14,334 research outputs found
Non-linear rheology of a nanoconfined simple fluid
We probe the rheology of the model liquid octamethylcyclotetrasiloxane
(OMCTS) confined into molecularly thin films, using a unique Surface Forces
Apparatus allowing to explore a large range of shear rates and confinement. We
thus show that OMCTS under increasing confinement exhibits the viscosity
enhancement and the non-linear flow properties characteristic of a sheared
supercooled liquid approaching its glass transition. Besides, we study the
drainage of confined OMCTS via the propagation of "squeeze-out" fronts. The
hydrodynamic model proposed by Becker and Mugele [Phys. Rev. Lett. {\bf 91},
166104 (2003)] to describe such front dynamics leads to a conclusion in
apparent contradiction with the dynamical slowdown evidenced by rheology
measurements, which suggests that front propagation is not controlled by large
scale flow in the confined films
Frictional dissipation of polymeric solids vs interfacial glass transition
We present single contact friction experiments between a glassy polymer and
smooth silica substrates grafted with alkylsilane layers of different coverage
densities and morphologies. This allows us to adjust the polymer/substrate
interaction strength. We find that, when going from weak to strong interaction,
the response of the interfacial junction where shear localizes evolves from
that of a highly viscous threshold fluid to that of a plastically deformed
glassy solid. This we analyse as resulting from an interaction-induced
``interfacial glass transition'' helped by pressure
Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses
Temperature modulated Alternating Differential Scanning Calorimetric (ADSC)
studies show that Se rich Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses are
microscopically phase separated, containing Ag2Se phases embedded in a
Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase
percolates in the Ge-Se matrix, with a well-defined percolation threshold at x
= 0.10. A signature of this percolation transition is shown up in the thermal
behavior, as the appearance of two exothermic crystallization peaks. Density,
molar volume and micro-hardness measurements, undertaken in the present study,
also strongly support this view of percolation transition. The super-ionic
conduction observed earlier in these glasses at higher silver proportions, is
likely to be connected with the silver phase percolation.Comment: 4 pages, 7 figure
Rate effects on layering of a confined linear alkane
We perform drainage experiments of a linear alkane fluid (n-hexadecane) down
to molecular thicknesses, and focus on the role played by the confinement rate.
We show that molecular layering is strongly influenced by the velocity at which
the confining walls are approached: under high enough shear rates, the confined
medium behaves as a structureless liquid of enhanced viscosity for film
thickness below 10 nm. Our results also lead us to conclude that a
rapidly confined film can be quenched in a metastable disordered state, which
might be related with recent intriguing results on the shear properties of
confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett.
{\bf 93}, 096101 (2004)]
The algebraic and Hamiltonian structure of the dispersionless Benney and Toda hierarchies
The algebraic and Hamiltonian structures of the multicomponent dispersionless
Benney and Toda hierarchies are studied. This is achieved by using a modified
set of variables for which there is a symmetry between the basic fields. This
symmetry enables formulae normally given implicitly in terms of residues, such
as conserved charges and fluxes, to be calculated explicitly. As a corollary of
these results the equivalence of the Benney and Toda hierarchies is
established. It is further shown that such quantities may be expressed in terms
of generalized hypergeometric functions, the simplest example involving
Legendre polynomials. These results are then extended to systems derived from a
rational Lax function and a logarithmic function. Various reductions are also
studied.Comment: 29 pages, LaTe
Long-term weight maintenance and cardiovascular risk factors are not different following weight loss on carbohydrate-restricted diets high in either monounsaturated fat or protein in obese hyperinsulinaemic men and women
The aim of this study was to determine after 52 weeks whether advice to follow a lower carbohydrate diet, either high in monounsaturated fat or low fat, high in protein had differential effects in a free-living community setting. Following weight loss on either a high monounsaturated fat, standard protein (HMF; 50 % fat, 20 % protein (67 g/d), 30 % carbohydrate) or a high protein, moderate fat (HP) (40 % protein (136 g/d), 30 % fat, 30 % carbohydrate) energy-restricted diet (6000 kJ/d) subjects were asked to maintain the same dietary pattern without intensive dietary counselling for the following 36 weeks. Overall weight loss was 6·2 (sd 7·3) kg (P < 0·01 for time with no diet effect, 7·6 (sd 8·1) kg, HMF v. 4·8 (sd 6·6) kg, HP). In a multivariate regression model predictors of weight loss at the end of the study were sex, age and reported percentage energy from protein (R2 0·22, P < 0·05 for the whole model). Fasting plasma insulin decreased (P < 0·01, with no difference between diets), 13·9 (sd 4·6) to 10·2 (sd 5·2) mIU/l, but fasting plasma glucose was not reduced. Neither total cholesterol nor LDL-cholesterol were different but HDL was higher, 1·19 (sd 0·26) v. 1·04 (sd 0·29) (P < 0·001 for time, no diet effect), while TAG was lower, 1·87 (sd 1·23) v. 2·22 (sd 1·15) mmol/l (P < 0·05 for time, no diet effect). C-reactive protein decreased (3·97 (sd 2·84) to 2·43 (sd 2·29) mg/l, P < 0·01). Food records showed that compliance to the prescribed dietary patterns was poor. After 1 year there remained a clinically significant weight loss and improvement in cardiovascular risk factors with no adverse effects of a high monounsaturated fat diet.Jennifer B. Keogh, Natalie D. Luscombe-Marsh, Manny Noakes, Gary A. Wittert and Peter M. Clifto
Developing Intensity-Duration-Frequency (IDF) Curves From Satellite-Based Precipitation: Methodology and Evaluation
Given the continuous advancement in the retrieval of precipitation from satellites, it is important to develop methods that incorporate satellite-based precipitation data sets in the design and planning of infrastructure. This is because in many regions around the world, in situ rainfall observations are sparse and have insufficient record length. A handful of studies examined the use of satellite-based precipitation to develop intensity-duration-frequency (IDF) curves; however, they have mostly focused on small spatial domains and relied on combining satellite-based with ground-based precipitation data sets. In this study, we explore this issue by providing a methodological framework with the potential to be applied in ungauged regions. This framework is based on accounting for the characteristics of satellite-based precipitation products, namely, adjustment of bias and transformation of areal to point rainfall. The latter method is based on previous studies on the reverse transformation (point to areal) commonly used to obtain catchment-scale IDF curves. The paper proceeds by applying this framework to develop IDF curves over the contiguous United States (CONUS); the data set used is Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks – Climate Data Record (PERSIANN-CDR). IDFs are then evaluated against National Oceanic and Atmospheric Administration (NOAA) Atlas 14 to provide a quantitative estimate of their accuracy. Results show that median errors are in the range of (17–22%), (6–12%), and (3–8%) for one-day, two-day and three-day IDFs, respectively, and return periods in the range (2–100) years. Furthermore, a considerable percentage of satellite-based IDFs lie within the confidence interval of NOAA Atlas 14
Non-Schlesinger Deformations of Ordinary Differential Equations with Rational Coefficients
We consider deformations of and matrix linear ODEs with
rational coefficients with respect to singular points of Fuchsian type which
don't satisfy the well-known system of Schlesinger equations (or its natural
generalization). Some general statements concerning reducibility of such
deformations for ODEs are proved. An explicit example of the general
non-Schlesinger deformation of -matrix ODE of the Fuchsian type with
4 singular points is constructed and application of such deformations to the
construction of special solutions of the corresponding Schlesinger systems is
discussed. Some examples of isomonodromy and non-isomonodromy deformations of
matrix ODEs are considered. The latter arise as the compatibility
conditions with linear ODEs with non-singlevalued coefficients.Comment: 15 pages, to appear in J. Phys.
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