Advanced Sample Preparation Techniques For Surface Spectroscopy Analysis Of Organic

Download Advanced Sample Preparation Techniques For Surface Spectroscopy Analysis Of Organic full books in PDF, epub, and Kindle. Read online Advanced Sample Preparation Techniques For Surface Spectroscopy Analysis Of Organic ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!

Advanced Sample Preparation Techniques for Surface Spectroscopy Analysis of Organic

Author : Smrutirekha Mishra
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (139 download)

DOWNLOAD NOW!

Book Synopsis Advanced Sample Preparation Techniques for Surface Spectroscopy Analysis of Organic by : Smrutirekha Mishra

Download or read book Advanced Sample Preparation Techniques for Surface Spectroscopy Analysis of Organic written by Smrutirekha Mishra and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silica due to its large inorganic amorphous wall and hydrophilic surface properties renders its suitability for designing different varieties of organic,Äìinorganic silica-based materials. Characterization of such hybrid silica-based materials is one of the fascinating as well as challenging topics to be covered. Surface analysis of these hybrid materials can be done utilizing various techniques, out of which X-ray photoelectron spectroscopy (XPS), 29Si Solid-state Nuclear magnetic resonance (NMR) spectroscopy, and Fourier-transform infrared spectroscopy (FTIR) is the most ideal ones. Thus, before analyzing these silica materials, it requires a massive study on its sample preparation for appropriate characterization of the organic molecules present in the inorganic network. Hence, this chapter will give a brief elucidation of the sample preparation techniques for analyzing the hybrid materials utilizing the above instrumentation techniques.

Sample Preparation Techniques for Chemical Analysis

Author : Massoud Kaykhaii
Publisher : BoD – Books on Demand
ISBN 13 : 1839692146
Total Pages : 109 pages
Book Rating : 4.8/5 (396 download)

DOWNLOAD NOW!

Book Synopsis Sample Preparation Techniques for Chemical Analysis by : Massoud Kaykhaii

Download or read book Sample Preparation Techniques for Chemical Analysis written by Massoud Kaykhaii and published by BoD – Books on Demand. This book was released on 2021-12-22 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite having powerful software, microchips, and solid-state detectors that enable analytical chemists to achieve fast, stable, and accurate signals from their instruments, sample preparation is the most important step in chemical analysis. Issues can arise at this step for various reasons, including a low concentration of analytes, incompatibility of the sample with the analytical instrument, and matrix interferences. This volume discusses the basics of sample preparation and examines modern techniques that can be used by both novice and expert analytical chemists. Chapters review microextraction, surface spectroscopy analysis, and techniques for particle, tissue, and cellular separation.

Sample Preparation Techniques in Analytical Chemistry

Author : Somenath Mitra
Publisher : John Wiley & Sons
ISBN 13 : 0471457825
Total Pages : 480 pages
Book Rating : 4.4/5 (714 download)

DOWNLOAD NOW!

Book Synopsis Sample Preparation Techniques in Analytical Chemistry by : Somenath Mitra

Download or read book Sample Preparation Techniques in Analytical Chemistry written by Somenath Mitra and published by John Wiley & Sons. This book was released on 2004-04-07 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: The importance of accurate sample preparation techniques cannot be overstated--meticulous sample preparation is essential. Often overlooked, it is the midway point where the analytes from the sample matrix are transformed so they are suitable for analysis. Even the best analytical techniques cannot rectify problems generated by sloppy sample pretreatment. Devoted entirely to teaching and reinforcing these necessary pretreatment steps, Sample Preparation Techniques in Analytical Chemistry addresses diverse aspects of this important measurement step. These include: * State-of-the-art extraction techniques for organic and inorganic analytes * Sample preparation in biological measurements * Sample pretreatment in microscopy * Surface enhancement as a sample preparation tool in Raman and IR spectroscopy * Sample concentration and clean-up methods * Quality control steps Designed to serve as a text in an undergraduate or graduate level curriculum, Sample Preparation Techniques in Analytical Chemistry also provides an invaluable reference tool for analytical chemists in the chemical, biological, pharmaceutical, environmental, and materials sciences.

Sample Preparation with Nanomaterials

Author : Chaudhery Mustansar Hussain
Publisher : John Wiley & Sons
ISBN 13 : 3527685618
Total Pages : 304 pages
Book Rating : 4.5/5 (276 download)

DOWNLOAD NOW!

Book Synopsis Sample Preparation with Nanomaterials by : Chaudhery Mustansar Hussain

Download or read book Sample Preparation with Nanomaterials written by Chaudhery Mustansar Hussain and published by John Wiley & Sons. This book was released on 2021-04-30 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discover this timely, comprehensive, and up-to-date exploration of crucial aspects of the use of nanomaterials in analytical chemistry Sample Preparation with Nanomaterials: Next Generation Techniques for Sample Preparation delivers insightful and complete overview of recent progress in the use of nanomaterials in sample preparation. The book begins with an overview of special features of nanomaterials and their applications in analytical sciences. Important types of nanomaterials, like carbon nanotubes and magnetic particles, are reviewed and biological sample preparation and lab-on-a-chip systems are presented. The distinguished author places special emphasis on approaches that tend to green and reduce the cost of sample treatment processes. He also discusses the legal, economical, and toxicity aspects of nanomaterial samples. This book includes extensive reference material, like a complete list of manufacturers, that makes it invaluable for professionals in analytical chemistry. Sample Preparation with Nanomaterials offers considerations of the economic aspects of nanomaterials, as well as the assessment of their toxicity and risk. Readers will also benefit from the inclusion of: A thorough introduction to nanomaterials in the analytical sciences and special properties of nanomaterials for sample preparation An exploration of the mechanism of adsorption and desorption on nanomaterials, including carbon nanomaterials used as adsorbents Discussions of membrane applications of nanomaterials, surface enhanced raman spectroscopy, and the use of nanomaterials for biological sample preparation A treatment of magnetic nanomaterials, lab-on-a-chip nanomaterials, and toxicity and risk assessment of nanomaterials Perfect for analytical chemists, materials scientists, and process engineers, Sample Preparation with Nanomaterials: Next Generation Techniques for Sample Preparation will also earn a place in the libraries of analytical laboratories, universities, and companies who conduct research into nanomaterials and seek a one-stop resource for sample preparation.

Comprehensive Sampling and Sample Preparation

Author : Josep M. Bayona
Publisher : Academic Press
ISBN 13 : 0123813743
Total Pages : 2998 pages
Book Rating : 4.1/5 (238 download)

DOWNLOAD NOW!

Book Synopsis Comprehensive Sampling and Sample Preparation by : Josep M. Bayona

Download or read book Comprehensive Sampling and Sample Preparation written by Josep M. Bayona and published by Academic Press. This book was released on 2012-12-31 with total page 2998 pages. Available in PDF, EPUB and Kindle. Book excerpt: Comprehensive Sampling and Sample Preparation is a complete treatment of the theory and methodology of sampling in all physical phases and the theory of sample preparation for all major extraction techniques. It is the perfect starting point for researchers and students to design and implement their experiments and support those experiments with quality-reviewed background information. In its four volumes, fundamentals of sampling and sample preparation are reinforced through broad and detailed sections dealing with Biological and Medical, Environmental and Forensic, and Food and Beverage applications. The contributions are organized to reflect the way in which analytical chemists approach a problem. It is intended for a broad audience of analytical chemists, both educators and practitioners of the art and can assist in the preparation of courses as well in the selection of sampling and sample preparation techniques to address the challenges at hand. Above all, it is designed to be helpful in learning more about these topics, as well as to encourage an interest in sampling and sample preparation by outlining the present practice of the technology and by indicating research opportunities. Sampling and Sample preparation is a large and well-defined field in Analytical Chemistry, relevant for many application areas such as medicine, environmental science, biochemistry, pharmacology, geology, and food science. This work covers all these aspects and will be extremely useful to researchers and students, who can use it as a starting point to design and implement their experiments and for quality-reviewed background information There are limited resources that Educators can use to effectively teach the fundamental aspects of modern sample preparation technology. Comprehensive Sampling and Sample Preparation addresses this need, but focuses on the common principles of new developments in extraction technologies rather than the differences between techniques thus facilitating a more thorough understanding Provides a complete overview of the field. Not only will help to save time, it will also help to make correct assessments and avoid costly mistakes in sampling in the process Sample and sample preparation are integral parts of the analytical process but are often less considered and sometimes even completely disregarded in the available literature. To fill this gap, leading scientists have contributed 130 chapters, organized in 4 volumes, covering all modern aspects of sampling and liquid, solid phase and membrane extractions, as well as the challenges associated with different types of matrices in relevant application areas

Development of Alternative Green Sample Preparation Techniques

Author : Emanuela Gionfriddo
Publisher : MDPI
ISBN 13 : 3039434683
Total Pages : 230 pages
Book Rating : 4.0/5 (394 download)

DOWNLOAD NOW!

Book Synopsis Development of Alternative Green Sample Preparation Techniques by : Emanuela Gionfriddo

Download or read book Development of Alternative Green Sample Preparation Techniques written by Emanuela Gionfriddo and published by MDPI. This book was released on 2020-11-23 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Special Issue of Separations, “Development of Alternative Green Sample Preparation Techniques”, provides an overview on recent trends in green sample preparation. This Special Issue of Separations collates 11 impressive contributions that describe the state-of-the-art in the development of green extraction technologies, from green materials for microextraction to the development of new sampling devices geometries for enhanced extraction efficiency and analysis throughput.

Sampling and Sample Preparation in Field and Laboratory

Author : Janusz Pawliszyn
Publisher : Elsevier
ISBN 13 : 9780444505101
Total Pages : 1170 pages
Book Rating : 4.5/5 (51 download)

DOWNLOAD NOW!

Book Synopsis Sampling and Sample Preparation in Field and Laboratory by : Janusz Pawliszyn

Download or read book Sampling and Sample Preparation in Field and Laboratory written by Janusz Pawliszyn and published by Elsevier. This book was released on 2002-09-09 with total page 1170 pages. Available in PDF, EPUB and Kindle. Book excerpt: This title is the first comprehensive book on sampling and modern sample preparation techniques and has several main objectives: to facilitate recognition of sample preparation as both an integral part of the analytical process; to present a fundamental basis and unified theoretical approach for the professional development of sample preparation; to emphasize new developments in sample preparation technology; and to highlight the future impact of sample preparation on new directions in analytical science, particularly automation, miniaturization and field implementation. Until recently, there has been relatively little scientific interest in sampling and sample preparation, however this situation is presently changing as sampling and sample preparation become integral parts of the analytical process with their own unique challenges and research opportunities. Sampling and Sample Preparation for Field and Laboratory is an essential resource for all analytical chemists, and in particular those involved in method development. Not only does it cover the fundamental aspects of extraction, it also covers applications in various matrices and includes sampling strategies and equipment and how these can be integrated into the analytical process for maximum efficiency.

Analytical Sample Preparation With Nano- and Other High-Performance Materials

Author : Rafael Lucena
Publisher : Elsevier
ISBN 13 : 0128221720
Total Pages : 573 pages
Book Rating : 4.1/5 (282 download)

DOWNLOAD NOW!

Book Synopsis Analytical Sample Preparation With Nano- and Other High-Performance Materials by : Rafael Lucena

Download or read book Analytical Sample Preparation With Nano- and Other High-Performance Materials written by Rafael Lucena and published by Elsevier. This book was released on 2021-10-23 with total page 573 pages. Available in PDF, EPUB and Kindle. Book excerpt: Analytical Sample Preparation With Nano- and Other High-Performance Materials covers advanced sample treatment techniques and the new materials that can be used to boost their performance. The evolution of sample treatment over the last two decades has resulted in the development of new techniques and application of new materials. This is a must-have resource for those studying advanced analytical techniques and the role of high-performance materials in analytical chemistry. The book explains the underlying principles needed to properly understand sample preparation, and also examines the latest materials - including nanomaterials - that result in greater sensitivity and specificity. The book begins with a section devoted to all the various sample preparation techniques and then continues with sections on high-performance sorbents and high-performance solvents. - Combines basic, fundamental principles and advanced concepts and applications for a comprehensive treatment of sample preparation with new materials - Defines nano- and other high-performance materials in this context, including carbon nanoparticles, inorganic nanoparticles, ionic liquids, supramolecular solvents, and more - Includes discussion of all the latest advancements and new findings in both techniques and materials used for proper sample preparation

Organic Trace Analysis

Author : Reinhard Nießner
Publisher : Walter de Gruyter GmbH & Co KG
ISBN 13 : 3111165205
Total Pages : 472 pages
Book Rating : 4.1/5 (111 download)

DOWNLOAD NOW!

Book Synopsis Organic Trace Analysis by : Reinhard Nießner

Download or read book Organic Trace Analysis written by Reinhard Nießner and published by Walter de Gruyter GmbH & Co KG. This book was released on 2024-09-23 with total page 472 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic contaminants even in very low concentrations can have toxic and ecotoxic effects on exposed organisms. Detection and quantification of such trace amounts in diverging matrices (e.g., water, air, soil, food, tissue, organisms) is challenging and great carefulness and strategic thinking is needed to get reliable results along the way from taking samples up to the final analysis. In the 2nd edition, besides revisions of existing chapters, new analytical technologies and recent application examples are presented: non-target mass spectrometric analysis, trace analysis of per- and polyfluoroalkylated "forever chemicals", organophosphorus esters (nerve agents), and micro- and nanoplastic particles in the environment. Students will learn about peculiarities and state of the art organic trace analysis and acquire basic and advanced principles of statistical evaluation of analytical results quality control strategies and good laboratory practices sampling techniques from various matrices sample treatment, enrichment and clean-up techniques chromatographic analyses including hyphenated techniques, and spectroscopy as well mass spectrometry and bioanalytical tools. An extended chapter on selected applications will transfer the theoretical understanding into applied scientific problems. Students will profit from a comprehensive and state of the art overview of organic trace analyses and from an extensive collection of relevant literature.

Advanced Topics in Organic Chemistry

Author : Cybellium
Publisher : Cybellium
ISBN 13 : 1836790481
Total Pages : 222 pages
Book Rating : 4.8/5 (367 download)

DOWNLOAD NOW!

Book Synopsis Advanced Topics in Organic Chemistry by : Cybellium

Download or read book Advanced Topics in Organic Chemistry written by Cybellium and published by Cybellium. This book was released on with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Welcome to the forefront of knowledge with Cybellium, your trusted partner in mastering the cutting-edge fields of IT, Artificial Intelligence, Cyber Security, Business, Economics and Science. Designed for professionals, students, and enthusiasts alike, our comprehensive books empower you to stay ahead in a rapidly evolving digital world. * Expert Insights: Our books provide deep, actionable insights that bridge the gap between theory and practical application. * Up-to-Date Content: Stay current with the latest advancements, trends, and best practices in IT, Al, Cybersecurity, Business, Economics and Science. Each guide is regularly updated to reflect the newest developments and challenges. * Comprehensive Coverage: Whether you're a beginner or an advanced learner, Cybellium books cover a wide range of topics, from foundational principles to specialized knowledge, tailored to your level of expertise. Become part of a global network of learners and professionals who trust Cybellium to guide their educational journey. www.cybellium.com

Surface Analysis

Author : John C. Vickerman
Publisher : John Wiley & Sons
ISBN 13 : 1119965519
Total Pages : 690 pages
Book Rating : 4.1/5 (199 download)

DOWNLOAD NOW!

Book Synopsis Surface Analysis by : John C. Vickerman

Download or read book Surface Analysis written by John C. Vickerman and published by John Wiley & Sons. This book was released on 2011-08-10 with total page 690 pages. Available in PDF, EPUB and Kindle. Book excerpt: This completely updated and revised second edition of Surface Analysis: The Principal Techniques, deals with the characterisation and understanding of the outer layers of substrates, how they react, look and function which are all of interest to surface scientists. Within this comprehensive text, experts in each analysis area introduce the theory and practice of the principal techniques that have shown themselves to be effective in both basic research and in applied surface analysis. Examples of analysis are provided to facilitate the understanding of this topic and to show readers how they can overcome problems within this area of study.

Green Sample Preparation Techniques

Author : Chaudhery Mustansar Hussain
Publisher : Royal Society of Chemistry
ISBN 13 : 1839166428
Total Pages : 317 pages
Book Rating : 4.8/5 (391 download)

DOWNLOAD NOW!

Book Synopsis Green Sample Preparation Techniques by : Chaudhery Mustansar Hussain

Download or read book Green Sample Preparation Techniques written by Chaudhery Mustansar Hussain and published by Royal Society of Chemistry. This book was released on 2023-06-30 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is a trend in analytical chemistry towards development of eco-friendly methods of sample preparation without loss of efficiency. This book provides a general, critical, and updated vision of the different green sample preparation approaches that have been developed. These include miniaturisation of the extraction techniques that allow a reduction not only of the chemicals used during the process, but also of the sample amount; the use of greener solvents, such as certain ionic liquids (ILs) or deep eutectic solvents (DES), instead of conventional organic solvents; and the use of new selective sorbent materials that allow both extraction and clean-up in the same step. All of these strategies have been successfully applied to the determination of a wide variety of organic and inorganic compounds. Advanced undergraduate and graduate students will find this book a good reference source and, because of the multidisciplinary nature of this topic, it will be of use to a broad audience including chemists, materials scientists, environmental analysts, forensic scientists, pharmacists, biologists and chemical engineers, who are involved and interested in the future frontiers of analytical chemistry.

Ion Spectroscopies for Surface Analysis

Author : Alvin W. Czanderna
Publisher : Springer Science & Business Media
ISBN 13 : 1461537088
Total Pages : 479 pages
Book Rating : 4.4/5 (615 download)

DOWNLOAD NOW!

Book Synopsis Ion Spectroscopies for Surface Analysis by : Alvin W. Czanderna

Download or read book Ion Spectroscopies for Surface Analysis written by Alvin W. Czanderna and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 479 pages. Available in PDF, EPUB and Kindle. Book excerpt: Determining the elemental composition of surfaces is an essential measurement in characterizing solid surfaces. At present, many ap proaches may be applied for measuring the elemental and molecular composition of a surface. Each method has particular strengths and limitations that often are directly connected to the physical processes involved. Typically, atoms and molecules on the surface and in the near surface region may be excited by photons, electrons, ions, or neutrals, and the detected particles are emitted, ejected, or scattered ions or electrons. The purpose of this book is to bring together a discussion of the surface compositional analysis that depends on detecting scattered or sputtered ions, and the methods emphasized are those where instruments are commercially available for carrying out the analysis. For each topic treated, the physical principles, instrumentation, qualitative analysis, artifacts, quantitative analysis, applications, opportunities, and limita tions are discussed. The first chapter provides an overview of the role of elemental composition in surface science; compositional depth profiling; stimulation by an electric field, electrons, neutrals, or photons and detection of ions; and then stimulation by ions, and detection of ions, electrons, photons, or neutrals.

Sample Preparation in Biological Mass Spectrometry

Author : Alexander R. Ivanov
Publisher : Springer Science & Business Media
ISBN 13 : 9400708289
Total Pages : 1081 pages
Book Rating : 4.4/5 (7 download)

DOWNLOAD NOW!

Book Synopsis Sample Preparation in Biological Mass Spectrometry by : Alexander R. Ivanov

Download or read book Sample Preparation in Biological Mass Spectrometry written by Alexander R. Ivanov and published by Springer Science & Business Media. This book was released on 2011-06-15 with total page 1081 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this book is to provide the researcher with important sample preparation strategies in a wide variety of analyte molecules, specimens, methods, and biological applications requiring mass spectrometric analysis as a detection end-point. In this volume we have compiled the contributions from several laboratories which are employing mass spectrometry for biological analysis. With the latest inventions and introduction of highly sophisticated mass spectrometry equipment sample preparation becomes an extremely important bottleneck of biomedical analysis. We have a goal of giving the reader several successful examples of sample preparation, development and optimization, leading to the success in analytical steps and proper conclusions made at the end of the day. This book is structured as a compilation of contributed chapters ranging from protocols to research articles and reviews. The main philosophy of this volume is that sample preparation methods have to be optimized and validated for every project, for every sample type and for every downstream analytical technique.

Instrumentation for Trace Organic Monitoring

Author : Raymond E. Clement
Publisher : CRC Press
ISBN 13 : 1351090623
Total Pages : 593 pages
Book Rating : 4.3/5 (51 download)

DOWNLOAD NOW!

Book Synopsis Instrumentation for Trace Organic Monitoring by : Raymond E. Clement

Download or read book Instrumentation for Trace Organic Monitoring written by Raymond E. Clement and published by CRC Press. This book was released on 2018-02-01 with total page 593 pages. Available in PDF, EPUB and Kindle. Book excerpt: Instrumentation for Trace Organic Monitoring provides comprehensive coverage of instrumental analysis techniques for trace organic analytes in environmental analysis. Sampling/sample preparation is discussed, in addition to mass spectrometry techniques, including GC-MS, HRMS, LCMS, APIMS, and MS-MS. This important book also covers new chromatography techniques, supercritical fluid, solid-phase extraction, and ion mobility spectrometry, which is a new ultra-sensitive technique. Difficult problems, such as dioxin/furan analysis, organometallic speciation, atmospheric organic vapors, water analysis, and flyash toxicity testing are addressed.

Miniaturization in Sample Preparation

Author : Francisco Pena Pereira
Publisher : Walter de Gruyter GmbH & Co KG
ISBN 13 : 3110427265
Total Pages : 411 pages
Book Rating : 4.1/5 (14 download)

DOWNLOAD NOW!

Book Synopsis Miniaturization in Sample Preparation by : Francisco Pena Pereira

Download or read book Miniaturization in Sample Preparation written by Francisco Pena Pereira and published by Walter de Gruyter GmbH & Co KG. This book was released on 2014-01-01 with total page 411 pages. Available in PDF, EPUB and Kindle. Book excerpt: Miniaturization is a challenge thrown down to analytical chemistry. The replacement of conventional analytical systems by miniaturized alternatives during the last years is noticeable. Specifically, the miniaturization of traditional sample preparation techniques (e.g., solid-phase extraction or solvent extraction) led to the development of environmentally benign analytical methods. This book aims to provide an overview of the challenges and achievements inthe application of the miniaturized sample preparation methods in analytical laboratories. It includes both theoretical and practical aspects of miniaturized sample preparation approaches and hence should be of interest to researchers, students and teachers of analytical and bioanalytical chemistry, environmental sciences and environmental engineering.

Sample Preparation Techniques in Analytical Chemistry

Author : Somenath Mitra
Publisher : Wiley-Interscience
ISBN 13 : 9780471328452
Total Pages : 488 pages
Book Rating : 4.3/5 (284 download)

DOWNLOAD NOW!

Book Synopsis Sample Preparation Techniques in Analytical Chemistry by : Somenath Mitra

Download or read book Sample Preparation Techniques in Analytical Chemistry written by Somenath Mitra and published by Wiley-Interscience. This book was released on 2003-09-26 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: The importance of accurate sample preparation techniques cannot be overstated--meticulous sample preparation is essential. Often overlooked, it is the midway point where the analytes from the sample matrix are transformed so they are suitable for analysis. Even the best analytical techniques cannot rectify problems generated by sloppy sample pretreatment. Devoted entirely to teaching and reinforcing these necessary pretreatment steps, Sample Preparation Techniques in Analytical Chemistry addresses diverse aspects of this important measurement step. These include: * State-of-the-art extraction techniques for organic and inorganic analytes * Sample preparation in biological measurements * Sample pretreatment in microscopy * Surface enhancement as a sample preparation tool in Raman and IR spectroscopy * Sample concentration and clean-up methods * Quality control steps Designed to serve as a text in an undergraduate or graduate level curriculum, Sample Preparation Techniques in Analytical Chemistry also provides an invaluable reference tool for analytical chemists in the chemical, biological, pharmaceutical, environmental, and materials sciences.