Scanning mirror on a vibrating membrane for dynamic optical trapping

A study of the variation of the spectral shape and the harmonic distribution of the high-order harmonics generated from silver plasma on the frequency chirp of the driving laser radiation (793 nm 48 fs) is reported. The results of the systematic study of the harmonic generation from the 21st order up to the 61st order (λ=13 nm) are presented. A tuning of the harmonic wavelength up to 0.8 nm can be accomplished by variation of the laser chirp. PACS 42.65.Ky; 42.79.Nv; 52.38.Mf     

Surface modification studies of edge-oriented molybdenum sulfide nanosheets

We have synthesized edge-oriented MoS2 nanosheets by the evaporation of a single source precursor based on Mo(IV)-tetrakis(diethylaminodithiocarbomato). The surface chemistry of the MoS2 nanosheets has been studied in order to evaluate the chemical reactivities of the basal planes and edges. By irradiating the MoS2 nanosheet with a scanning infrared laser, micron-scale lithographical structures can be created due to laser-induced oxidation of MoS2 to form nanocrystalline MoO3. Preferential reactivities of the MoS2 basal edges in an electrochemical environment and during vapor phase deposition have been demonstrated. Functionalization of the basal plane with 1-pyrene acetic acid allows the immobilization of DNA and immunoglobins on the MoS2 basal plane.     

Tasumatrols P – T,Five New Taxoids from Taxus sumatrana

The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells.     

New Clerodane Diterpenoids from Casearia membranacea

Bioassay‐guided fractionation of an AcOEt extract of Casearia membranacea resulted in the isolation of six new clerodane diterpenes, caseamembrins G–L ( 1 – 6 ). The structures of the new compounds, including their relative configurations, were established by an extensive study of their spectral data, especially 2D NMR. The cytotoxic activities of the isolated diterpenes against human oral epidermoid (KB), cervical epitheloid (Hela), and liver (Hep59T/VGH) carcinoma cell lines were investigated.     

Fabrication of size-tunable gold nanoparticles array with nanosphere lithography, reactive ion etching, and thermal annealing

Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique. First, ordered arrays of polystyrene nanospheres on Si substrate were used as deposition masks through which gold films were deposited by electron beam evaporation. After the removal of the nanospheres, an array of triangular Au nanodisks was left on the Si substrate. After thermal annealing at increasing temperature, systematic shape transition of the nanostructures from original triangular Au nanodisks to rounded nanoparticles was observed. This approach allows us to systematically vary the size and morphology of the particles. In the second and novel technique, we made use of reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films. These samples were subsequently annealed, which resulted in size-tunable and ordered Au nanoparticle arrays with the nanoparticles nested in the nanopores of the templated substrate. With the nanoparticles anchored in the nanopores, the substrate could be useful as a template for growth of other nanomaterials.     

Probabilistic interpretation of a system of quasilinear parabolic PDEs

Using a forward–backward stochastic differential equations (FBSDE) associated to a transmutation process driven by a finite sequence of Poisson processes, we obtain a probabilistic interpretation for a non-degenerate system of quasilinear parabolic partial differential equations (PDEs). The novetly is that the linear second order differential operator is different on each line of the system.     

Computational Study of the One‐ and Two‐Dimensional Infrared Spectra of a Proton‐Transfer Mode in a Hydrogen‐Bonded Complex Dissolved in a Polar Nanocluster

The signatures of nanosolvation on the one‐ and two‐dimensional (1D and 2D) IR spectra of a proton‐transfer mode in a hydrogen‐bonded complex dissolved in polar solvent molecule nanoclusters of varying size are elucidated by using mixed quantum–classical molecular dynamics simulations. For this particular system, increasing the number of solvent molecules successively from N=7 to N=9 initiates the transition of the system from a cluster state to a bulk‐like state. Both the 1D and 2D IR spectra reflect this transition through pronounced changes in their peak intensities and numbers, but the time‐resolved 2D IR spectra also manifest spectral features that uniquely identify the onset of the cluster‐to‐bulk transition. In particular, it is observed that in the 1D IR spectra, the relative intensities of the peaks change such that the number of peaks decreases from three to two as the size of the cluster increases from N=7 to N=9. In the 2D IR spectra, off‐diagonal peaks are observed in the N=7 and N=8 cases at zero waiting time, but not in the N=9 case. It is known that there are no off‐diagonal peaks in the 2D IR spectrum of the bulk version of this system at zero waiting time, so the disappearance of these peaks is a unique signature of the onset of bulk‐like behavior. Through an examination of the trajectories of various properties of the complex and solvent, it is possible to relate the emergence of these off‐diagonal peaks to an interplay between the vibrations of the complex and the solvent polarization dynamics.     

Effect of boundary layer losses on 2D detonation cellular structures

We evaluate the effect of boundary layer losses on two-dimensional H2/O2/Ar cellular detonations obtained in narrow channels. The experiments provide the details of the cellular structure and the detonation speed deficits from the ideal CJ speed. We model the effect of the boundary layer losses by incorporating the flow divergence in the third dimension due to the negative boundary layer displacement thickness, modeled using Mirels’ theory. The cellular structures obtained numerically with the resulting quasi-2D formulation of the reactive Euler equations with two-step chain-branching chemistry are found in excellent agreement with experiment, both in terms of cell dynamics and velocity deficits, provided the boundary layer constant of Mirels is modified by a factor of 2. A significant increase in the cell size is found with increasing velocity deficit. This is found to be very well captured by the induction zone increase in slower detonations due to the lower temperatures in the induction zone.     

Phytoquinoids and Secoprezizaane‐Type Sesquiterpenes from Illicium arborescens

A phytochemical investigation of the MeOH extract of Illicium arborescens yielded the two new phytoquinoid epimers, 2,3‐didehydro‐5‐O‐methyl‐11‐epiillifunone E ( 1 ) and 2,3‐didehydro‐5‐O‐methylillifunone E ( 2 ), as well as five new sesquiterpene lactones (8,9‐secoprezizaane‐type sesquiterpenes). Two of them, i.e., 3 and 4 , were minwanensin‐type sesquiterpenes, the other two, i.e., 5 and 6 , had the anisatin‐type (or floridanolide type) skeleton, and the fifth, i.e., 7 , was a dunnianin‐type sesquiterpene. Their structures were established by analyses of 1D‐ and 2D‐NMR, HR‐MS, and chemical evidence. The in vitro cytotoxic activity of compounds 1 – 7 was tested against four human tumor cell lines, including HeLa (cervical epitheloid), WiDr (colon), Daoy (medulloblastoma), and Hep2 (liver carcinoma) human‐tumor cells.     

Properties of a vector soliton laser passively mode-locked by a fiber-based semiconductor saturable absorber operating in transmission

We experimentally demonstrate a passively mode-locked fiber laser employing a fiber-based semiconductor saturable absorber (SSA) operating in transmission. Polarization rotation locked vector solitons are observed in the laser. Due to the intrinsic dynamic feature of the laser, period-doubling of these vector solitons has also been observed. Furthermore, extra spectral sidebands are formed on the optical spectrum, caused by the energy exchange between the two orthogonal polarization components of the vector solitons. By careful reduction of the pump power together with fine adjustment to the cavity birefringence, period-one state can further be obtained. Additionally, the phase noise properties of the vector soliton fiber laser have also been characterized experimentally and analytically.