25,890 research outputs found
Towards active microfluidics: Interface turbulence in thin liquid films with floating molecular machines
Thin liquid films with floating active protein machines are considered.
Cyclic mechanical motions within the machines, representing microscopic
swimmers, lead to molecular propulsion forces applied to the air-liquid
interface. We show that, when the rate of energy supply to the machines exceeds
a threshold, the flat interface becomes linearly unstable. As the result of
this instability, the regime of interface turbulence, characterized by
irregular traveling waves and propagating machine clusters, is established.
Numerical investigations of this nonlinear regime are performed. Conditions for
the experimental observation of the instability are discussed.Comment: 9 pages, 8 figures, RevTeX, submitted to Physical Review
Metallicity of high stellar mass galaxies with signs of merger events
We focus on an analysis of galaxies of high stellar mass and low metallicity.
We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital
Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high
resolution imaging and both spectroscopic and photometric information available
in the SDSS database. For each galaxy in our sample, we conducted a systematic
morphological analysis by visual inspection of MGC images using their
luminosity contours. The galaxies are classified as either disturbed or
undisturbed objects. We divide the sample into three metallicity regions,
within wich we compare the properties of disturbed and undisturbed objects. We
find that the fraction of galaxies that are strongly disturbed, indicative of
being merger remnants, is higher when lower metallicity objects are considered.
The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed
galaxies (for high, medium, and low metallicity, respectively). Moreover, the
ratio of the disturbed to undisturbed relative distributions of the population
age indicator, Dn(4000), in the low metallicity bin, indicates that the
disturbed objects have substantially younger stellar populations than their
undisturbed counterparts. In addition, we find that an analysis of colour
distributions provides similar results, showing that low metallicity galaxies
with a disturbed morphology are bluer than those that are undisturbed. The
bluer colours and younger populations of the low metallicity, morphologically
disturbed objects suggest that they have experienced a recent merger with an
associated enhanced star formation rate. [abridged]Comment: Astronomy & Astrophysics, in pres
Wheel–rail contact: experimental study of the creep forces–creepage relationships
The wheel–rail contact problem plays an important role in the simulation methods used to solve railway dynamics problems. As a consequence, many different mathematical models have been developed to calculate wheel–rail contact forces. However, most of them tackle this problem purely from a theoretical point of view and need to be experimentally validated. Such validation could also reveal the influence of certain parameters not taken into account in the mathematical developments. This paper presents the steps followed in building a scaled test-bench to experimentally characterise the wheel–rail contact problem. The results of the longitudinal contact force as a function of the longitudinal creepage are obtained and the divergences with respect to Kalker's simplified theory are analysed. The influence of lateral creepage, angular velocity and certain contaminants such as cutting fluid or high positive friction modifier is also discussed
Quicksort with unreliable comparisons: a probabilistic analysis
We provide a probabilistic analysis of the output of Quicksort when
comparisons can err.Comment: 29 pages, 3 figure
Theoretical simulation of the anisotropic phases of antiferromagnetic thin films
We simulate antiferromagnetic thin films. Dipole-dipole and antiferromagnetic
exchange interactions as well as uniaxial and quadrupolar anisotropies are
taken into account. Various phases unfold as the corresponding parameters, J, D
and C, as well as the temperature T and the number n of film layers vary. We
find (1) how the strength Delta_m of the anisotropy arising from dipole-dipole
interactions varies with the number of layers m away from the film's surface,
with J and with n; (2) a unified phase diagram for all n-layer films and bulk
systems; (3) a layer dependent spin reorientation (SR) phase in which spins
rotate continuously as T, D, C and n vary; (4) that the ratio of the SR to the
ordering temperature depends (approximately) on n only through (D+Delta/n)/C,
and hardly on J; (5) a phase transformation between two different magnetic
orderings, in which spin orientations may or may not change, for some values of
J, by varying n.Comment: 10 LaTeX pages, 13 eps figures. Submitted to PRB on 30 June 2006.
Accepted on 10 October 200
Spectroscopic characterization and detection of Ethyl Mercaptan in Orion
New laboratory data of ethyl mercaptan, CHCHSH, in the millimeter
and submillimeter-wave domains (up to 880 GHz) provided very precise values of
the spectroscopic constants that allowed the detection of
-CHCHSH towards Orion KL. 77 unblended or slightly blended
lines plus no missing transitions in the range 80-280 GHz support this
identification. A detection of methyl mercaptan, CHSH, in the spectral
survey of Orion KL is reported as well. Our column density results indicate
that methyl mercaptan is 5 times more abundant than ethyl mercaptan in
the hot core of Orion KL.Comment: Accepted for publication in ApJL (30 January 2014)/ submitted (8
January 2014
`Interpolating' differential reductions of multidimensional integrable hierarchies
We transfer the scheme of constructing differential reductions, developed
recently for the case of the Manakov-Santini hierarchy, to the general
multidimensional case. We consider in more detail the four-dimensional case,
connected with the second heavenly equation and its generalization proposed by
Dunajski. We give a characterization of differential reductions in terms of the
Lax-Sato equations as well as in the framework of the dressing method based on
nonlinear Riemann-Hilbert problem.Comment: Based on the talk at NLPVI, Gallipoli, 15 page
Curved dilatonic brane-worlds and the cosmological constant problem
We construct a model for dilatonic brane worlds with constant curvature on
the brane, i.e. a non-zero four-dimensional cosmological constant, given in
function of the dilaton coupling and the cosmological constant of the bulk. We
compare this family of solutions to other known dilatonic domain wall solutions
and apply a self-tunning mechanism to check the stability of our solutions
under quantum fluctuations living on the brane.Comment: latex, 6 pages. (v2): considerable changes in the conclusion. (v3):
added new discussion on the solutions and some references; version to appear
in CQ
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