On the capacity of packet reservation multiple access with capturein personal communication systems

A new Markovian model is developed to analyze the packet reservation multiple access (PRMA) protocol over Rician fading channels with lognormal shadowing. The packet dropping probability and the voice user capacity are defined as the performance measures. A new formula is derived to evaluate the dropping probability in the fading environment. The analytical results from our new formula show close agreement with those from computer simulations. The capture effect on the PRMA system performance is also studied. We found that, with capture, the user capacity will be improved and the service quality will degrade gracefully when the number of active users in the system increases. Using the dropping probability as the criterion, we also determine the optimal permission probability in a microcellular environment     

A novel soft-switching full-bridge DC/DC converter: analysis,design considerations, and experimental results at 1.5 kW, 100 kHz

The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM (pulsewidth modulated) full-bridge DC/DC converter substantially reduces the switching losses of the transistors and the rectifier diodes, under all loading conditions. The authors give analyses, practical design considerations, and experimental results for a 1.5 kW converter with 60 V, 25 A output, operating at 100 kHz clock frequency and 95% efficiency     

Full-wafer technology-A new approach to large-scale laserfabrication and integration

A concept for full-wafer processing (FWP) and full-wafer testing (FWT) for semiconductor laser fabrication in the AlGaAs-GaAs material system is presented. The approach is based on chemically assisted ion beam etching for the laser-mirror formation. Record values for mirror scattering, optimum mirror reflectivity, and equivalence to cleaved mirrors in terms of laser threshold and efficiency have been achieved. Promising results for uniformity and reproducibility for major laser diode characteristics on processed 2-in wafers have been found. The FWP technology has been extensively used for designing test sites to determine various materials, process, and laser parameters, such as sheet resistance, ridge dimensions, lithographic alignment errors, mirror surface leakage, etc     

Coupled-cavity passive mode-locked injection laser

Experimental results on the observation of the self-initiating passive mode-locking operation of an injection laser with a nonlinear external-coupled-cavity configuration are presented. Michelson and Fabry-Perot cavity arrangements with similar laser diodes as both the gain medium and nonlinear element have been investigated. This technique can be used for generating short pulses with ultrahigh repetition rates without utilizing both high-modulation bandwidth laser diodes and ultrafast electronics, which do not require special saturable absorbers.<>     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>     

Novel four quadrant DC-link soft switching inverter generating sinusoidal waveforms

A novel high frequency resonant link inverter using zero-voltage switching (except for one device where zero-current switching is used) operable in four quadrants is proposed. It provides several excellent advantages over the conventional resonant link inverters, such as low VA ratings, low acoustic noise and low harmonic distortion.<>     

Binary [18,11]2 codes do not exist-Nor do [64,53]2 codes

A binary, linear block code C with block length n and dimension n is commonly denoted by [n, k] or, if its minimum distance is d, by [n, k,d]. The code's covering radius r(C) can be defined as the smallest number r such that any binary column vector of length (n-k) can be written as a sum of r or fewer columns of a parity-check matrix of C. An [n,k] code with covering radius r is denoted by [n,k]r. R.A. Brualdi et al., (1989) showed that l(m,r) is defined to be the smallest n such that an [n,n-m]r code exists. l(m,2) is known for m⩽6, while it is shown by Brualdi et al. that 17⩽l(7,2)⩽19. This lower bound is improved by A.R. Calderbank et al. (1988), where it is shown that [17,10]2 codes do not exist. The nonexistence of [18,11]2 codes is proved, so that l(7,2)=19. l[7.2)=19 is established by showing that [18,11]2 codes do not exist. It is also shown that [64,53]2 codes do not exist, implying that l(11,2)⩾65     

Observation of low-chirp modulation in InGaAs-InAlAs multiple-quantum-well optical modulators under 30 GHz

Modulated light spectra were measured in long-wavelength InGaAs-InAlAs multiple-quantum-well intensity modulators under 30-GHz large-signal modulations. The linewidth broadening factor alpha is determined from the relation between the intensity modulation index and the sideband strength relative to the carrier. The minimum alpha value is estimated to be 0.70 at 1.54 mu m, which is almost the same as the lowest value so far reported in a bulk Franz-Keldysh modulator. This is significantly lower than what is obtained from direct-intensity modulation of injection lasers, making this a useful device for application to high-bit-rate long-haul optical communication systems.<>     

Alpha-particle-induced charge collection in p-n junction diodes insemi-insulating GaAs substrates

The bias and angle dependences of the alpha-particle-induced charge collected by GaAs p-n junction diodes are investigated. These diodes, in which the n-layer overlays the p-layer, are fabricated in a semi-insulating GaAs substrate by Si and Mg ion implantation. ²⁴¹ Am placed in a vacuum is used as an alpha-particle source with an initial energy of 4.03 MeV and a fluence of 5.4×10^-5/s/μm². The results show that the collected charge is nearly independent of the applied bias. This bias independence may be further evidence that the charge funneling process is not important in semi-insulating GaAs. A model not incorporating funneling can explain the measured angular dependence. Based on this model, the design principle for the buried p-layer structure is discussed     

95W-Ni-Fe 合金工艺缺陷的 SAM 和 XPS 分析

藉助扫描俄歇探针、Ｘ射线光电子谱等分析了９５Ｗ－Ｎｉ－Ｆｅ合金碳污染和氧化的本质。发现，碳污染试样中碳的化学状态主要为石墨，少量为铁或镍的有机化合物，这些物质的界面富集使材料脆化。钨合金氧化后，氧大量富集于钨／粘结相界面，使沿着该界面的断裂更容易发生。