Influence of Evaporation on Marangoni-Benard Instability

Evaporative convection and instability give rise to both scientific and technological interests. Practically, a number of the industrial applications such as thin-film evaporators, boiling technologies and heat pipes concern with the evaporation process of which through the vapor-liquid interface the heat and mass transfer occur. From a physical viewpoint, one of interesting questions is the mechanisms of convection instability in thin-liquid layers induced by the coupling of evaporation phenomenon and Marangoni effect at the mass exchanged interface. Classical theories, including Rayleigh’s and Pearson’s, have only successfully explained convection in a liquid layer heated from below without evaporation. However these theories are unable to explain the convection in an evaporating thin layer, especially liquid layer is cooled from below. In present paper, a new two-sided model is put forward rather than the one-sided model in previous works. In previous works, the vapor is treated as passive gas and dynamics of vapor has been ignored. In this case, the vapor liquid system can be described by one-sided model. In our two-sided model, the dynamics of vapor should be considered. Linear instability analysis of the Marangoni-Bénard convection in the two-layer system with an evaporation interface is performed. We define a new evaporating Biot number which is different from the Biot number in one-sided model and obtain the curves of critical Marangoni number versus wave number. In our theoretical results, the Biot number and the evaporating velocity play a major role in the stability of the vapor-liquid system.

Few-cycle relativistic solitons in plasmas

A set of exact one-dimensional solutions to coupled nonlinear equations describing the propagation of a relativistic ultrashort circularly polarized laser pulse in a cold collisionless and bounded plasma where electrons have an initial velocity in the laser propagating direction is presented. The solutions investigated here are in the form of quickly moving envelop solitons at a propagation velocity comparable to the light speed. The features of solitons in both underdense and overdense plasmas with electrons having different given initial velocities in the laser propagating direction are described. It is found that the amplitude of solitons is larger and soliton width shorter in plasmas where electrons have a larger initial velocity. In overdense plasmas, soliton duration is shorter, the amplitude higher than that in underdense plasmas where electrons have the same initial velocity.

Short-pulse laser absorption in very steep plasma density gradients

An analytical fluid model for resonance absorption during the oblique incidence by femtosecond laser pulses on a small-scale-length density plasma [k(0)L is an element of(0.1,10)] is proposed. The physics of resonance absorption is analyzed more clearly as we separate the electric field into an electromagnetic part and an electrostatic part. It is found that the characteristics of the physical quantities (fractional absorption, optimum angle, etc.) in a small-scale-length plasma are quite different from the predictions of classical theory. Absorption processes are generally dependent on the density scale length. For shorter scale length or higher laser intensity, vacuum heating tends to be dominant. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking. This can lead to heating of the plasma at the expanse of the wave energy. It is found that the optimum angle is independent of the laser intensity while the absorption rate increases with the laser intensity, and the absorption rate can reach as high as 25%. (c) 2006 American Institute of Physics.

Vacuum heating in the interaction of ultrashort, relativistically strong laser pulses with solid targets

An analytical fluid model for vacuum heating during the oblique incidence by an ultrashort ultraintense p-polarized laser on a solid-density plasma is proposed. The steepening of an originally smooth electron density profile as the electrons are pushed inward by the laser is included self-consistently. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking since the front part of the returning electrons always move slower than the trailing part. This can lead to heating of the plasma at the expense of the wave energy. An estimate for the efficiency of laser energy absorption by the vacuum heating is given. It is also found that for the incident laser intensity parameter, a(L)> 0.5, the absorption rate peaks at an incident angle 45 degrees-52 degrees and it reaches a maximum of 30% at a(L)approximate to 1.5.

Generation of strong quasistatic magnetic fields in interactions of ultraintense and short laser pulses with overdense plasma targets

An analytical fluid model is proposed for the generation of strong quasistatic magnetic fields during normal incidence of a short ultraintense Gaussian laser pulse with a finite spot size on an overdense plasma. The steepening of the electron density profile in the originally homogeneous overdense plasma and the formation of electron cavitation as the electrons are pushed inward by the laser are included self-consistently. It is shown that the appearance of the cavitation plays an important role in the generation of quasistatic magnetic fields: the strong plasma inhomogeneities caused by the formation of the electron cavitation lead to the generation of a strong axial quasistatic magnetic field B-z. In the overdense regime, the generated quasistatic magnetic field increases with increasing laser intensity, while it decreases with increasing plasma density. It is also found that, in a moderately overdense plasma, highly intense laser pulses can generate magnetic fields similar to 100 MG and greater due to the transverse linear mode conversion process.

基于U型塑料光纤和邻啡咯啉钌的溶解氧传感器

本文提出了一种基于U型塑料光纤和邻啡咯啉钌的溶解氧传感器。光纤传感头放在样品池中，测量了不同氮氧体积比情况下荧光强度和寿命。研究了邻啡咯啉钌的浓度、传感头的退火时间和U型光纤的弯曲半径对系统灵敏度的影响。我们提出了双层模型来解释实验结果不符合S-V方程的实验现象，并用双层模型分析了弯曲半径对系统灵敏度的影响。通过对溶解氧浓度和荧光寿命亚线性曲线的拟合，我们得出敏感层的厚度和S-V系数分别为0.59和0.61。

Prescription for optimizing holograms in LiNbO3 : Fe : Mn

The photorefractive holographic dynamics of grating formation in photochromic doubly doped LiNbO3:Fe:Mn crystal is studied numerically and analytically in terms of the two-center model of Kukhtarev Et al. [Ferroelectrics 22, 949 (1979)]. The relations among the recorded and fixed space-charge fields and the doping densities, the oxidation-reduction states of the fields, and the intensities of UV-sensitizing and red recording beams are studied. Important conditions and effects are feued, and an optimal prescription for material doping and oxidation-reduction processing is suggested in which the crystal can be strongly oxidized and the Mn-doping density is smaller than the Fe-doping density. (C) 2000 Optical Society of America. OCIS codes: 050.7330, 190.5330, 090.2900.

Ultrafast double pulses ablation of Cr film on glass

Ultrafast lasers ablation of Cr film was investigated by using double-pulse method. Experimental results show that there exists a temporal ablation window effect with each of the double pulses adjusted just smaller than the threshold. When the delay between the double pulses is within the order of 400 ps, the ablation of Cr film could happen. When the delay between the double pulses is beyond the order of 400 ps, the ablation of Cr film would not happen, and the reflectivity from the surface of the Cr film shows a sharp rise at the same time. The two-temperature model was developed into the form of double pulses to explain the experimental phenomena. Furthermore, microbump structures were formed on the surface of Cr film after ablation by ultrafast double pulses. Their heights exhibit an obvious drop between 1 and 10 ps double pulses delay, which is involved with the electron-phonon coupling process according to the numerical simulation. These results should be helpful for understanding the dynamic processes during ultrafast lasers ablation of metal films. (C) 2008 Elsevier B.V. All rights reserved.

Characterization of a dissolved oxygen sensor made of plastic optical fiber coated with ruthenium-incorporated solgel

A dissolved oxygen sensor made of plastic optical fiber as the substrate and dichlorotris (1, 10-phenanthroline) ruthenium as a fluorescence indicator is studied. Oxygen quenching characteristics of both intensity and phase were measured; the obtained characteristics showed deviation from the linear relation described by the Stern-Volmer equation. A two-layer model is proposed to explain the deviation, and main parameters can be deduced with the model. (C) 2009 Optical Society of America

Respiratory pattern of captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis)

Cetacean respiration usually happen in bouts. The most widely applied quantitative method used to analyze the structure of these bouts is the log(e)-survivorship analysis, based on the assumption that the respiratory intervals are distributed as negative exponentials. However, for the data collected from three captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis), we failed to obtain a convergent result with the application of log,survivorship analysis. However, the two-Gaussian model, which was recently proposed to analyze the feeding behavior of cows, was successfully fitted to the data. According to the fitting results, the overall respiratory pattern of the captive Yangtze finless porpoises can be described as a dive with a mean duration of around 30-40 s, followed by two or three ventilations with a mean interval of approximately 9 s. The average intra-bout intervals during both active and inactive periods are constant at 7.7-9.9 s for all individuals. However, when shifting from active to inactive states, the adult male and female decrease their mean numbers of respirations per bout and average length of inter-bout respiratory intervals, while the estimates of both parameters increase for the juvenile female. It was pointed out that the two-Gaussian model might be more adequate for cetacean respiratory-bout structure analyses than the log(e)-survivorship technique.

Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field is varied. An interesting beat pattern in the TMR and spin polarization is found for different nonmagnetic semiconductor/diluted magnetic semiconductor double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are split by the s-d exchange interaction.

Hydrostatic pressure effect on photoluminescence from a GaN0.015As0.985/GaAs quantum well

Photoluminescence from a GaN0.015As0.985/GaAs quantum well has been measured at 15 K under hydrostatic pressure up to 9 GPa. Both the emissions from the GaNAs well and GaAs barrier are observed. The GaNAs-related peak shows a much weaker pressure dependence compared to that of the GaAs band gap. A group of new peaks appear in the spectra when the pressure is beyond 2.5 GPa, which is attributed to the emissions from the N isoelectronic traps in GaAs. The pressure dependence of the GaNAs-related peaks was calculated using the two-level model with the measured pressure coefficients of the GaAs band gap and N level as fitting parameters. It is found that the calculated results deviate seriously from the experimental data. An increasing of the emission intensity and the linewidth of the GaNAs-related peaks was also observed and briefly discussed. (C) 2001 American Institute of Physics.

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

We have investigated the optical transitions in Ga1-yInyNxAs1-x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Q(c), electron effective mass m(e)*, and band gap energy E-g were estimated. It was found that the Q(c) is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0-1)%. The m(e)* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the m(e)* and E-g of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. (C) 2001 American Institute of Physics.

Determination of the macroscopic optical properties for the NAEC/PEK-c guest-host polymer films

The polyetherketone (PEK-c) guest-host polymer films doped with (4'-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The films were poled by corona-onset poling at elevated temperature (COPET). The orientational order parameter of the chromophores NAEC in poled polymer film was determined by measuring the absorption spectra of the films before and after being poled. By using the two-level model, the measured dispersion of the refractive index of the polymer film, and the dispersion of the first hyperpolarizability of chromophore NAEC, the dispersion of the macroscopic second-order nonlinear optical (NLO) and linear electrooptic (EO) coefficients was evaluated for the NAEC/PEK-c guest-host polymer film. (C) 2001 Elsevier Science Ltd. All rights reserved.

Investigation on the nonlinear optical properties of the DCNP/PEK-c guest-host polymer films

The polyetherketone (PEK-c) guest-host polymer thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. The polymer films were investigated with in situ second-harmonic generation (SHG) measurement. The corona poling temperature was optimized by the temperature dependence of the in situ SHG signal intensity under the poling electric field applying. The temporal and temperature stability of the second-order properties of the poled polymer film were measured by the in situ SHG signal intensity probing. The second-order NLO coefficient chi ((2))(33) = 32.65 pm/V at lambda = 1064 nm was determined by using the Makel fringe method after poling under the optimal poling condition. The dispersion of the NLO coefficient of the guest-host polymer system was determined by the measured value of chi ((2))(33) at 1064 nm and the two-level model.