Direct computation of solution spaces

In engineering, it is often desirable to find a subset of the set of feasible designs, a solution space, rather than a single solution. A feasible design is defined as a design which does not violate any constraints and has a performance value below a desired threshold. Performance measure, threshold value and constraints depend on the specific problem. For evaluation of a design with respect to feasibility, a model is required which maps the design parameters from the input space onto the performance measures in the output space. In state-of-the-art methodology, iterative sampling is used to generate an estimate of the frontier between feasible and infeasible regions in the input space. By evaluating each sample point with respect to feasibility, areas which contain a large fraction of feasible designs are identified and subsequently resampled. The largest hypercube containing only feasible designs is sought, because this results in independent intervals for each design parameter. Estimating this hypercube with sufficient precision may require a large number of model evaluations, depending on the dimensionality of the input space. In this paper, a novel approach is proposed for modeling the inequality constraints and an objective function in a way for which a linear formulation can be used, independently of the dimensionality of the problem. Thereby the exact solution for the largest feasible hypercube can be calculated at much lower cost than with stochastic sampling as described above, as the problem is reduced to solving a linear system of equations. The method is applied to structural design with respect to the US-NCAP frontal impact. The obtained solution is compared to numerical solutions of an identical system, which are computed using reduced order models and stochastic methods. By this example, the high potential of the new direct method for solution space computation is shown.     

Photoinduced Tetrazole‐Based Functionalization of Off‐Stoichiometric Clickable Microparticles

We report the preparation of tetrazole‐containing step‐growth microparticles and the subsequent use of photoinduced nitrile imine‐mediated tetrazole‐ene cycloaddition (NITEC) reactions on the particles with spatiotemporal control. Microparticles with an average diameter of 4.1 µm and with inherent tetrazole‐ene dual functionality are prepared by a one‐pot off‐stoichiometric thiol‐Michael addition dispersion polymerization. The NITEC reaction is performed efficiently in the solid phase by UV irradiation, leading to the formation of fluorescent pyrozoline adducts, with an estimated quantum yield of 0.7. Particle concentration‐independent reaction kinetics are observed and full conversion is reached within 10 min of UV exposure at an intensity of 8 mW cm^?2. Temporal control is demonstrated with either UV or rooftop sunlight irradiation of variable duration. By using two‐photon writing with a laser centered around 700 nm wavelength, spatial control is demonstrated with micrometer‐scale resolution via surface patterning of the microparticles. Further, microparticles with exclusive tetrazole functionality are prepared by a one‐pot, two‐step thiol‐Michael addition dispersion polymerization. The NITEC reaction between tetrazole‐functional particles and acrylates in solution is examined at various tetrazole/alkene molar ratios, and a 10:1 excess of alkenes in solution is found necessary for efficient functionalization.     

Determinants of nitrogen surplus at farm level in Swiss agriculture

This paper investigated the determinants of nitrogen surplus, also denoted as nitrogen balance, at farm level in Swiss agriculture. Our analysis was based on a cross-section of 210 farms from the year 2010. The nitrogen surplus of each farm was estimated according to the OECD soil-surface approach and decomposed in two components—nitrogen intensity and nitrogen inefficiency. The average nitrogen surplus of the farms investigated amounted to 89 kg/ha, resulting from an average nitrogen intensity of 255 kg/ha and an average nitrogen inefficiency of 34%. The determinants of nitrogen surplus and its two components were analyzed by means of a three-equation regression model estimated using a robust seemingly unrelated regression approach. Farm size, part-time farming, organic farming, arable cropping and farmer’s age were found to decrease nitrogen surplus, whereas dairy, pig and poultry farming were associated with an increase in nitrogen surplus.     

Struktursynthese und Optimierung nichtidealer Rektifizierprozesse

Optimization processes with MINLP are inherently capable of dramatically reducing the effort and time required for synthesis and analysis of separation processes. This approach represents an extremely powerful tool whose use, however, requires an understanding of process engineering. The principal advantage of the method lies in the simultaneous optimization of both the structure and also the operating conditions of a process. Reliable convergence to the global optimum requires careful limitation, scaling, and prior assignment of all variables. Starting values can be obtained by thermodynamic analysis of the phase equilibrium and by an overall balancing of the individual separation steps. Heuristic reduction of the superstructure generated on the basis of the preferred separation, appears appropriate given the present status of available models and solution algorithms. Under these conditions, the outer approximation algorithm recommended for this model will find the optimum solution after just a few iteration steps.     

Elastic Moduli and Hardness of Cubic Silicon Nitride

The bulk modulus B ₀= 290(5) GPa and its first pressure derivative B '₀= 4.9(6) were obtained for c -Si₃N₄ from volume versus pressure dependence. Measurements were performed under quasi-hydrostatic conditions in a diamond anvil cell to 53 GPa using synchrotron radiation and energy dispersive X-ray powder diffraction. This combined with nanoindentation measurements determined the shear modulus G ₀ of c -Si₃N₄ to be 148(16) GPa. The Vickers microhardness H _V(0.5) for dense, oxygen-free c -Si₃N₄ was estimated to be between 30 and 43 GPa. Both the elastic moduli and microhardness of c -Si₃N₄ exceed those of the hexagonal counterparts, α- and β-phases.     

The strength of hybrid glass/carbon fibre composites

The tensile mechanical properties of hybrid composites fabricated from glass and carbon fibres in an epoxy matrix have been evaluated over a range of glass: carbon ratios and states of dispersion of the two phases. The failure strain of the carbon phase increased as the relative proportion of carbon fibre was decreased, and as the carbon fibre was more finely dispersed. This behaviour is commonly termed the hybrid effect, and failure strain enhancement of up to 50% has been measured. Only part of the effect may be attributed to internal compressive strains induced in the carbon phase by differential thermal contraction as the composite is cooled from its cure temperature. The laminae or ligaments of carbon fibre dispersed in the glass fibre phase show a multiple failure mode, and when the constitution is favourable catastrophic failure does not occur until a considerable number of ligament fractures have accumulated. Failure is thus progressive, and the material is effectively tougher than equivalent all-carbon fibre composites.     

Photosensitizedcis-trans isomerization of jojoba wax

Jojoba wax solutions were irradiated at wavelengths longer than 366 nm, in the presence of sensitizers, at room temperature.Cis-trans isomerization took place only with sensitizers with triplet energy greater than 68 kcal/mol. Quantum yields were low and a conversion of up to 25% of thetrans isomer was achieved at the photostationary state.     

Structure of an antioxidant from fermented soybeans (tempeh)

In an exhaustive investigation of the antioxidative properties of tempeh constituents, the substance at R _f 0.58 (cyclohexane/ethyl ether, 9:1) was isolated and purified. Until now, only the ultraviolet and fluorescence data of the substance were known, and the presence of an OH group was indicated. In the present paper, the structure of the substance at R _f 0.58 was elucidated by the application of spectroscopic methods and found to be 5-(δ-tocopheroxy)-δ-tocopherol. That previous researchers did not confirm antioxidant activity in tempeh oil has been related to the way the tempeh oil was prepared. Previous suggestions regarding the substance at R _f 0.58 as being one of the main tempeh antioxidants could not be proved. The antioxidative effect of tempeh oil seems to be the result of a synergistic effect of tocopherols (present in the soybeans) and amino acids (liberated during the fermentation process with Rhizopus oligosporus).     

Switching on the photochemical reactivity in heterodimetallic Os–Ru bipyridyl complexes containing a bis(bidentate) phosphine

For the first time the excited states of the RuP₂N₄ moiety belonging to a new heterodimetallic Os^II–Ru^II bipyridyl complex are successfully designed in order to introduce photochemical reactivity. This dramatic effect is achieved via the use of the sterically demanding bis(bidentate) phosphine cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb). Thus, the temperature dependence of the luminescence lifetimes ranging from 77 to 298 K for the novel homodimetallic species meso-(ΔΛ/ΛΔ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (1) and rac-(ΔΔ/ΛΛ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (2) clearly indicates that the d–d state responsible for photochemistry is not populated. By contrast, the analogous temperature dependence for the new heterodimetallic species ΔΛ/ΛΔ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (3) and ΔΔ/ΛΛ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (4) unequivocally shows that as a consequence of the population of the d–d state the photochemical reactivity is switched on. Since single crystal X-ray structure analyses are a major clue to the understanding of photophysical and photochemical properties, also the X-ray structures of 1–3 are given.