Contention-TDMA protocol: performance evaluation

A hybrid access protocol known, as contention time-division multiple access (C-TDMA), is presented and analyzed in a radio cellular multiuser system scenario. C-TDMA shows some features of contention-based (slotted-ALOHA) and reservation-based (packet reservation multiple access, PRMA) protocols. It has been recommended for use in the uplink of future European multimedia distribution systems. A simple Markov model is proposed to describe C-TDMA behavior. A complete statistical analysis of the model has been made in order to evaluate the performance of the protocol. However, due to the long computation time required in the presence of a large number of users, a simpler approach known as equilibrium point analysis (EPA) is used. Moreover, on the basis of the EPA analysis and the C-TDMA design parameters, a fast algorithm has been developed to improve the achievable throughput of C-TDMA. Results in terms of throughput and delay under variable traffic conditions indicate that C-TDMA is able to grant optimum throughput/delay figures for typical multiuser systems. Moreover, for a digital speech scenario, a performance comparison with PRMA demonstrates that C-TDMA yields equivalent performance to PRMA in terms of number of users supported by the system with a limited packet dropping rate     

Phenanthrene sorption by aliphatic-rich natural organic matter

Contaminant sorption, an important process that may limit bioavailability, hinder remediation, encourage environmental persistence, and control mobility in the environment, has been the focus of numerous studies. Despite these efforts, the fundamental understanding of sorptive processes in soil and sedimentary environments has not been resolved. For instance, many have suggested that contaminants, such as polycyclic aromatic hydrocarbons (PAHs), solely interact with aromatic domains of organic matter. Until now, studies have neglected the aliphatic components that are known to be a recalcitrant and significant part of soil and sedimentary organic matter (SOM). In this investigation, the sorption of phenanthrene to several aliphatic-rich SOM samples was measured. The samples included the following: SOM precursors (algae, degraded algae, cellulose, collagen, cuticle, and lignin), two kerogen samples, and a highly aromatic humic acid. All samples were characterized by cross polarization magic angle spinning carbon-13 (CPMAS 13C) NMR and carbon, hydrogen, and nitrogen analysis. Batch experiments demonstrated that the highest organic carbon normalized sorption coefficients (Koc values) were obtained with the Pula kerogen sample (log Koc = 4.88) that only contains 6.5% aromatic carbon. Other aliphatic-rich samples, namely the Green River kerogen, degraded algae, and collagen samples produced comparable log Koc values (4.64, 4.66, and 4.72, respectively) to that of the highly aromatic humic acid (log Koc = 4.67). Phenanthrene uptake was the least for cellulose and lignin, two major soil components. A comparison of phenanthrene Koc values and paraffinic carbon content revealed a positive correlation (Koc = 798 +/- 96.1 * paraffinic carbon (%), r2 = 0.56) and indicates that amorphous polymethylene carbon is an important consideration in phenanthrene sorption. This study establishes that aliphatic SOM domains have a strong affinity for phenanthrene and likely, other PAHs. Therefore, aliphatic structures, that are an important component of SOM, require more attention in the examination of sorption processes in terrestrial and sedimentary environments.     

Olive oil authentication,traceability and adulteration detection using DNA‐based approaches

Olive oil is the fresh juice produced by pressing olive fruits. It serves as the main component of the Mediterranean diet and one of the most valuable products of the agro‐food industry, not only for its taste, but also for its high nutritional value. As it is considered the lipid constituent of the olive fruits, it is composed mainly of triglycerides and phenolics. Authentication and traceability of extra virgin olive oil is a challenging research task due to the complexity of fraudulent practices. Various chemical and biochemical techniques have been developed for determining the authenticity of olive oil. Olive oil DNA‐based analyses have gained attention in recent years, due to high specificity, sensitivity and reliability. DNA analyses have very high discriminating power because ultimately the unique identity of a variety or species is to a great extent genetically dependent. Polymorphisms are genetic variations which refer to the variation in populations or species. Molecular markers provide information on genetic variations and are valuable tools to determine olive oil authenticity. Molecular markers such as SNPs, microsatellites, SCARs and AFLPs have been used for the identification of the varietal origin of olive oils. This feature provides an overview of the current trends and critical issues on DNA‐targeted approaches used for traceability and authenticity of olive oil.     

Sequential flow membraneless microfluidic fuel cell with porous electrodes

A novel convective flow membraneless microfluidic fuel cell with porous disk electrodes is described. In this fuel cell design, the fuel flows radially outward through a thin disk shaped anode and across a gap to a ring shaped cathode. An oxidant is introduced into the gap between anode and cathode and advects radially outward to the cathode. This fuel cell differs from previous membraneless designs in that the fuel and the oxidant flow in series, rather than in parallel, enabling independent control over the fuel and oxidant flow rate and the electrode areas. The cell uses formic acid as a fuel and potassium permanganate as the oxidant, both contained in a sulfuric acid electrolyte. The flow velocity field is examined using microscale particle image velocimetry and shown to be nearly axisymmetric and steady. The results show that increasing the electrolyte concentration reduces the cell Ohmic resistance, resulting in larger maximum currents and peak power densities. Increasing the flow rate delays the onset of mass transport and reduces Ohmic losses resulting in larger maximum currents and peak power densities. An average open circuit potential of 1.2 V is obtained with maximum current and power densities of 5.35 mA cm⁻² and 2.8 mW cm⁻², respectively (cell electrode area of 4.3 cm²). At a flow rate of 100 μL min⁻¹ a fuel utilization of 58% is obtained.     

Distributed multi-tenant RAN slicing in 5G networks

Wireless Networks - Network slicing is a promising technology in 5G networks. The key concept is to divide the physical network into multiple logical networks, that are tailored to fulfill diverse...     

Design and manufacturing of parts for functional prototypes on five-axis milling machines

This paper presents the manufacturing process for complex parts in the aim of building functional prototype mechanisms. Functional prototypes are used during testing in order to validate new product design. Their layouts are very similar to the final product, wherein lies the interest of testing many modifications. The mechanism must respect the functional geometrical requirements and be capable of withstanding forces or, for example, ensuring a tight seal. The principle being proposed consists of decomposing the complex parts into several simple ones that can then be manufactured on a five-axis, high-speed milling machine from thick (approximately 40 mm) sheets made of resistant materials, notably aluminum. The problem at hand is threefold: the choice of slicing in order to avoid cutting functional areas; the choice of both positioning mode and sheet fastening mode; and lastly, the choice of machining process. This paper also presents a detailed application with a machining simulation, using CATIA (Dassault Systèmes) for a five-axis MIKRON UCP 710 milling machine.     

DECT-based return channel for 42 GHz broadband wireless systems

A modern approach for the implementation of the return channel of broadband wireless systems based on DECT-like layers is described. The physical and MAC features are illustrated and the system performance is evaluated by computer simulations. Numerical results show that the proposed approach yields a high throughput and minimum message delay     

Potential applications of sonet in BISDN customer premises network management

Future broadband customer premises networks (CPNs) may employ synchronous optical network (SONET) transmission, carrying asynchronous transfer mode (ATM) cells, to interconnect intrapremises stations. This prospect, driven by current standardization efforts in ANSI T1 committees and CCITT, can lead to ubiquitous and cost-effective, high-speed interfaces capable of supporting a variety of services. Similar to the way they will support operations functions for SONET network elements in future broadband public networks, the embedded overhead channels in the SONET frame structure can assist in management of the CPN. In this paper, we suggest means of supporting CPN management in the functions of network configuration, fault location and notification, and performance monitoring, by taking advantage of the SONET overhead capabilities.     

Fluoxetine in depressed alcoholics. A double-blind, placebo-controlled trial

BACKGROUND: The selective serotonergic medication fluoxetine has demonstrated efficacy in the treatment of major depression and has suggested efficacy in the treatment of alcoholism. However, no completed trials with any selective serotonergic medication have been reported in patients who display both major depression and alcoholism, despite previous observations that both depression and alcoholism are associated with low serotonergic functioning. METHODS: Fifty-one patients diagnosed as having comorbid major depressive disorder and alcohol dependence were randomized to receive fluoxetine (n = 25) or placebo (n = 26) in a 12-week, double-blind, parallel-group trial. Weekly ratings of depression and alcohol consumption were obtained throughout the 12-week course of the study. RESULTS: The improvement in depressive symptoms during the medication trial was significantly greater in the fluoxetine group than in the placebo group. Total alcohol consumption during the trial was significantly lower in the fluoxetine group than in the placebo group. CONCLUSIONS: Fluoxetine is effective in reducing the depressive symptoms and the alcohol consumption of patients with comorbid major depressive disorder and alcohol dependence. It is unknown whether these results generalize to the treatment of less depressed and less suicidal alcoholics.