108 research outputs found
Existence and large time behavior for generalized Kelvin-Voigt equations governing nonhomogeneous and incompressible fluids
Generalized Kelvin-Voigt equations governing nonhomogeneous and incompressible
fluids are considered in this work. We assume that, in the momentum equation, the diffusion
and relaxation terms are described by two distinct power-laws. Moreover, we assume that the
momentum equation is perturbed by an extra term, which, depending on whether its signal is
positive or negative, may account for the presence of a source or a sink within the system. For
the associated initial-boundary value problem, we study the existence of weak solutions as well
as the large time behavior of the solutions.Portuguese Foundation for Science and Technology: UID/MAT/04561/2019info:eu-repo/semantics/publishedVersio
3D Gamma-ray and Neutron Mapping in Real-Time with the Localization and Mapping Platform from Unmanned Aerial Systems and Man-Portable Configurations
Nuclear Scene Data Fusion (SDF), implemented in the Localization and Mapping
Platform (LAMP) fuses three-dimensional (3D), real-time volumetric
reconstructions of radiation sources with contextual information (e.g. LIDAR,
camera, etc.) derived from the environment around the detector system. This
information, particularly when obtained in real time, may be transformative for
applications, including directed search for lost or stolen sources, consequence
management after the release of radioactive materials, or contamination
avoidance in security-related or emergency response scenarios. 3D
reconstructions enabled by SDF localize contamination or hotspots to specific
areas or objects, providing higher resolution over larger areas than
conventional 2D approaches, and enabling more efficient planning and response,
particularly in complex 3D environments.
In this work, we present the expansion of these gamma-ray mapping concepts to
neutron source localization. Here we integrate LAMP with a custom
(CLLBC) scintillator detector sensitive to both
gamma-rays and neutrons, which we dub Neutron Gamma LAMP (NG-LAMP). NG-LAMP
enables simultaneous neutron and gamma-ray mapping with high resolution
gamma-ray spectroscopy. We demonstrate the ability to detect and localize
surrogate Special Nuclear Materials (SNM) in real-time and in 3D based on
neutron signatures alone, which is critical for the detection of heavily
shielded SNM, when gamma-ray signatures are attenuated. In this work, we show
for the first time the ability to localize, in 3D and realtime, a neutron
source in the presence of a strong gamma-ray source, simultaneous and
spectroscopic localization of three gamma-ray sources and a neutron source, and
finally the localization of a surrogate SNM source based on neutron signatures
alone, where gamma-ray data are consistent with background
The Massive Star Content of NGC 3603
We investigate the massive star content of NGC 3603, the closest known giant
H II region. We have obtained spectra of 26 stars in the central cluster using
the Baade 6.5-m telescope (Magellan I). Of these 26 stars, 16 had no previous
spectroscopy. We also obtained photometry of all of the stars with previous or
new spectroscopy, primarily using archival HST ACS/HRC images. We use these
data to derive an improved distance to the cluster, and to construct an H-R
diagram for discussing the masses and ages of the massive star content of this
cluster.Comment: Accepted by the Astronomical Journal. This revision updates the
coordinates in Table 1 by (-0.18sec, +0.2") to place them on the UCAC2 syste
The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at zeta approx. 5
We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in starburst, or the fraction of high mass stars in the bursts is increased towards the bright end of the LF
V838 Monocerotis: A Geometric Distance from Hubble Space Telescope Polarimetric Imaging of its Light Echo
Following the outburst of the unusual variable star V838 Monocerotis in 2002,
a spectacular light echo appeared. A light echo provides the possibility of
direct geometric distance determination, because it should contain a ring of
highly linearly polarized light at a linear radius of ct, where t is the time
since the outburst. We present imaging polarimetry of the V838 Mon light echo,
obtained in 2002 and 2005 with the Advanced Camera for Surveys onboard the
Hubble Space Telescope, which confirms the presence of the highly polarized
ring. Based on detailed modeling that takes into account the outburst light
curve, the paraboloidal echo geometry, and the physics of dust scattering and
polarization, we find a distance of 6.1+-0.6 kpc. The error is dominated by the
systematic uncertainty in the scattering angle of maximum linear polarization,
taken to be theta_{max}=90^o +- 5^o. The polarimetric distance agrees
remarkably well with a distance of 6.2+-1.5 kpc obtained from the entirely
independent method of main-sequence fitting to a sparse star cluster associated
with V838 Mon. At this distance, V838 Mon at maximum light had M_V\simeq-9.8,
making it temporarily one of the most luminous stars in the Local Group. Our
validation of the polarimetric method offers promise for measurement of
extragalactic distances using supernova light echoes.Comment: 43 pages, 17 figures, 3 tables; accepted for publication in the
Astronomical Journal. Version with high-quality figures available at
http://www.stsci.edu/~bond/v838monpolariz.pd
Star-formation in the HI bridge between M81 and M82
We present multi-wavelength observations of stellar features in the HI tidal
bridge connecting M81 and M82 in the region called Arp's Loop. We identify
eight young star-forming regions from Galaxy Evolution Explorer ultraviolet
observations. Four of these objects are also detected at H\alpha. We determine
the basic star formation history of Arp's Loop using F475W and F814W images
obtained with the Advanced Camera for Surveys on board the Hubble Space
Telescope. We find both a young (1 Gyr) stellar
population with a similar spatial distribution and a metallicity Z~0.004. We
suggest that the old stellar population was formed in the stellar disk of M82
and/or M81 and ejected into the intergalactic medium during a tidal passage (~
200-300 Myr ago), whereas the young UV-bright stars have formed in the tidal
debris. The UV luminosities of the eight objects are modest and typical of
small clusters or OB associations. The tidal bridge between M81-M82 therefore
appears to be intermediate between the very low levels of star formation seen
in the Magellanic bridge and actively star-forming tidal tails associated with
major galaxy mergers.Comment: Astronomical Journal accepte
The UDF05 Follow-up of the HUDF: II. Constraints on Reionization from z-dropout Galaxies
[Abridged] We detect three (plus one less certain) z-dropout sources in two
separate fields of our UDF05 HST NICMOS images. These z~7 Lyman-Break Galaxy
(LBG) candidates allow us to constrain the Luminosity Function (LF) of the star
forming galaxy population at those epochs. By assuming a change in only M* and
adopting a linear evolution in redshift, anchored to the measured values at
z~6, the best fit evolution coefficient is found to be 0.43+-0.19 mag per unit
redshift (0.36+-0.18, if including all four candidates), which provides a value
of M*(z=7.2)=-19.7+-0.3. This implies a steady evolution for the LBG LF out to
z~7, at the same rate that is observed throughout the z~3 to 6 period. This
puts a strong constraint on the star-formation histories of z~6 galaxies, whose
ensemble star-formation rate density must be lower by a factor 2 at ~170 Myr
before the epoch at which they are observed. In particular, a large fraction of
stars in the z~6 LBG population must form at redshifts well above z~7.
Extrapolating this steady evolution of the LF out to higher redshifts, we
estimate that galaxies would be able to reionize the universe by z~6, provided
that the faint-end slope of the z>7 LF steepens to alpha~-1.9, and that faint
galaxies, with luminosities below the current detection limits, contribute a
substantial fraction of the required ionizing photons. This scenario gives
however an integrated optical depth to electron scattering that is ~2sigma
below the WMAP-5 measurement. Therefore, altogether, our results indicate that,
should galaxies be the primary contributors to reionization, either the
currently detected evolution of the galaxy population slows down at z>7, or the
LF evolution must be compensated by a decrease in metallicity and a
corresponding increase in ionization efficiency at these early epochs.Comment: Accepted for publication in ApJ, 7 pages, 4 figures; minor revisions
to match accepted versio
The International Consensus Classification of Mature Lymphoid Neoplasms: a report from the Clinical Advisory Committee
Since the publication of the Revised European-American Classification of Lymphoid Neoplasms in 1994, subsequent updates of the classification of lymphoid neoplasms have been generated through iterative international efforts to achieve broad consensus among hematopathologists, geneticists, molecular scientists, and clinicians. Significant progress has recently been made in the characterization of malignancies of the immune system, with many new insights provided by genomic studies. They have led to this proposal. We have followed the same process that was successfully used for the third and fourth editions of the World Health Organization Classification of Hematologic Neoplasms. The definition, recommended studies, and criteria for the diagnosis of many entities have been extensively refined. Some categories considered provisional have now been upgraded to definite entities. Terminology for some diseases has been revised to adapt nomenclature to the current knowledge of their biology, but these modifications have been restricted to well-justified situations. Major findings from recent genomic studies have impacted the conceptual framework and diagnostic criteria for many disease entities. These changes will have an impact on optimal clinical management. The conclusions of this work are summarized in this report as the proposed International Consensus Classification of mature lymphoid, histiocytic, and dendritic cell tumors
BIOTIC DIVERSITY OF KARELIA: CONDITIONS OF FORMATION, COMMUNITIES AND SPECIES
The monograph generalises vast data characterising the diversity of the biota in Russian Karelia. The data pool includes both materials of long-term studies, and new data collected in 1997–2000 within the Russian-Finnish project “Inventory and studies of biological diversity in Republic of Karelia”. The volume is composed of four interrelated chapters. Chapter one provides a detailed account of the climatic, geological, geomorphological, hydrological and soil conditions in which the regional biota has been forming. Chapter two describes and evaluates the diversity of forest, mire and meadow communities, and the third chapter details the terrestrial biota at the species level (vascular plants, mosses, aphyllophoroid fungi, lichens, mammals, birds, insects). A special section is devoted to the flora and fauna of aquatic ecosystems (algae, zooplankton, periphyton, macrozoobenthos, fishes). Wide use is made of various zoning approaches based on biodiversity-related criteria. Current status of the regional biota, including its diversity in protected areas, is analysed with elements of the human impact assessment. A concise glossary of the terms used is annexed.
This is an unprecedentally multi-faceted review, at least for the taiga zone of European Russia. The volume offers extensive reference materials for researchers in a widest range of ecological and biological fields, including graduate and post-graduate students. The monograph is also available in Russian
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