Laser Field Induced Birefringence and Enhancement of Magneto-optical Rotation

An initially isotropic medium, when subjected to either a magnetic field or a coherent field, can induce anisotropy in the medium and can cause the polarization of a probe field to rotate. Therefore the rotation of probe polarization, due to magnetic field alone, can be controlled efficiently with the use of a coherent control field. We demonstrate this enhancement of the magneto-optical rotation (MOR) of a linearly polarized light, by doing detailed calculations on a system with relevant transitions $j=0\leftrightarrow j=1\leftrightarrow j=0$.Comment: 9 pages including 4 Figure

Mathematical modelling of the catalyst layer of a polymer-electrolyte fuel cell

In this paper we derive a mathematical model for the cathode catalyst layer of a polymer electrolyte fuel cell. The model explicitly incorporates the restriction placed on oxygen in reaching the reaction sites, capturing the experimentally observed fall in the current density to a limiting value at low cell voltages. Temperature variations and interfacial transfer of O2 between the dissolved and gas phases are also included. Bounds on the solutions are derived, from which we provide a rigorous proof that the model admits a solution. Of particular interest are the maximum and minimum attainable values. We perform an asymptotic analysis in several limits inherent in the problem by identifying important groupings of parameters. This analysis reveals a number of key relationships between the solutions, including the current density, and the composition of the layer. A comparison of numerically computed and asymptotic solutions shows very good agreement. Implications of the results are discussed and future work is outlined

Color Flux Profiles in SU(2) Lattice Gauge Theory

Results of a high statistics study of chromo field distributions around static sources in pure SU(2) gauge theory on lattices of volumes $16^4$, $32^4$, and $48^3\times 64$ at $\beta=2.5$, $2.635$, and $2.74$ are presented. We establish string formation up to physical distances as large as 2 fm.Comment: Contribution to Lattice '94, 3 pages uu-compressed LaTeX + 3 psfig

Two-loop corrections to the decay rate of parapositronium

Order $\alpha^2$ corrections to the decay rate of parapositronium are calculated. A QED scattering calculation of the amplitude for electron-positron annihilation into two photons at threshold is combined with the technique of effective field theory to determine an NRQED Hamiltonian, which is then used in a bound state calculation to determine the decay rate. Our result for the two-loop correction is $5.1243(33)$ in units of $(\alpha/\pi)^2$ times the lowest order rate. This is consistent with but more precise than the result $5.1(3)$ of a previous calculation.Comment: 26 pages, 7 figure

SU(2) Colour Fields Around Static Sources

First results of an ongoing high statistics study of the colour flux distribution around static quark sources in SU(2) gauge theory are presented. The flux tube profiles and widths have been investigated for several quark separations at beta=2.5 and beta=2.74. The results are tested against Michael's sum rules.Comment: 3 pages (LaTeX) with 4 epsf incl. PS figs., To be publ. in Proc. of Lattice '9

Spin dependent potentials from SU(2) gauge theory

We present results on spin dependent potentials from lattice simulations of SU(2) gauge theory. The Coulomb like short range part of the central potential is identified as a mixed vector-scalar exchange while the linear long range part is pure scalar.Comment: Talk held at LAT 94 conference, 3 pages, latex, uses epscrc2.st

Frozen section evaluation of lymph nodes in Oral squamous cell carcinoma: a retrospective study

The principal indication of performing a frozen section is to obtain a definite immediate diagnosis, on the basis of which a surgical decision will be made. Immediate diagnosis allows the surgeon to proceed with further therapy without any delay. A definite immediate diagnosis is said to be dependent on the reliability of frozen sections. Many authors have carried out frozen section study on soft tissue tumors and lymph node evaluation in different parts of the body with varying percentages of reliability. However, it appears that lymph node evaluations specifically in oral squamous cell carcinoma cases were not performed, or limited. Hence the present study was undertaken to determine the reliability of frozen section diagnosis in the lymph nodes of oral squamous cell carcinomas. This study was performed so that the surgeons would have an intraoperative assessment of the extent of local metastasis and to determine the adequacy of resection before the wound is closed. The objectives of the present study are to assess microscopically the frozen section of the palpable and non palpable lymph nodes of neck for metastasis in patients with squamous cell carcinoma of oral cavity. To compare the micros- copic features of paraffin embedded lymph node sections with those of frozen sections. To assess the reliability of frozen section evaluation of cervical lymph nodes in oral squamous cell carcinoma. The present research work gives 100% accuracy of frozen sections with due care by additional staining to frozen sections by phloxine methylene blue stain, however cannot be in any way superior to the magnetic resonance imaging, computed tomography, immunoscintigraphy and lymphangioscintigraphy

String breaking with dynamical Wilson fermions

We present results of our ongoing determination of string breaking in full QCD with N_f=2 Wilson fermions. Our investigation of the fission of the static quark-antiquark string into a static-light meson-antimeson system is based on dynamical configurations of size 24^3 x 40 produced by the TxL collaboration. Combining various optimization methods we determine the matrix elements of the two-by-two system with so far unprecedented accuracy. The all-to-all light quark propagators occurring in the transition element are computed from eigenmodes of the Hermitian Wilson-Dirac matrix complemented by stochastic estimates in the orthogonal subspace. We observe a clear signature for level-splitting between ground state and excited potential. Thus, for the first time, string breaking induced by sea quarks is observed in a simulation of 4-dimensional lattice-QCD.Comment: 3 pages, 3 figures, contribution to Lattice 200

The Running Coupling from SU(3) Gauge Theory

We present high precision results on the static quark-antiquark-potential on 32^4 and smaller lattices, using the standard Wilson action at BETA = 6.0, 6.2, 6.4, and 6.8 on the Connection Machine CM-2. Within our statistical errors (1%) we did not observe any finite size effects affecting the potential values, on varying the spatial lattice extent from 0.9 fm up to 3.3 fm. We find violations of asymptotic scaling in the bare coupling up to BETA = 6.8. We demonstrate that scaling violations on the string tension can be considerably reduced by introducing effective coupling schemes, which allow for a safer extrapolation of LAMBDA_Lattice to its continuum value. We are also able to see and to quantify the running of the coupling from the interquark force. From this we extract the ratio \sqrt{SIGMA}/LAMBDA_L. Both methods yield consistent values for the LAMBDA-parameter: LAMBDA_MSbar = 0.558(-0.007+0.017)\sqrt{SIGMA} = 246(-3+7) MeV.Comment: (Talk G. Bali at Lattice 92, Amsterdam), 4 Pages, 4 Postscript figures, LaTeX with espcrc2, and epsf style file