Showing papers by "Ensenada Center for Scientific Research and Higher Education published in 2008"

Activity-Aware Computing for Healthcare

Abstract: In this article, we introduce activity-aware computing, which uses activity-based computing to enhance pervasive environments in two ways: to help users associate resources and services with activities, resulting in seamless interaction with those resources and services, and to enable pervasive environments to automatically infer activities and thus opportunistically offer services that support the user's current goal. Thus, activity-aware applications persuade users to commit themselves to the technology, moving from a paradigm of activity-based ";interaction"; toward one of activity-aware ";engagement"; with a computationally augmented environment. We present a set of tools for developing activity-aware applications, including a computational representation of human activities that we defined using data from a hospital case study we conducted. We also used the data to create an activity recognition approach and a set of design principles for developing activity-aware applications. The mobile activity monitor we designed to create a wearable connection between patients and nurses exemplifies our design principles.

Second-order sliding mode control of underactuated mechanical systems I: Local stabilization with application to an inverted pendulum

Abstract: Second order sliding mode control synthesis is developed for underactuated mechanical systems, operating under uncertainty conditions. In order to locally stabilize an underactuated system around an unstable equilibrium, an output is specified in such a way that the corresponding zero dynamics is locally asymptotically stable. Then, the desired stability property of the closed-loop system is provided by applying a quasihomogeneous second order sliding mode controller, driving the system to the zero dynamics manifold in finite time. Although the present synthesis exhibits an infinite number of switches on a finite time interval, it does not rely on the generation of first order sliding modes, while providing robustness features similar to those possessed by their standard sliding mode counterparts. A second order sliding mode appears on the zero dynamics manifold which is of co-dimension greater than the control space dimension. Performance issues of the proposed synthesis are illustrated in numerical and experimental studies of a cart-Pendulum system.

Dynamic population gratings in rare-earth-doped optical fibres

Abstract: Dynamic Bragg gratings can be recorded in rare-earth (e.g. Er, Yb) doped optical fibres by two counter-propagating mutually coherent laser waves via local saturation of the fibre optical absorption or gain (in optically pumped fibres). Typical recording cw light power needed for efficient grating formation is of sub-mW–mW scale which results in characteristic recording/erasure times of 10–0.1 ms. This review paper discusses fundamental aspects of the population grating formation, their basic properties, relating wave-mixing processes and also considers different applications of these dynamic gratings in single-frequency fibre lasers, tunable filters, optical fibre sensors and adaptive interferometry.

Online scheduling in grids

Abstract: This paper addresses nonclairvoyant and non-preemptive online job scheduling in Grids. In the applied basic model, the grid system consists of a large number of identical processors that are divided into several machines. Jobs are independent, they have a fixed degree of parallelism, and they are submitted over time. Further, a job can only be executed on the processors belonging to the same machine. It is our goal to minimize the total makespan. We show that the performance of Garey and Graham's list scheduling algorithm is significantly worse in grids than in multiprocessors. Then we present a Grid scheduling algorithm that guarantees a competitive factor of 5. This algorithm can be implemented using a "job stealing" approach and may be well suited to serve as a starting point for Grid scheduling algorithms in real systems.

Second‐order sliding mode control of underactuated mechanical systems II: Orbital stabilization of an inverted pendulum with application to swing up/balancing control

Abstract: Orbital stabilization of an underactuated cart-pendulum system is under study. The quasihomogeneous control synthesis is utilized to design a second order sliding mode controller that drives the actuated cart to a periodic reference orbit in finite time, while the non-actuated pendulum produces bounded oscillations. A modified Van der Pol oscillator is introduced into the synthesis as an asymptotic generator of the periodic motion. The resulting closed-loop system is capable of moving from one orbit to another by simply changing the parameters of the Van der Pol modification. Performance issues of the proposed synthesis are illustrated in numerical and experimental studies of the swing up/balancing control problem of moving a pendulum, located on an actuated cart, from its stable downward position to the unstable inverted position and stabilizing it about the vertical.

Influences of climate on fire regimes in montane forests of north‐western Mexico

Abstract: Aim To identify the influence of interannual and interdecadal climate variation on the occurrence and extent of fires in montane conifer forests of north-western Mexico. Location This study was conducted in Jeffrey pine (Pinus jeffreyi Grev. & Balf.)-dominated mixed-conifer forests in the central and northern plateau of the Sierra San Pedro Martir, Baja California, Mexico. Methods Fire occurrence was reconstructed for 12 dispersed sites for a 290-year period (1700–1990) from cross-dated fire-scarred samples extracted from live trees, snags and logs. Superposed epoch analysis was used to examine the relationships of tree-ring reconstructions of drought, the El Nino/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) with fire occurrence and extent. Results Years with no recorded fire scars were wetter than average. In contrast, years of widespread fires were dry and associated with phase changes of the PDO, usually from positive (warm) to negative (cold). The influence of the PDO was most evident during the La Nina phase of the ENSO. Widespread fires were also associated with warm/wet conditions 5 years before the fire. We hypothesize that the 5-year lag between warm/wet conditions and widespread fires may be associated with the time necessary to build up sufficient quantity and continuity of needle litter to support widespread fires. Two periods of unusually high fire activity (1770–1800 and 1920–1950) were each followed by several decades of unusually low fire activity. The switch in each case was associated with strong phase changes in both PDO and ENSO. Main conclusions Climate strongly influences fire regimes in the mountains of north-western Mexico. Wet/warm years are associated with little fire activity. However, these years may contribute to subsequent fire years by encouraging the production of sufficient needle litter to support more widespread fires that occur in dry/cool years.

Identification of behavior patterns in household solid waste generation in Mexicali's city: Study case

Abstract: A strategy of household waste data analysis is proposed in this work, based on the WEKA workbench, developed on the Pattern Recognition community. The analysis was conducted on data collected from homes at residential areas in the city of Mexicali, Mexico. The data included information about solid waste produced and also the householder's commitment to the environment, assessed in a Likert's scale based on a questionnaire. A cluster analysis and a tree classifier constructed using the clustered data are presented. An analysis of the decision tree allowed to translate the resulting tree in a set of production rules. After the interpretation of these rules, we were able to predict an environmental behavior, based on the information about waste generation and the questionnaire answers. The rules showed a tendency to bring together members of the same family, concurring in all cases the reference to the same period of waste generation. The elements identified on each rule indicate that the socioeconomic stratum is an important factor, related to behavioral attributes and consumption habits, the main relationship is based on attributes of waste generation as glass, organics, paper, inert, mixer containers and sanitary. The discovered relationships between the cluster, socio-demographic, behavioral and waste attributes are presented and discussed.

Summer circulation in the Mexican tropical Pacific

Abstract: The main components of large-scale circulation of the eastern tropical Pacific were identified in the mid 20th century, but the details of the circulation at length scales of 10 2 km or less, the mesoscale field, are less well known particularly during summer. The winter circulation is characterized by large mesoscale eddies generated by intense cross-shore wind pulses. These eddies propagate offshore to provide an important source of mesoscale variability for the eastern tropical Pacific. The summer circulation has not commanded similar attention, the main reason being that the frequent generation of hurricanes in the area renders in situ observations difficult. Before the experiment presented here, the large-scale summer circulation of the Gulf of Tehuantepec was thought to be dominated by a poleward flow along the coast. A drifter-deployment experiment carried out in June 2000, supported by satellite altimetry and wind data, was designed to characterize this hypothesized Costa Rica Coastal Current. We present a detailed comparison between altimetry-estimated geostrophic and in situ currents estimated from drifters. Contrary to expectation, no evidence of a coherent poleward coastal flow across the gulf was found. During the 10-week period of observations, we documented a recurrent pattern of circulation within 500 km of shore, forced by a combination of local winds and the regional-scale flow. Instead of the Costa Rica Coastal Current, we found a summer eddy field capable of influencing large areas of the eastern tropical Pacific. Even in summer, the cross-isthmus wind jet is capable of inducing eddy formation.

An experimental analysis of Zigbee networks

Abstract: Zigbee has been touted as a technology that can be embedded in a wide range of products and applications across consumer, commercial, industrial and government markets. However, given the varying requirements for applications in these sectors, we question if Zigbee can really satisfy the needs of these diverse markets. We performed several experiments using commercially available Zigbee software and hardware in order to determine several aspects concerning the reach and limitations of the technology. We analyze the results of our tests and show evidence of where Zigbee can be applied and where it is not suited for.

A framework to analyze information systems as knowledge flow facilitators

Abstract: This paper presents a framework which can be used to analyze information systems as knowledge flow facilitators in organizational processes. This framework may be useful, particularly to small organizations, for two main reasons: it can help them to start seeing the implications of KM in their current technical infrastructure, and as a result, they should be in a better position to know how to include their current working tools in part of a KM strategy, thus facilitating the alignment of such a strategy to the daily work of the organization. Second, identifying the role that their current tools play in the flow of knowledge should help such organizations to identify means by which to improve such tools as KM enablers, before becoming engaged in costly KM efforts that could require the acquisition of new tools and often also big changes in their current work processes. The applicability of the framework is illustrated with a case study conducted in a software development environment in which it was successfully applied.

Shape and Dimensions of the Cerro Prieto Pull-Apart Basin, Mexicali, Baja California, Mexico, Based on the Regional Seismic Record and Surface Structures

Abstract: The Salton Trough is a wide, actively subsiding basin where a system of an en-echelon dextral transform faults and pull-apart basins is operating. This tectonic province represents the connection between the Gulf of California fault system and the San Andreas transform fault. Within the depression, several sub-basins, such as the Cerro Prieto geothermal field in Mexicali, Baja California, Mexico, represent an incipient spreading center along the southern limits of the Salton Trough. The Cerro Prieto Basin has developed between two major, subparallel, right-stepping active transforms, the Imperial and Cerro Prieto faults. General agreement exists regarding the regional tectonic interpretation of the Cerro Prieto Basin; however, published documentation is lacking regarding its shape and dimensions. In this paper, we address this problem. We have integrated seismic data available for the whole study area and evidence from surface breaks. Our study shows that the most important factor controlling formation of...

Coastal typology: An integrative “neutral” technique for coastal zone characterization and analysis

Abstract: Typology, the ‘study or systematic classification of types that have characteristics or traits in common’, has become a commonly used term and technique in coastal zone studies over the past two decades. At least part of this is due to adoption by the first Land–Ocean Interactions in the Coastal Zone (LOICZ) project of a typological approach as a way to understand and organize the daunting diversity of natural and human systems comprising the world coastal zone, and to the concurrent development of tools and databases to support systematic applications. This paper reviews some of the history of the term ‘typology’ and the concepts and techniques that it subsumes, and discusses its adoption and adaptation in coastal studies. It also addresses the continued and increasing relevance of typology to the continuation of the LOICZ project and its objectives, and outlines the opportunities and challenges involved in realizing the potentials of the approach – both within LOICZ and for the scientific and coastal zone communities in general.

Extreme precipitation trends associated with tropical cyclones in the core of the North American monsoon

Abstract: [1] We estimate trends of extreme daily precipitation (P95 > 95th percentile) events in the core of the North American monsoon region in Northwest Mexico during JJAS of 1961–1998. The intensity and seasonal contribution of P95 show significant upward linear trends in the mountain sites, which appear to be related to an increased contribution from heavy precipitation derived from tropical cyclones (TCs). Frequency of P95, total monsoon precipitation, and P95 in coastal stations did not change significantly. TC-derived P95 events are associated with SST anomalies similar to weak La Nina conditions in the eastern Equatorial Pacific, SSTs > 28.5°C in the Caribbean Sea, and strong land-sea thermal contrast over Northwest Mexico and the U.S. Southwest two weeks prior to their onset.

Seismic Attenuation in Northeastern Sonora, Mexico

Abstract: We studied the attenuation of local and regional earthquake body waves recorded by the seismic network of northeastern Sonora, Mexico (Red Sismica del Noreste de Sonora [RESNES]). The source-station paths of the selected data set cover the epicentral region of the May 1887 ( M w 7.5) Sonora earthquake. We used the best-located earthquakes recorded by RESNES between 2003 and 2004 to analyze the spectral amplitude decay of body waves with hypocentral distance. The database consists of 44 earthquakes with magnitudes between 1.8 and 3.2 and hypocentral distances between 25 and 150 km. We calculated Fourier spectral amplitudes from more than 400 records and defined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes at 23 individual frequencies between 0.4 and 63.1 Hz. We determined regional attenuation curves based on events located more than 100 km northwest of the center of the network and local curves based on earthquakes located near the fault zone that ruptured in the 1887 earthquake. The obtained attenuation curves indicate that the spectral amplitudes decay faster in the area of the 1887 rupture than in the surrounding region. To analyze the possible sources of attenuation, we parameterized the attenuation functions considering three terms: one that accounts for geometrical spreading, another one for anelastic attenuation, and a third for near-surface attenuation. We found the S -wave quality factor Q to be similar in both the general region and near the 1887 rupture. However, in the region of the 1887 rupture, the near-surface attenuation exceeds the regional average. Finally, in the region of the 1887 rupture, the nonparametric attenuation functions and the estimates of Q indicate that at between 0.6 and 63.1 Hz, P waves attenuate more than S waves ( Q P =20.8 f 1.1, whereas Q S =83.8 f 0.9).

Sampling Strategies and the Anisotropy of Magnetic Susceptibility of Dykes.

Abstract: Most studies of the anisotropy of magnetic susceptibility (AMS) of dykes have assumed that susceptibility axes should define a unique orientation relative to the dyke walls and magma flow direction. Theoretical considerations, however, predict systematic variations of AMS as a function of the amount of shear experienced by the flowing magma. Although this feature of AMS might seem undesirable at first sight, based in a theoretical model it has been suggested that actually we can take advantage of such variation in the orientation of the AMS axes to infer magma flow directions more confidently than until now if proper attention is given to the scheme followed during sample collection. In this work we report the results of a pilot study made to test those theoretical predictions. We resampled two dykes from the Ko'olau dyke complex in O'ahu and for which magma flow direction was previously inferred albeit with some uncertainty. The resampling was made following the guidelines suggested by the theoretical work as closely as possible (i.e., collecting more than one profile parallel to the dyke walls and across the dyke). The results of our measurements provide the first empirical evidence supporting the occurrence of a cyclic fabric acquisition during the emplacement of at least some dykes. The procedure described in this paper therefore constitutes a self-contained approach that can be followed to test in a case by case basis the occurrence of such fabric behavior. This in turn should provide enough elements to increase the reliability of the interpretation in the obtained results.

Asymptotic harmonic generator and its application to finite time orbital stabilization of a friction pendulum with experimental verification

Abstract: A second order sliding mode approach to orbital stabilization is presented and tested on a friction pendulum, operating under uncertain conditions. The quasihomogeneous control synthesis is utilized to design a variable structure controller that drives the pendulum to a model orbit in finite time in spite of the presence of external disturbances with an a priori known magnitude bound. A well-known Van der Pol oscillator is modified to be introduced into the synthesis as a reference model. This modification is made to shape the oscillator limit cycle to a harmonic one, thereby yielding an asymptotic harmonic generator of the periodic motion. The parameters of the asymptotic harmonic generator are shown to specify amplitude and frequency of the limit cycle production and damping of non-linear oscillations of the generator. The resulting closed-loop system is capable of moving from one orbit to another by changing these parameters dynamically. Performance issues of the controller constructed are illustrated ...

Cover and Colonization of Commercial Oyster (Crassostrea gigas) Shells by Fouling Organisms in San Quintin Bay, Mexico

Abstract: Fouling communities of commercial oyster crops in San Quintin Bay (Baja California, Mexico) were investigated to understand patterns of shell cover, species composition, and colonization. Historically dominated by soft sediment systems, San Quintin Bay currently supports a large oyster (Crassostrea gigas) aquaculture industry. Oyster shells are the main source of hard substratum in the bay, without which fouling communities would be mostly absent. Fouling communities are a nuisance to oyster farming because they result in increased handling time in cleaning and packaging oysters. To investigate the previously undocumented fouling communities of San Quintin, 3 sites within the bay were surveyed for 18 mo (2004 to 2005). Every month between July 2004 and December 2005 samples were deployed and collected so as to obtain shells that had been submerged for either 1, 2, 3, 6, or 12 mo. The majority of the fouling organisms were ascidians, with bryozoans, sponges, hydrozoans, and algae also present. Res...

Discovering several robot behaviors through speciation

Abstract: This contribution studies speciation from the standpoint of evolutionary robotics (ER). A common approach to ER is to design a robot's control system using neuro-evolution during training. An extension to this methodology is presented here, where speciation is incorporated to the evolution process in order to obtain a varied set of solutions for a robotics problem using a single algorithmic run. Although speciation is common in evolutionary computation, it has been less explored in behavior-based robotics. When employed, speciation usually relies on a distance measure that allows different individuals to be compared. The distance measure is normally computed in objective or phenotypic space. However, the speciation process presented here is intended to produce several distinct robot behaviors; hence, speciation is sought in behavioral space. Thence, individual neurocontrollers are described using behavior signatures, which represent the traversed path of the robot within the training environment and are encoded using a character string. With this representation, behavior signatures are compared using the normalized Levenshtein distance metric (N-GLD). Results indicate that speciation in behavioral space does indeed allow the ER system to obtain several navigation strategies for a common experimental setup. This is illustrated by comparing the best individual from each species with those obtained using the Neuro-Evolution of Augmenting Topologies (NEAT) method which speciates neural networks in topological space.

Reproductive biology of the brown smoothhound shark Mustelus henlei, in the northern Gulf of California, México

Abstract: Female brown smoothhound sharks Mustelus henlei were found to reproduce annually. A mature female carried both developing oocytes in the ovary and developing embryos in the uteri concurrently for c. 1 year. A great variability in the size of embryos was recorded each month, and the maximum embryo sizes were found from late January to mid-March. The largest oocytes in mature females were observed in mid-March. Gestation lasted c. 10 months. A linear relationship between maternal total length (LT) and the number of pups per litter (litter size one to 21) was estimated. Birth LT was reached in c. 280 mm. Females and males matured at 570–660 and 550–560 mm LT, respectively. Difference in the litter size among Californian coast (one to 10) and northern Gulf of California (one to 21) populations existed for this smoothhound shark.

Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film

Abstract: Using a self-diffraction experiment with 7ns pulses at 532nm we studied a silicon nitride film containing silicon nanoclusters (nc-Si) of 3.1+/-0.37 nm mean size. The sample was prepared by remote plasma-enhanced chemical vapor deposition (RPECVD), and we found that its nonlinearity consists of a combination of electronic and thermal contributions. By varying the repetition rate of the laser, we discriminated the responsible mechanisms for the nonlinear response. Using this procedure we determined a total /chi((3))1111/ = 3.3x10(-10)esu, n2 = 2.7x10(-16) m(2)/W, beta = 1x10(-9) m/W and dn/dT =1x10(-4) degrees C(-1) for our sample. We also show results for the optical Kerr effect using 80 fs pulses at 820 nm. The purely electronic nonlinearity measured is characterized by /chi((3))1111/=9.5 x10(-11) esu.