Base pairing and fidelity in codon-anticodon interaction

On the basis of chemical considerations and model building, the Watson-Crick concept of complementary base pairing is extended to a wider range of DNA pairs that A-T and G-C (including A-C, G-T, A-A, G-G and G-A) by invoking imino or enol tautomers (or protonated species) and synisomers. The virtual absence of these additional base pairs from DNA is explained in terms of the low frequency with which these unfavoured forms occur and the two-step mechanism of DNA synthesis, whereby residues are first incorporated by the DNA polymerase and then checked. This base-pairing hypothesis is used to explain the origin, nature and level of spontaneous substitution mutations, their enhancement by base analogues, and the unique effects of certain mutator alleles.     

Efficient mode transformations of degenerate Laguerre-Gaussian beams

We present an approach for efficient conversion of a single-high-order-mode distribution from a laser to a nearly Gaussian distribution and vice versa. It is based on dividing the high-order mode distribution into equal parts that are then combined together coherently. We implement our approach with several optical arrangements that include a combination of discrete elements and some with single interferometric elements. These arrangements are analyzed and experimentally evaluated for converting the TEM01 mode distribution with Mx(2) = 3 to a nearly Gaussian beam with Mx(2) = 1.045 or Mx(2) = 1.15. The basic principle, design, and experimental results obtained with several conversion arrangements are presented. The results reveal that conversion efficiency is typically greater than 90%, compared with theoretical ones. In addition, some arrangement is exploited for converting the fundamental Gaussian-beam distribution into the TEM01 mode distribution.     

Modeling study of the light stimulation of a neuron cell with channelrhodopsin-2 mutants

Channelrhodopsin-2 (ChR2) has become a widely used tool for stimulating neurons with light. Nevertheless, the underlying dynamics of the ChR2-evoked spikes are still not yet fully understood. Here, we develop a model that describes the response of ChR2-expressing neurons to light stimuli and use the model to explore the light-to-spike process. We show that an optimal stimulation yield is achieved when the optical energies are delivered in short pulses. The model allows us to theoretically examine the effects of using various types of ChR2 mutants. We show that while increasing the lifetime and shuttering speed of ChR2 have limited effect, reducing the threshold irradiance by increased conductance will eliminate adaptation and allow constant dynamic range. The model and the conclusion presented in this study can help to interpret experimental results, design illumination protocols, and seek improvement strategies in the nascent optogenetic field.     

Structural Effects in the Electrodeposition of CdSe Quantum Dots on Mechanically Strained Gold

CdSe nanoparticles were electrodeposited on mechanically strained gold, the latter achieved by controlled bending of gold films evaporated on mica. It is shown that the size and bandgap of the electrodeposited CdSe quantum dots (QDs) can be varied by applying mechanical strain to the Au substrate during deposition. This is attributed to change in the lattice spacing of the strained {111} Au and consequently in the lattice mismatch between the Au and the CdSe. Negative mechanical strain promotes the formation of rocksalt (RS) CdSe nanocrystals, normally existing only at high pressures. This is attributed to surface tension compression in the small crystals, together with enhancement of the phase transition by the CdSe/substrate interface.     

A Multiphase Dynamic Labeling Model for Variational Recognition-driven Image Segmentation

We propose a variational framework for the integration of multiple competing shape priors into level set based segmentation schemes. By optimizing an appropriate cost functional with respect to both a level set function and a (vector-valued) labeling function, we jointly generate a segmentation (by the level set function) and a recognition-driven partition of the image domain (by the labeling function) which indicates where to enforce certain shape priors. Our framework fundamentally extends previous work on shape priors in level set segmentation by directly addressing the central question of where to apply which prior. It allows for the seamless integration of numerous shape priors such that—while segmenting both multiple known and unknown objects—the level set process may selectively use specific shape knowledge for simultaneously enhancing segmentation and recognizing shape.     

Effect of yttrium additions on the properties of grain-refined Mg–3%Nd alloy

A systematic study was carried out to evaluate the effect of up to 2.5% yttrium additions on the properties of Mg–3%Nd alloy designated for high-temperature gravity casting applications. All the tested alloys were grain-refined by zirconium. The results show that additions of yttrium significantly improved the tensile yield strength, fatigue strength, and creep resistance while reducing the ductility. However, other properties such as the ultimate tensile strength and corrosion resistance in 5% NaCl solution were nearly not affected. The strengthening effect obtained by the yttrium additions is explained in terms of solid-solution strengthening and due to formation of a ternary phase of Mg–Nd–Y. The improved creep resistance was due to the large solubility of yttrium in solid-solution magnesium matrix and to the effective creep deformation barriers created by the ternary phase. The casting performance of the tested alloys in terms of fluidity was similar and no significant effect of the yttrium was evident