2,654 research outputs found
Dye lasing in optically manipulated liquid aerosols
We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging between 7.7 and 11.0 mu m, which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Our experiments revealed nonlinear dependence of the intensity of the droplet whispering gallery modes (WGMs) on the pump laser fluence, indicating dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by changing the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium
Dimer coverings on the Sierpinski gasket with possible vacancies on the outmost vertices
We present the number of dimers on the Sierpinski gasket
at stage with dimension equal to two, three, four or five, where one of
the outmost vertices is not covered when the number of vertices is an
odd number. The entropy of absorption of diatomic molecules per site, defined
as , is calculated to be
exactly for . The numbers of dimers on the generalized
Sierpinski gasket with and are also obtained
exactly. Their entropies are equal to , , ,
respectively. The upper and lower bounds for the entropy are derived in terms
of the results at a certain stage for with . As the
difference between these bounds converges quickly to zero as the calculated
stage increases, the numerical value of with can be
evaluated with more than a hundred significant figures accurate.Comment: 35 pages, 20 figures and 1 tabl
Spanning Trees on Graphs and Lattices in d Dimensions
The problem of enumerating spanning trees on graphs and lattices is
considered. We obtain bounds on the number of spanning trees and
establish inequalities relating the numbers of spanning trees of different
graphs or lattices. A general formulation is presented for the enumeration of
spanning trees on lattices in dimensions, and is applied to the
hypercubic, body-centered cubic, face-centered cubic, and specific planar
lattices including the kagom\'e, diced, 4-8-8 (bathroom-tile), Union Jack, and
3-12-12 lattices. This leads to closed-form expressions for for these
lattices of finite sizes. We prove a theorem concerning the classes of graphs
and lattices with the property that
as the number of vertices , where is a finite
nonzero constant. This includes the bulk limit of lattices in any spatial
dimension, and also sections of lattices whose lengths in some dimensions go to
infinity while others are finite. We evaluate exactly for the
lattices we considered, and discuss the dependence of on d and the
lattice coordination number. We also establish a relation connecting to the free energy of the critical Ising model for planar lattices .Comment: 28 pages, latex, 1 postscript figure, J. Phys. A, in pres
Two-frequency shell model for hypernuclei and meson-exchange hyperon-nucleon potentials
A two-frequency shell model is proposed for investigating the structure of hypernuclei starting with a hyperon-nucleon potential in free space. In a calculation using the folded-diagram method for Λ¹⁶O, the Λ single particle energy is found to have a saturation minimum at an oscillator frequency ħωΛ≈10MeV, for the Λ orbit, which is considerably smaller than ħωN=14MeV for the nucleon orbit. The spin-dependence parameters derived from the Nijmegen NSC89 and NSC97f potentials are similar, but both are rather different from those obtained with the Jülich-B potential. The ΛNN three-body interactions induced by ΛN-ΣN transitions are important for the spin parameters, but relatively unimportant for the low-lying states of Λ¹⁶O.Yiharn Tzeng, S. Y. Tsay Tzeng, T. T. S. Kuo, T.-S.H. Lee, and V. G. D. Stok
Influence of realistic parameters on state-of-the-art LWFA experiments
We examine the influence of non-ideal plasma-density and non-Gaussian
transverse laser-intensity profiles in the laser wakefield accelerator
analytically and numerically. We find that the characteristic amplitude and
scale length of longitudinal density fluctuations impacts on the final energies
achieved by electron bunches. Conditions that minimize the role of the
longitudinal plasma density fluctuations are found. The influence of higher
order Laguerre-Gaussian laser pulses is also investigated. We find that higher
order laser modes typically lead to lower energy gains. Certain combinations of
higher order modes may, however, lead to higher electron energy gains.Comment: 16 pages, 6 figures; Accepted for publication in Plasma Physics and
Controlled Fusio
Spanning trees on the Sierpinski gasket
We obtain the numbers of spanning trees on the Sierpinski gasket
with dimension equal to two, three and four. The general expression for the
number of spanning trees on with arbitrary is conjectured. The
numbers of spanning trees on the generalized Sierpinski gasket
with and are also obtained.Comment: 20 pages, 8 figures, 1 tabl
Portable Inter-workgroup Barrier Synchronisation for GPUs
Despite the growing popularity of GPGPU programming, there is not yet a portable and formally-specified barrier that one can use to synchronise across workgroups. Moreover, the occupancy-bound execution model of GPUs breaks assumptions inherent in traditional software execution barriers, exposing them to deadlock. We present an occupancy discovery protocol that dynamically discovers a safe estimate of the occupancy for a given GPU and kernel, allowing for a starvation-free (and hence, deadlock-free) inter-workgroup barrier by restricting the number of workgroups according to this estimate. We implement this idea by adapting an existing, previously non-portable, GPU inter-workgroup barrier to use OpenCL 2.0 atomic operations, and prove that the barrier meets its natural specification in terms of synchronisation.
We assess the portability of our approach over eight GPUs spanning four vendors, comparing the performance of our method against alternative methods. Our key findings include: (1) the recall of our discovery protocol is nearly 100%; (2) runtime comparisons vary substantially across GPUs and applications; and (3) our method provides portable and safe inter-workgroup synchronisation across the applications we study
Novel pulsatile-release microparticles for single-injection vaccination
Many controlled release devices are designed to achieve near zero-order release kinetics, however for some applications, such as vaccination, non-continuous or pulsatile release is desired. Such pulsatile release systems may enable the creation of single-injection vaccines that eliminate the need for subsequent booster immunizations by spontaneously releasing antigen at time points that correspond to normal vaccination regimens. This would be especially important in the developing world where a lack of consistent access to healthcare contributes to approximately 1.5 million vaccine-preventable deaths each year.1 Here we present the fabrication and characterization of biodegradable core-shell microparticles that exhibit pulsatile release kinetics due to their unique structure. These particles are produced using a novel fabrication process that combines soft lithography, picoliter dispensing, optical alignment, and a gentle heat-based sintering step to generate microparticles with a biodegradable polymeric shell surrounding an antigen-filled core. By altering the composition (e.g. copolymer ratio or molecular weight) of the poly(lactic-co-glycolic acid) shell, particles can be tuned to release discrete pulses of a model antigen at times ranging from four days to two months. This fabrication method is also compatible with sensitive biologics, such as the inactivated polio virus, which retains \u3e80% of its antigenicity after encapsulation. Further, because the shell of the particle is physically separated from the core, these particles can be filled with any aqueous vaccine solution without affecting release kinetics and be easily scaled via massively parallel fabrication. As a result, these particles have exciting potential as single-injection vaccines that fully mimic the antigen presentation profile of traditional bolus injections administered over the course of months or years.
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Probabilistic Bisimulation: Naturally on Distributions
In contrast to the usual understanding of probabilistic systems as stochastic
processes, recently these systems have also been regarded as transformers of
probabilities. In this paper, we give a natural definition of strong
bisimulation for probabilistic systems corresponding to this view that treats
probability distributions as first-class citizens. Our definition applies in
the same way to discrete systems as well as to systems with uncountable state
and action spaces. Several examples demonstrate that our definition refines the
understanding of behavioural equivalences of probabilistic systems. In
particular, it solves a long-standing open problem concerning the
representation of memoryless continuous time by memory-full continuous time.
Finally, we give algorithms for computing this bisimulation not only for finite
but also for classes of uncountably infinite systems
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