High‐capacity resource sharing schemes for broadband wireless networks

The unique capabilities of new cellular systems are expected to provide users with integrated multimedia services. Since the air interface still represents the system bottleneck, this paper proposes novel scheduling techniques to integrate efficiently the support of real‐time traffic (i.e. voice and video) and data bursty traffic under quality of service (QoS) guarantees. Prioritization among traffic classes is adopted and a polling service discipline is employed within a class, where the permission rights of each traffic source are determined on the basis of token bucket regulators. Two polling‐based approaches are compared to serve the sources of a class: (i) when a source is enabled to transmit, a burst of packets is sent at once; (ii) within the time interval destined to a traffic class, a cyclic service of the sources is allowed on a packet basis. With realistic assumptions on both radio channel conditions and protocol signaling overhead, this paper compares these two different approaches and the dynamic slot assignment++ (DSA++) scheme appeared in the literature. The obtained results highlight that our second scheme (case ii) allows increasing the number of supported video traffic sources of many units with respect to DSA++. Finally, an analytical approach has been proposed for our second polling scheme. Copyright © 2004 John Wiley & Sons, Ltd.     

High and low surface area NiO–MgO and CoO–MgO solid solutions: a study of XPS surface composition and CO oxidation activity

Oxide solid solutions NiO–MgO of high surface area were studied by XPS. The surface Ni²⁺ concentration was found to be equal, within experimental errors, to the bulk concentration. The result is analogous to that found previously for the low surface area NiO–MgO system and for both the high and low surface area systems of CoO–MgO. The catalytic oxidation of CO by O₂, on high and low surface area NiO–MgO and CoO–MgO materials, was investigated with the aim of relating the catalytic activity with transition metal ion nature and concentration. Turnover frequency data (CO₂ molecules produced per second per surface atom) show that the activity is due primarily to the transition metal ions and is not subject to the ions being in special configurations (dimers or trimers) or in special positions (edges, corners). The activity of CoO–MgO is higher than that of NiO–MgO solid solution. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterisation of volatile compounds in an alcoholic beverage produced by whey fermentation

An alcoholic beverage (35.4% v/v ethanol) was produced by distillation of the fermented broth obtained by continuous whey fermentation with a lactose-fermenting yeast Kluyveromyces marxianus. Forty volatile compounds were identified in this drink by gas chromatography. Higher alcohols were the most abundant group of volatile compounds present, with isoamyl, isobutyl, 1-propanol, and isopentyl alcohols being found in highest quantities (887, 542, 266, and 176 mg/l, respectively). Ethyl acetate had the highest concentration (138 mg/l) among the esters. Besides higher alcohols and esters, other components, including aldehydes, acids and terpenes were also identified in the whey spirit. Considering that the quality of an alcoholic beverage can be evaluated by the relation between isoamyl alcohol/2-methyl-1-propanol and 2-methyl-1-propanol/1-propanol, which have to be higher than unity, it was concluded that a novel spirit of acceptable organoleptic characteristics can be produced by cheese whey continuous fermentation with K. marxianus.     

Bio-hythane production from food waste by dark fermentation coupled with anaerobic digestion process: A long-term pilot scale experience

In this paper are presented the results of the investigation on optimal process operational conditions of thermophilic dark fermentation and anaerobic digestion of food waste, testing a long-term run, applying an organic loading rate of 16.3 kgTVS/m³d in the first phase and 4.8 kgTVS/m³d in the second phase. The hydraulic retention times (HRTs) were maintained at 3.3 days and 12.6 days, respectively, for the first and second phase. Recirculation of anaerobic digested sludge, after a mild solid separation, was applied to the dark fermentation reactor in order to control the pH in the optimal hydrogen production range of 5–6. It was confirmed the possibility to obtain a stable hydrogen production, without using external chemicals for pH control, in a long-term test, with a specific hydrogen production of 66.7 l per kg of total volatile solid (TVS) fed and a specific biogas production in the second phase of 0.72 m³ per kgTVS fed; the produced biogas presented a typical composition with a stable presence of hydrogen and methane in the biogas mixture around 6 and 58%, respectively, carbon dioxide being the rest.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

Pure hydrogen co-production by membrane technology in an IGCC power plant with carbon capture

The CO₂ capture in Integrated Gasification Combined Cycle (IGCC) plants causes a significant increase of the cost of electricity (COE) and thus determines high CO₂ mitigation cost (cost per ton of avoided CO₂ emissions). In this work the economic sustainability of the co-production of pure hydrogen in addition to the electricity production was assessed by detailed process simulations and a techno-economic analysis. To produce pure hydrogen a Water Gas Shift reactor and a Selexol^® process was combined with H₂ selective palladium membranes. This innovative process section was compared with the more conventional Pressure Swing Adsorption in order to produce amount of pure hydrogen up to 20% of the total hydrogen available in the syngas.Assuming for a base case a hydrogen selling price of 3 €/kg and a palladium membrane cost of 9200 €/m², a cost of electricity (COE) of 64 €/MWh and a mitigation cost of 20 €/ton_CO2 were obtained for 90% captured CO₂ and 10% hydrogen recovery. An increase of the hydrogen recovery up to 20% determines a reduction of the COE and of the mitigation cost to 50 €/MWh and 5 €/ton_CO2, respectively. A sensitivity analysis showed that even a 50% increase of cost of the membrane per unit surface could determine a COE increase of only about 10% and a maximum increase of the mitigation cost of further 5 €/ton_CO2.     

Learning organisation and human resources management practices: an exploratory research in medium-sized enterprises undergoing a lean implementation

Despite the fact that Lean Manufacturing (LM) implementation has been widely discussed in the literature, a reduced number of works focus on medium-sized enterprises (MEs). Such gap becomes more evident when searching for works exploring the dimensions of learning organisation (DLO) that surround LM implementation in MEs. This paper aims at assessing DLO maturity and the importance of human resources management (HRM) practices in MEs that are starting LM implementation. We verify the applicability of a method for assessing maturity levels of DLO and HRM practices in seven different MEs. The method was originally conceived for large enterprises well advanced in the lean implementation process; it combines concepts of HRM and organisational learning with lean implementation roadmaps. Adapting the method for application in MEs allows such companies to anticipate and minimise organisational learning problems by conducting appropriate HRM practices, leading to a more effective LM implementation. We conclude that the method is a suitable diagnostic tool for MEs, indicating which phases of the lean roadmap are better prepared to be implemented.     

LLDPE with Exclusively Ethyl Branches by Tandem Catalysis with Single-Site Zr(IV)/Co(II) Catalysts

Semicrystalline linear low density polyethylenes (LLDPEs) with exclusively ethyl branching (from 7 to 56 branches per 1,000 carbon atoms) were prepared from ethylene by homogeneous tandem catalytic systems comprising (imino)pyridine cobalt(II) dichlorides as oligomerization precursors, bis(cyclopentadienyl)zirconium(IV) dichloride as copolymerization precursor and methyaluminoxane as activator. The activity of the tandem systems was evaluated by varying either the molar fraction of the cobalt precursors or the ethylene pressure. The latter parameter was of crucial importance to control both the productivity and the extent of 1-butene incorporation. In particular, increasing the ethylene pressure from 2 bar to 4 bar changed the “comonomer effect” from positive to negative.     

Surface decorated platinum carbonyl clusters

Four molecular Pt-carbonyl clusters decorated by Cd-Br fragments, i.e., [Pt(13)(CO)(12){Cd(5)(μ-Br)(5)Br(2)(dmf)(3)}(2)](2-) (1), [Pt(19)(CO)(17){Cd(5)(μ-Br)(5)Br(3)(Me(2)CO)(2)}{Cd(5)(μ-Br)(5)Br(Me(2)CO)(4)}](2-) (2), [H(2)Pt(26)(CO)(20)(CdBr)(12)](8-) (3) and [H(4)Pt(26)(CO)(20)(CdBr)(12)(PtBr)(x)](6-) (4) (x = 0-2), have been obtained from the reactions between [Pt(3n)(CO)(6n)](2-) (n = 2-6) and CdBr(2)·H(2)O in dmf at 120 °C. The structures of these molecular clusters with diameters of 1.5-2 nm have been determined by X-ray crystallography. Both 1 and 2 are composed of icosahedral or bis-icosahedral Pt-CO cores decorated on the surface by Cd-Br motifs, whereas 3 and 4 display a cubic close packed Pt(26)Cd(12) metal frame decorated by CO and Br ligands. An oversimplified and unifying approach to interpret the electron count of these surface decorated platinum carbonyl clusters is suggested, and extended to other low-valent organometallic clusters and Au-thiolate nanoclusters.