Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources

I suggest that the beaming factor in bright ULXs varies as $b \propto \dot m^{-2}$, where $\dot m$ is the Eddington ratio for accretion. This is required by the observed universal $L_{\rm soft} \propto T^{-4}$ relation between soft--excess luminosity and temperature, and is reasonable on general physical grounds. The beam scaling means that all observable properties of bright ULXs depend essentially only on the Eddington ratio $\dot m$, and that these systems vary mainly because the beaming is sensitive to the Eddington ratio. This suggests that bright ULXs are stellar--mass systems accreting at Eddington ratios of order 10 -- 30, with beaming factors b \ga 0.1. Lower--luminosity ULXs follow bolometric (not soft--excess) $L \sim T^4$ correlations and probably represent {\it sub}--Eddington accretion on to black holes with masses \sim 10\msun. High--mass X-ray binaries containing black holes or neutron stars and undergoing rapid thermal-- or nuclear--timescale mass transfer are excellent candidates for explaining both types. If the $b \propto \dot m^{-2}$ scaling for bright ULXs can be extrapolated to the Eddington ratios found in SS433, some objects currently identified as AGN at modest redshifts might actually be ULXs (`pseudoblazars'). This may explain cases where the active source does not coincide with the centre of the host galaxy.Comment: MNRAS Letters, in pres

Managing Uncertainty: Lessons from Xenophon\u27s Retreat

Propositions on dynamic capabilities and organizational politics are developed from management literature and are then evaluated using case analysis. The goal is to identify complementary aspects of these perspectives to change from an ancient example that can offer insights for management thought and practice today. Initially chronicled by Xenophon, roughly 10,000 Greek mercenaries spent over two years confronting demanding circumstances as they fought their way into and out of ancient Persia. The mercenaries\u27 response to changing circumstances offers a unique case for integrating literature on responses to uncertainty that range between rational and haphazard explanations. The analysis suggests uncertainty management is a complex phenomenon imperfectly represented by existing models

Black-Hole Transients and the Eddington Limit

I show that the Eddington limit implies a critical orbital period P_crit(BH) = 2d beyond which black-hole LMXBs cannot appear as persistent systems. The unusual behaviour of GRO J1655-40 may result from its location close to this critical period.Comment: 3 pages, no figures; to appear in MNRA

The American Aircraft Industrial Base: On the Brink

An article reviewing the decline in the American aircraft industrial base

Generating Opportunity from Uncertainty

Learning to deal with uncertainty makes organizations more robust. Leaders can take steps to help their organizations take advantage uncertainty. When continued success transitions from informed decision to luck, small differences in the ability of organizations to handle uncertainty can have a large impact. An example from military history is used to outline current day lessons for military and business leaders

Improved high volume air sampler

Sampler permits size separations of particles by directing sampled air through cross-sectional area sufficiently large that air velocity is reduced to point where particles or larger size will settle out. Sampler conducts air downward and through slots around periphery of unit into relatively open interior of house

Magnetic Fields, Accretion, and the Central Engine of Gamma-Ray Bursts

I briefly review magnetic effects in accretion physics, and then go on to discuss a possible central engine for gamma-ray bursts. A rotating black hole immersed in a non-axisymmetric magnetic field experiences a torque trying to align spin and field. I suggest that gamma-ray burst hosts may provide conditions where this effect allows rapid extraction of a significant fraction of the hole's rotational energy. I argue that much of the electromagnetic emission is in two narrow beams parallel and antiparallel to the asymptotic field direction. This picture suggests that only a mass 10^-5 Msun is expelled in a relativistic outflow, as required by the fireball picture.Comment: 8 pages, Invited talk to appear in the Proceedings of Magnetic Fields in the Universe, Angra dos Reis, Brazil, November 28 - December 3 200

Implications of Technological Uncertainty on Firm Outsourcing Decisions

Outsourcing inherently considers what activity needs to reside within a given firm. The difficulty of exchanges between firms in the face of uncertainty affects where work on developing and producing new products is performed. Theory is developed and explored using a case study that explains firm sourcing decisions as a response to uncertainty within the context of industry structure and related transaction costs. Viewing outsourcing broadly results in a better delineation of outsourcing options. Implications for management research and practice are identified