bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning X-Ray Microscopy
Authors: Rarback H.
Published: June 2020

From a theoretical viewpoint, a scanning transmission soft x-ray microscope is an excellent instrument for imaging unmodified thick (1 - 10μm) biological specimens at moderate (10 - 100 nm) resolution . Such specimens include wet intact cells, cell cultures, and isolated organelles. It may even be possible to study the dynamics of a living cell at such resolution, a feat beyond the ability of most competing techniques.

Two basic features of the scanning x-ray microscope account for these theoretical advantages: the soft x-ray photon is well matched to such specimens, and the scanning technique minimizes the specimen damage which will probably set the achievable resolution limit for such specimens. X rays with wavelengths between 1 and 10 nm have a penetration depth of the order of 1 μm in wet biological material; the predominant interaction is photoelectric absorption which simply removes a photon from the incident beam without degrading the resolution.
Elemental Mapping by Core Level Excitations in the Analytical Electron Microscope
Authors: Leapman R.D.
Published: June 2020

Elemental distributions can be obtained in the analytical electron microscope by detecting core level excitations resulting from interaction of the scanned electron beam with atoms in the sample. This core level signal is recorded either through inelastic scattering measured by electron energy loss spectroscopy (EELS) or through x-ray emission measured by energy dispersive x-ray spectroscopy (EDXS). EELS is well suited to analysis of light elements for which the fluorescence yield is low whereas EDXS is sensitive to heavier elements; for several elements the two methods are competitive. The spatial resolution can approach the probe diameter, typically 1 to 50 nm, provided (i) the sample is thin enough to limit beam spreading effects, (ii) the counting statistics are adequate to detect a particular element, (iii) radiation damage is not a limiting factor, and (iv) delocalization of the scattering events is smaller than the probe diameter (in the case of high resolution studies).
Structure Studies of Supported Metal Catalyst Particles by Microdiffraction Technique
Authors: Pan M. , Cowley J.M. , Chan I.Y. , Garcia R.
Published: June 2020

Understanding the structures of the small metal particles (<5nm) in supported metal catalysts can provide some basis for understanding the properties and performance of these catalysts. High resolution transmission electron microscopy (HRTEM) has been extensively used to characterize the structures of small particles in the past few years. As a complement to HRTEM, microdiffraction technique has its unique advantage of being able to provide local structure information within regions of diameter 1-2nm.

In our VG HB-5 STEM an electron beam with diameter of 1-1.5nm can be easily generated at the specimen level and microdiffraction patterns from such small regions are routinely observed with the help of the attached optical system. Two series of catalyst samples, Pt/γ-Al2 O3 and Rh/CeO2 with various metal loadings and reduction temperatures, have been studied. The series of Pt/γ-Al2 O3 catalyst included both calcined and reduced samples. Both series of catalysts contain high dispersions of metal particles (<5nm). In the case of Rh/CeO2 Rh particles usually have sizes of 2-3nm.
High-resolution tem of transformation interfaces in metals
Authors: Howe J. M.
Published: June 2020

The advent of medium and high-voltage transmission electron microscopes with point-to-point resolutions below 0.2 nm has made it possible to study transformation interfaces in metals at the atomic level. Understanding the atomic structures of these interfaces is critical to understanding microstructural development and the resulting physical and mechanical properties of metals. One area of transformation interfaces in metals that has been investigated by high- resolution transmission electron microscopy (HRTEM), is the structures of interphase boundaries of metastable aging precipitates in Al alloys. The presence of these precipitates is largely responsible for the high strengths of many Al alloys and the low atomic number of Al alloys makes them ideally suited for study by HRTEM. The results from HRTEM Investigations of transformation Interfaces in Al-2%LI-1%Cu and Al-4%Ag alloys which follow, illustrate the wealth of information that HRTEM can provide about transformation interfaces in metals.
Measurement of compositional changes accompanying solid-state transformations at grain boundaries in metals
Authors: Hall Ernest L. , Briant Clyde L.
Published: June 2020

In many multicomponent metallic systems, solid-state precipitation processes can occur upon slow cooling or isothermal aging of solutionized material. Frequently, the precipitates form at grain boundaries, which are preferred sites for the nucleation and growth of the second phase. The precipitates generally grow through a combination of matrix and grain boundary diffusion, in which the grain boundary acts as a collector plate for the delivery of the solute to the growing precipitate. The precipitation process is thus accompanied by significant changes in the chemistry of the grain boundary and matrix regions near the grain boundary. These grain boundary chemistry changes can have a profound effect on the macroscopic properties of the material, including corrosion resistance, strength, and ductility. In order to understand the mechanism associated with these property changes, it is necessary to obtain a complete and precise description of the magnitude and extent of the compositional changes which have occurred at the grain boundaries.
Friedel'S law breakdown and interpretation of stacking fault images in tetrahedral semiconductors
Authors: Glaisher Rob. W. , Spargo A.E.C.
Published: June 2020

Images of <11> oriented crystals with diamond structure (i.e. C,Si,Ge) are dominated by white spot contrast which, depending on thickness and defocus, can correspond to either atom-pair columns or tunnel sites. Olsen and Spence have demonstrated a method for identifying the correspondence which involves the assumed structure of a stacking fault and the preservation of point-group symmetries by correctly aligned and stigmated images. For an intrinsic stacking fault, a two-fold axis lies on a row of atoms (not tunnels) and the contrast (black/white) of the atoms is that of the {111} fringe containing the two-fold axis. The breakdown of Friedel's law renders this technique unsuitable for the related, but non-centrosymmetric binary compound sphalerite materials (e.g. GaAs, InP, CdTe). Under dynamical scattering conditions, Bijvoet related reflections (e.g. (111)/(111)) rapidly acquire relative phase differences deviating markedly from thin-crystal (kinematic) values, which alter the apparent location of the symmetry elements needed to identify the defect.
Early stages of the M-Inp (M=Ni,Pd) reaction: Solid-state amorphization and subsequent crystallization
Authors: Krishnan Kannan M. , Sands Tim , Caron R'Sue
Published: June 2020

The fabrication and reproducibility of stable metal (M) contacts to compound semiconductor (AB) devices are largely dependent on the knowledge or ability to predict both the phase formation sequence and the phases that are finally in thermodynamic equilibrium within the substrate at any given temperature. In addition to forming stable and metastable ternary phases, these M-AB reactions (particularly the Ni-InP and Pd-InP systems) are prime candidates for solid-state amorphization reactions. Hence, thermodynamic data from the binary M-A and M-B systems are insufficient to predict the compounds that will form during these M-AB reactions. In this paper, the formation of the initial products of the M-AB (M=Ni, Pd) reactions were characterized by TEM, energy dispersive x-ray microanalysis and in-situ heating experiments.
Twin boundaries in GaAs grown on Ge
Authors: Cho N.-H.
Published: June 2020

Interest in the structure of grain boundaries in semiconductors has been increasing for many reasons including the important role of boundaries on the electrical behavior of polycrystalline materials. GaAs is of interest because of its particular electrical properties such as its direct band gap and high electron mobility. Specific bicrystals of GaAs were produced on substrates cut from Czochralski-grown germanium bicrystals in a low-pressure organometallic vapor- phase epitaxy system. When the growth surface was parallel to the (110) plane, many microtwins were produced in the GaAs epilayer. The structure of twin boundaries in GaAs can take two forms depending on the relative polarities of the two adjoining grains because GaAs has a sphalerite structure which is a face-centered cubic lattice with a two atom basis. The polarity of the two grains meeting at the grain boundaries can be determined by using the dynamical coupling effects of high-order Laue-zone reflections on the (200) and (200) diffracted beams.
Electron optical studies of the formation of vanadium pentoxide catalyst
Authors: Legrouri A.
Published: June 2020

The oxides of vanadium, especially vanadium pentoxide, have been extensively studied because of their interesting physical properties particularly in catalysis. Vanadium pentoxide is generally used in the oxidation and ammoxidation of hydrocarbons.

This catalyst has been prepared via the thermal decomposition of ammonium metavanadate (AMV) in air. Thermogravimetric analysis (TGA), infrared spectroscopy (IRS) and x-ray diffraction (XRD) techniques together with high resolution electron microscopy (HREM) and scanning electron microscopy (SEM) have enabled us to elucidate the physicochemical changes occurring during the decomposition process.

According to TGA results, the decomposition of AMV commences at 150°C and is complete by 320°C leading to vanadium pentoxide by loss of ammonia and water with the formation of two intermediate compounds, namely at 190°C, ammonium bivanadate: (NH4)2V4 O11, and at 230°C, ammonium hexavanadate AHV: (NH4)2V6O16 . Samples for structural correlation studies were prepared by heating AMV in a stream of air for 2 hours at selected temperatures of 140, 190, 230, 320 and 400°C.
Freezing Dynamical Sol-gel processes with the controlled environment vitrification system (CEVS)
Authors: Bellare J. R. , Bailey J. K. , Mecartney M. L.
Published: June 2020

A sol is a stable suspension of submicron particles in a liquid while a gel is a three dimensional network of these particles which is bicontinuous with the liquid phase. Sol particles are stabilized by surface charges or by steric hindrance of molecules on the particle surface. Sols can be gelled by the agglomeration of the particles; for example, by reducing the inter-particle repulsion with the addition of a salt. The sol-gel transformation is an important industrial, biological and household process. Novel ceramic processing techniques, blood-clotting, and white-sauce manufacturing are some diverse examples. Therefore, there has been extensive interest in relating the gel structure to changes in the physical properties that occur during gelation.

Direct observation of thin vitrified films is the preferred technique for microstructural determination of colloidal dispersions in the size range of 1-1000nm.
Structural investigations of mixed-layer smectite-illite clay minerals from North Sea oil source rocks
Authors: Hansen Poul Lenvig , Lindgreen Holger
Published: June 2020

The purpose of the present investigation is to identify mixed-layering between illite and smectite in oil source rocks with HREM and electron diffraction. Smectite and mica are both groups within the 2:1 type of layer silicates. Illite is a commonly used term for micas in the fraction less than 2 microns. Illite has a fixed d(001) spacing of 10A. Smectite is able to swell from 10A to more than 18A under uptake of water or organic polar molecules. Mixed-layer illite-smectite is built of alternating layers of illite and smectite. Smectite and illite layers are recognized by x-ray diffraction (XRD) from their swelling characteristics, but cannot be distinguished in this way in HREM, because smectite layers tend to contract to 10A by evaporation of water in the vacuum of the microscope. Illites are identified by HREM as small packets showing very regular lattice fringes and smectites as highly imperfect, anastomosing layers showing very irregular lattice fringes (1).
Transmission electron microscopy of alpha-decay damage and alteration of betafite
Authors: Lumpkin G. R. , Ewing R. C.
Published: June 2020

The pyrochlore structure type occurs as a constituent of crystalline nuclear waste form assemblages proposed for the long term isolation of actinides. Betafite, the Ti-rich end-member of the pyrochlore group, is a natural analogue similar in composition to waste form pyrochlores. This study examines the effects of alpha-recoil damage and geochemical alteration on a specimen of betafite from Antanifotsy, Madagascar (Harvard no. 87876, UNM no. 205).

Electron microprobe analyses were performed using a JEOL 733 Superprobe operated at 15 kV and 20 nA sample current crushed fragments of the sample were dispersed on holey-carbon grids and examined with a JEOL 2000 EX TEM operated at 200 kV. Phase compositions were checked using a Tracor TN5500 EDS.

The 1.5 cm diameter betafite crystal displays an unusual zonal sequence of alteration. The core consists of relatively unaltered betafite containing ca. 27 wt.% U02 and 2.5 wt.% CaO (TABLE 1, analysis 1).
Topography of gallium arsenide substrates following various surface treatments
Authors: Mescher J. A. , Grant J. T.
Published: June 2020

The preparation of a clean and defect-free GaAs surface is an ideal starting point for making GaAs based devices. Contaminants can also dramatically affect the adhesion of metals on GaAs. The effect of particulates or pits is more obvious. The purpose of this study was to evaluate differences in morphology and elemental composition of GaAs substrates subjected to commonly used wet etching techniques.

The samples used in this study were cut from a polished LEC Zn-doped (100) GaAs wafer and were approximately 5x5 mm in size. Samples were treated by various means including organic solvents, freon vapor, acid etchants, alkaline etchants as well as no treatment. The solvents appeared to clean the wafer of particulates and polishing residues. The most extensive etching was observed on three samples now to be described.
EELS characterization of bulk crystal surfaces in Rem: Surface micro analysis and surface channelling effect
Authors: Wang Z.L. , Cowley J.M.
Published: June 2020

Electron energy-loss spectroscopy (EELS) is used in parallel with reflection electron microscopy (REM) for studying surface chemical characterization. The successful observation of Pt and Au M4,5 edge modifications in the REM case has shown that it is possible to do surface chemical analysis for those heavy elements [1]. The reflection of electrons from the surface is critically affected by the surface resonance condition; it has been shown that the electrons will propagate parallel to the surface for some distance if the incident angle satisfies the surface resonance (SR) condition[2-3], then surface channeling is likely to be observed in this SR case. There is less propagation along the surface under the surface non-resonance (SNR) condition.

The GaAs bulk crystal (011) surface was chosen for observing the surface channeling effect in REM case, using a Philips 400T TEM. The surface absorbed oxygen is identified with the O-K edge (fig.l(A)).
High-resolution electron microscopy study of a Si-Mo x-ray mirror
Authors: Gronsky R. , Punglia J.
Published: June 2020

The science of x-ray optics has undergone rapid growth in recent years, spurned by the availability of high intensity light sources with tunable optical characteristics in the XUV spectral region which includes soft x-rays and ultraviolet radiation. The development of optical elements for use with XUV radiation has followed a parallel path of development with most recent emphasis being placed upon multilayer coatings that enhance the reflectivity of x-ray mirrors and at the same time provide spectral selectivity. In their simplest form, these coatings consist of alternating thin layers of two materials with different refractive indices that yield both the desired high reflectivity and a relatively broad wavelength bandpass. Additional considerations are based on their materials science: the multilayers must have atomically smooth interfaces and be resistant to interdiffusion or chemical reaction. A summary of their preparation and utilization is given in reference 3.
Atomic inner shell excitations with eels in REM: Pt and Au M4,5 edge shapes modifications in REM
Authors: Wang Z.L. , Cowley J.M.
Published: June 2020

Electron energy-loss spectroscopy (EELS) has been used in parallel with reflection electron microscopy (REM) to investigate the inner shell structure of the surface atoms in bulk single crystals of Pt and Au. A Phillips 400T TEM is used for the experiment, with the arrangement shown in fig. 4. The observed M4,5 edge from the bulk crystal surface (REM case) is compared with that from a thin metal foil (TEM case), such that the surface atomic inner shell modifications, relative to the atoms in the bulk, can be obtained. Fig. 1(A) and 1(B) show the REM image of the Pt (111) surface and the corresponding EELS Pt-M4,5 edge. This observed edge in the REM case is compared with the edge observed in the TEM from a thin Pt foil (fig.l(B)). Comparing the results in fig 1(B) and fig. 2(B) for the REM and TEM cases, the shape modification at the M4,5 edge maximum part is related to the strong multiple surface plasmon scattering[l].
Generation of surface plasmons in a supported metal particles with an external electron beam:II Classical energy loss theory
Authors: Wang Z.L. , Cowley J.M.
Published: June 2020

The theoretical predictions of the relative excitation probabilities of surface plasmons, using the coherent-state theory, are in good agreement with the experimentally observed relative heights of the surface plasmon peaks, This is partially because the field created by the induced charges on the support surface is not properly taken into account in the quantum theory.

The Classical energy loss theory is based on Ritchie's work. Consider the total potential distribution in the space created by an incident electron under the non-retardation approximation (as shown in fig. 1),
is the field created by the induced charges. Matching the solution of ψ on the boundaries, as a function of the incident electron position rt, the excitation probability of the surface plasmon as a function of ω is:
The role of silicon in forages: A quantitative X-Ray study
Authors: Woodward Janet H. , Akin D. E.
Published: June 2020

Silicon (Si) is distributed throughout plant tissues, but its role in forages has not been clarified. Although Si has been suggested as an antiquality factor which limits the digestibility of structural carbohydrates, other research indicates that its presence in plants does not affect digestibility. We employed x-ray microanalysis to evaluate Si as an antiquality factor at specific sites of two cultivars of bermuda grass (Cynodon dactvlon (L.) Pers.). “Coastal” and “Tifton-78” were chosen for this study because previous work in our lab has shown that, although these two grasses are similar ultrastructurally, they differ in in vitro dry matter digestibility and in percent composition of Si.

Two millimeter leaf sections of Tifton-7 8 (Tift-7 8) and Coastal (CBG) were incubated for 72 hr in 2.5% (w/v) cellulase in 0.05 M sodium acetate buffer, pH 5.0. For controls, sections were incubated in the sodium acetate buffer or were not treated.
Low-Voltage Scanning Electron Microscopy in polymer characterization
Authors: Berry V. K.
Published: June 2020

The application of low voltage scanning electron microscopy (LVSEM) to the characterization of polymers and non-conducting materials, other than semiconductors, has not been well explored yet. Some of the theoretical considerations and practical limitations which prevented the development of commercial instruments have mostly been addressed with the result that machines are now available which are optimized for low voltage (≥ 0.5 kV) operation. The advantages of working at low voltages are beginning to be recognized outside the semi-conductor industry. When we image uncoated polymer surfaces at low beam energies (0.5-1.5 kV), no beam damage or charging artifacts are experienced, because in this region the emitted electrons are equal to or more than the incident electrons and there is no deposition of charge underneath the surface due to the lower penetration of the incident electrons.
Crystal structure analysis of linear polysaccharides
Authors: Pérez Serge , Chanzy Henri
Published: June 2020

Carbohydrates molecules are ubiquitous in Nature, where they play a crucial rôle in promoting structure, texture or establishing storage; furthermore, their implications in biological recognition is now established. Such a spectrum of functions for carbohydrates arises from their ability to generate a large number of highly specific structures from only a small number of monomeric residues. To understand the molecular basis of such native arrangements, the elucidation at the atomic level of the 3-dimensional structures has to be performed. Fiber diffraction provides a method for the structure determination of crystalline polymers. However, despite the efforts of the fiber-diffraction community, it has not always been possible to mimic classical crystallographic studies so as to reach credible solutions using non controversial methods of elucidation. The present communication illustrates hows the use of electron diffraction data coupled with realistic molecular modelling can yield unambiguous structural elucidations.
Making every electron count: Detectors for scanning electron microscopy
Authors: McMullan D.
Published: June 2020

Fifty years ago, in December 1937, Manfred von Ardenne submitted his first paper on the scanning electron microscope (SEM) to Zeitschrift für Physik. Moreover his eightieth birthday was on January 20th this year and it is therefore now very appropriate that we should remember the great contribution he made to the subject by that mainly theoretical paper and by the one he published a few months later on the practical realisation of the first scanning transmission electron microscope (STEM); both papers have been frequently cited in the literature. Von Ardenne designed a two-lens microscope and calculated the current in a 10nm focussed spot to be 10-12A; he also discussed how the detector should be arranged to give bright and dark field images from a transparent specimen and secondary electron images from a solid specimen. Unfortunately, at that time the only device available to him for amplifying such small currents was the thermionic valve and he quickly realised that the noise level would be much too high.
Some biological materials observed by a new high-resolution SEM
Authors: Tanaka K. , Mitsushima A. , Takayama H.
Published: June 2020

Recently we made a high resolution SEM (UHS-T1) with a aid of Hitachi Co. Ltd. It was equipped with a field emission source and the objective lens with short focal length (3.6 mm). The electron probe is estimated to 0.4 nm on calculation, and the probe diameter of 0.5 nm is confirmed by observation in STEM mode. On observation of a biological material (a rat motor nerve cell) which was coated with platinum by an ion sputter coater, the SEM shows 0.5 nm resolution when the width of the dark space criterion was used. In the present study some biological materials are observed with this new SEM. The results are as follows.

Specimens were prepared by the aldehyde prefix osmium-DMSO-osmium method. In the specimens, mitochondria, Golgi complex, endoplasmic reticulum and so on, were very clearly observed (Fig.1) in comparison with those observed by ordinary SEM.
The application of three-dimensional tomographic reconstruction methods to high-voltage electron microscopy
Authors: McEwen B. F. , Rieder C. L. , Radermacher M. , Grassucci R. A. , Turner J. N. , Frank J.
Published: June 2020

High-voltage electron microscopy (HVEM) has considerably increased the thickness limit of biological specimens that can be visualized at high resolution. Because of its increased penetration power, HVEM is potentially the most powerful tool available for obtaining three-dimensional (3D) information concerning the structure of cells. In the past, such information was primarily obtained from serial thin sections or techniques based on surface shadowing, but these methods have severe problems and limitations which can only be overcome by imaging greater depths in the samples (see refs. 1 and 2). HVEM has yet to realize its potential for 3D structural determination because of the confusion arising from the overlap of features at different depths in the sample. Due to the relatively large depth of field, which exceeds the specimen thickness, HVEM (like all electron microscopy) produces an image that is essentially a projection of the sample.
Analytical Electron Microscopy of mineral fibers from human lungs
Authors: Roggli V.L.
Published: June 2020

A major application of analytical electron microscopy is in the analysis of mineral fibers recovered from lung tissue and the correlation of these findings with various human diseases. The best studied group of mineral fibers in this regard is asbestos, which is a generic term for fibrous crystalline silicates which possess the properties of high tensile strength, heat resistance, and relative resistance to various chemicals. Chrysotile is the form of asbestos which accounts for the great majority of industrial consumption in this country, with the commercial amphiboles amosite and crocidolite providing the remainder. Non-commercial varieties of amphibole asbestos, including tremolite, anthophyllite, and actinolite, are important primarily as contaminants of other mineral ores. A number of diseases or pathologic abnormalities have been described as resulting from exposure to airborne asbestos fibers, including a form of pulmonary interstitial fibrosis referred to as asbestosis, malignant (diffuse) mesothelioma of the pleura or peritoneum, parietal pleural plaques, and bronchogenic carcinoma, especially among asbestos workers who smoke.
Electron microscopic pathology of urinary stones
Authors: Kim K. M.
Published: June 2020

Urolithiasis occurs commonly. With modern technology, stones can be easily removed. However, the major threat of urolithiasis is in its high recurrence rate. Many recurrences can be medically prevented. For medical prevention, proper knowledge of stone components is essential.

Urinary stones have been analyzed mainly by x-ray diffraction, infrared spectroscopy and chemical analysis. Each method suffers from limitations in sensitivity and reliability. Primarily because of their inability to detect minor components of the stones, two or more methods are frequently combined. Recently it has become apparent that scanning electron microscopy (SEM), especially when combined with x-ray analysis (XA), has a sensivity in stone analysis exceeding other conventional methods.

SEM of urinary stones did not gain popularity mainly due to the perceived high cost, the difficulty of sectioning stones, and the variability of crystal morphology.
Ultrastructural alterations in the fetal mouse myocardium in response to genetic and environmental factors
Authors: Feng-Chen K.C. , Essien F.B. , Prestwidge K.J. , Cheng J.T. , Shen C.L.
Published: June 2020

The physiology of the fetal heart differs significantly from that of the mature post-natal organ: e.g., the metabolic supply for adult cardiac contraction relies mainly on fatty acids; whereas, the fetal heart uses carbohydrates as its primary energy source. Limited morphological descriptions of the developing myocardium have appeared. However, additional studies are required to elucidate the ultrastructural changes occuring in the perinatal period when enormous physiological adjustments are made. Although adult animals are most often used in toxocological and pathological analyses, it is also important to investigate fetal cardiac responsiveness to various agents. The vulnerability of the ultrastructure of the fetal mouse myocardium to genetic and environmental assault is the subject of this report. The genetically determined effect on the heart was observed in mouse embryos homozygous for the cab (cardiac abnormality) mutation discovered by Essien.
The cytochemical demonstration of bacteria in total artificial heart implant specimens
Authors: Hanker J. , Giammara B. , Dobbins J. , DeVries W.
Published: June 2020

Implantation of the total artificial heart and its associated systems, such as the pneumatic driving system, or other cardiovascular prostheses such as ventricular assist devices, intravenous catheters, ventriculo-atrial shunts, pacemaker electrodes and prosthetic heart valves can be complicated by the problem of bacterial infection.Staphylococcus epidermidis.a ubiquitous commensal of human skin and mucous membranes normally does not cause disease in man. It is now recognized, however, as an opportunistic pathogen of biomaterial implants especially cardiovascular protheses. This is due to its ability to undergo transformation to produce mucoid or polysaccharide extracellular coating substances which promote its adherence to biomaterial surfaces and protect the bacteria against antibiotics and host defense mechanisms; this results in increased virulence of the slime-producing strains.
High-resolution, low-dose electron cryomicroscopy of negatively stained matrix porin, a transmembrane protein from Escherichia coli outer membranes
Authors: Massalski A. , Sass H. J. , Zemlin F. , Beckmann E. , van Heel M. , Buldt G. , Dorset D.L. , Zeitler E. , Rosenbusch J. P.
Published: June 2020

Porin (ompF gene product), an integral channel-forming protein in the outer membrane of Escherichia coli, is regarded as a molecular sieve allowing non-specific passive diffusion for low-molecular-weight (Mr < 700d) hydrophilic solutes.

Electron microscopic studies of the negatively stained membrane vesicles reconstituted with porin and phospholipids have shown the presence of the stain-filled triplet indentation. Subsequent 3D image reconstruction demonstrated that three channels on the outer surface of the cell merge into a single channel at the periplasmatic face. Both 2D and 3D image reconstructions, based on electron micrographs from negatively stained preparations, are very informative about the size and distribution of the transmembrane channels but they contain very little or no information on the protein trimers which form the channels. This lack of information about the trimer structure and location is not surprising since the diffraction resolution limit, in our previous studies, is around 22Å.
Scanning Transmission EM (STEM) of dynein ATPases
Authors: Johnson Kenneth A. , Marchese-Ragona Silvio P. , Wall Joseph S.
Published: June 2020

The structure and molecular weight of the microtubule-dependent ATPase, dynein, was first established by scanning transmission electron microscopy (STEM) of dynein isolated from the cilia of Tetrahymena. It was shown that dynein consists of three globular heads joined to a common base by three slender, flexible strands. The globular heads have a diameter of 10-12 nm and the strands are 24 nm in length, such that the particles are 35 nm overall. Mass analysis by integration of electron scattering intensities in the STEM established a molecular weight of 1.9 million, with each head contributing 420,000. Several lines of evidence suggested that the base anchors the dynein to the A-tubule and the three independent, globular heads interact with the B-tubule of the adjacent outerdoublet in an ATP-dependent reaction to produce a force for sliding.
Morphologic differences between abdominal and inguinal testes in stallions
Authors: Al-Bagdadi F. , Hoyt D. , Karns P. , Martin G. , Memon M. , McClure J. , McCoy D.
Published: June 2020

The most frequently occuring abnormality of the male genital system in mammals is the failure of one or both testes to descend into the scrotum. The reasons for abdominal or inguinal retention of testes could be anatomic malformation, faulty development or hormone imbalance.

Cryptorchidism has been associated with either greatly reduced or absent spermatogenesis (Kaueakami et al, 1984), and being a source of neoplasia. According to Stick (1980), germinal carcinoma cells have been believed to be the cause of teratomas in equine cryptorchid testicles. Neoplasia has been reported in descended testes of unilateral cryptorchid patients (Martin et al, 1981).

No distinction has been made in relating the problem of cryptorchid testes to inguinal or abdominal retention. The purpose of this study is to record the morphological differences between inguinal and abdominal cryptorchid testes as an aid in diagnosis and prognosis.
Electron microscopic localization of sulfated glycosaminoglycansans and proteoglycans in chordoma
Authors: Lam Ronald , McGowan Mary Ellen
Published: June 2020

Although several electron microscopic studies of chordoma have been published, the origin of the chondroitin sulfate rich extracellular matrix is still not clear. Based on the ultrastructural similarities between the extracellular matrix, contents of the rough endoplasmic reticulum and cytoplasmic vacuoles, some authors assume that the two latter structures of chordoma cells contain mucosubstance. The intent of this study is to localize the sulfated glycosaminoglycans intracellularly in a chordoma, which provides cytochemical evidence of the origin of extracellular matrix.

A sacrococcygeal chordoma from a 65 year old man was examined by electron microscopy after fixation in 2.5% gluta-raldehyde, 0.2% ruthenium red-glutaraldehyde, and pre-embedment staining with high iron diamine (HID), a method specific for sulfated glycoconjugates. Routine electron microscopic examination revealed stellate nonvacuolated and vacuolated “physaliferous” cells embedded in an abundant extracellular matrix. In general the chordoma cells possessed prominent Golgi complex, rough endoplasmic reticulum, mitochondria, glycogen and intermediate filaments.
Ultrastructural changes in isolated rat liver perfused with cyclic heptapeptide toxins from norwegian freshwater cyanobacteria (blue-green algae)
Authors: Dabholkar A.S. , Carmichael W.W. , Berg K. , Wyman J.
Published: June 2020

Intracellular changes in the hepatocytes of isolated rat livers perfused with cyclic heptapeptide toxins are described. The toxins used are 1) -Ala-Leu- β-methyl isoAsp-Arg-ADDA-isoGlu-mdha (M.W. 944) from Microcystis aeruginosa- Lake Akersvatn, Norway; 2) -Ala-Arg-isoAsp-Arg-ADDA-isoGlu-mdha (M.W. 1023) from Oscillatoria agardhii var. - Lake Kolbatnvatn, Norway; 3) -Ala-Arg-isoAsp-Arg-ADDA-isoGlu-dha (M.W. 1009) from Oscillatoria agardhii var. isothrix - Lake Froylandsvatn, Norway. Approximate LD intraperitoneal mouse for the toxins is 50, 500 and 1000 μg/kg respectively.

Livers were removed from male Sprague Dawley rats and perfused for 15 min with a blood-free perfusate (50 ml) followed by 60 min with perfusate containing i) 25, 50, or 200 μg of M. aeruginosa toxin ii) 50, 250, 500 or 1000 μg of O. agardhii var. toxin and iii) 1000, 2000, 2500 or 5000 μg of O. agardhii var. isothrix toxin. Control livers were perfused for 75 min with the blood-free perfusate.
Use of lanthanum to detect changes in the permeability barrier of rat skin after dermal exposure to organic chemicals
Authors: Mattie D. R. , McDougal J. N. , Chase M. R. , Hixson C. J.
Published: June 2020

Occupational dermal exposures to organic solvents are of importance due to local effects in the skin and systemic toxicity if penetration occurs through the skin. Repeated or prolonged contact with organic solvents may cause dry skin and cutaneous irritation. Although organic solvents have been shown to penetrate the skin, little information is available concerning the effects on the barrier properties of skin after dermal exposure to solvents. The purpose of this investigation was to examine the ultra- structural changes in rat skin after exposure to 3 organic chemicals and to correlate changes with the location of an electron dense tracer, lanthanum, which is normally excluded by the permeability barrier in the stratum corneum.

Male rats, 6 for saline and 6 for each chemical, were exposed for 24 h to sterile saline, trichloroethylene (TCE), perchloroethylene (PERC), or toluene using dermal exposure cells developed in this laboratory. The cells were filled with 2 mL of saline or the neat chemical.
Electron microscopic study of rat myocardial infarcts induced by a free radical generator system
Authors: Feldman Dorothy , Cavallo Gary , Rosenberger Lois
Published: June 2020

The role of oxygen free radicals in the development of tissue injury and necrosis, including myocardial ischemic damage, is well documented. In this investigation, application of a free radical generator system (FRG) to rat myocardium resulted in ECG alterations typical of myocardial infarction; 24 hours after treatment, plasma lactate dehydrogenase (LDH) levels were elevated and 20% of the left ventricle was infarcted. In order to characterize the type of cellular damage and the ultrastructural changes in the affected cells, myocardial infarcts and myocardium from control rats were examined in the electron microscope.

Six spontaneously hypertensive rats were lightly anesthetized with sodium pentobarbital and infused for 10 minutes through a carotid cannula near the ostium of the coronary artery. Three rats were infused with a FRG consisting of purine (2.3 mM), xanthine oxidase (0.02 μ/ml), and Fe -loaded transferrin (0.06 μM), and 3 sham-operated rats served as controls.
Comparative SEM analyses of primary palate fusion in mouse and ferret embryos
Authors: Steffek A.J. , Lenke J.W.
Published: June 2020

Formation of the medial nasal, lateral nasal and maxillary midfacial processes is accomplished by extensive migrations of cranial neural crest cells followed by cellular and tissue interactions that lead to the fusion of these processes at the region of the isthmus. Fusion of the midfacial processes is an important developmental event since any genetic and/or environmental factors that prevent it produce cleft lip. SEM analyses were undertaken during midfacial fusion in mouse and ferret embryos to determine the surface similarities or differences that occur during this critical time of primary palate development.

Mice of the A/J strain and ferret embryos were obtained by laparotomy at the appropriate stage of midfacial fusion and washed with cold physiological saline (0.85%). They were then fixed in cold phosphate buffered (pH 7.3) glutaraldehyde for at least 48 hours, after which they were subsequently washed in cold, phosphate buffer and then placed in 70% ethyl alchohol.
Ultrastructural morphology of nontumorous lactotrophs in human pituitaries exposed to high prolactin levels
Authors: Jalalah S. , Kovacs K. , Horvath E.
Published: June 2020

Lactotrophs, as many other endocrine cells, change their morphology in response to factors influencing their secretory activity. Secretion of prolactin (PRL) from lactotrophs, like that of other anterior pituitary hormones, is under the control of the hypothalamus. Unlike most anterior pituitary hormones, PRL has no apparent target gland which could modulate the endocrine activity of lactotrophs. It is generally agreed that PRL regulates its own release from lactotrophs via the short loop negative feedback mechanism exerted at the level of the hypothalamus or the pituitary. Accordingly, ultrastructural morphology of lactotrophs is not constant; it is changing in response to high PRL levels showing signs of suppressed hormone synthesis and secretion.

By transmission electron microscopy and morphometry, we have studied the morphology of lactotrophs in nontumorous (NT) portions of 7 human pituitaries containing PRL-secreting adenoma; these lactotrophs were exposed to abnormally high PRL levels.
Different neurofilament densities show identical random distributions in side-by-side axons
Authors: Price R.L. , Paggi P. , Lasek R.J. , Katz M.J.
Published: June 2020

Neurofilaments (NF) are architectural polymers that contribute to the radial dimensions of an axon. In general, the diameter of an axon Increases as a function of the number of neurofilaments. We have studied the space-filling properties of neurofilaments in two different types of axons that have a large neurofilament content -- somatic motor axons and parasympathetic axons of the oculomotor system. Both types of axons originate from neurons in the oculomotor nucleus and they course together (side-by-side) through the oculomotor nerve; nonetheless, the packing density of neurofilaments in the parasympthetic axons is 30% greater than the neurofilament density in the somatic motor axons. Visual inspection of electron micrographs of parasympathetic and somatic motor axons suggests that the neurofilaments are uniformly distributed in both types of axons. To test this possibility, we quantified the distributions of the neurofilaments and then compared those distributions with a randomly generated (Poisson) distribution.
MacMeasure: A low cost, easy-to-operate quantitative morphometrics system for the Macintosh computer
Authors: Hook G.R. , Rasband W.
Published: June 2020

We have developed a new software package called MacMeasure for counting and measuring structures in photographs by use of a Macintosh computer and a Micro Digi-Pad digitizing tablet. The length, perimeter and area of structures can be easily measured, sequentially numbered, scaled, mapped and stored on floppy disk. The hardware for the system (Fig. 1) costs under $2000 and MacMeasure is available at no cost from the authors.

The intuitive Macintosh point and click paradigm for command selection is used to operate the software. The commands available include Point, Line, Area, Scale, Map and Help (Fig. 2). Point is used to count the number and location of items in the photograph. Line is used to measure the length of lines and Area measures the perimeter and area from which the shape factor F is calculated. The measured line or area is displayed on the Macintosh screen at high magnification after each measurement is made.
Immunoelectron microscopy of retinoblastoma
Authors: Rodrigues M.M. , Hackett J. , Wiggert B. , Chader G.
Published: June 2020

The histogenesis of retinoblastoma is uncertain. The derivation of this tumor has been attributed to neuronal and/or glial cells, by routine transmission electron microscopy and light microscopic immunocytochemical staining. Immunoelectron microscopy can provide more precise localization of retinal proteins. We investigated the immunoelectron microscopic localization of photoreceptor cell specific proteins to determine their distribution in eyes enucleated for retinoblastoma.

Surgically excised tissues were fixed in 1% glutaraldehyde 2%- paraformaldehyde in 0.1M phosphate buffer for 2 h at 4°C, dehydrated in 50%, 75% and 90% dimethyl-formamide and embedded in Lowicryl. Polymerization of Lowicryl was performed by exposure to UV light for 24 h at 4°, followed by polymerization at room temperature for 48-72 hr. Thin sections were incubated for 1 h at room temperature with primary antibodies against interphotoreceptor retinoid-binding protein (IRBP) (1:200 dilution), S-antigen (1:500 dilution) and opsin (1:500 dilution). Appropriate secondary antibodies either to mouse or rabbit IgG (1:20 dilution) were linked to colloidal gold (10-20 nm) and incubated for 30 min.
Three-dimensional reconstruction of the 40S ribosomal subunit from rabbit reticulocytes
Authors: Zhang Neng-Yu , Wagenknecht Terence , Radermacher Michael , Obrig Tom , Frank Joachim
Published: June 2020

We have reconstructed the 40S ribosomal subunit at a resolution of 4 nm using the single-exposure pseudo-conical reconstruction method of Radermacher et al.

Small (40S) ribosomal subunits were Isolated from rabbit reticulocytes, applied to grids and negatively stained (0.5% uranyl acetate) in a manner that “sandwiches” the specimen between two layers of carbon. Regions of the grid exhibiting uniform and thick staining were identified and photographed twice (magnification 49,000X). The first micrograph was always taken with the specimen tilted by 50° and the second was of the Identical area untilted (Fig. 1). For each of the micrographs the specimen was subjected to an electron dose of 2000-3000 el/nm2.

Three hundred thirty particles appearing in the L view (defined in [4]) were selected from both tilted- and untilted-specimen micrographs. The untilted particles were aligned and their rotational alignment produced the azimuthal angles of the tilted particles in the conical tilt series.
All that glisters is not gold: The physical basis of protein coloration in silver-stained gels
Authors: Steven A.C. , Bisher M.E. , Harrington M. , Merril C.R.
Published: June 2020

The introduction of silver-staining to detect electrophoretically separated proteins in polyacrylamide gels has provided a method that, with the most responsive proteins, is more sensitive by a factor of ∼100 than Coomassie Blue, the most commonly used organic stain. With silver staining, most proteins take on a brownish hue. However, under appropriate conditions, certain proteins have been found to exhibit distinct and vivid colors. Yellow, blue, red and green bands have all been observed. Colorability is a property with considerable analytical potential, in that it may become possible to infer chemical properties of proteins on the basis of their propensities for coloration upon silver-staining. Such information would considerably enhance the analytical capabilities of gel electrophoresis, which for the most part have been restricted to estimates of molecular weights and isoelectric points. To help realize this potential, we have investigated the physical basis of the colorability of proteins.
Ultrastructural preservation of the cortical region of sea urchin embryonic ectoderm
Authors: Nislow C. , Summers R. G. , Morrill J. B.
Published: June 2020

Recent studies using immunocytochemical techniques have renewed interest in the sea urchin embryo as a model system for development, particularly with respect to cellular interactions during morphogenesis. The bulk of these studies have been performed with the light microscope (LM) using fluorescently labeled antibodies, (i.e. Wessel and McClay, 1986)

Transmission electron microscopy (TEM) reveals that the cortex of the embryonic ectoderm includes membranous vesicles, yolk platelets, mitochondria, Golgi complexes, and the hyaline layer. The proximity of these compartments to the cell surface warrants a detailed study of their ultrastructure.

We have examined the quality of preservation with simultaneous and sequential fixation using glutaraldehyde and osmium tetroxide. Also examined are the effects of several additives and the quality of preservation with Bouin's fixative, which has been used in immunocytochemical preparations.

Embryos of Lytechinus variegatus were fertilized and reared according to the methods of Morrill and Santos (1986).
Development of propane jet freezing methods for cultured cardiac cells
Authors: Dalen H. , Lefurgey A. , Hawkey L. , Lieberman M.
Published: June 2020

Physiologically viable and synchronously beating heart cells can be grown in varying geometric configurations for parallel biochemical, electrophysiological, ultrastructural and x-ray microanalytical studies. Our objective in these experiments was to develop a method by which heart cells grown to confluency either as a sheet, spherical aggregate or polystrand could be rapidly frozen prior to cryosectioning and electron probe x-ray microanalysis.

A single-sided propane jet freezer, which has been shown to achieve excellent freezing of confluent cell sheets prior to freeze fracture, was constructed according to Pscheid et al.; a specimen holder was also designed and constructed which facilitated rapid transfer (<10 sec) of the various cultured cells from media to the jet freezer (FIG. 1a,b).