1,082 research outputs found
Comparative analysis of techniques for evaluating the effectiveness of aircraft computing systems
Performability analysis is a technique developed for evaluating the effectiveness of fault-tolerant computing systems in multiphase missions. Performability was evaluated for its accuracy, practical usefulness, and relative cost. The evaluation was performed by applying performability and the fault tree method to a set of sample problems ranging from simple to moderately complex. The problems involved as many as five outcomes, two to five mission phases, permanent faults, and some functional dependencies. Transient faults and software errors were not considered. A different analyst was responsible for each technique. Significantly more time and effort were required to learn performability analysis than the fault tree method. Performability is inherently as accurate as fault tree analysis. For the sample problems, fault trees were more practical and less time consuming to apply, while performability required less ingenuity and was more checkable. Performability offers some advantages for evaluating very complex problems
The eVALuate study: two parallel randomised trials, one comparing laparoscopic with abdominal hysterectomy, the other comparing laparoscopic with vaginal hysterectomy
OBJECTIVE: To compare the effects of laparoscopic hysterectomy
and abdominal hysterectomy in the abdominal trial, and
laparoscopic hysterectomy and vaginal hysterectomy in the
vaginal trial.
DESIGN: Two parallel, multicentre, randomised trials.
Setting 28 UK centres and two South African centres.
Participants 1380 women were recruited; 1346 had surgery;
937 were followed up at one year.
PRIMARY OUTCOME: outcome Rate of major complications.
RESULTS: In the abdominal trial laparoscopic hysterectomy was
associated with a higher rate of major complications than
abdominal hysterectomy (11.1% v 6.2%, P = 0.02; difference
4.9%, 95% confidence interval 0.9% to 9.1%) and the number
needed to treat to harm was 20. Laparoscopic hysterectomy
also took longer to perform (84 minutes v 50 minutes) but was
less painful (visual analogue scale 3.51 v 3.88, P = 0.01) and
resulted in a shorter stay in hospital after the operation (3 days
v 4 days). Six weeks after the operation, laparoscopic
hysterectomy was associated with less pain and better quality of
life than abdominal hysterectomy (SF-12, body image scale, and
sexual activity questionnaires).
In the vaginal trial we found no evidence of a difference in
major complication rates between laparoscopic hysterectomy
and vaginal hysterectomy (9.8% v 9.5%, P = 0.92; difference
0.3%, − 5.2% to 5.8%), and the number needed to treat to harm
was 333.We found no evidence of other differences between
laparoscopic hysterectomy and vaginal hysterectomy except
that laparoscopic hysterectomy took longer to perform (72
minutes v 39 minutes) and was associated with a higher rate of
detecting unexpected pathology (16.4% v 4.8%, P = < 0.01).
However, this trial was underpowered.
CONCLUSIONS: Laparoscopic hysterectomy was associated with a
significantly higher rate of major complications than abdominal
hysterectomy. It also took longer to perform but was associated
with less pain, quicker recovery, and better short term quality of
life. The trial comparing vaginal hysterectomy with laparoscopic
hysterectomy was underpowered and is inconclusive on the rate
of major complications; however, vaginal hysterectomy took less
time
Tricritical Phenomena at the Cerium Transition
The isostructural transition in the
CeLaTh system is measured as a function of La alloying
using specific heat, magnetic susceptibility, resistivity, thermal
expansivity/striction measurements. A line of discontinuous transitions, as
indicated by the change in volume, decreases exponentially from 118 K to close
to zero with increasing La doping and the transition changes from being
first-order to continuous at a critical concentration . At the tricritical point, the coefficient of the linear term in the
specific heat and the magnetic susceptibility start to increase
rapidly near = 0.14 and gradually approaches large values at =0.35
signifying that a heavy Fermi-liquid state evolves at large doping. Near ,
the Wilson ratio, , has a value of 3.0, signifying the presence of
magnetic fluctuations. Also, the low-temperature resistivity shows that the
character of the low-temperature Fermi-liquid is changing
Einstein's "Zur Elektrodynamik..." (1905) Revisited, with Some Consequences
Einstein, in his "Zur Elektrodynamik bewegter Korper", gave a physical
(operational) meaning to "time" of a remote event in describing "motion" by
introducing the concept of "synchronous stationary clocks located at different
places". But with regard to "place" in describing motion, he assumed without
analysis the concept of a system of co-ordinates. In the present paper, we
propose a way of giving physical (operational) meaning to the concepts of
"place" and "co-ordinate system", and show how the observer can define both the
place and time of a remote event. Following Einstein, we consider another
system "in uniform motion of translation relatively to the former". Without
assuming "the properties of homogeneity which we attribute to space and time",
we show that the definitions of space and time in the two systems are linearly
related. We deduce some novel consequences of our approach regarding
faster-than-light observers and particles, "one-way" and "two-way" velocities
of light, symmetry, the "group property" of inertial reference frames, length
contraction and time dilatation, and the "twin paradox". Finally, we point out
a flaw in Einstein's argument in the "Electrodynamical Part" of his paper and
show that the Lorentz force formula and Einstein's formula for transformation
of field quantities are mutually consistent. We show that for faster-than-light
bodies, a simple modification of Planck's formula for mass suffices. (Except
for the reference to Planck's formula, we restrict ourselves to Physics of
1905.)Comment: 55 pages, 4 figures, accepted for publication in "Foundations of
Physics
Positive-Operator-Valued Time Observable in Quantum Mechanics
We examine the longstanding problem of introducing a time observable in
Quantum Mechanics; using the formalism of positive-operator-valued measures we
show how to define such an observable in a natural way and we discuss some
consequences.Comment: 13 pages, LaTeX, no figures. Some minor changes, expanded the
bibliography (now it is bigger than the one in the published version),
changed the title and the style for publication on the International Journal
of Theoretical Physic
Simultaneous Observations of GRS 1758-258 in 1997 by VLA, IRAM, SEST, RXTE and OSSE: Spectroscopy and Timing
We report the results of our multi-wavelength observations of GRS 1758-258
made in August 1997. The energy bands include radio, millimeter, X-ray, and
gamma-ray. The observations enable us to obtain a complete spectrum of the
source over an energy range of 2 - 500 keV. The spectrum shows that GRS
1758-258 was in its hard state. It is well fitted by the Sunyaev-Titarchuk (ST)
Compton scattering model. The spectrum is also fit by a power law with an
exponential cutoff (PLE) plus a soft black-body component. The temperature of
the soft component is about 1.2 keV, and the energy flux is less than 1.5% of
the total X- and gamma-ray flux. The deduced hydrogen column density is in the
range of (0.93 - 2.0) 10^{22} cm^{-2}. No significant iron lines are detected.
The radio emission has a flat energy spectrum. The daily radio, X-ray and
gamma-ray light curves show that GRS 1758-258 was stable during the observation
period, but was highly variable on smaller time scales in X- and gamma-rays.
The power density spectra are typical for the low-state, but we find the photon
flux for the 5 to 10 keV band to be more variable than that in the other two
energy bands (2 - 5 keV and 10 - 40 keV). Harmonically spaced quasi-periodic
oscillations (QPOs) are observed in the power spectra. The phase lags between
the hard photons and the soft photons have a flat distribution over a wide
range of frequencies. A high coherence of about 1.0 (0.01 - 1 Hz) between the
hard photons and the soft photons is also obtained in our observations. We
compare these results with two variation models. Our millimeter observations
did not reveal any conclusive signatures of an interaction between the jet from
GRS 1758-258 and the molecular cloud that lies in the direction of GRS
1758-258.Comment: 32 pages, 13 figures, to appear in ApJ, 2000, V.533, no. 1, Apr. 10.
For better figure resolution, please directly download the paper from
http://spacsun.rice.edu/~lin/publication.htm
Origin of complex crystal structures of elements at pressure
We present a unifying theory for the observed complex structures of the
sp-bonded elements under pressure based on nearly free electron picture (NFE).
In the intermediate pressure regime the dominant contribution to crystal
structure arises from Fermi-surface Brillouin zone (FSBZ) interactions -
structures which allow this are favoured. This simple theory explains the
observed crystal structures, transport properties, the evolution of internal
and unit cell parameters with pressure. We illustrate it with experimental data
for these elements and ab initio calculation for Li.Comment: 4 pages 5 figure
Benefits, barriers and enablers of mentoring female health academics: An integrative review
This integrative literature review synthesizes the primary research evidence on mentoring female health academics published from 2000 to 2018, to identify the benefits, enablers and barriers to mentoring women. The need for this review is underpinned by the magnitude of change in higher education, the high number of women in health disciplines, limited progress in advancing women's academic careers, escalating role expectations, faculty shortages and staff turnover. Data were sourced from Scopus, PubMed, EMBASE and Cumulative Index of Nursing and Allied Health Literature. Twenty-seven studies were included. Although effective mentoring facilitates personal and career development, academic craftsmanship, psychosocial support and job satisfaction, it is complicated by organizational factors and personal and relational dynamics. Enablers of mentoring are mentor availability and expertise, supportive relationships, mutuality and responsiveness. Lack of, or inadequate mentoring compromise women's job satisfaction, career development and academic productivity. Providing female health academics access to experienced, well-connected mentors with common interests who are committed to advancing their career, is an investment in optimizing potential, promoting supportive work environments and increasing productivity and retention. Realizing the institutional potential that mentoring female health academics offers, is contingent on academic leaders valuing mentorship as faculty business and understanding the role that the contemporary academic environment plays in achieving mentoring outcomes. Further empirical and longitudinal research is needed to evaluate effective approaches for mentoring women in the contemporary academic environment
Exactly solvable model for cosmological perturbations in dilatonic brane worlds
We construct a model where cosmological perturbations are analytically solved
based on dilatonic brane worlds. A bulk scalar field has an exponential
potential in the bulk and an exponential coupling to the brane tension. The
bulk scalar field yields a power-law inflation on the brane. The exact
background metric can be found including the back-reaction of the scalar field.
Then exact solutions for cosmological perturbations which properly satisfy the
junction conditions on the brane are derived. These solutions provide us an
interesting model to understand the connection between the behavior of
cosmological perturbations on the brane and the geometry of the bulk. Using
these solutions, the behavior of an anisotropic stress induced on the
inflationary brane by bulk gravitational fields is investigated.Comment: 30 pages, typos corrected, reference adde
Ellipsoidal universe in the brane world
We study a scenario of the ellipsoidal universe in the brane world cosmology
with a cosmological constant in the bulk . From the five-dimensional Einstein
equations we derive the evolution equations for the eccentricity and the scale
factor of the universe, which are coupled to each other. It is found that if
the anisotropy of our universe is originated from a uniform magnetic field
inside the brane, the eccentricity decays faster in the bulk in comparison with
a four-dimensional ellipsoidal universe. We also investigate the ellipsoidal
universe in the brane-induced gravity and find the evolution equation for the
eccentricity which has a contribution determined by the four- and
five-dimensional Newton's constants. The role of the eccentricity is discussed
in explaining the quadrupole problem of the cosmic microwave background.Comment: 15 pages, 1 figure, Version 3, references added, contents expande
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