bluuebunny/crossref_metadata_2025 huggingface dataset:
Mesoscale simulations of atmospheric CO2 variations using a high‐resolution model system with process‐based CO2 fluxes
Authors: Uebel M. , Herbst M. , Bott A.
Published: March 2017

A new coupled high‐resolution biosphere–atmosphere model (TerrSysMP‐CO2) is applied to simulate mesoscale and diurnal variations of atmospheric CO2 mixing ratios. The model is characterized by process‐based parametrization calculating atmospheric dynamics and biogenic processes considering the prognostically varying CO2 content at the surface. An advanced parametrization of soil respiration is used distinguishing between heterotrophic and autotrophic respiration and explicitly considering the effect of varying soil moisture. In addition to biogenic CO2 fluxes, high‐resolution anthropogenic emissions are included in the simulations.

The model performance is verified with eddy‐covariance fluxes and meteorological and CO2 concentration measurements at various heights of a tower. It is found that a correct representation of turbulent mixing is most critical for a precise prediction of near‐surface CO2 mixing ratios and respective vertical gradients. High‐resolution simulations were performed for a region with complex terrain, heterogeneous land use and densely populated areas. The relative influence of diverse land use, orography as well as of synoptic and mesoscale transport on the spatio‐temporal CO2 distribution is analyzed. The results indicate that, in regions with hilly terrain at night and in the morning, the CO2 patterns are strongly influenced by terrain‐induced local circulations. Moreover, in densely populated regions, fossil fuel emissions are an important source of atmospheric CO2. Finally, the simulated canopy fluxes and atmospheric conditions, calculated using two different crop physiological parameter sets, are compared.
Control design for discrete‐time bilinear systems using the scalarized Schur complement
Authors: Vatani M. , Hovd M. , Olaru S.
Published: March 2017

In this paper, controller design for discrete‐time bilinear systems is investigated by using sum of squares programming methods and quadratic Lyapunov functions. The class of rational polynomial controllers is considered, and necessary conditions on the degree of controller polynomials for quadratic stability are derived. Next, a scalarized version of the Schur complement is proposed. For controller design, the Lyapunov difference inequality is converted to a sum of squares problem, and an optimization problem is proposed to design a controller, which maximizes the region of quadratic stability of the bilinear system. Input constraints can also be accounted for. Copyright © 2017 John Wiley & Sons, Ltd.
Regio‐Selective C−H Halogenation of 8‐Amido‐Quinolines under Transition Metal Free Conditions
Authors: Sen Chiranjit , Sahoo Tapan , Ghosh Subhash Chandra
Published: March 2017

A transition metal free highly regioselective remote C−H halogenation has been developed. Oxidative halogenation (Cl, Br, I) of C5‐H of 8‐amido quinolone with inexpensive potassium persulfate as an oxidant and cheap halogenating agents like N‐halosuccinimide (NXS) or tetrabutylammonium halides (TBAX) were employed. Two reaction conditions were developed and in both routes have advantages such as C5‐selectivity, high to excellent yields (up to 98 %) and broad substrate scope. The reaction also carried out in water, open to air condition.
Application of Drainage Basin Morphotectonic Analysis for Assessment of Tectonic Activities over Two Regional Structures of the Northeast India
Authors: Sharma Sangeeta , Sarma Jogendra Nath
Published: March 2017

The analysis of drainage basin morphotectonic indices is applied in assessment of the influence of tectonic activity on thirteen selected drainage basins of the streams having linear courses and flowing over two very prominent regional structures of northeast India, viz. the Belt of Schuppen and the Dauki fault. Such analysis has been made in order to assess the influence of tectonic activity of these structures on the morphology of the drainage basins of those streams. The different morphotectonic indices considered are: Basin elongation ratio, hypsometric integral, steepness index and profile concavity, drainage basin asymmetry, valley floor width to valley height ratio, longitudinal profiles, stream length gradient index and mountain front sinuosity. Results of the analysis of the morphotectonic indices of the drainage basins infer that morphology of both the streams and drainage basins have been influenced by the regional structures and the present tectonic status of these two structures varies from active to slightly active phase. No significant influence of lithology is seen in the distribution pattern of the anomalous knick points along the longitudinal profiles. The study also reveals that presently the state of tectonic activity is not uniform within the same regional structure and the Belt of Schuppen is relatively more active as compared to the Dauki fault.
Sagediopsis bayozturkiisp. nov. on the lichenAcarospora macrocyclosfrom Antarctica with a key to the known species of the genus (Ascomycota, Adelococcaceae)
Authors: Halıcı Mehmet Gökhan , Güllü Mithat , Parnikoza Ivan
Published: March 2017

Sagediopsis bayozturkii, a lichenicolous fungus growing on Antarctic endemic speciesAcarospora macrocyclos, is described as new to science from three collections made at 65° south in the Argentine Islands (Graham Land, maritime Antarctica). The fungus has a distinct internal apical beak in the ascus and ellipsoid three-septate ascospores; therefore, it is the member ofSagediopsissubgenusHawksworthiella. Morphologically and anatomicallyS. bayozturkiiis most similar toS. campsterianaandS. pertusariicola, which are confined to the lichen hostsOchrolechiaspp. andPertusariaspp., respectively. In addition to having different hosts,S. bayozturkiidiffers from these two species by having smaller ascomata and shorter ascospores. Its similarities to other species of the genus are discussed, and an artificial key based on the published descriptions of the ten species now known in the genusSagediopsisis presented.
‘Olde worlde’ urban? Reconstructing historic urban environments at exhibitions, 1884–1908
Authors: HILL KATE
Published: March 2017

From 1884 until the Franco-British Exhibition in 1908, international and national exhibitions had a fad for including reconstructed historic urban streets in their attractions. This article investigates the meaning of such forms of urban heritage in the light of modernizing cities. It shows that ideas about historical authenticity were complex, and traces this to the ways in which staff and employees, and also the big crowds at the displays, co-produced this meaning. It suggests that visitors particularly constructed meaning through haptic and emotional encounters with the past, providing evidence of the development of new memory practices for modernity.
‘Biracial’-Looking Twins: A New Twin Type?/Twin Research: Twins with Cystic Teratomas; Sleep Quality and Body Mass Index; Previable Membrane Rupture/Print and Online Reports: Twins Born to a Sister Surrogate; NASA Twin Study; African-Cosmopolitan Twin Fashion Inspirations; Triplet Hockey Stars
Authors: Segal Nancy L.
Published: March 2017

Dizygotic (DZ) co-twins born to mothers and fathers from different racial or ethnic backgrounds often resemble one parent much more than the other. As such, these pairs comprise a unique subset of twins for investigating how others’ responses to their different looks may affect their personalities and self-esteem. This article describes some of these twin pairs and some challenges of raising them, and suggests ways they may be used in research. Next, recent twin research on cystic teratomas, relations between sleep quality and body mass index, and previable membrane rupture is described. The final section concerns twins, twin studies, and related events in the media, namely: twins born to a sister surrogate, the NASA twin investigation, inspiring African-Cosmopolitan twins in fashion, and triplet Hockey Stars.
Realizing Haldane model in Fe-based honeycomb ferromagnetic insulators
Authors: Kim Heung-Sik , Kee Hae-Young
Published: March 2017

The topological Haldane model on a honeycomb lattice is a prototype of systems hosting topological phases of matter without external fields. It is the simplest model exhibiting the quantum Hall effect without Landau levels, which motivated theoretical and experimental explorations of topological insulators and superconductors. Despite its simplicity, its realization in condensed matter systems has been elusive due to a seemingly difficult condition of spinless fermions with sublattice-dependent magnetic flux terms. While there have been theoretical proposals including elaborate atomic-scale engineering, identifying candidate topological Haldane model materials has not been successful, and the first experimental realization was recently made in ultracold atoms. Here, we suggest that a series of Fe-based honeycomb ferromagnetic insulators, AFe2(PO4)2 (A=Ba, Cs, K, La) possess Chern bands described by the topological Haldane model. How to detect the quantum anomalous Hall effect is also discussed.
Comprehensive definition of human immunodominant CD8 antigens in tuberculosis
Authors: Lewinsohn Deborah A. , Swarbrick Gwendolyn M. , Park Byung , Cansler Meghan E. , Null Megan D. , Toren Katelynne G. , Baseke Joy , Zalwango Sarah , Mayanja-Kizza Harriet , Malone LaShaunda L. , Nyendak Melissa , Wu Guanming , Guinn Kristi , McWeeney Shannon , Mori Tomi , Chervenak Keith A. , Sherman David R. , Boom W. Henry , Lewinsohn David M.
Published: March 2017

Despite widespread use of the Bacillus Calmette-Guerin vaccine, tuberculosis, caused by infection with Mycobacterium tuberculosis, remains a leading cause of morbidity and mortality worldwide. As CD8+ T cells are critical to tuberculosis host defense and a phase 2b vaccine trial of modified vaccinia Ankara expressing Ag85a that failed to demonstrate efficacy, also failed to induce a CD8+ T cell response, an effective tuberculosis vaccine may need to induce CD8+ T cells. However, little is known about CD8, as compared to CD4, antigens in tuberculosis. Herein, we report the results of the first ever HLA allele independent genome-wide CD8 antigen discovery program. Using CD8+ T cells derived from humans with latent tuberculosis infection or tuberculosis and an interferon-γ ELISPOT assay, we screened a synthetic peptide library representing 10% of the Mycobacterium tuberculosis proteome, selected to be enriched for Mycobacterium tuberculosis antigens. We defined a set of immunodominant CD8 antigens including part or all of 74 Mycobacterium tuberculosis proteins, only 16 of which are previously known CD8 antigens. Immunogenicity was associated with the degree of expression of mRNA and protein. Immunodominant antigens were enriched in cell wall proteins with preferential recognition of Esx protein family members, and within proteins comprising the Mycobacterium tuberculosis secretome. A validation study of immunodominant antigens demonstrated that these antigens were strongly recognized in Mycobacterium tuberculosis-infected individuals from a tuberculosis endemic region in Africa. The tuberculosis vaccine field will likely benefit from this greatly increased known repertoire of CD8 immunodominant antigens and definition of properties of Mycobacterium tuberculosis proteins important for CD8 antigenicity.
Influences of surface treatments with abrasive paper and sand-blasting on surface morphology, hydrophilicity, mineralization and osteoblasts behaviors of n-CS/PK composite
Authors: Tang Xiaoming , Huang Kai , Dai Jian , Wu Zhaoying , Cai Liang , Yang Lili , Wei Jie , Sun Hailang
Published: March 2017

The surfaces of nano-calcium silicate (n-CS)/polyetheretherketone (PK) composites were treated with abrasive paper and sand-blasting, and the surfaces performances of the as-treated composites were studied. The results showed that the surface roughness, hydrophilicity and mineralization of the simulated body fluid (SBF) of the composites surfaces were significantly improved, and the properties of the composites treated by with sand-blasting were better than those treated with abrasive paper. Moreover, the treated composites significantly promoted osteoblasts responses, such as cell attachment, spreading, proliferation and alkaline phosphatase (ALP) activity, compared to un-treated composites, and the cellular responses to the composites treated with sand-blasting were better than those treated with abrasive paper. The results suggested that surface treatment with sand-blasting was an effective method to greatly improve the surface bioperformances of the n-CS/PK composite, and this treated composite with improved bioactivity and cytocompatibility might be a promising implant material for orthopedic applications.
Identification of genes related to salt stress tolerance using intron-length polymorphic markers, association mapping and virus-induced gene silencing in cotton
Authors: Cai Caiping , Wu Shuang , Niu Erli , Cheng Chaoze , Guo Wangzhen
Published: March 2017

Intron length polymorphisms (ILPs), a type of gene-based functional marker, could themselves be related to the particular traits. Here, we developed a genome-wide cotton ILPs based on orthologs annotation from two sequenced diploid species, A-genome Gossypium arboreum and D-genome G. raimondii. We identified 10,180 putative ILP markers from 5,021 orthologous genes. Among these, 535 ILP markers from 9 gene families related to stress were selected for experimental verification. Polymorphic rates were 72.71% between G. arboreum and G. raimondii and 36.45% between G. hirsutum acc. TM-1 and G. barbadense cv. Hai7124. Furthermore, 14 polymorphic ILP markers were detected in 264 G. hirsutum accessions. Coupled with previous simple sequence repeats (SSRs) evaluations and salt tolerance assays from the same individuals, we found a total of 25 marker-trait associations involved in nine ILPs. The nine genes, temporally named as C1 to C9, showed the various expressions in different organs and tissues, and five genes (C3, C4, C5, C7 and C9) were significantly upregulated after salt treatment. We verified that the five genes play important roles in salt tolerance. Particularly, silencing of C4 (encodes WRKY DNA-binding protein) and C9 (encodes Mitogen-activated protein kinase) can significantly enhance cotton susceptibility to salt stress.
Efficient collective influence maximization in cascading processes with first-order transitions
Authors: Pei Sen , Teng Xian , Shaman Jeffrey , Morone Flaviano , Makse Hernán A.
Published: March 2017

In many social and biological networks, the collective dynamics of the entire system can be shaped by a small set of influential units through a global cascading process, manifested by an abrupt first-order transition in dynamical behaviors. Despite its importance in applications, efficient identification of multiple influential spreaders in cascading processes still remains a challenging task for large-scale networks. Here we address this issue by exploring the collective influence in general threshold models of cascading process. Our analysis reveals that the importance of spreaders is fixed by the subcritical paths along which cascades propagate: the number of subcritical paths attached to each spreader determines its contribution to global cascades. The concept of subcritical path allows us to introduce a scalable algorithm for massively large-scale networks. Results in both synthetic random graphs and real networks show that the proposed method can achieve larger collective influence given the same number of seeds compared with other scalable heuristic approaches.
Soil classification predicts differences in prokaryotic communities across a range of geographically distant soils once pH is accounted for
Authors: Kaminsky Rachel , Trouche Blandine , Morales Sergio E.
Published: March 2017

Agricultural land is typically managed based on visible plant life at the expense of the belowground majority. However, microorganisms mediate processes sustaining plant life and the soil environment. To understand the role of microbes we first must understand what controls soil microbial community assembly. We assessed the distribution and composition of prokaryotic communities from soils representing four geographic regions on the South Island of New Zealand. These soils are under three different uses (dairy, sheep and beef, and high country farming) and are representative of major soil classification groups (brown, pallic, gley and recent). We hypothesized that pH would account for major community patterns based on 16S profiles, but that land use and location would be secondary modifiers. Community diversity and structure was linked to pH, coinciding with land use. Soil classification correlated with microbial community structure and evenness, but not richness in high country and sheep and beef communities. The impact of land use and pH remained significant at the regional scale, but soil classification provided support for community variability not explained by either of those factors. These results suggest that several edaphic properties must be examined at multiple spatial scales to robustly examine soil prokaryotic communities.
Extremely high-performance visible light photodetector in the Sb2SeTe2 nanoflake
Authors: Huang Shiu-Ming , Huang Shih-Jhe , Yan You-Jhih , Yu Shih-Hsun , Chou Mitch , Yang Hung-Wei , Chang Yu-Shin , Chen Ruei-San
Published: March 2017

The photocurrent was performed in the Sb2SeTe2 topological insulator at a wavelength of 532 nm. It exhibits extremely high performance that the responsivity and the photoconductive gain reach 2293 AW−1 and 5344 at 1 V. This high photoresponse is orders of magnitude higher than most reported values in topological insulators and two-dimensional transitional metal dichalcogenides. This finding suggests that the Sb2SeTe2 nanoflake has great potential for future optoelectronic device applications.
Organization of prefrontal network activity by respiration-related oscillations
Authors: Biskamp Jonatan , Bartos Marlene , Sauer Jonas-Frederic
Published: March 2017

The medial prefrontal cortex (mPFC) integrates information from cortical and sub-cortical areas and contributes to the planning and initiation of behaviour. A potential mechanism for signal integration in the mPFC lies in the synchronization of neuronal discharges by theta (6–12 Hz) activity patterns. Here we show, using in vivo local field potential (LFP) and single-unit recordings from awake mice, that prominent oscillations in the sub-theta frequency band (1–5 Hz) emerge during awake immobility in the mPFC. These oscillation patterns are distinct from but phase-locked to hippocampal theta activity and occur synchronized with nasal respiration (hence termed prefrontal respiration rhythm [PRR]). PRR activity modulates the amplitude of prefrontal gamma rhythms with greater efficacy than theta oscillations. Furthermore, single-unit discharges of putative pyramidal cells and GABAergic interneurons are entrained by prefrontal PRR and nasal respiration. Our data thus suggest that PRR activity contributes to information processing in the prefrontal neuronal network.
Flower-shaped cobalt oxide nano-structures as an efficient, flexible and stable electrocatalyst for the oxygen evolution reaction
Authors: Ranaweera C. K. , Zhang C. , Bhoyate S. , Kahol P. K. , Ghimire M. , Mishra S. R. , Perez Felio , Gupta Bipin Kumar , Gupta Ram K.
Published: March 2017

A binder free approach was used for the synthesis of flower-shaped Co3O4 nanosheets for the oxygen evolution reaction.
Osteoarthritis Patients’ Experiences of Pharmacotherapy for Pain Management in Iran: A Qualitative Study
Authors: Zamanzadeh Vahid , Ahmadi Fazlollah , Behshid Mozhgan , Irajpoor Alireza , Zakeri-Milani Parvin
Published: March 2017

Despite the effectiveness of pharmacotherapy for pain management in patients with osteoarthritis (OA), personal biases in the selection, administration, and continuation of pharmacotherapy challenge the proper management of symptoms and the effectiveness of the therapy. This study was conducted to carry out an in-depth examination of the experiences of patients with OA about their use of pharmacotherapy for the OA pain management and the existing challenges.

The present qualitative study was conducted on 17 patients with OA, 5 of their family members and 8 healthcare personnel using a conventional content analysis approach. Data were collected through 35 interviews, which were unstructured at first but became semi-structured later on. Data collection continued until data saturation and analyzed simultaneously. The criteria used to determine the rigor of the study included the credibility, transferability, dependability and conformability of the data.

The analysis of the data revealed 3 main categories and 8 subcategories. The main categories including preference for non-pharmacological modalities, preference for symptomatic slow-acting drugs for osteoarthritis (SySADOAs) and preference for vitamins and minerals.

Briefing the patients on the therapeutic goals, participating them in the clinical decision-making process, modifying drug administration patterns through prescribing the minimum effective dosage and substituting alternative therapies whenever possible, consistently monitoring the therapeutic responses and any unexpected complications and use of complementary treatments, makes up strategies that can help improve OA pain management.
National German Audit of Diagnosis, Treatment, and Teaching in Secondary Adrenal Insufficiency
Authors: Petersenn Stephan , Honegger Jürgen , Quinkler Marcus
Published: March 2017

Great heterogeneity seems to exist regarding diagnosis, therapy, and teaching of patients with secondary adrenal insufficiency (SAI) across Germany resulting in different diagnosis and treatment strategies. The aim of the work was to present the first national audit on diagnosis, treatment, and patient teaching of SAI reflecting common clinical practice in Germany. A self-designed questionnaire was sent via e-mail to all members of the German Endocrine Society (approx. 120 centers). Returned questionnaires (response rate 38.3%) were checked for duplicity of institutions and analyzed. Diagnostic testing focuses on those patients with relevant risk for adrenal insufficiency. Basal serum cortisol is mostly used as screening test. Short synacthen and CRH tests are the preferred confirmatory tests, however, cut-off values vary due to different assays used. Patients with radiation, second surgery, progressive disease or new symptoms are followed by serial re-testing. Perioperative management and frequency of postoperative re-evaluations differ among centers. Hydrocortisone is the preferred glucocorticoid for replacement therapy, but daily doses vary considerably (10–30 mg/day). Some centers perform hormone measurements for dose adjustment of glucocorticoid replacement therapy whereas others rely on clinical judgement. Patients’ teaching is done in 84% of centers, but only half of the centers include patients’ relatives. Homogeneity exists in patients’ teaching regarding intercurrent illnesses (fever, diarrhoea). Recommendations regarding dose adaptations in situations such as sport-activities, dental-procedures, or coughing are highly variable. This first national audit reveals great heterogeneity among German centers and could improve patients’ care in SAI, for example, by initiating new trials and developing clinical practice guidelines.
A generalized AZ-non-Maxwellian velocity distribution function for space plasmas
Authors: Abid A. A. , Khan M. Z. , Lu Quanming , Yap S. L.
Published: March 2017

A more generalized form of the non-Maxwellian distribution function, i.e., the AZ-distribution function is presented. Its fundamental properties are numerically observed by the variation of three parameters: α (rate of energetic particles on the shoulder), r (energetic particles on a broad shoulder), and q (superthermality on the tail of the velocity distribution curve of the plasma species). It has been observed that (i) the AZ- distribution function reduces to the (r,q)- distribution for α→0; (ii) the AZ- distribution function reduces to the q- distribution for α→0, and r→0; (iii) the  AZ-distribution reduces to Cairns-distribution function for r→0, and q→∞; (iv) the AZ-distribution reduces to Vasyliunas Cairns distribution for r→0, and q=κ+1; (v) the AZ-distribution reduces to kappa distribution for α→0, r→0, and q=κ+1; and (vi) finally, the AZ-distribution reduces to Maxwellian distribution   for α→0,r→0, and q→∞. The uses of this more generalized AZ- distribution function in various space plasmas are briefly discussed.
Experimental measurements of energy transfer and nonlinear interaction in turbulence at the sino-united spherical tokamak
Authors: Chai Song , Xu Yuhong , Gao Zhe , Wang Wenhao , Liu Yangqing , Tan Yi
Published: March 2017

The characteristics of the energy transfer and nonlinear coupling among edge electromagnetic turbulence have been dedicatedly studied in various discharge stages at the sino-united spherical tokamak using multiple Langmuir and magnetic probe arrays. The wavelet bispectral analysis and the modified Kim's method are applied to investigate turbulence properties and their linear growth/damping and nonlinear energy transfer rates, along with multi-field turbulence interactions. The results show diverse features in the linear growth and nonlinear energy transfer between multi-field fluctuations during the current ramp-up, stationary, and internal connection event discharge phases. The diversity implies the importance to develop more sophisticated multi-field models to directly estimate the energy transfer rate among multiple turbulent fields.
The design of a multi-harmonic step-tunable gyrotron
Authors: Qi Xiang-Bo , Du Chao-Hai , Zhu Juan-Feng , Pan Shi , Liu Pu-Kun
Published: March 2017

The theoretical study of a step-tunable gyrotron controlled by successive excitation of multi-harmonic modes is presented in this paper. An axis-encircling electron beam is employed to eliminate the harmonic mode competition. Physics images are depicted to elaborate the multi-harmonic interaction mechanism in determining the operating parameters at which arbitrary harmonic tuning can be realized by magnetic field sweeping to achieve controlled multiband frequencies' radiation. An important principle is revealed that a weak coupling coefficient under a high-harmonic interaction can be compensated by a high Q-factor. To some extent, the complementation between the high Q-factor and weak coupling coefficient makes the high-harmonic mode potential to achieve high efficiency. Based on a previous optimized magnetic cusp gun, the multi-harmonic step-tunable gyrotron is feasible by using harmonic tuning of first-to-fourth harmonic modes. Multimode simulation shows that the multi-harmonic gyrotron can operate on the 34 GHz first-harmonic TE11 mode, 54 GHz second-harmonic TE21 mode, 74 GHz third-harmonic TE31 mode, and 94 GHz fourth-harmonic TE41 mode, corresponding to peak efficiencies of 28.6%, 35.7%, 17.1%, and 11.4%, respectively. The multi-harmonic step-tunable gyrotron provides new possibilities in millimeter–terahertz source development especially for advanced terahertz applications.
Self-consistent perturbed equilibrium with neoclassical toroidal torque in tokamaks
Authors: Park Jong-Kyu , Logan Nikolas C.
Published: March 2017

Toroidal torque is one of the most important consequences of non-axisymmetric fields in tokamaks. The well-known neoclassical toroidal viscosity (NTV) is due to the second-order toroidal force from anisotropic pressure tensor in the presence of these asymmetries. This work shows that the first-order toroidal force originating from the same anisotropic pressure tensor, despite having no flux surface average, can significantly modify the local perturbed force balance and thus must be included in perturbed equilibrium self-consistent with NTV. The force operator with an anisotropic pressure tensor is not self-adjoint when the NTV torque is finite and thus is solved directly for each component. This approach yields a modified, non-self-adjoint Euler-Lagrange equation that can be solved using a variety of common drift-kinetic models in generalized tokamak geometry. The resulting energy and torque integral provides a unique way to construct a torque response matrix, which contains all the information of self-consistent NTV torque profiles obtainable by applying non-axisymmetric fields to the plasma. This torque response matrix can then be used to systematically optimize non-axisymmetric field distributions for desired NTV profiles.
On the amplitude of dust-density waves in inhomogeneous dusty plasmas
Authors: Tadsen Benjamin , Greiner Franko , Piel Alexander
Published: March 2017

Density waves in a cloud of submicron dust particles confined in an rf plasma are examined with respect to their amplitude. The plasma shows a strong inhomogeneity in its densities and the dust particle charge. An ion density gradient appears due to ambipolar diffusion and leads to a dust charge gradient provided by charge depletion. Using dust-density wave frequency and wave number as a diagnostic for the plasma parameters, it is found that the wave amplitude increases or decreases as the wave travels into regions with decreasing or increasing particle charge. The experimental amplitude profile is similar to the theoretical curve predicted by a formula from Singh and Rao [Phys. Plasmas 6, 3157–3162 (1999)].
New scheme for enhancement of maximum proton energy with a cone-hole target irradiated by a short intense laser pulse
Authors: Yang Siqian , Zhou Weimin , Jiao Jinlong , Zhang Zhimeng , Cao Leifeng , Gu Yuqiu , Zhang Baohan
Published: March 2017

Improvement of proton energy from short intense laser interaction with a new proposal of a cone-hole target is investigated via two-dimensional particle-in-cell simulations. The configuration of the target is a cone structure with a hole of changeable diameter through the center of the tip, with proton layers contaminated both on the target rear surface and at the rear part of the hole. In the interacting process, the cone-hole geometry enables the focus of the laser pulse by the cone structure and the consequent penetration of the intensified laser through the tip along the hole instead of reflection, which can increase the energy coupling from laser field to plasmas. The heated electrons, following the target normal sheath acceleration scheme, induce a much stronger electrostatic field in the longitudinal direction at the rear surface of the target than that in the traditional foil case. The simulation results indicate that the accelerated proton beam from the cone-hole target has a cutoff energy about 5.7 and 2.1 times larger than the foil case and the hollow cone case, respectively. Furthermore, the case of the cone-hole target without the proton layer in the hole is also analyzed to demonstrate the effect of the proton layer position and the results show that not only can the existence of the central proton layer improve the proton energy but also lead to a better collimation. The dependence of proton energy on the hole diameter and the scaling law of the maximum proton energy relative to laser intensity are also presented.
Rapid sampling of stochastic displacements in Brownian dynamics simulations
Authors: Fiore Andrew M. , Balboa Usabiaga Florencio , Donev Aleksandar , Swan James W.
Published: March 2017

We present a new method for sampling stochastic displacements in Brownian Dynamics (BD) simulations of colloidal scale particles. The method relies on a new formulation for Ewald summation of the Rotne-Prager-Yamakawa (RPY) tensor, which guarantees that the real-space and wave-space contributions to the tensor are independently symmetric and positive-definite for all possible particle configurations. Brownian displacements are drawn from a superposition of two independent samples: a wave-space (far-field or long-ranged) contribution, computed using techniques from fluctuating hydrodynamics and non-uniform fast Fourier transforms; and a real-space (near-field or short-ranged) correction, computed using a Krylov subspace method. The combined computational complexity of drawing these two independent samples scales linearly with the number of particles. The proposed method circumvents the super-linear scaling exhibited by all known iterative sampling methods applied directly to the RPY tensor that results from the power law growth of the condition number of tensor with the number of particles. For geometrically dense microstructures (fractal dimension equal three), the performance is independent of volume fraction, while for tenuous microstructures (fractal dimension less than three), such as gels and polymer solutions, the performance improves with decreasing volume fraction. This is in stark contrast with other related linear-scaling methods such as the force coupling method and the fluctuating immersed boundary method, for which performance degrades with decreasing volume fraction. Calculations for hard sphere dispersions and colloidal gels are illustrated and used to explore the role of microstructure on performance of the algorithm. In practice, the logarithmic part of the predicted scaling is not observed and the algorithm scales linearly for up to 4×106 particles, obtaining speed ups of over an order of magnitude over existing iterative methods, and making the cost of computing Brownian displacements comparable to the cost of computing deterministic displacements in BD simulations. A high-performance implementation employing non-uniform fast Fourier transforms implemented on graphics processing units and integrated with the software package HOOMD-blue is used for benchmarking.
Destabilization of a cylindrically confined electron cloud by impact ionization of background neutrals: 2D3v PIC simulation with Monte-Carlo-collisions
Authors: Sengupta M. , Ganesh R.
Published: March 2017

In this paper, we have investigated, through simulation, the process of destabilization of a cylindrically confined electron cloud due to the presence of a single species of neutral atoms, Ar in the background of the trap at a pressure relevant to experiments. The destabilization occurs because of a gradual accumulation of Ar+ in the cloud by the electron-impact ionization of the background neutrals. The trapped ions gradually collectively form a sizeable ion cloud which engages in a rotational two-stream instability (the ion resonance instability) with the electron cloud. The instability excites a growing fundamental diocotron mode on both components of the mixed non-neutral cloud. With the help of a set of numerical diagnostics, we have investigated the nonlinear evolution of the excited fundamental mode under the combined influence of two ongoing processes viz, (i) the changing electron and ion populations caused by electron impact ionization of the background Ar, and also by the radial loss of both charged species to the grounded trap wall at later stages and (ii) the elastic scattering of electrons and ions that make non-ionizing collisions with the background neutrals. The 2D collisionless dynamics of the instability has been simulated using a 2D Particle-in-Cell code operating on a Cartesian grid laid out on the cylindrical trap's cross-section, and the 3D ionizing and non-ionizing collisions between charged particles and background neutrals have been simulated using the technique of Monte-Carlo-Collisions.
On the evaluation of Pierce parameters C and Q in a traveling wave tube
Authors: Simon D. H. , Wong P. , Chernin D. , Lau Y. Y. , Hoff B. , Zhang P. , Dong C. F. , Gilgenbach R. M.
Published: March 2017

A study of an exactly solvable model of a traveling wave tube (TWT) shows that Pierce gain parameter C and space charge parameter Q generally depend on wavenumber k in addition to frequency ω. The choice of k at which C and Q are evaluated may strongly affect their values and, consequently, the values of the small signal gain obtained from 3- and 4-wave Pierce theory. In order to illustrate this effect, we calculate the spatial amplification rate, ki, from the exact dispersion relation for a dielectric TWT model which is exactly solvable. We compare this exact value of ki with approximate values obtained from Pierce's classical 3-wave and 4-wave dispersion relations, obtained by making various assumptions on k in the evaluation of C and Q. We find that the various ways to approximate C and Q will have a significant influence on the numerical values of ki. For our dielectric TWT example, Pierce's 4-wave TWT dispersion relation generally yields the most accurate values of ki if Q is evaluated for k = ω/v0, where v0 is the beam velocity, and if the complete frequency and wavelength dependence of C is retained. Pierce's 3-wave theory also yields accurate values of ki using a different form of Q from the 4-wave theory. The implications of this result for TWT design are explored.
HSX as an example of a resilient non-resonant divertor
Authors: Bader A. , Boozer A. H. , Hegna C. C. , Lazerson S. A. , Schmitt J. C.
Published: March 2017

This paper describes an initial description of the resilient divertor properties of quasi-symmetric (QS) stellarators using the HSX (Helically Symmetric eXperiment) configuration as a test-case. Divertors in high-performance QS stellarators will need to be resilient to changes in plasma configuration that arise due to evolution of plasma pressure profiles and bootstrap currents for divertor design. Resiliency is tested by examining the changes in strike point patterns from the field line following, which arise due to configurational changes. A low strike point variation with high configuration changes corresponds to high resiliency. The HSX edge displays resilient properties with configuration changes arising from the (1) wall position, (2) plasma current, and (3) external coils. The resilient behavior is lost if large edge islands intersect the wall structure. The resilient edge properties are corroborated by heat flux calculations from the fully 3-D plasma simulations using EMC3-EIRENE. Additionally, the strike point patterns are found to correspond to high curvature regions of magnetic flux surfaces.
Numerical study of influence of hydrogen backflow on krypton Hall effect thruster plasma focusing
Authors: Yan Shilin , Ding Yongjie , Wei Liqiu , Hu Yanlin , Li Jie , Ning Zhongxi , Yu Daren
Published: March 2017

The influence of backflow hydrogen on plasma plume focusing of a krypton Hall effect thruster is studied via a numerical simulation method. Theoretical analysis indicates that hydrogen participates in the plasma discharge process, changes the potential and ionization distribution in the thruster discharge cavity, and finally affects the plume focusing within a vacuum vessel.
Polarizable charge equilibration model for predicting accurate electrostatic interactions in molecules and solids
Authors: Naserifar Saber , Brooks Daniel J. , Goddard William A. , Cvicek Vaclav
Published: March 2017

Electrostatic interactions play a critical role in determining the properties, structures, and dynamics of chemical, biochemical, and material systems. These interactions are described well at the level of quantum mechanics (QM) but not so well for the various models used in force field simulations of these systems. We propose and validate a new general methodology, denoted PQEq, to predict rapidly and dynamically the atomic charges and polarization underlying the electrostatic interactions. Here the polarization is described using an atomic sized Gaussian shaped electron density that can polarize away from the core in response to internal and external electric fields, while at the same time adjusting the charge on each core (described as a Gaussian function) so as to achieve a constant chemical potential across all atoms of the system. The parameters for PQEq are derived from experimental atomic properties of all elements up to Nobelium (atomic no. = 102). We validate PQEq by comparing to QM interaction energy as probe dipoles are brought along various directions up to 30 molecules containing H, C, N, O, F, Si, P, S, and Cl atoms. We find that PQEq predicts interaction energies in excellent agreement with QM, much better than other common charge models such as obtained from QM using Mulliken or ESP charges and those from standard force fields (OPLS and AMBER). Since PQEq increases the accuracy of electrostatic interactions and the response to external electric fields, we expect that PQEq will be useful for a large range of applications including ligand docking to proteins, catalytic reactions, electrocatalysis, ferroelectrics, and growth of ceramics and films, where it could be incorporated into standard force fields as OPLS, AMBER, CHARMM, Dreiding, ReaxFF, and UFF.
A molecular Debye-Hückel theory and its applications to electrolyte solutions: The size asymmetric case
Authors: Xiao Tiejun , Song Xueyu
Published: March 2017

A molecular Debye-Hückel theory for electrolyte solutions with size asymmetry is developed, where the dielectric response of an electrolyte solution is described by a linear combination of Debye-Hückel-like response modes. As the size asymmetry of an electrolyte solution leads to a charge imbalanced border zone around a solute, the dielectric response to the solute is characterized by two types of charge sources, namely, a bare solute charge and a charge distribution due to size asymmetry. These two kinds of charge sources are screened by the solvent differently, our theory presents a method to calculate the mean electric potential as well as the electrostatic contributions to thermodynamic properties. The theory has been successfully applied to binary as well as multi-component primitive models of electrolyte solutions.
A setup for element specific magnetization dynamics using the transverse magneto-optic Kerr effect in the energy range of 30-72 eV
Authors: Jana S. , Terschlüsen J. A. , Stefanuik R. , Plogmaker S. , Troisi S. , Malik R. S. , Svanqvist M. , Knut R. , Söderström J. , Karis O.
Published: March 2017

In this paper, we present a spectrometer that is designed for element-specific and time-resolved transverse magneto-optic Kerr effect experiments at the high-harmonic generation pump-probe facility High Energy Laser Induced Overtone Source (HELIOS) laboratory. HELIOS delivers photons with energies between 30 eV and 72 eV with an overall time resolution of less than 40 fs. The spectrometer is based on a Rowland-circle geometry and allows for simultaneous measurements of all magnetic transition-metal elements. The setup also features easy sample transfer and alignment, and it combines high photon throughput, optimized data acquisition, and a fast switching of the magnetic field at the sample. The spectrometer performance is demonstrated by measuring the ultrafast demagnetization of permalloy. Our data are, for all practical purposes, identical to what have been reported in the earlier high-order harmonic generation work of a similar sample by Mathias et al. [Proc. Natl. Acad. Sci. U. S. A. 109, 4792–4797 (2012)], however, obtained within 15% of the acquisition time compared to their study. Furthermore, our data show a shift of the demagnetization curve of Ni relative to Fe, which has previously been interpreted as a delay of the Ni demagnetization to that of Fe [S. Mathias et al., Proc. Natl. Acad. Sci. U. S. A. 109, 4792–4797 (2012)].
Invited Review Article: Tip modification methods for tip-enhanced Raman spectroscopy (TERS) and colloidal probe technique: A 10 year update (2006-2016) review
Authors: Yuan C. C. , Zhang D. , Gan Y.
Published: March 2017

Engineering atomic force microscopy tips for reliable tip enhanced Raman spectroscopy (TERS) and colloidal probe technique are becoming routine practices in many labs. In this 10 year update review, various new tip modification methods developed over the past decade are briefly reviewed to help researchers select the appropriate method. The perspective is put in a large context to discuss the opportunities and challenges in this area, including novel combinations of seemingly different methods, potential applications of some methods which were not originally intended for TERS tip fabrication, and the problems of high cost and poor reproducibility of tip fabrication.
Wavelength conversion of QAM signals in a low loss CMOS compatible spiral waveguide
Authors: Da Ros Francesco , Porto da Silva Edson , Zibar Darko , Chu Sai T. , Little Brent E. , Morandotti Roberto , Galili Michael , Moss David J. , Oxenløwe Leif K.
Published: March 2017

We demonstrate wavelength conversion of quadrature amplitude modulation (QAM) signals, including 32-GBd quadrature phase-shift keying and 10-GBd 16-QAM, in a 50-cm long high index doped glass spiral waveguide. The quality of the generated idlers for up to 20 nm of wavelength shift is sufficient to achieve a BER performance below the hard decision forward error correction threshold BER performance (<3.8 × 103), with an optical signal-to-noise ratio penalty of less than 0.3 dB compared to the original signal. Our results confirm that this is a promising platform for nonlinear optical signal processing, as a result of both very low linear propagation loss (<0.07 dB/cm) and a large material bandgap, which in turn ensures negligible nonlinear loss at telecom wavelengths.
Predictability of large-scale atmospheric motions: Lyapunov exponents and error dynamics
Authors: Vannitsem Stéphane
Published: March 2017

The deterministic equations describing the dynamics of the atmosphere (and of the climate system) are known to display the property of sensitivity to initial conditions. In the ergodic theory of chaos, this property is usually quantified by computing the Lyapunov exponents. In this review, these quantifiers computed in a hierarchy of atmospheric models (coupled or not to an ocean) are analyzed, together with their local counterparts known as the local or finite-time Lyapunov exponents. It is shown in particular that the variability of the local Lyapunov exponents (corresponding to the dominant Lyapunov exponent) decreases when the model resolution increases. The dynamics of (finite-amplitude) initial condition errors in these models is also reviewed, and in general found to display a complicated growth far from the asymptotic estimates provided by the Lyapunov exponents. The implications of these results for operational (high resolution) atmospheric and climate modelling are also discussed.
Enhanced electrical properties, color-tunable up-conversion luminescence, and temperature sensing behaviour in Er-doped Bi3Ti1.5W0.5O9 multifunctional ferroelectric ceramics
Authors: Zhang Ying , Li Jun , Chai Xiaona , Wang Xusheng , Li Yongxiang , Yao Xi
Published: March 2017

Er-doped Bi3Ti1.5W0.5O9 (BTW-x) ferroelectric ceramics were prepared by a conventional solid-state reaction synthesis method, and their structure, electrical properties, up-conversion (UC) luminescence, and temperature sensing behaviour were investigated. A high piezoelectric coefficient d33 (9.6 pC/N), a large remnant polarization Pr (12.75 μC/cm2), a high Curie temperature Tc (730.2 °C), and the optimal luminescent intensity are obtained for the samples at x = 0.05. By changing the Er doped concentration, the BTW-x ceramics are capable of generating various UC spectra and the color could be tunable from green to yellow. According to the fluorescence intensity ratio of green emissions at 532.6 nm and 549.2 nm in the temperature range from 83 K to 423 K, optical temperature sensing properties are investigated and the maximum sensing sensitivity is found to be 0.00314 K−1 at 423 K. The results conclude that BTW-x would be a candidate in high temperature sensor, fluorescence thermometry, and opto-electronic integration applications.