8,587 research outputs found
A deductive statistical mechanics approach for granular matter
We introduce a deductive statistical mechanics approach for granular
materials which is formally built from few realistic physical assumptions. The
main finding is an universal behavior for the distribution of the density
fluctuations. Such a distribution is the equivalent of the Maxwell-Boltzmann's
distribution in the kinetic theory of gasses. The comparison with a very
extensive set of experimental and simulation data for packings of monosized
spherical grains, reveals a remarkably good quantitative agreement with the
theoretical predictions for the density fluctuations both at the grain level
and at the global system level. Such agreement is robust over a broad range of
packing fractions and it is observed in several distinct systems prepared by
using different methods. The equilibrium distributions are characterized by
only one parameter () which is a quantity very sensitive to changes in the
structural organization. The thermodynamical equivalent of and its relation
with the `granular temperature' are also discussed.Comment: 15 pages, 6 figure
Quantum Measurement and the Aharonov-Bohm Effect with Superposed Magnetic Fluxes
We consider the magnetic flux in a quantum mechanical superposition of two
values and find that the Aharonov-Bohm effect interference pattern contains
information about the nature of the superposition, allowing information about
the state of the flux to be extracted without disturbance. The information is
obtained without transfer of energy or momentum and by accumulated nonlocal
interactions of the vector potential with many charged particles
forming the interference pattern, rather than with a single particle. We
suggest an experimental test using already experimentally realized superposed
currents in a superconducting ring and discuss broader implications.Comment: 6 pages, 4 figures; Changes from version 3: corrected typo (not
present in versions 1 and 2) in Eq. 8; Changes from version 2: shortened
abstract; added refs and material in Section IV. The final publication is
available at: http://link.springer.com/article/10.1007/s11128-013-0652-
Smoothing tautologies, hidden dynamics, and sigmoid asymptotics for piecewise smooth systems
Switches in real systems take many forms, such as impacts, electronic relays,
mitosis, and the implementation of decisions or control strategies. To
understand what is lost, and what can be retained, when we model a switch as an
instantaneous event, requires a consideration of so-called hidden terms. These
are asymptotically vanishing outside the switch, but can be encoded in the form
of nonlinear switching terms. A general expression for the switch can be
developed in the form of a series of sigmoid functions. We review the key steps
in extending the Filippov's method of sliding modes to such systems. We show
how even slight nonlinear effects can hugely alter the behaviour of an
electronic control circuit, and lead to `hidden' attractors inside the
switching surface.Comment: 12 page
Deformation of lamellar TiAl alloys by longitudinal twinning
© 2016 Elsevier Ltd. The occurrence of longitudinal twinning in the engineering alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol.% TiB2 has been studied by measuring the changes in crystallographic orientation within individual lamellae during microcompression. Twinning in this alloy appeared to be a nucleation-limited process with the twins growing from lamellar boundaries at resolved shear stresses as low as 100 MPa, consistent with observations elsewhere. However, instead of forming twins ∼ 10-200 nm in thickness, as in polysynthetically twinned crystals, the longitudinal twins in this alloy were initiated at a lamellar boundary and then spread through the whole lamella.The work was supported by the EPSRC / Rolls-Royce Strategic Partnership (EP/H500375/1). Alberto Palomares Garcia, Claire Davis and Robert Jones are acknowledged for discussions and help with the TEM respectively
Upward Three-Dimensional Grid Drawings of Graphs
A \emph{three-dimensional grid drawing} of a graph is a placement of the
vertices at distinct points with integer coordinates, such that the straight
line segments representing the edges do not cross. Our aim is to produce
three-dimensional grid drawings with small bounding box volume. We prove that
every -vertex graph with bounded degeneracy has a three-dimensional grid
drawing with volume. This is the broadest class of graphs admiting
such drawings. A three-dimensional grid drawing of a directed graph is
\emph{upward} if every arc points up in the z-direction. We prove that every
directed acyclic graph has an upward three-dimensional grid drawing with
volume, which is tight for the complete dag. The previous best upper
bound was . Our main result is that every -colourable directed
acyclic graph ( constant) has an upward three-dimensional grid drawing with
volume. This result matches the bound in the undirected case, and
improves the best known bound from for many classes of directed
acyclic graphs, including planar, series parallel, and outerplanar
Measurement of enhanced ductility in nanolayered ceramics via micro-compression testing and digital image correlation
The use of ceramic or intermetallic structures in industrial applications is limited by their brittleness. However, it has been shown that nanolayered ceramics, such as the MAX phases, show unusually high levels of plasticity, with resolved shear yield stresses being reported to be as low as 77 MPa [1]. Our aim is to show that the origin of this behaviour is related to electron density shifts between layers, which enable eased dislocation movement compared to non-layered ceramics [2]. For an accurate study of this effect, and to prove its generality, a reliable determination of the onset of plastic deformation in form of dislocation movement is crucial.
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Comparison of Two Different Pasture Species Compositions for Recovery of Deep Soil Nitrogen during Winter
Surplus nitrate (NO3-) beneath animal urine patches is highly vulnerable to leaching, particularly during winter when soil drainage is often highest. Most common pastures in New Zealand (i.e. Lolium perenne) have relatively shallow root systems and produce low dry matter (DM) yields during winter months. Recent investigations suggest that alternative pasture species may be able to recover more soil nitrogen (N) during winter and consequently reduce NO3- leaching losses (Moir et al., 2013; Malcolm et al., 2014; 2015). However, further work is required to better understand the importance of root system architecture and plant growth of these alternative species during this cool period.
The objective was to determine the ability of L. multiflorum (Italian ryegrass) and F. arundinacea (tall fescue)-based pastures to recover mineral-N from different soil depths under simulated winter conditions and determine the relative importance of plant growth/metabolic activity and root system architecture
The topological susceptibility and f_pi from lattice QCD
We study the topological susceptibility, chi, in QCD with two quark flavours
using lattice field configurations that have been produced with an O(a)
improved quark action. We find clear evidence for the expected suppression at
small quark mass, and examine the variation of chi with this mass. The
resulting estimate of the pion decay constant, f_pi = 105 +/- 6 ^{+18}_{-10}
MeV, is consistent with the experimental value of ~93 MeV. We compare chi to
the large-N_c prediction and find consistency over a large range of quark
masses. We discuss the benefits of the non-perturbative action improvement
scheme and of the stategy of keeping the lattice spacing (nearly) fixed as the
quark mass is varied. We compare our results with other studies and suggest why
such a quark mass dependence has not always been seen.Comment: LaTeX. Supercedes our preprint hep-ph/0004180. Version to appear in
Phys. Lett.
Stable Speckle Patterns for Nano-scale Strain Mapping up to 700 °C
The digital image correlation (DIC) of speckle patterns obtained by vapour-assisted gold remodelling at 200 – 350 °C has already been used to map plastic strains with submicron resolution. However, it has not so far proved possible to use such patterns for testing at high temperatures. Here we demonstrate how a gold speckle pattern can be made that is stable at 700 °C, to study deformation in a commercial TiAl alloy (Ti-45Al-2Nb- 2Mn(at%)-0.8 vol% TiB). The pattern is made up of a uniformly sized random array of Au islands as small as 15 nm in diameter, depending on reconstruction parameters, with a sufficiently small spacing to be suitable for nano-scale, nDIC, strain mapping at a subset size of 60 × 60 nm . It can be used at temperatures up to 700 °C for many hours, for high cycle fatigue testing for instance. There is good particle attachment to the substrate. It can withstand ultra-sound cleaning, is thermally stable and has a high atomic number contrast for topography-free backscatter electron imaging.EPSRC / Rolls-Royce Strategic Partnership (EP/M005607/1
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