1,688 research outputs found
Precision determination of absolute neutron flux
A technique for establishing the total neutron rate of a highly-collimated
monochromatic cold neutron beam was demonstrated using a method of an
alpha-gamma counter. The method involves only the counting of measured rates
and is independent of neutron cross sections, decay chain branching ratios, and
neutron beam energy. For the measurement, a target of 10B-enriched boron
carbide totally absorbed the neutrons in a monochromatic beam, and the rate of
absorbed neutrons was determined by counting 478keV gamma rays from neutron
capture on 10B with calibrated high-purity germanium detectors. A second
measurement based on Bragg diffraction from a perfect silicon crystal was
performed to determine the mean de Broglie wavelength of the beam to a
precision of 0.024 %. With these measurements, the detection efficiency of a
neutron monitor based on neutron absorption on 6Li was determined to an overall
uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and
present details of how the measurement was performed including the systematic
effects. We also describe how this method may be used for applications in
neutron dosimetry and metrology, fundamental neutron physics, and neutron cross
section measurements.Comment: 44 page
Discovery of a Reproducing Wild Population of the Swamp Eel Amphipnous Cuchia (Hamilton, 1822) in North America.
We report discovery of an established population of the Asian swamp eel Amphipnous cuchia (Hamilton, 1822) in Bayou St. John, an urban waterway in New Orleans, Louisiana, USA. This fish, commonly referred to as cuchia (kuchia), is a member of the family Synbranchidae and is native to southern and southeastern Asia. Recently-used synonyms include Monopterus cuchia and Ophichthys cuchia. We collected both adult and young-of-year cuchia from dense mats of littoral vegetation at several locations in Bayou St. John. Presence of multiple age and size classes is the first documented evidence of reproduction of this species outside of its native range. Establishment of this air-breathing, burrowing, salt-tolerant, opportunistic predator is of concern given that Bayou St. John is a tributary of Lake Pontchartrain, which provides a direct pathway for dispersal into the Mississippi River basin and coastal wetlands of the Gulf of Mexico
Inflammatory monocytes require type I interferon receptor signaling to activate NK cells via IL-18 during a mucosal viral infection
The requirement of type I interferon (IFN) for natural killer (NK) cell activation in response to viral infection is known, but the underlying mechanism remains unclear. Here, we demonstrate that type I IFN signaling in inflammatory monocytes, but not in dendritic cells (DCs) or NK cells, is essential for NK cell function in response to a mucosal herpes simplex virus type 2 (HSV-2) infection. Mice deficient in type I IFN signaling, Ifnar(-/-) and Irf9(-/-) mice, had significantly lower levels of inflammatory monocytes, were deficient in IL-18 production, and lacked NK cell-derived IFN-gamma. Depletion of inflammatory monocytes, but not DCs or other myeloid cells, resulted in lower levels of IL-18 and a complete abrogation of NK cell function in HSV-2 infection. Moreover, this resulted in higher susceptibility to HSV-2 infection. Although Il18(-/-) mice had normal levels of inflammatory monocytes, their NK cells were unresponsive to HSV-2 challenge. This study highlights the importance of type I IFN signaling in inflammatory monocytes and the induction of the early innate antiviral response
Search for a T-odd, P-even Triple Correlation in Neutron Decay
Background: Time-reversal-invariance violation, or equivalently CP violation,
may explain the observed cosmological baryon asymmetry as well as signal
physics beyond the Standard Model. In the decay of polarized neutrons, the
triple correlation D\cdot(p_{e}\timesp_{\nu}) is a parity-even,
time-reversal- odd observable that is uniquely sensitive to the relative phase
of the axial-vector amplitude with respect to the vector amplitude. The triple
correlation is also sensitive to possible contributions from scalar and tensor
amplitudes. Final-state effects also contribute to D at the level of 1e-5 and
can be calculated with a precision of 1% or better. Purpose: We have improved
the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods:
We measured proton-electron coincidences from decays of longitudinally
polarized neutrons with a highly symmetric detector array designed to cancel
the time-reversal-even, parity-odd Standard-Model contributions to polarized
neutron decay. Over 300 million proton-electron coincidence events were used to
extract D and study systematic effects in a blind analysis. Results: We find D
= [-0.94\pm1.89(stat)\pm0.97(sys)]e-4. Conclusions: This is the most sensitive
measurement of D in nuclear beta decay. Our result can be interpreted as a
measurement of the phase of the ratio of the axial-vector and vector coupling
constants (CA/CV= |{\lambda}|exp(i{\phi}_AV)) with {\phi}_AV = 180.012{\deg}
\pm0.028{\deg} (68% confidence level) or to constrain time-reversal violating
scalar and tensor interactions that arise in certain extensions to the Standard
Model such as leptoquarks. This paper presents details of the experiment,
analysis, and systematic- error corrections.Comment: 21 pages, 22 figure
emiT: an apparatus to test time reversal invariance in polarized neutron decay
We describe an apparatus used to measure the triple-correlation term (\D
\hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons.
The \D-coefficient is sensitive to possible violations of time reversal
invariance. The detector has an octagonal symmetry that optimizes
electron-proton coincidence rates and reduces systematic effects. A beam of
longitudinally polarized cold neutrons passes through the detector chamber,
where a small fraction beta-decay. The final-state protons are accelerated and
focused onto arrays of cooled semiconductor diodes, while the coincident
electrons are detected using panels of plastic scintillator. Details regarding
the design and performance of the proton detectors, beta detectors and the
electronics used in the data collection system are presented. The neutron beam
characteristics, the spin-transport magnetic fields, and polarization
measurements are also described.Comment: 15 pages, 13 figure
13C Incorporation as a tool to estimate biomass yields in thermophilic and mesophilic nitrifying communities
Current methods determining biomass yield require sophisticated sensors for in situ measurements or multiple steady-state reactor runs. Determining the yield of specific groups of organisms in mixed cultures in a fast and easy manner remains challenging. This study describes a fast method to estimate the maximum biomass yield (Y-max ), based on C-13 incorporation during activity measurements. It was applied to mixed cultures containing ammonia oxidizing bacteria (AOB) or archaea (AOA) and nitrite oxidizing bacteria (NOB), grown under mesophilic (15-28 degrees C) and thermophilic (50 degrees C) conditions. Using this method, no distinction could be made between AOB and AOA co-existing in a community. A slight overestimation of the nitrifier biomass due to C-13 redirection via SMP to heterotrophs could occur, meaning that this method determines the carbon fixation activity of the autotrophic microorganisms rather than the actual nitrifier biomass yield. Thermophilic AOA yields exceeded mesophilic AOB yields (0.22 vs. 0.06-0.11 g VSS g(-1) N), possibly linked to a more efficient pathway for CO(2 )incorporation. NOB thermophilically produced less biomass (0.025-0.028 vs. 0.048-0.051 g VSS g(-1) N), conceivably attributed to higher maintenance requirement, rendering less energy available for biomass synthesis. Interestingly, thermophilic nitrification yield was higher than its mesophilic counterpart, due to the dominance of AOA over AOB at higher temperatures. An instant temperature increase impacted the mesophilic AOB yield, corroborating the effect of maintenance requirement on production capacity. Model simulations of two realistic nitrification/denitrification plants were robust toward changing nitrifier yield in predicting effluent ammonium concentrations, whereas sludge composition was impacted. Summarized, a fast, precise and easily executable method was developed determining Y(max )of ammonia and nitrite oxidizers in mixed communities
Comparison of two experiments on radiative neutron decay
Over 10 years ago we proposed an experiment on measuring the characteristics
of radiative neutron decay in papers [1, 2]. At the same time we had published
the theoretical spectrum of radiative gamma quanta, calculated within the
framework of the electroweak interactions, on the basis of which we proposed
the methodology for the future experiment [3,4]. However, because we were
denied beam time on the intensive cold neutron beam at ILL (Grenoble, France)
for a number of years, we could only conduct the experiment in 2005 on the
newly opened FRMII reactor of Technical University of Muenchen. The main result
of this experiment was the discovery of radiative neutron decay and the
measurement of its relative intensity B.R.= (3.2+-1.6)10-3 with C.L.=99.7% for
radiative gamma quanta with energy over 35 kev [5,6]. Over a year after our
first announcement about the results of the conducted experiment, "Nature" [7]
published a letter asserting that its authors have also measured the branching
ratio of radiative neutron decay B.R.= (3.13+-0.34)10-3 with C.L.=68% and gamma
quanta energy from 15 to 340 kev. This article aims to compare these two
experiments. It is shown that the use of strong magnetic fields in the NIST
(Washington, USA) experiment methodology not only prevents any exact
measurement of the branching ratio and identification of radiative neutron
decay events, but also makes registration of ordinary neutron decay events
impossible.Comment: contribution on conference ISINN-1
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