非常见问题解答——来自ADI公司的电话记录中奇怪但真实的故事

小心多个时钟沿! 问题：在使用多个时钟时，如何改善系统性能？ 回答：在使用同一时钟源产生多个时钟时，一个常见的问题是噪声，通常表现为存在于噪底之上的杂散，这是因为单一时钟源被倍频或分频为多个时钟。偏移各时钟的相邻沿可以降低哚声杂散，或者完全消除杂散，这具体取决于系统的时序裕量。     

The forecasting model based on modified SVRM and PSO penalizing Gaussian noise

The ε-insensitive loss function has no penalizing capability for white (Gaussian) noise from training series in support vector regression machine (SVRM). To overcome the disadvantage, the relation between Gaussian noise model and loss function of SVRM is studied. And then, a new loss function is proposed to penalize the Gaussian noise in this paper. Based on the proposed loss function, a new ν-SVRM, which is called g-SVRM, is put forward to deal with training set. To seek the optimal parameters of g-SVRM, an improved particle swarm optimization is also proposed. The results of application in car sale forecasts show that the forecasting approach based on the g-SVRM model is effective and feasible, the comparison between the method proposed in this paper and other ones is also given, which proves this method is better than ν-SVRM and other traditional methods.     

Urban Computing and Mobile Devices

In this issue's Works in Progress department, we have 12 urban computing and mobile device entries that span a wide range of computing and social areas. The first entry examines how an urban environment could operate as a large-scale, real-time control system. One project focuses on annotating public spaces and sharing the tags with others. Two projects tie together social networking in cyberspace with local urban communities. Two projects examine computing and social interactions in physical spaces. Two entries explore how to combine synthetic and physical views of urban environments. Four entries investigate how we explore urban spaces, interact with technology in those spaces, and create shared community histories.     

The development of MDDS-COMPASS. Compatibility of plasters with salt loaded substrates

The use of expert systems in building practice and more specifically a system meant to mitigate the effects of decay and damage to buildings belonging to the cultural heritage is a quite recent development.MDDS, the Masonry Damage Diagnostic System, is an expert system developed for the diagnosis of damage to ancient masonry structures. The principles of this system, dating back to 1995, were used as a basis for a new system focusing attention on damage to plasters due to salts. This development took place in the framework of the EU COMPASS project. The project focused on salt damage to plasters in historic buildings. The main aim of the project was to provide end-users with guidelines for decision support, including diagnostic support and support in planning of interventions. The new System is called Monument Damage Diagnostic System.     

Reverse combustion: Kinetically controlled and mass transfer controlled conversion front structures

Under most conditions for reverse fixed bed combustion, transport effects of heat and gaseous species to and within fuel bed particles are important phenomena that limit the conversion rate. At present there is only one model that (1) claims to take transport limitations into account and (2) for which analytical solutions are given. Here, we present a numerical study of reverse combustion analysis on the basis of this model to show the effect of transport limitations on the reaction front structure and the consequences of these effects for the applicability and accuracy of the analytical solution procedure. A parameter set for coal combustion was used to perform the study. Results of numerical simulations indicate that the model solutions contain two limiting cases: kinetically controlled and mass-transfer-controlled conversion front structures. The kinetically controlled solutions consist of a preheat zone at the upstream side of the front and a thin reaction zone at the downstream side. The mass-transfer-controlled solutions consist of a wide reaction zone with a maximum source term situated at the upstream part of the front. The analytical solution to the model equations is shown to give correct predictions in the kinetically controlled case only. In the presence of mass transfer, the solution predicts the trend of decreasing front velocity with increasing transport limitations correctly but does not show the correct functional dependence on the parameter describing transport limitations. In addition, the predictions become highly inaccurate. This is related to the fact that the effect of transport limitations is not accounted for in the analytical solution method. Therefore, numerical methods should be used to obtain generally valid solutions.