Soliton switching and propagation in two-core nonlinear fiber coupler with high order coupling coefficient

We use the variational approach (VA) and the split-step Fourier transforms (SSFT) to study the transmission and switching characteristics inside the fiber nonlinear directional coupler (NDLC). The results, based on the VA, indicate that the second-order coupling coefficient dispersion and initiative chirp all reduce the coupling length, and the second-order coupling coefficient dispersion makes the switching characteristics become sharper and threshold power become bigger under the case of not having initiative chirp. The outcomes, based on the SSFT, indicate that the first order intermodal dispersion coefficient make optical pulses splitting in the propagation of fundamental solitons, and the second-order coupling coefficient dispersion reduces the coupling length, sharpens the switching characteristics and increases the switching threshold power, the results agrees well with those from the VA.     

热膨胀系数异性轴夹角优化分析

高超声速飞行器需要先进的材料进行热防护,比如增强碳/碳材料.有两种将碳纤维制作成碳/碳球锥外形的工艺,研究表明在每种工艺中,碳/碳块体或碳纤维热膨胀系数异性轴角度对结构热应力影响很大,为此本文发展了一套优化设计方法,对给定的对流加热温度场可以实现球锥热应力的最小化.分析结果表明对于热膨胀系数异性轴角度,存在某些取值点,那时结构热应力分别达到最大和最小值.在异性轴模晕小于同性平面模量的条件下,对于工艺1,如果将球锥对称轴设置成垂直于碳/碳块体的同性平面,可以将热应力减至最小;对于工艺2,如果能将编制面内的碳纤维束异性轴角度取成负值(即指向来流方向),则球锥热应力也可以得到相当程度的减小.     

Low frequency in situ metrology of absorption and dispersion of sound absorbing porous materials based on high power ultrasonic non-linearly demodulated waves

The present work is related to acoustic in situ free-field measurements of sound absorption in porous materials, such as cellular plastic foams, glass-wool or recycled felt materials. The emphasis is given towards fine metrology of absorption in view of potential industrial applications. A powerful ultrasonic array working at 40 kHz is used. It enables to measure absorption acoustical data down to 100 Hz due to the exploitation of the non-linear ultrasonic demodulation phenomenon in air. Fine measurements of acoustic absorption are compared to numerical predictions based on the “equivalent-fluid” model (when the squeleton frame is motionless), and to some measurements performed on a Brüel and Kjaer impedance tube. Dispersion curves are also measured and compared to the numerical predictions for some automotive felt materials which are compressed at various ratios. Data obtained with a dedicated portable instrument are also discussed for the same type of materials and configurations.     

Bounding the Bogoliubov coefficients

While over the last century or more considerable effort has been put into the problem of finding approximate solutions for wave equations in general, and quantum mechanical problems in particular, it appears that as yet relatively little work seems to have been put into the complementary problem of establishing rigourous bounds on the exact solutions. We have in mind either bounds on parametric amplification and the related quantum phenomenon of particle production (as encoded in the Bogoliubov coefficients), or bounds on transmission and reflection coefficients. Modifying and streamlining an approach developed by one of the present authors [M. Visser, Phys. Rev. A 59 (1999) 427-438, arXiv:quant-ph/9901030], we investigate this question by developing a formal but exact solution for the appropriate second-order linear ODE in terms of a time-ordered exponential of 2×2 matrices, then relating the Bogoliubov coefficients to certain invariants of this matrix. By bounding the matrix in an appropriate manner, we can thereby bound the Bogoliubov coefficients.     

Absorptivity and fluorescence properties of 9,10-diiodoanthracene in solutions

The molar extinction coefficient, oscillator strength, natural fluorescence lifetime, and fluorescence quantum yield have been determined for 9,10-diiodoanthracene in ethanol at 20°C. The temperature effect on the quantum yield was studied in the range 120–300 K. The fluorescence lifetime was measured at 77 K. During glassification of ethanol, the fluorescence intensity of 9,10-diiodoanthracene increases by more than 50 times due to the activation nature of the intersystem crossing from the S₁(¹B_2u⁺) state. The activation energy and pre-exponential factor for the probability of the intersystem {ie319-01}-crossing are found. The long-wavelength shift of the absorption spectrum with increasing bulk polarizability of the solvent is interpreted as evidence of changes in the nonspecific interactions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 304–308, May–June, 2008.     

Complexation of heterocyclic ligands with DNA in aqueous solution

We have used spectrophotometry to study self-association and complexation with DNA by organic heterocyclic compounds in the acridine and phenothiazine series: proflavin, thionine, and methylene blue. Based on the experimental concentration dependences of the molar absorption coefficient of the molecules in an aqueous buffer solution (0.01 M NaCl, 0.01 M Na₂EDTA, 0.01 M Tris, pH 7.4, T = 298 K), we have determined the equilibrium dimerization constants for the dyes and the DNA complexation parameters using the Scatchard and McGhee-von Hippel models. The observed increase in the cooperativity parameters as the dimerization constants of the ligands increase allowed us to hypothesize that the same interactions occur between dye molecules adsorbed on DNA as in their self-association. The equilibrium DNA-binding constants for the ligands, obtained using the McGhee-von Hippel cooperative model, are (20.9 ± 2.7)·10³ M⁻¹ for proflavin and (33.8 ± 4.1)·10³ M⁻¹ for thionine. Using the Scatchard model, taking into account intercalation and “external” binding of ligands with DNA, we determined the DNA complexation constants for methylene blue: (26.4 ± 4.6)·10³ and (96 ± 17)·10³ M⁻¹ respectively. Based on analysis of the data obtained, we hypothesized that the predominant type of binding with DNA is intercalation binding in the case of proflavin and thionine, and “external” binding with the DNA surface in the case of methylene blue. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 242–249, March–April, 2008.     

渤海近岸水体后向散射系数反演模型

水体后向散射系数bb是重要的海洋光学参数,在以悬浮物为主要组分的浑浊二类水体中,其对于水体光学性质起着决定性的作用,该参数的遥感反演对于海洋光学与水色遥感研究具有重要意义.利用2005年渤海近岸水体实测数据集,建立了基于水体遥感反射率光谱数据的后向散射系数bb(λ)经验反演模型(λ=442 nm,488 nm,532 nm,589 nm,676 nm),经实测数据检验,bb(442)和bb(589)反演平均相对误差约为30%;bb(488)和bb(676)反演半均相对误差优于40%;bb(532)反演半均相埘误差约为57%.通过分析模型对于输入误差的敏感性发现,当输入端引入±5%的误差时,模型反演值的误差波动在绝大多数情形下可控制在±10%以内,模型足稳定可靠的.模型适用于渤海近岸浑浊水体,可用丁水体光学参数的时空分布特征分析以及基丁固有光学参数的水色组分遥感反演.     

Low-temperature specific heat of Ni–Mn–Ga ferromagnetic shape memory alloys

Results of the low-temperature specific heat measurements (2–80 K) for one austenitic and three martensitic Ni–Mn–Ga ferromagnetic alloys are presented. The alloy compositions are chosen to comprise a wide span of valence electron concentrations e/a=7.3–7.78. Debye temperature (261–345 K) is found to be an increasing function of e/a while the experimental values of the Sommerfeld coefficient (2.9–3.4 mJ/mol K²) appear to be increasing in the martensitic region only. Observation of those trends rekindles the discussion about the role of vibrational and electronic contributions to the lattice instability and transformation mechanism of studied alloys.     

The effect of magnetic field heat treatment on magnetostriction of Terfenol-D 2-2 composites

Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d₃₃ of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10⁻⁶ at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10⁻⁶ without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10⁻⁶. The dynamic magnetostrictive coefficient d₃₃ of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d₃₃ of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment.     

Correlation of fluctuation field and temperature coefficient of coercivity in a CoCrPtB thin film

The effect of the ratio of fluctuation field (H_f) to coercivity (H_c) on the temperature coefficient of coercivity [α(H_c)] was investigated for Co₅₅Cr_15.5Pt₂₈B_1.5/Co₆₃Cr₃₇/Cr, Co₆₉Cr₁₉Pt₉Ta₃/Cr, and Co₈₆Cr₁₀Ta₄/Cr thin films (longitudinal recording media) with very small average grain volume (V_phy). α(H_c) increases markedly with increase in temperature between near 250 and 350 K for Co₅₅Cr_15.5Pt₂₈B_1.5/Co₆₃Cr₃₇/Cr thin films. α(H_c) is approximately proportional to the ratio H_f/H_c for all thin films, as in the case of advanced data backup tapes prepared from ultrafine particles. α(H_c) and the ratio H_f/H_c increase as V_phy decreases. Smaller H_f/H_c values are necessary for small α(H_c) values, which is very important for the thermal stability of high-density recording media with very small V_phy.