621 research outputs found
Proving Termination Starting from the End
We present a novel technique for proving program termination which introduces
a new dimension of modularity. Existing techniques use the program to
incrementally construct a termination proof. While the proof keeps changing,
the program remains the same. Our technique goes a step further. We show how to
use the current partial proof to partition the transition relation into those
behaviors known to be terminating from the current proof, and those whose
status (terminating or not) is not known yet. This partition enables a new and
unexplored dimension of incremental reasoning on the program side. In addition,
we show that our approach naturally applies to conditional termination which
searches for a precondition ensuring termination. We further report on a
prototype implementation that advances the state-of-the-art on the grounds of
termination and conditional termination.Comment: 16 page
Astrophysical structures from primordial quantum black holes
The characteristic sizes of astrophysical structures, up to the whole
observed Universe, can be recovered, in principle, assuming that gravity is the
overall interaction assembling systems starting from microscopic scales, whose
order of magnitude is ruled by the Planck length and the related Compton
wavelength. This result agrees with the absence of screening mechanisms for the
gravitational interaction and could be connected to the presence of Yukawa
corrections in the Newtonian potential which introduce typical interaction
lengths. This result directly comes out from quantization of primordial black
holes and then characteristic interaction lengths directly emerge from quantum
field theory.Comment: 11 page
A Binary Lensing Event Toward the LMC: Observations and Dark Matter Implications
The MACHO collaboration has recently analyzed 2.1 years of photometric data
for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis
has revealed 8 candidate microlensing events and a total microlensing optical
depth of . This significantly
exceeds the number of events (1.1) and the microlensing optical depth predicted
from known stellar populations: , but it is
consistent with models in which about half of the standard dark halo mass is
composed of Machos of mass \sim 0.5 \msun. One of these 8 events appears to
be a binary lensing event with a caustic crossing that is partially resolved
which allows us to estimate the distance to the lenses. If the source star is
not a short period binary star, then we show that the lens system is very
likely to reside in the LMC. However, if we assume that the optical depth for
LMC-LMC lensing is large enough to account for our entire lensing signal, then
the binary event does not appear to be consistent with lensing of a single LMC
source star by a binary residing in the LMC. Thus, while the binary lens may
indeed reside in the LMC, there is no indication that most of the lenses reside
in the LMC.Comment: 5 pages, 3 postscript figures included; To appear in the Proceedings
of the Dark Matter '96 Conference held in Santa Monica, CA, Feb., 199
Origin and Evolution of Saturn's Ring System
The origin and long-term evolution of Saturn's rings is still an unsolved
problem in modern planetary science. In this chapter we review the current
state of our knowledge on this long-standing question for the main rings (A,
Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During
the Voyager era, models of evolutionary processes affecting the rings on long
time scales (erosion, viscous spreading, accretion, ballistic transport, etc.)
had suggested that Saturn's rings are not older than 100 My. In addition,
Saturn's large system of diffuse rings has been thought to be the result of
material loss from one or more of Saturn's satellites. In the Cassini era, high
spatial and spectral resolution data have allowed progress to be made on some
of these questions. Discoveries such as the ''propellers'' in the A ring, the
shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume
provide new constraints on evolutionary processes in Saturn's rings. At the
same time, advances in numerical simulations over the last 20 years have opened
the way to realistic models of the rings's fine scale structure, and progress
in our understanding of the formation of the Solar System provides a
better-defined historical context in which to understand ring formation. All
these elements have important implications for the origin and long-term
evolution of Saturn's rings. They strengthen the idea that Saturn's rings are
very dynamical and rapidly evolving, while new arguments suggest that the rings
could be older than previously believed, provided that they are regularly
renewed. Key evolutionary processes, timescales and possible scenarios for the
rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from
Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009)
537-57
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
The MACHO Project 2nd Year LMC Microlensing Results and Dark Matter Implications
The MACHO Project is searching for galactic dark matter in the form of
massive compact halo objects (Machos). Millions of stars in the Large
Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge are
photometrically monitored in an attempt to detect rare gravitational
microlensing events caused by otherwise invisible Machos. Analysis of two years
of photometry on 8.5 million stars in the LMC reveals 8 candidate microlensing
events, far more than the event expected from lensing by low-mass stars
in known galactic populations. From these eight events we estimate the optical
depth towards the LMC from events with 2 < \that < 200 days to be
\tau_2^{200} \approx 2.9 ^{+1.4}_{-0.9} \ten{-7}. This exceeds the optical
depth of 0.5\ten{-7} expected from known stars and is to be compared with an
optical depth of 4.7\ten{-7} predicted for a ``standard'' halo composed
entirely of Machos. The total mass in this lensing population is \approx
2^{+1.2}_{-0.7} \ten{11} \msun (within 50 kpc from the Galactic center). Event
timescales yield a most probable Macho mass of 0.5^{+0.3}_{-0.2}\msun,
although this value is quite model dependent.Comment: 10 pages, 6 epsf figures and style file included, 451k, also at
http://wwwmacho.mcmaster.ca/Pubs/Pubs.html; To appear in the Proceedings of
"Sources and Detection of Dark Matter in the Universe", Santa Monica, CA,
Feb., 199
Исследовательская деятельность эколого-биологической направленности в НОУ "Эврика" - эффективное средство профессиональной ориентации учащихся
В статье научно-исследовательская деятельность эколого-биологической направленности старшеклассников НОУ "Эврика" г. Нижнего Новгорода рассматривается как одна из значимых инновационных форм профессионального самоопределения. Материалом исследования послужил анализ программ конференции городского научного общества учащихся "Эврика" и судьбы выпускников данного общества. Отмечена тенденция роста популярности эколого-биологических исследований среди старшеклассников г. Нижнего Новгорода и успешное вхождение в профессию выпускников научного общества учащихся.In the article, the research activity of the ecology and biology of senior pupils of the scientific society of the pupils "Eureka" in Nizhny Novgorod is considered as one of the significant innovative forms of professional self-determination. The material of the study was the analysis of the programs of the conference of the city scientific society of the students "Eureka" and the fate of the graduates of this society. The tendency of growth of popularity of ecological and biological researches among senior pupils of Nizhny Novgorod and successful entry into the profession of graduates of the scientific society of students is noted
Arthroscopic subacromial decompression for subacromial shoulder pain (CSAW):a multicentre, pragmatic, parallel group, placebo-controlled, three-group, randomised surgical trial
Background: Arthroscopic sub-acromial decompression (decompressing the sub-acromial space by removing bone spurs and soft tissue arthroscopically) is a common surgery for subacromial shoulder pain, but its effectiveness is uncertain. We did a study to assess its effectiveness and to investigate the mechanism for surgical decompression.
Methods: We did a multicentre, randomised, pragmatic, parallel group, placebo-controlled, three-group trial at 32 hospitals in the UK with 51 surgeons. Participants were patients who had subacromial pain for at least 3 months with intact rotator cuff tendons, were eligible for arthroscopic surgery, and had previously completed a non-operative management programme that included exercise therapy and at least one steroid injection. Exclusion criteria included a full-thickness torn rotator cuff. We randomly assigned participants (1:1:1) to arthroscopic subacromial decompression, investigational arthroscopy only, or no treatment (attendance of one reassessment appointment with a specialist shoulder clinician 3 months after study entry, but no intervention). Arthroscopy only was a placebo as the essential surgical element (bone and soft tissue removal) was omitted. We did the randomisation with a computer-generated minimisation system. In the surgical intervention groups, patients were not told which type of surgery they were receiving (to ensure masking). Patients were followed up at 6 months and 1 year after randomisation; surgeons coordinated their waiting lists to schedule surgeries as close as possible to randomisation. The primary outcome was the Oxford Shoulder Score (0 [worst] to 48 [best]) at 6 months, analysed by intention to treat. The sample size calculation was based upon a target difference of 4·5 points (SD 9·0). This trial has been registered at ClinicalTrials.gov, number NCT01623011.
Findings: Between Sept 14, 2012, and June 16, 2015, we randomly assigned 313 patients to treatment groups (106 to decompression surgery, 103 to arthroscopy only, and 104 to no treatment). 24 [23%], 43 [42%], and 12 [12%] of the decompression, arthroscopy only, and no treatment groups, respectively, did not receive their assigned treatment by 6 months. At 6 months, data for the Oxford Shoulder Score were available for 90 patients assigned to decompression, 94 to arthroscopy, and 90 to no treatment. Mean Oxford Shoulder Score did not differ between the two surgical groups at 6 months (decompression mean 32·7 points [SD 11·6] vs arthroscopy mean 34·2 points [9·2]; mean difference −1·3 points (95% CI −3·9 to 1·3, p=0·3141). Both surgical groups showed a small benefit over no treatment (mean 29·4 points [SD 11·9], mean difference vs decompression 2·8 points [95% CI 0·5–5·2], p=0·0186; mean difference vs arthroscopy 4·2 [1·8–6·6], p=0·0014) but these differences were not clinically important. There were six study-related complications that were all frozen shoulders (in two patients in each group).
Interpretation: Surgical groups had better outcomes for shoulder pain and function compared with no treatment but this difference was not clinically important. Additionally, surgical decompression appeared to offer no extra benefit over arthroscopy only. The difference between the surgical groups and no treatment might be the result of, for instance, a placebo effect or postoperative physiotherapy. The findings question the value of this operation for these indications, and this should be communicated to patients during the shared treatment decision-making process.
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