Conventional cells--the last step toward general acceptance of standard conventional cells for the reporting of crystallographic data.In 1969, a seminal seminal /sem·i·nal/ (sem´i-n'l) pertaining to semen or to a seed. sem·i·nal adj. Of, relating to, containing, or conveying semen or seed. section on reduced forms In social science and statistics, particularlly econometrics, a reduced form equation is a method of dealing with endogeneity. A reduced form equation is defined by James Stock & Mark Watson (2007) in the following way: and conventional cells was published in the International Tables for X-Ray Crystallography X-ray crystallography, the study of crystal structures through X-ray diffraction techniques. When an X-ray beam bombards a crystalline lattice in a given orientation, the beam is scattered in a definite manner characterized by the atomic structure of the lattice. . The section contains a table that gives a metric classification of the 44 reduced forms. In 2001, this table with appropriate revisions was republished in the Journal of Research of the National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. . An especially valuable feature of the table is that it defines and allows the user to determine a standard conventional cell. Since 1969, there has been an evolution toward acceptance and widespread use of such conventional cells. An inspection of the articles in key crystallographic crys·tal·log·ra·phy n. The science of crystal structure and phenomena. crys  tal·log journals reveals that most cells follow the
conventions. However, one major exception remains-the centered
monoclinic mon·o·clin·ic adj. Of or relating to three unequal crystal axes, two of which intersect obliquely and are perpendicular to the third. monoclinic Adjective Crystallog lattices. In approximately one-third of these cases, non-conventional C-centered cells are used, apparently to avoid the use of I-centered cells. It is recommended that the crystallographic community routinely use the I-centered conventional cell in s uch cases. Key words: C-centered cell; centered monoclinic cells; conventional cells; I-centered cell; mathematical lattices. 1. Introduction In 1969, a seminal section (1) on reduced forms and conventional cells was published in the International Tables for X-Ray Crystallography. The section contains a table that gives a metric classification of the 44 reduced forms. In 2001, this table with appropriate revisions was republished in the Journal of Research of the National Institute of Standards and Technology (2). An especially valuable feature of the table is that it allows the user to determine a standard conventional cell. From the nature of the reduced form, one can determine the reduced form number, Bravais lattice Noun 1. Bravais lattice - a 3-dimensional geometric arrangement of the atoms or molecules or ions composing a crystal crystal lattice, space lattice lattice - an arrangement of points or particles or objects in a regular periodic pattern in 2 or 3 dimensions , and the transformation matrix to a standard conventional cell (or simply conventional cell). The table is widely used by the scientific community as it is imbedded imbedded, adj See embedded. in scientific software associated with automated au·to·mate v. au·to·mat·ed, au·to·mat·ing, au·to·mates v.tr. 1. To convert to automatic operation: automate a factory. 2. x-ray diffractometers as well as in other distributed software. This conventional cell is rigorously defined mathematically, unique, and can be calculated using a computer program. The cell is logical. For example, for those cases in which cell edges are not determined by symmetry symmetry, generally speaking, a balance or correspondence between various parts of an object; the term symmetry is used both in the arts and in the sciences. , one selects the shortest possible vectors. Thus in the triclinic system, the reduced cell which is based on the shortest three non-coplanar vectors of the lattice (theory) lattice - A partially ordered set in which all finite subsets have a least upper bound and greatest lower bound. This definition has been standard at least since the 1930s and probably since Dedekind worked on lattice theory in the 19th century; though he may not is chosen with the edges obeying a [less than or equal to] b [less than or equal to] c. In the monoclinic system, the cell is based on the shortest possible vectors in the ac plane with b the unique axis. The angle [beta] is taken as non-acute. This choice allows a primitive, a side-centered, and a body-centered lattice. In the primitive and body-centered lattices, a and c obey Obey can refer to:
There are many advantages to using conventional cells for the reporting of crystallographic data. For example, one can readily compare cells to ascertain if a new compound is the same as or related to a previously reported material. Accordingly, to facilitate the evaluation and use of data, several of the crystallographic data centers transform each original literature cell to the Crystal Data (CD) cell (CD cell = the conventional cell or a closely related cell determined by relabeling of axes axes [L., Gr.] plural of axis. The straight lines which intersect at right angles and on which graphs are drawn. Usually the horizontal axis is the x-axis and the vertical one the y-axis. Called also axes of reference. ). For this purpose, the NBS (National Bureau of Standards) See NIST. NBS - National Bureau of Standards: part of the US Department of Commerce, now NIST. *AIDS83 (3) program has been used for over 20 years. This program determines the CD cell directly from the literature cell. In a verification sequence, the program also calculates the CD cell from the reduced form using the table in the above references (1,2). As NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. *LATTICE (4) is a powerful tool for the evaluation and determination of metric lattice symmetry via matrix methods (5), it is often used in the determination of symmetry and the reduced form especially for difficult cases. A recommended goal for the crystallographic community would be to strive for the universal acceptance of standard conventional cells and to publish crystallographic results therein. This is especially important today, as so many cells are determined in so many laboratories and reported in such diverse journals. Use of such cells aids both the experimentalist, the journal reader, and the data centers as it eliminates the need to transform cells and coordinates in order to compare structural parameters. Fortunately, the crystallographic community is very close-to achieving such a goal. As shown in the next section, proper determination of conventional cells to characterize a subset A group of commands or functions that do not include all the capabilities of the original specification. Software or hardware components designed for the subset will also work with the original. of the centered monoclinic lattices represents the final major hurdle HURDLE, Eng. law. A species of sledge, used to draw traitors to execution. . 2. Discussion 2.1 Conventional Cells: Current Status Since 1969, there has been an evolution toward the general use of the standard conventional cells. An inspection of articles in key crystallographic journals (e.g. Acta Crystallographic Section C--Crystal Structure Communications) reveals that most cells reported in the literature follow the conventions (1) specified in the above two articles (1,2). For example, for the most populous pop·u·lous adj. Containing many people or inhabitants; having a large population. [Middle English, from Latin popul space group (No. 14), the shortest vectors in the ac plane, with the b-axis unique, are usually selected which results in either the space group setting [P2.sub.1]/c or [P2.sub.1]/n. For triclinic crystals, the reduced cell is routinely used. Both the editors of the International Tables for Crystallography and the instrument manufacturers have played an essential role in this evolutionary progress Three billion years ago, life on Earth consisted of single-celled organisms, but now there is a tremendous variety of complex multi-celled creatures. It may seem obvious that there is progress in evolution, but the topic has inspired much controversy. . Recent versions of Volume A of the International Tables for Crystallography (6) explicitly give the required space group settings to assist the experimentalist in the low symmetry systems. For example, the equivalent positions for [P2.sub.1]/n and I2/a are explicitly given. In addition, the software provided with many of the automated x-ray diffractometers makes it possible to readily obtain the conventional cell in the low symmetry crystal systems for most cases. 2.2 Conventional Cells: The Problem with Centered Monoclinic Cells The general use of non-conventional C-centered monoclinic cells--when conventional I-centered cells should have been selected--remains the principal remaining problem. An understanding of the problem can be gained by inspection of Tables 1 and 2. Table 1 is derived from the table of 44 reduced forms published originally in the International Tables for X-Ray Crystallography (1) and later, with revisions, in the Journal of Research of NIST (2). It contains the 13 reduced forms that correspond to centered monoclinic lattices. As the Table 1 shows, there are two possible standard conventional settings for the centered monoclinic cells--C and I. An analysis of approximately 11 000 centered monoclinic cells in the Crystal Data File (7) shows that the centered monoclinic literature cells transform to 1-centered and C-centered conventional cells in one-third and two-thirds of the cases, respectively. However, an analysis of the authors' cells reported in the literature shows that the I-centered cell is rarely used. Today, this avoidance continues unabated un·a·bat·ed adj. Sustaining an original intensity or maintaining full force with no decrease: an unabated windstorm; a battle fought with unabated violence. as can be seen by inspection of recent publications in the major crystallographic journals. A review of all 80 centered monoclinic cells published in 2001 in Acta Crystallographic Section C, shows that the I-centered cell is still infrequently in·fre·quent adj. 1. Not occurring regularly; occasional or rare: an infrequent guest. 2. used to report the experimental results. A detailed analysis of recent publications shows that the conventions are not entirely ignored. In fact for most cases in which a C-centered cell is the conventional cell, it is indeed selected (i.e., in approximately two-thirds of the cases). But for those cases, in which the I-centered cell is the conventional cell, the author usually selects a non-conventional C-centered unit cell. Clearly there is an aversion a·ver·sion n. 1. A fixed, intense dislike; repugnance, as of crowds. 2. A feeling of extreme repugnance accompanied by avoidance or rejection. to using the I-cell for those cases in which it is the conventional cell based on the shortest vectors in the ac plane (b-unique)! Table 2 shows examples of the selection of the nonstandard non·stan·dard adj. 1. Varying from or not adhering to the standard: nonstandard lengths of board. 2. C-centered cells by experimentalists (8-12). Note that in each case, the C-centered cell can be transformed to an 1-centered cell with a [beta] angle closer to 90[degrees]. (To facilitate comparisons, the rows with [beta] angles have been shaded.) In case 3, for example, the C-centered cell with a [beta] angle of 131.61[degrees] can be transformed to an I-cell with a [beta] of 9l.41[degrees]. The selection of such highly skewed skewed curve of a usually unimodal distribution with one tail drawn out more than the other and the median will lie above or below the mean. skewed Epidemiology adjective Referring to an asymmetrical distribution of a population or of data cells, such as the C-centered cell in case 3, is not recommended because it is often associated with experimental errors such as missed symmetry. The reluctance to use the I-centered cell is a bit puzzling in view of the fact that recent editions of Volume A of the International Tables for Crystallography explicitly give all the symmetry related positions for the I-cell. The most likely explanation is that the software associated with diffractometers continues to steer steer castrated male cattle beast over a year of age. See also bullock, buller steer. steer bulling see bulling. steer Medtalk verb the experimentalist toward the C-centered cell even in th ose cases when it should be I. 3. Conclusion and Recommendation Because many compounds crystallize crys·tal·lize also crys·tal·ize v. crys·tal·lized also crys·tal·ized, crys·tal·liz·ing also crys·tal·iz·ing, crys·tal·liz·es also crys·tal·iz·es v.tr. 1. in centered monoclinic lattices, the widespread use of the non-standard cells to characterize approximately one-third of these lattices is a nontrivial nontrivial - Requiring real thought or significant computing power. Often used as an understated way of saying that a problem is quite difficult or impractical, or even entirely unsolvable ("Proving P=NP is nontrivial"). The preferred emphatic form is "decidedly nontrivial". problem. An analysis of the NIST Crystal Data (7) shows that approximately 9 % of all compounds crystallize in lattices characterized char·ac·ter·ize tr.v. character·ized, character·iz·ing, character·iz·es 1. To describe the qualities or peculiarities of: characterized the warden as ruthless. 2. by a centered monoclinic unit cell. In fact, space group 15 (C2/c, 12/a) is one of the more populous space groups. Both I- and C-centered conventional unit cells can occur with monoclinic centered lattices. The maximum in utility of crystallographic data will be achieved if in each case, the experimentalist follows the conventions in Table (1,2) and selects the type of cell centering (1 or C) that leads to a conventional cell based on the shortest vectors in the ac plane (b-axis unique). By discontinuing the use of a non-conventional C-centered cell with a [beta] angle greater than that in the conventional I-centered cell, uniformity in crystallographic practice will be achieved. In all cases then, the practice for the monoclinic system would be to select a conventional cell based on the shortest vectors in the ac plane (b-axis unique) for primitive as well as centered cells. An effective way to promote this harmonization har·mo·nize v. har·mo·nized, har·mo·niz·ing, har·mo·niz·es v.tr. 1. To bring or come into agreement or harmony. See Synonyms at agree. 2. Music To provide harmony for (a melody). of crystallographic data could be achieved if journals were to modify their rules and policies to require or, at least, recommend that the standard conventional cell be used for reporting the monoclinic centered lattices. Likewise journal editors and reviewers should support this policy in the review process. In addition, the diffractometer A Diffractometer (Main Entry: dif·frac·tom·e·ter Pronunciation: di-"frak-'tä-m&-t&r Function: noun) is a measuring instrument for analyzing the structure of a usually crystalline substance from the scattering pattern produced when a beam of radiation or particles (as X rays or makers should modify and enhance their software so that experimentalists routinely are guided to select the I-centered cell when it is the standard conventional cell. Finally, other widely disseminated disseminated /dis·sem·i·nat·ed/ (-sem´i-nat?ed) scattered; distributed over a considerable area. dis·sem·i·nat·ed adj. Spread over a large area of a body, a tissue, or an organ. software packages, such as indexing programs, should be appropriately modified.
Table 1
Metric classification of the 13 reduced forms (a) corresponding to the
monoclinic centered lattices. From the nature of the reduced form, one
can determine the reduced form number and the transformation matrix to
the conventional cell. To assure that one obtains a conventional cell
(h) based on the shortest translations in the ac plane, the conditions
in the footnote for the specified centered monoclinic lattices must be
checked. in those cases for which the transformation matrix in the
footnote premultiples a given table matrix, the resultant cell centering
is indicated in parentheses following the transformation matrix
Reduced form matrix
Reduced First row Second row
form
No. a*a b*b c*c b*c
a = b
10 a*a a*a c*c b*c
14 a*a a*a c*c -\b*c17 a*a a*a c*c -\b*c
b = c
20 a*a b*b b*b b*c
25 a*a b*b b*b -\b*c
a [less than or equal to] b
[less than or equal to]c (g)
27 a*a b*b c*c b*c
28 a*a b*b c*c a*b/2
29 a*a b*b c*c a*c/2
30 a*a b*b c*c b*b/2
37 a*a b*b c*c -\b*c39 a*a b*b c*c -\b*c41 a*a b*b c*c -b*b/2
43 a*a b*b c*c -b*b - \a*b\/2
Reduced Second row
form
No. a*c a*b
a = b
10 b*c a*b
14 -\b*c\ -\a*b17 -\a*c\ -(a*a-\b*c\-\a*c\)
b = c
20 a*c a*c
25 -\a*c\ -\a*c
a [less than or equal to] b
[less than or equal to]c (g)
27 a*a/2 a*a/2
28 a*a/2 a*b
29 a*c a*a/2
30 a*b/2 a*b
37 -a*a/2 0
39 0 -a*a/2
41 -\a*c\ 0
43 - a*a - \a*b\/2 -\a*b
Reduced Reduced
form form Bravais
No. type lattice
a = b
10 + Monoclinic C (d)
14 - Monoclinic C (d)
17 - Monoclinic I (e)
b = c
20 + Monoclinic C (b)
25 - Monoclinic C (b)
a [less than or equal to] b
[less than or equal to]c (g)
27 + Monoclinic I (f)
28 + Monoclinic C
29 + Monoclinic C
30 + Monoclinic C
37 - Monoclinic C (c)
39 - Monoclinic C (d)
41 - Monoclinic C (b)
43 - Monoclinic I
Cell
Reduced transformation
form reduced [right
No. arrow] conventional
a = b
10 110/110/001
14 110/110/001
17 101/110/011
b = c
20 011/011/100
25 011/011/100
a [less than or equal to] b
[less than or equal to]c (g)
27 011/100/111
28 100/102/010
29 100/120/001
30 010/012/100
37 102/100/010
39 120/100/001
41 012/010/100
43 100/112/010
(a)Derived from the metric classification of the 44 reduced forms (1,2).
(b)If a*a < 4\a*c\ Premultiply tabe matrix by 001/010/101 (I-centered).
(c)If b*b < 4\b*c
(d)If c*c < 4\b*c
(e)If 3a*a < c*c + 2\a*c\ Premultiply table matrix by 101/010/100
(C-centered).
(f)If 3b*b < c*c + 2\b*c
(g)No required relationships between symmetrical scalars for reduced
forms 27-44.
(h) For the conventional cell in the monoclinic system, b is taken as
the unique axis, and a and c are chosen coincident with the shortest two
translations in the net perpendicular to b. The angle [beta] is taken to
be non-acute. This choice allows primitive, side-centered, and
body-centered lattices. In the primitive and body-centered lattices a
and c obey a < c. The side-centered lattice is taken as C-centered.
Table 2
crystallographic parameters reported for five centered monoclinic cells
selected from the recent literature (8-12). The Table shows that each
literature C-centered cell can be transformed to a conventional
I-centered cell in which the [beta] angle is closer to 90 [degrees].
Numbers in parentheses represent standard deviations
No. 1(8) 2(9) 3(10)
Lattice I Lattice II Lattice III
Literature cells--
monoclinic C-centered
Cell LC1 LC2 LC3
a([Angstrom]) 21.4179(6) 19.3044(4) 14.744(3)
b([Angstrom]) 11.1466(2) 10.6009(3) 8.850(3)
c([Angstrom]) 14.9649(3) 11.6549(3) 10.062(3)
[beta]([degrees]) 133.4280(6) 125.527(2) 131.609(19)
V([[Angstrom].sup.3]) 2594.61(10) 1941.10(8) 981.7(5)
Sp. Gr. C2 Cc C2/c
Yr. Pub. 2001 2000 2000
Standard conventional
cells--monoclinic
I-centered
Cell SC1 SC2 SC3
a([Angstrom]) 14.965 11.655 10.062
b([Angstrom]) 11.147 10.601 8.850
c([Angstrom]) 15.556 15.717 11.027
[beta]([degrees]) 90.89 91.59 91.41
V([[Angstrom].sup.3]) 2594.61 1941.10 981.7
Sp. Gr. I2 Ia I2/a
Reduced forms (a)
Form RF1 RF2 RF3
a*a 1.00 1.00 1.00
b*b 1.17 1.08 1.00
c*c 1.20 1.12 1.04
b*c 0.29 0.50 -0.20
a*c 0.50 0.50 -0.33
a*b 0.50 0.50 -0.47
Form No. 27 27 17
No. 4(11) 5(12)
Lattice IV Lattice V
Literature cells--
monoclinic C-centered
Cell LC4 LC5
a([Angstrom]) 27.4540(10) 23.785(9)
b([Angstrom]) 12.2738(10) 13.610(3)
c([Angstrom]) 16.2792(10) 19.080(7)
[beta]([degrees]) 123.118(10) 121.927(l2)
V([[Angstrom].sup.3]) 4594.4(5) 5242(3)
Sp. Gr. C2/c C2
Yr. Pub. 2001 2001
Standard conventional
cells--monoclinic
I-centered
Cell SC4 SC5
a([Angstrom]) 16.279 19.08
b([Angstrom]) 12.274 13.610
c([Angstrom]) 23.029 21.208
[beta]([degrees]) 93.18 107.85
V([[Angstrom].sup.3]) 4594.4 5242
Sp. Gr. I2/a I2
Reduced forms (a)
Form RF4 RF5
a*a 1.00 1.00
b*b 1.50 1.01
c*c 1.64 1.68
b*c 0.69 0.37
a*c 0.50 0.50
a*b 0.50 0.50
Form No. 27 27
(a) Reduced forms have been normalized.
Acknowledgment acknowledgment, in law, formal declaration or admission by a person who executed an instrument (e.g., a will or a deed) that the instrument is his. The acknowledgment is made before a court, a notary public, or any other authorized person. The author thanks Ronald Munro for his valuable suggestions and insightful comments. Accepted: May 15, 2002 Available online: http://www.nist.gov/jres (1.) In certain cases, there are trivial TRIVIAL. Of small importance. It is a rule in equity that a demurrer will lie to a bill on the ground of the triviality of the matter in dispute, as being below the dignity of the court. 4 Bouv. Inst. n. 4237. See Hopk. R. 112; 4 John. Ch. 183; 4 Paige, 364. deviations from strict adherence adherence /ad·her·ence/ (ad-her´ens) the act or condition of sticking to something. immune adherence to the conventions such as relabeling of the axes (e.g. the interchange An interchange is a location where two things meet, usually perform some kind of exchange, and possibly go on their ways again. It is most commonly used in four contexts:
4. References (1.) A. D. Mighell, A. Santoro, and J. D. H. Donnay, Reduced-cells section, in International Tables for X-Ray Crystallography, Vol. I., 3rd ed., Birmingham, Kynoch Press (1969) pp. 530-535. (2.) A. D. Mighell, Lattice Symmetry and Identification--The Fundamental Role of Reduced Cells in Materials Characterization A rather long and fancy word for analyzing a system or process and measuring its "characteristics." For example, a Web characterization would yield the number of current sites on the Web, types of sites, annual growth, etc. , J. Res. Natl. Inst. Stand. Technol. 106, 983-995 (2001). (3.) A. D. Mighell, C. R. Hubbard, and J. K. Stalick, NBS*AIDS80: A FORTRAN Program Noun 1. FORTRAN program - a program written in FORTRAN computer program, computer programme, programme, program - (computer science) a sequence of instructions that a computer can interpret and execute; "the program required several hundred lines of code" for Crystallographic Data Evaluation, National Bureau of Standards National Bureau of Standards: see National Institute of Standards and Technology. National Bureau of Standards - National Institute of Standards and Technology (USA), Tech. Note 1141 (1981). (NBS*AIDS83 is a later version of NBS*AIDS80). (4.) V. L. Karen and A. D, Mighell, NIST*LATl7ICE--A Program to Analyze Lattice Relationships, Version of Spring 1991, NIST Technical Note 1290(1991), National Institute of Standards and Technology, Gaithersburg, MD 20899. See also NIST Technical Note 1214 (1985). (5.) V. L. Karen (Himes) and A. D. Mighell, A Matrix Approach to Symmetry, Acta Cryst. A43, 375-384 (1987). (6.) International Tables for Crystallography, Vol. A, Th. Hahn, ed., Dordrecht, Kluwer Academic Publishers (1996). (7.) NIST Crystal Data, A Database with Chemical and Crystallographic Information. NIST Crystallographic Data Center, National Institute of Standards and Technology, Gaithersburg MD 20899. (8.) J. N. Low, D. Cannon, A. Quesada, A. Marchal, M. Melguizo, M. Nogueras, A. Sanchez, and C. Glidewell, N-(2-Amino-1,6-dihydro-5-nitroso-6-oxopyrimidin-4-yl)-L-isoleucine-wa ter (4/1): interplay in·ter·play n. Reciprocal action and reaction; interaction. intr.v. in·ter·played, in·ter·play·ing, in·ter·plays To act or react on each other; interact. of molecular and supramolecular su·pra·mo·lec·u·lar adj. 1. Consisting of more than one molecule. 2. Of greater complexity than a molecule. structures, Acta Cryst. C57, 604-607 (2001). (9.) B. J. Coe, J. A. Harris, T. Gelbrich, and M. B. Hursthouse, trans-4-[4-(Dimethylamino)phenyl-iminomethyl]-N-phenylpyridinium hexafluorophosphate, Acta Cryst. C56, 1487-1489 (2000). (10.) H.-M. Yuan Yuan (yüän), river, 540 mi (869 km) long, rising in S Guizhou prov. and flowing generally NE to Donting lake, Hunan prov., SE China. Navigation above Changde is limited by rapids to small craft. , J.-S. Chen, G.-S. Zhu, J.-Y. Li, J.-H. Yu, G.-D. Yang yang (yang) [Chinese] in Chinese philosophy, the active, positive, masculine principle that is complementary to yin; see yin, under principle. , and R.-R. Xu, The First Organo-Templated Cobalt Phosphate phosphate, salt or ester of phosphoric acid, H3PO4. Because phosphoric acid is tribasic (having three replaceable hydrogen atoms), it forms monophosphate, diphosphate, and triphosphate salts in which one, two, or three of the hydrogens of the with a Zeolite zeolite Any member of a family of hydrated aluminosilicate minerals that have a framework structure enclosing interconnected cavities occupied by large metal cations (positively charged ions)—generally sodium, potassium, magnesium, calcium, and barium—and water Topology topology, branch of mathematics, formerly known as analysis situs, that studies patterns of geometric figures involving position and relative position without regard to size. , Inorg. Chem. 39, 1476-1479 (2000). (11.) A. S. Pandi, D. Velmurugan, S. Shanmuga Sundara Raj raj also Raj n. Dominion or rule, especially the British rule over India (1757-1947). [Hindi r , H.-K. Fun, P. R. Seshadri, and D. Thirumalai, 10-(4-Fluorophenyl)-3,3,6,6,9-Pentamethyl-3,4,6,7,9,10-hexahydroacrid ine-1,8(2H,5H)-dione and l0-(4-fluorophenyl)-3,3,6,6-tetramethyl-9-propyl-3,4,6,7,9,10-hexahyd roacridine-1,8(2H,5H)-dione, Acta Cryst. C57, 821-824 (2001). (12.) D. R. Boer, H. Kooijman, M. Groen, J. van der Louw, J. Kelder, and J. Kroon kroon n. pl. kroon·i See Table at currency. [Estonian, from German Krone, from Middle High German kr , Conformational comparison of five follicular fluid Follicular fluid is a liquid which fills the follicular antrum and surrounds the ovum in an ovarian follicle. This fluid is rich in hyaluronic acid. External links
adj. 1. Not active or tending to be active. 2. a. Not functioning or operating; out of use: inactive machinery. b. compounds, Acta Cryst. C57, 1177-1181 (2001). About the author: Alan D. Mighell has been a research scientist at NIST since 1964. His research interests include structural crystallography and the design and development of mathematical procedures for materials identification, for establishing lattice relationships, and for the evaluation of crystallographic data. The National Institute of Standards and Technology is an agency of the Technology Administration, U.S. Department of Commerce. |
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