1,395 research outputs found
Wear effects and mechanisms of soot-contaminated automotive lubricants
A study has been carried out to investigate the influence of soot-contaminated automotive lubricants in the wear process of a simulated engine valve train contact. Previous research on this topic has been mainly performed from a chemical point of view in fundamental studies, with insufficient relevance to real engine conditions, i.e. load and geometry. This study investigates the conditions under which wear occurs through specimen testing. The objective of the work was to understand the wear mechanisms that occur within the contaminated contact zone, to help in future development of a predictive wear model to assist in the valve-train design process. The effects of soot in lubricants have been tested using a reciprocating test-rig specifically designed for this application, where a steel disc is held in a bath of oil and a steel ball (replicating a valve train contact) is attached to a reciprocating arm. The materials, contact geometry and loading conditions are all related to specific conditions experienced within an engine's valve train. The testing was carried out under various contact conditions, using carbon black as a soot simulant. Wear measurements were taken during the tests and wear scar morphology was studied. The results have revealed how varying lubrication conditions changes the wear rate of engine components and determines the wear mechanism that dominates for specific situations
Determination of Li-6 -- He-4 interaction from multi-energy scattering data
We present the first successful potential model description of Li-6 -- He-4
scattering. The differential cross-sections for three energies and the vector
analyzing powers for two energies were fitted by a single potential with energy
dependent imaginary components. An essential ingredient is a set of Majorana
terms in each component. The potential was determined using a recently
developed direct data-to-potential inversion method which is a generalisation
of the IP S-matrix-to-potential inversion algorithm. We discuss the problems
related to this phenomenological approach, and discuss the relationship of our
results to existing and future theories.Comment: 9 pages plain LaTeX, 6 postscript figue
Supersymmetry from a braided point of view
We show that one-dimensional superspace is isomorphic to a non-trivial but
consistent limit as of the braided line. Supersymmetry is identified
as translational invariance along this line. The supertranslation generator and
covariant derivative are obtained in the limit in question as the left and
right derivatives of the calculus on the braided line.Comment: LateX file. 10 pages. To appear in Phys. Lett.
An Improved Description of the Dielectric Breakdown in Oxides Based on a Generalized Weibull distribution
In this work, we address modal parameter fluctuations in statistical
distributions describing charge-to-breakdown and/or
time-to-breakdown during the dielectric breakdown regime of
ultra-thin oxides, which are of high interest for the advancement of electronic
technology. We reobtain a generalized Weibull distribution (-Weibull), which
properly describes data when oxide thickness fluctuations are
present, in order to improve reliability assessment of ultra-thin oxides by
time-to-breakdown extrapolation and area scaling. The incorporation
of fluctuations allows a physical interpretation of the -Weibull
distribution in connection with the Tsallis statistics. In support to our
results, we analyze data of SiO-based MOS devices obtained
experimentally and theoretically through a percolation model, demonstrating an
advantageous description of the dielectric breakdown by the -Weibull
distribution.Comment: 5 pages, 3 figure
Mask formulas for cograssmannian Kazhdan-Lusztig polynomials
We give two contructions of sets of masks on cograssmannian permutations that
can be used in Deodhar's formula for Kazhdan-Lusztig basis elements of the
Iwahori-Hecke algebra. The constructions are respectively based on a formula of
Lascoux-Schutzenberger and its geometric interpretation by Zelevinsky. The
first construction relies on a basis of the Hecke algebra constructed from
principal lower order ideals in Bruhat order and a translation of this basis
into sets of masks. The second construction relies on an interpretation of
masks as cells of the Bott-Samelson resolution. These constructions give
distinct answers to a question of Deodhar.Comment: 43 page
Modeling water waves beyond perturbations
In this chapter, we illustrate the advantage of variational principles for
modeling water waves from an elementary practical viewpoint. The method is
based on a `relaxed' variational principle, i.e., on a Lagrangian involving as
many variables as possible, and imposing some suitable subordinate constraints.
This approach allows the construction of approximations without necessarily
relying on a small parameter. This is illustrated via simple examples, namely
the Serre equations in shallow water, a generalization of the Klein-Gordon
equation in deep water and how to unify these equations in arbitrary depth. The
chapter ends with a discussion and caution on how this approach should be used
in practice.Comment: 15 pages, 1 figure, 39 references. This document is a contributed
chapter to an upcoming volume to be published by Springer in Lecture Notes in
Physics Series. Other author's papers can be downloaded at
http://www.denys-dutykh.com
Recommended from our members
Thin film coatings which inhibit spin relaxation of polarized potassium atoms
A prototype of a polarized deuterium target which employs the spin exchange method is being developed. The mixing cell for mixing deuterium atoms and potassium vapor requires a surface that will reflect these atoms without being destroyed by the corrosive potassium. Thin film coating methods and a technique for coating pyrex are described. Results of spin relaxation measurements are given. (LEW
The measurement of liner - piston skirt oil film thickness by an ultrasonic means
The paper presents a novel method for the
measurement of lubricant film thickness in the
piston-liner contact. Direct measurement of the film
in this conjunction has always posed a problem,
particularly under fired conditions. The principle is
based on capturing and analysing the reflection of
an ultrasonic pulse at the oil film. The proportion of
the wave amplitude reflected can be related to the
thickness of the oil film. A single cylinder 4-stroke
engine on a dyno test platform was used for
evaluation of the method. A piezo-electric
transducer was bonded to the outside of the
cylinder liner and used to emit high frequency short
duration ultrasonic pulses. These pulses were used
to determine the oil film thickness as the piston
skirt passed over the sensor location. Oil films in the
range 2 to 21 ÎŒm were recorded varying with
engine speeds. The results have been shown to be
in agreement with detailed numerical predictions
Herd-level risk factors of bovine tuberculosis in England and Wales after the 2001 foot-and-mouth disease epidemic
We present the results of a 2005 caseâcontrol study of bovine tuberculosis (bTB) breakdowns in English and Welsh herds. The herd management, farming practices, and environmental factors of 401matched pairs of case and control herds were investigated to provide a picture of herd-level risk factors in areas of varying bTB incidence. A global conditional logistic regression model, with region-specific variants, was used to compare case herds that had experienced a confirmed bTB breakdown to contemporaneous control herds matched on region, herd type, herd size, and parish testing interval. Contacts with cattle from contiguous herds and sourcing cattle from herds with a recent history of bTB were associated with an increased risk in both the global and regional analyses. Operating a farm over several premises, providing cattle feed inside the housing, and the presence of badgers were also identified as significantly associated with an increased bTB risk. Steps taken to minimize cattle contacts with neighboring herds and altering trading practices could have the potential to reduce the size of the bTB epidemic. In principle, limiting the interactions between cattle and wildlife may also be useful; however this study did not highlight any specific measures to implement
- âŠ