Chemiosmotic coupling − the harnessing of electrochemical ion gradients across membranes to drive metabolism − is as universally conserved as the genetic code. As argued previously in these pages, such deep conservation suggests that ion gradients arose early in evolution, and might have played a role in the origin of life. Alkaline hydrothermal vents harbour pH gradients of similar polarity and magnitude to those employed by modern cells, one of many properties that make them attractive models for (...) life's origin. Their congruence with the physiology of anaerobic autotrophs that use the acetyl CoA pathway to fix CO2 gives the alkaline vent model broad appeal to biologists. Recently, however, a paper by Baz Jackson criticized the hypothesis, concluding that natural pH gradients were unlikely to have played any role in the origin of life. Unfortunately, Jackson mainly criticized his own interpretations of the theory, not what the literature says. This counterpoint is intended to set the record straight. (shrink)

The concept of wild food does not play a significant role in contemporary nutritional science and it is seldom regarded as a salient feature within standard dietary guidelines. The knowledge systems of wild edible taxa are indeed at risk of disappearing. However, recent scholarship in ethnobotany, field biology, and philosophy demonstrated the crucial role of wild foods for food biodiversity and food security. The knowledge of how to use and consume wild foods is not only a means to deliver high-end (...) culinary offerings, but also a way to foster alternative models of consumption. Our aim in this paper is to provide a conceptual framework for wild foods, which can account for diversified wild food ontologies. In the first section of the paper, we survey the main conception of wild foods provided in the literature, what we call the Nature View. We argue that this view falls short of capturing characteristics that are core to a sound account of wilderness in a culinary sense. In the second part of the paper, we provide the foundation for an improved model of wild food, which can countenance multiple dimensions and degrees connoting wilderness in the culinary world. In the third part of the paper we argue that thanks to a more nuanced ontological analysis, the gradient framework can serve ethnobiologists, philosophers, scientists, and policymakers to represent and negotiate theoretical conflicts on the nature of wild food. (shrink)

For the safe and economical construction of embankment dams, the mechanical behaviour of the rockfill materials used in the dam’s shell must be analyzed. The characterization of rockfill materials with specified shear strength is difficult and expensive due to the presence of particles greater than 500 mm in diameter. This work investigates the feasibility of using an extreme gradient boosting computing paradigm to estimate the shear strength of rockfill materials. To train and validate the proposed XGBoost model, a total of (...) 165 databases obtained from the literature are chosen. The XGBoost model was compared against support vector machine, adaptive boosting, random forest, and K-nearest neighbor models described in the literature. XGBoost beats SVM, RF, AdaBoost, and KNN models in terms of performance evaluation metrics such as coefficient of determination, Nash–Sutcliffe coefficient, and error in the root mean square ratio to the standard deviation of the measured data. The results demonstrated that the XGBoost model has the highest prediction performance with, followed by the SVM model with, RF, the AdaBoost model with and the KNN model with. A sensitivity analysis has been conducted to ascertain the impact of each investigated input parameter. This study demonstrates that the established XGBoost model for estimating the shear strength of rockfill materials is reliable. (shrink)

The two parameters of leaf dimension namely, length and width, show inverse correlation with the third parameter, the thickness. A thermal diffusion model is proposed which explains the inverse relationship between these and envisages that while leaf length and width are directly influenced by the microclimate the thickness is affected by the microclimate through endoclimate and energy balance in the leaves. The significance of the model is discussed in the light of its importance in assessing the survival range of plant (...) species along the altitudinal gradient. (shrink)

Recent decades have witnessed the rapid evolution of robotic applications and their expansion into a variety of spheres with remarkable achievements. This article researches a crucial technique of robot manipulators referred to as visual servoing, which relies on the visual feedback to respond to the external information. In this regard, the visual servoing issue is tactfully transformed into a quadratic programming problem with equality and inequality constraints. Differing from the traditional methods, a gradient-based recurrent neural network for solving the visual (...) servoing issue is newly proposed in this article in the light of the gradient descent method. Then, the stability proof is presented in theory with the pixel error convergent exponentially to zero. Specifically speaking, the proposed method is able to impel the manipulator to approach the desired static point while maintaining physical constraints considered. After that, the feasibility and superiority of the proposed GRNN are verified by simulative experiments. Significantly, the proposed visual servo method can be leveraged to medical robots and rehabilitation robots to further assist doctors in treating patients remotely. (shrink)

Mental representations have continuous as well as discrete, combinatorial properties. For example, while predominantly discrete, phonological representations also vary continuously; this is reflected by gradient effects in instrumental studies of speech production. Can an integrated theoretical framework address both aspects of structure? The framework we introduce here, Gradient Symbol Processing, characterizes the emergence of grammatical macrostructure from the Parallel Distributed Processing microstructure (McClelland, Rumelhart, & The PDP Research Group, 1986) of language processing. The mental representations that emerge, Distributed Symbol Systems, (...) have both combinatorial and gradient structure. They are processed through Subsymbolic Optimization–Quantization, in which an optimization process favoring representations that satisfy well-formedness constraints operates in parallel with a distributed quantization process favoring discrete symbolic structures. We apply a particular instantiation of this framework, λ-Diffusion Theory, to phonological production. Simulations of the resulting model suggest that Gradient Symbol Processing offers a way to unify accounts of grammatical competence with both discrete and continuous patterns in language performance. (shrink)

Major contributions emanating from Sagvolden et al.'s theory include elucidation of the role in attention-deficit/hyperactivity disorder (ADHD) of temporal information processing, social learning, and response extinction learning. Key issues include a need for clearer explanation of the relative role of impulsivity versus response suppression/inhibition in the dual process model, and delineation of genotype-environment correlations versus interactions in the social and experiential mechanisms posited.