175 research outputs found
Expression profiling of human glial precursors
<p>Abstract</p> <p>Background</p> <p>We have generated gene expression databases for human glial precursors, neuronal precursors, astrocyte precursors and neural stem cells and focused on comparing the profile of glial precursors with that of other populations.</p> <p>Results</p> <p>A total of 14 samples were analyzed. Each population, previously distinguished from each other by immunocytochemical analysis of cell surface markers, expressed genes related to their key differentiation pathways. For the glial precursor cell population, we identified 458 genes that were uniquely expressed. Expression of a subset of these individual genes was validated by RT-PCR. We also report genes encoding cell surface markers that may be useful for identification and purification of human glial precursor populations.</p> <p>Conclusion</p> <p>We provide gene expression profile for human glial precursors. Our data suggest several signaling pathways that are important for proliferation and differentiation of human glial precursors. Such information may be utilized to further purify glial precursor populations, optimize media formulation, or study the effects of glial differentiation.</p
Searches for Neutrinos from LHAASO ultra-high-energy {\gamma}-ray sources using the IceCube Neutrino Observatory
Galactic PeVatrons are Galactic sources theorized to accelerate cosmic rays
up to PeV in energy. The accelerated cosmic rays are expected to interact
hadronically with nearby ambient gas or the interstellar medium, resulting in
{\gamma}-rays and neutrinos. Recently, the Large High Altitude Air Shower
Observatory (LHAASO) identified 12 {\gamma}-ray sources with emissions above
100 TeV, making them candidates for PeV cosmic-ray accelerators (PeVatrons).
While at these high energies the Klein-Nishina effect suppresses exponentially
leptonic emission from Galactic sources, evidence for neutrino emission would
unequivocally confirm hadronic acceleration. Here, we present the results of a
search for neutrinos from these {\gamma}-ray sources and stacking searches
testing for excess neutrino emission from all 12 sources as well as their
subcatalogs of supernova remnants and pulsar wind nebulae with 11 years of
track events from the IceCube Neutrino Observatory. No significant emissions
were found. Based on the resulting limits, we place constraints on the fraction
of {\gamma}-ray flux originating from the hadronic processes in the Crab Nebula
and LHAASOJ2226+6057
Searching for High-energy Neutrino Emission from Galaxy Clusters with IceCube
Galaxy clusters have the potential to accelerate cosmic rays (CRs) to ultrahigh energies via accretion shocks or embedded CR acceleration sites. The CRs with energies below the Hillas condition will be confined within the cluster and eventually interact with the intracluster medium gas to produce secondary neutrinos and gamma rays. Using 9.5 yr of muon neutrino track events from the IceCube Neutrino Observatory, we report the results of a stacking analysis of 1094 galaxy clusters with masses âł10 Mâ and redshifts between 0.01 and âŒ1 detected by the Planck mission via the SunyaevâZelâdovich effect. We find no evidence for significant neutrino emission and report upper limits on the cumulative unresolved neutrino flux from massive galaxy clusters after accounting for the completeness of the catalog up to a redshift of 2, assuming three different weighting scenarios for the stacking and three different power-law spectra. Weighting the sources according to mass and distance, we set upper limits at a 90% confidence level that constrain the flux of neutrinos from massive galaxy clusters (âł10 Mâ) to be no more than 4.6% of the diffuse IceCube observations at 100 TeV, assuming an unbroken Eâ power-law spectrum
Searches for Neutrinos from Gamma-Ray Bursts using the IceCube Neutrino Observatory
Gamma-ray bursts (GRBs) are considered as promising sources of
ultra-high-energy cosmic rays (UHECRs) due to their large power output.
Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic
accelerators of UHECRs. Previous IceCube analyses, which primarily focused on
neutrinos arriving in temporal coincidence with the prompt gamma rays, found no
significant neutrino excess. The four analyses presented in this paper extend
the region of interest to 14 days before and after the prompt phase, including
generic extended time windows and targeted precursor searches. GRBs were
selected between May 2011 and October 2018 to align with the data set of
candidate muon-neutrino events observed by IceCube. No evidence of correlation
between neutrino events and GRBs was found in these analyses. Limits are set to
constrain the contribution of the cosmic GRB population to the diffuse
astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from
GRBs is limited to 1% of the observed diffuse neutrino flux, and
emission on timescales up to s is constrained to 24% of the total
diffuse flux
Characteristics of the diffuse astrophysical electron and tau neutrino flux with six years of IceCube high energy cascade data
We report on the first measurement of the astrophysical neutrino flux using
particle showers (cascades) in IceCube data from 2010 -- 2015. Assuming
standard oscillations, the astrophysical neutrinos in this dedicated cascade
sample are dominated () by electron and tau flavors. The flux,
observed in the sensitive energy range from to
, is consistent with a single power-law model as expected
from Fermi-type acceleration of high energy particles at astrophysical sources.
We find the flux spectral index to be and a flux
normalization for each neutrino flavor of
at , in agreement with IceCube's complementary muon
neutrino results and with all-neutrino flavor fit results. In the measured
energy range we reject spectral indices at
significance level. Due to high neutrino energy resolution and low atmospheric
neutrino backgrounds, this analysis provides the most detailed characterization
of the neutrino flux at energies below compared to
previous IceCube results. Results from fits assuming more complex neutrino flux
models suggest a flux softening at high energies and a flux hardening at low
energies (p-value ). The sizable and smooth flux measured below remains a puzzle. In order to not violate the isotropic
diffuse gamma-ray background as measured by the Fermi-LAT, it suggests the
existence of astrophysical neutrino sources characterized by dense environments
which are opaque to gamma-rays.Comment: 4 figures, 4 tables, includes supplementary materia
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
A muon-track reconstruction exploiting stochastic losses for large-scale Cherenkov detectors
IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole.
The main goal of IceCube is the detection of astrophysical neutrinos and the
identification of their sources. High-energy muon neutrinos are observed via
the secondary muons produced in charge current interactions with nuclei in the
ice. Currently, the best performing muon track directional reconstruction is
based on a maximum likelihood method using the arrival time distribution of
Cherenkov photons registered by the experiment's photomultipliers. A known
systematic shortcoming of the prevailing method is to assume a continuous
energy loss along the muon track. However at energies TeV the light yield
from muons is dominated by stochastic showers. This paper discusses a
generalized ansatz where the expected arrival time distribution is parametrized
by a stochastic muon energy loss pattern. This more realistic parametrization
of the loss profile leads to an improvement of the muon angular resolution of
up to for through-going tracks and up to a factor 2 for starting tracks
over existing algorithms. Additionally, the procedure to estimate the
directional reconstruction uncertainty has been improved to be more robust
against numerical errors
LeptonInjector and LeptonWeighter: A neutrino event generator and weighter for neutrino observatories
We present a high-energy neutrino event generator, called LeptonInjector,
alongside an event weighter, called LeptonWeighter. Both are designed for
large-volume Cherenkov neutrino telescopes such as IceCube. The neutrino event
generator allows for quick and flexible simulation of neutrino events within
and around the detector volume, and implements the leading Standard Model
neutrino interaction processes relevant for neutrino observatories:
neutrino-nucleon deep-inelastic scattering and neutrino-electron annihilation.
In this paper, we discuss the event generation algorithm, the weighting
algorithm, and the main functions of the publicly available code, with
examples.Comment: 28 pages, 10 figures, 3 table
All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data
We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained
Strong Constraints on Neutrino Nonstandard Interactions from TeV-Scale Μ Disappearance at IceCube
We report a search for nonstandard neutrino interactions (NSI) using eight years of TeV-scale atmospheric muon neutrino data from the IceCube Neutrino Observatory. By reconstructing incident energies and zenith angles for atmospheric neutrino events, this analysis presents unified confidence intervals for the NSI parameter ΔΌÏ. The best-fit value is consistent with no NSI at a p value of 25.2%. With a 90% confidence interval of â0.0041â€Î”ÎŒÏâ€0.0031 along the real axis and similar strength in the complex plane, this result is the strongest constraint on any NSI parameter from any oscillation channel to date
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