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| A '''group contribution method''' is a technique to estimate and predict thermodynamic and other properties from molecular structures.
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| == Introduction ==
| | The Internet is a vast open market where businesses and consumers congregate. Some of the Wordpress development services offered by us are:. This is the reason for the increased risk of Down Syndrome babies in women over age 35. So if you want to create blogs or have a website for your business or for personal reasons, you can take advantage of free Word - Press installation to get started. Aided by the completely foolproof j - Query color selector, you're able to change the colors of factors of your theme a the click on the screen, with very little previous web site design experience. <br><br>It is very easy to install Word - Press blog or website. Word - Press has ensured the users of this open source blogging platform do not have to troubleshoot on their own, or seek outside help. You can now search through the thousands of available plugins to add all kinds of functionality to your Word - Press site. To turn the Word - Press Plugin on, click Activate on the far right side of the list. So, if you are looking online to hire dedicated Wordpress developers, India PHP Expert can give a hand you in each and every best possible way. <br><br>If all else fails, please leave a comment on this post with the issue(s) you're having and help will be on the way. As an example, if you are promoting a product that cures hair-loss, you most likely would not wish to target your adverts to teens. Specialty about our themes are that they are easy to load, compatible with latest wordpress version and are also SEO friendly. The company gains commission from the customers' payment. See a product, take a picture, and it gives you an Amazon price for that product, or related products. <br><br>When you beloved this post along with you would like to acquire more details regarding [http://GET7.pw/wordpress_backup_4105 wordpress dropbox backup] generously go to the website. You will know which of your Word - Press blog posts are attracting more unique visitors which in turn will help you develop better products and services for your customers. Here's a list of some exciting Word - Press features that have created waves in the web development industry:. It can be concluded that white label SEO comprise of a third party who resells a contract involving IT expert or consultant, SEO professional and end user. And, it is better that you leave it on for the duration you are writing plugin code. Verify whether your company has a team of developers or programmers having hands-on experience and knowledge about all Word - Press concepts. |
| In today's chemical processes hundreds of thousands of components are used. The [[Chemical Abstracts Service]] registry lists 56 million substances,<ref>http://www.cas.org/newsevents/releases/research120810.html</ref> but many of these are only of scientific interest.
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| Process designers need to know some basic chemical properties of the components and their mixtures. Experimental measurement is often too expensive.
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| Predictive methods can replace measurements if they provide sufficiently good estimations. The estimated properties cannot be as precise as well-made measurements but for many purposes the quality of estimated properties is sufficient. Predictive methods can also be used to check the results of experimental work.
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| == Principles ==
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| [[Image:Gruppenbeitragsmethodenprinzip.png|thumb|Principle of a Group Contribution Method]]
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| A group contribution method uses the principle that some simple aspects of the structures of chemical components are always the same in many different molecules. The smallest common constituents are the atoms and the bonds. The vast majority of organic components, for example, are built of [[carbon]], [[hydrogen]], [[oxygen]], [[nitrogen]], [[halogen]]s, and maybe [[sulfur]] or [[phosphorus]]. Together with a single, a double, and a triple bond there are only ten atom types (not including [[astatine]]) and three bond types to build thousands of components. The next slightly more complex building blocks of components are [[functional group]]s which are themselves built of few atoms and bonds.
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| A group contribution method is used to predict properties of pure components and mixtures by using group or atom properties. This reduces the number of needed data dramatically. Instead of needing to know the properties of thousands or millions of compounds, only data for a few dozens or hundreds of groups have to be known.
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| === Additive group contribution method ===
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| The simplest form of a group contribution method is the determination of a component property by summing up the group contribution.
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| <math>T_b \, = \, 198.2 + \sum {G_i}</math> | |
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| This simple form assumes that the property (normal boiling point in the example) is strictly linear dependent from the number of groups and additionally no interaction between groups and molecules are assumed. This simple approach is used for example in the [[Joback method]] for some properties and it works well in a limited range of components and property ranges but leads to quite large errors if used outside the applicable ranges.
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| === Additive group contributions and correlations ===
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| This technique uses the pure additive group contributions to correlate the wanted property with an easy accessible property. This is often done for the [[critical temperature]], where the [[Guldberg rule]] implies that T<sub>c</sub> is <sup>3</sup>/<sub>2</sub> of the normal boiling point and the group contributions are used to give a more precise value than <sup>3</sup>/<sub>2</sub>.
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| <math>T_c \, = \, T_b \left[0.584 + 0.965 \sum {G_i} - {G_i}^2 \right]^{-1}</math> | |
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| This approach often gives better results than pure additive equations because the relation with a known property introduces some knowledge about the molecule. Commonly used additional properties are the molecular weight, the number of atoms, chain length, and ring sizes and counts.
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| === Group interactions ===
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| For the prediction of mixture properties it is in most cases not sufficient to use a purely additive method. Instead the property is determined from group interaction parameters.
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| <math>P \, = \, f(G_{ij})</math>
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| where P stands for property and G<sub>ij</sub> for group interaction value.
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| A typical group contribution method using group interaction values is the [[UNIFAC]] method which estimates activity coefficients. A big disadvantage of the group interaction model is the need for many more model parameters. Where a simple additive model only needs ten parameters for ten groups a group interaction model needs already needs 45 parameters. Therefore a group interaction model has normally not parameter for all possible combinations.
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| === Group contributions of higher orders ===
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| Some newer methods<ref>Constantinou L., Gani R., "New Group Contribution Method for Estimating Properties of Pure Compounds", AIChE J., 40(10), 1697-1710, 1994</ref> introduce second-order groups. The second-order order groups can be super-groups containing several first-order (standard) groups. This allows the introduction of new parameters for the position of groups. Another possibility is to modify first-order group contributions if specific other groups are also present.<ref>Nannoolal Y., Rarey J., Ramjugernath J., "Estimation of pure component properties Part 2. Estimation of critical property data by group contribution", Fluid Phase Equilib., 252(1-2), 1-27, 2007</ref>
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| If the majority of Group Contribution Methods give results in gas phase, recently, a new Group Contribution Method<ref>Jankowski, M. D., C. S. Henry,L. J. Broadbelt, and V. Hatzimanikatis. Group Contribution Method for Thermodynamic Analysis of Complex Metabolic Networks. Biophys. J. 95(3): 1487-1499, 2008</ref> was created for estimating the standard Gibbs free energy of formation (ΔfG′°) and reaction (ΔrG′°) in biochemical systems: aqueous solution, temperature of 25℃ and pH=7 (biochemical conditions). This new aqueous system method is based on the group contribution method of Mavrovouniotis.<ref>Mavrovouniotis, M. L. Estimation of standard Gibbs energy changes of biotransformations. J. Biol. Chem. 266:14440-14445, 1991</ref><ref>Mavrovouniotis, M. L. Group contributions for estimating standard Gibbs energies of formation of biochemical-compounds in aqueous-solution. Biotechnol. Bioeng. 36:1070-1082, 1990</ref>
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| A free access tool of this new method in aqueous condition is available <ref>http://lcsbweb.epfl.ch/GCMWebSite/</ref> on the web.
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| == Determination of group contributions ==
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| Group contributions are obtained from known experimental data of well defined pure components and mixtures. Common sources are thermophysical data banks like the [[Dortmund Data Bank]], [[Beilstein database]], or the DIPPR data bank (from [[AIChE]]). The given pure component and mixture properties are then assigned to the groups by statistical correlations like e. g. (multi-)linear regression.
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| Important steps during the development of a new method are the
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| # evaluation of the quality of available experimental data, elimination of wrong data, finding of outliers
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| # construction of groups
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| # searching additional simple and easily accessible properties that can be used to correlate the sum of group contributions with the examined property
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| # finding a good but simple mathematical equation for the relation of the group contribution sum with the wanted property. The critical pressures, for example, is often determined as P<sub>c</sub>=f(ΣG<sub>i</sub><sup>2</sup>)
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| # fitting the group contribution
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| The reliability of a method mainly relies on a comprehensive data bank where sufficient source data have been available for all groups. A small data base may lead to a precise reproduction of the used data but will lead to significant errors when the model is used for the prediction of other systems.
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| == See also ==
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| *[[UNIFAC]]
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| *[[Benson group increment theory]]
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| *[[Activity coefficient]]
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| == References ==
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| <references/>
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| {{DEFAULTSORT:Group Contribution Method}}
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| [[Category:Thermodynamic models]]
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It involves expertise and knowledge of various tools and technologies used for creating websites. Offshore expert Word - Press developers high level of interactivity, accessibility, functionality and usability of our website can add custom online to using. Your parishioners and certainly interested audience can come in to you for further information from the group and sometimes even approaching happenings and systems with the church. Keep reading for some great Word - Press ideas you can start using today. The number of options offered here is overwhelming, but once I took the time to begin to review the video training, I was amazed at how easy it was to create a squeeze page and a membership site.
The Internet is a vast open market where businesses and consumers congregate. Some of the Wordpress development services offered by us are:. This is the reason for the increased risk of Down Syndrome babies in women over age 35. So if you want to create blogs or have a website for your business or for personal reasons, you can take advantage of free Word - Press installation to get started. Aided by the completely foolproof j - Query color selector, you're able to change the colors of factors of your theme a the click on the screen, with very little previous web site design experience.
It is very easy to install Word - Press blog or website. Word - Press has ensured the users of this open source blogging platform do not have to troubleshoot on their own, or seek outside help. You can now search through the thousands of available plugins to add all kinds of functionality to your Word - Press site. To turn the Word - Press Plugin on, click Activate on the far right side of the list. So, if you are looking online to hire dedicated Wordpress developers, India PHP Expert can give a hand you in each and every best possible way.
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