基于混合遗传算法的网络拓扑设计

提出了一种由启发式算法和遗传算法混合使用的混合遗传算法用于通信网络中的骨干网拓扑设计。文中骨干网拓扑设计问题是在满足R边连通和跳数约束的情况下使得网络费用最小。在遗传算法中,交叉和变异操作会产生不可行解,可通过增加链路来使不可行解变为可行解。增加链路后,其费用一般要比父代个体大,并且有多余的链路。该文的混合遗传算法是在遗传算法中加入启发式策略,来消除多余的链路,降低子代的费用,加快算法的收敛速度。仿真结果验证了算法的有效性。     

Comparison of the most odour-active volatiles in different hop varieties by application of a comparative aroma extract dilution analysis

Application of a comparative aroma extract dilution analysis on the volatiles isolated from five different hops (Hallertau Perle, Hallertau Hersbrucker Spät, Slowenian Golding, Hallertau Smaragd, US Cascade) revealed linalool and myrcene with the highest Flavour Dilution (FD)-factors in all varieties, followed by 2-isopropyl-3-methoxypyrazine, 3-methylbutanoic acid and geraniol. Some odourants, however, showed high FD-factors only in certain varieties, for example, (5Z)-octa-1,5-dien-3-one and germacrene B in Hersbrucker Spät, (3E,5Z)-undeca-1,3,5-triene in Hersbrucker Spät and Cascade and nonanal in Cascade. The overall odour profile of the Cascade sample clearly differed from the other varietes, and was dominated by a black currant like odour note. The identification experiments revealed 4-methyl-4-sulfanylpentan-2-one, so far unknown as hop constituent, as key contributor to this odour. In addition, an odour-active undecatetraene was present, in particular, in Perle and Cascade. Synthesis and structural assignment of the four stereoisomers of (3E)-undeca-1,3,5,9-tetraene allowed the identification of the fresh, pineapple-like smelling compound as (3E,5Z,9E)-undeca-1,3,5,9-tetraene. Among the four isomers synthesised, this compound showed by far the lowest odour threshold of 0.01 ng/L in air.     

USE OF A CHROMATOGRAPHY DATA SYSTEM TO IDENTIFY VARIETIES IN BINARY MIXTURES OF HOPS

Comparison of essential oil chromatograms and α-acid and β-acid analyses indicated differences between Tettnanger hops grown in the Tettnang district of Germany and those grown in the Hallertau district. Use of a chromatography data system to combine chromatograms of different varieties showed that the Hallertau samples were mixtures of Tettnanger with either Hersbruker Spät or Hallertau mittelfrüher .     

酒花制品的开发利用

介绍了酒花的植物性状、化学成分及其作用,阐述了酒花在啤酒酿造中的作用,详细论述了酒花制品在啤酒工业中的应用。     

SIMULTANEOUS DETERMINATION OF α, β AND ISO-α ACIDS IN HOPS AND HOP PRODUCTS

A method for the simultaneous analysis of α, β and iso-α acid in hops, hop extracts and isomerised hop extracts is described. It is based on the use of reversed phase high performance liquid chromatography and quantitative evaluation of the hop compounds is carried out with a computing integrator. The isomerisation reaction can be examined in detail, particularly in connection with the production of hop derived haze forming compounds in isomerised hop extracts used for post fermentation bittering.     

Dietary supplement of isohumulones inhibits the formation of aberrant crypt foci with a concomitant decrease in prostaglandin E2 level in rat colon

Male Fischer 344 rats were subcutaneously injected with azoxymethane (AOM) twice weekly at a dose of 15 mg/kg and were fed with freeze-dried (FD) samples of beer brewed without hops (non-hops beer), beer with hops at 4 times the amount of regular lager beer (x 4-hops beer), and isomerized hop extract (IHE) for the whole experimental period (I/PI) or for the post-initiation period (PI) only. Feeding FD beer samples at a dose of 1% significantly decreased the number of aberrant cryp foci (ACF) in the PI protocol over five weeks.x4-hops beer showed stronger inhibitory effects on the development of the numbers of aberrant crypts per focus and large ACF with four or more crypts than non-hops beer. Feeding IHE to rats at a dose of 0.01% or 0.05% in either the I/PI or PI experiment significantly reduced the numbers of ACF. Prostaglandin E2 (PGE2) levels in colonic mucosa of AOM-treated rats were significantly reduced by feeding of IHE. PGE2 production induced by lipopolysaccharide/interferon-gamma (LPS/IFN-gamma) in RAW264.7 cells was also reduced by treatment with IHE and isohumulone in a dose-dependent manner. These observations suggest that isohumulones show chemopreventive effects on ACF formation in rat colon by inhibiting the production of PGE2.     

THE SELF-HEATING AND IGNITION OF HOPS

Hops obtained from a brewery in Australia were examined for propensity to spontaneous combustion. The method used was basket heating and monitoring of the central temperature, so that supercritical behaviour could be clearly distinguished from subcritical. Frank Kamenetskii ignition theory was applied to the results and an extrapolation performed to gain insight into safe stockpiling heights.     

THE HOP MARKET—PRESENT AND PROSPECTIVE

The world production of hops currently exceeds the demand by brewers. Factors contributing to this situation are reviewed together with the effect that this has produced on price levels.     

WORT BOILING TODAY—OLD AND NEW ASPECTS

The requirements of the hop boiling process are reviewed together with the advantages of modern equipment.