13,319 research outputs found
Burner rig corrosion of SiC at 1000 deg C
Sintered alpha-SiC was examined in both oxidation and hot corrosion with a burner rig at 400 kPa (4 atm) and 1000 C with a flow velocity of 310 ft/sec. Oxidation tests for times to 46 hr produced virtually no attack, whereas tests with 4 ppm Na produced extensive corrosion in 13-1/2 hr. Thick glassy layers composed primarily of sodium silicate formed in the salt corrosion tests. This corrosion attack caused severe pitting of the silicon carbide substrate which led to a 32 percent strength decrease below the as-received material. Parallel furnace tests of Na2SO4/air induced attacked yielded basically similar results with some slight product composition differences. The differences are explained in terms of the continuous sulfate deposition which occurs in a burner rig
Black hole entropy: inside or out?
A trialogue. Ted, Don, and Carlo consider the nature of black hole entropy.
Ted and Carlo support the idea that this entropy measures in some sense ``the
number of black hole microstates that can communicate with the outside world.''
Don is critical of this approach, and discussion ensues, focusing on the
question of whether the first law of black hole thermodynamics can be
understood from a statistical mechanics point of view.Comment: 42 pages, contribution to proceedings of Peyresq
Transportation systems evaluation methodology development and applications, phase 3
Transportation systems or proposed changes in current systems are evaluated. Four principal evaluation criteria are incorporated in the process, operating performance characteristics as viewed by potential users, decisions based on the perceived impacts of the system, estimating what is required to reduce the system to practice; and predicting the ability of the concept to attract financial support. A series of matrix multiplications in which the various matrices represent evaluations in a logical sequence of the various discrete steps in a management decision process is used. One or more alternatives are compared with the current situation, and the result provides a numerical rating which determines the desirability of each alternative relative to the norm and to each other. The steps in the decision process are isolated so that contributions of each to the final result are readily analyzed. The ability to protect against bias on the part of the evaluators, and the fact that system parameters which are basically qualitative in nature can be easily included are advantageous
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Implementation issues in product line scoping
Often product line engineering is treated similar to the waterfall model in traditional software engineering, i.e., the different phases (scoping, analysis, architecting, implementation) are treated as if they could be clearly separated and would follow each other in an ordered fashion. However, in practice strong interactions between the individual phases become apparent. In particular, how implementation is done has a strong impact on economic aspects of the project and thus how to adequately plan it. Hence, assessing these relationships adequately in the beginning has a strong impact on performing a product line project right. In this paper we present a framework that helps in exactly this task. It captures on an abstract level the relationships between scoping information and implementation aspects and thus allows to provide rough guidance on implementation aspects of the project. We will also discuss the application of our framework to a specific industrial project
Model-Independent Test of General Relativity: An Extended post-Einsteinian Framework with Complete Polarization Content
We develop a model-independent test of General Relativity that allows for the
constraint of the gravitational wave (GW) polarization content with GW
detections of binary compact object inspirals. We first consider three modified
gravity theories (Brans-Dicke theory, Rosen's theory and Lightman-Lee theory)
and calculate the response function of ground-based detectors to gravitational
waves in the inspiral phase. This allows us to see how additional polarizations
predicted in these theories modify the General Relativistic prediction of the
response function. We then consider general power-law modifications to the
Hamiltonian and radiation-reaction force and study how these modify the
time-domain and Fourier response function when all polarizations are present.
From these general arguments and specific modified gravity examples, we infer
an improved parameterized post-Einsteinian template family with complete
polarization content. This family enhances General Relativity templates through
the inclusion of new theory parameters, reducing to the former when these
parameters acquire certain values, and recovering modified gravity predictions
for other values, including all polarizations. We conclude by discussing
detection strategies to constrain these new, polarization theory parameters by
constructing certain null channels through the combination of output from
multiple detectors.Comment: 20 pages, 1 figure, added erratum correcting some intermediate
equation
Resonance NLS Solitons as Black Holes in Madelung Fluid
A new resonance version of NLS equation is found and embedded to the
reaction-diffusion system, equivalent to the anti-de Sitter valued Heisenberg
model, realizing a particular gauge fixing condition of the Jackiw-Teitelboim
gravity. The space-time points where dispersion change the sign correspond to
the event horizon, and the soliton solutions to the AdS black holes. The
soliton with velocity bounded above describes evolution on the hyperboloid with
nontrivial winding number and create under collisions the resonance states with
a specific life time.Comment: Plain Tex, 12 pages, 6 figure
The association among diet, dietary fiber, and bowel preparation at colonoscopy
BACKGROUND AND AIMS: Pre-colonoscopy dietary restrictions vary widely and lack evidence-based guidance. We investigated whether fiber and various other foods/macronutrients consumed during the 3 days before colonoscopy are associated with bowel preparation quality.
METHODS: This was a prospective observational study among patients scheduled for outpatient colonoscopy. Patients received instructions including split-dose polyethylene glycol, avoidance of vegetables/beans 2 days before colonoscopy, and a clear liquid diet the day before colonoscopy. Two 24-hour dietary recall interviews and 1 patient-recorded food log measured dietary intake on the 3 days before colonoscopy. The Nutrition Data System for Research was used to estimate dietary exposures. Our primary outcome was the quality of bowel preparation measured by the Boston Bowel Preparation Scale (BBPS).
RESULTS: We enrolled 201 patients from November 2015 to September 2016 with complete data for 168. The mean age was 59 years (standard deviation, 7 years), and 90% of colonoscopies were conducted for screening/surveillance. Only 17% and 77% of patients complied with diet restrictions 2 and 1 day(s) before colonoscopy, respectively. We found no association between foods consumed 2 and 3 days before colonoscopy and BBPS scores. However, BPPS was positively associated with intake of gelatin, and inversely associated with intake of red meat, poultry, and vegetables on the day before colonoscopy.
CONCLUSIONS: Our findings support recent guidelines encouraging unrestricted diets >1 day before colonoscopy if using a split-dose bowel regimen. Furthermore, we found no evidence to restrict dietary fiber 1 day before colonoscopy. We also found evidence to promote consumption of gelatin and avoidance of red meat, poultry, and vegetables 1 day before colonoscopy.Dr Jacobson has acted as a consultant for MOTUS GI and Remedy Partners. All other authors disclosed no financial relationships relevant to this publication. Supported by NIH/NIDDK R21DK105476. (R21DK105476 - NIH/NIDDK)Accepted manuscrip
On the effects of the Dvali-Gabadadze-Porrati braneworld gravity on the orbital motion of a test particle
In this paper we explicitly work out the secular perturbations induced on all
the Keplerian orbital elements of a test body to order O(e^2) in the
eccentricity e by the weak-field long-range modifications of the usual
Newton-Einstein gravity due to the Dvali-Gabadadze-Porrati (DGP) braneworld
model. The Gauss perturbative scheme is used. It turns out that the argument of
pericentre and the mean anomaly are affected by secular rates which are
independent of the semimajor axis of the orbit of the test particle. The first
nonvaishing eccentricity-dependent corrections are of order O(e^2). For
circular orbits the Lue-Starkman (LS) effect on the pericentre is obtained.
Some observational consequences are discussed for the Solar System planetary
mean longitudes lambda which would undergo a 1.2\cdot 10^-3 arcseconds per
century braneworld secular precession. According to recent data analysis over
92 years for the EPM2004 ephemerides, the 1-sigma formal accuracy in
determining the Martian mean longitude amounts to 3\cdot 10^-3 milliarcseconds,
while the braneworld effect over the same time span would be 1.159
milliarcseconds. The major limiting factor is the 2.6\cdot 10^-3 arcseconds per
century systematic error due to the mismodelling in the Keplerian mean motion
of Mars. A suitable linear combination of the mean longitudes of Mars and Venus
may overcome this problem. The formal, 1-sigma obtainable observational
accuracy would be \sim 7%. The systematic error due to the present-day
uncertainties in the solar quadrupole mass moment, the Keplerian mean motions,
the general relativistic Schwarzschild field and the asteroid ring would amount
to some tens of percent.Comment: LaTex2e, 23 pages, 5 tables, 1 figure, 37 references. Second-order
corrections in eccentricity explicitly added. Typos corrected. References
update
Stochastically Fluctuating Black-Hole Geometry, Hawking Radiation and the Trans-Planckian Problem
We study the propagation of null rays and massless fields in a black hole
fluctuating geometry. The metric fluctuations are induced by a small
oscillating incoming flux of energy. The flux also induces black hole mass
oscillations around its average value. We assume that the metric fluctuations
are described by a statistical ensemble. The stochastic variables are the
phases and the amplitudes of Fourier modes of the fluctuations. By averaging
over these variables, we obtain an effective propagation for massless fields
which is characterized by a critical length defined by the amplitude of the
metric fluctuations: Smooth wave packets with respect to this length are not
significantly affected when they are propagated forward in time. Concomitantly,
we find that the asymptotic properties of Hawking radiation are not severely
modified. However, backward propagated wave packets are dissipated by the
metric fluctuations once their blue shifted frequency reaches the inverse
critical length. All these properties bear many resemblences with those
obtained in models for black hole radiation based on a modified dispersion
relation. This strongly suggests that the physical origin of these models,
which were introduced to confront the trans-Planckian problem, comes from the
fluctuations of the black hole geometry.Comment: 32 page
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