Microprobe Imaging Research Articles

Extreme nickel hyperaccumulation in the vascular tracts of the tree Phyllanthus balgooyi from Borneo.

Phyllanthus balgooyi (Phyllanthaceae), one of >20 nickel (Ni) hyperaccumulator plant species known in Sabah (Malaysia) on the island of Borneo, is remarkable because it contains >16wt% Ni in its phloem sap, the second highest concentration of Ni in any living material in the world (after Pycnandra acuminata (Sapotaceae) from New Caledonia with 25wt% Ni in latex). This study focused on the tissue-level distribution of Ni and other elements in the leaves, petioles and stem of P.balgooyi using nuclear microprobe imaging (micro-PIXE). The results show that in the stems and petioles of P.balgooyi Ni concentrations were very high in the phloem, while in the leaves there was significant enrichment of this element in the major vascular bundles. In the leaves, cobalt (Co) was codistributed with Ni, while the distribution of manganese (Mn) was different. The highest enrichment of calcium (Ca) in the stems was in the periderm, the epidermis and subepidermis of the petiole, and in the palisade mesophyll of the leaf. Preferential accumulation of Ni in the vascular tracts suggests that Ni is present in a metabolically active form. The elemental distribution of P.balgooyi differs from those of many other Ni hyperaccumulator plant species from around the world where Ni is preferentially accumulated in leaf epidermal cells.

Imaging liver and brain glycogen metabolism at the nanometer scale

In mammals, glycogen synthesis and degradation are dynamic processes regulating blood and cerebral glucose-levels within a well-defined physiological range. Despite the essential role of glycogen in hepatic and cerebral metabolism, its spatiotemporal distribution at the molecular and cellular level is unclear. By correlating electron microscopy and ultra-high resolution ion microprobe (NanoSIMS) imaging of tissue from fasted mice injected with 13C-labeled glucose, we demonstrate that liver glycogenesis initiates in the hepatocyte perinuclear region before spreading toward the cell membrane. In the mouse brain, we observe that 13C is inhomogeneously incorporated into astrocytic glycogen at a rate ~25 times slower than in the liver, in agreement with prior bulk studies. This experiment, using temporally resolved, nanometer-scale imaging of glycogen synthesis and degradation, provides greater insight into glucose metabolism in mammalian organs and shows how this technique can be used to explore biochemical pathways in healthy and diseased states. From the Clinical EditorBy correlating electron microscopy and ultra-high resolution ion microprobe imaging of tissue from fasting mice injected with 13C-labeled glucose, the authors demonstrate a method to image glycogen metabolism at the nanometer scale.

Zircon crystal morphology and internal structures as a tool for constraining magma sources: Examples from northern Portugal Variscan biotite-rich granite plutons

In northern Portugal, large volumes of granitoids were emplaced during the last stage (D3) of the Variscan orogeny and display a wide range of petrological signatures. We studied the morphologies and internal structures of zircons from syn-, late- and post-D3 granitoids. The sin-D3 granitoids include the Ucanha–Vilar, Lamego, Felgueiras, Sameiro, and Refoios do Lima plutons, the late- and post-D3 granitoids are represented by the Vieira do Minho and the Vila Pouca de Aguiar plutons, respectively. Typological investigations after Pupin (1980) along with scanning electron microprobe imaging reveal that the external morphology of zircon changes consistently with a decrease in the crystallization temperature. Zircon populations from the Refoios do Lima and the Vieira do Minho granites show gradual changes in the internal morphologies and their typologic evolution trends are consistent with their mainly crustal origin. The Sameiro, Felgueiras, Lamego and Ucanha-Vilar granites have more complex internal and external morphology and typological evolution trends that cross the domain of the calc-alkaline to the aluminous granites compatible with a mixing process. Finally, the morphological types of the Vila Pouca de Aguiar granites are found both in calc-alkaline and sub-alkaline granites and their typological evolutionary trends follow the calc-alkaline/sub-alkaline trend, suggesting crustal sources with some mantle contribution.

Exploring the dissolution effect on the intrashell Mg/Ca variability of the planktic foraminifer Globigerinoides ruber

AbstractThe Mg/Ca ratio of the planktic foraminifer Globigerinoides ruber is widely used for reconstructing past sea surface temperatures. The shell Mg/Ca ratio is also lowered by dissolution, which results in lower sea surface temperature estimates in partially dissolved shells. Here we use an electron microprobe image mapping technique to map the intrashell variability of the Mg/Ca ratio in G. ruber (white) sensu stricto shells to explore changes in the intrashell Mg/Ca ratio associated with dissolution. We examine shells from shallow and deep cores (Ceara Rise, western tropical Atlantic) from the Holocene and Last Glacial Maximum that represent a preservational gradient. Image map results show that the Mg/Ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval. Our results show that intrashell Mg/Ca variability is retained in samples that have undergone dissolution. Quantitative analysis of the data from Mg/Ca mapping suggests that preferential loss of high‐Mg/Ca calcite alone cannot account for the difference in intrashell Mg/Ca variability of shells from shallow and deep cores in both time periods. Rather, the data imply that, in G. ruber analyzed in this study, there is a loss of high Mg/Ca ratios accompanied by a more uniform lowering of Mg/Ca over the range of intershell Mg/Ca variability of shells subjected to dissolution at the 1 µm resolution of the microprobe analysis in this study.

Quantifying crystallization and devitrification of rhyolites by means of X-ray diffraction and electron microprobe analysis

Devitrification of silicic volcanic rocks is a relatively common process, resulting in the production of microcrystalline silica and feldspar components. Here we investigate how the products of pervasive devitrification may be characterized using the combined techniques of X-ray powder diffraction, electron microprobe analysis, and X-ray fluorescence analysis to provide a new calibrated approach to calculating the crystallinity and mineral modes in both glassy vitrophyre and devitrified volcanics. Using the integrated areas of the X-ray diffraction peaks associated with both the crystalline and amorphous components, the relative proportions of groundmass crystallites and amorphous material from both glassy and devitrified material can be calculated. A detailed calibration indicates a linear relationship among the ratio of the integrated counts and bulk crystallinity. Mineral proportions are also calculated from X-ray fluorescence measurements of whole-rock and groundmass separates and are well correlated to crystallinities calculated from both X-ray diffraction and electron microprobe image analysis for vitrophyre samples. Devitrification products in a pervasively devitrified sample are tridymite, quartz, sanidine, and a Ca-rich aluminosilicate component. Mineral analysis and X-ray mapping by electron microprobe analysis indicates that the Ca-rich aluminosilicate component appears to be the dominant metastable or amorphous phase in the devitrified sample with proportions calculated from X-ray mapping (~32%) in reasonable agreement with the calculated proportion of amorphous material determined by means of X-ray diffraction (~38%). These results demonstrate the robustness of this combined X-ray diffraction and electron microprobe imagery technique for quantifying and characterizing crystallization in complex samples.

Phosphorus Retention in a 20‐Year‐Old Septic System Filter Bed

Septic systems in lakeshore environments often occur where thin soils overlie bedrock and, consequently, filter beds may be constructed of imported filter sand. The objective of this study was to assess the mobility of wastewater phosphorus (P) in such a potentially vulnerable setting by examining a 20-yr-old domestic septic system located near Parry Sound, ON, Canada, where the filter bed is constructed of imported noncalcareous sand. The groundwater plume is acidic (pH 6.0) and has a zone of elevated PO-P (up to 3.1 ± 1.7 mg L) below the tile lines but no elevated PO-P is present beyond 5 m from the tile lines. Elevated concentrations of desorbable P (up to 137 mg kg) and acid-extractable P (up to 3210 mg kg) occur in the filter sand within 1 m below four of seven tile lines present and the total mass of excess acid-extractable P (39 kg) is similar to the estimated total lifetime P loading to the system (33 kg). Microprobe images reveal abundant Fe and Al-rich authigenic mineral coatings on the sand grains that are increasingly P rich (up to 10% w/w P) near the tile lines. Additionally, 6 yr of monitoring data show that groundwater PO concentrations are not increasing. This indicates that mineral precipitation, not adsorption, dominates P immobilization at this site. This example of robust long-term P retention opens up the possibility of improving P removal in on-site treatment systems by prescribing specific sand types for filter bed construction.

Scanning electron microscopic imaging and nano-secondary ion microprobe analyses of bacteria-like nanoball structures in oncoids from the Ediacaran Boonall Dolomite of Kimberley, northwestern Australia: testing their biogenicity

Nanoball structures have been frequently detected in modern and ancient sedimentary rocks worldwide. They are widely believed to be biological in origin due to their similar morphology to modern bacteria. Abundant, well-preserved nanoball structures from the oncoids of the Boonall Dolomite of Ediacaran age in the Kimberley region, northwestern Australia are being described. Scanning electron microscopic imaging indicates that these minute objects are identical with nanobacteria previously documented elsewhere. However, nano-secondary ion microprobe (NanoSIMS) imaging analysis could not reveal the presence of organic elements such as C, N and S in the nanoball-like structures. Therefore, a biological origin for the Ediacaran nanoball structures seems unlikely. NanoSIMS imaging analysis may well be needed for other occurrences of nanoball structures in order to determine if all of these similar objects are really of biological origin.

A single-cell view of ammonium assimilation in coral–dinoflagellate symbiosis

Assimilation of inorganic nitrogen from nutrient-poor tropical seas is an essential challenge for the endosymbiosis between reef-building corals and dinoflagellates. Despite the clear evidence that reef-building corals can use ammonium as inorganic nitrogen source, the dynamics and precise roles of host and symbionts in this fundamental process remain unclear. Here, we combine high spatial resolution ion microprobe imaging (NanoSIMS) and pulse-chase isotopic labeling in order to track the dynamics of ammonium incorporation within the intact symbiosis between the reef-building coral Acropora aspera and its dinoflagellate symbionts. We demonstrate that both dinoflagellate and animal cells have the capacity to rapidly fix nitrogen from seawater enriched in ammonium (in less than one hour). Further, by establishing the relative strengths of the capability to assimilate nitrogen for each cell compartment, we infer that dinoflagellate symbionts can fix 14 to 23 times more nitrogen than their coral host cells in response to a sudden pulse of ammonium-enriched seawater. Given the importance of nitrogen in cell maintenance, growth and functioning, the capability to fix ammonium from seawater into the symbiotic system may be a key component of coral nutrition. Interestingly, this metabolic response appears to be triggered rapidly by episodic nitrogen availability. The methods and results presented in this study open up for the exploration of dynamics and spatial patterns associated with metabolic activities and nutritional interactions in a multitude of organisms that live in symbiotic relationships.

Trace metal concentrations in the tropical sponge Spheciospongia vagabunda at a sewage outfall: synchrotron X-ray imaging reveals the micron-scale distribution of accumulated metals

Major and trace elements were measured in sponges, seawater and sediment in Darwin Harbour (Australia) to test the hypothesis that metals are elevated in sponges closer to a sewage outfall compared with unimpacted sites. Seawater and sediment at the sewage discharge site contained high, but localised, concentrations of phosphorus (P), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) compared with background sites. Metal concentrations in the sponge Spheciospongia vagabunda were highly elevated compared with other sponges and, although site specific, high metal concentrations were unrelated to the presence of sewage effluent. X-ray fluorescence microprobe imaging was used to investigate the metal distribution pattern in S. vagabunda. High Fe, Ni and Zn concentrations were either localised in circular patches (100–200 μm size) near water canals or in the pinacoderm, or scattered in spots (approximately 10 μm) throughout the tissue. This supports a microflora-mediated metal bioaccumulation hypothesis. In contrast, Co and Mn were highly dispersed and probably associated with aluminium- and iron-oxide rich sediment inclusions. Although the lack of association between sewage effluent and metal accumulation precludes the use of S. vagabunda as a biomonitor, the apparent differential mechanisms of metal accumulation warrants further investigation.

Far-IR/THz spectral characterization of the coherent synchrotron radiation emission at diamond IR beamline B22

Diamond is the new UK 3rd generation light source that opened to users since 2007 and now allocates more than 22 operational beamlines. Beamline B22 is dedicated to Infrared microspectroscopy and started operations in December 2009. By exploiting the Diamond SR source brightness it is optimized for mid-IR (2–25 μm wavelength) absorption spectroscopy, for fingerprint microprobe analysis and imaging mostly in Life Sciences but also Materials Sciences and Cultural Heritage. Vibrational spectroscopy analysis on condensed matter and material sciences can be performed at B22 by means of Fourier transform IR interferometry in a broader range from the visible up to the so-called THz region. Due to the uniquely wide B22 front end design (30 × 50 mrad2 angle and about 32 mm vacuum vessel internal height), the IR beamline B22 operational range spans across the far-IR/THz region, with effective performances tested up to 2 mm wavelength or, equivalently, well below 0.15 THz (FE cut off ~4 mm wavelength). Especially in low-alpha mode of operation of Diamond, by compressing the e− bunch length to a few millimeters coherent SR emission can be stimulated at comparable wavelengths. In the far-IR, a dramatic intensity increase can be observed at Diamond even at only a few μA of circulating current. A summary of the first performances so far achieved in the Far-IR/THz on the IR beamline B22 is here reported for what concerns the CSR emission at Diamond; this is for the storage ring running in dedicated low-alpha mode both in a stable configuration, as well as in the so-called “bursting” or unstable CSR emission. The former is particularly interesting to reach the longest wavelengths (<20 cm−1) so to address the lower energy vibrational modes in condensed matter, the latter is promising for the wider spectral far-IR/THz coverage allowed (around 100 cm−1), and consequently appealing for extending the spectroscopy capability into a broader range of applications.

Automated electron diffraction tomography – a new tool for nano crystal structure analysis

AbstractAutomated electron Diffraction Tomography (ADT) comprises an upcoming method for “ab intio” structure analysis of nano crystals. ADT allows fine sampling of the reciprocal space by sequential collection of electron diffraction patterns while tilting a nano crystal in fixed tilt steps around an arbitrary axis. Electron diffraction is collected in nano diffraction mode (NED) with a semi‐parallel beam with a diameter down to 50 nm. For crystal tracking micro‐probe STEM imaging is used. Full automation of the acquisition procedure allowed optimisation of the electron dose distribution and therefore analysis of highly beam sensitive samples. Cell parameters, space group and reflection intensities can be determined directly within a reconstructed 3d diffraction volume using a dedicated software package (ADT3D). Intensity data sets extracted from such a volume usually show a high coverage and significantly reduced dynamical effects due to “off‐zone” acquisition. The use of this data for “ab initio” structure solution by direct methods implemented in standard programs for X‐ray crystallography is demonstrated. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Mapping ion beam induced current changes in a commercial MOSFET

We demonstrate a novel nuclear microprobe imaging and analysis modality for micrometre-scale field effect transistor devices probed with focused beams of MeV ions. By recording the drain current as a function of time during ion irradiation it is possible to identify current transients induced by the passage of single ions through the sensitive structures of the device. This modality takes advantage of the fact that the ionization produced by the passage of a single ion acts in an equivalent way to a transient change in the gate bias which therefore modulates the drain current as a function of time. This differs from the traditional ion beam induced charge technique where the ionization drifts in an internal electric field and induces a single charge pulse in an electrode applied to the device. Instead a richer variety of phenomena are observed, with different time constants which depend on the proximity of the ion strike to the channel of the device. The signals may be used to examine device function, radiation sensitivity or to count ion impacts within the channel.

Cl-bearing lizardite in metamorphosed kimberlites from the Udachnaya Vostochnaya Pipe, Yakutia

Anhydrite-bearing dolomites and kimberlites from the contact zone of the Udachnaya Vostochnaya pipe, northern part of the Eastern Siberian Platform, were affected by low-grade metamorphism to the zeolite facies. The kimberlites are serpentinized and carbonatized and contain metasomes of anhydrite and saponite pockets. Twenty lizardite pseudomorphs after olivine (Fo91–82) in the kimberlites were examined on an electron microprobe. The lizardite is rimmed by saponite and contains dolomite, calcite, magnetite, and anhydrite inclusions. Lizardite in the central parts of the pseudomorphs contains 1.5–1.9 wt % Cl and 6–9 wt % Fe2O3, and this mineral in the outer portions of the pseudomorphs bears 0.7–1.0 wt % Cl and 2–6 wt % Fe2O3 (the paper presents nine microprobe analyses and images showing the distribution of Cl, Mg, Al, Si, S, Ca, Ti, and Fe obtained in characteristic X-ray radiation). The amounts of Fe3+ in octahedrally and tetrahedrally coordinated sites of the Cl-bearing lizardite are roughly equal. Cl was borrowed in the course of serpentinization from the host Early Paleozoic evaporites and brines contained in them. The Cl concentration in our lizardite from the metamorphosed kimberlites from the Eastern Siberian Platform (continental lizardite) is much higher than the Cl concentration in oceanic lizardite from serpentine replacing peridotites (0.03–0.2 wt % Cl). This is likely explained by differences in the Cl concentrations in the metamorphic fluids, their salinity (3% for oceanic water and 65% for brines in the platform cover).

Mg/Ca variability of the planktonic foraminifera G. ruber s.s. and N. dutertrei from shallow and deep cores determined by electron microprobe image mapping

The Mg/Ca ratio of planktonic foraminifera is widely used for reconstructing sea surface and thermocline temperatures. Dissolution, driven by changes in the bottom water calcite saturation state (a function of water mass chemistry and depth/pressure), lowers the bulk Mg/Ca ratio which results in an implied cooler reconstructed temperature. Here we employ electron microprobe analysis (EMPA) to characterize how dissolution alters shell Mg/Ca variability. Using EMPA we have generated Mg/Ca image maps of two species widely used in paleoceanographic reconstructions: Globogerinoides ruber sensu stricto (G. ruber s.s.) and Neogloboquadrina dutertrei (N. dutertrei). We first characterize the Mg/Ca ratio in the better-preserved shells from a shallow core (2.8 km) and compare those characteristics to the samples from a deep core (4.0 km) obtained from the same locality (Ceara Rise, western equatorial Atlantic). Though preliminary, results suggest EMPA Mg/Ca ratio mapping can reveal characteristics of well preserved shells that can be used to assess changes in the Mg/Ca ratio that occur with dissolution.

Mineralized soft-tissue structure and chemistry in a mummified hadrosaur from the Hell Creek Formation, North Dakota (USA)

An extremely well-preserved dinosaur (Cf. Edmontosaurus sp.) found in the Hell Creek Formation (Upper Cretaceous, North Dakota) retains soft-tissue replacement structures and associated organic compounds. Mineral cements precipitated in the skin apparently follow original cell boundaries, partially preserving epidermis microstructure. Infrared and electron microprobe images of ossified tendon clearly show preserved mineral zonation, with silica and trapped carbon dioxide forming thin linings on Haversian canals within apatite. Furthermore, Fourier transform infrared spectroscopy (FTIR) of materials recovered from the skin and terminal ungual phalanx suggests the presence of compounds containing amide groups. Amino acid composition analyses of the mineralized skin envelope clearly differ from the surrounding matrix; however, intact proteins could not be obtained using protein mass spectrometry. The presence of endogenously derived organics from the skin was further demonstrated by pyrolysis gas chromatography mass spectrometry (Py-GCMS), indicating survival and presence of macromolecules that were in part aliphatic (see the electronic supplementary material).

Multiple protective activities of neuroglobin in cultured neuronal cells exposed to hypoxia re‐oxygenation injury

Oxidative stress is associated with the pathology of acute and chronic neurodegenerative disease. We have cloned a human neuroglobin (Nb) construct and over-expressed this protein in cultured human neuronal cells to assess whether Nb ameliorates the cellular response to experimental hypoxia-reoxygenation (H/R) injury. Parental cells transfected with a blank (pDEST40) vector responded to H/R injury with a significant decrease in cellular ATP at 5 and 24 h after insult. This was coupled with increases in the cytosolic Ca(2+), and the transition metals iron (Fe), copper (Cu), and zinc (Zn) within the cell body, as monitored simultaneously using X-ray fluorescence microprobe imaging. Parental cell viability decreased over the same time period with a approximately 4 to 5-fold increase in cell death (maximum approximately 25%) matched by an increase in caspase 3/7 activation (peaking at a 15-fold increase after 24 h) and condensation of beta-actin along axonal processes. Over-expression of Nb inhibited ATP loss and except for significant decreases in the sulfur (S), chlorine (Cl), potassium (K) and Ca(2+) contents, maintained cellular ion homeostasis after H/R insult. This resulted in increased cell viability, significantly diminished caspase activation and maintenance of the beta-actin cytoskeletal structure and receptor-mediated endocytosis. These data indicate that bolstering the cellular content of Nb inhibits neuronal cell dysfunction promoted by H/R insult through multiple protective actions including: (i) maintenance of cellular bioenergetics; (ii) inhibition of Ca(2+) influx; (iii) a reduction in cellular uptake of Fe, Cu and Zn at the expense of S, Cl and K; and (iv) an enhancement of cell viability through inhibiting necrosis and apoptosis.

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2–2 m thick zone of partially weathered rock layers (∼2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive Δ V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 Å, forming “altered biotite”. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 × 10 −14 mol biotite m −2 s −1. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 μm resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet–saprolite interface, hornblende dissolves to completion at a rate of 6.3 × 10 −13 mol hornblende m −2 s −1: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O 2 at the bedrock–saprolite interface.

In Vivo Quantitative Microvasculature Phenotype Imaging of Healthy and Malignant Tissues Using a Fiber-Optic Confocal Laser Microprobe

Real-time in vivo imaging of the microvasculature may help both earlier clinical detection of disease and the understanding of tumor.host interaction at various stages of progression. In vivo confocal and multiphoton microscopy is often hampered by bulky optics setup and has limited access to internal organs. A fiber-optic setup avoids these limitations and offers great user maneuverability. We report here the in vivo validation of a fiber-optic confocal fluorescence microprobe imaging system. In addition, we developed an automated fractal-based image analysis to characterize microvascular morphology based on vessel diameter distribution, density, volume fraction, and fractal dimension from real-time data. The system is optimized for use in the far-red and near-infrared region. The flexible 1.5-mm-diameter fiber-optic bundle and microprobe enable great user maneuverability, with a field of view of 423 × 423 μm and a tissue penetration of up to 15 μm. Lateral and axial resolutions are 3.5 and 15 μm. We show that it is possible to obtain high temporal and spatial resolution images of virtually any abdominal viscera in situ using a far-red blood pool imaging probe. Using an orthotopic model of pancreatic ductal adenocarcinoma, we characterized the tumor surface capillary and demonstrated that the imaging system and analysis can quantitatively differentiate between the normal and tumor surface capillary. This clinically approved fiber-optic system, together with the fractal-based image analysis, can potentially be applied to characterize other tumors in vivo and may be a valuable tool to facilitate their clinical evaluation.

Crystal chemical significance of chemical zoning in dissakisite-(Ce)

Dissakisites from Trimouns dolomite mine, France, have two kinds of single crystals: chemical-zoned and homogeneous types. Back-scattered electron microprobe (BSE) images of these dissakisites reveal both Ca–Al rich dark zones and Fe-ΣREE rich bright zones. Crystal structures of three dark and two bright zones in a chemical-zoned dissakisite and of a homogeneous zone in unzoned dissakisite were refined to individual R indices (about 3.0–5.0%) based on 1,400 observed [|F 0| > 4σF 0] reflections measured with MoKα X-radiation using the single crystal diffractometer. The differences in brightness between their BSE images arise from those in coupled substitutions of the elements occupying A2 and M3 sites. The main reason for these differences is that ten-coordinated A2 polyhedra and M3 octahedra are directly linked through their shared edge, which creates a great potential for making this coupled substitution. This zoning indicates that formation of the whole zoned crystal, where each zone could be grown steadily with its crystallographic axes mutually parallel to each other, may be identified as autoepitaxy.

Microscopic and Macroscopic Signatures of Antiferromagnetic Domain Walls

Magnetotransport measurements on small single crystals of Cr, the elemental antiferromagnet, reveal the hysteretic thermodynamics of the domain structure. The temperature dependence of the transport coefficients is directly correlated with the real-space evolution of the domain configuration as recorded by x-ray microprobe imaging, revealing the effect of antiferromagnetic domain walls on electron transport. A single antiferromagnetic domain wall interface resistance is deduced to be of order 5 x 10(-5) mu Omega cm(2) at a temperature of 100 K.