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The authors demonstrate the detection of magnetic particles carried by water in a continuous flow using an atomic magnetic gradiometer. Studies on three types of magnetic particles are presented: a single cobalt particle (diameter ∼150 μm, multidomain), a suspension of superparamagnetic magnetite particles (diameter ∼1 μm), and ferromagnetic cobalt nanoparticles (diameter ∼10 nm). Estimated detection limits are 20 μm diameter for a single cobalt particle at a water flow rate of 30 ml/min, 5×103 magnetite particles at 160 ml/min, and 50 pl for the ferromagnetic fluid of cobalt nanoparticles at 130 ml/min. Possible applications of their method are discussed. [ABSTRACT FROM AUTHOR]

Observers (O's) were presented with a two-alternative forced-choice (2AFC) duration-discrimination task. In separate experimental runs, O's were asked to choose either the longer of two increments or the longer of two decrements from a continuous white noise background. Direct determinations of the increase in duration (ΔT) necessary for 75% and for 90% correct response were made at each of four base durations (T = 10, 25, 50, and 100 msec). These measurements were possible through the use of Delta, a combination of the PEST (parameter estimation by sequential testing) technique with ΔT as dependent variable. To establish whether Delta yielded results comparable to the more traditional 2AFC measurement of per cent correct, psychometric functions for the same observers were obtained for the same base durations. From these functions, the value of ΔT needed by an observer to achieve 75% and 90% correct discrimination was found for each T. In general, the estimated values of ΔT did not differ from those obtained directly by the Delta technique. [Supported by the National Research Council of Canada.] [ABSTRACT FROM AUTHOR]

We present experimental, analytical, and numerical methods developed for reconstruction (deconvolution) of one-dimensional (1D) surface slope profiles over the spatial frequency range where the raw data are significantly perturbed due to the limited resolution of the measurement instrument. We characterize the spatial resolution properties of a profiler with the instrument's transfer function (ITF). To precisely measure the ITF, we apply a recently developed method utilizing test surfaces with 1D linear chirped height profiles of constant slope amplitude. Based on the results of the ITF calibration, we determine parameters of an analytical model for the ITF that is used in the original reconstruction software. Here, we treat surface slope metrology data obtained with the Optical Surface Measuring System (OSMS), using as a sensor an electronic autocollimator (AC) ELCOMAT-3000. The spatial resolution of the OSMS is limited by the size of the AC light-beam-collimating aperture. For the purposes of this investigation, the OSMS is equipped with a circular aperture with a diameter of 2.5 mm. This is a typical arrangement of most AC-based slope profilers developed for surface slope metrology of state-of-the-art x-ray mirrors. Using the example of surface slope metrology of two state-of-the-art elliptically shaped x-ray focusing mirrors, we demonstrate that the developed data reconstruction procedure allows us to significantly improve the accuracy of surface slope metrology with the OSMS over the spatial wavelength range from ∼1.6 mm to 7 mm. Thus, the amplitude of the quasi-periodic error characteristic of the deterministic polishing process used appears to be higher by a factor of ∼2 than is apparent from the rough metrology data. Underestimation of the surface slope errors in this spatial wavelength range can lead to serious errors in the expected performance of x-ray mirrors in synchrotron beamlines, especially at modern light sources utilizing coherent x rays, where the perturbations can lead to increased speckle-like intensity variation.