7,010 research outputs found
Target Mass Monitoring and Instrumentation in the Daya Bay Antineutrino Detectors
The Daya Bay experiment measures sin^2 2{\theta}_13 using functionally
identical antineutrino detectors located at distances of 300 to 2000 meters
from the Daya Bay nuclear power complex. Each detector consists of three nested
fluid volumes surrounded by photomultiplier tubes. These volumes are coupled to
overflow tanks on top of the detector to allow for thermal expansion of the
liquid. Antineutrinos are detected through the inverse beta decay reaction on
the proton-rich scintillator target. A precise and continuous measurement of
the detector's central target mass is achieved by monitoring the the fluid
level in the overflow tanks with cameras and ultrasonic and capacitive sensors.
In addition, the monitoring system records detector temperature and levelness
at multiple positions. This monitoring information allows the precise
determination of the detectors' effective number of target protons during data
taking. We present the design, calibration, installation and in-situ tests of
the Daya Bay real-time antineutrino detector monitoring sensors and readout
electronics.Comment: 22 pages, 20 figures; accepted by JINST. Changes in v2: minor
revisions to incorporate editorial feedback from JINS
Control of Ultra-cold Inelastic Collisions by Feshbash Resonances and Quasi-One-Dimensional Confinement
Cold inelastic collisions of atoms or molecules are analyzed using very
general arguments. In free space, the deactivation rate can be enhanced or
suppressed together with the scattering length of the corresponding elastic
collision via a Feshbach resonance, and by interference of deactivation of the
closed and open channels. In reduced dimensional geometries, the deactivation
rate decreases with decreasing collision energy and does not increase with
resonant elastic scattering length. This has broad implications; e.g.,
stabilization of molecules in a strongly confining two-dimensional optical
lattice, since collisional decay of the highly vibrationally excited states due
to inelastic collisions is suppressed. The relation of our results with those
based on the Lieb-Liniger model are addressed.Comment: 5 pages, 1 figur
Pauli problem for a spin of arbitrary length: A simple method to determine its wave function
The problem of determining a pure state vector from measurements is investigated for a quantum spin of arbitrary length. Generically, only a finite number of wave functions is compatible with the intensities of the spin components in two different spatial directions, measured by a Stern-Gerlach apparatus. The remaining ambiguity can be resolved by one additional well-defined measurement. This method combines efficiency with simplicity: only a small number of quantities have to be measured and the experimental setup is elementary. Other approaches to determine state vectors from measurements, also known as the ‘‘Pauli problem,’’ are reviewed for both spin and particle systems
On the reliability of the theoretical internal conversion coefficients
Possible sources of uncertainties in the calculations of the internal
conversion coefficients are studied. The uncertainties induced by them are
estimated.Comment: 16 pages (including 3 figures inserted by 'epsfig' macro
Diversity of antigenic determinants of porcine zona pellucida revealed by monoclonal antibodies
Monoclonal antibodies derived from ten hybrid cell clones, generated against porcine zona pellucida gave strong immunofluorescence with zona but the pattern varied from patchy, thin rim to heavy precipitation type of rim. Five of the 6 monoclonals studied prevented the binding of the porcine epididymal sperm to homologous oocytesin vitro, whereas the sixth one was partially effective. All of the 6 monoclonale of this batch inhibited the lysis of zonae by proteolytic enzymes even at dilutions up to 1×10−3. Three of the four monoclonals prepared in a subsequent batch gave strong immunofluorescent reactions and had high titres as determined by enzyme immunoassay. These monoclonals did not, however, protect the zonae against lysis by proteolytic enzymes. These properties are suggestive of the heterogeneity of the antigenic determinants in zona and emphasize the employment of appropriate bioassays for screening and selection of bioeffective antibodies
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
EXIST's Gamma-Ray Burst Sensitivity
We use semi-analytic techniques to evaluate the burst sensitivity of designs
for the EXIST hard X-ray survey mission. Applying these techniques to the
mission design proposed for the Beyond Einstein program, we find that with its
very large field-of-view and faint gamma-ray burst detection threshold, EXIST
will detect and localize approximately two bursts per day, a large fraction of
which may be at high redshift. We estimate that EXIST's maximum sensitivity
will be ~4 times greater than that of Swift's Burst Alert Telescope. Bursts
will be localized to better than 40 arcsec at threshold, with a burst position
as good as a few arcsec for strong bursts. EXIST's combination of three
different detector systems will provide spectra from 3 keV to more than 10 MeV.
Thus, EXIST will enable a major leap in the understanding of bursts, their
evolution, environment, and utility as cosmological probes.Comment: 25 pages, 10 figures, accepted by Ap
Empirical determination of severe trauma in seals from collisions with tidal turbine blades
This work was funded by Marine Scotland Science (Marine Mammal Scientific Support Program 2, MRE2). It was also supported by NERC National Capability Funding to the Sea Mammal Research Unit (grant no. SMRU10001).1. Tidal energy converters (turbines) are being developed in many countries as part of attempts to reduce reliance on hydrocarbon fuels. However, the moving blades of tidal turbines pose potential collision risks for marine animals. Accurate assessment of mortality risk as a result of collisions is essential for risk management during planning and consenting processes for marine energy developments. In the absence of information on the physical consequences of such collisions, predicting likely risks relies on theoretical collision risk models. The application of these at a population level usually assumes that all collisions result in mortality. This is unlikely and the approach therefore produces upwardly biased estimates of population consequences. 2. In this study, we estimate the pathological consequences of direct collisions with tidal turbines using seal carcasses and physical models of tidal turbine blades. We quantify severe trauma at a range of impact speeds and to different areas of seal carcasses. A dose–response model was developed with associated uncertainty to determine an impact speed threshold of severe trauma to use in future collision risk models. 3. Results showed that severe trauma was restricted to the thoracic region, with no evidence of injury to the lumbar or cervical spine. Pathological indicators of mortality were only predicted to occur in collision speeds in excess of 5.1 m/s (95% C.I. 3.2–6.6) and was affected by body condition; increasing blubber depth reduced the likelihood of severe trauma. 4. Synthesis and applications. This study provides important information for policy makers and regulators looking to predict the potential impacts of tidal turbines on marine mammals. We demonstrate that the probability of severe trauma in seals due to collisions with turbine blades is highly dependent upon collision speed, and that the majority of predicted collisions are unlikely to cause fatal skeletal trauma. We recommend that collision risk models incorporate appropriate mortality assumptions to ensure accurate estimates of the population consequences are produced in risk assessments for tidal turbine deployments.PostprintPeer reviewe
Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields
We derive and apply an optical Bloch equation (OBE) model for describing
collisions of ground and excited laser cooled alkali atoms in the presence of
near-resonant light. Typically these collisions lead to loss of atoms from
traps. We compare the results obtained with a quantum mechanical complex
potential treatment, semiclassical Landau-Zener models with decay, and a
quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate
the OBE method in both adiabatic and diabatic representations. We calculate the
laser intensity dependence of collision probabilities and find that the
adiabatic OBE results agree quantitatively with those of the MCWP calculation,
and qualitatively with the semiclassical Landau-Zener model with delayed decay,
but that the complex potential method or the traditional Landau-Zener model
fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also
http://www.physics.helsinki.fi/~kasuomin
Discovery and characterization of 91 novel transcripts expressed in cattle placenta
<p>Abstract</p> <p>Background</p> <p>Among the eutherian mammals, placental architecture varies to a greater extent than any other tissue. The diversity of placental types, even within a single mammalian order suggests that genes expressed in placenta are under strong Darwinian selection. Thus, the ruminant placenta may be a rich source of genes to explore adaptive evolutionary responses in mammals. The aim of our study was to identify novel transcripts expressed in ruminant placenta, and to characterize them with respect to their expression patterns, organization of coding sequences in the genome, and potential functions.</p> <p>Results</p> <p>A combination of bioinformatics, comparative genomics and transcript profiling was used to identify and characterize 91 novel transcripts (NTs) represented in a cattle placenta cDNA library. These NTs have no significant similarity to any non-ferungulate DNA or RNA sequence. Proteins longer than 100 aa were predicted for 29 NTs, and 21 are candidate non-coding RNAs. Eighty-six NTs were found to be expressed in one or more of 18 different tissues, with 39 (42%) showing tissue-preference, including six that were expressed exclusively in placentome. The authenticity of the NTs was confirmed by their alignment to cattle genome sequence, 42 of which showed evidence of mRNA splicing. Analysis of the genomic context where NT genes reside revealed 61 to be in intergenic regions, whereas 30 are within introns of known genes. The genes encoding the NTs were found to be significantly associated with subtelomeric regions.</p> <p>Conclusion</p> <p>The 91 lineage-specific transcripts are a useful resource for studying adaptive evolutionary responses of the ruminant placenta. The presence of so many genes encoding NTs in cattle but not primates or rodents suggests that gene loss and gain are important mechanisms of genome evolution in mammals. Furthermore, the clustering of NT genes within subtelomeric regions suggests that such regions are highly dynamic and may foster the birth of novel genes. The sequencing of additional vertebrate genomes with defined phylogenetic relationships will permit the search for lineage-specific genes to take on a more evolutionary context that is required to understand their origins and functions.</p
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