Study of the competition between forward and backward stimulated Raman scattering in methane

Simultaneous forward and backward stimulated Raman scattering (SRS) in methane pumped by a single longitudinal mode Nd:YAG laser at 355 nm has been investigated both experimentally and numerically. For forward SRS, a maximum energy-conversion efficiency of 55% was obtained under 24 atm, while for backward SRS the corresponding figure was 58% under 4.7 atm. Under low pressures or at low pump energies, the conversion efficiency for backward SRS was found to be much higher than that for forward SRS, while the situation is quite the contrary under high pressures and at high pump energies. A quasi-two-dimensional numerical model is introduced to elucidate the competition between forward and backward SRS; we conclude that the high-pressure and high-pump-energy experimental results should be caused by the thermal defocusing effect in the SRS process. This is confirmed by the experimental fact that a decrease of the pulse-repetition rate increases the conversion efficiency for backward SRS but decreases that for forward SRS under high pressures. Our calculated results are in good agreement with the experimental results at a pulse-repetition rate of 2 Hz. PACS 42.55.Ye; 42.65.Dr; 42.65.Es     

计算机单缝衍射光强分布曲线的拟合

先将单缝衍射光强分布的实验数据用五点三次平滑处理,以减少误差。再用牛顿插值求出光强分布公式中的单缝宽度。从而用计算机得出拟合曲线。     

Pulse self-compression in normally dispersive bulk media

We experimentally demonstrate that high-power femtosecond pulses can be compressed during the nonlinear propagation in the normally dispersive solid bulk medium. The self-compression behavior was detailedly investigated under a variety of experimental conditions, and the temporal and spectral characteristics of resulted pulses were found to be significantly affected by the input pulse intensity, with higher intensity corresponding to shorter compressed pulses. By passing through a piece of BK7 glass, a self-compression from 50 to 20 fs was achieved, with a compression factor of about 2.5. However, the output pulse was observed to be split into two peaks when the input intensity is high enough to generate supercontinuum and conical emission.     

β-delayed proton decay of the proton drip-line nucleus142Ho in the rare-earth region

New β-delayed proton precursor¹⁴²Ho was produced via heavy ion induced reaction¹⁰⁶Cd(⁴⁰Ca, p3n), and identified for the first time by using a He-jet fast tape transport system in combination with “p-γ” coincidence measurements. The β-delayed proton decay of¹⁴²Ho was observed and its half life was determined to be (0.4±0.1) s. By fitting the experimental relative branching ratios to final states in the proton daughter nucleus¹⁴¹Tb and the energy spectrum of β-delayed protons with a statistical model calculation, the ground-state spin of¹⁴²Ho was assigned as 5, 6 or 7. Nuclear energy-potential-surface (EPS) calculations were performed using the Woods-Saxon Strutinsky method. The calculated results favored the assignments of 7⁻ to¹⁴²Ho. As the by-products, some γ-transitions in the proton daughter nuclei following the β-delayed proton decays of precursors¹³⁹Gd,¹⁴⁰Tb,¹⁴²Tb, and¹⁴³Dy were reported here for the first time.     

Non-equilibrium,nonlinear critical layers in laminar-turbulent transition

We describe some recent developments of high-Reynolds-number asymptotic theory for the nonlinear stage of laminar-turbulent transition in nearly parallel flows. The classic weakly nonlinear theory of Landau and Stuart is briefly revisited with the dual purposes of highlighting its fundamental ideas, which continue to underlie much of current theoretical thinking, as well as its difficulty in dealing with unbounded flows. We show that resolving such a difficulty requires an asymptotic approach based on the high-Reynolds-number assumption, which leads to a nonlinear critical-layer theory. Major recent results are reviewed with emphasis on the non-equilibrium effect. Future directions of investigation are indicated.     

Experiment Study on Active-passive Mode-locking Using Cr4+∶YAG as Saturable Absorber

Cr4+∶YAG crystal was used as a saturable absorber in an active-passive mode-locked Nd∶YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm. The duration of ～0.8 ns to 2.4 ns for a single pulse was obtained by using Cr4+∶YAG crystals with the different initial transmissions, and there was a shortest pulse width. The mode-locking dynamic process of Cr4+∶YAG crystal was discussed to explain the experimental result, and the effect of excited-state absorption was considered.     

Nanosecond Dynamics Regulate the MIF‐Induced Activity of CD74

Macrophage migration inhibitory factor (MIF) activates CD74, which leads to severe disorders including inflammation, autoimmune diseases and cancer under pathological conditions. Molecular dynamics (MD) simulations up to one microsecond revealed dynamical correlation between a residue located at the opening of one end of the MIF solvent channel, previously thought to be a consequence of homotrimerization, and residues in a distal region responsible for CD74 activation. Experiments verified the allosteric regulatory site and identified a pathway to this site via the MIF β‐strands. The reported findings provide fundamental insights on a dynamic mechanism that controls the MIF‐induced activation of CD74.     

A highly selective and sensitive dual-channel chemosensor for cyanide based on sulfahydrazone derivative

A colorimetric and fluorescent cyanide probe bearing naphthol and sulfahydrazone groups has been designed and synthesized. This structurally simple probe displays a rapid response and high selectivity for cyanide in DMSO/EtOH (v/v = 2:8) solution. The addition of CN^? to the sensor p-toluenesulfonyl-2-hydroxy-1-naphthylhydrazone (L3) induced a remarkable color change from pale-yellow to yellow, and green fluorescence changed to yellow. The ¹H NMR titration and DFT calculations suggested that the selective sensing process is based on a nucleophilic addition reaction of cyanide to imine. Test strips based on sensor L3 were fabricated, which could act as a convenient and efficient test kit to detect CN^? for “in-the-field” measurements.     

Hydroxylation of phenol over MeAPO molecular sieves synthesized by vapor phase transport

In this study, MeAPO-25 (Me = Fe, Cu, Mn) molecular sieves were first synthesized by a vapor phase transport method using tetramethyl guanidine as the template and applied to hydroxylation of phenol. The zeolites were characterized by XRD, SEM, FT-IR, and DR UV–Vis. As a result, MeAPO-21 and MeAPO-15 were synthesized by changing the Me/Al ratio. UV–Visible diffuse reflectance study suggested incorporation of heteroatoms into the framework and FT-IR study also supported these data. Effects of heteroatoms, contents of Me in MeAPO-25, reaction temperature, phenol/H₂O₂ mole ratios, reaction time and concentration of catalyst on the conversion of phenol, as well as on the selectivity were studied. FeAPO-25 exhibited a high catalytic activity at the mole ratio of FeO and Al₂O₃ equal to 0.1 in the synthesis gel, giving the phenol conversion of 88.75% and diphenols selectivity of 66.23% at 60°C within 3 h [n(phenol)/n(H₂O₂) = 0.75, m(FeAPO-25)/m(phenol) = 7.5%]. Experimental results indicated that the FeAPO-25 molecular sieve was a fairly promising candidate for the application in hydroxylation of phenol.     

Quality evaluation of moluodan concentrated pill using high‐performance liquid chromatography fingerprinting coupled with chemometrics

In this study, a fast and effective high‐performance liquid chromatography method was developed to obtain a fingerprint chromatogram and quantitative analysis simultaneously of four indexes including gallic acid, chlorogenic acid, albiflorin and paeoniflorin of the traditional Chinese medicine Moluodan Concentrated Pill. The method was performed by using a Waters X‐bridge C₁₈ reversed phase column on an Agilent 1200S high‐performance liquid chromatography system coupled with diode array detection. The mobile phase of the high‐performance liquid chromatography method was composed of 20 mmol/L phosphate solution and acetonitrile with a 1 mL/min eluent velocity, under a detection temperature of 30°C and a UV detection wavelength of 254 nm. After the methodology validation, 16 batches of Moluodan Concentrated Pill were analyzed by this high‐performance liquid chromatography method and both qualitative and quantitative evaluation results were achieved by similarity analysis, principal component analysis and hierarchical cluster analysis. The results of these three chemometrics were in good agreement and all indicated that batch 10 and batch 16 showed significant differences with the other 14 batches. This suggested that the developed high‐performance liquid chromatography method could be applied in the quality evaluation of Moluodan Concentrated Pill.