730 research outputs found
Biomedical applications of NASA technology
Through the active transfer of technology, NASA Technology Utilization (TU) Program assists private companies, associations, and government agencies to make effective use of NASA's technological resources to improve U.S. economic competitiveness and to provide societal benefit. Aerospace technology from such areas as digital image processing, space medicine and biology, microelectronics, optics, and electro-optics, and ultrasonic imaging have found many secondary applications in medicine. Examples of technology spinoffs are briefly discussed to illustrate the benefits realized through adaptation of aerospace technology to solve health care problems. Successful implementation of new technologies increasingly requires the collaboration of industry, universities, and government and the TU Program serves as the liaison to establish such collaborations with NASA. NASA technology is an important resource to support the development of new medical products and techniques that will further advance the quality of health care available in the U.S. and worldwide
Topological Censorship
All three-manifolds are known to occur as Cauchy surfaces of asymptotically
flat vacuum spacetimes and of spacetimes with positive-energy sources. We prove
here the conjecture that general relativity does not allow an observer to probe
the topology of spacetime: any topological structure collapses too quickly to
allow light to traverse it. More precisely, in a globally hyperbolic,
asymptotically flat spacetime satisfying the null energy condition, every
causal curve from \scri^- to {\scri}^+ is homotopic to a topologically
trivial curve from \scri^- to {\scri}^+. (If the Poincar\'e conjecture is
false, the theorem does not prevent one from probing fake 3-spheres).Comment: 12 pages, REVTEX; 1 postscript figure in a separate uuencoded file.
Our earlier version (PRL 71, 1486 (1993)) contained a secondary result,
mistakenly attributed to Schoen and Yau, regarding ``passive topological
censorship'' of a certain class of topologies. As Gregory Burnett has pointed
out (gr-qc/9504012), this secondary result is false. The main topological
censorship theorem is unaffected by the erro
Nonexistence of marginally trapped surfaces and geons in 2+1 gravity
We use existence results for Jang's equation and marginally outer trapped
surfaces (MOTSs) in 2+1 gravity to obtain nonexistence of geons in 2+1 gravity.
In particular, our results show that any 2+1 initial data set, which obeys the
dominant energy condition with cosmological constant \Lambda \geq 0 and which
satisfies a mild asymptotic condition, must have trivial topology. Moreover,
any data set obeying these conditions cannot contain a MOTS. The asymptotic
condition involves a cutoff at a finite boundary at which a null mean convexity
condition is assumed to hold; this null mean convexity condition is satisfied
by all the standard asymptotic boundary conditions. The results presented here
strengthen various aspects of previous related results in the literature. These
results not only have implications for classical 2+1 gravity but also apply to
quantum 2+1 gravity when formulated using Witten's solution space quantization.Comment: v3: Elements from the original two proofs of the main result have
been combined to give a single proof, thereby circumventing an issue with the
second proof associated with potential blow-ups of solutions to Jang's
equation. To appear in Commun. Math. Phy
Adherence to
(MWM) for palliative care has prioritized data collection efforts for evaluating quality in clinical practice. How these measures can be implemented across diverse clinical settings using point-of-care data collection on quality is unknown.To evaluate the implementation of MWM measures by exploring documentation of quality measure adherence across six diverse clinical settings inherent to palliative care practice.We deployed a point-of-care quality data collection system, the Quality Data Collection Tool, across five organizations within the Palliative Care Research Cooperative Group. Quality measures were recorded by clinicians or assistants near care delivery.During the study period, 1989 first visits were included for analysis. Our population was mostly white, female, and with moderate performance status. About half of consultations were seen on hospital general floors. We observed a wide range of adherence. The lowest adherence involved comprehensive assessments during the first visit in hospitalized patients in the intensive care unit (2.71%); the highest adherence across all settings, with an implementation of >95%, involved documentation of management of moderate/severe pain. We observed differences in adherence across clinical settings especially with MWM Measure #2 (Screening for Physical Symptoms, range 45.7%–81.8%); MWM Measure #5 (Discussion of Emotional Needs, range 46.1%–96.1%); and MWM Measure #6 (Documentation of Spiritual/Religious Concerns, range 0–69.6%).Variations in clinician documentation of adherence to MWM quality measures are seen across clinical settings. Additional studies are needed to better understand benchmarks and acceptable ranges for adherence tailored to various clinical settings
Single-exterior black holes and the AdS-CFT conjecture
In the context of the conjectured AdS-CFT correspondence of string theory, we
consider a class of asymptotically Anti-de Sitter black holes whose conformal
boundary consists of a single connected component, identical to the conformal
boundary of Anti-de Sitter space. In a simplified model of the boundary theory,
we find that the boundary state to which the black hole corresponds is pure,
but this state involves correlations that produce thermal expectation values at
the usual Hawking temperature for suitably restricted classes of operators. The
energy of the state is finite and agrees in the semiclassical limit with the
black hole mass. We discuss the relationship between the black hole topology
and the correlations in the boundary state, and speculate on generalizations of
the results beyond the simplified model theory.Comment: 27 pages, LaTeX, using REVTeX v3.1 with amsfonts and epsf, with two
eps figures. (v3: references updated
Centerscope
Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.
Inextendible Schwarzschild black hole with a single exterior: How thermal is the Hawking radiation?
Several approaches to Hawking radiation on Schwarzschild spacetime rely in
some way or another on the fact that the Kruskal manifold has two causally
disconnected exterior regions. We investigate the Hawking(-Unruh) effect for a
real scalar field on the \RPthree geon: an inextendible, globally hyperbolic,
space and time orientable eternal black hole spacetime that is locally
isometric to Kruskal but contains only one exterior region. The
Hartle-Hawking-like vacuum~\hhvacgeon, which can be characterized
alternatively by the positive frequency properties along the horizons or by the
complex analytic properties of the Feynman propagator, turns out to contain
exterior region Boulware modes in correlated pairs, and any operator in the
exterior that only couples to one member of each correlated Boulware pair has
thermal expectation values in the usual Hawking temperature. Generic operators
in the exterior do not have this special form; however, we use a Bogoliubov
transformation, a particle detector analysis, and a particle
emission-absorption analysis that invokes the analytic properties of the
Feynman propagator, to argue that \hhvacgeon appears as a thermal bath with
the standard Hawking temperature to any exterior observer at asymptotically
early and late Schwarzschild times. A~(naive) saddle-point estimate for the
path-integral-approach partition function yields for the geon only half of the
Bekenstein-Hawking entropy of a Schwarzschild black hole with the same ADM
mass: possible implications of this result for the validity of path-integral
methods or for the statistical interpretation of black-hole entropy are
discussed. Analogous results hold for a Rindler observer in a flat spacetime
whose global properties mimic those of the geon.Comment: 53 pages, REVTex v3.1 with amsfonts and epsf, includes 5 eps figures.
(v2: Title and abstract expanded, minor comments added. v3: Minor typos
corrected.
Black Holes and Instabilities of Negative Tension Branes
We consider the collision in 2+1 dimensions of a black hole and a negative
tension brane on an orbifold. Because there is no gravitational radiation in
2+1 dimensions, the horizon area shrinks when part of the brane falls through.
This provides a potential violation of the generalized second law of
thermodynamics. However, tracing the details of the dynamical evolution one
finds that it does not proceed from equilibrium configuration to equilibrium
configuration. Instead, a catastrophic space-time singularity develops similar
to the `big crunch' of FRW space-times. In the context of classical
general relativity, our result demonstrates a new instability of constructions
with negative tension branes.Comment: 18 pages, 3 figures, uses RevTeX. Minor typos fixed. References and
one footnote adde
Galaxy Clustering in Early SDSS Redshift Data
We present the first measurements of clustering in the Sloan Digital Sky
Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies
with redshifts 5,700 km/s < cz < 39,000 km/s, distributed in several long but
narrow (2.5-5 degree) segments, covering 690 square degrees. For the full,
flux-limited sample, the redshift-space correlation length is approximately 8
Mpc/h. The two-dimensional correlation function \xi(r_p,\pi) shows clear
signatures of both the small-scale, ``fingers-of-God'' distortion caused by
velocity dispersions in collapsed objects and the large-scale compression
caused by coherent flows, though the latter cannot be measured with high
precision in the present sample. The inferred real-space correlation function
is well described by a power law, \xi(r)=(r/6.1+/-0.2 Mpc/h)^{-1.75+/-0.03},
for 0.1 Mpc/h < r < 16 Mpc/h. The galaxy pairwise velocity dispersion is
\sigma_{12} ~ 600+/-100 km/s for projected separations 0.15 Mpc/h < r_p < 5
Mpc/h. When we divide the sample by color, the red galaxies exhibit a stronger
and steeper real-space correlation function and a higher pairwise velocity
dispersion than do the blue galaxies. The relative behavior of subsamples
defined by high/low profile concentration or high/low surface brightness is
qualitatively similar to that of the red/blue subsamples. Our most striking
result is a clear measurement of scale-independent luminosity bias at r < 10
Mpc/h: subsamples with absolute magnitude ranges centered on M_*-1.5, M_*, and
M_*+1.5 have real-space correlation functions that are parallel power laws of
slope ~ -1.8 with correlation lengths of approximately 7.4 Mpc/h, 6.3 Mpc/h,
and 4.7 Mpc/h, respectively.Comment: 51 pages, 18 figures. Replaced to match accepted ApJ versio
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