5,050 research outputs found
The -ray Milky Way above 10 GeV: Distinguishing Sources from Diffuse Emission
One of the most prominent features of the -ray sky is the emission
from our own Galaxy. The Galactic plane has been observed by Fermi-LAT in GeV
and H.E.S.S. in TeV light. Fermi has modeled the Galactic emission as the sum
of a complex 'diffuse' emission model with the predominately point source
catalogs of 1FHL and 2FGL, while H.E.S.S. has primarily detected extended TeV
sources. At GeV energies, Galactic diffuse emission dominates the -ray
Milky Way but, as sources have hard spectra, it is likely their emission
dominates at TeV energies. Generally the spatial shape and fraction of source
emission compared to diffuse emission in the Galactic plane is not well known
and is dependent on the source detection method, threshold and diffuse emission
modeling methods used.
We present a simple image-analysis based method applied to Fermi-LAT data
from 10 GeV to 500 GeV, covering a region of +/- 5 degrees in Galactic latitude
and +/- 100 degrees in Galactic longitude, to separate source and diffuse
emission. This method involves elongated filter smoothing, combined with
significance clipping to exclude sources. We test the method against models
based on the 1FHL catalog and very simple model Galaxies to evaluate the
response for an input of known fraction and shape of diffuse and source
emission.Comment: 6 pages, 5 figures; Proceedings of the 10th Workshop on Science with
the New Generation of High-Energy Gamma-ray experiments (SciNeGHE) -
PoS(Scineghe2014)03
Cosmic rays as a feedback agent in primordial galactic ecosystems
High-redshift primordial galaxies have recently been found with evolved
stellar populations and complex star-formation histories reaching back to 250
Myr after the Big Bang. Their intense bursts of star-formation appear to be
interspersed with sustained periods of strong quenching, however the processes
underlying this evolutionary behaviour remain unclear. Unlike later epochs,
galaxies in the early Universe are not located in large associations like
clusters. Instead, they co-evolve with their developing circumgalactic halo as
relatively isolated ecosystems. Thus, the mechanisms that could bring about the
downfall of their star-formation are presumably intrinsic, and feedback
processes associated with their intense starburst episodes likely play an
important role. Cosmic rays are a viable agent to deliver this feedback, and
could account for the star-formation histories inferred for these systems. The
cosmic ray impact on galaxies may be investigated using the wealth of
multi-wavelength data soon to be obtained with the armada of new and upcoming
facilities. Complementary approaches to probe their action across the
electromagnetic spectrum can be arranged into a distance ladder of cosmic ray
feedback signatures. With a clear understanding of how cosmic ray activity in
primordial systems can be traced, it will be possible to extend this ladder to
high redshifts and map-out the role played by cosmic rays in shaping galaxy
evolution over cosmic time.Comment: Presented at the 27th European Cosmic Ray Symposium, Nijmegen, July
2022 (ECRS 2022). 8 pages, 3 figure
Roles and regulation of membrane-associated serine proteases
Pericellular proteolytic activity affects many aspects of cellular behaviour, via mechanisms involving processing of the extracellular matrix, growth factors and receptors. The serine proteases have exquisitely sensitive regulatory mechanisms in this setting, involving both receptor-bound and transmembrane proteases. Receptor-bound proteases are exemplified by the uPA (urokinase plasminogen activator)/uPAR (uPAR receptor) plasminogen activation system. The mechanisms initiating the activity of this proteolytic system on the cell surface, a critical regulatory point, are poorly understood. We have found that the expression of the TTSP (type II transmembrane serine protease) matriptase is highly regulated in leucocytes, and correlates with the presence of active uPA on their surface. Using siRNA (small interfering RNA), we have demonstrated that matriptase specifically activates uPAR-associated pro-uPA. The uPA/uPAR system has been implicated in the activation of the plasminogen-related growth factor HGF (hepatocyte growth factor). However, we find no evidence for this, but instead that HGF can be activated by both matriptase and the related TTSP hepsin in purified systems. Hepsin is of particular interest, as the proteolytic cleavage sequence of HGF is an ‘ideal substrate’ for hepsin and membrane-associated hepsin activates HGF with high efficiency. Both of these TTSPs can be activated autocatalytically at the cell surface, an unusual mechanism among the serine proteases. Therefore these TTSPs have the capacity to be true upstream initiators of proteolytic activity with subsequent downstream effects on cell behaviour
Cosmic rays in early star-forming galaxies and their effects on the interstellar medium
Galaxies at high redshifts with strong star formation are sources of
high-energy cosmic rays. These cosmic rays interact with the baryon and
radiation fields of the galactic environment via photo-pair, photo-pion and
proton-proton processes to produce charged and neutral pions, neutrons and
protons. The cosmic rays thereby deposit energy into the interstellar medium
(ISM) as they propagate. We show how energy transport and deposition by ultra
high-energy cosmic rays is regulated by the evolution of the galaxy, in
particular by the development of the galactic magnetic field. We show how the
particle-driven energy deposition can influence the thermal evolution of the
host and its surroundings. Using a parametric protogalaxy model, we calculate
the heating effect on the ISM as the cosmic rays are increasingly confined by
the magnetic evolution of the galaxy.Comment: 8 pages, 2 figures; Proceedings of the 35th International Cosmic Ray
Conference (ICRC2017), 10-20 July 2017, Bexco, Busan, Korea -
PoS(ICRC2017)28
Starburst and post-starburst high-redshift protogalaxies: The feedback impact of high energy cosmic rays
Quenching of star-formation has been identified in many starburst and
post-starburst galaxies, indicating burst-like star-formation histories (SFH)
in the primordial Universe. We have investigated the role of high energy cosmic
rays (CRs) in such environments, particularly how they could contribute to this
burst-like SFH via quenching and feedback. These high energy particles interact
with the baryon and radiation fields of their host via hadronic processes to
produce secondary leptons. The secondary particles then also interact with
ambient radiation fields to generate X-rays through inverse-Compton scattering.
In addition, they can thermalise directly with the semi-ionised medium via
Coulomb processes. Heating at a rate of can be attained by Coulomb processes
in a star-forming galaxy with one core-collapse SN event per decade, and this
is sufficient to cause quenching of star-formation. At high-redshift, a
substantial amount of CR secondary electron energy can be diverted into
inverse-Compton X-ray emission. This yields an X-ray luminosity of above
by redshift which drives a further
heating effect, operating over larger scales. This would be able to halt
inflowing cold gas filaments, strangulating subsequent star-formation. We
selected a sample of 16 starburst and post-starburst galaxies at and determine the star-formation rates they could have sustained.
We applied a model with CR injection, propagation and heating to calculate
energy deposition rates in these 16 sources. Our calculations show that CR
feedback cannot be neglected as it has the strength to suppress star-formation
in these systems. We also show that their currently observed quiescence is
consistent with the suffocation of cold inflows, probably by a combination of
X-ray and CR heating.Comment: 30 pages, 14 figures, 4 tables, accepted for publication in A&A;
abstract abridged. V2: updates to match published version (minor typo
corrections
Secondary peritoneal hydatidosis, the challenges of echinococcal disease in South Sudan: A case report
A 28 year old male presented to the Juba Teaching Hospital with progressive shortness of breath. 18 months prior to admission, he presented to a rural hospital with severe abdominal pain. An emergency laparotomy was performed, and a large hepatic cyst was removed. Examination at the Juba Teaching hospital revealed a grossly distended abdomen with multiple palpable masses per abdomen. An Abdominal Ultrasound revealed multiple loculated cysts throughout the abdomen. A diagnosis of Secondary Peritoneal Hydatidosis resulting from incorrectly performed surgery was made. The patient was conservatively treated and at 14 weeks, the cysts showed a moderate reduction in size. Cystic Echinococcus(CE) is common in South Sudan and has a considerable disease burden throughout the developing world. Greater governmental and international support is required to develop effective control measures for these diseases
Effects of large-scale magnetic fields on the observed composition of ultra high-energy cosmic rays
Ultra high-energy (UHE) cosmic rays (CRs) from distant sources interact with
intergalactic radiation fields, leading to their spallation and attenuation.
They are also deflected in intergalactic magnetic fields (IGMFs), particularly
those associated with Mpc-scale structures. These deflections extend the
propagation times of CR particles, forming a magnetic horizon for each CR
species. The cumulative cooling and interactions of a CR ensemble also modifies
their spectral shape and composition observed on Earth. We construct a
transport formulation to calculate the observed UHE CR spectral composition for
4 classes of source population. The effects on CR propagation brought about by
IGMFs are modeled as scattering processes during transport, by centers
associated with cosmic filaments. Our calculations demonstrate that IGMFs can
have a marked effect on observed UHE CRs, and that source population models are
degenerate with IGMF properties. Interpretation of observations, including the
endorsement or rejection of any particular source classes, thus needs careful
consideration of the structural properties and evolution of IGMFs. Future
observations providing tighter constraints on IGMF properties will
significantly improve confidence in assessing UHE CR sources and their
intrinsic CR production properties.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Phys. Rev.
Effects of large-scale magnetic fields on the observed composition of ultrahigh-energy cosmic rays
Ultrahigh-energy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation. They are also deflected in intergalactic magnetic fields (IGMFs), particularly those associated with megaparsec-scale structures. These deflections extend the propagation times of CR particles, forming a magnetic horizon for each CR species. The cumulative cooling and interactions of a CR ensemble also modifies their spectral shape and composition observed on Earth. We construct a transport formulation to calculate the observed UHE CR spectral composition for four classes of source population. The effects on CR propagation brought about by IGMFs are modeled as scattering processes during transport, by centers associated with cosmic filaments. Our calculations demonstrate that IGMFs can have a marked effect on observed UHE CRs and that source population models are degenerate with IGMF properties. Interpretation of observations, including the endorsement or rejection of any particular source classes, thus needs careful consideration of the structural properties and evolution of IGMFs. Future observations providing tighter constraints on IGMF properties will significantly improve confidence in assessing UHE CR sources and their intrinsic CR production properties
Vapor Phase Oxidation of Chloropropenes Over Heterogeneous Catalyst Systems
Propylene Dichloride (PDC) is a byproduct of several Dow processes. The thermal cracking of PDC produces 1-cis-chloropropene, 1-trans-chloropropene, 2-chloropropene, and allyl chloride . By oxidizing the l- and 2-chloropropenes to 3- and 2- chloroacrylic acids, respectively, a potentially valuable product could be made. The chloropropenes, air, and steam were passed over various heterogeneous oxidation catalyst systems to attempt this oxidation. Contact time was varied between 0.0951 to 0.915 sec. Temperature was varied between 275C to .25C. The air content of the feed was varied between .1 to 75%. The chloropropene content of the feed was varied between 2.9% to 5.0% . The following supported catalysts were tested Co/Mo (3/7)-alumina pellets , CoMoO4-alumina granules, CoMo04-silica gel, AcNbMo-alumina pellets, two bed catalyst MoFeTeRe- MoVGeMo- silica gel, CoMoTe- silica gel, and CoMoBi-alumina pellets. No chloroacroleins, or chloroacrylic acids were detected in the reaction products. In general, no CO and from 5- 15% CO2 was obtained in the reaction products with the alumina and silica support materials. Oxidation over the metal catalysts produced 0-10% CO and 5-40% CO2. Severe carbonization of the supports with and without the metal catalysts was observed at the reaction conditions described above. Chloropropenes were found to be unstable, decomposing to carbon at 300°C in an empty reactor at a contact time greater than 0.1 sec. Chloroacrylic acids at a 0.1 sec contact time were tested in the reactor over alumina and silica support materials at 200°C and above, and found to be unstable with regard to decomposition to coke. It was concl uded that the vapor phase oxidation of chloropropenes over heterogeneous catalysts to chloroacrylic acids is not feasible because of their decomposition to car bon at the prevailing reaction conditions
Hadronic Interactions of Energetic Charged Particles in Protogalactic Outflow Environments and Implications for the Early Evolution of Galaxies
We investigate the interactions of energetic hadronic particles with the
media in outflows from star-forming protogalaxies. These particles undergo
pion-producing interactions which can drive a heating effect in the outflow,
while those advected by the outflow also transport energy beyond the galaxy,
heating the circumgalactic medium. We investigate how this process evolves over
the length of the outflow and calculate the corresponding heating rates in
advection-dominated and diffusion-dominated cosmic ray transport regimes. In a
purely diffusive transport scenario, we find the peak heating rate reaches
at the base of the outflow
where the wind is driven by core-collapse supernovae at an event rate of 0.1
, but does not extend beyond 2 kpc. In the advection limit, the
peak heating rate is reduced to , but its extent can reach to tens of kpc. Around 10% of the cosmic
rays injected into the system can escape by advection with the outflow wind,
while the remaining cosmic rays deliver an important interstellar heating
effect. We apply our cosmic ray heating model to the recent observation of the
high-redshift galaxy MACS1149-JD1 and show that it could account for the
quenching of a previous starburst inferred from spectroscopic observations.
Re-ignition of later star-formation may be caused by the presence of
filamentary circumgalactic inflows which are reinstated after cosmic ray
heating has subsided.Comment: 29 pages, 16 figures, accepted for publication in MNRAS. v2: updated
to match published version (reference added, minor typos corrected
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