2,570 research outputs found
Transport Properties of Highly Aligned Polymer Light-Emitting-Diodes
We investigate hole transport in polymer light-emitting-diodes in which the
emissive layer is made of liquid-crystalline polymer chains aligned
perpendicular to the direction of transport. Calculations of the current as a
function of time via a random-walk model show excellent qualitative agreement
with experiments conducted on electroluminescent polyfluorene demonstrating
non-dispersive hole transport. The current exhibits a constant plateau as the
charge carriers move with a time-independent drift velocity, followed by a long
tail when they reach the collecting electrode. Variation of the parameters
within the model allows the investigation of the transition from non-dispersive
to dispersive transport in highly aligned polymers. It turns out that large
inter-chain hopping is required for non-dispersive hole transport and that
structural disorder obstructs the propagation of holes through the polymer
film.Comment: 4 pages, 5 figure
Application of a single-objective, hybrid genetic algorithm approach to pharmacokinetic model building.
A limitation in traditional stepwise population pharmacokinetic model building is the difficulty in handling interactions between model components. To address this issue, a method was previously introduced which couples NONMEM parameter estimation and model fitness evaluation to a single-objective, hybrid genetic algorithm for global optimization of the model structure. In this study, the generalizability of this approach for pharmacokinetic model building is evaluated by comparing (1) correct and spurious covariate relationships in a simulated dataset resulting from automated stepwise covariate modeling, Lasso methods, and single-objective hybrid genetic algorithm approaches to covariate identification and (2) information criteria values, model structures, convergence, and model parameter values resulting from manual stepwise versus single-objective, hybrid genetic algorithm approaches to model building for seven compounds. Both manual stepwise and single-objective, hybrid genetic algorithm approaches to model building were applied, blinded to the results of the other approach, for selection of the compartment structure as well as inclusion and model form of inter-individual and inter-occasion variability, residual error, and covariates from a common set of model options. For the simulated dataset, stepwise covariate modeling identified three of four true covariates and two spurious covariates; Lasso identified two of four true and 0 spurious covariates; and the single-objective, hybrid genetic algorithm identified three of four true covariates and one spurious covariate. For the clinical datasets, the Akaike information criterion was a median of 22.3 points lower (range of 470.5 point decrease to 0.1 point decrease) for the best single-objective hybrid genetic-algorithm candidate model versus the final manual stepwise model: the Akaike information criterion was lower by greater than 10 points for four compounds and differed by less than 10 points for three compounds. The root mean squared error and absolute mean prediction error of the best single-objective hybrid genetic algorithm candidates were a median of 0.2 points higher (range of 38.9 point decrease to 27.3 point increase) and 0.02 points lower (range of 0.98 point decrease to 0.74 point increase), respectively, than that of the final stepwise models. In addition, the best single-objective, hybrid genetic algorithm candidate models had successful convergence and covariance steps for each compound, used the same compartment structure as the manual stepwise approach for 6 of 7 (86 %) compounds, and identified 54 % (7 of 13) of covariates included by the manual stepwise approach and 16 covariate relationships not included by manual stepwise models. The model parameter values between the final manual stepwise and best single-objective, hybrid genetic algorithm models differed by a median of 26.7 % (q₁ = 4.9 % and q₃ = 57.1 %). Finally, the single-objective, hybrid genetic algorithm approach was able to identify models capable of estimating absorption rate parameters for four compounds that the manual stepwise approach did not identify. The single-objective, hybrid genetic algorithm represents a general pharmacokinetic model building methodology whose ability to rapidly search the feasible solution space leads to nearly equivalent or superior model fits to pharmacokinetic data
Relationship between Secondary Metabolites, Antiradical Activities, and Colour Characteristics of Cochlospermum Tinctorium A. Rich. (Bixaceae) Root
Cochlospermum tinctorium A. Rich. (Bixaceae) is a widespread herbaceous plant in the African sahelian and soudanian zones. Its root is used as food and medicinal plant. Studies of secondary metabolites, functional activities and trichromatic parameters were realized according to standard methods of laboratory. At a threshold of α = 0.05, significant correlations (p < 0.05) were found between secondary metabolites contents and functional activities such as radical scavenging activity of antioxidant component or hydroxyl radical scavenging activity. The value of DPPHH was 95.56 ± 0.94% for CT inner Matrix with variation of 0.12% for CT Soaked inner Matrix and 1.63% for CT Peeler. But HSRA was 37.14 ± 5.71 for CT inner Matrix with variation of -38.46% for CT Soaked inner Matrix and -71.79% for CT Peeler. Cochlospermum tinctorium root has exhibited efficiency to heal many diseases thanks to multiple bioactive compounds. In addition, the colour of powders depended upon chemical compounds. Finally, Cochlospermum tinctorium root was found to neutralize organic radicals and reactive oxygen species
Quantitative analysis of single particle trajectories: mean maximal excursion method
An increasing number of experimental studies employ single particle tracking
to probe the physical environment in complex systems. We here propose and
discuss new methods to analyze the time series of the particle traces, in
particular, for subdiffusion phenomena. We discuss the statistical properties
of mean maximal excursions, i.e., the maximal distance covered by a test
particle up to time t. Compared to traditional methods focusing on the mean
squared displacement we show that the mean maximal excursion analysis performs
better in the determination of the anomalous diffusion exponent. We also
demonstrate that combination of regular moments with moments of the mean
maximal excursion method provides additional criteria to determine the exact
physical nature of the underlying stochastic subdiffusion processes. We put the
methods to test using experimental data as well as simulated time series from
different models for normal and anomalous dynamics, such as diffusion on
fractals, continuous time random walks, and fractional Brownian motion.Comment: 10 pages, 7 figures, 2 tables. NB: Supplementary material may be
found in the downloadable source file
Scaling relation for determining the critical threshold for continuum percolation of overlapping discs of two sizes
We study continuum percolation of overlapping circular discs of two sizes. We
propose a phenomenological scaling equation for the increase in the effective
size of the larger discs due to the presence of the smaller discs. The critical
percolation threshold as a function of the ratio of sizes of discs, for
different values of the relative areal densities of two discs, can be described
in terms of a scaling function of only one variable. The recent accurate Monte
Carlo estimates of critical threshold by Quintanilla and Ziff [Phys. Rev. E, 76
051115 (2007)] are in very good agreement with the proposed scaling relation.Comment: 4 pages, 3 figure
Are we providing patient-centered care? Preferences about paracentesis and thoracentesis procedures
Procedures performed at the bedside are as safe and less expensive than Interventional Radiology (IR) procedures. Patient preferences regarding location are rarely taken into account. Therefore, in this study we compared patient satisfaction with bedside and IR paracentesis and thoracentesis procedures, and identified reasons for patient location preferences. We performed a cross-sectional survey of medical inpatients undergoing paracentesis or thoracentesis procedures at a tertiary care academic medical center. The survey had eight domains: overall experience, pain control, expertise, courtesy, bedside manner of the physician, time required, explanation of risks/benefits, comfort and privacy. Patients were also asked about their preference for procedure location.
Two hundred and twenty surveys (162 paracentesis and 58 thoracentesis) were completed on 152 patients. Patient satisfaction was similar for bedside and IR procedures across all domains. A location preference was expressed in 151 surveys (68.6%). Thirty-five of 108 responses (32.4%) from patients with a paracentesis expressed a preference for bedside procedures while 73/108 (67.6%) responses expressed a preference for IR. Twenty-eight of 43 responses (65.1%) from patients with a thoracentesis expressed a preference for bedside procedures while 15/43 (34.9%) responses expressed a preference for IR. Comfort was listed as the most common reason for preferring the bedside while specialized equipment and safety were the most common reasons for preferring IR. Patients are equally and highly satisfied with bedside and IR paracentesis and thoracentesis procedures. Because both approaches are safe and effective, clinicians should pursue informed discussions with patients when a choice is available
Electrical transport and percolation in magnetoresistive manganite / insulating oxide composites: case of La0.7Ca0.3MnO3 / Mn3O4
We report the results of electrical resistivity measurements carried out on
well-sintered La0.7Ca0.3MnO3 / Mn3O4 composite samples with almost constant
composition of the magnetoresistive manganite phase (La0.7Ca0.3MnO3). A
percolation threshold (fc) occurs when the La0.7Ca0.3MnO3 volume fraction is ~
0.19. The dependence of the electrical resistivity as a function of
La0.7Ca0.3MnO3 volume fraction (fLCMO) can be described by percolation-like
phenomenological equations. Fitting the conducting regime (fLCMO > fc) by the
percolation power law returns a critical exponent t value of 2.0 +/- 0.2 at
room temperature and 2.6 +/-0.2 at 5 K. The increase of t is ascribed to the
influence of the grain boundaries on the electrical conduction process at low
temperature.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
A continuous time random walk model for financial distributions
We apply the formalism of the continuous time random walk to the study of
financial data. The entire distribution of prices can be obtained once two
auxiliary densities are known. These are the probability densities for the
pausing time between successive jumps and the corresponding probability density
for the magnitude of a jump. We have applied the formalism to data on the US
dollar/Deutsche Mark future exchange, finding good agreement between theory and
the observed data.Comment: 14 pages, 5 figures, revtex4, submitted for publicatio
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