Organized into 15 chapters, this book begins with an overview of the spectral analysis and the dependence of chemical shifts and J couplings on structure. This text then discusses the isomerism in polymer chains without special reference to NMR. Other chapters consider the interpretation of synthetic polymer spectra in terms of structure, stereochemical configuration, conformation, and chain growth mechanism. This book discusses as well the application of high resolution NMR to the study of nucleic acids, which has not been so well developed as that of polypeptides and proteins. The final chapter deals with biopolymers and their model compounds.
This book is a valuable resource for chemists and research workers.
As a new mom, Jessica Alba wanted to create the safest, healthiest environment for her family. But she was frustrated by the lack of trustworthy information on how to live healthier and cleaner--delivered in a way that a busy mom could act on without going to extremes. In 2012, with serial entrepreneur Brian Lee and environmental advocate Christopher Gavigan, she launched The Honest Company, a brand where parents can find reliable information and products that are safe, stylish, and affordable. The Honest Life shares the insights and strategies she gathered along the way.
The Honest Life recounts Alba's personal journey of discovery and reveals her tips for making healthy living fun, real, and stylish, while offering a candid look inside her home and daily life. She shares strategies for maintaining a clean diet (with favorite family-friendly recipes) and embraces nontoxic choices at home and provides eco-friendly decor tips to fit any budget. Alba also discusses cultivating a daily eco beauty routine, finding one's personal style without resorting to yoga pants, and engaging in fun, hands-on activities with kids. Her solutions are easy, chic, and down-to-earth: they're honest. And discovering everyday ways to live naturally and authentically--true to you--could be honestly life-changing.
The highly-anticipated paperback edition of The Elements is finally available.
An eye-opening, original collection of gorgeous, never-before-seen photographic representations of the 118 elements in the periodic table.
The elements are what we, and everything around us, are made of. But how many elements has anyone actually seen in pure, uncombined form? The Elements provides this rare opportunity. Based on seven years of research and photography, the pictures in this book make up the most complete, and visually arresting, representation available to the naked eye of every atom in the universe. Organized in order of appearance on the periodic table, each element is represented by a spread that includes a stunning, full-page, full-color photograph that most closely represents it in its purest form. For example, at -183°C, oxygen turns from a colorless gas to a beautiful pale blue liquid.
Also included are fascinating facts, figures, and stories of the elements as well as data on the properties of each, including atomic weight, density, melting and boiling point, valence, electronegativity, and the year and location in which it was discovered. Several additional photographs show each element in slightly altered forms or as used in various practical ways. The element's position on the periodic table is pinpointed on a mini rendering of the table and an illustrated scale of the element's boiling and/or melting points appears on each page along with a density scale that runs along the bottom.
Packed with interesting information, this combination of solid science and stunning artistic photographs is the perfect gift book for every sentient creature in the universe.
Includes a tear-out poster of Theodore Gray's iconic Photographic Periodic Table!
Fortunately, there's Schaum's. This all-in-one-package includes more than 650 fully solved problems, examples, and practice exercises to sharpen your problem-solving skills. Plus, you will have access to 16 detailed videos featuring Chemistry instructors who explain the most commonly tested concepts--it's just like having your own virtual tutor! You'll find everything you need to build confidence, skills, and knowledge for the highest score possible.
More than 40 million students have trusted Schaum's to help them succeed in the classroom and on exams. Schaum's is the key to faster learning and higher grades in every subject. Each Outline presents all the essential course information in an easy-to-follow, topic-by-topic format. You also get hundreds of examples, solved problems, and practice exercises to test your skills.
This Schaum's Outline gives you673 fully solved problems Hundreds of examples with explanations of chemistry concepts Support for all the major textbooks for beginning chemistry courses
Fully compatible with your classroom text, Schaum's highlights all the important facts you need to know. Use Schaum’s to shorten your study time--and get your best test scores!Schaum’s Outlines--Problem Solved.
Herbal remedies have been around for years and many people count on them every day. Some carry a strong belief that there is no need to rely on medications. Among the alternative medicine approaches, essential oils are used for a number of different conditions and offer a variety of benefits.
After a stress filled day, it would be nice to come home and just relax. Some have found that they can get fast relaxation by taking a warm bath using essential oils. A mix of the oils and the aromas can relax one so much that it puts the client to sleep.
Because essential oils are extracted from plant material, they often contain the nutritional essence of the plants themselves. In concentrated form, they can impart huge health benefits, when they are ingested into the body.
Essential Oils will guide you through the various uses and benefits of essential oils, highlighting how to use them to lose weight, relieve pain, maintain your skin, as well as strengthen your hair. The various uses of essential oils is nearly limitless. Come discover what many others have: that there is now a safer, more natural way to protect yourself and your family.
Whether you're new to biosynthesis, integrated metabolism, and the molecular cloning of DNA or just brushing up on those topics, CliffsQuickReview Organic Chemistry II can help. This guide introduces each topic, defines key terms, and walks you through each sample problem step-by-step. In no time, you'll be ready to tackle other concepts in this book such asThe reactions of aromatic compoundsAldol, cross-aldol, and ketonic aldol condensationEster formationOxidationMass spectra
CliffsQuickReview Organic Chemistry II acts as a supplement to your textbook and to classroom lectures. Use this reference in any way that fits your personal style for study and review — you decide what works best with your needs. You can either read the book from cover to cover or just look for the information you want and put it back on the shelf for later. What's more, you canGet a glimpse of what you’ll gain from a chapter by reading through the introduction at the beginning of each chapterStudy your formulas in the Summary of Preparations or the Summary of ReactionsUse the glossary to find key terms fast.
With titles available for all the most popular high school and college courses, CliffsQuickReview guides are a comprehensive resource that can help you get the best possible grades.
Assuming no prior knowledge, the book discusses everything from the simplest mixed acid nitration of toluene, to the complex synthesis of highly energetic caged nitro compounds.Reviews laboratory and industrial methods, which can be used to introduce aliphatic C-nitro, aromatic C-nitro, N-nitro, and nitrate ester functionality into organic compounds Discusses the advantages and disadvantages of each synthetic method or route, with scope, limitations, substrate compatibility and other important considerations Features numerous examples in the form of text, reaction diagrams, and tables.
Drawing on the expertise of leading researchers in their fields, Current Topics in Elastomers Research provides the first comprehensive overview of rubber research activities from around the world. Divided into seven sections, this seminal work begins with a general introduction before presenting the chemistry and structure-property relationships of a variety of new materials and composites. The second section covers the most important rubber ingredients along with the current thinking on their mechanism of action.
Two important new characterization techniques, 3D-TEM and AFM, are evaluated in the third section, while the fourth considers the physics and engineering aspects of elastomers, including reinforcement mechanisms, viscoelastic properties, fatigue life, abrasion, adhesion, rheology, mixing and processing, and the effects of time, temperature and fluids. The fifth section pays respect to the tire, a driving impetus for research and one of the major applications of rubber. Finally, the book includes two chapters on eco-friendly technology and recycling, perhaps the most important engineering topic in this age of globalization and environmental responsibility.
Barring the inaccessibility of truly classified information, Current Topics in Elastomers Research is a complete review of current elastomers research and applications, compiling once-guarded knowledge and outlining the future directions of the field.
The first book to consider this topic, Click Chemistry for Biotechnology and Materials Science examines the fundamentals of click chemistry, its application to the precise design and synthesis of macromolecules, and its numerous applications in materials science and biotechnology. The book surveys the current research, discusses emerging trends and future applications, and provides an important nucleation point for research.
Edited by one of the top 100 young innovators with the greatest potential to have an impact on technology in the 21st century according to Technology Review and with contributions from pioneers in the field, Click Chemistry for Biotechnology and Materials Science provides an ideal reference for anyone wanting to learn more about click reactions.
• first to provide exam data-mining in study guide
• allow students to focus on most examined concepts – cut study time and increase efficiency
• an expert guide to lead one abstract knowledge and wisdom
• provides exact, accurate, complete and independent self–education
• the only guide currently that covers Planning Questions
• advanced trade book
• complete and concise eBook editions available
• also suitable for
• Cambridge GCE AL (H1/H2)
• Cambridge International A & AS Level
• Books available for other subjects including Physics, Chemistry, Biology, Mathematics, Economics, English
• Primary level, Secondary level, GCE O-level, GCE A-level, iGCSE, Cambridge A-level, Hong Kong DSE
• visit www.yellowreef.com for sample chapters and more
Aimed at a wide readership ranging from educated laypeople and students to practitioners in engineering and environmental science.
Microorganisms in Foods 5, 7, and the second edition of Microorganisms in Foods 6 are for anyone using microbiological testing and/or engaged in setting Microbiological Criteria, whether for the purpose of Governmental Food Inspection and Control or in Industry, and for those identifying the most effective use of microbiological testing in the food chain. The contents are essential reading for food processors, food microbiologists, food technologists, veterinarians, public health workers and regulatory officials. For students in Food Science and Technology they offer a wealth of information on Food Microbiology and Food Safety Management, with many references for further study.
The information has been prepared by the International Commission on Microbiological Specifications for Foods (ICMSF). The ICMSF was formed in response to the need for internationally acceptable and authoritative decisions on microbiological limits for foods moving in international commerce. Currently the membership consists of eighteen food microbiologists from eleven countries, drawn from governmental laboratories in public health, agriculture, and food technology, from universities and from the food industry.
* The first reference work on named reactions to present colored schemes for easier understanding
* 250 frequently used named reactions are presented in a convenient two-page layout with numerous examples
* An opening list of abbreviations includes both structures and chemical names
* Contains more than 10,000 references grouped by seminal papers, reviews, modifications, and theoretical works
* Appendices list reactions in order of discovery, group by contemporary usage, and provide additional study tools
* Extensive index quickly locates information using words found in text and drawings
Note: CD-ROM/DVD and other supplementary materials are not included as part of eBook file.
This comprehensive, well structured handbook presents the fundamental principles and the recent advances in carbene complex chemistry. Arranged according to structure and reactivity, all relevant classes of carbene complexes, their generation, and application in organic synthesis are discussed in detail. Critically selected, up-to-date references and valuable experimental procedures await the reader. Every chemist searching for a concise introduction and reference work for carbene complex chemistry will welcome this practical guide.
"...this concise presentation of all the aspects of the use of carbene complexes in synthesis will help provide the impetus for even more rapid developments in this field of research." R. H. Grubbs (Caltech)
Providing a comprehensive overview of chemosensors—organic molecules designed to bind and sense small molecules or metal ions—and their applications, Chemosensors: Principles, Strategies, and Applications is an accessible one-stop resource for analysts, clinicians, and graduate students studying advanced chemistry and chemosensing.
Chemosensors function on a molecular level, generating a signal upon binding. The book reviews their synthesis, design, and applications for detecting biological and organic molecules as well as metal ions. The text highlights applications in drug discovery and catalyses that have not been well covered elsewhere.
Covering such topics as molecular recognition, detection methods, design strategies, and important biological issues, the book is broken into four sections that examine intermolecular interactions, strategies in sensor design, detection methods, and case studies in metal, saccharide, and amino acid sensing.
An indispensable source of information for chemical and biomedical experts using sensors, Chemosensors includes case studies to make the material both accessible and understandable to chemists of all backgrounds.
Important Notice: Media content referenced within the product description or the product text may not be available in the ebook version.
This book serves as a complete compendium of three important methods widely used for the characterization of synthetic and natural polymers—light scattering, size exclusion chromatography (SEC), and asymmetric flow field flow fractionation (A4F). Featuring numerous up-to-date examples of experimental results obtained by light scattering, SEC, and A4F measurements, Light Scattering, Size Exclusion Chromatography and Asymmetric Flow Field Flow Fractionation takes an all-in-one approach to deliver a complete and thorough explanation of the principles, theories, and instrumentation needed to characterize polymers from the viewpoint of their molar mass distribution, size, branching, and aggregation. This comprehensive resource:
Is the only book gathering light scattering, size exclusion chromatography, and asymmetric flow field flow fractionation into a single text
Systematically compares results of size exclusion chromatography with results of asymmetric flow field flow fractionation, and how these two methods complement each other
Provides in-depth guidelines for reproducible and correct determination of molar mass and molecular size of polymers using SEC or A4F coupled with a multi-angle light scattering detector
Offers a detailed overview of the methodology, detection, and characterization of polymer branching
Light Scattering, Size Exclusion Chromatography and Asymmetric Flow Field Flow Fractionation should be of great interest to all those engaged in the polymer analysis and characterization in industrial and university research, as well as in manufacturing quality control laboratories. Both beginners and experienced can confidently rely on this volume to confirm their own understanding or to help interpret their results.
*A one-stop source for proven methods and protocols for synthesizing bioconjugates in the lab
*Step-by-step presentation makes the book an ideal source for researchers who are less familiar with the synthesis of bioconjugates
*More than 600 figures that visually describe the complex reactions associated with the synthesis of bioconjugates
*Includes entirely new chapters on the latest areas in the field of bioconjugation as follows:
Microparticles and nanoparticles
Silane coupling agents
Dendrimers and dendrons
Discrete PEG compounds
Buckyballs,fullerenes, and carbon nanotubes
Mass tags and isotope tags
Bioconjugation in the study of protein interactions
This title is an ideal introductory book for anybody starting work in this field.
This book is comprised of 11 chapters and begins with a brief overview of plasma polymerization and its growing importance for the formation of entirely new kinds of materials. The discussion then shifts to a comparison between plasma-state polymerization and plasma-induced polymerization, between plasma polymerization and graft polymerization, and between plasma polymerization and radiation polymerization. The reader is also introduced to fundamental aspects of gas-phase reactions, paying particular attention to the classical kinetic theory of gas, as well as the mechanisms of formation of polymeric materials in plasma, competitive ablation and polymer formation in plasma, and polymer deposition in plasma polymerization. The operational parameters of plasma polymerization are described and a chapter devoted to the electrical properties of plasma-polymerized thin organic films concludes the book.
This book will be of interest to students and researchers of material science.
Polymers constitute the basis for the plastics, rubber, adhesives, fiber, and coating industries. The Fourth Edition of Introduction to Physical Polymer Science acknowledges the industrial success of polymers and the advancements made in the field while continuing to deliver the comprehensive introduction to polymer science that made its predecessors classic texts.
The Fourth Edition continues its coverage of amorphous and crystalline materials, glass transitions, rubber elasticity, and mechanical behavior, and offers updated discussions of polymer blends, composites, and interfaces, as well as such basics as molecular weight determination. Thus, interrelationships among molecular structure, morphology, and mechanical behavior of polymers continue to provide much of the value of the book.
Newly introduced topics include:
* Nanocomposites, including carbon nanotubes and exfoliated montmorillonite clays
* The structure, motions, and functions of DNA and proteins, as well as the interfaces of polymeric biomaterials with living organisms
* The glass transition behavior of nano-thin plastic films
In addition, new sections have been included on fire retardancy, friction and wear, optical tweezers, and more.
Introduction to Physical Polymer Science, Fourth Edition provides both an essential introduction to the field as well as an entry point to the latest research and developments in polymer science and engineering, making it an indispensable text for chemistry, chemical engineering, materials science and engineering, and polymer science and engineering students and professionals.
In order to establish links and similarities the book places prominence on principles and deductive reasoning with cross-referencing. This informal text also places the main emphasis on understanding and predicting reactivity rather than synthetic methodology as well as utilising a mechanism based layout and featuring annotated schemes to reduce the need for textual explanations.
* tailored specifically to the needs of students of Pharmacy Medical Chemistry and Biological Chemistry
* numerous pharmaceutical and biochemical examples
* mechanism based layout
* focus on principles and deductive reasoning
This will be an invaluable reference for students of Pharmacy Medicinal and Biological Chemistry.
The Essentials For Dummies Series
Dummies is proud to present our new series, The Essentials For Dummies. Now students who are prepping for exams, preparing to study new material, or who just need a refresher can have a concise, easy-to-understand review guide that covers an entire course by concentrating solely on the most important concepts. From algebra and chemistry to grammar and Spanish, our expert authors focus on the skills students most need to succeed in a subject.
In order to be able to reflect the development of today's science and to cover all modern aspects of thin films, the series, starting with Volume 20, has moved beyond the basic physics of thin films. It now addresses the most important aspects of both inorganic and organic thin films, in both their theoretical as well as technological aspects. Therefore, in order to reflect the modern technology-oriented problems, the title has been slightly modified from Physics of Thin Films to Thin Films.
This volume, part of the Thin Films Series, has been wholly written by two authors instead of showcasing several edited manuscripts.
This is a revised edition of a very successful book, which appeals to both academic and industrial markets.Illustrates the organic mechanism associated with each enzyme-catalyzed reactionMakes the connection between organic reaction mechanisms and enzyme mechanismsCompiles the latest information about molecular mechanisms of enzyme reactionsAccompanied by clearly drawn structures, schemes, and figuresIncludes an extensive bibliography on enzyme mechanisms covering the last 30 yearsExplains how enzymes can accelerate the rates of chemical reactions with high specificityProvides approaches to the design of inhibitors of enzyme-catalyzed reactionsCategorizes the cofactors that are appropriate for catalyzing different classes of reactionsShows how chemical enzyme models are used for mechanistic studiesDescribes catalytic antibody design and mechanismIncludes problem sets and solutions for each chapter Written in an informal and didactic style
With lively prose and an eye for colorful and unusual details, Le Couteur and Burreson offer a novel way to understand the shaping of civilization and the workings of our contemporary world.
Science of Fullerenes and Carbon Nanotubes introduces materials scientists, chemists, and solid state physicists to the field of fullerenes, and discusses the unique properties and applications. both current and future, of all classes of fullerenes.
* First comprehensive resource on fullerenes and their applications
* Provides an introduction to the topic
* Presents an extensive discussion of current and future applications of Fullerenes
* Covers all classes of fullerenes
Why This Title
This title is written in a clear and logical manner that is accessible to environmental professionals of all disciplines. It contains hundreds of practical tips on planning, sampling, and interactions with analytical laboratories. Having this text as a desk reference will greatly improve skills in planning and sampling, and elevate understanding of chemical data to a new level.
This topic is of importance to a wide range of environmental professionals from a variety of disciplines (see audience). Written by a practicing professional for practicing professionals, this handbook provides everything an environmental professional needs to know to competently collect environmental chemical data.
* Helps readers to understand where models come from, so they don't use them blindly and
* Provides many visual and geometric models for understanding a largely mathematical method
* Allows readers to judge whether recently published models are of sufficiently high quality and detail to be useful in their own work
* Allows readers to study macromolecular structure independently and in an open-ended fashion on their own computers, without being limited to textbook or journals illustrations
* Provides access to web tools in a format that will not go out of date. Links will be updated and added as existing resources change location or are added
In Uncle Tungsten we meet Sacks’ extraordinary family, from his surgeon mother (who introduces the fourteen-year-old Oliver to the art of human dissection) and his father, a family doctor who imbues in his son an early enthusiasm for housecalls, to his “Uncle Tungsten,” whose factory produces tungsten-filament lightbulbs. We follow the young Oliver as he is exiled at the age of six to a grim, sadistic boarding school to escape the London Blitz, and later watch as he sets about passionately reliving the exploits of his chemical heroes–in his own home laboratory. Uncle Tungsten is a crystalline view of a brilliant young mind springing to life, a story of growing up which is by turns elegiac, comic, and wistful, full of the electrifying joy of discovery.
From formulas and lab techniques to the periodic table, Chemistry for the Utterly Confused focuses on the areas of maximum confusion and breaks down the most difficult chemistry topics into easy-to-understand concepts. This invaluable guide also teaches problem-solving skills you need to master this imposing subject. Whether you're in high school, in college, or simply brushing up on chemistry knowledge, this fun, easily accessible book will make understanding chemistry a breeze.
College success for virtually all science, computing, engineering, and premedical majors depends in part on passing chemistry. The skills learned in chemistry courses are applicable to a number of fields, and chemistry courses are essential to students who are studying to become nurses, doctors, pharmacists, clinical technicians, engineers, and many more among the fastest-growing professions. But if you're like a lot of students who are confused by chemistry, it can seem like a daunting task to tackle the subject. That's where Chemistry II For Dummies can help!
Here, you'll get plain-English, easy-to-understand explanations of everything you'll encounter in your Chemistry II class. Whether chemistry is your chosen area of study, a degree requirement, or an elective, you'll get the skills and confidence to score high and enhance your understanding of this often-intimidating subject. So what are you waiting for?Presents straightforward information on complex concepts Tracks to a typical Chemistry II course Serves as an excellent supplement to classroom learning Helps you understand difficult subject matter with confidence and ease
Packed with approachable information and plenty of practice opportunities, Chemistry II For Dummies is just what you need to make the grade.
Featuring a mix of philosophy, rituals, spiritual practice, and lifestyle issues, The Druidry Handbook is one-stop shopping for those seriously interested in practicing a traditional form of Druidry. It offers equal value to eclectics and solitary practitioners eager to incorporate more earth-spirituality into their own belief system; it also appeals to the merely curious.
John Michael Greer has been a student of the occult traditions and nature spirituality for more than 25 years. He began following the Druid path in 1993 with initiation in the Order of Bards, Ovates, and Druids (OBOD). In 2003, he received OBOD's Mount Haemus Award for Druid scholarship and later the same year was elected Grand Archdruid of the Ancient Order of Druids in America (AODA). Greer is the author of numerous articles and ten books, including Paths of Wisdom, Circles of Power, Inside a Magical Lodge, Natural Magic, Monsters, and The New Encyclopedia of the Occult. He recently coauthored Learning Ritual Magic.
Philip Carr-Gomm is Chief of the Order of Bards, Ovates and Druids. Philip is the author of a number of works on Druidry, and since the publication of his first book in 1991 he has been in demand worldwide for radio, television and newspaper interviews.
Trying to understand chemistry but feel like the information's just not bonding with your brain? Here's your solution. Chemistry Demystified, Second Edition, helps you grasp both fundamental and complex concepts with ease.
Written in a step-by-step format, this practical guide first covers atomic theory, elements, symbols, and the Periodic Table of the Elements. The book then delves into solids, liquids, gases, solutions, orbitals, chemical bonds, acids, and bases. Electrochemistry, thermodynamics, biochemistry, and organic, environmental, and nuclear chemistry are discussed. In-depth examples, detailed illustrations, and worked-out problems make it easy to understand the material, and end-of-chapter quizzes and a final exam help reinforce learning.
It's a no-brainer! You'll learn about:Molecular and structural formulas Metallurgy Gas laws Molar mass Molecular orbital theory Covalent and ionic bonds Oxidation/reduction The laws of thermodynamics Organic reactions Biological and environmental markers
Simple enough for a beginner, but challenging enough for an advanced student, Chemistry Demystified, Second Edition, helps you master this fascinating subject.
Kratom and Other Mitragynines: The Chemistry and Pharmacology of Opioids from a Non-Opium Sourcepresents an introduction to the chemical and biological properties of alkaloids isolated from M. speciosa as well as their synthetic analogs. The book covers various topics including phytochemistry, medicinal chemistry, and pharmacology. Current research, analgesic effects, and addiction potential are also discussed. As the first extensive text on the basic science and clinical use of Kratom, the book provides readers with a concise yet comprehensive introduction to nature’s "other opioid."
Each chapter is self-contained and features an introduction that identifies its basic goals, their significance, and a general plan for their achievement. This text's important aims are to demonstrate that the basic kinetic principles are essential to the solution of modern chemical problems, and to show how the underlying question — "How do chemical reactions occur?" — leads to exciting, vibrant fields of modern research. The first aim is achieved by using relevant examples in presenting the basic material, and the second is attained by inclusion of chapters on surface processes, photochemistry, and reaction dynamics.
Incident Management Systems (IMS) provide the means by which to coordinate the efforts of individual agencies in order to stabilize an incident and protect life, property, and the environment. Born from the FireScope project of the late 1960s, which was developed in response to the major wildfires that regularly plagued Southern California, these systems have evolved with many similarities and certain fundamental differences.
Emergency Incident Management Systems: Fundamentals and Applications contrasts the major forms of Incident Management/Incident Command Systems. The author illuminates these differences and offers a fresh perspective on the concepts on which these systems are founded in order to make them more accessible and user-friendly. Without suggesting major changes in the systems, he bridges the gap between their theoretical and academic foundations and their real-world applications, and makes them more applicable to the professional's daily needs.
Timely features of the book include:
* An "in the field" point of view
* Coverage of incidents of mass destruction
* Filled-out sample forms designed to aid professionals in completing reports
In post-9/11 America, where incident management has become a national priority-one that must be easilyunderstood and applicable across all emergency systems-this book provides a useful tool for helping today's emergency workers be more informed and more prepared than ever.
Note: CD-ROM/DVD and other supplementary materials are not included as part of eBook file.
New chapters include: high-temperature oxidation of metals and alloys, nanomaterials, and dental materials, anodic protection. Also featured are chapters dealing with standards for corrosion testing, microbiological corrosion, and electrochemical noise.