Reassessment of the Rates at which Oil from Natural Sources Enters the Marine Environment

Previous estimates of the world-wide input of oil to the marine environment by natural seeps ranged from 0 ·2 to 6 ·0 million (metric) tonnes per year with a \u27best estimate\u27 of 0 ·6 million tonnes per year. Based on considerations of the availability of oil for seepage from the world\u27s known and assumed oil resources, we believe that the world-wide natural oil seepage over geological time should be revised to about 0 ·2 million tonnes per ),ear with a range upward or downward of a factor of ten leading to estimates between 0 ·02 and 2 million tonnes per year. Our estimate of the amount of oil eroding from the land and being transported to the oceans is about 0 ·05 million tonnes per year with an order of magnitude uncertainty. Therefore, while the uncertainties are large, we estimate that the total amount of oil entering the marine environment by natural, geological processes, is about 0 ·25 million tonnes per year, and the estimate may range from about 0 ·025 to 2 ·5 million tonnes per year

Eigenstates of a Small Josephson Junction Coupled to a Resonant Cavity

We carry out a quantum-mechanical analysis of a small Josephson junction coupled to a single-mode resonant cavity. We find that the eigenstates of the combined junction-cavity system are strongly entangled only when the gate voltage applied at one of the superconducting islands is tuned to certain special values. One such value corresponds to the resonant absorption of a single photon by Cooper pairs in the junction. Another special value corresponds to a {\em two-photon} absorption process. Near the single-photon resonant absorption, the system is accurately described by a simplified model in which only the lowest two levels of the Josephson junction are retained in the Hamiltonian matrix. We noticed that this approximation does not work very well as the number of photons in the resonator increases. Our system shows also the phenomenon of ``collapse and revival'' under suitable initial conditions, and our full numerical solution agrees with the two level approximation result.Comment: 7 pages, and 6 figures. To be published in Phys. Rev.

Several small Josephson junctions in a Resonant Cavity: Deviation from the Dicke Model

We have studied quantum-mechanically a system of several small identical Josephson junctions in a lossless single-mode cavity for different initial states, under conditions such that the system is at resonance. This system is analogous to a collection of identical atoms in a cavity, which is described under appropriate conditions by the Dicke model. We find that our system can be well approximated by a reduced Hamiltonian consisting of two levels per junction. The reduced Hamiltonian is similar to the Dicke Hamiltonian, but contains an additional term resembling a dipole-dipole interaction between the junctions. This extra term arises when states outside the degenerate group are included via degenerate second-order (L\"{o}wdin) perturbation theory. As in the Dicke model, we find that, when N junctions are present in the cavity, the oscillation frequency due to the junction-cavity interaction is enhanced by $\sqrt{N}$. The corresponding decrease in the Rabi oscillation period may cause it to be smaller than the decoherence time due to dissipation, making these oscillations observable. Finally, we find that the frequency enhancement survives even if the junctions differ slightly from one another, as expected in a realistic system.Comment: 11 pages. To be published in Phys. Rev.

Resonant-Cavity-Induced Phase Locking and Voltage Steps in a Josephson Array

We describe a simple dynamical model for an underdamped Josephson junction array coupled to a resonant cavity. From numerical solutions of the model in one dimension, we find that (i) current-voltage characteristics of the array have self-induced resonant steps (SIRS), (ii) at fixed disorder and coupling strength, the array locks into a coherent, periodic state above a critical number of active Josephson junctions, and (iii) when $N_a$ active junctions are synchronized on an SIRS, the energy emitted into the resonant cavity is quadratic with $N_a$. All three features are in agreement with a recent experiment [Barbara {\it et al}, Phys. Rev. Lett. {\bf 82}, 1963 (1999)]}.Comment: 4 pages, 3 eps figures included. Submitted to PRB Rapid Com

Pass/Fail, A-F, or 0-100? Optimal Grading of Eager Students

This paper analyzes optimal grading in a world that focuses on top grades. Students choose an effort level, their performance is graded, and their grade correlates with their future income. Ex-ante, the policy maker chooses the optimal coarseness of the grading scale to maximize student welfare. When choosing their effort, students overweight outstanding - or salient - grades. I show that this behavior leads to excessive effort levels when grading is fully informative, and that coarse grading can be used to counterbalance incentives. Thus, salience can help explain why grading ranges from Pass/Fail scales (tenure decisions) via A-F-scales (school) to fully disclosing scores (e.g. SAT)

Benevolent characteristics promote cooperative behaviour among humans

Cooperation is fundamental to the evolution of human society. We regularly observe cooperative behaviour in everyday life and in controlled experiments with anonymous people, even though standard economic models predict that they should deviate from the collective interest and act so as to maximise their own individual payoff. However, there is typically heterogeneity across subjects: some may cooperate, while others may not. Since individual factors promoting cooperation could be used by institutions to indirectly prime cooperation, this heterogeneity raises the important question of who these cooperators are. We have conducted a series of experiments to study whether benevolence, defined as a unilateral act of paying a cost to increase the welfare of someone else beyond one's own, is related to cooperation in a subsequent one-shot anonymous Prisoner's dilemma. Contrary to the predictions of the widely used inequity aversion models, we find that benevolence does exist and a large majority of people behave this way. We also find benevolence to be correlated with cooperative behaviour. Finally, we show a causal link between benevolence and cooperation: priming people to think positively about benevolent behaviour makes them significantly more cooperative than priming them to think malevolently. Thus benevolent people exist and cooperate more

Learned Generosity? A Field Experiment with Parents and Their Children

An active area of research within the social sciences concerns the underlying motivation for sharing scarce resources and engaging in other pro-social actions. We develop a theoretical framework that sheds light on the developmental origins of social preferences by providing mechanisms through which parents transmit preferences for generosity to their children. Then, we conduct a field experiment with nearly 150 3-5 year old children and their parents, measuring (1) whether child and parent generosity is correlated, (2) whether children are influenced by their parents when making sharing decisions and (3) whether parents model generosity to children. We observe no correlation of independently measured parent and child sharing decisions at this young age. Yet, we find that apart from those choosing an equal allocation of resources between themselves and another child, children adjust their behaviors to narrow the gap with their parent's or other adult's choice. We find that fathers, and parents of initially generous children, increase their sharing when informed that their child will be shown their choice