bluuebunny/crossref_metadata_2025 huggingface dataset:
David Garrick Presents The Padlock: An 18th-Century “Hit”
Authors: Fahrner Robert
Published: July 2009

The importance of the afterpiece in David Garrick's managerial scheme is generally acknowledged, though most grant too casually, perhaps, that the “English Roscius” was also a practical and clever theatrical entrepreneur. He understood the popular taste and, even as he attempted to improve that taste, he catered to it for obvious financial reasons. Had a Londoner visited Drury Lane on the night of 3 October 1768, therefore, and dutifully witnessed the “prisons, racks, and death” of The Earl of Warwick, Dr. Thomas Francklin's patriotic exercise in pseudo-istorical, blank verse tragedy, he would have been rewarded with the premiere of The Padlock, a delightful afterpiece by Isaac Bickerstaffe and Charles Dibdin.
A Fragmented Autobiography
Authors: Morley Malcolm
Published: July 2009

Back in London I devoted myself to playgoing, the crowning experience of which was seeing Forbes-Robertson as Hamlet at the Theatre Royal, Drury Lane: a noble actor in a noble role at a noble theatre—and, as I remember it, a production without gimmicks or recondite interpretations of the text. Before returning to the States I wished to see all kinds and conditions of English theatre, and after visits to the West End, I sought Suburbia.
EXTERNAL NORMS AND RATIONALITY OF CHOICE
Authors: Bossert Walter , Suzumura Kotaro
Published: July 2009

Ever since Sen criticized the notion of internal consistency of choice, there exists a widespread perception that the standard rationalizability approach to the theory of choice has difficulties in coping with the existence of external norms. We introduce a concept of norm-conditional rationalizability and show that external norms can be made compatible with the methods underlying the traditional rationalizability approach. To do so, we characterize norm-conditional rationalizability by means of suitable modifications of revealed preference axioms that are well established in the theory of rational choice on general domains as analysed in contributions by Richter and Hansson, for example. We compare our approach to alternative suggestions that have appeared in response to Sen's criticisms, and we discuss its links to Sen's notion of self-imposed choice constraints.
ON MUTUAL BENEFIT AND SACRIFICE: A COMMENT ON BRUNI AND SUGDEN'S ‘FRATERNITY’
Authors: Gui Benedetto
Published: July 2009

This note comments on Bruni and Sugden's interesting notion of fraternity among contract partners as joint commitment to cooperate for mutual benefit. I raise two points on their paper, both concerning the role of sacrifice. First I maintain that, differently from other social preferences, guilt aversion (or warm glow) does not imply self-sacrifice. Secondly, I argue that aiming for mutual benefit does not prevent individuals from facing trade-offs between their own and their partners’ surplus, so the notion of sacrifice cannot be entirely eschewed. To the contrary, reciprocal ‘sacrifices’ enhance cooperative intentions and help create feelings of friendliness.
A RESPONSE TO BRUNI AND SUGDEN
Authors: Nelson Julie A.
Published: July 2009

An article by Luigino Bruni and Robert Sugden published in this journal argues that market relations contain elements of what they call ‘fraternity’. This Response demonstrates that my own views on interpersonal relations and markets – which originated in the feminist analysis of caring labour – are far closer to Bruni and Sugden's than they acknowledge in their article, and goes on to discuss additional important dimensions of sociality that they neglect.
FRATERNITY, INTRINSIC MOTIVATION AND SACRIFICE: A REPLY TO GUI AND NELSON
Authors: Bruni Luigino , Sugden Robert
Published: July 2009

This paper responds to Gui and Nelson's separate comments on our paper ‘Fraternity’, which analysed sociality in markets as joint commitment to mutual assistance. We argue that our analysis is fundamentally different both from Nelson's analysis (a mixture of self-interested and intrinsic motivations) and from that provided by theories of warm glow or guilt aversion, as discussed by Gui. We agree with Gui that, in initiating and maintaining cooperative relationships, individuals sometimes incur personal costs to benefit others without any certainty of reciprocation, but we argue that the intentions underlying such actions are cooperative rather than self-sacrificing.
Hopf bifurcation analysis in a model of oscillatory gene expression with delay
Authors: Wei Junjie , Yu Chunbo
Published: July 2009

The dynamics of a gene expression model with time delay are investigated. The investigation confirms that a Hopf bifurcation occurs due to the existence of stability switches when the delay varies. An explicit algorithm for determining the direction of the Hopf bifurcations and the stability of the bifurcating periodic solutions has been derived by using the theory of the centre manifold and the normal forms method. The global existence of periodic solutions has been established using a global Hopf bifurcation result by Wu and a Bendixson criterion for higher-dimensional ordinary differential equations due to Li and Muldowney.
Scattering theory for the Dirac equation with a non-local term
Authors: Machihara Shuji , Tsutaya Kimitoshi
Published: July 2009

Consider a scattering problem for the Dirac equation with a non-local term including the Hartree type, say the cubic convolution term. We show the existence of scattering operators for small initial data in the subcritical and critical Sobolev spaces.
On the scattering of two-dimensional elastic point sources and related near-field inverse problems for small discs
Authors: Athanasiadis C. E. , Pelekanos G. , Sevroglou V. , Stratis I. G.
Published: July 2009

The problem of scattering of a point-generated elastic dyadic field by a bounded obstacle or a penetrable body in two dimensions is considered. The direct scattering problem for each case is formulated in a dyadic form. For two point sources, dyadic far-field pattern generators are defined and general scattering theorems and mixed scattering relations are presented. The direct scattering problem for a rigid circular disc is considered, and the exact Green function and the elastic far-field patterns of the radiating solution in the form of infinite series are obtained. Under the low-frequency assumption, approximations for the longitudinal and transverse far-field patterns of the scattered field are obtained, in addition to an asymptotic expansion for the corresponding scattering cross-section. A simple inversion scheme that locates the radius and the position of a rigid circular disc, which is based on a closed-form approximation of the scattered field at the location of the incident point source, is proposed.
Relaxed model for the hysteresis in micromagnetism
Authors: Carbou G. , Efendiev M. A. , Fabrie P.
Published: July 2009

We study a model of ferromagnetic material with hysteresis effects. The magnetic moment behaviour is described by the nonlinear Landau–Lifshitz equation with an additional term modelling the hysteresis. This term takes the form of a maximal monotone operator acting on the time derivative of the magnetic moment. In our model, it is approximated via a relaxing heat equation. For this relaxed model we prove local existence of regular solutions.
Adversative conjunction choice in Russian (no, da, odnako): Semantic and syntactic influences on lexical selection
Authors: Kapatsinski Vsevolod
Published: July 2009

This article presents a multivariate analysis of adversative conjunction choice (among no, da, and odnako) in Russian, drawing implications for sentence production and semantic theory. The two main factors shown to influence conjunction choice are the types of the conjoined constituents and the semantic subtype of the adversative relation. One of the conjunctions, da, is favored when the conjoined elements are of different syntactic types and disfavored when they are of the same type, which is argued to suggest that the conjunction is chosen at a point in sentence production when the types of both of the conjoined constituents are known (Uryson, 2006). In addition, the conjunction da is heavily favored by the “preventive” adversative meaning (Sannikov, 1989:177; Serebrjanaja, 1976), as in I would go but I don't have the money. This quantitative meaning-construction association is argued to support the view that the preventive adversative is a distinct semantic subtype of adversativity (Payne, 1985; contra Foolen, 1991:84).
Phonological variation and change in Australian and New Zealand Sign Languages: The location variable
Authors: Schembri Adam , McKee David , McKee Rachel , Pivac Sara , Johnston Trevor , Goswell Della
Published: July 2009

In this study, we consider variation in a class of signs in Australian and New Zealand Sign Languages that includes the signsthink, name, andclever. In their citation form, these signs are specified for a place of articulation at or near the signer's forehead or above, but are sometimes produced at lower locations. An analysis of 2667 tokens collected from 205 deaf signers in five sites across Australia and of 2096 tokens collected from 138 deaf signers from three regions in New Zealand indicates that location variation in these signs reflects both linguistic and social factors, as also reported for American Sign Language (Lucas, Bayley, & Valli, 2001). Despite similarities, however, we find that some of the particular factors at work, and the kinds of influence they have, appear to differ in these three signed languages. Moreover, our results suggest that lexical frequency may also play a role.
Stem cell therapy for cardiac repair: benefits and barriers
Authors: Joggerst Steven J. , Hatzopoulos Antonis K.
Published: July 2009

Cardiovascular disease remains the leading cause of death worldwide. Acute ischaemic injury and chronic cardiomyopathies lead to permanent loss of cardiac tissue and ultimately heart failure. Current therapies aim largely to attenuate the pathological remodelling that occurs after injury and to reduce risk factors for cardiovascular disease. Studies in animal models indicate that transplantation of mesenchymal stem cells, bone-marrow-derived haematopoietic stem cells, skeletal myoblasts, or embryonic stem cells has the potential to improve the function of ventricular muscle after ischaemic injury. Clinical trials using primarily bone-marrow-derived cells and skeletal myoblasts have also produced some encouraging results. However, the current experimental evidence suggests that the benefits of cell therapy are modest, the generation of new cardiac tissue is low, and the predominant mechanisms of action of transplanted stem cells involve favourable paracrine effects on injured myocardium. Recent studies show that the adult heart possesses various pools of putative resident stem cells, raising the hope that these cells can be isolated for therapy or manipulated in vivo to improve the healing of cardiac muscle after injury. This article reviews the properties and potential of the various stem cell populations for cardiac repair and regeneration as well as the barriers that might lie ahead.
Epidemiologie der chronisch venösen Insuffizienz - Schweizer Befragung liefert überraschende Ergebnisse
Authors: Traber  , Mazzolai  , Läuchli
Published: July 2009

Die chronisch venöse Insuffizienz (CVI) der Beine ist eine der häufigsten Krankheiten der Erwachsenen in der westlichen Bevölkerung mit beträchtlicher sozioökonomischer Bedeutung. Aufgrund der jetzigen Datenlage darf davon ausgegangen werden, dass die Entstehung variköser Beinvenenveränderungen multifaktorieller Genese ist und dass neben Umweltfaktoren vor allem dem Lebensstil eine wichtigere Rolle in ihrer Entstehung zukommt als bisher angenommen. Dies zeigt auch die im Sommer 2008 in 40 verschiedenen Schweizer Apotheken durchgeführte Umfrage mit 1099 Teilnehmern.
Correlation between global lightning and whistlers observed at Tihany, Hungary
Authors: Collier A. B. , Delport B. , Hughes A. R. W. , Lichtenberger J. , Steinbach P. , Öster J. , Rodger C. J.
Published: July 2009

Although the generation and propagation mechanisms for whistlers are fairly well understood, the location and extent of the lightning source region for the whistlers observed at a given station are currently unknown. The correlation of whistler observations against global lightning data allows an estimate of the size and position of the source region. For whistlers detected at Tihany, Hungary, an area of positive correlation with radius of ∼1000 km was found to be centered on the conjugate point. Although the maximal sample correlation coefficient was relatively low, r = 0.065, it has a high statistical significance, indicating that it is extremely improbable that the whistlers and lightning in this region are actually uncorrelated. Other smaller areas of positive correlation were found further afield in South America and the Maritime Continent. Lightning in the northern hemisphere displayed a negative correlation with whistlers at Tihany.
Simultaneous ground‐satellite optical observations of postnoon shock aurora in the Southern Hemisphere
Authors: Motoba T. , Kadokura A. , Ebihara Y. , Frey H. U. , Weatherwax A. T. , Sato N.
Published: July 2009

On 14 June 2005, a transient postnoon shock aurora, induced by an interplanetary (IP) shock, was observed simultaneously with the FUV imager onboard the IMAGE satellite and the all‐sky imager (ASI) at the South Pole Station (−74.3° magnetic latitude (MLAT), ∼15 magnetic local time). The global evolution of the shock aurora was identified by the FUV, whereas the detailed spatial‐temporal structure was identified by the ASI. Both optical emissions for the shock aurora showed a reasonable agreement in a common field of view. During the transient auroral brightenings in the dayside oval detected by the FUV, a two‐step development of the shock aurora was identified by the ASI in the afternoon sector of the oval. Just after the IP shock, the ASI first observed a diffuse 557.7 nm aurora expanding duskward at the equatorward edge of the oval (−70° to −73° MLAT). About 5 min later, new discrete auroral forms (arcs) were detected in the middle of the oval (−73° to −76° MLAT) by both 557.7 nm and 630.0 nm ASI images. The discrete arcs developed with relatively brighter emissions, and had a lifetime of the order of 10 min, during the main impulse (MI) of geomagnetic sudden commencement. The spectrographic auroral imagers onboard the IMAGE satellite indicated that proton precipitation played an effective role in the first shock auroral emission observed with the ASI, while intense electron precipitation played an effective role in the second one. Mechanisms of the first and second postnoon shock auroras presented here are speculated to be associated with the wave‐particle interaction process, and the field‐aligned acceleration process in the region of the MI‐related upward field‐aligned currents, respectively.
Alfvénic plasma velocity variations observed at the inner edge of the low‐latitude boundary layer induced by the magnetosheath mirror mode waves: A THEMIS observation
Authors: Nowada M. , Shue J.‐H. , Lin C.‐H. , Sakurai T. , Sibeck D. G. , Angelopoulos V. , Carlson C. W. , Auster H.‐U.
Published: July 2009

With unique simultaneous observations both in the magnetosheath and magnetosphere by the THEMIS probes, Alfvénic variations in the plasma velocity are observed at the inner edge of low‐latitude boundary layer (LLBL) and are induced by the mirror mode waves in the magnetosheath near the subsolar magnetopause on 31 July 2007. These Alfvénic variations appeared as the wavy perturbations in the Vx and Vy components observed by THEMIS C, D, and E, which had the same periodicity as associated magnetic field variations. Simultaneously, THEMIS B observed the mirror mode waves in the magnetosheath. The periodicities of the magnetic and plasma pressure variations of mirror modes in the magnetosheath were consistent with those of the Alfvénic wavy variations in the LLBL. Therefore, the mirror mode waves can induce the magnetopause undulations, launching Alfvén waves, and resultant Alfvénic variations are observed in the LLBL. Also, in the succeeding magnetosheath interval by THEMIS B, we examined whether the mirror mode waves occurred and associated Alfvénic variations were observed in the LLBL. However, no clear evidence for an existence of the mirror mode waves was obtained, and THEMIS C, D, and E do not also observe associated magnetic field and plasma Alfvénic responses in the LLBL. These results suggest that the Alfvénic variations in the LLBL are strongly related to the mirror mode waves in the magnetosheath. On the basis of these results, we emphasize that the magnetosheath energy is transmitted and transported into the magnetosphere via magnetopause surface waves.
Moment release rate of Cascadia tremor constrained by GPS
Authors: Aguiar Ana C. , Melbourne Timothy I. , Scrivner Craig W.
Published: July 2009

A comparison of GPS and seismic analyses of 23 distinct episodic tremor and slip events, located throughout the Cascadia subduction zone over an 11‐year period, yields a highly linear relationship between moment release, as estimated from GPS, and total duration of nonvolcanic tremor, as summed from regional seismic arrays. The events last 1–5 weeks, typically produce ∼5 mm of static forearc deformation, and show cumulative totals of tremor that range from 40 to 280 h. Moment released by each event is estimated by inverting GPS‐measured deformation, which is sensitive to all rates of tremor‐synchronous faulting, including aseismic creep, for total slip along the North American‐Juan de Fuca plate interface. Tremor, which is shown to be largely invariant in amplitude and frequency content both between events and with respect to its duration, is quantified using several different parameterizations that agree to within 10%. All known Cascadia events detected since 1997, which collectively span the Cascadia arc from northern California to Vancouver Island, Canada, release moment during tremor at a rate of 5.2 ± 0.4 × 1016 N m per hour of recorded tremor. This relationship enables estimation of moment dissipation, via seismic monitoring of tremor, along the deeper Cascadia subduction zone that poses the greatest threat to its major metropolitan centers.
Spatial and temporal variability of the phytoplankton carbon to chlorophyll ratio in the equatorial Pacific: A basin‐scale modeling study
Authors: Wang Xiujun , Le Borgne Robert , Murtugudde Raghu , Busalacchi Antonio J. , Behrenfeld Michael
Published: July 2009

The relationship between phytoplankton carbon biomass and chlorophyll is nonlinear because of the complex impacts of light, nutrient conditions, and temperature. A basin‐scale ocean circulation‐biogeochemistry model implemented with a dynamic phytoplankton model is employed to explore the spatial and temporal variability of the phytoplankton carbon to chlorophyll (C:Chl) ratio in the equatorial Pacific Ocean. The dynamic model computes the phytoplankton C:Chl ratio as a function of light, nitrate, iron, and temperature. The model reproduces well the general features of phytoplankton dynamics in this region, e.g., the deeper chlorophyll maximum (DCM) in the western warm pool and shallower DCM in the upwelling region. The model predicts large spatial and temporal variations of the C:Chl ratio. The mixed layer C:Chl ratio increases from <100 in the eastern upwelling region to >150 in the warm pool, whereas subsurface ratio is ∼50 below 100 m. The model produces a weak seasonality in the mixed layer C:Chl ratio but strong interannual variability that is associated with the El Niño‐Southern Oscillation (ENSO) events. The warm pool has strong anomalies during the cold phase of the ENSO with a reduced C:Chl ratio and a shoaled DCM. However, the upwelling region reveals strong anomalies during the warm phase of the ENSO, showing an increased C:Chl ratio in the euphotic zone and a deepened DCM. The predicted large spatial and temporal variations of the C:Chl ratio have potential implications for the carbon uptake in the equatorial Pacific.
Characterization of Tumor Angiogenesis in Rat Brain Using Iron-Based Vessel Size Index MRI in Combination with Gadolinium-Based Dynamic Contrast-Enhanced MRI
Authors: Beaumont Marine , Lemasson Benjamin , Farion Régine , Segebarth Christoph , Rémy Chantal , Barbier Emmanuel L
Published: July 2009

This study aimed at combining an iron-based, steady-state, vessel size index magnetic resonance imaging (VSI MRI) approach, and a gadolinium (Gd)-based, dynamic contrast-enhanced MRI approach (DCE MRI) to characterize tumoral microvasculature. Rats bearing an orthotopic glioma (C6, n=14 and RG2, n=6) underwent DCE MRI and combined VSI and DCE MRI 4 h later, at 2.35 T. Gd-DOTA (200 μmol of Gd per kg) and ultrasmall superparamagnetic iron oxide (USPIO) (200 μmol of iron per kg) were used for DCE and VSI MRI, respectively. C6 and RG2 gliomas were equally permeable to Gd-DOTA but presented different blood volume fractions and VSI, in good agreement with histologic data. The presence of USPIO yielded reduced Ktrans values. The Ktrans values obtained with Gd-DOTA in the absence and in the presence of USPIO were well correlated for the C6 glioma but not for the RG2 glioma. It was also observed that, within the time frame of DCE MRI, USPIO remained intravascular in the C6 glioma whereas it extravasated in the RG2 glioma. In conclusion, VSI and DCE MRI can be combined provided that USPIO does not extravasate with the time frame of the DCE MRI experiment. The mechanisms at the origin of USPIO extravasation remain to be elucidated.
Reduced ADAMTS13 Activity in Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage
Authors: Vergouwen Mervyn DI , Bakhtiari Kamran , van Geloven Nan , Vermeulen Marinus , Roos Yvo BWEM , Meijers Joost CM
Published: July 2009

The pathogenesis of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) remains unknown. Besides vasospasm, microthrombosis might have an important function. As in patients with thrombotic thrombocytopenic purpura an A Disintegrin And Metalloprotease with ThromboSpondin repeats-13 (ADAMTS13) deficiency leads to higher concentrations of large von Willebrand factor (vWF) multimers resulting in microthrombosis, our purpose was to compare ADAMTS13 and vWF in patients with and without DCI after aneurysmal SAH. We measured ADAMTS13 activity, vWF antigen, vWF propeptide, and vWF ristocetin cofactor activity in plasma at standard intervals. Thirty-one patients were included. Eleven patients (35%) developed DCI. No differences were observed in baseline characteristics between patients with and without DCI. Patients with DCI had a stronger decrease in ADAMTS13 activity, and a more profound increase in vWF antigen, vWF propeptide, and vWF activity in the first few days after the hemorrhage ( P-values for difference in polynomial time trend 0.0001, 0.020, 0.004, and 0.188, respectively). No indication of correlation between vWF antigen and ADAMTS13 was found ( r=−0.027, P=0.736). Our results suggest that microthrombosis has a role in the pathogenesis of DCI, as a result of decreased ADAMTS13 activity and endothelium dysfunction.
Comparison of Eight Methods for the Estimation of the Image-Derived Input Function in Dynamic [18F]-FDG PET Human Brain Studies
Authors: Zanotti-Fregonara Paolo , Fadaili El Mostafa , Maroy Renaud , Comtat Claude , Souloumiac Antoine , Jan Sebastien , Ribeiro Maria-Joao , Gaura Véronique , Bar-Hen Avner , Trébossen Régine
Published: July 2009

The aim of this study was to compare eight methods for the estimation of the image-derived input function (IDIF) in [18F]-FDG positron emission tomography (PET) dynamic brain studies. The methods were tested on two digital phantoms and on four healthy volunteers. Image-derived input functions obtained with each method were compared with the reference input functions, that is, the activity in the carotid labels of the phantoms and arterial blood samples for the volunteers, in terms of visual inspection, areas under the curve, cerebral metabolic rates of glucose (CMRglc), and individual rate constants. Blood-sample-free methods provided less reliable results as compared with those obtained using the methods that require the use of blood samples. For some of the blood-sample-free methods, CMRglc estimations considerably improved when the IDIF was calibrated with a single blood sample. Only one of the methods tested in this study, and only in phantom studies, allowed a reliable calculation of the individual rate constants. For the estimation of CMRglc values using an IDIF in [18F]-FDG PET brain studies, a reliable absolute blood-sample-free procedure is not available yet.
ECoG-based short-range recurrent stimulation techniques to stabilize tissue at risk of progressive damage: Theory based on clinical observations
Authors: Dahlem Markus , Schneider Felix , Dreier Jens , Strong Anthony , Schoell Eckehard
Published: July 2009

We introduce theoretical concepts based on chaos control to stabilize in acute stroke the tissue at risk of progressive damage by preventing adverse effects of waves of mass neuronal depolarization. Moreover, we present clinical electrocorticography (ECoG) recordings of relevant signals suggested for the feedback control. The recordings are performed in combination with novel subdural opto-electrode technology for simultaneous laser-Doppler flowmetry in patients with aneurysmal subarachnoid haemorrhage (aSAH). In aSAH patients waves of spreading depolarization (SD) have a high incidence and cause hypoxia in tissue at risk, and, importantly, the haemodynamic response is the inverse of that seen in healthy tissue. In previous clinical studies, clusters of prolonged SDs have been measured in aSAH patients in close proximity to structural brain damage as assessed by neuroimaging, and, in theoretical studies, a mechanism was presented, suggesting how a failure of internal feedback could be a putative mechanism of such SD cluster patterns in acute stroke. This failing internal feedback control is now suggested to be replaced by ECoG-based short-range recurrent functional stimulation that initiates the normal hyperperfusion haemodynamic response in a demand-controlled way and stabilizes the tissue at risk during the critical phase of SD passage. The suggested method has three key features: (i) it is short-range, i.e., in the order of the distance of the ECoG electrode strip, (ii) it is demand-controlled, and (iii) it uses no prior knowledge of the target state, in particular, it adapts to conditions in the healthy physiological range. On-demand type stimulation provides minimal invasive feedback as the control force is off when the target state is reached, i.e., the tissue at risk is without SD or it is back to the physiological range (out of risk). These last two features (ii-iii) are shared with classical methods of chaos control, where major progress was made in the last years with respect to extensions for spatio-temporal wave patterns. A detailed bifurcation analysis of the nonlinear model is presented, in particular, the SD cluster forming cortical state is suggested to be caused by a delay-induced saddle-node bifurcation.
Stabilization of the ionization overheating thermal instability in atmospheric pressure microplasmas
Authors: Staack D. , Farouk B. , Gutsol A. , Fridman A.
Published: July 2009

Stable direct current atmospheric pressure plasmas can regularly be generated in air using microplasma systems, and rapid cooling due to the small size is typically suggested as the thermally stabilizing mechanism. However, temperatures of the stable discharges are significantly higher than ambient, and stable operation is not easily achieved in all gases at similar sizes. Revisiting a traditional analysis of the thermal instability, we find that the inclusion of the simple ballasted external circuit in the analysis leads to additional stabilizing mechanisms. This stabilization occurs in microplasmas due to the characteristic times of the external circuit and the instability being comparable, which allows the electric field to change during the time frame of the instability. Experimentally this is implemented by reducing the stray capacitance of the external circuit. This stabilizing mechanism is verified in several gases and its application in a plasma enhanced chemical vapor deposition system leads to a more uniform film deposition.
Effect of large strain on dielectric and ferroelectric properties of Ba0.5Sr0.5TiO3 thin films
Authors: Xiao Bo , Avrutin Vitaliy , Liu Hongrui , Rowe Emmanuel , Leach Jacob , Gu Xing , Özgür Ümit , Morkoç Hadis , Chang W. , Alldredge L. M. B. , Kirchoefer S. W. , Pond J. M.
Published: July 2009

Ba x Sr 1 − x TiO 3 is ideally suited as a tunable medium for radio frequency passive component. In this context we have studied the effect of biaxial strain on the dielectric and ferroelectric properties of Ba0.5Sr0.5TiO3 thin films grown epitaxially on SrTiO3 (001) substrates. The lattice parameters of the films determined by high-resolution x-ray diffraction with the thickness varying from 160 to 1000 nm indicated large biaxial compressive strain which decreased from 2.54% to 1.14% with increasing film thickness. Temperature-dependent measurements of the dielectric constant in our strained Ba0.5Sr0.5TiO3 thin films revealed a significant increase in the Curie temperature as the film thickness is below 500 nm. Enhanced ferroelectric behavior was observed for highly strained films with a remanent polarization of 15 μC/cm2 in the 160-nm-thick layer. However, the thick films (≥500 nm) exhibited weak temperature dependence of the dielectric constant without any pronounced peak corresponding to the Curie temperature, which may suggest inhomogeneous strain distribution in the thick films.
Terahertz-range free-electron laser electron spin resonance spectroscopy: Techniques and applications in high magnetic fields
Authors: Zvyagin S. A. , Ozerov M. , Čižmár E. , Kamenskyi D. , Zherlitsyn S. , Herrmannsdörfer T. , Wosnitza J. , Wünsch R. , Seidel W.
Published: July 2009

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave terahertz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4–250 μm) with pulsed magnetic fields up to 70 T allows for multifrequency ESR spectroscopy in a frequency range of 1.2–75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl and the low-dimensional organic material (C6H9N2)CuCl3.
A combined effective fragment potential–fragment molecular orbital method. I. The energy expression and initial applications
Authors: Nagata Takeshi , Fedorov Dmitri G. , Kitaura Kazuo , Gordon Mark S.
Published: July 2009

The effective fragment potential (EFP) method, a model potential for treating solvent effects and other intermolecular interactions, is interfaced with an electronic structure method, the fragment molecular orbital (FMO) method, that is able to retain high accuracy for ab initio calculations on large molecular systems. The accuracy of the total energies in this novel combined FMO/EFP method is assessed by comparisons with the conventional quantum mechanics (QM)/EFP method. The test cases are water clusters, a peptide, and a dianionic protein (treated with full QM and FMO) combined with water clusters (treated with EFP) at the RHF, B3LYP, and MP2 levels of theory. The basis sets employed range from minimal to augmented double zeta plus polarization. The energy differences between FMO/EFP and the conventional QM/EFP methods are within “chemical accuracy” (1 kcal/mol≈4 kJ/mol).
High giant magnetoresistance and thermal annealing effects in perpendicular magnetic [Co/Ni]N-based spin valves
Authors: Li Zhenya , Zhang Zongzhi , Zhao Hui , Ma Bin , Jin Q. Y.
Published: July 2009

The thermal stability and giant magnetoresistance (GMR) of pseudo- and FeMn-biased spin valves with perpendicular magnetic [Co/Ni]N multilayer as free and reference layers are investigated. The observed GMR ratio for the pseudo-spin-valve is as high as 7.7%, but it rapidly decreases below 1.0% after annealing in a perpendicular field at 200 °C. Such poor temperature stability is ascribed to simultaneous switching of the free and reference multilayers caused by loss of their coercivity difference. In contrast, an FeMn-biased sample with a similar structure has a slightly lower GMR signal of 6.5% but exhibits much better thermal stability, with the GMR reduction occurring at an elevated anneal temperature of over 300 °C. This GMR reduction is due to Mn diffusion and a reduction in perpendicular anisotropy.
Self-lubricating carbon nanotube reinforced nickel matrix composites
Authors: Scharf T. W. , Neira A. , Hwang J. Y. , Tiley J. , Banerjee R.
Published: July 2009

Nickel (Ni)—multiwalled carbon nanotube (CNT) composites have been processed in a monolithic form using the laser-engineered net shape (LENS™) processing technique. Auger electron spectroscopy maps determined that the nanotubes were well dispersed and bonded in the nickel matrix and no interfacial chemical reaction products were determined in the as-synthesized composites. Mechanisms of solid lubrication have been investigated by micro-Raman spectroscopy spatial mapping of the worn surfaces to determine the formation of tribochemical products. The Ni-CNT composites exhibit a self-lubricating behavior, forming an in situ, low interfacial shear strength graphitic film during sliding, resulting in a decrease in friction coefficient compared to pure Ni.
High-pressure phase transformation of nanometric ZnSb prepared by mechanical alloying
Authors: Trichês D. M. , Souza S. M. , de Lima J. C. , Grandi T. A. , Campos C. E. M. , Polian A. , Itié J. P. , Baudelet F. , Chervin J. C.
Published: July 2009

Nanometric orthorhombic ZnSb was prepared by mechanical alloying and its structural stability was studied as a function of pressure. The changes were followed by Raman and x-ray absorption spectroscopy. Between 11.0 and 14.6 GPa, we observed an irreversible phase transformation from the orthorhombic phase to a hexagonal hP1 phase. A similar transformation had been previously observed at 7 GPa for bulk ZnSb. The difference in the phase transformation pressures is attributed to an interfacial component of the nanometric structure.
Ferromagnetism induced by Zn vacancy defect and lattice distortion in ZnO
Authors: Kim Dongyoo , Yang Jeong-hwa , Hong Jisang
Published: July 2009

Through the full potential linearized augmented plane wave method, we have explored the vacancy defect induced magnetism in wurtize ZnO. It has been found that the Zn vacancy defect brings a spin polarized state in the nearest neighbor oxygen atoms, whereas the oxygen vacancy defect has no influence on the magnetism. However, it is found that the lattice distortion is a crucial factor for the Zn vacancy induced ferromagnetism because the ferromagnetic ground state cannot be achieved if there is no lattice distortion due to Zn vacancy defect. The magnetic moment of oxygen atom in the nearest neighbor from the Zn vacancy site is ranged from 0.10 to 0.19 μB and the spin polarized oxygen atoms have metallic feature in both spin states. These results are quite different from those found in other calculation [Q. Wang et al., Phys. Rev. B 77, 205411 (2008)]. In addition, we have found that the ferromagnetic exchange interaction among oxygen atoms is mediated by Zn 3d state. Along with these, the theoretically calculated x-ray absorption spectroscopy and x-ray magnetic circular dichroism are presented.
Coupled-cluster and density functional theory studies of the electronic excitation spectra of trans-1,3-butadiene and trans-2-propeniminium
Authors: Lehtonen Olli , Sundholm Dage , Send Robert , Johansson Mikael P.
Published: July 2009

The electronic excitation spectra of trans-1,3-butadiene (CH2=CH–CH=CH2) and trans-2-propeniminium (CH2=CH–CH=NH2+) have been studied at several coupled-cluster and time-dependent density functional theory levels using the linear response approach. Systematic studies employing large correlation-consistent basis sets show that approximate singles and doubles coupled-cluster calculations yield excitation energies in good agreement with experiment for all states except for the two lowest excited Ag states of trans-1,3-butadiene which have significant multiconfigurational character. Time-dependent density functional theory calculations employing the generalized gradient approximation and hybrid functionals yield too low excitation energies in the basis set limit. In trans-1,3-butadiene, increasing the basis set size by augmenting multiple diffuse functions is observed to reduce the high-lying excitation energies with most density functionals. The decrease in the energies is connected to the incorrect asymptotic behavior of the exchange-correlation potential. The results also demonstrate that standard density functionals are not capable of providing excitation energies of sufficient accuracy for experimental assignments.
First-principles study on the tension-induced magnetic phase transition in Fe3C-single walled carbon nanotube compounds
Authors: Yuan Shijun , Li Fashen
Published: July 2009

We report a first-principles investigation on the mechanical and magnetic properties of the compound of a single Fe3C cluster and single walled carbon nanotubes (SWNT) under uniaxial tensile stress. We find that the external tensile strain can induce a remarkably magnetic phase transition in the Fe3C-SWNT compounds. The results on geometrical and electronic structure suggest that the strong Fe-SWNT interaction plays an important role in determining the magnetic properties of the compounds.
Effects of material parameters on elastic band gaps of two-dimensional solid phononic crystals
Authors: Zhou Xiao-Zhou , Wang Yue-Sheng , Zhang Chuanzeng
Published: July 2009

In this paper we study the influences of the material parameters on phononic band gaps of two-dimensional solid phononic crystals. The analysis begins with the basic wave equations and derives the material parameters directly determining band gaps. These parameters include the mass density ratio, the shear modulus ratio, and Poisson’s ratios of the scatterer and host materials (or equivalently, the wave velocity ratio, the acoustic impedance ratio, and Poisson’s ratios). The effects of these parameters on phononic band gaps are discussed in details for phononic crystals with different filling fractions and lattice forms for both antiplane and in-plane wave modes. Band gaps are calculated by the plane wave expansion method. The results show that for the antiplane mode, the mass density ratio predominantly determines the band gap, while that for the in-plane mode, both mass density ratio and shear modulus ratio play equally important roles. The maximum band gap will appear at both large density ratio and shear modulus ratio (i.e., large acoustic impedance ratio with small mismatch in wave velocities) for either antiplane or in-plane wave mode; but band gaps may appear in other situations depending on the filling fraction and lattice forms. It is also shown that neither acoustic impedance ratio nor wave velocity ratio can determine the band gap independently. The present analysis can be applied to artificial design of band gaps.
Temperature dependent and time-resolved photoluminescence studies of InAs self-assembled quantum dots with InGaAs strain reducing layer structure
Authors: Kong Lingmin , Feng Zhe Chuan , Wu Zhengyun , Lu Weijie
Published: July 2009

Four types of self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy and studied via temperature-dependent and time-resolved photoluminescence (PL) spectroscopy measurements. A thin InGaAs stain reducing layer (SRL) is adopted which extends the emission wavelength to 1.3 μm and the influence of strain on QDs is investigated. The SRL releases the strain between the wetting layer and QDs, and enlarges the size of QDs, as shown by atomic force microscopy measurements. As the thickness of InAs layer decreases to 1.7 ML, the QDs with the SRL are chained to strings and the density of QDs increases significantly, which leads to an abnormal redshift of 1.3 μm PL peak at room temperature. PL peaks of InAs QDs with the SRL show redshift compared with the QDs directly deposited on GaAs matrix. The dependences of PL lifetime on the QD size, density and temperature (T) are systematically studied. It is observed that the PL lifetime of QDs is insensitive to T below 50 K. Beyond 50 K, increases and then drops at higher temperature, with a peak at TC, which was determined by the SRL and the thickness of InAs. We have also observed an obvious PL spectral redshift of the QDs with 1.7 ML InAs coverage on SRL at low T as the measuring time delays. The PL lifetime of QDs with the SRL is smaller than that of QDs without the SRL. The QDs with different densities have different PL lifetime dependence on the QDs size. These observations can be explained by the competition between the carrier redistribution and thermal emission.
Melt dynamics of aluminum irradiated with ultrafast laser radiation at large intensities
Authors: Mingareev Ilya , Horn Alexander
Published: July 2009

Ablation of bulk aluminum has been investigated in situ using ultrafast laser radiation produced by chirped-pulse amplification technique (tp=80fs, λ=800nm). Melt dynamics and the contribution of the amplified spontaneous emission (ASE) to the ablation have been studied experimentally and numerically for laser fluences well above ablation threshold (F≲103×Fthr). Using transient quantitative phase microscopy (TQPm), dimensions and volume of ejected vapor, melt droplets, and liquid jets has been investigated. Computational analysis of the optical phase images has been used to determine the total volume of ejected material. A series of time-resolved phase images of vaporized material and/or melt, which are induced by n=1..8 pulses on an aluminum target, are obtained by means of TQPm up to temporal delay τ=1.65μs after irradiation. Increase in material ejection rate is observed at delays τ≈300ns and τ≈1.1μs after the incident pulse. For large irradiation intensities a considerable contribution of ASE to ablation dynamics has been detected. Ex situ measurements of the ablated material by means of white-light interferometry and scanning electron microscopy provides corresponding factual removed volumes and highlight the pulse-to-pulse morphology changes.
Noise characteristics of the gas ionization cascade used in low vacuum scanning electron microscopy
Authors: Tileli Vasiliki , Knowles W. Ralph , Toth Milos , Thiel Bradley L.
Published: July 2009

The noise characteristics of gas cascade amplified electron signals in low vacuum scanning electron microscopy (LVSEM) are described and analyzed. We derive expressions for each component contributing to the total noise culminating in a predictive, quantitative model that can be used for optimization of LVSEM operating parameters. Signal and noise behavior is characterized experimentally and used to validate the model. Under most operating conditions, the noise is dominated by the excess noise generated in the gas amplification cascade. At high gains, the excess noise increases proportionally with gain such that the signal-to-noise ratio is constant. The effects of several instrument operating parameters, including working distance, gas pressure, beam current, and detector bias, are condensed and presented in the form of a master curve.
Photoluminescent properties of K2GeF6:Mn4+ red phosphor synthesized from aqueous HF/KMnO4 solution
Authors: Adachi Sadao , Takahashi Toru
Published: July 2009

A simple method of synthesizing K2GeF6:Mn4+ red phosphor has been demonstrated by wet chemical etching of Ge shots in HF/KMnO4 mixed solution. The x-ray diffraction pattern suggests that the synthesized phosphor has the trigonal structure (space group=D3d3–P3¯m1). The optical properties of K2GeF6:Mn4+ are investigated using photoluminescence (PL) and PL excitation spectroscopies. The room-temperature zero-phonon line emission and excitation energies in K2GeF6:Mn4+ are determined to occur at ∼1.99 eV (E2→A42), ∼2.44 eV (A42→T42), and ∼2.80 eV (A42→T41). Some local vibronic emission modes are split in energies of about 5 meV due to the trigonal distortion of the MnF6−2 octahedra. The temperature-dependent PL properties can be reasonably explained on the basis of the Bose–Einstein statistics.
Effect of nonlinear Landau damping in plasma-based backward Raman amplifier
Authors: Yampolsky N. A. , Fisch N. J.
Published: July 2009

A plasma wave can mediate laser coupling in a plasma-based resonant backward Raman amplifier for high power amplification of short laser pulses. The resonant nature of amplification requires a long lifetime of the plasma wave. However, the plasma wave can be heavily Landau damped in warm plasma. On the other hand, Landau damping can be saturated in the presence of a strong plasma wave. We study backward Raman amplifier in the nonlinear regime of Landau damping using a simplified fluid model. We find the regime in which initially high linear Landau damping can be significantly saturated. Because of the saturation effect, higher temperatures can be tolerated in achieving efficient amplification. The plasma temperature can be as much as 50% larger compared to the case of unsaturated Landau damping.
Accurate thermochemistry for transition metal complexes from first-principles calculations
Authors: DeYonker Nathan J. , Williams T. Gavin , Imel Adam E. , Cundari Thomas R. , Wilson Angela K.
Published: July 2009

The “correlation consistent Composite Approach” or ccCA is an ab initio model chemistry based on the single reference MP2 level of theory. By adjusting the basis set and level of theory of the core valence additive correction, ccCA is capable of reliable thermochemical predictions of inorganic and organometallic transition metal-containing molecules, as well as achieving chemical accuracy on main group species, with a mean absolute deviation of 0.89 kcal mol−1 against the 147 enthalpies of formation in the G2/97 test set. For a set of 52 complexes containing elements Sc–Zn, ranging in size from diatomics to Ni(PF3)4 and Fe(C5H2)2, ccCA on average predicts enthalpies of formation to within ±3 kcal mol−1 of the experimental result with a mean absolute deviation of 2.85 kcal mol−1 and a root mean square deviation of 3.77 kcal mol−1. The ccCA methodology is a significant step toward quantitative theoretical modeling of transition metal thermodynamics.
An assessment of full wave effects on the propagation and absorption of lower hybrid waves
Authors: Wright J. C. , Bonoli P. T. , Schmidt A. E. , Phillips C. K. , Valeo E. J. , Harvey R. W. , Brambilla M. A.
Published: July 2009

Lower hybrid (LH) waves (Ωci⪡ω⪡Ωce, where Ωi,e≡Zi,eeB/mi,ec) have the attractive property of damping strongly via electron Landau resonance on relatively fast tail electrons and consequently are well-suited to driving current. Established modeling techniques use Wentzel–Kramers–Brillouin (WKB) expansions with self-consistent non-Maxwellian distributions. Higher order WKB expansions have shown some effects on the parallel wave number evolution and consequently on the damping due to diffraction [G. Pereverzev, Nucl. Fusion 32, 1091 (1991)]. A massively parallel version of the TORIC full wave electromagnetic field solver valid in the LH range of frequencies has been developed [J. C. Wright et al., Comm. Comp. Phys. 4, 545 (2008)] and coupled to an electron Fokker–Planck solver CQL3D [R. W. Harvey and M. G. McCoy, in Proceedings of the IAEA Technical Committee Meeting, Montreal, 1992 (IAEA Institute of Physics Publishing, Vienna, 1993), USDOC/NTIS Document No. DE93002962, pp. 489–526] in order to self-consistently evolve nonthermal electron distributions characteristic of LH current drive (LHCD) experiments in devices such as Alcator C-Mod and ITER (B0≈5 T, ne0≈1×1020 m−3). These simulations represent the first ever self-consistent simulations of LHCD utilizing both a full wave and Fokker–Planck calculation in toroidal geometry.