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991.
Laser welding is an important joining process for magnesium alloys. These materials are being increasingly used in different applications such as in aerospace, aircraft, automotive, electronics, etc. To date, carbon dioxide (CO2) neodymium-doped yttrium aluminum garnet (Nd:YAG) and the high power diode laser have been extensively used to investigate the weldability of magnesium alloys. The present work describes an analytical thermal model for the weldability of magnesium alloys (WE43) using an industrial (CO2) laser source. The main target of the project is to present to the industrial community a simple and rapid tool for the determination of the penetration depth and the bead width as a function of both the incident laser power and welding speed. The proposed model is based on the Davis thermal approach, largely considered for the characterization of the average radius of the liquid zone, aiming at predicting the joint shape. Moreover, since during the welding process considered in this study, a protecting gas is used to avoid joint oxidation, both thermal convection and radiation phenomena in the welding area have been estimated and introduced in our model for a better characterization of the welding process. The obtained results have been compared to the experimental ones and a satisfactory correlation has been observed, indicating the reliability of the model developed in this study. 相似文献
992.
In the paper, we study the problem on the number of zeros of eigenfunctions of the fourth-order boundary-value problem with
spectral and physical parameters in the boundary conditions. We show that the number of zeros of the eigenfunctions corresponding
to eigenvalues of positive type behaves in a usual way (it is equal to the serial number of an eigenvalue increased by 1),
but, however, the number of zeros of the eigenfunction corresponding to an eigenvalue of negative type can be arbitrary. In
the case of a sufficient smoothness of coefficients of the differential expression, we write the asymptotics in the physical
parameter for such a number.
__________
Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 12, No. 4, pp. 41–52, 2006. 相似文献
993.
Ben Justice 《Fiber and Integrated Optics》1977,1(2):115-133
An important aspect of optical waveguide fiber made of glass is whether it will break under a wide variety of service and manufacturing conditions. This paper covers some of the testing in which stress, length, time, and environment were vaned. The use of Weibull statistics with these data indicates that a statistically predictable behavior exists for populations of glass fibers. Extrapolation from short lengths and short times to very long lengths and very long times must be based on an understanding of the “constants” in the prediction equation. That is, these “constants” can be shown to vary when the three basic parameters cover orders of magnitude in range. 相似文献
994.
We describe a partition of the double flag variety G/B+ × G/B- of a complex semisimple algebraic group G analogous to the Deodhar partition on the flag variety G/B+. This partition is a refinement of the stratification into orbits both for B+ × B- and for the diagonal action of G, just as Deodhar's partition refines the orbits of B+ and B-. We give a coordinate system on each stratum, and show that all strata are coisotropic subvarieties. Also, we discuss possible
connections to the positive and cluster geometry of G/B+ × G/B-, which would generalize results of Fomin and Zelevinsky on double Bruhat cells and Marsh and Rietsch on double Schubert cells. 相似文献
995.
Huaji Liu Zhong Shen Salah‐Eddine Stiriba Yu Chen Wenqin Zhang Liuhe Wei 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4165-4173
Novel multiarm star copolymers with poly(?‐caprolactone) (PCL) as the arms and hyperbranched polyethylenimine (HPEI) as the core have been successfully prepared by the tin(II) 2‐ethylhexanoate catalyzed ring‐opening polymerization of ?‐caprolactone (CL) with HPEI used directly as a macroinitiator. Not only primary but also secondary amine groups of HPEI participate in initiating the ring‐opening polymerization of CL with almost 100% initiation efficiency. The average degree of polymerization of the PCL arms can be controlled by the feed ratio of the monomers to the initiating sites. Because of the polarity difference of the PCL arms and HPEI core, the obtained multiarm star polymers display an inverted micellar structure with potential extraction and encapsulation of water‐soluble guests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4165–4173, 2006 相似文献
996.
Elisa Guerrero Pedro Galindo Andrés Yá?ez Teresa Ben Sergio I Molina 《Microscopy and microanalysis》2007,13(5):320-328
In this article a method for determining errors of the strain values when applying strain mapping techniques has been devised. This methodology starts with the generation of a thickness/defocus series of simulated high-resolution transmission electron microscopy images of InAsxP1-x/InP heterostructures and the application of geometric phase. To obtain optimal defocusing conditions, a comparison of different defocus values is carried out by the calculation of the strain profile standard deviations among different specimen thicknesses. Finally, based on the analogy of real state strain to a step response, a characterization of strain mapping error near an interface is proposed. 相似文献
997.
Ben Brüggemann Tnu Pullerits Volkhard May 《Journal of photochemistry and photobiology. A, Chemistry》2007,190(2-3):372-377
Femtosecond laser pulse control of exciton dynamics in a biological chromophore complex is studied theoretically. The computations use the optimal control theory specified to open quantum systems and formulated in the framework of the rotating wave approximation. Based on the laser pulse induced formation of an excitonic wave packet the possibility to localize excitation energy at a certain chromophore within a photosynthetic antenna system (FMO complex of green bacteria) is investigated. Details of exciton dynamics driven by a polarization shaped pulse are discussed. 相似文献
998.
Shu‐Ben Li 《中国化学》2001,19(1):16-21
W‐Mn/SiO2 catalyst has been developed in our laboratory (LICP), which is active, selective and stable for oxidative coupling of methane (OCM) in fixed bed and fluidized bed reactors. The research results have been reproduced at different reaction conditions by two groups of J. H. Lunsford (JH‐LL) from Texas A & M University and R. M. Lambert (RMLL) from University of Cambridge respectively. The basic research aspects on this catalyst systems, reaction performances, structure characterization and reaction mechanism were reviewed. A model on two active sites related to W6+/5+ and Mn3+/2+ has been suggested for activation of methane and oxygen respectively. 相似文献
999.
Idempotency of linear combinations of three idempotent matrices, two of which are commuting 总被引:1,自引:0,他引:1
The considerations of the present paper were inspired by Baksalary [O.M. Baksalary, Idempotency of linear combinations of three idempotent matrices, two of which are disjoint, Linear Algebra Appl. 388 (2004) 67-78] who characterized all situations in which a linear combination P=c1P1+c2P2+c3P3, with ci, i=1,2,3, being nonzero complex scalars and Pi, i=1,2,3, being nonzero complex idempotent matrices such that two of them, P1 and P2 say, are disjoint, i.e., satisfy condition P1P2=0=P2P1, is an idempotent matrix. In the present paper, by utilizing different formalism than the one used by Baksalary, the results given in the above mentioned paper are generalized by weakening the assumption expressing the disjointness of P1 and P2 to the commutativity condition P1P2=P2P1. 相似文献
1000.
The 2ν3 overtone (A1, E) and the ν1 + ν3 (E) combination bands of the oblate symmetric top 14NF3 were studied by FTIR spectroscopy with a resolution of 2.5 × 10−3 cm−1. Nearly 500 lines up to Kmax/Jmax = 30/43 were observed for the weak A1 component reaching the v3 = 20 substate (1803.1302 cm−1), the majority of which corresponded to reinforced K = 3p-type transitions. For the strong E component reaching the v3 = 2±2 substate (1810.4239 cm−1), about 3550 transitions were assigned up to Kmax/Jmax = 65/69, favoring a clear observation of the ℓ(4, −2) and ℓ(4, 4) splittings within the kℓ = −2 and +4 sublevels, respectively. The two v3 = 2 substates are linked by the ℓ(2, 2)- and ℓ(2, −1)-type interactions, providing severe crossings, respectively, at K′ = 6 and near K′ = 24 on the v3 = 2+2 side. A model working in the D-reduction and including all these ℓ-type interactions could reproduce together 3695 nonzero weighted experimental data (NZW) through 33 free parameters with a standard deviation of σ = 0.357 × 10−3 cm−1. As for the ν1 + ν3 (E) combination band, about 3690 lines were assigned up to Kmax/Jmax = 45/55. Its v1 = v3 = 1 upper state (1931.577 5 cm−1) was treated using the same model recently applied to the v3 = 1 (E, 907.5413 cm−1) state. It yielded 21 free parameters through 3282 NZW experimental data, adjusted with σ = 0.344 × 10−3 cm−1 in the D-reduction. For the two excited states, the small and unobserved ℓ(0, 6) interaction was tested as useless. To confirm the adequacy of the vibrationally isolated models used, some other reductions of the Hamiltonian were tried. For the v3 = 2 state, the D-, L-, and LD-reductions led to similar σ’s, while the Q one was not successful. For the v1 = v3 = 1 state, the D- and Q-reductions gave comparable σ’s, while the QD-reduction was not as good. The corresponding unitary equivalence relations are generally more nicely fulfilled for the v3 = 2 state than for the v1 = v3 = 1 state. The three derivable anharmonicity constants in cm−1 are x33 = −4.1528, g33 = +1.8235 and x13 = −7.9652. 相似文献