7,064 research outputs found
Dynamics of nearly spherical vesicles in an external flow
We analytically derive an equation describing vesicle evolution in a fluid
where some stationary flow is excited regarding that the vesicle shape is close
to a sphere. A character of the evolution is governed by two dimensionless
parameters, and , depending on the vesicle excess area, viscosity
contrast, membrane viscosity, strength of the flow, bending module, and ratio
of the elongation and rotation components of the flow. We establish the ``phase
diagram'' of the system on the plane: we find curves corresponding
to the tank-treading to tumbling transition (described by the saddle-node
bifurcation) and to the tank-treading to trembling transition (described by the
Hopf bifurcation).Comment: 4 pages, 1 figur
The strong influence of substrate conductivity on droplet evaporation
We report the results of physical experiments that demonstrate the strong influence of the thermal conductivity of the substrate on the evaporation of a pinned droplet. We show that this behaviour can be captured by a mathematical model including the variation of the saturation concentration with temperature, and hence coupling the problems for the vapour concentration in the atmosphere and the temperature in the liquid and the substrate. Furthermore, we show that including two ad hoc improvements to the model, namely a Newton's law of cooling on the unwetted surface of the substrate and the buoyancy of water vapour in the atmosphere, give excellent quantitative agreement for all of the combinations of liquid and substrate considered
Magnetic studies of multi-walled carbon nanotube mats: Evidence for the paramagnetic Meissner effect
We report magnetic measurements up to 1200 K on multi-walled carbon nanotube
mats using Quantum Design vibrating sample magnetometer. Extensive magnetic
data consistently show two ferrromagnetic-like transitions at about 1000 K and
1275 K, respectively. The lower transition at about 1000 K is associated with
an Fe impurity phase and its saturation magnetization is in quantitative
agreement with the Fe concentration measured by an inductively coupled plasma
mass spectrometer. On the other hand, the saturation magnetization for the
higher transition phase (1.0 emu/g) is about four orders of magnitude
larger than that expected from the measured concentration of Co or CoFe, which
has a high enough Curie temperature to explain this high transition. We show
that this transition at about 1275 K is not consistent with a magnetic
proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based
materials or magnetic impurities but with the paramagnetic Meissner effect due
to the existence of Josephson junctions in a granular superconductor.Comment: 5 pages, 4 figure
Low Energy Supersymmetry from the Heterotic Landscape
We study possible correlations between properties of the observable and
hidden sectors in heterotic string theory. Specifically, we analyze the case of
the Z6-II orbifold compactification which produces a significant number of
models with the spectrum of the supersymmetric standard model. We find that
requiring realistic features does affect the hidden sector such that hidden
sector gauge group factors SU(4) and SO(8) are favoured. In the context of
gaugino condensation, this implies low energy supersymmetry breaking.Comment: 4 pages, 3 figures; to appear in Phys. Rev. Let
Decay of scalar turbulence revisited
We demonstrate that at long times the rate of passive scalar decay in a
turbulent, or simply chaotic, flow is dominated by regions (in real space or in
inverse space) where mixing is less efficient. We examine two situations. The
first is of a spatially homogeneous stationary turbulent flow with both viscous
and inertial scales present. It is shown that at large times scalar
fluctuations decay algebraically in time at all spatial scales (particularly in
the viscous range, where the velocity is smooth). The second example explains
chaotic stationary flow in a disk/pipe. The boundary region of the flow
controls the long-time decay, which is algebraic at some transient times, but
becomes exponential, with the decay rate dependent on the scalar diffusion
coefficient, at longer times.Comment: 4 pages, no figure
Resilience of the Spectral Standard Model
We show that the inconsistency between the spectral Standard Model and the
experimental value of the Higgs mass is resolved by the presence of a real
scalar field strongly coupled to the Higgs field. This scalar field was already
present in the spectral model and we wrongly neglected it in our previous
computations. It was shown recently by several authors, independently of the
spectral approach, that such a strongly coupled scalar field stabilizes the
Standard Model up to unification scale in spite of the low value of the Higgs
mass. In this letter we show that the noncommutative neutral singlet modifies
substantially the RG analysis, invalidates our previous prediction of Higgs
mass in the range 160--180 Gev, and restores the consistency of the
noncommutative geometric model with the low Higgs mass.Comment: 13 pages, more contours added to Higgs mass plot, one reference adde
The Viscous Lengths in Hydrodynamic Turbulence are Anomalous Scaling Functions
It is shown that the idea that scaling behavior in turbulence is limited by
one outer length and one inner length is untenable. Every n'th order
correlation function of velocity differences \bbox{\cal
F}_n(\B.R_1,\B.R_2,\dots) exhibits its own cross-over length to
dissipative behavior as a function of, say, . This length depends on
{and on the remaining separations} . One result of this Letter
is that when all these separations are of the same order this length scales
like with
, with being
the scaling exponent of the 'th order structure function. We derive a class
of scaling relations including the ``bridge relation" for the scaling exponent
of dissipation fluctuations .Comment: PRL, Submitted. REVTeX, 4 pages, I fig. (not included) PS Source of
the paper with figure avalable at http://lvov.weizmann.ac.il/onlinelist.htm
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