143174 research outputs found
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Motivic invariants in birational geometry and singularity theory
No full textThis thesis is mainly concerned with computing motivic invariants in two particular cases. Given two polynomials f and g in disjoint sets of variables, we compute the motivic zeta function of f + g in terms of strictly toroidal resolutions of f and g. Using this, we show that the motivic Thom-Sebastiani formula of Denef–Loeser holds already in the Grothendieck ring of varieties without inverting the affine line. We also compute weak strictly toroidal resolutions for singularities of the form P(f,g) for certain non-degenerate polynomials P, and show that the motivic monodromy conjecture holds in this case.
Limits of these zeta functions have interesting properties as well, and Nicaise– Shinder showed that they can be used as an obstruction to stable rationality. Building on the combinatorial framework of Nicaise–Ottem to study stable rationality of hypersurfaces in toric varieties (in terms of the associated polytope), we give a purely combinatorial strategy to prove stable irrationality of hypersurfaces in toric varieties. We apply this strategy to give many new examples of stably irrational hypersurfaces in projective space and products of projective spaces.Open Acces
Eco-driving optimal control for electric vehicles with driver preferences
No full textAn optimal control formulation of an eco-driving system for front-wheel drive electric vehicles is proposed in this paper, demonstrating that including an optimal control model of driver preferences in such systems can successfully blend the objective of energy-efficiency with the subjective goals of human drivers, including desired following distances and time headways, a desired vehicle speed, smooth vehicle acceleration, and a comfortable corner negotiation speed. This builds on previous works that developed driver preference models for optimal control, but did not apply them to a realistic model of an EV powertrain to evaluate potential energy savings in practice. The resulting optimal control problem (OCP) is simplified for implementation by using a polynomial approximation of vehicle losses, and a relaxation of regenerative braking constraints that accurately accounts for required braking bias in a front-wheel drive vehicle. In testing, over a simulated 25km journey involving rural, motorway and urban sections, blending driver preferences with energy efficiency in this framework achieves energy savings of 21% with only a 7% decrease in average speed. For car-following scenarios, 10–15% energy savings are achievable with no decrease in average speed
Neural network based surrogates for scalable Bayesian inference on a complex malaria model
No full textBayesian inference on complex models is challenging, as long simulation times and large observational data sets can make computation infeasible and posterior samplers can struggle with high-dimensional parameter spaces with complex posterior geometries. However, several active areas of research offer methods to address some of these challenges, such as Hamiltonian Monte Carlo (HMC) to use gradient information for robust posterior sampling, Stochastic Variational Inference (SVI) for faster inference which is robust to noisy data, Neural Networks (NNs) and Neural Density Estimators (NDEs) for fast and scalable approximations of deterministic functions and stochastic processes. However, they are yet to find adoption for the more complex, realistic, long running models in the sciences, such as climate, astrological or disease transmission models. Fast and scalable inference for these models would result in timely scientific understanding and policy making which could have a far-reaching impact on our societies. Newer methods of inference are of particular interest in global malaria research, where models have grown in complexity. These often include hundreds of parameters which influence an intricate combination of non-linear dynamics, need to be fit to several decades of global prevalence and incidence data, and simulations for each location take many hours to execute. Researchers have developed these models to meet the growing demands for malaria control and elimination in a widening landscape of potential interventions and confounding dynamics-such as new vaccines, insecticide resistance and a changing climate. Bayesian inference of model parameters affects the predictive power of malaria transmission forecasts when estimating burden or planning intervention strategies, which impacts hundreds of millions of lives globally. New methods are needed to ensure that researchers can perform inference on malaria transmission models as they grow to capture the nuances of modern malaria. This thesis documents my investigations into new methods which could address these needs.Open Acces
Novel universality classes in polar active fluids using nonperturbative renormalization group methods
No full textThe compressible Toner-Tu equations are investigated with respect to novel universality classes, describing the structure of its phase diagram. This is achieved using the nonperturbative functional renormalization group. In particular, the ordered flocking phase and a multicritical region, where the critical order-disorder and critical phase-separation points coincide, are studied. The flocking phase is studied in two levels of approximation. In the incompressible limit, it is confirmed that the scaling exponents, previously obtained using perturbative methods, are indeed exact also within a nonperturbative approximation. Further, this work revealed an active Goldstone regime, where novel scaling laws for the previously neglected parallel and longitudinal modes emerge. In a second approximation, compressibility effects are taken into account using a simplified model, where density fluctuations are only minimally coupled. In dimensions d < 11/3, this model is described by a novel compressible universality class, which in two and three dimensions matches state-of-the-art simulation results of the celebrated Vicsek model. I therefore believe to have uncovered the universality class describing the flocking phase of the Vicsek model, a question that has remained unanswered since the early beginnings of active matter. Around the multicritical point, three novel fixed points are discovered, including the one describing generically the scaling behaviour of the multicritical point. All three universality classes carry the hallmarks of a nonequilibrium universality class.Open Acces
Spatio-temporal variability in forest biodiversity associated with human well-being across socio-economic deprivation gradients
No full textBiodiversity declines are accelerating globally, impacting ecosystem functioning, with consequences for human health. Interactions with biodiversity can be associated with human well-being benefits at the individual level, leading to substantial gains for society when scaled up across populations. However, existing research has not accounted for the species within ecological communities and their effect traits (for example, colours, sounds) that can elicit well-being responses. Many species’ effect traits are seasonal, and spatial variation in exposure to ecosystems by different sectors of society can lead to unequal opportunities to gain well-being. Here we use an interdisciplinary analytical approach to explore how the association between forest biodiversity and well-being fluctuates: (1) temporally, between different seasons and (2) spatially, across socio-economic deprivation gradients at a national scale (England and Wales). Species’ effect traits and participant well-being were derived through a series of seasonal participatory workshops and questionnaires that incorporated BIO-WELL (a biodiversity–well-being psychometric scale). By generating spatially explicit data, we could examine variability in forest biodiversity associated with human well-being across socio-economic deprivation gradients. Forest species’ effect trait richness was spatially heterogeneous, particularly in autumn, spring and summer. Broadleaf forests had greater species’ effect trait richness than other categories of forest. Forests with higher species’ effect trait richness and forests that were associated with higher self-reported participant well-being were in areas with the least socio-economic deprivation. Forest creation/restoration and nature–health interventions must recognize this ecological and social diversity to ensure initiatives are equitable and socially just
Digitalization of access to primary care: is there an equity-efficiency trade-off?
No full textIn the English National Health Service, most patients can use an online platform to send a written request to the practice, in addition to calling or visiting the practice in person. However, there are concerns that the availability of an online access route to primary care can adversely impact healthcare provision for older or lower socioeconomic groups. To examine those concerns, we explore the differential timing of online platforms' implementation between 2019 and 2020 across 289 practices covering over 2.5 million patients in North West London. We find no evidence of an impact of the online access route on age and socioeconomic-related inequity in synchronous interactions in primary care, but observe an increase in all interactions in this setting and in some cases, a small reduction (worst case, no changes) in unplanned hospital care. These findings suggest that having an online access route to primary care can improve the provision of healthcare services, at no detriment to patients from older and lower socioeconomic groups
The nitrogen-vacancy defect in Si1-xGex
No full textDefect processes and energetics in semiconducting alloys is scientifically and technologically important as silicon germanium (Si1 − xGex) is a mainstream nanoelectronic material. It is established that point defects and defect clusters have an increasing role in the physical properties of Si1 − xGex particularly with the ever-decreasing critical dimensions of nanoelectronic devices. Nitrogen-vacancy defects in Si1 − xGex are bound and have the potential to change the optical and electronic properties and thus need to be investigated as absolute control is required in nanoelectronic devices. The nitrogen-vacancy defects are not extensively studied in Si1 − xGex random semiconductor alloys. Here we employ density functional theory (DFT) in conjunction with the special quasirandom structures (SQS) method to calculate the binding energies of substitutional nitrogen-vacancy pairs (NV) in Si1 − xGex alloys. This is a non-trivial problem as the energetics of these defect pairs are dependent upon the nearest neighbour Ge concentration and the composition of Si1 − xGex. The criterion for NV stability is binding energy and here it is shown that the most bound NV defects will form in high Si-content Si1 − xGex alloys
Trends and disparities in the prevalence of diagnosed arthritis among united states adults from 2019 to 2022
No full textArthritis is a predominant cause of disability in the United States, imposing substantial economic burdens and public health challenges. This study aimed to analyze the trends and disparities in the prevalence of arthritis among US adults from 2019 to 2022. The National Health Interview Survey (NHIS) database of the Center for Disease Control and Prevention was analyzed, employing Joinpoint regression analysis for determining annual percentage changes (APCs) and prevalence percentages with 95% confidence intervals (CI). The prevalence of diagnosed arthritis among US adults remained relatively stable and slightly increased from 21.4% (95% CI: 20.9, 22.0) in 2019 to 21.6% (95% CI: 21.0, 22.2) in 2022 (APC: 0.4698; 95% CI: ‐1.0841, 2.0577). Females had a higher prevalence, which also increased from 24.3% to 25.0% (APC: 1.0218; 95% CI: ‐0.4408, 2.5223) with male prevalence ranging from 18.3% to 18.0% (APC: ‐0.3254; 95% CI: ‐2.6590, 2.0817). Age-related differences were particularly evident, with rates peaking in individuals aged ≥ 75 years at 53.9% in 2022. Racial disparities were observed, with White adults having a higher prevalence each year (23.8% in 2022). Geographic factors influenced prevalence, with higher rates noted in areas outside metropolitan areas and in the Midwest. Analysis of the NHIS database indicated a slight rise in arthritis prevalence overall, accompanied by notable demographic disparities. These results emphasize the necessity for tailored public health interventions and efficient disease management approaches tailored to specific populations
Phase-space measurements, decoherence and classicality
No full textThe emergence of classical behavior in quantum theory is often ascribed to the interaction of a quantum system with its environment, which can be interpreted as environmental monitoring of the system. As a result, off-diagonal elements of the density matrix of the system are damped in the basis of a preferred observable, often taken to be the position, leading to the phenomenon of decoherence. This effect can be modeled dynamically in terms of a Lindblad equation driven by the position operator. Here the question of decoherence resulting from a monitoring of position and momentum, i.e., a phase-space measurement, by the environment is addressed. There is no standard quantum observable corresponding to the detection of phase-space points, which is forbidden by Heisenberg's uncertainty principle. This issue is addressed by use of a coherent-state-based positive operator-valued measure for modeling phase-space monitoring by the environment. In this scheme, decoherence in phase space implies the diagonalization of the density matrix in both position and momentum representations. This is shown to be linked to a Lindblad equation where position and momentum appear as two independent Lindblad operators
Allergy and ferroptosis
No full textAllergic responses are defined by hypersensitive reactions against foreign antigens that activate immune cell interactions, leading B lymphocytes to produce IgE. This results in tissue mast cells and circulating basophil cells releasing leukotrienes and histamine, which causes an early inflammatory response; in the late phase, immune cells release chemokines and cytokines. Ferroptosis is an iron-dependently regulated cell death process in which excessive production of reactive oxygen species (ROS) causes massive lipid peroxidation–mediated membrane damage. Allergens, IgE regulation, inflammatory cytokines, and lipid metabolism from an allergic response can induce ferroptosis, which can then enhance the allergic response. This review summarizes the mechanism of ferroptosis and its key regulators. We particularly focus on the potential roles of allergen triggers, IgE regulation, inflammatory cytokines, and lipid metabolism in ferroptosis. We also describe recent research progress regarding ferroptosis in allergic asthma, allergic rhinitis, and allergic dermatitis. Further research on the process of ferroptosis in allergic responses and diseases can aid potential novel therapeutic tools