1,125 research outputs found
Characteristics of the wavelength of ripples on icicles
It is known that the wavelength of the ripples on icicles in nature is of
centimeter-scale. Such study on morphological instability of ice-water
interface during ice growth from flowing supercooled water film with one side
being a free surface has recently been made [K. Ueno, Phys. Rev. E 68, 021603
(2003)]. This is a first theoretical study taking into account the influence of
the shape of the water-air surface on the growth condition of infinitesimal
disturbances of the ice-water interface. A simpler formula to determine the
wavelength of the ripples than that in the previous paper is derived. It seems
that the wavelength of ripples is insensitive to the water supply rates,
diameters of the icicles and surrounding air temperatures. The details of
dependence of the wavelengh of ripples on these parameters are investigated.Comment: 15 pages, 6 figure
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
Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow
Ring-like ripples on the surface of icicles are an example of morphological
instability of the ice-water interface during ice growth under supercooled
water film flow. The surface of icicles is typically covered with ripples of
about 1 cm in wavelength, and the wavelength appears to be almost independent
of external temperature, icicle radius, and volumetric water flow rate. One
side of the water layer consists of the water-air surface and growing ice is
the other. This is one of the more complicated moving phase boundary problems
with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68,
(2003) 021603] to address the underlying instability that produces ripples is
based on the assumption of the absence of airflow around icicles. In this
paper, we extend the previous theoretical framework to include a natural
convection airflow ahead of the water-air surface and consider whether the
effect of natural convection airflow on the wavelength of ripples produced on
an ice surface is essential or not.Comment: 19 pages, 5 figure
Stability of hexagonal solidification patterns
We investigate the dynamics of cellular solidification patterns using
three-dimensional phase-field simulations. The cells can organize into stable
hexagonal patterns or exhibit unsteady evolutions. We identify the relevant
secondary instabilities of regular hexagonal arrays and find that the stability
boundaries depend significantly on the strength of crystalline anisotropy. We
also find multiplet states that can be reached by applying well-defined
perturbations to a pre-existing hexagonal array.Comment: Minor changes, mainly in introduction and conclusion, one reference
adde
Midgap spectrum of the fermion-vortex system
I study the midgap spectrum of the fermion-vortex system in two spatial
dimensions. The existence of bound states, in addition to the zero modes found
by Jackiw and Rossi, is established. For a singly quantized vortex, I present
complete analytical solutions in terms of generalized Laguerre polynomials in
the opposite limits of vanishing and large vortex core size. There is an
infinite number of such bound states, with a spectrum that is, when squared,
given by, respectively, the Coulomb potential and the isotropic harmonic
oscillator. Possible experimental signatures of this spectrum in
condensed-matter realizations of the system are pointed out.Comment: 10 pages, no figure
Expected performances of a Laue lens made with bent crystals
In the context of the LAUE project devoted to build a Laue lens prototype for
focusing celestial hard X-/soft gamma-rays, a Laue lens made of bent crystal
tiles, with 20 m focal length, is simulated. The focusing energy passband is
assumed to be 90--600 keV. The distortion of the image produced by the lens on
the focal plane, due to effects of crystal tile misalignment and radial
distortion of the crystal curvature, is investigated. The corresponding
effective area of the lens, its point spread function and sensitivity are
calculated and compared with those exhibited by a nominal Laue lens with no
misalignment and/or distortion. Such analysis is crucial to estimate the
optical properties of a real lens, in which the investigated shortcomings could
be present.Comment: 20 pages, 14 figure
Results of the simulations of the petal/lens as part of the LAUE project
In the context of the LAUE project for focusing hard X-/gamma rays, a petal
of the complete lens is being assembled at the LARIX facility in the Department
of Physics and Earth Science of the University of Ferrara. The lens petal
structure is composed of bent Germanium and Gallium Arsenide crystals in
transmission geometry. We present the expectations derived from a mathematical
model of the lens petal. The extension of the model for the complete LAUE
project in the 90 -- 600 keV energy range will be discussed as well. A
quantitative analysis of the results of these simulations is also presented.Comment: 12 pages, 26 figures, SPIE optics + Photonics conference 2013, Vol:
886
Perturbation of Tunneling Processes by Mechanical Degrees of Freedom in Mesoscopic Junctions
We investigate the perturbation in the tunneling current caused by
non-adiabatic mechanical motion in a mesoscopic tunnel junction. A theory
introduced by Caroli et al. \cite{bi1,bi2,bi3} is used to evaluate second order
self-energy corrections for this non-equilibrium situation lacking
translational invariance. Inelastic signatures of the mechanical degrees of
freedom are found in the current-voltage characteristics. These give
rise to sharp features in the derivative spectrum, .Comment: 22 pages LaTeX + 3 uuencoded PS picture
Stability of critical bubble in stretched fluid of square-gradient density-functional model with triple-parabolic free energy
The square-gradient density-functional model with triple-parabolic free
energy, that was used previously to study the homogeneous bubble nucleation [J.
Chem. Phys. 129, 104508 (2008)], is used to study the stability of the critical
bubble nucleated within the bulk under-saturated stretched fluid. The stability
of the bubble is studied by solving the Schr\"odinger equation for the
fluctuation. The negative eigenvalue corresponds to the unstable growing mode
of the fluctuation. Our results show that there is only one negative eigenvalue
whose eigenfunction represents the fluctuation that corresponds to the
isotropically growing or shrinking nucleus. In particular, this negative
eigenvalue survives up to the spinodal point. Therefore the critical bubble is
not fractal or ramified near the spinodal.Comment: 9 pages, 8 figures, Journal of Chemical Physics accepted for
publicatio
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