bluuebunny/crossref_metadata_2025 huggingface dataset:
Postprandial Endothelial Function, Inflammation, and Oxidative Stress in Obese Children and Adolescents
Authors: Metzig Andrea M. , Schwarzenberg Sarah J. , Fox Claudia K. , Deering Mary M. , Nathan Brandon M. , Kelly Aaron S.
Published: January 2011

Most studies in adults suggest that acute glucose consumption induces a transient impairment in endothelial function. We hypothesized that obese youth would demonstrate reduced endothelial function and increased inflammation and oxidative stress following acute glucose ingestion and that transient elevations in plasma glucose would correlate with endothelial dysfunction, inflammation, and oxidative stress. Thirty‐four obese (BMI ≥95th percentile) children and adolescents (age 12.4 ± 2.6 years; BMI = 37.9 ± 6.7 kg/m2; 50% females) underwent measurement of endothelial function (reactive hyperemic index (RHI)), glucose, insulin, C‐reactive protein (CRP), interleukin‐6 (IL‐6), circulating oxidized low‐density lipoprotein (oxLDL), and myeloperoxidase (MPO) in a fasting state and at 1‐ and 2‐h following glucose ingestion. Repeated measures ANOVA with Tukey post‐tests and Pearson correlations were performed. Glucose and insulin levels significantly increased at 1‐ and 2‐h (all P values < 0.001). Compared to baseline, there were no statistically significant differences in 1‐ and 2‐h RHI, CRP, IL‐6, and oxLDL. However, MPO significantly decreased at the 1‐ (P < 0.05) and 2‐h (P < 0.001) time points. At the 1‐h time point, glucose level was significantly inversely correlated with RHI (r = −0.40, P < 0.05) and at the 2‐h time point, glucose level was positively correlated with MPO (r = 0.40, P < 0.05). An acute oral glucose load does not reduce endothelial function or increase levels of inflammation or oxidative stress in obese youth. However, associations of postprandial hyperglycemia with endothelial function and oxidative stress may have implications for individuals with impaired glucose tolerance or frank type 2 diabetes.
Multilocus Analyses of Seven Candidate Genes Suggest Interacting Pathways for Obesity‐Related Traits in Brazilian Populations
Authors: Angeli Cláudia B. , Kimura Lilian , Auricchio Maria T. , Vicente João P. , Mattevi Vanessa S. , Zembrzuski Verônica M. , Hutz Mara H. , Pereira Alexandre C. , Pereira Tiago V. , Mingroni‐Netto Regina C.
Published: January 2011

We investigated whether variants in major candidate genes for food intake and body weight regulation contribute to obesity‐related traits under a multilocus perspective. We studied 375 Brazilian subjects from partially isolated African‐derived populations (quilombos). Seven variants displaying conflicting results in previous reports and supposedly implicated in the susceptibility of obesity‐related phenotypes were investigated: β2‐adrenergic receptor (ADRB2) (Arg16Gly), insulin induced gene 2 (INSIG2) (rs7566605), leptin (LEP) (A19G), LEP receptor (LEPR) (Gln223Arg), perilipin (PLIN) (6209T > C), peroxisome proliferator‐activated receptor‐γ (PPARG) (Pro12Ala), and resistin (RETN) (−420C > G). Regression models as well as generalized multifactor dimensionality reduction (GMDR) were employed to test the contribution of individual effects and higher‐order interactions to BMI and waist‐hip ratio (WHR) variation and risk of overweight/obesity. The best multilocus association signal identified in the quilombos was further examined in an independent sample of 334 Brazilian subjects of European ancestry. In quilombos, only the PPARG polymorphism displayed significant individual effects (WHR variation, P = 0.028). No association was observed either with the risk of overweight/obesity (BMI ≥ 25 kg/m2), risk of obesity alone (BMI ≥ 30 kg/m2) or BMI variation. However, GMDR analyses revealed an interaction between the LEPR and ADRB2 polymorphisms (P = 0.009) as well as a third‐order effect involving the latter two variants plus INSIG2 (P = 0.034) with overweight/obesity. Assessment of the LEPR‐ADRB2 interaction in the second sample indicated a marginally significant association (P = 0.0724), which was further verified to be limited to men (P = 0.0118). Together, our findings suggest evidence for a two‐locus interaction between the LEPR Gln223Arg and ADRB2 Arg16Gly variants in the risk of overweight/obesity, and highlight further the importance of multilocus effects in the genetic component of obesity.
Efficacy of a School‐Based Childhood Obesity Intervention Program in a Rural Southern Community: TEAM Mississippi Project
Authors: Greening Leilani , Harrell Kristopher T. , Low Annette K. , Fielder Carrie E.
Published: January 2011

A healthy lifestyle school‐based obesity intervention was evaluated in a rural southern community where the rate of obesity ranks as the highest. School‐age children (N = 450) ranging from 6 to 10 years of age (Mage = 8.34) participated in monthly physical activity and nutritional events during a 9‐month academic year. The children's nutritional knowledge, number of different physical activities, fitness level, dietary habits, waist circumference, BMI percentile, and percentage body fat were measured pre‐ and postintervention. Changes on these measures were compared to students in a school employing the school system's standard health curriculum. Regression analyses with residualized change scores revealed that the intervention school showed statistically significant improvement in percentage body fat, physical activity, performance on fitness tests, and dietary habits compared to the control school. There was no evidence of differences in outcomes based on gender or ethnicity/race. With rates of obesity and overweight reaching 50% in southern rural communities, intervening early in development may offer the best outcome because of the difficulties with changing lifestyle behaviors later in adulthood. A population‐based approach is recommended over a targeted approach to cultivate a culture of healthy lifestyle behaviors when children are developing their health‐care habits. Evidence suggests that both boys and girls, and African‐American and white children can benefit equally from such interventions.
Accurate Measurement of Body Weight and Food Intake in Environmentally Enriched Male Wistar Rats
Authors: Beale Kylie E.L. , Murphy Kevin G. , Harrison Eleanor K. , Kerton Angela J. , Ghatei Mohammad A. , Bloom Stephen R. , Smith Kirsty L.
Published: January 2011

Laboratory animals are crucial in the study of energy homeostasis. In particular, rats are used to study alterations in food intake and body weight. To accurately record food intake or energy expenditure it is necessary to house rats individually, which can be stressful for social animals. Environmental enrichment may reduce stress and improve welfare in laboratory rodents. However, the effect of environmental enrichment on food intake and thus experimental outcome is unknown. We aimed to determine the effect of environmental enrichment on food intake, body weight, behavior and fecal and plasma stress hormones in male Wistar rats. Singly housed 5–7‐week‐old male rats were given either no environmental enrichment, chew sticks, a plastic tube of 67 mm internal diameter, or both chew sticks and a tube. No differences in body weight or food intake were seen over a 7‐day period. Importantly, the refeeding response following a 24‐h fast was unaffected by environmental enrichment. Rearing, a behavior often associated with stress, was significantly reduced in all enriched groups compared to controls. There was a significant increase in fecal immunoglobulin A (IgA) in animals housed with both forms of enrichment compared to controls at the termination of the study, suggesting enrichment reduces hypothalamo‐pituitary‐adrenal (HPA) axis activity in singly housed rats. In summary, environmental enrichment does not influence body weight and food intake in singly housed male Wistar rats and may therefore be used to refine the living conditions of animals used in the study of energy homeostasis without compromising experimental outcome.
RGS6 Variants Are Associated With Dietary Fat Intake in Hispanics: The IRAS Family Study
Authors: Sibbel Scott P. , Talbert Matthew E. , Bowden Donald W. , Haffner Steve M. , Taylor Kent D. , Chen Yii‐Der I. , Wagenknecht Lynne E. , Langefeld Carl D. , Norris Jill M.
Published: January 2011

Recently, a genome‐wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic‐American cohort. Multiple single‐nucleotide polymorphisms (SNPs) in the G‐protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar‐laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat‐laden food intake.
Reversing Compiled Executables for Malware Analysis via Visualization
Authors: Quist Daniel A , Liebrock Lorie M
Published: January 2011

Reverse engineering-compiled executables is a task with a steep learning curve. It is complicated by the task of translating assembly into a series of abstractions that represent the overall flow of a program. Most of the steps involve finding interesting areas of an executable and determining their general functionality. This article presents a method using dynamic analysis of program execution to visually represent the general flow of a program. We use the Ether hypervisor framework to covertly monitor a program. The data are processed and presented for the reverse engineer. The VERA (Visualization of Executables for Reversing and Analysis) system specifically accelerates the location of the original entry point and understanding of overall executable functionality. Using this method, the amount of time needed to extract key features of an executable is greatly reduced, improving productivity. Two malware samples are used to demonstrate the advantages of using the VERA system to reverse engineer malware. Further, these examples exemplify a reversing process enhanced through effective use of dynamic analysis tools. Preliminary user study indicates that the tool is useful for both new and experienced users.
Deuterium retention in tungsten exposed to low-energy pure and helium-seeded deuterium plasmas
Authors: Ogorodnikova O. V. , Schwarz-Selinger T. , Sugiyama K. , Alimov V. Kh.
Published: January 2011

Influence of helium (He) on the deuterium (D) retention in tungsten (W) under simultaneous He-D plasma exposure was investigated. Bulk polycrystalline tungsten and two W coatings on carbon substrate, namely, plasma-sprayed tungsten and combined magnetron-sputtered and ion implanted tungsten (CMSII-W) were exposed to pure and He-seeded D plasmas generated by electron-cyclotron-resonance plasma source. The D retention in each sample was subsequently analyzed by various methods such as nuclear reaction analysis for the D depth profiling up to 6 μm and thermal desorption spectroscopy for the determination of total amount of D retention. It is shown that seeding of helium into D plasma with helium ion flux fraction of 10% reduces the deuterium retention for all tungsten grades but more significant reduction was observed for polycrystalline W and less significant effect was found for W coatings. From the thermal desorption spectroscopy measurements, we conclude that the presence of He modifies the density of existing traps for D but does not modify the nature of traps. Maximum effect of a reduction in the deuterium retention due to helium seeding was observed at around 500 K for bulk polycrystalline W. Mechanisms of deuterium retention and He effect in different W materials are discussed.
The water–amorphous silica interface: Analysis of the Stern layer and surface conduction
Authors: Zhang Hui , Hassanali Ali A. , Shin Yun Kyung , Knight Chris , Singer Sherwin J.
Published: January 2011

To explain why dynamical properties of an aqueous electrolyte near a charged surface seem to be governed by a surface charge less than the actual one, the canonical Stern model supposes an interfacial layer of ions and immobile fluid. However, large ion mobilities within the Stern layer are needed to reconcile the Stern model with surface conduction measurements. Modeling the aqueous electrolyte–amorphous silica interface at typical charge densities, a prototypical double layer system, the flow velocity does not vanish until right at the surface. The Stern model is a good effective model away from the surface, but cannot be taken literally near the surface. Indeed, simulations show no ion mobility where water is immobile, nor is such mobility necessary since the surface conductivity in the simulations is comparable to experimental values.
Practical solutions for reliable triple probe measurements in magnetized plasmas
Authors: Theiler C. , Furno I. , Kuenlin A. , Marmillod Ph. , Fasoli A.
Published: January 2011

The triple probe method to obtain local, time-resolved measurements of density, electron temperature and plasma potential is investigated in detail. The difficulties in obtaining reliable measurements with this technique are discussed and overcome. These include phase delay errors, ion sheath expansion and limited bandwidth due to stray capacitance to ground. In particular, a relatively simple electronic circuit is described to strongly reduce stray capacitance. Measurements with the triple probe are presented in a plasma characterized by interchange-driven turbulence in the TORPEX device. The measured time-averaged and time-dependent, conditionally averaged parameters are cross-checked with other Langmuir probe based techniques, and show good agreement. Triple probe measurements show that electron temperature fluctuations are sufficiently large, such that the identification of plasma potential fluctuations with fluctuations of the floating potential is not a good approximation. Over a large radial region, the time-averaged fluctuation-induced particle flux can, however, be deduced from floating potential only. This is because the phase shift between density and electron temperature is close to zero there and temperature fluctuations do not give rise to a net radial particle transport.
Estimating equilibrium ensemble averages using multiple time slices from driven nonequilibrium processes: Theory and application to free energies, moments, and thermodynamic length in single-molecule pulling experiments
Authors: Minh David D. L. , Chodera John D.
Published: January 2011

Recently discovered identities in statistical mechanics have enabled the calculation of equilibrium ensemble averages from realizations of driven nonequilibrium processes, including single-molecule pulling experiments and analogous computer simulations. Challenges in collecting large data sets motivate the pursuit of efficient statistical estimators that maximize use of available information. Along these lines, Hummer and Szabo developed an estimator that combines data from multiple time slices along a driven nonequilibrium process to compute the potential of mean force. Here, we generalize their approach, pooling information from multiple time slices to estimate arbitrary equilibrium expectations. Our expression may be combined with estimators of path-ensemble averages, including existing optimal estimators that use data collected by unidirectional and bidirectional protocols. We demonstrate the estimator by calculating free energies, moments of the polymer extension, the thermodynamic metric tensor, and the thermodynamic length in a model single-molecule pulling experiment. Compared to estimators that only use individual time slices, our multiple time-slice estimators yield substantially smoother estimates and achieve lower variance for higher-order moments.
A new ab initio potential energy surface for the NeCO complex with the vibrational coordinate dependence
Authors: Wang Zhongquan , Feng Eryin , Yu Haijun , Zhang Chunzao , Du Jianming
Published: January 2011

A new high quality three-dimensional potential energy surface for the Ne–CO van der Waals complex is developed using the CCSD(T) method and avqz/avqz+33221 basis set. The ab initio calculation is performed in a total of 1365 configurations with supermolecule method. There is a single global minimum located in a nearly T-shaped geometry. The global minimum energy is −49.4090 ${\rm cm}^{ - 1}$ cm −1 at $R_e = 6.40a_0$Re=6.40a0 and $\theta _e =82.5^ \circ$θe=82.5∘ for $V_{00} $V00. Using the three-dimensional potential energy surface, we have calculated bound rovibrational energy levels up to J = 10 including the Coriolis coupling terms. Compared with the experimental transition frequencies, the theoretical results are in good agreement with the experimental results.
Stress transmission in porous materials impacted by shock waves
Authors: Kazemi-Kamyab Vahid , Subramaniam Kolluru , Andreopoulos Yiannis
Published: January 2011

The interaction of moving shock waves with short length elastic porous aluminum samples of various porosities was investigated in a shock tube facility in a setup where the specimens were placed in front of a long rod of a modified Hopkinson Bar. High frequency response miniature pressure transducers and semiconductor strain gages were used to measure the pore gas pressure and the transmitted stress wave to the rod respectively. It was found that the effect of pore gas flow on the total stress history was inversely proportional to the material’s porosity, permeability and length. For low porosity aluminum samples due to the very low and very confined volumetric gas flow rate within the foam, a minimal contribution of the gas pressure within the pores to the total stress was observed and the magnitude of stress wave transmitted to the rod was amplified mainly due to the lower acoustic impedance of the foams relative to the rod. However, in a high porosity aluminum specimens with a high permeability and low inertial coefficient, there is a high volumetric gas flow rate within the foam, where faster wave interactions within the gas phase take place resulting in an earlier arrival of the rarefaction wave and restricting the magnitude of the total stress to reach its value when no gas flow into the pores is allowed. Due to this out of phase interaction between the wave propagating within the gas phase and the fast wave propagating in the solid matrix, the magnitude of the stress wave transmitted to the rod was slightly attenuated when the high porous foam was placed in front of the rod. It was also found that the aluminum foams deviate from a linearly elastic medium behavior and demonstrate dispersive and dissipative properties which result in the gradual rise or fall of the stress and damping of the oscillations. The pore gas flow influences the profile of the oscillations by introducing dissipation and dispersion into the propagating wave in the solid phase due to the nonlinear nature of the solid-fluid interaction. Further data analysis included a decomposition of the measured time-dependent signals into two components, one with low frequency content which is argued that it is associated with Biot’s slow wave and one with high frequency contributions which corresponds to the fast wave propagation. It is also argued that this decomposition can differentiate the effects of gas pressure in the pores from the stress in the matrix of the porous medium.
Structures and energetics of small lead cluster ions
Authors: Kelting Rebecca , Otterstätter Robin , Weis Patrick , Drebov Nedko , Ahlrichs Reinhart , Kappes Manfred M.
Published: January 2011

By a combination of gas phase ion mobility measurements and relativistic density functional theory calculations with inclusion of spin-orbit coupling, we assign structures of lead cluster cations and anions in the range between 4 and 15 atoms. We find a planar rhombus for the tetramer, a trigonal bipyramid for the pentamer, and a pentagonal bipyramid for the heptamer, independent of charge state. For the hexamer, the cation and anion structures differ: we find an octahedron for the anion while the cation consists of fused tetrahedra. For the octamer, we find in both cases structures based on the pentagonal bipyramid motif plus adatom. For the larger clusters investigated we always find different structures for cations and anions. For example, Pb12− is confirmed to be a hollow icosahedron while Pb12+ is a truncated filled icosahedron. Pb13+ is a filled icosahedron but Pb13− is a hollow icosahedron with the additional atom capping a face. In order to get experimental information on the relative stabilities, we investigated the collision induced dissociation mass spectra for the different cluster sizes and charge states, and observe a strong correlation with the calculated fragmentation energies. Up to n = 13 the main fragmentation channel is atom loss; for the larger cluster sizes we observe fission into two large fragments. This channel is dominant for larger anions, less pronounced but clearly present for the cations.
Quasielastic small-angle neutron scattering from heavy water solutions of cyclodextrins
Authors: Kusmin André , Lechner Ruep E. , Saenger Wolfram
Published: January 2011

We present a model for quasielastic neutron scattering (QENS) by an aqueous solution of compact and inflexible molecules. This model accounts for time-dependent spatial pair correlations between the atoms of the same as well as of distinct molecules and includes all coherent and incoherent neutron scattering contributions. The extension of the static theory of the excluded volume effect [A. K. Soper, J. Phys.: Condens. Matter 9, 2399 (1997)] to the time-dependent (dynamic) case allows us to obtain simplified model expressions for QENS spectra in the low Q region in the uniform fluid approximation. The resulting expressions describe the quasielastic small-angle neutron scattering (QESANS) spectra of D \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2O solutions of native and methylated cyclodextrins well, yielding in particular translational and rotational diffusion coefficients of these compounds in aqueous solution. Finally, we discuss the full potential of the QESANS analysis (that is, beyond the uniform fluid approximation), in particular, the information on solute–solvent interactions (e.g., hydration shell properties) that such an analysis can provide, in principle.
Density, structure, and dynamics of water: The effect of van der Waals interactions
Authors: Wang Jue , Román-Pérez G. , Soler Jose M. , Artacho Emilio , Fernández-Serra M.-V.
Published: January 2011

It is known that ab initio molecular dynamics (AIMD) simulations of liquid water at ambient conditions, based on the generalized gradient approximation (GGA) to density functional theory (DFT), with commonly used functionals fail to produce structural and diffusive properties in reasonable agreement with experiment. This is true for canonical, constant temperature simulations where the density of the liquid is fixed to the experimental density. The equilibrium density, at ambient conditions, of DFT water has recently been shown by Schmidt et al. [J. Phys. Chem. B, 113, 11959 (2009)] to be underestimated by different GGA functionals for exchange and correlation, and corrected by the addition of interatomic pair potentials to describe van der Waals (vdW) interactions. In this contribution we present a DFT-AIMD study of liquid water using several GGA functionals as well as the van der Waals density functional (vdW-DF) of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. As expected, we find that the density of water is grossly underestimated by GGA functionals. When a vdW-DF is used, the density improves drastically and the experimental diffusivity is reproduced without the need of thermal corrections. We analyze the origin of the density differences between all the functionals. We show that the vdW-DF increases the population of non-H-bonded interstitial sites, at distances between the first and second coordination shells. However, it excessively weakens the H-bond network, collapsing the second coordination shell. This structural problem is partially associated to the choice of GGA exchange in the vdW-DF. We show that a different choice for the exchange functional is enough to achieve an overall improvement both in structure and diffusivity.
Turning symmetric an asymmetric hydrogen bond with the inclusion of nuclear quantum effects: The case of the [CN···H···NC]− complex
Authors: Moreno Diego V. , González Sergio A. , Reyes Andrés
Published: January 2011

Nuclear quantum effects (NQE) on the geometry, energy, and electronic structure of the \documentclass[12pt]{minimal}\begin{document}$[\mbox{CN}\cdot \mbox{L} \cdot \mbox{NC}]^{-}$\end{document}[CN·L·NC]− complex (L = H, D, T) are investigated with the recently developed APMO/MP2 code. This code implements the nuclear molecular orbital approach (NMO) at the Hartree–Fock (HF) and MP2 levels of theory for electrons and quantum nuclei. In a first study, we examined the H/D/T isotope effects on the geometry and electronic structure of the CNH molecule at NMO/HF and NMO/MP2 levels of theory. We found that when increasing the hydrogen nuclear mass there is a reduction of the \documentclass[12pt]{minimal}\begin{document}$R_{\mbox{N-H}}$\end{document}RN-H bond distance and an increase of the electronic population on the hydrogen atom. Our calculated bond distances are in good agreement with experimental and other theoretical results. In a second investigation, we explored the hydrogen NQE on the geometry of [CNHNC] \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}− complex at the NMO/HF and NMO/MP2 levels of theory. We discovered that while a NMO/HF calculation presented an asymmetric hydrogen bond, the NMO/MP2 calculation revealed a symmetric H-bond. We also examined the H/D/T isotope effects on the geometry and stabilization energy of the [CNHNC] \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}− complex. We noted that gradual increases in hydrogen mass led to reductions of the \documentclass[12pt]{minimal}\begin{document}$R_{\mbox{NN}}$\end{document}RNN distance and destabilization of the hydrogen bond (H-bond). A discussion of these results is given in terms of the hydrogen nuclear delocalization effects on the electronic structure and energy components. To the best of our knowledge, this is the first ab initio NMO study that reveals the importance of including nuclear quantum effects in conventional electronic structure calculations for an enhanced description of strong-low-barrier H-bonded systems.
Kinetic study on the H+SiH4 abstraction reaction using an ab initio potential energy surface
Authors: Cao Jianwei , Zhang Zhijun , Zhang Chunfang , Bian Wensheng , Guo Yin
Published: January 2011

Variational transition state theory calculations with the correction of multidimensional tunneling are performed on a 12-dimensional ab initio potential energy surface for the ${\rm H} + {\rm SiH}_{\rm 4}$H+ SiH 4 abstraction reaction. The surface is constructed using a dual-level strategy. For the temperature range 200−1600 K, thermal rate constants are calculated and kinetic isotope effects for various isotopic species of the title reaction are investigated. The results are in very good agreement with available experimental data.
Quantum confinement effects on charge-transfer between PbS quantum dots and 4-mercaptopyridine
Authors: Fu Xiaoqi , Pan Yi , Wang Xin , Lombardi John R.
Published: January 2011

We obtain the surface enhanced Raman spectra of 4-mercaptopyridine on lead sulfide (PbS) quantum dots as a function of nanoparticle size and excitation wavelength. The nanoparticle radii are selected to be less than the exciton Bohr radius of PbS, enabling the observation of quantum confinement effects on the spectrum. We utilize the variation of nontotally symmetric modes of both b1 and b2 symmetry as compared to the totally symmetric a1 modes to measure the degree of charge-transfer between the molecule and quantum dot. We find both size dependent and wavelength dependent resonances in the range of these measurements, and attribute them to charge-transfer resonances which are responsible for the Raman enhancement.
Theoretical study of carbon-nanotube-based gas pressure sensors
Authors: Tooski S. B.
Published: January 2011

We investigate microwave absorption properties of carbon nanotubes under different gas pressures, using a combination of fluid and perturbation theories. We demonstrate that microwave absorption of the system shifts toward high frequency with increasing gas pressure. A linear relationship between resonant frequency shift and gas pressure is also found. The model is useful for designing carbon nanotubes based gas pressure sensors. The change in microwave absorption of the carbon nanotubes due to exposure of different gas pressures is utilized as the principle of this gas sensor. The presented model has also great potential for different types of nanomaterials applications.
From caging to Rouse dynamics in polymer melts with intramolecular barriers: A critical test of the mode coupling theory
Authors: Bernabei Marco , Moreno Angel J. , Zaccarelli Emanuela , Sciortino Francesco , Colmenero Juan
Published: January 2011

By means of computer simulations and solution of the equations of the mode coupling theory (MCT), we investigate the role of the intramolecular barriers on several dynamic aspects of nonentangled polymers. The investigated dynamic range extends from the caging regime characteristic of glass-formers to the relaxation of the chain Rouse modes. We review our recent work on this question, provide new results, and critically discuss the limitations of the theory. Solutions of the MCT for the structural relaxation reproduce qualitative trends of simulations for weak and moderate barriers. However, a progressive discrepancy is revealed as the limit of stiff chains is approached. This disagreement does not seem related with dynamic heterogeneities, which indeed are not enhanced by increasing barrier strength. It is not connected either with the breakdown of the convolution approximation for three-point static correlations, which retains its validity for stiff chains. These findings suggest the need of an improvement of the MCT equations for polymer melts. Concerning the relaxation of the chain degrees of freedom, MCT provides a microscopic basis for time scales from chain reorientation down to the caging regime. It rationalizes, from first principles, the observed deviations from the Rouse model on increasing the barrier strength. These include anomalous scaling of relaxation times, long-time plateaux, and nonmonotonous wavelength dependence of the mode correlators.
Single center method: A computational tool for ionization and electronic excitation studies of molecules
Authors: Demekhin Ph. V. , Ehresmann A. , Sukhorukov V. L.
Published: January 2011

We discuss the recent progress in the development of the single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules. Basic equations of the SC method are presented, and an efficient scheme for the numerical solution of a system of coupled Hartree–Fock equations for a photoelectron is described. Several illustrative applications of the method to photoionization and electronic excitation processes in diatomic molecules are considered. Thereby, we demonstrate its potential for theoretically studying angularly resolved molecular photoionization processes.
Excitation energy calculation of conjugated hydrocarbons: A new Pariser–Parr–Pople model parameterization approaching CASPT2 accuracy
Authors: Zhang Dawei , Qu Zexing , Liu Chungen , Jiang Yuansheng
Published: January 2011

A new parameterization for the Pariser–Parr–Pople (PPP) model for conjugated hydrocarbons is proposed in this work. The distance-dependence of PPP parameters are obtained from CASPT2 ground state and low-lying excited state energies of ethylene and its cation at various C–C single bond lengths and are fitted to a set of carefully chosen mathematical functions. Our new PPP model is applied to the calculation of vertical singlet–triplet energy gaps and the excitation energies for low-lying $\pi \rightarrow \pi ^*$π→π* valence excitations in various π-conjugated molecules. Results with the new PPP model are consistently better than the standard PPP model in use. It often surpasses density functional theory and single-reference excited state methods such as configuration interaction singles or time-dependent density functional theory in terms of its accuracy and agrees reasonably well with high-level theories or experiments.
In vivomolecular labeling of halogenated volatile anesthetics via intrinsic molecular vibrations using nonlinear Raman spectroscopy
Authors: Nagashima Yu , Suzuki Takayuki , Terada Sumio , Tsuji Shoji , Misawa Kazuhiko
Published: January 2011

Halogenated volatile anesthetics are frequently used for inhaled anesthesia in clinical practice. No appropriate biological method has been available for visualizing their localization in action. Therefore, despite their frequent use, the mechanism of action of these drugs has not been fully investigated. We measured coherent anti-Stokes Raman scattering (CARS) spectra of sevoflurane and isoflurane, two of the most representative volatile anesthetics, and determined the low-frequency vibrational modes without nonresonant background disturbance. Molecular dynamics calculations predict that these modes are associated with multiple halogen atoms. Because halogen atoms rarely appear in biological compounds, the entire spectral landscape of these modes is expected to be a good marker for investigating the spatial localization of these drugs within the intracellular environment. Using live squid giant axons, we could detect the unique CARS spectra of sevoflurane for the first time in a biological setting.
Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains
Authors: Liu Chun-Sheng , An Hui , Guo Ling-Ju , Zeng Zhi , Ju Xin
Published: January 2011

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2σ orbitals contributes to the H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 adsorption. However, the binding mechanism of the H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 molecules on Na arises only from the polarization interaction between the charged Na atom and the H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2. Interestingly, additional H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60 fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60-C\documentclass[12pt]{minimal}\begin{document}$_{n}$\end{document}n-C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60 (n = 5, 8), the Li\documentclass[12pt]{minimal}\begin{document}$_{12}$\end{document}12C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60-C\documentclass[12pt]{minimal}\begin{document}$_n$\end{document}n-Li\documentclass[12pt]{minimal}\begin{document}$_{12}$\end{document}12C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60 complex, keeping the number of adsorbed H\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li\documentclass[12pt]{minimal}\begin{document}$_{12}$\end{document}12C\documentclass[12pt]{minimal}\begin{document}$_{60}$\end{document}60)\documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.
Structural study of low concentration LiCl aqueous solutions in the liquid, supercooled, and hyperquenched glassy states
Authors: Winkel K. , Seidl M. , Loerting T. , Bove L. E. , Imberti S. , Molinero V. , Bruni F. , Mancinelli R. , Ricci M. A.
Published: January 2011

Neutron diffraction experiments on a solution of LiCl in water (R = 40) at ambient conditions and in the supercooled and hyperquenched states are reported and analyzed within the empirical potential structure refinement framework. Evidence for the modifications of the microscopic structure of the solvent in the presence of such a small amount of salt is found at all investigated thermodynamic states. On the other hand, it is evident that the structure of the hyperquenched salty sample is similar to that of pure low density amorphous water, although all the peaks of the radial distribution functions are broader in the present case. Changes upon supercooling or hyperquenching of the ion's hydration shells and contacts are of limited size and evidence for segregation phenomena at these states does not clearly show up, although the presence of water separated contacts between ion of the same sign is intriguing.
Structural and dynamical properties of solid ammonia borane under high pressure
Authors: Wang Liancheng , Bao Kuo , Meng Xing , Wang Xiaoli , Jiang Tingting , Cui Tian , Liu Bingbing , Zou Guangtian
Published: January 2011

The structural and dynamical properties of solid ammonia borane were investigated by means of extensive density functional theory calculation up to 60 GPa. Molecular dynamics simulations suggest that the Cmc21 phase found by recent room-temperature x-ray diffraction experiments can be obtained from the Pmn21 structure at high pressure and low temperature. Two new high-pressure phases were found on further compression at room temperature. We also found that all three high-pressure phases have proton-ordered structures, and the separation of the NH3 and BH3 rotation observed in the simulations can be explained by their distinct rotational energy barriers. The role of dihydrogen bonds in the high-pressure phases is discussed.
Ostwald ripening of binary alloy particles
Authors: Burlakov V. M. , Kantorovich L.
Published: January 2011

Classical Lifshitz–Slyozov–Wagner theory is generalized for Ostwald ripening of particles composed of random binary alloy. We show that the steady state ripening process is characterized by self-similar particle size and composition distributions. The shape of particle size distribution depends on whether the process is diffusion controlled (Lifshitz–Slyozov) or reaction controlled (Wagner) and is consistent with the predictions of classical theory for one-component materials. The steady state composition distribution, in contrast, has the same functional form in both extreme cases featuring a universal dependence of the composition upon particle size. We also found that transients in particle's composition can be very quick resulting in a steady state distribution well before it is reached by particles sizes. These transients involve significant changes in particle sizes and open an opportunity for producing metastable particle size distributions of required shape.
Design of selective emitting media within a cylindrical tube for conversion of wasted heat energy to electrical energy
Authors: Starvaggi P. , Hoffman M. , Clemons C. B. , Young G. W.
Published: January 2011

Thermophotovoltaic (TPV) energy conversion is the conversion of heat energy to electrical energy via light. This manuscript focuses on the geometric design of emitting material within an exhaust tube to convert wasted heat energy to light, and achieve an optimal amount of irradiance at the PV diode cells. Due to the large value of the absorption coefficient for the selectively emitting erbia-doped nanofibers under discussion, the diffusion approximation to the equation of radiation transfer is used. This approximate equation is solved for emission from hot-spot sources within the emitting material. Several geometric distributions of the emitting material are considered. Within an axisymmetric geometry all erbia-doped nanofibers, all quartz wool, and mixtures of disk-shaped or cylindrical shell shaped distributions of nanofibers and wool are investigated. Within a polar geometry all erbia-doped nanofibers, all quartz wool, and mixtures of spoke-shaped or cylindrical shell shaped distributions are investigated. In both geometries the mixture distributions consist of alternating thin layers of emitting and non-emitting material. Homogenization techniques are applied to these distributions to define expressions for the effective absorption and scattering coefficients for these spatially distributed emitting structures. The effective expressions are input into the diffusion approximation that is solved for the spectral irradiance. The net radiation obtained from these emitting structures is examined to optimize the geometry of the TPV material to maximize emission with use of minimal TPV material. Results show that disk-shaped bands or spokes allow for maximum irradiation in the radial direction toward the diode collectors. A large volume fraction of erbia-doped nanofibers is optimal when hot spots are close to the diodes. Smaller volume fractions work better when hot spots are away from the diodes due to reabsorption of emitted light by the emitting material.
Mechanisms of nanodot formation under focused ion beam irradiation in compound semiconductors
Authors: Grossklaus K. A. , Millunchick J. M.
Published: January 2011

We have examined the responses of GaAs, InP, InAs, and AlAs to 30 keV focused ion beam (FIB) irradiation and applied a unified model that consistently explains the observed effects. Nanodots were observed to form on GaAs, InP, and InAs under irradiation at normal incidence, while nanodots are not observed on AlAs. The FIB response and nanodot formation behavior of each material is discussed with regard to a few basic material properties and a model for nanodot creation and growth by the action of preferential sputtering and Ostwald ripening. The model predicts the development of a stable average nanodot size with increasing ion dose, with the average nanodot size depending on the excess group III adatom yield, adatom surface diffusion rate, and surface tension. These predictions qualitatively agree with the experimentally observed trends for GaAs and InP. They also agree for the initial nanodot formation on InAs, but this material system exhibits a sudden transition in the nanodot size distribution. The model predicts that nanodots will have difficulty forming and growing on AlAs, which is also in agreement with our experimental results.
Effects of barrier height inhomogeneities on the determination of the Richardson constant
Authors: Sarpatwari K. , Mohney S. E. , Awadelkarim O. O.
Published: January 2011

Extraction of the Richardson constant and Schottky barrier height from the current-voltage-temperature (I−V−T) characteristics of Schottky barrier contacts is greatly influenced by a variety of nonideal effects. Starting with an overview of the original Richardson plot and relevant modifications of the Richardson plot, this article discusses limitations of previous analytical approaches that attempt to account for the effects of barrier height inhomogeneities on the extracted Richardson constant. A temperature-driven fundamental change in the current conduction in an inhomogeneous Schottky diode from conduction dominated by low barrier height patches to conduction dominated by high barrier height regions is identified as a likely source for the bowing of the Richardson plot, and knowledge of which regime dominates the current transport is critical for accurate determination of the Richardson constant. A simple linear relation between the effective Richardson constant and effective barrier height is described, and this recently-reported linear relation provides a consistent method for estimating the Richardson constant of inhomogeneous Schottky diodes when transport is primarily through high barrier height regions. The method is applied to I−V−T characteristics of Au/Ni/n-GaN Schottky diodes measured from 320–440 K. A homogeneous Richardson constant of 29±6 A cm−2 K−2 is extracted using the proposed approach and is in very good agreement with the theoretical value of 26.4 A cm−2 K−2.
Photovoltaic devices based on high density boron-doped single-walled carbon nanotube/n-Si heterojunctions
Authors: Saini Viney , Li Zhongrui , Bourdo Shawn , Kunets Vasyl P. , Trigwell Steven , Couraud Arthur , Rioux Julien , Boyer Cyril , Nteziyaremye Valens , Dervishi Enkeleda , Biris Alexandru R. , Salamo Gregory J. , Viswanathan Tito , Biris Alexandru S.
Published: January 2011

A simple and easily processible photovoltaic device has been developed based on boron-doped single-walled carbon nanotubes (B-SWNTs) and n-type silicon (n-Si) heterojunctions. The SWNTs were substitutionally doped with boron atoms by thermal annealing, in the presence of B2O3. The samples used for these studies were characterized by Raman spectroscopy, thermal gravimetric analysis, transmission electron microscopy, and x-ray photoelectron spectroscopy. The fully functional solar cell devices were fabricated by airbrush deposition that generated uniform B-SWNT films on top of the n-Si substrates. The carbon nanotube films acted as exciton-generation sites, charge collection, and transportation while the heterojunctions formed between B-SWNTs and n-Si acted as charge dissociation centers. The current-voltage characteristics in the absence of light and under illumination, as well as optical transmittance spectrum are reported here. It should be noted that the device fabrication process can be made amenable to scalability by depositing direct and uniform films using airbrushing, inkjet printing, or spin-coating techniques.