744 research outputs found
General technique of calculating drift velocity and diffusion coefficient in arbitrary periodic systems
We develop a practical method of computing the stationary drift velocity V
and the diffusion coefficient D of a particle (or a few particles) in a
periodic system with arbitrary transition rates. We solve this problem both in
a physically relevant continuous-time approach as well as for models with
discrete-time kinetics, which are often used in computer simulations. We show
that both approaches yield the same value of the drift, but the difference
between the diffusion coefficients obtained in each of them equals V*V/2.
Generalization to spaces of arbitrary dimension and several applications of the
method are also presented.Comment: 12 pages + 2 figures, RevTeX. Submitted to J. Phys. A: Math. Ge
Hopping motion of lattice gases through nonsymmetric potentials under strong bias conditions
The hopping motion of lattice gases through potentials without
mirror-reflection symmetry is investigated under various bias conditions. The
model of 2 particles on a ring with 4 sites is solved explicitly; the resulting
current in a sawtooth potential is discussed. The current of lattice gases in
extended systems consisting of periodic repetitions of segments with sawtooth
potentials is studied for different concentrations and values of the bias.
Rectification effects are observed, similar to the single-particle case. A
mean-field approximation for the current in the case of strong bias acting
against the highest barriers in the system is made and compared with numerical
simulations. The particle-vacancy symmetry of the model is discussed.Comment: 8 pages (incl. 6 eps figures); RevTeX 3.
Stimuli-responsive local drug molecule delivery to adhered cells in a 3D nanocomposite scaffold
Drug delivery systems capable of providing controlled and localized drug release are a highly important tool in the biomedical field because they can provide site-specific, sustained, and controlled drug release at the place where the drug is most needed, and they allow for significantly lower doses of the drug at other parts of the body, reducing the drug\u2019s potential side effects. In this respect, we describe pH-responsive PMO/alginate nanocomposite (NC) scaffolds with different pH-responsive strengths for controlled local drug delivery applications. To prepare the PMO/alginate NC scaffolds, PMOs were first loaded with anti-cancer molecules and then coated with a non-biopolymer or a biopolymer, after which the PMOs were embedded into an alginate network. We found that drug release from the PMOs was regulated by the pH of the environment and the surface coating of the PMOs due to the different pHdependent levels of electrostatic interactions between all the charged components of the NC scaffolds. The non-biopolymer-coated formulation of the NC scaffold can be utilized to deliver higher dosages of drug molecules directly to cells, while the biopolymer-coated system is useful for slow and prolonged release of drugs and for enhanced cell adhesion. Nonetheless, both systems can be utilized, in particular, to deliver higher dosages of drug molecules directly to cancer cells while delivering less of the drug to healthy cells
Absence of self-averaging in the complex admittance for transport through random media
A random walk model in a one dimensional disordered medium with an
oscillatory input current is presented as a generic model of boundary
perturbation methods to investigate properties of a transport process in a
disordered medium. It is rigorously shown that an admittance which is equal to
the Fourier-Laplace transform of the first-passage time distribution is
non-self-averaging when the disorder is strong. The low frequency behavior of
the disorder-averaged admittance, where , does not coincide with the low frequency behavior of the admittance for any
sample, . It implies that the Cole-Cole plot of
appears at a different position from the Cole-Cole plots of of any
sample. These results are confirmed by Monte-Carlo simulations.Comment: 7 pages, 2 figures, published in Phys. Rev.
Characteristics of ferroelectric-ferroelastic domains in N{\'e}el-type skyrmion host GaVS
GaVS is a multiferroic semiconductor hosting N{\'e}el-type magnetic
skyrmions dressed with electric polarization. At T = 42K, the compound
undergoes a structural phase transition of weakly first-order, from a
non-centrosymmetric cubic phase at high temperatures to a polar rhombohedral
structure at low temperatures. Below T, ferroelectric domains are formed
with the electric polarization pointing along any of the four axes. Although in this material the size and the shape of the
ferroelectric-ferroelastic domains may act as important limiting factors in the
formation of the N{\'e}el-type skyrmion lattice emerging below T=13\:K, the
characteristics of polar domains in GaVS have not been studied yet.
Here, we report on the inspection of the local-scale ferroelectric domain
distribution in rhombohedral GaVS using low-temperature piezoresponse
force microscopy. We observed mechanically and electrically compatible lamellar
domain patterns, where the lamellae are aligned parallel to the (100)-type
planes with a typical spacing between 100 nm-1.2 m. We expect that the
control of ferroelectric domain size in polar skyrmion hosts can be exploited
for the spatial confinement and manupulation of N{\'e}el-type skyrmions
Calidad microbiológica de una fórmula enteral lista para usar
Indexación: ScieloTo determinate and compare the microbiological quality of a ready to use enteral formula (EF): liquid ADN™ during different periods of time. Methods: The study was developed in the Hospital formula-preparing room. Twenty liters of EF were delivered in 40 plastic sterile bottles using aseptic technique, and were maintained at room temperature during 24 hours. Feed samples of 50 ml at time 0 and at 24 hours were obtained and frozen at _70º C, until they were investigated (40 feed samples of EF were cultivated at preparation time 0, and 24 hours). Mesophile count (Me), total coliform (TC) and faecal coliform (FC) bacteria were investigated. The feed samples were analized at the Microbiologic Laboratory of CESMEC. The microbial quality standards (MQS) were at time 0:
< 10² UFC/ml of (Me), and no (TC) and (FC). At 24 hours: < 10³ UFC/ml of (Me), < 10 UFC/ml of (TC) and no (FC).The statistical data analysis was done using Stata program and Z test was used for proportions. The level of p < 0,05 was considered statistically significant. Results: The average of fulfilment (MQS) for liquid ADN™ at time 0, and 24 hours was 100% and 95% (p = 0,3) for Me. TC got 100% fulfilment (MQS) at any time. FC were not detected at any time. Conclusions: Liquid ADN™can be hung during 24 hours at room temperature.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-10182004000400005&nrm=is
Effects of cariprazine on extracellular levels of glutamate, GABA, dopamine, noradrenaline and serotonin in the medial prefrontal cortex in the rat phencyclidine model of schizophrenia studied by microdialysis and simultaneous recordings of locomotor activity
Aberrant glutamatergic, dopaminergic, and GABAergic neurotransmission has been implicated in schizophrenia. Cariprazine reverses the behavioral effects observed in the rat phencyclidine (PCP)-induced model of schizophrenia; however, little is known about its in vivo neurochemistry. The study aims to compare the effects of cariprazine and aripiprazole on PCP-induced changes in the extracellular levels of glutamate, dopamine, serotonin, noradrenaline, and GABA in the rat medial prefrontal cortex (mPFC), and on locomotor activation. Microdialysis was performed in awake rats with probes placed into the mPFC. Rats (n = 7/group) received vehicle (saline), cariprazine (0.05, 0.2, or 0.8 mg/kg), or aripiprazole (3 or 20 mg/kg) via gavage. After 60 min, 5 mg/kg PCP was administered intraperitoneally (i.p.). Samples were taken before drug administration, during pretreatment, and after PCP injection. Locomotor activity recording and microdialysis sampling occurred simultaneously. PCP treatment increased extracellular levels of all the neurotransmitters tested except GABA, for which there were no significant changes. Cariprazine and aripiprazole dose-dependently inhibited the PCP-induced increases of tested neurotransmitters. Overall effects were significant for higher cariprazine doses and both aripiprazole doses for glutamate and noradrenaline, for higher cariprazine doses and 20 mg/kg aripiprazole for dopamine, and for 0.8 mg/kg cariprazine and 20 mg/kg aripiprazole for serotonin and locomotor activity. Both cariprazine and aripiprazole dose-dependently attenuated PCP-induced hyperlocomotion and acute increases in glutamate, dopamine, noradrenaline, and serotonin levels in the mPFC; cariprazine was approximately 5-fold more potent than aripiprazole
A Salt Metathesis Route To Ruthenium Carbene Complex Isomers With Pyridine Dicarboxamide-Derived Chelate Pincer Ligands
Reaction of the doubly deprotonated pyridine 2,6-dicarboxamido ligand (1) with (PCy_3)_2Cl_2 Ru=CHPh (3a) in THF gave a mixture of (lig)(PCy_3)Ru=CHPh isomers (4). The pentane soluble N,N,O-4 isomer was isolated by extraction and characterized by X-ray diffraction. The O,N, O-4 isomer was identified in the residue. Single crystals of the closely related complex (lig)(NHC) Ru=CHPh, O,N,O-5, were obtained from the reaction of 1 with (NHC)(PCy_3)Cl_2Ru=CHPh (3b) and used for the X-ray crystal structure analysis of the system
Comparación entre nutrición enteral precoz y nutrición enteral tardía en el estado nutricional de pacientes gastrectomizados
Indexación: ScieloLa nutrición enteral (NE) es un método efectivo para cubrir los requerimientos nutricionales en pacientes que presentan un estado nutricional deteriorado. Objetivos: Comparar la Nutrición Enteral Precoz (NEP) versus Nutrición Enteral Tardía (NET) en la evolución clínica y nutricional de pacientes sometidos a gastrectomía total por Cáncer Gástrico. Material y Método: 18 pacientes con cáncer gástrico resecable, fueron estudiados con parámetros antropométricos, funcionales y bioquímicos que evalúan el estado nutricional, en el período preoperatorio y postoperatorio. Recibieron una fórmula enteral polimérica (1 kcal/ml) en el período postoperatorio. De manera aleatoria fueron asignados al tipo de nutrición (precoz o tardía). Resultados: El grupo con NEP presentó mejoría significativa del porcentaje de adecuación del pliegue bicipital y dinamometría. El grupo con NET presentó disminución significativa de la albuminemia. La distensión abdominal fue más frecuente en grupo con NEP. Conclusión: La Nutrición Enteral Precoz es un soporte nutricional seguro, eficaz y que trae consigo ventajas nutricionales en comparación con la Nutrición Enteral Tardía en el grupo de pacientes gastrectomizados totales por presentar cáncer gástrico.Enteral nutrition (EN) is an effective method to meet the nutritional requirements in patients who have a deteriorated nutritional status. Objectives: To compare clinical and nutritional performance oftwo groups: Early Enteral Nutrition (EEN) versus Late Enteral Nutrition (LEN) of patients undergoing to total gastrectomy for gastric cancer. Material and Methods: 18 patients with resectable gastric cancer were studied with anthropometric, functional and biochemical parameters to assess nutritional status in the preoperative and postoperative period. They received a polimeric enteral formula (1 kcal/ml) in the postoperative period. They were randomly assigned to the type of nutrition (early or late). Results: The group with EEN had a significant improvement in the bicipital fold adequacy percentage and dynamometry. The LEN group had a significant decrease of albumin. The bloating was more fre quent in the group with EEN. Conclusion: Early enteral nutrition is a safe nutritional support, effective and that brings nutritional benefits compared with late enteral nutrition in patients undergoing to total gastrectomy for gastric cancer.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-75182009000100002&nrm=is
Critical dimensions for random walks on random-walk chains
The probability distribution of random walks on linear structures generated
by random walks in -dimensional space, , is analytically studied
for the case . It is shown to obey the scaling form
, where is
the density of the chain. Expanding in powers of , we find that
there exists an infinite hierarchy of critical dimensions, ,
each one characterized by a logarithmic correction in . Namely, for
, ; for ,
; for , ; for , ; for , , {\it etc.\/} In particular, for
, this implies that the temporal dependence of the probability density of
being close to the origin .Comment: LATeX, 10 pages, no figures submitted for publication in PR
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