Water and simulation

The fatigue behaviour of pure hydroxy- and fluorhydroxyapatite-sintered bioceramics has been studied in ambient air, distilled water and simulated human saliva [86]. The authors observed that, as a general trend, HA ceramics exhibited a lower resistance to fatigue than fluoridated ones. Another work [87] showed that the hardness remained essentially unchanged until 80% of OH were replaced with F , whereas it noticeably increased with greater fluoride contents. The elastic... 

Barcelo, D., G. Durand, V. Bouvot, and M. Nielen (1993). Use of extraction disks for trace enrichment of various pesticides from river water and simulated seawater samples followed by liquid chromatography-rapid-scanning UV-visible and thermospray-mass spectrometry detection. Environ. Sci. Technol., 27(2) 271-277. 

The concentration profile during the dissolution testing of melphalan tablets in water and simulated gastric fluid was determined by HPLC. A method of data analysis was developed to take into account the spontaneous drug degradation [111]. 

Single extractants water and simulated acid rain at pH 4... 

Nordli et al. (146), using the Langmuir-balance technique, studied the monolayer properties of the interfacially active fractions extracted from six North Sea crude oils over a subphase of distilled water and simulated formation water. The pH and salinity were varied. They compared additives such as butanol, benzyl alcohol, and octylamine, added to the subphase, to note changes in film compressibilities. A typical phase-change pattern for Langmuir ciuves of siuface pressure versus area was observed for all cases. The smallest specific area attributed to the liquid ex-... 

Table 8.6 Retention time stabilities and recoveries for nine haloacetic acids in deionized water and simulated matrix l...

The solubilities of some steroids in water and simulated intestinal fluid are related to increased anabolic and androgenic efficiency. 

Thus, we have found unexpected complexities and even in this simple system have not yet been unable to accurately extrapolate the results of simulations done over periods varying from 1 to several hundred ps, to the low-friction conditions of extraction experiments performed in times on the oi dc r of ms. The present results indicate that one should not expect agreement between extraction experiments and simulations in more complex situations typically found in experiments, involving also a reverse flow of water molecules to fill the site being evacuated by the ligand, unless the simulation times are prolonged well beyond the scope of current computational resources, and thereby strengthen the conclusion reached in the second theoretical study of extraction of biotin from it.s complex with avidin [19]. 

Calculations of relative partition coefficients have been reported using the free energy perturbation method with the molecular dynamics and Monte Carlo simulation methods. For example, Essex, Reynolds and Richards calculated the difference in partition coefficients of methanol and ethanol partitioned between water and carbon tetrachloride with molecular dynamics sampling [Essex et al. 1989]. The results agreed remarkably well with experiment... 

Molecular dynamics simulations of proteins often begin with a known structure (such as an X-ray diffraction structure) that you want to maintain during equilibration. Since the solvent may contain high energy hot spots, equilibration of the protein and solvent at the same time can change the protein conformation. To avoid this, select only the water molecules and run a molecular dynamics equilibration. This relaxes the water while fixing the protein structure. Then deselect the water and equilibrate the whole system. 

HyperChem allows solvation of arbitrary solutes (including no solute) in water, to simulate aqueous systems. HyperChem uses only rectangular boxes and applies periodic boundary conditions to the central box to simulate a constant-density large system. The solvent water molecules come from a pre-equilibrated box of water. The solute is properly immersed and aligned in the box and then water molecules closer than some prescribed distance are omitted. You can also put a group of non-aqueous molecules into a periodic box. 

If an opportunistic preconcentration of the feed is used instead, an entirely different flow sheet results. In this case the MSA composition is a two-phase mixture of methylene chloride and water. Detailed simulations ate requited to determine which of these (or other) 2-ptopanol dehydration flow sheet alternatives is the economically advantaged process. 

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