Energy limits imposed by two-photon absorption for pulse amplification in high-power semiconductor optical amplifiers

We study the combined effects of dynamic gain saturation and two-photon absorption on the amplification of short pulses in semiconductor optical amplifiers and show that two-photon absorption can saturate the amplifier gain and limit the output pulse energies even for amplifiers with large gain saturation energies. We discuss the upper limits for the pulse energies obtainable from semiconductor optical amplifiers in the presence of two-photon absorption and show that for single transverse mode waveguide amplifiers these upper limits can range from values as small as a few picojoules to several hundred picojoules for pulse widths in the 0.5 ps to 20 ps range, respectively.     

Total Fragmentation Cross Section of 158A GeV Lead Projectiles in Cu Target

Total fragmentation cross section for the reaction 158A Pb ions ＋ Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region （63 ≤ Z ≤ 83） are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented.     

Size-induced effect on nano-crystalline CoFe2O4

Cobalt ferrite (CoFe₂O₄) nano-particles have been synthesized successfully and we studied the effect of temperature on them. The particles have been annealed at different temperatures ranging from 373 to 1173 K. Significant effect on the physical parameters like crystalline phase, crystallite size, particle size, lattice strain and magnetic properties of the nano-particles has been investigated. The studies have been carried out using a powder X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a vibrating sample magnetometer (VSM). A thorough study of the variation of specific surface area and particle size with annealing is presented here, with their effects on saturation magnetization.     

LTNE thermoconvective instability in Newtonian rotating layer under magnetic field utilizing nanoparticles

Journal of Thermal Analysis and Calorimetry - In the present framework, the simultaneous effect of rotation, magnetic field, heat source and local thermal non-equilibrium (LTNE) is investigated on...     

Epoxidation of trans-stilbene with molecular oxygen over an eco-friendly heterogeneous cobalt oxide/reduced graphene oxide composite material

Research on Chemical Intermediates - We report the synthesis of 1, 5, 10 wt% cobalt oxide/reduced graphene oxide (CoO–RGO) composite materials by a simple solvothermal method. We assessed...     

Experimental and theoretical assessment of Fe-doped indium-oxide-based dilute magnetic semiconductors

Specimens of iron-doped indium oxide (In_1-xFe_x)₂O₃ with x?=?0.015, 0.03, 0.045 and 0.06, amalgamated through a traditional solid-state reaction method followed by H₂/air sintering, were characterised using an X-ray diffractometer (XRD), a vibrating sample magnetometer (VSM), and a scanning electron microscope (SEM) to investigate their structural, magnetic and morphological properties respectively. According to XRD plots, all the specimens exhibit cubic bixbyite structures along with ancillary phases. Magnetic assessment showed that In₂O₃ has a negative susceptibility, exhibiting diamagnetic behaviour at room temperature. The doping of Fe ions induces ferromagnetic (FM) ordering, which is enhanced with increasing doping content. The strength of the magnetisation increases when the specimens are exposed to H₂ but is reduced on further air sintering. A bound magnetic polaron (BMP) model is successfully fitted to the observed FM data involving localised carriers and magnetic cations. A multivariate assessment viz. a hierarchical cluster analysis (HCA) was used to corroborate and strengthen the experimental determined magnetic properties. A homogeneous particle distribution was observed in all SEM micrographs and is validated through MATLAB-based simulation by applying a watershed segmentation algorithm. Surface plots also confirm the change in magnetic properties with increase in doping concentration.     

Luminescent amphiphilic nanogels by terpyridine-Zn(II) complexation of polymeric micelles

In this work, we investigated terpyridine (tpy)/Zn(II) complexation for the crosslinking of polymeric micelles of the branched poly(ethylene oxide)–poly(propylene oxide) block copolymer Tetronic® 1107 (T1107) in water and produce physically stable amphiphilic luminescent nanogels. Nanoparticles displayed a size of 235 ± 25 and 318 ± 57 nm before and after Zn(II) crosslinking, respectively, as measured by dynamic light scattering. High-resolution scanning electron microscopy analysis revealed the multimicellar nature of the crosslinked nanoparticles. In addition, Zn(II) complexation prevented nanoparticle disassembly after extreme dilution below the critical micellar concentration and reduced the minimum concentration required for the reverse thermal gelation of concentrated aqueous T1107 systems. The cell compatibility and uptake were initially assessed in the murine macrophage cell line RAW 264.7. Results showed that complexation increases the cell compatibility of the nanoparticles with respect to the non-complexed counterparts. In addition, non-crosslinked nanoparticles accumulated in the cell membrane, while the complexed ones were internalized, as observed by confocal laser scanning fluorescence microscopy. Then, the antiproliferative activity of the crosslinked nanoparticles was confirmed in the rhabdomyosarcoma cell line Rh30; their inhibitory concentration 50 (IC₅₀) being 101 μg/mL (6.7 μM). Finally, the encapsulation and release of the hydrophobic antiretroviral efavirenz was characterized in vitro. Complexation slightly reduced the release kinetics with respect to the pristine nanoparticles. Overall results demonstrate the promise of this simple modification strategy to produce amphiphilic nanogels with a set of advantageous physicochemical, optical, and biological properties.     

Beyond microstructures: Using the Kerr Effect to characterize the macrostructures of synthetic polymers

The macrostructures of synthetic polymers are essentially the complete molecular chain architectures, including the types and amounts of constituent short‐range microstructures, such as the regio‐ and stereosequences of the inserted monomers, the amounts and sequences of monomers found in co‐, ter‐, and tetra‐polymers, branching, inadvertent, and otherwise, etc. Currently, the best method for characterizing polymer microstructures uses high field, high resolution ¹³C‐nuclear magnetic resonance (NMR) spectroscopy observed in solution. However, even ¹³C‐NMR is incapable of determining the locations or positions of resident polymer microstructures, which are required to elucidate their complete macrostructures. The sequences of amino acid residues in proteins, or their primary structures, cannot be characterized by NMR or other short‐range spectroscopic methods, but only by decoding the DNA used in their syntheses or, if available, X‐ray analysis of their single crystals. Similarly, there are currently no experimental means to determine the sequences or locations of constituent microstructures along the chains of synthetic macromolecules. Thus, we are presently unable to determine their macrostructures. As protein tertiary and quaternary structures and their resulting ultimate functions are determined by their primary sequence of amino acids, so too are the behaviors and properties of synthetic polymers critically dependent on their macrostructures. We seek to raise the consciousness of both synthetic and physical polymer scientists and engineers to the importance of characterizing polymer macrostructures when attempting to develop structure–property relations. To help achieve this task, we suggest using the electrical birefringence or Kerr effects observed in their dilute solutions. The molar Kerr constants of polymer solutes contributing to the birefringence of their solutions, under the application of a strong electric field, are highly sensitive to both the types and locations of their constituent microstructures. As a consequence, we may begin to characterize the macrostructures of synthetic polymers by means of the Kerr effect. To simplify implementation of the Kerr effect to characterize polymer macrostructures, we suggest that NMR first be used to determine the types and amounts of constituent microstructures present. Subsequent comparison of observed Kerr effects with those predicted for different microstructural locations along the polymer chains can then be used to identify the most likely macrostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 155–166     

Tri-amine functionalized graphene oxide for co-operative catalyst in the Henry reaction

Research on Chemical Intermediates - Novel tri-amine functionalized graphene oxide (TGO) material was synthesized using organo silane {3-[2-(2-amino ethyl amino) ethyl amino] propyl trimethoxy...