Laser Microprobe Research Articles

Structural and geochronological constraints on the tectono-thermal evolution of the Danba domal terrane, eastern margin of the Tibetan plateau

The Songpan-Ganze terrane of the Tibetan plateau is underlain by Neoproterozoic crystalline basement rocks of the Yangtze block. These basement rocks are exposed as a series of extensional tectonic domes that form a nearly north–south trending extensional belt more than 1000 km long in the eastern margin of the Tibetan plateau. In the Danba area, detachment faults separate the basement core complexes (e.g., the Gezong and Gongcai complexes) from the Paleozoic strata which have been thinned or removed completely. The cover sequences have undergone upper greenschist to lower amphibolite facies metamorphism to form the Danba schist and are overlain by the Triassic Xikang Group, a thick flysch sequence. Both the basement rocks and the Paleozoic rocks have undergone multiple stages of deformation and thus provide an excellent opportunity to study the tectono-thermal evolution of the eastern margin of the Tibetan plateau. Two stages of deformation, corresponding to three generations of foliation (S 1, S 2 1 , and S 2 2 ), have been recognized on the basis of structural and microscopic observations. We selected amphibole and biotite separates associated with distinct generations of foliation for 40Ar/ 39Ar dating using laser microprobe incremental heating technique to place numerical constraints on the major tectono-thermal events within the Danba area. The geochronogical results reveal an earliest metamorphic event at 258.6 ± 0.5 Ma (S 1 biotite) and 263.6 ± 0.8 Ma (S 1 amphibole), coinciding temporally with the mantle plume that produced the voluminous Emeishan flood basalts. The second event was a progressive extensional deformation first occurred at 159–166 Ma ( S 2 1 amphibole) responsible for the earlier tectonic doming of the crystalline basement, and then the final tectono-thermal overprint recorded by S 2 2 foliation and M 2 2 metamorphism locally in the core complexes at 47–58 Ma for the Gezong complex and 64–81 Ma for the Gongcai complex. This major post-orogenic extensional event is believed to be a consequence of collision between the North China and South China blocks. The apparent discrepancy of the 40Ar/ 39Ar ages observed between localities suggests a slow cooling process associated with progressive uplift.

Quantitative analysis of domain texture in polycrystalline barium titanate by polarized Raman microprobe spectroscopy

A quantitative determination of domain distribution in polycrystalline barium titanate (BaTiO3, henceforth BT) ceramics has been pursued with the aid of a microprobe polarized Raman spectrometer. The crystallographic texture and domain orientation distribution of BT ceramics, which switched upon applying stress according to ferroelasticity principles, were determined from the relative intensity of selected phonon modes, taking into consideration a theoretical analysis of the angular dependence of phonon mode intensity for the tetragonal BT phase. Furthermore, the angular dependence of Raman intensity measured in polycrystalline BT depended on the statistical distribution of domain angles in the laser microprobe, which was explicitly taken into account in this work for obtaining a quantitative analysis of domain orientation for in-plane textured BT polycrystalline materials.

Aluminium and Alzheimer's disease.

The hypothesis that aluminium (Al) is a cause of (or a risk factor in) the development of beta-amyloid plaques and neurofibrillary tangles (NFT) and dementia in Alzheimer's disease (AD) is based on studies by Wisniewski et al, Klatzo et al and Terry & Peña in 1965 that showed that injection of experimental animals with Al compounds induces the formation of NFT. Other publications revealed that Al affects cognitive functions in experimental animals and humans undergoing dialysis for renal failure. Electron probe and laser microprobe mass analysis (LAMMA) studies have demonstrated the presence of Al in NFT and cores of amyloid stars and nuclei of neurons in AD patients. Other studies have indicated the association between amyotrophic lateral sclerosis/Guam parkinsonism-dementia complex and Al in the environment. A recent report suggests that the chelating agent desferrioxamine slows the rate of cognitive decline in AD patients. Extensive studies of the pathology of AD and Al-induced encephalopathy by our group and others indicate that Al does not cause Alzheimer's disease neuropathology. However, under certain conditions, cognition can be affected when Al enters the brain. Therefore, for individuals with renal failure or undergoing dialysis or individuals with a damaged blood-brain barrier, the intake of Al should be controlled.

Aluminium and the neurofibrillary tangle: results of tissue microprobe studies.

Despite the contradictory results of studies attempting to compare the bulk brain tissue aluminium content of specimens from Alzheimer's disease patients and controls, microprobe studies from our laboratory have consistently documented evidence of selective accumulation of the element within the neurofibrillary tangle-bearing cells associated with this condition. Laser microprobe mass analysis (a highly sensitive and precise technique for trace elemental microprobe analysis) has now demonstrated that the most prominent aluminium accumulations occur within the neurofibrillary tangle itself. Similar findings have been obtained from microprobe studies of the neurofibrillary tangles which are a characteristic feature of amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam. Although the intraneuronal localization of aluminium in the Guam-derived specimens is similar to that of Alzheimer's disease, the concentration of aluminium is considerably higher than is encountered in Alzheimer's disease specimens. We conclude that aluminium is an integral component of the neurofibrillary tangle and raise the possibility that the cross-linking properties of this highly reactive metal may stabilize the constituent cytoskeletal proteins which make up this pathological structure.

Morphological and chemical studies of pathological human and mice brain at the subcellular level: Correlation between light, electron, and nanosims microscopies

Neurodegenerative diseases induce morphological and chemical alterations in well-characterized regions of the brain. Understanding their pathological processes requires the use of methods that assess both morphological and chemical alterations in the tissues. In the past, microprobe approaches such as scanning electron microscopy combined with an X-ray spectrometer, Proton induced X-ray emission, secondary ion mass spectrometry (SIMS), and laser microprobe mass analysis have been used for the study of pathological human brain with limited success. At the present, new SIMS instruments have been developed, such as the NanoSIMS-50 ion microprobe, that allow the simultaneous identification of five elements with high sensitivity, at subcellular spatial resolution (about 50-100 nm with the Cs(+) source and about 150-200 nm with O(-) source). Working in scanning mode, 2D distribution of five elements (elemental maps) can be obtained, thus providing their exact colocalization. The analysis can be performed on semithin or ultrathin embedded sections. The possibility of using transmission electron microscopy and SIMS on the same ultrathin sections allows the correlation between structural and analytical observations at subcellular and ultrastructural level to be established. Our observations on pathological brain areas allow us to establish that the NanoSIMS-50 ion microprobe is a highly useful instrument for the imaging of the morphological and chemical alterations that take place in these brain areas. In the human brain our results put forward the subcellular distribution of iron-ferritin-hemosiderin in the hippocampus of Alzheimer disease patients. In the thalamus of transgenic mice, our results have shown the presence of Ca-Fe mineralized amyloid deposits.

Millimeter scale variations in the isotopic composition of vein sulphide minerals in the Kupferschiefer deposits, Lubin area, SW Poland†

A slice of black shale rock cut by various metal sulphide veins of different generations from the Kupferschiefer deposits of Lubin, Poland was subjected to bombardment in a Laser Microprobe Combustion Reactor to produce SO2 for S-isotope analyses. The δ34S values ranged from−22 to−29 ‰ consistent with previous findings using conventional IRMS and attributable to primary generation of H2S by bacterial sulphate reduction. Systematic trends in δ34S values of a few per mil over distances of the order of mm attest to low temperatures of mineralization with accompanying change in the isotope composition of the fluids due to kinetic or equilibrium isotope fractionation. †Revised version of a paper presented at the VIII Isotope Workshop of the European Society for Isotope Research (ESIR), June 25 to 30, 2005, Leipzig-Halle, Germany

SEU Error Signature Analysis of Gbit/s SiGe Logic Circuits Using a Pulsed Laser Microprobe

We present, for the first time, an analysis of the error signatures captured during pulsed laser microprobe testing of high-speed digital SiGe logic circuits. 127-bit shift registers, configured using various circuit level latch hardening schemes and incorporated into the circuit for radiation effects self test serve as the primary test vehicle. Our results indicate significant variations in the observed upset rate as a function of strike location and latch architecture. Error information gathered on the sensitive transistor nodes within the latches and characteristic upset durations agree well with recently reported heavy-ion microprobe data. These results support the growing credibility in using pulsed laser testing as a lower-cost alternative to heavy-ion microprobe analysis of sensitive device and circuit nodes, as well as demonstrate the efficiency of the autonomous detection and error approach for high speed bit-error rate testing. Implications for SEU hardening in SiGe are addressed and circuit-level and device-level Radiation Hardening By Design recommendations are made

Laser Microprobe with Fourier Transform Ion Cyclotron Resonance Mass Spectrometer for Surface Analysis

Fourier transform ion cyclotron resonance laser microprobe mass spectrometry (FTICR LMMS) uses focused laser irradiation of solids with a spot of 5 microm and a FTICR mass analyzer for local analysis with high mass resolution. A new ion source design has been developed to improve the extraction and transfer of ions generated in an external laser microprobe source. Calculations predicted trapping of ions initially emitted with angles up to 40 degrees and 60 degrees from the surface and from a distance of 1 mm above the sample, respectively. The analytical performances of the method have been verified on two sets of test samples. First, detection of chemisorbed benzotriazole on copper, average of two monolayers, has been shown with less sample consumption than typically required in static secondary ion mass spectrometry with a time-of-flight analyzer. Second, experiments on a thermal plate for offset printing have shown the feasibility of analysis and quantification of dyes embedded in a polymer matrix.

Pyrite metamorphism in the devonian hunsruck slate of Germany: Insights from laser microprobe sulfur isotope analysis and thermodynamic modeling

The Devonian Hunsruck Slate of Altlay, Rhenish Massif, Germany, contains an exceptional spectrum of pyrite textures, recording progressive recrystallization and remobilization of sedimentary/diagenetic pyrite during very low grade metamorphism. Sedimentary/diagenetic pyrite is very fine-grained and forms distinct enrichments, including thin layers, elongate concretions, and pyritized fish coprolites. These pyrites show abundant idioblastic overgrowths, which are very coarse-grained and are always located at the interface between the sedimentary/diagenetic pyrite and the slate matrix. Progressive recrystallization resulted in the formation of porphyroblasts and an almost complete obliteration of the original internal structures. A detailed, texturally-resolved sulfur isotope study of the different pyrite types has been carried out, using an in situ laser microprobe technique. The δ34S values of sedimentary/diagenetic pyrite, idioblastic overgrowths, and porphyroblasts are very homogeneous and lie in the range of +7.9 to +12.8 permil (mean: +10.6 ‰), +8.6 to +12.4 permil (mean: +10.8 ‰), and +8.3 to +12.1 permil (mean: +10.3 ‰), respectively. The sulfur isotope data for each population and the isotopic relationships on the sample scale indicate that metamorphic recrystallization has not resulted in a significant modification of the original isotopic composition. Calculation of phase relations and modeling of fluid-rock equilibria place important constraints on the conditions and mechanisms of pyrite remobilization during metamorphism. The calculations show that pressure variations have no detectable influence on pyrite solubility, indicating that pressure solution was not important in the metamorphic mass transfer of pyrite. The effects of temperature and oxidation state are more pronounced, and infiltration of fluids originating from deeper crustal levels could have caused the remobilization of pyrite. Modeling of the isotopic fractionation shows that remobilization driven by interaction with such fluids having a higher temperature and oxidation state would have resulted in a significant negative shift of the δ34S values, which is not consistent with the observed isotopic pattern. We envisage an alternative model that involves fluid-assisted reduction of the grain surface area (and surface energy) per unit volume of pyrite as the dominant mechanism driving recrystallization and porphyroblast growth. The difference in surface energy between the fine-grained sedimentary/diagenetic and the idioblastic pyrite resulted in establishment of a small-scale chemical potential gradient, which evolved along a self-enhancing path during progressive idioblastic growth. The results of our modeling have implications for the preservation of primary sulfur isotopic signatures and emphasize the importance of constraining the history of fluid-rock interaction for a meaningful interpretation of sedimentary/diagenetic processes in pyrite-rich metasediments.

Aluminum and Alzheimer's disease, a personal perspective after 25 years

It is now 25 years since the publication of our original paper investigating the association aluminum with Alzheimer's disease. This publication reported on the results of scanning electron microscopy coupled x-ray spectrometry microprobe elemental studies of both neurofibrillary tangle-bearing and tangle-free neurons in the hippocampus of cases of Alzheimer's disease and controls. Peaks related to the presence of aluminum were consistently detected within the tangle-bearing neurons. This paper supported the association of aluminum and Alzheimer's disease on the cellular level of resolution and caused considerable interest and discussion. Subsequent work demonstrated prominent evidence of aluminum accumulation in the tangle-bearing neurons of cases of amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam. This latter observation has now been replicated using five different forms of microanalysis. Finally, using laser microprobe mass analysis, we demonstrated that the abnormally high aluminum-related signal which we originally detected was actually located within the neurofibrillary tangle, itself, and was accompanied by excess concentrations of iron. Although it is unlikely that aluminum represents an etiologic cause of Alzheimer's disease, we believe that this highly reactive element, known to cross-link hyperphosphorylated proteins, may play an active role in the pathogenesis of critical neuropathologic lesion in Alzheimer's disease and other related disorders.

Sulfur and carbon isotope analyses of 2.7 Ga stromatolites, cherts and sandstones in the Jeerinah Formation, Western Australia

Microbial consortia are found in modern stromatolites. It has been uncertain if such microbial consortia already existed in late Archean stromatolites. Stable carbon and sulfur isotope analyses were performed on organic matter and pyrite in stromatolites, cherts and sandstones of the Jeerinah Formation. Fine-grained microscopic pyrite crystals occur predominantly inside the stromatolites. Sulfur isotope compositions of individual pyrite crystals were determined using the Nd-YAG laser microprobe system. Variable δ 34S values (−2.5 to +5.6‰ (CDT)) of pyrite were found in the examined samples, suggesting that pyrite crystals were formed by either abiotic or biotic sulfate reduction in stromatolite. Geological and petrographic evidence suggest that microbial sulfate reduction was the more likely pathway of the pyrite formation. δ 13C values of organic matter range from −39.7 to −27.1‰ (PDB). These values indicate that microorganisms capable of photosynthesis were active around stromatolites in addition to the activity of methanotrophic microorganism. These stable isotope data suggest that various type of microorganisms existed during stromatolite formation, although the role of each microorganism in stromatolite accretion is still uncertain.

Laser microprobe (U–Th)/He geochronology

A new analytical method had been developed to enable high-spatial-resolution (U–Th)/He dating of accessory minerals. It involves the use of a focused ArF excimer to ablate pits in a polished grain surface, with the evolved gases spiked for isotope-dilution measurement of radiogenic 4He. These data are converted to concentrations by precise measurement of each pit using an optical interferometric microscope. U, Th, and Sm concentration measurements are made using one of several alternative microanalytical techniques (e.g., wavelength-dispersive electron microprobe analysis or laser-ablation, inductively coupled plasma mass spectrometry). By way of illustration, we present both conventional and laser microprobe (U–Th)/He dating results for a Brazilian monazite sample. Laser microprobe data (28 measurements on two crystal fragments) yield a weighted mean (U–Th)/He date of 455.3 ± 3.7 Ma (2SE). This result is statistically indistinguishable from the mean conventional (U–Th)/He date for three separate grain fragments: 449.6 ± 9.8 Ma (2SE). The agreement of conventional and laser ablation dates should encourage a wide variety of applications of the technique, including: (1) detrital mineral dating for provenance and unroofing studies; (2) the dating of broken, included, highly zoned, or irregular grains which are not easily corrected for α-ejection; and (3) measuring 4He loss profiles that can be inverted to determine cooling histories.

Environmental Phase Stability of Next Generation Ceramic Composite for Hip Prostheses

A hip-joint femoral head, made of alumina matrix composite, has been evaluated with respect to its surface degradation upon increasing elongation time in water vapor environment. A microscopic evaluation of surface degradation phenomena was obtained according to laser microprobe Raman and fluorescence spectroscopies. According to a confocal configuration of the optical probe, the spectroscopic assessments were performed in volumes limited to the very neighborhood of the material surface, thus minimizing the effect of the sub-surface, which was less affected by environmental degradation. Two main features were observed: (i) significant transformation of zirconia occurred in moist environment from the tetragonal to the monoclinic polymorph; such an environmentally induced phase transformation, conspicuously increased the fraction of monoclinic polymorph (i.e., ≅ 18 vol.% in average) already present in the as-received femoral head; (ii) the equilibrium residual stress field stored at the joint surface changed from a tensile field in the as-received material to a slightly compressive stress field after several hours aging in moist atmosphere and, after exposures >50 h to an increasingly tensile stress state. A residual stress field of tensile nature in the joint surface may trigger wear degradation in the femoral head in presence of microscopic (local) weight impingements due to micro-separation and third-body wear phenomena.

Laser ablation 40 Ar/ 39 Ar dating of metamorphic fabrics in the Caledonides of north Ireland

In situ 40 Ar/ 39 Ar dating of two texturally distinct biotite generations within a phyllite from the Caledonian orogen of Ireland was performed using a high spatial resolution laser microprobe. In this sample, an older generation of biotite (Bt 1 ) is aligned subparallel to a steeply dipping crenulation foliation, which itself is overprinted by a regionally developed shallow-dipping foliation. The second biotite generation (Bt 2 ) occurs as randomly oriented porphyroblasts that overprint and therefore postdate both foliations. A dataset of 89 ages from a single thick section was acquired for six Bt 1 and eight Bt 2 crystals. The two biotite generations yielded two statistically distinct age distributions with Bt 1 maxima at c . 433 Ma and Bt 2 maxima at c . 417 Ma. A small number of analyses (11% Bt 1 and 26% Bt 2 ) from within crystals yielded ‘main population’ ages that conflict with the dominant age populations and relative chronology established by field relationships. Discordant analyses from the earlier Bt 1 crystals are younger (than the Bt 2 population) and probably reflect intracrystalline partial resetting during a later thermal perturbation. The discordant Bt 2 analyses are predominantly older (than the Bt 2 population) and are interpreted as indicating localized excess 40 Ar. Such dis cordant analyses indicate intracrystalline variation reflecting both excess 40 Ar (Bt 2 population) and 40 Ar loss (Bt 1 population), and were therefore discarded when determining geologically meaningful ages.

Polycyclic aromatic hydrocarbons in flames, in diesel fuels, and in diesel emissions

Numerous chemical analyses of gaseous and particulate samples from laboratory flames provide a library of data on the polycyclic aromatic hydrocarbon (PAH) species found in diverse flame types burning fuels consisting of pure gaseous hydrocarbons. The diesel fuels utilized by the more complex combustion in compression ignition engines are composed of thousands of hydrocarbon species. Mass spectrometry by the laser microprobe and gas chromatography were used in a complementary manner to distinguish the PAHs originating in the fuel from those produced by engine combustion. The C x H y PAH products of premixed and diffusion flame processes, which also occur in the unsteady diesel combustion, range in mass from 128 u (two rings, x = 10 , y = 8 ) to beyond 350 u (eight rings, x = 28 , y = 14 ). Graphs of the number of hydrogen atoms y vs the number of carbon atoms x for the species found by many investigators of laboratory flames show these pyrogenic PAHs to lie on or near the staircase curve that describes the most stable, pericondensed, benzenoid PAHs. In contrast, samples of diesel fuels from the United Kingdom and the United States contain petrogenic alkyl-PAHs with high hydrogen contents. Samples of diesel particulate emissions typical of the 1990s from two different sources display the full mass range of PAHs from 128 to 350 u, including both the benzenoid PAHs and the alkyl-PAHs. Thus diesel emissions, in general, may contain petrogenic fuel components ranging up to 206 u and also the combustion-generated four- to seven-ring species in the 228 to 302 u mass range that have greater carcinogenic potency. The absence of petrogenic components larger than 206 u facilitates their detection and delineation from pyrogenic PAHs by methods of chemical analysis.

A high resolution record of multiple diagenetic events: Ultraviolet laser microprobe Ar/Ar analysis of zoned K-feldspar overgrowths

High spatial resolution UV laser Ar/Ar analyses were performed in situ on K-feldspar overgrowths from sandstone hosted Pb–Zn bodies from central Sweden. Two different populations of ages were detected—Precambrian–Cambrian (528 ± 10 to 567 ± 8 Ma) and late Silurian (403 ± 6 to 453 ± 8 Ma). These were both detected in single pore spaces, with the older population adjacent to the detrital feldspar whilst the younger population was always distal to the detrital grain. This younging of authigenic K-feldspar ages with distance from the detrital grain margin is discussed in terms of disturbance to the argon system within an authigenic overgrowth that is of a single age: (a) the overgrowths are Precambrian–Cambrian in age and the late Silurian population might be an artefact of argon-loss due to partial resetting, (b) the overgrowths are late Silurian and the Precambrian–Cambrian population might have resulted from excess argon uptake, and (c) the overgrowths are late Silurian but the Precambrian–Cambrian population is an experimental artefact arising from the analysis of overlapping detrital/authigenic feldspars. Diffusion modelling shows that the partial resetting scenario is a very unlikely cause for the observed age variation because it requires a very particular arrangement of sub-grain sizes. Excess argon was not detected in either the K-feldspar or quartz. The data are best interpreted as the ages of two discrete diagenetic events—an early burial diagenesis and a later tectonically induced fluid flow event relating to the collapse of the Caledonian orogen. Further, the use of 38Ar Cl/ 39Ar K as a proxy for Cl/K ratio highlights the physical boundaries between feldspar populations, where all other petrographic, SEM and CL analyses have failed to do so. This study shows that high spatial resolution UV laserprobe Ar/Ar analysis is a powerful tool for extracting age information from complex hydrothermal minerals as a means to investigating fluid flow events.

Complementary use of Fourier transform laser microprobe mass spectrometry and time‐of‐flight static secondary ion mass spectrometry for the study of the surface adsorption of organic dyes on silicate materials

The adsorption of organic ionic dyes on different pore size engineered silica materials with potential application for industrial wastewater treatment has been investigated using Fourier transform laser microprobe mass spectrometry (FT-LMMS) and time-of-flight secondary ion mass spectrometry (TOF-S-SIMS). The complementary use of the two methods with different information depth allowed data on the subsurface distribution and pore penetration of the adsorbed organic compounds. Macroscopic methods were employed to determine the amount adsorbed on the particles and the specific external surface area. Local MS analysis allows identification of the organic dyes exclusively at the outer particle surface when the pore size is inferior to the size of the adsorbing molecule, or at the surface of the channels inside the material. Specifically, the monolayer information depth of TOF-S-SIMS causes a signal to refer essentially to the adsorbate at the outer particle surface, which is only a fraction of the total adsorption in mesoporous materials, while FT-LMMS allowed detection of the presence of adsorbates at the outer surface as well as inside the subsurface of 10 to 50 nm depending on the material under study. The observed data open perspectives for the molecular monitoring of the adsorption behaviour of different materials at the (sub) microm scale.

Matrix-Assisted Laser Desorption/Ionization, Time of Flight, and Angiotensin II

Elsewhere in this issue, Jankowski et al show that mononuclear cells produce sufficient angiotensin II (Ang II) to stimulate Ang II type 1 receptors.1 That finding alone is noteworthy; however, my attention was riveted by the methods the authors used to measure Ang II. Ang II is generally measured by radioimmunoassay. Because of antibody specificity, the samples are first purified by high-performance liquid chromatography (HPLC). The assay is difficult, tedious, and fraught with pitfalls. The sample collections, standardization of collection conditions, and use of appropriate inhibitors are only some of the problems. Only a few investigators do this assay well. An alternative, more accurate, method would be most welcome. Were the method sufficiently established, and were the method routinely available, direct Ang II measurements could be of great clinical utility. After reading the article and meeting with the senior author, I hedge the hope that matrix-assisted laser desorption/ionization (MALDI)–time of flight (TOF) might bring this wish to reality. Jankowski et al adapted MALDI-TOF to measure Ang II or other small peptides and proteins with interesting biological activities in a previous study.2 In their article, they outlined a MALDI-TOF–based strategy to screen protein fractions for defined enzymatic activities. The authors prepared porcine kidney extracts that were then immobilized by covalent coupling to activated affinity beads. The immobilized proteins were incubated with probes …

U–Pb isotopic ages and Hf isotopic composition of single zircons: The search for juvenile Precambrian continental crust

U–Pb isotopic ages and Hf isotope compositions by laser microprobe ICPMS and MC-ICPMS can be useful in identifying detrital zircons derived from juvenile continental sources. Hf isotopes in detrital zircons from modern river deposits in Brazil, Australia, India and the Ukraine show evidence for production of juvenile crust at about 2.5 Ga. However, if detrital zircon populations in the 2.4–2.2 Ga time window are representative of the proportion of juvenile crust in their primary sources, they yield little evidence for significant volumes of juvenile crust of this age. Hf isotopic compositions of detrital zircons from the Ukraine and eastern Australia also record production of juvenile continental crust between 1.65 and 1.40 Ga. Zircons from granitoids in south-central Laurentia and in western Brazil have E Hf( T) values that fall near the depleted mantle growth curve recording production of juvenile continental crust in these regions between 1.5 and 1.3 Ga. Although Hf isotope compositions of detrital zircons can be useful in identifying detrital zircons derived from juvenile continental sources, the results do not necessarily equate to the volume of juvenile continental crust produced during specific time intervals.

Interfacial properties of sapphire/epoxy composites: Comparison of fluorescence spectroscopy and fiber push-in techniques

Experiments and analyses leading to the assessment of interfacial sliding friction and residual stresses in sapphire filament reinforced epoxy matrix composite by two different techniques are described in this paper. The first technique was based on measurements of stresses in filaments bridging a steady-state matrix crack using a laser microprobe to stimulate fluorescence from the sapphire filaments. The measured stress variation was consistent with un-bonded, frictionally constrained filaments with a constant friction stress along the sliding zone length. The second technique involved measurements of load–displacement records in filament push-in tests using a mechanical microprobe. The sliding friction stress and the residual stress in the filaments assessed by the two techniques were essentially identical. Analyses of the experimental results with different theoretical models indicated that the assessed values of the sliding friction stress and the residual stresses were not affected significantly by accounting for the mismatch in the Poisson’s ratios of the filaments and the matrix and taking into account the elastic anisotropy of the filaments.