Relation between configurational entropy and relaxation dynamics of glass-forming systems under volume and temperature reduction

SUMMARY The structural relaxation dynamics of two molecular glass-forming systems have been analyzed by means of dielectric spectroscopy, under cooling and compression conditions. The relation of the dynamic slowing down with the reduction of the configurational entropy, SC, as predicted by Adam and Gibbs (AG), was also investigated. As SC is not directly accessible by experiments, it was estimated, following a common procedure in literature, from the excess entropy Sexc of the supercooled liquid with respect to the crystal, determined from calorimetric and expansivity measurements over the same T–P range of dynamics investigation. The AG relation, predicting linear dependence between the logarithmic of structural relaxation time and the reciprocal of the product of temperature with configurational entropy, was successfully tested. Actually, a bilinear relation between Sexc and SC was found, with different proportionality factors in isothermal and isobaric conditions. Using such results, we derived an equation for predicting the pressure dependence of the glass transition temperature, in good accordance with the experimental values in literature

Laser spectroscopy studies of relaxation dynamics in polymers

Polymer molecular systems are complicated and difficult to study, even in this modern age. Nowadays, there is big effort to understand mechanical and electrical behavior of these systems and many experimental methods are developed for this reason. Laser spectroscopy techniques are excellent methods to study fast and slow dynamics of the complicated polymeric systems. In our present work we used two different laser spectroscopic methods to study the plexiglass polymers. First Second Harmonic Generation (SHG) that deals with nonlinear optical properties of guest-host polymer. In this method, initially a nonlinear system is created.The evaluation of this nonlinearity is coupled to the physical properties of the guest-host polymer. So this evaluation gives us important informations on mobility of the chain and charge treatment in the system. Second method is Transient Grating (TG) that is very powerful optoacoustic technique. In a TG experiment, the sample is excited by two spatially crossed and time coincident laser pulses producing an interference pattern. This spatially modulated excitation creates high frequency acoustic wave due to thermal and electrostriction effect. This technique gives information on sound velocity, acoustic damping time and thermal diffusion

Automotive Electric Power Steering Control With Robust Observer Based Neuroadaptive Type-2 Radial Basis Function Methodology

In this article, a simplified type-2 (ST2) radial basis function (RBF) based neuroadaptive technique for controlling an automotive electric power steering (AEPS) system is designed. The dynamics of the AEPS are assumed to be unknown and the system is subjected to certain disturbances. A ST2-RBF system is proposed for approximating the unknown nonlinear functions. The ST2-RBF parameters are tuned online based on the adaptation laws obtained via Lyapunov stability analysis. A robust observer is also used in this process. The effects of uncertainties as well as approximation and estimation errors are compensated by means of an adaptive component. The parameters of the robust observer-based neuroadaptive ST2-RBF network are optimally determined by applying the Coronavirus disease optimization algorithm (COVIDOA), which mimics the replication mechanism of Coronaviruses taking over the human cells. The results indicate that the COVIDOA can reduce the cost function for neuroadaptive ST2-RBF controller compared to other strategies. Comparison of numerical results is presented to show the efficacy of the suggested technique. Interestingly, based on implementation results, the designed methodology is able to control the AEPS system successfully

Determining the Causes and Extent of Negligence of Occupational Accidents Assessed by Labor Office Inspectors and Official Experts of Judiciary

Background: The purpose of this study was to model the causes and extent of negligence of occupational accidents assessed by labor office inspectors and official experts of the Judiciary of Isfahan Province, Iran, from the perspective of health, safety, and environment (HSE) management. Methods: This descriptive-analytical cross-sectional study was conducted to determine the causes and extent of negligence of agent or agents of occupational accidents in some industries and workshops in Isfahan Province. In this study, the data were collected by census, which after reviewing all the cases, finally 367 cases were completed and examined. Findings: The lowest agreement on the percentage of negligence of the victims was related to the opinion of the inspector and the opinion of the seven-member board [intraclass correlation coefficient (ICC) = 31.5%]. Most agreement between the five-member and seven-member boards was in determining the percentage of the employer's failure. Moreover, disagreement was observed more in determining the percentage of negligence of the victim. Statistically, there was no significant difference between the three-member and five-member staff in any of the potential causes of the accidents (P > 0.05). For the cause of carelessness and negligence, there was a weak agreement between the inspector's opinion and the opinions of three-member and seven-member boards. Conclusion: Based on the results, people who have more work experience receive less failure percentage. However, if the injured person has a higher work experience in the current job, he has a higher percentage of negligence in the accident which has occurred

The effect of different polymer length on water droplets of reverse AOT microemulsion

We study the effect of polyethylene glycol (PEG) on the dynamic and structure of water droplets at the reverse sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) microemulsion. The mixture of water and oil with anionic surfactant AOT can form microemulsion. The dynamic of microemulsion in the presence of PEG is investigated by photon correlation spectroscopy technique. We mainly focus on the variation of the translational diffusion behaviour as a function of the polymer concentration and polymer length scale. By increasing the content of the lowest PEG length scale (Mn = 285), the dynamic of microemulsion slows down. In addition, one relaxation process is distinguished for all polymer concentration. However, for the two higher polymer length scale (Mn = 2200 and 6000), two relaxations are observed and the dynamic of microemulsion speeds up. We used the small angle X-ray scattering technique to monitor the size and the polydispersity of the mixture system (AOT microemulsion/PEG)

Force decay of polyethylene terephthalate glycol aligner materials during simulation of typical clinical loading/unloading scenarios

Background!#!This in vitro study investigated the effect of three distinct daily loading/unloading cycles on force delivery during orthodontic aligner therapy. The cycles were applied for 7 days and were designed to reflect typical clinical aligner application scenarios.!##!Materials and methods!#!Flat polyethylene terephthalate glycol (PET-G) specimens (Duran®, Scheu Dental, Iserlohn, Germany) with thicknesses ranging between 0.4 and 0.75 mm were tested in a three-point-bending testing machine. Measurements comprised loading/unloading intervals of 12 h/12 h, 18 h/6 h, and 23 h/1 h, and specimens were exposed to bidistilled water during loading to simulate intraoral conditions.!##!Results!#!A very large decay in force for the PET‑G specimens could already be observed after the first loading period, with significantly different residual force values of 24, 20, and 21% recorded for the 12 h/12 h, 18 h/6 h, and 23 h/1 h loading/unloading modes, respectively (Mann-Whitney U test, p < 0.01). In addition, further decays in force from the first to the last loading period at day 7 of 13.5% (12 h/12 h), 9.7% (18 h/6 h), and 8.4% (23 h/1 h) differed significantly among the three distinct loading modes (Mann-Whitney U test, p < 0.01).!##!Conclusion!#!Although the initial material stiffness of PET‑G is relatively high, the transmission of excessive forces is attenuated by the high material-related force decay already within a few hours after intraoral insertion

Relation between Configurational Entropy and Relaxation Dynamics of Glass-Forming Systems under Volume and Temperature Reduction

Abstract The structural relaxation dynamics of two molecular glass forming systems have been analyzed by means of dielectric spectroscopy, under cooling and compression conditions. The relation of the dynamic slowing down with the reduction of the configurational entropy, S C , as predicted by Adam and Gibbs (AG), was also investigated. As S C is not directly accessible by experiments, it was estimated, following a common procedure in literature, from the excess entropy S exc of the supercooled liquid with respect to the crystal, determined from calorimetric and expansivity measurements over the same T-P range of dynamics investigation. The AG relation, predicting linear dependence between the logarithmic of structural relaxation time and the product of temperature with configurational entropy, was successfully tested. Actually, a bilinear relation between S exc and S C was found, with different proportionality factors in isothermal and isobaric conditions. Using such results, we derived an equation for predicting the pressure dependence of the glass transition temperature, in good accordance with the experimental values in literature

A rapid sonication based method for preparation of stromal vascular fraction and mesenchymal stem cells from fat tissue

Introduction: Much attention has been paid to the idea of cell therapy using stem cells from different sources of the body. Fat-derived stem cells that are called adipose derived stem cells (ADSCs) from stromal vascular fraction (SVF) are the subject of many studies in several cell therapy clinical trials. Despite production of some GMP-grade enzymes to isolate SVF for clinical trials, there are critical conditions like inconsistency in lot-to-lot enzyme activity, endotoxin residues, other protease activities and cleavage of some cell surface markers which significantly narrow the options. So we decided to develop a new method via sonication cavitation to homogenize fat tissue and disrupt partially adipose cells to obtain SVF and finally ADSCs at a minimum of time and expenses. Methods: The fat tissue was chopped in a sterile condition by a blender mixer and then sonicated for 2 s before centrifugation. The next steps were performed as the regular methods of SVF harvesting, and then it was characterized using flow cytometry. Results: Analysis of the surface markers of the cells revealed similar sets of surface antigens. The cells showed slightly high expression of CD34, CD73 and CD105. The differentiation capacity of these cells indicates that multipotent properties of the cells are not compromised after sonication. But we had the less osteogenic potential of cells when compared with the enzymatic method. Conclusion: The current protocol based on the sonication-mediated cavitation is a rapid, safe and cost-effective method, which is proposed for isolation of SVF and of course ADSCs cultures in a large scale for the clinical trials or therapeutic purposes

Rejuvenation of facial skin and improvement in the dermal architecture by transplantation of autologous stromal vascular fraction: a clinical study

Introduction: The rejuvenation characteristics of fat tissue grafting has been established for many years. Recently it has been shown that stromal vascular fraction (SVF) of fat tissue contributes to its rejuvenation properties. As the SVF is a minimal processed cell population (based on FDA guidance), therefore it is a suitable cell therapy for skin rejuvenation. This clinical trial was aimed to evaluate the ultrastructural improvement of aging skin in the facial nasolabial region after transplantation of autologous SVF. Methods: Our study was conducted in 16 patients aged between 38 and 56 years old that were interested in face lifting at first. All of the cases underwent the lipoaspiration procedure from the abdomen for sampling of fat tissue. Quickly, the SVF was harvested from 100 mL of harvested fat tissue and then transplanted at dose of 2.0×107 nucleated cells in each nasolabial fold. The changes in the skin were evaluated using Visioface scanner, skin-scanner DUB, Visioline, and Cutometer with multi probe adopter. Results: By administration of autologous SVF, the elasticity and density of skin were improved significantly. There were no changes in the epidermis density in scanner results, but we noticed a significant increase in the dermis density and also its thickness with enrichment in the vascular bed of the hypodermis. The score of Visioface scanner showed slight changes in wrinkle scores. The endothelial cells and mesenchymal progenitors from the SVF were found to chang the architecture of the skin slightly, but there was not obvious phenotypic changes in the nasolabial grooves. Conclusion: The current clinical trial showed the modification of dermis region and its microvascular bed, but no changes in the density of the epidermis. Our data represent the rejuvenation process of facial skin by improving the dermal architecture

Rejuvenation of facial skin and improvement in the dermal architecture by transplantation of autologous stromal vascular fraction: a clinical study

Introduction: The rejuvenation characteristics of fat tissue grafting has been established for many years. Recently it has been shown that stromal vascular fraction (SVF) of fat tissue contributes to its rejuvenation properties. As the SVF is a minimal processed cell population (based on FDA guidance), therefore it is a suitable cell therapy for skin rejuvenation. This clinical trial was aimed to evaluate the ultrastructural improvement of aging skin in the facial nasolabial region after transplantation of autologous SVF. Methods: Our study was conducted in 16 patients aged between 38 and 56 years old that were interested in face lifting at first. All of the cases underwent the lipoaspiration procedure from the abdomen for sampling of fat tissue. Quickly, the SVF was harvested from 100 mL of harvested fat tissue and then transplanted at dose of 2.0×107 nucleated cells in each nasolabial fold. The changes in the skin were evaluated using Visioface scanner, skin-scanner DUB, Visioline, and Cutometer with multi probe adopter. Results: By administration of autologous SVF, the elasticity and density of skin were improved significantly. There were no changes in the epidermis density in scanner results, but we noticed a significant increase in the dermis density and also its thickness with enrichment in the vascular bed of the hypodermis. The score of Visioface scanner showed slight changes in wrinkle scores. The endothelial cells and mesenchymal progenitors from the SVF were found to chang the architecture of the skin slightly, but there was not obvious phenotypic changes in the nasolabial grooves. Conclusion: The current clinical trial showed the modification of dermis region and its microvascular bed, but no changes in the density of the epidermis. Our data represent the rejuvenation process of facial skin by improving the dermal architecture