All-fiber coherent beam combining of fiber lasers

One half of a 2x2 fused taper single-mode fiber coupler is used for the all-fiber spatial and spectral beam combining of two fiber lasers.     

Calculation of the propagator for a time-dependent damped,forced harmonic oscillator using the Schwinger action principle

A calculation of the quantum mechanical propagator for a general time-dependent one-dimensional damped, forced harmonic oscillator based on a direct application of the Schwinger action principle is presented. Contact with an earlier general method of calculation is made and in particular two previously found results are recovered from our general expression. The apparent dependence of one of them upon some unphysical parameters is clarified. The method presented here can be applied to any system described by a quadratic Hamiltonian and is an immediate extension of the calculation for the propagator of a simple harmonic oscillator with constant frequency.     

Fluorescence lifetime enhancement of organic chromophores attached to gold nanoparticles

We present for the first time experimental evidence of fluorescence lifetime enhancement of organic chromophores attached to metal nanospheres via radiative decay engineering. The hybrid system (HS) was a modified "diconjugated" molecular probe, 4-acetamido-4'-maleimidylstilbene-2,2'-dithiol (AMDT), covalently bound to the surface of 5-nm-diameter Au nanospheres by its two sulfur atoms, at a distance d < 1 nm and with its molecular axis parallel to the surface of the nanoparticle surface. We measured a fluorescence lifetime increase of a factor of 2 at room temperature (tau(AMDT) = (4.32 +/- 0.10) ns and tau(HS) = (8.73 +/- 0.23) ns) and a factor of 3.4 at 4.2 K (tau(AMDT) = (2.64 +/- 0.07) ns and tau(HS) = (7.96 +/- 0.14) ns). We also found that the fluorescence quantum yield of this hybrid system is not reduced, proof of a weak energy transfer between the molecular probe and the nanoparticle. These results demonstrate that a molecular dipole oriented parallel to the metal surface tends to be reduced by the coupling with its image.     

Metastability for Markov processes with detailed balance

We present a definition for metastable states applicable to arbitrary finite state Markov processes satisfying detailed balance. In particular, we identify a crucial condition that distinguishes metastable states from other slow decaying modes and which allows us to show that our definition has several desirable properties similar to those postulated in the restricted ensemble approach. The intuitive physical meaning of this condition is simply that the total equilibrium probability of finding the system in the metastable state is negligible.     

Phase diagram of silicon from atomistic simulations

In this Letter we present a calculation of the temperature-pressure phase diagram of Si in a range of pressures covering from -5 to 20 GPa and temperatures up to the melting point. The phase boundaries and triple points between the diamond, liquid, beta-Sn, and Si34 clathrate phases are reported. We have employed efficient simulation techniques to calculate free energies and to numerically integrate the Clausius-Clapeyron equation, combined with a tight-binding model capable of an accuracy comparable to that of first-principles methods. The resulting phase diagram agrees well with the available experimental data.     

Application of PLS regression to fluorimetric data for the determination of furosemide and triamterene in pharmaceutical preparations and triamterene in urine

Multivariate calibration methods that use fluorescence data for the simultaneous determination of furosemide and triamterene were developed. One of the most salient advantages of them is that the vast amount of information provided by the whole spectrum of the sample is not required. This makes analyses simple and fast. The methods require selecting chemometric parameters such as the specific spectral region and number of factors to be used. Both spectral region and number of factors are selected, simultaneously, by minimising the prediction residual error sum of squares (PRESS).The proposed methods were used for the simultaneous determination of the two drugs in real samples (pharmaceutical preparations) with no excipient separation pre-treatment, with furosemide and triamterene contents of 1.68E−3 to 4.31E−2 and 1.03E−3 to 3.12E−2 μg ml⁻¹, respectively; as well as that of triamterene at concentrations of 5.00E−4 to 5.80E−3 μg ml⁻¹ in urine samples. The ability to construct the calibration validation sets directly from the urine samples itself avoids the need to consider matrix interferences or to pre-treat the sample and/or separate some analytes The results were quite good in all cases.     

Formation of trinuclear palladium orthometalated complexes with unprecedented asymmetrical (mu 3-S)(mu 3-X) bridges (X = OH, SR, O2CR) from mu 2-hydroxo dimeric complexes and CS2

Complexes [Pd(3)(mu(3)-S)(mu(3)-X)(L)(3)] (L = orthometalated imine), obtained by an unusual reaction of mu(2)-OH dimeric complexes and CS(2), are an unprecedented type of asymmetrical bridges between metallatriangles, which force an all-cis arrangement of the three orthometalated ligands relative to the metallatriangle.     

Phosphate diester hydrolysis and DNA damage promoted by new cis-aqua/hydroxy copper(II) complexes containing tridentate imidazole-rich ligands

The tridentate Schiff base [(2-(imidazol-4-yl)ethyl)(1-methylimidazol-2-yl)methyl)imine (HISMIMI) and its reduced form HISMIMA were synthesized and characterized, as well their mononuclear cis-dihalo copper(II) complexes 1 and 2, respectively. In addition, the dinuclear [CuII(mu-OH)2CuII](2+) complexes (3) and (4) obtained from complexes 1 and 2, respectively, were also isolated and characterized by several physicochemical techniques, including magnetochemistry, electrochemistry, and EPR and UV-vis spectroscopies. The crystal structures of 1 and 2 were determined by X-ray crystallography and revealed two neutral complexes with their tridentate chelate ligands meridionally coordinated. Completing the coordination spheres of the square-pyramidal structures, a chloride ion occupies the apical position and another is bonded in the basal plane. In addition, complexes 1 and 2 were investigated by infrared, electronic, and EPR spectroscopies, cyclic voltammetry, and potentiometric equilibrium studies. The hydrolytic activity on phosphate diester cleavage of 1 and 2 was investigated utilizing 2,4-BDNPP as substrate. These experiments were carried out at 50 degrees C, and the data treatment was based on the Michaelis-Menten approach, giving the following kinetic parameters (complex 1/complex 2): vmax (mol L(-1) s(-1))=16.4x10(-9)/7.02x10(-9); KM (mol L(-1))=17.3x10(-3)/3.03x10(-3); kcat (s(-1))=3.28x10(-4)/1.40x10(-4). Complex 1 effectively promoted the hydrolytic cleavage of double-strand plasmid DNA under anaerobic and aerobic conditions, with a rate constant of 0.28 h(-1) for the decrease of form I, which represents about a 10(7) rate increase compared with the estimated uncatalyzed rate of hydrolysis.     

Continuous-Time Controlled Markov Chains with Discounted Rewards

This paper studies denumerable state continuous-time controlled Markov chains with the discounted reward criterion and a Borel action space. The reward and transition rates are unbounded, and the reward rates are allowed to take positive or negative values. First, we present new conditions for a nonhomogeneous Q(t)-process to be regular. Then, using these conditions, we give a new set of mild hypotheses that ensure the existence of -optimal (0) stationary policies. We also present a martingale characterization of an optimal stationary policy. Our results are illustrated with controlled birth and death processes.