Gender patterns of tuberculosis testing and disease in South Africa.

SETTING: In South Africa, tuberculosis (TB) has been the leading cause of death for over a decade. The TB incidence rate is the second highest in the world, and continues to rise. OBJECTIVE: To examine gender patterns in South Africa's TB epidemic. This is one of the first studies to use National Health Laboratory Service (NHLS) data to evaluate the epidemic at the national level. DESIGN: Observational study using NHLS retrospective data for every TB test performed in public health facilities between 2009 and 2011. RESULTS: Despite an increase in the number of TB tests performed, the number of TB cases remained relatively constant. Although prevalence rates differ between health districts, we find a similar female-to-male ratio (0.70) in each district. The age profile for TB resembles that of human immunodeficiency virus (HIV), with peak TB prevalence in women occurring 7 years earlier than in men. The female-to-male ratio of TB cases and 3+ positive (severe) cases decreases rapidly between ages 25 and 35 years. CONCLUSION: These age and gender patterns are driven by the HIV epidemic and risks associated with pregnancy and childbearing. Increasing the quality and quantity of active TB case finding at existing points of care would be a sustainable and cost-effective intervention for both treatment and prevention.

X-ray microprobe of orbital alignment in strong-field ionized atoms.

We have developed a synchrotron-based, time-resolved x-ray microprobe to investigate optical strong-field processes at intermediate intensities (10(14) - 10(15) W/cm2). This quantum-state specific probe has enabled the direct observation of orbital alignment in the residual ion produced by strong-field ionization of krypton atoms via resonant, polarized x-ray absorption. We found strong alignment to persist for a period long compared to the spin-orbit coupling time scale (6.2 fs). The observed degree of alignment can be explained by models that incorporate spin-orbit coupling. The methodology is applicable to a wide range of problems.

Interaction of atomic systems with X-ray free-electron lasers.

The planned construction of an X-ray free-electron laser (XFEL) will provide new opportunities for research in various areas of physics, chemistry and biology. The proposed design of the XFELs at DESY (Deutsches Elektronen-Synchrotron) and SLAC (Stanford Linear Accelerator Center) is built on the concept of a fourth-generation synchrotron source and will provide an intense pulse (I(0) approximately 10(16) W cm(-2), tau(gamma) approximately 100 fs) for photon wavelengths down to 1 A. Some guidelines for applications of these sources pertaining to atomic physics are presented here. Issues such as the onset of strong photon-field effects, multiple ionization and hollow-atom formation are analyzed. Attention is especially given to studying the interaction with rare-gas atoms, for which some numerical estimates are provided.

In situ preparation of thin sodium films as an expendable filter in the vacuum ultraviolet.

The use of a sodium film as a filter for wavelengths between 40 and 80 nm is discussed, and a technique to prepare these films is described. Sodium films of 230 nm thickness were demonstrated to have a transmission of 55% at 100 degrees K at a wavelength 41 nm. The transmission decreased to 40% after 18 h in a vacuum of 5x10(-8) Torr. Films of this thickness were shown to attenuate 20.5-nm radiation appearing in second order at 41 nm by at least a factor of 50.

The Use of Synchrotron Radiation as an Absolute Source of VUV Radiation.

Synchrotron radiation has been used as a standard source to calibrate spectrographic instruments at the National Bureau of Standards (NBS). Conceptually it is straightforward to apply the calculable continuum distribution of synchrotron radiation to problems requiring a source of known irradiance if the electron energy, the radius of the electron orbit, and the beam current are known. In practice many factors affect the accuracy of such a calibration, such as temporal and spatial variations in the electron beam, uncertainties in the orbital radius and maximum energy of the orbiting electron beam. These sources of error are discussed and the method of calibration on SURF-I is specified. A storage ring synchrotron radiation facility (SURF-II) is now operational at NBS. The calibration techniques developed for SURF-I are applied to SURF-II with anticipated improvements in calibration accuracy. For SURF-I the incident flux was determined with an accuracy of 15 percent while for SURF-II we anticipate accuracies of about 7 percent.

Absolute Radiometric Calibration of Detectors Between 200-600A.

Radiometric transfer standards consisting of windowless diodes with cathodes made of anodized aluminum oxide on aluminum are now available from the National Bureau of Standards with calibrations in the 200-600-A wavelength range. This extends the previously existing range of calibration for these diodes (600-1200 A). For wavelengths shorter than 600 A, synchrotron radiation at NBS-SURF is used as the source of radiant energy. A noble gas double ionization chamber is used to calibrate a secondary standard diode that is then intercompared with the transfer standards. Monitors take into account variations in the intensity of synchrotron radiation and in beam position. Methods of accounting for the effects of second-order radiation in the incident flux and secondary ionization in the double ionization chamber are discussed. Calibration uncertainties are about 10%.

Computer analysis of resonance profiles by the method of least squares.

The method of least squares has been applied to the analysis of resonance profiles described by the Beutler-Fano (BF) absorption cross section. To illustrate the method, parameters were determined for experimental data having BF profiles of (a) the asymmetric, enhanced absorption type; (b) the window type, and (c) the lorentzian absorption type. Systematic and random errors and correlation among the parameters were studied as a function of the slitwidth-to-resonance width ratio by applying the least squares fitting method to data computed by folding the BF transmission profile with a gaussian slit function. High correlation among the parameters and parameter fractional standard deviations of 10-20% for data with a standard deviation of 0.01 are an incentive to keep the slitwidth-to-resonance width ratio less than two for window type resonances. In addition it was found that the parameters describing a resonance could be determined with the greatest precision in a given time when the slitwidth-to-resonance width ratio was approximately 1. It was found that systematic errors greater than about 1% resulted if the number of mesh points used to approximate the convolution integral in the fitting procedure was less than at least two per resonance width. Also, for resonances whose width was equal to the slitwidth, systematic errors in the parameter values of about 10% resulted if the width of slit function used in the fitting procedure differed from the actual slit function by 10%.

Instrumental aspects of synchrotron XUV spectroscopy.

Electron synchrotrons are becoming increasingly important as sources of extreme uv radiation for physical experiments. The NBS 180-MeV machine has been utilized for gas absorption studies over a four-year period, during which a 3-m grazing incidence spectrograph and monochromator have been designed, constructed and put into operation. The instruments are extremely stable to vibration and temperature variation, and are operating with a slit limited resolution of the order of 0.06 A. The design principles and features of these instruments are described, and a highly successful prealignment procedure for grazing incidence spectrometers is outlined. The effect of the unusual characteristics of this light source on the illumination and performance of the spectroscopic instruments is discussed.