12,376 research outputs found
On the IMF in a Triggered Star Formation Context
The origin of the stellar initial mass function (IMF) is a fundamental issue
in the theory of star formation. It is generally fit with a composite power
law. Some clues on the progenitors can be found in dense starless cores that
have a core mass function (CMF) with a similar shape. In the low-mass end,
these mass functions increase with mass, albeit the sample may be somewhat
incomplete; in the high-mass end, the mass functions decrease with mass. There
is an offset in the turn-over mass between the two mass distributions. The
stellar mass for the IMF peak is lower than the corresponding core mass for the
CMF peak in the Pipe Nebula by about a factor of three. Smaller offsets are
found between the IMF and the CMFs in other nebulae. We suggest that the offset
is likely induced during a starburst episode of global star formation which is
triggered by the formation of a few O/B stars in the multi-phase media, which
naturally emerged through the onset of thermal instability in the cloud-core
formation process. We consider the scenario that the ignition of a few massive
stars photoionizes the warm medium between the cores, increases the external
pressure, reduces their Bonnor?Ebert mass, and triggers the collapse of some
previously stable cores. We quantitatively reproduce the IMF in the low-mass
end with the assumption of additional rotational fragmentation.Comment: 3 figure
Study of Xenopus orthologs of novel genes expressed in the mouse AVE
info:eu-repo/semantics/publishedVersio
Action of metronidazole in combination with isoniazid & rifampicin on persisting organisms in experimental murine tuberculosis
To study the activity of metronidazole on persisting tubercle bacilli, BALB/c mice were infected with
Mycobacterium tuberculosis and, after 14 days, treated with isoniazid (H) or rifampicin (R) or isoniazid
+ rifampicin (HR) for 2 months. An untreated group and a group treated with metronidazole (M)
alone served as controls. At the end of 2 months, M was added to the H, R, and HR regimen in half
the mice, and the treatment was continued for 1 more month in all mice. At the end of treatment, no
viable organisms were detected in the lung or spleen of mice treated with HR or HRM regimens. In
contrast, compared to the mice treated with R alone, the log10 colony forming units (cfu) of mice
treated with RM were lower by 1.84 and 0.52 in the lung and spleen, respectively. Similarly, compared
to the H group, the log10 cfu were lower by 0.67 in the spleen of mice treated with HM, and no
additional effect due to M was seen in the lung. Three months after stopping treatment, viable
organisms were isolated from both the organs of all the groups. However, the log10 cfu in the lung and
spleen for the groups with metronidazole were below the log10 cfu for the respective single or 2 drug
groups, except the log10 cfu in the lung for the RM group. These findings suggest that metronidazole,
given with bactericidal drugs such as rifampicin and isoniazid may be of value in eliminating
persisting tubercle bacilli, but further studies are warranted
BCG: Do we have an alternative?
Vaccination is generally used as a form of immunoprophylaxis,
so that administration of the vaccine even a
long. time before exposure to the wild-type infectious
organism should afford protection. Since effector T
and B cells are short-lived, a prime requisite for a
vaccine is to generate immunological memory.1 In the
case organisms such as mycobacteria which are
obligate intracellular pathogens and which elicit
granulomatous tissue reactions, artificial immunisation
with live bacteria is required to induce protection.2,3
The only existing vaccine against tuberculosis is the
BCG (Bacille Calmette - Guerin), an attenuated strain
of M.bovis and it is mandatory or officially recommended
in 182 countries or territories. Under the
Expanded Programme on Immuisation (EPT) started
by the Government of India in 1978, BCG is recommended
to be given to all infants 3-9 months after
birth.
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
Bactericidal action of pulsed exposure to rifampicin, ethambutol, isoniazid & pyrazinamide on Mycobacterium tuberculosis in vitro
The bactericidal action of pulsed exposure to rifampicin (R), ethambutol (Emb), isoniazid (I) and
pyrazinamide (Z) togcthcr on alternate days (REmbIZ) and as REmb and IZ separately on alternate
days (REmb/IZ) on M.tuberculosis H37Rv, two isolates of M.tuberculosis sensitive to these drugs, as
well as four isolates resistant to one or more drugs, was studied using an in vitro method. The
experimental duration was 6 days. REmbIZ and REmb/IZ appeared to have equally good bactericidal
action on M.tuberculosis strains in the in vitro system. The results suggest that splitting REmbIZ into
REmb and IZ on alternate days in short course chemotherapy regimens for tuberculosis may not affect
the bactericidal action of the regimens
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
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
Protective response in guineapigs exposed to Mycobacterium avium intracellulare/ M. scrofulaceum, BCG & south Indian isolates of M. tuberculosis
The protective immunity resulting from exposure to nontuberculous mycobacteria (NTM), BCG and
virulent mycobacteria in different sequences was studied in the guineapig model employing strains
prevalent in the south Indian BCG trial area and time kinetics to observe the immuno-modulation. The
findings suggest that during the early course of challenge infection in guineapigs there was no
interference with the immunity due to BCG, by prior exposure to NTM. In the animals sensitised with
M. avium intracellulare before immunisation, the challenge infection was localised and confined to the
site of inoculation, and only a few organisms reached the spleen.. However, at the later stages of the
infection, as seen by the spleen viable counts at 12 wk, it appeared that the barrier at the localised site of
infection may not be intact in the animals with prior exposure to NTM, and a few organisms disseminate
to the spleen
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