Oscar A. Lindemann

Bio: Oscar A. Lindemann is an academic researcher. The author has contributed to research in topics: Radiation impedance & Piston. The author has an hindex of 1, co-authored 4 publications receiving 12 citations.

Transient fluid reaction on a baffled plane piston of arbitrary shape

Abstract: The inverse Laplace transform of the frequency‐dependent radiation impedance of a baffled piston, i.e., its impulse response, is a function which is more directly related to the geometry of the piston than the impedance itself. It is here shown how this function can be described in terms of a finite pulse called the characteristic pulse, whose shape depends on that of the piston, and that its evaluation depends on a relatively simple integration around the piston's contour. A number of examples show that the characteristic pulse can be evaluated exactly for certain piston shapes. Geometrical features of the piston's shape, such as corners, have a predictable effect on the characteristic pulse, and hence on the radiation impedance; some of these fundamental relationships are derived in the form of simple theorems.

Radiation Impedance of a Long Narrow Rectangular Piston in a Plane Baffle

Abstract: The radiation impedance of a long narrow rectangular baffled piston is investigated order to discover whether its frequency dependence is in any way markedly different from that of a disk. A first assumption that its width is negligibly small in comparison with a wavelength leads to an asymptotic expression valid for frequencies in a neighborhood of zero, and a second assumption that its length is infinite gives an asymptotic expression valid for frequencies in a neighborhood of infinity. For a finite rectangle of large aspect ratio the two approximations overlap and are compatible, enabling composite graph of the radiation impedance to be drawn over the entire frequency range. The result shows that the piston behaves differently in three distinct frequency bands, corresponding to spherical, cylindrical, and plane‐wave radiation. The circular piston, in contrast, has no cylindrical middle band.

Transformation of the Helmholtz Integral into a Line Integral

Abstract: The quadruple Helmholtz integral, which appears in the expression for the radiation impedance of a piston in a plane baffle, can be very simply transformed into a double contour integral. This can simplify computation, particularly in the case of a rectangular piston.

Radiation Impedance of a Rectangular Piston at Very Low Frequencies

Abstract: In order to demonstrate how the radiation reactance of a piston, at low frequencies, depends on its shape, the solution for a rectangle of varying aspect ratio is obtained by contour integration The method gives in a few short steps the exact value of the asymptotic accession to inertia, previously available only by means of a much longer computation The result is graphed as a function of the piston's aspect ratio, and compared with the known value for the circle

Parental caregivers of children with developmental disabilities mount a poor antibody response to pneumococcal vaccination

Abstract: In older populations, caregiving for a spouse with dementia has been associated with a poor antibody response to vaccination. The present study examined whether younger caregivers, specifically the parents of children with developmental disabilities, would also show a diminished antibody response to vaccination. At baseline assessment, 30 parents of children with developmental disabilities and 29 parents of typically developing children completed standard measures of depression, perceived stress, social support, caregiver burden, and child problem behaviours. They also provided a blood sample and were then vaccinated with a pneumococcal polysaccharide vaccine. Further blood samples were taken at 1- and 6-month follow-ups. Caregivers mounted a poorer antibody response to vaccination than control parents at both follow-ups. This effect withstood adjustment for a number of possible confounders and appeared to be, at least in part, mediated by child problem behaviours. The negative impact of caregiving on antibody response to vaccination is not restricted to older spousal caregivers, but is also evident in younger parents caring for children with developmental disabilities. The behavioural characteristics of the care recipients may be a key consideration in whether or not immunity is compromised in this context.

Acoustic properties of micro-perforated panel absorber having arbitrary cross-sectional perforations

Abstract: Micro-perforated panel absorber is used in many noise control applications as a next-generation absorbing material. Perforation shapes of micro-perforated panel studied are usually circular in the past. However, in practice, the perforations are often non-circular or irregular shape due to manufacturing techniques. Sound absorption coefficient and absorption bandwidth of the micro-perforated panel absorber may be further improved, when the perforations in shape are changed. In view of the existing exact solutions of sound propagation in tubes, the simple formulas of specific acoustic impedances of the tubes for triangle and square cross-sectional perforations are derived. Mass reactance end correction of the micro-perforated panel is obtained based on the sound radiation of a shaped piston. The specific acoustic impedance ratio of the micro-perforated panel absorber is calculated and analyzed, which can predict its sound absorption bandwidth. Finally, for closed perforations, the influences of the perforations in shape (including triangle, circle, square and irregular circle) on sound absorption of the MPP absorber are discussed in collaboration with FE simulations.

Extensions to the Mode Matching Method for Horn Loudspeaker Simulation

Abstract: For loudspeaker horns, the throat acoustic impedance and the far field directional characteristics are important measures of performance. Both quantities depend greatly on the shape of the horn, and the acoustical conditions at the mouth of the horn. The Mode Matching Method (MMM) is a semianalytical method for the simulation of sound propagation in ducts, and is the method used as the fundamental building block in this work. In previous work using this method, the horn has usually been assumed to be mounted in an infinite baffle, a condition that is not realistic for most real-world applications. Most horns are usually mounted in finite baffles or cabinets, or placed close to reflecting surfaces or in rooms. This work has therefore focused on extending the MMM to new cases closer to real-world applications. For horns without baffle, or with finite baffles or flanges, two methods have been explored; one for axisymmetric horns based on the solution for a semi-infinite unflanged duct, and one for general geometries based on edge diffraction. For horns near infinite reflecting surfaces, a method has been derived to compute the modal mutual radiation impedance. For the final radiation condition, a horn mounted in the wall of a room, two methods have been explored, where in both cases analytical expressions for radiation impedance and radiated pressure are found for shoebox shaped rooms. Experimental verification of some of the cases mentioned above is provided. The MMM is restricted to certain cross-sectional geometries; round and rectangular geometries are treated in this work. In many practical cases a rectangular horn is connected to a circular loudspeaker, and in order to simulate this and similar configuration, a method has been developed to interface the MMM with the Boundary Element Method. By modifying the MMM, it has also been possible to simulate radiation from concave structures like loudspeaker diaphragms. Using this approach it is also possible to simulate concave reflectors, as long as the source is not outside of the cavity. A final application of the MMM in this work, is the use of the method to compute the transfer function and resonance frequencies of non-shoebox shaped rooms. While the shape of the room is still somewhat restricted compared to Finite Element Method simulations, a wide range of rooms can be simulated.

Estimation of treatment preference effects in clinical trials when some participants are indifferent to treatment choice

Abstract: In the two-stage randomised trial design, a randomly sampled subset of study participants are permitted to choose their own treatment, while the remaining participants are randomised to treatment in the usual way. Appropriate analysis of the data from both arms of the study allows investigators to estimate the impact on study outcomes of treatment preferences that patients may have, in addition to evaluating the usual direct effect of treatment. In earlier work, we showed how to optimise this design by making a suitable choice of the proportion of participants who should be assigned to the choice arm of the trial. However, we ignored the possibility of some participants being indifferent to the treatments under study. In this paper, we extend our earlier work to consider the analysis of two-stage randomised trials when some participants have no treatment preference, even if they are assigned to the choice arm and allowed to choose. We compare alternative characterisations of the response profiles of the indifferent or undecided participants, and derive estimates of the treatment and preference effects on study outcomes. We also present corresponding test statistics for these parameters. The methods are illustrated with data from a clinical trial contrasting medical and surgical interventions. Expressions are obtained to estimate and test the impact of treatment choices on study outcomes, as well as the impact of the actual treatment received. Contrasts are defined between patients with stated treatment preferences and those with no preference. Alternative assumptions concerning the outcomes of undecided participants are described, and an approach leading to unbiased estimation and testing is identified. Use of the two-stage design can provide important insights into determinants of study outcomes that are not identifiable with other designs. The design can remain attractive even in the presence of participants with no stated treatment preference.

The radiation impedance of a rectangular piston

Abstract: The radiation impedance of a rectangular piston is expressed as the Fourier transform of its impulse response, which is obtained from the recent work of Lindermann [1]. The analytical evaluation of the transform is performed and new integral expressions are presented for both the radiation resistance and reactance. The integrals are readily evaluated in terms of elementary functions at both the low and high frequency limits. The integrals are also expressed as series of Bessel functions which are valid for all frequencies and aspect ratios. Numerical results are presented to illustrate the behavior of the radiation resistance and reactance as a function of the aspect ratio of the piston and a normalized frequency parameter. Additional numerical results are then presented to illustrate the accuracy of the analytical expressions for the radiation resistance and reactance at low and high frequencies. Finally, numerical results are presented to illustrate the application and accuracy of using standard FFT algorithms to evaluate the radiation resistance and reactance directly from the impulse responses.