7,721 research outputs found
gem-Dibromocyclopropanes and enzymatically derived cis-1,2-dihydrocatechols as building blocks in alkaloid synthesis
The application of the title building blocks, the 6,6-dibromobicyclo[3.1.0]hexanes
and the cis-1,2-dihydrocatechols, to the total synthesis of crinine and lycorinine alkaloids is
described.We thank the Australian Research Council and the Institute of Advanced Studies for generous financial
support
RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap
We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt
Telescope Photometric Survey (XDSS). The area we consider is located in the
North Galactic Cap, covering 376.75 sq deg at RA 150 deg and Dec
27 deg down to a magnitude limit of i 19. Using the
variability information afforded by the multi-epoch nature of our XDSS data,
combined with colors from the Sloan Digital Sky Survey, we are able to identify
candidate RRLs. We find 318 candidates, derive distances to them and estimate
the detection efficiency. The majority of our candidates have more than 12
observations and for these we are able to calculate periods. These also allows
us to estimate our contamination level, which we predict is between 30% to 40%.
Finally we use the sample to probe the halo density profile in the 9-49 kpc
range and find that it can be well fitted by a double power law. We find good
agreement between this model and the models derived for the South Galactic Cap
using the Watkins et al. (2009) and Sesar et al. (2010) RRL data-sets, after
accounting for possible contamination in our data-set from Sagittarius stream
members. We consider non-spherical double power law models of the halo density
profile and again find agreement with literature data-sets, although we have
limited power to constrain the flattening due to our small survey area. Much
tighter constraints will be placed by current and future wide-area surveys,
most notably ESA's astrometric Gaia mission. Our analysis demonstrates that
surveys with a limited number of epochs can effectively be mined for RRLs. Our
complete sample is provided as accompanying online material.Comment: 14 pages, ApJ (in press
PARISROC, a Photomultiplier Array Integrated Read Out Chip
PARISROC is a complete read out chip, in AMS SiGe 0.35 !m technology, for
photomultipliers array. It allows triggerless acquisition for next generation
neutrino experiments and it belongs to an R&D program funded by the French
national agency for research (ANR) called PMm2: ?Innovative electronics for
photodetectors array used in High Energy Physics and Astroparticles?
(ref.ANR-06-BLAN-0186). The ASIC (Application Specific Integrated Circuit)
integrates 16 independent and auto triggered channels with variable gain and
provides charge and time measurement by a Wilkinson ADC (Analog to Digital
Converter) and a 24-bit Counter. The charge measurement should be performed
from 1 up to 300 photo- electrons (p.e.) with a good linearity. The time
measurement allowed to a coarse time with a 24-bit counter at 10 MHz and a fine
time on a 100ns ramp to achieve a resolution of 1 ns. The ASIC sends out only
the relevant data through network cables to the central data storage. This
paper describes the front-end electronics ASIC called PARISROC.Comment: IEEE Nuclear Science Symposium an Medical Imaging Conference (2009
NSS/MIC
Gene dosage compensation calibrates four regulatory RNAs to control Vibrio cholerae quorum sensing
Quorum sensing is a mechanism of cell-to-cell communication that allows bacteria to coordinately regulate gene expression in response to changes in cell-population density. At the core of the Vibrio cholerae quorum-sensing signal transduction pathway reside four homologous small RNAs (sRNAs), named the quorum regulatory RNAs 1–4 (Qrr1–4). The four Qrr sRNAs are functionally redundant. That is, expression of any one of them is sufficient for wild-type quorum-sensing behaviour. Here, we show that the combined action of two feedback loops, one involving the sRNA-activator LuxO and one involving the sRNA-target HapR, promotes gene dosage compensation between the four qrr genes. Gene dosage compensation adjusts the total Qrr1–4 sRNA pool and provides the molecular mechanism underlying sRNA redundancy. The dosage compensation mechanism is exquisitely sensitive to small perturbations in Qrr levels. Precisely maintained Qrr levels are required to direct the proper timing and correct patterns of expression of quorum-sensing-regulated target genes
Submillimeter Wave ESR Study of Spin Gap Excitations in CuGeO3
Transitions between the ground singlet state to the excited triplet state has
been observed in CuGeO3 by means of submillimeter wave electron spin resonance.
The strong absorption intensity shows the break down of the selection rule. The
energy gap at zero field is evaluated to be 570 GHz(2.36 meV) and this value is
nearly identical to the gap at the zone center observed by inelastic neutron
scattering. The absorption intensity shows strong field orientation dependence
but shows no significant dependence on magnetic field intensity. These features
have been explained by considering the existence of Dzyaloshinsky-Moriya (DM)
antisymmetric exchange interaction. The doping effect on this singlet-triplet
excitation has been also studied. A drastic broadening of the absorption line
is observed by the doping of only 0.5 % of Si.Comment: 6 pages, 8figures submitted to J. Phys. Soc. Jp
PARISROC, a photomultiplier array readout chip
PARISROC is a complete read out chip, in AMS SiGe 0.35 micron technology, for
photomultipliers array. It is a front-end electronics ASIC which allows
triggerless acquisition for the next generation of neutrino experiments. These
detectors have place in megaton size water tanks and will require very large
surface of photo-detection. An R & D program, funded by French national agency
for research and called PMm2, proposes to segment the very large surface of
photo-detection in macro pixels made of 16 photomultiplier tubes connected to
an autonomous front-end electronics. The ASIC allows triggerless acquisition
and only send out the relevant data by network to the central data storage.
This data management reduces considerably the cost of these detectors. This
paper describes the front-end electronics ASIC called PARISROC which integrates
totally independents 16 channels with a variable gain and provides charge and
time measurement with a 12-bit ADC and a 24-bits Counter.Comment: 1st international conference on Technology and Instrumentation in
Particle Physics (TIPP09), Tsukuba, Japan (2009
Characterization of HIV-1 RNA forms in the plasma of patients undergoing successful HAART
An assay to characterize plasma human immunodeficiency virus 1 (HIV-1) sequences for patients with low viral loads was developed by combining the selective binding of anti-CD44 MicroBeads with a nested RT-PCR targeting the env C2V4 region. Sequences were obtained from 10 of 20 HIV+ patients who had viral loads below 48 copies/ml. Sequences derived from plasma were compared to those from CD14+ CD16 +monocytes and CD4+ T cells. The plasma sequences were most closely related to those amplified from monocytes, suggesting that during successful antiretroviral therapy, the predominant plasma virus originates from myeloid cells. By characterizing HIV-1 RNA sequences from 8 ml of plasma while avoiding multiple steps, which can lead to contamination and deterioration, this method can help elucidate the viral forms in patients with therapeutically suppressed HIV-1. Understanding the source of residual viremia is crucial in developing approaches for viral eradication
Avionics System and Attitude Algorithms for a Deorbit Device Based on an Electrodynamic Tether
The main goal of the Electrodynamic Tether technology for PAssive Consumable-less deorbit Kit (E.T.PACK) project is to develop a deorbit device based on an electrodynamic tether with TRL 4 by 2022. In September 2022, its continuation, i.e. the E.T.PACK-F project, will carry on with the activities of E.T.PACK to prepare a flight model with TRL 8 that will be tested in an in-orbit demonstration mission in 2025. This work (i) describes the attitude determination and control strategy of the mission, which is used as a means of explaining its different phases and the dynamics of each one of them, (ii) provides a description of the avionics elements of the whole system, (iii) describes some of the tests performed until this moment, and (iv) summarizes the current status and the future work
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