bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of the gill of Palaemonetes pugio as compared to the structure of uropod setae throughout the molt cycle
Authors: Andon Nancy L. , Dillaman Richard M.
Published: June 2020

In order to grow, crustaceans must shed their old cuticle (molt) and replace it with a new, larger one. To achieve this, it is necessary to form a new, preexuvial, cuticle under the old cuticle prior to molting. In most of the integument this does not present a problem; however, in the gill, the addition of the preexuvial layer might create an extended barrier to ion and gas exchange. In order to determine whether gills have devised a strategy to deal with this potential problem, the ultrastructure of the gills from the grass shrimp Palaemonetes pugio were examined throughout the molt cycle. The timing of the sequential steps of the molt in the cuticle other than the gills was determined by examining the light microscopic appearance of the setae at the margin of the uropods. Stevenson described the cuticle of the dorsal carapace throughout the molt cycle and correlated those events with setae formation. Consequently, separation and subsequent retraction of the hypodermis from the old cuticle and deposition of the new cuticle have been widely used as a convenient, non-invasive means of determining molt stage in crustaceans.
Ultrastructural characterization of an extracellular matrix produced by Leishmania mexicana pifanoi
Authors: Argüello Carlos
Published: June 2020

In a previous study it was shown that Leishmania braziliensis promastigotes secreted metabolic products to the culture media. These metabolites called “excreted factors” were chemically characterized as polysaccharides and glycoproteins that reacted with antileishmania sera. These observations together with the recent characterization of lipophosphoglycans and phosphoglycan lead us to investigate by ultrastructural procedues if leishmania is able to produce an extracellular matrix, in axenic culture conditions. In this study, Leishmania mexicana were cultured in minimum essential medium, supplemented with 10% fetal calf serum, at 22°C. Under these conditions, the parasites tend to associate forming small aggregates, called “rosettes” in which the flagellum is oriented inwards and the cell body outwards (Fig.1). In order to retain their association I supposed the existance of an adhesive substance that kept the parasites together. To test this possibility, rosettes were fixed with glutaraldehyde in cacodylate buffer 0.1 M, or with glutaraldehyde containing 1 mg of ruthenium red, that binds to glycoproteins or polyanionic polysaccharides of extracellular matrices.
Use of low-temperature SEM to observe seasonal variation in wax deposition and stomatal apertures in three common tree species
Authors: Wergin William P. , Brakke Thomas W. , Erbe Eric F.
Published: June 2020

The waxy covering or cuticle that covers the outer epidermal cells of leaves protects most plants from desiccation, pollution and many types of pathogens. This covering is generally interrupted only by the guard cells which form a stoma or pore that allows for the necessary gas exchange that occurs between the inner tissues of the leaf and the surrounding environment. The SEM has frequently been used to study the ultrastructure of the cuticle and the stomates because of their importance in the taxonomy, pathology and physiology of plants However, the results have been contradictory because chemical fixatives, dehydrating agents and critical point drying, procedures that are used to prepare specimens for conventional SEM studies, probably alter the waxy cuticle and the status or turgor of the guard cells. To avoid these problems we have utilized a technique for biological specimens that allows us to quickly freeze tissue in liquid nitrogen and to coat and observe the frozen samples. To accomplish this a Hitachi S-570 SEM was equipped with an EMscope SP2000A Sputter Ciyo System. Leaf samples were collected from the field, mounted on stubs, quenched in liquid nitrogen slush, sputter coated with gold and transferred to the cryostage for low temperature SEM observation.
Ultrastructure of the basal body apparatus in epidermal cells of a sponge larva (Aplysilla SP: Demospongiae)
Authors: Pinto R.L. , Woollacott R.M.
Published: June 2020

The basal body and its associated rootlet are the organelles responsible for anchoring the flagellum or cilium in the cytoplasm. Structurally, the common denominators of the basal apparatus are the basal body, a basal foot from which microtubules or microfilaments emanate, and a striated rootlet. A study of the basal apparatus from cells of the epidermis of a sponge larva was initiated to provide a comparison with similar data on adult sponges.

Sexually mature colonies of Aplysillasp were collected from Keehi Lagoon Marina, Honolulu, Hawaii. Larvae were fixed in 2.5% glutaraldehyde and 0.14 M NaCl in 0.2 M Millonig’s phosphate buffer (pH 7.4). Specimens were postfixed in 1% OsO4 in 1.25% sodium bicarbonate (pH 7.2) and embedded in epoxy resin. The larva ofAplysilla sp was previously described (as Dendrilla cactus) based on live observations and SEM by Woollacott and Hadfield.
Assessing the Fundamental Limits of Electron-Beam Imaging
Authors: Hobbs Linn W.
Published: June 2020

A long-overdue Nobel Prize in Physics for the development of the transmission electron microscope was awarded in 1986 to Professor Dr. Ernst Ruska, some fifty-three years after his demonstration of the superiority of electron-beam imaging. The microscope originally designed by Ruska did not differ significantly from the instruments in use today, a half century later, nor were early practitioners unaware of the image resolution potential inherent in electron-beam optics. We are now, at last, running into the limits of that potential, at least as judged by the quantity of effort expended for increasingly diminishing returns. The present point-resolution limit under axial illumination stands at about 0.15 nm and is unlikely to be lowered significantly without signal successes in design and application of novel correction schemes for spherical aberration or in sophistication of interactive image processing methods.
Electron microscopy of high-temperature oxide superconductors
Authors: Bentley J. , Fisher A.T. , Haltom C.P. , Brynestad J. , Lauf R.J. , Williams R.K. , Kroeger D.M.
Published: June 2020

The discovery of superconductivity, first at temperatures above 35 K in materials with the formula La2-x(Ba,Sr)xCuO4, and subsequently at temperatures above 90 K in a polyphase material of nominal composition Y1.2Ba0.8CuOx, has generated considerable excitement and has prompted widespread experimental and theoretical research activity because of the implications both for practical applications and also our understanding of superconductivity. In the 35 K material the highest temperature superconducting phase has the K2NiF4-type structure of composition La1.85(Ba,Sr)0.15CuO4-y with the oxygen content dependent on specimen preparation and processing methods. The superconducting phase in Y-Ba-Cu-O has been widely reported to have the formula YBa2Cu3O9-x and a proposed tetragonal structure with a=0.389 nm and c= 1.165 nm.

La1.85Sr0.15CuO4 was made by thermal denitration at <500 K. The sintered powder was hot isostatically pressed to ∼96% theoretical density and annealed to ensure oxygen contents that produce superconductivity. Y-Ba-Cu-O materials were prepared from mixtures of Y2O3, CuO, and BaCO3 powders that were ground and sintered. Specimens were prepared for electron microscopy by several methods.
Image localization: imaging conditions
Authors: Luzzi D.E. , Marks L.D.
Published: June 2020

The study of localized phenomena, defect structures, relaxations, surface impurities, etc., all require the ability to resolve small deviations from equilibrium (average) positions of the atoms. Thus, a useful HREM image must have the property of being a one-to-one mapping of the atomic columns in the image to those in the specimen. This localisation of the image depends on the imaging parameters of the microscope and on the spatial frequency of the information. Therefore, each microscope should be calibrated for the imaging conditions under which the maximum localisation of the information of any given spatial frequency is obtained. We have done this for the Hitachi H-9000 HREM which is operated typically at 300 kV, with a Cs of 0.9 and a focal spread of approximately 80 A (fwhm).
Processing of x-ray and electron spectra
Authors: Joy David C
Published: June 2020

A spectrum is a linear compilation of the output data, i.e signal intensity as a function of wavelength or energy, from an X-ray or electron energy loss spectrometer. In the earliest forms of the instrumentation the spectra existed only as traces on an oscilloscope or as the output plot of a chart recorder, and the operations that could be performed on them were therefore restricted to the identification of major features, and to manipulations that could be performed manually or graphically, such as estimating a background or integrating the area beneath a peak. In current instrumentation the spectrum is stored digitally in the memory of a computer. Since the data forming the spectral set can now be examined at will and transformed mathematically in any desired manner the spectrum can be processed to yield additional types of information. This paper will examine how spectral processing must be applied to obtain data from the X-ray and electron energy loss spectra generated from thin foils in the analytical electron microscope.
Atomic structure analysis of small particles supported on amorphous material
Authors: Sattler M.L. , O'Keefe M.A.
Published: June 2020

The direct observation of atomic features in small crystalline particles supported by a thicker substrate is useful when characterizing materials such as electrocatalysts. However, particle definition becomes difficult to establish for catalyst crystallites less than 5nm in diameter on a support 5 to 10 times thicker, since the background contrast obscures the HREM image of the particle. Previous image calculations of 2.4nm sized particles on 10nm amorphous support have demonstrated further the problems associated with image interpretation of these small particles. The present method incorporates the matching of simulated images at varying thicknesses with computer enhanced images of small particles on amorphous supports in order to characterize atomic details at the surfaces of these particles.

Catalyst material consisting of crystalline Ti02 particles on an amorphous Si02 support was developed so that the average particle size measured 7.0nm.
Electron energy loss spectroscopy (EELS) by scanning transmission electron microscopy (STEM) at low doses
Authors: Reichelt R. , Engel A. , Leapman R.
Published: June 2020

A scanning transmission electron microscope (STEM) has the unique feature to record simultaneously two types of images with high collection efficiencies. The first type, collected by an annular detector (AD), contains high resolution structural information which is primarily transmitted by elastically scattered electrons. The second type, formed by an electron spectrometer (SP), yields information on the local energy loss spectrum of the inelastically scattered electrons at lower structural resolution. Thus useful quantitative information from biological matter can be obtained: the AD-signal provides the basis for mass mapping and the inelastic one allows the estimation of the local chemical element concentration.

For a very thin specimen (T<< ^, T: thickness, A: mean free path between two scattering events) the signal S of the imaging modes mentioned above can be linearly related to the properties of the sample:
Analytical TEM of grain boundary phases in yttria-zirconia ceramics
Authors: Mecartney M.L. , Angelini P.
Published: June 2020

Yttria-zirconia ceramics have a broad range of applications, from use as structural materials (tetragonal zirconia) to ionic conductors (cubic zirconia). Similar to many ceramic materials, these zirconia ceramics often contain small amounts of amorphous silicate phases at grain boundaries and multiple grain junctions. These phases are a result of impurities, introduced during processing or from the original raw material, or are deliberate additions to aid in the densification via liquid phase sintering. Despite the universality of these grain boundary phases, as of yet little work has been undertaken to understand their effect on the microstructural development, chemistry, and physical properties of the materials. We report here our results on analyzing a series of yttria doped zirconia ceramics to which deliberate additions of various glass phases have been added.

Samples were fabricated from zirconia powders which contained 3 mol% yttria and 8 mol% yttria. Aluminosilicate glass or borosilicate glass (5 wt%) was added to the powders before sintering. The samples were hot-isostatically pressed at 1650°C for 1-100 minutes.
Scanning ion microscopy images
Authors: Levi-Setti R. , Chabala J.M. , Wang Y.L.
Published: June 2020

Finely focused beams extracted from liquid metal ion sources (LMIS) provide a wealth of secondary signals which can be exploited to create high resolution images by the scanning method. The images of scanning ion microscopy (SIM) encompass a variety of contrast mechanisms which we classify into two broad categories: a) Emission contrast and b) Analytical contrast.

Emission contrast refers to those mechanisms inherent to the emission of secondaries by solids under ion bombardment. The contrast-carrying signals consist of ion-induced secondary electrons (ISE) and secondary ions (ISI). Both signals exhibit i) topographic emission contrast due to the existence of differential geometric emission and collection effects, ii) crystallographic emission contrast, due to primary ion channeling phenomena and differential oxidation of crystalline surfaces, iii) chemical emission or Z-contrast, related to the dependence of the secondary emission yields on the Z and surface chemical state of the target.
Low voltage scanning electron microscopy of interplanetary dust particles
Authors: Blake D.F. , Reilly T.W. , Brownlee D.E. , Bunch T.E.
Published: June 2020

Interplanetary Dust Particles (IDPs) are a relatively new class of extraterrestrial materials which are collected by high-flying aircraft in the stratosphere. The particles, ∼1.0-50 μm in size, enter the earth's atmosphere at ballistic velocities, but are sufficiently small to be decelerated without burning up. IDPs commonly have solar elemental abundances, and are thoughfto have undergone very little differentiation since the formation of the solar system. While these materials are called “particles,” they are in fact aggregates of a variety of mineral phases, glass, and carbonaceous material. Grains within IDPs commonly range from a few microns to a few tens of nanometers. The extraterrestrial origin of IDPs has been established by the discovery of solar flare tracks in some mineral grains, and recent D/H isotopic ratios recorded from individual particles. The source and formational history of the particles is a topic of active research. At present, the primary means of screening and classifying IDPs is Scanning Electron Microscopy, although a variety of electron microbeam and X-ray techniques is used for subsequent analysis.
Microstructure of pores in N+-silicon layers
Authors: Kaushik V. S.
Published: June 2020

Oxidized porous silicon has drawn considerable interest as one of the alternatives for implementing silicon-on-insulator technology. Buried porous layers can be formed by utilizing the preferential pore formation in highly doped silicon during anodic etching in hydrofluoric acid. This porous silicon layer (PSL) can be subsequently oxidized rapidly at low temperatures to yield a device-quality silicon island layer, which is dielectrically isolated from the substrate. Although pores can be formed in both n-type and p-type silicon, the latter has received more attention. This paper presents the results of cross-sectional TEM (XTEM) observations of the microstructure of pores in n+ silicon.

Samples used in this study were n- /n+/n- doped silicon (001) wafers which had been anodically etched in a hydrofluoric acid solution to form the PSL in the n+ layer via trenches etched through the n- surface layer.
A static and dynamic electron microscope study of slip propagation across grain boundaries in polycrystalline metals
Authors: Clark William A. T.
Published: June 2020

The deformation of polycrystalline metals proceeds by the movement of individual dislocations both within the grains and across the grain boundaries which separate them. It is therefore apparent that these grain boundaries have an important role in controlling the mechanical properties of materials. It is known, for example, that the yield stress is directly affected by the density of grain boundaries in a metal; in the familiar Hall—Petch relationship it is inversely proportional to the grain diameter. Various models have been proposed to account for this behaviour, all of which involve the interaction between dislocations and grain boundaries (for a review see e.g. ref. 1). Microscopically, these interactions can be accomplished by one of several different mechanisms, such as the nucleation of new dislocations, direct transmission of dislocations across the interface, the absorption and desorption of dislocations into and out of the interface, among others.
Analysis of boundaries
Authors: Garratt-Reed Anthony J.
Published: June 2020

As the understanding of the importance of grain boundary structure and chemistry in determining material properties grows, the need for high quality analysis of grain boundary segregation becomes more and more critical. In this paper we shall discuss briefly the three common direct methods of grain boundary analysis. We shall loosely use the term “grain boundary” to include phase boundaries and precipitate interfaces.

The earliest technique employed to study grain boundary segregation was Auger electron spectroscopy of intergranular fracture surfaces. Since the depth sensitivity of Auger analysis, is, in general, only a few atomic layers, it is possible in principle to detect only a few percent of saturation coverage of the boundary.
Interface characterization of metal matrix composites by transmission electron microscopy
Authors: Hall I. W. , Diwanji A. P.
Published: June 2020

Carbon fiber reinforced metal matrix composites (MMC's) are an attractive class of materials for automotive and aerospace structural applications because of their high strength and stiffness to weight ratios and their low coefficients of thermal expansion. Successful development of these new materials demands a thorough understanding of the structure/property/processing relationships and, in particular, a detailed understanding of the fiber/matrix interface since this region strongly influences the final mechanical properties of the system. This interface is affected by many factors including the manufacturing method, heat treatment, matrix alloy composition and wettability of the fibers but, since it is a region which is typically much less than lμm wide, it is inaccessible to direct detailed observation by any means other than transmission electron microscopy.
Morphological studies of III-V thin layers and SLS'S
Authors: Jones K.M. , Al-Jassim M.M. , Olson J.M. , Kibbler A.
Published: June 2020

Thin layers of III-V semiconductors, such as quantum well structures and strained layer superlattices (SLS's), are currently of great interest. However, there have been widely scattered reports suggesting that thin layers and SLS's with arbitrarily large strain and thicknesses are difficult if not impossible to grow. In this work we studied the nucleation, morphology and structural perfection of a wide variety of thin layers in the GaAs/GalnAsP system. These epitaxial layers were grown by atmospheric pressure MOCVD. The GaAs/GalnAs system is mismatched through the entire compositional range, the extreme mismatch being 7% for GaAs/lnAs. The nucleation and growth morphology of GalnAs layers on GaAs were observed to be very strongly dependent on the mismatch (i.e. the In concentration x) This is clearly depicted in Fig. 1 which shows secondary electron micrographs of the surface of three GalnAs layers grown for 30 sec. using the same growth rate of 600 Å min-1.
A TEM/Low-Temperature Photoluminescence Examination of MBE-grown (001) CdTe films
Authors: Burke M.G. , Choyke W.J. , Feng Z.C. , Hanes M.H.
Published: June 2020

CdTe, a large band gap semiconductor, is used for a variety of applications such as infrared detectors, solar cells, and other opto-electronic devices. These applications require that CdTe thin films or buffer layers are made with high structural perfection. To date, a variety of substrates have been employed in CdTe thin film production, including GaAs, sapphire, and InSb. InSb is particularly attractive due to the small lattice mismatch with CdTe across {100}. We will report results of a combined TEM/low temperature photoluminescence (LT-PL) investigation into the defect structures present in MBE grown (001) CdTe films produced on InSb substrates, and initial observations of MOCVD CdTe on CdTe substrates.

Several high quality MBE CdTe/InSb specimens were initially selected based upon initial PL measurements and DCRC (double crystal rocking curve) results.
SEM determination of optimum processing conditions for microwave dielectrics in the (Ca,Sr,Ba) zirconate system
Authors: Borglum B.P. , Buchanan R.C.
Published: June 2020

Ceramic components for microwave applications, such as dielectric resonators, typically must possess low dielectric loss (high Q), high dielectric constant (εr) and small temperature coefficient of permittivity (τε). Non-stoichiometric CaZrO3 doped with Sr and Ba has been shown to possess these necessary characteristics Compact and highly reliable microwave components can, therefore, be fabricated using these materials. In this study, the effect of heat-treatment on the final microstructure was investigated.

A chemical solution technique was used to synthesize powders of the composition Ca0.965(Sr0.030Ba0.005)Zr0.990O4 Chemical preparation methods offer the advantages of precise stoichiometric control, atomistic homogeneity, high purity, and fine particle size of the resultant powders. Appropriate amounts of the nitrate salts in aqueous solution were mixed to prepare the desired composition. The solution was converted to a powder by evaporation and calcined at 600°C and 800°C for 2 hours.
Computer averaging of lattice images of poly-4-methyl-pentene-1 (P4mp1): Noise created artifacts
Authors: Pradère P. , Revol J.F. , John Manley R. St.
Published: June 2020

Although radiation damage is the limiting factor in HREM of polymers, new techniques based on low dose imaging at low magnification have permitted lattice images to be obtained from very radiation sensitive polymers such as polyethylene (PE). This paper describes the computer averaging of P4MP1 lattice images. P4MP1 is even more sensitive than PE (total end point dose of 27 C m-2 as compared to 100 C m-2 for PE at 120 kV). It does, however, have the advantage of forming flat crystals from dilute solution and no change in d-spacings is observed during irradiation.

Crystals of P4MP1 were grown at 60°C in xylene (polymer concentration 0.05%). Electron microscopy was performed with a Philips EM 400 T microscope equipped with a Low Dose Unit and operated at 120 kV. Imaging conditions were the same as already described elsewhere. Enlarged micrographs were digitized and processed with the Spider image processing system.
Examinations of low-density polymer foams with a low-voltage FESEM
Authors: Price C. W. , McCarthy P. L. , Letts S. A. , Kong F. M.
Published: June 2020

The cell structure of low-density polymer foams is extremely delicate, and the application of conductive coatings for SEM examinations can obliterate much of the fine structural detail. In extreme cases, the structure can be significantly altered by the coating. This problem has been found to be particularly critical in low-density polymer foams. The thin membranes of polymer foams also are exceptionally susceptable to electron-beam damage. Consequently, both the improved low-voltage resolution and the low beam currents now available on an SEM equipped with a field-emission gun (FESEM) have proven to be highly beneficial for the examination of low-density polymer foams. This will be demonstrated for polystyrene foams; equally successful results have been obtained on other types of polymer foams.

The simplest technique to examine the cell structure of polystyrene foams is to fracture specimens and examine the fracture surface. Since polystyrene is nonconductive, it must be coated to be examined in the conventional SEM.
Using the scanning electron microscope for failure analysis of high density magnetic media
Authors: Ackerman Evelyn R. , Burnett Gary D.
Published: June 2020

Advancements in state of the art high density Head/Disk retrieval systems has increased the demand for sophisticated failure analysis methods. From 1968 to 1974 the emphasis was on the number of tracks per inch. (TPI) ranging from 100 to 400 as summarized in Table 1. This emphasis shifted with the increase in densities to include the number of bits per inch (BPI). A bit is formed by magnetizing the Fe203 particles of the media in one direction and allowing magnetic heads to recognize specific data patterns. From 1977 to 1986 the tracks per inch increased from 470 to 1400 corresponding to an increase from 6300 to 10,800 bits per inch respectively. Due to the reduction in the bit and track sizes, build and operating environments of systems have become critical factors in media reliability.

Using the Ferrofluid pattern developing technique, the scanning electron microscope can be a valuable diagnostic tool in the examination of failure sites on disks.
Preparation And elemental analysis of ancient fibers
Authors: Angel Allen , Jakes Kathryn A.
Published: June 2020

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).

Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.
Microanalysis and electron energy loss spectroscopy of polymers
Authors: Briber R. M.
Published: June 2020

Analytical electron microscopy has progressed in recent years such that quantitative chemical information can be obtained from very small volumes of sample. In principle, the composition of regions on the order of a few namometers in both diameter and thickness can be determined using energy dispersive x-ray analysis (EDS) and electron energy loss spectroscopy (EELS) [1,2], In the case of organic polymers the limitations to quantitative microanalysis are generally due to the sample and not to the instrument. Radiation damage induced mass loss often proves to be the constraining factor in obtaining quantitative information from small volumes of sample [3], The principles and processes of radiation damage in organic materials and polymers can be found in various review articles [4,5].

The principles underlying both analytical x-ray spectroscopy and electron energy loss spectroscopy are closely related. When an electron in the incident beam loses energy (i.e. inelastically scattered) by "knocking" out an inner shell electron from an atom present in the sample there are two aspects that are of value for compositional analysis.
Low-voltage, high-resolution scanning electron microscopy of polymers
Authors: Krause S. J. , Adams W.W. , Kumar S. , Reilly T. , Suziki T.
Published: June 2020

Scanning electron microscopy (SEM) of polymers at routine operating voltages of 15 to 25 keV can lead to beam damage and sample image distortion due to charging. Imaging polymer samples with low accelerating voltages (0.1 to 2.0 keV), at or near the “crossover point”, can reduce beam damage, eliminate charging, and improve contrast of surface detail. However, at low voltage, beam brightness is reduced and image resolution is degraded due to chromatic aberration. A new generation of instruments has improved brightness at low voltages, but a typical SEM with a tungsten hairpin filament will have a resolution limit of about 100nm at 1keV. Recently, a new field emission gun (FEG) SEM, the Hitachi S900, was introduced with a reported resolution of 0.8nm at 30keV and 5nm at 1keV. In this research we are reporting the results of imaging coated and uncoated polymer samples at accelerating voltages between 1keV and 30keV in a tungsten hairpin SEM and in the Hitachi S900 FEG SEM.
High-resolution electron images of linear polymers
Authors: Revol J.F. , Chanzy H.
Published: June 2020

Polymer crystals are damaged and changed to an amorphous state by a relatively small electron irradiation dose. For this reason, lattice imaging of polymer crystals was restricted until recently to ones that are relatively resistant to irradiation. To overcome irradiation damage, R.M. Glaeser proposed the use of a low-dose imaging technique followed by averaging techniques to produce statistically well defined information. This pioneering technique was then first applied by Unwin and Henderson who obtained a two dimensional molecular structure of the purple membrane protein, bacteriorhodopsin, at 0.7 nm resolution. For the usual linear polymer crystals, however, no structural information is available at this level and a better resolution must be reached to have access to molecular features. The following is a brief description of low-dose imaging at molecular dimensions of the two most abundant naturally occurring polymers in the world: cellulose and chitin, and of two common synthetic polymers: polyethylene (PE) and polytetrafluoro-ethylene (PTFE).
Domains in single crystals of poly-4-methyl-pentene-1
Authors: Pradère P. , Revol J.-F. , John Manley R. St.
Published: June 2020

Polymer single crystals are generally considered to be structurally homogeneous. In this paper it is shown that in a given single crystal of poly-4-methyl-pentene-1 (P4MP1) there exist narrowly delimited domains that give rise to different electron diffraction (ED) patterns. The shape and location of these domains is characterized by diffraction contrast imaging in the dark field (DF) mode.

Monolayer single crystals of P4MP1 polymorphs I and III were prepared in dilute solution (concentration ranging from 0.01 to 0.05%). Form I was obtained by slow cooling of a hexadecane solution whereas form III was prepared by isothermal crystallisation in xylene at 60°C. Crystals were deposited on carbon coated grids and observed with a Philips EM 400 T electron microscope operated at 120 kV. The crystals are very radiation sensitive and the total end point dose, measured by the fading of the ED pattern is 27 C m-2.
Electron diffraction and imaging of epitaxially grown crystals of monogalactosyldiacylglycerol
Authors: Sen A. , Hurley E.L. , Hui S.W. , Dorset D.L. , McConnell C.M.
Published: June 2020

The molecular structure of 1,2-3-distearyl-monogalactosyldiacylglycerol (MGDG) was studied by electron microscopy and electron diffraction. MGDG was extracted from spinach leaves, purified and hydrogenated to a distearate compound. Crystals of MGDG were obtained in two orientations. Thin crystals grown from solutions by evaporation of non-polar solvent on the carbon coated grid showed the long axis of the molecules nearly perpendicular to the carbon film substrate. The acyl chains were packed in a hexagonal lattice commonly found in phospholipid crystals. In order to study the structure along the long axis of the molecule, an epitaxial method of crystal growth was used to obtain crystals with the long axis of the molecule parallel to the carbon substrate. Epitaxial crystals was grown from solutions in naphthalene or benzoic acid on 400 mesh, carbon coated grids.
Structural transitions and organization of micelles in block copolymer/hompolymer blends
Authors: Thomas Edwin L. , Kinning David J.
Published: June 2020

Spherical and cylindrical micelles are quite common in lipid/water systems. The self assembly of amphiphilic molecules into well defined geometries has been extensively studied and is explained in terms of geometric and packing properties in addition to electrostatic, van der Waals and solvation forces. While macromolecular self assembly may seem more complex than for such small molecule systems, it is actually a simpler physical situation to model. Much can be learned from the combined study of each type of system.

In block copolymer/homopolymer blends the scale of the phase separation is restricted to the radius of gyration of the polymer blocks (typically several hundred A). By varying the composition and the molecular weights of the blocks and of the homopolymer, a wide range of morphologies and therefore physical properties can be achieved.
Combination of cryo-SEM and WET-SEM
Authors: Makita Takashi , Hirabara Kazumi , Hirose Haruko
Published: June 2020

WET-SEM is a version of commercially available SEM equipped with Robinson's type of wide-angle backscattered electron detector to observe wet samples under low vacuum(0.3-0.5 torr) and it has been used to variable biological samples with or without chemical fixation. Its versatility to observe hydrated specimens without any metalic coating is obviously advantageous to application of cryo-SEM to biological samples.

Recent improvement of nitrogen gas cooled cold stage, and vacuum transfer device(Hexland, England) made the WET-SEM(ISI, Akashi, Japan) as a tool for quick survey of unfixed, hydrated, uncoated, and frozen fractured tissue blocks of animals. For examples, tissue from the rat liver or the mice kidney was quickly frozen in nitrogen slush for several minutes and then transfered to prechamber with a type of vacuum transfer system. Within the prechamber the surface of frozen sample is sublimated or fractured under vacuum and then the sample is ready to be seen on the cryo stage which is cooled by nitrogen gas.
Cryo-electron microscopy of chromosome fibers is consistent with the crossed-linker model for chromatin structure
Authors: Athey B. , Langmore J. , Williams S. , Smith M. , Chang C.F. , Grant R. , Chiu W.
Published: June 2020

Although there is general agreement that inactive chromosome fibers consist of helically packed nucleosomes, the pattern of packing is still disputed. The nucleosome itself is composed of a highly conserved “core” comprised of 146bp of DNA and a histone octamer, and a variable “linker” comprised of 20-100bp of DNA bound to histone H1. The models of chromatin structure can be distinguished by their dependence upon linker length. The solenoid model for chromatin structure is a single helix with constant pitch (11 nm) and constant diameter (25-30nm). The twisted-ribbon model is a double helix with variable pitch (26-40nm) and constant diameter (30nm). The crossed-linker model is a double helix with conserved pitch (26-28nm) and variable diameter (26-40nm). Measurements of the diameter and apparent helical parameters of negatively-stained chromatin from Thyone sperm (87bp linker) and Necturus erythrocytes (48bp linker) are in agreement with a left-handed crossed-linker model, and in disagreement with the solenoid and twisted-ribbon models.
Revealing gross three-dimensional structure in the SEM
Authors: Newberry Sterling P.
Published: June 2020

The beautiful three dimensional representation of small object surfaces by the SEM leads one to search for ways to open up the sample and look inside. Could this be the answer to a better microscopy for gross biological 3-D structure? We know from X-Ray microscope images that Freeze Drying and Critical Point Drying give promise of adequately preserving gross structure. Can we slice such preparations open for SEM inspection? In general these preparations crush more readily than they slice. Russell and Dagihlian got around the problem by “deembedding” a section before imaging. This some what defeats the advantages of direct dry preparation, thus we are reluctant to accept it as the final solution to our problem. Alternatively, consider fig 1 wherein a freeze dried onion root has a window cut in its surface by a micromanipulator during observation in the SEM.
Alterations of ultrastructure and elemental composition in cultured human epidermal keratinocytes after treatment with nitrofurazone and silver sulfadiazine
Authors: Crooker A. R. , Myers M. C. , Beard T. L. , Graham E. S.
Published: June 2020

Cell culture systems have become increasingly popular as a means of screening toxic agents and studying toxic mechanisms of drugs and other chemicals at the cellular and subcellular levels. These in vitro tests can be conducted rapidly in a broad range of relevant mammalian culture systems; a variety of biological and biochemical cytotoxicity endpoints can be examined. The following study utilized human keratinocytes to evaluate the relative cytotoxicities of nitrofurazone (NF) and silver sulfadiazine (SS), the active ingredients of FURACIN(R) Topical Cream and SILVADENE(R) Cream, respectively. These compounds are anti-infectives used in the treatment of burn patients. Cell ultrastructure and elemental composition were utilized as cytotoxicity endpoints.

Normal Human Epidermal Keratinocytes (HK) were prepared from the EpiPackTM culture system (Clonetics Corporation, Boulder, CO). For scanning electron microscopy (SEM) and transmission electron microscopy (TEM), cells were seeded on sterile 35 mm Falcon plastic dishes; for elemental microanalysis, cells were plated on polished pyrolytic carbon discs (E. Fullam, Latham, NY) placed in the culture dishes.
Resolution assessment from spectral signal-to-noise ratios
Authors: Unser M. , Trus B.L. , Steven A.C.
Published: June 2020

Since the resolution-limiting factor in electron microscopy of biological macromolecules is not instrumental, but is rather the preservation of structure, operational definitions of resolution have to be based on the mutual consistency of a set of like images. The traditional measure of resolution for crystalline specimens in terms of the extent of periodic reflections in their diffraction patterns is such a criterion. With the advent of correlation averaging techniques for lattice rectification and the analysis of non-crystalline specimens, a more general - and desirably, closely compatible - resolution criterion is needed. Two measures of resolution for correlation-averaged images have been described, namely the differential phase residual (DPR) and the Fourier ring correlation (FRC). However, the values that they give for resolution often differ substantially. Furthermore, neither method relates in a straightforward way to the long-standing resolution criterion for crystalline specimens.
Estimation of the noise in TEM image recorded on “imaging plate”
Authors: Oikawa T. , Mori N. , Katoh T. , Harada Y. , Miyahara J. , Matsuo T.
Published: June 2020

The “Imaging Plate”(IP) is a highly sensitive image recording plate for X-ray radiography. It has been ascertained that the IP has superior properties and high practicability as an image recording material in a TEM. The sensitivity, one of the properties, is about 3 orders higher than that of conventional photo film. The IP is expected to be applied to low dose techniques. In this paper, an estimation of the quantum noise on the TEM image which appears in case of low electron dose on the IP is reported.

In this experiment, the JEM-2000FX TEM and an IP having the same size as photo film were used.

Figure 1 shows the schematic diagram of the total system including the TEM used in this experiment. In the reader, He-Ne laser light is scanned across the IP, then blue light is emitted from the IP.
Image enhancement and dynamic range control with unsharp masking
Authors: Guettler R. D. , Bellare J. R. , Davis H. T. , Scriven L. E.
Published: June 2020

Prints containing the maximum amount of micrograph detail are the objective of all microscopists. Due to the limited dynamic range of printing papers (Fig. 1), much darkroom time is spent in printing wide tonal-range micrographs that require contrast manipulation. We have applied the technique of unsharp masking to simplify contrast reduction and developed a process that yields significantly better results in a shorter time than the conventional method of dodging and burning. Spiegler and Juris's early works in unsharp masking have been applied by various researchers to aerial mapping, graphic arts, astronomy, and, to a limited extent, to electron micrographs. We have built upon this work and developed a simple procedure for using unsharp masking and studied the quantitative effects of its use in dynamic range control and image enhancement.
A new antibody label 5-10 times smaller than previous ones
Authors: Hainfeld James F.
Published: June 2020

By covalently coupling an undecagold complex to an Fab’ fragment, the smallest gold-conjugated antibody label yet devised has been synthesized. Its overall dimension is 50 x 30 x 20 Å and when bound to an antigen, the gold cluster is 40-50 Å from the antigen surface. The preparation procedure does not alter the activity and specificity of the antibody since coupling of the gold cluster is at a crystallographically known position at the opposite end of the Fab’ fragment from the antigen combining site.

One significance of this new label is that with a smaller E.M. antibody label, higher resolution of labeling is possible. In fact, if monoclonals are used, specific sites on a single macromolecule, or subunits of a protein complex could be mapped.
High-resolution, low-dose electron cryomicroscopy of sugar embedded porin, a transmembrane protein from Eschrichia coli outer membrane
Authors: Sass H. J. , Massalski A. , Zemlin F. , Beckman E. , van Heel M. , Büldt G. , Dorset D. L. , Zeitler E. , Rosenbusch J. P.
Published: June 2020

The secondary structure of porin, which form voltage-dependent channels across outer membrane of Escherichia coli, consists mostly (two-thirds of polypeptides) of anti-parallel (β-pleated strands. However, information on the tertiary and quaternary structure of porin is still far from complete. The β-pleated strands, which have a mean length of 10-12 residues, span the outer membrane in an orientation approximately perpendicular to the membrane surface. Porins are so far the only class of membrane proteins for which the predominant β-structure has been established unequivocally. However, the exact arrangement of β-strands (β- barrels or stacked sheets) is still unknown. Depending on the method of investigation, one being the turn identification, and the second the Raman spectroscopy, 16 or 18 β-strands respectively were calculated as a building block required for one protein monomer. Both models predict the β-strands delineating the pore, as amphipatic molecules with hydrophobic residues forming protein-lipid interface and hydrophilic residues facing the lumen of the pore.
Comparative surface and ultrastructural views of methylotrophic bacteria by TEM, STEM, SE, and freeze-etch electron microscopy.
Authors: Fassel T.A. , Schaller M.J. , Lidstrom M.E. , Remsen C.C.
Published: June 2020

Methylotrophic bacteria play an Important role in the environment in the oxidation of methane and methanol. Extensive intracytoplasmic membranes (ICM) have been associated with the oxidation processes in methylotrophs and chemolithotrophic bacteria. Classification on the basis of ICM arrangement distinguishes 2 types of methylotrophs. Bundles or vesicular stacks of ICM located away from the cytoplasmic membrane and extending into the cytoplasm are present in Type I methylotrophs. In Type II methylotrophs, the ICM form pairs of peripheral membranes located parallel to the cytoplasmic membrane. Complex cell wall structures of tightly packed cup-shaped subunits have been described in strains of marine and freshwater phototrophic sulfur bacteria and several strains of methane oxidizing bacteria. We examined the ultrastructure of the methylotrophs with particular view of the ICM and surface structural features, between representatives of the Type I Methylomonas albus (BG8), and Type II Methylosinus trichosporium (OB-36).
Nuclear lamina and regulation of nuclear envelofe structure
Authors: Gerace Larry , Aebi Ueli , Burke Brian , Suprynowicz Frank
Published: June 2020

The nuclear lamina is a protein meshwork that lines the nucleoplasmic surface of the nuclear envelope. In numerous higher eukaryotic cells, the lamina is known to contain a polymer of 1-3 major polypeptides (“lamins“) that form an insoluble supramolecular assembly during interphase. The lamina is thought to provide both a skeletal framework for the nuclear envelope (that regulates its disassembly and reformation during mitosis) and an anchoring site at the nuclear periphery for interphase chromosomes. Recent structural and functional studies on the nuclear lamina have yielded important new insight on its roles in nuclear architecture.

Using electron microscopy, we found that the nuclear lamina of Xenopus oocytes is a meshwork of intermediate-sized (8-12 nm) filaments arranged in a near-tetragonal lattice having a spacing of 52 nm.
Actin: High-resolution electron microscopy on its subunit and filamentous structure, and its molecular interactions
Authors: Aebi U. , Millonig R. , Sütterlin R. , Engel A.
Published: June 2020

Elucidation of the 3-D molecular structure of actin has been a challenge to protein crystallo-graphers and electron microscopists ever since the pivotal role of this 43-kDa protein in muscle contraction - and later in cellular motility and cytoskeletal architecture - has been recognized. In its functional form actin is polymerized into filaments (F-actin) which are made of two linear strands of actin subunits helically twisted around each other with a pitch of about 72 nm and an axial stagger of 2.75 nm. In most in vivo situations F-actin is complexed with stoichiometric amounts of accessory proteins - e.g. tropomyosin, troponin, crosslinking or capping proteins - via specific binding sites the actin molecule has for these proteins. While ultimately one would like to reveal a near-atomic resolution model of the actin filament, as a first step towards this goal one would be quite happy to obtain a high resolution electron density map of the actin molecule which, in turn, requires the availability of large and well ordered 3-D crystals.
Fine structure of the cupula
Authors: Cohen G. M. , Domeier M. L.
Published: June 2020

The cupula functions as a sensitive biological transducer that undergoes extremely limited mechanical displacements in its normal dynamic range. Cupular displacements are coupled to the bending and stimulation of hair cell cilia. However, details of cupular-ciliary coupling and of cupular attachments to the ampullary crest are unsettled because of difficulties in preserving the cupula without severe distortion from fixation and dehydration. With conventional fixation procedures, the cupula either pulls away from crest or collapses to a fraction of its original volume. Our objective was to reduce cupular shrinkage.

We used the inner ears of 1 day-old chicks (White Leghorn) and 3 month-old mice (C57BL/6). The inner ears were fixed 3-72 h in 1.5-1.75% glutaraldehyde in 150 mM KC1 buffered with potassium phosphate, pH 7.3. To the basic solution, we sometimes added spermine (0.1%) or lysine (0.25%).