Inter-dependence of the volume and stress ensembles and equipartition in statistical mechanics of granular systems

We discuss the statistical mechanics of granular matter and derive several significant results. First, we show that, contrary to common belief, the volume and stress ensembles are inter-dependent, necessitating the use of both. We use the combined ensemble to calculate explicitly expectation values of structural and stress-related quantities for two-dimensional systems. We thence demonstrate that structural properties may depend on the angoricity tensor and that stress-based quantities may depend on the compactivity. This calls into question previous statistical mechanical analyses of static granular systems and related derivations of expectation values. Second, we establish the existence of an intriguing equipartition principle - the total volume is shared equally amongst both structural and stress-related degrees of freedom. Third, we derive an expression for the compactivity that makes it possible to quantify it from macroscopic measurements.Comment: 5 pages, including 2 figures, To appear in Phys. Rev. Let

Duration of unassisted swimming activity for spotted dolphin (Stenella attenuata) calves: implications for mother-calf separation during tuna purse-seine sets

Size-related differences in power production and swim speed duration may contribute to the observed deficit of nursing calves in relation to lactating females killed in sets by tuna purse-seiners in the eastern tropical Pacific Ocean (ETP). Power production and swim-speed duration were estimated for northeastern spotted dolphins (Stenella attenuata), the species (neonate through adult) most often captured by the fishery. Power required by neonates to swim unassisted was 3.6 times that required of an adult to swim the same speed. Estimated unassisted burst speed for neonates is only about 3 m/s compared to about 6 m/s for adults. Estimated long-term sustainable speed is about 1 m/s for neonates compared to about 2.5 m/s for adults. Weight-specific power requirements decrease as dolphin calves increase in size, but power estimates for 2-year-old spotted dolphin calves are still about 40% higher than power estimates for adults, to maintain the same speed. These estimated differences between calves and adults are conservative because the calculations do not include accommodation for reduced aerobic capacity in dolphin calves compared to adults. Discrepancies in power production are probably ameliorated under normal circumstances by calves drafting next to their mothers, and by employing burst-coast or leap-burst-coast swimming, but the relatively high speeds associated with evasion behaviors during and after tuna sets likely diminish use of these energy-saving strategies by calves

Statistical Mechanics of Vibration-Induced Compaction of Powders

We propose a theory which describes the density relaxation of loosely packed, cohesionless granular material under mechanical tapping. Using the compactivity concept we develope a formalism of statistical mechanics which allows us to calculate the density of a powder as a function of time and compactivity. A simple fluctuation-dissipation relation which relates compactivity to the amplitude and frequency of a tapping is proposed. Experimental data of E.R.Nowak et al. [{\it Powder Technology} 94, 79 (1997) ] show how density of initially deposited in a fluffy state powder evolves under carefully controlled tapping towards a random close packing (RCP) density. Ramping the vibration amplitude repeatedly up and back down again reveals the existence of reversible and irreversible branches in the response. In the framework of our approach the reversible branch (along which the RCP density is obtained) corresponds to the steady state solution of the Fokker-Planck equation whereas the irreversible one is represented by a superposition of "excited states" eigenfunctions. These two regimes of response are analyzed theoretically and a qualitative explanation of the hysteresis curve is offered.Comment: 11 pages, 2 figures, Latex. Revised tex

Ownership of Renewable Ocean Resources

Much of the recent fisheries economics literature promotes usufructuary rights policies to lessen the dissipation of resource rents. However, this literature does not count institutional inefficiencies which result from rent-seeking and the principal-agent problem when a centralized government controls access to renewable ocean resources. As a result, the efficiency of usufructuary rights programs, including ITQs, throughout the economy could be exaggerated. From a dynamic standpoint, though, usufructuary rights policies remain an important avenue for residual claimants to contract for less attenuated institutions of common or private property rights. These conclusions are drawn from a survey of the property rights and public choice literatures.U.S. fisheries, fisheries management, open access, common pool resources, property rights, economic efficiency, rent-seeking, principal-agent problem, common property, self-governance, private property, Environmental Economics and Policy, Resource /Energy Economics and Policy,

ETHICAL PREFERENCES AND THE ASSESSMENT OF EXISTENCE VALUES: DOES THE NEOCLASSICAL MODEL FIT?

Some of the implications of ethical preferences for traditional welfare analyses of existence values are discussed in this paper and illustrated with a lexicographic model for preference structures. Although willingness-to-pay and willingness-to-sell are well-defined, their connection with Hicksian surpluses is lost when a person is motivated by an ethical commitment to others welfare. Researchers need to expand contingent valuation methods to collect information on underlying motives and types of preferences in order to identify respondents who fit the neoclassical model of egoistic man.Institutional and Behavioral Economics,

ON ESTIMATING HOUSEHOLD DEMAND FOR OUTDOOR RECREATION FROM PROPERTY VALUES: AN EXPLORATION

This paper explores how hedonic price analysis might be used to estimate the surplus benefits of local outdoor recreation when distance to the recreational site is captured in property values. The model is characterized by the endogenous choice of distance to a local recreational area by households in coastal property markets and by the capitalization of proximity in property values. Equilibrium occurs when the reduction in the cost of a property due to a marginal increase in distance to the recreational area equals the associated loss in recreational surplus resulting from increased travel costs. The theoretical model is applied in an exploratory analysis of the "demand" for distance to the nearest public beach from which total surplus benefits are estimated.Resource /Energy Economics and Policy,

RENT-SEEKING AND PROPERTY RIGHTS FORMATION IN THE U.S. ATLANTIC SEA SCALLOP FISHERY

This paper chronicles rent-seeking in the U.S. Atlantic sea scallop fishery, including its influence on property rights formation. Decades of lobbying by the U.S. fishing industry against foreign fishing and seafood imports caused Congress to extend federal jurisdiction to 200 miles in 1977. Scallop fishermen initially earned high profits for their efforts, but by about 1990 the overcapitalized fishery was surviving on new year classes. Limited access and a stock rebuilding program were introduced in 1994, but an asymmetric distribution of potential gains in favor of relatively few, multi-permit companies has preoccupied public debate on the transferability and consolidation of fishing rights. Rent-seeking by the limited-access permit holders is now also focused on claims by the growing open-access sector of the scallop fishery, groundfish bycatch limitations, and gear-induced habitat damage, which has drawn lawsuits from environmental organizations.Resource /Energy Economics and Policy,

Determination of pilot and vehicle describing functions from the Gemini 10 mission

Three types of manual control maneuvers conducted during the Gemini-10 mission have been analyzed in order to measure and document the describing function of the pilot, the vehicle and the pilot-vehicle combination during an actual space mission. Measurements made from the data records of the reentry maneuver (a single axis control task) indicate that the pilot's control behavior changes during critical portions of the reentry. Measurements made of the deorbit maneuver and of a terminal phase initiation maneuver (three axis tasks) show that the pilot assigns priorities to the separate axes and controls them differently. His control technique is also influenced by the magnitude of the thrust disturbance present during the maneuvers. The results for all three types of maneuvers show that the pilot adapts to the nonlinear spacecraft control system in such a way that the combined pilot-vehicle dynamics take the form of the linear crossover model

Use of reaction wheels and nonlinear control for a satellite scanning a small celestial area

Reaction wheel control torque for satellite system scanning of small celestial are