336 research outputs found
Understanding the social in a digital age
Datafication, algorithms, social media and their various assemblages enable massive connective processes, enriching personal interaction and amplifying the scope and scale of public networks. At the same time, surveillance capitalists and the social quantification sector are committed to monetizing every aspect of human communication, all of which threaten ideal social qualities, such as togetherness and connection. This Special Issue brings together a range of voices and provocations around ‘the social’, all of which aim to critically interrogate mediated human connection and their contingent socialities. Conventional methods may no longer be adequate, and we must rethink not only the fabric of the social but the very tools we use to make sense of our changing social formations. This Special Issue raises shared concerns with what the social means today, unpicking and rethinking the seams between digitization and social life that characterize today’s digital age
Transient contractions of urinary bladder smooth muscle are drivers of afferent nerve activity during filling
Activation of afferent nerves during urinary bladder (UB) filling conveys the sensation of UB fullness to the central nervous system (CNS). Although this sensory outflow is presumed to reflect graded increases in pressure associated with filling, UBs also exhibit nonvoiding, transient contractions (TCs) that cause small, rapid increases in intravesical pressure. Here, using an ex vivo mouse bladder preparation, we explored the relative contributions of filling pressure and TC-induced pressure transients to sensory nerve stimulation. Continuous UB filling caused an increase in afferent nerve activity composed of a graded increase in baseline activity and activity associated with increases in intravesical pressure produced by TCs. For each ∼4-mmHg pressure increase, filling pressure increased baseline afferent activity by ∼60 action potentials per second. In contrast, a similar pressure elevation induced by a TC evoked an ∼10-fold greater increase in afferent activity. Filling pressure did not affect TC frequency but did increase the TC rate of rise, reflecting a change in the length-tension relationship of detrusor smooth muscle. The frequency of afferent bursts depended on the TC rate of rise and peaked before maximum pressure. Inhibition of small- and large-conductance Ca(2+)-activated K(+) (SK and BK) channels increased TC amplitude and afferent nerve activity. After inhibiting detrusor muscle contractility, simulating the waveform of a TC by gently compressing the bladder evoked similar increases in afferent activity. Notably, afferent activity elicited by simulated TCs was augmented by SK channel inhibition. Our results show that afferent nerve activity evoked by TCs represents the majority of afferent outflow conveyed to the CNS during UB filling and suggest that the maximum TC rate of rise corresponds to an optimal length-tension relationship for efficient UB contraction. Furthermore, our findings implicate SK channels in controlling the gain of sensory outflow independent of UB contractility
Moduli-Space Approximation for BPS Brane-Worlds
We develop the moduli-space approximation for the low energy regime of
BPS-branes with a bulk scalar field to obtain an effective four-dimensional
action describing the system. An arbitrary BPS potential is used and account is
taken of the presence of matter in the branes and small supersymmetry breaking
terms. The resulting effective theory is a bi-scalar tensor theory of gravity.
In this theory, the scalar degrees of freedom can be stabilized naturally
without the introduction of additional mechanisms other than the appropriate
BPS potential. We place observational constraints on the shape of the potential
and the global configuration of branes.Comment: 10 pages, 1 figur
Gravitational Radiation and Very Long Baseline Interferometry
Gravitational waves affect the observed direction of light from distant
sources. At telescopes, this change in direction appears as periodic variations
in the apparent positions of these sources on the sky; that is, as proper
motion. A wave of a given phase, traveling in a given direction, produces a
characteristic pattern of proper motions over the sky. Comparison of observed
proper motions with this pattern serves to test for the presence of
gravitational waves. A stochastic background of waves induces apparent proper
motions with specific statistical properties, and so, may also be sought. In
this paper we consider the effects of a cosmological background of
gravitational radiation on astrometric observations. We derive an equation for
the time delay measured by two antennae observing the same source in an
Einstein-de Sitter spacetime containing gravitational radiation. We also show
how to obtain similar expressions for curved Friedmann-Robertson-Walker
spacetimes.Comment: 31 pages plus 3 separate figures, plain TeX, submitted to Ap
Low Energy Branes, Effective Theory and Cosmology
The low energy regime of cosmological BPS-brane configurations with a bulk
scalar field is studied. We construct a systematic method to obtain
five-dimensional solutions to the full system of equations governing the
geometry and dynamics of the bulk. This is done for an arbitrary bulk scalar
field potential and taking into account the presence of matter on the branes.
The method, valid in the low energy regime, is a linear expansion of the system
about the static vacuum solution. Additionally, we develop a four-dimensional
effective theory describing the evolution of the system. At the lowest order in
the expansion, the effective theory is a bi-scalar tensor theory of gravity.
One of the main features of this theory is that the scalar fields can be
stabilized naturally without the introduction of additional mechanisms,
allowing satisfactory agreement between the model and current observational
constraints. The special case of the Randall-Sundrum model is discussed.Comment: 19 pages, 4 figure
Quasar Proper Motions and Low-Frequency Gravitational Waves
We report observational upper limits on the mass-energy of the cosmological
gravitational-wave background, from limits on proper motions of quasars.
Gravitational waves with periods longer than the time span of observations
produce a simple pattern of apparent proper motions over the sky, composed
primarily of second-order transverse vector spherical harmonics. A fit of such
harmonics to measured motions yields a 95%-confidence limit on the mass-energy
of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the
closure density of the universe.Comment: 15 pages, 1 figure. Also available at
http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm
Report of the panel on earth rotation and reference frames, section 7
Objectives and requirements for Earth rotation and reference frame studies in the 1990s are discussed. The objectives are to observe and understand interactions of air and water with the rotational dynamics of the Earth, the effects of the Earth's crust and mantle on the dynamics and excitation of Earth rotation variations over time scales of hours to centuries, and the effects of the Earth's core on the rotational dynamics and the excitation of Earth rotation variations over time scales of a year or longer. Another objective is to establish, refine and maintain terrestrial and celestrial reference frames. Requirements include improvements in observations and analysis, improvements in celestial and terrestrial reference frames and reference frame connections, and improved observations of crustal motion and mass redistribution on the Earth
Cosmic String Wakes in Scalar-Tensor Gravities
The formation and evolution of cosmic string wakes in the framework of a
scalar-tensor gravity are investigated in this work. We consider a simple model
in which cold dark matter flows past an ordinary string and we treat this
motion in the Zel'dovich approximation. We make a comaprison between our
results and previous results obtained in the context of General Relativity. We
propose a mechanism in which the contribution of the scalar field to the
evolution of the wakes may lead to a cosmological observation.Comment: Replaced version to be published in the Classical and Quantum Gravit
Vacuum Polarization in the Spacetime of a Scalar-Tensor Cosmic String
We study the vacuum polarization effect in the spacetime generated by a
magnetic flux cosmic string in the framework of a scalar-tensor gravity. The
vacuum expectation values of the energy-momentum tensor of a conformally
coupled scalar field are calculated. The dilaton's contribution to the vacuum
polarization effect is shown explicitly.Comment: 11 pages, LATEX file, 2 eps figure
Reconstruction of a scalar-tensor theory of gravity in an accelerating universe
The present acceleration of the Universe strongly indicated by recent
observational data can be modeled in the scope of a scalar-tensor theory of
gravity. We show that it is possible to determine the structure of this theory
(the scalar field potential and the functional form of the scalar-gravity
coupling) along with the present density of dustlike matter from the following
two observable cosmological functions: the luminosity distance and the linear
density perturbation in the dustlike matter component as functions of redshift.
Explicit results are presented in the first order in the small inverse
Brans-Dicke parameter 1/omega.Comment: 4 pages, LaTeX 2.09, REVTeX 3.0, two-column forma
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