Reprogramming of Stem Cell Activity to Convert Thorns into Branches.

Thorns arise from axillary shoot apical meristems that proliferate for a time and then terminally differentiate into a sharp tip. Like other meristems, thorn meristems contain stem cells but, in the case of thorns, these stem cells undergo a programmed cessation of proliferative activity. Using Citrus, we characterize a gene network necessary for thorn development.

Type-B ARABIDOPSIS RESPONSE REGULATORs Directly Activate WUSCHEL.

The WUSCHEL (WUS) gene is necessary for the maintenance of stem cells in the shoot apical meristem. Four recent reports show that cytokinin responsive type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) directly activate WUS expression, providing a long-awaited explanation for how cytokinin influences the maintenance of the stem cell niche.

Probing Toluene and Ethylbenzene Stable Glass Formation Using Inert Gas Permeation.

Inert gas permeation is used to investigate the formation of stable glasses of toluene and ethylbenzene. The effect of deposition temperature (T(dep)) on the kinetic stability of the vapor deposited glasses is determined using Kr desorption spectra from within sandwich layers of either toluene or ethylbenzene. The results for toluene show that the most stable glass is formed at T(dep) = 0.

Desorption Kinetics of Ar, Kr, Xe, N2, O2, CO, Methane, Ethane, and Propane from Graphene and Amorphous Solid Water Surfaces.

The desorption kinetics for Ar, Kr, Xe, N2, O2, CO, methane, ethane, and propane from graphene-covered Pt(111) and amorphous solid water (ASW) surfaces are investigated using temperature-programmed desorption (TPD). The TPD spectra for all of the adsorbates from graphene have well-resolved first, second, third, and multilayer desorption peaks. The alignment of the leading edges is consistent the zero-order desorption for all of the adsorbates.

Mobility of supercooled liquid toluene, ethylbenzene, and benzene near their glass transition temperatures investigated using inert gas permeation.

We investigate the mobility of supercooled liquid toluene, ethylbenzene, and benzene near their respective glass transition temperatures (Tg). The permeation rate of Ar, Kr, and Xe through the supercooled liquid created when initially amorphous overlayers are heated above their glass transition temperature is used to determine the diffusivity. Amorphous benzene crystallizes at temperatures well below its Tg, and as a result, the inert gas underlayer remains trapped until the onset of benzene desorption.

The release of trapped gases from amorphous solid water films. II. "Bottom-up" induced desorption pathways.

In this (Paper II) and the preceding companion paper (Paper I; R. May, R. Smith, and B.

The release of trapped gases from amorphous solid water films. I. "Top-down" crystallization-induced crack propagation probed using the molecular volcano.

In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B.

The Molecular Volcano Revisited: Determination of Crack Propagation and Distribution During the Crystallization of Nanoscale Amorphous Solid Water Films.

Temperature programmed desorption (TPD) is utilized to determine the length distribution of cracks formed through amorphous solid water (ASW) during crystallization. This distribution is determined by monitoring how the thickness of an ASW overlayer alters desorption of an underlayer of O2. As deposited, ASW prevents desorption of O2.

Reactive ballistic deposition of nanostructured model materials for electrochemical energy conversion and storage.

Porous, high surface area materials have critical roles in applications including catalysis, photochemistry, and energy storage. In these fields, researchers have demonstrated that the nanometer-scale structure modifies mechanical, optical, and electrical properties of the material, greatly influencing its behavior and performance. Such complex chemical systems can involve several distinct processes occurring in series or parallel.

Probing the interaction of amorphous solid water on a hydrophobic surface: dewetting and crystallization kinetics of ASW on carbon tetrachloride.

Desorption of carbon tetrachloride from beneath an amorphous solid water (ASW) overlayer is explored utilizing a combination of temperature programmed desorption and infrared spectroscopy. Otherwise inaccessible information about the dewetting and crystallization of ASW is revealed by monitoring desorption of the CCl(4) underlayer. The desorption maximum of CCl(4) on graphene occurs at ~140 K.

Patterning high surface area silica with lysozyme: adsorption kinetics, fluorescence quenching, and protein readsorption studies to evaluate the templated surface.

A method was developed for using an inexpensive and widely available protein, hen egg white lysozyme, as a patterning agent for commercial high surface area silicas. The basic patterning methodology involved spontaneous adsorption of the protein from aqueous solution, alkylation of the uncovered surface with an alkylsiloxane, and protein desorption in a slightly alkaline solution of morpholine. Adsorption kinetic studies using Bradford assays assisted in determining protein deposition conditions.

Flow-based multiadsorbate ellipsometric porosimetry for the characterization of mesoporous Pt-TiO2 and Au-TiO2 nanocomposites.

Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO2 interactions and the influence of adsorbate polarity upon adsorption isotherms for mesoporous TiO2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Psi and Delta when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data.

Evaluation of lithium ion insertion reactivity via electrochromic diffraction-based imaging.

A microscope-CCD setup has been developed as an analytical tool for the detection of diffraction from one-dimensional redox-active transition-metal oxide gratings prepared with a combination of microtransfer molding (microTM) and cathodic electrodeposition. The diffraction efficiencies (DE) of tungsten trioxide, WO3, and binary molybdenum-tungsten trioxide, Mo0.6W0.

Electrochemical deposition and characterization of mixed-valent rhenium oxide films prepared from a perrhenate solution.

Cathodic electrodeposition of mixed-valent rhenium oxides at indium tin oxide, gold, rhenium, and glassy carbon electrodes from acidic perrhenate solutions (pH = 1.5 +/- 0.1) prepared from hydrogen peroxide and zerovalent rhenium metal is described.

Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts.

In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer.