4,548 research outputs found
Thermodynamic properties and bulk viscosity near phase transition in the Z(2) and O(4) models
We investigate the thermodynamic properties including equation of state, the
trace anomaly, the sound velocity and the specific heat, as well as transport
properties like bulk viscosity in the Z(2) and O(4) models in the Hartree
approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism. We study these
properties in different cases, e.g. first order phase transition, second order
phase transition, crossover and the case without phase transition, and discuss
the correlation between the bulk viscosity and the thermodynamic properties of
the system. We find that the bulk viscosity over entropy density ratio exhibits
an upward cusp at the second order phase transition, and a sharp peak at the
1st order phase transition. However, this peak becomes smooth or disappears in
the case of crossover. This indicates that at RHIC, where there is no real
phase transition and the system experiences a crossover, the bulk viscosity
over entropy density might be small, and it will not affect too much on
hadronization. We also suggest that the bulk viscosity over entropy density
ratio is a better quantity than the shear viscosity over entropy density ratio
to locate the critical endpoint.Comment: 19 pages, 30 figures, 1 tabl
Chiral selection and frequency response of spiral waves in reaction-diffusion systems under a chiral electric field
Chirality is one of the most fundamental properties of many physical,
chemical and biological systems. However, the mechanisms underlying the onset
and control of chiral symmetry are largely understudied. We investigate
possibility of chirality control in a chemical excitable system (the BZ
reaction) by application of a chiral (rotating) electric field using the
Oregonator model. We find that unlike previous findings, we can achieve the
chirality control not only in the field rotation direction, but also opposite
to it, depending on the field rotation frequency. To unravel the mechanism, we
further develop a comprehensive theory of frequency synchronization based on
the response function approach. We find that this problem can be described by
the Adler equation and show phase-locking phenomena, known as the Arnold
tongue. Our theoretical predictions are in good quantitative agreement with the
numerical simulations and provide a solid basis for chirality control in
excitable media.Comment: 21 pages with 9 figures; update references; to appear in J. Chem.
Phy
Aspect ratio dependence of heat transport by turbulent Rayleigh-B\'{e}nard convection in rectangular cells
We report high-precision measurements of the Nusselt number as a
function of the Rayleigh number in water-filled rectangular
Rayleigh-B\'{e}nard convection cells. The horizontal length and width
of the cells are 50.0 cm and 15.0 cm, respectively, and the heights ,
25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios
, , ,
, , and . The measurements were carried out
over the Rayleigh number range and the
Prandtl number range . Our results show that for
rectangular geometry turbulent heat transport is independent of the cells'
aspect ratios and hence is insensitive to the nature and structures of the
large-scale mean flows of the system. This is slightly different from the
observations in cylindrical cells where is found to be in general a
decreasing function of , at least for and larger. Such a
difference is probably a manifestation of the finite plate conductivity effect.
Corrections for the influence of the finite conductivity of the top and bottom
plates are made to obtain the estimates of for plates with
perfect conductivity. The local scaling exponents of are calculated and found to increase from 0.243 at
to 0.327 at .Comment: 15 pages, 7 figures, Accepted by Journal of Fluid Mechanic
Type III Secretion System of Phytopathogenic Bacterium Pseudomonas syringae : From Gene to Function
The type III secretion system (T3SS) is an essential requirement for the virulence of many Gram-negative bacteria which infect plants, animals and men. Pathogens use the T3SS to deliver effector proteins from the bacterial cytoplasm to the eukaryotic host cells, where the effectors subvert host defenses. The best candidates for directing effector protein traffic are the bacterial type III-associated appendages, called needles or pili.
In plant pathogenic bacteria, the best characterized example of a T3SS-associated appendage is the HrpA pilus of the plant pathogen Pseudomonas syringae pv. tomato DC3000. The components of the T3SS in plant pathogens are encoded by a cluster of hrp (hypersensitive reaction and pathogenicity) genes. Two major classes of T3SS-secreted proteins are: harpin proteins such as HrpZ which are exported into extracellular space, and avirulence (Avr) proteins such as AvrPto which are translocated directly to the plant cytoplasm.
This study deals with the structural and functional characterization of the T3SS-associated HrpA pilus and the T3SS-secreted harpins. By insertional mutagenesis analysis of HrpA, we located the optimal epitope insertion site in the amino-terminus of HrpA, and revealed the potential application of the HrpA pilus as a carrier of antigenic determinants for vaccination. By pulse-expression of proteins combined with immuno-electron microscopy, we discovered the Hrp pilus assembly strategy as addition of HrpA subunits to the distal end of the growing pilus, and we showed for the first time that secretion of HrpZ occurs at the tip of the pilus. The pilus thus functions as a conduit delivering proteins to the extracellular milieu. By using phage-display and scanning-insertion mutagenesis methods we identified a conserved HrpZ-binding peptide and localized the peptide-binding site to the central domain of HrpZ. We also found that the HrpZ specifically interacts with a host bean protein.
Taken together, the current results provide deeper insight into the molecular mechanism of T3SS-associated pilus assembly and effector protein translocation, which will be helpful for further studies on the pathogenic mechanisms of Gram-negative bacteria and for developing new strategies to prevent bacterial infection
Phase-locked scroll waves defy turbulence induced by negative filament tension
Scroll waves in a three-dimensional media may develop into turbulence due to negative tension of the filament. Such negative tension-induced instability of scrollwaves has been observed in the Belousov-Zhabotinsky reaction systems. Here we propose a method to restabilize scroll wave turbulence caused by negative tension in three-dimensional chemical excitable media using a circularly polarized (rotating) external field. The stabilization mechanism is analyzed in terms of phase-locking caused by the external field, which makes the effective filament tension positive. The phase-locked scrollwaves that have positive tension and higher frequency defy the turbulence and finally restore order. A linear theory for the change of filament tension caused by a generic rotating external field is presented and its predictions closely agree with numerical simulations
Activation of extracellular signal-regulated protein kinase 5 is essential for cystitis- and nerve growth factor-induced calcitonin gene-related peptide expression in sensory neurons
Background Cystitis causes considerable neuronal plasticity in the primary afferent pathways. The molecular mechanism and signal transduction underlying cross talk between the inflamed urinary bladder and sensory sensitization has not been investigated.
Results In a rat cystitis model induced by cyclophosphamide (CYP) for 48 h, the mRNA and protein levels of the excitatory neurotransmitter calcitonin gene-related peptide (CGRP) are increased in the L6 dorsal root ganglia (DRG) in response to bladder inflammation. Cystitis-induced CGRP expression in L6 DRG is triggered by endogenous nerve growth factor (NGF) because neutralization of NGF with a specific NGF antibody reverses CGRP up-regulation during cystitis. CGRP expression in the L6 DRG neurons is also enhanced by retrograde NGF signaling when NGF is applied to the nerve terminals of the ganglion-nerve two-compartmented preparation. Characterization of the signaling pathways in cystitis- or NGF-induced CGRP expression reveals that the activation (phosphorylation) of extracellular signal-regulated protein kinase (ERK)5 but not Akt is involved. In L6 DRG during cystitis, CGRP is co-localized with phospho-ERK5 but not phospho-Akt. NGF-evoked CGRP up-regulation is also blocked by inhibition of the MEK/ERK pathway with specific MEK inhibitors U0126 and PD98059, but not by inhibition of the PI3K/Akt pathway with inhibitor LY294002. Further examination shows that cystitis-induced cAMP-responsive element binding protein (CREB) activity is expressed in CGRP bladder afferent neurons and is co-localized with phospho-ERK5 but not phospho-Akt. Blockade of NGF action in vivo reduces the number of DRG neurons co-expressing CGRP and phospho-CREB, and reverses cystitis-induced increases in micturition frequency.
Conclusions A specific pathway involving NGF-ERK5-CREB axis plays an essential role in cystitis-induced sensory activation
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