508 research outputs found
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Dislocation imaging of an InAlGaAs opto-electronic modulator using IBICC
This paper presents ion beam induced charge collection (IBICC) contrast images showing regions of differing charge collection efficiency within optoelectronic modulator devices. The experiments were carried out at the Sandia nuclear microprobe using 18 MeV carbon and 2 MeV helium ions. Lines of varying densities are observed to run along the different {l_brace}110{r_brace} directions which correlate with misfit dislocations within the 392nm thick strained layer superlattice quantum well of the modulator structure. Independent cross-sectional TEM studies and the electrical properties of the devices under investigation suggest the presence of threading dislocations in the active device region at a density of {approximately} 10{sup 6} cm{sup {minus}2}. However, no clear evidence of threading dislocations was observed in the IBICC images as they are possibly masked by the strong contrast of the misfit dislocations. Charge carrier transport within the modulator is used to explain the observed contrast. The different signal to noise levels and rates of damage of the incident ions are assessed
volumetric characterisation and correlation to established classification systems
Objective and sensitive assessment of cartilage repair outcomes lacks suitable
methods. This study investigated the feasibility of 3D ultrasound
biomicroscopy (UBM) to quantify cartilage repair outcomes volumetrically and
their correlation with established classification systems. 32 sheep underwent
bilateral treatment of a focal cartilage defect. One or two years post-
operatively the repair outcomes were assessed and scored macroscopically
(Outerbridge, ICRS-CRA), by magnetic resonance imaging (MRI, MOCART), and
histopathology (O'Driscoll, ICRS-I and ICRS-II). The UBM data were acquired
after MRI and used to reconstruct the shape of the initial cartilage layer,
enabling the estimation of the initial cartilage thickness and defect volume
as well as volumetric parameters for defect filling, repair tissue, bone loss
and bone overgrowth. The quantification of the repair outcomes revealed high
variations in the initial thickness of the cartilage layer, indicating the
need for cartilage thickness estimation before creating a defect. Furthermore,
highly significant correlations were found for the defect filling estimated
from UBM to the established classification systems. 3D visualisation of the
repair regions showed highly variable morphology within single samples. This
raises the question as to whether macroscopic, MRI and histopathological
scoring provide sufficient reliability. The biases of the individual methods
will be discussed within this context. UBM was shown to be a feasible tool to
evaluate cartilage repair outcomes, whereby the most important objective
parameter is the defect filling. Translation of UBM into arthroscopic or
transcutaneous ultrasound examinations would allow non-destructive and
objective follow-up of individual patients and better comparison between the
results of clinical trials
An evaluation of Deccan Traps eruption rates using geochronologic data
Recent attempts to establish the eruptive history of the Deccan Traps large igneous province have used both U−Pb (Schoene et al., 2019) and
40Ar/39Ar (Sprain et al., 2019) geochronology. Both of these studies report dates with high precision and unprecedented coverage
for a large igneous province and agree that the main phase of eruptions began near the C30n–C29r magnetic reversal and waned shortly after the
C29r–C29n reversal, totaling ∼ 700–800 kyr duration. These datasets can be analyzed in finer detail to determine eruption rates, which
are critical for connecting volcanism, associated volatile emissions, and any potential effects on the Earth's climate before and after the
Cretaceous–Paleogene boundary (KPB). It is our observation that the community has frequently misinterpreted how the eruption rates derived from
these two datasets vary across the KPB. The U−Pb dataset of Schoene et al. (2019) was interpreted by those authors to indicate four major
eruptive pulses before and after the KPB. The 40Ar/39Ar dataset did not identify such pulses and has been largely interpreted by
the community to indicate an increase in eruption rates coincident with the Chicxulub impact (Renne et al., 2015; Richards et al., 2015). Although
the overall agreement in eruption duration is an achievement for geochronology, it is important to clarify the limitations in comparing the two
datasets and to highlight paths toward achieving higher-resolution eruption models for the Deccan Traps and for other large igneous provinces. Here,
we generate chronostratigraphic models for both datasets using the same statistical techniques and show that the two datasets agree very well. More
specifically, we infer that (1)Â age modeling of the 40Ar/39Ar dataset results in constant eruption rates with relatively large
uncertainties through the duration of the Deccan Traps eruptions and provides no support for (or evidence against) the pulses identified by the
U−Pb data, (2) the stratigraphic positions of the Chicxulub impact using the 40Ar/39Ar and U−Pb datasets do not
agree within their uncertainties, and (3)Â neither dataset supports the notion of an increase in eruption rate as a result of the Chicxulub
impact. We then discuss the importance of systematic uncertainties between the dating methods that challenge direct comparisons between them, and we
highlight the geologic uncertainties, such as regional stratigraphic correlations, that need to be tested to ensure the accuracy of eruption
models. While the production of precise and accurate geochronologic data is of course essential to studies of Earth history, our analysis
underscores that the accuracy of a final result is also critically dependent on how such data are interpreted and presented to the broader community
of geoscientists.</p
Geochronological and geochemical effects of zircon chemical abrasion: insights from single-crystal stepwise dissolution experiments
Chemical abrasion in hydrofluoric acid (HF) is routinely applied to zircon grains prior to U–Pb dating by isotope dilution thermal ionization mass spectrometry (ID-TIMS) to remove radiation-damaged portions of grains affected by Pb loss. Still, many chemically abraded datasets exhibit evidence of residual Pb loss. Here we test how the temperature and duration of chemical abrasion affect zircon U–Pb and trace element systematics in a series of 4 h, single-crystal stepwise dissolution experiments at 180 and 210 ∘C. Microtextural data for the zircon samples studied are presented in a companion paper by McKanna et al. (2023). We find that stepwise dissolution at 210 ∘C is more effective at eliminating material affected by open-system behavior and enriched in U, common Pb (Pbc), and light rare earth elements (LREEs); reduces the presence of leaching-induced artifacts that manifest as reverse discordance; and produces more consistent and concordant results in zircon from the three rocks studied. We estimate that stepwise dissolution in three 4 h steps is roughly equivalent to a single ∼ 8 h leaching step due to the insulating properties of the PTFE sleeve in the Parr pressure dissolution vessel, whereas traditionally labs utilize a single 12 h leaching step. We conclude that a single 8 h leaching step at 210 ∘C should remove Pb loss effects in the majority of zircon and that this can be used as an effective approach for routine analysis. Further, we calculate time-integrated alpha doses for leachates and residues from measured radionuclide concentrations to investigate (1) the alpha dose of the material dissolved under the two leaching conditions and (2) the apparent minimum alpha dose required for Pb loss susceptibility: ≥ 6×1017 α g−1.</p
Quantitative ultrasound biomicroscopy for the analysis of healthy and repair cartilage tissue
The increasing spectrum of different cartilage repair strategies requires the introduction of adequate non-destructive methods to analyse their outcome in-vivo, i.e. arthroscopically. The validity of non-destructive quantitative ultrasound biomicroscopy (UBM) was investigated in knee joints of five miniature pigs. After 12 weeks, six 5-mm defects, treated with different cartilage repair approaches, provided tissues with different structural qualities. Healthy articular cartilage from each contralateral unoperated knee joint served as a control. The reflected and backscattered ultrasound signals were processed to estimate the integrated reflection coefficient (IRC) and apparent integrated backscatter (AIB) parameters. The cartilage repair tissues were additionally assessed biomechanically by cyclic indentation, histomorphologically and immunohistochemically. UBM allowed high-resolution visualisation of the structure of the joint surface and subchondral bone plate, as well as determination of the cartilage thickness and demonstrated distinct differences between healthy cartilage and the different repair cartilage tissues with significant higher IRC values and a steeper negative slope of the depth-dependent backscatter amplitude AIBslope for healthy cartilage. Multimodal analyses revealed associations between IRC and the indentation stiffness. Furthermore, AIBslope and AIB at the cartilage-bone boundary (AIBdC) were associated with the quality of the repair matrices and the subchondral bone plate, respectively. This ex-vivo pilot study confirms that UBM can provide detailed imaging of articular cartilage and the subchondral bone interface also in repaired cartilage defects, and furthermore, contributes in certain aspects to a basal functional characterization of various forms of cartilage repair tissues. UBM could be further established to be applied arthroscopically in-vivo
Hamstring stretch reflex:could it be a reproducible objective measure of functional knee stability?"
Background: The anterior cruciate ligament (ACL) plays an important role in anterior knee stability by preventing anterior translation of the tibia on the femur. Rapid translation of the tibia with respect to the femur produces an ACL-hamstring stretch reflex which may provide an object measure of neuromuscular function following ACL injury or reconstruction. The aim of this study was to determine if the ACL-hamstring stretch reflex could be reliably and consistently obtained using the KT-2000 arthrometer. Methods: A KT-2000 arthrometer was used to translate the tibia on the femur while recording the electromyography over the biceps femoris muscle in 20 participants, all with intact ACLs. In addition, a sub-group comprising 4 patients undergoing a knee arthroscopy for meniscal pathology, were tested before and after anaesthetic and with direct traction on the ACL during arthroscopy. The remaining 16 participants underwent testing to elicit the reflex using the KT-2000 only. Results: A total number of 182 trials were performed from which 70 trials elicited stretch reflex (38.5 %). The mean onset latency of the hamstring stretch reflexes was 58.9 ± 17.9 ms. The average pull force was 195 ± 47 N, stretch velocity 48 ± 35 mm/s and rate of force 19.7 ± 6.4 N/s. Conclusions Based on these results, we concluded that the response rate of the anterior cruciate ligament-hamstring reflex is too low for it to be reliably used in a clinical setting, and thus would have limited value in assessing the return of neuromuscular function following ACL injuries
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HRTEM of extended defects in Tl-2212 thin films
Many applications of high temperature superconductors, HTS, require the presence of lattice defects in the material structure to suppress the motion of magnetic vortices and enhance the critical current density, J{sub c}. The microstructure of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8{minus}{delta}} (Tl-2212) thin films which have extended defects induced by high energy Au and Cu ion irradiation is studied using high resolution transmission electron microscopy, HRTEM, with slow scan digital imaging. In order to optimize the HTS properties and better analyze the consequent microstructural modification, the fluence is varied. At moderate fluences, resulting in {approximately}4% reduction of the superconducting transition, large enhancements of J{sub c} and vortex pinning potential are observed. The density and microstructure of isolated defects and surrounding structure will be discussed and compared to damage profiles calculated using the TRIM code. Correlation will be made between the HRTEM results and the changes in HTS properties
Chemical abrasion: the mechanics of zircon dissolution
Chemical abrasion is a technique that combines thermal annealing and partial
dissolution in hydrofluoric acid (HF) to selectively remove
radiation-damaged portions of zircon crystals prior to U–Pb isotopic
analysis, and it is applied ubiquitously to zircon prior to U–Pb isotope
dilution thermal ionization mass spectrometry (ID-TIMS). The mechanics of
zircon dissolution in HF and the impact of different leaching conditions on
the zircon structure, however, are poorly resolved. We present a
microstructural investigation that integrates microscale X-ray computed
tomography (µCT), scanning electron microscopy, and Raman
spectroscopy to evaluate zircon dissolution in HF. We show that µCT
is an effective tool for imaging metamictization and complex dissolution
networks in three dimensions. Acid frequently reaches crystal interiors via
fractures spatially associated with radiation damage zoning and inclusions
to dissolve soluble high-U zones, some inclusions, and material around
fractures, leaving behind a more crystalline zircon residue. Other acid paths
to crystal cores include the dissolution of surface-reaching inclusions and
the percolation of acid across zones with high defect densities. In highly
crystalline samples dissolution is crystallographically controlled with
dissolution proceeding almost exclusively along the c axis. Increasing the
leaching temperature from 180 to 210 ∘C results in
deeper etching textures, wider acid paths, more complex internal dissolution
networks, and greater volume losses. How a grain dissolves strongly depends
on its initial radiation damage content and defect distribution as well as
the size and position of inclusions. As such, the effectiveness of any
chemical abrasion protocol for ID-TIMS U–Pb geochronology is likely
sample-dependent. We also briefly discuss the implications of our findings
for deep-time (U-Th)/He thermochronology.</p
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