Optimal Surveys for Weak Lensing Tomography

Weak lensing surveys provide a powerful probe of dark energy through the measurement of the mass distribution of the local Universe. A number of ground-based and space-based surveys are being planned for this purpose. Here, we study the optimal strategy for these future surveys using the joint constraints on the equation of state parameter wn and its evolution wa as a figure of merit by considering power spectrum tomography. For this purpose, we first consider an `ideal' survey which is both wide and deep and exempt from systematics. We find that such a survey has great potential for dark energy studies, reaching one sigma precisions of 1% and 10% on the two parameters respectively. We then study the relative impact of various limitations by degrading this ideal survey. In particular, we consider the effect of sky coverage, survey depth, shape measurements systematics, photometric redshifts systematics and uncertainties in the non-linear power spectrum predictions. We find that, for a given observing time, it is always advantageous to choose a wide rather than a deep survey geometry. We also find that the dark energy constraints from power spectrum tomography are robust to photometric redshift errors and catastrophic failures, if a spectroscopic calibration sample of 10^4-10^5 galaxies is available. The impact of these systematics is small compared to the limitations that come from potential uncertainties in the power spectrum, due to shear measurement and theoretical errors. To help the planning of future surveys, we summarize our results with comprehensive scaling relations which avoid the need for full Fisher matrix calculations.Comment: Submitted to MNRAS. 10 pages, including 13 figures and 2 table

Systematic Bias in Cosmic Shear: Beyond the Fisher Matrix

We describe a method for computing the biases that systematic signals introduce in parameter estimation using a simple extension of the Fisher matrix formalism. This allows us to calculate the offset of the best fit parameters relative to the fiducial model, in addition to the usual statistical error ellipse. As an application, we study the impact that residual systematics in tomographic weak lensing measurements. In particular we explore three different types of shape measurement systematics: (i) additive systematic with no redshift evolution; (ii) additive systematic with redshift evolution; and (iii) multiplicative systematic. In each case, we consider a wide range of scale dependence and redshift evolution of the systematics signal. For a future DUNE-like full sky survey, we find that, for cases with mild redshift evolution, the variance of the additive systematic signal should be kept below 10^-7 to ensure biases on cosmological parameters that are sub-dominant to the statistical errors. For the multiplicative systematics, which depends on the lensing signal, we find the multiplicative calibration m0 needs to be controlled to an accuracy better than 10^-3. We find that the impact of systematics can be underestimated if their assumes redshift dependence is too simplistic. We provide simple scaling relations to extend these requirements to any survey geometry and discuss the impact of our results for current and future weak lensing surveys.Comment: Submitted to MNRAS. 11 pages, including 11 figures and 4 table

The KH-Theory of Complete Simplicial Toric Varieties and the Algebraic K-Theory of Weighted Projective Spaces

We show that, for a complete simplicial toric variety $X$, we can determine its homotopy \KH-theory entirely in terms of the torus pieces of open sets forming an open cover of $X$. We then construct conditions under which, given two complete simplicial toric varieties, the two spectra \KH(X) \otimes \Q and \KH(Y) \otimes \Q are weakly equivalent. We apply this result to determine the rational \KH-theory of weighted projective spaces. We next examine \K-regularity for complete toric surfaces; in particular, we show that complete toric surfaces are \K_{0}-regular. We then determine conditions under which our approach for dimension 2 works in arbitrary dimensions, before demonstrating that weighted projective spaces are not \K_{1}-regular, and for dimensions bigger than 2 are also not in general \K_{0}-regular.Comment: 14 pages. Updated version, strengthening the proofs to hold true over any regular ring. To appear in the Journal of Pure and Applied Algebr

Memory, space and time: Researching children's lives

This article discusses the research approach in 'Pathways through Childhood', a small qualitative study drawing on memories of childhood. The research explores how wider social arrangements and social change influence children's everyday lives.The article discusses the way that the concepts of social memory, space and time have been drawn on to access and analyse children's experiences, arguing that attention to the temporal and spatial complexity of childhood reveals less visible yet formative influences and connections. Children's everyday engagements involve connections between past and present time, between children, families, communities and nations, and between different places. Children carve out space and time for themselves from these complex relations. © The Author(s) 2010

On Point Spread Function modelling: towards optimal interpolation

Point Spread Function (PSF) modeling is a central part of any astronomy data analysis relying on measuring the shapes of objects. It is especially crucial for weak gravitational lensing, in order to beat down systematics and allow one to reach the full potential of weak lensing in measuring dark energy. A PSF modeling pipeline is made of two main steps: the first one is to assess its shape on stars, and the second is to interpolate it at any desired position (usually galaxies). We focus on the second part, and compare different interpolation schemes, including polynomial interpolation, radial basis functions, Delaunay triangulation and Kriging. For that purpose, we develop simulations of PSF fields, in which stars are built from a set of basis functions defined from a Principal Components Analysis of a real ground-based image. We find that Kriging gives the most reliable interpolation, significantly better than the traditionally used polynomial interpolation. We also note that although a Kriging interpolation on individual images is enough to control systematics at the level necessary for current weak lensing surveys, more elaborate techniques will have to be developed to reach future ambitious surveys' requirements.Comment: Accepted for publication in MNRA

Native Apps versus Web Apps: which is best for healthcare applications?

Smartphone applications (Apps) provide a new way to deliver healthcare, illustrated by the fact that healthcare Apps are estimated to make up over 30% of new Apps currently being developed; with this number seemingly set to increase as the benefits become more apparent. In this paper, using the development of an In Vitro Fertilisation (IVF) treatment stress study App as the exemplar, the alternatives of Native App and Web App design and implementa-tion are considered across several factors that include: user interface, ease of development, capabilities, performance, cost, and potential problems. Development for iOS and Android platforms and a Web App using JavaScript and HTML5 are discussed

Mental health in the UK during the COVID-19 pandemic: cross-sectional analyses from a community cohort study

Objectives: Previous pandemics have resulted in significant consequences for mental health. Here, we report the mental health sequelae of the COVID-19 pandemic in a UK cohort and examine modifiable and non-modifiable explanatory factors associated with mental health outcomes. We focus on the first wave of data collection, which examined short-term consequences for mental health, as reported during the first 4–6 weeks of social distancing measures being introduced.Design: Cross-sectional online survey.Setting: Community cohort study.Participants: N=3097 adults aged ≥18 years were recruited through a mainstream and social media campaign between 3 April 2020 and 30 April 2020. The cohort was predominantly female (n=2618); mean age 44 years; 10% (n=296) from minority ethnic groups; 50% (n=1559) described themselves as key workers and 20% (n=649) identified as having clinical risk factors putting them at increased risk of COVID-19.Main outcome measures: Depression, anxiety and stress scores.Results: Mean scores for depression (Embedded Image =7.69, SD=6.0), stress (Embedded Image =6.48, SD=3.3) and anxiety (Embedded Image = 6.48, SD=3.3) significantly exceeded population norms (all p < 0.0001). Analysis of non-modifiable factors hypothesised to be associated with mental health outcomes indicated that being younger, female and in a recognised COVID-19 risk group were associated with increased stress, anxiety and depression, with the final multivariable models accounting for 7%–14% of variance. When adding modifiable factors, significant independent effects emerged for positive mood, perceived loneliness and worry about getting COVID-19 for all outcomes, with the final multivariable models accounting for 54%–57% of total variance.Conclusions: Increased psychological morbidity was evident in this UK sample and found to be more common in younger people, women and in individuals who identified as being in recognised COVID-19 risk groups. Public health and mental health interventions able to ameliorate perceptions of risk of COVID-19, worry about COVID-19 loneliness and boost positive mood may be effective

User requirements for the development of smartphone self-reporting applications in healthcare

Two case studies of the development of Smartphone self-reporting mHealth applications are described: a wellness diary for asthma management combined with Bluetooth pulse oximeter and manual peak flow measurements; and a questionnaire for ecological assessment of distress during fertility treat-ment. Results are presented of user experiences with the self-reporting applica-tion and the capture of physiological measurements in the case of the asthma diary project and the findings from a phone audit at an early stage of design in the case of the in vitro fertilisation (IVF) study. Issues raised by ethics commit-tees are also discussed. It is concluded that the optimal adoption of Smartphone self-reporting applications will require a good appreciation of user and ethics panel requirements at an early stage in their development, so that the correct de-sign choices can be made