974 research outputs found
Effects of the variation of fundamental constants on Pop III stellar evolution
A variation of the fundamental constants is expected to affect the
thermonuclear rates important for stellar nucleosynthesis. In particular,
because of the very small resonant energies of Be8 and C12, the triple
process is extremely sensitive to any such variations. Using a microscopic
model for these nuclei, we derive the sensitivity of the Hoyle state to the
nucleon-nucleon potential allowing for a change in the magnitude of the nuclear
interaction. We follow the evolution of 15 and 60 solar mass, zero metallicity
stellar models, up to the end of core helium burning. These stars are assumed
to be representative of the first, Population III stars. We derive limits on
the variation of the magnitude of the nuclear interaction and model dependent
limits on the variation of the fine structure constant based on the calculated
oxygen and carbon abundances resulting from helium burning. The requirement
that some C12 and O16 be present are the end of the helium burning phase allows
for permille limits on the change of the nuclear interaction and limits of
order 10^{-5} on the fine structure constant relevant at a cosmological
redshift of z ~ 15-20.Comment: 14 pages, 12 figure
Perylene and pyrromethene doped xerogels for solid state pulsed laser
International audienceHydrophobic photostable dye molecules such as perylenes or pyrromethenes were trapped in xerogel matrices. Using these new materials as solid-state dye lasers, we have demonstrated efficient laser operation. Slope efficiencies of up to 30% were obtained in the millijoule output-energy range. Tunabilities of up to 60 nm were observed, and more than 150,000 pulses were emitted by the same spot of a given sample when the laser was pumped at millijoule energy level
Toward millions of laser pulses using pyrromethene and perylene doped xerogels
International audienceSignificant improvements have been obtained for solid-state dye lasers with doped xerogels. By using longitudinal pumping with a frequency-doubled Q-switched Nd: YAG laser, we obtained as much as 86% slope efficiency and 5 3 105 pulses lifetime. Furthermore, newly prepared deoxygenated samples exhibited even greater lifetime
High-contrast Ultrabroadband Frontend Source for High Intensity Few-Cycle Lasers
An ultrabroadband seed source for high-power, high-contrast OPCPA systems at
800 nm is presented. The source is based on post compression in a hollow-core
fiber followed by crossed polarized waves (XPW) filtering and is capable of
delivering 80J, 5fs, CEP-stable (0.3rad RMS) pulses with excellent
spectral and temporal qualit
Reverse saturable absorption in solid xerogel matrices
International audienceAluminophthalocyanine (APC) and fullerene carbon 60 (C,) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C&,. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matri
Development of recombinant nucleoprotein-based diagnostic systems for lassa fever
Diagnostic systems for Lassa fever (LF), a viral hemorrhagic fever caused by Lassa virus (LASV), such as enzyme immunoassays for the detection of LASV antibodies and LASV antigens, were developed using the recombinant nucleoprotein (rNP) of LASV (LASV-rNP). The LASV-rNP was expressed in a recombinant baculovirus system. LASV-rNP was used as an antigen in the detection of LASV-antibodies and as an immunogen for the production of monoclonal antibodies. The LASV-rNP was also expressed in HeLa cells by transfection with the expression vector encoding cDNA of the LASV-NP gene. An immunoglobulin G enzyme-linked immunosorbent assay (ELISA) using LASV-rNP and an indirect immunofluorescence assay using LASV-rNP-expressing HeLa cells were confirmed to have high sensitivity and specificity in the detection of LASV-antibodies. A novel monoclonal antibody to LASV-rNP, monoclonal antibody 4A5, was established. A sandwich antigen capture (Ag-capture) ELISA using the monoclonal antibody and an anti-LASV-rNP rabbit serum as capture and detection antibodies, respectively, was then developed. Authentic LASV nucleoprotein in serum samples collected from hamsters experimentally infected with LASV was detected by the Ag-capture ELISA. The Ag-capture ELISA specifically detected LASV-rNP but not the rNPs of lymphocytic choriomeningitis virus or Junin virus. The sensitivity of the Ag-capture ELISA in detecting LASV antigens was comparable to that of reverse transcription-PCR in detecting LASV RNA. These LASV rNP-based diagnostics were confirmed to be useful in the diagnosis of LF even in institutes without a high containment laboratory, since the antigens can be prepared without manipulation of the infectious viruses.Instituto de Biotecnologia y Biologia Molecula
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