Allocating data for broadcasting over wireless channels subject to transmission errors

Broadcasting is an efficient and scalable way of transmitting data over wireless channels to an unlimited number of clients. In this paper the problem of allocating data to multiple channels is studied, assuming flat data scheduling per channel and the presence of unrecoverable channel transmission errors. The objective is that of minimizing the average expected delay experienced by the clients. Two different channel error models are considered: the Bernoulli model and the simplified Gilbert–Elliot one. In the former model, each packet transmission has the same probability to fail and each transmission error is independent from the others. In the latter one, bursts of erroneous or error-free packet transmissions due to wireless fading channels are modeled. Particular cases are detected where optimal solutions can be found in polynomial time. For general cases, simulations show that good sub-optimal solutions can be found on benchmarks whose item popularities follow Zipf distributions.     

Cold shut formation analysis on a free lead yellow brass tap

In order to minimize the risk of the lead in the health, the chemical composition of the plumbing components have suffered changes. However, lead improves machinability and castability in copper alloys. In this work a failure created during solidification process on a lead free tap of yellow brass alloy was investigated. Visual inspection, SEM, EDS and a ProCast V.2008 simulation were carried out in order to determine the cause of this failure. The results exhibited a close correlation between the failure formation and a convergent metal flow and solidification involved during the tilt process and determines that failure was caused by a cold shut, also inclusions carrying from the core and metal oxide films were also found.     

Sorption equilibrium of Cr(VI) ions by strong base anion exchangers with pyridine structures

Chromate sorption on pyridine strong base anion exchangers with different functional groups (methyl, ethyl, and butyl groups), at the quaternary nitrogen atoms, was studied as a function of various initial concentrations (100–1500 mg Cr/L) and counterion type. The studied resins in the Cl^?[ form have higher Cr(VI)‐retention capacities than those in the SO form. The pyridine strong base anion exchangers showed a selectivity reversal for the sulfate and chromate anions compared to that of the commercial resins. The alkyl substituent length of the quaternary nitrogen atoms exerted a substantial influence on the Cr(VI)‐retention capacity values for the resins in the Cl^? form; the chromate anions preferred resins with methyl functional groups, that is, resins with a greater hydrophilic structure. For the resins in the SO form the length of the substituent at the quaternary nitrogen atom had only a negligible influence on their Cr(VI)‐retention values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1957–1963, 2004     

Enantiomer separation by countercurrent chromatography using cinchona alkaloid derivatives as chiral selectors

Cinchona-derived anion-exchange-type chiral selectors have been adapted and employed in countercurrent chromatography (CCC) for the separation of enantiomers of N-derivatized amino acids and 2-aryloxypropionic acids. The accurate optimization of the enantioseparation in terms of solvent system composition, pH values, ionic strength, and CCC operating conditions was performed. A wide range of solvent mixtures was evaluated. Successful resolutions were achieved in systems such as ammonium acetate buffer/tert-amyl alcohol/methanol/heptane and especially ammonium acetate buffer/methyl isobutyl ketone or diisopropyl ether. Up to 300 mg (0.92 mmol) of N-(3,5-dinitrobenzoyl)-(+/-)-leucine was totally resolved in a single run using a 10 mM concentration of chiral selector in 122 mL of stationary phase. This amount could be increased up to 900 mg (2.77 mmol) when pH-zone-refining mode was applied. The results here presented account for the high potential of CCC as a preparative enantiomer separation technique.     

Enhanced osteoinductive capacity and decreased variability by enrichment of demineralized bone matrix with a bone protein extract

Osteoinductive capacity of demineralized bone matrix (DBM) is sometimes insufficient or shows high variability between different batches of DBM. Here, we tried to improve its osteoinductive activity by alkali-urea or trypsin treatment but this strategy was unsuccessful. Then, we tested the enrichment of DBM with a bone protein extract (BPE) containing osteogenic growth factors comparing two sources: cortical bone powder and DBM. The osteoinductive capacity (alkaline phosphatase activity) of the obtained BPEs was evaluated in vitro in C2C12 cells. Specific protein levels present in the different BPE was determined by enzyme-linked immunosorbent assay or by a multiplex assay. BPE from cortical bone powder showed a lack of osteoinductive effect, in agreement with the low content on osteoinductive factors. In contrast, BPE from DBM showed osteoinductive activity but also high variability among donors. Thus, we decided to enrich DBM with BPE obtained from a pool of DBM from different donors. Following this strategy, we achieved increased osteoinductive activity and lower variability among donors. In conclusion, the use of a BPE obtained from a pool of demineralized bone to enrich DBM could be used to increase its osteoinductive effect and normalize the differences between donors.

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Freeze drying optimization of polymeric nanoparticles for ocular flurbiprofen delivery: effect of protectant agents and critical process parameters on long-term stability

Context: The stabilization of flurbiprofen loaded poly-?-caprolactone nanoparticles (FB-P?CL-NPs) for ocular delivery under accurate freeze-drying (FD) process provides the basis for a large-scale production and its commercial development.

Objective: Optimization of the FD to improve long-term stability of ocular administration’s FB-P?CL-NPs.

Methods: FB-P?CL-NPs were prepared by solvent displacement method with poloxamer 188 (P188) as stabilizer. Freezing and primary drying (PD) were studied and optimized through freeze-thawing test and FD microscopy. Design of experiments was used to accurate secondary drying (SD) conditions and components concentration. Formulations were selected according to desired physicochemical properties. Furthermore, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to study interactions components.

Results: Optimized FB-P?CL-NPs, stabilized with 3.5% (w/w) P188 and protected with 8% (w/w) poly(ethylene glycol), was submitted to precooling at +10?°C for 1?h, freezing at ?50?°C for 4?h, PD at +5?°C and 0.140 mbar for 24?h and a SD at +45?°C during 10?h. These conditions showed 188.4?±?1.3?nm, 0.087?±?0.014, 85.5?±?1.4%, 0.61?±?0.12%, ?16.4?±?0.1?mV and 325?±?7 mOsm/kg of average size, polydispersity index, entrapment efficiency, residual moisture, surface charge and osmolality, respectively. It performed a long-term stability >12 months. DSC and XRD spectra confirmed adequate chemical interaction between formulation components and showed a semi-crystalline state after FD.

Conclusions: An optimal freeze dried ocular formulation was achieved. Evidently, the successful design of this promising colloidal system resulted from rational cooperation between a good formulation and the right conditions in the FD process.     

Time, Narratives and Participation Frameworks in Software Troubleshooting

The paper problematizes diagnostic work as a solely technical and rational activity by presenting an analysis focused on the social and organizational practices in which diagnosis is embedded. The analysis of a troubleshooting episode in an Italian internet company shows how diagnostic work is realized: 1) through collaboration sustained by specific knowledge distribution among designers (different but overlapping competences); 2) intersubjectively and discursively as an activity characterized by specific and diverse forms of participation and interwined with material intervention in the system; 3) following a situated rationality which proceeds by gradual approximations to achieve partial or provisional solutions while also taking account of organizational goals and needs. In particular the paper discusses how diagnosis is shaped by time pressure, flexible roles and distributed responsibilities, absent participants, narratives as specialized discourses.