The primary quantities of interest in EMC problems are conducted emissions [voltage in volts (V), and current in amperes (A)] and radiated emissions [electric field in volts per meter (V/m) and magnetic field in amperes per meter (A/m)]. Associated with these primary quantities are the quantities of power in watts (W) or power density in watts per square meter (W/m²). The numerical range of these quantities can be quite large. 继续阅读“Introduction to Electromagnetic Compatibility (EMC) II”
Introduction to Electromagnetic Compatibility (EMC) I
This series is concerned with the ability of these types of electromagnetic emissions to cause interference in electronic devices. This series is also concerned with the design of electronic systems such that interference from or to that system will be minimized. An electronic system that is able to function compatibly with other electronic systems and not produce or be susceptible to interference is said to be electromagnetically compatible with its environment. 继续阅读“Introduction to Electromagnetic Compatibility (EMC) I”
Sorting～Elementary Sorting Methods III
The development of a string data type implementation similar to Program 5 and 6 is of particular interest, because character strings are widely used as sort keys. 继续阅读“Sorting～Elementary Sorting Methods III”
Sorting～Elementary Sorting Methods II
Selection sort, insertion sort, and bubble sort are all quadratic-time algorithms both in the worst and in the average case, and none requires extra memory. Their running times thus differ by only a constant factor, but they operate quite differently, as illustrated in Figures 1 through 3. 继续阅读“Sorting～Elementary Sorting Methods II”
Sorting～Elementary Sorting Methods I
For our first excursion into the area of sorting algorithms, we shall study several elementary methods that are appropriate for small files, or for files that have a special structure. 继续阅读“Sorting～Elementary Sorting Methods I”
Recursion and Trees～Graph Traversal
For our final example of a recursive program in this series, we consider one of the most important of all recursive programs: recursive graph traversal, or depth-first search. This method for systematically visiting all the nodes in a graph is a direct generalization of the tree-traversal methods that we considered in Recursion and Trees～ Mathematical Properties of Trees and Tree Traversal, and it serves as the basis for many basic algorithms for processing graph. 继续阅读“Recursion and Trees～Graph Traversal”
Database Design ~ Database Design and the E-R Model V
A diagrammatic representation of the data model of an application is a very important part of designing a database schema. Creation of a database schema requires not only data modeling experts, but also domain experts who know the requirements of the application but may not be familiar with data modeling. An intuitive diagrammatic representation is particularly important since it eases communication of information between these groups of experts. 继续阅读“Database Design ~ Database Design and the E-R Model V”
Database Design ~ Database Design and the E-R Model IV
Although the basic E-R concepts can model most database features, some aspects of a database may be more aptly expressed by certain extensions to the basic E-R model. In this section, we discuss the extended E-R features of specialization, generalization, higher-and lower-level entity sets, attribute inheritance, and aggregation.
To help with the discussions, we shall use a slightly more elaborate database schema for the university. In particular, we shall model the various people within a university by defining an entity set person, with attributes ID, name, and address. 继续阅读“Database Design ~ Database Design and the E-R Model IV”
Database Design ~ Database Design and the E-R Model III
We can represent a database that conforms to an E-R database schema by a collection of relation schemas. For each entity set and for each relationship set in the database design, there is a unique relation schema to which we assign the name of the corresponding entity set or relationship set. 继续阅读“Database Design ~ Database Design and the E-R Model III”