84,028 research outputs found
High-speed ultrasound imaging in dense suspensions reveals impact-activated solidification due to dynamic shear jamming
A remarkable property of dense suspensions is that they can transform from
liquid-like at rest to solid-like under sudden impact. Previous work showed
that this impact-induced solidification involves rapidly moving jamming fronts;
however, details of this process have remained unresolved. Here we use
high-speed ultrasound imaging to probe non-invasively how the interior of a
dense suspension responds to impact. Measuring the speed of sound we
demonstrate that the solidification proceeds without a detectable increase in
packing fraction, and imaging the evolving flow field we find that the shear
intensity is maximized right at the jamming front. Taken together, this
provides direct experimental evidence for jamming by shear, rather than
densification, as driving the transformation to solid-like behavior. Based on
these findings we propose a new model to explain the anisotropy in the
propagation speed of the fronts and delineate the onset conditions for dynamic
shear jamming in suspensions.Comment: 9 pages, 3 figure
Dynamic shear jamming in dense granular suspensions under extension
Unlike dry granular materials, a dense granular suspension like cornstarch in
water can strongly resist extensional flows. At low extension rates, such a
suspension behaves like a viscous liquid, but rapid extension results in a
response where stresses far exceed the predictions of lubrication hydrodynamics
and capillarity. To understand this remarkable mechanical response, we
experimentally measure the normal force imparted by a large bulk of the
suspension on a plate moving vertically upward at a controlled velocity. We
observe that above a velocity threshold, the peak force increases by orders of
magnitude. Using fast ultrasound imaging we map out the local velocity profiles
inside the suspension which reveal the formation of a growing jammed region
under rapid extension. This region interacts with the rigid boundaries of the
container through strong velocity gradients, suggesting a direct connection to
the recently proposed shear-jamming mechanism.Comment: Accepted for publication in Phys. Rev.
Studying High Energy Final State Interactions by N/D Method
We discuss the final state interaction effects at high energies via a
multi-channel N/D method. We find that the 2 by 2 charge--exchange final state
interactions typically contribute an enhancement factor of a few times
in the meson decay amplitudes, both for the real and the
imaginary part. We also make some discussions on the elastic rescattering
effects.Comment: 10 pages, revte
Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Euclidean Theory
We study the large-j asymptotics of the Euclidean EPRL/FK spin foam amplitude
on a 4d simplicial complex with arbitrary number of simplices. We show that for
a critical configuration (j_f, g_{ve}, n_{ef}) in general, there exists a
partition of the simplicial complex into three regions: Non-degenerate region,
Type-A degenerate region and Type-B degenerate region. On both the
non-degenerate and Type-A degenerate regions, the critical configuration
implies a non-degenerate Euclidean geometry, while on the Type-B degenerate
region, the critical configuration implies a vector geometry. Furthermore we
can split the Non-degenerate and Type-A regions into sub-complexes according to
the sign of Euclidean oriented 4-simplex volume. On each sub-complex, the spin
foam amplitude at critical configuration gives a Regge action that contains a
sign factor sgn(V_4(v)) of the oriented 4-simplices volume. Therefore the Regge
action reproduced here can be viewed as a discretized Palatini action with
on-shell connection. The asymptotic formula of the spin foam amplitude is given
by a sum of the amplitudes evaluated at all possible critical configurations,
which are the products of the amplitudes associated to different type of
geometries.Comment: 27 pages, 5 figures, references adde
Induced Magnetic Ordering by Proton Irradiation in Graphite
We provide evidence that proton irradiation of energy 2.25 MeV on
highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism.
Measurements performed with a superconducting quantum interferometer device
(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering
is stable at room temperature.Comment: 3 Figure
Stokes Parameters as a Minkowskian Four-vector
It is noted that the Jones-matrix formalism for polarization optics is a
six-parameter two-by-two representation of the Lorentz group. It is shown that
the four independent Stokes parameters form a Minkowskian four-vector, just
like the energy-momentum four-vector in special relativity. The optical filters
are represented by four-by-four Lorentz-transformation matrices. This
four-by-four formalism can deal with partial coherence described by the Stokes
parameters. A four-by-four matrix formulation is given for decoherence effects
on the Stokes parameters, and a possible experiment is proposed. It is shown
also that this Lorentz-group formalism leads to optical filters with a symmetry
property corresponding to that of two-dimensional Euclidean transformations.Comment: RevTeX, 22 pages, no figures, submitted to Phys. Rev.
A scheme for demonstration of fractional statistics of anyons in an exactly solvable model
We propose a scheme to demonstrate fractional statistics of anyons in an
exactly solvable lattice model proposed by Kitaev that involves four-body
interactions. The required many-body ground state, as well as the anyon
excitations and their braiding operations, can be conveniently realized through
\textit{dynamic}laser manipulation of cold atoms in an optical lattice. Due to
the perfect localization of anyons in this model, we show that a quantum
circuit with only six qubits is enough for demonstration of the basic braiding
statistics of anyons. This opens up the immediate possibility of
proof-of-principle experiments with trapped ions, photons, or nuclear magnetic
resonance systems.Comment: 4 pages, 3 figure
Towards Work-Efficient Parallel Parameterized Algorithms
Parallel parameterized complexity theory studies how fixed-parameter
tractable (fpt) problems can be solved in parallel. Previous theoretical work
focused on parallel algorithms that are very fast in principle, but did not
take into account that when we only have a small number of processors (between
2 and, say, 1024), it is more important that the parallel algorithms are
work-efficient. In the present paper we investigate how work-efficient fpt
algorithms can be designed. We review standard methods from fpt theory, like
kernelization, search trees, and interleaving, and prove trade-offs for them
between work efficiency and runtime improvements. This results in a toolbox for
developing work-efficient parallel fpt algorithms.Comment: Prior full version of the paper that will appear in Proceedings of
the 13th International Conference and Workshops on Algorithms and Computation
(WALCOM 2019), February 27 - March 02, 2019, Guwahati, India. The final
authenticated version is available online at
https://doi.org/10.1007/978-3-030-10564-8_2
Assessment of different urban traffic control strategy impacts on vehicle emissions
This paper investigates the influence of traffic signal control strategy on vehicle emissions, vehicle journey time and total throughput flow within a single isolated four-armed junction. Two pre-timed signal plans are considered, one with two-stages involving permissive-only opposing turns and the other with four-stages which has no conflicting traffic. Additionally, the increase in efficiency by utilising actuated signal timing where green time is re-optimised as flow values vary is investigated. A microscopic traffic simulation model is used to model flows and AIRE (Analysis of Instantaneous Road Emissions) microscopic emissions model is utilised to out- put emission levels from the flow data. A simple junction model shows that the two-stage signal plan is more efficient in both emis- sions and journey time. However, as the level of opposed turning vehicles and conflicting movement increases, the two-stage model moves to being the inferior signal plan choice and the four-stage plan outputs fewer emissions than the two-stage plan. A real-world example of a four-armed junction has been used in this study and from the traffic survey data and existing junction layout; it is rec- ommended that a two-stage plan is used as it produces lower amounts of emissions and shorter journey times compared to a four-stage plan. The results also show that nitrogen oxides (NOx) are the most sensitive to changes in flow followed by carbon dioxide (CO2), Black Carbon and then particulate matter (PM10)
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