The Effect of Different Polishing Sequences on the Adhesion of Streptococcus mutans to Feldspathic Porcelain

The aim of this research was to determine whether extra-oral surface treatments on feldspathic porcelain surfaces influence initial adhesion of Streptococcus mutans. Ninety-six porcelain specimen discs were fabricated and divided into six equal groups according to surface treatment: fine-grit diamond polishing (Group 1); self-glazing (Group 2); overglazing (Group 3); overglazing followed by a finishing procedure and then overglazing (Group 4); Pearl Surface polishing (Group 5); and Diamond Twist SCL^TM polishing (Group 6). Surface roughness and hydrophobicity were assessed. An S. mutans suspension was incubated on each specimen group and evaluated. A one-way analysis of variance, post-hoc Tukey honestly significantly different test, Friedman test, and t-test were used for statistical analysis. Group 1 showed the highest surface roughness (p < 0.001) and bacterial adhesion (p < 0.05). Groups 5 and 6 specimen surfaces presented significantly higher contact angles (p < 0.05). Group 1 had the highest S. mutans adhesion, followed by Groups 3, 5, 6, 2, and 4 (p < 0.05). Reglazing after grinding may therefore decrease bacterial adhesion beneficially.     

Formation of dynamic virtual enterprises and enterprise networks

This paper addresses the preparation and set up of virtual enterprises and enterprise networks. A virtual enterprise (VE) can be perceived as a customer solution delivery system created by a temporary and re-configurable information and communications technology (ICT) enabled aggregation of competencies. The main achievements of the research include: (1) Clarification and definition of the concept for virtual enterprises and enterprise networks including preparation of these. (2) Development of a framework and a reference architecture for virtual enterprises named as Structured Methodology and ICT Reference Architecture respectively. Structured methodology structures the body of knowledge related to preparation, setup, and operation of virtual enterprises and enterprise networks. ICT reference architecture consists of three levels with seven layers to portray in a diagrammatic fashion how different enterprises may exchange and use information between their respective organizations’ specific proprietary systems and a central server. (3) Development of a methodology for virtual enterprise named as virtual enterprise methodology (VEM). VEM consists of a set of guidelines, which systematically describes activities that enterprises should consider in relation to set up and preparation of own enterprise networks with the aim to set up virtual enterprises. (4) Testing and validation of the developed VEM with the realization of a virtual case study. Virtual case study demonstrates and validates the application of the developed VE methodology with the illustration of the key activities related to setting up breeding environment, setting up and operating VE and dissolution of VE.     

Subsurface mechanoelectromagnetic phenomena in thermoelastic polarized bodies in the case of local displacements of mass

We deduce a complete system of relations of electromagnetothermomechanics of conducting polarized media with regard for the local displacements of masses. It is shown that the set of conjugated parameters specifying the equilibrium thermodynamic state, parallel with temperature and entropy, the strain and stress tensors, electric-field intensity, and polarization, includes two couples of new parameters, namely, the induced mass and the energy measure μ′_π of the influence of the displacement of masses on the internal energy and the vector of displacement of masses and the space gradient of the energy measure μ′_π appearing if we take into account the local displacements of masses The indicated extension of the space of parameters of state enables us to describe the subsurface inhomogeneity of the stress-stain state and electric polarization, as well as the formation of the surface charge and electromagnetic signal in the process formation of a new surface. The relations obtained with regard for the indicated parameters can be used for the investigation of the electromagnetic emission accompanying the process of formation of new surfaces in the body or the electromagnetic response to the action of external forces. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 5–17, July–August, 2007.     

Bio-methanization of energy crops through mono-digestion for continuous production of renewable biogas

The aim of this laboratory-scale study was to investigate the long-term anaerobic fermentation of an extremely sour substrate, an energy crop, for continuous production of methane (CH₄) as a source of renewable energy. The sugar beet silage was used as the mono-substrate, which had a low pH of around 3.3–3.4, without the addition of manure. The mesophilic biogas digester was operated in a hydraulic retention time (HRT) range between 15 and 9.5 days, and an organic loading rate (OLR) range of between 6.33 and 10 g VS l⁻¹ d⁻¹. The highest specific gas production rate (spec. GPR) and CH₄ content were 0.67 l g VS⁻¹ d⁻¹ and 74%, respectively, obtained at an HRT of 9.5 days and OLR of 6.35 g VS l⁻¹ d⁻¹. The digester worked within the neutral pH range as well. Since this substrate lacked the availability of macro and micro nutrients, and the buffering capacity as well, external supplementation was definitely required to provide a stable and efficient operation, as provided using NH₄Cl and KHCO₃ in this case. The findings of this ongoing long-term fermentation of an extremely acidic biomass substrate without manure addition have reflected crucial information about how to appropriately maintain the operational and particularly the environmental parameters in an agricultural biogas plant.     

A Lagrangean heuristic for integrated production and transportation planning problems in a dynamic, multi-item, two-layer supply chain

We present a Lagrangean-based decomposition that is used to generate solutions for an integrated production and transportation planning problem in a two-stage supply chain. This supply chain consists of a number of facilities, each capable of producing the final products, and a number of retailers. It is assumed that the retailers' demands are known and deterministic, and that there are production capacity constraints. The problem is formulated as a multi-commodity network flow problem with fixed charge costs which is a NP-hard problem. An alternative formulation is provided whose linear programming relaxation gives tighter lower bounds. The quality of the lower and upper bounds from the Lagrangean decomposition is tested on a large set of randomly generated problems.     

Numerical research of cavitation on Francis turbine runners

Francis turbines, as other hydraulic turbines, are custom-designed for nominal operating conditions specific to each power plant. However, they may need to be operated at off-design flow conditions because of variable reservoir levels and flowrates. Operating the turbine at off-design points can cause cavitation. Four cavitation types can be observed on Francis turbine runners. These are leading edge, travelling bubble, draft tube swirl and inter-blade vortex cavitation. They may cause erosion, reduction in efficiency, vibration, instability of operation and noise. Runner blades must be designed taking the flow characteristics into account for design conditions to prevent cavitation. Cavitation limits for the off-design points must also be determined. In this study, the runner geometry of an actual hydroelectric power plant that was designed and implemented in 1960s, is redesigned with the help of the state of the art computational fluid dynamics techniques for cavitation free operation. The cavitation limits for the off-design points are also determined.     

Defect prediction from static code features: current results,limitations, new approaches

Building quality software is expensive and software quality assurance (QA) budgets are limited. Data miners can learn defect predictors from static code features which can be used to control QA resources; e.g. to focus on the parts of the code predicted to be more defective.     

Exploring the role of stearic acid in modified zinc aluminum layered double hydroxides and their acrylonitrile butadiene rubber nanocomposites

The proposed study attempted to explore the role of stearic acid modification on the properties of zinc‐aluminum based layered double hydroxides (LDH) and their composites with acrylonitrile butadiene rubber (NBR). Three distinctive LDH systems were adapted for such comparison; an unmodified LDH and two stearic acid modified LDH. The use of zinc oxide and stearic acid in the rubber formulation was avoided as the modified LDH would be able to deliver the necessary activators for the vulcanization process. Emphasis was predominantly given to reconnoiter the merits of stearic acid modification on the increase in interlayer distance of the LDH. X‐ray diffraction studies and transmission electron microscope morphological investigations of LDH powders indicated that modification with stearic acid increased the interlayer spacing which would favor the intercalation of NBR polymer chains into the layered space. However, stress–strain studies indicated better mechanical properties for composites with unmodified LDH. Composites with LDH showed higher crosslinking densities than conventionally sulfur cured control compounds using zinc oxide/stearic acid as activators. This was evident from equilibrium swelling method as well as statistical theory of rubber elasticity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41539.