Decoherence in Phase Space

Much of the discussion of decoherence has been in terms of a particle moving in one dimension that is placed in an initial superposition state (a Schr\"{o}dinger "cat" state) corresponding to two widely separated wave packets. Decoherence refers to the destruction of the interference term in the quantum probability function. Here, we stress that a quantitative measure of decoherence depends not only on the specific system being studied but also on whether one is considering coordinate, momentum or phase space. We show that this is best illustrated by considering Wigner phase space where the measure is again different. Analytic results for the time development of the Wigner distribution function for a two-Gaussian Schrodinger "cat" state have been obtained in the high-temperature limit (where decoherence can occur even for negligible dissipation) which facilitates a simple demonstration of our remarks.Comment: in press in Laser Phys.13(2003

Note on the derivative of the hyperbolic cotangent

In a letter to Nature (Ford G W and O'Connell R F 1996 Nature 380 113) we presented a formula for the derivative of the hyperbolic cotangent that differs from the standard one in the literature by an additional term proportional to the Dirac delta function. Since our letter was necessarily brief, shortly after its appearance we prepared a more extensive unpublished note giving a detailed explanation of our argument. Since this note has been referenced in a recent article (Estrada R and Fulling S A 2002 J. Phys. A: Math. Gen. 35 3079) we think it appropriate that it now appear in print. We have made no alteration to the original note

The PHASES Differential Astrometry Data Archive. I. Measurements and Description

The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) monitored 51 sub-arcsecond binary systems to determine precision binary orbits, study the geometries of triple and quadruple star systems, and discover previously unknown faint astrometric companions as small as giant planets. PHASES measurements made with the Palomar Testbed Interferometer (PTI) from 2002 until PTI ceased normal operations in late 2008 are presented. Infrared differential photometry of several PHASES targets were measured with Keck Adaptive Optics and are presented.Comment: 33 pages emulateapj, Accepted to A

Laplace transform of spherical Bessel functions

We provide a simple analytic formula in terms of elementary functions for the Laplace transform j_{l}(p) of the spherical Bessel function than that appearing in the literature, and we show that any such integral transform is a polynomial of order l in the variable p with constant coefficients for the first l-1 powers, and with an inverse tangent function of argument 1/p as the coefficient of the power l. We apply this formula for the Laplace transform of the memory function related to the Langevin equation in a one-dimensional Debye model.Comment: 5 pages LATEX, no figures. Accepted 2002, Physica Script

A Note on Frame Dragging

The measurement of spin effects in general relativity has recently taken centre stage with the successfully launched Gravity Probe B experiment coming toward an end, coupled with recently reported measurements using laser ranging. Many accounts of these experiments have been in terms of frame-dragging. We point out that this terminology has given rise to much confusion and that a better description is in terms of spin-orbit and spin-spin effects. In particular, we point out that the de Sitter precession (which has been mesured to a high accuracy) is also a frame-dragging effect and provides an accurate benchmark measurement of spin-orbit effects which GPB needs to emulate

Aspects of the limnology of Long Pond, St. John's, in relation to a changing environment

Certain physiocochemical parameters, benthos and plankton were examined on a seasonal basis in Long Pond, C. A. Pippy Park, St. John's. This pond receives both rural and urban runoff and is characterized by a high flushing rate. -- The physicochemical environment was studied from June 1971 to May 1973 at five stations. Of the parameters studied, concentrations of total suspended matter, BOD, total CO₂ and free CO₂ were significantly greater in a small pool prior to the main body of the pond near the entry of Learys Brook where current speed is noticeably reduced. Sedimentation rate was also greatest at this location. No significant differences were found between stations with respect to pH, dissolved O₂, TDS, total hardness, Ca hardness, alkalinity, ammonium-N, nitrite-N, nitrate-N, orthophosphate and polyphosphate. Water quality in Long Pond is compared with unpolluted lakes and streams in the area; nutrient levels are indicative of eutrophic conditions. -- Benthos was studied at the same station as above from June 1971 to August 1972. Adverse physicochemical conditions which prevailed near the point of entry of Learys Brook were reflected in the components comprising the benthos. Numbers of Tubifex tubifex (maximum: 720,000/m²) increased with time, which paralleled increases in BOD (maximum: 12.9 mg/1). Opposed to the almost monospecific nature of this station, diversity was greater at the other stations. Diversity index values were computed for all stations. -- Plankton was studied quantitatively at one station (mid-pond) from April 1972 to May 1973. A comparison is made with Clarkes Pond, Hogans Pond and Bauline Long Pond. Long Pond phytoplankton was characterized by nannoplankton (particularly phytoflagellates). The most important zooplankters were Bosmina coregoni and Daphina catawba. -- Significant negative correlations were obtained between total phytoplankton and nitrate-N and total phytoplankton and free CO₂. Significant positive correlations were obtained between total phytoplankton and temperature, total zooplankton and total phytoplankton and total zooplankton and temperature

Architecture and Selectivity in Aquaporins: 2.5 Å X-Ray Structure of Aquaporin Z

Aquaporins are a family of water and small molecule channels found in organisms ranging from bacteria to animals. One of these channels, the E. coli protein aquaporin Z (AqpZ), has been shown to selectively conduct only water at high rates. We have expressed, purified, crystallized, and solved the X-ray structure of AqpZ. The 2.5 Å resolution structure of AqpZ suggests aquaporin selectivity results both from a steric mechanism due to pore size and from specific amino acid substitutions that regulate the preference for a hydrophobic or hydrophilic substrate. This structure provides direct evidence on the molecular mechanisms of specificity between water and glycerol in this family of channels from a single species. It is to our knowledge the first atomic resolution structure of a recombinant aquaporin and so provides a platform for combined genetic, mutational, functional, and structural determinations of the mechanisms of aquaporins and, more generally, the assembly of multimeric membrane proteins

Primary reading exercises for use with the Durrell Analysis of Reading Difficulty

Thesis (Ed.M.)--Boston Universit