THE STRUCTURE OF THE LOCAL HOT BUBBLE Liu, W.; Chiao, M.; Collier, M. R. ...
The Astrophysical journal,
01/2017, Letnik:
834, Številka:
1
Journal Article
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ABSTRACT Diffuse X-rays from the Local Galaxy (DXL) is a sounding rocket mission designed to quantify and characterize the contribution of Solar Wind Charge eXchange (SWCX) to the Diffuse X-ray ...Background and study the properties of the Local Hot Bubble (LHB). Based on the results from the DXL mission, we quantified and removed the contribution of SWCX to the diffuse X-ray background measured by the ROSAT All Sky Survey. The "cleaned" maps were used to investigate the physical properties of the LHB. Assuming thermal ionization equilibrium, we measured a highly uniform temperature distributed around kT = 0.097 keV 0.013 keV (FWHM) 0.006 keV (systematic). We also generated a thermal emission measure map and used it to characterize the three-dimensional (3D) structure of the LHB, which we found to be in good agreement with the structure of the local cavity measured from dust and gas.
The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. ...Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.
ABSTRACT DXL (Diffuse X-ray emission from the Local Galaxy) is a sounding rocket mission designed to estimate the contribution of solar wind charge eXchange (SWCX) to the diffuse X-ray background and ...to help determine the properties of the Local Hot Bubble. The detectors are large area thin-window proportional counters with a spectral response that is similar to that of the PSPC used in the ROSAT All Sky Survey (RASS). A direct comparison of DXL and RASS data for the same part of the sky viewed from quite different vantage points in the solar system, and the assumption of approximate isotropy for the solar wind, allowed us to quantify the SWCX contribution to all six RASS bands (R1-R7, excluding R3). We find that the SWCX contribution at , where the DXL path crosses the Galactic plane, is for R1, for R2, for R4, for R5, and negligible for the R6 and R7 bands. Reliable models for the distribution of neutral H and He in the solar system permit estimation of the contribution of interplanetary SWCX emission over the the whole sky and correction of the RASS maps. We find that the average SWCX contribution in the whole sky is for R1, for R2, for R4, for R5, and negligible for R6 and R7.
Three recent results related to the heliosphere and the local interstellar medium (ISM) have provided an improved insight into the distribution and conditions of material in the solar neighborhood. ...These are the measurement of the magnetic field outside of the heliosphere by Voyager 1, the improved mapping of the three-dimensional structure of neutral material surrounding the Local Cavity using extensive ISM absorption line and reddening data, and a sounding rocket flight which observed the heliospheric helium focusing cone in X-rays and provided a robust estimate of the contribution of solar wind charge exchange emission to the ROSAT All-Sky Survey 1/4 keV band data. Combining these disparate results, we show that the thermal pressure of the plasma in the Local Hot Bubble (LHB) is P/k = 10,700 cm super(-3) K. If the LHB is relatively free of a global magnetic field, it can easily be in pressure (thermal plus magnetic field) equilibrium with the local interstellar clouds, eliminating a long-standing discrepancy in models of the local ISM.
Ethnopharmacological knowledge is common and import among tribal populations but much of the information is empirical at best lacking scientific validation. Despite widespread use of plant resources ...in traditional medicines, bioassay analysis of very few plant species have been conducted to investigate their medicinal properties, and to ascertain safety and efficacy of traditional remedies. The present study analyses indigenous uses of medicinal plants of far-west Nepal and compares with earlier ayurveda studies, phytochemical assessments and pharmacological actions. A field study was carried out in Baitadi and Darchula districts of far-west Nepal. Group discussions, informal meetings, questionnaire surveys and field observations were employed for primary data collection. Voucher specimens were collected with field notes and codes and deposited at Tribhuvan University Central Herbarium (TUCH), Kathmandu. Only 50% of species surveyed shared common uses with ayurvedic medicine. This implies that these herbal remedies are part of an independent health care system in the Nepal Himalaya, which is indigenous and influenced by ayurveda. The folk uses of some of the species were contradicting to those of ayurveda and phytochemical bioassays. A detailed phytochemical study on those species would be an important line of research.
Vitis genus comprised about 70 species. Concerning its pharmacological properties, V. vinifera is the most studied one, but there are other species with interest.
Therefore, this review aims to ...provide an updated overview on bioactive phytochemicals present in food products (grapes and wine) of V. vinifera and other Vitis species, as well as in different underused bioresources (stem, leaves, seeds, wine pomace, etc.). Moreover, due to their promising perspectives in the field of anticancer drug discovery, this bioactivity has been covered as well as the contribution that Vitis phenolic compounds has.
Among the plant products reviewed, grape seed extracts was the most investigated at preclinical phase, hence exhibiting a promising potential as anticancer drugs. However, an evidence-based clinical efficacy is still lacking.
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•V. vinifera comprises of more than 140 phenolic compounds.•Vitis phenolic compounds exhibit a promising potential as anticancer agents.•V. vinifera grape seed extracts was the most investigated part at preclinical phase.•An evidence-based clinical efficacy is still lacking.
The effective mass of the electron neutrino can be probed by studying the
163
Ho electron capture decay with cryogenic microcalorimeters. The goal is to perform a calorimetric experiment, where all ...the energy released in the decay is measured except for the kinetic energy of the neutrino. To achieve such a goal, multiple approaches are being investigated to enclose the radioactive source in a microcalorimeter absorber without affecting the thermal properties of the absorber material. One such approach is to implant the radioactive isotope into a gold absorber, as gold is successfully used in similar applications. We measured the heat capacity of gold films, implanted with various concentrations of holmium and erbium (a byproduct of the
163
Ho fabrication), in the temperature range 70–300 mK. Our results show that the specific heat capacity of the films is not affected by the implant, making this a viable option for a future experiment. We also verified that the implant does not affect the crystal structure of the gold film.
Nepal is located in the central part of the greater Himalayan range with a unique series of mountain chains formed by recent mountain building geological events. As one of the youngest mountains in ...the world it contributes to diversity of plants and also provided barriers to and corridors through which plants migrated during the ice ages. The higher altitudinal variation with the high mountains, deep river valleys and lowland plains combine with the effects of the summer monsoon and dry winter result with an extraordinary diversity of ecosystems including flora and fauna in a relatively small land area. The existing checklists for Nepal record some 6000 species of flowering plants and about 530 ferns. However, the botanical experts estimate that numbers may go up to 7000 when the poorly known remote regions are fully explored. The information on plant endemism in Nepal Himalaya is not adequately known as Nepal is still struggling to complete long awaited Flora of Nepal project. Endemic species are confined to specific areas and are the first to be affected by land use and other global changes. We sought to explore the spatial distribution of endemic plant species in Nepal in relation to the consequences associated with climatic and geologic changes over time in the region with the help of published literature. It was found that the endemism showed marked spatial variation between open moist habitat and dry inner valleys, the former with higher endemism. The updated records showed 312 flowering plant species to be endemic to Nepal with higher endemism around the elevation of 3800–4200 m at sea level. The recent human population explosion, intensified deforestation, habitat fragmentation and modern day environmental changes are posing greater threats to endemic plant in Nepal. The conservation status and threats to these peculiar species are unknown. Nevertheless, environmental degradation and high poverty rates create a potent mix of threats to biodiversity in this landscape.
Homoepitaxial growths of 4H-SiC(1
1
2¯
0) epitaxial layers have been achieved using chemical vapor deposition from 1250 to 1600
°C and two process routes: (1) with and (2) without the addition of SiH
...4 and C
2H
4 to the growth ambient. An activation energy of 3.72
eV/atom (359
kJ/mol) was determined for the former route and associated with either reactions in the gas phase or the potential barrier associated with the temperature-dependent sticking coefficient. The activation energy for the latter route was 5.64
eV/atom (544
kJ/mol), which is consistent with published values for SiC sublimation epitaxy. Sublimation dominated the growth process at temperature ⩾1600
°C. The same effect resulted in the
in-situ deposition of a thin film during the heating stage of route (1). At 1450
°C this layer was ∼100
nm thick and exhibited a specular surface microstructure with a roughness of 0.31
nm RMS. The
in-situ-deposited layer was thus employed as an intermediate layer prior to epitaxial layer growth using route (1) at ∼1450
°C. Regions free of one- and two-dimensional defects were observed using cross-sectional transmission electron microscopy. Distinct interfaces were not observed between the substrate and the epitaxial layers.
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