bluuebunny/crossref_metadata_2025 huggingface dataset:
Multimodal mechanism of action of allosteric HIV-1 integrase inhibitors
Authors: Jurado Kellie Ann , Engelman Alan
Published: November 2013

Integrase (IN) is required for lentivirus replication and is a proven drug target for the prevention of AIDS in HIV-1-infected patients. While clinical strand transfer inhibitors disarm the IN active site, allosteric inhibition of enzyme activity through the disruption of IN–IN protein interfaces holds great therapeutic potential. A promising class of allosteric IN inhibitors (ALLINIs), 2-(quinolin-3-yl) acetic acid derivatives, engage the IN catalytic core domain dimerisation interface at the binding site for the host integration co-factor LEDGF/p75. ALLINIs promote IN multimerisation and, independent of LEDGF/p75 protein, block the formation of the active IN–DNA complex, as well as inhibit the IN–LEDGF/p75 interaction in vitro. Yet, rather unexpectedly, the full inhibitory effect of these compounds is exerted during the late phase of HIV-1 replication. ALLINIs impair particle core maturation as well as reverse transcription and integration during the subsequent round of virus infection. Recapitulating the pleiotropic phenotypes observed with numerous IN mutant viruses, ALLINIs provide insight into underlying aspects of IN biology that extend beyond its catalytic activity. Therefore, in addition to the potential to expand our repertoire of HIV-1 antiretrovirals, ALLINIs afford important structural probes to dissect the multifaceted nature of the IN protein throughout the course of HIV-1 replication.
Organized large structure in the post-transition mixing layer. Part 1. Experimental evidence
Authors: D’Ovidio A. , Coats C. M.
Published: November 2013

New flow-visualization experiments on mixing layers of various velocity and density ratios are reported. It is shown that, in mixing layers developing from laminar initial conditions, the familiar mechanism of growth by vortex amalgamation is replaced at the mixing transition by a previously unrecognized mechanism in which the spanwise-coherent large structures individually undergo continuous linear growth. In the organized post-transition flow it is this continuous linear growth of the individual structures that produces the self-similar growth of the mixing-layer thickness, with the occasional interactions between neighbouring structures occurring as a consequence of their growth, not its cause. It is also observed that periods during which the post-transition mixing layer comprises orderly processions of large structures alternate with periods during which no large-scale organization is apparent downstream of the transition location. These two fully turbulent flow states are characterized by different growth rates, entrainment ratios and orientations of the mixing layer relative to the free streams. The implications of these findings are discussed.
Endoscopic transsphenoidal drainage of an aggressive petrous apex cholesterol granuloma: unusual complications and lessons learnt
Authors: Park K C , Wong G , Stephens J C , Saleh H A
Published: November 2013

Objectives:

This case report describes the endoscopic transsphenoidal management of a cholesterol granuloma situated in a technically challenging part of the petrous apex, and the associated peri- and post-operative complications that arose. The literature on diagnosis and management of petrous apex cholesterol granulomas is reviewed.

Method and results:

Surgical intervention was attempted on three occasions, each time via an endoscopic, transsphenoidal approach with image guidance. The procedure was abandoned on the first occasion as there was a significant risk to the carotid artery; only a small drainage ostium was created because of the proximity of the carotid artery. The second attempt, complicated by copious bleeding from the clival venous plexus, was arrested prematurely. Successful drainage was achieved at the third attempt, but recovery was complicated by tension pneumocephalus.

Conclusion:

The transnasal route is less invasive than a lateral labyrinthine or cochlear approach, and spares cochlear and vestibular function. However, this approach is not without risk. It is important to consider the natural anatomical variance of vasculature when planning surgical intervention for a lesion situated in a technically challenging part of the petrous apex. Additional magnetic resonance venography is recommended to circumnavigate the venous plexus, thereby avoiding an unexpected breach.
A fern cultured from Antarctic glacier detritus
Authors: Smith R.I. Lewis
Published: November 2013

A fem, Elaphoglossum hybridum (Bory) Brack., has been cultured from mineral sediment in cryoconite holes in the ice cap of Signy Island, South Orkney Islands. Its provenance, mode of transport to its Maritime Antarctic destination and the significance of viable exotic propagules as potential colonists are discussed.
Beyond allostatic load: Rethinking the role of stress in regulating human development
Authors: Ellis Bruce J. , Del Giudice Marco
Published: November 2013

How do exposures to stress affect biobehavioral development and, through it, psychiatric and biomedical disorder? In the health sciences, the allostatic load model provides a widely accepted answer to this question: stress responses, while essential for survival, have negative long-term effects that promote illness. Thus, the benefits of mounting repeated biological responses to threat are traded off against costs to mental and physical health. The adaptive calibration model, an evolutionary–developmental theory of stress–health relations, extends this logic by conceptualizing these trade-offs as decision nodes in allocation of resources. Each decision node influences the next in a chain of resource allocations that become instantiated in the regulatory parameters of stress response systems. Over development, these parameters filter and embed information about key dimensions of environmental stress and support, mediating the organism's openness to environmental inputs, and function to regulate life history strategies to match those dimensions. Drawing on the adaptive calibration model, we propose that consideration of biological fitness trade-offs, as delineated by life history theory, is needed to more fully explain the complex relations between developmental exposures to stress, stress responsivity, behavioral strategies, and health. We conclude that the adaptive calibration model and allostatic load model are only partially complementary and, in some cases, support different approaches to intervention. In the long run, the field may be better served by a model informed by life history theory that addresses the adaptive role of stress response systems in regulating alternative developmental pathways.
Understanding rating addiction: US courts and the origins of rating agencies' regulatory license (1900–1940)
Authors: Flandreau Marc , Sławatyniec Joanna Kinga
Published: November 2013

This article challenges the ‘regulatory license’ view that reliance by regulators on the output of rating agencies in the 1930s ‘caused’ the agencies to become a central part of the fabric of the US financial system. We argue that long before the 1930s, courts began using ratings as financial-community-produced norms of prudence. This created ‘a legal license’ problem, very analogous to the ‘regulatory license’ problem, and gave rise to conflicts of interest not unlike those that have been discussed in the context of the subprime crisis. Rating agencies may have had substantial responsibility for the Great Depression of the 1930s.
Can Corrective Information Reduce Negative Appraisals of Intrusive Thoughts in a Community Sample?
Authors: Rees Clare S. , Austen Tomas , Anderson Rebecca A. , Egan Sarah J.
Published: November 2013

Background: Improving mental health literacy in the general population is important as it is associated with early detection and treatment-seeking for mental health problems. Target areas for mental health literacy programs should be guided by research that tests the impact of improving knowledge of psychological constructs associated with the development of mental health problems. Aims: This study investigated the impact of providing corrective information about the nature of intrusive thoughts on their subsequent appraisal in a community sample. Method: In an online, experimental design, 148 community participants completed measures of obsessive-compulsive symptoms and appraisals (Obsessive Compulsive Inventory-Revised [OCI-R]; Intrusions Inventory [III]). Individuals were instructed to read either a brief informational text about the nature of intrusive thoughts or a control text. All participants then completed post-test measurements of appraisals. Intervention effectiveness was analysed using hierarchical multiple regression. Results: Individuals in the intervention group reported significantly lower levels of maladaptive appraisals than those in the control group (α = .05). Conclusions: The results of this study support the efficacy of provision of brief written information in reducing negative appraisals of intrusive thoughts in a community sample. It suggests a possible role for education about intrusive thoughts as a prevention strategy for obsessive-compulsive disorder.
Capturing Enveloped Viruses on Affinity Grids for Downstream Cryo-Electron Microscopy Applications
Authors: Kiss Gabriella , Chen Xuemin , Brindley Melinda A. , Campbell Patricia , Afonso Claudio L. , Ke Zunlong , Holl Jens M. , Guerrero-Ferreira Ricardo C. , Byrd-Leotis Lauren A. , Steel John , Steinhauer David A. , Plemper Richard K. , Kelly Deborah F. , Spearman Paul W. , Wright Elizabeth R.
Published: November 2013

Electron microscopy (EM), cryo-electron microscopy (cryo-EM), and cryo-electron tomography (cryo-ET) are essential techniques used for characterizing basic virus morphology and determining the three-dimensional structure of viruses. Enveloped viruses, which contain an outer lipoprotein coat, constitute the largest group of pathogenic viruses to humans. The purification of enveloped viruses from cell culture presents certain challenges. Specifically, the inclusion of host-membrane-derived vesicles, the complete destruction of the viruses, and the disruption of the internal architecture of individual virus particles. Here, we present a strategy for capturing enveloped viruses on affinity grids (AG) for use in both conventional EM and cryo-EM/ET applications. We examined the utility of AG for the selective capture of human immunodeficiency virus virus-like particles, influenza A, and measles virus. We applied nickel-nitrilotriacetic acid lipid layers in combination with molecular adaptors to selectively adhere the viruses to the AG surface. This further development of the AG method may prove essential for the gentle and selective purification of enveloped viruses directly onto EM grids for ultrastructural analyses.
Why do some oil exporters experience civil war but others do not?: investigating the conditional effects of oil
Authors: Basedau Matthias , Richter Thomas
Published: November 2013

According to quantitative studies, oil seems the only natural resource that is robustly linked to civil war onset. However, recent debates on the nexus of oil and internal conflict have neglected the fact that there are a number of peaceful rentier oil states in existence. Few efforts have been made to explain why some oil-exporting countries have experienced civil war while others have not. We thus address this puzzle, by arguing that civil war risks depend on the specific conditions of oil production and how they come to structure state–society relations. Specifically, we expect that states that are either highly dependent on oil or who have problematic relations with oil regions are prone to civil war. However, these risks will be mitigated either when democratic institutions can manage conflicts peacefully or when abundant oil revenues can be spent in such a way as to buy peace. We test this conditional argument by comparing 39 net oil exporters, using a (crisp-set) Qualitative Comparative Analysis – a methodology particularly suited to test conditional relationships in medium-Nsamples. Our results largely confirm our conditional hypotheses. Conditions of oil production are ambiguous, and particular combinations thus explain the onset of civil war. Specifically, we find that high abundance is sufficient to ensure peace, while two distinct pathways lead to civil war: the combination of high dependence and low abundance, as well as the overlap of ethnic exclusion and oil reserves in non-abundant and non-democratic oil states.
Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6
Authors: Li Yan-Ling , Luo Wei , Chen Xiao-Jia , Zeng Zhi , Lin Hai-Qing , Ahuja Rajeev
Published: November 2013

Pressure can tune material's electronic properties and control its quantum state, making some systems present disconnected superconducting region as observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6 superconductor (Tc of 11.5 K), applying pressure first Tc increases and then suppresses and the superconductivity of this compound is eventually disappeared at about 18 GPa. Here, we report a theoretical finding of the re-emergence of superconductivity in heavily compressed CaC6. The predicted phase III (space group Pmmn) with formation of carbon nanofoam is found to be stable at wide pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has bad metallic behavior, indicating again departure from superconductivity. Re-emerged superconductivity in compressed CaC6 paves a new way to design new-type superconductor by inserting metal into nanoporous host lattice.
Influence of doping on charge carrier collection in normal and inverted geometry polymer:fullerene solar cells
Authors: Dibb George F. A. , Muth Mathis-Andreas , Kirchartz Thomas , Engmann Sebastian , Hoppe Harald , Gobsch Gerhard , Thelakkat Mukundan , Blouin Nicolas , Tierney Steve , Carrasco-Orozco Miguel , Durrant James R. , Nelson Jenny
Published: November 2013

While organic semiconductors used in polymer:fullerene photovoltaics are generally not intentionally doped, significant levels of unintentional doping have previously been reported in the literature. Here, we explain the differences in photocurrent collection between standard (transparent anode) and inverted (transparent cathode) low band-gap polymer:fullerene solar cells in terms of unintentional p-type doping. Using capacitance/voltage measurements, we find that the devices exhibit doping levels of order 1016 cm−3, resulting in space-charge regions ~100 nm thick at short circuit. As a result, low field regions form in devices thicker than 100 nm. Because more of the light is absorbed in the low field region in standard than in inverted architectures, the losses due to inefficient charge collection are greater in standard architectures. Using optical modelling, we show that the observed trends in photocurrent with device architecture and thickness can be explained if only charge carriers photogenerated in the depletion region contribute to the photocurrent.
Altered transition metal homeostasis in Niemann–Pick disease, type C1
Authors: Hung Ya Hui , Faux Noel G. , Killilea David W. , Yanjanin Nicole , Firnkes Sally , Volitakis Irene , Ganio George , Walterfang Mark , Hastings Caroline , Porter Forbes D. , Ory Daniel S. , Bush Ashley I.
Published: November 2013

The Niemann–Pick type C1 disease protein, NPC1 may have a critical role in transition metal homeostasis.
“Dirty nanostructures”: aerosol-assisted synthesis of temperature stable mesoporous metal oxide semiconductor spheres comprising hierarchically assembled zinc oxide nanocrystals controlled via impurities
Authors: Lehr Daniela , Großmann Dennis , Grünert Wolfgang , Polarz Sebastian
Published: November 2013

The thermal stability of mesoporous ZnO nanostructures could be enhanced by intentional introduction of impurity atoms like Al or S.
Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation
Authors: Martínez-Martínez A. J. , Armstrong D. R. , Conway B. , Fleming B. J. , Klett J. , Kennedy A. R. , Mulvey R. E. , Robertson S. D. , O'Hara C. T.
Published: November 2013

The synthesis, structure and reactivity of donor-free sodium and potassium magnesiates are assessed culminating in the unique 1,4-dimetallation of naphthalene.
Remarkable photocurrent of p-type dye-sensitized solar cell achieved by size controlled CuGaO2 nanoplates
Authors: Xu Zhen , Xiong Dehua , Wang Huan , Zhang Wenjun , Zeng Xianwei , Ming Liqun , Chen Wei , Xu Xiaobao , Cui Jin , Wang Mingkui , Powar Satvasheel , Bach Udo , Cheng Yi-Bing
Published: November 2013

This work demonstrates CuGaO2 as an efficient alternative to NiO as a photocathode material in dye-sensitized solar cells. A remarkable photocurrent has been achieved by the CuGaO2 photocathode.
TheEscherichia coliRNA processing and degradation machinery is compartmentalized within an organized cellular network
Authors: Taghbalout Aziz , Yang Qingfen , Arluison Véronique
Published: November 2013

Bacterial RNA processing and degradation involves the co-ordinated action of a large number of RNases, RNA helicases and other proteins. It is not known how this functional network is organized within the cell nor how it is co-ordinated or regulated. In the present study, we show that multiple components of the RNA degradation and processing network of Escherichia coli are localized within extended cellular structures that appear to coil around the periphery of the cell. These include Orn, Hfq, PAP I, RNase III, RppH, RraA and RraB in addition to the previously reported proteins RNase II and RNaseE. Double-label localization studies of several of the proteins showed co-localization of the proteins within the observed structures. Assembly of the proteins into the structures was independent of the MreBCD or MinCDE cytoskeletal systems, RNA synthesis, or nucleoid positioning within the cell. Our results indicate that the components of the RNA processing and degradation network are compartmentalized within the cell rather than diffusely distributed in the cytoplasm. This sequestration provides the cell with a possible mechanism to control access to RNA substrates and to functionally co-ordinate the multiple players of the RNA processing and degradation pathways.
Laser‐scanner‐based powered two‐wheeler traffic monitoring
Authors: Vivet D. , Prabhakar Y. , Subirats P. , Lecomte C. , Violette E. , Bensrhair A.
Published: November 2013

Powered two wheelers (PTWs) represent only 2% of the traffic, but 30% of all deaths on the road. European governments have made this particular point a priority for road safety. This presented study overcomes the lack of PTW traffic‐analyser systems in real traffic conditions. A detection technique based on a single two‐dimensional LIDAR sensor is proposed. This system is able to accurately detect and count PTWs with a single sensor in dense traffic on a highway with multiple carriageways. The method consists, firstly, in generating spatio‐temporal observations of vehicles crossing under the LIDAR, then, in classifying vehicles using machine‐learning techniques, and finally, in evaluating PTW traffic. Such a system has direct industrial applications since it is a non‐intrusive traffic‐analyser system that is reliable, easily deployable and inexpensive compared with existing industrial solutions.
Improved dual‐feed single‐beam power‐combining reflectarray antenna
Authors: Almajali E. , McNamara D.A. , Shaker J. , Chaharmir M.R.
Published: November 2013

The power combining efficiency of a dual‐feed single‐beam power combining reflectarray is shown to be substantially improved by reducing the spacing between the reflectarray elements. This improvement has been confirmed experimentally.
Orthodontie et finitions cosmétiques composites : approche
ultra-conservatrice de la restauration du sourire
Authors: Grossetti François
Published: November 2013

Une nouvelle pratique a vu le jour dans le traitement dentaire cosmétique par le biais de
l’alignement, de l’éclaircissement et du collage. Les patients présentés dans cet article
résument certains cas types en dentisterie cosmétique, susceptibles d’être traités sans
aucune mutilation tissulaire grâce à un traitement orthodontique préalable.
Analytical investigation of collector optimum tilt angle at low latitude
Authors: Chikere Aja Ogboo , Al-Kayiem Hussain H. , Ambri Abdul Karim Zainal
Published: November 2013

An analytical investigation on the optimum tilt angle for solar collectors at low latitude, a case study of Universiti Teknologi PETRONAS (UTP), 4.39°N and 100.98°E, Malaysia is presented in this work. The study employed Hay, Davies, Klucher, and Reindl (HDKR) anisotropic sky model to evaluate the available hourly solar radiation on inclined surface using the location metrological data. The tilt angles considered were 0° to 30° in step of 3° with the inclusion of the location latitude angle. The study employed the ratio of global solar radiation on tilted surface to the global solar radiation on horizontal surface in the decision of the optimum tilt. The system equations were converted to MATLAB codes to solve for the optimum tilt angles. The results show that the optimum tilt varies monthly but gave zero degree for south facing collector for the months of April to August; thus, the investigation also considered north facing orientation for the months of April to September. The optimum annual tilt angle for the location using the tilt to horizontal radiation ratio was found to be equal to the location latitude angle. Using the conventional average of the monthly optimum tilt angles, the annual optimum tilt angle was found to be 9.75° for south facing collector. Considering seasonal optimum tilt angle for the location using the tilt to horizontal radiation ratio, 18° facing south was found to be the optimum tilt angle for rainy season (September to March) and 15° facing north for dry season (April to August). Employing the average of monthly optimum tilt method, the seasonal optimum tilt angle was found to be 17° for rainy season and 12° facing north dry season. The effect of dust on the collector was considered with reference to literature and the annual tilt angle of 15° facing south was recommended for the location in the case of large solar collector that cannot be monthly or seasonally adjusted.
Delay time calculation for dual-wavelength quantum cascade lasers
Authors: Hamadou A. , Lamari S. , Thobel J.-L.
Published: November 2013

In this paper, we calculate the turn-on delay (tth) and buildup (Δt) times of a midinfrared quantum cascade laser operating simultaneously on two laser lines having a common upper level. The approach is based on the four-level rate equations model describing the variation of the electron number in the states and the photon number present within the cavity. We obtain simple analytical formulae for the turn-on delay and buildup times that determine the delay times and numerically apply our results to both the single and bimode states of a quantum cascade laser, in addition the effects of current injection on tth and Δt are explored.
Low-temperature EPR spectra of synthetic diamond and type Ib nanodiamond
Authors: Vaisnoras R. , Kulbickas A. , Kobets M. , Dergachev K. , Khatsko E.
Published: November 2013

Low-frequency resonance studies of single crystal diamond and type Ib nanodiamond (powder) unirradiated and irradiated by protons at temperatures of 300 and 500 K are reported. EPR spectra typical of paramagnetic nitrogen centers are observed. It is shown that when synthetic diamond crystals are irradiated by protons, additional lines appear in the EPR spectra which can be attributed to radiation induced nitrogen-vacancy centers (NV defects).
The Nernst spin effect in a two-dimensional electron gas
Authors: Lyapilin I. I.
Published: November 2013

The response of two-dimensional conduction electrons with spin-orbit coupling to a thermal perturbation is studied using the method of nonequilibrium statistical operator. It is shown that in this case, a spin current orthogonal to the direction of the temperature gradient is generated in the system of two-dimensional electrons. Expressions for the spin-Hall conductivity are derived with electron scattering taken into account.
On the stability of ethanol nanoclusters in a nitrogen cryomatrix
Authors: Drobyshev A. , Aldiyarov A. , Katpaeva K. , Korshikov E. , Kurnosov V. , Sokolov D.
Published: November 2013

Investigating the processes of recondensation of ethanol molecules from a nitrogen cryomatrix onto a substrate we have previously found that the state of ethanol molecules in the matrix is not stable. A slight increase of temperature of the solid nitrogen long before its sublimation changes the vibrational spectrum of the bicomponent film ethanol-nitrogen. The results of study of this phenomenon are presented here. The measurements were carried out in the temperature range 12–40 K at the initial vacuum in the chamber of at least 10−8 Torr. The concentration of ethanol in nitrogen was from 0.5% to 3%. The methodology of obtaining the information on the state of ethanol molecules in a nitrogen matrix is based on an analysis of amplitudes of the absorption bands corresponding to vibrations of an ethanol molecule in an unbound state. In particular, the amplitude of the absorption of the strain δ(OH)-vibrations at a frequency ν = 1259 cm−1 which is a sign of the presence in this object of monomers or dimers of ethanol in the anti-conformal state was measured. On the basis of reflection spectra it is concluded that the nitrogen matrix contains poly-aggregates of ethanol formed during the condensation of a mixture of nitrogen and ethanol. A part of the ethanol molecules forming poly-aggregates is not connected by hydrogen bonds with neighboring molecules, creating in the near-surface zone of clusters an assembly of quasi-free ethanol molecules with the absorption bands corresponding to these states. An increase of temperature of the matrix leads to a decrease of the amplitude of absorption at the frequency ν = 1259 cm−1, which can be explained by the anti-gauche conversion with a corresponding decrease in the concentration of anti-component. This is confirmed by a simultaneous reduction of the amplitude of absorption of ethanol at the frequency ν = 1028 cm−1, which corresponds to vibrations of anti-conformers of ethanol. Thus, the observed decrease in the amplitude of absorption is a manifestation of reducing the number of anti- conformal states of an ethanol molecule.
Raman scattering investigation of the structural phase transition in single crystal KDy(WO4)2
Authors: Peschanskii A. V.
Published: November 2013

The Raman scattering spectrum of a KDy(WO4)2 single crystal has been investigated in the frequency range 3–950 cm−1 at temperatures 2, 5, 25, 80, and 300 K. All 36 vibrational modes predicted by the group-theoretical analysis for the high-temperature phase were detected and their symmetries were determined. The analysis of the temperature behavior of the Raman spectra indicates that the monoclinic symmetry of the crystal remains unchanged upon the phase transition. Low-energy electronic transitions are observed between the levels of the ground multiplet 6H15/2 of the Dy3+ ion split by the crystal field of symmetry C2. It is established that in the region of the first excited Kramers doublet of the Dy3+ ion in the KDy(WO4)2 crystal, the Raman spectrum above the phase transition temperature of 6.38 K contains two lines (11.0 and 13.6 cm−1 at 25 K), while at lower temperatures it contains four lines (9.0, 16.2, 16.6, and 18.6 cm−1 at 2 K). This fact shows the presence of four nonequivalent dysprosium ions in the low-temperature phase. Three additional phonon lines (41.5, 76.7, 182.3 cm−1) observed in the low-temperature phase at 2 K also indicate that the primitive translation cell is doubled upon the phase transition. The measurements in an external magnetic field directed along the a-axis of the monoclinic cell revealed a considerable transformation of the scattering spectrum in the region of the first exited Kramers doublet of the Dy3+ ion in KDy(WO4)2. This transformation indicates a magnetic-field-induced phase transition.
A temperature dependent screening tool for high throughput thermoelectric characterization of combinatorial films
Authors: Yan Y. G. , Martin J. , Wong-Ng W. , Green M. , Tang X. F.
Published: November 2013

Combinatorial metrology has evolved as a useful approach to rapidly determine the composition-structure-property relationships for solid solution systems in a far more efficient way than the traditional one composition at a time approach. The success of this method applied in thermoelectric (TE) research relies on screening tools to evaluate the TE properties for a combinatorial library. We report here on a thermoelectric screening tool capable of performing temperature dependent measurement of the Seebeck coefficient and electrical resistivity from 300 K to 800 K. The validity of the apparatus is demonstrated by screening the power factor of a filled skutterudite combinatorial film at room temperature and at elevated temperatures as well. The accuracy of the measurement is verified using the low temperature Seebeck coefficient Standard Reference Material (NIST SRM 3451) and a heavily doped SiGe specimen for high temperature comparison. Several important parameters, such as measurement atmosphere, film substrate, and probe configuration, are identified that directly affect the Seebeck coefficient measurement in this and other similar apparatus.
Fluctuation theory of single-walled carbon nanotube formation
Authors: Vosel Sergey V. , Onischuk Andrei A. , Purtov Peter A. , Nasibulin Albert G.
Published: November 2013

In the framework of classical fluctuation theory an analytical formula is derived for the reversible work of formation of just detached carbon cap on the surface of catalyst nanoparticle (NP). This cap is considered as single walled carbon nanotube (SWCNT) formation center. The work of cap formation depends on the source carbon chemical potential μC. Using the derived formula for this work an expression for the rate of SWCNT formation is determined. From this expression the SWCNT diameter distributions can be obtained. The obtained distributions have sharp maxima. It is found that the modal SWCNT diameter dm increases weakly with μC being in the narrow window of 1.0 < dm < 1.8 nm when changing the source carbon chemical potential in a wide range. The determined diameter distributions proved to be in a good agreement with the typical values of the SWCNT diameters as experimentally measured in the chemical vapor deposition process. The increase of dm is accompanied by the increase of the distribution width Δd. The selectivity dm/Δd is a function of μC, the higher values of μC the worse selectivity is observed. Although the value of the SWCNT formation rate I cannot be calculated precisely the relationship between I and the system parameters, such as the NP radius RS, can be obtained. This relationship is derived for the solid-liquid-solid system. To determine the function I(RS) for nanotubes of a certain diameter d, formulas for catalyst/amorphous carbon mutual solubilities as functions of NP radius are derived in the framework of the rigorous Gibbs theory of interface. Using the derived formulas an expression giving the dependence I(RS) is obtained. The expression predicts an increase of I with the radius RS. The estimations carried out for the metal/carbon interface surface tension of 1000 mN/m show that the SWCNT formation rate increases by a few orders of magnitude with the radius increase from 1 to 10 nm.
Cluster-continuum quantum mechanical models to guide the choice of anions for Li+-conducting ionomers
Authors: Shiau Huai-Suen , Liu Wenjuan , Colby Ralph H. , Janik Michael J.
Published: November 2013

A quantum-mechanical investigation on Li poly(ethylene oxide)-based ionomers was performed in the cluster-continuum solvation model (CCM) that includes specific solvation in the first shell surrounding the cation, all surrounded by a polarizable continuum. A four-state model, including a free Li cation, Li+-anion pair, triple ion, and quadrupole was used to represent the states of Li+ within the ionomer in the CCM. The relative energy of each state was calculated for Li+ with various anions, with dimethyl ether representing the ether oxygen solvation. The population distribution of Li+ ions among states was estimated by applying Boltzmann statistics to the CCM energies. Entropy difference estimates are needed for populations to better match the true ionomer system. The total entropy change is considered to consist of four contributions: translational, rotational, electrostatic, and solvent immobilization entropies. The population of ion states is reported as a function of Bjerrum length divided by ion-pair separation with/without entropy considered to investigate the transition between states. Predicted concentrations of Li+-conducting states (free Li+ and positive triple ions) are compared among a series of anions to indicate favorable features for design of an optimal Li+-conducting ionomer; the perfluorotetraphenylborate anion maximizes the conducting positive triple ion population among the series of anions considered.
Multi-transmission-line-beam interactive system
Authors: Figotin Alexander , Reyes Guillermo
Published: November 2013

We construct here a Lagrangian field formulation for a system consisting of an electron beam interacting with a slow-wave structure modeled by a possibly non-uniform multiple transmission line (MTL). In the case of a single line we recover the linear model of a traveling wave tube due to J. R. Pierce. Since a properly chosen MTL can approximate a real waveguide structure with any desired accuracy, the proposed model can be used in particular for design optimization. Furthermore, the Lagrangian formulation provides: (i) a clear identification of the mathematical source of amplification, (ii) exact expressions for the conserved energy and its flux distributions obtained from the Noether theorem. In the case of uniform MTLs we carry out an exhaustive analysis of eigenmodes and find sharp conditions on the parameters of the system to provide for amplifying regimes.
Correlation between oxygen adsorption energy and electronic structure of transition metal macrocyclic complexes
Authors: Liu Kexi , Lei Yinkai , Wang Guofeng
Published: November 2013

Oxygen adsorption energy is directly relevant to the catalytic activity of electrocatalysts for oxygen reduction reaction (ORR). In this study, we established the correlation between the O2 adsorption energy and the electronic structure of transition metal macrocyclic complexes which exhibit activity for ORR. To this end, we have predicted the molecular and electronic structures of a series of transition metal macrocyclic complexes with planar N4 chelation, as well as the molecular and electronic structures for the O2 adsorption on these macrocyclic molecules, using the density functional theory calculation method. We found that the calculated adsorption energy of O2 on the transition metal macrocyclic complexes was linearly related to the average position (relative to the lowest unoccupied molecular orbital of the macrocyclic complexes) of the non-bonding d orbitals ($d_{z^2 },\,d_{xy},\,d_{xz}$dz2,dxy,dxz, and dyz) which belong to the central transition metal atom. Importantly, our results suggest that varying the energy level of the non-bonding d orbitals through changing the central transition metal atom and/or peripheral ligand groups could be an effective way to tuning their O2 adsorption energy for enhancing the ORR activity of transition metal macrocyclic complex catalysts.
Influence of soft ferromagnetic substrate on magneto-elastic behavior in a superconducting coated conductor strip
Authors: He An , Xue Cun , Yong Huadong , Zhou Youhe
Published: November 2013

Ferromagnetic materials will affect not only the electromagnetic response but also the mechanical behaviors of coated conductors. The influence of soft ferromagnetic substrate on magneto-elastic behavior in a superconductor/ferromagnetic (SC/FM) bilayer exposed to a transverse magnetic field is investigated theoretically. The ferromagnetic substrate is regarded as ideal soft magnets with high permeability and small magnetic hysteresis. Due to the composite structure of SC/FM hybrids, magneto-elastic behavior will be subjected to combined effect of equivalent force and flexural moment. Analytical expressions for internal stress and strain components are derived by virtue of a two-dimensional elasticity analysis. It is worth pointing out that the y component of strain has much larger positive value during field ascent, which may result in the delamitation at the interface. Irreversible magnetostrictive behaviors are observed both along x direction and along y direction. For the thickness dependence of magnetostriction, the flexural moment dominates when the SC thickness is small while the equivalent force plays a critical role at higher SC thickness.
Relationship between open-circuit voltage in Cu(In,Ga)Se2 solar cell and peak position of (220/204) preferred orientation near its absorber surface
Authors: Chantana J. , Watanabe T. , Teraji S. , Kawamura K. , Minemoto T.
Published: November 2013

Cu(In,Ga)Se2 (CIGS) absorbers with various Ga/III, Ga/(In+Ga), profiles are prepared by the so-called “multi-layer precursor method” using multi-layer co-evaporation of material sources. It is revealed that open-circuit voltage (VOC) of CIGS solar cell is primarily dependent on averaged Ga/III near the surface of its absorber. This averaged Ga/III is well predicted by peak position of (220/204) preferred orientation of CIGS film near its surface investigated by glancing-incidence X-ray diffraction with 0.1° incident angle. Finally, the peak position of (220/204) preferred orientation is proposed as a measure of VOC before solar cell fabrication.
Effect of sidewall surface recombination on the quantum efficiency in a Y2O3 passivated gated type-II InAs/GaSb long-infrared photodetector array
Authors: Chen G. , Hoang A. M. , Bogdanov S. , Haddadi A. , Darvish S. R. , Razeghi M.
Published: November 2013

Y2O3 was applied to passivate a long-wavelength infrared type-II superlattice gated photodetector array with 50% cut-off wavelength at 11 μm, resulting in a saturated gate bias that was 3 times lower than in a SiO2 passivated array. Besides effectively suppressing surface leakage, gating technique exhibited its ability to enhance the quantum efficiency of 100 × 100 μm size mesa from 51% to 57% by suppressing sidewall surface recombination. At 77 K, the gated photodetector showed dark current density and resistance-area product at −300 mV of 2.5 × 10−5 A/cm2 and 1.3 × 104 Ω cm2, respectively, and a specific detectivity of 1.4 × 1012 Jones.
Phonon and thermal properties of exfoliated TaSe2 thin films
Authors: Yan Z. , Jiang C. , Pope T. R. , Tsang C. F. , Stickney J. L. , Goli P. , Renteria J. , Salguero T. T. , Balandin A. A.
Published: November 2013

We report on the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe2) obtained via the “graphene-like” mechanical exfoliation of crystals grown by chemical vapor transport. The ratio of the intensities of the Raman peak from the Si substrate and the E2g peak of TaSe2 presents a convenient metric for quantifying film thickness. The temperature coefficients for two main Raman peaks, A1g and E2g, are −0.013 and −0.0097 cm−1/oC, respectively. The Raman optothermal measurements indicate that the room temperature thermal conductivity in these films decreases from its bulk value of ∼16 W/mK to ∼9 W/mK in 45-nm thick films. The measurement of electrical resistivity of the field-effect devices with TaSe2 channels shows that heat conduction is dominated by acoustic phonons in these van der Waals films. The scaling of thermal conductivity with the film thickness suggests that the phonon scattering from the film boundaries is substantial despite the sharp interfaces of the mechanically cleaved samples. These results are important for understanding the thermal properties of thin films exfoliated from TaSe2 and other metal dichalcogenides, as well as for evaluating self-heating effects in devices made from such materials.
Silicon-compatible high-hole-mobility transistor with an undoped germanium channel for low-power application
Authors: Cho Seongjae , Man Kang In , Rok Kim Kyung , Park Byung-Gook , Harris James S.
Published: November 2013

In this work, Ge-based high-hole-mobility transistor with Si compatibility is designed, and its performance is evaluated. A 2-dimensional hole gas is effectively constructed by a AlGaAs/Ge/Si heterojunction with a sufficiently large valence band offset. Moreover, an intrinsic Ge channel is exploited so that high hole mobility is preserved without dopant scattering. Effects of design parameters such as gate length, Ge channel thickness, and aluminum fraction in the barrier material on device characteristics are thoroughly investigated through device simulations. A high on-current above 30 μA/μm along with a low subthreshold swing was obtained from an optimized planar device for low-power applications.
Photoconduction efficiencies of metal oxide semiconductor nanowires: The material's inherent properties
Authors: Chen R. S. , Wang W. C. , Chan C. H. , Lu M. L. , Chen Y. F. , Lin H. C. , Chen K. H. , Chen L. C.
Published: November 2013

The photoconduction (PC) efficiencies of various single-crystalline metal oxide semiconductor nanowires (NWs) have been investigated and compared based on the materials' inherent properties. The defined PC efficiency (normalized gain) of SnO2 NWs is over one to five orders of magnitude higher than that of its highly efficient counterparts such as ZnO, TiO2, WO3, and GaN. The inherent property of the material allowed the photoconductive gain of an SnO2 single-NW photodetector to easily reach 8 × 108 at a low bias of 3.0 V and a low light intensity of 0.05 Wm−2, which is the optimal reported value so far for the single-NW photodetectors. The probable physical origins, such as charged surface state density and surface band bending, that caused the differences in PC efficiencies and carrier lifetimes are also discussed.
Transparent p-type SnO nanowires with unprecedented hole mobility among oxide semiconductors
Authors: Caraveo-Frescas J. A. , Alshareef H. N.
Published: November 2013

p-type tin monoxide (SnO) nanowire field-effect transistors with stable enhancement mode behavior and record performance are demonstrated at 160 °C. The nanowire transistors exhibit the highest field-effect hole mobility (10.83 cm2 V−1 s−1) of any p-type oxide semiconductor processed at similar temperature. Compared to thin film transistors, the SnO nanowire transistors exhibit five times higher mobility and one order of magnitude lower subthreshold swing. The SnO nanowire transistors show three times lower threshold voltages (−1 V) than the best reported SnO thin film transistors and fifteen times smaller than p-type Cu2O nanowire transistors. Gate dielectric and process temperature are critical to achieving such performance.
Room temperature ferromagnetism in defective TiO2 nanoparticles: Role of surface and grain boundary oxygen vacancies
Authors: Choudhury Biswajit , Choudhury Amarjyoti
Published: November 2013

Unexpected room temperature ferromagnetism (RTFM) in nonmagnetic metal oxide nanoparticles have been reported previously. This unconventional behaviour is primarily attributed to the presence of oxygen vacancies, and in this regard TiO2 is not an exception. This article, therefore, explores the effect of oxygen vacancies on the magnetic properties of TiO2 nanoparticles. TiO2 nanoparticles are prepared by sol-gel method and annealed in vacuum for 3 h and 8 h. These defective TiO2 nanoparticles are found to display RTFM and the highest magnetization is shown by the sample which is exposed for the maximum period of 8 h under vacuum. It is further observed that the RTFM is transformed to paramagnetism on air annealing of the defective TiO2 for 8 h. It is anticipated that oxygen vacancies on the surface and on the grain boundary triggers ferromagnetism in this otherwise nonmagnetic metal oxide system. The localized oxygen vacancies in these regions form oxygen vacancy clusters and undergo strong ferromagnetic exchange interaction. Switching of magnetism from ferro-to para is observed as disappearance of these oxygen vacancies set in.
In situ study of e-beam Al and Hf metal deposition on native oxide InP (100)
Authors: Dong H. , KC Santosh , Azcatl A. , Cabrera W. , Qin X. , Brennan B. , Zhernokletov D. , Cho K. , Wallace R. M.
Published: November 2013

The interfacial chemistry of thin Al (∼3 nm) and Hf (∼2 nm) metal films deposited by electron beam (e-beam) evaporation on native oxide InP (100) samples at room temperature and after annealing has been studied by in situ angle resolved X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. The In-oxides are completely scavenged forming In-In/In-(Al/Hf) bonding after Al and Hf metal deposition. The P-oxide concentration is significantly decreased, and the P-oxide chemical states have been changed to more P-rich oxides upon metal deposition. Indium diffusion through these metals before and after annealing at 250 °C has also been characterized. First principles calculation shows that In has lower surface formation energy compared with Al and Hf metals, which is consistent with the observed indium diffusion behavior.
Oxygen surfactant-assisted growth and dewetting of Co films on O-3 × 3/W(111)
Authors: Hsueh Kun-Jen , Tsai Cheng-Jui , Wu Shih-Yu , Chou Hsin-Lei , Bisio Francesco , Kuo Chien-Cheng , Lin Wen-Chin
Published: November 2013

Following the cyclic heating in oxygen and annealing, an oxygen-induced 3 × 3 reconstruction was found on the W(111) surface. The growth, crystalline structure, thermal stability, and magnetism of Co ultrathin films deposited on the O-3 × 3/W(111) surface were investigated. The Auger signal of the oxygen was always observable and nearly invariant after either Co deposition or annealing, indicating the role of the surfactant played by oxygen. Auger electron spectroscopy and scanning tunneling microscopy measurements revealed the 2-dimensional growth of Co on O-3 × 3/W(111). Following the annealing procedures, the surfactant oxygen was always observed to float on the film surface while the Co film transformed to 3-dimensional islands with a wetting layer. In contrast to the thermodynamically stable wetting layer of 1 physical monolayer (PML) Co on clean W(111) between 700 and 1000 K, the oxygen surfactant led to a reduction of the wetting layer to ≈1/3 PML after thermal annealing. The 6 and 9.6 PML Co/O-3 × 3/W(111) revealed a stable in-plane magnetic anisotropy. A 6-fold symmetry corresponding to the crystalline structure was observed in the in-plane angle-dependent magneto-optical Kerr effect measurement.
Low interface defect density of atomic layer deposition BeO with self-cleaning reaction for InGaAs metal oxide semiconductor field effect transistors
Authors: Shin H. S. , Yum J. H. , Johnson D. W. , Harris H. R. , Hudnall Todd. W. , Oh J. , Kirsch P. , Wang W.-E. , Bielawski C. W. , Banerjee S. K. , Lee J. C. , Lee H. D.
Published: November 2013

In this paper, we discuss atomic configuration of atomic layer deposition (ALD) beryllium oxide (BeO) using the quantum chemistry to understand the theoretical origin. BeO has shorter bond length, higher reaction enthalpy, and larger bandgap energy compared with those of ALD aluminum oxide. It is shown that the excellent material properties of ALD BeO can reduce interface defect density due to the self-cleaning reaction and this contributes to the improvement of device performance of InGaAs MOSFETs. The low interface defect density and low leakage current of InGaAs MOSFET were demonstrated using X-ray photoelectron spectroscopy and the corresponding electrical results.