bluuebunny/crossref_metadata_2025 huggingface dataset:
A Device for Accurate Sampling of Tissue After Perfusion-Fixation
Authors: Estable R.F.de , Estable-Puig J.F. , Weibel J.
Published: June 2020

The main technical problems involved in the routine fine structural study of normal and pathological tissue have already been solved. In recent years, considerable attention has been focused on the diverse techniques of fixation by perfusion. Osmium tetroxide perfusion as well as aldehydic perfusion have been shown to preserve remarkably well the different elements of the nervous system. Conventional light and histochemical studies can be carried out in perfused tissue. A fairly good fixation of deeply located structures is now possible without the artifacts involved in the procedure of fixation by immersion. These studies have been extended to other tissues.

Nevertheless the conventional sampling of tissue with razor blades usually lacks anatomical precision. Indeed, the study of pathological or neuroanatomical material involve very serious problems in relation to an accurate sampling of a precisely located cell group or tract or that of a minute lesion. Furthermore, the area to be studied may not necessarily be located on the surface of the organ studied and then their excision involves a considerable disruption of the surrounding tissue. The samples are in general very irregular in shape and this makes their orientation very cumbersome.
Particle Counting and Detection
Authors: Ball Frances L. , Harris W. W.
Published: June 2020

The limit of detection of viral particles with UV absorption is 1010 particles per milliliter and that of the routinely employed electron microscopy technique is 107 to 108 particles per milliliter so that low titre virus preparations such as hepatitis serum must be concentrated severalfold if these physical methods are to be used.

The sensitivity of the electron microscope can be increased if all the particles in a given volume of sample can be sedimented onto one microscope grid and a study of this has been made using polio virus which titred 4 X 1012 by light scattering and 6 X 1011 by sedimentation. The number of micrographs and the necessary magnification to detect 105 particles per milliliter were calculated.
Ultrastructural Effects of Antimetabolites, Amino Acid Deprivation and Starvation on Myeloma Cells
Authors: Sorenson G. D. , Pettengill O. S.
Published: June 2020

The availability of antimetabolites with specific metabolic effects permits the evaluation of ultrastructural alterations produced by the inhibition of known biochemical processes. In these studies puromycin and chloramphenicol have been utilized to evaluate the effect of antimetabolites acting at different stages of macromolecular synthesis. Suspension cultures of murine myeloma cells were exposed to concentrations of puromycin (10-200 ug/ml) for 72 hrs. and then examined for incorporation of H3-Leucine and by electron microscopy. In other experiments, cultures treated with a single concentration, (50 ug/ml) were examined periodically over 72 hrs. by the same two methods. Under the latter conditions, amino acid incorporation was diminished within the first hour and ultrastructural effects were apparent by 10-12 hrs. Nuclear alterations, e.g. condensation of the chromatin and budding of the nuclear membrane, were early changes followed by the formation of cytoplasmic chromatin granules, dilatation and alteration of the granular endoplasmic reticulum and aggregation of ribosomes (Fig. 1).
On the Location of Stain in Mitochondria
Authors: Haydon G. B. , Smith S. O.
Published: June 2020

The degree of matrical staining in isolated and tissue mitochondria has been shown to be a function of their state of oxidative-phosphorylation at the time of fixation (J. Histochem. Cytochem. 15:752, 1967). High resolution EM in conjunction with these studies revealed amplitude contrast images 10 AU and larger in diameter which are independent of the focal plane. These amplitude densities have been interpreted as individual aggregates of heavy metal stain (J. Cell Biol. 35:55A, 1967). Two approaches have been used in an effort to locate such stain aggregates.

(1) Four micron epoxy sections of skeletal muscle, cardiac muscle, and liver were stained with uranyl acetate, lead citrate, or both, following the methods used to stain 500 AU sections for EM. After staining, the thick epon sections were re-embedded and thin sections cut perpendicular to the stained surface. Either or both of these metal stains penetrate 500 to 1000 AU into the thick section and give the tissue increased contrast similar to that due to staining after thin sectioning. The mitochondrial matrices are lightly stained indicating that they are not in a state of active oxidative-phosphorylation. Figure 1 shows such mitochondria at low magnification before (Figure 1a) and after (Figure lb) restaining with uranyl acetate and lead citrate. After restaining it is no longer possible to identify the original stained surface.
Nuclear Morphogenesis During Spermiogenesis in the Pulmonate Snail Lymnaea Stagnalis
Authors: Ihle James , Humphreys Walter J.
Published: June 2020

A study by Rebhun on nuclear changes during spermiogenesis in the pulmonate snail Otala lactea has presented evidence that nuclear elongation is accompanied by orientation of nuclear material into 60 A° sheets. The exact nature of the formation of these sheets, however, was not ascertained. In current work on gametogenesis in the pulmonate snail Lymnaea stagnalis observations were made of nuclear morphogenesis which describes this process.

The nucleus of a Lymnaea spermatid is spheriod or somewhat ellipsoidal in the early stages of differentiation. The karoplasm consists of a nonhomogeneous matrix of granules. Thereafter, the shape of the nucleus changes to that of an oblate spheriod. The granular nuclear material becomes fibrous in nature and is either clumped together or randomly dispersed in the karoplasm. The nuclear membrane becomes thickened at the prospective anterior and posterior regions of the sperm nucleus.
Fertilization Membrane Structure as Revealed by Freeze Etching
Authors: Humphreys Walter J. , Kreutziger G. Oscar
Published: June 2020

Many evenly spaced papillae on the surface of the unfertilized egg of Strongylocentrotus purpuratus are revealed with great clarity by freeze etching. They measure about 0.25 μ in diameter and 0.5 μ in length. When flat fracture planes through the cortical granules are obtained, differential etching causes the internal components to appear similar to the structures seen in sectioned eggs. The folded laminar component stands out with a distinctive texture. At fertilization, basic structural subunits 40-45 A° in diameter, originating from ruptured cortical granules, become organized on the inner surface of the vitelline membrane to form an array of closely packed, parallel, 197 A° wide strands diagonally striated by regularly repeating units 108 A° apart at an angle of about 72° to the long axes of the strands.

Figure 1 is a surface replica of the fertilization membrane as it appears 90 seconds after fertilization. As in the replicas of isolated and dried fertilization membranes made by Inoue et al. the strands extend into the somewhat regularly spaced shallow protrusions on the membrane surface.
Some Secretory Products of the Invasive Stage of a Digenetic Trematode
Authors: Krupa Paul L. , Bal Arya K. , Cousineau Gilles H.
Published: June 2020

The fine structure of various gland cells and their secretory products was studied in the invasive stage (cercaria) of the platyhelminth parasite, Cryptocotyle lingua. Secretory granules or droplets occur in several different specialized cell types, but those that we call attention to here are found in the (1) surface cytoplasmic tegument or “cuticle”, (2) ducts of cephalic (penetration) glands, and (3) epithelial lining of the “excretory bladder”.

The tegumental granules appear as numerous, membrane-bounded circular or oval profiles of uniform density (Fig. 1). They are scattered more or less randomly among mitochondria and other inclusion bodies of the tegument. Some of the longer granules, with a length to width ratio of about 7 to 1, have their long axes oriented perpendicularly to the surface plasma membrane of the parasite. In cercariae tested for acid hydrolases with sodium β-glycerophosphate in Barka and Anderson's modification of Gomori's medium, clumps of reaction product appear in the vicinity of the granules and elsewhere within the tegument, but not within the granules themselves. As granules that stain with periodic acid-Schiff, they are seen in certain subsurface gland cells as well as in the tegument under the light microscope.
Electron Microscopy of Caprine Cloisonne Renal Proximal Tubular Basement Membranes
Authors: Altman Norman H. , Grossman I. William , Jernigan Norman B.
Published: June 2020

The pigmented thickening of renal proximal convoluted tubular basement membranes in the goat (Capra hircus), resembling metal wires separating colored areas of enamelwork, has been termed Cloisonne kidney by Light. An associated hemosiderosis of the proximal tubule is occasionally present and the thickened basement membranes yield variable histochemical reactions for iron. The electron microscopy of the thickened basement membranes was studied and correlated with clinicopathological observations in an attempt to determine the pathogenesis of the Cloisonne lesion.

Percutaneous renal biopsies were performed on 300 goats, and 5 of these goats were found to have the Cloisonne lesion by light microscopy. Two of the involved kidneys were examined by electron microscopy and were found to have thickened proximal convoluted tubular basement membranes of uniform electron-density approximately 3 times wider than those of a normal goat (figs. 1 and 2). One of the involved kidneys displayed electron-dense deposits measuring approximately 160 A in diameter which were aggregated into larger clumps of varying size on the outer portion of the basement membrane (fig. 2). The 160 A deposits had subunits of approximately 40 A diameter and were consistent with the electron microscopic appearance of ferritin. This particular kidney did not have an associated hemosiderosis of the proximal convoluted tubule. There was no clinicopathological evidence of hemolytic, erythrocytic or urinary abnormalities in the goats with the Cloisonne lesion when compared with a group of control goats with normal renal biopsies.
Langerhans’ Granules in Cells of an Eosinophilic Histiocytoma
Authors: Watson John H. L. , Swedo John L. , Morales A. R.
Published: June 2020

Recent papers describe Langerhans’ granules in cells of normal skin, in Letterer-Siwe disease, and associated with osseous and pulmonary lesions of histiocytosis X. The present report concerns the structure and occurrence of these granules in a solitary tumor of the human posterior anal wall, diagnosed as an eosinophilic histiocytoma, confirmed by the electron microscopy. The investigation supports the hypothesis that the epidermal Langerhans’ cell is a macrophage. Samples of the recurrent tumor were fixed in cacodylate-buffered 6.4% glutaraldehyde, washed in cacodylate-buffered 0.2M sucrose, and postfixed in OSO4 for electron microscopy. Embedment was in Araldite, and sections were contrasted with uranyl acetate and lead hydroxide.

The surface of the tumor cells was very irregular, with numerous microvillus-like projections, and was without both desmosomes and basement membrane. The nuclei were lobulated, and possessed both finely dispersed and coagulated chromatin, with multiple nucleoli. The system of parallel tubules and sacs which composed the Golgi was prominent in most cells. Numerous linear profiles of RER occurred. The RNA particles were also abundant throughout the cytoplasm in groups unrelated to the RER. Centrioles were seen frequently paranuclearly. The mitochondria, with well developed cristae, were frequently altered, being locally swollen, vacuolated or containing myelin figures, Fig. A. The most striking organelles were (i) the Langerhans’ granules (L), observed in abundance throughout the cytoplasm of most of the tumor cells, but predominantly in those cells which contained (ii) the fusiform or ovoid, membrane-bound, electron-dense bodies (B). Many of these rounded, dense bodies contained concentric, double-membranous structures, Figs. C and D.
The Development and Structure of Measles Virus
Authors: Nakai T. , Shand F. L. , Howatson A. F.
Published: June 2020

Measles virus and the closely related distemper and rinderpest viruses are members of the paramyxovirus group. A feature that distinguishes these viruses from other members of the group is the occurrence in infected cells of intranuclear inclusions. These are present in addition to the cytoplasmic inclusions which are a common feature of infection by all paramyxoviruses.

In electron microscopic studies on thin sections of measles-infected primary monkey kidney cells and BSC-1 cells (a continuous line of monkey kidney cells) it was found that the intranuclear inclusions consisted of masses of tubular structures associated with a filamentous matrix. The tubules were 140 Å in diameter and had well-marked cross striations with a spacing of 50 Å. The latter were interpreted as rings of a helix forming the wall of the tubule. Aggregates of identical tubules and associated matrix material were observed in the cytoplasm of infected cells. In any one cell, tubules were usually present either in the nucleus or in the cytoplasm and there was no indication that tubules migrated from one site to another.
Techniques for Transmission Electron Microscopy of the Microstructure and Dislocation Morphology Associated with Fatigue Crack Nucleation
Authors: Shaw G.G.
Published: June 2020

Fatigue crack nucleation studies By transmission electron microscopy have been limited by the lack of a general technique for sample preparation, and while the work described herein was done with 2024-T4 aluminum alloy, the method may be adapted to a host of metals and alloys.

A fatigue sample having the geometry shown in Figure 1 was prepared. The shallow dimple shown was machined to a depth of 12 mils after which it was polished with 600 grit powder to remove burrs. The sample was then carefully heat treated to the T4 condition. The sample was painted with microstop to lines A and B and the central area including the dimple was electropolished removing about 2 mils of metal. Then the sample was mounted in a Sontag fatigue machine and cycled, at an appropriate load, until a starting crack was observed by optical microscopy. Due to the sample geometry cracks usually started at the bottom of the dimple. Some samples were stopped before crack nucleation to observe by transmission electron microscopy precrack microstructure and dislocation morphology.
Analysis of Contrast from Lattice Defects
Authors: Bell W. L.
Published: June 2020

The differential equations of the two-beam dynamical theory of electron diffraction in an absorbing single crystal are, ignoring unimportant phase factors:

where T(z) and S(z) are the transmitted and diffracted amplitudes,

the mean and anomalous absorption distances; to is the extinction distance, z the foil thickness, Sg the macroscopic deviation parameter, ḡ the reciprocal lattice vector and R the displacement function of any defect present in the crystal. Occasionally, but not often, these equations can be handled by standard techniques; the wave vectors allowed in the crystal can be determined and the transmitted and diffracted waves expressed as linear combinations of waves with these wave vectors.
Dislocation Configurations in the γ’ Phase Ni3(AlTi)
Authors: Thornton P. H. , Davies R. G.
Published: June 2020

The γ’ phase Ni3Al, as with all f.c.c. metals and also the isomorphous phase CU3Au, deforms by octahedral slip over a wide temperature range. However, in contrast to these other materials cube slip can also occur in γ'. This extra slip mode, which is very unusual in metals, has been observed to operate at temperatures near 800°C. In the present study of the deformation behavior of the γ' phase Ni3(AlTi), the critical resolved shear stress for cube slip was found to become equal to that of octahedral slip at 400°C approximately and was less than that of octahedral slip at 700°C.

An examination of slip plane sections of <100> oriented crystals of Ni3(AlTi), in which deformation is restricted to the ﹛111﹜ mode, revealed mainly screw dislocations in samples deformed at temperatures between 25°C and 750°C. At the lower temperatures, the screw dislocations were straight (Fig. 1) whereas at the higher temperatures the dislocations were more heavily jogged (Fig. 2). In contrast, slip plane sections taken from crystals which could deform by cube slip showed both edge and screw dislocations (Fig. 3).
Stacking Fault Contrast in an Ordered L12 Lattice
Authors: Oblak J. M. , Kear B. H.
Published: June 2020

Stacking fault contrast arises from the phase shift α = 2π ḡ · experienced by the diffracted wave at the fault. In an ordered L12 lattice, the displacement <111> is not necessarily equivalent to a displacement of the type <112>. 1 and 2 differ by a displacement <110> which can introduce a phase shift of π when ḡ is a superlattice diffraction vector. The physical difference can be seen by examining the formation of an intrinsic fault. When the fault is produced by removal of a close packed plane, <111>, no nearest neighbor violations of order result; on the other hand,nearest neighbor order is disrupted by shear of the <112> type.

Similarly, there are two types of extrinsic faults. Values of α are listed in Table I for [111] and [112] with ḡ of the form 100, 200, and 300. As expected, the two representations are equivalent when ḡ is a fundamental reflection. For g = 100, 010 the values of α for 1 and 2 differ by π because of the antiphase boundary associated with the latter displacement.
Dislocations and Growth Occlusions in Tungsten Selenide
Authors: Richman M. H. , Prince K. D. , Wold A.
Published: June 2020

Tungsten selenide, WSe2, crystallizes in the molybdenite structure and has the space group . The cations are arranged in close-packed hexagonal layers surrounded by two adjacent close-packed planes of anions - in such a way that the metal ions occupy trigonal prismatic sites. The basic unit cell consists of three of these AX2 units and exhibits basal plane cleavage. WSe2 is a semiconductor and is transparent to light; transmitting it in the long-wavelength red region of the spectrum. The existence of these properties makes it interesting to study, at the electron microscope level, the structural effects which could influence the electrical and optical properties of this material.

Samples of WSe2 single crystals were grown by vapor transport with iodine using the technique of Kershaw, Vlasse, and Wold. By using repeated cellophane tape strippings, thin flakes were obtained with a basal plane orientation. These were then floated from the tape in benzene, rinsed in acetone, and mounted on grids.
A Simplified Electron Beam Gun for Producing Evaporated Films in Electron Microscopy
Authors: Schneidniller R. F. , Richardson J. H.
Published: June 2020

The use of an electron beam as the source of heat for the vacuum evaporation of materials has increased rapidly in the past few years. Some of the advantages of electron beam over resistance heating are; 1) it can be easily controlled and manipulated. However, even with these significant advantages it has not found extensive application in most electron microscopy laboratories. The main reason for its limited use is that the commercial instruments available are for heavy production work; as a result they are overdesigned for this purpose. The object of this study was to design an electron beam instrument specifically for this field. This would require the instrument to be: 1) easily constructed using readily available commercial parts, 2) nominal in cost and 3) uncomplicated to operate.

The initial phase of this study was concerned with the electron gun design. A television picture tube gun was chosen because it produces a fine beam of electrons, it has incorporated into its design all of the elements necessary for critical control of the electron beam and it is readily available.
A Newly Designed 650kv Electron Microscope
Authors: Shiraishi K. , Katsuta T. , Ozasa S. , Todokoro H.
Published: June 2020

We have recently completed a newly designed 650KV electron microscope. An external view of this advanced instrument is shown in Figure 1. A symmetrical Cockcroft-Walton circuit has been adopted as the high voltage generator. The cathode is heated by high frequency power; a battery is not employed. The high voltage stability is better than 1 x 10-5/min.

The sectional diagram of the column shown in Figure 2 is 420mm in diameter and 2750mm in height. The illuminating system consists of a double condenser lens and a magnetic alignment device. Dual deflector assemblies for dark and bright field images, selectable by push button, are built beneath the condenser lens. Two selectable stigmator power supplies are also provided for dark and bright field image operation.
Objective Lens Properties of Very High Excitation
Authors: Suzuki S. , Akashi K. , Tochigi H.
Published: June 2020

Recently the image quality of the electron microscope has been highly improved, because of technical advances made for the exclusion of mechanical and electrical instabilities in the instrument itself. To further improve the resolution, it is important to minimize the chromatic aberration, as well as the spherical aberration. This is true, even though the accelerating voltage has excellent stability; because of the unavoidable velocity fluctuations of electrons, resulting from thermal emission from the cathode, and the energy-loss in the specimen.

Therefore, the specimen should be immersed deeply into the lens field, to make these aberrations small. The result will be very high lens excitation. In 1962, Professor E. Ruska and Dr. W. Riecke had investigated the single field condenser-objective lens at the center of which the specimen is placed. Prior to that, in 1960, Dr. S. Suzuki, one of the authors, had pointed out that this new objective lens, in which the specimen is placed at the image side from the center of the lens field,(of the condenser-objective lens: but no special illuminating system is necessary.
High Voltage Electron Microscopy
Authors: Fisher R. M.
Published: June 2020

The striking results obtained by Dupouy and Perrier using the Toulouse microscope sparked extensive interest in high voltage microscopy throughout the world. Several similar instruments are now in use and others will be operational in the near future.

The Physical basis for high voltage microscopy is a marked reduction in electron wavelength and scattering cross section with increasing voltage (Fig. 1) which promise improved resolution and penetration. Because of the relativistic increase in electron mass, the refractive power of the lenses in the electron optical column would have to be increased 20x to maintain the dimensions of 100 kv microscopes. The maximum peak field (Hm) magnetic lenses is limited by saturation of the iron pole-pieces resulting an increase in minimum focal length (Fig. 2) and hence of column dimensions. The suitability of superconducting lenses for high voltage microscopy has not escaped attention and no doubt they will be utilized in the near future.
The Potentials of Scanning Microscopy
Authors: Crewe A. V.
Published: June 2020

If the resolving power of a scanning electron microscope can be improved until it is comparable to that of a conventional microscope, it would serve as a valuable additional tool in many investigations.

The salient feature of scanning microscopes is that the image-forming process takes place before the electrons strike the specimen. This means that several different detection systems can be employed in order to present information about the specimen. In our own particular work we have concentrated on the use of energy loss information in the beam which is transmitted through the specimen, but there are also numerous other possibilities (such as secondary emission, generation of X-rays, and cathode luminescence).

Another difference between the pictures one would obtain from the scanning microscope and those obtained from a conventional microscope is that the diffraction phenomena are totally different. The only diffraction phenomena which would be seen in the scanning microscope are those which exist in the beam itself, and not those produced by the specimen.
Thermal Stress Effects of Thin Superconducting Films
Authors: Connella M. , Deck R. J. , Morriss R. H.
Published: June 2020

In order to completely understand the role of microstructural defects in superconductivity, it is very desirable to have quantitative correlations between superconducting properties and structural properties. This research is part of a study to correlate grain-sizes with “flux creep phenomena” which occur in the mixed state of Type II superconducting films. Since the superconducting properties in our study must be observed at liquid helium temperatures, whereas the films are evaporated at elevated temperatures, the structural changes produced in some films by cycling to 4.2°K have been investigated.

As the temperature of a film is lowered, the difference in thermal expansion coefficients of a film and its substrate results in thermal stress. This stress can produce structural changes. Films have been examined by electron microscopy techniques before and after a temperature cycle down to 4.2°K and back to room temperature. All temperature cycles were carried out in approximately 20 minutes. Both transmission and replication techniques have been employed. The direct replication method was employed using carbon. The carbon replica was separated from the film and post-shadowed with Pt-C.
Structure of Amorphous Films Using Direct Recording Electron Diffraction
Authors: Dove D. B.
Published: June 2020

Vapor deposited layers of certain materials show a diffuse, amorphous diffraction pattern; carbon is an example. Such patterns may not be interpreted by identification of Bragg peaks, instead the intensity profile is measured with all possible precision and the data is then treated by computer, yielding what is, in effect, a spectrum of interatomic distances within the specimen.

The direct recording electron diffraction technique is particularly suited to the measurement of diffuse patterns. The electron beam from a conventional electron gun and magnetic lens arrangement produces a transmission diffraction pattern of a thin film specimen. Coils beneath the specimen produce a magnetic field which deflects the diffraction pattern across a very small aperture.
Systematic-Reflection Effects in Electron Diffraction
Authors: Fukuhara A.
Published: June 2020

Many workers have recently noticed what is called many-beam effects In the electron diffraction by crystals. In particular it was found and studied by several people that some second-order reflections vanish even at the exact Bragg position when the acceleration energy coincides with a particular characteristic value EC. This phenomenon has been confirmed to be due to the effect of the first order reflection which is not exactly excited at this position. Systematic reflections sometimes have a decisive role as in this example depending upon the crystal and the reflection. Furthermore it must be noted that the effect is intensified with the rise of the acceleration energy owing to the relativistic change in the electron diffraction.

In this study the effects of systematic reflections on extinction contours obserable in an electron-microscopic image of a crystal have been investigated on the basis of dynamical theory taking more than two beams into account. Suppose a wedge-shaped crystal which bends uniformly. As is well known extinction fringes are observed in a bright-field image of such a crystal. This intensity distribution due to diffraction contrast has been computed and printed as in half-tone process by a line-printer of an electronic computor Hitac 5020. Four groups of systematic reflections are studied in the present report: Al(nnn) at 100kv, Al(nnn) at 1000kv, Si(nnn) at 100kv and hexagonal CdS(noo) at 150kv.
Multi Beam Calculations of Dislocation Contrast
Authors: Cann C.D. , Foxon C.T.B. , Sheinin S.S.
Published: June 2020

Calculations of the diffraction contrast of dislocations are of great importance in understanding the nature of dislocation images observed by the technique of thin film electron microscopy. The calculations which have been carried out up to the present time have been based on the two beam approximation of the dynamical theory and thus neglect the effects of systematic reflections. The results presented in this report take these reflections into account by using the scattering matrix formulation of the general dynamical theory taking effects of absorption into account. The variation of intensity across a dislocation was found by considering the crystal to be made up of a large number of slices each of which is perfect but which are displaced with respect to one another by a displacement function based on the elastic continuum model of a dislocation. This method of calculation was chosen because of its convenience in computer calculation and because it avoids the approximation required in the usual differential equation formulation of the dynamical theory for an imperfect crystal.
Detection of Hyperfine Precipitates in Nickel-Base Alloys
Authors: Beardmore P.
Published: June 2020

One of the primary objectives of the use of the electron microscope in the examination of metal foils is to ascertain the exact details of the microstructure in order that a realistic interpretation of the deformation mechanisms can be made. However, problems can arise in two phase structures in which the second phase is present as particles of widely differing size. In such cases it is possible to overlook the extremely fine particles because of the predominance of the larger particles on the fluorescent screen. Thus, fine details of the microstructure can remain undetected. This is particularly true in alloys in which both the precipitate and matrix have a common crystal structure and differ only in state of order. In such a structure, the detection and clarity of the precipitates is enhanced by dark field microscopy.
Charge transfer in binary alloys: A future for electron energy loss spectroscopy in materials science
Authors: Ahn C. C. , Pearson D. H. , Fultz B. T.
Published: June 2020

The redistribution of atomic charge which takes place from an atom of one type to that of another in a binary alloy system is fundamental to the formulation of models of enthalpies of formation of these systems. Of special interest are charge transfers where one of the alloy constituents is from the first row transition series. The extent to which the 3d band is filled, ultimately plays an important role in the propensity with which alloys will form intermetallic phases. An understanding of electron charge transfer is important not only in crystalline systems but can also serve as the basis for the determination of the extent of chemical short range order (CSRO) in amorphous binary alloys.

Electron energy loss spectroscopy (EELS) in the electron microscope can probe unoccupied bound states and unlike other spectroscopies which probe core levels, is not surface sensitive. The features of the energy loss spectra of the 3d metals which make charge transfer studies possible are the L23 transitions. These spectra are characterized by two “white lines” at the threshold energy which result from ionizations from the 2p3/2 and 2p1/2 spin orbit subshells to a narrow bound 3d state. Beneath and beyond the white line transitions are transitions to the continuum states.
Electron microscopy and the deep sea: Discovery and exploration of symbioses between invertebrates and bacteria
Authors: Cavanaugh Colleen M.
Published: June 2020

Electron microscopy has played an important role in the discovery of symbioses between sulfur-oxidizing chemoautotrophic bacteria and marine invertebrates. Initially proposed for deep-sea hydrothermal vent tubeworms, associations between chemoautotrophs and invertebrate hosts appear to be widespread in nature (see review). In these proposed mutualistic symbioses, bacterial endosymbionts are thought to provide the host animal with an internal source of nutrition via the autotrophic fixation of CO2, analogous to the role of chloroplasts in plants. Reduced inorganic compounds, e.g., sulfide, serve as the symbionts' source of energy and reducing power. The host, in turn, provides its symbionts with the necessary inorganic nutrients for chemosynthesis.

Transmission and scanning electron microscopy have indicated that numerous procaryotic-like cells, resembling Gram-negative bacteria in ultrastructure, comprise the bulk of the trophosome tissue in Riftia pachyptila, the vent vestimentiferan tubeworm. Further transmission electron microscopy (TEM) studies show that the symbionts are contained within membrane-bound vacuoles and appear intracellular. Activities of enzymes associated with sulfur metabolism and with carbon fixation, notably ribulose-1,5-bisphosphate carboxylase (RuBPCase), the key enzyme of the Calvin Benson cycle, have been detected in the trophosome tissue, indicating that the symbionts are chemoautotrophs.
3-D organization of fibrinogen receptors using computer reconstruction and whole-mount microscopy
Authors: O'Toole E. T. , Hantgan R. R. , Lewis J. C.
Published: June 2020

Thrombocytes (TC), the avian equivalent of blood platelets, support hemostasis by aggregating at sites of injury. Studies in our lab suggested that fibrinogen (fib) is a requisite cofactor for TC aggregation but operates by an undefined mechanism. To study the interaction of fib with TC and to identify fib receptors on cells, fib was purified from pigeon plasma, conjugated to colloidal gold and used both to facilitate aggregation and as a receptor probe. Described is the application of computer assisted reconstruction and stereo whole mount microscopy to visualize the 3-D organization of fib receptors at sites of cell contact in TC aggregates and on adherent cells.

Pigeon TC were obtained from citrated whole blood by differential centrifugation, washed with Ca++ free Hank's balanced salts containing 0.3% EDTA (pH 6.5) and resuspended in Ca++ free Hank's. Pigeon fib was isolated by precipitation with PEG-1000 and the purity assessed by SDS-PAGE. Fib was conjugated to 25nm colloidal gold by vortexing and the conjugates used as the ligand to identify fib receptors.
Fluorescent microtubules break up under illumination
Authors: Vigers G.P.A. , Coué M. , McIntosh J.R.
Published: June 2020

The dynamic behavior of microtubules (MTs) in living cells has recently been elucidated by the use of tubulin tagged with a fluorescent molecule and then injected into cultured cells. The dynamics of the labelled tubulin are then followed either by watching the incorporation of the fluorescence immediately after injection, or by monitoring fluorescence redistribution after photobleaching (FRAP).

Until recently, the best fluorescent analogue of tubulin appeared to be dichlorotriazinyl-amino-fluorescein tubulin (DTAF-tubulin). We have now made fluorescein, rhodamine and X-rhodamine n-hydroxy-succinimidyl derivatives of tubulin. These analogues all have a higher fluorescence to protein (f-to-p) ratio and better in-vitro assembly characteristics than the DTAF-tubulin previously used. They have been injected into cultured PtKl cells, where they incorporate well into the microtubule cytoskeltons of the cells. However, while characterising the properties of these four analogues we discovered that they all suffer from a major problem: Microtubules formed from them, either in vitro or in vivo, are destroyed as the bound fluorophore becomes photobleached. We have characterised the photolability of the fluorescent microtubules both in vivo, using epifluorescence microscopy, and in vitro with DIC microscopy.
Preparatory techniques for the quantitative analysis of asbestos in tissues
Authors: Roggli V. L.
Published: June 2020

With the heightened awareness of various diseases related to asbestos exposure in the workplace, there is an increasing demand for the analysis of tissue for its asbestos fiber content. Quantitative analysis of tissue asbestos burden is not only a valuable research technique, but also has medical implications regarding etiology in patients with suspected asbestos-related diseases and legal implications regarding product liability. It is the purpose of this article to briefly review the various techniques used in the preparation of tissues for quantitative analysis of asbestos fiber content. These can be conveniently divided into four steps: 1) tissue selection; 2) digestion; 3) filtration; and 4) mounting.

Tissue selection. The first requirement for tissue asbestos analysis is that an adequate sample is available. Since there is some variation in tissue asbestos content from one site in the lung to another, the more tissue that is available to sample the better.
Confocal microscopy at the integrated microscopy resource for biomedical research (IMR) of the university of wisconsin
Authors: Schatten G. , Paddock S. , Cooke P. , Pawley J.
Published: June 2020

Confocal microscopy holds great promise for improved imaging of fluorescent or reflective biomedical specimens. The IMR is actively investigating the advantages and optimal usage of the Medical Research Council's Lasersharp laser - scanning confocal microscope and Tracor/Northern's Tandem Scanning Microscope, which benefits from the principles outlined by Petran et al. and Boyde.

Quantitative evaluation of microscopic images has always been complicated by the effect of out-of-focus structures on the final image. These effects can be greatly reduced if the conventional light microscope is replaced by a scanning-confocal light microscope. In such an instrument two conditions are met: 1) only a single point of the sample is illuminated at any time and 2) this point on the sample is then imaged onto the pinhole at the entrance to the photodetector. Because little light from out-of-focus planes will pass through the pinhole, only in-focus data is recorded.
Cryotransfer device for cryo-SEM to observe unfixed frozen biological samples
Authors: Makita T. , Asahina T. , Manba K. , Kagabu S.
Published: June 2020

Further to our previous reports on the combination of CRYO-SEM and WET-SEM, this is application of another type of cryo-SEM device(SP2000 Sputter cryo, ST2000 Semtran, and SC2000 Semcool of Emscope Lab,England) attached to WET- SEM(W-40,Akashi Beam Technol.Tokyo) and SEM(DS130,ABT.Tokyo) to observe unfixed tissues of rats. The main check points of this system were how its cryotransfer device could prevent frost and ample space of cryo chamber which is independent to SEM chamber could safely utilized.

Briefly preparation steps before observation were as follows;

To insert thin specimen into two metalic tubies and install this assembly in specimen holder

For rapid freezing immerse this whole assembly into semi-solid nitrogen.

Enclose this frozen specimen within a small chamber of transfer device and evacuate the chamber.

Transfer to precooled (less than-170°C) specimen preparation chamber.

By a stroke of handle,crack two metalic tubes in which frozen samples are contained. Alternatively scrach the surface of samples by a surgical knife.
Low-temperature specimen preparation apparatus and techniques for low-temperature scanning electron microscopy (LTSEM) and synchrotron soft x-ray microscopy
Authors: Bastacky Jacob , Hayes Thomas L. , Lee Joong , Lee Charles , Goerke John , Ferreira Steve , Thrasher Ralph , Garcia Edwin
Published: June 2020

We have developed equipment and techniques for low-temperature scanning electron microscope (LTSEM) and x-ray microscope examinations of animal tissue samples. A cryoprobe for rapidly freezing tissue in vivo, a low-temperature saw for cutting large blocks of frozen tissue without warming, cardboard containers for sample storage in liquid nitrogen (LN2), tools for holding and manipulating frozen specimens, and an under-LN2 specimen viewer are described here. An LTSEM specimen holder for small blocks of tissue and a low-temperature trim saw for precisely cutting such blocks are described elsewhere. We have found such equipment, along with various commercial and specially fabricated dewars, to greatly facilitate our LTSEM experiments.

To minimize ice crystal size by freezing as rapidly as possible and to maintain tissue in as close to normal physiologic state as possible during freezing, we use a cryoprobe for freezing 1 cm2 surfaces of tissue in vivo. The cryoprobe (Fig. 1) is a highly-polished 1 mm thick, 10 mm diam.
Motile microtubles in foraminifera: Correlative video-enhanced contrast light and transmission electron microscopy
Authors: Travis J.L. , Bowser S.S.
Published: June 2020

Analog and digital contrast-enhanced video light microscopy have provided exciting new views of subcellular architecture and dynamics. One such example is recent work on the motility of the pseudopodia of Allogromia and other foraminifera. Because of the unsurpassed clarity with which their cytoplasmic microtubules can be visualized, these organisms have been used extensively as model systems in which to study microtubule- associated cell motility in vivo. We have employed correlative electron microscopy to further resolve the subcellular processes imaged by the video microscope. Our studies indicate that the bidirectional axial and lateral movements of cytoplasmic microtubules drives the formation and movement of the pseudopodia. Furthermore, organelle and cell surface transport occur exclusively along the motile microtubules.

The exceptional visibility of foraminiferan microtubules in vivo is due to the fact that when the organisms are plated on cationized substrates, the normally cylindrical pseudopodia spread along the substrate and become highly flattened (generally to a thickness of ≤ 0.5μm).
high-resolution cryomicroscopy of porin (OmpF)
Authors: Sass H.J. , Massalski A. , Beckmann E. , Büldt G. , Dorset D. , Heel M.v. , Rosenbusch J.P. , Zeitler E. , Zemlin F.
Published: June 2020

Porin (OmpF) is one of the major outer membrane proteins of Escherichia coli /1/. This integral membrane protein functions as a molecular sieve for hydrophilic molecules with an exclusion limit of around 600 dalton /2/.

For our investigation, purified porin was reconstituted in di-myristoyllecithin vesicles, where it formed 2D-lattices. The crystallinity was considerably improved by subsequent treatment with phospholipase. Electron microscopy was done on the “Suleika”, a cryo-electron microscope which permits low-dose imaging under “cryo-protection” conditions (4K) /3/. The embedding medium was glucose, which allows the visualisation of integral membrane proteins at high resolution /4/. Under these conditions, we obtained several electron micrographs showing optical diffraction of up to 0.8nm resolution. Image prossessing was performed by using the correlation averaging method to overcome the imperfections of the porin lattice. Only about 80% of the lattice shows well defined cross-correlation peaks which are marked in Figure 1. Dislocations along the lattice lines are clearly discernable. The averaged image of the porin trimer (Fig. 2 ) was built up from unit cells corresponding to positions with correlation peaks above the noise level.
Herpesvirus Nucleocapsids Imaged in the Frozen-Hydrated State
Authors: Booy F. P. , Newcomb W. W. , Brown J. C. , Steven A. C.
Published: June 2020

Herpesviruses are an extensive family of double-stranded DNA-containing animal viruses. The typical herpes-virion consists of a loosely-fitting envelope derived from the nuclear membrane of the host cell, within which a proteinaceous "tegument" layer encloses an icosahedral nucleocapsid. The capsid is a thick-walled shell of triangulation class T=16, whose major constituent is a protein of monomer mass ∽ 155kDa. Hexamers of this protein occupy the hexavalent sites of the icosahedral surface lattice. The nucleocapsid also contains several minor proteins and the linear genome of 80-150 MDa

Despite investigations extending over more than 20 years, many basic questions concerning the HSV nucleocapsid structure remain unanswered; e.g. where are the minor proteins located? and what is the structure and chemical identity of the vertex capsomers? Moreover, although several models have been proposed for the packing of DNA inside the capsid, further, more detailed, evidence is needed to settle this issue. Conventional electron microscopic approaches having been constrained by difficulties in preserving and conveying the native structures of intact nucleocapsids, we have started to explore the potentialities of cryo-electron microscopy for this system.
Fourier Analysis of Digital STEM Images in the Study of Transparency in Human Cornea And Sclera
Authors: Vaezy S .
Published: June 2020

The structure of transparent human cornea is similar to that of the opaque human sclera, and they both consist of collagen fibers embedded in a mucopolysaccharide matrix.[1] This similarity in structure and composition, in contrast to a large difference in turbidity, presents an important question regarding the basis of transparency in the cornea.

In general, a transparent structure permits most of the incident light to be transmitted, whereas an opaque structure scatters it. Scattering of an incident light wave occurs when the spatial fluctuations in the index of the refraction of the medium have dimensions close to the wavelength of visible light.[2] To analyze spatial fluctuations in cornea and sclera we have developed techniques based on Fourier analysis of digital STEM images.

Fourier analysis allows direct quantitative measurements of the fluctuations in any signal. The signal is resolved into its constituent sinusoids or Fourier components. Amplitude, and frequency of each component are quantitatively obtained using the Fourier Transform (FT).
Image Contrast in the SEM from 1 to 30 keV
Authors: Joy David C
Published: June 2020

The image produced by the SEM is not an intrinsic property of the object viewed but is also a function of the electron-optical conditions used to generate the image as well as of the chemical and geometric characteristics of the specimen itself. The image is therefore not a simple representation of the specimen, but must be interpreted to yield the desired information. A general purpose method for image interpretation is to perform a detailed contrast simulation for the specified object and to then examine the influence of various factors such the beam energy or signal mode on the form of the image so as to deduce the rules which relate the form of the image to the form of the specimen.

In the computations shown here a Monte Carlo simulation is used to model the interaction of the incident beam. The generation of the secondary electron signal is incorporated using the method proposed by Salow, and the escape probability of these secondary electrons is computed using a simple exponential approximation.
Edge Penetration Effects in the Low-Loss Electron Image in the SEM
Authors: Wells Oliver C.
Published: June 2020

The low-loss electron (LLE) image in the scanning electron microscope (SEM) is useful for the study of uncoated photoresist and some other poorly conducting specimens because it is less sensitive to specimen charging than is the secondary electron (SE) image. A second advantage can arise from a significant reduction in the width of the “penetration fringe” close to a sharp edge. Although both of these problems can also be solved by operating with a beam energy of about 1 keV, the LLE image has the advantage that it permits the use of a higher beam energy and therefore (for a given SEM) a smaller beam diameter. It is an additional attraction of the LLE image that it can be obtained simultaneously with the SE image, and this gives additional information in many cases. This paper shows the reduction in penetration effects given by the use of the LLE image.