bluuebunny/crossref_metadata_2025 huggingface dataset:
Who switches sickness funds in Israel?
Authors: SHMUELI AMIR , BENDELAC JACQUES , ACHDUT LEAH
Published: August 2007

A competitive national health insurance system was introduced in Israel in 1995. Comsumer mobility has been traditionally a signal of market (managed) competition. However, since 1998, sickness funds’ switching rate has been stable at around 1% of the population. The low switching rate is explained by limited real options and similarity in the sickness funds functioning, and reluctance to change providers. The paper aims to characterize the 1% of the population who switches sickness fund in relation to the stayers, and to examine the implications for public policy. The National Insurance Institute Health Registry was used to conduct two analyses: (i) bivariate comparisons on selected socio-demographic characteristics of the switchers to those of the stayers in the years 1999–2000, and (ii) a multivariate logistic analysis of the propensity to switch for the entire adult (21+) population in the years 2005–2006. The main result is that switching is an inferior good. Both the bivariate and the multivariate analysis show that persons with lower labor-income, receiving income support or unemployment benefits are more likely to switch. Switchers have more children up to age 18. Arabs and Orthodox Jews are more likely to switch sickness funds. The 1% of switchers does not form a random draw from the age–sex-adjusted population. The over-representation of poor persons among switchers is unique to the Israeli scene, which might have resulted from demand-side initiatives, but also from implicit risk-selection strategies exercised by the sickness funds under the Israeli incomplete age-based risk-adjustment system.
Lawsuit activity, defensive medicine, and small area variation: the case of cesarean sections revisited
Authors: BROWN, III H. SHELTON
Published: August 2007

This paper examines whether delivery practice patterns (Cesarean sections or vaginal) are influenced by lawsuits or whether the hypothesized relationship is confounded by small area variation. The analysis uses multilevel analysis to deal with hospital- and Dartmouth Hospital Referral Region-level variation. The model includes patient clinical variables, patient socio-economic status, and hospital characteristics as control variables. The secondary data sources include hospital discharges from the 2002 Texas Health Care Information Council as well as 1988–2001 Texas Department of Insurance Closed Claim File data. After extracting the variation in delivery practice between hospitals and between Dartmouth Hospital Referral Regions in a multilevel model, the effects of lawsuits on defensive medicine are reduced but are still significant.
The political economy of Chinese health reform
Authors: HSIAO WILLIAM C.
Published: August 2007

Political economy studies of health policy offer more than simple economic or political studies. Politics can have a greater influence on health policy decisions and their implementation than either economic or health considerations. Politics constrain how much of an optimal economic or health programme can be adopted and implemented. At the same time, the economic interests of the stakeholders drive their political positions on any potential policy change. We need more political economy studies to understand how to craft and execute politically viable ‘best’ health policies. This editorial uses the decision choices facing China’s health reform to illustrate the importance of political economic analysis and argues for more integrated political economy studies, particularly ones examining the roles of the health bureaucracy and the medical profession.
The ICRC: a unique humanitarian protagonist
Authors: Forsythe David P.
Published: August 2007

The International Committee of the Red Cross, associated with four Nobel Peace Prizes, is a unique and widely respected humanitarian actor. There were times in its past, however, when it was not as independent, neutral and impartial as is sometimes pictured. Since about 1970 it has made important changes in its structure and functioning so as to improve on the past. In contemporary times the ICRC has carved out an enduring place for neutral humanitarianism in conflicts, but one that is not free from controversies and challenges.
In search of symbiosis: the Security Council in the humanitarian domain
Authors: Viotti Aurélio
Published: August 2007

While the Security Council's incursion into the protection of individuals or groups could appear necessary – or even praiseworthy – it should be viewed with caution. The author argue that the search for perfect complementarity between the powers of the Security Council and humanitarian action should not overlook the political nature of the Council, the omissions and inconsistencies in its decisions regarding grave offences against human dignity and the effects of coercive action – including armed force – on the provision of neutral and impartial assistance to the victims of an armed conflict.
Non-governmental organizations: an indispensable player of humanitarian aid
Authors: Ryfman Philippe
Published: August 2007

Although the humanitarian landscape is constantly evolving, one factor which stands out among the players of aid, and particularly non-governmental organizations (NGOs), is the significance of the private, not-for-profit dimension. After tracing the historical origin of those organizations, defining them and stressing how well known and well regarded they are, the article goes on to discuss the main questions they set. It points out that although each one has its own specific characteristics, their operating methods have much in common. In conclusion the role NGOs play on the international stage is also mentioned, as well as their position regarding UN plans to overhaul the international humanitarian system. Faced with a transnational environment and a growing demand for accountability both to beneficiaries and to sponsors, with uncertain times ahead and difficult choices to make, NGOs must be even more humanitarian in the approach they take.
Beyond the Red Cross: the protection of independent humanitarian organizations and their staff in international humanitarian law
Authors: Mackintosh Kate
Published: August 2007

Members of independent humanitarian organizations have less protection, legally speaking, than most of them probably think. Two key features of their work – their neutrality and independence – as well as practical steps they take to implement these principles, actually place them outside much of the protection afforded to either civilians or authorized medical staff. This article examines the international legal protection currently available to independent humanitarian organizations, and considers whether there is scope for improvement of both the content of this framework and respect for the same.
Temporal variations of the 18O/16O signal of the whole‐canopy transpiration in a temperate forest
Authors: Lee Xuhui , Kim Kyounghee , Smith Ronald
Published: August 2007

Biosphere‐atmosphere exchange of water vapor isotopes plays an important role in the global atmospheric 18O‐CO2 and 18O‐O2 budgets. In this paper, we report the results of the first continuous measurements of isotope ratios of water vapor and the evapotranspiration flux in a temperate forest over one full growing season. We found that the 18O/16O isotopic signal of the whole‐canopy transpiration (δT) was not in steady state with respect to plant source water. The departure from steady state was greatest at night and on days of low transpiration rates. Relative humidity was an important driver on timescales shorter than a few hours; on the diurnal timescale, the nonsteady state behavior was driven by relative humidity and the covarying transpiration rate. On average, δT was lowest in midmorning and highest at midnight, with an average peak‐to‐peak variation on the order of 15‰ over the growing season. A diurnal variation of 60‰ or more was observed on some days. On the seasonal timescale, δT was tightly coupled with the precipitation isotope ratio in the early growing season and fluctuated around the isotope ratio of the stem water of overstory trees in the late growing season. The temporal shift suggests that the forest switched its water source from the shallow to the deep soil pool and that the overstory trees dominated the whole stand transpiration in the late growing season. Using isotopic partitioning, we estimated that the overstory trees contributed roughly 70% to the whole‐stand transpiration water loss during the growing season.
Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms
Authors: Basu S. , Basu Su. , Rich F. J. , Groves K. M. , MacKenzie E. , Coker C. , Sahai Y. , Fagundes P. R. , Becker‐Guedes F.
Published: August 2007

We investigate the response of the equatorial ionosphere at dusk to the intense magnetic storms of 30 October 2003 and 20 November 2003, different aspects of which have been widely studied by the community. We present here a very complete set of space and ground‐based diagnostics that provide the vertical and latitudinal structures of the ionosphere within the South Atlantic magnetic anomaly (SAMA) region and the contiguous parts of South America and Africa. We show that for both storms, the dusk sector corresponding to the universal time (UT) interval between the fast decrease of the SYM‐H index and minimum SYM‐H value determines uniquely the longitude interval populated by equatorial plasma bubbles and depletions. Further, we find that the UT of these storms is such that the ionospheric density perturbations occur in the SAMA region, which are most extended in latitude and altitude compared with other regions of the globe. In the dusk sector, the eastward penetration electric field, associated with rapid SYM‐H decrease, adds to the postsunset eastward E‐field because of the F region dynamo, which may be specially enhanced in this longitude interval because of the increased zonal conductivity gradient caused by energetic particle precipitation. This enhanced E‐field at dusk causes a rapid uplift of the ionosphere and sets off plasma instabilities to form bubbles or bite‐outs. The decreased ion density seen in the Defense Meteorological Satellite Program (DMSP) in situ data at 840 km indicates that the ionospheric plasma has been lifted above the DMSP altitude and transported away from the region by diffusion along magnetic field lines. Plasma bubbles and bite‐outs impact satellite communication and navigation systems by introducing scintillations and steep density gradients. This paper corroborates that intense magnetic storms follow the framework, developed by Su. Basu et al. (2001) for moderate storms, that specifies the longitude interval in which such disturbances are most likely to occur.
Subregional precipitation climate of the Caribbean and relationships with ENSO and NAO
Authors: Jury Mark , Malmgren Björn A. , Winter Amos
Published: August 2007

Thirty‐five meteorological stations encompassing the Caribbean region (Cuba, Bahamas, Jamaica, Dominican Republic, Puerto Rico, US Virgin Islands, St. Maarten, and Barbados) were analyzed over the time interval 1951–1981 to assess regional precipitation patterns and their relationships with the North Atlantic Oscillation (NAO) and El Niño‐Southern Oscillation (ENSO). Application of factor analysis to these series revealed the existence of four geographically distinct precipitation regions, (C1) western Cuba and northwestern Bahamas, (C2) Jamaica, eastern Cuba, and southeastern Bahamas, (C3) Dominican Republic and northwestern Puerto Rico, and (C4) eastern Puerto Rico, US Virgin Islands, St. Maarten, and Barbados. This regionalization is related to different annual cycles and interannual fluctuations of rainfall. The annual cycle is more unimodal and largest in the northwest Caribbean (C1) and becomes increasingly bimodal toward lower latitudes (C4) as expected. Year‐to‐year variations of precipitation are compared with two well‐known climatic indices. The ENSO relationship, represented by Niño 3.4 sea surface temperatures (SST), is positive and stable at all lags, but tends to reverse over the SE Caribbean (C4) in late summer. The NAO influence is weak and seasonally dependent. Early summer rainfall in the northwest Caribbean (C1) increases under El Niño conditions. Clusters 2 and 3 are less influenced by the global predictors and more regional in character.
Analysis of the global distribution of water isotopes using the NCAR atmospheric general circulation model
Authors: Lee Jung‐Eun , Fung Inez , DePaolo Donald J. , Henning Cara C.
Published: August 2007

We have incorporated the cycling of water isotopes into the NCAR atmospheric general circulation model, CAM2. Isotope dynamics mostly follow those of previous isotope GCMs, with fractionation being produced by evaporation at the surface and by cloud processes. A new feature that we have added is the direct estimation of the degree of isotopic equilibration between vapor and raindrops as a function of temperature and rain rate. The model yields a reasonable global pattern of water isotopes in precipitation, but detailed comparison with observations is limited by known inaccuracies in precipitation and temperatures yielded by CAM2. We use the results to evaluate the fundamental controls on water isotopic composition in precipitation. We emphasize that, over much of the surface of the Earth, the concept of Rayleigh distillation is inadequate to understand the large‐scale geographic distribution of water isotopes in precipitation, because the effects of surface fluxes are more important than those of distillation, in particular at low and midlatitudes and over the oceans. In oceanic regions the balance between precipitation and evaporation (P − E), which reflects the large‐scale atmospheric circulation, is the primary determinant of the isotopic composition of precipitation and vapor. Variations of P − E at low latitudes over the oceans produce about 7‰ variation of precipitation δ18O that is independent of temperature variation. Where P > E, the convergence of atmospheric vapor derived from various sources leads to low values and a particularly wide range in δppt. In the tropical and subtropical troposphere the vertical decrease of δ18O in vapor is different from the values expected from Rayleigh distillation because of entrainment, convective mixing, detrainment, evaporation of detrained water, and subsidence of low‐δ18O high‐altitude air. The low δ18O of atmospheric vapor over the oceans at high (ca. 55°) latitudes produces, as a result of kinetic effects associated with evaporation, a zone of heavy (high‐δ18O) evaporation from the oceans. This effect may account for the low δ18O of some high‐latitude ocean surface waters and also helps attenuate the effects of global temperature changes on the isotopic composition of polar precipitation.
Dissecting the polar dichotomy of the noncondensable gas enhancement on Mars using the NASA Ames Mars General Circulation Model
Authors: Nelli Steven M. , Murphy James R. , Sprague Ann L. , Boynton William V. , Kerry Kris E. , Janes Daniel M. , Metzger Albert E.
Published: August 2007

The atmospheric processes underlying the observed spatial and temporal enhancement of noncondensing gases in Mars' atmosphere are investigated. The Gamma Ray Spectrometer (GRS) on board Mars Odyssey has obtained measurements indicating that the absolute and relative column abundance of noncondensing gases (primarily argon and nitrogen) maximizes at high latitudes in both hemispheres during winter as CO2 gas condenses and forms the seasonal polar ice cap. This condensing CO2 “leaves behind” noncondensing gases whose local absolute and relative column abundances can increase at a rate controlled by mixing with less‐enhanced air from lower latitudes. Understanding the processes responsible for the magnitude and seasonal variations of these enhancement values is an aid in understanding atmospheric transport processes. The NASA Ames Mars General Circulation Model is employed to help understand the atmospheric thermodynamical mechanisms that give rise to the observed temporal and magnitude variations in the polar enhancement values. The model produces a threefold noncondensable gas enhancement in the south polar region and an approximate 1.4‐fold increase in noncondensables in the north polar region. These model results are temporally consistent with observed values, but the observed enhancement magnitudes exceed those modeled by up to a factor of two. The difference in strength and the season of formation between transient eddies in the southern and northern hemispheres may play a large role in determining the different character of the two polar enhancements. Model simulations also illuminate the effect that topography, orbital eccentricity, and atmospheric dust opacity have on producing the north versus south polar enhancement dichotomy.
Wildfires drive interannual variability of organic carbon aerosol in the western U.S. in summer
Authors: Spracklen Dominick V. , Logan Jennifer A. , Mickley Loretta J. , Park Rokjin J. , Yevich Rosemarie , Westerling Anthony L. , Jaffe Dan A.
Published: August 2007

Forest wildfire area burned in the western U.S. has increased in recent decades resulting in a substantial organic carbon (OC) source with large interannual variability. We derive OC emissions from wildfires using data for area burned for 1980–2004 and ecosystem specific fuel loadings. For the period 1989–2004 we analyze OC observations in the western U.S. from the IMPROVE network and use a global chemical transport model to simulate OC concentrations. Modeled and observed OC concentrations are highly correlated when we use interannually varying fire emissions (R2 = 0.88); the correlation is smaller with climatological emissions (R2 = 0.4). We estimate that the observed increase in wildfire activity after the mid 1980s has caused mean OC concentrations in summer over the western U.S. to increase by 30% relative to 1970–1984. In the coming decades, climate change will likely cause further increases in wildfires resulting in increased OC concentrations with implications for health and visibility.
Dynamical influences of precipitation assimilation on regional downscaling
Authors: Nunes Ana M. B. , Roads John O.
Published: August 2007

Precipitation assimilation has previously been found to be useful for improving regional climate model simulations of the surface water and energy cycles. Here we show that upper‐level dynamical features are also better simulated. In particular, noticeable improvements in the intensity and location of the subtropical upper‐level westerly jet and associated transverse circulations were found in a regional climate model simulation of the 1993 heavy summertime precipitation over the midwestern United States. We suggest that the increased rainfall directly over the upper Mississippi River Basin during the 1993 summer was linked with the location of the upper‐level jet, and its associated transverse circulation, in addition to increased low‐level summertime meridional moisture transport from the Gulf of Mexico.
Joint inversion of teleseismic receiver functions and magnetotelluric data using a genetic algorithm: Are seismic velocities and electrical conductivities compatible?
Authors: Moorkamp M. , Jones A. G. , Eaton D. W.
Published: August 2007

Joint inversion of different kinds of geophysical data has the potential to improve model resolution, under the assumption that the different observations are sensitive to the same subsurface features. Here, we examine the compatibility of P‐wave teleseismic receiver functions and long‐period magnetotelluric (MT) observations, using joint inversion, to infer one‐dimensional lithospheric structure. We apply a genetic algorithm to invert teleseismic and MT data from the Slave craton; a region where previous independent analyses of these data have indicated correlated layering of the lithosphere. Examination of model resolution and parameter trade‐off suggests that the main features of this area, the Moho, Central Slave Mantle Conductor and the Lithosphere‐Asthenosphere boundary, are sensed to varying degrees by both methods. Thus, joint inversion of these two complementary data sets can be used to construct improved models of the lithosphere. Further studies will be needed to assess whether the approach can be applied globally.
Photodissociation yields for vibrationally excited states of sulfuric acid under atmospheric conditions
Authors: Miller Yifat , Gerber R. B. , Vaida Veronica
Published: August 2007

Theoretical investigations of the dynamics of the sunlight initiated dehydration of sulfuric acid are performed under atmospheric conditions. The relevant time scales for collisional deactivation and for vibrational fluorescence, which may compete with sulfuric acid dehydration in the upper stratosphere and the mesosphere are evaluated to provide a realistic quantum yield consistent with spectroscopic and theoretical results. The results obtained allow evaluation of the J values for this photochemical reaction in the atmosphere. At the higher altitudes of the upper stratosphere and the mesosphere the J values obtained are sufficiently large to satisfy model requirements and explain field observations of SO2 vertical profiles and the concentration of condensation nuclei in the stratosphere for air of recent polar origin.
Modernising Healthcare – is the NPfIT for Purpose?
Authors: Mark Annabelle L
Published: August 2007

This paper responds to the findings of the research by Currie and Guah on the introduction of the National Programme for Information Technology through an institutional theory perspective. It considers both the appropriateness and applicability of the method chosen in the light of what is already known about UK healthcare organisations and the complex and changing process that is involved in both the organisation and any research that takes place. This is further confounded by an unstable political environment both nationally and locally and a failure to understand the changing location, role and status of the medical record. Only when this is resolved will a transformational change occur, in line with the new patient-focused government agenda and the external world of technology that must engage with the emotional as well as the rational role that both technology and health play in people's lives.
E-government: Towards the E-Bureaucratic Form?
Authors: Cordelia Antonio
Published: August 2007

Bureaucratic institutions not only provide mechanisms to coordinate work activities in the public sector, but also serve to enforce the democratic values of equality and impartiality. This paper explores how recent approaches to e-government neglect these important dimensions of bureaucracy and proposes an alternative approach to e-government. This paper sets the wider new public management reform context to help explain some of the difficulties the NHS IT Projects are running into by 2007. The e-bureaucratic form is proposed as an e-government solution, which, while taking advantages of the information and communication technology as means of coordination, also help to enforce the values of equality and impartiality underpinned through the actions emanating from bureaucratic structures.
Outer-layer similarity in the presence of a practical rough-wall topography
Authors: Wu Y. , Christensen K. T.
Published: August 2007

High-resolution particle image velocimetry measurements are made in the streamwise–wall-normal plane of a zero-pressure-gradient turbulent boundary layer over smooth and rough walls at Reθ≈13000. The roughness considered herein is replicated from a surface scan of a turbine blade damaged by deposition of foreign materials and its topography is highly irregular and contains a broad range of topographical scales. Two physical scalings of the same roughness topography are considered, yielding two different rough surfaces: RF1 with k=4.2mm and RF2 with k=2.1mm, where k is the average peak-to-valley roughness height. At Reθ≈13000, these roughness conditions yield k+≡k∕y*=207, δ∕k=28, ks+=115, and δ∕ks=48 for RF1 and k+=91, δ∕k=50, ks+=29, and δ∕ks=162 for RF2 (where δ is the boundary-layer thickness, ks is the equivalent sand-grain height, and y* is the viscous length scale). The mean velocity deficits along with the Reynolds normal and shear stress profiles for both roughness conditions collapse on the smooth-wall baseline in the outer layer when appropriately scaled by the friction velocity, uτ. Probability density functions and quadrant analysis of the instantaneous events contributing to the mean Reynolds shear stress show similar outer-layer consistency between the smooth and rough cases when scaled appropriately with uτ. In addition, one-dimensional, two-point streamwise, and wall-normal velocity autocorrelation coefficients are also found to collapse in the outer region, indicating a similarity in the spatial structure of the outer-layer turbulence. The observed collapse of the smooth- and rough-wall turbulence statistics in the outer layer supports Townsend’s wall similarity hypothesis for flow over the unique surface topography considered herein.
Extrapolation of electron correlation energies to finite and complete basis set targets
Authors: Bakowies Dirk
Published: August 2007

The electron correlation energy of two-electron atoms is known to converge asymptotically as ∼(L+1)−3 to the complete basis set limit, where L is the maximum angular momentum quantum number included in the basis set. Numerical evidence has established a similar asymptotic convergence ∼X−3 with the cardinal number X of correlation-consistent basis sets cc-pVXZ for coupled cluster singles and doubles (CCSD) and second order perturbation theory (MP2) calculations of molecules. The main focus of this article is to probe for deviations from asymptotic convergence behavior for practical values of X by defining a trial function X−β that for an effective exponent β=βeff(X,X+1,X+N) provides the correct energy EX+N, when extrapolating from results for two smaller basis sets, EX and EX+1. This analysis is first applied to “model” expansions available from analytical theory, and then to a large body of finite basis set results (X=D,T,Q,5,6) for 105 molecules containing H, C, N, O, and F, complemented by a smaller set of 14 molecules for which accurate complete basis set limits are available from MP2-R12 and CCSD-R12 calculations. βeff is generally found to vary monotonically with the target of extrapolation, X+N, making results for large but finite basis sets a useful addition to the limited number of cases where complete basis set limits are available. Significant differences in effective convergence behavior are observed between MP2 and CCSD (valence) correlation energies, between hydrogen-rich and hydrogen-free molecules, and, for He, between partial-wave expansions and correlation-consistent basis sets. Deviations from asymptotic convergence behavior tend to get smaller as X increases, but not always monotonically, and are still quite noticeable even for X=5. Finally, correlation contributions to atomization energies (rather than total energies) exhibit a much larger variation of effective convergence behavior, and extrapolations from small basis sets are found to be particularly erratic for molecules containing several electronegative atoms. Observed effects are discussed in the light of results known from analytical theory. A carefully calibrated protocol for extrapolations to the complete basis set limit is presented, based on a single “optimal” exponent βopt(X,X+1,∞) for the entire set of molecules, and compared to similar approaches reported in the literature.
Propulsion in a viscoelastic fluid
Authors: Lauga Eric
Published: August 2007

Flagella beating in complex fluids are significantly influenced by viscoelastic stresses. Relevant examples include the ciliary transport of respiratory airway mucus and the motion of spermatozoa in the mucus-filled female reproductive tract. We consider the simplest model of such propulsion and transport in a complex fluid, a waving sheet of small amplitude free to move in a polymeric fluid with a single relaxation time. We show that, compared to self-propulsion in a Newtonian fluid occurring at a velocity UN, the sheet swims (or transports fluid) with velocity U∕UN=(1+De2ηs∕η)∕(1+De2), where ηs is the viscosity of the Newtonian solvent, η is the zero-shear-rate viscosity of the polymeric fluid, and De is the Deborah number for the wave motion, product of the wave frequency by the fluid relaxation time. Similar expressions are derived for the rate of work of the sheet and the mechanical efficiency of the motion. These results are shown to be independent of the particular nonlinear constitutive equations chosen for the fluid, and are valid for both waves of tangential and normal motion. The generalization to more than one relaxation time is also provided. In stark contrast with the Newtonian case, these calculations suggest that transport and locomotion in a non-Newtonian fluid can be conveniently tuned without having to modify the waving gait of the sheet but instead by passively modulating the material properties of the liquid.
Spatiotemporal dynamics in a ring of N mutually coupled self-sustained systems
Authors: Enjieu Kadji H. G. , Chabi Orou J. B. , Woafo P.
Published: August 2007

In this paper, we consider the spatiotemporal dynamics in a ring of N mutually coupled self-sustained oscillators in the regular state. When there are no parameter mismatches, the good coupling parameters leading to full, partial, and no synchronization are derived using the properties of the variational equations of stability. The effects of the spatial dimension of the ring on the stability boundaries of the synchronized states are performed. Numerical simulations validate and complement the results of analytical investigations. The influences of coupling parameter mismatch on the forecasted stability boundaries are also highlighted.
Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: I. Transitions in the one-phase liquid region
Authors: Tóth Gyula I. , Gránásy László
Published: August 2007

The phase field theory (PFT) has been applied to predict equilibrium interfacial properties and nucleation barrier in the binary eutectic system Ag–Cu using double well and interpolation functions deduced from a Ginzburg-Landau expansion that considers fcc (face centered cubic) crystal symmetries. The temperature and composition dependent free energies of the liquid and solid phases are taken from CALculation of PHAse Diagrams-type calculations. The model parameters of PFT are fixed so as to recover an interface thickness of ∼1nm from molecular dynamics simulations and the interfacial free energies from the experimental dihedral angles available for the pure components. A nontrivial temperature and composition dependence for the equilibrium interfacial free energy is observed. Mapping the possible nucleation pathways, we find that the Ag and Cu rich critical fluctuations compete against each other in the neighborhood of the eutectic composition. The Tolman length is positive and shows a maximum as a function of undercooling. The PFT predictions for the critical undercooling are found to be consistent with experimental results. These results support the view that heterogeneous nucleation took place in the undercooling experiments available at present. We also present calculations using the classical droplet model [classical nucleation theory (CNT)] and a phenomenological diffuse interface theory (DIT). While the predictions of the CNT with a purely entropic interfacial free energy underestimate the critical undercooling, the DIT results appear to be in a reasonable agreement with the PFT predictions.
Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: II. Nucleation in the metastable liquid immiscibility region
Authors: Tóth Gyula I. , Gránásy László
Published: August 2007

In the second part of our paper, we address crystal nucleation in the metastable liquid miscibility region of eutectic systems that is always present, though experimentally often inaccessible. While this situation resembles the one seen in single component crystal nucleation in the presence of a metastable vapor-liquid critical point addressed in previous works, it is more complex because of the fact that here two crystal phases of significantly different compositions may nucleate. Accordingly, at a fixed temperature below the critical point, six different types of nuclei may form: two liquid-liquid nuclei: two solid-liquid nuclei; and two types of composite nuclei, in which the crystalline core has a liquid “skirt,” whose composition falls in between the compositions of the solid and the initial liquid phases, in addition to nuclei with concentric alternating composition shells of prohibitively high free energy. We discuss crystalline phase selection via exploring∕identifying the possible pathways for crystal nucleation.
Coupled molecular dynamics-Monte Carlo model to study the role of chemical processes during laser ablation of polymeric materials
Authors: Prasad Manish , Conforti Patrick F. , Garrison Barbara J.
Published: August 2007

The coarse grained chemical reaction model is enhanced to build a molecular dynamics (MD) simulation framework with an embedded Monte Carlo (MC) based reaction scheme. The MC scheme utilizes predetermined reaction chemistry, energetics, and rate kinetics of materials to incorporate chemical reactions occurring in a substrate into the MD simulation. The kinetics information is utilized to set the probabilities for the types of reactions to perform based on radical survival times and reaction rates. Implementing a reaction involves changing the reactants species types which alters their interaction potentials and thus produces the required energy change. We discuss the application of this method to study the initiation of ultraviolet laser ablation in poly(methyl methacrylate). The use of this scheme enables the modeling of all possible photoexcitation pathways in the polymer. It also permits a direct study of the role of thermal, mechanical, and chemical processes that can set off ablation. We demonstrate that the role of laser induced heating, thermomechanical stresses, pressure wave formation and relaxation, and thermochemical decomposition of the polymer substrate can be investigated directly by suitably choosing the potential energy and chemical reaction energy landscape. The results highlight the usefulness of such a modeling approach by showing that various processes in polymer ablation are intricately linked leading to the transformation of the substrate and its ejection. The method, in principle, can be utilized to study systems where chemical reactions are expected to play a dominant role or interact strongly with other physical processes.
Emission intensities and line ratios from a fast neutral helium beam
Authors: Ahn J-W. , Craig D. , Fiksel G. , Den Hartog D. J. , Anderson J. K. , O’Mullane M. G.
Published: August 2007

The emission intensities and line ratios from a fast neutral helium beam is investigated in the Madison Symmetric Torus (MST) [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 1991]. Predicted He I line intensities and line ratios from a recently developed collisional-radiative model are compared with experiment. The intensity of singlet lines comes mostly (>95%) from the contribution of the ground state population and is very weakly dependent on the initial metastable fraction at the observation point in the plasma core. On the other hand, the intensity of triplet lines is strongly affected by the local metastable state (21S and 23S) populations and the initial metastable fraction plays an important role in determining line intensities. The fraction of local metastable states can only be estimated by making use of electron temperature (Te), electron density (ne), and effective ion charge (Zeff) profiles as inputs to the population balance equations. This leads triplet lines to be unusable for the investigation of their local plasma parameter dependence. The ratio of singlet lines at 667.8nm and 492.2nm (I667∕I492) as well as the ratio of 667.8nm and 501.6nm lines (I667∕I501) has been investigated for the dependence on Te and ne both theoretically and experimentally. I667∕I492 shows strong dependence on ne with weak sensitivity to Te. Measurements and predictions agree quantitatively within a factor of 2. There has been no ratio of singlet lines identified to have strong enough Te dependence yet. The ratios are expected to be reasonably insensitive to the variation of Zeff.
Derivations of extended Navier-Stokes equations from upscaled molecular transport considerations for compressible ideal gas flows: Towards extended constitutive forms
Authors: Chakraborty Suman , Durst Franz
Published: August 2007

This paper deals with the derivations of the extended forms of the continuum conservation equations for ideal gas flows with heat and mass transfer, from upscaled molecular transport considerations. It is shown that for strong local temperature and/or density gradients, diffusive transport of momentum, heat, and mass over subcontinuum length scales gives rise to additional terms in the corresponding continuum level constitutive relationships. An exact analogy with kinematically hypothesized extended rheological forms is established by casting the expression for momentum flux in an equivalent linear form, with the postulation of a gradient-based hypothesis. Possible considerations of extending the theory to more general flow conditions are also discussed.
Gadolinium (III) ion in liquid water: Structure, dynamics, and magnetic interactions from first principles
Authors: Yazyev Oleg V. , Helm Lothar
Published: August 2007

We applied first principles molecular dynamics (MD) technique to study structure, dynamics, and magnetic interactions of the Gd3+ aqua ion dissolved in liquid water, a prototypical system for Gd-based complexes used as contrast agents for magnetic resonance imaging. The first coordination sphere contains eight water molecules with an average Gd-O distance of 2.37 Å and an average geometric arrangement close to a square antiprism. The mean tilt angle of the electric dipole vector of these water molecules is θ=145°. In our picosecond time scale simulation we observe no exchange event from the first coordination sphere but only fast “wagging” motions. The second coordination sphere is well pronounced though water molecules in this sphere are subjected to large amplitude dynamic motions. The isotropic hyperfine coupling constants for the inner sphere water molecules [⟨Aiso(O17I)⟩=0.65±0.03 MHz, ⟨Aiso(H1I)⟩=0.085±0.005 MHz] are in good agreement with experimental data and with an earlier study using classical MD. Second sphere Fermi contact hyperfine coupling constants calculated are more than one order of magnitude smaller and of opposite sign as those of the first coordination sphere. The effect of spin polarization induced by the paramagnetic Gd3+ ion on the dipolar hyperfine interaction was found to be sizable only for the O17 nuclei of inner sphere water molecules and has a screening character.
Elastic stability of a dual-coated optical fiber of finite length
Authors: Suhir E.
Published: August 2007

Dual-coated optical fibers are fabricated at elevated temperatures and operated at low temperature conditions. It is imperative that the fibers remain elastically stable, i.e., do not buckle as a result of the thermal contraction mismatch of the dissimilar materials of the fiber and the secondary coating or, in the case of an optical fiber interconnect, of the fiber and the material of an enclosure, if any. We develop a simple and easy-to-use predictive model that enables one to establish the condition of elastic stability for a dual-coated optical fiber of finite length, and/or to select the coating materials with the most favorable physical properties for such a fiber, and/or to establish the adequate thickness of the primary coating. The fiber is idealized as a free-free beam (i.e., a beam not supported at the ends), and the effect of the embedding medium is mimicked by a continuous elastic foundation. The obtained results can be applied also, with some minor modifications, for the evaluation of the elastic stability of short fibers in fiber-reinforced composites, including nanocomposites.
Theoretical modeling of the O–H stretching IR bands of hydrogen-bonded dimers of benzoic acid in S and S1 electronic states
Authors: Boczar Marek , Boda Łukasz , Wójcik Marek J.
Published: August 2007

Theoretical model for vibrational interactions in the hydrogen-bonded dimer of benzoic acid is presented. The model takes into account anharmonic-type couplings between the high-frequency O–H and the low-frequency O⋯O stretching vibrations in two hydrogen bonds, resonance interactions (Davydov coupling) between two hydrogen bonds in the dimer, and Fermi resonance between the O–H stretching fundamental and the first overtone of the O–H in-plane bending vibrations. The vibrational Hamiltonians and selection rules for the C2h geometry in the S0 state and for the Cs in-plane bent geometry in the S1 state of the dimer are derived. The model is used for theoretical simulation of the O–H stretching IR absorption bands of benzoic acid dimers in the gas phase in the electronic ground and first excited singlet states. Ab initio CIS and CIS(D)∕6-311++G(d,p) calculations have been performed to determine geometry, frequencies, and excited state energies of benzoic acid dimer in the S1 state.
Nonlinear buoyant-thermocapillary flows in a three-layer system with a temperature gradient along the interfaces
Authors: Simanovskii Ilya B.
Published: August 2007

The nonlinear buoyant-thermocapillary flows in three superposed liquid layers bounded by two solid planes and subjected to a temperature gradient directed along the interfaces, are investigated. Two types of boundary conditions, periodic boundary conditions and heat-insulated lateral walls, are considered. The nonlinear simulations of the wavy convective regimes are performed by the finite-difference method.
Kinetic modeling of a sheath layer in a magnetized collisionless plasma
Authors: Kawamura G. , Fukuyama A.
Published: August 2007

A sheath layer in a magnetized collisionless plasma is analyzed by the one-dimensional kinetic equation. The plasma is bounded by an absorbing wall and a plasma source with a shifted Maxwellian velocity distribution function that is characterized by a temperature, a drifting velocity parallel to the magnetic field, and a cutoff velocity. The magnetic field is assumed to be strong enough so that the ion Larmor radius is comparable to the Debye length. In order to include the polarization effect of ions due to a strong electric field, equations describing the potential profile are derived from the gyrokinetic Vlasov equation in a frame moving with the E×B drift. A new algorithm for evaluating the loss of particles in gyration at the wall is introduced. The condition of the stable sheath formation for a magnetized plasma is discussed. The dependence of the electric field at the wall on the angle and the strength of the magnetic field is examined and compared with the results of full-kinetic particle-in-cell simulation. The effect of the polarization and the loss of gyration particles on the wall electric field are also discussed.
Filamentation of ultrashort laser pulses propagating in tenuous plasmas
Authors: Andreev N. E. , Gorbunov L. M. , Mora P. , Ramazashvili R. R.
Published: August 2007

The filamentation of ultrashort laser pulses (shorter than a plasma period) propagating in tenuous plasmas is studied. In this regime relativistic and ponderomotive nonlinearities tend to cancel each other. Time-dependent residual nonlinear plasma response brings about the dynamical filamentation with the maximum unstable transverse wave number decreasing in the course of laser pulse propagation. Dynamics of a hot spot that seeds the filamentation instability is studied numerically and reveals a good agreement with the analytical results.
Dust density waves in a complex plasma layer
Authors: Yaroshenko V. V. , Thomas H. M. , Morfill G. E.
Published: August 2007

Modifications of dust density waves in a complex plasma layer imbedded in a bulk of electron ion plasmas are studied. In view of laboratory experiments, we consider a layer of finite thickness to be able to examine various cases of interest. Different electron and ion populations inside and outside of the complex plasma layer are assumed. It is found that (i) the geometric factor leads to a splitting of the surface dust-density modes in a specific region of wavenumbers and the appearance of a backward surface mode in case of a thin layer (d∼λD); (ii) due to spatial restriction of a complex plasma, the bulk dust-acoustic mode appears to have the lowest cutoff frequency, whose value is strongly dependent on the ratio between the screening length and the thickness of the layer. Observations of the features discussed can be used for complex plasma diagnostics.
Polymer brushes in solvents of variable quality: Molecular dynamics simulations using explicit solvent
Authors: Dimitrov D. I. , Milchev A. , Binder K.
Published: August 2007

The structure and thermodynamic properties of a system of end-grafted flexible polymer chains grafted to a flat substrate and exposed to a solvent of variable quality are studied by molecular dynamics methods. The macromolecules are described by a coarse-grained bead-spring model, and the solvent molecules by pointlike particles, assuming Lennard-Jones-type interactions between pairs of monomers (ϵpp), solvent molecules (ϵss), and solvent monomer (ϵps), respectively. Varying the grafting density σg and some of these energy parameters, we obtain density profiles of solvent particles and monomers, study structural properties of the chain (gyration radius components, bond orientational parameters, etc.), and examine also the profile of the lateral pressure P‖(z), keeping in the simulation the normal pressure P⊥ constant. From these data, the reduction of the surface tension between solvent and wall as a function of the grafting density of the brush has been obtained. Further results include the stretching force on the monomer adjacent to the grafting site and its variation with solvent quality and grafting density, and dynamic characteristics such as mobility profiles and chain relaxation times. Possible phase transitions (vertical phase separation of the solvent versus lateral segregation of the polymers into “clusters,” etc.) are discussed, and a comparison to previous work using implicit solvent models is made. The variation of the brush height and the interfacial width of the transition zone between the pure solvent and the brush agrees qualitatively very well with corresponding experiments.
Scattering of surface acoustic waves by a phononic crystal revealed by heterodyne interferometry
Authors: Kokkonen Kimmo , Kaivola Matti , Benchabane Sarah , Khelif Abdelkrim , Laude Vincent
Published: August 2007

Surface acoustic wave propagation within a two-dimensional phononic band gap structure has been studied using a heterodyne laser interferometer. Acoustic waves are launched by interdigital transducers towards a square lattice of holes etched in a piezoelectric medium. Interferometer measurements performed at frequencies lying below, within, and above the expected band gap frequency range provide direct information of the wave interaction with the phononic crystal, revealing anisotropic scattering into higher diffraction orders depending on the apparent grating pitch at the boundary between the phononic crystal and free surface. Furthermore, the measurements also confirm the existence of an elastic band gap, in accordance with previous electrical measurements and theoretical predictions.