8,723 research outputs found
Non trivial generalizations of the Schwinger pair production result
We present new, non trivial generalizations of the recent Tomaras, Tsamis and
Woodard extension of the original Schwinger formula for charged pair production
in a constant field.Comment: 11 page
Non-abelian Eikonals
A functional formulation and partial solution is given of the non-abelian
eikonal problem associated with the exchange of non-interacting, charged or
colored bosons between a pair of fermions, in the large /small limit. A
simple, functional ``contiguity" prescription is devised for extracting those
terms which exponentiate, and appear to generate the leading, high-energy
behavior of each perturbative order of this simplest non-abelian eikonal
function; the lowest non-trivial order agrees with the corresponding SU(N)
perturbative amplitude, while higher-order contributions to this eikonal
generate an ``effective Reggeization" of the exchanged bosons, resembling
previous results for the perturbative amplitude. One exact and several
approximate examples are given, including an application to self-energy
radiative corrections. In particular, for this class of graphs and to all
orders in the coupling, we calculate the leading-log eikonal for SU(2). Based
on this result, we conjecture the form of the eikonal scattering amplitude for
SU(N).Comment: 19 pages, late
Measurement of Thermal Conductance of Multilayer and Other Insulation Materials
Thermal conductance measurements on space suit thermal insulation candidate
Theory for solvent, momentum, and energy transfer between a surfactant solution and a vapor atmosphere
We develop a complete set of equations governing the evolution of a sharp interface separating a volatile-solvent/nonvolatile-surfactant solution from a vapor atmosphere. In addition to a sorption isotherm equation and the conventional balances for mass, linear momentum, and energy, these equations include a counterpart of the Hertz???Knudsen???Langmuir equation familiar from conventional theories of evaporation-condensation. This additional equation arises from a consideration of configurational forces within a thermodynamical framework. While the notion of configurational forces is well-developed and understood for the description of materials, like crystalline solids, that possess natural reference configurations, very little has been done regarding their role in materials, such as viscous fluids, that do not possess preferred reference states. We therefore provide a comprehensive discussion of configurational forces, the balance of configurational momentum, and configurational thermodynamics that does not require a choice of reference configuration. The general evolution equations arising from our theory account for the thermodynamic structure of the solution and the interface and for sources of dissipation related to the transport of surfactant, momentum, and heat in the solution, the transport of surfactant and momentum within the interface, and the transport of solute, momentum, kinetic energy, and heat across the interface. Due to the complexity of these equations, we provide approximate equations which we compare to relations that appear in the literature.published or submitted for publicationis peer reviewe
Proton network flexibility enables robustness and large electric fields in the ketosteroid isomerase active site
Hydrogen bond networks play vital roles in biological functions ranging from
protein folding to enzyme catalysis. Here we combine electronic structure
calculations and ab initio path integral molecular dynamics simulations, which
incorporate both nuclear and electronic quantum effects, to show why the
network of short hydrogen bonds in the active site of ketosteroid isomerase is
remarkably robust to mutations along the network and how this gives rise to
large local electric fields. We demonstrate that these properties arise from
the network's ability to respond to a perturbation by shifting proton positions
and redistributing electronic charge density. This flexibility leads to small
changes in properties such as the partial ionization of residues and
isotope effects upon mutation of the residues, consistent with recent
experiments. This proton flexibility is further enhanced when an extended
hydrogen bond network forms in the presence of an intermediate analog, which
allows us to explain the chemical origins of the large electric fields in the
enzyme's active site observed in recent experiments.Comment: 13 pages, 10 figures (7 main text and 3 SI
Herding Cats: Improving Law School Teaching
What makes a good law teacher? Is excellence in teaching largely a matter of intellectual brilliance, of superior organization and delivery of material, of friendliness and fairness to one\u27s students? Or does it have more to do with style, with stage presence, with the ability to engage an audience in the act of reflective and spontaneous thinking?
While the question of how to define and evaluate teaching necessarily bedevils deans and tenure committees who must make personnel decisions, the focus on defining the competent teacher has obscured from faculty attention the more fundamental question: how can we implement a system to improve faculty performance across the board? It is this question that law schools around the country have not adequately addressed.
Three years ago, the faculty of Franklin Pierce Law Center adopted a program to improve our classroom teaching. This article describes and evaluates that program, in which all three authors played a role
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