Degrees of Freedom of an Image in the Presence of Noise and ‘a Priori’ Information

Abstract

The mathematical technique applied by Gori and Guttari for calculation of degrees of freedom in images formed by point-like elemental pupils is extended to continuous pupils. Eigenvalues of the imaging equation are calculated for the sinc as well as the sinc² kernel. The effect of noise and ‘a priori’ information are taken into account.     

Spectral Matched Filters in Coherent Laser Radar

Abstract

Insight into the properties of maximum likelihood Doppler frequency shift estimators, which function as spectral domain matched filters, is often obtained more readily from examination of their spectral correlating functions, and lag windows than from simulated performance data. These functions are compared and contrasted with reference to lidar applications for the three principal estimators.     

Lowpass filters with near‐maximally flat passband

Abstract

A new class of low‐pass filters, referred to as Near‐Maximally Flat (NMF) filters, with a zero passband loss at the origin and some fixed frequency near the passband edge are investigated. The magnitude response exhibits one controllable ripple in the passband and provides more stopband attentuation than the classical Butterworth filters and monotonic response class L filters. A systematic procedure is also presented to generate normalized near‐maximally flat filters with pairs of finite transmission zeros in the filter function.     

Choice of Filtration Methods for Monitoring the Dissolution of Frusemide

Abstract

Although the British Pharmacopoeia indicates the need for filtration during the removal of samples in the course of dissolution tests, there is little guidance as to the type of filters that should be used to clarify fluids during their removal. On the basis of results obtained using frusemide as a model drug, the following recommendations are made regarding the use of filters in dissolution testing.

[1] If membrane filters are to be used to clarify dissolution fluids, filters with the smallest diameter and the highest pore size as practically permissible should be utilized to minimise drug loss into the filters.

[2] Whatman Paper filters, or equivalent, are probably to be preferred to membrane filters since they do not seem susceptible to drug sorption.

[3] The membrane type should be varied to the pH of the dissolution fluid. At pH 5.8, cellulose acetate filters sorbed less frusemide than cellulose nitrate filters but with 0.1M HC1 more sorption occurred into the cellulose acetate filters.     

Influence of Amplitude-only Filters in Optical Systems with Residual Longitudinal Chromatic Aberration

Abstract

The transverse and axial polychromatic responses of optical systems with residual chromatic aberration and an achromatic correction are studied. The influence of amplitude-only filters that produce apodization or hyper-resolution in a transverse section is shown. Filters that modify the responses along the axis are also shown. The differences between the responses of the aberration-free system with a filter and the aberrant systems with the same filter are compared.     

Carbon and Beryllium Extreme Ultraviolet Filters: Far-ultraviolet Performance

Abstract

Designs for extreme-ultraviolet filters using thin carbon and beryllium foils are presented and their far-ultraviolet performance summarized. The transmission data yield values for the linear-absorption coefficients of beryllium and carbon in the wavelength range 1200–2000 Å which are compared with other published data in this and in the adjacent extreme-ultraviolet wavebands. Use of multiple foils is demonstrated to be an effective means of eliminating pin-holes, which may contribute significantly to the far-ultraviolet transmission.     

Integrated intensity and confocal imaging through scattering media

Abstract

It is shown how the integrated intensity, discussed previously elsewhere, can be used to investigate in a simple way, the process of confocal imaging though a weakly scattering medium. The effect of annular pupils and half-plane apertures are investigated.     

New formulae for switch ed‐capacitor band pass filters

Abstract

The governing equations for switched‐capacitor band pass filters are greatly simplified into a new set of much simpler equations, with no approximation involved. For sharp band pass filters with narrow bandwidths, we expand the new set, cancel out many leading terms, and get a set of new formulae. Based on these formulae, we obtain and tabulate numerical design data for sharp 4th to 8th order Butterworth band pass filters, including values for the required resistors. The application of switched‐capacitor filters MF5 and MF10 is then greatly expanded to cover sharp and very sharp band pass filters.     

GENERAL PRINCIPLES OF VEHICLE CAB FILTRATION

ABSTRACT

The basic requirements to be satisfied by cab filters are discussed, and the behaviour of fibrous filters with respect to airflow resistance and the capture of particles by mechanical and electrostatic means are outlined. Optimisation of filter performance by means of pleating, to increase the area, is briefly reviewed, and the behaviour of both mechanical and electrically charged filters on loading is discussed. Finally, the requirements for tests of cab filter performance, both in the field and in the laboratory, are considered.     

Optical Intensity Filters for Pattern Recognition

Abstract

All the shape information of an object is preserved in its quarter-spectrum (QS). Some new uses of optical filters for pattern recognition based on QS are introduced. These filters are intensity functions so that amplitude modulating spatial light modulators or photographic film can be used. Some of the new filters yield better correlation performances than the phase-only filter and the amplitude-encoded phase-only filter. Computer simulations and optical experiments show the results.     

On realization of modified maximally flat group delay low‐pass filters

Abstract

This paper presents four tables of element values for designing maximally flat group delay low‐pass filters with Chebyshev attenuation in stopband and flat attenuation in passband.     

Fringe visibility analysis with different scale apertures in speckle photography

Abstract

The use of different scale aperture pupils for image recording in speckle photography is analysed. In particular a double-exposure specklegram is considered. The ensemble-average intensity in the Fourier plane is analytically derived and fringe visibility is investigated. The theoretical results are verified by in-plane displacement translation experiments.     

Coherence filters and their uses. I. Basic theory and examples

Abstract

The phenomenon of correlation-induced spectral changes, discovered several years ago and extensively studied since then, is shown to offer the possibility of contructing novel types of spectral filter which have several properties that are not achievable with conventional filters. For example such filters can have different prescribed filtering properties in different directions of observation. In this paper the underlying theory is discussed and is illustrated by a few examples.     

Stability of UV Filters in Different Vehicles: Solvents and Emulsions

Abstract

In this paper, we analyzed the stability of several ultraviolet (UV) filters exposed to simulated solar light. Evaluation of the photostability of UV-A/UV-B filters has an important impact on the efficiency of sunscreen preparations. The purpose of this study is first to relate some of the solvent shifts that can interact with UV filters; secondly, it is to formulate sunscreen emulsions (oil in water and water in oil) in order to evaluate the photostability of sunscreens in the mixture, and therefore their efficiency in solar protection, because photostability and protection are closely linked together.     

Polychromatic Self-imaging

Abstract

The necessary condition for self-imaging in incoherent polychromatic light is derived from the McCutchen and central-slice theorems. Two types of self-imaging pupils are analysed: a pupil produced by a diffracting mask which gives self-images at positions depending on the wavelength, and an interferential pupil using a Fabry-Perot etalon which produces achromatic self-images. Experimental verifications are presented.     

Image Intensity at the Edge of a Straight Edge Object

Abstract

We consider the value of the intensity image at the geometrical position of a general, flat, straight edge object. We adopt a Fourier optical transfer function approach and obtain, rigorously, analytic expressions for the cases of coherent, incoherent and equal aperture, partially coherent imaging. Aberration-free, circular pupils are considered and the analytic results are found to agree with earlier numerical calculations. We also obtain expressions for the intensity gradient at the edge.     

Unbounded increase in the dimension of chaotic attractors in linear filtering

An analysis is made of the limiting possibilities for adding complexity to chaotic oscillations in high-order filters. It is found that the limiting dimension of chaotic oscillation attractors in linear filters may increase to infinity, so that deterministic chaotic test oscillations with any desired dimension can be generated. “Kolledzh” State Education and Science Center Pis’ma Zh. Tekh. Fiz. 23, 8–13 (April 12, 1997)     

The Use of Annular Pupil Plane Filters to Tune the Imaging Properties in Confocal Microscopy

Abstract

We consider the use of pupil plane filters to modify the imaging properties of confocal optical systems. We specialize to the annular filter as it is useful in itself and as part of a more complex filter. We show, inter alia, that by changing the size of the annular obscuration we can tune the strength of the optical sectioning. The question of spherical aberration is considered and it is found both theoretically and experimentally that the effects are reduced in the annular case. We also discuss the problem of where best to place the filters in reflection systems where different filter functions are required for the two imaging lenses. The use of filters in both bright-field and fluorescence imaging modes is considered.     

A MATHEMATICAL MODEL FOR THE DYNAMIC PARTICIPATE FILTRATION IN DIESEL FOAM FILTERS

ABSTRACT

Diesel Particulate Filters (DPFs) are probably the most effective means for trapping the exhaust-emitted participate from diesel engines. Foam type filters become a promising alternative to the common wall flow filters, since they are effective in filtering small size particles and provide a larger specific surface area for catalytic coatings. A mathematical model taking into account the significant phenomena during the dynamic filtration of foam filters is developed. The model predicts the filtration efficiency and the induced backpressure as function of the geometric filter properties and operating conditions. Due to the particular structure properties of the foam filters it is necessary to employ a tunable parameter, which accounts for the influence of non-Stokes flow in foam filters. This parameter is easily derived by simple measurements. The model is employed to identify and understand the critical parameters of the filtration in foam filters. Indicative parametric runs are presented, which illustrate the applicability of the model in system optimization procedures.