Influence of the biological fluid on the corrosion of dental amalgam

An electrochemical study of corrosion of Tytin^® dental amalgam was carried out in electrolytes similar to body fluids: artificial saliva with or without lactic acid, a polymer-containing product of the same composition as Glandosane^® and in Krebs-Ringer solution. The electrochemical techniques of open circuit potential, polarisation curves, cyclic voltammetry and electrochemical impedance were employed as a function of immersion time to characterise the surface processes occurring and bring out the differences between the different solutions. The influence of pH was tested in solutions of artificial saliva with or without lactic acid. The results demonstrated the importance of the organic component on the rate of corrosion and of adsorption phenomena on the amalgam surface.     

Synthesis and characterization of thermosensitive poly(N-isopropylacrylamide-co-hydroxyethylacrylamide) microgels as potential carriers for drug delivery

Thermoresponsive colloidal microgels were prepared by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and N-hydroxyethylacrylamide (HEAM) with various concentrations of a cross-linker in the presence of an anionic surfactant, sodium dodecylsulphate (SDS). The volume phase transition temperature (VPTT) of the prepared microgels was studied by dynamic light scattering (DLS), ultraviolet–visible spectroscopy (UV–vis) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. In addition, atomic force microscopy (AFM) was used to characterize the polydispersity and morphology of the microgels. Results indicated that poly(NIPAM-co-HEAM) microgels are spherical and monodisperse. VPTTs of microgels determined by DLS and UV–vis methods are almost the same and very close to the human body temperature, presenting the microgels as candidates for biomedical application. The temperature at which the phase transition occurred is nearly independent of the cross-linking density, whereas the transition range is deeply influenced by temperature. Also, the SDS concentration was increased to decrease the average hydrodynamic size of the microgels, due to the electrostatic repulsion between the charged particles during the polymerization process. ¹H-NMR spectra of the microgels show a decrease in peak intensity with an increased temperature due to a reduction in molecular mobility of the polymer segments. Release rates of propranolol from microgels are deeply influenced by temperature; below the VPTT at 25 °C, the drug is rapidly released at a rate comparable to that of a free drug, whereas above the VPTT (37 and 42 °C), a fraction of the drug is mechanically expulsed in the first five min, followed by a prolonged release.     

Teaching an automated agent to monitor the electrical power system of an orbital satellite

This paper illustrates an application of the Disciple knowledge acquisition methodology to build an intelligent adaptive agent for monitoring the electrical power system of an orbital satellite. This methodology is used by an expert to build and train an agent in much the same way that the expert would teach a human apprentice—by giving the agent specific examples of problems and solutions, explanations of these solutions, and supervising the agent as it solves new problems. During these interactions, the agent acquires general rules and concepts, continuously extending and improving its knowledge base. The agent learns by synergistically integrating the basic learning strategies: explanation-based learning, learning by analogy, and empirical inductive learning from examples. An important feature of Disciple-based agents is their ability to reason with incomplete and even partially incorrect information. The agent distinguishes between routine problems (problems it knows that it can solve correctly), innovative problems (problems to which it can recommend solutions, but for which it is not certain of the result), and creative problems (problems it is not able to solve). This allows the agent to solve a problem independently (for a routine problem), to ask confirmation of its solution (for an innovative problem), or simply to ask the expert to solve the problem (for a creative problem).     

Fuzzy Multicriteria Decision Aid Method for Conceptual Design

A general fuzzy multicriteria decision aid method for conceptual design is proposed. It is used for selecting the best compromise alternative, among a finite set of design concepts, considering environmental and economic performance. At the conceptual design phase most of the environmental impact is committed, whereas at that stage the design concepts are imprecisely defined and should be selected based on multiple, often conflicting criteria. Three vacuum cleaners, using different design principles for the dust storage, are analyzed. The best compromise design alternative is selected, considering trade offs between end-of-life profit and environmental criteria.     

Quad-band GSM/GPRS/EDGE polar loop transmitter

An enhanced data-rates for GSM evolution (EDGE) transmitter using a nonlinear GSM-type PA is presented. It is based on a novel polar loop architecture that employs separate feedback control of the amplitude and the phase of the output signal. With this approach, the problems with AM-to-PM as well as AM-to-AM of the nonlinear PA are essentially eliminated. In addition, this architecture allows for a large dynamic output power control range, as required by the GSM specification. The transmitter uses a standard I/Q interface and does not require the extraction of amplitude and phase modulation in the digital domain. The dual feedback loop ensures robust performance even under voltage-standing wave ratio variations without using an isolator. No external PA filtering is required to meet the transmitter noise in the receive band. The EDGE spectral mask is met with an rms error vector magnitude of <3% at 29 dBm at the antenna, corresponding to 2 dB above nominal maximum output power. There is no mode change between GMSK and EDGE, and the transmitter operates seamlessly in multislot Enhanced General Packet Radio Service. The polar modulation transmitter meets or exceeds the GSM-type approval requirements for both EDGE and GMSK in quad band (850/900/1800/1900 MHz).     

A system analysis of technological changes in the Romanian high voltage power network

Increasing demand for energy requires large-scale construction of power plants and adequate growth of the transmission network. Currently, several high-voltage transmission subsystems (110, 220, 400, 500, and 750 kV) coexist in the same network. We investigate the mechanism of substitution of voltage for the medium-size energy system in Romania by using the Marchetti-Nakicenovic model and Romanian data of the period 1965–1981. The horizon of our prediction is up to the year 2030.     

The effect of arginine on gold nanoparticles in colloidal solutions and in thin films

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.