A new map-making algorithm for CMB polarisation experiments

With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by removed using our algorithms. The algorithms require no prior knowledge of the imperfections or temperature sky to remove the temperature leakage. Instead, they calculate the systematic and polarisation maps in one step directly from the time ordered data (TOD). The first algorithm is designed to work with scan strategies that have a good range of crossing angles for each map pixel and the second for scan strategies that have a limited range of crossing angles. The first algorithm can also be used to identify if systematic errors that have a particular spin are present in a TOD. We demonstrate the use of both algorithms and the ability to identify systematics with simulations of TOD with realistic scan strategies and instrumental noise.Comment: 11 pages, 6 figure

Optimal scan strategies for future CMB satellite experiments

The B-mode polarisation power spectrum in the Cosmic Microwave Background (CMB) is about four orders of magnitude fainter than the CMB temperature power spectrum. Any instrumental imperfections that couple temperature fluctuations to B-mode polarisation must therefore be carefully controlled and/or removed. We investigate the role that a scan strategy can have in mitigating certain common systematics by averaging systematic errors down with many crossing angles. We present approximate analytic forms for the error on the recovered B-mode power spectrum that would result from differential gain, differential pointing and differential ellipticity for the case where two detector pairs are used in a polarisation experiment. We use these analytic predictions to search the parameter space of common satellite scan strategies in order to identify those features of a scan strategy that have most impact in mitigating systematic effects. As an example we go on to identify a scan strategy suitable for the CMB satellite proposed for the ESA M5 call. considering the practical considerations of fuel requirement, data rate and the relative orientation of the telescope to the earth. Having chosen a scan strategy we then go on to investigate the suitability of the scan strategy.Comment: 21 pages, 11 figures, Comments welcom

Engineering design of sub-micron topographies for simultaneously adherent and reflective metal-polymer interfaces

The approach of the project is to base the design of multi-function, reflective topographies on the theory that topographically dependent phenomena react with surfaces and interfaces at certain scales. The first phase of the project emphasizes the development of methods for understanding the sizes of topographic features which influence reflectivity. Subsequent phases, if necessary, will address the scales of interaction for adhesion and manufacturing processes. A simulation of the interaction of electromagnetic radiation, or light, with a reflective surface is performed using specialized software. Reflectivity of the surface as a function of scale is evaluated and the results from the simulation are compared with reflectivity measurements made on multi-function, reflective surfaces

voxEUROPP Episode 2: Eastern Europe and Democracy

Today EUROPP launches the second episode in our voxEUROPP series of podcasts. Presented by Chris Gilson and Stuart A Brown, voxEUROPP draws on academic experts from EUROPP to discuss the latest issues across European governance, economics, politics, culture and society, both at the European Union and national levels

Removing beam asymmetry bias in precision CMB temperature and polarisation experiments

Asymmetric beams can create significant bias in estimates of the power spectra from CMB experiments. With the temperature power spectrum many orders of magnitude stronger than the B-mode power spectrum any systematic error that couples the two must be carefully controlled and/or removed. Here, we derive unbiased estimators for the CMB temperature and polarisation power spectra taking into account general beams and general scan strategies. A simple consequence of asymmetric beams is that, even with an ideal scan strategy where every sky pixel is seen at every orientation, there will be residual coupling from temperature power to B-mode power if the orientation of the beam asymmetry is not aligned with the orientation of the co-polarisation. We test our correction algorithm on simulations of two temperature-only experiments and demonstrate that it is unbiased. The simulated experiments use realistic scan strategies, noise levels and highly asymmetric beams. We also develop a map-making algorithm that is capable of removing beam asymmetry bias at the map level. We demonstrate its implementation using simulations and show that it is capable of accurately correcting both temperature and polarisation maps for all of the effects of beam asymmetry including the effects of temperature to polarisation leakage.Comment: 18 pages, 9 figure

Short Convergent Synthesis of the Mycolactone Core Through Lithiation-Borylation Homologations

Abstract: Using iterative lithiation-borylation homologations, the mycolactone toxin core has been synthesized in 13 steps and 17 %o verall yield. The rapid build-up of molecular complexity,h igh convergencea nd high stereoselectivitya re noteworthy features of this synthesis. The third most common Mycobacterium infection( after M. tuberculosis and M. leprae)i sthat of M. ulcerans,t he pathogen responsible for the severeu lcerative skin disease,B uruli ulcer. [1] Endemic in tropical Africa, it infects over 5000 patients per annum with 48 %o fc ases being aged under 15. [1a, 2] Transmission is thought to occur by an aquatic organism bite, [3] with initial manifestation occurring as ap ainless skin nodule. If diagnosed early, simple antibiotic chemotherapyi seffective (80 %), [4] however, if untreated, propagation of the infection results in large skin lesions of necrotic tissue and bone loss which are only treatable througha ggressive surgery,r esulting in scarring and loss of limb function. [1a, c] Small and coworkers [8] successfully isolated milligram quantities of 1 allowing structure elucidation by NMR [17] These efforts have enabled furtherr esearch into the pathogenesis of Buruli ulcer, [18] aid the invention of new/simplerd iagnostic techniques [20a] The side chain of 1 has alreadyb een synthesized by the groups of Kishi, Our retrosynthetic analysisb egan with disconnection to the knowni ntermediate 3 (Scheme 2). We began with the synthesis of boronic ester 10,w hich was achieved in three high yielding steps (Scheme3). Copper-catalyzed formal hydroboration [27] of alkynol 11 with B 2 pin 2 in the presence of MeOH gave the desiredv inyl boronate in 83 % yield as as ingle regio-and stereoisomer.S ubsequent carbaScheme1.Structure of mycolactone A/B 1 and core 2. [a] C. A. Brown, Prof. Dr.V .K.A ggarwal SchoolofC hemistry,University of Bristol Cantock's Close Bristol, BS8 1TS (UK

Removing beam asymmetry bias in precision CMB temperature and polarisation experiments

Asymmetric beams can create significant bias in estimates of the power spectra from CMB experiments. With the temperature power spectrum many orders of magnitude stronger than the B-mode power spectrum any systematic error that couples the two must be carefully controlled and/or removed. Here, we derive unbiased estimators for the CMB temperature and polarisation power spectra taking into account general beams and general scan strategies. A simple consequence of asymmetric beams is that, even with an ideal scan strategy where every sky pixel is seen at every orientation, there will be residual coupling from temperature power to B-mode power if the orientation of the beam asymmetry is not aligned with the orientation of the co-polarisation. We test our correction algorithm on simulations of two temperature-only experiments and demonstrate that it is unbiased. The simulated experiments use realistic scan strategies, noise levels and highly asymmetric beams. We also develop a map-making algorithm that is capable of removing beam asymmetry bias at the map level. We demonstrate its implementation using simulations and show that it is capable of accurately correcting both temperature and polarisation maps for all of the effects of beam asymmetry including the effects of temperature to polarisation leakage.Comment: 18 pages, 9 figure