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Harmon M.E.,Oregon State University | Bond-Lamberty B.,Pacific Northwest National Laboratory | Tang J.,Ecosystems Center | Vargas R.,Research Center Cientifica Educacion Superior Of Ensenada
Journal of Geophysical Research: Biogeosciences | Year: 2011

Heterotrophic respiration (RH) is a major process releasing carbon to the atmosphere and is essential to understanding carbon dynamics in terrestrial ecosystems. Here we review what is known about this flux as related to forest disturbance using examples from North America. The global R H flux from soils has been estimated at 53-57 Pg C yr-1, but this does not include contributions from other sources (i.e., dead wood, heart-rots). Disturbance-related inputs likely account for 20-50% of all R H losses in forests, and disturbances lead to a reorganization of ecosystem carbon pools that influences how RH changes over succession. Multiple controls on RH related to climate, the material being decomposed, and the decomposers involved have been identified, but how each potentially interacts with disturbance remains an open question. An emerging paradigm of carbon dynamics suggests the possibility of multiple periods of carbon sinks and sources following disturbance; a large contributing factor is the possibility that postdisturbance RH does not always follow the monotonic decline assumed in the classic theory. Without a better understanding and modeling of RH and its controlling factors, it will be difficult to estimate, forecast, understand, and manage carbon balances of regions in which disturbance frequency and severity are changing. Meeting this challenge will require (1) improved field data on processes and stores, (2) an improved understanding of the physiological and environmental controls of R H, and (3) a more formal analysis of how model structure influences the RH responses that can be predicted. Copyright 2011 by the American Geophysical Union.

Olague G.,Research Center Cientifica Educacion Superior Of Ensenada | Trujillo L.,Tijuana Institute of Technology
Applied Soft Computing Journal | Year: 2012

The detection of stable and informative image points is one of the most important low-level problems in modern computer vision. This paper proposes a multiobjective genetic programming (MO-GP) approach for the automatic synthesis of operators that detect interest points. The proposal is unique for interest point detection because it poses a MO formulation of the point detection problem. The search objectives for the MO-GP search consider three properties that are widely expressed as desirable for an interest point detector, these are: (1) stability; (2) point dispersion; and (3) high information content. The results suggest that the point detection task is a MO problem, and that different operators can provide different trade-offs among the objectives. In fact, MO-GP is able to find several sets of Pareto optimal operators, whose performance is validated on standardized procedures including an extensive test with 500 images; as a result, we could say that all solutions found by the system dominate previously man-made detectors in the Pareto sense. In conclusion, the MO formulation of the interest point detection problem provides the appropriate framework for the automatic design of image operators that achieve interesting trade-offs between relevant performance criteria that are meaningful for a variety of vision tasks. © 2011 Elsevier B.V.

Cudney R.S.,Research Center Cientifica Educacion Superior Of Ensenada
Optics Express | Year: 2011

A modified Shack-Hartmann wavefront sensor based on an array of electrically controlled zone plates made of ferroelectric domains is presented. The camera used for image acquisition is also used for wavefront sensing. An experimental simulation of the use of this sensor to enhance astronomical images obtained by "Lucky Imaging" is presented. © 2011 Optical Society of America.

Robles-Agudo M.,Research Center Cientifica Educacion Superior Of Ensenada | Cudney R.S.,Research Center Cientifica Educacion Superior Of Ensenada
Applied Physics B: Lasers and Optics | Year: 2011

We present a simple method to design aperiodically poled crystals to obtain multiple nonlinear optical processes simultaneously. We use this technique to design and make an aperiodically poled lithium niobate crystal with which we obtained eight distinct sum-frequency generation processes, and another sample with which we obtained four distinct optical parametric generation processes. We also show that the peak effective nonlinearities of aperiodic crystals designed with this technique are larger and their widths are narrower than what can be obtained with a crystal of the same length with separate sections with well-defined poling periodicities. © Springer-Verlag 2010.

O'Donnell K.A.,Research Center Cientifica Educacion Superior Of Ensenada
Physical Review Letters | Year: 2011

An experimental study of the dispersion cancellation occurring in frequency-entangled photon pairs is presented. The approach uses time-resolved up-conversion of the pairs, which has temporal resolution at the femtosecond level, and group-delay dispersion sensitivity of 20fs2 under experimental conditions. The cancellation is demonstrated with dispersion stronger than ±103fs2 in the signal (-) and idler (+) modes. © 2011 American Physical Society.

Alvarez-Borrego S.,Research Center Cientifica Educacion Superior Of Ensenada
Botanica Marina | Year: 2012

The Gulf of California has three main natural fertilization mechanisms: upwelling, tidal mixing, and water exchange with the Pacifi c Ocean. Waters high in nutrients occur at very shallow depths in the gulf, and little energy is required for these nutrients to reach the euphotic zone. Upwelling off the eastern coast is strong, chlorophyll a concentration (Chl) can exceed 10 mg m -3, and because of eddy circulation it increases the phytoplankton biomass across the gulf. Because of strong stratifi cation during summer, upwelling off the western coast causes Chl to increase only to - 0.5 mg m -3. The annual cycle is the dominant mode of Chl variability in most of the gulf. El Niño events cause the suppression of Chl mostly in areas on the eastern side of the central and southern gulf, with the effect decreasing from the mouth to the central gulf. 14C data show that highest productivities occur during winter - spring, and in the Guaymas Basin (up to > 4 g C m -2 day -1). Averages of total integrated production (P Tint) for " winter " and for whole regions within the gulf estimated from satellite imagery are in good agreement with averages of 14C estimates (∼ 1.8 g C m -2 day -1). P Tint values for " summer " are ∼ 30 % of those for " winter.". © 2012 by Walter de Gruyter.

Aguilar-Gonzalez P.M.,Research Center Cientifica Educacion Superior Of Ensenada | Kober V.,Research Center Cientifica Educacion Superior Of Ensenada
Optics Communications | Year: 2012

We present the design of correlation filters for detection of a target in a noisy input scene when the object of interest is given in a noisy reference image. The target signal, shape and location in the reference image are assumed to be unknown. Two signal models are considered for the input scene: additive and nonoverlapping. The design of the filters consists of automated estimation of needed parameters from a noisy reference image and maximization of the peak-to-output energy ratio criterion. Two filter variants are proposed. The matching error metric is used to determine the regions of the parameter space where each filter variant performs better. Computer simulation results obtained with the proposed filters are presented and evaluated in terms of discrimination capability, location errors, and tolerance to input noise. © 2011 Elsevier B.V. All rights reserved.

Water exchange between the Gulf of California and the Pacific has a significant vertical component. Surface (0-200 m) gulf water flows out into the Pacific and deep (200-600 m) water flows into the gulf. A biogeochemical method is proposed to estimate this vertical component of water exchange assuming steady state for the concentration of nutrients in the gulf and using the net average annual input of nitrate needed to support new phytoplankton production in the whole Gulf of California (P NEW). An annual average P NEW of (2586.7 ± 131.7) × 10 9 mol C yr -1 was deduced from the literature for the whole gulf and for non-El Niño years. Using the Redfield N:C ratio (16:122), the nitrate needed to support P NEW was estimated as (339 ± 17)× 10 9 mol yr -1. Annual representative averages of NO 3, for the mouth of the gulf and for the depth intervals 0-200 m and 200-600 m, were used to calculate the annual average vertical component of water exchange between the gulf and the Pacific to balance the nitrate needed to support P NEW with the net input of nitrate from the Pacific, and the result was (0.67 ± 0.10) Sv in and out of the gulf. This relatively low value, possibly only ~7% of the whole water exchange, indicates that when considering a particular depth most of the time the inflow from the Pacific is equal or very similar to the outflow. Thus, most of the exchange between the gulf and the Pacific consists of the horizontal component.

Contreras J.,Research Center Cientifica Educacion Superior Of Ensenada
International Geology Review | Year: 2013

The Trans-Mexican Volcanic Belt (TMVB) is an igneous arc built above the Middle America subduction zone. Its western section is being extended orthogonally to its axis by several arrays of active normal faults with a combined length of 450 km and including up to 1.5 km of throw. Until now, intra-arc extension in the TMVB has been considered the result of either rifting or retreat of the Rivera and Cocos plates. Observations worldwide and numerical models, however, appear to contradict these ideas. Continental extension in convergent margins takes place where the upper plate moves away from the trench, and the subduction zone is only weakly coupled with the overlying plate. In western Mexico, neither of these relationships applies. A new numerical model presented here is able to explain satisfactorily the state of brittle failure of the TMVB. The model embodies the first-order physics of the northern Middle America subduction zone, and its boundary conditions are consistent with the convergence history of the Rivera and North America plates. Modelling results show that periods of accelerated subduction between the Rivera and North America plates give rise to an increase in suction force under the fore arc. The over-riding plate then bends downwards, building up tensional stress inside the volcanic arc. Failure of the arc follows within 1 million years of pulse initiation. Analysis of the results shows that the steep subduction angle of the Rivera slab, the relief of the volcanic plateau, and the thermal weakening of the lower crust facilitated the failure of the arc. The model demonstrates that a highly coupled subduction zone can cause extension, albeit limited, in the over-riding plate. © 2013 Taylor & Francis.

Cavazos T.,Research Center Cientifica Educacion Superior Of Ensenada | Arriaga-Ramirez S.,Research Center Cientifica Educacion Superior Of Ensenada
Journal of Climate | Year: 2012

Regional climate change scenarios for Baja California/Southern California (BCC) and the North American monsoon (NAM) were produced as part of the Baja California State Climate Change Action Program (PEACC-BC). Bias-corrected and spatially downscaled scenarios (BCSD) from six general circulation models (GCMs) with a total of 12 realizations were analyzed for two scenarios of the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES): B1 (low emissions) and A2 (high emissions) during the twenty-first century. A validation of the original GCM realizations and the BCSD scenarios with observed data during 1961-90 show that the ensemble GCM produces too much precipitation during autumn and winter, which could be the cause of the observed delay of the summer monsoon rains; the ensemble BCSD considerably improves the mean annual cycles and spatial distributions of precipitation and temperature in the region. However, both ensembles greatly underestimate the observed interannual variability of precipitation. BCSD scenarios of temperature and precipitation during the twenty-first century were evaluated on the basis of the multimodel median change relative to 1961-90. The scenarios of precipitation change show large interannual variations and larger uncertainties than the scenarios of temperature change. The A2 scenarios show the largest reductions of precipitation in the last 20 yr of the twenty-first century; a decrease of 30% is projected for BCC mainly in winter and spring, while precipitation in the NAM region could be weakened by 20% during winter, spring, and summer. After 2050, a significant reduction of precipitation is expected in northwestern Mexico and the southwestern United States south of 35°N, and temperature changes larger than 2°C warming. © 2012 American Meteorological Society.

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