3,271 research outputs found
Interfacial deflection and jetting of a paramagnetic particle-laden fluid: theory and experiment
We describe the results of experiments and mathematical analysis of the deformation of a free surface by an aggregate of magnetic particles. The system we study is differentiated from ferrofluid systems because it contains regions rich with magnetic material as well as regions of negligible magnetic content. In our experiments, the magnetic force from a spherical permanent magnet collects magnetic particles to a liquidâair interface, and deforms the free surface to form a hump. The hump is composed of magnetic and non-magnetic regions due to the particle collection. When the magnet distance falls below a threshold value, we observe the transition of the hump to a jet. The mathematical model we develop, which consists of a numerical solution and an asymptotic approximation, captures the shape of the liquidâair interface during the deformation stage and a scaling prediction for the critical magnet distance for the hump to become a jet
Instantaneous Bethe-Salpeter Equation and Its Exact Solution
We present an approach to solve a Bethe-Salpeter (BS) equation exactly
without any approximation if the kernel of the BS equation exactly is
instantaneous, and take positronium as an example to illustrate the general
features of the solutions. As a middle stage, a set of coupled and
self-consistent integration equations for a few scalar functions can be
equivalently derived from the BS equation always, which are solvable
accurately. For positronium, precise corrections to those of the Schr\"odinger
equation in order (relative velocity) in eigenfunctions, in order in
eigenvalues, and the possible mixing, such as that between () and
() components in () states as well, are
determined quantitatively. Moreover, we also point out that there is a
problematic step in the classical derivation which was proposed first by E.E.
Salpeter. Finally, we emphasize that for the effective theories (such as NRQED
and NRQCD etc) we should pay great attention on the corrections indicated by
the exact solutions.Comment: 4 pages, replace for shortening the manuscrip
Electrochemical Deposition and Dissolution of Aluminum in NaAlCl4 Melts:Influence of MnCl2 and Sulfide Addition
Recurrence and higher ergodic properties for quenched random Lorentz tubes in dimension bigger than two
We consider the billiard dynamics in a non-compact set of R^d that is
constructed as a bi-infinite chain of translated copies of the same
d-dimensional polytope. A random configuration of semi-dispersing scatterers is
placed in each copy. The ensemble of dynamical systems thus defined, one for
each global realization of the scatterers, is called `quenched random Lorentz
tube'. Under some fairly general conditions, we prove that every system in the
ensemble is hyperbolic and almost every system is recurrent, ergodic, and
enjoys some higher chaotic properties.Comment: Final version for J. Stat. Phys., 18 pages, 4 figure
An adaptive large neighborhood search heuristic for the share-a-ride problem
The Share-a-Ride Problem (SARP) aims at maximizing the profit of serving a set of passengers and parcels using a set of homogeneous vehicles. We propose an adaptive large neighborhood search (ALNS) heuristic to address the SARP. Furthermore, we study the problem of determining the time slack in a SARP schedule. Our proposed solution approach is tested on three sets of realistic instances. The performance of our heuristic is benchmarked against a mixed integer programming (MIP) solver and the Dial-a-Ride Problem (DARP) test instances. Compared to the MIP solver, our heuristic is superior in both the solution times and the quality of the obtained solutions if the CPU time is limited. We also report new best results for two out of twenty benchmark DARP instances
Dynamics of quantum Hall stripes in double-quantum-well systems
The collective modes of stripes in double layer quantum Hall systems are
computed using the time-dependent Hartree-Fock approximation. It is found that,
when the system possesses spontaneous interlayer coherence, there are two
gapless modes, one a phonon associated with broken translational invariance,
the other a pseudospin-wave associated with a broken U(1) symmetry. For large
layer separations the modes disperse weakly for wavevectors perpendicular to
the stripe orientation, indicating the system becomes akin to an array of
weakly coupled one-dimensional XY systems. At higher wavevectors the collective
modes develop a roton minimum associated with a transition out of the coherent
state with further increasing layer separation. A spin wave model of the system
is developed, and it is shown that the collective modes may be described as
those of a system with helimagnetic ordering.Comment: 16 pages including 7 postscript figure
Towards the understanding of vertical-axis wind turbines in double-rotor configuration
Vertical-axis wind turbines (VAWTs) in double-rotor configuration, meaning two rotors in close proximity, have the ability to enhance the power performance. In this study, we work towards the understanding of vertical-axis wind turbines in double-rotor configuration. Numerical simulations are performed to gain insight in the physics behind the double-rotor concept. Furthermore, a parametric study is performed to explore the effect of the double-rotor lay-out, rotor loading, rotor spacing and wind direction on the flow characteristics and the power generation.</p
Observation of Enhanced Beaming from Photonic Crystal Waveguides
We report on the experimental observation of the beaming effect in photonic
crystals enhanced via surface modes. We experimentally map the spatial field
distribution of energy emitted from a subwavelength photonic crystal waveguide
into free-space, rendering with crisp clarity the diffractionless beaming of
energy. Our experimental data agree well with our numerical studies of the
beaming enhancement in photonic crystals with modulated surfaces. Without loss
of generality, we study the beaming effect in a photonic crystal scaled to
microwave frequencies and demonstrate the technological capacity to deliver
long-range, wavelength-scaled beaming of energy.Comment: 4 pages, 6 figure
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