5,457 research outputs found
Pair creation in boost-invariantly expanding electric fields and two-particle correlations
Pair creation of scalar particles in a boost-invariant electric field which
is confined in the forward light cone is studied. We present the proper-time
evolution of momentum distributions of created particles, which preserve the
boost invariance of the background field. The two-particle correlation of the
created particles is also calculated. We find that long-range rapidity
correlations may arise from the Schwinger mechanism in the boost-invariant
electric field.Comment: 21 pages, 10 figures; v2: minor changes, to appear in Phys. Rev.
Tasting edge effects
We show that the baking of potato wedges constitutes a crunchy example of
edge effects, which are usually demonstrated in electrostatics. A simple model
of the diffusive transport of water vapor around the potato wedges shows that
the water vapor flux diverges at the sharp edges in analogy with its
electrostatic counterpart. This increased evaporation at the edges leads to the
crispy taste of these parts of the potatoes.Comment: to appear in American Journal of Physic
Maximal extension of the Schwarzschild spacetime inspired by noncommutative geometry
We derive a transformation of the noncommutative geometry inspired
Schwarzschild solution into new coordinates such that the apparent unphysical
singularities of the metric are removed. Moreover, we give the maximal
singularity-free atlas for the manifold with the metric under consideration.
This atlas reveals many new features e.g. it turns out to describe an infinite
lattice of asymptotically flat universes connected by black hole tunnels.Comment: 17 pages LaTex, 2 figure
On the origin of the unusual behavior in the stretching of single-stranded DNA
Force extension curves (FECs), which quantify the response of a variety of
biomolecules subject to mechanical force (), are often quantitatively fit
using worm-like chain (WLC) or freely-jointed chain (FJC) models. These models
predict that the chain extension, , normalized by the contour length
increases linearly at small and at high forces scale as where = 0.5 for WLC and unity for FJC. In contrast,
experiments on ssDNA show that over a range of and ionic concentration,
scales as , which cannot be explained using WLC or FJC models.
Using theory and simulations we show that this unusual behavior in FEC in ssDNA
is due to sequence-independent polyelectrolyte effects. We show that the arises because in the absence of force the tangent correlation function,
quantifying chain persistence, decays algebraically on length scales on the
order of the Debye length. Our theory, which is most appropriate for monovalent
salts, quantitatively fits the experimental data and further predicts that such
a regime is not discernible in double stranded DNA.Comment: Accepted for publication in JC
Contact resistance and shot noise in graphene transistors
Potential steps naturally develop in graphene near metallic contacts. We
investigate the influence of these steps on the transport in graphene Field
Effect Transistors. We give simple expressions to estimate the
voltage-dependent contribution of the contacts to the total resistance and
noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde
Approximative analytical solutions of the Dirac equation in Schwarzschild spacetime
Approximative analytic solutions of the Dirac equation in the geometry of
Schwarzschild black holes are derived obtaining information about the discrete
energy levels and the asymptotic behavior of the energy eigenspinors.Comment: 8 page
Stability analysis of the Witten black hole (cigar soliton) under world-sheet RG flow
We analyze the stability of the Euclidean Witten black hole (the cigar
soliton in mathematics literature) under first-order RG (Ricci) flow of the
world-sheet sigma model. This analysis is from the target space point of view.
We find that the Witten black hole has no unstable normalizable perturbative
modes in a linearized mode analysis in which we consider circularly symmetric
perturbations. Finally, we discuss a result from mathematics that implies the
existence of a non-normalizable mode of the Witten black hole under which the
geometry flows to the sausage solution studied by Fateev, Onofri and
Zamolodchikov.Comment: 17 pages, version to appear in Physical Review D, and now has
complete proof of stability for circularly symmetric perturbations, in
response to referee comment
Controlled collisions of a single atom and ion guided by movable trapping potentials
We consider a system composed of a trapped atom and a trapped ion. The ion
charge induces in the atom an electric dipole moment, which attracts it with an
r^{-4} dependence at large distances. In the regime considered here, the
characteristic range of the atom-ion interaction is comparable or larger than
the characteristic size of the trapping potential, which excludes the
application of the contact pseudopotential. The short-range part of the
interaction is described in the framework of quantum-defect theory, by
introducing some short-range parameters, which can be related to the s-wave
scattering length. When the separation between traps is changed we observe
trap-induced shape resonances between molecular bound states and vibrational
states of the external trapping potential. Our analysis is extended to
quasi-one-dimensional geometries, when the scattering exhibit
confinement-induced resonances, similar to the ones studied before for
short-range interactions. For quasi-one-dimensional systems we investigate the
effects of coupling between the center of mass and relative motion, which
occurs for different trapping frequencies of atom and ion traps. Finally, we
show how the two types of resonances can be employed for quantum state control
and spectroscopy of atom-ion molecules.Comment: 17 pages, 16 figure
Reflection above the barrier as tunneling in momentum space
Quantum mechanics predicts an exponentially small probability that a particle
with energy greater than the height of a potential barrier will nevertheless
reflect from the barrier in violation of classical expectations. This process
can be regarded as tunneling in momentum space, leading to a simple derivation
of the reflection probability.Comment: 7 pages, 3 figures, submitted to American Journal of Physics. Version
2: MIT preprint number added, typographical error in caption to Figure 2
correcte
Critical role of canonical transient receptor potential channel 7 in initiation of seizures
Status epilepticus (SE) is a life-threatening disease that has been recognized since antiquity but still causes over 50,000 deaths annually in the United States. The prevailing view on the pathophysiology of SE is that it is sustained by a loss of normal inhibitory mechanisms of neuronal activity. However, the early process leading to the initiation of SE is not well understood. Here, we show that, as seen in electroencephalograms, SE induced by the muscarinic agonist pilocarpine in mice is preceded by a specific increase in the gamma wave, and genetic ablation of canonical transient receptor potential channel (TRPC) 7 significantly reduces this pilocarpine-induced increase of gamma wave activity, preventing the occurrence of SE. At the cellular level, TRPC7 plays a critical role in the generation of spontaneous epileptiform burst firing in cornu ammonis (CA) 3 pyramidal neurons in brain slices. At the synaptic level, TRPC7 plays a significant role in the long-term potentiation at the CA3 recurrent collateral synapses and Schaffer collateral-CA1 synapses, but not at the mossy fiber-CA3 synapses. Taken together, our data suggest that epileptiform burst firing generated in the CA3 region by activity-dependent enhancement of recurrent collateral synapses may be an early event in the initiation process of SE and that TRPC7 plays a critical role in this cellular event. Our findings reveal that TRPC7 is intimately involved in the initiation of seizures both in vitro and in vivo. To our knowledge, this contribution to initiation of seizures is the first identified functional role for the TRPC7 ion channel.Fil: Phelan, K. D.. University of Arkansas for Medical Sciences; Estados UnidosFil: Shwe, U. T.. University of Arkansas for Medical Sciences; Estados UnidosFil: Abramowitz, J.. National Institute of Environmental Health Sciences; Estados Unidos. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Birnbaumer, Lutz. National Institute of Environmental Health Sciences; Estados UnidosFil: Zheng, F.. University of Arkansas for Medical Sciences; Estados Unido
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