Base-catalyzed oxidation of poly (ethylene glycol) by alkaline permanganate: Part I. Kinetics and mechanism of formation of coordination intermediate complex

A spectrophotometric investigation has been applied to study the kinetics of oxidation of poly (ethylene glycol) (PEG) as a synthetic polymer by alkaline permanganate at a constant ionic strength of 1.0 mol.dm^?3. The reaction was found to proceed through two distinct measurable stages. The first stage was relatively fast and corresponding to the formation of coordination polymer intermediate complexes involving blue hypomanganate (V) and/or green manganate (VI) transient species. The influence of variable factors on the oxidation rates such as the concentration of permanganate ion and PEG substrate concentrations as well as the pH and ionic strength have been examined. Under the pseudo-first-order reaction conditions of [PEG] ? [MnO₄^?], the experimental results showed a first-order dependence in [MnO₄^?] and fractional first-order kinetics in each of [PEG] and alkali concentration. The oxidation process was of base-catalyzed nature where the oxidation rates were increased with increasing the alkali concentration. The observed first-order rate constant was found to be 1.1 ×10^?3 s^?1 with deprotonation constant of 0.72 dm³ mol^?1 at 45 °C. Blue hypomanganate (V) was detected for the first time by using a conventional spectrophotometer. The oxidation process has proceeded without the intervention of a free-radical mechanism. Colloidal manganese (IV) and the acid derivatives of PEG were identified as final oxidation products. The activation parameters of the second-order reaction have been calculated and found to be ΔH^≠ = 40.66 kJmol^?1; ΔS^≠ = ? 145.41 Jmo^l?K^?1 and ΔG^≠ = 83.99 kJmol^?1. A plausible reaction mechanism for oxidation based on the evaluated activation parameters and in good consistent with the observed kinetic data was suggested and discussed.     

Distributed channel selection in CRAHNs: A non-selfish scheme for mitigating spectrum fragmentation

In this paper, we consider the problem of spectrum sharing in CRAHNs and propose a distributed channel selection scheme. The key functionality of our proposal, best-fit channel selection (BFC) is that it accounts both the primary channel traffic activity and CR traffic activity in channel selection. We assume CR nodes have the capability of estimating the primary channel traffic activities. In BFC, each CR selects a channel among the primary user (PU) channels for transmission that best fits to its transmission time requirement. We compare the performance of BFC to the widely known longest idle time channel selection (LITC) scheme. In LITC, a CR selects the channel that has the longest expected idle time independent of its transmission needs. In a multi-user CRN, this may degrade the network performance compared to the non-selfish BFC approach. LITC is considered selfish since each CR aims to maximize its own benefit and thus wastes resources that may be utilized by other nodes in the network. BFC providing an efficient spectrum sharing mechanism implicitly mitigates the effect of spectrum fragmentation which is a significant issue degrading the CR spectrum utilization. In CRNs, spectrum may be fragmented in various dimensions, e.g. time and frequency, such that some parts of the spectrum can not be used although being idle. Our proposal provides a solution to the spectrum fragmentation issue in time dimension at the medium access control (MAC) layer. By a set of simulations, we highlight the performance improvement by BFC over the conventional LITC under various CR/PU traffic, number of CRs, estimation accuracy and buffering capability. Simulation results show that the performance of the proposed BFC is significantly superior to that of LITC in terms of probability of successful transmission, spectrum opportunity utilization and fragmentation.     

Do ozone and boric acid affect microleakage in class V composite restorations?

The aim of this in vitro study was to evaluate the effects of chlorhexidine gluconate (2%), sodium hypochloride (2.5%), ozone gas, and boric acid at different concentrations (1%, 3%, 5%, and 7%) on microleakage from composite restorations.

In a total of 80 extracted human canine teeth, a class V cavity was opened on the buccal surface and the samples were separated into eight groups. In the control group, no procedure was applied for cavity disinfection, then composite restoration (Z250, 3M) was made using single-stage, self-etch adhesive (Single Bond 3M). In the other groups, seven different disinfectants were used, then the cavity was restored. The teeth were split into two in the buccolingual direction, parallel to the long axes. Stain penetration was examined under stereomicroscope and scored. Examination with SEM was made on one sample from each group, selected at random. Statistical evaluations were made using Dunnett C Post Hoc Comparison and Kruskal–Wallis H tests.

In the occlusal region evaluation, the groups with the lowest level of leakage were the 3% and 5% boric acid groups, and the highest levels of microleakage were determined in the chlorhexidine group and the 1% boric acid group. In the gingival region, the lowest level of microleakage was in the 5% boric acid group and the highest levels were determined in the 1% and 7% boric acid groups.

Boric acid disinfectants used at suitable concentrations were not seen to create a risk in respect of microleakage.     

Bilaterally Microstructured Thin Polydimethylsiloxane Film Production

Thin PDMS films with complex microstructures are used in the manufacturing of dielectric electro active polymer (DEAP) actuators, sensors and generators, to protect the metal electrode from large strains and to assure controlled actuation. The current manufacturing process at Danfoss Polypower A/S produces films with a one-sided microstructured surface only. It would be advantageous to produce a film with both surfaces microstructured, as this increases the film’s performance efficiency. The new technique introduced herein produces bilaterally microstructured film by combining an embossing method with the existing manufacturing process. In employing the new technique, films with microstructures on both surfaces are successfully made with two different liquid silicone rubber (LSR) formulations: 1) pure XLR630 and 2) XLR630 with titanium dioxide (TiO₂). The LSR films (～70 µm) are cast on a carrier web substrate using a coating blade. The carrier web, which has a sinusoidal corrugation with wave height of 7 µm and a wave period of 7 µm on its surface, imparts corrugations to the bottom surface of the film. The elastomer film on the carrier web is preheated to the gel point, where the elastomer film can retain an imprint made on it. The preheated film at gel point is embossed between the rolls of a gravure lab coater, which corrugates the top surface of the film. The films are then heated, in order to cure completely. For the LSR systems used in this process, the optimum conditions for preheating are 110°C for 4–7 s, while for embossing the temperature is 110°C with 25 psi pressure between the rolls at a speed of 1.4 rpm. Scanning electron microscope (SEM) images confirm the formation of microstructures on both the surfaces of the film.     

Hydrolysis of freshly prepared wheat starch fractions and commercial wheat starch using α-amylase

The enzymic hydrolysis of commercial wheat starch and freshly prepared wheat starch fractions was studied in batch and flow systems. Fresh starch was prepared by wet separation of wheat flour into starch milk and gluten, followed by processing the starch milk using a serially connected hydrocyclone system to produce underflow and overflow streams. The underflow stream consisted mainly of the larger (> 30 w m) granules, while the overflow stream contained only the smaller (< 10 w m) granules. In batch system, the hydrolysis behavior of wheat starch fractions was investigated under the action of Sigma f -amylase ( Bacillus licheniformis ), either as soon as they were prepared or after spray drying. The two fractions of fresh wheat starch showed different hydrolysis behavior, the difference getting larger as the separation improves. Underflow streams were found to be much more susceptible to hydrolysis than overflow streams, regardless of whether the hydrolysis was carried out right away or on dried samples, and also regardless of whether rinsing was applied. In flow system, dried underflow stream and commercialwheat starch were hydrolyzed using Orbamil-T ( Bacillus licheniformis ), Orbamil-BHT ( Bacillus stearothermophilus ), and Sigma f -amylase ( Bacillus licheniformis ). Hydrolysis of fresh starch was found to be significantly faster than commercial wheat starch. Commercial f -amylase Orbamil-T was found to be almost as effective as the purified Sigma f -amylase.     

Creating a reference data set for the summarization of discussion forum threads

In this paper we address extractive summarization of long threads in online discussion fora. We present an elaborate user evaluation study to determine human preferences in forum summarization and to create a reference data set. We showed long threads to ten different raters and asked them to create a summary by selecting the posts that they considered to be the most important for the thread. We study the agreement between human raters on the summarization task, and we show how multiple reference summaries can be combined to develop a successful model for automatic summarization. We found that although the inter-rater agreement for the summarization task was slight to fair, the automatic summarizer obtained reasonable results in terms of precision, recall, and ROUGE. Moreover, when human raters were asked to choose between the summary created by another human and the summary created by our model in a blind side-by-side comparison, they judged the model’s summary equal to or better than the human summary in over half of the cases. This shows that even for a summarization task with low inter-rater agreement, a model can be trained that generates sensible summaries. In addition, we investigated the potential for personalized summarization. However, the results for the three raters involved in this experiment were inconclusive. We release the reference summaries as a publicly available dataset.     

Participatory Irrigation Management and Transfer: Setting the Guiding Principles for a Sustaining Monitoring &amp; Evaluation System – a Focus on the Mediterranean

A major shortcoming of Participatory Irrigation Management and Irrigation Management Transfer (PIM/IMT) is the absence of Monitoring & Evaluation (M&E) systems that accompany these processes and become a major instrument to correct, improve and learn. Although at the global level some countries have exerted efforts to implement M&E systems, these still present limitations, as the review of the international experiences shows. The Mediterranean situation is even more dramatic since only Tunisia implements an M&E system, whereas Egypt has shyly moved in this direction with a limited practical application. This state of affairs led the authors to develop a set of guiding principles to develop an M&E system to be applied in countries where PIM/IMT is adopted. This paper revises the main international efforts devoted to assess the performance of PIM/IMT and the state of the art of these processes in Southern and Eastern Mediterranean Countries. Moreover, it sets the framework and analyses the main sustaining factors for the development of a new M&E system for these countries.     

Characterization of Biogenic Silica Generated by Thermo Chemical Treatment of Rice Husk

This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323 K for 180 min and then at 353 K for 60 min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well.