Influence of the state of light on the optically induced interparticle interaction

A general expression for the energy of interparticle interaction induced by an arbitrary mode of light is determined using quantum electrodynamics, and it is shown that the Casimir-Polder potential is included within this quantum result. Equations are also derived for the corresponding coupling induced by multimode number states of light, and the dependence of the pair energy on the Poynting vector and polarization state is determined. Attention is then focused on the interactions between particles trapped in counterpropagating coherent beams, both with and without interference, and it is shown that the results afford insights into the multiparticle structures that can be optically fabricated with counterpropagating input. Brief consideration is also given to the effect of squeezing the optical coherent state. Extending previous studies of optical binding in Laguerre-Gaussian beams, results are given for the case of particles trapped at radially different locations within the beam structure. Finally, consideration is given to interparticle interactions induced by broadband light, and it is shown how the length of optically fabricated particle chains can be controlled by the use of wavelength filters

Picosecond imaging of sprays

Preliminary results from applying a Kerr-Fourier imaging system to a water/air spray produced by a shear coaxial element are presented. The physics behind ultrafast time-gated optical techniques is discussed briefly. A typical setup of a Kerr-Fourier time gating system is presented

Multimodal nested sampling: an efficient and robust alternative to MCMC methods for astronomical data analysis

In performing a Bayesian analysis of astronomical data, two difficult problems often emerge. First, in estimating the parameters of some model for the data, the resulting posterior distribution may be multimodal or exhibit pronounced (curving) degeneracies, which can cause problems for traditional MCMC sampling methods. Second, in selecting between a set of competing models, calculation of the Bayesian evidence for each model is computationally expensive. The nested sampling method introduced by Skilling (2004), has greatly reduced the computational expense of calculating evidences and also produces posterior inferences as a by-product. This method has been applied successfully in cosmological applications by Mukherjee et al. (2006), but their implementation was efficient only for unimodal distributions without pronounced degeneracies. Shaw et al. (2007), recently introduced a clustered nested sampling method which is significantly more efficient in sampling from multimodal posteriors and also determines the expectation and variance of the final evidence from a single run of the algorithm, hence providing a further increase in efficiency. In this paper, we build on the work of Shaw et al. and present three new methods for sampling and evidence evaluation from distributions that may contain multiple modes and significant degeneracies; we also present an even more efficient technique for estimating the uncertainty on the evaluated evidence. These methods lead to a further substantial improvement in sampling efficiency and robustness, and are applied to toy problems to demonstrate the accuracy and economy of the evidence calculation and parameter estimation. Finally, we discuss the use of these methods in performing Bayesian object detection in astronomical datasets.Comment: 14 pages, 11 figures, submitted to MNRAS, some major additions to the previous version in response to the referee's comment

Evidence for a Noachian-Aged Ephemeral Lake in Gusev Crater, Mars

Gusev crater was selected as the landing site for the Spirit rover because of the likelihood that it contained an ancient lake. Although outcrops rich in Mg-Fe carbonate dubbed Comanche were discovered in the Noachian-aged Columbia Hills, they were inferred to result from volcanic hydrothermal activity. Spirit encountered other mineral and chemical indicators of aqueous activity, but none was recognized as definitive evidence for a former lake in part because none was associated with obvious lacustrine sedimentary deposits. However, water discharge into Martian crater basins like Gusev may have been episodic, producing only small amounts of sediment and shallow ephemeral lakes. Evaporative precipitation from such water bodies has been suggested as a way of producing the Mg- and Fe-rich carbonates found in ALH84001 and carbonates and salts in some nakhlites a hypothesis we examine for the Comanche carbonate

The Static Failure of Adhesively Bonded Metal Laminate Structures: A Cohesive Zone Approach

Data on distribution, ecology, biomass, recruitment, growth, mortality and productivity of the West African bloody cockle Anadara senilis were collected at the Banc d'Aguuin, Mauritania, in early 1985 and 1986. Ash-free dry weight appeared to be correlated best with shell height. A. senilis was abundant on the tidal flats of landlocked coastal bays, but nearly absent on the tidal flats bordering the open sea. The average biomass for the entire area of tidal flats was estimated at 5.5 g·m−2 ash-free dry weight. The A. senilis population appeared to consist mainly of 10 to 20-year-old individuals, showing a very slow growth and a production: biomass ratio of about 0.02 y−1. Recruitment appeared negligible and mortality was estimated to be about 10% per year. Oystercatchers (Haematopus ostralegus), the gastropod Cymbium cymbium and unknown fish species were responsible for a large share of this. The distinction of annual growth marks permitted the assessment of year-class strength, which appeared to be correlated with the average discharge of the river Senegal. This may be explained by assuming that year-class strength and river discharge both are correlated with rainfall at the Banc d'Arguin.

Gossip as a Burdened Virtue

Gossip is often serious business, not idle chitchat. Gossip allows those oppressed to privately name their oppressors as a warning to others. Of course, gossip can be in error. The speaker may be lying or merely have lacked sufficient evidence. Bias can also make those who hear the gossip more or less likely to believe the gossip. By examining the social functions of gossip and considering the differences in power dynamics in which gossip can occur, we contend that gossip may be not only permissible but virtuous, both as the only reasonable recourse available and as a means of resistance against oppression

Mineralización del herbicida comercial 2,4-D Amina en laboratorio y en reactor solar a escala piloto

Se estudian las eficiencias cuánticas de mineralización para la degradación foto-Fenton del herbicida comercial 2,4-D Amina empleando un reactor de laboratorio. Para todos los ensayos la concentración inicial del contaminante es de 30 ppm expresado en términos de la sal de dimetil amina del ácido 2,4 diclorofenoxiacético (TOC equivalente 13.5 ppm). A partir de los resultados experimentales y los cálculos de la velocidad promedio de absorción de fotones, se computaron las eficiencias cuánticas de mineralización aparente y absoluta. Para 30 min de reacción (T=25ºC), se alcanzaron valores máximos de eficiencias cuánticas de mineralización aparente y absoluta de 0.378 y 0.590 mol/Einstein, respectivamente. Para ensayos realizados empleando el reactor solar escala planta piloto, la mineralización completa del contaminante es alcanzada luego de 180 min (R=50). Además, para condiciones similares de operación solares se obtuvo una reducción 43 % mayor de TOC en la degradación del principio activo respecto al herbicida comercial.A study of the quantum efficiency of the photo-Fenton mineralization of a commercial herbicide 2,4-D amine in a laboratory reactor is presented. All the experimental runs were performed with an initial concentration of contaminant of 30 ppm expressed in terms of the dimethyl amine salt of 2,4-dichlorophenoxyacetic acid (equivalent to 13.5 ppm TOC). A set of experimental runs were performed to study the effects of the operating parameters on the Total Organic Carbon (TOC) conversion as a function of time. Different values of the hydrogen peroxide and ferric iron initial concentrations, and reaction temperatures were studied. From the experimental results and the average photon absorption calculations for the photo-Fenton treatment of this commercial herbicide, apparent and absolute quantum efficiencies of mineralization were defined and computed. For 25 °C and a reaction time equal to 30 min, maximum apparent and absolute quantum efficiencies of mineralization equal to 0.378 and 0.590 mol/Einstein, respectively, were obtained. Results of the commercial herbicide degradation using a solar reactor at pilot plant scale are also presented. The complete mineralization of pollutants is achieved after 180 min of reaction (R = 50). In addition, for similar solar operating conditions, a 43% greater TOC reduction was achieved for the degradation of the active principle with respect to the commercial herbicide.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES