A graph grammar-based formal validation of object-process diagrams

Two basic requirements from a system’s conceptual model are correctness and comprehensibility. Most modeling methodologies satisfy only one of these apparently contradicting requirements, usually comprehensibility, leaving aside problems of correctness and ambiguousness that are associated with expressiveness. Some formal modeling languages do exist, but in these languages a complete model of a complex system is fairly complicated to understand. Object-process methodology (OPM) is a holistic systems modeling methodology that combines the two major aspects of a system—structure and behavior—in one model, providing mechanisms to manage the complexity of the model using refinement-abstraction operations, which divide a complex system into many interconnected diagrams. Although the basic syntax and semantics of an OPM model are defined, they are incomplete and leave room for incorrect or ambiguous models. This work advances the formal definition of OPM by providing a graph grammar for creating and checking OPM diagrams. The grammar provides a validation methodology of the semantic and syntactic correctness of a single object-process diagram.     

From Raster to Vectors: Extracting Visual Information from Line Drawings

Vectorisation of raster line images is a relatively mature subject in the document analysis and recognition field, but it is far from being perfect as yet. We survey the methods and algorithms developed to-date for the vectorisation of document images, and classify them into six categories: Hough transform-based, thinning-based, contour-based, run-graph-based, mesh-pattern-based, and sparse-pixel-based. The purpose of the survey is to provide researchers with a comprehensive overview of this technique, to enable a judicious decision while selecting a vectorisation algorithm for a system under development or a newly developed vectorisation algorithm. Received: 10 November 1998?Received in revised form: 7 January 1999?Accepted: 7 January 1999     

Determining production sequences for single-stage multifunctional machining systems based on the tradeoff between fixture cost, re-fixturing and tool replenishment

The main advantage of a Single-Stage Multifunctional machining System (SSMS) is its ability to combine many operations and processes, previously done on different machines in several stages, into a single stage. The flexibility and process variety these machining systems offer have ensured their widespread adoption in industry. As a result SSMSs frequently constitute the bottleneck of a manufacturing system and therefore control system throughput. Hence, it is imperative to use these resources efficiently. This study considers three possible costs and the tradeoffs between them that are pertinent to any job sequence: (i) the Tool Magazine Replenishment (TMR) cost; (ii) the Re-Fixturing (RF) cost; and (iii) the fixture cost. A job sequencing algorithm that minimizes these costs as well as the machine non-operational time, which stems from TMRs and RFs, is developed. The algorithm takes into account the tools and fixture requirements as well as the tool magazine capacity. The algorithm also recommends purchasing additional fixtures when economically justified. The algorithm is used to solve a job sequencing problem that occurs in a real industrial setting.     

Microwave pulses compressed in a quasi-optical resonator with corrugated mirror

A microwave pulse compressor, representing a three-mirror resonator supplied with a radiation beam reflected from a corrugated mirror, was constructed and experimentally tested. A fivefold compression of microwave pulses with a 70% efficiency was obtained in a 9-mm wavelength range.     

Reduction of the incidence of postharvest quality losses,and future prospects

Both quantitative and qualitative food losses of extremely variable magnitude occur during all harvest and postharvest stages, from harvesting, through handling, storage, processing and marketing, to final delivery to the consumer. The latest values published indicated that industrialized and developing countries dispose of roughly similar quantities of food. Whereas in developed countries the losses occur at the retailer and consumer stages, in the developing countries the losses occur during the production, harvest, postharvest and processing phases, because of poor infrastructure, low levels of technology, and low investment in food production systems. Quality cannot be improved after harvest, only maintained; therefore it is important to harvest fruits, vegetables and flowers at the proper stage and size and at peak quality. Preharvest production practices and factors such as cultivation practices, water supply, type of soil, environmental temperature and mechanical damage may seriously affect postharvest quality and result in the rejection or downgrading of produce at the point of sale. In addition, after harvest, improper temperature and humidity management as well as packaging and handling may have adverse effects on storage life and quality. Thus, integration of treatment methods calls for specific differential combinations of treatments for each product in each country.