A Cellular Automata Model of Oncolytic Virotherapy in Pancreatic Cancer

Oncolytic virotherapy is known as a new treatment to employ less virulent viruses to specifically target and damage cancer cells. This work presents a cellular automata model of oncolytic virotherapy with an application to pancreatic cancer. The fundamental biomedical processes (like cell proliferation, mutation, apoptosis) are modeled by the use of probabilistic principles. The migration of injected viruses (as therapy) is modeled by diffusion through the tissue. The resulting diffusion–reaction equation with smoothed point viral sources is discretized by the finite difference method and integrated by the IMEX approach. Furthermore, Monte Carlo simulations are done to quantitatively evaluate the correlations between various input parameters and numerical results. As we expected, our model is able to simulate the pancreatic cancer growth at early stages, which is calibrated with experimental results. In addition, the model can be used to predict and evaluate the therapeutic effect of oncolytic virotherapy.

Hydrodynamic advantages of swimming by salp chains

Salps are marine invertebrates comprising multiple jet-propelled swimming units during a colonial life-cycle stage. Using theory, we show that asynchronous swimming with multiple pulsed jets yields substantial hydrodynamic benefit due to the production of steady swimming velocities, which limit drag. Laboratory comparisons of swimming kinematics of aggregate salps (Salpa fusiformis and Weelia cylindrica) using high-speed video supported that asynchronous swimming by aggregates results in a smoother velocity profile and showed that this smoother velocity profile is the result of uncoordinated, asynchronous swimming by individual zooids. In situ flow visualizations of W. cylindrica swimming wakes revealed that another consequence of asynchronous swimming is that fluid interactions between jet wakes are minimized. Although the advantages of multi-jet propulsion have been mentioned elsewhere, this is the first time that the theory has been quantified and the role of asynchronous swimming verified using experimental data from the laboratory and the field.

Stability versus Maneuvering: Challenges for Stability during Swimming by Fishes

Fishes are well known for their remarkable maneuverability and agility. Less visible is the continuous control of stability essential for the exploitation of the full range of aquatic resources. Perturbations to posture and trajectory arise from hydrostatic and hydrodynamic forces centered in a fish (intrinsic) and from the environment (extrinsic). Hydrostatic instabilities arise from vertical and horizontal separation of the centers of mass (CM) and of buoyancy, thereby creating perturbations in roll, yaw, and pitch, with largely neglected implications for behavioral ecology. Among various forms of hydrodynamic stability, the need for stability in the face of recoil forces from propulsors is close to universal. Destabilizing torques in body-caudal fin swimming is created by inertial and viscous forces through a propulsor beat. The recoil component is reduced, damped, and corrected in various ways, including kinematics, shape of the body and fins, and deployment of the fins. We postulate that control of the angle of orientation, θ, of the trailing edge is especially important in the evolution and lifestyles of fishes, but studies are few. Control of stability and maneuvering are reflected in accelerations around the CM. Accelerations for such motions may give insight into time-behavior patterns in the wild but cannot be used to determine the expenditure of energy by free-swimming fishes.

The stimuli evoking the aerial-righting-posture of falling pea aphids

Some wingless insects possess aerial righting reflexes, suggesting that adaptation for controlling body orientation while falling through air could have preceded flight. When threatened by a predator, wingless pea aphids (Acyrthosiphon pisum) may drop off their host plant and assume a stereotypic posture that rotates them in midair to land on their feet. The sensory information triggering aphids to assume this posture has so far been unknown. We subjected aphids to a series of tests, isolating the sensory cues experienced during free-fall. Falling aphids assumed the righting posture and landed upright irrespective of whether the experiments were carried out in the light or in complete darkness. Detachment of the tarsi from the substrate triggered the aphids to assume the posture rapidly, but only for a brief period. Rotation (mainly roll and yaw) of the body in air, in the light, caused aphids to assume the posture and remain in it throughout rotation. In contrast, aphids rotated in the dark did not respond. Acceleration associated with falling or airflow over the body per se did not trigger the posture. However, sensing motion relative to air heightened the aphids’ responsiveness to rotation in the light. These results suggest that the righting posture of aphids is triggered by a tarsal reflex, but once airborne, vision and a sense of motion relative to air can augment the response. Hence, aerial righting in a wingless insect could have emerged as a basic tarsal response and developed further to include secondary sensory cues typical of falling.

Hydrodynamics and energy-saving swimming techniques of Pacific bluefin tuna

Weihs theoretically revealed that during the movement of fish with negative buoyancy, more kinetic energy is saved in the glide and upward (GAU) swimming mode than in the continuous horizontal swimming mode. Because kinetic energy saving depends on dynamic parameters such as the drag and lift of the body, the effects of variations in these parameters on energy saving for different species remain unknown. Here, the kinetic energy saving of Pacific bluefin tuna (PBT), Thunnus orientalis, exhibiting the GAU swimming mode was investigated. The dynamic properties of PBT were estimated by carrying out CFD analysis. The CFD model was produced by using a three-dimensional laser surface profiler, and the model was controlled such that it exhibited swimming motion similar to that of a live PBT swimming in a flume tank. The drag generated by tail beating, which significantly affects the kinetic energy during motion, was twice that generated in the glide mode. The faster the upward swimming speed, the lesser is the kinetic energy saving; therefore, when the upward swimming speed is more than twice the glide speed, there is no gain in the GAU mode. However, when SMR (Standard Metabolic Rate) is considered, if the energy based on SMR is assumed to be 30% of the total energy spent during motion, the most efficient upward swimming speed is 1.4 times the glide speed. The GAU swimming mode of PBT leads to energy saving during motion, and the upward swimming speed and the lift force produced by the pectoral fins for the most efficient drive are unique for different species of different sizes.

Why are there no long distance jumpers among click-beetles (Elateridae)?

Click-beetles jump from an inverted position without using their legs. This unique mechanism results in high vertical jumps with the jump angle restricted by the rigid morphology of the exoskeleton. We explored the option to exploit this jumping mechanism for application to small mechanical devices having to extricate themselves from rough terrain. We combined experiments on a biomimetic jumping device with a physical-mathematical model of the jump to assess the effect of morphological variation on the jumping performance. We found that through morphological change of two non-dimensional (size independent) parameters, the propulsive force powering the jump can be directed at angles as small as 40°. However, in practice jumping at such angles is precluded by loss of traction with the ground during the push-off phase. This limitation to steep jump angles is inherent to the jumping mechanism which is based on rotation of body parts about a single hinge. Such a rotation dictates a curvilinear trajectory for the center of mass during takeoff so that the vertical and horizontal accelerations occur out of phase, implying loss of traction with the ground before substantial horizontal acceleration can be reached. Thus click-beetle inspired jumping is effective mainly for making steep-angle righting jumps.

Stability versus maneuverability in aquatic locomotion

The dictionary definition of stability as "Firmly established, not easily to be changed" immediately indicates the conflict between stability and maneuverability in aquatic locomotion. The present paper addresses several issues resulting from these opposing requirements. Classical stability theory for bodies moving in fluids is based on developments in submarine and airship motions. These have lateral symmetry, in common with most animals. This enables the separation of the equations of motion into two sets of 3 each. The vertical (longitudinal) set, which includes motions in the axial (surge), normal (heave) and pitching directions, can thus be separated from the lateral-horizontal plane which includes yaw, roll and sideslip motions. This has been found useful in the past for longitudinal stability studies based on coasting configurations but is not applicable to the analysis of turning, fast starts and vigorous swimming, where the lateral symmetry of the fish body is broken by bending motions. The present paper will also examine some of the aspects of the stability vs. maneuverability tradeoff for these asymmetric motions. An analysis of the conditions under which the separation of equations of motions into vertical and horizontal planes is justified, and a definition of the equations to be used in cases where this separation is not accurate enough is presented.

Dynamics of dolphin porpoising revisited

Porpoising is the popular name for the high-speed surface piercing motion of dolphins and other species, in which long, ballistic jumps are alternated with sections of swimming close to the surface. The first analysis of this behavior (Au and Weihs, 1980) showed that above a certain "crossover" speed this behavior is energetically advantageous, as the reduction in drag due to movement in the air becomes greater than the added cost of leaping.Since that publication several studies documented porpoising behavior at high speeds. The observations indicated that the behavior was more complex than previously assumed. The leaps were interspersed with relatively long swimming bouts, of about twice the leap length. In the present paper, the possibility of dolphins using a combination of leaping and burst and coast swimming is examined. A three-phase model is proposed, in which the dolphin leaps out of the water at a speed U(f), which is the final speed obtained at the end of the burst phase of burst and coast swimming. The leap is at constant speed and so the animal returns to the water at U(f), goes to a shallow depth and starts horizontal coasting while losing speed, till it reaches U(i). At that point it starts active swimming, accelerating to U(f). It then starts the next leap. Ranges of speeds for which this three-stage swimming is advantageous are calculated as a function of animal and physical parameters.NotationC-Constant defined in equation (12)C(D)-Coasting drag coefficientD-Dragg-Gravitational accelerationH-Height of jumpJ-Energy required for jumpk-Ratio of swim length to jump lengthl-DistanceL-Total distance (eq. 28)m-Added massM-Animal massM(1)-Total massr-Coefficient defined in eq. (22)R-Ratio of energies, for three-phase swimmingR(2)-Ratio of energies, for burst and coast swimmingt-TimeT-ThrustU-SpeedV-Body volumeW-Weightα-Emergence (=return) angleβ-Swim / coast drag penalty ratioγ-Surface effects drag ratioρ-Density of seawater and cetacean.Subscriptsa-airav-Averageb-Burst phasec-Coast phasee-Reference (maximal) thrustf-Final, at end of bursti-Initial, at start of burstj-Jump phasen-Nominal reference thrusto-Optimals-Surface swimmingw-Water.

Hydrodynamics of sailing of the Portuguese man-of-war Physalia physalis

Physalia physalis, commonly known as the Portuguese man-of-war (PMW), is a peculiar looking colony of specialized polyps. The most conspicuous members of this colony are the gas-filled sail-like float and the long tentacles, budding asymmetrically beneath the float. This study addresses the sailing of the PMW, and, in particular, the hydrodynamics of its trailing tentacles, the interaction between the tentacles and the float and the actual sailing performance. This paper attempts to provide answers for two of the many open questions concerning P. physalis: why does it need a sail? and how does it harness the sail?

Locomotion in diving elephant seals: physical and physiological constraints

To better understand how elephant seals (Mirounga angustirostris) use negative buoyancy to reduce energy metabolism and prolong dive duration, we modelled the energetic cost of transit and deep foraging dives in an elephant seal. A numerical integration technique was used to model the effects of swim speed, descent and ascent angles, and modes of locomotion (i.e. stroking and gliding) on diving metabolic rate, aerobic dive limit, vertical displacement (maximum dive depth) and horizontal displacement (maximum horizontal distance along a straight line between the beginning and end locations of the dive) for aerobic transit and foraging dives. Realistic values of the various parameters were taken from previous experimental data. Our results indicate that there is little energetic advantage to transit dives with gliding descent compared with horizontal swimming beneath the surface. Other factors such as feeding and predator avoidance may favour diving to depth during migration. Gliding descent showed variable energy savings for foraging dives. Deep mid-water foraging dives showed the greatest energy savings (approx. 18%) as a result of gliding during descent. In contrast, flat-bottom foraging dives with horizontal swimming at a depth of 400m showed less of an energetic advantage with gliding descent, primarily because more of the dive involved stroking. Additional data are needed before the advantages of gliding descent can be fully understood for male and female elephant seals of different age and body composition. This type of data will require animal-borne instruments that can record the behaviour, three-dimensional movements and locomotory performance of free-ranging animals at depth.

Consequences of buoyancy to the maneuvering capabilities of a foot-propelled aquatic predator, the great cormorant (Phalcrocorax carbo sinensis)

Great cormorants are foot-propelled aquatic divers utilizing a region of the water column where their underwater foraging behavior is affected by their buoyancy. While swimming horizontally underwater, cormorants use downward lift forces generated by their body and tail to overcome their buoyancy. Here we assess the potential of this swimming strategy for controlling maneuvers in the vertical plane. We recorded the birds swimming through a submerged obstacle course and analyzed their maneuvers. The birds reduced swimming speed by only 12% to maneuver and were able to turn upward and then downward in the sagittal plane at a minimal turning radius of 32±4 cm (40% body length). Using a quasi-steady approach, we estimated the time-line for hydrodynamic forces and the force-moments produced while maneuvering. We found that the tail is responsible for the pitch of the body while motions of the body, tail, neck and feet generate forces normal (vertically) to the swimming direction that interact with buoyancy to change the birds' trajectory. Vertical maneuvers in cormorants are asymmetric in energy cost. When turning upward, the birds use their buoyancy but they must work harder to turn downward. Lift forces generated by the body were always directed ventrally. Propulsion improves the ability to make tight turns when the center of the turn is ventral to the birds. The neck produced only a small portion (10%) of the normal vertical forces but its length may allow prey capture at the end of pursuit, within the minimum turning radius.

Speed limits on swimming of fishes and cetaceans

Physical limits on swimming speed of lunate tail propelled aquatic animals are proposed. A hydrodynamic analysis, applying experimental data wherever possible, is used to show that small swimmers (roughly less than a metre long) are limited by the available power, while larger swimmers at a few metres below the water surface are limited by cavitation. Depending on the caudal fin cross-section, 10-15 m s(-1) is shown to be the maximum cavitation-free velocity for all swimmers at a shallow depth.

Evidence of self-correcting spiral flows in swimming boxfishes

The marine boxfishes have rigid keeled exteriors (carapaces) unlike most fishes, yet exhibit high stability, high maneuverability and relatively low drag given their large cross-sectional area. These characteristics lend themselves well to bioinspired design. Based on previous stereolithographic boxfish model experiments, it was determined that vortical flows develop around the carapace keels, producing self-correcting forces that facilitate swimming in smooth trajectories. To determine if similar self-correcting flows occur in live, actively swimming boxfishes, two species of boxfishes (Ostracion meleagris and Lactophrys triqueter) were induced to swim against currents in a water tunnel, while flows around the fishes were quantified using digital particle image velocimetry. Significant pitch events were rare and short lived in the fishes examined. When these events were observed, spiral flows around the keels qualitatively similar to those observed around models were always present, with greater vortex circulation occurring as pitch angles deviated from 0 degrees . Vortex circulation was higher in live fishes than models presumably because of pectoral fin interaction with the keel-induced flows. The ability of boxfishes to modify their underlying self-correcting system with powered fin control is important for achieving high levels of both stability and maneuverability. Although the challenges of performing stability and maneuverability research on fishes are significant, the results of this study together with future studies employing innovative new approaches promise to provide valuable inspiration for the designers of bioinspired aquatic vehicles.

Optimal descent angles for shallow-diving cormorants

Air-breathing divers should attempt to maximize foraging efficiency under the constraint of limited oxygen availability. For diving water birds, high buoyancy (owing to the air in the plumage) and the associated change in buoyancy with diving depth impose further constraints on the adaptation to aquatic life. Diving birds are expected to descend as fast as possible to escape the higher buoyancy near the water surface, but in practice, shallow-diving cormorants (genus Phalacrocorax Brisson, 1760) are often observed descending the water column in relatively small angles with respect to the water surface. We derive a theoretical biomechanical model for the energetics of the descent phase of a dive of foot-propelled cormorants feeding on benthic prey at shallow depth. The model shows that visually guided benthic feeders benefit energetically from diving at small descent angles when optical conditions and bottom depth allow. The model also explains the high variation in descent angles observed in free-ranging birds, as well as the observed correlation between descent angle and bottom depth in cormorants.

Adjustment of submerged swimming to changes in buoyancy in cormorants

Waterbirds are buoyant because of volumes of air in their plumage and respiratory tract. When they are submerged, their buoyancy is reduced, owing to compression of these volumes of air with depth. We tested how the horizontal submerged swimming of cormorants (Phalacrocorax carbo sinensis (Blumelbach, 1798)) changed when their buoyancy was artificially reduced. Birds were filmed swimming under water once with lead weights (density 11 000 kg·m–3) and again with "dummy" weights (density 1100 kg·m–3) attached to their body. The dummy weights had negligible weight under water and served as control for the increased drag in the experiment. Cormorants swimming with weights tilted their bodies at an angle of 3°–7° below the swimming direction, whereas the body of birds in the control groups was tilted at 14°–16°. The tilt of the body affected the orientation and trajectory of the tail and feet during swimming. A hydrodynamic analysis showed that the lesser tilt of the body (while swimming with weights equivalent to 26% of body weight) resulted in a 55%–57% reduction of the vertical hydrodynamic forces (lift, drag, and thrust) generated by the birds to overcome buoyancy. When more weights were added and the birds became negatively buoyant, these vertical forces changed direction to prevent sinking. Thus, by adjusting the tilt of the body, the birds may dynamically control their buoyancy to maintain straight horizontal swimming despite changes in buoyancy.

Dynamics of the aerial maneuvers of spinner dolphins

The spinner dolphin (Stenella longirostris) performs spectacular leaps from the water while rotating around its longitudinal axis up to seven times. Although twisting of the body while airborne has been proposed as the mechanism to effect the spin, the morphology of the dolphin precludes this mechanism for the spinning maneuver. A mathematical model was developed that demonstrates that angular momentum to induce the spin was generated underwater, prior to the leap. Subsurface corkscrewing motion represents a balance between drive torques generated by the flukes and by hydrodynamic forces at the pectoral fins, and resistive torques, induced by the drag forces acting on the rotating control surfaces. As the dolphin leaps clear of the water, this balance is no longer maintained as the density of the air is essentially negligible, and a net drive torque remains, which permits the dolphin's rotation speed to increase by as much as a factor of three for a typical specimen. The model indicates that the high rotation rates and orientation of the dolphin's body during re-entry into the water could produce enough force to hydrodynamically dislodge unwanted remoras.

Submerged swimming of the great cormorantPhalacrocorax carbo sinensisis a variant of the burst-and-glide gait

Cormorants are water birds that forage by submerged swimming in search and pursuit of fish. Underwater they swim by paddling with both feet simultaneously in a gait that includes long glides between consecutive strokes. At shallow swimming depths the birds are highly buoyant as a consequence of their aerial lifestyle. To counter this buoyancy cormorants swim underwater with their body at an angle to the swimming direction. This mechanical solution for foraging at shallow depth is expected to increase the cost of swimming by increasing the drag of the birds. We used kinematic analysis of video sequences of cormorants swimming underwater at shallow depth in a controlled research setup to analyze the swimming gait and estimate the resultant drag of the birds during the entire paddling cycle. The gliding drag of the birds was estimated from swimming speed deceleration during the glide stage while the drag during active paddling was estimated using a mathematical`burst-and-glide' model. The model was originally developed to estimate the energetic saving from combining glides with burst swimming and we used this fact to test whether the paddling gait of cormorants has similar advantages.

We found that swimming speed was correlated with paddling frequency(r=0.56, P<0.001, N=95) where the increase in paddling frequency was achieved mainly by shortening the glide stage(r=–0.86, P<0.001, N=95). The drag coefficient of the birds during paddling was higher on average by two- to threefold than during gliding. However, the magnitude of the drag coefficient during the glide was positively correlated with the tilt of the body(r=0.5, P<0.003, N=35) and negatively correlated with swimming speed (r=–0.65, P<0.001, N=35), while the drag coefficient during the stroke was not correlated with tilt of the body (r=–0.11, P>0.5, N=35) and was positively correlated with swimming speed(r=0.41, P<0.015, N=35). Therefore, the difference between the drag coefficient during the glide and during propulsion diminished at lower speeds and larger tilt. The mean drag of the birds for a single paddling cycle at an average swimming speed of 1.5 m s–1 was 5.5±0.68 N. The burst-and-glide model predicts that energy saving from using burst-and-glide in the paddling cycle is limited to relatively fast swimming speeds (>1.5 m s–1), but that as the birds dive deeper (>1 m where buoyancy is reduced), the burst-and-glide gait may become beneficial even at lower speeds.

Body-induced vortical flows: a common mechanism for self-corrective trimming control in boxfishes

Boxfishes (Teleostei: Ostraciidae) are marine fishes having rigid carapaces that vary significantly among taxa in their shapes and structural ornamentation. We showed previously that the keels of the carapace of one species of tropical boxfish, the smooth trunkfish, produce leading edge vortices (LEVs) capable of generating self-correcting trimming forces during swimming. In this paper we show that other tropical boxfishes with different carapace shapes have similar capabilities. We conducted a quantitative study of flows around the carapaces of three morphologically distinct boxfishes (spotted boxfish, scrawled cowfish and buffalo trunkfish) using stereolithographic models and three separate but interrelated analytical approaches: digital particle image velocimetry (DPIV), pressure distribution measurements, and force balance measurements. The ventral keels of all three forms produced LEVs that grew in circulation along the bodies, resembling the LEVs produced around delta-winged aircraft. These spiral vortices formed above the keels and increased in circulation as pitch angle became more positive, and formed below the keels and increased in circulation as pitch angle became more negative. Vortices also formed along the eye ridges of all boxfishes. In the spotted boxfish, which is largely trapezoidal in cross section, consistent dorsal vortex growth posterior to the eye ridge was also present. When all three boxfishes were positioned at various yaw angles, regions of strongest concentrated vorticity formed in far-field locations of the carapace compared with near-field areas, and vortex circulation was greatest posterior to the center of mass. In general, regions of localized low pressure correlated well with regions of attached, concentrated vorticity, especially around the ventral keels. Although other features of the carapace also affect flow patterns and pressure distributions in different ways, the integrated effects of the flows were consistent for all forms: they produce trimming self-correcting forces, which we measured directly using the force balance. These data together with previous work on smooth trunkfish indicate that body-induced vortical flows are a common mechanism that is probably significant for trim control in all species of tropical boxfishes.

How do cormorants counter buoyancy during submerged swimming?

Buoyancy is a de-stabilizing force for diving cormorants that forage at shallow depths. Having to counter this force increases the cost of transport underwater. Cormorants are known to be less buoyant than most water birds but are still highly buoyant (ρ=∼0.8 kg m–3) due to their adaptations for aerial flight. Nevertheless, cormorants are known to dive at a wide range of depths, including shallow dives where buoyancy is maximal. We analyzed the kinematics of underwater swimming of the great cormorant(Phalacrocorax carbo sinensis) in a shallow pool to discover and evaluate the mechanisms countering buoyancy while swimming horizontally. The birds maintained a very uniform cyclic paddling pattern. Throughout this cycle, synchronized tilting of the body, controlled by the tail, resulted in only slight vertical drifts of the center of mass around the average swimming path. We suggest that this tilting behavior serves two purposes: (1) the elongated bodies and the long tails of cormorants, tilted at a negative angle of attack relative to the swimming direction, generate downward directed hydrodynamic lift to resist buoyancy and (2) during the propulsive phase, the motion of the feet has a significant vertical component, generating a vertical component of thrust downward, which further helps to offset buoyancy. The added cost of the drag resulting from this tilting behavior may be reduced by the fact that the birds use a burst-and-glide pattern while swimming.

The hydrodynamics of dolphin drafting

Background

Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here.

Results

Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers.

Conclusions

A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members.

Hydrodynamic stability of swimming in ostraciid fishes: role of the carapace in the smooth trunkfish Lactophrys triqueter (Teleostei: Ostraciidae)

The hydrodynamic bases for the stability of locomotory motions in fishes are poorly understood, even for those fishes, such as the rigid-bodied smooth trunkfish Lactophrys triqueter, that exhibit unusually small amplitude recoil movements during rectilinear swimming. We have studied the role played by the bony carapace of the smooth trunkfish in generating trimming forces that self-correct for instabilities. The flow patterns, forces and moments on and around anatomically exact, smooth trunkfish models positioned at both pitching and yawing angles of attack were investigated using three methods: digital particle image velocimetry (DPIV), pressure distribution measurements, and force balance measurements. Models positioned at various pitching angles of attack within a flow tunnel produced well-developed counter-rotating vortices along the ventro-lateral keels. The vortices developed first at the anterior edges of the ventro-lateral keels, grew posteriorly along the carapace, and reached maximum circulation at the posterior edge of the carapace. The vortical flow increased in strength as pitching angles of attack deviated from 0 degrees, and was located above the keels at positive angles of attack and below them at negative angles of attack. Variation of yawing angles of attack resulted in prominent dorsal and ventral vortices developing at far-field locations of the carapace; far-field vortices intensified posteriorly and as angles of attack deviated from 0 degrees. Pressure distribution results were consistent with the DPIV findings, with areas of low pressure correlating well with regions of attached, concentrated vorticity. Lift coefficients of boxfish models were similar to lift coefficients of delta wings, devices that also generate lift through vortex generation. Furthermore, nose-down and nose-up pitching moments about the center of mass were detected at positive and negative pitching angles of attack, respectively. The three complementary experimental approaches all indicate that the carapace of the smooth trunkfish effectively generates self-correcting forces for pitching and yawing motions--a characteristic that is advantageous for the highly variable velocity fields experienced by trunkfish in their complex aquatic environment. All important morphological features of the carapace contribute to producing the hydrodynamic stability of swimming trajectories in this species.

Head stabilization in herons

We examined head stabilization in relation to body mass and length of legs in four heron species (little egrets, Egretta garzetta; night herons, Nycticorax nycticorax; squacco herons, Ardeola ralloides; and cattle egrets, Bubulcus ibis: Aves: Ardeidae). Head stabilization, under controlled, sinusoidal, perch perturbations was mostly elicited at frequencies lower than 1 Hz. Maximal perturbation amplitudes sustained were positively correlated with leg length and maximal perturbation frequencies sustained were negatively correlated with body mass and with leg length. The species differed significantly in average maximal perturbation amplitudes sustained. Combinations of amplitude and frequency for which stabilization was achieved were bounded by a decreasing concave "envelope" curve in the frequency-amplitude plane, with inter specific differences in "envelope". As physical constraints, we tested maximal vertical acceleration, which translates into a line defined by the product of frequency2 x amplitude, and maximal vertical velocity, which translates into a line defined by the product of frequency x amplitude. Both relations were in good agreement with the experimental results for all but squacco herons. The results support predictions based on mechanical considerations and may explain the predominance of motor patterns employed by herons while foraging.

Boxfishes (Teleostei: Ostraciidae) as a model system for fishes swimming with many fins: kinematics

Swimming movements in boxfishes were much more complex and varied than classical descriptions indicated. At low to moderate rectilinear swimming speeds (<5 TL s(−1), where TL is total body length), they were entirely median- and paired-fin swimmers, apparently using their caudal fins for steering. The pectoral and median paired fins generate both the thrust needed for forward motion and the continuously varied, interacting forces required for the maintenance of rectilinearity. It was only at higher swimming speeds (above 5 TL s(−1)), when burst-and-coast swimming was used, that they became primarily body and caudal-fin swimmers. Despite their unwieldy appearance and often asynchronous fin beats, boxfish swam in a stable manner. Swimming boxfish used three gaits. Fin-beat asymmetry and a relatively non-linear swimming trajectory characterized the first gait (0--1 TL s(−1)). The beginning of the second gait (1--3 TL s(−1)) was characterized by varying fin-beat frequencies and amplitudes as well as synchrony in pectoral fin motions. The remainder of the second gait (3--5 TL s(−1)) was characterized by constant fin-beat amplitudes, varying fin-beat frequencies and increasing pectoral fin-beat asynchrony. The third gait (>5 TL s(−1)) was characterized by the use of a caudal burst-and-coast variant. Adduction was always faster than abduction in the pectoral fins. There were no measurable refractory periods between successive phases of the fin movement cycles. Dorsal and anal fin movements were synchronized at speeds greater than 2.5 TL s(−1), but were often out of phase with pectoral fin movements.

Boxfishes as unusually well-controlled autonomous underwater vehicles

Boxfishes (family Ostraciidae) are tropical reef-dwelling marine bony fishes that have about three-fourths of their body length encased in a rigid bony test. As a result, almost all of their swimming movements derive from complex combinations of movements of their median and paired fins (MPF locomotion). In terms of both body design and swimming performance, they are among the most sophisticated examples known of naturally evolved vertebrate autonomous underwater vehicles. Quantitative studies of swimming performance, biomechanics, and energetics in one model species have shown that (i) they are surprisingly strong, fast swimmers with great endurance; (ii) classical descriptions of how they swim were incomplete: they swim at different speeds using three different gaits; (iii) they are unusually dynamically well controlled and stable during sustained and prolonged rectilinear swimming; and (iv) despite unusually high parasite (fuselage) drag, they show energetic costs of transport indistinguishable from those of much better streamlined fishes using body and caudal fin (BCF) swimming modes at similar water temperatures and over comparable ranges of swimming speeds. We summarize an analysis of these properties based on a dynamic model of swimming in these fishes. This model accounts for their control, stability, and efficiency in moving through the water at moderate speeds in terms of gait changes, of water-flow patterns over body surfaces, and of complex interactions of thrust vectors generated by fin movements.

Microstructural evolution of lipid aggregates in nucleating model and human biles visualized by cryogenic transmission electron microscopy

Obtaining reliable information on the physical state and ultrastructure of bile is difficult because of its mixed aqueous-lipid composition and thermodynamic metastability. We have used time-lapse cryogenic transmission electron microscopy (cryo-TEM) combined with video-enhanced light microscopy (VELM) to study microstructural evolution in nucleating bile. A well-characterized model bile and gallbladder biles from cholesterol and pigment gallstone patients were studied sequentially during cholesterol nucleation and precipitation. In model bile, cholesterol crystallization was preceded by the appearance of the following distinct microstructures: spheroidal micelles (3-5 nm), discoidal membrane patches (50-150 nm) often in multiple layers (2-10), discs (50-100 nm), and unilamellar (50-200 nm) and larger multilamellar vesicles (MLVs). The membrane patches and discs appeared to be short-lived intermediates in a micelle-to-vesicle transition. Vesicular structures formed by growth and closure of patches as well as by budding off from vesicles with fewer bilayers. MLVs became more abundant, uniform, and concentric as a function of time. In native bile, all the above microstructures, except discoidal membrane patches, were observed. However, native MLVs were more uniform and concentric from the beginning. When cholesterol crystals appeared by light microscopy, MLVs were always detected by cryo-TEM. Edges of early cholesterol crystals were lined up with micelles and MLVs in a way suggesting an active role in feeding crystal growth from these microstructures. These findings, for the first time documented by cryo-TEM in human bile, provide a microstructural framework that can serve as a basis for investigation of specific factors that influence biliary cholesterol nucleation and crystal formation.

Hydrostatic stability of fish with swim bladders: not all fish are unstable

The center of mass and the center of buoyancy were found to occur at the same relative longitudinal location along the body of the elongate-bodied European eel (Anguilla anguilla), the fusiform yellow perch (Perca flavescens), and two gibbose species, rock bass (Ambloplites rupestris) and bluegill (Lepomis macrochirus). The locations of these centers were not affected by fish size. Therefore the fish were neutral in hydrostatic pitching equilibrium. The vertical location of the centers of mass and buoyancy were the same for bluegill, but the center of mass was dorsal to the center of buoyancy in yellow perch. The observations on bluegill show that neutral hydrostatic rolling equilibrium is possible. Our conclusions on similarity or separation between the locations of the centers of mass and buoyancy derive from tests of significance and differ from conclusions reported elsewhere on the basis of mean values only. In general, fish with swim bladders can be at or close to neutral hydrostatic equilibrium but any disturbance will be destabilizing. This probably explains continuous fin-beating of fish in apparently still water.

Size-related hydrodynamic characteristics of the giant scallop, Placopecten magellanicus (Bivalvia: Pectinidae)

The giant scallop, Placopecten magellanicus (Gmelin, 1791), exhibits a three-stage life history: an early sedentary phase with byssal attachment (1–30 mm shell height), a motile phase (30–100 mm), and a later, sedentary phase, recessed in the bottom (100–160 mm). If hydrodynamics have an adaptive advantage, ontogeny of form and functional kinetics should reflect changes in life stage, and medium-sized Placopecten would be the best swimmers, with optimum hydrodynamic characteristics. Comparison of morphological characteristics of P. magellanicus in relation to size (5–160 mm) suggested that peak hydrodynamic efficiency for this species occurs between 40 and 80 mm shell height. Fineness, aspect ratio, wing loading, and potential power relationships were optimal in this range. Underwater video sequences of swimming Placopecten revealed that the angle of valve opening during sustained level flight averaged 9° per contraction and calculated jet volume expelled per unit weight peaked at 55 mm shell height. Swimming Placopecten between 30 and 100 mm exhibited a steep angle of attack only during takeoff and then swam level at velocities of 30–60 cm/s (4–9 body lengths/s), with associated Reynolds numbers of 0.6–7.2 × 104. Swimming speed, both absolute and adjusted for body length, was maximal between 50 and 70 mm shell height. Calculated Reynolds numbers increased for individuals between 30 and 70 mm but remained constant for those over 70 mm.

Energetic advantages of burst-and-coast swimming of fish at high speeds

A theoretical model describes how an intermittent swimming style can be energetically advantageous over continuous swimming at high average velocities. Kinematic data are collected from high-speed cine pictures of free swimming cod and saithe at high velocities in a burst-and-coast style. These data suggest that fish make use of the advantages shown by choosing initial and final burst velocities close to predicted optimal values. The limiting role of rapid glycogen depletion in fast white anaerobic muscle fibres is discussed.

[Enzymatic lecithin determination in amniotic fluid for antepartal diagnosis of lung maturity - a multi-center study (author's transl)]

A new test-combination for the enzymatic determination of lecithin in amniotic fluid for the assessment of fetal lung maturity has been developed by Boehringer Mannheim. This test was evaluated by 12 hospitals and has been compared with the L/S ratio, the foam-test or the densitometric determination of lecithin. The assay is based on the hydrolysis of lecithin by phospholipase C which starts an enzymatic chain reaction in which NADH consumption if measured photometrically. The intra- and interassay precision were characterized by CV values below 10%. Average recoveries of lecithin were 95-102%. It is recommended to centrifuge the samples (10 min, 700 g) and to start the analysis as soon as possible after receipt of the specimen. The total amount of time required is 2 hours for a single determination. Batches of up to 10 samples require little extra time. An opened test-combination can be used for a maximum of 30 single determinations. Comparison of the quantitative enzymatic lecithin determination with other methods showed that the critical value for lecithin is 5.0 mg/100 ml. Above 5.1 mg/100 ml no case respiratory distress syndrome was observed. The good precision accuracy and the simple handling make the enzymatic lecithin determination suitable for routine use.