886 research outputs found

    Galaxy-Galaxy Flexion: Weak Lensing to Second Order

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    In this paper, we develop a new gravitational lensing inversion technique. While traditional approaches assume that the lensing field varies little across a galaxy image, we note that this variation in the field can give rise to a ``Flexion'' or bending of a galaxy image, which may then be used to detect a lensing signal with increased signal to noise. Since the significance of the Flexion signal increases on small scales, this is ideally suited to galaxy-galaxy lensing. We develop an inversion technique based on the ``Shapelets'' formalism of Refregier (2003). We then demonstrate the proof of this concept by measuring a Flexion signal in the Deep Lens Survey. Assuming an intrinsically isothermal distribution, we find from the Flexion signal alone a velocity width of v_c=221\pm 12 km/s for lens galaxies of r < 21.5, subject to uncertainties in the intrinsic Flexion distribution.Comment: 11 pages, Latex, 4 figures. Accepted by ApJ, changes include revision of errors from previous draf

    Testing Bekenstein's Relativistic MOND gravity with Lensing Data

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    We propose to use multiple-imaged gravitational lenses to set limits on gravity theories without dark matter, specificly TeVeS (Bekenstein 2004), a theory which is consistent with fundamental relativistic principles and the phenomenology of MOdified Newtonian Dynamics (MOND) theory. After setting the framework for lensing and cosmology, we derive analytically the deflection angle for the point lens and the Hernquist galaxy profile, and fit galaxy-quasar lenses in the CASTLES sample. We do this with three methods, fitting the observed Einstein ring sizes, the image positions, or the flux ratios. In all cases we consistently find that stars in galaxies in MOND/TeVeS provide adequate lensing. Bekenstein's toy μ\mu function provides more efficient lensing than the standard MOND μ\mu function. But for a handful of lenses [indicated in Table 2,3, fig 16] a good fit would require a lens mass orders of magnitude larger/smaller than the stellar mass derived from luminosity unless the modification function μ\mu and modification scale a0a_0 for the universal gravity were allowed to be very different from what spiral galaxy rotation curves normally imply. We discuss the limitation of present data and summarize constraints on the MOND μ\mu function. We also show that the simplest TeVeS "minimal-matter" cosmology, a baryonic universe with a cosmological constant, can fit the distance-redshift relation from the supernova data, but underpredicts the sound horizon size at the last scattering. We conclude that lensing is a promising approach to differentiate laws of gravity (see also astro-ph/0512425).Comment: reduced to 17p, 16 figs, discussed cosmology and constraints on mu-function, MNRAS accepte

    CamFlow: Managed Data-sharing for Cloud Services

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    A model of cloud services is emerging whereby a few trusted providers manage the underlying hardware and communications whereas many companies build on this infrastructure to offer higher level, cloud-hosted PaaS services and/or SaaS applications. From the start, strong isolation between cloud tenants was seen to be of paramount importance, provided first by virtual machines (VM) and later by containers, which share the operating system (OS) kernel. Increasingly it is the case that applications also require facilities to effect isolation and protection of data managed by those applications. They also require flexible data sharing with other applications, often across the traditional cloud-isolation boundaries; for example, when government provides many related services for its citizens on a common platform. Similar considerations apply to the end-users of applications. But in particular, the incorporation of cloud services within `Internet of Things' architectures is driving the requirements for both protection and cross-application data sharing. These concerns relate to the management of data. Traditional access control is application and principal/role specific, applied at policy enforcement points, after which there is no subsequent control over where data flows; a crucial issue once data has left its owner's control by cloud-hosted applications and within cloud-services. Information Flow Control (IFC), in addition, offers system-wide, end-to-end, flow control based on the properties of the data. We discuss the potential of cloud-deployed IFC for enforcing owners' dataflow policy with regard to protection and sharing, as well as safeguarding against malicious or buggy software. In addition, the audit log associated with IFC provides transparency, giving configurable system-wide visibility over data flows. [...]Comment: 14 pages, 8 figure

    Weak lensing predictions for coupled dark energy cosmologies at non-linear scales

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    We present non-linear weak lensing predictions for coupled dark energy models using the CoDECS simulations. We calculate the shear correlation function and error covariance expected for these models, for forthcoming ground-based (such as DES) and space-based (Euclid) weak lensing surveys. We obtain predictions for the discriminatory power of a ground-based survey similar to DES and a space-based survey such as Euclid in distinguishing between Λ\LambdaCDM and coupled dark energy models; we show that using the non-linear lensing signal we could discriminate between Λ\LambdaCDM and exponential constant coupling models with β0≥0.1\beta_0\geq0.1 at 4σ4\sigma confidence level with a DES-like survey, and β0≥0.05\beta_0\geq0.05 at 5σ5\sigma confidence level with Euclid. We also demonstrate that estimating the coupled dark energy models' non-linear power spectrum, using the Λ\LambdaCDM Halofit fitting formula, results in biases in the shear correlation function that exceed the survey errors.Comment: 9 pages, 5 figures, v2: accepted for publication in MNRA

    Simulink-Based Simulation Architecture for Evaluating Controls for Aerospace Vehicles (SAREC-ASV)

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    The Simulation Architecture for Evaluating Controls for Aerospace Vehicles (SAREC-ASV) is a Simulink-based approach to providing an engineering quality desktop simulation capability for finding trim solutions, extracting linear models for vehicle analysis and control law development, and generating open-loop and closed-loop time history responses for control system evaluation. It represents a useful level of maturity rather than a finished product. The layout is hierarchical and supports concurrent component development and validation, with support from the Concurrent Versions System (CVS) software management tool. Real Time Workshop (RTW) is used to generate pre-compiled code for substantial component modules, and templates permit switching seamlessly between original Simulink and code compiled for various platforms. Two previous limitations are addressed. Turn around time for incorporating tabular model components was improved through auto-generation of required Simulink diagrams based on data received in XML format. The layout was modified to exploit a Simulink "compile once, evaluate multiple times" capability for zero elapsed time for use in trimming and linearizing. Trim is achieved through a Graphical User Interface (GUI) with a narrow, script definable interface to the vehicle model which facilitates incorporating new models

    Twist and Turn: Weak Lensing Image Distortions to Second Order

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    We account for all the image distortions relevant to weak gravitational lensing to second order. Besides the familiar shear, convergence, rotation and flexions, we find a new image distortion with two distinct descriptions, the twist and the turn. Like rotation, this distortion is not activated gravitationally to first order, but will be activated by systematic effects. We examine the rotational properties of twist and turn, and their effect on images in real and shapelet space. We construct estimators for the new distortion, taking into account the centroid shift which it generates. We then use these estimators to make first constraints on twist using the STAGES HST survey; we find that the mean twist estimator is consistent with zero. We measure correlation functions for our twist estimator on the survey, again finding no evidence of systematic effects.Comment: 9 pages, 9 figures. Accepted by MNRAS; expands discussion of distortions and estimator

    Density mapping with weak lensing and phase information

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    The available probes of the large scale structure in the Universe have distinct properties: galaxies are a high resolution but biased tracer of mass, while weak lensing avoids such biases but, due to low signal-to-noise ratio, has poor resolution. We investigate reconstructing the projected density field using the complementarity of weak lensing and galaxy positions. We propose a maximum-probability reconstruction of the 2D lensing convergence with a likelihood term for shear data and a prior on the Fourier phases constructed from the galaxy positions. By considering only the phases of the galaxy field, we evade the unknown value of the bias and allow it to be calibrated by lensing on a mode-by-mode basis. By applying this method to a realistic simulated galaxy shear catalogue, we find that a weak prior on phases provides a good quality reconstruction down to scales beyond l=1000, far into the noise domain of the lensing signal alone.Comment: 11 pages, 9 figures, published in MNRA

    Measuring galaxy [OII] emission line doublet with future ground-based wide-field spectroscopic surveys

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    The next generation of wide-field spectroscopic redshift surveys will map the large-scale galaxy distribution in the redshift range 0.7< z<2 to measure baryonic acoustic oscillations (BAO). The primary optical signature used in this redshift range comes from the [OII] emission line doublet, which provides a unique redshift identification that can minimize confusion with other single emission lines. To derive the required spectrograph resolution for these redshift surveys, we simulate observations of the [OII] (3727,3729) doublet for various instrument resolutions, and line velocities. We foresee two strategies about the choice of the resolution for future spectrographs for BAO surveys. For bright [OII] emitter surveys ([OII] flux ~30.10^{-17} erg /cm2/s like SDSS-IV/eBOSS), a resolution of R~3300 allows the separation of 90 percent of the doublets. The impact of the sky lines on the completeness in redshift is less than 6 percent. For faint [OII] emitter surveys ([OII] flux ~10.10^{-17} erg /cm2/s like DESi), the detection improves continuously with resolution, so we recommend the highest possible resolution, the limit being given by the number of pixels (4k by 4k) on the detector and the number of spectroscopic channels (2 or 3).Comment: 5 pages, 1 figur

    Welfare of non-traditional pets

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    The keeping of non-traditional or ‘exotic’ pets has been growing in popularity worldwide. In addition to the typical welfare challenges of keeping more traditional pet species like dogs and cats, ensuring the welfare of non-traditional pets is complicated by factors such as lack of knowledge, difficulties meeting requirements in the home and where and how animals are obtained. This paper uses examples of different species to highlight three major welfare concerns: ensuring that pets under our care i) function well biologically, ii) are free from negative psychological states and able to experience normal pleasures, and iii) lead reasonably natural lives. The keeping of non-traditional pets also raises ethical concerns about whether the animal poses any danger to others (e.g. transmission of zoonotic diseases) and whether the animal might cause environmental damage (e.g. invading non-native habitats when released). The authors used these considerations to create a checklist, which identifies and organises the various concerns that may arise over keeping non-traditional species as pets. An inability to address these concerns raises questions about how to mitigate them or even whether or not certain species should be kept as pets at all. Thus, the authors propose five categories, which range from relatively unproblematic pet species to species whose keeping poses unacceptable risks to the animals, to humans, or to the environment. This approach to the evaluation and categorisation of species could provide a constructive basis for advocacy and regulatory actions

    Complementarity of Weak Lensing and Peculiar Velocity Measurements in Testing General Relativity

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    We explore the complementarity of weak lensing and galaxy peculiar velocity measurements to better constrain modifications to General Relativity. We find no evidence for deviations from GR on cosmological scales from a combination of peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital Sky Survey) with weak lensing measurements (from the CFHT Legacy Survey). We provide a Fisher error forecast for a Euclid-like space-based survey including both lensing and peculiar velocity measurements, and show that the expected constraints on modified gravity will be at least an order of magnitude better than with present data, i.e. we will obtain 5% errors on the modified gravity parametrization described here. We also present a model--independent method for constraining modified gravity parameters using tomographic peculiar velocity information, and apply this methodology to the present dataset.Comment: 8 pages, 5 figure
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