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Biomedical subjects

J D Maynard

Publications and source records attributed to J D Maynard.

11 recordsLinked to original sources
PubMed2004

Resonant ultrasound spectroscopy measurements of the elastic constants of human dentin.

The technique of resonant ultrasound spectroscopy (RUS) was used to measure the second-order elastic constants of hydrated human dentin. Specimens were placed between two transducers, and the resonant frequencies of vibration were measured between 0.5 and 1.4 MHz. The elastic constants determined from the measured resonant frequencies in hydrated dentin exhibited slight hexagonal anisotropy, with the stiffest direction being perpendicular to the axis of the tubules (E11 = 25.1GPA) This hexagonal anisotropy was small (E33/E11 = 0.92), and almost disappeared when the specimens were dried. In addition, there was a pronounced anisotropy in the Poisson's ratio of wet dentin: v21 = 0.45; v31 = 0.29. With drying in air, this anisotropy vanished: v21 = v31 = 0.29. The isotropic Young's modulus of dried dentin was 28.1 GPa. RUS shows promise for determining the elastic constants in mineralized tissues.

Anisotropy↗
PubMed2003

Measurements of elastic constants in thin films of colossal magnetoresistance material.

Measurements of elastic constants of strained 200 and 400 nm thin films, as well as unstrained samples, of the colossal magnetoresistance (CMR) material La0.67Ca0.33MnO3 are presented. Since the peak resistance temperature of a strained CMR film decreases as the film thickness decreases, it is of interest to see if features in the elastic constants, reflecting structural or magnetic changes, follow the peak resistance temperature. It is observed that features in the elastic constants appear not only at the peak resistance temperatures of the CMR samples, but also at a temperature about 17 K higher. A new technique, thin-film resonant ultrasound spectroscopy, was used to make the measurements.

Journal Article↗
PubMed1992

The use of piezoelectric film and ultrasound resonance to determine the complete elastic tensor in one measurement.

The ultrasonic and elastic properties of materials are conventionally measured using quartz, lithium niobate, etc., transducers and a pulse-echo technique with the transducer driven at resonance. Problems with the technique include transducer ringing, transducer-sample coupling, parallelism of sample faces, beam diffraction, and the necessity of remounting transducers in order to measure all of the elastic constants. Usually, these problems can be minimized, but with samples that are only a fraction of a millimeter in size, conventional ultrasound measurements become difficult if not impossible. However, nearly all of these problems may be avoided if a resonance technique is used, and all of the elastic constants may be determined with a single measurement. For the broadband response and minimum transducer loading required for a resonance measurement in a small sample, polyvinylidene fluoride (PVDF) piezoelectric film (as thin as 9 microns) is ideally suitable.

Computer Simulation↗
PubMed1992

Tumours of the accessory lobe of the parotid gland.

Three cases of tumour of the accessory lobe of the parotid gland are reported and the surgical aspects discussed. An approach through a routine parotidectomy incision is preferred to direct incision over the mass.

Aged↗
PubMed1992

Carcinoma of the major salivary glands.

The results of a prospective survey of planned management of 28 primary carcinomas of the parotid, and five primary carcinomas of the submandibular gland over a period of 22 years are discussed. High- and low-grade carcinomas are distinguished and less radical treatment for the latter appears justified.

Aged↗
PubMed1988

Management of pleomorphic adenoma of the parotid.

A series of 336 parotidectomies, carried out for benign disease has been followed for up to 20 years. One hundred and thirty primary pleomorphic adenomas were treated by wide excision of the tumour after identification of the facial nerve. Recurrence occurred in only one patient and, although 20 patients (15 per cent) experienced some degree of facial nerve weakness postoperatively, there was only one case of permanent weakness.

Adenoma, Pleomorphic↗
PubMed1988

Enucleated parotid tumours.

Five pleomorphic, one monomorphic adenoma and one acinic cell lower pole parotid tumours were thought to be lymph nodes and enucleated. Wide excision of the operative site within 2 months revealed microscopic recurrence in three cases. Three carcinomas were enucleated and two had recurred rapidly. It is suggested that such cases of inadvertent enucleation should undergo wide resection of the operative site with nerve dissection.

Adenocarcinoma↗