121 research outputs found
Disorder-induced superconductivity in ropes of carbon nanotubes
We study the interplay between disorder and superconductivity in a rope of
metallic carbon nanotubes. Based on the time dependent Ginzburg Landau theory,
we derive the superconducting transition temperature T taking into account
the critical superconducting fluctuations which are expected to be
substantially strong in such low dimensional systems. Our results indicate
that, contrary to what is expected, T increases by increasing the amount of
disorder. We argue that this behavior is due to the dynamics of the tubes which
reduces the drastic effect of the local disorder on superconductivity by
enhancing the intertube Josephson tunneling. We also found that T is
enhanced as the effective dimensionality of the rope increases by increasing
the number N of the tubes forming the rope. However, T tends to saturate
for large values of N, expressing the establishment of a bulk three dimensional
(3D) superconducting order.Comment: 9 pages, 4 figur
Antiferromagnetic Excitations and Van Hove Singularities in YBaCuO
We show that in quasi-two-dimensional -wave superconductors Van Hove
singularities close to the Fermi surface lead to novel magnetic quasi-particle
excitations. We calculate the temperature and doping dependence of dynamical
magnetic susceptibility for YBCO and show that the proposed excitations are in
agreement with inelastic neutron scattering experiments. In addition, the
values of the gap parameter and in-plane antiferromagnetic coupling are much
smaller than usually believed.Comment: REVTeX, 4 pages + 3 PostScript (compressed) figures; to appear in
Phys. Rev. B (Rap. Comm.
Velocity autocorrelation function of a Brownian particle
In this article, we present molecular dynamics study of the velocity
autocorrelation function (VACF) of a Brownian particle. We compare the results
of the simulation with the exact analytic predictions for a compressible fluid
from [6] and an approximate result combining the predictions from hydrodynamics
at short and long times. The physical quantities which determine the decay were
determined from separate bulk simulations of the Lennard-Jones fluid at the
same thermodynamic state point.We observe that the long-time regime of the VACF
compares well the predictions from the macroscopic hydrodynamics, but the
intermediate decay is sensitive to the viscoelastic nature of the solvent.Comment: 7 pages, 6 figure
Effect of growth stages on phenolics content and antioxidant activities of shoots in sweet marjoram (Origanum majorana L.) varieties under salt stress
We investigated the contributions of salinity and development stage on total polyphenols, flavonoids, condensed tannins contents, phenolic content, 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide scavenging activities at three phenolic stages: early vegetative stage (EVS), late or prefloral vegetative (LVS) stage and flowering stage (FS). The total phenolic, flavonoids and condensed tannins contents were more important in the presence and absence of salt at prefloral or building stage than at EVS and FS. In addition, salt stress increased total polyphenol and individual phenolic contents in shoots of Origanum majorana. This increase was more important in LVS than in EVS and FS. Moreover, the antiradical activity of the shoots (DPPH) decreased with the addition of NaCl. In fact, LVS extracts showed the highest antioxidant properties. Furthermore, at LVS, marjoram grown at 75 mM showed a higher antiradical ability against DPPH radical and antioxidant activity, compared to EVS and LVS. Data reported here revealed the variation of phenolic compound contents at different stages of growth of O. majorana, and the possible role of these changes in the response of the plant to salt was also discussed.Key words: Antiradical activity, Origanum majorana, early vegetative stage (EVS), late or prefloral vegetative (LVS) stage and flowering stage (FS), phenolic content
Aquaporin-3 Re-Expression Induces Differentiation in a Phospholipase D2-Dependent Manner in Aquaporin-3-Knockout Mouse Keratinocytes
Aquaporin-3 (AQP3) is a water and glycerol channel expressed in epidermal keratinocytes. Despite many studies, controversy remains about the role of AQP3 in keratinocyte differentiation. Previously, our laboratory has shown co-localization of AQP3 and phospholipase D2 (PLD2) in caveolin-rich membrane microdomains. We hypothesized that AQP3 transports glycerol and “funnels” this primary alcohol to PLD2 to form a pro-differentiative signal, such that the action of AQP3 to induce differentiation should require PLD2. To test this idea, we re-expressed AQP3 in mouse keratinocytes derived from AQP3-knockout mice. The re-expression of AQP3, which increased [3H]glycerol uptake, also induced mRNA and protein expression of epidermal differentiation markers such as keratin 1, keratin 10, and loricrin, with or without the induction of differentiation by an elevated extracellular calcium concentration. Re-expression of AQP3 had no effect on the expression of the proliferation markers keratin 5 and cyclin D1. Furthermore, a selective inhibitor of PLD2, CAY10594, and a lipase-dead (LD) PLD2 mutant, but not a LD PLD1 mutant, significantly inhibited AQP3 re-expression–induced differentiation marker expression with calcium elevation, suggesting a role for PLD2 in this process. Thus, our results indicate that AQP3 has a pro-differentiative role in epidermal keratinocytes and that PLD2 activity is necessary for this effect
Inhomogeneous superconductivity in organic conductors: role of disorder and magnetic field
Several experimental studies have shown the presence of spatially
inhomogeneous phase coexistence of superconducting and non superconducting
domains in low dimensional organic superconductors. The superconducting
properties of these systems are found to be strongly dependent on the amount of
disorder introduced in the sample regardless of its origin. The suppression of
the superconducting transition temperature shows clear discrepancy with
the result expected from the Abrikosov-Gor'kov law giving the behavior of
with impurities. Based on the time dependent Ginzburg-Landau theory, we derive
a model to account for the striking feature of in organic superconductors
for different types of disorder by considering the segregated texture of the
system. We show that the calculated quantitatively agrees with
experiments. We also focus on the role of superconducting fluctuations on the
upper critical fields of layered superconductors showing slab
structure where superconducting domains are sandwiched by non-superconducting
regions. We found that may be strongly enhanced by such fluctuations.Comment: to appear in Journal of Physics: Condensed Matte
Human Immunodeficiency Virus (HIV) Infection and Use of Illicit Substances Promote Secretion of Semen Exosomes that Enhance Monocyte Adhesion and Induce Actin Reorganization and Chemotactic Migration
Semen exosomes (SE) from HIV-uninfected (HIV−) individuals potently inhibit HIV infection in vitro. However, morphological changes in target cells in response to SE have not been characterized or have the effect of HIV infection or the use of illicit substances, specifically psychostimulants, on the function of SE been elucidated. The objective of this study was to evaluate the effect of HIV infection, psychostimulant use, and both together on SE-mediated regulation of monocyte function. SE were isolated from semen of HIV− and HIV-infected (HIV+) antiretroviral therapy (ART)-naive participants who reported either using or not using psychostimulants. The SE samples were thus designated as HIV−Drug−, HIV−Drug+, HIV+Drug−, and HIV+Drug+. U937 monocytes were treated with different SEs and analyzed for changes in transcriptome, morphometrics, actin reorganization, adhesion, and chemotaxis. HIV infection and/or use of psychostimulants had minimal effects on the physical characteristics of SE. However, different SEs had diverse effects on the messenger RNA signature of monocytes and rapidly induced monocyte adhesion and spreading. SE from HIV infected or psychostimulants users but not HIV−Drug− SE, stimulated actin reorganization, leading to the formation of filopodia-like structures and membrane ruffles containing F-actin and vinculin that in some cases were colocalized. All SE stimulated monocyte chemotaxis to HIV secretome and activated the secretion of matrix metalloproteinases, a phenotype exacerbated by HIV infection and psychostimulant use. SE-directed regulation of cellular morphometrics and chemotaxis depended on the donor clinical status because HIV infection and psychostimulant use altered SE function. Although our inclusion criteria specified the use of cocaine, humans are poly-drug and alcohol users and our study participants used psychostimulants, marijuana, opiates, and alcohol. Thus, it is possible that the effects observed in this study may be due to one of these other substances or due to an interaction between different substances
Targeting Cattle-Borne Zoonoses and Cattle Pathogens Using a Novel Trypanosomatid-Based Delivery System
Trypanosomatid parasites are notorious for the human diseases they cause throughout Africa and South America. However, non-pathogenic trypanosomatids are also found worldwide, infecting a wide range of hosts. One example is Trypanosoma (Megatrypanum) theileri, a ubiquitous protozoan commensal of bovids, which is distributed globally. Exploiting knowledge of pathogenic trypanosomatids, we have developed Trypanosoma theileri as a novel vehicle to deliver vaccine antigens and other proteins to cattle. Conditions for the growth and transfection of T. theileri have been optimised and expressed heterologous proteins targeted for secretion or specific localisation at the cell interior or surface using trafficking signals from Trypanosoma brucei. In cattle, the engineered vehicle could establish in the context of a pre-existing natural T. theileri population, was maintained long-term and generated specific immune responses to an expressed Babesia antigen at protective levels. Building on several decades of basic research into trypanosomatid pathogens, Trypanosoma theileri offers significant potential to target multiple infections, including major cattle-borne zoonoses such as Escherichia coli, Salmonella spp., Brucella abortus and Mycobacterium spp. It also has the potential to deliver therapeutics to cattle, including the lytic factor that protects humans from cattle trypanosomiasis. This could alleviate poverty by protecting indigenous African cattle from African trypanosomiasis
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