Numerical simulation of gas-lubricated journal bearings for microfabricated machines

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Includes bibliographical references (p. 203-208).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Numerical simulations of gas-lubricated journal bearings for microfabricated machines are performed with specialized tools. To maximize flexibility, an orbit method formulation is chosen for the primary tool. Its pseudospectral fluid equation solver enables run-time resolution adjustment while maintaining the efficiency advantage of spectral methods. A design framework is established for microfabricated bearings, including several new charts that reflect the unique constraints of MEMS. A duality between applied load and imbalance level is demonstrated and a method for experimentally determining appropriate loads for unknown imbalance is suggested. A large-amplitude whirling mode is shown to exist on both sides of the fixed-point threshold speed, in agreement with experimental observation. A quasi-static method for calculating shock tolerance is suggested and evaluated against unsteady simulations. Simulations of loads applied via non-circumferentially-uniform pressure at the bearing end are shown to increase the attitude angle and decrease the allowable nondimensional mass compared to the equivalent gravity-loaded case. Furthermore, the associated axial pressure gradients are shown to produce a hydrostatic stiffness via inertial effects. A nondimensional model is constructed for this stiffness and its dependence on various parameters is studied. It is shown that the load capacity advantage reported in the literature for noncircular bearings can be canceled by microfabrication constraints. The stability advantage, however, survives. Tapered axial clearance is shown to have an extremely deleterious effect on performance while bowed clearance proves less detrimental. Navier-Stokes solutions of infinite-length bearings with unity inertial parameters are performed using a second specially-built tool. Little change is found in the steady-state results from inertial and curvature effects in the MIT microengine’s parameter space.by Edward Stanley Piekos.Ph.D

The terminal branch of the posterior interosseous nerve : an anatomic and histologic study

Background: The aim of this study was to evaluate the terminal branch of the posterior interosseous nerve (PIN) by anatomically and histologically assessing the number, dimension, and area of its individual fascicles, by determining the dimension and area of the whole nerve itself, and by calculating the nerve density ratio (ratio of the sum of the areas of individual fascicles to the area of the whole nerve) of the terminal branch of the PIN. Materials and methods: Twenty-eight terminal branches of the PIN nerve samples were collected from patients undergoing partial denervation of the wrist. The nerve samples were fixed in 10% buffered formalin and stained with haematoxylin and eosin to visualise their nerve bundles. Quantitative analysis of individual fascicles and the whole nerve itself were carried out. Results: Ten nerve samples (35.7%) had one single fascicle (group 1) while the remaining 18 nerve samples (64.3%) contained 2-9 fascicles (group 2). The difference in the sum of the areas of individual fascicles between the two groups did not constitute a statistical difference. Statistically significant between-group differences (p < 0.05) were seen in the area of whole nerve, the ratio of fascicle area to the nerve cross-sectional area and the cross-section maximum nerve length and width. Conclusions: The number of nerve fascicles in the terminal branch of the PIN does not affect the overall size of the nerve. The majority of the volume of multi-fascicle nerves, therefore, primarily consists of the internal perineurium. However, due to the low number of nerves, this question cannot be clearly answered. This sets a further direction for further research on a larger group

Accelerating DSMC data extraction.

In many direct simulation Monte Carlo (DSMC) simulations, the majority of computation time is consumed after the flowfield reaches a steady state. This situation occurs when the desired output quantities are small compared to the background fluctuations. For example, gas flows in many microelectromechanical systems (MEMS) have mean speeds more than two orders of magnitude smaller than the thermal speeds of the molecules themselves. The current solution to this problem is to collect sufficient samples to achieve the desired resolution. This can be an arduous process because the error is inversely proportional to the square root of the number of samples so we must, for example, quadruple the samples to cut the error in half. This work is intended to improve this situation by employing more advanced techniques, from fields other than solely statistics, for determining the output quantities. Our strategy centers on exploiting information neglected by current techniques, which collect moments in each cell without regard to one another, values in neighboring cells, nor their evolution in time. Unlike many previous acceleration techniques that modify the method itself, the techniques examined in this work strictly post-process so they may be applied to any DSMC code without affecting its fidelity or generality. Many potential methods are drawn from successful applications in a diverse range of areas, from ultrasound imaging to financial market analysis. The most promising methods exploit relationships between variables in space, which always exist in DSMC due to the absence of shocks. Disparate techniques were shown to produce similar error reductions, suggesting that the results shown in this report may be typical of what is possible using these methods. Sample count reduction factors of approximately three to five were found to be typical, although factors exceeding ten were shown on some variables under some techniques

The anatomical landmarks effective in the localisation of the median nerve during orthopaedic procedures

Background: The aim of this study was to create a safe zone for surgeons who perform procedures in the wrist to avoid iatrogenic damage to the median nerve (MN) by identifying anatomical landmarks using ultrasound (USG).Materials and methods: We measured the distances between the MN and two easily identifiable anatomical landmarks at the level of the proximal border of carpal ligament using USG.Results: A total of 57 volunteers (n = 114 upper limbs) were included in this study. Our main findings revealed that the distance from the flexor carpi radialis tendon to MN (FCR-MN) was 7.87 mm (95% confidence interval 7.37–8.37) and the distance from flexor carpi ulnaris tendon to MN (FCU-MN) was 19.09 mm (95% confidence interval 18.51–19.67).Conclusions: The tendons of FCR and FCU are easily identifiable landmarks that can be distinguished using simple palpation. Based on our USG findings, the area around FCR should be carefully navigated to avoid iatrogenic injury to the MN during surgical procedures around the carpal tunnel

The terminal branch of the posterior interosseous nerve: an anatomic and histologic study

Background: The aim of this study was to evaluate the terminal branch of the posterior interosseous nerve (PIN) by anatomically and histologically assessing the number, dimension, and area of its individual fascicles, by determining the dimension and area of the whole nerve itself, and by calculating the nerve density ratio (ratio of the sum of the areas of individual fascicles to the area of the whole nerve) of the terminal branch of the PIN. Materials and methods: Twenty-eight terminal branches of the PIN nerve samples were collected from patients undergoing partial denervation of the wrist. The nerve samples were fixed in 10% buffered formalin and stained with haematoxylin and eosin to visualise their nerve bundles. Quantitative analysis of individual fascicles and the whole nerve itself were carried out. Results: Ten nerve samples (35.7%) had one single fascicle (group 1) while the remaining 18 nerve samples (64.3%) contained 2–9 fascicles (group 2). The difference in the sum of the areas of individual fascicles between the two groups did not constitute a statistical difference. Statistically significant between-group differences (p &lt; 0.05) were seen in the area of whole nerve, the ratio of fascicle area to the nerve cross-sectional area and the cross-section maximum nerve length and width. Conclusions: The number of nerve fascicles in the terminal branch of the PIN does not affect the overall size of the nerve. The majority of the volume of multi-fascicle nerves, therefore, primarily consists of the internal perineurium. However, due to the low number of nerves, this question cannot be clearly answered. This sets a further direction for further research on a larger group

Using evaluation techniques and performance claims to demonstrate public relations impact: An Australian perspective

Public relations professionals use many methods to demonstrate their contribution to organizational goals, yet it is unclear how their attitudes towards evaluation and the reporting of success matches real outcomes. Ten years after the International Public Relations Association produced an evaluation gold paper, this study combines research on Australian practitioners’ evaluation practices and attitudes, and data from industry awards to identify how practitioners demonstrate their accountability. Data suggest that despite the attention paid to evaluation by the academy and industry, practitioners still focus on measuring outputs, not outcomes to demonstrate performance and continue to rely heavily on media-based evaluation methods