Despite the significant progress achieved in recent years, the physical mechanisms underlying the origin of solar energetic particles (SEPs) are still a matter of debate. The complex nature of both ...particle acceleration and transport poses challenges to developing a universal picture of SEP events that encompasses both the low-energy (from tens of keV to a few hundreds of MeV) observations made by space-based instruments and the GeV particles detected by the worldwide network of neutron monitors in ground-level enhancements (GLEs). The high-precision data collected by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment offer a unique opportunity to study the SEP fluxes between ∼80 MeV and a few GeV, significantly improving the characterization of the most energetic events. In particular, PAMELA can measure for the first time with good accuracy the spectral features at moderate and high energies, providing important constraints for current SEP models. In addition, the PAMELA observations allow the relationship between low- and high-energy particles to be investigated, enabling a clearer view of the SEP origin. No qualitative distinction between the spectral shapes of GLE, sub-GLE and non-GLE events is observed, suggesting that GLEs are not a separate class, but are the subset of a continuous distribution of SEP events that are more intense at high energies. While the spectral forms found are to be consistent with diffusive shock acceleration theory, which predicts spectral rollovers at high energies that are attributed to particles escaping the shock region during acceleration, further work is required to explore the relative influences of acceleration and transport processes on SEP spectra.
Oxides containing only one metallic component as well as mixed oxides with several cations may form during oxidation of multicomponent alloys. It is demonstrated that regardless of an intricacy of a ...particular situation, there exists a simple, general, practical, and elegant expression for Pilling–Bedworth ratio underpinned by a realistic assumption. Limits of formula’s applicability are delineated.
Precision measurements of the positron component in the cosmic radiation provide important information about the propagation of cosmic rays and the nature of particle sources in our Galaxy. The ...satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray positron flux and fraction that extends previously published measurements up to 300 GeV in kinetic energy. The combined measurements of the cosmic-ray positron energy spectrum and fraction provide a unique tool to constrain interpretation models. During the recent solar minimum activity period from July 2006 to December 2009, approximately 24,500 positrons were observed. The results cannot be easily reconciled with purely secondary production, and additional sources of either astrophysical or exotic origin may be required.
Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these ...particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.
More efficient and preferably more convenient and greener synthetic solutions in coumarin scaffold functionalization are in steady demand. The Duff
-formylation of unsubstituted umbelliferone was ...revised in this study. The reaction conditions were optimized based upon data from the literature analysis and resulted in unexpectedly rapid
-formylation of umbelliferone, yielding a mixture of
-formyl position isomers. Thorough studies on the separation of
-formylated umbelliferones using chromatographic and recrystallization methods as well as the evaluation of their solubility in common organic solvents led to complete resolution of 8-formyl- and 6-formylumbelliferones. The precise protocol for simultaneous preparation, extraction, and purification of 8-formyl- and 6-formylumbelliferones is provided, and the prospective studies of biological and pharmacological activities of these compounds are synopsized.
We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions ...containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues. We observed a statistical difference between the THz optical constants of intact tissues and gliomas of grades I to IV, while the response of edema was similar to that of tumor. The results of this paper justify a potential of THz technology in the intraoperative label-free diagnosis of human brain gliomas for ensuring the gross-total resection.
Origin of Echinodermata Ezhova, O. V.; Malakhov, V. V.
Paleontological journal,
12/2022, Letnik:
56, Številka:
8
Journal Article
Recenzirano
The common ancestor of Ambulacraria was a mobile bilaterally symmetrical organism. Its body was subdivided into a preoral (proboscis) region, a perioral (collar) region with ciliated tentacles, and a ...trunk region with a metameric coelom and metameric gill slits. Like in other Bilateria, the preoral and tentacular regions of Ambulacraria are free of
Hox
gene expression, which begins in the area of the first pair of gill slits in compliance with the colinearity. The axial complex is a synapomorphy of the Ambulacraria clade. A bilaterally symmetrical ancestor of Echinodermata lay on its dorsal side, so its anus was shifted to the ventral side as in present-day echinoderm larvae. This stage of evolution corresponds to the Early Paleozoic bilaterally symmetrical forms, such as
Protocinctus, Ctenocystis
, and
Ctenoimbricata
. The common ancestor of echinoderms had a symmetrical tentacular apparatus consisting of five ciliated tentacles on each side of a collar. At the next stage, the ancestors of echinoderms lay on the right side that resulted in the reduction of the tentacles on the right side and the right hydrocoel. This evolution stage includes various Early Paleozoic forms (
Cothurnocystis
,
Dendrocystoides
,
Syringocrinus
,
Castericystis
,
Coleicarpus
,
Rhenocystis
, etc.). The next stage is related to the sedentary lifestyle. During this stage, the mouth and tentacles occupied an apical position, the anus has shifted up, and thus an intestinal loop was formed. The five primary tentacles of the left side of the ancestor of Ambulacraria predestined the formation of pentaradial symmetry of echinoderms. The primary tentacles remained only in Holothuroidea. The secondary ciliary grooves were formed between the primary tentacles. These grooves were accompanied by hydrocoelic canals, which gave rise to the water-vascular (ambulacral) system. The present-day echinoderms are characterized by several metameric rings formed by the derivatives of the left somatocoel. They derive from the coelomic segments of the left side of the trunk of the ambulacrarian ancestor and, thus, the echinoderms retain coelomic metamerism. The attachment of the crinoid larvae by the preoral lobe reflects the ancient method of locomotion of deuterostomes using the proboscis, but, in reality, the Pelmatozoa stalk is homologous to the Pterobranchia stalk, i.e., the posterior end of the body, because the right somatocoel grows into it. During metamorphosis, the internal coelomic complex of the larva is inverted by 180°. The significance of this inversion for the translocation of the anterior genes of the
Hox
cluster is discussed. The ancestors of Eleutherozoa began to crawl on the oral surface, which led to a shift of the anus to the aboral side. Thus, the ontogeny and phylogeny of echinoderms exhibits a change from bilateral symmetry to dissymmetry, and then the development of pentameric symmetry.
ExoMars is a two-launch mission undertaken by Roscosmos and European Space Agency. Trace Gas Orbiter, a satellite part of the 2016 launch carries the Fine Resolution Neutron Detector instrument as ...part of its payload. The instrument aims at mapping hydrogen content in the upper meter of Martian soil with spatial resolution between 60 and 200 km diameter spot. This resolution is achieved by a collimation module that limits the field of view of the instruments detectors. A dosimetry module that surveys the radiation environment in cruise to Mars and on orbit around it is another part of the instrument.
This paper describes the mission and the instrument, its measurement principles and technical characteristics. We perform an initial assessment of our sensitivity and time required to achieve the mission goal. The Martian atmosphere is a parameter that needs to be considered in data analysis of a collimated neutron instrument. This factor is described in a section of this paper. Finally, the first data accumulated during cruise to Mars is presented.
Precise measurements of the time-dependent intensity of the low-energy (<50 GeV) galactic cosmic rays (GCRs) are fundamental to test and improve the models that describe their propagation inside the ...heliosphere. In particular, data spanning different solar activity periods, i.e., from minimum to maximum, are needed to achieve comprehensive understanding of such physical phenomena. The minimum phase between solar cycles 23 and 24 was peculiarly long, extending up to the beginning of 2010 and followed by the maximum phase, reached during early 2014. In this Letter, we present proton differential spectra measured from 2010 January to 2014 February by the PAMELA experiment. For the first time the GCR proton intensity was studied over a wide energy range (0.08-50 GeV) by a single apparatus from a minimum to a maximum period of solar activity. The large statistics allowed the time variation to be investigated on a nearly monthly basis. Data were compared and interpreted in the context of a state-of-the-art three-dimensional model describing the GCRs propagation through the heliosphere.
•LEND/LRO instrument neutron counting data sets have been analyzed to create high resolution maps of epithermal neutron flux at polar regions of the Moon.•The conversion from epithermal neutron flux ...to the H/H2O abundances is presented based on the simple subsurface models.•The polar lunar maps (poleward 70S/70N) of homogeneous hydrogen distribution are derived and discussed.
We present a method of conversion of the lunar neutron counting rate measured by the Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) instrument collimated neutron detectors, to water equivalent hydrogen (WEH) in the top ∼1m layer of lunar regolith. Polar maps of the Moon's inferred hydrogen abundance are presented and discussed.
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