Transitional Butterworth?Chebyshev filters

Based on the fact that the Butterworth and Chebyshev filters differ in the number of points of flatness, a new variety of simple and elegant Butterworth-Chebyshev transitional filter is proposed. Their time and frequency domain characteristics confirm their transitional nature.     

Development of Injectable Biodegradable Multi-Arms PEG-Based Hydrogels: Swelling and Degradation Investigations

Summary : Injectable biodegradable hydrogels have been developed to determine the efficacy of biomaterials for the treatment of periodontitis through control delivery of bone-healing bioactives. The hydrogels were prepared from the PEG-ylated macromer of Boltorn™ H20 (BH20) and an acrylated triblock copolymer of polylactide-polyethylene glycol (2k)-polylactide (PLA) in various molar ratios using ammonium persulfate and sodium ascorbate as a free radical initiating system. Preliminary investigations involving the synthesis of PLA hydrogels with different PLLA block lengths were studied in order to determine the swelling ratios and degradation rates of the biodegradable component of the hydrogels prior to copolymerization with BH20. The swelling and degradation studies of PLA with PEG diacrylate (FW 700) hydrogels were established in phosphate buffered saline (PBS) at 37 °C, pH 7.4 and in water (pH ∼5.5). They have been shown to have low swelling ratios (Q_max = 4.4 to 3.6) and degradation times of 20–30 days. The swelling and degradation parameters were found to be dependent on the molar ratio of the PEG diacrylate to PLA in the copolymer.     

Thermal infrared lines of methane broadened by nitrogen at low temperatures

Measurements of spectral transmittance in the v₄-fundamental band of ¹²CH₄ have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 cm^-1. With applications to lines formed in the atmospheres of Titan and Earth in mind, N₂ has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N₂-broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 cm^-2-atm^-1 at 296 K. Line widths were found to vary as Tⁿ with n = -1.0 for lines of the F-species and 0.63 for the A-species. Our measured line widths are considerably larger than those used in the AFGL compilation.     

Measurement of line intensities of linear molecules under low resolution

By using the relation k_v?S_J/δ_J applicable at sufficiently high pressures, at which the rotational fine structure in a band is smeared out completely, line intensities S_J may be determined from measured spectral absorption coefficients and known local line spacings δ_J. First, the validity of the approximation is ascertained by comparing the spectral absorption coefficient data of Penner and Weber and of Varanasi and Penner for the fundamental bands of CO and NO, respectively, with S_J/δ_J derived from the high resolution measurements of Benedict et al. (for CO) and of Abels and Shaw (for NO). Line intensity data obtained using this method are in good agreement with the high-resolution measurements of Toth (grating spectroscopy) for some unblended lines in the 00°0?02°1 band of N₂O and of Lacome et al. (laser- spectroscopy) for lines in the 10°0?00°1 band of N₂O.     

On the determination of the quadrupole moment of oxygen from self-broadened line widths in the microwave spectrum

The large discrepancy between the value 0·4 D Å measured by Buckingham for the quadrupole moment of oxygen and the recent value 1·21 D Å used by Yamamoto and Cattani and by Bouanich in line-broadening calculations is examined. When hexadecapolar and repulsive interactions are included, the discrepancy in the values of the quadrupole moment obtained by the bi-refringence method and line width calculations is resolved provided a value of Φ ～ 8 D ų is used for the hexadecapole moment of oxygen.     

Effects of platinum and oxygenation on microstructure in YBa2Cu3O7−δ/Y2BaCuO5 bulk materials

Transmission electron microscopy examinations have been conducted on undoped and PtO₂ doped YBa₂Cu₃O_7−δ, with excess Y₂BaCuO₅ (211) in the molar ratio of 5∶1 (123/211), processing using the solid liquid melt growth technique. Magnetization hysteresis suggests that addition of Pt strongly influences the pinning behavior. Considerable differences in dislocation and stacking fault densities were observed. Dislocation nets and tangles were commonly observed in the Pt doped samples. In both samples, stacking faults were observed near 211 precipitates, interplatelet boundaries, and dislocations. Dislocations appear to be formed during high temperature processing, while stacking faults appear to be generated during the final oxygenation step. The density and distribution of fine precipitates (∼25–100 nm) were comparable in both specimens suggesting that Pt additon affects the size and acicular morphology of only the coarser 211 (∼1–10 μm). It is proposed that the observed increase in J_c due to Pt addtion may be attributed to the increase in defect density rather than fine precipitates.     

Unsteady motion of receding contact lines of surfactant solutions: the role of surfactant re-self-assembly

Re-self-assembly of surfactant molecules must occur at moving contact lines of soluble surfactant solutions. Molecules are transported into and out of the contact line region from four sources: the three interfaces meeting at the contact line and the fluid confined between the solid-liquid and liquid-vapor interfaces. As molecules move among these sources at the contact line, they must rearrange. The dynamics of this re-self-assembly has been shown to have a dominating effect on the structure of advancing contact lines, causing unsteady motion and complex structure of the contact line. It might be assumed that the re-self-assembly for receding contact lines leads to more steady contact line movement. However, in this article we show that for a wide variety of systems this is not true. Quasi-static distortions of the contact line occur as it retreats because of the inability of the surfactant to completely re-self-assemble at localized positions along the contact line.     

Decision feedback multiuser detection: a systematic approach

A systematic approach to decision feedback multiuser detection is introduced for the joint detection of symbols of K simultaneously transmitting users of a synchronous correlated waveform multiple-access (CWMA) channel with Gaussian noise. A new performance criterion called symmetric energy is defined which is a low-noise indicator of the joint error rate that at least one user is detected erroneously. Even the best linear detectors can perform poorly in terms of symmetric energy compared to the maximum-likelihood detector. A general class of decision feedback detectors (DFDs) is defined with O(K) implementational complexity per user. The symmetric energy of arbitrary DFD and bounds on their asymptotic effective energy (AEE) performance are obtained along with an exact bit-error rate and AEE analysis for the decorrelating DFD. The optimum DFD that maximizes symmetric energy is obtained. Each one of the K! optimum, decorrelating, and conventional DFDs, that correspond to the K! orders in which the users can be detected, are shown to outperform the linear optimum, decorrelating, and conventional detectors, respectively, in terms of symmetric energy. Moreover, algorithms are obtained for determining the choice of order of detection for the three DFDs which guarantee that they uniformly (user-wise) outperform their linear counterparts. In addition to optimality in symmetric energy, it is also shown that under certain conditions, the optimum DFD achieves the AEE performance of the exponentially complex maximum-likelihood detector for all users simultaneously. None of the results of this paper make the perfect feedback assumption. The implications of our work on power control for multiuser detection are also discussed     

Optimally near-far resistant multiuser detection in differentiallycoherent synchronous channels

The noncoherent demodulation of differentially phase-shift keyed signals transmitted simultaneously via a synchronous code-division multiple-access (CDMA) channel is studied under the assumption of white Gaussian background noise. A class of noncoherent linear detectors is defined with the objective of obtaining the optimal one. The performance criterion considered is near-far resistance that denotes worst-case multiuser asymptotic efficiency over near-far environments. It is shown that the optimal linear detector is a noncoherent decorrelating detector. The commonality between the properties of the decorrelating detectors for coherent and noncoherent channels is established. In particular, it is shown that no other differential phase-shift keying (DPSK), multiuser detector achieves a higher near-far resistance than does the noncoherent decorrelator     

2-vinyloxy ethyl phthalimide polymerization initiated by 1-(isobutoxy) ethyl acetate in the presence of ethyl aluminum dichloride and either ethyl acetate or ethyl benzoate

2-Vinyloxy ethyl phthalimide (ImVE) was polymerized using 1-(isobutoxy) ethyl acetate as the initiator in the presence of ethyl aluminum dichloride and either ethyl acetate or ethyl benzoate. The resulting polymers have a narrow molecular weight distribution, and their molecular weight can be controlled within a narrow range by varying the monomer and initiator concentrations. Diblock copolymers with n-butyl vinyl ether can also be formed. The behavior of the polymerization is consistent with a living cationic mechanism. A brief comparison of the title system with other initiating systems is also presented. © 1996 John Wiley & Sons, Inc.