bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐performance X‐ray detection in a new analytical electron microscope
Authors: LYMAN C. E. , GOLDSTEIN J. I. , WILLIAMS D. B. , ACKLAND D. W. , VON HARRACH S. , NICHOLLS A. W. , STATHAM P. J. 
Published: August 2011

SummaryX‐ray detection by energy‐dispersive spectrometry in the analytical electron microscope (AEM) is often limited by low collected X‐ray intensity (P), modest peak‐to‐background (P/B) ratios, and limitations on total counting time (τ) due to specimen drift and contamination. A new AEM has been designed with maximization of P, P/B, and τ as the primary considerations. Maximization of P has been accomplished by employing a field‐emission electron gun, X‐ray detectors with high collection angles, high‐speed beam blanking to allow only one photon into the detector at a time, and simultaneous collection from two detectors. P/B has been maximized by reducing extraneous background signals generated at the specimen holder, the polepieces and the detector collimator. The maximum practical τ has been increased by reducing specimen contamination and employing electronic drift correction. Performance improvements have been measured using the NIST standard Cr thin film. The 0·3 steradian solid angle of X‐ray collection is the highest value available. The beam blanking scheme for X‐ray detection provides 3–4 times greater throughput of X‐rays at high count rates into a recorded spectrum than normal systems employing pulsepileup rejection circuits. Simultaneous X‐ray collection from two detectors allows the highest X‐ray intensity yet recorded to be collected from the NIST Cr thin film. The measured P/B of 6300 is the highest level recorded for an AEM. In addition to collected X‐ray intensity (cps/nA) and P/B measured on the standard Cr film, the product of these can be used as a figure‐of‐merit to evaluate instruments. Estimated minimum mass fraction (MMF) for Cr measured on the standard NIST Cr thin film is also proposed as a figure‐of‐merit for comparing X‐ray detection in AEMs. Determinations here of the MMF of Cr detectable show at least a threefold improvement over previous instruments.
The preparation of cryosections from plant tissue: An alternative method appropriate for secondary ion mass spectrometry studies of nutrient tracers and trace metals
Authors: LAZOF D. B. , GOLDSMITH J. K. G. , RUFTY T. W. , SUGGS C. , LINTON R. W. 
Published: August 2011

SummaryA method involving cryostat sectioning (10 μm thickness) and freeze‐drying is presented for the preparation of plant tissue for microanalytical studies. The method is well suited for semi‐quantitative imaging by secondary ion mass spectrometry (SIMS) and offers significant advantages over bulk freeze‐dried or freeze‐substitution preparations. Segments of corn or soybean root (5 mm) are quench‐frozen, embedded externally, sectioned in a cryostat (10 μm), pressed onto ultrapure Si and slowly freeze‐dried. Images of these sections with secondary electron microscopy and SIMS indicated good morphological preservation. It was possible to section tissues of a wide developmental range, as well as roots varying sixfold in diameter. SIMS images are presented which demonstrate the ability to detect and localize nutrient tracers, such as Rb+, following brief exposures (10 min) to the intact plant. Likewise, a toxic metal (Al) was localized in root tissue after brief exposure (<1 day) of the intact plant root to micromolar external concentrations. Elemental redistribution during processing was minimal, as demonstrated most explicitly by the lack of movement of loosely bound Ca from the outer cell walls into the adjacent embedding material. Preservation of compositional differences between cellular content and cell wall was supported by a semi‐quantitative treatment of SIMS images.
A versatile 2π‐tilting device for fluorescence microscopes
Authors: BRADL J. , HAUSMANN M. , SCHNEIDER B. , RINKE B. , CREMER C. 
Published: August 2011

A tilting device for biological specimens (rotation angle up to 2π), especially fluorescence‐labelled cell nuclei, was developed. It consists of a quartz glass capillary and a mounting adapter for the microscope stage. The applicability of the device was tested for several epifluorescence and confocal scanning laser fluorescence microscopes. The axis of rotation is perpendicular to the optical axis of the microscope. The capillary can be tilted around its axis at any desired angle or in equiangular steps. This can be done manually or by remote control using a stepping motor.The three‐dimensional (3‐D) image‐forming properties of the capillary system were experimentally examined using an inverse confocal scanning laser microscope. The results were compared with measurements obtained from the same microscope with the standard stage for plane slides with cover glasses. The measured point spread function suggested that in spite of aberration effects, the optical arrangement used allows a gain in the 3‐D resolution by tilting the object.A low‐cost, fully automated 3‐D imaging system was built on the basis of a conventional epifluorescence microscope with a cooled black‐and‐white CCD camera. The system was operated by a personal computer. The online visualization (‘movie’) of rotating objects indicates the feasibility of the system.
Studies of porphyrin‐containing specimens using an optical spectrometer connected to a confocal scanning laser microscope
Authors: TREPTE O. , ROKAHR I. , ANDERSSON‐ENGELS S. , CARLSSON K. 
Published: August 2011

A spectrometer has been developed for use with a confocal scanning laser microscope. With this unit, spectral information from a single point or a user‐defined region within the microscope specimen can be recorded. A glass prism is used to disperse the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit keeps the detector at 277 K, thereby allowing integration times of up to 60 s. The spectral resolving power, λ/Δλ, ranges from 350 at λ = 400 nm to 100 at λ = 700 nm. Since the entrance aperture of the spectrometer has the same size as the detector pinhole used during normal confocal scanning, the three‐dimensional spatial resolution is equivalent to that of normal confocal scanning. Light from the specimen is deflected to the spectrometer by a solenoid controlled mirror, allowing fast and easy switching between normal confocal scanning and spectrometer readings.With this equipment, studies of rodent liver specimens containing porphyrins have been made. The subcellular localization is of interest for the mechanisms of photo‐dynamic therapy (PDT) of malignant tumours. Spectroscopic detection is necessary to distinguish the porphyrin signal from other fluorescent components in the specimen. Two different substances were administered to the tissue, Photofrin, a haematoporphyrin derivative (HPD) and δ‐amino levulinic acid (ALA), a precursor to protoporphyrin IX and haem in the haem cycle. Both are substances under clinical trials for PDT of malignant tumours. Following administration of these compounds to the tissue, the potent photosensitizer and fluorescent compound Photofrin, or protoporphyrin IX, respectively, is accumulated. For our study Wistar/Furth rats were injected either with Photofrin or with ALA 3–5 h before they were killed. The organs were removed directly after, and snap‐frozen in carbon dioxide ice with isopentane. No further staining or fixation procedures were adopted.
Modelling of inclined and curved surfaces in the reflection scanning acoustic microscope
Authors: WEISE W. , ZININ P. , BOSECK S. 
Published: August 2011

SummaryAn expression is derived for the output signal when an inclined plane surface is imaged by the reflection scanning acoustic microscope, which is modelled as a spherical transducer. This expression is applied to model non‐planar surfaces. The accuracy of this approach is tested for perfectly reflecting spherical surfaces. The influence of inclination on V(z) curves is considered when Rayleigh waves occur.
Atomic force microscopy in the photochemistry of chalcones
Authors: KAUPP G. 
Published: August 2011

SummaryThe application of atomic force microscopy (AFM) to photodimerization of crystalline chalcones provides new insights into the detailed mechanisms of solid‐state reactions on the molecular level. Well‐directed long‐range transport phenomena are found which reach far beyond the crystal lattice distances. Reactions occur in the surface region where the light is absorbed. Characteristic features are built up that depend on crystal structure and crystal face. This could not be foreseen by previous theories based solely on a topochemical postulate/principle. There is now a much more intimate correlation of crystal structure with solid‐state reactivity and this is directly studied and proven experimentally by AFM. Even solid‐state reactions which are in opposition to topochemistry can be studied and understood on a molecular basis. The three‐dimensional resolution of undisturbed insulating surfaces which is obtained by AFM is not available by any other technique.
In vivo determination of fibril orientation in plant cell walls with polarization CSLM
Authors: VERBELEN J.‐P. , STICKENS D. 
Published: August 2011

SummaryCongo Red fluorescence is used to detect cellulose in the wall of plant cells. The orientation of the cellulose fibrils is determined by using polarized light for excitation. The absorption characteristics of Congo Red make this approach a method of choice for applications with any standard confocal scanning laser microscope (CSLM). The semiquantitative character of CSLM observations combined with the non‐toxicity of the stain allow a very fast and reliable assessment of cellulose orientation in the wall of living plant cells.
Confocal microscopy in the analysis of the etched nuclear particle tracks in polymers
Authors: JAKES J. , GAIS P. , SCHRAUBE H. 
Published: August 2011

SummaryThe possibility of the morphometric analysis of etched tracks, induced by protons and alpha particles in the organic polymer allyl diglycol carbonate (CR‐39), using the confocal scanning laser microscope (CSLM), was studied. The detectors were investigated in two groups of irradiation experiments, namely: (a) irradiated with mono‐energetic neutrons of energy 1–2 MeV, (b) exposed to the alpha radiation from 222Rn and its progeny. Both groups were irradiated at normal incidence. Radiation‐induced latent tracks were electrochemically etched, and their morphometric parameters were investigated in the reflection mode by using the 488‐nm spectral line of an argon ion laser. A constant number of up to 200 optical sections in Z‐scan mode was taken through each selected etched track at vertical spacings of 0·642 μm. Successive reconstructions of Z‐sections were used to determine the following parameters: the mean radius of the opening channel, the maximum diameter and the length of the track, and the angle of the track wall to the surface of the sample. The results show that tracks produced by alpha particles differ from those induced by protons. The radius of the opening channel of alpha‐particle‐induced tracks ranges from 7·9 to 11 μm, whereas for protons the same parameter ranges between 2·0 and 3·8 μm for a specific electrochemical etch procedure.
A method to compensate for light attenuation with depth in three‐dimensional DNA image cytometry using a confocal scanning laser microscope
Authors: LILJEBORG A. , CZADER M. , PORWIT A. 
Published: August 2011

SUMMARYA method to compensate for attenuation of detected light with increased depth of the collected optical section, and its application in three‐dimensional (3‐D) DNA image cytometry is described. The method is based on studying the stack of 2‐D histograms that can be formed from each consecutive pair of sections in a stack of optical serial sections. An attenuation factor is calculated interactively and a new compensated section series is computed. Formalin‐fixed paraffin‐embedded rat tissue was stained with propidium iodide. Each cell nucleus is extracted by thresholding and its total intensity is calculated. The coefficient of variation (CV) of the total intensity of all cells in each stack is computed. For comparison the CV of the same cells is computed in the uncompensated stacks. This study shows a significantly lower CV for the compensated data, thus contributing to the accuracy of DNA quantification in 3‐D DNA image cytometry.
Comparison of three‐dimensional imaging properties between two‐photon and single‐photon fluorescence microscopy
Authors: GU MIN , SHEPPARD C. J. R. 
Published: August 2011

SUMMARYThe imaging performance in single‐photon (1‐p) and two‐photon (2‐p) fluorescence microscopy is described. Both confocal and conventional systems are compared in terms of the three‐dimensional (3‐D) point spread function and the 3‐D optical transfer function. Images of fluorescent sharp edges and layers are modelled, giving resolution in transverse and axial directions. A comparison of the imaging properties is also given for a 4Pi confocal system. Confocal 2‐p 4Pi fluorescence microscopy gives the best axial resolution in the sense that its 3‐D optical transfer function has the strongest response along the axial direction.
Double‐pulse fluorescence lifetime imaging in confocal microscopy
Authors: MÜLLER M. , GHAUHARALI R. , VISSCHER K. , BRAKENHOFF G. 
Published: August 2011

SUMMARYA theoretical analysis of a new technique for fluorescence lifetime measurement, relying on (near steady state) excitation with short optical pulses, is presented. Application of the technique to confocal microscopy enables local determination of the fluorescence lifetime, which is a parameter sensitive to the local environment of fluorescent probe molecules in biological samples. The novel technique provides high time resolution, since it relies on the laser pulse duration, rather than on electronic gating techniques, and permits, in combination with bilateral confocal microscopy and the use of a (cooled) CCD, sensitive signal detection over a large dynamic range. The principle of the technique is discussed within a theoretical framework. The sensitivity of the technique is analysed, taking into account: photodegradation, the effect of the laser repetition rate and the effect of non‐steady‐state excitation. The features of the technique are compared to more conventional methods for fluorescence lifetime determination.
Influence of matrix precursors on the microstructure and mechanical properties of C/C composites
Authors: FIGUEIRAS A. , FERNÁNDEZ J. J. , GRANDA M. , BERMEJO J. , CASAL E. , MENÉNDEZ R. 
Published: August 2011

SummaryThe microstructure and properties of uni‐directional pitch‐based carbon‐carbon composites are explained in terms of the chemical composition of pitch precursors. Pitches are characterized by standard procedures (elemental analysis, softening point and solubility tests), extrography which is a simple and rapid silica gel adsorption chromatographic technique, Fourier transform infra‐red and gas chromatography of the toluene‐soluble fraction. Pitch pyrolysis behaviour is monitored by hot‐stage microscopy. The main microstructural features of uni‐directional composites from pitches and commercial PAN‐based carbon fibres are determined by light microscopy and scanning electron microscopy.
Processing and properties of Al2O3/SiC nanocomposites
Authors: BORSA C. E. , JIAO S. , TODD R. I. , BROOK R. J. 
Published: August 2011

SummaryAlumina/SiC nanocomposites were produced by mechanical mixture of commercial powders. The preparation steps involved the vigorous mixing of the powders and drying under conditions where the homogeneous mixture was kept stable. Pressureless sintering of die‐pressed powders achieved reasonable densities (∼97% theoretical density) for 2·5wt% of SiC on sintering at 2073 K. Higher SiC contents strongly reduced the sintered density. The use of a more reactive alumina (finer matrix powder) gave similar results. Hot pressing at 1973 K/1 h/25 MPa produced high‐density materials for SiC contents as high as 20 wt%. Transmission and scanning electron microscopy analysis showed that the SiC particles were well distributed and were situated both inside the grains and on the grain boundaries of the alumina matrix. The SiC strongly inhibited grain growth in the matrix in keeping with the Zener model. The bend strength increased as the SiC content increased, a result partly explained by the grain size refinement. The strength improvement of 20% over monolithic was explained in terms of the change to an intergranular fracture mode.
Spatially resolved electron energy‐loss studies of metal–ceramic interfaces in transition metal/alumina cermets
Authors: BRYDSON R. , MÜLLEJANS H. , BRULEY J. , TRUSTY P. A. , SUN X. , YEOMANS J. A. , RÜHLE M. 
Published: August 2011

SummaryComposites consisting of an alumina matrix and 20 vol.% transition metal (Ni or Fe) particles, prepared by hot pressing powder blends, have been studied using spatially resolved transmission electron energy‐loss spectroscopy (EELS), and, to a lesser extent, by high‐resolution electron microscopy (HREM). Particular attention was paid to the elucidation of the chemical bonding mechanisms at the metal‐ceramic interface; EELS spectra from interfacial regions being obtained via a spatial difference technique. From both qualitative and quantitative interpretation of EELS near‐edge structures, as well as observed HREM images, the data appear to be consistent with the presence of an Al‐terminated alumina at the interface and the formation of direct transition metal – aluminium bonds in Al(O3M) (M = Ni or Fe) tetrahedral units, possibly as a result of the dissolution and interfacial reprecipitation of Al during processing. These results correlate well with similar model studies on diffusion‐bonded Nb/Al2O3 interfaces and may, in the light of recent theoretical electronic structure calculations, have implications for the resultant interfacial bond strength in such materials.
Identification and surface structure of crystalline cellulose studied by atomic force microscopy
Authors: KUUTTI L. , PELTONEN J. , PERE J. , TELEMAN O. 
Published: August 2011

SummaryA combination of molecular modelling and atomic force microscopy (AFM) techniques was used to study the surface structure of crystalline cellulose. Two‐dimensional Fourier analysis of the AFM raw data gave crystal parameters as well as a highly filtered inverse‐transformed image. Molecular modelling was used to generate Connolly surfaces based on electron diffraction data for crystalline cellulose. The modelled surfaces were used to interpret the experimental AFM images. Monoclinic () crystal faces were identified. The method used enables the structural analysis of cellulose surfaces at the molecular level, where all biological processes involving cellulose take place.
A scanning near‐field optical microscope having scanning electron tunnelling microscope capability using a single metallic probe tip
Authors: INOUYE Y. , KAWATA S. 
Published: August 2011

SummaryA new microscope system that has the combined capabilities of a scanning near‐field optical microscope (SNOM) and a scanning tunnelling microscope (STM) is described. This is achieved with the use of a single metallic probe tip. The distance between the probe tip and the sample surface is regulated by keeping the tunnelling current constant. In this mode of operation, information about the optical properties of the sample, such as its refractive index distribution and absorption characteristics, can be disassociated from the information describing its surface structure. Details of the surface structure can be studied at resolutions smaller than the illumination wavelength. The performance of the microscope is evaluated by analysing a grating sample that was made by coating a glass substrate with gold. The results are then compared with the corresponding SNOM and STM images of the grating.
Three‐dimensionally resolved NAD(P)H cellular metabolic redox imaging of the in situ cornea with two‐photon excitation laser scanning microscopy
Authors: PISTON D. W. , MASTERS B. R. , WEBB W. W. 
Published: August 2011

SummaryThree‐dimensional maps of cellular metabolic oxidation/reduction states of rabbit cornea in situ were obtained by imaging the fluorescence of the naturally occurring reduced pyridine nucleotides (both reduced nicotinamide‐adenine dinucleotide, NADH, and reduced nicotinamide‐adenine dinucleotide phosphate, NADPH, denoted here as NAD(P)H). Autofluorescence images with submicrometre lateral resolution were obtained throughout the entire 400 μm thickness of the cornea. Two‐photon excitation scanning laser microscopy with near‐infrared excitation provided high fluorescence collection efficiency, reduced photodamage, and eliminated ultraviolet chromatic aberration, all of which have previously degraded the visualization of pyridine nucleotide fluorescence. Sharp autofluorescence images of the basal epithelium (40 μm within the cornea) show substantial subcellular detail, providing the ability to monitor autofluorescence intensity changes over time, which reflect changes in oxidative metabolism and cellular dynamics necessary for maintenance of the ocular surface. The autofluorescence was confirmed to be mostly of NAD(P)H origin by cyanide exposure, which increased the fluorescence from all cell types in the cornea by about a factor of two. Autofluorescence images of individual keratocytes in the stroma were observed only after cyanide treatment, while in the predominant extracellular collagen (> 90% of the stromal volume), fluorescence was not distinguished from the background. Observation of keratocyte metabolism demonstrates the sensitivity made available by two‐photon microscopy for future redox fluorescence imaging of cellular metabolic states.
A hybrid scanning force and light microscope for surface imaging and three‐dimensional optical sectioning in differential interference contrast
Authors: STEMMER A. 
Published: August 2011

SummaryThe design of a scanned‐cantilever‐type force microscope is presented which is fully integrated into an inverted high‐resolution video‐enhanced light microscope. This set‐up allows us to acquire thin optical sections in differential interference contrast (DIC) or polarization while the force microscope is in place. Such a hybrid microscope provides a unique platform to study how cell surface properties determine, or are affected by, the three‐dimensional dynamic organization inside the living cell.The hybrid microscope presented in this paper has proven reliable and versatile for biological applications. It is the only instrument that can image a specimen by force microscopy and high‐power DIC without having either to translate the specimen or to remove the force microscope. Adaptation of the design features could greatly enhance the suitability of other force microscopes for biological work.
Maximum entropy reconstruction of compositional depth profiles from electron probe microanalysis data
Authors: SMITH G. C. , PARK D. , COCHONNEAU O. 
Published: August 2011

SummaryElectron probe microanalysis (EPMA) is a powerful method for the quantitative determination of the elemental composition of micro‐regions of a sample surface. Here, we report on the development of a method of reconstructing compositional depth profiles in thin films from EPMA data measured over a range of electron beam energies, using maximum entropy data processing. The method gives quantitative information on film compositions up to approximately 1 μm in depth, with a lateral spatial resolution of approximately 1 μm. The method is tested using both simulated data and measured experimental data from well‐characterized model sample structures.