic disorder induced modification of magnetization in MnCrVAl
Authors: Herran Juliana , Dalal Rishabh , Gray Paul , Kharel Parashu , Lukashev Pavel V.
Published: October 2017

We have investigated the physical mechanism behind magnetization reduction in a potential spin-gapless semiconducting compound MnCrVAl by analyzing various atomic disorder schemes. In particular, we show that depending on the degree of disorder, exchanging atomic positions between Mn/Cr and V/Al leads to reduced total magnetization due to either spin flip, or vanishing spin magnetic moments. The latter is attributed to the itinerant character of magnetism in Cr-, Mn-, and V-containing Heusler alloys, and to the frustration of antiferromagnetic exchange interactions, and is accompanied by a tetragonal distortion, but such distortion alone (i.e., in a fully ordered crystal, with no atomic disorder) is not sufficient for a transition to zero magnetization. Besides, we demonstrate that in certain disordered structures the spin polarization of MnCrVAl significantly increases, reaching the half-metallic state. Our calculations indicate that exchange of atomic positions of Mn with Cr, and V with Al has no significant effect on electronic and magnetic properties of MnCrVAl. We also show that antisite disorder does not result in significant reduction of magnetization. At the same time, some types of antisite disorder result in essentially 100% spin-polarized structures. These findings may contribute to understanding the role of atomic disorder on magnetic properties of materials with potential applications in spin-based electronics.
Ion trapping by the graphene electrode in a graphene-ITO hybrid liquid crystal cell
Authors: Basu Rajratan , Lee Andrew
Published: October 2017

A monolayer graphene coated glass slide and an indium tin oxide (ITO) coated glass slide with a planar-aligning polyimide layer were placed together to make a planar hybrid liquid crystal (LC) cell. The free-ion concentration in the LC was found to be significantly reduced in the graphene-ITO hybrid cell compared to that in a conventional ITO-ITO cell. The free-ion concentration was suppressed in the hybrid cell due to the graphene-electrode's ion trapping process. The dielectric anisotropy of the LC was found to increase in the hybrid cell, indicating an increase in the nematic order parameter of the LC due to the reduction of ionic impurities.
Full-wave and ray-based modeling of cross-beam energy transfer between laser beams with distributed phase plates and polarization smoothing
Authors: Follett R. K. , Edgell D. H. , Froula D. H. , Goncharov V. N. , Igumenshchev I. V. , Shaw J. G. , Myatt J. F.
Published: October 2017

Radiation-hydrodynamic simulations of inertial confinement fusion (ICF) experiments rely on ray-based cross-beam energy transfer (CBET) models to calculate laser-energy deposition. The ray-based models assume locally plane-wave laser beams and polarization-averaged incoherence between laser speckles for beams with polarization smoothing. The impact of beam speckle and polarization smoothing on CBET are studied using the 3-D wave-based laser–plasma interaction code LPSE. The results indicate that ray-based models underpredict CBET when the assumption of spatially averaged longitudinal incoherence across the CBET interaction region is violated. A model for CBET between linearly polarized speckled beams is presented that uses ray tracing to solve for the real speckle pattern of the unperturbed laser beams within the eikonal approximation and gives excellent agreement with the wave-based calculations. OMEGA-scale 2-D LPSE calculations using ICF-relevant plasma conditions suggest that the impact of beam speckle on laser absorption calculations in ICF implosions is small (<1%).
Electric and magnetic properties of magnetic (CoFeTaB)(100−x)Ox films
Authors: Sun Wen , Saleemi Awais Siddique , Luo Zhaochu , Guo Zhengang , Xiong Chengyue , Lu Ziyao , Zhang Xiaozhong
Published: October 2017

By the controlling of oxygen flow rate, the oxygen content has been altered in the (CoFeTaB)(100−x)Ox system, a newly reported possible magnetic semiconductor. The electric and magnetic properties of (CoFeTaB)(100−x)Ox films are dependent on the oxygen content of (CoFeTaB)(100−x)Ox films. The resistivity of the grown (CoFeTaB)(100−x)Ox films could be altered from 3.77×10−4 Ω·cm to insulator. Correspondingly, the magnetic behavior of the grown (CoFeTaB)(100−x)Ox films was varied from ferromagnetism to paramagnetism. The increase in the resistivity was mainly attributed to the enhanced oxidization of metal Co; and the magnetism conversion was resulted from the decrease of ferromagnetic Fe3+ and increase of paramagnetic Co2+ in the grown films. These findings provide the fundamental reference for tailoring the electric and magnetic properties of (CoFeTaB)(100−x)Ox materials for potential applications in spintronics.
Verification of linear resistive tearing instability with gyrokinetic particle code VirtEx
Authors: Feng Hongying , Zhang Wenlu , Dong Chao , Cao Jintao , Li Ding
Published: October 2017

Current-driven resistive tearing instability is verified using the newly developed global first-principles particle-in-cell code called VirtEx, which was coded from scratch in conformity with the C++'11 specifications. The tearing instability is first verified in the fluid limit in a cylinder geometry by ignoring the gyrokinetic effect of ions, and the numerical results agree well with the analytical predictions of the resistive tearing theory. Then, the effect of toroidicity on resistive tearing instability is investigated.
Sensitive measurement of spin-orbit torque driven ferromagnetic resonance detected by planar Hall geometry
Authors: Bose Arnab , Dutta Sutapa , Bhuktare Swapnil , Singh Hanuman , Tulapurkar Ashwin A.
Published: October 2017

The magnetization of a nano-magnet can be manipulated and even switched by spin-orbit torques. Hence, accurate characterization of these torques is essential from the application perspective. In this work, we present an alternative method to characterize the spin-orbit torque utilizing the planar Hall effect of a ferromagnet. We show that while the ferromagnet is excited to resonance due to spin-orbit torque, its planar Hall resistance also varies, which leads to sensitive detection of spin-orbit torque. We further demonstrate that planar Hall geometry enables us to estimate spin Hall angle measuring change in magnetic damping very accurately while rf current and dc current are applied perpendicular to each other. Using these techniques, we show that in the Pt/Py bilayer, the spin-Hall effect dominates over interfacial field like spin-orbit torques, which is consistent with previous studies.
Optical diagnosis of spatiotemporal development of plasma discharge in high power microwave sources
Authors: Fan Zhiqiang , Sun Jun , Song Zhimin , Cao Yibing , Zhu Meng , Wu Ping , Teng Yan
Published: October 2017

The breakdown and plasma discharge phenomena in high power microwave sources were studied using an imaging fiber bundle and an intensified-charged-coupled device. By implanting the imaging fiber bundle into the resonant cavity of a relativistic backward wave oscillator, nanosecond-scale plasma light emission could be observed during the experiments. The intensities of the plasma light emission on both sides of the resonant cavity were found to increase initially during the microwave pulse, before reaching a maximum value after tens of nanoseconds following the end of the microwave pulse. Subsequently, the plasma light emission ceased because the microwave energy could no longer maintain the plasma discharge. Additionally, the spatial distribution of the plasma light emission was found to coincide with the surface damage that occurred on both sides of the resonant cavity during the experiment. The spatiotemporal evolution of the plasma discharge during high-gradient breakdown in the relativistic backward wave oscillator was determined via a statistical analysis of the optical imaging results.
A semi-analytical model of a near-field optical trapping potential well
Authors: Zaman Mohammad Asif , Padhy Punnag , Hesselink Lambertus
Published: October 2017

A semi-analytical model is proposed to describe the force generated by a near-field optical trap. The model contains fitting parameters that can be adjusted to resemble a reference force-field. The model parameters for a plasmonic near-field trap consisting of a C-shaped engraving are determined using least squares regression. The reference values required for the regression analysis are calculated using the Maxwell stress tensor method. The speed and accuracy of the proposed model are compared with the conventional method. The model is found to be significantly faster with an acceptable level of accuracy.