9,871 research outputs found
Swift Pointing and the Association Between Gamma-Ray Bursts and Gravitational-Wave Bursts
The currently accepted model for gamma-ray burst phenomena involves the
violent formation of a rapidly rotating solar mass black hole. Gravitational
waves should be associated with the black-hole formation, and their detection
would permit this model to be tested, the black hole progenitor (e.g.,
coalescing binary or collapsing stellar core) identified, and the origin of the
gamma rays (within the expanding relativistic fireball or at the point of
impact on the interstellar medium) located. Even upper limits on the
gravitational-wave strength associated with gamma-ray bursts could constrain
the gamma-ray burst model. To do any of these requires joint observations of
gamma-ray burst events with gravitational and gamma-ray detectors. Here we
examine how the quality of an upper limit on the gravitational-wave strength
associated with gamma-ray burst observations depends on the relative
orientation of the gamma-ray-burst and gravitational-wave detectors, and apply
our results to the particular case of the Swift Burst-Alert Telescope (BAT) and
the LIGO gravitational-wave detectors. A result of this investigation is a
science-based ``figure of merit'' that can be used, together with other mission
constraints, to optimize the pointing of the Swift telescope for the detection
of gravitational waves associated with gamma-ray bursts.Comment: aastex, 14 pages, 2 figure
Expenditure-based segmentation and visitor profiling at The Quays in Salford, UK
There is a substantial body of literature relating to tourismâs
economic impact at the macro level, but less is known about tourist
expenditure at a micro scale. This paper reports findings from a
survey of day-visitor expenditure by category at The Quays in Salford,
UK. Expenditure is influenced strongly by the visitorâs age,
frequency of visitation and visit motivation. Heavy, medium and
light expenditure segments and associated profiles are identified.
âHeavy spendersâ are more likely to be female, in a family group and
have shopping as the main motivation for the visit. The implications
of the findings are discussed
Information Preserving Component Analysis: Data Projections for Flow Cytometry Analysis
Flow cytometry is often used to characterize the malignant cells in leukemia
and lymphoma patients, traced to the level of the individual cell. Typically,
flow cytometric data analysis is performed through a series of 2-dimensional
projections onto the axes of the data set. Through the years, clinicians have
determined combinations of different fluorescent markers which generate
relatively known expression patterns for specific subtypes of leukemia and
lymphoma -- cancers of the hematopoietic system. By only viewing a series of
2-dimensional projections, the high-dimensional nature of the data is rarely
exploited. In this paper we present a means of determining a low-dimensional
projection which maintains the high-dimensional relationships (i.e.
information) between differing oncological data sets. By using machine learning
techniques, we allow clinicians to visualize data in a low dimension defined by
a linear combination of all of the available markers, rather than just 2 at a
time. This provides an aid in diagnosing similar forms of cancer, as well as a
means for variable selection in exploratory flow cytometric research. We refer
to our method as Information Preserving Component Analysis (IPCA).Comment: 26 page
Magnetic Flux Tube Reconnection: Tunneling Versus Slingshot
The discrete nature of the solar magnetic field as it emerges into the corona
through the photosphere indicates that it exists as isolated flux tubes in the
convection zone, and will remain as discrete flux tubes in the corona until it
collides and reconnects with other coronal fields. Collisions of these flux
tubes will in general be three dimensional, and will often lead to
reconnection, both rearranging the magnetic field topology in fundamental ways,
and releasing magnetic energy. With the goal of better understanding these
dynamics, we carry out a set of numerical experiments exploring fundamental
characteristics of three dimensional magnetic flux tube reconnection. We first
show that reconnecting flux tubes at opposite extremes of twist behave very
differently: in some configurations, low twist tubes slingshot while high twist
tubes tunnel. We then discuss a theory explaining these differences: by
assuming helicity conservation during the reconnection one can show that at
high twist, tunneled tubes reach a lower magnetic energy state than slingshot
tubes, whereas at low twist the opposite holds. We test three predictions made
by this theory. 1) We find that the level of twist at which the transition from
slingshot to tunnel occurs is about two to three times higher than predicted on
the basis of energetics and helicity conservation alone, probably because the
dynamics of the reconnection play a large role as well. 2) We find that the
tunnel occurs at all flux tube collision angles predicted by the theory. 3) We
find that the amount of magnetic energy a slingshot or a tunnel reconnection
releases agrees reasonably well with the theory, though at the high
resistivities we have to use for numerical stability, a significant amount of
magnetic energy is lost to diffusion, independent of reconnection.Comment: 21 pages, 15 figures, submitted to Ap
Productive tensions - engaging geography students in participatory action research with communities
ArticleCopyright © 2013 copyright Taylor & Francis.This study discusses the benefits and challenges of an undergraduate module on participatory geographies, involving students in co-producing research with community partners. The module challenges the knowledge production model predominant in Geography curricula. We argue that it develops students' skills and understanding through engaging them intellectually, socially and emotionally outside the university. As a student, two community partners and a professor, we offer our perspectives on the opportunities and conflicts that arose. We do not gloss over tensions in achieving the module's diverse aims, but suggest that these are productive for teaching, learning, research and the needs of community organizations
Resolution of Cosmological Singularities
We show that a class of 3+1 dimensional Friedmann-Robertson-Walker
cosmologies can be embedded within a variety of solutions of string theory. In
some realizations the apparent singularities associated with the big bang or
big crunch are resolved at non-singular horizons of higher-dimensional
quasi-black hole solutions (with compactified real time); in others plausibly
they are resolved at D-brane bound states having no conventional space-time
interpretation.Comment: 11 pages, latex. Two references added, one typo correcte
Improving the efficiency of the detection of gravitational wave signals from inspiraling compact binaries: Chebyshev interpolation
Inspiraling compact binaries are promising sources of gravitational waves for
ground and space-based laser interferometric detectors. The time-dependent
signature of these sources in the detectors is a well-characterized function of
a relatively small number of parameters; thus, the favored analysis technique
makes use of matched filtering and maximum likelihood methods. Current analysis
methodology samples the matched filter output at parameter values chosen so
that the correlation between successive samples is 97% for which the filtered
output is closely correlated. Here we describe a straightforward and practical
way of using interpolation to take advantage of the correlation between the
matched filter output associated with nearby points in the parameter space to
significantly reduce the number of matched filter evaluations without
sacrificing the efficiency with which real signals are recognized. Because the
computational cost of the analysis is driven almost exclusively by the matched
filter evaluations, this translates directly into an increase in computational
efficiency, which in turn, translates into an increase in the size of the
parameter space that can be analyzed and, thus, the science that can be
accomplished with the data. As a demonstration we compare the present "dense
sampling" analysis methodology with our proposed "interpolation" methodology,
restricted to one dimension of the multi-dimensional analysis problem. We find
that the interpolated search reduces by 25% the number of filter evaluations
required by the dense search with 97% correlation to achieve the same
efficiency of detection for an expected false alarm probability. Generalized to
higher dimensional space of a generic binary including spins suggests an order
of magnitude increase in computational efficiency.Comment: 23 pages, 5 figures, submitted to Phys. Rev.
On the mechanism of titanium-tartrate catalyzed asymmetric epoxidation
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCEVita.Bibliography: leaves 273-288.M.G. Finn.Ph.D
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