Hydrogen atom in phase space. The Kirkwood-Rihaczek representation

We present a phase-space representation of the hydrogen atom using the Kirkwood-Rikaczek distribution function. This distribution allows us to obtain analytical results, which is quite unique because an exact analytical form of the Wigner functions corresponding to the atom states is not known. We show how the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom wave functions in position and momentum representations.Comment: 5 pages (and 5 figures

Dynamics of Diblock Copolymers in Dilute Solutions

We consider the dynamics of freely translating and rotating diblock (A-B), Gaussian copolymers, in dilute solutions. Using the multiple scattering technique, we have computed the diffusion and the friction coefficients D_AB and Zeta_AB, and the change Eta_AB in the viscosity of the solution as functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments of the A block and of the whole copolymer, respectively, and l_A, l_B are the Kuhn lengths of the A and B blocks. Specific regimes that maximize the efficiency of separation of copolymers with distinct "t" values, have been identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty, submitted to Macromolecule

Revisiting Clickers: In-Class Questions Followed by At-Home Reflections Are Associated with Higher Student Performance on Related Exam Questions

Clicker questions are a commonly used active learning technique that stimulates student interactions to help advance understanding of key concepts. Clicker questions are often administered with an initial vote, peer discussion, and a second vote, followed by broader classroom explanation. While clickers can promote learning, some studies have questioned whether students maintain this performance on later exams, highlighting the need to further understand how student answer patterns relate to their understanding of the material and to identify ways for clickers to benefit a broader range of students. Systematic requizzing of concepts during at-home assignments represents a promising mechanism to improve student learning. Thus, we paired clicker questions with at-home follow-up reflections to help students articulate and synthesize their understandings. This pairing of clickers with homework allowed us to decipher how student answer patterns related to their underlying conceptions and to determine if revisiting concepts provided additional benefits. We found that students answering both clicker votes correctly performed better on isomorphic exam questions and that students who corrected their answers after the first vote did not show better homework or exam performance than students who maintained an incorrect answer across both votes. Furthermore, completing the followup homework assignment modestly boosted exam question performance. Our data suggest that longer-term benefits of clickers and associated homework may stem from students having repeated opportunities to retrieve, refine, and reinforce emerging conceptions

On the ecology, distribution and conservation status of Vittadinia blackii (Asteraceae) in Australia

Distribution records of Vittadinia blackii (family Asteraceae) across southern Australia show the species has a strong and moderately common presence across a broad range of climate zones and sites in South Australia, but a much more restricted occurrence in other mainland state’s. Using the IUCN criteria, adopted by the separate state regulatory authorities vested with listing threatened species, Vittadinia blackii is considered to be not threatened in South Australia, but endangered in Western Australia, Victoria and New South Wales

Why do ultrasoft repulsive particles cluster and crystallize? Analytical results from density functional theory

We demonstrate the accuracy of the hypernetted chain closure and of the mean-field approximation for the calculation of the fluid-state properties of systems interacting by means of bounded and positive-definite pair potentials with oscillating Fourier transforms. Subsequently, we prove the validity of a bilinear, random-phase density functional for arbitrary inhomogeneous phases of the same systems. On the basis of this functional, we calculate analytically the freezing parameters of the latter. We demonstrate explicitly that the stable crystals feature a lattice constant that is independent of density and whose value is dictated by the position of the negative minimum of the Fourier transform of the pair potential. This property is equivalent with the existence of clusters, whose population scales proportionally to the density. We establish that regardless of the form of the interaction potential and of the location on the freezing line, all cluster crystals have a universal Lindemann ratio L = 0.189 at freezing. We further make an explicit link between the aforementioned density functional and the harmonic theory of crystals. This allows us to establish an equivalence between the emergence of clusters and the existence of negative Fourier components of the interaction potential. Finally, we make a connection between the class of models at hand and the system of infinite-dimensional hard spheres, when the limits of interaction steepness and space dimension are both taken to infinity in a particularly described fashion.Comment: 19 pages, 5 figures, submitted to J. Chem. Phys; new version: minor changes in structure of pape

The role of marine reserves in achieving sustainable fisheries (One contribution of 15 to a Theme Issue 'Fisheries: a Future?')

Many fishery management tools currently in use have conservation value. They are designed to maintain stocks of commercially important species above target levels. However, their limitations are evident from continuing declines in fish stocks throughout the world. We make the case that to reverse fishery declines, safeguard marine life and sustain ecosystem processes, extensive marine reserves that are off limits to fishing must become part of the management strategy. Marine reserves should be incorporated into modern fishery management because they can achieve many things that conventional tools cannot. Only complete and permanent protection from fishing can protect the most sensitive habitats and vulnerable species. Only reserves will allow the development of natural, extended age structures of target species, maintain their genetic variability and prevent deleterious evolutionary change from the effects of fishing. Species with natural age structures will sustain higher rates of reproduction and will be more resilient to environmental variability. Higher stock levels maintained by reserves will provide insurance against management failure, including risk-prone quota setting, provided the broader conservation role of reserves is firmly established and legislatively protected. Fishery management measures outside protected areas are necessary to complement the protection offered by marine reserves, but cannot substitute for it

Environmental factors influencing pipe failures

This report details work carried out under NERC grants NE/M008339/1 and NE/NO13026/1 which were collaborations between the British Geological Survey and Yorkshire Water, with an additional knowledge transfer component involving Scottish Water and Dŵr Cymru Welsh Water. The work examines whether models developed using environmental, topographical and geohazard information could complement existing management tools, and increase the understanding as to how pipe networks of different materials interact with their broader environment. This can be seen as a first step in identifying ways in which greater resilience could be built into pipe networks

Equilibrium Sampling From Nonequilibrium Dynamics

We present some applications of an Interacting Particle System (IPS) methodology to the field of Molecular Dynamics. This IPS method allows several simulations of a switched random process to keep closer to equilibrium at each time, thanks to a selection mechanism based on the relative virtual work induced on the system. It is therefore an efficient improvement of usual non-equilibrium simulations, which can be used to compute canonical averages, free energy differences, and typical transitions paths