•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.
Abstract
The direction and magnitude of the dipole anisotropy of ultra-high-energy cosmic rays with energies above 8 EeV observed by the Pierre Auger Observatory indicate their extragalactic origin. ...The observed dipole on Earth does not necessarily need to correspond to the anisotropy of the extragalactic cosmic-ray flux due to the effects of propagation in the Galactic magnetic field. We estimate the size of these effects via numerical simulations using the CRPropa 3 package. The Jansson-Farrar and Terral-Ferrière models of the Galactic magnetic field are used to propagate particles within the Galaxy. We identify allowed directions and amplitudes of the dipole outside the Galaxy that are compatible with the measured features of the dipole on Earth for various mass composition scenarios at the 68% and 95% confidence level.
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Mercedes water Cherenkov detector Assis, P.; Bakalová, A.; Barres de Almeida, U. ...
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report a measurement of the energy spectrum of cosmic rays for energies above 2.5 × 1018 eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the ...estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above 5 × 1019 eV. The principal conclusions are (1) The flattening of the spectrum near 5 × 1018 eV, the so-called "ankle," is confirmed. (2) The steepening of the spectrum at around 5 × 1019 eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux ( ∝ E−γ ) changes from 2.51 ± 0.03 ( stat ) ± 0.05 ( syst ) to 3.05 ± 0.05 ( stat ) ± 0.10 ( syst ) before changing sharply to 5.1 ± 0.3 ( stat ) ± 0.1 ( syst ) above 5 × 1019 eV. (4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above 8 × 1018 eV.
The Pierre Auger Cosmic Ray Observatory Aab, A.; Abreu, P.; Aglietta, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2015, Letnik:
798, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The Pierre Auger Observatory, located on a vast, high plain in western Argentina, is the world׳s largest cosmic ray observatory. The objectives of the Observatory are to probe the origin and ...characteristics of cosmic rays above 1017eV and to study the interactions of these, the most energetic particles observed in nature. The Auger design features an array of 1660 water Cherenkov particle detector stations spread over 3000km2 overlooked by 24 air fluorescence telescopes. In addition, three high elevation fluorescence telescopes overlook a 23.5km2, 61-detector infilled array with 750m spacing. The Observatory has been in successful operation since completion in 2008 and has recorded data from an exposure exceeding 40,000km2sryr. This paper describes the design and performance of the detectors, related subsystems and infrastructure that make up the Observatory.
We report a measurement of the energy spectrum of cosmic rays above 2.5 × 1018 eV based on 215 030 events. New results are presented: at about 1.3 × 1019 eV , the spectral index changes from 2.51 ± ...0.03 (stat) ± 0.05 (syst) to 3.05 ± 0.05 (stat) ± 0.10 (syst), evolving to 5.1 ± 0.3 (stat) ± 0.1 (syst) beyond 5 × 1019 eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above 5 × 1018 eV is 5.66 ± 0.03 (stat) ± 1.40 (syst) × 1053 erg Mpc−3.
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