11,677 research outputs found
The Ultrarelativistic Kerr-Geometry and its Energy-Momentum Tensor
The ultrarelativistic limit of the Schwarzschild and the Kerr-geometry
together with their respective energy-momentum tensors is derived. The approach
is based on tensor-distributions making use of the underlying Kerr-Schild
structure, which remains stable under the ultrarelativistic boost.Comment: 16 pages, (AMS-LaTeX), TUW-94-0
Synopsis of biological data on the pink shrimp, Pandalus borealis Kroyer, 1838
This synopsis of the literature was designed to summarize the biological and biochemical studies involving Pandalus borealis as well as to provide a summary of the literature regarding the fisheries data published before early 1984. Included are many unpublished observations, drawn from studies at the State of Maine Department of Marine Resources Laboratory in West Boothbay Harbor, Maine. (PDF file contains 63 pages.
Boosting the Kerr-geometry into an arbitrary direction
We generalize previous work \cite{BaNa3} on the ultrarelativistic limit of
the Kerr-geometry by lifting the restriction on boosting along the axis of
symmetry.Comment: latex2e, no figure
Symmetries of pp-Waves with Distributional Profile
We generalize the classification of (non-vacuum) pp-waves \cite{JEK} based on
the Killing-algebra of the space-time by admitting distribution-valued profile
functions. Our approach is based on the analysis of the (infinite-dimensional)
group of ``normal-form-preserving'' diffeomorphisms.Comment: 10 pages, latex2e, no figures, statement about the combination of
symmetry classes of impulsive waves correcte
Head-on collision of ultrarelativistic charges
We consider the head-on collision of two opposite-charged point particles
moving at the speed of light. Starting from the field of a single charge we
derive in a first step the field generated by uniformly accelerated charge in
the limit of infinite acceleration. From this we then calculate explicitly the
burst of radiation emitted from the head-on collision of two charges and
discuss its distributional structure. The motivation for our investigation
comes from the corresponding gravitational situation where the head-on
collision of two ultrarelativistic particles (black holes) has recently aroused
renewed interest.Comment: 4 figures, uses the AMSmat
A Note on the Symmetries of the Gravitational Field of a Massless Particle
It is shown that the metric of a massless particle obtained from boosting the
Schwarzschild metric to the velocity of light, has four Killing vectors
corresponding to an E(2)\times \RR symmetry-group. This is in agreement with
the expectations based on flat-space kinematics but is in contrast to previous
statements in the literature \cite{Schueck}. Moreover, it also goes beyond the
general Jordan-Ehlers-Kundt-(JEK)-classification of gravitational pp-waves as
given in \cite{JEK}.Comment: 10pages, amslatex, TUW-94-12 and UWThPh-1994-2
Minimal inhibitory concentrations of sulbactam/ampicillin against drug sensitive and drug resistant isolates of Mycobacterium tuberculosis
A total of 92 isolates of Mycobacteriurn tuberculosis consisting of equal numbers of
sensitive and resistant strains was tested for their susceptibility to sulbactam and
ampicillin (in the ratio of 1:2) on Lowenstein-Jensen (LJ) and 7H11 agar media. The
geometric mean MIC was 63.97 μg/ml for the drug sensitive strains and 65.92 μg/ml
for the resistant strains, and the overall mean was 65.01 μg/ml. The high MIC on LJ
medium could be attributed to the higher protein content which resulted in greater
binding of sulbactam/ampicillin. On the other hand, the geometric mean MIC on
7H11 medium was 26.73 μg/ml for sensitive strains and 23.82 μg/ml for resistant
strains; the overall mean being 25.23 μg/ml. Although these MlCs of sulbactamampicillin
are higher than those reported earlier, they can be easily achieved in
serum. Further studies on experimental tuberculosis and in humans will be needed
to prove the efficacy of sulbactam/ampicillin in the treatment of patients with
multidrug resistant tuberculosis
Evaluation of the BACTEC radiometric method in the early diagnosis of tuberculosis
A comparison of the BACTEC radiometric method with the conventional culture and drug
susceptibility testing methods on isolates from clinical specimens in pulmonary and extrapulmonary
tuberculosis, childhood TB and TB in HIV-infected individuals was undertaken. In the case of
pulmonary TB, the rate of isolation of positive cultures was significantly faster with the BACTEC
method, with 87 per cent of the positives being obtained by 7 days, and 96 per cent by 14 days.
However, while there was no difference in the total number of positive cultures by the two methods
in smear positive pulmonary tuberculosis, in smear negative pulmonary TB, the BACTEC method
yielded more number of positive cultures. In extrapulmonary TB, HIV-TB and childhood TB,
although the BACTEC method did not yield additional positives, the detection of positives was
considerably faster than by the conventional methods, in which the degree of growth was also scanty.
The agreement in drug susceptibility tests was 94 per cent for streptomycin and isoniazid, 99 per cent
for rifampicin and 91 per cent for ethambutol. Further, most of the drug susceptibility test results
became available within 8 days by the BACTEC method. By facilitating early diagnosis, the BACTEC
method may prove to be cost effective in a population with a high prevalence of tuberculosis,
particularly in the extrapulmonary and paucibacillary forms of the disease
ADM and Bondi four-momenta for the ultrarelativistic Schwarzschild black hole
We argue that it is possible to assign Bondi as well as ADM four-momentum to
the ultrarelativistic limit of the Schwarzschild black hole in agreement to
what is expected on physical grounds: The Bondi-momentum is lightlike and equal
to the ADM-momentum up to the retarded time when particle and radiation escape
to infinity and drops to zero thereafter, leaving flat space behind.Comment: Changes in the expression used for the ADM four-momentum without
altering the result, correction of some minor typing error
Signal processing in local neuronal circuits based on activity-dependent noise and competition
We study the characteristics of weak signal detection by a recurrent neuronal
network with plastic synaptic coupling. It is shown that in the presence of an
asynchronous component in synaptic transmission, the network acquires
selectivity with respect to the frequency of weak periodic stimuli. For
non-periodic frequency-modulated stimuli, the response is quantified by the
mutual information between input (signal) and output (network's activity), and
is optimized by synaptic depression. Introducing correlations in signal
structure resulted in the decrease of input-output mutual information. Our
results suggest that in neural systems with plastic connectivity, information
is not merely carried passively by the signal; rather, the information content
of the signal itself might determine the mode of its processing by a local
neuronal circuit.Comment: 15 pages, 4 pages, in press for "Chaos
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