1,785 research outputs found
Immobilization of Polyethylene Oxide Surfactants for Non-Fouling Biomaterial Surfaces Using an Argon Glow Discharge Treatment
A non-fouling (protein-resistant) polymer surface is achieved by the covalent immobilization of polyethylene oxide (PEO) surfactants using an inert gas discharge treatment. Treated surfaces have been characterized using electron spectroscopy for chemical analysis (ESCA), static secondary ion mass spectrometry (SSIMS), water contact angle measurement, fibrinogen adsorption, and platelet adhesion. This paper is intended to review our recent work in using this simple surface modification process to obtain wettable polymer surfaces in general, and non-fouling biomaterial surfaces in particular
Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor
The band structure of a prototypical dilute ferromagnetic semiconductor,
GaMnAs, is studied across the phase diagram via optical
spectroscopy. We prove that the Fermi energy () resides in a Mn induced
impurity band (IB). This conclusion is based upon careful analysis of the
frequency and temperature dependence of the optical conductivity
(). From our analysis of we infer
a large effective mass () of the carriers, supporting the view that
conduction occurs in an IB. Our results also provide useful insights into the
transport properties of Mn-doped GaAs.Comment: 4 pages, 4 figure
Capping-induced suppression of annealing in Ga(1-x)Mn(x)As epilayers
We have studied the effects of capping ferromagnetic Ga(1-x)Mn(x)As epilayers
with a thin layer of undoped GaAs, and we find that even a few monolayers of
GaAs have a significant effect on the ferromagnetic properties. In particular,
the presence of a capping layer only 10 monolayers thick completely suppresses
the enhancement of the ferromagnetism associated with low temperature
annealing. This result, which demonstrates that the surface of a Ga(1-x)Mn(x)As
epilayer strongly affects the defect structure, has important implications for
the incorporation of Ga(1-x)Mn(x)As into device heterostructures.Comment: 13 pages with figures attatche
Stochastic Ballistic Annihilation and Coalescence
We study a class of stochastic ballistic annihilation and coalescence models
with a binary velocity distribution in one dimension. We obtain an exact
solution for the density which reveals a universal phase diagram for the
asymptotic density decay. By universal we mean that all models in the class are
described by a single phase diagram spanned by two reduced parameters. The
phase diagram reveals four regimes, two of which contain the previously studied
cases of ballistic annihilation. The two new phases are a direct consequence of
the stochasticity. The solution is obtained through a matrix product approach
and builds on properties of a q-deformed harmonic oscillator algebra.Comment: 4 pages RevTeX, 3 figures; revised version with some corrections,
additional discussion and in RevTeX forma
Magnetothermopower and Magnetoresistivity of RuSr2Gd1-xLaxCu2O8 (x=0, 0.1)
We report measurements of magnetothermopower and magnetoresistivity as a
function of temperature on RuSr2Gd1-xLaxCu2O8 (x = 0, 0.1). The normal-state
thermopower shows a dramatic decrease after applying a magnetic field of 5 T,
whereas the resistivity shows only a small change after applying the same
field. Our results suggest that RuO2 layers are conducting and the magnetic
field induced decrease of the overall thermopower is caused by the decrease of
partial thermopower decrease associated with the spin entropy decrease of the
carriers in the RuO2 layers.Comment: 21 pages, 6 figure
The Static and Dynamic Lattice Changes Induced by Hydrogen Adsorption on NiAl(110)
Static and dynamic changes induced by adsorption of atomic hydrogen on the
NiAl(110) lattice at 130 K have been examined as a function of adsorbate
coverage. Adsorbed hydrogen exists in three distinct phases. At low coverages
the hydrogen is itinerant because of quantum tunneling between sites and
exhibits no observable vibrational modes. Between 0.4 ML and 0.6 ML, substrate
mediated interactions produce an ordered superstructure with c(2x2) symmetry,
and at higher coverages, hydrogen exists as a disordered lattice gas. This
picture of how hydrogen interacts with NiAl(110) is developed from our data and
compared to current theoretical predictions.Comment: 36 pages, including 12 figures, 2 tables and 58 reference
Adsorption of Reactive Particles on a Random Catalytic Chain: An Exact Solution
We study equilibrium properties of a catalytically-activated annihilation reaction taking place on a one-dimensional chain of length () in which some segments (placed at random, with mean concentration
) possess special, catalytic properties. Annihilation reaction takes place,
as soon as any two particles land onto two vacant sites at the extremities
of the catalytic segment, or when any particle lands onto a vacant site on
a catalytic segment while the site at the other extremity of this segment is
already occupied by another particle. Non-catalytic segments are inert with
respect to reaction and here two adsorbed particles harmlessly coexist. For
both "annealed" and "quenched" disorder in placement of the catalytic segments,
we calculate exactly the disorder-average pressure per site. Explicit
asymptotic formulae for the particle mean density and the compressibility are
also presented.Comment: AMSTeX, 27 pages + 4 figure
Association of LEC and tnpA Helicobacter pylori genes with gastric cancer in a Brazilian population
<p>Abstract</p> <p>Background</p> <p><it>H. pylori </it>seroprevalence in Brazilians varies and is dependent on socioeconomic status, sanitation conditions and ethnicity; furthermore, <it>H. pylori </it>is not always associated with the incidence of gastric cancer, suggesting the role of more virulent strains. The purpose of this study was to analyze the association of more virulent <it>H. pylori </it>strains with gastric cancer.</p> <p>Methods</p> <p>DNA was extracted from gastric biopsies of thirty-four cases of gastric cancer (11 intestinal-type, 23 diffuse-type), and thirty-four of patients with endoscopic gastritis. The presence of <it>cag</it>PAI genes (<it>cagA</it>, <it>cagA </it>promoter, <it>cagE</it>, <it>cagM</it>, <it>tnpB</it>, <it>tnpA</it>, <it>cagT </it>and the left end of the <it>cag</it>II (LEC)) and <it>babA </it>were analyzed by PCR.</p> <p>Results</p> <p>Comparison of <it>H. pylori </it>isolates from gastric cancer and gastritis patients showed significant associations of <it>tnpA </it>and LEC with gastric cancer (73.5% [OR, 6.66; 95% CI, 2.30-19.25] and 58.8% [OR, 10.71; 95% CI, 3.07-37.28] of cases, respectively). Other <it>cag</it>PAI genes were detected in both groups at similar frequencies.</p> <p>Conclusions</p> <p><it>tnpA </it>and LEC of <it>H. pylori cag</it>PAI were associated with gastric cancer; nonetheless, these results were restricted within this group of patients and further studies are needed to confirm these results in a larger sample and determine their role in gastric carcinogenesis.</p
Reaction Front in an A+B -> C Reaction-Subdiffusion Process
We study the reaction front for the process A+B -> C in which the reagents
move subdiffusively. Our theoretical description is based on a fractional
reaction-subdiffusion equation in which both the motion and the reaction terms
are affected by the subdiffusive character of the process. We design numerical
simulations to check our theoretical results, describing the simulations in
some detail because the rules necessarily differ in important respects from
those used in diffusive processes. Comparisons between theory and simulations
are on the whole favorable, with the most difficult quantities to capture being
those that involve very small numbers of particles. In particular, we analyze
the total number of product particles, the width of the depletion zone, the
production profile of product and its width, as well as the reactant
concentrations at the center of the reaction zone, all as a function of time.
We also analyze the shape of the product profile as a function of time, in
particular its unusual behavior at the center of the reaction zone
Genetic diversity of Bromeliaceae species from the Atlantic Forest
ABSTRACT. The Bromeliaceae family includes a range of species used for many purposes, including ornamental use and use as food, medicine, feed, and fiber. The state of EspÃrito Santo, Brazil is a center of diversity for this family in the Atlantic Forest. We evaluated the genetic diversity of five populations of the Bromeliaceae family, including specimens of the genera Aechmea, Billbergia (subfamily Bromelioideae), and Pitcairnia (subfamily Pitcairnioidea), all found in the Atlantic Forest and distributed in the state of EspÃrito Santo. The number of alleles per locus in populations ranged from two to six and the fixation index (F), estimated for some simple sequence repeats in bromeliad populations, was less than zero in all populations. All markers in the Pitcairnia flammea population were in Hardy-Weinberg equilibrium (P < 0.05). Moreover, significant deviations from Hardy-Weinberg equilibrium were observed at some loci in populations of the five bromeliad species. In most cases, this can be attributed to the presence of inbreeding or the Wahlund effect. The genetic diversity indices of five species showed greater allelic richness in P. flammea (3.55). Therefore, we provide useful information for the characterization of genetic diversity in natural populations of Aechmea ramosa, Aechmea nudicaulis, Billbergia horrid, Billbergia euphemia, and P. flammea in Atlantic Forest remnants in the south of EspÃrito Santo state
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