A systematic method to create reaction constraints for stoichiometric matrices

Modeling rate-controlled chemically reactive systems in biocatalysis, fuel combustion, material science, and chemical process engineering involves the quantification and exploitation of interactions between many chemical species. These dynamic chemical systems, having relatively few limiting reactions, can be conceived as a series of snapshots where reactions have fixed extents but otherwise idle. Since the reactions affect the stoichiometric matrix of the internal constraints, such constrained equilibrium states cannot be defined in terms of conventional atomic mass balances.A systematic method for obtaining generalized equilibrium constraints for reaction mechanisms of arbitrary complexity is presented. Reaction matrices are converted into entity conservation matrices using row operations. The simultaneously introduced virtual components enable Gibbs energy calculations for complex reaction schemes including organic systems and enzyme-catalyzed biochemical transformations having multiple limiting reactions. Classical Gibbs energy minimization, which would otherwise readily model phase transformations and solvent interactions, is thereby made accessible to these emerging application fields.     

Hexaferrite/Polyester Composite Coatings for Electromagnetic-Wave Absorbers

Composite coatings, consisting of a ceramic barium hexaferrite and polyester, were manufactured by atmospheric plasma spraying. The crystalline structure of the barium hexaferrite was preserved during the spraying process while the polyester first (partly) melted and then resolidified. The high magnetic losses of the barium hexaferrite at mm-waves were coupled to the dielectric losses of the polyester in the composite coating and the superior electromagnetic absorption of the composite coating with respect to the pure materials was determined.     

Solubility and phase separation of poly(L,D‐lactide) copolymers

In this study, the solubility and precipitation properties of medical‐grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D ‐lactide) stereocopolymers was highly dependent on the L /D ratio of the copolymer. The phase‐separation ability was tested by cloud‐point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n‐hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n‐hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L /D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interband transitions and interference effects in superconducting qubits

We investigate phase-sensitive interference effects in a periodically sin(2π f _rf t)-driven, artificial two-state system connected to a microwave resonator at f _LC ? 800 MHz. We observe two kinds of multiphoton transitions in the two-state system, accompanied by: (1) Several quanta from the drive at f _rf and (2) one quantum at f _rf and several at f _LC . The former are described using phase-sensitive Landau–Zener transitions, while the latter are discussed in terms of vibronic transitions in diatomic molecules. Interference effects in the vibronic transitions governed by Franck–Condon coefficients are also considered.     

Primary and secondary context in mobile video communication

The new video capabilities of mobile phones are starting to change the field of mobile communication. It is now dramatically easier to publish video in quasi-real time. We discuss how this change will affect the way people perceive video-recording, in terms of privacy, transparency, and the notion of context. We use a model of primary and secondary contexts to analyze usage situations, highlighting newly relevant research issues.     

Selenium in Finnish foods after beginning the use of selenate-supplemented fertilisers

In Finland all agricultural multinutrient fertilisers have been supplemented with sodium selenate since 1984 in order to increase the selenium (Se) content of domestic foods and to raise the population's low Se intake. In the present study the Se contents of 125 food items, most of them produced locally but some imported, have been analysed using electrothermal atomic absorption spectrophotometry. The quality of Se analyses was verified by accuracy and precision measures of certified references and non-certified controls. In all cases the Se-supplemented fertilisation increased the Se levels of domestic agricultural products. The mean Se values (mg kg^?1 dry weight) in different food groups varied as follows: cereals 0.05–0.35; vegetables and fruit < 0.01,–1.20; meat and meat products 0.16–4.90; fish 0.54–3.80; dairy products and eggs 0.05–1.30; and ready to eat foods 0.04–0.78. The highest Se contents were in kidney, liver and roe whereas the lowest concentrations were found in some fruits and berries. Generally, foods of high protein content, such as meat, fish and high protein dairy products, were abundant sources of Se. The present Se intake, calculated according to Finnish national food statistics and the present results, is about 0.11 mg day^?1 at an energy level of 10 MJ (2400 keal). Cereals, meat, dairy products, eggs and fish, respectively, contributed 26%, 29%, 20%, 10% and 9% of the total intake. The Se intake now very probably meets the recommendations. Only diets with a very exceptional composition provide less than 0.05 mg or more than 0.2 mg per 10 MJ.     

Modelling of airborne dust emissions in CNC MDF milling

All dust control measures are necessary to reduce dust exposure in MDF (Medium Density Fibreboard)-milling, because of the high amount and fineness of the dust produced and a potential risk of exposure to formaldehyde or other glue chemicals during the machining of MDF. The most effective way of reducing dust exposure is to reduce the emission of dust at the source. Airborne dust emission was studied and modelled in the milling. In the milling of MDF, airborne dust emission was much higher than in the milling of solid materials. Milling of MDF produced airborne particles with a mass median diameter of 6–7 µm. The most significant factor affecting the amount of dust created from milling was average chip thickness. In order to reduce the amount of dust, milling parameters should be chosen so that the average chip thickness is greater than 0.05 mm. The average chip thickness could be obtained with different milling parameters, for example with different combinations of feed and traverse rates. The same chip thicknesses resulted in around the same percentage fraction of fine dust mass regardless of how the average chip thickness was obtained. The relationship between the percentage fraction of fine dust mass from the removed mass (c_%) and the chip thickness (h_m) was modelled and presented in the form of c_% = 0.194 h _m ^-1. The model developed can be used to estimate the percentage fraction of fine dust mass as a function of chip thickness. The model can be used in optimisation programs for CNC milling machines to minimize the airborne dust generated and to reduce dust exposure.     

Calculation of constrained equilibria by Gibbs energy minimization

The Gibbs energy minimization encompasses active use of the chemical potentials (partial molar Gibbs energies) of the constituents of the system. Usually, these appear at their equilibrium values as a result of the minimization calculation, the mass balance constraints being the necessary subsidiary conditions. Yet, there are several such physico-chemical circumstances where the system is also constrained by other factors, such as surface effects, potential fields or even by chemical reaction kinetics. In this paper a particular method is presented by which constrained chemical potentials can be applied in a multi-phase Gibbs energy minimization. The constrained potentials arise typically from work-related thermodynamic displacements in the system. When Gibbs energy minimization is performed by the Lagrange method, these constraints appear as additional Lagrangian multipliers. Examples of the constrained potential method are presented in terms of the electrochemical Donnan equilibria in aqueous systems containing semi-permeable interfaces, the phase formation in surface-energy controlled systems and in systems with affinities controlled by chemical reaction kinetics. The methods have been applied successfully in calculating distribution coefficients for metal ions together with pH-values in pulp suspensions, in the calculation of surface tension of alloys, and in thermochemical process modeling involving chemical reaction rates.     

Effect of process parameters on properties of wet‐spun poly(L,D‐lactide) copolymer multifilament fibers

Poly(L,D ‐lactide) [P(L,D )LA], LL/D ratio 96/4, and poly(L,DL ‐lactide) [P(L,DL )LA], L/DL ratio 70/30, multifilament fibers were prepared by wet‐spinning and the effects of the spin draw ratio and the coagulant on the morphological, thermal, and mechanical properties of the filaments were studied. The hydrolytic degradation of filaments was studied in vitro. The filament diameter and the mechanical properties of filaments were highly dependent on the spin draw ratio, whereas the coagulant had no or minor effect. The filament diameters were in the range of 11–36 μm and the maximum tenacity of 150 MPa was obtained at the spin draw ratio of 7.0 for both copolymers. The copolymer had the main importance on the crystallinity of filaments, but it was also affected by the duration of the coagulation process. The crystallinities of P(L,D )LA 96/4 filaments were in the range of 5–16%, whereas P(L,DL )LA 70/30 filaments were totally amorphous. The degree of crystallinity had effect on the hydrolytic degradation of filaments. The tenacity loss of P(L,D )LA 96/4 filaments was about 10% and that of P(L,DL )LA 70/30 filaments was as high as 50% after 24 weeks in vitro. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Shear-load carrying capacities of the distal rat femora after osteotomy fixed with self-reinforced polyglycolic acid and poly-L-lactic acid pins

Distal femora of 40 rats were osteotomized and fixed with self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) pin 2.0 mm in diameter and 15 mm in length. The shear-load carrying capacities of the osteotomized bones were compared with each other and with the intact control rat distal femora of the same age of 20 pairs. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities reached their highest values at 24 weeks in the SR-PGA-fixed specimens, after that decreasing to the level where they remained. In the SR-PLLA-fixed specimens the strength values of the pins increased after three weeks, but there was a decrease at 24 weeks. After that the shear-load carrying capacities started to raise because of the influence of the healed osteotomy. In the control bones the shear-load carrying capacities were weaker than in the SR-PGA-and SR-PLLA-fixed specimens except at three weeks, as the osteotomies had not yet healed. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA-fixed specimens was 199.1 N, in the SR-PLLA-fixed specimens 214.6 N, the corresponding value of the control specimens being 148.2 N.