922017 research outputs found
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Theoretical study of the stability of the tetradymite-like phases of Sb2S3, Bi2S3, and Sb2Se3
No full textWe report a comparative theoretical study of the Pnma and R-3m phases of Sb2S3, Bi2S3, and Sb2Se3 close to ambient pressure. Our enthalpy calculations at 0 K show that at ambient pressure the R-3m (tetradymite-like) phase of Sb2Se3 is energetically more stable than the Pnma phase, contrary to what is observed for Sb2S3 and Bi2S3, and irrespective of the exchange-correlation functional employed in the calculations. The result for Sb2Se3 is in contradiction to experiments where all three compounds are usually grown in the Pnma phase. This result is further confirmed by free-energy calculations taking into account the temperature dependence of the unit-cell volumes and phonon frequencies. Lattice dynamics and elastic tensor calculations further show that both Pnma and R-3m phases of Sb2Se3 are dynamically and mechanically stable at zero applied pressure. Since these results suggest that the formation of the R-3m phase for Sb2Se3 should be feasible at close to ambient conditions, we provide a theoretical crystal structure and simulated Raman and infrared spectra to help in its identification. We also discuss the results of the two published works that have claimed to have synthesized tetradymite-like Sb2Se3. Finally, the stability of the R-3m phase across the three group-15 A2X3 sesquichalcogenides is analysed based on their van der Waals gap and X-X in-plane geometry
Dry heterometallic resist processing based on thermal sublimation deposition and development
No full textA negative tone heterometallic ring resist (HRR) based on a supramolecular assembly [NH2(allyl)2][Cr7NiF8(piv)16] with previously demonstrated resolution down to sub-10nm lines is evaluated in terms of its flexibility to be processed either ‘wet’ (spin-cast, solvent-developed) or ‘dry’ (deposition and development by vacuum sublimation). The implemented sublimation hardware fits easily in the wafer load-lock chamber of EUV and electron beam exposure systems dedicated to R&D activities and allows for HRR films to be uniformly deposited or developed in the same vacuum environment. The HRR shows a sublimation rate dependence on temperature that obeys a Clausius-Clapeyron relation, with thermal stability up to 275°C. Flood exposures of the HRR show identical sensitivity between wet and dry deposited films, while contrast degradation is observed when dry development is initiated by increasing the temperature prior to system pump down. A modified sublimation setup allows for the dry development of exposed HRR samples inside the electron beam tool without breaking vacuum. In this case, nominally patterned 25nm L/S are identically resolved at 30 keV for wet- or dry-developed HRR
A Bibliometric Mapping Study of the Literature on Oral Health-related Quality of Life
No full textBackgroundOral health is an indispensable component of overall health, and oral health status significantly influences people’s physical, mental, and social well-being. Oral health-related quality of life (OHRQoL), an important and widely used dental patient-reported outcome (dPRO), is attracting more and more researchers’ attention and interest. This study aimed to analyze and map the existing scientific literature regarding OHRQoL through a bibliometric approach, including a summary of the characteristics of OHRQoL-related publications, the identification of prolific entities, high-frequency keywords analysis and research trend analysis via periodic high-impact keywords.MethodsA literature search was conducted in the Web of Science Core Collection to collect OHRQoL-related original research and review articles. After examination and deduplication, the following bibliometric information was extracted from each article: title, abstract, keywords, authors, affiliations, geographic origin (countries/regions), year of publication, journal name, and references. Various scientometric mapping tools including Microsoft Office spreadsheet, VOSviewer, Biblioshiny R-package software, and Scimago Graphica were used to analyze basic bibliometric parameters, leading producers, highimpact keywords, and research trends.ResultsA total of 3324 OHRQoL-related articles (3119 original research articles and 205 review papers) were collected, which received 65704 citations. A total of 9950 authors from 2429 organizations contributed to this body of research. Prolific authors from Europe, USA, Brazil, New Zealand, China, and Canada were identified, and they also centered collaboration clusters in the co-author network. Community Dentistry and Oral Epidemiology was the most prolific journal. Twenty-one keywords with more than 200 occurrences, and 23 keywords with more than 150 occurrences, were identified for publications of 1994-2021 and 2012-2021, respectively. Keyword analysis revealed hot topics such as instrument development and validation, studies targeting children and adolescents, as well as clinical studies in operative dentistry, implantology, orthodontics, and community dentistry. Oral Health Impact Profile is the most commonly used instrument in OHRQoL-related research.ConclusionsOHRQoL is an impactful topic in dental health care as it is not only useful in dental research and patient-centered clinical outcome measures but also provides valuable guidance in dental public health administration and policy making. OHRQoL-related research presents a dynamic landscape and is expected to continue presenting high productivity and broad application in the future
Self-assembled 1T-MoS2/Functionalized Graphene Composite Electrodes for Supercapacitor Devices
No full textTwo-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS2) have been investigated widely for applications in energy storage, including supercapacitors, due to their high specific surface area, potential redox activity and mechanical flexibility. However, electrodes comprised of either pure graphene and MoS2 have failed to reach their potential due to restacking of the layered structure and poor electrical conductivity. It has been shown previously that composite electrodes made from a mixture of graphene and MoS2 partially counteract these issues, however performance is still limited by poor mixing at the nanoscale. Herein, we form a true composite electrode by chemically functionalizing the graphene so that the negatively charged surface can self-assemble with the positively charged 1T-MoS2 to give an alternating layer structure. These alternately restacked 2D materials were then used to produce supercapacitor electrodes, and their energy storage properties characterized. This stacked structure has increased the interlayer spacing of 1T-MoS2 which was indicated by the increase of the intensity of the (001) peak in the XRD spectra. Furthermore, the typically metastable 1T-MoS2 was stabilized by the interaction with the functionalized graphene, preventing it reverting back to the 2H phase, which was observed when pristine graphene was used. The graphene was functionalized using either 4-bromobenzenediazonium (BBD) or 4-nitrobenzenediazonium (NBD), with the later giving optimal capacitance when mixed with the MoS2. The alternative layer graphene-MoS2 structure was confirmed by Raman spectroscopy and electron microscopy and lead to high specific capacitance (290 F cm-3 at 0.5 A g-1) and 90 % retention of capacitance after 10,000 cycles
Hierarchical zeolites: controllable synthesis, diffusion study and catalysis
No full textHierarchical zeolites refer to zeolitic materials having bi-/multi-modal interconnective pores arranged in order of certain ranks, which improve the molecular diffusion within their frameworks, and hence the performance in their applications such as adsorption and heterogeneous catalysis. Hierarchical zeolites are commonly produced via the ‘top-down’ post-synthetic treatments (such as dealumination and/or desilication) of pre-synthesised zeolites (i.e. the parent zeolites) and the ‘bottom-up’ synthesis-by-design methods (such as soft/hard templating). This review presents the recent advances (from 2001 to 2020) in the strategies of making hierarchical zeolites, with the emphasis on the ‘top-down’ approaches due to their relatively high practicality. Since hierarchical zeolites are proposed to improve intracrystalline diffusion, experimental studies of guest molecules diffusion in hierarchical zeolites is also reviewed. Additionally, catalytic applications of hierarchical zeolites, in comparison with the conventional microporous pristine zeolites, are also commented to highlight the advantages of hierarchical zeolites to improve catalysis.Keywords Hierarchical zeolites; Post-synthetic treatment; Diffusion; Pulsed-field gradient nuclear magnetic resonance (PFG-NMR); Catalysis<br/
Did the Siebel Systems Case Limit the SEC's Ability to Enforce Regulation Fair Disclosure?
No full textWe examine whether a shock to the enforceability of Regulation Fair Disclosure (Reg FD) limited its ability to restrict the flow of private information between managers and investors. While prior work provides evidence that Reg FD reduced managers’ selective disclosure of material information immediately following its promulgation, we posit that private information flows returned as a result of the SEC’s public enforcement failure in SEC v. Siebel Systems, Inc. Using multiple settings, we find consistent evidence suggesting that Siebel changed the cost-benefit tradeoff for Reg FD compliance and effectively reversed the initial effects of the regulation. We also find that Siebel disrupted the equilibrium of selective disclosure activity, resulting in an unleveling effect among investors with respect to private information advantages. Finally, we find that Siebel also had real effects by altering managers’ capital structure decisions. Our findings run counter to the prevailing “mosaic theory” and gradual learning explanations for private information advantages in the extended post-Reg FD period and highlight the importance of enforcement in achieving intended regulatory outcomes
Recall of exposure in UK farmers and pesticide applicators:trends with follow-up time
No full textBACKGROUND: Occupational epidemiological studies on pesticide use commonly rely on self-reported questionnaire or interview data to assess exposure. Insight into recall accuracy is important, as misclassification of exposures due to imperfect recall can bias risk estimates.METHODS: We assessed the ability of workers in three UK cohorts (Prospective Investigation of Pesticide Applicators' Health [PIPAH], Pesticide Users' Health Study [PUHS], and Study of Health in Agricultural Work [SHAW]) to remember their working history related to pesticide exposure over time periods ranging from 3 to 14 years prior. During 2019-2020, cohort participants were re-surveyed using a similar questionnaire to that used previously. We compared recall of responses at follow-up to those reported at baseline related to crops/areas of work, use of personal protective equipment (PPE) items, hygiene habits, frequency of pesticide use, and application method. To assess the extent of recall, we used sensitivity, specificity, the percentage of overall agreement, and area under the curve (AUC) values. We also examined the presence of over or underestimation of recalled years, and days and hours per year, of working with pesticides using geometric mean ratios (GMR) and regression analysis to investigate any trends based on demographic characteristics.RESULTS: There were 643 individuals who completed both the baseline and follow-up surveys in the three cohorts with response rates ranging from 17 to 46%. There was a strong correlation (rho = 0.77) between the baseline and recalled years working with pesticides, though higher values were reported at follow-up (GMR = 1.18 [95% confidence interval: 1.07-1.30]) with no consistent differences by demographic characteristics. There was stronger agreement in the recalled days compared to hours per year in two of the cohorts. Recall for a number of exposure determinants across short and longer periods entailed overall agreement of >70%, though with some differences: for example, sensitivity for long-term recall of crops was poor (<43% in PUHS), whereas short-term recall of hygiene practices was good (AUC range = 0.65-1.00 in PIPAH).CONCLUSION: Results indicate that recall ability may deteriorate over a longer period. Although low-response rates may require these findings to be interpreted with caution, recall for a number of exposure determinants appeared reliable, such as crops and hygiene practices within 3 years, as well as days per year working with pesticides.</p
Modelling annual scintillation arc variations in PSR J1643−1224 using the large european array for pulsars
No full textIn this work we study variations in the parabolic scintillation arcs of the binary millisecond pulsar PSR J1643−1224 over five years using the Large European Array for Pulsars (LEAP). The 2D power spectrum of scintillation, called the secondary spectrum, often shows a parabolic distribution of power, where the arc curvature encodes the relative velocities and distances of the pulsar, ionised interstellar medium (IISM), and Earth. We observe a clear parabolic scintillation arc which varies in curvaturethroughout the year. The distribution of power in the secondary spectra are inconsistent with a single scattering screen which is fully 1D, or entirely isotropic. We fit the observed arc curvature variations with two models; an isotropic scattering screen, and a model with two independent 1D screens. We measure the distance to the scattering screen to be in the range 114-223 pc, depending on the model, consistent with the known distance of the foreground large-diameter HII region Sh 2-27 (112 ± 17 pc), suggesting that it is the dominant source of scattering. We obtain only weak constraints on the pulsar’s orbital inclination and angle of periastron, since the scintillation pattern is not very sensitive to the pulsar’s motion, since the screen is much closer to the Earth than the pulsar. More measurements of this kind - where scattering screens can be associated with foreground objects - will help to inform the origins and distribution of scattering screens within our galaxy.Key words: pulsars: general – pulsars:individual ( PSR J1643−1224) – ISM:HII regio
An asymptotic approach to proving sufficiency of Stein characterisations
No full textIn extending Stein's method to new target distributions, the first step is to find a Stein operator that suitably characterises the target distribution. In this paper, we introduce a widely applicable technique for proving sufficiency of these Stein characterisations, which can be applied when the Stein operators are linear differential operators with polynomial coefficients. The approach involves performing an asymptotic analysis to prove that only one characteristic function satisfies a certain differential equation associated to the Stein characterisation. We use this approach to prove that all Stein operators with linear coefficients characterise their target distribution, and verify on a case-by-case basis that all polynomial Stein operators in the literature with coefficients of degree at most two are characterising. For X denoting a standard Gaussian random variable and Hp the p-th Hermite polynomial, we also prove, amongst other examples, that the Stein operators for Hp(X), p = 3; 4; : : : ; 8, with coefficients of minimal possible degree characterise their target distribution, and that the Stein operators for the products of p = 3; 4; : : : ; 8 independent standard Gaussian random variables are characterising (in both settings the Stein operators for the cases p = 1; 2 are already known to be characterising). We leverage our Stein characterisations of H3(X) and H4(X) to derive characterisations of these target distributions in terms of iterated Gamma operators from Malliavin calculus, that are natural in the context of the Malliavin-Stein method