<Superscript>29</Superscript>Si NMR Chemical Shift Tensor and Electronic Structure of 7-Silanorbornadienes

The structure and bonding of 7-silanorbornadienes was investigated using X-ray Diffraction (XRD), solid-state NMR spectroscopy and density functional calculations. The solid state structures of four benzo-7-silanorbornadienes (4a, c, d, e) and of one dibenzo-7-silabenzonorbornadiene (5a) are reported and compared with the results of previous structural investigations. The most prominent features of the molecular structures of all 7-silanorbornadienes are very long Si-C(bridgehead) bonds (d(SiC) = 190.6–196.8 pm) and very acute CSiC bond angles α (α(CSiC) = 78.7–83.9°). All newly investigated 7-silanorborndienes show for tetracoordinated silicon nuclei extremely deshielded ²⁹Si NMR resonances (δ²⁹Si = 65.6–31.6). Solid State NMR investigations for 7-silanorbornadienes anti-4a, b reveal highly anisotropic chemical shift tensors of axial or nearly axial symmetry (4a: δ₁₁ = 161, δ₂₂ = δ₃₃ = −11; 4b: δ₁₁ = 113, δ₂₂ = 14, δ₃₃ = −15). The dominating, strongly deshielding δ₁₁ component is oriented almost perpendicular to the plane spanned by the two bridgehead carbon atoms and the bridging silicon atom. The DFT calculations suggest that the origin of the strong deshielding is a small energy difference between the frontier orbitals, which are strongly localized at the silicon atom. In addition the computations reveal that both the long SiC bonds and the strongly deshielded ²⁹Si NMR chemical shift are direct consequences of the bonding situation in 7-silanorbornadienes which are characterized by through space interaction of the C=C double bonds and by hyperconjugation between the SiC σ-bonds and the unoccupied orbitals of the C=C double bonds.     

How does industry specialization affect the efficiency of regional innovation systems?

This study analyzes the relationship between the specialization of a region in certain industries and the efficiency of the region in generating new knowledge. The efficiency measure is constructed by relating regional R&D input and output. An inversely u-shaped relationship is found between regional specialization and R&D efficiency, indicating the presence of externalities of both Marshall and Jacobs’ type. Further factors influencing efficiency are externalities resulting from high R&D intensity of the local private sector as well as knowledge from local public research institutions. The impact of both the specialization and the additional factors is, however, different for regions at different efficiency levels.     

Application of Plasma-Sprayed Complex Perovskites as Thermal Barrier Coatings

In an effort to improve the performance of heat engines at high temperatures, advanced surface coatings have been developed from complex perovskites. Materials of Ba(Mg_1/3Ta_2/3)O₃ and La(Al_1/4Mg_1/2Ta_1/4)O₃ composition were synthesized and applied as ceramic topcoats of thermal barrier coating (TBC) systems by atmospheric plasma spraying (APS) in single layer and in double-layer combination with conventional yttria stabilized zirconia (YSZ). Microstructural and phase analyses reveal that plasma spraying of complex perovskites is accompanied with the formation of vertical crack networks and secondary oxide phases which influence the failure mechanism of the TBCs. The low value of fracture toughness for the complex perovskites and the thermally grown oxide at the topcoat-bondcoat interface of the TBCs are, however, the major factors which lead to the coating failure on thermal cycling at about 1250 °C.     

A novel test approach for plasma-sprayed coatings tested simultaneously under CMAS and thermal gradient cycling conditions

Plasma-sprayed ceramic coatings, used as thermal barrier or abradable coatings in high-pressure stages of gas turbines, are exposed to high thermo-mechanical loading due to harsh operating conditions. Under certain conditions they also have to withstand attack by calcium-magnesium-alumino-silicate (CMAS) deposits resulting from the ingestion of siliceous minerals with the intake air.Resistance to this kind of attack becomes more important at higher temperatures, when the melting temperature of the CMAS deposits is exceeded and a penetration into the coating microstructural features (cracks and pores) can take place. During cooling the CMAS solidifies and the coating loses its strain tolerance, which can lead to coating failure. Although the basic principles of failure seem to be understood, a detailed analysis of the mechanisms and the possibilities of avoiding delamination are still lacking, especially because there are as yet no adequate test beds.This paper investigates the possibility of testing such coatings in a burner rig test facility under thermal gradient cycling conditions and at the same time CMAS deposition. This novel and unique test approach promises a coating screening and characterization test under service conditions. The CMAS rig was established because the test conditions simulated here are closer to actual engine conditions, as compared to previous tests with primarily CMAS deposition and subsequent thermal furnace testing.The experimental setup of this new test approach is described and the applicability is confirmed. Furthermore, a first evaluation for plasma-sprayed coatings is presented. A significantly reduced lifetime was found for samples tested with CMAS attack in comparison to tests with water deposition only. The lifetime was also reduced compared to older results without any corrosive media. A decrease of nearly two orders of magnitude was found. A microstructural evaluation of the coatings is presented and the mechanisms and reasons for the very early failure are discussed.     

Monoterpene and sesquiterpene emission estimates for the United States

Biogenic volatile organic compounds (BVOC) contribute significantly to the formation of ozone and secondary organic aerosol (SOA). The Model of Emissions of Gases and Aerosols from Nature (MEGANv2.02) is used to estimate emissions of isoprene, monoterpenes (MT), and sesquiterpenes (SQT) across the United States. Compared to the Biogenic Emission Inventory System (BEIS3.0), MEGANv2.02 estimates higher isoprene but lower MT emissions for July 2001 and January 2002. A sensitivity study of SQT and MT emission factors and algorithm parameters was conducted by assigning values to four plant functional types (PFTs) using both recent measurements and literature values. The standard deviations of the emissions factors within these PFTs were two to four times the averages because of the variation in experimental basal emissions rate data. More recently published SQT and MT basal emission rates are generally lower than those reported in the literature through 2004. With the new emissions factors, monthly average SQT emission rates for the contiguous United States are equal to 16% of the MT emissions during July and 9% of the emissions during January. The SQT emissions distribution is strongly influenced by the grass and crop PFT, for which SQT emissions data are quite limited.     

Shelf life and quality of skim milk processed by cold microfiltration with a 1.4-μm pore size membrane,with or without heat treatment

The objective of this study was to evaluate the effectiveness of cold microfiltration (MF), alone or in combination with heat treatment, in extending the shelf life of skim milk. Raw skim milk underwent MF at 6 ± 1°C with a ceramic membrane of 1.4-μm pore size, at a transmembrane pressure of 75.8 kPa and a crossflow velocity of 7 m/s. Samples of raw skim milk; MF skim milk; high-temperature, short-time (HTST)-pasteurized milk; and MF+HTST-pasteurized skim milk were stored at 6°C for 92 d. During the shelf-life study, the total bacterial count and degree of proteolysis were evaluated weekly. The study was replicated 3 times. Cold MF was very effective in reducing the microbial load in skim milk, and an average of 3.4 log reduction in vegetative bacteria was obtained. Although HTST pasteurization reduced the bacterial load by ～2 log, the MF+HTST process resulted in near complete elimination of vegetative microflora, with a total of ～4 log reduction. A 9-member sensory panel found no significant differences between skim milk samples processed with or without MF. The MF+HTST skim milk had only minor microbial growth after 92 d at 6°C, but its proteolytic shelf life was limited by plasmin activity. A reduction of plasmin activity and a slower rate of proteolysis were obtained by increasing the heat treatment temperature to 85°C. The results of this study can be used to make decisions regarding processing strategies that lead to increased skim milk shelf life.     

Fields of knowledge in higher education institutions,and innovative start‐ups: An empirical investigation

We investigate the role played by different fields of academic knowledge and various types of higher education institutions in the emergence of innovative start‐ups in a region. We show that education and research in the applied and natural sciences have the strongest effect on the emergence of new businesses in innovative industries. Distinguishing between different indicators for these types of knowledge, the strongest effects are found for the number of professors, the number of students and the amount of external funds attracted.     

Impacts of forebrain neuronal glycine transporter 1 disruption in the senescent brain: Evidence for age-dependent phenotypes in Pavlovian learning.

Genetic deletion of glycine transporter 1 (GlyT1) in forebrain neurons gives rise to multiple-procognitive phenotypes, presumably due to enhanced N-methyl-d-aspartate receptor (NMDAR) functions. However, concerns over possible harmful excitotoxic effects under lifelong elevation of synaptic glycine have been raised. Such effects might accelerate the aging process, weakening or even reversing the procognitive phenotypes identified in adulthood. Here, we examined if one of the most robust phenotypes in the mutant mouse line (CamKIIαCre;GlyT1tm1.2fl/fI), namely, enhanced aversive Pavlovian conditioning, might be modified by age. Comparison between 3-month-old (adult) and 22-month-old (aged) mutants confirmed the presence of this phenotype at both ages. However, the temporal expression of the Pavlovian phenotype was modified in senescence; while adult mutants showed a pronounced within-session extinction, aged mutants did not. Expression of NR2B subunits of NMDAR and neural proliferation were examined in the same animals by immunohistochemistry. These were reduced in the aged mice as expected, but not exacerbated by the mutation. Thus, our results do not substantiate the concerns of neurotoxic effects through lifelong GlyT1 disruption in forebrain neurons, but provide evidence for a modification of phenotypic expression as a function of age. The latter points to the need to further investigate other procognitive phenotypes identified at adulthood in this mutant line. In addition, we revealed here for the first time a clear increase in the number of immature neurons in the hippocampus of the mutants, although the behavioral significance of this phenotype remains to be determined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling Evapotranspiration Effects on Air Flowing in a Small Glass Roofed Tunnel

A preliminary investigation into the feasibility of erecting a solar chimney power plant requires a model incorporating all possible aspects of such a power plant and giving results on an hourly basis. Possible agricultural activities underneath the outer section of the solar collector would require a model predicting the changing state of the air due to evapotranspiration effects as it flows from the perimeter of the collector to the chimney in the center. The vegetation temperature and irrigation requirements need to be determined in order to ascertain how far inward crops may be planted without being subjected to heat stress. A small experimental glass roofed tunnel was constructed, planted with grass, and the changing state of the air, drawn over the grass by a fan, was determined using wet- and dry-bulb temperature measurements and the mass flow rate of the air. Starting off with a known air state inlet condition, conservation and the Penman-Monteith equations were applied to subsequent 1-m lengths of the tunnel and the state of the air at the outlet was predicted and compared with the measured state of the air. The predicted and measured values were found to be in agreement within experimental limits giving confidence in incorporating this model into the larger model of the solar chimney.     

Application of optical broadband monitoring to quasi-rugate filters by ion-beam sputtering

Methods for the manufacture of rugate filters by the ion-beam-sputtering process are presented. The first approach gives an example of a digitized version of a continuous-layer notch filter. This method allows the comparison of the basic theory of interference coatings containing thin layers with practical results. For the other methods, a movable zone target is employed to fabricate graded and gradual rugate filters. The examples demonstrate the potential of broadband optical monitoring in conjunction with the ion-beam-sputtering process. First-characterization results indicate that these types of filter may exhibit higher laser-induced damage-threshold values than those of classical filters.