Body symmetry

An important characteristic of the body plan of an animal is its symmetry. Symmetry refers to the equivalence in size and shape of sections of an animal s body. Most animals exhibit body symmetry, but a few species of sponges are asymmetrical. If a plane were passed through the body of an asymmetrical sponge, slicing it in two, the parts would not be the same. 

Some animals are radially symmetrical. Shaped like either short or long cylinders, these stationary or slow-moving organisms have distinct top and bottom surfaces but lack fronts and backs, heads or tails. A plane could pass through a radially symmetrical animal in several places to create two identical halves. Starfish, jellyfish, sea cucumbers, sea lilies, and sand dollars are a few examples of radially symmetrical animals. 

The bodies of most animals are bilaterally symmetrical, a form in which a plane could pass through the animal only in one place to divide it into two equal parts. The two halves of a bilaterally symmetrical animal are mirror images of each other. Bilateral symmetry is associated with animals that move around. The leading part of a bilaterally symmetrical animal s body contains sense organs such as eyes and nose. Fish, whales, birds, snakes, and humans are all bilaterally symmetrical. 

The cnidarian body has only one opening, the mouth, through which food is taken in and wastes are expelled. The mouths of cnidarians are surrounded with rings of tentacles. The body wall is made of two layers, the epidermis and endo-dermis, with a jellylike mesoglea between them. 

Anemones are cnidarians that develop as polyps. The body of an anemone is a thick column with two distinctive ends, as shown in the lower color insert on page C-l. The upper end, or oral disk, is a ring of tentacles around a narrow slit at the center, the mouth. Grooves beside the mouth continuously bring in water to provide oxygen to interior tissues. Depending on the species, oral disks vary in diameter from a fraction of an inch to 12 inches (30 cm). 

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Doyen [158] was one who theoretically examined the reflection of metastable atoms from a solid surface within the framework of a quantum- mechanical model based on the general properties of the solid body symmetry. From the author s viewpoint the probability of metastable atom reflection should be negligibly small, regardless of the chemical nature of the surface involved. However, presence of defects and inhomogeneities of a surface formed by adsorbed layers should lead to an abrupt increase in the reflection coefficient, so that its value can approach the relevant gaseous phase parameter on a very inhomogeneous surface. 

Rybak, S., Jeziorski,B. and Szalewicz, K. (1991)Many-body symmetry-adapted perturbation theory of intermolecular interactions. FhOandHF dimers,/. Chem. Phys., 95, 6576-6601. 

Jeziorski B, Moszynski R, Ratkiewicz A, Rybak S, Szalewicz K, Williams HL (1993) SAPT A program for many-body symmetry-adapted perturbation theory calculations of intermolecular interaction energies. In Clementi E (ed) Methods and techniques in computational chemistry METECC-94, vol B. STEF, Cagliari, pp 79-129... 

Recently, a new theoretical method of calculating potential energy and dipole/polarizability surfaces for van der Waals molecules based on symmetry-adapted perturbation theory (sapt) of intermolecular forces (12)— (15) has been developed (16)-(24). In this method, referred to as many-body symmetry-adapted perturbation theory, all physically important contributions to the potential and the interaction-induced properties, such as electrostatics, exchange, induction, and dispersion are identified and computed separately. By making a perturbation expansion in the intermolecular interaction as well as in the intramolecular electronic correlation, it is possible to sum the correlation contributions to the different physical... 

B. Jeziorski, R. Moszynski, A. Ratkiewicz, S. Rybak, K. Szalewicz, and H.L. Williams SAPT A Program for Many-Body Symmetry-Adapted Perturbation Theory Calculations of Intermolecular Interactions , in Methods and Techniques in Computational Chemistry METECC-94, vol. B Medium Size Systems, edited by E. Clementi, (STEP, Cagliari 1993), p. 79. 

R. Bukowski, W. Cencek, P. Jankowski, B. Jeziorski, M. Jeziorska, S.A. Kucharski, A.J. Misquitta, R. Moszynski, K. Patkowski, S. Rybak, K. Szalewicz, H.L. Williams and P.E.S. Wormer, SAPT2002 An ab initio program for many-body symmetry-adapted perturbation theory calculations of inter-molecular interaction energies, University of Delaware and University of Warsaw http //www.physics, udel.edu/— szalewic/SAPT/SAPT.html... 

The word S5mimetry comes from the Greek syn — together — and metron — measure — which tells us that we compare the relation of two or more things to observe symmetry. For example, we associate the word with beauty of the human form by comparing the two parts of the face and body with respect to a mirror plane bisecting our body. Symmetry is also related to the proportions of the various parts of our body with respect to each other. 

General observation of gross body symmetry and asymmetry... 

S. Rybak, B. Jeziorski, and K. Szalewicz, J. Chem. Phys., 95, 6576 (1991). Many-Body Symmetry-Adapted Perturbation Theory of Intermolecular Interactions. H2O and HF Dimers. 

Bukowski, R., Cencek, W., Jankowski, P., Jeziorski, B., Jeziorska, M., Lotrich, V., Kucharski, S., Misquitta, A. J., Moszynski, R., Patkowski, K., Podeszwa, R., Rybak, S., Szalewicz, K., Williams, H., Wheatley, R. J., Wormer, P. E. S., 8c Zuchowski, P. S. (2002). SAPT2008 An ab initio program for many-body symmetry-adapted perturbation theory calculations of intermolecular interaction energies. University of Delaware and University of Warsaw, http //www.physics.udel. edu/ szalewic/. Accessed 18 July 2011... 

Podeszwa, R., 8c Szalewicz, K. (2007). Three-body symmetry-adapted perturbation theory based on Kohn-Sham description of the monomers. Journal of Chemical Physics, 126,194101. 

Eisenschitz R, London F (1930) Z Phys 60 491 Rybak S, Jeziorski B, Szalewicz K (1991) J Chem Phys 95 6579 SAPT2002 An Ab Initio Program for Many-Body Symmetry-Adapted Perturbation Theory Calculations of Intermolecular Interaction Energies Bukowski R, Cencek W, Jankowski P, Jeziorska M, Jeziorski B, Kucharski SA, Lotrich VF, Misquitta AJ, Moszyhski R, Patkowski K, Rybak S, Szalewicz K, Williams HL, Wormer PES, University of Delaware and University of Warsaw (http //www.physics.udel.edu/ szalewic/ SAPT/SAPT.html)... 

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