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Biomedical subjects

L J Jacobs

Publications and source records attributed to L J Jacobs.

13 recordsLinked to original sources
PubMed2001

Time-frequency representations of Lamb waves.

The objective of this study is to establish the effectiveness of four different time-frequency representations (TFRs)--the reassigned spectrogram, the reassigned scalogram, the smoothed Wigner-Ville distribution, and the Hilbert spectrum--by comparing their ability to resolve the dispersion relationships for Lamb waves generated and detected with optical techniques. This paper illustrates the utility of using TFRs to quantitatively resolve changes in the frequency content of these nonstationary signals, as a function of time. While each technique has certain strengths and weaknesses, the reassigned spectrogram appears to be the best choice to characterize multimode Lamb waves.

Journal Article↗
PubMed2001

Crack characterization using guided circumferential waves.

This paper examines the propagation of guided circumferential waves in a hollow isotropic cylinder that contains a crack, with the goal of using these guided waves to both locate and size the crack. The crack is sized using a modified Auld's formula, which relates the crack's length to a reflected energy coefficient. The crack is then located by operating on the backscattered signal with a time-frequency digital signal processing (DSP) technique, and then comparing these results to those obtained if the cylinder is perfect. The guided circumferential waves are generated with a commercial finite element method (FEM) code. One objective of this work is to demonstrate the effectiveness of using sophisticated DSP techniques to describe the effect of scattering on dispersive waves, showing it is possible to characterize cracks systematically and accurately by quantifying this scattering effect. The results show that the need for high frequency signals to detect small cracks is significantly decreased by using these techniques.

Journal Article↗
PubMed2000

Multiplex PCR of polymorphic markers flanking the CFTR gene; a general approach for preimplantation genetic diagnosis of cystic fibrosis.

Cystic fibrosis (CF) is the first monogenic disorder for which single cell preimplantation genetic diagnosis (PGD) has been successfully applied. The spectrum of mutations in CF is extremely heterogeneous, and hence, the development of mutation-specific PGD protocols is impracticable. The current study reports the development and evaluation of a general multiplex marker polymerase chain reaction (PCR) protocol for PGD of CF. Four closely linked highly polymorphic (CA)(n) repeat markers D7S523, D7S486, D7S480 and D7S490, flanking the cystic fibrosis transmembrane regulator (CFTR) gene, were used. In 99% of the single cells tested (100 leukocytes and 50 blastomeres), multiplex PCR results were obtained and the overall allelic drop out (ADO) rate varied from 2 to 5%. After validation for the presence of ADO and additional alleles, 95% of the multiplex PCR results were accepted to construct the marker genotypes. Depending on the genotype of the couple, and taking into account the embryos lost for transfer due to validation criteria (5%), ADO (0-2%) and single recombination (1.1-3%), in general >90% of the embryos could be reliably genotyped by PGD using a single blastomere. The risk of misdiagnosis equals the chance of a double recombination between informative flanking markers and is <0.05%. Therefore, this polymorphic and multi-allelic marker system is a reliable and generally applicable alternative for mutation-directed PGD protocols. Furthermore, it provides a test for the origin of the detected genotype and also gives an indication of the chromosomal ploidy status of the blastomere tested.

Blastomeres↗
PubMed1989

Reversible dilated cardiomyopathy induced by methamphetamine.

This brief report details the case of a woman who was thought, after extensive evaluation, to have idiopathic congestive cardiomyopathy. It was subsequently found that systolic ventricular dysfunction was due to amphetamine abuse, and that ventricular function normalized after discontinuation of this drug.

Cardiomyopathy, Dilated↗
PubMed1981

Ventricular arrhythmias during Swan-Ganz catheterization of the critically ill.

The incidence of ventricular arrhythmias in critically-ill patients during bedside right-sided heart catheterization with a flow-directed balloon-tipped catheter was determined. Twenty-nine of 60 catheterizations (48 percent) were associated with premature ventricular contractions and 20 (33 percent) were associated with ventricular tachycardia. Two patients required antiarrhythmic therapy or a precordial thump to convert ventricular tachycardia. One patient developed ventricular tachycardia and fibrillation and died. Serious catheter-induced arrhythmias, including sustained ventricular tachycardia, may occur during Swan-Ganz catheterization of the critically ill.

Arrhythmias, Cardiac↗
PubMed1979

Imitative behavior by Down's syndrome persons.

Three scales of imitative behavior (nonverbal, vocal, and verbal) were administered to 28 Down's syndrome subjects and 56 subjects with other diagnoses. All of the subjects were severely retarded and had at least partial vision and hearing, and the two groups were closely comparable with respect to sex, CA, and IQ. The results provided no support for the hypothesis--backed by a century of clinical observation--that individuals with Down's syndrome "are outstanding in their mimicry" (Belmont, 1971, p. 38).

Adolescent↗