592 research outputs found
Status epilepticus results in reversible neuronal injury in infant rat hippocampus: novel use of a marker.
Despite ready induction of severe limbic status epilepticus by systemic kainic acid (KA) in infant rats, excitotoxic neuronal injury has not been observed. The mechanisms of this resistance of the immature hippocampus to excitotoxicity are unknown. Acid fuchsin stain has been used as a marker of irreversibly injured neurons in the adult brain. We speculated that the dye might map reversibly injured neurons in the infant. Subsequent to KA-induced status epilepticus in 11-day-old rats, acid fuchsin stain was evident in the hippocampal CA3, CA1, dentate gyrus and hilus by 24 h, peaked at 48 h and disappeared by 6 days, without evidence for neuronal loss. Acid fuchsin may be a useful tool for delineating the distribution of reversibly injured immature neurons in experimental seizure paradigms
Deposition of general ellipsoidal particles
We present a systematic overview of granular deposits composed of ellipsoidal
particles with different particle shapes and size polydispersities. We study
the density and anisotropy of such deposits as functions of size polydispersity
and two shape parameters that fully describe the shape of a general ellipsoid.
Our results show that, while shape influences significantly the macroscopic
properties of the deposits, polydispersity plays apparently a secondary role.
The density attains a maximum for a particular family of non-symmetrical
ellipsoids, larger than the density observed for prolate or oblate ellipsoids.
As for anisotropy measures, the contact forces show are increasingly preferred
along the vertical direction as the shape of the particles deviates for a
sphere. The deposits are constructed by means of an efficient molecular
dynamics method, where the contact forces are efficiently and accurately
computed. The main results are discussed in the light of applications for
porous media models and sedimentation processes.Comment: 7 pages, 8 figure
Calculation of the Density of States Using Discrete Variable Representation and Toeplitz Matrices
A direct and exact method for calculating the density of states for systems
with localized potentials is presented. The method is based on explicit
inversion of the operator . The operator is written in the discrete
variable representation of the Hamiltonian, and the Toeplitz property of the
asymptotic part of the obtained {\it infinite} matrix is used. Thus, the
problem is reduced to the inversion of a {\it finite} matrix
Diffusional Relaxation in Random Sequential Deposition
The effect of diffusional relaxation on the random sequential deposition
process is studied in the limit of fast deposition. Expression for the coverage
as a function of time are analytically derived for both the short-time and
long-time regimes. These results are tested and compared with numerical
simulations.Comment: 9 pages + 2 figure
An algorithm for series expansions based on hierarchical rate equations
We propose a computational method to obtain series expansions in powers of
time for general dynamical systems described by a set of hierarchical rate
equations. The method is generally applicable to problems in both equilibrium
and nonequilibrium statistical mechanics such as random sequential adsorption,
diffusion-reaction dynamics, and Ising dynamics. New result of random
sequential adsorption of dimers on a square lattice is presented.Comment: LaTeX, 9 pages including 1 figur
Investigation of the Multiple Method Adaptive Control (MMAC) method for flight control systems
The stochastic adaptive control of the NASA F-8C digital-fly-by-wire aircraft using the multiple model adaptive control (MMAC) method is presented. The selection of the performance criteria for the lateral and the longitudinal dynamics, the design of the Kalman filters for different operating conditions, the identification algorithm associated with the MMAC method, the control system design, and simulation results obtained using the real time simulator of the F-8 aircraft at the NASA Langley Research Center are discussed
Glass Transition in a 2D Lattice Model
The dynamics of compaction of hard cross-shaped pentamers on the 2D square
lattice is investigated. The addition of new particles is controlled by
diffusive relaxation. It is shown that the filling process terminates at a
glassy phase with a limiting coverage density \rho_{rcp}=0.171626(3), lower
than the density of closest packing \rho_{cp}=0.2, and the long time filling
rate vanishes like (\rho_{rcp}-\rho(t))^2. For the entire density regime the
particles form an amorphous phase, devoid of any crystalline order. Therefore,
the model supports a stable random packing state, as opposed to the hard disks
system. Our results may be relevant to recent experiments studying the
clustering of proteins on bilayer lipid membranes
Rhythmic coma in children.
We describe a syndrome of rhythmic coma in children that consists of an invariant, nonreactive, diffuse cortical activity of a specific frequency, such as alpha, beta, spindle, or theta, recorded from a comatose child. We report 11 cases of children who were found to be in rhythmic coma during their acute illnesses. Their ages ranged from 2 to 15 years, and their diagnoses included encephalitis, head trauma, seizures, near drowning, brain tumors, stroke, and metabolic derangements. The specific frequency of the electroencephalographic pattern, ie, alpha, beta, spindle, or theta, did not influence the outcome. The clinical outcome appeared to depend on the primary disease process rather than the electroencephalographic finding. The prognosis of alpha-frequency rhythmic coma as well as of rhythmic coma in general was better in children than in adults. The pathophysiology in children may be similar, ie, the interruption of reticulothalamocortical pathways by metabolic or structural abnormalities, but the expression of this deafferentation may be more varied in the developing brain. Thus, we propose the term rhythmic coma as a unified concept for alpha, beta, spindle, and theta coma in children
Dimensional Reduction for Directed Branched Polymers
Dimensional reduction occurs when the critical behavior of one system can be
related to that of another system in a lower dimension. We show that this
occurs for directed branched polymers (DBP) by giving an exact relationship
between DBP models in D+1 dimensions and repulsive gases at negative activity
in D dimensions. This implies relations between exponents of the two models:
(the exponent describing the singularity of the
pressure), and (the correlation length exponent of
the repulsive gas). It also leads to the relation ,
where is the Yang-Lee edge exponent. We derive exact expressions
for the number of DBP of size N in two dimensions.Comment: 7 pages, 1 eps figure, ref 24 correcte
The Importance of Patch Size in Estimating Steady-State Bite Rate in Grazing Cattle
Since the pioneering work of Black and Kenney (1984), various intake studies have been conducted at the spatial scale of a single feeding station ( patch ) to elucidate the processes that determine instantaneous intake rate (e.g. Laca et al., 1994). While these are well-suited for patch depletion studies, it is less clear how well they represent non-patchy and relatively homogeneous environments (Ungar & Griffiths, 2002). Clearly, grazing should be restricted to the upper grazing horizon (i.e. layer of bites), but sample duration may be insufficient to characterize steady-state behaviour, especially when grazing commences on an empty mouth. We examined the impact of feeding station size on bite rate and jaw movement allocation between bites and chews
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