Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts

The slurry-based Three Dimensional Printing (3DP^TM) process requires the production of an easily redispersible powder bed from a well-dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle–particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle–particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low-molecular-weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.     

Self-Catalyzed Synthesis of Organo-Silica Nanoparticles

A procedure has been developed which utilizes aminopropyltriethoxysilane (APS) as the catalyst and a comonomer in the production of hybrid organo-silica nanoparticles. Particles ranging from ca. 100 to 500 nm can be prepared using organo-silanes of the type R'Si(OR)₃, where R'= Me, vinyl, allyl, or other hydrophobic groups and R = Me or Et, in a water/surfactant solution. Based on elemental analysis, up to 10 mol% of APS was incorporated into the siloxane particle network. It is thought that the amino groups are located mainly on the surface due to their hydrophilicity and APS' relatively slow rate of hydrolysis and condensation.     

Self-Propagating High-Temperature Synthesis of Aluminum Nitride under Lower Nitrogen Pressures

The synthesis of aluminum nitride (AlN) via self-propagating high-temperature synthesis (SHS) was attempted, using aluminum powder that was mixed with AlN powder as a diluent. The AlN content in the reactant was varied over a range of 30%–70%, and the nitrogen pressure was varied over a range of 0.1–1.0 MPa. The SHS reaction that was performed using a reactant that contained 50% AlN diluent, under a nitrogen-gas pressure of 0.8 MPa, yielded the highest conversion ratio of aluminum powder to AlN powder. A mechanism for the reaction of aluminum with nitrogen gas during the SHS process was discussed, based on observations of the microstructures of the reaction zone and products.     

Discrimination of Prey, But Not Plant, Chemicals by Actively Foraging, Insectivorous Lizards, the Lacertid Takydromus sexlineatus and the Teiid Cnemidophorus gularis

Sampling environmental chemicals to reveal prey and predators and to provide information about conspecifics is highly developed in lizards. Actively foraging lizards can discriminate between prey chemicals and control stimuli, but ambush foragers do not exhibit prey chemical discrimination. Recent experiments on a few species of herbivorous lizards have also demonstrated an ability to identify plant food chemicals. We studied chemosensory responses to chemicals from prey and palatable plants in two species of actively foraging, insectivorous lizards. Both the lacertid Takydromus sexlineatus and the teiid Cnemidophorus gularis exhibited strong responses to prey chemicals, but not to plant chemicals. These findings increase confidence in the relationship between prey chemical discrimination and foraging mode, which is based on data for very few species per family. They also provide data showing that actively foraging insectivores in two families do not respond strongly to plant cues. Such information is essential for eventual comparative studies of the relationship between plant diet and responses to food chemicals. The traditional method of presenting stimuli by using hand-held cotton swabs worked well for T. sexlineatus but could not be used for C. gularis due to repeated escape attempts. When stimuli were presented to C. gularis on ceramic tiles and no experimenter was visible, the lizards responded readily. Presentation of stimuli on tiles in the absence of a visible experimenter may be a valuable approach to study of food chemical discrimination by active foragers in which antipredatory behavior interferes with responses to swabs.     

玩转巧手坊

经常有朋友问：“我想自己动手做点东西,你知道哪里有合适的地方？”我的答案通常都是南坪步行街上的巧艺手工坊。     

Valid KIC Determination via In-Test Subcritical Precracking of Chevron-Notched Bend Bars

The initiation of the crack in a chevronnotched bend bar was studied. Ideal testing conditions depend strongly on specimen preparation and material; valid K_IC values do not always result. An in-test precracking technique was developed for ceramics at room and elevated temperatures. A yttria-partially-stabilized zirconia ceramic was tested, and the results showed that ideal testing conditions were obtained, which guaranteed valid K_IC determination.     

Thermal Properties of Hf‐Doped ZrB2 Ceramics

The effect of Hf additions on the thermal properties of ZrB₂ ceramics was studied. Reactive hot pressing of ZrH₂, B, and HfB₂ powders was used to synthesize (Zr_1?x,Hf_x)B₂ ceramics with Hf contents ranging from x = 0.0001 (0.01 at.%) to 0.0033 (0.33 at.%). Room‐temperature heat capacity values decreased from 495 J·(kg·K)^?1 for a Hf content of 0.01 at.% to 423 J·(kg·K)^?1 for a Hf content of 0.28 at.%. Thermal conductivity values decreased from 141 to 100 W·(m·K)^?1 as Hf content increased from 0.01 to 0.33 at.%. This study revealed, for the first time, that small Hf contents decreased the thermal conductivity of ZrB₂ ceramics. Furthermore, the results indicated that reported thermal properties of ZrB₂ ceramics are affected by the presence of impurities and do not represent intrinsic behavior.     

Aquaporins in Salivary Glands: From Basic Research to Clinical Applications

Salivary glands are involved in saliva secretion that ensures proper oral health. Aquaporins are expressed in salivary glands and play a major role in saliva secretion. This review will provide an overview of the salivary gland morphology and physiology of saliva secretion, and focus on the expression, subcellular localization and role of aquaporins under physiological and pathophysiological conditions, as well as clinical applications involving aquaporins. This review is highlighting expression and localization of aquaporins in human, rat and mouse, the most studied species and is pointing out possible difference between major salivary glands, i.e., parotid, submandibular and sublingual glands.     

The Fungus <Emphasis Type="Italic">Raffaelea lauricola</Emphasis> Modifies Behavior of Its Symbiont and Vector,the Redbay Ambrosia Beetle (<Emphasis Type="Italic">Xyleborus Glabratus</Emphasis>), by Altering Host Plant Volatile Production

The redbay ambrosia beetle Xyleborus glabratus is the vector of the symbiotic fungus, Raffaelea lauricola that causes laurel wilt, a highly lethal disease to members of the Lauraceae family. Pioneer X. glabratus beetles infect live trees with R. lauricola, and only when tree health starts declining more X. glabratus are attracted to the infected tree. Until now this sequence of events was not well understood. In this study, we investigated the temporal patterns of host volatiles and phytohormone production and vector attraction in relation to laurel wilt symptomology. Following inoculations with R. lauricola, volatile collections and behavioral tests were performed at different time points. Three days after infection (DAI), we found significant repellency of X. glabratus by leaf odors of infected swamp bay Persea palustris as compared with controls. However, at 10 and 20 DAI, X. glabratus were more attracted to leaf odors from infected than non-infected host plants. GC-MS analysis revealed an increase in methyl salicylate (MeSA) 3 DAI, whereas an increase of sesquiterpenes and leaf aldehydes was observed 10 and 20 DAI in leaf volatiles. MeSA was the only behaviorally active repellent of X. glabratus in laboratory bioassays. In contrast, X. glabratus did not prefer infected wood over healthy wood, and there was no associated significant difference in their volatile profiles. Analyses of phytohormone profiles revealed an initial increase in the amount of salicylic acid (SA) in leaf tissues following fungal infection, suggesting that the SA pathway was activated by R. lauricola infection, and this activation caused increased release of MeSA. Overall, our findings provide a better understanding of X. glabratus ecology and underline chemical interactions with its symbiotic fungus. Our work also demonstrates how the laurel wilt pathosystem alters host defenses to impact vector behavior and suggests manipulation of host odor by the fungus that attract more vectors.     

An Engineered Tryptophan Synthase Opens New Enzymatic Pathways to β‐Methyltryptophan and Derivatives

β‐Methyltryptophans (β‐mTrp) are precursors in the biosynthesis of bioactive natural products and are used in the synthesis of peptidomimetic‐based therapeutics. Currently β‐mTrp is produced by inefficient multistep synthetic methods. Here we demonstrate how an engineered variant of tryptophan synthase from Salmonella (StTrpS) can catalyse the efficient condensation of l ‐threonine and various indoles to generate β‐mTrp and derivatives in a single step. Although l ‐serine is the natural substrate for TrpS, targeted mutagenesis of the StTrpS active site provided a variant (βL166V) that can better accommodate l ‐Thr as a substrate. The condensation of l ‐Thr and indole proceeds with retention of configuration at both α‐ and β‐positions to give (2S,3S)‐β‐mTrp. The integration of StTrpS (βL166V) with l ‐amino acid oxidase, halogenase enzymes and palladium chemocatalysts provides access to further d ‐configured and regioselectively halogenated or arylated β‐mTrp derivatives.