Preparation of Chiral Amino Esters by Asymmetric Phase‐Transfer Catalyzed Alkylations of Schiff Bases in a Ball Mill

The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified.     

A vectorial algorithm with finite element method for prediction of powder segregation in metal injection molding

The design of the mold and the choice of the injection parameters for metal injection molding (MIM) is required to maintain homogeneity of the filled mixture. However, powder segregation is unavoidable in MIM because of the significant difference in densities of the metallic powder and the polymer binder. To achieve an effective prediction of segregation effect, a biphasic model based on mixture theory is employed. The viscous behaviors of each phase and the interaction coefficient between the flows of the two phases should be determined. The solution of two coupled Navier–Stokes equations results in a tremendous computation effort. The previous development of an explicit algorithm makes the biphasic simulation much faster than that of the classic methods. However, it is strongly desired to reduce or even eliminate the numerous global solutions for pressure fields at each time step. Hence, a new vectorial algorithm is proposed and developed to perform the simulation only by vectorial operations. It provides the anticipated efficiency in the simulation of biphasic modeling, and the advantage to use the classic elements of equal‐order interpolations. Some results produced by the two algorithms are compared with the experimental values to validate the new vectorial algorithm. Copyright © 2012 John Wiley & Sons, Ltd.     

Sub‐picosecond Raman spectrometer for time‐resolved studies of structural dynamics in heme proteins

We describe a pump–probe Raman spectrometer based on a femtosecond Ti:sapphire laser, an optical parametric generator and two optical parametric amplifiers for time‐resolved studies, with emphasis on the structural dynamics in heme proteins. The system provides a 100‐fs pump pulse tunable in the range 500–600 nm and a transform‐limited sub‐picosecond probe pulse tunable in the range 390–450 nm. The spectrometer has spectral (25 cm⁻¹) and temporal (∼0.7 ps) resolutions which constitute an effective compromise for identifying transient heme protein species and for following their structural evolution by spontaneous Raman scattering in the time range 0.5 ps to 2 ns. This apparatus was applied to time‐resolved studies of a broad range of heme proteins, monitoring the primary dynamics of photoinduced heme coordination state and structural changes, its interaction with protein side‐chains and diatomic gaseous ligands, as well as heme vibrational cooling. The treatment of transient Raman spectra is described in detail, and the advantages and shortcomings of spontaneous resonance Raman spectroscopy for ultrafast heme proteins studies are discussed. We demonstrate the efficiency of the constructed spectrometer by measuring Raman spectra in the sub‐picosecond and picosecond time ranges for the oxygen‐storage heme protein myoglobin and for the oxygen‐sensor heme protein FixLH in interaction with the diatomic gaseous ligands CO, NO, and O₂. Copyright © 2010 John Wiley & Sons, Ltd.     

Finite size effects on structure and magnetism in mass-selected CoPt nanoparticles

In this paper, the one-way absorption property in one-dimensional dielectric/metal photonic crystal structure with a dielectric defect layer is studied. The effects of incident angle and state of polarization on one-way absorption behaviour of the anti-resonant (AR) mode are investigated. The normally incident wave from left to right propagation is totally allowed to penetrate to the structure but right to left propagation totally reflected at the same wavelength. It is found that, with increasing of the incident angle, the AR mode shifts to the lower wavelengths and its intensity decreases. Simultaneously, another AR mode with reversed one-way property appears at higher wavelength. The one-way behaviour on absorption is observed at the both states of polarizations but is localized on different wavelengths. Those effects, are suggesting that the proposed structure can be used as a direction sense polarization splitter or reflector/antireflector device.     

Observation of phase defects in quasi-two-dimensional Bose-Einstein condensates

We have observed phase defects in quasi-2D Bose-Einstein condensates close to the condensation temperature. Either a single or several equally spaced condensates are produced by selectively evaporating the sites of a 1D optical lattice. When several clouds are released from the lattice and allowed to overlap, dislocation lines in the interference patterns reveal nontrivial phase defects.     

Self-similarities in the frequency-amplitude space of a loss-modulated CO2 laser

We show the standard two-level continuous-time model of loss-modulated CO2 lasers to display the same regular network of self-similar stability islands known so far to be typically present only in discrete-time models based on mappings. Our results suggest that the two-parameter space of class B laser models and that of a certain class of discrete mappings could be isomorphic.     

Theoretical investigations of the processes of laser interaction with ocular tissues for laser applications in ophthalmology

Theoretical investigations and the results of computer modeling of the optical, thermophysical, and thermochemical processes during laser interaction with ocular tissues are reviewed in this paper. Physical-mathematical models and results of numerical simulation of the processes are presented. The computer modeling was applied for investigations of laser heating and coagulation of ocular tissues for treatment of retina diseases and intraocular tumors, cyclophotocoagulation of the ciliary body for treatment of glaucoma, and laser thermal keratoplasty of the cornea. The influence of radiation parameters on the selectivity of laser coagulation of laminated ocular tissues is considered. The results obtained are of essential interest for laser applications in ophthalmology and can be used for investigation of heating and coagulation of tissues in different fields of laser medicine.     

High-power laser with Nd:YAG single-crystal fiber grown by the micro-pulling-down technique

We present optical characterization and laser results achieved with single-crystal fibers directly grown by the micro-pulling-down technique. We investigate the spectroscopic and optical quality of the fiber, and we present the first laser results. We achieved a cw laser power of 10 W at 1064 nm for an incident pump power of 60 W at 808 nm and 360 kW peak power for 12 ns pulses at 1 kHz in the Q-switched regime. It is, to the best of our knowledge, the highest laser power ever achieved with directly grown single-crystal fibers.     

Thermodynamic non-additivity in disordered systems with extended phase space

Non-additivity effects in coupled dynamic-stochastic systems are investigated. It is shown that there is a mapping of the replica approach to disordered systems with finite replica indexn on Tsallis non-extensive statistics, if the average thermodynamic entropy of the dynamic subsystem differs from the information entropy for the probability distribution in the stochastic subsystem. The entropic indexq is determined by the entropy difference ΔS. In the case of incomplete information, the entropic indexq=1−n is shown to be related to the degree of lost information.