Sunday, May 17, 2015



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía

rss_1.0 Recursos de colección

Caltech Authors (105,723 recursos)
Repository of works by Caltech published authors.

Type = Book Section

Mostrando recursos 1 - 20 de 4,662

1. Considerations in the design of optimum compaction filters for subband coders - Lin, Yuan-Pei; Vaidyanathan, P. P.
Recently there has been considerable interest in the design of optimal paraunitary filter banks for a given class of inputs. In this paper we address a number of practical considerations associated with the design and implementation of optimal paraunitary filter banks.

2. The evaluation of SCIAMACHY CO and CH_4 scientific data products, using ground-based FTIR measurements - Dils, B.; De Mazière, M.; Müller, J. F.; Buchwitz, M.; de Beek, R.; Frankenberg, C.; Gloudemans, A.; Schrijver, H.; Van den Broek, M.
In the framework of the European EVERGREEN project, three scientific algorithms, namely WFM-DOAS, IMAPDOAS and IMLM, have been developed to retrieve the total column amounts of key atmospheric trace gases including CO and CH_4 from SCIAMACHY nadir observations in its near-infrared channels. These channels offer the capability to detect trace gases in the planetary boundary layer, potentially making the associated retrieval products suited for regional source-sink studies. The retrieval products of these three algorithms, in their present status of development, have been compared to independent data from a ground-based quasi-global network of Fourier-transform infrared (FTIR) spectrometers, for the year 2003. Comparisons have been made for individual data,...

3. Reactive Synthesis from Signal Temporal Logic Specifications - Raman, Vasumathi; Donzé, Alexandre; Sadigh, Dorsa; Murray, Richard M.; Seshia, Sanjit A.
We present a counterexample-guided inductive synthesis approach to controller synthesis for cyber-physical systems subject to signal temporal logic (STL) specifications, operating in potentially adversarial nondeterministic environments. We encode STL specifications as mixed integer-linear constraints on the variables of a discrete-time model of the system and environment dynamics, and solve a series of optimization problems to yield a satisfying control sequence. We demonstrate how the scheme can be used in a receding horizon fashion to fulfill properties over unbounded horizons, and present experimental results for reactive controller synthesis for case studies in building climate control and autonomous driving.

4. Satellite Remote Sensing of Atmospheric SO_2: Volcanic Eruptions and Anthropogenic Emissions - Khokhar, Muhammad Fahim; Frankenberg, C.; Hollwedel, J.; Beirle, S.; Kühl, S.; Grzegorski, M.; Wilms-Grabe, W.; Platt, U.; Wagner, Thomas
In this article, we present satellite data analysis of atmospheric Sulfur Dioxide (SO_2) from volcanic eruptions and anthropogenic activities. Data from Global Ozone Monitoring Experiment (GOME) on board ERS-2 for the years 1996 to 2002 is analyzed using a DOAS based algorithm with the aim of retrieving SO_2 Slant Column Densities (SCDs). Difficulties in the retrieval of SO_2 SCDs due to instrumental effects are investigated in detail and significantly improved. The retrieved SCDs can be used to identify and monitor several volcanic eruptions. A brief introduction of different volcanic eruptions around the globe is presented Also informations about the anthropogenic...

5. 3-D measurements using conoscopy and application to ophthalmology - Moser, Christophe; Barbastathis, George; Psaltis, Demetri
In this paper we present a novel method to measure 3-D quasi planar or quasi spherical reflective surfaces with submicron depth accuracy. Two implementations are presented: a scanning and a non-scanning system. The non-scanning device allows fast measurements and can be applied for eye-shape measurements. The paper is organized as follows: in the introductory section, we first demonstrate the principle of the conoscopic effect leading to the formation of the interferogram. The second and third sections explain respectively. the scanning and non-scanning methods based on the conoscopic effect. We present the experimental results from a simple measurement and show how...

6. Image halftoning using optimized dot diffusion - Meşe, Murat; Vaidyanathan, P. P.
The dot diffusion method for digital halftoning has the advantage of parallelism unlike the error diffusion method. However, image quality offered by error diffusion is still regarded as superior to other known methods. In this paper we show how the dot diffusion method can be improved by optimization of the so-called class matrix. By taking the human visual characteristics into account we show that such optimization consistently results in images comparable to error diffusion, without sacrificing the parallelism.

7. Nonlinear and cooperative control of multiple hovercraft with input constraints - Dunbar, William B.; Olfati-Saber, Reza; Murray, Richard M.
In this paper, we introduce an approach for distributed nonlinear control of multiple hovercraft-type underactuated vehicles with bounded and unidirectional inputs. First, a bounded nonlinear controller is given for stabilization and tracking of a single vehicle, using a cascade backstepping method. Then, this controller is combined with a distributed gradient-based control for multi-vehicle formation stabilization using formation potential functions previously constructed. The vehicles are used in the Caltech Multi-Vehicle Wireless Testbed (MVWT). We provide simulation and experimental results for stabilization and tracking of a single vehicle, and a simulation of stabilization of a six-vehicle formation, demonstrating that in all cases...

8. Optimization of filter banks based on properties of the input signal - Vaidyanathan, P. P.
Filter banks and wavelets have found applications in signal compression, noise removal, and in many other signal processing contexts. In this tutorial we review a number of recent results on the optimization of filter banks based on the knowledge of the input. The main emphasis will be the minimization of error due to subband quantization, and its connection to principal component reconstruction. Both uniform and nonuniform filter banks are considered.

9. Classification of human actions into dynamics based primitives with application to drawing tasks - Del Vecchio, D.; Murray, R. M.; Perona, P.
We develop the study of primitives of human motion, which we refer to as movemes. The idea is to understand human motion by decomposing it into a sequence of elementary building blocks that belong to a known alphabet of dynamical systems. How can we construct an alphabet of movemes from human data? In this paper we address this issue by introducing the notion of well-posednes. Using examples from human drawing data, we show that the well-posedness notion can be applied in practice so to establish if sets of actions, viewed as signals in time, can define movemes.

10. Global analysis of piecewise linear systems using impact maps and quadratic surface Lyapunov functions - Gonçalves, Jorge M.; Megretski, Alexandre; Dahleh, Munther A.
In this paper we develop an entirely new constructive global analysis methodology for a class of hybrid systems known as Piecewise Linear Systems (PLS). This methodology consists in inferring global properties of PLS solely by studying their behavior at switching surfaces associated with PLS. The main idea is to analyze impact maps, i.e., maps from one switching surface to the next switching surface, by constructing quadratic Lyapunov functions on switching surfaces. We found that an impact map induced by an LTI flow between two switching surfaces can be represented as a linear transformation analytically parameterized by a scalar function of...

11. Satellite Chartography of Atmospheric Methane and carbon monoxide from SCIAMACHY onboard ENVISAT - Frankenberg, C.; Meirink, J. F.; Bergamaschi, P.; Platt, U.; Wagner, T.
The UV/Vis/near infrared spectrometer SCIAMACHY on board the European ENVISAT satellite enables total column retrieval of atmospheric methane with high sensitivity to the lower troposphere. The vertical column density of methane is converted to column averaged mixing ratio by using carbon dioxide retrievals as proxy for the probed atmospheric column. For this purpose, we apply concurrent total column measurements of CO_2 in combination with modeled column-averaged CO_2 mixing ratios. Possible systematic errors are discussed in detail while the precision error is 1.8% on average. This paper focuses on methane retrievals from January 2003 through December 2004. The measurements with global...

12. Ionic Charge States Inferred from Elemental and Isotopic Composition in ^3He-rich Solar Energetic Particle Events - Wiedenbeck, M. E.; Cohen, C. M. S.; Leske, R. A.; Mewaldt, R. A.; Cummings, A. C.; Stone, E. C.; von Rosenvinge, T. T.
Data from the ACE Solar Isotope Spectrometer have been used to study heavy ion elemental and isotopic abundances at energies above 10MeV/nuc in a number of ^3He-rich solar energetic particle events. The isotopic composition observations have revealed a fractionation pattern in which heavy isotopes are enhanced relative to lighter isotopes of the same element as a power law in the ratio of the masses. Adopting the assumption that this represents a special case of a general fractionation law in which different ion species are fractionated as a power law in Q/M , we infer ionic charge state values (Q) for a number...

13. One Tile to Rule Them All: Simulating Any Tile Assembly System with a Single Universal Tile - Demaine, Erik D.; Demaine, Martin L.; Fekete, Sándor P.; Patitz, Matthew J.; Schweller, Robert T.; Winslow, Andrew; Woods, Damien
In the classical model of tile self-assembly, unit square tiles translate in the plane and attach edgewise to form large crystalline structures. This model of self-assembly has been shown to be capable of asymptotically optimal assembly of arbitrary shapes and, via information-theoretic arguments, increasingly complex shapes necessarily require increasing numbers of distinct types of tiles. We explore the possibility of complex and efficient assembly using systems consisting of a single tile. Our main result shows that any system of square tiles can be simulated using a system with a single tile that is permitted to flip and rotate. We also show...

14. First Results on the DOAS-Retrieval of OClO from SCIAMACHY Nadir Measurements - Kühl, Sven; Wilms-Grabe, Walburga; Frankenberg, Christian; Kraus, Stefan; Platt, Ulrich; Wagner, Thomas
The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography was launched successfully onboard ENVISAT on March 1, 2002. It observes solar radiation transmitted, backscattered from the atmosphere and reflected from the ground in nadir, limb and occultation viewing modes. Chlorinedioxide (OClO), an important indicator for stratospheric chlorine activation, can be measured in the UV spectral range by Differential Optical Absorption Spectroscopy (DOAS). First results of the DOAS retrieval of OClO slant column densities (SCDs) from the SCIAMACHY measurements are presented. The influence of several parameters like the wavelength range chosen as fitting window or the reference spectra included in the fit on the quality of the retrieval is examined. It is found that a...

15. Determination of Cloud Parameters from SCIAMACHY Data for the Correction of Tropospheric Trace Gases - Grzegorski, Michael; Frankenberg, Christian; Platt, U.; Wenig, Mark; Fournier, Nicolas; Stammes, Piet; Wagner, Thomas
For the accurate retrieval of tropospheric trace gases from SCIAMACHY the availability of cloud parameters is crucial. In this paper we present a new algorithm for the retrieval of cloud fraction from SCIAMACHY data, the Heidelberg Iterative Cloud Retrieval Utilities (HICRU). The reliability of the results are proven through intercomparision with cloud fractions from the FRESCO algorithm and images from Meteosat. The new algorithm for SCIAMACHY is based on the already well validated HICRU algorithm developed for the retrieval of cloud fractions from GOME data. We use broad band spectrometers with high spatial resolution, the Polarization Monitoring Devices. The retrieval applies the widely used threshold method. Our sophisticated, iterative calculation of thresholds including image sequence...

16. Global Monitoring of Atmospheric Trace Gases, Clouds and Aerosols from UV/vis/NIR Satellite Instruments: Currents Status and Near Future Perspectives - Wagner, T.; Beirle, S.; Deutschmann, T.; Frankenberg, C.; Grzegorski, M.; Khokhar, M. F.; Kühl, S.; Marbach, T.; Mies, K.; de Vries, M. Penning; Platt, U.; Pukite, J.; Sanghavi, S.
A new generation of UV/vis/near‐IR satellite instruments like GOME (since 1995), SCIAMACHY (since 2002), OMI (since 2004), and GOME‐2 (since 2006) allows to measure several important stratospheric and tropospheric trace gases like O_3, NO_2, OClO, HCHO, SO_2, BrO, and H_2O as well as clouds and aerosols from space. Because of its extended spectral range, the SCIAMACHY instrument also allows the retrieval of Greenhouse gases (CO_2, CH_4) and CO in the near IR. Almost all of the tropospheric trace gases are observed by these instruments for the first time. From satellite data it is possible to investigate the temporal and spatial...

17. Identification of tropospheric trace gas sources: synergistic use of HCHO and other satellite observations - Marbach, Thierry; Beirle, Steffen; Frankenberg, Christian; Platt, Ulrich; Wagner, Thomas
Satellite observations provide unique opportunities for the identifications of trace gas sources on a global scale. In our case, the satellite Formaldehyde (HCHO) observations provide information concerning the localization of biomass burning (intense source of HCHO over the Amazon basin region and in central Africa) and biogenic isoprene emissions. The HCHO data can be compared with NO2, glyoxal and CO results to identify more precisely the tropospheric sources (biomass burning events, biogenic emissions, human activities). We present case studies for combined satellite observations, derived from GOME measurements aboard the ERS-2 satellite and SCIAMACHY aboard ENVISAT as well as other satellite instrument...

18. Satellite observations of atmospheric SO_2 from volcanic eruptions during the time-period of 1996–2002 - Khokhar, M. F.; Frankenberg, C.; Van Roozendael, M.; Beirle, S.; Kühl, S.; Richter, A.; Platt, U.; Wagner, T.
In this article, we present satellite observations of atmospheric sulfur dioxide (SO_2) from volcanic eruptions. Global ozone monitoring experiment (GOME) data for the years 1996–2002 is analyzed using a DOAS based algorithm with the aim of retrieving SO_2 slant column densities (SCD). The retrieval of SO_2 SCD in the UV spectral region is difficult due to strong and interfering ozone absorptions. It is also likely affected by instrumental effects. We investigated these effects in detail to obviate systematic biases in the SO_2 retrieval. A quantitative study of about 20 volcanoes from Italy, Iceland, Congo/Zaire, Ecuador, Japan, Vanuatu Island and Mexico...

19. Relationship between ATSR fire counts and CO vertical column densities retrieved from SCIAMACHY onboard ENVISAT - Liu, C.; de Vries, M. Penning; Beirle, S.; Hoor, P.; Marbach, T.; Frankenberg, C.; Platt, U.; Wagner, T.
SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric ChartographY) is the first instrument to allow retrieval of CO by measuring absorption in the near infrared from reflected and scattered sunlight instead of from thermal emission. Thus, in contrast to thermal-infrared satellites (MOPITT), SCIAMACHY is highly sensitive to the lower layers of the troposphere where the sources, such as biomass burning, are located, and where the bulk of the CO is usually found. In many regions of the world, the burning of vegetation has a repeating seasonal pattern, but the amount of CO emitted from biomass burning varies considerably from place to...

20. Dictionary approaches for identifying periodicities in data - Tenneti, Srikanth; Vaidyanathan, P. P.
We propose several dictionary representations for periodic signals and use them for estimating their periodicity. This includes estimating concurrent multiple periodicities. These are inspired from the recently proposed DFT based Farey dictionary, where period estimation was cast as a sparse vector recovery problem. We show that this can instead be framed as an l2 norm based data-fitting problem with closed form solutions and much faster computations. We also generalize the complex valued Farey dictionary to simpler integer valued dictionaries. We find that dictionaries constructed using the recently proposed Ramanujan Periodicity Transforms provide the best trade-off between complexity and noise immunity.

Página de resultados:

Busque un recurso