An interferometer with an efficient confocal layout is described. Similar in structure to a folded Linnik microscope, the interferometer employs broadband illumination to improve rejection of out-of-focus light. A pro...
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An interferometer with an efficient confocal layout is described. Similar in structure to a folded Linnik microscope, the interferometer employs broadband illumination to improve rejection of out-of-focus light. A prototype reflectometry system based on the new interferometer achieved an axial resolution of less than 10 mu m within a probing depth of 1 mm in samples containing particulate scatterers and specularly reflecting objects. Options for mechanical and electronic scanning are discussed.
An editorial discusses an approach to finding effective pharmaceutical agents. Researchers have suggested that the behavior of biochemical networks may provide an approach for discovering pharmaceuticals.
An editorial discusses an approach to finding effective pharmaceutical agents. Researchers have suggested that the behavior of biochemical networks may provide an approach for discovering pharmaceuticals.
An assembly of resistive paper and liquid crystal sheet, conveniently and cheaply constructed for visual detection of the electric fields associated with an rf probe, is presented. Electrical asymmetries, and &ldq...
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An assembly of resistive paper and liquid crystal sheet, conveniently and cheaply constructed for visual detection of the electric fields associated with an rf probe, is presented. Electrical asymmetries, and “hot-spots” usually associated with conservative electric fields, are easily visualized by the color patterns displayed. The device is of considerable assistance in probe design and the minimization of dielectric loss.
The SLIM experiment ( X. Hu, D. N. Levin, P. C. Lauterbur, and T. Spraggins, spectral l ocalization by im aging, Magn. Reson. Med. 8 , 314, 1988 ) promises to be an efficient technique for localized spectroscopy in vi...
The SLIM experiment ( X. Hu, D. N. Levin, P. C. Lauterbur, and T. Spraggins, spectral l ocalization by im aging, Magn. Reson. Med. 8 , 314, 1988 ) promises to be an efficient technique for localized spectroscopy in vivo , allowing simultaneous acquisition of regional spectra from several, arbitrarily shaped compartments. In the present contribution, we evaluate how sensitivity is affected in this experiment, and we identify a source of localization errors stemming from inhomogeneities within the compartments. We present SLOOP (“spectral lo calization with o ptimal p ointspread function”) as an extension of the SLIM technique. SLOOP optimizes sensitivity and minimizes localization errors by choosing an optimal set of phase-encoding gradients that matches the pointspread function to the shape of the volumes of interest. Experimental results obtained in vitro on a rabbit kidney are shown. SLOOP is also compared to Fourier series localization techniques and to spectroscopic imaging and is presented as a generalization of both of these that samples k space in a nonuniform fashion.
In the bidomain model, two alternative sets of boundary conditions at the interface between cardiac tissue and a saline bath have been used. It is shown that these boundary conditions are equivalent if the length cons...
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In the bidomain model, two alternative sets of boundary conditions at the interface between cardiac tissue and a saline bath have been used. It is shown that these boundary conditions are equivalent if the length constant of the tissue in the direction transverse to the fibers is much larger than the radius of the individual cardiac cells. If this is not the case, the relative merits of the two boundary conditions are closely related to the question of the applicability of a continuum model, such as the bidomain model, to describe a discrete multicellular tissue.
Progress has been made in the identification of experimental and analytical procedures that allow for a more reliable determination of equilibrium and kinetic constants, Possible origins of the frequently observed dev...
Progress has been made in the identification of experimental and analytical procedures that allow for a more reliable determination of equilibrium and kinetic constants, Possible origins of the frequently observed deviations of the measured binding progress from that expected for chemical binding of pseudo-first order, and appropriate experimental controls have been proposed. Improved analytical approaches include the application of global analysis and analytical corrections for the influence of mass transport.
This work analyses the method of correlational accumulation (averaging) of a set of multiple copies of a signal from the same object arbitrarily displaced with relation to one another and observed in a mixture with ad...
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This work analyses the method of correlational accumulation (averaging) of a set of multiple copies of a signal from the same object arbitrarily displaced with relation to one another and observed in a mixture with additive signal independent sensor noise in which the signal displacements are measured by localization of maximum of the signal cross-correlation function. Three main problems are addressed and investigated both analytically and by computer simulation: optimality of the correlational accumulation method, signal distortions which originate from the signal registration errors and noise reduction capability of the correlational accumulation as a function of signal-to-noise ratio in the observed signal-plus-noise realizations.
This paper describes a set of efficient filtering techniques for the processing and representation of signals in terms of continuous B-spline basis functions. We first consider the problem of determining the spline co...
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This paper describes a set of efficient filtering techniques for the processing and representation of signals in terms of continuous B-spline basis functions. We first consider the problem of determining the spline coefficients for an exact signal interpolation (direct B-spline transform). The reverse operation is the signal reconstruction from its spline coefficients with an optional zooming factor m (indirect B-spline transform). We derive general expressions for the z transforms and the equivalent continuous impulse responses of B-spline interpolators of order n. We present simple techniques for signal differentiation and filtering in the transformed domain. We then derive recursive filters that efficiently solve the problems of smoothing spline and least squares approximations. The smoothing spline technique approximates a signal with a complete set of coefficients subject to certain regularization or smoothness constraints. The least squares approach, on the other hand, uses a reduced number of B-spline coefficients with equally spaced nodes;this technique is in many ways analogous to the application of antialiasing low-pass filter prior to decimation in order to represent a signal correctly with a reduced number of samples.
This paper describes two ways of improving Burt and Adelson's Laplacian pyramid, a technique developed for image compression. The Laplacian pyramid is a multi-resolution image representation that captures the loss...
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This paper describes two ways of improving Burt and Adelson's Laplacian pyramid, a technique developed for image compression. The Laplacian pyramid is a multi-resolution image representation that captures the loss of information occurring through repeated reduction of the spatial resolution. The generation of this data structure involves the use of two complementary functions: EXPAND, which increases the size of an image by a factor of 2, and REDUCE, which performs the reverse operation. The first modification is the adjunction of a pre-filter to the initial EXPAND function in order to guarantee an image extrapolation that is an exact interpolation of the coarser resolution level. The second refinement is a REDUCE operation modified to. minimize information loss. The corresponding least squares Laplacian pyramid (LSLP) is generated by adding a post-filter to the initial REDUCE function. These new functions have an efficient implementation using recursive algorithms. Preliminary experiments indicate improved performance: for a Gaussian-like kernel (a=3/8), the new EXPAND function exhibits a 2 to 2.5 dB attenuation of the first level of the Laplacian pyramid, while the complete scheme (LSLP) leads to a 4.7 to 8.5 dB improvement in the two images used to test the procedure. For comparable compression ratios, the subjective image quality for the LSLP appears to be significantly better. A theoretical relationship between the present approach and the family of quadrature mirror filter image pyramids is also derived.
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