2,468 research outputs found
Solving the 100 Swiss Francs Problem
Sturmfels offered 100 Swiss Francs in 2005 to a conjecture, which deals with
a special case of the maximum likelihood estimation for a latent class model.
This paper confirms the conjecture positively
Restricted ambiguity of erasing morphisms
A morphism h is called ambiguous for a string s if there
is another morphism that maps s to the same image as h; otherwise,
it is called unambiguous. In this paper, we examine some fundamental
problems on the ambiguity of erasing morphisms. We provide a detailed
analysis of so-called ambiguity partitions, and our main result uses this
concept to characterise those strings that have a morphism of strongly
restricted ambiguity. Furthermore, we demonstrate that there are strings
for which the set of unambiguous morphisms, depending on the size of
the target alphabet of these morphisms, is empty, finite or infinite. Finally,
we show that the problem of the existence of unambiguous erasing
morphisms is equivalent to some basic decision problems for nonerasing
multi-pattern languages
Numerical investigation of conjugated heat transfer in a channel with a moving depositing front
This article presents numerical simulations of conjugated heat transfer in a fouled channel with a moving depositing front. The depositing front separating the fluid and the deposit layer is captured using the level-set method. Fluid flow is modeled by the incompressible NavierâStokes equations. Numerical solution is performed on a fixed mesh using the finite volume method. The effects of Reynolds number and thermal conductivity ratio between the deposit layer and the fluid on local Nusselt number as well as length-averaged Nusselt number are investigated. It is found that heat transfer performance, represented by the local and length-averaged Nusselt number reduces significantly in a fouled channel compared with that in a clean channel. Heat transfer performance decreases with the growth of the deposit layer. Increases in Reynolds, Prandtl numbers both enhance heat transfer. Besides, heat transfer is enhanced when the thermal conductivity ratio between the deposit layer and the fluid is lower than 20 but it decreases when the thermal conductivity ratio is larger than 2
Transitional Cell Carcinoma of the Bladder Manifestating as Malignant Lymphoma with Generalized Lymphadenopathy
Bladder cancer usually spreads via the lymphatic and hematogenous routes, the most common sites of metastases of urinary bladder cancers being the regional lymph nodes, liver, lung, bone, peritoneum, pleura, kidney, adrenal gland and intestines. Generalized lymph node metastasis of transitional cell cancer of the bladder is extremely rare. According to our literature search, there has been no case report of transitional cell cancer of the bladder that manifests as an extensive large lymph node metastasis involving the intraparotid, supraclavicular thoracic inlet, axillary and regional abdominal and pelvic lymph nodes without bone or visceral organs involved. Such a presentation could be mistaken as malignant lymphoma and the importance of a biopsy of the lymph nodes is emphasized. The clinical course of rapid progression of the disease and the presence of wild-type p53 with rapid response to chemotherapy and a short remission may represent a unique case, which is discussed here
Novel microstructured fibres for supercontinuum generation
We report recent progress on the fabrication of photonic crystal fibre from ZBLAN and tellurite glasses and their application to generating broadband supercontinua
Theory of Current-Induced Magnetization Precession
We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.Comment: Submitted to Physical Review
Response of alluvial systems to Late Pleistocene climate changes recorded by environmental magnetism in the Añavieja Basin (Iberian Range, NE Spain)
Environmental magnetic proxies were analyzed in a relatively monotonous, ~25.3m thick alluvial sedimentary sequence drilled in the Añavieja Basin (NE Spain). Results from the core AĂ2 suggest that the concentrationdependent magnetic parameters mainly reflect variations in the content of detrital magnetite, sourced in the catchment rocks and soils of the basin, via changes in the dynamics of alluvial fans due to temperature changes in the northern hemisphere during the Late Pleistocene. The correspondence between the magnetic proxies and the temperature variations in the North Atlantic region (NGRIP curve) indicates that higher (lower) concentrations and finer (coarser) magnetite grains coincide with warm (cold) periods. We propose that during cold periods, a sparser vegetation cover favored the incoming of higher energy runoff bearing coarser sediments to the basin that are relatively impoverished in magnetite. In contrast, during warm periods, the wider distribution of the vegetation cover associated with the lower runoff energy lead to finer, magnetite-richer sediment input to the basin. Maghemite, presumably of pedogenic origin, appears to be present also in the studied alluvial sediments. Further studies are necessary to unravel its palaeoclimatic significance
Epitaxially strained [001]-(PbTiO)(PbZrO) superlattice and PbTiO from first principles
The effect of layer-by-layer heterostructuring and epitaxial strain on
lattice instabilities and related ferroelectric properties is investigated from
first principles for the [001]-(PbTiO)(PbZrO) superlattice and
pure PbTiO on a cubic substrate. The results for the superlattice show an
enhancement of the stability of the monoclinic r-phase with respect to pure
PbTiO. Analysis of the lattice instabilities of the relaxed centrosymmetric
reference structure computed within density functional perturbation theory
suggests that this results from the presence of two unstable zone-center modes,
one confined in the PbTiO layer and one in the PbZrO layer, which
produce in-plane and normal components of the polarization, respectively. The
zero-temperature dielectric response is computed and shown to be enhanced not
only near the phase boundaries, but throughout the r-phase. Analysis of the
analogous calculation for pure PbTiO is consistent with this
interpretation, and suggests useful approaches to engineering the dielectric
properties of artificially structured perovskite oxides.Comment: 8 pages, 5 figure
Limitation of energy deposition in classical N body dynamics
Energy transfers in collisions between classical clusters are studied with
Classical N Body Dynamics calculations for different entrance channels. It is
shown that the energy per particle transferred to thermalised classical
clusters does not exceed the energy of the least bound particle in the cluster
in its ``ground state''. This limitation is observed during the whole time of
the collision, except for the heaviest system.Comment: 13 pages, 15 figures, 1 tabl
From semiclassical transport to quantum Hall effect under low-field Landau quantization
The crossover from the semiclassical transport to quantum Hall effect is
studied by examining a two-dimensional electron system in an AlGaAs/GaAs
heterostructure. By probing the magneto-oscillations, it is shown that the
semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the
minima of the longitudinal resistivity approach zero. The extension of the
applicable range of the SdH theory could be due to the damping effects
resulting from disorder and temperature. Moreover, we observed plateau-plateau
transition like behavior with such an extension. From our study, it is
important to include the positive magnetoresistance to refine the SdH theory.Comment: 11 pages, 5 figure
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