376 research outputs found
Light sterile neutrino sensitivity of 163Ho experiments
We explore the sensitivity of Ho electron capture experiments to
neutrino masses in the standard framework of three-neutrino mixing and in the
framework of 3+1 neutrino mixing with a sterile neutrino which mixes with the
three standard active neutrinos, as indicated by the anomalies found in
short-baseline neutrino oscillations experiments. We calculate the sensitivity
to neutrino masses and mixing for different values of the energy resolution of
the detectors, of the unresolved pileup fraction and of the total statistics of
events, considering the expected values of these parameters in the two planned
stages of the ECHo project (ECHo-1k and ECHo-1M). We show that an extension of
the ECHo-1M experiment with the possibility to collect events will be
competitive with the KATRIN experiment. This statistics will allow to explore
part of the 3+1 mixing parameter space indicated by the global analysis of
short-baseline neutrino oscillation experiments. In order to cover all the
allowed region, a statistics of about events will be needed.Comment: 11 page
First Calorimetric Measurement of OI-line in the Electron Capture Spectrum of Ho
The isotope Ho undergoes an electron capture process with a
recommended value for the energy available to the decay, , of about
2.5 keV. According to the present knowledge, this is the lowest
value for electron capture processes. Because of that, Ho is the best
candidate to perform experiments to investigate the value of the electron
neutrino mass based on the analysis of the calorimetrically measured spectrum.
We present for the first time the calorimetric measurement of the atomic
de-excitation of the Dy daughter atom upon the capture of an electron
from the 5s shell in Ho, OI-line. The measured peak energy is 48 eV.
This measurement was performed using low temperature metallic magnetic
calorimeters with the Ho ion implanted in the absorber.
We demonstrate that the calorimetric spectrum of Ho can be measured
with high precision and that the parameters describing the spectrum can be
learned from the analysis of the data. Finally, we discuss the implications of
this result for the Electron Capture Ho experiment, ECHo, aiming to
reach sub-eV sensitivity on the electron neutrino mass by a high precision and
high statistics calorimetric measurement of the Ho spectrum.Comment: 5 pages, 3 figure
Prospects for measuring the 229Th isomer energy using a metallic magnetic microcalorimeter
The Thorium-229 isotope features a nuclear isomer state with an extremely low
energy. The currently most accepted energy value, 7.8 +- 0.5 eV, was obtained
from an indirect measurement using a NASA x-ray microcalorimeter with an
instrumental resolution 26 eV. We study, how state-of-the-art magnetic metallic
microcalorimeters with an energy resolution down to a few eV can be used to
measure the isomer energy. In particular, resolving the 29.18 keV doublet in
the \gamma-spectrum following the \alpha-decay of Uranium-233, corresponding to
the decay into the ground and isomer state, allows to measure the isomer
transition energy without additional theoretical input parameters, and increase
the energy accuracy. We study the possibility of resolving the 29.18 keV line
as a doublet and the dependence of the attainable precision of the energy
measurement on the signal and background count rates and the instrumental
resolution.Comment: 32 pages, 8 figures, eq. (3) correcte
Unsupervised Monitoring System for Predictive Maintenance of High Voltage Apparatus
The online monitoring of a high voltage apparatus is a crucial aspect for a predictive maintenanceprogram. Partialdischarges(PDs)phenomenaaffecttheinsulationsystemofanelectrical machine and\u2014in the long term\u2014can lead to a breakdown, with a consequent, signi\ufb01cant economic loss; wind turbines provide an excellent example. Embedded solutions are therefore required to monitor the insulation status. The paper presents an online system that adopts unsupervised methodologies for assessing the condition of the monitored machine in real time. The monitoring process does not rely on any prior knowledge about the apparatus; nonetheless, the method can identify the relevant drifts in the machine status. In addition, the system is speci\ufb01cally designed to run on low-cost embedded devices
Spontaneous Magnetization in Heterometallic NiFe-MOF-74 Microporous Magnets by Controlled Iron Doping
We report the direct synthesis of mixed-metal NiFe-MOF-74 solids that display combination of porosity with ferrimagnetic ordering. Compared to the undoped Ni phase, controlled doping with Fe enables to modify intra and interchain magnetic interactions for the onset of spontaneous magnetization at temperatures fixed by the doping level. Synthesis of porous magnets remains somewhat elusive due to the difficulties in isolating foreseeable metal-organic architectures that combine small bridging linkers, for strong magnetic coupling, with polyaromatic connectors responsible for porosity. In turn, we demonstrate that metal doping is better fitted to modify the magnetism of Metal-Organic Frameworks already available simply by suitable choice of their nature and relative ratio in isostructural solid solutions
HighSTEPS. A high strain temperature pèressure and speed apparatus to study earthquake mechanics
We present a state of-the-art biaxial apparatus able to study both earthquake rupture nucleation and propagation at conditions typical of the seismogenic crust. The HighSTEPS, High Strain TEmperature Pressure Speed, apparatus simulates fault deformation in a wide range of slip velocities, i.e., from 10-5m/s to 0.25 m/s. Within this velocity range, it is possible to study, the rate-and-state friction, the fault dynamic weakening, and healing under unique boundary conditions, i.e., normal stress up to 100 MPa, confining pressure up to 100 MPa, pore fluid pressure up to 100 MPa and temperature up to 120 °C. The apparatus consists of a hydraulic system integrated with four linear motors. The hydraulic system allows
for the application of normal stress, confining pressure and pore fluid pressure. The main peculiarity of this apparatus is the system of four linear motors that are mounted in series in order to apply shearing velocities up to 0.25 m/s, accelerations up to 10 m/s2 and shear stresses up to 200 MPa. Moreover, both experiments in sliding velocity control or shear stress control on the experimental faults are possible. Preliminary experiments on carbonate and silicate bearing rocks are coherent with the previous literature. The investigation of fault friction under a wide range of velocities, normal stresses, confining pressures and pore fluid pressures will provide insights into the mechanics of earthquakes and reduce the gap between
natural and laboratory observations
Data assimilation of radar reflectivity volumes in a LETKF scheme
Quantitative precipitation forecast (QPF) is still a
challenge for numerical weather prediction (NWP), despite the continuous
improvement of models and data assimilation systems. In this regard, the
assimilation of radar reflectivity volumes should be beneficial, since the
accuracy of analysis is the element that most affects short-term QPFs. Up to
now, few attempts have been made to assimilate these observations in an
operational set-up, due to the large amount of computational resources needed
and due to several open issues, like the rise of imbalances in the analyses
and the estimation of the observational error. In this work, we evaluate the
impact of the assimilation of radar reflectivity volumes employing a local
ensemble transform Kalman filter (LETKF), implemented for the
convection-permitting model of the COnsortium for Small-scale MOdelling
(COSMO). A 4-day test case on February 2017 is considered and the
verification of QPFs is performed using the fractions skill score (FSS) and
the SAL technique, an object-based method which allows one to decompose the
error in precipitation fields in terms of structure (S), amplitude (A)
and location (L). Results obtained assimilating both conventional data and
radar reflectivity volumes are compared to those of the operational system of
the Hydro-Meteo-Climate Service of the Emilia-Romagna Region (Arpae-SIMC), in
which only conventional observations are employed and latent heat nudging
(LHN) is applied using surface rainfall intensity (SRI) estimated from the
Italian radar network data. The impact of assimilating reflectivity volumes
using LETKF in combination or not with LHN is assessed. Furthermore, some
sensitivity tests are performed to evaluate the effects of the length of the
assimilation window and of the reflectivity observational error
(roe). Moreover, balance issues are assessed in terms of kinetic
energy spectra and providing some examples of how these affect prognostic
fields. Results show that the assimilation of reflectivity volumes has a
positive impact on QPF accuracy in the first few hours of forecast, both when
it is combined with LHN or not. The improvement is further slightly enhanced
when only observations collected close to the analysis time are assimilated,
while the shortening of cycle length worsens QPF accuracy. Finally, the
employment of too small a value of roe introduces imbalances into
the analyses, resulting in a severe degradation of forecast accuracy,
especially when very short assimilation cycles are used.</p
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