159 research outputs found
On the discrete spectrum of spin-orbit Hamiltonians with singular interactions
We give a variational proof of the existence of infinitely many bound states
below the continuous spectrum for spin-orbit Hamiltonians (including the Rashba
and Dresselhaus cases) perturbed by measure potentials thus extending the
results of J.Bruening, V.Geyler, K.Pankrashkin: J. Phys. A 40 (2007)
F113--F117.Comment: 10 pages; to appear in Russian Journal of Mathematical Physics
(memorial volume in honor of Vladimir Geyler). Results improved in this
versio
From Model Specification to Simulation of Biologically Constrained Networks of Spiking Neurons.
A declarative extensible markup language (SpineML) for describing the dynamics, network and experiments of large-scale spiking neural network simulations is described which builds upon the NineML standard. It utilises a level of abstraction which targets point neuron representation but addresses the limitations of existing tools by allowing arbitrary dynamics to be expressed. The use of XML promotes model sharing, is human readable and allows collaborative working. The syntax uses a high-level self explanatory format which allows straight forward code generation or translation of a model description to a native simulator format. This paper demonstrates the use of code generation in order to translate, simulate and reproduce the results of a benchmark model across a range of simulators. The flexibility of the SpineML syntax is highlighted by reproducing a pre-existing, biologically constrained model of a neural microcircuit (the striatum). The SpineML code is open source and is available at http://bimpa.group.shef.ac.uk/SpineML
Novel techniques for alpha/beta pulse shape discrimination in Borexino
Borexino could efficiently distinguish between alpha and beta radiation in
its liquid scintillator by the characteristic time profile of their
scintillation pulse. This alpha/beta discrimination, first demonstrated at the
tonne scale in the Counting Test Facility prototype, was used throughout the
lifetime of the experiment between 2007 and 2021. With this method, alpha
events are identified and subtracted from the beta-like solar neutrino events.
This is particularly important in liquid scintillator as alpha scintillation is
quenched many-fold. In Borexino, the prominent Po-210 decay peak was a
background in the energy range of electrons scattered from Be-7 solar
neutrinos. Optimal alpha-beta discrimination was achieved with a "multi-layer
perceptron neural network", which its higher ability to leverage the timing
information of the scintillation photons detected by the photomultiplier tubes.
An event-by-event, high efficiency, stable, and uniform pulse shape
discrimination was essential in characterising the spatial distribution of
background in the detector. This benefited most Borexino measurements,
including solar neutrinos in the \pp chain and the first direct observation of
the CNO cycle in the Sun. This paper presents the key milestones in alpha/beta
discrimination in Borexino as a term of comparison for current and future large
liquid scintillator detectorsComment: 13 pages, 14 figure
Borexino's search for low-energy neutrinos associated with gravitational wave events from GWTC-3 database
The search for neutrino events in correlation with gravitational wave (GW)
events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has
been performed using the Borexino data-set of the same period. We have searched
for signals of neutrino-electron scattering with visible energies above 250 keV
within a time window of 1000 s centered at the detection moment of a particular
GW event. The search was done with three visible energy thresholds of 0.25, 0.8
and 3.0 MeV.Two types of incoming neutrino spectra were considered: the
mono-energetic line and the spectrum expected from supernovae. The same spectra
were considered for electron antineutrinos detected through inverse beta-decay
(IBD) reaction. GW candidates originated by merging binaries of black holes
(BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were
analysed separately. Additionally, the subset of most intensive BHBH mergers at
closer distances and with larger radiative mass than the rest was considered.
In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3
catalog were analyzed and no statistically significant excess over the
background was observed. As a result, the strongest upper limits on
GW-associated neutrino and antineutrino fluences for all flavors (\nu_e,
\nu_\mu, \nu_\tau) have been obtained in the (0.5 - 5.0) MeV neutrino energy
range.Comment: 13 pages, 8 figure
The Hidden Sexuality of Alexandrium Minutum: An Example of Overlooked Sex in Dinoflagellates
Dinoflagellates are haploid eukaryotic microalgae in which rapid proliferation causes dense
blooms, with harmful health and economic effects to humans. The proliferation mode is
mainly asexual, as the sexual cycle is believed to be rare and restricted to stressful environmental
conditions. However, sexuality is key to explaining the recurrence of many dinoflagellate
blooms because in many species the fate of the planktonic zygotes (planozygotes)
is the formation of resistant cysts in the seabed (encystment). Nevertheless, recent
research has shown that individually isolated planozygotes in the lab can enter other routes
besides encystment, a behavior of which the relevance has not been explored at the population
level. In this study, using imaging flow cytometry, cell sorting, and Fluorescence In
Situ Hybridization (FISH), we followed DNA content and nuclear changes in a population of
the toxic dinoflagellate Alexandrium minutum that was induced to encystment. Our results
first show that planozygotes behave like a population with an “encystment-independent”
division cycle, which is light-controlled and follows the same Light:Dark (L:D) pattern as the
cycle governing the haploid mitosis. Resting cyst formation was the fate of just a small fraction
of the planozygotes formed and was restricted to a period of strongly limited nutrient
conditions. The diploid-haploid turnover between L:D cycles was consistent with two-step
meiosis. However, the diel and morphological division pattern of the planozygote division
also suggests mitosis, which would imply that this species is not haplontic, as previously
considered, but biphasic, because individuals could undergo mitotic divisions in both the
sexual (diploid) and the asexual (haploid) phases. We also report incomplete genome duplication
processes. Our work calls for a reconsideration of the dogma of rare sex in
dinoflagellates.Versión del edito
First Directional Measurement of sub-MeV Solar Neutrinos with Borexino
We report the measurement of sub-MeV solar neutrinos through the use of their associated Cherenkov radiation, performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The measurement is achieved using a novel technique that correlates individual photon hits of events to the known position of the Sun. In an energy window between 0.54 to 0.74 MeV, selected using the
dominant scintillation light, we have measured 10 887þ2386 ðstatÞ � 947ðsystÞ (68% confidence interval) −2103 solar neutrinos out of 19904 total events. This corresponds to a 7Be neutrino interaction rate of 51.6þ13.9 counts=ðday · 100 tonÞ, which is in agreement with the standard solar model predictions and the −12.5 previous spectroscopic results of Borexino. The no-neutrino hypothesis can be excluded with > 5σ confidence level. For the first time, we have demonstrated the possibility of utilizing the directional Cherenkov information for sub-MeV solar neutrinos, in a large-scale, high light yield liquid scintillator detector. This measurement provides an experimental proof of principle for future hybrid event reconstruction using both Cherenkov and scintillation signatures simultaneously
Experimental Detection of the CNO Cycle
Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe
Solar and geoneutrinos
Thanks to the progress of neutrino physics, today we are able of exploiting neutrinos as a tool to study astrophysical objects. The latter in turn serve as unique sources of elusive neutrinos, which fundamental properties are still to be understood. This contribution attempts to summarize the latest results obtained by measuring neutrinos emitted from the Sun and geoneutrinos produced in radioactive decays inside the Earth, with a particular focus on a recent discovery of the CNO-cycle solar neutrinos by Borexino. Comprehensive measurement of the pp-chain solar neutrinos and the first directional detection of sub-MeV solar neutrinos by Borexino, the updated 8B solar neutrino results of Super-Kamiokande, as well as the latest Borexino and KamLAND geoneutrino measurements are also discussed
Identification of the cosmogenic 11C background in large volumes of liquid scintillators with Borexino
Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic 11C decays outnumber solar pep and CNO neutrino events by about ten to one. In order to extract the flux of these two neutrino species, a highly efficient identification of this background is mandatory. We present here the details of the most consolidated strategy, used throughout Borexino solar neutrino measurements. It hinges upon finding the space-time correlations between 11C decays, the preceding parent muons and the accompanying neutrons. This article describes the working principles and evaluates the performance of this Three-Fold Coincidence (TFC) technique in its two current implementations: a hard-cut and a likelihood-based approach. Both show stable performances throughout Borexino Phases II (2012–2016) and III (2016–2020) data sets, with a 11C tagging efficiency of ∼90 % and ∼ 63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically 11C produced in high-multiplicity during major spallation events. Such 11C appear as a burst of events, whose space-time correlation can be exploited. Burst identification can be combined with the TFC to obtain about the same tagging efficiency of ∼90% but with a higher fraction of the exposure surviving, in the range of ∼ 66–68 %
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