376 research outputs found
Amylase release from streptolysin O-permeabilized pancreatic acinar cells. Effects of Ca2+, guanosine 5'-[gamma-thio]triphosphate, cyclic AMP, tetanus toxin and botulinum A toxin
The molecular requirements for amylase release and the intracellular effects of botulinum A toxin and tetanus toxin on amylase release were investigated using rat pancreatic acinar cells permeabilized with streptolysin O. Micromolar concentrations of free Ca2+ evoked amylase release from these cells. Maximal release was observed in the presence of 30 microM free Ca2+. Ca(2+)-stimulated, but not basal, amylase release was enhanced by guanosine 5'-[gamma-thio]triphosphate (GTP[S]) (3-4 fold) or cyclic AMP (1.5-2 fold). Neither the two-chain forms of botulinum A toxin and tetanus toxin, under reducing conditions, nor the light chains of tetanus toxin, inhibited amylase release triggered by Ca2+, or combinations of Ca2+ + GTP[S] or Ca2+ + cAMP. The lack of inhibition was not due to inactivation of botulinum A toxin or tetanus toxin by pancreatic acinar cell proteolytic enzymes, as toxins previously incubated with permeabilized pancreatic acinar cells inhibited Ca(2+)-stimulated [3H]noradrenaline release from streptolysin O-permeabilized adrenal chromaffin cells. These data imply that clostridial neurotoxins inhibit a Ca(2+)-dependent mechanism which promotes exocytosis in neural and endocrine cells, but not in exocrine cells
Effects due to a scalar coupling on the particle-antiparticle production in the Duffin-Kemmer-Petiau theory
The Duffin-Kemmer-Petiau formalism with vector and scalar potentials is used
to point out a few misconceptions diffused in the literature. It is explicitly
shown that the scalar coupling makes the DKP formalism not equivalent to the
Klein-Gordon formalism or to the Proca formalism, and that the spin-1 sector of
the DKP theory looks formally like the spin-0 sector. With proper boundary
conditions, scattering of massive bosons in an arbitrary mixed vector-scalar
square step potential is explored in a simple way and effects due to the scalar
coupling on the particle-antiparticle production and localization of bosons are
analyzed in some detail
Exact Solution of Photon Equation in Stationary G\"{o}del-type and G\"{o}del Space-Times
In this work the photon equation (massless Duffin-Kemmer-Petiau equation) is
written expilicitly for general type of stationary G\"{o}del space-times and is
solved exactly for G\"{o}del-type and G\"{o}del space-times. Harmonic
oscillator behaviour of the solutions is discussed and energy spectrum of
photon is obtained.Comment: 9 pages,RevTeX, no figure, revised for publicatio
Quantum Mechanics of Proca Fields
We construct the most general physically admissible positive-definite inner
product on the space of Proca fields. Up to a trivial scaling this defines a
five-parameter family of Lorentz invariant inner products that we use to
construct a genuine Hilbert space for the quantum mechanics of Proca fields. If
we identify the generator of time-translations with the Hamiltonian, we obtain
a unitary quantum system that describes first-quantized Proca fields and does
not involve the conventional restriction to the positive-frequency fields. We
provide a rather comprehensive analysis of this system. In particular, we
examine the conserved current density responsible for the conservation of the
probabilities, explore the global gauge symmetry underlying the conservation of
the probabilities, obtain a probability current density, construct position,
momentum, helicity, spin, and angular momentum operators, and determine the
localized Proca fields. We also compute the generalized parity (\cP),
generalized time-reversal (\cT), and generalized charge or chirality (\cC)
operators for this system and offer a physical interpretation for its
\cP\cT-, \cC-, and \cC\cP\cT-symmetries.Comment: Published version, typos fixed, a change in symbol, 1 fi
On Equivalence of Duffin-Kemmer-Petiau and Klein-Gordon Equations
A strict proof of equivalence between Duffin-Kemmer-Petiau (DKP) and
Klein-Gordon (KG) theories is presented for physical S-matrix elements in the
case of charged scalar particles interacting in minimal way with an external or
quantized electromagnetic field. First, Hamiltonian canonical approach to DKP
theory is developed in both component and matrix form. The theory is then
quantized through the construction of the generating functional for Green
functions (GF) and the physical matrix elements of S-matrix are proved to be
relativistic invariants. The equivalence between both theories is then proved
using the connection between GF and the elements of S-matrix, including the
case of only many photons states, and for more general conditions - so called
reduction formulas of Lehmann, Symanzik, Zimmermann.Comment: 23 pages, no figures, requires macro tcilate
Solving the inhomogeneous Bethe-Salpeter equation
We develop an advanced method of solving homogeneous and inhomogeneous
Bethe-Salpeter equations by using the expansion over the complete set of
4-dimensional spherical harmonics. We solve Bethe-Salpeter equations for bound
and scattering states of scalar and spinor particles for the case of one meson
exchange kernels. Phase shifts calculated for the scalar model are in agreement
with the previously published results. We discuss possible manifestations of
separability for one meson exchange interaction kernels.Comment: 9 pages, 11 eps-figures. Talk presented by S. S. Semikh at XVII
International Baldin Seminar on High Energy Physics Problems "Relativistic
Nuclear Physics and Quantum Chromodynamics", September 27 - October 2, 2004,
Dubna, Russia; to appear in the proceedings of this conferenc
Silicon pixel detector for the TTF-FEL beam trajectory monitor
Abstract In order to achieve the high brightness promised by the single-pass Free Electron Laser (FEL) at the TESLA Test Facility (TTF) at DESY, the electron beam position must be controlled better than 10 m over a distance of 15 m. The design of a monitor system with this accuracy is described. The silicon pixel detector, which is critical to this monitor, must have a position resolution of 1 m and an excellent sensitivity for soft X-rays above 150 eV. The silicon pixel detector and its readout electronics are also described
The GRA Beam-Splitter Experiments and Particle-Wave Duality of Light
Grangier, Roger and Aspect (GRA) performed a beam-splitter experiment to
demonstrate the particle behaviour of light and a Mach-Zehnder interferometer
experiment to demonstrate the wave behaviour of light. The distinguishing
feature of these experiments is the use of a gating system to produce near
ideal single photon states. With the demonstration of both wave and particle
behaviour (in two mutually exclusive experiments) they claim to have
demonstrated the dual particle-wave behaviour of light and hence to have
confirmed Bohr's principle of complementarity. The demonstration of the wave
behaviour of light is not in dispute. But we want to demonstrate, contrary to
the claims of GRA, that their beam-splitter experiment does not conclusively
confirm the particle behaviour of light, and hence does not confirm
particle-wave duality, nor, more generally, does it confirm complementarity.
Our demonstration consists of providing a detailed model based on the Causal
Interpretation of Quantum Fields (CIEM), which does not involve the particle
concept, of GRA's which-path experiment. We will also give a brief outline of a
CIEM model for the second, interference, GRA experiment.Comment: 24 pages, 4 figure
The source ambiguity problem: Distinguishing the effects of grammar and processing on acceptability judgments
Judgments of linguistic unacceptability may theoretically arise from either grammatical deviance or significant processing difficulty. Acceptability data are thus naturally ambiguous in theories that explicitly distinguish formal and functional constraints. Here, we consider this source ambiguity problem in the context of Superiority effects: the dispreference for ordering a wh-phrase in front of a syntactically “superior” wh-phrase in multiple wh-questions, e.g., What did who buy? More specifically, we consider the acceptability contrast between such examples and so-called D-linked examples, e.g., Which toys did which parents buy? Evidence from acceptability and self-paced reading experiments demonstrates that (i) judgments and processing times for Superiority violations vary in parallel, as determined by the kind of wh-phrases they contain, (ii) judgments increase with exposure, while processing times decrease, (iii) reading times are highly predictive of acceptability judgments for the same items, and (iv) the effects of the complexity of the wh-phrases combine in both acceptability judgments and reading times. This evidence supports the conclusion that D-linking effects are likely reducible to independently motivated cognitive mechanisms whose effects emerge in a wide range of sentence contexts. This in turn suggests that Superiority effects, in general, may owe their character to differential processing difficulty
Hamilton Operator and the Semiclassical Limit for Scalar Particles in an Electromagnetic Field
We successively apply the generalized Case-Foldy-Feshbach-Villars (CFFV) and
the Foldy-Wouthuysen (FW) transformation to derive the Hamiltonian for
relativistic scalar particles in an electromagnetic field. In contrast to the
original transformation, the generalized CFFV transformation contains an
arbitrary parameter and can be performed for massless particles, which allows
solving the problem of massless particles in an electromagnetic field. We show
that the form of the Hamiltonian in the FW representation is independent of the
arbitrarily chosen parameter. Compared with the classical Hamiltonian for point
particles, this Hamiltonian contains quantum terms characterizing the
quadrupole coupling of moving particles to the electric field and the electric
and mixed polarizabilities. We obtain the quantum mechanical and semiclassical
equations of motion of massive and massless particles in an electromagnetic
field.Comment: 17 page
- …