Positive and negative circuits in discrete neural networks

We study the relationships between the positive and negative circuits of the connection graph and the fixed points of discrete neural networks (DNNs). As main results, we give necessary conditions and sufficient conditions for the existence of fixed points in a DNN. Moreover, we exhibit an upper bound for the number of fixed points in terms of the structure and number of positive circuits in the connection graph. This allows the determination of the maximum capacity for storing vectors in DNNs as fixed points, depending on the architecture of the network.     

Large scale cathodic exfoliation of graphite using deep eutectic solvent and water mixture

A short-time and low-cost synthesis route was used to produce large lateral size (from 2 to 15 μm) from monolayers to few layers of graphene by a two-step process of electrochemical exfoliation with a deep eutectic solvent in a mixture with water that can be reused, and ultrasonic bath. The graphene was characterized by SEM, TEM, AFM, Raman and electrochemical activity. During the electrochemical exfoliation, high expanded graphene particles were obtained and these were dispersed in a mixture of water with 5%wt ethylene glycol by an ultrasonic bath in order to complete the exfoliation process. An enhancement of the electrical conductivity of these dispersions was obtained with the increase of graphene concentration, 0.38 mg/mL, which best result was achieved with 30 wt% water and a DC voltage of 10 V. It was possible to add a conductive layer to a glass substrate with the graphene obtained and Tyndall effect was observed.     

Kinetics of Dissolution of Tenorite in Ammonium Media

In this work, the dissolution kinetics of tenorite (CuO) in a NH₄OH-H₂O system was studied. The studied temperature range was 5–55°C, ammonium hydroxide concentration between 0.1 and 0.75 M, and a particle size range of 5–24 µm. The stirring speed, pH of the ammonia solution, and various agents were also studied. The results indicated that the leaching of tenorite occurred quickly with a particle size of 5 µm in a 0.45 M solution of NH₄OH for a pH value equal to 10.5. Dissolution of CuO also increases as temperature and the concentration of NH₄OH increase. For concentrations less than 0.10 M, there is almost no leaching tenorite. By decreasing the particle size, the dissolution of CuO increase. Results show the stirring speed had no significant effect on the leaching rate of tenorite for values above 250 rpm. Leaching kinetics was analyzed using the model of the surface chemical reaction. The reaction rate was of the order of 2.2 with respect to the concentration of ammonium hydroxide and inversely proportional to the initial particle size. Activation energy of 59 kJ/mol was estimated for the temperature range of 5–55°C.     

Uptake of Zn2+ from dilute aqueous solutions using protonated dry alginate beads

The uptake of zinc ions from dilute aqueous solutions was studied at 25°C using protonated dry alginate beads (PDAB) of around 1 mm in diameter. The Zn²⁺ uptake increases with the pH of the Zn bearing solution, reaching a value of around 90 mg of Zn per gram of beads (dry weight) at pH 4·5. For an initial Zn concentration as low as 10 mg L^?1, the removal reached was complete.

The mechanism of Zn uptake was found to be ion exchange between zinc ions and protons form the functional groups of the beads, which followed a pseudo-second order kinetic behaviour. In equilibrium condition the experimental data followed the Langmuir adsorption model.

The maximum uptake reached were around 145 and 165 mg g^?1 at pH values of 3·5 and 4·5, respectively, which is higher than most of the sorbents used for zinc removal. EPMA-EDX analysis shows that the functional groups of the PDAB were homogeneously distributed during preparation of beads, and that zinc ions were able to reach functional groups in the entire structure of the beads without a concentration gradient across the beads.

On a étudié le changement d′ions de le Zinc depuis des solutions aqueuses diluées à 25°C en utilisant des sphères protonadas sèches d′alginatos (PDAB) d′autour de 1 mm de diamètre. Le changement de Zn²⁺ augmente avec le pH de la solution, en atteignant une valeur d′autour de 90 mg de Zn par gramme de sphères (un poids sec) à un pH 4.5. Pour un concetración initial de Zn plus bas que 10 mg L^?1, le changement à court d'argent a été complet. Le mécanisme de changement de Zn est été par un échange ionique entre des ions de zinc et protones provenants depuis les groupes fonctionnels des sphères, qui a un comportement cinétique du pseudo-deuxième ordre. Dans des conditions d′équilibre, les données expérimentales suivent un modèle d′adsorpcin de Langmuir. Le changement maximal à court d′argent a été de 145 et 165 mg g^?1 aux valeurs de pH de 3.5 et 4.5, respectivement, où elles ont été plus hautes que les sorbentes utilisés pour le changement de Zn. Des analyses par EPMA-EDX ont montré que les groupes fonctionnels du PDAB ont été distribués de façon homogène durant la préparation des sphères, et que les ions de zinc ont été capables d′atteindre les groupes fonctionnels dans toute la structure des sphères sans une pente de concentration à travers des sphères.     

Maximum number of fixed points in AND–OR–NOT networks

We are interested in the number of fixed points in AND–OR–NOT networks, i.e. Boolean networks in which the update function of each component is either a conjunction or a disjunction of positive or negative literals. As the main result, we prove that the maximum number of fixed points in a loop-less connected AND–OR–NOT network with n components is at most the maximum number of maximal independent sets in a loop-less connected graph with n vertices, a quantity already known.     

Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures

Roasting of enargite (Cu₃AsS₄) in the temperature range of 648?K to 898?K (375?°C to 625?°C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:

1. $4{\text{Cu}}_{ 3} {\text{AsS}}_{ 4} \left( {\text{s}} \right){\text{ + 13O}}_{ 2} \left( {\text{g}} \right){\text{ = As}}_{ 4} {\text{O}}_{ 6} \left( {\text{g}} \right){\text{ + 6Cu}}_{ 2} {\text{S}}\left( {\text{s}} \right){\text{ + 10SO}}_{ 2} \left( {\text{g}} \right) $
2. $ 6{\text{Cu}}_{ 2} {\text{S}}\left( {\text{s}} \right){\text{ + 9O}}_{ 2} \left( {\text{g}} \right){\text{ = 6Cu}}_{ 2} {\text{O}}\left( {\text{s}} \right){\text{ + 6SO}}_{ 2} \left( {\text{g}} \right) $
3. $ 6{\text{Cu}}_{ 2} {\text{O}}\left( {\text{s}} \right){\text{ + 3O}}_{ 2} \left( {\text{g}} \right){\text{ = 12CuO}}\left( {\text{s}} \right) $

The three reactions occurred sequentially, each with constant rate, and they were affected significantly by temperature and partial pressure of oxygen. The kinetics of the first stage were analyzed by using the model X?=?k ₁ t. The first stage reaction was on the order of 0.9 with respect to oxygen partial pressure and the activation energy was 44?kJ/mol for the temperature range of 648?K to 898?K (375?°C to 625?°C).     

Mathematical modeling in genetic networks: relationships between the genetic expression and both chromosomic breakage and positive circuits

The human genome with its 23 pairs of chromosomes, is the result of evolution. This evolution has been ruled by the mutation process and also by the physiological and pathological reorganization of the genomic material inside or between the chromosomes, which are conditioning the genomic variability. This reorganization is starting at singular points on the short or long chromosomic arms, called crossing-over, or translocations, insertions, break points. In this paper, we will show that these points, also called weak points or hot spots of the genome are correlated, independently of their origin. In addition, we will give some properties of the genetic interaction matrices in terms of attractors of the genetic expression dynamics.     

Discrete Particle Model for Analyzing Bedform Development

A discrete element model is used to simulate the emergence and evolution in time of wind ripples with the use of simple rules for the motion of individual sediment particles. It is shown, by analyzing the probabilities for the particles to be entrained and deposited over the bed implied by the selected rules, that the same model can be used to simulate the development of underwater bedforms. The results of the model show that the particle-transport processes implied by the simple rules used in the model can represent many different complex aspects of the physics of bedforms. The results of the model are compared with experimental results on underwater ripples obtained by the authors, and a surprisingly good agreement is found in terms of the main dynamical properties of the bedforms, such as growth rate of the amplitude, evolution of the steepness, growth saturation, and bedform celerity. Even though the simulated bedforms do not reproduce the exact geometry of their physical counterparts, the richness of the strongly nonlinear processes that this simple model is able to simulate makes this kind of approach useful to explain many of the observed features of underwater bedforms, which are otherwise very difficult to address theoretically.