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Biomedical subjects

M J Richardson

Publications and source records attributed to M J Richardson.

8 recordsLinked to original sources
PubMed1999

Boundary effects in reaction-diffusion processes.

The effects of a boundary on reaction systems are examined in the framework of the general single-species reaction/coalescence process. The boundary naturally represents the reactants' container, but is applicable to exciton dynamics in a doped TMMC crystal. We show that a density excess, which extends into the system diffusively from the boundary, is formed in two dimensions and below. This implies a surprising result for the magnetization near a fixed spin in the coarsening of the one-dimensional critical Ising model. The universal, dimensionally dependent functional forms of this density excess are given by an exact solution and the field-theoretic renormalization group.

Journal Article↗
PubMed1998

Giant cell tumor of bone.

Giant cell tumor of bone is an unusual neoplasm and treatment commonly leads to local recurrence. This can be related to the aggressiveness of the tumor or to the incompleteness of its removal. This study includes 27 cases that presented to our institution between the 1984 and 1994. One case was as a consultation only and 9 cases, either Campanacci Grade 3 or patients with considerable joint destruction, were treated by resection and reconstruction. One case was treated by curettage and cementation. Sixteen cases were treated with a combination of radical curettage, high speed burring, pulsatile lavage, and bone graft (either autograft or allograft mixed with autograft). No other adjuvant therapy was used. All of these 16 cases had a minimum follow-up of 5 years and none had a local recurrence. This study demonstrates that local control of giant cell tumors can be obtained by appropriate staging, resection of aggressive tumors, and by conservative management of the others. Such conservative management provides a bony matrix for the subchondral bone that is preferable to other treatments that have become popular in recent years, including cementation. This should provide better joint function in the longer term. High local recurrence rates have been reported in other series, but by a combination of appropriate selection of cases and by careful treatment of the Campanacci Grade 1 and 2 cases, these patients can have an uncomplicated outcome.

Adolescent↗
PubMed1991

New materials for dielectric simulation of tissues.

Two novel materials have been developed to simulate the dielectric properties of human muscle and fat at 1000 MHz. These materials, which are based on ethanediol set with gelatine, are easily made and have good mechanical properties. The complex permittivity, epsilon *, of each material was measured with an open-ended coaxial sensor in conjunction with an automatic network analyser. Values of epsilon * at 1000 MHz and room temperature (49.4-24.4j for the muscle-equivalent material, 8.2-3.6j for the fat-equivalent) compared well with literature values for tissue at body temperature. Thermal properties were also considered. Specific heat capacities of the materials at room temperature were measured by differential scanning calorimetry and found to be very close to values predicted by theory. Densities were also measured and the thermal conductivities estimated. For comparison, new measurements were made of the specific heat and density of human muscle and fat at body temperature.

Adipose Tissue↗
PubMed1990

Self-concepts of Costa Rican elementary school children.

The Martinek-Zaichkowsky Self-concept Scale was administered to 797 Costa Rican children in Grades 1 to 6. A three-way analysis of variance and Scheffé tests, used in conjunction with a 7 x 6 x 2 factorial design, showed significant differences between school types based on enrollment, grades, and sex. The highest self-concepts were found in the first grade and girls. Children in schools with enrollments under 50 scored significantly lower than those in larger schools. Findings were discussed in relation to literature for children in the USA.

Child↗
PubMedDate not supplied

Effects of narcotic and non-narcotic continuous epidural anesthesia on intrapartum fetal heart rate tracings as measured by computer analysis.

OBJECTIVE: To evaluate the effect of narcotic and non-narcotic continuous epidural anesthesia on intrapartum fetal heart rate (FHR) tracings as measured by computer analysis. METHODS: We studied 37 women with uncomplicated pregnancies at term with reactive FHR tracings. The women were randomized to receive epidural anesthesia with either bupivicaine with fentanyl or bupivicaine alone. One-hour FHR tracings were obtained before epidural anesthesia. Thirty minutes after the initial bolus of the epidural a repeat computer analysis of 60-minute FHR tracing was obtained. Median values are reported for FHR parameters with statistical analysis performed by the Mann-Whitney U and Wilcoxon signed rank tests where appropriate. A power calculation was performed using a power of 90% to determine a required sample size of 28 patients. Statistical significance was set at P < .05. RESULTS: In early first stage of labor, there was no significant difference in pre- and postepidural anesthesia FHR baseline, accelerations of 10 and 15 beats per minute, episodes of high and low variation, and short- and long-term variation when using either narcotic or non-narcotic anesthetic agents. CONCLUSIONS: Thus, the clinician can consider the use of narcotic as well as non-narcotic continuous epidural anesthesia in the dosages used in our study with its attendant advantages without fear of obscuring the fetal heart rate tracing.

Anesthesia, Epidural↗
PubMedDate not supplied

Determination of sulfur dioxide in grapes: comparison of the Monier-Williams method and two ion exclusion chromatographic methods.

Results for determination of sulfur dioxide in grapes were compared by 3 methods: the modified Monier-Williams method, acid distillation/ion exclusion chromatography with electrochemical detection (AD/IEC-EC), and alkali extraction/ion exclusion chromatography with electrochemical detection (AE/IEC-EC). An unusual positive response was observed during the later stage of the Monier-Williams distillation of both control grapes and sulfited grapes. Development of volatile acidic compounds in parallel with this Monier-Williams response and darkening of sample was also observed by collection in an alkali trap and analysis using anion exclusion chromatography and photodiode array detection. No parallel increase in sulfite was observed by the more selective AD/IEC-EC method, which clearly demonstrated that the response observed during the later stage of the Monier-Williams method is a false positive, probably due to caramelization reaction products. Monier-Williams results for grapes containing ca 10 ppm sulfite were in reasonably good agreement with those by either the AD/IEC-EC or AE/IEC-EC methods, presumably because the false positive response in the Monier-Williams analysis compensated for the somewhat incomplete recovery of sulfite. The AE/IEC-EC method is recommended because it is rapid, sensitive, straightforward, and free from interference. Accurate results by Monier-Williams analysis could be obtained by limiting distillation to 60 min and correcting for recovery.

Chromatography, Liquid↗