Excess noise measurement in In0.53Ga0.47As

The excess noise due to impact ionization has been measured explicitly for the first time in In/sub 0.53/Ga/sub 0.47/As. By using a phase sensitive detection technique, the noise due to avalanche current was determined even in the presence of high tunneling currents. The excess noise due to pure electron injection measured on a series of thick In/sub 0.53/Ga/sub 0.47/As p/sup +/-i-n/sup +/ diodes suggests large electron to hole ionization coefficient ratio between 3.7 at electric field of 310 kV/spl middot/cm/sup -1/ to 5.3 at 260 kV/spl middot/cm/sup -1/. Excess noise was also measured at fields as low as 155 kV/spl middot/cm/sup -1/ suggesting that significant impact ionization occurs at these low fields. The multiplication and excess noise calculated using published ionization coefficients and ignoring dead space effects, gave good agreement with the experimental data for mixed and pure electron injection

A Hybrid Approach to Case Teaching

We structure case based teaching using a combination of computer-support echnology and in-class activities. We create and design an on-line learning tool, Case Study On-line (CSOL) that enables instructor to structure the delivery of teaching resources and set up assignment tasks in the system. The tool enables tasks to be set in a way that they can be completed sequentially, and learning resources can be accessed only when required by students. Upon submission of their assignments, students can promptly receive instructor’s explanations to the tasks. Follow up activities take place in class, with the objective to promote active learning. The tool was adopted over two semesters in an undergraduate economics course and surveys were conducted among the students to evaluate the effectiveness of the tool. The results of the survey were very positive, providing support to our belief that a system of well-designed case teaching delivery tool, together with classroom activities, is able to increase the level of students’ engagement and interest. The paper helps to address some concerns about teaching methods in undergraduate economics courses.Technologies-based Instruction, In-class Activities, Scaffolding, Active-based Learning

The complement of the Bowditch space in the SL(2,C) character variety

Let ${\mathcal X}$ be the space of type-preserving \SL(2,C) characters of the punctured torus $T$. The Bowditch space ${\mathcal X}_{BQ}$ is the largest open subset of ${\mathcal X}$ on which the mapping class group acts properly discontinuously, this is characterized by two simple conditions called the $BQ$-conditions. In this note, we show that $[\rho]$ is in the interior of the complement of ${\mathcal X}_{BQ}$ if there exists an essential simple closed curve $X$ on $T$ such that $|{\rm tr} \rho(X)|<0.5$.Comment: 6 page

Effect of impact ionization in the InGaAs absorber on excess noise of avalanche photodiodes

The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer

Time for Cloud? Design and implementation of a time-based cloud resource management system

The current pay-per-use model adopted by public cloud service providers has influenced the perception on how a cloud should provide its resources to end-users, i.e. on-demand and access to an unlimited amount of resources. However, not all clouds are equal. While such provisioning models work for well-endowed public clouds, they may not always work well in private clouds with limited budget and resources such as research and education clouds. Private clouds also stand to be impacted greatly by issues such as user resource hogging and the misuse of resources for nefarious activities. These problems are usually caused by challenges such as (1) limited physical servers/ budget, (2) growing number of users and (3) the inability to gracefully and automatically relinquish resources from inactive users. Currently, cloud resource management frameworks used for private cloud setups, such as OpenStack and CloudStack, only uses the pay-per-use model as the basis when provisioning resources to users. In this paper, we propose OpenStack Café, a novel methodology adopting the concepts of 'time' and booking systems' to manage resources of private clouds. By allowing users to book resources over specific time-slots, our proposed solution can efficiently and automatically help administrators manage users' access to resource, addressing the issue of resource hogging and gracefully relinquish resources back to the pool in resource-constrained private cloud setups. Work is currently in progress to adopt Café into OpenStack as a feature, and results of our prototype show promises. We also present some insights to lessons learnt during the design and implementation of our proposed methodology in this paper

A Hybrid Approach to Case Teaching

We structure case based teaching using a combination of computer-support technology and in-class activities. We create and design an on-line learning tool, Case Study On-line (CSOL) that enables instructor to structure the delivery of teaching resources and set up assignment tasks in the system. The tool enables tasks to be set in a way that they can be completed sequentially, and learning resources can be accessed only when required by students. Upon submission of their assignments, students can promptly receive instructors explanations to the tasks. Follow up activities take place in class, with the objective to promote active learning. The tool was adopted over two semesters in an undergraduate economics course and surveys were conducted among the students to evaluate the effectiveness of the tool. The results of the survey were very positive, providing support to our belief that a system of well-designed case teaching delivery tool, together with classroom activities, is able to increase the level of students engagement and interest. The paper helps to address some concerns about teaching methods in undergraduate economics courses.Technologies-based Instruction, In-class Activities, Scaffolding, Active-based Learning

A theoretical comparison of the breakdown behavior of In0.52Al0.48As and InP near-infrared single-photon avalanche photodiodes

We study the breakdown characteristics and timing statistics of InP and In0.52Al0.48As single-photon avalanche photodiodes (SPADs) with avalanche widths ranging from 0.2 to 1.0 mu m at room temperature using a random ionization path-length model. Our results show that, for a given avalanche width, the breakdown probability of In0.52Al0.48As SPADs increases faster with overbias than InP SPADs. When we compared their timing statistics, we observed that, for a given breakdown probability, InP requires a shorter time to reach breakdown and exhibits a smaller timing jitter than In0.52Al0.48As. However, due to the lower dark count probability and faster rise in breakdown probability with overbias, In0.52Al0.48As SPADs with avalanche widths <= 0.5 mu m are more suitable for single-photon detection at telecommunication wavelengths than InP SPADs. Moreover, we predict that, in InP SPADs with avalanche widths <= 0.3 mu m and In0.52Al0.48As SPADs with avalanche widths <= 0.2 mu m, the dark count probability is higher than the photon count probability for all applied biases

Performance-based control system design automation via evolutionary computing

This paper develops an evolutionary algorithm (EA) based methodology for computer-aided control system design (CACSD) automation in both the time and frequency domains under performance satisfactions. The approach is automated by efficient evolution from plant step response data, bypassing the system identification or linearization stage as required by conventional designs. Intelligently guided by the evolutionary optimization, control engineers are able to obtain a near-optimal ‘‘off-thecomputer’’ controller by feeding the developed CACSD system with plant I/O data and customer specifications without the need of a differentiable performance index. A speedup of near-linear pipelineability is also observed for the EA parallelism implemented on a network of transputers of Parsytec SuperCluster. Validation results against linear and nonlinear physical plants are convincing, with good closed-loop performance and robustness in the presence of practical constraints and perturbations

Field dependence of impact ionization coefficients in In0.53Ga0.47As

Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes