bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Obesity Stigmatization in Children and Adolescents: Modernizing a Standard Measure
Authors: Latner Janet D. , Simmonds Murray , Rosewall Juliet K. , Stunkard Albert J.
Published: July 2008

Objective: Stigmatization of overweight children is highly prevalent. However, the measurement of stigma has varied widely across studies. An up‐to‐date version of a commonly used measure of weight‐related stigma is needed.

Research Methods and Procedures: Poser 5 (DAZ software) was used to develop 12 modernized figures, using three‐dimensional models rendered as high‐resolution images. They depicted one overweight, one non‐overweight, and four disabled children of each sex. Children recruited from public and private schools (N = 261; mean age, 11.3 years; median BMI z‐score = 0.33; 77.0% white, 11.5% Asian, and 7.7% Maori) ranked these figures in order of liking. Participants also ranked traditionally used line drawings depicting comparable images. Participants rated each new figure on measures of liking and stereotypical attributes on 100‐mm visual analog scales (VASs).

Results: Rankings of liking of the new figures were highly correlated with rankings of corresponding old figures, especially for overweight figures [boys: ρ (77) = 0.72, p < 0.001; girls: ρ (153) = 0.68, p < 0.001]. Rankings of overweight and other figures were also highly correlated with VAS assessment of liking and with a composite, internally consistent VAS measure of liking and stereotypical attributes. Only negative stereotypes about the intelligence of overweight boys and girls contributed significantly to the variance in liking.

Discussion: An updated and modernized tool for assessing children's weight stigma was developed and its construct validity supported. The present findings suggest that stereotypes about low intelligence may contribute to weight stigma among children. More research is needed on the causes and components of weight stigma so that it can be effectively reduced.
Failure to Meet Weight Loss Expectations Does Not Impact Maintenance in Successful Weight Losers
Authors: Gorin Amy A. , Pinto Angela Marinilli , Tate Deborah F. , Raynor Hollie A. , Fava Joseph L. , Wing Rena R.
Published: July 2008

Objective: The objective was to examine whether having a weight loss experience that lives up to one's expectations is related to maintenance in a group of successful weight losers participating in the STOP Regain trial.

Research Methods and Procedures: Participants (N = 314, 81% women, mean age, 51.3 ± 10.1 years; BMI = 28.6 ± 4.8 kg/m2) who lost ≥10% of their body weight within the past 2 years were randomly assigned to a maintenance program delivered either face‐to‐face or via the Internet or to a control group and assessed at 0, 6, 12, and 18 months.

Results: At study entry, participants had lost 19% of their body weight, yet 86% of participants were currently trying to lose more weight. Further losses of 13% of body weight were needed to reach self‐selected ideal weights, with heavier participants wanting to lose more (p < 0.001). The weight loss‐related benefits participants achieved did not live up to their expectations (p ≤ 0.01). However, neither satisfaction with current weight, nor amount of further weight loss desired, nor discrepancies between actual and expected benefits predicted regain after adjusting for treatment group, gender, baseline weight, and percent weight loss before entry.

Discussion: Even among very successful weight losers, expectations were not met and substantial further weight losses were desired; however, these factors were not related to subsequent weight maintenance outcomes.
Predictive Value of Weight‐for‐Age to Identify Overweight Children
Authors: Stettler Nicolas , Zomorrodi Arezoo , Posner Jill C.
Published: July 2008

Objective: The objective was to assess the predictive value of weight‐for‐age to identify overweight children and adolescents in the unusual research or public health situations where height is not available to calculate BMI.

Research Methods and Procedures: Data from the National Health and Nutrition Examination Survey 1999 to 2004 were used to calculate the sensitivity, specificity, and positive and negative predictive values of selected weight‐for‐age cut‐off points to identify overweight children and adolescents (as defined by BMI ≥95th percentile). Positive and negative predictive values are dependent on prevalence and are reported here for this study population only.

Results: The 50th and 75th weight‐for‐age percentiles had good sensitivity (100% and 99.6%, respectively), but poor positive predictive value (23.7% and 37.0%, respectively), while the 95th and 97th percentiles had reasonable positive predictive value (80.3% and 91.5%, respectively), but limited sensitivity (82.0% and 66.7%, respectively) to identify overweight subjects. The properties of weight‐for‐age percentiles to identify overweight subjects differed between sex, age, and race/ethnicity but remain within a relatively narrow range.

Discussion: No single weight‐for‐age cut‐off point was found to identify overweight children and adolescents with acceptable values for all properties and, therefore, cannot be used in the clinical setting. Furthermore, the positive predictive values reported here may be lower in populations with a lower prevalence of obesity. However, in unusual research or public health situations where height is not available, such as existing databases, weight‐for‐age percentiles may be useful to target limited resources to groups more likely to include overweight children and adolescents than the general population.
Trends in Obesity and Associations with Education and Urban or Rural Residence in Thailand
Authors: Aekplakorn Wichai , Hogan Margaret C. , Chongsuvivatwong Virasakdi , Tatsanavivat Pyatat , Chariyalertsak Suwat , Boonthum Angsana , Tiptaradol Siriwat , Lim Stephen S.
Published: July 2008

Objective: To measure trends in the prevalence of overweight and obesity and the relationship with urban or rural residence and education in Thailand.

Research Methods and Procedures: Data were from two nationally representative surveys of 38,323 individuals ≥18 years old (19,156 were 18 to 59 years old) in 2004 and 3375 individuals 18 to 59 years old in 1997. Overweight and obesity were defined using the World Health Organization's Asian criteria.

Results: Among those ≥18 years old in 2004, 17.8% of men (95% confidence interval, 16.6% to 19.0%) were overweight, 18.4% (17.3% to 19.5%) had Class I obesity, 4.8% (4.1% to 5.5%) had Class II obesity, and 15.9% (14.6% to 17.1%) had abdominal obesity. In women, 18.2% (17.1% to 19.2%) were overweight, 26.1% (24.9% to 27.3%) had Class I obesity, 9.3% (8.6% to 10.0%) had Class II obesity, and 37.3% (35.3% to 39.2%) had abdominal obesity. In those 18 to 59 years old, the prevalence of Class I obesity in men and all four categories in women significantly increased between 1997 and 2004. There was an inverse relationship in women but a positive relationship in men between education and the odds of being overweight or obese. In 2004, there were significantly lower odds of being overweight or obese in rural compared with urban men but similar odds between urban and rural women.

Discussion: The prevalence of overweight and obesity in Thailand is high and increasing. Although the transition of overweight and obesity to those of lower socioeconomic status is not complete, it is well on the way.
The Medical Cost of Cardiometabolic Risk Factor Clusters in the United States
Authors: Sullivan Patrick W. , Ghushchyan Vahram , Wyatt Holly R. , Hill James O.
Published: July 2008

Objective: Diabetes, hypertension, hyperlipidemia, and overweight/obesity often cluster together. The prevalence of these cardiometabolic risk factor clusters (CMRFCs) is increasing significantly for all sociodemographic groups, but little is known about their economic impact.

Research Methods and Procedures: The nationally representative Medical Expenditure Panel Survey was used (2000 and 2002). The current study estimated the national cost of CMRFCs independent of the cost of cardiovascular disease in the U.S., as well as the cost for all major payers and the marginal cost per individual using a Heckman selection model with Smearing retransformation. CMRFCs included BMI ≥ 25 and two of the following three: diabetes, hyperlipidemia, and/or hypertension. All amounts are expressed in 2005 $U.S.

Results: National medical expenditures attributable to CMRFCs in the U.S. totaled $80 billion, of which $27 billion was spent on prescription drugs. Private insurance paid the largest amount of the national bill ($28 billion), followed by Medicare ($11 billion), Medicaid ($6 billion), and the Veterans Administration ($4 billion), whereas individuals paid $28 billion out‐of‐pocket. For each individual with CMRFCs, $5477 in medical expenditures was attributable to CMRFCs, of which $1832 was for prescription drugs. On average, individuals with CMRFCs spent $1668 out‐of‐pocket, of which $830 was for prescription drugs.

Discussion: The results of this study show that CMRFCs result in significant medical cost in the U.S. independent of the cost of cardiovascular disease. Individuals, private insurers, Medicare, Medicaid, the Veterans Administration, and other payers all share this burden.
Energy transfer in hybrid quantum dot light-emitting diodes
Authors: Chin Patrick T. K. , Hikmet Rifat A. M. , Janssen René A. J.
Published: July 2008

Energy transfer in a host-guest system consisting of a blue-emitting poly(2,7-spirofluorene) (PSF) donor and red-emitting CdSe∕ZnS core shell quantum dots (QDs) as acceptor is investigated in solid films, using time-resolved optical spectroscopy, and in electroluminescent diodes. In the QD:PSF composite films, the Förster radius for energy transfer is found to be 4–6nm. In electroluminescent devices lacking an electron transport layer, the electroluminescence (EL) spectrum of the QD:PSF polymer composite is similar to the photoluminescence (PL), giving evidence for energy transfer from PSF to the QDs. The addition of an electron transport layer between the emitting layer and the cathode results in a significant change in the EL spectrum and a considerable improved device performance, providing almost pure monochromatic emission at 630nm with a luminance efficiency of 0.32cd∕A. The change in spectrum signifies that the electron transport layer changes the dominant pathway for QD emission from energy transfer from the polymer host to direct electron-hole recombination on the QDs.
Time-resolved x-ray diffraction experiments to examine the elastic-plastic transition in shocked magnesium-doped LiF
Authors: Jensen B. J. , Gupta Y. M.
Published: July 2008

Time-resolved x-ray diffraction measurements were used to examine the lattice deformation during elastic-plastic deformation in Mg-doped (approximately 100 ppm) LiF single crystals shocked along [100]. The magnesium impurities significantly increase the elastic limit of the LiF crystals, as compared to the low values observed for ultrapure LiF crystals, leading to a large amplitude elastic wave and significant stress relaxation behind the elastic wave. The objective of the current work was to examine lattice deformation throughout this wave profile using time-resolved, x-ray diffraction methods (2 ns resolution) for plate impact experiments to gain insight into time-dependent, elastic-plastic deformation at the microscopic level. The diffraction data were analyzed using an x-ray model coupled to an existing wave propagation code that incorporated dislocation mechanisms for elastic-plastic deformation including stress relaxation. All experimental results revealed a uniaxial lattice compression at the elastic wave front followed by a rapid transition toward isotropic unit cell compression during stress relaxation. Furthermore, comparison between the experimental data and the calculated streak records indicated that the lattice transition proceeds at a faster rate than predicted by the model. Further implications of these results are discussed.
Mechanism of critical catalyst size effect on MgO nanowire growth by pulsed laser deposition
Authors: Yanagida Takeshi , Nagashima Kazuki , Tanaka Hidekazu , Kawai Tomoji
Published: July 2008

The size controllability of oxide nanowires formed via vapor-liquid-solid (VLS) mechanism is desired for the oxide nanowire-based device applications. However, the complex nature of oxide nanowire VLS growth has held back such size controllability. Here we demonstrate the critical size effect of a Au catalyst on MgO nanowire VLS growth by pulsed laser deposition. The presence of a critical catalyst size was found. Above such critical size, an oxide nanowire VLS growth is no longer feasible. Interestingly, such critical size increased with increasing growth temperature. The mechanism of the critical phenomenon is interpreted in terms of the catalyst size dependence on the amount of adatoms diffused from surroundings into the catalyst.
Basic nanosystems of early 4d and 5d transition metals: Electronic properties and the effect of spin-orbit interaction
Authors: Bala Anu , Nautiyal Tashi , Auluck Sushil
Published: July 2008

There are various possibilities for the structure as well as for the growth of nanosystems, particularly of nanowires. The ultimate one-dimensional material—linear chains—are difficult to exploit for applications due to their transient nature. Nonetheless these are a good prototype for studying one-dimensional materials and project the kind of behavior one may expect from ultrathin nanowires. Likewise monolayers are the ultimate two-dimensional materials and their study is helpful in understanding the behavior of two-dimensional materials. We present a theoretical study on basic nanosystems—linear chains and monolayers—of the 4d (Y, Zr, Nb, Mo, and Tc) and 5d (Hf, Ta, W, and Re) transition metals of groups 3–7 by means of an all-electron density functional approach. We have explored all kinds of magnetic configurations: nonmagnetic, ferromagnetic, and antiferromagnetic, by (i) inclusion and (ii) omission of spin-orbit interaction. We find that though this interaction has a marginal effect on nanosystems of 4d transition metals, its impact becomes stronger with lowering of dimensionality. Further it has a significant effect on properties of nanosystems of 5d transition metals as well as those of bulk. It is interesting to note that the monolayers of 5d transition metals seem reluctant to order magnetically despite the general tendency of nanosystems of 4d transition metals and linear chains of 5d transition metals to woo magnetic ordering. The nanosystems with preference for antiferromagnetic ordering are found to be stable at larger nearest-neighbor distances compared to the ferromagnetic and nonmagnetic phases. Specially, antiferromagnetic monolayers of Nb and Mo are predicted to exhibit larger separations with respect to bulk, a feature observed only for some low-dimensional systems. All the monolayers, except Y, are predicted to have a nonmagnetic state almost degenerate with ferromagnetic or antiferromagnetic state. Therefore suitable substrate selection is likely to play an important role in controlling the magnetic ordering in monolayers. Interestingly, Mo linear chains are predicted to have a small energy gap at the Fermi energy, a feature not predicted for any other low-dimensional system of studied transition metals. The stable value of magnetic moment in the vicinity of the equilibrium nearest-neighbor separation for monolayers of Y and for linear chains of Zr, Mo, Tc, and Ta suggests potential of these low-dimensional systems as thermally stable nanoscale devices. Comparison with available experimental data on similar systems confirms consistency of our results. We feel that the results predicted here can be helpful guides to experimentalists as well as theorists.
Enhanced piezoelectric properties of grain-oriented Bi4Ti3O12–BaBi4Ti4O15 ceramics obtained by magnetic-field-assisted electrophoretic deposition method
Authors: Suzuki Muneyasu , Miyayama Masaru , Noguchi Yuji , Uchikoshi Tetsuo
Published: July 2008

We report novel grain-orientation technology, magnetic-field-assisted electrophoretic deposition (B-assisted EPD), for synthesizing bismuth layer–structured ferroelectric ceramics. Grain-oriented Bi4Ti3O12–BaBi4Ti4O15 ceramics obtained by the B-assisted EPD is shown to exhibit enhanced polarization and piezoelectric properties with a remanent polarization (Pr) of 30 μC/cm2 and an electromechanical coupling coefficient (k33) of 24%, which are much superior to those of randomly oriented ceramics (Pr of 9 μC/cm2 and k33 of 16%). High-temperature piezoelectric measurements show that the grain-oriented ceramics maintained a k33 value of 24% up to an extremely high temperature of 370 °C. These results will open up innovative piezoelectric applications at high temperatures above 300 °C, where commercial Pb(Zr,Ti)O3 ceramics are not available due to its low TC.
Anisotropic exchange splitting of excitons in (001)GaAs/Al0.3Ga0.7As superlattice studied by reflectance difference spectroscopy
Authors: Zhou Z. Y. , Tang C. G. , Chen Y. H. , Wang Z. G.
Published: July 2008

Anisotropic exchange splitting (AES) is induced by the joint effects of the electron-hole exchange interaction and the symmetry reduction in quantum wells and quantum dots. A model has been developed to quantitatively obtain the electron-hole exchange energy and the hole-mixing energy of quantum wells and superlattices. In this model, the AES and the degree of polarization can both be obtained from the reflectance difference spectroscopy. Thus the electron-hole exchange energy and the hole-mixing energy can be completely separated and quantitatively deduced. By using this model, a (001)5 nm GaAs/7 nm Al0.3Ga0.7As superlattice sample subjected to [110] uniaxial strains has been investigated in detail. The n=1 heavy-hole (1H1E) exciton can be analyzed by this model. We find that the AES of quantum wells can be linearly tuned by the [110] uniaxial strains. The small uniaxial strains can only influence the hole-mixing interaction of quantum wells, but have almost no contribution to the electron-hole exchange interaction.
Electric field modulation of exciton recombination in InAs/GaAs quantum dots emitting at 1.3μm
Authors: Miyazawa Toshiyuki , Nakaoka Toshihiro , Usuki Tatsuya , Tatebayashi Jun , Arakawa Yasuhiko , Hirose Shinichi , Takemoto Kazuya , Takatsu Motomu , Yokoyama Naoki
Published: July 2008

Changing the electric field applied to InAs quantum dots embedded in a p-i-n diode was found to modulate the radiative recombination rate of excitons in the dots. The quantum dots were capped with a strain-reducing layer to realize 1.3 μm photoemission and a large dipole moment to the exciton states. The exciton states in a quantum dot were investigated by measuring the quantum-confined Stark shift for various applied electric fields and were compared with the theoretical electron and hole wave functions calculated using an eight-band k⋅p model. When the absolute value of the applied electric field was reduced from −82.4 kV/cm to 0, the radiative recombination rate increased from 0.88 to 1.11 ns−1. Comparison of the experimental rate with the calculated one revealed that the increase in the radiative recombination rate was due to a decrease in the overlap integral between the electrons and holes. These optical characteristics of InAs quantum dots are especially important for developing optical devices that use single photons and single charges because the contribution of nonradiative processes is smaller than that of the radiative process.
The filtering formulation of the mixed subgrid model
Authors: Germano M.
Published: July 2008

In this paper a new mixed model consistent with the filtering formulation has been derived as the subgrid model associated with the product GF of a similarity filter G with a functional filter F. The case where F is the Smagorinsky eddy viscosity filter is discussed in detail, and, in particular, it is shown that some ambiguities concerning the additive coefficient of the usual mixed subgrid model are automatically removed.
High-Tc superconducting quantum interference devices: Status and perspectives
Authors: Yang Hong-Chang , Chen Ji-Chen , Chen Kuen-Lin , Wu Chiu-Hsien , Horng Herng-Er , Yang S. Y.
Published: July 2008

In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ∼30–50fT∕Hz1∕2 or better at 100Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed.
Magnetization decay in neutron irradiated MgB2 bulk samples
Authors: Tarantini C. , Manfrinetti P. , Palenzona A. , Putti M. , Ferdeghini C. , Gambardella U. , Lehmann E. , Cimberle M. R.
Published: July 2008

In this paper the magnetization decay behavior of neutron irradiated MgB2 bulk samples and an estimate of the strength of the introduced pinning centers are presented. The magnetization decay measurements appear much more complex than usual, in fact, they may be logarithmic or not, depending on the values of temperature and magnetic field and, as the region of low temperatures and fields is approached, they are affected by a “noise” that is out of experimental uncertainties. This “noisy” behavior is attributed to the small flux jumps, related to the dendritic flux penetration, widely observed in MgB2 samples. We identify a phase diagram that divides the H-T plane in two regions: one, at relatively low temperatures and fields, where the decay observed is noisy, the other, outside it, where the decay is “clean.” This noisy region extends up to T/Tc≅0.5 and up to a field of some teslas, i.e., in a range of instability much more extended than that found in previous measurements. At high magnetic field the pinning energy turns out to be higher in irradiated samples than in the pristine one, in agreement with the observed increase in the critical current density. However, at high enough fields and temperatures, pinning is no longer effective and, by varying the measurement frequency, differences in the magnetic valuation of critical current density are observed. This fact may be of importance because it occurs at magnetic field and temperature conditions where technological applications of MgB2 are expected.
Observation of wakefield generation in left-handed band of metamaterial-loaded waveguide
Authors: Antipov S. , Spentzouris L. , Gai W. , Conde M. , Franchini F. , Konecny R. , Liu W. , Power J. G. , Yusof Z. , Jing C.
Published: July 2008

We report on a design of a TM-mode based metamaterial-loaded waveguide. Network analyzer measurements demonstrated a left-handed propagation region for the TM11 mode at around 10 GHz. A beamline experiment was performed with the metamaterial-loaded waveguide. In this experiment, a 6 MeV electron beam passes through the waveguide and generates a wakefield via the Cherenkov radiation mechanism. We detected a signal in the left-handed frequency band at 10 GHz. This is an indirect demonstration of reverse Cherenkov radiation as predicted in the work of Veselago [Sov. Phys. Usp. 10, 509 (1968)] and discussed in the works of Lu et al. [Opt. Express 11, 723 (2003)], Averkov and Yakovenko [Phys. Rev. B 72, 205110 (2005)], and Tyukhtin et al. [IEEE, Proceedings of the PAC, 2007 (unpublished), pp. 4156–4158]. Cherenkov radiation in artificially constructed materials [metamaterials (MTMs)] can provide unusual engineered features that can be advantageous for particle detector design.
Optimizing the Ar–Xe infrared laser on the Naval Research Laboratory’s Electra generator
Authors: Apruzese J. P. , Giuliani J. L. , Wolford M. F. , Sethian J. D. , Petrov G. M. , Hinshelwood D. D. , Myers M. C. , Dasgupta A. , Hegeler F. , Petrova Ts.
Published: July 2008

The Ar–Xe infrared laser has been investigated in several series of experiments carried out on the Naval Research Laboratory’s Electra generator. Our primary goals were to optimize the efficiency of the laser (within Electra’s capabilities) and to gain understanding of the main physical processes underlying the laser’s output as a function of controllable parameters such as Xe fraction, power deposition, and gas pressure. We find that the intrinsic efficiency maximizes at ∼3% at a total pressure of 2.5 atm, Xe fraction of 1%, and electron beam power deposition density of 50–100 kW cm−3. We deployed an interferometer to measure the electron density during lasing; the ionization fractions of 10−5–10−4 that it detected well exceed previous theoretical estimates. Some trends in the data as a function of beam power and xenon fraction are not fully understood. The as-yet incomplete picture of Ar–Xe laser physics is likely traceable in large part to significant uncertainties still present in many important rates influencing the atomic and molecular kinetics.
Magnetization reversal in nanowires with a spiral shape
Authors: Westphalen A. , Remhof A. , Zabel H.
Published: July 2008

Magnetic nanowires have been shaped in the form of spirals and arranged in different patterns. A two-dimensional periodic array of Fe spiral structures was fabricated by electron-beam lithography. The spirals had a radius of 2.8 μm, a linewidth of 100 nm, and a thickness of 20 nm. The magnetization reversal was studied by longitudinal vector magneto-optic Kerr effect (MOKE) in specular geometry as well as in Bragg MOKE geometry, using the diffraction spots from the grating for hysteresis measurements. The measurements are compared with the results of micromagnetic simulation, which allows a detailed interpretation of the experimental data. The magnetization reversal is characterized by an onion state in remanence and a coercivity which is different for the inner and outer parts of the spiral structures. In general the inner parts of the spiral are more stable and switch later than the outer ones. The switching of the outer parts depends on the boundary condition.
Tensile strength of randomly perforated aluminum plates: Weibull distribution parameters
Authors: Klein Claude A.
Published: July 2008

Recently, Yanay and collaborators [J. Appl. Phys. 101, 104911 (2007)] addressed issues regarding the fracture strength of randomly perforated aluminum plates subjected to tensile loads. Based on comprehensive measurements and computational simulations, they formulate statistical predictions for the tensile strength dependence on the hole density but conclude that their data are inadequate for the purpose of deriving the strength distribution function. The primary purpose of this contribution is to demonstrate that, on dividing the totality of applicable data into seven “bins” of comparable population, the strength distribution of perforated plates of similar hole density obeys a conventional two-parameter Weibull model. Furthermore, on examining the fracture stresses as recorded in the vicinity of the percolation threshold, we find that the strength obeys the expression σo(P−Pth)β with Pth≃0.64 and β≃0.4. In this light, and taking advantage of percolation theory, we formulate equations that specify how the two Weibull parameters (characteristic strength and shape factor) depend on the hole density. This enables us to express the failure probability as a function of the tensile stress, over the entire range of hole densities, i.e., P=0.02 up to the percolation threshold.
Structure and relaxor behavior of BaTiO3–CaTiO3–SrTiO3 ternary system ceramics
Authors: Zhang Lingling , Wang Xusheng , Yang Wei , Liu Hong , Yao Xi
Published: July 2008

This study prepared (1−x)BaTiO3–xCaTiO3 (x=0–1) (denoted as BCT), (0.95−x)BaTiO3–xCaTiO3–0.05SrTiO3 (x=0.00–0.95) (denoted as BS5CT), and (0.90–x)BaTiO3–xCaTiO3–0.10SrTiO3 (x=0.00–0.90) (denoted as BS10CT) ceramics. Their preparation and structural and dielectric properties were characterized. The results show that the x-ray diffraction (XRD) peaks of the BCT, BS5CT, and BS10CT ceramics shift toward higher angles with increasing Ca. All samples were uniform and dense by 1400 °C sintering and the grain size decreased with the Ca addition. With the Sr and Ca cosubstitutions, the phase transition temperature (TC) decreased and the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transition points disappeared. The dielectric peaks became increasingly broad and the relative dielectric constant of the BCT, BS5CT, and BS10CT samples decreased with increasing Ca. The replacement of Ba2+ ions by Sr2+ and Ca2+ ions reduced the lattice constant with increasing hydrostatic pressure and moved the Curie point downwards. The index of relaxation (γ) and the broadening parameter were estimated from a linear fit of the modified Curie–Weiss law.
Magnetoelectric behavior of BaTiO3 films directly grown on CoFe2O4 ceramics
Authors: Wang Jing , Zhang Yi , Ma Jing , Lin Yuanhua , Nan C. W.
Published: July 2008

BaTiO 3 films were grown on highly dense CoFe2O4 ceramics via pulsed laser deposition. Microstructural characterization showed that polycrystalline BaTiO3 thin films with grain size of about 70 nm were grown on the CoFe2O4 ceramics. BaTiO3 films showed good ferroelectric feature. An obvious magnetoelectric response, which had the same bias-dependent trend as the piezomagnetic coupling coefficient of CoFe2O4 ceramics, was observed in the multiferroic film-ceramic composites. Phenomenological theoretical analysis shows that there is plenty of room for further enhancing the magnetoelectric response of such film-substrate composites.
Influence of balancing parameters in achieving magnetic field uniformity in a large cylindrical volume
Authors: Masood Khalid , Iqbal Munawer , Zakaullah Mohammad , Zafar Junaid , Gibson A. A. P
Published: July 2008

Large diameter, air-cored, coaxially configured magnetic coils of rectangular winding cross sections have been envisaged for generating extremely homogenous magnetic fields over a large volume of space. Optimized magnetic field balancing parameters and dimensions for a coil configuration were experimentally developed, verified, and their results are presented. The developed design has made it possible to generate extremely homogenous magnetic fields in a large extended cylindrical region of more than 12 of the coil’s diameter, which requires the winding cross-section thickness to have a width ratio of a relatively small integer. Furthermore, field uniformity regions can be extended to more than one and a half times as can be achieved with coils of negligible winding cross section by employing balancing parameters method.
Numerical simulation of the postformation evolution of a laminar vortex ring
Authors: Danaila Ionut , Hélie Jérôme
Published: July 2008

Direct numerical simulations are used to study the postformation evolution of a laminar vortex ring. The vortex structure is described by calculating the embedded boundaries of the vortex inner core, vortex core, and vortex bubble. The topology of the vortex ring is found to be self-similar during the entire postformation phase. We also show that extracting the vortex inner core provides an objective method in setting the upper value for the cutoff vorticity level separating the vortex from its tail. The computed power laws describing the decay of the translation velocity and integrals of motion (circulation, impulse, and energy) are shown to be consistent with both studies of Dabiri and Gharib [J. Fluid Mech. 511, 311 (2004)] and Maxworthy [J. Fluid Mech. 51, 15 (1972)]. We prove that the apparently different scaling laws reported in these two studies collapse if a virtual time origin is properly defined. Finally, the computationally generated vortex rings are matched to the classical Norbury–Fraenkel model and the recent model proposed by Kaplanski and Rudi [Phys. Fluids 17, 087101 (2005)]. The former model provides not only a good prediction of normalized energy and circulation but also a good estimation of individual integrals of motion. The latter model offers, in addition to a good prediction of integral quantities, a more accurate description of the vortex ring topology when comparing the contours of the inner cores or vortex signatures. Both models underestimate the volume of fluid carried inside the vortex bubble.
On the decrease of intermittency in decaying rotating turbulence
Authors: Seiwert J. , Morize C. , Moisy F.
Published: July 2008

The scaling of the longitudinal velocity structure functions, Sq(r)=⟨∣δu(r)∣q⟩∼rζq, is analyzed up to order q=8 in a decaying rotating turbulence experiment from a large particle image velocimetry dataset. The exponent of the second order structure function ζ2 increases throughout the self-similar decay regime, up to the Ekman time scale. The normalized higher-order exponents ζq∕ζ2 are close to those of the intermittent nonrotating case at small times, but show a marked departure at larger times, on a time scale Ω−1 (Ω is the rotation rate), although a strictly nonintermittent linear law ζq∕ζ2=q∕2 is not reached.
Copper precipitation in nitrogen-doped Czochralski silicon
Authors: Wang Weiyan , Yang Deren , Ma Xiangyang , Que Duanlin
Published: July 2008

Copper (Cu) precipitation behaviors in p-type conventional Czochralski (CZ) and nitrogen-doped Czochralski (NCZ) silicon have been comparatively investigated by means of transmission electron microscopy and optical microscopy. Within the CZ silicon, the Cu precipitates exhibited as spheres with size of about 100 nm and generated stress in the matrix. In this case, they were preferentially delineated as etching pits. On the other hand, within the NCZ silicon, the Cu precipitates were revealed as colonies in which spherelike Cu precipitates with sizes of 10–30 nm assembled on and around the climbing dislocations. As a result, they were preferentially etched as aggregated rods. The formation of Cu precipitate colonies in NCZ silicon was explained in terms of the effect of large grown-in oxygen precipitates on Cu precipitation.
Role of elastic anisotropy in evolution of microstructure and texture in orthorhombic YBa2Cu3O7−δ thin film deposits
Authors: Lee Sung Bo , Ko Rock-Kil , Song Kyu-Jeong , Kim Doh-Yeon , Phillipp Fritz , Lee Dong Nyung
Published: July 2008

We have investigated the microstructure of YBa2Cu3O7−δ films deposited on SrTiO3(100) by pulsed laser deposition and then postdeposition annealed in the temperature range between 200 and 400 °C. By postdeposition annealing, in the matrix oriented with the c-axis normal to the substrate surface, domains oriented with the c-axis parallel to the surface are nucleated and grown in the crystalline solid state, revealing the rectangular shape or the network structure. Strain energy minimization calculated based on the elastic anisotropy of the orthorhombic YBa2Cu3O7−δ favors the development of the domains and their anisotropic growth shape.
Site-directed electronic tunneling in a dissipative molecular environment
Authors: Volkovich Roie , Toroker Maytal Caspary , Peskin Uri
Published: July 2008

The ability to control electronic tunneling in complex molecular networks of multiple donor/acceptor sites is studied theoretically. Our past analysis, demonstrating the phenomenon of site-directed transport, was limited to the coherent tunneling regime. In this work we consider electronic coupling to a dissipative molecular environment including the effect of decoherence. The nuclear modes are classified into two categories. The first kind corresponds to the internal molecular modes, which are coupled to the electronic propagation along the molecular bridges. The second kind corresponds to the external solvent modes, which are coupled to the electronic transport between different segments of the molecular network. The electronic dynamics is simulated within the effective single electron picture in the framework of the tight binding approximation. The nuclear degrees of freedom are represented as harmonic modes and the electronic-nuclear coupling is treated within the time-dependent Redfield approximation. Our results demonstrate that site-directed tunneling prevails in the presence of dissipation, provided that the decoherence time is longer than the time period for tunneling oscillations (e.g., at low temperatures). Moreover, it is demonstrated that the strength of electronic coupling to the external nuclear modes (the solvent reorganization energy) controls the coherent intramolecular tunneling dynamics at short times and may be utilized for the experimental control of site-directed tunneling in a complex network.
Magnetism of amorphous Ge1−xMnx magnetic semiconductor films
Authors: Deng Jiang-xia , Tian Yu-feng , Yan Shi-shen , Cao Qiang , Liu Guo-lei , Chen Yan-xue , Mei Liang-mo , Ji Gang , Zhang Ze
Published: July 2008

Amorphous Ge1−xMnx magnetic semiconductor films with high Mn concentrations were prepared on liquid-nitrogen (LN2)-cooled glass substrates by ultrahigh vacuum thermal coevaporation. Hysteresis loops measured at 5K show coexistence of ferromagnetism and paramagnetism. The maximum Curie temperature of 220K was found in Ge0.48Mn0.52 film. Moreover, exchange bias occurs in magnetization hysteresis loops for samples with higher Mn concentrations, which can be explained by the antiferromagntic exchange coupling between ferromagnetic phase and antiferromagnetic phase. All the Ge1−xMnx magnetic semiconductor films show semiconducting transport behavior and anomalous Hall effects below the Curie temperature, indicating carrier-mediated ferromagnetism.
Refinements in the characterization of the heterogeneous dynamics of Li ions in lithium metasilicate
Authors: Habasaki J. , Ngai K. L.
Published: July 2008

We have performed the molecular dynamics simulations of ionically conducting lithium metasilicate, Li2SiO3, to get a more in depth understanding of the heterogeneous ion dynamics by separating out the partial contributions from localized and diffusive ions to the mean square displacement (MSD) ⟨r2(t)⟩, the non-Gaussian parameter α2(t), and the van Hove function Gs(r,t). Several different cage sizes lc have been used for the definition of localized ions. Behaviors of fast ions are obtained by the subtraction of the localized component from the ⟨r2(t)⟩ of all ions, and accelerated dynamics is found in the resultant subensemble. The fractional power law of MSD is explained by the geometrical correlation between successive jumps. The waiting time distribution of jumps also plays a role in determining ⟨r2(t)⟩ but does not affect the exponent of its fractional power law time dependence. Partial non-Gaussian parameters are found to be instructive to learn how long length-scale motions contribute to various quantities. As a function of time, the partial non-Gaussian parameter for the localized ions exhibits a maximum at around tx2, the onset time of the fractional power law regime of ⟨r2(t)⟩. The position of the maximum is slightly dependent on the choice of lc. The power law increases in the non-Gaussian parameter before the maximum are attributed to the Lévy distribution of length scales of successive (long) jumps. The decreases with time, after the maximum has been reached, are due to large back correlation of motions of different length scales. The dynamics of fast ions with superlinear dependence in their MSD also start at time around the maximum. Also investigated are the changes of the characteristic times demarcating different regimes of ⟨r2(t)⟩ on increasing temperatures from the glassy state to the liquid state. Relation between the activation energies for short time and long time regimes of ⟨r2(t)⟩ is in accord with interpretation of ion dynamics by the coupling model.
Size effects on the magnetization reversal behavior of exchange bias modulated thin films
Authors: Hamann Christine , Mönch Ingolf , Kaltofen Rainer , Schäfer Rudolf , Gemming Thomas , Schultz Ludwig , McCord Jeffrey
Published: July 2008

Thin films of NiFe/IrMn/Ta with spatially modulated unidirectional anisotropy have been prepared by local oxidation of the antiferromagnetic IrMn layer. Varying the lateral dimensions and orientation of the stripe structures with respect to the direction of exchange bias, the films exhibited different magnetization reversal behavior. While stripes aligned parallel to the unidirectional anisotropy direction display a two-step hysteresis loop, those with perpendicular orientation show a single-step, shifted hysteresis loop. Magnetic domain observation reveals separate switching of the magnetically different stripes for the parallel structures. For decreased lateral dimensions as well as perpendicularly aligned stripes quasidomain states are observed. The different magnetization reversal phenomena are discussed in terms of direct exchange coupling of the bimodal magnetic properties at the stripe interfaces.
The isotropic nuclear magnetic shielding constants of acetone in supercritical water: A sequential Monte Carlo/quantum mechanics study including solute polarization
Authors: Fonseca Tertius L. , Coutinho Kaline , Canuto Sylvio
Published: July 2008

The nuclear isotropic shielding constants σ(O17) and σ(C13) of the carbonyl bond of acetone in water at supercritical (P=340.2atm and T=673K) and normal water conditions have been studied theoretically using Monte Carlo simulation and quantum mechanics calculations based on the B3LYP∕6-311++G(2d,2p) method. Statistically uncorrelated configurations have been obtained from Monte Carlo simulations with unpolarized and in-solution polarized solute. The results show that solvent effects on the shielding constants have a significant contribution of the electrostatic interactions and that quantitative estimates for solvent shifts of shielding constants can be obtained modeling the water molecules by point charges (electrostatic embedding). In supercritical water, there is a decrease in the magnitude of σ(C13) but a sizable increase in the magnitude of σ(O17) when compared with the results obtained in normal water. It is found that the influence of the solute polarization is mild in the supercritical regime but it is particularly important for σ(O17) in normal water and its shielding effect reflects the increase in the average number of hydrogen bonds between acetone and water. Changing the solvent environment from normal to supercritical water condition, the B3LYP∕6-311++G(2d,2p) calculations on the statistically uncorrelated configurations sampled from the Monte Carlo simulation give a C13 chemical shift of 11.7±0.6ppm for polarized acetone in good agreement with the experimentally inferred result of 9–11ppm.
Modeling of avalanche multiplication and excess noise factor in In0.52Al0.48As avalanche photodiodes using a simple Monte Carlo model
Authors: Mun S. C. Liew Tat , Tan C. H. , Goh Y. L. , Marshall A. R. J. , David J. P. R.
Published: July 2008

A simple Monte Carlo model has been developed to simulate the avalanche multiplication process in In0.52Al0.48As. The model reproduces avalanche multiplication and excess noise factor measured on a wide range of In0.52Al0.48As p+-n-n+, n+-n-p+, and p+-n+ diodes and confirms that very low excess noise factor can be obtained using pure electron injection in very thick diodes with avalanche region greater than 2.21 μm or in very thin diodes with avalanche region lesser than 0.11 μm. In addition we investigated the effect of an electric field gradient in the avalanche region of avalanche photodiodes and found that the excess noise factor can be reduced with electric field gradients. However in thin diodes with avalanche region lesser than 0.20 μm, the onset of tunneling current negates the excess noise reduction achieved using the electric field gradient. Therefore ideal p+-i-n+ diodes still provide the overall preferred structure.
Sensitivity of global instability of spatially developing flow in weakly and fully nonlinear regimes
Authors: Hwang Yongyun , Choi Haecheon
Published: July 2008

In the present study, we investigate the sensitivity of global instability in weakly and fully nonlinear regimes using the supercritical Ginzburg–Landau equation. In the weakly nonlinear regime, the sensitivity of global instability is determined by linear global mode and its adjoint mode, and the variation of sensitivity with the departure from the criticality does not change. On the other hand, it is shown that in the fully nonlinear regime, the sensitivity of global instability is characterized by nonlinear global mode and adjoint mode of secondary-instability equation, and the Kolmogorov front acts as a wavemaker of nonlinear global mode. The sensitive region of nonlinear global mode in the fully nonlinear regime is similar to that of linear global mode in the weakly nonlinear regime, but this Kolmogorov front layer becomes less sensitive to the perturbation as the departure from the criticality increase.
Experimental investigation of electron transport properties of gallium nitride nanowires
Authors: Motayed Abhishek , Davydov Albert V. , Mohammad S. N. , Melngailis John
Published: July 2008

We report transport properties of gallium nitride (GaN) nanowires grown using direct reaction of ammonia and gallium vapor. Reliable devices, such as four-terminal resistivity measuring structures and field-effect transistors, were realized by dielectrophoretically aligning the nanowires on an oxidized silicon substrate and subsequently applying standard microfabrication techniques. Room-temperature resistivity in the range of (1.0–6.2)×10−2 Ω cm was obtained for the nanowires with diameters ranging from 200 to 90 nm. Temperature-dependent resistivity and mobility measurements indicated the possible sources for the n-type conductivity and high background charge carrier concentration in these nanowires. Specific contact resistance in the range of 5.0×10−5 Ω cm2 was extracted for Ti/Al/Ti/Au metal contacts to GaN nanowires. Significant reduction in the activation energy of the dopants at low temperatures (<200 K) was observed in the temperature-dependent resistivity measurement of these nanowires, which is linked to the onset of degeneracy. Temperature-dependent field-effect mobility measurements indicated that the ionized impurity scattering is the dominant mechanism in these nanowires at all temperatures.
Temperature compensation method for resonant microsensors based on a controlled stiffness modulation
Authors: Seo Jae Hyeong , Demirci Kemal Safak , Byun Albert , Truax Stuart , Brand Oliver
Published: July 2008

A strategy to compensate for frequency drifts caused by temperature changes in resonant microstructures is presented. The proposed compensation method is based on a controlled stiffness modulation of the resonator by an additional feedback loop to extract the frequency changes caused by temperature changes. The feasibility of the suggested method is verified experimentally by compensating for temperature-induced frequency fluctuations of a micromachined resonator. The developed compensation scheme requires only one additional feedback loop and is applicable to any resonant microstructure featuring excitation and detection elements.