Observation of Seven Astrophysical Tau Neutrino Candidates with IceCube.

We report on a measurement of astrophysical tau neutrinos with 9.7 yr of IceCube data. Using convolutional neural networks trained on images derived from simulated events, seven candidate ν_{τ} events were found with visible energies ranging from roughly 20 TeV to 1 PeV and a median expected parent ν_{τ} energy of about 200 TeV. Considering backgrounds from astrophysical and atmospheric neutrinos, and muons from π^{±}/K^{±} decays in atmospheric air showers, we obtain a total estimated background of about 0.5 events, dominated by non-ν_{τ} astrophysical neutrinos. Thus, we rule out the absence of astrophysical ν_{τ} at the 5σ level. The measured astrophysical ν_{τ} flux is consistent with expectations based on previously published IceCube astrophysical neutrino flux measurements and neutrino oscillations.

Observation of high-energy neutrinos from the Galactic plane.

The origin of high-energy cosmic rays, atomic nuclei that continuously impact Earth's atmosphere, is unknown. Because of deflection by interstellar magnetic fields, cosmic rays produced within the Milky Way arrive at Earth from random directions. However, cosmic rays interact with matter near their sources and during propagation, which produces high-energy neutrinos. We searched for neutrino emission using machine learning techniques applied to 10 years of data from the IceCube Neutrino Observatory. By comparing diffuse emission models to a background-only hypothesis, we identified neutrino emission from the Galactic plane at the 4.5σ level of significance. The signal is consistent with diffuse emission of neutrinos from the Milky Way but could also arise from a population of unresolved point sources.

Search for Unstable Sterile Neutrinos with the IceCube Neutrino Observatory.

We present a search for an unstable sterile neutrino by looking for a resonant signal in eight years of atmospheric ν_{µ} data collected from 2011 to 2019 at the IceCube Neutrino Observatory. Both the (stable) three-neutrino and the 3+1 sterile neutrino models are disfavored relative to the unstable sterile neutrino model, though with p values of 2.8% and 0.81%, respectively, we do not observe evidence for 3+1 neutrinos with neutrino decay. The best-fit parameters for the sterile neutrino with decay model from this study are Δm_{41}^{2}=6.7_{-2.5}^{+3.9} eV^{2}, sin^{2}2θ_{24}=0.33_{-0.17}^{+0.20}, and g^{2}=2.5π±1.5π, where g is the decay-mediating coupling. The preferred regions of the 3+1+decay model from short-baseline oscillation searches are excluded at 90% C.L.

Pore formation by tetanus toxin, its chain and fragments in neuronal membranes and evaluation of the underlying motifs in the structure of the toxin molecule.

The pore-forming activity of tetanus toxin, its chains and fragments was studied on membrane patches from spinal cord neurons of fetal mice using the outside-out patch-clamp configuration. 1. The dichain tetanus toxin forms pores at pH 5, but not at pH 7.4. The elementary pore conductance is 38.4 +/- 1.1 pS and nonselective for small cations. The open probability of the pores is voltage-dependent and increases with membrane depolarisation. The pores activate at +80 mV with a time constant of about 20 ms and deactivate at -80 mV with two time constants of about 2 ms and 10 ms. Besides the elementary pore conductance, larger pore conductances which are multiples of the elementary conductance were observed. With increasing conductances, their frequency of occurrence decreases exponentially. 2. The light chain of tetanus toxin alone does not form pores in neuronal membranes at pH 5 or at pH 7.4. 3. The heavy chain of tetanus toxin forms pores at pH 5 as well as at pH 7.4. The single pore conductance increases from 35.0 +/- 1.2 pS at pH 5 to 43.2 +/- 1.8 pS at pH 7.4. The pores allow mono- and divalent cations and chloride ions to pass. Only at pH 5 do they have a voltage dependence with time constants identical to those obtained with tetanus toxin. 4. Secondary structure predictions show a high density of presumably helically organized elements in fragment beta 2 (45 kDa) of the heavy chain between residues 700-850.(ABSTRACT TRUNCATED AT 250 WORDS)

Profound differences in potassium current properties of normal and Rous sarcoma virus-transformed chicken embryo fibroblasts.

The membrane currents of chicken embryo fibroblasts (CEFs) transformed by Rous sarcoma virus (RSV) were compared with the currents of their nontransformed counterparts by using the whole-cell patch-clamp technique. In nontransformed CEFs, the main membrane current is a delayed outward K+ current that is sensitive to tetraethylammonium ion but insensitive to 4-aminopyridine. This K+ current is almost independent of the intracellular Ca2+ concentration and becomes completely inactivated at positive membrane potentials with a time constant of about 10 s at +30 mV. In contrast, transformed CEFs exhibit a noninactivating K+ current that strongly depends on the intracellular Ca2+ concentration. This Ca(2+)-dependent K+ current is blocked by the scorpion toxin charybdotoxin with an IC50 value of 19 nM, whereas the K+ current of normal CEFs is insensitive to charybdotoxin (up to 300 nM). The K+ current properties of transformed CEFs were also found after microinjection of purified, enzymatically active pp60v-src into normal CEFs but not after infection of CEFs with the Rous-associated virus RAV5, which lacks the v-src oncogene. Our results suggest that the oncogene product pp60v-src modulates existing K+ channel proteins, leading to profound electrophysiological and pharmacological alterations of the K+ current properties in RSV-transformed CEFs. Furthermore, our experiments identify for the first time K+ channels as possible substrates of pp60v-src.