Detector-induced dephasing in quantum-dot cellular automata qubit

We investigate the quantum dynamics of the quantum-dot cellular automata qubit in the presence of a quantum point contact detector by modified rate equations. It is demonstrated that the qubit information can be resolved by measuring the detector current variation. Furthermore, we show that this oscillating current and the electron occupation probabilities in states \b> and \c> decay drastically as the dephasing rate increases, clearly revealing the influence of the dephasing induced by the detector. Moreover, it is shown that the operation speed of the quantum-dot cellular automata qubit may be adjusted by varying the interdot coupling strength. (C) 2003 American Institute of Physics.

On equations for regular languages, finite automata, and sequential networks

We consider systems of equations of the form where A is the underlying alphabet, the Xi are variables, the Pi,a are boolean functions in the variables Xi, and each δi is either the empty word or the empty set. The symbols υ and denote concatenation and union of languages over A. We show that any such system has a unique solution which, moreover, is regular. These equations correspond to a type of automation, called boolean automation, which is a generalization of a nondeterministic automation. The equations are then used to determine the language accepted by a sequential network; they are obtainable directly from the network.

An automata theoretic decision procedure for the propositional mu-calculus

The propositional mu-calculus is a propositional logic of programs which incorporates a least fixpoint operator and subsumes the propositional dynamic logic of Fischer and Ladner, the infinite looping construct of Streett, and the game logic of Parikh. We give an elementary time decision procedure, using a reduction to the emptiness problem for automata on infinite trees. A small model theorem is obtained as a corollary.

Modeling of Hillslope Runoff and Soil Erosion at Rainfall Events Using Cellular Automata Approach

National Science Fund for Distinguished Young Scholars of China [40225004]; National Natural Science Foundation of China [40471048]

Cellular automata: Simulating alpine tundra vegetation dynamics in response to global warming

This study attempts to model alpine tundra vegetation dynamics in a tundra region in the Qinghai Province of China in response to global warming. We used Raster-based cellular automata and a Geographic Information System to study the spatial and temporal vegetation dynamics. The cellular automata model is implemented with IDRISI's Multi-Criteria Evaluation functionality to simulate the spatial patterns of vegetation change assuming certain scenarios of global mean temperature increase over time. The Vegetation Dynamic Simulation Model calculates a probability surface for each vegetation type, and then combines all vegetation types into a composite map, determined by the maximum likelihood that each vegetation type should distribute to each raster unit. With scenarios of global temperature increase of I to 3 degrees C, the vegetation types such as Dry Kobresia Meadow and Dry Potentilla Shrub that are adapted to warm and dry conditions tend to become more dominant in the study area.

Long-range automaton models of earthquakes: Power-law accelerations, correlation evolution, and mode-switching

We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r(-p) dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.

基于Yices对时间自动机的有界模型检测

随着工业化程度的提高，对模型的检测方法受到越来越大的重视。通常的检测方法有推理验证和模型检测。而相对于推理验证，模型检测由于其高度自动化的检测过程，在工业界有着更广泛的应用。 模型检测自从概念雏形开始之时，就受到状态爆炸问题的困扰。为了解决这个问题，不同的技术被提了出来。McMillan提出利用OBDD的符号模型检测方法在一定程度上解决了这个问题。另外，本文所主要讲述的有界模型检测，经大量的实践证明，对符号模型检测也是一个很好的补充。 由于问题的特殊性，科学家提出来不同的模型来描述不同情况的系统。由于时间自动机能够很好地描述异步系统，而且这种系统广泛地存在于现实生活中，对时间自动机这种特殊模型的验证方法的研究变得很有必要。另外，由于时间自动机带有实数域的时钟变量，这导致了时间自动机有一个无限域的状态迁移图。为了利用模型检测的方法对其进行验证，需要对时间变量进行预处理。一般的方法是把时钟所对应的时钟区或时钟域根据等价性，化为有限的域，相应地，把时间自动机转化为有限的状态迁移图。 为了避免在对时间自动机有界模型检测过程中对变量进行布尔编码以及对时间自动机模型中的时钟进行预处理，本文给出一个利用SMT工具进行的对时间自动机进行有界模型检测的方法。该方法的主要优点是无需将时间自动机中的时钟进行预处理，也不需要将模型中的变量进行布尔编码，只需将时间自动机转变为SMT工具可解的逻辑公式，利用SMT的高效求解来进行模型检测。实验结果表明，对于某些可达性性质的验证，这种方法的效率有一定的优势。