Preferential sampling

A consideration of the transition probabilities allows us to prove that microscopic reversibility holds, and that canonical ensemble averages are generated. This approach has greatly extended the range of simulations that can be perfonned. An early example was the preferential sampling of molecules near solutes [77], but more recently, as we shall see, polymer simulations have been greatly accelerated by tiiis method. 

Owicki J C and Scheraga H A 1977 Preferential sampling near solutes in Monte Carlo calculations on dilute solutions Chem. Phys. Lett. 47 600-2... 

Gawler Craton, located on the edge of the Great Victoria Desert (GVD). In this part of the GVD, regolith landforms are comprised of scarce hills of weathered bedrock outcrops surrounded by sand spreads, dunes and colluvial materials the hills act as windows to the otherwise covered weathered bedrock. The outcrops themselves have been silicified and, more recently, have been overprinted with calcrete. Calcrete sampling is relatively easy on the exposed outcrops and is preferentially sampled by mineral explorers due to its near-surface location (<10-20 cm depth). However, calcrete on the colluvial slopes and in the swales is not as easily located because of concealment by GVD sand and colluvium. 

This is the most versatile approach to LC-MS, as it keeps most of the mobile phase ont of the high-vacnnm region. API interfaces are special gas-phase analyte enrichment interfaces, becanse analyte ionization takes place already in the spray chamber, and the ions generated are preferentially sampled into the vacuum system. 

When such a texture gradient exists, it must be remembered that the transmission and reflection methods preferentially sample different layers of the same specimen and that the thicknesses of the layers so sampled vary with a in a systematic way. 

Fig. 3.2.3 Relationships between coordinate systems for the description of molecular order. The orientation of the laboratory coordinate system in the principal axes system of the coupling tensor determines the angular dependence of the resonance frequency. The orientations of the preferential sample direction in a molecule-fixed coordinate frame determines the orientational distribution function.

Ordinary chondrites. The ordinary chondrites, the most common meteorites, do not show a strong signature of a cataclysm at 3.9 Ga. Bogard (1995), in pointing this out, suggested that it was a selection effect, that chondritic asteroids that suffered large impacts in the cataclysm were simply destroyed, so we preferentially sample those that were not affected. There are, however, more recent impact events that are clearly recorded in ordinary chondrites. 

A somewhat related concept is preferential sampling [46], in which molecules in the vicinity of a given point are sampled more often than the rest of the system. The reference point might, for example, be centered at a solute site conformations resulting from important solute-solvent inter-... 

---