bluuebunny/crossref_metadata_2025 huggingface dataset:
Decrease in heliospheric magnetic flux in this solar minimum: Recent Ulysses magnetic field observations
Authors: Smith Edward J. , Balogh Andre
Published: November 2008

The Ulysses spacecraft has traveled from the solar equator at 1.3 and 5.3 AU to above the polar caps at 2.2 AU three times during the last 17 years and has provided measurements of the solar–heliospheric magnetic field. The open magnetic flux, i.e., the radial component, BR, multiplied by the square of the radial distance, r, is independent of latitude at both solar minimum and maximum. Measurements of r2 BR contain information about the average polar cap field strength when allowance is made for the non‐radial expansion of the magnetic field and solar wind near the Sun that eliminates the latitude gradient in magnetic pressure. Recent Earth‐based magnetograph observations indicate that the Sun's polar cap field strength, BP, has decreased by a factor of about two between the previous and present latitude scans. Ulysses measurements show that the average value of r2 BR has decreased from 3.6 nT (AU)2 in 1993.5 to 1995.0 to 2.3 nT (AU)2 in 2006.1 to 2007.4, a decrease by 0.64. The two Ulysses scans are not precisely at solar minimum. However, in‐ecliptic BR is highly correlated with the Ulysses measurements at all latitudes and can be used to determine the open flux at the two solar minima. Averages of BR at the two solar minima are 2.82 and 2.45 nT. This decrease is contrary to the suggestion based on previous solar cycles that BR returns to the same value of ≈ 3 nT at solar minimum. The ratio of BP to the expansion factor, fE, is proportional to the measured open flux and observed and assumed values of BP are used to determine the corresponding values of fE. Another property of the fast solar wind is that it is highly turbulent compared to lower latitudes. To determine if the decrease in r2 BR and BP has affected the intensity of the magnetic fluctuations, the total variances in the magnetic field fluctuations are derived and found to decrease by a factor of 0.75.
Reduced Antarctic meridional overturning circulation reaches the North Atlantic Ocean
Authors: Johnson Gregory C. , Purkey Sarah G. , Toole John M.
Published: November 2008

We analyze abyssal temperature data in the western North Atlantic Ocean from the 1980s–2000s, showing that reductions in Antarctic Bottom Water (AABW) signatures have reached even that basin. Trans‐basin oceanographic sections occupied along 52°W from 1983–2003 and 66°W from 1985–2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between AABW and North Atlantic Deep Water (NADW), hence a local AABW volume reduction. Repeat section data taken from 1981–2004 along 24°N also show a reduced zonal gradient in abyssal temperatures, consistent with decreased northward transport of AABW. The reduction in the Antarctic limb of the MOC within the North Atlantic highlights the global reach of climate variability originating around Antarctica.
Simultaneous THEMIS observations in the near‐tail portion of the inner and outer plasma sheet flux tubes at substorm onset
Authors: Sergeev V. A. , Apatenkov S. V. , Angelopoulos V. , McFadden J. P. , Larson D. , Bonnell J. W. , Kuznetsova M. , Partamies N. , Honary F.
Published: November 2008

We analyzed the measurements made by two Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes in ideal observational conditions (quiet background, near midnight, inside the substorm current wedge) during two distinct isolated substorm onsets, with probe P2 measuring the inner plasma sheet at ∼8 Re and P1 near the plasma sheet–lobe interface at 11–12 Re. The earliest onset‐related strong perturbations were observed by P1; they include the increase of both Bz (dipolarization) and Ey (a few mV/m) as well as the simultaneous drop in total pressure, indicating the unloading process. This was also accompanied by fast inward plasma motion (up to 100 km/s, toward the neutral sheet) and fast plasma sheet thinning while the poleward auroral expansion was in progress in the conjugate ionosphere. These perturbations were followed after 6–8 min by the rapid expansion of the already heated plasma sheet. While in the adjacent lobe during this thinning phase, probe P1 continued to observe intense flux transfer toward the sheet center plane. The inner probe observed intense dipolarization and inward plasma injection but with a smaller flux transfer and starting 1–2 min after the perturbations at P1, supporting the conclusion that onset instability took place tailward of 12 Re. We also demonstrate the global MHD simulations to show that a nontrivial combination of dipolarization and the plasma sheet thinning may be observed simultaneously in the outmost part of the dipolelike region during a sudden increase of the reconnection rate at the nearby active X line, staying a few Re from the observation point. These observations provide constraints for the choice of substorm onset mechanism and indicate near‐Earth magnetic reconnection as the most probable source process.
A multi‐instrument view of tail reconnection at Saturn
Authors: Jackman C. M. , Arridge C. S. , Krupp N. , Bunce E. J. , Mitchell D. G. , McAndrews H. J. , Dougherty M. K. , Russell C. T. , Achilleos N. , Jones G. H. , Coates A. J.
Published: November 2008

Three instances of tail reconnection events at Saturn involving the ejection of plasmoids downtail have been reported by Jackman et al. (2007) using data from Cassini's magnetometer (MAG). Here we show two newly discovered events, as identified in the MAG data by northward/southward turnings and intensifications of the field. We discuss these events along with the original three, with the added benefit of plasma and energetic particle data. The northward/southward turnings of the field elucidate the position of the spacecraft relative to the reconnection point and passing plasmoids, while the variability of the azimuthal and radial field components during these events indicates corresponding changes in the angular momentum of the magnetotail plasma following reconnection. Other observable effects include a reversal in flow direction of energetic particles, and the apparent evacuation of the plasma sheet following the passage of plasmoids.
Validation of Aura Microwave Limb Sounder OH measurements with Fourier Transform Ultra‐Violet Spectrometer total OH column measurements at Table Mountain, California
Authors: Wang Shuhui , Pickett Herbert M. , Pongetti Thomas J. , Cheung Ross , Yung Yuk L. , Shim Changsub , Li Qinbin , Canty Timothy , Salawitch Ross J. , Jucks Kenneth W. , Drouin Brian , Sander Stanley P.
Published: November 2008

The first seasonal and interannual validation of OH measurements from the Aura Microwave Limb Sounder (MLS) has been conducted using ground‐based OH column measurements from the Fourier Transform Ultra‐Violet Spectrometer (FTUVS) over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) during 2004–2007. To compare with FTUVS total column measurements, MLS OH vertical profiles over TMF are integrated to obtain partial OH columns above 21.5 hPa, which covers nearly 90% of the total column. The tropospheric OH and the lower stratopheric OH not measured by MLS are estimated using GEOS (Goddard Earth Observing System)‐Chem and a Harvard 2‐D model implemented within GEOS‐Chem, respectively. A number of field observations and calculations from a photochemical box model are compared to OH profiles from these models to estimate the variability in the lower atmospheric OH and thus the uncertainty in the combined total OH columns from MLS and models. In general, the combined total OH columns agree extremely well with TMF total OH columns, especially during seasons with high OH. In winter with low OH, the combined columns are often higher than TMF measurements. A slightly weaker seasonal variation is observed by MLS relative to TMF. OH columns from TMF and the combined total columns from MLS and models are highly correlated, resulting in a mean slope of 0.969 with a statistically insignificant intercept. This study therefore suggests that column abundances derived from MLS vertical profiles have been validated to within the mutual systematic uncertainties of the MLS and FTUVS measurements.
In vivo effects of cytokines on pancreatic β‐cells in models of type I diabetes dependent on CD4+ T lymphocytes
Authors: Angstetra Eveline , Graham Kate L , Emmett Sarah , Dudek Nadine L , Darwiche Rima , Ayala‐Perez Rochelle , Allison Janette , Santamaria Pere , Kay Thomas W H , Thomas Helen E
Published: November 2008

CD4+ T cells can actively kill β‐cells in type I diabetes as well as help CD8+ T cells become cytolytic. Cytokines have the potential to kill β‐cells, or upregulate Fas on β‐cells, and increase their susceptibility to FasL. We investigated the direct effects of cytokines on β‐cells in perforin‐deficient non‐obese diabetic (NOD) mice and NOD4.1 TCR transgenic mice, two models in which CD8+ T cells play a less dominant role. Inhibiting the effects of cytokines by the overexpression of suppressor of cytokine signalling‐1 (SOCS1) in β‐cells did not reduce diabetes or insulitis in perforin‐deficient NOD, NOD4.1 or interleukin (IL)‐1 receptor‐deficient NOD4.1 mice. SOCS1 overexpression prevented Fas upregulation on NOD4.1 β‐cells, but did not prevent islet destruction because SOCS1 transgenic islets were killed when grafted into NOD4.1.scid mice. Likewise, Fas‐deficient NOD.lpr islets were destroyed in NOD4.1 mice. Although blocking the effects of interferon (IFN)γ on β‐cells did not affect diabetes in NOD4.1 mice, global deficiency of IFNγR2 reduced diabetes and insulitis, suggesting that IFNγ is involved in CD4+ T‐cell activation or migration. Our data show that β‐cells under attack by CD4+ T cells are not destroyed by the effects of cytokines including IFNγ and IL‐1 or Fas‐dependent cytotoxicity.
Gene Expression Profiling of the Hepatic Transcriptome in Presence of TNF-alpha
Authors: Pandey Amit Kumar , Munjal Neha , Datta Malabika
Published: November 2008

Diabetes mellitus, often simply termed Diabetes, is a syndrome characterized by disordered metabolism and high blood sugar. It is caused due to low levels of insulin hormone or from abnormal resistance to insulin in its target tissues. World Health Organization estimates that India will alone have 79.4 million diabetic patients in 2030. One of its major form Type 2 diabetes, is often associated with obesity, hypertension, elevated cholesterol and metabolic syndrome. Changes in life style, such as consumption of high-calorie diet and lack of exercise, have increased the global prevalence not only of diabetes but also of obesity. Type 2 diabetes is characterized by insulin resistance in target tissue, occurs due to several reasons and one of them being the proinflammatory cytokine, TNF-α. It is also known as the link between diabetes and obesity. High levels of TNF-α interfere with insulin signaling to cause the effect and to further investigate into the situation, gene transcription profiling was examined in control and TNF-α treated HepG2 cells. Results indicated that TNF-α could significantly alter the expression of a significant number of genes that were identified to be related to lipid and fat metabolism on one hand and to immunoglobulin receptor activity and IgE binding thereby on the other thereby indicating global dysregulation of fat metabolism and compromise in immune defense mechanism(s) within the hepatocyte by TNF-α. Pathway analysis revealed “biosynthesis of steroids” to be most effected. All these indicate TNF-α to be significantly altering the transcriptome profiling within HepG2 cells with genes involved in lipid and steroid metabolism being the most favoured and this could explain one of the underlying mechanisms of TNF-α action in the liver.
Management of Obesity: A Challenge for Medical Training and Practice
Authors: Thande Njeri K. , Hurstak Emily E. , Sciacca Robert E. , Giardina Elsa‐Grace V.
Published: November 2008

Health‐care providers are in a unique position to encourage people to make healthy lifestyle choices. However, lifestyle modification counseling is a complex task, made even more so by the cultural and socioeconomic diversity of patient populations. The objective of this study is to evaluate the prevalence and predictors of attending and physician‐in‐training weight control counseling in an urban academic internal medicine clinic serving a unique low‐income multiethnic high‐risk population. In 2006, patients (n = 256) from the Associates in Internal Medicine clinic (Division of General Medicine at the New York Presbyterian Hospital, Columbia University Medical Center, New York, NY) were recruited and completed a questionnaire, which assessed demographic variables, health conditions, access to health‐care services, physician weight control counseling, and weight loss attempts. Seventy‐nine percent of subjects were either overweight or obese. Only 65% of obese subjects were advised to lose weight. Attending physicians were more likely than physicians‐in‐training to counsel subjects on weight control (P < 0.01). Factors that were significantly (P < 0.05) associated with different types of weight control counseling included obesity, cardiovascular disease (CVD) risk factors, female gender, nonblack race, college education, married status, and attending physician. Subjects advised to lose weight were more likely to report an attempt to lose weight (P < 0.01). Rates of weight control counseling among physicians are suboptimal, particularly among physicians‐in‐training. Training programs need to promote effective clinical obesity prevention and treatment strategies that address socioeconomic, linguistic, and cultural factors.
Influence of Waist on Adiponectin and Insulin Sensitivity in Adolescence
Authors: Rasmussen‐Torvik Laura J. , Pankow James S. , Jacobs David R. , Steinberger Julia , Moran Antoinette M. , Sinaiko Alan R.
Published: November 2008

It has been hypothesized that abdominal obesity leads to insulin resistance partly through decreased adiponectin. However, the cross‐sectional and longitudinal associations among waist, adiponectin, and insulin sensitivity have not been examined in older adolescents. Non‐Hispanic white and black children were recruited from the Minneapolis school district and underwent three examinations at mean ages 13, 15, and 19. Insulin sensitivity (measured using the gold‐standard euglycemic clamp) and waist circumference were measured at all exams. Adiponectin was measured at mean ages 15 and 19. Partial correlations were used to examine associations among waist, adiponectin, and insulin sensitivity at mean age 15 (n = 308) and mean age 19 (n = 218). Longitudinal correlations and a longitudinal regression model were used to predict adiponectin and insulin sensitivity measured at ages 15 and 19, from age 13 waist and change in waist. At age 15, waist and adiponectin were significantly correlated (r = −0.32). At age 19, waist and adiponectin were significantly correlated (r = −0.36), as were waist and insulin sensitivity (r = −0.16). Both baseline waist and change in waist were significantly inversely associated with age 19 adiponectin but with age 19 insulin sensitivity only in men. In conclusion, in adolescents, the association between waist and adiponectin appears to develop several years before the association between waist and insulin sensitivity and there is a longitudinal association between waist and adiponectin. These results support the hypothesis that adiponectin may contribute to the association of waist and insulin sensitivity.
Regulation of Pituitary Gene Expression by Adrenalectomy
Authors: Nishida Yuichiro , Yoshioka Mayumi , Ray Chester A. , Bolduc Carl , Tanaka Hiroaki , St‐Amand Jonny
Published: November 2008

Excessive secretion of adrenal hormones, such as glucocorticoid and mineralocorticoid, leads to metabolic syndrome, including insulin resistance, obesity, and hypertension. These metabolic abnormalities are ameliorated by adrenalectomy (ADX). To identify pituitary mediators for ADX‐induced physiological alterations, such as weight loss and hypotension, we investigated the effect of ADX on the pituitary transcriptome using serial analysis of gene expression (SAGE). SAGE method is based on isolation of short sequence tags, which usually correspond to unique mRNA species. The SAGE libraries were constructed from pituitary gland of intact (n = 51) and ADX (n = 12) mice. Thirty‐one transcripts were differentially expressed between intact and ADX. Three transcripts encoding for proopiomelanocortin and three other transcripts involved in regulation of hormone secretion (neuromedin B, proprotein convertase subtilisin/kexin type 2, and IA‐2) were induced by ADX. In addition, ADX increased the expression levels of genes encoding for cation extracellular matrix (matrix γ‐carboxyglutamate protein) and transport (solute carrier family 22 member 17). Conversely, ADX downregulated two transcripts involved in mitochondrial oxidative phosphorylation (nicotinamide adenine dinucleotide (NADH) dehydrogenase 3 and cytochrome c oxidase 3). Moreover, ADX significantly modulated the expression levels of one gene with uncharacterized function and 20 novel transcripts. This study reveals alterations of pituitary gene expressions that may be associated with ADX‐induced physiological changes including weight loss.
Gender‐ethnic Disparity in BMI and Waist Circumference Distribution Shifts in US Adults
Authors: Beydoun May A. , Wang Youfa
Published: November 2008

While obesity has been increasing in the United States, little is known about the variation in recent BMI and waist circumference (WC) distribution shifts across socio‐demographic groups. We assessed shifts in BMI and WC distributions and compared between‐group differences over the past decade, and projected future BMI and WC distributions and prevalence of obesity and central obesity using National Health and Nutrition Examination Survey (NHANES) 1988–1994 and 1999–2004 data. BMI/WC distributional shifts overall and in percentiles were compared across groups. Average yearly shift was calculated and used for projecting future distributions and prevalence. Both BMI and WC increased more in their uppermost percentile distribution, though BMI shift declined toward the uppermost percentiles among women. Heavier Americans gained more adiposity over the past decade. Ethnic (non‐Hispanic (NH) white vs. black) disparities in mean BMI and WC became wider. Over the survey period, mean BMI increased by 1.3 units vs. 1.8 units among men and women, whereas WC, by 4.2 cm vs. 4.8 cm. Young adults had the largest increase. Shift in women's WC was stable between the 25th and 75th percentiles, but gained pace at higher WC, while women's BMI and men's BMI and WC shifts increased linearly. NH black women had the largest shifts and would have central obesity and obesity prevalence of 90.8 and 70.7% by 2020. Shifts in BMI and WC distribution varied across age‐, gender‐, and ethnic groups. Future rise in the obesity and central obesity prevalence rates are expected, but would vary by demographic groups.
An Endoluminal Sleeve Induces Substantial Weight Loss and Normalizes Glucose Homeostasis in Rats with Diet‐Induced Obesity
Authors: Aguirre Vincent , Stylopoulos Nicholas , Grinbaum Ronit , Kaplan Lee M.
Published: November 2008

To investigate the contributions of two surgical gut manipulations—exclusion of the proximal intestine from alimentary flow and exposure of the jejunum to partially digested nutrients—to body weight regulation and metabolism, we have developed a rat model of an investigational device, the endoluminal sleeve (ELS). The ELS is a 10 cm, nutrient‐impermeable, flexible tube designed for endoluminal implantation. ELS devices were surgically implanted in the duodenal bulb of rats with diet‐induced obesity. Body weight, food intake, stool caloric content, and glucose homeostasis were subsequently evaluated. ELS‐implanted rats demonstrated a 20% reduction of body weight compared to sham‐operated (SO) controls. ELS‐treated animals consumed an average of 27% fewer kcal/day than SO, and there was no evidence of malabsorption. ELS treatment improved fasting glycemia and glucose tolerance after oral and intraperitoneal (IP) administration. ELS treatment enhanced insulin sensitivity, as demonstrated by decreased fasting and glucose‐stimulated insulin levels and confirmed by calculation of homeostasis model assessment of insulin resistance (IR). These data suggest that selective bypass of the proximal intestine by ELS, with enhanced delivery of partially digested nutrients to the jejunum, mimics many of the effects of Roux‐en‐Y gastric bypass (RYGB) on body weight and glucose metabolism. Thus, ELS implantation may be an effective treatment for obesity and diabetes. Since the ELS device is amenable to endoscopic placement, it may offer a valuable alternative to more invasive surgical approaches in selected patients with obesity and its metabolic complications.
Lys‐110 is essential for targeting PCNA to replication and repair foci, and the K110A mutant activates apoptosis
Authors: Kim Byung Ju , Lee Hoyun
Published: November 2008

Background information. PCNA (proliferating cell nuclear antigen) is required for a wide range of cellular functions, including DNA replication and damage repair. To be functional, PCNA must associate with the replication and repair foci. In addition, PCNA also mediates targeting of certain replication and repair proteins to these foci. However, the mechanism is not yet known by which PCNA is imported into the nucleus, and then localized to the replication and repair foci.

Results. We have found that an NLS (nuclear localization sequence) is present within the amino acid 101–120 segment of PCNA. An NLS‐deleted PCNA was localized in the cytoplasm and showed 5‐fold lower affinity for importin‐β than wild‐type, suggesting that PCNA may be imported into the nucleus by importin‐β via its NLS. We previously reported that the functional unit of PCNA is a double trimer (as opposed to single homotrimer), and Lys‐110 is essential for the formation of the double trimer complex [Naryzhny, Zhao and Lee (2005) J. Biol. Chem. 280, 13888–13894]. The present study shows that the substitution of Lys‐110 within the NLS to an alanine residue did not affect its nuclear localization. However, the double‐trimer‐defective PCNA(K110A) was not localized at replication or repair foci. In contrast, the double‐trimer‐intact PCNA(K117A) mutant was targeted normally to replication and repair foci. Interestingly, in cells transfected with PCNA(K110A), but not PCNA(K117A), caspase‐3‐mediated chromosome fragmentation was activated.

Conclusions. The present study suggests that the regulation of PCNA is intimately connected with that of DNA replication, repair and cell death signals, and raises the possibility that defects in the formation of the PCNA double‐trimer complex can cause apoptosis.
Low specific contact resistance of heavily phosphorus-doped diamond film
Authors: Kato Hiromitsu , Umezawa Hitoshi , Tokuda Norio , Takeuchi Daisuke , Okushi Hideyo , Yamasaki Satoshi
Published: November 2008

Low resistive contacts were formed on heavily phosphorus-doped diamond (n+) films with phosphorus concentration of over ∼1020cm−3 grown on (111) diamond substrates by microwave plasma enhanced chemical vapor deposition with precise control of growth conditions. The specific contact resistance was determined by characterizing the current-voltage relations by means of transfer length method. It was found that the resistance of Ti∕n+ contact was significantly reduced down to the order of ∼10−3Ωcm2 even at room temperature, which indicates that the barrier width would be narrow for tunneling through the barrier to take place by heavy phosphorus doping.
Mechanical and electrical coupling at metal-insulator-metal nanoscale contacts
Authors: Kim Doo-In , Pradeep Namboodiri , DelRio Frank W. , Cook Robert F.
Published: November 2008

Mechanical and electrical coupling at nanoscale metallic contacts was investigated using a conducting-probe atomic force microscope (AFM). The current-voltage responses were non-Ohmic, symmetric about zero bias, with conductance values smaller than the quantum conductance limit, which indicate electron tunneling through an insulating layer. Using a self-consistent contact mechanics model and a parabolic tunneling model for thin insulating layers, we determined the contact area, barrier height, and barrier thickness as a function of applied contact load. The results suggest the presence of two insulating layers: an oxide layer on the AFM tip and an organic contaminant layer on the metallic surface.
Spontaneous charging and crystallization of water droplets in oil
Authors: de Graaf Joost , Zwanikken Jos , Bier Markus , Baarsma Arjen , Oloumi Yasha , Spelt Mischa , van Roij René
Published: November 2008

We study the spontaneous charging and the crystallization of spherical micron-sized water droplets dispersed in oil by numerically solving, within a Poisson–Boltzmann theory in the geometry of a spherical cell, for the density profiles of the cations and anions in the system. We take into account screening, ionic Born self-energy differences between oil and water, and partitioning of ions over the two media. We find that the surface charge density of the droplet as induced by the ion partitioning is significantly affected by the droplet curvature and by the finite density of the droplets. We also find that the salt concentration and the dielectric constant regime in which crystallization of the water droplets is predicted is enhanced substantially compared to results based on the planar oil-water interface, thereby improving quantitative agreement with recent experiments.
Molecular dynamics simulation of confined fluids in isosurface-isothermal-isobaric ensemble
Authors: Eslami Hossein , Mozaffari Farkhondeh , Moghadasi Jalil , Müller-Plathe Florian
Published: November 2008

A method for the simulation of fluids confined between surfaces is developed. The molecular dynamics, with coupling to an external bath, simulation method of Berendsen et al. [J. Chem. Phys. 81, 3684 (1984)] is extended for this purpose. We keep the temperature and the parallel component of pressure fixed and change the box length in the perpendicular direction with respect to the confining surfaces to archive equilibrium. The simulation is easy to perform, especially in the case of solvation force computation. Employing this method, the simulation results on the confined Lennard-Jones and water are presented and are compared to previous grand canonical ensemble Monte Carlo and molecular dynamics simulation results. While consistent with other methods, our results show that spherical Lennard-Jones particles and water form layered structures parallel to the confining surfaces with enhanced layering with increasing pressure. Also we studied the oscillatory behaviors of solvation force and number density of confined particles as well as the stepwise variation of particle numbers as a function of separation between confining surfaces.
Perturbative calculation of spin-orbit splittings using the equation-of-motion ionization-potential coupled-cluster ansatz
Authors: Klein Kerstin , Gauss Jürgen
Published: November 2008

Spin-orbit splittings for Π2 states are calculated within coupled-cluster (CC) theory via first-order degenerate perturbation theory. Using the equation-of-motion CC variant for ionization potentials (EOMIP-CC), the two components of the considered Π2 state are treated in a balanced way by generating both radical states via annihilation of one electron out of the CC wave function of the corresponding anion. We report on the implementation of the described approach within the CC singles and doubles approximation. To ensure computational efficiency, an atomic mean-field approximation for the spin-orbit integrals is used, resulting in a formulation in terms of one-electron transition-density matrices. Calculations for XH radicals (X=O, S, Se) lead to satisfactory agreement with experiment. For Π2 systems that within an EOMIP-CC treatment can only be reached from a triplet reference state (e.g., CF and O2+) the influence of spin contamination is found to be negligible.
Bond dissociation and correlation effects in molecular electronic devices
Authors: Goker Ali , Goyer Francois , Ernzerhof Matthias
Published: November 2008

We present a simple model for a fundamental process in molecular electronics: The change in conductance upon bond breaking. In our model, a diatomic molecule is attached to spin-polarized contacts. Employing a Hubbard Hamiltonian, electron interaction is explicitly considered in the molecule and neglected in the contacts, enabling us to study the impact of electron interaction on the molecular conductance. In the limit where the electron repulsion is strong compared to the binding energy (as is the case upon dissociation), electron transmission is strongly suppressed compared to the noninteracting case. On the other hand, the spin-polarized contacts introduce a coupling between the molecular singlet and triplet states, as a consequence of which the energy gap between the lowest resonances is reduced.
CoCrPt-oxide based perpendicular recording media with hybrid soft magnetic underlayers
Authors: Piramanayagam S. N. , Srinivasan K. , Sbiaa R. , Dong Yan , Victora R. H.
Published: November 2008

Writability of magnetic recording media with high anisotropy constant (Ku) is one of the major challenges encountered in extremely high density recording. A possible avenue to improve writability in perpendicular magnetic recording is to reduce the spacing between the writing head and the soft magnetic underlayer (SUL) or head-to-keeper spacing (HKS). A hybrid layer structure for reducing the HKS between the SUL and the writing head is investigated. The proposed structure makes use of a crystalline SUL with in-plane anisotropy together with an amorphous SUL to form a hybrid SUL (H-SUL). The H-SUL design helps to achieve better surface smoothness, thinner HKS, and good c-axis dispersion for the recording layer while still maintaining small and exchange-decoupled grains. Micromagnetic simulation demonstrates that the H-SUL scheme helps in improving writing field effectiveness and increasing field gradient along down-track and cross-track directions.
Blue-green upconversion emission in ZrO2:Yb3+ nanocrystals
Authors: de la Rosa E. , Solis D. , Díaz-Torres L. A. , Salas P. , Angeles-Chavez C. , Meza O.
Published: November 2008

Strong blue-green cooperative upconversion emission was observed under infrared excitation in 70 nm average crystallite size ZrO2:Yb3+ nanocrystals prepared by sol-gel process. The structural characterization was performed by x-ray diffraction and high resolution transmission electron microscopy suggesting that crystalline phase of nanoparticles is controlled by active ion concentration. The cooperative absorption coefficient η∼2.5×10−22 is four orders of magnitude larger than the ones reported from bulk crystals. The highest emission intensity was obtained from the doped sample at 4 mol % and was the result of the simultaneous relaxation of two excited Yb ions. Decay time of the upconverted signal τCUC≈0.310 ms is half from the near infrared effective decay time confirming the cooperative process among Yb ions. Such strong cooperative effect is explained in terms of interaction enhancement due to the diminishing of Yb–Yb separation promoted partly by the surface recombination of nanocrystals.
Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods
Authors: Riaz M. , Fulati A. , Yang L. L. , Nur O. , Willander M. , Klason P.
Published: November 2008

Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid (VLS) method, a relatively high temperature approach, and the aqueous chemical growth (ACG) method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 μN on the SiC substrates and 114 μN on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15×10−12 and 2.337×10−12 J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 μN and 7.03×10−12 J on the SiC substrates, and 19 μN and 1.805×10−13 J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.
Lorentzian Lie n-algebras
Authors: Figueroa-O’Farrill José
Published: November 2008

We classify Lie n-algebras possessing an invariant Lorentzian inner product.
Mechanical behavior of stressed films on anisotropic substrates
Authors: Murray Conal E. , Saenger K. L.
Published: November 2008

The effects of stressed thin films on substrates that possess anisotropic elasticity have been measured and modeled. Substrate curvature induced by a uniform, stressed film will be axisymmetric for substrates possessing greater than twofold in-plane symmetry, and anisotropic for twofold symmetric substrates. For a (011) Si substrate, the difference between the curvature along the ⟨110⟩ and ⟨100⟩ principal axes varies by approximately 47%. A simple, analytical formulation of the force and moment balance equations for elastically anisotropic films and substrates has been employed to calculate the dependence of curvature and strain on substrate orientation for several cases.
Piezoelectric forceps actuator: Theory and experiments
Authors: Susanto Ken
Published: November 2008

This paper studies the characteristic performances of a novel piezoelectric forceps actuator (PFA) that has several potential applications for minimally invasive surgery and assembly lines of semiconductor industries. The first part of the paper treats the PFA model, which is comprised of a piezoelectric slightly curved composite beam derived using Hamilton’s principle. In the latter part of the paper, the distributed transfer function method is applied to evaluate the transfer function formulation of the cantilevered PFA associated with its boundary conditions. This method will be used to resolve the radial displacements and natural frequencies of the PFA in an exact and closed-form solution, which is validated by in situ fiber optic curvature sensing measurements. The theoretical model predicted the natural frequencies of the first- and second-mode responses of the experimental quite accurately. For a cyclical low-field input, the field-induced displacement appears approximately linear, which seems comparable to the theoretical prediction and reflects primarily the converse piezoelectric effect. A cyclical high-field butterfly-shaped displacement behavior is also analogous to the behavior predicted by the model in that it demonstrates the range of validity of the linear converse piezoelectric effect without consideration of the ferroelectric domain switch effect.
Single dominant distribution of Ge nanogranule embedded in Al oxide thin film
Authors: Abe Seishi , Ohnuma Masato , Ping D. H. , Ohnuma Shigehiro
Published: November 2008

This paper investigates size distribution of Ge nanogranules embedded in Al oxide thin film prepared by rf reactive sputtering method. It is found from the results of x-ray diffraction and small angle x-ray diffraction spectroscopy that their mean sizes distribute bimodally or single dominantly with respect to sputtering process parameter of additional oxygen ratio in Ar and Ge concentrations. Compositional plane of these distribution types reveals that single dominant distribution appears along the line of stoichiometric composition of Al2O3, and deviation from stoichiometry results in bimodal distribution. Thus, size uniformity of Ge nanogranules seems to be enhanced when the Al oxide matrix forms stoichiometric composition.
Reflection chromaticity of multilayered structures incorporating cholesteric liquid crystals
Authors: Nascimento E. M. , de Oliveira I. N. , Lyra M. L.
Published: November 2008

We investigate the chromaticity of the light reflected by multilayered structures containing cholesteric liquid crystals (ChLCs). We considered a single-pitched ChLC multilayered system with quasiperiodic Fibonaccian phase defects as well as an alternate sequence of single-pitched ChLC and isotropic dielectric layers. Using the Berreman 4×4 matrix formalism, we numerically obtain the reflection spectrum and the chromaticity diagram of these structures. The associated chromaticity is shown to depend on the incidence angle. However, for the ChLC Fibonaccian phase defect system, the color shift can be controlled by the defect angle α. For the F4 generation and α=π/3, the chromaticity of the reflected light remains close to the white color region for a wide range of incidence angles, followed by a blueshift at intermediate incidence angles. This is the setup that produces the nearest omnidirectional red-green-blue condition for the reflection spectrum. On the other hand, the structure with alternate ChLC and isotropic layers exhibits a complex sequence of color shifts when the incidence angle is increased.
Alternative to classic annealing treatments for fractally patterned TiO2 thin films
Authors: Van Overschelde O. , Guisbiers G. , Hamadi F. , Hemberg A. , Snyders R. , Wautelet M.
Published: November 2008

Titanium dioxide thin films have been deposited by reactive magnetron sputtering on glass and subsequently irradiated by UV radiation using a KrF excimer laser. The influence of the laser fluence (F) on the constitution and microstructure of the deposited films is studied for 0.05<F<0.40 J/cm2. The diffraction data reveal that as deposited films are amorphous, while irradiated films present an anatase structure. Additional Raman spectroscopy study shows better crystal quality for the films irradiated with F<0.13 J/cm2. The film morphology appears to be strongly modified after laser treatment. Atomic force microscopy and scanning electron microscopy measurements reveal fractally textured films presenting characteristics of high porosity and high specific surface area. Finally, contact angle analysis suggests hydrophobic or wetting behavior depending on F. In order to explain the laser-induced structuration mechanisms, we have successfully applied a fractal as well as the nucleation theories. We propose that electronics effects could be responsible for the observed crystallization.
Simulation of the bulk and surface modes supported by a diamond lattice of metal wires
Authors: Shapiro M. A. , Samokhvalova K. R. , Sirigiri J. R. , Temkin R. J. , Shvets G.
Published: November 2008

We present a numerical study of the electromagnetic properties of the three-dimensional metallic wire lattices operating at microwave frequencies with applications to advanced accelerating structures and microwave sources. The metallic lattices can be considered as “artificial plasmas” because they demonstrate the properties of plasmas with a negative dielectric constant. Bulk modes in a diamond lattice of metal wires and surface modes on its interface are calculated. It is shown that the lattice can be modeled as an anisotropic medium with spatial dispersion. In contrast to a simple cubic lattice, the diamond lattice allows the existence of three different interfaces—one isotropic and two anisotropic. The surface modes supported by these interfaces are affected by spatial dispersion, in sharp contrast with the surface mode on an isotropic vacuum/plasma interface. For particle accelerator applications, we identify the electromagnetic mode confined by a plasmonic waveguide formed as a defect in a diamond lattice. All deleterious higher order modes excited as wakefields from the accelerating particle are found to be leaky. The diamond lattice is also useful as a research tool for studying particle radiation in media with spatial dispersion.
Characterization of a controlled plasma expansion in vacuum for laser driven ion acceleration
Authors: Flacco A. , Guemnie-Tafo A. , Nuter R. , Veltcheva M. , Batani D. , Lefebvre E. , Malka V.
Published: November 2008

We present experimental and numerical results on the formation of a controlled plasma density gradient in front of a solid target irradiated with a subpicosecond, moderate intensity laser pulse. Interferometry with femtosecond probe is used to map the temporal evolution of the spatial density distribution of the generated plasma. Experimental results are found to be in good agreement with 1D1/2 hydrodynamic simulations. Moreover, these numerical simulations enable us to determine the impact of such a heating beam on the target rear surface and to correlate the plasma gradient that can be produced on the illuminated surface with the position of the shock wave in the bulk.
Structure and photoinduced volume changes of obliquely deposited amorphous selenium
Authors: Lukács R. , Hegedüs J. , Kugler S.
Published: November 2008

Atomic scale computer simulations on structures and photoinduced volume changes of flatly and obliquely deposited amorphous selenium (a-Se) films have been carried out in order to understand how the properties of chalcogenide glasses are influenced by their preparation method. Obliquely deposited a-Se thin films contain more coordination defects and larger voids than the flatly deposited ones. To model the photoinduced volume changes the electron excitation and hole creation were treated independently within the framework of tight-binding formalism. Covalent and interchain bond breakings and formations were found. The obliquely deposited samples containing voids showed a wide spectrum of photoinduced structural changes in the microscopic level and volume changes in the macroscopic level.
Stabilizing of low frequency oscillation in Hall thrusters
Authors: Yu Daren , Wang Chunsheng , Wei Liqiu , Gao Chao , Yu Guang
Published: November 2008

Numerical simulations and experiments have been conducted to investigate the effects of a filter on low frequency oscillation in Hall thrusters. With one-dimensional quasineutral hydrodynamic model, the effects of filter components are studied by way of simulation computations. The simulation results show that with proper filter parameters, low frequency oscillation can be stabilized. Further, an eigenvalue study of the linear stability has been performed and the stability conditions according to filter parameters are given. Finally, the theoretical analysis is validated qualitatively through experiments.
Polarization-induced two-dimensional electron gases in ZnMgO/ZnO heterostructures
Authors: Tampo H. , Shibata H. , Maejima K. , Yamada A. , Matsubara K. , Fons P. , Kashiwaya S. , Niki S. , Chiba Y. , Wakamatsu T. , Kanie H.
Published: November 2008

Both the formation mechanism and the origin of the two-dimensional electron gas (2DEG) in ZnMgO/ZnO heterostructures have been investigated. The 2DEG in the heterostructures was confirmed to originate from polarization-induced charge and was found to be dominant for transport at low temperatures as well as room temperature (RT) by transport measurements. The origin of 2DEG was concluded to be the surface of the ZnMgO layer based on both capacitance-voltage measurements and the dependence of the carrier concentration on the ZnMgO layer thickness. The largest sheet carrier concentration was 1.1×1013 cm−2 and the highest mobility for the heterostructure was obtained for a Mg composition of 0.61 at RT.
Comparison of the effects of Ar and H2 plasmas on the performance of homojunctioned amorphous indium gallium zinc oxide thin film transistors
Authors: Du Ahn Byung , Shin Hyun Soo , Kim Hyun Jae , Park Jin-Seong , Jeong Jae Kyeong
Published: November 2008

We proposed a homojunctioned amorphous InGaZnO (a-IGZO) thin film transistor (TFT) and compared its performance to that of a conventional structured TFT. The source/drain regions were formed in the a-IGZO channel layer using Ar and H2 plasma treatments, respectively. Hydrogen itself was found to act as a carrier of donors with H2 plasma treatment, which had effects to a depth of 50 nm. Our TFT had a field-effect mobility of 7.27 cm2/V s, an on/off ratio of 1.2×107, a threshold voltage of 0.96 V, and a subthreshold swing of 0.49 V/decade.
Compact 2×2 tapered multimode interference couplers based on SU-8 polymer rectangular waveguides
Authors: Yang Liu , Yang Bo , Sheng Zhen , Wang Jianwei , Dai Daoxin , He Sailing
Published: November 2008

A 2×2 tapered multimode interference (MMI) coupler is designed and fabricated by using air-cladded SU-8 rectangular waveguide, which is effective in reducing the device size and improving the self-imaging quality. The parabolically tapered MMI section is used to reduce further the size of the MMI coupler. A compact 2×2 coupler with a total MMI size of about 5.3×34.2μm2 is demonstrated and characterized. The measurement results show that the fabricated 2×2 MMI coupler has relatively small excess loss and nonuniformity for both polarizations in a broad wavelength range (from 1480to1630nm).
A polymer/fullerene based photodetector with extremely low dark current for x-ray medical imaging applications
Authors: Agostinelli T. , Campoy-Quiles M. , Blakesley J. C. , Speller R. , Bradley D. D. C. , Nelson J.
Published: November 2008

Organic photodetectors for use in medical x-ray digital imaging applications are fabricated from poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester using a solution-based, temperature assisted deposition protocol. In comparison to bulk heterojunction structures, the proposed protocol leads to much lower dark currents while still offering useful external quantum efficiency values. Devices made by this protocol lead to dark currents of around 50pA∕cm2 at −0.8V, well within the requirements for x-ray digital imaging. When coupled to a scintillating phosphor screen the device yields a linear response of photocurrent to x-ray exposure (from 0to7mGy∕s) for a range of operating biases.
Separation enhancement in pinched flow fractionation
Authors: Vig Asger Laurberg , Kristensen Anders
Published: November 2008

A method for enhancing the separation in the microfluidic size separation technique called pinched flow fractionation (PFF) is demonstrated experimentally and analyzed by numerical calculations. The enhancement is caused by a geometrical modification of the original PFF design. Seven different polystyrene bead sizes ranging from 0.25to2.5μm in radius were separated in a PFF and in an enhanced PFF device. The separation in the two types of devices were compared and an amplification in the separation of up to 70% was achieved. Numerical calculations, which include an edge effect, are used to analyze the device.