381 research outputs found
Thermal runaway of metal nano-tips during intense electron emission
When an electron emitting tip is subjected to very high electric fields, plasma forms even under ultra high vacuum conditions. This phenomenon, known as vacuum arc, causes catastrophic surface modifications and constitutes a major limiting factor not only for modern electron sources, but also for many large-scale applications such as particle accelerators, fusion reactors etc. Although vacuum arcs have been studied thoroughly, the physical mechanisms that lead from intense electron emission to plasma ignition are still unclear. In this article, we give insights to the atomic scale processes taking place in metal nanotips under intense field emission conditions. We use multi-scale atomistic simulations that concurrently include field-induced forces, electron emission with finite-size and space-charge effects, Nottingham and Joule heating. We find that when a sufficiently high electric field is applied to the tip, the emission-generated heat partially melts it and the field-induced force elongates and sharpens it. This initiates a positive feedback thermal runaway process, which eventually causes evaporation of large fractions of the tip. The reported mechanism can explain the origin of neutral atoms necessary to initiate plasma, a missing key process required to explain the ignition of a vacuum arc. Our simulations provide a quantitative description of in the conditions leading to runaway, which shall be valuable for both field emission applications and vacuum arc studies.Peer reviewe
An Archival Search for Very-High-Energy Counterparts to Sub-Threshold Neutron-Star Merger Candidates
The recent discovery of electromagnetic signals in coincidence with
gravitational waves from neutron-star mergers has solidified the importance of
multimessenger campaigns for studying the most energetic astrophysical events.
Pioneering multimessenger observatories, such as the LIGO/Virgo gravitational
wave detectors and the IceCube neutrino observatory, record many candidate
signals that fall short of the detection significance threshold. These
sub-threshold event candidates are promising targets for multimessenger
studies, as the information provided by these candidates may, when combined
with time-coincident gamma-ray observations, lead to significant detections. In
this contribution, I describe our use of sub-threshold binary neutron star
merger candidates identified in Advanced LIGO's first observing run (O1) to
search for transient events in very-high-energy gamma rays using archival
observations from the VERITAS imaging atmospheric Cherenkov telescope array. I
describe the promise of this technique for future joint sub-threshold searches
Have hierarchical three-body mergers been detected by LIGO/Virgo?
One of the proposed channels of binary black hole mergers involves dynamical
interactions of three black holes. In such scenarios, it is possible that all
three black holes merge in a so-called hierarchical merger chain, where two of
the black holes merge first and then their remnant subsequently merges with the
remaining single black hole. Depending on the dynamical environment, it is
possible that both mergers will appear within the observable time window. Here
we perform a search for such merger pairs in the public available LIGO and
Virgo data from the O1/O2 runs. Using a frequentist p-value assignment
statistics we do not find any significant merger pair candidates, the most
significant being GW170809-GW151012 pair. Assuming no observed candidates in
O3/O4, we derive upper limits on merger pairs to be , corresponding to a rate that relative to the total merger
rate is . From this we argue that both a detection and a
non-detection within the next few years can be used to put useful constraints
on some dynamical progenitor models.Comment: 7 pages, 4 figure
Characterization of a new full length TMPRSS3 isoform and identification of mutant alleles responsible for nonsyndromic recessive deafness in Newfoundland and Pakistan
BACKGROUND: Mutant alleles of TMPRSS3 are associated with nonsyndromic recessive deafness (DFNB8/B10). TMPRSS3 encodes a predicted secreted serine protease, although the deduced amino acid sequence has no signal peptide. In this study, we searched for mutant alleles of TMPRSS3 in families from Pakistan and Newfoundland with recessive deafness co-segregating with DFNB8/B10 linked haplotypes and also more thoroughly characterized the genomic structure of TMPRSS3. METHODS: We enrolled families segregating recessive hearing loss from Pakistan and Newfoundland. Microsatellite markers flanking the TMPRSS3 locus were used for linkage analysis. DNA samples from participating individuals were sequenced for TMPRSS3. The structure of TMPRSS3 was characterized bioinformatically and experimentally by sequencing novel cDNA clones of TMPRSS3. RESULTS: We identified mutations in TMPRSS3 in four Pakistani families with recessive, nonsyndromic congenital deafness. We also identified two recessive mutations, one of which is novel, of TMPRSS3 segregating in a six-generation extended family from Newfoundland. The spectrum of TMPRSS3 mutations is reviewed in the context of a genotype-phenotype correlation. Our study also revealed a longer isoform of TMPRSS3 with a hitherto unidentified exon encoding a signal peptide, which is expressed in several tissues. CONCLUSION: Mutations of TMPRSS3 contribute to hearing loss in many communities worldwide and account for 1.8% (8 of 449) of Pakistani families segregating congenital deafness as an autosomal recessive trait. The newly identified TMPRSS3 isoform e will be helpful in the functional characterization of the full length protein
An Archival Search for Neutron-Star Mergers in Gravitational Waves and Very-High-Energy Gamma Rays
The recent discovery of electromagnetic signals in coincidence with
neutron-star mergers has solidified the importance of multimessenger campaigns
in studying the most energetic astrophysical events. Pioneering multimessenger
observatories, such as LIGO/Virgo and IceCube, record many candidate signals
below the detection significance threshold. These sub-threshold event
candidates are promising targets for multimessenger studies, as the information
provided by them may, when combined with contemporaneous gamma-ray
observations, lead to significant detections. Here we describe a new method
that uses such candidates to search for transient events using archival
very-high-energy gamma-ray data from imaging atmospheric Cherenkov telescopes
(IACTs). We demonstrate the application of this method to sub-threshold binary
neutron star (BNS) merger candidates identified in Advanced LIGO's first
observing run. We identify eight hours of archival VERITAS observations
coincident with seven BNS merger candidates and search them for TeV emission.
No gamma-ray emission is detected; we calculate upper limits on the integral
flux and compare them to a short gamma-ray burst model. We anticipate this
search method to serve as a starting point for IACT searches with future
LIGO/Virgo data releases as well as in other sub-threshold studies for
multimessenger transients, such as IceCube neutrinos. Furthermore, it can be
deployed immediately with other current-generation IACTs, and has the potential
for real-time use that places minimal burden on experimental operations.
Lastly, this method may serve as a pilot for studies with the Cherenkov
Telescope Array, which has the potential to observe even larger fields of view
in its divergent pointing mode
Genotype–Phenotype Correlation in DFNB8/10 Families with TMPRSS3 Mutations
In the present study, genotype–phenotype correlations in eight Dutch DFNB8/10 families with compound heterozygous mutations in TMPRSS3 were addressed. We compared the phenotypes of the families by focusing on the mutation data. The compound heterozygous variants in the TMPRSS3 gene in the present families included one novel variant, p.Val199Met, and four previously described pathogenic variants, p.Ala306Thr, p.Thr70fs, p.Ala138Glu, and p.Cys107Xfs. In addition, the p.Ala426Thr variant, which had previously been reported as a possible polymorphism, was found in one family. All affected family members reported progressive bilateral hearing impairment, with variable onset ages and progression rates. In general, the hearing impairment affected the high frequencies first, and sooner or later, depending on the mutation, the low frequencies started to deteriorate, which eventually resulted in a flat audiogram configuration. The ski-slope audiogram configuration is suggestive for the involvement of TMPRSS3. Our data suggest that not only the protein truncating mutation p.T70fs has a severe effect but also the amino acid substitutions p.Ala306Thr and p.Val199Met. A combination of two of these three mutations causes prelingual profound hearing impairment. However, in combination with the p.Ala426Thr or p.Ala138Glu mutations, a milder phenotype with postlingual onset of the hearing impairment is seen. Therefore, the latter mutations are likely to be less detrimental for protein function. Further studies are needed to distinguish possible phenotypic differences between different TMPRSS3 mutations. Evaluation of performance of patients with a cochlear implant indicated that this is a good treatment option for patients with TMPRSS3 mutations as satisfactory speech reception was reached after implantation
IceCube Search for Neutrinos Coincident with Compact Binary Mergers from LIGO-Virgo's First Gravitational-Wave Transient Catalog
Using the IceCube Neutrino Observatory, we search for high-energy neutrino
emission coincident with compact binary mergers observed by the LIGO and Virgo
gravitational wave (GW) detectors during their first and second observing runs.
We present results from two searches targeting emission coincident with the sky
localization of each gravitational wave event within a 1000 second time window
centered around the reported merger time. One search uses a model-independent
unbinned maximum likelihood analysis, which uses neutrino data from IceCube to
search for point-like neutrino sources consistent with the sky localization of
GW events. The other uses the Low-Latency Algorithm for Multi-messenger
Astrophysics, which incorporates astrophysical priors through a Bayesian
framework and includes LIGO-Virgo detector characteristics to determine the
association between the GW source and the neutrinos. No significant neutrino
coincidence is seen by either search during the first two observing runs of the
LIGO-Virgo detectors. We set upper limits on the time-integrated neutrino
emission within the 1000 second window for each of the 11 GW events. These
limits range from 0.02-0.7 . We also set limits on the
total isotropic equivalent energy, , emitted in high-energy
neutrinos by each GW event. These limits range from 1.7 10 -
1.8 10 erg. We conclude with an outlook for LIGO-Virgo
observing run O3, during which both analyses are running in real time
IceCat-1: The IceCube Event Catalog of Alert Tracks
We present a catalog of likely astrophysical neutrino track-like events from the IceCube Neutrino Observatory. IceCube began reporting likely astrophysical neutrinos in 2016, and this system was updated in 2019. The catalog presented here includes events that were reported in real time since 2019, as well as events identified in archival data samples starting from 2011. We report 275 neutrino events from two selection channels as the first entries in the catalog, the IceCube Event Catalog of Alert Tracks, which will see ongoing extensions with additional alerts. The Gold and Bronze alert channels respectively provide neutrino candidates with a 50% and 30% probability of being astrophysical, on average assuming an astrophysical neutrino power-law energy spectral index of 2.19. For each neutrino alert, we provide the reconstructed energy, direction, false-alarm rate, probability of being astrophysical in origin, and likelihood contours describing the spatial uncertainty in the alert\u27s reconstructed location. We also investigate a directional correlation of these neutrino events with gamma-ray and X-ray catalogs, including 4FGL, 3HWC, TeVCat, and Swift-BAT
Constraining High-energy Neutrino Emission from Supernovae with IceCube
Core-collapse supernovae are a promising potential high-energy neutrino source class. We test for correlation between seven years of IceCube neutrino data and a catalog containing more than 1000 core-collapse supernovae of types IIn and IIP and a sample of stripped-envelope supernovae. We search both for neutrino emission from individual supernovae as well as for combined emission from the whole supernova sample, through a stacking analysis. No significant spatial or temporal correlation of neutrinos with the cataloged supernovae was found. All scenarios were tested against the background expectation and together yield an overall p-value of 93%; therefore, they show consistency with the background only. The derived upper limits on the total energy emitted in neutrinos are 1.7 × 10 erg for stripped-envelope supernovae, 2.8 × 10 erg for type IIP, and 1.3 × 10 erg for type IIn SNe, the latter disfavoring models with optimistic assumptions for neutrino production in interacting supernovae. We conclude that stripped-envelope supernovae and supernovae of type IIn do not contribute more than 14.6% and 33.9%, respectively, to the diffuse neutrino flux in the energy range of about [ 10–10] GeV, assuming that the neutrino energy spectrum follows a power-law with an index of −2.5. Under the same assumption, we can only constrain the contribution of type IIP SNe to no more than 59.9%. Thus, core-collapse supernovae of types IIn and stripped-envelope supernovae can both be ruled out as the dominant source of the diffuse neutrino flux under the given assumptions
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