6,122 research outputs found
Thermal conduction of carbon nanotubes using molecular dynamics
The heat flux autocorrelation functions of carbon nanotubes (CNTs) with
different radius and lengths is calculated using equilibrium molecular
dynamics. The thermal conductance of CNTs is also calculated using the
Green-Kubo relation from the linear response theory. By pointing out the
ambiguity in the cross section definition of single wall CNTs, we use the
thermal conductance instead of conductivity in calculations and discussions. We
find that the thermal conductance of CNTs diverges with the CNT length. After
the analysis of vibrational density of states, it can be concluded that more
low frequency vibration modes exist in longer CNTs, and they effectively
contribute to the divergence of thermal conductance.Comment: 15 pages, 6 figures, submitted to Physical Review
Hawking radiation of Dirac particles via tunneling from Kerr black hole
We investigated Dirac Particles' Hawking radiation from event horizon of Kerr
black hole in terms of the tunneling formalism. Applying WKB approximation to
the general covariant Dirac equation in Kerr spacetime background, we obtain
the tunneling probability for fermions and Hawking temperature of Kerr black
hole. The result obtained by taking the fermion tunneling into account is
consistent with the previous literatures.Comment: 7 pages, no figures, to appear in CQ
Ginsenoside Rb1 Reduces Nitric Oxide Production via Inhibition of Nuclear Factor-κB Activation in Interleukin-1β- Stimulated SW1353 Chondrosarcoma Cells
Purpose: To investigate the effect and the potential mechanisms of ginsenoside Rb1 on nitric oxide (NO) production in chondrocytes.Methods: SW1353 chondrosarcoma cells were stimulated with interleukin-1β (IL-1β) in the presence of 20, 40, 80 μM ginsenoside Rb1. NO concentration was assessed by the Griess reaction. Expression of inducible nitric oxide synthase (iNOS), content of inhibitor of NF-κB (IκB)α and nuclear level of nuclear factor (NF)-κB p65 were determined by Western blot. DNA binding activity of NF-κB was evaluated with Trans AM™ kit for NF-κB p65.Results: Ginsenoside Rb1 (40 and 80 μM) significantly decreased NO level by 24 (p < 0.05) and 46 % (p < 0.01), as well as iNOS protein expression by 40 and 55 % (p < 0.01), respectively, in IL-1β- stimulated SW1353 cells. Ginsenoside Rb1 (40 and 80 μM) also markedly elevated IκBα protein content by 200 and 260 % (p < 0.01), reduced the nuclear level of p65 protein by 30 and 40 % (p < 0.01), as well as decreased the DNA binding activity of NF-κB by 40 and 50 % (both p < 0.01), respectively, in IL- 1β-stimulated SW1353 cells.Conclusion: These results suggest that ginsenoside Rb1 inhibits IL-1β-induced NO production through downregulation of NF-κB-dependent iNOS expression in chondrocytes, and also underlines the potential mechanisms of ginseng activity in OA treatment of TCM. Keywords: Ginsenoside Rb1, Nitric oxide, Nuclear factor-κB, Chondrocytes, Osteoarthriti
Differentiation of cultured epithelial cells: response to toxic agents.
Cell culture systems are instrumental in elucidating regulation of normal function and mechanisms of its perturbation by toxic substances. To this end, three applications of epithelial cells cultured with 3T3 feeder layer support are described. First, treatment of the premalignant human epidermal keratinocyte line SCC-12F2 with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate suppressed cell growth and differentiation. This agent produced a biphasic growth response greatly inhibiting cell growth at 1 to 10 nM, but much less above 100 nM. Expression of the differentiated functions involucrin and transglutaminase was found to be inhibited markedly at concentrations above 10 nM. Second, 3-methylcholanthrene toxicity was surveyed in a variety of rat epithelial cell types. The two most sensitive to growth inhibition were epidermal and mammary epithelial cells, while those from bladder, prostate, thyroid, and endometrium were insensitive to growth inhibition. Great differences were evident even among those cells derived from stratified squamous epithelia (epidermal, esophageal, vaginal, forestomach) despite their expression of aryl hydrocarbon hydroxylase activities to similar degrees. Finally, expression of estrogen receptors in rat endometrial cells was shown to be stimulated by the cAMP-elevating agent forskolin. Maximal stimulation of 3- to 6-fold occurred in 6 hr, compatible with a requirement for protein synthesis. Although expressing keratinocyte character (transglutaminase activity and envelope forming ability), the cells thus retain some hormonal character that may be modulated by cAMP-dependent kinase activity. Pursuit of such results will aid in understanding differences in response among cell types and species, in elucidating mechanisms of action of known toxic substances and, ultimately, in predicting toxicity of less well understood agents
Persistence, extinction and spatio-temporal synchronization of SIRS cellular automata models
Spatially explicit models have been widely used in today's mathematical
ecology and epidemiology to study persistence and extinction of populations as
well as their spatial patterns. Here we extend the earlier work--static
dispersal between neighbouring individuals to mobility of individuals as well
as multi-patches environment. As is commonly found, the basic reproductive
ratio is maximized for the evolutionary stable strategy (ESS) on diseases'
persistence in mean-field theory. This has important implications, as it
implies that for a wide range of parameters that infection rate will tend
maximum. This is opposite with present results obtained in spatial explicit
models that infection rate is limited by upper bound. We observe the emergence
of trade-offs of extinction and persistence on the parameters of the infection
period and infection rate and show the extinction time having a linear
relationship with respect to system size. We further find that the higher
mobility can pronouncedly promote the persistence of spread of epidemics, i.e.,
the phase transition occurs from extinction domain to persistence domain, and
the spirals' wavelength increases as the mobility increasing and ultimately, it
will saturate at a certain value. Furthermore, for multi-patches case, we find
that the lower coupling strength leads to anti-phase oscillation of infected
fraction, while higher coupling strength corresponds to in-phase oscillation.Comment: 12page
Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry
We study the effect of a single non-magnetic impurity in
AFeSe (A=K, Rb, or Cs) superconductors by considering
various pairing states based on a three-orbital model consistent with the
photoemission experiments. The local density of states on and near the impurity
site has been calculated by solving the Bogoliubov-de Gennes equations
self-consistently. The impurity-induced in-gap bound states are found only for
attractive impurity scattering potential, as in the cases of doping of Co or
Ni, which is characterized by the strong particle-hole asymmetry, in the
nodeless wave pairing state. This property may be used to probe
the pairing symmetry of FeSe-based 122-type superconductors.Comment: 7 pages, 7 figure
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