Natural Polymers Based Green Adsorbents for Water Treatment

Natural Polymers Based Green Adsorbents for Water Treatment
Author: Susheel Kalia
Publsiher: Elsevier
Total Pages: 356
Release: 2021-09-10
ISBN 10: 0128205415
ISBN 13: 9780128205419
Language: EN, FR, DE, ES & NL

Natural Polymers Based Green Adsorbents for Water Treatment Book Review:

Natural Polymers-Based Green Adsorbents for Water Treatment focuses on the recent development of novel polymeric adsorbents that are green and eco-friendly or biodegradable in nature. The book reviews the synthesis, properties and adsorption applications of natural and green polymer-based adsorbents. It discusses adsorption processes in biopolymer systems, remediation technologies developed to remove environmental pollutants, the usage of natural polymer-based cost-effective and green novel adsorbent materials for the removal of organic and inorganic contaminants, and the efficiency of functionalized polymers, nanosorbents, hydrogels, composites, graft copolymers in the sorption of various pollutants from the environment as well as from the industrial effluents. Researchers working on environmental remediation need a single book, where all data on natural and green adsorbents for water treatment are discussed comprehensively. Natural Polymers-Based Green Adsorbents for Water Treatment addresses this need by providing world-wide leading experts' observations and research. So, this book is a valuable reference for early-career scientist, academic researchers and graduate students in chemical engineering and material science. Presents step-by-step review of processing and modification of natural polymers and their applications in water remediation Analyzes data on natural and green adsorbents for water treatment, meanwhile provides world-wide experts' knowledge to pave the way for further research Includes extensive tables, graphs, figures, bibliographies and references to enhance key concepts

Natural Polymers Based Green Adsorbents for Water Treatment

Natural Polymers   Based Green Adsorbents for Water Treatment
Author: Susheel Kalia
Publsiher: Elsevier
Total Pages: 356
Release: 2021-08-22
ISBN 10: 0128205423
ISBN 13: 9780128205426
Language: EN, FR, DE, ES & NL

Natural Polymers Based Green Adsorbents for Water Treatment Book Review:

Natural Polymers-Based Green Adsorbents for Water Treatment focuses on the recent development of novel polymeric adsorbents that are green and eco-friendly or biodegradable in nature. The book reviews the synthesis, properties and adsorption applications of natural and green polymer-based adsorbents. It discusses adsorption processes in biopolymer systems, remediation technologies developed to remove environmental pollutants, the usage of natural polymer-based cost-effective and green novel adsorbent materials for the removal of organic and inorganic contaminants, and the efficiency of functionalized polymers, nanosorbents, hydrogels, composites, graft copolymers in the sorption of various pollutants from the environment as well as from the industrial effluents. Researchers working on environmental remediation need a single book, where all data on natural and green adsorbents for water treatment are discussed comprehensively. Natural Polymers-Based Green Adsorbents for Water Treatment addresses this need by providing world-wide leading experts’ observations and research. So, this book is a valuable reference for early-career scientist, academic researchers and graduate students in chemical engineering and material science. Presents step-by-step review of processing and modification of natural polymers and their applications in water remediation Analyzes data on natural and green adsorbents for water treatment, meanwhile provides world-wide experts’ knowledge to pave the way for further research Includes extensive tables, graphs, figures, bibliographies and references to enhance key concepts

Advanced Green Materials

Advanced Green Materials
Author: Shakeel Ahmed
Publsiher: Woodhead Publishing
Total Pages: 494
Release: 2020-11-24
ISBN 10: 0128226757
ISBN 13: 9780128226759
Language: EN, FR, DE, ES & NL

Advanced Green Materials Book Review:

Advanced Green Materials: Fabrication, Characterization and Applications of Biopolymers and Biocomposites looks at their extraction, purification, modification, and processing for various industrial, biomedical, pharmaceutical, and construction applications. The book comprehensively summarizes recent technical research accomplishments in natural materials and discusses various aspects of natural materials from a chemistry/engineering point of view. The book is unique with contributions from experts working on hybrid biopolymers and bio- composites, bioactive and biodegradable materials, bio-inert polymers and composites, natural polymer and composites, and metallic natural materials. The book will be a useful reference for scientists, academicians, research scholars, and biotechnologists. Advanced biocomposite materials continue to become increasingly popular and important for a broad range of different science and engineering applications. In the race to exploit the unique mechanical, thermal, and electrical properties of these materials, researchers must also address new challenges to predict, understand, and manage the potentially adverse effects they could have on the environment and human lives. The book describes recent developments and applications of biopolymers and biocomposites for applications in various industrial fields. Chapters include original research and the latest reviews in similar fields. Biopolymers and biocomposites occupy an exceptional position in the exciting new world of novel biomaterials. Considering their sustainability, non-toxic properties, and their ability to have tailored properties and functions, they should be considered as a smart candidate in the advancement of biomaterials technology. Covers all types of biopolymers and advanced industrial applications, from packaging to biomedical therapeutics Discusses the shift from research to industrial large-scale application of biopolymers and biocomposites Emphasizes new strategic trends, such as bio-based and biodegradable additives for bioplastics, PHAs, new lignin-based biopolymers, and new polymers based on terpenes and biosensor applications

Green Composites

Green Composites
Author: Sabu Thomas,Preetha Balakrishnan
Publsiher: Springer Nature
Total Pages: 617
Release: 2021-01-18
ISBN 10: 9811596433
ISBN 13: 9789811596438
Language: EN, FR, DE, ES & NL

Green Composites Book Review:

This book presents important developments in green chemistry, with a particular focus on composite materials chemistry. In recent years, natural polymers have generated much interest due to their unique morphology and physical properties. The book gives an introductory overview of green composites, and discusses their emerging interdisciplinary applications in various contemporary fields. The chapters, written by leading experts from industry and academia, cover different aspects of biodegradable green composites and natural polymers including their processing, manufacturing, properties, and applications. This book will be a valuable reference for beginners, researchers as well as industry professionals interested in biodegradable composites.

Green Adsorbents to Remove Metals Dyes and Boron from Polluted Water

Green Adsorbents to Remove Metals  Dyes and Boron from Polluted Water
Author: Inamuddin,Mohd Imran Ahamed,Eric Lichtfouse,Abdullah M. Asiri
Publsiher: Springer Nature
Total Pages: 462
Release: 2020
ISBN 10: 3030474003
ISBN 13: 9783030474003
Language: EN, FR, DE, ES & NL

Green Adsorbents to Remove Metals Dyes and Boron from Polluted Water Book Review:

This book reviews adsorption techniques to clean wastewater, with focus on pollution by dyes and heavy metals. Advanced adsorbents include carbon nanomaterials, biomass, cellulose, polymers, clay, composites and chelating materials.

Current Advances in Mechanical Engineering

Current Advances in Mechanical Engineering
Author: Saroj Kumar Acharya,Dipti Prasad Mishra
Publsiher: Springer Nature
Total Pages: 1018
Release: 2021-03-17
ISBN 10: 9813347953
ISBN 13: 9789813347953
Language: EN, FR, DE, ES & NL

Current Advances in Mechanical Engineering Book Review:

This book presents select proceedings of the International Conference on Recent Advances in Mechanical Engineering Research and Development (ICRAMERD 2020). The contents focus on latest research and current problems in various branches of mechanical engineering. Some of the topics discussed here include fracture and failure analysis, fuels and alternative fuels, combustion and IC engines, advanced manufacturing technologies, powder metallurgy and rapid prototyping, industrial engineering and automation, supply chain management, design of mechanical systems, vibrations and control engineering, automobile engineering, fluid mechanics and machines, heat transfer, composite materials, micro and nano-engineering for energy storage and conversion, and modeling and simulations. The wide range of topics presented in this book can make it useful for beginners, researchers as well as professionals in mechanical engineering.

Biodegradation Pollutants and Bioremediation Principles

Biodegradation  Pollutants and Bioremediation Principles
Author: Ederio Dino Bidoia,Renato Nallin Montagnolli
Publsiher: CRC Press
Total Pages: 352
Release: 2021-04-20
ISBN 10: 1000264513
ISBN 13: 9781000264517
Language: EN, FR, DE, ES & NL

Biodegradation Pollutants and Bioremediation Principles Book Review:

This book presents a broad compendium of biodegradation research and discussions on the most up-to-date bioremediation strategies. The most relevant microbiological, biochemical and genetic concepts are presented alongside the fundamentals of bioremediation. The topics include: a wide variety of contaminant impacts evaluation, key methodologies required to measure biodegradation and propose new bioremediation protocols, as well as the handling of microbial communities related to such processes. The selected collaborating authors are renowned for their microbiology expertise and will provide an in-depth reference for students and specialists. The contents provide a valuable source of information for researchers, professionals, and policy makers alike.

Functional Hybrid Nanomaterials for Environmental Remediation

Functional Hybrid Nanomaterials for Environmental Remediation
Author: Ahmad Fauzi Ismail,Pei Sean Goh
Publsiher: Royal Society of Chemistry
Total Pages: 308
Release: 2021-09-24
ISBN 10: 1839165294
ISBN 13: 9781839165290
Language: EN, FR, DE, ES & NL

Functional Hybrid Nanomaterials for Environmental Remediation Book Review:

Functional and structural nanomaterials are emerging materials that display interesting physical and chemical properties because of their size and surface area to volume ratio. Applications for these materials include uses in removing pollutants from the environment. Looking at the current state-of-the-art as well as future trends in the use of nanomaterials for tackling environmental issues this book covers everything from the synthesis and characterisation of these materials to their use in the removal of specific contaminants. Functional Hybrid Nanomaterials for Environmental Remediation is a useful resource both for nanomaterial scientists interested in the real world application of hybrid nanomaterials and for environmental chemists and environmental engineers interested in novel materials for environmental remediation.

New Polymer Nanocomposites for Environmental Remediation

New Polymer Nanocomposites for Environmental Remediation
Author: Chaudhery Mustansar Hussain,Ajay Kumar Mishra
Publsiher: Elsevier
Total Pages: 756
Release: 2018-02-19
ISBN 10: 0128110341
ISBN 13: 9780128110348
Language: EN, FR, DE, ES & NL

New Polymer Nanocomposites for Environmental Remediation Book Review:

New Polymer Nanocomposites for Environmental Remediation summarizes recent progress in the development of materials’ properties, fabrication methods and their applications for treatment of contaminants, pollutant sensing and detection. This book presents current research into how polymer nanocomposites can be used in environmental remediation, detailing major environmental issues, and key materials properties and existing polymers or nanomaterials that can solve these issues. The book covers the fundamental molecular structure of polymers used in environmental applications, the toxicology, economy and life-cycle analysis of polymer nanocomposites, and an analysis of potential future applications of these materials. Recent research and development in polymer nanocomposites has inspired the progress and use of novel and cost-effective environmental applications. Presents critical, actionable guidelines to the structure and property design of nanocomposites in environmental remediation Focuses on taking technology out of the lab and into the real world Summarizes the latest developments in polymer nanocomposites and their applications in catalytic degradation, adsorptive removal and detection of contaminants in the environment Enables researchers to stay ahead of the curve, with a full discussion of regulatory issues and potential new applications and materials in this area

Natural Polymers

Natural Polymers
Author: Maya J. John,Sabu Thomas
Publsiher: Royal Society of Chemistry
Total Pages: 332
Release: 2012
ISBN 10: 1849734038
ISBN 13: 9781849734035
Language: EN, FR, DE, ES & NL

Natural Polymers Book Review:

This two volume set provides a valuable reference on natural polymer composites, including both natural and protein fibres, and natural polymer nanocomposites.

Bionanocomposites in Tissue Engineering and Regenerative Medicine

Bionanocomposites in Tissue Engineering and Regenerative Medicine
Author: Shakeel Ahmed,Annu Tomer
Publsiher: Woodhead Publishing
Total Pages: 672
Release: 2021-06-03
ISBN 10: 0128216344
ISBN 13: 9780128216347
Language: EN, FR, DE, ES & NL

Bionanocomposites in Tissue Engineering and Regenerative Medicine Book Review:

Bionanocomposites in Tissue Engineering and Regenerative Medicine explores novel uses of these in tissue engineering and regenerative medicine. This book offers an interdisplinary approach, combining chemical, biomedical engineering, materials science and pharmacological aspects of the characterization, synthesis and application of bionanocomposites. Chapters cover a broad selection of bionanocomposites including chitosan, alginate and more, which are utilized in tissue engineering, wound healing, bone repair, drug formulation, cancer therapy, drug delivery, cartilage regeneration and dental implants. Additional sections of Bionanocomposites in Tissue Engineering and Regenerative Medicine discuss, in detail, the safety aspects and circular economy of bionanocomposites – offering an insight into the commercial and industrial aspects of these important materials. Bionanocomposites in Tissue Engineering and Regenerative Medicine will prove a highly useful text for for those in the fields of biomedical engineering, chemistry, pharmaceutics and materials science, both in academia and industrial R&D groups. Each bionanocomposite type is covered individually, providing specific and detailed information for each material Covers a range of tissue engineering and regenerative medicine applications, from dental and bone engineering to cancer therapy Offers an integrated approach, with contributions from authors across a variety of related disciplines, including biomedical engineering, chemistry and materials science

Biopolymer Based Metal Nanoparticle Chemistry for Sustainable Applications

Biopolymer Based Metal Nanoparticle Chemistry for Sustainable Applications
Author: Mahmoud Nasrollahzadeh
Publsiher: Elsevier
Total Pages: 724
Release: 2021-03-05
ISBN 10: 0323898912
ISBN 13: 9780323898911
Language: EN, FR, DE, ES & NL

Biopolymer Based Metal Nanoparticle Chemistry for Sustainable Applications Book Review:

Biopolymers are becoming an increasingly important area of research as traditional chemical feedstocks run low and concerns about environmental impacts increase. One area of particular interest is their use for more sustainable development of metal nanoparticles. Biopolymer-Based Metal Nanoparticle Chemistry for Sustainability Applications, Volume 2 reviews key uses of biopolymers and biopolymer-based metal nanoparticles for a range of key sustainability-focused applications. After providing contextual examples of applications across the fields of food science, biomedicine and biochemistry, the book goes on to explore further sustainability-focused applications of Biopolymer-Based Metal Nanoparticles in such important areas as catalysis, environmental science, biosensing, and energy. Provides an overview of biopolymer-based metal nanoparticles for a wide range of applications Provides technological details on the synthesis of natural polymer-based metal nanoparticles Explores the role of biopolymer-based metal nanoparticles for more sustainable catalytic processes

Polymer Based Advanced Functional Materials for Energy and Environmental Applications

Polymer Based Advanced Functional Materials for Energy and Environmental Applications
Author: Nithin Kundachira Subramani
Publsiher: Springer Nature
Total Pages: 135
Release: 2022
ISBN 10: 9811687552
ISBN 13: 9789811687556
Language: EN, FR, DE, ES & NL

Polymer Based Advanced Functional Materials for Energy and Environmental Applications Book Review:

Polysaccharides as a Green and Sustainable Resources for Water and Wastewater Treatment

Polysaccharides as a Green and Sustainable Resources for Water and Wastewater Treatment
Author: Nurudeen A. Oladoja,Emmanuel I. Unuabonah,OMOTAYO S. AMUDA,Olatunji M. Kolawole
Publsiher: Springer
Total Pages: 110
Release: 2017-05-16
ISBN 10: 3319565990
ISBN 13: 9783319565996
Language: EN, FR, DE, ES & NL

Polysaccharides as a Green and Sustainable Resources for Water and Wastewater Treatment Book Review:

This brief critically reviews the structure and applications of polysaccharide based materials as a green and sustainable resource in water and water treatment operations. The authors present a fascinating insight into the application of this renewable resource in water and wastewater treatment operations approached from multiple perspectives: mechanistic insight into the coagulation efficiency of polysaccharides based coagulants; progress and prospects of polysaccharide composites as adsorbent for water and wastewater treatment; structural modifications of polysaccharides for enhanced performance as adsorbents; tuning polysaccharides framework for optimal coagulation efficiency; and tapping into microbial polysaccharides for water and wastewater purifications.This brief is aimed at professionals active in the science and engineering aspects of water and wastewater treatment operations.

Handbook of Polymer Nanocomposites for Industrial Applications

Handbook of Polymer Nanocomposites for Industrial Applications
Author: Chaudhery Mustansar Hussain
Publsiher: Elsevier
Total Pages: 782
Release: 2020-10-29
ISBN 10: 0128226692
ISBN 13: 9780128226698
Language: EN, FR, DE, ES & NL

Handbook of Polymer Nanocomposites for Industrial Applications Book Review:

Handbook of Polymer Nanocomposites for Industrial Applications summarizes the properties of polymer nanocomposites, discusses their industrial scale fabrication methods, and presents their applications for various industrial sectors at both experimental and theoretical models scales. The book also addresses existing challenges for the use of polymer nanocomposites in major industrial sectors. Overall, the aim of this book is to summarize the recent advancements in the use of PNCs in a variety of industry sectors. Particular attention is paid to those approaches that enable green and sustainable industrial developments. The legal, economical and toxicity aspects of polymer nanocomposite are also presented in detail. Comprehensively explores how polymer nanocomposites are being used to create more efficient products and devices in a variety of industry sectors Explores the environmental, legal, health and safety issues of using polymer nanocomposites in an industrial context Develops a roadmap to the wider commercial utilization of polymer nanocomposites Emphasizes the use of polymer nanocomposites in green and sustainable technologies

Eco friendly Functional Polymers

Eco friendly Functional Polymers
Author: Manuel Palencia,Tulio A. Lerma,Viviana Garcés,Mayra A. Mora,Jina M. Martínez,Sixta L. Palencia
Publsiher: Elsevier
Total Pages: 466
Release: 2021-07-25
ISBN 10: 0128218541
ISBN 13: 9780128218549
Language: EN, FR, DE, ES & NL

Eco friendly Functional Polymers Book Review:

There is a growing demand for strategies to address the impact of polymers and plastics in ecosystems. The principles of green chemistry offer a good source of such strategies. Ecofriendly Functional Polymers: An Approach from Application-Targeted Green Chemistry provides a holistic overview of polymer chemistry, development, and applications in the context of these sustainability-driven principles. It encourages researchers to consider the principles of green chemistry, environmental impacts, and end-user needs as integral aspects for consideration at the earliest stages of any design process, and draws together key aspects of polymer chemistry, organic synthesis, experimental design, and applications in a single volume. Beginning with an authoritative guide to fundamental polymer chemistry and its impact in the current environmental context, the book then discusses a range of key theoretical and experimental aspects of designing eco-friendly functional polymers. Applications of ecofriendly functional polymers across an entire range of fields are discussed, and a selection of case studies highlights the implementation of theoretical and experimental information to address a broad selection of issues. Highlights the physicochemical principles of green chemistry and the development of biodegradable and recyclable polymers in this context Compiles key information connecting structural features with properties, experimental strategies, and appropriate applications into a single volume Discusses requirements and applications across a broad range of fields, supported by practical examples

Polymer based Nanocomposites for Energy and Environmental Applications

Polymer based Nanocomposites for Energy and Environmental Applications
Author: Mohammad Jawaid,Mohammad Mansoob Khan
Publsiher: Woodhead Publishing
Total Pages: 700
Release: 2018-01-03
ISBN 10: 0081019114
ISBN 13: 9780081019115
Language: EN, FR, DE, ES & NL

Polymer based Nanocomposites for Energy and Environmental Applications Book Review:

Polymer-Based Nanocomposites for Energy and Environmental Applications provides a comprehensive and updated review of major innovations in the field of polymer-based nanocomposites for energy and environmental applications. It covers properties and applications, including the synthesis of polymer based nanocomposites from different sources and tactics on the efficacy and major challenges associated with successful scale-up fabrication. The chapters provide cutting-edge, up-to-date research findings on the use of polymer based nanocomposites in energy and environmental applications, while also detailing how to achieve material’s characteristics and significant enhancements in physical, chemical, mechanical and thermal properties. It is an essential reference for future research in polymer based nanocomposites as topics such as sustainable, recyclable and eco-friendly methods for highly innovative and applied materials are current topics of importance. Covers a wide range of research on polymer based nanocomposites Provides updates on the most relevant polymer based nanocomposites and their prodigious potential in the fields of energy and the environment Demonstrates systematic approaches and investigations from the design, synthesis, characterization and applications of polymer based nanocomposites Presents a useful reference and technical guide for university academics and postgraduate students (Masters and Ph.D.)

Carbon Nanomaterial Based Adsorbents for Water Purification

Carbon Nanomaterial Based Adsorbents for Water Purification
Author: Suprakas Sinha Ray,Rashi Gusain,Neeraj Kumar
Publsiher: Elsevier
Total Pages: 420
Release: 2020-06-27
ISBN 10: 0128219602
ISBN 13: 9780128219607
Language: EN, FR, DE, ES & NL

Carbon Nanomaterial Based Adsorbents for Water Purification Book Review:

The deterioration of water quality and unavailability of drinkable water are pressing challenges worldwide. The removal of toxic organic and inorganic pollutants from water is vital for a clean environment, as a response to water scarcity. Adsorption-based water technologies are among the most widely used because of their high efficiency and low cost, without relying on a complex infrastructure. In recent years, carbon nanomaterials (CNMs), such as graphene and derivatives, carbon nanotubes, carbon nanofibers, nanoporous carbon, fullerenes, graphitic carbon nitride, and nanodiamonds have been extensively exploited as adsorbents due to their extraordinary surface properties, ease of modification, large surface area, controlled structural varieties, high chemical stability, porosity, low density, ease of regeneration, and reusability. This book provides a thorough overview of the state of the art in carbon nanomaterials as they are used for adsorption applications in water purifications, as well as addressing their toxicological challenges. This volume primarily explores the fundamentals of adsorption, its mechanical aspects, synthesis and properties of CNMs, and adsorption performances of CNMs and their nanocomposites with organic and inorganic materials. Structural engineering and activation processes produce materials with enhanced adsorptive properties and separation efficiencies. Furthermore, the formation of CNMs with 2D and 3D macro-and microstructures and high porosities is a potential approach to improve adsorption performances and extend CNM use at the industrial level. The book also addresses important issues regarding these adsorbents that potentially affect future research and industrial applications of carbon-based nanoadsorbents in water security. Presents advances in multifunctional 3D superstructures of carbon nanomaterials and their composites for adsorption applications Outlines the fundamentals on synthesis and characterization techniques of carbon-based nanostructures and their composites Assesses the major toxicological challenges in using nanostructured materials as adsorbents for water purification

Green Composites for Automotive Applications

Green Composites for Automotive Applications
Author: Georgios Koronis,Arlindo Silva
Publsiher: Woodhead Publishing
Total Pages: 332
Release: 2018-11-10
ISBN 10: 008102178X
ISBN 13: 9780081021781
Language: EN, FR, DE, ES & NL

Green Composites for Automotive Applications Book Review:

Green Composites for Automotive Applications presents cutting-edge, comprehensive reviews on the industrial applications of green composites. The book provides an elaborative assessment of both academic and industrial research on eco-design, durability issues, environmental performance, and future trends. Particular emphasis is placed on the processing and characterization of green composites, specific types of materials, such as thermoset and thermoplastic, nanocomposites, sandwich, and polymer biofoams. Additional sections cover lifecycle and risk analysis. As such, this book is an essential reference resource for R&D specialists working in materials science, automotive, chemical, and environmental engineering, as well as R&D managers in industry. Contains contributions from leading experts in the field Covers experimental, analytical and numerical analysis Deals with most important automotive aspects Provides a special section dedicated to lifecycle assessment

Green Synthesis Characterization and Applications of Nanoparticles

Green Synthesis  Characterization and Applications of Nanoparticles
Author: Ashutosh Kumar Shukla,Siavash Iravani
Publsiher: Elsevier
Total Pages: 548
Release: 2018-11-26
ISBN 10: 0081025807
ISBN 13: 9780081025802
Language: EN, FR, DE, ES & NL

Green Synthesis Characterization and Applications of Nanoparticles Book Review:

Green Synthesis, Characterization and Applications of Nanoparticles shows how eco-friendly nanoparticles are engineered and used. In particular, metal nanoparticles, metal oxide nanoparticles and other categories of nanoparticles are discussed. The book outlines a range of methodologies and explores the appropriate use of each. Characterization methods include spectroscopic, microscopic and diffraction methods, but magnetic resonance methods are also included as they can be used to understand the mechanism of nanoparticle synthesis using organisms. Applications covered include targeted drug delivery, water purification and hydrogen generation. This is an important research resource for those wishing to learn more about how eco-efficient nanoparticles can best be used. Theoretical details and mathematical derivations are kept to a necessary minimum to suit the need of interdisciplinary audiences and those who may be relatively new to the field. Explores recent trends in growth, characterization, properties and applications of nanoparticles Gives readers an understanding on how they are applied through the use of case studies and examples Assesses the advantages and disadvantages of a variety of synthesis and characterization techniques for green nanoparticles in different situations