750 research outputs found
Species concepts and relationships in wild and cultivated potatoes
Wild and cultivated potatoes (Solanum section Petota) present challenges to taxonomists arising from lack of clearly defined morphological character differences among many species, phenotypic plasticity, a range of ploidy levels from diploid to hexaploid, and hybrid speciation and introgression. Taxonomic treatments of the group have differed greatly regarding numbers of species and hypotheses of their interrelationships at the series level. Recent morphological phenetic studies and molecular studies have confirmed the general lack of clearly defined species, have shown the need to use a number of character states with overlapping ranges for species delimitation (polythetic support), and have suggested the need for the reduction of species in section Petota. Molecular studies have sometimes confirmed hypotheses of hybridization and sometimes have failed to support them. Molecular studies have suggested the need for a reconsideration of the traditionally held series concepts. Currently, section Petota contains 196 wild species and a single cultivated species, Solanum tuberosum, with eight landrace cultivar groups, exclusive of the modern cultivars that are not yet classified into cultivar groups. The number of wild species likely will decrease with future study. These points are here illustrated by (1) a discussion of published species level studies in Solanum series Longipedicellata, the Solanum brevicaule complex, and the cultivated landrace populations of potatoes; (2) reinvestigations of hybridization in S. chacoense, S. raphanifolium and S. xrechei; and (3) studies of ingroup and outgroup relationships of section Petota
Approximating the Maximum Overlap of Polygons under Translation
Let and be two simple polygons in the plane of total complexity ,
each of which can be decomposed into at most convex parts. We present an
-approximation algorithm, for finding the translation of ,
which maximizes its area of overlap with . Our algorithm runs in
time, where is a constant that depends only on and .
This suggest that for polygons that are "close" to being convex, the problem
can be solved (approximately), in near linear time
Long Cycles in a Perturbed Mean Field Model of a Boson Gas
In this paper we give a precise mathematical formulation of the relation
between Bose condensation and long cycles and prove its validity for the
perturbed mean field model of a Bose gas. We decompose the total density
into the number density of
particles belonging to cycles of finite length () and to
infinitely long cycles () in the thermodynamic limit. For
this model we prove that when there is Bose condensation,
is different from zero and identical to the condensate density. This is
achieved through an application of the theory of large deviations. We discuss
the possible equivalence of with off-diagonal long
range order and winding paths that occur in the path integral representation of
the Bose gas.Comment: 10 page
Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence
Band tailing is a major contributing factor to the large open circuit voltage (Voc) deficit that is currently limiting Cu2ZnSnS4 (CZTS) photovoltaic devices. It occurs in highly doped, highly compensated semiconductors and gives rise to a non-uniform electronic band structure. Here we report spatially resolved fluctuations in CZTS optical properties using low temperature cathodoluminescence (CL) in a scanning electron microscope (SEM). Principal component analysis reveals three CL peaks whose relative intensity vary across domains ~ 100 nm in size. It is not known whether the non-uniform optical properties are due to changes in composition or due to structural order-disorder at constant composition. Measurement of composition with energy dispersive X-ray (EDX) analysis in an SEM and ordering with Micro-Raman mapping revealed CZTS to be uniform within the spatial resolution (estimated at ~ 0.4 µm and 1.1 µm respectively) and sensitivity of the two techniques. The CL results are consistent with the presence of band tailing in CZTS
The Mythology of Game Theory
Non-cooperative game theory is at its heart a theory of cognition, specifically a theory of how decisions are made. Game theory\u27s leverage is that we can design different payoffs, settings, player arrays, action possibilities, and information structures, and that these differences lead to different strategies, outcomes, and equilibria. It is well-known that, in experimental settings, people do not adopt the predicted strategies, outcomes, and equilibria. The standard response to this mismatch of prediction and observation is to add various psychological axioms to the game-theoretic framework. Regardless of the differing specific proposals and results, game theory uniformly makes certain cognitive assumptions that seem rarely to be acknowledged, much less interrogated. Indeed, it is not widely understood that game theory is essentially a cognitive theory. Here, we interrogate those cognitive assumptions. We do more than reject specific predictions from specific games. More broadly, we reject the underlying cognitive model implicitly assumed by game theory
Hydrodynamic flow of expanding Bose-Einstein condensates
We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC)
after switching off the confining harmonic potential. Exact solution of
dynamical equations is obtained in framework of the hydrodynamic approximation
and it is compared with the direct numerical simulation of the full problem
showing excellent agreement at realistic values of physical parameters. We
analyze the maximum of the current density and estimate the velocity of
expansion. The results of the 1D analysis provides also qualitative
understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review
Beyond the MSSM Higgs with d=6 effective operators
We continue a previous study of the MSSM Higgs Lagrangian extended by all
effective operators of dimension d=6 that can be present beyond the MSSM,
consistent with its symmetries. By supersymmetry, such operators also extend
the neutralino and chargino sectors, and the corresponding component fields
Lagrangian is computed onshell. The corrections to the neutralino and chargino
masses, due to these operators, are computed analytically in function of the
MSSM corresponding values. For individual operators, the corrections are small,
of few GeV for the constrained MSSM (CMSSM) viable parameter space. We
investigate the correction to the lightest Higgs mass, which receives, from
individual operators, a supersymmetric correction of up to 4 (6) GeV above the
2-loop leading-log CMSSM value, from those CMSSM phase space points with: EW
fine tuning Delta<200, consistent with WMAP relic density (3), and for
a scale of the operators of M=10 (8) TeV, respectively. Applied to the CMSSM
point of minimal fine tuning (Delta=18), such increase gives an upper limit
GeV, respectively. The increase of m_h from individual
operators can be larger ( 10-30 GeV) for those CMSSM phase space points
with Delta>200; these can now be phenomenologically viable, with reduced Delta,
and this includes those points that would have otherwise violated the LEP2
bound by this value. The neutralino/chargino Lagrangian extended by the
effective operators can be used in studies of dark matter relic density within
extensions of the MSSM, by implementing it in public codes like micrOMEGAs.Comment: 36 pages, Latex, 16 figures (v2: minor changes, corrected typos
Stress Transmission through Three-Dimensional Ordered Granular Arrays
We measure the local contact forces at both the top and bottom boundaries of
three-dimensional face-centered-cubic and hexagonal-close-packed granular
crystals in response to an external force applied to a small area at the top
surface. Depending on the crystal structure, we find markedly different results
which can be understood in terms of force balance considerations in the
specific geometry of the crystal. Small amounts of disorder are found to create
additional structure at both the top and bottom surfaces.Comment: 9 pages including 9 figures (many in color) submitted to PR
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