Klimabelastung und Lastverteilung bei Mehrscheiben‐Isolierglas

Internal loads and load sharing of insulating glass units. A change of temperature or barometric pressure results in a pressure difference between the cavities of an insulating glass unit and the exterior and causes a load to the single panes. On the other hand external loads acting on one pane are borne by the panes together. In general, the performance of an unit depends on the stiffness of the system. Common rectangular insulating glass units of reasonable size show the expected load sharing and only low climatic loads. Small units or units with thicker glass panes, triple glazing, triangular or point supported units and units with curved panes will bear a considerably higher load and that may result in damage of the glass or the edge seal. The technical bases are described and the theory is developed in a general form for any size and shape of the unit and different types of external loads. For practical purpose the formulae will be given in a linearised form and are adapted to common constructions such as double and symmetric triple glazing. Deflection and stress can be calculated by the definition of the isochore pressure and the insulating glass factor as usual. The consequences of the load sharing and climatic loads and the step by step calculation are demonstrated for typical examples. The formulae and the necessary coefficients are tabulated in an Annex.     

Wahrscheinlichkeitsdichteverteilungen der Konzentration in isothermen Luft-Freistrahlen

Zusammenfassung Zur Berechnung der ?rtlichen Verteilungen von zeitlichen Mittelwerten der Konzentration und der Konzentrationsschwankungen in isothermen Strahlen und in Flammen werden die Wahrscheinlichkeitsverteilungen der Konzentration als Normal- oder schiefe Verteilungen vorausgesetzt. Es fehlen jedoch experimentelle Untersuchungen, um die Richtigkeit solcher Annahmen zu überprüfen. Um diese Lücke zu schlie?en, wurden in einem isothermen Freistrahl, der als Modell einer Freistrahldiffusionsflamme betrachtet werden kann, nach der Streulichtmethode und mittels eines Korrelators die ?rtlichen Konzentrations-Wahrscheinlichkeitsdichteverteilungen sowie die Intermittenzfaktoren ermittelt. Die Verfasser danken der Deutschen Forschungsgemeinschaft für die Bereitstellung von Me?ger?ten, die diese Untersuchungen erm?glichten. Au?erdem sei der Alexander-von-Humboldt-Stiftung für die Gew?hrung eines Dozentenstipendiums herzlich gedankt.     

Determination of Caffeine,Myosmine, and Nicotine in Chocolate by Headspace Solid‑Phase Microextraction Coupled with Gas Chromatography‑Tandem Mass Spectrometry

The occurrence of the bioactive components caffeine (xanthine alkaloid), myosmine and nicotine (pyridine alkaloids) in different edibles and plants is well known, but the content of myosmine and nicotine is still ambiguous in milk/dark chocolate. Therefore, a sensitive method for determination of these components was established, a simple separation of the dissolved analytes from the matrix, followed by headspace solid?phase microextraction coupled with gas chromatography‐tandem mass spectrometry (HS?SPME?GC?MS/MS). This is the first approach for simultaneous determination of caffeine, myosmine, and nicotine with a convenient SPME technique. Calibration curves were linear for the xanthine alkaloid (250 to 3000 mg/kg) and the pyridine alkaloids (0.000125 to 0.003000 mg/kg). Residuals of the calibration curves were lower than 15%, hence the limits of detection were set as the lowest points of the calibration curves. The limits of detection calculated from linearity data were for caffeine 216 mg/kg, for myosmine 0.000110 mg/kg, and for nicotine 0.000120 mg/kg. Thirty samples of 5 chocolate brands with varying cocoa contents (30% to 99%) were analyzed in triplicate. Caffeine and nicotine were detected in all samples of chocolate, whereas myosmine was not present in any sample. The caffeine content ranged from 420 to 2780 mg/kg (relative standard deviation 0.1 to 11.5%) and nicotine from 0.000230 to 0.001590 mg/kg (RSD 2.0 to 22.1%).     

Chemical basis of egg cannibalism in a caterpillar (Utetheisa ornatrix)

Larvae of the mothUtetheisa ornatrix are shown to cannibalize eggs in the laboratory. They proved most cannibalistic if they were systemically deficient in pyrrolizidine alkaloid (PA), the defensive agent that protectsUtetheisa at all stages of development against predation, and whichUtetheisa acquire as larvae from their food plant. In exercising cannibalistic choice,Utetheisa larvae feed preferentially on eggs that are PA-Iaden rather than PA-free. Egg cannibalism can therefore provideUtetheisa with a supplemental means of PA procurement. Moreover, presence of PA in the egg, while providing the egg with defense against predation, can increase its vulnerability to cannibalism. Although evidence is presented thatUtetheisa larvae cannibalize eggs in nature, it is argued that such feeding may occur only opportunistically in the wild, rather than as a matter of course.Paper No. 104 of the series Defense Mechanisms of Arthropods, No. 103 in Eisner and Eisner, 1991.Psyche 98:111–118.     

Potential of roof-integrated solar collectors for preheating air at drying facilities in Northern Thailand

Longan is one of the most widely cropped fruits in Northern Thailand, where a significant amount of the annual harvest is commercially dried and exported as a commodity. Liquefied petroleum gas is generally used as the energy source for heating the drying air, but concern is growing as fuel prices are expected to increase for the foreseeable future. Meanwhile, with the ample solar radiation in Thailand, the roofs of drying facilities could be adapted to serve as solar collectors to preheat the drying air, thus reducing the energy requirement from fossil fuels. In this study, a simulation program for a flat-plate solar air heater was used to estimate the potential to preheat drying air given the conditions of several longan drying facilities. Results showed that solar collectors can replace up to 19.6% of the thermal energy demand during the drying season. Bigger collectors and smaller air channels result in more useful heat, but attention has to be paid to costs and pressure drop, respectively. Annual monetary savings can reach up to THB 56,000 (≈US$ 1800 at US$ 1 = THB 31).