bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Structure of One and Two Dimensional Polymers of Tubulin and their Role in Nucleation of Microtubule Assembly
Authors: Erickson H.P. 
Published: June 2020

The microtubule is a long hollow cylinder, 23 nm outside diameter and of indeterminate length, often many micrometers long. The wall of the microtubule, a curved sheet of 5 nm thickness, is seen to best advantage where it is split open and flattened against the carbon film as a non-overlapping, single sheet (fig. 1). Optical diffraction and image reconstruction techniques show that the wall is composed of subunits arranged on a 4 x 5 nm lattice (fig. 2). Each of these 4 x 5 nm subunits corresponds to a 55,000 MW protein subunit characterized biochemically and called tubulin.It is well established that microtubules are composed of two similar but distinct types of tubulin, called alpha and beta. In most negatively stained specimens, however, the 4 x 5 nm subunits are identical in structure. A small structural difference between alternate 4 x 5 nm subunits is seen under certain conditions (Amos and Klug, 1974; Baker and Amos, 1978), but in the present discussion we will ignore the distinction between alpha and beta subunits and pretend that the microtubule is composed of a single type of subunit.
Transcription in the Interphase Nucleus
Authors: Simard R. , Royal A. , Lacoste-Royal G. , Banville D. 
Published: June 2020

Normal Nuclear Fine Structure
The Nucleolus
Excellent reviews on nucleolar fine structure have been published in
past and recent years, and it is not our intention to duplicate them. There
are four distinct nucleolar components in most mammalian cells: (1) 150- to
200-A dense granules randomly dispersed in the nucleolus, (2) a loose
fibrillar reticulum composed of 50- to 80-A fibrils, (3) an amorphous matrix
of low electron opacity, and (4) nucleolus-associated chromatin with
intranucleolar ramifications. The granular and fibrillar components are
partially extracted with ribonuclease and disappear completely if digestion
with the nuclease is followed by pepsin (Marinozzi and Bernhard, 1963). They
can be referred to as granular and fibrillar ribonucleoproteins (RNP). The
granular RNP are similar to the cytoplasmic ribosomes in their staining
properties, but they are smaller, more irregular, and never arranged in
subunits. Thin filaments about 20 A in width have been demonstrated in the
granules; these filaments are RNase-sensitive (Smetana et al.,
1968a).
Electron Microscopy of Cytoplasmic Contractile Proteins
Authors: Pollard T.D. , Maupin P. 
Published: June 2020

In this paper we review some of the contributions that electron microscopy has made to the analysis of actin and myosin from nonmuscle cells. We place particular emphasis upon the limitations of the ultrastructural techniques used to study these cytoplasmic contractile proteins, because it is not widely recognized how difficult it is to preserve these elements of the cytoplasmic matrix for electron microscopy.The structure of actin filaments is well preserved for electron microscope observation by negative staining with uranyl acetate (Figure 1). In fact, to a resolution of about 3nm the three-dimensional structure of actin filaments determined by computer image processing of electron micrographs of negatively stained specimens (Moore et al., 1970) is indistinguishable from the structure revealed by X-ray diffraction of living muscle.
Possible indirect transmission of COVID-19 at a squash court, Slovenia, March 2020: case report
Authors: Brlek A. , Vidovič Š. , Vuzem S. , Turk K. , Simonović Z. 
Published: June 2020

Abstract
Since the beginning of the COVID-19 epidemic, there is an ongoing debate and research regarding the possible ways of virus transmission. We conducted an epidemiological investigation which revealed a cluster of five COVID-19 cases, linked to playing squash at a sports venue in Maribor, Slovenia. Acquired data raises possibility that the transmission occurred indirectly through contaminated objects in changing room or squash hall or via aerosolisation in squash hall.
Dark-Field Imaging with the Albany 1.2 MV High-Voltage Electron Microscope
Authors: Mannella C.A. , Ratkowski A.J. , Marko M. , Parsons D.F. 
Published: June 2020

High-resolution images of naked biological structures have been produced with conventional electron microscopes operated in dark-field mode. The use of higher accelerating voltages offers several important advantages, including decreased plural scattering and decreased chromatic aberration for thin, low-Z specimens. Despite impressive early results at the Toulouse HVEM facility there has been little application of high-voltage dark-field techniques to the study of biological specimens of low mass-thickness.The increased contrast inherrent to dark-field imaging is illustrated in Fig. 1 for a conventionally-stained, very thin (20nm) section of rat brain taken at an accelerating voltage of 1.0 MV. Fig. 1A is a bright-field micro-graph taken with a 30-μm diam Pt object apenture. Micrographs B and C are dark-field images of the same field generated, respectively, by tilting the zero-order beam into the edge of the 30-μm aperture (“beam-tilt” dark-field) or by blocking the zero-order beam with a 20-μm-thick Cu bar (“strioscopy”). The much higher collection efficiency of strioscopic relative to beam-tilt dark-field is reflected in the exposure times for micrographs B and C (10vs1 sec). Although all 3 micrographs display features (e.g., myelin intraperiod line widths) at the effective specimen preparation resolution limit (2.5-3.0 nm), dark-field HVEM micrographs taken using strioscopic techniques are generally not as sharp as those obtained with beam-tilt. Because radiation damage associated with the latter dark-field mode may be excessive in proposed studies of unstained biological structures, we have undertaken a study of the factors limiting the resolution and contrast of the more efficient strioscopy. Our findings suggest that dark-field resolution with non-crystalline, low-Z specimens may be a sensitive function of HVEM lens design and of collimation as well as dark-field aperture arrangement.
Microprobe and Nanoprobe Analysis in TEM
Authors: Thompson M.N. 
Published: June 2020

The application of TEM/S(T)EM systems to problems in the materials
science and life science is an accepted and growing trend. Considerable
information benefits have been derived from the new information which
secondary electron, back-scattered electron and X-ray line scan and mapping
images have provided. This is also true of the STEM mode with respect to the
visualisation of low-contrast specimens, the application of annular D.F.
detectors and signal mixing techniques.
In the general case, however, the STEM mode is used specifically to view
an area for the purpose of locating a small probe for point X-ray analysis
or microdiffraction. As there is no clear evidence to date that the STEM
mode has specific advantages under conditions analogous to normal TEM
observation the greater proportion of normal thin specimen work has remained
the domain of the basic TEM mode. The reasons for this TEM preference for
transmission work are the intrinsically simple operation, the convenience of
real time, wide-field imaging and the high resolution images available for
viewing and recording particularly at relatively low
magnifications.
Sputter-Deposited Films as Standards for Tem X-Ray Analysis
Authors: Marshall A. F. , Zercher C. 
Published: June 2020

Quantitative energy dispersive x-ray analysis in the transmission
electron microscope is generally obtained in the form of relative
concentrations using the equation:
where CA, CB are the
concentrations and IA, IB are the
peak intensities of elements A and B, and kAB is a
constant which is independent of specimen composition and specimen
thickness, assuming the thin film criterion is satisfied.
kAB may be determined experimentally from standards
(Cliff-Lorimer technique1), or may be calculated from
considerations of x-ray generation and detector efficiency for the elements
being analyzed2. Due to differences in detector
parameters, kAB may vary from instrument to
instrument.
Scanning Transmission Electron Microscopy of Polyethylene
Crystals
Authors: Khoury F. , Bolz L. H. 
Published: June 2020

The lateral growth habits and non-planar conformations of polyethylene
crystals grown from dilute solutions (<0.1% wt./vol.) are known to vary
depending on the crystallization temperature.1-3 With
the notable exception of a study by Keith2, most
previous studies have been limited to crystals grown at <95°C. The trend
in the change of the lateral growth habit of the crystals with increasing
crystallization temperature (other factors remaining equal, i.e. polymer
mol. wt. and concentration, solvent) is illustrated in Fig.l.
The lateral growth faces in the lozenge shaped type of crystal (Fig.la)
which is formed at lower temperatures are {110}. Crystals formed at higher
temperatures exhibit 'truncated' profiles (Figs. lb,c) and are bound
laterally by (110) and (200} growth faces. In addition, the shape of the
latter crystals is all the more truncated (Fig.lc), and hence all the more
elongated parallel to the b-axis, the higher the crystallization
temperature.
Accurate Determination of Foil Surface Normal in a Material with Stacking
Faults
Authors: Allen Samuel M. 
Published: June 2020

This paper describes a method for determining the foil surface normal in
a transmission electron microscopy (TEM) sample containing stacking faults.
The method makes use of observed dihedral angles at stacking fault
intersections to compute the foil normal, when the beam direction is
known.
Dihedral angles are angles formed at the intersections of surfaces. The
true dihedral angle is observed when viewed parallel to the line of
intersection of the surfaces. For optical metallography, where observations
are made by viewing normal to a plane of polish, the observed dihedral angle
is the angle formed by thetraces of the intersecting surfaces on the plane
of polish. The geometry of this problem was considered by Harker and Parker,
who demonstrated that the observed angle could be either greater or less
than the true angle.
Structural Investigation of Iron Particles Used for Magnetic Recording
Media
Authors: Baltz Alfred 
Published: June 2020

As part of a program to develop iron particles for next generation
recording disk medium, their structural properties were investigated using
transmission electron microscopy and electron diffraction. Iron particles
are a more desirable recording medium than iron oxide, the most widely used
material in disk manufacturing, because they offer a higher magnetic output
and a higher coercive force.
The particles were prepared by a method described elsewhere. Because of
their strong magnetic interaction, a method had to be developed to separate
the particles on the electron microscope grids.
Ultrastructural Changes in Rough Endoplasmic Reticulum of Renal Proximal
Tubule Cells in Tetraethyllead Poisoning
Authors: Wade P. R. , Chang L. W. , Wade V. L. 
Published: June 2020

Tetraethyllead (TEL), a gasoline antiknock additive, poses an
occupational and environmental risk to human health. Renal damage is a
prominent finding in human TEL intoxication. Levels of urinary and
erythrocyte ALA-D are altered. Histological examination of the renal
parenchyma reveals degenerative changes in the proximal tubules.
Experimental TEL studies also demonstrate kidney damage in mice, rats,
rabbits, and dogs by various investigators.
The basic pathogenetic mechanism of TEL poisoning is unknown. However,
in view of the disruption of rough endoplasmic reticulum (RER) and protein
synthesis which constitutes the pathogenetic mechanism of methylmercury
poisoning, alteration of the RER may also underl ie the toxic impact of
organolead in the cells. This report presents unique ultrastructural
findings of such an investigation.
Localization of Immune Complexes in the Basement Membrane of the Ductuli
Efferentes of the Rhesus Monkey
Authors: Marsh D. 
Published: June 2020

As a result of vasectomy, spermatozoa are confined to the epididymis and
vas deferens, where they degenerate, releasing antigens that enter the
circulation or are engulfed by macrophages. Multiple antigens of the sperm
can elicit production of autoantibodies; circulating anti-sperm antibodies
are found in a large percentage of vasectomized men, indicating the
immunogenicity of the sperm.
The increased prevalence of macrophages in the liomen of the rhesus
monkey testicular efferent ducts after vasectomy led to further study of
this region. Frozen sections were used for evaluation of immunopathological
status by fluorescence microscopy with fluorescein-conjugated antibody.
Subsequent granular deposits of immune complexes were revealed by positive
immunofluorescence staining for complement. The immune complex deposition in
the basement membrane surrounding the efferent ducts implies that this
region is involved in antigen leakage (Fig. 1).
A Quantitative Scanning Electron Microscopic Investigation of Aquatic
Bacterial Populations: Diel Variability
Authors: Dreier Thomas M. 
Published: June 2020

Two important variables in sampling aquatic bacterial populations are
the sampling interval (time and space) and the species of bacteria that
compose the bacterial population. Scanning electron microscopy (SEM) has
proven to be an accurate method for estimation of both the density and
composition (based on morphological characters) of aquatic bacterial
populations (1). This investigation was undertaken to quantify the diel
population dynamics of a morphologically distinct population from a
stratified aquatic environment. This type of information has not been
previously obtainable with other enumeration techniques.
Samples were taken from a stratified pond located in Central Texas.
Water samples (n=4) were collected employing sterile techniques from the 2.0
m strata every three hours from 1000 hrs, 24 August to 1000 hrs, 25 August
1979. Bacterial samples were prepared for SEM according to the methods of
Dreier and Thurston (2). Bacteria were classified and enumerated with SEM
into 54 morphologically identifiable types (fig. 1a and 1b). The frequency
of dividing cells (FDC) for R26 was calculated as the percentage of R26
showing septum formation (fig. 1b) to the total number of R26.
Electron Microscopic Analysis of Asymmetry within the Cell Nucleus of DNA
Helix Openings During Human Cell Activation and Cell Differentiation
Authors: Frenster J. H. 
Published: June 2020

Most of the DNA molecules within an animal cell are repressed for RNA
synthesis at any one time, and those DNA molecules that are active are
characteristic of the particular tissue or organ within which the cell has
differentiated (1). This phenomena of differential gene transcription is
thought to be the epigenetic basis for such diverse cell activities as cell
differentiation organ regeneration, neoplastic transformation, immune
activation, and the response to steroid hormones (2).
Carcinogenic chemicals, oncogenic viruses, embryogenic RNA, immune RNA,
and steroid hormones all prefer to bind to single-stranded regions within
DNA molecules of the host cell (3). DNA molecules which are active in RNA
synthesis display short loops of such single-stranded DNA (4), which are a
necessary prerequisite for the gene de-repression characteristic of animal
neoplasms (5).
Ribosomal Structure and Functional Sites Mapped by Immune Electron
Microscopy
Authors: Lake James A. 
Published: June 2020

Ribosomal protein locations have been mapped on the ribosomal surface by
using antibodies directed against specific ribosomal proteins. Relative
orientations of the large and the small subunits in the monomeric ribosome
have been determined using a double labeling approach; and functional
regions such as the codon-anticodon interaction site, the tRNA binding sites
and the peptidyl transferase have been suggested from the locations of
ribosomal proteins.
The small ribosomal subunit (see Figure 1) is divided by a constriction
into a one-third, or head, and a two-thirds, or base, region (1). A
platform, located on the base, forms a cleft between it and the upper
one-third of the subunit. The cleft, the upper one-third and the platform
are thought to comprise the binding sites for mRNA and for initiation
factors IFl, IF2 and IF3. The locations of some of the proteins involved in
tRNA binding that have been mapped in collaboration with Dr. L. Kahan
(Department of Physiological Chemistry, University of Wisconsin) are
summarized in Figure 1. In addition, some proteins such as S4 are not
accessible for IgG binding (2). Protein S4 is being mapped using
reconstituted subunits lacking S5 and S12 (3). The binding sites for
proteins Si, S11, S12 and S18 (not shown) are located on the platform and
suggest that the site of the codon-anticodon interaction is also
there.
Function of the Cortical Actin Lattice in the Motor of Macrophages
Authors: Stossel T.P. 
Published: June 2020

Macrophages are cells of the hematopoietic system with important defensive functions in the tissues of higher animals. Movement is an important aspect of the execution of these functions, which include locomotion, spreading on surfaces and the phagocytosis of foreign debris and microorganisms. These cells also secrete lysosomal enzymes by the process of exocytosis, and the released enzymes may play a part in the pathogenesis of tissue destruction during inflammation.The “motor” region of macrophages appears to reside in the peripheral cytoplasm beneath the plasma membrane. This cortical region ordinarily excludes lysosomes and other organelles, and, although evident throughout the entire cell periphery, it is particularly prominent in veils, pleats and pseudopodia extended by the cell ( 1 ).
Ultrastructural Immunocytochemistry of Five Rat Pituitary
Adenomas
Authors: McComb D. J. , Ryan N. , Horvath E. , Kovacs K. , Nagy E. , Berczi I. , Domokos I. , LaszIo F. A. 
Published: June 2020

Conventional light and electron microscopic techniques failed to clarify
the cellular composition and derivation of spontaneous and induced,
intrasellar and transplanted pituitary adenomas in rats (1). In the present
work, electron microscopic immunocytochemistry was applied to evaluate five
adenohypo-physial tumors using a technique described by Moriarty and Garner
(2).
Spontaneously occurring pituitary adenomas (group 1) were harvested from
aging female Long-Evans rats. R-Amsterdam rats were treated with 2 x 1.0 mg
estrone acetate (HogivaI) s.c. weekly for 6 months. Pituitary adenomas in
excess of 30 mg were removed from these animals to make up the tumors of
group 2. Groups 3 and 4 consisted of estrogen-induced autonomous
transplan¬ted pituitary tumors MtT.WlO and MtT.F4. Group 5 was a
radiation-induced transplanted autonomous pituitary tumor MtT.W5. The tumors
of groups 3,4 and 5 were allowed to proliferate in host rats 6-8 weeks prior
to removal for processing. Tissue was processed for transmission electron
microscopy (glutaraldehyde fixation, OsO4 postfixation
and epoxy resin embedding), and electron microscopic immunocytochemistry (3%
paraformaldehyde fixation and Araldite embedding).
An X-Ray Projection Microscope Stage for the Cambridge S.180 S.E.M. and
its Biological Applications
Authors: Fletcher S. , Hannah R. S. , Hollenberg M. J. 
Published: June 2020

The purpose of this study was to develop a functional microscope system
to overcome the inherent disadvantages of using the light microscope/camera
lucida system to reconstruct sections of biological material. The problem is
perhaps most acute in the nervous system, where reconstruction of
3-dimensional neurons or the tracing of neuronal pathways over extensive
distances must be attempted. The camera lucida system suffers from many
inaccuracies and is an extremely time-consuming and tedious
procedure.
Point projection x-ray microscopy in the SEM, entails utilizing the
primary electron beam in the spot mode to generate a point source of x-rays
from a suitable target (Al, Cu, Au). This technique was first successfully
demonstrated by Horn and Waltinger (1978).
Efficacy of experimental phage therapies in livestock
Authors: Dec Marta , Wernicki Andrzej , Urban-Chmiel Renata 
Published: June 2020

AbstractBacteriophages are the most abundant form of life on earth and are present everywhere. The total number of bacteriophages has been estimated to be 1032 virions. The main division of bacteriophages is based on the type of nucleic acid (DNA or RNA) and on the structure of the capsid. Due to the significant increase in the number of multi-drug-resistant bacteria, bacteriophages could be a useful tool as an alternative to antibiotics in experimental therapies to prevent and to control bacterial infections in people and animals. The aim of this review was to discuss the history of phage therapy as a replacement for antibiotics, in response to EU regulations prohibiting the use of antibiotics in livestock, and to present current examples and results of experimental phage treatments in comparison to antibiotics. The use of bacteriophages to control human infections has had a high success rate, especially in mixed infections caused mainly by Staphylococcus, Pseudomonas, Enterobacter, and Enterococcus. Bacteriophages have also proven to be an effective tool in experimental treatments for combating diseases in livestock.
Playful Work Design: Introduction of a New Concept
Authors: Bakker Arnold B. , Scharp Yuri S. , Breevaart Kimberley , de Vries Juriena D. 
Published: June 2020

Abstract
This article introduces the concept of playful work design—the process through which employees proactively create conditions within work activities that foster enjoyment and challenge without changing the design of the job itself. First, we review play theory and the motives people may have to play during work. In addition, we use the literature on proactive work behavior to argue that individuals can take personal initiative to increase person-job fit. Combining these literatures, we provide a theoretical framework for playful work design. We discuss the development and validation of an instrument to assess playful work design, and review recent studies to elucidate the psychological effects of playful work design and its possible outcomes. Finally, we briefly discuss practical implications.
Long‐Term Variations of >16‐MeV Proton Fluxes: Measurements From NOAA POES and EUMETSAT MetOp Satellites
Authors: Lin Ruilin , Zhang Jichun , Zhang Xiaoxin , Ni Binbin , Liu Siqing , Shi Liqin , Gong Jiancun , Wang Hong , Cao Yong 
Published: June 2020

AbstractBased on the recalibrated data of >16‐MeV proton omnidirectional integral fluxes obtained from NOAA POES and EUMETSAT MetOp satellites during the period from 1978 to 2014, solar cycle phase lags, the variations of proton radiation belt, and the relationships between trapped proton fluxes and F10.7 flux, cosmic ray, or sunspot number are investigated in detail. It is found that (a) the solar cycle phase lags between energetic proton fluxes and sunspot number are within 2.5 years, dependent on solar cycle, Lm, B/B0, and proton energy; (b) at the magnetic equator, the ratios of the maximal to minimal values of 4‐month smoothed monthly >16‐MeV proton fluxes during the period from 1978 to 2014 increase and then decrease with increasing Lm, showing the maximal value ~11.24 at Lm = 1.15; and (c) at a magnetic field line with Lm ≤ 1.15, the ratios of the maximal values in 1987 to the minimal values in 2002 for yearly >16‐MeV proton fluxes decrease with increasing B/B0, while at a magnetic field line with Lm ≥ 1.16, they increase and then decrease with increasing B/B0, and the maximal ratio for all magnetic field lines can reach above 20. An exponential equation with an offset is feasible to describe the relationship between the logarithm of >16‐MeV proton fluxes and F10.7 flux. It can be readily used to improve the NOAAPRO model.