Relative angular momentum balances of quasi-geostrophic circulation models

Calculations of the local vertical component of relative angular momentum are considered for quasi-geostrophic circulation models. The angular momentum diagnostic measures the net horizontal spin of the flow within an ocean basin and complements traditional budgets of energy, vorticity and linear momentum. In particular, the diagnostic can help identify the role of bottom topographic stresses in driving ocean circulation. Calculations of torque balances are presented for several numerical experiments with single-layer and multi-layer models. Experiments with an idealized continental slope topography develop a cyclonic circulation in the abyssal layer which is driven by a significant topographic form torque

Contrast effects : incentive value of N-lengths

E.J. Capaldi has developed a sequential explanation of the partial reinforcement effect. The central assumption of this explanation is that non reinforced trials occasion a specific and distinctive internal stimulus and that this stimulus is progressively modified by successive non reinforcements. In this experiment, forty, male albino Holtzman rats traversed a straight alley runway under different patterns of partial reinforcement. Group One received an N3-length, i.e., three successive non-reinforced trials followed by a reinforced trial. Group Two received an N1-length, i.e., one non-reinforced trial followed by a reinforced trial. Group Three received an N3-length for the first ten days of acquisition training and was then shifted to an N1-length for the last five days of acquisition training. Group Four received an N1-length for the first ten days of acquisition training and an N3-length for the last five days of acquisition training. All groups received five days of extinction training. The results indicate that partial reinforcement patterns not only effect extinction performance but also effect acquisition performance in extended training

Regulatory solvency prediction in property-liability insurance: risk-based capital, audit ratios, and cash flow simulation

This paper analyzes the accuracy of the principal models used by U.S. insurance regulators to predict insolvencies in the property-liability insurance industry and compares these models with a relatively new solvency testing approach--cash flow simulation. Specifically, we compare the risk-based capital (RBC) system introduced by the National Association of Insurance Commissioners (NAIC) in 1994, the FAST (Financial Analysis and Surveillance Tracking) audit ratio system used by the NAIC, and a cash flow simulation model developed by the authors. Both the RBC and FAST systems are static, ratio-based approaches to solvency testing, whereas the cash flow simulation model implements dynamic financial analysis. Logistic regression analysis is used to test the models for a large sample of solvent and insolvent property-liability insurers, using data from the years 1990-1992 to predict insolvencies over three-year prediction horizons. We find that the FAST system dominates RBC as a static method for predicting insurer insolvencies. Further, we find the cash flow simulation variables add significant explanatory power to the regressions and lead to more accurate solvency prediction than the ratio-based models taken alone.Insurance industry

Observations and modeling of seasonal variability in the Straits of Georgia and Juan de Fuca

The Strait of Georgia is a large semi-enclosed basin on the southern coast of British Columbia. Its main connection to the Pacific is to the south, through Juan de Fuca Strait. Abundant freshwater discharge, mainly from the Fraser River, forces an estuarine exchange with oceanic shelf water. The resulting circulation is modulated by tides and winds. Both the coastal wind stress and the flux of freshwater are subject to strong seasonal modulations, producing a marked seasonal cycle in the water properties and circulation of the region. The seasonal variability of the Strait of Georgia and Juan de Fuca Strait is described using data from a series of recent cruises conducted over a five-year period, in addition to longer term historical data sets. To complement the observations, the data are compared with numerical simulations based on the Princeton Ocean Model (POM). Forced with tides, freshwater discharge and seasonal wind stress, the model is integrated over a few years until the system approaches statistical equilibrium. Results show good agreement with observations from Juan de Fuca Strait, as well as over the upper part of the water column within the Strait of Georgia. However, simulation of the seasonal cycle of the deeper waters of the Strait of Georgia is more problematic. The deep water properties apparently are determined by a delicate balance between dense intrusions from the sill area and local vertical mixing

Fortnightly modulation of the estuarine circulation in Juan de Fuca Strait

Riverine discharge into the Strait of Georgia sets up a well-defined estuarine circulation within Juan de Fuca Strait, the main path for the freshwater outflow to the continental shelf. At the landward end of Juan de Fuca Strait, the water flows through narrow channels in which strong tidal currents are known to induce significant mixing of the water column, and a spring-neap modulation of the estuarine exchange. A three-dimensional prognostic numerical model has been developed to study the circulation around Vancouver Island, British Columbia. In a series of simulations, the estuarine circulation within Juan de Fuca Strait is established by the Fraser River freshwater discharge. A fortnightly modulation is imposed on the mixing over the various sills to simulate the spring-neap tidal mixing regime. The resulting variation in the estuarine circulation is found to be largely limited to the eastern section of Juan de Fuca Strait, in the vicinity of the sills. Data from current meter moorings and surface salinity data from lighthouse stations compare favorably with the model results. The effect of local wind forcing on the estuarine exchange is also examined. The model is capable of simulating those rare events during which a concurrence of river freshet, neap tide and northwest wind allows a stronger pulse of fresh surface water to escape relatively unmixed into the eastern end of Juan de Fuca Strait. The disturbance then propagates along the northern shore of the strait as a first mode internal Kelvin wave. Finally, the effect of the fortnightly modulation on the export of freshwater onto the continental shelf is examined. It is found that small amplitude coastal trapped waves are generated near the mouth of Juan de Fuca. However, this fortnightly signal is weak in comparison to the energetic wind-induced variations typically found over the shelf

Hedgehog Pathway Activation Alters Ciliary Signaling in Primary Hypothalamic Cultures

Primary cilia dysfunction has been associated with hyperphagia and obesity in both ciliopathy patients and mouse models of cilia perturbation. Neurons throughout the brain possess these solitary cellular appendages, including in the feeding centers of the hypothalamus. Several cell biology questions associated with primary neuronal cilia signaling are challenging to address in vivo. Here we utilize primary hypothalamic neuronal cultures to study ciliary signaling in relevant cell types. Importantly, these cultures contain neuronal populations critical for appetite and satiety such as pro-opiomelanocortin (POMC) and agouti related peptide (AgRP) expressing neurons and are thus useful for studying signaling involved in feeding behavior. Correspondingly, these cultured neurons also display electrophysiological activity and respond to both local and peripheral signals that act on the hypothalamus to influence feeding behaviors, such as leptin and melanin concentrating hormone (MCH). Interestingly, we found that cilia mediated hedgehog signaling, generally associated with developmental processes, can influence ciliary GPCR signaling (Mchr1) in terminally differentiated neurons. Specifically, pharmacological activation of the hedgehog-signaling pathway using the smoothened agonist, SAG, attenuated the ability of neurons to respond to ligands (MCH) of ciliary GPCRs. Understanding how the hedgehog pathway influences cilia GPCR signaling in terminally differentiated neurons could reveal the molecular mechanisms associated with clinical features of ciliopathies, such as hyperphagia-associated obesity

Microscopic theory for the glass transition in a system without static correlations

We study the orientational dynamics of infinitely thin hard rods of length L, with the centers-of-mass fixed on a simple cubic lattice with lattice constant a.We approximate the influence of the surrounding rods onto dynamics of a pair of rods by introducing an effective rotational diffusion constant D(l),l=L/a. We get D(l) ~ [1-v(l)], where v(l) is given through an integral of a time-dependent torque-torque correlator of an isolated pair of rods. A glass transition occurs at l_c, if v(l_c)=1. We present a variational and a numerically exact evaluation of v(l).Close to l_c the diffusion constant decreases as D(l) ~ (l_c-l)^\gamma, with \gamma=1. Our approach predicts a glass transition in the absence of any static correlations, in contrast to present form of mode coupling theory.Comment: 6 pages, 3 figure