bluuebunny/crossref_metadata_2025 huggingface dataset:
Palaeoenvironmental implications derived from a piston core from east lobe Bonney, Taylor Valley, Antarctica
Authors: Wagner Bernd , Ortlepp Sabrina , Kenig Fabien , Doran Peter T. , Melles Martin
Published: August 2010

A 270 cm long sediment sequence was recovered with a piston corer from east lobe Bonney, Taylor Valley, Antarctica, and characterized according to its sedimentological, mineralogical, and geochemical properties. It is the first record of such length recovered from east lobe Bonney. The sediment core is mainly composed of halite crystals of different sizes, water, and a relatively low and stable proportion of clastic particles. Although the sediment surface was probably disturbed by the coring process and absence or low contents of organic material or carbonates hampers the establishment of a robust chronology by radiocarbon dating, the core probably contains at least several hundred years of information about the history of the lake and the Bonney basin. Variations in halite crystal sizes and amount as well as variations in the composition of clastic material can be related to past lake level changes and evaporation cycles.
Cognitive tests used in chronic adult human randomised controlled trial micronutrient and phytochemical intervention studies
Authors: Macready Anna L. , Butler Laurie T. , Kennedy Orla B. , Ellis Judi A. , Williams Claire M. , Spencer Jeremy P. E.
Published: August 2010

In recent years there has been a rapid growth of interest in exploring the relationship between nutritional therapies and the maintenance of cognitive function in adulthood. Emerging evidence reveals an increasingly complex picture with respect to the benefits of various food constituents on learning, memory and psychomotor function in adults. However, to date, there has been little consensus in human studies on the range of cognitive domains to be tested or the particular tests to be employed. To illustrate the potential difficulties that this poses, we conducted a systematic review of existing human adult randomised controlled trial (RCT) studies that have investigated the effects of 24 d to 36 months of supplementation with flavonoids and micronutrients on cognitive performance. There were thirty-nine studies employing a total of 121 different cognitive tasks that met the criteria for inclusion. Results showed that less than half of these studies reported positive effects of treatment, with some important cognitive domains either under-represented or not explored at all. Although there was some evidence of sensitivity to nutritional supplementation in a number of domains (for example, executive function, spatial working memory), interpretation is currently difficult given the prevailing ‘scattergun approach’ for selecting cognitive tests. Specifically, the practice means that it is often difficult to distinguish between a boundary condition for a particular nutrient and a lack of task sensitivity. We argue that for significant future progress to be made, researchers need to pay much closer attention to existing human RCT and animal data, as well as to more basic issues surrounding task sensitivity, statistical power and type I error.
The impact of the food-based and nutrient-based standards on lunchtime food and drink provision and consumption in primary schools in England
Authors: Haroun Dalia , Harper Clare , Wood Lesley , Nelson Michael
Published: August 2010

Objective

To assess lunchtime provision of food and drink in English primary schools and to assess both choices and consumption of food and drink by pupils having school lunches. These findings were compared with similar data collected in 2005.

Design

Cross-sectional data collected between February and April 2009. In each school, food and drink provision, including portion weights and number of portions of each item served at lunchtime, were recorded over five consecutive days. Caterers provided school lunchtime menus and recipes.

Setting

England.

Subjects

A random selection of 6696 pupils having school lunches in a nationally representative sample of 136 primary schools in England.

Results

Compared with 2005, schools in 2009 provided significantly more fruit, fruit-based desserts, vegetables and salad, water and fruit juice, and less ketchup, sauces and gravy, starchy foods cooked in fat, snacks and confectionery (P < 0·01). Pupils were also making healthier choices, choosing an average of 2·2 portions of fruit and vegetables from their ‘five a day’, but about one-third to two-fifths of these were wasted.

Conclusions

Lunchtime food provision and consumption in primary schools have improved substantially since 2005, following the introduction of new standards for school food in 2008. However, improvements still need to be made to increase the Fe and Zn content and to decrease the Na content of recipes, and in encouraging pupils to eat more of the fruits and vegetables taken at lunchtime.
Choice and privatisation in Swedish primary care
Authors: Anell Anders
Published: August 2010

In 2007, a new wave of local reforms involving choice for the population and privatisation of providers was initiated in Swedish primary care. Important objectives behind reforms were to strengthen the role of primary care and to improve performance in terms of access and responsiveness. The purpose of this article was to compare the characteristics of the new models and to discuss changes in financial incentives for providers and challenges regarding governance from the part of county councils. A majority of the models being introduced across the 21 county councils can best be described as innovative combinations between a comprehensive responsibility for providers and significant degrees of freedom regarding choice for the population. Key financial characteristics of fixed payment and comprehensive financial responsibility for providers may create financial incentives to under-provide care. Informed choices by the population, in combination with reasonably low barriers for providers to enter the primary care market, should theoretically counterbalance such incentives. To facilitate such competition is indeed a challenge, not only because of difficulties in implementing informed choices but also because the new models favour large and/or horizontally integrated providers. To prevent monopolistic behaviour, county councils may have to accept more competition as well as more governance over clinical practice than initially intended.
POSITIVE LOGIC WITH ADJOINT MODALITIES: PROOF THEORY, SEMANTICS, AND REASONING ABOUT INFORMATION
Authors: SADRZADEH MEHRNOOSH , DYCKHOFF ROY
Published: August 2010

We consider a simple modal logic whose nonmodal part has conjunction and disjunction as connectives and whose modalities come in adjoint pairs, but are not in general closure operators. Despite absence of negation and implication, and of axioms corresponding to the characteristic axioms of (e.g.) T, S4, and S5, such logics are useful, as shown in previous work by Baltag, Coecke, and the first author, for encoding and reasoning about information and misinformation in multiagent systems. For the propositional-only fragment of such a dynamic epistemic logic, we present an algebraic semantics, using lattices with agent-indexed families of adjoint pairs of operators, and a cut-free sequent calculus. The calculus exploits operators on sequents, in the style of “nested” or “tree-sequent” calculi; cut-admissibility is shown by constructive syntactic methods. The applicability of the logic is illustrated by reasoning about the muddy children puzzle, for which the calculus is augmented with extra rules to express the facts of the muddy children scenario.
Comparative genomics reveals a deep-sea sediment-adapted life style of Pseudoalteromonas sp. SM9913
Authors: Qin Qi-Long , Li Yang , Zhang Yan-Jiao , Zhou Zhe-Min , Zhang Wei-Xin , Chen Xiu-Lan , Zhang Xi-Ying , Zhou Bai-Cheng , Wang Lei , Zhang Yu-Zhong
Published: August 2010

Deep-sea sediment is one of the most important microbial-driven ecosystems, yet it is not well characterized. Genome sequence analyses of deep-sea sedimentary bacteria would shed light on the understanding of this ecosystem. In this study, the complete genome of deep-sea sedimentary bacterium Pseudoalteromonas sp. SM9913 (SM9913) is described and compared with that of the closely related Antarctic surface sea-water ecotype Pseudoalteromonas haloplanktis TAC125 (TAC125). SM9913 has fewer dioxygenase genes than TAC125, indicating a possible sensitivity to reactive oxygen species. Accordingly, experimental results showed that SM9913 was less tolerant of H2O2 than TAC125. SM9913 has gene clusters related to both polar and lateral flagella biosynthesis. Lateral flagella, which are usually present in deep-sea bacteria and absent in the related surface bacteria, are important for the survival of SM9913 in deep-sea environments. With these two flagellar systems, SM9913 can swim in sea water and swarm on the sediment particle surface, favoring the acquisition of nutrients from particulate organic matter and reflecting the particle-associated alternative lifestyle of SM9913 in the deep sea. A total of 12 genomic islands were identified in the genome of SM9913 that may confer specific features unique to SM9913 and absent from TAC125, such as drug and heavy metal resistance. Many signal transduction genes and a glycogen production operon were also present in the SM9913 genome, which may help SM9913 respond to food pulses and store carbon and energy in a deep-sea environment.
Looking inside the box: using Raman microspectroscopy to deconstruct microbial biomass stoichiometry one cell at a time
Authors: Hall Edward K , Singer Gabriel A , Pölzl Marvin , Hämmerle Ieda , Schwarz Christian , Daims Holger , Maixner Frank , Battin Tom J
Published: August 2010

Stoichiometry of microbial biomass is a key determinant of nutrient recycling in a wide variety of ecosystems. However, little is known about the underlying causes of variance in microbial biomass stoichiometry. This is primarily because of technological constraints limiting the analysis of macromolecular composition to large quantities of microbial biomass. Here, we use Raman microspectroscopy (MS), to analyze the macromolecular composition of single cells of two species of bacteria grown on minimal media over a wide range of resource stoichiometry. We show that macromolecular composition, determined from a subset of identified peaks within the Raman spectra, was consistent with macromolecular composition determined using traditional analytical methods. In addition, macromolecular composition determined by Raman MS correlated with total biomass stoichiometry, indicating that analysis with Raman MS included a large proportion of a cell's total macromolecular composition. Growth phase (logarithmic or stationary), resource stoichiometry and species identity each influenced each organism's macromolecular composition and thus biomass stoichiometry. Interestingly, the least variable peaks in the Raman spectra were those responsible for differentiation between species, suggesting a phylogenetically specific cellular architecture. As Raman MS has been previously shown to be applicable to cells sampled directly from complex environments, our results suggest Raman MS is an extremely useful application for evaluating the biomass stoichiometry of environmental microorganisms. This includes the ability to partition microbial biomass into its constituent macromolecules and increase our understanding of how microorganisms in the environment respond to resource heterogeneity.
DamID in C. elegans reveals longevity‐associated targets of DAF‐16/FoxO
Authors: Schuster Eugene , McElwee Joshua J , Tullet Jennifer M A , Doonan Ryan , Matthijssens Filip , Reece‐Hoyes John S , Hope Ian A , Vanfleteren Jacques R , Thornton Janet M , Gems David
Published: August 2010

Insulin/IGF‐1 signaling controls metabolism, stress resistance and aging in Caenorhabditis elegans by regulating the activity of the DAF‐16/FoxO transcription factor (TF). However, the function of DAF‐16 and the topology of the transcriptional network that it crowns remain unclear. Using chromatin profiling by DNA adenine methyltransferase identification (DamID), we identified 907 genes that are bound by DAF‐16. These were enriched for genes showing DAF‐16‐dependent upregulation in long‐lived daf‐2 insulin/IGF‐1 receptor mutants (P=1.4e−11). Cross‐referencing DAF‐16 targets with these upregulated genes (daf‐2 versus daf‐16; daf‐2) identified 65 genes that were DAF‐16 regulatory targets. These 65 were enriched for signaling genes, including known determinants of longevity, but not for genes specifying somatic maintenance functions (e.g. detoxification, repair). This suggests that DAF‐16 acts within a relatively small transcriptional subnetwork activating (but not suppressing) other regulators of stress resistance and aging, rather than directly regulating terminal effectors of longevity. For most genes bound by DAF‐16∷DAM, transcriptional regulation by DAF‐16 was not detected, perhaps reflecting transcriptionally non‐functional TF ‘parking sites’. This study demonstrates the efficacy of DamID for chromatin profiling in C. elegans.
Association Between Body Composition and Pulmonary Function in Elderly People: The Korean Longitudinal Study on Health and Aging
Authors: Lim Soo , Kwon Sung‐Youn , Yoon Ji Won , Kim So Yeon , Choi Sung Hee , Park Young Joo , Yoon Ho Il , Chang Yoon Seok , Lee Jae Ho , Lee Choon‐Taek , Kim Ki Woong , Park Kyong Soo , Jang Hak Chul
Published: August 2010

The age‐related increase in body fat and decrease in muscle mass are associated with increased morbidity in elderly populations. Pulmonary function also decreases with age, but no study has investigated whether regional body composition is associated with pulmonary function in an older population. The Korean Longitudinal Study on Health and Aging is a community‐based cohort study of people aged >65 years selected by random stratified sampling. Anthropometrics, biochemical factors, and lung function by spirometry were evaluated in 439 men (mean age of 75.9 ± 8.6 years) and 561 women (mean age of 76.0 ± 8.8 years). Dual‐energy X‐ray absorptiometry (DXA) was performed to assess the whole and regional body composition. Computed tomography (CT) was also used to measure fat or muscle distribution at the abdominal and mid‐thigh levels. Although pulmonary function and muscle mass were inversely related to age, fat mass was not. After adjusting for age, height, BMI, smoking and exercise status, and high sensitivity C‐reactive protein (hsCRP), fat mass in trunk or central area was inversely associated with lung function in both sexes (P < 0.01). Men with more muscle in trunk and mid‐thigh level had better lung function (P < 0.01). The results of this community‐based study show that regional body composition is significantly associated with lung function. Augmentation of muscle in the trunk and low extremity in men, and reduction of fat in the trunk and upper body in men and women may be helpful in maintaining lung function in the elderly population.
Obesity‐Induced Diabetes in Mouse Strains Treated With Gold Thioglucose: A Novel Animal Model for Studying β‐Cell Dysfunction
Authors: Karasawa Hiroshi , Takaishi Kiyosumi , Kumagae Yoshihiro
Published: August 2010

An obesity‐induced diabetes model using genetically normal mouse strains would be invaluable but remains to be established. One reason is that several normal mouse strains are resistant to high‐fat diet‐induced obesity. In the present study, we show the effectiveness of gold thioglucose (GTG) in inducing hyperphagia and severe obesity in mice, and demonstrate the development of obesity‐induced diabetes in genetically normal mouse strains. GTG treated DBA/2, C57BLKs, and BDF1 mice gained weight rapidly and exhibited significant increases in nonfasting plasma glucose levels 8–12 weeks after GTG treatment. These mice showed significantly impaired insulin secretion, particularly in the early phase after glucose load, and reduced insulin content in pancreatic islets. Interestingly, GTG treated C57BL/6 mice did not become diabetic and retained normal early insulin secretion and islet insulin content despite being as severely obese and insulin resistant as the other mice. These results suggest that the pathogenesis of obesity‐induced diabetes in GTG‐treated mice is attributable to the inability of their pancreatic β‐cells to secrete enough insulin to compensate for insulin resistance. Mice developing obesity‐induced diabetes after GTG treatment might be a valuable tool for investigating obesity‐induced diabetes. Furthermore, comparing the genetic backgrounds of mice with different susceptibilities to diabetes may lead to the identification of novel genetic factors influencing the ability of pancreatic β‐cells to secrete insulin.
The Prevalence of Metabolically Healthy Obese Subjects Defined by BMI and Dual‐Energy X‐Ray Absorptiometry
Authors: Shea Jennifer L. , Randell Edward W. , Sun Guang
Published: August 2010

Nearly one‐third of obese (OB) people are reported to be metabolically healthy based on BMI criteria. It is unknown whether this holds true when more accurate adiposity measurements are applied such as dual‐energy X‐ray absorptiometry (DXA). We compared differences in the prevalence of cardiometabolic abnormalities among adiposity groups classified using BMI vs. DXA criteria. A total of 1,907 adult volunteers from Newfoundland and Labrador participated. BMI and body fat percentage (%BF; measured using DXA) were measured following a 12‐h fasting period. Subjects were categorized as normal weight (NW), overweight (OW), or OB based on BMI and %BF criteria. Cardiometabolic abnormalities considered included elevated triglyceride, glucose, and high‐sensitivity C‐reactive protein (hsCRP) levels, decreased high‐density lipoprotein (HDL) cholesterol levels, insulin resistance, and hypertension. Subjects were classified as metabolically healthy (0 or 1 cardiometabolic abnormality) or abnormal (≥2 cardiometabolic abnormalities). We found low agreement in the prevalence of cardiometabolic abnormalities between BMI and %BF classifications (κ = 0.373, P < 0.001). Among NW and OW subjects, the prevalence of metabolically healthy individuals was similar between BMI and %BF (77.6 vs. 75.7% and 58.8 vs. 62.5%, respectively) however, there was a pronounced difference among OB subjects (34.0 vs. 47.7%, P < 0.05). Similar trends were evident using three additional definitions to characterize metabolically healthy individuals. Our findings indicate that approximately one‐half of OB people are metabolically healthy when classified using %BF criteria which is significantly higher than previously reported using BMI. Caution should therefore be taken when making inferences about the metabolic health of an OB population depending on the method used to measure adiposity.
Association of Prescription H1 Antihistamine Use With Obesity: Results From the National Health and Nutrition Examination Survey
Authors: Ratliff Joseph C. , Barber Jessica A. , Palmese Laura B. , Reutenauer Erin L. , Tek Cenk
Published: August 2010

The incidence of obesity in the United States has reached epidemic proportions. Previous research has shown several medications exert noticeable effects on body‐weight regulation. Histamine‐1 (H1) receptor blockers commonly used to alleviate allergy symptoms are known to report weight gain as a possible side effect. Therefore, we investigated the association between prescription H1 antihistamine use and obesity in adults using data from the 2005–2006 National Health and Nutrition Examination Survey (NHANES). Adults taking prescription H1 antihistamines were matched by age and gender with controls and compared on the basis of body measurements, plasma glucose, insulin concentrations, and lipid levels. Prescription H1 antihistamine users had a significantly higher weight, waist circumference, and insulin concentration than matched controls. The odds ratio (OR) for being overweight was increased in prescription H1 antihistamine users. H1 antihistamine use may contribute to the increased prevalence of obesity and the metabolic syndrome in adults given these medications are also commonly used as over‐the‐counter remedies.
Effect of degree of fluid saturation on transport coefficients in disturbed soils
Authors: Tuli A. , Hopmans J. W.
Published: August 2010

To improve the predictive capability of transport models in soils we need experimental data that improve their understanding of properties at the scale of pores, including the effect of degree of fluid saturation. All transport occurs in the same soil pore space, so that one may intuitively expect a link between the different transport coefficients and key geometrical characteristics of the pores such as tortuosity and connectivity, and pore‐size distribution. To understand the combined effects of pore geometry and pore‐size distribution better, we measured the effect of degree of water saturation on hydraulic conductivity and bulk soil electrical conductivity, and of degree of air saturation on air conductivity and gaseous diffusion for a fine sand and a sandy loam soil. To all measured data were fitted a general transport model that includes both pore geometry and pore‐size distribution parameters. The results show that both pore geometry and pore‐size distribution determine the functional relations between degree of saturation, hydraulic conductivity and air conductivity. The control of pore size on convective transport is more for soils with a wider pore‐size distribution. However, the relative contribution of pore‐size distribution is much larger for the unsaturated hydraulic conductivity than for gaseous phase transport. For the other transport coefficients, their saturation dependency could be described solely by the pore‐geometry term. The contribution of the latter to transport was much larger for transport in the air phase than in the water phase, supporting the view that connectivity dominates gaseous transport. Although the relation between effective fluid saturation and all four relative transport coefficients for the sand could be described by a single functional relation, the presence of a universal relationship between fluid saturation and transport for all soils is doubtful.
Microliter-bioreactor array with buoyancy-driven stirring for human hematopoietic stem cell culture
Authors: Luni Camilla , Feldman Hope C. , Pozzobon Michela , De Coppi Paolo , Meinhart Carl D. , Elvassore Nicola
Published: August 2010

This work presents the development of an array of bioreactors where finely controlled stirring is provided at the microliter scale (100–300 μl). The microliter-bioreactor array is useful for performing protocol optimization in up to 96 parallel experiments of hematopoietic stem cell (HSC) cultures. Exploring a wide range of experimental conditions at the microliter scale minimizes cost and labor. Once the cell culture protocol is optimized, it can be applied to large-scale bioreactors for stem cell production at the clinical level. The controlled stirring inside the wells of a standard 96-well plate is provided by buoyancy-driven thermoconvection. The temperature and velocity fields within the culture volume are determined with numerical simulations. The numerical results are verified with experimental velocity measurements using microparticle image velocimetry (μPIV) and are used to define feasible experimental conditions for stem cell cultures. To test the bioreactor array’s functionality, human umbilical cord blood-derived CD34+ cells were cultured for 7 days at five different stirring conditions (0.24–0.58 μm/s) in six repeated experiments. Cells were characterized in terms of proliferation, and flow cytometry measurements of viability and CD34 expression. The microliter-bioreactor array demonstrates its ability to support HSC cultures under stirred conditions without adversely affecting the cell behavior. Because of the highly controlled operative conditions, it can be used to explore culture conditions where the mass transport of endogenous and exogenous growth factors is selectively enhanced, and cell suspension provided. While the bioreactor array was developed for culturing HSCs, its application can be extended to other cell types.
Binary spinning black hole Hamiltonian in canonical center-of-mass and rest-frame coordinates through higher post-Newtonian order
Authors: Rothe Tilman J. , Schäfer Gerhard
Published: August 2010

The recently constructed Hamiltonians for spinless binary black holes through third post-Newtonian order and for spinning ones through formal second post-Newtonian order, where the spins are counted of zero post-Newtonian order, are transformed into fully canonical center-of-mass and rest-frame variables. The mixture terms in the Hamiltonians between center-of-mass and rest-frame variables are in accordance with the relation between the total linear momentum and the center-of-mass velocity as demanded by global Lorentz invariance. The various generating functions for the center-of-mass and rest-frame canonical variables are explicitly given in terms of the single-particle canonical variables. The no-interaction theorem does not apply because the world-line condition of Lorentz covariant position variables is not imposed.
Structural and optical characterization of infrared hot electron transistor
Authors: Jung Hyeson , Pinsukanjana Paul , Dutta Mitra , Choi Kwong-Kit , Tidrow Meimei Z.
Published: August 2010

We present structural, optical, and transport characterization of long wave infrared hot electron transistor (IHET) based on doped quantum wells of InGaAs/AlGaAs. The atomic resolution images and x-ray diffraction patterns verified a lattice matched and band-gap engineered device structure of IHET. Measured values of the photocurrent were less than the theoretically expected values and indicated a loss of photocurrent between the base of the IHET and the collector. A higher filter height due to high unexpected dopant in the filter barrier was suggested as a possible cause of the current loss. Photoluminescence data in the near infrared showed the existence of such a dopant.
Long-lived laser-induced microwave plasma guides in the atmosphere: Self-consistent plasma-dynamic analysis and numerical simulations
Authors: Shneider M. N. , Zheltikov A. M. , Miles R. B.
Published: August 2010

A detailed model of plasma dynamics, which self-consistently integrates plasma-kinetic, Navier–Stokes, electron heat conduction, and electron-vibration energy transfer equations, is used to quantify the limitations on the lifetime of microwave plasma waveguides induced in the atmosphere through filamentation with high-intensity ultrashort laser pulses further sustained by long laser pulses. We demonstrate that a near-infrared or midinfrared laser pulse can tailor plasma decay in the wake of a filament, efficiently suppressing, through electron temperature increase, the attachment of electrons to neutral species and dissociative recombination, thus substantially increasing the plasma-guide lifetime and facilitating long-distance transmission of microwaves.
Validation of the transition state theory with Langevin-dynamics simulations
Authors: Schratzberger J. , Lee J. , Fuger M. , Fidler J. , Fiedler G. , Schrefl T. , Suess D.
Published: August 2010

Finite-element Langevin-dynamics simulations are performed in order to extract the attempt frequency of small magnetic particles as a function of an applied perpendicular field. The obtained values of the attempt frequency are in excellent agreement with the analytical results of [Kalmykov, J. Appl. Phys. 96, 1138 (2004)]. It is shown that an external field that is applied perpendicularly to the easy axis with a strength of just about 1% of the anisotropy field is strong enough that the framework of the transition state theory (TST) for broken symmetries can be applied. It is concluded that for most realistic structures, the attempt frequency can be numerically calculated by broken symmetry—TST formulism.
On the interpretation of lateral manganin gauge stress measurements in polymers
Authors: Appleby-Thomas Gareth J. , Hazell Paul J. , Wilgeroth James M. , Wood David C.
Published: August 2010

Encapsulated wire-element stress gauges enable changes in lateral stress during shock loading to be directly monitored. However, there is substantial debate with regards to interpretation of observed changes in stress behind the shock front; a phenomenon attributed both to changes in material strength and shock-dispersion within the gauge-encapsulation. Here, a pair of novel techniques which both modify or remove the embedding medium where such stress gauges are placed within target materials have been used to try and inform this debate. The behavior of three polymeric materials of differing complexity was considered, namely polystyrene, the commercially important resin transfer moulding (RTM) 6 resin and a commercially available fat (lard). Comparison to the response of embedded gauges has suggested a possible slight decrease in the absolute magnitude of stress. However, changing the encapsulation has no detectable effect on the gradient behind the shock in such polymeric systems.
Construction of orthonormal wavelet-like bases
Authors: Morillas Patricia Mariela
Published: August 2010

A general method for constructing wavelet-like bases in a Hilbert space H starting from any orthonormal basis in H and any periodic orthonormal wavelet basis is presented. With this method we can take advantage of the characteristics of both types of bases to obtain orthonormal wavelet-like bases that are suitable to represent functions and operators efficiently.
Determination of core and hydrodynamic size distributions of CoFe2O4 nanoparticle suspensions using ac susceptibility measurements
Authors: Ludwig F. , Guillaume A. , Schilling M. , Frickel N. , Schmidt A. M.
Published: August 2010

The complex susceptibility was measured on CoFe2O4 nanoparticle suspensions in the frequency range between 1 kHz and 1 MHz for different values of a superimposed static magnetic field. The maximum in the imaginary part χ″ of the ac susceptibility shifts to higher frequencies with increasing static magnetic field. The shift is theoretically modeled utilizing the magnetic field dependence of the Brownian relaxation time constant and assuming a distribution of hydrodynamic particle sizes. The mean hydrodynamic size as determined from the maximum of χ″ in zero field and the mean core size as obtained from the shift of the χ″ peak with static field agree very well with the data from transmission electron microscopy and dynamic light scattering measurements, respectively. The results indicate that both core and hydrodynamic size distributions can be determined from measurements on nanoparticle suspensions proposed that magnetic dipole-dipole interactions are negligible.
Reflection of acoustodiffusive waves from the boundary of a semiconductor halfspace
Authors: Sharma J. N. , Sharma A.
Published: August 2010

The paper concentrates on the study of reflection characteristics of acoustodiffusive waves from the surface of a semiconductor halfspace which is subjected to stress free, isoconcentrated and stress free, impermeable conditions. The effect of life and relaxation times of charge carriers (electron or holes) fields on the wave characteristics is also investigated. The amplitude ratios (reflection coefficients) of reflected waves to that of incident wave are obtained for incident quasilongitudinal (qP), quasitransverse (qSV), and electron-(N) and hole (P) wave cases. The special cases of normal and grazing incidence are also derived and discussed. Finally, the numerical computations of reflection coefficients are carried out with the help of Gauss elimination method by using MATLAB programming software. The computer simulated results in respect of stress free conditions have been plotted graphically for silicon (Si) and presented in tabular form in case of germanium (Ge) semiconductors. The study may be useful in semiconductors and surface acoustic wave devices in addition to geophysical applications.
Recombination processes controlling the carrier lifetime in n−4H–SiC epilayers with low Z1/2 concentrations
Authors: Klein P. B. , Myers-Ward R. , Lew K.-K. , VanMil B. L. , Eddy C. R. , Gaskill D. K. , Shrivastava A. , Sudarshan T. S.
Published: August 2010

The dominant recombination processes controlling the carrier lifetime in n-type 4H–SiC epitaxial layers grown with low concentrations of the Z1/2 defect (the dominant bulk lifetime killer), where Z1/2 no longer determines the lifetime, have been investigated by studying the variation in the carrier lifetime with temperature. The temperature dependent lifetimes were obtained primarily by low-injection photoluminescence decay for several low-Z1/2 epilayers over a wide temperature range. The results were fitted to simulations of the temperature dependent recombination rate, where bulk, surface and interface recombination was considered. No significant contribution from other bulk defects was observed, and upper limits to the bulk recombination rate were found to be consistent with the low Z1/2 concentrations measured in these materials. There was also no significant contribution from carrier capture at the epilayer/substrate interface, which is consistent with behavior expected at low injection for low-doped epilayers grown on n+ substrates. Corresponding high-injection measurements exhibited very different behavior, consistent with the surface/interface under flat-band conditions. Consequently, it is concluded that for low-Z1/2 materials, control of the carrier lifetime has not been transferred from Z1/2 to another bulk defect, but is instead dominated by surface and interface recombination. Simulations suggest that further enhancement of the total lifetime under the high injection conditions of a device structure would require very thick epilayers, effectively passivated surface and interface recombination and a further reduction in the remaining Z1/2 concentrations. The temperature dependence of the low-injection carrier lifetime was also found to provide a method to estimate the surface band bending and the surface defect density.
Electro-osmotic flow in a wavy microchannel: Coherence between the electric potential and the wall shape function
Authors: Shu Y. C. , Chang C. C. , Chen Y. S. , Wang C. Y.
Published: August 2010

The electro-osmotic flow through a wavy microchannel is studied under the Debye–Hückel approximation. An analytic solution by perturbation with appropriate averaging is carried out up to the second-order in terms of the small amplitude of corrugation. It is shown that the wavelength and phase difference of the corrugations can be utilized to control the flow relative to the case of flat walls. In particular, for thick electric double layers the electro-osmotic flow can be enhanced at long-wavelength corrugations because of the coherence between the electric potential and the wall shape function. Notably, these findings are not restricted to small amplitudes of corrugation. By applying the Ritz method to solve for the electro-osmotic flow, it is found that the enhancement becomes even greater (up to 30%) with increases in corrugation. Moreover, the nonlinear Poisson–Boltzmann equation is solved by finite difference to study the electro-osmotic flow in terms of the relative strength of the zeta potential. The issue of overlapped electric double layers when they are very thick is also discussed. The relative flow rate is shown to increase under the following conditions: (i) completely out-of-phase corrugations with long wavelength and large amplitude, (ii) small zeta potential, and (iii) slight overlapping of electric double layers.
Klein tunneling and zitterbewegung and the formation of a polarized p-n junction in graphene
Authors: Martinez J. C. , Jalil M. B. A. , Tan S. G.
Published: August 2010

The Klein tunneling of charge pairs in an electrostatically created p-n junction of monolayer graphene is shown to occur at an observable rate for moderate fields. The pairs undergo zitterbewegung (ZBW) in opposite directions leading to their separation and transverse dipole moment, since the valleys contribute constructively. The dipole moment depends critically on the exponential collimation characteristic of Klein tunneling and serves as a diagnostic signature of ZBW.
Real-space self-consistent mean-field theory study of ABC star triblock copolymers
Authors: Li Weihua , Xu Yuci , Zhang Guojie , Qiu Feng , Yang Yuliang , Shi An-Chang
Published: August 2010

The phase behavior of ABC star triblock copolymers is examined using real-space self-consistent mean-field theory. The central part of the triangular phase diagram for ABC triblock copolymers with equal A/B, B/C, and C/A interactions is determined by comparing the free energy of a number of candidate ordered phases. In this region of the phase diagram, the dominant microstructures are cylinders with polygonal cross sections or two-dimensional polygon-tiling patterns. Most of the known polygon-tiling patterns observed in experiments and simulations, plus some neighboring morphologies, are considered in the construction of the phase diagram. The resulting phase behavior is consistent with experiments and computer simulations.
Vector coherent state realization of representations of the affine superalgebra A(1)(,1)
Authors: Wu Yuezhu
Published: August 2010

The method of vector coherent states is generalized to study the representations of the affine superalgebra A(1)(0,1). A new realization of all the irreducible highest weight representations of this affine superalgebra is obtained in terms of holomorphic superdifferential operators in infinitely many Grassmannian and bosonic variables.
Contactless measurement of critical current of high temperature superconductor tape by magnetic circuit
Authors: Gu C. , Qu T.-M. , Zou S.-N. , Han Z.
Published: August 2010

A method based on the principle of the magnetic circuit is proposed and realized for contactless measurement of critical current (Ic) of high temperature superconductor tapes. This method has two unique features: first, it eliminates noises caused by mechanical fluctuations and thus makes high speed and high stability measurement possible and second, adapts for both Bi2Si2Ca2Cu3Ox (Bi2223) and YBa2Cu3O7−x (YBCO) tape, which even has a magnetic substrate. Theoretical analysis is given and an apparatus for the reel-to-reel measurement has been constructed, by which continuous inspection of Ic uniformity of YBCO and Bi2223 tapes measured at different speeds is reported.
Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier
Authors: Amaral G. A. , Arregui A. , Rubio-Lago L. , Rodríguez J. D. , Bañares L.
Published: August 2010

The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S1, which, in turn, undergoes intersystem crossing to the first excited triplet state T1. On the triplet surface, the molecule dissociates into CH3 and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T1. However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S0 after internal conversion from S1. We have characterized the fragments’ KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T1 is presented.
Miniaturized ultrasound scanner by electrowetting
Authors: Deladi S. , Suijver J. F. , Shi Y. S. , Shahzad K. , de Boer B. M. , Rademakers A. J. J. , van der Vleuten C. , Jankovic L. , Bongers E. , Harks E. , Kuiper S.
Published: August 2010

An ultrasound imaging technology based on electrowetting has been developed and integrated in a miniaturized ultrasound scanner. The feasibility of scanning the ultrasound beam of a single-piston transducer in a three-dimensional space by using electrowetting is demonstrated. The technology has a high potential to be embedded in devices where size restrictions do not allow the use of traditional ultrasound phased-array transducers.
Thulium pumped high power supercontinuum in loss-determined optimum lengths of tellurite photonic crystal fiber
Authors: Buccoliero Daniel , Steffensen Henrik , Bang Ole , Ebendorff-Heidepriem Heike , Monro Tanya M.
Published: August 2010

We demonstrate the formation of an ultrabroad supercontinuum (SC) generated in short lengths of highly nonlinear tellurite photonic crystal fibers (PCFs) specifically designed for high power picosecond pumping at the thulium wavelength 1930 nm. The fibers exhibit high losses caused by material absorption below ∼500 nm and at long wavelengths >4000 nm by both material and confinement loss. The fibers are endlessly single-mode with a relative hole size of 0.4 and we tune the pitch (Λ) from 3 to 7 μm to achieve zero-dispersion wavelengths both below and above the pump. We show how the SC has a maximum width at an optimum fiber length after which the bandwidth and power decay due to losses. We thus obtain a maximum bandwidth of 4.6 μm for the PCF with the smallest Λ, i.e., 3 μm at an optimum length of only ∼2.8 cm.
Carbon nanotube films change Poisson’s ratios from negative to positive
Authors: Ma Yin Ji , Yao Xue Feng , Zheng Quan Shui , Yin Ya Jun , Jiang Dong Jie , Xu Guang Hui , Wei Fei , Zhang Qiang
Published: August 2010

In this paper, a discovery is reported that carbon nanotube (CNT) films can change in-plane Poisson’s ratios from negative to positive during a uniaxial tensile loading. First, in situ experimental investigations of the deformation fields about the CNT films fabricated using vertically aligned CNT arrays are performed by digital speckle correlation method, the novel phenomenon for changing Poisson’s ratio from negative to positive during the stretching process is discovered. Furthermore, the physical mechanisms for changing the Poisson’s ratio from negative to positive are explained based on the interactions among CNTs. Finally, a potential engineering application for designing intelligent connector is proposed based on the intriguing Poisson’s ratio of CNT films.
Terahertz instability of optical phonons interacting with plasmons in two-dimensional electron channels
Authors: Sydoruk O. , Kalinin V. , Solymar L.
Published: August 2010

A terahertz (THz) instability can occur when optical phonons interact with drifting solid-state plasmas. We developed a theoretical model for the optical-phonon instability in two-dimensional electron channels. The paper derives the dispersion relation and analyzes the instability using parameters measured in InSb. As the calculations show, strong instability occurs around the longitudinal optical-phonon frequency, and both the growth rate and the unstable frequency band are larger for higher electron densities and lower drift velocities. The results demonstrate the potential of the optical-phonon instability for active THz devices.
Electronic structures of MoO3-based charge generation layer for tandem organic light-emitting diodes
Authors: Bao Q. Y. , Yang J. P. , Li Y. Q. , Tang J. X.
Published: August 2010

The role of MoO3 in charge generation layers for tandem organic light-emitting diodes is investigated. The electronic structure of a typical MoO3-based charge generation layer, consisting of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine, MoO3, and Mg doped 4,7-diphenyl-1,10-phenanthroline (NPB/MoO3/Mg:Bphen) is identified to be a p/n/n junction. It is shown that MoO3 can pronouncedly modify the energy level alignment, beneficial to charge separation at the NPB/MoO3 interface and electron injection at the MoO3/Mg:Bphen interface from MoO3 into suitable molecular energy levels of adjacent emission units. Moreover, Mg:Bphen is favorable to block holes flowing from the anode side directly into the adjacent emission unit.
Transport properties of two laterally coupled vertical quantum dots in series with tunable interdot coupling
Authors: Hatano T. , Amaha S. , Kubo T. , Teraoka S. , Tokura Y. , Gupta J. A. , Austing D. G. , Tarucha S.
Published: August 2010

We describe the electronic properties of a double dot for which the lateral coupling between the two vertical dots can be controlled in situ with a center gate voltage (Vc) and the current flows through the two dots in series. When Vc is large and positive, the two dots merge. As Vc is made less positive, two dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.
Bistable resistance memory switching effect in amorphous InGaZnO thin films
Authors: Kim C. H. , Jang Y. H. , Hwang H. J. , Song C. H. , Yang Y. S. , Cho J. H.
Published: August 2010

We report a bistable resistance switching effect in amorphous InGaZnO (a-IGZO) thin films deposited by a pulsed laser deposition method. The electrical properties of a-IGZO thin films were controlled by the oxygen partial pressure during deposition and this determined the resistance switching effect. We also observed the resistance switching effect with various electrodes such as Pt, Au, and Al. We suggest that the resistance switching effect is related to the formation of a conducting path by metal and/or oxygen vacancy defects in the a-IGZO matrix.
Polarization switching in quasiplanar BiFeO3 capacitors
Authors: You Lu , Liang Elvin , Guo Rui , Wu Di , Yao Kui , Chen Lang , Wang Junling
Published: August 2010

Polarization switching in multiferroic BiFeO3 is studied using a quasiplanar capacitor geometry. Macroscopic quantitative hysteresis measurements using single-pair electrodes yield results that agree well with the theoretical predictions. Nanoscale ferroelectric domain analyses reveal that highly aligned 71° stripe domains are created upon electrical switching. Careful reconstruction of the polarization configuration demonstrates that in-plane polarization reversal is achieved by a coherent 71° switching mechanism, consistent with the macroscopic measurement results. Such control of polarization switching in quasiplanar BiFeO3 capacitors is crucial for the electrical control of the multifunctionality of BiFeO3.
Sequence dependence of DNA bending rigidity
Authors: Geggier Stephanie , Vologodskii Alexander
Published: August 2010

For many aspects of DNA–protein interaction, it is vital to know how DNA bending rigidity (or persistence length,
a
) depends on its sequence. We addressed this problem using the method based on cyclization of short DNA fragments, which allows very accurate determination of
a
. Our approach was based on assigning specific values of
a
to each of 10 distinct dinucleotide steps. We prepared DNA fragments, each about 200 bp in length, with various quasi-periodic sequences, measured their cyclization efficiencies (
j
factors), and fitted the data by the theoretical equation to obtain the values of
a
for each fragment. From these data, we obtained a set of
a
for the dinucleotide steps. To test this set, we used it to design DNA sequences that should correspond to very low and very high values of
a
, prepared the corresponding fragments, and determined their values of
a
experimentally. The measured and calculated values of
a
were very close to one another, confirming that we have found the correct solution to this long-standing problem. The same experimental data also allowed us to determine the sequence dependence of DNA helical repeat.