Synthesis of polyacrylamide flocculants with poly(ethylene glycol) segments by redox polymerization

The polymerization of acrylamide (AAm) initiated by polyazoesters (PAE) possessing poly(ethylene glycol) (PEG) segments and azo functions was investigated in aqueous solution at 70°C. Polymerization of AAm initiated by PAE yields polymers with PEG segments and appropriate hydroxy functions for the subsequent redox polymerization. Polymerization of AAm induced by these polymers in conjunction with Ce(IV) provided increase in the molecular weight of the initial polymer without formation of insoluble polymer. The water-soluble polymers obtained at various stages were tested in the flocculation of suspension of tincal concentrate and showed good flocculating properties.     

The effect of bulk-fill flowable composites on the fracture resistance and cuspal deflection of endodontically treated premolars

The aim of this study was to evaluate the effect of bulk-fill flowable composites on cuspal deflection and fracture resistance of endodontically treated teeth. Forty-two maxillary premolars were subjected to endodontic treatment followed by the preparation of mesioocclusodistal cavities. Teeth were divided into six groups according to restorative materials as follows: Group 1: Clearfil Majesty Flow and Clearfil Majesty Posterior; Group 2: Venus Bulk Fill and Clearfil Majesty Posterior; Group 3: Clearfil Majesty Posterior; Group 4: Vertise Flow and Clearfil Majesty Posterior; Group 5: SDR and Clearfil Majesty Posterior; and Group 6: x-tra base and Clearfil Majesty Posterior. A single-step self-etch adhesive (OptiBond All-in-One) was applied to all groups, except Group 4. The cavities were restored with a centripetal incremental insertion technique and flowable composites using a 2-mm-thick base material, except for Group 3. The distance between cusp tips was measured before and after the cavity preparations, after the restorations, and after thermal cyclus with a digital micrometer. After measuring, each tooth was subjected to compressive loading with a stainless steel ball (4 mm diameter) perpendicular to the occlusal surface with a crosshead speed of 1 mm/min, and mean loads necessary to fracture were recorded in Newtons. The data were statistically analyzed by Kruskal–Wallis test. No statistically significant differences were found between groups in fracture strength or cuspal deflections (p > 0.05). Bulk-fill flowable composite bases did not change the cuspal deflection or fracture resistance of endodontically treated teeth, compared with that of a conventional flowable base and conventional resin composite.     

Production of oil-based binder by RAFT polymerization technique

In this study, air-blown linseed oil was styrenated by reversible addition–fragmentation chain transfer polymerization (RAFT). For this purpose, hydroperoxide groups were formed in the structure of linseed oil by blowing air through it. The oxidized oil was used as a macroinitiator in the styrenation process by RAFT technique using phenacyl morpholine dithiocarbamate (PMDC) as a RAFT agent. The obtained samples were characterized by GPC and FT-IR measurements. The effects of various parameters, such as the amount of PMDC, the number of peroxide groups, and the reaction time were investigated on polydispersity and molecular weight. For comparison, a copolymer sample was also prepared in the absence of PMDC. The film properties of all the samples were determined according to the related standards and compared. The sample obtained by the RAFT technique exhibited better film properties and a relatively narrow polydispersity, showing that the RAFT technique provides good control over the polymerization system in this study.     

On dielectric data analysis. Using the Monte Carlo method to obtainrelaxation time distribution and comparing non-linear spectral functionfits

In this paper, we present a technique for analyzing dielectric response data in the frequency domain, χ(ω)=ϵ(ω)-ϵ_∞ =ϵ'(ω)-ϵ_∞-iϵ(ω). We use a predistribution of relaxation times and reconstruct the original data by single Debye relaxations using a box constraint, least squares algorithm. The resulting relaxation times τ(D_i) and their amplitudes Δϵ_i,, yield the relaxation time spectrum, where i is equal or less than the number of data points. Two different predistributions of relaxation times are considered, log-uniform and adaptive. The adaptive predistribution is determined by the real part of the dielectric susceptibility χξ', and it allows for the increase of the number of effective relaxation times used in the fitting procedure. Furthermore, since the number of unknowns is limited to the number of data points, the Monte Carlo technique is introduced. In this way, the fitting procedure is repeated many times with randomly selected relaxation times, and the number of relaxation times treated in the procedure becomes continuous. The proposed method is tested for `ideal' and measured data. Finally, the method is compared with a nonlinear curve fitting by a spectral function which consists of three contributions, i.e. the Havriliak-Negami relaxation polarization, low frequency dispersion and de conductivity. It has been found that more information can be obtained from a particular data set if it is compared with a nonlinear curve fitting procedure. The method also can be used instead of the Kramers-Kronig transformation     

Nonsimilar boundary layers on the leeside of cones at incidence

It is known that the similarity equations for the leeward line of symmetry of a cone have no solutions for $\text{?1 < k}{}_2{}^1\text{< k < k}{}_1\text{1 < 0}$, where k is the incidence parameter of Moore, and $\text{k}{}_1{}^1\text{, k}{}_2{}^1$ depend on the external Mach number and enthalpy ratio. In this paper we present evidence that a leeside integration for such k terminates at a finite distance from the vertex in a singularity of the type analyzed by Stewartson and Simpson for entry flow in a curved pipe, and compare the theory with a representative numerical solution at $\text{k = ?}\text{1}\text{2}$. A possible interpretation of this singularity is that the boundary layers growing from the windward line of symmetry have collided, and support for this view is given by windward to leeward integrations for a range of values of k. For k such that the similarity equations have solutions, these are interpreted as limits of more general solutions.     

An Integration Algorithm for Constitutive Models with Two Intersecting Yield Surfaces

Abstract: In this paper, the constitutive models involving two active intersecting yield surfaces, such as Lade's model, are considered and a new integration algorithm is formulated. The formulation introduces a new class of the return mapping algorithm within the framework of the operator splitting methodology. The proposed algorithm is applicable to a general class of elastoplastic constitutive models exhibiting associative or nonassociative flow rule, arbitrary yield criteria and hardening laws. The algorithm can handle one or two active yield surfaces at a time. The development leads to a relatively simple, straightforward algorithm for updating the stresses at Gauss point.
Finally, the new algorithm is implemented in a generalized nonlinear finite element computer program incorporating Lade's model. The results of a number of boundary value problems are presented and compared with available experimental data and theoretical formulas. The comparisons indicate that incorporating the new class of return mapping algorithm gives reasonable solutions.     

Determination of antibiotic susceptibility and decarboxylase activity of coagulase‐negative Staphylococcus and Macrococcus caseolyticus strains isolated from fermented Turkish sausage (sucuk)

The aim of this research was to detect antibiotic susceptibility patterns and amino acid decarboxylase activity of 61 presumptive coagulase‐negative Staphylococcus (CNS) strains from the Turkish dry fermented sausage (sucuk). The presumptive CNS strains were identified at species levels as 21 S. saprophyticus, 16 S. epidermidis, 10 Macrococcus caseolyticus, 4 S. xylosus, 3 S. sciuri, 2 S. hominis, 2 S. warneri, 1 S. cohnii, 1 S. pasteuri, and 1 S. vitulinus by 16S rDNA sequence analysis. S. saprophyticus and S. epidermidis species were found highly resistant to antibiotics than other species. In addition, most of the CNS and M. caseolyticus strains showed multiple antibiotic resistance profiles. None of the CNS and M. caseolyticus strains did not decarboxylate histidine, lysine, or ornithine, but only three CNS strains produced tyramine from tyrosine. A 100% correlation was found between the presence of tdc gene and tyramine production in tyraminogenic strains.

Practical applications

Coagulase‐negative Staphylococcus (CNS) strains play an important role in production of traditional fermented sausages such as sucuk. In this study, S. saprophyticus and S. epidermidis were found the most common isolated CNS species from sucuk. Antibiotic resistance was detected widespread in CNS and M. caseolyticus strains. Most of the CNS strains were found resistant to clinically relevant antibiotics. Antibiotic resistance strains may be dangerous for consumer health. These strains can be a potential reservoir to spread of antibiotic resistance gene between staphylococci and other species of bacteria. In addition, biogenic amine production was not found widespread in CNS strains.     

Pore structure of air-entrained hardened cement paste

The effect of air entrainment on the pore structure of hardened cement paste was investigated. Air-entrained and air-free samples of various water-cement ratios and ages were prepared by a well-defined procedure. The first and second-intrusion pore-size distribution curves of the samples were determined by mercury intrusion porosimetry. It was observed that sample preparation technique affects the pore-size distributions of hardened cement pastes. The second-intrusion curves indicated a decrease in the total volume and a reduction in the size of pores that are uniform in cross section with decreasing age and water: cement ratio. The second-intrusion curves of air-entrained and air-free pastes of equal water: cement ratio and age matched with each other. It was concluded that air entrainment introduces only large air voids observable by a naked eye and does not alter the characteristic fine pore structure of hardened cement paste appreciably.     

A novel anti islanding detection method for grid connected fuel cell power generation systems

Renewable energy sources have been developed rapidly all around the world, and one of these green energy sources is hydrogen energy. The fuel cell systems have become prominent in renewable energy sources because of its minimal dimensions and energy conversion method. There have been developed, some applications, especially in domestic and automotive areas, and fuel cell systems are also have been started to use in grid connected systems. Fuel cell systems must have some electrical connection standards while they connected to an electrical grid. One of these electrical conditions and may be the most important one is unplanned islanding condition. Islanding is a very dangerous situation because it can damage to the fuel cell and related electrical systems and also working people have been at risk in islanding situation on the grid. In this study, a novel islanding detection method was introduced for grid connected fuel cell systems. 0.5 kW solid oxide fuel cell (SOFC) system used in developed experimental system and a novel anti islanding detection method was researched by using an effective method. The proposed method was also developed by using Matlab Simulink and its useful tools. The developed islanding detection method is robust, reliable and has a fast response time, according to present methods. The results confirm the suggested conditions, and it can be seen in this method, it can also be adapted easily to the grid connected fuel cell systems.