Aromaticity as a Quantitative Concept. 2. Sixteen familiar five- and six-membered monocyclic heterocycles

Restudy of an almost complete data set of 12 characteristics for 16 common heterocycles confirms the previous conclusion [1] of the independence of „classical”︁ and of „magnetic”︁ aromaticity. The scores for the individual heterocycles correlate well with their chemical structure.     

Redesigning the active site of Geotrichum candidum lipase

Attempts to engineer enzymes with unique catalytic propertieshave largely focused on altering the existing specificitiesby reshaping the substrate binding pockets. Few experimentshave aimed at modifying the configuration of the residues essentialfor catalysis. The difference in the topological location ofthe triad acids of Geotrichum candidum lipase (GCL) and thecatalytic domain of human pancreatic lipase (HPL), despite greatsimilarities in their topologies and 3-D structures, suggestthat these are related enzymes whose catalytic triads have beenrearranged in the course of evolution (Schrag et aL, 1992).In this study we prepared a double mutant GCL in which the catalytictriad acid is shifted to the position equivalent to the locationof the triad acid of HPL. The double mutant maintains 10% ofthe wild type activity against triglycerides and the fluorogenicester 4-methylumbelliferyl-oleate. The only significant differencesbetween the 3-D structures of the double mutant and wild typeGCL are at the mutated sites. Even the water structure in theregion of the triad is unchanged. The hydrogen bonding patternof the catalytic triad of the double mutant is very similarto that of pancreatic lipase. The acid of the double mutantis stabilized by only two hydrogen bonds, whereas three hydrogenbonds are observed in the wild type enzyme. These results stronglysupport the hypothesis that the pancreatic Upases are evolutionaryswitchpoints between the two observed arrangements of the catalytictriads supported by the /ß hydrolase fold and suggestthat this fold provides a stable protein core for engineeringenzymes with unique catalytic properties.     

均质压燃(HCCI)单区和多区燃烧模型的比较

利用耦合化学动力学软件包CHEMKIN建立了汽油HCCI发动机的单区和多区燃烧模型。与试验数据的对比表明：虽然单区模型在参数化研究中能较准确地预测混合气的自燃定时,但其准确性在很大程度上取决于缸内的均匀性;包含缝隙区、淬熄区、质量交换区和绝热核心区的九区燃烧模型通过设置特定的功能分区能更好地模拟HCCI的燃烧过程,它在对自燃定时的预测和对热量释放过程和排放物的形成机理的模拟等方面都有很好的性能。     

Total number of coding open reading frames in the yeast genome

At the end of 1996 we approximated the total number of protein coding ORFs in the Saccharomyces cerevisiae genome, based on their properties, as 4700–4800. The number is much smaller than the 5800 which is widely accepted. According to our calculations, there remain about 200–300 orphans—ORFs without known function or homology to already discovered genes, which is only about 5% of the total number of genes. Our results would be questionable if the analysed set of known genes was not a statistically representative sample of the whole set of protein coding genes in the S. cerevisiae genome. Therefore, we repeated our estimation using recently updated databases. In the course of the last 18 months, previously unknown functions of about 500 genes have been found. We have used these to check our method, former results and conclusions. Our previous estimation of the total number of coding ORFs was confirmed. Copyright © 1999 John Wiley & Sons, Ltd.     

Electrical and thermophysical properties of mechanochemically obtained lanthanide hafnates

This contribution presents the synthesis and thermophysical characterization of seven lanthanide hafnates Ln₂Hf₂O₇ (Ln=Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Y³⁺, Ho³⁺, Yb³⁺); the title samples were prepared at room temperature by mechanically milling stoichiometric mixtures of the corresponding elemental oxides. Irrespective of the lanthanide ion involved, milling promotes the formation of highly disordered fluoritelike materials. Postmilling thermal treatments facilitate the formation of the fluorite ordered derivative, the pyrochlore structure, but only for the larger lanthanides (Sm³⁺, Eu³⁺, Gd³⁺). Impedance spectroscopy measurements revealed that these materials show a moderate‐to‐good oxygen ion conductivity at high temperatures; furthermore, those adopting the pyrochlore structure give higher σ_dc and lower E_dc than their fluorite analogues (σ_dc at 750°C>10^?3 S·cm^?1 vs <5·10^?4 S·cm^?1, respectively). The same trend also holds for the thermal resistivity at high temperatures; the highest thermal resistivity and thus, lowest κ was obtained for Eu₂Hf₂O₇ (κ~1.3·W·m^?1·K^?1 at 800°C). Therefore, Ln₂Hf₂O₇ phases might be attractive component materials for electrochemical devices and thermal insulating coatings.     

Effect of spark timing and load on a DISI engine fuelled with 2,5-dimethylfuran

Currently, bioethanol leads the automotive fuel market as the main substitute for gasoline in spark-ignition engines. However, worldwide interest has been triggered in the potential of 2,5-dimethylfuran, known as DMF, since the discovery of improved production methods. Although the energy content of DMF is comparable to that of gasoline, little is known about its combustion characteristics and emissions. Therefore, this work examines the effect of DMF in a single cylinder direct-injection spark-ignition engine. The results are compared to ethanol and gasoline using the optimized spark timings for gasoline and the respective fuel. In summary, DMF produces competitive combustion and emissions qualities to gasoline, which, in some cases surpass ethanol. The two biofuels have a higher burning rate and lower initial combustion duration than gasoline. They also produce greater combustion efficiency, which helps to lower hydrocarbon and carbon monoxide emissions. These initial results highlight how DMF, which was originally only considered as an octane improver, has the potential to become a competitive renewable gasoline alternative.     

Correction of the metrological properties of the pneumatic length measuring gauges through changes of the measuring nozzle head surface shape

In this paper, the geometry of the measuring nozzle head surface used in an air gauging system has been examined. The concept of conical correction of the surface in order to influence the metrological properties of the air gauge has been described. Geometrical correction has a substantial impact on the conditions of the outflow and the metrological properties of the air gauge. The outflow surfaces for a corrected nozzle have been calculated for different slots, and the transition point has been defined for the smallest outflow surface. The analysis of possible static characteristics enabled us to examine the influence of other parameters like inlet nozzle diameter or multiplication on the linearity. As a result of analysis, the method of the measuring head nozzle profile calculation has been presented. The experimental verification of the concept of conical surface correction in order to influence the metrological properties of an air gauge has been described. Dozens of corrected measuring nozzles have been manufactured and undergone experimental research. Comparative analysis of the static characteristics gained enabled us to examine the influence of other parameters such as inlet nozzle diameter or multiplication on the linearity and to contrast the results with the theoretical expectations.     

汽油和柴油混合燃料均质压燃(HCCI)的试验研究

汽油和柴油这两种不同特性的燃料被用作HCCI发动机的燃料。汽油具有高挥发性、易雾化和易于形成混合气的特性,被用来形成均质混合气;柴油具有良好的着火性和可燃性,被用来控制自燃和限制爆震燃烧。期望这两种特性不同而又相互补充的燃料混合后能够达到一个折衷的HCCI的燃烧性能。试验在一个专用于HCCI研究的单缸发动机上实施,采用两种中等的压缩比(10．4和15)和两种HCCI模式(进气加热和负气门叠开),试验结果证实了这种期望。结果是:随着混合燃料中柴油比例的增加,对于进气加热模式,HC- CI能稳定工作所需要的进气温度有所降低,对于负气门叠开模式,缸内平均指示压力和过量空气系数的范围有所扩展,并且两种方式下HC和NOx的排放均有所减少。     

An evaluation of MODIS and SeaWiFS bio-optical algorithms in the Baltic Sea

An extensive bio-optical data set from field measurements was used to evaluate the performance of standard Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color (in-water) algorithms in the Baltic Sea, which represents an example of optically complex Case 2 waters with high concentration of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities, chlorophyll a concentration (Chl a), and absorption coefficient of CDOM, which were taken on 25 cruises between 1993 and 2001. The data cover a wide range of variability with Chl a in surface waters from about 0.3 to 100 mg m⁻³. All the MODIS pigment algorithms examined as well as the SeaWiFS OC4v4 algorithm showed a systematic and large overestimation in chlorophyll retrievals. The mean systematic and random errors based on our entire data set exceeded 150% or even 200% in some cases, making these standard algorithms inadequate for pigment determinations in the Baltic. Although new parameterization of the standard pigment algorithms based on our field measurements in the Baltic resulted in a significant reduction of errors, the overall performance of such regionally tuned algorithms remained unsatisfactory. For example, the mean normalized bias (MNB) for the regionally tuned MODIS chlor_a_2 algorithm was reduced to 26% (from over 200% for the standard algorithm), but the root mean square (RMS) error was still large (>100%). The MODIS K_490 algorithm for estimating the diffuse attenuation coefficient of downwelling irradiance showed the best performance among all the algorithms examined. With the new coefficients based on our field data, the regional version of this algorithm showed an acceptable level of errors, MNB=4% and RMS=30%. In addition to the apparent problems of the standard in-water bio-optical algorithms, we found that the atmospheric correction currently in use for MODIS and SeaWiFS imagery usually fails to retrieve upwelling radiances emerging from the Baltic Sea. The match-up comparisons of the coincident in situ and satellite determinations of normalized water-leaving radiances showed generally poor agreement, especially in the blue spectral region. It appears that new approaches for ocean color algorithms are required in the Baltic Sea.     

Circularly orthogonal moments for geometrically robust image watermarking

Circularly orthogonal moments, such as Zernike moments (ZMs) and pseudo-Zernike moments (PZMs), have attracted attention due to their invariance properties. However, we find that for digital images, the invariance properties of some ZMs/PZMs are not perfectly valid. This is significant for applications of ZMs/PZMs. By distinguishing between the ‘good’ and ‘bad’ ZMs/PZMs in terms of their invariance properties, we design image watermarks with ‘good’ ZMs/PZMs to achieve watermark's robustness to geometric distortions, which has been considered a crucial and difficult issue in the research of digital watermarking. Simulation results show that the embedded information can be decoded at low error rates, robust against image rotation, scaling, flipping, as well as a variety of other common manipulations such as lossy compression, additive noise and lowpass filtering.