bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling, control, and stability analysis of quasi‐Z‐source matrix converter as the grid interface of a PMSG‐WECS
Authors: Alizadeh Mojtaba , Kojuri Shokrollah Shokri
Published: June 2017

This work aims to carry out a comprehensive analytical evaluation of a quasi‐Z‐source matrix converter (qZSMC), which is comprised of a three‐phase quasi‐Z‐source network (TPQZSN) followed by an MC, as the grid interface of a permanent magnet synchonous generator (PMSG)‐based wind energy conversion system (PMSG‐WECS). First, the small‐signal model of the TPQZSN in space domain is obtained by the state‐space averaging method, while the parasitic elements are also considered. The TPQZSN's transfer functions are further calculated and analysed. The results together with a frequency‐domain analysis are used to render a comprehensive guide for the selection of proper passive components of the TPQZSN. The qZSMC is then employed as the grid interface of a PMSG‐WECS. A control system is designed for the grid‐connected operation. The small‐signal model of the whole system is developed. The qZSMC is compared with conventional MC (CMC) from stability point of view, indicating that, unlike the CMC, the qZSMC has no trouble working stable for all ranges of output power. Furthermore, it is shown that the proposed WECS can operate stably without using digital filter. The system performance is compared with CMC‐based WECS.
Improving the convergence time of DCTCP to reduce the completion time of short flows: a congestion window‐based method
Authors: Wu Hangxing , Wang Hongbin , Wan Yadong , Zhang Ming
Published: June 2017

Data Center Transmission Control Protocol (DCTCP) is an excellent transmission control protocol for data centre network (DCN). Although DCTCP can achieve the high throughput and stability, it trades off the convergence time. It takes a long time for a new flow to increase its congestion window (cwnd), which greatly increases the completion time of some delay sensitive short flows, such as query traffic, short messages existing extensively in DCN. An improved DCTCP (IDCTCP) is proposed to improve the convergence of DCTCP. IDCTCP utilises the receive window field in TCP header to communicate sender's current cwnd to a switch. The switch only marks the packets with large cwnd. So the flows with small cwnd are protected and can increase their cwnd quickly, which can effectively improve the convergence time of DCTCP. As a result, the short flows completion time (SFCT) can be reduced. The performance of IDCTCP has been validated by NS2 simulations.
Current Trends towards the Synthesis of Bioactive Heterocycles and Natural Products Using 1,3-Dipolar Cycloadditions (1,3-DC) with Azomethine Ylides
Authors: Döndas H. , de Gracia Retamosa María , Sansano José
Published: June 2017

This review summarizes the trends in the formation of complex or not so complex heterocyclic structures through 1,3-dipolar cy­cloadditions of azomethine ylides. Diastereo- and enantioselective processes as well as non-asymmetric cycloadditions constitute very important synthetic tools for achieving these compounds. This review covers the literature from 2015 through 2016 and organizes the research in terms of biologically important heterocycles and natural products from cascade 1,3-dipolar cycloadditions of azomethine ylides to the simpler forms of 1,3-dipolar cycloaddition.

1 Introduction

2 Synthesis of Spirooxindoles

3 Synthesis of Spiropyrrolidines

4 Synthesis of Spiropiperidines and Piperidines

5 Synthesis of Pyrrolidines and Fused Pyrrolidines

6 Synthesis of Pyrrolizidines and Indolizidines

7 Synthesis of Quinolone and Isoquinolines

8 Conclusions
C4 Pictet–Spengler Reactions for the Synthesis of Core Structures in Hyrtiazepine Alkaloids
Authors: Abe Takumi , Yamada Koji , Haruyama Tomohiro
Published: June 2017

The hyrtiazepine alkaloids are a family of bisindole natural products that have the azepinoindole backbone. We developed a biomimetic approach by constructing the azepinoindole core in a one-pot manner through 1,4-diazabicyclo[2.2.2]octane/2,2,2-trifluoroethanol (DABCO/TFE) promoted Pictet–Spengler reaction onto the C-4 position of tryptophan. This strategy allowed the synthesis of common key structures of these families. The key intermediate can be converted into the 3H-pyrano[2,3-b:5,6-e′]diindol intermediate present in hyrtimomines A and B, as well as the azepinoindole core present in fargesine.
On the Oxidation of Hydroxylamines with o-Iodoxybenzoic Acid (IBX)
Authors: Matassini Camilla , Goti Andrea , Parmeggiani Camilla , Cardona Francesca
Published: June 2017

o-Iodoxybenzoic acid (IBX) is confirmed as a powerful tool for the oxidation of hydroxylamines. The synthetic route is demonstrated as efficient and user friendly, and is exploited on various carbohydrate-derived N,N-disubstituted hydroxylamines (cyclic, acyclic, and functionalized ones), affording the corresponding nitrones in good yields and regioselectivity. N-Monosubstituted hydroxylamines revealed an interesting divergent behavior depending on the reaction conditions. While IBX oxidation in dimethyl sulfoxide at 45 °C furnished oximes as reported, the oxidation in dichloromethane at room temperature afforded efficiently the unusual corresponding nitroso dimers.
Synthesis of Silatrane-Containing Organic Sensitizers as Precursors for the Silyloxyl Anchoring Group in Dye-Sensitized Solar Cells
Authors: Bessi Matteo , Monini Marco , Calamante Massimo , Mordini Alessandro , Sinicropi Adalgisa , Basosi Riccardo , Di Donato Mariangela , Foggi Paolo , Iagatti Alessandro , Zani Lorenzo , Reginato Gianna
Published: June 2017

A series of organic D-π-A dyes, endowed with different silicon-based anchoring groups, has been prepared to assess the stability of such anchoring moieties on nanocrystalline TiO2 in dye-sensitized solar cells. Due to the difficulties encountered in finding a reliable and robust preparation protocol to obtain pure trialkoxysilanes, replacement with a silatrane moiety was evaluated. It was found that the silatrane group could be easily introduced on three different molecular scaffolds by using a simple amide coupling reaction mediated by EDC-Cl. Furthermore, the spectroscopic properties and anchoring mode on nanocrystalline TiO2 of the silatrane dyes were found to be nearly identical to those of the trialkoxysilane compounds, and both gave a much more stable attachment to the semiconductor compared with their cyano­acrylic acid counterpart, as shown by desorption experiments.
Chemoselectivity in the Synthesis of 1,2,3-Triazoles from Enolizable Ketones, Primary Alkylamines, and 4-Nitrophenyl Azide
Authors: Thomas Joice , Dehaen Wim , Opsomer Tomas
Published: June 2017

In recent years, several organocatalytic/metal-free synthetic pathways towards 1,2,3-triazoles have been reported. One of them is a general metal-free route towards the synthesis of 1,5-di- or fully-substituted 1,2,3-triazoles, designed by our group and named the ‘triazolization’ reaction of ketones. Limitations of this route were encountered in reactions with more activated ketones, where the corresponding 1-(4-nitrophenyl)-1,2,3-triazole was found back as the major product. Interestingly, three different triazoles are formed when 1,3-diphenylacetone is used as the ketone. In the present work, 1,3-diphenylacetone was used as a model substrate to investigate the chemoselectivity of our metal-free route under different reaction circumstances. This led to the conclusion that the formation of the desired 1,2,3-triazole is favored in apolar solvents, at high temperatures, and in the presence of acetic acid. By using one equivalent of acetic acid, previously inaccessible fully decorated 1,2,3-triazoles can be synthesized from simple α-arylketones in moderate to high yields.
Facile Approaches to 2-Deoxy-d-glucose and 2-Deoxy-α-d-glucopyranonucleosides from d-Glucal
Authors: Liu Feng-Wu , Xu Wenke , Yang Hui , Liu Yingju , Hua Yingchun , He Bin , Ning Xin , Qin Zhiyan , Liu Hong-Min
Published: June 2017

Convenient and stereoselective methods for the preparation of 2-deoxy-d-glucose and purine 2-deoxy-α-d-glucopyranonucleosides were developed. Halogen-mediated O-glycosidation of d-glucal by bromine in MeOH followed by reductive removal of the halo group and hydrolysis of methoxy group by zinc in saturated aqueous sodium dihydrogen phosphate gave 2-deoxy-d-glucose. Treatment of 3,4,6-tri-O-acetyl-d-glucal with IBr and 2,6-dichloropurine based on haloetherification and subsequent reductive removal of iodine and deprotection allowed the isolation of purin-9-yl 2-deoxy-α-d-glucopyranonucleoside. Preparation of several purin-9-yl 2-deoxy-α-d-glucopyranoside derivatives is also reported. Their configuration was confirmed by single crystal X-ray analysis of the key intermediate 2,6-dichloro-9-(2-iodo-2-deoxy-α-d-glucopyranosyl)purine.
Rater Reliability of the Hardy Classification for Pituitary Adenomas in the Magnetic Resonance Imaging Era
Authors: Mooney Michael , Hardesty Douglas , Sheehy John , Bird C. , Chapple Kristina , White William , Little Andrew
Published: June 2017

Objectives The Hardy classification is used to classify pituitary tumors for clinical and research purposes. The scale was developed using lateral skull radiographs and encephalograms, and its reliability has not been evaluated in the magnetic resonance imaging (MRI) era.

Design Fifty preoperative MRI scans of biopsy-proven pituitary adenomas using the sellar invasion and suprasellar extension components of the Hardy scale were reviewed.

Setting This study was a cohort study set at a single institution.

Participants There were six independent raters.

Main Outcome Measures The main outcome measures of this study were interrater reliability, intrarater reliability, and percent agreement.

Results Overall interrater reliability of both Hardy subscales on MRI was strong. However, reliability of the intermediate scores was weak, and percent agreement among raters was poor (12–16%) using the full scales. Dichotomizing the scale into clinically useful groups maintained strong interrater reliability for the sellar invasion scale and increased the percent agreement for both scales.

Conclusion This study raises important questions about the reliability of the original Hardy classification. Editing the measure to a clinically relevant dichotomous scale simplifies the rating process and may be useful for preoperative tumor characterization in the MRI era. Future research studies should use the dichotomized Hardy scale (sellar invasion Grades 0–III versus Grade IV, suprasellar extension Types 0–C versus Type D).
High Tibial Osteotomy for the Correction of Varus Knee Deformity
Authors: Lobenhoffer Philipp , Kfuri Mauricio
Published: June 2017

Knee varus deformity is a condition where the mechanical axis of the lower extremity is displaced medially. As a result, the medial compartment of the knee is overloaded and is prone to degenerative changes. The mechanical compromise of the medial compartment of the knee is very disabling, especially if affecting young and active individuals. Valgus-producing high tibial osteotomies (HTOs) were designed to shift the mechanical axis laterally, transferring the load to the knee compartment which is asymptomatic. HTO is a well-accepted concept for the management of medial unicompartmental knee arthritis. Medial joint line pain associated with metaphyseal varus deformity in a young patient is the essential criteria to indicate an HTO. Symptomatic young patients who do not have a bone-on-bone pathology may be benefited from HTO since for those individuals a unicompartmental knee replacement is contraindicated. Surgical technique matters in cases of HTO. Dome, lateral closing wedge, and medial opening wedge techniques have been reported with mixed results. Recent developments in fixation techniques, namely, the development of implants with angular stability, introduced safety, and reproducibility to open wedge HTOs, which became the preferred correction method for varus deformity of the knee. This article aims to cover the indications and contraindications of HTO with a focus on the unique aspects of the biplanar open wedge tibial osteotomy.
Kommunikativ-pragmatisches Screening (KOPS)
Authors: Glindemann Ralf , Ziegler Wolfram
Published: June 2017

Das Kommunikativ-pragmatische Screening (KOPS) ist ein neues Diagnostikverfahren zur Untersuchung kommunikativ-pragmatischer Fähigkeiten bei Patienten mit Aphasie. Das Verfahren umfasst 44 Aufgaben in 9 Untertests, mit denen rezeptive und expressive Fähigkeiten im Rahmen kommunikativer Handlungen geprüft werden. Die Antworten der Patienten sind nicht auf die mündliche Modalität beschränkt, vielmehr werden auch gestische, zeichnerische oder schriftliche Reaktionen bewertet. Der Test beinhaltet außerdem ein System abgestufter Hilfestellungen, die bei der Bewertung der Leistungen berücksichtigt werden.

Es wird über eine klinische Erprobung des Verfahrens mit 20 aphasischen Patienten berichtet. Dabei werden Angaben zur relativen Schwierigkeit der neun Untertests gemacht und Zusammenhänge mit den Untertests des Aachener Aphasie Tests beschrieben. Die spezifischen Anwendungsmöglichkeiten des Verfahrens werden anhand von Einzelfällen erläutert.
Intraoperative Ultrasound as a Screening Modality for the Detection of Liver Metastases during Resection of Primary Colorectal Cancer - A Systematic Review
Authors: Ellebæk Signe , Fristrup Claus , Mortensen Michael
Published: June 2017

Colorectal cancer (CRC) is one of the most common cancer diseases worldwide. One in 4 patients with CRC will have a disseminated disease at the time of diagnosis and often in the form of synchronous liver metastases. Studies suggest that up to 30% of patients have non-recognized hepatic metastases during primary surgery for CRC. Intraoperative ultrasonography examination (IOUS) of the liver to detect liver metastases was considered the gold standard during open CRC surgery. Today laparoscopic surgery is the standard procedure, but laparoscopic ultrasound examination (LUS) is not performed routinely.

Aim To perform a systematic review of the test performance of IOUS and LUS regarding the detection of synchronous liver metastases in patients undergoing surgery for primary CRC.

Method The literature was systematically reviewed using the search engines: PubMed, Cochrane, Embase and Google. 21 studies were included in the review and the key words: intraoperative ultrasound, laparoscopic ultrasound, staging colon and rectum cancer.

Results Intraoperative ultrasound showed a higher sensitivity, specificity, positive predictive value and overall accuracy for the detection liver metastases during surgery for primary CRC, compared to preoperative imaging modalities (ultrasound, computed tomography (CT) and contrast-enhanced computed tomography (CE-CT)). LUS showed a higher detection rate for liver metastases compared to CT, CE-CT and magnetic resonance imaging (MRI).

Conclusion This systematic review found that both IOUS and LUS had a higher detection rate regarding liver metastases during primary CRC surgery, especially liver metastases<10 mm in diameter, when compared to US, CT, CE-CT and MRI.
Morbus Alzheimer: Polyätiologie und multifaktorielle Schrittmacher
Authors: Mosetter Kurt
Published: June 2017

Aus der Analyse zahlreicher wissenschaftlicher Arbeiten zu kausalen Ursachen der Alzheimer-Erkrankung geht hervor, dass das Risiko
für die Neurodegeneration durch mehrere ätiologische Faktoren mit verschiedenen Belastungen aus Umwelt, Verhalten und Lebensstil
erhöht wird. Dysregulationen des Mikrobioms und der Darm-Gehirn-Achse sowie der Stoffwechselachse um Leber und Gehirn stellen
dabei wichtige Schrittmacher dar. Genauso wie Schwermetalle, Toxine oder ein Mangel an Omega-3-Fettsäuren, B-Vitaminen und
Vitamin D. Faktoren wie Schädel-Hirn-Traumata, Verletzungen der Halswirbelsäule, Postinfektionssyndrome und mitochondriale
Dysfunktionen münden in Energiemangel, Insulinresistenz, oxidativen Stress, Entzündungen und entgleiste Signalkaskaden für
Advanced Glycation Endproduct (AGE) und der zugehörigen Rezeptoren (RAGE).
Opportunities and Challenges in Realizing Universal Access to Obstetric Ultrasound in Sub-Saharan Africa
Authors: Wanyonyi Sikolia , Mariara Charles , Vinayak Sudhir , Stones William
Published: June 2017

The potential benefits of obstetric ultrasound have yet to be fully realized in sub-Saharan Africa (SSA), despite the region bearing the greatest burden of poor perinatal outcomes. We reviewed the literature for challenges and opportunities of universal access to obstetric ultrasound and explored what is needed to make such access an integral component of maternity care in order to address the massive burden of perinatal morbidity and mortality in SSA. Original peer-reviewed literature was searched in various electronic databases using a ‘realist’ approach. While the available data were inconclusive, they identify many opportunities for potential future research on the subject within the region that can help build a strong case to justify the provision of universal access to ultrasound as an integral component of comprehensive antenatal care.
Bedeutung von Hitzeaktionspläne für den präventiven Gesundheitsschutz in Deutschland
Authors: Zielo Birgit , Matzarakis Andreas
Published: June 2017

Hintergrund Hitzewellen zählen zu den Extremwetterereignissen und stellen eine zunehmende Gesundheitsgefährdung für die Bevölkerung in Europa dar. Nach den derzeit vorliegenden Klimastudien steigt die Wahrscheinlichkeit für eine Zunahme und eine Intensivierung von Hitzewellen seit Jahren weiter an. Besonders betroffen von ungewohnt hoher Hitzeexposition sind Menschen, deren Organismus durch Alter oder Krankheit bereits geschwächt ist. Da der Anteil der Seniorinnen und Senioren aufgrund des demografischen Wandels in Deutschland weiter steigt, gewinnen die gesundheitlichen Auswirkungen von Hitzewellen zunehmend an Bedeutung.

Ziel Hitzebedingter Morbidität und Mortalität kann durch Aufklärung und zeitig initiierten Präventionsmaßnahmen wirksam entgegengewirkt werden. Die Hitzewelle des Sommers 2003, welcher europaweit etwa 70000 Menschen zum Opfer fielen, führte in weiten Teilen Europas zu einer Etablierung von nationalen Hitzewarnsystemen und/oder Hitzemaßnahmenplänen. In Deutschland wurde im Jahr 2005 bundesweit das Hitzewarnsystem des Deutschen Wetterdienstes eingerichtet. Damit kann über einen 2-stufigen Warnprozess umfassend und rechtzeitig über eine bevorstehende Hitzewelle informiert werden, woraufhin entsprechende Präventionsmaßnahmen eingeleitet werden können. Darüber hinaus empfiehlt sich die Etablierung eines Hitzeaktionsplans, der neben einer Hitzewarnung auch umfassende Interventionsmaßnahmen zum Gesundheitsschutz berücksichtigt.

Material und Methoden Der vorliegende Artikel erläutert Hintergründe, Bedeutung und Aufbau eines Hitzeaktionsplans nach Maßgabe der Weltgesundheitsorganisation (WHO). Grundlage hierfür bilden der im Jahr 2008 erstellte Leitfaden und die ergänzenden Dokumenten der Jahre 2009 und 2011.

Ergebnisse und Diskussion Um einen nachhaltigen Schutz vor hitzebedingten Gesundheitsschäden zu gewährleisten, empfiehlt die Weltgesundheitsorganisation (WHO) ihren Mitgliedsstaaten die Einführung eines nationalen Hitzeaktionsplans. Zwischen einem Hitzewarnsystem und einem Hitzeaktionsplan gibt es grundlegende Unterschiede. Während die Warnung vor einer kurz bevorstehenden Hitzeperiode zentrale Aufgabe des Hitzewarnsystems ist, verfolgt der Hitzeaktionsplan einen integrativen Ansatz, der kurz-, mittel- und langfristige Maßnahmen zum Gesundheitsschutz in einem gemeinsamen Rahmen vereint.
Zum 100. Todestag von James Tyler Kent (1849–1916)
Authors: Gypser Von Klaus-Henning
Published: June 2017

Der vierte Teil von insgesamt vier Beiträgen zumLeben undWerk James Tyler Kents anlässlich seines 100. Todestags widmet sich der Zeit Kents als Homöopath in St. Louis (1880–1888).
Erfolg der Privatisierung von Krankenhäusern – Eine Einschätzung aus der Sicht ehemaliger öffentlicher
Krankenhausträger
Authors: Negele Daniel , Ott Robert , Wellisch Ulrich
Published: June 2017

Zielsetzung In den letzten Jahren konnte eine Steigerung der Anzahl privater Krankenhäuser und Betten festgestellt werden. Die
Probleme der Investitionsfinanzierung deutscher Krankenhäuser in Kombination mit verstärkenden Faktoren wie der Einführung der DRGs, aber
auch die Erwartung einer höheren Effizienz nach der Privatisierung einer Klinik können als Hauptgründe bei Privatisierungsentscheidungen
genannt werden. Es soll untersucht werden, wie ehemalige öffentliche Krankenhausträger den Erfolg der Privatisierung einschätzen.

Methodik Alle 99 identifizierten ehemaligen öffentlichen Träger, die ihr Krankenhaus in den Jahren 2003–2013 an einen privaten
Eigentümer verkauft hatten, wurden hinsichtlich ihrer Einschätzung von Zielen sowie Befürchtungen vor und nach der Privatisierung anonym und
schriftlich befragt.

Ergebnisse und Schlussfolgerung Zusammenfassend lässt sich feststellen, dass bei einer ausreichenden Finanzierung der Krankenhäuser
aus Krankenkassenbeiträgen (Betriebsmittel) und Ländermittel (Investitionskosten) der Privatisierungsdruck rapide sinken würde. Wenn jedoch
privatisiert wurde, hatte dies aus Sicht der ehemaligen Träger weder einen negativen Einfluss auf die medizinische Versorgung in der Region,
noch auf die Qualität der medizinischen Behandlung und auf den Umgang mit den Mitarbeitern. Die Einschätzungen der ehemaligen Träger weisen
eine statistisch überprüfte Übereinstimmung auf. Die mit einer Privatisierung verbundenen Erwartungen und Ziele werden prinzipiell als
erfüllt wahrgenommen.
Nano-second time resolved investigations on thermal implications of high-field transport through MWCNTs
Authors: Mishra Abhishek , Nandan Ravi , Raghavan Srinivasan , Shrivastava Mayank
Published: June 2017

The high-current carrying capacity of Multi-walled Carbon Nanotubes (MWCNTs) is the central idea behind their possible applications as interconnects. Joule-heating due to transport of high current through constricted quasi-1D electron channel results in various temperature-driven phenomena. Two such phenomena are current annealing and irreversible breakdown, which play vital roles in deciding electron transport and interconnect reliability, respectively. These phenomena occur at the time scale of 1–100 ns and hence cannot be precisely captured by conventional steady-state or DC measurement techniques. In this work, we explore these two phenomena by investigating electro-thermal transport through the inner and outer shells of MWCNTs, both suspended and substrate-supported, at the time scale of nano-seconds.
Surprising behaviors in the temperature dependent kinetics of diatomic interhalogens with anions and cations
Authors: Shuman Nicholas S. , Martinez Oscar , Ard Shaun G. , Wiens Justin P. , Keyes Nicholas R. , Guo Hua , Viggiano Albert A.
Published: June 2017

Rate constants and product branching fractions of reactions between diatomic interhalogens (ICl, ClF) and a series of anions (Br−, I−) and cations (Ar+, N2+) are measured using a selected ion flow tube apparatus and reported over the temperature range 200–500 K. The efficiency of both anion reactions with ICl is 2%-3% at 300 K to yield Cl−, increasing with temperature in a manner consistent with the small endothermicities of the reactions. The anion reactions with ClF are 10%–20% efficient at 300 K to yield Cl− and also show a positive temperature dependence despite being highly exothermic. The stationary points along the anion + ClF reaction coordinates were calculated using density functional theory, showing no endothermic barriers inhibiting reaction. The observed temperature dependence can be rationalized by a decreasing dipole attraction with increasing rotational energy, but confirmation requires trajectory calculations of the systems. All four cation reactions are fairly efficient at 300 K with small positive temperature dependences, despite large exothermicities to charge transfer. Three of the four reactions proceed exclusively by dissociative charge transfer to yield Cl+. The N2+ + ClF reaction proceeds by both non-dissociative and dissociative charge transfer, with the non-dissociative channel surprisingly increasing with increasing temperature. The origins of these behaviors are not clear and are discussed within the framework of charge-transfer reactions.
Phase transformations upon doping in WO3
Authors: Wang Wennie , Janotti Anderson , Van de Walle Chris G.
Published: June 2017

High levels of doping in WO3 have been experimentally observed to lead to structural transformation towards higher symmetry phases. We explore the structural phase diagram with charge doping through first-principles methods based on hybrid density functional theory, as a function of doping the room-temperature monoclinic phase transitions to the orthorhombic, tetragonal, and finally cubic phase. Based on a decomposition of energies into electronic and strain contributions, we attribute the transformation to a gain in energy resulting from a lowering of the conduction band on an absolute energy scale.
Liquid jets produced by an immersed electrical explosion in round tubes
Authors: Zhang Guifu , Zhu Yujian , Yang Jiming , Sun Mingyu
Published: June 2017

Liquid jets produced by an electrical explosion in water in round, centimeter-wide tubes are investigated experimentally and theoretically. Several jet flow patterns including sharp conical forms and annular forms are observed through high-speed photography. The general features of these patterns are presented and examined herein. It is found that the jet pattern is influenced mainly by the tube diameter, with narrow tubes producing conical jets and wide tubes producing annular jets. The jet maintains a nearly constant velocity, which increases with the explosion energy and decreases with the tube diameter and the standoff distance. A quasi-one-dimensional theoretical model that includes the bubble dynamics is proposed. With the model proposed herein, the effective explosion energy is calibrated first by matching the maximum bubble size. The results show that the confinement imposed by the tube tends to reduce the effective energy and that tubes with smaller diameters collect less effective energy. A theoretical analysis of the jet velocity indicates that the jet has to overcome a threshold energy level to obtain a constant velocity and that in narrower tubes, the jet velocity is amplified. The amplification factor, which is defined as the ratio of the actual jet velocity to the theoretical maximum bulk velocity, generally decreases with the tube diameter. It approaches unity when the jet is annular or blunt, indicating that the kinematic focusing effect with this type of jet is negligible. A parametric analysis of the calibrated explosion energy and the amplification factor provides a relation that comprehensively represents the experimental data. The relation is found to be different from those obtained in previous investigations, and the reasons for this difference are discussed.
Metalorganic vapor phase epitaxy of AlN on sapphire with low etch pit density
Authors: Koleske D. D. , Figiel J. J. , Alliman D. L. , Gunning B. P. , Kempisty J. M. , Creighton J. R. , Mishima A. , Ikenaga K.
Published: June 2017

Using metalorganic vapor phase epitaxy, methods were developed to achieve AlN films on sapphire with low etch pit density (EPD). Key to this achievement was using the same AlN growth recipe and only varying the pre-growth conditioning of the quartz-ware. After AlN growth, the quartz-ware was removed from the growth chamber and either exposed to room air or moved into the N2 purged glove box and exposed to H2O vapor. After the quartz-ware was exposed to room air or H2O, the AlN film growth was found to be more reproducible, resulting in films with (0002) and (10–12) x-ray diffraction (XRD) rocking curve linewidths of 200 and 500 arc sec, respectively, and EPDs < 100 cm−2. The EPD was found to correlate with (0002) linewidths, suggesting that the etch pits are associated with open core screw dislocations similar to GaN films. Once reproducible AlN conditions were established using the H2O pre-treatment, it was found that even small doses of trimethylaluminum (TMAl)/NH3 on the quartz-ware surfaces generated AlN films with higher EPDs. The presence of these residual TMAl/NH3-derived coatings in metalorganic vapor phase epitaxy (MOVPE) systems and their impact on the sapphire surface during heating might explain why reproducible growth of AlN on sapphire is difficult.
Magnetic antivortex dynamics in a two nanocontact disk
Authors: Zaspel C. E.
Published: June 2017

Stable magnetic vortex-antivortex-vortex structures can form on a thin ferromagnetic disk at two separated nanocontacts with the vortices at the nanocontacts and the antivortex between the nanocontacts. When the vortices are pinned to the nanocontacts, the antivortex gyrotropic motion can be isolated about the stable equilibrium between the pinned vortices. The restoring force in the antivortex is from the combined exchange, magnetostatic, and Oersted fields where the exchange and the magnetostatic interactions will result in an attractive vortex-antivortex force, but the net Oersted field from the nanocontacts tends to stabilize the antivortex between both nanocontacts. A small ac driving current on one of the nanocontacts provides an efficient driving force for this antivortex oscillator that is tunable through the nanocontact current. Owing to the competing magnetostatic and Oersted forces, the oscillator can be soft along the direction between the nanocontact resulting in a high amplitude oscillation. Moreover, because of this competition, nonlinear effects are important at low ac current amplitudes. An interesting nonlinear effect is an amplitude jump that is shown to be a result of a time-dependent asymmetry of the antivortex potential.
Anomalous compression behavior of ∼12 nm nanocrystalline TiO2
Authors: Wang Qiming , Li Shourui , Peng Fang , Lei Li , Hu Qiwei , Wang Pei , Nan Xiaolong , Liu Jing , Zhu Wenjun , He Duanwei
Published: June 2017

When the grain size decreases, there inevitably exists a critical size (dc) where the contribution of surface atoms to the physical properties is competitive with that of the interior atoms, giving rise to a wide variety of new phenomena. The behavior of granular materials near dc is particularly interesting because of the crossover, a continuous transition from one type of mechanism to another. In situ high-pressure x-ray diffraction experiments showed that the compression curve of nanocrystalline anatase TiO2 with grain size near dc reached a platform after about 5%–6% of deformation under hydrostatic compression. Eventually, the unit cell volume of anatase expanded at ∼14–16 GPa. We propose that the anomalous compression behavior is attributed to the formation and thickening of the stiff high density amorphous shell under high pressure, giving rise to a great arching effect at the grain boundary at the nanolevel. This process results in a remarkable difference in stress between inside and outside of the shell, generating the illusions of the hardening and the negative compressibility. This study offers a new insight into the mechanical properties of nanomaterials under extreme conditions.
Continuous reading SQUID magnetometer and its applications
Authors: Janů Zdeněk , Soukup František
Published: June 2017

We show a continuous reading superconducting quantum interference detector magnetometer used to measure the magnetic moment of small samples of materials as a function of an applied magnetic field, temperature, and time. A sample is held stationary while the magnetic field and sample temperature may be varied continuously in an arbitrary way, determined by the user. The applied field range is ±25 mT and the temperature range is 4.2–150 K. The advantage of a stationary sample technique is that the sample is not exposed to variations in the magnetic field or temperature, which may set in when the sample is moving. An evaluation of the measurements is not bound by the dipolar magnetic moment of the sample. High linearity of the detection system, low harmonic distortion of the applied time-varying magnetic field, and precise sample temperature control make this device suitable for studies of phase transitions, hysteretic phenomena, and nonlinear phenomena in magnetic materials and superconductors. The magnetometer’s sensitivity (noise floor), i.e., magnetic moment noise spectral density, is 10 pA m2 Hz−1/2 in the white noise region.
Novel design of high voltage pulse source for efficient dielectric barrier discharge generation by using silicon diodes for alternating current
Authors: Truong Hoa Thi , Hayashi Misaki , Uesugi Yoshihiko , Tanaka Yasunori , Ishijima Tatsuo
Published: June 2017

This work focuses on design, construction, and optimization of configuration of a novel high voltage pulse power source for large-scale dielectric barrier discharge (DBD) generation. The pulses were generated by using the high-speed switching characteristic of an inexpensive device called silicon diodes for alternating current and the self-terminated characteristic of DBD. The operation started to be powered by a primary DC low voltage power supply flexibly equipped with a commercial DC power supply, or a battery, or DC output of an independent photovoltaic system without transformer employment. This flexible connection to different types of primary power supply could provide a promising solution for the application of DBD, especially in the area without power grid connection. The simple modular structure, non-control requirement, transformer elimination, and a minimum number of levels in voltage conversion could lead to a reduction in size, weight, simple maintenance, low cost of installation, and high scalability of a DBD generator. The performance of this pulse source has been validated by a load of resistor. A good agreement between theoretically estimated and experimentally measured responses has been achieved. The pulse source has also been successfully applied for an efficient DBD plasma generation.
Electron and thermal transport via variable range hopping in MoSe2 single crystals
Authors: Suri Dhavala , Patel R. S.
Published: June 2017

Bulk single crystal molybdenum diselenide has been studied for its electronic and thermal transport properties. We perform resistivity measurements with current in-plane (CIP) and current perpendicular to plane (CPP) as a function of temperature. The CIP measurements exhibit metal to semiconductor transition at ≃31 K. In the semiconducting phase (T > 31 K), the transport is best explained by the variable range hopping (VRH) model. Large magnitude of resistivity in the CPP mode indicates strong structural anisotropy. The Seebeck coefficient as a function of temperature measured in the range of 90–300 K also agrees well with the VRH model. The room temperature Seebeck coefficient is found to be 139 μV/K. VRH fittings of the resistivity and the Seebeck coefficient data indicate high degree of localization.
Monolayer graphene-insulator-semiconductor emitter for large-area electron lithography
Authors: Kirley Matthew P. , Aloui Tanouir , Glass Jeffrey T.
Published: June 2017

The rapid adoption of nanotechnology in fields as varied as semiconductors, energy, and medicine requires the continual improvement of nanopatterning tools. Lithography is central to this evolving nanotechnology landscape, but current production systems are subject to high costs, low throughput, or low resolution. Herein, we present a solution to these problems with the use of monolayer graphene in a graphene-insulator-semiconductor (GIS) electron emitter device for large-area electron lithography. Our GIS device displayed high emission efficiency (up to 13%) and transferred large patterns (500 × 500 μm) with high fidelity (<50% spread). The performance of our device demonstrates a feasible path to dramatic improvements in lithographic patterning systems, enabling continued progress in existing industries and opening opportunities in nanomanufacturing.
Electrostatic simulation of a complete cluster deposition apparatus
Authors: Elger B. , Schmidt T. , Krähling S. , Neuberger F. , Schäfer R.
Published: June 2017

A complete electrostatic model of a cluster deposition apparatus is presented using SIMION. It consists of fifteen different ion optical components including a quadrupole mass filter and a quadrupole ion deflector. The accuracy of the model was tested by comparing calculated cationic cluster transmissions with experimental ion currents by varying the electrostatic potential of different components. Considering the negatively charged particles produced by the magnetron cluster source as a charged background with a density of 5⋅10−7 cm−3, the influence of the first components on cluster transmission is well reproduced in comparison to the experimental results. This background was included by increasing the charge of the clusters from zero to an elementary charge using a sigmoidal function. The inflection point of this function was found to depend on the first components’ electrostatic potential but in good approximation, not on later ones. All of the calculated transmissions represent the experimental data quite well; therefore, the simulation is validated and helps us to understand the influence of the electrostatic components on cluster transmission and improve the target efficiency. Furthermore, this understanding opens the possibility for a global optimization scheme to be employed in the ion optics’ geometries.
Statistical analysis of Hasegawa-Wakatani turbulence
Authors: Anderson Johan , Hnat Bogdan
Published: June 2017

Resistive drift wave turbulence is a multipurpose paradigm that can be used to understand transport at the edge of fusion devices. The Hasegawa-Wakatani model captures the essential physics of drift turbulence while retaining the simplicity needed to gain a qualitative understanding of this process. We provide a theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent events in Hasegawa-Wakatani turbulence with enforced equipartition of energy in large scale zonal flows, and small scale drift turbulence. We find that for a wide range of adiabatic index values, the stochastic component representing the small scale turbulent eddies of the flow, obtained from the autoregressive integrated moving average model, exhibits super-diffusive statistics, consistent with intermittent transport. The PDFs of large events (above one standard deviation) are well approximated by the Laplace distribution, while small events often exhibit a Gaussian character. Furthermore, there exists a strong influence of zonal flows, for example, via shearing and then viscous dissipation maintaining a sub-diffusive character of the fluxes.
Nonlinear space charge dynamics and modulational instability in the interaction of intense laser pulses with electron-positron plasmas
Authors: Hashemzadeh M. , Niknam A. R.
Published: June 2017

Nonlinear space charge dynamics and modulational instability in the interaction between ultrashort, intense laser pulses and electron-positron pair plasmas are investigated taking into account the relativistic ponderomotive force and the relativistic mass of electrons and positrons. By coupling Maxwell's equations and hydrodynamic model, the electron and positron density distributions and the dispersion relation for the modulational instability are obtained. Moreover, two coupled nonlinear equations for the scalar and vector potentials are derived and numerically solved. The results show that the growth rate of instability increases with the decrease in the electron and positron temperatures. Moreover, it is shown that when the temperatures of electrons and positrons are not equal to each other, the profiles of scalar potential are similar to bright-like or dark-like solitons.
Edge wrinkling of a soft ridge with gradient thickness
Authors: Zhao Yan , Shao Zhi-Chun , Li Guo-Yang , Zheng Yang , Zhang Wan-Yu , Li Bo , Cao Yanping , Feng Xi-Qiao
Published: June 2017

We investigate the edge wrinkling of a soft ridge with gradient thickness under axial compression. Our experiments show that the wrinkling wavelength undergoes a considerable increase with increasing load. Simple scaling laws are derived based on an upper-bound analysis to predict the critical buckling conditions and the evolution of wrinkling wavelength during the post-buckling stage, and the results show good accordance with our finite element simulations and experiments. We also report a pattern transformation triggered by the edge wrinkling of soft ridge arrays. The results and method not only help understand the correlation between the growth and form observed in some natural systems but also inspire a strategy to fabricate advanced functional surfaces.
Energy thresholds of discrete breathers in thermal equilibrium and relaxation processes
Authors: Ming Yi , Ling Dong-Bo , Li Hui-Min , Ding Ze-Jun
Published: June 2017

So far, only the energy thresholds of single discrete breathers in nonlinear Hamiltonian systems have been analytically obtained. In this work, the energy thresholds of discrete breathers in thermal equilibrium and the energy thresholds of long-lived discrete breathers which can remain after a long time relaxation are analytically estimated for nonlinear chains. These energy thresholds are size dependent. The energy thresholds of discrete breathers in thermal equilibrium are the same as the previous analytical results for single discrete breathers. The energy thresholds of long-lived discrete breathers in relaxation processes are different from the previous results for single discrete breathers but agree well with the published numerical results known to us. Because real systems are either in thermal equilibrium or in relaxation processes, the obtained results could be important for experimental detection of discrete breathers.
A magneto-fluidic nanoparticle trapping platform for surface-enhanced Raman spectroscopy
Authors: Huang Po-Jung , Marks Haley L. , Coté Gerard L. , Kameoka Jun
Published: June 2017

A microfluidic device utilizing magnetically activated nickel (Ni) micropads has been developed for controlled localization of plasmonic core-shell magnetic nanoparticles, specifically for surface enhanced Raman spectroscopy (SERS) applications. Magnetic microfluidics allows for automated washing steps, provides a means for easy reagent packaging, allows for chip reusability, and can even be used to facilitate on-chip mixing and filtration towards full automation of biological sample processing and analysis. Milliliter volumes of gold-coated 175-nm silica encapsulated iron oxide nanoparticles were pumped into a microchannel and allowed to magnetically concentrate down into 7.5 nl volumes over nano-thick lithographically defined Ni micropads. This controlled aggregation of core-shell magnetic nanoparticles by an externally applied magnetic field not only enhances the SERS detection limit within the newly defined nanowells but also generates a more uniform (∼92%) distribution of the SERS signal when compared to random mechanical aggregation. The microfluidic flow rate and the direction and strength of the magnetic field determined the overall capture efficiency of the magneto-fluidic nanoparticle trapping platform. It was found that a 5 μl/min flow rate using an attractive magnetic field provided by 1 × 2 cm neodymium permanent magnets could capture over 90% of the magnetic core-shell nanoparticles across five Ni micropads. It was also observed that the intensity of the SERS signal for this setup was 10-fold higher than any other flow rate and magnetic field configurations tested. The magnetic concentration of the ferric core-shell nanoparticles causes the SERS signal to reach the steady state within 30 min can be reversed by simply removing the chip from the magnet housing and sonicating the retained particles from the outlet channel. Additionally, each magneto-fluidic can be reused without noticeable damage to the micropads up to three times.
Geometrically nonlinear analysis of composite beams using Wiener-Milenković parameters
Authors: Wang Qi , Yu Wenbin
Published: June 2017

This paper presents a geometrically nonlinear analysis of composite beams including static, dynamic, and eigenvalue analyses. With the increase in size and flexibility of engineering components such as wind turbine blades, geometric nonlinearity plays an increasingly significant role in structural analysis. The Geometric Exact Beam Theory (GEBT), pioneered by Reissner and extended by Hodges, is adopted as the foundation for this work. Special emphasis is placed on the vectorial parameterization of finite rotation, which is a fundamental aspect in the geometrically nonlinear formulation. This method is introduced based on Euler's rotation theorem and the property of rotation operation: the length preservation of the rotated vector. The GEBT is then implemented with the Wiener-Milenković parameters using a mixed formulation. Several numerical examples are studied based on the derived theory, and the results are compared with analytical solutions and those available in the literature. The analysis of a realistic composite wind turbine blade is provided to show the capability of the present model for generalized composite slender structures. It concludes that the proposed model can be used as a beam tool in a multibody framework whose valid range of rotation is up to 2π.
Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity
Authors: Sahu Siddharth S. , Siva Vantari , Pradhan Paresh C. , Nayak Maheswar , Senapati Kartik , Sahoo Pratap K.
Published: June 2017

We report a study of the structural and magnetic behavior of the topmost magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing angle X-ray diffraction measurements performed on a series of multilayers showed a gradual decrease in the grain size of the topmost magnetic layer with the increasing number of bilayers. Concurrently, the magnetic hardness and magneto-crystalline anisotropy of the top Co layer were found to decrease, as observed by magneto-optical Kerr effect measurements. This magnetic softening has been discussed in the light of Herzer's random anisotropy model. Micromagnetic simulations of the multilayer system also corroborated these observations.
Fast and efficient STT switching in MTJ using additional transient pulse current
Authors: Pathak Sachin , Cha Jongin , Jo Kangwook , Yoon Hongil , Hong Jongill
Published: June 2017

We propose a profile of write pulse current-density to switch magnetization in a perpendicular magnetic tunnel junction to reduce switching time and write energy as well. Our simulated results show that an overshoot transient pulse current-density (current spike) imposed to conventional rectangular-shaped pulse current-density (main pulse) significantly improves switching speed that yields the reduction in write energy accordingly. For example, we could dramatically reduce the switching time by 80% and thereby reduce the write energy over 9% in comparison to the switching without current spike. The current spike affects the spin dynamics of the free layer and reduces the switching time mainly due to spin torque induced. On the other hand, the large Oersted field induced causes changes in spin texture. We believe our proposed write scheme can make a breakthrough in magnetic random access memory technology seeking both high speed operation and low energy consumption.