José Paredes - Academia.edu (original) (raw)

Papers by José Paredes

Mecanografiado Tesis (Ing. Eléctrico)-- Universidad de los Andes, Facultad de Ingeniería, Escuela... more Mecanografiado Tesis (Ing. Eléctrico)-- Universidad de los Andes, Facultad de Ingeniería, Escuela de Ingeniería Eléctrica, Mérida, 2003 Incluye bibliografía

_________________________________________________________________________________________________... more _____________________________________________________________________________________________________________________ RESUMEN: La incidencia de los cálculos intrahepáticos en las sociedades occidentales es muy baja, sin embargo, la presencia de estos es todo un reto, ya que el manejo con colangiopancreatografía retrógrada endoscópica, es efectivo sólo en un pequeño porcentaje de los pacientes. Las opciones quirúrgicas son muy variables. El objetivo de este trabajo es describir un caso clínico de litiasis biliar intrahepática resuelto con el uso de colangioscopia intraoperatoria mediante coledocotomía y extracción de cálculos bajo visión directa con canastillas helicoidales, la cual es considerada como una de las mejores opciones quirúrgicas.

In this paper, a coordinate descent algorithm for robust sparse signal representation in overcomp... more In this paper, a coordinate descent algorithm for robust sparse signal representation in overcomplete dictionaries is proposed. Under the coordinate descent framework, each target coefficient is robustly estimated applying the weighted median (WM) to a scaled-and-shifted version of the input signal weighted by the magnitude of the atom associated to the underlying coefficient. Sparsity is induced by appending a zero-valued sample weighted by an adaptive parameter in WM operation. This leads to a generalized thresholding operation over each coefficient of the target vector minimizing, thus, both the bias in nonzero estimates and the sensitivity to small noise levels. Furthermore, a continuation strategy is included in order to set a suitable value of the regularization parameter that leads the best representation at a current noise level. In the context of compressive sensing, numerical simulations are presented to compare the performance of the proposed algorithm to those yielded by...

In this paper, matched subspace detectors based on the framework of Compressive Sensing (CS) are ... more In this paper, matched subspace detectors based on the framework of Compressive Sensing (CS) are developed. The proposed approach, called compressive matched subspace detectors, exploits the sparsity model of the signal-of-interest in the design of the random projection operator. By tai-loring the CS measurement matrix (projection operator) to the subspace where the signal-of-interest is known to lie, the compressive matched subspace detectors can effectively cap-ture the signal energy while the interference and noise ef-fects are mitigated at sub-Nyquist rate. The proposed detec-tion approach is particularly suitable for detection of wide-band signals that emerge in modern communication systems that demand high-speed ADCs. The performance of the sub-space compressive detectors are studied by analytically de-riving closed-form expressions for the detection probability and through extensive simulations.

En este trabajo se proponen dos metodologías de acelerar el algoritmo de mediana ponderada regres... more En este trabajo se proponen dos metodologías de acelerar el algoritmo de mediana ponderada regresiva (MPR) basados en la estimación previa del soporte de la señal a reconstruir antes de la etapa de estimación de la magnitud de la señal. El primer método propuesto, determina iterativamente el subespacio donde se encuentra la mayor energía de la señal poco densa, mientras que el segundo método se basa en determinar la dirección sobre el cual se produce la mayor variación del gradiente. Una vez determinado el posible soporte de la señal, la magnitud de la misma es determinada iterativamente siguiendo el algoritmo de mediana ponderada regresiva. Con los algoritmos propuestos se consiguen niveles de aceleración que van desde 4 a 12 veces más rápido que el algoritmo original [2] y que dependen del número de elementos no nulos de la señal poco densa a recuperar. Palabras clave: Algoritmo de reconstrucción, compressive sensing, mediana ponderada, aceleración. INTRODUCCIÓN Un problema comúnm...

In this paper, the efficiency of the algorithm for compressive sensing (CS) signal reconstruction... more In this paper, the efficiency of the algorithm for compressive sensing (CS) signal reconstruction based on weighted median regression (WMR) is analyzed through a Cox-regression model. We perform 1620 reconstructions for signals with different dimension (N), sparsity (K), number of measurements (M) and regularization parameter (α) that induces sparsity in the solution. Among the most relevant results, we find that the algorithm efficiency, as a function of the regularization parameter, follows an inverted parabolic function reaching its maximum at α = 0.8. Furthermore, we show that the reconstruction algorithm is quite sensible to α and M. Thus, a slight change on those parameters leads to a notable variation on the algorithm’s convergence speed. Therefore, by suitably tunning the number of measurements, we can control the volatile described above. Thus, if the ratio N/M goes from 7 to 9, the probability of having a good performance increases from 0.4 to 0.7. Furthermore, if α change...

IEEE Transactions on Signal Processing

The output distribution formula for stack filters based on mirrored threshold decomposition is de... more The output distribution formula for stack filters based on mirrored threshold decomposition is derived. This formula allows one to compute the cumulative distribution function of the output of a stack filter for a given independent and identically distributed (i.i.d.) input noise distribution. Mirrored threshold decomposition permits us to analyze the input-output characteristics of the stack filter in the binary domain. The sliding window operation of the stack filter is modeled by a deterministic finite automaton. The output distribution of the filter is obtained by interpreting the automaton as a Markov chain whose transition probabilities depend on the probabilistic description of the binary input signal. An example illustrating the use of the output distribution formula is provided.

2000 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.00CH37100), 2000

2009 IEEE International Conference on Acoustics, Speech and Signal Processing, 2009

In this paper, a new framework for confocal microscopy based on the novel theory of compressive s... more In this paper, a new framework for confocal microscopy based on the novel theory of compressive sensing is proposed. Unlike wide field microscopy or conventional parallel beam confocal imaging systems that use charge-coupled devices (CCD) as acquisition devices in addition to complex mechanical scanning system, the proposed compressive confocal microscopy is a kind of parallel beam confocal imaging system which exploits the rich theory of compressive sensing by using a single pixel detector and a digital micromirror device (DMD) to capture linear projections of the in-focus image. With the proposed system, confocal imaging of high optical sectioning ability can be achieved at sub-Nyquist sampling rates. Theoretical analysis, simulations and experimental results are shown to demonstrate the characteristics and potential of the proposed approach.

Gastroenterologia y hepatologia, Jan 23, 2015

Information received by IBD patients about their disease is of particular importance. The objecti... more Information received by IBD patients about their disease is of particular importance. The objective of the study was to determine the information resources these patients used, together with their perceived information gaps and expected preferences. A prospective, observational, cross-sectional study conducted on IBD patients attending 13 Spanish hospitals during 2008. Patients completed a semi-structured 52-question survey. Survey was adequately completed by 379 of 385 patients (98%), of whom 57% had Crohn's disease and 43% ulcerative colitis. Mean patient age was 37.9 years (range, 16-76 years). Gastroenterologists were the most commonly used resource (98%), followed by the Internet (60%), and general practitioners (50%). More than 90% reported good to excellent satisfaction with gastroenterologists, nurses, and patients' associations. Only 56% considered their information needs to be covered. The Internet was mostly used by young patients and those with a high education l...

IBM Journal of Research and Development, 2015

ABSTRACT The IBM POWER8™ processor is a 649-mm , 4.2-billion transistor, high-frequency microproc... more ABSTRACT The IBM POWER8™ processor is a 649-mm , 4.2-billion transistor, high-frequency microprocessor fabricated in the IBM 22-nm silicon on insulator (SOI) technology with embedded dynamic random access memory (eDRAM) and 15 layers of metal. With its twelve architecturally enhanced, eight-way multithreaded cores, 96-MB high-bandwidth shared third-level cache, and increased on and off-chip bandwidth, the POWER8 processor delivers industry-leading performance. This paper describes the circuit techniques and design methodologies that were employed for implementing this chip and that allowed it to maintain the power dissipation at the level of its predecessor while delivering a threefold increase in per-socket performance. Among the innovative technologies employed by the processor are resonant clocking, on-chip per-core voltage regulation, and enhanced eDRAM arrays.

Emerging Digital Micromirror Device Based Systems and Applications, 2009

In this paper, a new approach for Confocal Microscopy (CM) based on the framework of compressive ... more In this paper, a new approach for Confocal Microscopy (CM) based on the framework of compressive sensing is developed. In the proposed approach, a point illumination and a random set of pinholes are used to eliminate out-of-focus information at the detector. Furthermore, a Digital Micromirror Device (DMD) is used to efficiently scan the 2D or 3D specimen but, unlike the conventional CM that uses CCD detectors, the measured data in the proposed compressive confocal microscopy (CCM) emerge from random sets of pinhole illuminated pixels in the specimen that are linearly combined (projected) and measured by a single photon detector. Compared to conventional CM or programmable array microscopy (PAM), the number of measurements needed for nearly perfect reconstruction in CCM is significantly reduced. Our experimental results are based on a testbed that uses a Texas Instruments DMD (an array of 1024×768; 13.68×13.68 µm 2 mirrors) for computing the linear projections of illuminated pixels and a single photon detector is used to obtain the compressive sensing measurement. The position of each element in the DMD is defined by the compressed sensing measurement matrices. Threedimensional image reconstruction algorithms are developed that exploit the inter-slice spatial image correlation as well as the correlation between different 2D slices. A comprehensive performance comparison between several binary projection patterns is shown. Experimental and simulation results are provided to illustrate the features of the proposed systems.

International Conference on Indoor Positioning and Indoor Navigation, 2013

This work benefits from the capability of the iPhone's or iPad's microphone to acquire high-frequ... more This work benefits from the capability of the iPhone's or iPad's microphone to acquire high-frequency sound for accurate acoustic code identification. Although the maximum theoretical value for the frequency response of the built-in iOS device microphone is 20 kHz, emissions with frequencies close to 22 kHz have been experimentally detected. The frequencies used in this work are in the range from 18 to 22 kHz, which are high enough to be inaudible for almost every people but low enough to be generated by standard sound hardware.

This work describes campaigns of measurements of propagation channel characteristics for Terrestr... more This work describes campaigns of measurements of propagation channel characteristics for Terrestrial Digital TV, carried on the metropolitan region of Rio de Janeiro, Brazil and Caracas, Venezuela. Measurements of propagation loss obtained from these experiment are compared with predictions using the ITU-R Recommendation P.1546–3 method. Measured multipath time delay profiles for LOS and NLOS reception are also presented.

American journal of physiology. Renal physiology, 2014

During kidney development, the vasculature develops via both angiogenesis (branching from major v... more During kidney development, the vasculature develops via both angiogenesis (branching from major vessels) and vasculogenesis (de novo vessel formation). The formation and perfusion of renal blood vessels are vastly understudied. In the present study, we investigated the regulatory role of renal blood flow and O2 concentration on nephron progenitor differentiation during ontogeny. To elucidate the presence of blood flow, ultrasound-guided intracardiac microinjection was performed, and FITC-tagged tomato lectin was perfused through the embryo. Kidneys were costained for the vasculature, ureteric epithelium, nephron progenitors, and nephron structures. We also analyzed nephron differentiation in normoxia compared with hypoxia. At embryonic day 13.5 (E13.5), the major vascular branches were perfused; however, smaller-caliber peripheral vessels remained unperfused. By E15.5, peripheral vessels started to be perfused as well as glomeruli. While the interior kidney vessels were perfused, th...

Signal Processing, 2015

ABSTRACT Active sensing is a growing research field with long-standing open problems, whose appli... more ABSTRACT Active sensing is a growing research field with long-standing open problems, whose applications range from CDMA communication systems, ultrasonic imaging or ranging systems to name a few. In those applications, spreading sequences are usually transmitted in a bursting manner, making their aperiodic correlation the most important feature to be considered, since it determines how easily the transmission can be detected by the receiver. Hence, the selection of the spreading sequence with good aperiodic correlation properties has a large impact on the final system performance. This paper presents a revision of the aperiodic spreading sequences used for active sensing systems available in the literature so it aims to serve as a reference for researchers in the field.