bluuebunny/crossref_metadata_2025 huggingface dataset:
SparRec: An effective matrix completion framework of missing data imputation for GWAS
Authors: Jiang Bo , Ma Shiqian , Causey Jason , Qiao Linbo , Hardin Matthew Price , Bitts Ian , Johnson Daniel , Zhang Shuzhong , Huang Xiuzhen
Published: October 2016

Genome-wide association studies present computational challenges for missing data imputation, while the advances of genotype technologies are generating datasets of large sample sizes with sample sets genotyped on multiple SNP chips. We present a new framework SparRec (Sparse Recovery) for imputation, with the following properties: (1) The optimization models of SparRec, based on low-rank and low number of co-clusters of matrices, are different from current statistics methods. While our low-rank matrix completion (LRMC) model is similar to Mendel-Impute, our matrix co-clustering factorization (MCCF) model is completely new. (2) SparRec, as other matrix completion methods, is flexible to be applied to missing data imputation for large meta-analysis with different cohorts genotyped on different sets of SNPs, even when there is no reference panel. This kind of meta-analysis is very challenging for current statistics based methods. (3) SparRec has consistent performance and achieves high recovery accuracy even when the missing data rate is as high as 90%. Compared with Mendel-Impute, our low-rank based method achieves similar accuracy and efficiency, while the co-clustering based method has advantages in running time. The testing results show that SparRec has significant advantages and competitive performance over other state-of-the-art existing statistics methods including Beagle and fastPhase.
Purification and Characterization of a Novel Cold Shock Protein-Like Bacteriocin Synthesized by Bacillus thuringiensis
Authors: Huang Tianpei , Zhang Xiaojuan , Pan Jieru , Su Xiaoyu , Jin Xin , Guan Xiong
Published: October 2016

Bacillus thuringiensis (Bt), one of the most successful biopesticides, may expand its potential by producing bacteriocins (thuricins). The aim of this study was to investigate the antimicrobial potential of a novel Bt bacteriocin, thuricin BtCspB, produced by Bt BRC-ZYR2. The results showed that this bacteriocin has a high similarity with cold-shock protein B (CspB). BtCspB lost its activity after proteinase K treatment; however it was active at 60 °C for 30 min and was stable in the pH range 5–7. The partial loss of activity after the treatments of lipase II and catalase were likely due to the change in BtCspB structure and the partial degradation of BtCspB, respectively. The loss of activity at high temperatures and the activity variation at different pHs were not due to degradation or large conformational change. BtCspB did not inhibit four probiotics. It was only active against B. cereus strains 0938 and ATCC 10987 with MIC values of 3.125 μg/mL and 0.781 μg/mL, and MBC values of 12.5 μg/mL and 6.25 μg/mL, respectively. Taken together, these results provide new insights into a novel cold shock protein-like bacteriocin, BtCspB, which displayed promise for its use in food preservation and treatment of B. cereus-associated diseases.
Molecular characterization of host-parasite cell signalling in Schistosoma mansoni during early development
Authors: Ressurreição Margarida , Elbeyioglu Firat , Kirk Ruth S. , Rollinson David , Emery Aidan M. , Page Nigel M. , Walker Anthony J.
Published: October 2016

During infection of their human definitive host, schistosomes transform rapidly from free-swimming infective cercariae in freshwater to endoparasitic schistosomules. The ‘somules’ next migrate within the skin to access the vasculature and are surrounded by host molecules that might activate intracellular pathways that influence somule survival, development and/or behaviour. However, such ‘transactivation’ by host factors in schistosomes is not well defined. In the present study, we have characterized and functionally localized the dynamics of protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) activation during early somule development in vitro and demonstrate activation of these protein kinases by human epidermal growth factor, insulin, and insulin-like growth factor I, particularly at the parasite surface. Further, we provide evidence that support the existence of specialized signalling domains called lipid rafts in schistosomes and propose that correct signalling to ERK requires proper raft organization. Finally, we show that modulation of PKC and ERK activities in somules affects motility and reduces somule survival. Thus, PKC and ERK are important mediators of host-ligand regulated transactivation events in schistosomes, and represent potential targets for anti-schistosome therapy aimed at reducing parasite survival in the human host.
A unified theory of calcium alternans in ventricular myocytes
Authors: Qu Zhilin , Liu Michael B. , Nivala Michael
Published: October 2016

Intracellular calcium (Ca2+) alternans is a dynamical phenomenon in ventricular myocytes, which is linked to the genesis of lethal arrhythmias. Iterated map models of intracellular Ca2+ cycling dynamics in ventricular myocytes under periodic pacing have been developed to study the mechanisms of Ca2+ alternans. Two mechanisms of Ca2+ alternans have been demonstrated in these models: one relies mainly on fractional sarcoplasmic reticulum Ca2+ release and uptake, and the other on refractoriness and other properties of Ca2+ sparks. Each of the two mechanisms can partially explain the experimental observations, but both have their inconsistencies with the experimental results. Here we developed an iterated map model that is composed of two coupled iterated maps, which unifies the two mechanisms into a single cohesive mathematical framework. The unified theory can consistently explain the seemingly contradictory experimental observations and shows that the two mechanisms work synergistically to promote Ca2+ alternans. Predictions of the theory were examined in a physiologically-detailed spatial Ca2+ cycling model of ventricular myocytes.
THz-circuits driven by photo-thermoelectric, gate-tunable graphene-junctions
Authors: Brenneis Andreas , Schade Felix , Drieschner Simon , Heimbach Florian , Karl Helmut , Garrido Jose A. , Holleitner Alexander W.
Published: October 2016

For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches.
Antigen-affinity controls pre-germinal center B cell selection by promoting Mcl-1 induction through BAFF receptor signaling
Authors: Wensveen Felix M. , Slinger Erik , van Attekum Martijn HA , Brink Robert , Eldering Eric
Published: October 2016

Upon antigen encounter, the responsive B cell pool undergoes stringent selection which eliminates cells with low B cell receptor (BCR) affinity. Already before formation of the germinal center, activated B cells of low-affinity are negatively selected in a process that is molecularly not well understood. In this study, we investigated the mechanism behind pre-GC affinity-mediated B cell selection. We applied affinity mutants of HEL antigen and found that rapidly after activation B cells become highly dependent on the cytokine BAFF. Moreover, expression of BAFF receptor CD268 is regulated in a BCR-affinity dependent fashion. High affinity responses via BAFF correlated with PI3K activation, which controlled expression of the pro-survival protein Mcl-1, and thereby increased survival. In the presence of excess BAFF, or in absence of the Mcl-1 antagonist Noxa, more low-affinity B cells survived the first two days after antigen encounter. This resulted in increased numbers of antigen-specific B cells of low affinity upon immunization and reduced the overall affinity of cells that contributed to the germinal center reaction. Our findings elucidate a crucial molecular pathway of B cell selection in the earliest phases of activation by identifying a novel link between BCR affinity and BAFF-R signaling towards Mcl-1.
Investigation of bacterial effects of Asian dust events through comparison with seasonal variability in outdoor airborne bacterial community
Authors: Park Jonguk , Ichijo Tomoaki , Nasu Masao , Yamaguchi Nobuyasu
Published: October 2016

Atmospheric bacterial dispersion with aeolian dust has been reported to have a potential impact on public health and ecosystems. Asian dust is a major aeolian event that results in an estimated 4 million tons of Asian dust particles falling in Japan annually, 3,000–5,000 km away from their source regions. However, most studies have only investigated the effects of Asian dust during dust seasons. Therefore, in this study, outdoor bacterial abundance and community composition were determined by 16S rRNA quantitative PCR and amplicon sequencing, respectively, and compared on Asian and non-Asian dust days (2013–2015; 44 samples over four seasons). Seasonal variations in bacterial abundance of non-Asian dust days were not observed. Bacterial abundance of individual samples collected on non-Asian dust days changed dynamically relative to Asian dust days, with bacterial abundance occasionally reaching those of Asian dust days. The bacterial community composition on non-Asian dust days was rather stable seasonally, and did not differ from that on Asian dust days. These results indicate that bacteria in Asian dust does not immediately influence indigenous bacterial communities at the phylum/class level in distant downwind areas; accordingly, further studies of bacterial communities in downwind areas closer to the dust source are warranted.
Improving O2reduction at an enzymatic biocathode: mimicking the lungs
Authors: Hickey David P. , Knoche Krysti L. , Albertson Kelan , Castro Carolina , Milton Ross D. , Minteer Shelley D.
Published: October 2016

Phospholipid micelles were used to enhance O2concentrations by two-fold at the surface of a bilirubin oxidase biocathode in an enzymatic fuel cell.
A simple way to fine tune the redox potentials of cobalt ions encapsulated in nitrogen doped graphene molecular catalysts for the oxygen evolution reaction
Authors: Wang Jiong , Lin Wen-Feng , Shi Yi , Wang Huai-Song , Rong Lian-Qing , Xia Xing-Hua
Published: October 2016

A simple approach to fine-tuning the redox potential of Co2+ ions encapsulated in nitrogen doped graphene (NG) has been proposed. We found that the redox potential determines the oxygen evolution reaction activity of the catalyst.
Oxidation of InP nanowires: a first principles molecular dynamics study
Authors: Berwanger Mailing , Schoenhalz Aline L. , dos Santos Cláudia L. , Piquini Paulo
Published: October 2016

InP nanowires are candidates for optoelectronic applications, and as protective capping layers of III–V core–shell nanowires.
Thermal transport properties of antimonene: an ab initio study
Authors: Wang Shudong , Wang Wenhua , Zhao Guojun
Published: October 2016

Searching for low thermal conductivity materials is crucial for thermoelectric devices.
Mechanisms of H- and OH-assisted CO activation as well as C–C coupling on the flat Co(0001) surface – revisited
Authors: Liu Shaoli , Li Yong-Wang , Wang Jianguo , Jiao Haijun
Published: October 2016

The mechanisms of H- and OH-assisted CO activation and the consecutive C–C coupling on the flat Co(0001) surface have been computed at the level of periodic RPBE density functional theory.
Raising the N-aryl fluoride content in unsymmetrical diaryliminoacenaphthylenes as a route to highly active nickel(ii) catalysts in ethylene polymerization
Authors: Wang Xinxin , Fan Linlin , Yuan Yichun , Du Shizhen , Sun Yang , Solan Gregory A. , Guo Cun-Yue , Sun Wen-Hua
Published: October 2016

The title nickel systems, incorporating fluorine content on one N-aryl group, display superior productivity.
Cell-laden microfluidic microgels for tissue regeneration
Authors: Jiang Weiqian , Li Mingqiang , Chen Zaozao , Leong Kam W.
Published: October 2016

This review provides an overview of how cell-laden microfluidic microgels are generated, summarizes their most recent applications in tissue regeneration, and discusses future applications as well as existing challenges.
Isothermal amplification detection of miRNA based on the catalysis of nucleases and voltammetric characteristics of silver nanoparticles
Authors: Xu Jianhua , Han Kun , Liu Dongdong , Lin Li , Miao Peng
Published: October 2016

We have developed an exonuclease and nicking endonuclease aided electrochemical biosensor for the isothermal amplification detection of miRNA.
The discovery of new acetylcholinesterase inhibitors derived from pharmacophore modeling, virtual screening, docking simulation and bioassays
Authors: Zhang Yunqin , Zhang Shuqun , Xu Guowei , Yan Hui , Pu Yinglan , Zuo Zhili
Published: October 2016

Novel AChE inhibitors are discovered using computer aided drug design and bioassays.
Correction: A new class of radiopeptides for PET imaging of neuromedin-B receptor: 68Ga-ranatensin analogs
Authors: Morgat C. , Varshney R. , Vimont D. , Savona-Baron C. , Riès C. , Chanseau C. , Bertrand S. S. , Mishra A. K. , Hindié E. , Fernandez P. , Schulz J.
Published: October 2016

Correction for ‘A new class of radiopeptides for PET imaging of neuromedin-B receptor: 68Ga-ranatensin analogs’ by C. Morgat et al., Med. Chem. Commun., 2016, 7, 1217–1223.
Highly selective direct azidation of alcohols over a heterogeneous povidone–phosphotungstic solid acid catalyst
Authors: Kamble Sumit , More Sagar , Rode Chandrashekhar
Published: October 2016

A heterogeneous povidone–phosphotungstic acid catalyzed direct selective azidation of alcohols gave excellent product yields at room temperature.
A facile approach for the trifluoromethylthiolation of methylenecyclopropanes
Authors: Chen Min-Tao , Tang Xiang-Ying , Shi Min
Published: October 2016

Trifluoromethylthiolation of methylenecyclopropanes (MCPs) has been developed by using AgSCF3/Na2S2O8as a trifluoromethylthiolation source (SCF3) to give trifluoromethylthiolated 1,2-dihydronaphthalene derivatives in moderate to good yields.
Copper-mediated annulation of 2-(1-arylvinyl) anilines and aryl nitrosos towards 2,3-diaryl-2H-indazoles
Authors: Hu Weiming , Yu Jin-Tao , Liu Suqin , Jiang Yan , Cheng Jiang
Published: October 2016

A copper-mediated annulation of 2-(1-substituted vinyl)anilines and aryl nitrosos is developed, giving 2,3-diaryl pyrazoles in moderate to good yields.
Formal [3 + 2] cycloaddition of α-unsubstituted isocyanoacetates and methyleneindolinones: enantioselective synthesis of spirooxindoles
Authors: Peng Xiao-Jiao , Ho Yee Ann , Wang Zhi-Peng , Shao Pan-Lin , Zhao Yu , He Yun
Published: October 2016

The first formal [3 + 2] cycloaddition of α-unsubstituted isocyanoacetates with methyleneindolinones was developed. A variety of optically enriched 3,3′-pyrrolidinyl spirooxindoles were obtained.
Fabrication and evaluation of polymeric membranes for blood dialysis treatments using functionalized MWCNT based nanocomposite and sulphonated-PES
Authors: Irfan Muhammad , Idris Ani , Nasiri Rozita , Almaki Javad Hamzehalipour
Published: October 2016

The use of polyethersulfone based membranes for dialysis therapy is increasing, but the poor bio-compatibility of the PES membrane can raise severe blood reactions affecting the rate of morbidity and mortality of hemodialysis (HD) patients.
Hydrogen-peroxide-fuelled platinum–nickel–SU-8 microrocket with steerable propulsion using an eccentric nanoengine
Authors: Hu Liangxing , Tao Kai , Miao Jianmin , Grüber Gerhard
Published: October 2016

Microrockets with eccentric nanoengines are able to realize the steerable propulsion in either a clockwise or a counter-clockwise direction.
Convenient and efficient synthesis of functionalized unsymmetrical alkynyl sulfides
Authors: Doroszuk J. , Musiejuk M. , Demkowicz S. , Rachon J. , Witt D.
Published: October 2016

We developed a simple and efficient method for the synthesis of functionalized unsymmetrical alkynyl sulfides under mild conditions in good yields.
Investigation on pH-switchable (itaconic acid/ethylene glycol/acrylic acid) based polymeric biocompatible hydrogel
Authors: Sakthivel M. , Franklin D. S. , Sudarsan S. , Chitra G. , Guhanathan S.
Published: October 2016

A new variety of pH-sensitive polymeric hydrogels (IAE) have been developed and evaluated as biocompatible hydrogels using synergetic combinations of itaconic acid (IA), acrylic acid (AA), and ethylene glycol (EG) in water medium by free radical polymerization.
An easily accessible and recyclable copper nanoparticle catalyst for the solvent-free synthesis of dipyrromethanes and aromatic amines
Authors: Megarajan Sengan , Ayaz Ahmed Khan Behlol , Rajmohan Rajamani , Vairaprakash Pothiappan , Anbazhagan Veerappan
Published: October 2016

A facile method to prepare a reusable copper nanocatalyst is reported.
Bionic creation of nano-engineered Janus fabric for selective oil/organic solvent absorption
Authors: Gore Prakash M. , Dhanshetty Mamta , K. Balasubramanian
Published: October 2016

We present a self-driven and tunable hydrophobic/oleophilic, wettability-modified Janus fabric composed of a cellulosic substrate engineered with nanofibersviafacile a electrospinning technique that exhibits one-step selective oil absorption capacity from water.
Carbon-coated Si micrometer particles binding to reduced graphene oxide for a stable high-capacity lithium-ion battery anode
Authors: Han Xiang , Chen Huixin , Zhang Ziqi , Huang Donglin , Xu Jianfang , Li Cheng , Chen Songyan , Yang Yong
Published: October 2016

Micrometer Si (MSi) particles are an attractive alternative as high energy-density lithium-ion battery anodes.
Localized and sustained release of brain-derived neurotrophic factor from injectable hydrogel/microparticle composites fosters spinal learning after spinal cord injury
Authors: Khaing Zin Z. , Agrawal Nikunj K. , Park James H. , Xin Shangjing , Plumton Glendon C. , Lee Kuan H. , Huang Yung-Jen , Niemerski Ashley L. , Schmidt Christine E. , Grau James W.
Published: October 2016

Injectable hydrogel allows for sustained delivery of growth factor resulting in spinal mediated learning after injury.
An emerging dual collaborative strategy for high-performance tumor therapy with mesoporous silica nanotubes loaded with Mn3O4
Authors: Zhang Yi , Tan Jieqiong , Long Mei , Yang Huaming , Yuan Shuwen , Tang Aidong , Chang Shi , Hu Yuehua
Published: October 2016

A highly integrated nanocomposite is constructed based on mesoporous silica nanotubes (SiNTs)-loaded with Mn3O4 nanoparticles for cervical cancer therapy via T1-weighted magnetic resonance imaging and doxorubicin-based chemotherapy.
Loss of lamin B receptor is necessary to induce cellular senescence
Authors: Lukášová Emilie , Kovarˇík Aleš , Bacˇíková Alena , Falk Martin , Kozubek Stanislav
Published: October 2016

Cellular transition to senescence is associated with extensive chromatin reorganization and changes in gene expression. Recent studies appear to imply an association of lamin B1 (LB1) reduction with chromatin rearrangement in human fibroblasts promoted to senescence, while the mechanisms and structural features of these relationships have not yet been clarified. In this work, we examined the functions of LB1 and the lamin B receptor (LBR) in human cancer cells. We found that both LB1 and LBR tend to deplete during cancer cell transfer to senescence by γ-irradiation. A functional study employing silencing of LBR by small hairpin ribonucleic acid (shRNA) constructs revealed reduced LB1 levels suggesting that the regulation of both proteins is interrelated. The reduced expression of LBR resulted in the relocation of centromeric heterochromatin (CSH) from the inner nuclear membrane (INM) to the nucleoplasm and is associated with its unfolding. This indicates that LBR tethers heterochromatin to INM in cycling cancer cells and that LB1 is an integral part of this tethering. Down-regulation of LBR and LB1 at the onset of senescence are thus necessary for the release of heterochromatin binding to lamina, resulting in changes in chromatin architecture and gene expression. However, the senescence phenotype was not manifested in cell lines with reduced LBR and LB1 expression suggesting that other factors, such as deoxyribonucleic acid (DNA) damage, are needed to trigger senescence. We conclude that the primary response of cells to various stresses leading to senescence consists of the down-regulation of LBR and LB1 to attain reversal of the chromatin architecture.
Molecular mapping of α-thrombin (αT)/β2-glycoprotein I (β2GpI) interaction reveals how β2GpI affects αT functions
Authors: Acquasaliente Laura , Peterle Daniele , Tescari Simone , Pozzi Nicola , Pengo Vittorio , De Filippis Vincenzo
Published: October 2016

β2-Glycoprotein I (β2GpI) is the major autoantigen in the antiphospholipid syndrome, a thrombotic autoimmune disease. Nonetheless, the physiological role of β2GpI is still unclear. In a recent work, we have shown that β2GpI selectively inhibits the procoagulant functions of human α-thrombin (αT; i.e. prolongs fibrin clotting time, tc, and inhibits αT-induced platelet aggregation) without affecting the unique anticoagulant activity of the protease, i.e. the proteolytic generation of the anticoagulant protein C (PC) from the PC zymogen, which interacts with αT exclusively at the protease catalytic site. Here, we used several different biochemical/biophysical techniques and molecular probes for mapping the binding sites in the αT–β2GpI complex. Our results indicate that αT exploits the highly electropositive exosite-II, which is also responsible for anchoring αT on the platelet GpIbα (platelet receptor glycoprotein Ibα) receptor, for binding to a continuous negative region on β2GpI structure, spanning domain IV and (part of) domain V, whereas the protease active site and exosite-I (i.e. the fibrinogen-binding site) remain accessible for substrate/ligand binding. Furthermore, we provided evidence that the apparent increase in tc, previously observed with β2GpI, is more likely caused by alteration in the ensuing fibrin structure rather than by the inhibition of fibrinogen hydrolysis. Finally, we produced a theoretical docking model of αT–β2GpI interaction, which was in agreement with the experimental results. Altogether, these findings help to understand how β2GpI affects αT interactions and suggest that β2GpI may function as a scavenger of αT for binding to the GpIbα receptor, thus impairing platelet aggregation while enabling normal cleavage of fibrinogen and PC.
Can a Commercially Available Auditory Training Program Improve Audiovisual Speech Performance?
Authors: Rishiq Dania , Rao Aparna , Koerner Tess , Abrams Harvey
Published: October 2016

Purpose

The goal of this study was to determine whether hearing aids in combination with computer-based auditory training improve audiovisual (AV) performance compared with the use of hearing aids alone.

Method

Twenty-four participants were randomized into an experimental group (hearing aids plus ReadMyQuips [RMQ] training) and a control group (hearing aids only). The Multimodal Lexical Sentence Test for Adults (Kirk et al., 2012) was used to measure auditory-only (AO) and AV speech perception performance at three signal-to-noise ratios (SNRs). Participants were tested at the time of hearing aid fitting (pretest), after 4 weeks of hearing aid use (posttest I), and again after 4 weeks of RMQ training (posttest II).

Results

Results did not reveal an effect of training. As expected, interactions were found between (a) modality (AO vs. AV) and SNR and (b) test (pretest vs. posttests) and SNR.

Conclusion

Data do not show a significant effect of RMQ training on AO or AV performance as measured using the Multimodal Lexical Sentence Test for Adults.
Exploring the Clinical Utility of Relative Fundamental Frequency as an Objective Measure of Vocal Hyperfunction
Authors: Roy Nelson , Fetrow Rebecca A. , Merrill Ray M. , Dromey Christopher
Published: October 2016

Purpose

Vocal hyperfunction, related to abnormal laryngeal muscle activity, is considered the proximal cause of primary muscle tension dysphonia (pMTD). Relative fundamental frequency (RFF) has been proposed as an objective acoustic marker of vocal hyperfunction. This study examined (a) the ability of RFF to track changes in vocal hyperfunction after treatment for pMTD and (b) the influence of dysphonia severity, among other factors, on the feasibility of RFF computation.

Method

RFF calculations and dysphonia severity ratings were derived from pre- and posttreatment recordings from 111 women with pMTD and 20 healthy controls. Three vowel–voiceless consonant–vowel stimuli were analyzed.

Results

RFF onset slope consistently varied as a function of group (pMTD vs. controls) and time (pretherapy vs. posttherapy). Significant correlations between RFF onset cycle 1 and dysphonia severity were observed. However, in many samples, RFF could not be computed, and adjusted odds ratios revealed that these unanalyzable data were linked to dysphonia severity, phonetic (vowel–voiceless consonant–vowel) context, and group (pMTD vs. control).

Conclusions

RFF onset appears to be sensitive to the presence and degree of suspected vocal hyperfunction before and after therapy. The large number of unanalyzable samples (related especially to dysphonia severity in the pMTD group) represents an important limitation.
Computationally efficient calculation of skew effects in brushless doubly‐fed induction machines
Authors: Wang Xuezhou , Strous Tim Dave , Lahaye Domenico , Polinder Henk , Ferreira Jan Abraham
Published: October 2016

Brushless doubly‐fed induction machines (DFIMs) have great potential as variable‐speed generators in wind turbines. Undesired space‐harmonics exist because the special rotor needs to couple to two stator windings with different pole‐pair numbers and different frequencies. These undesired space‐harmonics could lead to noise, vibrations and low power quality. Applying skewed slots can overcome the above drawbacks. Previously, a two‐dimensional (2D) multi‐slice finite element (FE) method was applied to study the effects of skew which was time consuming. In the stage of initial design, it is not efficient to use such a model to predict how much the average torque and the torque ripple would be reduced by skewing slots. This study makes use of normal 2D FE results and applies skew factors in post‐processing to investigate the influence of rotor skew. It also proves that to apply skew factors appropriately, not only the space‐harmonic order needs to be considered, but also the time‐harmonic order. The proposed method can give an approximate prediction of skew effects with limited computing time. The results also indicate that skewing the rotor slot over one stator slot pitch could be a good choice to minimise the torque ripple in a brushless DFIM with a nested‐loop rotor.
A revised moving cluster distance to the Pleiades open cluster
Authors: Galli P. A. B. , Moraux E. , Bouy H. , Bouvier J. , Olivares J. , Teixeira R.
Published: October 2016

Context.The distance to the Pleiades open cluster has been extensively debated in the literature over several decades. Although different methods point to a discrepancy in the trigonometric parallaxes produced by the Hipparcosmission, the number of individual stars with known distances is still small compared to the number of cluster members to help solve this problem.

Aims.We provide a new distance estimate for the Pleiades based on the moving cluster method, which will be useful to further discuss the so-called Pleiades distance controversy and compare it with the very precise parallaxes from theGaiaspace mission.

Methods.We apply a refurbished implementation of the convergent point search method to an updated census of Pleiades stars to calculate the convergent point position of the cluster from stellar proper motions. Then, we derive individual parallaxes for 64 cluster members using radial velocities compiled from the literature, and approximate parallaxes for another 1146 stars based on the spatial velocity of the cluster. This represents the largest sample of Pleiades stars with individual distances to date.

Results.The parallaxes derived in this work are in good agreement with previous results obtained in different studies (excluding Hipparcos) for individual stars in the cluster. We report a mean parallax of 7.44 ± 0.08 mas and distance of 134.4+2.9-2.8pc that is consistent with the weighted mean of 135.0 ± 0.6 pc obtained from the non-Hipparcosresults in the literature.

Conclusions.Our result for the distance to the Pleiades open cluster is not consistent with the Hipparcoscatalog, but favors the recent and more precise distance determination of 136.2 ± 1.2 pc obtained from Very Long Baseline Interferometry observations. It is also in good agreement with the mean distance of 133 ± 5 pc obtained from the first trigonometric parallaxes delivered by theGaiasatellite for the brightest cluster members in common with our sample.
Theoretical predictions on efficiency of bi-exciton formation and dissociation in chiral carbon nanotubes
Authors: Kryjevski Andrei , Gifford Brendan , Kilina Svetlana , Kilin Dmitri
Published: October 2016

Efficient multiple exciton generation (MEG) in chiral single-wall carbon nanotubes (SWCNTs) is present within the solar spectrum range as shown by the many-body perturbation theory calculations combined with the density functional theory simulations. To describe the impact ionization process, we calculate exciton-to-biexciton decay rates R1→2 and biexciton-to-exciton rates R2→1 in the (6,2) and (10,5) SWCNTs. Within the solar energy range, we predict R1→2 ∼ 1014 s−1, while biexciton-to-exciton recombination is weak with R2→1/R1→2 ≤ 10−2. Also we calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, for which we find QE ≃ 1.2–1.6, that is 20%–60%. However, MEG strength in these SWCNTs varies strongly with the excitation energy due to highly non-uniform density of states at the low energy. We hypothesize that MEG efficiency in the chiral SWCNTs can be enhanced by altering the low-energy electronic spectrum via surface functionalization, or by mixing SWCNTs of different chiralities.
On the origin of multiexponential fluorescence decays from 2-aminopurine-labeled dinucleotides
Authors: Remington Jacob M. , Philip Abbey M. , Hariharan Mahesh , Kohler Bern
Published: October 2016

The fluorescent probe 2-aminopurine (2Ap) has been used for decades to study local conformational fluctuations in DNA. Steady-state and time-resolved measurements of 2Ap fluorescence have been used to predict specific conformational states through suitable modeling of the quenching of the fluorescence of a 2Ap residue incorporated site-specifically into a DNA strand. The success of this approach has been limited by a lack of understanding of the precise factors responsible for the complex, multiexponential decays observed experimentally. In this study, dinucleotides composed of 2Ap and adenine were studied by the time-correlated single-photon counting technique to investigate the causes of heterogeneous emission kinetics. Contrary to previous reports, we argue that emission from 2Ap that is stacked with a neighboring base contributes negligibly to the emission signals recorded more than 50 ps after excitation, which are instead dominated by emission from unstacked 2Ap. We find that the decay kinetics can be modeled using a continuous lifetime distribution, which arises from the inherent distance dependence of electron transfer rates without the need to postulate a small number of discrete states with decay times derived from multiexponential fits. These results offer a new perspective on the quenching of 2Ap fluorescence and expand the information that can be obtained from experiments.
Surface photovoltage studies of p-type AlGaN layers after reactive-ion etching
Authors: McNamara J. D. , Phumisithikul K. L. , Baski A. A. , Marini J. , Shahedipour-Sandvik F. , Das S. , Reshchikov M. A.
Published: October 2016

The surface photovoltage (SPV) technique was used to study the surface and electrical properties of Mg-doped, p-type AlxGa1−xN (0.06 < x < 0.17) layers. SPV measurements reveal significant deviation from previous SPV studies on p-GaN:Mg thin films and from the predictions of a thermionic model for the SPV behavior. In particular, the SPV of the p-AlGaN:Mg layers exhibited slower-than-expected transients under ultraviolet illumination and delayed restoration to the initial dark value. The slow transients and delayed restorations can be attributed to a defective surface region which interferes with normal thermionic processes. The top 45 nm of the p-AlGaN:Mg layer was etched using a reactive-ion etch which caused the SPV behavior to be substantially different. From this study, it can be concluded that a defective, near-surface region is inhibiting the change in positive surface charge by allowing tunneling or hopping conductivity of holes from the bulk to the surface, or by the trapping of electrons traveling to the surface by a high concentration of defects in the near-surface region. Etching removes the defective layer and reveals a region of presumably higher quality, as evidenced by substantial changes in the SPV behavior.
Structure and dynamics of liquid CS2: Going from ambient to elevated pressure conditions
Authors: Skarmoutsos Ioannis , Mossa Stefano , Samios Jannis
Published: October 2016

Molecular dynamics simulation studies were performed to investigate the structural and dynamic properties of liquid carbon disulfide (CS2) from ambient to elevated pressure conditions. The results obtained have revealed structural changes at high pressures, which are related to the more dense packing of the molecules inside the first solvation shell. The calculated neutron and X-ray structure factors have been compared with available experimental diffraction data, also revealing the pressure effects on the short-range structure of the liquid. The pressure effects on the translational, reorientational, and residence dynamics are very strong, revealing a significant slowing down when going from ambient pressure to 1.2 GPa. The translational dynamics of the linear CS2 molecules have been found to be more anisotropic at elevated pressures, where cage effects and librational motions are reflected on the shape of the calculated time correlation functions and their corresponding spectral densities.
Molecular and electronic structures of cerium and cerium suboxide clusters
Authors: Kafader Jared O. , Topolski Josey E. , Jarrold Caroline Chick
Published: October 2016

The anion photoelectron (PE) spectra of Ce2Oy− (y = 1, 2), Ce3Oy− (y = 0–4), Ce4Oy− (y = 0–2), and Ce5Oy− (y = 1, 2) are reported and analyzed with supporting results from density functional theory calculations. The PE spectra all exhibit an intense electronic transition to the neutral ground state, all falling in the range of 0.7 to 1.1 eV electron binding energy, with polarization dependence consistent with detachment from diffuse Ce 6s-based molecular orbitals. There is no monotonic increase in electron affinity with increasing oxidation. A qualitative picture of how electronic structure evolves with an oxidation state emerges from comparison between the spectra and the computational results. The electronic structure of the smallest metallic cluster observed in this study, Ce3, is similar to the bulk structure in terms of atomic orbital occupancy (4f 5d2 6s). Initial cerium cluster oxidation involves largely ionic bond formation via Ce 5d and O 2p orbital overlap (i.e., larger O 2p contribution), with Ce—O—Ce bridge bonding favored over Ce=O terminal bond formation. With subsequent oxidation, the Ce 5d-based molecular orbitals are depleted of electrons, with the highest occupied orbitals described as diffuse Ce 6s based molecular orbitals. In the y ≤ (x + 1) range of oxidation states, each Ce center has a singly occupied non-bonding 4f orbital. The PE spectrum of Ce3O4− is unique in that it exhibits a single nearly vertical transition. The highly symmetric structure predicted computationally is the same structure determined from Ce3O4+ IR predissociation spectra [A. M. Burow et al., Phys. Chem. Chem. Phys. 13, 19393 (2011)], indicating that this structure is stable in −1, 0, and +1 charge states. Spectra of clusters with x ≥ 3 exhibit considerable continuum signal above the ground state transition; the intensity of the continuum signal decreases with increasing oxidation. This feature is likely the result of numerous quasi-bound anion states or two-electron transitions possible in molecules with abundant nearly degenerate partially occupied orbitals.
On the development of a magnetoresistive sensor for blade tip timing and blade tip clearance measurement systems
Authors: Tomassini R. , Rossi G. , Brouckaert J.-F.
Published: October 2016

A simultaneous blade tip timing (BTT) and blade tip clearance (BTC) measurement system enables the determination of turbomachinery blade vibrations and ensures the monitoring of the existing running gaps between the blade tip and the casing. This contactless instrumentation presents several advantages compared to the well-known telemetry system with strain gauges, at the cost of a more complex data processing procedure. The probes used can be optical, capacitive, eddy current as well as microwaves, everyone with its dedicated electronics and many existing different signal processing algorithms. Every company working in this field has developed its own processing method and sensor technology. Hence, repeating the same test with different instrumentations, the answer is often different. Moreover, rarely it is possible to achieve reliability for in-service measurements. Developments are focused on innovative instrumentations and a common standard. This paper focuses on the results achieved using a novel magnetoresistive sensor for simultaneous tip timing and tip clearance measurements. The sensor measurement principle is described. The sensitivity to gap variation is investigated. In terms of measurement of vibrations, experimental investigations were performed at the Air Force Institute of Technology (ITWL, Warsaw, Poland) in a real aeroengine and in the von Karman Institute (VKI) R2 compressor rig. The advantages and limitations of the magnetoresistive probe for turbomachinery testing are highlighted.
Peculiarities of tunneling current in w-AlN/GaN(0001) two-barrier structures induced by deep-level defects
Authors: Grinyaev S. N. , Razzhuvalov A. N.
Published: October 2016

The influence of deep-level defects localized in spacer layers on the tunneling current in a w-AlN/GaN (0001) double-barrier structure is studied. It is shown that the current value essentially depends on the nature and spatial distribution of defects. New effects (screening of built-in fields, negative feedback, fixing of current peaks at high temperature) and a new mechanism of formation of resonances and tunneling current hysteresis caused by deep centers are established. The results of calculation agree with a number of experimental data on the position and temperature dependence of the current peak. It is noted that the current bistability can be caused by multicharged deep centers localized near the heteroboundaries of a double-barrier structure. Due to the defects, electric field in the barriers can reach values, at which the Poole-Frenkel effect should be taken into account.
Chaotic millimeter wave generation in a helical-waveguide gyro-TWT with delayed feedback
Authors: Ginzburg N. S. , Rozental R. M. , Sergeev A. S. , Zotova I. V. , Tarakanov V. P.
Published: October 2016

We demonstrate the possibility of chaotic millimeter wave generation in broadband helical-waveguide gyrotron travelling wave tubes (gyro-TWTs) by introducing external delayed feedback. It is shown that for the realization of “developed” chaos the amplitude characteristic of the amplifier should have the maximum slope in the overdrive regime upon saturation. This can be achieved by proper choosing of cyclotron resonance detuning. According to the time-domain averaged model and 3D particle-in-cell simulations with the parameters of the experimentally realized 35 GHz gyro-TWT, the power of chaotic generation can achieve 50 kW for an electron mean efficiency of about 7% and a spectrum width of 3–4 GHz.
Photoelectron spectroscopic study of carbon aluminum hydride cluster anions
Authors: Zhang Xinxing , Wang Haopeng , Ganteför Gerd , Eichhorn Bryan W. , Kiran Boggavarapu , Bowen Kit H.
Published: October 2016

Numerous previously unknown carbon aluminum hydride cluster anions were generated in the gas phase, identified by time-of-flight mass spectrometry and characterized by anion photoelectron spectroscopy, revealing their electronic structure. Density functional theory calculations on the CAl5−9H− and CAl5−7H2− found that several of them possess unusually high carbon atom coordination numbers. These cluster compositions have potential as the basis for new energetic materials.
Improving electrical properties of sol-gel derived zinc oxide thin films by plasma treatment
Authors: Talukder Al-Ahsan , Pokharel Jyotshna , Shrestha Maheshwar , Fan Qi H.
Published: October 2016

Being a direct and wide bandgap semiconductor, zinc oxide is a suitable material for various optoelectronic applications. These applications require tuning and controlling over the electrical and optical properties of zinc oxide films. In this work, zinc oxide thin films were prepared by a solution method that led to oriented crystal growth along (002) plane. The zinc oxide thin films were treated with oxygen, hydrogen, and nitrogen plasmas. The films were characterized to reveal the effects of plasma treatments on transmittance, crystallinity, carrier density, carrier mobility, and electrical resistivity. Oxygen plasma treatment improved the crystallinity of the zinc oxide thin film without affecting the film's transmittance. Hydrogen plasma treatments were found very effective in improving the electrical conductivity sacrificing the film's transmittance. Nitrogen plasma treatment led to improved electrical conductivity without compromising the crystallinity and optical transmittance. Sequential oxygen, hydrogen, and nitrogen plasma treatments significantly reduced the resistivity of zinc oxide thin films by over two orders and maintained the transmittance close to the as-deposited films of ∼80% in visible wavelength range. This is the first work on the improvement of conductivity of solution-based zinc oxide films using the plasma treatment.
Simulations of Ar gas-puff Z-pinch radiation sources with double shells and central jets on the Z generator
Authors: Tangri V. , Harvey-Thompson A. J. , Giuliani J. L. , Thornhill J. W. , Velikovich A. L. , Apruzese J. P. , Ouart N. D. , Dasgupta A. , Jones B. , Jennings C. A.
Published: October 2016

Radiation-magnetohydrodynamic simulations using the non-local thermodynamic equilibrium Mach2-Tabular Collisional-Radiative Equilibrium code in (r, z) geometry are performed for two pairs of recent Ar gas-puff Z-pinch experiments on the refurbished Z generator with an 8 cm diameter nozzle. One pair of shots had an outer-to-inner shell mass ratio of 1:1.6 and a second pair had a ratio of 1:1. In each pair, one of the shots had a central jet. The experimental trends in the Ar K-shell yield and power are reproduced in the calculations. However, the K-shell yield and power are significantly lower than the other three shots for the case of a double-shell puff of 1:1 mass ratio and no central jet configuration. Further simulations of a hypothetical experiment with the same relative density profile of this configuration, but higher total mass, show that the coupled energy from the generator and the K-shell yield can be increased to levels achieved in the other three configurations, but not the K-shell power. Based on various measures of effective plasma radius, the compression in the 1:1 mass ratio and no central jet case is found to be less because the plasma inside the magnetic piston is hotter and of lower density. Because of the reduced density, and the reduced radiation cooling (which is proportional to the square of the density), the core plasma is hotter. Consequently, for the 1:1 outer-to-inner shell mass ratio, the load mass controls the yield and the center jet controls the power.
Dynamics of nonspherical compound capsules in simple shear flow
Authors: Luo Zheng Yuan , Bai Bo Feng
Published: October 2016

The dynamics of an initially ellipsoidal compound capsule in a simple shear flow is investigated numerically using a three-dimensional front-tracking finite-difference model. Membrane bending resistance is included based on Helfrich’s energy function besides the resistances against shear deformation and area dilatation governed by the constitutive law of Skalak et al. In this paper, we focus specifically on how the presence of a spherical inner capsule and its size affects the characteristics and transition of various dynamical states of nonspherical compound capsules (i.e., the outer capsule). Significant differences in the dynamical characteristics are observed between compound capsules and homogeneous capsules in both qualitative and quantitative terms. We find the transition from swinging to tumbling can occur at vanishing viscosity mismatch through increasing the inner capsule size alone to a critical value regardless of the initial shape of the nonspherical compound capsule (i.e., prolate or oblate). Besides, for compound capsules with viscosity mismatch, the critical viscosity ratio for the swinging-to-tumbling transition remarkably decreases by increasing the inner capsule size. It is thus concluded that the inner capsule size is a key governing parameter of compound capsule dynamics apart from the capillary number, aspect ratio, and viscosity ratio that have been long identified for homogeneous capsules. Further, we discuss the mechanisms underlying the effects of the inner capsule on the compound capsule dynamics from the viewpoint of the effective viscosity of internal fluid and find that the effects of the inner capsule on compound capsule dynamics are qualitatively similar to that of increasing the internal viscosity on homogeneous capsule dynamics. However, in quantitative terms, the compound capsule cannot be viewed as a homogeneous capsule with higher viscosity as obvious inhomogeneity in fluid stress distribution is induced by the inner membrane.