236 research outputs found
Quantitative Estimation of the Ratio of GABA-Immunoreactive Cells in Neocortical Grafts
Somatosensory anlage from 17-18 day old rat
embryos were transplanted in place of the
removed barrel cortex in adult rats. Six to eight
months after transplantation, the grafts were
either completely separated by glial scar or
partly separated and partly confluent with the
host neocortex. Each was studied histologically
and immunostained for GABA. It was found that
in partly confluent grafts the neuronal density
was similar or even higher than in the host
cortex, while the cell number in the separate
grafts was much lower than in the nearby host
cortex. The number of GABA-positive cells,
however, was in all grafts significantly lower
(2.9% on average) than in the normal cortex
(11.8% on average).The decline in GABA-stained
nerve cells was highest in separated
grafts, but was somewhat less marked in
transplants partly confluent with the host tissue.
The possible role of partial or total
deafferentation as well as the relative
vulnerability of the transplanted tissue by
temporary hypoxia and other metabolic
disturbances are discussed as the probable
factors in selective decline of GABA-ergic cells in
the transplanted somatosensory cortex
Investigation of activation cross-sections of proton induced nuclear reactions on natTl up to 42 MeV: review, new data and evaluation
Cross-sections of proton induced nuclear reactions on natural thallium have
been studied for investigation of the production of the medical important 201Tl
diagnostic radioisotope. The excitation functions of 204mPb, 203Pb, 202mPb,
201Pb, 200Pb, 199Pb, 202Tl (direct, cumulative), 201Tl (direct, cumulative),
200Tl(direct), and 203Hg were measured up to 42 MeV proton energy by stacked
foil technique and activation method. The experimental data were compared with
the critically analyzed experimental data in the literature, with the IAEA
recommended data and with the results of model calculations by using the
ALICE-IPPE, EMPIRE-II and TALYS codes
The effective bandwidth problem revisited
The paper studies a single-server queueing system with autonomous service and
priority classes. Arrival and departure processes are governed by marked
point processes. There are buffers corresponding to priority classes,
and upon arrival a unit of the th priority class occupies a place in the
th buffer. Let , denote the quota for the total
th buffer content. The values are assumed to be large, and
queueing systems both with finite and infinite buffers are studied. In the case
of a system with finite buffers, the values characterize buffer
capacities.
The paper discusses a circle of problems related to optimization of
performance measures associated with overflowing the quota of buffer contents
in particular buffers models. Our approach to this problem is new, and the
presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in
Stochastic Model
Age-Related Loss of GABA-Positive and GABA-Negative Neurons in Neocortical Transplants
The numerical density of GABA
immunopositive and GABA immunonegative
neurons was quantitatively determined in 0, 12,
30 and 90 day-old neocortical transplants,
derived from E17 rat embryos and transplanted
into adult hosts. It was found that the original,
very high neuronal density in the fetal
transplant declined steadily after
transplantation to the somatosensory cortex of
adult rat. The decline in numerical density of
GABA-positive neurons, however, was
disproportionately larger than that of GABA-negative
nerve cells: At 90 days the proportion
of GABA-positive cells was 2.3% (in contrast to
the 11.8% in the adult host cortex). The density
of GABA-negative neurons, on the other hand,
remained slightly higher than comparable
values in the control cortex. The decline in
density Of GABA-positive neurons was
continuous until the 90th post-transplantation
day, while final, close to normal density values
of GABA-negative nerve cells were already
reached in 30 day-old grafts, with no significant
change afterwards
Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet
The electronic structure of the single molecule magnet system
M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray
photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission
spectroscopy, and density functional calculations. There is good agreement
between theoretical calculations and experimental data. The valence band mainly
consists of three bands between 2 eV and 30 eV. Both theory and experiments
show that the top of the valence band is dominated by the hybridization between
Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe
in the molecule is most likely in the 2+ charge state. Its neighboring atoms
(O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron
atom, giving a high spin state molecule with a total S=5 effective spin for the
case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy
Latrocimicinae completes the phylogeny of Cimicidae: meeting old morphologic data rather than modern host phylogeny.
The family Cimicidae includes obligate hematophagous ectoparasites (bed bugs and their relatives) with high veterinary/medical importance. The evolutionary relationships of Cimicidae and their hosts have recently been reported in a phylogenetic context, but in the relevant study, one of the six subfamilies, the bat-specific Latrocimicinae, was not represented. In this study the only known species of Latrocimicinae, i.e., Latrocimex spectans, was analyzed with molecular and phylogenetic methods based on four (two nuclear and two mitochondrial) genetic markers. The completed subfamily-level phylogeny of Cimicidae showed that Latrocimicinae is most closely related to Haematosiphoninae (ectoparasites of birds and humans), with which it shares systematically important morphologic characters, but not hosts. Moreover, in the phylogenetic analyses, cimicid bugs that are known to infest phylogenetically distant bat hosts clustered together (e.g., Leptocimex and Stricticimex within Cacodminae), while cimicid subfamilies (Latrocimicinae, Primicimicinae) that are known to infest bat hosts from closely related superfamilies clustered distantly. In conclusion, adding Latrocimicinae significantly contributed to the resolution of the phylogeny of Cimicidae. The close phylogenetic relationship between Latrocimicinae and Haematosiphoninae is consistent with long-known morphologic data. At the same time, phylogenetic relationships of genera within subfamilies are inconsistent with the phylogeny of relevant hosts
Persistence exponents of non-Gaussian processes in statistical mechanics
Motivated by certain problems of statistical physics we consider a stationary
stochastic process in which deterministic evolution is interrupted at random
times by upward jumps of a fixed size. If the evolution consists of linear
decay, the sample functions are of the "random sawtooth" type and the level
dependent persistence exponent \theta can be calculated exactly. We then
develop an expansion method valid for small curvature of the deterministic
curve. The curvature parameter g plays the role of the coupling constant of an
interacting particle system. The leading order curvature correction to \theta
is proportional to g^{2/3}. The expansion applies in particular to exponential
decay in the limit of large level, where the curvature correction considerably
improves the linear approximation. The Langevin equation, with Gaussian white
noise, is recovered as a singular limiting case.Comment: 20 pages, 3 figure
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