bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulated detection of syndromic classical swine fever on a Finnish pig-breeding farm
Authors: RAULO S. M. , LYYTIKÄINEN T.
Published: February 2007

Although Finland has not experienced a classical swine fever (CSF) epidemic since 1917, the concern about early detection is relevant. The time until detection of CSF on a pig-breeding farm was predicted by simulation, and earlier detection of CSF-infected farms was assessed. Eight to 12 weeks will pass before CSF is detected on a Finnish pig-breeding farm, which resembles detection of the index farm for actual CSF epidemics in Europe. Although notification of suspected CSF on the infected farm accelerates detection the most, interventions aimed at promoting investigations of the general health problem noticed on the farm, or a more comprehensive testing of samples currently arriving from pig farms to the investigating laboratory could shorten detection time by 3 weeks. Results are applicable for further simulation of an event of a CSF epidemic in Finland, and for studying contingency options to promote more rapid detection of infectious diseases of swine not found at present in the country.
Randomization and baseline transmission in vaccine field trials
Authors: STRUCHINER C. J. , HALLORAN M. E.
Published: February 2007

In randomized trials, the treatment assignment mechanism is independent of the outcome of interest and other covariates thought to be relevant in determining this outcome. It also allows, on average, for a balanced distribution of these covariates in the vaccine and placebo groups. Randomization, however, does not guarantee that the estimated effect is an unbiased estimate of the biological effect of interest. We show how exposure to infection can be a confounder even in randomized vaccine field trials. Based on a simple model of the biological efficacy of interest, we extend the arguments on comparability and collapsibility to examine the limits of randomization to control for unmeasured covariates. Estimates from randomized, placebo-controlled Phase III vaccine field trials that differ in baseline transmission are not comparable unless explicit control for baseline transmission is taken into account.
Design and analysis of small-scale transmission experiments with animals
Authors: VELTHUIS A. G. J. , BOUMA A. , KATSMA W. E. A. , NODELIJK G. , DE JONG M. C. M.
Published: February 2007

Interactions between pathogens and hosts at the population level should be considered when studying the effectiveness of control measures for infectious diseases. The advantage of doing transmission experiments compared to field studies is that they offer a controlled environment in which the effect of a single factor can be investigated, while variation due to other factors is minimized. This paper gives an overview of the biological and mathematical aspects, bottlenecks and solutions of developing and executing transmission experiments with animals. Different methods of analysis and different experimental designs are discussed. Final size methods are often used for analysing transmission data, but have never been published in a refereed journal; therefore, they will be described in detail in this paper. We hope that this information is helpful for scientists who are considering performing transmission experiments.
A population-based estimate of the substantial burden of diarrhoeal disease in the United States; FoodNet, 1996–2003
Authors: JONES T. F. , McMILLIAN M. B. , SCALLAN E. , FRENZEN P. D. , CRONQUIST A. B. , THOMAS S. , ANGULO F. J.
Published: February 2007

From 1996 to 2003, four 12-month population-based surveys were performed in FoodNet sites to determine the burden of diarrhoeal disease in the population. Acute diarrhoeal illness (ADI) was defined as [ges ]3 loose stools in 24 hours with impairment of daily activities or duration of diarrhoea >1 day. A total of 52840 interviews were completed. The overall weighted prevalence of ADI in the previous month was 5·1% (95% CI±0·3%), corresponding to 0·6 episodes of ADI per person per year. The average monthly prevalence of ADI was similar in each of the four survey cycles (range 4·5–5·2%). Rates of ADI were highest in those age <5 years. Of those with ADI, 33·8% (95% CI±2·7%) reported vomiting, 19·5% (95% CI±2·1%) visited a medical provider, and 7·8% (95% CI±1·4%) took antibiotics. Rates of ADI were remarkably consistent over time, and demonstrate the substantial burden placed on the health-care system.
Outbreak of cryptosporidiosis at a California waterpark: employee and patron roles and the long road towards prevention
Authors: WHEELER C. , VUGIA D. J. , THOMAS G. , BEACH M. J. , CARNES S. , MAIER T. , GORMAN J. , XIAO L. , ARROWOOD M. J. , GILLISS D. , WERNER S. B.
Published: February 2007

In August–September 2004, a cryptosporidiosis outbreak affected >250 persons who visited a California waterpark. Employees and patrons of the waterpark were affected, and three employees and 16 patrons admitted to going into recreational water while ill with diarrhoea. The median illness onset date for waterpark employees was 8 days earlier than that for patrons. A case-control study determined that getting water in one's mouth on the waterpark's waterslides was associated with illness (adjusted odds ratio 7·4, 95% confidence interval 1·7–32·2). Laboratory studies identified Cryptosporidium oocysts in sand and backwash from the waterslides' filter, and environmental investigations uncovered inadequate water-quality record keeping and a design flaw in one of the filtration systems. Occurring more than a decade after the first reported outbreaks of cryptosporidiosis in swimming pools, this outbreak demonstrates that messages about healthy swimming practices have not been adopted by pool operators and the public.
A family outbreak of Escherichia coli O157 haemorrhagic colitis caused by pork meat salami
Authors: CONEDERA G. , MATTIAZZI E. , RUSSO F. , CHIESA E. , SCORZATO I. , GRANDESSO S. , BESSEGATO A. , FIORAVANTI A. , CAPRIOLI A.
Published: February 2007

A family outbreak of Escherichia coli O157 infection was microbiologically associated with consumption of dry-fermented salami made with pork meat only and produced in a local plant. E. coli O157 strains isolated from a wife and husband, both hospitalized with bloody diarrhoea, and from the salami carried vt1, vt2 and eae genes and shared the same PFGE pattern. The food vehicle implicated in this outbreak is unusual because of both the animal species from which it originates and the fermentation and drying steps of the manufacturing process. This could be the first report of an outbreak associated with a product containing pork meat only. Even though sources of contamination other than pork meat could not be excluded, pork products should not be neglected in E. coli O157 outbreak investigations.
An outbreak of E. coli O157 associated with a swimming pool: an unusual vehicle of transmission
Authors: VERMA A. , BOLTON F. J. , FIEFIELD D. , LAMB P. , WOLOSCHIN E. , SMITH N. , McCANN R.
Published: February 2007

Escherichia coli O157 causes a range of illnesses from mild diarrhoea to haemolytic uraemic syndrome (HUS) which carries a mortality rate of 3·7%. Infection is more common in the under-5s. Between 1995 and 2000, 106 outbreaks of E. coli O157 were reported in England and Wales. Recreational water is well documented as a transmission route for infectious diseases worldwide. In the United Kingdom there have been very few reported outbreaks associated with swimming pools due to the relative susceptibility of E. coli O157 to adequate levels of free chlorine. This report describes the investigation of an outbreak associated with a local leisure centre pool and makes recommendations about the safe management of such facilities.
A community outbreak ofCampylobacter jejuniinfection from a chlorinated public water supply
Authors: RICHARDSON G. , THOMAS D. Rh. , SMITH R. M. M. , NEHAUL L. , RIBEIRO C. D. , BROWN A. G. , SALMON R. L.
Published: February 2007

An outbreak ofCampylobacter jejuniinfection occurred in a South Wales Valleys housing estate. Illness in estate residents was associated with tap water consumption [population attributable risk (PAR) 50%, relative risk (RR) 2·53, 95% confidence interval (CI) 1·9–3·37] and residence in the upper estate (PAR 49%, RR 2·44, 95% CI 1·83–3·24). Amongst upper estate residents, rates of diarrhoeal illness increased with rates of water consumption (OR 18, 95% CI 3·5–92·4 for heaviest consumers, χ2trendP<0·0001). The upper estate received mains water via a covered holding reservoir. A crack in the wall of the holding reservoir was identified. Contamination with surface water from nearby pasture land was the likely cause of this outbreak. Service reservoirs are common in rural communities and need regular maintenance and inspection. The role of water in sporadic cases of campylobacter enteritis may be underestimated.
Long and short vowels in Swiss French: Their production and perception
Authors: GROSJEAN FRANÇOIS , CARRARD SÉVERINE , GODIO CORALIE , GROSJEAN LYSIANE , DOMMERGUES JEAN-YVES
Published: February 2007

Contrary to what is stated in much of the literature which is based in large part on Parisian French, many dialects of French still have long and short vowels (e.g. in Switzerland and Belgium). This study had two aims. The first was to show that Swiss French speakers, as opposed to Parisian French speakers, produce long vowels with durations that are markedly different from those of short vowels. The second aim was to show that, for these two groups, vowel duration has a different impact on word recognition. A production study showed that Swiss French speakers make a clear duration difference between short and long vowels (the latter are more than twice the length of the former on average) whereas the Parisian French do not. In an identification study which used stimuli pronounced in Swiss French, it was shown that words articulated with long vowels created no recognition problem for Swiss French listeners whereas they did so for Parisian French listeners. These results are discussed in terms of models of speech perception and word recognition.
“Contents May Vary”: A Pilot Study of Treatment Histories of OCD Patients
Authors: Stobie Blake , Taylor Tracey , Quigley Alexandra , Ewing Sandra , Salkovskis Paul M.
Published: February 2007

Definitions of treatment failure and the labelling of patients as non-responsive typically require treatments to have been offered and failed. For pharmacological treatments, treatment quality is relatively easy to define; this is much more difficult with psychological treatments. This study examined patient recollections of previous therapy for obsessive compulsive disorder (OCD). A Treatment History Questionnaire was administered to a sample of 57 apparently treatment refractory OCD patients from a specialist national OCD treatment unit and a national charity for OCD sufferers. On average, respondents reported an 8$\frac{1}{2}$ year wait between the obsessional symptoms interfering significantly with their lives and being diagnosed. Forty-three percent recalled having received either cognitive behaviour therapy (CBT) or behaviour therapy as the first treatment; 31% of the group did not know what type of therapy they had received. The components of therapy that respondents recalled were analysed and contrasted with minimal therapy criteria. These criteria appear not to have been met in most patients who understood that they had received “CBT”. The implications of this study for assessment of treatment integrity and the classification of patients as “treatment resistant” are discussed.
Removing redundant arguments automatically
Authors: ALPUENTE M. , ESCOBAR S. , LUCAS S.
Published: February 2007

The application of automatic transformation processes during the formal development and optimization of programs can introduce encumbrances in the generated code that programmers usually (or presumably) do not write. An example is the introduction of redundant arguments in the functions defined in the program. Redundancy of a parameter means that replacing it by any expression does not change the result. In this work, we provide methods for the analysis and elimination of redundant arguments in term rewriting systems as a model for the programs that can be written in more sophisticated languages. On the basis of the uselessness of redundant arguments, we also propose an erasure procedure which may avoid wasteful computations while still preserving the semantics (under ascertained conditions). A prototype implementation of these methods has been undertaken, which demonstrates the practicality of our approach.
Demand analysis with partial predicates
Authors: MARIÑO JULIO , HERRANZ ÁNGEL , MORENO-NAVARRO JUAN JOSÉ
Published: February 2007

To alleviate the inefficiencies caused by the interaction of the logic and functional sides, integrated languages may take advantage ofdemandinformation, i.e. knowing in advance which computations are needed and, to which extent, in a particular context. This work studiesdemand analysis– which is closely related tobackwards strictness analysis– in a semantic framework ofpartial predicates, which in turn are constructive realizations of ideals in a domain. This will allow us to give a concise, unified presentation of demand analysis, to relate it to other analyses based on abstract interpretation or strictness logics, some hints for the implementation, and, more important, to prove the soundness of our analysis based ondemand equations. There are also some innovative results. One of them is that a set constraint-based analysis has been derived in a stepwise manner using ideas taken from the area of program transformation. The other one is the possibility of using program transformation itself to perform the analysis, specially in those domains of properties where algorithms based on constraint solving are too weak.
Evaluating the influence of land cover on seasonal water budgets using Next Generation Radar (NEXRAD) rainfall and streamflow data
Authors: Jayawickreme Dushmantha H. , Hyndman David W.
Published: February 2007

Accurate estimates of fluxes between different components of the hydrosphere are needed for water resources management at the watershed scale. Runoff and evapotranspiration are critical fluxes that are heavily influenced by land cover characteristics; however, our understanding of the interactions between land cover attributes and these fluid fluxes is generally limited by inadequate regional data to capture variations in both climatic conditions and landscape characteristics. This limitation is largely avoided by integrating data from Next Generation Radar (NEXRAD) precipitation systems with widely available streamflow, land cover, and other Geographic Information System data sets. Such data integration facilitates development of rapid and reliable methods for estimating hydrologic fluxes at desirable temporal and spatial scales. In this study, we calculate ratios of streamflow to NEXRAD rainfall over the peak growing season for 40 watersheds across Michigan and use these to evaluate the landscape factors that influence groundwater recharge rates. Results indicate that ratios of streamflow and baseflow to rainfall are strongly influenced by land cover attributes. Stream baseflow analyses indicate that approximately 5% of the July to September rainfall becomes recharge in high‐intensity agriculture (>70%) watersheds compared to 15% in moderate‐intensity agriculture (<50%) watersheds across our study region during the same period. A strong negative correlation was also found between intensive agriculture and the streamflow:rainfall ratio during summer and early fall periods.
Optimization of concentration control by evolution strategies: Formulation, application, and assessment of remedial solutions
Authors: Bayer Peter , Finkel Michael
Published: February 2007

The uniqueness and mathematical complexity of typical groundwater remediation or control problems involving numerical models necessitate appropriate solvers that find optimal solutions reliably and within reasonable computational time. The aim of this paper is to introduce an innovative evolutionary algorithm, the evolution strategies with covariance matrix adaptation and rank μ update (CMA‐ES), used as an external solver in combination with groundwater transport models. A broad range of hypothetical pump‐and‐treat design problems is set up to derive recommendations for a robust CMA‐ES configuration. One‐ and five‐well cases are distinguished, for which both extraction rates and well positions have to be optimized in order to partly capture a contaminant plume. Intrinsic natural attenuation of the contaminant that emanates from a continuous source is considered. During this study, it is revealed that when pumping rates are minimized, well positions should be focused close to the source. In contrast, when contaminant mass extraction is minimized, positions distant from the source close to the plume fringes prove to be preferable.
Inverse estimates of the oceanic sources and sinks of natural CO2 and the implied oceanic carbon transport
Authors: Mikaloff Fletcher S. E. , Gruber N. , Jacobson A. R. , Gloor M. , Doney S. C. , Dutkiewicz S. , Gerber M. , Follows M. , Joos F. , Lindsay K. , Menemenlis D. , Mouchet A. , Müller S. A. , Sarmiento J. L.
Published: February 2007

We use an inverse method to estimate the global‐scale pattern of the air‐sea flux of natural CO2, i.e., the component of the CO2 flux due to the natural carbon cycle that already existed in preindustrial times, on the basis of ocean interior observations of dissolved inorganic carbon (DIC) and other tracers, from which we estimate ΔCgasex, i.e., the component of the observed DIC that is due to the gas exchange of natural CO2. We employ a suite of 10 different Ocean General Circulation Models (OGCMs) to quantify the error arising from uncertainties in the modeled transport required to link the interior ocean observations to the surface fluxes. The results from the contributing OGCMs are weighted using a model skill score based on a comparison of each model's simulated natural radiocarbon with observations. We find a pattern of air‐sea flux of natural CO2 characterized by outgassing in the Southern Ocean between 44°S and 59°S, vigorous uptake at midlatitudes of both hemispheres, and strong outgassing in the tropics. In the Northern Hemisphere and the tropics, the inverse estimates generally agree closely with the natural CO2 flux results from forward simulations of coupled OGCM‐biogeochemistry models undertaken as part of the second phase of the Ocean Carbon Model Intercomparison Project (OCMIP‐2). The OCMIP‐2 simulations find far less air‐sea exchange than the inversion south of 20°S, but more recent forward OGCM studies are in better agreement with the inverse estimates in the Southern Hemisphere. The strong source and sink pattern south of 20°S was not apparent in an earlier inversion study, because the choice of region boundaries led to a partial cancellation of the sources and sinks. We show that the inversely estimated flux pattern is clearly traceable to gradients in the observed ΔCgasex, and that it is relatively insensitive to the choice of OGCM or potential biases in ΔCgasex. Our inverse estimates imply a southward interhemispheric transport of 0.31 ± 0.02 Pg C yr−1, most of which occurs in the Atlantic. This is considerably smaller than the 1 Pg C yr−1 of Northern Hemisphere uptake that has been inferred from atmospheric CO2 observations during the 1980s and 1990s, which supports the hypothesis of a Northern Hemisphere terrestrial sink.
Micro pulse lidar observation of high altitude aerosol layers at Visakhapatnam located on the east coast of India
Authors: Niranjan K. , Madhavan B. L. , Sreekanth V.
Published: February 2007

Aerosol back scatter profiles obtained using a micro pulse lidar at Visakhapatnam, a station located on the east coast of peninsular India show certain high altitude aerosol layers during the months of March/April 2005, 2006. Co‐located aerosol optical depth measurements show an increase in AOD by 0.05 to 0.25 during the event when the layers were observed. The prevailing meteorology does not indicate any possible local entrainment of aerosol leading to the formation of elevated layers due to boundary layer dynamics. The 7 day back trajectory analysis shows that the possible origin of the layers could be from Arabia in 60% of the cases while it is from Indian sub‐continent during the rest of the events. When the air mass flow is from the Indian sub‐continent, there is a proportional increase in MODIS derived aerosol column fine mode fraction though it is not observed at the surface level. During the events when air mass flow is from Arabia, such an increase in column fine mode fraction was not observed but the angstrom size index which is a measure of the aerosol size distribution was low indicating that the elevated layers of Arabian origin could contain significant fraction of dust aerosol.
TRAMS: A new dynamic cloud model for Titan's methane clouds
Authors: Barth Erika L. , Rafkin Scot C. R.
Published: February 2007

Convective clouds on Titan may play an important role in climate dynamics, atmospheric chemistry, and the overall volatile cycle. To study the formation and evolution of these clouds, we have developed the Titan Regional Atmospheric Modeling System (TRAMS). TRAMS is a three‐dimensional, time‐dependent, coupled fully compressible dynamic and microphysical model capable of simulating methane and ethane clouds in Titan's atmosphere. In initial model tests over a two‐dimensional domain, a warm bubble or random temperature perturbations trigger a parcel of air to rise. For an initial methane profile with a 60% surface humidity, convection occurs for positive temperature perturbations of 1 K or greater. Cloud tops are between 25 and 35 km, consistent with observations of the south polar clouds. For a drier methane environment in the lower atmosphere, characteristic of the Huygens landing site, convection does not occur, but a layer of stratiform clouds is able to form at altitudes around 10 km.
Airborne measurements of HCHO and HCOOH during the New England Air Quality Study 2004 using a pulsed quantum cascade laser spectrometer
Authors: Herndon Scott C. , Zahniser Mark S. , Nelson David D. , Shorter Joanne , McManus J. Barry , Jiménez Rodrigo , Warneke Carsten , de Gouw Joost A.
Published: February 2007

Atmospheric mixing ratios of formaldehyde and formic acid have been measured from the NOAA WP‐3 aircraft during the New England Air Quality Study (NEAQS) of July and August 2004 using a newly developed quantum cascade laser (QCL) spectrometer operating at a wavelength of 5.6 μm. The laser operates in pulsed mode with thermoelectric cooling. The detection is based on direct absorption in a compact 76‐m multiple pass absorption cell. The laser is swept over a 0.5 cm−1 spectral region containing multiple lines of both HCHO and HCOOH. Absolute concentrations are retrieved by simultaneous spectral fitting routines with a detection limit (2σ) for HCHO of 0.3 parts in 109 (ppbv) with an averaging time of 60 s under stable flight conditions. HCHO mixing ratios in the range from 0.3 to 5 ppb were encountered during flight conditions. Some of the highest mixing ratios of HCHO were observed over heavily vegetated areas of Florida during the test flights where the ratios of HCHO to methacrolein and methyl vinyl ketone, measured by proton transfer mass spectroscopy, are consistent with formaldehyde production by isoprene oxidation. The highest mixing ratios of HCOOH, up to 10 ppbv, were observed in an aged forest fire plume encountered over northern Canada, in which ratios of HCOOH/CO are greater than previous observations, while the ratios of HCHO/CO are less than previous reports from forest fire plumes. Observations of HCHO/CO and HCOOH/CO in urban plumes are indicative of a mixture of sources from direct emissions and secondary oxidation of anthropogenic and biogenic hydrocarbons. The ability to measure both HCHO and HCOOH simultaneously is of value in assessing the oxidation mechanisms of atmospheric hydrocarbons and secondary organic aerosol formation and oxidation.
Perceptions, data, and river management: Lessons from the Mekong River
Authors: Campbell Ian C.
Published: February 2007

Workshops to identify transboundary and basin‐wide environmental issues and a diagnostic study by consultants identified priority environmental concerns of resource managers in the lower Mekong River basin. The issues identified, in priority order, were water quality, reduction in dry season flows, sedimentation, fisheries decline, wetland degradation, and flooding. An analysis of the available data found no evidence that water quality was poor except in the delta, where nutrient levels were high and increasing. Dry season flows have not decreased, and in the immediate future they are more likely to increase. Suspended sediment levels in the river are not high, and there is no indication that sediment loads are substantially increasing. Fish catch per unit effort has declined over the past decades, as have catches of large fish, but total fish catch has increased. Flooding does not appear to have increased in frequency or extent. There is no reliable quantitative information available on changes in wetland extent or condition, although it is reasonable to assume that both have declined. Reasons for the mismatch between perceptions and the data may include a failure by management agencies to analyze and publish data and provide adequate responses to issues raised in the popular press. This results from a lack of capacity in many government agencies and the Mekong River Commission, where there are high staff turnover rates and a dependence on short‐term experts with limited experience in the basin.
On the cause of the electrical activity of superfluid helium upon excitation of a second sound wave and normal-component velocity oscillations in it
Authors: Pashitskii E. A. , Ryabchenko S. M.
Published: February 2007

An explanation is proposed for a new, previously unknown effect that was recently observed experimentally: the appearance of an electric field in superfluid helium during the propagation of second sound waves or in the presence of induced oscillations of the velocity of the normal component. It is shown that the electrical potential that arises upon excitation of second sound on account of the polarization of the He atoms under acceleration because of the strong mass difference of the electrons and nuclei (the inertial effect) is proportional to the total entropy of the HeII. The analysis makes use of the idea that superfluid component of HeII is a superposition of two oppositely charged coherent Bose condensates, electronic and nuclear, coupled strongly by the Coulomb interaction. These condensates consist, respectively, of the zero-spin helium nuclei and of the strongly correlated pairs of electrons found in the singlet state and forming the completely filled 1s shell of the helium atoms. It is taken into account that, because of the interatomic interaction, the effective coherent condensate constituting the microscopic basis of the superfluid component of HeII contains intense pair and higher multiparticle condensates in addition to the “depleted” single-particle Bose–Einstein condensate. Because of this, the entropy of the superfluid quantum liquid He4 has a constant, temperature-independent contribution. It follows from the analysis that the amplitude ratio of the temperature and potential oscillations in the second sound wave, which was obtained by A. S. Rybalko, Fiz. Nizk. Temp. 30, 1321 (2004) [Low Temp. Phys. 30, 994 (2004)], can be used to determine the entropy of HeII. The appearance of electrical activity upon excitation of induced oscillations of the normal-component velocity arising as a result of torsional oscillations of the vessel containing the HeII, which was observed by A. S. Rybalko and S. P. Rubets, Fiz. Nizk. Temp. 31, 820 (2005) [Low Temp. Phys. 31, 623 (2005)], is explained qualitatively by a correction to the chemical potential quadratic in the velocity difference of the superfluid and normal components of HeII. It is shown, however, that this contribution, like the contribution due to centripetal acceleration discussed by Rybalko and Rubtsa (op. cit.), does not agree quantitatively with experiment.
Electrotransport and Hall effect in Y1−xPrxBa2Cu3O7−y films
Authors: Solovjov A. L. , Dmitriev V. M.
Published: February 2007

The longitudinal and transverse resistivities ρxx(T) and ρxy(T), respectively, and the Hall effect are investigated in Y1−xPrxCu3O7−y films with x≈0.1. Despite the low value of Tc≈78K, the temperature dependence ρxx(T) is linear over a wide temperature range. At the same time, ρxy(T) has a pronounced semiconductor character. The measured Hall coefficient has a value RH≈1.3, which is 3 times less than in a YBa2Cu3O7−y film with a similar Tc. The interaction constant λ≈1.26, on the contrary, is ≈3.5 times greater. It is shown that these and other features revealed can be explained by charge-carrier localization effects in Y1−xPrxCu3O7−y systems.
On the influence of the internal structure of the atom on Bose–Einstein condensationin an ideal gas of hydrogenlike atoms
Authors: Slyusarenko Yu. V. , Sotnikov A. G.
Published: February 2007

The features of Bose condensation in an equilibrium ideal gas consisting of two types of charged fermions and their bound states—hydrogenlike atoms—in the presence of equilibrium between the photons and matter are investigated. It is shown that under such conditions the main influence on the Bose–Einstein condensation comes from the existence of levels concerned with the hyperfine splitting of the ground state of the hydrogenlike atom. The critical temperature and condensate density as functions of magnetic field are determined by considering effects due to the additional splitting of the levels of the hyperfine structure of the ground state in an external uniform static magnetic field (the Zeeman and Paschen–Back effects). It is found that under conditions of total statistical equilibrium in the system, a condensate is formed only by atoms found in the lowest energy state. It is shown that in the absence of equilibrium between radiation and matter, in the region of ultralow temperatures and low densities, the system can be treated as a multicomponent ideal gas of hydrogenlike atoms. The existence of a hierarchy of individual transition temperatures of each of the samples to the state with Bose–Einstein condensation is established. Expressions are found for the critical temperatures and number densities of particles in the condensate for each of the system components.
Magnetic and transport properties driven by lattice strain in La0.7Ca0.3MnO3∕BaTiO3 and La0.7Sr0.3MnO3∕BaTiO3 bilayer films
Authors: Prokhorov V. G. , Komashko V. A. , Kaminsky G. G. , Yu K. K. , Jun S. J. , Park S. Y. , Park J. S. , Lee Y. P. , Svetchnikov V. L.
Published: February 2007

The microstructure and the magnetic and transport properties of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 films deposited on a BaTiO3 layer (LCMO/BTO and LSMO/BTO) and on a LaAlO3(001) single crystal (LCMO/LAO and LSMO/LAO) by rf-magnetron sputtering using “soft” (or powder) targets are investigated. The films grown on BTO demonstrate biaxial tensile in-plane and compressive out-of-plane strains, while the films grown on LAO, in contrast, manifest compressive in-plane and tensile out-of-plane strains. The films with biaxial tensile in-plane lattice strain undergo the magnetic transition at a higher temperature than that for the biaxial compressive case. This argues that the Mn–O–Mn bond-angle variation, controlled by the lattice strain, plays a more important role in the formation of the spin ordering than the attendant modification of the Mn–O bond length. It is shown that the magnetic inhomogeneity, expressed by a significant difference between the field-cooled and zero-field-cooled temperature-dependent magnetization, has a metallurgical rather than an electronic nature, and is controlled by the crystal lattice distortion and the microstructure defects. The observed enhancement of the magnetoresistance effect in the LSMO/BTO bilayer at room temperature makes this object greatly beneficial in the development of new hybrid ferromagnetic/ferroelectric devices.
Influence of exchange properties of the interface on the reflection of surface spin waves from a uniaxial multilayer ferromagnet
Authors: Reshetnyak S. A.
Published: February 2007

The coefficient of reflection of surface spin waves from a multilayer ferromagnetic structure with periodically modulated exchange interaction parameter, uniaxial magnetic anisotropy parameter, and saturation magnetization is calculated for a nonideal exchange between layers. The influence of the wave frequency, external uniform static magnetic field, and surface exchange parameter at the interface on the coefficient of reflection of surface spin waves from a multilayer ferromagnet is investigated.
X-ray studies of the effects of intercalation of C60 fullerite crystals by Ne atoms
Authors: Legchenkova I. V. , Prokhvatilov A. I. , Stetsenko Yu. E. , Strzhemechny M. A. , Yagotintsev K. A.
Published: February 2007

The process of intercalation of polycrystalline C60 fullerite by Ne atoms at room temperature and a gas pressure of 1atm and the temperature dependence of the lattice parameter in the temperature interval 30–293K are investigated by an x-ray method. It is established that the occupation of the octahedral interstitial cavities of the fcc lattice of C60 by neon is accompanied by a noticeable increase in the lattice parameter and volume. These changes as a function of saturation time are described satisfactorily by an exponential law. The intercalation time constant τ is determined to be 179±24h, which is almost two orders of magnitude longer than the time τ obtained at increased pressure. The maximal saturation of fullerite by neon reaches nearly (48±3)%. The presence of a neon impurity in the C60 lattice has practically no influence on the intensity of the x-ray scattering, but as a consequence of the nonuniformity of the impurity distribution in the first stage of intercalation it appreciably alters the width of the reflections. It is determined as a result of energy calculations that the most probable path of migration of the Ne atoms in fullerite crystals during the intercalation is via the octa–tetra–octahedral cavities. In the region of the orientational phase transition significant hysteresis is observed in the temperature dependence of the lattice parameters. The results are discussed and compared with published data.
Measurement of the shear strength of pure tungsten during one-dimensional shock loading
Authors: Millett J. C. F. , Gray G. T. , Bourne N. K.
Published: February 2007

The behavior of a pure tungsten under conditions of one-dimensional shock loading has been monitored using Manganin stress gauges, in longitudinal and lateral orientations. The shock induced equation of state, in terms of stress and particle velocity (from the longitudinal gauges), shows that the Hugoniot of this pure material agrees with the results of previous workers, both in pure tungsten and tungsten alloys. Lateral stress traces show an increase in stress (and hence decrease in shear strength) behind the shock front, in a manner similar to that observed in a tungsten heavy alloy and pure tantalum. It has been proposed that this is due to the high Peierl’s stress initially restricting dislocation generation, followed by a later increased in dislocation density. However, the brittle manner in which tungsten fails under shock loading indicates that other mechanisms are in operation. It has been suggested that the shock front nucleates cracking, which progressively grows behind it, which in combination with the proposed dislocation mechanisms reduces shear strength. Finally, we show that the variation of shear strength with shock stress is in agreement with a number of other workers until a stress level of ∼10GPa, where it is significantly higher. We have suggested that this is due to the higher strength of pure tungsten compared to the liquid phase sintered materials studied previously.
A nonmagnetic spintronic adder
Authors: Sarkar Angik , Bhattacharyya T. K.
Published: February 2007

A one-bit adder based on electron spin has been presented in this paper. The adder can be implemented in ballistic nanowires with separate circuits for sum and carry. Two implementations of the carry circuit have been presented. The choice of the carry circuit is dependent on the spin injection device. The spin injection and detection schemes have also been discussed. Though magnetic field may be required for spin injection, the operation of the adder does not require any magnetic field or magnetic materials.
Composition effects on the early-stage oxidation kinetics of (001) Cu–Au alloys
Authors: Zhou G.-W. , Eastman J. A. , Birtcher R. C. , Baldo P. M. , Pearson J. E. , Thompson L. J. , Wang L. , Yang J. C.
Published: February 2007

An in situ environmental transmission electron microscopy study of the nucleation and growth of oxide islands during the early-stage oxidation of (001) Cu1−xAux alloys (x⩽38at.%) was undertaken in order to investigate the effects of alloying on oxide island nucleation behavior and growth kinetics. The kinetic data reveal that Au enhances the nucleation density of oxide islands and suppresses their growth rate. Our results provide insight into reasons for the decreased passivation properties of Cu when alloyed with Au.
Reaction analysis of initial oxidation of silicon by UV-light-excited ozone and the application to rapid and uniform SiO2 film growth
Authors: Tosaka Aki , Nonaka Hidehiko , Ichimura Shingo , Nishiguchi Tetsuya
Published: February 2007

UV-light-excited O3 prepared by irradiation of nearly 100% pure O3 with a KrF excimer laser (λ=248nm, irradiated area=30×10mm2) was utilized for low-temperature Si oxidation. The initial oxidation rate was determined, and the activation energy was shown to be almost zero (0.049eV). To clarify the optimum oxidation conditions, the dependence of the SiO2 film growth rate on the total photon number and the photon density was investigated. The evolution of O3 density after UV-light irradiation was experimentally measured, and the O(D1) density change is discussed. O(D1) density changes are successfully explained by using a second-order reaction model, indicating that a pulse supply of oxygen atoms is essential in the initial oxidation process. The uniform oxidation of 8in. Si wafer has been carried out using a wafer-transfer type chamber by irradiating the wafer with KrF excimer laser light expanded linearly to the wafer width by a concave lens.
Interface effects in ferroelectric bilayers and heterostructures
Authors: Misirlioglu I. B. , Akcay G. , Zhong S. , Alpay S. P.
Published: February 2007

We study the role of interlayer interfaces on the polarization response of ferroelectric-paraelectric bilayers using a nonlinear thermodynamic model. We carry out a numerical analysis for prototypical BaTiO3–SrTiO3 bilayers ranging from 40to800nm total thickness as a function of SrTiO3 fraction. There exists a critical fraction of SrTiO3 at which the polarization is suppressed due to the depolarization field arising from the interlayer coupling and a large dielectric response is predicted. It is shown that this critical fraction decreases with decreasing total bilayer thickness, indicating that the interfacial effects are more pronounced in thinner bilayers.
Modeling microscopic swimmers at low Reynolds number
Authors: Earl David J. , Pooley C. M. , Ryder J. F. , Bredberg Irene , Yeomans J. M.
Published: February 2007

The authors employ three numerical methods to explore the motion of low Reynolds number swimmers, modeling the hydrodynamic interactions by means of the Oseen tensor approximation, lattice Boltzmann simulations, and multiparticle collision dynamics. By applying the methods to a three bead linear swimmer, for which exact results are known, the authors are able to compare and assess the effectiveness of the different approaches. They then propose a new class of low Reynolds number swimmers, generalized three bead swimmers that can change both the length of their arms and the angle between them. Hence they suggest a design for a microstructure capable of moving in three dimensions. They discuss multiple bead, linear microstructures and show that they are highly efficient swimmers. They then turn to consider the swimming motion of elastic filaments. Using multiparticle collision dynamics the authors show that a driven filament behaves in a qualitatively similar way to the micron-scale swimming device recently demonstrated by Dreyfus et al. [Nature (London) 437, 862 (2005)].
Cross sections and oscillator strengths for electron-impact excitation of the ÃB11 electronic state of water
Authors: Thorn P. A. , Brunger M. J. , Teubner P. J. O. , Diakomichalis N. , Maddern T. , Bolorizadeh M. A. , Newell W. R. , Kato H. , Hoshino M. , Tanaka H. , Cho H. , Kim Y.-K.
Published: February 2007

The authors report absolute differential and integral cross section measurements for electron-impact excitation of the ÃB11 electronic state of water. This is an important channel for the production of the OH (X̃Π2) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20–200eV, while the angular range of the differential cross section data is 3.5°–90°. This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment.
Role of a pore network for band energy configuration in mesostructured materials
Authors: Filho Djalma Albuquerque Barros
Published: February 2007

This work is focused on the charge transfer process of mesoporous amorphous titania to build a band energy diagram by spectro- and photoelectrochemical characterization. The surface topology of mesoporous titania is completely different from a nanocrystalline film, as transmission electron microscopy confirmed. Mesoporous titania consists of an amorphous framework of titania walls where cylindrical pores are ordered in a hexagonal arrangement. Two features have been attributed to the surface topology of mesoporous titania during electrochemical characterization: (i) dominance of capacitive surface-confined electrochemical processes due to the huge surface area of amorphous titania walls showing a metallic behavior; (ii) a band energy denominated “mesoscopic” band which intermediated charge transfer from the substrate into the surface states and defect sites (Ti4+∕Ti3+) resulting in a cathodic current when mesoporous titania acted as photovoltaic solar cells. The spectroelectrochemical characterization confirmed that mesostructured titania has a different band energy diagram determined by analysis of the filling of empty electronic states during a lithium intercalation process. A surface model for mesostructured materials is introduced in this work where quantum sized particles are surrounded by hollow titania particles, modifying their optical and electrical properties. These hollow particles contain surface states and defect sites (Ti4+∕Ti3+) ordered in a hexagonal arrangement due to a porous network of mesoporous titania and, consequently, a mesoscopic band appears. This conception of band energy can give a different insight to build functional devices like solar cells, electrochromical windows and batteries where mesostructured materials can act as a cathode transporting holes through their pore network.
Optical limiting behavior of zinc phthalocyanines in polymeric matrix
Authors: Ostuni R. , Larciprete M. C. , Leahu G. , Belardini A. , Sibilia C. , Bertolotti M.
Published: February 2007

Phthalocyanines are promising molecules which present very attractive properties for nonlinear optical applications of both second and third orders. Different solutions of zinc phthalocyanine in toluene at increasing concentration were investigated by spectroscopic analysis in order to get the best conditions for the realization of films in poly(methyl methacrylate). Some films of zinc phthalocyanine in polymeric matrix were realized and their nonlinear optical behavior was characterized. The ratio by weight of the compound to the host polymer was varied between 0.004% and 0.15%. In this range all samples show a low degree of aggregation. The nonlinear optical behavior of the films was evaluated by measuring nonlinear transmission. The measurements of nonlinear transmission were carried out at 532nm using a nanosecond Nd:YAG laser followed by an optical parametric oscillator, and a nonlinear response was observed for the two highest concentrations (0.083% and 0.15%). Finally, the nonlinear absorption coefficient β was retrieved by fitting experimental data and found to be 29 and 43cm∕GW, respectively.
Enhanced thermal stability in organic light-emitting diodes through nanocomposite buffer layers at the anode/organic interface
Authors: Grozea D. , Turak A. , Yuan Y. , Han S. , Lu Z. H. , Kim W. Y.
Published: February 2007

The effect of doped buffer layers at the anode/organic interface in small molecule organic light-emitting diodes was investigated. Appropriate doping of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and Cu-phthalacyanine (CuPc) layers using LiF or C60 molecules leads to improved interfacial morphology and thermal stability for both standard indium tin oxide or metals anodes, such as Au and Ag. Graded interfaces remain stable at temperatures well above the hole transport layer (i.e., NPB) glass transition temperature.
Ideal basis sets for the Dirac Coulomb problem: Eigenvalue bounds and convergence proofs
Authors: Munger Charles Thomas
Published: February 2007

Basis sets are developed for the Dirac Coulomb Hamiltonian for which the resulting numerical eigenvalues and eigenfunctions are proved mathematically to have all the following properties: to converge to the exact eigenfunctions and eigenvalues, with necessary and sufficient conditions for convergence being known; to have neither missing nor spurious states; to maintain the Coulomb symmetries between eigenvalues and eigenfunctions of the opposite sign of the Dirac quantum number κ; to have positive eigenvalues bounded from below by the corresponding exact eigenvalues; and to have negative eigenvalues bounded from above by −mc2. All these properties are maintained using functions that may be analytic or nonanalytic (e.g., Slater functions or splines); that match the noninteger power dependence of the exact eigenfunctions at the origin, or that do not; or that extend to +∞ as do the exact eigenfunctions, or that vanish outside a cavity of large radius R (convergence then occurring after a second limit, R→∞). The same basis sets can be used without modification for potentials other than the Coulomb, such as the potential of a finite distribution of nuclear charge, or a screened Coulomb potential; the error in a numerical eigenvalue is shown to be second order in the departure of the potential from the Coulomb. In certain bases of Sturmian functions the numerical eigenvalues can be related to the zeros of the Pollaczek polynomials.