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Influence of co-reactants on surface passivation by nanoscale hafnium oxide layers grown by atomic layer deposition on silicon
No full textHafnium oxide thin films have attracted considerable interest for passivation layers, protective barriers, and anti-reflection coatings. Atomic layer deposition offers a route to produce conformal films at the nanometre scale, but there is a lack of clarity over how the growth conditions affect the film properties. Here we present a study into the role of different co-reactants (O2 plasma, O3 and H2O) for the atomic layer deposition of HfOx on n-type silicon from a tetrakis(dimethylamido)hafnium (TDMAH) precursor at 200 °C followed by post-deposition annealing (up to 500 °C). Through X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate variations in film composition, stoichiometry and crystallinity with co-reactant. Depth profiling conducted with X-ray photoelectron spectroscopy reveals differences in composition between the HfOx surface and the HfOx/Si interface. We also determine differences in the charge level and chemical passivation through photoconductance decay measurements and Kelvin probe analysis. We find that surface recombination velocities <10 cm s-1 are possible for HfOx films, with the best passivation achieved for H2O-based HfOx (SRVs as low as ~5 cm s-1). We show that with TDMAH as a hafnium precursor, neither co-reactant choice nor annealing ambient influence resulting charge polarity
Union-closed sets and Horn Boolean functions
Get PDFA family of sets is union-closed if the union of any two sets from belongs to. The union-closed sets conjecture states that if is a finite union-closed family of finite sets, then there is an element that belongs to at least half of the sets in. The conjecture has several equivalent formulations in terms of other combinatorial structures such as lattices and graphs. In its whole generality the conjecture remains wide open, but it was verified for various important classes of lattices, such as lower semimodular lattices, and graphs, such as chordal bipartite graphs. In the present paper we develop a Boolean approach to the conjecture and verify it for several classes of Boolean functions, such as submodular functions and double Horn functions
The Unified Tradeoff Model
Get PDFEvidence is steadily mounting that attribute-based models offer a more accurate description of intertemporal choices than traditional alternative-based models. Among the attribute-based models, the tradeoff model offers the broadest coverage of research findings, but at the cost of considerable complexity: There now are various instantiations of the model dealing with partially overlapping universes of choice options and preference patterns. Moreover, there are reports of preference patterns in intertemporal decisions about monetary losses that contradict all attribute-based models proposed so far. Taking stock of these core challenges, and all other evidence, we develop an account of intertemporal choice, the unified tradeoff model, that is simpler, yet more comprehensive, than all currently available versions of the tradeoff model taken together. It borrows extensively from its predecessors, but it introduces a new element, time bias, that enables it to accommodate an extraordinarily broad range of preference patterns, and also generate new predictions that contradict all existing models of intertemporal choice. We report four studies that test and confirm its predictions regarding delay, interval, sign, and magnitude dependence in choices between single-dated outcomes, and a fifth study that tests and confirms its predictions regarding the relation between delay preference in choices that only involve single-dated payments and duration preference in choices that also involve sequences of payments. Having subjected the unified tradeoff model to an elevated risk of disconfirmation, we discuss its parsimony and scope in relation to yet other phenomena, most notably, preference patterns in consumption decisions, the final frontier for attribute-based models
Minimising bias and increasing relevance in clinical trials : basis for the international standard
No full textSystematic review of computed tomography parameters used for the assessment of subchondral bone in osteoarthritis
Get PDFObjective:
To systematically review the published parameters for the assessment of subchondral bone in human osteoarthritis (OA) using computed tomography (CT) and gain an overview of current practices and standards.
Design:
A literature search of Medline, Embase and Cochrane Library databases was performed with search strategies tailored to each database (search from 2010 to January 2023). The search results were screened independently by two reviewers against pre-determined inclusion and exclusion criteria. Studies were deemed eligible if conducted in vivo/ex vivo in human adults (>18 years) using any type of CT to assess subchondral bone in OA. Extracted data from eligible studies were compiled in a qualitative summary and formal narrative synthesis.
Results:
This analysis included 202 studies. Four groups of CT modalities were identified to have been used for subchondral bone assessment in OA across nine anatomical locations. Subchondral bone parameters measuring similar features of OA were combined in six categories: (i) microstructure, (ii) bone adaptation, (iii) gross morphology (iv) mineralisation, (v) joint space, and (vi) mechanical properties.
Conclusions:
Clinically meaningful parameter categories were identified as well as categories with the potential to become relevant in the clinical field. Furthermore, we stress the importance of quantification of parameters to improve their sensitivity and reliability for the evaluation of OA disease progression and the need for standardised measurement methods to improve their clinical value
Cryopreservation of assay-ready hepatocyte monolayers by chemically-induced ice nucleation : preservation of hepatic function and hepatotoxicity screening capabilities
Get PDFCell culture plays a critical role in biomedical discovery and drug development. Primary hepatocytes and hepatocyte-derived cell lines are especially important cellular models for drug discovery and development. To enable high-throughput screening and ensure consistent cell phenotypes, there is a need for practical and efficient cryopreservation methods for hepatocyte-derived cell lines and primary hepatocytes in an assay-ready format. Cryopreservation of cells as adherent monolayers in 96-well plates presents unique challenges due to low volumes being susceptible to supercooling, leading to low recovery and well-to-well variation. Primary cell cryopreservation is also particularly challenging due to the loss of cell viability and function. In this study, we demonstrate the use of soluble ice nucleator materials (IN) to cryopreserve a hepatic-derived cell line (HepG2) and primary mouse hepatocytes, as adherent monolayers. HepG2 cell recovery was near 100% and ∼75% of primary hepatocytes were recovered 24 hours post-thaw compared to just 10% and 50% with standard 10% DMSO, respectively. Post-thaw assessment showed that cryopreserved HepG2 cells retain membrane integrity, metabolic activity, proliferative capacity and differentiated hepatic functions including urea secretion, cytochrome P450 levels and lipid droplet accumulation. Cryopreserved primary hepatocytes exhibited reduced hepatic functions compared to fresh hepatocytes, but functional levels were similar to commercial suspension-cryopreserved hepatocytes, with the added benefit of being stored in an assay-ready format. In addition, normal cuboidal morphology and minimal membrane damage were observed 24 hours post-thaw. Cryopreserved HepG2 and mouse hepatocytes treated with a panel of pharmaceutically active compounds produced near-identical dose–response curves and EC50 values compared to fresh hepatocytes, confirming the utility of cryopreserved bankable cells in drug metabolism and hepatotoxicity studies. Cryopreserved adherent HepG2 cells and primary hepatocytes in 96 well plates can significantly reduce the time and resource burden associated with routine cell culture and increases the efficiency and productivity of high-throughput drug screening assays
A scientometric analysis of Africa’s health science journals indexed in international and regional databases : a comparative analysis
No full textObjectives: This study aimed to compare the geographic coverage, citation impact, subject trends and authorship collaboration pattern of African health science journals indexed in international and regional databases. Methods: Data was collected from Ulrichs web serials directory, Web of Science (WoS), Scopus, PubMed, Google scholar, African Index Medicus (AIM) and African Journals Online (AJOL) between February 2023 and May 2023. Data was analysed using summary descriptive statistics such as percentages and interquartile ranges, and through network visualisation. Results: More than 40 African countries had no any health science journal indexed in WoS, whereas 20 African countries did not have any health science journal indexed in AJOL and AIM. The Journal of Advanced research was the top performing journal on almost all journal metric lists such as Google scholar’s H5-Index, SNIP, Journal Impact Factor, and Citescore, except Journal Citation indicator. Conclusion: The coverage of African health science journals by international citation databases is still limited which result in low scientific impact of many African health science journals. Authorship collaboration is related to historical ties among countries
Measuring the Mass–Radius Relation of White Dwarfs Using Wide Binaries
No full textMeasuring the mass–radius relation of individual white dwarfs is an empirically challenging task that has been performed for only a few dozen stars. We measure the white dwarf mass–radius relation using the gravitational redshifts and radii of 135 white dwarfs in wide binaries with main-sequence companions. We obtain the radial velocities of these systems using the main-sequence companion, and subtract these Doppler redshifts from the white dwarfs’ apparent motions, isolating their gravitational redshifts. We use Gaia data to calculate the surface temperatures and radii of these white dwarfs, thereby deriving an empirical gravitational redshift–radius relation. This work demonstrates the utility of low-resolution Galactic surveys to measure the white dwarf equation of state. Our results are consistent with theoretical models, and represent the largest sample of individual white dwarf gravitational redshift measurements to date
Novel battery power capability assessment for improved eVTOL aircraft landing
No full textA key aspect in the deployment of electric vertical take-off and landing (eVTOL) aircraft is the safety and performance capabilities of the batteries used. A component of the safety requirements is the need for reserve energy, which would only be utilised in case of emergencies. In the literature, it has been observed that the lower bound of the reserve region of battery energy should be limited to avoid the area where a precipitous drop in voltage would occur. Here, a method for defining the lower bound is proposed. This seeks to extend the amount of time the aircraft can cruise before landing can no longer be completed. A novel power capability testing procedure is used to measure the lowest state-of-charge (SoC) at which a constant power pulse can be completed. This differs from existing power capability tests that perform pulses at predetermined SoC points. The goal of the proposed method is to replicate the conditions of landing to understand the power capability performance at low SoC. The test is performed for a variety of environmental conditions and use cases, which includes temperature and power pulses, as well as two sets of differently aged cells. For the defined test conditions, the lowest SoC values for the calendar aged cells ranges from 6% to 14% SoC, whereas the range for cycle aged cells is 8% to 27% SoC. The outcome of this test is a characteristic map which correlates temperature, pulse power and pulse duration to the lowest SoC the pulse can be completed. The characteristic map indicates the lowest SoC value allowed for the battery before landing needs to be performed. The accuracy of the characteristic map is compared to a battery equivalent circuit model, parametrised from the test data. The defined approaches are experimentally validated based on a set of previously unmeasured experimental conditions. Overall, the characteristic map provides good accuracy compared to measured values, with both map and model methods having an average maximum absolute percentage error of at most 7.5%. Additionally, the test results show that if the worst case landing scenario is used as the lower bound of the reserve region, the useable SoC range for nominal flight would be greatly affected if cell degradation is not considered
Atmospheric chemistry of secondary and hybrid atmospheres of super earths and sub-Neptunes
No full textThe atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. Secondary atmospheres, such as those of Earth, Mars, and Venus, are sourced by outgassing. Persistent outgassing into long-lived, primordial, hydrogen–helium envelopes produces hybrid atmospheres of which there are no examples in the solar system. We construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation, and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium, and nitrogen content. Nonideal gases (quantified by the fugacity coefficient) and nonideal mixing of gaseous components (quantified by the activity coefficient) are considered. Both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. The abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by James Webb Space Telescope spectra in the near future. Methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding ∼10 bar, a reduced (poorly oxidized) mantle, and diminished magma temperatures (compared to modern Earth). Future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. Exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super Earths and sub-Neptunes; such an empirical relationship already exists for solar system bodies