bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucosinolate assessment in Brassica oleracea leaves by near-infrared spectroscopy
Authors: FONT R. , DEL RÍO-CELESTINO M. , ROSA E. , AIRES A. , DE HARO-BAILÓN A.
Published: June 2005

Glucosinolates and their hydrolysis products are of great concern because they are responsible for many of both the beneficial and harmful properties of glucosinolate-containing plants. Cabbage (Brassica oleracea L.) is a species highly consumed as a leaf vegetable in many countries showing high qualitative and quantitative differences in glucosinolate composition among cultivars. The standard analytical techniques for determining glucosinolate composition using conventional methods lead to high costs, labour input and delays, all of which affect both the availability of data and the taking of swift decisions. In contrast, near-infrared spectroscopy (NIRS) has emerged as a rapid and cost-effective technique of analysis for many agro-food products. In this work we test the potential of NIRS for screening the total glucosinolates (t-GSL), gluconapin (GNA), gluconasturtiin (GNAST) and neoglucobrassicin (NGBS) contents of cabbage leaf cultivars coming from Portugal and Spain. NIRS calibrations resulted in coefficients of determination and standard deviation to standard error of cross-validation ratio of 0·83 and 2·38 for t-GSL; 0·70 and 1·85 for GNA; 0·62 and 1·63 for GNAST; and 0·60 and 1·58 for NGBS, respectively. An examination of the loadings of the equation for t-GSL suggested that O-H groups of water, C-H combinations of the methylene group and also N-H groups of amides were the molecular associations most strongly used in modelling total glucosinolates. It was concluded that NIRS shows a high potential as an analytical method for total and individual glucosinolate routine analysis in cabbage.
The possible use of n-alkanes, long-chain fatty alcohols and long-chain fatty acids as markers in studies of the botanical composition of the diet of free-ranging herbivores
Authors: ALI H. A. M. , MAYES R. W. , HECTOR B. L. , VERMA A. K. , ØRSKOV E. R.
Published: June 2005

Few methods exist for estimating quantitatively the diet composition of free-ranging herbivores. The current study examined whether long-chain fatty alcohols (alcohols) or long-chain fatty acids (acids) could be used along with n-alkanes to allow reliable diet composition estimates to be made in herbivores consuming complex diets. Twelve Scottish Blackface wether sheep housed in metabolism crates were fed four different mixtures of three plant species (three animals per mixture) for a seven-period experiment. Concentrations of cuticular wax n-alkanes, alcohols and acids were estimated in samples of individual plant species, and the faeces from animals that consumed mixtures of these species. These concentrations were then used to calculate the dietary proportions of each species by a least-squares optimization procedure. To explore the differences between the estimation methods (individual markers and their combinations), the mean squares of errors (EMS) between the actual and predicted proportions of plant species were calculated.

In three out of the four mixtures, alcohols had the lowest discrepancies (lowest EMS values), followed by n-alkanes and then acids. Acids yielded the lowest discrepancy in one mixture and the highest in the others.

It is concluded that, for this particular set of mixtures, alcohols had great potential to estimate composition of complex diets. However, the estimation using acids was less good and n-alkanes were of intermediate potential. Estimation from the combination of the three marker classes was always better than using the poorest individual marker.
The zoom-on-possessee construction in Kam (Dong): the anatomy of a new construction type
Authors: GERNER MATTHIAS
Published: June 2005

Kam, a Kadai language spoken in Guizhou province (People's Republic of China), has a family of intransitive possessive constructions with the word order ‘Possessor–Verb–Possessee’. (The basic word order in Kam is SV and AVO.) While two recent papers have featured this unique construction type for an array of other Southeast Asian languages, they fail to acknowledge its distinct semantic value in contrast to the related construction type ‘Possessee–Possessor–Verb’. The former construction type displays a so-called ‘zoom-effect’: the possessor is predicated IN, AT or THROUGH his/her/its possessee; the predication zooms from the possessor on his/her/its possessee. The latter construction, in contrast, views the possessee as an entity separated from its possessor, and the predicate as applying solely to the possessee. After illustrating the ‘zoom-effect’ for a representative sample of Kam constructions, I demonstrate that ‘zoom-effects’ do not merely exist when the possessee–possessor compound has the zero-role (=intransitive subject) as above, but also when it assumes other semantic roles (e.g. patient, force, etc.). A general definition of this construction type, called ‘zoom-on-possessee construction’, is proposed; it enables us to unify and account for an array of hitherto disparate construction types that run in the literature under labels such as ‘proprioceptive state expressions’, ‘body part locative constructions’, ‘dative of affect’, etc. Furthermore, I discuss in some detail whether zoom-on-possessee constructions are better accounted for within a multi-stratal or a mono-stratal framework and, finally, whether the concept of noun-incorporation has any relevance.
Hungarian in focus
Authors: KENESEI ISTVÁN
Published: June 2005

Katalin É. Kiss,The syntax of Hungarian (Cambridge Syntax Guides). Cambridge: Cambridge University Press, 2002. Pp. xii+278.

László Varga,Intonation and stress: evidence from Hungarian. Houndmills: Palgrave MacMillan, 2002. Pp. xvii+229.

László Hunyadi,Hungarian sentence prosody and universal grammar. Frankfurt am Main: Peter Lang, 2002. Pp. 328.

It seems it's harvest time in Hungarian linguistics: a number of respectable publishers have in recent years put out books on various aspects of the Hungarian language by authors working in or outside Hungary. In addition to the monographs under review here, one can mention Szabolcsi (1997), Kenesei, Vago & Fenyvesi (1998), Koopman & Szabolcsi (2000) or Siptár & Törkenczy (2000).
Density dependence and overdispersion in the transmission of helminth parasites
Authors: CHURCHER T. S. , FERGUSON N. M. , BASÁÑEZ M.-G.
Published: June 2005

The influence of density-dependent processes on the transmission of parasitic helminths is determined by both the severity of the regulatory constraints and the degree of parasite overdispersion among the host population. We investigate how overdispersed parasite distributions among humans influence transmission levels in both directly- and indirectly-transmitted nematodes (Ascaris lumbricoides and Onchocerca volvulus). While past work has assumed, for simplicity, that density dependence acts on the average worm load, here we model density-dependence as acting on individual parasite burdens before averaging across hosts. A composite parameter, which we call the effective transmission contribution, is devised to measure the number of transmission stages contributed by a given worm burden after incorporating overdispersion in adult worm mating probabilities and other density-dependent mechanisms. Results indicate that the more overdispersed the parasite population, the greater the effect of density dependence upon its transmission dynamics. Strong regulation and parasite overdispersion make the relationship between mean worm burden and its effective contribution to transmission highly non-linear. Consequently, lowering the intensity of infection in a host population using chemotherapy may produce only a small decline in transmission (relative to its initial endemic level). Our analysis indicates that when parasite burden is low, intermediate levels of parasite clustering maximize transmission. Implications are discussed in relation to existing control programmes and the spread of anthelmintic resistance.
Asymptomatic giardiasis and growth in young children; a longitudinal study in Salvador, Brazil
Authors: PRADO M. S. , CAIRNCROSS S. , STRINA A. , BARRETO M. L. , OLIVEIRA-ASSIS A. M. , REGO S.
Published: June 2005

This study sought to assess the effect of giardiasis on growth of young children. In Salvador, northeast Brazil, 597 children initially aged 6 to 45 months were followed for a year in 1998/9, measured anthropometrically thrice, every 6 months, and monitored for diarrhoea prevalence twice weekly. Stool samples were collected and examined during the second round of anthropometry, and infected children were treated 39 days later, on average (S.D. 20 days). For each 6-month interval, the gains in z-scores of infected and uninfected children were compared, after adjustment for potential confounding factors, including longitudinal prevalence of diarrhoea. No significant difference was found for the first interval but in the second, the gain in adjusted height-for-age z-score was 0·09 less in infected than uninfected children, equivalent to a difference in height gain of 0·5 cm. The shortfall in growth was greater in children who remained free of diarrhoea, and was significantly correlated with the proportion of the second interval during which the child had remained untreated. We conclude that Giardia can impede child growth even when asymptomatic, presumably through malabsorption. This finding challenges the view that young children found to have asymptomatic giardiasis in developing countries should not be treated.
A regional ocean modeling system for the Long‐term Ecosystem Observatory
Authors: Wilkin John L. , Arango Hernan G. , Haidvogel Dale B. , Lichtenwalner C. Sage , Glenn Scott M. , Hedström Katherine S.
Published: June 2005

A coastal ocean forecasting system was developed for the Long‐term Ecosystem Observatory (LEO) on New Jersey's inner shelf. The forecast system comprised an ocean model, the Regional Ocean Modeling System, forced by a high‐resolution atmospheric forecast, with assimilation of ocean data from ships and coastal radar systems. The forecasts were used to aid the deployment of real‐time adaptive sampling observing systems during the July 2001 Coastal Predictive Skill Experiment. Temperature and salinity assimilation data were prepared by optimal interpolation of shipboard towed‐body data. Surface current observations from coastal radar were projected vertically for assimilation using a statistically based extrapolation. The assimilation methods tested with the operational forecast system in July 2001 were continuous nudging and intermittent melding of the model forecast and gridded data. Observations from a validation array of current meter and thermistor moorings deployed on a cross‐shore line through the center of the LEO intensive observing area were used to formulate a set of quantitative model skill metrics that focused on aspects of the two‐layer wind‐driven upwelling and downwelling circulation that characterizes ocean dynamics during the stratified summer season along this coast. An ensemble of model and data assimilation configurations were tested, showing that the k profile parameterization for vertical turbulence closure, and assimilation by intermittent melding, comprised the forecast system with the more significant skill as measured by the mean squared error of the validation metric time series.
Radio frequency emissions from a runaway electron avalanche model compared with intense, transient signals from thunderstorms
Authors: Tierney Heidi E. , Roussel‐Dupré Robert A. , Symbalisty Eugene M. D. , Beasley William H.
Published: June 2005

We present a one‐dimensional model of a runaway electron avalanche in a thunderstorm electric field. Previous simulations have calculated the ionization rates and energy distribution functions for runaway electrons, for various atmospheric values of E/p, through the solution of the modified relativistic Boltzmann equation. We use the field‐ and pressure‐dependent ionization rates in a hydrodynamic macroscopic treatment. The runaway electron avalanche modeled here includes the production of runaway and low‐energy electrons, electric field relaxation, electron attachment, and runaway electron loss. The model ambient electric field is established from two disks of charge with a sinusoidally spatially varying charge density of 9 nC/m3 peak amplitude. The peak ambient electric field from this configuration is 538 kV/m at 5 km. The numerically calculated radio frequency radiation exhibits relativistic effects. We hypothesize that runaway electron avalanches are sources of intense HF/VHF impulses radiated from within electrified clouds. The results from this case study are compared with ground‐based and FORTE satellite observations of HF and VHF radiation observed during the rise portion of narrow bipolar pulses (NBP). Given the specified rates and ambient environment, the radiation electric field HF and VHF spectra covering 3–25, 26–48, and 60–66 MHz are in agreement with observations for limited angular ranges. The modeled peak radiation electric field in the time domain is just below one standard deviation from the observed mean for NBPs.
A mesoscale model study of summertime atmospheric circulations in the north polar region of Mars
Authors: Tyler Daniel , Barnes Jeffrey R.
Published: June 2005

The Oregon State University Mars MM5 was used in a comprehensive high‐resolution study of northern polar summertime circulations. Three simulations (Ls = 120, Ls = 135, and Ls = 150) characterize the changing circulation. The atmosphere is dry, and model dynamics are hydrostatic. A modified TES thermal inertia map provides a realistic simulation of the polar thermal environment. The highest‐resolution nest (18 km) resolves complex flows near the cap; zonal‐mean easterlies (∼10 m/s) and zonal‐mean katabatic winds (∼5 m/s) near the surface are relatively steady during this study. Katabatic flows are shallow (∼300 m); the easterlies are deeper (∼1.5 km). Transient eddies are very important within the first scale height; they are excited by mechanisms, and at locations, that change dramatically during this short study period. At Ls = 120 they form along the residual cap edge with a zonal wave number one structure, producing strong excursion winds (10–15 m/s) that blow consistently across the cap. By Ls = 135, strong eddies are seen to form on the northern slopes of Alba Patera and Tharsis. These eddies are quite suggestive of the large annular cloud structures seen in Hubble Space Telescope and Mars Orbital Camera imagery at this location and season and can traverse the high latitudes to reach the residual cap before dissipating. Eddies in the earlier two simulations appear to be primarily excited by energetic flows near the surface. By Ls = 150 an early fall polar jet causes strong winter‐like baroclinic eddies to develop. The transient eddies found in this study are probably important in the water cycle of the northern residual cap.
Empirical studies of cloud effects on UV radiation: A review
Authors: Calbó Josep , Pagès David , González Josep‐Abel
Published: June 2005

The interest in solar ultraviolet (UV) radiation from the scientific community and the general population has risen significantly in recent years because of the link between increased UV levels at the Earth's surface and depletion of ozone in the stratosphere. As a consequence of recent research, UV radiation climatologies have been developed, and effects of some atmospheric constituents (such as ozone or aerosols) have been studied broadly. Correspondingly, there are well‐established relationships between, for example, total ozone column and UV radiation levels at the Earth's surface. Effects of clouds, however, are not so well described, given the intrinsic difficulties in properly describing cloud characteristics. Nevertheless, the effect of clouds cannot be neglected, and the variability that clouds induce on UV radiation is particularly significant when short timescales are involved. In this review we show, summarize, and compare several works that deal with the effect of clouds on UV radiation. Specifically, works reviewed here approach the issue from the empirical point of view: Some relationship between measured UV radiation in cloudy conditions and cloud‐related information is given in each work. Basically, there are two groups of methods: techniques that are based on observations of cloudiness (either from human observers or by using devices such as sky cameras) and techniques that use measurements of broadband solar radiation as a surrogate for cloud observations. Some techniques combine both types of information. Comparison of results from different works is addressed through using the cloud modification factor (CMF) defined as the ratio between measured UV radiation in a cloudy sky and calculated radiation for a cloudless sky. Typical CMF values for overcast skies range from 0.3 to 0.7, depending both on cloud type and characteristics. Despite this large dispersion of values corresponding to the same cloud cover, it is clear that the cloud effect on UV radiation is 15–45% lower than the cloud effect on total solar radiation. The cloud effect is usually a reducing effect, but a significant number of works report an enhancement effect (that is increased UV radiation levels at the surface) due to the presence of clouds. The review concludes with some recommendations for future studies aimed to further analyze the cloud effects on UV radiation.
Tropical cyclones and the flood hydrology of Puerto Rico
Authors: Smith James A. , Sturdevant‐Rees Paula , Baeck Mary Lynn , Larsen Matthew C.
Published: June 2005

Some of the largest unit discharge flood peaks in the stream gaging records of the U.S. Geological Survey (USGS) have occurred in Puerto Rico. Many of these flood peaks are associated with tropical cyclones. Hurricane Georges, which passed directly over the island on 21–22 September 1998, produced record flood peaks at numerous USGS stations in Puerto Rico. The hydrology and hydrometeorology of extreme flood response in Puerto Rico are examined through analyses of rainfall, based on Weather Surveillance Radar–1988 Doppler (WSR‐88D) radar reflectivity observations and USGS rain gage observations and discharge from USGS stream gaging stations. Peak rainfall accumulations of more than 700 mm occurred in the central mountain region of the island. The largest unit discharge flood peaks, however, were located in the eastern portion of the island in areas with smaller storm total rainfall accumulations but markedly larger rainfall rates at 5–60 min timescale. Orographic precipitation mechanisms played an important role in rainfall distribution over the island of Puerto Rico. Amplification of rainfall accumulations was associated with areas of upslope motion. Elevated low‐level cloud water content in regions of upslope motion played an important role in the maximum rainfall accumulations in the central mountain region of Puerto Rico. The largest unit discharge flood peaks, however, were produced by a decaying eye wall mesovortex, which resulted in a 30–45 min period of extreme rainfall rates over the eastern portion of the island. This storm element was responsible for the record flood peak of the Río Grande de Lóiza. The role of terrain in development and evolution of the eye wall mesovortex is unclear but is of fundamental importance for assessing extreme flood response from the storm. Hydrologic response is examined through analyses of rainfall and discharge from five pairs of drainage basins, extending from east to west over the island. These analyses point to the importance of short‐term rainfall rates for extreme flood response. The hydrologic response of Puerto Rico is compared with two other extreme flood environments, the central Appalachians and Edwards Plateau of Texas. These analyses suggest that the high rainfall environment of Puerto Rico is linked to the development of a hydraulically efficient drainage system.
Optical satellite imagery detection of internal wave effects from a submerged turbulent outfall in the stratified ocean
Authors: Keeler R. Norris , Bondur Valery G. , Gibson Carl H.
Published: June 2005

Sea surface brightness anomalies caused by a municipal wastewater discharge are detected from space in areas much larger than their submerged turbulence source. The mechanism involves a complex interaction between currents, topography, tides, vertical and horizontal mixing, internal waves and stratified turbulence.
Magnetic anisotropy and magnetization reversal in Ga1−xMnxAs layers studied by polarized neutron reflectometry
Authors: Primus Jean-Louis , Fritzsche Helmut , Malfait Mathieu , Van Bael Margriet J. , De Boeck Jo , Temst Kristiaan
Published: June 2005

The magnetic anisotropy and the in-plane magnetization reversal mechanism of Ga0.945Mn0.055As thin films, grown on GaAs(001), were investigated. Samples A and B, with sample A grown 45 °C lower than sample B, were analyzed by magnetization hysteresis measurements and polarized neutron reflectivity (PNR) magnetization reversal experiments. Magnetization hysteresis loops and temperature-dependent magnetization curves accounted for an in-plane uniaxial magnetic anisotropy, with a significant out-of-plane magnetization, for sample A, while an in-plane biaxial magnetic anisotropy with in-plane ⟨100⟩ as easy axes was evidenced for sample B. PNR magnetization reversal experiments showed the occurrence of a spin-flip maximum upon magnetization reversal only for sample B. A mechanism of magnetization reversal proceeding by 180° domain-wall nucleation and propagation is proposed for sample A, while an incoherent rotation mechanism by 90° domains is proposed for sample B. The reversal mechanism is shown to be correlated to the anisotropy of the samples which depends on the T∕Tc ratio.
Temperature effects for isothermal polymer crystallization kinetics
Authors: Yang Jiao , McCoy Benjamin J. , Madras Giridhar
Published: June 2005

We adopt the cluster size distribution model to investigate the effect of temperature on homogeneous nucleation and crystal growth for isothermal polymer crystallization. The model includes the temperature effects of interfacial energy, nucleation rate, growth and dissociation rate coefficients, and equilibrium solubility. The time dependencies of polymer concentration, number and size of crystals, and crystallinity (in Avrami plots) are presented for different temperatures. The denucleation (Ostwald ripening effect) is also investigated by comparing moment and numerical solutions of the population balance equations. Agreement between the model results and temperature-sensitive experimental measurements for different polymer systems required strong temperature dependence for the crystal-melt interfacial energy.
Suspended glass nanochannels coupled with microstructures for single molecule detection
Authors: Verbridge Scott S. , Edel Joshua B. , Stavis Samuel M. , Moran-Mirabal Jose M. , Allen Scott D. , Coates Geoffrey , Craighead H. G.
Published: June 2005

We present a nonlithographic approach for forming free standing nanochannels, made of a variety of materials, that can be easily integrated with microfabricated structures. The approach uses a deposited polymeric fiber as a sacrificial template around which a deposited coating forms a tube. We formed suspended nanochannels of silica glass spanning a trench on a silicon wafer and used these structures for detection of single fluorescently labeled proteins. This geometry provides excellent isolation of the molecules of interest and also separates them from surrounding material that could create unwanted background fluorescence. The same geometry provides a platform for observing motion and mechanical response of the suspended nanochannel, and we measured the mechanical resonance of a glass channel of the type used for the fluorescent detection. This type of structure provides a general approach for integrating fluid carrying nanochannels with microstructures.
HF in clusters of molecular hydrogen. I. Size evolution of quantum solvation by parahydrogen molecules
Authors: Jiang Hao , Bačić Zlatko
Published: June 2005

We present a theoretical study of the quantum solvation of the HF molecule by a small number of parahydrogen molecules, having n=1–13 solvent particles. The minimum-energy cluster structures determined for n=1–12 have all of the H2 molecules in the first solvent shell. The first solvent shell closes at n=12 and its geometry is icosahedral, with the HF molecule at the center. The quantum-mechanical ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. The zero-point energy of (p-H2)nHF clusters is unusually large, amounting to 86% of the potential well depth for n>7. The radial probability distribution functions (PDFs) confirm that the first solvent shell is complete for n=12, and that the 13th p-H2 molecule begins to fill the second solvent shell. The p-H2 molecules execute large-amplitude motions and are highly mobile, making the solvent cage exceptionally fluxional. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n∼8–9 the solvent environment is practically isotropic. The analysis of the pair angular PDF reveals that for a given n, the parahydrogen solvent density around the HF is modulated in a pattern which clearly reflects the lowest-energy cluster configuration. The rigidity of the solvent clusters displays an interesting size dependence, increasing from n=6to9, becoming floppier for n=10, and increasing again up to n=12, as the solvent shell is filled. The rigidity of the solvent cage appears to reach its maximum for n=12, the point at which the first solvent shell is closed.
The 4051-Å band of C3 (ÃΠu1−X̃Σg+1, 000-000): Perturbed low-J lines and lifetime measurements
Authors: Zhang Guiqiu , Chen Kan-Sen , Merer Anthony J. , Hsu Yen-Chu , Chen Wei-Jan , Shaji S. , Liao Yean-An
Published: June 2005

Rotational analyses have been carried out at high resolution for the 000-000 and 000-100 bands of the ÃΠu1−X̃Σg+1 transition of supersonic jet-cooled C3. Two different spectra have been recorded for each band, using time gatings of 20–150 and 800–2300 ns. At the shorter time delay the spectra show only the lines observed by many previous workers. At the longer time delay many extra lines appear, some of which have been observed previously by [McCall et al.Chem. Phys. Lett. 374, 583 (2003)] in cavity ring-down spectra of jet-cooled C3. Detailed analysis of these extra lines shows that at least two long-lived states perturb the ÃΠu1, 000 state. One of these appears to be a Σu−3 vibronic state, which may possibly be a high vibrational level of the b̃Πg3 state, and the other appears to be a P=1 state with a low rotational constant B. Our spectra also confirm the reassignment by McCall et al. of the R(0) line of the 000-000 band, which is consistent with the spectra recorded towards a number of stars that indicate the presence of C3 in the interstellar medium. Fluorescence lifetimes have been measured for a number of upper-state rotational levels. The rotational levels of the ÃΠu1 state have lifetimes in the range of 230–190 ns, decreasing slightly with J; the levels of the perturbing states have much longer lifetimes, with some of them showing biexponential decays. An improved value has been obtained for the ν1 vibrational frequency of the ground state, ν1=1224.4933±0.0029cm−1.
Dispersion of the local parameters of quasilocalized low-frequency vibrational modes in a low-temperature glass: Direct observation via single-molecule spectroscopy
Authors: Vainer Yuri G. , Naumov Andrei V. , Bauer Markus , Kador Lothar
Published: June 2005

Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6<T<40K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses.
Exploratory study of the electron-density relocalization process in benzene through a time-dependent topological analysis
Authors: Chevreau Hilaire
Published: June 2005

A time-dependent topological analysis of the electron density in benzene provides quantitative information about charge oscillation processes, and particularly about the two highest π orbitals contributions to carbon topological basins. In this exploratory study coupling one molecular-dynamic trajectory to a topological analysis, Fourier transform of the topological time data autocorrelation functions indicates frequencies of oscillations, and shows that carbon atoms, though identical in average, would be more or less highest occupied molecular-orbital reactive with a cyclic behavior.
A heuristic approach to precisely represent optical absorption and refractive index data for photon energies below, at, and above the band gap of semiconductors: The case of high-purity GaAs. Part I
Authors: Reinhart F. K.
Published: June 2005

The existence of band tails even in nominally undoped and uncompensated GaAs, and the nonparabolic absorption shape above the band gap are the prime examples for the discrepancy between theory and experiments. To overcome this difficulty, we propose a heuristic approach that is guided by the fundamental theoretical aspects and the experimental facts. For this reason, we fit the available absorption data with exponential functions over a photon energy interval from below the band gap to 3eV. This analytical representation remains well within the known experimental uncertainties over a temperature range from cryogenic to room temperature and beyond. The fitting functions are interpreted to represent the absorption contributions by the band tails, the continuum, and the excitons. This descriptive absorption function implicitly results from a perturbation of the imaginary part of the dielectric function that takes a host of unspecified contributions into account. The real part of the dielectric function due to the high-energy critical points is represented by Lorentzian functions with critical energies taken at 3 and 5eV. Its square root defines the refractive index due to these critical points, nh. The refractive index, n, is represented by the sum of nh and the truncated Kramers–Krönig transformation of the absorption function. The determination of nh is made by fitting n to the precise refractive index data of Marple [J. Appl. Phys. 35, 1241 (1964)]. This procedure yields a very precise description (<0.1% below and within experimental uncertainty at and above the band gap) of the published refractive index data from 0to2.2eV (except for the narrow reststrahl band near 0.033eV) over a temperature range similar to that mentioned for the absorption function. We feel confident to predict the refractive index for temperatures as low as 4K. An analytical expression for the refractive index describes the temperature and energy dependences very precisely below the band gap. The analytic expression is also very precise in the band-gap region for a temperature range estimated from 80to400K. We also compare the form of the absorption function derived from photoluminescence spectra. We find that low quasiequilibrium carrier densities lead to important modifications of the absorption function. These experimental findings together with the fitting procedures serve as a basis for a heuristic theory to calculate the electronic and optical properties under injection.
Full orbit computations of ripple-induced fusion α-particle losses from burning tokamak plasmas
Authors: McClements K. G.
Published: June 2005

A full orbit code is used to compute collisionless losses of fusion α particles from three proposed burning plasma tokamaks: the International Tokamak Experimental Reactor (ITER); a spherical tokamak power plant (STPP) [T. C. Hender, A. Bond, J. Edwards, P. J. Karditsas, K. G. McClements, J. Mustoe, D. V. Sherwood, G. M. Voss, and H. R. Wilson, Fusion Eng. Des. 48, 255 (2000)]; and a spherical tokamak components test facility (CTF) [H. R. Wilson, G. M. Voss, R. J. Akers, L. Appel, A. Dnestrovskij, O. Keating, T. C. Hender, M. J. Hole, G. Huysmans, A. Kirk, P. J. Knight, M. Loughlin, K. G. McClements, M. R. O’Brien, and D. Yu. Sychugov, Proceedings of the 20th IAEA Fusion Energy Conference, Invited Paper FT∕3-1Ra]. It has been suggested that α particle transport could be enhanced due to cyclotron resonance with the toroidal magnetic field ripple. However, calculations for inductive operation in ITER yield a loss rate that appears to be broadly consistent with the predictions of guiding center theory, falling monotonically as the number of toroidal field coils N is increased (and hence the ripple amplitude is decreased). For STPP and CTF the loss rate does not decrease monotonically with N, but collisionless losses are generally low in absolute terms. As in the case of ITER, there is no evidence that finite Larmor radius effects would seriously degrade fusion α-particle confinement.
Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
Authors: Paskaleva A. , Ciechonski R. R. , Syväjärvi M. , Atanassova E. , Yakimova R.
Published: June 2005

The electrical properties of Al2O3 as a gate dielectric in metal-oxide-semiconductor structures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by capacitance–voltage (C–V) and current–voltage (I–V) methods. The results show that the type as well as spatial and energy distributions of defects in Al2O3∕SiC and SiO2∕SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better electrical characteristics than the p-type 4H-SiC∕SiO2 structures. It is demonstrated that the conduction process in the former is governed by Fowler–Nordheim electron tunneling from the Al gate whereas in the latter the hole tunneling from SiC is the more probable process. This difference combined with the higher defect density in p-type SiC∕SiO2 structures defines the higher leakage currents compared to the structures utilizing Al2O3.
Energetics of forced magnetic reconnection in a visco-resistive plasma
Authors: Bian Nicolas , Vekstein Grigory
Published: June 2005

The rate of energy dissipation provided by the ongoing magnetic reconnection in a force-free magnetic field is investigated in the framework of visco-resistive magnetohydrodynamics (MHD). It is shown that viscous effects are important even under small magnetic Prandtl number Pm≡ν∕η, namely for Pm>S−2∕5, where ν and η are the plasma viscosity and resistivity, respectively, and S⪢1 is the Lundquist number of a highly conducting plasma. Various regimes of plasma heating, which are determined by the nondimensional parameters Pm, S, and ωτA, are identified, where τA is the Alfvén transit time of the magnetic configuration and ω is the frequency of an external driver.
Properties of the H-bond network for two-dimensional lattice water model
Authors: Lishchuk Sergey V. , Lokotosh Tatjana V. , Malomuzh Nikolay P.
Published: June 2005

A microscopic Hamiltonian of the hydrogen-bond network in two-dimensional lattice water is proposed, which describes the formation and disruption of the H bonds, their bending, and which satisfies the Bernal–Fowler rules [J. D. Bernal and R. H. Fowler, J. Chem. Phys. 1, 515 (1933)]. The thermodynamic properties of the H-bond network are studied using the method of many-particle irreducible distribution functions, which is a generalization of the Kikuchi cluster approach [R. Kikuchi, Phys. Rev. 81, 988 (1951)] and the Bethe–Peierls quasiactivities method [H. A. Bethe, Prog. R. Soc. A 150, 552 (1935)]. The temperature dependencies of the average number of H bonds per molecules, the contribution of the H bonds into the heat capacity of the system, and the parameters describing the correlations between the states of molecules on the neighboring sites are investigated. It is shown that depending on the magnitude of the interaction between the H bonds in the H-bond subsystem either smooth or sharp first-order phase transition can occur. The role of different factors in the formation of the properties of the H-bond network is discussed.
Clustering and collisions of heavy particles in random smooth flows
Authors: Bec J. , Celani A. , Cencini M. , Musacchio S.
Published: June 2005

Finite-size impurities suspended in incompressible flows distribute inhomogeneously, leading to a drastic enhancement of collisions. A description of the dynamics in the full position-velocity phase space is essential to understand the underlying mechanisms, especially for polydisperse suspensions. These issues are studied here for particles much heavier than the fluid by means of a Lagrangian approach. It is shown that inertia enhances collision rates through two effects: correlation among particle positions induced by the carrier flow and uncorrelation between velocities due to their finite size. A phenomenological model yields an estimate of collision rates for particle pairs with different sizes. This approach is supported by numerical simulations in random flows.
Valence photoionization dynamics in circular dichroism of chiral free molecules: The methyl-oxirane
Authors: Stranges S. , Turchini S. , Alagia M. , Alberti G. , Contini G. , Decleva P. , Fronzoni G. , Stener M. , Zema N. , Prosperi T.
Published: June 2005

The dynamical behavior of circular dichroism for valence photoionization processes in pure enantiomers of randomly oriented methyl-oxirane molecules has been studied by circularly polarized synchrotron radiation. Experimental results of the dichroism coefficient obtained for valence photoionization processes as a function of photon energy have been compared with theoretical values predicted by state-of-the-art ab initio density-functional theory. The circular dichroism measured at low electron kinetic energies was as large as 11%. Trends in the experimental dynamical behavior of the dichroism coefficients Di(ω) have been observed. Agreement between experimental and theoretical results permits unambiguous identification of the enantiomer and of the individual orbitals.
Structure and energy difference of two isomers of He–CH3F
Authors: Higgins Kelly J. , Klemperer William
Published: June 2005

The intermolecular potential surface of He–CH3F is investigated through ab initio calculations and microwave and millimeter-wave spectroscopies. The intermolecular potential is calculated at the fourth-order Møller–Plesset level with a large basis set including bond functions. Three minimums exist, the deepest of which is at the carbon end of the C–F axis and has a depth of 46.903cm−1, the second deepest is in a T-shaped position relative to the C–F axis with a depth of 44.790cm−1, and the shallowest is at the fluorine end of the C–F axis with a depth of 30.929cm−1. The barrier to internal rotation of the CH3F subunit about its C–F axis is very low, thus leading to essentially free internal rotation and two separate sets of bound states correlating to ortho-CH3F (∣K∣=3n) for the ground, or A, internal rotor state upon which this study focuses, and to para-CH3F (∣K∣=3n±1) for the excited, or E, internal rotor state. Bound-state calculations of the A state performed using two different techniques show the lowest-energy state to have the helium localized in the T-shaped well with an energy of −11.460cm−1, while two excited configurations of the A state have the helium localized either in the well at the carbon end (“linear”) with an energy of −7.468cm−1 or in the well at the fluorine end (“antilinear”) with an energy of −4.805cm−1. Spectroscopic observations confirm the predicted energy-level structure of the ground and first excited states. Sixteen transitions between 12 distinct energy levels have been observed, including pure rotational transitions of both the T-shaped ground state and the linear excited state, as well as rovibrational transitions between the ground state and the linear excited state. The energy difference between the T-shaped state and the linear state is measured to be 132374.081(16)MHz. There is significant Coriolis mixing of the ground state JKaKc=220 and the linear JK=20 levels which aided in the observation of the T to linear transitions. This mixing and the T to linear energy difference are sensitive probes of the relative well depths of the two lowest minimums and are well predicted by the ab initio potential. Improved agreement between experiment and theory is obtained by morphing the correlation energy of the potential. He–CH3F is one of just a few atom-molecule complexes for which the ground-state geometry does not coincide with the global potential minimum.
Structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering
Authors: Liu C. , Yun F. , Xiao B. , Cho S.-J. , Moon Y. T. , Morkoç H. , Abouzaid Morad , Ruterana R. , Yu K. M. , Walukiewicz W.
Published: June 2005

We report on the structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering, using transmission electron microscopy (TEM), high-resolution x-ray diffraction, and Rutherford backscattering spectroscopy (RBS) measurements. The ferromagnetic Mn-doped ZnO film showed magnetization hysteresis at 5 and 300K. A TEM analysis revealed that the Mn-doped ZnO included a high density of round-shaped cubic and elongated hexagonal MnZn oxide precipitates. The incorporation of Mn caused a large amount of structural disorder in the crystalline columnar ZnO lattice, although the wurtzite crystal structure was maintained. The observed ferromagnetism is discussed based on the structural characteristics indicated by TEM and the behavior of Mn when it is substituted into a ZnO lattice derived from RBS measurements.
Two-photon absorption in solution by means of time-dependent density-functional theory and the polarizable continuum model
Authors: Frediani Luca , Rinkevicius Zilvinas , Ågren Hans
Published: June 2005

We present the first study of two-photon absorption (TPA) of solvated molecules based on direct evaluation of TPA cross sections from the quadratic response of time-dependent perturbations. A set of prototypical two-photon (TP) chromophores has been selected and analyzed: a pure π system (t-stilbene) and its substituted homologs obtained employing a donor (D) and an acceptor (A) group to probe the solvent effects along the series π, D−π−D, A−π−D, and A−π−A. For the selected systems we have calculated the TPA cross sections in different environments by means of the polarizable continuum model. The data have been analyzed to evaluate how the structural and environmental parameters contribute to the final two-photon absorption cross section. These include molecular structure, geometry relaxation in solution, polarity, and refractive index of the solvent. The performances of the three common functionals SVWN, BLYP, and B3LYP have been compared. The results show a significant solvent dependence of the TPA cross section and an unusual trend when passing from cyclohexane to water. The data have also been rationalized in terms of the main orbital excitations leading to the transitions. Finally, trends along the series have been described and comparison with experiments and previous calculations has been drawn.
High-mobility pentacene organic field-effect transistors with a high-dielectric-constant fluorinated polymer film gate dielectric
Authors: Stadlober Barbara , Zirkl Martin , Beutl Michael , Leising Günther , Bauer-Gogonea Simona , Bauer Siegfried
Published: June 2005

High-performance pentacene organic thin-film transistors with double layers of the terpolymer electret poly(vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene) and the polymer poly(vinyl cinnamate) as a gate dielectric are reported. The electret is a high-k dielectric polymer with a static dielectric constant of ε=14. The transistors show an intrinsic field-effect mobility in the range of μi=1cm2∕Vs and an on- to off-current ratio of about 105. High-k polymer gate dielectrics seem promising for organic nonvolatile memory and sensor field-effect transistors.
Opening of aligned carbon nanotube ends via room-temperature sputter etching process
Authors: AuBuchon Joseph F. , Chen Li-Han , Gapin Andrew I. , Jin Sungho
Published: June 2005

Top ends of aligned carbon nanotubes were opened via room-temperature sputter etching of the nanotubes in the same chemical-vapor deposition (CVD) chamber that the nanotubes were grown. The mechanism of the sputter etching process involves incident positive ions in the plasma, such as hydrogen or argon, colliding with the nanotube material and preferentially eroding the nanotube walls around the catalyst metal particles. The cut-off nanotube segments are removed from the sample in the CVD chamber together with the catalyst particles. This process is entirely physical in nature with no wet chemical processing steps involved. The sputter etching process is found to be faster with larger ion size, higher applied voltage forming the plasma, and higher pressure of the sputtering gas.
Adjustment of sand ripples under changing water waves
Authors: Testik F. Y. , Voropayev S. I. , Fernando H. J. S.
Published: June 2005

The results of an experimental investigation on the adjustment of vortex sand ripples under shoaling waves to changing of wave conditions are presented in this paper. A large wave tank was used to generate shoaling waves. Waves with small (S), moderate (M), and large (L) intensities (as specified by the wave paddle excursion) were used to model three basic cases of cyclic variation of wave forcing, namely, M-L-M, L-M-L, and L-S-L. Depending on the forcing transitions (L-M, M-L, or L-S), three main ripple adjustment processes were identified: (i) ripple splitting, (ii) ripple regrowth, and (iii) ripple flattening. Quantitative data on the time evolution of ripple characteristics were collected using the structured light technique. The results of the observations were explained by extending a simplified physical model proposed earlier for ripples under constant wave forcing to the case of changing wave forcing.
Activation volume and density of mobile dislocations in plastically deforming nanocrystalline Ni
Authors: Wang Y. M. , Hamza A. V. , Ma E.
Published: June 2005

We report the analysis of repeated transients to monitor the coupled evolution of dislocation velocity and mobile dislocation density in plastically deforming nanocrystalline Ni. The stress relaxation series allowed the determination of the physical activation volume, indicating a rate-controlling mechanism different from that in coarse-grained Ni. The mobile dislocation exhaustion observed is correlated with the unusually high apparent work-hardening rate during the early stage of straining.
Changes in nonlinear potential scattering theory in electron gases brought about by reducing dimensionality
Authors: March N. H. , Howard I. A. , Nagy I. , Echenique P. M.
Published: June 2005

Recent work has shown the essential equivalence of stopping power, force-force correlation function, and phase-shift analysis for nonlinear potential scattering in a three-dimensional electron gas. In the present study, we first demonstrate that the above situation is markedly different when the scattering occurs from a localized potential in a two-dimensional (2D) electron gas. Only to second order in the potential do the three methods referred to above precisely agree. However, all these methods can still be applied in 2D, some fully nonlinear evaluation proving possible. The one-dimensional case is also discussed, albeit more briefly. Scattering from a two-center modeling of the localized potential is also calculated, but now only in the Born approximation, due to the added complication of a noncentral potential.