Development Of A Slide-Rolling Contact Fatigue Tester

Contact fatigue failure is a common problem experienced in many applications such as bearings, gears and railway tracks. In recent years, research companies have developed finishing processes which aim to improve a component\u27s contact fatigue life. One such process has been patented by REM Chemicals in Texas. Preliminary contact fatigue tests have shown that this superfinishing process could potentially improve a component’s contact fatigue life by 300%. Before this technology can move from the laboratory to an industrial platform, more tests are needed to verify the claim. To the best of the author’s knowledge, no standard process or test machine exists to assess the fatigue endurance of superfinished contacting surfaces. The objective of this thesis is to discuss the completion and verification of a sliding-rolling contact fatigue (S-RCF) test rig. A majority of the development and fabrication was performed by a group of students at the University of North Dakota before May 2007. After this, completion of the tester was finished by the graduate student of this thesis. Unlike other contact fatigue testers built for specific purposes, the proposed tester allows for more flexible testing parameters such as any combination of slide-roll ratio between the surfaces, any operating speed and dry or lubricated testing. For failure detection, the proposed tester is equipped with a state-of-the-art eddy current crack detection system. However, it can be easily modified to use ultrasonic or vibration based crack detection devices. The eddy current crack detection system can also be used to monitor and investigate crack growth for different materials, levels of superfinish and operating conditions. Three preliminary tests on a common gear material (A1S1 8620 steel) were performed mechanical limits as well as the software performance of the tester. Two of the 8620 specimens exhibited signs of failure during testing, while one specimen was suspended after running for several days. While the last specimen was being tested, a shaft broke and further testing could not be performed. The tester failure was caused due to poor manufacturing of the shafts and a slight misalignment of the rollers. During the three tests, the various systems of the S-RCF tester were left running for several days and only minor problems were found. These problems were either inconsequential or fixed. Several Matlab scripts were developed and modified to control the tester and analyze the data online and offline. The S-RCF tester has a few components that need to be fixed before further testing can be performed. Two options exist to continue testing. The first option is to repair the current S-RCF tester and continue testing. The second option is to design a second generation machine with several upgrades and improvements. Either option will provide the University of North Dakota\u27s Engineered Surfaces Center the ability to test and compare the fatigue endurance for different surface finishes

Data Processing in Multiport-Based Reflectometer System

The paper describes operations with DC output voltage of multiport based system. Proposed system is based on the same principle as common six ports systems, however the used coupler has more outputs. This allows extension of bandwidth and higher precision of the measurement. To process measured data standard six port system calculations are used. To get more accurate results than in the case of simple six port system additional statistical methods can be used. The higher number of outputs produces large amount of measurement and calibration data, however using described technique this amount of data were reduced

Mast cell clones: a model for the analysis of cellular maturation.

Cloned mouse mast cells resemble, by ultrastructure, immature mast cells observed in vivo. These mast cell clones can be grown in the absence of any other cells, facilitating direct investigations of their biochemistry and function. We find that cloned mast cells express plasma membrane receptors (Fc epsilon R) that bind mouse IgE with an equilibrium constant (KA) similar to that of normal mouse peritoneal mast cells. In addition, cloned mast cells do not display detectable la antigens and cannot enhance lg secretion when added to lymphocyte cultures or mediate natural killer lysis. In the presence of 1 mM sodium butyrate, cloned mast cells stop dividing and acquire abundant electron-dense cytoplasmic granules similar to those of mature mast cells. Their histamine content increases concomitant with cytoplasmic granule maturation and may exceed that of untreated mast cells by 50-fold. Unlike peritoneal mast cells, cloned mast cells incorporate 35SO4 into chondroitin sulfates rather than heparin. These findings demonstrate that, unlike fully differentiated mouse peritoneal mast cells, cloned immature mouse mast cells contain no heparin and low levels of histamine. In addition, they establish that high-affinity Fc epsilon R are expressed early in mast cell maturation, well before completion of cytoplasmic granule synthesis and mediator storage

Epidemiology and potential preventative measures for viral infections in children with malignancy and those undergoing hematopoietic cell transplantation.

In pediatric patients with malignancy and those receiving hematopoietic stem cell transplants, bacterial and fungal infections have been the focus of fever and neutropenia episodes for decades. However, improved diagnostic capabilities have revealed viral pathogens as a significant cause of morbidity and mortality. Because of limited effective antiviral therapies, prevention of viral infections is paramount. Pre-exposure and post-exposure prophylaxis and antiviral suppressive therapeutic approaches are reviewed. Additionally, infection control practices specific to this patient population are discussed. A comprehensive approach utilizing each of these can be effective at reducing the negative impact of viral infections

“Changing Relationships with Wilderness: A New Focus for Research and Stewardship

Wilderness managers strive to provide quality recreation experiences. Because of this commitment, a need exists to further incorporate experiential aspects into current planning and management frameworks. This article suggests a focus on relationships with wilderness, moving beyond the examination of single transactions with a setting toward a consideration of the dynamic engagements visitors accumulate with wilderness over time. Understanding these relationships relative to social and cultural change may allow managers to incorporate diverse meanings into management planning and provide better protection of wilderness characte

Spectroscopy of PTCDA attached to rare gas samples: clusters vs. bulk matrices. I. Absorption spectroscopy

The interaction between PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) and rare gas or para-hydrogen samples is studied by means of laser-induced fluorescence excitation spectroscopy. The comparison between spectra of PTCDA embedded in a neon matrix and spectra attached to large neon clusters shows that these large organic molecules reside on the surface of the clusters when doped by the pick-up technique. PTCDA molecules can adopt different conformations when attached to argon, neon and para-hydrogen clusters which implies that the surface of such clusters has a well-defined structure and has not liquid or fluxional properties. Moreover, a precise analysis of the doping process of these clusters reveals that the mobility of large molecules on the cluster surface is quenched, preventing agglomeration and complex formation

Asteroid flux towards circumprimary habitable zones in binary star systems: I. Statistical Overview

So far, multiple stellar systems harbor more than 130 extra solar planets. Dynamical simulations show that the outcome of planetary formation process can lead to various planetary architecture (i.e. location, size, mass and water content) when the star system is single or double. In the late phase of planetary formation, when embryo-sized objects dominate the inner region of the system, asteroids are also present and can provide additional material for objects inside the habitable zone (hereafter HZ). In this study, we make a comparison of several binary star systems and their efficiency to move icy asteroids from beyond the snow-line into orbits crossing the HZ. We modeled a belt of 10000 asteroids (remnants from the late phase of planetary formation process) beyond the snow-line. The planetesimals are placed randomly around the primary star and move under the gravitational influence of the two stars and a gas giant. As the planetesimals do not interact with each other, we divided the belt into 100 subrings which were separately integrated. In this statistical study, several double star configurations with a G-type star as primary are investigated. Our results show that small bodies also participate in bearing a non-negligible amount of water to the HZ. The proximity of a companion moving on an eccentric orbit increases the flux of asteroids to the HZ, which could result into a more efficient water transport on a short timescale, causing a heavy bombardment. In contrast to asteroids moving under the gravitational perturbations of one G-type star and a gas giant, we show that the presence of a companion star can not only favor a faster depletion of our disk of planetesimals but can also bring 4 -- 5 times more water into the whole HZ.Comment: Accepted for publication in A&

Relativistic effects in the chaotic Sitnikov problem

We investigate the phase space structure of the relativistic Sitnikov problem in the first post-Newtonian approximation. The phase space portraits show a strong dependence on the gravitational radius which describes the strength of the relativistic pericentre advance. Bifurcations appearing at increasing the gravitational radius are presented. Transient chaotic behavior related to escapes from the primaries are also studied. Finally, the numerically determined chaotic saddle is investigated in the context of hyperbolic and non-hyperbolic dynamics as a function of the gravitational radius.Comment: 8 pages, 11 figure

Dynamical Stability and Habitability of Gamma Cephei Binary-Planetary System

It has been suggested that the long-lived residual radial velocity variations observed in the precision radial velocity measurements of the primary of Gamma Cephei (HR8974, HD222404, HIP116727) are likely due to a Jupiter-like planet around this star (Hatzes et al, 2003). In this paper, the orbital dynamics of this plant is studied and also the possibility of the existence of a hypothetical Earth-like planet in the habitable zone of its central star is discussed. Simulations, which have been carried out for different values of the eccentricity and semimajor axis of the binary, as well as the orbital inclination of its Jupiter-like planet, expand on previous studies of this system and indicate that, for the values of the binary eccentricity smaller than 0.5, and for all values of the orbital inclination of the Jupiter-like planet ranging from 0 to 40 degrees, the orbit of this planet is stable. For larger values of the binary eccentricity, the system becomes gradually unstable. Integrations also indicate that, within this range of orbital parameters, a hypothetical Earth-like planet can have a long-term stable orbit only at distances of 0.3 to 0.8 AU from the primary star. The habitable zone of the primary, at a range of approximately 3.1 to 3.8 AU, is, however, unstable.Comment: 25 pages, 7 figures, 3 tables, submitted for publicatio