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United States households' consumption expenditures and car purchases collapsed during the Great Recession and more so than income changes would have predicted. Using CEX data, we show that both the extensive and the intensive car spending margins contracted sharply in the Great Recession. We also document significant cross‐cohort differences in the impact of the Great Recession including a stronger reduction in car spending by younger cohorts. We draw inference on the sources of the Great Recession by investigating which shocks can explain household choices in a 60 period life‐cycle model with idiosyncratic and aggregate shocks fitted to aggregate and life‐cycle moments. We find that the Great Recession was caused by a combination of large aggregate income and wealth shocks, while cross‐cohort adjustment patterns imply a role for life‐cycle income profile shocks. We also find a role for car loan premia shocks in accounting for car spending and car loans.

This article contrasts the experiences of the United States and United Kingdom during and after the Great Recession to understand the role of financial shocks in the magnitude of the crises and length of the recoveries. It starts from the common consensus that the Great Recession first and foremost was a financial crisis. It shows that relative to the United States, the Great Recession in the United Kingdom was more closely associated with a decline in productivity. Motivated by the similar behavior of financial variables at a business cycle frequency, it contrasts the behavior of the U.S. and U.K. economies through the lens of a simple real business cycle model augmented with financial shocks. A credit channel that operates on firm hiring decisions captures the magnitude of the output decline in both the United States and United Kingdom but exaggerates the response of the hours margin for the United Kindgom. The conclusion is that the financial channel supported in the U.S. data seems less appropriate for understanding the U.K. experience.

US households’ consumption and car purchases collapsed during the Great Recession, for reasonsthat are still poorly understood. In this paper we use the Consumer Expenditure Survey to derive cohort and business cycle decompositions of consumption profiles. When decomposing the car expenditure data into its extensive and intensive margins, we find that the intensive margin contracted sharply in the Great Recession, a finding in stark contrast to conventional wisdom and to the experience of prior recessions. We interpret the evidence through the prism of a very rich life-cycle model where individuals are subject to idiosyncratic uninsurable income shocks, aggregate income shocks, wealth shocks, and credit shocks. We show that, because of their salience and the transaction costs, cars are particularly sensitive to changes in the perception of fu- ture expected income and its variability. We find that on top of a large aggregate income shock, life-cycle income profile shocks and wealth shocks are important determinants of consumption choices during the Great Recession., Also published as CEPR Discussion Paper No. 15361.

We propose an innovative low-cost mission capable of detecting potentially habitable planets around a sample of solar-type stars near the sun. Our mission will deliver relative measurements of stellar position and motion at sub-micro acrsecond precision. These data, in turn, will reveal the presence of orbiting exoplanets. For the case of our primary targets Alpha Centauri A & B, objects below one Earth mass will be accessible when the end-of-mission astrometric precision requirement of 0.4 micro-arcsecond is achieved. The technique will directly reveal not only the presence of the planet but deliver fundamental data such as masses and 3-D orbital parameters including eccentricity and inclination. This paper describes the optical and mechanical architecture of the mission and first-order instrument design. We also explain the instrument stability requirements imposed by the diffractive pupil post-processing calibration limitations. Our design baseline is a stable two-mirror telescope that images the field directly on CCD camera minimizing the number of reflections and optical components.

The TOLIMAN space telescope is a low-cost, agile mission concept dedicated to astrometric detection of exoplanets in the near-solar environment, and particularly targeting the Alpha Cen system. Although successful discovery technologies are now populating exoplanetary catalogs into the thousands, contemporary astronomy is still poorly equipped to answer the basic question of whether there are any rocky planets orbiting any particular star system. Toliman will make a first study of stars within 10 PC of the sun by deploying an innovative optical and signal encoding architecture that leverages the most promising technology to deliver data on this critical stellar sample: high precision astrometric monitoring. Here we present results from the Foundational Mission Study, jointly funded by the Breakthrough Prize Foundation and the University of Sydney which has translated innovative underlying design principles into error budgets and potential spacecraft systems designs.

Author Posting. © Society of Photo Optical Instrumentation Engineers, 2017. This article is posted here by permission of Society of Photo Optical Instrumentation Engineers for personal use, not for redistribution. The definitive version was published in Journal of Biomedical Optics 22 (2017): 016006, doi:10.1117/1.JBO.22.1.016006., We describe the principles of using orientation-independent differential interference contrast (OI-DIC) microscopy for mapping optical path length (OPL). Computation of the scalar two-dimensional OPL map is based on an experimentally received map of the OPL gradient vector field. Two methods of contrast enhancement for the OPL image, which reveal hardly visible structures and organelles, are presented. The results obtained can be used for reconstruction of a volume image. We have confirmed that a standard research grade light microscope equipped with the OI-DIC and 100×/1.3 NA objective lens, which was not specially selected for minimum wavefront and polarization aberrations, provides OPL noise level of ∼0.5 nm and lateral resolution if ∼300 nm at a wavelength of 546 nm. The new technology is the next step in the development of the DIC microscopy. It can replace standard DIC prisms on existing commercial microscope systems without modification. This will allow biological researchers that already have microscopy setups to expand the performance of their systems., This publication was made possible by Grant No. R01-GM101701 from the National Institute of General Medical Sciences, National Institutes of Health.

Author Posting. © Society of Photo Optical Instrumentation Engineers, 2017. This article is posted here by permission of Society of Photo Optical Instrumentation Engineers for personal use, not for redistribution. The definitive version was published in Journal of Biomedical Optics 22 (2017): 016006, doi:10.1117/1.JBO.22.1.016006., We describe the principles of using orientation-independent differential interference contrast (OI-DIC) microscopy for mapping optical path length (OPL). Computation of the scalar two-dimensional OPL map is based on an experimentally received map of the OPL gradient vector field. Two methods of contrast enhancement for the OPL image, which reveal hardly visible structures and organelles, are presented. The results obtained can be used for reconstruction of a volume image. We have confirmed that a standard research grade light microscope equipped with the OI-DIC and 100×/1.3 NA objective lens, which was not specially selected for minimum wavefront and polarization aberrations, provides OPL noise level of ∼0.5 nm and lateral resolution if ∼300 nm at a wavelength of 546 nm. The new technology is the next step in the development of the DIC microscopy. It can replace standard DIC prisms on existing commercial microscope systems without modification. This will allow biological researchers that already have microscopy setups to expand the performance of their systems., This publication was made possible by Grant No. R01-GM101701 from the National Institute of General Medical Sciences, National Institutes of Health.

It is not obvious how to extend Shannon's original information entropy to higher dimensions, and many different approaches have been tried. We replace the English text symbol sequence originally used to illustrate the theory by a discrete, bandlimited signal. Using Shannon's later theory of sampling we derive a new and symmetric version of the second order entropy in 1D. The new theory then naturally extends to 2D and higher dimensions, where by naturally we mean simple, symmetric, isotropic and parsimonious. Simplicity arises from the direct application of Shannon's joint entropy equalities and inequalities to the gradient (del) vector field image embodying the second order relations of the scalar image. Parsimony is guaranteed by halving of the vector data rate using Papoulis' generalized sampling expansion. The new 2D entropy measure, which we dub delentropy, is underpinned by a computable probability density function we call deldensity. The deldensity captures the underlying spatial image structure and pixel co-occurrence. It achieves this because each scalar image pixel value is nonlocally related to the entire gradient vector field. Both deldensity and delentropy are highly tractable and yield many interesting connections and useful inequalities. The new measure explicitly defines a realizable encoding algorithm and a corresponding reconstruction. Initial tests show that delentropy compares favourably with the conventional intensity-based histogram entropy and the compressed data rates of lossless image encoders (GIF, PNG, WEBP, JP2K-LS and JPG-LS) for a selection of images. The symmetric approach may have applications to higher dimensions and problems concerning image complexity measures., Comment: 47 pages,9 figures, preprint for submission to an image science and optics journal

The Structural Similarity Index (SSIM) is generally considered to be a milestone in the recent history of Image Quality Assessment (IQA). Alas, SSIM's accepted development from the product of three heuristic factors continues to obscure it's real underlying simplicity. Starting instead from a symmetric-antisymmetric reformulation we first show SSIM to be a contrast or visibility function in the classic sense. Furthermore, the previously enigmatic structural covariance is revealed to be the difference of variances. The second step, eliminating the intrinsic quadratic nature of SSIM, allows a near linear correlation with human observer scores, and without invoking the usual, but arbitrary, sigmoid model fitting. We conclude that SSIM can be re-interpreted in terms of perceptual masking: it is essentially equivalent to a normalised error or noise visibility function (NVF), and, furthermore, the NVF alone explains it success in modelling perceptual image quality. We use the term Dissimilarity Quotient (DQ) for the specifically anti/symmetric SSIM derived NVF. It seems that IQA researchers may now have two choices: 1) Continue to use the complex SSIM formula, but noting that SSIM only works coincidentally since the covariance term is actually the mean square error (MSE) in disguise. 2) Use the simplest of all perceptually-masked image quality metrics, namely NVF or DQ. On this choice Occam is clear: in the absence of differences in predictive ability, the fewer assumptions that are made, the better., Comment: Updated abstract and references. 4 pages total, main analysis 2 pages, notes and minimal references 1 page

We describe a method for attaching persistent metadata to an image. The method can be interpreted as a template-based blind watermarking scheme, robust to common editing operations, namely: cropping, rotation, scaling, stretching, shearing, compression, printing, scanning, noise, and color removal. Robustness is achieved through the reciprocity of the embedding and detection invariants. The embedded patterns are real onedimensional Mellin monomial patterns distributed over two-dimensions. The embedded patterns are scale invariant and can be directly embedded in an image by simple pixel addition. Detection achieves rotation and general affine invariance by signal projection using implicit Radon transformation. Embedded signals contract to one-dimension in the two-dimensional Fourier polar domain. The real signals are detected by correlation with complex Mellin monomial templates. Using a unique template of 4 chirp patterns we detect the affine signature with exquisite sensitivity and moderate security. The practical implementation achieves efficiencies through fast Fourier transform (FFT) correspondences such as the projection-slice theorem, the FFT correlation relation, and fast resampling via the chirp-z transform. The overall method utilizes orthodox spread spectrum patterns for the payload and performs well in terms of the classic robustness-capacity-visibility performance triangle. Tags are entirely imperceptible with a mean SSIM greater than 0.988 in all cases tested. Watermarked images survive almost all Stirmark attacks. The method is ideal for attaching metadata robustly to both digital and analogue images., Comment: Previous MS rejected as the journal no longer accepts purely image processing articles. Reworked with emphasis on the embedded patterns: Mellin monomials, which underpin optical rotation and scale invariant pattern recognition. Noted visual imperceptibility. Kept animation sequence showing how correlation detection survives image distortions. Submitted to an "optics and image science" journal