496 research outputs found
MPTP-induced degeneration: interference with glutamatergic toxicity
Parkinson's disease (PD) is characterised by the progressive degeneration of nigrostriatal dopamine (DA) neurons resulting in the major symptoms of akinesia and rigidity. Although the primary cause of PD is still not known some features make this disorder a model for neurodegenerative diseases in general. It has been known for some time that symptomatic PD can be attributed to insults with symptoms occurring many years later such as post-encephalitic PD or PD following manganese poisoning. More recently, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) has been identified as a neurotoxin selective for melanin-containing dopaminergic neurons in humans and non-human primates. The specificity of this neurotoxin and the striking clinical similarities to idiopathic PD, seen in primates, make MPTP-induced parkinsonism the most useful animal model of a neurological disease. There are numerous theoretical possibilities to interfere with both MPTP-induced neurotoxicity and the symptomatology of PD. In recent years excitatory amino acids have gained considerable interest since they can cause excitotoxic lesion of neurons under a number of pathological conditions (Olney et al., 1989; Choi, 1988). Here we summarise the present data and provide new experimental evidence indicating that MPTP-induced degeneration of dopaminergic neurons does involve glutamate-mediated toxicity. It is concluded that glutamate-mediated excitotoxicity results in the destruction of DAergic somata in the substantia nigra. Non-competitive or competitive NMDA antagonists protect nigral neurons from MPTP-induced degeneration whereas their striatal terminals still seem to degenerate
Wave Propagation and Diffusive Transition of Oscillations in Pair Plasmas with Dust Impurities
In view of applications to electron-positron pair-plasmas and fullerene
pair-ion-plasmas containing charged dust impurities a thorough discussion is
given of three-component Plasmas. Space-time responses of multi-component
linearized Vlasov plasmas on the basis of multiple integral equations are
invoked. An initial-value problem for Vlasov-Poisson -Ampere equations is
reduced to the one multiple integral equation and the solution is expressed in
terms of forcing function and its space-time convolution with the resolvent
kernel. The forcing function is responsible for the initial disturbance and the
resolvent is responsible for the equilibrium velocity distributions of plasma
species. By use of resolvent equations, time-reversibility, space-reflexivity
and the other symmetries are revealed. The symmetries carry on physical
properties of Vlasov pair plasmas, e.g., conservation laws. Properly choosing
equilibrium distributions for dusty pair plasmas, we can reduce the resolvent
equation to: (i) the undamped dispersive wave equations, (ii) wave-diffusive
transport equation (iii) and diffusive transport equations of oscillations. In
the last case we have to do with anomalous diffusion employing fractional
derivatives in time and space. Fractional diffusion equations account for
typical anomalous features, which are observed in many systems, e.g. in the
case of dispersive transport in amorphous semiconductors, liquid crystals,
polymers, proteins and biosystems.Comment: 6 page
Measured residual stress distributions for low and high heat input single weld beads deposited on to SA508 steel
Effects of stop-start features on residual stresses in a multipass austenitic stainless steel weld
Domain Wall Dynamics of Phase Interfaces
The statics and dynamics of a surface separating two phases of a relativistic
quantum field theory at or near the critical temperature typically make use of
a free energy as a functional of an order parameter. This free energy
functional also affords an economical description of states away from
equilibrium. The similarities and differences between using a scalar field as
the order parameter versus the energy density are examined, and a peculiarity
is noted. We also point out several conceptual errors in the literature dealing
with the dynamical prefactor in the nucleation rate.Comment: 12 pages plus 5 figure
On the evolution of local material properties and residual stress in a three-pass SA508 steel weld
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
Nucleation of Quark--Gluon Plasma from Hadronic Matter
The energy densities achieved during central collisions of large nuclei at
Brookhaven's AGS may be high enough to allow the formation of quark--gluon
plasma. Calculations based on relativistic nucleation theory suggest that rare
events, perhaps one in every 10 or 10, undergo the phase transition.
Experimental ramifications may include an enhancement in the ratio of pions to
baryons, a reduction in the ratio of deuterons to protons, and a larger source
size as seen by hadron interferometry.Comment: 22 pages, 7 figures available upon request, NUC--MINN--94/5--
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