Reduced complexity models for water management and anode purge scheduling in DEA operation of PEMFCs

In this work, the dynamic behavior of Fuel Cell operation under Dead-Ended Anode conditions is shown. A DEA can be fed with dry hydrogen, since water crossing through the membrane is sufficient to humidify the fuel. The reduced requirements for inlet humidification yield a system with lower cost and weight compared to FCs with flow-through or recirculated anodes. The accumulation of water and nitrogen in the anode channel is first observed near the outlet. A stratified pattern develops in the channel where a hydrogen-rich area sits above a depleted region and is stabilized by the effect of gravity. A model is presented which describes the dynamic evolution of a blanketing N2 front in the anode channel and a hydrogen starved region. Understanding, modeling, and predicting the front evolution can reduce the H2 wasted during purges, avoid over drying the membrane, and mitigate degradation associated with hydrogen starved areas

Running anti-de Sitter radius from QCD-like strings

We consider renormalization effects for a bosonic QCD-like string, whose partons have $1/p^{2}$ propagators instead of Gaussian. Classically this model resembles (the bosonic part of) the projective light-cone (zero-radius) limit of a string on an AdS${}_5$ background, where Schwinger parameters give rise to the fifth dimension. Quantum effects generate dynamics for this dimension, producing an AdS${}_5$ background with a running radius. The projective light-cone is the high-energy limit: Holography is enforced dynamically.Comment: 12 page

The Covariant Quantum Superstring and Superparticle from their Classical Actions

We develop an approach based on the Noether method to construct nilpotent BRST charges and BRST-invariant actions. We apply this approach first to the holomorphic part of the flat-space covariant superstring, and we find that the ghosts b, c_z which we introduced by hand in our earlier work, are needed to fix gauge symmetries of the ghost action. Then we apply this technique to the superparticle and determine its cohomology. Finally, we extend our results to the combined left- and right-moving sectors of the superstring.Comment: 14 pages, harmva

Concepts for autonomous flight control for a balloon on Mars

Balloons operating as airborne rovers have been suggested as ideal candidates for early exploration of the Martian surface. An international study team composed of scientists from the U.S.S.R., France, and the U.S.A. is planning the launching in 1994 of a balloon system to fly on Mars. The current likely design is a dual thermal/gas balloon that consists of a gas balloon suspended above a solar-heated thermal balloon. At night, the thermal balloon provides no lift, and the balloon system drifts just above the Martian surface; the lift of the gas balloon is just sufficient to prevent the science payload from hitting the ground. During the day, the balloon system flies at an altitude of 4 to 5 kilometers, rising due to the added lift provided by the thermal balloon. Over the course of a single Martian day, there may be winds in several directions, and in fact it can be expected that there will be winds simultaneously in different directions at different altitudes. Therefore, a balloon system capable of controlling its own altitude, via an autonomous flight control system, can take advantage of these different winds to control its direction, thereby greatly increasing both its mission utility and its longevity

Experimental validation of equilibria in fuel cells with dead-ended anodes

This paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. Surprisingly the dynamic evolution of nitrogen and water accumulation in the dead-ended anode (DEA) of a PEM fuel cell arrives to a steady-state suggesting the existence of equilibrium behavior. We use a multi-component model of the two-phase one-dimensional (along-the-channel) system behavior to analyze and exploit this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized for showing the evolution towards equilibrium. The full order model is reduced to a second-order ordinary differential equation (ODE) with one state, which can be used to predict and amalyse the surprising but experimentally observed steady state DEA behavior

Challenging The Distinct Population Segment Definition Of Atlantic Salmon Under The Endangered Species Act

In October 1993, a citizen petition was filed under the Endangered Species Act of 1973 (ESA or Act) to list the anadromous Atlantic salmon as an endangered species throughout its historic range in the contiguous United States. The National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife Service (FWS) responded in January 1994, by forming a joint biological review team to perform a detailed Status Review of the requested listing. Following completion of the Status Review, the two Services announced that the petitioned U.S.-wide listing was not warranted, but acknowledged that listings for populations in certain New England rivers might be. In September 1995, the Services proposed listing only a distinct population segment (DPS) of the Atlantic salmon, found only in certain Maine rivers, as threatened. The NMFS and FWS issued a proposed rule (Rule) establishing joint regulations, prohibitions, and protective measures. On the day before the comment period closed, Maine Governor Angus King delivered a letter to the Services objecting to the listing in the strongest possible terms, and called on the Services to enter into a cooperative agreement with Maine to implement an alternative plan to listing developed in early 1996 by a task force appointed by Governor King. Thus, at the time this Comment goes to print it will not be known whether the Services will change their Rule or what impact Governor King\u27s comments will have on concurrent jurisdiction and federal-state cooperation in protecting Atlantic salmon. This Comment addresses several debated aspects of the proposed listing, proposes an alternative method of deciding listings more in keeping with the goals and purposes of the Endangered Species Act, and describes several congressional attempts to limit the scope of the ESA. Specifically, Part II summarizes the threshold tests used in the listing process and describes how these tests were applied to the listing of the Atlantic salmon. Part III begins by criticizing the standard the Services used to determine which populations to list and the eventual limitation of ESA protection to seven downeast Maine rivers instead of the dozens of other rivers throughout the species\u27 historic range. Part III continues by criticizing the Services\u27 proposed rule for failing to consider threats to the ecosystem and the habitat of the Atlantic salmon, as well as ignoring other federal requirements and agreements. Part HI concludes that in addition to scholarly criticism and debate, the legality of the proposed rule may be challenged as being arbitrary and capricious. Part IV describes an alternative standard that is more consistent with ESA goals and purposes. Part V discusses the significance of several misguided proposed amendments to the ESA that would prohibit federal agencies from even considering listings below the species level in the future. The Comment concludes that the Services\u27 proposed rule is a prime example of the interplay between biology and law in a political context. Even if one believes that the Services used a logical method to define which populations to list, they did so to minimize political pressure calling for limited federal involvement and greater state control. Additionally, the Services\u27 sensitivity to this atmosphere of reform may be indicative of future approaches to administering the Act. This result would be unfortunate because the Services\u27 proposed rule fails to extend ESA protection to populations which may be crucial to the survival of Atlantic salmon, and whose habitat is similarly important