bluuebunny/crossref_metadata_2025 huggingface dataset:
Subcutaneous Abdominal Adipose Tissue Subcompartments: Potential Role in Rosiglitazone Effects
Authors: Walker Gillian E. , Marzullo Paolo , Verti Barbara , Guzzaloni Gabriele , Maestrini Sabrina , Zurleni Francesco , Liuzzi Antonio , Di Blasio Anna Maria
Published: August 2008

Abdominal visceral tissue (VAT) and subcutaneous adipose tissue (SAT), comprised of superficial‐SAT (sSAT) and deep‐SAT (dSAT), are metabolically distinct. The antidiabetic agents thiazolidinediones (TZDs), in addition to their insulin‐sensitizing effects, redistribute SAT suggesting that TZD action involves adipose tissue depot‐specific regulation. We investigated the expression of proteins key to adipocyte metabolism on differentiated first passage (P1) preadipocytes treated with rosiglitazone, to establish a role for the diverse depots of abdominal adipose tissue in the insulin‐sensitizing effects of TZDs. Adipocytes and preadipocytes were isolated from sSAT, dSAT, and VAT samples obtained from eight normal subjects. Preadipocytes (P1) left untreated (U) or treated with a classic differentiation cocktail (DI) including rosiglitazone (DIR) for 9 days were evaluated for strata‐specific differences in differentiation including peroxisome proliferator‐activated receptor‐γ (PPAR‐γ) and lipoprotein lipase (LPL) expression, insulin sensitivity via adiponectin and glucose transport‐4 (GLUT4), glucocorticoid metabolism with 11β‐hydroxysteroid dehydrogenase type‐1 (11βHSD1), and alterations in the adipokine leptin. While depot‐specific differences were absent with the classic differentiation cocktail, with rosiglitazone sSAT had the most potent response followed by dSAT, whereas VAT was resistant to differentiation. With rosiglitazone, universal strata effects were observed for PPAR‐γ, LPL, and leptin, with VAT in all cases expressing significantly lower basal expression levels. Clear dSAT‐specific changes were observed with decreased intracellular GLUT4. Specific sSAT alterations included decreased 11βHSD1 whereas secreted adiponectin was potently upregulated in sSAT with respect to dSAT and VAT. Overall, the subcompartments of SAT, sSAT, and dSAT, appear to participate in the metabolic changes that arise with rosiglitazone administration.
Baseline Correlates of Insulin Resistance in Inner City High‐BMI African‐American Children
Authors: Raman Aarthi , Fitch Mark D. , Hudes Mark L. , Lustig Robert H. , Murray Carolyn B. , Ikeda Joanne P. , Fleming Sharon E.
Published: August 2008

To characterize the influence of diet‐, physical activity–, and self‐esteem‐related factors on insulin resistance in 8–10‐year‐old African‐American (AA) children with BMI greater than the 85th percentile who were screened to participate in a community‐based type 2 diabetes mellitus (T2DM) prevention trial. In 165 subjects, fasting glucose‐ and insulin‐derived values for homeostasis model assessment of insulin resistance (HOMA‐IR) assessed insulin resistance. Body fatness was calculated following bioelectrical impedance analysis, and fitness was measured using laps from a 20‐m shuttle run. Child questionnaires assessed physical activity, dietary habits, and self‐esteem. Pubertal staging was assessed using serum levels of sex hormones. Parent questionnaires assessed family demographics, family health, and family food and physical activity habits. Girls had significantly higher percent body fat but similar anthropometric measures compared with boys, whereas boys spent more time in high‐intensity activities than girls. Scores for self‐perceived behavior were higher for girls than for boys; and girls desired a more slender body. Girls had significantly higher insulin resistance (HOMA‐IR), compared with boys (P < 0.01). Adjusting for age, sex, pubertal stage, socioeconomic index (SE index), and family history of diabetes, multivariate regression analysis showed that children with higher waist circumference (WC) (P < 0.001) and lower Harter's scholastic competence (SC) scale (P = 0.044) had higher insulin resistance. WC and selected self‐esteem parameters predicted insulin resistance in high‐BMI AA children. The risk of T2DM may be reduced in these children by targeting these factors.
Energy Expenditure and Adiposity in Nigerian and African‐American Women
Authors: Ebersole Kara E. , Dugas Lara R. , Durazo‐Arvizu Ramon A. , Adeyemo Adebowale A. , Tayo Bamidele O. , Omotade Olayemi O. , Brieger William R. , Schoeller Dale A. , Cooper Richard S. , Luke Amy H.
Published: August 2008

Objective: Obesity is a prevalent condition in industrialized societies and is increasing around the world. We sought to assess the relative importance of resting energy expenditure (REE) and activity EE (AEE) in two populations with different rates of obesity.

Methods and Procedures: Women of African descent between 18 and 59 years of age were recruited from rural Nigeria and from metropolitan Chicago. Total EE (TEE) was measured using the doubly labeled water (DLW) technique and REE by indirect calorimetry; AEE was calculated as the difference between TEE and the sum of REE plus a factor for the thermic effect of food. In the analyses all EE parameters were adjusted for body size using a regression method. Comparisons were made between the groups and associations between EE and adiposity examined.

Results: A total of 149 Nigerian and 172 African‐American women completed the protocol. All body size measurements were lower in the Nigerian women. Adjusted TEE and REE were higher in the Nigerian cohort but adjusted AEE did not differ significantly. Adjustment for parity, seasonality, and recent illness did not modify mean AEE or adiposity. In neither cohort was there a meaningful association between measures of AEE and adiposity.

Discussion: In these cohorts of women from very different environments, AEE did not differ significantly nor was it associated cross‐sectionally with adiposity. If generalizable, these findings suggest that reduction in AEE may have less of a role in the development of obesity than anticipated. The possibility remains that variation in type and duration of activity plays a role not captured by total AEE.
Reformulation of BMI and Percent Body Fat to Remove the Height Bias in 8‐year‐olds
Authors: Telford Richard D. , Cunningham Ross B.
Published: August 2008

BMI and percent body fat (%BF) are both related to height (Ht) in prepubertal children, so may misrepresent childhood adiposity, especially in tall or short children. We sought to construct replacement functions for BMI and %BF that are independent of Ht. Fat mass (FM) was measured using dual‐energy X‐ray absorptiometry, together with Ht and body mass (BM) in 746 healthy boys and girls aged 8 years (0.34 s.d.). Relationships between BM, FM, and Ht were measured and values of p and q derived such that the functions BM. Ht−p and FM.BM−q were unrelated to Ht. BM was not directly proportional to Ht2, BMI being significantly related to Ht in both boys and girls (P < 0.001). BM was proportional to Ht3, BM. Ht−3 being independent of Ht. Similarly, FM was not directly proportional to BM and %BF was significantly related to Ht (P < 0.001). While FM was proportional to BM2, FM.BM−1.5 was the function found to be independent of Ht. Using the 85th and 95th percentiles as the cutoffs for overweight and obesity respectively, 6.4% of the boys and 6.8% of the girls were classified differently by BMI and the Ht independent measure BM. Ht−3. Similarly, 10.1% boys and 13.7% girls were classified differently by %BF and the Ht independent measure FM.BM−1.5. We propose that improved diagnostic accuracy of body composition in 8‐year‐olds is provided by the BM function (BMF, BM. Ht−3) and FM function (FMF, FM.BM−1.5) replacing BMI and %BF, which both overestimate the adiposity of taller children and underestimate it in shorter children.
Maternal Treatment With Oleoyl‐estrone Induces Resistance to Lipid Accrual in Their Descendants
Authors: García‐Peláez Beatriz , Vilà Ruth , Remesar Xavier
Published: August 2008

Objective: To determine whether treatment of rat dams with oleoyl‐estrone (OE) has an effect on the offspring's long‐term response to diet restriction during lactation.

Methods and Procedures: Control, OE‐treated, and diet‐restricted dams were treated up to day 15 of lactation. Changes in food intake and body weight were recorded for dams and their pups. After weaning, pups received a 4‐week standard diet followed by a 4‐week period of high‐fat diet. Lipid, protein, and energy content of pups plus energy intake and efficiency. Serum metabolites (glucose, urea, and cholesterol) and serum hormones (adiponectin, leptin, insulin, and sexual hormones).

Results: Neither pups from dams in the OE‐treated nor in the diet‐restricted group showed significant changes in weight, though these two groups ingested 79% of food ingested by controls. At weaning, the pups from OE‐treated rats were smaller than those of the control or diet‐restricted groups. These pups maintained the differences in size and lipid content during the 4‐week standard‐diet period, whereas pups from diet‐restricted dams showed a sharp decrease in their lipid content. During the 4 weeks of high‐fat diet, the male offspring from OE‐treated dams increased the difference in lipid content in relation to the pups from control dams whereas in females the differences decreased. Female offspring from diet‐restricted dams showed the most marked changes in metabolite and hormone levels in relation to controls.

Discussion: Treatment of lactating dams with OE programs the metabolic response of their offspring to resist the challenge of a high‐fat diet that would lead to obesity in adulthood.
Weight Regain and Health‐related Quality of Life in Postmenopausal Women
Authors: Yankura David J. , Conroy Molly B. , Hess Rachel , Pettee Kelley K. , Kuller Lewis H. , Kriska Andrea M.
Published: August 2008

Weight loss improves health‐related quality of life (HRQoL). However, regain after loss is common; little is known about the impact of weight regain on HRQoL in postmenopausal women. Woman on the Move through Activity and Nutrition (WOMAN) is a randomized lifestyle intervention trial of diet, physical activity, and weight loss in 508 postmenopausal women aged 52–62 years. This analysis focused on the women who lost ≥5 lb during the initial phase of the study, baseline to 6 months (n = 248). This cohort was divided into three groups based on subsequent weight change between 6 and 18 months: weight loss (WL; ≥5 lb loss), weight stable (WS; <±5 lb change), and weight regain (WR; ≥5 lb gain). HRQoL was measured at baseline, 6, and 18 months using the Short Form‐36. Of the 248 women studied, 51 (21%) continued to lose weight after initial weight loss, while 127 (51%) maintained a stable weight, and 70 (28%) regained weight. Between baseline and 6 months, women in WR group had decreased mental health and social‐functioning scores, while the WL and WS groups improved in these subscales. Between baseline and 18 months, energy improved most significantly in those with continued weight loss (P = 0.0003). Weight loss was correlated with a small to moderate improvement in perceived general health and energy, which was reversed by weight gain. Further study is needed to investigate the impact of a decline in mental health and social functioning on future weight regain.
Weight‐specific Health‐related Quality of Life in Adolescents With Extreme Obesity
Authors: Modi Avani C. , Loux Tara J. , Bell Stephen K. , Harmon Carroll M. , Inge Thomas H. , Zeller Meg H.
Published: August 2008

The objectives of this multisite study were to: (i) examine differences by gender and race on generic and weight‐ specific health‐related quality of life (HRQOL) in adolescents with extreme obesity (BMI ≥ 40 kg/m2) and (ii) explore HRQOL differences based on treatment pursued (behavioral vs. bariatric surgery). Study participants included 145 obese adolescents (mean age = 15.3 years; 68% female; 46% black; mean BMI = 50.6) referred to pediatric weight management programs. Participants completed generic (PedsQL) and weight‐specific (Impact of Weight on Quality of Life‐Kids (IWQOL‐Kids)) HRQOL measures. Generic and weight‐specific measures indicated global (e.g., all domains) HRQOL impairment and significant differences by race. Physical, emotional, and social scores of the PedsQL (Ps < 0.01) and the physical comfort and body esteem scores of the IWQOL‐Kids (Ps < 0.001) were significantly higher for black compared to white adolescents with extreme obesity. Extremely obese adolescents pursuing bariatric surgery reported similar HRQOL to adolescents pursuing behavioral treatment (n = 30 matched pairs). HRQOL did not differ for extremely obese adolescents based on type of treatment sought, but race/ethnicity should be considered when characterizing these youth. Although racial differences in adolescent body image/esteem have been reported, it is unknown why black adolescents with extreme obesity would report less impact of weight on their physical functioning. Overall, these data suggest that HRQOL is not homogenous in adolescents with extreme obesity.
Effects of Ritonavir on Adipocyte Gene Expression: Evidence for a Stress‐related Response
Authors: Adler‐Wailes Diane C. , Guiney Evan L. , Koo Jashin , Yanovski Jack A.
Published: August 2008

To understand the molecular mechanisms underlying the development of dyslipidemia and lipodystrophy that occurs after administration of aspartic acid protease inhibitors, we examined transcriptional profiles using cDNA microarrays in 3T3‐L1 adipocytes exposed to 10 μmol/l ritonavir for 2–21 days. The expression levels of ∼12,000 transcripts were assessed using the MgU74Av2 mouse microarray chip. Ritonavir altered gene expression of inflammatory cytokines, stress response genes localized to endoplasmic reticulum, oxidative stress genes, apoptosis‐related genes, and expression of genes involved in cell adhesion and extracellular matrix remodeling. Microarray analysis also identified a novel gene downregulated by ritonavir, Cidea, whose expression levels may affect free‐fatty acid metabolism. These changes suggest a unique, stress‐related pattern in adipocytes induced by chronic exposure to the protease inhibitor, ritonavir.
Role of Estrogen Receptor‐α and −β in Regulating Leptin Expression in 3T3‐L1 Adipocytes
Authors: Yi Kyong Wook , Shin Jung‐Ho , Seo Hong Seog , Lee Jae Kwan , Oh Min‐Jeong , Kim Tak , Saw Ho Suk , Kim Sun‐Haeng , Hur Jun‐Young
Published: August 2008

We investigated the effects of the estrogen receptor‐α (ERα) and ‐β (ERβ) in the regulation of leptin, resistin, and adiponectin expression in 3T3‐L1 adipocytes. Mature adipocytes were exposed to estradiol (E2), ERα agonist (PPT (4,4′,4″‐(4‐propyl‐[1H]‐pyrazole‐1,3,5‐triyl)trisphenol)), ERβ agonist (DPN (2,3‐bis(4‐Hydroxyphenyl)‐propionitrile)), E2 with ERα antagonist (MPP (1,3‐Bis(4‐hydroxyphenyl)‐4‐methyl‐5‐[4‐(2‐piperidinylethoxy)phenol]‐1H‐pyrazole dihydrochloride)), and E2 with ERβ antagonist (R, R‐THC ((R, R)‐5,11‐diethyl‐5,6,11,12‐tetrahydro‐2,8‐chrysenediol)) at different concentrations. To clarify the expression and regulation of adipokines by ER subtypes, total RNA was extracted from cells and measured using quantitative PCR. Western blot analysis was performed to evaluate the protein expression of adipokines, ERα, and ERβ. The leptin expression was significantly increased in the cells treated with high concentrations (10−5 and 10−6 mol/l) of the PPT (P < 0.01, P < 0.05). By contrast, the leptin expression decreased in a dose‐dependent manner in the MPP‐treated groups (P < 0.05). High concentrations (10−5 mol/l) of R, R‐THC with E2 (10−7 mol/l) caused a significant increase of the leptin expression (P < 0.01). The leptin mRNA levels were positively correlated with the ERα mRNA levels (r = 0.584, P < 0.01) and negatively correlated with the ERβ mRNA levels (r = −0.236, P = 0.03) in the adipocytes. The ratio of the ERα to ERβ mRNA levels in the adipocytes was significantly associated with leptin mRNA levels (r = 0.454, P < 0.01). ERα induced leptin expression and ERβ inhibited its expression in 3T3‐L1 adipocytes. The ratio of the ERα‐to‐ERβ expression in 3T3‐L1 adipocytes may be an important potential regulatory factor in leptin expression.
Glucose‐dependent Insulinotropic Polypeptide (GIP) Stimulates Transepithelial Glucose Transport
Authors: Singh Satish K. , Bartoo Aaron C. , Krishnan Selvi , Boylan Michael O. , Schwartz John H. , Wolfe M. Michael
Published: August 2008

The purpose of this study was to characterize the effects of glucose‐dependent insulinotropic peptide (GIP) on small intestinal glucose transport in vitro. Stripped proximal jejunum from fasted mice was mounted in Ussing chambers. The serosal side was bathed in Regular Ringer solution containing 5 mmol/l glucose, and the mucosal side, with solution containing 10 mmol/l 3‐O‐methyl glucose (3OMG). Intercellular cyclic adenosine monophosphate (cAMP), mucosa‐to‐serosa fluxes of 3OMG (Jms3OMG), and short‐circuit current (ISC) were measured in the presence and absence of GIP. GIP increased cAMP by 2.5‐fold in isolated enterocytes, consistent with a direct effect of GIP on these epithelial cells. GIP also increased ISC and Jms3OMG by 68 and 53%, respectively, indicating that the increase in Jms3OMG was primarily electrogenic, with a small electroneutral component. The stimulatory effect of GIP on Jms3OMG was concentration dependent. In addition, 1,000 nmol/l and 10 nmol/l GIP increased Jms3OMG by 70 and 30% over control, respectively, consistent with receptor activation. Phlorizin (20 μmol/l), an inhibitor of Na+‐glucose cotransporter (SGLT‐1), abolished the increase in ISC and decreased Jms3OMG by ∼65%. These results indicate that stimulation of SGLT‐1 activity by GIP partially accounts for the increase in Jms30MG. These studies are the first to demonstrate direct stimulation of intestinal glucose transport by GIP independent of its insulinotropic properties. GIP stimulates cellular accumulation of cAMP and thereby upregulates glucose transport. The GIP‐induced increase in glucose transport appears to be mediated, at least in part, by SGLT‐1.
Near-to-far-field spectral evolution in a plasmonic crystal: Experimental verification of the equipartition of diffraction orders
Authors: Park D. J. , Lee K. G. , Kihm H. W. , Byun Y. M. , Kim D. S. , Ropers C. , Lienau C. , Kang J. H. , Park Q-Han
Published: August 2008

We report on drastic changes in the near-field spectrum as it evolves into the far field in periodically corrugated metallic nanoslit arrays. The far-field spectral minimum is located exactly at the near-field spectral maximum, where a quasimonochromatic standing wave pattern is observed in the near field. These results are in excellent agreement with the equipartition of diffraction orders recently proposed [K. G. Lee and Q-Han Park, Phys. Rev. Lett. 95, 103902 (2005)].
Inverse scattering method and soliton double solution family for the general symplectic gravity model
Authors: Gao Ya-Jun
Published: August 2008

A previously established Hauser–Ernst-type extended double-complex linear system is slightly modified and used to develop an inverse scattering method for the stationary axisymmetric general symplectic gravity model. The reduction procedures in this inverse scattering method are found to be fairly simple, which makes the inverse scattering method applied fine and effective. As an application, a concrete family of soliton double solutions for the considered theory is obtained.
Simulation study of the symmetry-breaking instability and the dipole field reversal in a rotating spherical shell dynamo
Authors: Nishikawa N. , Kusano K.
Published: August 2008

The reversal mechanism of a dipole magnetic field generated by dynamo action in a rotating spherical shell is investigated by a three-dimensional nonlinear magnetohydrodynamic simulation as well as a linear stability analysis. The emphasis of the study is on understanding the relationship between dipole reversal and the symmetry properties of the dynamo solution. As a result, first, it is found that there is a threshold of the magnetic Prandtl number, below which the dipole field is never reversed, and above which the reversal occurs at irregular intervals like the paleomagnetic evolution of the geodynamo. Second, it is shown that the dynamo process responsible for the generation of a dipole field (called “a-dynamo” in this paper) consists only of the antimirror symmetric magnetic field and the mirror symmetric velocity field with respect to the equatorial plane. Third, it is found that the components of the opposite symmetry to the a-dynamo grow only during the polarity reversal events and quickly decay afterwards. This indicates that the dipole field reversal and the loss of equatorial symmetry are tightly connected. In fact, it is clearly demonstrated by numerical analyses that the a-dynamo process is linearly unstable for the perturbation of opposite symmetry when the magnetic Prandtl number exceeds the threshold for dipole reversal. Mode coupling between the longitudinal Fourier components plays a crucial role in creating the instability. Based on the above results, it is proposed that symmetry-breaking instability could be the mechanism for dipole field reversal in the geodynamo process. The energy conversion between components of different symmetry is also analyzed in the quasistable polarity phase and in the polarity reversal phase, respectively.
Experimental and theoretical study of the ion-ion mutual neutralization reactions Ar++SFn− (n=6, 5, and 4)
Authors: Bopp Joseph C. , Miller Thomas M. , Viggiano Albert A. , Troe Jürgen
Published: August 2008

The ion-ion mutual neutralization reactions Ar++SFn−→Ar+SFn (n=6, 5, and 4) have been studied in a flowing afterglow-Langmuir probe (FALP) apparatus at 300K and 1Torr of He buffer gas. Electron concentrations and product ion fractions were measured, and neutralization rate constants of 4.0×10−8, 3.8×10−8, and 4×10−8cm3s−1 for SF6−, SF5−, and SF4−, respectively, were derived, with uncertainties of ±25% (±35% for SF4−). During the neutralization process, excited neutrals are generated that are able to dissociate to neutral fragments. In the case of SF6, the formation of SF5 and SF4, and similarly in the case of SF5, the formation of SF4 and SF3 were observed and quantified. The mechanism of primary and secondary reaction was analyzed in detail, and rate constants for the dissociative electron attachments e−+SF5→F−+SF4 (k=3×10−9cm3s−1,±40%) and e−+SF3→F−+SF2 (k=2×10−8cm3s−1,+400%,−75%) were also derived. The experimental ion-ion neutralization rate constants were found to be in good agreement with estimates from an optimum two-state double-passage Landau–Zener model. It was also found that energy partitioning in the neutralization is related to the extent of electronic excitation of Ar generated by the electron transfer processes.
Effects of orbit squeezing on neoclassical toroidal plasma viscosity in tokamaks
Authors: Shaing K. C. , Sabbagh S. A. , Chu M. S. , Becoulet M. , Cahyna P.
Published: August 2008

The effects of orbit squeezing are important to neoclassical and anomalous transport fluxes in the region where plasma confinement is improved. This occurs in the edge region after the transition from the low confinement mode (L-mode) to the high confinement mode (H-mode) or in the vicinity of low-order rational surfaces. Neoclassical toroidal viscosity in tokamaks induced by the broken toroidal symmetry resulting from the activity of magnetohydrodynamic instabilities or error fields is calculated to include orbit squeezing effects. It is found that in the 1∕ν regime, the magnitude of the neoclassical toroidal viscosity is enhanced by a factor of ∣S∣3∕2, where ν is the collision frequency and S is the orbit squeezing factor; while in the ν regime, it is reduced by a factor of ∣S∣1∕2. A boundary layer analysis is performed to remove the singularity in the vicinity of the trapped-circulating boundary in the ν regime. As a result, the well-known ν regime is recovered. Orbit squeezing has little effect in the ν regime. The implications on the physics of H-mode confinement are also discussed.
Quantum chemistry of the minimal CdSe clusters
Authors: Yang Ping , Tretiak Sergei , Masunov Artëm E. , Ivanov Sergei
Published: August 2008

Colloidal quantum dots are semiconductor nanocrystals (NCs) which have stimulated a great deal of research and have attracted technical interest in recent years due to their chemical stability and the tunability of photophysical properties. While internal structure of large quantum dots is similar to bulk, their surface structure and passivating role of capping ligands (surfactants) are not fully understood to date. We apply ab initio wavefunction methods, density functional theory, and semiempirical approaches to study the passivation effects of substituted phosphine and amine ligands on the minimal cluster Cd2Se2, which is also used to benchmark different computational methods versus high level ab initio techniques. Full geometry optimization of Cd2Se2 at different theory levels and ligand coverage is used to understand the affinities of various ligands and the impact of ligands on cluster structure. Most possible bonding patterns between ligands and surface Cd∕Se atoms are considered, including a ligand coordinated to Se atoms. The degree of passivation of Cd and Se atoms (one or two ligands attached to one atom) is also studied. The results suggest that B3LYP/LANL2DZ level of theory is appropriate for the system modeling, whereas frequently used semiempirical methods (such as AM1 and PM3) produce unphysical results. The use of hydrogen atom for modeling of the cluster passivating ligands is found to yield unphysical results as well. Hence, the surface termination of II–VI semiconductor NCs with hydrogen atoms often used in computational models should probably be avoided. Basis set superposition error, zero-point energy, and thermal corrections, as well as solvent effects simulated with polarized continuum model are found to produce minor variations on the ligand binding energies. The effects of Cd–Se complex structure on both the electronic band gap (highest occupied molecular orbital–lowest unoccupied molecular orbital energy difference) and ligand binding energies are systematically examined. The role played by positive charges on ligand binding is also explored. The calculated binding energies for various ligands L are found to decrease in the order OPMe3>OPH3>NH2Me⩾NH3⩾NMe3>PMe3>PH3 for neutral clusters and OPMe3>OPH3>PMe3⩾NMe3⩾NH2Me⩾NH3>PH3 and OPMe3>OPH3>NH2Me⩾NMe3⩾PMe3⩾NH3>PH3 for single and double ligations of positively charged Cd2Se22+ cluster, respectively.
Spinodal decomposition of asymmetric binary fluids in a micro-Couette geometry simulated with molecular dynamics
Authors: Thakre Amol K. , den Otter W. K. , Padding J. T. , Briels W. J.
Published: August 2008

The spinodal decomposition of quenched polymer/solvent and liquid-crystal/solvent mixtures in a miniature Taylor–Couette cell has been simulated by molecular dynamics. Three stacking motifs, each reflecting the geometry and symmetry of the cell, are most abundant among the fully phase separated stationary states. At zero or low angular velocity of the inner cylindrical drum, the two segregated domains have a clear preference for the stacking with the lowest free energy and hence the smallest total interfacial tension. For high shear rates, the steady state appears to be determined by a minimum dissipation mechanism, i.e., the mixtures are likely to evolve into the stacking demanding the least mechanical power by the rotating wall. The partial slip at the polymer-solvent interfaces then gives rise to a new pattern: A stack of three concentric cylindrical shells with the viscous polymer layer sandwiched between two solvent layers. Neither of these mechanisms can explain all simulation results, as the separating mixture easily becomes kinetically trapped in a long-lived suboptimal configuration. The phase separation process is observed to proceed faster under shear than in a quiescent mixture.
Organic photovoltaic cells made from sandwich-type rare earth phthalocyaninato double and triple deckers
Authors: Wang Qi , Li Yong , Yan Xingzhong , Rathi Monika , Ropp Michael , Galipeau David , Jiang Jianzhuang
Published: August 2008

This work presents organic-inorganic hybrid solar cells, which possess the capability for broad band photon harvesting from an ultraviolet-visible to a near infrared range. These solar cells are bulk heterojunction devices, which have been fabricated by free base phthalocyanine and rare earth phthalocyaninato double or triple deckers (electron donors) with a perylenediimide derivative (electron acceptor). Two-type cell structures with or without nanostructured TiO2 layers have been presented. A characterization of the structures, steady state spectroscopy, fluorescence dynamics, and photoelectrical property of these cells and the active materials has been carried out. A cell structure of In2O3:SnO2∕TiO2-active material-TiO2∕Al has shown a significant improvement in conversion efficiency.
A parametric study of collisional and pulse attenuation on Raman threshold intensity in cluster plasmas
Authors: Tiwari Pawan K. , Mok Chinook , Ryu C. M. , Lee J. K.
Published: August 2008

Coulombic expansion of an atomic cluster can significantly affect the growth of stimulated Raman backscattering in cluster embedded plasmas. The pulse attenuation and the collisional absorption occur during the early phase of cluster expansion, competing against each other in determining the Raman threshold intensity in a cluster plasma. The threshold laser intensities estimated for various wave numbers of the electron plasma waves are found to be consistent with the previous result [P. K. Tiwari et al., Phys. Plasmas 14, 103101 (2007)]: Collisional threshold intensities are to be of 1∼105W∕cm2 at the electron-ion collisional frequency ≈1013s−1, and the pulse attenuated threshold intensities are to be of ∼1013W∕cm2 for short pulse length ∼20fs. The pulse attenuation and collisional absorption of Raman threshold intensities are found to be inversely proportional to both the pulse duration and attenuation length.
Systematic study of Rayleigh–Taylor growth in directly driven plastic targets in a laser-intensity range from ∼2×1014to∼1.5×1015W∕cm2
Authors: Smalyuk V. A. , Hu S. X. , Goncharov V. N. , Meyerhofer D. D. , Sangster T. C. , Stoeckl C. , Yaakobi B.
Published: August 2008

Direct-drive, Rayleigh–Taylor (RT) growth experiments were performed using planar plastic targets on the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at laser intensities between ∼2×1014 and ∼1.5×1015W∕cm2. The primary purpose of the experiments was to test fundamental physics in hydrocodes at the range of drive intensities relevant to ignition designs. The target acceleration was measured with a streak camera using side-on, x-ray radiography, while RT growth was measured with a framing camera using face-on radiography. In a laser-intensity range from 2to5×1014W∕cm2, the measured RT growth agrees well with two-dimensional simulations, based on a local model of thermal-electron transport. The RT growth at drive intensities above ∼1.0×1015W∕cm2 was strongly stabilized compared to the local model predictions. The experiments demonstrate that standard simulations, based on a local model of electron thermal transport, break down at peak intensities of ignition designs, although they work well at lower intensities. These results also imply that direct-drive ignition targets are significantly more stable than previously calculated using local electron-transport models at peak intensities of ignition designs. The preheating effects by nonlocal electron transport and hot electrons were identified as some of the stabilizing mechanisms.
Local potentiometry using a multiprobe scanning tunneling microscope
Authors: Bannani A. , Bobisch C. A. , Möller R.
Published: August 2008

Scanning tunneling potentiometry (STP) is a powerful tool to analyze the conductance through thin conducting layers with lateral resolution in the nanometer range. In this work, we show how a commercial ultrahigh vacuum multiprobe system, equipped with four independent tips, can be used to perform STP experiments. Two tips are gently pushed into the surface applying a lateral current through the layer of interest. Simultaneously, the topography and the potential distribution across the metal film are measured with a third tip. The signal-to-noise ratio of the potentiometry signal may be enhanced by using a fourth tip, providing a reference potential in close vicinity of the studied area. Two different examples are presented. For epitaxial (111) oriented Bi films, grown on a Si(100)-(2×1) surface, an almost constant gradient of the potential as well as potential drops at individual Bi-domain boundaries were observed. On the surface of the Si(111)(3×3)–Ag superstructure the potential variation at individual monoatomic steps could be precisely resolved.
Evolution of photoluminescence as a function of the structural order or disorder in CaMoO4 nanopowders
Authors: Marques A. P. A. , Motta F. V. , Leite E. R. , Pizani P. S. , Varela J. A. , Longo E. , de Melo D. M. A.
Published: August 2008

CaMoO 4 nanopowders were prepared by the complex polymerization method. The materials were characterized by x-ray diffraction (XRD) and by Fourier transform infrared, Raman, and optical reflectance spectroscopies. The data revealed the presence of crystalline scheelite-type phase CaMoO4 and the absence of additional phases. The surface morphology was monitored by high-resolution scanning electron microscopy (HR-SEM). The HR-SEM and XRD characterizations both revealed a tendency for the particle size to increase with rising treatment temperatures. The disordered nanopowders showed strong emission of photoluminescence, which dropped to minimal levels in the ordered nanopowders. These differences in the photoluminescence of disordered and ordered nanopowders were attributed to complex cluster vacancies.
Acoustic wave propagation in uniform glow discharge plasma at an arbitrary angle between the electric field and wave vectors
Authors: Soukhomlinov Vladimir , Gerasimov Nikolay , Sheverev Valery A.
Published: August 2008

This paper extends the recently reported one-dimensional model for sound propagation in glow discharge plasma to arbitrary mutual orientation of the plasma electric field and acoustic wave vectors. The results demonstrate that an acoustic wave in plasma may amplify, attenuate, or remain unchanged depending on the angle between these vectors and on the power input into the discharge. Quantitative evaluations indicate that for glow discharge plasma of a self-sustained discharge in air at the electric current densities of the order of 100 mA cm−2, a gain of as much as 1 m−1 at 0° angle between the vectors changes to similar strength attenuation for the 90° angle.
The effect of thermal anisotropies during crystallization in phase-change recording media
Authors: Belmont M. R. , Aziz M. M. , Wright C. D.
Published: August 2008

The problem discussed is the significance of anisotropies in the thermal parameters of different phases of phase-change materials as used for data storage purposes during recording. The particular phase change in interest is from the amorphous-to-crystalline state. Applying the method of correlation moment analysis produced upper estimators for the time dependence of the width of the crystalline mark and the time at which phase change ceases based on the heat flow process alone. These upper estimators are closed-form analytical expressions that can be used to estimate the recording resolution for any general spatial profile of initial temperature in the medium. This analysis showed that, up to a first order, the specific heat anisotropies have considerably less influence on the heat flow than the thermal conductivity differences. In general, for the material parameters used in phase-change data storage applications, the theory showed that the anisotropy in thermal parameters can be neglected.
Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems
Authors: Knorr Daniel B. , Gray Tomoko O. , Overney René M.
Published: August 2008

Energy dissipation in single asperity sliding friction was directly linked to submolecular modes of mobility by intrinsic friction analysis, involving time-temperature superposition along with thermodynamic stress and reaction rate models. Thereby, polystyrene served as a representative tribological sample for organic and amorphous complex systems. This study reveals the significance of surface and subsurface (α-, β-, and γ-) relaxational modes, which couple under appropriate external conditions (load, temperature, and rate) with shear induced disturbances, and thus gives rise to material specific frictional dissipation. At low pressures and temperatures below the glass transition point, the phenyl pendant side groups of polystyrene, known for their preferential orientation at the free surface, were noticed to be the primary channel for dissipation of kinetic sliding-energy. While this process was found to be truly enthalpic (activation energy of 8kcal∕mol), energy dissipation was shown to possess both enthalpic and cooperative entropic contributions above the loading capacity of the surface phenyl groups (9.9kcal∕mol) or above the glass transition. Apparent Arrhenius activation energies of frictional dissipation of 22 and 90kcal∕mol, respectively, and cooperative contributions up to 80% were found. As such, this study highlights issues critical to organic lubricant design, i.e., the intrinsic enthalpic activation barriers of mobile linker groups, the evaluation of cooperative mobility phenomena, and critical tribological parameters to access or avoid coupling between shear disturbances and molecular actuators.
Photoelectron spectroscopic and theoretical studies of Fem−(coronene)n (m=1,2, n=1,2) complexes
Authors: Li Xiang , Eustis Soren , Bowen Kit H. , Kandalam Anil K. , Jena Puru
Published: August 2008

Fe m ( coronene ) n (m=1,2, n=1,2) cluster anions were generated by a laser vaporization source and studied by anion photoelectron spectroscopy. Density functional theory was used to calculate the structures and the spin multiplicities of those clusters as well as the electron affinities and photodetachment transitions. The calculated magnetic moments of Fe1(coronene)1 and Fe2(coronene)1 clusters suggest that coronene could be a suitable template on which to deposit small iron clusters and that these in turn might form the basis of an iron cluster-based magnetic material. Fe1(coronene)2 and Fe2(coronene)2 cluster anions and their corresponding neutrals prefer the sandwich-type structures, and the ground state structures of these clusters are all staggered sandwiches.
Shock-tube study of relaxation in HCN
Authors: Srinivasan N. K. , Gupte K. S. , Kiefer J. H.
Published: August 2008

Thermal vibrational relaxation in HCN mixtures with Kr has been observed with the laser-schlieren technique. The experiments cover the temperatures 750–2900K and a large pressure range of 13–420Torr in 5% and 20% HCN∕Kr mixtures. Relaxation is extremely fast but appears to occur in two well-separated stages that are assigned to the vibrational transitions (000)→(010) and (000)→(100) with perhaps some lesser contribution from (000)→(001). This interpretation is strongly supported by a comparison of net density changes to thermodynamic calculations. The first and faster process shows near constant relaxation times whereas the latter slower stage has a slight decrease of these with T. Relaxation times in pure HCN obtained by neglecting the small contribution of krypton are as follows: (a) PτHCN–HCN=27exp(1.473∕T1∕3)nsatm (000)→(010); (b) PτHCN–HCN=11exp(32.6∕T1∕3)nsatm (000)→(100). Probabilities suggested by these results are around 0.05 for the fast step and 0.0035 to 0.005 for the slow process. These results are close to those found by laser fluorescence measurements for deactivation of levels involving excitation of the C–H stretch (001) at 3312cm−1. These results are also consistent with the notion of a dominance of the fast stage by T,R-V transfer (thermal relaxation) occurring in a weakly bound complex. However, the slow step most likely occurs through a V–V process (0301)→(100), ΔE=27.7cm−1, after multiple excitation of the (010) mode. These are the first thermal measurements of relaxation in HCN and the first to see energy transfer involving the low-frequency modes.
Piezoelectric response of nanoscale PbTiO3 in composite PbTiO3−CoFe2O4 epitaxial films
Authors: Tan Zhuopeng , Roytburd Alexander L. , Levin Igor , Seal Katyayani , Rodriguez Brian J. , Jesse Stephen , Kalinin Sergei , Baddorf Art
Published: August 2008

Piezoelectric properties of PbTiO3 in 1/3PbTiO3−2/3CoFe2O4 transverse epitaxial nanostructures on differently oriented SrTiO3 were analyzed using conventional and switching-spectroscopy piezoelectric force microscopy. The results confirmed that the individual PbTiO3 nanocolumns in the CoFe2O4 matrix exhibit a detectable piezoelectric response regardless of substrate orientation. For the {100} and {110} orientations, a bias of ±10 V produced ferroelectric domain switching; however, no switching was observed for the {111} films. Small values of piezoelectric constants dzz(100)≈11 pm/V, dzz(110)≈5 pm/V, and dzz(111)≈3 pm/V are attributed to the weak intrinsic response of the nano-PbTiO3 under strong mechanical and depolarizing-field constraints in the composite films.
Half-metallic NiO in zinc-blende structure from ab initio calculations
Authors: Wu R. Q. , Feng Y. P. , Ouyang Y. F. , Zhou P. , Hu C. H.
Published: August 2008

Structural and electronic properties of NiO in the zinc-blende (zb) structure have been studied by ab initio calculations based on density functional theory. The results show that zb-NiO has a half-metallic band structure and its lattice constant is compatible to that of wide gap semiconductors such as SiC, GaN, and ZnO. The half-metallic character can survive the in-plane strain from the wide gap semiconductor substrates. Thus, our calculations indicate that NiO can be a potential half metal for these wide gap semiconductors for spin injection.
Observation of superluminal and negative group velocities in a Mach–Zehnder interferometer
Authors: Sánchez-López M. M. , Sánchez-Meroño A. , Arias J. , Davis J. A. , Moreno I.
Published: August 2008

We demonstrate superluminal and negative group velocity regimes in a linear passive Mach–Zehnder interferometer. This phenomenon occurs in a narrow frequency region around the interferometer’s transmission minima. Experiments are performed in the radio frequency range by using coaxial cables and 1×2 wave splitters. Group velocities of 2c and tunneling with a maximum fractional advancement of 0.12 were measured for electromagnetic sinusoidal wave packets of 2 μs width. These results agree with theoretical predictions using the interferometer’s transmission phase function. This system is proposed as a simpler alternative to photonic crystals and active or microstructured multiple-beam interferometers for sustaining anomalous group velocities.
Collisional boundary layer analysis for neoclassical toroidal plasma viscosity in tokamaks
Authors: Shaing K. C. , Cahyna P. , Becoulet M. , Park J.-K. , Sabbagh S. A. , Chu M. S.
Published: August 2008

It is demonstrated that the pitch angle integrals in the transport fluxes in the ν regime calculated in K. C. Shang [Phys. Plasmas 10, 1443 (2003)] are divergent as the trapped-circulating boundary is approached. Here, ν is the collision frequency. The origin of this divergence results from the logarithmic dependence in the bounce averaged radial drift velocity. A collisional boundary layer analysis is developed to remove the singularity. The resultant pitch angle integrals now include not only the original physics of the ν regime but also the boundary layer physics. The transport fluxes, caused by the particles inside the boundary layer, scale as ν.
Optimal Langevin modeling of out-of-equilibrium molecular dynamics simulations
Authors: Micheletti Cristian , Bussi Giovanni , Laio Alessandro
Published: August 2008

We introduce a scheme for deriving an optimally parametrized Langevin dynamics of a few collective variables from data generated in molecular dynamics simulations. The drift- and the position-dependent diffusion profiles governing the Langevin dynamics are expressed as explicit averages over the input trajectories. The proposed strategy is applicable to cases when the input trajectories are generated by subjecting the system to an external time-dependent force (as opposed to canonically equilibrated trajectories). Second, it provides an explicit control on the statistical uncertainty in the drift and diffusion profiles. These features lend to the possibility of designing the external force driving the system to maximize the accuracy of the drift and diffusion profiles throughout the phase space of interest. Quantitative criteria are also provided to assess a posteriori the satisfiability of the requisites for applying the method, namely, the Markovian character of the stochastic dynamics of the collective variables.
Molecular dynamics study of the repulsive form influence of the interaction potential on structural, thermodynamic, interfacial, and transport properties
Authors: Galliero Guillaume , Boned Christian
Published: August 2008

In this work, using extensive molecular dynamics simulations of several thermophysical properties, it is proposed to analyze possible relationships (in the corresponding state sense) between monoatomic fluids for which the repulsive interactions are modeled by an inverse n-power form, the Lennard-Jones 12-6 (LJ), or by an exponential one, the exponential-6 (Exp-6). To compare results between them, two possible definitions of Exp-6 potentials “equivalent” to the LJ one are proposed. In pure fluids, for a large range of thermodynamic conditions, the properties computed are the surface tension, liquid/vapor equilibrium densities, one-phase potential energy, pressure, isometric heat capacity, thermal pressure coefficient, self-diffusion, shear viscosity, and thermal conductivity. Additionally, thermodiffusion (Soret effect) has been considered in “isotopic” equimolar mixtures. It is shown that despite similarities exhibited by alike radial distribution functions, differences exist between the thermodynamic properties values provided by the LJ fluid and the two equivalent Exp-6 fluids. Nevertheless, quite surprisingly, when temperature and density are used as inputs, all three direct transport properties are shown to be nearly independent of the choice of the potential tested. Unexpectedly, these similarities hold even for thermodiffusion which is a priori very sensitive to the nature of the interactions. These results indicate that the use of an Exp-6 potential form to describe nonbonded/nonpolar interaction in molecular simulation is an alternative (more physically acceptable) to the LJ potential when dealing simultaneously with thermodynamic and transport properties. However, when only transport properties are considered (including thermodiffusion), the Exp-6 potential form should not lead to any differences compared to the LJ one.
Slow photoelectron imaging spectroscopy of CCO− and CCS−
Authors: Garand Etienne , Yacovitch Tara I. , Neumark Daniel M.
Published: August 2008

High-resolution photodetachment spectra of CCO− and CCS− using slow photoelectron velocity-map imaging spectroscopy are reported. Well-resolved transitions to the neutral XΣ−3, aΔ1, bΣ+1, and AΠ3 states are seen for both species. The electron affinities of CCO and CCS are determined to be 2.3107±0.0006 and 2.7475±0.0006eV, respectively, and precise term energies for the aΔ1, bΣ+1, and AΠ3 excited states are also determined. The two low-lying singlet states of CCS are observed for the first time, as are several vibronic transitions within the four bands. Analysis of hot bands finds the spin-orbit orbit splitting in the XΠ2 ground state of CCO− and CCS− to be 61 and 195cm−1, respectively.