Real-time monitoring of proton exchange membrane fuel cell stack failure

Uneven pressure drops in a 75-cell 9.5-kWe proton exchange membrane fuel cell stack with a U-shaped flow configuration have been shown to cause localised flooding. Condensed water then leads to localised cell heating, resulting in reduced membrane durability. Upon purging of the anode manifold, the resulting mechanical strain on the membrane can lead to the formation of a pin-hole/membrane crack and a rapid decrease in open circuit voltage due to gas crossover. This failure has the potential to cascade to neighbouring cells due to the bipolar plate coupling and the current density heterogeneities arising from the pin-hole/membrane crack. Reintroduction of hydrogen after failure results in cell voltage loss propagating from the pin-hole/membrane crack location due to reactant crossover from the anode to the cathode, given that the anode pressure is higher than the cathode pressure. Through these observations, it is recommended that purging is avoided when the onset of flooding is observed to prevent irreparable damage to the stack

Software for Exact Integration of Polynomials over Polyhedra

We are interested in the fast computation of the exact value of integrals of polynomial functions over convex polyhedra. We present speed ups and extensions of the algorithms presented in previous work. We present the new software implementation and provide benchmark computations. The computation of integrals of polynomials over polyhedral regions has many applications; here we demonstrate our algorithmic tools solving a challenge from combinatorial voting theory.Comment: Major updat

Coefficients of Sylvester's Denumerant

For a given sequence $\mathbf{\alpha} = [\alpha_1,\alpha_2,\dots,\alpha_{N+1}]$ of $N+1$ positive integers, we consider the combinatorial function $E(\mathbf{\alpha})(t)$ that counts the nonnegative integer solutions of the equation $\alpha_1x_1+\alpha_2 x_2+\cdots+\alpha_{N} x_{N}+\alpha_{N+1}x_{N+1}=t$, where the right-hand side $t$ is a varying nonnegative integer. It is well-known that $E(\mathbf{\alpha})(t)$ is a quasi-polynomial function in the variable $t$ of degree $N$. In combinatorial number theory this function is known as Sylvester's denumerant. Our main result is a new algorithm that, for every fixed number $k$, computes in polynomial time the highest $k+1$ coefficients of the quasi-polynomial $E(\mathbf{\alpha})(t)$ as step polynomials of $t$ (a simpler and more explicit representation). Our algorithm is a consequence of a nice poset structure on the poles of the associated rational generating function for $E(\mathbf{\alpha})(t)$ and the geometric reinterpretation of some rational generating functions in terms of lattice points in polyhedral cones. Our algorithm also uses Barvinok's fundamental fast decomposition of a polyhedral cone into unimodular cones. This paper also presents a simple algorithm to predict the first non-constant coefficient and concludes with a report of several computational experiments using an implementation of our algorithm in LattE integrale. We compare it with various Maple programs for partial or full computation of the denumerant.Comment: minor revision, 28 page

The Mercury-Tolerant Microbiota of the Zooplankton Daphnia Aids in Host Survival and Maintains Fecundity under Mercury Stress.

Many aquatic organisms can thrive in polluted environments by having the genetic capability to withstand suboptimal conditions. However, the contributions of microbiomes under these stressful environments are poorly understood. We investigated whether a mercury-tolerant microbiota can extend its phenotype to its host by ameliorating host survival and fecundity under mercury-stress. We isolated microbiota members from various clones of Daphnia magna, screened for the mercury-biotransforming merA gene, and determined their mercury tolerance levels. We then introduced the mercury-tolerant microbiota, Pseudomonas-10, to axenic D. magna and quantified its merA gene expression, mercury reduction capability, and measured its impact on host survival and fecundity. The expression of the merA gene was up-regulated in Pseudomonas-10, both in isolation and in host-association with mercury exposure. Pseudomonas-10 is also capable of significantly reducing mercury concentration in the medium. Notably, mercury-exposed daphnids containing only Pseudomonas-10 exhibited higher survival and fecundity than mercury-exposed daphnids supplemented with parental microbiome. Our study showed that zooplankton, such as Daphnia, naturally harbor microbiome members that are eco-responsive and tolerant to mercury exposure and can aid in host survival and maintain host fecundity in a mercury-contaminated environment. This study further demonstrates that under stressful environmental conditions, the fitness of the host can depend on the genotype and the phenotype of its microbiome

L'arc lémanique se trouve-t-il dans une bulle immobilière ?

Le marché de l’immobilier suscite depuis longtemps un vif intérêt auprès des investisseurs, des promoteurs mais aussi des banques spécialisées dans l’octroi de crédits hypothécaires. Cet attrait peut avoir un rapport avec le fait que son évolution soit fortement corrélée avec l’évolution de l’économie du pays concerné. La preuve en est ce qu’il s’est produit aux Etats-Unis en 2008. Ces dernières années, le secteur a, en effet, beaucoup fait parler de lui avec la crise des « subprimes » qu’ont connus les Etats-Unis. Crise qui s’est ensuite généralisée et s’est propagée jusqu’en Europe. Le secteur de l’immobilier était pourtant réputé solide. Mais les Etats-Unis ne sont pas le seul pays à avoir connu un marché immobilier en panique. En effet, la Suisse à la fin des années 1980 a vu son marché s’écrouler. Les raisons qui ont causé ces effondrements n’étaient, certes, pas les mêmes mais les conséquences sur l’économie furent tout aussi désastreuses. Aujourd’hui, en Suisse, certains professionnels du secteur commencent à tirer la sonnette d’alarme. Les prix sont en effet très élevés et on commence à se demander si le scénario de 1989 n’est pas en train de se reproduire. L’objectif de mon travail est de déterminer si, dans la région lémanique (de Genève à Montreux en passant par Lausanne) le marché immobilier résidentiel se trouve dans une bulle spéculative. Pour répondre à cette question, je vais parler du secteur du marché immobilier en général, pour ensuite me concentrer sur le marché suisse et plus précisément sur le marché lémanique. Je dois, de plus, expliquer comment le prix d’un bien immobilier est déterminé pour pouvoir introduire la notion de « bulle immobilière ». Il est aussi important de connaître le fonctionnement de ce secteur en Suisse, comme par exemple, le processus d’achat d’un bien immobilier sans oublier les aspects juridiques et légaux (droit suisse) mais aussi les mesures qui ont été prises afin d’éviter que ce genre d’événement ne se reproduise. Il faut savoir qu’à l’inverse de plusieurs autres actifs (actions, obligations par exemple), un bien immobilier est complexe à évaluer et qu’il y a plusieurs facteurs à considérer

ORCSim: a generalized Organic Rankine cycle simulation tool

An increasing interest in organic Rankine cycle (ORC) technology has led to numerous simulation and optimization studies. In the open-literature different modeling approaches can be found, but general software tools available to the academic/industrial community are limited. A generalized ORC simulation tool, named ORCSim, is proposed in this paper. The framework is developed using object-oriented programming that easily allows improvements and future extensions. Currently two cycle configurations are implemented, i.e. a basic ORC and an ORC with liquid-flooded expansion. The software architecture, the thermo-physical property wrappers, the component library and the solution algorithm are discussed with particular emphasis on the ORC with liquid-flooded expansion. A thorough validation both at component and cycle levels is proposed by considering the aforementioned cycle architectures

Schooling in Rural East Texas: Contextualizing and Responding to the Needs of African American Students

This critical analysis contextualizes and responds to the current state of education for persons of African descent in rural East Texas, specifically Region VII. The researchers analyzed assessment data, attendance data, demographic data, and discipline data from the Texas Education Agency. Selected data provided a pathway to explore variables that directly impact students’ academic performance and identities. Findings from this study highlight concerns that range from discrepancies in out-of-school suspensions, disproportionate representation of faculty with the student populations, and challenges faced by East Texas schools and school districts to meet state and federal policies and accountability standards. The authors recommend that students, families, teachers, administrators within these communities must work together to create an environment that all parties are valued

Computational approach to the Schottky problem

We present a computational approach to the classical Schottky problem based on Fay's trisecant identity for genus $g\geq 4$. For a given Riemann matrix $\mathbb{B}\in\mathbb{H}^{g}$, the Fay identity establishes linear dependence of secants in the Kummer variety if and only if the Riemann matrix corresponds to a Jacobian variety as shown by Krichever. The theta functions in terms of which these secants are expressed depend on the Abel maps of four arbitrary points on a Riemann surface. However, there is no concept of an Abel map for general $\mathbb{B} \in \mathbb{H}^{g}$. To establish linear dependence of the secants, four components of the vectors entering the theta functions can be chosen freely. The remaining components are determined by a Newton iteration to minimize the residual of the Fay identity. Krichever's theorem assures that if this residual vanishes within the finite numerical precision for a generic choice of input data, then the Riemann matrix is with this numerical precision the period matrix of a Riemann surface. The algorithm is compared in genus 4 for some examples to the Schottky-Igusa modular form, known to give the Jacobi locus in this case. It is shown that the same residuals are achieved by the Schottky-Igusa form and the approach based on the Fay identity in this case. In genera 5, 6 and 7, we discuss known examples of Riemann matrices and perturbations thereof for which the Fay identity is not satisfied