2,069 research outputs found
Naked Singularity and Thunderbolt
We consider quantum theoretical effects of the sudden change of the boundary
conditions which mimics the occurrence of naked singularities. For a simple
demonstration, we study a massless scalar field in -dimensional
Minkowski spacetime with finite spatial interval. We calculate the vacuum
expectation value of the energy-momentum tensor and explicitly show that
singular wave or {\em thunderbolt} appears along the Cauchy horizon. The
thunderbolt possibly destroys the Cauchy horizon if its backreaction on the
geometry is taken into account, leading to quantum restoration of the global
hyperbolicity. The result of the present work may also apply to the situation
that a closed string freely oscillating is traveling to a brane and changes
itself to an open string pinned-down by the ends satisfying the Dirichlet
boundary conditions on the brane.Comment: 12 pages, 1 figure, references added, to appear in Phys. Rev.
Acupuncture is a feasible treatment for post-thoracotomy pain: results of a prospective pilot trial
BACKGROUND: Thoracotomy is associated with severe pain that may persist for years. Acupuncture is a complementary therapy with a proven role in pain control. A randomized trial showed that acupuncture was effective in controlling pain after abdominal surgery, but the efficacy of this technique for the treatment of thoracotomy pain has not been established. We developed a novel technique for convenient application of acupuncture to patients undergoing thoracotomy, and in a Phase II trial evaluated the safety of this intervention and the feasibility of doing a randomized trial. METHODS: Adult patients scheduled for unilateral thoracotomy with preoperative epidural catheter placement received acupuncture immediately prior to surgery. Eighteen semi-permanent intradermal needles were inserted on either side of the spine, and four were inserted in the legs and auricles. Needles were removed after four weeks. Using a numerical rating scale, pain was measured on the first five postoperative days. After discharge, pain was assessed using the Brief Pain Inventory at 7, 30, 60 and 90 days. RESULTS: Thirty-six patients were treated with acupuncture. Of these, 25, 23, and 22 patients provided data at 30, 60, and 90 days, respectively. The intervention was well tolerated by patients with only one minor and transient adverse event of skin ulceration. CONCLUSION: The rate of data completion met our predefined criterion for determining a randomized trial to be feasible (at least 75% of patients tolerated the intervention and provided evaluable data). This novel intervention is acceptable to patients undergoing thoracotomy and does not interfere with standard preoperative care. There was no evidence of important adverse events. We are now testing the hypothesis that acupuncture significantly adds to standard perioperative pain management in a randomized trial
Understanding concurrent earcons: applying auditory scene analysis principles to concurrent earcon recognition
Two investigations into the identification of concurrently presented, structured sounds, called earcons were carried out. One of the experiments investigated how varying the number of concurrently presented earcons affected their identification. It was found that varying the number had a significant effect on the proportion of earcons identified. Reducing the number of concurrently presented earcons lead to a general increase in the proportion of presented earcons successfully identified. The second experiment investigated how modifying the earcons and their presentation, using techniques influenced by auditory scene analysis, affected earcon identification. It was found that both modifying the earcons such that each was presented with a unique timbre, and altering their presentation such that there was a 300 ms onset-to-onset time delay between each earcon were found to significantly increase identification. Guidelines were drawn from this work to assist future interface designers when incorporating concurrently presented earcons
Complex actions in two-dimensional topology change
We investigate topology change in (1+1) dimensions by analyzing the
scalar-curvature action at the points of metric-degeneration
that (with minor exceptions) any nontrivial Lorentzian cobordism necessarily
possesses. In two dimensions any cobordism can be built up as a combination of
only two elementary types, the ``yarmulke'' and the ``trousers.'' For each of
these elementary cobordisms, we consider a family of Morse-theory inspired
Lorentzian metrics that vanish smoothly at a single point, resulting in a
conical-type singularity there. In the yarmulke case, the distinguished point
is analogous to a cosmological initial (or final) singularity, with the
spacetime as a whole being obtained from one causal region of Misner space by
adjoining a single point. In the trousers case, the distinguished point is a
``crotch singularity'' that signals a change in the spacetime topology (this
being also the fundamental vertex of string theory, if one makes that
interpretation). We regularize the metrics by adding a small imaginary part
whose sign is fixed to be positive by the condition that it lead to a
convergent scalar field path integral on the regularized spacetime. As the
regulator is removed, the scalar density approaches a
delta-function whose strength is complex: for the yarmulke family the strength
is , where is the rapidity parameter of the associated
Misner space; for the trousers family it is simply . This implies that
in the path integral over spacetime metrics for Einstein gravity in three or
more spacetime dimensions, topology change via a crotch singularity is
exponentially suppressed, whereas appearance or disappearance of a universe via
a yarmulke singularity is exponentially enhanced.Comment: 34 pages, REVTeX v3.0. (Presentational reorganization; core results
unchanged.
Gravitational waves, black holes and cosmic strings in cylindrical symmetry
Gravitational waves in cylindrically symmetric Einstein gravity are described
by an effective energy tensor with the same form as that of a massless Klein-
Gordon field, in terms of a gravitational potential generalizing the Newtonian
potential. Energy-momentum vectors for the gravitational waves and matter are
defined with respect to a canonical flow of time. The combined energy-momentum
is covariantly conserved, the corresponding charge being the modified Thorne
energy. Energy conservation is formulated as the first law expressing the
gradient of the energy as work and energy-supply terms, including the energy
flux of the gravitational waves. Projecting this equation along a trapping
horizon yields a first law of black-hole dynamics containing the expected term
involving area and surface gravity, where the dynamic surface gravity is
defined with respect to the canonical flow of time. A first law for dynamic
cosmic strings also follows. The Einstein equation is written as three wave
equations plus the first law, each with sources determined by the combined
energy tensor of the matter and gravitational waves.Comment: 10 pages, revtex. Published version with further detail
Evaluation of pressurized water cleaning systems for hardware refurbishment
Historically, refurbishment processes for RSRM motor cases and components have employed environmentally harmful materials. Specifically, vapor degreasing processes consume and emit large amounts of ozone depleting compounds. This program evaluates the use of pressurized water cleaning systems as a replacement for the vapor degreasing process. Tests have been conducted to determine if high pressure water washing, without any form of additive cleaner, is a viable candidate for replacing vapor degreasing processes. This paper discusses the findings thus far of Engineering Test Plan - 1168 (ETP-1168), 'Evaluation of Pressurized Water Cleaning Systems for Hardware Refurbishment.
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National interest to global reform: patterns of reasoning in British foreign policy discourse
Discussion of the national interest often focuses on how Britain's influence can be maximized, rather than on the goals that influence serves. Yet what gives content to claims about the national interest is the means-ends reasoning which links interests to deeper goals. In ideal-typical terms, this can take two forms. The first, and more common, approach is conservative: it infers national interests and the goals they advance from existing policies and commitments. The second is reformist: it starts by specifying national goals and then asks how they are best advanced under particular conditions. New Labour's foreign policy discourse is notable for its explicit use of a reformist approach. Indeed, Gordon Brown's vision of a 'new global society' not only identifies global reform as a key means of fulfilling national goals, but also thereby extends the concept of the national interest well beyond a narrow concern with national security
Gravitational Phase Operator and Cosmic Strings
A quantum equivalence principle is formulated by means of a gravitational
phase operator which is an element of the Poincare group. This is applied to
the spinning cosmic string which suggests that it may (but not necessarily)
contain gravitational torsion. A new exact solution of the Einstein-
Cartan-Sciama-Kibble equations for the gravitational field with torsion is
obtained everywhere for a cosmic string with uniform energy density, spin
density and flux. A novel effect due to the quantized gravitational field of
the cosmic string on the wave function of a particle outside the string is used
to argue that spacetime points are not meaningful in quantum gravity.Comment: 22 pages, to be published Phys. Rev. D. Some minor changes have been
made and a reference has been added to the paper of D.V. Gal'tsov and P.S.
Letelier, Phys. Rev. D 47 (1993) 4273, which first contained the metric (2.2)
external to the cosmic string. The present paper extends this solution to a
regular solution inside the string as wel
On the combination of omics data for prediction of binary outcomes
Enrichment of predictive models with new biomolecular markers is an important
task in high-dimensional omic applications. Increasingly, clinical studies
include several sets of such omics markers available for each patient,
measuring different levels of biological variation. As a result, one of the
main challenges in predictive research is the integration of different sources
of omic biomarkers for the prediction of health traits. We review several
approaches for the combination of omic markers in the context of binary outcome
prediction, all based on double cross-validation and regularized regression
models. We evaluate their performance in terms of calibration and
discrimination and we compare their performance with respect to single-omic
source predictions. We illustrate the methods through the analysis of two real
datasets. On the one hand, we consider the combination of two fractions of
proteomic mass spectrometry for the calibration of a diagnostic rule for the
detection of early-stage breast cancer. On the other hand, we consider
transcriptomics and metabolomics as predictors of obesity using data from the
Dietary, Lifestyle, and Genetic determinants of Obesity and Metabolic syndrome
(DILGOM) study, a population-based cohort, from Finland
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