145 research outputs found
Globular Cluster Population of Hickson Compact Group 22a and 90c
We present the first measurement of the globular cluster populations of
galaxies in Hickson compact groups, in order to investigate the effect of these
high density environments on the formation and evolution of globular cluster
systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c
with the ESO New Technology Telescope (NTT), we find a total globular cluster
population of for HCG 22a and for 90c. The specific
frequency for HCG 22a was found to be and for HCG 90c. A power-law fit to the globular cluster radial profile of HCG
22a yields and for HCG 90c we found . A comparison of the globular cluster radial profiles with
the surface brightness of the parent galaxy shows that the globular cluster
systems are at least as extended as the halo light. The measured values for the
specific frequency are consistent with a scenario in which the host galaxies
were in a low density ``field-like'' environment when they formed their
globular cluster systems.Comment: 28 pages, 13 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Self-referenced characterization of space-time couplings in near single-cycle laser pulses
We report on the characterization of space-time couplings in high energy
sub-2-cycle 770nm laser pulses using a self-referencing single-shot method.
Using spatially-encoded arrangement filter-based spectral phase interferometry
for direct electric field reconstruction (SEA-F-SPIDER) we characterize
few-cycle pulses with a wave-front rotation of 2.8x?10^11 rev/sec (1.38 mrad
per half-cycle) and pulses with pulse front tilts ranging from to -0.33 fs/um
to -3.03 fs/um.Comment: 6 pages, 6 figure
The Dynamics of Poor Systems of Galaxies
We assemble and observe a sample of poor galaxy systems that is suitable for
testing N-body simulations of hierarchical clustering (Navarro, Frenk, & White
1997; NFW) and other dynamical halo models (e.g., Hernquist 1990). We (1)
determine the parameters of the density profile rho(r) and the velocity
dispersion profile sigma(R), (2) separate emission-line galaxies from
absorption-line galaxies, examining the model parameters and as a function of
spectroscopic type, and (3) for the best-behaved subsample, constrain the
velocity anisotropy parameter, beta, which determines the shapes of the galaxy
orbits.
The NFW universal profile and the Hernquist (1990) model both provide good
descriptions of the spatial data. In most cases an isothermal sphere is ruled
out. Systems with declining sigma(R) are well-matched by theoretical profiles
in which the star-forming galaxies have predominantly radial orbits (beta > 0);
many of these galaxies are probably falling in for the first time. There is
significant evidence for spatial segregation of the spectroscopic classes
regardless of sigma(R).Comment: 36 pages, 20 figures, and 5 tables. To appear in the Astrophysical
Journa
Integrated human-animal sero-surveillance of Brucellosis in the pastoral Afar and Somali regions of Ethiopia
BACKGROUND: Brucellosis is widespread in Ethiopia with variable reported prevalence depending on the geographical area, husbandry practices and animal species. However, there is limited information on the disease prevalence amongst pastoral communities, whose life is intricately linked with their livestock. METHODOLOGY: We conducted an integrated human-animal brucellosis sero-surveillance study in two adjacent pastoral regions, Afar and Somali region (SRS). This cross-sectional study included 13 woredas (districts) and 650 households. Blood samples were collected from people and livestock species (cattle, camel, goats and sheep). Sera were analyzed with C-ELISA for camels and shoats (sheep and goats), with I-ELISA for cattle and IgG ELISA for humans. Descriptive and inferential statistics analyses were performed. RESULTS: A total of 5469 sera were tested by ELISA. Prevalence of livestock was 9.0% in Afar and 8.6% in SRS (ranging from 0.6 to 20.2% at woreda level). In humans, prevalence was 48.3% in Afar and 34.9% in SRS (ranging from 0.0 to 74.5% at woreda level). 68.4% of all households in Afar and 57.5% of households in SRS had at least one animal reactor. Overall, 4.1% of animals had a history of abortion. The proportion of animals with abortion history was higher in seropositive animals than in seronegative animals. Risk factor analysis showed that female animals were significantly at higher risk of being reactors (p = 0.013). Among the species, cattle had the least risk of being reactors (p = 0.014). In humans, there was a clear regional association of disease prevalence (p = 0.002). The older the people, the highest the odds of being seropositive. CONCLUSION: Brucellosis is widespread in humans and animals in pastoral communities of Afar and SRS with the existence of geographical hotspots. No clear association was seen between human and particular livestock species prevalence, hence there was no indication as whether B. abortus or B. melitensis are circulating in these areas, which warrants further molecular research prior to embarking on a national control programs. Such programs will need to be tailored to the pastoral context
Radio emission of Shakhbazian Compact Galaxy Groups
Three hundred fifty three radio sources from the NRAO VLA Sky Survey (NVSS)
(Condon et al. 1998) and the FIRST Survey (White et al. 1997}, are detected in
the areas of 179 Shakhbazian Compact Groups (ShCGs) of galaxies. Ninety three
of them are identified with galaxies in 74 ShCGs. Six radio sources have
complex structure. The radio spectra of 22 sources are determined. Radio
luminosities of galaxies in ShCGs are in general higher than that of galaxies
in Hickson Compact Groups (HCGs). The comparison of radio (at 1.4 GHz) and FIR
(at 60 m) fluxes of ShCG galaxies with that of HCG galaxies shows that
galaxies in ShCGs are relatively stronger emitters at radio wavelengths, while
galaxies in HCGs have relatively stronger FIR emission. The reasons of such
difference is discussed.Comment: 35 pages, 6 Postscript figures, ApJS in pres
Chaotic scattering on surfaces and collisional damping of collective modes
The damping of hot giant dipole resonances is investigated. The contribution
of surface scattering is compared with the contribution from interparticle
collisions. A unified response function is presented which includes surface
damping as well as collisional damping. The surface damping enters the response
via the Lyapunov exponent and the collisional damping via the relaxation time.
The former is calculated for different shape deformations of quadrupole and
octupole type. The surface as well as the collisional contribution each
reproduce almost the experimental value, therefore we propose a proper
weighting between both contributions related to their relative occurrence due
to collision frequencies between particles and of particles with the surface.
We find that for low and high temperatures the collisional contribution
dominates whereas the surface damping is dominant around the temperatures
of the centroid energy.Comment: PRC su
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning
Free-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers
Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule
The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or hole) dynamics prior to significant structural change was first recognized more than 20 years ago and termed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specific hole within the molecule. We report an investigation of the dynamics of inner valence hole states in isopropanol where we use an x-ray pumpâx-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an ab initio theoretical treatment. We record the signature of transient hole dynamics and make the first tentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify that the effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localized in space and time in molecules and thus to charge transfer phenomena that are fundamental in chemical and material physics
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