force field
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2022 ◽  
Vol 579 ◽  
pp. 121370
Author(s):  
Fumiya Noritake ◽  
Tomoko Sato ◽  
Akane Yamamoto ◽  
Daisuke Wakabayashi ◽  
Satoru Urakawa ◽  
...  

Author(s):  
Mengmeng Ai ◽  
Wenhui Liu ◽  
Yi Shan

In the process of Ultra high voltage direct current (UHVDC) transmission, the direct current (DC) bias of power transformer is easily induced, which makes the transformer exciting current distorted, the ferromagnetic material saturated and the magnetic leakage increased, and then leads to the increase of core vibration and noise. Aiming at this problem, taking a 240 MVA, 330 kV three-phase five-column power transformer as an example, the coupling of the electromagnetic field, structural force field and acoustic field is studied, and the influence of DC bias on vibration and noise of power transformer core is analyzed in this paper. According to the magnetic density and electric density of transformer core under different magnetic bias degree, the structural force field is solved, and the displacement and surface acceleration of core are obtained, which can be as the excitation of sound field to determine the noise distribution of transformer. In order to avoid the natural frequencies which easily cause resonance, the modal analysis is needed to obtain the natural frequencies and modal modes of the core. The transformer noise under no-load and DC bias conditions of the prototype is tested experimentally and compared with the theoretical calculation, the results prove the accuracy of the simulation calculation method in this paper.


Minerva ◽  
2022 ◽  
Author(s):  
Aitor Anduaga

AbstractThe why and the how of knowledge production are examined in the case of the transnational cooperation between the directors of observatories in the Far East who drew up unified typhoon-warning codes in the period 1900–1939. The why is prompted by the socioeconomic interests of the local chambers of commerce and international telegraphic companies, although this urge has the favourable wind of Far Eastern meteorologists’ ideology of voluntarist internationalism. The how entails the persistent pursuit of consensus (on ends rather than means) in international meetings where non-binding resolutions on codes and procedures are adopted. The outcome is the co-production of standardised knowledge, that is, the development of a series of processes and practices that co-produce both knowledge and ideas about the social order in a force field characterised by negotiations and power struggles.


Author(s):  
Jun Chen ◽  
Hao Liu ◽  
Xiaochen Cui ◽  
Zhengxin Li ◽  
Hai-Feng Chen
Keyword(s):  

Molecules ◽  
2022 ◽  
Vol 27 (2) ◽  
pp. 427
Author(s):  
Igor Kochikov ◽  
Anna Stepanova ◽  
Gulnara Kuramshina

The model of Regularized Quantum Mechanical Force Field (RQMFF) was applied to the joint treatment of ab initio and experimental vibrational data of the four primary nucleobases using a new algorithm based on the scaling procedure in Cartesian coordinates. The matrix of scaling factors in Cartesian coordinates for the considered molecules includes diagonal elements for all atoms of the molecule and off-diagonal elements for bonded atoms and for some non-bonded atoms (1–3 and some 1–4 interactions). The choice of the model is based on the results of the second-order perturbation analysis of the Fock matrix for uncoupled interactions using the Natural Bond Orbital (NBO) analysis. The scaling factors obtained within this model as a result of solving the inverse problem (regularized Cartesian scale factors) of adenine, cytosine, guanine, and thymine molecules were used to correct the Hessians of the canonical base pairs: adenine–thymine and cytosine–guanine. The proposed procedure is based on the block structure of the scaling matrix for molecular entities with non-covalent interactions, as in the case of DNA base pairs. It allows avoiding introducing internal coordinates (or coordinates of symmetry, local symmetry, etc.) when scaling the force field of a compound of a complex structure with non-covalent H-bonds.


Author(s):  
Jinfeng Chen ◽  
Gerhard König

The correct reproduction of conformational substates of amino acids was tested for the CHARMM Drude polarizable force field. This was achieved by evaluating the reorganization energies for all low lying energy minima occurring in all 15 neutral blocked amino acids on a quantum-mechanical (QM) energy surface at the MP2/cc-pVDZ level. The results indicate that the bonded parameters of the N-acetyl (ACE) and N-Methylamide (CT3) blocking groups lead to significant discrepancies. A reparametrization of five bond angles significantly improved the agreement with the QM energy surface. The corrected Drude force field exhibits almost the same average reorganization energies relative to the MP2 energy surface as the AM1 and PM3 semi-empirical methods.


2022 ◽  
Author(s):  
Michael J. Robertson ◽  
Georgios Skiniotis

G protein-coupled receptors (GPCRs) and other membrane proteins are valuable drug targets, and their dynamic nature makes them attractive systems for study with molecular dynamics simulations and free energy approaches. Here, we report the development, implementation, and validation of OPLS-AA/M force field parameters to enable simulations of these systems. These efforts include the introduction of post-translational modifications including lipidations and phosphorylation. We also modify previously reported parameters for lipids to be more consistent with the OPLS-AA force field standard and extend their coverage. These new parameters are validated on a variety of test systems, with the results compared to high-level quantum mechanics calculations, experimental data, and simulations with CHARMM36m where relevant. The results demonstrate that the new parameters reliably reproduce the behavior of membrane protein systems.


2022 ◽  
Author(s):  
Darian Yang ◽  
Angela Gronenborn ◽  
Lillian Chong

We developed force field parameters for fluorinated aromatic amino acids enabling molecular dynamics (MD) simulations of fluorinated proteins. These parameters are tailored to the AMBER ff15ipq protein force field and enable the modeling of 4, 5, 6, and 7F-tryptophan, 3F- and 3,5F-tyrosine, and 4F- or 4-CF3-phenylalanine. The parameters include 181 unique atomic charges derived using the Implicitly Polarized Charge (IPolQ) scheme in the presence of SPC/Eb explicit water molecules and 9 unique bond, angle, or torsion terms. Our simulations of benchmark peptides and proteins maintain expected conformational propensities on the μs-timescale. In addition, we have developed an open-source Python program to calculate fluorine relaxation rates from MD simulations. The extracted relaxation rates from protein simulations are in good agreement with experimental values determined by 19F NMR. Collectively, our results illustrate the power and robustness of the IPolQ lineage of force fields for modeling structure and dynamics of fluorine containing proteins at the atomic level.


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