The effects of carrier accumulation at the cathode on the negative resistance induced by avalanche injection in Si bulk devices

An analytical model for the negative resistance induced by avalanche injection in bulk semiconductors is developed including diffusion, recombination and accounting for the properties of the majority carrier injecting electrode with respect to the avalanche generated carriers.

Two limiting situations are discussed in detail namely that of a n⁺-n cathode which is blocking for the avalanche generated holes and that of a metal-semiconductor ohmic contact with an infinite surface recombination rate.

The calculations show that in the first case the avalanche ionization is extremely low and the negative resistance occurs because a low-field neutral region creates into the solid thus reducing the voltage; in the other case, the multiplication is relatively high and the negative resistance is due to the lowering of the field in the region of scattering-limited velocity. As a consequence, from the first to the second situation the peak voltage changes by a factor of two and the peak current by a factor of three or more.

These results give a new insight of a number of experimental observations reported in the literature. The performance of devices made with different techniques which approximate one or the other limiting situations mentioned above is accurately predicted by the proposed model.     

Chloride/sulfate exchange on anion resins. Kinetic investigations. Chemical control in selective exchanges

Rate determinations for the Cl^-/SO⁼₄ exchange on anion resins in very diluted systems (1 ÷ 6 × 10^-3N), where resin selectivities for the divalent ion are drastically raised by the electroselectivity effect, show convincing evidence that the chemical reaction rate on fixed charges controls the overall process kinetics. Activation energies, in particular, (up to 16.83 kcal/eq) are definitely out of the range for usual diffusion-controlled kinetics.A spherically-symmetrical diffusion model with a billiard-ball-like mechanism of site-to-site jumping of ions inside the resin is suggested.     

Influence of microorganisms on retinol isomerization in milk

In order to have a deeper insight into the retinol isomerization phenomenon, in this work different milk samples have been analysed for their content of trans retinol and its cis-isomers, by means of reliable HPLC techniques. Levels of the different isomers and the degree of retinol isomerization (13-cis/all-trans ratio, %) have been monitored during milk storage at different temperatures and after addition of specific microorganisms. In raw milk stored at 4 degrees C for 96 h the degree of retinol isomerization shifted from 1.1 to 2.3%, while in raw milk stored at 22 degrees C for 24 h it increased from 1.1 to 12.7%. Among microorganisms tested in pasteurized milk, the most active in causing an increment in the 13-cis/all-trans ratio (%), from 3.4 to 33.4% in 8 h, was Streptococcus thermophilus. The results obtained demonstrated a relationship between microbial evolution and retinol isomerization. Therefore, the determination of retinol isomers is of importance not only for a more precise evaluation of vitamin A activity but also for the evaluation of the microbiological quality of milk.     

Distribution system minimum loss reconfiguration in the Hyper-Cube Ant Colony Optimization framework

This paper presents an original application of the Ant Colony Optimization concepts to the optimal reconfiguration of distribution systems, with the objective of minimizing the distribution system losses in the presence of a set of structural and operational constraints. The proposed algorithm starts from the current configuration of the system and proceeds by progressively introducing variations in the configuration according to local and global heuristic rules developed within the Hyper-Cube Ant Colony Optimization framework. Results of numerical tests carried out on a classical system and on a large real urban distribution system are presented to show the effectiveness of the proposed approach.     

Different Stages of Quiescence,Senescence, and Cell Stress Identified by Molecular Algorithm Based on the Expression of Ki67, RPS6, and Beta-Galactosidase Activity

During their life span, cells have two possible states: a non-cycling, quiescent state (G0) and a cycling, activated state. Cells may enter a reversible G0 state of quiescence or, alternatively, they may undergo an irreversible G0 state. The latter may be a physiological differentiation or, following a stress event, a senescent status. Discrimination among the several G0 states represents a significant investigation, since quiescence, differentiation, and senescence are progressive phenomena with intermediate transitional stages. We used the expression of Ki67, RPS6, and beta-galactosidase to identify healthy cells that progressively enter and leave quiescence through G0-entry, G0 and G0-alert states. We then evaluated how cells may enter senescence following a genotoxic stressful event. We identified an initial stress stage with the expression of beta-galactosidase and Ki67 proliferation marker. Cells may recover from stress events or become senescent passing through early and late senescence states. Discrimination between quiescence and senescence was based on the expression of RPS6, a marker of active protein synthesis that is present in senescent cells but absent in quiescent cells. Even taking into account that fixed G0 states do not exist, our molecular algorithm may represent a method for identifying turning points of G0 transitional states that continuously change.     

Autochthonous white grape pomaces as bioactive source for functional jams

Seeds and skins from grape pomaces of Pecorello and Mantonico cv underwent extraction (ultrasound–assisted or maceration), in order to obtain added-value ingredients for the production of a functional pear jam. The antioxidant features of the extracts were tested by in vitro colorimetric assays. Among seeds, Mantonico by maceration (MSC) showed the best results, as well as Mantonico by ultrasound-assisted extraction (MBs) among skin extracts. The selected extracts were fully characterised by NMR and MS techniques, confirming the presence of many polyphenols, flavonoids and tannins among others. Pectin was then derivatised by the grafting procedure with the active molecules of MBs and MSC. The latter produced the best antioxidant polymer also without toxicity evaluated using Caco-2 cells and was used for the jam preparation. The functional pear jam showed improved antioxidant performances in comparison with its non-functional counterparts as well as its maintenance over time (15 days).     

Dry versus hydrated collagen scaffolds: are dry states representative of hydrated states?

Collagen composite scaffolds have been used for a number of studies in tissue engineering. The hydration of such highly porous and hydrophilic structures may influence mechanical behaviour and porosity due to swelling. The differences in physical properties following hydration would represent a significant limiting factor for the seeding, growth and differentiation of cells in vitro and the overall applicability of such hydrophilic materials in vivo. Scaffolds based on collagen matrix, poly(DL-lactide) nanofibers, calcium phosphate particles and sodium hyaluronate with 8 different material compositions were characterised in the dry and hydrated states using X-ray microcomputed tomography, compression tests, hydraulic permeability measurement, degradation tests and infrared spectrometry. Hydration, simulating the conditions of cell seeding and cultivation up to 48?h and 576?h, was found to exert a minor effect on the morphological parameters and permeability. Conversely, hydration had a major statistically significant effect on the mechanical behaviour of all the tested scaffolds. The elastic modulus and compressive strength of all the scaffolds decreased by ~95%. The quantitative results provided confirm the importance of analysing scaffolds in the hydrated rather than the dry state since the former more precisely simulates the real environment for which such materials are designed.

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Model Predictive Control of Glucose Concentration Based on Signal Temporal Logic Specifications with Unknown-Meals Occurrence

Abstract

The glycemia regulation is a significant challenge in the Artificial Pancreas (AP) scenario. Several control systems have been developed in the last years, many of them requiring meal announcements. Therefore, if the patients skip the meal announcement or make a mistake in the estimation of the amount of carbohydrates, the control performance will be negatively affected. In this extended version of our previous work, we present a Model Predictive Controller (MPC) for the AP in which the meal is treated as a disturbance to be estimated by an Unknown Input Observer (UIO). The MPC constraints are expressed in terms of Signal Temporal Logic (STL) specifications. Indeed, in the AP some requirements result in hard constraints (in particular, absolutely avoid hypoglycemia and absolutely avoid severe hyperglycemia) and some other in soft constraints (avoid a prolonged hyperglycemia) and STL is suitable for expressing such requirements. The achieved results are obtained using the BluSTL toolbox, which allows to synthesize model predictive controllers with STL constraints. We report simulations showing that the proposed approach, avoiding unnecessary restrictions, provides safe trajectories in correspondence of higher unknown disturbance.     

Formulation of muds for pelotherapy: effects of “maturation” by different mineral waters

Spa centres in northern Italy use clayey admixtures for the formulation of muds to be used in pelotherapy. The basic ingredient (“virgin” clay) is a dressed bentonitic geomaterial with mineralogical composition: smectite 60–70%, illite 5–10%, kaolinite 10–15%, quartz 5–10%, calcite 5–10% and feldspars 2–3%.The peloid muds are obtained by “maturation” of the virgin clay with mineral waters gushing out in situ which have different geochemistry: sulphureous, Ca-sulphate, Ca–Mg-sulphate and Br–I-salty (after the Italian regulation DPR 105/92). The maturation treatment is varying with respect to the mixing procedure and lasting time.Peculiar parameters have been tested to verify the effects of various maturation treatments, i.e., changes with respect to virgin clay.Formation of organic matter is due to the presence of microorganisms and algae in the maturation habitat. The <2 μm fraction is generally decreased due to clay particles agglomeration. Mineralogical changes are mainly concerning the degradation of clay minerals, as smectite and illite, and subordinately to the dissolution of calcite. Cation exchange capacity (CEC), soluble salts, water retention, swelling index, activity, consistency parameters (WL, WP and PI), thermal behaviour and cooling kinetics are influenced by the geochemistry of mineral waters used for the maturation treatments but with some opposite trends for Br–I-salty water, and for sulphureous and Ca-sulphate waters, respectively.Noteworthy was the influence of high-pH value of the virgin clay on the pH of peloid muds (in fact, the pH of the used mineral waters is ranging around the natural value). Furthermore, the temperature reached by the peloid muds after 20 min of application (calculated after an innovative mathematical model) is influenced by water retention. An increase in plasticity index and a slower cooling are considered to improve the quality of the obtained peloid muds for pelotherapy.The observed different cation exchange behaviour and soluble salt content could be discriminant for either dermatological masks or thermal body cataplasms.A need of regulation (standard procedures) is suggested to certificate the clay geomaterials suitable for pelotherapy and also for drugs formulation.