Two-junction tuning circuits for submillimeter SIS mixers

The capacitance of superconducting tunnel junctions can seriously degrade the performance of quasiparticle (SIS) mixers operating in the submillimeter band, so it is essential to provide a circuit for tuning out this capacitance at the operating frequency. In this article, we present two new tuning circuits for SIS mixers which use a pair of SIS junctions connected by an inductance. Compared to previously proposed tuning circuits, ours have a broader bandwidth, are easier to scale to higher frequencies, and may be easier to fabricate. We have constructed quasi-optical mixers which employ these tuning circuits, using Nb/Al-Oxide/Nb SIS junctions defined by optical lithography. The performance of these devices is excellent, giving receiver noise temperatures of 113 K (DSB) at 490 GHz and 230 K DSB at 612 GHz. In addition to demonstrating the effectiveness of our tuning circuit, these results show that quasi-optical mixers can be competitive with or superior to waveguide mixers at submillimeter wavelengths. The mixers continue to perform well at frequencies up to 672 GHz, which is about 95% of the Nb gap frequency

Optimizing Habitat Protection Using Demographic Models of Population Viability

Expanding habitat protection is a common tactic for species conservation. When unprotected habitat is privately owned, decisions must be made about which areas to protect by land purchase or conservation easement. To address this problem, we developed an optimization framework for choosing the habitat-protection strategy that minimizes the risk of population extinction subject to an upper bound on funding. The framework is based on the idea that an extinction-risk function that predicts the relative effects of varying the quantity and quality of habitat can be estimated from the results of a demographic model of population viability. We used the framework to address the problem of expanding the protected habitat of a core population of the endangered San Joaquin kit fox (Vulpes macrotis mutica) in the Panoche area in central California. We first developed a stochastic demographic model of the kit fox population. Predictions from the simulation model were used to estimate an extinction-risk function that depended on areas of good- and fair-quality habitat. The risk function was combined with costs of habitat protection to determine cost-efficient protection strategies and risk-cost curves showing how extinction risk could be reduced at minimum cost for increasing levels of funding. One important result was that cost-efficient shares of the budget used to protect different types of habitat changed as the budget increased and depended on the relative costs of available habitat and the relative effects of habitat protection on extinction risk. Another important finding was the sensitivity of the location and slope of the risk-cost curve to assumptions about the spatial configuration of available habitat. When the location and slope of the risk-cost curve are sensitive to model assumptions, resulting predictions of extinction risk and risk reduction per unit cost should be used very cautiously in ranking conservation options among different species or populations. The application is an example of how the results of a complex demographic model of population viability can be synthesized for use in optimization analyses to determine cost-efficient habitat-protection strategies and risk-cost tradeoffs

What kind of local and regional development and for whom?

This paper asks the question, what kind of local and regional development and for whom? It examines what is meant by local and regional development, its historical context, its geographies in space, territory, place and scale and its different varieties, principles and values. The socially uneven and geographically differentiated distribution of who and where benefits and loses from particular forms of local and regional development is analysed. A holistic, progressive and sustainable version of local and regional development is outlined with reflections upon its limits and political renewal. Locally and regionally determined development models should not be developed independently of more foundational principles and values such as democracy, equity, internationalism and justice. Specific local and regional articulations are normative questions and subject to social determination and political choices in particular national and international contexts