Pulsar Bound on the Photon Electric Charge Reexamined

If photons had a small electric charge $Q_\gamma$ their path in the galactic magnetic field would be curved, leading to a time delay between photons of different frequency from a distant source. Cocconi's previous application of this argument led to a limit which is too restrictive by a factor of about 200; the corrected bound is Q_\gamma/e\lapprox10^{-29}.Comment: 3 pages, LaTe

Information technology, capabilities and Asset Ownership: Evidence from Taxicab Fleets

We examine how information technology (IT) influences asset ownership through its impact on firms’ and agents’ capabilities. In particular, we propose that when IT is a substitute for agents’ industry-specific human capital, IT adoption leads to increased vertical integration. We test this prediction using micro data on vehicle ownership patterns from the Economic Census during a period when computerized dispatching systems were first adopted by taxicab firms. The empirical tests exploit exogenous variation in local market conditions, to identify the impact of dispatching technology on firm asset ownership. The results show that firms increase the proportion of taxicabs owned by 12% when they adopt new computerized dispatching systems. The findings suggest that firms increasingly vertically integrate when they acquire resources that substitute for their agents’ capabilities.

Information Technology, Productivity, and Asset Ownership: Evidence from Taxicab Fleets

We develop a simple model that links the adoption of a productivity-enhancing technology to increased vertical integration and a less skilled workforce. We test the model's key prediction using novel microdata on vehicle ownership patterns from the Economic Census during a period when computerized dispatching systems were first adopted by taxicab firms. Controlling for time-invariant firm-specific effects, firms increase the proportion of taxicabs under fleet ownership by 12% when they adopt new computerized dispatching systems. An instrumental variables analysis suggests that the link between dispatching technology and vertical integration is causal. These findings suggest that increasing a firm's productivity can lead to increased vertical integration, even in the absence of asset specificity

Diversification, Diseconomies of Scope, and Vertical Contracting: Evidence from the Taxicab Industry

This paper studies how firms reorganize following diversification, proposing that firms use outsourcing, or vertical disintegration, to manage diseconomies of scope. We also consider the origins of scope diseconomies, showing how different underlying mechanisms generate contrasting predictions about the link between within-firm task heterogeneity and the incentive to outsource following diversification. We test these propositions using microdata on taxicab and limousine fleets from the Economic Census. The results show that taxicab firms outsource, by shifting the composition of their fleets toward owner-operator drivers, when they diversify into the limousine business. The magnitude of the shift toward driver ownership is larger in less urban markets, where the tasks performed by taxicab and limousine drivers are more similar. These findings suggest that (1) firms use outsourcing to manage diseconomies of scope at a particular point in the value chain and (2) interagent conflicts can be an important source of scope diseconomies

How Do Mobile Information Technology Networks Affect Firm Strategy and Performance? Firm-Level Evidence from Taxicab Fleets

This paper examines how the adoption of mobile information technology networks impact firm strategy and performance in the U.S. taxicab industry. Using a rich, novel firm-level data set from the Economic Census, I test transaction cost economics' prediction that adoption of mobile IT networks leads to shifts in the boundary of the firm toward increased fleet ownership of vehicles. I then exploit the homogeneity of the industry's production function and exogenous variation in local market conditions to precisely measure the impact of adoption of mobile IT networks on productivity. I find strong evidence that firms respond to adoption of mobile IT networks by changing their organizational structure, shifting toward owning a greater fraction of vehicles in their fleets (as opposed to contracting with independent driver-owners for vehicles). I then use a precise and economically meaningful measure of firm performance to show that adoption of mobile IT networks causes firms to become more productive. The results suggest that adoption of mobile IT networks increases asset utilization by improving within-firm coordination but that firms must simultaneously shift toward a more highly vertically integrated structure to fully capture the benefits of mobile IT networks

Information Technology, Productivity, and Asset Ownership: Evidence from Taxicab Fleets

We develop a simple model that links the adoption of a productivity-enhancing technology to increased vertical integration and a less skilled workforce. We test the model's key prediction using novel microdata on vehicle ownership patterns from the Economic Census during a period when computerized dispatching systems were first adopted by taxicab firms. Controlling for time-invariant firm-specific effects, firms increase the proportion of taxicabs under fleet ownership by 12% when they adopt new computerized dispatching systems. An instrumental variables analysis suggests that the link between dispatching technology and vertical integration is causal. These findings suggest that increasing a firm's productivity can lead to increased vertical integration, even in the absence of asset specificity

Skill, Luck, and the Multiproduct Firm: Evidence from Hedge Funds

We formalize the idea that when managers require external investment to expand, higher-skilled firms will be more likely to diversify in equilibrium, even though managers can exploit asymmetric information about their ability to raise capital from investors. We exploit the timing of new fund launches in the hedge fund industry to distinguish between agency and capability effects in firm product diversification decisions, using a large survivor-bias-free panel data set on the hedge fund industry from 1994 to 2006. Empirically we show that diversifying firms' excess returns are high relative to those of other firms prior to diversification and fall within firm following diversification, but are six basis points higher per month per unit of risk ex post compared to a matched sample of focused firms. The evidence suggests that managers exploit asymmetric information about their own ability to time diversification decisions; yet, the discipline of markets ensures that better firms diversify, on average. The results provide large-sample empirical evidence that agency effects and firm capabilities jointly influence diversification decisions

Diversification, Coordination Costs, and Organizational Rigidity: Evidence From Microdata

This paper examines the impact of coordination costs and organizational rigidity on the returns to diversification. The central thesis is that coordination costs offset economies of scope, while organizational rigidity increases coordination costs, further constraining economies of scope. The empirical tests of this proposition identify the effects of coordination and organizational rigidity costs on business unit and firm productivity, using novel data from the Economic Census on taxicab and limousine firms. The key results show that coordination and organizational rigidity costs are economically and statistically significant, while organizational rigidity itself accounts for a 16 percent decrease in paid ride-miles per taxicab in incumbent diversifiers, controlling for the other costs and benefits of diversification and incumbency. The findings suggest that coordination costs, in general, and organizational rigidity costs, in particular, limit the scope of the firm

Diversification, Coordination Costs and Organizational Rigidity: Evidence from Microdata

This paper examines the impact of coordination costs and organizational rigidity on the returns to diversification. The central thesis is that coordination costs offset economies of scope, while organizational rigidity increases coordination costs, further constraining economies of scope. The empirical tests of this proposition identify the effects of coordination and organizational rigidity costs on business-unit and firm productivity, using novel data from the Economic Census on taxicab and limousine firms. The key results show that coordination and organizational rigidity costs are economically and statistically significant, while organizational rigidity itself accounts for a 16% decrease in paid ride-miles per taxicab in incumbent diversifiers, controlling for the other costs and benefits of diversification and incumbency. The findings suggest that coordination costs, in general, and organizational rigidity costs, in particular, limit the scope of the fir

Diurnal changes in the heterotrophic uptake of glycolate and glucose in two lakes

A study was made of diurnal changes in the heterotrophic uptake kinetics of both ¹⁴C-glucose and ¹⁴C- glycolate in two small stratified lakes, Lake Rotomanuka in New Zealand and Lake Fryxell in Antarctica. The purpose of the investigation was to study the effect that diurnal changes in the extracellular release of certain substrates by algae might have on the uptake of those substrates by aquatic microheterotrophs. The heterotrophic uptake technique of Parsons and Strickland.(196l) was modified to provide a technique which was more convenient for field-work. In an effort to exclude the effects of migration and heterogeneous population distribution on substrate uptake, the microbial population in each lake was observed using a combination of (a) direct counts of bacteria (using acridine orange staining and epi-fluorescent microscopy); (b) measurement of chlorophyll α and bacterio-chlorophyll and (c) measurement of the reduction of INT dye. The natural concentration of glycolate was measured on some occasions using a modification of the technique of Shah and Wright (1974)