Hierarchical Nets: A Structured Petri Net Approach to Concurrency

Liveness and safeness are two key properties Petri nets should have when they are used to model asynchronous systems. The analysis of liveness and safeness for general Petri nets, though shown to be decidable by Mayr [1981], is still computa- tionally expensive (Lipton [1976]1). In this paper an hierarchical approach is taken: a class of Petri nets is recursively defined starting with simple, live and safe struc- tures, becoming progressively more complex using net transformations designed to preserve liveness and safeness. Using simple net transformations, nice nets, which are live and safe, are defined. Their behavior is too restrictive for modeling non-trivial systems, so the mutual exclusion and the repetition constructs are added to get p-p-nets. Since the use of mutual exclusions can cause deadlock, and the use of repetitions can cause loss of safeness, restrictions for their use are given. Using u-p-nets as the building blocks, hierarchical nets are defined. When the mutual exclusion and repetition constructs are allowed between hierarchical nets, distributed hierarchical nets are obtained. Examples of distributed hierarchical nets used to solve synchronization problems are given. General net transformations not preserving liveness or safeness, and a notion of duality are presented, and their effect on Petri net behavior is considered

An Inverse Limit Construction of a Domain of Infinite Lists

A domain of infinite lists is constructed by taking the inverse limit of a chain of finite list domain ordered by projection. The resulting space, called L infinity, is shown to be a complete partial order. I use as a semantic domain for nonterminating programs is illustrated

Logic from Programming Language Semantics

Logic for reasoning about programs must proceed from the programming language semantics. It is our thesis that programs be considered as mathematical objects that can be reasoned about directly, rather than as linguistic expressions whose meanings are embedded in an intermediate formalism.Since the semantics of many programming language features (including recursion, type-free application, infinite structures, self-reference, and reflection) require models that are constructed as limits of partial objects, a logic for dealing with partial objects is required. Using the D infinity, model of the lambda-calculus, a logic (called continuous logic) for reasoning about partial objects is presented. In continuous logic, the logical operations (negation, implication, and quantification) are defined for each of the finite levels and then extended to the limit, giving us a model of type-free logic. The triples of Hoare Logic are interpreted as partial assertions over the domain of partial states, and contradictions arising from rules for function definitions are analyzed. Recursive procedures and recursive functions are both proved using mathematical induction. A domain of infinite lists is constructed as a model for languages with lazy evaluation and it is compared to an ordinal-heirarchic construction. A model of objects and multiple inheritance is constructed where objects are self-referential states and multiple inheritance is defined using the notion of product of classes. The reflective processor for a language with environment and continuation reflection is constructed as the projective limit of partial reflective processors of finite height

Lateral Decubitus Positioning Stereotactic Vacuum-Assisted Breast Biopsy with True Lateral Mammography

Stereotactic vacuum-assisted breast biopsy (VAB) has been used to evaluate microcalcifications or non-palpable breast lesions on mammography. Although stereotactic VAB is usually performed in a prone or upright position, an expensive prone table is necessary and vasovagal reactions often occur during the procedure. For these reasons, the lateral decubitus position can be applied for stereotactic VAB, and true lateral mammography can be used to detect the lesion. We report on 15 cases of lateral decubitus positioning for stereotactic VAB with true lateral mammography for non-palpable breast lesions or microcalcifications. The mean procedure time was approximately 30.1 minutes, and no complications occurred during the procedures. Fourteen cases had benign breast lesions and one case had a ductal carcinoma in situ. The lateral decubitus stereotactic VAB with true lateral mammography can be applied for microcalcifications or non-palpable breast lesions and helps to minimize anxiety and vasovagal reactions in patients

Imaging Features of Gray-Scale and Contrast-Enhanced Color Doppler US for the Differentiation of Transient Renal Arterial Ischemia and Arterial Infarction

No publisher copyright information found in the SHERPA/RoMEO list.OBJECTIVE: To characterize the imaging features on gray-scale and contrast-enhanced color Doppler US images which differentiate renal ischemia from renal infarction. MATERIALS AND METHODS: The segmental renal arteries of eight healthy rabbits were surgically ligated. In four of these rabbits, the ligated renal artery was released 60 minutes after arterial occlusion to cause transient ischemia. In the remaining four rabbits, the arterial ligation was retained to cause a permanent infarction. The gray-scale and contrast-enhanced color Doppler US imaging features of the involved renal parenchyma of both ischemia and infarction groups were compared with respect to the presence or absence of parenchymal swelling, echogenicity changes, tissue loss and perfusion defects. RESULTS: Parenchyma swelling, echogenic changes, tissue loss and perfusion defects were found to be more extensive in the infarction than the ischemia group. The hyperechoic areas reperfused with blood flow recovered normal echogenicity and perfusion, whereas the hyperechoic areas without reperfusion became renal infarcts. CONCLUSION: Gray-scale and contrast-enhanced color Doppler US showed that the hyperechoic areas with reperfusion may reverse to normal parenchyma and allow the differentiation of renal ischemia from renal infarction

The effects of different pilot-drilling methods on the mechanical stability of a mini-implant system at placement and removal: a preliminary study

Objective: To investigate the effects of different pilot-drilling methods on the biomechanical stability of self-tapping mini-implant systems at the time of placement in and removal from artificial bone blocks. Methods: Two types of artificial bone blocks (2-mm and 4-mm, 102-pounds per cubic foot [102-PCF] polyurethane foam layered over 100-mm, 40-PCF polyurethane foam) were custom-fabricated. Eight mini-implants were placed using the conventional motor-driven pilot-drilling method and another 8 mini-implants were placed using a novel manual pilot-drilling method (using a manual drill) within each of the 2-mm and 4-mm layered blocks. The maximum torque values at insertion and removal of the mini-implants were measured, and the total energy was calculated. The data were statistically analyzed using linear regression analysis. Results: The maximum insertion torque was similar regardless of block thickness or pilot-drilling method. Regardless of the pilot-drilling method, the maximum removal torque for the 4-mm block was statistically higher than that for the 2-mm block. For a given block, the total energy at both insertion and removal of the mini-implant for the manual pilot-drilling method were statistically higher than those for the motor-driven pilot-drilling method. Further, the total energies at removal for the 2-mm block was higher than that for the 4-mm block, but the energies at insertion were not influenced by the type of bone blocks. Conclusions: During the insertion and removal of mini-implants in artificial bone blocks, the effect of the manual pilot-drilling method on energy usage was similar to that of the conventional, motor-driven pilot-drilling method. (Korean J Orthod 2011;41(5):354-360)Supported by a grant from Kyung Hee University in 2010 (KHU-20100696).

Urban and rural Differences in the Prevalence of Gender and Age specific Obesity and related Health Behaviors in Korea

The objective of this study was to discuss the residential difference in gender and age specific prevalence of obesity by body mass index (BMI) and obesity related health behaviors in the Republic of Korea. A total of nationally representative 2,583 men and 3,087 women (age: 20-64 yr) was used as subjects from 1998 National Health and Nutrition Survey. All statistics were calculated using SUDAAN to consider a stratified multistage probability sampling design. The prevalence of obesity (BMI≥25) was significantly different by age, gender and residential areas. Although younger men aged 20-49 yr did not show a residential difference in the prevalence of obesity, men aged 50-64 yr showed differences, highest in big cities and lowest in rural areas. However, in women, a higher prevalence was observed in rural areas compared to urban areas in the younger age group (20-49 yr), but not in the older age group. Residential differences of obesity related health behaviors existed mostly in the older population, but not in the younger population. The urban-rural differences demonstrate the various stages of behavioral transition that Korea is currently undergoing. Therefore, different strategies considering those factors are needed to manage obesity problems in Korea