We present a new approach for the identification of ultra-high energy cosmic rays from sources using dynamic graph convolutional neural networks. These networks are designed to handle sparsely ...arranged objects and to exploit their short- and long-range correlations. Our method searches for patterns in the arrival directions of cosmic rays, which are expected to result from coherent deflections in cosmic magnetic fields. The network discriminates astrophysical scenarios with source signatures from those with only isotropically distributed cosmic rays and allows for the identification of cosmic rays that belong to a deflection pattern. We use simulated astrophysical scenarios where the source density is the only free parameter to show how density limits can be derived. We apply this method to a public data set from the AGASA Observatory.
The present white paper is submitted as part of the “Snowmass” process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy ...physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.
Abstract The Tarantula Nebula in the Large Magellanic Cloud is known for its high star formation activity. At its center lies the young massive star cluster R136, providing a significant amount of ...the energy that makes the nebula shine so brightly at many wavelengths. Recently, young massive star clusters have been suggested to also efficiently produce very high-energy cosmic rays, potentially beyond PeV energies. Here, we report the detection of very-high-energy γ -ray emission from the direction of R136 with the High Energy Stereoscopic System, achieved through a multicomponent, likelihood-based modeling of the data. This supports the hypothesis that R136 is indeed a very powerful cosmic-ray accelerator. Moreover, from the same analysis, we provide an updated measurement of the γ -ray emission from 30 Dor C, the only superbubble detected at TeV energies presently. The γ -ray luminosity above 0.5 TeV of both sources is (2–3) × 10 35 erg s −1 . This exceeds by more than a factor of 2 the luminosity of HESS J1646−458, which is associated with the most massive young star cluster in the Milky Way, Westerlund 1. Furthermore, the γ -ray emission from each source is extended with a significance of >3 σ and a Gaussian width of about 30 pc. For 30 Dor C, a connection between the γ -ray emission and the nonthermal X-ray emission appears likely. Different interpretations of the γ -ray signal from R136 are discussed.
The present white paper is submitted as part of the "Snowmass" process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy ...physics. Further, it summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.
Abstract We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the ...spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
Lysosomal degradation of ganglioside GM2 by hexosaminidase A requires the presence of a small, non‐enzymatic cofactor, the GM2‐activator protein (GM2AP). Lack of functional protein leads to the AB ...variant of GM2‐gangliosidosis, a fatal lysosomal storage disease.
Although its possible mode of action and functional domains have been discussed frequently in the past, no structural information about GM2AP is available so far. Here, we determine the complete disulfide bond pattern of the protein. Two of the four disulfide bonds present in the protein were open to classical determination by enzymatic cleavage and mass spectrometry. The direct localization of the remaining two bonds was impeded by the close vicinity of cysteines 136 and 138. We determined the arrangement of these disulfide bonds by MALDI‐PSD analysis of disulfide linked peptides and by partial reduction, cyanylation and fragmentation in basic solution, as described recently (Wu F, Watson JT, 1997, Protein Sci 6:391‐398).
Abstract The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented ...precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$ 2×1017 and $$2\times 10^{18}$$ 2×1018 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$ 1017.5eV and $$10^{{18}}\, {\mathrm{eV}} $$ 1018eV . We find that, for the models to explain the data, an increase in the muon density of $$38\%$$ 38% $$\pm 4\% (12\%)$$ ±4%(12%) $$\pm {}^{21\%}_{18\%}$$ ±18%21% for EPOS-LHC, and of $$50\% (53\%)$$ 50%(53%) $$\pm 4\% (13\%)$$ ±4%(13%) $$\pm {}^{23\%}_{20\%}$$ ±20%23% for QGSJetII-04, is respectively needed.
Sphingolipid activator proteins (SAPs) are non-enzymatic glycoproteins required for lysosomal degradation of various sphingolipids
with short oligosaccharide chains by their respective exohydrolases. ...Four of these (SAP-A to SAP-D or saposins A to D) are
derived from a common precursor by proteolytic processing. Alternative splicing of the SAP-precursor gene results in insertion
of additional 6 or 9 bases of exon 8â² or 8, respectively, into the SAP-B coding region of the transcribed mRNAs.
To examine the features of the three different SAP-precursor proteins (prosaposins), the respective cDNAs were stably expressed
in baby hamster kidney cells. Pulse-chase experiments with transfected cells and endocytosis studies on human fibroblasts
showed that synthesis, transport, and maturation of all SAP-precursor led to formation of the four mature SAPs (SAP-A to SAP-D).
In order to determine the biological function of the three different SAP-B isoforms, SAP-precursor-deficient human fibroblasts
were loaded with recombinant SAP-precursor proteins with or without 2- and 3-amino acid insertions, respectively, purified
from the medium of the baby hamster kidney cells. They were found to stimulate at nanomolar concentrations the turnover of
biosynthetically labeled ceramide, glucosylceramide, and lactosylceramide. Since the physiological function of SAP-B is to
stimulate the degradation of sulfatide by arylsulfatase A (EC 3.1.6.1) and globotriaosylceramide by β-galactosidase (EC 3.2.1.23)
loading studies with the respective exogenously labeled lipids on SAP-precursor-deficient fibroblasts were performed. Addition
of different purified SAP-precursors to the medium of the lipid-loaded fibroblasts showed positive stimulation of the lipid
degradation by all three SAP-B isoforms derived from the SAP-precursors. These findings establish that all three forms of
the SAP-B can function as sulfatide/globotriaosylceramide activator.
The carbene precursor 3-azi-1-(6-3H-2-acetamido-2-deoxy-1-beta-D-galactopyranosyl)thi o -butane (also designated 3H-1-ATB-GalNAc) has been used as a photoaffinity label for human lysosomal ...beta-hexosaminidase B (Hex B, EC 3.2.1.52) purified to apparent homogeneity from postmortal liver. 3H-1-ATB-GalNAc behaved as an active site-directed inhibitor, which bound covalently to Hex B upon photolysis at 350 nm and resulted in 15% inactivation of enzyme activity. Up to 75% of the inactivation of Hex B was prevented by including the competitive inhibitor 2-acetamido-2-deoxy-D-glucono-1,5-lactone in the photoaffinity experiment. Incubation of 3H-1-ATB-GalNAc with the enzyme followed by irradiation and subsequent separation of the three polypeptides composing the beta-subunit led mainly to labeling of the beta a-polypeptide. Subsequent proteolysis of beta a with trypsin and separation of the resulting peptides by high pressure liquid chromatography yielded one prominently labeled peptide fraction. Edman degradation resulted in the sequence E339ISEVFPDQFIHLGGD-EVEFK359. However, no modified amino acid was detected, indicating that the photoaffinity label was presumably bound to the peptide by a labile ester linkage. This was proven when the radiolabel was almost completely released from the peptide by treatment with aqueous ammonium hydroxide. Simultaneously, Glu-355 was converted into Gln-355, which is located within a region of Hex B that shows considerable homology with the alpha-subunit of human hexosaminidase A and other hexosaminidases from various species.
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