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Uncertain Location Transmitter and UAV-Aided Warden-Based LEO Satellite Covert Communication Systems
Full text linkWe propose a novel covert communication system in which a ground user, Alice, transmits unauthorized message fragments to Bob, a low-Earth orbit satellite (LEO), and an unmanned aerial vehicle (UAV) warden (Willie) attempts to detect these transmissions. The key contribution is modeling a scenario where Alice and Willie are unaware of each other’s exact locations and move randomly within a specific area. Alice utilizes environmental obstructions to avoid detection and only transmits when the satellite is directly overhead. LEO satellite technology allows users to avoid transmitting messages near a base station. We introduce two key performance metrics: catch probability (Willie detects and locates Alice during a message chunk transmission) and overall catch probability over multiple message chunks. We analyze how two parameters impact these metrics: 1) the size of the detection window and 2) the number of message chunks. The paper proposes two algorithms to optimize these parameters. The simulation results show that the algorithms effectively reduce the detection risks. This work advances the understanding of covert communication under mobility and uncertainty in satellite-aided systems
IdeFN : Identifying Unclicked Space False Negatives via Relaxed Partial Optimal Transport for Conversion Rate Prediction
Full text linkAccurate conversion rate (CVR) prediction is critical for recommender systems to capture user conversion intent and increase platform revenues. Traditional CVR models commonly suffer from sample selection bias (SSB) and data sparsity (DS), which has led to the adoption of click-through & conversion rate (CTCVR) multi-task learning frameworks to alleviate these issues. However, existing methods implicitly mislabel some unclicked samples with genuine conversion potential as negatives, thereby exacerbating the false negative sample (FNS) problem. To address this, we propose IdeFN, a multi-task CVR framework that identifies false negatives in the unclicked space to enable CVR prediction across the entire exposure space and leverages click-through rates (CTR) as an auxiliary task for shared-parameter learning. Specifically, IdeFN consists of two main components, i.e., relaxed partial optimal transport (RPOT) module and sample relabeling mechanism (SRM). The former estimates the soft matching strengths between unclicked samples and positive samples under a relaxed partial optimal transport formulation, establishing corresponding relationships between these samples. The latter adaptively re-labels the unclicked samples according to the derived matching strengths, without relying on static or heuristic thresholds, thus enhancing the reliability of the generated pseudo-labels. Experimental results demonstrate that IdeFN effectively mitigates the FNS problem, achieving substantial improvements in CVR prediction accuracy
Ultrashort-pulse optical manipulation of anisotropic nanoparticles via photonic nanojets and hooks in aqueous environments
No full textWe present a computational study on the optical manipulation of anisotropic gold nanoparticles, rods, and disks in aqueous environments using ultrashort pulsed photonic nanojets and photonic hooks. Using three-dimensional finite-difference time-domain simulations and analytical models of anisotropic polarizability, we analyze how shape, orientation, and surrounding medium influence the optical force landscape. Our results show that deviations from spherical particle geometry introduce strong orientation dependence, with optical forces varying by up to a factor of 5-10 across particle orientations and structured-field configurations. In particular, force minima emerge at intermediate tilt angles due to destructive coupling between polarizability axes. We also demonstrate that the surrounding medium significantly alters field confinement and force magnitude, with water enhancing field localization and modifying the dominant particle geometry. These findings provide design guidelines for structured-light-based nanoparticle manipulation, particularly for applications in nanomedicine, sensing, and fabrication, where real-world particles are non-spherical and operate in aqueous conditions
Culture and environmental relational values at Amazonian farm-forest frontiers
Full text linkLarge-scale tropical deforestation threatens biodiversity, global climatic stability, and the livelihoods of forest-dependent people. The Brazilian Amazon harbours tremendous cultural diversity, rooted in Indigenous cosmologies, forest management practices, and centuries of adaptations by Amazonian peasantry. Yet annual deforestation has been high for decades, driven primarily by agricultural frontier expansion, characterized by violent dispossession of forest-dependent communities by illegal loggers and cattle ranchers. Quantitative analyses have focused on economic, spatial and political factors, largely neglecting the role of culture in land-use decisions. In contrast, ethnographic work demonstrates that forest clearance for pasture coincides with the emergence of an Amazonian cattle culture. This thesis examines the relationship between culture and regional-scale environmental change, investigating how cultural expression and environmental relational values are associated with land-use and land-cover change (LULCC) at deforestation frontiers. I employ novel demographic approaches to quantifying cultural expression at largespatial scales, analysing 3,427 songs played on 1,069 local radio stations across the Brazilian Amazon to perform the first cross-sectional culture~environment study to my knowledge. To link cultural expression and relational values to environmental histories and rural modes of production thousands of kilometres apart, I conducted fieldwork in four municipalities, ranging from one with 98% remaining forest cover and few cattle to another with 73% forest remaining and over 2.4 million cattle, the largest herd in Brazil. I developed and administered a novel survey to rural and urban people in each municipality, examining cultural expression associated with traditional Amazonian identities, cattle culture, and people’s relationships with their local environment. My results demonstrate that cultural identities and relational values across Amazonia are highly heterogenous and are associated with local land use, migration histories, and frontier expansion. I show that deforestation has complex and significant cultural dimensions and provide evidence that cattle culture is displacing traditional forest cultures as deforestation transforms landscapes. Recognising the cultural dimensions of LULCC in Amazonia is therefore critical to protecting forests and cultures of forestproximate people who have underpinned people-centred conservation in Brazil and elsewhere
A Novel Constrained Car-Following Control System for Autonomous Vehicles with Only Relative Distance and Angle Measurements
Full text linkThis paper proposes a novel coordinated car-following controller for two connected Ackermann steering vehicles subjected to actuator saturation, model uncertainties, limited filed-of-view, limited sensing and communication ranges, without velocity measurements, without collision between vehicles, and with path curvature compensation. To comply with the controller design, relative constrained distance and angle between vehicles are transformed into an efficient Euler-Lagrange formulation in terms of unconstrained errors. Then, two new sets of nonlinear filtered error variables are devised to propose a novel saturated proportional-integral-derivative observer-based control scheme which takes the advantages of the amplitude-limited PID control structure. The unknown model parameters and external disturbances are compensated via an operational combination of an adaptive robust control (ARC) scheme and a neural network (NN). The controller stability is proved by Lyapunov's direct method. Comparative simulation results will show the main benefits of the proposed control system
Black Hole and Host Galaxy Co-Evolution
Full text linkThe origins and the evolution of the observed correlations between supermassive black holes (SMBHs) and their host galaxies are still under debate. A merger-driven co-evolution framework has been a popular hypothesis, and suggests that mergers fuel both star formation and SMBH accretion. However, there is now evidence that the majority of black hole growth has occurred in the absence of mergers; moreover, a merger-driven scenario does not account for the rapidly accreting SMBHs, known as active galactic nuclei (AGN), observed in galaxies with morphologies indicative of a secular evolutionary history. The nature of co-evolution in disc-dominated galaxies is unclear, with different studies of unobscured (Type 1) AGN drawing contradictory conclusions. We analyse three such samples, applying their selection functions to a mock population of Type 1 AGN. We find that the different samples from the published studies are consistent with being drawn from the same underlying population. The mock AGN population is agnostic to the specifics of galaxy mass accretion and assembly. The fact that the disc galaxy samples are in agreement with the mock sample supports the growing consensus that merger-free black hole growth is typical and can lead to co-evolution between supermassive black holes and galaxies. We then use multicomponent 2D decomposition to examine the morphological dependence, as traced by bulge-to-total (B/T ) ratio, of the correlations between SMBH mass and both total and bulge stellar mass for a sample of 415 Type 1 AGN at z < 0.35. We use mock synthetic AGN host galaxies, generated by inserting point sources into inactive galaxies, to show that the decomposition process is reliable with small systematics. We find no morphological dependence on the SMBH mass-total stellar mass relation, while we find that the SMBH mass-bulge stellar mass relation is a shallower relation and dependent on B/T , with SMBHs in disc-dominated galaxies being offset above SMBHs hosted in bulge-dominated galaxies for a given bulge stellar mass. This further supports the hypothesis that secular evolution plays a strong role in driving co-evolution. In summary, regardless of the mechanism driving bulge growth, coevolution of the galaxy and SMBH clearly occurs, and is more strongly tied to the total stellar mass than to bulge properties. Thus, AGN growth may be more related to the total gravitational potential, which is better traced by the total stellar mass than the bulge stellar mass. The new and upcoming surveys are well placed to further this work with larger or higher resolution samples
Challenges for ionosphere-thermosphere science
No full textReport on the RAS Specialist Discussion Meeting about one of the grand challenges for Earth system scientist
Models for algorithm selection for combinatorial optimisation problems
No full textCombinatorial optimisation (CO) problems are often solved using approximate methods, such as heuristics, in practice. These solvers exhibit varying strengths in terms of solution quality and resource usage, making CO problems well-suited to automated algorithm selection. Effectively solving the algorithm selection problem (ASP) enables users to predict the most suitable algorithm for a given problem instance, thereby improving performance. Appropriate models also provide insights into the relationship between problem characteristics and algorithm behaviour. In this thesis, we explore multiple models for and elements of the algorithm selection problem. First, we assess the benefits of including dimensionality reduction (DR) in the ASP framework. We evaluate multiple classifiers paired with both unsupervised and supervised DR methods, as well as classifiers that inherently perform DR, across several combinatorial optimisation problem domains. We also study the impact of using regularisation during dimensionality reduction to obtain sparse representations of the feature space and promote feature elimination. We then apply the ASP and recent extensions of the framework to novel problem domains. Metadata is first generated for Sudoku puzzles as an illustrative example, then for the capacitated vehicle routing problem. For both domains, we evaluate the effect of using different performance metrics on the results from instance space analysis. We then propose the use of mixture discriminant analysis within the ISA framework to obtain both a low-dimensional representation of the instance space and a classifier of algorithm performance
Dark Energy Survey Year 6 Results : Photometric Dataset for Cosmology
Full text linkWe describe the photometric dataset assembled from the full 6 yr of observations by the Dark Energy Survey (DES) in support of static-sky cosmology analyses. DES Y6 Gold is a curated dataset derived from DES Data Release 2 (DR2) that incorporates improved measurement, photometric calibration, object classification and value-added information. Y6 Gold comprises nearly 5000 deg2 of grizY imaging in the south Galactic cap and includes 669 million objects with a depth of iAB ∼ 23.4 mag at a signal-to-noise ratio ∼ 10 for extended objects and a top-of-the-atmosphere photometric uniformit
OPTIMISATION OF TIDAL RANGE ELECTRICITY GENERATION AND ECONOMICS
Full text linkThe purpose of this study is to improve knowledge and understanding of tidal range power by investigating the potential for generation and its economics. The approach used an existing model of electricity generation (Lancaster 0-D tidal model) to investigate optimal generation and financial return. The thesis examines the question of the feasibility of tidal range power and the issues that are commonly presented as barriers preventing deployment. Those barriers include economics (finance, scale, rate of construction and power generation), environment (climate change, habitat loss, pollution) and engineering (mechanical, civil and electrical).Two case study sites were selected for investigation using scenarios with multiple configurations of: - numbers and size of turbines - sluice ratios - generator ratings. The economic issues were partly addressed by developing a simple financial model for the capital cost of schemes (CAPEX). It was used to indicate how specific components within a scheme best contribute to the financial return of investment. It can also be used to compare schemes in different locations and rank them in order of profitability. A major environmental consideration is climate change; it is especially important as tidal range schemes are designed to have a functional life of at least 120-years. The climate change driven challenge of sea level rise (SLR) over the proposed operation life must be considered in both planning and operation. This study models tidal range power schemes so that they protect coastal habitats and communities by maintaining the existing tidal range. For the two sites studied, as sea level begins to rise, the annual electricity production (AEP) increases due to the greater water head in flood tides. As SLR continues, the AEP falls due to increased pumping required to achieve low tide levels. Initially, pumping can be performed by the turbines used as pumps (TaP). The TaPs are not sufficient for higher levels of SLR, so after about 40-years it may be necessary to install submersible pumps to effectively match the desired low tide limits. The disciplines within engineering run as a constant thread through this thesis, essential in design, deployment, operation, maintenance and decommissioning. The time taken to deploy a barrage is constrained by the civil engineering options. A preliminary analysis of precast concrete barrage designs was made, with both existing vertical units and my proposed horizontal units. The latter can be cast on shore and floated out in shallower water, the sloping sides reduce both ground bearing pressures and the volume of concrete needed. The times of high and low tide are predictable for any site even though the tidal range varies for each cycle. A simplified 0-D program has been proposed based on varying the start of generation relative to the time of the previous high or low tide. The aim is to analyse a whole year of individual tides and include an efficiency reduction for reverse flow generation. During the development a simple spreadsheet was produced for a period of 22-days from the start of 2024 to be used to check the program. This identified that the simple time base program was effective but that it was not sufficient for operational use; there were several periods of generating at negative price which need not happen during operation. Consequently, a modified model was proposed that weighted the flow according to price and so better reflect demand. The adjustment created a significant increase in financial return whilst the total generation reduced. The algorithm will be complex and there was not sufficient time to write a program during this study. It is hoped to continue this work in future. Finally, the methods of comparing costs of different energy generating technologies have been examined and a new metric developed. It overcomes some of the problems with the commonly used levelised cost of energy by comparing continuous generation over the longest lifespan of the technologies considered (120-years). For example, a tidal barrage is equivalent to two nuclear sites of 60-years operational life or four gas turbine stations with 30-year operational lives. The analysis shows how tidal range power is economically viable and would fit into the national power generation system. If the annual benefits of flood protection are included in the analysis, tidal range power becomes the cheapest of all grid scale renewable technologies