An in situ correlative STEM-EDS and HRTEM based nanoscale chemical characterization of solid-liquid interfaces in an aluminium alloy.

The chemistry and the structure of solid-liquid interface in an Al-Si based alloy during high temperature phase transformation were characterized at nanoscale using scanning Transmission Electron Microscopy-EDS and HRTEM. Such studies were until recently limited by large sample drift associated with conventional heating holders. This study was made possible thanks to the modern low-drift MEMS-chip based localized heating technology. The results reveal that (i) the structural interface between solid (111) oriented Si phase and the liquid phase (i.e. decay of crystalline order) coexisting at 600°C is 3.2 nm wide (ii) the STEM-EDS chemical maps show inhomogeneous distribution of the elements with the solid phase being rich in Si and the liquid phase rich in Al (iii) the HRTEM and the HAADF images display respectively dark and bright intensity bands along the interface which could be due to apparent enrichment of Cu at the interface region resulting in enhanced amplitude-contrast (darker band in HRTEM) and Z-contrast (bright band in HAADF) and (iv) intriguingly, the concentration profiles within (i.e. compositional width) and across the solid-liquid interface display element-specific complex and asymmetric variation in the chemical widths.

Crystallography of a new metastable phase in Zr-N alloy.

Selected-area and convergent-beam electron diffraction were used to determine the lattice, point and space groups of a new metastable phase (designated the pi phase) in the Zr-N system. The pi phase has a body-centered tetragonal lattice with a approximately 0.66 nm and a c/a ratio of 0.81. The point-group symmetry of the phase is 4/mmm and the space group is I4/mmm.

In situ transmission-electron-microscopy investigation of melting in submicron Al-Si alloy particles under electron-beam irradiation.

In situ heating and electron-beam irradiation in the transmission electron microscope were performed to study melting of submicron Al-11.6 at. % Si particles supported on a C thin film. It was found that electron irradiation could be used to melt the particles, even when the hot-stage sample holder was kept at a much lower temperature ( approximately 125 degrees C) than the initial melting point of the particles. Comparison between the experimentally observed melting behavior and analytical calculations indicate that melting of the submicron Al-Si particles under electron-beam irradiation is caused by a temperature rise due to electron thermal spikes in the particles and poor thermal conduction away from the particles. These results have important implications in transmission electron microscopy studies of nanoparticles supported on thin films or poorly conducting substrates.

Atomic-level observation of disclination dipoles in mechanically milled, nanocrystalline Fe.

Plastic deformation of materials occurs by the motion of defects known as dislocations and disclinations. High-resolution transmission electron microscopy was used to directly reveal the individual dislocations that constitute partial disclination dipoles in nanocrystalline, body-centered cubic iron that had undergone severe plastic deformation by mechanical milling. The mechanisms by which the formation and migration of such partial disclination dipoles during deformation allow crystalline solids to fragment and rotate at the nanometer level are described. Such rearrangements are important basic phenomena that occur during material deformation, and hence, they may be critical in the formation of nanocrystalline metals by mechanical milling and other deformation processes.

A tilting procedure to enhance compositional contrast and reduce residual diffraction contrast in energy-filtered TEM imaging of planar interfaces.

This paper systematically demonstrates that energy-filtered transmission electron microscope (EFTEM) images of a planar interface between two single crystals have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the electron beam is parallel to the interface, but not directly on a zone axis. This off-axis orientation reduces diffraction contrast in the unfiltered (and zero-loss) image, which in turn, reduces residual diffraction contrast in single energy-filtered TEM (EFTEM) images, thickness maps, jump-ratio images, and elemental maps. Most importantly, this procedure produces EFTEM images that are more directly interpretable and, in most cases, possess superior spatial resolution compared to EFTEM images acquired directly on a zone axis.

Human immunodeficiency virus infection and hepatitis: biosafety in radiology.

Radiologists frequently perform invasive diagnostic and therapeutic procedures involving needles and/or vascular access, and often they do so in darkened rooms. Therefore, they are at risk of exposure to blood-borne pathogens. The risk of HIV infection with a single sharp injury is low (0.3%), and on average 99.7% of exposures will not result in infection. However, this seroconversion rate is increased when a high volume of blood or a high concentration of virus is inoculated, and it is decreased by 79% when postexposure prophylaxis is used. An estimated 800,000 needle-stick injuries and other injuries from sharp objects to health care workers occur annually in the United States (25). Approximately 16,000 of these involve HIV-contaminated blood, and even more are contaminated with HBV or HCV (46). Needle-stick injury therefore poses the single greatest risk to health care workers regarding occupational transmission of HIV. Because most patients in the radiology department have an unknown HIV or hepatitis serostatus, all patients should be regarded as potentially infectious, and precautions should be universal. In fact, the 1991 OSHA ruling made compliance with the CDC Universal Precautions Guidelines the enforceable national standard. Real-time oral communication among all members of the radiology team and scrupulous attention to safe technique are absolutely essential. Radiologists are not in agreement regarding the use of precautions against injury with a sharp object and splashing (47-50). Many have adapted some of their habits to conform well to the CDC and OSHA guidelines regarding universal precautions, but some remain skeptical regarding the risk of exposure to themselves. Consequently, in some areas resistance to the above recommendations persists. However, the data to date provide a compelling argument for protection against occupational exposure to blood either by percutaneous sharp injury or splashing on mucous membranes or interrupted skin. A number of resources were made available in early 1997 for easy access to the most current data regarding occupational transmission of HIV or hepatitis. For instance, the CDC has a World Wide Web site (http://www.cdc.gov) and a facsimile information service through the Hospital Infections Program directory (telephone 404-332-4565). Also, the National AIDS Clearinghouse can be reached by telephone (800-458-5231), as can the HIV/AIDS Treatment Information Service (800-448-0440). The postexposure prophylaxis protocol used at the University of California, San Francisco, can be reviewed by visiting its World Wide Web site at http://epi-center.ucsf.edu. And up-to-date information is available to both Veterans Administration and other health care staff worldwide by J. Michael Howe, MSLS, of the AIDS Information Center, a service of the VA HIV/AIDS National Training Program, located at the Veterans Administration Medical Center, San Francisco, University of California, San Francisco (hivinfo@itsa.ucsf.edu).

Effect of crystal and beam tilt on simulated high-resolution TEM images of interfaces.

The effects of crystal and beam tilt on high-resolution transmission electron microscope (HRTEM) images of planar coherent interfaces were investigated by multislice image simulations. It was found that a beam tilt of 0.5 Bragg angle (theta B) was sufficient to introduce detrimental artifacts into most images of interfaces in crystals only 1/8 xi 000 thick, while crystal tilt had a much smaller effect even for crystals 1 xi 000 thick. Effects produced in HRTEM images of interfaces by crystal and beam tilt included the introduction of additional periodicities and loss of compositional detail across a boundary, translation of a boundary from its actual position, and apparent mismatch of atomic planes across a perfectly coherent interface. These results indicate that alignment of the electron beam parallel to the optic axis is critical for reliable HRTEM imaging of interfaces in materials. Techniques for obtaining accurate alignment are also discussed.

Choroidal involvement in lymphomatoid granulomatosis.

A 13-year-old boy with evidence of pulmonary lymphomatoid granulomatosis developed monocular diplopia. Fluorescein angiography revealed bilateral choroidal involvement. Following treatment with vincristine, cyclophosphamide, and prednisone his diplopia resolved and the angiographic appearances returned to normal.

Mayonnaise, Sandwiches and Salmonella.

Sandwiches, prepared with home-cooked or commercially purchased turkey meat and made with or without commercially available mayonnaise, were inoculated with approximately 600-700 cells of a nalidixic acid-resistant strain of Salmonella typhimurium per gram of each sandwich. The sandwiches were incubated at 4, 21, and 30 C and samples analyzed at 4, 8 and 24 h for the number of S. typhimurium cells. Significant increases in the number of S. typhimurium cells were found in sandwiches prepared without mayonnaise and containing home cooked turkey meat after 8 h of incubation at 30 C and 24 h of incubation at 21 or 30 C. The increase in numbers of S. typhimurium in sandwiches prepared with commercially processed turkey meat was significantly lower than the increase in sandwiches prepared with home-cooked turkey meat. Mayonnaise had a significant inhibitory effect on growth of S. typhimurium in sandwiches prepared with turkey breast meat; however, mayonnaise did not prevent Salmonella from multiplying when the sandwiches were stored at 21 or 30 C for 8 or 24 h.

Relationship between the nutritional efficacy of a rice and bean diet and energy intake in preschool children.

Nitrogen balance and urea excretion were measured in a group of 4- to 6-year-old children receiving a rice and bean diet providing 1 g of protein per kilogram of body weight per day and three levels of calories. With diets providing 2300 and 3000 kcal/day, nitrogen retention was 41.16 +/- 29.04 and 53.30 +/- 18.46 mg/kg of body weight per day, respectively. With 1400 kcal/day, diet nitrogen retention decreased to 25.38 +/- 13.88 mg/kg body weight and urea nitrogen excretion increased. The importance of adequate caloric intake for optimum utilization of dietary protein from a rice and bean diet for growing children is demonstrated.