The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Y T Chew - One of the best experts on this subject based on the ideXlab platform.
-
a model for the frequency response of a near wall hot wire Velocity Perturbation and sine wave voltage Perturbation tests
Experimental Thermal and Fluid Science, 2003Co-Authors: Boo Cheong Khoo, Y T ChewAbstract:Abstract A simplified 1-D model is developed to compute the response of a near-wall hot wire as subjected to a Velocity Perturbation and sine-wave voltage Perturbation tests. The calculated frequency response, f D (according to the Velocity Perturbation test) and f bulge (according to the sine-wave Perturbation test) are compared to previous experimental works, and to ascertain the relationship proposed by Teo et al. [Meas. Sci. Technol. 12 (2001) 37] between f D and f bulge . The behavioral trends of f D and f bulge are evaluated in terms of varying convection Velocity, influence of wall effects and other pertinent factors. Although f D and f bulge share many similar characteristics and trends, the differences between the two responses give rise to the suggestion that while f D measures the response of heat lost from the wire in near-wall vicinity by Velocity Perturbation, f bulge measures the frequency response to the total heat lost from the wire.
-
the dynamic response of a hot wire anemometer iii voltage Perturbation versus Velocity Perturbation testing for near wall hot wire film probes
Measurement Science and Technology, 1999Co-Authors: Boo Cheong Khoo, Y T ChewAbstract:Experiments were performed for the first time using the electronic square-wave voltage-Perturbation test to systematically quantify the frequency response of near-wall hot-wire probes subjected in turn to varying magnitudes of convective Velocity, different substrate materials and changes in wall-substrate temperature. In addition, quartz-substrate hot-film gauges with various thicknesses of quartz coating were also tested. Results of were compared against the dynamic frequency response previously obtained in parts I and II using a known near-wall fluctuating flow field. Although the observed trends for and were similar, their magnitudes were vastly different, notably for the commercially available hot-film gauges, or which was up to five orders of magnitude greater than . This signifies that there are possibly inherent differences between square-wave voltage-Perturbation and Velocity-Perturbation tests for quantifying the frequency response of a hot-wire/hot-film system. These differences are then analysed in relation to the equation of a CTA unit put forth by Freymuth.
Boo Cheong Khoo - One of the best experts on this subject based on the ideXlab platform.
-
a model for the frequency response of a near wall hot wire Velocity Perturbation and sine wave voltage Perturbation tests
Experimental Thermal and Fluid Science, 2003Co-Authors: Boo Cheong Khoo, Y T ChewAbstract:Abstract A simplified 1-D model is developed to compute the response of a near-wall hot wire as subjected to a Velocity Perturbation and sine-wave voltage Perturbation tests. The calculated frequency response, f D (according to the Velocity Perturbation test) and f bulge (according to the sine-wave Perturbation test) are compared to previous experimental works, and to ascertain the relationship proposed by Teo et al. [Meas. Sci. Technol. 12 (2001) 37] between f D and f bulge . The behavioral trends of f D and f bulge are evaluated in terms of varying convection Velocity, influence of wall effects and other pertinent factors. Although f D and f bulge share many similar characteristics and trends, the differences between the two responses give rise to the suggestion that while f D measures the response of heat lost from the wire in near-wall vicinity by Velocity Perturbation, f bulge measures the frequency response to the total heat lost from the wire.
-
the dynamic response of a hot wire anemometer iii voltage Perturbation versus Velocity Perturbation testing for near wall hot wire film probes
Measurement Science and Technology, 1999Co-Authors: Boo Cheong Khoo, Y T ChewAbstract:Experiments were performed for the first time using the electronic square-wave voltage-Perturbation test to systematically quantify the frequency response of near-wall hot-wire probes subjected in turn to varying magnitudes of convective Velocity, different substrate materials and changes in wall-substrate temperature. In addition, quartz-substrate hot-film gauges with various thicknesses of quartz coating were also tested. Results of were compared against the dynamic frequency response previously obtained in parts I and II using a known near-wall fluctuating flow field. Although the observed trends for and were similar, their magnitudes were vastly different, notably for the commercially available hot-film gauges, or which was up to five orders of magnitude greater than . This signifies that there are possibly inherent differences between square-wave voltage-Perturbation and Velocity-Perturbation tests for quantifying the frequency response of a hot-wire/hot-film system. These differences are then analysed in relation to the equation of a CTA unit put forth by Freymuth.
Daniel Sebastiani - One of the best experts on this subject based on the ideXlab platform.
-
vibrational circular dichroism from ab initio molecular dynamics and nuclear Velocity Perturbation theory in the liquid phase
Journal of Chemical Physics, 2016Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear Velocity Perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liq...
-
nuclear Velocity Perturbation theory for vibrational circular dichroism an approach based on the exact factorization of the electron nuclear wave function
Journal of Chemical Physics, 2015Co-Authors: Arne Scherrer, Daniel Sebastiani, Federica Agostini, E K U Gross, Rodolphe VuilleumierAbstract:The nuclear Velocity Perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear Velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.
-
nuclear Velocity Perturbation theory of vibrational circular dichroism
Journal of Chemical Theory and Computation, 2013Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first implementation of vibrational circular dichroism (VCD) within density functional theory (DFT) using the nuclear Velocity Perturbation (NVP) theory. In order to support VCD calculations in large-scale systems such as solvated (bio)molecules and supramolecular assemblies, we have chosen a plane-wave electronic structure code (CPMD). This implementation allows the incorporation of fully anharmonic effects in VCD spectra on the basis of ab initio molecular dynamics simulations. On the conceptual level, we compare our NVP results for rigid molecules with an existing implementation based on the magnetic field Perturbation (MFP) technique using a Gaussian basis set and find an excellent agreement. Regarding numerical aspects, we analyze our results for their correct origin dependence and gauge invariance of the physical observables. The correlation with experimental data is very satisfactory, with certain deviations mainly due to the level of electronic structure theory used.
Arne Scherrer - One of the best experts on this subject based on the ideXlab platform.
-
vibrational circular dichroism from ab initio molecular dynamics and nuclear Velocity Perturbation theory in the liquid phase
Journal of Chemical Physics, 2016Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear Velocity Perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liq...
-
nuclear Velocity Perturbation theory for vibrational circular dichroism an approach based on the exact factorization of the electron nuclear wave function
Journal of Chemical Physics, 2015Co-Authors: Arne Scherrer, Daniel Sebastiani, Federica Agostini, E K U Gross, Rodolphe VuilleumierAbstract:The nuclear Velocity Perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear Velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.
-
nuclear Velocity Perturbation theory of vibrational circular dichroism
Journal of Chemical Theory and Computation, 2013Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first implementation of vibrational circular dichroism (VCD) within density functional theory (DFT) using the nuclear Velocity Perturbation (NVP) theory. In order to support VCD calculations in large-scale systems such as solvated (bio)molecules and supramolecular assemblies, we have chosen a plane-wave electronic structure code (CPMD). This implementation allows the incorporation of fully anharmonic effects in VCD spectra on the basis of ab initio molecular dynamics simulations. On the conceptual level, we compare our NVP results for rigid molecules with an existing implementation based on the magnetic field Perturbation (MFP) technique using a Gaussian basis set and find an excellent agreement. Regarding numerical aspects, we analyze our results for their correct origin dependence and gauge invariance of the physical observables. The correlation with experimental data is very satisfactory, with certain deviations mainly due to the level of electronic structure theory used.
Rodolphe Vuilleumier - One of the best experts on this subject based on the ideXlab platform.
-
vibrational circular dichroism from ab initio molecular dynamics and nuclear Velocity Perturbation theory in the liquid phase
Journal of Chemical Physics, 2016Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear Velocity Perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liq...
-
nuclear Velocity Perturbation theory for vibrational circular dichroism an approach based on the exact factorization of the electron nuclear wave function
Journal of Chemical Physics, 2015Co-Authors: Arne Scherrer, Daniel Sebastiani, Federica Agostini, E K U Gross, Rodolphe VuilleumierAbstract:The nuclear Velocity Perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear Velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.
-
nuclear Velocity Perturbation theory of vibrational circular dichroism
Journal of Chemical Theory and Computation, 2013Co-Authors: Arne Scherrer, Rodolphe Vuilleumier, Daniel SebastianiAbstract:We report the first implementation of vibrational circular dichroism (VCD) within density functional theory (DFT) using the nuclear Velocity Perturbation (NVP) theory. In order to support VCD calculations in large-scale systems such as solvated (bio)molecules and supramolecular assemblies, we have chosen a plane-wave electronic structure code (CPMD). This implementation allows the incorporation of fully anharmonic effects in VCD spectra on the basis of ab initio molecular dynamics simulations. On the conceptual level, we compare our NVP results for rigid molecules with an existing implementation based on the magnetic field Perturbation (MFP) technique using a Gaussian basis set and find an excellent agreement. Regarding numerical aspects, we analyze our results for their correct origin dependence and gauge invariance of the physical observables. The correlation with experimental data is very satisfactory, with certain deviations mainly due to the level of electronic structure theory used.
