Experiments and Theory of Induced Optical Magnetization.

This thesis reports the results of light scattering experiments at moderate optical intensities (~10^8 W/cm^2) in which the magnetic component of light induces magnetic dipolar response of unprecedented intensity by a novel nonlinear mechanism. Both experimentally and theoretically the amplitude of induced magnetization is found to be as large as electric polarization (M=cP) at intensities above ~10^8 W/cm^2 in different materials, greatly exceeding the conventional bounds of the multipole expansion. The transverse nature of the magnetization, its frequency, and its quadratic dependence on incident light intensity are in agreement with an exact theory which identifies the importance of magnetically-induced torque in achieving 2-photon resonance of this ultrafast process. In this work we report and compare the intensity dependence of cross-polarized scattering in the transparent molecular liquids CCl_4, SiCl_4, SiBr_4, SnCl_4, C_6H_6, C_6D_6, C_6H_5NH_2, and C_6H_5CN and the crystalline solid Gd_3Ga_5O_{12}. Complete radiation patterns of co-polarized and cross-polarized light scattering were recorded as a function of intensity in these homogeneous media and subsequently decomposed into polarized and unpolarized components to provide a more complete picture of scattering dynamics than has been possible in past experiments. The cross-polarized scattering observed from spherical-top molecules CCl_4, SiCl_4, SiBr_4, and SnCl_4 and crystalline GGG is argued to originate from magnetic dipoles induced by a second-order optical nonlinearity driven jointly by the E and B fields of light. Among the spherical top molecular liquids, SnCl_4 developed more intense magnetic scattering at a fixed intensity than CCl_4, in agreement with the predicted dependence on rotational frequency and damping. Cross-polarized scattering in anisotropic molecules C_6H_6, C_6D_6, C_6H_5NH_2, and C_6H_5CN, on the other hand, is known to originate from optical orientation of permanent electric dipole moments in first-order or differential polarizability in third-order. The importance of rotational dynamics to depolarization in all the liquids studied is outlined and confirmed through observation of an isotopic effect in the scattering from C_6H_6 vs. C_6D_6. Finally, the new nonlinear optical process investigated here provides a method for generating oriented rotations of molecules.PhDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120880/1/alxfshr_1.pd

Resistive Anomalies at Ferromagnetic Transitions Revisited: the case of SrRuO_3

We show that recent resistivity data on SrRuO_3 for T->T_c are consistent with conventional theory when corrections to scaling are included and a small shift in T_c is allowed.Comment: 2 pages, 1 figure; revte

A patient with amyotrophic lateral sclerosis and atypical clinical and electrodiagnostic features: a case report

INTRODUCTION: Amyotrophic lateral sclerosis is a rapidly progressive, fatal neurodegenerative disorder for which there is no effective treatment. The diagnosis is dependent on the clinical presentation and consistent electrodiagnostic studies. Typically, there is a combination of upper and lower motor neuron signs as well as electrodiagnostic studies indicative of diffuse motor axonal injury. The presentation of amyotrophic lateral sclerosis, however, may be variable. At the same time, the diagnosis is essential for patient prognosis and management. It is therefore important to appreciate the range of possible presentations of amyotrophic lateral sclerosis. CASE PRESENTATION: We present the case of a 57-year-old Caucasian man with pathological findings on postmortem examination consistent with amyotrophic lateral sclerosis but atypical clinical and electrodiagnostic features. He died after a rapid course of progressive weakness. The patient did not respond to immunosuppressive therapy. CONCLUSION: Amyotrophic lateral sclerosis should be considered in patients with a rapidly progressive, unexplained neuropathic process. This should be true even if there are atypical clinical and electrodiagnostic findings. Absence of response to therapy and the development of upper motor neuron signs should reinforce the possibility that amyotrophic lateral sclerosis may be present. Since amyotrophic lateral sclerosis is a fatal illness, however, the possibility of this disease in patients with atypical clinical features should not diminish the need for a thorough diagnostic evaluation and treatment trials

An Inversion Method for Measuring Beta in Large Redshift Surveys

A precision method for determining the value of Beta= Omega_m^{0.6}/b, where b is the galaxy bias parameter, is presented. In contrast to other existing techniques that focus on estimating this quantity by measuring distortions in the redshift space galaxy-galaxy correlation function or power spectrum, this method removes the distortions by reconstructing the real space density field and determining the value of Beta that results in a symmetric signal. To remove the distortions, the method modifies the amplitudes of a Fourier plane-wave expansion of the survey data parameterized by Beta. This technique is not dependent on the small-angle/plane-parallel approximation and can make full use of large redshift survey data. It has been tested using simulations with four different cosmologies and returns the value of Beta to +/- 0.031, over a factor of two improvement over existing techniques.Comment: 16 pages including 6 figures Submitted to The Astrophysical Journa