Variable time lag and backward ejection in full-dimensional analysis of strong-field double ionization

Ensembles of 400,000 two-electron trajectories in three space dimensions are used with Newtonian equations of motion to track atomic double ionization under very strong laser fields. We report a variable time lag between e-e collision and double ionization, and find that the time lag plays a key role in the emergence directions of the electrons. These are precursors to production of electron momentum distributions showing substantial new agreement with experimental data.     

Fluorimetric Determination of Cerium(IV) with Ascorbic Acid

A simple, sensitive, and selective method for the determination of cerium(IV), based on the oxidative reaction between cerium(IV) and ascorbic acid, has been described. The fluorescence comes from Ce(III) at λ_excitation 298 nm and λ_emission 358 nm, which, in turn, is obtained from the oxidation of ascorbic acid by Ce(IV) in the presence of sulfuric acid. The optimum conditions such as concentrations of ascorbic acid, sulfuric acid media and pH of the buffer solution were investigated. The fluorescent intensity of the system is linear over the range 0.0531 μg/ml to 0.3322 mg/ml Ce(IV) and detection limit and correlation coefficient are 0.0145 μg/ml and R=0.99987,respectively.     

A Batch Chemiluminescence Determination of Enoxacin Using a Tris-(1,10-phenanthroline)ruthenium(II)–Cerium(IV) System

A batch type chemiluminescence (CL) determination of enoxacin is described. In this work, it was observed that enoxacin could enhance the chemiluminescence (CL) emission Ru(phen)₃ ²⁺–Ce(IV) system and this enhancement effect was dependent on the concentration of enoxacin, based on which, CL system was established for the determination of enoxacin. Under the optimum experimental conditions, the linear range and detection limit are 0.6406–64.06 μg/ml and 0.0210 μg/ml, respectively. The R.S.D. is 1.75%. (n=10). The proposed method has been applied to detect the content of enoxacin in pharmaceutical formulation and human serum with satisfactory results. The possible mechanism of the CL reaction was discussed.     

New DEFT sequences for the acquisition of one-dimensional carbon NMR spectra of small unlabelled molecules

The acquisition time and quality of 1D 13C{1H} spectra can be improved substantially by using a modified driven equilibrium Fourier transform (DEFT) sequence, which is specifically designed to compensate for the effects of B1 inhomogeneity, pulse miscalibration and frequency offsets. The new sequence, called uniform driven equilibrium Fourier transform (UDEFT), returns the carbon magnetization with a high accuracy along its equilibrium position after each transient is complete. Thus, the sequence allows the use of relaxation delays (RD), which are much shorter than the carbon T1 of the molecule, thereby speeding up the acquisition process of 1D 13C{1H} spectra. To achieve this level of performance, UDEFT employs a refocusing element constituted by a composite adiabatic carbon pulse surrounded by two 90 degrees carbon pulses whose phases are designed to compensate for 90 degrees pulse miscalibrations in an MLEV manner (90 degrees+x-tau(FID)-180+y(Adia)-tau-90 degrees+x-180 degrees+x(Adia)). A version of the UDEFT sequence allows recording 1D 13C{1H} spectra devoid of heteronuclear NOE by using a matched adiabatic 1H decoupling scheme where an even number of 180 degrees adiabatic pulses is applied during the UDEFT module. Spectra of a solution of 300 mM camphor that contains some carbon nuclei with very long T1 relaxation times (90 s and 78 s) were acquired with 128 scans in 10 min using a 5 s relaxation delay.     

Analysis of salicylic acid based on the fluorescence enhancement of the As(III)-salicylic acid system

A new, simple and sensitive spectrofluorimetric method for the determination of salicylic acid (λ_ex = 315 nm, λ_em = 408 nm) using As(III) as a sensitizing reagent has been investigated by measuring the increase of fluorescence intensity of salicylic acid due to the complexation of As(III)-salicylic acid in presence of sodium dodecyl sulfate (SDS) 10⁻³ M. Under optimum conditions, a significant relationship was obtained between the fluorescence intensity and salicylic acid concentration. A linear calibration curve was obtained in the range 13.8-13812 μg l⁻¹ with product-moment correlation coefficient (R) 0.99985 and detection limit 4.2 μg l⁻¹. The R.S.D. is 2.35% (n = 5).The method was applied successfully to the determination of salicylic acid in human serum.     

Spectrophotometric studies of alkali and alkali earth metal ions complexes of mono amino derivative of calix[4]arene

The synthesis and complexive abilities of 5,11,17-tris(tert-butyl)-23 amino-25,26,27,28-tetra-propoxycalix[4]arene towards alkali cations Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and alkali earth cations Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ in methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex with all the cations by 1: 1 metal to ligand ratios. The selectivity presented considering the calculated formation constants are in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺ and Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ with the ligand.     

Synthesis and characterization of nanostructured-segmented block copolyetheramide based on nylon6 and poly(ethylene oxide)

<正>Segmented block copolymer based on nylon6(N6) and polyethylene oxide(PEO) with stochiometric ratio was synthesized via a two-step process.The first step represents end capping of N6 in the presence of adipic acid leading to carboxy terminated N6,and the second one is polycondensation of the latter product with PEO in the presence of catalyst and thermostabilizer to form a high molecular weight multi-block copolymer.Several methods were applied to characterize the synthesized copolymer such as Fourier transform infrared spectroscopy,proton nuclear magnetic resonance spectroscopy,differential thermal analysis,differential scanning calorimetry,X-ray diffraction and atomic force microscopy. The obtained results confirmed the multi-block structure for copolymer with a very high degree of micro-phase separation. Atomic force microscopy micrographs indicated that the morphology was the dispersion of high stiffness nanostructured polyamide(PA) domains in the amorphous region of PEO matrix,which can be very important in their performance for membrane processes.     

ℓ-group homomorphisms between reduced archimedean f-rings

Let A and B be reduced archimedean f-rings, A with identity e; let $A\,\mathop \to \limits^\gamma\,BLet A and B be reduced archimedean f-rings, A with identity e; let A \mathop ? ^g BA\,\mathop \to \limits^\gamma\,B be an ℓ-group homomorphism, and set w = γ (e). We show (with some vagaries of phrasing here) (1) γ = w·ρ for a canonical ℓ-ring homomorphism A \mathop ? ^r B (w)A\,\mathop \to \limits^\rho\,B (w), where B (w) is an extension of B in which w is a von Neumann regular element, and (2) for X _A ,X _B canonical representation spaces for A, B, γ is realized via composition with a unique partially defined continuous function from X _B to X _A .     

On the Brown–Shields conjecture for cyclicity in the Dirichlet space

Let be the Dirichlet space, namely the space of holomorphic functions on the unit disk whose derivative is square-integrable. We establish a new sufficient condition for a function to be cyclic, i.e. for to be dense in . This allows us to prove a special case of the conjecture of Brown and Shields that a function is cyclic in iff it is outer and its zero set (defined appropriately) is of capacity zero.