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M C Nolan

Publications and source records attributed to M C Nolan.

5 recordsLinked to original sources

Dynamical configuration of binary near-Earth asteroid (66391) 1999 KW4.

Dynamical simulations of the coupled rotational and orbital dynamics of binary near-Earth asteroid 66391 (1999 KW4) suggest that it is excited as a result of perturbations from the Sun during perihelion passages. Excitation of the mutual orbit will stimulate complex fluctuations in the orbit and rotation of both components, inducing the attitude of the smaller component to have large variation within some orbits and to hardly vary within others. The primary's proximity to its rotational stability limit suggests an origin from spin-up and disruption of a loosely bound precursor within the past million years.

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Binary asteroids in the near-Earth object population.

Radar images of near-Earth asteroid 2000 DP107 show that it is composed of an approximately 800-meter-diameter primary and an approximately 300-meter-diameter secondary revolving around their common center of mass. The orbital period of 1.755 +/- 0.007 days and semimajor axis of 2620 +/- 160 meters constrain the total mass of the system to 4.6 +/- 0.5 x 10(11) kilograms and the bulk density of the primary to 1.7 +/- 1.1 grams per cubic centimeter. This system and other binary near-Earth asteroids have spheroidal primaries spinning near the breakup point for strengthless bodies, suggesting that the binaries formed by spin-up and fission, probably as a result of tidal disruption during close planetary encounters. About 16% of near-Earth asteroids larger than 200 meters in diameter may be binary systems.

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Asteroid 1950 DA's encounter with Earth in 2880: physical limits of collision probability prediction.

Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft.

Journal Article↗

The role of palliative radiotherapy for brain metastases.

Brain metastases (BRM) are common complications of malignancy, frequently associated with disability and death. Clinical trials have addressed a few of the issues arising from treatment options for BRM. Phase III trials have shown superior survival for patients with solitary resectable BRM (SRBRM) when palliative radiation treatment (RT) to the brain is preceded by resection compared to brain RT alone, but no trial has explored resection plus brain RT compared to resection alone. One Phase III trial in patients with solitary unresected BRM comparing lower to higher doses of RT has shown a small survival advantage with higher-dose radiotherapy. All other trials, however, comparing different radiation doses and fractionation schedules have failed to indicate improved outcomes from treatment more intense than 2000 cGy in 5 fractions over 1 week (in any subset of patients with unresected BRM). A panel of radiation oncologists and medical oncologists discussed a literature review and results of Phase III trials of therapy for BRM. The panel was instructed to identify from these trials any evidence for the efficacy, indications, toxicity and fractionation of palliative RT for BRM. The panel concluded that unresected BRM is a possible indication for brain RT. The panel concluded that the benefits and toxicities of brain RT for unresected BRM are not characterized adequately to allow a stronger recommendation. The panel concluded that there is no evidence for superiority for any dose or schedule of brain RT for BRM more protracted or intense than 2000 cGy in 5 fractions over one week. The panel recommended further study in order to characterize the benefits and toxicities of brain RT for unresectable BRM. The panel considered the potential value of conducting a Phase III trial comparing palliative care and strategies that included brain RT to the same strategies excluding brain RT; the panel did not, however, reach consensus on the feasibility of such a trial.

Brain Neoplasms↗

A clinical audit of glottic cancer in Nova Scotia: a paradigm for effectiveness research.

We conducted a clinical audit of the recurrence-free rates and absolute survival of 146 patients who presented with T1-T3 glottic cancer and received primary radiotherapy treatment at the Nova Scotia Cancer Centre between 1984 and 1990. The outcomes are compared with a review of published results from other centres. We used stage T3 glottic cancer as an example to illustrate concepts of effectiveness research which are used to determine at what level interventions operate in the day to day practice of medicine. The actuarial recurrence-free rates at 5 years are: T1 91%, T2 73%, and T3 44%. The actuarial absolute survival rates are: T1 84%, T2 68%, and T3 52%. Effectiveness research may utilize efficacy research, clinical audit, quality of life assessment and decision making theory. Its objective is to aid the implementation of appropriate clinical management for specific individuals and defined communities. Expert computer systems may be necessary to synthesize the data and to enhance communication and decision making.

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