Fast-swimming hydromedusae exploit velar kinematics to form an optimal vortex wake

Fast-swimming hydromedusan jellyfish possess a characteristic funnel-shaped velum at the exit of their oral cavity that interacts with the pulsed jets of water ejected during swimming motions. It has been previously assumed that the velum primarily serves to augment swimming thrust by constricting the ejected flow in order to produce higher jet velocities. This paper presents high-speed video and dye-flow visualizations of free-swimming Nemopsis bachei hydromedusae, which instead indicate that the time-dependent velar kinematics observed during the swimming cycle primarily serve to optimize vortices formed by the ejected water rather than to affect the speed of the ejected flow. Optimal vortex formation is favorable in fast-swimming jellyfish because, unlike the jet funnelling mechanism, it allows for the minimization of energy costs while maximizing thrust forces. However, the vortex `formation number' corresponding to optimality in N. bachei is substantially greater than the value of 4 found in previous engineering studies of pulsed jets from rigid tubes. The increased optimal vortex formation number is attributable to the transient velar kinematics exhibited by the animals. A recently developed model for instantaneous forces generated during swimming motions is implemented to demonstrate that transient velar kinematics are required in order to achieve the measured swimming trajectories. The presence of velar structures in fast-swimming jellyfish and the occurrence of similar jet-regulating mechanisms in other jet-propelled swimmers (e.g. the funnel of squid) appear to be a primary factor contributing to success of fast-swimming jetters, despite their primitive body plans

Morphological diversity of medusan lineages constrained by animal–fluid interactions

Cnidarian medusae, commonly known as jellyfish, represent the earliest known animal taxa to achieve locomotion using muscle power. Propulsion by medusae requires the force of bell contraction to generate forward thrust. However, thrust production is limited in medusae by the primitive structure of their epitheliomuscular cells. This paper demonstrates that constraints in available locomotor muscular force result in a trade-off between high-thrust swimming via jet propulsion and high-efficiency swimming via a combined jet-paddling propulsion. This trade-off is reflected in the morphological diversity of medusae, which exhibit a range of fineness ratios (i.e. the ratio between bell height and diameter) and small body size in the high-thrust regime, and low fineness ratios and large body size in the high-efficiency regime. A quantitative model of the animal–fluid interactions that dictate this trade-off is developed and validated by comparison with morphological data collected from 660 extant medusan species ranging in size from 300 µm to over 2 m. These results demonstrate a biomechanical basis linking fluid dynamics and the evolution of medusan bell morphology. We believe these to be the organising principles for muscle-driven motility in Cnidaria

Sedimentology of a Lower Middle Pleistocene Reservoir in Garden Banks Area, Northern Gulf of Mexico: Integration of 3D Seismic, Cores, and Well Logs

Garden Banks field 236, known as Pimento, is part of a lower middle Pleistocene submarine-fan deposit in the north central Gulf of Mexico. Pimento field represents a classic example of a prograding fan across the continental shelf continuing across the continental slope filling and spilling minibasins. Channel complexes cut through the field as sediment migrated across the shelf and slope to the basin floor. This thesis consists of two papers which utilized donated 3D seismic data on six of the blocks in Pimento field. Public domain data was incorporated with these data to explore the producing reservoir sand in the field. Mapped horizons revealed the overall structural elements of the field including the fill and spill facies of the minibasin that directly influences the deposition of the field. In these papers, channel complexes have been resolved using seismic geomorphological techniques and cross sections. Two potential drilling targets have also been discovered and one has been initially investigated as a drilling target

Sedimentology of a Lower Middle Pleistocene Reservoir in Garden Banks Area, Northern Gulf of Mexico: Integration of 3D Seismic, Cores, and Well Logs

Garden Banks field 236, known as Pimento, is part of a lower middle Pleistocene submarine-fan deposit in the north central Gulf of Mexico. Pimento field represents a classic example of a prograding fan across the continental shelf continuing across the continental slope filling and spilling minibasins. Channel complexes cut through the field as sediment migrated across the shelf and slope to the basin floor. This thesis consists of two papers which utilized donated 3D seismic data on six of the blocks in Pimento field. Public domain data was incorporated with these data to explore the producing reservoir sand in the field. Mapped horizons revealed the overall structural elements of the field including the fill and spill facies of the minibasin that directly influences the deposition of the field. In these papers, channel complexes have been resolved using seismic geomorphological techniques and cross sections. Two potential drilling targets have also been discovered and one has been initially investigated as a drilling target

Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses

Flow patterns generated by medusan swimmers such as jellyfish are known to differ according the morphology of the various animal species. Oblate medusae have been previously observed to generate vortex ring structures during the propulsive cycle. Owing to the inherent physical coupling between locomotor and feeding structures in these animals, the dynamics of vortex ring formation must be robustly tuned to facilitate effective functioning of both systems. To understand how this is achieved, we employed dye visualization techniques on scyphomedusae (Aurelia aurita) observed swimming in their natural marine habitat. The flow created during each propulsive cycle consists of a toroidal starting vortex formed during the power swimming stroke, followed by a stopping vortex of opposite rotational sense generated during the recovery stroke. These two vortices merge in a laterally oriented vortex superstructure that induces flow both toward the subumbrellar feeding surfaces and downstream. The lateral vortex motif discovered here appears to be critical to the dual function of the medusa bell as a flow source for feeding and propulsion. Furthermore, vortices in the animal wake have a greater volume and closer spacing than predicted by prevailing models of medusan swimming. These effects are shown to be advantageous for feeding and swimming performance, and are an important consequence of vortex interactions that have been previously neglected

Extreme Minimum Wages: Effects on the U.S. Hotel Industry

The subject report analyzes literature regarding minimum wages to explore the potential effects of what could be described as extreme increases in the minimum wage on the American hotel industry. The current presidential administration as well as several large municipalities are actively seeking, or recently passed laws that increase the minimum wage by an extreme amount. The subject report quantifies the forecasted effect on the U.S. hotel industry. The study concludes that the hotel industry in the U.S. would have a negative economic impact estimated at $2.53 billion if the current national minimum wage proposal is approved.Mi

CTD electromechanical termination users manual

This report desribes a new, easy to install, reliable electromechanical cable termination to mechanically attach and electrically connect cable lowered instrument packages to their lowering cable.Funding was provided by the National Science Foundation through Grant No. OCE 8821977

Editorial Board

Editors-in Chief Hertha L. Lund Stephanie C. Stimpson Articles Editors Brendan R. Beatty Greg E. Overturf Citations Editors Tiffany B. Lonnevik Lisa A. Rodeghiero Managing Editor Robert J. Guite Staff Abbott Cooper Christopher J. Flann Sean S. Frampton Jamie J. Gaghwiler James M. Hughes Jason P. Loble Robert C. Lukes M. Scott Regan Jon. O. Shields David M. Wagner Faculty Advisor Carl Tobia