4,744 research outputs found
Media Literacy and Its Use as a Method to Encourage Civic Engagement
Changes in technology have opened up a new kind of participatory citizenry; one in which engaged citizens’ blog, post, tweet, upload, create, and otherwise interact with others online. This paper explores the intersection of media and information literacy with civic participation by examining three specific programs operating in the United States. These projects include «Powerful Voices for Kids», «The Salzburg Academy on Media and Social Change»; and «Cultivating the NetGeneration of Youth as Global Citizens and Media Literate Leaders in a Digital Age», in which educators and students at schools in the USA and Africa meet virtually and physically to explore collaborative methods that use media to build bridges of understanding. Through analysis of each program’s practices and personal interviews with the program director, consistent methods for developing a strong media and information literacy program with a focus on democratic participation are revealed. These include a need for programs to reflect a respect for student interest in popular culture, willingness for program educators to put aside assumptions that students lack an interest in current events, recognition that technology use is a means to an end, not the ultimate goal, and the utilization of a support team for the instructors or educator
Black holes in Einstein-aether and Horava-Lifshitz gravity
We study spherical black-hole solutions in Einstein-aether theory, a
Lorentz-violating gravitational theory consisting of General Relativity with a
dynamical unit timelike vector (the "aether") that defines a preferred timelike
direction. These are also solutions to the infrared limit of Horava-Lifshitz
gravity. We explore parameter values of the two theories where all presently
known experimental constraints are satisfied, and find that spherical
black-hole solutions of the type expected to form by gravitational collapse
exist for all those parameters. Outside the metric horizon, the deviations away
from the Schwarzschild metric are typically no more than a few percent for most
of the explored parameter regions, which makes them difficult to observe with
electromagnetic probes, but in principle within reach of future
gravitational-wave detectors. Remarkably, we find that the solutions possess a
universal horizon, not far inside the metric horizon, that traps waves of any
speed relative to the aether. A notion of black hole thus persists in these
theories, even in the presence of arbitrarily high propagation speeds.Comment: 18 pages, 12 figures; v2: typos corrected, matches published versio
Spinning Black Holes as Particle Accelerators
It has recently been pointed out that particles falling freely from rest at
infinity outside a Kerr black hole can in principle collide with arbitrarily
high center of mass energy in the limiting case of maximal black hole spin.
Here we aim to elucidate the mechanism for this fascinating result, and to
point out its practical limitations, which imply that ultra-energetic
collisions cannot occur near black holes in nature.Comment: 3 pages; v2: references added, minor modifications to match version
published in PR
Status of the Pacific Mackerel resource during 1997 and management recommendations for the fishery
Based on a California Department of Fish and Game (CDFG) projected biomass estimate of 91,200 metric tons for July 1, 1997, the recommended commercial fishery quota for the 1997/98 fishing season is 22,000 metric tons. Age-specific abundance for 1996 was estimated using output from a stock
assessment model called ADEPT and certain assumptions about growth and fishing mortality during the first half of 1997. In this year's assessment, abundance estimates made by ADEPT were expanded back in time to cover the 68-year period of 1929 through 1996. The commercial fishery quota recommendation is based upon the prescribed harvest formula for Pacific mackerel that is specified in the California Fish and Game Code.
Several sources of information are available for the Pacific mackerel stock, all of which suggest a smaller biomass than was present in the 1980's. Landings from both California and Ensenada, Mexico have sharply decreased and catch rates from the southern California Commercial Passenger Fishing Vessel (CPFV) fleet have declined. Fishery-independent indices of abundance from aerial spotter observations and California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton surveys show similar trends.
The 1997 biomass estimate is higher than last year's estimate of 47,160 metric tons because data added to the model this year increased abundance for fish of 1994 and older year classes (age 2+). This year's results indicate there were more fish in the older year classes than estimated in previous assessments. (27pp.
Destroying black holes with test bodies
If a black hole can accrete a body whose spin or charge would send the black
hole parameters over the extremal limit, then a naked singularity would
presumably form, in violation of the cosmic censorship conjecture. We review
some previous results on testing cosmic censorship in this way using the test
body approximation, focusing mostly on the case of neutral black holes. Under
certain conditions a black hole can indeed be over-spun or over-charged in this
approximation, hence radiative and self-force effects must be taken into
account to further test cosmic censorship.Comment: Contribution to the proceedings of the First Mediterranean Conference
on Classical and Quantum Gravity (talk given by T. P. S.). Summarizes the
results of Phys. Rev. Lett. 103, 141101 (2009), arXiv:0907.4146 [gr-qc] and
considers further example
Understanding the Jobs-Affordable Housing Balance in the Richmond Region
The mismatch between location of jobs and housing has a significant impact on the efficiency and quality of life within metropolitan areas. A well-planned region strives to be a “community of short distances.” A wide range of housing choices located close to employment centers could shorten commuting distances and substantially reduce government outlays for transportation facilities, reduce household transportation expenses, and increase feasibility of pedestrian movement. These needs are particularly important to families earning modest wages.
CURA, with support from The Community Foundation Serving Richmond and Central Virginia and the Richmond Association of Realtors, has analyzed the spatial pattern of lower-wage jobs and lower-cost housing within the Richmond Metropolitan Statistical Area (MSA). The analysis reveals how low-cost housing and modest-wage jobs in the Richmond region are not well-balanced. Few areas in which modest-wage jobs cluster have comparable levels of low-cost housing. The established suburban areas north, west, and south of Richmond’s urban center have a large number of retail and service jobs that pay modest wages, yet these areas provide few affordable-dwelling units for these wage earners.
The second part of this study addressed a major obstacle to the construction of new, affordable-housing units: fears. Many new, affordable dwelling units, by financial necessity, will be built at higher densities and smaller size to reduce cost. Homeowners in nearby neighborhoods often oppose construction of these units over fear of reduced property values, higher crime, and other factors. Six higher-density, 3 lower-cost housing projects were studied for their impact on the nearby middle-income neighborhoods. Documentation of home sale prices, assessment values, and crime rates before and after construction of the more affordable dwelling units did not reveal any notable long-term impact on crime rates, property values, or property sales
String dynamics and ejection along the axis of a spinning black hole
Relativistic current carrying strings moving axisymmetrically on the
background of a Kerr black hole are studied. The boundaries and possible types
of motion of a string with a given energy and current are found. Regions of
parameters for which the string falls into the black hole, or is trapped in a
toroidal volume, or can escape to infinity, are identified, and representative
trajectories are examined by numerical integration, illustrating various
interesting behaviors. In particular, we find that a string can start out at
rest near the equatorial plane and, after bouncing around, be ejected out along
the axis, some of its internal (elastic or rotational kinetic) energy having
been transformed into translational kinetic energy. The resulting velocity can
be an order unity fraction of the speed of light. This process results from the
presence of an outer tension barrier and an inner angular momentum barrier that
are deformed by the gravitational field. We speculatively discuss the possible
astrophysical significance of this mechanism as a means of launching a
collimated jet of MHD plasma flux tubes along the spin axis of a gravitating
system fed by an accretion disk.Comment: 14 pages, 11 figures; v.2: minor edits, references added, typos
corrected, published versio
Over-spinning a black hole with a test body
It has long been known that a maximally spinning black hole can not be
over-spun by tossing in a test body. Here we show that if instead the black
hole starts out with below maximal spin, then indeed over-spinning can be
achieved when adding either orbital or spin angular momentum. We find that
requirements on the size and internal structure of the test body can be met as
well. Our analysis neglects radiative and self-force effects,which may prevent
the over-spinning.Comment: 4 pages; v2: reference added, incorporates the missed case of an
oblate test body, which appears with the published version only as an
erratum, other minor edits (with respect to v1
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