Propagation of a laser beam in a plasma

This paper shows that for a nonabsorbing medium with a prescribed index of refraction, the effects of beam stability, line focusing, and beam distortion can be predicted from simple ray optics. When the paraxial approximation is used, diffraction effects are examined for Gaussian, Lorentzian, and square beams. Most importantly, it is shown that for a Gaussian beam, diffraction effects can be included simply by adding imaginary solutions to the paraxial ray equations. Also presented are several procedures to extend the paraxial approximation so that the solution will have a domain of validity of greater extent

Direct observation of the phonon energy in a Bose-Einstein condensate by tomographic imaging

The momentum and energy of phonons in a Bose-Einstein condensate are measured directly from a time-of-flight image by computerized tomography. We find that the same atoms that carry the momentum of the excitation also carry the excitation energy. The measured energy is in agreement with the Bogoliubov spectrum. Hydrodynamic simulations are performed which confirm our observation.Comment: Letter, 5 figure

Improved mortality among U.S. blacks, 1968-1978: The role of antiracist struggle

A marked improvement in health status for black adults took place over the last decade in the United States. Life expectancy for black men increased 4.6 years between 1968 and 1978, while for black women the increase was 5.7 years. Death rates for the age group 35-74 decreased approximately 25 percent for blacks over the same period. The largest contribution to this improvement was made by cardiovascular diseases (coronary heart disease and stroke). Although similar improvement was observed in the white population, on both a percentage and absolute basis the change was greater for blacks. For the first time in the U.S. important progress was made in the effort to narrow the gap in mortality rates between black and white adults. Hypertension detection and control appears to have played the key role in this positive public trend. The community-based demand for greater access to medical care, which emerged from the social struggle of the 1960s, also can be accorded a major social role. The current policies of the Reagan Administration pose a serious threat to these antiracist programs, as well as to the effort to close the gap in black-white mortality

Low Power Superconducting Microwave Applications and Microwave Microscopy

We briefly review some non-accelerator high-frequency applications of superconductors. These include the use of high-Tc superconductors in front-end band-pass filters in cellular telephone base stations, the High Temperature Superconductor Space Experiment, and high-speed digital electronics. We also present an overview of our work on a novel form of near-field scanning microscopy at microwave frequencies. This form of microscopy can be used to investigate the microwave properties of metals and dielectrics on length scales as small as 1 mm. With this microscope we have demonstrated quantitative imaging of sheet resistance and topography at microwave frequencies. An examination of the local microwave response of the surface of a heat-treated bulk Nb sample is also presented.Comment: 11 pages, including 6 figures. Presented at the Eight Workshop on RF Superconductivity. To appear in Particle Accelerator

Near-Field Scanning Microwave Microscopy: Measuring Local Microwave Properties and Electric Field Distributions

We describe the near-field microwave microscopy of microwave devices on a length scale much smaller than the wavelength used for imaging. Our microscope can be operated in two possible configurations, allowing a quantitative study of either material properties or local electric fields.Comment: 4 pages, 8 figures, minor corrections to text and 2 figure