bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Structure of Chromatin
Authors: Jones Janice L. , Beer Michael 
Published: June 2020

Chromatin from calf thymus has been reinvestigated.If the extraction procedure of Zubay and Doty is altered through the omission of EDTA and the resulting fibrils are picked up on grids by the method of Koller et al from a solution containing no added salt, one observes fibrils of diameter about 230 Å. (Figure A). This is the same diameter as was found by DuPraw and Bahr for the component fibrils of isolated honey-bee chromosome's. If the salt concentration is increased, strands of diameter approximately 100 Å are found. The transition from 230 Å to 100 Å fibrils occurs not as a separation into two fibrils but as a thinning and elongation.
Whole Mount Electron Microscopy of Chicken Microchromosomes
Authors: A. Okada Tadashi , E. Comings David 
Published: June 2020

Although many observations have been made on the ultrastructure of chromosomes by whole mount electron microscopy, the large size of most chromosomes has made it difficult to trace the chromatin fibers throughout the entire course of a given chromatid.In the present study, microchromosomes of the chicken were used to provide information on this facet of chromosome structure. Cells from a tissue culture of chicken embryo fibroblasts were exposed to colcemid 0.1 ug/ml for 3 hours and the cells in mitosis were selectively removed by shaking with 0.05% trypsin.
Pipes Buffer: Effect Of Osmolality On Morphology Of Squash R00t Tips
Authors: Martin Albert R. , Bystrom Barbara G. 
Published: June 2020

Buffers routinely used in electron microscope work are often unsuitable for non-routine work. We have found that piperazi ne-N,N bis(ethane sulfonic acid), monosodium salt, (PIPES) is a suitable buffer for both routine and non-routine work. PIPES is one of a class of buffers specifically designed for biological use by Good et al(1), and has many useful properties.From the work of Schultz and Karlsson (2), we knew that buffer osmolality was an important parameter in preserving tissue morphology. Thus before we could use PIPES as a buffer for electron microscope work, a study on the effect of PIPES osmolality on morphology was needed. The results of this study are summarized below.
Cytochemical and Morphological Differentiation of Epithelial Cells in Ductuli Efferentes of Chinese Hamster.
Authors: Yokoyama Masao , P. Chang Jeffrey 
Published: June 2020

Light microscopy and histochemistry of ductuli efferentes have been frequent subjects of investigation among various species of animals. Only a limited number of ultrastructural studies on this organ have been published. Adequate data on the fine structure and ultracytochemistry of ductuli efferentes of Chinese hamster are not available in the literature. Investigation of this subject therefore was initiated in this laboratory. Some preliminary findings are reported herein.Two distinctive types of cells, namely ciliated and nonciliated, are observed in the epithelia. The ciliated cells ('Fig. 1) always have typical kineto-cilia with 9 + 2 groups of microtubules. A few microvilli may be intermingled with the cilia on the apical surface of the plasma membrane. Also in the apical region, a peculiar structure (Fig. 1, arrow) resembling the “fibrogranular material” of respiratory epithelium is present. Its presence in the ductuli efferentes has not been reported previously.
Cilia in Endometrial Stromal Cells of the Hamster Uterus
Authors: Clark M. V. , Brinsfield T. H. 
Published: June 2020

During an investigation on the ultrastructure of the hamster uterus cilia-like structures were frequently observed in the cells of endometrial stroma. The occurrence of these structures stimulated further investigation to determine if their morphological characteristics were similar to typical cilia.Specimens of uterine endometrium from hamsters in estrus or during various stages of pseudopregnancy were fixed for 1 hour at 4° C in Millonig's 1% buffered osmium tetroxide at pH 7.4, dehydrated, and embedded in an Araldite-Epon mixture and cured for 48 hours at 60° C. Sections for electron microscopy were cut with a MT-1 Porter-Blum Ultra-Microtome and stained with a saturated solution of methanolic uranyl acetate and viewed in a Philips EM 200 electron microscope.
Thermal Considerations in Lens Regulator Systems
Authors: Newton K.C. 
Published: June 2020

Thermal effects in lens regulator systems have become a major problem with the extension of electron microscope resolution capabilities below 5 Angstrom units. Larger columns with immersion lenses and increased accelerating potentials have made solutions more difficult by increasing the power being handled. Environmental control, component choice, and wiring design provide answers, however. Figure 1 indicates with broken lines where thermal problems develop in regulator systemsExtensive environmental control is required in the sampling and reference networks. In each case, stability better than I ppm/min. is required. Components with thermal coefficients satisfactory for these applications without environmental control are either not available or priced prohibitively.
A Shelved Structure for the Support of An Electron Optical Column
Authors: McLaughlin P.H. 
Published: June 2020

A shelved structure for the support of an electron optical column affords advantages both to the designer and the user. A lens may be removed for cleaning for example, without demounting the remaining lenses. A custom device for another example, may be placed on a shelf, substituting for the standard lens perhaps so that some specialized research may be undertaken. Especially advantageous is a shelved arrangement if the column assembly is designed to hang from a supporting structure such as a gas borne floating platform, as is the case with the system described below.As shown on the schematic, a floating platform (I) supports the electron source apparatus (2) and a U-shaped column support shelf (3). The column support shelf acts as a key for locating and supporting three struts (4) which with nuts (5) support the condenser shelf (6), the objective shelf (7), the upper projector shelf (8), and the lower projector shelf (9).
Characterisation of Polycrystalline Silicon Carbide by Scanning and Transmission Electron Microscopy
Authors: Faulkner D. , Stevens R. 
Published: June 2020

Silicon carbide is an extremely hard refractory material. Corrosion resistance, which is a general limitation of most carbides, is also good. These features alone make silicon carbide an important engineering material, but in addition, its low neutron absorption cross-section, and its behaviour under irradiation make it a particularly attractive material for use in a nuclear environment.The mechanical strength of self-bonded silicon carbide is primarily dependent on grain size and on the presence of free silicon in the material. Figure 1 shows a scanning electron micrograph of a fracture surface. The morphology is typical of a brittle transgranular fracture, although there is evidence of some ductility in the free silicon phase.
Observations oh Nucleation and Growth of Voids in Nickel
Authors: Brimhall J. L. , Kissinger H. E. , Mastel B. 
Published: June 2020

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.
Resistivity and Electron Microscopy Study of Precipitates in Fe-Ni-Co-Mo
Authors: Christou A. , Lowry R.W. 
Published: June 2020

The details of the precipitation hardening mechanisms have been studied previously. Peters and Cupp have measured the kinetics of precipitation in an 18 pet Ni-Co-Mo steel. Hardy and Heal have studied the reversion processes caused by annealing for short times at temperatures above the aging temperature. This paper reports studies of the pre-precipitation and reversion stages in an 18 pct. Ni-Co-Mo steel (maraging with .46 pct Ti).The annealed microstructure of the parent steel consists of BCC martensitic grains. Within the matrix lies a fairly high density of dislocations whose configurations appear irregular. These dislocations are nucleation sites and are shown in Figure 1.
A Comment on Mica as Electron Microscope Specimen Support Film
Authors: Heinemann Klaus 
Published: June 2020

Single crystal mica substrate films thin and stable enough for high resolution electron microscopy can be prepared in a variety of ways, e.g., by adhesive tape cleavage, direct mechanical stripping, and by ion bombardment thinning from one side.High resolution electron microscopic studies of such thin mica substrate films exhibit the following characteristic features:
— Relatively high rate of radiation damage during electron microscope observation— Comparatively low amount of background phase contrast, even after complete decomposition due to radiation damage— Good mechanical and electrical stability, especially in areas which have been exposed to a high electron flux and show radiation damage.
Electron Microscope Image-Recording System for Dynamical Observation
Authors: Mayeda M. , Tukahara S. , Yotsumoto M. , Taoka T. 
Published: June 2020

Recent advance in high voltage electron microscope has entailed an expanded application of a continuous observation of non-static structures in specimens at elevated temperature or under stress. In order to attain this end, the need for a VTR system capable of recording structural changes is increasingly felt. Through several investigations, we eventually decided to adopt an Image Orthicon tube, as pick-up tube, considering its high recording speed, reliability and ease of operation.In this paper, a detectable speed of the specimen depending upon the specified resolution, electron beam flux and size of the specimen is experimentally discussed by adjusting the gain of the amplifier so as to obtain an optimal condition. The TV system consists of a high-gain Image Orthicon tube and a transformer circuit which has a band width of 8MHz and a frame speed of 1/30 sec, as shown in Fig. 1.
Some Applications of the U. S. Steel MVEM
Authors: Lally J. S. , Thomas L. E. , Fisher R. M. 
Published: June 2020

A variety of materials containing many different microstructures have been examined with the USS MVEM. Three topics have been selected to illustrate some of the more recent studies of diffraction phenomena and defect, grain and multi-phase structures of metals and minerals.(1) Critical Voltage Effects in Metals and Alloys - This many-beam dynamical diffraction phenomenon, in which some Bragg resonances vanish at certain accelerating voltages, Vc, depends sensitively on the spacing of diffracting planes, Debye temperature θD and structure factors. Vc values can be measured to ± 0.5% in the HVEM ana used to obtain improved extinction distances and θD values appropriate to electron diffraction, as well as to probe local bonding effects and composition variations in alloys.
High Voltage Electron Microscopy of Defects in Lithium Ferrite
Authors: Van der Biest O. 
Published: June 2020

Above 750°C lithium ferrite (LiFe5 O8) has an inverted spinel structure, i.e. With Fe3+ on tetrahedrally coordinated sites and a 3:1 mixture of Fe3+ and Li3+ on the octahedral sites. The latter take on an ordered arrangement below 750°C. It has been shown that the ordered structure contains antiphase boundaries (APB), with a displacement-vector of 1/2 <110=. In this paper observations on stacking faults and dislocations in the ordered and disordered structure are reported.Slices of a flux grown single crystal were thinned using the ion bombardment technique. Observations were made in the 650 kV Hitachi microscope, equipped with a high angle tiltstage which allows a tilt over an angle of ± 30°.
Electron Diffraction Study of Cellulose
Authors: Hebert Jacques J. , Muller Linda L. 
Published: June 2020

Cellulose is the most abundant polymer occurring in nature. It constitutes the cell wall of most, if not all, green plants. In the form of wood, wood pulp and cotton, cellulose represents a very valuable agricultural commodity and is, therefore, the subject of much intensive research.Chemical modifications of cotton are brought about predominately by the reaction of various reagents upon the surface of the crystalline elementary fibrils which make up the sub-fiber structure. For this reason, electron diffraction studies were undertaken to evaluate this microstructure and its various modifications. Electron-diffraction techniques offered several advantages over x-ray methods. Electrons have intensity; therefore, much smaller samples can be used.
Row-Nucleated and “Shish Kebab” Structures in Crystalline Polymers
Authors: Tucker Paul , George Waller , Holland V. F. 
Published: June 2020

Traditionally, polymer crystallization studies have been conducted on quiescent systems, but most polymers in commercial use are crystallized while under the influence of external dynamic stress fields. Only during the last decade has attention been given to the structure and morphology of polymers crystallized in systems that resemble those used for producing fibrous products.Although phenomenological studies of stress crystallization are now being conducted, scant attention is given to the basic theoretical raison d'etre. It is fairly well understood how stress increases the nucleation rate, but it is not well understood as to why a fibrous product results.
Chromic Acid Etching of Polyethylene
Authors: Muzzy J. D. , Hester R. D. , Hubbard J. L. 
Published: June 2020

Polyethylene is one of the most important plastics produced today because of its good physical properties, ease of fabrication and low cost. Studies to improve the properties of polyethylene are leading to an understanding of its crystalline morphology. Polyethylene crystallized by evaporation from dilute solutions consists of thin crystals called lamellae. The polyethylene molecules are parallel to the thickness of the lamellae and are folded since the thickness of the lamellae is much less than the molecular length. This lamellar texture persists in less perfect form in polyethylene crystallized from the melt.Morphological studies of melt crystallized polyethylene have been limited due to the difficulty of isolating the microstructure from the bulk specimen without destroying or deforming it.
Preparation of Thin Single Crystal Silicon Substrates for in situ Electron Microscope Studies
Authors: Maa J. S. , Lee J. I. , Hutchinson Thos. E. 
Published: June 2020

The in-situ electron microscope technique has been shown to be a powerful method for understanding the nucleation and growth of thin films formed both by vacuum vapor deposition and ion beam sputter-deposition. Single crystal silicon which has only been chosen as substrate for thin film deposition outside the electron microscope has now been prepared in a form suitable for in-situ deposition.The method of the preparation of thin silicon substrate is a combination of jet chemical etching and modified ion beam thinning. A specimen of thickness roughly 0.010 inch is first etched from both sides by the jet etching technique. After jet etching, it is transferred to the Commonwealth Scientific ion micro-milling instrument and bombarded from both sides with Argon ion beam. A pin hole occurs in the center of the specimen after about 30 minutes of ion bombardment.
Phosphorus Precipitation in Si-Ge (30 at. %) Alloy
Authors: Hills C. R. , Thomas G. J. , Maurin J. K. 
Published: June 2020

Solution treated and quenched Si-Ge (30 at. %) alloy doped with phosphorus to a level of 1.54 × 1020 atoms/cm3 has been shown to increase in resistivity following aging at elevated temperatures. This effect is indicative of a loss of phosphorus from substitutional sites in the Si-Ge lattice and consequent precipitation of the excess phosphorus into electrically inactive centers. The structural changes occurring as a result of aging have been studied using transmission electron microscopy.Examination of the solution heat-treated material (1 hr. at 1000°C, then quenched) prior to aging revealed the presence of small defect clusters ranging in size from 20-80 Å, as well as larger defects approximately 200 Å in diameter exhibiting large strain field contrast.
Neutron Radiation Damage in Zr-2.5 wt % Nb Alloys
Authors: Faulkner D. , Styles R.C. 
Published: June 2020

There has been much speculation recently concerning the nature of radiation induced defects in zirconium and its alloys. In particular, the absence of voids in pure zirconium and in Zircaloy-2 at high fluences and at temperatures in the range 0.3 to 0.5 Tm is inconsistent with observations made on most elemental f.c.c., b.c.c., c.p.h. metals, on stainless steels and on Nimonic PE16 alloys. Wolfenden and Farrell have reviewed the evidence and discuss the importance of dislocation density and/or gas content on void formation.The specimens examined in this study were.3 m.m. discs of Zr-2.5 wt % Nb fuel sheath material irradiated to 1.24 × 102 1 n. cm−2 (E > 1 MeV) at 380-390°C (∼ 0.31 Tm, where Tm is the melting temperature of the β phase) and to 1.37 × 102 1 n. cm−2 at 470 - 490°C (∼ 0.36 Tm) in the WR-1 organic cooled reactor.
Observation of Superlattice Dislocations on Cube Planes in Ni3Al
Authors: Oblak J. M. , Rand W. H. 
Published: June 2020

The energy of an a/2 <110> shear antiphase. boundary in the Ll2 expected to be at a minimum on {100} cube planes because here strue ture is there is no violation of nearest-neighbor order. The latter however does involve the disruption of second nearest neighbors. It has been suggested that cross slip of paired a/2 <110> dislocations from octahedral onto cube planes is an important dislocation trapping mechanism in Ni3Al; furthermore, slip traces consistent with cube slip are observed above 920°K.Due to the high energy of the {111} antiphase boundary (> 200 mJ/m2), paired a/2 <110> dislocations are tightly constricted on the octahedral plane and cannot be individually resolved.
Electron Mtcroscope Study of the Structure of Natural Pyrolusite (Pseudo-Psilomelane)
Authors: Staudhammer K. P. , Murr L. E. 
Published: June 2020

A manganese-bearing mineral characterized by a black hair-like surface crystal growth, and somewhat unique to the Socorro County, New Mexico area, has been referred to as psilomelane (pseudo-pyrolusite). Psilomelane, however, is a hydrated barium manganese oxide, generally A 3 X6Mn8016 (A= B2+, Mn3+, Al3+, Fe3+, S14+, etc. and X=O, OH). Natural psllomelane 1s a smooth, black, uniform or botryoidal mineral possessing an or- thorhombic crystal structure.Large specimens of the hair-like c·rystalline mineral (Fig. 1 (a) were analyzed by X-ray diffraction utilizing Debye-Scherrer nd diffractometer techniques and found to be tetragonal (a=4.42A, c = 2.87A).
Observations on Virgula Structure in Two Graptoloid Graptolites
Authors: Berry W. B. N. , Takagi R. S. 
Published: June 2020

The sexually-produced individual in the fossil colonial organisms, the graptolites was housed in a conical structure, the prosicula. Prosiculae in many graptoloid graptolites, those graptolites that were planktonic, have a tubular extension from their apices. That extension in graptoloids with uniserial and biserial scandent rhabdosome form has the aspect of a relatively rigid, rod-like structure that extends through the thecate part of the rhabdosome and beyond. Details of the virgula structure are most readily observed using electron microscopy.Virgula structure has been examined in a uniserial scandent graptoloid, a monograptid of the M. priodon group, and in a biserial scandent graptoloid, an Orthograptus of the O. quadrimucronatus group.
Electron Energy Analyzer Design
Authors: Kuyatt Chris E. 
Published: June 2020

The use of electron energy analyzers has increased dramatically in the last few years. Monochromator-analyzer combinations have achieved resolutions of a few milli-electron volts for electron energies from a few tenths of an electron volt to tens of thousands of electron volts. Figure 1 shows an energy loss spectrum of nitrogen which is typical of the performance of low energy electron spectrometers, and illustrates the wide dynamic range of these instruments.Various energy dispersing elements have been used in electron energy analyzers, some of the most popular being cylindrical and spherical electrostatic deflectors and the Wien filter.
A Prototype Field-Emission Scanning Transmission Electron Microscope
Authors: Banbury J.R. , Bance U. R. 
Published: June 2020

A prototype field emission scanning transmission electron microscope has been constructed and is under further development at AEI Scientific Apparatus Limited.The field emission gun has a triode construction, with geometry such as to produce a divergent beam from a virtual source whose position remains substantially constant over a wide range of total accelerating voltages. The gun has been operated satisfactorily from below 10 kV to over 90 kV (upper limit set by power supplies), with the field emission diode voltage typically between 2 kV and 4 kV and total emission of a few microamps. Single-crystal tungsten tips of either (111) or (310) orientation are used, though (310) tips normally produce a superior probe current stability.
Contrast Enhancement of Glutaraldehyde Cross-Linked, Ethylene Glycol Dehydrated Tissue With Triafol Nets
Authors: Kretzer Frank 
Published: June 2020

When tissue is prepared for thin section, high resolution electron microscopy with the specific goal of minimally denaturing membrane protein and with the least lipid solubilization possible, the method of choice is cross-linking membrane protein with a short exposure to 1% glutaraldehyde, brief dehydration in O°C ethylene glycol, and Vestopal infiltration. After such a procedure, the resultant contrast, even after uranyl acetate section staining, is extremely low. This low contrast is due to the few charged groups on native proteins available for interaction with the stain and the protein's compact structure which prohibits stain ions from penetrating into the nonpolar interior.To optimally increase the resultant low contrast in an effort to study the complex, three dimensional, condensed state of heterogeneous membrane proteins (10-100A) in the 300A-thick mitochondrial inner membranes (Figures 1-2) and the 270A-thick chloroplast partition membranes, sections were mounted over Triafol nets (Figure 3) spanning one hole slot grids.
Prolonged Fixation Studies For Spaceflight
Authors: Corbett Robert , Philpott Delbert E. , Black Sam 
Published: June 2020

Observation of subtle or early signs of change in spaceflight induced alterations on living systems require precise methods of sampling. In-flight analysis would be preferable but constraints of time, equipment, personnel and cost dictate the necessity for prolonged storage before retrieval. Because of this, various tissues have been stored in fixatives and combinations of fixatives and observed at various time intervals. High pressure and the effect of buffer alone have also been tried.Of the various tissues embedded, muscle, cartilage and liver, liver has been the most extensively studied because it contains large numbers of organelles common to all tissues (Fig. 1).