bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevalence of Tritrichomonas foetus infection in cats with diarrhoea in the UK
Authors: Gunn-Moore Danièlle A. , McCann Theresa M. , Reed Nicki , Simpson Kerry E. , Tennant Bryn
Published: April 2007

Faecal samples from 111 cats with diarrhoea that were living in the UK were submitted for the assessment of Tritrichomonas foetus infection by polymerase chain reaction (PCR). Sixteen (14.4%) samples were found to be positive. In agreement with studies from the USA, infected cats were predominantly of a year of age or less and of a pedigree breed, with Siamese and Bengal cats specifically over-represented in this population.
Nuts: source of energy and macronutrients
Authors: Brufau Gemma , Boatella Josep , Rafecas Magda
Published: April 2007

On the basis of the high fat content of nuts, they are traditionally considered as foods that provide a high amount of energy. However, epidemiologic and clinical observations do not indicate an association between nut intake and increased BMI. There is a notorious variability in macronutrient composition among nuts, although they have some consistent patterns. Nuts contain all major macronutrients: protein, carbohydrate, and fat. The total protein content is relatively high, which makes them a good source of plant protein (especially for vegetarians). Although nuts contain low amounts of some essential amino acids, this is not a nutritional concern due to the complement of protein. In addition, nuts have a low lysine:arginine ratio, which is inversely associated with the risk of developing hypercholesterolemia and atherosclerosis. Carbohydrates are the second highest macronutrient in nuts in terms of total calories provided. The fat fraction is characterized by a high amount of unsaturated fatty acids and a low content of saturated fatty acids. In conclusion, the high content in unsaturated fatty acids, the low lysine:arginine ratio, and the presence of other bioactive molecules (such as fibre, phytosterols, vitamin and other antioxidants, and minerals) make the addition of nuts to healthy diets a useful tool for the prevention of cardiovascular heart diseases.
Fatty acid composition of nuts – implications for cardiovascular health
Authors: Ros Emilio , Mataix José
Published: April 2007

It is well established that, due to their high content of saturated fatty acids (SFA), the intake of meat and meat products is strongly associated with elevated blood cholesterol concentrations and an increased risk of hypertension, diabetes and cardiovascular diseases. Conversely, the intake of foods rich in unsaturated fatty acids, such as those contained in most vegetable fats and oils and oily fish, is associated with improved lipid profiles, a lower potency of intermediate biomarkers of atherosclerosis and lesser incidence of cardiovascular diseases. There are persuasive evidences that dietary substitution of monounsaturated fatty acids (MUFA) or n-6 polyunsaturated fatty acids (PUFA) for SFA lowers blood cholesterol and may have beneficial effects on inflammation, thrombosis, and vascular reactivity. MUFA may have an advantage over PUFA because enrichment of lipoprotein lipids with MUFA increases their resistance to oxidation. Marine n-3 PUFA have a number of anti-atherosclerotic effects, including anti-arrhythmic properties and, at relatively high doses, reduce serum triglycerides. These effects appear to be shared in part by vegetable n-3 PUFA. Nuts are natural foods rich in unsaturated fatty acids; most nuts contain substantial amounts of MUFA, while walnuts are especially rich in both n-6 and n-3 PUFA. Healthy fats in nuts contribute to the beneficial effects of frequent nut intake observed in epidemiological studies (prevention of coronary heart disease, diabetes, and sudden death) and in short-term feeding trials (cholesterol lowering, LDL resistance to oxidation, and improved endothelial function).
Dietary fibre, nuts and cardiovascular diseases
Authors: Salas-Salvadó Jordi , Bulló Mónica , Pérez-Heras Ana , Ros Emilio
Published: April 2007

Dietary fibre has a range of metabolic health benefits. Through a variety of mechanisms, dietary fibre, and the viscous variety in particular, slows down gastric emptying and intestinal transit, decreases the rate of intestinal carbohydrate absorption, and increases faecal bile acid excretion. Therefore, consumption of some types of soluble fibre can enhance satiety, which is associated with a lower BMI, and reduce blood cholesterol and the postprandial glucose response. Surprisingly, the consumption of insoluble fibre from whole grains, though metabolically inert, has been associated with a reduction in the risk of developing coronary heart disease and diabetes in epidemiological studies. The likely reason is that whole grains, like nuts, legumes and other edible seeds, contain many bioactive phytochemicals and various antioxidants. After cereals, nuts are the vegetable foods that are richest in fibre, which may partly explain their benefit on the lipid profile and cardiovascular health.
Tree nuts and the lipid profile: a review of clinical studies
Authors: Griel Amy E. , Kris-Etherton Penny M.
Published: April 2007

Tree nuts have a fatty acid profile that favourably affects blood lipids and lipoproteins. They are low in saturated fat and high in unsaturated fatty acids and are rich sources of other nutrients. An extensive database consistently shows total and LDL cholesterol-lowering effects of diets low in saturated fat and cholesterol and high in unsaturated fat provided by a variety of tree nuts. Collectively, a summary of studies conducted to date shows that tree nuts reduce LDL cholesterol by 3–19 % compared with Western and lower-fat diets. Nuts also contain many nutrients and bioactive compounds that appear to contribute to the favourable effects on lipids and lipoproteins – these include plant sterols, dietary fibre and antioxidants. Because of their unique nutrient profile, nuts can be part of a diet that features multiple heart-healthy foods resulting in a cholesterol lowering response that surpasses that of cholesterol-lowering diets typically used to reduce CVD risk.
The potential of nuts in the prevention of cancer
Authors: González Carlos A. , Salas-Salvadó Jordi
Published: April 2007

Cancer is a disease that is characterized by the loss of genetic control over cell growth and proliferation, mainly as a result of the exposure to environmental factors. Cessation of smoking and a high consumption of fruits and vegetables are the most important means of reducing the risk of cancer in our society. Like fruits and vegetables, nuts are a source of vegetable protein, monounsaturated fatty acids, vitamin E, phenolic compounds, selenium, vegetable fibre, folic acid and phytoestrogens. There are numerous mechanisms of action by which these components can intervene in the prevention of cancer, although they have not been fully elucidated. There are very few epidemiological studies analyzing the relationship between nuts consumption and risk of cancer. One of the greatest difficulties in interpreting the results is that the consumption of nuts, seeds and legumes are often presented together. The most commonly studied location is the colon/rectum, an organ in which the effect of nuts is biologically plausible. Although the results are not conclusive, a protective effect on colon and rectum cancer is possible. Likewise, some studies show a possible protective effect on prostate cancer, but there is insufficient data on other tumour locations. New epidemiological studies are required to clarify the possible effects of nuts on cancer, particularly prospective studies that make reliable and complete estimations of their consumption and which make it possible to analyse their effects independently of the consumption of legumes and seeds.
Prenatal exposure to undernutrition and programming of responses to high-fat feeding in the rat
Authors: Erhuma Aml , Bellinger Leanne , Langley-Evans Simon C. , Bennett Andrew J.
Published: April 2007

Fetal undernutrition programmes risk of later metabolic disorders. Postnatal factors modify the programmed phenotype. This study aimed to assess the effects of a postnatal high-fat (HF) challenge on body weight gain, adiposity and gene expression following prenatal undernutrition. Pregnant rats were fed either a control diet or a low-protein (LP) diet, targeted at days 0–7 (LPE), days 8–14 (LPM), or days 15–22 (LPL) gestation. At 12 weeks of age offspring were either fed standard laboratory chow diet (4·13 % fat), or a 39·5 % fat diet, for 10 weeks. LP exposure had no effect on weight gain or abdominal fat in males. Females exposed to LP dietin uteroexhibited a similar weight gain on HF diet as on the chow diet. Programming of fat deposition was noted in LPE females and males of the LPM and LPL groups (P = 0·019). Hypothalamic expression of galanin mRNA was similar in all groups, but expression of the galanin-2 receptor was modified by LP exposure in female offspring. Hepatic expression of sterol response element binding protein (SREBP-1c) was decreased by LP at both the mRNA (P = 0·008) and protein (P < 0·001) level. HF feeding increased expression of SREBP-1c mRNA three-fold in controls, with little response noted in the LP groups. Interactions of factors such as postnatal diet, age and sex act together with prenatal factors to determine metabolic function and responsiveness at any stage of postnatal life. This study further establishes a role for prenatal nutrition in programming the genes involved in lipid metabolism and appetite regulation.
Nutritional status and subsequent all-cause mortality in men and women aged 75 years or over living in the community
Authors: Jia Xueli , Aucott Lorna S. , McNeill Geraldine
Published: April 2007

We prospectively investigated relationships between blood markers of Fe, vitamin B12, folate, vitamin C and vitamin D status and subsequent all-cause mortality in 208 men and 191 women aged 75 years or over living in the community in Aberdeen, Scotland. The participants had been recruited for a cross-sectional study in 1999–2000 when they completed health and lifestyle questionnaires and had blood samples taken for analysis of serum ferritin, serum vitamin B12, erythrocyte folate, plasma vitamin C and serum 25-hydroxycholecalciferol. Mortality was ascertained on national databases up to December 2005, with a median time of follow up of 69·2 (range 1·0–79·9) months. Participants were divided into sex-specific quintiles of baseline levels for each nutrient, and hazard ratios were estimated with Cox proportional hazard models adjusted for age and sex with the significance of linear trends in the associations assessed by logistic regression. There was no significant association between blood markers of Fe, vitamin B12 or folate status at baseline and mortality, but vitamin D status at baseline was inversely related to mortality (P for trend < 0·001). For vitamin C there was no evidence of a linear trend but participants in the lowest quintile of plasma levels had a significantly higher risk of death than those in the highest quintile. Randomized controlled trials of lifestyle changes which improve vitamin status are needed to assess whether these associations could be causal.
Particle dynamics and pattern formation in a rotating suspension
Authors: LEE JONGHOON , LADD ANTHONY J. C.
Published: April 2007

A rotating suspension of non-neutrally buoyant particles, confined by a horizontal cylinder, can be unstable to axial perturbations in concentration. A highly regular pattern of particle density and fluid flow then coexists in a non-equilibrium stationary state. The density profile along the cylinder axis is roughly sinusoidal, with a well-defined wavelength close to the cylinder diameter, and has a magnitude of approximately 30% of the average number density. We have used numerical simulations within the Stokes-flow approximation to investigate the mechanism underlying axial-band formation. Our results show that bands develop from an inhomogeneous particle distribution in the radial plane, which is itself driven by the competition between gravity and the viscous drag of the rotating fluid. We have discovered that the mean angular velocity of the particles is an order parameter which distinguishes between a low-frequency segregated phase and a high-frequency dispersed phase, where the particles fill the whole volume uniformly. The order parameter is a function of a single dimensionless frequency, with a characteristic length that is the mean interparticle separation. As the rotational frequency increases, the particle distribution becomes more homogeneous and the band structure disappears. Hydrodynamic diffusion stabilizes the suspension against centrifugal forces, allowing for a uniformly dispersed phase that can be used to grow three-dimensional cell cultures in an artificial microgravity environment.
Gravity currents in horizontal porous layers: transition from early to late self-similarity
Authors: HESSE M. A. , TCHELEPI H. A. , CANTWEL B. J. , ORR F. M.
Published: April 2007

We investigate the evolution of a finite release of fluid into an infinite, two-dimensional, horizontal, porous slab saturated with a fluid of different density and viscosity. The vertical boundaries of the slab are impermeable and the released fluid spreads as a gravity current along a horizontal boundary. At early times the released fluid fills the entire height of the layer, and the governing equation admits a self-similar solution that is a function of the viscosity ratio between the two fluids. This early similarity solution describes a tilting interface with tips propagating as x ∝ t1/2. At late times the released fluid has spread along the boundary and the height of the current is much smaller than the thickness of the layer. The governing equation simplifies and admits a different similarity solution that is independent of the viscosity ratio. This late similarity solution describes a point release of fluid in a semi-infinite porous half-space, where the tip of the interface propagates as x ∝ t1/3. The same simplification of the governing equation occurs if the viscosity of the released fluid is much higher than the viscosity of the ambient fluid. We have obtained an expression for the time when the solution transitions from the early to the late self-similar regime. The transition time increases monotonically with increasing viscosity ratio. The transition period during which the solution is not self-similar also increases monotonically with increasing viscosity ratio, for mobility ratios larger than unity. Numerical computations describing the full evolution of the governing equation show good agreement with the theoretical results. Estimates of the spreading of injected fluids over long times are important for geological storage of CO2, and for the migration of pollutants in aquifers. In all cases it is important to be able to anticipate when the spreading regime transitions from x ∝ t1/2 to x ∝ t1/3.
The effect of confining boundaries on viscous gravity currents
Authors: TAKAGI DAISUKE , HUPPERT HERBERT E.
Published: April 2007

Newtonian viscous gravity currents propagating along horizontal and inclined channels with semicircular and V-shaped boundaries are examined. Similarity solutions are obtained from the governing mathematical equations and compared with closely matching data from laboratory experiments in which the propagation of glycerine along different channels was recorded. Geological applications of the results are discussed briefly.
Akutes Abdomen aus gynäkologisch-sonographischer Sicht – Eine Darstellung der häufigsten Ursachen
Authors: Bajka
Published: April 2007

Ein sinnvoller Ansatz zur Abklärung beim akuten Abdomen in der Gynäkologie, respektive bei Unterbauchschmerzen, ist die Unterteilung in Schwangerschaftstest positiv (resp. bekannte Schwangerschaft) und Schwangerschaftstest negativ (resp. postmenopausale) Situationen. Frühschwangerschaftsassoziiert sind die verschiedenen Formen der Extrauteringravidität und des Abortes. Bei Ausschluss einer Schwangerschaft kommen vor allem Schmerzen im Zusammenhang mit Adnexbefunden, Adnextorsionen, Myomen und Infektionen in Frage. Die Sonographie, zur Beurteilung der Morphologie wie auch der Durchblutung von Organen und Strukturen, ist dabei ein Diagnostikum von hohem Stellenwert, sollte aber nur im Verbund mit Anamnese, Klinik, Labor und ggf. weiteren bildgebenden Verfahren gewertet werden. Bauchschmerzen erfordern durchaus auch eine intensive interdisziplinäre Zusammenarbeit. Nicht selten stellen sich mehrere relevante Ursachen bei Unterbauchschmerzen heraus.
A comparison of statistical and dynamical downscaling for surface temperature in North America
Authors: Spak Scott , Holloway Tracey , Lynn Barry , Goldberg Richard
Published: April 2007

Projections from general circulation model (GCM) simulations must be downscaled to the high spatial resolution needed for assessing local and regional impacts of climate change, but uncertainties in the downscaling process are difficult to quantify. We employed a multiple linear regression model and the MM5 dynamical model to downscale June, July, and August monthly mean surface temperature over eastern North America under greenhouse gas‐driven climate change simulation by the NASA GISS GCM. Here we examine potential sources of apparent agreement between the two classes of models and show that arbitrary parameters in a statistical model contribute significantly to the level of agreement with dynamical downscaling. We found that the two methods and all permutations of regression parameters generally exhibited comparable skill at simulating observations, although spatial patterns in temperature across the region differed. While the two methods projected similar regional mean warming over the period 2000–2087, they developed different spatial patterns of temperature across the region, which diverged further from historical differences. We found that predictor domain size was a negligible factor for current conditions, but had a much greater influence on future surface temperature change than any other factor, including the data sources. The relative importance of SD model inputs to downscaled skill and domain‐wide agreement with MM5 for summertime surface temperature over North America in descending order is Predictor Domain; Training Data/Predictor Model; Predictor Variables; and Predictor Grid Resolution. Our results illustrate how statistical downscaling may be used as a proxy for dynamical models in sensitivity analysis.
Estimating cirrus cloud properties from MIPAS data
Authors: Mendrok J. , Schreier F. , Höpfner M.
Published: April 2007

High resolution mid‐infrared limb emission spectra observed by the spaceborne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) showing evidence of cloud interference are analyzed. Using the new line‐by‐line multiple scattering [Approximate] Spherical Atmospheric Radiative Transfer code (SARTre), a sensitivity study with respect to cirrus cloud parameters, e.g., optical thickness and particle size distribution, is performed. Cirrus properties are estimated by fitting spectra in three distinct microwindows between 8 and 12μm. For a cirrus with extremely low ice water path (IWP = 0.1 g/m2) and small effective particle size (De= 10μm) simulated spectra are in close agreement with observations in broadband signal and fine structures. We show that a multi‐microwindow technique enhances reliability of MIPAS cirrus retrievals compared to single microwindow methods.
Modeling ground level enhancements: Event of 20 January 2005
Authors: Plainaki C. , Belov A. , Eroshenko E. , Mavromichalaki H. , Yanke V.
Published: April 2007

The solar cosmic ray event associated with an X7.1 class solar flare on 20 January 2005 was one of the greatest enhancements ever recorded by the ground level worldwide network of neutron monitors. The event occurred during a Forbush decrease, almost at the end of the 23rd cycle of solar activity. In this work a ground level enhancement model for getting the broadest possible picture, as well as for understanding the physics of solar cosmic ray particles under extreme solar conditions, is proposed. Neutron monitors responses from 41 stations widely distributed around the Earth have been modeled to an anisotropic solar proton flux, using an optimization method based on the Levenberg‐Marquardt algorithm. The parameters of the primary solar particles outside the magnetosphere and their dynamics, as well as the characteristics of solar cosmic rays during this event are obtained and discussed.
Self‐consistent model of magnetospheric ring current and propagating electromagnetic ion cyclotron waves: 2. Wave‐induced ring current precipitation and thermal electron heating
Authors: Khazanov G. V. , Gamayunov K. V. , Gallagher D. L. , Kozyra J. U. , Liemohn M. W.
Published: April 2007

This paper continues presentation and discussion of the results from our new global self‐consistent theoretical model of interacting ring current ions and propagating electromagnetic ion cyclotron waves (Khazanov et al., 2006) currently developing in NASA Marshall Space Flight Center. To study the effects of electromagnetic ion cyclotron wave propagation and refraction on the wave induced ring current precipitation and heating of the thermal plasmaspheric electrons, we simulate the May 1998 storm. The main findings after the simulation can be summarized as follows. First, the wave induced ring current precipitation exhibits quite a lot of fine structure and is highly organized by location of the plasmapause gradient. The strongest fluxes of about 4 × 106 (cm2 s sr)−1 are observed during the main and early recovery phases of the storm. The very interesting and probably more important finding is that in a number of cases the most intense precipitating fluxes are not connected to the most intense waves in simple manner. The characteristics of the wave power spectral density distribution over the wave normal angle are extremely crucial for the effectiveness of the ring current ion scattering. Second, comparison of the global proton precipitating patterns with the results from RAM (Kozyra et al., 1997a) reveals that although we observe a qualitative agreement between the localizations of the wave induced precipitations in the models, there is no quantitative agreement between the magnitudes of the fluxes. The quantitative differences are mainly due to a qualitative difference between the characteristics of the wave power spectral density distributions over the wave normal angle in RAM and in our model. Third, the heat fluxes to plasmaspheric electrons caused by Landau resonate energy absorption from electromagnetic ion cyclotron waves are observed in the postnoon‐premidnight MLT sector and can reach the magnitude of 1011 eV/(cm2 s). The Coulomb energy degradation of the RC H+ and O+ ions maximizes at about 1011 eV/(cm2 s) and typically leads to electron energy deposition rates of about 2 × 1010 eV/(cm2 s) which are observed during two periods, 32–48 hours and 76–86 hours after 1 May, 0000 UT. The theoretically derived spatial structure of the thermal electron heating caused by interaction of the ring current with the plasmasphere is strongly supported by concurrent and conjugate plasma measurements from the plasmasphere, ring current, and topside ionosphere (Gurgiolo et al., 2005). Finally, the wave induced intense electron heating has a structure of the spot‐like patches along the most enhanced density gradients in the plasmasphere boundary layer and can be a possible driver of the observed but still not explained small‐scale structures of enhanced emissions in the stable auroral red arcs.
A simulation study of thermospheric neutral winds over the MU radar
Authors: Lei Jiuhou , Roble Raymond G. , Kawamura Seiji , Fukao Shoichiro
Published: April 2007

The climatological thermospheric winds observed by the Shigaraki middle and upper atmosphere (MU) radar in East Asia are compared for the first time with simulation results from the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM). The comparisons show that the predicted meridional winds are in excellent agreement with the observations; their differences generally fall within 20 m/s except for the summer nighttime at high solar activity. A harmonic analysis of the observed and model meridional winds is carried out to extract the mean winds and the amplitudes and phases of diurnal, semidiurnal, and terdiurnal components. The model tidal waves are also in good agreement with the observed values except for the summer diurnal amplitude at high solar activity. Comparisons of the model electron densities with the radar observations suggest that the solar activity variation of the meridional winds can be mainly explained by the role of ion drag. Interestingly, the numerical simulations predict a feature not previously interpreted well: the diurnal amplitude and the mean wind depend nonlinearly on solar activity because the electron density saturates at high solar activity levels. It is further shown that both the observed and predicted diurnal phases remain almost stable at different solar activity levels, regardless of season.
Ice core paleovolcanic records from the St. Elias Mountains, Yukon, Canada
Authors: Yalcin Kaplan , Wake Cameron P. , Kreutz Karl J. , Germani Mark S. , Whitlow Sallie I.
Published: April 2007

We previously reported a record of regionally significant volcanic eruptions in the North Pacific using an ice core from Eclipse Icefield (St. Elias Mountains, Yukon, Canada). The acquisition of two new ice cores from Eclipse Icefield, along with the previously available Eclipse Icefield and Mount Logan Northwest Col ice cores, allows us to extend our record of North Pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3–5 km. Comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible, especially for the largest eruptions such as Katmai (A.D. 1912). Correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one‐third of the eruptions recorded in St. Elias ice cores are from Alaskan and Kamchatkan volcanoes. Although there are several moderately large (volcanic explosivity index (VEI) ≥ 4) eruptions recorded in only one core from Eclipse Icefield, the use of multiple cores provides signals in at least one core from all known VEI ≥ 4 eruptions in Alaska and Kamchatka since A.D. 1829. Tephrochronological evidence from the Eclipse ice cores documents eruptions in Alaska (Westdahl, Redoubt, Trident, and Katmai), Kamchatka (Avachinsky, Kliuchevoskoi, and Ksudach), and Iceland (Hekla). Several unidentified tephra‐bearing horizons, with available geochemical evidence suggesting Alaskan and Kamchatkan sources, were also found. We present a reconstruction of annual volcanic sulfate loading for the North Pacific troposphere based on our ice core data, and we provide a detailed assessment of the atmospheric and climatic effects of the Katmai eruption.
Some characteristics and purification of anti‐(human ovarian carcinoma)×anti‐(human CD3) single‐chain bispecific antibody
Authors: Zhou Feng , Wei Dong‐Zhi , Tong Wang‐Yu , Zhu Yi‐Qi , Jiang Yun‐Mei
Published: April 2007

To obtain high‐quality AhOC×AhCD3 [anti‐(human ovarian carcinoma)×anti‐(human CD3)] with high biological activity economically and easily, some characteristics and purification of AhOC×AhCD3, a single chain bispecific antibody, were investigated. During the present study, some important properties of AhOC×AhCD3, such as molecular mass, pI, solubility, stability, hydrophobic ability, molecular status and bioactivity were primarily studied. The molecular mass of AhOC×AhCD3 was determined to be approx. 58.0 kDa by SDS/PAGE (theoretical molecular mass: 56972.5 Da, calculated on the basis of the primary structure) and the pI was approx. 7.5±0.4 by IEF (isoelectric focusing; theoretical pI: 8.5, predicted by the ProtParam software tool) respectively. Experiments showed that the solubility of AhOC×AhCD3 increased with the pH increase and that the AhOC×AhCD3 was easily degraded into several fragments during the storage time of samples and the mixtures of both fragment B and fragment C retained normal bioactivity. Particularly, the soluble aggregate/polymer status of AhOC×AhCD3 with bioactivity was verified by non‐reducing SDS/PAGE. After optimization of purification process, AhOC×AhCD3 with electrophoretic homogeneity was successfully obtained and the yield was approx. 20%. Some important properties of AhOC×AhCD3 were first observed and a procedure for soluble AhOC×AhCD3 purification in scale‐up was first established. Some characteristics of AhOC×AhCD3, especially the stability of AhOC×AhCD3, are critical for the development of this protein pharmaceutical and useful for reference to other proteins.
Experimental verification of apparent negative refraction in low-epsilon material in the microwave regime
Authors: von Rhein A. , Pergande D. , Greulich-Weber S. , Wehrspohn R. B.
Published: April 2007

We analyze the effect of negative refraction in dielectric photonic crystals with almost circular equifrequency surfaces experimentally and theoretically. We found experimental evidence for negative refraction in the microwave regime in low-epsilon material and suggest an improved interpretation. The apparent negative refraction originates from Bragg refraction and its combination with noncoupling bands.
Spin-flop transition driven by exchange springs in ErFe2∕YFe2 multilayers
Authors: Martin K. N. , Wang K. , Bowden G. J. , de Groot P. A. J. , Zimmermann J. P. , Fangohr H. , Ward R. C. C.
Published: April 2007

Magnetization loops for (110) ErFe2∕YFe2 multilayer films grown by molecular beam epitaxy are presented and discussed. The easy axis for the hard ErFe2 layers is near an out of plane ⟨111⟩-type crystal axis. At low temperatures there is just one irreversible switch of the hard layers, accompanied by the formation of magnetic exchange springs in the soft YFe2 layers. However, above a certain temperature the coercivity changes sign and there are additional high field transitions. This crossover temperature, TCO, depends on the composition of the multilayers. In sufficiently high fields, perpendicular to the multilayer film plane, the energy is minimized by an exchange spring driven multilayer spin-flop state. The composition dependence of TCO is explained with a simple energy argument.
Electronic Raman scattering in magnetite
Authors: Gasparov L. V. , Choi K.-Y. , Güntherodt G. , Berger H. , Forro L.
Published: April 2007

Raman spectra of optimally doped magnetite (Fe3O4) single crystals reveal broad electronic background extending up to 900 wave numbers (∼110meV). Redistribution of this background is observed when sample is cooled below the Verwey transition temperature (TV=123K). In particular, spectra of the low temperature phase show diminished background below 300 wave numbers followed by an enhancement of the electronic background between 300 and 400 wave numbers with subsequent decrease of the background below 400 wave numbers. Such redistribution may be assigned to an opening of the charge gap at about 350±80 wave numbers (∼43±10meV). The value of the gap is within the range of recent photoemission data on freshly fractured magnetite sample.
Automatic discovery of metastable states for the construction of Markov models of macromolecular conformational dynamics
Authors: Chodera John D. , Singhal Nina , Pande Vijay S. , Dill Ken A. , Swope William C.
Published: April 2007

To meet the challenge of modeling the conformational dynamics of biological macromolecules over long time scales, much recent effort has been devoted to constructing stochastic kinetic models, often in the form of discrete-state Markov models, from short molecular dynamics simulations. To construct useful models that faithfully represent dynamics at the time scales of interest, it is necessary to decompose configuration space into a set of kinetically metastable states. Previous attempts to define these states have relied upon either prior knowledge of the slow degrees of freedom or on the application of conformational clustering techniques which assume that conformationally distinct clusters are also kinetically distinct. Here, we present a first version of an automatic algorithm for the discovery of kinetically metastable states that is generally applicable to solvated macromolecules. Given molecular dynamics trajectories initiated from a well-defined starting distribution, the algorithm discovers long lived, kinetically metastable states through successive iterations of partitioning and aggregating conformation space into kinetically related regions. The authors apply this method to three peptides in explicit solvent—terminally blocked alanine, the 21-residue helical Fs peptide, and the engineered 12-residue β-hairpin trpzip2—to assess its ability to generate physically meaningful states and faithful kinetic models.
Microstructure morphology of shock-induced melt and rapid resolidification in bismuth
Authors: Colvin Jeffrey D. , Reed Bryan W. , Jankowski Alan F. , Kumar Mukul , Paisley Dennis L. , Swift Damian C. , Tierney Thomas E. , Frank Alan M.
Published: April 2007

With the growing importance of nanotechnology, there is increased emphasis on rapid solidification processing to produce materials microstructures with a finer length scale. However, few studies have focused on the question of how a material restructures itself on the microstructural scale when it refreezes at very high cooling rates. Here we report on the development of microstructures in pure bismuth metal as it is subjected to rapid shock-driven melting and subsequent resolidification (on release of pressure), where the estimated effective undercooling rates are on the order of 1010K∕s, orders of magnitude faster than any achieved before in bulk material. Microscopic examination of the recovered material indicates that the melting transformation was far from homogeneous, and substantial morphological changes are observed compared to the starting microstructure.
Nanoscale polarization relaxation kinetics in polycrystalline ferroelectric thin films
Authors: Anbusathaiah V. , Nagarajan V. , Aggarwal S.
Published: April 2007

We report on the nanoscale kinetics of ferroelectric domain wall motion in polycrystalline ferroelectric thin films. High-resolution piezoresponse force microscopy is employed to investigate the changes that occur at the domain wall surface during the polarization relaxation process. 50×50nm2 domain images reveal that domain wall motion is a very jerky process. The domain wall motion shows two distinct cycles—one where it breaks into several segments to advance, following which it recombines to form a continuous surface. This “pinning-depinning” cycle continues throughout the relaxation process. A kinetic model based on the concept of domain wall mobility and a thermodynamic driving force is developed to explain this jagged motion.
Internal friction study of oxygen ion conductors La1.95K0.05Mo2−xTxO9−δ (T=Fe,Mn)
Authors: Li C. , Fang Q. F. , Wang X. P. , Wang J. X. , Li D. , Zhuang Z.
Published: April 2007

Based on the oxygen ion conductor La2Mo2O9, a series of K, Fe, and Mn doped samples La1.95K0.05Mo2−xTxO9−δ (T=Fe,Mn; x=0,0.025,0.05,0.1) were prepared with conventional solid-state reaction method. The effects of Fe and Mn doping on the cationic and anionic ions diffusion, phase transition, and electrical conductivity were studied. The mechanical spectroscopy (or internal friction) technique was exploited to investigate the microscopic transport mechanism and to deduce the dynamical relaxation parameters. Three internal friction peaks (PL, PH, and PM) were observed in the La1.95K0.05Mo2−xTxO9−δ samples, among which PL and PM are of relaxational type while PH is associated with a kind of phase transition. The results revealed that peak PL is originated from the short-distance jumps of oxygen vacancies, while peak PM is associated with the short-distance diffusion of Mn (Fe) ions and peak PH with the phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution. Based on the results of conductivity measurements, it can be concluded that the high-temperature conductivity of La2Mo2O9 can be improved obviously by the Fe or Mn doping at Mo site and the low-temperature conductivity can be increased by the simultaneous K doping at La site.
First-principles molecular dynamics study on aqueous sulfuric acid solutions
Authors: Choe Yoong-Kee , Tsuchida Eiji , Ikeshoji Tamio
Published: April 2007

The properties of aqueous sulfuric acid have been studied employing density functional theory–based molecular dynamics simulations in conjunction with norm-conserving pseudopotentials. The simulations were carried out for two different concentrations whose molar concentrations were fixed at 0.84 and 10.2mol∕l. The structural features of aqueous sulfuric acid solutions show a strong dependency on the concentration. The Grötthuss-type proton transfer mechanism is not effectively operative at the higher concentration because of the broken hydrogen bond network of water induced by ions generated by the dissociation of sulfuric acid. In addition, to evaluate electrical properties, we carried out a simulation that takes an electric field into account. Results are compared with those of the simulation undertaken with no external electric field.
Experimental and numerical investigation into buckling instability of carbon nanotube probes under nanoindentation
Authors: Jeng Yeau-Ren , Tsai Ping-Chi , Fang Te-Hua
Published: April 2007

This study employs a series of experimental nanoindentation tests and molecular dynamics simulations to investigate buckling instabilities of carbon nanotube probes. It is found that the buckling mechanism varies as a function of probe lengths and initial inclination angles. The experimental results show that longer nanotubes buckle in local-buckling mode, whereas shorter nanotubes undergo global buckling. This study also suggests that the inclination angle also plays a key role in determining buckling behaviors of nanotube probes.
Structure of flexible and semiflexible polyelectrolyte chains in confined spaces of slit micro/nanochannels
Authors: Jeon Jonggu , Chun Myung-Suk
Published: April 2007

Understanding the behavior of a polyelectrolyte in confined spaces has direct relevance in design and manipulation of microfluidic devices, as well as transport in living organisms. In this paper, a coarse-grained model of anionic semiflexible polyelectrolyte is applied, and its structure and dynamics are fully examined with Brownian dynamics (BD) simulations both in bulk solution and under confinement between two negatively charged parallel plates. The modeling is based on the nonlinear bead-spring discretization of a continuous chain with additional long-range electrostatic, Lennard-Jones, and hydrodynamic interactions between pairs of beads. The authors also consider the steric and electrostatic interactions between the bead and the confining wall. Relevant model parameters are determined from experimental rheology data on the anionic polysaccharide xanthan reported previously. For comparison, both flexible and semiflexible models are developed accompanying zero and finite intrinsic persistence lengths, respectively. The conformational changes of the polyelectrolyte chain induced by confinements and their dependence on the screening effect of the electrolyte solution are faithfully characterized with BD simulations. Depending on the intrinsic rigidity and the medium ionic strength, the polyelectrolyte can be classified as flexible, semiflexible, or rigid. Confined flexible and semiflexible chains exhibit a nonmonotonic variation in size, as measured by the radius of gyration and end-to-end distance, with changing slit width. For the semiflexible chain, this is coupled to the variations in long-range bond vector correlation. The rigid chain, realized at low ionic strength, does not have minima in size but exhibits a sigmoidal transition. The size of confined semiflexible and rigid polyelectrolytes can be well described by the wormlike chain model once the electrostatic effects are taken into account by the persistence length measured at long length scale.
Hyperpolarizability of GaAs dimer is not negative
Authors: Maroulis George , Karamanis Panaghiotis , Pouchan Claude
Published: April 2007

We present a systematic study of the static electric hyperpolarizability of Ga2As2. The authors rely on finite-field high-level ab initio calculations with carefully optimized basis sets. Their best values for the mean and the anisotropy of the dipole polarizability are α¯=158.57 and Δα=130.33e2a02Eh−1. For the hyperpolarizability we propose an estimate γ¯=(155±15)×103e4a04Eh−3, which does not agree with the negative value predicted by Lan et al. [J. Chem. Phys. 124, 094302 (2006)]. Density functional theory based methods yield values close to those predicted by conventional ab initio methods. The (hyper)polarizability components are particularly enhanced along the direction defined by the Ga–Ga axis.
Temperature dependence of the persistent critical current and instabilities in MgB2 thin films
Authors: Mansour A. I. , Egilmez M. , Fan I. , Chow K. H. , Jung J. , Choi E. M. , Lee H. S. , Lee S. I. , Darhmaoui H.
Published: April 2007

Temperature dependences of the persistent critical current density Jc(T) and its relaxation rate S=dlnJ∕dlnt were measured from 8.0K to Tc in MgB2 ring-shaped thin films. Jc(T) was observed to approach a Ginzburg-Landau-like temperature dependence with a decreasing Tc in magnesium deficient films. No correlation was found between the current density and the magnitude of the relaxation rate, suggesting percolative (filamentary) flow of the supercurrent. A suppression of the supercurrent density (instability) was observed between 8.0 and 10.5K in MgB2 thin films of Tc above 30K, but not in films of lower transition temperatures. Vacuum annealing shifts the instability to lower temperatures.
Textured crystallization of ultrathin hafnium oxide films on silicon substrate
Authors: Bohra Fakhruddin , Jiang Bin , Zuo Jian-Min
Published: April 2007

The effects of rapid thermal annealing are reported here on the structure of 2nm thick hafnium oxide films grown on silicon (100) substrates. The films grown by atomic layer deposition have a 1nm SiO2 transition layer between silicon and the HfO2 layer. The amorphous structure of the as-deposited films is retained after annealing at 600°C. The HfO2 films crystallized into an orthorhombic phase with an out-of-plane texture after annealing at 800°C or higher. In contrast, films grown on thick amorphous SiO2 substrates crystallize without any texture. The authors attribute the texture of HfO2 on Si (100) to the role of interfacial SiO2 transition layer.
Influence of applied electric field annealing on the microwave properties of (Ba0.5Sr0.5)TiO3 thin films
Authors: Cho Kwang-Hwan , Lee Chil-Hyoung , Kang Chong-Yun , Yoon Seok-Jin , Lee Young-Pak
Published: April 2007

The effect of heat treatment in electric field on the structure and dielectric properties at microwave range of rf magnetron sputtering derived (Ba0.5Sr0.5)TiO3 thin films have been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability. The increased out-of-plane lattice constant in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature. And in dielectric loss, as the Ti–O bonding lengths increase, the energy scattering on the ferroelectric mode also increases. So, the value of dielectric loss is slightly increased.
Absolute in situ measurement of surface dangling bonds during a-Si:H growth
Authors: Aarts I. M. P. , Pipino A. C. R. , van de Sanden M. C. M. , Kessels W. M. M.
Published: April 2007

Hydrogenated amorphous silicon (a-Si:H) is regarded as a model system in mechanistic studies of amorphous semiconductor film growth, where the key reactive site is generally considered to be a surface “dangling bond.” Employing an ultrahigh-Q (≈1010) monolithic optical resonator, the authors probe the creation of dangling-bond defects during growth of a-Si:H from a predominantly SiHx (x=0–3) radical flux by detecting the associated near-IR subgap absorption with evanescent wave cavity ringdown spectroscopy. They find the apparent dangling-bond creation rate [(5±3)×1012cm−2s−1] and steady-state surface density [(5±2)×1011cm−2] to be considerably lower than expected from dangling-bond-based growth mechanisms.
Power enhancement in chemical oxygen-iodine lasers by iodine predissociation via corona/glow discharge
Authors: Katz A. , Dahan Z. , Rybalkin V. , Waichman K. , Barmashenko B. D. , Rosenwaks S.
Published: April 2007

The gain and power in a supersonic chemical oxygen-iodine laser (COIL) are enhanced by applying dc corona/glow discharge in the transonic section of the secondary flow in the supersonic nozzle, dissociating I2 prior to its mixing with O2(Δ1). The loss of O2(Δ1) consumed for dissociation is thus reduced, and the consequent dissociation rate downstream of the discharge increases, resulting in up to 80% power enhancement. The implication of this method for COILs operating beyond the specific conditions reported here is assessed.
Enhanced red electroluminescence from a polycrystalline diamond film/Si heterojunction structure
Authors: Liang Xingbo , Wang Lei , Ma Xiangyang , Li Dongsheng , Cheng Peihong , Yang Deren , Chen Jun , Sekiguchi Takashi
Published: April 2007

Strongly enhanced red electroluminescence (EL) was realized at room temperature (RT) from a polycrystalline diamond film (PDF)∕n−-Si heterojunction fabricated by direct chemical vapor deposition of PDF on silicon substrate. The red EL peaks featuring fairly narrow linewidth (∼12nm) were obtained when the device was under sufficient reverse bias with the positive voltage applied on the silicon substrate. Cathodoluminescence spectra measured from 77K to RT suggested that the enhanced red EL peaks originated from the neutral vacancy induced intrinsic defects of the PDF rather than the Si-related centers. The carrier transport mechanism of the PDF∕n−-Si heterojunction was elucidated based on the proposed energy band diagram of the PDF∕n−-Si heterojunction.