332 research outputs found
Molecular basis of glutamate toxicity in retinal ganglion cells
Loss of retinal ganglion cells (RGCs) is a hallmark of many ophthalmic diseases including glaucoma, retinal ischemia due to central artery occlusion, anterior ischemic optic neuropathy and may be significant in optic neuritis, optic nerve trauma, and AIDS. Recent research indicates that neurotoxicity is caused by excessive stimulation of receptors for excitatory amino acids (EAAs). In particular, the amino acid glutamate has been shown to act as a neurotoxin which exerts its toxic effect on RGCs predominantly through the N-methyl-d-aspartate (NMDA) subtype of glutamate receptor. NMDA-receptor-mediated toxicity in RGCs is dependent on the influx of extracellular Ca2+. The increase in [Ca2+]i acts as a second messenger that sets in motion the cascade leading to eventual cell death. Glutamate stimulates its own release in a positive feedback loop by its interaction with the non-NMDA receptor subtypes. Ca2+-induced Ca2+ release and further influx of Ca2+ through voltage-gated Ca2+ channels after glutamate-induced depolarization contribute to glutamate toxicity. In vitro and in vivo studies suggest that the use of selective NMDA receptor antagonists or Ca2+ channel blockers should be useful in preventing or at least abating neuronal loss in the retina. Of particular importance for future clinical use of NMDA receptor antagonists in the treatment of acute vascular insults is the finding that some drugs can prevent glutamate-induced neurotoxicity, even when administered a few hours after the onset of retinal ischemia
Stability and Instability of Relativistic Electrons in Classical Electro magnetic Fields
The stability of matter composed of electrons and static nuclei is
investigated for a relativistic dynamics for the electrons given by a suitably
projected Dirac operator and with Coulomb interactions. In addition there is an
arbitrary classical magnetic field of finite energy. Despite the previously
known facts that ordinary nonrelativistic matter with magnetic fields, or
relativistic matter without magnetic fields is already unstable when the fine
structure constant, is too large it is noteworthy that the combination of the
two is still stable provided the projection onto the positive energy states of
the Dirac operator, which defines the electron, is chosen properly. A good
choice is to include the magnetic field in the definition. A bad choice, which
always leads to instability, is the usual one in which the positive energy
states are defined by the free Dirac operator. Both assertions are proved here.Comment: LaTeX fil
Long Range Forces from Pseudoscalar Exchange
Using dispersion theoretic techniques, we consider coherent long range forces
arising from double pseudoscalar exchange among fermions. We find that Yukawa
type coupling leads to spin independent attractive potentials whereas
derivative coupling renders spin independent repulsive potentials.Comment: 27 pages, REVTeX, 3 figures included using epsfi
How to obtain a covariant Breit type equation from relativistic Constraint Theory
It is shown that, by an appropriate modification of the structure of the
interaction potential, the Breit equation can be incorporated into a set of two
compatible manifestly covariant wave equations, derived from the general rules
of Constraint Theory. The complementary equation to the covariant Breit type
equation determines the evolution law in the relative time variable. The
interaction potential can be systematically calculated in perturbation theory
from Feynman diagrams. The normalization condition of the Breit wave function
is determined. The wave equation is reduced, for general classes of potential,
to a single Pauli-Schr\"odinger type equation. As an application of the
covariant Breit type equation, we exhibit massless pseudoscalar bound state
solutions, corresponding to a particular class of confining potentials.Comment: 20 pages, Late
On the validity of the reduced Salpeter equation
We adapt a general method to solve both the full and reduced Salpeter
equations and systematically explore the conditions under which these two
equations give equivalent results in meson dynamics. The effects of constituent
mass, angular momentum state, type of interaction, and the nature of
confinement are all considered in an effort to clearly delineate the range of
validity of the reduced Salpeter approximations. We find that for
the solutions are strikingly similar for all
constituent masses. For zero angular momentum states the full and reduced
Salpeter equations give different results for small quark mass especially with
a large additive constant coordinate space potential. We also show that
corrections to heavy-light energy levels can be accurately
computed with the reduced equation.Comment: Latex (uses epsf macro), 24 pages of text, 12 postscript figures
included. Slightly revised version, to appear in Phys. Rev.
The exact Darwin Lagrangian
Darwin (1920) noted that when radiation can be neglected it should be
possible to eliminate the radiation degrees-of-freedom from the action of
classical electrodynamics and keep the discrete particle degrees-of-freedom
only. Darwin derived his well known Lagrangian by series expansion in
keeping terms up to order . Since radiation is due to acceleration the
assumption of low speed should not be necessary. A Lagrangian is suggested that
neglects radiation without assuming low speed. It cures deficiencies of the
Darwin Lagrangian in the ultra-relativistic regime.Comment: 2.5 pages, no figure
Ionization Potential of the Helium Atom
Ground state ionization potential of the He^4 atom is evaluated to be 5 945
204 221 (42) MHz. Along with lower order contributions, this result includes
all effects of the relative orders alpha^4, alpha^3*m_e/m_alpha and
alpha^5*ln^2(alpha).Comment: 4 page
Coordinate-space approach to the bound-electron self-energy: Self-Energy screening calculation
The self-energy screening correction is evaluated in a model in which the
effect of the screening electron is represented as a first-order perturbation
of the self energy by an effective potential. The effective potential is the
Coulomb potential of the spherically averaged charge density of the screening
electron. We evaluate the energy shift due to a , ,
, or electron screening a , ,
, or electron, for nuclear charge Z in the range . A detailed comparison with other calculations is made.Comment: 54 pages, 10 figures, 4 table
Multiparticle equations for interacting Dirac fermions in magnetically confined graphene quantum dots
We study the energy of quasi-particles in graphene within the Hartree-Fock approximation. The quasi-particles are confined via an inhomogeneous magnetic field and interact via the Coulomb potential. We show that the associated functional has a minimizer and determines the stability conditions for the N-particle problem in such a graphene quantum dot
The Standard Model in Strong Fields: Electroweak Radiative Corrections for Highly Charged Ions
Electroweak radiative corrections to the matrix elements are calculated for highly charged hydrogenlike ions. These
matrix elements constitute the basis for the description of the most parity
nonconserving (PNC) processes in atomic physics. The operator
represents the parity nonconserving relativistic effective atomic Hamiltonian
at the tree level. The deviation of these calculations from the calculations
valid for the momentum transfer demonstrates the effect of the strong
field, characterized by the momentum transfer ( is the
electron mass). This allows for a test of the Standard Model in the presence of
strong fields in experiments with highly charged ions.Comment: 27 LaTex page
- âŠ