Xem 1-20 trên 218 kết quả The chemical nature
  • There are two main reasons why the chemical process industry should be motivated to reduce energy consumption and CO 2 emissions: rising concerns in companies, the public and scientifi c community about climate change or global warming, and the increasing fraction of energy in manufacturing costs. ‘ Climate change ’ [1] in this context, means a change of climate, which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods....

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  • Tham khảo sách 'the vitamine manual', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả

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  • The first edition of Toxicological Chemistry (1989) was written to bridge the gap between toxicology and chemistry. It defined toxicological chemistry as the science that deals with the chemical nature and reactions of toxic substances, their origins and uses, and the chemical aspects of their exposure, transformation, and elimination by biological systems. It emphasized the chemical formulas, structures, and reactions of toxic substances. The second edition of Toxicological Chemistry (1992) was significantly enlarged and increased in scope compared to the first edition.

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  • Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials.[1] Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of one or more of these components. The separation of components is often performed prior to analysis

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  • Essential oil of Cinnamomum longepetiolatum Costerm. apud Phamh. Obtained by hydro distillation. The essential oil yield was 0.91% in fresh leaves. The chemical composition of this oil was study by GC and GC/MS. Twelve compounds were identified representing 98.8% of this oil with camphor as major constituent (87.5%). Eleven other compounds were found with lower content. The results of this study shows that Cinnamomum longepetiolatum Costerm. apud Phamh. was a new natural source of camphor in Vietnam. ...

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  • The compounds of La1-xCaxMnO3- δ with x=0.46 and 0.50 occupy special positions in the phase diagram of La1-xCaxMnO3-δ system due to their interesting properties and charge-ordering phase transition. The samples were prepared by a solid-state reaction method. The XPD patterns show that the samples are of a single-phase orthorhombic-perovskite structure. The chemical compositions of the samples are investigated by EDS. The concentrations of oxygen and Mn3+; Mn4+ ions have been determined by dichromate method.

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  • Although the chemical nature of the catalytic mechanism of the serine pro-tease a-chymotrypsin (a-CT) is largely understood, the influence of the enzyme’s structural dynamics on its catalysis remains uncertain. Here we investigate whether a-CT’s structural dynamics directly influence the kinet-ics of enzyme catalysis.

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  • RecD is essential for growth at low temperature in the Antarctic psychro-trophic bacterium Pseudomonas syringaeLz4W. To examine the essential nature of its activity, we analyzed wild-type and mutant RecD proteins with substitutions of important residues in each of the seven conserved helicase motifs.

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  • Human activities have a large and important impact on the environment. Naturally occurring elements or compounds are often concentrated and redistributed in the environment through industrial processes, power production, and consumer activity. For example, lead, which is found in naturally occurring mineral deposits, has become a major pollutant through its use in batteries, paints, and gasoline additives.

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  • Risk assessment is an inexact science. Successful risk assessment practitioners rely heavily on extensive and well-documented databases.

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  • As early as the middle of the 19th century, scientists were beginning to isolate and characterize organic compounds from nature. Modern studies of the nature of natural products, those compounds not involved in primary metabolic processes, began in the 1930s and 1940s. In the decades that followed, scientists began to focus on why organisms produce these compounds.

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  • Economic and environmental consequences of natural and man-made disasters have grown exponentially during the past few decades. Whether from hurricanes, chemical spills, terrorist incidents, or other catastrophes, the negative impacts can often be felt on a global scale. Natural Hazards Analysis: Reducing the Impacts of Disasters evaluates critical preparedness issues that emergency managers must face before, during, and after disasters of any kind.

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  • Food safety is of great importance to consumers. To ensure the safety of the food supply and to facilitate international trade, government agencies and international bodies establish standards, guidelines, and regulations that food producers and trade partners need to meet, respect, and follow. A primary goal of national and international regulatory frameworks for the use of veterinary drugs, including antimicrobials, in food-producing animals is to ensure that authorized products are used in a manner that will not lead to non-compliance residues.

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  • Forty-five years ago, agricultural and pharmaceutical chemistry appeared to be following divergent paths. On the agricultural scene industrial companies were concentrating on the synthesis of various classes of compounds and when a successful chemical candidate was discovered, there was a good deal of joy among the synthetic chemists. We were told that as a result of chemistry life would be better and, indeed, it was. Armed with synthetic agrochemicals, the American farmer became the envy of the world....

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  • Natural gas is a vital component of the world's supply of energy and an important source of many bulk chemicals and speciality chemicals. It is one of the cleanest, safest, and most useful of all energy sources, and helps to meet the world’s rising demand for cleaner energy into the future. However, exploring, producing and bringing gas to the user or converting gas into desired chemicals is a systematical engineering project, and every step requires thorough understanding of gas and the surrounding environment.

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  • Due to the success of the first edition of The Engineering Handbook published in 1995 I am pleased to provide the second edition ten years later fully updated and expanded. Purpose The purpose of The Engineering Handbook, Second Edition is to provide in a single volume a ready reference for the practicing engineer in industry, government, and academia. The book in its comprehensive format is divided into 30 sections which encompass the field of engineering and includes 19 brand new chapters and 131 fully updated contributions.

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  • Wet processing of textiles uses large quantities of water, and electrical and thermal energy. Most of these processes involve the use of chemicals as assisting, accelerating or retarding their rates and are carried out at elevated temperatures to transfer mass from processing liquid medium across the surface of textile material in a reasonable time. So, we can use some natural materials and some physical tools to reduce the chemicals, water, energy and pollution.

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  • The Tertiary Publications Committee of the Chemical Society decided that after the appearance of Volume 5 the Specialist Periodical Report ‘Aliphatic Chem- istry’ should be replaced by two new titles: ‘General and Synthetic Methods’ and ‘Aliphatic and Related Natural Product Chemistry’. This latter will be produced biennially and this represents the first volume in this series.

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  • The heroine of this book is nature’s simplest atom, the hydrogen atom. With one exception—the helium atom—hydrogen is the mother of all atoms and molecules. The hydrogen atom consists of a single electron and a single proton; the proton is the nucleus of the hydrogen atom and serves as the electron’s anchor. The universe is teeming with hydrogen: every cubic centimeter of dark interstellar space, essentially void of any other known matter,1 contains a few atoms of hydrogen

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  • Sewage sludge as an uncalled for product of wastewater treatment poses the challenge to society of disposing of it, but at the same time gives us the opportunity of beneficial use by closing the cycle of nutrients: sludge derived from agricultural activity must return to soil if a sustainable and ecologically sound management of these materials is desirable (SEQUI et al. 2000). At present the major ways of disposing of sewage sludges are deposition, landfill and incineration, only part of the sludges are used in agriculture. ...

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