bluuebunny/crossref_metadata_2025 huggingface dataset:
Bottom-up and top-down effects on algal community dynamics in an aridland river: the Middle Rio Grande, New Mexico*
Authors: Burdett Ayesha , Bixby Rebecca
Published: August 2009

Background/Question/Methods

In this study, we examined interactive effects of nutrient availability, river flow and food web structure on algal growth and species composition in the Middle Rio Grande, New Mexico. Algal community dynamics can be affected by both bottom-up and top-down factors. Algal production may be limited by low levels of nutrients or low light availability. Conversely, production is expected to increase when nutrient levels are high and light availability is not limited. Top-down factors such as grazing by invertebrates can also alter periphyton growth and community composition. Generally, a reduction in grazers results in periphyton biomass increases and shifts in growth forms (to more upright taxa).Nutrient diffusing substrates (NDS) were used in combination with grazer exclusion to investigate bottom-up and top-down effects on periphyton growth and species composition. Previously, NDS has been used in small, headwater streams and not in large sandy rivers like the Middle Rio Grande. NDS were made from inverted terracotta saucers, with four nutrient treatments – control, N, P and N+P. Large invertebrates were excluded from a subset of the saucers using an electrical field. The saucers were placed in a slow-flowing area of the Middle Rio Grande, and samples were collected weekly for a month.

Results/Conclusions

River conditions made it challenging to conduct the NDS experiment. Water levels were variable and turbidity levels were extremely high (>4000NTU). Algal growth was extremely low on all treatments, largely due to light limitation caused by consistently high turbidity levels and a series of flooding and drying events which also decimated organismal growth on the substrates. Initial surveys of the diatom communities indicate extremely low densities and chlorophyll biomass was very low (mean ± se = 0.31 ± 0.09mg/m2). While dense periphyton communities did not develop on the NDS saucers, there was evidence of colonization by invertebrate populations. Blackfly larvae (Simuliidae) were most abundant in earlier samples whereas chironomid larvae (Chironomidae) were more abundant later in the experiment. Also, blackfly larvae were significantly more abundant on control saucers than on N+P saucers in the grazer/non-grazer experiment (P = 0.044). However, it was difficult to detect differences in the abundance of invertebrate grazers among nutrient treatments. Relationships among invertebrate population densities and the availability and diversity of periphyton for grazing will be described. These results are not definitive, but there are indications that nutrients, flow and grazers do influence algal community dynamics.
Web‐based Weight Loss in Primary Care: A Randomized Controlled Trial
Authors: Bennett Gary G. , Herring Sharon J. , Puleo Elaine , Stein Evelyn K. , Emmons Karen M. , Gillman Matthew W.
Published: August 2009

Evidence is lacking regarding effective and sustainable weight loss approaches for use in the primary care setting. We conducted a 12‐week randomized controlled trial to evaluate the short‐term efficacy of a web‐based weight loss intervention among 101 primary care patients with obesity and hypertension. Patients had access to a comprehensive website that used a moderate‐intensity weight loss approach designed specifically for web‐based implementation. Patients also participated in four (two in‐person and two telephonic) counseling sessions with a health coach. Intent‐to‐treat analysis showed greater weight loss at 3 months (−2.56 kg; 95% CI −3.60, −1.53) among intervention participants (−2.28 ± 3.21 kg), relative to usual care (0.28 ± 1.87 kg). Similar findings were observed among intervention completers (−3.05 kg; 95% CI −4.24, −1.85). High rates of participant retention (84%) and website utilization were observed, with the greatest weight loss found among those with a high frequency of website logins (quartile 4 vs. 1: −4.16 kg; 95% CI −1.47, −6.84). The intervention's approach promoted moderate weight loss at 12 weeks, though greater weight loss was observed among those with higher levels of website utilization. Efficacious web‐based weight loss interventions can be successfully offered in the primary care setting.
Testosterone and Visceral Fat in Midlife Women: The Study of Women's Health Across the Nation (SWAN) Fat Patterning Study
Authors: Janssen Imke , Powell Lynda H. , Kazlauskaite Rasa , Dugan Sheila A.
Published: August 2009

Visceral fat (VF) increases with the menopause and is an independent predictor of the metabolic syndrome, diabetes, and cardiovascular disease (CVD) in women. Little is known about how hormonal changes during the menopausal transition are related to the increase in VF. We aimed to determine the relationship between bioavailable testosterone and VF in middle‐aged women at various stages of the menopausal transition and whether this relationship is independent of age and other CVD risk factors. The Study of Women's Health Across the Nation (SWAN) is a longitudinal, community‐based study. This report uses baseline data from a population‐based longitudinal ancillary study at the Chicago site to examine the cross‐sectional relationship between testosterone and computed tomography (CT)–assessed VF in women at different stages of the menopausal transition. Included are 359 women (47.2% black), aged 42–60 years, who were randomly selected from a complete community census in which a 72% participation rate was achieved. In multivariate models, bioavailable testosterone was associated with VF independent of age, race, percent total body fat, and other cardiovascular risk factors. Bioavailable testosterone was a stronger predictor than estradiol and was interchangeable in its strength of association with sex hormone–binding globulin (SHBG). As bioavailable testosterone was associated with VF even after adjusting for insulin resistance, this suggests that it plays an important role in regional fat distribution. Our findings may have direct implications in explaining the effect of menopause‐related testosterone predominance on VF accumulation and subsequent cardiovascular risk.
Parametrial Adipose Tissue and Metabolic Dysfunctions Induced by Fructose‐rich Diet in Normal and Neonatal‐androgenized Adult Female Rats
Authors: Alzamendi Ana , Castrogiovanni Daniel , Ortega Hugo H. , Gaillard Rolf C. , Giovambattista Andres , Spinedi Eduardo
Published: August 2009

Hyperandrogenemia predisposes an organism toward developing impaired insulin sensitivity. The aim of our study was to evaluate endocrine and metabolic effects during early allostasis induced by a fructose‐rich diet (FRD) in normal (control; CT) and neonatal‐androgenized (testosterone propionate; TP) female adult rats. CT and TP rats were fed either a normal diet (ND) or an FRD for 3 weeks immediately before the day of study, which was at age 100 days. Energy intake, body weight (BW), parametrial (PM) fat characteristics, and endocrine/metabolic biomarkers were then evaluated. Daily energy intake was similar in CT and TP rats regardless of the differences in diet. When compared with CT‐ND rats, the TP‐ND rats were heavier, had larger PM fat, and were characterized by basal hypoadiponectinemia and enhanced plasma levels of non‐esterified fatty acid (NEFA), plasminogen activator inhibitor‐1 (PAI‐1), and leptin. FRD‐fed CT rats, when compared with CT‐ND rats, had high plasma levels of NEFA, triglyceride (TG), PAI‐1, leptin, and adiponectin. The TP‐FRD rats, when compared with TP‐ND rats, displayed enhanced leptinemia and triglyceridemia, and were hyperinsulinemic, with glucose intolerance. The PM fat taken from TP rats displayed increase in the size of adipocytes, decrease in adiponectin (protein/gene), and a greater abundance of the leptin gene. PM adipocyte response to insulin was impaired in CT‐FRD, TP‐ND, and TP‐FRD rats. A very short duration of isocaloric FRD intake in TP rats induced severe metabolic dysfunction at the reproductive age. Our study supports the hypothesis that the early‐androgenized female rat phenotype is highly susceptible to developing endocrine/metabolic dysfunction. In turn, these abnormalities enhance the risk of metabolic syndrome, obesity, type 2 diabetes, and cardiovascular disease.
Effect of Diet‐induced Obesity on Acute Pancreatitis Induced by Administration of Interleukin‐12 Plus Interleukin‐18 in Mice
Authors: Pini Maria , Sennello Joseph A. , Cabay Robert J. , Fantuzzi Giamila
Published: August 2009

Obesity is associated with increased severity of acute pancreatitis (AP). We recently developed a model of AP induced by administration of interleukin (IL)‐12+IL‐18, two cytokines that are elevated in patients with AP. In this model, severe AP develops in obese leptin‐deficient ob/ob mice compared to lean littermates. In the present report, we evaluated the pancreatic response of diet‐induced obesity (DIO) mice to IL‐12+IL‐18. Body weight loss and adipose tissue necrosis were more severe and prolonged in cytokine‐injected DIO compared to lean mice. Edematous AP developed in lean mice, whereas DIO mice developed necrotizing AP. Obese DIO mice developed more severe hypocalcemia, increased liver damage and a heightened acute‐phase response compared to lean mice, although leukopenia and thrombocytopenia were of comparable severity in lean and DIO mice. Serum levels of IL‐6, IL‐10, and IL‐22 were significantly higher in DIO compared to lean mice, whereas interferon‐γ and tumor necrosis factor‐α did not differ between the two groups. In conclusion, obesity induced by high‐fat diet is associated with increased disease severity and duration in the model of AP induced by administration of IL‐12+IL‐18.
Association of the MC4R V103I Polymorphism With Obesity: A Chinese Case–control Study and Meta‐analysis in 55,195 Individuals
Authors: Wang Du , Ma Jun , Zhang Su , Hinney Anke , Hebebrand Johannes , Wang Yan , Wang Hai‐Jun
Published: August 2009

Recently, large‐scaled studies suggested a negative association of the infrequent allele of the melanocortin‐4 receptor (MC4R) V103I polymorphism with obesity. We conducted a Chinese case–control study, meta‐analysis in East Asians and in all populations, in order to further assess the association between the V103I polymorphism and reduced body weight and to explore whether the association varies among different ethnic groups. We conducted a case–control study to analyze this polymorphism in 2,012 children of two independent study groups from Beijing, China, no association was found between the V103I polymorphism and obesity or obesity‐related phenotypes (P > 0.10). In the meta‐analysis of 3,526 individuals from six East Asian studies, I103 carriers had a 31% lower risk for obesity (odds ratio (OR) = 0.69, 95% confidence interval (CI): 0.50–0.94, P = 0.02). Subsequently, we performed a large meta‐analysis of the six East Asian studies and 31 studies of other ethnic groups, involving 55,195 individuals with 19,822 obese cases and 35,373 nonobese controls. In total, the individuals with I103 allele had a 21% lower risk for obesity (OR = 0.79, 95% CI: 0.71–0.88, P < 0.0001). In conclusion, this study confirmed and extended the previous findings, suggesting the MC4R V103I polymorphism is negatively associated with human obesity. It provides significant evidence for the association in East Asian populations. Further large‐scaled studies in East Asian populations are needed to validate the association.
Quantitative Magnetic Resonance (QMR) for Longitudinal Evaluation of Body Composition Changes With Two Dietary Regimens
Authors: Myint Khin Swe , Napolitano Antonella , Miller Sam R. , Murgatroyd Peter R. , Elkhawad Maysoon , Nunez Derek J.R. , Finer Nick
Published: August 2009

We have recently reported a validation study of a prototype low‐field strength quantitative magnetic resonance (QMR) instrument for measurement of human body composition (EchoMRI‐AH). QMR was very precise, but underreported fat mass (FM) by 2–4 kg when compared to a 4‐compartment (4C) model in this cross‐sectional study. Here, we report the performance of an updated instrument in two longitudinal studies where FM was decreasing. Healthy obese volunteers were given a modest energy deficit diet for 8 weeks (study A) and obese patients with heart failure and/or at high cardiovascular risk were prescribed a low energy liquid diet for 6 weeks (study B). FM was measured at the start and end of these periods by QMR, dual‐energy X‐ray absorptiometry (DXA) and 4C. A higher proportion of the weight lost came from fat in study A compared with study B, where loss of total body water (TBW) played a greater part. The intraclass correlation between QMR and 4C estimates of FM loss (ΔFat) was 0.95, but 20 of 22 estimates of ΔFat by QMR were lower than the corresponding estimate by the 4C model. Bland–Altman analysis demonstrated that estimates of FM loss by QMR were ∼1.0 and 0.7 kg lower than those obtained with 4C (P = 0.0008) and DXA (P = 0.049), respectively. Measurement precision remained high. QMR measurement should prove valuable for quantifying modest changes of FM in small trials.
A 12‐Week Aerobic Exercise Program Reduces Hepatic Fat Accumulation and Insulin Resistance in Obese, Hispanic Adolescents
Authors: van der Heijden Gert‐Jan , Wang Zhiyue J. , Chu Zili D. , Sauer Pieter J.J. , Haymond Morey W. , Rodriguez Luisa M. , Sunehag Agneta L.
Published: August 2009

The rise in obesity‐related morbidity in children and adolescents requires urgent prevention and treatment strategies. Currently, only limited data are available on the effects of exercise programs on insulin resistance, and visceral, hepatic, and intramyocellular fat accumulation. We hypothesized that a 12‐week controlled aerobic exercise program without weight loss reduces visceral, hepatic, and intramyocellular fat content and decreases insulin resistance in sedentary Hispanic adolescents. Twenty‐nine postpubertal (Tanner stage IV and V), Hispanic adolescents, 15 obese (7 boys, 8 girls; 15.6 ± 0.4 years; 33.7 ± 1.1 kg/m2; 38.3 ± 1.5% body fat) and 14 lean (10 boys, 4 girls; 15.1 ± 0.3 years; 20.6 ± 0.8 kg/m2; 18.9 ± 1.5% body fat), completed a 12‐week aerobic exercise program (4 × 30 min/week at ≥70% of peak oxygen consumption (VO2peak)). Measurements of cardiovascular fitness, visceral, hepatic, and intramyocellular fat content (magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS)), and insulin resistance were obtained at baseline and postexercise. In both groups, fitness increased (obese: 13 ± 2%, lean: 16 ± 4%; bothP< 0.01). In obese participants, intramyocellular fat remained unchanged, whereas hepatic fat content decreased from 8.9 ± 3.2 to 5.6 ± 1.8%;P< 0.05 and visceral fat content from 54.7 ± 6.0 to 49.6 ± 5.5 cm2;P< 0.05. Insulin resistance decreased indicated by decreased fasting insulin (21.8 ± 2.7 to 18.2 ± 2.4 µU/ml;P< 0.01) and homeostasis model assessment of insulin resistance (HOMAIR) (4.9 ± 0.7 to 4.1 ± 0.6;P< 0.01). The decrease in visceral fat correlated with the decrease in fasting insulin (R2= 0.40;P< 0.05). No significant changes were observed in any parameter in lean participants except a small increase in lean body mass (LBM). Thus, a controlled aerobic exercise program, without weight loss, reduced hepatic and visceral fat accumulation, and decreased insulin resistance in obese adolescents.
Mediators of Weight Loss and Weight Loss Maintenance in Middle‐aged Women
Authors: Teixeira Pedro J. , Silva Marlene N. , Coutinho Sílvia R. , Palmeira António L. , Mata Jutta , Vieira Paulo N. , Carraça Eliana V. , Santos Teresa C. , Sardinha Luís B.
Published: August 2009

Long‐term behavioral self‐regulation is the hallmark of successful weight control. We tested mediators of weight loss and weight loss maintenance in middle‐aged women who participated in a randomized controlled 12‐month weight management intervention. Overweight and obese women (N = 225, BMI = 31.3 ± 4.1 kg/m2) were randomly assigned to a control or a 1‐year group intervention designed to promote autonomous self‐regulation of body weight. Key exercise, eating behavior, and body image variables were assessed before and after the program, and tested as mediators of weight loss (12 months, 86% retention) and weight loss maintenance (24 months, 81% retention). Multiple mediation was employed and an intention‐to‐treat analysis conducted. Treatment effects were observed for all putative mediators (Effect size: 0.32–0.79, P < 0.01 vs. controls). Weight change was −7.3 ± 5.9% (12‐month) and −5.5 ± 5.0% (24‐month) in the intervention group and −1.7 ± 5.0% and −2.2 ± 7.5% in controls. Change in most psychosocial variables was associated with 12‐month weight change, but only flexible cognitive restraint (P < 0.01), disinhibition (P < 0.05), exercise self‐efficacy (P < 0.001), exercise intrinsic motivation (P < 0.01), and body dissatisfaction (P < 0.05) predicted 24‐month weight change. Lower emotional eating, increased flexible cognitive restraint, and fewer exercise barriers mediated 12‐month weight loss (R2 = 0.31, P < 0.001; effect ratio: 0.37), but only flexible restraint and exercise self‐efficacy mediated 24‐month weight loss (R2 = 0.17, P < 0.001; effect ratio: 0.89). This is the first study to evaluate self‐regulation mediators of weight loss and 2‐year weight loss maintenance, in a large sample of overweight women. Results show that lowering emotional eating and adopting a flexible dietary restraint pattern are critical for sustained weight loss. For long‐term success, interventions must also be effective in promoting exercise intrinsic motivation and self‐efficacy.
Admixture Mapping of Obesity‐related Traits in African Americans: The Atherosclerosis Risk in Communities (ARIC) Study
Authors: Cheng Ching‐Yu , Reich David , Coresh Josef , Boerwinkle Eric , Patterson Nick , Li Man , North Kari E. , Tandon Arti , Bailey‐Wilson Joan E. , Wilson James G. , Kao W.H. Linda
Published: August 2009

Obesity is an important cause of morbidity and mortality worldwide. In the United States, the prevalence of obesity is higher in African Americans than whites, even after adjustment for socioeconomic status (SES). This leads to the hypothesis that differences in genetic background may contribute to racial/ethnic differences in obesity‐related traits. We tested this hypothesis by conducting a genome‐wide admixture mapping scan using 1,350 ancestry‐informative single‐nucleotide polymorphisms (SNPs) in 3,531 self‐identified blacks from the Atherosclerosis Risk in Communities (ARIC) study. We used these markers to estimate the overall proportions of European ancestry (PEAs) for each individual and then scanned for the association between PEA and obesity‐related traits (both continuous and dichotomous) at each locus. The median (interquartile range) PEA was 0.151 (0.115). PEA was inversely correlated with continuous BMI, weight, and subscapular skinfold thickness, even after adjusting for socioeconomic factors. In contrast, PEA was positively correlated with BMI‐adjusted waist circumference. Using admixture mapping on dichotomized traits, we identified a locus on 2p23.3 to be suggestively associated with BMI (locus‐specific lod = 4.11) and weight (locus‐specific lod = 4.07). After adjusting for global PEA, each additional copy of a European ancestral allele at the 2p23.3 peak was associated with a BMI decrease of ∼0.92 kg/m2 (P = 2.9 × 10−5). Further mapping in this region on chromosome 2 may be able to uncover causative variants underlying obesity, which may offer insights into the control of energy homeostasis.
Interactions of the 67 kDa laminin receptor and its precursor with laminin
Authors: Fatehullah Aliya , Doherty Caroline , Pivato Géraldine , Allen George , Devine Lynda , Nelson John , Timson David J.
Published: August 2009

The 67LR (67 kDa laminin receptor) enables cells to interact with components of the extracellular matrix. The molecule is derived from the 37LRP (37 kDa laminin receptor precursor); however, the precise molecular mechanism of this conversion is unknown. Recombinant 37LRP, expressed in and purified from Escherichia coli, bound to human laminin in a SPR (surface plasmon resonance) experiment. 67LR isolated from human breast-cancer-derived cells in culture was also shown to bind to laminin by SPR. However, the kinetics of association are qualitatively different. 37LRP, but not 67LR, binds to heparan sulfate. The binding of 37LRP to heparan sulfate did not affect the interaction of 37LRP with laminin. In contrast, heparan sulfate reduces the extent of binding of laminin to 67LR. Taken together, these results show that 37LRP has some of the biological activities of 67LR, even prior to the conversion event. However, the conversion affects the sites of interaction with both laminin and heparan sulfate.
Inhibition of transcription factor assembly and structural stability on mitoxantrone binding with DNA
Authors: Khan Shahper N. , Danishuddin Mohd , Khan Asad U.
Published: August 2009

MTX (mitoxantrone) is perhaps the most promising drug used in the treatment of various malignancies. Comprehensive literature on the therapeutics has indicated it to be the least toxic in its class, although its mechanism of action is still not well defined. In the present study, we have evaluated the associated binding interactions of MTX with naked DNA. The mechanism of MTX binding with DNA was elucidated by steady-state fluorescence and a static-type quenching mechanism is suggested for this interaction. Thermodynamic parameters from van 't Hoff plots showed that the interaction of these drugs with DNA is an entropically driven phenomenon. The binding mode was expounded by attenuance measurements and competitive binding of a known intercalator. Sequence specificity of these drug–DNA complexes was analysed by FTIR (Fourier-transform infrared) spectroscopy and molecular modelling studies. CD spectroscopy and the plasmid nicking assay showed that the binding of this drug with DNA results in structural and conformational perturbations. EMSA (electrophoretic mobility-shift assay) results showed that these drug–DNA complexes prevent the binding of octamer TF (transcription factor) to DNA. In summary, the study implicates MTX-induced conformational instability and transcription inhibition on DNA binding.
Knowledge Generation through Human-Centered Information Visualization
Authors: Einsfeld Katja , Ebert Achim , Kerren Andreas , Deller Matthias
Published: August 2009

One important intention of human-centered information visualization is to represent huge amounts of abstract data in a visual representation that allows even users from foreign application domains to interact with the visualization, to understand the underlying data, and finally, to gain new, application-related knowledge. The visualization will help experts as well as non-experts to link previously or isolated knowledge-items in their mental map with new insights. Our approach explicitly supports the process of linking knowledge-items with three concepts. At first, the representation of data items in an ontology categorizes and relates them. Secondly, the use of various visualization techniques visually correlates isolated items by graph-structures, layout, attachment, integration or hyperlink techniques. Thirdly, the intensive use of visual metaphors relates a known source domain to a less known target domain. In order to realize a scenario of these concepts, we developed a visual interface for non-experts to maintain complex wastewater treatment plants. This domain-specific application is used to give our concepts a meaningful background.
Dynamic Collaboration: A Personal Reflection
Authors: Aron Dave
Published: August 2009

This paper explores the nature of, and possibilities arising from, dynamic collaboration, where large numbers of people can collaborate on an evolving set of initiatives, without prior knowledge of each other. It references early examples of dynamic collaboration including Topcoder, Innocentive, Zopa, and Wikipedia. It then speculates about the future of dynamic collaboration.
Influence of nozzle sharpness on the flow fields of V-notched nozzle jets
Authors: New T. H. , Tsovolos D.
Published: August 2009

This study reports on an experimental investigation on laminar jets discharging from V-notched nozzles of different relative sharpness. Each nozzle consists of two smooth peaks and two sharp troughs and its sharpness is defined by the aspect ratio (AR) of the half ellipses which make up each half of the V-notch. Two ARs of AR=2 and 4 are used here to look at how changes in relative sharpness affect the vortex dynamics and quantifiable flow characteristics. Flow visualization results reveal the formation of coherent streamwise vortices at both peaks and troughs, as well as the bending of the large-scale vortex roll-ups. Digital particle-image velocimetry measurements reveal that peaks produce vortex roll-ups which are stronger than those associated with the troughs and that their strength difference increases with nozzle sharpness. Correspondingly, flow stresses show that the peaks and troughs tend to confer more significant effects upon the Reynolds normal stresses when nozzle sharpness increases, with Reynolds shear stresses remaining relatively invariant. Comparisons with an earlier study using an AR=1.5 nozzle show that depending on the nozzle sharpness, the large-scale vortex-bending behavior linked to axis switching can reverse in direction. Unlike the earlier study which produced vortex bending toward the upstream direction, the present sharper nozzles resulted in vortex bending in the downstream direction. Earlier formation of streamwise vortices at the troughs and associated vortex disconnection/reconnection processes are deduced to produce such a discrepancy and flow interpretations are presented for further clarifications.
Molecular dynamics simulation of the thin film deposition of Co/Cu(111) with Pb surfactant
Authors: Kim Byung-Hyun , Chung Yong-Chae
Published: August 2009

Using molecular dynamics simulation, the effect of Pb surfactant for the thin film growth of Co atoms on Cu(111) substrate was investigated. Specifically, the behavior of Co atoms being deposited on Cu(111) substrate with predeposited Pb layer was extensively investigated and compared with the case of without Pb layer to explain the effect of Pb surfactant. It was observed that Pb layer was floating during the Co deposition. It was, quantitatively, found that Pb surfactant played an important role in suppression of active diffusion of Co atoms, which was accomplished by the increase in the surface diffusion barrier energy. The energy change in the deposited Co adatom on the Cu(111) substrate with predeposited Pb layer showed that the approaching Co adatom penetrated into the Pb layer; then, the Co adatom settled down on the Cu(111) substrate. Consequently, Pb atoms around Co adatom suppressed the further diffusion of Co adatom.
Ultraviolet Raman microscopy of single and multilayer graphene
Authors: Calizo Irene , Bejenari Igor , Rahman Muhammad , Liu Guanxiong , Balandin Alexander A.
Published: August 2009

We investigated Raman spectra of single-layer and multilayer graphene under ultraviolet laser excitation at the wavelength λ=325 nm. It was found that while graphene’s G peak remains pronounced in UV Raman spectra, the 2D-band intensity undergoes severe quenching. The evolution of the ratio of the intensities of the G and 2D peaks, I(G)/I(2D), as the number of graphene layers n changes from n=1 to n=5, is different in UV Raman spectra from that in conventional visible Raman spectra excited at the 488 and 633 nm wavelengths. The 2D band under UV excitation shifts to larger wave numbers and is found near 2825 cm−1. The observed UV Raman features of graphene were explained by invoking the resonant scattering model. The obtained results contribute to the Raman nanometrology of graphene by providing an additional metric for determining the number of graphene layers and assessing its quality.
Optical conductance and transmission in bilayer graphene
Authors: Dong H. M. , Zhang J. , Peeters F. M. , Xu W.
Published: August 2009

We present a theoretical study of the optoelectronic properties of bilayer graphene. The optical conductance and transmission coefficient are calculated using the energy-balance equation derived from a Boltzmann equation for an air/graphene/dielectric-wafer system. For short wavelengths (λ<0.2 μm), we obtain the universal optical conductance σ=e2/(2ℏ). Interestingly, there exists an optical absorption window in the wavelength range 10–100 μm, which is induced by different transition energies required for inter- and intra-band optical absorptions in the presence of the Moss–Burstein effect. As a result, the position and width of this absorption window depend sensitively on temperature, carrier density, and sample mobility of the system. These results are relevant for applications of recently developed graphene devices in advanced optoelectronics such as the infrared photodetectors.
Structural stability and compressibility of group IV transition metals-based bulk metallic glasses under high pressure
Authors: Stemshorn Andrew K. , Vohra Yogesh K.
Published: August 2009

High-pressure x-ray diffraction studies have been carried out on the two group IV transition metals-based bulk metallic glasses (BMGs) Zr57Cu15.4Ni12.6Al10Nb5 and Ti42Zr24Cu15.5Ni14.5Be4 to a pressure of 30 GPa at ambient temperature in a diamond anvil cell. Image plate x-ray diffraction studies under high pressure were carried out at a synchrotron source and the two BMG diffraction bands can be followed to the highest pressure using an internal copper pressure standard. The amorphous phase is observed to be stable to the highest static pressure of 30 GPa suggesting that the phase change observed in dynamical pressure experiments is related to an increase in temperature. The measured bulk modulus (B0) and its pressure derivative (B′) are 118 GPa and 3.11 for Zr-based BMG and 116 GPa and 2.84 for Ti-based BMG. The measured bulk modulus for BMG’s by x-ray diffraction technique is consistent with the ultrasonic measurements. The decompression data reveal an increase in density by 3%–4% at ambient condition after pressure cycling to 30 GPa indicating reduction in excess free volume.
Nanoscale phase transformation in Ge2Sb2Te5 using encapsulated scanning probes and retraction force microscopy
Authors: Bhaskaran Harish , Sebastian Abu , Pauza Andrew , Pozidis Haralampos , Despont Michel
Published: August 2009

Encapsulated conducting probes that can sustain high currents are used to study the nanoscale properties of thin-film stacks comprising of a phase-change chalcogenide, Ge2Sb2Te5. Scaling studies on this promising candidate for random-access memory devices had thus far required extensive lithography and nanoscale growth. This seriously hampers rapid materials characterization. This article describes the use of two key techniques, an encapsulated conductive probe and its use in retraction mode, whereby the attractive force between tip and sample is used to maintain electrical contact. The effective transformation of nanoscale dots of amorphous Ge2Sb2Te5 into the crystalline state is achieved and the electrical conductivity of the transformed structures is probed. The use of retraction force microscopy in a robust manner is demonstrated by reading the conductivity of the crystalline dots. Both these techniques could enable rapid electrical characterization of nanoscale materials, without extensive nanopatterning, thus reducing material development cycles.
Vapor-solid-solid radial growth of Ge nanowires
Authors: Li C. B. , Usami K. , Mizuta H. , Oda S.
Published: August 2009

The radial growth of Ge nanowire via chemical vapor deposition is discussed in detail. Vapor-solid-solid (VSS) growth mechanism is believed to dominate the nanowire growth in radial direction, which contributes to the increase of the diameter of nanowire. After the Au catalysts on the tip are consumed for a long growth time, the nanowire with a rough surface will be grown due to the selective VSS radial growth.
Erratum: “Parametric instability of a driven ion-acoustic wave” [Phys. Plasmas 12, 092101 (2005)]
Authors: Pesme D. , Riconda C. , Tikhonchuk V. T.
Published: August 2009

In this erratum, (i) we repair a typographical error in Eq. (44) of our publication [D. Pesme, C. Riconda, and V. T. Tikhonchuk, Phys. Plasmas 12, 092101 (2005)] and (ii) we correct an algebraic mistake concerning the Korteweg-de-Vries (KdV) limits (44) and (49) of the general dispersion relation (39) of our publication. This algebraic error invalidates some of our statements concerning the existence of the decay H2 instability in the KdV limit. We consequently correct the approximate equation governing the decay H2 instability in the KdV limit. We display the corrected figures corresponding to the numerical solutions of the general dispersion relation (39).
A uniaxial tension system and its applications in testing of thin films and small components
Authors: Wu Wenwang , Li Xide , Liu Liang
Published: August 2009

The aim of this investigation is to develop a uniaxial tension system for testing very small samples that allows observation of the gauge section by optical or atomic force microscopy. Major parts of the system consist of a pair of identical piezoelectric actuators, two symmetrical double-cantilevered force sensors, and two symmetrical universal coupling joints. It can accomplish both-end loaded uniaxial tension to produce centrosymmetric deformations of the tested objects in the field of view and can apply tensile loads in the range from 7.8 μN to 15 N to the samples. Sample extensions from submicrometers to 100 μm can be measured with displacement resolution of several tens of nanometers. The system’s performance is demonstrated by tests of a polycrystalline aluminum alloy thin sheet, a mica thin sheet, and a fibril of bamboo.
A versatile dual spot laser scanning confocal microscopy system for advanced fluorescence correlation spectroscopy analysis in living cell
Authors: Ferrand Patrick , Pianta Martina , Kress Alla , Aillaud Alexandre , Rigneault Hervé , Marguet Didier
Published: August 2009

A fluorescence correlation spectroscopy system based on two independent measurement volumes is presented. The optical setup and data acquisition hardware are detailed, as well as a complete protocol to control the location, size, and shape of the measurement volumes. A method that allows to monitor independently the excitation and collection efficiency distribution is proposed. Finally, a few examples of measurements that exploit the two spots in static and/or scanning schemes are reported.
Numerical and experimental study of microwave-excited microplasma and micronozzle flow for a microplasma thruster
Authors: Takahashi Takeshi , Takao Yoshinori , Eriguchi Koji , Ono Kouichi
Published: August 2009

Plasma and aerodynamic features have been investigated for a microplasma thruster of electrothermal type using azimuthally symmetric microwave-excited microplasmas. The thruster developed consisted of a microplasma source 1.5 mm in diameter, 10 mm long with a rod antenna on axis, and a converging-diverging micronozzle 1 mm long with a throat 0.2 mm in diameter. The feed or propellant gas employed was Ar at pressures of 10–50 kPa with flow rates of 10–70 SCCM (SCCM denotes standard cubic centimeter per minute at STP) and the surface wave-excited plasmas were established by 4.0 GHz microwaves at powers of ≤6 W. Numerical analysis was made for the plasma and flow properties by developing a self-consistent, two-dimensional model, where a two-temperature fluid model was applied to the entire region through the microplasma source to the micronozzle (or through subsonic to supersonic); in the former, an electromagnetic model based on the finite difference time-domain approximation was also employed for analysis of microwaves interacting with plasmas. In experiments, optical emission spectroscopy was employed with a small amount of additive gases of H2 and N2, to measure the plasma electron density and gas temperature in the microplasma source around the top of the microwave antenna, just upstream of the micronozzle inlet; in practice, the numerical analysis exhibited a maximum thereabout for the microwave power density absorbed, plasma density, and gas temperature. The Stark broadening of H Balmer line and the vibronic spectrum of N2 second positive band indicated that the electron density was in the range of (3–12)×1019 m−3 and the gas or rotational temperature was in the range of 700–1000 K. The thrust performance was also measured by using a microthrust stand with a combination of target and pendulum methods, giving a thrust in the range of 0.2–1.4 mN, a specific impulse in the range of 50–80 s, and a thrust efficiency in the range of 2%–12%. These experimental results were consistent with those of numerical analysis, depending on microwave power and gas flow rate.
Deconvolution-based correction of alkali beam emission spectroscopy density profile measurements
Authors: Pusztai I. , Pokol G. , Dunai D. , Réfy D. , Pór G. , Anda G. , Zoletnik S. , Schweinzer J.
Published: August 2009

A deconvolution-based correction method of the beam emission spectroscopy (BES) density profile measurement is demonstrated by its application to simulated measurements of the COMPASS and TEXTOR tokamaks. If the line of sight is far from tangential to the flux surfaces, and the beam width is comparable to the scale length on which the light profile varies, the observation may cause an undesired smoothing of the light profile, resulting in a non-negligible underestimation of the calculated density profile. This effect can be reduced significantly by the emission reconstruction method, which gives an estimate of the emissivity along the beam axis from the measured light profile, taking the finite beam width and the properties of the measurement into account in terms of the transfer function of the observation. Characteristics and magnitude of the mentioned systematic error and its reduction by the introduced method are studied by means of the comprehensive alkali BES simulation code RENATE.
Are isomers of the vinyl cyanide ion missing links for interstellar pyrimidine formation?
Authors: Bera Partha P. , Lee Timothy J. , Schaefer Henry F.
Published: August 2009

In the interstellar medium (ISM) there are many regions where the formation of molecules is kinetically driven rather than thermochemically, which can lead to the formation of many isomers even though some may be fairly higher in energy relative to the molecular global minimum. Recent laboratory experiments where noble gas cations are reacted with pyrimidine favored the formation of C3H3N+, but the molecular structure(s) of this fragment was not determined. Microscopic reversibility means that pyrimidine could form under interstellar conditions should the required C3H3N+ reactant be detected in the ISM. Hence C3H3N+ could be a strong candidate for involvement in the formation of heterocyclic biomolecules such as pyrimidine in the ISM. In this study, we have investigated the low energy isomers of the acrylonitrile ion (C3H3N+) using density functional theory as well as high levels of ab initio theory, namely, the singles and doubles coupled-cluster theory that includes a perturbational correction for connected triple excitations, denoted as CCSD(T). An automated stochastic search procedure, Kick, has been employed to find isomers on the ground state doublet potential energy surface. Several new structures, along with all the previously reported minima, have been found. The global minimum H2CCCNH+ is energetically much lower than either H2CC(H)CN+, the acrylonitrile ion, or HCC(H)NCH+, the most likely intermediate of the reaction between HCCH+ and HCN. These isomers are connected to the global minimum via several transition states and intermediates. The results indicate that not only the global minimum but also several higher energy isomers of the C3H3N+ ion could be important in interstellar pyrimidine formation. The isomeric molecules have the necessary CCNC backbone needed for the reaction with HCN to form the cyclic pyrimidine framework. The structural and rotational parameters of all the isomers studied in this work have been predicted at the CCSD(T) level of theory with the anticipation that it will expedite their laboratory as well as astronomical identification.
Comment on “Guiding center plasma models in three dimensions” [Phys. Plasmas 15, 092112 (2008)]
Authors: Krommes John A.
Published: August 2009

Recent assertions that guiding-center theory breaks down at second order for three-dimensional magnetic fields with nonzero torsion are argued to be incorrect.
A density-functional study of the structures and electronic properties of neutral, anionic, and endohedrally doped InxPx clusters
Authors: Longo R. C. , Carrete J. , Aguilera-Granja F. , Vega A. , Gallego L. J.
Published: August 2009

We report extensive ab initio calculations of the structures, binding energies, and magnetic moments of InxPx and InxPx− clusters (x=1–15) using a density-functional method that employs linear combinations of pseudoatomic orbitals as basis sets, nonlocal norm-conserving pseudopotentials, and the generalized gradient approximation for exchange and correlation. Our results, which are compared with those obtained previously for some of these clusters by means of all-electron calculations, show that hollow cages with alternating In–P bonds are energetically preferred over other structures for both the neutral and anionic species within the range x=6–15. We also consider the endohedrally doped X@In10P10 (X=Cr,Mn,Fe,Co) and Ti@InxPx (x=7–12) clusters. Our results show that, except for Ti@In7P7 and Ti@In8P8, the transition metal atoms preserve their atomic spin magnetic moments when encapsulated in the InP cages, instead of suffering either a spin crossover or a spin quenching due to hybridization effects. We also show that the stabilities of some empty and doped InP cages can be explained on the basis of the jellium model.
100 ps precessional spin-transfer switching of a planar magnetic random access memory cell with perpendicular spin polarizer
Authors: Papusoi C. , Delaët B. , Rodmacq B. , Houssameddine D. , Michel J.-P. , Ebels U. , Sousa R. C. , Buda-Prejbeanu L. , Dieny B.
Published: August 2009

Ultrafast spin-transfer precessional switching between two stable states of a magnetic random access memory device is demonstrated in structures comprising a perpendicularly magnetized polarizing layer (PL⊥), an in-plane magnetized free layer (FL), and an in-plane magnetized analyzing layer (AL) in a PL⊥/spacer/FL/spacer/AL stack. Back and forth switching can be achieved with sub-ns current pulses of the same polarity. The spin-torque influence from the analyzer leads to an asymmetric dependence of the switching properties as a function of the current sign and initial state.
Observation of dielectric dispersion of BaTiO3 ceramics in the gigahertz frequency region by scattering parameter measurement using a pair of surface electrodes
Authors: Nakayama A. , Yoshikawa H.
Published: August 2009

A measurement method is proposed for observing dielectric dispersion of ferroelectric ceramics in the gigahertz region. This method is based on scattering parameter (S11) measurements using a pair of electrodes. Using this method, relaxation-type dielectric dispersion of BaTiO3 ceramics is observed in the range from 100 MHz to 20 GHz. The relaxation frequency shifts to lower frequencies with larger grain size. In coarse-grain BaTiO3 ceramics, two peaks of the imaginary part of permittivity are observed, depending on the amount of time after thermal treatment. The contribution of the ferroelectric domain and ionic vibration to the dielectric dispersion is discussed.
Phase space method for identification of driven nonlinear systems
Authors: Carroll T. L.
Published: August 2009

We seek in this paper to differentiate driven nonlinear systems using only a single output signal from the driven system. We do not have access to the driving signal. We demonstrate the phase space identification techniques with an experimental model of a radio transmitter. We restrict the driving signals to nearly periodic signals, because these types of signals are the most common signals used in real transmitters. We find that by studying our transmitter as a driven nonlinear system, we are able to distinguish one transmitter from another. This work may have consequences for real transmitters.
Natural versus forced convection in laminar starting plumes
Authors: Rogers Michael C. , Morris Stephen W.
Published: August 2009

A starting plume or jet has a well-defined, evolving head that is driven through the surrounding quiescent fluid by a localized flux of either buoyancy or momentum, or both. We studied the scaling and morphology of starting plumes produced by a constant flux of buoyant fluid from a small, submerged outlet. The plumes were laminar and spanned a wide range of plume Richardson numbers Ri. Ri is the dimensionless ratio of the buoyancy forces to inertial effects and thus our measurements crossed over the transition between buoyancy-driven plumes and momentum-driven jets. We found that the ascent velocity of the plume, nondimensionalized by Ri, exhibits a power law relationship with Re, the Reynolds number of the injected fluid in the outlet pipe. We also found that as the threshold between buoyancy-driven and momentum-driven flows was crossed, two distinct types of plume head morphologies exist: confined heads, produced in the Ri>1 regime, and dispersed heads, which are found in the Ri<1 regime. Head dispersal is caused by a breakdown of overturning motion in the head and a local Kelvin–Helmholtz instability on the exterior of the plume.
Experimental study of gravitation effects in the flow of a particle-laden thin film on an inclined plane
Authors: Ward Thomas , Wey Chi , Glidden Robert , Hosoi A. E. , Bertozzi A. L.
Published: August 2009

The flow of viscous, particle-laden wetting thin films on an inclined plane is studied experimentally as the particle concentration is increased to the maximum packing limit. The slurry is a non-neutrally buoyant mixture of silicone oil and either solid glass beads or glass bubbles. At low concentrations (ϕ<0.45), the elapsed time versus average front position scales with the exponent predicted by Huppert [Nature (London) 300, 427 (1982)]. At higher concentrations, the average front position still scales with the exponent predicted by Huppert on some time interval, but there are observable deviations due to internal motion of the particles. At the larger concentration values and at later times, the departure from Huppert is seen to strongly depend on total slurry volume VT, inclination angle α, density difference, and particle size range.
Effective viscosity model for electron heating in warm magnetized inductively coupled plasma discharges
Authors: Aman-ur-Rehman  , Lee J. K.
Published: August 2009

An effective viscosity model for warm magnetized inductively coupled plasma (MICP) discharges has been derived. It calculates the power absorbed inside MICP discharges that takes nonlocal behavior into account with the help of effective viscosity terms in the momentum equations for right-handed and left-handed components of the wave. The validity of this model for warm MICP discharges has been checked by comparing it with self-consistent kinetic model for warm MICP discharges. This effective viscosity model shows nonmonotonic decay for right- and left-handed components of the electric field inside MICP discharges. It also shows regions of negative power absorption which cannot be shown using conventional fluid models. The power absorbed per unit area (for right- and left-handed components) calculated using effective viscosity model is similar to that calculated using computationally extensive kinetic models over a wide range of MICP discharge conditions.