739 research outputs found
Unidimensional model of the ad-atom diffusion on a substrate submitted to a standing acoustic wave I. Derivation of the ad-atom motion equation
The effect of a standing acoustic wave on the diffusion of an ad-atom on a
crystalline surface is theoretically studied. We used an unidimensional space
model to study the ad-atom+substrate system. The dynamic equation of the
ad-atom, a Generalized Langevin equation, is analytically derived from the full
Hamiltonian of the ad-atom+substrate system submitted to the acoustic wave. A
detailed analysis of each term of this equation, as well as of their
properties, is presented. Special attention is devoted to the expression of the
effective force induced by the wave on the ad-atom. It has essentially the same
spatial and time dependences as its parent standing acoustic wave
Study of vibrational kinetics of CO2 and CO in CO2-O2 plasmas under non-equilibrium conditions
This work explores the effect of O2 addition on CO2 dissociation and on the
vibrational kinetics of CO2 and CO under various non-equilibrium plasma
conditions. A self-consistent model, previously validated for pure CO2
discharges, is further extended by adding the vibrational kinetics of CO,
including electron impact excitation and de-excitation (e-V),
vibration-to-translation relaxation (V-T) and vibration-to-vibration energy
exchange (V-V) processes. The vibrational kinetics considered include levels up
to v = 10 for CO and up to v1=2 and v2=v3=5, respectively for the symmetric
stretch, bending and asymmetric stretch modes of CO2, and accounts for e-V, V-T
in collisions between CO, CO2 and O2 molecules and O atoms and V-V processes
involving all possible transfers involving CO2 and CO molecules. The kinetic
scheme is validated by comparing the model predictions with recent experimental
data measured in a DC glow discharge, operating at pressures in the range 0.4 -
5 Torr (53.33 - 666.66 Pa). The experimental results show a lower vibrational
temperature of the different modes of CO2 and a decreased dissociation fraction
of CO2 when O2 is added to the plasma but an increase of the vibrational
temperature of CO. On the one hand, the simulations suggest that the former
effect is the result of the stronger V-T energy-transfer collisions with O
atoms which leads to an increase of the relaxation of the CO2 vibrational
modes; On the other hand, the back reactions with O2 contribute to the lower
CO2 dissociation fraction with increased O2 content in the mixture.Comment: 34 pages 15 figure
Driven Tunneling Dynamics: Bloch-Redfield Theory versus Path Integral Approach
In the regime of weak bath coupling and low temperature we demonstrate
numerically for the spin-boson dynamics the equivalence between two widely used
but seemingly different roads of approximation, namely the path integral
approach and the Bloch-Redfield theory. The excellent agreement between these
two methods is corroborated by a novel efficient analytical high-frequency
approach: it well approximates the decay of quantum coherence via a series of
damped coherent oscillations. Moreover, a suitably tuned control field can
selectively enhance or suppress quantum coherence.Comment: 4 pages including 3 figures, submitted for publicatio
System size resonance in coupled noisy systems and in the Ising model
We consider an ensemble of coupled nonlinear noisy oscillators demonstrating
in the thermodynamic limit an Ising-type transition. In the ordered phase and
for finite ensembles stochastic flips of the mean field are observed with the
rate depending on the ensemble size. When a small periodic force acts on the
ensemble, the linear response of the system has a maximum at a certain system
size, similar to the stochastic resonance phenomenon. We demonstrate this
effect of system size resonance for different types of noisy oscillators and
for different ensembles -- lattices with nearest neighbors coupling and
globally coupled populations. The Ising model is also shown to demonstrate the
system size resonance.Comment: 4 page
Coherence Resonance and Noise-Induced Synchronization in Globally Coupled Hodgkin-Huxley Neurons
The coherence resonance (CR) of globally coupled Hodgkin-Huxley neurons is
studied. When the neurons are set in the subthreshold regime near the firing
threshold, the additive noise induces limit cycles. The coherence of the system
is optimized by the noise. A bell-shaped curve is found for the peak height of
power spectra of the spike train, being significantly different from a
monotonic behavior for the single neuron. The coupling of the network can
enhance CR in two different ways. In particular, when the coupling is strong
enough, the synchronization of the system is induced and optimized by the
noise. This synchronization leads to a high and wide plateau in the local
measure of coherence curve. The local-noise-induced limit cycle can evolve to a
refined spatiotemporal order through the dynamical optimization among the
autonomous oscillation of an individual neuron, the coupling of the network,
and the local noise.Comment: five pages, five figure
Strong coupling theory for driven tunneling and vibrational relaxation
We investigate on a unified basis tunneling and vibrational relaxation in
driven dissipative multistable systems described by their N lowest lying
unperturbed levels. By use of the discrete variable representation we derive a
set of coupled non-Markovian master equations. We present analytical treatments
that describe the dynamics in the regime of strong system-bath coupling. Our
findings are corroborated by ``ab-initio'' real-time path integral
calculations.Comment: 4 LaTeX pages including 3 figure
The Right to Code and Share Arms
Glycerol is, to date, the most widely used cryoprotectant to freeze stallion spermatozoa at concentrations between 2% and 5%. Cryoprotectant toxicity has been claimed to be the single most limiting factor for the success of cryopreservation. In order to evaluate the toxic effects of the concentrations of glycerol used in practice, stallion spermatozoa were incubated in Biggers Whitten and Whittingham (BWW) media supplemented with 0%, 0.5%, 1.5%, 2.5%, 3.5%, and 5% glycerol. In two additional experiments, a hyposmotic (75 mOsm/kg) and a hyperosmotic (900 mOsm/kg) control media were included. Sperm parameters evaluated included cell volume, membrane integrity, lipid peroxidation, caspase 3, 7, and 8 activation, mitochondrial membrane potential, and integrity of the cytoskeleton. Glycerol exerted toxicity at concentrations 3.5% and the maximal toxicity was observed at 5%. The actin cytoskeleton was especially sensitive to glycerol presence, inducing rapid F actin depolymerization at concentrations over 1.5%. The sperm membrane and the mitochondria were other structures affected. The toxicity of glycerol is apparently related to osmotic and nonosmotic effects. In view of our results the concentration of glycerol in the freezing media for stallion spermatozoa should not surpass 2.5%.Funding Agencies|Ministerio de Ciencia e Innovacion-FEDER Madrid, Spain|AGL 2010 20758 (GAN)|Inia|RZ2008-00018-00-00|Junta de Extremadura FEDER GR|10010
Does native Trypanosoma cruzi calreticulin mediate growth inhibition of a mammary tumor during infection?
IndexaciĂłn: Web of Science.Background: For several decades now an antagonism between Trypanosoma cruzi infection and tumor development has been detected. The molecular basis of this phenomenon remained basically unknown until our proposal that T. cruzi Calreticulin (TcCRT), an endoplasmic reticulum-resident chaperone, translocated-externalized by the parasite, may mediate at least an important part of this effect. Thus, recombinant TcCRT (rTcCRT) has important in vivo antiangiogenic and antitumor activities. However, the relevant question whether the in vivo antitumor effect of T. cruzi infection is indeed mediated by the native chaperone (nTcCRT), remains open. Herein, by using specific modified anti-rTcCRT antibodies (Abs), we have neutralized the antitumor activity of T. cruzi infection and extracts thereof, thus identifying nTcCRT as a valid mediator of this effect.
Methods: Polyclonal anti-rTcCRT F(ab')(2) Ab fragments were used to reverse the capacity of rTcCRT to inhibit EAhy926 endothelial cell (EC) proliferation, as detected by BrdU uptake. Using these F(ab')(2) fragments, we also challenged the capacity of nTcCRT, during T. cruzi infection, to inhibit the growth of an aggressive mammary adenocarcinoma cell line (TA3-MTXR) in mice. Moreover, we determined the capacity of anti-rTcCRT Abs to reverse the antitumor effect of an epimastigote extract (EE). Finally, the effects of these treatments on tumor histology were evaluated.
Results: The rTcCRT capacity to inhibit ECs proliferation was reversed by anti-rTcCRT F(ab')(2) Ab fragments, thus defining them as valid probes to interfere in vivo with this important TcCRT function. Consequently, during infection, these Ab fragments also reversed the in vivo experimental mammary tumor growth. Moreover, anti-rTcCRT Abs also neutralized the antitumor effect of an EE, again identifying the chaperone protein as an important mediator of this anti mammary tumor effect. Finally, as determined by conventional histological parameters, in infected animals and in those treated with EE, less invasive tumors were observed while, as expected, treatment with F(ab')(2) Ab fragments increased malignancy.
Conclusion: We have identified translocated/externalized nTcCRT as responsible for at least an important part of the anti mammary tumor effect of the chaperone observed during experimental infections with T. cruzi.http://bmccancer.biomedcentral.com/articles/10.1186/s12885-016-2764-
Stochastic resonance between dissipative structures in a bistable noise-sustained dynamics
We study an extended system that without noise shows a monostable dynamics,
but when submitted to an adequate multiplicative noise, an effective bistable
dynamics arise. The stochastic resonance between the attractors of the
\textit{noise-sustained dynamics} is investigated theoretically in terms of a
two-state approximation. The knowledge of the exact nonequilibrium potential
allows us to obtain the output signal-to-noise ratio. Its maximum is predicted
in the symmetric case for which both attractors have the same nonequilibrium
potential value.Comment: RevTex, 13 pages, 6 figures, accepted in Physical Review
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