Effect of Long-Term Potato Starch Retention with Citric Acid on Its Properties

The present study aimed to determine changes in the properties of starch triggered by its long-lasting (1, 2, 4, 7, 10, or 14 days) retention with citric acid (5 g/100 g) at a temperature of 40 °C. The starch citrates obtained under laboratory conditions had a low degree of substitution, as confirmed via NMR and HPSEC analyses. The prolonging time of starch retention with citric acid at 40 °C contributed to its increased esterification degree (0.05–0.11 g/100 g), swelling power (30–38 g/g), and solubility in water (19–35%) as well as to decreased viscosity of the starch pastes. Starch heating with citric acid under the applied laboratory conditions did not affect the course of DSC thermal characteristics of starch pasting. The low-substituted starch citrates exhibited approximately 15% resistance to amylolysis.     

β-Lactone as intermediate in the perkin reaction catalyzed by tertiary amines

The Perkin reaction catalyzed by tertiary amines is found to run not according to the aldol-type condensation mechanism but according to the mechanism in which the first stage is the formation and cycloaddition of ketene, yielding a β-lactone, which cleaves to the unsaturated acid.     

Kink instability in applied-field magneto-plasma-dynamic thrusters

Measurements of magnetic and electrostatic fluctuations in an applied field magneto-plasma-dynamic thruster have shown that a m/n=1/1 kink mode becomes unstable whenever the Kruskal-Shafranov limit is violated. A positive correlation is established between the kink and performance degradation at high current, which has until now prevented the use of this kind of thruster in space missions.     

Ultrasonic inspection of batters for on-line process monitoring

A new method for on-line batter monitoring using ultrasound techniques is presented. Air or gas incorporation is done during the beating process which produces bubbles in the mixture. The density and the compressibility of the batter vary as a function of mixing time and are quality index of batter. Traditionally, a batter sample of a fixed volume is removed and weighted in order to determine its density. This is a time consuming process. Batters are air filled mixtures of high viscosity which do not support significant transmission of ultrasound. For this reason conventional ultrasonic density sensors for liquids are not suitable for this application. Therefore, a special transducer has been developed. The sensor was constructed using a piezoelectric ceramic at the fundamental frequency of 1 MHz. Instead of measuring density, in this work, changes in compressibility in batters are monitored by measuring the acoustic impedance of the batter. Main advantage of this novel approach is that changes in acoustic impedance are easier to detect than changes in density especially when air incorporation is in small quantities. Experimental results on different liquids and batters with different gas contents are presented and discussed.     

Eavesdropping on the "ping-pong" quantum communication protocol

Security of the "ping-pong" quantum communication protocol recently proposed by Bostr?m and Felbinger [Phys. Rev. Lett. 89, 187902 (2002)]] is analyzed in the case of considerable quantum channel losses. The eavesdropping scheme is presented, which reveals that the ping-pong protocol is not secure for transmission efficiencies lower than 60%. Our scheme induces 50% losses, which, however, can be hidden in the channel losses if one replaces the original lossy channel with a less lossy one. Finally, a possible improvement of the ping-pong protocol security is proposed.     

Modular amino alcohol ligands containing bulky alkyl groups as chiral controllers for Et2Zn addition to aldehydes: illustration of a design principle

A new family of enantiomerically pure (1S,2R)-1-alkyl-2-(dialkylamino)-3-(R-oxy)-1-propanols containing a very bulky alkyl substituent (tert-butyl or 1-adamantyl) on their hydrocarbon chains has been synthesized from the corresponding enantiopure epoxy alcohols, arising from the catalytic Sharpless epoxidation, by protection of the primary hydroxy group and subsequent regioselective ring opening of the epoxide by a secondary cyclic amine (C-2 attack). The performance of these amino alcohols as ligands for the catalytic enantioselective addition of diethylzinc to benzaldehyde has been studied, with enantioselectivities of 92-96% being recorded. The best performing ligands, those with a bulky R-oxy group, also depict a convenient activity and selectivity profile in the addition of Et(2)Zn to a representative family of aldehydes. An anomalous structure/enantioselectivity relationship of some ligands in the tert-butyl series has been studied using PM3 calculations, and conclusions have been drawn on the possible effects of including in modular designs structural fragments giving rise to a variety of rotameric transition states.