Laser spectroscopy of LaF: Determination of the separation of the singlet and triplet state manifolds

Tunable dye lasers have been used to excite several known transitions in LaF. Resolved fluorescence spectra obtained after excitation of B¹Π-X¹Σ⁺ and C¹Π-X¹Σ⁺ bands showed transitions to both X¹Σ⁺ and a³Δ states. Analysis of the spectra shows that the state is 1432 cm⁻¹ above X¹Σ⁺, is at 1808 cm⁻¹, and there is an Ω = 2 state (probably ¹Δ) at 5478 cm⁻¹. A new 0⁺-X¹Σ⁺ (v = 0) band has been observed in the vicinity of the B¹Π-X¹Σ⁺ 1-0 band. High resolution excitation spectra of both bands have been obtained, term energies and rotational constants calculated, and the Λ-doubling in B¹Π, v = 1 has been studied. The principal constants (in cm⁻¹) obtained from the analyses wereThe assignments of the low lying states are discussed in terms of their electron configurations and are shown to be in accord with predictions of Ligand Field Theory.     

Molecular orientation by surface forces ii. on the prediction of orientation of crystal overgrowths

Previous workers have attempted to explain epitaxy and oriented crystal growth by various approaches but none of the models had significant predictive power for predetermining the orientation of a specific substrate-deposit interaction.We present an empirical approach based upon mathematically determining relative potential minima on the substrate surface and the alignment of the deposition nucleus within this energy well. This model has been tested on a wide variety of substrate-deposit systems and found to exhibit a high degree of orientational predictive capacity.     

Orbits under actions of affine groups over GF (2)

Let G be a group (or vector space) and A a group of transformations of G. A then acts as a group of transformations of P(G), the set of subsets of G. It is meaningful to study the orbit structure of P(G) under the action of A. The question of the existence of elements of P(G) with trivial isotropy subgroup seems to be of interest in studying the action of A on G. In this paper actions of affine groups over GF (2) are considered. It is proved, by an inductive construction, that every vector space over GF (2) of dimension at least six contains a subset with trivial isotropy subgroup.     

Measurement of asymmetric optical pumping of ions accelerating in a magnetic-field gradient

We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic-field gradient. The signature is a difference in the laser-induced-fluorescence emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities.     

Mixed data rate and format transmission (40-Gbit/s non-return-to-zero, 40-Gbit/s duobinary, and 10-Gbit/s non-return-to-zero) by mid-link spectral inversion

A polarization-diverse subsystem based on periodically poled lithium niobate waveguides is used as an optical phase conjugator for compensation for linear and nonlinear distortion. We show successful transmission formats of 13 x 40 Gbit/s non-return-to-zero mixed with 6 x 10 Gbit/s non-return-to-zero and 40-Gbit/s duobinary over 8 x 100 km of standard single-mode fiber. A single phase conjugator is used to conjugate all data formats, including the alternative duobinary format, simultaneously.     

Enhancement of high-order harmonic generation at tuned wavelengths through adaptive control

An adaptive learning loop enhances the efficiency and tuning of high-order harmonic generation. In comparison with simple chirp tuning, we observe a broader tuning range and a twofold to threefold enhancement in integrated photon flux in the cutoff region. The driving pulse temporal phase varies significantly for different tunings and is more complicated than a simple chirp. We compare our experimental results with a one-dimensional, time-dependent model that incorporates the intrinsic atomic response, the experimental pulse temporal phase, ionization effects, and transverse coherence of the spatial mode of the laser. The model agrees with our experimental results and indicates that a specific quantum path coupled with ionization effects determines the optimized harmonic spectrum.     

Hydroxystilbene isomer-specific photoisomerization versus proton transfer

The ground- and excited-state acidities of 3- and 4-hydroxystilbene have been investigated in aqueous solution. Approximate pKa* values determined from the F?rster equation are similar for the two isomers; however, 3-hydroxystilbene behaves as a photoacid in water, whereas 4-hydroxystilbene does not. Singular value decomposition with self-modeling is used to obtain more accurate pKa* values for 3-hydroxystilbene. The different behavior of the isomeric hydroxystilbenes is attributed to differences in their excited-state C=C torsional barriers. 3-Hydroxystilbene has a high barrier and a long singlet lifetime, permitting proton transfer to compete with other singlet decay pathways, whereas 4-hydroxystilbene has a low barrier, and thus proton transfer cannot compete with C=C torsion.     

Preparation,X-ray structure and reactivity of a stable glycosyl iodide

Highly selective reaction of methyl tetra-O-pivaloyl-beta-D-glucopyranuronate 2 with iodotrimethylsilane or (Me3Si)2 and I2 affords, in excellent yield, the 'disarmed' glycosyl iodide 1 which has good stability at 20 degrees C and excellent stability at 0 degrees C; the X-ray crystal structure of 1 is described, along with a comparison of its utility as a glycosyl donor to that of the corresponding bromide.     

Theoretical strength and cleavage of diamond

The theoretical strength of diamond has been calculated for the <100>, <110>, and <111> directions using a first principles approach and is found to be strongly dependent on crystallographic direction. This elastic anisotropy, found at large strains, and particularly the pronounced minimum in cohesion in the <111> direction, is believed to be the reason for the remarkable dominance of the 111 cleavage plane when diamond is fractured. The extra energy required to cleave a crystal on planes other than 111 is discussed with reference to simple surface energy calculations and also the introduction of bond-bending terms.     

In Situ Self-Assembly of Quantum Dots at the Plasma Membrane Mediates Energy Transfer-Based Activation of Channelrhodopsin

The use of nanoparticle (NP) bioconjugates to control the activity of membrane ion channels has recently emerged as a new paradigm for the activation of electrically excitable cells. An NP-based strategy is reported for the specific activation of channelrhodopsin C1V1 (ChR-C1V1) expressed in the plasma membrane of HEK 293T/17 cells. Hydrophilic CdSe/ZnS core–shell semiconductor quantum dots (QDs) are self-assembled to the exofacial face of recombinantly expressed ChR-C1V1 by metal affinity-driven interaction of the QD ZnS shell with an N-terminal hexahistidine tag displayed on ChR-C1V1. This configuration enables the Förster resonance energy transfer (FRET)-based excitation and activation of the 11-cis-retinal moiety of ChR-C1V1 using the QD as a light harvesting transducer/energy donor. It is shown that the specific laser-induced opening of the ChR-C1V1 channel wherein the photoexcited QD (405 nm excitation, 530 nm emission) iteratively activates ChR-C1V1 channels as confirmed using the voltage-sensitive dye (VSD) bis-(1,3-diethylthiobarbituric acid)trimethine oxonol (DiSBAC ₂ (3)). In the absence of the QD transducer, excitation of ChR-C1V1-expressing cells at 405 nm results in no activation of ChR-C1V1. The results demonstrate the ability to controllably interface QDs with living cells for the activation of ChR membrane proteins and detail a new NP-bioconjugate hybrid system for the specific activation of ion channels.