111 research outputs found
Earnings Extrapolation And Predictable Stock Market Returns
The U.S. stock marketâs return during the first month of a quarter correlates strongly with returns in future months, but the correlation is negative if the future month is the first month of a quarter, and positive if it is not. These effects offset, leaving the market return with its weak unconditional predictive ability known to the literature. The pattern accords with a model in which investors extrapolate announced earnings to predict future earnings, not recognizing that earnings in the first month of a quarter are inherently less predictable than in other months. Survey data support this model, as does out-of-sample return predictability across industries and international markets. These results challenge the Efficient Market Hypothesis and advance a novel mechanism of expectation formation
Nanoscale Texture and Microstructure in a NdFeAs(O,F)/IBAD-MgO Superconducting Thin Film with Superior Critical Current Properties
This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y2O3/Hastelloy substrate. The NdFeAs(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the ab-plane as well as grain boundaries perpendicular to the ab-plane, good superconducting properties are measured: a critical temperature, T-c, of 46 K and a self-field critical current density, J(c), of 2 x 10(6) A/cm(2) at 4.2 K. Automated crystal orientation mapping by scanning precession electron diffraction in transmission electron microscope is employed to analyze the misorientation angles between adjacent grains in a large ensemble (247 grains), and 99% of the grain boundaries show in-plane misorientation angles (Delta gamma) less than the critical angle theta(c), which satisfies one of the necessary conditions for the high J(c). Comparing the columnar grain size distribution with the mean distance of the flux line lattice, the triple junctions of low-angle grain boundaries are found to be effective pinning centers, even at high temperatures (>= 35 K) and/or low magnetic fields
Potential immune evasion of the severe acute respiratory syndrome coronavirus 2 Omicron variants
Coronavirus disease 2019 (COVID-19), which is caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a global pandemic. The Omicron variant (B.1.1.529) was first discovered in November 2021 in specimens collected from Botswana, South Africa. Omicron has become the dominant variant worldwide, and several sublineages or subvariants have been identified recently. Compared to those of other mutants, the Omicron variant has the most highly expressed amino acid mutations, with almost 60 mutations throughout the genome, most of which are in the spike (S) protein, especially in the receptor-binding domain (RBD). These mutations increase the binding affinity of Omicron variants for the ACE2 receptor, and Omicron variants may also lead to immune escape. Despite causing milder symptoms, epidemiological evidence suggests that Omicron variants have exceptionally higher transmissibility, higher rates of reinfection and greater spread than the prototype strain as well as other preceding variants. Additionally, overwhelming amounts of data suggest that the levels of specific neutralization antibodies against Omicron variants decrease in most vaccinated populations, although CD4+ and CD8+ T-cell responses are maintained. Therefore, the mechanisms underlying Omicron variant evasion are still unclear. In this review, we surveyed the current epidemic status and potential immune escape mechanisms of Omicron variants. Especially, we focused on the potential roles of viral epitope mutations, antigenic drift, hybrid immunity, and âoriginal antigenic sinâ in mediating immune evasion. These insights might supply more valuable concise information for us to understand the spreading of Omicron variants
The competition and equilibrium in power markets under decarbonization and decentralization
Equilibrium analysis has been widely studied as an effective tool to model gaming interactions and predict market results. However, as competition modes are fundamentally changed by the decarbonization and decentralization of power systems, analysis techniques must evolve. This article comprehensively reviews recent developments in modelling methods, practical settings and solution techniques in equilibrium analysis. Firstly, we review equilibrium in the evolving wholesale power markets which feature new entrants, novel trading products and multi-stage clearing. Secondly, the competition modes in the emerging distribution market and distributed resource aggregation are reviewed, and we compare peer-to-peer clearing, cooperative games and Stackelberg games. Furthermore, we summarize the methods to treat various information acquisition degrees, risk preferences and rationalities of market participants. To deal with increasingly complex market settings, this review also covers refined analytical techniques and agent-based models used to compute the equilibrium. Finally, based on this review, this paper summarizes key issues in the gaming and equilibrium analysis in power markets under decarbonization and decentralization
Household, community, sub-national and country-level predictors of primary cooking fuel switching in nine countries from the PURE study
Introduction. Switchingfrom polluting (e.g. wood, crop waste, coal)to clean (e.g. gas, electricity) cooking
fuels can reduce household air pollution exposures and climate-forcing emissions.While studies have
evaluated specific interventions and assessed fuel-switching in repeated cross-sectional surveys, the role
of different multilevel factors in household fuel switching, outside of interventions and across diverse
community settings, is not well understood. Methods.We examined longitudinal survey data from
24 172 households in 177 rural communities across nine countries within the Prospective Urban and
Rural Epidemiology study.We assessed household-level primary cooking fuel switching during a
median of 10 years offollow up (âŒ2005â2015).We used hierarchical logistic regression models to
examine the relative importance of household, community, sub-national and national-level factors
contributing to primary fuel switching. Results. One-half of study households(12 369)reported
changing their primary cookingfuels between baseline andfollow up surveys. Of these, 61% (7582)
switchedfrom polluting (wood, dung, agricultural waste, charcoal, coal, kerosene)to clean (gas,
electricity)fuels, 26% (3109)switched between different polluting fuels, 10% (1164)switched from clean
to polluting fuels and 3% (522)switched between different clean fuels
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Development of applications of liquid crystalline elastomers from Materials to Applications
Liquid crystalline elastomer (LCE) is a class of "smart polymer" with constituent molecules called mesogens, exhibiting orientational ordering. These mesogens can self-assemble into many types of ordering and transition to being isotropic reversibly subjected to external stimuli. In the last four decades, this field has seen many advancements: the first generation of polysiloxane LCEs successfully introduced this wonderful material to the world; the second generation of LCEs deployed much more robust and easier synthesis procedure, bringing in researcher from many other disciplines; the third generation of LCE utilised the bond-exchange behaviour in vitrimers to produce exchangeable LCE (xLCE), which enabled post-polymerisation alignment, welding and recycling of LCE. Stemming from such unique network structures and a wide range of synthetic chemistries, LCEs have a variety of remarkable properties. LCEs are renowned for the "soft elasticity", which is the ability to be elongated without increasing the stress; as well as the enormous viscoelastic dissipation originating from the rotation of internal nematic orders. LCEs are also famous for the reversible actuation properties which can be triggered by a wide range of external stimuli. LCEs have promising practical applications such as artificial muscles, smart textiles, sensors and soft robotics.
This thesis aims to contribute to the field of LCE in the following three key aspects: (1) developing new LCE materials with novel synthesis routes and network structures, in order to find new or improved material properties; (2) investigating new fundamental physical effects associated with LCE in order to find new application areas; and (3) Designing and constructing demonstrator devices to illustrate the great potential of LCE materials.
**New materials** First, novel side-chain LCEs based on the robust thiol-acrylate click reaction were developed. The effects of mesogen structures on the LCEsâ phase transition behaviours and network structures were investigated. The unusual features were the semi-crystalline nature of elastomers with non-polar mesogens, and the clear role of side-by-side rod dimerisation of polar mesogens leading to the higher smectic layer spacing. When stretching beyond the full alignment, the smectic structures were found to evolve in two ways: forming the coarsened Helfrich-Hurault zig-zag layer texture, or the large-scale stripe domains of uniform layer rotation in the systems with lower order parameter and the associated layer constraints.
This then led to a new composite liquid crystalline elastomer, combining main-chain nematic and side-chain smectic together, which resulted in micro-phase separated regions of nematic and smectic ordering in the macroscopically homogeneous elastomer. Thermal phase transitions of both phases coexisting in the material were detected by calorimetry, and the nematic/smectic structure investigated by X-Ray scattering. The tensile stressâstrain data revealed the key effect of such a multi-phase composite, where the nematic fraction adds
ductility while the smectic fraction increases the modulus and mechanical stiffness. Thus, mechanical properties of this material type can be optimised by varying the composition.
**New physical effects** Next, the effect of LCE viscoelastic impact damping was investigated, in comparison with a reference silicone rubber. This project focused not only on the energy dissipation, but also on the momentum conservation and transfer during the collision, because the latter determines the maximum force exerted, which is responsible for damaging the target and/or the impactor. To better assess the momentum transfer, I compared the collision with a very heavy object and the collision with a comparable mass, when some of the impact momentum is retained in the target receding away from the collision. A method to estimate the optimal thickness of an elastomer damping pad was proposed for minimising the energy in impactor rebound. It has been found that thicker pads introduce a large elastic rebound and the optimal thickness is therefore the thinnest possible pad that does not suffer from mechanical failure.
This anomalously high vibration/impact damping in nematic poly-domain LCEs has also been assumed to be the cause of their anomalously high pressure-sensitive adhesion (PSA). The mechanism behind enhanced PSA was investigated by manufacturing generic LCE coated adhesive tapes with varying cross-linking densities. Industrial standard adhesion tests were performed to characterise LCE adhesion behaviours, which helped to reveal the strong dependence of adhesion strength on contact time. The long saturation time (sometimes exceeding 24 hours) is caused by the slow relaxation of local stress and director orientation in nematic domains after pressing against the surface. This mechanism was further confirmed by a freshly pressed and annealed tape reaching the same maximum bonding strength on cooling, when the returning nematic order is forming in its optimal configuration in the pressed film. Based on these findings, a class of much stronger, multi-use amine-acrylate LCE adhesive materials was developed. These adhesives exhibit low tackiness at room temperature; however, upon heating and annealing, they can be activated, enabling effective deployment. The LCEs were formulated to have tunable glass transition temperatures which is crucial for the low tackiness at ambient temperature. All formulations showed high adhesion strength (peel force) in the nematic region (1.0 to 1.6 N/mm) and low peel force in the isotropic region. Furthermore, the adhesive materials demonstrated the capability for reuse in more than five heating and cooling peeling cycles and have shown remarkable contamination tolerance to sand, oil, and dirt. Moreover, these adhesive materials displayed adhesion strengths (lap shear) that comparable to those of traditional PSAs, reaching up to 3 MPa, with a clean detachment.
**New device** Finally, a spontaneous heliotracking prototype device was designed and constructed based on the differential light-induced actuation of LCE. The design drew inspiration from nature itself with many living organisms responding to light stimulus and track the light source. The synthesis of the actuator material involves a robust thiol-acrylate "click" polymerisation, while the addition of indocyanine green (ICG) dye imparts the sensitivity to broad-spectrum and near-infrared light. Highly reproducible thermal and photo-induced linear actuation was demonstrated. The device is based on a freely pivoting payload platform held in place by several linear LCE actuators around the 360° circumference. The side of the device, when exposed to light, has the actuators contracting and tilting the platform towards the light source. As the light source was moving around the device, the platform tilt followed, always exposing the payload face to the light; in the dark, the device recovers its neutral position.The Cambridge Commonwealth, European & International Trust
Chinese Scholarship Council (CSC
Earnings Extrapolation and Predictable Stock Market Returns
The U.S. stock marketâs return during the first month of a quarter correlates strongly with returns in future months, but the correlation is negative if the future month is the first month of a quarter, and positive if it is not. These effects offset, leaving the market return with its weak unconditional predictive ability known to the literature. The pattern accords with a model in which investors extrapolate announced earnings to predict future earnings, not recognizing that earnings in the first month of a quarter are inherently less predictable than in other months. Survey data support this model, as does out-of-sample return predictability across industries and international markets. These results challenge the Efficient Market Hypothesis and advance a novel mechanism of expectation formation
Thiol-acrylate side-chain liquid crystal elastomers
The Michael addition âclickâ chemistry was used to graft acrylate-terminated mesogenic groups onto the polysiloxane backbone polymer chain with thiol functional groups, with a constant 15% fraction of diacrylate reacting monomers as crosslinkers. Three different types of mesogens were used, and also their 50:50 mixtures, and in all cases we have obtained the smectic-A phase of the resulting liquid crystalline elastomer. Using the Xray diffraction, calorimetry and dynamic mechanical testing, we investigated the relationship between the molecular structure of mesogenic side groups and the structure and properties of the elastomers. The shape-memory of smectic elastomers was verified. The unusual features were the semi-crystalline nature of elastomers with non-polar mesogens, and the clear role of of side-by-side rod dimerization of polar mesogens leading to the higher smectic layer spacing. We investigated the evolution of the smectic alignment on uniaxial stretching along the layer normal, and identified two distinct ways the elastomer response: the coarsened Helfrich-Hurault zig-zag layer texture, and the large-scale stripe domains of uniform layer rotation in the systems with lower order parameter and the associated layer constraints
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