The study of a two-dimensional (2-D) system started nearly half a century ago when Peierls and Landau showed the lack of long range translational order in a two-dimensional solid. In 1968, Mermin proved that despite the absence of long range translational order, two-dimensional solids can still exhibit a different kind of long range bond orientation. During the last decade, fascinating theories were put forward to explain the role of topological defects in the melting of two-dimensional solids, starting with Kosterlitz and Thouless. Recent surge of interest in melting is also due to the theoretical ideas of Halperin, Nelson and Young. They have suggested that the transition may be fundamentally different from that observed in ordinary three-dimensional systems. Computer SIMULATIONs suggest that the transition is of the usual first-order type observed in a three-dimensional system. A large body of experimental and SIMULATION research into the two-dimensional melting followed the announcement of the KTHNY theory. In spite of all this effort, the question as to the nature of two dimensional melting remains unresolved. Recent experimental work supporting the existence of continuous melting transitions in some two dimensional systems indicates the need for further theoretical and computational work to lead to an understanding of the experimental results.In this paper we intend to summarize and clarify the current situation with regard to research in the two-dimensional melting with an emphasis on computer SIMULATIONs. The paper begins with an overview of the current status of relevant theoretical, experimental and SIMULATION research, then a two-dimensional SIMULATION of an ionic salt system is studied in detail. This SIMULATION has been done by using the MOLECULAR DYNAMICS method. The most important parameters that have been determined are: The transition temperature, the total energy of the system, the mean square displacement and the bond angle distribution. The transition temperature of the system has been specified by plotting some of these parameters as a function of temperature and time. The first order transition is observed. It is difficult to distinguish a hexatic phase from a two-phase coexistence region.

A new MOLECULAR DYNAMICS SIMULATION technique for simulating fluids in confinement [H. Eslami, F. Mozaffari, J. Moghadasi, F. Müller-Plathe, J. Chem. Phys. 129 (2008) 194702] is employed to simulate the diffusion coefficient of nanoconfined Lennard-Jones fluid. The diffusing fluid is liquid Ar and the confining surfaces are solid Ar fcc (100) surfaces, which are kept frozen during the SIMULATION. In this SIMULATION just the fluid in confinement is simulated at a constant temperature and a constant parallel component of pressure, which is assumed to be equal to the bulk pressure. It is shown that the calculated parallel (to the surfaces) component of the diffusion coefficients depends on the distance between the surfaces (pore size) and shows oscillatory behavior with respect to the intersurface separations. Our results show that on formation of well-organized layers between the surfaces, the parallel diffusion coefficients decrease considerably with respect to the bulk fluid. The effect of pressure on the parallel diffusion coefficients has also been studied. Better organized layers, and hence, lower diffusion coefficients are observed with increasing the pressure.

Amylin is a 37 residue peptide with a disulfide bridge between the residues 2 and 7. This hormone co-secreted with insulin by pancreatic islet b-cells. It has been reported that amylin is able to form amyloid fibrils. Although these fibrils are not related with the manifestation of type 2 diabetes, they have a significant role in the aggravation of diabetic condition. In this study, the potential of amyloid formation and stability of amylin has been studied in 10 species with high sequence similarity (80%), with the use of MOLECULAR DYNAMICS SIMULATION. Based on the structure of human amylin (2L86.pdb from Protein Data Bank) homology modeling technique was used to create 10 different species amylin. SIMULATION was performed using GROMACS version 4.6.1, with a 10 ns duration and 500K. The systems were solvated with SPC water molecules. Secondary structure content was calculated using DSSP. Other analyses such as energy, solvent accessible surface, radius of gyration, RMSD and RMSF were performed, using GROMACS. Human and Rat amylin were selected as non-aggregating peptides respectively. During SIMULATION amylin showed remarkable structural changes, and in most cases α-helical structures were lost. In some species with aggregating amylin, b -sheets were formed at the end of the SIMULATION. Between the studied species, Pongoabelii peptide, one of the two species of orangutans used in this study, showed more stability alongside with more similarity to human amylin. Based on these results, this amylin specie could be proposed as a potential therapeutic peptide, as an alternative to rat amylin.