Fast Back-Projection for Non-Line of Sight Reconstruction

Recent works have demonstrated non-line of sight (NLOS) reconstruction by using the time-resolved signal frommultiply scattered light. These works combine ultrafast imaging systems with computation, which back-projects the recorded space-time signal to build a probabilistic map of the hidden geometry. Unfortunately, this computation is slow, becoming a bottleneck as the imaging technology improves. In this work, we propose a new back-projection technique for NLOS reconstruction, which is up to a thousand times faster than previous work, with almost no quality loss. We base on the observation that the hidden geometry probability map can be built as the intersection of the three-bounce space-time manifolds defined by the light illuminating the hidden geometry and the visible point receiving the scattered light from such hidden geometry. This allows us to pose the reconstruction of the hidden geometry as the voxelization of these space-time manifolds, which has lower theoretic complexity and is easily implementable in the GPU. We demonstrate the efficiency and quality of our technique compared against previous methods in both captured and synthetic dat

Charged Particle-like Branes in ABJM: A Summary

We study the effect of adding lower dimensional brane charges to the 't Hooft monopole, di-baryon and baryon vertex configurations in AdS_4 x CP^3. We show that these configurations capture the background fluxes in a way that depends on the induced charges, requiring additional fundamental strings to cancel the worldvolume tadpoles. The dynamics reveal that the charges must lie inside some interval, a situation familiar from the baryon vertex in AdS_5 x S^5 with charges. For the baryon vertex and the di-baryon the number of fundamental strings must also lie inside an allowed interval. Some ideas about the existence of these bounds in relation to the stringy exclusion principle are given.Comment: 6 pages. Contribution to the proceedings of the XVIth European Workshop on String Theory, Madrid, Spain, June 14-18 2010; based on a talk given by N. Gutierre

Genocide is the tip of the iceberg: reviewing the Guatemalan case

In 2013 the former Guatemalan dictator Efraín Ríos-Montt was tried in a national court for genocide and crimes against humanity. He was found guilty and sent to prison, but the verdict was quickly overturned on technical grounds. Local reactions to these events were varied, since the Mayan genocide is one of the most controversial issues for Guatemalan society today. In this article, I draw on the Ríos-Montt case to discuss the Mayan genocide not as an isolated event, but only as the momentary surfacing of a set of institutional arrangements that also explain the astonishing inequality that prevails in this Central American country

An intuitive control space for material appearance

Many different techniques for measuring material appearance have been proposed in the last few years. These have produced large public datasets, which have been used for accurate, data-driven appearance modeling. However, although these datasets have allowed us to reach an unprecedented level of realism in visual appearance, editing the captured data remains a challenge. In this paper, we present an intuitive control space for predictable editing of captured BRDF data, which allows for artistic creation of plausible novel material appearances, bypassing the difficulty of acquiring novel samples. We first synthesize novel materials, extending the existing MERL dataset up to 400 mathematically valid BRDFs. We then design a large-scale experiment, gathering 56,000 subjective ratings on the high-level perceptual attributes that best describe our extended dataset of materials. Using these ratings, we build and train networks of radial basis functions to act as functionals mapping the perceptual attributes to an underlying PCA-based representation of BRDFs. We show that our functionals are excellent predictors of the perceived attributes of appearance. Our control space enables many applications, including intuitive material editing of a wide range of visual properties, guidance for gamut mapping, analysis of the correlation between perceptual attributes, or novel appearance similarity metrics. Moreover, our methodology can be used to derive functionals applicable to classic analytic BRDF representations. We release our code and dataset publicly, in order to support and encourage further research in this direction

A Similarity Measure for Material Appearance

We present a model to measure the similarity in appearance between different materials, which correlates with human similarity judgments. We first create a database of 9,000 rendered images depicting objects with varying materials, shape and illumination. We then gather data on perceived similarity from crowdsourced experiments; our analysis of over 114,840 answers suggests that indeed a shared perception of appearance similarity exists. We feed this data to a deep learning architecture with a novel loss function, which learns a feature space for materials that correlates with such perceived appearance similarity. Our evaluation shows that our model outperforms existing metrics. Last, we demonstrate several applications enabled by our metric, including appearance-based search for material suggestions, database visualization, clustering and summarization, and gamut mapping.Comment: 12 pages, 17 figure

Fermion mass hierarchy and non-hierarchical mass ratios in SU(5) x U(1)_F

We consider a SU(5) x U(1)_F GUT-flavor model in which the number of effects that determine the charged fermions Yukawa matrices is much larger than the number of observables, resulting in a hierarchical fermion spectrum with no particular regularities. The GUT-flavor symmetry is broken by flavons in the adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that gives rise to a large number of effective operators. By assuming a common mass for the heavy fields and universality of the fundamental Yukawa couplings, we reduce the number of free parameters to one. The observed fermion mass spectrum is reproduced thanks to selection rules that discriminate among various contributions. Bottom-tau Yukawa unification is preserved at leading order, but there is no unification for the first two families. Interestingly, U(1)_F charges alone do not determine the hierarchy, and can only give upper bounds on the parametric suppression of the Yukawa operators.Comment: 14 pages, one figure. Few typos correcte

Anuncios macroeconómicos y mercados Accionarios: El caso Latinoamericano

Reflejan los mercados accionarios los fundamentales macroeconómicos de un país?. La hipótesis de eficiencia semifuerte (Fama 1970) implica que los mercados accionarios deben reaccionar inmediatamente, y sin sobre ni subreacción predecible, a las sorpresas en los anuncios macroeconómicos relevantes. Ponemos a prueba esta implicación en los seis principales mercados accionarios de Latinoamérica: Argentina, Brasil, Chile, Colombia, México y Perú ante los anuncios de inflación, tasa de interés del banco central, PIB, balanza comercial y desempleo. Se discute el efecto esperado de una sorpresa en el anuncio de cada variable económica. Siguiendo a Flannery y Protopapadakis (2002), se estima el efecto sobre la media y la volatilidad de dichos anuncios mediante modelos de serie de tiempo univariados de volatilidad heterocesdástica controlando por los efectos de los rendimientos de índices internacionales y de la tasa de cambio. Entre los principales hallazgos se encuentra que los efectos de los anuncios solo son significativos y con el signo esperado para la inflación en México, para la tasa de interés en Chile y Colombia, y para el desempleo en estos tres mercados. Se encuentra además que, en determinados casos, los mercados no incorporan toda la información en el día del anuncio, y en otros, que reaccionan ante el anuncio en sí mismo controlando por la sorpresa, contrario a lo postulado por la hipótesis de eficiencia de mercado. Se concluye que los mercados accionarios latinoamericanos, solo reaccionan parcialmente a la información macro, y no con total eficiencia.Do stock markets reflect changes on the macroeconomic fundamentals? . The semi-strong form of the Efficient market hypothesis (HEM - Fama 1970) asserts that stock prices should react immediately to the surprise content on announcements of macroeconomic variables, without predictable over or under reaction. We test this in the six main Latin-American equity markets: Argentina, Brazil, Chile, Colombia, México and Perú, for the announcements of Consumer Price Inflation, Central Bank interest rate, GDP growth, Trade Balance and Unemployment rate. Following Flannery and Protopapadakis (2002), we estimate the effect of the surprises of such announcements, using time series models of conditional volatility, controlling of the exchange rate and international stock markets. We found that the effects on the market returns are significant and with the expected sign only for the CPI in Mexico, for the interest rate in Chile and Colombia, and for Unemployment on those three markets. Moreover, in some cases the stock markets incorporate the announcement with a lag, whereas in others, they react to the announcement rather than to the surprise, in conflict with the HEM. We conclude that the Latin-American stock markets react only partially to the macroeconomic announcements and not fully incorporating the new information in an efficient manner