Effects of Substrate Orientation and Metal Film Thickness on the Intrinsic Strength, Intrinsic Fracture Energy, and Total Fracture Energy of Tantalum–Sapphire Interfaces

Parameters that characterize interface fracture are defined, and procedures to measure them are discussed. The interface strength σ_o is measured by using a novel laser spallation experiment, which uses a laser-induced stress wave to separate the interface. The intrinsic ( G _o) and total ( G _c) fracture energies are measured using a double cantilever beam experiment performed at ambient and cryogenic temperatures, respectively. These experiments are used to obtain relationships between G _c and G _o, and between σ_o and G _o, for interfaces between sputter-deposited polycrystalline Ta coatings and sapphire substrates. The intrinsic toughness and strength were modified by changing the orientation of the sapphire surface (basal and prismatic), while G _c was varied by changing the test temperature (ambient and cryogenic) and the thickness (1–3 μm) of the ductile Ta layer. Besides providing values that have interest in their own right, the work presented here provides a general framework for designing interfaces in bonded structures and serves as a basis to develop atomistic and continuum interface fracture models.     

Dry Sliding Tribological Behavior of Brake Oil Conditioned Ceramic Matrix Composites Reinforced With Carbon Fabric

Silicon - Ceramic composites are extremely sensitive to the surrounding environment. Their tribological performance may degrade drastically if they are polluted by some external agent. The present...     

1-[2-(1-Cyclobutylpiperidin-4-yloxy)-6,7-dihydro-4H-thiazolo[5,4-c]pyridin-5-yl]propan-1-one: a Histamine H3 Receptor Inverse Agonist with Efficacy in Animal Models of Cognition

A series of chemical optimizations, which was guided by in vitro affinity at histamine H₃ receptor (H₃R), modulation of lipophilicity, ADME properties and preclinical efficacy resulted in the identification of 1-[2-(1-cyclobutylpiperidin-4-yloxy)-6,7-dihydro-4H-thiazolo[5,4-c]pyridin-5-yl]propan-1-one ( 45 e ) as a potent and selective (K_i=4.0 nM) H₃R inverse agonist. Dipsogenia induced by (R)-α-methylhistamine was dose dependently antagonized by 45 e , confirming its functional antagonism at H₃R. It is devoid of hERG and phospholipidosis issues. Compound 45 e has adequate oral exposures and favorable half-life in both rats and dogs. It has demonstrated high receptor occupancy (ED₈₀=0.22 mg/kg) and robust efficacy in object recognition task and, dose dependently increased acetylcholine levels in brain. The sub-therapeutic doses of 45 e in combination with donepezil significantly increased acetylcholine levels. The potent affinity, selectivity, in vivo efficacy and drug like properties together with safety, warrant for further development of this molecule for potential treatment of cognitive disorders associated with Alzheimer's disease.     

A Review on Wear and Friction Performance of Carbon–Carbon Composites at High Temperature

Carbon–carbon (C/C) composite is one of the best ceramic matrix composite due to its high mechanical properties and applications at control environments in various sectors. Carbon–carbon composite is made of woven carbon fibers; carbonaceous polymers and hydrocarbons are used as matrix precursors. These composites generally have densities <2.0 g/cm³ even after densification. C/C composites have good frictional properties and thermal conductivity at high temperature. Also C/C composite can be used as brake pads in high‐speed vehicles. In spite of various applications, C/C composites are very much prone to oxidation at high temperature. Therefore, C/C composites must be protected from oxidation for the use at high temperature.     

Polyaniline / carbon nanotube composites: starting with phenylamino functionalized carbon nanotubes

Summary Composites of carbon a nanotube with polymers are a developing and interesting area of research. The dispersion of the nanotube in polymer matrices is an important factor while making its nanocomposites. Even though in-situ polymerization approach offers a better approach for synthesizing homogeneous polymer nanotube composites, the dispersion of the nanotubes in the monomer solution is a problem. In this article we report a new chemical method for dispersing nanotubes in monomer and the preparation of uniform tubular composite of polyaniline (PANI) and multiwalled carbon nanotube (MWNT). For this the oxidized multiwalled nanotube (o-MWNT) was functionalized with p-phenylenediamine, which gave phenylamine functional groups on the surface. This functionalization helped to disperse the nanotubes in acidic solution. The in-situ polymerization of aniline in the presence of these well dispersed nanotubes gave a new tubular composite of carbon nanotube having an ordered uniform encapsulation of doped polyaniline. The phenylamine functional groups on the surface were grown into polyaniline chain so that the composite contains polyaniline functionalized CNT and they were no more an impurity in the final nanocomposite. The microscopic and structural properties of this composite were compared with that of a composite prepared under identical condition using o-MWNT.     

Amyloidogenic Properties of Peptides Derived from the VHL Tumor Suppressor Protein

The von Hippel-Lindau tumor suppressor protein (pVHL) is involved in maintaining cellular oxygen homeostasis through the regulated degradation of HIF-α. The intrinsically disordered nature of pVHL makes it prone to aggregation that impairs its function, and this is further aggravated in mutant versions of the protein, thus promoting tumor development. By using in silico analysis, we predicted six peptide fragments from pVHL to be amyloidogenic. This was verified for two of the peptides by biophysical approaches, which demonstrated self-assembly and formation of β-sheet-rich aggregates, which, under transmission electron microscopy, atomic force microscopy, and X-ray diffraction, displayed typical fibrillar amyloid characteristics. These motifs may serve as proxies for exploring the nature of pVHL aggregation.     

Adhesion and Debonding of Soft Elastic Films on Rough and Patterned Surfaces

With the help of simulations based on energy minimization, we have studied the effect of roughness of a rigid contactor with sinusoidal and step patterns on the adhesion-debonding cycle of a soft thin elastic film. The surface instability engendered by attractive forces between the contactor and the film produces a regularly spaced array of columns in the bonding phase. The inter-column spacing is governed largely by periodicity of the contactor pattern. Decreased periodicity of the pattern favors intermittent collapse of columns rather than a continuous peeling of contact zones. An increase in the amplitude of roughness decreases the maximum force required for debonding and increases the snap-off distance. The net effect results in a reduced work for debonding. Introduction of noise and increased step-size in simulations decreases the pull-off force and the snap-off distance, as in the case of a smooth contactor. Finally the study reveals that a patterned contactor can be used as a potential template in the patterning of soft interfaces.     

Application of the phase extension method in virus crystallography

The procedure for phase extension (PX) involves gradually extending the initial phases from low resolution (e.g. ～8?Å) to the high-resolution limit of a diffraction data set. Structural redundancy present in the viral capsids that display icosahedral symmetry results in a high degree of non-crystallographic symmetry (NCS), which in turn translates into higher phasing power and is critical for improving and extending phases to higher resolution. Greater completeness of the diffraction data and determination of a molecular replacement solution, which entails accurately identifying the virus particle orientation(s) and position(s), are important for the smooth progression of the PX procedure. In addition, proper definition of a molecular mask (envelope) around the NCS-asymmetric unit has been found to be important for the success of density modification procedures, such as density averaging and solvent flattening. Regardless of the degree of NCS, the PX method appears to work well in all space groups, provided an accurate molecular mask is used along with reasonable initial phases. However, in the cases with space group P1, in addition to requiring a molecular mask, starting the PX at a higher resolution (e.g. 6?Å) overcame the previously reported problems due to Babinet phases and phase flipping errors.     

Enhancement of resistance to galvanic corrosion of ZE41 Mg alloy by equal channel angular pressing

The galvanic corrosion behavior of as-received and ECAPed ZE41 Mg alloy coupled with Al7075 alloy is investigated using zero resistance ammeter in three different corrosive environments, 0, 0.1, and 1 M NaCl, to mimic the conditions experienced in engineering applications. The mechanism of galvanic corrosion for the ZE41 Mg–Al7075 aluminum alloy is explained. It is observed that a robust surface film containing a composite layer of oxide/hydroxide of magnesium and aluminum is established in deionized water (0 M). However, only a single layer of magnesium oxide/hydroxide is detected in chloride-containing environments. Equal channel angular pressing (ECAP) improved the resistance to galvanic corrosion by 58% and 54% when compared with the as-cast counterparts in 0 and 1 M NaCl solution, respectively. In contrast, galvanic corrosion resistance decreased by 26% in 0.1 M NaCl after ECAP while the as-received samples evinced pits unfavorable to be used in engineering applications. ECAP is a promising method to combat galvanic corrosion encountered by ZE41 magnesium alloy used in automobiles and components of military vehicles.     

Sol-gel auto-combustion synthesis of Ba–Sr hexaferrite ceramic powders

We report the mechanism involved in sol-gel auto-combustion synthesis of Ba–Sr-hexaferrite (Ba_1-xSr_xFe₁₂O₁₉; x = 0, 0.25, 0.5, 0.75 and 1, BSFO) ceramic powders through the analysis of the phases evolved during annealing of the as-synthesized powders, along with their structure and morphological studies. The XRD patterns of the as-synthesized samples indicate the formation of barium/strontium monoferrite ((Ba/Sr)Fe₂O₄) and maghemite (γ-Fe₂O₃) phases along with a minute amount of hematite (α-Fe₂O₃) phase. Annealing of these samples facilitates formation of BSFO phase through the solid state reaction between BaFe₂O₄ and γ-Fe₂O₃ phase. Interestingly, after annealing the samples with x = 0, 0.5 and 1, at 1000 °C for 2 h, we observed that phase pure Ba–Sr hexaferrite structure forms, but for samples with x = 0.25 and 0.75, high amount of hematite (α-Fe₂O₃) phase is observed, especially for x = 0.75. The reason associated with this could be the large difference between the ionic radii of Ba²⁺ and Sr²⁺ ions occupying the oxygen site. Furthermore, our study on annealing dependent phase evolution confirms that, this difference in ionic radii forbids the formation of a single phase Ba–Sr hexaferrite. The growth of clear hexagonal-shaped plate-like particles with varied particle sizes was observed for all the samples. The particle size variation may be due to the influence of the ionic radii difference on the sinterability of the samples. Our study provides a better understanding of synthesis mechanism of Ba–Sr hexaferrite samples.