Analysis of a substitute for the impact damper to damp near-resonant mechanical vibrations

This report investigates a substitute for the impact damper which, although highly effective in reducing vibration amplitudes of near-resonant mechanical systems, in operation causes often unacceptable intensive noise. The present damper consists of a piston free to move in a cylinder, at either end of which is a ball valve set to open at a preset pressure, and in the middle along its length an intake port. An approximate analytical study is made to determine the conditions for the existence of noiseless periodic operation of the damper, periodic operation without the occurence of impacts. This approach is based on the describing function method which harmonically linearizes the nonlinear damping force involved in the equations of motion of the system. The excitation force to produce this periodic operation and the response results from this operation may be predicted by this analytical approach. Digital simulation of the system is used to verify the predictions by analytical approach. A study on a given system indicates that appropriate design parameters may be selected for a damper of this type to obtain a reduction in response amplitude of the primary system at resonance to 1/5 of its value without the damper. This is essentially the reduction that might be obtained with a properly designed impact damper. Unlike the impact damper, the new damper is expected to operate relatively noiselessly --Abstract, pages ii-iii

TRACKING ANISOTROPIC OPTICAL TRACERS TO STUDY BIOPHYSICAL PROCESSES AND CYTOTOXICITY

We use anisotropic optical tracers (also called magnetically modulated optical nanoprobes – MagMOONs or MOONs for non-magnetic nanoprobes in this dissertation) to study biophysical processes such as enzyme-catalyzed cleavage through tissue, intracellular transport of these tracers and cytotoxicity based on this transport. The anisotropic optical properties cause these tracers to blink when rotating. This blinking is distinguishable from the background and can be tracked on a single-particle level in the absence of tissue, or for an ensemble average of tracers blinking through tissue. An alginate gel containing these tracers in the form of a thin film can be used as a sensor to detect alginate lyase, a protease of alginate gel. As the protease cleaves the gel, the tracers are released, free to rotate and give a blinking signal that can be tracked under the microscope. The tracers started blinking approximately 10 minutes after 2 mg/mL alginate lyase addition, and this blinking was clearly detected through up to 4 mm of chicken breast. Similar tracer-integrated gel films may potentially be employed to detect bacterial biofilm formation on medical implants by sensing specific proteases that either activate a related function or regulate biofilm formation. It can also be applied to other biosensors and drug delivery systems based on enzyme-catalyzed breakdown of gel components. For intracellular transport and cytotoxicity, we apply the advantages of rotational and translational single particle tracking in cytotoxicity studies by observing the tracers’ behavior with and without the presence of toxic substances. Both cyanide and 2-deoxy-D-glucose or azide and 2-deoxy-D-glucose combinations immediately inhibited intracellular motion in J774A.1 macrophages upon addition. This result suggested our method can potentially be applied to study cytotoxicity of particulate matter. More importantly, tracking simultaneously the tracers’ translation and rotation reveals interesting information about macrophage intracellular transport; for instance, tracers do not rotate when sliding along microtubules. The data analysis also confirmed that sliding periods contributed to a major portion of total movement but comprised a very small portion of total observation time

On hole approximation algorithms in wireless sensor networks

Routing holes in sensor network are regions without operating nodes. They may occur due to several reasons, including cases caused by natural obstacles or disaster suffering areas. Determining the location and shape of holes can help monitor these disaster events (such as volcano, tsunami, etc.) or make smart, early routing decisions for circumventing a hole. However, given the energy limit of sensor nets, the determination and dissemination of the information about the exact shape of a large hole could be unreasonable. Therefore, there are some techniques to approximate a hole by a simpler shape. In this paper, the authors analyze and compare two existing approximation approaches that are considered as the most suitable for the sensor network, namely the grid-based and the convex-hull-based approaches. And a new algorithm of the grid-based approach is also introduced. The performances of all the mentioned algorithms are under analysis and evaluation in both theoretical and experimental perspectives. The findings show that grid-based approach has advantages in saving network energy and providing a finer image of the hole while the convex hull approach is better for making a shorter hole-bypassing the route but not much