Über sterische Hinderung bei der Verseifung von Benzalchloriden

Zusammenfassung Die Verseifung von Benzalchloriden kann durch Substitution beider orthoständigen Wasserstoffatome durch Chloratome derart gehemmt werden, daß unter Bedingungen, wo beim unsubstituierten Benzalchlorid bereits vollständige Verseifung stattfindet, beim 2, 6-Dichlorbenzalchlorid keine wesentliche Abspaltung von Chlorionen zu beobachten ist. Es tritt also bei der Verseifung von Benzalchloriden sterische Hinderung im SinneViktor Meyers auf.Ferner wurde gefunden, daß auch beim 2-Chlor-benzalchlorid, wenn auch in geringerem Maße, eine Verseifungshemmung auftritt, was in bezug auf die Angabe vonOlivier, daßo-Brombenzoylchlorid rascher verseift wird als das unsubstituierte Benzoylchlorid, erwähnenswert ist.Bei Versuchen mit drei verschiedenen Verseifungsmitteln, nämlich wässeriges Azeton, konzentrierte Schwefelsäure und wasserfreie Oxalsäure, wurden keinerlei wesentliche Unterschiede bezüglich der Verseifungshemmung beobachtet.Auch beim 2, 6-Dichlor-benzalchlorid tritt bei Anwendung extremerer Bedingungen Abspaltung von Chlorwasserstoff ein, die Reaktionshemmung ist also auch hier keine absolute, sondern nur gradueller Natur.Die vonOlivier geäußerten Ansichten über den Verseifungsvorgang von Benzylchlorid und Benzoylchlorid lassen sich nicht ohneweiters auf den der Benzalchloride übertragen.     

Flow visualisation of the external flow from a converging slot-hole film-cooling geometry

This paper presents flow visualisation experiments for a novel film-cooling hole, the converging slot-hole or console for short. Previously published experimental results have demonstrated that the console improved both the heat transfer and the aerodynamic performance of turbine vane and rotor blade cooling systems. Flow visualisation data for a row of consoles were compared with that of cylindrical and fan-shaped holes and a slot at the same inclination angle of 35° to the surface, on a large-scale, flat-plate model at engine-representative Reynolds numbers in a low speed tunnel with ambient temperature mainstream flow. In the first set of experiments, the flow was visualised by using a fine nylon mesh covered with thermochromic liquid crystals, allowing the measurement of gas temperature contours in planes perpendicular to the flow. This data demonstrated that the console film was similar to a slot film, and remained thin and attached to the surface for the coolant-to-mainstream momentum flux ratios of 1.1 to 40 and for a case with no crossflow (infinite momentum flux ratio). A second set of flow visualisation experiments using water/dry-ice fog have confirmed these results and have shown that the flow through all coolant geometries is unsteady.     

The Challenges of Scanner Data

Data capture at point of sale, using laser scanning technology, is now commonplace in retail outlets in developed economies. The volume of data collected is enormous (a single UK grocery superstore carries over 15 000 different lines, each with a unique 13 digit barcode and will sell 600 000 items per week). It has been recognized that, where point of sale data can be translated into meaningful information, there is scope for efficiency savings and exploitable competitive advantage. In UK grocery retailing the uses of scanner data have concentrated on operational aspects such as improved ordering systems and staff scheduling. There have, however, been many recent studies, predominantly in the USA, which have examined, using scanner data, the relationship between marketing variables (price, display, advertising, coupons, and other promotions) and customer purchasing behaviour. This paper presents an overview of these studies and identifies the opportunities for operational researchers to further the understanding of such relationships through modelling and data handling.     

Gravity effects on partially premixed flames: an experimental-numerical investigation

While premixed and nonpremixed microgravity flames have been extensively investigated, the corresponding literature regarding partially premixed flames (PPFs) is sparse. We report the first experimental investigation of burner-stabilized microgravity PPFs. Partially premixed flames with multiple reaction zones are established in microgravity on a Wolfhard–Parker slot burner in the 2.2 s drop tower at the NASA Glenn Research Center. Microgravity measurements include flame imaging, and thermocouple and radiometer data. Detailed simulations are also used to provide further insight into the steady and transient response of these flames to variations in g. The flame topology and interactions between the various reaction zones are strongly influenced by gravity. The flames widen substantially in microgravity. During the transition from normal to microgravity, the flame structure experiences a fast change and another relatively slower transient change. The fast response is due to the altered advection as the value of g is reduced, while the slow response is due to the changes in the diffusive fluxes. The radiative heat loss from the flames increases in microgravity. A scaling analysis based on a radiation Damköhler number is able to characterize the radiation heat loss.     

MRI studies of the neurotoxic effects of L-2-chloropropionic acid on rat brain

L-2-Chloropropionic acid (L-CPA) is selectively toxic to rat cerebellar granule cells; necrosis is first observed about 36 hours after administration of L-CPA (750 mg/kg p.o.) becoming more marked by 48 h. Parallel to the onset of cell death an increase in cerebellar water content and sodium concentration has been reported suggesting an oedematous reaction. In this study T(2)-weighted (T(2)WI) and diffusion weighted (DWI) imaging were used to detect the development of neuronal damage in the cerebellum of rats as a result of exposure to L-CPA. T(2)WI and DWI were not able to detect cerebellar abnormalities at 37 h post-dosing except for a slight swelling of the cerebellum. However, at 48 h post-dosing when cerebellar swelling and granule cell necrosis were marked, T(2)WI and DWI hyperintensities were observed in the cerebellum. Therefore, under the conditions of this study, MRI was not able to detect abnormalities in the cerebellum prior to the onset of the clinical signs of neurotoxicity or at the time of early histological changes. T(2)WI also suggested a marked increase in the amount of fluid in the ventricular system of rats 37 and 48 h after dosing; fluid accumulation was observed in all animals studied whether or not necrosis was detected. The occurrence of T(2)WI hyperintensity in the forebrain lead us to discover a new lesion in the habenular nucleus.     

The mechanism of antiparallel <Emphasis Type="Italic">β</Emphasis>-sheet formation based on conditioned self-avoiding walk

By introducing an additional hydrogen bond to hydrogen bond interaction in the force field of the CSAW (Conditioned Self-Avoiding Walk) model, we investigate into the mechanism of antiparallel β-sheet formation based on the folding of a short polyalanine in gas phase. Through our numerical simulation, we detect the possible presence of a transient helix during β-sheet formation, whose presence is shown to have slowed the formation of β-sheets by an order of magnitude. While we observe the mechanisms of nucleation, zipping and induction that drives the formation of a β-sheet, we uncover a new mechanism that involves transient β-turns and short β-sheets during the formation of long β-sheets. Our results have enabled us to provide an overview on the mechanisms of β-sheet formation via two main folding pathways: slow folding through the intermediate state of transient helix, and fast folding from the nucleation of β-turn.     

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation,Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 °C) and supercritical (300 bar, 400 °C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)₃ within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate‐determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub‐ and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub‐ and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X‐ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 °C and gives a two‐phase product of hydrated and non‐hydrated aluminium oxide.