Pricing VoWLAN services through a micro-economic framework

This article investigates the issue of determining an appropriate pricing strategy for voice over WLAN provisioning. This is performed by first framing the voice services in a tunable QoS scenario. The analysis is then performed with the awareness that in a WLAN system the tariff payment determines price-based access regulation, which implies a different service perception because of the modified network conditions. For this reason, we apply a micro-economic framework that considers the trade-off between perceived QoS and paid price in the users' request (i.e., including in a tunable way both service requirements and willingness to pay). This allows us to investigate the provider's task of having a suitable price policy, both identifying the subsequently involved trade-offs and providing insight on how to efficiently cut them.     

Computational Studies Identifying Entry Inhibitor Scaffolds Targeting the Phe 43 Cavity of HIV‐1 gp120

Targeting protein–protein interactions, such as the HIV‐1 gp120—CD4 interface, has become a cutting‐edge approach in the current drug discovery scenario. Many small molecules have been developed so far as inhibitors of the interaction between CD4 and HIV‐1 gp120. However, due to a variety of reasons such as solubility, drug toxicity and drug resistance, these inhibitors have failed to prove clinically useful. As such, the identification of novel compounds that bind to protein–protein interactions is still a research area of considerable interest. Here, a structure‐based virtual screening approach was successfully applied with the aim of identifying novel HIV‐1 entry inhibitors targeting the Phe 43 pocket of HIV‐1 gp120. Several compounds able to inhibit viral replication in cell culture were identified, with the best agent endowed with an EC₅₀ value of 0.9 μM . Inactivity of all the identified hits toward a mutant (Met 475 Ile) strain strongly suggests that they interact in the Phe 43 cavity of gp120, as intended. Remarkably, all of these small molecules have a chemical scaffold unrelated to any known class of entry inhibitors reported thus far. Overall, our strategy led to the identification of four novel chemical scaffolds that inhibit HIV‐1 replication through the destabilization of the HIV‐1 gp120–CD4 interface.     

Middle term immersion corrosion tests on metal‐salt hydrate pairs used for latent heat storage in the 32 to 36°C temperature range

Thermal energy storage is required in order to utilize alternative energy sources, which often are available at times when energy is not needed. The main applications of phase change materials (PCMs) in thermal energy storage are when space restrictions limit larger thermal storage units. To ensure long term stability of recipients and containers in energy storage facilities, corrosion must be avoided. In the present work, we studied corrosion stability of different common metals (aluminum, brass, copper, steel, and stainless steel) and tested their corrosion resistance in contact with salt hydrates that are used as PCMs (zinc nitrate hexahydrate, sodium phosphate dodecahydrate, calcium chloride hexahydrate) using the immersion corrosion test method. In a former paper, short term tests were presented. As a consequence of the results from those experiments several combinations of construction material and PCM could be ruled out. In this paper, middle term tests were performed in different conditions, such as the accessibility to oxygen in the sample and contact with graphite. These experiments allowed us to choose the best metal to be used with each salt hydrate, and combinations that should be definitely avoided.     

Supporting quantified queries in distributed databases

We show that some relational queries, which we call quantified queries are not well supported in distributed environments. We give a formal definition of quantified queries, propose a language in which to express said queries and provide a procedure to compute answers in this new language in the context of distributed databases. The proposed language is made up of high-level, declarative operators (called generalised quantifiers), and therefore it can be used in combination with several distributed frameworks. Our approach is designed to be as general as possible; it assumes horizontally partitioned relations, but nothing else, so no data placement or replication is used. We present an implementation and algorithms for the new language, propose some basic optimisations and give experimental results which show that the new approach is indeed quite efficient and scales well.     

Critical Properties of Two-dimensional Anisotropic Ising Model on a Square Lattice

We study the critical behavior of two-dimensional anisotropic Ising model on a square lattice by the finite cluster approximation based on a single-site cluster theory and by Monte Carlo techniques. We analize the influence of the report of the interactions J _h /J v on the critical temperature of the system, and we show that the critical exponents depend only on the very general properties of the systems and not on the detail of the interactions. Finally, we do a comparison between the finite cluster approximation, the mean-field approximation, and the Monte Carlo method on the level of the phase diagram in the plan \(\left (J_{h}/T_{c}\text { },\text { } J_{v}/T_{c}\right ).\)     

Improved Resource Management through User Aggregation in Heterogeneous Multiple Access Wireless Networks

In this letter we discuss the exploitation of aggregated mobility patterns in mobile networks including heterogeneous multiple access techniques. We advocate the use of knowledge about neighboring devices to create routing groups (RGs) of adjacent nodes in order to optimize radio resource management. Basically, RGs consist of aggregated logical structures which are built and maintained at the application layer. Their use allows decreased signaling overhead between groups of nodes and access points (AP) and, at the same time, improved connectivity, which is achieved through the exploitation of technology diversity and relaying schemes. We illustrate a simple yet effective analytical model, and validate it through accurate simulation results. Finally, we show the effectiveness of the RG approach in terms of resource efficiency, throughput and multiple access performance.     

Markov analysis of selective repeat type II hybrid ARQ using block codes

This paper presents an analytical model for the study of Hybrid ARQ techniques on Discrete Time Markov Channels by means of an appropriate Markov chain, which tracks the transmission outcome and can be used to evaluate several performance metrics, including throughput, loss probability, number of retransmissions, and delay. The analysis is carried out with the assumptions that the information frame is encoded by the source with a linear block code and hard decoding is used at the receiver side. We finally present numerical evaluations for the performance of a truncated Type II Hybrid ARQ technique based on Reed Solomon erasure codes.     

Effect of an External Magnetic Field on the 3-D Oscillatory Natural Convection of Molten Gallium During Phase Change

In this article, a numerical study of the effect of an external magnetic field on three-dimensional (3-D) oscillatory natural convection during phase change is carried out. A parallelepiped enclosure filled with a molten gallium and subjected to an external magnetic field applied in X-, Y-, and Z-directions, separately, is considered. The finite-volume method with enthalpy formulation is used to solve the mathematical model in the solid and liquid phases. The Hartmann number is fixed to Ha = 20.The computer program developed in this study was validated with the experimental data founded in the literature. The critical Grashof numbers Gr _Cr and critical corresponding frequencies F r _Cr are determined with and without magnetic field. The results show that the oscillatory natural convection during phase change are characterized by low-frequency oscillations in the presence and absence of the magnetic field. The pattern flow shows a spiral development of the flow in Z- direction. A strong dependence between the direction of the magnetic field and the critical Grashof number and their corresponding frequency is determined. A strong stabilization of the flow field is shown when the magnetic field is oriented horizontally.     

Study of phenolic composition and sensory properties of red grape varieties in danger of extinction from the Spanish region of Castilla-La Mancha

This paper reports on a study of the profiles of different phenolic compounds (anthocyanins, flavonols, hydroxycinnamic acids and stilbenes) of five minor red grape varieties from the Spanish region of Castilla-La Mancha (Bobal, Moravia Agria, Moravia Dulce, Rojal and Tortosí) and a traditional variety from this growing region (Cencibel) as reference. Grape skin extracts of each variety were analysed by High Performance Liquid Chromatography coupled to Diode Array Detector (HPLC–DAD). The content of grape skins in anthocyanins (21.1–453 mg kg⁻¹), flavonols (26.9–288 mg kg⁻¹) and hydroxycinnamic acids (6.80–18.2 mg kg⁻¹) showed differences according to mainly varietal origin, although other important factors have to be taken into account such as the degree of ripeness, berry size or vintage year. In all the studied varieties, the major anthocyanin was malvidin 3-glucoside (>40%) with the exception of Rojal variety, which major one was peonidin 3-glucoside together with cyanidin 3-glucoside. Moravia Dulce and Rojal varieties contained more than 46% of quercetin 3-glucuronide; the rest of them contained less than 27%. No relation was found between profiles of hydroxycinnamic acids in the studied samples and their variety or year of vintage. All the studied grapes presented high concentrations of stilbenes that could be interesting due to the health benefits.