Crocodylus acutus

Number of Pages: 17Integrative BiologyGeological Science

Vegetation Effects on Fish Distribution in Impounded Salt Marshes

We compared the density and biomass of resident fish in vegetated and unvegetated flooded habitats of impounded salt marshes in the northern Indian River Lagoon (IRL) Estuary of east-central Florida. A 1-m2 throw trap was used to sample fish in randomly located, paired sample plots (n = 198 pairs) over 5 seasons in 7 impoundments. We collected a total of 15 fish taxa, and 88% of the fishes we identified from the samples belonged to three species: Cyprinodon variegatus (Sheepshead Minnow), Gambusia holbrooki (Eastern Mosquitofish), and Poecilia latipinna (Sailfin Molly). Vegetated habitat usually had higher density and biomass of fish. Mean fish density (and 95% confidence interval) for vegetated and unvegetated sites were 8.2 (6.7–9.9) and 2.0 (1.6–2.4) individuals m-2, respectively; mean biomass (and 95% confidence interval) for vegetated and unvegetated sites were 3.0 (2.5–3.7) and 1.1 (0.9–1.4) g m-2, respectively. We confirmed previous findings that impounded salt marshes of the northern IRL Estuary produce a high standing stock of resident fishes. Seasonal patterns of abundance were consistent with fish moving between vegetated and unvegetated habitat as water levels changed in the estuary. Differences in density, mean size, and species composition of resident fishes between vegetated and unvegetated habitats have important implications for movement of biomass and nutrients out of salt marsh by piscivores (e.g., wading birds and fishes) via a trophic relay

Scale-Dependent Habitat Selection of Nesting Great Egrets and Snowy Egrets

Foraging habitat selection of nesting Great Egrets ( Ardea alba ) and Snowy Egrets ( Egretta thula ) was investigated within an estuary with extensive impounded salt marsh habitat. Using a geographic information system, available habitat was partitioned into concentric bands at five, ten, and 15 km radius from nesting colonies to assess the relative effects of habitat composition and distance on habitat selection. Snowy Egrets were more likely than Great Egrets to depart colonies and travel to foraging sites in groups, but both species usually arrived at sites that were occupied by other wading birds. Mean flight distances were 6.2 km (SE = 0.4, N = 28, range 1.8-10.7 km) for Great Egrets and 4.7 km (SE = 0.48, N = 31, range 0.7-12.5 km) for Snowy Egrets. At the broadest spatial scale both species used impounded (mostly salt marsh) and estuarine edge habitat more than expected based on availability while avoiding unimpounded (mostly fresh water wetland) habitat. At more local scales habitat use matched availability. Interpretation of habitat preference differed with the types of habitat that were included and the maximum distance that habitat was considered available. These results illustrate that caution is needed when interpreting the results of habitat preference studies when individuals are constrained in their choice of habitats, such as for central place foragers

Lorentz contraction, Bell's spaceships, and rigid body motion in special relativity

The meaning of Lorentz contraction in special relativity and its connection with Bell's spaceships parable is discussed. The motion of Bell's spaceships is then compared with the accelerated motion of a rigid body. We have tried to write this in a simple form that could be used to correct students' misconceptions due to conflicting earlier treatments.Comment: Modified the discussion in Sec. 2. This version to be published in European Journal of Physic

Two-region model for positive and negative plasma sheaths and its application to Hall thruster metallic anodes.

An asymptotic presheath/sheath model for positive and negative sheaths in front of a conducting electrode, with a continuous parametric transition at the no-sheath case, is presented. Key aspects of the model are as follows: full hydrodynamics of both species in the presheath; a kinetic formulation with a truncated distribution function for the repelled species within the sheath; and the fulfillment of the marginal Bohm condition at the sheath edge, in order to match the two formulations of the repelled species. The sheath regime depends on the ratios of particle fluxes and sound speeds between the two species. The presheath model includes the effect of a magnetic field parallel to the wall on electrons. An asymptotic, parametric study of the anode presheath is carried out in terms of the local ion-to-electron flux ratio and Hall parameter. The drift-diffusive model of magnetized electrons fails in a parametric region that includes parts of the negative sheath regime. In the case of the Hall parameter vanishing near the electrode and a weakly collisional plasma, a quasisonic, quasineutral plateau forms next to the sheath edge

Integrated control and display research for transition and vertical flight on the NASA V/STOL Research Aircraft (VSRA)

Results of a substantial body of ground-based simulation experiments indicate that a high degree of precision of operation for recovery aboard small ships in heavy seas and low visibility with acceptable levels of effort by the pilot can be achieved by integrating the aircraft flight and propulsion controls. The availability of digital fly-by-wire controls makes it feasible to implement an integrated control design to achieve and demonstrate in flight the operational benefits promised by the simulation experience. It remains to validate these systems concepts in flight to establish their value for advanced short takeoff vertical landing (STOVL) aircraft designs. This paper summarizes analytical studies and simulation experiments which provide a basis for the flight research program that will develop and validate critical technologies for advanced STOVL aircraft through the development and evaluation of advanced, integrated control and display concepts, and lays out the plan for the flight program that will be conducted on NASA's V/STOL Research Aircraft (VSRA)

Hierarchical Discrete-Event Simulation on Hypercube Architecture

This paper presents model of hierarchical discrete-event simulation algorithm running on a hypercube architecture. We assume a static allocation of system components to processors in the hypercube. We also assume a global clock algorithm, with an event-based time increment. Following development of the performance model, we describe an application of the model in the area of digital systems simulation. Hierarchical levels included are gate level (NAND, NOR, and NOT gates) and MSI level (multiplexors, shift registers, etc.). Example values (gathered from simulations running on standard von Neumann architectures) are provided at the model inputs to show the effect of different model parameters and partitioning strategies on the simulation performance

A Unified Approach to Mixed-Mode Simulation

This paper presents a unified approach to mixed-mode simulation. It investigates the algorithms for both logic and circuit simulation, considering their similarities and differences, and a general framework is presented for integrating the two algorithms in uniform manner. The time advance mechanisms and component functional evaluations of the algorithms are show to be similar in nature, and mechanisms for the translation of information represented uniquely in the two algorithms are given. The resulting integrated algorithms is capable of performing mixed-mode simulation, where a circuit is partitioned into discrete and continuous regions, and each region is simulated at the appropriate level. In addition, several of the issues relating to the implementation of mixed-mode simulation on multiprocessors are presented

Using Interviews to Understand Patients’ Post-operative Pain Management Educational Needs Before and After Elective Total Joint Replacement Surgery

Objective: To better understand the education needs of patients electing to have TJR in managing their pain in the post-operative period after discharge from the hospital. Methods: An exploratory, descriptive, qualitative design. Convenience sample of people who reported that they had not received information about pain management prior to TJR surgery were recruited from 9 surgeon practices in 8 states to participate in telephone interviews, utilizing open-ended questions. Questions included: recollection of pre-op class attended and content; experiences with surgical pain after surgery and how it was managed; experiences with pain medicine; experience using non-medicine related pain reduction methods; suggestions for delivery of pain management information. Interviews were recorded and transcribed. Data were categorized using content analysis techniques. Results: Seventeen patients were interviewed. Although all remembered attending a pre-operative class prior to their joint replacement surgery, none remembered receiving information during that class about managing pain once they were discharged. All had been prescribed an opioid for pain management post-operatively; however no patients reported receiving any information regarding use of the medication other than the information on the pill bottle. Many had concerns regarding the use of opioids to control their pain, including side effects, such as constipation and the risk of addiction. The most common non-medicine method used to manage pain was the use of ice. Participants believed that information about pain management, including both non-medicine approaches and instructions for taking opioids would be helpful and should be delivered at multiple time points, including pre-operatively, at discharge, and within the first few days after discharge. Conclusion: With trends toward shorter hospital stays, home based pain management is a priority. Understanding the pain management education needs of patients considering elective TJR could inform interventions for this population as well as provide insight into the needs of other patients undergoing surgery