Showing papers by "University of South Carolina published in 2004"

Electrophoretic analysis and purification of fluorescent single-walled carbon nanotube fragments.

Abstract: Arc-synthesized single-walled carbon nanotubes have been purified through preparative electrophoresis in agarose gel and glass bead matrixes. Two major impurities were isolated: fluorescent carbon and short tubular carbon. Analysis of these two classes of impurities was done. The methods described may be readily extended to the separation of other water-soluble nanoparticles. The separated fluorescent carbon and short tubule carbon species promise to be interesting nanomaterials in their own right.

Stable recovery of sparse overcomplete representations in the presence of noise

Abstract: Overcomplete representations are attracting interest in signal processing theory, particularly due to their potential to generate sparse representations of signals. However, in general, the problem of finding sparse representations must be unstable in the presence of noise. This paper establishes the possibility of stable recovery under a combination of sufficient sparsity and favorable structure of the overcomplete system. Considering an ideal underlying signal that has a sufficiently sparse representation, it is assumed that only a noisy version of it can be observed. Assuming further that the overcomplete system is incoherent, it is shown that the optimally sparse approximation to the noisy data differs from the optimally sparse decomposition of the ideal noiseless signal by at most a constant multiple of the noise level. As this optimal-sparsity method requires heavy (combinatorial) computational effort, approximation algorithms are considered. It is shown that similar stability is also available using the basis and the matching pursuit algorithms. Furthermore, it is shown that these methods result in sparse approximation of the noisy data that contains only terms also appearing in the unique sparsest representation of the ideal noiseless sparse signal.

Movement Disorder Society Task Force report on the Hoehn and Yahr staging scale: status and recommendations.

Abstract: The Movement Disorder Society Task Force for Rating Scales for Parkinson's disease (PD) prepared a critique of the Hoehn and Yahr scale (HY). Strengths of the HY scale include its wide utilization and acceptance. Progressively higher stages correlate with neuroimaging studies of dopaminergic loss, and high correlations exist between the HY scale and some standardized scales of motor impairment, disability, and quality of life. Weaknesses include the scale's mixing of impairment and disability and its non-linearity. Because the HY scale is weighted heavily toward postural instability as the primary index of disease severity, it does not capture completely impairments or disability from other motor features of PD and gives no information on nonmotor problems. Direct clinimetric testing of the HY scale has been very limited, but the scale fulfills at least some criteria for reliability and validity, especially for the midranges of the scale (Stages 2-4). Although a "modified HY scale" that includes 0.5 increments has been adopted widely, no clinimetric data are available on this adaptation. The Task Force recommends that: (1) the HY scale be used in its original form for demographic presentation of patient groups; (2) when the HY scale is used for group description, medians and ranges should be reported and analysis of changes should use nonparametric methods; (3) in research settings, the HY scale is useful primarily for defining inclusion/exclusion criteria; (4) to retain simplicity, clinicians should "rate what you see" and therefore incorporate comorbidities when assigning a HY stage; and (5) because of the wide usage of the modified HY scale with 0.5 increments, this adaptation warrants clinimetric testing. Without such testing, however, the original five-point scales should be maintained.

Room temperature, high-yield synthesis of multiple shapes of gold nanoparticles in aqueous solution.

Abstract: A seed-mediated growth method was used to control the morphology and dimensions of Au nanocrystals by the manipulation of the experimental parameters in aqueous solution at room temperature. This chemical route produces various structural architectures with rod-, rectangle-, hexagon-, cube-, triangle-, and starlike profiles and branched (such as bi-, tri-, tetra-, and multipod) Au nanocrystals of various dimensions in high yield in the presence of a single surfactant, cetyltrimethylammonium bromide.

Seeded high yield synthesis of short Au nanorods in aqueous solution.

Abstract: Short gold nanorods of average lengths ranging between 20 and 100 nm (with corresponding aspect ratios of 2 and 4) were synthesized in excellent yield (approximately 97%). These nanorods were characterized by dark-field microscopy, UV-visible spectrophotometry, and transmission electron microscopy. Temporal evolution of rod shape had also been followed by UV-visible spectrophotometry and transmission electron microscopy and indicates that the nanorods briefly increase in length, then increase slightly in width, as they grow. The effect of the synthetic parameters on the rod dimension and yield was explored to find out suitable conditions to produce short nanorods; short nanorods have both plasmon bands in the visible region of the spectrum, which is a valuable property for sensor applications.

Seed-Mediated Synthesis of Gold Nanorods: Role of the Size and Nature of the Seed

Abstract: We report studies on the synthesis of gold nanorods by a three-step seeding protocol method using a variety of different gold seeds. The synthetic method is adapted from one we published earlier (Jana et al. J. Phys. Chem. B 2001, 105, 4065). The seeds chosen for these studies have average diameters in the range from 4 to 18 nm, with positively charged as well as negatively charged surface groups. In all the cases, along with a large concentration of long rods, a small number of different shapes such as triangles, hexagons, and small rods are observed. The proportion of small rods increases with an increase in the seed size used for nanorod synthesis. For long nanorods synthesized by different seeds a comparison of various parameters such as length, width, and aspect ratio has been made. A dependence of the nanorod aspect ratio on the size of the seed is observed. Increasing the seed size results in lowering of the gold nanorod aspect ratios for a constant concentration of reagents. The charge on the seed...

Bayesian Survival Analysis

Abstract: Great strides in the analysis of survival data using Bayesian methods have been made in the past ten years due to advances in Bayesian computation and the feasibility of such methods. In this chapter, we review Bayesian advances in survival analysis and discuss the various semiparametric modeling techniques that are now commonly used. We review parametric and semiparametric approaches to Bayesian survival analysis, with a focus on proportional hazards models. Reference to other types of models are also given. Keywords: beta process; Cox model; Dirichlet process; gamma process; Gibbs sampling; piecewise exponential model; Weibull model

Individual Equity Return Data from Thomson Datastream: Handle with Care!

Abstract: We compare individual equity return data from Thomson Datastream (TDS) for one large national equity market, the United States, to the source most often used by academics, the Center for Research in Security Prices (CRSP) for the period 1975-2002. Our purpose is not to advocate for the use of a particular source of U.S. equity data but to evaluate the suitability of TDS for use in studies involving large numbers of individual equities in markets outside the U.S. We discover important issues of coverage, classification, and data integrity and find that naive use of TDS data can have a large impact on economic inferences, particularly earlier in the period of coverage and among smaller stocks. We show that after careful screening of the TDS data that although differences still remain, inferences drawn from TDS data are similar to those drawn from CRSP. We also apply our screens to a sample of four European equity markets and show that screening the data has a measurable impact on the time series of country portfolio returns.

The Neglect of Power in Recent Framing Research

Abstract: This article provides a critique of recent developments in research examining media frames and their influence. We contend that a number of trends in framing research have neglected the relationship between media frames and broader issues of political and social power. This neglect is a product of a number of factors, including conceptual problems in the definition of frames, the inattention to frames sponsorship, the failure to examine framing contests within wider political and social contexts, and the reduction of framing to a form of media effects. We conclude that framing research needs to be linked to the political and social questions regarding power central to the media hegemony thesis, and illustrate this focus by exploring how framing research can contribute to an understanding of the interaction between social movements and the news media. Examinations of the production, character, and influence of news stories represent an enduring focus of media scholarship. A variety of approaches, including gatekeeping, agenda setting, organizational studies of news work, and analyses of news bias, have explored either the gathering of news or journalism’s political role. In recent decades, a rapidly expanding research literature on news frames has sought to provide a comprehensive perspective on the production, reception, and influence of news texts. This article provides a critique of recent developments in research examining media frames and their influence. We contend that a number of trends in framing research have neglected the relationship between media frames and broader issues of political and social power. This neglect is a product of conceptual problems in the definition of frames, the inattention to frame sponsorship, the failure to examine framing contests within wider political and social contexts, and the reduction of framing to a form of media effects. In keeping with early sociological research on framing (Gitlin, 1980; Tuchman, 1978), we suggest that framing processes need to be examined within the contexts of the distribution of political and social power. We, therefore, call for the integration of framing research with the

Development of First Principles Capacity Fade Model for Li-Ion Cells

Abstract: A first principles-based model has been developed to simulate the capacity fade of Li-ion batteries. Incorporation of a continuous occurrence of the solvent reduction reaction during constant current and constant voltage (CC-CV) charging explains the capacity fade of the battery. The effect of parameters such as end of charge voltage and depth of discharge, the film resistance, the exchange current density, and the over voltage of the parasitic reaction on the capacity fade and battery performance were studied qualitatively. The parameters that were updated for every cycle as a result of the side reaction were state-of-charge of the electrode materials and the film resistance, both estimated at the end of CC-CV charging. The effect of rate of solvent reduction reaction and the conductivity of the film formed were also studied. © 2004 The Electrochemical Society. All rights reserved.

Simple non-invasive assessment of advanced glycation endproduct accumulation

Abstract: Aims/hypothesis The accumulation of AGE is thought to play a role in the pathogenesis of chronic complications of diabetes mellitus and renal failure. All current measurements of AGE accumulation require invasive sampling. We exploited the fact that several AGE exhibit autofluorescence to develop a non-invasive tool for measuring skin AGE accumulation, the Autofluorescence Reader (AFR). We validated its use by comparing the values obtained using the AFR with the AGE content measured in extracts from skin biopsies of diabetic and control subjects.

Defining Accelerometer Thresholds for Activity Intensities in Adolescent Girls

Abstract: Purpose To derive a regression equation that estimates metabolic equivalent (MET) from accelerometer counts, and to define thresholds of accelerometer counts that can be used to delineate sedentary, light, moderate, and vigorous activity in adolescent girls.

Physical Activity Among Children Attending Preschools

Abstract: Objectives. Obesity rates are increasing among children of all ages, and reduced physical activity is a likely contributor to this trend. Little is known about the physical activity behavior of preschool-aged children or about the influence of preschool attendance on physical activity. The purpose of this study was to describe the physical activity levels of children while they attend preschools, to identify the demographic factors that might be associated with physical activity among those children, and to determine the extent to which children9s physical activity varies among preschools. Methods. A total of 281 children from 9 preschools wore an Actigraph (Fort Walton Beach, FL) accelerometer for an average of 4.4 hours per day for an average of 6.6 days. Each child9s height and weight were measured, and parents of participating children provided demographic and education data. Results. The preschool that a child attended was a significant predictor of vigorous physical activity (VPA) and moderate-to-vigorous physical activity (MVPA). Boys participated in significantly more MVPA and VPA than did girls, and black children participated in more VPA than did white children. Age was not a significant predictor of MVPA or VPA. Conclusions. Children9s physical activity levels were highly variable among preschools, which suggests that preschool policies and practices have an important influence on the overall activity levels of the children the preschools serve.

Gravitational vacuum condensate stars

Abstract: A new final state of gravitational collapse is proposed By extending the concept of Bose–Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate pv = -ρv and an exterior Schwarzschild geometry of arbitrary total mass M is constructed These regions are separated by a shell with a small but finite proper thickness l of fluid with equation of state p = +ρ, replacing both the Schwarzschild and de Sitter classical horizons The new solution has no singularities, no event horizons, and a global time Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of the order kBlMc/, instead of the Bekenstein–Hawking entropy formula, SBH = 4πkBGM2/c Hence, unlike black holes, the new solution is thermodynamically stable and has no information paradox

Adaptive Finite Element Methods with convergence rates

Abstract: Adaptive Finite Element Methods for numerically solving elliptic equations are used often in practice. Only recently [12], [17] have these methods been shown to converge. However, this convergence analysis says nothing about the rates of convergence of these methods and therefore does, in principle, not guarantee yet any numerical advantages of adaptive strategies versus non-adaptive strategies. The present paper modifies the adaptive method of Morin, Nochetto, and Siebert [17] for solving the Laplace equation with piecewise linear elements on domains in ℝ2 by adding a coarsening step and proves that this new method has certain optimal convergence rates in the energy norm (which is equivalent to the H1 norm). Namely, it is shown that whenever s>0 and the solution u is such that for each n≥1, it can be approximated to accuracy O(n−s) in the energy norm by a continuous, piecewise linear function on a triangulation with n cells (using complete knowledge of u), then the adaptive algorithm constructs an approximation of the same type with the same asymptotic accuracy while using only information gained during the computational process. Moreover, the number of arithmetic computations in the proposed method is also of order O(n) for each n≥1. The construction and analysis of this adaptive method relies on the theory of nonlinear approximation.

Research on Assessment of Life Satisfaction of Children and Adolescents

Abstract: Over the years, various psychologists have issued calls for greater attention to a science of positive psychology, which focuses on studying conditions that promote optimal human and societal development. Recent calls (e.g., McCullough and Snyder, 2000; Seligman and Csikszentmihalyi, 2000) have furthered interest in studies of the nature and determinants of the good life. Such a science, along with the creation of prevention and intervention programs informed by the expanded scientific framework, is expected to improve the quality of life for all individuals, not just individuals who are at risk or who already demonstrate psychopathological conditions. To contrast with the previous emphasis on psychopathology, the development of a positive psychology requires constructs and measures that reflect the full range of human functioning, incorporating indicators of high levels of wellness as well as psychopathological functioning. This article discusses one such construct, life satisfaction, that has been studied extensively in adulthood (see Diener et al., 1999), but which has only recently gained attention with children and adolescents (see Bender, 1997; Huebner, 1997). This article reviews life satisfaction assessment research with children and adolescents, specifically with regard to construct validity. In doing so, the following areas are addressed: models of life satisfaction; convergent validity; discriminant validity; relationships with other well-being measures; relationships with external, environmental circumstances; relationships with demographic variables; cultural factors; group differences on life satisfaction measures; predictive relationships; and stability of life satisfaction reports. Conclusions regarding the validity of the life satisfaction construct are formulated. Recommendations for future research are also discussed.

Dietary carbohydrate (amount and type) in the prevention and management of diabetes: a statement by the american diabetes association.

Abstract: Diabetes has long been viewed as a disorder of carbohydrate metabolism due to its hallmark feature of hyperglycemia. Indeed, hyperglycemia is the cause of the acute symptoms associated with diabetes such as polydypsia, polyuria, and polyphagia (1). The long-term complications (retinopathy, nephropathy, and neuropathy) associated with diabetes are also believed to result from chronically elevated blood glucose levels (2–6). In addition, hyperglycemia may contribute to the development of macrovascular disease, which is associated with the development of coronary artery disease, the leading cause of death in individuals with diabetes (7–9). Thus, a primary goal in the management of diabetes is the regulation of blood glucose to achieve near-normal blood glucose. Blood glucose concentration following a meal is determined by the rate of appearance of glucose into the blood stream (absorption) and its clearance/disappearance from the circulation (10). The rate of disappearance of glucose is largely influenced by insulin secretion and its action on target tissues (11). The component of the diet that has the greatest influence on blood glucose is carbohydrate. Other macronutrients in the diet, i.e., fat and protein, can influence the postprandial blood glucose level, however. For example, dietary fat slows glucose absorption, delaying the peak glycemic response to the ingestion of a food that contains glucose (12–14). In addition, although glucose is the primary stimulus for insulin release, protein/amino acids augment insulin release when ingested with carbohydrate, thereby increasing the clearance of glucose from the blood (15–17). Both the quantity and the type or source of carbohydrate found in foods influence postprandial glucose level (18,19). Although most experts agree that the total carbohydrate intake from a meal or snack is a relatively reliable predictor of postprandial blood glucose (18,20–22), the impact …

Oxoiron(IV) in chloroperoxidase compound II is basic: implications for P450 chemistry.

Abstract: With the use of x-ray absorption spectroscopy, we have found that the Fe-O bond in chloroperoxidase compound II (CPO-II) is much longer than expected for an oxoiron(IV) (ferryl) unit; notably, the experimentally determined bond length of 1.82(1) A accords closely with density functional calculations on a protonated ferryl (Fe^(IV)-OH, 1.81 A). The basicity of the CPO-II ferryl [pK_a > 8.2 (where K_a is the acid dissociation constant)] is attributable to strong electron donation by the axial thiolate. We suggest that the CPO-II protonated ferryl is a good model for the rebound intermediate in the P450 oxygenation cycle; with elevated pK_a values after one-electron reduction, thiolate-ligated ferryl radicals are competent to oxygenate saturated hydrocarbons at potentials that can be tolerated by folded polypeptide hosts.

Transformation of Dissolved and Particulate Materials on Continental Shelves Influenced by Large Rivers: Plume Processes

Abstract: The world's ten largest rivers transport approximately 40% of the fresh water and particulate materials entering the ocean. The impact of large rivers is important on a regional/continental scale (e.g. the Mississippi drains ∼40% of the conterminous US and carries approximately 65% of all the suspended solids and dissolved solutes that enter the ocean from the US) and on a global scale (e.g. the Amazon River annually supplies approximately 20% of all the freshwater that enters the ocean; e.g. approximately 85% of all sedimenting organic carbon in the ocean accumulates in coastal margin regions). River plume processes are affected by a suite of complex factors that are not fully understood. It is clear however, that the composition, concentration and delivery of terrestrial materials by large rivers cannot be understood by simply scaling up the magnitudes and impacts of dominant processes in smaller rivers. Because of high rates of particulate and water discharge, the estuarine processes associated with major rivers usually take place on the adjacent continental shelf instead of in a physically confined estuary. This influences the magnitude and selectivity of processes that transform, retain or export terrestrial materials. Buoyancy is a key mediating factor in transformation processes in the coastal margin. In this paper we review and synthesize current understanding of the transformation processes of dissolved and particulate organic and inorganic materials associated with large river (buoyant) plumes. Chemical and biological activities are greatly enhanced by the changed physical and optical environment within buoyant plumes. Time and space scales over which these transformation processes occur vary greatly, depending on factors such as scales of discharge, suspended sediment loads, light and temperature. An adequate understanding of transformation processes in these highly dynamic, buoyancy-driven systems is lacking. In this paper, we review the biogeochemical processes that occur in large river plumes.

Efficacy of an HIV Prevention Intervention for African American Adolescent Girls: A Randomized Controlled Trial

Abstract: ContextAfrican American adolescent girls are at high risk for human immunodeficiency virus (HIV) infection, but interventions specifically designed for this population have not reduced HIV risk behaviors.ObjectiveTo evaluate the efficacy of an intervention to reduce sexual risk behaviors, sexually transmitted diseases (STDs), and pregnancy and enhance mediators of HIV-preventive behaviors.Design, Setting, and ParticipantsRandomized controlled trial of 522 sexually experienced African American girls aged 14 to 18 years screened from December 1996 through April 1999 at 4 community health agencies. Participants completed a self-administered questionnaire and an interview, demonstrated condom application skills, and provided specimens for STD testing. Outcome assessments were made at 6- and 12-month follow-up.InterventionAll participants received four 4-hour group sessions. The intervention emphasized ethnic and gender pride, HIV knowledge, communication, condom use skills, and healthy relationships. The comparison condition emphasized exercise and nutrition.Main Outcome MeasuresThe primary outcome measure was consistent condom use, defined as condom use during every episode of vaginal intercourse; other outcome measures were sexual behaviors, observed condom application skills, incident STD infection, self-reported pregnancy, and mediators of HIV-preventive behaviors.ResultsRelative to the comparison condition, participants in the intervention reported using condoms more consistently in the 30 days preceding the 6-month assessment (unadjusted analysis, intervention, 75.3% vs comparison, 58.2%) and the 12-month assessment (unadjusted analysis, intervention, 73.3% vs comparison, 56.5%) and over the entire 12-month period (adjusted odds ratio, 2.01; 95% confidence interval [CI], 1.28-3.17; P = .003). Participants in the intervention reported using condoms more consistently in the 6 months preceding the 6-month assessment (unadjusted analysis, intervention, 61.3% vs comparison, 42.6%), at the 12-month assessment (unadjusted analysis, intervention, 58.1% vs comparison, 45.3%), and over the entire 12-month period (adjusted odds ratio, 2.30; 95% CI, 1.51-3.50; P<.001). Using generalized estimating equation analyses over the 12-month follow-up, adolescents in the intervention were more likely to use a condom at last intercourse, less likely to have a new vaginal sex partner in the past 30 days, and more likely to apply condoms to sex partners and had better condom application skills, a higher percentage of condom-protected sex acts, fewer unprotected vaginal sex acts, and higher scores on measures of mediators. Promising effects were also observed for chlamydia infections and self-reported pregnancy.ConclusionInterventions for African American adolescent girls that are gender-tailored and culturally congruent can enhance HIV-preventive behaviors, skills, and mediators and may reduce pregnancy and chlamydia infection.

Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch

Abstract: In the present-day climate, surface water salinities are low in the western tropical Pacific Ocean and increase towards the eastern part of the basin. The salinity of surface waters in the tropical Pacific Ocean is thought to be controlled by a combination of atmospheric convection, precipitation, evaporation and ocean dynamics, and on interannual timescales significant variability is associated with the El Nino/Southern Oscillation cycles. However, little is known about the variability of the coupled ocean-atmosphere system on timescales of centuries to millennia. Here we combine oxygen isotope and Mg/Ca data from foraminifers retrieved from three sediment cores in the western tropical Pacific Ocean to reconstruct Holocene sea surface temperatures and salinities in the region. We find a decrease in sea surface temperatures of approximately 0.5 degrees C over the past 10,000 yr, whereas sea surface salinities decreased by approximately 1.5 practical salinity units. Our data imply either that the Pacific basin as a whole has become progressively less salty or that the present salinity gradient along the Equator has developed relatively recently.

Key factors in the rising cost of new drug discovery and development

Abstract: The public desire for new therapies, their increasing cost and the increased role of government as a payer for innovative new drugs all converge on the issue of the rapidly rising cost of new drug development — now thought to be greater than US $800 million — and highlight the necessity for an efficient use of resources. With this in mind, here we review studies on the cost of developing new drugs and consider how this cost has, and could be, affected by the changing environment for pharmaceutical research and development.

Theory and research on desistance from antisocial activity among serious adolescent offenders

Abstract: Improving juvenile court decision making requires information about how serious adolescent offenders desist from antisocial activity. A systematic research agenda on this topic requires consideration of several processes, including normative development in late adolescence, what constitutes desistance, and the factors likely to promote the end of involvement in antisocial behavior and successful adjustment in early adulthood. This article presents an overview of the major points to consider in pursuing this research agenda.

Reversion of CTL escape-variant immunodeficiency viruses in vivo.

Abstract: Engendering cytotoxic T-lymphocyte (CTL) responses is likely to be an important goal of HIV vaccines. However, CTLs select for viral variants that escape immune detection. Maintenance of such escape variants in human populations could pose an obstacle to HIV vaccine development. We first observed that escape mutations in a heterogeneous simian immunodeficiency virus (SIV) isolate were lost upon passage to new animals. We therefore infected macaques with a cloned SIV bearing escape mutations in three immunodominant CTL epitopes, and followed viral evolution after infection. Here we show that each mutant epitope sequence continued to evolve in vivo, often re-establishing the original, CTL-susceptible sequence. We conclude that escape from CTL responses may exact a cost to viral fitness. In the absence of selective pressure upon transmission to new hosts, these original escape mutations can be lost. This suggests that some HIV CTL epitopes will be maintained in human populations.