31,245 research outputs found
Thrust reverser for a long duct fan engine
A bypass duct outer cowl includes a fixed cascade disposed between axially spaced fixed cowl portions and a translatable cowl sleeve and blocker doors movably disposed on the respective radially outer and inner sides of the cascade. Actuation and linkage structure located entirely within the outer cowl provides for selectively moving the cowl sleeve rearwardly and rotating the blocker doors to a position across the bypass duct to cause the fan airflow to pass through the cascade in a thrust reversing manner
Combustion chemistry of solid propellants
Several studies are described of the chemistry of solid propellant combustion which employed a fast-scanning optical spectrometer. Expanded abstracts are presented for four of the studies which were previously reported. One study of the ignition of composite propellants yielded data which suggested early ammonium perchlorate decomposition and reaction. The results of a study of the spatial distribution of molecular species in flames from uncatalyzed and copper or lead catalyzed double-based propellants support previously published conclusions concerning the site of action of these metal catalysts. A study of the ammonium-perchlorate-polymeric-fuel-binder reaction in thin films, made by use of infrared absorption spectrometry, yielded a characterization of a rapid condensed-phase reaction which is likely important during the ignition transient and the burning process
Surgical salvage in patients with advanced testicular cancer: indications, risks and outcomes
The purpose of this review is to present a comprehensive and updated review of the literature and summary of the indications, risks and outcomes related to salvage, desperation and late relapse surgery for advanced testicular cancer. After completing a thorough review of the current literature, this review has attempted to provide an overview of the indications for salvage, desperation and late relapse retroperitoneal lymph node dissection (RPLND) followed by a summary of the histopathologic and clinical outcomes regarding each. Recent literature, combined with a significant contribution from historical studies suggest that while testicular cancer is a relatively uncommon malignancy overall, it represents the most common solid organ malignancy for young men. Although a significant number of men are cured with a combination of first-line treatments, the remaining men are a diverse and often challenging cohort who require the benefit of expertise to improve their outcomes. The role of surgical strategies in the salvage, desperation and late relapse settings is unquestionable, although the most important question remains who will benefit. This often requires a multi-disciplinary approach at centers specializing in this disease process in order to recognize who should get surgery, what surgery to do and how to minimize the potential morbidity associated with the operation
Ammonium-perchlorate diffusion flames - A spectrographic investigation
Spectroscopic analyses on ammonium perchlorate diffusion flames with various fuel
Radiation-reaction-induced evolution of circular orbits of particles around Kerr Black Holes
It is demonstrated that, in the adiabatic approximation, non-Equatorial
circular orbits of particles in the Kerr metric (i.e. orbits of constant
Boyer-Lindquist radius) remain circular under the influence of gravitational
radiation reaction. A brief discussion is given of conditions for breakdown of
adiabaticity and of whether slightly non-circular orbits are stable against the
growth of eccentricity.Comment: 23 pages. Revtex 3.0. Inquiries to [email protected]
A Proof of Entropy Minimization for Outputs in Deletion Channels via Hidden Word Statistics
From the output produced by a memoryless deletion channel from a uniformly
random input of known length , one obtains a posterior distribution on the
channel input. The difference between the Shannon entropy of this distribution
and that of the uniform prior measures the amount of information about the
channel input which is conveyed by the output of length , and it is natural
to ask for which outputs this is extremized. This question was posed in a
previous work, where it was conjectured on the basis of experimental data that
the entropy of the posterior is minimized and maximized by the constant strings
and and the alternating strings
and respectively. In the present
work we confirm the minimization conjecture in the asymptotic limit using
results from hidden word statistics. We show how the analytic-combinatorial
methods of Flajolet, Szpankowski and Vall\'ee for dealing with the hidden
pattern matching problem can be applied to resolve the case of fixed output
length and , by obtaining estimates for the entropy in
terms of the moments of the posterior distribution and establishing its
minimization via a measure of autocorrelation.Comment: 11 pages, 2 figure
Risk evaluations and condom use decisions of homeless youth: a multi-level qualitative investigation.
BackgroundHomeless youth are at higher risk for sexually transmitted infections and unwanted pregnancy than non-homeless youth. However, little is known about how they evaluate risk within the context of their sexual relationships. It is important to understand homeless youths' condom use decisions in light of their sexual relationships because condom use decisions are influenced by relationship dynamics in addition to individual attitudes and event circumstances. It is also important to understand how relationship level factors, sexual event circumstances, and individual characteristics compare and intersect.MethodsTo explore these issues, we conducted semi-structured interviews with 37 homeless youth in Los Angeles County in 2011 concerning their recent sexual relationships and analyzed the data using systematic methods of team-based qualitative data analysis.ResultsWe identified themes of risk-related evaluations and decisions at the relationship/partner, event, and individual level. We also identified three different risk profiles that emerged from analyzing how different levels of risk intersected across individual respondents. The three profiles included 1) Risk Takers, who consistently engage in risk and have low concern about consequences of risk behavior, 2) Risk Avoiders, who consistently show high concern about protection and consistently avoid risk, and 3) Risk Reactors, those who are inconsistent in their concerns about risk and protection and mainly take risks in reaction to relationship and event circumstances.ConclusionsInterventions targeting homeless youth should reflect multiple levels of risk behavior and evaluation in order to address the diversity of risk profiles. Relationship/partner-, event-, and individual-level factors are all important but have different levels of importance for different homeless youth. Interventions should be tailored to address the most important factor contributing to homeless youth reproductive needs
A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283
Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron
capture processes: the s- and r-process. Metal-poor stars should contain fewer
isotopes that form via the s-process, according to currently accepted theory.
It has been shown in several investigations that theory and observation do not
agree well, raising questions on the validity of either the methodology or the
theory. We analyse the metal-poor star HD140283, for which we have a high
quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum
synthesis code permits a more reliable analysis of the iron abundance and
barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we
examine 91 iron lines of varying strength and formation depth. This provides us
with the star's rotational speed. With this, we model the barium isotope ratio
by exploiting the hyperfine structure of the singly ionised 4554 resonance
line, and study the impact of the uncertainties in the stellar parameters.
HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm
show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form
via the r-process, where errors represent the assigned random and systematic
errors, respectively. We find that 3D LTE fits reproduce iron line profiles
better than those in 1D, but do not provide a unique abundance (within the
uncertainties). However, we demonstrate that the isotopic ratio is robust
against this shortcoming. Our barium isotope result agrees well with currently
accepted theory regarding the formation of the heavy-elements during the early
Galaxy. The improved fit to the asymmetric iron line profiles suggests that the
current state of 3D LTE modelling provides excellent simulations of fluid
flows. However, the abundances they provide are not yet self-consistent. This
may improve with NLTE considerations and higher resolution models.Comment: 16 pages, 10 figures, 5 tables. Accepted for publication in A&
Simultaneous Arithmetic Progressions on Algebraic Curves
A simultaneous arithmetic progression (s.a.p.) of length k consists of k
points (x_i, y_\sigma(i)), where x_i and y_i are arithmetic progressions and
\sigma is a permutation. Garcia-Selfa and Tornero asked whether there is a
bound on the length of an s.a.p. on an elliptic curve in Weierstrass form over
Q. We show that 4319 is such a bound for curves over R. This is done by
considering translates of the curve in a grid as a graph. A simple upper bound
is found for the number of crossings and the 'crossing inequality' gives a
lower bound. Together these bound the length of an s.a.p. on the curve. We then
use a similar method to extend the result to arbitrary real algebraic curves.
Instead of considering s.a.p.'s we consider k^2/3 points in a grid. The number
of crossings is bounded by Bezout's Theorem. We then give another proof using a
result of Jarnik bounding the number of grid points on a convex curve. This
result applies as any real algebraic curve can be broken up into convex and
concave parts, the number of which depend on the degree. Lastly, these results
are extended to complex algebraic curves.Comment: 11 pages, 6 figures, order of email addresses corrected 12 pages,
closing remarks, a reference and an acknowledgment adde
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