Suspension flow: do particles act as mixers?

Recently, Roht et al. [J. Contam. Hydrol. 145, 10-16 (2013)] observed that the presence of suspended non-Brownian macroscopic particles decreased the dispersivity of a passive solute, for a pressure-driven flow in a narrow parallel-plates channel at low Reynolds number. This result contradicts the idea that the streamline distortion caused by the random diffusive motion of the particles increases the dispersion and mixing of the solute. Therefore, to estimate the influence of this motion on the dispersivity of the solute, and investigate the origin of the reported decrease, we experimentally studied the probability density functions (pdf) of the particle velocities, and spatio-temporal correlations, in the same experimental configuration. We observed that, as the mean suspension velocity exceeds a critical value, the pdf of the streamwise velocities of the particles markedly changes from a symmetric distribution to an asymmetric one strongly skewed to high velocities and with a peak of most probable velocity close to the maximum velocity. The latter observations and the analysis of suspension microstructure indicate that the observed decrease in the dispersivity of the solute is due to particle migration to the mid-plane of the channel, and consequent flattening of the velocity profile. Moreover, we estimated the contribution of particle diffusive motion to the solute dispersivity to be three orders of magnitude smaller than the reported decrease, and thus negligible. Solute dispersion is then much more affected by how particles modify the flow velocity profile across the channel, than by their diffusive random motion

Method for analyzing radiation sensitivity of integrated circuits

A method for analyzing the radiation sensitivity of an integrated circuit is described to determine the components. The application of a narrow radiation beam to portions of the circuit is considered. The circuit is operated under normal bias conditions during the application of radiation in a dosage that is likely to cause malfunction of at least some transistors, while the circuit is monitored for failure of the irradiated transistor. When a radiation sensitive transistor is found, then the radiation beam is further narrowed and, using a fresh integrated circuit, a very narrow beam is applied to different parts of the transistor, such as its junctions, to locate the points of greatest sensitivity

_Limusaurus_ and bird digit identity

_Limusaurus_ is a remarkable herbivorous ceratosaur unique among theropods in having digits II, III and IV, with only a small metacarpal vestige of digit I. This raises interesting questions regarding the controversial identity of avian wing digits. The early tetanuran ancestors of birds had tridactyl hands with digital morphologies corresponding to digits I, II & III of other dinosaurs. In bird embryos, however, the pattern of cartilage formation indicates that their digits develop from positions that become digits II, III, & IV in other amniotes. _Limusaurus_ has been argued to provide evidence that the digits of tetanurans, currently considered to be I, II and III, may actually be digits II, III, & IV, thus explaining the embryological position of bird wing digits. However, morphology and gene expression of the anterior bird wing digit specifically resemble digit I, not II, of other amniotes. We argue that digit I loss in _Limusaurus_ is derived and thus irrelevant to understanding the development of the bird wing

Credit default swaps and financial stability: risks and regulatory issues.

The credit default swap (CDS) market has grown much faster than other derivatives markets since its inception. Even though it is dwarfed by the interest rate derivatives market, which is eight times larger, its growth has affected the stability of the financial system. CDS were originally designed as a risk transfer tool to allow investors to hedge their position in the debt of a reference entity, but much of the activity in this market is also speculative (Olléon-Assouan, 2004). Risk management in the CDS market has certainly improved significantly, reflected in the fact that gross notional volumes have fallen remarkably as a result of trade compression. Nevertheless there is still no accurate indication of how much risk has actually been transferred with these instruments, and this is a major concern for financial stability. Even a rough estimate of market size ranges from USD 29 trillion to USD 38 trillion at end-2008. Clarifying and harmonising information is vitally important, particularly since the uncertainty surrounding market participants’ risk exposure contains the seeds of systemic contagion. There is now a pressing need for better market supervision based on the active participation of regulators. The task has already been made easier by a number of public and private initiatives aimed at improving the functioning of the market and monitoring risks more effectively. The most tangible evidence of these combined efforts can be found in various plans for a clearinghouse that emerged in 2008 and 2009. Aside from its practical limitations, however, this solution cannot be extended to all CDS classes. And regulators still face the sizeable challenge of assessing overall counterparty risk on the CDS market and preventing concentration and formation of systemic exposures.

High-order optical nonlinearity at low light levels

We observe a nonlinear optical process in a gas of cold atoms that simultaneously displays the largest reported fifth-order nonlinear susceptibility \chi^(5) = 1.9x10^{-12} (m/V)^4 and high transparency. The nonlinearity results from the simultaneous cooling and crystallization of the gas, and gives rise to efficient Bragg scattering in the form of six-wave-mixing at low-light-levels. For large atom-photon coupling strengths, the back-action of the scattered fields influences the light-matter dynamics. This system may have important applications in many-body physics, quantum information processing, and multidimensional soliton formation.Comment: 5 pages, 3 figure

Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number

A study on the spatial organization and velocity fluctuations of non Brownian spherical particles settling at low Reynolds number in a vertical Hele-Shaw cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while the distance between cell plates ranged from 5 to 15 times the particle radius. Particle tracking revealed that particles were not uniformly distributed in space but assembled in transient settling clusters. The population distribution of these clusters followed an exponential law. The measured velocity fluctuations are in agreement with that predicted theoretically for spherical clusters, from the balance between the apparent weight and the drag force. This result suggests that particle clustering, more than a spatial distribution of particles derived from random and independent events, is at the origin of the velocity fluctuations.Comment: 13 pages, 8 figure

The Bonhomie Project: An Anti-Bullying Program for Middle School Students

Bullying is a prevalent issue in society today. The Bonhomie Project is a program developed to engage sixth grade students in learning about bullying and methods to help halt the cycle of bullying in their school. Students learn about the three key players of bullying, the various types of bullying, and how to stand up against bullies. This program utilizes R.J. Palacio\u27s award winning novel, Wonder, with students answering questions and discussing the parts of the novel in small groups; students also participate in activities that build up kindness instead of tearing each other down with bullying, and at the end of the program, students will develop their own anti-bullying policies to implement in their school