Biomedical subjects

Mark McDonald

Publications and source records attributed to Mark McDonald.

4 recordsLinked to original sources

PubMed2005

Detecting a currency's dominance or dependence using foreign exchange network trees.

In a system containing a large number of interacting stochastic processes, there will typically be many nonzero correlation coefficients. This makes it difficult to either visualize the system's interdependencies, or identify its dominant elements. Such a situation arises in foreign exchange (FX), which is the world's biggest market. Here we develop a network analysis of these correlations using minimum spanning trees (MSTs). We show that not only do the MSTs provide a meaningful representation of the global FX dynamics, but they also enable one to determine momentarily dominant and dependent currencies. We find that information about a country's geographical ties emerges from the raw exchange-rate data. Most importantly from a trading perspective, we discuss how to infer which currencies are "in play" during a particular period of time.

Journal Article↗

PubMed2004

Multi-modality tissue-mimicking phantom for thermal therapy.

A tissue-mimicking phantom material has been developed for use with thermal therapy devices and techniques. This material has magnetic resonance properties (primarily T2) which change drastically upon thermal coagulation, enabling its use for device characterization and treatment verification using simple T2-weighted imaging techniques. The coagulation temperature of the phantom can be changed from 50-60 degrees C by adjusting the pH from 4.3 to 4.7. The energy absorption properties can be adjusted to match the acoustical and optical properties of tissues. T2 relaxation measurements are provided as a function of temperature, along with T2-weighted MR images to illustrate the visualization of heating patterns. A complete recipe for fabricating phantoms is provided.

Acrylic Resins↗

PubMed2003

Laser-polarized 129Xe NMR at 1.88 T and 8.5 mT: a signal-to-noise ratio comparison.

The signal-to-noise ratio of nuclear magnetic resonance signals from laser-polarized 129Xe gas was investigated at 8.5 mT and compared to that of signals acquired at 1.88 T. A dedicated 8.5 mT resistive magnet was constructed and used to acquire the signals. The SNR for 1 atm of xenon gas with a polarization of 1% was measured to be 1900 at a field of 1.88 T. Under identical acquisition conditions, the SNR at 8.5 mT was about 60 (or 32 times lower). After measuring and including all of the electrical factors of the detection systems at each field strength, theory indicates the SNR value measured at 8.5m T should be about 36 times lower. Considering the widely differing frequencies and completely different detection systems the agreement is quite good and indicates that extrapolating the frequency dependence of the SNR down to very low fields does work as long as the detection system parameters are carefully accounted for. This work suggests that magnetic resonance (MR) imaging is achievable on ideal gas samples at 8.5 mT using laser-polarized 129Xe gas down to the practical resolution limit of about 0.5mm, although the SNR will be very low (approximately 1.4). The feasibility of imaging small animals at 8.5 mT is discussed and it is suggested that a field of about 50 mT is required.

Journal Article↗

PubMedDate not supplied

Communication and health protection issues arising from a flooding emergency.

OBJECTIVE: To identify and describe the key communication and health protection issues surrounding a flooding emergency. METHODS: A telephone questionnaire was used to assess health and safety information sources, information recalled, and behavioral responses among residents of the town of Feilding, New Zealand following a major flood in February 2004. This was supplemented by key informant interviews and a newspaper content analysis. RESULTS: A total of 154 adult residents were surveyed (76% of those successfully contacted and eligible). Of the respondents, 79% recalled being provided with health and safety information from authorities. The major sources were: radio (41%), pamphlets (23%), and newspapers (20%). The regional newspaper had extensive coverage of this flooding emergency but "health" only was mentioned in 46 (7%) of the 664 flood-related articles. Of those who recalled receiving information from authorities, most (89%) perceived that it was adequate. Nevertheless, 18% actively sought out information (mainly about water safety and availability). In the post-flood period, 73% of all respondents boiled water; however, only 4% maintained boiling water or bottled water use for the necessary nine-week period. Some forms of emergency preparations did not change substantially from before the flood, compared to four months afterwards (e.g., having a radio with batteries increased from 62% to 68%). Perceived health concerns around the flooding were low, though 59% were concerned about the risk of water contamination. Actual self-reported, health consequences from the flood were rare, as only two (1%) people out of 154 reported flood-related health problems. CONCLUSIONS: Health and safety information generally was communicated successfully and was regarded as appropriate by the population of this flood-affected town. Nevertheless, there are further improvements needed in the emergency response by both residents and authorities.

Adult↗