bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-equilibrium phase formation
Authors: Fujita Hiroshi
Published: June 2020

The most important advantage of EM’s is in situ experiments on detailed processes of the same phenomena that occur in bulk materials. In recent years, in situ experiments with HVEM’s, in particular with a 3MV ultra-HVEM , has made it possible to create non-equilibrium phases, which do not exist in nature, or to control and design materials on an atomic scale. Namely, HVEM’s have developed to “Micro-Laboratory”, in which various material-treatments can be done, for natural science from powerful tools for characterization and/or identification of materials.

l.The General Rule for Solid Amorphization
The author and his cowerkers have succeeded in making amorphous solids of intermetallic compounds by high energy electron irradiation. Using the electron irradiation effect, necessary conditions for the formation of both non-equilibrium phases and extremly supersaturated solid structures[3,4] can be easily and precisely controlled.
A new system for in-situ observation of dynamic process of structural and chemical changes during dual ion beam irradiation in a 400 Kv Electron Microscope
Authors: Furuno Shigemi , Hojou Kiichi , Otsu Hitoshu , Izui Kazuhiko , Sasaki Teikichi , Tsukamoto Tetsuo , Hata Takao
Published: June 2020

In order to simulate radiation damage of fusion reactor materials, we have developed an in-situ observation system in 1986, which consisted of an electron microscope of JEM-100C type combined with a 10 keV ion gun and parallel EELS. Using this system, we have observed dynamic processes of structural and chemical changes of materials during ion irradiation. In this paper, we have developed a new in-situ observation system, with which it is possible to observe dynamic process of structural and chemical changes of materials during dual ion beam irradiation.

This system consists of an analytical electron microscope of 4000FX type linked with two 40 keV ion beam accelerators, as shown in fig. 1. The maximum possible ion current on the specimen is 50μA/cm2 for 40keV He ion. Ion beams emmitted from duo-plasmatron ion guns are deflected downward by an angle of 30° with selecting magnet and are introduced into the specimen chamber. Ion beams are deflected downward again by an angle of 30° with electrostatic plism and are incident finally at an angle of 60° with the surface of the specimen, as shown in fig. 2. The images of electron microscope during irradiation are recorded with a VTR through a TV camera. It is possible to control the temperature of the specimen during irradiation within the range from 10 K to 1575 K by using both low and high temperature specimen holders. Test of tension for the specimen under irradiation is also possible. The in-situ chemical analysis in the region of 10 nm under irradiation is possible with EDS (UTW type, Tracor Nothern) and parallel EELS (666 type, Gatan). A quadrapole mass spectrometer is attached near specimen chamber to carry out TDS analysis.
HRTEM observations of schottky barrier interfaces at WSi0.4/GaAs contacts
Authors: Mitwalsky A. , Willer J. , Oppolzer H.
Published: June 2020

WSix is one of the most favored Schottky gate metallizations due to its self-aligned contact formation capability and high temperature resistance (∽800°C) for x ∽ 0.45. It will be demonstrated that fine details of the microstructure at this WSi0.4/GaAs Schottky interface change clearly when temperature is increased up to 800°C. These findings are relevant for explaining Schottky barrier measurements usually implying the existence of an intimate and uniform contact between metallization and semiconductor. Similar investigations have been performed on related WSix (x = 0.1 and 0.6) systems.

The WSi0.4 Schottky contact was sputtered from a planar magnetron compound target at a power level of 4 W·cm−2 and a deposition rate of 45 nm·min−1. As described previously films were deposited in dc-mode with an rf-bias of 50 V. Initial wafer surface preparation of bulk doped GaAs (Si : 7·1016cm−3) involved standard H2SO4 etch followed by a surface etch in diluted NH4OH. The sputtering chamber was evacuated to a base pressure of 2·10−7 Torr. A heat treatment at 250°C for 10 min of the substrate was performed immediately prior to silicide deposition. The temperature stability and interface structure of this metallization was investigated by cross-sectional transmission electron microscopy (TEM) at specimens annealed for 20 min at 400°C, 720°C and 800°C, respectively. In particular, atomic scale information was attained by high-resolution TEM (HRTEM) using a 400 kV TEM with a point resolution of 0·18 nm.
HREM study of M, Y and W hexagonal type ferrites
Authors: Vallet-Regí M. , Nicolopoulos S. , González-Calbet J.M.
Published: June 2020

Hexagonal ferrites have similar structural symmetries and are built by the same structural units. HREM has proved to be an excellent tool to identify individual stacking bloks, in M, Y and W hexaferrites.

M, Y and W hexagonal type ferrites are well-known magnetic materials for applications. Some previous electron microscopy studies on these ferrites, reveal a variety of new phases coming from the microsyntactic intergrowth of M, Y and W structures. We report in this paper some microstructural features of these ferrites.

BaFe12O19 (M) hexagonal ferrite was synthetized by using the standard ceramic technique. Crystals of Y type ferrite (nominal composition: BaLi0.5Fe0.5ZnFe16027) were prepared from stoichiometric amounts of BaCO3, ZnO and LiCO3. The synthesis of W-type ferrite (formula: Ba2Zn2Fe16027) is described elsewhere.Samples for observation were prepared by grinding powders of the above ferrites under acetone. HREM study was performed at the "Centro de Microscopía Electrónica, Univ. Complutense" using both 400 Kv and 200 Kv electron microscopes (JEM-400EX and JEM-200FX)
HREM observations of microstructrues of silicon carbide whiskers
Authors: Ning X.G. , Ye H.Q. , Cao W.
Published: June 2020

As we know, SiC whiskers take an important role in lightweight composite materials such as Al-Li-SiC material and etc. The study on microstructures of SiC whiskers is needed for well understanding the properties of the composite materials reinforced by SiC whiskers. Microstructures such as multi-twins and polytypes of bulk crystal of SiC have been studied in detail. Information of microstructures of SiC whiskers in atomic resolution, however, has not been reported yet.

Defects in SiC whiskers made from rice hulls were identified and analyzed using TEM. The whiskers were characterized by a high density of planar faults lying on closed planes perpendicular to the whisker axis. Defects in SiC whiskers here (made by solid reaction method, IMR, Academia Sinica) were different. The basic structure of SiC whiskers here is β-type (f.c.c.) (Fig.1a). There were many twins and some polytypes, too. Fig.1a shows normal structure with many twins formed on the (111) planes perpendicular to the growth direction of the whiskers. There were two kinds of microtwins. Multiple twins, which may occurred on four sets of the {111} twin planes ( Fig.1b gives its diffraction patterns). Normally, only multiple twins on two sets of {111} twin planes, which were parallel to the direction of electron beams (viewed along a [110] axis), could be seen (Fig.1c). Thin lamellar twins of predominant β phase interspersed with stacking faults (Fig.1a). Within the twinned lamellae, microtwins sometimes terminated in the matrix (B in Fig.1a). Fig.1d gives clear image of this kind of termination in another area. The interfacial structures between such twins and the matrix were twinning dislocations and Shockley partials. It will be discussed in detailed elsewhere. It can be seen in Fig. 2 that there was a intrinsic stacking fault interrupted by a intersected twin and closed by two twins. Generally, there were few intrinsic stacking faults but many extrinsic ones as indicated by the arrows in Fig.1a. This is because that the energy of intrinsic stacking fault is higher than that of extrinsic one. Polytypes of 2H (Fig. 3a), 4H (Fig.b), 6H (Fig.c), 9R (Fig.d) and 15R (Fig.e) were observed in SiC whiskers by HREM. It is interesting that Fig.3c was taken from a bar of the whisker with strange [1010] growth direction, because the normal growth axis should be [0001] in α-SiC.
EM of hot-dip zinc-iron (galvannealed) coatings
Authors: 'Ecuyer J.D.L , Gagné M. , Cheng C.C. , 'Espérance G.L.
Published: June 2020

Galvannealed coatings have superior weldability and paintability characteristics than conventional zinc coatings. As a result, the market for galvannealed steel sheets is steadily increasing especially in the automotive industry. The formation of the brittle intermetallic Zn-Fe phases, Γ, Γ1, δ, and Z also affects the for- mability properties of the coated steel product. In order to minimize powdering and flaking, the microstructure of the coating must be closely controlled.

The characterization of the galvannealed coating microstructure is essential but has proven to be quite difficult. The individual phases cannot be resolved using optical microscopy. X-ray diffraction appears promising, however some of the intermetallic phases are too thin to produce a detectable signal. Electrochemical stripping has been used, but phase identification is ambiguous. Direct observation of the phases using electron microscopy appears to be the best method for characterizing these coatings.
EM of a macro defect-free cement
Authors: Popoola O. , Kriven W. M. , Young J.F.
Published: June 2020

Engineering materials application of silicate or aluminate cements are limited because of their low strength and toughness. These poor properties can be easily attributed to the inherent macro and micro porosity of cement pastes. However in the last decade it has been found that by the addition of a water soluble polymer, high shear mixing and the by application of modest pressure during processing, cement with mechanical properties comparable to most ceramics can be obtained. The water soluble polymer, apart from filling the pores, also act as a rheological aid, reducing the interparticle friction coefficient and providing for optimum particle packing in the microstructure. Although a brief account of the microstructure of this new composite (called Macro Defect Free Cement) has been reported, a close and detailed examination of the cement particle/polymer interface remains to be performed. The aim of this communication is to report the microstructure of a macro defect free cement with particular emphasis on the cement particle/polymer interfaces. Cement nomenclature is used in this report: C= CaO, A= Al2O3, H=H2O
Morphological and structural studies on ATS terpolymers
Authors: Braglia R. , Ayroldi G. , Fumagalli M.
Published: June 2020

The outdoor resistance of ABS terpolymers (acrylonitrile-co-styrene-graft-polybutadiene) can be greatly improved by substitution of diene rubber with a nearly saturated ethylene-co-propylene-co-diene (EPDM) elastomer terpolymer. The grafting reaction of styrene and acrylo= nitrile onto EPDM (ATS terpolymer) can be carried out, for example, by suspension polymerization using coarse milled rubber!

Transmission electron microscopy (TEM) and dynamic-mechanical spectro= scopy (DMS) at about I Hz are used to understand the grafting reaction and the morphological changes induced by processing the graft or by dilution of the graft with styrene-acrylonitrile (SAN) copolymer. TEM investigation is carried out either on grafted material, embedded in a hard matrix to facilitate sectioning operation, or on pelletized diluted or undiluted materia 1.0smium tetroxide is used as a staining agent.
Imaging of polymer single crystals in low-voltage, high-resolution scanning electron microscopy
Authors: Adams W.W. , Price G. , Krause A.
Published: June 2020

It has been shown that there are numerous advantages in imaging both coated and uncoated polymers in scanning electron microscopy (SEM) at low voltages (LV) from 0.5 to 2.0 keV compared to imaging at conventional voltages of 10 to 20 keV. The disadvantages of LVSEM of degraded resolution and decreased beam current have been overcome with the new generation of field emission gun SEMs. In imaging metal coated polymers in LVSEM beam damage is reduced, contrast is improved, and charging from irregularly shaped features (which may be unevenly coated) is reduced or eliminated. Imaging uncoated polymers in LVSEM allows direct observation of the surface with little or no charging and with no alterations of surface features from the metal coating process required for higher voltage imaging. This is particularly important for high resolution (HR) studies of polymers where it is desired to image features 1 to 10 nm in size. Metal sputter coating techniques produce a 10 - 20 nm film that has its own texture which can obscure topographical features of the original polymer surface. In examining thin, uncoated insulating samples on a conducting substrate at low voltages the effect of sample-beam interactions on image formation and resolution will differ significantly from the effect at higher accelerating voltages. We discuss here sample-beam interactions in single crystals on conducting substrates at low voltages and also present the first results on HRSEM of single crystal morphologies which show some of these effects.
Crystal chemistry of high-Tc superconductors
Authors: Hervieu Maryvonne
Published: June 2020

Four years after the discovery of superconductivity at high temperature in the Ba-La-Cu-O system, more than thirty new compounds have been synthesized, which can be classified in six series of copper oxides: La2CuO4 - type oxides, bismuth cuprates, YBa2Cu3O7 family, thallium cuprates, lead cuprates and Nd2CuO4 - type oxides. Despite their quite different specific natures, close relationships allow their structures to be simply described through a single mechanism. The fifth first families can indeed be described as intergrowths of multiple oxygen deficient perovskite slabs with multiple rock salt-type slabs, according to the representation [ACuO3-x]m [AO]n.

The n and m values are integer in the parent structures, n varying from 0 to 3 and m from 1 to 4; every member of this large family can thus be symbolized by [m,n]. The oxygen deficient character of the perovskite slabs involves the existence or the co-existence of several types of copper environment: octahedral, pyramidal and square planar.

Both mechanisms, oxygen deficiency and intergrowth, are well known to give rise easily to nonstoichiometry phenomena. Numerous and various phenomena have actually been characterized in these cuprates, strongly depending on the thermal history of the samples.
Imaging of Silicon (111) at 1.92Å Resolution using a 100keV STEM
Authors: Xu Peirong
Published: June 2020

Atomic structure imaging using bright field phase contrast at less than 2Å resolution has become routinely possible in medium and high voltage microscopes (>200 keV). Radiation damage at these elevated voltages can be serious and this limits the length of useful observation time. For example, the knock-on threshold energy for silicon is 120-190keV. Recently, a VG HB501A STEM equipped with a newly developed ultra-high resolution pole piece (Cs=0.7mm) has demonstrated the capability of achieving sub-2Å resolution in imaging the (111) silicon latticer using both bright field (BF) and annular dark field (ADF) modes at an operating voltage of l00keV (Fig.1).

A thin silicon specimen was prepared through successive steps of chemical etching, anodic etching and reactive ion etching. Large flat thin areas about 100Å thick were produced in the specimen. Since there is no tilting mechanism for the stage used with this ultra-high resolution pole piece, the specimen was not oriented exactly along the (111) zone axis as indicated by CBED but was less than 1-2° off.
Identification of {110} Inversion Boundaries in GaAs Layers Grown on Si by High Resolution Electron Microscopy
Authors: Mazur J.H.
Published: June 2020

Epitaxical growth of GaAs on (001)Si substrates can result in formation of inversion boundaries resulting from the presence of monatomic height (a/4[001]Si) steps on the Si substrate surface or nucleation of GaAs initiated with As or Ga in two areas in the same plane. The lack of TEM evidence for the presence of the inversion boundaries in the GaAs film which characterized earlier research in this area has been a source of speculation about the mechanism of inversion boundary elimination. Recently Liliental-Weber et al. have shown, both experimentally and by computer simulation, that the energetically most favorable (110) inversion boundaries could be imaged edge-on in an atomic resolution microscope for thicknesses in the narrow range of 21-26 nm. Earlier multislice calculations indicated no contrast changes across the boundary for imaging at 200 kV for samples thinner than 18 nm.

In the present work image simulations were performed for the (110) inversion boundary in GaAs. The aim was to interpret the high resolution image contrast observed in the GaAs thin film grown on Si on JEOL 200CX microscope operating at 200 kV. Other microscope parameters used for computation were: Cs=1.2 mm, DEL=8 nm (half width of a Gaussian spread of focus due to chromatic aberration), ALPHA=0.9 mrd (semi-angle of beam convergence), R=7 nm-1 (objective aperture radius). Simulation were performed for a wide range of thicknesses (up to 31 nm) and focus (-17 to -127 nm) and the results are shown on the simulated image map in Fig. 1. The simulated image map demonstrates that the contrast change ({111} fringe shift) indicating the (110) inversion boundary in the GaAs thin film imaged along <110> direction can be observed for specimens 11 nm thick for focus -127 nm, for 15 nm and above 23 nm thick specimens for a wide range of calculated focus values.
Slow-Scan CCD Camera for Transmission Electron Microscopy
Authors: Mooney P.E. , Fan G.Y. , Meyer C.E. , Truong K.V. , Bui D.B. , Krivanek O.L.
Published: June 2020

Transmission electron microscopes aretraditionally equipped with three imaging devices: 1) the main viewing screen, which shows a large portion of the specimen in real time, 2) the focussing screen, which is viewed through binoculars and shows a small area of the specimen at a high magnification also in real time, and 3) a film camera, which permits time-integrated images to be recorded with a large number of pixels and a good detective quantum efficiency (DQE). In many laboratories, TV cameras have replaced the real-time viewing devices 1 and 2. The slow-scan CCD technology now promises to replace the photographic film.

Slow-scan charge coupled device (CCD) sensors differ from the CCDs found in home video cameras in several aspects: their pixels are typically 10x larger in area, there is no frame-transfer buffer which would enable the CCD to function at TV rate, and the CCDs are optimized for operation at low temperature and slow readout speed. The increased size permits more electrons to be stored per pixel, which increases the dynamic range of the CCD. The elimination of the frame-transfer buffer allows the whole area of the CCD to be used for image detection. The low temperature and slow readout speed minimize the CCD dark current and readout noise.
Surface Magnetic Microstructural Analysis using Scanning Electron Microscopy with Polarization Analysis (SEMPA)
Authors: Scheinfein Michael R. , Unguris John , Pierce Daniel T. , Celotta Robert J.
Published: June 2020

High resolution imaging of magnetic microstructure has important ramifications for both fundamental studies of magnetism and the technology surrounding the magnetic recording industry. In SEMPA, a focused beam of electrons excites secondary electrons on a ferromagnet's surface. The secondaries leave the solid with an electron spin polarization which is characteristic of the net spin density in the ferromagnet. This is related directly to the sample magnetization. By scanning the beam and analyzing the secondary electron spin polarization at each point, a magnetization map of the ferromagnet's surface is generated.

As SEMPA is a surface sensitive, magnetic microstructural analysis technique, the environment local to the specimen must be ultra-high vacuum. A schematic of our SEMPA instrument is shown in figure 1. The probe forming electron optical column of a SEMPA system must produce small probes with high currents (> 1 nA) at long working distances ( > 10 mm). The SEMPA system may be equipped with a single, or multiple spin detectors as in figure 1. Two detectors are used for the acquisition of all three orthogonal components of the polarization vector signal. The inefficiency of all polarimeters makes SEMPA time consuming when compared to conventional SEM. The polarized secondary electrons must be extracted efficiently without introducing any deleterious effects into the focused incident electron beam. This imposes limits on incident beam energies and extraction voltages for the transport optics. Additionally, the transport optics must map the scanned spot of the secondary electrons produced under the incident rastered beam, to a (stationary) position on the spin detector such that undesirable instrumental asymmetries are not introduced.
Hepatitis A Virus Aggregation in Suspensions of Purified Virus
Authors: Humphrey Charles D. , Robertson Betty H. , Khanna B.
Published: June 2020

Virus capsid structure as determined by x-ray crystallography or by elec imaging of virus particles in thefrozen hydrated state has received con interest during the past decade. Specific functional proteins were localized recently on the Rotavirus capsid by using cryo-electron microscopy, indicating the potential for morphological studies that rel directly to capsid protein function.

Most cryo-electron microscopy studies have involved investigation of vir were 40 nm or greater in diameter. Smaller viruses may provide a greate practical difficulty in their preparation and imaging.

Highly purified virus for study by x-ray crystallographic studies or ele microscopic evaluation of frozen hydrated particles requires stringent c particle aggregation. Preparations for x-ray crystallography should agg an orderly manner to form arrays and ordered crystals of sufficient size Preparations for cryo-electron microscopy are more desirable when the pa numerous but not over-lapping (Fig. 1). We have experienced uncontrolla aggregation including considerable over-lapping of hepatitis A virus (HA particles when purified preparations were stored in phosphate or tris buffers (Fig. 2).
The Panoramic Rheed Patterns
Authors: Kim Yootaek , Hsu Tung
Published: June 2020

When applying the reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) methods[1] on the study of crystal surfaces it is necessary to index the RHEED spots and recognize the azimuth of the electron beam direction. This can be difficult because the RHEED pattern, unlike the transmission electron diffraction (TED) pattern, is distorted by the inner potential of the specimen and only one half of the pattern is shown. We found that it is useful, at the beginning of working on a certain surface of a certain crystal, to record a panoramic RHEED pattern by rotating the crystal through a large azimuth angle. This produces a map which is similar to the Kikuchi maps[2] used in transmission electron microscopy (TEM).

Two examples of these panoramic RHEED patterns, one from the Pt(111) [3] and the other from α-Al203 (0001) [4,5,6), are shown in Figs. 1 and 2.

The transmission Kikuchi maps are recorded using a specimen of suitable thickness such that the Kikuchi lines are strong and the diffraction spots are practically invisible. On the contrary, in making the panoramic RHEED patterns (or RHEED maps) we have no control over the thickness of the specimen. The electron beam enters and exits the same surface of the crystal; therefore, the relative intensities of the Bragg diffracted spots and the Kikuchi lines are not adjustable. The only adjustment lies in choosing the accelerating voltage and the incidence angle of the electrons such that the RHEED pattern has relatively low diffuse scattering.
The Characterization of the Low-Index α-Al203 Surfaces by REM
Authors: Kim Yootaek
Published: June 2020

Four low-index surfaces; (A-surface), (0001) (basal surface), (R-surface), and of the α-Al203 single crystals were investigated by reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) techniques[1] and the characteristics of these surfaces are reported. Specimens were prepared by polishing and annealing[2, 3], Orientation of each surface was confirmed with x-ray diffraction using a Laue camera. Microscopy observation was carried out on a JEOL JEM-200CX TEM operated at 100 KV.

To facilitate a fair comparison, the surface areas which were obviously affected by a macroscopic tilt, localized contamination, etc., were avoided. Only the flat, clean, and smooth areas were compared. The surface (Fig. 1. The scale in this figure also applies to all other figures.) shows large atomically flat areas divided by steps running in <000 1> and directions. The steps in this image are not of the same height. Some are one or two atoms high and others are much higher. Fig. 2 shows the
surface which is periodically facetted. One type of the facets is flat and atomically smooth while the other type is rough. The (0001) planes display curved and/or straight steps[4]. An example of curved step configuration is shown in Fig. 3. Most of the steps in this image have the same height. This step configuration is similar to the surface shown in Fig. 4. However, the contrast of the steps are very different; on the (0001) surfaces the steps are much darker and well-defined. A summary of these four surfaces is presented in the table below.
REM Observation of the Prismatic Faces of Sapphire
Authors: Ndubuisi G. C. , Liu J. , Cowley J. M.
Published: June 2020

The structures and properties of the prismatic faces and
of as-grown single-crystal sapphire are still not well understood. Known information have been limited to calculated surface energies and TEM characterization . The TEM characterization has been limited to identification of the orientation of the structures. For better understanding of the behavior of these surfaces, the use of the RHEED and REM techniques, which have proved their value for purely surface analysis, is necessary. In this paper we report the characterization of these surfaces by the RHEED and REM techniques.

The sapphire ribbons were purchased, as-grown, from Saphikon, Inc.. The method of preparation of the REM samples has been reported. The samples were oxygen-annealed for 3 6h at 1500°C. The experiments were performed in a Philips 400T TEM with a vacuum pressure of 10-6 Torr.

Fig. 1(a) is a REM image showing the structural features that characterize the
surface in the
beam direction. The surface can be seen to exhibit periodic bright and dark domains, with parallel small steps (S) in average direction oriented 7° from the
(after de-foreshortening). The appearence of two domains may be due to a difference in termination of the lattice at the surface. The THREED pattern (insert) shows the specular reflection used for imaging. Fig. 1(b) shows the structural features on the
surface in the
beam direction. Two domains (grey, G and white, W) can also be seen here, and may be attributed to the same effect. A well defined step can be seen at the boundary of the two domains. The faceted steps in the white domain can be seen to adopt average direction oriented 5° from the
. Strain field of dislocation (D) can be seen to run across the steps, and is displaced at the steps. The RHEED pattern (insert) shows the specular spot used for imaging. Fig. 2 shows the structural features on the
surface in the
beam direction, with the spot (insert) used for imaging. Emerging dislocation (D) can be seen terminating at kink of the large step.
Detection by Induction in the Environmental SEM
Authors: Danilatos Gerasimos D.
Published: June 2020

The advent of environmental SEM (ESEM) has revealed the true mechanism of detection, when the current mode is used. The ESEM allows the introduction of gas in the specimen chamber with a pressure at least sufficient to maintain specimens in their wet state. The gas is also used to suppress charge accumulation on insulating specimens and, furthermore, it can be used as a detection and amplification medium. The resolving power of the instrument is not impaired by the presence of gas, whereas new contrast mechanisms are now possible. The foundations of this technology have been outlined in an extended survey previously.

It has been shown that the products of interaction between various signals and gas can be used for imaging. Ionization, in particular, was first used for imaging by Danilatos. A comprehensive theoretical survey of the gaseous detector device can be found elsewhere. Here, the principle of pulse induction by moving charge carriers between electrodes is highlighted. Any charge moving between two electrodes induces a charge of opposite sign on each electrode with a concomitant current flow in the external circuit. The current flow stops when the charge carriers terminate their motion. Therefore, pulses are generated by each electron in the beam and in the signals emerging from the beam-specimen interaction. The sum of all pulses corresponding to a given pixel element results in the total signal pulse carrying information from the specimen. This way of looking at signal formation would be superfluous, if one could always arrive at the same result by simply counting the number of charge carriers that arrive at a particular electrode. However, the creation of ions in the gas of an ESEM and the possibility of imaging non-conducting surfaces has compelled us to resort to first principles in order to properly understand, explain and evaluate new phenomena. First, the ions are more than 1000 times slower than electrons, and they may limit the frequency response of the system; the simple counting of electrons that arrive at the anode, while the corresponding ions have not yet reached the cathode, provides an incorrect signal intensity. Second, microscopists would not use the “specimen absorbed current mode” with insulating specimens in vacuum SEM, whereas a new situation exists in ESEM.
HVEM Cryomicroscopy of Frozen Hydrated PTK1 Cells
Authors: O’Toole E.T. , Wray G.P. , Kremer J.R. , Mcintosh J.R.
Published: June 2020

Ultrarapid freezing and cryomicroscopy of frozen hydrated material makes it possible to visualize samples that have never been exposed to chemical fixatives, dehydration, or stains. In principle, freezing and cryoimaging methods avoid artifacts associated with chemical fixation and processing and allow one to visualize the specimen in a condition that is close to its native state. Here we describe a way to use a high voltage electron microscope (HVEM) for the cryoimaging of frozen hydrated PTK1 cells.

PTK1 cells were cultured on formvar-coated, carbon stabilized gold grids. After three days in culture, the grids were removed from the culture medium and blotted in a humidity chamber at 35° C. In some instances, the grids were rinsed briefly in 0.16 M ammonium acetate buffer (pH 7.2) prior to blotting. After blotting, the grids were transferred to a plunging apparatus and plunged into liquid ethane held directly above its freezing point. The plunging apparatus consists of a vertical slide rail that guides the fall of a mounted pair of forceps that clamp the specimen. The forceps are surrounded by a plexiglass humidity chamber mounted over a dewar of liquid nitrogen containing an ethane chamber. After freezing, the samples were transferred to liquid nitrogen and viewed in a JEOL JEM 1000 equipped with a top entry cold stage designed and built by Mr. George Wray (Univ. Colorado). The samples were routinely exposed to electron doses of 1 e/Å2/sec, and viewed at a temperature of −150° C. A GATAN video system was used to enhance contrast and to estimate the correct amount of underfocus needed to obtain phase contrast at various magnifications. Low dose micrographs were taken using two second exposures of Kodak 4463 film. The state of the solid water in the specimen was determined by diffraction using a 30/μm field limiting aperture and a camera length of 1 meter.
Observations of Frozen-Hydrated Microtubules
Authors: Chrétien D. , Job D. , Wade R.H.
Published: June 2020

Microtubules are filamentary structures found in the cytoplasm of eukaryotic cells, where, together with actin and intermediate filaments, they form the components of the cytoskeleton. They have many functions and show various levels of structural complexity as witnessed by the singlet, doublet and triplet structures involved in the architecture of centrioles, basal bodies, cilia and flagella. The accepted microtubule model consists of a 25 nm diameter hollow tube with a wall made up of 13 paraxial protofilaments (pf). Each pf is a string of aligned tubulin dimers. Some results have suggested that the pfs follow a superhelix. To understand how microtubules function in the cell an accurate model of the surface lattice is one of the requirements. For example the 9x2 architecture of the axoneme will depend on the organisation of its component microtubules. We should also note that microtubules with different numbers of pfs have been observed in thin sections of cellular and of in-vitro material. An outstanding question is how does the surface lattice adjust to these different pf numbers?

We have been using cryo-electron microscopy of frozen-hydrated samples to study in-vitro assembled microtubules. The experimental conditions are described in detail in this reference. The results obtained in conjunction with thin sections of similar specimens and with axoneme outer doublet fragments have already allowed us to characterise the image contrast of 13, 14 and 15 pf microtubules on the basis of the measured image widths, of the the image contrast symmetry and of the amplitude and phase behaviour along the equator in the computed Fourier transforms. The contrast variations along individual microtubule images can be interpreted in terms of the geometry of the microtubule surface lattice. We can extend these results and make some reasonable predictions about the probable surface lattices in the case of other pf numbers, see Table 1. Figure 1 shows observed images with which these predictions can be compared.
Possibilities of the Bend-Contour Method in the Analysis of the Lattice Disorientations in Crystals on Thin-Film Transformations
Authors: Yu. Kolosov V.
Published: June 2020

The paper summarized some of the authors data on the transmission electron microscope (TEM) investigations using bend-contours(BC)the transformations of crystal lattice orientations on crystallization of amorphous films and recrystallization. Most investigations were made in situ in JEOL and TESLA microscopes under the influence of the electron beam, Fig.3-5, 8,9. In some cases the video record was produced, some clippings supposed to be demonstrated.

1. The possibilities of BC method were outlined earlier (e.g.1). In particular they are similar to Kikuchi lines method and sometimes are more powerful. However these and some other options are rarely used in practice though BC patterns often present on the TEM images and carry the unique diffraction information written in the image plane. The merits of BC method in the evaluation of the lattice orientation, if compared with traditional selected area diffraction(SAD)-high locality, the possibilities of simultaneous analysis of large areas(fields of orientations) and visual ability, the demerits - fitness only to crystals with large orientation gradients(more than 10−2rad/μm).
Writing the Precarious Self inFalling Man
Authors: Ventéjoux Aliette
Published: June 2020

The terrorist attacks on American soil of 11 September 2001 have reminded people how easily they can be submitted to the will of the other. This article will analyse how literature, and more particularly post-9/11 literature, deals with a new world order where the self seems to have become subjected to terrorism, being today its potential victim rather than a subject. More precisely, how have American novelists dealt with the demise of the sovereign self after the attacks of 11 September 2001 and what is the role played by memory? Focusing onFalling Man(2007) by Don DeLillo, this article will demonstrate the importance of art and literature to fight against the demise of the sovereign self.
Die Welt der andern entdecken
Authors: Bachmann Monika
Published: June 2020

Zusammenfassung. Der Trend hält an: Im Gesundheitswesen werden immer mehr Leistungen in vor- und nachgelagerte ambulante Bereiche verschoben. Es entsteht eine „Interprofessionelle Versorgungskette“. In einem neuen Modul lernen Studierende die Kompetenzen anderer Berufsgruppen kennen und versetzen sich in die Rolle einer Patientin.
The Regional Earth System Model RegCM‐ES: Evaluation of the Mediterranean Climate and Marine Biogeochemistry
Authors: Reale Marco , Giorgi Filippo , Solidoro Cosimo , Di Biagio Valeria , Di Sante Fabio , Mariotti Laura , Farneti Riccardo , Sannino Gianmaria
Published: June 2020

We introduce a new version of the Earth System Regional Climate model RegCM‐ES and evaluate its performances for the first time over the Mediterranean region. The novel aspect of this coupled system is the possibility to simulate the dynamics of the marine ecosystem through a biogeochemical model, BFM (Biogeochemical Flux Model), coupled online with the ocean circulation model MITgcm (MIT general circulation model). The validation of atmosphere and ocean components has shown that the model is able to capture interannual and intermonthly variabilities of the atmospheric heat fluxes and spatial patterns of land surface temperature, precipitation, evaporation, and sea surface temperature with a general improvement compared to previous versions. At the same time, we diagnosed some prominent deficiencies as a warm and dry bias associated in summer with the resolution of the atmospheric module and the tuning of the boundary layer and convective precipitation scheme. On the biogeochemical side, RegCM‐ES shows good skills in reproducing mean values and spatial patterns of net primary production, phosphate, and horizontal/vertical patterns of chlorophyll‐a. Limitations in this case include deficiencies mainly in the simulation of mean values of nitrate and dissolved oxygen in the basin which have been associated with too large vertical mixing throughout the water column, deficiencies in the boundary conditions, and solubility computations. Overall, RegCM‐ES has the potential to become a suitable tool for the analysis of the impacts of climate change on the ocean and marine biogeochemistry in the Mediterranean region and many other domains.
Evaluating Precipitation Features and Rainfall Characteristics in a Multi‐Scale Modeling Framework
Authors: Chern Jiun‐Dar , Tao Wei‐Kuo , Lang Stephen E. , Li Xiaowen , Matsui Toshihisa
Published: June 2020

Cloud and precipitation systems are simulated with a multi‐scale modeling framework (MMF) and compared over the Tropics and Subtropics against the Tropical Rainfall Measuring Mission (TRMM) Radar‐defined Precipitation Features (RPFs) product. A methodology, in close analogy to the TRMM RPFs, is developed to produce simulated precipitation features (PFs) from the output of the embedded two‐dimensional (2D) cloud‐resolving models (CRMs) within an MMF. Despite the limitations of 2D CRMs, the simulated population distribution, horizontal and vertical structure of PFs, and the geographical location and local rainfall contribution of mesoscale convective systems (MCSs) are in good agreement with the TRMM observations. However, some model discrepancies are found and can be identified and quantified within the PF distributions. Using model biases in relative population and rainfall contributions, PFs can be characterized into four size categories: small, medium to large, very large, and extremely large. Four different major mechanisms might account for the model biases in each different category: (1) the two‐dimensionality of the CRMs, (2) a positive convection‐wind‐evaporation feedback loop, (3) an artificial dynamic constraint in a bounded CRM domain with cyclic boundaries, and (4) the limited CRM domain size. The second and fourth mechanisms tend to contribute to the excessive tropical precipitation biases commonly found in most MMFs, whereas the other mechanisms reduce rainfall contributions from small and very large PFs. MMF sensitivity experiments with various CRM domain sizes and grid spacings showed that larger domains (higher resolutions) tend to shift PF populations toward larger (smaller) sizes.
Strong Intensification of Hourly Rainfall Extremes by Urbanization
Authors: Li Yafei , Fowler Hayley J. , Argüeso Daniel , Blenkinsop Stephen , Evans Jason P. , Lenderink Geert , Yan Xiaodong , Guerreiro Selma B. , Lewis Elizabeth , Li Xiao‐Feng
Published: June 2020

Although observations and modeling studies show that heavy rainfall is increasing in many regions, how changes will manifest themselves on sub‐daily timescales remains highly uncertain. Here, for the first time, we combine observational analysis and high‐resolution modeling results to examine changes to extreme rainfall intensities in urbanized Kuala Lumpur, Malaysia. We find that hourly intensities of extreme rainfall have increased by ~35% over the last three decades, nearly 3 times more than in surrounding rural areas, with daily intensities showing much weaker increases. Our modeling results confirm that the urban heat island effect creates a more unstable atmosphere, increased vertical uplift and moisture convergence. This, combined with weak surface winds in the Tropics, causes intensification of rainfall extremes over the city, with reduced rainfall in the surrounding region.
Wind Wave Effects on Remote Sensing of Sea Surface Currents From SAR
Authors: Li Shuiqing , Liu Baochang , Shen Hui , Hou Yijun , Perrie Will
Published: June 2020

Wind waves contribute a significant component to the sea surface currents detected by synthetic aperture radar (SAR) systems via the orbital velocity; this component is typically referred to as the wind wave‐induced artifact surface velocity (WASV). Accordingly, it is essential to precisely describe the WASV effect, so that the real sea surface currents can be obtained from SAR measurements. In order to enhance our understanding about WASV, we carried out a numerical analysis of the sea state dependence of WASV under various radar configurations. The simulated WASV compares reasonably well with observations reported in the literature. It is found that WASV not only depends on the wind speed but also increases considerably with the development of the wind waves, as characterized by wave age. WASV may increase by two to three times, in fully developed wind wave conditions, as compared to young waves. The wave age dependence appears to largely account for the observed uncertainty in WASV at a given wind speed; moreover, swell is also found to significantly influence WASV through hydrodynamic modulation of wind wave properties. These effects are stronger at higher wind speeds and vary significantly with the different radar configurations that are possible, in terms of polarizations and incidence angles. The variations in WASV using different shortwave spectral functions and angular spreading functions are examined in this manuscript.
Antarctic Circumpolar Current Transport Through Drake Passage: What Can We Learn From Comparing High‐Resolution Model Results to Observations?
Authors: Xu Xiaobiao , Chassignet Eric P. , Firing Yvonne L. , Donohue Kathleen
Published: June 2020

Uncertainty exists in the time‐mean total transport of the Antarctic Circumpolar Current (ACC), the world's strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12° global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1,000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, that is, approximately the average of the cDrake and DRAKE estimates, is actually representative of the time‐mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near‐surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated; thus, monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.
Berberine mediates root remodeling in an immature tooth with apical periodontitis by regulating stem cells from apical papilla differentiation
Authors: Cui Yujia , Xie Jing , Fu Yujie , Li Chuwen , Zheng Liwei , Huang Dingming , Zhou Changchun , Sun Jianxun , Zhou Xuedong
Published: June 2020

Once pulp necrosis or apical periodontitis occurs on immature teeth, the weak root and open root apex are challenging to clinicians. Berberine (BBR) is a potential medicine for bone disorders, therefore, we proposed to apply BBR in root canals to enhance root repair in immature teeth. An in vivo model of immature teeth with apical periodontitis was established in rats, and root canals were filled with BBR, calcium hydroxide or sterilized saline for 3 weeks. The shape of the roots was analyzed by micro-computed tomography and histological staining. In vitro, BBR was introduced into stem cells from apical papilla (SCAPs). Osteogenic differentiation of stem cells from apical papilla was investigated by alkaline phosphatase activity, mineralization ability, and gene expression of osteogenic makers. The signaling pathway, which regulated the osteogenesis of SCAPs was evaluated by quantitative real time PCR, Western blot analysis, and immunofluorescence. In rats treated with BBR, more tissue was formed, with longer roots, thicker root walls, and smaller apex diameters. In addition, we found that BBR promoted SCAPs osteogenesis in a time-dependent and concentration-dependent manner. BBR induced the expression of β-catenin and enhanced β-catenin entering into the nucleus, to up-regulate more runt-related nuclear factor 2 downstream. BBR enhanced root repair in immature teeth with apical periodontitis by activating the canonical Wnt/β-catenin pathway in SCAPs.