Fast-processing statistical methods for measurement of BER in optical fiber communication systems

We propose two fast-processing statistical methods for the determination of transmission performance, in particular the eye diagram and BER in optical fiber communication systems. Detailed guidelines for optimizing the accuracies of the statistical techniques are given. These methods provide BERs within one decade, hence more superior than those offered by Monte-Carlo and semi-analytical techniques.     

An insight into CH···N hydrogen bond and stability of the complexes formed by trihalomethanes with ammonia and its monohalogenated derivatives

A theoretical study of the C?H···N hydrogen bond in the interactions of trihalomethanes CHX₃ (X = F, Cl, Br) with ammonia and its halogen derivatives NH₂Y (Y = F, Cl, Br) has been carried out thoroughly. The complexes are quite stable, and their stability increases in going from CHF₃ to CHCl₃ then to CHBr₃ when Y keeps unchanged. With the same CHX₃ proton donor, enhancement of the gas phase basicity of NH₂Y strengthens stability of the CHX₃···NH₂Y complex. The C?H···N hydrogen bond strength is directly proportional to the increase of proton affinity (PA) at N site of NH₂Y and the decrease of deprotonation enthalpy (DPE) of C?H bond in CHX₃. The CHF₃ primarily appears to favor blue shift while the red‐shift is referred to the CHBr₃. The blue‐ or red‐shift of CHCl₃ strongly depends on PA at N site of NH₂Y. We suggest the ratio of DPE/PA as a factor to predict which type of hydrogen bond is observed upon complexation. The SAPT2+ results show that all C?H···N interactions in the complexes are electrostatically driven regardless of the type of hydrogen bond, between 48% and 61% of the total attractive energy, and partly contributed by both induction and dispersion energies.     

Facile isomerization of glucose into fructose using anion-exchange resins in organic solvents and application to direct conversion of glucose into furan compounds

The facile isomerization of glucose into fructose has been developed using commercially available anion-exchange resins (AERs) in organic solvents. Following extensive screening for the amount and type of AERs, solvents and reaction time, glucose was transformed into fructose in yields of up to 50% using Amberlite A-26 with macroreticular morphology and tertiary amine functionality in a protic solvent (ethanol). AERs could be used five times without a significant loss of activity. This isomerization method could be applied to the direct conversion of glucose into furan compounds by integrating the dehydration of fructose with cation-exchange resins.     

Oscillatory and simple shear flows of a flour-water dough: a constitutive model

We reported some dynamic and viscometric data on an Australia strong flour-water dough. In oscillatory shear flow experiments, we found the linear viscoelastic strain limit is extremely low, of O(10^–3), consistent with other published data on doughs. The relaxation spectrum derived from the dynamic data is broad, indicating the blend nature of dough. In the start-up of a simple shear flow, we found the shear stress increases nonlinearly with time to a peak value and then decreases rapidly, with no steady-state response. The concept of steady-state viscosity is not very meaningful here, unless the strain at which the measurements are taken is also specified. The stress peaks are strain-rate dependent; but they occur at a strain of O(10), for the strong flour/water dough used, over four decades of strain rates. The experimental data were used to construct a phenomenological model for dough, consisting of an hyperelastic term (representing the elastic gluten network of permanent cross-linked long chain polymers), and a viscoelastic contribution (representing the suspension of starch globules and other long-chain components in dough that are not parts of the permanent cross-linked gluten network). The model predictions compared favourably with experimental data in oscillatory and shear flows.     

The Sprague–Grundy function of the real game Euclid

The game Euclid, introduced and named by Cole and Davie, is played with a pair of nonnegative integers. The two players move alternately, each subtracting a positive integer multiple of one of the integers from the other integer without making the result negative. The player who reduces one of the integers to zero wins. Unfortunately, the name Euclid has also been used for a subtle variation of this game due to Grossman in which the game stops when the two entries are equal. For that game, Straffin showed that the losing positions (a,b) with a<b are precisely the same as those for Cole and Davie’s game. Nevertheless, the Sprague–Grundy functions are not the same for the two games. We give an explicit formula for the Sprague–Grundy function for the original game of Euclid and we explain how the Sprague–Grundy functions of the two games are related.     

Determination of the dissociation energy of the C-At bond in substituted astatobenzenes

The dissociation energy of C–At bond /D_C–At/ in a number of astatobenzene derivatives has been determined by pyrolytic method. The values of D_C–At for the astatoaromatic compounds investigated have been found to be independent of the substituents and their relative position in the astatoaromatic system.Dedicated to Prof. V.D. Nefedov on the occasion of his 70th birhtday     

Drag force on a sphere in creeping motion throug a carreau model fluid

In the report of Chhabra and Uhlherr [1], a theoretical formulation for the drag force on a sphere in a fluid governed by the Carreau viscosity equation was presented. The formulation gave a good representation of the drag force when compared with experimental measurements, although the experiments were carried out on fluids exhibiting both shear-thinning and elastic behaviour. In the present work the ‘boundary element method’ has been used to obtain a fully numerical solution for comparison with the theoretical predictions. The two sets of results agree closely. We also present a simple empirical relation which gives a good first approximation to the drag force (～ 10%).     

Cone-and-plate flow of the Oldroyd-B fluid is unstable

It is shown that the creeping cone-and-plate flow of an Oldroyd-B fluid is unstable with respect to an infinitesimal disturbance. The critical Weissenberg number for the case of the Maxwell fluid is about 2.