Stress Rupture Behavior of Silicon Carbide Coated, Low Modulus Carbon/Carbon Composites

The disadvantages of carbon-carbon composites, in addition to the oxidation problem, are low thermal expansion, expensive fabrication procedures, and poor off axis properties. The background of carbon-carbon composites, their fabrication, oxidation, oxidation protection and mechanical testing in flexure are discussed

The transition of ground-based space environmental effects testing to the space environment

The goal of the space flight program at the Center for Commercial Development of Space (CCDS)--Materials for Space Structures is to provide environmentally stable structural materials to support the continued humanization and commercialization of the space frontier. Information on environmental stability will be obtained through space exposure, evaluation, documentation, and subsequent return to the supplier of the candidate material for internal investigation. This program provides engineering and scientific service to space systems development firms and also exposes CCDS development candidate materials to space environments representative of in-flight conditions. The maintenance of a technological edge in space for NASA suggests the immediate search for space materials that maintain their structural integrity and remain environmentally stable. The materials being considered for long-lived space structures are complex, high strength/weight ratio composites. In order for these new candidate materials to qualify for use in space structures, they must undergo strenuous testing to determine their reliability and stability when subjected to the space environment. Ultraviolet radiation, atomic oxygen, debris/micrometeoroids, charged particles radiation, and thermal fatigue all influence the design of space structural materials. The investigation of these environmental interactions is the key purpose of this center. Some of the topics discussed with respect to the above information include: the Space Transportation System, mission planning, spaceborne experiments, and space flight payloads

Effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientation of (0(2),90(2))2S and (90(2),0(2))2S are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0 deg ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the 'apparent' strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to +85 C, 500 cycles). Mechanical cycling (0 to 50 percent of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue

The Social Structure of the Information Systems Collaboration Network: Centers of Influence and Antecedents of Tie Formation

In this study, we examine the historical information systems research collaboration network. We build the network using coauthorship information in the Senior Scholars’ basket of eight journals from the publication of MISQ’s first issue in April, 1977, to November, 2015. The different journals vary widely in their network configurations. We examine the influence of gender homophily, geographic homophily, and field tenure heterophily on coauthorship in the network. From using exponential random graph modeling (ERGM) on a randomly selected subset of the network, we present preliminary evidence that suggests that ties in the IS collaboration network exhibit homophily according to gender and geography. Conversely, coauthorship seems to exhibit heterophily along the temporal dimension: short-tenured researchers in the field prefer to collaborate with long-tenured researchers. ERGM enables one to make statistical inferences concerning the influence of node attributes and structural variables on network formation, which is hard to do with logistical regression because network relationships violate the independence of observations assumption. We also reveal the current center of the IS collaboration network. Based on this center, we propose a metric to measure a researcher’s connectedness in the network

Lost Dunkirk

Lost Dunkirk The Lost Dunkirk project came out of a class called Digital History. Our main goal for this project was to digitize the history of some buildings of Dunkirk, NY and create a public Internet exhibit on Lost Dunkirk. In order to digitize the history of Dunkirk we used a website builder known as Omeka. We selected buildings that we felt had the most significance in a local perspective and we gave a brief history of each building that we chose. With each building’s history the group included pictures of the building from various perspectives and times. Each building had its own demise whether through local urban renewal and tear down, while others met their end through fire. Some of these buildings still stand today as a test of time but see a new purpose. Research for this project was done at the Dunkirk Historical Society as well as online and at the on campus archive. We spent hours going through many old newspapers and photographs to get the information we used. Through our research we discovered that each building had a significant place in the hearts of those from Dunkirk as well as some historical significance. The site that we built can be edited and is changing with new information being found

ENTRAINMENT DURING BICYCLE ERGOMETRY IN ELITE CYCLISTS

While it is widely accepted that ventilation increases abruptly at the onset of muscular exercise (D'Angelo and Torelli, 1971; Jensen, Vejby-Christensen and Petersen, 1972; Krogh and Lin~~ard, 1913) the control of the respiratory pattern, i.e., the relationship between ventilation (V', Vi', Ve'), tidal volume (Vt), and respiratory frequency (fR) or respiratory cycle times (Tt, Ti, Te) is not clearly understood (Wasserman, 1978). There are a number of factors, which may be classified as humoral, neurogenic, or neurohumoral, involved in respiratory regulation (Dejours, 1960), but the importance of any single factor is difficult to determine because of the associated problems of controlling for the other variables involved in the total response. One such factor is the coordination of the respiratory pattern to the movement pattern referred to as entrainment. The purpose of the present study was to examine the relationship between the variables that control the respiratory pattern and to test the hypothesis that entrainment would be more prevalent in athletes who were highly trained for a particular mode of exercise, based on a work minimization theory (Priban and Fincham, 1965; Yamashiro and Grodins, 1973; Cherniack, 1980), than in non-athletes unaccustomed to the exercise

RENAL DEPOSITION OF SOLUBLE IMMUNE COMPLEXES IN MICE BEARING B-16 MELANOMA : CHARACTERIZATION OF COMPLEXES AND RELATIONSHIP TO TUMOR PROGRESS

Histologic and immunofluorescence studies of the kidneys of mice bearing a progressive melanoma show a proliferative glomerulonephritis associated with immune complex deposition in the mesangium and along the glomerular basement membrane This immune complex disease is distinct from the age-associated disease of the C57BL/6J host strain and the complexes can be shown to consist of soluble tumor antigen and antitumor antibody. Furthermore, the intensity of IgG complex deposition correlates directly with tumor progress (size and metastases) and inversely with mononuclear leukocyte infiltration of the tumor. In vitro assays for lymphocyte cytotoxicity and humoral antibody were found to be less reliable indicators of tumor progress. The possible role of circulating soluble tumor antigen in modifying the immune response to tumors is discussed

QUANTITATIVE CLINICAL NEUROLOGICAL TESTING. I. A STUDY OF A BATTERY OF TESTS DESIGNED TO EVALUATE IN PART THE NEUROLOGICAL FUNCTION OF PATIENTS WITH MULTIPLE SCLEROSIS AND ITS USE IN A THERAPEUTIC TRIAL *

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73100/1/j.1749-6632.1965.tb20231.x.pd

Telomeres Cluster De Novo before the Initiation of Synapsis: A Three-dimensional Spatial Analysis of Telomere Positions before and during Meiotic Prophase

We have analyzed the progressive changes in the spatial distribution of telomeres during meiosis using three-dimensional, high resolution fluorescence microscopy. Fixed meiotic cells of maize (Zea mays L.) were subjected to in situ hybridization under conditions that preserved chromosome structure, allowing identification of stage-dependent changes in telomere arrangements. We found that nuclei at the last somatic prophase before meiosis exhibit a nonrandom, polarized chromosome organization resulting in a loose grouping of telomeres. Quantitative measurements on the spatial arrangements of telomeres revealed that, as cells passed through premeiotic interphase and into leptotene, there was an increase in the frequency of large telomere-to-telomere distances and a decrease in the bias toward peripheral localization of telomeres. By leptotene, there was no obvious evidence of telomere grouping, and the large, singular nucleolus was internally located, nearly concentric with the nucleus. At the end of leptotene, telomeres clustered de novo at the nuclear periphery, coincident with a displacement of the nucleolus to one side. The telomere cluster persisted throughout zygotene and into early pachytene. The nucleolus was adjacent to the cluster at zygotene. At the pachytene stage, telomeres rearranged again by dispersing throughout the nuclear periphery. The stagedependent changes in telomere arrangements are suggestive of specific, active telomere-associated motility processes with meiotic functions. Thus, the formation of the cluster itself is an early event in the nuclear reorganizations associated with meiosis and may reflect a control point in the initiation of synapsis or crossing over