An orthogonal-plane PIV technique for the investigations of three-dimensional vortical structures in a turbulent boundary layer flow

An experimental investigation was carried out regarding a three-dimensional topology of a zero-pressure gradient turbulent boundary layer. In this study, the polarization separation technique has been applied to the PIV measurements. Two mutually perpendicular measurement planes have been employed in x–y and x–z planes, respectively. Synchronization between a stereoscopic PIV with another plane PIV system was made toward the detection of such salient features of the coherent structure as the legs and the head of the hairpin vortices. Polarization rotation via a half-waveplate and subsequent particle image separation using polarizer minimized the spurious particle images. The PIV results clearly demonstrate the presence of hairpin-like coherent vortical structures and coincidence between the near-wall quasi-streamwise vortex pair and the legs of the hairpin vortex.     

Orthotropic strain rate potential for the description of anisotropy in tension and compression of metals

In this paper, a macroscopic anisotropic strain rate potential, which can describe both the anisotropy and tension-compression asymmetry of the plastic response of textured metals is derived. This strain rate potential is the exact work-conjugate of the anisotropic stress potential CPB06 of Cazacu et al. (2006). Application of the developed strain rate potential to HCP high-purity alpha-titanium is presented.     

On the existence of indeterminate solutions to the equations of motion under non-associated flow

Under certain conditions, an indeterminate solution exists to the equations of motion for dynamic elastic–plastic deformation of materials using constitutive laws based on non-associated flow that suggests that an initially unbounded dynamic perturbation in the stress can develop from a quiescent state on the yield surface. The existence of this indeterminate solution has been alleged to discourage use of non-associated flow rules for both dynamic and quasi-static analysis theoretically. It is shown in this paper that the indeterminate solution that may solve the equations of motion is intrinsically dynamic, and it determinately goes to zero in the quasi-static limit regardless of other indeterminate parameters. Consequently, the existence of this unstable dynamic solution has no impact on stability and use of non-associated flow rules for analysis of the quasi-static problem. More importantly, for dynamic applications, it is also shown that the indeterminate solution solves the equations of motion only if critical restrictions are applied to the constitutive equations such that the effective modulus during loading is constant and the direction of the perturbation is unidirectional over a finite time interval. It is shown that common components of the constitutive laws used in metal forming and deformation analysis are inconsistent with these restrictions. So, these common models can be generalized to include non-associated flow for analysis of the dynamic problem without concern that the solution will become indeterminate.     

Interlaminar fracture toughness of graphite/epoxy composite under mixed-mode deformations

An antisymmetric test fixture is employed to investigate interlaminar fracture behavior in graphite/epoxy composite material under mixed-mode deformations. Finite correction factors for the graphite/epoxy fracture specimen with various crack lengths are used to determine the interlaminar fracture toughness by finite-element stress analysis. Interlaminar fracture characteristics of graphite/epoxy composite material under mode-I, mode-II and mixed-mode deformations are evaluated experimentally. A mixed-mode fracture criterion is also investigated to obtain information on mixedmode interlaminar fracture behavior of graphite/epoxy composite material.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

Optical parametric chirped pulse amplification of Cr:forsterite laser pulses in periodically poled stoichiometric LiTaO3 at 1 kHz

The first praseodymium-ytterbium up-conversion ZBLAN fiber laser in an all-fiber ring configuration is reported. The laser operates at 635 nm, is pumped at 835 nm, and consists of only the active ZBLAN fiber and two-fused-fiber couplers. PACS 42.55.Wd; 42.60.By     

Growth dynamics and optimization of Ga(In)AsN/GaAs towards 1.3 μm and 1.55 μm

It is demonstrated that a nitrogen supply, manifested as both a direct nitrogen beam from a rf-activated plasma source and dispersive nitrogen radicals from the growth-chamber background, is appropriate for the growth of GaAs-based nitrides. The nitrogen incorporation efficiency shows a linear relationship with increasing rf power when the nitrogen is supplied dispersively, and a saturation behavior when the nitrogen is supplied as a direct nitrogen beam. The indium composition causes a decrease in the nitrogen incorporation efficiency, which is suspected to be brought about by the increase of the growth rate due to the indium flux, because our experiments have proven that the nitrogen composition of GaAsN epilayers apparently decreases as the growth rate increases. It is more controllable to fix the indium flux first than to fix the nitrogen source condition, so as to facilitate wavelength control. The temperature window for the growth of quality nitride is concluded to be between 440 °C and 500 °C. For a quantum well with a certain well width, it is better to add more indium and less nitrogen to reach the desired wavelength in order that the quality of the InGaAs material is kept acceptable. PACS 81.15.Hi; 81.05.Ea; 42.70.-a     

Preparation and characterization of biodegradable poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers

A series of poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(ε‐caprolactone) random copolymer was synthesized with stannous‐2‐ethylhexanoate and followed by adding p‐dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by ¹H and ¹³C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790–2799, 2005     

Synthesis of novel N-acyclonucleosides: Benzotriazole,benzothiazinone and pyridooxazinone acyclonucleosides

Some novel benzotriazole, benzothiazinone and pyridooxazinone acyclonucleosides containing 4-hydroxybutyl, 4-hydroxybutoxy, 4-iodobutyl, 2-oxopropyl and 2,3-epoxypropoxy groups as a side chain was prepared.     

Morphology and thermal properties of poly(L‐lactide)/poly(butylene succinate‐co‐butylene adipate) compounded with twice functionalized clay

Poly(L ‐lactide) (PLLA)/poly(butylene succinate‐co‐butylene adipate) (PBSA) blends were compounded with Cloisite 25A® (C25A) and C25A functionalized with epoxy groups, respectively. Epoxy groups on the surface of C25A were introduced by treating C25A with (glycidoxypropyl)trimethoxy silane (GPS) to produce so called Twice Functionalized Organoclay (TFC). Variation of morphology and properties of PLLA/PBSA/C25A composites was investigated before and after the treatment with GPS. The morphological structure of the composites was analyzed by using X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The silicate layers of PLLA/PBSA/TFC were exfoliated to a larger extent than PLLA/PBSA/C25A. Incorporation of the epoxy groups on C25A improved significantly elongation at break as well as tensile modulus and tensile strength of PLLA/PBSA/C25A. The larger amount of exfoliation of the silicate layers in PLLA/PBSA/TFC as compared with that in PLLA/PBSA/C25A was attributed to the increased interfacial interaction between the polyesters and the clay due to chemical reaction. Thermo gravimetric analysis revealed that both T_5%, which was the temperature corresponding to 5% weight loss, and activation energy of thermal decomposition of PLLA/PBSA/TFC were far superior to those of PLLA/PBSA/C25A as well as to those of PLLA/PBSA, indicating that the composites with exfoliated silicate layers were more thermally stable than those with intercalated silicate layers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 478–487, 2005     

Molecular weight dependence of mechanical properties of poly(p,p′-oxydiphenylene pyromellitimide) films

The mechanical properties, i.e., Young's modulus, elongation, and tensile stress, were determined as functions of the molecular weight for films of poly(oxydi-p-phenylene pyromellitimide) prepared by thermal cyclization of the precursor poly(amic acid). The molecular weights of the samples were controlled by the monomer stoichiometry employed for the solution condensation of pyromellitic dianhydride and p,p′-oxydianiline. Weight-average molecular weights were determined by light scattering of the precursor poly(amic acid) as well as the fully cyclized polyimide. The elongation-at-break is most sensitive to the molecular weight, undergoing a rapid increase at M _w ? 8000 and reaching a limiting value of about 60% for M _w > 20,000.