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Borrowing and lending between sovereign parties is modelled as intertemporal barter that smooths the consumption of a risk-averse party subject to endowment shocks. The surplus anticipated in the relationship offers sufficient incentive for cooperation by all parties, including any other competitive lenders who may be potential entrants. The sole punishments consist of renegotiation-proof changes in the paths of future payments. This implicit long-term relationship may be fulfilled as the continual renegotiation of a simple, incomplete short-term debt contract with associated "debt overhang." The analysis suggests that the crucial role of the explicit contract is the identification of the parties to the relationship.

Song is a learned vocal behavior influenced by social interactions. Prior work has suggested that the anterior forebrain pathway (AFP), a specialized pallial-basal ganglia circuit critical for vocal plasticity, mediates the influence of social signals on song. Here, we investigate the signals the AFP sends to song motor areas and their dependence on social context by characterizing singing-related activity of single neurons in the AFP output nucleus LMAN (lateral magnocellular nucleus of the anterior nidopallium). We show that interaction with females causes marked, real-time changes in firing properties of individual LMAN neurons. When males sing to females ("directed"), LMAN neurons exhibit reliable firing of single spikes precisely locked to song. In contrast, when males sing alone ("undirected"), the same LMAN neurons exhibit prominent burst firing and trial-by-trial variability. Burst structure and timing vary substantially across repeated undirected trials. Despite context-dependent differences in firing statistics, the average pattern of song-locked firing for an individual neuron is similar across behavioral contexts, suggesting a common underlying signal. Different LMAN neurons in the same bird, however, exhibit distinct firing patterns, suggesting that subsets of neurons jointly encode song features. Together, our findings demonstrate that behavioral interactions reversibly transform the signaling mode of LMAN neurons. Such changes may contribute to rapid switching of motor activity between variable and precise states. More generally, our results suggest that pallial-basal ganglia circuits contribute to motor learning and production through multiple mechanisms: patterned signals could guide changes in motor output while state-dependent variability could subserve motor exploration.

Recent volatility of prices of major grains has generated a wide array of analyses and policy prescriptions that reveal the inability of economists to approach a consensus on the nature of the phenomenon and its implications for policy. This review of market events and their economic interpretations finds that recent price spikes are not as unusual as many discussions imply. Further, the balance between consumption, available supply, and stocks seems to be as relevant for our understanding of these markets as it was decades ago. Though there is much to be learned about commodity markets, the tools at hand are capable of explaining the main forces at work, and of giving good guidance to policymakers confronted with a bewildering variety of expensive policy prescriptions.

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We run all the couplings of the minimal supersymmetric (SUSY) extension of the standard model, taking account of the Yukawa sector. After identifying the scale at which the gauge couplings unify, we place bounds on the top-quark mass by requiring equality of the bottom-quark and r Yukawa couplings at that scale. For MSUSY = 1 TeV, M b =4.6 GeV, we find 139

The status of the sentinel node (SN) confers important prognostic information for patients with thin melanoma.Design, Setting, and Patients: We queried our melanoma database to identify patients undergoing sentinel lymph node biopsy for thin (Յ1.00-mm) cutaneous melanoma at a tertiary care cancer institute. Slides of tumor-positive SNs were reviewed by a melanoma pathologist to confirm nodal status and intranodal tumor burden, defined as isolated tumor cells, micrometastasis, or macrometastasis (Յ0.20, 0.21-2.00, or Ͼ2.00 mm, respectively). Nodal status was correlated with patient age and primary tumor depth (Յ0.25, 0.26-0.50, 0.51-0.75, or 0.76-1.00 mm). Survival was determined by log-rank test.Main Outcome Measures: Disease-free and melanomaspecific survival.Results: Of 1592 patients who underwent sentinel lymph node biopsy from 1991 to 2004, 631 (40%) had thin melanomas; 31 of the 631 patients (5%) had a tumor-positive SN. At a median follow-up of 57 months for the 631 patients, the mean (SD) 10-year rate of disease-free survival was 96% (1%) vs 54% (10%) for patients with tumornegative vs tumor-positive SNs, respectively (PϽ.001); the mean (SD) 10-year rate of melanoma-specific survival was 98% (1%) vs 83% (8%), respectively (PϽ.001). Tumorpositive SNs were more common in patients aged 50 years and younger (P=.04). The SN status maintained importance on multivariate analysis for both disease-free survival (PϽ.001) and melanoma-specific survival (PϽ.001). Conclusions:The status of the SN is significantly linked to survival in patients with thin melanoma. Therefore, sentinel lymph node biopsy should be considered to obtain complete prognostic information.

"The empirical relevance of models of competitive storage arbitrage in explaining commodity price behavior has been seriously challenged in a series of pathbreaking papers by Deaton and Laroque (1992, 1995, 1996). Here we address their major criticism, that the model is in general unable to explain the degree of serial correlation observed in prices of twelve major commodities. First, we present a simple numerical version of their model which, contrary to Deaton and Laroque (1992), can generate the high levels of serial correlation observed in commodity prices, if it is parameterized to generate realistic levels of price variation. Then, after estimating the Deaton and Laroque (1995, 1996) model using their data set, model specification and econometric approach, we show that use of a much finer grid to approximate the equilibrium price function yields quite different estimates for most commodities. Results are obtained for coffee, copper, jute, maize, palm oil, sugar and tin that support the specifications of the storage model with positive constant marginal storage cost and no deterioration as in Gustafson (1958a). Consumption demand has low response to price and, except for sugar, there are infrequent stockouts. Observed magnitudes of serial correlation of price match those implied by the estimated model." [author's abstract