3,226 research outputs found
Interface Collisions
We provide a theoretical framework to analyze the properties of frontal
collisions of two growing interfaces considering different short range
interactions between them. Due to their roughness, the collision events spread
in time and form rough domain boundaries, which defines collision interfaces in
time and space. We show that statistical properties of such interfaces depend
on the kinetics of the growing interfaces before collision, but are independent
of the details of their interaction and of their fluctuations during the
collision. Those properties exhibit dynamic scaling with exponents related to
the growth kinetics, but their distributions may be non-universal. These
results are supported by simulations of lattice models with irreversible
dynamics and local interactions. Relations to first passage processes are
discussed and a possible application to grain boundary formation in
two-dimensional materials is suggested.Comment: Paper with 12 pages and 2 figures; supplemental material with 4 pages
and 3 figure
Nonlinear wavelength selection in surface faceting under electromigration
We report on the control of the faceting of crystal surfaces by means of
surface electromigration. When electromigration reinforces the faceting
instability, we find perpetual coarsening with a wavelength increasing as
. For strongly stabilizing electromigration, the surface is stable.
For weakly stabilizing electromigration, a cellular pattern is obtained, with a
nonlinearly selected wavelength. The selection mechanism is not caused by an
instability of steady-states, as suggested by previous works in the literature.
Instead, the dynamics is found to exhibit coarsening {\it before} reaching a
continuous family of stable non-equilibrium steady-states.Comment: 5 pages, 4 figures, submitte
Development of adenocarcinoma in chronic fistula in Crohn's disease
The authors report the case of a 55 yr-old woman suffering from Crohn's disease since 31 years with stricture and fistulas developed in the ileocolic junction and anorectal portion. Long-standing anorectal fistulas and stricture led to adenocarcinoma and finally fistulisation in the vagina. Diagnosis was made by perineal examination with biopsies under general anaesthesia. Treatment was first posterior pelvectomy with resection of the anterior wall of vagina. Secondarily, radiochemotherapy was administrated. The authors discuss the incidence and risk factors of carcinoma in Crohn's disease with chronic fistulas
Creep stability of the proposed AIDA mission target 65803 Didymos: I. Discrete cohesionless granular physics model
As the target of the proposed Asteroid Impact & Deflection Assessment (AIDA)
mission, the near-Earth binary asteroid 65803 Didymos represents a special
class of binary asteroids, those whose primaries are at risk of rotational
disruption. To gain a better understanding of these binary systems and to
support the AIDA mission, this paper investigates the creep stability of the
Didymos primary by representing it as a cohesionless self-gravitating granular
aggregate subject to rotational acceleration. To achieve this goal, a
soft-sphere discrete element model (SSDEM) capable of simulating granular
systems in quasi-static states is implemented and a quasi-static spin-up
procedure is carried out. We devise three critical spin limits for the
simulated aggregates to indicate their critical states triggered by reshaping
and surface shedding, internal structural deformation, and shear failure,
respectively. The failure condition and mode, and shear strength of an
aggregate can all be inferred from the three critical spin limits. The effects
of arrangement and size distribution of constituent particles, bulk density,
spin-up path, and interparticle friction are numerically explored. The results
show that the shear strength of a spinning self-gravitating aggregate depends
strongly on both its internal configuration and material parameters, while its
failure mode and mechanism are mainly affected by its internal configuration.
Additionally, this study provides some constraints on the possible physical
properties of the Didymos primary based on observational data and proposes a
plausible formation mechanism for this binary system. With a bulk density
consistent with observational uncertainty and close to the maximum density
allowed for the asteroid, the Didymos primary in certain configurations can
remain geo-statically stable without including cohesion.Comment: 66 pages, 24 figures, submitted to Icarus on 25/Aug/201
Tunable Superconducting Properties of a-NbSi Thin Films and Application to Detection in Astrophysics
We report on the superconducting properties of amorphous NbxSi1-x thin films.
The normal-state resistance and critical temperatures can be separately
adjusted to suit the desired application. Notably, the relatively low
electron-phonon coupling of these films makes them good candidates for an "all
electron bolometer" for Cosmological Microwave Background radiation detection.
Moreover, this device can be made to suit both high and low impedance readouts
Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements
The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured
in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152,
in the underdoped regime. In fields large enough to suppress superconductivity,
R_H(T) is seen to go from positive at high temperature to negative at low
temperature, for p > 0.08. This change of sign is attributed to the emergence
of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the
normal-state R_H(T) remains positive at all temperatures, increasing
monotonically as T \to 0. We attribute the change of behaviour across p = 0.08
to a Lifshitz transition, namely a change in Fermi-surface topology occurring
at a critical concentration p_L = 0.08, where the electron pocket vanishes. The
loss of the high-mobility electron pocket across p_L coincides with a ten-fold
drop in the conductivity at low temperature, revealed in measurements of the
electrical resistivity at high fields, showing that the so-called
metal-insulator crossover of cuprates is in fact driven by a Lifshitz
transition. It also coincides with a jump in the in-plane anisotropy of ,
showing that without its electron pocket the Fermi surface must have strong
two-fold in-plane anisotropy. These findings are consistent with a
Fermi-surface reconstruction caused by a unidirectional spin-density wave or
stripe order.Comment: 16 pages, 13 figures, see associated Viewpoint: M. Vojta, Physics 4,
12 (2011
Spherically symmetric scalar field collapse in any dimension
We describe a formalism and numerical approach for studying spherically
symmetric scalar field collapse for arbitrary spacetime dimension d and
cosmological constant Lambda. The presciption uses a double null formalism, and
is based on field redefinitions first used to simplify the field equations in
generic two-dimensional dilaton gravity. The formalism is used to construct
code in which d and Lambda are input parameters. The code reproduces known
results in d = 4 and d = 6 with Lambda = 0. We present new results for d = 5
with zero and negative Lambda.Comment: 16 pages, 6 figures, typos corrected, presentational changes, PRD in
pres
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