bluuebunny/crossref_metadata_2025 huggingface dataset:
Data representation for time series data mining: time domain approaches
Authors: Wilson Seunghye J.
Published: December 2016

In most time series data mining, alternate forms of data representation or data preprocessing is required because of the unique characteristics of time series, such as high dimension (the number of data points), presence of random noise, and nonlinear relationship of the data elements. Therefore, any data representation method aims to achieve substantial data reduction to a manageable size, while preserving important characteristics of the original data, and robustness to random noise. Moreover, appropriate choice of a data representation method may result in meaningful data mining. Many high level representation methods of time series data are based on time domain approaches. These methods preprocess the original data in the time domain directly and are useful to understand the behavior of data over time. Piecewise approximation, data representation by identification important points, and symbolic representation are some of the main ideas of time domain approaches, and widely used in various fields. WIREs Comput Stat 2017, 9:e1392. doi: 10.1002/wics.1392

This article is categorized under:

Statistical and Graphical Methods of Data Analysis > Dimension Reduction

Statistical and Graphical Methods of Data Analysis > Data Reduction, Smoothing, and Filtering
Microbial community composition regulates SOC decomposition response to forest conversion in a Chinese temperate forest
Authors: Qi Lin , Yang Jian
Published: December 2016

Forest conversion influences soil organic carbon (SOC) decomposition through cascading effects on forest structure, soil properties, and soil microbial communities. However, interactive effects of these drivers and the key pathways that mediate forest SOC decomposition remain relatively unexplored. In this study, we compared relative importance of variables describing forest structure, soil properties, and soil microbial community on affecting SOC decomposition response to the conversion of a broadleaved Korean pine mixed forest into three other forests in the Changbai Mountains of China. We quantified SOC decomposition rate of these four forest types by measuring incubation soil respiration (SR). We then employed univariate regressions to quantify effect size of individual factor on SOC decomposition rate. A structural equation model (SEM) was developed to analyze pathways, relative importance, and interactive effects of these factors on SR. Our results showed strong marginal effects of dissolved organic carbon (DOC) content, fungal Phospholipid fatty acids (PLFAs) to bacterial PLFAs ratio (F/B), broadleaved to conifer ratio (B/C), and total PLFAs content (TPC) on SR. Measured SOC decomposition rate was most closely related to F/B, which was in turn influenced primarily by soil C/N ratio and fraction of non‐oxidized carbon (NOC%). Our study identified “Aboveground forest composition → SOC chemistry → Soil microbial composition → SOC decomposition” as the key pathway by which forest conversion affected SOC decomposition. This research work highlights the critical role of soil microbial community composition in altering SOC decomposition response to forest conversion.
A developmentally informed adaptation of minority stress for sexual minority adolescents
Authors: Goldbach Jeremy T. , Gibbs Jeremy J.
Published: December 2016

Sexual minority adolescents (lesbian, gay, bisexual) experience disparities in behavioral health outcomes compared to their heterosexual peers, generally attributed to minority stress. Although evidence of the applicability of the minority stress model among adolescents exists, it is based on a primarily adult literature. Developmental and generational differences demand further examination of minority stress to confirm its applicability. Forty‐eight life history interviews with sexual minority adolescents in California (age 14–19; M = 19.27 SD = 1.38; 39.6% cismale, 35.4% cisfemale, 25% other gender) were completed, recorded, transcribed, and analyzed using thematic analysis in QSR NVivo. Following a consensus model, all transcripts were double coded. Results suggest that minority stress is appropriate for use with adolescents; however, further emphasis should be placed on social context, coping resources, and developmental processes regarding identity development. A conceptual model is provided, as are implications for research and practice.
SFPQ associates to LSD1 and regulates the migration of newborn pyramidal neurons in the developing cerebral cortex
Authors: Saud K. , Cánovas J. , Lopez C.I. , Berndt F.A. , López E. , Maass J.C. , Barriga A. , Kukuljan M.
Published: December 2016

The development of the cerebral cortex requires the coordination of multiple processes ranging from the proliferation of progenitors to the migration and establishment of connectivity of the newborn neurons. Epigenetic regulation carried out by the COREST/LSD1 complex has been identified as a mechanism that regulates the development of pyramidal neurons of the cerebral cortex. We now identify the association of the multifunctional RNA‐binding protein SFPQ to LSD1 during the development of the cerebral cortex. In vivo reduction of SFPQ dosage by in utero electroporation of a shRNA results in impaired radial migration of newborn pyramidal neurons, in a similar way to that observed when COREST or LSD1 expressions are decreased. Diminished SFPQ expression also associates to decreased proliferation of progenitor cells, while it does not affect the acquisition of neuronal fate. These results are compatible with the idea that SFPQ, plays an important role regulating proliferation and migration during the development of the cerebral cortex.
Operative Reduction and Fixation of a Sternomanubrial Dislocation: A Case Report and Literature Review
Authors: Wood Thomas J. , Kellee Stephens , Matthew Denkers
Published: December 2016

A dislocation of the sternomanubrial joint is a rare injury with varied treatment methods including both nonoperative and operative described methods. There is a paucity of literature regarding the optimal method of treatment as well as a lack of consensus on the best surgical construct. This case demonstrates the successful use of dual locking plate fixation for an acute type II sternomanubrial dislocation in a 22-year-old man. In principle, locking plate fixation affords greater unicortical fixation than traditional nonlocking fixation, and allows for minimising the risk of damage to pulmonary tree structures. The patient achieved good pain relief and regained physical function.
Metabolite profiling of isoflavones and anthocyanins in black soybean [Glycine max (L.) Merr.] seeds by HPLC-MS and geographical differentiation analysis in Southwest China
Authors: Wu Hai-jun , Deng Jun-cai , Yang Cai-qiong , Zhang Jing , Zhang Qing , Wang Xiao-chun , Yang Feng , Yang Wen-yu , Liu Jiang
Published: December 2016

Twelve isoflavones and eight anthocyanins were quantified in black soybean seeds by HPLC-MS analyses; the coupled OPLS-DA multivariate statistical analysis helped us to determine their geographical origin.
Variable coordination and C–S bond cleavage activity of N-substituted imidazolidine-2-thiones towards copper: synthesis, spectroscopy, structures, ESI-mass and antimicrobial studies
Authors: Aulakh Jaspreet K. , Lobana Tarlok S. , Sood Henna , Arora Daljit S. , Garcia-Santos Isabel , Hundal Geeta , Kaur Manpreet , Smolenski Victoria A. , Jasinski Jerry P.
Published: December 2016

N-substituted imidazoldine-2-thiones with copper(i) halides have shown variable nuclearity, C–S bond cleavage, antimicrobial activity and non-toxicity in some cases to living cells.
Probing the magnetic relaxation and magnetic moment arrangement in a series of Dy4 squares
Authors: Wu Jianfeng , Lin Shuang-Yan , Shen Si , Li Xiao-Lei , Zhao Lang , Zhang Li , Tang Jinkui
Published: December 2016

Modulations of the first and secondary coordination geometries by dimerizing and reducing the Schiff base ligands result in the enhancement of the magnetic relaxation and rearrangement of the magnetic moments in μ4-O2− bridged Dy4 squares.
A hybrid-type Li–air battery based on a polypyrrole/carbon nanocomposite catalyst as the cathode
Authors: Kim Kyoungho , Lee Wang-Geun
Published: December 2016

A polypyrrole/carbon nanocomposite-based battery showed charge/discharge reversibility over 20 cycles and a round-trip efficiency as high as 92.9%.
NiCo2S4/tryptophan-functionalized graphene quantum dot nanohybrids for high-performance supercapacitors
Authors: Wang Huiying , Yang Yongqiang , Zhou Xiaoyan , Li Ruiyi , Li Zaijun
Published: December 2016

This paper reports a facile synthesis of NiCo2S4via a one-step hydrothermal reaction and its hybrid with tryptophan-functionalized graphene quantum dots. The nanohybrid electrode exhibits significantly enhanced electrochemical performance for supercapacitors.
High-color-quality white electroluminescence and amplified spontaneous emission from a star-shaped single-polymer system with simultaneous three-color emission
Authors: Jiu Yuanda , Wang Jianyun , Yi Jianpeng , Liu Cheng-Fang , Zhang Xin-Wen , Lai Wen-Yong , Huang Wei
Published: December 2016

A star-shaped single-polymer system with simultaneous RGB emission has been developed, achieving high-color-quality saturated white electroluminescence.
Variations in Echogenicity in Carotid and Femoral Atherosclerotic Plaques with Pycnogenol + Centella Asiatica Supplementation
Authors: Cornelli Umberto , Belcaro Gianni
Published: December 2016

This registry study evaluated echogenicity of carotid–femoral plaques in asymptomatic subjects with increased oxidative stress and risk factors (mild hypertension, hypercholesterolemia). Supplementation with the combination Pycnogenol–CA (centella asiatica) on the echogenicity of plaques was assessed at 6 months (79 subjects). A standard management (SM) plan was used in all subjects (control of risk factors, lifestyle changes); 36 subjects used the supplements +SM; 43 SM only. The groups were comparable. High-resolution ultrasound evaluated echogenicity and plaque structure. Pycnogenol (150 mg/day) and CA (Centellicum, 450 mg/day) were used.

At 6 months, cholesterol was reduced (p < 0.05) in both groups (difference between groups not significant). At 6 months, plasma free radicals were decreased with the supplements (17.64%; p < 0.05; vs <2% in controls). The plaque stability index increased from 11.22;2.3 to 22.4;1.1 (p < 0.05) with the supplements; no significant changes were seen in controls. Plaque echogenicity (% of “whiter” component in images) increased with supplementation from 16.7;1.7% to 34.2;2% (p < 0.05); no variations were observed in controls. The maximum plaque height decreased (p < 0.05) with the supplements. No significant variations were observed in controls. Plaque length was decreased (p < 0.05) in the supplement group with no changes in controls. The number of plaques (carotid, femoral bifurcations) decreased with supplementation; no significant changes were observed in controls. No adverse events, tolerability problems, or variations in routine blood tests were recorded. The combination Pycnogenol–CA appears to improve echogenicity and stability of complex plaques in 6 months.
A Canine Arthroscopic Anterior Cruciate Ligament Reconstruction Model for Study of Synthetic Augmentation of Tendon Allografts
Authors: Smith Pat , Stannard James , Pfeiffer Ferris , Kuroki Keiichi , Bozynski Chantelle , Cook Cristi , Cook James
Published: December 2016

Novel graft types, fixation methods, and means for augmenting anterior cruciate ligament (ACL) reconstructions require preclinical validation prior to safe and effective clinical application. The objective of this study was to describe and validate a translational canine model for all-inside arthroscopic complete ACL reconstruction using a quadriceps tendon allograft with internal brace (QTIB). With institutional approval, adult research hounds underwent complete transection of the native ACL followed by all-inside ACL reconstruction using the novel QTIB construct with suspensory fixation (n = 10). Contralateral knees were used as nonoperated controls (n = 10). Dogs were assessed over a 6-month period using functional, diagnostic imaging, gross, biomechanical, and histologic outcome measures required for preclinical animal models. Study results suggest that the novel QTIB construct used for complete ACL reconstruction can provide sustained knee stability and function without the development of premature osteoarthritis in a rigorous and valid preclinical model. The unique configuration of the QTIB construct—the combination of a tendon allograft with a synthetic suture tape internal brace—allowed for an effective biologic–synthetic load-sharing ACL construct. It prevented early failure, allowed for direct, four-zone graft-to-bone healing, and functional graft remodeling while avoiding problems noted with use of all-synthetic grafts.
Ab initio quantum–chemical computations of the electronic states in HgBr2 and IBr: Molecules of interest on the Earth’s atmosphere
Authors: Sitkiewicz Sebastian P. , Oliva Josep M. , Dávalos Juan Z. , Notario Rafael , Saiz–Lopez Alfonso , Alcoba Diego R. , Oña Ofelia B. , Roca-Sanjuán Daniel
Published: December 2016

The electronic states of atmospheric relevant molecules IBr and HgBr2 are reported, within the UV-Vis spectrum range (170nm≤λphoton≤600 nm) by means of the complete–active–space self–consistent field/multi–state complete–active–space second–order perturbation theory/spin–orbit restricted–active–space state–interaction (CASSCF/MS–CASPT2/SO–RASSI) quantum–chemical approach and atomic–natural–orbital relativistic–correlation–consistent (ANO–RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 eV. The presented analyses shall allow upcoming studies aimed to accurately determine the absorption cross sections of interhalogen molecules and compounds with Hg that are relevant to better comprehend the photochemical processes taking place in the atmosphere.
Relaxation pathways of the OD stretch fundamental of HOD in liquid H2O
Authors: Miguel Beatriz , Zúñiga José , Requena Alberto , Bastida Adolfo
Published: December 2016

The molecular dynamics with quantum transitions method is used to study the vibrational relaxation of the OD stretching mode of HOD dissolved in liquid H2O water at 303 K. All the vibrational modes of the solute and solvent molecules that participate in the relaxation process are described by quantum mechanics, while the rotational and translational degrees of freedom are treated classically. A modification of the water intramolecular SPC/E (Simple Point Charge/Extended) force field providing vibrational frequencies in solution closer to the experimental values is proposed to analyze the influence of the vibrational energy gaps on the relaxation channels. The relaxation times obtained are in satisfactory agreement with experimental values. The energy transfer during the relaxation process alters significantly the H-bond network around the HOD molecule. The analysis of the vibrational transitions during the relaxation process reveals a complex mechanism which involves the participation of both intra- and intermolecular channels and provides a compromise for the different interpretations of the experimental data reported for this system in recent years.
Self-consistent implementation of ensemble density functional theory method for multiple strongly correlated electron pairs
Authors: Filatov Michael , Liu Fang , Kim Kwang S. , Martínez Todd J.
Published: December 2016

The spin-restricted ensemble-referenced Kohn-Sham (REKS) method is based on an ensemble representation of the density and is capable of correctly describing the non-dynamic electron correlation stemming from (near-)degeneracy of several electronic configurations. The existing REKS methodology describes systems with two electrons in two fractionally occupied orbitals. In this work, the REKS methodology is extended to treat systems with four fractionally occupied orbitals accommodating four electrons and self-consistent implementation of the REKS(4,4) method with simultaneous optimization of the orbitals and their fractional occupation numbers is reported. The new method is applied to a number of molecular systems where simultaneous dissociation of several chemical bonds takes place, as well as to the singlet ground states of organic tetraradicals 2,4-didehydrometaxylylene and 1,4,6,9-spiro[4.4]nonatetrayl.
On the tautomerisation of porphycene on copper (111): Finding the subtle balance between van der Waals interactions and hybridisation
Authors: Novko Dino , Tremblay Jean Christophe , Blanco-Rey María
Published: December 2016

We use density-functional theory (DFT) to analyse the interaction of trans- and cis-porphycene with Cu(111) and their interconversion by intramolecular H-transfer. This tautomerisation reaction is characterised by small values for the reaction energy and barrier, on the order of ∼0.1 eV, where the trans configuration is thermodynamically more stable upon adsorption according to the experiments [J. N. Ladenthin et al., ACS Nano 9, 7287–7295 (2015)]. To gain even a qualitatively correct description of this reaction at the DFT level, an accurate treatment of dispersion interactions and a careful choice of the exchange contribution are required in order to predict the subtle energetics. Analysis of the electronic structure shows that adsorption is contributed by a van der Waals (vdW) interaction, mainly responsible for stabilising the polyaromatic fragments, and by a significant charge redistribution localised between Cu and the unsaturated N atoms of the molecule central cavity. We find that different vdW functionals can produce qualitatively different electronic structures, while yielding small trans vs. cis energy differences. Unlike other functionals surveyed here, vdW-DF with PBE exchange satisfactorily reproduces not only the experimental energetics but also the scanning tunneling microscopy images. This gives us confidence that this functional achieves a reliable balance between the two mechanisms contributing to the adsorption of porphycene.
Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids
Authors: Lu Hongduo , Li Bin , Nordholm Sture , Woodward Clifford E. , Forsman Jan
Published: December 2016

An asymmetric restricted primitive model (ARPM) of electrolytes is proposed as a simple three parameter (charge q, diameter d, and charge displacement b) model of ionic liquids and solutions. Charge displacement allows electrostatic and steric interactions to operate between different centres, so that orientational correlations arise in ion-ion interactions. In this way the ionic system may have partly the character of a simple ionic fluid/solid and of a polar fluid formed from ion pairs. The present exploration of the system focuses on the ion pair formation mechanism, the relative concentration of paired and free ions and the consequences for the cohesive energy, and the tendency to form fluid or solid phase. In contrast to studies of similar (though not identical) models in the past, we focus on behaviours at room temperature. By MC and MD simulations of such systems composed of monovalent ions of hard-sphere (or essentially hard-sphere) diameter equal to 5 Å and a charge displacement ranging from 0 to 2 Å from the hard-sphere origin, we find that ion pairing dominates for b larger than 1 Å. When b exceeds about 1.5 Å, the system is essentially a liquid of dipolar ion pairs with a small presence of free ions. We also investigate dielectric behaviours of corresponding liquids, composed of purely dipolar species. Many basic features of ionic liquids appear to be remarkably consistent with those of our ARPM at ambient conditions, when b is around 1 Å. However, the rate of self-diffusion and, to a lesser extent, conductivity is overestimated, presumably due to the simple spherical shape of our ions in the ARPM. The relative simplicity of our ARPM in relation to the rich variety of new mechanisms and properties it introduces, and to the numerical simplicity of its exploration by theory or simulation, makes it an essential step on the way towards representation of the full complexity of ionic liquids.
Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy
Authors: Lackner Florian , Chatterley Adam S. , Pemmaraju C. D. , Closser Kristina D. , Prendergast David , Neumark Daniel M. , Leone Stephen R. , Gessner Oliver
Published: December 2016

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C4H4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (∼58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field induced ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se+ ions within an overall time scale of approximately 170 fs. We propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se+ and ring-open cations within an additional τ2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. The findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.
An efficient quantum mechanical method for radical pair recombination reactions
Authors: Lewis Alan M. , Fay Thomas P. , Manolopoulos David E.
Published: December 2016

The standard quantum mechanical expressions for the singlet and triplet survival probabilities and product yields of a radical pair recombination reaction involve a trace over the states in a combined electronic and nuclear spin Hilbert space. If this trace is evaluated deterministically, by performing a separate time-dependent wavepacket calculation for each initial state in the Hilbert space, the computational effort scales as O(Z2log⁡Z), where Z is the total number of nuclear spin states. Here we show that the trace can also be evaluated stochastically, by exploiting the properties of spin coherent states. This results in a computational effort of O(MZlog⁡Z), where M is the number of Monte Carlo samples needed for convergence. Example calculations on a strongly coupled radical pair with Z>106 show that the singlet yield can be converged to graphical accuracy using just M=200 samples, resulting in a speed up by a factor of >5000 over a standard deterministic calculation. We expect that this factor will greatly facilitate future quantum mechanical simulations of a wide variety of radical pairs of interest in chemistry and biology.
Use of solid N2 surfaces in metastable particle detection
Authors: Kedzierski W. , McConkey J. W.
Published: December 2016

A novel detector is described in which solid nitrogen at 17 K is used as the most significant element. Metastable particles impinge on this element and immediately transfer their internal energy to the solid nitrogen producing photons, via excimer formation or otherwise, whose wavelength depends on the metastable being detected and the energy transfer process. The performance of the instrument for the detection of atomic oxygen and molecular nitrogen metastables is discussed.
High duty cycle inverse Compton scattering X-ray source
Authors: Ovodenko A. , Agustsson R. , Babzien M. , Campese T. , Fedurin M. , Murokh A. , Pogorelsky I. , Polyanskiy M. , Rosenzweig J. , Sakai Y. , Shaftan T. , Swinson C.
Published: December 2016

Inverse Compton Scattering (ICS) is an emerging compact X-ray source technology, where the small source size and high spectral brightness are of interest for multitude of applications. However, to satisfy the practical flux requirements, a high-repetition-rate ICS system needs to be developed. To this end, this paper reports the experimental demonstration of a high peak brightness ICS source operating in a burst mode at 40 MHz. A pulse train interaction has been achieved by recirculating a picosecond CO2 laser pulse inside an active optical cavity synchronized to the electron beam. The pulse train ICS performance has been characterized at 5- and 15- pulses per train and compared to a single pulse operation under the same operating conditions. With the observed near-linear X-ray photon yield gain due to recirculation, as well as noticeably higher operational reliability, the burst-mode ICS offers a great potential for practical scalability towards high duty cycles.
A retarding potential analyzer design for keV-level ion thruster beams
Authors: Zhang Zhe , Tang Haibin , Zhang Zun , Wang Joseph , Cao Shuai
Published: December 2016

We present a new Retarding Potential Analyzer (RPA) design that is capable of measuring keV-level energy, high-density plasma beams. This instrument overcomes the limitations of existing RPAs and can operate in plasmas with densities in excess of 1 × 1015 m−3 and ion energies up to 1200 eV. The RPA design parameters were determined by analyzing the electron density and temperature, the sheath thickness, and the ion density in the beam based on the Faraday probe and Langmuir probe measurements. A previously unobserved grid spacing arcing phenomenon was observed in experiments. This arcing phenomenon was also investigated and a grid spacing criterion was proposed to eliminate the arcing. We present measurement results on the plasma beam emitted from the 20 cm Xenon ion thruster used on the Chinese SJ-9A satellite.
Spectral dependence of carrier lifetimes in silicon for photovoltaic applications
Authors: Roller John F. , Li Yu-Tai , Dagenais Mario , Hamadani Behrang H.
Published: December 2016

Charge carrier lifetimes in photovoltaic-grade silicon wafers were measured by a spectral-dependent, quasi-steady-state photoconductance technique. Narrow bandwidth light emitting diodes were used to excite excess charge carriers within the material, and the effective lifetimes of these carriers were measured as a function of wavelength and intensity. The dependence of the effective lifetime on the excitation wavelength was then analyzed within the context of an analytical model relating effective lifetime to the bulk lifetime and surface recombination velocity of the material. The agreement between the model and the experimental data provides validation for this technique to be used at various stages of the solar cell production line to investigate the quality of the passivation layers and the bulk properties of the material.
Thermodynamics of supersaturated steam: Molecular simulation results
Authors: Moučka Filip , Nezbeda Ivo
Published: December 2016

Supersaturated steam modeled by the Gaussian charge polarizable model [P. Paricaud, M. Předota, and A. A. Chialvo, J. Chem. Phys. 122, 244511 (2005)] and BK3 model [P. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)] has been simulated at conditions occurring in steam turbines using the multiple-particle-move Monte Carlo for both the homogeneous phase and also implemented for the Gibbs ensemble Monte Carlo molecular simulation methods. Because of these thermodynamic conditions, a specific simulation algorithm has been developed to bypass common simulation problems resulting from very low densities of steam and cluster formation therein. In addition to pressure-temperature-density and orthobaric data, the distribution of clusters has also been evaluated. The obtained extensive data of high precision should serve as a basis for development of reliable molecular-based equations for properties of metastable steam.
Improving three-dimensional target reconstruction in the multiple scattering regime using the decomposition of the time-reversal operator
Authors: Zhang Ting , Chaumet Patrick C. , Sentenac Anne , Belkebir Kamal
Published: December 2016

The singular vectors of the time reversal operator (décomposition de l'opérateur de retournement temporel, time reversal operator decomposition (DORT) processing) are often used for localizing small echogeneous targets in a cluttered environment. In this work, we show that they can also improve the imaging of relatively large and contrasted targets in a homogeneous environment. It is observed that non-linear inversion schemes, minimizing iteratively the discrepancy between experimental data and simulated field scattered by target estimates, are more efficient when the illuminations correspond to the DORT singular vectors. In addition, DORT preprocessing permits a drastic diminution of the data load and computer burden. This study is conducted with experimental microwave data of targets with size comparable or greater than the wavelength.
Consequences of plasma oxidation and vacuum annealing on the chemical properties and electron accumulation of In2O3 surfaces
Authors: Berthold Theresa , Rombach Julius , Stauden Thomas , Polyakov Vladimir , Cimalla Volker , Krischok Stefan , Bierwagen Oliver , Himmerlich Marcel
Published: December 2016

The influence of oxygen plasma treatments on the surface chemistry and electronic properties of unintentionally doped and Mg-doped In2O3(111) films grown by plasma-assisted molecular beam epitaxy or metal-organic chemical vapor deposition is studied by photoelectron spectroscopy. We evaluate the impact of semiconductor processing technology relevant treatments by an inductively coupled oxygen plasma on the electronic surface properties. In order to determine the underlying reaction processes and chemical changes during film surface–oxygen plasma interaction and to identify reasons for the induced electron depletion, in situ characterization was performed implementing a dielectric barrier discharge oxygen plasma as well as vacuum annealing. The strong depletion of the initial surface electron accumulation layer is identified to be caused by adsorption of reactive oxygen species, which induce an electron transfer from the semiconductor to localized adsorbate states. The chemical modification is found to be restricted to the topmost surface and adsorbate layers. The change in band bending mainly depends on the amount of attached oxygen adatoms and the film bulk electron concentration as confirmed by calculations of the influence of surface state density on the electron concentration and band edge profile using coupled Schrödinger-Poisson calculations. During plasma oxidation, hydrocarbon surface impurities are effectively removed and surface defect states, attributed to oxygen vacancies, vanish. The recurring surface electron accumulation after subsequent vacuum annealing can be consequently explained by surface oxygen vacancies.
Micro and nano patternable magnetic carbon
Authors: Sharma Swati , Rostas Arpad M. , Bordonali Lorenzo , MacKinnon Neil , Weber Stefan , Korvink Jan G.
Published: December 2016

Carbon is conventionally not associated with magnetism, causing much of the discussion of its perspectives in nanotechnology to be centred on its electron-transport properties. Among the few existing examples of magnetic carbon production, none has found a direct route into scalable micro- and nanofabrication. Here we introduce a magnetic form of carbon whose precursor polymers can be lithographically patterned into micro- and nano-structures prior to pyrolysis. This unreactive and thermally robust material features a strong, room-temperature magnetism owing to a large number of unpaired electron spins with restricted mobility, which is achieved by controlling the progression of bond dissociation and formation during pyrolysis. The micro-manufacture of pyrolytic magnetic carbon, having (3.5±0.7)×1015 spins/mg, can immediately benefit a number of spintronic and magnetic-microelectromechanical system applications, and the fabrication of composite magnetic materials. The material could also complement the magnetic resonance spectroscopy and imaging techniques. Additionally, this contribution sheds light on the controversial theories concerning the existence and mechanism of magnetic phenomena in carbon.
Electric-field induced quantum broadening of the characteristic energy level of traps in semiconductors and oxides
Authors: Mohammed Mazharuddin , Verhulst Anne S. , Verreck Devin , Van de Put Maarten , Simoen Eddy , Sorée Bart , Kaczer Ben , Degraeve Robin , Mocuta Anda , Collaert Nadine , Thean Aaron , Groeseneken Guido
Published: December 2016

The trap-assisted tunneling (TAT) current in tunnel field-effect transistors (TFETs) is one of the crucial factors degrading the sub-60 mV/dec sub-threshold swing. To correctly predict the TAT currents, an accurate description of the trap is required. Since electric fields in TFETs typically reach beyond 106 V/cm, there is a need to quantify the impact of such high field on the traps. We use a quantum mechanical implementation based on the modified transfer matrix method to obtain the trap energy level. We present the qualitative impact of electric field on different trap configurations, locations, and host materials, including both semiconductors and oxides. We determine that there is an electric-field related trap level shift and level broadening. We find that these electric-field induced quantum effects can enhance the trap emission rates.
Characteristics of nonlinear dust acoustic waves in a Lorentzian dusty plasma with effect of adiabatic and nonadiabatic grain charge fluctuation
Authors: Denra Raicharan , Paul Samit , Sarkar Susmita
Published: December 2016

In this paper, characteristics of small amplitude nonlinear dust acoustic wave have been investigated in a unmagnetized, collisionless, Lorentzian dusty plasma where electrons and ions are inertialess and modeled by generalized Lorentzian Kappa distribution. Dust grains are inertial and equilibrium dust charge is negative. Both adiabatic and nonadiabatic fluctuation of charges on dust grains have been taken under consideration. For adiabatic dust charge variation reductive perturbation analysis gives rise to a KdV equation that governs the nonlinear propagation of dust acoustic waves having soliton solutions. For nonadiabatic dust charge variation nonlinear propagation of dust acoustic wave obeys KdV-Burger equation and gives rise to dust acoustic shock waves. Numerical estimation for adiabatic grain charge variation shows the existence of rarefied soliton whose amplitude and width varies with grain charges. Amplitude and width of the soliton have been plotted for different electron Kappa indices keeping ion velocity distribution Maxwellian. For non adiabatic dust charge variation, ratio of the coefficients of Burger term and dispersion term have been plotted against charge fluctuation for different kappa indices. All these results approach to the results of Maxwellian plasma if both electron and ion kappa tends to infinity.
Flow-field differences and electromagnetic-field properties of air and N2 inductively coupled plasmas
Authors: Yu Minghao , Yamada Kazuhiko , Takahashi Yusuke , Liu Kai , Zhao Tong
Published: December 2016

A numerical model for simulating air and nitrogen inductively coupled plasmas (ICPs) was developed considering thermochemical nonequilibrium and the third-order electron transport properties. A modified far-field electromagnetic model was introduced and tightly coupled with the flow field equations to describe the Joule heating and inductive discharge phenomena. In total, 11 species and 49 chemical reactions of air, which include 5 species and 8 chemical reactions of nitrogen, were employed to model the chemical reaction process. The internal energy transfers among translational, vibrational, rotational, and electronic energy modes of chemical species were taken into account to study thermal nonequilibrium effects. The low-Reynolds number Abe-Kondoh-Nagano k-ε turbulence model was employed to consider the turbulent heat transfer. In this study, the fundamental characteristics of an ICP flow, such as the weak ionization, high temperature but low velocity in the torch, and wide area of the plasma plume, were reproduced by the developed numerical model. The flow field differences between the air and nitrogen ICP flows inside the 10-kW ICP wind tunnel were made clear. The interactions between the electromagnetic and flow fields were also revealed for an inductive discharge.
Observation of mode transition and low-frequency oscillations in magnetically constricted anode
Authors: Chauhan S. , Ranjan M. , Bandyopadhyay M. , Mukherjee S.
Published: December 2016

We report on the discharge behaviour and the mode transition observed in a magnetically constricted anode device. With an increase in pressure, the central droplet shaped glow shrunk and abruptly switched to peripheral glow mode for pressure above 5×10−2 mbar. This transition is observed when the width of the droplet shaped glow at the anode approaches the diameter of the central magnet. The mode transition is observed as a sudden jump in the discharge current, which obeys a different power law than the previous discharge mode. Further, this new mode is observed to accompany the global oscillations in the range of few kHz.
The sources of super-high energetic electron at relativistic circularly-polarized laser-solid interactions in the presence of large scale pre-plasmas
Authors: Wu D. , Krasheninnikov S. I. , Luan S. X. , Yu W.
Published: December 2016

The two stage electron acceleration model [Wu et al., Nucl. Fusion 57, 016007 (2017)] is extended to investigate the sources of super-hot electrons at intense circularly polarized (CP) laser solid interactions. It is found that in the presence of large scale pre-formed plasmas, super-high energetic electrons can be generated. For laser of intensity 1020 W/cm2 and pre-plasma of scale-length 10 μm, the cut-off energy of electrons by CP laser can be as high as 120 MeV compared with 100 MeV by linearly polarized laser. This unexpected acceleration can be also explained by the two-stage acceleration model. The envelop modulation of reflected CP laser is figured out, and a modified scaling law of the maximal-possible energy gain when including the modulation effect is obtained.
Numerical demonstration of high-Z doping scheme on ignition-relevant scale implosion
Authors: Shiroto T. , Ohnishi N. , Sunahara A. , Fujioka S. , Sasaki A.
Published: December 2016

Although it has been demonstrated that high-Z doped plastic can suppress the Rayleigh–Taylor instability, its usability in direct-drive implosion design on mega-joule class reactors is still controversial. In this study, the radiation hydrodynamics code was validated by a planar target experiment of a brominated plastic target, since the result including high-Z strongly depends on the opacity model. Opacity for bromine ion based on the detailed configuration accounting model has better agreement with the experimental results compared to that of the average-ion model. Two-dimensional implosion simulations assuming a mega-joule driver were also conducted to estimate whether a brominated plastic ablator can suppress the hydrodynamic instability. It was revealed that a brominated plastic, which has an appropriate fraction of doping, can assist the generation of a high-density core by suppression of the hydrodynamic instability. A high-Z doped target can suppress the Rayleigh–Taylor instability at the foot-drive phase when the laser intensity is relatively low.
Comparison of device structures for the dielectric breakdown measurement of hexagonal boron nitride
Authors: Hattori Yoshiaki , Taniguchi Takashi , Watanabe Kenji , Nagashio Kosuke
Published: December 2016

Improving the film quality in the synthesis of large-area hexagonal boron nitride films (h-BN) for two-dimensional material devices remains a great challenge. The measurement of electrical breakdown dielectric strength (EBD) is one of the most important methods to elucidate the insulating quality of h-BN. In this work, the EBD of high quality exfoliated single-crystal h-BN was investigated using three different electrode structures under different environmental conditions to determine the ideal electrode structure and environment for EBD measurement. A systematic investigation revealed that EBD is not sensitive to contact force or electrode area but strongly depends on the relative humidity during measurement. Once the measurement environment is properly managed, it was found that the EBD values are consistent within experimental error regardless of the electrode structure, which enables the evaluation of the crystallinity of synthesized h-BN at the microscopic and macroscopic level by utilizing the three different electrode structures properly for different purposes.
Destructive quantum interference in electron transport: A reconciliation of the molecular orbital and the atomic orbital perspective
Authors: Zhao Xin , Geskin Victor , Stadler Robert
Published: December 2016

Destructive quantum interference (DQI) in single molecule electronics is a purely quantum mechanical effect and is entirely defined by the inherent properties of the molecule in the junction such as its structure and symmetry. This definition of DQI by molecular properties alone suggests its relation to other more general concepts in chemistry as well as the possibility of deriving simple models for its understanding and molecular device design. Recently, two such models have gained a wide spread attention, where one was a graphical scheme based on visually inspecting the connectivity of the carbon sites in conjugated π systems in an atomic orbital (AO) basis and the other one puts the emphasis on the amplitudes and signs of the frontier molecular orbitals (MOs). There have been discussions on the range of applicability for these schemes, but ultimately conclusions from topological molecular Hamiltonians should not depend on whether they are drawn from an AO or a MO representation, as long as all the orbitals are taken into account. In this article, we clarify the relation between both models in terms of the zeroth order Green’s function and compare their predictions for a variety of systems. From this comparison, we conclude that for a correct description of DQI from a MO perspective, it is necessary to include the contributions from all MOs rather than just those from the frontier orbitals. The cases where DQI effects can be successfully predicted within a frontier orbital approximation we show them to be limited to alternant even-membered hydrocarbons, as a direct consequence of the Coulson-Rushbrooke pairing theorem in quantum chemistry.
Thermodynamic and kinetic solid-liquid interface properties from transition path sampling
Authors: Şopu Daniel , Rogal Jutta , Drautz Ralf
Published: December 2016

We perform transition path sampling simulations to determine two of the key quantities in solidification, the solid-liquid interface energy and velocity, in a Lennard-Jones system. Our approach is applicable to a wide range of temperature and pressure conditions, at the melting temperature and out-of-equilibrium. We show that small system sizes are sufficient for good values of interface energies and velocities. The transition path sampling method thus offers an attractive and robust alternative for the evaluation of solid-liquid interface properties.
A unifying metric for comparing thermomagnetic transduction utilizing magnetic entropy
Authors: Wetzlar Kyle P. , Keller Scott M. , Phillips Makita R. , Carman Gregory P.
Published: December 2016

A method to compare the thermal to magnetic transduction efficiencies of different thermomagnetic systems was developed. The efficiencies of operating about a spin reorientation transition and the alternative ferromagnetic to paramagnetic transformation at the Curie point were directly compared. A case study was performed comparing Gd operating about its spin reorientation temperature and its Curie point. Additionally, a case study on NdCo5 operating about its spin reorientation temperature using experimentally derived values of the materials' temperature dependent magnetic properties was conducted. Analysis suggests that choosing the appropriate material and operating it about its transition produces considerable efficiencies (∼22%) as well as large harvestable energy densities (∼2.6 MJ/m3), which is an order of magnitude larger than Gd single domains operating about their Curie point (∼100 kJ/m3).
Interface-enhanced sensitivity of photoconductivity to the electric current and magnetic field in La0.67Ca0.33MnO3/Nb-SrTiO3 p-n junctions
Authors: Wang S. , Ma Z. Z. , Xiong J. J. , Li C. J. , Hou Y. H. , Ma T. X. , Xiong C. M. , Dou R. F. , Nie J. C.
Published: December 2016

The effects of electric current and magnetic field on the photoconductivity (PC) of La0.67Ca0.33MnO3 (LCMO) films have been investigated within a comparative study on LCMO films on an n-type semiconducting Nb-doped SrTiO3 (NSTO) and insulating SrTiO3 (STO) substrates separately. At room temperature, LCMO on NSTO (LCMO/NSTO) was found to show remarkable PC effect than that on STO (LCMO/STO). More attractive is that, compared with that of LCMO/STO, the room-temperature PC of LCMO/NSTO also shows a high sensitivity to the change of current or magnetic field: for LCMO/NSTO under a light illumination with an intensity of 60 mW/cm2, the increment of current yields a decreases of PC at a rate of 7.6%/μA, while an application of magnetic field of 1.2 T can suppress PC by a percentage as high as ∼20%. In contrast, under the same stimulus of current or field, PC of LCMO/STO remains almost unchanged. The phenomena can be explained based on the interface effects correlated with the photocarrier injection, current shunting, and magnetic tunability occurred at the interface. This work demonstrates that manganite-based heterojunctions with interface engineering are promising for developing a new type of photoelectric device with high sensitivity and multifunctionality.
Large magnetoresistance effect in nitrogen-doped silicon
Authors: Wang Tao , Yang Zhaolong , Wang Wei , Si Mingsu , Yang Dezheng , Liu Huiping , Xue Desheng
Published: December 2016

In this work, we reported a large magnetoresistance effect in silicon by ion implantation of nitrogen atoms. At room temperature, the magnetoresistance of silicon reaches 125 % under magnetic field 1.7 T and voltage bias -80 V. By applying an alternating magnetic field with a frequency (f) of 0.008 Hz, we find that the magnetoresistance of silicon is divided into f and 2f two signal components, which represent the linear and quadratic magnetoresistance effects, respectively. The analysis based on tuning the magnetic field and the voltage bias reveals that electric-field-induced space-charge effect plays an important role to enhance both the linear and quadratic magnetoresistance effects. Observation as well as a comprehensive explanation of large MR in silicon, especially based on semiconductor CMOS implantation technology, will be an important progress towards magnetoelectronic applications.