Nuclear magnetic resonance of poly-β-alanine

Nuclear magnetic resonance of poly-β-alanine samples differing in solubility in water was studied over a wide temperature range as part of an investigation of their physical properties. Water-soluble poly-β-alanine has more branches and a lower degree of crystallinity than water-insoluble poly-β-alanine. NMR spectra of poly-β-alanine show one component at 77°K. which splits into two components, broad and narrow, at room temperature. Two transition regions were observed in curves for line width and second moment versus temperature. The higher transition temperature, corresponding to the glass transition of the polymer, appears to decrease with increasing water content. The second moment for the water-soluble polymer differs from that of the water-insoluble polymer at 77°K. This is interpreted in terms of the difference in the degree of crystallinity of the polymers.     

Visible nonlinear band-edge luminescence in ZnSe and CdS excited by a mid-infrared free-electron laser

Visible nonlinear band-edge luminescence in ZnSe and CdS bulk crystals was observed upon excitation by a mid-infrared free-electron laser (mid-IR FEL) at approximately 9 mm. The emission intensity is proportional to the 74th and 45th powers of the excitation intensity for ZnSe and CdS, respectively. For ZnSe, the temporal profile of the emission intensity does not follow the profile of the excitation macropulse of the FEL, but sharply rises and decays only at the maximum of the macropulse profile. These features are in marked contrast to those of a previous report, where the emission profile follows that of the macropulse, and the emission intensity scales with the 4th power of the excitation intensity. The experimental observations were reproduced by a numerical simulation based on impact ionization and avalanche ionization by electrons accelerated by the optical electric field of the FEL. The large nonlinearity in the bandedge emission comes from the macropulse temporal structure, which consists of micropulses densely spaced to allow excited carriers to survive when the next micropulse arrives. They work as seed carriers in the next carrier multiplication step.     

Relaxational behavior of the piezoelectric constant and the electrostriction constant in polymers

Piezoelectricity in polymer films is classified by its mechanism into three groups: A-1, intrinsic piezoelectricity due to internal strain in nonpolar crystals; A-2, intrinsic piezoelectricity due to the strain-dependence of the spontaneous polarization in polar crystals; and B, piezoelectricity due to the heterogeneity of macroscopic strain.

The relaxational behavior of piezoelectricity in Type A-1 is discussed for two cases: (a) the piezoelectric phase is relaxing, and (b) the piezoelectric phase is nonrelaxing but the nonpiezoelectric phase is relaxing. For Case a, a thermody-namic theory is developed, yielding relations among relaxation strengths of piezoelectric constant, dielectric constant, and elastic modulus. For Case b, on the other hand, the inequalities e″/e′ < 0 and d″/d′ > 0 are verified for a generalized composite model of two phases, where e′ — ie” and d′ — id″ are complex piezoelectric stress and strain constants, respectively.

Relaxational behavior of the piezoelectric constant for Type A-2 and Type B is expected to reflect that of the electrostriction constant as suggested by theories. The complex electrostriction constant in a range from 30 Hz to 500 kHz is presented for unrolled and rolled poly(vinylidene fluoride) films. The frequency dependence of the complex electrostriction constant can explain the relaxational behavior of the piezoelectric constant of Types A-2 and B, and at the same time gives a new aspect of the relaxational character of polymers, the strain-dependence of the relaxation time, and its anisotropy.     

Front shock behavior of stable curved detonation waves in rectangular-cross-section curved channels

The propagation of curved detonation waves of gaseous explosives stabilized in rectangular-cross-section curved channels is investigated. Three types of stoichiometric test gases, C₂H₄ + 3O₂, 2H₂ + O₂, and 2C₂H₂ + 5O₂ + 7Ar, are evaluated. The ratio of the inner radius of the curved channel (r_i) to the normal detonation cell width (λ) is an important factor in stabilizing curved detonation waves. The lower boundary of stabilization is around r_i/λ = 23, regardless of the test gas. The stabilized curved detonation waves eventually attain a specific curved shape as they propagate through the curved channels. The specific curved shapes of stabilized curved detonation waves are approximately formulated, and the normal detonation velocity (D_n)?curvature (κ) relations are evaluated. The D_n nondimensionalized by the Chapman–Jouguet (CJ) detonation velocity (D_CJ) is a function of the κ nondimensionalized by λ. The D_n/D_CJ?λκ relation does not depend on the type of test gas. The propagation behavior of the stabilized curved detonation waves is controlled by the D_n/D_CJ?λκ relation. Due to this propagation characteristic, the fully-developed, stabilized curved detonation waves propagate through the curved channels while maintaining a specific curved shape with a constant angular velocity. Self-similarity is seen in the front shock shapes of the stabilized curved detonation waves with the same r_i/λ, regardless of the curved channel and test gas.     

Eigenvalues of some distal functions

In this paper we construct distal functions of another type discussed by Salehi (1991). Let be an almost periodic function with the mean value 0, which has unbounded integral, and a continuous periodic function with the prime period 1. If satisfies some additional condition, then is a distal function, which is not almost periodic, and the set of eigenvalues of is the module of .

     

Effects of Y (Ⅲ) Ions on the Fluorescence Properties of Ce(Ⅲ) Ion and the Organic Ligands in the Complex

The enhancement effects of Y ( Ⅲ) ions on the fluorescence of Ce ( Ⅲ) in Ce ( Ⅲ)-Y ( Ⅲ)-PMMA (polymethylmethacrylate ) or Ce ( Ⅲ)-Y ( Ⅲ)-PVC (polyvinyl chloride ) complex systems were observed. The influence of Y ( Ⅲ) ions on the emission spectra of PMMA ligands in PMMA-Y ( Ⅲ) and the fluorescent enhance- ment of Y( Ⅲ) on Ce( Ⅲ) emission in PMMA-Ce-Y by Y( Ⅲ) ion were studied. It was also of interest to note that when Y ( Ⅲ) ions were added into PMMA and into bpy(bipyridine ), respectively, the emission spectrum of PMMA ligands was split into fine structure bands by Y ( Ⅲ), and the fluorescence intensities of bpy ligands in bpy-Y ( Ⅲ) complexes were considerably increased.