bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability of Discrete Linear Feedback Systems with Pulse-Width-Modulation Power Dispatch
Authors: Barry Noel 
Published: July 2017

Stability of discrete linear feedback systems with pulse-width-modulation power dispatch An adaptation of the circle criterion to pulse-width-modulation type nonlinearities in a digital control loop is presented. Formulae are derived for both gain and the mode of oscillations of the system response. Standard examples are taken, including that of a plant with a pole at the origin.
A New Automatic Design Method of Compensators in the Frequency Domain
Authors: Sandoval Juan Ma , Ibarrola Julio J. , Martinez Gamaliel 
Published: July 2017

A new automatic design method of compensators in the frequency domain The present work develops a new compensatory technique on the Black's plane with simple phase-advance and phase-lag networks, which is more systematic and yields a family of possible compensators fulfilling the specifications required. Among these compensators the best solution can be chosen according to some additional criteria, not specified initially.
Appliance Rigid Foams Blown with Cyclopentane and Cyclopentane/Isopentane Blends
Authors: Schilling S. L. 
Published: July 2017

Since CFC 11 was eliminated from use in rigid foams in the mid 1990s, the blowing agent of choice in North America has primarily been HCFC 141b. In the USA, we are now faced with the phase-out of HCFC 141b by the year 2003. The blowing agent that will replace HCFC 141b must be non-ozone depleting and should also have low thermal conductivity and a low global warming potential. Hydrocarbons are some of the few blowing agents that meet these criteria and are approved by the United States Environmental Protection Agency to replace HCFC 141b in rigid polyurethane foams for appliance insulation [1]. Of the hydrocarbons being considered, cyclopentane is preferred, either by itself or in blends with other hydrocarbons. This is because of cyclopentane's favorable combination of low thermal conductivity, good solubility in polyols and reasonable boiling point, compared to other hydrocarbons. Not only is the thermal conductivity of cyclopentane lower than that of most other hydrocarbons, it is also lower than that of HFC 134a, another blowing agent which is approved for use after 2002. This paper will examine the effect of two important factors, both theoretically and experimentally, on cyclopentane blown foams. These factors are (1) the amount of blowing obtained from carbon dioxide that is formed from the reaction between water and isocyanate, and (2) the ratio of cyclopentane to isopentane, which is used as the hydrocarbon blowing agent.
HFC-365mfc and HFC-245fa Progress in Application of New HFC Blowing Agents
Authors: Zipfel L. , Krucke W. , Borner K. , Barthtlemy P. , Dournel P. 
Published: July 2017

For a few years now we have regularly reported our progress in the evaluation of possible 3rd generation blowing agents, and we have come to the conclusion that HFC-245fa and HFC-365mfc are the two leading candidates. Previous work included lab scale evaluation of foam samples, measurements of the main relevant physico-chemical characteristics, as well as a thorough evaluation of the chemical stability of HFC-365mfc and HFC-245fa in rigid polyurethane foams [1]. With larger quantities now available from our micropilot plant in Hannover, Germany, we have been able to enlarge our knowledge of HFC-365mfc to allow a sound comparison with the data already available for HFC-245fa. In particular, physico-chemical characteristics have been refined and new ones have been measured; the evaluation of the chronic toxicity of HFC-365mfc is ongoing with first data reported here. Most importantly, additional lab scale tests and large scale trials on industrial lines have been performed to allow an in-depth study of performances in rigid polyurethane foams. This paper completes our previous reports to offer the unique comprehensive comparison of HFC-365mfc and HFC-245fa.
Utilization of HFC-245fa in the Construction Industry
Authors: Bogdan M. C. , Parker R. C. , Williams D. J. 
Published: July 2017

The effective use of insulation in both commercial and residential buildings is the key to energy conservation. The effectiveness of an insulation is dependent upon many factors. If the insulation is a foam plastic, the blowing agent used in the insulation is critical to its performance. There has been a transition in blowing agents over the last decade from CFC's to HCFC's and the industry will soon see another transition from HCFC's to a third generation blowing agent. The exact timing of these transitions is dependent upon the Montreal Protocol national and local regulations. Each transition in blowing agents requires modifications to the manufacturing process for the foam products. AlliedSignal is dedicated to providing an HFC blowing agent to the construction industry and has identified HFC-245fa (1,1,1,3,3-pentafluoropropane) as our third generation blowing agent. Since 1994, we have published a series of papers on the development of this blowing agent. This paper discusses some of the key considerations required in making the transition from HCFC-141b to HFC-245fa in areas of polyisocyanurate boardstock and spray foam. It also discusses progress made in the application of HFC-245fa in bunstock and pour in place panel applications. It will discuss the progress in areas such as raw materials and formulation optimization, possible equipment and processing parameters changes required to optimize performance, and a general discussion of foam properties, including flammability, in comparison to HCFC-141b blown foams. It will focus on providing the information which board and system manufacturers and spray foam applicators will need to make a successful transition. This includes information on gasket compatibility, gloves, system vapor pressures, system packaging and shipping requirements and product performance.
Fundamental Study of Fluorinated Ethers as New Generation Blowing Agents
Authors: Takada N. , Tamai R. , Yamamoto H. , Sekiya A. , Tsukida N. , Takeyasu H. 
Published: July 2017

The development of blowing agents that exhibit lower thermal conductivity, shorter atmospheric lifetime, and less adverse effects on the atmosphere is an urgent issue. We investigated three fluorinated ethers as blowing agent alternatives [2,2,2-trifluoroethyl difluoromethyl ether (HFE-254mf), 2,2,3,3,3-pentafluoropropyl difluoromethyl ether (HFE-347mcf), and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE-347pc-f)] in terms of physical properties (boiling point and gaseous thermal conductivity), environmental adaptability (atmospheric lifetime), toxicity, flammability, solubility in polyols, and thermal stability. By using these fluorinated ethers as blowing agents, we experimentally produced rigid polyurethane foams, all of which showed thermal conductivities lower than or equal to foams produced with the blowing agent alternative candidates, HFC-245fa and cyclopentane.
Evaluation of the Next Generation HFC Blowing Agents in Rigid Polyurethane Foams
Authors: Wu J. , Albouy A. , Mouton D. 
Published: July 2017

The development of a third generation HFC blowing agent has achieved significant progress in the past few years. Several candidates have been identified as promising substitutes for HCFC-141b in foam applications. Elf Atochem has striven to provide alternatives after HCFC-141b phases out in foam applications. This paper summarizes our recent research activities in HFCs in rigid polyurethane foam applications. It includes determinations of the weight loss of blowing agents during the foaming process. To predict long term aging behavior of polyurethane foams, we measured effective diffusion coefficients of HFC-245fa, HFC-365mfc and HCFC-141b. Also, stability of the foam systems (PUR and PIR) using HFC-365mfc as the blowing agent will be reported. The stability is indicated by the amount of decomposition during a certain period of time. Furthermore, we have studied effects of HFC-245fa foam density on the foam insulation (k-factor), dimensional stability and compressive strength. In this study, we also determined aged k-factors of HFC-245fa and HCFC-141b foams with different foam densities. Finally, we investigated HFC-134a in PUR foam as well as its solubility in several polyols.
Dimensional Stability of Polyurethane Rigid Foams Blown with CO2
Authors: Cecchini C. , Zannetti R. , Stefani A. 
Published: July 2017

In recent years, water level in rigid foam formulations has been increased to such a point that the use of only the water/isocyanate reaction to provide all of the blowing has become a reality, at least for certain applications. Nevertheless, two limiting factors penalize the use of only CO2 blown foams: a too high λ aged value and a poor dimensional stability. The objective of this research work was to record the variations with time of some parameters that affect dimensional stability of only CO2 blown foams, in order to establish eventual correlation between them and foam behavior.
A Study of Nonsense Syllables Spoken by Two Language Groups in Varying Conditions of Sidetone and Reading Rate
Authors: Singh Sadanand , Black John W. 
Published: July 2017

Twenty-eight experimental subjects, 14 English-speaking and 14 Hindi-speaking, were assigned to record an equal number of paired nonsense syllables under two conditions of three variables: (1) delayed and normal sidetone, (2) noisy and quiet conditions of listening, and (3) fast and normal rates of speaking. The results show that the two language groups did not differ statistically significantly in the mean duration of the syllables nor in mean syllabic speech power. The duration of speech was universally lengthened under the condition of delayed sidetone, as compared to the normal. The duration was also longer under the condition of normal rate of reading as compared to the fast. Both delayed sidetone and noise in the earphones increased the mean syllabic speech power of the speakers. Presumably the noise reduced the talkers' awareness of the delayed sidetone. Although delayed sidetone increased the number of phonetic errors as compared to the normal sidetone for all, the two language groups differed significantly in scores that were derived from the phonetic transcriptions of recorded verbal material.
Response Strategies in the Partial Comprehension of Sentences
Authors: Graham Norman C. 
Published: July 2017

In a sentence comprehension task subjects had to select a correct picture from an array of four presented immediately after hearing a relevant sentence. Sentences were representative of twelve different grammatical structures and were eight words in length. In each array three incorrect pictures (distractors) were representations of lexical variants of the presented sentence. Each variant was derived from the original sentence by changing a content word in either an initial, middle or terminal location respectively of the sentence. Three groups of subjects were tested. They were drawn from Nursery Schools, Primary Schools and from Special Schools for the Educationally Subnormal (ESN). All subjects could be regarded as having a pre-school level of language development. Gross differences in overall error rate between groups were observed though patterns of choices among distractors were the same for all groups. No part of the sentences (in terms of lexical content) appeared to be more vulnerable to information loss than any other. Analysis of successive choices within items showed that failure to comprehend was associated with loss of information about specific lexical items. Theoretically, results are interpreted in relation to a limited capacity information processing model of speech perception.
A Design for Multivariate Analysis of Language Behaviour and Language Development
Authors: Moerk Ernst L. 
Published: July 2017

By means of a short integrative survey of studies of language development the complexity of this area is demonstrated. Consequently, the use of multivariate designs and the concentration upon the performance aspects of verbal behaviour is advocated. The pragmatic and semantic aspects are analysed as the two main dimensions affecting the verbal statement. The pragmatic dimension is subdivided into person variables and variables of the behaviour setting. Further subdivisions of the person variables are made and possibilities to subdivide the other dimensions are suggested. The theoretical argument is supported by illustrative examples of the verbal behaviour of two young children. The changing composition of the communicative acts of children, which are composed of verbal and non-verbal messages are further analysed and illustrated. It is concluded that the search for language competence has to be a search for a multitude of psychological variables including competence in non-verbal communication and in the evaluation of the information needs of the receiver.
Vacuum Cross-Linking of Chemically Modified Cotton
Authors: Soignet Donald M. , Benerito Ruth R. , Pilkington Mary W. 
Published: July 2017

Cottons containing carboxylic acid groups display good wrinkle recovery properties after the simultaneous application of heat and vacuum. This wrinkle recovery can be removed by soaking the fabric in dilute base which converts the acid to the carboxylate salt. To reintroduce the cross link, as shown by electron microscopy, it is first necessary to convert the salt to the free acid and then subject the fabric to the heat and vacuum treatment. Wrinkle recovery values can be further improved by first treating the cotton to introduce either primary or tertiary amine groups and then treating with chloroacetic acid to introduce the carboxyl groups. Wrinkle recovery imparted by heat and vacuum is stable to acid and neutral washes. The procedure can also be used to impart and remove creases in fabrics. Because of the prolonged heating, the fabric tends to discolor, but this discoloration can be removed by mild chlorine bleaching without affecting the wrinkle recovery.
Selective Accessibilities of Hydroxyl Groups in the Microstructure of Cotton Cellulose
Authors: Rowland S. P. , Roberts E. J. , Wade C. P. 
Published: July 2017

The reactions of 2-chloroethyldiethylamine with the hydroxyl groups at C-2, C-3, and C-6 of the d-glucopyranosyl unit of cotton cellulose were investigated as a means of evaluating the relative accessibilities of these hydroxyl groups in heterogeneous reactions of fibrous cellulose. The relative rate constants for reactions of the individual types of hydroxyl groups were determined from reactions of cellulose in solution and from reactions of disordered cellulose in heterogeneous systems. Quantitative determinations of the distributions of 2-(diethylamino)ethyl substituents in the mono-substituted d-glucopyranosyl units involved hydrolysis of the chemically modified cellulose to glucose and substituted glucoses followed by gas-liquid chromatographic analysis. The relative accessibilities of the hydroxyl groups at C-2 and C-3 vs those at C-6 were estimated for crystalline celluloses by employing the relative rate constants (noted above) together with the experimentally measured distributions of substituents resulting from heterogeneous reactions of crystalline celluloses and appropriate kinetic expressions. The relative accessibilities of the hydroxyl groups at C-2, C-3, and C-6 in cellulose in strong mercerizing media approach those of cellulose in solution. In media of lower concentration of sodium hydroxide (i.e., 4 N or 13.9%), selective accessibilities of the individual types of hydroxyl groups become evident, and these selective accessibilities become pronounced in sodium hydroxide solutions of still lower concentrations (e.g., N and 2 N).
Improved Resilience by Formation of Elastomers inside Cotton Fibers
Authors: Meimoun D. , Parisot A. 
Published: July 2017

The introduction of elastomeric substances between the cellulose fibrils and/or histological elements of cotton fibers could lead to wrinkle-resistant cottons. Such substances, polyenes obtained by polymerization in situ after inclusion within the structure, are unable to penetrate the intermolecular structure, but are able to link together the elements of the fiber. This might result in a fiber with greater delayed elastic recovery and reduced permanent set, permitting wrinkle recovery of cotton fabrics to be increased. The study of optimum reaction parameters resulted in a reproducible process for including the polymer. The location of the polymer has been determined through the development of a new method for revealing the structure of cellulose. The desired mechanical properties of woven treated fabrics are improved, as indicated by various measurements. The first results concerning single fibers seem to corroborate the preceding.
Phosphazene Elastomers for Fuel Service under Arctic Conditions
Authors: Touchet P. , Gatza P. E. 
Published: July 2017

Polyphosphazene fluoroelastomers, developed through Government in-house and contractual efforts, exhibit good resistance to aromatic fuels as well as capability for performance at temperatures as low as −57° C. This combination of properties is necessary in fabrication of end items or components for arctic fuel handling equipment and in many other military and civilian applications. These polymers, having a C2-C5 [(CF3CH2, O)2 PN-(HCF2C3F6CH2O)2 PN] ***n configuration, can contain varying degrees of unsaturation (cure sites) and fluorine content. The inherent heat, fuel, water and low temperature properties of phosphazene rubber are compared with those of commonly used fuel resistant elastomers. These properties are also compared in a study of several structurally modified polymers containing varying amounts of fluorine. Further discussion includes results of a compounding study of two polymer types, wherein experimental design and computerized data analysis are used to ascertain the effects of various cross-linking agents and fillers.
Bone Erosion in Experimental Cholesteatoma — The Effects of Implanted Barriers
Authors: Macri John R. , Chole Richard A. 
Published: July 2017

Mongolian gerbils and man are the only animals known to spontaneously develop bone‐eroding aural cholesteatoma. The pathophysiology of bone erosion in cholesteatoma is controversial. The majority of investigators believe that direct contact between cholesteatoma and bone is necessary for erosion to occur. We implanted glass, Silastic, and micropore barriers in the middle ear between the advancing cholesteatoma and cochlea in 50 Mongolian gerbils. The barriers prevented direct contact of cholesteatoma and cochlea but did not inhibit bone erosion. We conclude that transmitted pressure may be responsible for bone erosion in aural cholesteatoma in gerbils.
Damage Analysis of Honeycomb Core Composite Sandwich Plate Subjected Low Velocity Impact
Authors: Zheng Qixuan , Li Zhengneng , Wu Di 
Published: July 2017

A systematic study on the impact process and damage characteristics of honeycomb core composite sandwich plates were completed on the basis of the ex-study on laminated composite plates. A series of quasi-static transverse indentation tests of composite sandwich plates are carried out to study the contact law of honeycomb core sandwich composites. An analysis program of the transient dynamic finite element analysis was developed to calculate the impact characteristics of the impactor and the composite sandwich plate, and to predict the damage to the composite sandwich plate during the low velocity impacts process. For estimating the occurrence and the extension of the damage to the composite sandwich plate subjected impact, an impact damage model of the honeycomb core composite sandwich plates was set up and applied in the program. This model consisted of the damage occurring criterion and the damage extension criterion. A simplified criterion of the damage to honeycomb core was proposed in this paper. The results of numerical calculation showed that the impact energy had significant effect on the impact contact face and the damage process of sandwich plates, and the impact characteristics of composite sandwich plate were different from laminated composite plate. Finally, a series of standard low velocity tests on honeycomb core composite sandwich plates were carried out to demonstrate the analysis results. The comparison between both showed that the predictions agree with the test data fairly well.
Theoretical Forecasting and Experimental Validation of Damage Tolerance and Accumulation in Glass/Epoxy Laminates
Authors: Bonora N. , Marchetti M. , Milella P. P. 
Published: July 2017

Damage and damage accumulation mechanisms under cyclic loads were studied in orthotropic cross-ply composite laminates realized in S-glass fibers with epoxy resin. Five different basic mechanisms of damage were observed and evaluated making use of x-ray and dye-penetrant nondestructive techniques. They are: transverse matrix cracks, fiber failure, fiber debonding, intralaminar delamination and random disperse longitudinal cracks. The effects of these different damage mechanisms are revealed through the reduction of the mechanical properties of the composite material. A comprehensive experimental analysis of GFRP and CFRP, with two different lay-ups for each one, was made. Variations of the elastic moduli in two different directions and Poisson's ratio were measured as a function of the number of cycles, for different stress levels, under alternate loads. The basic relations, developed by Talreja et al., which permit the prediction of the reduction of the elastic moduli for a given damage state, were directly related to the number of cycles N and to the stress levels employed in the fatigue tests. Tests to evaluate an eventual frequency effect on damage accumulation processes in composite material were made. Cumulative damage tests were also conducted to analyse material response under different and alternate load spectra. A damage index based on residual normalized strain energy ratio, which can describe a global damage state, is also proposed.