bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Faulting in Laves Phase TiCr2 Alloys
Authors: Kolar H. R. , Allen C. W. , Spence J.C.H. 
Published: June 2020

The Laves phases TiCr2 have shown polytypism dependent on temperature. TiCr2 is 2H (C14, MgZn2 structure) above 1100°C (C15, MgCu2 structure) at lower temperatures with 4, 6, and 12 layer variants occurring as intermediate structures. Of particular interest are the phase transformations which presumably proceed by a shear mechanism.Laves phase structures and their stacking variants can be described in terms of the stacking sequence of six similar compound layers. These layers form topologically close packed structures of AB2 composition in which the metallic radius of the A atom is approximately 1.22 times larger than that of the B atom. Fig. 1 shows the atomic arrangement within a single compound layer. Similar layers are then stacked as in close packed structures. In TiCr2 the most common transition structures seem to be the 4H, 6H1, and 6H2 with the latter being less prominent. It is possible to form all these structures by the glide of arrays of Shockley type partial dislocation dipoles which are highly mobile at practical transformation temperatures. Models for each of the transformations have been proposed but have not been confirmed by direct observation. The partial dislocation dipoles may arise from the dissociation of perfect dipoles, emission from grain boundaries (or interfaces), or by nucleation from perfect crystal.
Lattice Image Analysis of the Metamict Transformation in Synthetic Quartz
Authors: Pascucci M. R. , Hobbs L. W. , Hutchison J. L. 
Published: June 2020

The irradiation-induced crystalline-to-amorphous transformation in quartz and other silicates has been investigated because of its importance to nuclear waste storage ard frequency control. The transformation to an amorphous (metamict) state is accompanied by up to 14% decrease in density.Recent in-situ electron damage studies of synthetic α-quartz using transmission electron microscopy have shown that the metamict transformation occurs in two stages at different rates: first, a rapid, heterogeneous nucleation of well-defined amorphous inclusions; and second, a more gradual, homogeneous loss of correlation in the surrounding matrix. The first stage initiates at doses less than ten times the second. Experiments at different electron energies have established that both stages can result from the ionizing component of the radiation alone. The proposed radiolytic damage mechanism involves localization of excitations resulting in bond breakage which provides the necessary topological freedom for reorientation of SiO4 tetrahedra. Water has been implicated in the first-stage heterogeneous nucleation.
Preparation of Particulates for Transmission Electron Microscopy: An Update
Authors: Lauf R. J. , Rawlston S. S. 
Published: June 2020

A method for preparing fragmented or particulate ceramic materials for transmission electron microscopy (TEM) by embedding in a solid metal matrix such as aluminum, using vacuum hot-pressing at about 550°C, followed by mechanical thinning and ion milling, has been published. This technique is useful for most high-melting ceramic materials but may introduce thermal damage to low-melting materials or to hydrated minerals. We describe here two relatively simple techniques that can be carried out at room temperature and that do not require vacuum hot-pressing equipment.The first technique disperses the sample in a dental amalgam. Premeasured capsules contain the silver alloy powder and mercury in separate compartments. The capsule is opened and a small amount of sample is added. The capsule is then closed and compressed to release the mercury and agitated for 1 to 2 min. The material is removed from the capsule and tightly packed into a 3-mm-diam cylindrical mold for hardening overnight. The resulting pellet is then sliced and thinned as in the earlier method. Figure 1 shows a coal fly ash particle prepared by this technique.
Pulsed Ion Beam Induced Silicide Formation
Authors: Chen L. J. , Hung L. S. , Mayer J. W. 
Published: June 2020

Metal silicides have found increasing use in microelectronic industry as contact material as well as interconnect between devices. Silicide formation is based on the reaction between metal film and substrate silicon. Thermal, laser, electron beam and ion-mixing induced silicide formation have been widely studied. Recently both scanning and pulsed ion beams have been used to anneal semiconductors. In this presentation, we report pulsed ion beam induced silicide formation.Ni films, 300 and 400 Å thick, were e-gun deposited on (001) oriented, 2 Ω-cm, n-type silicon with substrate temperature maintained at 150°C. A magnetically insulated diode driven by a Marx generator, constructed and run by J. Neri and D. Hammer of Laboratory for Plasma Studies at Cornell in conjunction with J. E. E. Baglin of IBM Research was used to produce pulsed proton and barium beams. Samples were irradiated with about 200 nsec, 200-300 keV, 10-100 A/cm2 ion pulses. A Gaussian-type radial profile was generally obtained. Thin foils for transmission electron microscope study were then chemically polished from silicon side. JEOL 100B and Siemens 102 electron microscopes were used to investigate microstructural changes.
Electron Channeling of Single Crystal Lithia-Disilicate
Authors: McCracken W. J. , Madden M. C. 
Published: June 2020

Electron beam channeling has been primarily applied to metals, which both conduct electrons and have cubic crystal structures. Ceramic materials are usually nonconductive and noncubic. However, determining the orientation of a single crystal ceramic is often necessary for subsequent materials analysis. This is the case with lithia-disilicate, the crystalline phase found in some technical glass-ceramics. To study lithia-disilicate single crystals with polarized infrared spectroscopy, it is required to know the crystallographic orientation of the sample.Lithia-disilicate has an orthorhombic crystal structure with a space group of Ccc2. The structure contains three cleavage planes perpendicular to the primary axes. The plane perpendicular to the (010) axis is micaceous. These features can be seen in Fig. 1, where the top surface is the 010 plane.
An EXELFS Analysis System and Preliminary Orientation Dependence Results
Authors: Disko M. , Krivanek O. , Spence J.C.H. 
Published: June 2020

A Fourier analysis of the core electron excitation Extended Electron Energy Loss Fine Structure (EXELFS) has been shown to yield information concerning the radial distribution of atoms about the ionized species. Theoretical descriptions of the EXELFS have been based to date on similarities with the Extended X-ray Absorption Fine Structure (EXAFS) for electron scattering within the dipole approximation. Differences between the EXELFS and the EXAFS phenomena have been stated, and remain to be investigated.The most important experimental EXELFS problem involves the difficulty of obtaining a sufficiently good EXELFS signal to noise ratio out to large postedge energy. The solution of this problem requires the correct combination of the convergence angle α, the collection angle β, the specimen thickness, and an efficient spectrometer system. Energy resolution is not a crucial limiting factor; 5eV resolution at the edge is sufficient. A computer program for EXELFS analysis has been developed that is versatile, and yet sufficiently compact to run on an LSI-11 minicomputer.
Simultaneous Collection and Processing of Energy-Filtered Images in Stem Using a Fast Digital System
Authors: Butler J. H. 
Published: June 2020

Hardware and software have been developed allowing concurrent acquisition of up to three electron energy-loss images formed by monitoring three separate regions of the energy-loss spectrum. This imaging mode provides display of three elemental contour maps or, after some digital image processing, an elemental contour map stripped of its spectrum background.Other systems proposed for simultaneous collection of these signals have not been realized because of the difficulties involved in manufacture of multiple parallel detectors consistent with the physical dimensions of the energy-loss spectrum. The technique described here requires just the single standard bright-field detector. The experimental apparatus consists of a Vacuum Generator's HB5 Scanning Transmission Electron Microscopy (STEM) under the control of a Fast Digital Acquisition System (FDDAS). A PDP11/34 minicomputer controls the electrostatic deflectors at the spectrometer exit so the spectrum can be shifted across the detector slits (Fig. 1). Circuitry enabling this has been incorporated directly into the FDDAS as an expansion device resident on the system bus.
Determination of Exact Orientation Relationships between Martensite and Austenite in Steels by Microdiffraction
Authors: Sarikaya M. 
Published: June 2020

A significant number of investigations have been performed on the determination of orientation relationships (OR) in high carbon, plate-martensitic steels. However, very little is known on the exact nature of ORs in technologically important lath martensitic steels. In the present study, in a series of low alloy steels with carbon contents between 0.1-0.4 wt%, the existence of retained austenite as thin films (∼200 Å thick) around the martensite lath boundaries, makes it possible to do direct crystallographic analysis between martensite and austenite by microdiffraction.The most commonly observed orientations for lath martensite-retained γ are <111>α'//<110>γ//<100>α'. Fig. 1 shows an example of a highly symmetric SAD pattern which was interpreted as follows: Considering only one martensite lath at a time, the <lll>α' and <110>γ combination corresponds to Kurdjumov-Sachs (K-S) OR, and <110>α and <100>γ corresponds to Nishiyama-Wassermann (N-W) OR. The coexistance of these two relationships may be taken as evidence that as many variants as necessary occur to provide maximum flexibility for martensite nucleation.
A Photodiode, Parallel Detection System for Energy Loss Spectrometry
Authors: Johnson D.E. , Csillag S. , Monson K.L. , Stern E.A. 
Published: June 2020

The advantages of parallel detection systems for energy loss spectometry are certainly clear. A variety of approaches are possible ranging from simple film recording to elaborate intensified television cameras. We are in the process of evaluating one approach to such a parallel detection system, which consists of; a magnetic post-spectrometer lens to increase dispersion, a phosphor conversion plate, glass coupling lenses, a dual channeltron image intensifier, and a cooled photodiode array (Reticon RL256C/17). A schematic diagram of the system is shown in Fig. 1.The post-spectrometer lens is an RCA-3G intermediate lens which typically magnifies (∼15x) the dispersion to ∼25μm/ev with a rotation of ∼90°. Although the dispersion plane of the straight edge sector magnet used is tilted at 30° from the beam axis, pre-spectrometer optics reduce the angular divergence of the beam entering and leaving the spectrometer to ∼1 mr and the consequently large depth of focus assures that the dispersed beam is in focus across the conversion plate, perpendicular to the beam axis.
Results from a New Analytical Electron Microscope
Authors: Parker N. W. , Utlaut M. , Crewe A. V. 
Published: June 2020

A new analytical electron microscope has been completed and is now in full operation in our lab. As described earlier, this microscope contains many new design features all of which have now been extensively tested. We report here on the success of each of these design experiments.The optical design utilized a magnetic lens above the accelerating gun, shielded from HV by a spool-shaped machinable glass insulator. While this system worked very well optically, some HV problems occurred which we are attempting to cure by minor design changes. The beam-defining aperture is contained within a differentially pumped Faraday cage and has worked very well, showing a vacuum differential (outside/inside) of 4 to 5 while allowing quick changes among the eight different apertures available.The specimen stage temperature control has demonstrated an attainable range of 98°K to above room temperature with no effect on either specimen mobility or microscope vacuum.
Enhanced Projections in Electron Micrographs of 40S Ribosomal Subunits from HeLa Cells
Authors: Boublik M. , Frank J. , Tesche B. , Verschoor A. 
Published: June 2020

Direct visualization by electron microscopy is of obvious advantage for conformational analysis of ribosomes. However, low contrast, small size, high degree of hydration, susceptibility to beam damage, recrystallization of the contrasting solution (usually uranyl acetate), and random structure of the support film are responsible for high noise level of the conventional electron micrographs of the ribosomes. Structural asymmetry and the fact that ribosomes do not normally form regular arrangements (exception cf. /l/) preclude the application of crystallographic averaging techniques. These conditions make interpretation of the morphologic parameters of ribosomes and topographic mapping of their constituents - proteins and rRNAs - challenging and controversial.In our efforts to interpret electron micrographs of ribosomal particles we have used two different techniques - filtering of arrays of images in reciprocal space (FAIRS) /2/ and computer alignment and averaging /3/ - to obtair averaged views of the particles.
Freeze Fracture-Electron Microscopy of Spermidine-Single DNA Double Helices
Authors: Ruben George C. , Marx Kenneth A. , Reynolds Thomas C. 
Published: June 2020

Torus shaped spermidine-DNA structures formed in vitro are thought to have a DNA organization similar to that in bacteriophage. In addition to toroidal structures in our preparations we have found large aggregates often interconnected with fibres comprised of one or more DNA double helices. The detailed organization of these interconnecting fibres will help illuminate little-understood theoretical aspects of the packing and bending properties of the DNA double helix. Previously, spermidine-DNA complexes have been dryed onto a substrate film and metal coated at an 11.3° angle. In contrast, the freeze-fracture, deep-etching technique was used because it could reveal hydrated spermidine-DNA complexes in their solution configuration. This preliminary report describes single double helical DNA-spermidine fibres suspended over unshadowed regions of the ice surface.Calf Thymus DNA (5 g/ml) was condensed with 1 mM spermidine at 0°C, for 1 hr in 1 mM NaCl, 10 mM Tris, pH 7.0. The solution was rapidly frozen on a Balzer's deep well pedestal in propane at -190°C. Samples were freeze-fractured and deepetched for 13 min at -97°C with a Balzer's 300 Freezing Microtome.
Distinguishing Characteristics of the Sub-Population of Squamous Cancer Cells with Invasive Motility—Light Microscope and HVEM Studies
Authors: Parsons D. F. , Marko M. , Braun S. 
Published: June 2020

The most active cells in a primary or metastatic carcinoma appear to interface the normal tissue (e.g., at the edge of the tumor mass or adjacent to other normal tissues). These cells, which are free of normal territory-restricting constraints, are characterized by a different morphology from the main mass of tumor cells by pseudopodia formation with pronounced filamentous actin organization, and (usually) with release of proteases including characteristic collagenases. We have developed two types of tissue culture models which give opportunity for 3-D thick-section HVEM and cytochemical study of the transition from the resting stage to the stage of invasive motility. We mean to define the conditions for this transition and to suggest therapies to control the leakage of invasive cells from the main tumor mass into normal tissues.The work is aimed at demonstrating the morphologic and cytochemical relationships between the invasive cells of human and mouse squamous cell tumors, the stem cells (“dark cells”) of normal and embryonic epithelial cells.
Osteogenesis Imperfecta: An SEM and TEM Study of Cellular and Matrix Characteristics
Authors: Kirchen M.E. , Marshall G.J. , Dietrich S.L. 
Published: June 2020

Samples of bone were obtained with appropriate consent from 27 patients with Osteogenesis imperfecta (O.I.). The samples were processed by conventional techniques and specimens viewed with a Novascan SEM, AEI Corinth TEM and a Cambridge SEM scope fitted with a Nuclear Semiconductor energy dispersive unit. For each bone sample specimens were conserved for light microscopy as well as SEM and TEM. The H & E slides were used to determine the architecture of the sample, to ascertain if a portion of the vascular bed was present and to obtain a ratio of osteocyte to matrix. SEM was used to compare the topography to that of normal bone. TEM was used for cellular and matrix details. The energy dispersive unit in association with the Cambridge SEM was used to estimate the concentration of bone minerals and to obtain the calcium phosphorus ratio for each specimen.O.I. is a familial disease which presents with a range of clinical entities
Differentiation of Fiber Types in a Mammalian Extraocular Muscle
Authors: Nag Asish C. , Cheng Mei 
Published: June 2020

The mammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. Superior rectus muscle of the adult cat and rat contains five morphological fiber types. The differentiation of these fiber types in the embryonic and postnatal rats was studied by light and electron microscopy, mapping the distribution of each developing fiber type with its distinctive features.A mixture of 4% paraformaldehyde and 4% glutaraldehyde was perfused through the superior rectus muscle of rats ranging from 18-day embryos through 4-week postnatal anesthetized animals. Muscles were removed, kept overnight in 4% glutaraldehyde, and processed for electron microscopy using standard methods of OsO4 postfixation and araldite embedding. Thick and thin sections were cut. Thick transverse sections were photographed, and maps of muscle fibers were prepared. In order to identify the fibers and their exact locations, electron micrographs of fibers were taken in conjunction with the light micrographs.The muscle fibers in the 18-day embryos did not differentiate into the specific structural fiber types (Fig. 1) that were observed in the adult muscle.
Ultrastructure of Cryptorchidism and Seminoma
Authors: Siew Shirley , James Susan C. 
Published: June 2020

Testicular maldescent is the most common endocrine gland abnormality, as 2.7% of mature neonates are cryptorchid. The significant complications are that there is a disturbance of normal maturation which results in diminished fertility and there is an increase in the malignant potential which is 35 times greater in the undescended than the descended testis. It is considered that genetic influences may be of etiological importance and recurrence has been described in some families. It is of interest, that the case reported here has 2 siblings who have also presented with cryptorchidism and malignant tumors.The propositus is 14 years old. He is well developed (described by some as obese) and shows normal secondary male characteristics except for an immature scrotum. Laparotomy showed both testes to be intraabdominal. A hard nodule (0.5cm) was palpated on the medial aspect of the left testis. Frozen section showed the presence of seminoma and bilateral orchiectomy was performed.
A Gaussian Small Particle Population is Transformed by Pt-C Replication into Distributions of Metal Cap Widths and Shadow Widths which Empirically Fit a Log-Normal Function
Authors: Ruben George C. 
Published: June 2020

The investigation of biological membranes would be greatly facilitated if the particle shadow widths (PSW) or particle cap width (PCW) distributions on freeze-fractured or freeze-etched membranes could be related to actual particle size and size diversity. By establishing how a gaussian population of small particles is transformed into its Pt-C PCW and its Pt-C particle shadow width distributions (PSWD), it may be possible to solve this problem.The negatively stained lac repressor (1% uranyl acetate, pH 4.8) which is roughly a gaussian population of diameters (fig. la) was used to investigate the distribution shape of Pt-C PCW's. Gold balls were only used to investigate the distribution shape of PSW's because they did not generally form a Pt-C metal cap (1,2). The preparation method for gold ball calibration grids has been reported (1,2). The Pt-C shadowing experiments (45° angle) were performed on a Balzer's model 360M freezing microtome at -97°C to -94°C in a 10-6 torr vacuum. An EKV 552 Pt-C electron beam gun was either degassed for 19 sec (film I) or for 120 sec (film II) at a current setting of 5 on the EVM 052 control unit.
Studies on Trifluoperazine Inhibition of Trichocyst Expansion and Secretion in Paramecium
Authors: Garofalo Robert S. , Satir. Birgit H. 
Published: June 2020

The importance of Ca2+ ion in regulation of many cellular processes is well established, as is its role as the mediator of “stimulus-secretion coupling” in exocytic release of secretory products. However, while the Ca2+ requirement in many secretory systems is clear, its mode of action is not.To probe the site of Ca2+ action, we have employed the protozoan, Paramecium tetraurelia as a model secretory system. Secretion in Paramecium requires Ca2+ as well as specific components in both the plasma and secretory vesicle membranes that can be visualized in freeze fracture as organized intramembrane particle arrays. The fusion of plasma and secretory organelle membranes, and subsequent release of vesicle contents, is routinely elicited by exposure to picric acid, and stimulation results in synchronous release of hundreds of secretory products called trichocysts. A rise in cytoplasmic Ca2+ triggers release and expansion of the trichocysts. This is accompanied by a reordering of the trichocysts' paracrystalline matrix, transforming the 5 μm long organelle to a 20-40 μm long needle-like structure.
The Demonstration of Hemoprotein Crystals in Secretory Lumina of Dimethyl-benzanthracene-Induced Mammary Tumors
Authors: Hanker J. S. , Silverman M. S. , deCamargo A. M. , Giammara B. L. , Bossen E. M. , Stein R. B. 
Published: June 2020

A number of hormone-dependent reproductive tract tissues synthesize a peroxidase and secrete it into their lumina. An estrogen-induced mammary gland peroxidase, probably lactoperoxidase, has been reported in the acinar cells of prelactating and lactating rats and has been found to be a marker of hormone-dependent 7,12-dimethylbenzanthracene (DMBA)-induced rat mammary tumors. Study of the enzyme in tumor acinar cells showed it in cisternae of the nuclear envelope, granular ER and apical secretory granules. Its presence in lumina of the acini has not been described. It was therefore of interest to determine whether lactoperoxidase could be demonstrated in their secretory lumina.Mammary tumors were induced in female rats by DMBA in the usual manner. Paraffin sections of tumor tissue were stained with H & E or the Leder stain.Fixed touch preparations, cryostat sections, and blocks of tumors for electron microscopy were treated for peroxidative activity with 3,3'-diaminobenzidine (DAB) or p-phenylenediamine/pyrocatechol (PPD/PC, available from Polysciences).