Marvin W. Luttges

Dragonfly Flight: Novel Uses of Unsteady Separated Flows

Studies of insect flight have revealed novel mechanisms of production of aerodynamic lift. In the present study, large lift forces were measured during flight episodes elicited from dragonflies tethered to a force balance. Simultaneously, stroboscopic photographs provided stop-action views of wing motion and the flowfield structure surrounding the insect. Wing kinematics were correlated with both instantaneous lift generation and vortex-dominated flow fields. The large lift forces appear to be produced by unsteady flow-wing interactions. This successful utilization of unsteady separated flows by insects may signal the existence of a whole new class of fluid dynamic uses that remain to be explored.

The physical and mechanical effects of suspension-induced osteopenia on mouse long bones

The present investigation addresses the extent of tail-suspension effects on the long bones of mice. The effects are explored in both sexes, in both forelimb and hindlimb bones, and in both diaphyseal and metaphyseal/epiphyseal bones. Two weeks of suspension provided unloading of the femora and tibiae and an altered loading of the humeri. Whole-bone effects included lower mass (approximately 10%) and length (approximately 4%) in the bones of suspended mice compared to controls. The geometric and material properties of the femora were considered along the entire length of the diaphysis and in the metaphysis/epiphysis portions as a unit. Geometric effects included lower cross-sectional cortical area (16%), cortical thickness (25%) and moment of inertia (21%) in the femora of suspended mice; these differences were observed in both distal and proximal portions of the femur diaphysis. The relative amount of bone comprising the middle 8 mm of the diaphysis was greater (3%) in the control mice than in the suspended mice. Significant mass differences between the group in the metaphysis/epiphysis were not observed. Material effects included lower %ash (approximately 2%) in the femora and tibiae as well as in the humeri of suspended mice compared to controls. With respect to the measured physical and material properties, suspension produced similar bone responses in male and female mice. The effects of suspension are manifested largely through geometric rather than through material changes.

Degenerative changes in mouse sciatic nerves: Electrophoretic and electrophysiologic characterizations

Abstract Mouse sciatic nerve degeneration was studied following various types of imposed damage. Gross characterizations of nerve weight and neural conduction changes were obtained. Slab gel, SDS-polyacrylamide electrophoresis was used for evaluating altered protein concentrations in degenerating nerve. Separate electrophoretic examinations were completed on experimental distal and proximal nerve samples and on contralateral control nerve samples. More than 40 major protein bands were reliably resolved by electrophoresis. During nerve degeneration, some proteins exhibited decreased whole-nerve concentrations whereas other proteins increased. Degenerative changes were most pronounced in nerve segments distal to the site of damage. The undamaged control nerves contralateral to the injured nerves showed what appeared to be compensatory changes including the appearance of proteins not resolved in normal control nerves. Simple subcellular fractionations and specific tissue dissections provided information regarding the major sources of proteins resolved in whole-nerve samples. Comparisons of the different types of damage used for initiating degeneration revealed temporal separation between decremental and incremental protein alterations associated with degeneration. A temporal difference also was observed for protein changes in proximal compared to distal nerve segments during degeneration. The protein changes are related to specific degenerative events associated with nerve damage.

Alterations in the mechanical properties of peripheral nerve following crush injury

The mechanical properties of injured nerves have been studied. At specific times following unilateral nerve crush, the sciatic nerves of mice were tested mechanically. Photographs and longitudinal force measurements were obtained as nerve segments were elongated to mechanical failure. Stress and strain at the proportional limit and apparent elastic modulus were used as indicators of strength, elasticity and stiffness. Injury led to time-dependent increases in strength and stiffness and decreases in elasticity. These changes were apparent in both damaged and contralateral, undamaged nerves. Many of the changes appear to be related to the epineurium. Some mechanical changes in nerve could have important consequences for the integrity and function of nerves and mechanically interfaced structures.

Structural properties of spinal nerve roots: Biomechanics

The biomechanics of spinal nerve roots obtained from normal and nerve-crushed mice were evaluated. Photographs and longitudinal force measurements were taken as nerve roots were elongated through mechanical failure. Proportional limit stress and strain as well as the apparent modulus were calculated from photographic and force measurements to characterize nerve root strength, elasticity, and stiffness, respectively. Resulting mechanical data were indicative of an extremely weak material. Comparisons of nerve and nerve root mechanical properties revealed major differences. While nerve root elasticity was comparable to nerve, nerve root strength was only 10% that of nerve and root stiffness was only 20% of nerve values. Differences in nerve and root mechanics are attributed to the large discrepancies in relative amounts of connective tissue. Also in sharp contrast with peripheral nerve, unilateral nerve crush produced no significant alterations in root mechanics. Comparisons of nerve and nerve root strengths suggested possible pathways for dissipation of peripherally applied forces through epineurial and dural structures.

Memory traces: experimental separation by cycloheximide and electroconvulsive shock.

Mice given cycloheximide or saline were trained with a single trial. Electroconvulsive shock was administered to both groups at various times after training. Cycloheximide led to memory that decayed with time. Cycloheximide plus electroconvulsive shock produced complete amnesia at times when neither treatment alone produced amnesia. Only two types of processes appear to support memory storage in our study.

Triethyltin toxicity as a model for degenerative disorders

Triethyltin (TET) toxicity in mice was examined as a model for certain degenerative disorders. Spontaneous and elicited behavioral tests, electrophysiological measures and nervous system protein characterizations were used to study anomalies resulting from TET treatments. TET animals exhibited lowered spontaneous locomotor activity levels, increased sciatic nerve excitation threshold and conduction velocities, and increased power levels in the slower frequency components of their electroencephalograms. Performance in an active avoidance task suggest that the gross ultrastructural changes commonly seen in TET intoxication are not primarily responsible for the observed neurophysiological changes. Possible sites of action of TET, in both the peripheral and central nervous systems, that would produce these neurophysiological changes and the relationship of these changes to the behavioral symptoms are discussed.

Neural network prediction of three-dimensional unsteady separated flowfields

Unsteady surface pressures were measured on a wing pitching beyond static stall. Surface pressure measurements confirmed that the pitching wing generated a rapidly evolving, three-dimensional unsteady surface pressure field. Using these data, both linear and nonlinear neural networks were developed. A novel quasilinear activation function enabled extraction of a linear equation system from the weight matrices of the linear network. This equation set was used to predict unsteady surface pressures and unsteady aerodynamic loads. Neural network predictions were compared directly to measured surface pressures and aerodynamic loads. The neural network accurately predicted both temporal and spatial variations for the unsteady separated flowfield as well as for the aerodynamic loads. Consistent results were obtained using either the linear or nonlinear neural network. In addition, fluid mechanics modeled by the linear equation set were consistent with established vorticity dynamics principles.

Accomplished Insect Fliers

The flight characteristics of dragonflies, and to a lesser extent hawk moths, have been summarized. Wing kinematics, aerodynamic force generation and flow-wing interactions are presented. It is clear that these insects generate and use unsteady separated flow structures to support flight. Prominent vortex-wing interactions are routinely documented in conjunction with significant force generation. The wing geometry and kinematics dictate optimal unsteady flow generation as long as the wingbeat frequencies are maintained within prescribed ranges. The dragonfly appears able to readily switch between the use of unsteady flows and the use of more conventional steady state aerodynamics. The latter is used for gliding, a major element of dragonfly territoriality defense as seen in patrolling. The hawk moth appears to use similar unsteady flow strategies but doesn’t exploit gliding. What we believe we have observed is (1) a mechanistic, self-correcting device for creating unsteady flows, (2) a set of devices for using these flows and (3) a set of principles for unsteady flow exploitation by other biological flight systems.

Unsteady Flow Separation and Attachment Induced by Pitching Airfoils

Abstract : The dynamics of induced, separated vortices generated from sinusoidal airfoil oscillations were examined across a range of unsteady flow parameters. Leading edge vortical initiation, development, and interaction with trailing edge vorticity were summarized via stroboscopic flow visualization and hotwire anemometry. Results indicate the sensitivity of vortical development at both leading and trailing edges to reduced frequency parameter and magnitude of oscillation angle. Certain optimal parametric conditions resulted in dramatic interactions of leading and trailing edge vorticity. At diminished oscillation angles, separated flow attachment was evident in the absence of the large induced vortical structures characteristic of large oscillation amplitudes. (sdw)