Evolution of material voids for highly anisotropic surface energy

In this paper we consider the evolution by surface diffusion of material voids in a linearly elastic solid, focusing on the evolution of voids with large surface energy anisotropy. It is well known that models for the time evolution of similar material surfaces can become mathematically ill-posed when the surface energy is highly anisotropic. In some cases, this ill-posedness has been associated with the formation of corners along the interface. Here the ill-posedness is removed through a regularization which incorporates higher order terms in the surface energy. Spectrally accurate numerical simulations are performed to calculate the steady-state solution branches and time-dependent evolution of voids, with a particular emphasis on inferring trends in the zero regularization (c→0) limit. For steady voids with large anisotropy we find that apparent corners form as c→0. In the presence of elastic stresses σ the limiting corner angles are most often found to differ from angles found on the (σ=0) Wulff shape. For large elastic stresses we find that steady solutions no longer exist; instead the void steadily lengthens via a filamenting instability referred to as tip streaming.     

Synthesis and Intracellular Redox Cycling of Natural Quinones and Their Analogues and Identification of Indoleamine‐2,3‐dioxygenase (IDO) as Potential Target for Anticancer Activity

Natural quinones, often linked with cellular oxidation processes, exhibit pronounced biological activity. In particular, the structurally unique isothiazolonaphthoquinone aulosirazole, isolated from blue‐green alga, possesses selective antitumor cytotoxicity, although its mechanism of action is unknown. The first synthesis of aulosirazole uses a route centered upon a late‐stage regioselective Diels–Alder reaction. The structurally related natural product pronqodine A, an inhibitor of prostaglandin release, and analogues thereof, were also prepared for comparison. Biological evaluation of the compounds identified one potential target as the immunoregulatory enzyme indoleamine‐2,3‐dioxygenase (IDO). The isothiazoloquinones are also efficient substrates for the human quinone reductase NQO1, and undergo intracellular NQO1‐dependent redox cycling resulting in the generation of reactive oxygen species, and at lower doses have the potential to alter the ratio of intracellular oxidized to reduced pyridine nucleotides.     

Phase Behavior of a Designed Cyclopropyl Analogue of Monoolein: Implications for Low‐Temperature Membrane Protein Crystallization

Lipidic cubic phases (LCPs) are used in areas ranging from membrane biology to biodevices. Because some membrane proteins are notoriously unstable at room temperature, and available LCPs undergo transformation to lamellar phases at low temperatures, development of stable low‐temperature LCPs for biophysical studies of membrane proteins is called for. Monodihydrosterculin (MDS) is a designer lipid based on monoolein (MO) with a configurationally restricted cyclopropyl ring replacing the olefin. Small‐angle X‐ray scattering (SAXS) analyses revealed a phase diagram for MDS lacking the high‐temperature, highly curved reverse hexagonal phase typical for MO, and extending the cubic phase boundary to lower temperature, thereby establishing the relationship between lipid molecular structure and mesophase behavior. The use of MDS as a new material for LCP‐based membrane protein crystallization at low temperature was demonstrated by crystallizing bacteriorhodopsin at 20 °C as well as 4 °C.     

A molecular half-wave rectifier

This paper describes the performance of junctions based on self-assembled monolayers (SAMs) as the functional element of a half-wave rectifier (a simple circuit that converts, or rectifies, an alternating current (AC) signal to a direct current (DC) signal). Junctions with SAMs of 11-(ferrocenyl)-1-undecanethiol or 11-(biferrocenyl)-1-undecanethiol on ultraflat, template-stripped Ag (Ag(TS)) bottom electrodes, and contacted by top electrodes of eutectic indium-gallium (EGaIn), rectified AC signals, while similar junctions based on SAMs of 1-undecanethiol-SAMs lacking the ferrocenyl terminal group-did not. SAMs in these AC circuits (operating at 50 Hz) remain stable over a larger window of applied bias than in DC circuits. AC measurements, therefore, can investigate charge transport in SAM-based junctions at magnitudes of bias inaccessible to DC measurements. For junctions with SAMs of alkanethiols, combining the results from AC and DC measurements identifies two regimes of bias with different mechanisms of charge transport: (i) low bias (|V| < 1.3 V), at which direct tunneling dominates, and (ii) high bias (|V| > 1.3 V), at which Fowler-Nordheim (FN) tunneling dominates. For junctions with SAMs terminated by Fc moieties, the transition to FN tunneling occurs at |V| ≈ 2.0 V. Furthermore, at sufficient forward bias (V > 0.5 V), hopping makes a significant contribution to charge transport and occurs in series with direct tunneling (V ? 2.0 V) until FN tunneling activates (V ? 2.0 V). Thus, for Fc-terminated SAMs at forward bias, three regimes are apparent: (i) direct tunneling (V = 0-0.5 V), (ii) hopping plus direct tunneling (V ≈ 0.5-2.0 V), and (iii) FN tunneling (V ? 2.0 V). Since hopping does not occur at reverse bias, only two regimes are present over the measured range of reverse bias. This difference in the mechanisms of charge transport at forward and reverse bias for junctions with Fc moieties resulted in large rectification ratios (R > 100) and enabled half-wave rectification.     

Hydroxyl-directed cyclizations of 1,6-enynes

The palladium-catalyzed, hydroxyl-directed cyclization reactions of 1,6-enynes provide a highly diastereoselective process for the syntheses of stereochemically defined cyclopentanes. Consistently high levels of cis-selectivity are possible using homopropargyl alcohols in contrast to the corresponding propargyl alcohols. Hydroborylative enyne cyclizations coupled with this directing group effect provide a useful method for the syntheses of multifaceted compounds bearing all carbon quaternary centers.     

Wavelength-Resolved 3-Dimensional Fluorescence Lifetime Imaging

We have developed a compact system for wide-field fluorescence imaging, resolved in three spatial dimensions, lifetime and wavelength, that is based on a gated optical intensifier and an all-solid-state diode pumped Cr:LiSAF oscillator-amplifier system. Exploiting spectral separation, the system has been applied to human teeth, obtaining good lifetime contrast between enamel, dentin and caries. Exploiting spectral separation combined with depth resolution, the study of fluorescent microspheres led to an enhancement in both lifetime contrast and lateral resolution.     

Correlation between mechanical and electrical properties on conductive SiC-fibre reinforced composites

Electrical and mechanical properties of ceramic composites are investigated to develop “smart materials” and establish a fracture prediction technique. The “smart materials” are based on silicon carbide fibre-reinforced composites. The SiC-fibres were checked to determine the changes in mechanical and electrical properties during the composites’ production. Samples were produced for the determination of the mechanical strength with in situ detection of the degree of damage by recording the electrical resistance.     

Distinguishable equivalent particles with symmetrized wave functions

The quantum formalism ofdistinguishable, yetequivalent particles (with symmetric or antisymmetric wave functions) is here worked out. The result is an entirely explicit formulation of the way in which classical mechanics emerges from quantum mechanics for such particles. Distinguishability is achieved at the cost of dynamical precision; the two are, in fact, complementary.Research sponsored in part by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR Grant No. 557–67.