Ignition of exterior building details in bushfires: An experimental study

A laboratory study of the ignition of building details incorporating timber, under bushfire conditions, using ‘mock-ups’ of these details and both realistic (leaves and twigs) and, mainly, artificial (cribs) ignition sources has been carried out. Parameters such as mock-up type, moisture content of the timber comprising the mock-ups, and temperature and relative humidity of the experimental atmosphere were examined. It was found that all these parameters affected the ignition and flame propagation induced and that under conditions typical of a severe bushfire, only very small amounts of fuel were required to cause ignition. These results support the belief, based on field studies, that ignition of exterior building details composed of timber plays an important role in the destruction of buildings in bushfires.     

An artificial life approach to dense stereo disparity

This article presents an adaptive approach to improving the infection algorithm that we have used to solve the dense stereo matching problem. The algorithm presented here incorporates two different epidemic automata along a single execution of the infection algorithm. The new algorithm attempts to provide a general behavior of guessing the best correspondence between a pair of images. Our aim is to provide a new strategy inspired by evolutionary computation, which combines the behaviors of both automata into a single correspondence problem. The new algorithm will decide which automata will be used based on the transmission of information and mutation, as well as the attributes, texture, and geometry, of the input images. This article gives details about how the rules used in the infection algorithm are coded. Finally, we show experiments with a real stereo pair, as well as with a standard test bed, to show how the infection algorithm works.     

Improved assay of hepatic microsomal cholesterol 7 alpha-hydroxylase activity by the use of hydroxypropyl-beta-cyclodextrin and an NADPH-regenerating system

Cholesterol 7 alpha-hydroxylase, the key enzyme in bile acid synthesis, has been implicated in atherosclerosis and gallstone disease. The aim of this study was to check if the use of hydroxypropyl-beta-cyclodextrin (HPBCD), a vehicle for solubilizing cholesterol, augmented the rate of 7 alpha-hydroxycholesterol formation in hamster liver microsomes compared to classical assays in which labeled cholesterol was delivered in Tween 80. We observed that [14C]cholesterol carried by HPBCD enhanced the sensitivity of the assay tenfold. However, linearity of 7 alpha-hydroxycholesterol formation with time was short because of the rapid transformation of 7 alpha-hydroxycholesterol into 7 alpha-hydroxy-cholesten-3-one and 7 alpha,12 alpha-dihydroxy-cholesten-3-one when NADPH alone was present in the incubation medium. In order to avoid the transformation of 7 alpha-hydroxycholesterol into 7 alpha-hydroxy-cholesten-3-one, which is essentially NAD(+)-dependent, but is also NADP(+)-dependent, NADPH (1 mmol/l) plus an NADPH-regenerating system must be present in the medium. In this improved assay, the optimal pH was 7.4 and the apparent Km for control and cholestyramine-fed hamsters had a similar value of 315 mumol/l; linearity in the formation of 7 alpha-hydroxycholesterol was also apparent after a relatively short time period (10 min), but with a markedly greater slope of the curve. With a short incubation time (6 min), microsomes from livers of hamsters (five and nine weeks old) that were fed with a commercial ground diet yielded rates of 7 alpha-hydroxycholesterol formation of 115 +/- 10 and 150 +/- 16 pmol/min.mg protein, respectively, whereas microsomes from hamsters fed with a lithogenic sucrose-rich diet (five weeks old) yielded rates of 7 alpha-hydroxycholesterol formation of 77 +/- 7 pmol/min.mg protein, which were significantly lower (-33%) than those of corresponding control hamsters. This improved cholesterol 7 alpha-hydroxylase assay is very sensitive, simple and rapid, and does not necessitate sophisticated equipment. It can be particularly useful for determining cholesterol 7 alpha-hydroxylase activity in liver biopsies from dyslipidemic or lithiasic patients.     

Hepatic apolipoprotein and LDL receptor gene expression in the genetically hypercholesterolemic (RICO) rat

Up and down-regulation of calcium and potassium conductances are associated with several forms of short-term synaptic modulation. Detailed investigation of synaptic plasticity in the marine gastropod Aplysia, and in other mollusks, indicates that synaptic transmission can be influenced in a number of ways by modulatory neurotransmitters acting through several second-messenger cascades. Modulation at the synapse itself occurs by means of the regulation of calcium current as well as through effects on processes directly involved in transmitter mobilization and exocytosis. Modulation of potassium current plays a major role in controlling neuronal excitability and may contribute to a lesser extent to the regulation of transmitter release through actions on the resting potential and on action potential configuration.     

Biliary cholesterol absorption in normal and L-thyroxin-fed rats

Infusion of bile containing labeled cholesterol into bile fistula rats has permitted an in vivo study of the movements and of the absorption of biliary cholesterol in the digestive tract. The specific activities of cholesterol were similar in the micelles and the sediment of the luminal content after a 6 hr infusion, indicating rapid exchange of cholesterol between these fractions. In animals fed a basal diet, the biliary cholesterol absorption was higher (83%) than that of dietary cholesterol (70%). Bile cholesterol is essentially absorbed in the jejunum while the absorption of cholesterol from the diet takes place all along the small intestine but preferentially in its second and third quarters. Both alimentary cholesterol and bile cholesterol enter the top cells of the villi in preference to those of the crypts. In L-thyroxin-fed rats, a parallel decrease in biliary and dietary cholesterol absorption was observed. The increase in the intestinal transit of cholesterol and epithelium cell renewal of the jejunum accounted for this observation.     

Preparation and phase behavior of positionally isomeric propylene glycol monoesters

Primary even-chain-length monoesters of propylene glycol (1,2-propanediol), myristate through behenate, have been prepared, and also the secondary monostearate. Phase behavior of the pure compounds and of the binary system of isomeric stearates has been studied. This behavior is one of considerable complexity. The highest-melting stable form of the primary stearate is a single-chain-length (SCL) perpendicular form (Form II) of very weak long-spacing intensities. A metastable perpendicular double-chain-length (DCL)a form occurs at the (metastable) melting point after chilling the primary esters; it transforms to a perpendicular DCL Form III on cooling. Low temp crystallization from dilute hexane gives a titled DCL Form I, the typical room temp form in crude preparations of primary ester. The secondary stearate exhibits a single similar DCL Form I at 25C and a perpendicular SCL a form just under the melting point of the chilled melt. Polymorphism is modified by mol wt and purity. Primary arachidate and behenate do not show Form II, hence show stable a at their (stable) melting points. Repeated crystallization of the 80% primary ester obtained on direct esterification with stearic acid yields pure primary ester. Special synthesis via 1-tetrahydropyranyl propylene glycol is necessary to prepare pure secondary ester. The pure primary monobehenate could be obtained only by acylation of 2-tetrahydropyranyl propylene glycol obtained by reduction of tetrahydropyranyl ethyl lactate. Removal of the tetrahydropyranyl blocking groups was accomplished without acyl migration by using boric acid as a cleaving agent.     

Postulated scheme forβ crystal structures of mixed palmitic-stearic triglycerides

A structural scheme is proposed forβ phases of the six palmitic-stearic triglycerides, based on known configurations of tricaprin and 2-11-bromoundecanoyl-1,1′-dicaprin. The scheme receives some support from short spacing and binary system data.     

Lipid structures

Much of the function of lipids, as in shortenings, confections, biological membranes, etc., depends on the structures they exhibit, i.e., their crystalline and mesomorphic states. Triglycerides may serve as a point of departure for considering the crystal state of lipids. The three principle cross-sectional arrangements of long chains-α, β′ and β-in which there is kinship to hydrocarbons, offer a major basis for classification. Different crystal forms are rheologically different. Complications in the chain length direction lead to stepped configurations in the methyl planes and to double and triple chain length structures. A detailed consideration of the time-honored melting point alternation of homologs sheds light on the lipid crystal picture. A startling feature is the catalysis of isomerization by the solid state of diglycerides, with a consequent shift in equilibrium far toward 100% 1,3-diglyceride. Stepwise reversible transformations, as in hydrocarbons, are documented for high molecular weight 1-monoglycerides. A common feature, the sharp drop with mixture of stable form melting points, to “expose” metastable forms as stable forms for intermediate compositions is strikingly exhibited by fatty alcohols. The two bases for mesomorphism, or liquid crystal formation, among lipids are discussed: (1) dichotomy between molecular moieties in degree of polarity, as in phospholipids; and (2) dichotomy in molecular geometry as in cholesteryl esters. The former type is associated with three main basic arrangements-smectic or lamellar, middle or hexagonal (normal and reversed), and viscous isotropic or cubic (normal and reversed). The latter is associated with two main arrangements-cholesteric (essentially limited to cholesteryl compounds) and smectic. The importance of mesomorphism in consideration of membranes and emulsions is emphasized. Developments in understanding the structures of interfacial lipid states (including monomolecular surface films) and the correspondence of interfacial with bulk states is a matter of great continuing interest. E.S. Lutton received the 1971 AOCS Award in Lipid Chemistry at the AOCS Meeting, Atlantic City, N.J., October 1971. The following is his Award Address, presented at the Plenary Session.     

Phase behavior of aqueous systems of monoglycerides

Monoglyceride-H₂O systems in the range above about 5% H₂O exhibit a varied phase behavior with a number of mesomorphic states reminiscent of those found for soap-H₂O systems. There are fluid neat, stiff and “short” viscous isotropic, and plastic or stringy middle states. In the case of saturated monoglycerides, neat states prevail at low molecular weight as with monolaurin, but viscous isotropic and finally middle states appear at higher chain length as with monoarchidin and monobehenin. The phase diagrams for systems of unsaturated compounds resemble those for systems of saturated compounds, with corresponding phase regions occurring at lower temperatures. The monoelaidin-H₂O system closely resembles a shifted monostearin-H₂O system, neither system showing middle. Middle phase appears in a small island for monoolein and monolinolein near 90C and 20% water. Water dissolves negligible amounts of monoglycerides so that phases which are nearly 100% H₂O exist for substantially all systems and conditions when H₂O content is 60% or more.     

The phases of saturated 1-monoglycerides C14-C22

Phase behavior of a homologous series of saturated even 1-monoglycerides, starting with monomyristin, has been reviewed and their study extended to monoarachidin and monobehenin. The occurrence of sub α, α, β' and β polymorphs was confirmed for all compounds, except in the case of β' for monomyristin. It has been firmly established that there is a reversible sub α₂ ⇄ sub α₁ transition, (indicated by Malkin for monostearin) below the reversible sub α (sub α₁)⇄α transition, for C₁₈ through C₂₂ compounds; it occurs at about 50 C and is apparently almost independent of chain length. The sub α₂ to sub α₁ transformation is particularly sensitive to impurity and disappears for 1-monobehenin at about 10% 2-monobehenin as produced by heating at 96 C. Heats of transformation are, for β' and β crystal melting, about 50 cal/g; for α melting, about 35; for sub α → α transition, about 15 and for sub α₂ to sub α₁ transition about 3, which is several times as large as typical heats of melting of mesomorphic states. Diffraction data confirm the essential identity of all long spacing values and the occurrence of tilted chains for all polymorphs of a given compound. Much similarity is encountered between sub α and β' patterns. Sub α₂ and sub α₁ are difficult to distinguish by diffraction pattern.