Short resolution proofs for a sequence of tricky formulas

 A class of propositional formulas, encoding the property that every finite, transitive digraph with no two-cycles must have a source, has been investigated by Krishnamurty and conjectured as hard for resolution. In this note we prove, opposed to that conjecture, that there are proofs of polynomial lengths (or even linear in the lengths of the formulas) of those formulas. Received March 15, 1994/November 28, 1994     

Objectives of Modelling Evacuation from Buildings during Accidents: Some Path-model Scenarios

The basic objective of developing an evacuation model is to supply the user with valid and valuable information on which conclusions concerning the safe evacuation from a building can be drawn. Several evacuation models have been developed over the last 15 years. In our opinion, many of these models are too narrowly focused, perhaps not meeting the needs of the decision maker. This paper discusses the objectives of evacuation studies and the selection of a suitable modelling technique relative to these objectives. We show that many different approaches to evacuation modelling are appropriate for different types of studies. In the discussion about different existing models and solution techniques, we present some of the basic philosophy lying behind the simulation model EVACSIM. EVACSIM has been developed to meet the need for an evacuation model that can combine knowledge about human behaviour with the ability to perform large-scale simulations of network processes. EVACSIM treats people as individuals and it has the capacity to collect any information of interest (in principle) regarding their movements, their exposure to potential accident effects and their time to exit the different parts of the structure. The role of an evacuation model in an evacuation analysis is also discussed.     

Scientific and structural base of manufacturing

Science comes from Latin scientia meaning knowledge. Science is difficult to define, but we can obtain an understanding of what we mean. Knowledge, however, is wider in scope than what we generally define as science. Engineering, of which manufacturing is a part, requires creativity, fantasy, scope, and imagination as well as scientific knowledge. These elements are also needed in the scientific work itself. Scientific quality and language to tell the result must be considered separately from each other. Scientific quality means true and accurate knowledge, and the language must be adapted to the problem and to the receiver of the scientific result. Axiomatic decision-rules are being proposed as a scientific method to help in sorting out good solutions in engineering. The manufacturing system can be described and analysed as three main production systems: the manufacturing production system (MPS), the data production system (DPS), and the innovation production system (IPS).     

Exposure to Volatile Organic Compounds of Microbial Origin (MVOC) during Indoor Application of Water-based Paints

The market for water-based paints (WBP) is growing, and these paints are favoured due to their low emission of volatile organic compounds (VOC). Because of the risk for microbial growth, biocides are usually added to WBP. Our study aimed to measure exposure to VOCs potentially of microbial origin (MVOC), during indoor application of typical Scandinavian WBP. Low concentrations of three MVOCs, 3-methyl-furan, 1-octen-3-ol, and 2-octen-1-ol, were detected during 5 out of 20 painting operations (25%). Mean exposures to MVOC and TVOC were 0.15 and 5000 μg/m³, respectively. No relation between MVOC and TVOC was observed. The highest exposure to MVOC was measured from an ecological paint, claimed to be low in VOCs and chemical additives. The results suggest that microbial growth in WBP may occur, and that measurements of MVOCs could be used as a means of quality control for WBP. The use of biocides in paint should be guided by the principle of a balance between the risk of contact allergies or other possible health hazards from the biocides, and the risk of microbial growth. If microbial growth occurs in paint, it may cause both unpleasant odor and potential health hazards for house painters and dwellers.     

Virtual origins of fire plumes

A model is proposed for correlating measurements of virtual origins of fire plumes, made possible in conjunction with a relation established recently for predicting mean flame heights. The model is consistent with plume theory and is shown to correlate available determinations of virtual origins quite well. However, precise experiments are needed to fully test the model and to investigate anticipated effects of fuel identity. It is shown that the results of this work lead to a rationale for the success of previously proposed temperature correlations which appear to be valid even into the flaming regions of plumes.     

Antiplasticization and transition to marked nonlinear viscoelasticity in poly(vinyl chloride)/acrylonitrile–butadiene copolymer blends

A series of PVC/NBR blends with varying acrylonitrile (AN) content in the NBR has been studied in uniaxial tension creep tests. The tests have been carried out at 21.5 ± 0.5°C covering creep times from 10 to 1000 sec. NBR with low AN content, having poor compatibility with PVC, gives the blends with higher compliance and increased time dependence of the compliance. A higher AN content in the NBR gives the blends with the opposite properties when the NBR is added in small amounts. NBR with 40 wt-% AN is found to act as an antiplasticizer giving minimal creep compliance when 7 wt-% NBR is added. The antiplasticization reveals a considerably increased stress level at which the transition from approximatively linear to marked nonlinear viscoelasticity occurs and a decreased stress dependence of the creep compliance in the nonlinear viscoelastic range. Since the antiplasticization is also associated with a suppression of the β-transition mechanism, the results provide a demonstration of the importance of β-mechanism in the stress activated processes responsible for the appearance of nonlinear viscoelasticity in solid polymers.     

Temperature transients in flowing boreholes

We consider the problem of temperature transients in a borehole which has been drilled into an isothermal homogeneous solid and which is flowing at a constant rate. At a fixed time, the temperature of the fluid entering the borehole at the bottom is raised by a given amount. We derive the theoretical expression for the temperature response of the borehole and give a few numerical data of practical value.     

The photochemical heat pipe

The performance of a solar collector system for high temperature heat delivery based on a photochromic reaction is discussed. The system consists of a non-focusing collector and a reactor integrated into a flow system. In the collector, kept close to ambient temperature, the chemical potential of the photochromic system is increased through an endothermic photochemical reaction and is used to drive the reverse thermal reaction taking place in the reactor at a high temperature. No separation of the photoproducts is involved. Accordingly, the highest temperature at which heat can be delivered from the reactor is determined by the maximum attainable photostationary state in the collector and not, as in a conventional flat-plate collector, by heat-loss from the collector to the surroundings. Accordingly, the highest temperature at which heat can be delivered from the reactor is determined by the maximum attainable photostationary state in the collector and not, as in a conventional flat-plate collector, by heat-loss from the collector to the surroundings. The functioning of the device is exemplified by calculations for a model system utilizing the photodissociation of gaseous nitrosylchloride. The results show that it should be possible to build a system which, on a clear day, delivers about 100 W heat at temperature above 200°C for each m² collector area. A tenfold reduction in the radiation flux density of the incident light will only slightly reduce output efficiency.