bluuebunny/crossref_metadata_2025 huggingface dataset:
Network for Observation of Volcanic and Atmospheric Change (NOVAC)—A global network for volcanic gas monitoring: Network layout and instrument description
Authors: Galle Bo , Johansson Mattias , Rivera Claudia , Zhang Yan , Kihlman Manne , Kern Christoph , Lehmann Thomas , Platt Ulrich , Arellano Santiago , Hidalgo Silvana
Published: March 2010

This paper presents the global project Network for Observation of Volcanic and Atmospheric Change (NOVAC), the aim of which is automatic gas emission monitoring at active volcanoes worldwide. Data from the network will be used primarily for volcanic risk assessment but also for geophysical research, studies of atmospheric change, and ground validation of satellite instruments. A novel type of instrument, the scanning miniaturized differential optical absorption spectroscopy (Mini‐DOAS) instrument, is applied in the network to measure volcanic gas emissions by UV absorption spectroscopy. The instrument is set up 5–10 km downwind of the volcano under study, and typically two to four instruments are deployed at each volcano in order to cover different wind directions and to facilitate measurements of plume height and plume direction. Two different versions of the instrument have been developed. Version I was designed to be a robust and simple instrument for measurement of volcanic SO2 emissions at high time resolution with minimal power consumption. Version II was designed to allow the best possible spectroscopy and enhanced flexibility in regard to measurement geometry at the cost of larger complexity, power consumption, and price. In this paper the project is described, as well as the developed software, the hardware of the two instrument versions, measurement strategies, data communication, and archiving routines. As of April 2009 a total of 46 instruments have been installed at 18 volcanoes worldwide. As a typical example, the installation at Tungurahua volcano in Ecuador is described, together with some results from the first 21 months of operation at this volcano.
Galileo constraints on the secular variation of the Jovian magnetic field
Authors: Yu Z. J. , Leinweber H. K. , Russell C. T.
Published: March 2010

The variations of the terrestrial magnetic field place important constraints on the behavior of the fluid in the Earth's magnetic dynamo. Jupiter is currently the only other planet for which magnetic measurements exist over a sufficiently long baseline to enable a study of the secular variation of the field to be undertaken. The average magnetic moment during the Galileo epoch was 4.334 ± 0.010 Gauss RJ3 or 1.584 ± 0.004 × 1020 Tm3. The tilt angle of the dipole was 9.71° ± 0.05°. We examine both the change in the magnetic field during the period in which Galileo operated in Jovian orbit and the change in the field between the initial observations with Pioneer 11 and the Galileo epoch. Neither approach definitively identifies secular change in the Jovian field but rather puts a limit on that rate of change. The only significant change is associated with the current imprecision of the International Astronomical Union‐defined System III period.
A subordinated kinematic wave equation for heavy‐tailed flow responses from heterogeneous hillslopes
Authors: Harman Ciaran J. , Reeves Donald M. , Baeumer Boris , Sivapalan Murugesu
Published: March 2010

Analytical expressions of hillslope‐scale subsurface stormflow discharge are currently restricted to hillslopes with homogeneous or mildly heterogeneous conductivity fields. In steep, straight hillslopes with uniform recharge these exhibit a classical piston flow response, which arises from an assemblage of impulses all moving at a constant velocity but with different starting locations. Heterogeneity within a hillslope soil creates variations in the downslope velocity of these impulses, which may lead to nonpiston flow responses with either exponential or heavy (power law) tails. The presence of heavy tails suggests that heterogeneity imparts a temporal memory on the motion of the impulses. Using this assumption, a subordinated kinematic wave equation is proposed for moderately to highly heterogeneous hillslopes. This equation convolves the piston response from a homogenous hillslope with a stable subordinator. The stable subordinator randomizes the time that impulses spend in motion and produces nonpiston solutions with heavy tails. Through comparisons of synthetic data generated from numerical hillslope simulations with physically realistic parameters, this equation faithfully reproduces both early and late time characteristics of heavy‐tailed flow responses from moderate to highly heterogenous hillslopes. A systematic evaluation of hillslope responses under different degrees of heterogeneity revealed a quantitative link between the statistical properties of the heterogeneous random fields and the parameters of the subordination framework. This suggests that the subordinator can be parameterized with the physical measurement of hillslope properties.
Regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data
Authors: Radić Valentina , Hock Regine
Published: March 2010

Very few global‐scale ice volume estimates are available for mountain glaciers and ice caps, although such estimates are crucial for any attempts to project their contribution to sea level rise in the future. We present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from ∼123,000 glaciers from a recently extended World Glacier Inventory. We compute glacier volumes and their sea level equivalent (SLE) for 19 glacierized regions containing all mountain glaciers and ice caps on Earth. On the basis of total glacierized area of 741 × 103 ± 68 × 103 km2, we estimate a total ice volume of 241 × 103 ± 29 × 103 km3, corresponding to 0.60 ± 0.07 m SLE, of which 32% is due to glaciers in Greenland and Antarctica apart from the ice sheets. However, our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried, i.e., Antarctica, North America, Greenland, and Patagonia. This emphasizes the need for more volume observations, especially of large glaciers and a more complete World Glacier Inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps.
Development and application of a catchment similarity index for subsurface flow
Authors: Lyon Steve W. , Troch Peter A.
Published: March 2010

In this study, we develop a similarity parameter to describe shallow subsurface hydrological response of small catchments on the basis of the hillslope‐Péclet number. This new similarity parameter, named the catchment‐Péclet (caPe) number, provides a theoretical framework to compare the relative hydrologic response derived from shallow subsurface flow of small catchments on the basis of geomorphic properties. Using 400,000 synthetically derived catchments to model catchment‐scale characteristic response functions (CRFs), we see good agreement between the synthetic and theoretical relationships relating the caPe number to the first two dimensionless moments of the CRF of small catchments. Working with real‐world data, however, requires the estimation of hydrologic parameters and delineation of hillslopes to apply the caPe number. Allowing for uncertainty in the estimation of hydrologic parameters and in the definition of the extent of the channel network, the caPe number is able to recreate the observed moments of an approximate catchment‐scale CRF for four small catchments ranging in size from 0.025 to 880 ha in two distinct climatic and geologic settings. By using physics to underpin the link between landscape and hydrological response, the caPe number creates a functional relationship between hydraulic theory and a catchment's pedogeomorphological structure. While this study is limited to small headwater catchments, it lays the groundwork for a catchment‐scale similarity parameter that could be expanded to larger scales where channel network structure and storage become more important.
The Sun's X‐ray Emission During the Recent Solar Minimum
Authors: Sylwester Janusz , Kowalinski Mirek , Gburek Szymon , Siarkowski Marek , Kuzin Sergey , Farnik Frantisek , Reale Fabio , Phillips Kenneth J. H.
Published: March 2010

The Sun recently underwent a period of a remarkable lack of major activity such as large flares and sunspots, without equal since the advent of the space age a half century ago. A widely used measure of solar activity is the amount of solar soft X‐ray emission, but until recently this has been below the threshold of the X‐ray‐monitoring Geostationary Operational Environmental Satellites (GOES). There is thus an urgent need for more sensitive instrumentation to record solar X‐ray emission in this range.

Anticipating this need, a highly sensitive spectrophotometer called Solar Photometer in X‐rays (SphinX) was included in the solar telescope/spectrometer TESIS instrument package on the third spacecraft in Russia's Complex Orbital Observations Near‐Earth of Activity of the Sun (CORONAS‐PHOTON) program, launched 30 January 2009 into a near‐polar orbit. SphinX measures X‐rays in a band similar to the GOES longer‐wavelength channel.
U.S. Geological Survey Would Fare Well in Proposed Federal Budget
Authors: Showstack Randy
Published: March 2010

The U.S. Geological Survey (USGS) is among the U.S. federal science agencies that would see significant funding increases if Congress approves the Obama administration's proposed budget for fiscal year (FY) 2011. The FY 2011 budget request would provide USGS with $1.13 billion, an increase of $21.6 million, or 1.9%, above the FY 2010 enacted level.

“In a time of budget austerity, to have the budget for a science agency like the USGS actually be at a level above 2010—and 2010 was a pretty good budget year for the USGS—is indeed a very good sign,” USGS director Marcia McNutt said at a 1 February budget briefing. “What we are seeing in the USGS budget is the reflection from both the president and the secretary [of the Department of the Interior, of which USGS is part] of their commitment that the problems that the nation is facing right now are problems to which science can help us find an answer,” she said.
Advocating for the Use of Informatics in the Earth and Space Sciences
Authors: Nativi Stefano , Fox Peter
Published: March 2010

Earth and space scientists are engaged in integrating knowledge stemming from different disciplines about the constituent parts of the complex Sun‐Earth system with the objective of understanding its properties as a whole system. Earth and space system analysis is a real challenge for scientists as well as for information technology (IT) experts. The scope and complexity of Earth and space system investigations demand the formation of distributed, multidisciplinary, collaborative teams [Foster and Kesselman, 2006]. The growing area of geoscience informatics is concerned with providing integrated access to a range of advanced information and processing resources for the environment.
Why Permafrost Is Thawing, Not Melting
Authors: Grosse Guido , Romanovsky Vladimir , Nelson Frederick E. , Brown Jerry , Lewkowicz Antoni G.
Published: March 2010

As global climate change is becoming an increasingly important political and social issue, it is essential for the cryospheric and global change research communities to speak with a single voice when using basic terminology to communicate research results and describe underlying physical processes. Experienced science communicators have highlighted the importance of using the correct terms to communicate research results to the media and general public [e.g., Akasofu, 2008; Hassol, 2008]. The consequences of scientists using improper terminology are at best oversimplification, but they more likely involve misunderstandings of the facts by the public.
Tridermal Tumorigenesis of Induced Pluripotent Stem Cells Transplanted in Ischemic Brain
Authors: Kawai Hiromi , Yamashita Toru , Ohta Yasuyuki , Deguchi Kentaro , Nagotani Shoko , Zhang Xuemei , Ikeda Yoshio , Matsuura Tohru , Abe Koji
Published: March 2010

Stroke is a major neurologic disorder. Induced pluripotent stem (iPS) cells can be produced from basically any part of patients, with high reproduction ability and pluripotency to differentiate into various types of cells, suggesting that iPS cells can provide a hopeful therapy for cell transplantation. However, transplantation of iPS cells into ischemic brain has not been reported. In this study, we showed that the iPS cells fate in a mouse model of transient middle cerebral artery occlusion (MCAO). Undifferentiated iPS cells (5 × 105) were transplanted into ipsilateral striatum and cortex at 24 h after 30 mins of transient MCAO. Behavioral and histologic analyses were performed at 28 day after the cell transplantation. To our surprise, the transplanted iPS cells expanded and formed much larger tumors in mice postischemic brain than in sham-operated brain. The clinical recovery of the MCAO+iPS group was delayed as compared with the MCAO+PBS (phosphate-buffered saline) group. iPS cells formed tridermal teratoma, but could supply a great number of Dcx-positive neuroblasts and a few mature neurons in the ischemic lesion. iPS cells have a promising potential to provide neural cells after ischemic brain injury, if tumorigenesis is properly controlled.
Human Recombinant Tissue-Plasminogen Activator (Alteplase): Why Not Use the ‘Human’ Dose for Stroke Studies in Rats?
Authors: Haelewyn Benoît , Risso Jean-Jacques , Abraini Jacques H
Published: March 2010

Since a pioneer work that has shown in vitro that the rat's fibrinolytic system is 10-fold less sensitive to recombinant tissue-plasminogen activator (rtPA) than the human system, most preclinical studies are performed with 10 instead of 0.9 mg/kg rtPA (the clinical dose in stroke patients). In this study, we compared the effects of these doses on mean time to reperfusion, reperfusion slope, brain infarct volume and edema in a rat model of thrombo-embolic stroke. Our data provide evidence that the dose of 0.9 mg/kg rtPA is as appropriate as that of 10 mg/kg for preclinical stroke studies in rodents.
17-β-Estradiol: A Powerful Modulator of Blood–Brain Barrier BCRP Activity
Authors: Hartz Anika MS , Mahringer Anne , Miller David S , Bauer Björn
Published: March 2010

The ATP-driven efflux transporter, breast cancer resistance protein (BCRP), handles many therapeutic drugs, including chemotherapeutics, limiting their ability to cross the blood–brain barrier. This study provides new insight into rapid, nongenomic regulation of BCRP transport activity at the blood–brain barrier. Using isolated brain capillaries from rats and mice as an ex vivo blood–brain barrier model, we show that BCRP protein is highly expressed in brain capillary membranes and functionally active in intact capillaries. We show that nanomolar concentrations of 17-β-estradiol (E2) rapidly reduced BCRP transport activity in the brain capillaries. This E2-mediated effect occurred within minutes and did not involve transcription, translation, or proteasomal degradation, indicating a nongenomic mechanism. Removing E2 after 1 h fully reversed the loss of BCRP activity. Experiments using agonists and antagonists for estrogen receptor (ER)α and ERβ and brain capillaries from ERα and ERβ knockout mice demonstrated that E2 could signal through either receptor to reduce BCRP transport function. We speculate that this nongenomic E2-signaling pathway could potentially be used for targeting BCRP at the blood–brain barrier, in brain tumors, and in brain tumor stem cells to improve chemotherapy of the central nervous system.
Informativeness of St14 VNTR Polymorphic Marker in the Carrier Detection of Hemophilia A
Authors: Arif Beenish , Baig Atif , Mahmood Saqib , Naeem Mohammad
Published: March 2010

Hemophilia A is the most common hereditary severe disorder of blood clotting. In families affected with hemophilia, genetic analysis provides opportunities to prevent recurrence of the disease. This study establishes a diagnostic strategy for carrier-ship determination in Pakistani population using an extragenic polymorphic marker for the first time. The analysis of St14 VNTR (DXS52) was carried out by polymerase chain reaction (PCR), in order to determine its informativeness in terms of heterozygosity in Pakistani population. This may be a milestone for further analysis of other polymorphic markers for carrier detection and prenatal diagnosis of hemophilia. Seventy eight blood samples (Hemophiliac = 23, Normal = 55) from 15 families were analyzed for determining informativeness of St14 VNTR in carrier detection of hemophilia A. A total of nine alleles (2400, 2100, 1750, 1690, 1630, 1570, 1390, 1300, 1220 bp) was detected in the pool of subjects. 19 out of 40 females were found to be carriers with respect to the St14 VNTR polymorphic marker. The marker was informative in 73.33% of families. The expected heterozygosity rate of the St14 VNTR was 0.86 while the observed heterozygosity was 0.7. This shows that St14 VNTR is 70% informative in our population, allowing it to be a useful marker in carrier detection, as informativeness is the direct reflection of heterozygosity of a polymorphic marker.
Interpreting the “Sounds of Silence” in Dual Language Preschools in Qatar: Teacher's Use of Story Retelling and Language Sampling
Authors: Kelly Karen L.
Published: March 2010

Analysis of English and Arabic story retelling in eight dual-language preschool classrooms in Qatar indicated that this method might provide useful data for monitoring children at risk for language delay. Language samples, elicited by teachers during five repeated story-retelling sessions, were obtained from a larger study of the vocabulary data of 157 children. Measures of language productivity included analysis of Total Utterances (TU) and number of Different Word Roots (DWR). Results revealed that 13% of the children who gave no response (NR) in English during the initial session were still non-productive 4 months later, at mid-year. Twenty-one percent of the children demonstrated English DWR more than 1 standard deviation below class means at mid-year and 17% remained below the mean at the end of the year. Review of concurrent Arabic language sampling at mid-year revealed that 7% of the children were non-productive in both languages and 13% achieved Arabic DWR levels that were more than 1 standard deviation below their class mean, with minimal change noted at the end of the year (12%), in spite of daily Arabic and English instruction. Recommendations are offered for SLP-supervised language sampling that facilitates dual language instruction in early childhood classrooms.
The Colorado Journey Towards Optimal Outcomes for Children With Hearing Loss
Authors: Yoshinaga-Itano Christine
Published: March 2010

It is possible for children who are deaf or hard of hearing to attain language development comparable to their hearing peers, but these outcomes are not guaranteed. The population of children with hearing loss is a diverse population and although the variable of the age of identification is less variable, there are numerous variables that could potentially and have historically impacted language outcomes of children who are deaf or hard of hearing. Variables such as hearing loss, maternal level of education, and maternal bonding can overcome the benefits of earlier identification and intervention.
Plasticity in the Human Motor System
Authors: Rothwell John C
Published: March 2010

It is well recognized that the number and effectiveness of synapses in the adult brain changes in response to learning and that similar processes contribute to the restoration of function after central nervous system damage. It is possible to use non-invasive methods of brain stimulation in humans (transcranial magnetic stimulation, TMS; or transcranial direct current stimulation, TDCS) to study and even manipulate these processes. Initial studies now are underway to test whether modification of synaptic plasticity by neurostimulation can improve recovery of motor function in patients after stroke.
Transient Cortical Stimulation To Alter Swallowing Physiology
Authors: Humbert Ianessa A.
Published: March 2010

Older adults are disproportionately affected by swallowing impairment, or dysphagia, a condition that can lead to increased morbidity and death. Delayed initiation of swallowing is a common and devastating pathophysiology of neurogenic dysphagia, and also is experienced by healthy older adults, making functional swallowing less safe. It is still not known if differences in activation of the cortex (primary sensory motor region) are responsible for delays in swallowing initiation, or if it is the consequence of advancing age. The goals of this proposal are to understand the functional role of the primary sensory-motor cortex on swallowing initiation and to characterize the effect of aging on swallowing initiation with transient cortical disruption. The overall hypothesis is that transient disruption of the primary sensory-motor cortex will produce measurable delays in swallowing initiation in young and old adults, but older adults will have more pronounced deficits. This investigation will determine whether cortical areas are involved in initiating swallowing as well as the importance of timing on this function.
Case Studies in Reimbursement: Material Adapted From Division 3 Reimbursement Committee Presentation at the 2009 ASHA Annual Convention
Authors: Von Berg Shelley , Hapner Edie R.
Published: March 2010

Special Interest Division 3 continues to focus on increasing awareness among affiliates of correct coding initiatives, updates on reimbursement guidelines, and a resource for questions regarding coding and reimbursement. In November 2009, Division 3 hosted an update on reimbursement issues for voice clinicians at the American Speech-Language-Hearing Association's (ASHA) annual convention in New Orleans. The purpose of this article is to summarize a number of case study highlights that were presented at the convention by Sandy Schwartz, Dee Nikjeh, Mary Sandage, Mark Kander, and Edie Hapner
Medicare Billing Update
Authors: Kander Mark
Published: March 2010

As of July 2009, speech-language pathologists (SLPs) may bill for Medicare services as private practitioners. This article directs SLPs to the rules for enrollment, necessary approvals by physicians and certain physician substitutes, and proper current procedural terminology (CPT) and International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) coding when submitting claims. Guidance for determination of the exact payment amount for specific geographic areas is covered as well as determination of local Medicare Administrative Contractor (MAC) Web sites and their local coverage policies for speech-language-voice and dysphagia services. Special rules apply to SLPs who are employees or contractors of physician groups, and these SLPs also may function as private practitioners in physician office settings if they follow certain rules that insulate SLPs from kickback accusations. The rules governing these SLPs are summarized in this article. Questions regarding reimbursement should be directed to the Division 3 Reimbursement Committee or toReimbursement@asha.org.
Multisoliton solutions to the lattice Boussinesq equation
Authors: Hietarinta Jarmo , Zhang Da-jun
Published: March 2010

The lattice Boussinesq equation (BSQ) is a three-component difference-difference equation defined on an elementary square of the two-dimensional lattice, having three-dimensional consistency. We write the equations in the Hirota bilinear form and construct their multisoliton solutions in terms of Casoratians, following the methodology in our previous papers. In the construction it turns out that instead of the usual discretization of the exponential as [(a+k)/(a−k)]n, we need two different terms [(a−ωk)/(a−k)]n and [(a−ω2k)/(a−k)]n, where ω is a cubic root of unity ≠1.
A high-resolution two-dimensional imaging velocimeter
Authors: Celliers P. M. , Erskine D. J. , Sorce C. M. , Braun D. G. , Landen O. L. , Collins G. W.
Published: March 2010

Velocity interferometers are typically used to measure velocities of surfaces at a single point or along an imaged line as a function of time. We describe an optical arrangement that enables high-resolution measurements of the two-dimensional velocity field across a shock front or shocked interface. The technique is employed to measure microscopic fluctuations in shock fronts that have passed through materials being considered as ablators for indirect-drive inertial confinement fusion. With picosecond time resolution the instrument captures velocity modes with wavelengths as short as 2.5 μm at a resolution of ∼10 m/s rms on velocity fields averaging many km/s over an 800 μm field of view.
Simulation of polarization charge on AlGaN/GaN high electron mobility transistors: Comparison to electron holography
Authors: Marino Fabio A. , Cullen David A. , Smith David J. , McCartney Martha R. , Saraniti Marco
Published: March 2010

The effects of polarization charge on the electrostatic potential distribution across the heterostructure of a AlGaN/GaN high electron mobility transistor device have been investigated. Simulations were performed using a full-band cellular Monte Carlo simulator, which included electronic dispersion and the phonon spectra. Quantum effects were taken into account using the effective potential method. Experimental extraction of potential profiles across the device was carried out using off-axis electron holography. Based on comparison to simulations, the differences between the theoretical predictions and experimental results could be explained, thereby providing better understanding of device operation.
Isothermal martensitic transformation in metamagnetic shape memory alloys
Authors: Kustov S. , Golovin I. , Corró M. L. , Cesari E.
Published: March 2010

We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase transition the direct transition from ferromagnetic austenite to nonmagnetic martensite is isothermal. In contrast to the direct transformation, the reverse one (nonmagnetic martensite–ferromagnetic austenite) is athermal, just as are athermal both direct and reverse martensitic transformations in conventional ferromagnetic shape memory alloys. The observed asymmetry of properties of the direct and reverse phase transitions in metamagnetic alloys, together with the data on entropy change during the magnetostructural transition, evidences that the magnetostructural transition is driven by the first order lattice modification. The change in magnetic ordering is an effect accompanying the lattice modification, opposing the direct transformation and promoting the reverse one. It has been shown that relaxation effects in metamagnetic shape memory alloys are intrinsic in the direct transformation itself and do not require the “arrest” of the transformation.
Transient growth analysis of flow through a sudden expansion in a circular pipe
Authors: Cantwell C. D. , Barkley D. , Blackburn H. M.
Published: March 2010

Results are presented from a numerical study of transient growth experienced by infinitesimal perturbations to flow in an axisymmetric pipe with a sudden 1–2 diametral expansion. First, the downstream reattachment point of the steady laminar flow is accurately determined as a function of Reynolds number and it is established that the flow is linearly stable at least up to Re=1400. A direct method is used to calculate the optimal transient energy growth for specified time horizon τ, Re up to 1200, and low-order azimuthal wavenumber m. The critical Re for the onset of growth with different m is determined. At each Re the maximum growth is found in azimuthal mode m=1 and this maximum is found to increase exponentially with Re. The time evolution of optimal perturbations is presented and shown to correspond to sinuous oscillations of the shear layer. Suboptimal perturbations are presented and discussed. Finally, direct numerical simulation in which the inflow is perturbed by Gaussian white noise confirms the presence of the structures determined by the transient growth analysis.
Iterative Monte Carlo with bead-adapted sampling for complex-time correlation functions
Authors: Jadhao Vikram , Makri Nancy
Published: March 2010

In a recent communication [V. Jadhao and N. Makri, J. Chem. Phys. 129, 161102 (2008)], we introduced an iterative Monte Carlo (IMC) path integral methodology for calculating complex-time correlation functions. This method constitutes a stepwise evaluation of the path integral on a grid selected by a Monte Carlo procedure, circumventing the exponential growth of statistical error with increasing propagation time, while realizing the advantageous scaling of importance sampling in the grid selection and integral evaluation. In the present paper, we present an improved formulation of IMC, which is based on a bead-adapted sampling procedure; thus leading to grid point distributions that closely resemble the absolute value of the integrand at each iteration. We show that the statistical error of IMC does not grow upon repeated iteration, in sharp contrast to the performance of the conventional path integral approach which leads to exponential increase in statistical uncertainty. Numerical results on systems with up to 13 degrees of freedom and propagation up to 30 times the “thermal” time ℏβ/2 illustrate these features.
New trace formulae for a quadratic pencil of the Schrödinger operator
Authors: Yang Chuan Fu
Published: March 2010

This work deals with the eigenvalue problem for a quadratic pencil of the Schrödinger operator on a finite closed interval with the two-point boundary conditions. We will obtain new regularized trace formulas for this class of differential pencil.
Electromechanical properties of tetragonal Pb(In1/2Nb1/2)O3−Pb(Mg1/3Nb2/3)O3−PbTiO3 ferroelectric crystals
Authors: Li Fei , Zhang Shujun , Xu Zhuo , Wei Xiaoyong , Luo Jun , Shrout Thomas R.
Published: March 2010

The ferroelectric, dielectric, elastic, piezoelectric, and electromechanical properties of tetragonal Pb(In1/2Nb1/2)O3−Pb(Mg1/3Nb2/3)O3−PbTiO3 (PIN–PMN–PT) crystals were investigated. The single domain piezoelectric coefficients d33, d15, and d31 were found to be 530, 2350, and −200 pC/N, respectively, with electromechanical coupling factors k33, k15, and k31 being on the order of 0.84, 0.85, and 0.58. The mechanical quality factor Q for longitudinal mode was found to be >700, with high coercive field (Ec) being on the order of 10 kV/cm. The temperature and dc bias electric-field characteristics of single domain tetragonal PIN–PMN–PT crystals were also investigated. In contrast to [001] oriented domain engineered rhombohedral crystals, tetragonal PIN–PMN–PT crystals exhibited broader temperature usage range and higher thermal/electric field stability, with improved coercive field and mechanical quality factor.
Temperature, concentration, and frequency dependence of the dielectric constant near the critical point of the binary liquid mixture nitrobenzene-tetradecane
Authors: Leys Jan , Losada-Pérez Patricia , Cordoyiannis George , Cerdeiriña Claudio A. , Glorieux Christ , Thoen Jan
Published: March 2010

Detailed results are reported for the dielectric constant ϵ as a function of temperature, concentration, and frequency near the upper critical point of the binary liquid mixture nitrobenzene-tetradecane. The data have been analyzed in the context of the recently developed concept of complete scaling. It is shown that the amplitude of the low frequency critical Maxwell–Wagner relaxation (with a relaxation frequency around 10 kHz) along the critical isopleth is consistent with the predictions of a droplet model for the critical fluctuations. The temperature dependence of ϵ in the homogeneous phase can be well described with a combination of a (1−α) power law term (with α the heat capacity critical exponent) and a linear term in reduced temperature with the Ising value for α. For the proper description of the temperature dependence of the difference Δϵ between the two coexisting phases below the critical temperature, it turned out that good fits with the Ising value for the order parameter exponent β required the addition of a corrections-to-scaling contribution or a linear term in reduced temperature. Good fits to the dielectric diameter ϵd require a (1−α) power law term, a 2β power law term (in the past considered as spurious), and a linear term in reduced temperature, consistent with complete scaling.
Nonlinear full-wave-interaction analysis of a gyrotron-traveling-wave-tube amplifier based on a lossy dielectric-lined circuit
Authors: Du Chao-Hai , Liu Pu-Kun
Published: March 2010

The stability of the millimeter-wave gyrotron-traveling-wave-tube (gyro-TWT) amplifier can be effectively improved via controlling the propagation characteristics of the operating modes using lossy dielectric-lined (DL) waveguide. Self-consistent nonlinear theory of the electron cyclotron maser (ECM) interaction in lossy DL circuit is developed based on a full-wave study of the propagation characteristics of the DL waveguide. This nonlinear theory fully takes into consideration the waveguide structure and the lossy dielectric characteristics. It is capable of accurately calculating the ECM instability between a cyclotron harmonic and a circular polarized mode, and effectively predicting the nonlinear stability of the DL waveguide-based gyro-TWT. Systematic investigation of a Ka-band TE01 mode DL waveguide-based gyro-TWT is carried out, and numerical calculation reveals a series of interesting results. This work provides a basic theoretical tool for further exploring the application of the lossy DL waveguide in millimeter-wave gyro-TWTs.
Electronic and optical properties of CdZnO quantum well structures with electric field and polarization effects
Authors: Jeon H. C. , Park S. H. , Lee S. J. , Kang T. W. , George T. F.
Published: March 2010

Electronic, optical, and electrical properties of CdZnO/MgZnO quantum well (QW) structures, considering internal field and polarization effect, are investigated by using many-body theory. The CdZnO/MgZnO QW structure with higher Cd composition, which has deeper and stronger confinement, is found to have smaller optical gain because the strain-induced piezoelectric polarization and spontaneous polarization in the well increase with the inclusion of Cd. The internal field and polarization is reduced effectively by using the ferroelectric dipole moment of the Li addition in the well region of the Li-doped CdZnO/ZnMgO QW structure. These results demonstrate that a high-performance optical devices operation can be realized in CdZnO/MgZnO QW structures by eliminating the droop phenomenon.
Thermomagnetically patterned micromagnets
Authors: Dumas-Bouchiat F. , Zanini L. F. , Kustov M. , Dempsey N. M. , Grechishkin R. , Hasselbach K. , Orlianges J. C. , Champeaux C. , Catherinot A. , Givord D.
Published: March 2010

Thermomagnetic patterning (TMP) of 4 μm thick high performance NdFeB hard magnetic films deposited on Si substrates has been achieved using single pulsed laser irradiation. Uniaxially magnetised chessboard and stripe patterns with lateral feature sizes in the range 50–100 μm were produced. The depth of reversal was estimated, using both global (vibrating sample magnetometry) and localized (scanning Hall probe) measurements, to be in the range of 1.1–1.2 μm. A simple model provides semiquantitative agreement with the experimental results. A linear Halbach array was fabricated to demonstrate the potential of TMP for the realization of complex multidirectional microflux sources.
Surface tension and orthobaric densities for vibrating square well dumbbells. I
Authors: Chapela Gustavo A. , Alejandre José
Published: March 2010

Surface tensions and liquid-vapor orthobaric densities are calculated for a wide variety of vibrating square well dumbbells using discontinuous molecular dynamics simulations. The size of the vibration well, the elongation or bond distance of the two particles of the dumbbell, the asymmetry in size (and interaction range) of the two particles, and the depth of the interaction well are the variables whose effects are systematically evaluated in this work. Extensive molecular dynamics simulations were carried out and the orthobaric liquid-vapor densities are compared with those obtained previously by other authors using different methods of simulation for rigid and vibrating square well dumbbells. Surface tension values are reported for the first time for homonuclear and heteronuclear vibrating square well dumbbells as well as for all the simulated series. The molecular dynamics results of tangent homonuclear dumbbells are compared with those from Monte Carlo simulations also obtained in this work, as a way of checking the order of magnitude of the molecular dynamics results. The size of the vibration well is shown to have a small influence on the resulting properties. Decreasing elongation and the size of the second particle increase critical temperatures, liquid densities, and surface tensions. Moderate increases in the depth of the interaction well have the same effect. For larger asymmetries of the depth of the interaction well on the dumbbell particles, a strong association phenomenon is observed and the main effects are a maximum on the critical temperature for increasing well depth and a decrease in the surface tension.
Bulk simulation of polar liquids in spherical symmetry
Authors: Stenhammar Joakim , Linse Per , Karlström Gunnar
Published: March 2010

Molecular simulations of strongly coupled dipolar systems of varying size have been carried out, using particles confined inside a dielectric cavity and an image charge approach to treat the dielectric response from the surroundings. A simple method using penalty functions was employed to create an isotropic and homogeneous distribution of particles inside the cavity. The dielectric response of the molecular system was found to increase as the number of particles N was increased. Nevertheless, a significant surface effect remained even for the largest systems (N=10 000), manifesting itself through a decrease in the dielectric constant of the system as the confining surface was approached. The surface effect was significantly reduced by using a negative dielectric constant of the surrounding dielectric medium, although accomplishing a full dielectric solvation of the molecular system was not possible.
Computer simulations of aqua metal ions for accurate reproduction of hydration free energies and structures
Authors: Li Xin , Tu Yaoquan , Tian He , Ågren Hans
Published: March 2010

Metal ions play essential roles in biological processes and have attracted much attention in both experimental and theoretical fields. By using the molecular dynamics simulation technology, we here present a fitting-refining procedure for deriving Lennard-Jones parameters of aqua metal ions toward the ultimate goal of accurately reproducing the experimentally observed hydration free energies and structures. The polarizable SWM4-DP water model {proposed by Lamoureux et al. [J. Chem. Phys. 119, 5185 (2003)]} is used to properly describe the polarization effects of water molecules that interact with the ions. The Lennard-Jones parameters of the metal ions are first obtained by fitting the quantum mechanical potential energies of the hexahydrated complex and are subsequently refined through comparison between the calculated and experimentally measured hydration free energies and structures. In general, the derived Lennard-Jones parameters for the metal ions are found to reproduce hydration free energies accurately and to predict hydration structures that are in good agreement with experimental observations. Dynamical properties are also well reproduced by the derived Lennard-Jones parameters.
Colloidal charge renormalization in suspensions containing multivalent electrolyte
Authors: dos Santos Alexandre P. , Diehl Alexandre , Levin Yan
Published: March 2010

A theory is proposed which allows us to self-consistently calculate the effective colloidal charge and the counterion and coion density profiles in suspensions containing both multivalent and monovalent electrolytes. The formation of counterion-coion clusters is explicitly taken into account. The theory predicts that sufficiently strongly charged colloidal particles will become overcharged. The addition of monovalent electrolyte decreases the counterion condensation and diminishes the amount of charge reversal. Predictions of the theory are compared with the Monte Carlo simulations and are found to be in excellent agreement without any adjustable parameters.
Coloring fluorescence emission with silver nanowires
Authors: Shegai Timur , Huang Yingzhou , Xu Hongxing , Käll Mikael
Published: March 2010

We demonstrate that emission from Rhodamine-6G fluorophores adsorbed on silver nanowires experiences a spectral redshift upon propagation to the distal ends of the nanowire, with the shift being proportional to the propagation distance. The end of a nanowire thus constitutes a tunable fluorescence source controlled by a single easily adjustable parameter, i.e., the position of the excitation focal spot. The effect is made possible by a combination of radiatively undamped plasmon propagation and dispersive ohmic losses in the silver nanowire. The results may be important for the development of plasmonic waveguides, fast fluorescent color switches and various nanoscale fluorescence sensors.
A computational study of electrolyte adsorption in a simple model for intercalated clays
Authors: Lomba E. , Weis J.-J.
Published: March 2010

A pillared interlayered clay is represented by a two-dimensional quenched charged disordered medium, in which the pillar configuration is produced by the quench of a two-dimensional electrolyte and the subsequent removal of the anions (that act as a template). The cation charge is counterbalanced by a neutralizing background that is an ideal representation of the layer’s negative charge in the experimental system. In this paper we investigate the adsorption of electrolyte particles in this charged disordered medium resorting both to the use of the replica Ornstein–Zernike equation in the hypernetted chain approximation and grand canonical Monte Carlo simulations. The theoretical approach qualitatively reproduces the simulated behavior of the adsorbed fluids. Theoretical estimates of the material porosities obtained for various types of pillar distributions are in good agreement with the simulation. We investigate the influence of the matrix on correlation functions and adsorption isotherms.
Effects of ambient atmosphere on the transfer characteristics and gate-bias stress stability of amorphous indium-gallium-zinc oxide thin-film transistors
Authors: Sung Sang-Yun , Choi Jun Hyuk , Han Un Bin , Lee Ki Chang , Lee Joon-Hyung , Kim Jeong-Joo , Lim Wantae , Pearton S. J. , Norton D. P. , Heo Young-Woo
Published: March 2010

We investigated the transfer characteristics and the gate-bias stability of amorphous indium-gallium-zinc oxide thin-film transistors when the channel layer was exposed to hydrogen, oxygen, air, or vacuum at room temperature during measurements. The threshold voltage and the drain current were changed by the ambient atmospheres. The threshold voltage shift (ΔVth) under gate-bias stress was faster in hydrogen than in oxygen and vacuum. It is suggested that hydrogen exposure degrades the gate-bias stress stability due to surface accumulation layer creation. The characteristic trapping times, τ, in H2, O2, air, and vacuum were 5×103, 1.5×104, 2×104, and 6.3×104 s, respectively.
Phase-locked arrays of surface-emitting terahertz quantum-cascade lasers
Authors: Kao Tsung-Yu , Hu Qing , Reno John L.
Published: March 2010

We report the demonstration of phase-locked arrays of surface-emitting distributed-feedback (DFB) terahertz quantum-cascade lasers with single-mode operations. Carefully designed “phase sector” locks several surface-emitting DFB laser ridges in-phase, creating tighter beam-patterns along the phased-array direction with full width at half maximum (FWHM)≈10°. In addition, the phase sector can be individually biased to provide a mechanism of frequency tuning through gain-induced optical index change, without significantly affecting the output power levels. A tuning range of 1.5 GHz around 3.9 THz was achieved. This fine tunability could be utilized to frequency- or phase-lock the DFB array to an external reference.
High performance tunnel injection quantum dot comb laser
Authors: Lee Chi-Sen , Guo Wei , Basu Debashish , Bhattacharya Pallab
Published: March 2010

A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (Δ−15 dB) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231–1252 nm and 1274–1311 nm, respectively, for a laser with 1040 μm cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300–323 K. The small signal modulation bandwidth is 7.5 GHz.
Optimal Extraction of Fibre Optic Spectroscopy
Authors: Sharp R. , Birchall M. N.
Published: March 2010

We report an optimal extraction methodology, for the reduction of multi-object fibre spectroscopy data, operating in the regime of tightly packed (and hence significantly overlapping) fibre profiles. The routine minimises crosstalk between adjacent fibres and statistically weights the extraction to reduce noise. As an example of the process we use simulations of the numerous modes of operation of the AAOmega fibre spectrograph and observational data from the SPIRAL Integral Field Unit at the Anglo-Australian Telescope.
Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation
Authors: Warren Jeffrey J. , Mayer James M.
Published: March 2010

Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold’s model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.