Wi-Fi Offload: Tragedy of the Commons or Land of Milk and Honey?

Fueled by its recent success in provisioning on-site wireless Internet access, Wi-Fi is currently perceived as the best positioned technology for pervasive mobile macro network offloading. However, the broad transitions of multiple collocated operators towards this new paradigm may result in fierce competition for the common unlicensed spectrum at hand. In this light, our paper game-theoretically dissects market convergence scenarios by assessing the competition between providers in terms of network performance, capacity constraints, cost reductions, and revenue prospects. We will closely compare the prospects and strategic positioning of fixed line operators offering Wi-Fi services with respect to competing mobile network operators utilizing unlicensed spectrum. Our results highlight important dependencies upon inter-operator collaboration models, and more importantly, upon the ratio between backhaul and Wi-Fi access bit-rates. Furthermore, our investigation of medium- to long-term convergence scenarios indicates that a rethinking of control measures targeting the large-scale monetization of unlicensed spectrum may be required, as otherwise the used free bands may become subject to tragedy-of-commons type of problems.Comment: Workshop on Spectrum Sharing Strategies for Wireless Broadband Services, IEEE PIMRC'13, to appear 201

An Ear for the Therapeutic in Stories of Religious Experience

It is a given that in our ministry we will hear our beloved patients or directeers' stories. When our clients are persons of faith, it is fruitful to listen to their stories with an ear for religious experience

Extraction and Formation of Iron(III) Thiocyanate Complexes: Application for Spectrophotometric Determination of Iron

Extraction of iron(III) from sulphuric and hydrochloric acid solutions containing an excess of thiocyanate ions with tetraphenylphosphonium (TPP) chloride and cetyltrimethylammonium (CTMA) bromide in chloroform was investigated. Optimum conditions for extraction by both extractants were determined. The extraction behaviour of CTMA was found to be more efficacious than that of TPP because less thiocyanate and extractant was required. Better extraction efficiency of CTMA can be attributed to surface-active properties of this substance. Formation of an extractable iron(III) thiocyanate complex with CTMA or TPP was also determined spectrophotometrically by measuring the absorbance of the organic phase at 473 nm or 506 nm, respectively. The composition of the extracted iron(III) complexes was determined by distribution and spectrophotometric methods. The molar ratio Fe:SCN:TPP of the extracted complex was 1:4:1; accordingly, its composition was [TPP][Fe(SCN)4]. The molar ratio Fe:CTMA of the extracted complex was 1:3. The molar ratio Fe:SCN in the complex extracted with CTMA could not be determined because of the turbidity in solutions containing less than 0.01 mol dm–3 thiocyanate ion, but it was concluded that the composition of the extracted complex was [CTMA]3[Fe(SCN)6]

Solvent Extraction of Copper as a Thiocyanate Complex. Reducing Effect of Thiocyanate

Extraction of copper(II) from sulphuric and hydrochloric acid Solutions containing an excess of thiocyanate ions with tetraphenylphosphonium (TPP) chloride and cetyltrimethylammonium (CTMA) bromide in chloroform was investigated. The optimum conditions for quantitative extraction (over 99%) by both extractants were determined. The extraction behaviour of CTMA was found to be more efficacious than that of TPP because a low excess of thiocyanate and extractant was required and extraction was feasible even from a higher concentration of sulphuric acid. The formation of an extractable copper(II) thiocyanate complex with CTMA could also be determined spectrophotometrically by measuring the absorbance of the organic phase at 409 nm. The presence of ascorbic acid decreased the absorbance at 409 nm but the formed copper(I) thiocyanate was quantitatively extracted with CTMA, independently of the ascorbic acid concentration. Thiocyanate ions also exercised a reducing effect on copper(II) at pH > 1.3; with increasing pH and/or prolonged shaking time of the aqueous and organic phases, the reducing effect increased. The composition of the extracted copper(II) complex was determined by the distribution and spectrophotometric methods. The molar ratio Cu:SCN:TPP (CTMA) of the extracted complex was 1:4:2; accordingly, its composition was [TPP]2 [Cu(SCN)4] or [CTMA]2 [Cu(SCN)4]

Extraction and Characterization of Niobium(V) Thiocyanate Complexes

Extraction of niobium(V) from sulphuric and hydrochloric acid Solutions containing an excess of thiocyanate ions with tetraphenylphosphonium (TPP) and tetraphenylarsonium (TPA) chloride into chloroform was investigated. The maximum extraction of niobium from sulphuric acid Solutions was about 91% and from hydrochloric acid Solutions about 94%. Chloride ions produced a moderate synergistic effect. Niobium(V) was quantitatively extracted (over 99%) from sulphuric and hydrochloric solutions only if chloride ions were also in excess and a lower excess of thiocyanate and extractant was required than in extraction without addition of chloride. The optimal conditions for the quantitative extraction of niobium were 0.2-0.5 M H2SO4 or 0.2-4 M HCl, 0.2-0.7 M thiocyanate and more than 4 M chloride in the aqueous phase, and TPP (TPA) concentration in the organic phase higher than 3 x 10-3 M. The extracted complexes in chloroform had an absorption maximum at 390 nm or at 390 and 320 nm, depending on the composition of the aqueous phase. Absorption spectra were studied as a function of H2SO4, HCl, thiocyanate and chloride concentrations in the aqueous phase. The optimal conditions for the spectrophotometric determination of niobium by measuring the absorbances of the organic phase at 390 nm were 1-2 M HCl, 0.1-0.5 M thiocyanate and TPP (TPA) chloride in chloroform of at least 5 x 10-3 M. A total chloride concentration lower than 2.2 M had no effect on absorbance. The mechanism of extraction based on the formation of ion-associated compounds between the onium cation and the thiocyanatoniobate(V) or mixed ligand chlorothiocyanatoniobate(V) anion is discussed

Extraction and Separation of Tantalum(V) with 3-Hydroxy-2-methyl-1-(4-tolyl)-4-pyridone

Extraction of tantalum(V) from aqueous oxalic solution with 3 hydroxy- 2-methyl-1-(4-tolyl)-4-pyridone (HY) dissolved in chloroform has been examined at different acidities and ionic strengths. Tantalum( V) is quantitatively extracted with HY from oxalic solution at pH = 2.3-2.5, probably as a mixed ligand Ta-oxalate-HY complex. Tantalum(V) can be quantitatively extracted even from a more acidic solution in the presence of sulphuric, hydrochloric or perchloric acids, in the acidity range from pH = 2.3 to 3.5 M H2S04 or HCI and from pH = 2.3 to 5.5 M HCI04. Thiocyanate, perchlorate and chloride ions produce a synergistic effect on the tantalum(V) extraction with HY. In the presence of an excess of thiocyanate, perchlorate or chloride ions, tantalumtV) is quantitatively extracted with HY in the acidity range from pH = 2.3 to 3.5 M H2S04 as a mixed ligand Ta-NCS-HY, Ta-CI04-HY or in the form of Ta-CI-HY complexes. Compositions of the complexes are studied and discussed. Tantalum(V) extraction with HY enables its separation from niobium(V), zirconium(IV) and hafnium(IV)