The photosensitized generation of reactive oxygen species, and particularly of singlet oxygen [O2 (a(1) Δg )], is the essence of photodynamic action exploited in photodynamic therapy. The ability to switch singlet oxygen generation on/off would be highly valuable, especially when it is linked to a cancer-related cellular parameter. Building on recent findings related to intersystem crossing efficiency, we designed a dimeric BODIPY dye with reduced symmetry, which is ineffective as a photosensitizer unless it is activated by a reaction with intracellular glutathione (GSH). The reaction alters the properties of both the ground and excited states, consequently enabling the efficient generation of singlet oxygen. Remarkably, the designed photosensitizer can discriminate between different concentrations of GSH in normal and cancer cells and thus remains inefficient as a photosensitizer inside a normal cell while being transformed into a lethal singlet oxygen source in cancer cells. This is the first demonstration of such a difference in the intracellular activity of a photosensitizer.

This paper develops an econometric model of stochastic production functions to quantify the impacts of climatic variables on the mean, variance, and covariance of crop yields. The estimates of the production function parameters and their elasticities are utilized to analyse the impacts of the projected climate change on agriculture. The results show that the climate change will have modest effects on the mean crop yields, but will significantly reduce the variance and covariance for most of the crops considered. The results have implications for allocations of agricultural land among crops and for crop production mix.

A model of farmer decision making is developed to determine the extent to which uncertainties about soil fertility and weather affect the value of site‐specific technologies (SSTs) using jointly estimated risk and technology parameters. Uncertainty can lead risk‐averse farmers to apply more fertilizers and generate more pollution than in the certainty case. Ignoring uncertainty and risk aversion would overestimate the economic and environmental benefits of SSTs and underestimate the subsidy required to induce adoption. Accounting for uncertainties and risk preferences might explain the low observed adoption rates of SSTs. Improving the accuracy of SSTs would increase the incentives for adoption.

Substantial public scrutiny about adverse environmental impacts of the dairy sector has resulted in increased environmental regulations. A behavioral model of location and production is developed to examine the impacts of environmental regulations, traditional location factors, and agglomeration economies on the spatial structure and geographical location of dairy production. The results show that counties in the states with more stringent environmental regulations tend to lose dairy inventories to those with less stringent policies. There are substantially meaningful spatial patterns of dairy production. Current dairy production levels are positively correlated while changes in production levels are negatively correlated across counties. Copyright 2004, Oxford University Press.

Judicious design of BODIPY dyes carrying nitroethenyl substituents in conjugation with the BODIPY core yields dyes that respond to biological thiols by both absorbance and emission changes. Incorporation of solubilizing ethyleneglycol units ensures water solubility. The result is bright signaling of biologically relevant thiols in the longer wavelength region of the visible spectrum and in aqueous solutions.

This paper quantitatively analyses the cost-effectiveness of alternative green payment policies designed to achieve a targeted level of pollution control by heterogeneous microunits. These green payment policies include cost-share subsidies that share the fixed costs of adoption of a conservation technology and/or input reduction subsidies to reduce the use of a polluting input. The paper shows that unlike a pollution tax that achieves abatement through three mechanisms, a negative extensive margin effect, a negative intensive margin effect and a technology switching effect, a cost-share subsidy and an input reduction subsidy are much more restricted in the types of incentives they provide for conservation of polluting inputs and adoption of a conservation technology to control pollution. Moreover, they may lead to varying levels of expansion of land under production. Costs of abatement with alternative policies and implications for production and government payments are compared using a simulation model for controlling drainage from irrigated cotton production in California, with drip irrigation as a conservation technology.

Various environmental policies have been proposed to control agricultural runoff of nutrients and pesticides. The impacts of these policies on input use are complicated because of the various sources of uncertainty farmers face and the precise nature of farmers' risk attitude. A risk-averse farmer's response to changed profit, input, and output taxes under output price and production uncertainty is examined. The impact of these policies on input use depends on the form of production uncertainty, risk-input relationships, risk attitudes, and degrees of output price and production uncertainty. These results have implications for the design and implementation of environmental and other production-related policies. Copyright 2002, Oxford University Press.

This paper applies an option-pricing model to analyze the impact of uncertainty about output prices and expectations of declining fixed costs on the optimal timing of investment in site-specific crop management (SSCM). It also analyzes the extent to which the level of spatial variability in soil conditions can mitigate the value of waiting to invest in SSCM and influence the optimal timing of adoption and create a preference for custom hiring rather than owner purchase of equipment. Numerical simulations show that while the net present value (NPV) rule predicts that immediate adoption is profitable under most of the soil conditions considered here, recognition of the option value of investment indicates that it is preferable to delay investment in SSCM for at least 3 years unless average soil quality is high and the variability in soil quality and fertility is high. The use of the option value approach reveals that the value of waiting to invest in SSCM raises the cost-share subsidy rates required to induce immediate adoption above the levels indicated by the NPV rule. 0 (M. Khanna). ent uptake as low as 30% of the applied nitrogen by plants (Legg and Meisinger, 1982).Site-specific crop management (SSCM) provides an input efficiency enhancing alternative to conventional methods by acquiring information about spatial variability in soil conditions and using it to target input applications to match that variability. It relies on several interrelated components that include grid-based soil sampling and yield monitors linked to satellite-based global positioning systems (GPS) that provide geo-referenced information about the agronomic conditions and yields at various points in the field and identify the need for spatial variation in input application. Variable rate technologies (VRT) then use this information to vary input flow rates on-the-go, 0169-5150/00/$ -see front matter 0 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 -5 1 5 0 ( 0 0 ) 0 0 1 11-0