bluuebunny/crossref_metadata_2025 huggingface dataset:
On the algebraic K-theory of truncated polynomial algebras in several variables
Authors: Angeltveit Vigleik , Gerhardt Teena , Hill Michael A. , Lindenstrauss Ayelet
Published: November 2013

We consider the algebraic K-theory of a truncated polynomial algebra in several commuting variables, . This naturally leads to a new generalization of the big Witt vectors. If k is a perfect field of positive characteristic we describe the K-theory computation in terms of a cube of these Witt vectors on ℕn. If the characteristic of k does not divide any of the ai we compute the K-groups explicitly. We also compute the K-groups modulo torsion for k = ℤ.

To understand this K-theory spectrum we use the cyclotomic trace map to topological cyclic homology, and write as the iterated homotopy cofiber of an n-cube of spectra, each of which is easier to understand.
Generalized phase average with applications to sensor-based flow estimation of the wall-mounted square cylinder wake
Authors: Bourgeois J. A. , Noack B. R. , Martinuzzi R. J.
Published: November 2013

We experimentally investigate the three-dimensional wake behind a finite wall-mounted square cylinder at$\mathit{Re}= 12\hspace{0.167em} 000$and aspect ratio of 4. Focus is placed on the base flow and oscillatory fluctuation. Time-resolved three-dimensional velocity fields are constructed from high-frame-rate particle image velocimetry (PIV) and simultaneously recorded surface pressure measurements. All three velocity components are resolved in a rectangular near-wake region by two orthogonal dense arrays of parallel PIV planes. A key enabler is a generalized phase average incorporating a slowly varying base flow, a variable oscillation amplitude and higher harmonics. These generalizations reduce the instantaneous residual 30 % below those of a traditional phase average. Moreover, the resolved variations reveal analytical constraints of the mean flow and oscillation levels, such as the mean-field paraboloid. The proposed methodology for generalized phase averaging and for construction of three-dimensional velocity fields from two-dimensional PIV data is applicable to a large class of turbulent flows with oscillatory dynamics.
Occupancy estimation of jaguar Panthera onca to assess the value of east-central Mexico as a jaguar corridor
Authors: Petracca Lisanne S. , Ramírez-Bravo O. Eric , Hernández-Santín Lorna
Published: November 2013

The use of wildlife corridors to maintain landscape connectivity has become increasingly relevant to the conservation of wide-ranging species, including the jaguar Panthera onca. Jaguars are particularly threatened in Mexico, where corridor linkages are tenuous as a result of habitat fragmentation. Our study assessed a section of potential corridor south of the Sierra Madre Oriental in eastern Mexico. We conducted 245 interviews with local inhabitants in 140 36-km2 sampling units over a 5-month period and compiled detection histories for jaguars and five prey species: collared peccary Pecari tajacu, red brocket deer Mazama americana, white-tailed deer Odocoileus virginianus, spotted paca Agouti paca, and nine-banded armadillo Dasypus novemcinctus. These detection histories were then analysed using site occupancy modelling. Each sampling unit was assigned a probability of habitat use based on (1) the two smaller prey species (paca and armadillo) and (2) at least two of the larger prey species (collared peccary and two deer species) using habitat in that unit. This probability estimate was considered a proxy for the prey base of each sampling unit and therefore the unit's suitability as a jaguar corridor. Although the prey base in some areas appears adequate to support a jaguar population, large-scale development projects and the paucity of jaguar sign are major obstacles to this region's potential as a jaguar corridor. Our results suggest that the eastern coast of Mexico may not be a priority area for range-wide jaguar conservation.
The English Evangelicals and the Pilgrim Tax in India. 1800–1862
Authors: Ingham Kenneth
Published: November 2013

The East India Company's accession to political and administrative responsibility in India in the late eighteenth and early nineteenth centuries was greatly complicated by the simultaneous development of the evangelical movement in England with its missionary agents overseas. India was one of the first areas of British expansion to feel the pressure of evangelical influence upon the conduct of its government; South Africa was to experience it soon afterwards, and in both areas the younger Charles Grant (1778–1866) played an important part, through his tenure of the offices of President of the Board of Control and Colonial Secretary.
Triggering word learning in children with Language Impairment: the effect of phonotactic probability and neighbourhood density
Authors: MCKEAN CRISTINA , LETTS CAROLYN , HOWARD DAVID
Published: November 2013

The effect of phonotactic probability (PP) and neighbourhood density (ND) on triggering word learning was examined in children with Language Impairment (3;04–6;09) and compared to Typically Developing children. Nonwords, varying PP and ND orthogonally, were presented in a story context and their learning tested using a referent identification task. Group comparisons with receptive vocabulary as a covariate found no group differences in overall scores or in the influence of PP or ND. Therefore, there was no evidence of atypical lexical or phonological processing. ‘Convergent’ PP/ND (High PP/High ND; Low PP/Low ND) was optimal for word learning in both groups. This bias interacted with vocabulary knowledge. ‘Divergent’ PP/ND word scores (High PP/Low ND; Low PP/High ND) were positively correlated with vocabulary so the ‘divergence disadvantage’ reduced as vocabulary knowledge grew; an interaction hypothesized to represent developmental changes in lexical–phonological processing linked to the emergence of phonological representations.
Mild cognitive impairment and mood: a systematic review
Authors: Yates Jennifer A , Clare Linda , Woods Robert T
Published: November 2013

This systematic review, with meta-analyses conducted where data were available, aimed to investigate the prevalence of symptoms of depression and anxiety in mild cognitive impairment (MCI), and to establish how symptoms of depression and anxiety relate to the progression from no cognitive impairment to MCI, and from MCI to dementia. Sixty studies were included in the review. Meta-analyses indicated that symptoms of depression and anxiety were more prevalent in people with MCI than in people with normal cognitive function, and increased the risk of progression from no cognitive impairment to MCI. There were mixed results regarding the effect of such symptoms on progression from MCI to dementia. The findings highlight the need for more research in this area, which can inform attempts to slow or halt the progression of cognitive impairment in later life, with resulting benefits for quality of life.
Praxisanleitung
Authors: Quernheim German , Keller Christian
Published: November 2013

Im ersten Teil einer dreiteiligen Artikelserie wird der problembehaftete aktuelle Zustand der praktischen Pflegeausbildung und die Situation der Praxisanleiter und -anleiterinnen dargestellt. Es wird auf die Freistellung, das Anrechnungsverhältnis und die aktuelle Finanzierung der Praxisanleitung eingegangen und der Ausbildungsrealität Verbesserungsvorschläge gegenübergestellt.
Die Akademisierung fängt schon vor dem Bachelor an
Authors: Wieschowski Sebastian
Published: November 2013

In den USA gehört die Akademisierung der Pflegeberufe längst zur professionellen Pflege – nicht zuletzt deshalb, weil der Weg in die akademische Bildung dort deutlich früher beginnt. Die enge Verknüpfung zwischen Ausbildung und Akademischer Qualifizierung wird inzwischen auch außerhalb der Vereinigten Staaten umgesetzt und könnte zum Vorbild für die Pflege in Deutschland werden.
Influence of O-Methylated Metabolite Penetrating the Blood–Brain Barrier to Estimation of Dopamine Synthesis Capacity in Human L-[β-11C]DOPA PET
Authors: Matsubara Keisuke , Ikoma Yoko , Okada Maki , Ibaraki Masanobu , Suhara Tetsuya , Kinoshita Toshibumi , Ito Hiroshi
Published: November 2013

O-methyl metabolite (L-[ β-11C]OMD) of 11C-labeled L-3,4-dihydroxyphenylalanine (L-[ β-11C]DOPA) can penetrate into brain tissue through the blood–brain barrier, and can complicate the estimation of dopamine synthesis capacity by positron emission tomography (PET) study with L-[ β-11C]DOPA. We evaluated the impact of L-[ β-11C]OMD on the estimation of the dopamine synthesis capacity in a human L-[ β-11C]DOPA PET study. The metabolite correction with mathematical modeling of L-[ β-11C]OMD kinetics in a reference region without decarboxylation and further metabolism, proposed by a previous [18F]FDOPA PET study, were implemented to estimate radioactivity of tissue L-[ β-11C]OMD in 10 normal volunteers. The component of L-[ β-11C]OMD in tissue time-activity curves (TACs) in 10 regions were subtracted by the estimated radioactivity of L-[ β-11C]OMD. To evaluate the influence of omitting blood sampling and metabolite correction, relative dopamine synthesis rate ( kref) was estimated by Gjedde–Patlak analysis with reference tissue input function, as well as the net dopamine synthesis rate ( Ki) by Gjedde–Patlak analysis with the arterial input function and TAC without and with metabolite correction. Overestimation of Ki was observed without metabolite correction. However, the kref and Ki with metabolite correction were significantly correlated. These data suggest that the influence of L-[ β-11C]OMD is minimal for the estimation of kref as dopamine synthesis capacity.
Measurement of 40 power system harmonics in real‐time on an economical ARM® Cortex™‐M3 platform
Authors: Roscoe A.J. , Sklaschus T. , Oldroyd G. , Blair S.M. , Burt G.M.
Published: November 2013

Within future homes and electrical power networks, emphasis is being placed on intelligent, distributed measurement devices. In particular, the recognition of individual or aggregated loads through harmonic signature has been proposed as a useful way to enhance the value of home energy monitoring/control. Clearly, the cost of implementing such measurement devices is a major barrier to acceptance. In a recent project, a challenge was set to implement real‐time software on an ARM® Cortex™ LPC1768 microcontroller platform (chip cost c. £4). The software must be capable of measuring a single‐phase AC frequency, real and reactive power flows and provide a full breakdown of the voltage and current (and power) behaviour via harmonic analysis from DC to the 40th, in real‐time with a new output every 20 ms. In addition, the algorithm must be capable of adapting the measurement when the frequency is not nominal (50 Hz) so that spectral leakage is minimised. It is found that the LPC1768 processor is capable of supporting such an algorithm when it is coded appropriately. This knowledge de‐risks the proposed use of such cheap microcontrollers for these relatively complex tasks.
Transient response optimisation for peak current mode buck converter in the application of dynamic voltage scaling
Authors: Xu Shen , Yao Yunpeng , Kan Mingjian , Sun Weifeng
Published: November 2013

For optimising the peak current mode buck converter's transient response in the application of dynamic voltage scaling, an accurate small signal model of the converter under continuous conduction mode is built. The switch conduction loss, dead‐time and other main parasitic parameters are considered in the presented model. Based on the model, a novel compensation network for the voltage loop is proposed, which eliminates the zero point of the voltage loop. The relationship between the gain of the proposed compensation network and the transient response of the output voltage relative to the reference voltage (Vref) at the input node of error amplifier is investigated. By this way, an optimal gain for the transient output voltage is obtained and the optimaltransient response without overshoot and oscillation relative to Vref is validated by the circuit simulations and tests.
Single stage soft switching ac/dc converter without any extra switch
Authors: Abasian Alireza , Farzaneh‐fard Hosein , Madani Seyed
Published: November 2013

This study presents a single‐stage single‐switch soft‐switching converter based on boost‐flyback power factor correction (PFC) scheme. In the proposed circuit, soft‐switching condition is achieved by only an auxiliary winding on the transformer and a resonant capacitor without any extra switch. The converter operating modes are discussed in details. The design guidelines for the proposed PFC converter, are provided and simulation results are presented. A prototype of this converter is realised to justify the validity of theoretical analysis.
Analytical evaluation of control strategies for participation of doubly fed induction generator‐based wind farms in power system short‐term frequency regulation
Authors: Akbari Mohammad , Madani Seyed M.
Published: November 2013

Increase in doubly fed induction generator (DFIG)‐based wind farms degrades the short‐term frequency regulation of power systems. However, such wind farms may have large amount of kinetic energy which can be rapidly injected into the power system to support system frequency by using an appropriate supplementary control loop. This study first analyses the impacts of DFIGs and their supplementary loop on power system short‐term frequency regulation. Then, the average power system frequency model is modified to include the participation of wind farms in frequency control. Moreover, a new method is proposed to derive an analytical expression for minimum frequency of a power system, as an important index of frequency regulation, after a power imbalance occurrence. This analytical expression provides a tool for better insight into frequency behaviour of power systems with high levels of wind generation. The results of the analysis are verified by simulation of the nine‐bus test system, using MATLAB/SIMULINK.
Production of energetic neutral particles and low energy electrons from four anode rods ion source
Authors: Mostafa O. A. , El-Khabeary H. , Abdel Reheem A. M.
Published: November 2013

The factors affecting the energetic neutral current, the low energy electron current, and the positive ion current emerging from a four-anode-rods ion source have been studied using argon gas. The neutral and electron current were measured using a simple, new technique. It was found that the energetic neutral current and the electron current depend on the positive ion current and the gas pressure. The ratio of the neutral and electron current to the positive ion current increases by increasing the gas pressure. Also it was found that at a pressure equal to 9 × 10−4 mmHg, the ratio of the neutral to the positive ion current reaches 2.34 while the ratio of the electron current to the positive ion current reaches 1.7.
Iron beam acceleration using direct plasma injection scheme
Authors: Okamura M. , Kanesue T. , Yamamoto T. , Fuwa Y.
Published: November 2013

A new set of vanes of radio frequency quadrupole (RFQ) accelerator was commissioned using highly charged iron beam. To supply high intensity heavy ion beams to the RFQ, direct plasma injection scheme (DPIS) with a confinement solenoid was adopted. One of the difficulties to utilize the combination of DPIS and a solenoid field is a complexity of electro magnetic field at the beam extraction region, since biasing high static electric field for ion extraction, RFQ focusing field, and the solenoid magnetic field fill the same space simultaneously. To mitigate the complexity, a newly designed magnetic field clamps were used. The intense iron beam was observed with bunched structure and the total accelerated current reached 2.5 nC.
Zero-multipole summation method for efficiently estimating electrostatic interactions in molecular system
Authors: Fukuda Ikuo
Published: November 2013

The zero-multipole summation method has been developed to efficiently evaluate the electrostatic Coulombic interactions of a point charge system. This summation prevents the electrically non-neutral multipole states that may artificially be generated by a simple cutoff truncation, which often causes large amounts of energetic noise and significant artifacts. The resulting energy function is represented by a constant term plus a simple pairwise summation, using a damped or undamped Coulombic pair potential function along with a polynomial of the distance between each particle pair. Thus, the implementation is straightforward and enables facile applications to high-performance computations. Any higher-order multipole moment can be taken into account in the neutrality principle, and it only affects the degree and coefficients of the polynomial and the constant term. The lowest and second moments correspond respectively to the Wolf zero-charge scheme and the zero-dipole summation scheme, which was previously proposed. Relationships with other non-Ewald methods are discussed, to validate the current method in their contexts. Good numerical efficiencies were easily obtained in the evaluation of Madelung constants of sodium chloride and cesium chloride crystals.
Effect of secondary electrons suppression on emittance measurement of an intense, low-energy beam
Authors: Weissman L.
Published: November 2013

Transversal emittance measurements of intense low-energy beams involve use of collimators. As most of the beam is stopped by a collimator, a question arises whether the special conditions in the vicinity of the collimator influence emittance measurement. In particular, the secondary electrons emitted from the slit surface may affect the measurement of the beam phase distribution. We have observed significant modification in the measured phase space distribution of a 5–6 mA DC proton beam at the Soreq Applied Research Accelerator Facility low-energy transport after application of a weak magnetic field in the plane of the slit collimator. The periphery region of the phase distribution was mostly affected. The overall effect on the emittance value was as large as 20%.
Development of three-dimension microelectrode array for bioelectric measurement using the liquidmetal-micromolding technique
Authors: Liu Ran , Yang Xueyao , Jin Cuiyun , Fu Jingjing , Chen Weixing , Liu Jing
Published: November 2013

A method of manufacturing three-dimension microneedle electrode arrays is presented in this paper using the micromolding technology with liquid metal at room temperature, based on the physical property of the Bi-In-Sn liquid metal alloy, being its melting point especially low. Observed under scanning electron microscopy, the needle body of the electrode chip manufactured using this method has a good consistency. Skin penetration test in-vitro indicates that the microneedle electrode can pierce the stratum corneum and cross the high-impedance layer to acquire electrical signals. Electrical impedance and polarization voltage experimental results show that the electrode chips have great electric characteristics and meet the practical application demands.
First charge breeding of a rare-isotope beam with the electron-beam ion trap of the ReA post-accelerator at the National Superconducting Cyclotron Laboratory
Authors: Lapierre A. , Schwarz S. , Baumann T. M. , Cooper K. , Kittimanapun K. , Rodriguez A. J. , Sumithrarachchi C. , Williams S. J. , Wittmer W. , Leitner D. , Bollen G.
Published: November 2013

An electron-beam ion trap (EBIT) charge breeder is being brought into operation at the National Superconducting Cyclotron Laboratory at Michigan State University. The EBIT is part of the ReA post-accelerator for reacceleration of rare isotopes, which are thermalized in a gas “stopping” cell after being produced at high energy by projectile fragmentation. The ReA EBIT has a distinctive design; it is characterized by a high-current electron gun and a two-field superconducting magnet to optimize the capture and charge-breeding efficiency of continuously injected singly charged ion beams. Following a brief overview of the reaccelerator system and the ReA EBIT, this paper presents the latest commissioning results, particularly, charge breeding and reacceleration of the highly charged rare isotopes, 76Ga24 +, 25 +.
The structure of mixed 3He-4He droplets doped with OCS: A density functional approach
Authors: Leal Antonio , Mateo David , Pi Martí , Barranco Manuel , Navarro Jesús
Published: November 2013

We have investigated the structure and energetics of mixed 3He-4He droplets doped with a carbonyl sulfide molecule within a density functional approach considering a small but finite temperature of 0.1 K. The molecule is treated as an external field to which the helium droplet is attached. The energetics and appearance of these droplets are discussed for selected numbers of helium atoms, identifying the first magic numbers of the fermionic component.
Benzene analogues of (quasi-)planar M@BnHn compounds (M = V−, Cr, Mn+): A theoretical investigation
Authors: Li Lifen , Xu Chang , Jin Baokang , Cheng Longjiu
Published: November 2013

The stability of M@BnHn (M = V−, Cr, Mn+; n = 5–8) is investigated by density functional theory. For n = 6–8, the isomers possess (quasi-)planar local minima showed by geometry optimization at TPSSh/6-311+G** level. All the optimized structures are thermodynamics stable according to the large HOMO-LUMO gap, binding energy, vertical ionization potential, and vertical electron affinity analysis. The peripheral and central atomic radius fit each other best at n = 7 confirmed by the variation of the binding energy values. The availability of d atom orbitals in M for participation in the π-delocalized bonding with the peripheral ring leads to the aromaticity of the (quasi-)planar structures and makes them the benzene analogues. This work establishes firmly the metal-doped borane rings as a new type of aromatic molecule.
Interactions in ion pairs of protic ionic liquids: Comparison with aprotic ionic liquids
Authors: Tsuzuki Seiji , Shinoda Wataru , Miran Md. Shah , Kinoshita Hiroshi , Yasuda Tomohiro , Watanabe Masayoshi
Published: November 2013

The stabilization energies for the formation (Eform) of 11 ion pairs of protic and aprotic ionic liquids were studied by MP2/6-311G** level ab initio calculations to elucidate the difference between the interactions of ions in protic ionic liquids and those in aprotic ionic liquids. The interactions in the ion pairs of protic ionic liquids (diethylmethylammonium [dema] and dimethylpropylammonium [dmpa] based ionic liquids) are stronger than those of aprotic ionic liquids (ethyltrimethylammonium [etma] based ionic liquids). The Eform for the [dema][CF3SO3] and [dmpa][CF3SO3] complexes (−95.6 and −96.4 kcal/mol, respectively) are significantly larger (more negative) than that for the [etma][CF3SO3] complex (−81.0 kcal/mol). The same trend was observed for the calculations of ion pairs of the three cations with the Cl−, BF4−, TFSA− anions. The anion has contact with the N–H bond of the dema+ or dmpa+ cations in the most stable geometries of the dema+ and dmpa+ complexes. The optimized geometries, in which the anions locate on the counter side of the cations, are 11.0–18.0 kcal/mol less stable, which shows that the interactions in the ions pairs of protic ionic liquids have strong directionality. The Eform for the less stable geometries for the dema+ and dmpa+ complexes are close to those for the most stable etma+ complexes. The electrostatic interaction, which is the major source of the attraction in the ion pairs, is responsible for the directionality of the interactions and determining the magnitude of the interaction energy. Molecular dynamic simulations of the [dema][TFSA] and [dmpa][TFSA] ionic liquids show that the N–H bonds of the cations have contact with the negatively charged (oxygen and nitrogen) atoms of TFSA− anion, while the strong directionality of the interactions was not suggested from the simulation of the [etma][CF3SO3] ionic liquid.
Liquid to solid nucleation via onion structure droplets
Authors: Barros Kipton , Klein W.
Published: November 2013

We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions d ⩾ 3 is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.
Nuclear quantum effects on the structure and the dynamics of [H2O]8 at low temperatures
Authors: Videla Pablo E. , Rossky Peter J. , Laria D.
Published: November 2013

We use ring-polymer-molecular-dynamics (RPMD) techniques and the semi-empirical q-TIP4P/F water model to investigate the relationship between hydrogen bond connectivity and the characteristics of nuclear position fluctuations, including explicit incorporation of quantum effects, for the energetically low lying isomers of the prototype cluster [H2O]8 at T = 50 K and at 150 K. Our results reveal that tunneling and zero-point energy effects lead to sensible increments in the magnitudes of the fluctuations of intra and intermolecular distances. The degree of proton spatial delocalization is found to map logically with the hydrogen-bond connectivity pattern of the cluster. Dangling hydrogen bonds exhibit the largest extent of spatial delocalization and participate in shorter intramolecular O-H bonds. Combined effects from quantum and polarization fluctuations on the resulting individual dipole moments are also examined. From the dynamical side, we analyze the characteristics of the infrared absorption spectrum. The incorporation of nuclear quantum fluctuations promotes red shifts and sensible broadening relative to the classical profile, bringing the simulation results in much more satisfactory agreement with direct experimental information in the mid and high frequency range of the stretching band. While RPMD predictions overestimate the peak position of the low frequency shoulder, the overall agreement with that reported using an accurate, parameterized, many-body potential is reasonable, and far superior to that one obtains by implementing a partially adiabatic centroid molecular dynamics approach. Quantum effects on the collective dynamics, as reported by instantaneous normal modes, are also discussed.
Hysteresis and memory factor of the Kerr effect in blue phases
Authors: Nordendorf Gaby , Lorenz Alexander , Hoischen Andreas , Schmidtke Jürgen , Kitzerow Heinz , Wilkes David , Wittek Michael
Published: November 2013

The performance of a polymer-stabilized blue phase system based on a nematic host with large dielectric anisotropy and a chiral dopant with high helical twisting power is investigated and the influence of the reactive monomer composition on the electro-optic characteristics is studied. Field-induced birefringence with a Kerr coefficient greater than 1 nm V−2 can be achieved in a large temperature range from well below 20 °C to above 55 °C. The disturbing influences of electro-optic hysteresis and memory effects can be reduced by diligent choice of the composition and appropriate electric addressing.
A comprehensive picture of Cu doping in CdTe solar cells
Authors: Perrenoud J. , Kranz L. , Gretener C. , Pianezzi F. , Nishiwaki S. , Buecheler S. , Tiwari A. N.
Published: November 2013

The importance of Cu for CdTe solar cell absorber doping has been increasingly recognized in recent years. Currently different models are being discussed how to understand the case of CuCd substitutional doping in polycrystalline CdTe solar cells. In this work, an understanding is developed, which is based on a low concentration deep acceptor doped CdTe layer (Na ∼ 5 × 1014 cm−3, Ea ∼ 300 meV above the valence band). Despite their non-shallow nature, CuCd acceptors are fully or at least heavily (>30%) ionized. The low hole concentration in CdTe (∼1 × 1014 cm−3) originates directly from low Cu solubility in CdTe bulk material and is not caused by partial ionization or compensation as proposed by earlier models. The three to four orders of magnitude difference between bulk acceptor concentration and average Cu concentration in polycrystalline CdTe is attributed to grain boundary segregation of Cu. Our model is derived from substrate and superstrate CdTe solar cell measurements, controlled CdTe doping and quenching, Hall Effect measurements of CdTe films, numerical and analytical calculations, and a broad literature survey. Based on these results, routes to improve the conversion efficiency of CdTe solar cells are discussed.
Photothermoelectric response in asymmetric carbon nanotube devices exposed to sub-terahertz radiation
Authors: Fedorov G. , Kardakova A. , Gayduchenko I. , Charayev I. , Voronov B. M. , Finkel M. , Klapwijk T. M. , Morozov S. , Presniakov M. , Bobrinetskiy I. , Ibragimov R. , Goltsman G.
Published: November 2013

We report on the voltage response of carbon nanotube devices to sub-terahertz (THz) radiation. The devices contain carbon nanotubes (CNTs), which are over their length partially suspended and partially Van der Waals bonded to a SiO2 substrate, causing a difference in thermal contact. We observe a DC voltage upon exposure to 140 GHz radiation. Based on the observed gate voltage and power dependence, at different temperatures, we argue that the observed signal is both thermal and photovoltaic. The room temperature responsivity in the microwave to THz range exceeds that of CNT based devices reported before.
Nucleation and growth of HfO2 layers on graphene by chemical vapor deposition
Authors: Lupina Grzegorz , Lukosius Mindaugas , Kitzmann Julia , Dabrowski Jarek , Wolff Andre , Mehr Wolfgang
Published: November 2013

We investigate a seed layer-free growth of HfO2 on commercially available chemical vapor deposited (CVD) graphene from various suppliers. It is revealed that the samples of monolayer graphene transferred from Cu to SiO2/Si substrates have different coverage with bi- and multi-layer graphene islands. We find that the distribution and number of such islands impact the nucleation and growth of HfO2 by CVD. In particular, we show that the edges and surface of densely distributed bi-layer graphene islands provide good nucleation sites for conformal CVD HfO2 layers. Dielectric constant of 16 is extracted from measurements on graphene-HfO2-TiN capacitors.
Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion source
Authors: Choi Seyong , Lee Byoung-Seob , Park Jin Yong , Ok Jung-Woo , Shin Chang Seouk , Yoon Jang-Hee , Won Mi-Sook , Kim Byoung-Chul
Published: November 2013

Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.
Permanent magnet electron beam ion source/trap systems with bakeable magnets for improved operation conditions
Authors: Schmidt M. , Zschornack G. , Kentsch U. , Ritter E.
Published: November 2013

The magnetic system of a Dresden electron beam ion source (EBIS) generating the necessary magnetic field with a new type of permanent magnet made of high energy density NdFeB-type material operable at temperatures above 100 °C has been investigated and tested. The employment of such kind of magnets provides simplified operation without the time-consuming installation and de-installation procedures of the magnets for the necessary baking of the ion source after commissioning and maintenance work. Furthermore, with the use of a new magnetization technique the geometrical filling factor of the magnetic Dresden EBIS design could be increased to a filling factor of 100% leading to an axial magnetic field strength of approximately 0.5 T exceeding the old design by 20%. Simulations using the finite element method software Field Precision and their results compared with measurements are presented as well. It could be shown that several baking cycles at temperatures higher than 100 °C did not change the magnetic properties of the setup.
Ferroelectric polarization switching kinetics process in Bi0.9La0.1FeO3 thin films
Authors: Gao R. L. , Yang H. W. , Chen Y. S. , Sun J. R. , Zhao Y. G. , Shen B. G.
Published: November 2013

Bi0.9La0.1FeO3 (BLFO) thin films with the thickness of ∼500 nm were deposited on (001) oriented SrTiO3 substrate with 30 nm LaNiO3 as buffer layer. The switching kinetics process of ferroelectric BLFO thin films was investigated by using pulse voltages. The result shows that one dimension and two dimensions are the prior grown modes of BLFO domains in the polarization switching process. The dimensionality of the domain growth n increases linearly with applied voltage, and the grown model varies from 1 D (n = 1, implies needlelike growth) to 2 D (n = 2, planar growth) with electric pulses increasing. This is explained due to the increase in the density of nucleating domains at high fields where sideway growth is limited. The higher value of n can be an indication of non-homogeneous distribution of domain nuclei. Under all our experimental conditions that the switching time tsw is instrumentally limited and therefore the intrinsic switching time of ferroelectric BLFO films is smaller than several nanoseconds. This very short polarization switching time can be explained as a switching mechanism controlled by nucleation rate. Considering the domain walls de-pinning and thermal disturbance, the saturated polarization increases with the temperature increasing under the same input voltage which in turn affects the he switching transient current and switching time.
Thermal equation of state and thermodynamic Grüneisen parameter of beryllium metal
Authors: Zhang Jianzhong , Zhu Jinlong , Velisavljevic Nenad , Wang Liping , Zhao Yusheng
Published: November 2013

We conducted in-situ high-pressure synchrotron x-ray experiments on beryllium metal at pressures up to 7.9 GPa and temperatures up to 1373 K. A complete pressure (P)–volume (V)–temperature (T) equation of state (EOS) is determined based on the experiment, which includes temperature derivatives of elastic bulk modulus (at both constant pressure and constant volume) and pressure dependence of thermal expansivity. From this EOS, we calculate thermal pressure, heat capacity at constant volume, and thermodynamic Grüneisen parameter as a function of temperature. Above ∼600 K, our results show notable deviation from theoretical predictions using the quasiharmonic and local-density approximations, indicating that the free energy calculations need to be further improved within the current scheme of approximations.
Direct evidence for self-trapping of excitons by indium nanowires at In/Si(111) surface
Authors: Xu Maojie , Zhang Yafei
Published: November 2013

We report on the real-space observation of self-trapped excitons using scanning tunneling microscope. Electrons of In nanowires transfer to the Si substrate, yielding charge-transfer excitons at In/Si interface. The strong coupling between excitons and lattice vibrations leads to the exciton localization at low carrier density and 80.0 K. Exciton condensation was observed at the proper carrier density and its microscopic origin is discussed.
Damage threshold and focusability of mid-infrared free-electron laser pulses gated by a plasma mirror with nanosecond switching pulses
Authors: Wang Xiaolong , Nakajima Takashi , Zen Heishun , Kii Toshiteru , Ohgaki Hideaki
Published: November 2013

The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusability is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.
On the dynamics of propeller-like dust grain in plasma
Authors: Krasheninnikov S. I.
Published: November 2013

The equations of motion of a dust grain with non-spherical shape in plasma are generalized by incorporating the effects associated with propeller-like features of the grain's shape. For the grain shape close to rotationally symmetric, the stability of “stationary” (in terms of variables used in the grain dynamic equations) solutions are considered. It is found that propeller-like features of the grain's shape can crucially alter stability of such “stationary” states.
The importance of metal transverse momentum for silicon contact resistivity
Authors: Weber Cory
Published: November 2013

Contact resistance is becoming an increasing performance limiter as complimentary metal oxide semiconductor devices are scaled. Non-equilibrium Green's function transport simulations are used to evaluate contact resistivity (ρc) to silicon for metals with different density of states (DOS) distributions in k-space and different Si surface orientations. It is shown that the overlap of the metal and silicon DOS in k-space can have orders of magnitude impact to ρc, as this overlap determines whether the low resistivity transverse valleys will conduct. Thus, technologists and materials researchers should search for contact metals with a DOS distribution overlapping the silicon Δ valleys as well metals with low barriers.
Stacked inverted top-emitting white organic light-emitting diodes composed of orange and blue light-emitting units
Authors: Najafabadi Ehsan , Knauer Keith A. , Haske Wojciech , Fuentes-Hernandez Canek , Kippelen Bernard
Published: November 2013

Stacked inverted top-emitting white electrophosphorescent organic light-emitting diodes (OLEDs) are demonstrated. The OLEDs consist of orange and blue light-emitting units interconnected with a connecting unit of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile/Al/LiF. These OLEDs combine the features of having inverted electrode positions, top-emission, and a stacked architecture. They exhibit an average current efficacy of 26.5 cd/A at a luminance of 100 cd/m2. Single-unit inverted top-emitting OLEDs based on the constituent orange and blue light-emitting units are also characterized for comparison. The current efficacies of the orange and blue OLEDs are 21.2 cd/A and 32.6 cd/A, respectively, at a luminance of 100 cd/m2.
In situ optical observations of keyhole dynamics during laser drilling
Authors: Chen Meng , Wang Yuren , Yu Gang , Lan Ding , Zheng Zhongyu
Published: November 2013

To better understand the laser drilling process and especially to clarify keyhole dynamics in metal drilling, a quasi-two-dimensional drilling assembly was set up with a thin sandwich structure. Keyhole dynamics coupling multiple physical processes were recorded using high-speed photography, and clear images were obtained. The formation of keyholes was found not to be a single unified process, and the whole drilling process could be divided into five stages: an initial melt ejection, mild melting, rapid drilling, hole expansion, and backflow and recasting. As the keyhole evolved, the removal of material changed.
Phase transitions in ferroelectric-paraelectric superlattices: Stability of single domain state
Authors: Levanyuk A. P. , Misirlioglu I. B.
Published: November 2013

We studied stability of the single-domain state with respect to domain formation within Landau-Ginzburg-Devonshire theory for ferroelectric-paraelectric superlattices having equal layer thickness. Single-domain state is possible if dielectric constant of the paraelectric is larger than that of the ferroelectric for non-polar directions as in the BaTiO3/SrTiO3 system, which was taken as an example. Stability limit of the single-domain state is found as a function of temperature and layer thickness where we show a strong dependence of this limit on character of near-electrode regions, a point often overlooked. We also show that transition between single- and multi-domain states is discontinuous.
Fracture and buckling of piezoelectric nanowires subject to an electric field
Authors: Zhang Jin , Wang Chengyuan , Adhikari Sondipon
Published: November 2013

Fracture and buckling are major failure modes of thin and long nanowires (NWs), which could be affected significantly by an electric field when piezoelectricity is involved in the NWs. This paper aims to examine the issue based on the molecular dynamics simulations, where the gallium nitride (GaN) NWs are taken as an example. The results show that the influence of the electric field is strong for the fracture and the critical buckling strains, detectable for the fracture strength but almost negligible for the critical buckling stress. In addition, the reversed effects are achieved for the fracture and the critical buckling strains. Subsequently, the Timoshenko beam model is utilized to account for the effect of the electric field on the axial buckling of the GaN NWs, where nonlocal effect is observed and characterized by the nonlocal coefficient e0a=1.1 nm. The results show that the fracture and buckling of piezoelectric NWs can be controlled by applying an electric field.
Deformation-induced nanoscale mixing reactions in Cu/Ni and Ag/Pd multilayers
Authors: Wang Z. , Perepezko J. H.
Published: November 2013

During the repeated cold rolling of Cu/Ni and Ag/Pd multilayers, a solid solution forms at the interfaces as nanoscale layer structure with a composition that replicates the overall multilayer composition. The interfacial mixing behavior was investigated by means of X-ray diffraction and scanning transmission electron microscopy. During deformation induced reaction, the intermixing behavior of the Cu/Ni and Ag/Pd multilayers is in contrast to thermally activated diffusion behavior. This distinct behavior can provide new kinetic pathways and offer opportunities for microstructure control that cannot be achieved by thermal processing.
Superconductivity at 28 K in CaB3C3 predicted from first-principles
Authors: Chen Wanjin
Published: November 2013

The structural parameters, electronic properties, and superconducting state in the graphite-like BxC1−x intercalation compound, CaB3C3, have been studied using pseudopotential density functional theory within the generalized gradient approximation. Electronic and electron–phonon coupling calculations reveal that CaB3C3 is hole conducting and superconducting with critical temperature 28.2 K, which is much higher than that of CaC6 (11.5 K). The excellent superconducting state in CaB3C3 stems from the simultaneous presence of highly mobile and extremely confined conduction electrons, which enhances electron pairing and superconductivity. The current calculations might stimulate further theoretical and experimental investigation in search of new superconducting states in graphite-like BxC1−x intercalated compounds.
Characterization of magnetically fractionated magnetic nanoparticles for magnetic particle imaging
Authors: Yoshida T. , Othman N. B. , Enpuku K.
Published: November 2013

We have characterized fractionated magnetic nanoparticles (MNPs) for magnetic particle imaging. Original Ferucarbotran particles were magnetically divided into three fractionated MNPs called MS1, MS2, and MS3. Harmonic spectra from the three fractionated MNPs were measured at excitation fields of 2.8 and 28 mT with a frequency of 10 kHz. MS1 showed a 2.5-fold increase in the harmonic spectrum over that of the original MNPs. To understand the origin of the enhancement in the harmonic spectrum from MS1, we explored the magnetic properties of the MS series, such as distributions of effective core size and anisotropy energy barrier, and the correlation between them. Using these results, we performed numerical simulations of the harmonic spectra based on the Langevin equation. The simulation results quantitatively explained the experimental results of the fractionated MS series. It was also clarified that MS1 includes a large portion of the MNPs that are responsible for the harmonic spectrum.
Magnetic properties of nanocrystalline KNbO3
Authors: Golovina I. S. , Shanina B. D. , Kolesnik S. P. , Geifman I. N. , Andriiko A. A.
Published: November 2013

Newly synthesized undoped and iron-doped nanoscale powders of KNbO3 are investigated using magnetic resonance and static magnetization methods in order to determine how the crystal size and doping affect the structure of magnetic defects and material properties. Although the bulk crystals of KNbO3 are nonmagnetic, the undoped KNbO3 powder with average particle size of 80 nm exhibits magnetic properties. The ferromagnetic resonance signal and the magnetization curve registered on the powder are thoroughly analyzed. It is concluded that the appearance of the defect driven ferromagnetism in the undoped powder is due to the nano-size of the particles. This effect disappears in the iron-doped KNbO3 powder with particle sizes above 300 nm. In case of low doping (<1 mol. % Fe), a new electron paramagnetic resonance signal with geff = 4.21 is found out in the KNbO3:Fe powder. Such a signal has not been observed in the bulk crystals of KNbO3:Fe. We suppose that this signal corresponds to individual paramagnetic Fe3+ ions having rhombic symmetry.
The geodynamo’s unique longevity
Authors: Olson Peter
Published: November 2013

New insights into how Earth’s magnetic field has been sustained for billions of years closely link the planet’s core and mantle in the dynamo process.
Relationships between Visual Figure Discrimination, Verbal Abilities, and Gender
Authors: Tammik Valdar , Toomela Aaro
Published: November 2013

This study investigated the relationships between verbal thinking and performance on visual figure discrimination tasks from a Vygotskian perspective in a large varied adult sample ( N = 428). A test designed to assess the structure of word meanings (ie tendency to think in ‘everyday’ or ‘scientific’ concepts as distinguished by Vygotsky) together with two contour picture tasks was presented. Visual tasks were a modified version of Poppelreuter's overlapping figures and a picture depicting a meaningful scene. On both tasks concrete objects and abstract meaningless shapes had to be identified. In addition to relationships between visual task performance and word meaning structure, the effects of the meaningful scene and relations with gender were examined. The results confirmed the expected relation between word meaning structure and visual performance. Furthermore, they suggested a specific effect of the meaningful whole and a male advantage, especially for the first task in which women seemed to benefit less from advanced word meaning structure.