The merits and limitations of local impact ionization theory

Multiplication measurements on GaAs p+-i-n+s with i-region thicknesses, w, between 1 μm and 0.025 μm and Monte Carlo (MC) calculations of the avalanche process are used to investigate the applicability of the local ionization theory. The local expressions for multiplication are able to predict the measured values surprisingly well in p+-i-n+s with i-region thicknesses, w, as thin as 0.2 μm before the effect of dead-space, where carriers have insufficient energy to ionize, causes significant errors. Moreover, only a very simple correction to the local expressions is needed to predict the multiplication accurately where the field varies rapidly in abrupt one-sided p+-n junctions doped up to 1018 cm-3. However, MC modeling also shows that complex dead-space effects cause the local ionization coefficients to be increasingly unrepresentative of the position dependent values in the device as w is reduced below 1 μm. The success of the local model in predicting multiplication is therefore attributed to the dead-space information already being contained within the experimentally determined values of local coefficients. It is suggested that these should therefore be thought of as effective coefficients which, despite the presence of dead-space effects, can be still be used with the existing local theory for efficiently quantifying multiplication and breakdown voltages

Fishy Gifts: Bribing with Shame and Guilt

The following is a model of psychological contracting with unmonitorable performance, implicit offers, and screening for non-performance by the announcement of the expectation of performance. It is motivated by the $250 billion prescription drug industry, which spends$19 billion per year on marketing to US doctors, mostly on `gifts', and often, as at Yale, with no monitoring for reciprocation. In one revealing incident, a drug firm representative closed her presentation to Yale medical residents by handing out $150 medical reference books and remarking, "one hand washes the other." By the next day, half the books were returned. I model this with a one shot psychological trust game with negative belief preferences and asymmetric information. I show that the `shame' of accepting a possible bribe can screen for reciprocation inducing `guilt'. An announcement can extend the effect. Current policies to deter reciprocation might aid such screening. I also discuss applications like vote buying when voting is unobservable and why taxis drivers in Naples announce inflated fares after their service is sunk

Optimization of InP APDs for high-speed lightwave systems

Calculations based on a rigorous analytical model are carried out to optimize the width of the indium phosphide avalanche region in high-speed direct-detection avalanche photodiode-based optical receivers. The model includes the effects of intersymbol interference (ISI), tunneling current, avalanche noise, and its correlation with the stochastic avalanche duration, as well as dead space. A minimum receiver sensitivity of -28 dBm is predicted at an optimal width of 0.18 mu m and an optimal gain of approximately 13, for a 10 Gb/s communication system, assuming a Johnson noise level of 629 noise electrons per bit. The interplay among the factors controlling the optimum sensitivity is confirmed. Results show that for a given transmission speed, as the device width decreases below an optimum value, increased tunneling current outweighs avalanche noise reduction due to dead space, resulting in an increase in receiver sensitivity. As the device width increases above its optimum value, the receiver sensitivity increases as device bandwidth decreases, causing ISI to dominate avalanche noise and tunneling current shot noise

Sensitivity of High-Speed Lightwave System Receivers Using InAlAs Avalanche Photodiodes

Calculations based on a rigorous analytical model are carried out to compare the sensitivity of optical receivers that use InP and In0.52Al0.48As avalanche photodiodes (APDs). The model includes the effects of intersymbol interference, tunneling current, avalanche noise and its correlation with the stochastic avalanche duration, dead space, and transimpedance amplifier noise. For a 10-Gb/s system with a bit-error rate of 10-12, the optimum receiver sensitivity predicted for In0.52Al0.48As and InP APDs is -28.6 and -28.1 dBm, respectively, corresponding to a reduction of 11% in optical signal power for receivers using In0.52Al0.48As APDs. Thus, considering overall receiver sensitivity, the improvement offered by In0.52Al0.48As APDs over InP is modest

Applying Cognitive Linguistics to teaching English prepositions in the EFL classroom

This paper reports on a quasi-experimental study investigating the effect of cognitive linguistics-grounded instruction on learning the prepositions in, on, and at, which are known to pose tremendous difficulty to English language learners due to their language-specific features and polysemous nature. The participants (N = 44) were adolescent learners at a school in Indonesia. They were assigned into the cognitive group and the rule group. The cognitive group was presented with pictorial representations of the prepositions and cognitive tools used to motivate non-spatial uses, while the rule group was provided with rules. Participants’ performance on the three uses (i.e. spatial, temporal and abstract) was measured with pre-, post-, and delayed post-tests in a form of gap filling. The study yielded mixed results. The findings demonstrate that the cognitive group outperformed the rule group in the overall immediate and delayed post-tests. The cognitive group improved significantly in the immediate post-test; however, the positive effect did not last until the delayed post-test. On the other hand, the rule group gained a little in the immediate post-test, but the group’s performance decreased significantly in the delayed post-test. Although there was no indication of long-term effects of the cognitive instruction, the results still indicate a value of applying cognitive linguistics to teaching the prepositions, and thus lend support to the applicability of cognitive linguistic theory in second language instruction