Adaptive modulation and combining for bandwidth and power efficient communication over fading channels

Traditional fading mitigation techniques are designed relative to the worst‐case channel conditions, resulting in a poor utilization of the spectrum and the available power a good percentage of the time. In contrast, we introduce and investigate in this paper new adaptive modulation and diversity combining techniques that jointly select the most appropriate constellation size and the most suitable diversity branches in response to the channel variation and given a desired bit error rate (BER) requirement. Numerical results show that these newly proposed adaptive modulation and combining schemes can reduce considerably the average receiver channel estimation complexity as well as the power drain from the battery while offering high spectral efficiency and satisfying the desired outage probability and BER requirements. Copyright © 2006 John Wiley & Sons, Ltd.     

Corrosion inhibition, hydrogen evolution and antibacterial properties of newly synthesized organic inhibitors on 316L stainless steel alloy in acid medium

Electrochemical corrosion behavior and hydrogen evolution reaction of 316L stainless steel has been investigated, in 0.5 M sulfuric acid solution containing four novel organic inhibitors as derivatives from one family, using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and surface examination via scanning electron microscope (SEM) technique. The effect of corrosion inhibitors on the hydrogen evolution reaction was related to the chemical composition, concentration and structure of the inhibitor. The inhibition efficiency, for active centers of the four used compounds, was found to increase in the order: -Cl < -Br < -CH₃ < -OCH₃. The corrosion rate and hydrogen evolution using the compound with methoxy group as a novel compound was found to increase with either increasing temperature or decreasing its concentration as observed by polarization technique and confirmed by EIS measurements. The compound with methoxy group (newly synthesized) has very good inhibition efficiency (IE) in 0.5 M sulfuric acid (98.3% for 1.0 mM concentration). EIS results were confirmed by surface examination. Also, antibacterial activity of these organic inhibitors was studied. The results showed that the highest inhibition efficiency was observed for the compound that posses the highest antibacterial activity.     

Thermal performance study of a vacuum integrated solar storage collector (ISSC) with compound parabolic concentrator (CPC)

This paper deals with the energy performance of a new integrated solar storage collector (ISSC) with compound parabolic concentrator (CPC) conceived in the Thermal Process Laboratory in CRTEn Borj Cedria (North of Tunisia). The novelty in this system is the use of transparent vacuum insulation in the annulus between double half-Cylindrical Plexiglass, and the use of automated nocturnal insulation system, which suppresses heat loss during night. Also, the system is equipped with a mobile support permitting to have many collector orientations toward south, east-south, and west-south in order to maximize the incident solar flux. The experimental study of the ISSC system showed that the thermal loss coefficient of ISSC system is equal to 6.16 W/K for ISSC without nocturnal insulation and without vacuum, 4.69W/K for ISSC without nocturnal insulation and with vacuum, and 4.00 W/K for ISSC with nocturnal insulation and with vacuum. The thermal efficiency of the solar collector is equal to 42.92% for ISSC system fixed without vacuum, 45.95% for ISSC system fixed with vacuum, and 50.56% for ISSC system mobile with vacuum. In order to determine the long-term performance of the vacuum ISSC with CPC, the TRNSYS simulations were carried out by using the component modules modeling the ISSC with CPC concentrator (type 74 and type 60f). Comparison between experimental and predicted results for the temperature difference inside the storage tank during 3 days of January showed reasonable agreement. The numerical results for the ISSC system showed that the annual total energy collected (solar) and auxiliary energy were about 4670 and 1561 MJ, respectively. The annual total auxiliary energy represents about 33.4% of the annual total energy collected (solar). During the summer months (June, July, and August), no auxiliary is needed and the solar fraction (SF) is equal to 100%, where as the annual average SF is about 75%.     

Characterization of Lactobacillus isolates from fermented olives and their bacteriocin gene profiles

Near one hundred isolates of Lactobacillus paraplantarum, Lactobacillus pentosus and Lactobacillus plantarum from table olives were studied. Strains were genotyped by rep-PCR. Although the technique failed to differentiate some isolates at the species level, it proved a robust and easy procedure that could be useful for distinguishing between related strains of L. paraplantarum, L. pentosus and L. plantarum from a large pool of unrelated strains of these species. A PCR-based screening revealed the presence of the plantaricin encoding genes plnA, plnB, plnC, plnD, plnE/F, plnF, plnI, plnJ, plnK, plnG and plnN in most isolates of the three species. Sequences of bacteriocin genes present in L. paraplantarum and L. pentosus were homologous to L. plantarum genes. Through a discriminating analysis of the bacteriocin gene profiles, it was possible to establish a relationship between the origin of isolation and the LAB isolates, regardless of species.     

Preconcentration and determination of copper and cadmium ions with 1,6-bis(2-carboxy aldehyde phenoxy)butane functionalized Amberlite XAD-16 by flame atomic absorption spectrometry

A new chelating resin, covalently linked 1,6-bis(2-carboxy aldehyde phenoxy)butane with the Amberlite XAD-16 was synthesized and used for preconcentration of Cu(II) and Cd(II) prior to their determination by flame atomic absorption spectrometry (FAAS). It was characterized by elemental analyses and Fourier Transform Infrared Spectroscopy (FT-IR). Cu(II) and Cd(II) ions were quantitatively preconcentrated on minicolumn loaded with synthesised resin at pH 4.00 and 6.00, respectively. They were eluated with 5 mL of 0.5 mol L⁻¹ HCl. Recoveries of Cu(II) and Cd(II) were found to be 100 ± 2.15, 100 ± 1.40 (N = 5), the limits of detection of Cu(II) and Cd(II) in the determination by FAAS (3s, N = 20) were found to be 0.33 and 1.19 μg L⁻¹, respectively. The effect of foreign ions on the recovery has been investigated. The proposed method has been applied for the determination of Cu(II) and Cd(II) ions to the real samples collected from Tigris river water in Diyarbak?r and Elaz?? cities in Turkey. Standard addition method and analysis of the certified reference material (NCS-DC 73350) was employed to check the accuracy of the method.     

Substitution mechanism of alkali metals for strontium in strontium hydroxyapatite

Strontium hydroxyapatites substituted by alkali metals are synthesized by double decomposition method in basic medium. Structures of Sr_9.50Na_0.30(PO₄)₆(OH)_1.30 (SrNaHAp) and Sr_9.81K_0.12(PO₄)₆(OH)_1.74 (SrKHAp) are determined by X-ray powder diffraction. Both compounds are isotypic and crystallize in hexagonal system (space group P63/m) with the following cells: a=9.751(3) Å and c=7.279(3) Å for SrNaHAp and a=9.755(4) Å and c=7.284(3) Å for SrKHAp. Results are compared to those of Sr₁₀(PO₄)₆(OH)₂. According to the site occupancy factors, in SrNaHAp sodium is localized in site (I) and in SrKHAp potassium in site (II). Both structures contain vacancies in hydroxyl and metal sites. The mechanism of alkali metals substitution for strontium proposed explains the vacancies formation.     

The importance of viscoplastic strain rate in the formation of center cracks during the start-up phase of direct-chill cast aluminum extrusion ingots

A comparison of experimental observations and computer simulations shows that trends in the occurrence and severity of center cracks in direct-chill (DC) cast ingots due to different initial casting speed histories may best be explained by the changes in viscoplastic strain rate close to the center of the base of the ingot. The thermomechanical histories of five ingots were simulated and correlations between stresses, strains, strain rates, and liquid pressure drops due to feeding restrictions were considered.     

Dynamic sorption of ionizable organic compounds (IOCs) and xylene from water using geomaterial-modified montmorillonite

Adsorption of phenols and xylene onto composite material, Na-montmorillonite, activated carbon, cement and water mixture, 70%, 7%, 7% and 16% (w/w/w/w), respectively, was studied at pH values of 5.15, 4.55, 5.2 and 4.9, respectively, of phenol, 2-CP, 2-NP and xylene. Equilibrium isotherms and fixed-bed column studies were undertaken to evaluate the performance of clay-active coal-coated cement (CACC) in removing phenols from aqueous solution. Investigations revealed CACC to be a very efficient media for the removal of phenols from water. The suitability of the Langmuir adsorption model to the equilibrium data was investigated for all phenols-adsorbent systems. At the maximum sorption capacity of the composite material it was found that the uptake (mg phenols/g) of phenols increased in the order 2-CP>2-NP>phenol approximately m-xylene as do their solubilities. The LUB design approach was used to determine the equivalent length of unused bed. The lower LUB values imply a better utilization of CACC composite. A model, which considered the effect of axial dispersion, was successfully used to describe the fixed-bed operation, the axial dispersion coefficient increased significantly with solubility.