20,521 research outputs found
Nevirapine-Induced Heratotoxicity: Incidence, Risk Factors and Associated Mortality in a Primary Care ART Programme in South Africa
CROI 200
Quantum Inequalities and Singular Energy Densities
There has been much recent work on quantum inequalities to constrain negative
energy. These are uncertainty principle-type restrictions on the magnitude and
duration of negative energy densities or fluxes. We consider several examples
of apparent failures of the quantum inequalities, which involve passage of an
observer through regions where the negative energy density becomes singular. We
argue that this type of situation requires one to formulate quantum
inequalities using sampling functions with compact support. We discuss such
inequalities, and argue that they remain valid even in the presence of singular
energy densities.Comment: 18 pages, LaTex, 2 figures, uses eps
Detection of Formaldehyde Towards the Extreme Carbon Star IRC+10216
We report the detection of H2CO (formaldehyde) around the carbon-rich AGB
star, IRC+10216. We find a fractional abundance with respect to molecular
hydrogen of x(H2CO)= (1.3 {+1.5}{-0.8}) x 10^{-8}. This corresponds to a
formaldehyde abundance with respect to water vapor of x(H2CO)/x(H2O)=(1.1 +/-
0.2) x 10^{-2}, in line with the formaldehyde abundances found in Solar System
comets, and indicates that the putative extrasolar cometary system around
IRC+10216 may have a similar chemical composition to Solar System comets.
However, we also failed to detect CH3OH (methanol) around IRC+10216 and our
upper limit of x(CH3OH)/x(H2O) < 7.7 x 10^{-4}, (3 sigma), indicates that
methanol is substantially underabundant in IRC+10216, compared to Solar System
comets. We also conclude, based on offset observations, that formaldehyde has
an extended source in the envelope of IRC+10216 and may be produced by the
photodissociation of a parent molecule, similar to the production mechanism for
formaldehyde in Solar System comet comae. Preliminary mapping observations also
indicate a possible asymmetry in the spatial distribution of formaldehyde
around IRC+10216, but higher signal-to-noise observations are required to
confirm this finding. This study is based on observations carried out with the
IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and
IGN (Spain). (abridged)Comment: accepted to ApJ, 45 pages, 11 figure
Effectiveness of highly active antiretroviral therapy in HIV-positive children: evaluation at 12 months in a routine program in Cambodia.
OBJECTIVE: Increasing access to highly active antiretroviral therapy to reach all those in need in developing countries (scale up) is slowly expanding to HIV-positive children, but documented experience remains limited. We aimed to describe the clinical, immunologic, and virologic outcomes of pediatric patients with >12 months of highly active antiretroviral therapy in 2 routine programs in Cambodia. METHODS: Between June 2003 and March 2005, 212 children who were younger than 13 years started highly active antiretroviral therapy. Most patients started a standard first-line regimen of lamivudine, stavudine, and nevirapine, using split adult fixed-dosage combinations. CD4 percentage and body weight were monitored routinely. A cross-sectional virologic analysis was conducted in January 2006; genotype resistance testing was performed for patients with a detectable viral load. RESULTS: Mean age of the subjects was 6 years. Median CD4 percentage at baseline was 6. Survival was 92% at 12 months and 91% at 24 months; 13 patients died, and 4 were lost to follow-up. A total of 81% of all patients had an undetectable viral load. Among the patients with a detectable viral load, most mutations were associated with resistance to lamivudine and non-nucleoside reverse-transcriptase inhibitor drugs. Five patients had developed extensive antiretroviral resistance. Being an orphan was found to be a predictor of virologic failure. CONCLUSIONS: This study provides additional evidence of the effectiveness of integrating HIV/AIDS care with highly active antiretroviral therapy for children in a routine setting, with good virologic suppression and immunologic recovery achieved by using split adult fixed-dosage combinations. Viral load monitoring and HIV genotyping are valuable tools for the clinical follow-up of the patients. Orphans should receive careful follow-up and extra support
The quantum inequalities do not forbid spacetime shortcuts
A class of spacetimes (comprising the Alcubierre bubble, Krasnikov tube, and
a certain type of wormholes) is considered that admits `superluminal travel' in
a strictly defined sense. Such spacetimes (they are called `shortcuts' in this
paper) were suspected to be impossible because calculations based on `quantum
inequalities' suggest that their existence would involve Planck-scale energy
densities and hence unphysically large values of the `total amount of negative
energy' E_tot. I argue that the spacetimes of this type may not be unphysical
at all. By explicit examples I prove that: 1) the relevant quantum inequality
does not (always) imply large energy densities; 2) large densities may not lead
to large values of E_tot; 3) large E_tot, being physically meaningless in some
relevant situations, does not necessarily exclude shortcuts.Comment: Minor corrections and addition
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