Comments, with reply, on `Passive equalization of semiconductordiode laser frequency modulation' by S.B. Alexander et al

Some flaws in a recent article by S.B. Alexander et al. (ibid., vol.7, no.1, p.11-23, Jan. 1989) on the theory of equalization of FM response of a laser diode using passive filters are noted. An error has occurred as a result of assuming a constant C as a positive instead of negative. When C is negative and large, the equalization network cannot be realized with passive networks. Also the simulated time waveform shown in the article for the optical frequency of an equalized laser does not show some spikes which are expected theoretically. The spikes occur as a result of an imperfect equalization provided by the proposed passive filters that were realized assuming C as positive. In replying the original author feels that the comments and observations result simply from attempting to extend the simple FM transfer-function model far beyond its limits while trying to introduce unnecessary theoretical rigor     

Structure determination of CaMgGeO4

The crystal structure of CaMgGeO₄ is described. CaMgGeO₄, M_r = 200.9, orthorhombic, Pnam, A = 11.285(5) Å, B = 5.016(2) Å, C = 6.435(2) Å, V = 364.36 ų, Dx = 3.664 Mg/m³.λ(MoK_a = 0.71069 Å, F(000) = 384, room temperature, final R = 0.045 for 1752 observed reflections. The structure is isomorphous with CaMgSiO₄ (monticellite).     

Long-wavelength infrared photoinduced switching of a resonanttunneling diode using the intersubband transition

Voltage switching induced by long-wavelength infrared light from a CO₂ laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed     

Rotative quadrature phase-shift keying

A rotative quadrature phase-shift keying (RQPSK) modulation scheme is proposed. By rotating the QPSK signal constellation by pi /2 either clockwise or anticlockwise during a symbol duration, the conventional QPSK scheme can be modified to transmit 3 bits per symbol to achieve both power and bandwidth efficiency.<>     

The integrated academic information management system at Columbia-Presbyterian Medical Center.

Over the past seven years, Columbia-Presbyterian Medical Center has been planning and implementing an integrated academic information management system. Accomplishments to date include establishing an institutional information architecture, installing a campus-wide network of workstations, recruiting the staff needed to develop and implement the system, and developing various applications. This paper presents the rationale and steps involved in these accomplishments, as well as data on use of the system so far.     

Ultrasonic welding using tie-layer materials. part II: Factors affecting the lap-shear strength of ultrasonic welds

The influence of tie-layer Melt Flow Index on the lap-shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie-layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap-shear strength properties were obtained using tie-layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie-layers, hot spot formation and concomitant changes in fusion zone and heat-affected-zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie-layers were used, the mode of failure during lap-shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie-layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo-oxidative processes.     

PMMA tacticity and alumina powder dispersion stability

Summary Sedimentation experiments and X-ray photoelectron spectroscopy (XPS or ESCA) analyses have been used to study the effect of poly(methylmethacrylate) (PMMA) tacticity on aluminum oxide powder dispersion stability in a common solvent medium. The relative trends from sedimentation densities, and from surface analyses after solvent washing show that (PMMA) adsorption is greatest with isotactic polymer, where isotactic>atactic>syndiotactic adsorption. These results suggest that surface adsorption and hence dispersion stability can be influenced by polymer chain configuration as well as by chain conformation.     

Hot-carrier aging of the MOS transistor in the presence of spin-onglass as the interlevel dielectric

The effect of introducing a polysilicate or polysiloxane spin-on glass (SOG) as a component of the interlevel dielectric in a multilevel integrated circuit on the hot-carrier aging of the MOS transistor is discussed. It was found that the presence of SOG led to accelerated aging of the MOS transistor: factors of 20 and 5 for silicate and siloxane, respectively. This effect is attributed to water absorbed in the SOG films. a correlation was found for the hot-carrier aging rate and the amount of absorbed water     

Conformational effects in the reversed-phase chromatographic behavior of recombinant human growth hormone (rhGH) and N-methionyl recombinant human growth hormone (Met-hGH).

This paper examines the retention behavior of recombinant DNA-derived human growth hormone (rhGH) in reversed-phase chromatography and its separation from the closely related N-methionyl variant (Met-hGH). It is first shown that retention for rhGH decreases with increasing column temperature when 1-propanol (1-PrOH) is used as organic modifier. On the other hand, retention increases with temperature when acetonitrile (CH3CN) is employed. The differences in behavior for the two organic modifiers could be related to conformational changes in the protein as determined by solution and adsorption intrinsic fluorescence spectroscopy. Specifically, desorption and elution of rhGH using 1-PrOH could be correlated with a solvent-induced conformational change, with retention decreasing with increasing temperature due to the increasing ease of structural alteration. On the other hand for CH3CN the increase in retention correlated with temperature rise was related to a partial structural change yielding a more hydrophobic species. In this case, a surface-driven process is suggested. The work then turned to the separation of rhGH and Met-hGH where it was found for both organic modifiers optimum separation occurred at 45 degrees C and pH 6.5. Separate studies revealed that during the conformational change Met-hGH appeared more hydrophobic than rhGH since protein-protein aggregation was observed at a lower 1-PrOH concentration. It is suggested that this hydrophobic difference, which was optimized under the conditions cited above, resulted in the separation. The study demonstrates the importance of conformational changes in retention behavior and separation of protein samples.