bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin films of block copolymer supramolecular assemblies: Microphase separation and nanofabrication
Authors: Böhme Marcus , Kuila Biplab , Schlörb Heike , Nandan Bhanu , Stamm Manfred
Published: September 2010

Block copolymer (BCP) thin films have received enormous interest for possible applications in nanotechnology due to their self‐assembled structure formation. However, synthesis of polymers with desired chemical and physical properties sometimes is not possible. During the past 6 years, our group developed a method to introduce certain functionality into self‐assembled structures via the formation of supramolecular assemblies from BCPs and low molecular weight additives. Among several other materials, the most noteworthy is a system consisting of polystyrene‐block‐poly(4‐vinylpyridine) and 2‐(4′‐hydroxybenzeneazo) benzoic acid which has been used as nanotemplate for the fabrication of materials with potentially exceptional electrical, optical, or magnetic properties. The present article summarizes the research done at our group on fundamental aspects of microphase separation in these supramolecular assemblies and also their further use as templates for nanofabrication.
Ab initio study of structural, electronic, elastic, and phonon properties of ScN and ScP at ambient and high pressure
Authors: Pandit Premlata , Rakshit Bipul , Sanyal Sankar P.
Published: September 2010

The structural, electronic, and elastic properties of ScN and ScP in NaCl (B1 phase) and CsCl (B2 phase) structures and the phonon dispersion at ambient and high pressure, close to phase transition, have been investigated by using first‐principles pseudopotential method in the framework of density functional theory with the generalized gradient approximation. It is found that both compounds are stable in B1 phase at ambient pressure and undergo a structural phase transition to B2 phase at 368.76 and 247.56 GPa, respectively. ScN is a semiconductor and ScP is semimetallic at ambient pressure (B1 phase), whereas both the compounds are metallic at high pressure (B2 phase). The calculated lattice parameter (a), bulk modulus (B), and their first‐order pressure derivative (B′) are in good agreement with previous calculations. The elastic constants (C11, C12, and C44) have been calculated in both phases. We also report the phonon structure of these compounds at ambient and close to the phase‐transition pressure and compared among themselves. It is shown that their phonon structures are consistent with electronic properties at ambient and high pressures. Near B1–B2 transition, the LA mode at X‐point softens considerably leading to structural instability.
The potential use of Echinacea in acne: control of Propionibacterium acnes growth and inflammation
Authors: Sharma M. , Schoop R. , Suter A. , Hudson J. B.
Published: September 2010

Acne is a chronic inflammatory disorder of skin follicles caused by the gram‐positive bacterium Propionibacterium acnes. The possibility was investigated that a standardized preparation of Echinacea purpurea (Echinaforce®), with known antiviral, antiinflammatory and antibacterial properties, might provide a useful alternative treatment in the control of the disease. The herbal extract readily killed a standard laboratory strain of the bacterium and several clinical isolates. In cell culture models of human bronchial epithelial cells and skin fibroblasts, P. acne induced the secretion of substantial amounts of several pro‐inflammatory cytokines, including IL‐6 and IL‐8 (CXCL8), as determined by means of cytokine–antibody arrays. However, the E. purpurea completely reversed this effect and brought the cytokine levels back to normal. Thus Echinaforce® could provide a safe two‐fold benefit to acne individuals by inhibiting proliferation of the organism and reversing the bacterial‐induced inflammation. Copyright © 2010 John Wiley & Sons, Ltd.
Antioxidant and anticholinesterase constituents from the petroleum ether and chloroform extracts of Iris suaveolens
Authors: Hacıbekiroğlu Işıl , Kolak Ufuk
Published: September 2010

The aim of this study was to investigate the phytochemical, antioxidant and anticholinesterase activities of Iris suaveolens. After determining total phenolic and flavonoid contents of the petroleum ether, chloroform and methanol extracts prepared from the rhizomes, the antioxidant capacity of the extracts was established using β‐carotene–linoleic acid and CUPRAC methods. The chloroform extract which was rich in phenolic content exhibited the highest inhibition of lipid peroxidation in the β‐carotene–linoleic acid system, and the best cupric reducing antioxidant capacity among the tested extracts. The petroleum ether extract indicated moderate anticholinesterase activity while the chloroform extract revealed significant butyrylcholinesterase inhibitory activity (75.03 ± 1.29%). Spectroscopic methods were used for the structural elucidation of the compounds (1–13) isolated from the petroleum ether and chloroform extracts. Coniferaldehyde (6), having the highest antioxidant activity in the β‐carotene–linoleic acid assay at 25 and 50 µg/mL, demonstrated also the best effect in the CUPRAC method among the tested compounds (1–12). 3‐Hydroxyirisquinone (10) showed the best anticholinesterase activity among the tested compounds (1–4, 6–12), and coniferaldehyde exhibited almost the same butyrylcholinesterase inhibitory activity (82.60 ± 2.33%) as galantamine (86.26 ± 0.66%). Copyright © 2010 John Wiley & Sons, Ltd.
Drift and retention of pelagic spawning minnow eggs in a regulated river
Authors: Widmer A. M. , Fluder J. J. , Kehmeier J. W. , Medley C. N. , Valdez R. A.
Published: September 2010

Long‐distance drift of eggs and larvae has been identified as a possible cause of downstream displacement and poor recruitment of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Seven experiments were conducted using artificial eggs to estimate silvery minnow egg drift and retention in the Albuquerque and Isleta reaches of the regulated Middle Rio Grande, New Mexico, USA over a range of flows during expected spawning times. Bead retention varied by reach, discharge, and shape of the hydrograph. Highest retention (6.9 and 9.7% per km in the Albuquerque and Isleta reaches, respectively) occurred on the ascending limb of a high flow in areas where there was substantial floodplain inundation. Retention was maximized at different flows in each reach (97 and 140 m3/s, respectively), possibly associated with reach‐specific floodplain inundation thresholds. Lowest retention in each reach (2.1 and 1.7%, respectively) occurred on the descending limb of low and high flows, respectively. Of the silvery minnow eggs produced in the combined Albuquerque and Isleta reaches in 2005, 8–14% are predicted to have been retained in the Albuquerque Reach (67 km) and 49–83% in the Isleta Reach (86 km) based on the distribution of adult fish and measured bead retention rates. Although silvery minnow propagules are capable of drifting long distances, our study suggests that considerable retention occurs in the Middle Rio Grande. Habitat restoration to increase channel habitat complexity, and flow management to promote floodplain inundation should help to retain a greater proportion of propagules in upstream reaches. Copyright © 2010 John Wiley & Sons, Ltd.
The Gondwana–Laurussia convergence process: evidence from the Middle Mississippian (Viséan) palynostratigraphic record
Authors: GONZÁLEZ FELIPE , MORENO CARMEN , PLAYFORD GEOFFREY
Published: September 2010

The Gondwana–Laurussia convergence process can be explored by studying the Middle Mississippian (Viséan) palynoflora of northwest Africa. Statistical analysis of the Viséan miospore assemblages reported from Morocco defines two populations, one with clear Laurussian affinity from the northern margin of the Western Meseta, and the other, more Gondwanan in composition, from the southern part of the Western Meseta and Anti-Atlas. Moreover, no transitional assemblages have been described from the region. These palynofloral variations are a consequence of the complex palaeogeography of the northwest African margin, which was controlled by the Variscan Orogeny during Viséan times. Taking into consideration the palynofloral affinity of the miospore assemblages reported throughout the entire North African margin and the Middle East, it is possible to envisage a Late Carboniferous Pangaea amalgamation process initially evolving from the west, while in the east the ocean separating Gondwana and Laurussia persisted as an effective barrier to floral migration.
A revised Aquitanian age for the emplacement of the Ronda peridotites (Betic Cordilleras, southern Spain)
Authors: ESTEBAN J. J. , CUEVAS J. , TUBÍA J. M. , SERGEEV S. , LARIONOV A.
Published: September 2010

The hot emplacement of the Ronda peridotites (Betic Cordilleras) developed a dynamothermal aureole and partial melts that led to the intrusion of granite dykes in the peridotites. Previous geochronological data place rather broad limits for this event between 22 and 19 Ma. Analyses of neocrystalline zircon rims from large zircon populations yield a U–Pb SHRIMP age of 22.3±0.7 Ma for the dynamothermal aureole formation, and intrusion ages of granite dykes between 22.6±1.8 and 21.5±3.8 support that conclusion. Therefore, these new ages provide a more robust constraint on the hot emplacement of the Ronda peridotites at middle crustal levels.
Moving On and Moving Back: Rethinking Inequality and Migration in the Latin American City
Authors: ROBERTS BRYAN R.
Published: September 2010

This paper focuses on the similarities and differences between contemporary urban organisation and that of the 1960s in Guatemala City and other Latin American cities, mainly using data taken from a re-study of low-income neighbourhoods in Guatemala City. It looks at the impact of sharper patterns of residential segregation, changes in migration patterns, rising levels of crime and violence, and the increase in the relationships of the urban poor with external actors, such as governments and NGOs. Severe inequality persists, but is mediated by an improvement in living standards, by the range of consumer goods accessible to the poor, and by community- and family-based adaptation.
Molecular characterization of Cystoisospora belli and unizoite tissue cyst in patients with Acquired Immunodeficiency Syndrome
Authors: VELÁSQUEZ JORGE NÉSTOR , OSVALDO GERMÁN ASTUDILLO , DI RISIO CECILIA , ETCHART CRISTINA , CHERTCOFF AGUSTÍN VÍCTOR , PERISSÉ GLADYS ELISABET , CARNEVALE SILVANA
Published: September 2010

Cystoisospora belli is a coccidian protozoan that can cause chronic diarrhoea, acalculous cholecystitis and cholangiopathy in AIDS patients. We applied molecular methods to identify Cystoisospora at species level in AIDS patients presenting with and without the presence of unizoites in lamina propria. Coprological and histological analyses were performed in stool and/or biopsy samples from 8 Cystoisospora-infected patients. DNA from the same samples was used to amplify 2 fragments of the SSU-rRNA gene and the ITS-1 region. Sequencing of the resulting amplicons identified C. belli infections in all cases, independent of the presence or absence of unizoite tissue cysts. Further work should be considered in order to find molecular targets related to strain variations in C. belli.
AN INTERVIEW WITH JAMES J. HECKMAN
Authors: Ginther Donna K.
Published: September 2010

James Heckman is one of the most important and influential scholars to have graced the economics profession. His work is deeply rooted at the intersection of economic theory and empirical microeconomics, and he has made significant contributions to the study of labor economics, microeconometrics, and the use of micro data in macroeconomic analysis. Heckman's work is motivated by the scientific method, in which theory is held up to the scrutiny of the data and empirical analysis is informed by economic theory. During the course of his work, he has made lasting contributions to the study of sample selection bias, duration analysis, heterogeneity, and treatment effects in microeconometrics. In labor economics, he has applied these econometric methods to the study of labor supply and life-cycle dynamic models of unemployment, wage growth, and skill formation. In addition, he is the leading scholar on the evaluation of active labor market programs. As an applied microeconomist, one cannot do research on labor supply, sample selection, duration models, or life-cycle dynamics without encountering Jim Heckman's work.
Is It Really Robust?
Authors: Schmider Emanuel , Ziegler Matthias , Danay Erik , Beyer Luzi , Bühner Markus
Published: September 2010

Empirical evidence to the robustness of the analysis of variance (ANOVA) concerning violation of the normality assumption is presented by means of Monte Carlo methods. High-quality samples underlying normally, rectangularly, and exponentially distributed basic populations are created by drawing samples which consist of random numbers from respective generators, checking their goodness of fit, and allowing only the best 10% to take part in the investigation. A one-way fixed-effect design with three groups of 25 values each is chosen. Effect-sizes are implemented in the samples and varied over a broad range. Comparing the outcomes of the ANOVA calculations for the different types of distributions, gives reason to regard the ANOVA as robust. Both, the empirical type I error α and the empirical type II error β remain constant under violation. Moreover, regression analysis identifies the factor “type of distribution” as not significant in explanation of the ANOVA results.
Measurement of atmospheric hydrogen peroxide and organic peroxides in Beijing before and during the 2008 Olympic Games: Chemical and physical factors influencing their concentrations
Authors: He S. Z. , Chen Z. M. , Zhang X. , Zhao Y. , Huang D. M. , Zhao J. N. , Zhu T. , Hu M. , Zeng L. M.
Published: September 2010

For the 2008 Beijing Olympic Games full‐scale control (FSC) of atmospheric pollution was implemented to improve the air quality from 20 July to 20 September 2008, resulting in a significant decrease in the emission of pollutants in urban Beijing, especially vehicular emissions. The combination of reduced emissions and weather condition changes provided us with a unique opportunity to investigate urban atmospheric chemistry. Hydrogen peroxide (H2O2) and organic peroxides play significant roles in atmospheric processes, such as the cycling of HOx radicals and the formation of secondary sulfate aerosols and secondary organic aerosols. We measured atmospheric H2O2 and organic peroxides in urban Beijing, at the Peking University campus, from 12 July to 30 September, before and during the FSC. The major peroxides observed were H2O2, methyl hydroperoxide (MHP), and peroxyacetic acid (PAA), having maximal mixing ratios of 2.34, 0.95, and 0.17 ppbv (parts per billion by volume), respectively. Other organic peroxides were detected occasionally, such as bis‐hydroxymethyl hydroperoxide, hydroxymethyl hydroperoxide, ethyl hydroperoxide, and 1‐hydroxyethyl hydroperoxide. On sunny days the concentrations of H2O2, MHP, and PAA exhibited pronounced diurnal variations, with a peak in the afternoon (1500–1900) and, occasionally, a second peak in the evening (2000–0200). The night peaks can be attributed to local night production from the ozonolysis of alkenes, coupled with the reaction between NO3 radicals and organic compounds. Sunny‐day weather dominated during 16–26 July, and we found that the concentrations of H2O2, MHP, and PAA increased strikingly on 22–26 July, compared with the concentrations during 16–19 July. This effect was mainly attributed to the NOx (NO and NO2) decline because of the FSC, due to (i) the suppressing effect of NO and NO2 on the production of peroxides and (ii) the indirect effect of reduced NOx on the concentration of peroxides via O3 production in the volatile organic compound‐sensitive area. Although the time period from 29 July to 15 August fell within the FSC, the concentrations of H2O2, MHP, and PAA decreased significantly. This can be explained by a combination of chemical and physical factors during this period, when rainy‐ and cloudy‐day weather dominated. Weaker irradiation and lower temperatures resulted in a lower photochemical production of peroxides; the higher humidity resulted in their greater loss through their aqueous‐phase oxidation of S(IV) and through heterogeneous removal, and lower temperatures and higher nighttime humidity resulted in a quicker surface deposition of peroxides. Furthermore, our observations seem to imply that the heterogeneous removal of H2O2 is faster than that of MHP, as indicated by the strong negative correlation between the H2O2‐to‐MHP ratio and the aerosol surface area.
A solution of the laminar flow for a gradual transition between porous and fluid domains
Authors: Duman Tomer , Shavit Uri
Published: September 2010

Despite its importance, the problem of transfer phenomena at the interface between porous domains and homogeneous free flows found no complete general solution. In this study we contribute to the solution of the problem by studying the effect of a gradual geometrical change at the interface. Such a geometrical change is common to all cases, depending on the scale of observation. We apply the one‐domain approach, assume that the porosity profile is given, use a permeability profile as a function of porosity, and generate excellent predictions by applying, when necessary, the concept of the apparent interface location. The apparent interface location serves as an empirical measure providing the degree of freedom needed to match the solution with measured quantities such as the flow rate or a known velocity.
An improved time series approach for estimating groundwater recharge from groundwater level fluctuations
Authors: Cuthbert M. O.
Published: September 2010

An analytical solution to a linearized Boussinesq equation is extended to develop an expression for groundwater drainage using estimations of aquifer parameters. This is then used to develop an improved water table fluctuation (WTF) technique for estimating groundwater recharge. The resulting method extends the standard WTF technique by making it applicable, as long as aquifer properties for the area are relatively well known, in areas with smoothly varying water tables and is not reliant on precipitation data. The method is validated against numerical simulations and a case study from a catchment where recharge is “known” a priori using other means. The approach may also be inverted to provide initial estimates of aquifer parameters in areas where recharge can be reliably estimated by other methods.
Attenuation of in situ UV radiation in Mackenzie Delta lakes with varying dissolved organic matter compositions
Authors: Gareis Jolie A. L. , Lesack Lance F. W. , Bothwell Max L.
Published: September 2010

In 2004, ultraviolet‐B (UVB) and ultraviolet‐A (UVA) attenuation were measured in Mackenzie Delta lakes spanning gradients in water renewal rate, dissolved organic carbon (DOC) concentration, and dissolved organic matter (DOM) composition. DOM compositions (ratio of chromophoric DOM (CDOM) to non‐chromophoric DOM) in Delta lakes are complex, evolving seasonally via flooding, dilution, macrophyte production, photobleaching, and bacterial metabolism. Attenuation was more strongly related to CDOM absorption coefficients (a330; UVB r2 = 0.69, p < 0.0001; UVA r2 = 0.58, p < 0.0001) than to DOC concentrations due to variable DOM compositions. Attenuation in one set of lakes was well related (linear models) to a330 and total suspended solids (UVB R2 = 0.80, p < 0.0001; UVA R2 = 0.81, p < 0.0001). When these models were applied to other Delta lakes, however, attenuation of UVB was overestimated in 17 of 19 cases and attenuation of UVA was overestimated in all 18 cases. This bias indicates that models are not transferrable among Delta lakes, and likely cannot be applied in other circumpolar delta lakes with similarly complex DOM compositions. Although attenuation is high in Delta lakes (KdUVB 17.1–33.4 m−1; KdUVA 7.7–19.2 m−1), plankton and photoreactive solutes may be exposed to high levels of ultraviolet radiation (UVR) because Delta lakes are shallow, UVB and UVA penetrate the top 19% and 31% of water columns, respectively, and day lengths are extended during open water. Thus, climate change effects on DOM compositions may significantly alter in situ UVR environments in circumpolar delta lakes.
Source contributions of volatile organic compounds to ozone formation in southeast Texas
Authors: Ying Qi , Krishnan Anupama
Published: September 2010

A source‐oriented SAPRC‐99 gas phase photochemical mechanism was incorporated into the Community Multiscale Air Quality (CMAQ) model to determine the contributions of volatile organic compounds (VOCs) to predicted net ozone (O3) formation rates during the Texas Air Quality Study (TexAQS) from 16 August to 7 September 2000. Contributions from biogenic sources, diesel vehicles, highway gasoline vehicles, off‐highway gasoline vehicles, solvent utilization, petroleum industries, other industries and wildfires were determined. Peak column‐averaged O3 formation rate due to industrial sources averaged over this episode was approximately 8.5 ppb hr−1. Contributions of gasoline vehicles and solvent utilization were large in urban areas to the west of the industrial region with highest column‐averaged formation rates of 3.7 and 1.4 ppb hr−1, respectively. Large regional contributions of biogenic sources to O3 formation were predicted with highest O3 formation rate of 11.9 ppb hr−1 in downwind rural areas. Wildfires could contribute to large O3 formation but their influence was generally localized. Analysis of 2400 back‐trajectories from areas with maximum daily 8‐h O3 greater than 90 ppb showed that industrial sources were the largest anthropogenic sources of VOC that contributed to the these high O3 events, followed by gasoline vehicle sources. The median of relative contributions from biogenic and anthropogenic sources from this analysis was approximately 60% and 40%, respectively. Analysis of the back‐trajectories where 1‐h peak O3 concentrations were greater than 120 ppb showed that the median relative contributions due to anthropogenic sources were increased to over 60%. This suggests that high O3 events in the HGB region were driven by anthropogenic VOC emissions from industrial sources.
Parents and Vehicle Purchases for Their Children: A Surprising Source of Weight Bias
Authors: Kraha Amanda , Boals Adriel
Published: September 2010

According to current estimates, 68% of the population in United States is considered either overweight or obese. Despite its relative frequency, prejudice and discrimination against overweight and obese Americans is a common occurrence. This study seeks to build on previous findings that overweight individuals are more likely than their skinnier peers to rely on themselves, rather than family, to fund their education. We examined whether this trend continued in car‐buying practices. Results suggest that overweight and obese individuals differentially rely on their own sources of income to finance a car, even after controlling for socioeconomic differences. Possible explanations and implications are discussed.
Economic Impact of the Clinical Benefits of Bariatric Surgery in Diabetes Patients With BMI ≥35 kg/m2
Authors: Klein Samuel , Ghosh Arindam , Cremieux Pierre Y. , Eapen Sara , McGavock Tamara J.
Published: September 2010

The medical costs for a type 2 diabetes patient are two to four times greater than the costs for a patient without diabetes. Bariatric surgery is the most effective weight‐loss therapy and has marked therapeutic effects on diabetes. We estimate the economic effect of the clinical benefits of bariatric surgery for diabetes patients with BMI ≥35 kg/m2. Using an administrative claims database of privately insured patients covering 8.5 million lives 1999–2007, we identify obese patients with diabetes, aged 18–65 years, who were treated with bariatric surgery identified using Healthcare Common Procedure Coding System codes. These patients were matched with nonsurgery control patients on demographic factors, comorbidities, and health‐care costs. The overall return on investment (RoI) associated with bariatric surgery was calculated using multivariate analysis. Surgery and control patients were compared postindex with respect to diagnostic claims for diabetes, diabetes medication claims, and adjusted diabetes medication and supply costs. Surgery costs were fully recovered after 26 months for laparoscopic surgery. At month 6, 28% of surgery patients had a diabetes diagnosis, compared to 74% of control patients (P < 0.001). Among preindex insulin users, insulin use dropped to 43% by month 3 for surgery patients, vs. 84% for controls (P < 0.001). By month 1, medication and supply costs were significantly lower for surgery patients (P < 0.001). The therapeutic benefits of bariatric surgery on diabetes translate into considerable economic benefits. These data suggest that surgical therapy is clinically more effective and ultimately less expensive than standard therapy for diabetes patients with BMI ≥35 kg/m2.
Surface order reconstruction in nematics
Authors: Ayeb H. , Lombardo G. , Ciuchi F. , Hamdi R. , Gharbi A. , Durand G. , Barberi R.
Published: September 2010

Investigations on π-cell, a sandwich cell with the director rotating by 180°, demonstrate the possibility to obtain nematic transitions between two textures with different topologies, for instance between an untwisted state and a π-twisted one. These fast textural changes can be obtained by bulk order reconstruction, which allows the director reorientation between two perpendicular directions without macroscopic rotations of the director itself, or by anchoring breaking, which transforms a weak planar anchoring in a homeotropic surface state. Now, we demonstrate that order reconstruction close to a boundary surface with strong or infinite anchoring conditions provides transitions equivalent to anchoring breaking.
Probability distributions of molecular observables computed from Markov models. II. Uncertainties in observables and their time-evolution
Authors: Chodera John D. , Noé Frank
Published: September 2010

Discrete-state Markov (or master equation) models provide a useful simplified representation for characterizing the long-time statistical evolution of biomolecules in a manner that allows direct comparison with experiments as well as the elucidation of mechanistic pathways for an inherently stochastic process. A vital part of meaningful comparison with experiment is the characterization of the statistical uncertainty in the predicted experimental measurement, which may take the form of an equilibrium measurement of some spectroscopic signal, the time-evolution of this signal following a perturbation, or the observation of some statistic (such as the correlation function) of the equilibrium dynamics of a single molecule. Without meaningful error bars (which arise from both approximation and statistical error), there is no way to determine whether the deviations between model and experiment are statistically meaningful. Previous work has demonstrated that a Bayesian method that enforces microscopic reversibility can be used to characterize the statistical component of correlated uncertainties in state-to-state transition probabilities (and functions thereof) for a model inferred from molecular simulation data. Here, we extend this approach to include the uncertainty in observables that are functions of molecular conformation (such as surrogate spectroscopic signals) characterizing each state, permitting the full statistical uncertainty in computed spectroscopic experiments to be assessed. We test the approach in a simple model system to demonstrate that the computed uncertainties provide a useful indicator of statistical variation, and then apply it to the computation of the fluorescence autocorrelation function measured for a dye-labeled peptide previously studied by both experiment and simulation.
Sequential thermoelastic multiscale analysis of nanoparticulate composites
Authors: Yang Seunghwa , Yu Suyoung , Cho Maenghyo
Published: September 2010

The thermoelastic properties of SiC/epoxy nanocomposites are investigated through a molecular dynamics (MDs) simulation and micromechanics bridging method. One major finding from the MD simulation is that not only the elastic modulus but also the thermal expansion coefficient of the nanocomposites exhibits particle-size dependency at fixed volume fractions. In order to describe such effects that are observed from atomistic simulations, a micromechanics-based scale bridging method is suggested that handles both the elastic and residual fields of the nanocomposites with the help of the effective interface concept and sequential information transfer.
Logarithmic based optical delay for time-resolved data collection
Authors: Cole Richard L. , Barisas B. George , Levinger Nancy E.
Published: September 2010

A method has been established that generates values spaced according to a mathematical function, specifically the logarithm function that can be applied to a stepper motor. Here, it is applied to yield logarithmically spaced time delay points for subnanosecond interferometric time-resolved experiments using a stepper motor controlled translation stage. Application of this method is discussed in terms of three input parameters: the optical delay stage time resolution, dt; the time of maximum delay, dstop; and the desired number of data points, N. The method improves the efficiency of interferometric time-resolved data collection while providing data collection effective to determine decay parameters. In principle, this technique could be generalized to any mathematical function.
Topological complexity and tangential discontinuity in magnetic fields
Authors: Janse Å. M. , Low B. C. , Parker E. N.
Published: September 2010

This is a study of the topological magnetostatic problem. A magnetic field embedded in a perfectly conducting fluid and rigidly anchored at its boundary has a specific topology invariant for all time. Subject to that topology, the force-free state of such a field generally requires the presence of tangential discontinuities (TDs). This property proposed and demonstrated by Parker [Spontaneous Current Sheets in Magnetic Fields (Oxford University Press, New York, 1994)] is explained in terms of (i) the overdetermined nature of the magnetostatic partial differential equations nonlinearly coupled to the integral equations imposing the field topology and (ii) the hyperbolic nature of the partial differential equation for the twist function α of the force-free field. The mathematical analysis elucidates a basic incompatibility between preserving a complex field topology and attaining equilibrium, if analyticity is assumed. Physics avoids this incompatibility via TD formation as a natural consequence of perfect conductivity. The study relates TD formation to topological complexity in two-dimensional and three-dimensional fields, as well as the topological connectivity and geometric shape of the field domain. Mathematical points made are given physical interpretations, but important topological concepts for understanding spontaneous TDs have remained incomplete. As an application, examples are presented to define twisted and untwisted potential fields found in simply and multiply connected domains, clarifying a confusion in several recent publications. Appendix A treats the expression of the frozen-in condition by a continuum of conserved, total generalized helicities. Appendix B reports briefly on concurrent developments showing that a published objection to the theory of spontaneous TDs is based upon a misunderstanding of the theory.
Field emission cathode with electron optics for use in Hall thrusters
Authors: Kronhaus I. , Kapulkin A. , Guelman M.
Published: September 2010

This paper is devoted to the development and numerical modeling of a field emission cathode for low power Hall thrusters (100–300 W). Generally, Hall thrusters use hollow cathodes, which require a relatively large mass flow rate of xenon-gas to operate. For lower emission currents the cathode gas consumption is still substantial, which contributes to the drop in efficiency when operating a Hall thruster in a low power regime. Conventional field emission cathodes, which are considered as an alternative, do not provide the required low power consumption with an acceptable lifetime. In order to increase the efficiency of the field emission cathode while retaining an acceptable lifetime, an acceleration-deceleration electron optics is proposed. This system is used for the extraction of electrons from carbon nanotubes and the formation of the electron beam. Numerical modeling of the processes in the proposed cathode was carried out using a particle-in-cell approach. It has been shown that (1) it is possible to provide adequate transmission of the electron beam at the required deceleration voltage; (2) injecting xenon-gas at the outlet of the cathode for the creation of a “plasma-bridge” between the cathode and ion beam does not lead to significant population of ions near the emitter surface. A cathode with electron current of 1 A was modeled using a particle-in-cell simulation. The cathode requires only ∼15 W of power and 0.11 mg/s of xenon mass flow rate. For the given current, these parameters are quite reasonable.
Proximity to a ferroelectric instability in Ba1−xCaxZrO3
Authors: Kim H. S. , Christen H. M. , Biegalski M. D. , Singh D. J.
Published: September 2010

Ferroelectricity in ABO3 perovskites driven by A-site disorder is seen as a powerful approach toward lead-free piezoelectrics and ferroelectrics as well as to forming multiferroic compounds. Here we investigate the Ba1−xCaxZrO3 solid solution by structural and dielectric measurements on pulsed laser deposition grown films and by first principles calculations. Films on SrRuO3-coated SrTiO3 substrates are studied for x between 0 and 0.44. Despite the expectation that the Ca-ions assume off-center positions in the perovskite lattice, dielectric measurements show no evidence for ferroelectricity. This behavior is explained by first principles supercell calculations that show ferroelectricity at expanded volume but a rapid suppression thereof as the volume is reduced, thus indicating that our paraelectric Ba1−xCaxZrO3 films are close to a ferroelectric instability. These results demonstrate the important interplay between unit cell volume and ferroelectricity arising from off-centered ions.
Electric current enhanced defect elimination in thermally annealed Bi–Sb–Te and Bi–Se–Te thermoelectric thin films
Authors: Liou K. M. , Liao C. N.
Published: September 2010

An electric-current assisted thermal treatment is demonstrated to be an effective process for eliminating crystal lattice defects and improving thermoelectric properties of both Bi–Sb–Te and Bi–Se–Te nanocrystalline thin films. A model based on electromigration-induced preferential Sb and Te diffusion is proposed to explain the observed Sb-rich and Te precipitation as well as the enhancement of Seebeck coefficient and electrical conductivity of the electrically stressed thin films. Owing to anisotropic diffusion and electrical transport properties, charged lattice defects are preferentially eliminated in the direction parallel to the basal plane of bismuth telluride crystal under electric current stressing. The presented current assisted annealing approach can be an efficient postdeposition treatment that prevents from gross grain growth and evaporation of volatile constituents in Bi–Te based nanocrystalline thin films during high-temperature annealing process.
Radio frequency-compensated Langmuir probe with auxiliary double probes
Authors: Oh Se-Jin , Oh Seung-Ju , Chung Chin-Wook
Published: September 2010

A radio frequency (rf) compensation design using auxiliary double probes connected in parallel with a main measurement probe was developed for Langmuir probe diagnostics. This probe structure can reduce the sheath impedance of the main probe. In our probe design, the sheath capacitance of the probe can be increased and its sheath resistance can be decreased with increasing dc bias differential voltage between the auxiliary double probes. The I-V characteristic curve and electron energy distribution functions measured by our probe system had sufficient rf compensation performance in inductively coupled plasmas.
Spin relaxation due to electron–electron magnetic interaction in high Lande g-factor semiconductors
Authors: Kamra Akashdeep , Ghosh Bahniman , Ghosh Tarun K.
Published: September 2010

We investigate spin transport in InSb/InAlSb heterostructure using the Monte Carlo approach, generalized by including density matrix description of spin for taking spin dynamics into account. In addition to the dominant Dyakonov–Perel (DP) mechanism for spin control and relaxation, we consider magnetic interaction between electrons which assumes importance due to high electronic Lande g-factor in the material. It is found that while the effect of magnetic interaction is not important at low densities, it reduces the spin relaxation length by as much as 50% at higher densities. We also present a calculation which elucidates the suppression of decoherence attributed to wave vector dependent magnetic field in the DP relaxation mechanism. We note that magnetic interaction is a general relaxation mechanism which may assume importance in materials with high electronic Lande g-factor.
Magnetic properties of carbon nanotube poly(ether-ester) nanocomposites
Authors: Glenis S. , Likodimos V. , Guskos N. , Yarmis D. , Zolnierkiewicz G. , Szymczyk A. , Lin C. L.
Published: September 2010

The magnetic and electronic properties of composites consisting of oxidized multiwall carbon nantubes (MWNTs) dispersed in elastomeric poly(ether-ester) segmented block copolymer have been studied by means of electron spin resonance (ESR) and dc magnetization measurements. A marked reduction in the MWNT diamagnetic response is identified, indicative of substantial hole doping related to the oxygen functional groups on the oxidized carbon nanotube’s surface. Both ESR and the static magnetization reveal considerable enhancement of the spin susceptibility due to an excessive increase in the density of paramagnetic defects, which are sensitive to the dynamical polymer relaxation and thus to the MWNT-polymer interfacial coupling.
Photosensitive biosensor array system using optical addressing without an addressing circuit on array biochips
Authors: Ahn Chang-Geun , Ah Chil Seong , Kim Tae-Youb , Park Chan Woo , Yang Jong-Heon , Kim Ansoon , Sung Gun Yong
Published: September 2010

This paper introduces a photosensitive biosensor array system with a simple photodiode array that detects photocurrent changes caused by reactions between probe and target molecules. Using optical addressing, the addressing circuit on the array chip is removed for low-cost application, and real cell addressing is achieved using an externally located computer-controllable light-emitting diode array module. The fabricated biosensor array chip shows a good dynamic range of 1–100 ng/mL under prostate-specific antigen detection, with an on-chip resolution of roughly 1 ng/mL.
Organic solar cells with submicron-thick polymer:fullerene bulk heterojunction films
Authors: Lee Seungsoo , Nam Sungho , Kim Hwajeong , Kim Youngkyoo
Published: September 2010

We report the viability of organic solar cells with submicron-thick bulk heterojunction films, which were fabricated by mixing poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester at a solid concentration of 90 mg/ml. To elucidate the physics behind the thick film solar cells, optical transmittance and electrical characteristics were compared for film thicknesses between 520 and 1000 nm. Results showed that the device (520 nm thick film; efficiency=3.68%) exhibited similar performance to that of a control device (170 nm thick). A decreasing device performance was measured for much thicker films (efficiency=0.34% for the 1000 nm thick device).
Recovery of gas density in a nitrogen gap after breakdown
Authors: Cai Xinjing , Zou Xiaobing , Wang Xinxin , Wang Liming , Guan Zhicheng , Jiang Weihua
Published: September 2010

The recovery of the gas density and the hold-off voltage of a spark gap after breakdown were investigated with Mach–Zehnder interferometry and two-pulse method, respectively. It was shown that the gas density in a 2.7 mm gap filled with atmospheric nitrogen almost fully recovers at t=50 ms but the breakdown voltage of the gap only recovers to its static hold-off voltage, about 21.4% of its original overvolted breakdown voltage. The mechanisms for the delayed recovery of the ability to be overvolted were discussed.
Highly sensitive, low-voltage, organic photomultiple photodetectors exhibiting broadband response
Authors: Chen Fang-Chung , Chien Shang-Chieh , Cious Guan-Lin
Published: September 2010

Highly sensitive polymer photodetectors exhibiting broad spectral responses, ranging from the ultraviolet to the near-infrared (NIR) region, are obtained after incorporating an organic NIR dye into the device active layer. As a result, high external quantum efficiencies (>7000%) and high responsivities (32.4 A/W) are achieved at an extremely low operating voltage (−1.5 V). The high photomultiplation could be attribute to trapping of electrons, originating from the photogenerated electron/hole pairs, at the dye molecules, which effectively facilitates hole injection from the external circuit. The device preparation scheme presented herein opens up the possibility fabricating lost-cost, flexible organic photodetectors.
Binding of a Flexibly-linked Dinuclear Ruthenium(II) Complex to Adenine-bulged DNA Duplexes
Authors: Buck Damian P. , Paul Jacob A. , Pisani Michelle J. , Collins J. Grant , Keene F. Richard
Published: September 2010

Using 1H NMR spectroscopy and molecular modelling, the DNA binding of a chiral dinuclear ruthenium(ii) complex {Δ,Δ-[{Ru(phen)2}2(μ-bb7)]4+; phen = 1,10-phenanthroline, bb7 = 1,7-bis[4(4′-methyl-2,2′-bipyridyl)]-heptane} involving a bridging ligand containing a flexible aliphatic chain has been studied. The binding of the ruthenium(ii) complex was examined with the non-self-complementary duplexes d(CCGAGAATCGGCC):d(GGCCGATTCCGG) (containing a single adenine bulge: designated SB) and d(CCGAGCCGTGCC):d(GGCACGAGCCGG) (containing two adenine bulge sites separated by two base-pairs: designated DB). The NMR data indicated that the ruthenium(ii) complex bound at the bulge site of SB, with one ruthenium centre located at the bulge site with the second metal centre binding with lower affinity and selectivity in the duplex region adjacent to the bulge site. Less specific binding is inferred from chemical shift changes of nucleotide protons two to five base pairs from the single adenine bulge. The ruthenium(ii) complex selectively bound the DB duplex with one metal centre located at each bulge site. The NMR results also suggested that the metal complex binding induced greater changes to the structure of the SB duplex, compared with the DB duplex. Modelling indicates the bridging ligand allowed each ruthenium(ii) metal centre to bind one adenine bulge of the doubly-bulged duplex without disrupting the DNA structure, using the additional torsional flexibility conferred by the aliphatic bridging ligand. However, the second ruthenium(ii) metal centre is not able to bind in the minor groove of the singly-bulged duplex without disrupting the structure, as the metal centre is too bulky. The results of this study suggest dinuclear ruthenium(ii) complexes have considerable potential as probes for DNA and RNA sequences that contain two bulge sites separated by a small number of base-pairs.
Tuning Coordination Environments Through Ligand Redox Chemistry: the Thiol - Disulfide Reaction
Authors: Constable Edwin C. , Housecroft Catherine E. , Neuburger Markus , Price Jason R. , Zampese Jennifer A.
Published: September 2010

Oxidative coupling of 6-(pyridin-2-yl)pyridine-2(1H)-thione yields 1,2-bis(2,2′-bipyridin-6-yl)disulfide (4), which can act as a bis(chelate) to a single zinc(ii) centre. The effects on the solid-state structure of introducing a methyl substituent into each 6-position of 4 have been examined. Ligand 4 functions as a bridging ligand in [Cu2(μ-4)(μ-6)]4+ in which ligand 6 is 1,2-bis(2,2′:6′,2″-terpyridin-4′-yl)disulfide; [Cu2(μ-4)(μ-6)]4+ self-assembles from the components according to the preference shown by copper(ii) for a five-coordinate {Cu(bpy)(tpy)} environment. Reaction of 4 with [Cu(NCMe)4][PF6] leads to a product, tentatively formulated as {[Cu(4)][PF6]}n, which, in air, undergoes oxidation of both copper and ligand to yield [Cu(5)2] (H5 = 2,2′-bipyridine-6-sulfonic acid), the solid state structure of which is presented.
Microfluidic Droplet Technique for In Vitro Directed Evolution
Authors: Wu Nan , Oakeshott John , Brown Sue , Easton Christopher , Zhu Yonggang
Published: September 2010

Increasingly over the past two decades, biotechnologists have been exploiting various molecular technologies for high-throughput screening of genes and their protein products to isolate novel functionalities with a wide range of industrial applications. One particular technology now widely used for these purposes involves directed evolution, an artificial form of evolution in which genes and proteins are evolved towards new or improved functions by imposing intense selection pressures on libraries of mutant genes generated by molecular biology techniques and expressed in heterologous systems such as Escherichia coli. Most recently, the rapid development of droplet-based microfluidics has created the potential to dramatically increase the power of directed evolution by increasing the size of the libraries and the throughput of the screening by several orders of magnitude. Here, we review the methods for generating and controlling droplets in microfluidic systems, and their applications in directed evolution. We focus on the methodologies for cell-based assays, in vitro protein expression and DNA amplification, and the prospects for using such platforms for directed evolution in next-generation biotechnologies.