298 research outputs found

    Lessons Learned from the Investigation of an Anomalous Termination of BETTII

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    The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) mission launched from Palestine, Texas in June 2017. After an exciting launch and successful cruise, the BETTII gondola suffered an anomalous event at termination. BETTII separated from its parachute and free-fell 136,000 feet into the west Texas desert. This event was classified as a "close-call" and investigated as such. We present here the recovery effort required to find the payload and extract the payload from its impact site. We also present lessons learned from the event and results from the investigation, the design for the next BETTII gondola, and a path forward for return to flight

    A Dispersive Backend Design for the 'Double-Fourier' Interferometer BETTII

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    BETTII (Balloon Experimental Twin Telescope for Infra-red Interferometry) is designed to provide high angular resolution spectroscopic data in the far-infrared (FIR) wavelengths. The most significant limitation for BETTII is its sensitivity; obtaining spectral signal-to-noise ratio greater than 5 in less than 10 minutes requires sources greater than 13 Janskys (Jy). One possible way to improve the signal-to-noise ratio (SNR) for future BETTII flights is by reducing the spectral bandwidth post beam-combination. This involves using a dispersive element to spread out a polychromatic point source PSF (Point Spread Function) on the detector array, such that each pixel corresponds to a small fraction of the bandwidth. This results in a broader envelope of the interferometric fringe pattern allowing more fringes to be detected, and thereby improving the spectral SNR. Here we present the analysis and optical design of the dispersive backend, discussing the tradeoffs and how it can be combined with the existing design

    Measurements of the Temperature and E-Mode Polarization of the CMB from 500 Square Degrees of SPTpol Data

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    We present measurements of the EE-mode polarization angular auto-power spectrum (EEEE) and temperature-EE-mode cross-power spectrum (TETE) of the cosmic microwave background (CMB) using 150 GHz data from three seasons of SPTpol observations. We report the power spectra over the spherical harmonic multipole range 50<ℓ≤800050 < \ell \leq 8000, and detect nine acoustic peaks in the EEEE spectrum with high signal-to-noise ratio. These measurements are the most sensitive to date of the EEEE and TETE power spectra at ℓ>1050\ell > 1050 and ℓ>1475\ell > 1475, respectively. The observations cover 500 deg2^2, a fivefold increase in area compared to previous SPTpol analyses, which increases our sensitivity to the photon diffusion damping tail of the CMB power spectra enabling tighter constraints on \LCDM model extensions. After masking all sources with unpolarized flux >50>50 mJy we place a 95% confidence upper limit on residual polarized point-source power of Dℓ=ℓ(ℓ+1)Cℓ/2π<0.107 μK2D_\ell = \ell(\ell+1)C_\ell/2\pi <0.107\,\mu{\rm K}^2 at ℓ=3000\ell=3000, suggesting that the EEEE damping tail dominates foregrounds to at least ℓ=4050\ell = 4050 with modest source masking. We find that the SPTpol dataset is in mild tension with the ΛCDM\Lambda CDM model (2.1 σ2.1\,\sigma), and different data splits prefer parameter values that differ at the ∼1 σ\sim 1\,\sigma level. When fitting SPTpol data at ℓ<1000\ell < 1000 we find cosmological parameter constraints consistent with those for PlanckPlanck temperature. Including SPTpol data at ℓ>1000\ell > 1000 results in a preference for a higher value of the expansion rate (H_0 = 71.3 \pm 2.1\,\mbox{km}\,s^{-1}\mbox{Mpc}^{-1} ) and a lower value for present-day density fluctuations (σ8=0.77±0.02\sigma_8 = 0.77 \pm 0.02).Comment: Updated to match version accepted to ApJ. 34 pages, 17 figures, 6 table

    TGF-beta(2)- and H2O2-Induced Biological Changes in Optic Nerve Head Astrocytes Are Reduced by the Antioxidant Alpha-Lipoic Acid

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    Background/Aims: The goal of the present study was to determine whether transforming growth factor-beta(2) (TGF-beta(2))- and oxidative stress-induced cellular changes in cultured human optic nerve head (ONH) astrocytes could be reduced by pretreatment with the antioxidant alpha-lipoic acid (LA). Methods: Cultured ONH astrocytes were treated with 1.0 ng/ml TGF-beta(2) for 24 h or 200 mu M hydrogen peroxide (H2O2) for 1 h. Lipid peroxidation was measured by a decrease in cis-pari-naric acid fluorescence. Additionally, cells were pretreated with different concentrations of LA before TGF-beta 2 or H2O2 exposure. Expressions of the heat shock protein (Hsp) alpha B-crystallin and Hsp27, the extracellular matrix (ECM) component fibronectin and the ECM-modulating protein connective tissue growth factor (CTGF) were examined with immunohistochemistry and real-time PCR analysis. Results: Both TGF-beta(2) and H2O2 increased lipid peroxidation. Treatment of astrocytes with TGF-beta(2) and H2O2 upregulated the expression of alpha B-crystallin, Hsp27, fibronectin and CTGF. Pretreatment with different concentrations of LA reduced the TGF-beta(2)- and H2O2-stimulated gene expressions. Conclusion: We showed that TGF-beta(2)- and H2O2-stimulated gene expressions could be prevented by pretreatment with the antioxidant LA in cultured human ONH astrocytes. Therefore, it is tempting to speculate that the use of antioxidants could have protective effects in glaucomatous optic neuropathy. Copyright (C) 2012 S. Karger AG, Base

    Fourier Analysis of Correlated Monte Carlo Importance Sampling

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    International audienceFourier analysis is gaining popularity in image synthesis, as a tool for the analysis of error in Monte Carlo (MC) integration. Still, existing tools are only able to analyze convergence under simplifying assumptions (such as randomized shifts) which are not applied in practice during rendering. We reformulate the expressions for bias and variance of sampling-based integrators to unify non-uniform sample distributions (importance sampling) as well as correlations between samples while respecting finite sampling domains. Our unified formulation hints at fundamental limitations of Fourier-based tools in performing variance analysis for MC integration. This non-trivial exercise also provides exciting insight into the effects of importance sampling on the convergence rate of estimators because of the introduction or removal of discontinuities. Specifically, we demonstrate that the convergence of multiple importance sampling (MIS) is determined by the strategy that converges slowest. We propose two simple and practical approaches to limit the impact of discontinuities on the convergence rate of estimators: The first one involves mirroring the integrand to cancel out the effect of boundary discontinuities. This is followed by two novel mirror sampling techniques for MC estimation in this mirrored domain. The second approach improves direct illumination light sampling by smoothing out discontinuities within the domain at the cost of introducing a small amount of bias. Our approaches are simple, practical and can be easily incorporated in production renderers
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