110 research outputs found
Molecular dynamics simulations of ultrathin water film confined between flat diamond plates
Molecular dynamics simulations of ultrathin water film confined between
atomically flat rigid diamond plates are described. Films with thickness of one
and two molecular diameters are concerned and TIP4P model is used for water
molecules. Dynamical and equilibrium characteristics of the system for
different values of the external load and shear force are investigated. An
increase of the external load causes the transition of the film to a solidlike
state. This is manifested in the decreasing of the diffusion constant and in
the ordering of the liquid molecules into quasidiscrete layers. For two-layer
film under high loads molecules also become ordered parallel to the surfaces.
Time dependencies of the friction force and the changes of its average value
with the load are obtained. In general, the behaviour of the studied model is
consistent with the experimental results obtained for simple liquids with
spherical molecules.Comment: 10 pages, 9 figures, PDFLaTe
Finite-size scaling in the interfacial stiffness of rough elastic contacts
The total elastic stiffness of two contacting bodies with a microscopically
rough interface has an interfacial contribution K that is entirely attributable
to surface roughness. A quantitative understanding of K is important because it
can dominate the total mechanical response and because it is proportional to
the interfacial contributions to electrical and thermal conductivity in
continuum theory. Numerical simulations of the dependence of K on the applied
squeezing pressure p are presented for nominally flat elastic solids with a
range of surface roughnesses. Over a wide range of p, K rises linearly with p.
Sublinear power-law scaling is observed at small p, but the simulations reveal
that this is a finite-size effect. We derive accurate, analytical expressions
for the exponents and prefactors of this low-pressure scaling of K by extending
the contact mechanics theory of Persson to systems of finite size. In agreement
with our simulations, these expressions show that the onset of the low-pressure
scaling regime moves to lower pressure as the system size increases.Comment: Supplementary material is available at arXiv:1210.4255, 5 pages, 3
figure
Planetary and Light Motions From Newtoinian Theory: An Amusing Exercise
We attempt to see how closely we can formally obtain the planetary and light
path equations of General Relativity by employing certain operations on the
familiar Newtonian equation. This article is intended neither as an alternative
to nor as a tool for grasping Einstein's General Relativity. Though the
exercise is understandable by readers at large, it is especially recommended to
the teachers of Relativity for an appreciative understanding of its peculiarity
as well as its pedagogical value in the teaching of differential equations.Comment: 7 page
Interfacial separation between elastic solids with randomly rough surfaces: comparison between theory and numerical techniques
We study the distribution of interfacial separations P(u) at the contact
region between two elastic solids with randomly rough surfaces. An analytical
expression is derived for P(u) using Persson's theory of contact mechanics, and
is compared to numerical solutions obtained using (a) a half-space method based
on the Boussinesq equation, (b) a Green's function molecular dynamics technique
and (c) smart-block classical molecular dynamics. Overall, we find good
agreement between all the different approaches.Comment: 25 pages, 12 figure
Induced Parity Breaking Term in Arbitrary Odd Dimensions at Finite Temperature
We calculate the exact parity odd part of the effective action
() for massive Dirac fermions in 2d+1 dimensions at finite
temperature, for a certain class of gauge field configurations. We consider
first Abelian external gauge fields, and then we deal with the case of a
non-Abelian gauge group containing an Abelian U(1) subgroup. For both cases, it
is possible to show that the result depends on topological invariants of the
gauge field configurations, and that the gauge transformation properties of
depend only on those invariants and on the winding number
of the gauge transformation.Comment: 10 pages, revtex, no figure
Recurrent Disease in Patients With Sporadic Pheochromocytoma and Paraganglioma
Supplemental Appendix for manuscript 'Recurrent disease in patients with sporadic pheochromocytoma and paraganglioma
Determinants of disease-specific survival in patients with and without metastatic pheochromocytoma and paraganglioma
BACKGROUND: Pheochromocytomas and paragangliomas (PPGLs) have a heterogeneous prognosis, the basis of which remains unclear. We, therefore, assessed disease-specific survival (DSS) and potential predictors of progressive disease in patients with PPGLs and head/neck paragangliomas (HNPGLs) according to the presence or absence of metastases. METHODS: This retrospective study included 582 patients with PPGLs and 57 with HNPGLs. DSS was assessed according to age, location and size of tumours, recurrent/metastatic disease, genetics, plasma metanephrines and methoxytyramine. RESULTS: Among all patients with PPGLs, multivariable analysis indicated that apart from older age (HR = 5.4, CI = 2.93-10.29, P < 0.0001) and presence of metastases (HR = 4.8, CI = 2.41-9.94, P < 0.0001), shorter DSS was also associated with extra-adrenal tumour location (HR = 2.6, CI = 1.32-5.23, P = 0.0007) and higher plasma methoxytyramine (HR = 1.8, CI = 1.11-2.85, P = 0.0170) and normetanephrine (HR = 1.8, CI = 1.12-2.91, P = 0.0160). Among patients with HNPGLs, those with metastases presented with longer DSS compared to patients with metastatic PPGLs (33.4 versus 20.2 years, P < 0.0001) and only plasma methoxytyramine (HR = 13, CI = 1.35-148, P = 0.0380) was an independent predictor of DSS. For patients with metastatic PPGLs, multivariable analysis revealed that apart from older age (HR = 6.2, CI = 3.20-12.20, P < 0.0001), shorter DSS was associated with the presence of synchronous metastases (HR = 4.9, CI = 2.78-8.80, P < 0.0001), higher plasma methoxytyramine (HR = 2.4, CI = 1.44-4.14, P = 0.0010) and extensive metastatic burden (HR = 2.1, CI = 1.07-3.79, P = 0.0290). CONCLUSIONS: DSS among patients with PPGLs/HNPGLs relates to several presentations of the disease that may provide prognostic markers. In particular, the independent associations of higher methoxytyramine with shorter DSS in patients with HNPGLs and metastatic PPGLs suggest the utility of this biomarker to guide individualized management and follow-up strategies in affected patients
- …