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The immune system maintains appropriate cell numbers through regulation of cell proliferation and death. Normal tissue distribution of lymphocytes is maintained through expression of specific adhesion molecules and chemokine receptors such as L-selectin and CCR7, respectively. Lymphocyte insufficiency or lymphopenia induces homeostatic proliferation of existing lymphocytes to increase cell numbers. Interestingly, homeostatic proliferation of T lymphocytes induces a phenotypic change from naïve- to memory-type cell. Naïve T cells recirculate between blood and lymphoid tissues whereas memory T cells migrate to nonlymphoid sites such as skin and gut. To assess effects of homeostatic proliferation on migratory ability of T cells, a murine model of lymphopenia-induced homeostatic proliferation was used. Carboxyfluorescein diacetate, succinimidyl ester-labeled wild-type splenocytes were adoptively transferred into recombination activation gene-1-deficient mice and analyzed by flow cytometry, in vitro chemotactic and in vivo migration assays, and immunofluorescence microscopy. Homeostatically proliferated T cells acquired a mixed memory-type CD44high L-selectinhigh CCR7low phenotype. Consistent with this, chemotaxis to secondary lymphoid tissue chemokine in vitro was reduced by 22%–34%. By contrast, no differences were found for migration or entry into lymph nodes during in vivo migration assays. Therefore, T lymphocytes that have undergone homeostatic proliferation recirculate using mechanisms similar to naïve T cells.
This paper focus on the analysis of the interfaces of nanocomposite TiAlN/Mo multilayers by high-resolution transmission electron microscopy (HRTEM). These thin films were deposited by reactive magnetron sputtering, with modulation periods below 7 nm. The structural disorder at the interfaces was probed by the analysis of the X-ray diffraction data, and afterwards correlated with the TEM observations on the cross-sections of the TiAlN/Mo multilayers. For specific deposition conditions, these structures can be prepared with relatively planar interfaces, revealing layer-by-layer growth. For modulation periods below 3 nm the intermixing acts a major role in the degradation of the multilayer chemical modulation.
The use of an alkane mixture that remains liquid at 77 K to freeze specimens has advantages over the use of a pure alkane that is solid at 77 K. It was found that a mixture of methane and ethane did not give a cooling rate adequate to produce vitreous ice, but a mixture of propane and ethane did result in vitreous ice. Furthermore, the latter mixture produced less damage to specimens mounted on a very thin, fragile holey carbon substrate.
Patterning of cells is critical to the formation and function of the normal organ, and it appears to be dependent upon internal and external signals. Additionally, the formation of most tissues requires the interaction of several cell types. Indeed, both extracellular matrix (ECM) components and cellular components are necessary for three-dimensional (3-D) tissue formation in vitro. Using 3-D cultures we demonstrate that ECM arranged in an aligned fashion is necessary for the rod-shaped phenotype of the myocyte, and once this pattern is established, the myocytes were responsible for the alignment of any subsequent cell layers. This is analogous to the in vivo pattern that is observed, where there appears to be minimal ECM signaling, rather formation of multicellular patterns is dependent upon cell–cell interactions. Our 3-D culture of myocytes and fibroblasts is significant in that it models in vivo organization of cardiac tissue and can be used to investigate interactions between fibroblasts and myocytes. Furthermore, we used rotational cultures to examine cellular interactions. Using these systems, we demonstrate that specific connexins and cadherins are critical for cell–cell interactions. The data presented here document the feasibility of using these systems to investigate cellular interactions during normal growth and injury.
Two-photon excitation microscopy (also referred to as multiphoton laser scanning microscopy) has gained increasing popularity during the past few years because of the distinct advantages over single-photon microscopy, which includes increased penetration depth and low out-of-focus photobleaching and photodamage. It allows superior imaging of thick specimen compared to single-photon microscopy, and it excels at imaging live cells either single or within intact tissue. This highly valuable tool has been used with great success to gain important new insights into brain tissue, embryos, whole organs, entire animals, and it has been most useful in numerous other applications.
A method for phase analysis, similar to the Rietveld method in X-ray diffraction, was not developed for electron diffraction (ED) in the transmission electron microscope (TEM), mainly due to the dynamic nature of ED. Nowadays, TEM laboratories encounter many thin samples with grain size in the 1–30 nm range, not too far from the kinematic ED conditions. This article describes a method that performs (semi)quantitative phase analysis for nanocrystalline samples from selected area electron diffraction (SAED) patterns. Fractions of the different nanocrystalline components are determined from rotationally symmetric ring patters. Both randomly oriented nanopowders and textured nanopowders, observed from the direction of the texture axis produce such SAED patterns. The textured fraction is determined as a separate component by fitting the spectral components, calculated for the previously identified phases with a priori known structures, to the measured distribution. The Blackman correction is applied to the set of kinematic diffraction lines to take into account dynamic effects for medium grain size. Parameters of the peak shapes and the other experimental parameters are refined by exploring the parameter space with the help of the Downhill-SIMPLEX. Part I presents the principles, while future publication of Parts II and III will elaborate on current implementation and will demonstrate its usage by examples, respectively.
The last decade has witnessed a revolution in electron microscopy as online correction of spherical aberration has become a reality in both fixed-beam and scanning instruments. The combination of improved resolution and higher beam currents coupled with the prospect of simpler image interpretation has stimulated great interest and excitement across the entire field of microscopy. The Microscopy Society of America has an active Focused Interest Group on the topic of “Materials Research in an Aberration-Free Environment,” and its goal is to provide a forum for discussion and dissemination of the latest advances in instrumentation and novel applications of aberration-corrected electron microscopy. This special issue of Microscopy and Microanalysis contains contributions from the Pre-Meeting Congress on this topic held in Chicago, Illinois, in late July 2006, immediately preceding Microscopy & Microanalysis 2006.
The successful correction of spherical aberration is an exciting and revolutionary development for the whole field of electron microscopy. Image interpretability can be extended out to sub-Ångstrom levels, thereby creating many novel opportunities for materials characterization. Correction of lens aberrations involves either direct (online) hardware attachments in fixed-beam or scanning TEM or indirect (off-line) software processing using either off-axis electron holography or focal-series reconstruction. This review traces some of the important steps along the path to realizing aberration correction, including early attempts with hardware correctors, the development of online microscope control, and methods for accurate measurement of aberrations. Recent developments and some initial applications of aberration-corrected electron microscopy using these different approaches are surveyed. Finally, future prospects and problems are briefly discussed.
Strontium titanate (SrTiO3, ST) has a perovskite type structure that is cubic at room temperature, but transforms into a tetragonal one at 105K. At very low temperatures, ST exhibits an extremely large dielectric permittivity and piezoelectric and superconducting characteristics. ST finds applications in tunable microwave devices, due to a dependence of its dielectric response on the electric field and low microwave losses. ST electrical properties are strongly dependent on grain boundaries features and directly influenced by grain size distribution. It was found in our previous studies that a small variation in the stoichiometry of ST has a significant effect on the grain size of the sintered ceramic and related electrical properties: increased grain size and dielectric permittivity values have been reported for Ti excess compositions whereas Sr excess caused a decrease of grain size and of the dielectric permittivity. The tailoring of the dielectric properties by small non-stoichiometric variations in ST needs, however, a full understanding of its effects on the microstructure, phases structure and on the structure / composition of the grain boundaries.
Understanding the Synthesis and Properties of Nanostructures and Nanomaterials
Gaining insight into how the nervous system functions is a challenge for scientists, particularly because the static morphology of the brain and the cells within tell little about how they actually work. Fixed specimens can provide critical structural information, but the jump to functional neurobiology in living cells is obviated with these preparations. In order to grasp the complexity of neuronal activity, it is necessary to observe the brain in action, from the level of subcellular signaling to the whole organism. Recent advances in nonlinear microscopy have given rise to a new era for biological research. In particular, the introduction of multiphoton excitation has drastically improved the depth and speed to which we can probe brain function. In order to better appreciate recent contributions of multiphoton microscopy to our current and future understanding of biological systems, an historical awareness of past microscopy applications is useful.
All common negative stains are salts of heavy metals. To remedy several technical defects inherent in the use of heavy metal compounds, this study investigates whether salts of the light metals sodium, magnesium, and aluminum can function as negative stains. Screening criteria require aqueous solubility at pH 7.0, formation of a smooth amorphous layer upon drying, and transmission electron microscope imaging of the 87-Å (8.7-nm) lattice periodicity in thin catalase crystals. Six of 23 salts evaluated pass all three screens; detection of the protein shell in ferritin macromolecules indicates that light metal salts also provide negative staining of single particle specimens. Appositional contrast is less than that given by heavy metal negative stains; image density can be raised by increasing electron phase contrast and by selecting salts with phosphate or sulfate anions, thereby adding strong scattering from P or S atoms. Low-dose electron diffraction of catalase crystals negatively stained with 200 mM magnesium sulfate shows Bragg spots extending out to 4.4 Å. Future experimental use of sodium phosphate buffer and magnesium sulfate for negative staining is anticipated, particularly in designing new cocktail (multicomponent) negative stains able to support and protect protein structure to higher resolution levels than are currently achieved.
The application of wide field-of-view detection systems to atom probe experiments emphasizes the importance of careful parameter selection in the tomographic reconstruction of the analyzed volume, as the sensitivity to errors rises steeply with increases in analysis dimensions. In this article, a self-consistent method is presented for the systematic determination of the main reconstruction parameters. In the proposed approach, the compression factor and the field factor are determined using geometrical projections from the desorption images. A three-dimensional Fourier transform is then applied to a series of reconstructions, and after comparing to the known material crystallography, the efficiency of the detector is estimated. The final results demonstrate a significant improvement in the accuracy of the reconstructed volumes.
Sertoli cells are very important to spermatogenesis homeostasis because they control germ cell proliferation, differentiation, and death. Damages to Sertoli cells cause germ cell death and affect fertility. Etoposide is a potent chemotherapeutic drug largely used against a variety of cancers. However, this drug also kills normal cells, especially those undergoing rapid proliferation. In the testis, etoposide acts predominantly on intermediate and type B spermatogonia. Etoposide was shown to permanently alter Sertoli cell function when administered to prepubertal rats. Based on this, we decided to investigate whether etoposide can affect Sertoli cell morphology. For this, 25-day-old rats were treated with etoposide during 8 consecutive days and killed at 32, 45, 64, 127, and 180 days old. Testes were fixed in Bouin's liquid or in a mixture of 2.5% glutaraldehyde and 2% formaldehyde for analysis under light and electron microscopes, respectively. Sertoli cells showed morphological alterations such as the presence of chromatin clumps close to the nuclear membrane, nucleus displacement, and cytoplasmic vacuolization. Some Sertoli cells also showed nuclear and cytoplasmic degenerative characteristics, suggesting that etoposide causes severe damages to Sertoli cell.
Roughness increases significantly after finishing procedures. The aim of this study was to assess by the atomic force microscope (AFM) the effect of finishing instruments on the surface roughness of composite resins. A nanofiller composite resin (Filtek Supreme, 3M–F) and a microhybrid composite resin (Point 4, Kerr–P) were selected. The finishing procedures were done with a 30-blade carbide bur (C) and a 30-μm finishing diamond bur (D). Standardized specimens were produced and divided into six experimental groups (n = 4) according to (1) composite resin, (2) absence of finishing (Mylar matrix–M), and (3) finishing instrument (FM, PM, FC, FD, PC, PD). The mean surface roughness was evaluated by AFM in the contact mode. FM and PM groups were assessed statistically by the Student's T test, and FC, FD, PC, PD groups were submitted to variance analysis (ANOVA), both at 5% significance. The mean surface roughness values, in nanometers, were FM, 23.63 (b); FC, 283.88 (c); FD, 510.55 (d); PM, 12.52 (a); PC, 343.98 (c); PD, 531.64 (d). Microhybrid composite displayed less roughness than nanofiller composite in the absence of finishing procedures. The 30-blade carbide bur produced less roughness compared to the extra fine diamond bur.
Intervessel pits play a key role in trees' water transport, lying at the base of drought-induced embolism, and in the regulation of hydraulic conductivity via hydrogels bordering pit canals. Recently, their microstructure has been the focus of numerous studies, but the considerable variation, even within species and the histochemistry of pit membranes, remains largely unexplained. In the present study, intervessel pits of the outermost wood were examined for Avicennia marina, of dry and rainy season wood separately for Rhizophora mucronata. The thickness of the pit membranes was measured on transmission electron micrographs while their topochemical nature was also analyzed via cellular UV microspectrophotometry. Pit membranes of R. mucronata were slightly thicker in dry season wood than in rainy season wood, but their spectra showed for both seasons a lignin and a yet unidentified higher wavelength absorbing component. It was suggested to be a derivative of the deposits, regularly filling pit canals. The vestures of A. marina chemically resembled pit membranes rather than cell walls.
Transition metal dichalcogenides (TMD) are widely used as self-lubricating material either as oil additive or directly as thin films. Magnetron sputtering is a deposition method allowing depositing such films with high density and adhesion. However, their spread use in practical applications is still hindered since their excellent sliding properties are deteriorated in the presence of humidity and under high contact pressures. MoSe2, one of the members of TMD family recently studied, has been co-sputtered with carbon in order to improve the mechanical and tribological properties when compared to pure MoSe2 films.