Visualising impregnated chitosan in Pinus radiata early wood cells using light and scanning electron microscopy

Chitosan, a deacetylated product of an abundant naturally occurring biopolymer chitin, has been used in a range of applications, particularly in food and health areas, as an antimicrobial agent. In the work reported here Pinus radiata wood was impregnated with chitosan as an environmentally compatible organic biocide (Eikenes et al., 2005a, Eikenes et al., 2005b) to protect wood against wood deteriorating microorganisms and to thus prolong the service life of wooden products. We developed sample preparation techniques targeted to visualise impregnated chitosan within wood tissues using light microscope and field-emission scanning electron microscope (FE-SEM). Sections were viewed with the light microscope without staining with a dye as well as after staining with the dye toluidine blue. Light microscopy was also undertaken on sections that had been stained with 1% aqueous osmium tetroxide (OsO₄). For SEM observations, the sections were treated with OsO₄ and then examined with the FE-SEM, first in the secondary electron imaging mode (SEI) and then in the backscattered electron imaging (BEI) mode, imaging the same areas of a section in both SEI and BEI modes. The preparation techniques employed and the combined use of light and scanning electron microscopy provided valuable complementary information, revealing that chitosan had penetrated into the cavities (cell lumens, intercellular spaces) of all sizes present within wood tissues and had also impregnated early wood cell walls. The information obtained is discussed in relation to its importance in further development of chitosan formulations and refinement of impregnation technologies to optimise chitosan impregnation into and distribution within wood tissues as well as in assessing chitosan efficacy.     

The formation of zona radiata in Pseudosciaena crocea revealed by light and transmission electron microscopy

The egg envelope is an essential structure occurring during oogenesis. It plays an important role during the process of fertilization in the large yellow croaker Pseudosciaena crocea. Elucidation of egg envelope formation helps us to understand fertilization mechanisms in teleosts. In the present work, we studied the formation of egg envelope in P. crocea by light microscopy, as well as by transmission and scanning electron microscopy. Four layers exist outside the oocyte plasmalemma, i.e., theca cell layer, basal membrane, granulosa cell layer and zona radiata. According to our observation, zona radiata is a multilaminar structure just like the same structure reported in teleosts, but the origin of this structure is a little different. Before it is formed, a peripheral space filled with different density of vesicles is the place where zona radiata is formed. Zona radiata (Z1) is secreted only by oocyte itself, it belongs to the primary envelope; zona radiata 2 (Z2) and zona radiata 3 (Z3) belong to the secondary envelope, because the two layers are formed after granulosa cells appear, and microvilli participate this process. It is very interesting that Z2 and Z3 are situated between Z1 and the granulosa cell first, but they translocate to the other side of Z1. This microanatomy difference may due to the participation of microvilli. The new finding about egg envelope formation in P. crocea will help us to do further investigation on fertilization mechanisms and will make artificial breeding possible which may contribute to the resource recovery of this species.     

Annealing effects on the microstructure of sputtered gold layers on oxidized silicon investigated by scanning electron microscopy and scanning probe microscopy

The structure of Au layers deposited by sputtering on oxidized p-type Si(100) substrates is investigated by a combination of scanning electron microscopy and scanning probe microscopy. The effect of the temperature on the grain structure of the layers has been determined, revealing that an annealing temperature of 300° C results in a larger grain size and smoother surfaces but generates some cracks in the film surface. At an annealing temperature of 500° C, further grain growth is observed, but a high density of cracks and voids also results while there is little enhancement regarding the smoothness of the grain surfaces.     

Correlated light and electron microscopy observations of the uterine epithelial cell actin cytoskeleton using fluorescently labeled resin-embedded sections

In order to perform correlative light and electron microscopy (CLEM) more precisely, we have modified existing specimen preparation protocols allowing fluorescence retention within embedded and sectioned tissue, facilitating direct observation across length scales. We detail a protocol which provides a precise correlation accuracy using accessible techniques in biological specimen preparation. By combining a pre-embedding uranyl acetate staining step with the progressive lowering of temperature (PLT) technique, a methacrylate embedded tissue specimen is ultrathin sectioned and mounted onto a TEM finder grid for immediate viewing in the confocal and electron microscope. In this study, the protocol is applied to rat uterine epithelial cells in vivo during early pregnancy. Correlative overlay data was used to track changes in filamentous actin that occurs in these cells from fertilization (Day 1) to implantation on Day 6 as part of the plasma membrane transformation, a process essential in the development of uterine receptivity in the rat. CLEM confirmed that the actin cytoskeleton is disrupted as apical microvilli are progressively lost toward implantation, and revealed the thick and continuous terminal web is replaced by a thinner and irregular actin band, with individually distinguishable filaments connecting actin meshworks which correspond with remaining plasma membrane protrusions.     

Mathematical and physical considerations on the spatial resolution in scanning Auger electron microscopy

A simple mathematical model is used to evaluate the spatial resolution in scanning Auger microscopy (SAM). This model includes for the first time all the possible causes of Auger electron production and broadening (impact parameter effect, backscattering effect, X-ray induced Auger electron production). The conclusions depend greatly upon the criteria of resolution used (Δ(50) or δ(10–90)). Physical limitations due to the impact parameter and influence of X-ray-induced electron production are established. This model is in good agreement with the experimental data. Applications to scanning electron microscopy and other microanalysis techniques are also suggested.     

Crystalline effects on Auger emission; The influence of the electron channeling of the probe in scanning Auger microscopy

The modification of the Auger emission by the electron channelling of the probe is studied in silicon. An important effect is measured on the amplitude of the KLL Auger peak; the height of this peak is modified by a factor close to 2 when the channelling of the probe is changed using the rocking beam method. Due to the experimental conditions chosen, it is possible to interpret the results using the dynamical theory with two wave approximation.     

Use of light and scanning electron microscopy to examine colonisation of barley rhizosphere by the nematophagous fungus Verticillium chlamydosporium

Barley roots were readily colonised by the nematophagous fungus Verticillium chlamydosporium. Light microscopy (LM) but also low temperature scanning electron microscopy (LTSEM) revealed details of the colonisation process. Hyphae were found on the rhizoplane often with dictyochlamydospores. Hyphae of V. chlamydosporium penetrated epidermal cells, often by means of appressoria. A hyphal network was formed in epidermal and cortical cells. Likewise, hyphal coils were found within root cells next to transverse cell walls. Cortical cells were the limits of fungal colonisation, since no hyphae were seen in the vascular cylinder. Modifications of root cell contents (phenolic droplets and callose appositions) were common three weeks after inoculation with V. chlamydosporium. These features may indicate induction of plant defence reactions in late stages of root colonisation by the fungus. Both LTSEM and LM have proved extremely useful to describe root colonisation by the fungus. The results found may have implications in the mode action of nematophagous fungi against plant parasitic nematodes.     

New possibilities and some artifacts of the cathodoluminescent mode in scanning electron microscopy

Lightning inside the chamber of a scanning electron microscope (SEM), caused by electrons being scattering from a sample (and parts of the chamber), is observed and analyzed. These electrons generate the luminescence in a Thornly–Everhart collector. This parasitic effect (artifact) must be considered and eliminated in all experiments with the cathodoluminescent (CL) mode of SEM. A new technique for measuring surface potential on dielectric samples is proposed. It is based on variations in the CL signal during electron irradiation of a sample in SEM.     

Strategies and results of field emission scanning electron microscopy (FE-SEM) in the study of parasitic protozoa

Field emission scanning electron microscopy (FE-SEM) provides a range of strategies for investigating the structural organization of biological systems, varying from isolated macromolecules to tissue organization and whole organisms. This review covers some of the results so far obtained using FE-SEM observation and various protocols of sample fixation to analyze the structural organization of parasitic protozoa and their interaction with host cells. The employment of FE-SEM can be broadened through the use of gold-labeled molecules or tracers, gradual extraction by detergents, and cleavage techniques. These analyses provide significant contributions to the characterization of these organisms concerning ultrastructure, cytoskeleton, motility and intracellular behavior.     

Analysis of the spatial orientation distribution of building blocks in polycrystals as determined using transmission electron microscopy and a backscattered electron beam in a scanning electron microscope

The advantages and disadvantages of the method of automatic analysis of electron backscattering diffraction (EBSD) patterns for studying spatial orientation distributions are considered as compared to transmission electron microscopy (TEM). A misorientation spectrum in a test alloy (Kh20N80 alloy) having a high content of annealing twins is experimentally studied using both TEM and EBSD, and the results obtained are compared.     

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应用电子和多光子集团非弹性碰撞模型和冷等离子体模型，研究了飞秒强激光与线性等离子体发生多光子非线性Compton散射时，散射激光与入射激光形成的飞秒耦合激光场对线性等离子体层中光场和电子密度分布的影响。研究发现，在耦合激光的有质动力作用下，电子密度分布和离子密度分布比Compton散射前的偏离更加严重，电子密度的变化比离子密度的变化更快，产生的静电场更强。即使耦合激光场非常弱，电子的运动仍表现出相对论效应，仍有静电场存在。     

Experimental study of the voids in the electroless copper deposits and the direct measurement of the void fraction based on the scanning electron microscopy images

Electroless copper deposits were plated on epoxy substrates in various plating solutions at either a high operating temperature (60 °C) or a low one (45 °C). Cross section samples were made using epoxy resin cured in room temperature, and then ground, polished and over-etched. The scanning electron microscopy (SEM) images of the over-etched cross section samples show voids in low temperature deposits and solid structure in high temperature ones. The surface morphology images also indicated such structures in low temperature samples. The SEM image of the cross section of a stand-alone deposit prepared on stainless steel substrate shows similar voids observed on etched cross section samples on epoxy board substrates. An image processing program was written using MATLAB to identify the voids in the over-etched cross sections of the deposits from low temperature solutions and thus the void fraction can be directly measured and compared with the previously published simulation results.     

Studies of electron irradiation and annealing effects on TiO2 surfaces in ultrahigh vacuum using high-resolution electron microscopy

Electron-beam-induced surface damage and subsequent annealing processes in rutile crystals have been investigated with a 300 keV high-resolution electron microscope which has been modified for ultrahigh vacuum and equipped with a specimen heating holder. Room temperature irradiation produced a reduction sequence identical to that observed previously in conventional microscope vacuum, except for some evidence of enhanced sputtering. Irradiation at higher temperatures (200–400°C) increased the damage rate resulting in approximately the same amount of the surface TiO phase but producing larger areas of the intermediate TiO₂-II phase. Sputter pits in both rutile and TiO₂-II phases became markedly more facetted as the temperature was increased. Irradiation at temperatures greater than 500°C resulted in the formation of well-facetted holes in the rutile, but no accumulation of crystalline reduced phases was observed. Annealing of the damaged areas in the absence of the electron beam, as shown by the reformation of crystalline rutile, revealed a temperature dependence for the restoration of the stoichiometry of the reduced areas, while complete removal of the sometimes extensive sputter pits was observed at temperatures in excess of 200 ° C.     

Use of light, scanning electron microscopy and bioassays to evaluate parasitism by entomopathogenic fungi of the red scale insect of palms (Phoenicococcus marlatti Ckll., 1899)

We have evaluated the parasitism of the red scale insect of the date palm (Phoenicococcus marlatti) by entomopathogenic fungi, using light microscopy (LM), scanning electron microscopy (SEM) and low temperature scanning electron microscopy (LTSEM). Beauveria bassiana, Lecanicillium dimorphum and Lecanicillium cf. psalliotae, were inoculated directly on the scale insects or on insect infested plant material. We found that L. dimorphum and L. cf. psalliotae developed on plant material and on scale insects, making infection structures. B. bassiana was a bad colonizer of date palm leaves (Phoenix dactylifera L.) and did not parasite the scale insects.     

Updating of the toroidal electron spectrometer intended for a scanning electron microscope and its new applications in diagnostics of micro- and nanoelectronic structures

A new version of the toroidal electron spectrometer installed in a scanning electron microscope is described. The new instrument has made it possible to carry out fundamental and applied research in the field of local nondestructive inspection of micro- and nanoelectronic materials and devices. The topology control of 3D microstructures by backscattered electron tomography is exemplified. A high efficiency of secondary electron energy filtering in monitoring of semiconductor regions locally doped by p- and n-type impurities is demonstrated. A physical substantiation for the high contrast of the doped regions is given. The feasibility of taking electron spectra using a scanning electron microscope in a wide range from slow secondary electrons to elastically scattered ones is proved.     

Theoretical insights into the effects of the diameter and helicity on the adsorption of formic acid on silicon carbide nanotube

The anchoring of small organic molecules onto the semiconductor surface has a great application for developing various molecular devices, such as novel solar cells, fuel cells, hybrid systems, sensors, and so on. In the present work, by carrying out detailed density-functional theory calculations, we have investigated the adsorption of the formic acid (HCOOH) molecule on planar and various curved silicon carbide (SiC) nanotubes. By considering both the molecular and dissociative adsorptions of HCOOH on these SiC nanomaterials, we found that the HCOOH molecule prefers to dissociate into HCOO and H group. Interestingly, different adsorption modes were found for HCOOH on SiC nanotubes, i.e. dissociative monodentate or bidentate adsorption, which depends on the tube diameter and helicity. For (n, 0) SiC nanotube, the monodentate adsorption mode is energetically favorable when n is less than 10. However, HCOOH prefers to be adsorbed on other (n, 0) SiC nanotubes in a bridged bidentate mode, which is similar to those of on (n, n) SiC nanotubes or planar SiC sheet. Moreover, upon HCOOH adsorption, these SiC nanomaterials remain to be of the semiconducting nature and their band gaps are decreased to different degrees. In addition, we also explored the effects of HCOOH coverage on its adsorption on SiC nanotube.     

Pulvinus functional traits in relation to leaf movements: a light and transmission electron microscopy study of the vascular system

Previous studies on legume pulvini suggest that the vascular system plays an important role in the redistribution of ions and transmission of stimuli during leaf's movements. However, the number of anatomical and ultrastructural studies is limited to few species. The aim of this paper is to investigate the structure and cellular features of the pulvinus vascular system of nine legume species from Brazilian cerrado, looking for structural traits pointing to its participation in the leaf's movements. Samples were excised from the medial region of opened pulvinus of Bauhinia rufa, Copaifera langsdorffii, Senna rugosa (Caesalpinioideae), Andira humilis, Dalbergia miscolobium, Zornia diphylla (Faboideae), Mimosa rixosa, Mimosa flexuosa and Stryphnodendron polyphyllum (Mimosoideae), and were prepared following light microscopy, transmission electron microscopy and histochemical standard techniques. The vascular system occupies a central position, comprises phloem and xylem and is delimited by a living sheath of septate fibers in all the species studied. This living cells sheath connects the cortex to the vascular tissues via numerous plasmodesmata. The absence of fibers and sclereids, the presence of phenolic idioblasts and the abundance and diversity of protein inclusions in the sieve tube members are remarkable features of the phloem. Pitted vessel elements, parenchyma cells with abundant cytoplasm and living fibriform elements characterize the xylem. The lack of lignified tissues and extensive symplastic continuity by plasmodesmata are remarkable features of the vascular system of pulvini of the all studied species.     

The effects of ultrasound on chromium gels in light of their catalytic activity and electron paramagnetic resonance

Investigations into the influence of ultrasound on the catalytical properties of chromium gels are presented. The changes of the EPR spectra and surface concentration of Cr on the sixth oxidation degree of certain preparations are described. These changes are then related to the increase in the velocity in the test reaction of H₂O₂ decomposition and the increased yield of cyclohexane dehydrogenation when the insonated preparations are used as catalysts.