402 research outputs found
What can GLAST say about the origin of cosmic rays in other galaxies ?
Gamma rays in the band from 20 MeV to 300 GeV, used in combination with data
from radio and X-ray bands, provide a powerful tool for studying the origin of
cosmic rays in our sister galaxies Andromeda and the Magellanic Clouds.
Gamma-ray Large Area Space Telescope (GLAST) will spatially resolve these
galaxies and measure the spectrum and intensity of diffuse gamma radiation from
the collisions of cosmic rays with gas and dust in them. Observations of
Andromeda will give an external perspective on a spiral galaxy like the Milky
Way. Observations of the Magellanic Clouds will permit a study of cosmic rays
in dwarf irregular galaxies, where the confinement is certainly different and
the massive star formation rate is much greater.Comment: 4 pages including 6 figures; to appear in Proc. ACE-2000 Symp. "The
Acceleration and Transport of Energetic Particles Observed in the
Heliosphere" (Jan. 5-8, 2000, Indian Wells, CA), AIP Conf. Proc. More details
can be found at the LHEA GLAST page at
http://lhea-glast.gsfc.nasa.gov/pub/science/index.htm
Multi-wavelength constraints on cosmic-ray leptons in the Galaxy
Cosmic rays (CRs) interact with the gas, the radiation field and the magnetic
field in the Milky Way, producing diffuse emission from radio to gamma rays.
Observations of this diffuse emission and comparison with detailed predictions
are powerful tools to unveil the CR properties and to study CR propagation. We
present various GALPROP CR propagation scenarios based on current CR
measurements. The predicted synchrotron emission is compared to radio surveys,
and synchrotron temperature maps from WMAP and Planck, while the predicted
interstellar gamma-ray emission is compared to Fermi-LAT observations. We show
how multi-wavelength observations of the Galactic diffuse emission can be used
to help constrain the CR lepton spectrum and propagation. Finally we discuss
how radio and microwave data could be used in understanding the diffuse
Galactic gamma-ray emission observed with Fermi-LAT, especially at low
energies.Comment: 8 pages, 5 figures; in Proceedings of the 34th International Cosmic
Ray Conference (ICRC 2015), The Hague (The Netherlands); Oral contributio
Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
It is widely accepted that cosmic rays (CRs) up to at least PeV energies are
Galactic in origin. Accelerated particles are injected into the interstellar
medium where they propagate to the farthest reaches of the Milky Way, including
a surrounding halo. The composition of CRs coming to the solar system can be
measured directly and has been used to infer the details of CR propagation that
are extrapolated to the whole Galaxy. In contrast, indirect methods, such as
observations of gamma-ray emission from CR interactions with interstellar gas,
have been employed to directly probe the CR densities in distant locations
throughout the Galactic plane. In this article we use 73 months of data from
the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV
to search for gamma-ray emission produced by CR interactions in several high-
and intermediate-velocity clouds located at up to ~ 7 kpc above the Galactic
plane. We achieve the first detection of intermediate-velocity clouds in gamma
rays and set upper limits on the emission from the remaining targets, thereby
tracing the distribution of CR nuclei in the halo for the first time. We find
that the gamma-ray emissivity per H atom decreases with increasing distance
from the plane at 97.5% confidence level. This corroborates the notion that CRs
at the relevant energies originate in the Galactic disk. The emissivity of the
upper intermediate-velocity Arch hints at a 50% decline of CR densities within
2 kpc from the plane. We compare our results to predictions of CR propagation
models.Comment: Accepted for publication in the Astrophysical Journa
The Origin of Cosmic Rays and the Diffuse Galactic Gamma-Ray Emission
Cosmic-ray interactions with interstellar gas and photons produce diffuse
gamma-ray emission. In this talk we will review the current understanding of
this diffuse emission and its relationship to the problem of the origin of
cosmic rays. We will discuss the open issues and what progress might be
possible with GLAST, which is planned for launch in 2006.Comment: 10 pages, 5 figures. Invited talk at the "Gamma 2001" Symp., April
4-6, 2001, Baltimore, MD. AIP Conf. Proc. v.587, eds. S. Ritz, N. Gehrels, &
C. R. Shrader, in pres
Physicochemical and Antibacterial Properties of Composite Films Based on Bacterial Cellulose and Chitosan for Wound Dressing Materials
New bacterial cellulose/chitosan (BC/Ch) nanocomposite films were obtained using a simple procedure by immersing BC synthesized by Komagataeibacter xylinus in 1% acetic acid solutions of Ch with the degree of deacetylation 75‒85% of medium molecular weight. The BC and BC/Ch composites chemical composition was examined by FTIR, the mechanical properties by a tensile tester, surface morphology by scanning electron microscopy, and antibacterial activity against S. aureus, E. coli and P. aeruginosa by diffusion and joint incubation methods. The FTIR spectra indicated the intermolecular interaction between BC and Ch. Due to addition of 0.6% (w/v) Ch, the films of BC/Ch become more homogeneous with a significantly denser fibril structure, smaller pore diameter and higher surface area in comparison to those of pure BC films. Micro- (15‒35 nm) and macrofibrils (50‒150 nm) in both BC and BC/Ch films are joined in ribbon-like fibers, providing a high degree of mechanical strength (Young’s modulus: 33‒36 MPa, tensile strength and elongation et break: 17, 22 MPa). The obtained hybrid material is transparent, flexible and displays good water absorption capacity and water vapor permeability. The films have reasonable thermal stability to be in contact with body or during steam sterilization, since maximum degradation temperature (Td) of both biocomposites is around 400‒600 °C. The disc diffusion method confirmed that the BC/Ch films have predominantly non-diffusible antibacterial properties. Antibacterial assessment by the joint incubation method proved that addition of Ch to BC films resulted in significant growth inhibition against target bacteria. The BC/Ch biocomposites’ notable properties make them suitable for wound healing applications
The distribution of cosmic-ray sources in the Galaxy, gamma-rays, and the gradient in the CO-to-H2 relation
We present a solution to the apparent discrepancy between the radial gradient
in the diffuse Galactic gamma-ray emissivity and the distribution of supernova
remnants, believed to be the sources of cosmic rays. Recent determinations of
the pulsar distribution have made the discrepancy even more apparent. The
problem is shown to be plausibly solved by a variation in the CO-to-N(H2)
scaling factor. If this factor increases by a factor of 5-10 from the inner to
the outer Galaxy, as expected from the Galactic metallicity gradient, we show
that the source distribution required to match the radial gradient of gamma-ray
can be reconciled with the distribution of supernova remnants as traced by
current studies of pulsars. The resulting model fits the EGRET gamma-ray
profiles extremely well in longitude, and reproduces the mid-latitude inner
Galaxy intensities better than previous models.Comment: Accepted for publication in Astronomy & Astrophysics Letter
From powder to solution: hydration dependence of human hemoglobin dynamics correlated to body temperature
A transition in hemoglobin (Hb), involving partial unfolding and aggregation, has been shown previously by various biophysical methods. The correlation between the transition temperature and body temperature for Hb from different species, suggested that it might be significant for biological function. In order to focus on such biologically relevant human Hb dynamics, we studied the protein internal picosecond motions as a response to hydration, by elastic and quasielastic neutron scattering. Rates of fast diffusive motions were found to be significantly enhanced with increasing hydration from fully hydrated powder to concentrated Hb solution. In concentrated protein solution, the data revealed that amino acid side-chains can explore larger volumes above body temperature than expected from normal temperature dependence. The body temperature transition in protein dynamics was absent in fully hydrated powder, indicating that picosecond protein dynamics responsible for the transition is activated only at a sufficient level of hydration. A collateral result from the study is that fully hydrated protein powder samples do not accurately describe all aspects of protein picosecond dynamics that might be necessary for biological function
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