1,049 research outputs found
Numerical wave propagation for the triangular - finite element pair
Inertia-gravity mode and Rossby mode dispersion properties are examined for
discretisations of the linearized rotating shallow-water equations using the
- finite element pair on arbitrary triangulations in planar
geometry. A discrete Helmholtz decomposition of the functions in the velocity
space based on potentials taken from the pressure space is used to provide a
complete description of the numerical wave propagation for the discretised
equations. In the -plane case, this decomposition is used to obtain
decoupled equations for the geostrophic modes, the inertia-gravity modes, and
the inertial oscillations. As has been noticed previously, the geostrophic
modes are steady. The Helmholtz decomposition is used to show that the
resulting inertia-gravity wave equation is third-order accurate in space. In
general the \pdgp finite element pair is second-order accurate, so this leads
to very accurate wave propagation. It is further shown that the only spurious
modes supported by this discretisation are spurious inertial oscillations which
have frequency , and which do not propagate. The Helmholtz decomposition
also allows a simple derivation of the quasi-geostrophic limit of the
discretised - equations in the -plane case, resulting in a
Rossby wave equation which is also third-order accurate.Comment: Revised version prior to final journal submissio
Thin-film and marginal lubrication of PolyEtherKetone-steel sliding contacts at high temperature and high speed
YesPolyEtherKetone (PEK) is a suitable material for tribological systems which specifically require
the properties of high chemical resistance, low component weight, seizure resistance under
starved lubrication conditions and operation at higher temperatures than many other engineering
polymers can survive. PEK is used with a liquid lubricant at high temperatures and
velocities to reduce friction and also to control unstable friction and wear, particularly in the
region of the material’s glass transition temperature, Tg.
Intermittent and marginal lubrication using representative high temperature synthetic lubricants
was applied to high speed, high temperature PEK/steel sliding contacts to determine the
effectiveness of lubrication under these conditions. Variations in the stability of the thin lubricant
films were observed, particularly under different load conditions. Under low load conditions,
the lubricant polarity and the related ability to form a film in the contact was important.
Under high load conditions, the thermal stability of the lubricant became more important in
retaining stability in the friction and wear mechanisms. Whilst not ideal practice, marginal lubrication
of PEK-steel sliding contacts can be achieved by selection of an appropriate lubricant,
even in the glass transition region of PEK.Innovate UK Knowledge Transfer Partnership (KTP) grant, No. 8092
Recommended from our members
Representative tribometer testing of wire rope fretting contacts: the effect of lubrication on fretting wear
YesFretting wear has a significant influence on wire rope fatigue life when in cyclic bending, particularly for crossed-wire
contacts, where the interfacial motion of the surfaces is complex and multi-axial. To simulate these contacts in a
controlled manner, a laboratory-scale, crossed-cylinder, reciprocating fretting wear test was developed. A broad range of
contemporary lubrication technologies were evaluated using this method and a systematic multivariate statistical analysis
was performed to identify the most significant lubrication-related parameters with respect to these fretting wear
conditions. Wear area increase per slip cycle was the most relevant measure of wear damage, as this captured the
influence of changes in the fretting wear regime during the test. The ability of a lubricant to reduce damaging fretting
wear during the run-in phase was the biggest influence on long-term fretting wear, particularly for grease-lubricated
contacts
The effect of distraction, response mode and age on peripheral target detection to inform studies of lighting for driving
It is expected that the detection of peripheral objects, a key visual task for safe driving, is affected by cognitive distraction, by observer age and by the manner in which action is undertaken following detection. An experiment was conducted to measure these effects, using a fixation cross and peripheral target discs displayed on a screen. The experiment was repeated with young (18–25 years) and old (60+years) age groups, with six distraction tasks, and with simple and choice response modes. The older group was found to respond more slowly than the younger group and detected fewer targets. The results suggest that distraction impairs detection, with the degree of impairment depending on the difficulty of the distraction task. Participants were generally slower at responding with choice response but this did not lead to a greater number of missed targets. Where lighting standards are informed by the ability to detect peripheral hazards, the research should represent older people, choice responses and impaired detection due to distraction
A Novel Sparse Graphical Approach for Multimodal Brain Connectivity Inference
International audienceDespite the clear potential benefits of combining fMRI and diffusion MRI in learning the neural pathways that underlie brain functions, little methodological progress has been made in this direction. In this paper, we propose a novel multimodal integration approach based on sparse Gaussian graphical model for estimating brain connectivity. Casting functional connectivity estimation as a sparse inverse covariance learning problem, we adapt the level of sparse penalization on each connection based on its anatomical capacity for functional interactions. Functional connections with little anatomical support are thus more heavily penalized. For validation, we showed on real data collected from a cohort of 60 subjects that additionally modeling anatomical capacity significantly increases subject consistency in the detected connection patterns. Moreover, we demonstrated that incorporating a connectivity prior learned with our multimodal connectivity estimation approach improves activation detection
Predicting the Presence of Companions for Stripped-envelope Supernovae:The Case of the Broad-lined Type Ic SN 2002ap
Integromic analysis of genetic variation and gene expression identifies networks for cardiovascular disease phenotypes
BACKGROUND - : Cardiovascular disease (CVD) reflects a highly coordinated complex of traits. Although genome-wide association studies have reported numerous single nucleotide polymorphisms (SNPs) to be associated with CVD, the role of most of these variants in disease processes remains unknown. METHODS AND RESULTS - : We built a CVD network using 1512 SNPs associated with 21 CVD traits in genome-wide association studies (at P≤5×10) and cross-linked different traits by virtue of their shared SNP associations. We then explored whole blood gene expression in relation to these SNPs in 5257 participants in the Framingham Heart Study. At a false discovery rate <0.05, we identified 370 cis-expression quantitative trait loci (eQTLs; SNPs associated with altered expression of nearby genes) and 44 trans-eQTLs (SNPs associated with altered expression of remote genes). The eQTL network revealed 13 CVD-related modules. Searching for association of eQTL genes with CVD risk factors (lipids, blood pressure, fasting blood glucose, and body mass index) in the same individuals, we found examples in which the expression of eQTL genes was significantly associated with these CVD phenotypes. In addition, mediation tests suggested that a subset of SNPs previously associated with CVD phenotypes in genome-wide association studies may exert their function by altering expression of eQTL genes (eg, LDLR and PCSK7), which in turn may promote interindividual variation in phenotypes. CONCLUSIONS - : Using a network approach to analyze CVD traits, we identified complex networks of SNP-phenotype and SNP-transcript connections. Integrating the CVD network with phenotypic data, we identified biological pathways that may provide insights into potential drug targets for treatment or prevention of CVD
Effect of tensor couplings in a relativistic Hartree approach for finite nuclei
The relativistic Hartree approach describing the bound states of both
nucleons and anti-nucleons in finite nuclei has been extended to include tensor
couplings for the - and -meson. After readjusting the parameters
of the model to the properties of spherical nuclei, the effect of
tensor-coupling terms rises the spin-orbit force by a factor of 2, while a
large effective nucleon mass sustains. The overall
nucleon spectra of shell-model states are improved evidently. The predicted
anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include
Differential cross sections, charge production asymmetry, and spin-density matrix elements for D*(2010) produced in 500 GeV/c pi^- nucleon interactions
We report differential cross sections for the production of D*(2010) produced
in 500 GeV/c pi^- nucleon interactions from experiment E791 at Fermilab, as
functions of Feynman-x (x_F) and transverse momentum squared (p_T^2). We also
report the D* +/- charge asymmetry and spin-density matrix elements as
functions of these variables. Investigation of the spin-density matrix elements
shows no evidence of polarization. The average values of the spin alignment are
\eta= 0.01 +- 0.02 and -0.01 +- 0.02 for leading and non-leading particles,
respectively.Comment: LaTeX2e (elsart.cls). 13 pages, 6 figures (eps files). Submitted to
Physics Letters
The delta-function-kicked rotor: Momentum diffusion and the quantum-classical boundary
We investigate the quantum-classical transition in the delta-kicked rotor and
the attainment of the classical limit in terms of measurement-induced
state-localization. It is possible to study the transition by fixing the
environmentally induced disturbance at a sufficiently small value, and
examining the dynamics as the system is made more macroscopic. When the system
action is relatively small, the dynamics is quantum mechanical and when the
system action is sufficiently large there is a transition to classical
behavior. The dynamics of the rotor in the region of transition, characterized
by the late-time momentum diffusion coefficient, can be strikingly different
from both the purely quantum and classical results. Remarkably, the early time
diffusive behavior of the quantum system, even when different from its
classical counterpart, is stabilized by the continuous measurement process.
This shows that such measurements can succeed in extracting essentially quantum
effects. The transition regime studied in this paper is accessible in ongoing
experiments.Comment: 8 pages, 4 figures, revtex4 (revised version contains much more
introductory material
- …