Computation in a single neuron: Hodgkin and Huxley revisited

A spiking neuron "computes" by transforming a complex dynamical input into a train of action potentials, or spikes. The computation performed by the neuron can be formulated as dimensional reduction, or feature detection, followed by a nonlinear decision function over the low-dimensional space. Generalizations of the reverse correlation technique with white noise input provide a numerical strategy for extracting the relevant low-dimensional features from experimental data, and information theory can be used to evaluate the quality of the low-dimensional approximation. We apply these methods to analyze the simplest biophysically realistic model neuron, the Hodgkin-Huxley (HH) model, using this system to illustrate the general methodological issues. We focus on the features in the stimulus that trigger a spike, explicitly eliminating the effects of interactions between spikes. One can approximate this triggering "feature space" as a two-dimensional linear subspace in the high-dimensional space of input histories, capturing in this way a substantial fraction of the mutual information between inputs and spike time. We find that an even better approximation, however, is to describe the relevant subspace as two dimensional but curved; in this way, we can capture 90% of the mutual information even at high time resolution. Our analysis provides a new understanding of the computational properties of the HH model. While it is common to approximate neural behavior as "integrate and fire," the HH model is not an integrator nor is it well described by a single threshold.     

Theoretical insights and experimental characterization of $$\hbox {HfO}_2$$-based OxRRAMs operation

The intensive research in resistive random access memories (RRAM) field has brought in significant improvements in the performance, optimization and reliability of the devices as well as more understanding on their operation. This was made possible through the combination of different tools starting from material engineering to device characterization, modeling and simulations. In this review, we bring an overview of our recent work on RRAM through experimental characterization and first-principles calculations. We explore the effects of metal electrodes on the switching performance and conductive filament (CF) stability of \(\hbox {HfO}_2\) oxide-based RRAM (OxRRAM). With the insight gained from the experimental data, we employ first-principles calculations to have a better microscopic understanding on OxRRAM operation. We show that CF stability and device operating voltages strongly depend on the electrode material. Ti being an electrode material of high interest, we investigate the type of \(\hbox {Ti/HfO}_2\) interface that may be formed and propose a probable composition. We also study the formation and migration of extended Frenkel-pair (EFP) defect in \(\hbox {HfO}_2\) which we consider to be the prototype defect responsible for OxRRAM degradation leading to CF formation. This EFP emission occurs through a cascading migration of O atoms inside \(\hbox {HfO}_2\) lattice. Based on EFP formation and diffusion, we present a simplified CF formation model. Finally, we study low resistance data retention failure in OxRRAM through \(\hbox {HfO}_2\), \(\hbox {Hf}_{1x}\hbox {Al}_{2x}\hbox {O}_{2+x}\) (HfAlO) and \(\hbox {Hf}_{1-x}\hbox {Ti}_{x}\hbox {O}_{2}\) (HfTiO) type of cells. We link its origin to the lateral diffusion of oxygen vacancies at the constriction/tip of the conductive filament in \(\hbox {HfO}_2\)-based RRAM.     

Central electric thermal storage (ETS) feasibility for residential applications: Part 2. Techno‐economic study

This techno‐economic feasibility study was performed to evaluate the viability of central electric thermal storage (ETS) systems for the residential sector. Numerical models have been used to study the effect of a number of parameters on the annual heating cost and unit storage capacity. The considered parameters were the type of central ETS heating system, the proposed rate electricity structure and the storage strategy. The viability of thermal storage systems is determined using a simple payback criteria. The results show that the implementation of thermal storage in the Montreal area is economically viable only if hourly based differential rates are in effect. Simple rules for the design of central ETS heating units were also developed. Copyright © 2001 John Wiley & Sons, Ltd.     

Reparametrization of the BKW Equation of State for the Triazoles and Comparison of the Detonation Properties of HMX,TNMA and NTO by means of Ab-Initio and Semiempirical Calculations

For some years, the research and the new composition development to low vulnerability make the many object works. In the perspective to realize new explosive formulation candidates to EIDS and more effective, the oxynitrotriazole(ONTA or NTO) is an interesting substance. Among melt cast formulations, the composition AFX-644, developed by the US Air Force⁽¹⁾, is considered as EIDS(Extremely Insensitive Detonating Substances) but its performances are too low. One of the possibilities to improve these formulations is to estimate detonation characteristics of these new substances by calculation codes so as to decrease the number of experimental tests and therefore to reduce the cost price. This paper describes the result of the reparametrization studies on the Becker-Kistiakowsky-Wilson(BKW) equation of state for the triazoles. The new set of BKW parameters(α=0.5; β=0.18; κ=11.8; θ=1850) give realistic values for the detonation properties and the predicted ab-initio F. BKW, semiempirical Kamlet and the experimental detonation celerities are in good agreement for each set of parameters for the Nitroaromatics, Nitramines and Triazoles.     

Nutrient Uptake and Balance of Cotton + Pigeonpea Strip Intercropping on Rainfed Vertisols of Central India

Nutrient uptake and balance of the cotton (Gossypium hirsutum L.) + pigeonpea (Cajanus cajan(L.) Millsp.), a traditional strip intercropping system practiced on the rainfed Vertisols of central India is not known to us. On-farm participatory trials were conducted on 10 farmer fields, five each on medium deep (MDS) and deep soils (DS) of Nagpur, central India to determine the effect of technological interventions on N, P and K uptake of cotton and pigeonpea. The nutrient balance was also quantified as a difference of nutrient inputs and removal. Nutrients accumulated by the crops (grain, stalk and leaves) and weeds removed off the field by hand weeding were considered as nutrient removal, while fertilizer was considered as nutrient input. The interventions included application of recommended dose of fertilizer (RDF), RDF + conservation tillage with in situ green manure (CT₁) and CT₁ + application of ZnSO₄ (CT₂) and compared with farmers’ practice (FP). Nutrient uptake, in general, was higher on DS than on MDS. Among the interventions, N, P and K uptake of cotton and pigeonpea followed the order: CT₂ > CT₁ > RDF > FP. Mean N and P balance was positive in all the treatments. The balance may become negative if nutrient losses are accounted. A negative K balance was observed in all the treatments and the magnitude was the greatest for the FP plots (−39.4 kg ha⁻¹ y⁻¹). In spite of fertilizer-K application in the intervention plots, K balance was negative (−14.4 to −19.5 kg ha⁻¹ y⁻¹). By way of leaf and fruit drop, cotton and pigeonpea litter recycled 12.2 kg N, 1.7 kg P and 6.7 kg K ha⁻¹ y⁻¹     

Accounting for self-selected drinking goals in the assessment of treatment outcome.

Many treatment outcome studies are abstinence-based and rely on achieved abstinence as an indicator of success, making the implicit assumption that participants have an abstinence goal. However, it is often the case that participants self-select controlled drinking goals, even in the context of an abstinence-based treatment. The current study explored the use of an outcome variable, percent weeks meeting goal (PWMG), which takes into account individual goal choice at baseline. The sample consisted of 57 women who participated in a cognitive-behavioral therapy treatment for alcohol dependence and were followed for 18 months after baseline. Twenty-two (39%) women self-selected controlled drinking goals, and 35 (61%) self-selected an abstinence goal at baseline. A repeated measures analysis of variance with PWMG as the dependent variable revealed that both goal groups were equally successful in meeting their goals during the 6-month treatment period. After treatment, participants with a goal of abstinence had more PWMG than did participants with a self-selected controlled drinking goal, but the difference was significant at a trend level. The two goal groups did not differ in outcome when the authors compared them using more traditional measures of outcome, percent days abstinent and percent heavy drinking days. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Review of the Existing Translational Pharmacokinetics Modeling Approaches Specific to Monoclonal Antibodies (mAbs) to Support the First-In-Human (FIH) Dose Selection

The interest in therapeutic monoclonal antibodies (mAbs) has continuously growing in several diseases. However, their pharmacokinetics (PK) is complex due to their target-mediated drug disposition (TMDD) profiles which can induce a non-linear PK. This point is particularly challenging during the pre-clinical and translational development of a new mAb. This article reviews and describes the existing PK modeling approaches used to translate the mAbs PK from animal to human for intravenous (IV) and subcutaneous (SC) administration routes. Several approaches are presented, from the most empirical models to full physiologically based pharmacokinetic (PBPK) models, with a focus on the population PK methods (compartmental and minimal PBPK models). They include the translational approaches for the linear part of the PK and the TMDD mechanism of mAbs. The objective of this article is to provide an up-to-date overview and future perspectives of the translational PK approaches for mAbs during a model-informed drug development (MIDD), since the field of PK modeling has gained recently significant interest for guiding mAbs drug development.     

Analytical modeling of H‐shape distributed topology with bandpass negative group delay behavior

This article describes an analytical modeling of a distributed negative group delay (NGD) circuit presenting a H‐shape topology. It acts as an innovative typical transmission line (TL) based topology with a feedback connected with an open‐stub termination. The equivalent circuit diagram is established based on TL representation of H‐topology constituting elements. The S‐matrix analytical model is developed. To validate the analytical model, a proof‐of‐concept prototype implemented in microstrip topology is designed, simulated, fabricated, and measured. The compared calculated, simulated, and measured S‐parameters are in very good agreement. In addition, the microstrip prototype confirm the bandpass NGD behavior of the H‐topology circuit with NGD value of approximately ?2 ns around the center frequency 1.67 GHz.     

A time-discrete model for dynamic fracture based on crack regularization

We propose a discrete time model for dynamic fracture based on crack regularization. The advantages of our approach are threefold: first, our regularization of the crack set has been rigorously shown to converge to the correct sharp-interface energy Ambrosio and Tortorelli (Comm. Pure Appl. Math., 43(8): 999–1036 (1990); Boll. Un. Mat. Ital. B (7), 6(1):105–123, 1992); second, our condition for crack growth, based on Griffith’s criterion, matches that of quasi-static settings Bourdin (Interfaces Free Bound 9(3): 411–430, 2007) where Griffith originally stated his criterion; third, solutions to our model converge, as the time-step tends to zero, to solutions of the correct continuous time model Larsen (Math Models Methods Appl Sci 20:1021–1048, 2010). Furthermore, in implementing this model, we naturally recover several features, such as the elastic wave speed as an upper bound on crack speed, and crack branching for sufficiently rapid boundary displacements. We conclude by comparing our approach to so-called “phase-field” ones. In particular, we explain why phase-field approaches are good for approximating free boundaries, but not the free discontinuity sets that model fracture.