157 research outputs found
Short-term changes in particulate fluxes measured by drifting sediment traps during end summer oligotrophic regime in the NW Mediterranean Sea
Short-term changes in the flux of particulate matter were determined in the central north western Mediterranean Sea (near DYFAMED site) using drifting sediment traps at 200 m depth in the course of the DYNAPROC 2 cruise (14 September–17 October 2004). In this period of marked water column stratification, POC fluxes varied by an order of magnitude, in the range of 0.03–0.29 mgC m<sup>&minus;2</sup> h<sup>&minus;1</sup> over the month and showed very rapid and high variations. Particulate carbon export represented less than 5% of integrated primary production, suggesting that phytoplankton production was essentially sustained by internal recycling of organic matter and retained within the photic zone. While PON and POP fluxes paralleled one another, the elemental ratios POC/PON and POC/POP, varied widely over short-term periods. Values of these ratios generally higher than the conventional Redfield ratio, together with the very low chlorophyll a flux recorded in the traps (mean 0.017 μg m<sup>&minus;2</sup> h<sup>&minus;1</sup>), and the high phaeopigment and acyl lipid hydrolysis metabolite concentrations of the settling material, indicated that the organic matter reaching 200 m depth was reworked (by grazing, fecal pellets production, degradation) and that algal sinking, dominated by nano- and picoplankton, made a small contribution to the downward flux. Over time, the relative abundance of individual lipid classes in organic matter (OM) changed from glycolipids-dominated to neutral (wax esters, triacylglycerols) and phospholipids-dominated, suggesting ecosystem maturation as well as rapid and continual exchanges between dissolved, suspended and sinking pools. Our most striking result was documenting the rapid change in fluxes of the various measured parameters. In the situation encountered here, with dominant regenerated production, a decrease of fluxes was noticed during windy periods (possibly through reduction of grazing). But fluxes increased as soon as calm conditions settle
Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide
We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C}
270K and ferromagnetic to canted spin glass state at T_f\leq$ 125K is
observed
Project 8 Phase III Design Concept
We present a working concept for Phase III of the Project 8 experiment,
aiming to achieve a neutrino mass sensitivity of ( C.L.)
using a large volume of molecular tritium and a phased antenna array. The
detection system is discussed in detail.Comment: 3 pages, 3 figures, Proceedings of Neutrino 2016, XXVII International
Conference on Neutrino Physics and Astrophysics, 4-9 July 2016, London, U
Results from the Project 8 phase-1 cyclotron radiation emission spectroscopy detector
The Project 8 collaboration seeks to measure the absolute neutrino mass scale
by means of precision spectroscopy of the beta decay of tritium. Our technique,
cyclotron radiation emission spectroscopy, measures the frequency of the
radiation emitted by electrons produced by decays in an ambient magnetic field.
Because the cyclotron frequency is inversely proportional to the electron's
Lorentz factor, this is also a measurement of the electron's energy. In order
to demonstrate the viability of this technique, we have assembled and
successfully operated a prototype system, which uses a rectangular waveguide to
collect the cyclotron radiation from internal conversion electrons emitted from
a gaseous Kr source. Here we present the main design aspects of the
first phase prototype, which was operated during parts of 2014 and 2015. We
will also discuss the procedures used to analyze these data, along with the
features which have been observed and the performance achieved to date.Comment: 3 pages; 2 figures; Proceedings of Neutrino 2016, XXVII International
Conference on Neutrino Physics and Astrophysics, 4-9 July 2016, London, U
First observation of cyclotron radiation from MeV-scale following nuclear beta decay
We present an apparatus for detection of cyclotron radiation that allows a
frequency-based beta energy determination in the 5 keV to 5 MeV range,
characteristic of nuclear beta decays. The cyclotron frequency of the radiating
beta particles in a magnetic field is used to determine the beta energy
precisely. Our work establishes the foundation to apply the cyclotron radiation
emission spectroscopy (CRES) technique, developed by the Project 8
collaboration, far beyond the 18-keV tritium endpoint region. We report initial
measurements of beta^-s from 6He and beta^+s from 19Ne decays to demonstrate
the broadband response of our detection system and assess potential systematic
uncertainties for beta spectroscopy over the full (MeV) energy range. This work
is an important benchmark for the practical application of the CRES technique
to a variety of nuclei, in particular, opening its reach to searches for
evidence of new physics beyond the TeV scale via precision beta-decay
measurements
Cyclotron radiation emission spectroscopy signal classification with machine learning in project 8
The cyclotron radiation emission spectroscopy (CRES) technique pioneered by Project 8measures electromagnetic radiation fromindividual electrons gyrating in a backgroundmagnetic field to construct a highly precise energy spectrumfor beta decay studies and other applications. The detector,magnetic trap geometry and electron dynamics give rise to amultitude of complex electron signal structures which carry information about distinguishing physical traits.Withmachine learningmodels, we develop a scheme based on these traits to analyze and classifyCRES signals. Proper understanding and use of these traits will be instrumental to improve cyclotron frequency reconstruction and boost the potential of Project 8 to achieveworld-leading sensitivity on the tritiumendpointmeasurement in the future
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