bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ fatigue of Al-Li-X alloys
Authors: Vecchio Kenneth S. 
Published: June 2020

The introduction of Al-Li based alloys into commercial applications has not occurred without some major difficulties in alloy development. Poor ductility and low fracture toughness in these alloys has hindered their use in structures where they must serve as integral load-carrying members. On the other hand, superior fatigue and stiffness properties of these alloys has provided great incentive to pursue further development. The reason for the low ductility and poor fracture toughness has been attributed to several possible mechanisms including: i) shear band formation due to planar slip., and ii) strain localization resulting from large grain boundary precipitates. The rather good fatigue crack propagation characteristics have been attributed to significant macroscopic out-of-plane crack growth. However, little work has aimed at understanding the micromechanisms of this out-of-plane crack growth during cyclic loading. In addition, the role of the numerous precipitates that can exist in these complex Al-Li-X alloys to the fatigue crack growth resistance has not been examined closely.In this research we have examined the microscopic evolution of fatigue deformation in two Al-Li-X alloys using in-situ fatigue experiments conducted within an intermediate voltage transmission electron microscope.
Dose rate and temperature dependence of the critical dose for amorphization of CuTi-irradiated by 1 MeV electrons
Authors: Xu Genbao , Koike Junichi , Meshii M. , Okamoto Paul 
Published: June 2020

The dose rate and temperature dependence of critical dose for amorphization of CuTi under electron irradiation was investigated in a temperature range from 10 to 260K and in a dose rate range from 1.0 × 10−4 to 1.5 × 10−3 dpa/sec, using the Argonne HVEM and a helium coding specimen stage. An alloy button of Cu-54at%Ti was prepared by arc-melting and subsequently annealed at 1173K for two days. HVEM samples were spark-cut and thinned by jet polishing. The irradiation was carried out in HVEM with a fully focused beam. The Gaussian flux distribution of the beam was utilized to study the dose rate dependence of amorphization.Fig. 1 shows a few example photographs taken during a sequence of irradiation. The irradiation was always carried out on a low index bend contour. An interruption in the bend contour appears at the beam center where the dose rate is highest, as the irradiation proceeds. With further irradiation, the interruption grows outward into regions of lower dose rate. The critical dose for amorphization was calculated from each micrograph by multiplying the irradiation time with the predetermined dose rate. The length of the interruption in the bend contour was taken as the diameter of a completely amorphized volume at the accumulated dose. About ten micrographs were usually taken during a sequence of irradiation.
Shear-induced changes in chain configuration of poly(acrylic acid) in dilute solution
Authors: Armistead J.P. , Price R.R. , Kim O.-K. , Choi L.-S. 
Published: June 2020

Small amounts (less than 30 ppm) of polymer dissolved in solution may significantly reduce the work required to pump fluids through a pipe at a given rate. In other words, the drag of the solution along the pipe walls is reduced. Drag reduction by polymers has been well characterized, however the molecular origin of the phenomena is not fully understood. Polymers that exhibit drag reduction characteristics typically have high molecular weight, have predominantly linear, flexible chains, and have an expanded molecular configuration in solution.Work in this laboratory has focused on the drag reduction behavior of poly(acrylic acid), PAA, in recent years. This polymer is one of the most shear stable water-soluble polymers and due to the ionic groups in the polymer chain its conformation in solution changes with pH and ionic strength. In a recent work, PAA solutions of 18 ppm, pH=8.1, showed an initial drag reduction of over thirty-five percent in rotating disc experiments. Over four minutes of shearing the drag reduction decreased to ten percent. This was surprising because of the known shear stability of PAA. When the sheared solution was left undisturbed for two weeks, it did not recover its drag reduction performance. However, the addition of NaCl to the solution during the shearing immediately restored drag reduction to its initial level. It was hypothesized that the shear flow induced interchain association that was possibly stabilized by hydrogen bonding and that the addition of the NaCl caused dissociation and drag reduction recovery. In additional work, fluorescence probe studies showed that shear flow induced local chain rigidity in the originally flexible polymer chains. In this study, the drag reduction experiments were repeated and the configurations of the sheared and unsheared polymer chains were viewed using electron microscopy.
High-resolution, extended views of membrane surfaces revealed by fracture-flip
Authors: da Silva Pedro Pinto 
Published: June 2020

I will describe a new method — fracture-flip — that uses commercially available equipment to produce extended views of cell and membrane surfaces. The resolution of this new method permits the routine identification of surface structures down to 5 nm diameter. Moreover, in contrast to freeze-etching/deep-etching, extended views are easily obtained.Conceptally, fracture-flip derives from label-fracture, another method developed in my laboratory. With label-fracture we showed that, after freeze-fracture, the exoplasmic (E) halves of cell membranes are stabilized by, and remain attached to, their platinum/carbon replicas. This allows the observation of co-incident views of the Pt/C replica of the E face, and of the distribution of colloidal gold labeled receptors or antigens. This is the sequence of steps in fracture-flip:
Organization and composition of the cytoskeleton of giant algal cells: Its role in wound healing
Authors: Goddard R. H. , La Claire II J. W. 
Published: June 2020

We have been using the giant algal cells of Ernodesmis verticillata as a model system to study the process of wound healing at the cellular level of organization. Using immuno-localization techniques we have observed changes in the distribution of tubulin-containing microtubules (MTs) and actin-containing microfilaments (MFs), that occur during wound healing. Based on these and new findings, we carried out correlative experiments with inhibitors to investigate the functional roles of the various cytoskeletal components in wound healing.Emodesmis cells were cultured, Wounded and Fixed as described previously. The cytoplasm from fixed cells was adhered to polylysine-coated coverslips for light microscopy, or to formvar coated gold grids for transmission electron microscopy (TEM).The attached cells were labeled with primary antibodies (against tubulin ,actin,calmodulin [CAM], intermediate filament [If] proteins, or myosin)followed by incubation in appropriate secondary antibodies conjugated with FITC or TRITC for fluorescence, or conjugated to gold beads for TEM.
Traffic to the endocytic compartment of plants
Authors: Griffing L. R. , Record R. D. , Mollenhauer H. H. 
Published: June 2020

The endocytic pathway of plants has been identified and partially characterized using nonspecific membrane-bound and fluid phase probes . The function of endocytosis in plants is, however, unknown. We shall describe how ultrastructural histochemistry, immunocytochemical analyses and fluorescence imaging have been used to explore the physiology and function of the endocytic pathway in plant protoplasts and whole cells.Cationized ferritin (CF) can be used as a marker of plasma membrane uptake in plant protoplasts. Several different organelles become labeled upon exposure of protoplasts to CF: clathrin-coated vesicles (CV), the partially coated reticulum (PCR), the Golgi complex (GC), the multivesicular body (MVB), and the vacuole (V). These organelles also participate in the pathways of secretion and delivery of protein to the lysosome (vacuole). What are the sites of overlap/divergence among the secretory, endocytic and lysosomal pathways in these cells?
Morphogenetic plastid migration and spindle dynamics in simple land plants
Authors: Brown R.C. , Lemmon B. E. 
Published: June 2020

In many of the simple land plants mitosis and/or meiosis occurs in cells that contain a single plastid. Preparation for division in these monoplastidic cells is especially obvious because of predictive migration and division of the single plastid. The plastids serve as foci for organization of spindle microtubules (Mts) resulting in infallible coordination of plastid and nuclear division. Thus unlike most plant cells where a distinct MTOC is difficult to distinguish, monoplastidic cells provide a system in which the material responsible for nucleating Mts is closely associated with the plastid envelope and can be followed throughout the cell cycle. The intimate association of plastids with spindle poles has suggested the concept of plastid polarity which holds that the behavior of plastids parallels that of animal centrosomes. This concept is supported by recent studies using correlated methods of modern botanical microscopy.Mitosis was studied in the basal meristem of hornwort sporophytes and in root tips of Isoetes and Selaginella.
Freeze fracture analysis of cellulose terminal synthesizing complexes in Vaucheria
Authors: Mizuta Shun , Brown R. Malcolm 
Published: June 2020

It is well known that cellulose is assembled by specialized enzyme complexes (known as terminal complexes = TCs) located on or within the plasma membrane.At least three types of TCs have been described: a single linear row of particles observed in the brown alga Pelvetia; linear multiple rows in Oocystis and in some green algae; and, hexagonally arranged particle “rosettes” in some algae and solitary rosettes in all land plants. A new linear type of TC has been found in a freshwater xanthophycean alga Vaucheria hamata. Fine structure of the TC has been analyzed by high resolution analytical techniques for freeze-replication. Further examination for its characteristics was carried out by the treatment with inhibitors for cellulose formation(2,6-dichlorobenzonitrile, DCB) and its crystallization (Tinopal LPW).v. hamata was cultured under appropriate light conditions and single cells were cut into small pieces and recultured for two days. They were plasmolyzed in 0.2M NaCl, washed with fresh medium, and then recultured with or without inhibitors for 4-10 h. The cells were placed on Balzers double replica supports and quickly frozen in liquid propane. The supports were inserted in a Balzers double replica holder cooled by liquid nitrogen and placed in the chamber of a Balzers BA 360. Cells were fractured at 2x10-4 Pa and etched for 1 min. Most of the specimens were rotary shadowed (1 rps) with Pt-C at an angle of 30° and coated with carbon. Replicas were cleaned with 50% sulfuric acid containing 5% sodium dichromate and distilled water, and observed at 80Kv on a Philips EM 420.
Scanning tunneling microscopy and atomic force microscopy: New tools for biology
Authors: Bracker CE , Hansma P. K. 
Published: June 2020

A new family of scanning probe microscopes has emerged that is opening new horizons for investigating the fine structure of matter. The earliest and best known of these instruments is the scanning tunneling microscope (STM). First published in 1982, the STM earned the 1986 Nobel Prize in Physics for two of its inventors, G. Binnig and H. Rohrer. They shared the prize with E. Ruska for his work that had led to the development of the transmission electron microscope half a century earlier. It seems appropriate that the award embodied this particular blend of the old and the new because it demonstrated to the world a long overdue respect for the enormous contributions electron microscopy has made to the understanding of matter, and at the same time it signalled the dawn of a new age in microscopy. What we are seeing is a revolution in microscopy and a redefinition of the concept of a microscope.Several kinds of scanning probe microscopes now exist, and the number is increasing. What they share in common is a small probe that is scanned over the surface of a specimen and measures a physical property on a very small scale, at or near the surface. Scanning probes can measure temperature, magnetic fields, tunneling currents, voltage, force, and ion currents, among others.
Fluorescence microscopy and image analysis studies showing how plastids grow
Authors: Coleman A.W. , Maguire M.J. 
Published: June 2020

Biochemical analyses have shown that leaf plastid material/cell, both genomes and other materials, increase during growth and in response to light and other cues. However, the biochemical methods inevitably express results as an average per cell, leaving the precise timing of events in the cell cycle and course of ontogeny uncertain, and the variation in guantity/cell largely unknown. The power of quantitative microscopy lies in the capability of determining information on the single cell or single plastid level.To test the feasibility of using microscopic methods to study plastid growth and variability, we chose as an analog of the plant meristematic cell, the photosynthetic alga Ochromonas danica. This unicellular Chrysophyte combines a number of advantageous features. It typically has but 1-2 plastids and these occupy only a small proportion of the cell volume. Secondly, Ochromonas grows rapidly both in light and in darkness to high cell densities. Thirdly, the cell lacks a wall, so that its contents can be examined in detail in living cells flattened beneath a coverslip. Thirdly, the organism synthesizes chlorophyll both in light and darkness, so that plastids in living cells, however small, can be distinguished by virtue of the autofluorescence of their chlorophyll. Finally, for measurement of DNA per plastid, the arrangement of plastid DNA in Ochromonas plastids, as a necklace closely underlying the perimeter of the plastid, ensures that when one has isolated, stained intact necklaces, one is measuring the entire DNA content of the plastid.
In situ analysis of cell lineage and axonal guidance in the developing nervous system
Authors: Fraser S.E. 
Published: June 2020

The development of the nervous system involves the same classes of cell movements and differentiations as seen in the development of other tissues; however, the nervous system adds the complication of axonal processes that can travel over large distances to establish selective connections. Typically, the lineages of the neuronal precursors, their migrations, or the migrations of neuronal growth cones are studied in tissues fixed at different stages. Such timed samples can be used to infer some aspect of the developmental processes, but cannot offer any direct information on the dynamic aspects of these processes. This is a severe limitation because it is becoming ever-apparent that cellular dynamics provide the driving force behind many developmental phenomena.This presentation will discuss techniques that permit individual cells to be uniquely identified and followed over time as development proceeds in intact vertebrate embryos. There are two challenges to be met in performing an in situ analysis of neural development: unique labeling of individual cells, and observation of the cells. Labeling of individual cells is accomplished by microinjection of the vital dyes lysinated fluorescein dextran (LFD) or lysinated rhodamine dextran (LRD). Observation of the labeled cells is simplified by the recent strides in computer enhanced video microscopy. Much of the work has utilized the embryos of the frog, Xenopus laevis. The embryos of this species are hardy and have been the subject of a large body of experimental work. An important feature for these experiments is that the tissues surrounding the brain become progressively more transparent as development proceeds, offering the possibility of directly observing the labeled cells non-invasively in an intact, living embryo. Other experiments utilize the chicken embryo, because of the careful experimental embryology of the past decades provides a fertile backdrop for these new experimental approaches.
Applications of post-embedding immunogold labelling in the study of human tumors
Authors: Hearn Stephen , Kontozoglou Theodosios , Cramer Harvey 
Published: June 2020

Post-embedding immunogold labelling (IEM) can provide an exact correlation between the ultrastructure of tumor cells and the location of specific antigens. This technology links the molecular features of tumor cells derived from immunohistochemistry with our knowledge of tumor ultrastructure from electron microscopy. Criteria for the use of IEM in the study of human tissues include: the ability to localize many different antigens with commercially available antibodies; specimen preparation that is rapid, standardized and effective for different biopsies and tissue culture; results should compare with immunoperoxidase labelling on formalin-fixed, paraffin-embedded tissue.The tumors examined in this study included: squamous carcinomas, melanomas, multiple myelomas, schwannomas, medullary carcinomas of the thyroid, adenocarcinomas, leiomyomas, germ-cell carcinoma, myeloid leukemia, lymphomas, merkel cell carcinoma, and carcinoid tumors. Fine-needle aspiration biopsies (FNAB), core biopsies of bone marrow, peripheral blood, cell culture monolayers and surgically removed tissues were fixed in 1.6% glutaraldehyde. Samples were dehydrated, infiltrated in Lowicryl K4M and UV polymerized (total preparation time: 3 days). Technique for FNAB samples used mesh filtration to purify tumor cells which were then entrapped in albumin prior to embedding to prevent loss of cells. Glass coverslips (4x2mm) bearing cell monolayers were fixed in situ, infiltrated, placed in gelatin capsules and the cells separated from the coverslips after polymerization for en face sectioning. Thin sections were immunolabelled with readily available monoclonal and polyclonal antibodies using the protein A-gold technique. Samples of normal tissues were labelled for each antigen as positive controls and the negative controls used had appropriate low levels of non-specific labelling.
Structure of agarose gels: Mean pore radius
Authors: Griess Gary A. , Serwer Philip 
Published: June 2020

To use an agarose gel's sieving for the biophysical characterization of macromolecules and supramolecular complexes, the effective gel's pore radius (PE) is determined as a function of the agarose percentage (A). In previous studies, performed by use of agarose gel electrophoresis, the sieving of spheres of known radius (R) was used, together with two different (unproven) theories of sieving, to obtain PE. The PE values obtained were self-consistent and independent of R. The PE vs. A relationship did not agree with that predicted by a model that represents the gel as straight, randomly-oriented fibers (random fiber model). To test the accuracy of both the empirical PE vs. A relationship and the previously assumed model of gel structure, in the present study thin sections of agarose gels have been examined by use of electron microscopy.Gels of the agarose previously used to quantify sieving (SeaKem LE, Marine Colloids) were cast in the buffer previously used: 0.025 M sodium phosphate, pH 7.4, 0.001M MgCl2. Pieces of gel were fixed with osmium tetroxide, dehydrated and embedded in Epon. Dark gold (120 nm) sections were examined with a JEM-100CX transmission electron microscope. Electron micrographs were captured with a DataTranslation QuickCapture video digitizer and were processed on a Macintosh II computer using the program, Image.4
Electron microscopic study of the membrane glycoproteins in the rat kidney after cisplatin treatment
Authors: Aggarwal S.K. 
Published: June 2020

The proposed primary mechanism of action of the anticancer drug cisplatin (Cis-DDP) is through its interaction with DNA, mostly through DNA intrastrand cross-links or DNA interstrand cross-links. DNA repair mechanisms can circumvent this arrest thus permitting replication and transcription to proceed. Various membrane transport enzymes have also been demonstrated to be effected by cisplatin. Glycoprotein alkaline phosphatase was looked at in the proximal tubule cells before and after cisplatin both in vivo and in vitro for its inactivation or its removal from the membrane using light and electron microscopy.Outbred male Swiss Webster (Crl: (WI) BR) rats weighing 150-250g were given ip injections of cisplatin (7mg/kg). Animals were killed on day 3 and day 5. Thick slices (20-50.um) of kidney tissue from treated and untreated animals were fixed in 1% buffered glutaraldehyde and 1% formaldehyde (0.05 M cacodylate buffer, pH 7.3) for 30 min at 4°C. Alkaline phosphatase activity and carbohydrates were demonstrated according to methods described earlier.
Focal adhesions to the synaptic matrix at mouse neuromuscular junctions
Authors: Robbins Norman , Polak Joseph 
Published: June 2020

Studies of identified synapses in living animals have revealed ongoing synaptic remodelling in the mature nervous system. We recently demonstrated the existence of filopodia and lamellipodia (structures associated with nerve outgrowth in developing or tissue culture systems) at the mature mouse neuromuscular junction (NMJ) . Evidence of motor nerve terminal retraction, regeneration and perisynaptic outgrowth indicated that even established synaptic contacts were not permanent. It now appears that variation in the stability of synaptic contacts, not the amount of nerve terminal outgrowth,is the basis for synaptic remodelling and extension. Although it has been documented that regenerating motor nerve terminals adhere to former synaptic matrix,and that the matrix contains information for inducing and aligning presynaptic and postsynaptic specializations,it was not clear whether the synaptic matrix was uniformly adhesive, or formed specialized adhesive foci with the preterminal membrane. To determine if there are specific sites of synaptic adhesion we utilized hypertonic fixatives to induce shrinkage at the NMJ.Male mice were anaesthetized, the soleus muscle was exposed, and the overlying skin was retracted to create a pool into which either 2% glutaraldehyde in HEPES Krebs (normal fixative) or 2% glutaraldehyde in HEPES Krebs with a 2X NaCl concentration (hypertonic fixative) was added continually for 30 minutes. The surface layer of each muscle was then removed and submerged in the same fixative for an additional 1.5 hours. Tissue was washed in buffer (pH 7.2) and immersed in cholinesterase stain for 5 minutes to localize endplate regions . Endplate regions were cut into 1 mm blocks, washed in buffer (pH 7.2) and post-fixed for 1 hour in HEPES Krebs buffered 2% osmium tetroxide (pH 7.2). Following fixation, specimens were dehydrated in a graded ethanol series and embedded in Polybed 812 (Polysciences). Mouse soleus muscle was stained for immunocytochemical localization of actin with a rabbit polyclonal antiserum against chicken gizzard actin (from Dr. James Lessard, University of Cincinnati) as previously described .