An Optical Implementation of Adaptive Resonance Utilizing Phase Conjugation

A novel adaptive resonance theory (ART) device has been conceived that is fully optical in the input-output processing path. This device is based on holographic information processing in a phase-conjugating crystal. This sets up an associative pattern retrieval in a resonating loop utilizing angle-multiplexed reference beams for pattern classification. A reset mechanism is used to reject any given beam, allowing an ART search strategy. The design is similar to that of an existing nonlearning optical associative memory, but is does allow learning and makes use of information the other device discards. This new device is expected to offer higher information storage density that alternative ART implementation

An Optical Adaptive Resonance Neural Network Utilizing Phase Conjugation

An adaptive resonance (ART) device has been conceived that is fully optical in the input-output processing path. It is based on holographic information processing in a phase-conjugating crystal. This sets up an associative pattern retrieval in a resonating loop utilizing angle-multiplexed reference beams for pattern classification. A reset mechanism is used to reject any given beam, allowing an ART search strategy. The design is similar to an existing nonlearning optical associative memory, but it does allow learning and makes use of information the other device discards. This device is expected to offer higher information storage density than alternative ART implementations

An Optoelectronic Adaptive Resonance Unit

The authors demonstrate a hardware implementation of the adaptive resonance theory ART 1 neural network architecture. The optoelectronic ART1 unit, is a novel application of an old device. This device-the 4-f or Van der Lugt correlator-has historically been used as a fast pattern classifier. Usually the correlation operation is employed as a matched filter, so that a maximum correlation peak corresponds to a well-matched pattern. The device described also uses the large peaks, but takes specific advantage of the fact that a zero-shift correlation is mathematically equivalent to a two-dimensional inner product. The authors describe a promising method for emulating an ART1 unit in optics. They review ART1 from an algorithmic point of view, which shows that inner products are a critical part of ART1. They then discuss its implementation, and show some experimental results. The device works by performing the most computationally intensive parts of the algorithm in optical hardware, and thus offers a suitable marriage of the strengths of electronics and optics

A Neural Architecture for Unsupervised Learning with Shift, Scale and Rotation Invariance, Efficient Software Simulation Heuristics, and Optoelectronic Implementation

A simple modification of the adaptive resonance theory (ART) neural network allows shift, scale and rotation invariant learning. The authors point out that this can be accomplished as a neural architecture by modifying the standard ART with hardwired interconnects that perform a Fourier-Mellin transform, and show how to modify the heuristics for efficient simulation of ART architectures to accomplish the additional innovation. Finally, they discuss the implementation of this in optoelectronic hardware, using a modification of the Van der Lugt optical correlato

An Optoelectronic Implementation of the Adaptive Resonance Neural Network

A solution to the problem of implementation of the adaptive resonance theory (ART) of neural networks that uses an optical correlator which allows the large body of correlator research to be leveraged in the implementation of ART is presented. The implementation takes advantage of the fact that one ART-based architecture, known as ART1, can be broken into several parts, some of which are better to implement in parallel. The control structure of ART, often regarded as its most complex part, is actually not very time consuming and can be done in electronics. The bottom-up and top-down gated pathways, however, are very time consuming to simulate and are difficult to implement directly in electronics due to the high number of interconnections. In addition to the design, the authors present experiments with a laboratory prototype to illustrate its feasibility and to discuss implementation details that arise in practice. This device can potentially outperform alternative implementations of ART1 by as much as two to three orders of magnitude in problems requiring especially large input field

Testing a pyroclimatic hypothesis on the Mexico-United States border

The “pyroclimatic hypothesis” proposed by F. Biondi and colleagues provides a basis for testable expectations about climatic and other controls of fire regimes. This hypothesis asserts an a priori relationship between the occurrence of widespread fire and values of a relevant climatic index. Such a hypothesis provides the basis for predicting spatial and temporal patterns of fire occurrence based on climatic control. Forests near the Mexico–United States border offer a place to test the relative influence of climatic and other controls in mountain ranges that are ecologically similar and subject to broadly similar top-down climatic influence, but with differing cultural influences. We tested the pyroclimatic hypothesis by comparing fire history information from the Mesa de las Guacamayas, a mountain range in northwestern Chihuahua, with previously published fire data from the Chiricahua Mountains, in southeastern Arizona, approximately 150 km away. We developed a priori hypothetical models of fire occurrence and compared their performance to empirical climate-based models. Fires were frequent at all Mesa de las Guacamayas study sites through the mid-20th century and continued uninterrupted to the present at one site, in contrast to nearly complete fire exclusion after 1892 at sites in the Chiricahua Mountains. The empirical regression models explained a higher proportion of the variability in fire regime associated with climate than did the a priori models. Actual climate–fire relationships diverged in each country after 1892. The a priori models predicted continuing fires at the same rate per century as prior to 1892; fires did in fact continue in Mexico, albeit with some alteration of fire regimes, but ceased in the United States, most likely due to changes in land use. The cross-border comparison confirms that a frequent-fire regime could cease without a climatic cause, supporting previous arguments that bottom-up factors such as livestock grazing can rapidly and drastically alter surface fire regimes. Understanding the historical patterns of climate controls on fire could inform the use of historical data as ecological reference conditions and for future sustainability

Assessing the Climate Change Vulnerability of Ecosystem Types of the Southwestern U.S.

Climate change is challenging scientists and decision-makers to understand the complexities of climate change and to predict the related effects at scales relevant to environmental policy and the management of ecosystem services. Extraordinary change in climate, and the ensuing impacts to ecosystem services, are widely anticipated for the southwestern United States. Predicting the vulnerability of Southwest ecosystems and their components has been a priority of natural resource organizations over the past decade. Supplementing vulnerability assessments in the region with geospatial inputs of high thematic and spatial detail has become vital for supporting local analyses, planning, and decisions. In this context has come the opportunity to build upon a framework of major ecosystem types of the Southwest and to assess vulnerability to climate change for each type. Herein are presented three studies that set the backdrop for vulnerability assessment, detail a novel correlative modeling procedure to predict the location and the magnitude of vulnerability to familiar vegetation patterns, and then explore applications of the resulting geospatial vulnerability surface: 1) considerations for evaluating or designing a vulnerability assessment; 2) an overview of the vegetation and climate of major ecosystem types, and 3) a climate change vulnerability assessment for all major ecosystem types of the Southwest. This work has resulted in a regionwide vulnerability surface of greater extent and higher spatial and thematic resolution than previous modeling efforts, giving local managers information on the location and degree of climate risk to vegetation resources

Linking old-growth forest composition, structure, fire history, climate and land-use in the mountains of northern México

Old-growth forests are biologically and ecologically valuable systems that are disappearing worldwide at a rapid rate. México still holds large areas covered by temperate forests in the mountains of the Sierra Madre Occidental, but few of these retain old-growth characteristics. We studied four sites with remnant old-growth forests in Mesa de las Guacamayas, a site in the Sierra Madre Occidental in northwestern Chihuahua, to assess their composition, structure, and age characteristics. Overstory tree densities and basal areas at each site were based on measurements of all trees \u3e1.3 m tall. The overstory was dominated by large Pinus durangensis, P. strobiformis, and Pseudotsuga menziesii (270–335 trees ha−1, basal area 24–42 m2 ha−1), with a subcanopy formed mostly of oaks. This species composition, combined with the lack of vertical structural development, and thus of fuel ladders, suggests that these forests are relatively resistant to severe wildfire. We evaluated forest attributes in the context of local fire regimes and regional climatic patterns, and found that frequent disturbance by surface fires has been part of the study sites\u27 histories for at least 250 years. While climate was a driver of fire regimes historically in this mountain range, humans appear to have played a role in interruptions of the fire regime in the second half of the 20th century. Age distributions showed recruitment to the canopy over ∼250 years, while fires in the four sites recurred every 6–12 years. Temporary interruption of the fire regime in the mid-20th century at three sites was associated with increased tree establishment, especially by broadleaved species. One site had an uninterrupted fire regime and showed continuous tree establishment, consistent with the self-reinforcing role of frequent fire in regulating live and dead fuel loads. Remnant old-growth forests such as those we sampled are becoming increasingly rare in the Sierra Madre Occidental. The biodiversity and ecological processes that they support are highly threatened and their conservation must be made a priority in the U.S.-México borderlands

Dismay, Dissembly and Geocide:Ways Through the Maze of Trumpist Geopolitics

Written in the still-unfolding aftermath of Donald Trump's accession to the office of President of the United States, this article picks up and expands upon some of the key points raised by Kyle McGee's Heathen Earth, particularly concerning the forms of political violence emergent in an age ever-increasingly defined by climate change and the strategies of analysis, theorisation and critique that these geohistorical developments demand. Much like McGee's book, it takes a particularly troubling contemporary political event as a spur to develop thoughts deriving from more long-term projects concerning the way we have come to divide up the world and the manner in which these divisions are contestedpublishersversionNon peer reviewe