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Swimming and sinking behavior by pelagic snails is poorly studied but is important in their ecology, predator-prey interactions, and vertical distributions. We used a low magnification, high speed stereophotogrammetry system to study the swimming and sinking kinematics of nine warm water pelagic snail species (seven thecosomes, one gymnosome, and one heteropod). As different thecosomatous pteropod species may have coiled, elongated, or globular shell morphologies, we focused on how the shell shape, body geometry, and body size affect their swimming behavior from a fluid mechanics perspective. In addition, ZooScan image analysis and metabarcoding of archived vertically stratified MOCNESS samples were used to relate swimming behaviors to night time and daytime vertical distributions. While different large scale swimming patterns were observed, all species exhibited small scale sawtooth swimming trajectories caused by reciprocal appendage flapping. Thecosome swimming and sinking behavior corresponded strongly with shell morphology and size, with the tiny coiled shell pteropods swimming and sinking the slowest, the large globular shelled pteropods swimming and sinking the fastest, and the medium-sized elongated shell pteropods swimming and sinking at intermediate speeds. However, the coiled shell species had the highest normalized swimming and sinking speeds, reaching swimming speeds of up to 45 body lengths s-1. The sinking trajectories of the coiled and elongated shell pteropods were nearly vertical, but globular shell pteropods use their hydrofoil-like shell to glide downwards at approximately 20° from the vertical, thus retarding their sinking rate. The swimming Reynolds number (Re) increased from the coiled shell species (Re ~ O(10)) to the elongated shell species (Re ~ O(100)) and again for the globular shell species (Re ~ O(1000)), suggesting that more recent lineages increased in size and altered shell morphology to access greater lift-to-drag ratios available at higher Re. Swimming speed does not correlate with the vertical extent of migration, emphasizing that other factors, likely including light, temperature, and predator and prey fields, influence this ecologically important trait. Size does play a role in structuring the vertical habitat, with larger individuals tending to live deeper in the water column, while within a species, larger individuals have deeper migrations.

The high-speed impact of a droplet on a bulk fluid at high Weber number (We) is not well understood but is relevant to the production of marine aerosol by raindrop impact on the sea surface. These splashes produce a subsurface cavity and a crown which closes into a bubble canopy, but a floating layer of immiscible oil, such as a crude oil slick, alters the splash dynamics. The effects of oil layer fluid properties and thickness, droplet size and impact speed are examined by high-speed visualization. Oil layer rupture and crown behaviour are classified by dimensional scaling. The subsurface cavity volume for impact on thick layers is shown to depend on the Reynolds number (Re), although canopy formation at high Re introduces a competing We effect since rapid canopy closure is found to retard cavity expansion. Time-resolved kinematic measurements show that thin crude oil slicks similarly alter crown closure and cavity growth. The size and spatial distributions of airborne droplets are examined using high-speed holographic microscopy. The droplets have a bimodal distribution with peaks at 50 and $225~{\\rm\\mu}\\text{m}$ and are clustered by size at different elevation angles. Small droplets ( $50~{\\rm\\mu}\\text{m}$ ) are ejected primarily at shallow angles, indicating production by splashing within the first $100~{\\rm\\mu}\\text{s}$ and by breakup of microligaments. Larger droplets ( $225~{\\rm\\mu}\\text{m}$ ) are found at steeper elevation angles, indicating later production by capillary instability acting on large ligaments protruding upward from the crown. Intermittent droplet release while the ligaments grow and sweep upward is thought to contribute to the size-dependent spatial ordering. Greater numbers of small droplets are produced at high elevation angles when a crude oil layer is present, indicating satellite droplet formation from ligament breakup. A crude oil layer also increases the target fluid Ohnesorge number, leading to creation of an intact ejecta sheet, which then ruptures to form aerosolized oil droplets.

Animal positions within moving groups may reflect multiple motivations including saving energy and sensing neighbors. These motivations have been proposed for schools of Antarctic krill, but little is known about their three-dimensional structure. Stereophotogrammetric images of Antarctic krill schooling in the laboratory are used to determine statistical distributions of swimming speed, nearest neighbor distance, and three-dimensional nearest neighbor positions. The krill schools swim at speeds of two body lengths per second at nearest neighbor distances of one body length and reach similarly high levels of organization as fish schools. The nearest neighbor position distribution is highly anisotropic and shows that Antarctic krill prefer to swim in the propulsion jet of their anterior neighbor. This position promotes communication and coordination among schoolmates via hydrodynamic signals within the pulsed jet created by the metachronal stroking of the neighboring krill’s pleopods. The hydrodynamic communication channel therefore plays a large role in structuring the school. Further, Antarctic krill avoid having a nearest neighbor directly overhead, possibly to avoid blockage of overhead light needed for orientation. Other factors, including the elongated body shape of Antarctic krill and potential energy savings, also may help determine the three dimensional spatial structure of tightly packed krill schools.

Blood damage and platelet activation are inherent problems with present day mechanical heart valve designs. We investigate the approach of passive flow control applied to bileaflet mechanical heart valve (BMHV) flows as a means of optimizing leakage flow hemodynamics at length scales relevant to blood damage and platelet activation. Rectangular and hemispherical vortex generator (VG) arrays were mounted on the downstream surfaces of a 25 mm St. Jude Medical valve adjacent to the b-datum leaflet edge (central line where the two leaflets touch in closed position). The effect of VGs on the flow structure emanating from the b-datum line under both pulsatile and steady flow conditions was measured using high resolution particle image velocimetry technique. The VGs were seen to spatially disperse and dissipate the coherent leakage jet structure emanating from the b-datum line. This resulted in a significant diminution of turbulence stresses, particularly with the rectangular VG configuration. This study shows that passive flow control techniques deployed on BHMVs is potentially beneficial as significant control of flow at small length scales may be achieved without altering large scale designs of the valve.

Copepods escape well by detecting minute gradients in the flow field; they react quickly, and swim away strongly. As a key link in the aquatic food web, these small planktonic organisms often encounter suction-feeding fish. Studies have identified certain hydrodynamic features that are created by the approach of this visual predator and the generation of its suction flow for capturing food. Similarly, studies have identified certain hydrodynamic features that evoke the evasive response of copepods. This is a review of the copepod sensory motor system as pertains to understanding their response to suction-feeding fish. Analyses of the reaction time, threshold sensitivity, structure of sensors, and evasive behavior by this key prey of fish can be useful for evaluating the effectiveness of feeding tactics in response to suction flow. To illustrate, we present results comparing a copepod from a fishless lake (Hesperodiaptomus shoshone) to a copepod from a rich fishing ground (Calanus finmarchicus). We designed a flow mimic that produces a realistic mushroom-cap-shaped flow field and realistic accelerations of flow; the copepods treated the mimic as a threat and performed jumps directed up and away from the siphon. Calanus finmarchicus responded at an average threshold strain rate of 18.7/s, escaped at 0.46 m/s, and traveled 5.99 mm, most frequently as a single jump. Hesperodiaptomus shoshone responded at a strain rate of 15.1/s that is not significantly different, escaped more slowly at 0.22 m/s and traveled a shorter distance of 3.01mm using a series of hops. The high variability noted in the initial angle of the body and the maximum change in body angle suggests that unpredictability in the escape maneuver is another aspect of the tactic of copepods. The speed of the escape by small copepods 2–3mm long is overwhelmed by the speed of the attack by the much larger, faster fish; if the copepod reacts when it is within the fish’s arena of capture (<1.5mm from mouth), it will be eaten. The copepod, however, has an acutely sensitive array of mechanosensors that perceive the flow field of the fish at distances of 3–6 mm, or outside the fish’s range of capture. The copepod also has a rapid and strong locomotory response, thereby increasing the odds that the copepod will survive—but speed is unlikely to be the best tactic for staying alive. Instead, the copepod accelerates from 61.3 to 96.5 m/s² or more than 20 times stronger than the lunge of a fish. This collection of capabilities of copepods enables them to remain one of the most abundant multicellular organisms on our planet.

Proponents of police officer residency requirements maintain that police officers who live in the area they serve contribute to the local tax base, provide better information dissemination, and represent community interests in their agencies. However, little research has been conducted to assess the extent to which residency requirements affect public perceptions of the police. This paper explores the relationship between police residency requirements at the municipal level and citizen satisfaction with law enforcement - specifically, the connection between residency requirements and reported confidence in the abilities of the police to prevent crime, solve crime, and protect citizens. Data derived from a national survey of citizen satisfaction with criminal justice institutions conducted during 1995 and from the 1993 Law Enforcement Management and Administrative Statistics survey of agencies with more than 100 sworn officers reveal, among other things, that residency requirements affect citizens' perceptions of the police in a negative way.

Shock incarceration programs have become increasingly popular as an alternative to traditional prisons. Critics state, however, that such programs are characterized by ultramasculine environments which may lead to a number of negative outcomes for inmates. This study compares inmates in a shock incarceration program with inmates in a traditional minimum-security prison on the degree to which they perceive their environments as masculine, and how these perceptions relate to institutional adjustment. Inmates who describe their environment as possessing ultramasculine attributes were more likely to report negative patterns of adjustment.

Character is a critical component of effective leadership, particularly in the chaotic and brutal combat environment. The extreme context of battle accentuates character to a degree not possible in other settings, but there is little research exploring character under fire. Military historiography features prominently in leadership literature, so research on military leaders contributes to the field of leadership studies, especially when juxtaposed against a modern understanding of the character construct. Case studies of small-unit combat leaders serve as a foundation to better understand character. One such leader was Lewis Millett, awarded the Medal of Honor during the Korean War for actions during a small engagement called the Battle of Bayonet Hill. Extant historiography on this action does not consider his combat leadership from a character perspective, nor in the context of his life experience. This gap in the historical understanding of Millett leads to the following research question: How did Captain Lewis Millett demonstrate wartime leadership character during the Korean War Battle of Bayonet Hill? Millett’s character, leadership, soldiering expertise, love of country, and love of his men all combined in a bloody, brief engagement. The way Millett told his story, like most veteran stories, did not always accurately reflect what happened but does serve to demonstrate the values that underpinned his character. The Christian faith that emerged in his post-World War II years developed into a worldview in which patriotism and faith deeply intertwined, promoting a nationalism previously identified by other research into different military leaders.

Locomotion is a key characteristic of almost all forms of life and is often accomplished, whether on land, in water, or in the air, by reciprocal motion of two or more appendages. Among the zooplankton, many species propel themselves by rhythmically beating multiple pairs of closely spaced leg-like appendages in a back-to-front (metachronal) pattern. The focus of this study is to understand the mechanical design, kinematic operation, and hydrodynamic result of metachrony in the zooplankton. In the first part of this study, Antarctic krill (Euphausia superba ) are investigated as an ecologically important model species that metachronally beats its swimming legs (pleopods) to perform drag-based propulsion. Based on high speed videos of freely swimming Antarctic krill, hovering, fast forward swimming, and upside down swimming are identified as three distinct swimming modes with significantly different stroke amplitudes and beat frequencies. When transitioning between hovering and fast forward swimming, Antarctic krill first increase beat amplitude and secondarily increase beat frequency. In considering the design components that contribute to metachrony being a successful swimming technique, a comparison among many different species shows that the ratio between the appendage separation distance and appendage length is limited to a narrow range of values (i.e. 0.2 – 0.65). In the second part of this study, metachrony is examined at smaller length and time scales by examining the impulsive escape jump of a calanoid copepod (Calanus finmarchicus). The wake generated by the copepod’s metachronally beating swimming legs is experimentally measured using a novel (and newly developed) tomographic particle image velocimetry (PIV) system capable of making volumetric 3D velocity measurements with high temporal and spatial resolution using IR illumination. The flow generated by the escaping copepod consisted of a stronger posterior vortex ring generated by the metachronally stroking swimming legs and a weaker one generated anteriorly around the body by the impulsive start of the escape, both of which decayed over time. The experiments also revealed azimuthal asymmetry in the vortices caused by body yawing and the action of the swimming legs, flow features not considered in previous axisymmetric computational and theoretical models of copepod jumps. While not accounting for this asymmetry, an impulsive stresslet is nonetheless useful in modeling the flow created by the escaping copepod and represents the flow more accurately than an impulsive Stokeslet. In the final part of this study, the flow associated with metachronal hovering in Antarctic krill is experimentally and theoretically investigated in regards to the energy requirements of the pelagic lifestyle. Volumetric flow measurements of a hovering Antarctic krill show that each stroking pleopod drags flow behind it such that a downward stream develops medially. The lateral exopodites induce tip vortices which add to the lift force on each appendage. Furthermore, the flow beneath the hovering krill develops into a pulsed jet with a Strouhal number in the ‘high-efficiency zone’ of 0.2 < St < 0.4. Actuator disk theory is used to make theoretical estimates of the induced power necessary to hover, the results of which match induced power values calculated from measured flow gradients contributing to viscous energy dissipation.