Generalized Frequency Spectrum Research Articles

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Thermal neutron cross-section libraries for aromatic hydrocarbons

Abstract Solid phases of aromatic hydrocarbons, such as benzene, toluene, mesitylene and a 3:2 mixture by volume of mesitylene and toluene, were studied as potential moderator materials for a cold neutron source. Existing information on the (lattice) translational and rotational modes of the different molecular species was used to produce generalized frequency spectra; the latter included the internal vibrational modes which in turn involved the analysis of the weights of the different modes. Cross-section libraries were generated in ENDF and ACE formats for hydrogen bounded in those materials at several temperatures, and were used in Monte Carlo calculations to analyze their neutron production compared with standard cryogenic materials like liquid hydrogen and solid methane, the best moderators in terms of cold neutron production. In particular, cross-section libraries were generated at 20 K, which is a typical operating temperature for the majority of the existing cold neutron sources. It was found that those aromatic hydrocarbons produce neutron spectra which are slightly warmer than that of solid methane while presenting a high resistance to radiation, conforming in this way a new and advantageous alternative to traditional moderator materials.

A method to correct optical fiber's spectrum attenuation based on Fourier transform in spectra-measuring systems

A method based on Fourier transform to revise the non-linear spectrum attenuation of optical fiber used as a probe in a spectrum-measuring system is proposed in this paper. Spectral curves of a normal light source are measured by a spectrum-measuring system with and without the optical fiber probe, respectively. The generalized frequency spectrum (GFS) of these spectral curves can be calculated based on Fourier transform. From them, an optical fiber spectrum correction function can be obtained and the non-linear spectrum attenuation of optical fiber can be revised with the SCF. The experiment results show that the method has the accuracy of 1% and it is more accurate than the Ratio Method (RM) and the Weighted Ratio Method (WRM).

Atomic dynamics of liquid lithium and lithium-hydrogen melt investigated by inelastic neutron scattering

From the experimental data on inelastic neutron scattering the frequency spectrum of lithium atomic vibrations is extracted at the temperature of 22, 227, 397 and 557°C. The frequency spectrum for lithium-hydrogen melt (98 at.% Li7, 2 at.% H) has been obtained at 557°C. Based on the frequency spectrum, the temperature dependencies of the mean-square of the lithium atoms displacements in time, the mean-square amplitude of atomic vibrations, velocity autocorrelation function of atoms are calculated. A generalized frequency spectrum of hydrogen atomic vibrations in lithium-hydrogen melt is obtained.

Study of the microdynamics of liquid lithium and lithium-hydrogen melt by inelastic neutron scattering

The frequency spectra of vibrations of Li atoms at temperatures of 22, 227, 397, and 557°C and the lithium-hydrogen melt (98 at % 7Li, 2 at % H) at 557°C have been obtained from the experimental neutron inelastic scattering data. On the basis of the frequency spectra, the temperature dependences of the mean-square displacement of Li atoms, the mean-square amplitudes of atomic vibrations, and the velocity autocorrelation function of atoms have been calculated. The speed of sound in liquid lithium has been estimated within the Debye model. The frequency spectra of lithium-hydrogen melt and solid lithium hydride are compared. A generalized frequency spectrum of vibrations of hydrogen atoms in lithium-hydrogen melt is obtained.

Generalized frequency spectra of water at both sides of the freezing transition

We report a comparison of the experimental frequency distributions of heavy water on both sides of the melting transition. The spectra for ice about 3 ∘ below melting point shows a still narrow first peak at about 6.5 meV as well as a gap centered at about 40 meV separating both the “translational” and “librational” bands. Such features are profoundly modified upon melting. The first peak is still present in the liquid as a well-defined entity although significantly broader than that shown by the hot crystal. The derived Z( ε) spectra is then used for a tentative assignment of features appearing on the Raman spectrum of the liquid.