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Evidence for involvement of both IKCa and SKCa channels in hyperpolarizing responses of the rat middle cerebral artery
Endothelium-derived hyperpolarizing factor responses in the rat middle cerebral artery are blocked by inhibiting IKCa channels alone, contrasting with peripheral vessels where block of both IKCa and SKCa is required. As the contribution of IKCa and SKCa to endothelium-dependent hyperpolarization differs in peripheral arteries, depending on the level of arterial constriction, we investigated the possibility that SKCa might contribute to equivalent hyperpolarization in cerebral arteries under certain conditions. METHODS: Rat middle cerebral arteries (approximately 175 microm) were mounted in a wire myograph. The effect of KCa channel blockers on endothelium-dependent responses to the protease-activated receptor 2 agonist, SLIGRL (20 micromol/L), were then assessed as simultaneous changes in tension and membrane potential. These data were correlated with the distribution of arterial KCa channels revealed with immunohistochemistry. RESULTS: SLIGRL hyperpolarized and relaxed cerebral arteries undergoing variable levels of stretch-induced tone. The relaxation was unaffected by specific inhibitors of IKCa (TRAM-34, 1 micromol/L) or SKCa (apamin, 50 nmol/L) alone or in combination. In contrast, the associated smooth-muscle hyperpolarization was inhibited, but only with these blockers in combination. Blocking nitric oxide synthase (NOS) or guanylyl cyclase evoked smooth-muscle depolarization and constriction, with both hyperpolarization and relaxation to SLIGRL being abolished by TRAM-34 alone, whereas apamin had no effect. Immunolabeling showed SKCa and IKCa within the endothelium. CONCLUSIONS: In the absence of NO, IKCa underpins endothelium-dependent hyperpolarization and relaxation in cerebral arteries. However, when NOS is active SKCa contributes to hyperpolarization, whatever the extent of background contraction. These changes may have relevance in vascular disease states where NO release is compromised and when the levels of SKCa expression may be altered
Will jams get worse when slow cars move over?
Motivated by an analogy with traffic, we simulate two species of particles
(`vehicles'), moving stochastically in opposite directions on a two-lane ring
road. Each species prefers one lane over the other, controlled by a parameter
such that corresponds to random lane choice and
to perfect `laning'. We find that the system displays one large cluster (`jam')
whose size increases with , contrary to intuition. Even more remarkably, the
lane `charge' (a measure for the number of particles in their preferred lane)
exhibits a region of negative response: even though vehicles experience a
stronger preference for the `right' lane, more of them find themselves in the
`wrong' one! For very close to 1, a sharp transition restores a homogeneous
state. Various characteristics of the system are computed analytically, in good
agreement with simulation data.Comment: 7 pages, 3 figures; to appear in Europhysics Letters (2005
Density Profile of the One-Dimensional Partially Asymmetric Simple Exclusion Process with Open Boundaries
The one-dimensional partially asymmetric simple exclusion process with open
boundaries is considered. The stationary state, which is known to be
constructed in a matrix product form, is studied by applying the theory of
q-orthogonal polynomials. Using a formula of the q-Hermite polynomials, the
average density profile is computed in the thermodynamic limit. The phase
diagram for the correlation length, which was conjectured in the previous
work[J. Phys. A {\bf 32} (1999) 7109], is confirmed.Comment: 24 pages, 6 figure
On Matrix Product Ground States for Reaction-Diffusion Models
We discuss a new mechanism leading to a matrix product form for the
stationary state of one-dimensional stochastic models. The corresponding
algebra is quadratic and involves four different matrices. For the example of a
coagulation-decoagulation model explicit four-dimensional representations are
given and exact expressions for various physical quantities are recovered. We
also find the general structure of -point correlation functions at the phase
transition.Comment: LaTeX source, 7 pages, no figure
Electronic correlation effects and the Coulomb gap at finite temperature
We have investigated the effect of the long-range Coulomb interaction on the
one-particle excitation spectrum of n-type Germanium, using tunneling
spectroscopy on mechanically controllable break junctions. The tunnel
conductance was measured as a function of energy and temperature. At low
temperatures, the spectra reveal a minimum at zero bias voltage due to the
Coulomb gap. In the temperature range above 1 K the Coulomb gap is filled by
thermal excitations. This behavior is reflected in the temperature dependence
of the variable-range hopping resitivity measured on the same samples: Up to a
few degrees Kelvin the Efros-Shkovskii ln law is obeyed,
whereas at higher temperatures deviations from this law are observed,
indicating a cross-over to Mott's ln law. The mechanism of
this cross-over is different from that considered previously in the literature.Comment: 3 pages, 3 figure
Finite Dimensional Representations of the Quadratic Algebra: Applications to the Exclusion Process
We study the one dimensional partially asymmetric simple exclusion process
(ASEP) with open boundaries, that describes a system of hard-core particles
hopping stochastically on a chain coupled to reservoirs at both ends. Derrida,
Evans, Hakim and Pasquier [J. Phys. A 26, 1493 (1993)] have shown that the
stationary probability distribution of this model can be represented as a trace
on a quadratic algebra, closely related to the deformed oscillator-algebra. We
construct all finite dimensional irreducible representations of this algebra.
This enables us to compute the stationary bulk density as well as all
correlation lengths for the ASEP on a set of special curves of the phase
diagram.Comment: 18 pages, Latex, 1 EPS figur
The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy
We have investigated the intermediate valence narrow-gap semiconductor SmB6
at low temperatures using both conventional spear-anvil type point contacts as
well as mechanically controllable break junctions. The zero-bias conductance
varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the
spectral anomalies, which are related to the different activation energies and
band gaps of SmB6, did not depend on the the contact size. Two different
regimes of charge transport could be distinguished: Contacts with large zero -
bias conductance are in the diffusive Maxwell regime. They had spectra with
only small non-linearities. Contacts with small zero - bias conductance are in
the tunnelling regime. They had larger anomalies, but still indicating a finite
45 % residual quasiparticle density of states at the Fermi level at low
temperatures of T = 0.1 K. The density of states derived from the tunelling
spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and
Ed = 4.5 meV wide gaps, respectively.Comment: 9 pages incl. 13 figure
Spurious phase in a model for traffic on a bridge
We present high-precision Monte Carlo data for the phase diagram of a
two-species driven diffusive system, reminiscent of traffic across a narrow
bridge. Earlier studies reported two phases with broken symmetry; the existence
of one of these has been the subject of some debate. We show that the disputed
phase disappears for sufficiently large systems and/or sufficiently low bulk
mobility.Comment: 8 pages, 3 figures, JPA styl
Stability of a Nonequilibrium Interface in a Driven Phase Segregating System
We investigate the dynamics of a nonequilibrium interface between coexisting
phases in a system described by a Cahn-Hilliard equation with an additional
driving term. By means of a matched asymptotic expansion we derive equations
for the interface motion. A linear stability analysis of these equations
results in a condition for the stability of a flat interface. We find that the
stability properties of a flat interface depend on the structure of the driving
term in the original equation.Comment: 14 pages Latex, 1 postscript-figur
Remarks on the multi-species exclusion process with reflective boundaries
We investigate one of the simplest multi-species generalizations of the one
dimensional exclusion process with reflective boundaries. The Markov matrix
governing the dynamics of the system splits into blocks (sectors) specified by
the number of particles of each kind. We find matrices connecting the blocks in
a matrix product form. The procedure (generalized matrix ansatz) to verify that
a matrix intertwines blocks of the Markov matrix was introduced in the periodic
boundary condition, which starts with a local relation [Arita et al, J. Phys. A
44, 335004 (2011)]. The solution to this relation for the reflective boundary
condition is much simpler than that for the periodic boundary condition
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