9,976 research outputs found
Effective slip-length tensor for a flow over weakly slipping stripes
We discuss the flow past a flat heterogeneous solid surface decorated by
slipping stripes. The spatially varying slip length, , is assumed to be
small compared to the scale of the heterogeneities, , but finite. For such
"weakly" slipping surfaces, earlier analyses have predicted that the effective
slip length is simply given by the surface-averaged slip length, which implies
that the effective slip-length tensor becomes isotropic. Here we show that a
different scenario is expected if the local slip length has step-like jumps at
the edges of slipping heterogeneities. In this case, the next-to-leading term
in an expansion of the effective slip-length tensor in powers of
becomes comparable to the leading-order term, but
anisotropic, even at very small . This leads to an anisotropy of the
effective slip, and to its significant reduction compared to the
surface-averaged value. The asymptotic formulae are tested by numerical
solutions and are in agreement with results of dissipative particle dynamics
simulations.Comment: 11 pages, 4 figures, submitted to Phys. Rev.
Effective slippage on superhydrophobic trapezoidal grooves
We study the effective slippage on superhydrophobic grooves with trapezoidal
cross-sections of various geometries (including the limiting cases of triangles
and rectangular stripes), by using two complementary approaches. First,
dissipative particle dynamics (DPD) simulations of a flow past such surfaces
have been performed to validate an expression [E.S.Asmolov and O.I.Vinogradova,
J. Fluid Mech. \textbf{706}, 108 (2012)] that relates the eigenvalues of the
effective slip-length tensor for one-dimensional textures. Second, we propose
theoretical estimates for the effective slip length and calculate it
numerically by solving the Stokes equation based on a collocation method. The
comparison between the two approaches shows that they are in excellent
agreement. Our results demonstrate that the effective slippage depends strongly
on the area-averaged slip, the amplitude of the roughness, and on the fraction
of solid in contact with the liquid. To interpret these results, we analyze
flow singularities near slipping heterogeneities, and demonstrate that they
inhibit the effective slip and enhance the anisotropy of the flow. Finally, we
propose some guidelines to design optimal one-dimensional superhydrophobic
surfaces, motivated by potential applications in microfluidics.Comment: 11 pages, 8 figures, submitted to J. Chem. Phy
Flows and mixing in channels with misaligned superhydrophobic walls
Aligned superhydrophobic surfaces with the same texture orientation reduce
drag in the channel and generate secondary flows transverse to the direction of
the applied pressure gradient. Here we show that a transverse shear can be
easily generated by using superhydrophobic channels with misaligned textured
surfaces. We propose a general theoretical approach to quantify this transverse
flow by introducing the concept of an effective shear tensor. To illustrate its
use, we present approximate theoretical solutions and Dissipative Particle
Dynamics simulations for striped superhydrophobic channels. Our results
demonstrate that the transverse shear leads to complex flow patterns, which
provide a new mechanism of a passive vertical mixing at the scale of a texture
period. Depending on the value of Reynolds number two different scenarios
occur. At relatively low Reynolds number the flow represents a transverse shear
superimposed with two co-rotating vortices. For larger Reynolds number these
vortices become isolated, by suppressing fluid transport in the transverse
direction.Comment: 8 pages, 10 figure
Somatostatin agonist pasireotide inhibits exercise stimulated growth in the male Siberian hamster (Phodopus sungorus)
R.Dumbell was supported by a University of Aberdeen PhD studentship and a research visit grant awarded by the British Society of Neuroendocrinology. Further support was provided by the Scottish Government Rural and Environment Science and Analytical Services Division (Barrett and the German Research Foundation (DFG; STE 331/8-1; Steinlechner lab). We are grateful for technical assistance from Dana Wilson at RINH and Siegried Hiliken at UVMH, and thank Dr Claus-Dieter Mayer of Biomathematics & Statistics Scotland for valuable advice on statistical analysis.Peer reviewedPostprin
Chemical ordering and composition fluctuations at the (001) surface of the Fe-Ni Invar alloy
We report on a study of (001) oriented fcc Fe-Ni alloy surfaces which
combines first-principles calculations and low-temperature STM experiments.
Density functional theory calculations show that Fe-Ni alloy surfaces are
buckled with the Fe atoms slightly shifted outwards and the Ni atoms inwards.
This is consistent with the observation that the atoms in the surface layer can
be chemically distinguished in the STM image: brighter spots (corrugation
maxima with increased apparent height) indicate iron atoms, darker ones nickel
atoms. This chemical contrast reveals a c2x2 chemical order (50% Fe) with
frequent Fe-rich defects on Invar alloy surface. The calculations also indicate
that subsurface composition fluctuations may additionally modulate the apparent
height of the surface atoms. The STM images show that this effect is pronounced
compared to the surfaces of other disordered alloys, which suggests that some
chemical order and corresponding concentration fluctuations exist also in the
subsurface layers of Invar alloy. In addition, detailed electronic structure
calculations allow us to identify the nature of a distinct peak below the Fermi
level observed in the tunneling spectra. This peak corresponds to a surface
resonance band which is particularly pronounced in iron-rich surface regions
and provides a second type of chemical contrast with less spatial resolution
but one that is essentially independent of the subsurface composition.Comment: 7 pages, 5 figure
Rapid attainment of a doubled haploid line from transgenic maize ( Zea mays L.) plants by means of anther culture
Summary: We present a strategy for establishing a transgenic doubled haploid maize line from heterozygous transgenic material by means of anther culture. Compared to conventional inbreeding, the in vitro androgenesis technique enables a faster generation of virtually fully homozygous lines. Since the androgenic response is highly genotype-dependent, we crossed transgenic, non-androgenic plants carrying a herbicide resistance marker gene (pat, encoding for phosphinothricin acetyl transferase) with a highly androgenic genotype. The transgenic progenies were used as donor plants for anther culture. One transgenic and three non-transgenic doubled haploid lines have been established within approximately 1 yr. The homozygosity of all four doubled haploid lines was tested by analysis of simple sequence repeat (SSR) markers at 19 different loci. Polymorphisms were found between the lines but not within the lines indicating the homozygous nature of the entire plant genome gained by anther culture. Southern blot analysis revealed that the transgenic donor plants and their doubled haploid progeny exhibited the same integration pattern of the pat gene. No segregation of the herbicide resistance trait has been observed among the progeny of the transgenic doubled haploid lin
Conduction through a quantum dot near a singlet-triplet transition
Kondo effect in the vicinity of a singlet-triplet transition in a vertical
quantum dot is considered. This system is shown to map onto a special version
of the two-impurity Kondo model. At any value of the control parameter, the
system has a Fermi-liquid ground state. Explicit expressions for the linear
conductance as a function of the control parameter and temperature are
obtained. At T=0, the conductance reaches the unitary limit at
the triplet side of the transition, and decreases with the increasing distance
to the transition at the singlet side. At finite temperature, the conductance
exhibits a peak near the transition point
Non-local Control of the Kondo Effect in a Double Quantum Dot-Quantum Wire Coupled System
We have performed low-temperature transport measurements on a double quantum
dot-quantum wire coupled device and demonstrated non-local control of the Kondo
effect in one dot by manipulating the electronic spin states of the other. We
discuss the modulation of the local density of states in the wire region due to
the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida (RKKY)
exchange interaction as the mechanisms responsible for the observed features.Comment: 4 pages, 4 figure
Peculiar properties of the cluster-cluster interaction induced by the Pauli exclusion principle
Role of the Pauli principle in the formation of both the discrete spectrum
and multi-channel states of the binary nuclear systems composed of clusters is
studied in the Algebraic Version of the resonating-group method. Solutions of
the Hill-Wheeler equations in the discrete representation of a complete basis
of the Pauli-allowed states are discussed for 4He+n, 3H+3H, and 4He+4He binary
systems. An exact treatment of the antisymmetrization effects are shown to
result in either an effective repulsion of the clusters, or their effective
attraction. It also yields a change in the intensity of the centrifugal
potential. Both factors significantly affect the scattering phase behavior.
Special attention is paid to the multi-channel cluster structure 6He+6He as
well as to the difficulties arising in the case when the two clustering
configurations, 6He+6He and 4He+8He, are taken into account simultaneously. In
the latter case the Pauli principle, even in the absence of a potential energy
of the cluster-cluster interaction, leads to the inelastic processes and
secures an existence of both the bound state and resonance in the 12Be compound
nucleus.Comment: 17 pages, 14 figures, 1 table; submitted to Phys.Rev.C Keywords:
light neutron-rich nuclei, cluster model
Geometrical Description of Quantum Mechanics - Transformations and Dynamics
In this paper we review a proposed geometrical formulation of quantum
mechanics. We argue that this geometrization makes available mathematical
methods from classical mechanics to the quantum frame work. We apply this
formulation to the study of separability and entanglement for states of
composite quantum systems.Comment: 22 pages, to be published in Physica Script
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