3,595 research outputs found
Aspect ratio dependence of heat transport by turbulent Rayleigh-B\'{e}nard convection in rectangular cells
We report high-precision measurements of the Nusselt number as a
function of the Rayleigh number in water-filled rectangular
Rayleigh-B\'{e}nard convection cells. The horizontal length and width
of the cells are 50.0 cm and 15.0 cm, respectively, and the heights ,
25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios
, , ,
, , and . The measurements were carried out
over the Rayleigh number range and the
Prandtl number range . Our results show that for
rectangular geometry turbulent heat transport is independent of the cells'
aspect ratios and hence is insensitive to the nature and structures of the
large-scale mean flows of the system. This is slightly different from the
observations in cylindrical cells where is found to be in general a
decreasing function of , at least for and larger. Such a
difference is probably a manifestation of the finite plate conductivity effect.
Corrections for the influence of the finite conductivity of the top and bottom
plates are made to obtain the estimates of for plates with
perfect conductivity. The local scaling exponents of are calculated and found to increase from 0.243 at
to 0.327 at .Comment: 15 pages, 7 figures, Accepted by Journal of Fluid Mechanic
N′-(4-Fluorobenzylidene)acetohydrazide
The title compound, C9H9FN2O, was prepared by the reaction of 4-fluorobenzophenone and acethydrazide. In the molecule, all non-H atoms are essentially coplanar [r.m.s. deviation = 0.065 (2) Å]. In the crystal, molecules are linked into centrosymmetric dimers by pairs of intermolecular N—H⋯O hydrogen bonds
Experimental Investigation of Longitudinal Space-Time Correlations of the Velocity Field in Turbulent Rayleigh-B\'{e}nard Convection
We report an experimental investigation of the longitudinal space-time
cross-correlation function of the velocity field, , in a cylindrical
turbulent Rayleigh-B\'{e}nard convection cell using the particle image
velocimetry (PIV) technique. We show that while the Taylor's frozen-flow
hypothesis does not hold in turbulent thermal convection, the recent elliptic
model advanced for turbulent shear flows [He & Zhang, \emph{Phys. Rev. E}
\textbf{73}, 055303(R) (2006)] is valid for the present velocity field for all
over the cell, i.e., the isocorrelation contours of the measured
have a shape of elliptical curves and hence can be related to
via with and
being two characteristic velocities. We further show that the fitted is
proportional to the mean velocity of the flow, but the values of are
larger than the theoretical predictions. Specifically, we focus on two
representative regions in the cell: the region near the cell sidewall and the
cell's central region. It is found that and are approximately
the same near the sidewall, while at cell center.Comment: 16 pages, 15 figures, submitted to J. Fluid Mec
N′-[1-(4-Chlorophenyl)ethylidene]acetohydrazide
In the title compound, C10H11ClN2O, the dihedral angle between the acetohydrazide group and the aromatic ring is 33.76 (9)°. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R
2
2(8) loops
Geometric bionics: Lotus effect helps polystyrene nanotube films get good blood compatibility
Various biomaterials have been widely used for manufacturing biomedical applications including artificial organs, medical devices and disposable clinical apparatus, such as vascular prostheses, blood pumps, artificial kidney, artificial hearts, dialyzers and plasma separators, which could be used in contact with blood^1^. However, the research tasks of improving hemocompatibility of biomaterials have been carrying out with the development of biomedical requirements^2^. Since the interactions that lead to surface-induced thrombosis occurring at the blood-biomaterial interface become a reason of familiar current complications with grafts therapy, improvement of the blood compatibility of artificial polymer surfaces is, therefore a major issue in biomaterials science^3^. After decades of focused research, various approaches of modifying biomaterial surfaces through chemical or biochemical methods to improve their hemocompatibility were obtained^1^. In this article, we report that polystyrene nanotube films with morphology similar to the papilla on lotus leaf can be used as blood-contacted biomaterials by virtue of Lotus effect^4^. Clearly, this idea, resulting from geometric bionics that mimicking the structure design of lotus leaf, is very novel technique for preparation of hemocompatible biomaterials
COCA: Classifier-Oriented Calibration for Source-Free Universal Domain Adaptation via Textual Prototype
Universal Domain Adaptation (UniDA) aims to distinguish common and private
classes between the source and target domains where domain shift exists.
Recently, due to more stringent data restrictions, researchers have introduced
Source-Free UniDA (SF-UniDA) in more realistic scenarios. SF-UniDA methods
eliminate the need for direct access to source samples when performing
adaptation to the target domain. However, existing SF-UniDA methods still
require an extensive quantity of labeled source samples to train a source
model, resulting in significant labeling costs. To tackle this issue, we
present a novel Classifier-Oriented Calibration (COCA) method. This method,
which leverages textual prototypes, is formulated for the source model based on
few-shot learning. Specifically, we propose studying few-shot learning, usually
explored for closed-set scenarios, to identify common and domain-private
classes despite a significant domain shift between source and target domains.
Essentially, we present a novel paradigm based on the vision-language model to
learn SF-UniDA and hugely reduce the labeling costs on the source domain.
Experimental results demonstrate that our approach outperforms state-of-the-art
UniDA and SF-UniDA models
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