262 research outputs found
Shear band formation in granular media as a variational problem
Strain in sheared dense granular material is often localized in a narrow
region called shear band. Recent experiments in a modified Couette cell
provided localized shear flow in the bulk away from the confining walls. The
non-trivial shape of the shear band was measured as the function of the cell
geometry. First we present a geometric argument for narrow shear bands which
connects the function of their surface position with the shape in the bulk.
Assuming a simple dissipation mechanism we show that the principle of minimum
dissipation of energy provides a good description of the shape function.
Furthermore, we discuss the possibility and behavior of shear bands which are
detached from the free surface and are entirely covered in the bulk.Comment: 4 pages, 5 figures; minor changes, typos and journal-ref adde
Center Vortices and the Gribov Horizon
We show how the infinite color-Coulomb energy of color-charged states is
related to enhanced density of near-zero modes of the Faddeev-Popov operator,
and calculate this density numerically for both pure Yang-Mills and gauge-Higgs
systems at zero temperature, and for pure gauge theory in the deconfined phase.
We find that the enhancement of the eigenvalue density is tied to the presence
of percolating center vortex configurations, and that this property disappears
when center vortices are either removed from the lattice configurations, or
cease to percolate. We further demonstrate that thin center vortices have a
special geometrical status in gauge-field configuration space: Thin vortices
are located at conical or wedge singularities on the Gribov horizon. We show
that the Gribov region is itself a convex manifold in lattice configuration
space. The Coulomb gauge condition also has a special status; it is shown to be
an attractive fixed point of a more general gauge condition, interpolating
between the Coulomb and Landau gauges.Comment: 19 pages, 17 EPS figures, RevTeX4; v2: added references, corrected
caption of fig. 11; v3: new data for higher couplings, clarifications on
color-Coulomb potential in deconfined phase, version to appear in JHE
Description of two new species of the groundstreak genus Arzecla Duarte et Robbins, 2010 (Lepidoptera: Lycaenidae: Theclinae: Eumaeini) from Colombia = Описание двух новых видов рода Arzecla Duarte et Robbins, 2010 (Lepidoptera: Lycaenidae: Theclinae: Eumaeini) из Колумбии
Two species of Arzecla Duarte et Robbins,
2010 are described from Colombia, namely: Arzecla
straboris Bálint, sp. n. (type locality: El Aguila, Manizales,
Caldas), and Arzecla straelena Bálint, sp. n. (type locality:
Cerro Ingrumá, Riosucio, Caldas), both on the basis of a
single male specimen. New species possess a combination of characters, unique in the genus, hence they are easy to identify. A checklist with biogeographic and country indications and a key for identification based on wing characters for all described Arzecla species is provided. Specimens examined for comparative purpose are listed as an Appendix. Eleven figures
Dynamic asset trees and Black Monday
The minimum spanning tree, based on the concept of ultrametricity, is
constructed from the correlation matrix of stock returns. The dynamics of this
asset tree can be characterised by its normalised length and the mean
occupation layer, as measured from an appropriately chosen centre called the
`central node'. We show how the tree length shrinks during a stock market
crisis, Black Monday in this case, and how a strong reconfiguration takes
place, resulting in topological shrinking of the tree.Comment: 6 pages, 3 eps figues. Elsevier style. Will appear in Physica A as
part of the Bali conference proceedings, in pres
Bound states in the 3d Ising model and implications for QCD at finite temperature and density
We study the spectrum of bound states of the three dimensional Ising model in
the (h,beta) plane near the critical point. We show the existence of an
unbinding line, defined as the boundary of the region where bound states exist.
Numerical evidence suggests that this line coincides with the beta=beta_c axis.
When the 3D Ising model is considered as an effective description of hot QCD at
finite density, we conjecture the correspondence between the unbinding line and
the line that separates the quark-gluon plasma phase from the superconducting
phase. The bound states of the Ising model are conjectured to correspond to the
diquarks of the latter phase of QCD.Comment: Lattice2001(hightemp
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Study of Crystal and Electronic Structure of Ti-Cr Alloys during Decomposition of b-Solid Solution
Thermal Decomposition of the B.C.C. Beta-Solid Solution of Titanium Alloy Containing 6.7 at% Mo, 3 at% Zr, and 1.8 at% Sn
- …