Dynamics of solid dispersions in oil during the lubrication of point of contacts. Part 2: Molybdenum disulfide

A Hertzian contact consisting of a steel ball in contact with a glass disk is lubricated with MoS2 dispersions and observed by optical microscopy at various slide/roll conditions. In general the behavior of MoS2 and graphite are similar. That is, the solids tend to enter the contact and form a film on the contacting surfaces whenever a rolling component of motion is used, but solid particles seldom enter the contact during pure sliding. The MoS2 has more pronounced plastic flow behavior than graphite. However, the polished steel ball is more readily scratched by MoS2 than by graphite. Under the conditions of these studies, lower friction and wear are observed with pure oil rather than with the dispersions. However under other conditions (such as different contact geometry or rougher surfaces) the solid lubricant dispersions might be beneficial

The influence of surface dents and grooves on traction in sliding EHD point contacts

Changes in traction, caused by dents and grooves on a highly polished ball,are investigated as these defects approach and go through sliding elastohydrodynamic point contacts. The contacts are formed with the ball loading against a transparent disk. The ball and thus the topographical features are held stationary at various locations in the vicinity and within the contact while the disk is rotating. These topographical features can cause substantial changes in the traction when compared to traction obtained with smooth surfaces

Effects of artificially produced defects on film thickness distribution in sliding EHD point contacts

The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness

Elastohydrodynamic contacts. Effects of dents and grooves on traction and local film thickness

Traction and film thickness were simultaneously measured under sliding elastohydrodynamic (EHD) conditions. The influence of surface topography was investigated by using simulated surfaces produced by depressing dents and grooves in highly polished steel balls. Significant changes in traction occurred depending on the orientation of the surface defects and their location with respect to the contact region. The results can be explained in terms of changes in overall film thickness and redistribution of pressure within the contact region due to micro-EHD effects. It can be concluded that the traction capability of mechanical components operating in thin film lubrication can be enhanced particularly by surface topographical orientation perpendicular to the surface motion. Associated with the higher traction are increases in local shear stress and normal stress as well as an increase in temperature at asperity sites. It is postulated that the local surface topography can become involved in run in or failure initiation even without actual asperity contact

Dynamics of solid dispersions in oil during the lubrication of point contacts. Part 1: Graphite

A Hertzian contact was lubricated with dispersed graphite in mineral oils under boundary lubrication conditions. The contact was optically observed under pure rolling, combined rolling and sliding, and pure sliding conditions. The contact was formed with a steel ball on the flat surface of a glass disk. Photomicrographs are presented which show the distribution of the graphite in and around the contact. Friction and surface damage are also shown for conditions when the base oils are used alone and when graphite is added to the base oils. Under pure rolling and combined rolling and sliding conditions, it is found that, for low speeds, a graphite film can form which will separate the contacting surfaces. Under pure sliding conditions, graphite accumulates at the inlet and sweeps around the contact, but very little of the graphite passes through the contact. The accumulated graphite appears to act as a barrier which reduces the supply of oil available to the contact for boundary lubrication. Friction data show no clear short term beneficial or detrimental effect caused by addition of graphite to the base oil. However, during pure sliding, more abrasion occurs on the polished balls lubricated with the dispersion than on those lubricated with the base oil alone. All observations were for the special case of a highly-polished ball on a glass surface and may not be applicable to other geometries and materials, or to rougher surfaces

The Effect of Dissolved Water on the Tribological Properties of Polyalkylene Glycol and Polyolester Oils

The effect of water dissolved in polyalkylene glycol and polyolester oils on the tribological behavior of two material contact pairs in three test environments is evaluated. The material contact pairs are M2 tool steel against 390 aluminum and M2 tool steel against gray cast iron. The three oils are a polyalkylene glycol (PAG) and two polyolester (PEl and PE2) oils. The test environments are R134a, air and argon. The tests are conducted in a specially designed high pressure tribometer which provides an accurate control of the test variables. The results indicate that the P AG oil performed better than the esters for both material contact pairs. The wear on the aluminum plates for the tests conducted with the P AG oil in all three environments is greatest at the lowest moisture content levels. From the stand point of friction and wear, it is beneficial to have a water content level of 5000 ppm or greater in the PAG oil when the plate material is 390 aluminum. The wear on the cast iron plates, when using a PAG oil as the lubricant showed a slight increase with water content in a R134a environment. This trend is opposite when air is the test environment. Both ester oils lubricated aluminum much better than the cast iron . The difference in the amount of wear can be as high as two orders of magnitude. This is probably due to the ability of the esters to form bidentate bonds with aluminum. Esters do not form such bonds with iron. The plate wear is greater for the PEl tests than for the PE2 tests for both material contact pairs. This is most likely due to the difference in the viscosity of the oils. In PE2 oil, water does not seem to affect the friction and wear of both aluminum/steel and cast iron/steel contacts when R134a is the test environment. On the contrary, for the aluminum/steel contacts, the water content significantly influences wear when argon or air is the test environment. For the cast iron/steel contacts, the wear is strongly influenced by the water content when the test is conducted in argon, but it is not influenced by the water content when the test is conducted in air.Air Conditioning and Refrigeration Center Project 0

Dynamic Characteristics of Externally Pressurized, Double-Pad, Circular Thrust Bearings with Membrane Restrictors

The dynamic characteristics of externally pressurized, double-pad, circula

Seismic activity and thermal regime of low temperature fumaroles at Mt. Vesuvius in 2004-2011: distinguishing among seismic, volcanic and hydrological signals

Seismological, soil temperature and hydrological data from Mt. Vesuvius are collected to characterize the present-day activity of the volcanic/hydrothermal system and to detect possible unrest-related phenomena. We present patterns of seismicity and soil temperature in the crater area during the period February 2004-December 2011. The temporal distribution of number and depth of Volcano-Tectonic earthquakes and the energy release are considered. Hourly data of soil temperature have been acquired since January 2004 in different locations along the rim and within the crater. The observed changes of temperature are studied to establish a temporal-based correlation with the volcanic activity and/or with external forcing, as variations of the regional and local stress field acting on the volcano or meteorological phenomena. The comparison between seismic activity and temperature data highlights significant variations possibly related to changes in fluid circulation in the hydrothermal system of the volcano. The common continuous observations start just before a very shallow earthquake occurred in August 2005, which was preceded by a thermal anomaly. This coincidence has been interpreted as related to fluid-driven rock fracturing, as observed in other volcanoes. For the successive temporal patterns, the seismicity rate and energy release are characterized by slight variations accompanied by changes in temperature. This evidence of reactivity of the fumarole thermal field to seismic strain can be used to discriminate between tectonic and volcanic signals at Mt. Vesuvius

Temozolomide for Anaplastic Astrocytoma: A Case Report of Aplastic Anemia, Sustained Treatment Response, and Spontaneous Marrow Recovery

Introduction:Temozolomide is an alkylating agent used in the treatment of high-grade glioma. Rarely, it can induce an aplastic anemia that is usually rapidly fatal if the patient is unable to undergo a bone marrow transplant. This is the first case report of a temozolomide-induced aplastic anemia in an anaplastic astrocyoma patient, and of spontaneous complete marrow recovery with supportive care.Presentation of Case: 21 year old Caucasian female presented with pancytopenia after 39 days of temozolomide at 75mg/m2/day concurrent with radiation. Hematologic nadir occurred and aplastic anemia was diagnosed 3 months after the first dose of temzolomide. She required multiple platelet and red cell transfusions in addition to granulocyte colony stimulating factor therapy. During this time, the patient also became pregnant and delivered a healthy baby. With supportive care, the patient's white cell count recovered after 6 months, red cell count after 1.5 years, and platelets after 3 years. Her tumour remains stable more than 4 years after temozolomide and radiation with no further treatment.Conclusions:Aplastic anemia may occur with low-dose temozolomide. Spontaneous marrow recovery using only supportive care is possible following temozolomide-induced aplastic anemia

Groundwater geochemistry of the Mt. Vesuvius area: implications for volcano surveillance and relationship with hydrological and seismic signals

Geochemical data obtained between 1998 and 2011 at the Mt. Vesuvius aquifer are discussed, focusing on the effects of both the hydrological regime and the temporal pattern of local seismicity. Water samples were collected in a permanent network of wells and springs located in the areas that are mostly affected by the ascent of magmatic volatiles, and their chemical composition and dissolved gas content were analyzed. As well as the geochemical parameters that describe the behavior of groundwater at Mt. Vesuvius, we discuss the temporal distribution of volcano-tectonic earthquakes. The seismological data set was collected by the stations forming the permanent and mobile network of the Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano (INGV-OV). Our analysis of seismic data collected during 1998-2011 identified statistically significant variations in the seismicity rate, marked by phases of decreasing activity from October 1999 to May 2001 and increasing activity from August 2004 to mid-2006. The water chemistry shows peculiar patterns, characterized by a changeable input of CO2-rich and saline water, which must be related to either a changing stress field or an increased input of CO2-rich vapor. The water chemistry data from 1999 to 2003 account for both higher fluid pressure (which induced the seismic crisis of 1999 that peaked with a 3.6-magnitude earthquake in October 1999) and the increased input of CO2-rich fluids. The highest emission of CO2 from the crater fumaroles and the corresponding increase in dissolved carbon in groundwater characterize the phase of low seismicity. The termination of the phase of intense deep degassing is associated with a change in water chemistry and a peculiar seismic event that was recorded in July 2003. All these seismic and geochemical patterns are interpreted according to temporal variations in the regional and local stress field