A stable dual-wavelength fiber laser with tunable wavelength spacing using a polarization-maintaining linear cavity

We propose and experimentally demonstrate a stable dual-wavelength erbium-doped polarization-maintaining (PM) fiber laser with tunable wavelength spacing using an all-PM linear cavity that makes use of two reflection peaks from the PM fiber Bragg grating (PM-FBG). Experimental results show stable dual lasing lines with a wavelength separation of ∼0.22 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. By applying axial strain to the PM-FBG, the center wavelengths of the two lasing lines can be tuned over several nanometers and the wavelength separation between the lasing lines can also be tuned to as small as 0.05 nm, which, to our knowledge, is the smallest wavelength spacing ever obtained from a stable room-temperature dual-wavelength fiber laser. The proposed laser configuration has the advantages of simple structure, low loss, stable dual-wavelength operation and a very small lasing linewidth of ∼5 kHz . PACS 42.55.Wd; 42.81.-i; 42.81.Gs     

Determination of uranium and thorium isotopes in soil samples by coprecipitation

Summary The paper presents a procedure to prepare soil samples for U and Th isotope measurement by alpha-spectrometry after coprecipitation with LaF₃. In this procedure the reduction of U(VI) to U(IV) was performed by Zn metal in 4M HCl solution. The recoveries of chemical separation equal to e_U-chemistry = 78±4% for uranium and e_Th-chemistry = 82±4% for thorium. Canberra alpha-spectrometer was used with PIPS detectors of A-1200-37-AM Model of 1200 mm² active area. The counting efficiency of the measuring system equals to e_counting = 18% and the total efficiencies were e_U = e_counting ^.e_U-chemistry = 14.0±0.7% for uranium and e_Th = e_counting ^.e_Th-chemistry = 14.7±0.7% for thorium. The recoveries of chemical separation were rather high (about 80%), that leads to the use of a small weight of soil sample (about 0.5 g). The efficiencies were also stable, that allows analyzing the soil sample without using radiotracers. They are advantages of the sample preparation procedure of this work.     

A chemoenzymatic synthesis of the linear triquinane (−)-hirsutene and identification of possible precursors to the naturally occurring (+)-enantiomer

An enantiomerically pure cis-1,2-dihydrocatechol, which is readily obtained via a toluene dioxygenase-mediated dihydroxylation of toluene in a whole-cell biotransformation process, has been converted over 17 steps into the linear triquinane (−)-hirsutene. Since the enantiomer of the starting material is also available this work constitutes a formal total synthesis of the naturally occurring (+)-form of hirsutene. Furthermore, minor modifications of the route used here offer the possibility of accessing (+)-hirsutene from the original starting material.     

Co-doped In2O3 thin films: Room temperature ferromagnets

Laser-ablated Co-doped In₂O₃ thin films were fabricated under various growth conditions on R-cut Al₂O₃ and MgO substrates. All Co:In₂O₃ films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μ_B/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In₂O₃ thin films has confirmed that doping few percent of magnetic elements such as Co into In₂O₃ could result in a promising magnetic material.     

Immunochromatographic flow-injection method for detection of human serum immunoglobulin G antibodies to Helicobacter pylori

This study reports on the development of an immunochromatographic flow-injection (FI) method for the quantitation of human serum IgG antibodies to Helicobacter pylori. Patients’ sera were injected into the carrier stream of a FI manifold incorporating an H. pylori immuno-adsorbent reactor. The immuno-adsorbent was prepared by covalently linking H. pylori antigens to periodate oxidized Sepharose CL-4B. Any H. pylori antibody present in the serum is bound to the immuno-sorbent. The bound antibody was quantified by injecting into the carrier stream anti-human IgG peroxidase conjugate followed by TMB/H₂O₂ as the enzyme substrate. The FI system was optimized with respect to antigen loading (1.0 mg/ml gel), bioreactor length (3.0 cm), enzyme conjugate (0.2 mg/ml) and sample loop size (250 μl). One hundred clinical samples were analyzed for their H. pylori antibody concentrations and the results evaluated with respect to their receiver-operator characteristics (ROC). When a cut-off absorbance of between 0.7 and 0.75 was used for positive and negative samples a specificity (>95%), a sensitivity (>90%)and an overall accuracy (>94%) were obtained.     

Carrier-mediated transport of yttrium(III) through a supported liquid membrane containing TOPO in n-dodecane

Transport of yttrium(III) from nitrate medium through liquid membrane containing tri-n-octyl-phosphine oxide (TOPO) in n-dodecane, supported on a nucleoporous filter, into a strip solution with ethylenediaminetetraacetic acid (EDTA) has been studied. The kinetic dependences of transport were obtained and compared with a model, resulting in calculation of permeability coeffients and initial fluxes of yttrium. The influence of salting-out agent, initial metal and nitric acid concentrations in the feed, and of concentration of carrier in membrane are discussed.     

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

Porphyrins have been widely used in the self‐assembly of metallo‐supramolecules. In this study, we introduced 2,2':6,2"‐terpyridine (tpy) into a porphyrin core to synthesize a tetratopic building block with multiple conformers. During the self‐assembly with Zn(II), such a mixture of conformers was able to form a discrete nanoprism with all building blocks in one conformation. Detailed characterizations, including NMR, ESI‐MS and traveling‐wave ion mobility‐mass spectrometry (TWIM‐MS), all supported the formation of the desired assemblies. AFM and TEM further confirmed the dimensions of assembled nanoprisms. Moreover, the photophysical properties of the ligands and complexes were noticeably different depending upon size and metal ion center.     

Synthesis of novel tryptamine and β-carboline derivatives via palladium-catalyzed reaction of bromotryptamine with organic boronic acids

New tryptamine 5, 7 and β-carboline derivatives 3 were preparated by palladium-catalyzed coupling reaction of 5-bromotryptamine 1 with aryl boronic acids. Dedicated to Professor András Lipták on his 70^th birthday.     

Hierarchical assembly of homochiral porous solids using coordination and hydrogen bonds

A family of homochiral metal carboxylate coordination polymers have been synthesized by treating 2,2'-dihydroxy-1,1'-binaphthalene-6,6'-dicarboxylic acid (H(2)BDA) with metal salts at elevated temperatures. BDA ligands link adjacent metal centers to form 1D coordination polymeric chains using the carboxylate functionality, while the hydroxyl groups of BDA ligands form H-bonds with carboxylate oxygen atoms to link 1D coordination polymeric chains into open frameworks of higher dimensionality. We also present evidence for the important role played by H-bonds in the stabilization of open framework structures which allows for the hierarchical assembly of chiral porous solids.     

Conformational and photophysical studies on porphyrin-containing donor-bridge-acceptor compounds. Charge separation in micellar nanoreactors

Photophysical studies with semi-rigid, 1, and flexible, 2, donor-bridge-acceptor (D-b-A2+) molecules with D a porphyrin and A2+ a methyl viologen moiety, were performed in neat polar solvents as well as included in surfactant (DTAB) aqueous and in reverse AOT/n-alkane micelles. The micelles acted as nanoreactors for the photoinduced electron transfer reaction upon laser excitation. In spite of the longer lifetime of the charge separated (CS) state in the semi-rigid tetrad 1(ca. 200 ns vs. ca. 100 ns for the flexible dyad 2), the CS formation quantum yield, for example in acetonitrile, was lower for the former (phi(CS) = 0.13) than for the latter (0.58). Comparison of the time-resolved fluorescence data in neat solvent and in the micelles yielded the phi(CS) values in the dilute micellar solutions. Application of laser-induced optoacoustic spectroscopy at various temperatures to 1 dissolved in a polar organic solvent (benzonitrile, BZN) included in aqueous DTAB nanoreactors afforded structural volume changes for the production in hundreds of ps of the CS state upon excitation of a polar molecule. The contraction during CS formation upon excitation of the collapsed conformer in BZN is attributed to the entering of solvent into the open molecular cavity. The opening upon formation of the CS state due to photoinduced electron transfer in the 1 collapsed conformation arises from the repulsion of the two positively charged ends in this state, as previously calculated. Inclusion of 1 in reverse AOT micelles in various n-alkanes also led to a contraction upon excitation, but the data had much more error due to the limited range of variability of the ratio of thermoelastic parameters. The data obtained with the more flexible "supermolecule" 2 showed the predicted large conformation flexibility of these molecules.