An optoelectronic recirculating sorter based on CMOS/vertical cavity surface emitting laser smart pixel arrays; architecture and system demonstration

The architecture of an optoelectronic recirculating sorter based on the hybrid integration of CMOS logic circuitry, silicon detector/receivers and vertical cavity surface emitting lasers is presented along with the demonstration of the system.     

Parallel acquisition of spread-spectrum signals with antennadiversity

The use of antenna diversity is investigated for improving the parallel acquisition performance of a direct-sequence spread-spectrum signal in both flat and frequency-selective fading channels. Noncoherent combining techniques are analyzed because coherent diversity techniques, such as maximal ratio combining, cannot be employed prior to initial acquisition. A major application of this work is to cellular communications     

仿真速度和容量的提升

速度、精度和易用性都是设计者使用仿真时的关键需求,他们要用仿真将自己的模拟、RF和混合信号设备推向市场。广受尊重的Spice仿真器仍是模拟仿真工具的选择,而EDA供应商正在通过创新技术改进自己工具的速度与精度,如使它们适合于多核处理器或多CPU系统的运行。其它公司则正在重新编写Spice算法,心加快仿真速度。当然也有一些公司关注自顶向下的设计。     

工作在扩展温度范围的计时器件

宽温范围的时钟计时需求正在不断增加,其应用涉及电表、工业、通信等带有部分嵌入式付费系统的设备、全球卫星导航接收机及其他行业应用。准确计时取决于几个重要参数,当然其他参数也会影响时间计时精度,但以下3个参数是最终用户需要特别关注的指标。     

Chutes and Ladders in Markov Chains

We investigate how the stationary distribution of a Markov chain changes when transitions from a single state are modified. In particular, adding a single directed edge to nearest neighbor random walk on a finite discrete torus in dimensions one, two, or three changes the stationary distribution linearly, logarithmically, or only locally. Related results are derived for birth and death chains approximating Bessel diffusions and for random walk on the Sierpinski gasket.     

Two phase transitions for the contact process on small worlds

In our version of Watts and Strogatz’s small world model, space is a d$d$-dimensional torus in which each individual has in addition exactly one long-range neighbor chosen at random from the grid. This modification is natural if one thinks of a town where an individual’s interactions at school, at work, or in social situations introduce long-range connections. However, this change dramatically alters the behavior of the contact process, producing two phase transitions. We establish this by relating the small world to an infinite “big world” graph where the contact process behavior is similar to the contact process on a tree. We then consider the contact process on a slightly modified small world model in order to show that its behavior is decidedly different from that of the contact process on a tree.     

Once edge-reinforced random walk on a tree

 We consider a nearest neighbor walk on a regular tree, with transition probabilities proportional to weights or conductances of the edges. Initially all edges have weight 1, and the weight of an edge is increased to $c > 1$ when the edge is traversed for the first time. After such a change the weight of an edge stays at $c$ forever. We show that such a walk is transient for all values of $c \ge 1$, and that the walk moves off to infinity at a linear rate. We also prove an invariance principle for the height of the walk. Received: 6 March 2001 / Revised version: 16 July 2001 / Published online: 15 March 2002     

Evolution in predator–prey systems

We study the adaptive dynamics of predator–prey systems modeled by a dynamical system in which the traits of predators and prey are allowed to evolve by small mutations. When only the prey are allowed to evolve, and the size of the mutational change tends to 0, the system does not exhibit long term prey coexistence and the trait of the resident prey type converges to the solution of an ODE. When only the predators are allowed to evolve, coexistence of predators occurs. In this case, depending on the parameters being varied, we see that (i) the number of coexisting predators remains tight and the differences in traits from a reference species converge in distribution to a limit, or (ii) the number of coexisting predators tends to infinity, and we calculate the asymptotic rate at which the traits of the least and most “fit” predators in the population increase. This last result is obtained by comparison with a branching random walk killed to the left of a linear boundary and a finite branching–selection particle system.     

Super-Tree Random Measures

We use supercritical branching processes with random walk steps of geometrically decreasing size to construct random measures. Special cases of our construction give close relatives of the super-(spherically symmetric stable) processes. However, other cases can produce measures with very smooth densities in any dimension.