8,873 research outputs found
Around the tangent cone theorem
A cornerstone of the theory of cohomology jump loci is the Tangent Cone
theorem, which relates the behavior around the origin of the characteristic and
resonance varieties of a space. We revisit this theorem, in both the algebraic
setting provided by cdga models, and in the topological setting provided by
fundamental groups and cohomology rings. The general theory is illustrated with
several classes of examples from geometry and topology: smooth quasi-projective
varieties, complex hyperplane arrangements and their Milnor fibers,
configuration spaces, and elliptic arrangements.Comment: 39 pages; to appear in the proceedings of the Configurations Spaces
Conference (Cortona 2014), Springer INdAM serie
Absorption characteristics of a quantum dot array induced intermediate band: implications for solar cell design
We present a theoretical study of the electronic and absorption properties of the intermediate band (IB) formed by a three dimensional structure of InAs/GaAs quantum dots (QDs) arranged in a periodic array. Analysis of the electronic and absorption structures suggests that the most promising design for an IB solar cell material, which will exhibit its own quasi-Fermi level, is to employ small QDs (~6–12 nm QD lateral size). The use of larger QDs leads to extension of the absorption spectra into a longer wavelength region but does not provide a separate IB in the forbidden energy gap
Chaotic dynamics of the planet in HD 196885 AB
Depending on the planetary orbit around the host star(s), a planet could
orbit either one or both stars in a binary system as S-type or P-type,
respectively. We have analysed the dynamics of the S-type planetary system in
HD 196885 AB with an emphasis on a planet with a higher orbital inclination
relative to the binary plane. The mean exponential growth factor of nearby
orbits (MEGNO) maps are used as an indicator to determine regions of
periodicity and chaos for the various choices of the planet's semimajor axis,
eccentricity and inclination with respect to the previously determined
observational uncertainties. We have quantitatively mapped out the chaotic and
quasi-periodic regions of the system's phase space which indicate a likely
regime of the planet's inclination. In addition, we inspect the resonant angle
to determine whether alternation between libration and circulation occurs as a
consequence of Kozai oscillations, a probable mechanism that can drive the
planetary orbit to a very large inclination. Also, we demonstrate the possible
higher mass limit of the planet and improve upon the current dynamical model
based on our analysis.Comment: 10 pages, 9 figures (Accepted for publication at MNRAS
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Ideas for the Arcturus personal workstation
In order to achieve more effective use of interpersonal collaboration, management lifecycle activities, and dynamic retrieval of as well as for ordinary programming chores, it may be useful to take a fresh look at the devices we use to help us conduct our transactions with computers.This paper presents some new ideas for using large flatscreen displays and dedicated computers as personal workstations
Subdiffusion and lateral diffusion coefficient of lipid atoms and molecules in phospholipid bilayers
We use a long, all-atom molecular dynamics (MD) simulation combined with
theoretical modeling to investigate the dynamics of selected lipid atoms and
lipid molecules in a hydrated diyristoyl-phosphatidylcholine (DMPC) lipid
bilayer. From the analysis of a 0.1 s MD trajectory we find that the time
evolution of the mean square displacement, [\delta{r}(t)]^2, of lipid atoms and
molecules exhibits three well separated dynamical regions: (i) ballistic, with
[\delta{r}(t)]^2 ~ t^2 for t < 10 fs; (ii) subdiffusive, with [\delta{r}(t)]^2
~ t^{\beta} with \beta<1, for 10 ps < t < 10 ns; and (iii) Fickian diffusion,
with [\delta{r}(t)]^2 ~ t for t > 30 ns. We propose a memory function approach
for calculating [\delta{r}(t)]^2 over the entire time range extending from the
ballistic to the Fickian diffusion regimes. The results are in very good
agreement with the ones from the MD simulations. We also examine the
implications of the presence of the subdiffusive dynamics of lipids on the
self-intermediate scattering function and the incoherent dynamics structure
factor measured in neutron scattering experiments.Comment: Submitted to Phys. Rev.
SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material
We present photometry, spectra, and spectropolarimetry of supernova (SN)
2012ab, mostly obtained over the course of days after discovery. SN
2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral
galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN
1998S, its spectral evolution does not. We see indications of CSM interaction
in the strong intermediate-width emission features, the high luminosity (peak
at absolute magnitude ), and the lack of broad absorption features in
the spectrum. The H emission undergoes a peculiar transition. At early
times it shows a broad blue emission wing out to km
and a truncated red wing. Then at late times (
100days) it shows a truncated blue wing and a very broad red emission wing
out to roughly km . This late-time broad red wing
probably arises in the reverse shock. Spectra also show an asymmetric
intermediate-width H component with stronger emission on the red side
at late times. The evolution of the asymmetric profiles requires a density
structure in the distant CSM that is highly aspherical. Our spectropolarimetric
data also suggest asphericity with a strong continuum polarization of % and depolarization in the H line, indicating asphericity in the
CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss
rate of for km extending back at least 75yr prior to the
SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest
that the progenitor was an eccentric binary system undergoing eruptive mass
loss.Comment: 18 pages, 12 figure
Complex Network Structure of Flocks in the Standard Vicsek Model
In flocking models, the collective motion of self-driven individuals leads to
the formation of complex spatiotemporal patterns. The Standard Vicsek Model
(SVM) considers individuals that tend to adopt the direction of movement of
their neighbors under the influence of noise. By performing an extensive
complex network characterization of the structure of SVM flocks, we show that
flocks are highly clustered, assortative, and non-hierarchical networks with
short-tailed degree distributions. Moreover, we also find that the SVM dynamics
leads to the formation of complex structures with an effective dimension higher
than that of the space where the actual displacements take place. Furthermore,
we show that these structures are capable of sustaining mean-field-like
orientationally ordered states when the displacements are suppressed, thus
suggesting a linkage between the onset of order and the enhanced dimensionality
of SVM flocks.Comment: 26 pages, 11 figures. To appear in J. Stat. Phy
Conditional expectations, traces, angles between spaces and Representations of the Hecke algebras
In this paper we extend the results in [Ra] on the representation of the
Hecke algebra, determined by the matrix coefficients of a projective, unitary
representation, in the discrete series of representations of the ambient group,
to a more general, vector valued case. This method is used to analyze the
traces of the Hecke operators.
We construct representations of the Hecke algebra of a group , relative to
an almost normal subgroup , into the von Neumann algebra of the group
, tensor matrices. The representations we obtain are a lifting of the Hecke
operators to this larger algebra. By summing up the coefficients of the terms
in the representation one obtains the classical Hecke operators.
These representations were used in the scalar case in [Ra], to find an
alternative representation of the Hecke operators on Maass forms, and hence to
reformulate the Ramanujan Petersson conjectures as a problem on the angle (see
e.g. A. Connes's paper [Co] on the generalization of CKM matrix) between two
subalgebras of the von Neumann algebra of the group : the image of the
representation of the Hecke algebra and the algebra of the almost normal
subgroup.Comment: This is print versio
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