1,721,025 research outputs found
Storing, learning and retrieving biased patterns
No full textThe formal equivalence between the Hopfield network (HN) and the Boltzmann Machine (BM) has been well established in the context of random, unstructured and unbiased patterns to be retrieved and recognised. Here we extend this equivalence to the case of “biased” patterns, that is patterns which display an unbalanced count of positive neurons/pixels: starting from previous results of the bias paradigm for the HN, we construct the BM's equivalent Hamiltonian introducing a constraint parameter for the bias correction. We show analytically and numerically that the parameters suggested by equivalence are fixed points under contrastive divergence evolution when exposed to a dataset of blurred examples of each pattern, also enjoying large basins of attraction when the model suffers of a noisy initialisation. These results are also shown to be robust against increasing storage of the models, and increasing bias in the reference patterns. This picture, together with analytical derivation of HN's phase diagram via self-consistency equations, allows us to enhance our mathematical control on BM's performance when approaching more realistic datasets
Impact of environmental factors on stilbene biosynthesis
Full text linkStilbenes are a small family of polyphenolic secondary metabolites that can be found in several distantly related plant species. These compounds act as phytoalexins, playing a crucial role in plant defense against phytopathogens, as well as being involved in the adaptation of plants to abiotic environmental factors. Among stilbenes, trans-resveratrol is certainly the most popular and extensively studied for its health properties. In recent years, an increasing number of stilbene compounds were subjected to investigations concerning their bioactivity. This review presents the most updated knowledge of the stilbene biosynthetic pathway, also focusing on the role of several environmental factors in eliciting stilbenes biosynthesis. The effects of ultraviolet radiation, visible light, ultrasonication, mechanical stress, salt stress, drought, temperature, ozone, and biotic stress are reviewed in the context of enhancing stilbene biosynthesis, both in planta and in plant cell and organ cultures. This knowledge may shed some light on stilbene biological roles and represents a useful tool to increase the accumulation of these valuable compounds
Atrio-ventricular junction: Can precision electrocardiology bridge cell and electrocardiogram?
No full textThe Atrio Ventricular Junction (AVJ) is a well-defined anatomical region of the heart the physiology of which, despite extensive and numerous observations, it is not fully understood. The aim of this review is to present an up to date summary of old and more recent findings on histology, cellular electrophysiology and intracellular connectivity of this region. We have also attempted to relate our increasing understanding of nodal pathophysiology to the interpretation of the electrocardiographic (ECG) manifestations of AVN behavior. Bridging cellular observations with ECG analysis in a process we call “Precision Electrocardiology” renders this tool far more sensitive and clinically useful than the pattern analysis too often employed in the ECG interpretation
Stemodane diterpenes and diterpenoids. Isolation, structure elucidation, biogenesis, biosynthesis, biological activity, biotransformations, metabolites and derivatives biological activity, rearrangements
Full text linkThe scientific activity carried out over forty-five years on stemodane diterpenes and diterpenoids structure elucidation, biogenesis, biosynthesis, biological activity and biotransformations was reviewed
On the effective initialisation for restricted Boltzmann machines via duality with Hopfield model
No full textRestricted Boltzmann machines (RBMs) with a binary visible layer of size N and a Gaussian hidden layer of size P have been proved to be equivalent to a Hopfield neural network (HNN) made of N binary neurons and storing P patterns ξ, as long as the weights w in the former are identified with the patterns. Here we aim to leverage this equivalence to find effective initialisations for weights in the RBM when what is available is a set of noisy examples of each pattern, aiming to translate statistical mechanics background available for HNN to the study of RBM's learning and retrieval abilities. In particular, given a set of definite, structureless patterns we build a sample of blurred examples and prove that the initialisation where w corresponds to the empirical average ξ ̄ over the sample is a fixed point under stochastic gradient descent. Further, as a toy application of the duality between HNN and RBM, we consider the simplest random auto-encoder (a three layer network made of two RBMs coupled by their hidden layer) and evidence that, as long as the parameter setting corresponds to the retrieval region of the dual HNN, reconstruction and denoising can be accomplished trivially, while when the system is in the spin-glass phase inference algorithms are necessary. This questions the need for larger retrieval regions which we obtain by applying a Gram–Schmidt orthogonalisation to the patterns: in fact, this procedure yields to a set of patterns devoid of correlations and for which the largest retrieval region can be accomplished. Finally we consider an application of duality also in a structured case: we test this approach on the MNIST dataset, and obtain that the network performs already ∼67% of successful classifications, suggesting it can be exploited as a computationally-cheap pre-training
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Precision Electrocardiology: A Rational Approach for Simple and Complex Arrhythmias
No full textElectrocardiography (ECG)in all its forms, from 12-lead ECG to long-term monitoring, is considered, an old and increasingly irrelevant test in this high technology era. This article reviews the clinical utility of this tool and argues that the obsolescence is due to an increasing inability to read electrocardiographic tracings. The usual interpretative pitfalls are discussed and a logical approach is proposed with illustrative examples. Finally, the concept of precision ECG is presented and its meaning reviewed
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