The Possible Role of Extra-ocular Photoreceptors in the Entrainment of Lobster Circadian Rhythms to Light:Dark Cycles

The American lobster, Homarus americanus, is a decapod crustacean whose daily nocturnal rhythms of activity are driven, in part, by an internal biological clock. While this circadian clock is capable of producing a rhythm of approximately 24 hours on its own, it can also be entrained to light:dark cycles. Recent findings in our laboratory suggest that lobsters have photosensitive neurons throughout their nervous system (extra-ocular photoreceptors). The objective of this research was to test the hypothesis that these extra-ocular photoreceptors aid in entraining their daily rhythm of activity. First, the locomotion of juvenile American lobsters was measured in trials under a normal 24 hour light:dark cycle. Then, after this “control” period, the lobsters’ eyes were painted with black nail polish and their activity was monitored under the same conditions. The lobsters were also exposed to DD conditions with their eyes covered in one of the trials. During the control LD cycle, lobsters expressed increased locomotion at night, demonstrating their daily rhythm. The DD cycle had a consistent rhythm with an elongated period of activity. Interestingly, half of the lobsters continued to follow the same pattern of activity despite the visual impairment and half expressed a diurnal rhythm. Although there was variation in the locomotor activity, a periodicity of ~24 hours was maintained throughout the LD cycles. This indicates that H. americanus receives photoperiod input from both their eyes and extra-ocular photoreceptors that help synchronize their locomotor activity to LD cycles

A Reconnection Switch to Trigger Gamma-Ray Burst Jet Dissipation

Prompt gamma-ray burst (GRB) emission requires some mechanism to dissipate an ultrarelativistic jet. Internal shocks or some form of electromagnetic dissipation are candidate mechanisms. Any mechanism needs to answer basic questions, such as what is the origin of variability, what radius does dissipation occur at, and how does efficient prompt emission occur. These mechanisms also need to be consistent with how ultrarelativistic jets form and stay baryon pure despite turbulence and electromagnetic reconnection near the compact object and despite stellar entrainment within the collapsar model. We use the latest magnetohydrodynamical models of ultrarelativistic jets to explore some of these questions in the context of electromagnetic dissipation due to the slow collisional and fast collisionless reconnection mechanisms, as often associated with Sweet-Parker and Petschek reconnection, respectively. For a highly magnetized ultrarelativistic jet and typical collapsar parameters, we find that significant electromagnetic dissipation may be avoided until it proceeds catastrophically near the jet photosphere at large radii ($r\sim 10^{13}--10^{14}{\rm cm}$), by which the jet obtains a high Lorentz factor ($\gamma\sim 100--1000), has a luminosity of$L_j \sim 10^{50}--10^{51}\ergs$, has observer variability timescales of order 1s (ranging from 0.001-10s), achieves$\gamma\theta_j\sim 10--20 (for opening half-angle $\theta_j$) and so is able to produce jet breaks, and has comparable energy available for both prompt and afterglow emission. This reconnection switch mechanism allows for highly efficient conversion of electromagnetic energy into prompt emission and associates the observed prompt GRB pulse temporal structure with dissipation timescales of some number of reconnecting current sheets embedded in the jet.[abridged]Comment: 21 pages main text + 11 pages appendices + 3 pages references, 12 figures, MNRAS in pres

Stabilization of Polystyrene by Friedel-Crafts Chemistry: Effect of Position of Alcohol and the Catalyst

Polystyrene has been copolymerized with 4-vinylbenzyl alcohol, 4-(2-hydroxyethyl)styrene, and 4-(3-hydroxypropyl)styrene and it has been shown that thermal cross-linking of these copolymers is dependent upon the alcohol content. When the alcohol content is low, no thermal cross-linking is observed. When various phosphate esters are present as catalysts with these low alcohol content copolymers, cross-linking is observed at temperatures of about 250°C but not at lower temperatures. Cross-linking enhances the thermal stability of the copolymers. Studies of the thermal stability of the copolymers and their blends with the catalysts have been performed using thermogravimetric analysis and thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. There is little difference in the thermal stability of all three copolymers and their blends with the catalysts

Polybutadiene Cross-Linked With Various Diols – Effect On Thermal Stability

The relationship between cross-linking and thermal stability as related to polybutadiene is the focus of current research. Cross-linked polybutadienes have been prepared using various diols as the cross-linking agent. Cross-linked polymers have been characterized by gel content, swelling ratios, infrared spectroscopy, and thermal analysis. These polymers are not highly cross-linked, as seen by gel content and swelling ratios, and cross-linking does not have a large effect on the onset temperature of the degradation. Nonetheless, extensive formation of a non-volatile residue occurs

Small Cities Blues: Looking for Growth Factors in Small and Medium-Sized Cities

The purpose of this exploratory study is to attempt to identify particular public policies which have the potential to increase the economic viability of smaller metropolitan areas and cities. We identify characteristics associated with smaller metro areas that performed better-than-expected (winners) and worse-than-expected (losers) during the 1990s, given their resources, industrial mix, and location as of 1990. Once these characteristics have been identified, we look for evidence that public policy choices may have promoted and enhanced a metro area's ability to succeed and to regain control of its own economic destiny. Methodologically, we construct a regression model which identifies the small metro areas that achieved higher-than-expected economic prosperity (winners) and the areas that saw lower-than-expected economic prosperity (losers) according to the model. Next, we explore whether indications exist that winners and losers are qualitatively different from other areas in ways that may indicate consequences of policy choices. A cluster analysis is completed to group the metro areas based on changes in a host of social, economic, and demographic variables between 1990 and 2000. We then use contingency table analysis and ANOVA to see if "winning" or "losing," as measured by the error term from the regression, is related to the grouping of metro areas in a way that may indicate the presence of deliberate and replicable government policy.economic, development, growth, factors, erickcek, mckinney, incentives, local, regional, small, medium, cities

Cloud cavitation on an oscillating hydrofoil

Cloud cavitation, often formed by the breakdown of a sheet or vortex cavity, is believed to be responsible for much of the noise and erosion damage that occurs under cavitating conditions. For this paper, cloud cavitation was produced through the periodic forcing of the flow by an oscillating hydrofoil. The present work examines the acoustic signal generated by the collapse of cloud cavitation, and compares the results to those obtained by studies of single travelling bubble cavitation. In addition, preliminary studies involving the use of air injection on the suction surface of the hydrofoil explore its mitigating effects on the cavitation noise

Equation of State in Relativistic Magnetohydrodynamics: variable versus constant adiabatic index

The role of the equation of state for a perfectly conducting, relativistic magnetized fluid is the main subject of this work. The ideal constant $\Gamma$-law equation of state, commonly adopted in a wide range of astrophysical applications, is compared with a more realistic equation of state that better approximates the single-specie relativistic gas. The paper focus on three different topics. First, the influence of a more realistic equation of state on the propagation of fast magneto-sonic shocks is investigated. This calls into question the validity of the constant $\Gamma$-law equation of state in problems where the temperature of the gas substantially changes across hydromagnetic waves. Second, we present a new inversion scheme to recover primitive variables (such as rest-mass density and pressure) from conservative ones that allows for a general equation of state and avoids catastrophic numerical cancellations in the non-relativistic and ultrarelativistic limits. Finally, selected numerical tests of astrophysical relevance (including magnetized accretion flows around Kerr black holes) are compared using different equations of state. Our main conclusion is that the choice of a realistic equation of state can considerably bear upon the solution when transitions from cold to hot gas (or viceversa) are present. Under these circumstances, a polytropic equation of state can significantly endanger the solution.Comment: 14 pages, 14 figure