Brillouin and ultrasonic study of the temperature dependence of the elastic constants in NaCN

The temperature dependence of the elastic constants of NaCN has been studied by propagation of ultrasonic waves at 15 MHz and by Brillouin scattering at 3 GHz over the temperature range from 287K to 355K. c₄₄ is observed to soften linearly with temperature as the order-disorder phase transition at 284K is approached from above. The other elastic constants also soften, except for c₁₂ which stiffens. Considerable dispersion is seen in the values of c₄₄ obtained ultrasonically and by Brillouin scattering. Measurements of the temperature dependence of the density are also reported.     

X-Ray Investigations on Celluloses Grafted by the Thiocarbonation Method

It is a pleasure for me to contribute to the symposium held in honor of my colleague and old friend Vivian Stannett. The topic of this contribution is results of x-ray investigations on graft modified cellulose fibers.     

Low-Temperature Polymerization of endo- and exo-2-Methyl-7-oxabicyclo-[2.2.1]-heptane

Abstract

Polymerization of the title compounds in methylene di-chloride with PF, catalyst have shown that the rate of polymer formation drops sharply with temperature and the polymerization ceases entirely around -60 to -70°C. Ex-periments carried out with the exo-2-Me isomer have shown that at -30°C a limiting conversion of approx 40% is attained and simultaneously the molecular weight and the molecular weight distribution level off. At -50°C the same limiting conversion level is reached; however, the molecular weight level is higher and a study of changes in molecular weight distribution with time indicates that at this tempera-ture a greater proportion of chains remain active throughout the polymerization. Even at -30°C, however, experiments with changing conditions, especially the temperature, during the runs have demonstrated that the systems are not “dead” after the limiting conversion has been reached. Polymeriza-tion of the endo-2-Me isomer at -50°C has shown that in the time interval studied the limiting viscosity number increases essentially linearly with time.     

A Convenient Synthesis of 2,4(3H,5H)-Furandione (β-Tetronic Acid)

The chemical versatility of 2,4(3H,5H)-furandione (β-tetronic acid, 1) and its synthetic applicability are of considerable current interest^1b,2a-k. The multifunctional character of this small molecule confers an intriguing synthetic potential which has prompted us to develop synthetic schemes utilizing it as a synthon for certain heterocyclic systems.     

Synthesis and mesogenic properties of several homologous series of aldose dialkyl dithioacetals. A model for their behaviour

Abstract

Ten homologous series (n-butyl through n-decyl) of aldose S,S-acetals (D-glucose, D-galactose, D-mannose, L-rhamnose, 2-deoxy-D-glucose, D-xylose, D-lyxose, D- or L-arabinose, D-ribose and 2-deoxy-D-ribose) have been prepared. Most of these compounds form thermotropic liquid crystals, the exceptions being the entire L-rhamnose series and some of the derivatives with the shortest alkyl chains. All of the compounds have been investigated with differential scanning calorimetry and polarization microscopy. Some temperature dependent powder X-ray data are also presented. A model is proposed which correlates the carbohydrate configuration with the melting behaviour. On the basis of now available behaviourial characteristics, visual inspection, mixing experiments and precedent, the mesophase is identified as smectic A_d, the partially overlapping carbohydrate moieties being in the centre and the aliphatic chains pointing outward at an angle of about 62°. Despite the intrinsic chirality of all the carbohydrate mesogens, no evidence for chiral mesophases was found, not even after introduction of a homochiral branched alkyl chain.     

Optimal spin squeezing inequalities detect bound entanglement in spin models

We determine the complete set of generalized spin squeezing inequalities. These are entanglement criteria that can be used for the experimental detection of entanglement in a system of spin-1/2 particles in which the spins cannot be individually addressed. They can also be used to show the presence of bound entanglement in the thermal states of several spin models.