3,625 research outputs found

    Casimir Energy and Entropy between perfect metal Spheres

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    We calculate the Casimir energy and entropy for two perfect metal spheres in the large and short separation limit. We obtain nonmonotonic behavior of the Helmholtz free energy with separation and temperature, leading to parameter ranges with negative entropy, and also nonmonotonic behavior of the entropy with temperature and with the separation between the spheres. The appearance of this anomalous behavior of the entropy is discussed as well as its thermodynamic consequences.Comment: 10 pages and 8 figures. Accepted for publication in the Proceedings of the tenth conference on Quantum Field Theory under the influence of external conditions - QFEXT'1

    Analytical method for the determination of trichlorobenzenes in marine biota (poster)

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    Trichlorobenzenes (TCBs) were intensively used in the last decades as essential components of dielectric fluids, intermediates in chemical synthesis, solvents, coolants, lubricants, heat-transfer medium; insecticide, additive in polyester dyeing and components of termite-control preparations (1, 2). Due to their widespread occurrence in the various environmental compartments they have been classified by OSPARCOM (Oslo and Paris Commissions) (3) as chemicals for priority action and have been proposed by the Marine Chemistry Working Group (MCWG) as chemical parameters in the Water Framework Directive (4). Based on their octanol-water partitioning coefficients (log Kow = 4.02-4.49) (5) and bioconcentration factors in fish (ranging from 182 to 3200, depending on the lipid content) (6), these chemicals are expected to bioaccumulate in aquatic organisms.Against their potential significance in the marine environment there is relatively little information available concerning the actual concentration levels and distribution of trichlorobenzenes in marine organisms (7, 8).The aim of this work was to develop an analytical method appropriate for the determination of TCBs in marine biota.The analytical method consists of saponification of the fish tissue with methanolic potassium hydroxide, liquid-liquid extraction of the solution with pentane, clean up of the concentrated extract on alumina column and analysis of the extract with gas chromatograph equipped with electron capture detector (ECD). The method proved to be appropriate for the detection of concentration levels typical of the organic contaminants in biota (7) (~1 ng /g wet weight of tissue). The relative standard deviation of the analysis of 1,3,5-, 1,2,4- and 1,2,3-trichlorobenzene was 8, 6 and 18% (n=4) respectively. Higher recoveries of the analytes were obtained with spiked fish samples than with standard solutions (88, 96 and 78 instead of 53, 50 and 32% of 1,3,5-, 1,2,4- and 1,2,3-trichlorobenzene respectively). One plausible explanation of the difference is that the proteins and glycerides of the fish tissue compete effectively with trichlorobenzenes for the base and their presence decrease their decomposition rate

    Preliminary results of passive microwave snow experiment during February and March 1978

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    The purpose of the experiment was to determine if remote microwave sensing of snowpack data could be used to predict runoff, thereby allowing more efficient management of the water supply. A four-frequency microwave radiometer system was attached to a truck-mounted aerial lift and was used to gather data on snowpacks at three different sites in the Colorado Rocky Mountains. Ground truth data measurements (density, temperature, grain size, hardness, and free-liquid water content) were taken at each site corresponding to each microwave scan

    Feasibility of free space quantum key distribution with coherent polarization states

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    We demonstrate for the first time the feasibility of free space quantum key distribution with continuous variables under real atmospheric conditions. More specifically, we transmit coherent polarization states over a 100m free space channel on the roof of our institute's building. In our scheme, signal and local oscillator are combined in a single spatial mode which auto-compensates atmospheric fluctuations and results in an excellent interference. Furthermore, the local oscillator acts as spatial and spectral filter thus allowing unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This is an author-created, un-copyedited version of an article accepted for publication in New Journal of Physics (Special Issue on Quantum Cryptography: Theory and Practice). IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

    Division of Continuing Education

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    This departmental history was written on the occasion of the UND Quasquicentennial in 2008.https://commons.und.edu/departmental-histories/1072/thumbnail.jp

    Self-Diffusion of a Polymer Chain in a Melt

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    Self-diffusion of a polymer chain in a melt is studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account. Polymer chains, each of which consists of NN segments, are located on an L×L×LL \times L \times L simple cubic lattice under periodic boundary conditions, where each segment occupies 2×2×22 \times 2 \times 2 unit cells. The results for N=32,48,64,96,128,192,256,384N=32, 48, 64, 96, 128, 192, 256, 384 and 512 at the volume fraction ϕ0.5\phi \simeq 0.5 are reported, where L=128L = 128 for N256N \leq 256 and L=192 for N384N \geq 384. The NN-dependence of the self-diffusion constant DD is examined. Here, DD is estimated from the mean square displacements of the center of mass of a single polymer chain at the times larger than the longest relaxation time. From the data for N=256N = 256, 384 and 512, the apparent exponent xdx_{\rm d}, which describes the apparent power law dependence of DD on NN as DNxdD \propto N^{- x_{\rm d}}, is estimated as xd2.4x_{\rm d} \simeq 2.4. The ratio Dτ/D \tau / seems to be a constant for N=192,256,384N = 192, 256, 384 and 512, where τ\tau and denote the longest relaxation time and the mean square end-to-end distance, respectively.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp

    Casimir forces between arbitrary compact objects

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    We develop an exact method for computing the Casimir energy between arbitrary compact objects, either dielectrics or perfect conductors. The energy is obtained as an interaction between multipoles, generated by quantum current fluctuations. The objects' shape and composition enter only through their scattering matrices. The result is exact when all multipoles are included, and converges rapidly. A low frequency expansion yields the energy as a series in the ratio of the objects' size to their separation. As an example, we obtain this series for two dielectric spheres and the full interaction at all separations for perfectly conducting spheres.Comment: 4 pages, 1 figur

    Reinventing College Physics for Biologists: Explicating an epistemological curriculum

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    The University of Maryland Physics Education Research Group (UMd-PERG) carried out a five-year research project to rethink, observe, and reform introductory algebra-based (college) physics. This class is one of the Maryland Physics Department's large service courses, serving primarily life-science majors. After consultation with biologists, we re-focused the class on helping the students learn to think scientifically -- to build coherence, think in terms of mechanism, and to follow the implications of assumptions. We designed the course to tap into students' productive conceptual and epistemological resources, based on a theoretical framework from research on learning. The reformed class retains its traditional structure in terms of time and instructional personnel, but we modified existing best-practices curricular materials, including Peer Instruction, Interactive Lecture Demonstrations, and Tutorials. We provided class-controlled spaces for student collaboration, which allowed us to observe and record students learning directly. We also scanned all written homework and examinations, and we administered pre-post conceptual and epistemological surveys. The reformed class enhanced the strong gains on pre-post conceptual tests produced by the best-practices materials while obtaining unprecedented pre-post gains on epistemological surveys instead of the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material

    The GREGOR Fabry-P\'erot Interferometer

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    The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution R of about 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012 (AN special issue to GREGOR
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