Reynolds number limits for jet propulsion: A numerical study of simplified jellyfish

The Scallop Theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number = 0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers (Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the two-dimensional Navier Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Reynolds numbers between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re < 10. Similarly, the work required to generate the pulsing motion increases significantly for Re < 10. When compared actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism

Leaf roll-up and aquaplaning in strong winds and floods

Flexible plants, fungi, and sessile animals are thought to reconfigure in the wind and water to reduce the drag forces that act upon them. In strong winds, for example, leaves roll up into cone shapes that reduce flutter and drag when compared to paper cut-outs with similar shapes and flexibility. During flash floods, herbaceous broad leaves aquaplane on the surface of the water which reduces drag. Simple mathematical models of a flexible beam immersed in a two-dimensional flow will also reconfigure in flow. What is less understood is how the mechanical properties of a two-dimensional leaf in a three-dimensional flow will passively allow roll up and aquaplaning. In this study, we film leaf roll-up and aquaplaning in tree and vine leaves in both strong winds and water flows

Exploiting Structural Complexity for Robust and Rapid Hyperspectral Imaging

This paper presents several strategies for spectral de-noising of hyperspectral images and hypercube reconstruction from a limited number of tomographic measurements. In particular we show that the non-noisy spectral data, when stacked across the spectral dimension, exhibits low-rank. On the other hand, under the same representation, the spectral noise exhibits a banded structure. Motivated by this we show that the de-noised spectral data and the unknown spectral noise and the respective bands can be simultaneously estimated through the use of a low-rank and simultaneous sparse minimization operation without prior knowledge of the noisy bands. This result is novel for for hyperspectral imaging applications. In addition, we show that imaging for the Computed Tomography Imaging Systems (CTIS) can be improved under limited angle tomography by using low-rank penalization. For both of these cases we exploit the recent results in the theory of low-rank matrix completion using nuclear norm minimization

Effects of a Geographically-Targeted Intervention and Creative Outreach to Reduce Shelter Intake in Portland, Oregon

Animal shelters focus much of their efforts towards decreasing euthanasia and one of the best ways to reduce euthanasia risk may be to prevent cats and dogs from ever entering a shelter. This study, conducted in Portland, Oregon, relied on the capabilities of Geographic Information Systems (GIS) to precisely and scientifically identify an intervention area (with high shelter intake) and to identify control areas to compare the project results with community-wide trends. The intervention itself was designed and implemented in a comprehensive way by seeking numerous paths to engage pet owners and reduce shelter intake of cats and Pit Bull type dogs. This research highlighted the ability of Geographic Information Systems (GIS) to significantly improve a community's capacity to identify the most appropriate locations to focus resources and to closely track and measure interventions. Portland's targeted intervention to reduce shelter intake utilized many outreach tools with varying levels of impact. The overall intervention yielded a reduction in intake of owned cats that was greater in total numbers and percentage than four control areas. Furthermore, this work identified a percentage of cat spay/neuter out of the estimated number of owned, originally intact cats within the intervention and control areas. As percentages approached or surpassed 20%, those areas realized larger intake reductions than control areas with lower percentages

The Influence of Test Colors on the Color Rendering Index Maximization in a Three Component Spectral Power Distribution

This thesis describes the technique of principle component analysis as applied to determining if a combination of three characteristic vectors would account for an underlying structure in the eight color test objects specified by the CIE for calculation of the color rendering index (CRI). Anticipated was that three vectors would account for 100 % of the variance in the eight test objects; however it was determined that three vectors account for only 96 % of the variance. Since the analysis of the reflectance functions showed no dependence within the functions a 3^3 factorial experiment was conducted. Its purpose was to determine if the point of maximization of CRI in a three component spectral power distribution would be at 610, 540, and 450 nm when using metameric gray objects. This was postulated by Mr. Thornton in his paper Luminosity and the Color Rendering Capability of White Light . The analysis of the resulting response surface indicated that the maximization point was not the same but if a valid point exists it lies outside the experimental boundaries of the experiment