The Pierre Auger Observatory is currently the largest detector of cosmic rays of ultrahigh energies (from ∼1017 to ∼1020 eV). The size of its accumulated exposure and the hybrid concept of the ...detector have provided measurements of unprecedented precision on the cosmic ray energy spectrum, mass composition, and anisotropy searches. There is an ankle in the energy spectrum at ∼4 EeV and a steepening at the end of the energy spectrum (above ∼40 EeV). The mass composition around the ankle is mixed and is uncertain at the highest energies due to the lack of statistics and high systematic uncertainties coming from predictions of different models of hadronic interactions. These models have, moreover, serious problems in describing the muon component of air showers. Still, the mean mass number of cosmic rays reaches its lowest value at energy ∼2 EeV and increases gradually above this energy. A dipole in the arrival directions is observed for energies above 8 EeV at more than 5σ significance level. It points ∼125° from the Galactic center, indicating the extra‐Galactic origin of these cosmic rays. The correlation of the arrival directions with starburst galaxies disfavors the isotropy hypothesis at energies above ∼40 EeV at the 4σ level without penalization for the catalog scan. The Observatory is currently being upgraded to improve its sensitivity to the mass of cosmic rays at the highest energies, which is crucial to constrain their sources.
The Mercedes water Cherenkov detector Assis, P.; Bakalová, A.; Barres de Almeida, U. ...
The European physical journal. C, Particles and fields,
10/2022, Letnik:
82, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The concept of a small, single-layer water Cherenkov detector, with three photomultiplier tubes (PMTs), placed at its bottom in a
120
∘
star configuration (
Mercedes
Water Cherenkov Detector) is ...presented. The PMTs are placed near the lateral walls of the stations with an adjustable inclination and may be installed inside or outside the water volume. To illustrate the technical viability of this concept and obtain a first-order estimation of its cost, an engineering design was elaborated. The sensitivity of these stations to low energy Extensive Air Shower (EAS) electrons, photons and muons is discussed, both in compact and sparse array configurations. It is shown that the analysis of the intensity and time patterns of the PMT signals, using machine learning techniques, enables the tagging of muons, achieving an excellent gamma/hadron discrimination for TeV showers. This concept minimises the station production and maintenance costs, allowing for a highly flexible and fast installation. Mercedes Water Cherenkov Detectors (WCDs) are thus well-suited for use in high-altitude large gamma-ray observatories covering an extended energy range from the low energies, closing the gap between satellite and ground-based measurements, to very high energy regions, beyond the PeV scale.
•Selectively oxidized 2,3-dicarboxypolysaccharides has number of unique properties.•Direct control over their molecular weight is achieved by addition of sulfamic acid.•Underlying mechanism is ...elucidated for cellulose and dextrin.•Role of reaction conditions to molecular weight of products is investigated.•Materials with adjustable molecular weight and degree of oxidation >90% prepared.
Oxidation of polysaccharides to 2,3-dicarboxypolysaccharides is a two-stage process, where selective oxidation by periodate is followed by secondary oxidation by chlorite. Addition of sulfamic acid before the secondary oxidation influences the molecular weight and degree of oxidation of the product. Here, mechanism of sulfamic acid-catalysed chain scission is elucidated for selectively oxidized cellulose and dextrin. Initially, sulfamic acid sulfonates the aldehyde groups of 2,3-dialdehydepolysaccharide. Introduced –SO3H groups are in ideal position to protonate the oxygen atom of 1-4′ glycosidic bond and to trigger acidic hydrolysis. This can be used to obtain a direct control over the molecular weight of the product. Observed slightly lower degree of oxidation was ascribed to the ability of sulfamic acid to scavenge the hypochlorite and thus protect the intermolecular hemiacetals from oxidation. Usually undesirable hypochlorite thus seems to be necessary for preparation of selectively oxidized polysaccharides with degree of oxidation above 90%.
The molecular weight (Mw) of dextran derivatives, such as regioselectively oxidized dicarboxydextran (DXA), is greatly influencing their faith in an organism, which could be possibly used to improve ...anticancer drug delivery. Here we present a modified method of sulfonation-induced chain scission allowing direct and accurate control over the Mw of DXA without increasing its polydispersity. Prepared DXA derivatives (Mw = 10–185 kDa) have been conjugated to cisplatin and the Mw of the carrier found to have a significant impact on cisplatin release rates, in vitro cytotoxicity, and migrastatic potential. Conjugates with the high-Mw DXA showed particularly increased anticancer efficacy. The best conjugate was four times more effective against malignant prostatic cell lines than free cisplatin and significantly inhibited the ovarian cancer cell migration. This was traced to the characteristics of spontaneously formed cisplatin-crosslinked DXA nanogels influenced by Mw of DXA and amount of loaded cisplatin.
•Method for control over the molecular weight of oxidized dextran developed.•Cisplatin loading resulted in spontaneous formation of nanogels.•Role of molecular weight to drug release and biological properties examined.•Highly improved in vitro efficacy and migrastatic potential compared to cisplatin.
A non-axial centerpiece based on 1,3-disubstituted adamantane was designed, and three new guests were prepared. In the structure of the heterotritopic guests, the central adamantane site was combined ...with two terminal butyl or 1-adamantyl sites. The new central binding motif displayed an extraordinarily high affinity towards CB8 ( K a = (5.3 ± 0.3) × 10 12 M −1 in water) to allow formation of quaternary assemblies with geometries which are dependent on the nature of macrocycles. Based on the individual binding strengths, the replacement of CB7 by CB8 led to inverse arrangements of the quaternary assemblies; i.e. , β-CD is capped at the central site by two CB7 units, while the CB8 prefers the central site to be capped with two β-CD units.
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.
A new concept for the direct measurement of muons in air showers is presented. The concept is based on resistive plate chambers (RPCs), which can directly measure muons with very good space and time ...resolution. The muon detector is shielded by placing it under another detector able to absorb and measure the electromagnetic component of the showers such as a water-Cherenkov detector, commonly used in air shower arrays. The combination of the two detectors in a single, compact detector unit provides a unique measurement that opens rich possibilities in the study of air showers.
PDF
