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This article presents historical and scientific analysis, as well as the conservation treatment of a newly rediscovered Roman wall painting fragment, now in the collection of the Harvard Art Museum...

This study assesses the potential of Uniform Manifold Approximation and Projection (UMAP) as an alternative tool to t-distributed Stochastic Neighbor Embedding (t-SNE) for the reduction and visualization of visible spectral images of works of art. We investigate the influence of UMAP parameters-such as, correlation distance, minimum embedding distance, as well as number of embedding neighbors- on the reduction and visualization of spectral images collected from Poemes Barbares (1896), a major work by the French artist Paul Gauguin in the collection of the Harvard Art Museums. The use of a cosine distance metric and number of neighbors equal to 10 preserves both the local and global structure of the Gauguin dataset in a reduced two-dimensional embedding space thus yielding simple and clear groupings of the pigments used by the artist. The centroids of these groups were identified by locating the densest regions within the UMAP embedding through a 2D histogram peak finding algorithm. These centroids were subsequently fit to the dataset by non-negative least square thus forming maps of pigments distributed across the work of art studied. All findings were correlated to macro XRF imaging analyses carried out on the same painting. The described procedure for reduction and visualization of spectral images of a work of art is quick, easy to implement, and the software is opensource thus promising an improved strategy for interrogating reflectance images from complex works of art.

We refine the crystal structures of a systematic series of compounds with the general composition Ho(x)Yb(2-x)TiO5 (x = 2, 1.6, 1.2, 1, 0.8, 0.4, 0) and Er2TiO5 and find a transition from defect-pyrochlore to defect-fluorite structure with increasing ytterbium content, decreasing lanthanide radius. Short-range structure modulations consisting of pyrochlore-like nano-domains are systematically characterised using transmission electron microscopy. We test the Kr2+ 1 MeV ion-irradiation response of Ho2TiO5, HoYbTiO5, Yb2TiO5, and Er2TiO5, via the crystalline to amorphous transition observed by using the in-situ TEM approach. The critical dose of amorphisation, Dc, was measured at various temperatures and used to calculate the critical temperature for maintaining crystallinity, Tc. A trend of lower Tc values with decreasing lanthanide radius is found. We describe a new approach for determining Tc values using cross-sectional TEM analysis of ex-situ bulk irradiated, 1 MeV Se+, samples; Ho2TiO5, HoYbTiO5 and Yb2TiO5. The results of Dc and Tc values using the two approaches vary; however the trends across the sample system remain the same.

The Ln 2 TiO 5 (Ln = lanthanides and yttrium) compounds find use in nuclear, electronic and battery applications but there is a lack of information correlating the synthesis, structure and properties of these materials. We give an in depth review of the current available literature on the Ln 2 TiO 5 compounds. New structural findings of the Tb x Yb 2−x TiO 5 (x = 0, 0.4, 0.8, 1, 1.2, 1.6, 2) compounds are detailed and their response to 1 MeV krypton ion exposure is discussed. A single phase Tb 2 TiO 5 sample with hexagonal symmetry is the first bulk, single phase, mono-lanthanide with this stoichiometry and symmetry to be reported. Thus this work brings together the current literature and illustrates the synthesis-structure-property relationships that are observed in this family.

This ion-irradiation study covers the four major crystal structure types in the Ln 2 TiO 5 series (Ln = lanthanide), namely orthorhombic Pnma , hexagonal P6 3 /mmc , cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m . This is the first systematic examination of the complete Ln 2 TiO 5 crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm (x) Yb (2-x) TiO 5 (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr 2+ ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation ( D c ), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature ( T c ), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb 2 TiO 5 and Sm 0.6 Yb 1.4 TiO 5 , were found to be the most radiation tolerant, with T c values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds.

The response of Ln2TiO5 (where Ln is a lanthanide) compounds exposed to high-energy ions was used to test their suitability for nuclear-based applications, under two different but complementary conditions. Eight samples with nominal stoichiometry Ln2TiO5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Dy), of orthorhombic (Pnma) structure were irradiated, at various temperatures, with 1 MeV Kr2+ ions in-situ within a transmission electron microscope. In each case, the fluence was increased until a phase transition from crystalline to amorphous was observed, termed critical dose Dc. At certain elevated temperatures, the crystallinity was maintained irrespective of fluence. The critical temperature for maintaining crystallinity, Tc, varied non-uniformly across the series. The Tc was consistently high for La, Pr, Nd and Sm2TiO5 before sequential improvement from Eu to Dy2TiO5 with Tc's dropping from 974 K to 712 K. In addition, bulk Dy2TiO5 was irradiated with 12 MeV Au+ ions at 300 K, 723 K and 823 K and monitored via grazing-incidence X-ray diffraction (GIXRD). At 300 K, only amorphisation is observed, with no transition to other structures, whilst at higher temperatures, specimens retained their original structure. The improved radiation tolerance of compounds containing smaller lanthanides has previously been attributed to their ability to form radiation-induced phase transitions. No such transitions were observed here.

Garnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca 3 Zr 2 FeAlSiO 12 , has been shown naturally to contain up to 30 wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca 3 Hf 2 FeAlSiO 12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca 3 Zr 2 FeAlSiO 12 , at 1000 K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring.

A series of single phase compounds with nominal stoichiometry Sm(x)Yb(2−x)TiO5 (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln2TiO5 series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types.

A pilot project was conducted in Dane County, Wisconsin, to evaluate the frequency of individuals driving under the influence of drugs (DUID). Evidentiary blood specimens, collected from subjects arrested for Operating While Intoxicated (OWI), were compared to oral fluid (OF) results obtained with the Alere DDS2®, a handheld screening device. The project objectives were to evaluate (i) the Alere DDS2® for use by police officers in the field, (ii) the frequency of individuals DUID and drugs combined with alcohol among OWI cases, (iii) the differences between detecting drugs in OF and in blood, and (iv) the effect of the laboratory drug testing cancellation policy (LCP) when the blood alcohol concentration (BAC) exceeds 0.100 g/100 mL. Following the arrest and collection of blood, subjects were asked to voluntarily participate in the project and provide an OF specimen. The OF was presumptively screened with the Alere DDS2® for six drug categories including (ng/mL) amphetamine (50), benzodiazepines (temazepam, 20), cocaine (benzoylecgonine, 30), methamphetamine (50), opioids (morphine, 40) and THC (delta-9-THC, 25). Results obtained with the OF screening instrument were not confirmed. A total of 104 subjects (22 female, 82 male), ages 18-72, were included in the project. Blood specimens were tested by gas chromatography-headspace (GCHS-FID) for volatiles, enzyme immunoassay (Siemens Viva-E Drug Testing System), and an alkaline basic drug screen with gas chromatography-mass spectrometry (GCMS) analysis. To compensate for differences between the EIA and the Alere DDS2® drug categories, results from the enzyme immunoassay and the alkaline basic drug screen were combined for purposes of comparing OF to blood. Seventy-six of 104 (73%) subjects arrested for OWI were driving under the influence of alcohol; 71 of the 76 had a BAC exceeding 0.10 g/100 mL. Subjects with a BAC exceeding the LCP, screened positive for drugs in both OF (n = 29) and blood (n = 28). Overall, one or more positive drug screening result was observed in 57 (55%) and 50 (48%) subjects for OF and blood specimens, respectively. THC was the most frequently detected drug category in both OF (n = 46) and whole blood (n = 44). Drug Recognition Expert (DRE) evaluations were performed on 18 subjects. In general, the Alere DDS2® results were consistent with the combined screening results observed in evidentiary blood specimens. This project was limited in scope as a second OF specimen was not collected for confirmation of drugs, however it did demonstrate that nearly 40% of the subjects with concentrations of alcohol exceeding 0.10 g/100 mL, screened positive for one or more drug categories in both OF and blood. The Alere DDS2® portable OF screening instrument may be useful in assisting law enforcement with identifying individuals driving under the influence of drugs and establishing probable cause at roadside for making DUID arrests.

Zirconolites based on the replacement of Ti 4+ with equimolar amounts of Nb 5+ and Fe 3+ , CaZrTi 2−2x Nb x Fe x O 7 , have been jointly refined using high-resolution neutron powder diffraction and resonant X-ray powder diffraction data, with extra information provided from 57 Fe Mossbauer spectroscopy, to determine cation disorder. The results indicate that the CaZrTi 2−2x Nb x Fe x O 7 series adopts the zirconolite-2 M polytype across the range, with the replacement of Ti 4+ by Fe 3+ and Nb 5+ located within the hexagonal tungsten bronze (HTB) layers. Mossbauer spectroscopy shows that Fe 3+ preferentially fills the Ti split (C2) site, with secondary filling of the C1 site and no observable occupancy of the C3 site. This has been confirmed by neutron and resonant X-ray diffraction. Niobium has been found to occupy both the C1 and C3 sites with no evidence for occupancy of the C2 site.

Recent climate analyses indicate that average global temperature is rising and both global drought occurrence and precipitation intensity are increasing. The nature of climate change is unique to each location, and its impact, both positive and negative, is predicted to be widespread. One area to be potentially affected includes management and use of outdoor natural resources such as the Appalachian Trail (AT), a 3500 km continuous hiking trail in the eastern United States. Observed historical (1895-2008) and projected future (to 2099) seasonal temperature and precipitation trends were examined along the AT. The AT has generally warmed since 1895, with greater warming occurring more recently. The warming has been greatest in the northern part of the AT and during winter. Precipitation trends show wide spatial variation depending upon the season, but generally precipitation has increased more in the northern than southern AT. Temperature and precipitation are projected to increase for all regions during al...

Thin crystals of La 2 O 3 , LaAlO 3 , La 2/3 TiO 3 , La 2 TiO 5 , and La 2 Ti 2 O 7 have been irradiated in situ using 1 MeV Kr 2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La 2 O 3 remained crystalline to a fluence greater than 3.1×10 16 ions cm −2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline–amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation ( T c ) of 647 K for LaAlO 3 , 840 K for La 2 Ti 2 O 7 , 865 K for La 2/3 TiO 3 , and 1027 K for La 2 TiO 5 . The T c values observed in this study, together with previous data for Al 2 O 3 and TiO 2 , are discussed with reference to the melting points for the La 2 O 3 –Al 2 O 3 and La 2 O 3 –TiO 2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T c and melting temperature ( T m ) in the two systems. More complex relationships exist between T c and crystal structure, with the stoichiometric perovskite LaAlO 3 being the most resistant to amorphisation.

Thin crystals of rutile, brookite, anatase, and cassiterite were irradiated in situ in the transmission electron microscope using 1.0 MeV Kr ions at 50-300 K. Synthetic rutile and natural cassiterite, with 0.1-0.2 wt% impurities, remain crystalline up to a fluence of 5 x 10{sup 15} ions cm{sup -2} without evidence for amorphization at 50 K. Natural brookite and anatase, with 0.3-0.5 wt% impurities, become amorphous at fluences of 8.1 x 10{sup 14} and 2.3 x 10{sup 14} ions cm{sup -2}, respectively. We have also studied two natural rutile samples containing {approx}1.7 and 1.2 wt% impurities. These samples became amorphous at 9.2 x 10{sup 14} and 8.6 x 10{sup 14} ions cm{sup -2} at 50 K, respectively. Further analyses of the fluence-temperature data for natural brookite, rutile, and anatase give critical amorphization temperatures of 168 {+-} 11, 209 {+-} 8, and 242 {+-} 6 K, respectively. Results are briefly discussed with respect to several criteria for radiation resistance, including aspects of the structure, bonding, and energetics of defect formation and migration.

Polycrystalline synthetic samples of Y2Ti2−xSnxO7 with x = 0.4, 0.8, 1.2, and 1.6, together with Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, were irradiated in situ in the intermediate voltage electron microscope (IVEM)-Tandem Facility at Argonne National Laboratory using 1.0 MeV Kr ions at temperatures of 50 to 650 K. Determination of the critical amorphization fluence (Fc) as a function of temperature has revealed a dramatic increase in radiation tolerance with increasing Sn content on the pyrochlore B site. Nonlinear least-squares analysis of the fluence-temperature curves gave critical temperatures (Tc) of 666 ± 4, 335 ± 12, and 251 ± 51 K for the Y2Ti2−xSnxO7 samples with x = 0.4, 0.8, and 1.2, respectively. The sample with x = 1.6 appears to disorder to a defect fluorite structure at a fluence below 1.25 × 1015 ions cm−2 and remains crystalline to 5 × 1015 ions cm−2 at 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd2Zr1.2Ti0.8O7 and La1.6Y0.4Hf2O7, and ...

A reduction in interhemispheric connectivity is thought to contribute to the etiology of schizophrenia. Diffusion Tensor Imaging (DTI) measures the diffusion of water and can be used to describe the integrity of the corpus callosum white matter tracts, thereby providing information concerning possible interhemispheric connectivity abnormalities. Previous DTI studies in schizophrenia are inconsistent in reporting decreased Fractional Anisotropy (FA), a measure of anisotropic diffusion, within different portions of the corpus callosum. Moreover, none of these studies has investigated corpus callosum systematically, using anatomical subdivisions.DTI and structural MRI scans were obtained from 32 chronic schizophrenic subjects and 42 controls. Corpus callosum cross sectional area and its probabilistic subdivisions were determined automatically from structural MRI scans using a model based deformable contour segmentation. These subdivisions employ a previously generated probabilistic subdivision atlas, based on fiber tractography and anatomical lobe subdivision. The structural scan was then co-registered with the DTI scan and the anatomical corpus callosum subdivisions were propagated to the associated FA map.Results revealed decreased FA within parts of the corpus interconnecting frontal regions in schizophrenia compared with controls, but no significant changes for callosal fibers interconnecting parietal and temporo-occipital brain regions. In addition, integrity of the anterior corpus was statistically significantly correlated with negative as well as positive symptoms, while posterior measures correlated with positive symptoms only.This study provides quantitative evidence for a reduction of interhemispheric brain connectivity in schizophrenia, involving corpus callosum, and further points to frontal connections as possibly disrupted in schizophrenia.

Sampling protocols for ichthyofaunal inventories have received considerable study at the stream reach level; however, no studies have examined the optimal allocation of sampling effort for watershed-level inventories. To address this question, we used data from surveys of four Great Lakes watersheds to compare rates of species accumulation among several watershed-level scenarios of sampling effort allocation (sampling strategies). To allow for quantitative comparisons among strategies, we (1) divided each sampling site into smaller sampling units and separately recorded fish capture data at the smallest unit; (2) stratified the allocation of sampling effort throughout each watershed by stream order; and (3) recorded all sampling and travel costs (i.e., time spent on different tasks). We used a Monte Carlo simulation program to resample the data from each of the four watershed surveys and calculated rates of species accumulation. This technique allowed us to quantitatively compare sampling strateg...

Molecular dynamics simulations are used to study amorphisation resistance in the rutile, brookite and anatase polymorphs of titania. As an alternative to the traditional large-scale cascade calculation, small thermal spike simulations are used to quantify recrystallisation on the picosecond scale. In agreement with experiment, the thermal spikes in rutile recover completely (within 5 ps), remain largely intact in anatase, while brookite exhibits intermediate behaviour. Analysis of the annealing response shows that the thermal spike approach captures much of the cascade physics at a fraction of the computational cost, and in doing so provide insight into the radiation response process.

The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation–anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation–anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature.

Addressing landscape-level threats to stream fishes such as habitat and hydrological alterations requires adequate watershed-level species inventories. Where watershed-level ichthyofaunal surveys are prohibitively expensive, existing (historical) data sources may provide an option for compiling species lists. However, it is critical that managers consider potential biases or limitations of species lists compiled from existing data. Here we assess the suitability of species lists compiled from existing data sources for making watershed-level fish management and conservation decisions. For nine Great Lakes watersheds, we developed existing species lists by compiling all available federal and state agency and museum fish survey data. We then compared the size and species composition of existing species lists to current species lists compiled from intensive field surveys, conducted in 2002, of the same watersheds. Species lists compiled from commonly available existing data sources, such as state and federal agency and museum data, missed many species detected during our 2002 field surveys. In most watersheds, more than 10 species were missed (range 5-21) on existing lists. Sampling over multiple years and seasons increased the size of both current (field) and existing species lists. Existing species lists compiled from surveys conducted over multiple years and seasons included an average of 15 species not captured during the 2002 field surveys. However, such multiyear existing datasets are rare and not available for many watersheds. In addition, species lists compiled from older existing surveys (e.g., before 1984) did not accurately represent current species composition of the watersheds and our results indicate several apparent misidentifications or errors on these lists. Lastly, while most game species were detected on existing lists, migratory species and recently introduced species were commonly missed on these lists. We conclude with recommendations for using existing data for watershed-level stream fish management and conservation decisions.

Garnets, A3B2C3O12, are an important group of minerals and have potential uses in the safe immobilisation of high-level nuclear waste. They have been found naturally to incorporate Zr, Ti and Fe, three elements of interest in the safe storage of nuclear waste. Kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, is a naturally occurring garnet that contains Zr in a high percentagenot, vert, similar30 wt%. For such a material to be of potential immobilisation for nuclear waste the structure needs to be completely understood. Electron channelling studies have shown that the Zr/Ti cations are located on the Y-site, with the Al/Fe cations located on the Z-site. This work has investigated synthetic analogues of kimzeyite, Ca3(Zr,Hf)2(Al,Fe,Si)3O12, by neutron powder diffraction, using the C2 spectrometer at the Chalk River nuclear facility, coupled with 57Fe Mossbauer spectroscopy. Such work has allowed the structure of the synthetic material to be determined along with the distribution of cations across the X (CN=8), Y (CN=6), and Z (CN=4) sites. Results have shown that it is possible to synthesise Ca3(Zr,Hf)2(Al,Fe,Si)3O12 with a range of Al/Fe ratios containing Zr and Hf. The Mossbauer data has indicated the Fe is located on the Z site. The structural analyses show that the unit cell changes linearly as a function of composition, and analysis of the disorder indicates that the Zr, Hf reside on the Y site and the Al, Fe, and Si reside on the Z site.

We have characterized thermally annealed perovskite (CaTiO3) surfaces, both before and after aqueous dissolution testing, using scanning electron microscopy, cross-sectional transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. It was shown that mechanical damage caused by polishing was essentially removed at the CaTiO3 surface by subsequent annealing; such annealed samples were used to study the intrinsic dissolution behavior of perovskite in deionized water at RT, 90 °C, and 150 °C. Our results indicate that, although mechanical damage caused higher Ca release initially, it did not affect the long-term Ca dissolution rate. However, the removal of surface damage by annealing did lead to the subsequent spatial ordering of the alteration product, which was identified as anatase (TiO2) by both x-ray and electron diffraction, on CaTiO3 surfaces after dissolution testing at150 °C. The effect of Ca2+ in the leachant on the dissolution reaction of perovskite at 150 °C was also investigated, and the results suggest that under repository conditions, the release of Ca from perovskite is likely to be significantly slower if Ca2+ is present in ground water.

Accurate assessments of watershed-level species composition are necessary for comparative ecological studies, ecosystem health assessments, monitoring, and aquatic conservation prioritization. Several studies have addressed sampling effort requirements for characterizing fish species composition at a section of stream, but none have examined watershed-level requirements. In the spring and summer of 2002, we extensively sampled nine Great Lakes watersheds to assess sampling-effort requirements. Sampling requirements increased with the targeted percentage of estimated species richness. Sampling 15–119 randomly selected reaches of stream, stratified by stream order, was on average sufficient to detect 80%–100% of estimated species richness. Watershed size (km2) and estimated species richness each showed a weak, negative correlation with sampling-effort requirements in our study streams, with Pearson's correlation coefficients of –5.06 and –0.590, respectively. Because of among-watershed variability in sampling effort requirements, field crews should plot species accumulation curves onsite to determine adequate inventory completion. Based on the difficulty of detecting the last 10% of species, random sampling should be conducted in conjunction with targeted sampling of rare species.

In this study, the valence states of uranium in synthetic and natural brannerite samples were studied using a combination of transmission electron microscopy-electron energy loss spectroscopy, scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) techniques. We used a set of five (UO2, CaUO4, SrCa2UO6, UTi2O6, and Y0.5U0.5Ti2O6) U standard samples, including two synthetic brannerites, to calibrate the EELS branching ratio, M5/(M4 +M5), against the number of f electrons. The EELS data were collected at liquid nitrogen temperature in order to minimise the effects of electron beam reduction of U6+ and U5+. Test samples consisted of three additional synthetic brannerites (Th0.7U0.3Ti2O6, Ca0.2U0.8Ti2O6, and Th0.55U0.3Ca0.15Ti2O6) and three natural brannerites from different localities. The natural brannerite samples are all completely amorphous, due to cumulative alpha decay events over geological time periods (24–508 Ma). Our U valence calibration results are in reasonable agreement with previous work, suggesting possibly a non-linear relationship between the branching ratio and the number of f electrons (and hence the average valence state) of U in solids. We found excellent agreement between the nominal valence states of U and the average valence states determined directly by EELS and estimated by EDX analysis (with assumptions regarding stoichiometry) in two of the three synthetic brannerite test samples. The average U oxidation states of the five synthetic brannerite samples, as derived from XPS analyses, are also in good agreement with those determined by other techniques. The average valence states of U in three amorphous (metamict) natural brannerite samples with alpha decay doses ranging from 3.6×1016 to 6.9×1017 α/mg were found to be 4.4, 4.7, and 4.8, consistent with the presence of U5+ and/or U6+ as well as U4+ in these samples. These results are in general agreement with previous wet chemical analyses of natural brannerite. However, the average valence states inferred by SEM-EDX for two of the natural brannerite samples do not show satisfactory agreement with the EELS determined valence. This may be due to the occurrence of OH− groups, cation vacancies, anion vacancies, or excess oxygen in the radiation-damaged structure of natural brannerite.

High angular resolution electron channelling X-ray spectroscopy (HARECXS) was used to monitor the intensity ratio of Ca Kα/Ti Kα X-rays emitted by perovskite (CaTiO3) as a function of incident electron beam orientation. The collected HARECXS data suggest that the displacement energies of calcium and titanium in perovskite (CaTiO3) are 82 ± 11 eV and 69 ± 9 eV, respectively. These values are approximately 40% larger than those currently used to convert ion doses applied to oxides into dpa using SRIM.

Synthetic samples of the pyrochlores La2Zr2O7 and La2Hf2O7 were irradiated in situ in the intermediate voltage electron microscope (IVEM-Tandem Facility) at Argonne National Laboratory using 1.0 MeV Kr2+. Results of this study demonstrate that both pyrochlores pass through the crystalline–amorphous transformation albeit with significantly different critical amorphization dose curves. The critical dose values extrapolated to 0 K (Dc0) are 11 ± 3 × 1014 ions cm−2 ( dpa) for La2Zr2O7 and 5.5 ± 0.7 × 1014 ions cm−2 ( dpa) for La2Hf2O7. Non-linear least squares analysis of the dose–temperature curves gave values of the critical temperature (Tc) of 339 ± 49 K for La2Zr2O7 and 563 ± 10 K for La2Hf2O7. This analysis also gave values of the activation energy (Ea) for thermal recovery of damage of 0.02 ± 0.01 and 0.05 ± 0.01 eV for the zirconium pyrochlore and the hafnium pyrochlore, respectively. These results demonstrate that there is a major difference in the dose–temperature response dependent upon the nature of the B-site cation of these two pyrochlores. Results are discussed in terms of the pyrochlore structural parameters rA/rB and x(48f) as well as the stopping powers, displacement energies, and defect energies of the materials.

New weberite-type Ca 2 Ta 2 O 7 and zirconolite-type CaZrTi 2 O 7 polytypes have been prepared by doping with Nd/Zr and Th/Al, respectively, and their structures have been refined using single-crystal X-ray diffraction intensity data. The 3T zirconolite polytype, Ca 0.8 Ti 1.35 Zr 1.3 Th 0.15 Al 0.4 O 7 , has a =7.228(1), c =16.805(1) A. The 3T weberite-type polytype, Ca 1.92 Ta 1.92 Nd 0.08 Zr 0.08 O 7 , has a =7.356(1), c =18.116(1) A. Both 3T polytypes have space group P 3 1 21, Z =6. The 4M Ca 2 Ta 2 O 7 polytype has the same composition, from electron microprobe analyses, as the 3T polytype, and has cell parameters: a =12.761(1), b =7.358(1), c =24.565(1) A, β =100.17(1)°, space group C 2, Z =16. The structural relationships between the different zirconolite and weberite polytypes are discussed. A consideration of the structures from the viewpoint of anion-centered tetrahedral arrays shows that zirconolite can be considered as an anion-deficient fluorite derivative phase. However, the fluorite-type topology of edge-shared O M 4 tetrahedra is not maintained in the Ca 2 Ta 2 O 7 weberite-type polytypes, even though they have a fluorite-like fcc packing of metal atoms. One of the oxygen atoms moves from a tetrahedral Ta 3 Ca interstice to an adjacent Ta 2 Ca 4 octahedral interstice in the weberite polytypes.

Optical emission spectra in the 300–700 nm range were collected from four perovskite-structured materials (CaTiO 3 , SrTiO 3 , BaTiO 3 and CaZrO 3 ), a pyrochlore-structured material (La 2 Zr 2 O 7 ) and zirconolite (CaZrTi 2 O 7 ), using either a Febetron 706 variable energy pulsed-electron-beam generator (pulse duration 3 ns) or a Vickers pulsed-electron LINAC (pulse duration 0.5 μs). The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ∼100 nm) bands centred around ∼400 nm. For the CaZrO 3 , La 2 Zr 2 O 7 and CaZrTi 2 O 7 samples, the emission intensity per unit dose was also measured as a function of electron beam energy over the range 0.2–0.6 MeV. The data for all three samples suggest a single stage dependence on electron beam energy. CaZrO 3 , La 2 Zr 2 O 7 , and CaZrTi 2 O 7 have emission thresholds of 0.28 ± 0.03, 0.27 ± 0.03, and 0.26 ± 0.03 MeV respectively, which give oxygen displacement values of 49 ± 5, 47 ± 5, and 45 ± 5 eV respectively. Data collected in this study are discussed in the context of previously measured and calculated oxygen displacement values.

This paper presents the results of a combined electron microprobe and analytical TEM study that describes the chemical and structural characteristics of non-metamict zirconolite from a volcanic ejectum collected within a pyroclastic formation of the Vico volcanic complex, near Tre Croci Community, Latium (Italy). The host rock is a foid-bearing alkali-syenite and consists of potassium-feldspar and plagioclase, with minor biotite, titanite, clinopyroxene and magnetite. Sodalite occurs as well-faceted crystals inside miarolitic cavities between intersecting feldspars and it is variably altered to a kaolinite-like product. Accessory minerals include zircon, baddeleyite, stillwellite, hellandite, fluorite, apatite and monazite. Zirconolite occurs both as elongated acicular crystals of orthorhombic symmetry (zirconolite-3 O ), space group Acam, with (in A) a = 10.13(1), b = 14.16(1) and c = 7.288(2), and as pseudo-hexagonal platy crystals of trigonal symmetry (zirconolite-3 T ), space group P 3 1 2, with a = 7.279(2) and c = 16.89(2). TEM studies revealed additionally the presence of polytype zirconolite-2 M in a subset of grains analyzed. Zirconolite displays pronounced compositional zoning, observed in backscattered electron images, resulting mainly from an antipathetic variation in the actinide elements (Th + U) and REE contents. Analytical TEM results indicate compositional differences exist between the zirconolite-3 T and zirconolite-2 M polytypes. Zirconolite, and associated accessory REE, Th, U minerals crystallized after the formation of the major rock-forming minerals of the ejectum, from metasomatic fluids rich in F and P.

Several natural and synthetic samples of pyrochlore, columbite, and brannerite were irradiated in situ in the high voltage electron microscope at Argonne National Laboratory using 1.5 MeV Kr+ ions at room temperature. The columbite samples were selected because they have the same stoichiometry as brannerite and they exhibit a range of cation order prior to irradiation. The results of this study demonstrate that all the samples pass through the crystalline–amorphous transformation at a relatively low ion dose. For the AB2O6 oxides, Dc ranges from 0.8 to 1.5×1014 ions cm−2, with little difference between the columbite and brannerite structure types. Within the group of columbite samples, there appears to be a systematic trend of increasing critical dose with increasing order parameter, although the critical doses are essentially within error of one another. Ordered columbites do not appear to revert to the subcell upon irradiation. The brannerite data set indicates a possible correlation between Dc and the mean atomic number of the A-site cation. The results for the two natural pyrochlores gave a slightly higher range of doses compared with the AB2O6 oxides. The pyrochlore data set indicates a possible correlation between Dc and the mean atomic number of the B-site cation. Electron diffraction results also suggest that the pyrochlore compositions irradiated in this work may not transform to the fluorite subcell until just before Dc is reached, if at all. For comparison, the samples investigated in this work have Dc values at room temperature that are generally on the low side of the range of values previously reported for synthetic zirconolite and pyrochlore samples (2–6×1014 ions cm −2 ) under similar irradiation conditions.

Optical emission spectra in the 300–700 nm range were collected from single crystal CaTiO 3 , SrTiO 3 and BaTiO 3 , and polycrystalline CaTiO 3 samples, that were irradiated at room temperature using a Febetron 706 variable energy pulsed-electron-beam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ∼100 nm) bands centred around 380, 425, and 445 nm for CaTiO 3 , SrTiO 3 and BaTiO 3 , respectively. These emission bands are similar to cathodoluminescence emissions from 25 keV electron irradiation attributed by others to direct conduction-valence band transitions in unreduced samples and oxygen vacancies in reduced samples. CaTiO 3 , SrTiO 3 and BaTiO 3 all have emission thresholds of 0.26±0.02 MeV. This corresponds to a threshold displacement energy for oxygen, E d of 45±4 eV.

Using the HVEM-tandem facility at Argonne National Laboratory, the critical dose of 1.5 MeV Kr + ions for amorphisation of freudenbergite ( D c (freudenbergite)) at room temperature was found to be 1.6±0.3×10 18 ions m −2 . D c (freudenbergite) is lower than D c (zirconolite) and D c (perovskite) (3.5–5.5 and 3.9–9.2 × 10 18 ion m −2 , respectively). Freudenbergite can occur in Synroc-C, a titanate wasteform designed for immobilising high level radioactive waste (HLW). In Synroc-C, zirconolite and perovskite will contain the majority of the actinides in HLW. Freudenbergite will contain less than 0.2 wt% actinides but will experience displacement damage due to the alpha decay of actinides in surrounding phases. In agreement with the experimental findings of previous authors, our calculations show that in Synroc-C, freudenbergite will remain crystalline after zirconolite and perovskite have become amorphous. Neither of the two current parameters (structural freedom, f or susceptibility to amorphisation, S ) for estimating the relative radiation resistance of different phases is capable of predicting the relative radiation resistance of freudenbergite, zirconolite and perovskite. The low D c of freudenbergite may result from Na + ions having significantly lower E d values compared to the other elements in freudenbergite, zirconolite and perovskite, in the electric fields induced by heavy ion irradiation of TEM specimens. If this hypothesis is true, it challenges the assumption that heavy ion irradiation can be used to compare the relative radiation resistance of different phases and will have serious implications for the predictive parameters of radiation resistance.

Words appear to be stored in memory in syllabic units that adhere to the phonology and morphology of the language (e.g., Marslen-Wilson, Tyler, Waksler, & Older, 1994; Treiman & Danis, 1988a). Three experiments investigated the formation of the syllabic representation of words using the structural induction phoneme monitoring paradigm in which stimulus lists are disproportionately weighted with words of one syllabic structure. In Experiment 1, two phonological principles of syllabification were compared to determine if one (maximum onset principle) might take precedence over the other (phonotactic illegality) during the formation of the initial structural representation of a word. Results suggest that phonotactic legality overrides the maximum onset principle. In Experiments 2 and 3, phonological and morphological parsings were pitted against each other to determine whether morphological influences in syllabification could be found as early as phonological influences. Results demonstrated that phonology, not morphology, guided syllabification. Experiment 4 demonstrated that the null effects of morphology were likely due to the stage of processing being tapped by the induction paradigm. Findings suggest that the formation of syllabic structure is guided by phonology prior to morphology.

The relative radiation resistance of the structures of zirconolite, pyrochlore and perovksite were investigated by in situ transmission electron microscopy using 1.5 MeV Kr+ ions in the HVEM-Tandem User Facility, at Argonne National Laboratory. A suite of six fabricated zirconolites, one fabricated pyrochlore and one natural perovskite was used. Damage accumulation essentially occurs in the same way in all three phases and is revealed by the following changes in SAD patterns: weakening of superlattice Bragg diffraction maxima, appearance of diffuse rings which increase in intensity with dose, disappearance of superlattice or other specific classes of maxima, and disappearance of remaining sublattice maxima leaving only diffuse rings. The average critical doses for amorphisation (Dc) for all the zirconolites (undoped, Nd-doped, U-doped and Th-doped) and the pyrochlore in this study varied by a factor of ∼ 2 (from 3.5 to 6.1 × 1018 ions m−2). No correlations were observed between Dc and the atomic weight of dopants in zirconolite or the mean atomic weight of the sample. The Dc value at room temperature of perovksite was found to be 1.8 × 1019 ions m−2, 3–5 times the Dc values for zirconolite. This observation is in line with what one expects from the topologic and chemical complexity of the two phases and is compared with the results of previous authors. Preliminary assessment was made of EELS as a tool for monitoring radiation damage.

The structure of a new polytype of zirconolite, zirconolite-4M, has been determined using X-ray and neutron powder diffraction, high resolution transmission electron microscopy, and selected area electron diffraction. Zirconolite-4M occurs when zirconolite is doped with 0.5–0.8 Nd per formula unit. Its structure consists of four hexagonal tungsten bronze (HTB) type layers interleaved alternately with layers of Ca, Zr polyhedra (as in zirconolite-2M) and Ca, Ti polyhedra (as in pyrochlore). Nd substitutes on the Ca and Zr sites. The compositions of the zirconolites were determined using an extrapolation technique based on an analysis of the impurity lines in the diffraction pattern. Cation site occupancies were determined with composition constraints applied and these were consistent with the expected zirconolite-4M cation site occupancies. Observed zirconolite-4M lattice parameters correlated with expected values for a zirconolite and pyrochlore type stacking sequence.

An AEM ratio technique for the analysis of 25 elements in finely zoned natural zirconolite was used in conjunction with electron diffraction and imaging techniques to examine the effects of alpha-decay damage on zirconolites from Bergell, Switzerland-Italy and Adamello, northern Italy. Comparison of AEM and EPMA results confirms that the AFM technique can be used to obtain accurate information on the chemical formula of zirconolite. The TEM images and diffraction patterns in this study are analogous to those of previous authors. They support the proposition that radiation damage ingrowth can be adequately described by the accumulation and overlap of isolated alpha-recoil collision cascades, producing progressively larger amorphous domains. Careful determination of Th and U contents by AEM gives an accurate indication of the dose range of the crystalline-amorphous transformation. For the samples from Bergell and Adamello, the transformation occurs over a dose range of 0.05 × 10 16 to just over 1 × 10 16 a/mg, consistent with studies of synthetic zirconolite doped with 238 Pu or 244 Cm. The Bergell zirconolites all exhibited diffraction patterns characteristic of the zirconolite-2M. Those grains containing REE and Th+U contents up to ≈0.1 and ≈0.03 atoms per formula unit, respectively, exhibit a high level of crystallographic perfection. While those grains containing ≈0.2 REE and 0.06 Th+U atoms per formula unit, exhibit twinning and stacking disorder.

Word production was examined in four aphasics diagnosed acutely with neologistic jargon and who displayed impairment to the lexical stage of phonological production (Kohn & Smith, 1993, 1994a). To investigate the major source of their nonword errors (i.e., neologisms, phonemic paraphasias), single word production was tested at three different times over the first 6 months postonset, with one subject receiving additional testing at 14 months postonset. Two subjects showed signs of recovery to the phonological output system with respect to: (1) improved word production scores, (2) increased frequency of phonemic paraphasias versus neologisms, and (3) increased production of target phonemes. These subjects also displayed above-chance production of target phonemes and no significant tendency to perseverate phonemes across picture-naming trials. It was argued that this pattern reflects a resolving disturbance in retrieving entries from the phonological lexicon. The other two subjects showed no improvement in word production. They also consistently produced target phonemes at chance levels and had a tendency to perseverate phonemes across picture-naming trials. This static pattern of performance was considered to reflect loss of information from the phonological lexicon. The neuroanatomical damage sustained by each case was consistent with these two recovery patterns.

This study addresses how fluent aphasics construct complete phonological representations, given the premise that their phonological speech errors result from faulty information about stored lexical representations. We explored whether consonant harmony, a common rule-governed process of feature copying, operates as a compensatory device for completing phonological representations in fluent aphasia. This was examined in a corpus of phonemic paraphasias (n = 543) produced by 8 fluent aphasics during picture naming. Consonant substitutions due to a single feature change (n = 143) were analyzed for the properties of consonant harmony predicted by the phonological principles embodied in a Universal Markedness version of Underspecification Theory (e.g., Chomsky and Halle, 1968). Results indicated that harmony constrained the feature substitution errors involving the feature class of voice (e.g., calendar-->/[symbol: see text]/), but not place of articulation (e.g., igloo-->/idlu/); substitutions due to an error in manner were rare. These findings were used to argue that for English-speaking fluent aphasics a consonant harmony rule for the feature voice is incorporated into a compensatory output mechanism that is used to complete faulty lexical-phonological representations.

AEM techniques employing digital filtering, least squares profile fitting, and experimental k-factor calibrations were used to investigate 16 Synroc samples containing simulated Purex (PW-4b-D) HLW at loadings of 10, 15, 19, and 23 wt%. A second group of Synroc samples with 10 wt% HLW also contained additional impurities of F, Na, MgO, P2O5, and Fe2O3. A third set of samples with 10 wt% HLW contained different metal additions of Al, Ni, and Ti, and a sample with no metal addition for comparison. In samples with low Na2O content, it was confirmed that element partitioning is mainly controlled by the ionic radius criterion, with smaller Y, Gd, and U ions having a preference for zirconolite and the larger Ce and Nd ions favoring perovskite. Average relative partitioning coefficients ( D Z P = metal oxide in zirconolite ÷ wt% metal oxide in perovskite ) of 8 samples with 10 wt% HLW and -∼0.5 wt% Na2O are 0.14 ± 0.01, 0.39 ± 0.03, 1.7 ± 0.2, 3.8 ± 1.0, and 2.2 ± 0.8 for Ce, Nd, Gd, Y, and U, respectively. Element partitioning is not strongly affected by additional impurities of F, MgO, P2O5, or Fe2O3; metal addition; or waste loading. Additions of up to ∼3.6 wt% Na2O lead to an increase in the amount of perovskite at the expense of zirconolite as well as a systematic shift in the partitioning of REEs and U from zirconolite into perovskite.

This study investigates the stage of word production during which the full phonemic specification of a word is developed from a more abstract stored form. We tested the proposal that this stage (i.e. phonemic planning) operates from left to right in accordance with the basic syllabic structure of the stored phonological representation. According to our production model, if phonemic planning were disrupted, evidence of such serial processing would involve the production of word-initial fragments and an increase in segmental errors across successive syllables in a word. To test the above proposal, and to determine whether the serial properties are unique to the phonemic stage, we compared the word production of three aphasics with impaired phonemic planning to that of three aphasics with impairment earlier in the system, at the level of activating the stored phonological representations on which phonemic planning operates. While both groups of subjects tended to preserve word onsets in their target...

The production of neologisms in fluent aphasia has been linked to both anomia and impaired phonological processing, but the supportive data are minimal. The current study uses longitudinal data to explore these explanations in an aphasic with acute neologistic jargon and severe word-finding difficulty (VN). Picture naming, conversation, and complex picture description were evaluated at 3 days, 6 weeks, 3 months, and 5 months post onset. Results were interpreted with respect to predictions based on a word-production model that associates anomia with breakdown in locating entries in the phonological lexicon and neologisms with impaired activation of these entries. VN's picture naming indicated disruption of both locating and activating stored phonological representations. Longitudinal changes helped to specify the source of his anomia, and to rule out this deficit as the source of his neologisms.