Heats of reaction of two common cellulose solvents with various model compounds

Heats of reaction of two common cellulose solvents, cadoxen and ferric sodium tartrate (FeTNa), with a variety of cellulose-related compounds were obtained with a sensitive adiabatic microcalorimeter. Both solvents require adjacent hydroxyl groups in the equatorial positions of ring systems for maximum reactivity (or maximum exothermic heat of reaction). The cellulose solvent cuprammonium has a significantly different pattern of reactivity toward a number of sugars compared with the patterns observed for cadoxen and FeTNa. These differences are explained in terms of the Jahn-Teller effect and the preferred sites of reaction and oxidation in ring systems. Calorimetric evidence indicates that complexes containing methoxy groups may be formed by both cadoxen and FeTNa.     

Equi-ripple design of quadratic-phase RF pulses

An improved strategy for the design of quadratic-phase RF pulses with high selectivity and broad bandwidths using the Shinnar-Le Roux (SLR) transformation is proposed. Unlike previous implementations, the required quadratic-phase finite impulse response (FIR) filters are generated using the complex Remez exchange algorithm, which ensures an equi-ripple deviation from the ideal response function. It is argued analytically that quadratic-phase pulses are near-optimal in terms of minimising the B1-amplitude for a given bandwidth and flip angle. Furthermore, several parameter relations are derived, providing practical design guidelines. The effectiveness of the proposed design method is demonstrated by examples of excitation and saturation pulses applied in vitro and in vivo.     

Energy element and its application in the dynamic calculation of continuous medium

The present paper which discusses the problem related to the combination of the finite difference method and the finite element method, describes an energy element calculating mode including the special features of the above two methods.     

Research challenges to ultra‐efficient inorganic solid‐state lighting

Solid‐state lighting is a rapidly evolving, emerging technology whose efficiency of conversion of electricity to visible white light is likely to approach 50% within the next several years. This efficiency is significantly higher than that of traditional lighting technologies, giving solid‐state lighting the potential to enable significant reduction in the rate of world energy consumption. Further, there is no fundamental physical reason why efficiencies well beyond 50% could not be achieved, which could enable even more significant reduction in world energy usage. In this article, we discuss in some detail: (a) the several approaches to inorganic solid‐state lighting that could conceivably achieve “ultra‐high,” 70% or greater, efficiency, and (b) the significant research questions and challenges that would need to be addressed if one or more of these approaches were to be realized.     

Two new heterocyclic [3.3.3.01,5]‐propellanoid compounds: 2,8‐dioxatricyclo[3.3.3.01,5]undecane‐3,7‐dione and a related dimer

2,8‐Dioxatri­cyclo­[3.3.3.0^1,5]­un­decane‐3,7‐dione, C₉H₁₀O₄, (I), is the dilactone acylal of cyclo­pentanone‐2,2‐di­acetic acid. Both mol­ecules in the asymmetric unit have conformational chirality and differ principally in the flexing of the carbon ring, which produces a resolvable conformational disorder in one of the mol­ecules. Three intermolecular C—H⋯O close contacts exist. 7,7′‐Oxybis(2,8‐dioxatri­cyclo­[3.3.3.0^1,5]­undecan‐3‐one), C₁₈H₂₂O₇, (II), a racemate, lies on a C₂ axis and is a non‐meso furan­osyl furan­oside dimer derived from the monoacid mono­aldehyde corresponding to (I). One intermolecular C—H⋯O close contact exists. Diminished intramolecular void space in these small propellanoids generates unusually high crystal density in both species, particularly (I).     

Repeated solid-phase fermentation and extraction for enzyme production

Solid-phase fermentation has been found to have a much higher productivity than the popular liquid submerged fermentation in producing cellulase enzymes. The highest reported productivity in the literature for cellulases by Trichoderma cultures in submerged fermentation is 158 filter paper units (FPU)/(h·L) of fermenting liquid. From preliminary experiments of solid-phase fermentation in 1000-m L flasks, a productivity of 234 FPU of cellulases/(h·L) of solid-bed volume was obtained. When two novel techniques—pressure pulsation and repeated extraction—were applied, a productivity of 806 FPU/(h·L) was achieved. The same techniques also greatly enhanced the productivity of other enzymes by fungal cultures in solid-phase fermentation.     

Unbinding of the streptavidin-biotin complex by atomic force microscopy: a hybrid simulation study

A hybrid molecular simulation technique, which combines molecular dynamics and continuum mechanics, was used to study the single-molecule unbinding force of a streptavidin-biotin complex. The hybrid method enables atomistic simulations of unbinding events at the millisecond time scale of atomic force microscopy (AFM) experiments. The logarithmic relationship between the unbinding force of the streptavidin-biotin complex and the loading rate (the product of cantilever spring constant and pulling velocity) in AFM experiments was confirmed by hybrid simulations. The unbinding forces, cantilever and tip positions, locations of energy barriers, and unbinding pathway were analyzed. Hybrid simulation results from this work not only interpret unbinding AFM experiments but also provide detailed molecular information not available in AFM experiments.     

Effects of multivalent salt addition on effective charge of dilute colloidal solutions

The effective charge Z* is often invoked to account for the accumulation of counterions near the colloid with intrinsic charge Z. Although the ion concentrations c(i) are not uniform in the solution due to the presence of the charged particle, their chemical potentials are uniform everywhere. Thus, on the basis of ion chemical potential, effective ion concentrations c(i)*, which can be experimentally measured by potentiometry, are defined with the pure salt solution as the reference state. The effective charge associated with the charged particle can then be determined by the global electroneutrality condition. Monte Carlo simulations are performed in a spherical Wigner-Seitz cell to obtain the effective charge of the colloid. In terms of the charge ratio alpha=Z*/Z, the effects of added salt concentration, counterion valency, and particle charge are examined. The effective charge declines with increasing salt concentration and the multivalent salt is much more efficient in reducing the effective charge of the colloidal solution. Moreover, the extent of effective charge reduction is decreased with increasing intrinsic charge for a given concentration of added salt. Those results are qualitatively consistent with experimental observations by electrophoresis.