Friedman Technique Research Articles

Mechanical and thermal degradation behavior of high-performance PDMS elastomer based on epoxy/silicone hybrid network

In this study, the high-performance PDMS elastomer was successfully prepared by constructing epoxy/silicone hybrid network through hydrosilylation and epoxide-opening reaction. The tensile strength, elongation at break and shear strength of the prepared hybrid material were increased by 200.0%, 59.6%, 140.6% respectively when compared with the pure PDMS. The thermal residual weight of the hybrid material at 800 °C in N2 was kept at 56.9%. The thermal degradation mechanism of hybrid material was investigated through TG-IR analysis. Friedman technique was used to compute the kinetic parameters of degradation reaction. Meanwhile, the composition and structure of residual char of hybrid material after thermal degradation at 800 °C was systematically characterized. Results indicated that the high-performance PDMS elastomer with excellent thermal and mechanical properties was expected to be applied in many prospects such as thermal protective coating, high temperature resistant adhesive and ablative material matrix.

Computed Tomography and Magnetic Resonance Imaging are Similarly Reliable in the Assessment of Glenohumeral Arthritis and Glenoid Version.

The purpose of this study was to compare the intraobserver and interobserver reliability of CT and T2-weighted MRI for evaluation of the severity of glenoid wear, glenohumeral subluxation, and glenoid version. Sixty-one shoulders with primary osteoarthritis had CT and MRI scans before shoulder arthroplasty. All slices were blinded and randomized before evaluation. Two fellowship-trained shoulder surgeons and three orthopaedic surgery trainees reviewed the images to classify glenoid wear (Walch and Mayo classifications) and glenohumeral subluxation (Mayo classification). Glenoid version was measured using Friedman's technique. After a minimum two-week interval, the process was repeated. Intraobserver reliability was good for the CT group and fair-to-good for the MRI group for the Walch, Mayo glenoid, and Mayo subluxation classifications; interobserver reliability was poor for the CT and fair-to-poor for the MRI group. For the measurement of glenoid version, intraobserver reliability was good for the CT and substantial for the MRI group; interobserver agreement was good for both groups. There were no significant differences in reliability between staff surgeons and trainees for any of the classifications or measurements. CT and MRI appear similarly reliable for the classification of glenohumeral wear patterns. For the measurement of glenoid version, MRI was slightly more reliable than CT within observers. Differences in training level did not produce substantial differences in agreement, suggesting these systems can be applied by observers of different experience levels with similar reliability.

Modified Friedman technique: a new proposed method of measuring glenoid version in the setting of glenohumeral dysplasia.

Glenoid version angles are measured to objectively follow changes related to glenohumeral dysplasia in the setting of brachial plexus birth palsy. Measuring glenoid version on cross-sectional imaging was initially described by Friedman et al. in 1992. Recent literature for non-dysplastic shoulders advocates time-consuming reconstructions and reformations for an accurate assessment of glenoid version. To compare Friedman's original method for measuring glenoid version to a novel technique we developed ("modified Friedman") with the reference standard of true axial reformations. With institutional review board approval, we retrospectively examined 30 normal and dysplastic shoulders obtained from magnetic resonance imaging examinations of 30 patients with an established diagnosis of brachial plexus birth palsy between January 2012 and September 2017. Four pediatric radiologists performed glenoid version measurements using Friedman's method, the modified Friedman method and a previously described true axial reformation method. The modified Friedman technique better accounts for scapular positioning by selecting a reference point related to the acromion-scapular body interface. Inter-rater reliability and inter-method agreement were assessed using intraclass correlation, paired t-tests and mixed linear model analysis. Equivalence tests between methods were performed per reader. Glenoid version measurements were significantly different when comparing Friedman's method to true axial reformations in normal (-10.8±5.7° [mean±standard deviation] vs. -8.8±5.3°; P≤0.001) and dysplastic shoulders (-34.6±17.7° vs. -28.1±17.5°; P≤0.001). Glenoid version measurements were not significantly different when comparing the modified Friedman's method to true axial reformations in normal (-6.3±5.8° vs. -8.8±5.3°; P=0.06) and dysplastic shoulders (-29.0±18.3° vs. -28.1±17.5°; P=0.06). Friedman's method was not equivalent to true axial reformations for measurements in dysplastic shoulders for all readers (P=0.68, 0.81, 0.86, 0.99); the modified Friedman method was equivalent to of true axial reformations for measurements in dysplastic shoulders for 3 of 4 readers (P≤0.001, P≤0.001, P≤0.001, P=0.10). In glenohumeral dysplasia, the modified Friedman method and post-processed true axial reformations provide statistically similar and reproducible values. We propose that our modified Friedman technique can be performed in lieu of post-processed true axial reformations to generate glenoid version measurements.

Analyzing Machine Learning Techniques for Fault Prediction Using Web Applications

Web applications are indispensable in the software industry and continuously evolve either meeting a newer criteria and/or including new functionalities. However, despite assuring quality via testing, what hinders a straightforward development is the presence of defects. Several factors contribute to defects and are often minimized at high expense in terms of man-hours. Thus, detection of fault proneness in early phases of software development is important. Therefore, a fault prediction model for identifying fault-prone classes in a web application is highly desired. In this work, we compare 14 machine learning techniques to analyse the relationship between object oriented metrics and fault prediction in web applications. The study is carried out using various releases of Apache Click and Apache Rave datasets. En-route to the predictive analysis, the input basis set for each release is first optimized using filter based correlation feature selection (CFS) method. It is found that the LCOM3, WMC, NPM and DAM metrics are the most significant predictors. The statistical analysis of these metrics also finds good conformity with the CFS evaluation and affirms the role of these metrics in the defect prediction of web applications. The overall predictive ability of different fault prediction models is first ranked using Friedman technique and then statistically compared using Nemenyi post-hoc analysis. The results not only upholds the predictive capability of machine learning models for faulty classes using web applications, but also finds that ensemble algorithms are most appropriate for defect prediction in Apache datasets. Further, we also derive a consensus between the metrics selected by the CFS technique and the statistical analysis of the datasets.

Thermoanalytical study of siloxane-polyurethane thermosets: Kinetic deconvolution of overlapping heterogeneous curing reactions

Abstract The curing behaviour and kinetics of siloxane-polyurethane coatings based on difunctional hydroxyl-terminated polydimethylsiloxane (PDMS-OH), polycaprolactone triol (PCL-triol) and isophorone diisocyanate (IPDI) were studied. The curing kinetics were elucidated by dynamic differential scanning calorimetry (DSC) using the model-free Friedman technique. The curing kinetics showed a constant value of 96.3 ± 1.5 kJ/mol over the range of 0.05 α y ( α ) and z ( α ) functions showed that the kinetic process does not follow a single-step curing reaction and that a combination of reactions of carbon-linked and silicone-linked hydroxyls with isocyanate control the kinetics during curing due to the different chemical activities of the hydroxyl species. The detailed kinetics of the curing reactions were analyzed by applying an empirical kinetic deconvolution method. The results showed that the thermal behaviour of these systems is characterized by the reaction of PCL-triol with isocyanate, followed by another overlapping exothermic reaction of PDMS-OH with isocyanate at a higher thermal range, resulting in a reaction-induced phase-separated system. The activation energy of the two separated reactions was calculated using a model-fitting method, and optimization was performed to minimize the sum of the squared errors. Moreover, the surface topography of the cured systems was observed using an atomic force microscope (AFM) in the tapping mode, and the different isocyanate curing reactions were confirmed using Fourier transform infrared (FT-IR) spectroscopy.

Degradation Behavior of Polypropylene–Organically Modified Clay Nanocomposites

The degradation mechanism of polypropylene (PP)–clay nanocomposites is investigated in the present study. The PP–clay nanocomposites are prepared through a solution process with 4 and 8 wt % incorporation of nanoclay in a polymer matrix. Nanoclay with two types of organic modifications (25–30 wt % methyl dihydroxyethyl hydrogenated tallow ammonium (TA) and 25–30 wt % octadecylamine (OA)) is used with isotactic PP, atactic PP, and ethylene propylene copolymer with ∼20 wt % rubber. Characterization of nanocomposites is done through X-ray diffraction (XRD) analysis while melting and crystallization behavior is studied through differential scanning calorimetry (DSC). XRD and DSC analysis shows formation of intercalated type nanocomposites with improved barrier properties. Degradation behavior of nanocomposites is studied through thermogravimetric analysis (TGA). Weight loss curves are further analyzed through the Friedman technique to find the rate of degradation. Nanoclay incorporation increases the lifetime...

Influence of world trade organization on Iran’s carpet industry compatibility

The article discusses the influence of accession to world trade organization (WTO) on Iran's carpet industry compatibility. Results of applying Pearson and regression tests show that by joining the world trade organization, carpet industry compatibility will be increased, domestic corporate resources will be improved, more international market segments will be captured and the industry's creativity strength will be promoted. The compatibility dimensions levels were calculated and its dimensions apart from “creativity and innovation strength” were placed in suitable situations. Then the dimensions weights were indicated by Friedman technique in direct order: industry's creativity and innovation strength; situation in the international market place; and domestic corporate resources. The most important strategies for improving the current situation are: raising advertisement and marketing researches, production in terms of global customer needs, making exporters accustom to modern international marketing methods and e-commerce to maintain market segments. Key words: World trade organization, Iran, carpet industry, compatibility.

Preparation, characterization and crystal structure of some imino Schiff bases

Bis[2-N(methyleneimino)ethylbutanoate] [(eaa) 2en] ( 1), 2-[1-(2-hydroxypropylimino)ethyl]phenol [ohap-1-a-2-pn] ( 2), and 3-(2-hydroxyethylimino)-1-phenylbutan-1-one [bzacmea] ( 3) were isolated from the condensation reactions between the corresponding ketone and amine at 303 K. The single crystal XRD analyses revealed that the packing of the molecules in the crystal structure of compounds ( 1), ( 2) and ( 3) are stabilized through hydrogen bonding interactions. Compounds ( 2) and ( 3) are zwitter ions. Thermal decomposition kinetics has been studied using model free evaluation techniques. The Friedman technique gave average activation energy ( E a) of 79, 78, and 73 kJ mol −1 for the non-isothermal decomposition of ( 1), ( 2), and ( 3) in nitrogen environment. The average activation energy of ( 1) was found to be 88, and 86 kJ mol −1, which are derived by Kissinger and Flynn–Wall techniques from non-isothermal TG plots at different heating rates.

Mechanical and Thermal Properties of Poly(Phthalazinone Ether Sulfone)/Poly(Ether Sulfone) Blends

The mechanical and thermal properties of poly(phthalazinone ether sulfone) (PPES)/poly(aryl ether sulfone) (PES) blends prepared by melt-mixing were investigated by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The dynamic mechanical thermal analysis results show that the incorporated PES has a large influence on the heat stability of PPES. The DMTA results display that the blends with a single glass transition temperature, which increases with increasing PPES content, indicates that PPES and PES are completely miscible over the studied composition range. The thermodegradative behavior of PPES/PES blends was used to analyze their thermal stability. The Friedman technique was used to determine the kinetic parameters (i.e., the apparent activation energy and order of reaction of the degradation process). The results indicate that the presence of the PES component influences the thermal stability of the PPES. On the basis of the kinetic data derived from Friedman' approach, the lifetime estimates for pure PPES, pure PES, and the blends generated from the weight loss of 5% were constructed.

Effect of the Alkyl Group Substituents on the Thermal and Enzymatic Degradation of Poly(n-alkyl acrylates)

The effect of alkyl group substituents on the thermal degradation kinetics of poly (n-alkyl acrylate) was investigated in pyrolysis and in solution. The activation energies for the pyrolytic degradation of poly (n-butyl acrylate) (PBA), poly (ethyl acrylate) (PEA), and poly (methyl acrylate) (PMA), determined by the Friedman's technique, were 150, 170 and 203 kJ/mol, respectively. For the thermal degradation of the polymers in solution, a continuous distribution kinetic model was used to determine the random chain degradation rate coefficients. The activation energies, determined from the temperature dependence of the rate coefficients, for PBA, PEA and PMA in solution were 109, 117, and 138 kJ/mol, respectively. This indicates that the variation of the activation energies with chain length of the substituent in the polymer is similar to degradation both by pyrolysis and in solution, though the values obtained are lower for degradation in solution. The enzymatic degradation of these polymers was also investigated at different temperatures with various enzymes (Novozym 435, Lipolase and Porcine Pancreas) in different solvents. A continuous distribution kinetic model was used to evaluate the polymer chain end scission rate coefficient. The degradation rates were highest when the acrylates were degraded in presence of Porcine Pancreas in toluene at $50\hspace{2mm}^oC$.

Thermal decomposition kinetics of thermotropic liquid crystalline p-hydroxy benzoic acid/poly(ethylene terephthalate) copolyester

The nonisothermal and isothermal thermogravimetry (TG) in nitrogen and in air of thermotropic liquid crystalline poly(oxybenzoate- co-ethylene terephthalate), a copolyester consisting of 60 mol% of p-hydroxy benzoic acid (HBA) and 40 mol% of poly(ethylene terephthalate) (PET), known as Rodrun LC3000, was performed. The Friedman technique based on a single heating-rate method was used to calculate the kinetic parameters of the nonisothermal degradation and the Flynn technique was employed to calculate the kinetic parameters of isothermal degradation. The nonisothermal degradation of Rodrun LC3000 in nitrogen and in air occurred in two steps. In air, Rodrun LC3000 became degraded leaving very small residues within the range of experimental temperature whereas, in nitrogen, it left some residues which were found to increase in amount with increasing heating rate. The respective activation energy, order and ln(frequency factor) for nonisothermal decomposition of Rodrun LC3000 are 159 kJ/mol, 2.2 and 28 min −1 in nitrogen and 121 kJ/mol, 2.4 and 20 min −1 in air. The respective activation energy, order and ln(frequency factor) for isothermal degradation are found to be 110 kJ/mol, 2.2 and 17.1 min −1 in nitrogen and 103 kJ/mol, 2.3 and 15.9 min −1 in air. The kinetic parameters obtained from the two modes of decomposition indicate that the thermal stability of Rodrun LC3000 is substantially better in nitrogen than in air. The estimated lifetimes at various temperatures suggest a good thermal stability of Rodrun LC3000.

Thermoanalytical study of the cure characteristics of a main-chain liquid crystalline oligoester: Model-free approach to kinetic analysis of non-isothermal data

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and sebacic acid in presence of a mixture 75:25 of diglycidyl terephthalate and triglycidyl trimellitic acid ester (D&TGE), as a curing agent, was studied by non-isothermal differential scanning calorimetry (DSC). The analysis of non-isothermal data was carried out using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, have been calculated by the Friedman technique. It shows a constant value of 95.5 ± 2.5 kJ/mol, in the 0.27 < α < 0.68 range. The activation energy, out of the above-mentioned interval, is strongly dependent on the degree of extent of the curing reaction. The y( α) and z( α) plots, which were obtained through transformation of DSC data, are not completely identical at a variety of heating rates. It indicates that the kinetic process dose not follow a single-step curing reaction model and a multi-step process controls it during curing. To approve the non-isothermal analysis result, we carried out further, depolarizing transmittance measurements and optical microscopy observations on the stoichiometric mixture of LCO/D&TGE during curing, at various heating rates. The results of these experiments exhibit that the kinetic process of the investigated system is strongly influenced by altering the mesomorphism features of the sample.

Liquid crystalline thermosets as binder for powder coatings: Thermoanalytical study of the cure characteristics of a carboxylated main chain liquid crystalline oligoester

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, has been calculated by the Friedman technique. It showed an ascending trend from about 133.7 kJ/mol, at α=0.1 to 177.2 kJ/mol, at α=0.4, then it reached approximately a constant value of about 150±5% kJ/mol in the range of 50–90%. The results indicated that the kinetic process does not follow a single-step curing reaction model. To verify the isothermal analysis result, we carried out further, non-isothermal differential scanning calorimetry and depolarizing transmittance measurements on the stoichiometric mixture of LCO/TGIC, at different heating rates. The results of these experiments exhibited that the kinetic process of the investigated system is strongly influenced by curing condition which alters the liquid crystalline state of the sample.

Thermal degradation kinetics of poly(vinyl chloride-co-vinyl acetate)

The kinetics of thermal degradation of three vinyl chloride-co-vinyl acetate (PVC-co-PVAc) copolymers with PVAc content of 14, 14 and 10 wt.% was investigated at various temperatures (220–250 °C) in solution. Reaction samples were analyzed by gel permeation chromatography (GPC) to obtain the molecular weight distribution (MWD). The degradation rate coefficients were determined from the time evolution of the MWDs. The energies of activation, determined from the temperature dependence of the rate coefficients, of the three copolymers were 92, 77 and 100 kJ/mol, respectively. The degradation of these copolymers was also investigated thermogravimetrically in the presence of nitrogen. The activation energies, determined from the Friedman technique, were 114, 92 and 131 kJ/mol, respectively. This indicated that the overall stability order of the copolymers remained same in both the methods. This also indicated that copolymers having the same PVAc content exhibit different stability. To our knowledge, this is the first paper that reports the activation energies, rate coefficients for the degradation of these copolymers as well as show that copolymers having the same composition degrade differently.

Thermal degradation of poly(ethylene terephthalate): A kinetic analysis of thermogravimetric data

The thermal decomposition of poly(ethylene terephthalate) has been studied using a conventional dynamic thermogravimetric technique in a flowing air atmosphere at several heating rates between 0.1°C and 100°C/min. The dynamic thermogravimetric analysis curve and its derivative have been analyzed using a variety of analytical methods reported in the literature to obtain information on the kinetic parameters. The degradation was found to be a complex process composed of at least three overlapping stages for which kinetic values can be calculated. The best approaches to solving the kinetics of the decomposition were found to be the multiple heating rate techniques of Friedman and Ozawa. The Friedman technique gave apparent activation energies (kJ/mol) for the three main decomposition stages of 122.2 ± 12.9, 201.0 ± 8.5, and 141.9 ± 12.7, with a value of 85.5 ± 10.2 for the prestage at low conversion. The Ozawa method, meanwhile, gave values of 101.6 ± 2.6, 182.6 ± 7.4, 142.5 ± 3.8, and 158.4 ± 26.1 for the prestage.

A routine method for 18O analysis of water vapor

A new routine method for 18O study of water vapor is presented. Microquantities (2–6 μl) of water vapor are used and analysed with the modified Hardcastle and Friedman technique for organic compounds. The sampling technique is very simple (opening of evacuated flasks at air temperature) and allows a very high sampling rate relative to natural isotopic variations of water vapor in space and time. This new method gives reproducible results with a standard error of ▪.

The permanent income hypothesis in an underdeveloped economy

After a concise but critical survey of several tests of the permanent income hypothesis (PIH), the authors advance their own test for India using annual data from 1919–1960. It employs Friedman's technique for calculating the permanent value of a variable. Two different specifications of the model are tested, using different values of the consumer's ‘horizon.’ In almost all cases it is found that the marginal propensity to consume out of transitory income is very similar to the marginal propensity to consume out of permanent income. The authors conclude that even a looser variant of the PIH is not valid for India. However, no valid generalization with respect to the appropriate planning horizon can be made, for the PIH was almost equally invalid with a horizon of one, two and two-and-a-half years. The authors briefly discuss the policy implications of their results for the savings efforts in underdeveloped countries.