Combination Of Model Calculations Research Articles

Assessment of N and P status at the landscape scale using environmental models and measurements

We assessed the compliance of a Dutch landscape, dominated by dairy farming, with environmental quality standards using a combination of model calculations and measurements. The total ammonia emission of 2.4 kton NH 3 yr −1 does not exceed the environmental quality standard (2.6 kton NH 3 yr −1). Nevertheless, the total N deposition (on average 24.4 kg N ha −1 yr −1) is such that critical N loads are exceeded at 53% of the nature areas. The deposited N mainly results from non-agricultural sources and agricultural sources outside the area (72%). The calculated average NO 3 − concentration in the upper groundwater does not exceed the 50 mg l −1 threshold. Calculated annual average N-total and P-total concentrations in discharge water are relatively high but these cannot be directly compared with thresholds for surface water. The results suggest that compliance monitoring at the landscape scale needs to include source indicators and cannot be based on state indicators alone.

Conformational analysis of dipeptide‐derived polyisocyanides

AbstractThe conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003

Orientationally Enhanced Photocurrent and Electrooptic Modulation Effects in Bacteriorhodopsin/Polyvinyl Alcohol Thin Films

Polymeric films of bacteriorhodopsin, formed by embedding purple membrane fragments into a poly(vinyl alcohol) matrix without field poling, exhibit modulated photocurrent and electrooptic effects when an AC modulating rectangular voltage or a sinusoidal voltage is applied across the films. When the modulating frequencies are lower than 100 Hz, both effects are enhanced by the orientation of the purple membrane fragments and exhibit two different orientational time constants. The orientational enhancement at low frequencies (∼7.1 Hz) arises from the permanent dipole moments of membranes, and the enhancement at higher frequencies (∼74.8 Hz) is attributed to the induced dipole moments of the purple membrane molecules. For quantitative analyses of these processes, a theoretical model is proposed. From the combination of model calculations and fitted experimental results, we determine that the permanent dipole moment of the membrane material is ∼33 kD and the induced dipole moment is ∼10-13 cm3. We also demonstrate that when a poling field is applied across the films, the electrooptic coefficients are increased linearly with increasing field strength.

Optimization of the Hydrodynamic Bead Model for the Analysis of DNA Conformations in Solution

The construction of detailed bead models with atomic resolution has been proposed to identify DNA and RNA conformations by hydrodynamic methods in solution. Comparison of model predictions with experimental values for the translational and rotational diffusion coefficients of a homologous series of double-helical B-DNA oligonucleotides has demonstrated the validity and consistency of this strategy when hydration of the molecules is properly accounted for. Further investigations of “hairpin” and quadruplex model oligonucleotides reveal the potential of this technique to differentiate between DNA conformations. This combination of model calculations with experimental hydrodynamic methods provides a powerful means to identify DNA or RNA conformations in solution, follow conformational changes under a wide variety of solvent conditions, or characterize intermolecular associations with other components of (bio)molecular importance.