bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS
Authors: Marshak A. , Knyazikhin Y. , Chiu J. C. , Wiscombe W. J.
Published: August 2009

The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1‐sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud‐free. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength‐independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear‐to‐cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.
Coexistence of turbulence and discrete modes in the solar wind
Authors: Ghosh S. , Thomson D. J. , Matthaeus W. H. , Lanzerotti L. J.
Published: August 2009

Motivated by apparently contradictory reports of turbulence and discrete frequency wave‐like signals in the interplanetary medium, we employ numerical simulations to investigate the persistence of wave‐like spatial structures in the presence of strong low‐frequency turbulence. We seek to identify the time scales and other conditions that permit them to remain as identifiable structures in the turbulent medium. The wave‐like structures are initialized as discrete modes in wave number in a series of spectral method magnetohydrodynamic turbulence computations. We find that discrete modes can survive from one to many nonlinear times and that the main factor that determines their survivability is the separation from turbulence in parallel wave number. This corresponds to a separation in their corresponding Alfvén mode frequency.
Ultrawideband pulse propagation through a homogeneous, isotropic, lossy plasma
Authors: Cartwright N. A. , Oughstun K. E.
Published: August 2009

We investigate a linearly polarized, plane wave electromagnetic step function modulated sine wave pulse traveling through an isotropic, homogeneous, lossy plasma with dielectric permittivity described by the Drude model. The results of this investigation extend the useful frequency domain below the plasma cutoff frequency. An asymptotic method of analysis is used to provide a closed‐form approximation to the integral representation of the propagated pulse that is valid for all input carrier frequencies. This closed‐form expression is the sum of its three asymptotic component fields: the Sommerfeld precursor, the Brillouin precursor and the signal contribution. These expressions reveal that, because of conductivity, each field component attenuates exponentially with distance at its own characteristic rate and that, for sufficiently large propagation distance, the Sommerfeld precursor will be the dominant contribution to the field. However, a study of the penetration capability of each field component shows that, for a large enough propagation distance with carrier frequencies below cutoff, the Brillouin precursor decays algebraically as z−2 with a minimal exponential attenuation with propagation distance while the Sommerfeld precursor decays at a rate that approaches a z−3/4 algebraic decay. Optimal signal penetration through a finite distance of a lossy plasma medium, for either radar imaging, remote sensing, or communication applications, may then be realized by using an appropriately constructed sequence of Brillouin precursor pulses.
Effect of a tapasin mutant on the assembly of the mouse MHC class I molecule H2‐Kd
Authors: Simone Laura C , Wang Xiaojian , Tuli Amit , Solheim Joyce C
Published: August 2009

Major histocompatibility complex (MHC) class I heavy chain/β2m heterodimers assemble with antigenic peptides through interactions with peptide‐loading complex proteins, including tapasin and ERp57. In human cells, a cysteine residue within tapasin (C95) has been shown to form a covalent bond with ERp57. In this study, we focused on the effect of this tapasin amino‐acid residue in mouse cells expressing the MHC class I molecule H2‐Kd. We showed that a large disulfide‐bonded complex was present in the mouse cells that included ERp57, tapasin, and Kd. Furthermore, in mouse cells, unlike human cells, we found that tapasin mutated at C95 can participate in a non‐covalent complex with ERp57. Comparison of our findings to earlier findings with a human molecule (HLA‐B∗4402) also revealed that a tapasin C95 mutation has a stronger effect on the maturation and stability of Kd than HLA‐B∗4402. Overall, our results characterize the influence of this tapasin cysteine residue on the stable surface expression of a mouse MHC class I molecule and reveal differences in tapasin C95 interactions and effects between mouse and human systems.
Moisture availability influences the effect of ultraviolet-B radiation on leaf litter decomposition
Authors: Smith William , Gao Wei , Steltzer Heidi , Wallenstein Matthew , Tree Roger
Published: August 2009

Altered surface ultraviolet-B (UV-B) radiation resulting from a combination of factors that include changes in stratospheric ozone concentrations, cloud cover, and aerosol conditions may affect litter decomposition and, thus, terrestrial nutrient cycling on a global scale. Although litter decomposition rates vary across biomes, patterns of decomposition suggest that UV-B radiation accelerates litter decay in xeric environments where precipitation is infrequent. However, under more frequent precipitation regimes where litter decay rates are characteristically high, the effect of UV-B radiation on litter decomposition has not been fully elucidated. To evaluate this association between moisture regime and UV-B exposure, a litter decomposition experiment was designed for aspen (Populus tremuloides) leaf litter, where conditions that influence both abiotic (photodegradation) and biotic (microbial) processes could be manipulated quantitatively. We found that experimentally increasing UV-B exposure (0, 7.4, and 11.2 kJ m-2 d-1, respectively) did not consistently increase litter decomposition rates across simulated precipitation frequencies of 4-, 12-, and 24-days. Instead, a UV-B exposure of 11.2 kJ m-2 d-1 resulted in a 13% decrease in decomposition rates under the 4-day precipitation frequency, but an increase of 80% under the 24-day frequency. Furthermore, the same UV-B dose increased litter decomposition rates under the 24-day precipitation frequency by 78% even in conditions where microbial activity was suppressed. Therefore, under more xeric conditions, greater exposure to UV-B radiation increased decomposition rates, presumably through photodegradation. In contrast, when decomposition was not moisture-limited, greater UV-B exposure slowed decomposition rates, most likely from the resulting inhibition of microbial activity. Ultimately, these experimental results highlight UV-B radiation as a potential driver of decomposition, as well as indicate that both the direction and magnitude of the UV-B effect is dependent on moisture availability, a factor that may change according to future patterns in global precipitation.
The Role of Bio-Ontologies in Data-Driven Research: A Philosophical Perspective
Authors: Leonelli Sabina
Published: August 2009

This project aims to reach a philosophical understanding of the role played by theory in the practices of data dissemination and re-use that characterise data-driven research. Bio-ontologies have the potential to play the epistemic role of theories in this context, insofar as they (1) express the knowledge underlying data-driven research and (2) guide such research towards future discoveries.
The Influence of Weekday Eating Patterns on Energy Intake and BMI Among Female Elementary School Personnel
Authors: Hartline‐Grafton Heather L. , Rose Donald , Johnson Carolyn C. , Rice Janet C. , Webber Larry S.
Published: August 2009

Many health practitioners recommend eating small, frequent meals for weight loss, yet the relationship of eating patterns, such as eating occasion frequency (EOF), to energy intake and body weight is controversial. Broad‐based efforts to promote worksite wellness programs increase the importance of this issue, as many work environments inherently restrict eating patterns. The eating patterns of school personnel are understudied, but are of particular interest, not only because they have limited eating opportunities during the day but also because their diet and weight outcomes are likely to influence behaviors of a much larger population. We examined relationships between weekday EOF and energy intake and BMI among female elementary school personnel in 22 schools in a suburban county of southeastern Louisiana. Two 24‐h dietary recalls were administered to randomly‐selected employees (n = 329) on nonconsecutive days by registered dietitians. Measured heights and weights were used to calculate BMI (weight/height2). On average, employees consumed 2.2 of their total 5.9 meals and snacks during the school day, accounting for 37% of daily energy. In multiple regression models controlling for demographic and health variables, EOF as well as separate counts of meal and snack frequency were each positively and significantly associated with energy intake. However, neither the number of meals, snacks, nor overall EOF was associated with BMI. The proportion of energy consumed during the school day and the positive association of weekday EOF with energy intake suggest an important role for worksite wellness programs that target the dietary improvement of elementary school personnel.
Patterns of Weight Control Strategies Predict Differences in Women's 4‐Year Weight Gain
Authors: Savage Jennifer S. , Birch Leann L.
Published: August 2009

The purpose of this study was to explore whether differences in patterns of weight control strategies predict 4‐year weight change among women. Participants (N = 176), were assessed at baseline and biennially on three occasions. Weight control strategies were assessed by the Weight Loss Behavior Scale. Height and weight were measured to calculate BMI. Latent class analysis (LCA) identified groups of women differing in their reported weight control strategies. Repeated measures were employed to examine the relationship between using different types of weight control strategies and weight change before and after adjusting for education, income, and initial BMI. LCA yielded a three‐group solution: use of none (N), healthy (H), and healthy plus unhealthy (H+U) weight control strategies. The N group had the lowest initial BMIs. Women's pattern of weight gain differed by latent group membership after adjusting for covariates: H+U group gained significantly more weight (4.56 kg) than the N group (1.51 kg) and H group (1.02 kg). Similar patterns emerged predicting weight change between years 2 and 4: H+U group gained significantly more weight (2.86 kg) than the H group (0.03 kg) and N group (0.44 kg). H+U weight control group had higher scores on weight concerns, dietary restraint, and eating attitudes than women in the H or N groups. These findings provide evidence that self‐reported weight control attempts do not necessarily lead to large weight gains; rather the amount of weight gain may depend on the type of weight control strategies that women are practicing.
Fat Overload Induces Changes in Circulating Lactoferrin That Are Associated With Postprandial Lipemia and Oxidative Stress in Severely Obese Subjects
Authors: Fernández‐Real José M. , García‐Fuentes Eduardo , Moreno‐Navarrete José M. , Murri‐Pierri Mora , Garrido‐Sánchez Lourdes , Ricart Wifredo , Tinahones Francisco
Published: August 2009

Lactoferrin is an innate immune system protein with anti‐inflammatory and antioxidant activities. We aimed to evaluate circulating lactoferrin levels in association with lipid concentrations, and parameters of oxidative stress and inflammation in subjects with morbid obesity after an acute fat intake. The effects of a 60 g fat overload on circulating lactoferrin and antioxidant activities were evaluated in 45 severely obese patients (15 men and 30 women, BMI 53.4 ± 7.2 kg/m2). The change in circulating lactoferrin after fat overload was significantly and inversely associated with the free fatty acid (FFA) change. In those subjects with the highest increase in lactoferrin (in the highest quartile), high‐density lipoprotein (HDL)‐cholesterol decreased after fat overload to a lesser extent (P = 0.03). In parallel to lipid changes, circulating lactoferrin concentrations were inversely linked to the variations in catalase (CAT) and glutathione reductase (GSH‐Rd). Baseline circulating lactoferrin concentration was also inversely associated with the absolute change in antioxidant activity after fat overload, and with the change in C‐reactive protein (CRP). Furthermore, those subjects with higher than the median value of homeostasis model assessment of insulin secretion (HOMAIS) had significantly increased lactoferrin concentration after fat load (885 ± 262 vs. 700 ± 286 ng/ml, P = 0.03). Finally, we further explored the action of lactoferrin in vitro. Lactoferrin (10 µmol/l) led to significantly lower triglyceride (TG) concentrations and lactate dehydrogenase activity (as expression of cell viability) in the media from adipose explants obtained from severely obese subjects. In conclusion, circulating lactoferrin concentrations, both at baseline and fat‐stimulated, were inversely associated with postprandial lipemia, and parameters of oxidative stress and fat‐induced inflammation in severely obese subjects.
Higher Free Fatty Acid Uptake in Visceral Than in Abdominal Subcutaneous Fat Tissue in Men
Authors: Hannukainen Jarna C. , Kalliokoski Kari K. , Borra Ronald J.M. , Viljanen Antti P.M. , Janatuinen Tuula , Kujala Urho M. , Kaprio Jaakko , Heinonen Olli J. , Viljanen Tapio , Haaparanta Merja , Iozzo Patricia , Parkkola Riitta , Nuutila Pirjo
Published: August 2009

Visceral adipose tissue has been shown to have high lipolytic activity. The aim of this study was to examine whether free fatty acid (FFA) uptake into visceral adipose tissue is enhanced compared to abdominal subcutaneous tissue in vivo. Abdominal adipose tissue FFA uptake was measured using positron emission tomography (PET) and [18F]‐labeled 6‐thia‐hepta‐decanoic acid ([18F]FTHA) and fat masses using magnetic resonance imaging (MRI) in 18 healthy young adult males. We found that FFA uptake was 30% higher in visceral compared to subcutaneous adipose tissue (0.0025 ± 0.0018 vs. 0.0020 ± 0.0016 µmol/g/min, P = 0.005). Visceral and subcutaneous adipose tissue FFA uptakes were strongly associated with each other (P < 0.001). When tissue FFA uptake per gram of fat was multiplied by the total tissue mass, total FFA uptake was almost 1.5 times higher in abdominal subcutaneous than in visceral adipose tissue. In conclusion, we observed enhanced FFA uptake in visceral compared to abdominal subcutaneous adipose tissue and, simultaneously, these metabolic rates were strongly associated with each other. The higher total tissue FFA uptake in subcutaneous than in visceral adipose tissue indicates that although visceral fat is active in extracting FFA, its overall contribution to systemic metabolism is limited in healthy lean males. Our results indicate that subcutaneous, rather than visceral fat storage plays a more direct role in systemic FFA availability. The recognized relationship between abdominal visceral fat mass and metabolic complications may be explained by direct effects of visceral fat on the liver.
Identification and Prediction of Latent Classes of Weight‐loss Strategies Among Women
Authors: Lanza Stephanie T. , Savage Jennifer S. , Birch Leann L.
Published: August 2009

We apply latent class analysis (LCA) to quantify multidimensional patterns of weight‐loss strategies in a sample of 197 women, and explore the degree to which dietary restraint, disinhibition, and other individual characteristics predict membership in latent classes of weight‐loss strategies. Latent class models were fit to a set of 14 healthy and unhealthy weight‐loss strategies. BMI, weight concern, body satisfaction, depression, dietary disinhibition and restraint, and the interaction of disinhibition and restraint were included as predictors of latent class membership. All analyses were conducted with PROC LCA, a recently developed SAS procedure available for download. Results revealed four subgroups of women based on their history of weight‐loss strategies: No Weight Loss Strategy (10.0%), Dietary Guidelines (26.5%), Guidelines+Macronutrients (39.4%), and Guidelines+Macronutrients+Restrictive (24.2%). BMI, weight concerns, the desire to be thinner, disinhibition, and dietary restraint were all significantly related to weight‐control strategy latent class. Among women with low dietary restraint, disinhibition increases the odds of engaging in any set of weight‐loss strategies vs. none, whereas among medium‐ and high‐restraint women disinhibition increases the odds of use of unhealthy vs. healthy strategies. LCA was an effective tool for organizing multiple weight‐loss strategies in order to identify subgroups of individuals who have engaged in particular sets of strategies over time. This person‐centered approach provides a measure weight‐control status, where the different statuses are characterized by particular combinations of healthy and unhealthy weight‐loss strategies.
Effect of pyruvate, lactate and insulin on ATP supply and demand in unpaced perfused rat heart
Authors: Korzeniewski Bernard , Deschodt-Arsac Véronique , Calmettes Guillaume , Gouspillou Gilles , Franconi Jean-Michel , Diolez Philippe
Published: August 2009

Mitochondrial respiration/oxidative phosphorylation is the main source of energy, in the form of ATP, in the heart under physiological conditions. Different respiratory substrates were used in various experiments during heart perfusion: glucose, pyruvate, lactate, glucose+pyruvate, glucose+lactate, glucose+insulin etc. Also under physiological conditions, the concentration of respiratory substrates/hormones in blood can vary significantly. In the present study, we tested the effect of pyruvate, lactate and insulin (all in the presence of glucose) and glucose (in the presence of pyruvate) on the ATP-producing and -consuming blocks in perfused rat heart, in a system where HR (heart rate) was allowed to vary (no pacing). Changes in RPP (rate-pressure product) and PCr (phosphocreatine) concentration were measured. PAA (Proportional Activation Approach) was used to visualize and quantitatively analyse the data. It was demonstrated that addition of glucose (in the presence of pyruvate) exerted essentially no effect on the system. Insulin (in the presence of glucose) activated only the ATP producer. The most interesting finding is that, in our system, pyruvate and lactate (added in the presence or instead of glucose) activated ATP producer, but significantly inhibited ATP consumer (their effect was quantitatively identical).
Urokinase-receptor-mediated phenotypic changes in vascular smooth muscle cells require the involvement of membrane rafts
Authors: Kiyan Julia , Smith Graham , Haller Hermann , Dumler Inna
Published: August 2009

The cholesterol-enriched membrane microdomains lipid rafts play a key role in cell activation by recruiting and excluding specific signalling components of cell-surface receptors upon receptor engagement. Our previous studies have demonstrated that the GPI (glycosylphosphatidylinositol)-linked uPAR [uPA (urokinase-type plasminogen activator) receptor], which can be found in lipid rafts and in non-raft fractions, can mediate the differentiation of VSMCs (vascular smooth muscle cells) towards a pathophysiological de-differentiated phenotype. However, the mechanism by which uPAR and its ligand uPA regulate VSMC phenotypic changes is not known. In the present study, we provide evidence that the molecular machinery of uPAR-mediated VSMC differentiation employs lipid rafts. We show that the disruption of rafts in VSMCs by membrane cholesterol depletion using MCD (methyl-β-cyclodextrin) or filipin leads to the up-regulation of uPAR and cell de-differentiation. uPAR silencing by means of interfering RNA resulted in an increased expression of contractile proteins. Consequently, disruption of lipid rafts impaired the expression of these proteins and transcriptional activity of related genes. We provide evidence that this effect was mediated by uPAR. Similar effects were observed in VSMCs isolated from Cav1−/− (caveolin-1-deficient) mice. Despite the level of uPAR being significantly higher after the disruption of the rafts, uPA/uPAR-dependent cell migration was impaired. However, caveolin-1 deficiency impaired only uPAR-dependent cell proliferation, whereas cell migration was strongly up-regulated in these cells. Our results provide evidence that rafts are required in the regulation of uPAR-mediated VSMC phenotypic modulations. These findings suggest further that, in the context of uPA/uPAR-dependent processes, caveolae-associated and non-associated rafts represent different signalling membrane domains.
MAC inhibitors suppress mitochondrial apoptosis
Authors: Peixoto Pablo M. , Ryu Shin-Young , Bombrun Agnes , Antonsson Bruno , Kinnally Kathleen W.
Published: August 2009

MAC (mitochondrial apoptosis-induced channel) forms in the mitochondrial outer membrane and unleashes cytochrome c to orchestrate the execution of the cell. MAC opening is the commitment step of intrinsic apoptosis. Hence closure of MAC may prevent apoptosis. Compounds that blocked the release of fluorescein from liposomes by recombinant Bax were tested for their ability to directly close MAC and suppress apoptosis in FL5.12 cells. Low doses of these compounds (IC50 values ranged from 19 to 966 nM) irreversibly closed MAC. These compounds also blocked cytochrome c release and halted the onset of apoptotic markers normally induced by IL-3 (interleukin-3) deprivation or staurosporine. Our results reveal the tight link among MAC activity, cytochrome c release and apoptotic death, and indicate this mitochondrial channel is a promising therapeutic target.
Measuring Effectiveness of Graph Visualizations: A Cognitive Load Perspective
Authors: Huang Weidong , Eades Peter , Hong Seok-Hee
Published: August 2009

Graph visualizations are typically evaluated by comparing their differences in effectiveness, measured by task performance such as response time and accuracy. Such performance-based measures have proved to be useful in their own right. There are some situations, however, where the performance measures alone may not be sensitive enough to detect differences. This limitation can be seen from the fact that the graph viewer may achieve the same level of performance by devoting different amounts of cognitive effort. In addition, it is not often that individual performance measures are consistently in favor of a particular visualization. This makes design and evaluation difficult in choosing one visualization over another. In an attempt to overcome the above-mentioned limitations, we measure the effectiveness of graph visualizations from a cognitive load perspective. Human memory as an information processing system and recent results from cognitive load research are reviewed first. The construct of cognitive load in the context of graph visualization is proposed and discussed. A model of user task performance, mental effort and cognitive load is proposed thereafter to further reveal the interacting relations between these three concepts. A cognitive load measure called mental effort is introduced and this measure is further combined with traditional performance measures into a single multi-dimensional measure called visualization efficiency. The proposed model and measurements are tested in a user study for validity. Implications of the cognitive load considerations in graph visualization are discussed.
On shear viscosity and the Reynolds number of magnetohydrodynamic turbulence in collisionless magnetized plasmas: Coulomb collisions, Landau damping, and Bohm diffusion
Authors: Borovsky Joseph E. , Gary S. Peter
Published: August 2009

For a collisionless plasma, the magnetic field Ḇ enables fluidlike behavior in the directions perpendicular to B; however, fluid behavior along Ḇ may fail. The magnetic field also introduces an Alfven-wave nature to flows perpendicular to Ḇ. All Alfven waves are subject to Landau damping, which introduces a flow dissipation (viscosity) in collisionless plasmas. For three magnetized plasmas (the solar wind, the Earth’s magnetosheath, and the Earth’s plasma sheet), shear viscosity by Landau damping, Bohm diffusion, and by Coulomb collisions are investigated. For magnetohydrodynamic turbulence in those three plasmas, integral-scale Reynolds numbers are estimated, Kolmogorov dissipation scales are calculated, and Reynolds-number scaling is discussed. Strongly anisotropic Kolmogorov k−5∕3 and mildly anisotropic Kraichnan k−3∕2 turbulences are both considered and the effect of the degree of wavevector anisotropy on quantities such as Reynolds numbers and spectral-transfer rates are calculated. For all three plasmas, Braginskii shear viscosity is much weaker than shear viscosity due to Landau damping, which is somewhat weaker than Bohm diffusion.
Two-photon photodissociation dynamics of H2O via the D̃ electronic state
Authors: Yuan Kaijun , Cheng Lina , Cheng Yuan , Guo Qing , Dai Dongxu , Yang Xueming
Published: August 2009

Photodissociation dynamics of H2O via the D̃ state by two-photon absorption have been investigated using the H-atom Rydberg tagging time-of-flight technique. The action spectrum of the D̃←X̃ transition band has been measured. The predissociation lifetime of the D̃ state is determined to be about 13.5 fs. The quantum state-resolved OH product translational energy distributions and angular distributions have also been measured. By carefully simulating these distributions, quantum state distributions of the OH product as well as the state-resolved angular anisotropy parameters were determined. The most important pathway of the H2O dissociation via the D̃ state leads to the highly rotationally excited OH(X,v=0) products. Vibrationally excited OH(X) products (up to v=10) and electronically excited OH(A,v=0,1,2) have also been observed. The OH(A)/OH(X) branching ratios are determined to be 17.9% at 244.540 nm (2ω1=81 761.4 cm−1) and 19.9% at 244.392 nm (2ω2=81 811 cm−1), which are considerably smaller than the value predicted by the theory. These discrepancies are attributed to the nonadiabatic coupling effect between the B̃ and D̃ surfaces at the bent geometry.
Reversible atomic modification of nanostructures on surfaces using direction-depended tip-surface interaction with a trimer-apex tip
Authors: Xie Yiqun , Ma Liuxue , Zhang Peng , Cai Xiulong , Zhang Wenxian , Gan Fuxi , Ning Xi-Jing , Zhuang Jun
Published: August 2009

Using first-principles simulations, we propose a simple mechanism and an easy-controlled method for reversible modification of supported nanoclusters on surfaces with atomic precision. As illustrated, individual atoms at edges of a Al nanocluster on a Al(111) surface can be extracted vertically and repositioned with a Al trimer-apex tip, which allows to rearrange a ten-atom hexagonal nanocluster to a triangular one in a reversible way. The governing mechanism is the atomic tip-surface interaction whose distinct dependence on directions plays a key role in manipulations.
Functionally grading the shape memory response in NiTi films: Laser irradiation
Authors: Birnbaum A. J. , Satoh G. , Yao Y. L.
Published: August 2009

A new process and mechanism are presented for controlling the shape memory response spatially within monolithic NiTi thin film structures. This technique is shown to effectively control the martensitic phase transformation temperature and exhibits control over aspects of the mechanical and shape memory responses as well. Specifically, the martensitic phase transformation temperature decreases with incident laser energy density. Concomitant modifications are observed in both the mechanical and shape memory responses in laser processed films. Analysis and characterization are performed via temperature controlled optical microscopy, x-ray diffraction, atomic force microscopy, and nanoindentation.
Emittance characterization of a hot-cavity laser ion source at Holifield Radioactive Ion Beam Facility
Authors: Liu Y. , Baktash C. , Beene J. R. , Geppert Ch. , Gottwald T. , Havener C. C. , Kessler T. , Krause H. F. , Schultz D. R. , Stracener D. W. , Vane C. R. , Wies K. , Wendt K.
Published: August 2009

The first investigation of the transverse emittance of a hot-cavity laser ion source based on all-solid-state Ti:sapphire lasers is presented. The emittances of C63u ion beams generated by three-photon resonant ionization are measured and compared with that of the G69a and K39 ion beams resulting from surface ionization in the same ion source. A self-consistent unbiased elliptical exclusion method is adapted for noise reduction and emittance analysis. Typical values of the rms and 90% fractional emittances of the Cu ion beams at 20 keV energy are found to be about 2 and 8πmm mrad, respectively, for the ion currents of 2–40 nA investigated. The emittances of the laser-produced Cu ion beams are smaller than those of the surface-ionized Ga and K ion beams.
On the variational computation of a large number of vibrational energy levels and wave functions for medium-sized molecules
Authors: Mátyus Edit , Šimunek Ján , Császár Attila G.
Published: August 2009

In a recent publication [J. Chem. Phys. 127, 084102 (2007)], the nearly variational DEWE approach (DEWE denotes Discrete variable representation of the Watson Hamiltonian using the Eckart frame and an Exact inclusion of a potential energy surface expressed in arbitrarily chosen coordinates) was developed to compute a large number of (ro)vibrational eigenpairs for medium-sized semirigid molecules having a single well-defined minimum. In this publication, memory, CPU, and hard disk usage requirements of DEWE, and thus of any DEWE-type approach, are carefully considered, analyzed, and optimized. Particular attention is paid to the sparse matrix-vector multiplication, the most expensive part of the computation, and to rate-determining steps in the iterative Lanczos eigensolver, including spectral transformation, reorthogonalization, and restart of the iteration. Algorithmic improvements are discussed in considerable detail. Numerical results are presented for the vibrational band origins of the C12H4 and C12H2D2 isotopologues of the methane molecule. The largest matrix handled on a personal computer during these computations is of the size of (4∙108)×(4∙108). The best strategy for determining vibrational eigenpairs depends largely on the actual details of the required computation. Nevertheless, for a usual scenario requiring a large number of the lowest eigenpairs of the Hamiltonian matrix the combination of the thick-restart Lanczos method, shift-fold filtering, and periodic reorthogonalization appears to result in the computationally most feasible approach.
Electronic structure of (Ge2Sb2Te5)1−x(In3SbTe2)x investigated by x-ray photoelectron spectroscopy
Authors: Benayad Anass , Kang YounSeon , Shin Hyun-Joon , Kim Kihong , Suh Dong-Seok , Kim KiJoon , Kim CheolKyu , Lee Tae-Yon , Noh Jin-Seo , Lee JaeCheol , Khang YoonHo
Published: August 2009

We have investigated the core levels and the valence band of (Ge2Sb2Te5)1−x(In3Sb1Te2)x quaternary phase system (IGST) by means of x-ray photoelectron spectroscopy. A systematic shift of Sb 3d and Ge 2p core-level peaks toward lower binding energies side was observed with increasing indium amount, whereas the In 3d and Te 3d core peaks showed less change. The Sb 3d and Ge 2p core-level shift is attributed to an increase in the electronic charge of p-electrons dependent of indium amount. The valence band spectra show a distinct change in the sp configuration with indium concentration change. The change in the local bonding as the indium amount increase has a profound impact on both local atomic arrangement and amorphous-to-crystalline transformation temperature. The difference in the photoemission spectra have been discussed according to a simple structural model suggesting that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.
Strain mapping of tensiley strained silicon transistors with embedded Si1−yCy source and drain by dark-field holography
Authors: Hüe Florian , Hÿtch Martin , Houdellier Florent , Bender Hugo , Claverie Alain
Published: August 2009

Dark-field holography, a new transmission electron microscopy technique for mapping strain distributions at the nanoscale, is used to characterize strained-silicon n-type transistors with a channel width of 65 nm. The strain in the channel region, which enhances electron mobilities, is engineered by recessed Si0.99C0.01 source and drain stressors. The strain distribution is measured across an array of five transistors over a total area of 1.6 μm wide. The longitudinal tensile strain reaches a maximum of 0.58%±0.02% under the gate oxide. Theoretical strain maps obtained by finite element method agree well with the experimental results.
Magnetohydrodynamic stability at a separatrix. I. Toroidal peeling modes and the energy principle
Authors: Webster A. J. , Gimblett C. G.
Published: August 2009

A potentially serious impediment to the production of energy by nuclear fusion in large tokamaks, such as ITER [R. Aymar, V. A. Chuyanov, M. Huguet, Y. Shimomura, ITER Joint Central Team, and ITER Home Teams, Nucl. Fusion 41, 1301 (2001)] and DEMO [D. Maisonner, I. Cook, S. Pierre, B. Lorenzo, D. Luigi, G. Luciano, N. Prachai, and P. Aldo, Fusion Eng. Des. 81, 1123 (2006)], is the potential for rapid deposition of energy onto plasma facing components by edge localized modes (ELMs). The trigger for ELMs is believed to be the ideal magnetohydrodynamic peeling-ballooning instability, but recent numerical calculations have suggested that a plasma equilibrium with an X-point—as is found in all ITER-like tokamaks, is stable to the peeling mode. This contrasts with analytical calculations [G. Laval, R. Pellat, and J. S. Soule, Phys. Fluids 17, 835 (1974)] that found the peeling mode to be unstable in cylindrical plasmas with arbitrary cross-sectional shape. Here, we re-examine the assumptions made in cylindrical geometry calculations and generalize the calculation to an arbitrary tokamak geometry at marginal stability. The resulting equations solely describe the peeling mode and are not complicated by coupling to the ballooning mode, for example. We find that stability is determined by the value of a single parameter Δ′ that is the poloidal average of the normalized jump in the radial derivative of the perturbed magnetic field’s normal component. We also find that near a separatrix it is possible for the energy principle’s δW to be negative (that is usually taken to indicate that the mode is unstable, as in the cylindrical theory), but the growth rate to be arbitrarily small.
Dephasing of Si spin qubits due to charge noise
Authors: Culcer Dimitrie , Hu Xuedong , Das Sarma S.
Published: August 2009

Spin qubits in silicon quantum dots can have long coherence times, yet their manipulation relies on the exchange interaction, through which charge noise can induce decoherence. Charge traps near the interface of a Si heterostructure lead to fluctuations in the quantum-dot confinement and barrier potentials, which cause gating errors and two-spin dephasing. We quantify these effects in Si double quantum dots using a realistic model of noise. Specifically, we consider both random telegraph noise from a few traps good for dots grown on submicron wafers and 1/f noise from many traps good for larger wafers appropriate for quantum dot arrays. We give estimates of gate errors for single-spin qubit architectures and dephasing in singlet-triplet qubits.
Competition between the barrier and injection mechanisms of nonlinearity of the current-voltage characteristic in Mott-barrier detector diodes
Authors: Shashkin V. I. , Vostokov N. V.
Published: August 2009

We obtain an analytical solution to the problem of transverse injection current in an undoped semiconductor i layer of arbitrary thickness with account of self-consistent boundary conditions. Charge transfer in the semiconductor bulk is described in the drift-diffusion approximation. Current transfer through the boundaries of an undoped layer is described in terms of the thermoelectron emission theory. Thus, the generalized thermoemission-diffusion approach applies for semiconductors with both low and high mobilities of charge carriers. On the basis of the obtained solution, we analyze the characteristics of the current nonlinearity of the Mott-barrier diodes. The generalized approach is used for describing current transfer in low-barrier diodes based on Mott contacts with near-surface δ-doping. Characteristics of detection of low-barrier diodes are analyzed. Limiting values of the volt-watt and threshold sensitivities of the detectors based on these diodes in the subterahertz frequency range (up to 1 THz) are determined.
Intensity distributions of enhanced H emission from laser-induced low-pressure He plasma and a suggested He-assisted excitation mechanism
Authors: Lie Zener Sukra , Pardede Marincan , Hedwig Rinda , Suliyanti Maria Margaretha , Steven Eden , Maliki  , Kurniawan Koo Hendrik , Ramli Muliadi , Abdulmadjid Syahrun Nur , Idris Nasrullah , Lahna Kurnia , Kagawa Kiichiro , Tjia May On
Published: August 2009

An experimental study was conducted on the spatial distributions of hydrogen emission intensities from low-pressure plasmas generated by laser ablation of zircaloy-4 and black stone targets in nitrogen and helium ambient gases. In addition to confirming the previously observed intensity enhancement effect in ambient helium gas, the hydrogen and helium emission intensities measured along the plasma expansion direction revealed remarkable extended spatial distributions featuring unexpected maxima near the far end of the plasma where the available shock-wave generated thermal excitation energy should have been significantly reduced. This “anomalous” feature necessarily implied the presence of an additional excitation process beside the well known shock-wave excitation process which is responsible for the plasma emission of heavy atoms in low-pressure ambient gas. Further analysis of the data led to a suggested physical mechanism explaining the possible contribution of a helium metastable excited state to the unusual phenomenon observed in this experiment.
Carbon nanotube induced enhancement of electroluminescence of phosphor
Authors: Bae Min Jong , Park Shang Hyeun , Jeong Tae Won , Lee Jeong Hee , Han In Taek , Jin Yong Wan , Kim Jong Min , Kim Jin-Young , Yoo Ji Beom , Yu Se Gi
Published: August 2009

Electroluminescence (EL) was observed on conventional cathodoluminescent (CL) phosphor with the incorporation of carbon nanotube (CNT) at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CL phosphor was significantly improved from no light emission in the case of no addition of CNT to 35 cd/m2 with 1 wt % CNT at 10 kHz of ac 300 V.
Effect of substitutional carbon concentration on Schottky-barrier height of nickel silicide formed on epitaxial silicon-carbon films
Authors: Lim Phyllis S. Y. , Lee Rinus T. P. , Sinha Mantavya , Chi Dong Zhi , Yeo Yee-Chia
Published: August 2009

The effective electron Schottky barrier height (ΦBN) of nickel silicide (NiSi:C) formed on silicon-carbon (Si1−yCy or Si:C) films with different substitutional carbon concentrations Csub was investigated. ΦBN was observed to decrease substantially with an increase in Csub. When Csub is increased from 0% to 1.5%, ΦBN is reduced by 200 meV. The results of this work could be useful for the reduction in contact resistance between nickel silicide and silicon-carbon source and drain in strained n-channel metal-oxide-semiconductor field-effect transistors.
The fusion algebra of an extraspecial p-group
Authors: Duman Ali Nabi
Published: August 2009

One can remark that the study of twisted fusion algebras for finite groups is closely related to the modular data associated with finite groups. Coste et al. [“Finite group modular data,” Nucl. Phys. B, 521, 679] undergo the study of this finite group modular data and write down the modular S and T matrices of the group G=(Z∕p)3 for a particular twist. Here we show that the modular data of G for a particular twist are the same as the modular data of the extraspecial p-group H of order p3 with exponent p. This result implies that the twisted fusion algebra of G is the same as the nontwisted fusion algebra of H.
Diffusion of Mn in GaAs studied by quantitative time-of-flight secondary ion mass spectrometry
Authors: Goacher Robyn E. , Hegde Shridhar , Luo Hong , Gardella Joseph A.
Published: August 2009

Diffusion coefficients and the activation energy for Mn diffusion in ion-implanted and layered epitaxial structures of Ga1−xMnxAs/GaAs are reported from quantitative time-of-flight secondary ion mass spectrometry. Samples are annealed between the growth temperature (as low as 200 °C) and approximately 400 °C. This temperature range is reported to improve the Curie temperature, which is important for the spintronic applications of these materials. Quantitative diffusion information is obtained by calibrating the Mn concentration to ion-implanted standards and the depth scale to profilometry measurements. Depth profiles obtained for ion-implanted Mn in GaAs at a dose of 1.35×1015 atoms/cm2 show increased Mn concentration within the top 5 nm of the sample but otherwise reveal no significant differences in the implantation shape after annealing up to 350 °C. For a higher implantation dose of 8.10×1015 Mn atoms/cm2, diffusion is initiated after annealing at 300 °C with more significant diffusion at higher temperatures. The analysis of annealed epitaxial films of even higher concentration (Ga0.89Mn0.11As) exhibits diffusion at all temperatures measured (200–400 °C) and an activation energy of 0.67±0.09 eV is calculated by fitting the profiles to an error function.
Equations for probability density and for the phase of wave function in quantum mechanics and superconductivity
Authors: Mkrtchyan A. R. , Avakyan R. M. , Hayrapetyan A. G. , Khachatryan B. V. , Petrosyan R. G.
Published: August 2009

The fourth order linear differential equation is obtained for the probability density considering the non-Hermitian Hamiltonian (the case of quasistationary states—complexity of energy). Third order nonlinear differential equation for the square of the modulus of the order parameter and for the phase is obtained by making use of Ginzburg–Landau equations. Three integrals of “motion” are found in the absence of the external magnetic field and two integrals are found in the presence of the external magnetic field. The analysis of these integrals is conducted. New analytical solutions are obtained.
Study of linear and nonlinear optical properties of dendrimers using density matrix renormalization group method
Authors: Mukhopadhyay S. , Ramasesha S.
Published: August 2009

We have used the density matrix renormalization group (DMRG) method to study the linear and nonlinear optical responses of first generation nitrogen based dendrimers with donor acceptor groups. We have employed Pariser–Parr–Pople Hamiltonian to model the interacting π electrons in these systems. Within the DMRG method we have used an innovative scheme to target excited states with large transition dipole to the ground state. This method reproduces exact optical gaps and polarization in systems where exact diagonalization of the Hamiltonian is possible. We have used a correction vector method which tacitly takes into account the contribution of all excited states, to obtain the ground state polarizibility, first hyperpolarizibility, and two photon absorption cross sections. We find that the lowest optical excitations as well as the lowest excited triplet states are localized. It is interesting to note that the first hyperpolarizibility saturates more rapidly with system size compared to linear polarizibility unlike that of linear polyenes.
Improving the relativistic self-focusing of intense laser beam in plasma using density transition
Authors: Sadighi-Bonabi R. , Habibi M. , Yazdani E.
Published: August 2009

The propagation of a Gaussian beam in underdense plasma with upward increasing density ramp is analyzed. In this work are shown that the spot size oscillations of laser beam increases and its amplitude shrinks with proper plasma density ramp. This causes the laser beam to become more focused and penetrations deep into the plasma by reduction of diffraction effect. The related focusing parameters are optimized to get the best possible focusing at the relativistic threshold intensity of Nd-glass laser and the effect of the laser intensity in the self-focusing parameters is also investigated. The analytical calculations are presented and showed more reliable results in comparison to the previous works.
Electrical anisotropy in multiscale nanotube/fiber hybrid composites
Authors: Thostenson Erik T. , Gangloff John J. , Li Chunyu , Byun Joon-Hyung
Published: August 2009

This letter reports an experimental and theoretical study on the electrical properties of carbon nanotube/glass fiber composites. Experimental measurements on unidirectional glass fiber composites with nanotubes dispersed in the polymer matrix show a high degree of anisotropy. The composites, manufactured with a vacuum infusion technique, do not show any significant process-induced anisotropy. Theoretical modeling reveals that the microstructure of the fiber composite plays a dominant role in the electrical behavior due to alteration of percolating paths in the carbon nanotube network.
The polarity origin of the bipolar resistance switching behaviors in metal/La0.7Ca0.3MnO3/Pt junctions
Authors: Yang R. , Li X. M. , Yu W. D. , Gao X. D. , Shang D. S. , Liu X. J. , Cao X. , Wang Q. , Chen L. D.
Published: August 2009

Bipolar resistance switching behaviors in the M/La0.7Ca0.3MnO3/Pt (M=Pt, Ag, Cu, Al, Ti, and W) junctions were investigated. We found that the switching polarities of the junctions for M=Pt, Ag, and Cu were opposite to those for M=Al, Ti, and W. This phenomenon was attributed to the different Gibbs free energy of the metal oxide formation. Based on Auger electron spectroscopy measurement of the M/La0.7Ca0.3MnO3 interfaces, the switching mechanisms were further discussed in terms of metal electrode redox reaction for M=Al, Ti, and W and oxygen vacancy generation/annihilation in the La0.7Ca0.3MnO3 film for M=Pt, Ag, and Cu, respectively.