Dynamically modified windows

Pearlman, D. A. Kollman, P. A., A new method for carrying out free energy perturbation calculations dynamically modified windows, J. Chem. Phys. 1989, 90, 2460-2470... 

An example of the first approach is method of Dynamically Modified Windows (DMW).18 DMW approximates the slope of the accumulated free... 

Pearlman D A and P A Kollman 1989. A New Method for Carrying Out Free-Energy Perturbation Calculations - Dynamically Modified Windows Journal Of Chemical Physics 90 2460-2470. 

D. A. Pearlman and P. A. Kollman,/. Ghent. Phys., 90, 2461 (1989). A New Method for Carrying Out Energy Perturbation Calculations Dynamically Modified Windows. 

This latter assumption was the inspiration behind the dynamically modified windows approach. In this method, the slope of the AG versus X curve over the last several windows, M, is used to predict the slope over the next window. This is used in turn to adjust 5X for the next window in an attempt to keep AG at each window approximately constant and equal to AGtarged... 

Carrying out Free Energy Perturbation Calculations Dynamically Modified Windows. 

Karcher and KruII [30] used complexometric calculations to determine the mobile phase concentrations of HIBA and tartaric acid needed to fine tune their separation of eleven metal cations on C and Ci silica-based reverse-phase columns which had been dynamically modified with n-octanesulfonate. Isocratic elution was used to separate the metals into three distinct windows each window corresponding to one of the three dififerent valence states spanned by the eleven metal cations. The metals eluted in the order of increasing valence, with the sole exception of La(III) which did not elute within the trivalent ion window. Figure 6.15 illustrates the separation of ZrdV), Ga(III), Sc(III), Y(III), Al(III), In(III), Zn(II), La(III), Cd(II), Ca(II), and Mg(II) using a Cis column and an eluent comprised of 2.27 mM n-octanesulfonate, 8.18 mM tartaric acid, 52.9 mM HIBA, and 10.7% (v/v) methanol. 

The distributions of (R)tw obtained for a polypeptide immobilized on the attractive surface are presented in Fig. 11. Surface-immobilization is seen once again not to affect the behavior of the folded state. In this case, surface immobilization is also seen to have a relatively minor effect on the behavior at the midpoint. However, the behavior in unfolded states a and fi is clearly influenced by surface immobilization in this case. More specifically, the (R)tw distributions are hardly affected by the time-window-averaging for values of Tw that were seen to significantly modify the (R)tw distributions in the freely diffusing and repulsive surface-immobilized cases. This can be attributed to the slower dynamics of the unfolded polypeptide on the attractive surface. At the same time, conformations with a small value of R are still seen to move faster than conformations with a large value of R, as for the freely diffusing polypeptide. 

Yan et al. [52] explored the use of IPN techniques to produce a composite vinyl-acrylic latex. The first-formed polymer was produced using VAc and divinyl benzene (DVB), while the second formed polymer constituted a BA/DVB copolymer. In both cases the DVB was added at 0.4 wt%. They compared this product with another product, a bidirectional interpenetrating netwodc (BIPN) in which VAc was again polymerized over the first IPN. They noted that the compatibility between the phases was more pronounced in the BIPN than in the IPN as determined using dynamic mechanical measurements and C nuclear magnetic resonance spectroscopy. The concept of polymer miscibility has also been used to produce composite latex particles and thus modify the pafamance properties of VAc latexes. Bott et al. [53] describe a process whereby they bloid VAc/ethylene (VAc/E) copolymers with copolymers of acrylic acid or maleic anhydride and determine windows of miscibility. Apparently an ethyl acrylate or BA copolymer with 10-25 wt% AA is compatible with a VAc/E copolymer of 5-30 wt% ethylene. The information obtained from this woik was then used to form blends of latex polymers by polymerizing suitable mixtures of monomers into preformed VAc/E copolymers. The products are said to be useful for coating adhesives and caulks. 

The last Windows version release of SPDM 3.0 (Shell 1998) contains modules for thickness design, rutting calculations and asphalt overlay design. Additionally, more emphasis was given to material properties incorporating the use of polymer-modified bitumen. The rutting calculations are now based on creep characteristics obtained from dynamic and not static tests, since it appeared not to be applicable to modified bitumen (Lijzenga 1997). 

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