Visualization of solvation structures in liquid mixtures.

Spatial distribution functions of atomic densities. SDFs, have been proposed as a natural starting point for analysis of local molecular structure in liquids and solutions. The local structure in these systems is often complex and this is reflected in the fact that SDFs can be difficult to visualize. Among the different methods that can be used to visualize SDFs we discuss 3D isodensity surfaces, cross-sections, and 'comic book' animations. We also discuss the possibility of a simultaneous visualization of SDFs and other 3D fields, such as the electron density. These techniques are all intended to emphasize and bring out aspects of SDFs that promote a further understanding of the local molecular structure. OpenGL-based software has been used under X-Windows to implement these techniques, and we argue that high-quality molecular graphics need not be expensive. Data from a molecular dynamics simulation of an equimolar binary mixture of water and acetonitrile have been used to illustrate the discussion.

Evaluation of four deoxyribonucleic acid (DNA) extraction protocols for DNA yield and variation in restriction fragment length polymorphism (RFLP) sizes under varying gel conditions.

This study originated from discussions and recommendations of the Technical Working Group on DNA Analysis Methods (TWGDAM). Four bloodstain deoxyribonucleic acid (DNA) extraction protocols and five semen stain DNA extraction protocols were evaluated. Nine laboratories participated in the extraction of DNA from 20 bloodstains and 20 semen stains using each protocol. All blood and semen stains originated from a single donor and were prepared under uniform conditions to permit the direct comparison of DNA yields and restriction fragment lengths. The extracted DNA from approximately 600 bloodstains and 700 semen stains was quantified by yield gel analysis and a slot blot hybridization technique. The extracted DNA was digested and restriction fragment length polymorphism (RFLP) patterns were generated using three single-locus probes. The RFLP sizing data produced from the blood and semen stains were evaluated with respect to (1) DNA extraction method, (2) gel length, (3) agarose type, (4) presence or absence of ethidium bromide in the gel, and (5) fragment sizes obtained from DNA isolated directly from the donor's liquid blood. This study demonstrates conclusively that high-molecular-weight DNA can be isolated using either organic or nonorganic DNA extraction protocols and that the resulting RFLP sizes are highly reproducible regardless of gel length, agarose type, or presence/absence of ethidium bromide.

Scaling properties of the placenta's arterial tree.

The purpose of the present work is to establish a basic knowledge about the scaling properties of the placenta's arterial tree. For this end we have analysed X-ray angiograms of 22 normal arterial trees by box counting. All the investigated arterial trees scale closely according to a power-law over a one decade wide range of scales. Perfectly self-similar fractals, of the same resolution as our representation of the arterial tree, do not follow a power-law more closely. The results support the hypothesis that a mechanism or rule--as regular as those which dictate the structure of perfectly self-similar fractals--also determines fundamental aspects of the arterial tree's morphology.

Topological and spatial aspects of the hydration of solutes of extreme solvation entropy.

The hydration of charged Lennard-Jones spheres by simple point charge water is considered. Molecular dynamics and expanded ensemble simulations were used to compare the hydration structures surrounding solutes with extreme solvation entropy. The variations in the solvation entropy were analyzed in terms of changes in the spatial and topological structure of the hydration shells. The solvation entropy was found to be maximal for solutes that can replace water molecules in the hydrogen-bond network. Further, using a Kirkwood-type factorization, the solvation entropy was expanded as a sum over the partial n-body distribution functions. The two-body solute-water contribution to the solvation entropy was found to exceed the full solvation entropy for solutes with low charge, whereas the converse is true for the other solutes. This is consistent with the idea that water-water correlations are enhanced by solvation of, for example, noble gases, whereas they are disrupted by solvation of ions. Further, the orientational and radial parts of the two-body solute-water entropy were calculated as functions of the charge of the solute. The orientational part has a single maximum, whereas the radial part maintains the bimodal form of the full solvation entropy.