7,231 research outputs found
A Model for Granular Texture with Steric Exclusion
We propose a new method to characterize the geometrical texture of a granular
packing at the particle scale including the steric hindrance effect. This
method is based on the assumption of a maximum disorder (entropy) compatible
both with strain-induced anisotropy of the contact network and steric
exclusions. We show that the predicted statistics for the local configurations
is in a fairly agreement with our numerical data.Comment: 9 pages, 5 figure
Motivic Milnor fibre for nondegenerate function germs on toric singularities
We study function germs on toric varieties which are nondegenerate for their
Newton diagram. We express their motivic Milnor fibre in terms of their Newton
diagram. We extend a formula for the motivic nearby fibre to the case of a
toroidal degeneration. We illustrate this by some examples.Comment: 14 page
Multiscale Analysis of the Stress State in a Granular Slope in Transition to Failure
By means of contact dynamics simulations, we analyze the stress state in a
granular bed slowly tilted towards its angle of repose. An increasingly large
number of grains are overloaded in the sense that they are found to carry a
stress ratio above the Coulomb yield threshold of the whole packing. Using this
property, we introduce a coarse-graining length scale at which all stress
ratios are below the packing yield threshold. We show that this length
increases with the slope angle and jumps to a length comparable to the depth of
the granular bed at an angle below the angle of repose. This transition
coincides with the onset of dilatation in the packing. We map this transition
into a percolation transition of the overloaded grains, and we argue that in
the presence of long-range correlations above the transition angle, the
granular slope is metastable.Comment: 11 pages, 14 Fig, submitted to PR
Dynamics of broken symmetry nodal and anti-nodal excitations in Bi_{2} Sr_{2} CaCu_{2} O_{8+\delta} probed by polarized femtosecond spectroscopy
The dynamics of excitations with different symmetry is investigated in the
superconducting (SC) and normal state of the high-temperature superconductor
BiSrCaCuO (Bi2212) using optical pump-probe (Pp)
experiments with different light polarizations at different doping levels. The
observation of distinct selection rules for SC excitations, present in A and B symmetries, and for the PG excitations, present in
A and B symmetries, by the probe and absence of any
dependence on the pump beam polarization leads to the unequivocal conclusion of
the existence of a spontaneous spatial symmetry breaking in the pseudogap (PG)
state
The a-number of hyperelliptic curves
It is known that for a smooth hyperelliptic curve to have a large -number,
the genus must be small relative to the characteristic of the field, ,
over which the curve is defined. It was proven by Elkin that for a genus
hyperelliptic curve to have , the genus is bounded by
. In this paper, we show that this bound can be lowered to . The method of proof is to force the Cartier-Manin matrix to have rank one
and examine what restrictions that places on the affine equation defining the
hyperelliptic curve. We then use this bound to summarize what is known about
the existence of such curves when and .Comment: 7 pages. v2: revised and improved the proof of the main theorem based
on suggestions from the referee. To appear in the proceedings volume of Women
in Numbers Europe-
Sheared force-networks: anisotropies, yielding and geometry
A scenario for yielding of granular matter is presented by considering the
ensemble of force networks for a given contact network and applied shear stress
. As is increased, the probability distribution of contact forces
becomes highly anisotropic, the difference between average contact forces along
minor and major axis grows, and the allowed networks span a shrinking subspace
of all force-networks. Eventually, contacts start to break, and at the yielding
shear stress, the packing becomes effectively isostatic. The size of the
allowed subspace exhibits simple scaling properties, which lead to a prediction
of the yield stress for packings of arbitrary contact number.Comment: 4 pages, 4 figure
Probing the Inflow/Out-flow and Accretion Disk of Cyg X-1 in the High State with HETG/Chandra
Cyg X-1 was observed in the high state at the conjunction orbital phase (0)
with HETG/Chandra. Strong and asymmetric absorption lines of highly ionized
species were detected, such as Fe XXV, Fe XXIV, Fe XXIII, Si XIV, S XVI, Ne X,
and etc. In the high state the profile of the absorption lines are composed of
an extended red wing and a less extended blue wing. The red wings of higher
ionized species are more extended than that of lower ionized species. The
detection of these lines provides a way to probe the properties of the flow
around the companion and the black hole in Cyg X-1 during the high state. A
broad emission feature around 6.5 keV was significantly detected from the both
spectra of HETG/Chandra and PCA/RXTE. This feature appears to be symmetric and
can be fitted with a Gaussian function rather than the Laor disk line model of
fluorescent Fe K line from an accretion disk. The implications of
these results on the structure of the accretion flow of Cyg X-1 in the high
state are discussed.Comment: 16 pages, 4 fiugres. accepted for publication in the v597 n2 ApJ
November 10, 2003 issu
Are Womenâs Mate Preferences for Altruism Also Influenced by Physical Attractiveness?
Altruism plays a role in mate choice, particularly in womenâs preferences, and particularly for long-term relationships. The current study analyzed how these preferences interacted with another important mate choice variable, physical attractiveness. Here, female participants were presented with photographs of men of varying levels of physical attractiveness, alongside descriptions of them behaving either altruistically or not in different scenarios. The results showed women preferred altruistic men, particularly in long-term relationships, and that this interacted with physical attractiveness such that being both attractive and altruistic made a man more desirable than just the sum of the two desirable parts. Also, being altruistic made low attractive men more desirable, but only for long-term relationships. Finally, men who were just altruistic were rated more desirable than men who were just attractive, especially for long-term relationships. Overall these findings are discussed in terms of the role of altruism in mate choice, particularly in long-term relationships and directions of future research
Free Differential Algebras and Pure Spinor Action in IIB Superstring Sigma Models
In this paper we extend to the case of IIB superstring sigma models the
method proposed in hep-th/10023500 to derive the pure spinor approach for type
IIA sigma models. In particular, starting from the (Free) Differential Algebra
and superspace parametrization of type IIB supergravity, extended to include
the BRST differential and all the ghosts, we derive the BRST transformations of
fields and ghosts as well as the standard pure spinor constraints for the
ghosts related to supersymmetry. Moreover, using the method first
proposed by us, we derive the pure spinor action for type IIB superstrings in
curved supergravity backgrounds (on shell), in full agreement with the action
first obtained by Berkovits and Howe.Comment: 24 page
Pure Spinor Approach to Type IIA Superstring Sigma Models and Free Differential Algebras
This paper considers the Free Differential Algebra and rheonomic
parametrization of type IIA Supergravity, extended to include the BRS
differential and the ghosts. We consider not only the ghosts lambda's of
supersymmetry but also the ghosts corresponding to gauge and Lorentz
transformations. In this way we can derive not only the BRS transformations of
fields and ghosts but also the standard pure spinor constraints on lambda's.
Moreover the formalism allows to derive the action for the pure spinor
formulation of type IIA superstrings in a general background, recovering the
action first obtained by Berkovits and Howe.Comment: 1+23 pages, v2: added clarifications and a reference, misprints
corrected, v3: presentation improved, results unchange
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