Ultrashort pulse generation by distributed feedback dye lasers. II

The properties of distributed feedback dye lasers as novel sources for wavelength tunable ultrashort pulses in the visible and ultraviolet range are studied. Calculated and measured energy characteristics of the laser are in very good agreement. The shot-to-shot stability of the single ultrashort pulses has been measured to be ±7.1%.     

Phase averaged velocity field in an axisymmetric jet subject to a sudden velocity decrease

An unsteady transient axisymmetric turbulent jet was studied experimentally. The initial flow perturbation consisted of a sudden and large decrease in the ejection velocity. The temporal evolution of the mean and fluctuating unsteady velocity field was measured by using X hot-wire probes. In the jet far field, adaptation of the externally imposed unsteadiness to the local jet time scale is confirmed quantitatively. The main features of the phase averaged velocity field are presented and comments are made about the instantaneous state of the turbulence energetics. Transient mean radial velocities are deduced and an important increase of the instantaneous rate of entraining external fluid into the jet is found. Finally, we show that the pressure effect due to radial impusle terms plays an important role in the propagation of the mean perturbation. The longitudinal adaptation of the perturbation time scale driven by the local jet time scale provides a turbulent flow that is intermediate to quasi-static flows and rapidly distorted flows.We wish to thank Professor H. Fiedler and Professor M. Wolfshtein for their helpful comments about this work. We have benefited greatly from discussions with Dr. H.J. Nuglisch, Professor E.K. Longmire and Dr. A. Sevrain and of the technical support of G. Couteau and J.F. Alquier.     

New Determination Scheme of p‐Aminophenol by MnO2 Modified Electrode Coupled with Flow Injection Analysis

New determination scheme of p‐aminophenol by using MnO₂ as a preoxidant is demonstrated in this work. In the flow injection system, the p‐aminophenol is oxidized to quinoneimine by MnO₂ at up‐stream, which can be detected at a suitable reductive potential. After optimization, the linear range of PAP is started from 1 μM to 30 μM (R²=0.999), the estimated detection limit (S/N=3) is 0.28 μM. Two real samples are studied and excellent recoveries are achieved by using standard addition method.     

Diterpenoids from the Wood of Cunninghamia konishii

Investigation of the wood of Cunninghamia konishii resulted in the isolation and characterization of one new abietane diterpenoid, (6α,7β)‐7,8‐epoxy‐6‐hydroxyabieta‐9(11),13‐dien‐12‐one ( 1 ), and two new labdane diterpenoids, (12R)‐12‐hydroxylabda‐8(17),13(16),14‐trien‐19‐oic acid ( 2 ) and (12R)‐12‐hydroxylabda‐8(17),13(16),14‐trien‐18‐oic acid ( 3 ). The structures of these new compounds were elucidated by analysis of their spectroscopic data.     

Adsorption model for retention in normal-phase liquid chromatography with ternary mobile phases

The review gives a link between the theory of adsorption from multicomponent solutions and liquid chromatography. The article surveys the methods developed to describe the retention in normal-phase chromatography with ternary mobile phases with emphasis on the results of the authors. In the model used the driving force for the separation is the difference in adsorption of a solute and all solvents onto the solid surface. The general equation generates a series of simple linear relationships to predict the retention factor in ternary mobile phase for which certain parameters remain fixed. Theoretical concepts are tested by comparison with experimental data. The correlations between parameters characterizing retention in ternary, binary and pure solvents are discussed.     

The distributed diagonal force decomposition method for parallelizing molecular dynamics simulations

Parallelization is an effective way to reduce the computational time needed for molecular dynamics simulations. We describe a new parallelization method, the distributed-diagonal force decomposition method, with which we extend and improve the existing force decomposition methods. Our new method requires less data communication during molecular dynamics simulations than replicated data and current force decomposition methods, increasing the parallel efficiency. It also dynamically load-balances the processors' computational load throughout the simulation. The method is readily implemented in existing molecular dynamics codes and it has been incorporated into the CHARMM program, allowing its immediate use in conjunction with the many molecular dynamics simulation techniques that are already present in the program. We also present the design of the Force Decomposition Machine, a cluster of personal computers and networks that is tailored to running molecular dynamics simulations using the distributed diagonal force decomposition method. The design is expandable and provides various degrees of fault resilience. This approach is easily adaptable to computers with Graphics Processing Units because it is independent of the processor type being used.     

Complex phase behavior of a fluid in slits with semipermeable walls modified with tethered chains

We study the phase behavior of a two-component fluid in a pore with the walls modified by tethered chains. The walls are completely permeable for one component of the fluid and completely impenetrable for the second component. The fluid is perfectly mixed in a bulk phase. We have found that depending on the details of the model the fluid undergoes capillary condensation inside the pore and wetting and layering transitions at the outer walls. Moreover, we have found transitions connected with the change of symmetry of the distribution of chains and fluid inside the pore.     

Drag force of a particle moving axisymmetrically in open or closed cavities

Hydrodynamic resistance to particle transport arising from the solid mass in porous media is of fundamental importance. We investigate an axisymmetric creeping flow caused by a spherical particle migrating in a spherical cavity or connected cavities of equal size by a boundary element method. Each cavity has either one or two circular apertures, through which a sufficiently small particle can pass. Drag force on the particle is calculated to determine the correction factor to the Stokes law. It is found that when passing through an aperture, the particle experiences a local maximum drag force larger than that located in the cavity center. This force is also greater than that for the particle near the closed end at the same smallest surface-to-surface distance. For connected cavities open to the exterior fluid, the drag force is smaller than that in the corresponding closed system.