1,887 research outputs found
DEIMOS Observations of WISE-Selected, Optically Obscured AGNs
While there are numerous criteria for photometrically identifying active
galactic nuclei (AGNs), searches in the optical and UV tend to exclude galaxies
that are highly dust obscured. This is problematic for constraining models of
AGN evolution and estimating the AGN contribution to the cosmic X-ray and IR
backgrounds, as highly obscured objects tend to be underrepresented in
large-scale surveys. To address this, we identify potentially obscured AGNs
using mid-IR color colors from the Wide-field Infrared Survey Explorer (WISE)
catalog. This paper presents the results of optical spectroscopy of obscured
AGN candidates using Keck DEIMOS, and their physical properties derived from
these spectra. We find that a color criterion effectively selects
AGNs with a higher median level of extinction compared to the AGNs
found in the SDSS DR7 survey. This optical extinction can be measured using SED
modeling or by using as a measure of optical to IR flux. We find that
specific, targeted observations are necessary to find the most highly optically
obscured AGNs, and that additional far-IR photometry is necessary to further
constrain the dust properties of these AGNs.Comment: 20 pages, 25 figures, accepted by MNRA
Hyperstaticity and loops in frictional granular packings
The hyperstatic nature of granular packings of perfectly rigid disks is
analyzed algebraically and through numerical simulation. The elementary loops
of grains emerge as a fundamental element in addressing hyperstaticity. Loops
consisting of an odd number of grains behave differently than those with an
even number. For odd loops, the latent stresses are exterior and are
characterized by the sum of frictional forces around each loop. For even loops,
the latent stresses are interior and are characterized by the alternating sum
of frictional forces around each loop. The statistics of these two types of
loop sums are found to be Gibbsian with a "temperature" that is linear with the
friction coefficient mu when mu<1.Comment: 4 pages; Powders and Grains 2009, Golden, Colorado, US
Modeling of the UNLV-Aro light-weight robot using Lagrange\u27s assumed mode method, symbolic manipulation, and numerical simulation
This thesis modeled the dynamics of the UNLV-ARO serially connected light-weight robot. The two outer-most links of the robot exhibited flexible behavior in the in-plane and the out-of-plane directions. Lagrangian mechanics were used to model this system. Assumed modes method was used to approximate the vibration mode shape of the links. Using these analytical techniques in conjunction with the inverse dynamics method, a set of equations of motion was formulated to describe the vibrations of the robot. Due to the complexity of the system, the equations of motion were derived using MACSYMA, a symbolic software. From MACSYMA, the equations of motion were translated into FORTRAN statements. FORTRAN programs were written using the equations obtained to numerically simulate the motions of the robot. The scheme discussed in this thesis provided a step towards modeling the dynamics of a light-weight robot accurately
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Modelling the Epidemiological Dynamics of Seasonal Influenza Viruses at Local Scales
Seasonal influenza viruses are a substantial source of disease burden globally, causing epidemics across all climatic regions. Through error-prone RNA replication, influenza viruses can escape pre-existing humoral immunity and reinfect humans, resulting in recurrent epidemics within populations. From year to year, individual epidemics differ substantially in timing, duration and size. Despite intensive study, characterising the spatiotemporal patterns of virus circulation and identifying the underlying sources of this variability at global, regional and local scales remain as ongoing challenges. There is a need to reconcile environmental, virological and host drivers of virus epidemiological dynamics across diverse contexts. Such insights can only be generated through a holistic approach that integrates observational, ecological, experimental and modelling studies: this would enable more accurate and timely epidemiological forecasts and more efficient allocation of public health resources.
In this thesis, I investigate the phylodynamical interactions between the seasonal influenza virus, environment and human host population, integrating analyses from observational study and theoretical modelling approaches. The current knowledge gap on the drivers of local city-level epidemics is identified in Chapter 2 and subsequently addressed over 4 research chapters. In Chapter 3, I review existing epidemic detection algorithms and present a novel statistical model that I developed for use with noisy disease surveillance data and is optimised for the context of seasonal influenza. In Chapter 4, I apply this novel algorithm and analyse a 15-year dataset of 18,250 typed, subtyped, and antigenically characterised seasonal influenza viruses from the five most populous cities in Australia. With the necessary geographical and virus resolution, I quantify the effects of previously hypothesised environmental and virological factors. Most surprisingly, despite an apparent lack of marked change in virus antigenicity, individual antigenic variants are capable of reinvading the same population over consecutive seasons, which runs contrary to predictions made by existing mathematical models.
In Chapters 5 and 6, I investigate how antigenic variants are capable of causing recurrent epidemics at local scales by building upon previous theoretical modelling studies and developing a modelling framework to investigate the interactions between and joint effects exerted by the topology of cross-immunity and host contact structure within a population. In Chapter 5, I investigate the effects of correlations between network structure and individual susceptibility. In Chapter 6, I examine the population-level significance of age-specific changes to an individual's immune response. In Chapter 7, I review my findings and discuss how these new insights into virus ecology can open new avenues for better influenza control and future research
Sitting Down with Dr. John Weg: Pulmonary Medicine Pioneer
Recently, the Quill & Scopeās Jenny Lam and Edward Hurley spoke with pulmonary medicine pioneer Dr. John Weg, Class of 1959, about his career, medicine in general and his time at New York Medical College
The counterintuitive role of efficiency : implications for the ecological impact of health care
Non peer reviewe
Microlensing of gamma ray bursts by stars and MACHOs
The microlensing interpretation of the optical afterglow of GRB 000301C seems
naively surprising, since a simple estimate of the stellar microlensing rate
gives less than one in four hundred for a flat Omega_Lambda=0.7 cosmology,
whereas one event was seen in about thirty afterglows. Considering baryonic
MACHOs making up half of the baryons in the universe, the microlensing
probability per burst can be roughly 5% for a GRB at redshift z=2. We explore
two effects that may enhance the probability of observing microlensed gamma-ray
burst afterglows: binary lenses and double magnification bias. We find that the
consideration of binary lenses can increase the rate only at the ~15% level. On
the other hand, because gamma-ray bursts for which afterglow observations exist
are typically selected based on fluxes at widely separated wavebands which are
not necessarily well correlated (e.g. localization in X-ray, afterglow in
optical/infrared), magnification bias can operate at an enhanced level compared
to the usual single-bias case. We find that existing estimates of the slope of
the luminosity function of gamma-ray bursts, while as yet quite uncertain,
point to enhancement factors of more than three above the simple estimates of
the microlensing rate. We find that the probability to observe at least one
microlensing event in the sample of 27 measured afterglows can be 3-4% for
stellar lenses, or as much as 25 Omega_lens for baryonic MACHOs. We note that
the probability to observe at least one event over the available sample of
afterglows is significant only if a large fraction of the baryons in the
universe are condensed in stellar-mass objects. (ABRIDGED)Comment: 22 pages, 4 figures, 2 table
Understanding the āriseā of the radical left in Europe: itās not just the economy, stupid
A considerable amount of attention has been paid to understanding the electoral rise of populist radical right parties in Europe. However, much less research has focused on understanding the recent electoral fortunes of the populist radical left across Europe. James F. Downes, Edward Chan, Venisa Wai and Andrew Lam argue that three key factors, in the form of the 2008ā13 economic crisis, the decline of the centre left and Euroscepticism can partly explain the post-crisis electoral growth of populist radical left parties in Europe. In addition, it is important to note that this electoral growth is higher than centre left and right parties, but considerably lower than populist radical right parties
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