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Luminescent coupling (LC) is a key phenomenon in monolithic tandem solar cells. This study presents a nondestructive technique to quantitatively evaluate the LC effect, addressing a gap in the existing predictions made by optical modeling. The method involves measuring the ratio of photons emitted from the high bandgap top cell that escape through the rear, contributing additional current to the bottom cell, and to those escaping from the front side of top cell. The findings indicate that in the analyzed monolithic perovskite/silicon tandem solar cells, more than 85% of the emitted photons escaping from the perovskite top cell are used to generate additional current in the bottom cell. This process notably reduces the mismatch in the generated current between each subcell, particularly when the current is limited by the low bandgap subcell. The presented method is applicable to a variety of monolithic tandem structures, providing vital information for subcell characterization, providing vital information for predicting energy output and optimization for outdoor applications.
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BACKGROUND: The first generation of titanium nitride (TiN) coatings for orthopaedic implants was clinically introduced in the 1990s because of their promising biocompatibility, wear resistance, and corrosion resistance. This study evaluated the in vivo performance of early TiN-coated knee and hip implants, focusing on the bearing surfaces and mechanisms of in vivo damage. METHODS: There were 13 TiN-coated implants (5 knee and 8 hip) retrieved from 8 patients as part of a multi-institutional implant retrieval program. The average implantation time was 4.25 years for knees and 17.5 years for hips. Implant revisions occurred for various reasons, including polyethylene wear, loosening, pain, infection, and instability. Components were examined using a semiquantitative scoring method, and surface roughness measurements were performed using white-light interferometry. Surface morphology, chemistry, and particle characterization were also assessed by scanning electron microscopy. RESULTS: For hips, mild corrosion was found on femoral head tapers, along with severe scratching on certain femoral heads. Knee implants exhibited low burnishing and scratching for both mechanisms. Roughness measurements (Sa) were 37.3 nm (interquartile range = 22.0 to 62.4) for hips and 85.3 nm (interquartile range = 66.3 to 110) for knees. The observed scratch depth in both hip and knee implants due to third-body particles ranged from 0.3 to 1.3 µm. The coating coverage remained intact in the majority of the implants, with 2 cases of small, localized cohesive chipping and substrate exposure. CONCLUSIONS: The results of this study confirm the potential in vivo durability of early TiN coatings and will be useful in benchmarking wear tests for modern TiN-coated orthopaedic implants.
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Materiais Revestidos Biocompatíveis , Prótese de Quadril , Prótese do Joelho , Falha de Prótese , Propriedades de Superfície , Titânio , Humanos , Materiais Revestidos Biocompatíveis/química , Idoso , Feminino , Pessoa de Meia-Idade , Masculino , Remoção de Dispositivo , Artroplastia de Quadril/instrumentação , Artroplastia do Joelho/instrumentação , Desenho de Prótese , Corrosão , Reoperação , Microscopia Eletrônica de VarreduraRESUMO
BACKGROUND: After clinical introduction in 2005, sequentially annealed, highly cross-linked polyethylene (SA HXLPE) was studied for retrievals with short implantation times; however, long-term follow-ups are lacking. The objective of this study was to examine and compare the revision reasons, damage mechanisms, and oxidation indices of SA HXLPE and conventional gamma inert-sterilized (Gamma Inert) ultra-high-molecular-weight polyethylene tibial inserts implanted for >5 years. METHODS: There were 74 total knee arthroplasty tibial inserts (46 SA HXLPEs, 28 Gamma Inerts) implanted for >5 years (mean 7 ± 2 years) retrieved as part of a multicenter retrieval program. Cruciate-retaining implants comprised 44% of the SA HXLPEs and 14% of the Gamma Inerts. Patient factors and revision reasons were collected from revision operating notes. A semiquantitative scoring method was used to assess surface damage mechanisms. Oxidation was measured using Fourier transform infrared microscopy according to American Society for Testing and Materials 2102. Differences between cohorts were assessed with Mann-Whitney U-tests. RESULTS: Loosening (Gamma Inert: 17 of 28, SA HXLPE: 15 of 46) and instability (Gamma Inert: 6 of 28, SA HXLPE: 15 of 46) were the most common revision reasons for both cohorts. The most prevalent surface damage mechanisms were burnishing, pitting, and scratching, with burnishing of the condyles being higher in Gamma Inert components (P = .022). Mean oxidation was higher in the SA HXLPE inserts at the articulating surface (P = .002) and anterior-posterior faces (P = .023). No difference was observed at the backside surface (P = .060). CONCLUSIONS: Revision reasons and surface damage mechanisms were comparable in the Gamma Inert and SA cohorts. Further studies are needed to continue to assess the in vivo damage and clinical relevance, if any, of oxidation in SA HXLPE over longer implantation times, particularly for implants implanted for more than 10 years.
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BACKGROUND: Highly cross-linked polyethylene (HXLPE) was introduced to improve wear in total hip arthroplasty, with manufacturers implementing different thermal treatments to reduce oxidation. It is important to understand how long-term time in vivo affects the wear of these materials. The purpose of this study was to investigate the wear and oxidative performance of first-generation HXLPE hip inserts implanted for greater than 10 years and compare annealed and remelted HXLPE formulations. METHODS: There were 49 total hip arthroplasty liners retrieved during routine revision surgery as part of an institutional review board-approved implant retrieval program. Penetration rates for the liners were calculated as the difference between the thickness of the unloaded and loaded regions divided by implantation time. Oxidation indices for the rim, locking mechanism, articulating surface, and backside regions were measured using Fourier-transform infrared spectroscopy according to American Society for Testing and Materials 2102. Mann-Whitney U tests were used to determine the statistical difference between annealed and remelted components. RESULTS: The cohort had an average implantation time of 13.1 ± 2.6 years for annealed and 12.1 ± 1.7 years for remelted components. The components were revised most often for polyethylene wear, instability, and loosening. The penetration rate averaged 0.0177 ± 0.014 mm/year for annealed components and 0.015 ± 0.022 mm/year for remelted components. Penetration rates did not differ between the remelted and annealed cohorts (P = .28). Oxidation indices were found to be significantly higher in the annealed cohort for all regions of interest (P < .001). CONCLUSIONS: Oxidation was found to be higher in the annealed HXLPE; however, this does not seem to be associated with greater wear as we found the average penetration rates for the cohorts were low, and the penetration rates were similar between the annealed and remelted cohorts.
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Artroplastia de Quadril , Cabeça do Fêmur , Prótese de Quadril , Oxirredução , Polietileno , Falha de Prótese , Humanos , Artroplastia de Quadril/instrumentação , Pessoa de Meia-Idade , Feminino , Masculino , Idoso , Polietileno/química , Desenho de Prótese , Reoperação , Teste de Materiais , Adulto , Fatores de TempoRESUMO
Amorphous thin-film TiOx prepared via atomic layer deposition (ALD) has been identified as one of the most promising materials for use in transparent passivating contacts in high-efficiency and low-cost crystalline silicon (c-Si) solar cells. As highlighted in this work, the passivation performance of ALD TiOx layers strongly depends on the metal precursor used, with films prepared using TiCl4 recently showing the best results. However, a full understanding of how such films achieve their high level of surface passivation has not yet been demonstrated. This study provides a clear demonstration that a key part of this passivation mechanism is due to chlorine (Cl) accumulation at the Si surface. This mechanism is demonstrated to be quite general in nature by showing how 2 nm of ALD TiOx (TiCl4 + H2O) can be applied as a capping layer for either ZnO or Al2O3 interlayers to dramatically reduce silicon surface recombination. Cl depth profiles obtained using secondary ion mass spectrometry confirm the presence of Cl extending through the depth of the interlayers with a peak at the silicon interface. Remarkably, this diffusion of Cl is observed following low-temperature (75 °C) deposition of the TiOx capping layer, without any subsequent thermal treatment. Contrary to earlier studies that treated residual Cl in ALD films as a general contamination issue, these findings reveal unequivocally that chlorine plays a crucial role in Si surface passivation and can be classed as an effective passivation element, similar to hydrogen in its ability to passivate Si dangling bonds. The outcomes of this research emphasize the importance of residual chlorine in enhancing the passivation of buried interfaces and provide additional motivation for employing metal chloride precursors for silicon surface passivation applications.
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BACKGROUND AND OBJECTIVE: Vessel geometry and hemodynamics are intrinsically linked, whereby geometry determines hemodynamics, and hemodynamics influence vascular remodeling. Both have been used for testing clinical outcomes, but geometry/morphology generally has less uncertainty than hemodynamics derived from medical image-based computational fluid dynamics (CFD). To provide clinical utility, CFD-based hemodynamic parameters must be robust to modeling errors and/or uncertainties, but must also provide useful information not more-easily extracted from shape alone. The objective of this study was to methodically assess the response of hemodynamic parameters to gradual changes in shape created using an unsupervised 3D shape interpolation method. METHODS: We trained the neural network NeuroMorph on 3 patient-derived intracranial aneurysm surfaces (labelled A, B, C), and then generated 3 distinct morph sequences (AâB, BâC, CâA) each containing 10 interpolated surfaces. From high-fidelity CFD simulation of these, we calculated a variety of common reduced hemodynamic parameters, including many previously associated with aneurysm rupture, and analyzed their responses to changes in shape, and their correlations. RESULTS: The interpolated surfaces demonstrate complex, gradual changes in branch angles, vessel diameters, and aneurysm morphology. CFD simulation showed gradual changes in aneurysm jetting characteristics and wall-shear stress (WSS) patterns, but demonstrated a range of responses from the reduced hemodynamic parameters. Spatially and temporally averaged parameters including time-averaged WSS, time-averaged velocity, and low-shear area (LSA) showed low variation across all morph sequences, while parameters of flow complexity such as oscillatory shear, spectral broadening, and spectral bandedness indices showed high variation between slightly-altered neighboring surfaces. Correlation analysis revealed a great deal of mutual information with easier-to-measure shape-based parameters. CONCLUSIONS: In the absence of large clinical datasets, unsupervised shape interpolation provides an ideal laboratory for exploring the delicate balance between robustness and sensitivity of nominal hemodynamic predictors of aneurysm rupture. Parameters like time-averaged WSS and LSA that are highly "robust" may, as a result, be effectively redundant to morphological predictors, whereas more sensitive parameters may be too uncertain for practical clinical use. Understanding these sensitivities may help identify parameters that are capable of providing added value to rupture risk assessment.
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Aneurisma Intracraniano , Humanos , Aneurisma Intracraniano/diagnóstico por imagem , Simulação por Computador , Hemodinâmica , Hidrodinâmica , Redes Neurais de ComputaçãoRESUMO
BACKGROUND: Previous retrieval studies of patellar components for total knee arthroplasty focused on historical designs and polyethylene materials that are no longer clinically relevant. Therefore, this study aimed to compare revision reasons and surface damage mechanisms of conventional, gamma inert sterilized polyethylene and highly cross-linked polyethylene (HXLPE) patellar components in contemporary designs from a single manufacturer. METHODS: A total of 114 gamma inert and 76 HXLPE patellar components were gathered in a multicenter orthopaedic implant retrieval program. Patient age and body mass index were similar between cohorts (P = .27 and P = .42, respectively); however, the gamma inert cohort was implanted longer (µdifference = 3.1 years; P = .005). A matched subset was created based on the total knee arthroplasty design, patellar shape, and implantation time. Revision reasons were gathered from revision operating notes, and surface damage was examined via the Hood scoring method. Differences between HXLPE and gamma inert cohorts were evaluated using Mann-Whitney U-tests. RESULTS: The most common revision reasons were infection, loosening, and instability, with the most common patellar complication resulting in revision being patellar loosening for both cohorts with similar incidences for both (chi-square; P = .60, P = .59). The most common surface damage modes were burnishing, scratching, and pitting in both cohorts. Total surface damage was significantly higher in the gamma inert components (P = .02), but not in the matched subset (P = .46). CONCLUSION: Overall, the clinical performance of HXLPE was similar to that of conventional polyethylene for patellar components with short implantation times. While this study provides much needed information on the performance of HXLPE patellae in short-term retrievals, long-term studies are still needed.
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Prótese do Joelho , Polietileno , Humanos , Falha de Prótese , Reoperação , Desenho de PróteseRESUMO
INTRODUCTION: Overestimation of intracranial aneurysm neck width by 3D angiography is a recognized clinical problem, and has long been a concern for image-based computational fluid dynamics (CFD). Recently, it was demonstrated that neck overestimation in 3D rotational angiography (3DRA) could be corrected via segmentation with upsampled resolution and gradient enhancement (SURGE). Our aim was to leverage this approach to determine whether and how neck overestimation actually impacts CFD-derived hemodynamics. MATERIALS AND METHODS: A subset of 17 cases having the largest neck errors from a consecutive clinical sample of 60 was segmented from 3DRA using both standard watershed and SURGE methods. High-fidelity, pulsatile CFD was performed, and a variety of scalar hemodynamic parameters that have been associated with aneurysm growth and/or rupture status were derived. RESULTS: With a few exceptions, flow and wall shear stress (WSS) patterns were qualitatively similar between neck-overestimated and corrected models. Sac-averaged WSS values were significantly lower after neck correction (p = 0.0005) but were highly correlated with their neck-overestimated counterparts (R2 = 0.98). Jet impingement was significantly more concentrated in the neck-corrected vs. -uncorrected models (p = 0.0011), and only moderately correlated (R2 = 0.61). Parameters quantifying velocity or WSS fluctuations were not significantly different after neck correction, but this reflected their poorer correlations (R2 < 0.4). Nevertheless, for all hemodynamic parameters, median absolute differences were < 26%, and no parameter had more than 5/17 cases with absolute differences > 50%. CONCLUSION: Differences in hemodynamics due to neck width overestimation were found to be at most equal to, and often less than, those reported for other sources of error/uncertainty in intracranial aneurysm CFD, such as solver settings or assumed inflow rates.
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Aneurisma Intracraniano , Humanos , Aneurisma Intracraniano/diagnóstico por imagem , Imageamento Tridimensional , Hemodinâmica , Estresse Mecânico , HidrodinâmicaRESUMO
BACKGROUND: Intracranial aneurysm neck width tends to be overestimated when measured with three-dimensional rotational angiography (3DRA) compared with two-dimensional digital subtraction angiography (2D-DSA), owing to high curvature at the neck. This may affect morphological and hemodynamic analysis in support of treatment planning. We present and validate a method for extracting high curvature features, such as aneurysm ostia, during segmentation of 3DRA images. METHODS: In our novel SURGE (segmentation with upsampled resolution and gradient enhancement) approach, the gradient of an upsampled image is sharpened before gradient-based watershed segmentation. Neck measurements were performed for both standard and SURGE segmentations of 3DRA for 60 consecutive patients and compared with those from 2D-DSA. Those segmentations were also qualitatively compared for surface topology and morphology. RESULTS: Compared with the standard watershed method, SURGE reduced neck measurement error relative to 2D-DSA by >60%: median error was 0.49 mm versus 0.17 mm for SURGE, which is less than the average pixel resolution (~0.33 mm) of the 3DRA dataset. SURGE reduced neck width overestimations >1 mm from 13/60 to 5/60 cases. Relative to 2D-DSA, standard segmentations were overestimated by 16% and 93% at median and 95th percentiles, respectively, compared with only 6% and 37%, respectively, for SURGE. CONCLUSION: SURGE provides operators with high-level control of the image gradient, allowing recovery of high-curvature features such as aneurysm ostia from 3DRA where conventional algorithms may fail. Compared with standard segmentation and tedious manual editing, SURGE provides a faster, easier, and more objective method for assessing aneurysm ostia and morphology.
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Imageamento Tridimensional , Aneurisma Intracraniano , Humanos , Imageamento Tridimensional/métodos , Angiografia Cerebral/métodos , Aneurisma Intracraniano/diagnóstico por imagem , Angiografia Digital/métodos , HemodinâmicaRESUMO
The Radiation and Dust Sensor is one of six sensors of the Mars Environmental Dynamics Analyzer onboard the Perseverance rover from the Mars 2020 NASA mission. Its primary goal is to characterize the airbone dust in the Mars atmosphere, inferring its concentration, shape and optical properties. Thanks to its geometry, the sensor will be capable of studying dust-lifting processes with a high temporal resolution and high spatial coverage. Thanks to its multiwavelength design, it will characterize the solar spectrum from Mars' surface. The present work describes the sensor design from the scientific and technical requirements, the qualification processes to demonstrate its endurance on Mars' surface, the calibration activities to demonstrate its performance, and its validation campaign in a representative Mars analog. As a result of this process, we obtained a very compact sensor, fully digital, with a mass below 1 kg and exceptional power consumption and data budget features.
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Poeira , Meio Ambiente Extraterreno , AtmosferaRESUMO
PURPOSE: Communicating complex blood flow patterns generated from computational fluid dynamics (CFD) simulations to clinical audiences for the purposes of risk assessment or treatment planning is an ongoing challenge. While attempts have been made to develop new software tools for such clinical visualization of CFD data, these often overlook established medical imaging/visualization practice and data infrastructures. Here, leveraging the clinical ubiquity of the DICOM file format, we present techniques for the translation of CFD data to DICOM series, facilitating interactive visualization in standard radiological software. METHODS: Unstructured CFD data (volumetric fields of velocity magnitude, Q-criterion, and pathlines) are resampled to structured grids. Novel raster-based techniques that simulate experimental optical blurring are presented for bringing simulated pathlines into structured image volumes. DICOM series are created by strategically encoding these data into the file's PixelArray tag. Lumen surface information is also strategically encoded into a different range of pixel intensities, allowing hemodynamics and morphology to be co-visualized in a single volume using opacity-based rendering transfer functions. RESULTS: We show that 3D temporal CFD data represented as structured DICOM series can be rendered interactively in Horos, a widely-used medical imaging/radiology software. Our transfer function-based approach allows for representations of scalar isosurfaces, volumetric rendering, and tubular pathlines to be modified in real-time, resembling conventional unstructured visualizations. Careful selection of voxelization ROIs helps to ensure that data are kept lightweight for real-time rendering and minimal storage. CONCLUSION: While our approach inherently sacrifices some of the advanced visualization capabilities of specialized software tools, we believe our closer consideration of standardization can help to facilitate meaningful clinical interaction. This work opens up possibilities for the complete integration of measured and simulated data in established radiological software environments and workflows from PACS storage to 3D/4D visualization.
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Hidrodinâmica , Software , Diagnóstico por Imagem , Hemodinâmica/fisiologia , Humanos , Fluxo de TrabalhoRESUMO
Recent studies using high-fidelity computational fluid dynamics (CFD) have revealed high-frequency flow instabilities consistent with clinical reports of bruits and "musical murmurs", which have been speculated to contribute to aneurysm growth and rupture. We hypothesized that harmonic flow instabilities ("spectral bandedness") in aneurysm CFD data may be associated with rupture status. Before testing this hypothesis, we first present a novel method for quantifying and visualizing spectral bandedness in cardiovascular CFD datasets based on musical audio-processing tools. Motivated by previous studies of aneurysm hemodynamics, we also computed a selection of existing metrics that have demonstrated association with rupture in large studies. In a dataset of 50 bifurcation aneurysm geometries modeled using high-fidelity CFD, our spectral bandedness index (SBI) was the only metric significantly associated with rupture status (AUC = 0.76, p = 0.002), with a specificity of 79% (correctly predicting 19/24 unruptured cases) and sensitivity of 65% (correctly predicting 17/26 ruptured cases). Three-dimensional flow visualizations revealed coherent regions of high SBI to be associated with strong near-wall inflow jets and vortex-shedding/flutter phenomena in the aneurysm sac. We speculate that these intracycle, coherent flow instabilities may preferentially contribute to the progressive degradation of the aneurysm wall through flow-induced vibrational mechanisms, and that their absence in high-fidelity CFD may be useful for identifying intracranial aneurysms at lower risk of rupture.
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Aneurisma Roto , Aneurisma Intracraniano , Hemodinâmica , Humanos , HidrodinâmicaRESUMO
It has previously been shown that ex situ phosphorus-doped polycrystalline silicon on silicon oxide (poly-Si/SiOx) passivating contacts can suffer a pronounced surface passivation degradation when subjected to a firing treatment at 800 °C or above. The degradation behavior depends strongly on the processing conditions, such as the dielectric coating layers and the firing temperature. The current work further studies the firing stability of poly-Si contacts and proposes a mechanism for the observed behavior based on the role of hydrogen. Secondary ion mass spectrometry is applied to measure the hydrogen concentration in the poly-Si/SiOx structures after firing at different temperatures and after removing hydrogen by an anneal in nitrogen. While it is known that a certain amount of hydrogen around the interfacial SiOx can be beneficial for passivation, surprisingly, we found that the excess amount of hydrogen can deteriorate the poly-Si passivation and increase the recombination current density parameter J0. The presence of excess hydrogen is evident in selected poly-Si samples fired with silicon nitride (SiNx), where the injection of additional hydrogen to the SiOx interlayer leads to further degradation in the J0, while removing hydrogen fully recovers the surface passivation. In addition, the proposed model explains the dependence of firing stability on the crystallite properties and the doping profile, which determine the effective diffusivity of hydrogen upon firing and hence the amount of hydrogen around the interfacial SiOx after firing.
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Defects and impurities in silicon limit carrier lifetimes and the performance of solar cells. This work explores the use of fluorine to passivate defects in silicon for solar cell applications. We present a simple method to incorporate fluorine atoms into the silicon bulk and interfaces by annealing samples coated with thin thermally evaporated fluoride overlayers. It is found that fluorine incorporation does not only improve interfaces but can also passivate bulk defects in silicon. The effect of fluorination is observed to be comparable to hydrogenation, in passivating grain boundaries in multicrystalline silicon, improving the surface passivation quality of phosphorus-doped poly-Si-based passivating contact structures, and recovering boron-oxygen-related light-induced degradation in boron-doped Czochralski-grown silicon. Our results highlight the possibility to passivate defects in silicon without using hydrogen and to combine fluorination and hydrogenation to further improve the overall passivation effect, providing new opportunities to improve solar cell performance.
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BACKGROUND: Dual mobility (DM) articulations were introduced for total hip arthroplasty to reduce the risk of instability for patients who have a high risk of dislocation. The use of DM constructs in both primary and revision total hip arthroplasty has been steadily increasing, leading to concerns regarding potential risks of fretting corrosion, polyethylene wear, metal release, and failure due to component positioning. METHODS: A total of 56 retrieved DM constructs were collected. The inner and outer polyethylene liner surfaces were assessed for 7 damage mechanisms, and fretting corrosion was evaluated for the femoral stem, head, and modular liner. Three polyethylene liners with the greatest amounts of embedded debris were examined using scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to determine the elemental content of the debris. Acetabular cup orientation was analyzed radiographically using the EBRA (Einzel-Bild-Roentgen-Analyse) method. RESULTS: The devices were revised most frequently for infection (36%), loosening (21%), and instability/dislocation (18%). The most common polyethylene damage mechanisms were scratching, pitting, burnishing, and embedded debris, and no difference in total damage was found between primary and revision cases. Scanning electron microscopy/energy-dispersive X-ray spectroscopy revealed that debris morphology and composition were consistent with porous titanium coating, resulting from cup loosening or broken screws and augments. A total of 71% and 50% of the constructs were determined to be within the Lewinnek safe zone for inclination and anteversion, respectively. CONCLUSION: The most notable mechanisms of surface damage were due to third-body debris, especially for the polyethylene surfaces which articulate against cobalt-chromium femoral heads and acetabular liners. Scratching of the femoral head and the metal liner from this debris may support the clinical use of ceramic for DM bearing surfaces in the future.
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Artroplastia de Quadril , Prótese de Quadril , Artroplastia de Quadril/efeitos adversos , Corrosão , Prótese de Quadril/efeitos adversos , Humanos , Polietileno , Desenho de Prótese , Falha de PróteseRESUMO
For Ti6Al4V orthopedic and spinal implants, osseointegration is often achieved using complex porous geometries created via additive manufacturing (AM). While AM porous titanium (pTi) has shown clinical success, concerns regarding metallic implants have spurred interest in alternative AM biomaterials for osseointegration. Insights regarding the evaluation of these new materials may be supported by better understanding the role of preclinical testing for AM pTi. We therefore asked: (a) What animal models have been most commonly used to evaluate AM porous Ti6Al4V for orthopedic bone ingrowth; (b) What were the primary reported quantitative outcome measures for these models; and (c) What were the bone ingrowth outcomes associated with the most frequently used models? We performed a systematic literature search and identified 58 articles meeting our inclusion criteria. We found that AM pTi was evaluated most often using rabbit and sheep femoral condyle defect (FCD) models. Additional ingrowth models including transcortical and segmental defects, spinal fusions, and calvarial defects were also used with various animals based on the study goals. Quantitative outcome measures determined via histomorphometry including ''bone ingrowth'' (range: 3.92-53.4% for rabbit/sheep FCD) and bone-implant contact (range: 9.9-59.7% for rabbit/sheep FCD) were the most common. Studies also used 3D imaging to report outcomes such as bone volume fraction (BV/TV, range: 4.4-61.1% for rabbit/sheep FCD), and push-out testing for outcomes such as maximum removal force (range: 46.6-3092 N for rabbit/sheep FCD). Though there were many commonalities among the study methods, we also found significant heterogeneity in the outcome terms and definitions. The considerable diversity in testing and reporting may no longer be necessary considering the reported success of AM pTi across all model types and the ample literature supporting the rabbit and sheep as suitable small and large animal models, respectively. Ultimately, more standardized animal models and reporting of bone ingrowth for porous AM materials will be useful for future studies.
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Ligas/química , Materiais Biocompatíveis/química , Alicerces Teciduais/química , Titânio/química , Animais , Osso e Ossos , Fêmur , Humanos , Teste de Materiais , Modelos Animais , Osseointegração , Avaliação de Resultados em Cuidados de Saúde , Porosidade , Impressão Tridimensional , Próteses e Implantes , Coelhos , Ovinos , Fusão Vertebral , Engenharia TecidualRESUMO
Two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors exhibit many important structural and optoelectronic properties, such as strong light-matter interactions, direct bandgaps tunable from visible to near-infrared regions, flexibility and atomic thickness, quantum-confinement effects, valley polarization possibilities, and so on. Therefore, they are regarded as a very promising class of materials for next-generation state-of-the-art nano/micro optoelectronic devices. To explore different applications and device structures based on 2D TMDs, intrinsic material properties, their relationships, and evolutions with fabrication parameters need to be deeply understood, very often through a combination of various characterization techniques. Among them, steady-state photoluminescence (PL) spectroscopy has been extensively employed. This class of techniques is fast, contactless, and nondestructive and can provide very high spatial resolution. Therefore, it can be used to obtain optoelectronic properties from samples of various sizes (from microns to centimeters) during the fabrication process without complex sample preparation. In this article, the mechanism and applications of steady-state PL spectroscopy in 2D TMDs are reviewed. The first part of this review details the physics of PL phenomena in semiconductors and common techniques to acquire and analyze PL spectra. The second part introduces various applications of PL spectroscopy in 2D TMDs. Finally, a broader perspective is discussed to highlight some limitations and untapped opportunities of PL spectroscopy in characterizing 2D TMDs.
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In the past decade, high-fidelity computational fluid dynamics (CFD) has uncovered the presence of high-frequency flow instabilities (on the order of 100 s of Hz) in a variety of cardiovascular applications. These fluctuations are typically reported as pulsatile velocity-time traces or fast-Fourier-transformed power-frequency spectra, often from a single point or at most a handful of points. Originally inspired by its use in spectral Doppler ultrasound, here we demonstrate the utility of the simplest form of time-frequency representation - the spectrogram - as a more comprehensive yet still-intuitive means of visualizing the potential harmonic complexity of pulsatile cardiovascular flows. After reviewing the basic theory behind spectrograms, notably the short-time Fourier transform (STFT), we discuss the choice of input parameters that inform the appearance and trade-offs of spectrograms. We show that spectrograms using STFT were able to highlight spectral features and were representative of those obtained from more complex methods such as the Continuous Wavelet transforms (CWT). While visualization properties (colourmap, filtering, smoothing/interpolation) are shown to affect the conspicuity of spectral features, the window properties (function, size, overlap) are shown to have the greatest impact on the resulting spectrogram appearance. Using a set of cerebral aneurysm CFD cases, we show that spectrograms can readily reveal the case-specific nature of the time-varying flow instabilities, whether broadband, suggesting intermittent turbulent-like flow, or narrowband, suggesting laminar vortex shedding, or some combination thereof.
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Aneurisma Intracraniano , Análise de Ondaletas , Velocidade do Fluxo Sanguíneo , Análise de Fourier , Humanos , Hidrodinâmica , Modelos Cardiovasculares , Fluxo PulsátilRESUMO
Long-range and fast transport of coherent excitons is important for the development of high-speed excitonic circuits and quantum computing applications. However, most of these coherent excitons have only been observed in some low-dimensional semiconductors when coupled with cavities, as there are large inhomogeneous broadening and dephasing effects on the transport of excitons in their native states in materials. Here, by confining coherent excitons at the 2D quantum limit, we first observed molecular aggregation-enabled 'supertransport' of excitons in atomically thin two-dimensional (2D) organic semiconductors between coherent states, with a measured high effective exciton diffusion coefficient of ~346.9 cm2/s at room temperature. This value is one to several orders of magnitude higher than the values reported for other organic molecular aggregates and low-dimensional inorganic materials. Without coupling to any optical cavities, the monolayer pentacene sample, a very clean 2D quantum system (~1.2 nm thick) with high crystallinity (J-type aggregation) and minimal interfacial states, showed superradiant emission from Frenkel excitons, which was experimentally confirmed by the temperature-dependent photoluminescence (PL) emission, highly enhanced radiative decay rate, significantly narrowed PL peak width and strongly directional in-plane emission. The coherence in monolayer pentacene samples was observed to be delocalised over ~135 molecules, which is significantly larger than the values (a few molecules) observed for other organic thin films. In addition, the supertransport of excitons in monolayer pentacene samples showed highly anisotropic behaviour. Our results pave the way for the development of future high-speed excitonic circuits, fast OLEDs, and other optoelectronic devices.
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BACKGROUND: The purpose of this study was to evaluate ultrahigh-molecular-weight polyethylene (UHMWPE) wear and damage from retrieved total elbow arthroplasty components and compare in vivo wear with wear produced in vitro. METHODS: Explanted total elbow components were collected at revision surgery. UHMWPE damage was characterized visually, whereas penetration and wear were quantified using micro-computed tomography and gas pycnometry. Volumetric wear rates were compared with historical hip data, and wear data were compared with reported in vitro wear test data. RESULTS: Humeral bushing damage primarily occurred in the form of burnishing, scratching, and pitting at the articular face in the region of contact with the ulnar component. Wear of the ulnar bushings was concentrated on the edge of the component at the point of contact with the axis pin. Pitting and embedded debris were dominant damage modes, in addition to burnishing and delamination. Backside wear was negligible. The median linear penetration rates of the lateral, medial, and ulnar bushings were 0.14 mm/yr (range, 0.01-0.78 mm/yr), 0.12 mm/yr (range, 0.03-0.55 mm/yr), and 0.11 mm/yr (range, 0.01-0.69 mm/yr), respectively. The volumetric wear rates of the lateral, medial, and ulnar bushings were 5.5 mm3/yr (range, 0.7-37.2 mm3/yr), 5.9 mm3/yr (range, 0.6-25.5 mm3/yr), and 5.5 mm3/yr (range, 1.2-51.2 mm3/yr), respectively. CONCLUSIONS: The observed wear rates were similar to those reported in well-functioning total hip replacement patients with conventional UHMWPE bearings. We found limitations in reported in vitro testing resulting in wear that was not consistent with our retrieval data. We recommend further investigation to clinically validate in vitro simulation to provide appropriate loading protocols for elbow wear simulation.