Shape Memory Effect and Properties Memory Effect of Polyurethane

The relationship between shape and properties memory effect, especially viscoelastic properties of polyurethane under study is the main aim of this research work. Tensile tests have been performed in order to introduce 100% of deformation in the polyurethane samples. Under this deformation, stress–relaxation experiments have been performed in order to eliminate the residual stresses. This deformation of the samples has been fixed by cooling. Recovery tests, then, were carried out at different isothermal temperatures that varied from 30 C to 60 C. Viscoelastic behavior has been studied by a biparabolic model and by using the Cole–Cole method. It was shown that this model describes the behavior of the polymer at the different states of shape memory tests. The constants of this model then have been determined. This study leads to a better understanding of the mechanism of shape memory effect. The comparison between the virgin polymer and the polymer after a recovery test by DMTA (dynamic mechanical thermal analysis) and by Cole–Cole method has illustrated that the polymer does not obtain its initial properties even when it was totally regained its initial shape. These results have been confirmed by three successive shape memory tests on the same sample and by comparing the mechanical characteristics of different cycles because ‘‘shape memory effect’’ and ‘‘properties memory effect’’ do not follow the same mechanisms

How Do MOHME-Affiliated Hospital Libraries Comply with the National Standards?

Introduction: : Hospital libraries have a special role in providing knowledge-evidence-based services to their users, including medical staff, patients, and their families. The present study aimed to evaluate the Ministry of Health and Medical Education (MOHME)-affiliated hospital libraries of Iran based on the national standard approved in 2021 by the National Standard Organization. Methods: The present research is an applied study regarding its purpose and a descriptive survey regarding its method. The study’s statistical population includes 213 hospital libraries of 60 universities of medical sciences affiliated with the MOHME of Iran. The data collection tool is a researcher-made checklist extracted from the national standard book of hospital libraries. SPSS software was used for data analysis. Results: The obtained results revealed that, in common, less than 50% of the hospital libraries of medical universities in Iran complied with two components of the Organization and nine components of Resources Management standards: five components of Human Resources Management and four components of Physical, Environment, and Equipment Management. Conclusion: MOHME-affiliated hospital libraries have fundamental weaknesses in the key components of Organization standard and Resource Management standards, i.e., human resource management and physical resource, environment, and equipment management, and do not comply with the standards. Therefore, taking practical measures by officials and stakeholders to improve the services, the quality of patient care, and, ultimately, the satisfaction of patients, their families, and users are essential

Conservative Management of Unset Mineral Trioxide Aggregate Root-End Filling: A Case Report

This case report presents conservative management of unset mineral trioxide aggregate (MTA) after being placed as a root-end filling material following periapical surgery. Periapical surgery was indicated for a maxillary lateral incisor of a 15-year-old male due to persistent exudate and a large periapical lesion. During surgery Angelus MTA was placed as root-end filling. The next session it was noticed that MTA had failed to completely set. In an orthograde approach, calcium-enriched mixture (CEM) cement was used to obturate the root canal space. The patient was followed up for 27 months and did not exhibit any clinical signs and symptoms. Radiographic images showed complete healing of the lesion.Keywords: Calcium-Enriched Mixture; Calcium Silicate; CEM Cement; Dens Invaginatus; Mineral Trioxide Aggregat

Some New Concepts of Shape Memory Effect of Polymers

In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation and recovery tests were performed on these samples at 70 °C. The results indicated that the blend can only regain 24% of its initial shape. It was shown that, this partial shape memory effect could be improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed into a shape memory polymer without any chemical modification. In this work, we have also shown the relationship between shape memory and property memory effect. Mono and multi-frequency DMA (dynamic mechanical analyzer) tests on virgin and 100% recovered samples of polyurethane (PU) revealed that the polymer at the end of the shape memory tests regains 100% of its initial form without regaining some of its physical properties like glass transition temperature, tensile modulus, heat expansion coefficient and free volume fraction. Shape memory (with and without stress-relaxation) tests were performed on the samples in order to show the role of residual stresses during recovery tests. On the basis of the results we have tried to show the origin of the driving force responsible for shape memory effect

Processing and Quality Control of Masks: A Review

It is clear that viruses, especially COVID-19, can cause infection and injure the human body. These viruses can transfer in different ways, such as in air transfer, which face masks can prevent and reduce. Face masks can protect humans through their filtration function. They include different types and mechanisms of filtration whose performance depends on the texture of the fabric, the latter of which is strongly related to the manufacturing method. Thus, scientists should enrich the information on mask production and quality control by applying a wide variety of tests, such as leakage, dynamic respiratory resistance (DBR), etc. In addition, the primary manufacturing methods (meltblown, spunlaid, drylaid, wetlaid and airlaid) and new additive manufacturing (AM) methods (such as FDM) should be considered. These methods are covered in this study

Production of Vitamins B3, B6 and B9 by Lactobacillus Isolated from Traditional Yogurt Samples from 3 Cities in Iran, Winter 2016

Background and Objective: B-group vitamins have important roles in many aspects of cellular metabolism and humans cannot synthesize them. So, they should be obtained from external resources. This project provides a new insight into assessing the production of vitamins B3, B6 and B9 by Lactobacillus, isolated from traditional yogurt samples from 3 different cities of Iran; Golpayegan, Sanandaj and Tehran (Damavand).Material and Methods: Following 72 h of anaerobic culture of the Lactic acid bacteria at 37°C in 5% CO2, some Lactobacillus species from traditional yogurt samples were isolated and characterized both morphologically and biochemically. Isolates were identified following 16S rRNA PCR-amplification and sequencing. Including Lactobacillus (L.) ozensis strain Gon2-7, L. acidophilus strain KU, L. helveticus strain D76, L. helveticus strain Dpc 4571, L. fermentum strain 1, L. rossiae strain DSM15814T, L. casei strain NCDO, L. delbrueckii strain ATCC 11842, L. crispatus strain MRS 54.4, L. delbrueckii strain SB3 and L. paracasei subsp. tolerans JCM1171 (T). The sequence of L. paracasei subsp. tolerans JCM1171 (T) was submitted to the NCBI. The ability to produce B-group vitamins was evaluated by high performance liquid chromatography. Lactobacillus strains and amount of vitamin B3, B6 and B9 production were analyzed by Analysis of Variance test.Results and Conclusion: Eleven isolates of Lactobacillus species from traditional yogurt samples were identified. Optimal conditions for Lactobacillus growth were pH 5-6 and temperatures 37-40°C. The isolates produced vitamins B3, B6 and B9. L. paracasei subsp. tolerance JCM 1171 (T) showed the highest amount of produced vitamins (p≤0.01) consist of vitamin B6 (1566.17 µg ml-1) and B9 (1279.72 µg ml-1). L. acidophilus strain KU showed the highest production of vitamin B3 (522.7 µg ml-1). L. fermentum produced the highest amount of vitamin B2. These strains are a natural and cost efficient source of vitamin. The Lactobacillus strains isolated in this research particularly, L. paracasei, could be applied in improving new fermented products, fortified with B-group vitamin that could be applied as substitution for enriching and supplementation with the controversial synthetic vitamins. Conflict of interest: The authors declare that there is no conflict of interest

Rheokinetic of polyurethane crosslinking time-temperature-transformation diagram for rotational molding

In this work, the rheokinetic of polyurethane crosslinking was studied by different methods: differential scanning calorimetric (DSC), rheometry, and infrared spectrometry. The conversion ratio and the glass transition temperature were followed by time of reaction. The results of the isothermal and nonisothermal test were compared. The evolution of viscosity was measured at different frequencies. The intersection of these curves is considered as gel point. A simplified mechanism has been proposed for crosslinking reactions. Based on this mechanism, a kinetic model describing the evolution of reactive system was developed. This model then was compared with the results of experiments performed by infrared spectrometry. The time-temperature- transformation diagram was established showing the evolution of physical state change of the reactive system. This diagram may be used to evaluate the zone of rotomoldability of the reactive polyurethane

Standards for Iranian Hospital Libraries: Why do Hospital Libraries Need to be Standardized?

The objective of developing the National Standard for Hospital Libraries (NSHL) is to present an efficient tool to replace scientific methods with traditional ones. The standards should be designed to be used as a comprehensive guide for librarians working in hospitals in various fields. Various standards are currently being developed for national, public, and academic libraries. Despite the activity of more than 200 educational and medical centers and a large number of public and private medical centers in Iran, there was no comprehensive standard that could meet this group of libraries' expectations. Therefore, the development of a standard for hospital libraries began based on national research. Finally, this standard was prepared in four chapters, including mission and organization, strategic planning, resources management, and service management. This standard was handed over to the Iranian National Standards Organization and the Deputy for Research and Technology of the Ministry of Health and Medical Education to be available to users and stakeholders. The NSHL is a comprehensive guideline for establishing and developing hospital libraries and applies to all public and private hospital libraries, both