Numerical Investigation of the Effects of Orientation and Gravity in a Closed Loop Pulsating Heat Pipe

The Closed Loop Pulsating Heat Pipe (CLPHP) is a very promising passive two-phase heat transfer device for relatively high heat fluxes (up to 30 W/cm²) patented by Akachi (1990, 1993). Although the CLPHP has a simple structure, its working principles are very complex compared to the standard heat pipe with a porous wick. One of the most debated issues deals on how the thermal performance is affected by the inclination and by the action of different gravity fields (terrestrial, lunar, martian and microgravity). Even if the internal tube diameter satisfies the conventional slug flow regime requirement on the Bond number, gravity force still plays an important role on the PHP behaviour. Heat input and the number of turns are two of the most important indirect parameters linked to the gravity issue. A complete numerical campaign has been performed by means of a FORTRAN code at different inclination angles and gravity levels on various PHP. The numerical model is able to estimate both the hydrodynamic and the thermal performance of a CLPHP with different working fluids. The analysis shows that the effect of local pressure losses due to bends is important and must be taken into account, in particular in the horizontal operation which is the reference point for space applications. Numerical results are matched with the experimental data quoted in literature and both good qualitative and quantitative agreement have been found.     

Transparente leitfähige Elektroden

Transparent conductive oxides and alternative transparent electrodes for organic photovoltaics and OLEDs Organic, photoactive devices, such as OLEDs or organic solar cells, currently use indium tin oxide (ITO) as transparent electrode. Whereas ITO is industry‐proven for many years and shows very good electrical and optical properties, its application for lowcost and flexible devices might not be optimal. For such applications innovative technologies such as networkbased metal nanowire or carbon nanotube electrodes, graphene, conductive polymers, metal thin‐films and alternative transparent conductive oxides emerge. Although some of these technologies are rather experimental and far from application, some of them have the potential to replace ITO in selected applications.     

Characterization of multifunctional nanosystems based on the avidin-nucleic acid interaction as signal enhancers in immuno-detection

The Avidin-Nucleic-Acids-Nano-Assembly (ANANAS) is a kind of soft poly avidin nanoparticle originating from the high affinity interaction between avidin and the nucleic acids. In this work we investigated the possibility of transforming ANANAS cores into stoichiometrically controlled multifunctional nanoparticles through a "one-pot" procedure, and we measured in a quantitative way their ability to work as reagents for enhanced immunodiagnostic detection. Initially, we measured the ANANAS loading capability for biotinylated proteins of different nature. About 200 molecules of biotin-horseradish-peroxidase (40KDa b-HRP) and 60 molecules of biotin-immunoglobulin-G (150KDa b-IgG) could be accommodated onto each nanoparticle, showing that steric limitations dictate the number of loadable entities. Stoichiometrically controlled functional assemblies were generated by mixing core particles with subsaturating amounts of b-HRP and b-IgG. When applied as detection reagents in an Enzyme-Linked-ImmunoSorbed-Assay (ELISA), these assemblies were up to two-orders of magnitude more sensitive than commercial HRP-based reagents. Assemblies of different composition displayed different efficacy, indicating that the system functionality can be fine-tuned. Within-assay variability (CV%), measured to assess if the assembly procedure is reproducible, was within 10%. Stability experiments demonstrated that the functionalyzed assemblies are stable in solution for more than one week. In principle, any biotinylated function can be loaded onto the core particle, whose high loading capacity and tunability may open the way toward further application in biomedicine.     

Recombination‐Limited Photocurrents in Low Bandgap Polymer/Fullerene Solar Cells

The charge transport and photogeneration in solar cells based on the low bandgap‐conjugated polymer, poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b; 3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (PCPDTBT) and fullerenes is studied. The efficiency of the solar cells is limited by a relatively low fill factor, which contradicts the observed good and balanced charge transport in these blends. Intensity dependent measurements display a recombination limited photocurrent, characterized by a square root dependence on effective applied voltage, a linear dependence on light intensity and a constant saturation voltage. Numerical simulations show that the origin of the recombination limited photocurrent stems from the short lifetime of the bound electron‐hole pairs at the donor/acceptor interface.     

Opioid-induced respiratory depression: a mathematical model for fentanyl

In this paper, respiratory depressant effects of fentanyl are described quantitatively by a mathematical model. The model is an extension of a previous one, which reproduces the human ventilatory control system on a physiological basis. It includes the following: three compartments for gas storage and exchange (lungs, body tissue, and brain tissue); the main mechanisms involved in ventilation control (peripheral chemoreceptors, central chemoreceptors, and the central hypoxic depression); and local blood flow regulation. The effects of fentanyl on the respiratory system include a decrease in peripheral and central chemoreceptor gains on ventilation and a direct inhibition of respiratory neural activity. All parameters in the model were chosen according to the literature. The model is able to reproduce the ventilatory effects of fentanyl in several conditions: 1) constant levels of fentanyl; 2) after a bolus injection; 3) at fixed levels of P(ETCO2); and 4) after artificial ventilation. According to the model, in spontaneously breathing subjects, minute ventilation depends on two opposing actions: fentanyl inhibitory influences, which depress ventilation, reducing oxygen tension and increasing CO2 tension, and the consequent activation of chemoreceptors, which stimulates ventilation. Simulations of anesthetized patients resuming spontaneous breathing after artificial ventilation demonstrate the risk of prolonged apnea and tissue hypoxemia. A safe transition can be achieved by increasing patient PCO2 toward the end of artificial ventilation, because an advanced chemoreceptor stimulation is produced, which promptly counteracts fentanyl-induced inhibition at cessation of artificial ventilation.     

Impact of the hypocaloric diet using food substitutes on the body weight and biochemical profile

Recent studies using balanced hypocaloric diets with food substitutes in some meals, have presented positive results. There are no studies with the Brazilian population on the efficacy of using food substitute, together with a hypocaloric diet. Main objective of this study was to verify the effects of a hypocaloric diet using food substitutes as meal replacement on the body weight, lipid profile, and glucose and insulin plasma levels. Seventy eight subjects of both genders were selected, 20-50 years old, and a body weight index between 25 kg/m2 and 35 kg/m2. The study lasted for six months and it was divided in 2 phases of three months each- mass reduction for 3 months and 3 months for maintenance. The sample was randomly divided in two groups: Group A (control- 3 months of general nutritional and physical orientation followed by 3 months with 1 meal replacement) and Group B (intervention- 2 meals replacement a day plus nutritional and physical orientation for 3 months followed by 3 months with 1 meal replacement). Anthropometric measurements, percent body fat (%BF), biochemical profile and intake survey were performed at moments 0, 3 and 6 months. Both groups showed a significant decrease in %BF, weight, and consequently in their BMI, in the third and sixth month of follow up. However, weight loss in group B was higher than in group A. At the end of the treatment, 0 and 25.0% of the patients of the group A and B, respectively, presented a weight loss higher than 10% of the initial weight. Comparing the triglycerides, LDL-cholesterol and glucose levels, between the beginning and after the three and six months of treatment, there was a significant reduction in the individuals only in group B. In conclusion, the use of food substitutes as meal replacement, together with a balanced, hypocaloric diet, proved to be efficient in weight loss for Brazilian overweighed individuals.     

Modeling segmentation of a visual scene via neural oscillators: fragmentation, discovery of details and attention

The present study analyses the problem of binding and segmentation of a visual scene by means of a network of neural oscillators, laying emphasis on the problems of fragmentation, perception of details at different scales and spatial attention. The work is based on a two-layer model: a second layer of Wilson-Cowan oscillators is inhibited by information from the first layer. Moreover, the model uses a global inhibitor (GI) to segment objects. Spatial attention consists of an excitatory input, surrounded by an inhibitory annulus. A single object is identified by synchronous oscillatory activity of neural groups. The main idea of this work is that segmentation of objects at different detail levels can be achieved by linking parameters of the GI (i.e. the threshold and the inhibition strength) with the dimension of the zone selected by attention and with the dimension of the smaller objects to be detected. Simulations show that three possible kinds of behavior can be attained with the model, through proper choice of the GI parameters and attention input: (i) large objects in the visual scene are perceived, while small details are suppressed; (ii) large objects are perceived, while details are assembled together to constitute a single 'noise term'; (iii) if attention is focused on a smaller area and the GI parameters modulated accordingly (i.e. the threshold and attention strength are reduced) details are individually perceived as separate objects. These results suggest that the GI and attention may represent two concurrent aspects of the same attentive mechanism, i.e. they should work together to provide flexible management of a visual scene at different levels of detail.     

Robustness of convergence in finite time for linear programming neural networks

A recent work has introduced a class of neural networks for solving linear programming problems, where all trajectories converge toward the global optimal solution in finite time. In this paper, it is shown that global convergence in finite time is robust with respect to tolerances in the electronic implementation, and an estimate of the allowed perturbations preserving convergence is obtained. Copyright © 2006 John Wiley & Sons, Ltd.     

Integrated Services on High Altitude Platform: Receiver Driven Smart Selection of HAP-Geo Satellite Wireless Access Segment and Performance Evaluation

A renewed interest in the development of high-altitude platforms (HAPs), which are stratospheric aircraft or airship carrying payloads tailored for a wide range of applications in telecommunications and remote sensing, is becoming progressively widespread. HAPs offer a reduced propagation delay and they are especially suitable for interactive multimedia services. In this paper, the inter-working between HAP and satellite segments in an integrated QoS architecture has been addressed. A new way to manage integrated services over a new hybrid wireless platform has been proposed. A smart terminal device has been considered in order to perform an intelligent switching on the wireless access segment. The switching criteria applied in the HAP/satellite architecture is based on the available bandwidth and on the admissible data packet end-to-end delay. Performance evaluations of the integrated HAP–satellite platform have been evaluated in terms of bandwidth utilization and number of admitted calls. The simulations show an improvement of admitted calls, reduced data packet end-to-end delay and increased bandwidth utilization.     

Synthesis of multiport resistors with piecewise‐linear characteristics: a mixed‐signal architecture

Non‐linear multiport resistors are the main ingredients in the synthesis of non‐linear circuits. Recently, a particular PWL representation has been proposed as a generic design platform (IEEE Trans. Circuits Syst.‐I 2002; 49 :1138–1149). In this paper, we present a mixed‐signal circuit architecture, based on standard modules, that allows the electronic integration of non‐linear multiport resistors using the mentioned PWL structure. The proposed architecture is fully programmable so that the unit can implement any user‐defined non‐linearity. Moreover, it is modular: an increment in the number of input variables can be accommodated through the addition of an equal number of input modules. Copyright © 2005 John Wiley & Sons, Ltd.