Direct observation of the saturation of stimulated Brillouin scattering by ion-trapping-induced frequency shifts

We report the first measurement of the saturation of stimulated Brillouin scattering (SBS) by an ion-trapping-induced frequency shift, which was achieved by directly measuring the amplitude and absolute frequency of SBS-driven ion-acoustic waves (IAW). A frequency shift of up to 30% and a simultaneous saturation of driven IAW and SBS reflectivity were observed. The scaling of the frequency shift with the IAW amplitude compares well with theoretical calculations. We have further measured fast 30 ps oscillations of the SBS-driven IAW amplitude induced by the frequency shift.     

Electrons are transported through phenylene-ethynylene oligomer monolayers via localized molecular orbitals

We report excellent correlations between the first negative threshold potentials (V(TH)s) for electric conduction, electrochemical potentials, and computed lowest unoccupied molecular orbital energies in a series of phenylene-ethynylene oligomers bearing a sulfur-based anchoring unit and different electroactive substituents on the central benzene ring. The theoretical and electrochemical results strongly suggest that the peaks observed in the i-V curves have a true molecular origin and are associated with distinct unoccupied molecular levels of the compounds that are strongly localized on the central ring (except for compound I). This localization might account for the existence of a long-lived radical-anion state that permits lateral electron hopping and leads to charge trapping and storage.     

Review and comparison of three methods for the solution of the car sequencing problem

The car sequencing problem is the ordering of the production of a list of vehicles which are of the same type, but which may have options or variations that require higher work content and longer operation times for at least one assembly workstation. A feasible production sequence is one that does not schedule vehicles with options in such a way that one or more workstations are overloaded. In variations of the problem, other constraints may apply. We describe and compare three approaches to the modeling and solution of this problem. The first uses integer programming to model and solve the problem. The second approaches the question as a constraint satisfaction problem (CSP). The third method proposes an adaptation of the Ant Colony Optimization for the car sequencing problem. Test-problems are drawn from CSPLib, a publicly available set of problems available through the Internet. We quote results drawn both from our own work and from other research. The literature review is not intended to be exhaustive but we have sought to include representative examples and the more recent work. Our conclusions bear on likely research avenues for the solution of problems of practical size and complexity. A new set of larger benchmark problems was generated and solved. These problems are available to other researchers who may wish to solve them using their own methods.     

On the physical transformations of processed pharmaceutical solids

Atomic force microscopy Phase Imaging, an adaptation of Tapping Mode AFM was used to visualise physico-mechanical variations on the surface of crystalline materials after being subjected to mechanically induced lattice damage. Large crystals (100-500 microm) of lactose were nucleated on AFM sample stubs, imaged and subjected to a milling process. The milled samples were then imaged at specific humidity using Phase Imaging. Phase and Amplitude images of the re-crystallised lactose suggested an ordered crystalline state with multiple platelets present across the surface. In comparison, the morphology and surface properties after a 1-min mill time suggested milling had a dramatic effect on the surface characteristics of the re-crystallised lactose. Phase and Topographical imaging during exposure to elevated humidities (70% RH) indicated both morphological and physico-mechanical changes that may be linked to surface amorphous re-crystallisation.     

Color-tunable organic microcavity laser array using distributed feedback

Distributed feedback microstructures play a fundamental role in confining and manipulating light to obtain lasing in media with gain. Here, we present an innovative array of organic, color-tunable microlasers which are intrinsically phase locked. Dye-doped helixed liquid crystals were embedded within periodic, polymeric microchannels sculptured by light through a single-step process. The helical superstructure was oriented along the microchannels; the lasing was observed along the same direction at the red edge of the stop band. Several physical and technological advantages arise from this engineered heterostructure: a high quality factor of the cavity, ultralow lasing threshold, and thermal and electric control of the lasing wavelength and emission intensity. This level of integration of guest-host systems, embedded in artificially patterned small sized structures, might lead to new photonic chip architectures.     

High-repetition-rate grazing-incidence pumped x-ray laser operating at 18.9 nm

We have demonstrated a 10 Hz Ni-like Mo x-ray laser operating at 18.9 nm with 150 mJ total pump energy by employing a novel pumping scheme. The grazing-incidence scheme is described, where a picosecond pulse is incident at a grazing angle to a Mo plasma column produced by a slab target irradiated by a 200 ps laser pulse. This scheme uses refraction of the short pulse at a predetermined electron density to increase absorption to pump a specific gain region. The higher coupling efficiency inherent to this scheme allows a reduction in the pump energy where 70 mJ long pulse energy and 80 mJ short pulse energy are sufficient to produce lasing at a 10 Hz repetition rate. Under these conditions and by optimizing the delay between the pulses, we achieve strong amplification and close to saturation for 4 mm long targets.     

Intramolecular carbolithiation reactions for the preparation of 3-alkenylpyrrolidines

Tin-lithium exchange allows the formation of alpha-amino-organolithium species that undergo anionic cyclization onto allylic ethers to give 3-alkenylpyrrolidines. The methodology has been applied to the synthesis of an advanced intermediate related to the natural product (-)-alpha-kainic acid.     

Enhanced load current delivery from the SHIVA star vacuum inductivestore/plasma flow switch

The SHIVA Star device is a 1313-μF, 120-kV capacitative storage device capable of storing 9.4-MJ electrical energy. The experimental operating voltage is 90 kV. An increased current delivery from the SHIVA Star capacitor band to a plasma-flow-switch-driven cylindrical foil load is reported. Modification of a plasma-flow-switch electrode produces a current delivery that is a factor of two better than the best previous comparable efforts. Peak driving current is 12.3 MA; the peak load current is over 9.4 MA. At peak load current, driving current is 11.2 MA for a current delivery of 85% or more. Current delivery in the experimental system is reported. The modification specified entails partially closing the outflow electrode of a plasma-flow switch