Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

sions: In the greater residential areas, the overall rating sound level does not exceed 53 dB(A). In the future this level might
decrease by 1 dB.
Author
Sound Propagation; Guns (Ordnance); Gunfire
20010022795 Institute TNO of Applied Physics, Delft, Netherlands
Literature Study on the Modelling of Target Echo Strength Final Report
Giling, E. J. M., Institute TNO of Applied Physics, Netherlands; Aug. 25, 2000; 32p; In English
Contract(s)/Grant(s): A97/KM/125; TNO Proj. 008.00762
Report No.(s): HAI-RPT-990015; TD-990308; Copyright; Avail: Issuing Activity
In this document, the results of a literature study and software search on the numerical modelling of Target Echo Strength
(also ”TES”, ”Target Strength” or ”TS”) are reported.
Author
Mathematical Models; Echoes; Computer Programs
262
72
ATOMIC AND MOLECULAR PHYSICS
�������� ������ ��� ��������� ���������� �������� ����������� ��� ������ ��� ��������� �������� ��� ���������� �������� ������� ���
�� ������� ��������
20010022632 Stanford Univ., Center for Turbulence Research, Stanford, CA USA
Calculating Free Energies Using Scaled-Force Molecular Dynamics Algorithm
Darve, Eric, Stanford Univ., USA; Wilson, Micahel A., NASA Ames Research Center, USA; Pohorille, Andrew, NASA Ames
Research Center, USA; Annual Research Briefs - 2000: Center for Turbulence Research; December 2000, pp. 3-16; In English;
See also 20010022631; No Copyright; Avail: CASI; A03, Hardcopy; A03, Microfiche
One common objective of molecular simulations in chemistry and biology is to calculate the free energy difference between
different states of the system of interest. Examples of problems that have such an objective are calculations of receptor-ligand or
protein-drug interactions, associations of molecules in response to hydrophobic, and electrostatic interactions or partition of molecules
between immiscible liquids. Another common objective is to describe evolution of the system towards a low energy (possibly
the global minimum energy), ’native’ state. Perhaps the best example of such a problem is folding of proteins or short RNA
molecules. Both types of problems share the same difficulty. Often, different states of the system are separated by high energy
barriers, which implies that transitions between these states are rare events. This, in turn, can greatly impede exploration of phase
space. In some instances this can lead to ’quasi non-ergodicity’, whereby a part of phase space is inaccessible on timescales of
the simulation. A host of strategies has been developed to improve efficiency of sampling the phase space. For example, some
Monte Carlo techniques involve large steps which move the system between low-energy regions in phase space without the need
for sampling the configurations corresponding to energy barriers (J-walking). Most strategies, however, rely on modifying probabilities
of sampling low and high-energy regions in phase space such that transitions between states of interest are encouraged.
Perhaps the simplest implementation of this strategy is to increase the temperature of the system. This approach was successfully
used to identify denaturation pathways in several proteins, but it is clearly not applicable to protein folding. It is also not a successful
method for determining free energy differences. Finally, the approach is likely to fail for systems with co-existing phases, such
as water-membrane systems, because it may lead to spontaneous mixing. A similar difficulty may be encountered in any method
relying on global modifications of phase space.
Author
Algorithms; Free Energy; Molecular Dynamics; Mathematical Models
20010026183 Oak Ridge National Lab., TN USA
Neutron Total Cross Sections of U-235 From Transmission Measurements in the Energy Range 2 keV to 300 keV and Statistical
Model Analysis of the Data
Derrien, H.; Harvey, J. A.; Larson, N. M.; Leal, L. C.; Wright, R. Q.; May 01, 2000; 44p; In English
Report No.(s): DE00-763240; ORNL/TM-2000/129; No Copyright; Avail: Department of Energy Information Bridge