THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE

In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT₅₀ (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT₅₀, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT₅₀, Escape from photoreversibility did not occur at 27°C in seeds in which the GT₅₀ had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action.     

Final-state effects in neutron Compton scattering measurements on zirconium deuteride and beryllium

We report inelastic neutron scattering measurements of the neutron Compton profile, J(y), for Be and for D in polycrystalline [Formula: see text] over a range of momentum transfers, q between 27 and [Formula: see text]. The measurements were performed using the inverse geometry spectrometer eVS which is situated at the UK pulsed spallation neutron source ISIS. We have investigated deviations from impulse approximation (IA) scattering which are generically referred to as final-state effects (FSEs) using a method described by Sears. This method allows both the magnitude and the q dependence of the FSE to be studied. Analysis of the measured data was compared with analysis of numerical simulations based on the harmonic approximation and good agreement was found for both [Formula: see text] and Be. Finally we have shown how [Formula: see text], where V is the interatomic potential, can be extracted from the antisymmetric component of J(y).     

Spatially Controlled Occlusion of Polymer‐Stabilized Gold Nanoparticles within ZnO

In principle, incorporating nanoparticles into growing crystals offers an attractive and highly convenient route for the production of a wide range of novel nanocomposites. Herein we describe an efficient aqueous route that enables the spatially controlled occlusion of gold nanoparticles (AuNPs) within ZnO crystals at up to 20 % by mass. Depending on the precise synthesis protocol, these AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. Remarkably, such efficient occlusion is mediated by a non‐ionic water‐soluble polymer, poly(glycerol monomethacrylate)₇₀ (G₇₀), which is chemically grafted to the AuNPs; pendent cis‐diol side groups on this steric stabilizer bind Zn²⁺ cations, which promotes nanoparticle interaction with the growing ZnO crystals. Finally, uniform occlusion of G₇₀‐AuNPs within this inorganic host leads to faster UV‐induced photodegradation of a model dye.     

Vacuum moulding of a superplastic in two dimensions

A mathematical model is proposed for the process of vacuum superplasticforming. The model exploits the fact that in most industrialapplications the sheet aspect ratio (thickness/sheet width)is small. After an initial consideration of some of the moregeneral properties and the literature of superplastic materials,the elastic/plastic deformation of an internally-inflated thin-walledcylinder is examined. Plates of arbitrary geometry are thenconsidered. A quasisteady model in which the sheet moves througha sequence of steady states is developed. Some simplified closed-formsolutions are examined, but for general cases a system of nonlinearpartial differential equations must be solved numerically. Anefficient and accurate semi-explicit numerical scheme is proposedand a simplified stability analysis is presented; the methodis then used to compute properties of superplastic vacuum mouldedsheets in a number of practically motivated cases.     

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2Ti3O7 in Na-Ion Batteries

Na₂Ti₃O₇ (NTO) is considered a promising anode material for Na-ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na⁺/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na₂Ti₆O₁₃. The enhanced electrochemical performance agrees with the higher Na⁺ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.     

Development of a new casting method to fabricate U–Zr alloy containing minor actinides

Metal fuel slugs of U–Zr alloys for a sodium-cooled fast reactor (SFR) have conventionally been fabricated using an injection casting method. However, casting alloys containing volatile radioactive constituents, such as Am, are problematic in a conventional injection casting method. As an alternative fabrication method, low pressure gravity casting has been developed. Casting soundness, microstructural characteristics, alloying composition, density, and fuel losses were evaluated for the following as-cast fuel slugs: U–10 wt% Zr, U–10 wt% Zr–5 wt% RE, and U–10 wt% Zr–5 wt% RE–5 wt% Mn. The U and Zr contents were uniform throughout the matrix, and impurities such as oxyen, carbon, and nitrogen satisfied the specification of total impurities less than 2,000 ppm. The appearance of the fuel slugs was generally sound, and the internal integrity was shown to be satisfactory based on gamma-ray radiography. In a volatile surrogate casting test, the U–Zr–RE–Mn fuel slug showed that nearly all of the manganese was retained when casting was done under an inert atmosphere.     

Zirconocene catalysis in the synthesis of 1,4-dimagnesium reagents: using competitive inhibition to suppress β-hydrogen abstraction

Substituted 1,4-dimagnesium reagents were synthesized by the zirconocene-catalyzed reaction of alkenes with ethylmagnesium reagents in the presence of a methylmagnesium containing additive. Improved selectivity for formation of dimagnesium reagents over monomagnesium reagents was obtained in the presence of the methylmagnesium containing additive. The ratio of mono- to dimagnesiated products was extrapolated from the ratio of alkene to diene in the products formed when the reaction was quenched with allyl bromide. The extent of the increase in the alkene/diene ratio was dependent on the type of organomagnesium halide, with greatest increases (59%) for the alkylmagnesium chlorides. A mechanism for improved selectivity by suppression of β-hydrogen abstraction in the catalytic cycle is presented. Quenching the 1,4-dimagnesium reagents with allyl bromide yielded decadienes.     

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.