The aim of this study was to evaluate the possibility of preparing starch-based porous matrixes using supercritical fluid technology. Supercritical immersion precipitation technique was used to prepare scaffolds of a polymeric blend of starch and poly(l-lactic acid) for tissue engineering purposes.Immersion precipitation experiments were carried out at different operational conditions and highly porous and interconnected scaffolds were obtained. Two organic solvents, dichloromethane and chloroform were tested, and from the results obtained chloroform was the more favourable for the process. The effect of polymer solution concentration (5 up to 20 wt{%}), temperature (35 up to 55 °C) and pressure (100 up to 200 bar) in the SPLA (50:50 wt{%}) membrane morphology, porosity and interconnectivity was evaluated. All the conditions tested were in the region of total miscibility between the organic solvent and carbon dioxide. Additionally, a blend with a different starch-poly(l-lactic acid) ratio (30:70 wt{%}) was tested. Bicontinuous structures were formed indicating that the L-L demixing process that governs the phase inversion is the spinodal decomposition. © 2008 Elsevier B.V. All rights reserved.

The aim of this study was to develop a new process for the production of bioactive 3D scaffolds using a clean and environmentally friendly technology. The possibility of preparing composite scaffolds of Bioglass?? and a polymeric blend of starch and poly(l-lactic acid) (SPLA50) was evaluated. Supercritical phase-inversion technique was used to prepare inorganic particles loaded starch-based porous composite matrixes in a one-step process for bone tissue engineering purposes. Due to their osteoconductive properties some glasses and ceramics are interesting materials to be used for bone tissue engineering purposes; however their poor mechanical properties create the need of a polymeric support where the inorganic fraction can be dispersed. Samples impregnated with different concentrations of Bioglass?? (10 and 15{%} wt/wt polymer) were prepared at 200??bar and 55????C. The presence of Bioglass?? did not affect the porosity or interconnectivity of the polymeric matrixes. Dynamic mechanical analysis has proven that the modulus of the SPLA50 scaffolds increases when glass particles are impregnated within the matrix. In vitro bioactivity studies were carried out using simulated body fluid and the results show that a calcium-phosphate layer started to be formed after only 1??day of immersion. Chemical analysis of the apatite layer formed on the surface of the scaffold was performed by different techniques, namely EDS and FTIR spectroscopy and X-ray diffraction (XRD). The ion concentration in the simulated body fluid was also carried out by ICP analysis. Results suggest that a bone-like apatite layer was formed. This study reports the feasibility of using supercritical fluid technology to process, in one step, a porous matrix loaded with a bioactive material for tissue engineering purposes. ?? 2009 Elsevier B.V. All rights reserved.

Over the past several years, the definition of a scaffold for tissue engineering has changed dramatically, from a material that acts only as an inert structural support for cell attachment to serving as a more complex and dynamic environment for tissue development. This paper is a review on the existing and on the new emerging techniques based on supercritical fluid technology for the preparation of scaffolds and particles for tissue engineering applications. Supercritical fluid technology has already proven to be feasible for many pharmaceutical applications and is now emerging as an alternative to conventional materials' processing methods for the preparation of three-dimensional structures and injectable particles suitable to be used in regenerative medicine. The basic principles underlying each technique are here presented as well as the advantages and disadvantages of each process. The state of the art is reviewed and the major conclusions of the studies reported in the literature are discussed.

The multicopper enzyme nitrous oxide reductase (N2OR) catalyzes the final step of denitrification, the two-electron reduction of N2O to N-2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome C-552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared [cytochrome vs methylviologen (MV)]. In the presence of cytochrome c(552), the reaction rate is dependent on the ET reaction and independent of the N2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c(552) concentration dependence, we estimate the following kinetic parameters: K-mc512 = 50.2 +/- 9.0 mu M and V-maxc551 1.8 +/- 10.6 units/mg. The N2O concentration dependence indicates a K-mN2O of 14.0 +/- 2.9 mu M using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c(552) is used as the electron donor (pK(a) = 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by H-1 NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c(552) is placed near a hydrophobic patch located around the CuA center.

Adenylate kinase (AK) mediates the reversible transfer of phosphate groups between the adenylate nucleotides and contributes to the maintenance of their constant cellular level, necessary for energy metabolism and nucleic acid synthesis. The AK were purified from crude extracts of two sulfate-reducing bacteria (SRB), Desulfovibrio (D.) gigas NCIB 9332 and Desulfovibrio desulfuricans ATCC 27774, and biochemically and spectroscopically characterised in the native and fully cobalt- or zinc-substituted forms. These are the first reported adenylate kinases that bind either zinc or cobalt and are related to the subgroup of metal-containing AK found, in most cases, in Gram-positive bacteria. The electronic absorption spectrum is consistent with tetrahedral coordinated cobalt, predominantly via sulfur ligands, and is supported by EPR. The involvement of three cysteines in cobalt or zinc coordination was confirmed by chemical methods. Extended X-ray absorption fine structure (EXAFS) indicate that cobalt or zinc are bound by three cysteine residues and one histidine in the metal-binding site of the ``LID{''} domain. The sequence (129)Cys-X(5)-His-X(15)-Cys-X(2)-Cys of the AK from D. gigas is involved in metal coordination and represents a new type of binding motif that differs from other known zinc-binding sites of AK. Cobalt and zinc play a structural role in stabilizing the LID domain. (C) 2008 Elsevier Inc. All rights reserved.

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Software transactional memory (STM) is a promising programming model that adapts many concepts borrowed from the databases world to control concurrent accesses to memory (RAM) locations. In this paper we propose a new classification for the active states of a transaction; a new memory quiescing algorithm, to allow the safe transition of a memory block form transactional to non-transactional space; we compare word and object transactional grain units; and evaluate the cost of consistent state validation, arguing that this cost can be minimized by performing partial validation on problematic code regions.

Software transactional memory (STM) is a promising programming model that adapts many concepts borrowed from the databases world to control concurrent accesses to memory (RAM) locations. In this paper we propose a new classification for the active states of a transaction; a new memory quiescing algorithm, to allow the safe transition of a memory block form transactional to non-transactional space; we compare word and object transactional grain units; and evaluate the cost of consistent state validation, arguing that this cost can be minimized by performing partial validation on problematic code regions.

This paper presents the mobile technology utilization in improving the remote access to the data acquisition processes of several automated monitoring system for air quality, water quality, and crop canopy microclimate. The system facilitates mobile environmental management and decision making by using in-situ measurements, GSM/GPRS informational fluxes, Pocket PCs, dGPS and mobile GIS resources. Data is retrieved via GSM/GPRS data modem to remote computer using digital (GSM) phone network. The main outcomes of this study were as follows: 1. designing the hardware, communication and software infrastructure of the system using telemetry features, 2. establishing the wireless connections and remote access from PDAs to the measurement servers, 3. programming and testing specific control virtual instruments (Vis) in NI LabVIEWTM, 4. obtaining a portable solution of statistical analysis and survey with PDA Vi (Virtual Instruments) interfaces for Pocket PC to gather, store, customize and report data combined with statistical processing functions, and 5. identifying mobile GIS applications for the environmental protection. The remote-accessing of the GIS server features, provided in-situ electronically reviews, mark up, and precise measurements of the site pollution plans. One possible solution to overcome the PDA hardware and software restraints is enabling the remote access and control of the DAQ and GIS software resources of the measurement server via internet.

Software transactional memory is a promising programming model that adapts many concepts borrowed from the databases world to control concurrent accesses to main memory (RAM). This paper discusses how to support revertible operations, such as memory allocation and release, within software libraries that will be used in software memory transactional contexts. The proposal is based in the extension of the transaction life cycle state diagram with new states associated to the execution of user-defined handlers. The proposed approach is evaluated in terms of functionality and performance by way of a use case study and performance tests. Results demonstrate that the proposal and its current implementation are flexible, generic and efficient

Software transactional memory (STM) is a promising programming model that adapts many concepts borrowed from the databases world to control concurrent accesses to main memory (RAM) locations. This paper aims at discussing how to support apparently irreversible operations within a memory transaction.

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The characterization of the bottom ashes produced by two Portuguese municipal solid waste incinerators (MSWI) was performed with the aim of assessing the feasibility of using this waste as raw material in the production of glass that can be further processed as glass-ceramics for application in construction. Density and particle size distribution measurements were carried out for physical characterization. Chemical characterization revealed that SiO2, a network glass former oxide, was present in a relatively high content (52-58 wt%), indicating the suitability for this waste to be employed in the development of vitreous materials. CaO, Na2O and K2O, which act as fluxing agents, were present in various amounts (2-17 wt%) together with several other oxides normally present in ceramic and glass raw materials. Mineralogical characterization revealed that the main crystalline phases were quartz (SiO2) and calcite (CaCO3) and that minor amounts of different alkaline and alkaline-earth aluminosilicate phases were also present. Thermal characterization showed that the decomposition of the different compounds occurred up to 1100 °C and that total weight loss was <10 wt%. Heating both bottom ashes at 1400 °C for 2 h resulted in a melt with suitable viscosity to be poured into a mould, and homogeneous black-coloured glasses with a smooth shiny surface were obtained after cooling. The vitrified bottom ashes were totally amorphous as confirmed by X-ray diffraction. The results from the present experimental work indicate that the examined bottom ashes can be a potential material to melt and to obtain a glass that can be further processed as glass-ceramics to be applied in construction. © 2007 Elsevier Ltd. All rights reserved.

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There is a sustained interest both from theoretical and from practical points of view to understand the isothermal charging and the isothermal discharging currents in dielectrics. The measured currents are analyzed either in terms of polarization mechanisms or in terms of charge injection/extraction at the metal-dielectric interface and the conduction current through the dielectric material. As long as we do not know the nature of the origin of the current, it is not clear what information we can get by analyzing the experimental data. We propose to measure the open-circuit isothermal charging and discharging currents just to overpass the difficulties related to the analysis of the conduction mechanisms in dielectric materials. We demonstrate that besides a polarization current, there is a current related with charge injection or extraction at the metal-dielectric contact and a reverse current related to the charge trapped into the superficial trap states of the dielectric and that can jump at the interface in a reverse way. An analytical expression for the current is proposed. By fitting the experimental data to this analytical equation, two important parameters can be determined: (i) the highest value of the relaxation time for the polarization mechanisms still involved into the transient current and (ii) the height of the potential barrier W-0 at the metal-dielectric interface at the initial time when the step voltage is applied. The value obtained for Al-polyethylene terephthalate interface is (0.43 +/- 0.02) eV. For a charging voltage of 220 V there are 6x10(14) trapped electrons/m(2). (c) 2008 American Institute of Physics.

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