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A minK-HERG complex regulates the cardiac potassium current I(Kr).
MinK is a widely expressed protein of relative molecular mass approximately 15K that forms potassium channels by aggregation with other membrane proteins. MinK governs ion channel activation, regulation by second messengers, and the function and structure of the ion conduction pathway. Association of minK with a channel protein known as KvLQT1 produces a voltage-gated outward K+ current (I[sK]) resembling the slow cardiac repolarization current (I[Ks]). HERG, a human homologue of the ether-a-go-go gene of the fruitfly Drosophila melanogaster, encodes a protein that produces the rapidly activating cardiac delayed rectifier (I[Kr]). These two potassium currents, I(Ks) and I(Kr), provide the principal repolarizing currents in cardiac myocytes for the termination of action potentials. Although heterologously expressed HERG channels are largely indistinguishable from native cardiac I(Kr), a role for minK in this current is suggested by the diminished I(Kr) in an atrial tumour line subjected to minK antisense suppression. Here we show that HERG and minK form a stable complex, and that this heteromultimerization regulates I(Kr) activity. MinK, through the formation of heteromeric channel complexes, is thus central to the control of the heart rate and rhythm
A test of the power law relationship between gamma-ray burst pulse width ratio and energy expected in fireballs or uniform jets
Recently, under the assumption that the Doppler effect of the
relativistically expanding fireball surface is important, Qin et al. showed
that in most cases the power law relationship between the pulse width and
energy of gamma-ray bursts (GRBs)would exist in a certain energy range. We
check this prediction with two GRB samples which contain well identified
pulses. A power law anti-correlation between the full pulse width and energy
and a power law correlation between the pulse width ratio and energy are seen
in the light curves of the majority (around 65%) of bursts of the two samples
within the energy range of BATSE, suggesting that these bursts are likely to
arise from the emission associated with the shocks occurred on a
relativistically expanding fireball surface. For the rest of the bursts, the
relationships between these quantities were not predicted previously. We
propose to consider other spectral evolutionary patterns or other radiation
mechanisms such as a varying synchrotron or Comptonized spectrum to check if
the observed relationships for these rest bursts can also be accounted for by
the Doppler model. In addition, we find that the upper limits of the width
ratio for the two samples do not exceed 0.9, in agrement with what predicted
previously by the Doppler model. The plateau/power law/plateau and the peaked
features predicted and detected previously by Qin et al. are generally
observed, with the exceptions being noticed only in a few cases. According to
the distinct values of two power law indices of FWHM and ratio and energy, we
divide the bursts into three subsets which are located in different areas of
the two indices plane. We suspect that different locations of the two indices
might correspond to different mechanisms.Comment: 16 pages, 7 figures, MNRAS accepte
Neutron and X-ray diffraction study of cubic [111] field cooled Pb(Mg1/3Nb2/3)O3
Neutron and x-ray diffraction techniques have been used to study the
competing long and short-range polar order in the relaxor ferroelectric
Pb(MgNb)O (PMN) under a [111] applied electric field.
Despite reports of a structural transition from a cubic phase to a rhombohedral
phase for fields E 1.7 kV/cm, we find that the bulk unit cell remains cubic
(within a sensitivity of 90- =0.03)for fields up to
8 kV/cm. Furthermore, we observe a structural transition confined to the near
surface volume or `skin' of the crystal where the cubic cell is transformed to
a rhombohedral unit cell at T=210 K for E 4 kV/cm, for which
90-=0.08 0.03 below 50 K. While the bulk unit
cell remains cubic, a suppression of the diffuse scattering and concomitant
enhancement of the Bragg peak intensity is observed below T=210 K,
indicating a more ordered structure with increasing electric field yet an
absence of a long-range ferroelectric ground state in the bulk. The electric
field strength has little effect on the diffuse scattering above T,
however below T the diffuse scattering is reduced in intensity and adopts
an asymmetric lineshape in reciprocal space. The absence of hysteresis in our
neutron measurements (on the bulk) and the presence of two distinct temperature
scales suggests that the ground state of PMN is not a frozen glassy phase as
suggested by some theories but is better understood in terms of random fields
introduced through the presence of structural disorder. Based on these results,
we also suggest that PMN represents an extreme example of the two-length scale
problem, and that the presence of a distinct skin maybe necessary for a relaxor
ground state.Comment: 12 pages, 9 figure
Classification of Swift's gamma-ray bursts
Two classes of gamma-ray bursts have been identified in the BATSE catalogs
characterized by durations shorter and longer than about 2 seconds. There are,
however, some indications for the existence of a third class. Swift satellite
detectors have different spectral sensitivity than pre-Swift ones for gamma-ray
bursts. Therefore, it is worth to reanalyze the durations and their
distribution. We analyze, the maximum likelihood estimation, the bursts
duration distribution, published in The First BAT Catalog, whether it contains
two, three or more groups. The three log-normal fit is significantly (99.54%
probability) better than the two for the duration distribution. Monte-Carlo
simulations also confirm this probability (99.2%). Similarly, in previous
results we found that the fourth component is not needed. The relative
frequencies of the distribution of the groups are 7% short 35% intermediate and
58% long. Although the relative frequencies of the groups are different than in
the BATSE GRB sample, the difference in the instrument spectral sensitivities
can explain this bias on a natural way. This means theoretical models may be
needed to explain three different type of gamma-ray bursts.Comment: Accepted in AA, added bibliograph
Electrical conductance at initial stage in epitaxial growth of Pb on modified Si(111) surface
The electrical conductance and RHEED intensities as a function of the
coverage have been measured during Pb depositions at 105 K on Si(111)-(6x6)Au
with up to 4.2 ML of annealed Pb. The experiments show the strong influence of
used substrates on the behavior of the conductance during the epitaxy of Pb
atoms, especially for very initial stage of growth. Oscillations of the
conductance during the layer-by-layer growth are correlated with RHEED
intensity oscillations. The analysis of the conductance behavior is made
according to the theory described by Trivedi and Aschcroft (Phys.Rev.B 38,12298
(1988)).Comment: 5 pages, 3 figures. Surf. Sci. - accepte
Chemically Induced Spin Hyperpolarization: Coherence Formation in Reaction Products
Chemically induced dynamic nuclear polarization (CIDNP) has emerged as a highly informative method to study spin-dependent radical reactions by analyzing enhanced NMR (nuclear magnetic resonance) signals of their diamagnetic reaction products. In this way, one can probe the structure of elusive radical intermediates and determine their magnetic parameters. A careful examination of experimental CIDNP data at variable magnetic fields shows that formation of hyperpolarized molecules in a coherent state is a ubiquitous though rarely discussed phenomenon. The presence of nuclear spin coherences commonly leads to subsequent polarization transfer among coupled spins in the diamagnetic products of radical recombination reaction that must be taken into account when analyzing the results of CIDNP experiments at low magnetic field. Moreover, such coherent polarization transfer can be efficiently exploited to polarize spins, which do not acquire CIDNP directly. Here we explain under what conditions such coherences can be generated, focusing on the key role of level anti-crossings in coherent polarization transfer, and provide experimental approaches to probing nuclear spin coherences and their time evolution. We illustrate the theoretical consideration of the outlined coherent spin phenomena in CIDNP by examples, obtained for the dipeptide tryptophan–tryptophan
UV/Optical Emission Accompanying Gamma-ray Burst
We discuss the possible simultaneously UV/optical emission accompanying
Gamma-ray bursts (GRBs). We show that as long as the intrinsic spectrum of GRB
can extend to 10 GeV or higher, there is a large amount of relativistic
pairs generated due to the annihilation of the soft rays with
the very energetic photons, which dominates over the electrons/positrons
associated with the fireball, no matter the fireball is highly magnetized or
not (For the highly magnetized fireball, the magnetic field is ordered, the
high linear polarization of the multi-wavelength emission is expected). We find
that these pairs can power an UV flash with
magnitude, and the corresponding optical emission can be up to magnitude. Such bright UV emission can be detected by
the upcoming satellite Swift, planned for launch in early 2004. The behavior of
the optical-UV spectrum () differs significantly from
that of the reverse shock emission (, ), which is a signature of the emission accompanying with GRB. The
mild optical emission can be detected with the ROTSE-IIIa telescope system, if
the response to the GRB alert is fast enough.Comment: 5 pages, no figures. MNRAS in pres
Equilibrium random-field Ising critical scattering in the antiferromagnet Fe(0.93)Zn(0.07)F2
It has long been believed that equilibrium random-field Ising model (RFIM)
critical scattering studies are not feasible in dilute antiferromagnets close
to and below Tc(H) because of severe non-equilibrium effects. The high magnetic
concentration Ising antiferromagnet Fe(0.93)Zn(0.07)F2, however, does provide
equilibrium behavior. We have employed scaling techniques to extract the
universal equilibrium scattering line shape, critical exponents nu = 0.87 +-
0.07 and eta = 0.20 +- 0.05, and amplitude ratios of this RFIM system.Comment: 4 pages, 1 figure, minor revision
Knotting probabilities after a local strand passage in unknotted self-avoiding polygons
We investigate the knotting probability after a local strand passage is
performed in an unknotted self-avoiding polygon on the simple cubic lattice. We
assume that two polygon segments have already been brought close together for
the purpose of performing a strand passage, and model this using Theta-SAPs,
polygons that contain the pattern Theta at a fixed location. It is proved that
the number of n-edge Theta-SAPs grows exponentially (with n) at the same rate
as the total number of n-edge unknotted self-avoiding polygons, and that the
same holds for subsets of n-edge Theta-SAPs that yield a specific
after-strand-passage knot-type. Thus the probability of a given
after-strand-passage knot-type does not grow (or decay) exponentially with n,
and we conjecture that instead it approaches a knot-type dependent amplitude
ratio lying strictly between 0 and 1. This is supported by critical exponent
estimates obtained from a new maximum likelihood method for Theta-SAPs that are
generated by a composite (aka multiple) Markov Chain Monte Carlo BFACF
algorithm. We also give strong numerical evidence that the after-strand-passage
knotting probability depends on the local structure around the strand passage
site. Considering both the local structure and the crossing-sign at the strand
passage site, we observe that the more "compact" the local structure, the less
likely the after-strand-passage polygon is to be knotted. This trend is
consistent with results from other strand-passage models, however, we are the
first to note the influence of the crossing-sign information. Two measures of
"compactness" are used: the size of a smallest polygon that contains the
structure and the structure's "opening" angle. The opening angle definition is
consistent with one that is measurable from single molecule DNA experiments.Comment: 31 pages, 12 figures, submitted to Journal of Physics
An analysis of the durations of Swift Gamma-Ray Bursts
We report the systematic analysis of the durations for Swift gamma-ray bursts
(GRBs) and compare the results with those of pre-Swift data. For 95 GRBs with
known redshift, we show that the observed durations have two lognormal
distributions that are clearly divided at s. This is consistent
with the earlier BATSE results. The intrinsic durations also show a bimodal
distribution but shift systematically toward the smaller value and the
distribution exhibits a narrower width compared with the observed one. We find
that the intrinsic distributions of long GRBs between Swift and pre-Swift are
significantly different particularly in the width and the median value. In
addition, the Swift data exhibit a wider dynamic range of duration. Our present
study not only confirms the spectra of short GRBs are in general harder than
the long GRBs in the observer frame but also shows this trend becomes weaker in
the source frame.Comment: 5 pages, 4 figures and 2 table; Accepted to A&A with minor changes;
Note that our previously main conclusions are unchange
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