Optimal trading strategies - a time series approach

Motivated by recent advances in the spectral theory of auto-covariance matrices, we are led to revisit a reformulation of Markowitz' mean-variance portfolio optimization approach in the time domain. In its simplest incarnation it applies to a single traded asset and allows to find an optimal trading strategy which - for a given return - is minimally exposed to market price fluctuations. The model is initially investigated for a range of synthetic price processes, taken to be either second order stationary, or to exhibit second order stationary increments. Attention is paid to consequences of estimating auto-covariance matrices from small finite samples, and auto-covariance matrix cleaning strategies to mitigate against these are investigated. Finally we apply our framework to real world data

Rare Earth Doped Silica for Integrated Optical Waveguide Lasers and Amplifiers

The aim of the project was to realise rare earth doped planar silica waveguide lasers. Research centred on two rare earth ions: neodymium taking advantage of the four level laser system near 1.05 mum and erbium with emission at 1.54 mum, in the important third telecommunication window. Research concentrated on SiO2-P2O5 glass films fabricated by the flame hydrolysis of SiCl4 and PCI3. The resultant low density glass soot was deposited onto silica or oxidised silicon substrates, which was then sintered at temperatures up to 135

Resource extraction and infrastructure threaten forest cover and community rights

Mineral and hydrocarbon extraction and infrastructure are increasingly significant drivers of forest loss, greenhouse gas emissions, and threats to the rights of forest communities in forested areas of Amazonia, Indonesia, and Mesoamerica. Projected investments in these sectors suggest that future threats to forests and rights are substantial, particularly because resource extraction and infrastructure reinforce each other and enable population movements and agricultural expansion further into the forest. In each region, governments have made framework policy commitments to national and cross-border infrastructure integration, increased energy production, and growth strategies based on further exploitation of natural resources. This reflects political settlements among national elites that endorse resource extraction as a pathway toward development. Regulations that protect forests, indigenous and rural peoples’ lands, and conservation areas are being rolled back or are under threat. Small-scale gold mining has intensified in specific locations and also has become a driver of deforestation and degradation. Forest dwellers’ perceptions of insecurity have increased, as have documented homicides of environmental activists. To explain the relationships among extraction, infrastructure, and forests, this paper combines a geospatial analysis of forest loss overlapped with areas of potential resource extraction, interviews with key informants, and feedback from stakeholder workshops. The increasing significance of resource extraction and associated infrastructure as drivers of forest loss and rights violations merits greater attention in the empirical analyses and conceptual frameworks of Sustainability Science

Psychological mechanisms mediating effects between trauma and psychotic symptoms: the role of affect regulation, intrusive trauma memory, beliefs, and depression

Evidence suggests a causal role for trauma in psychosis, particularly for childhood victimization. However, the establishment of underlying trauma-related mechanisms would strengthen the causal argument. In a sample of peo-ple with relapsing psychosis (n = 228), we tested hypoth-esized mechanisms specifically related to impaired affect regulation, intrusive trauma memory, beliefs, and depres-sion. The majority of participants (74.1%) reported vic-timization trauma, and a fifth (21.5%) met symptomatic criteria for Posttraumatic Stress Disorder. We found a specific link between childhood sexual abuse and auditory hallucinations (adjusted OR = 2.21, SE = 0.74, P = .018). This relationship was mediated by posttraumatic avoid-ance and numbing (OR = 1.48, SE = 0.19, P = .038) and hyperarousal (OR = 1.44, SE = 0.18, P = .045), but not intrusive trauma memory, negative beliefs or depression. In contrast, childhood emotional abuse was specifically associated with delusions, both persecutory (adjusted OR = 2.21, SE = 0.68, P = .009) and referential (adjusted OR = 2.43, SE = 0.74, P = .004). The link with persecutory delusions was mediated by negative-other beliefs (OR = 1.36, SE = 0.14, P = .024), but not posttraumatic stress symptoms, negative-self beliefs, or depression. There was no evidence of mediation for referential delusions. No rela-tionships were identified between childhood physical abuse and psychosis. The findings underline the role of cognitive-affective processes in the relationship between trauma and symptoms, and the importance of assessing and treating victimization and its psychological consequences in people with psychosis

The evolution of delayed dispersal and different routes to breeding in social birds

Many animals live in stable groups, where sexually mature individuals delay dispersal and stay as nonbreeding subordinates, seemingly counter to their own evolutionary interests. Revealing what circumstances drive the evolution of delayed dispersal is central to understanding sociality, family living and cooperative breeding across the animal kingdom, but there is as yet no general consensus about the relative importance of the various ecological and social conditions and the reproductive benefits proposed to drive delayed dispersal. We argue that two components may facilitate further progress in this respect: firstly, full consideration of the various routes that individuals can follow to obtain an independent breeding position. Here, we provide a comprehensive review of these routes: inheritance of a natal territory, budding off part of the natal territory, shifting to a neighboring vacancy, making temporary prospecting trips throughout the population; or permanently leaving to float in search of a breeding position or to stage as subordinate in a non-natal territory. Second, we illustrate that in order to understand delayed dispersal, we need to consider that the fitness consequences of these different routes apply across the lifetime: as subordinate (e.g., benefits of philopatry and indirect fitness); while waiting or searching for a position; and after obtaining a breeding position. Overall, we conclude that by which route and under what circumstances individuals can obtain a breeding position must be considered in order to make more comprehensive inferences about the evolution of delayed dispersal, cooperative breeding and animal sociality as a whole.</p

Delayed dispersal and the cost and benefits of different routes to independent breeding in a cooperative breeding bird

Why sexually mature individuals stay in groups as non-reproductive subordinates is central to the evolution of sociality and cooperative breeding. To understand such delayed dispersal, its costs and benefits need to be compared with those of permanently leaving to float through the population. However, comprehensive comparisons, especially regarding differences in future breeding opportunities, are rare. Moreover, extra-territorial prospecting by philopatric individuals has generally been ignored, even though the factors underlying this route to independent breeding may differ from those of strict philopatry or floating. We use a comprehensive predictive framework to explore how various costs, benefits and intrinsic, environmental and social factors explain philopatry, prospecting and floating in Seychelles warblers (Acrocephalus sechellensis). Floaters more likely obtained an independent breeding position before the next season than strictly philopatric individuals, but also suffered higher mortality. Prospecting yielded similar benefits to floating but lower mortality costs, suggesting that it is overall more beneficial than floating and strict philopatry. Whereas prospecting is probably individual-driven, though limited by resource availability, floating likely results from eviction by unrelated breeders. Such differences in proximate and ultimate factors underlying each route to independent breeding highlight the need for simultaneous consideration when studying the evolution of delayed dispersal

Co-Occurrence Patterns of Common and Rare Leaf-Litter Frogs, Epiphytic Ferns and Dung Beetles across a Gradient of Human Disturbance

Indicator taxa are commonly used to identify priority areas for conservation or to measure biological responses to environmental change. Despite their widespread use, there is no general consensus about the ability of indicator taxa to predict wider trends in biodiversity. Many studies have focused on large-scale patterns of species co-occurrence to identify areas of high biodiversity, threat or endemism, but there is much less information about patterns of species co-occurrence at local scales. In this study, we assess fine-scale co-occurrence patterns of three indicator taxa (epiphytic ferns, leaf litter frogs and dung beetles) across a remotely sensed gradient of human disturbance in the Ecuadorian Amazon. We measure the relative contribution of rare and common species to patterns of total richness in each taxon and determine the ability of common and rare species to act as surrogate measures of human disturbance and each other. We find that the species richness of indicator taxa changed across the human disturbance gradient but that the response differed among taxa, and between rare and common species. Although we find several patterns of co-occurrence, these patterns differed between common and rare species. Despite showing complex patterns of species co-occurrence, our results suggest that species or taxa can act as reliable indicators of each other but that this relationship must be established and not assumed

Consequences of sibling rivalry vary across life in a passerine bird

Many studies have assessed the costs of sibling rivalry in systems where offspring always have competitors, but conclusions about sibling rivalry in these species are restricted to interpreting the cost of changes in the relative level of competition and are often complicated by the expression of potentially costly rivalry related traits. Additionally, the majority of studies focus on early-life sibling rivalry, but the costs of competition can also affect later-life performance. We test a suite of hypothesized immediate (early-life body mass, telomere length, and survival) and delayed (adult reproductive potential and lifespan) costs of sibling rivalry for offspring of differing competitive ability in Seychelles warblers, where most offspring are raised singly and hence competitor success can be compared to a competition-free scenario. Compared to those raised alone, all competing nestlings had lower body mass and weaker competitors experienced reduced survival. However, the stronger competitors appeared to have longer adult breeding tenures and lifespan than those raised alone. We propose that comparisons with competition-free groups, as well as detailed fitness measures across entire lifetimes, are needed to understand the evolution of sibling rivalry and thus individual reproductive strategy in wild systems

Joint care can outweigh costs of nonkin competition in communal breeders

Competition between offspring can greatly influence offspring fitness and parental investment decisions, especially in communal breeders where unrelated competitors have less incentive to concede resources. Given the potential for escalated conflict, it remains unclear what mechanisms facilitate the evolution of communal breeding among unrelated females. Resolving this question requires simultaneous consideration of offspring in noncommunal and communal nurseries, but such comparisons are missing. In the Seychelles warbler Acrocephalus sechellensis, we compare nestling pairs from communal nests (2 mothers) and noncommunal nests (1 mother) with singleton nestlings. Our results indicate that increased provisioning rate can act as a mechanism to mitigate the costs of offspring rivalry among nonkin. Increased provisioning in communal broods, as a consequence of having 2 female parents, mitigates any elevated costs of offspring rivalry among nonkin: per-capita provisioning and survival was equal in communal broods and singletons, but lower in noncommunal broods. Individual offspring costs were also more divergent in noncommunal broods, likely because resource limitation exacerbates differences in competitive ability between nestlings. It is typically assumed that offspring rivalry among nonkin will be more costly because offspring are not driven by kin selection to concede resources to their competitors. Our findings are correlational and require further corroboration, but may help explain the evolutionary maintenance of communal breeding by providing a mechanism by which communal breeders can avoid these costs