Static Fluctuations Research Articles

Энергетический спектр и спектр оптического поглощения фуллерена C-=SUB=-24-=/SUB=- в модели Хаббарда

Anticommutator Green’s functions and energy spectra of fullerene C24 with the D6, D6d, and Oh symmetry groups have been obtained in an analytical form within the Hubbard model and static fluctuation approximation. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of fullerene C24 with the D6, D6d, and Oh symmetry groups have been determined.

Энергетический спектр и спектр оптического поглощения фуллерена С-=SUB=-28-=/SUB=- в модели Хаббарда

Anticommutator Green’s functions and energy spectra of fullerene C28 and endofullerene Zr@C28 with the Td symmetry groups have been obtained in an analytical form within the Hubbard model and static fluctuation approxima-tion. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of fullerene C28 and endofull-erene Zr@C28 with the Td symmetry groups have been determined.

Influence of T-128 wind tunnel perforated walls on aerodynamic characteristics of reentry vehicles at transonic speed

The paper is devoted to the study of the influence of wind tunnel perforated walls on the aerodynamic characteristics of the reentry vehicle model at transonic speed. An experimental investigations were conducted with a model at zero angle of attack in the T-128 TsAGI transonic wind tunnel within the range of Mach numbers M = 0.9–1.1 at three perforation ratios of test section walls F = 2; 6; 10%. Aerodynamic forces and moments acting on the model were measured with a six-component internal strain-gauge balance. A distribution of static pressure on the model surface and on the test section perforated walls was measured along with static pressure fluctuations. Integral parameters of the boundary layer on the perforated wall were measured by means of the rake with total pressure probes. Numerical investigations of the flow around the model in the test section were performed by solving Reynolds Averaged Navier–Stocks (RANS) equations using the Electronic Wind Tunnel software (EWT-TsAGI). Satisfactory agreement was obtained between the computational and experimental data on the effect of the test section perforated walls on the aerodynamic characteristics of the model and the flow parameters on the wall. The influence of the perforation coefficient on the model drag coefficient in the calculations and in the experiment had the same trend. The maximum error of the drag coefficient at a simplified computational model is estimated to be 0.05. The highest effect of perforation on the drag coefficient of reentry vehicle is comprised if 1.05 < M < 1.1 and makes ΔCD ≈ 0.03–0.04.

Numerical simulation of inlet buzz

Comprehensive numerical analyses are conducted to simulate and capture “Buzz” phenomenon in a supersonic mixed compression air inlet. The buzz is an unsteady self-sustained feature that occurs in supersonic inlets, especially when operating in their subcritical condition. In such a situation, the shock waves oscillate along the inlet and cause mass flow fluctuations inside the inlet that will deteriorate the engine performance significantly. An axisymmetric unsteady numerical simulation was used to solve the Navier–Stokes equations combined with the URANS SST k–ω turbulence model. The simulations for two different free-stream Mach numbers of M∞=2.0 and 2.2 and at two specific subcritical conditions of the inlet operation, where the buzz was experimentally detected, were performed. The numerical solution was able to accurately capture the buzz and its oscillation which is seen to be periodic for this specific inlet. The results show that a large separation region on the compression ramp blocks the duct entry and causes conical and lambda shocks, which are formed on the compression ramp, to move upstream and creates the self-sustained oscillation. The predicted buzz frequencies are in a good agreement with the experimental frequencies calculated based on the surface pressure data with a discrepancy of less than 2%. Further, the peak and trough of both total and static pressure fluctuations and, as a result, the amplitude of buzz all are accurately predicted. The inlet performance curve during the buzz cycle indicates that both TPR and MFR values fluctuate about 70% and 60% of their maximum possible values, respectively. In addition, the influence of the Hysteresis-Effect on the inlet operation and its performance curve is beheld clearly.

Empirical proton-neutron interaction of even Ra isotopes probed by the quadrupole-octupole collective Hamiltonian based on the covariant density functional

The empirical proton-neutron interaction $\ensuremath{\delta}{V}_{pn}$ for even-even Ra isotopes is analyzed by using the covariant density functional theory and the quadrupole-octupole collective Hamiltonian approach. It is shown that the static deformation and collective fluctuation are crucial ingredients for good reproduction of the data. Particularly, the introduction of octupole deformation ${\ensuremath{\beta}}_{3}$ dramatically changes the $\ensuremath{\delta}{V}_{pn}$ with $N=134,136,140$. The collective fluctuation smoothly corrects the $\ensuremath{\delta}{V}_{pn}$ with good trend. Taking $^{224}\mathrm{Ra}$ as an example, the detailed contributions from the static deformation and the collective fluctuation are analyzed, and the microscopic single-particle levels, the octupole driving pairs, and the enhancement of proton-neutron interaction are discussed.

The Energy Spectrum and the Optical Absorption Spectrum of С36 Fullerene Within the Hubbard Model

Using the Hubbard model in an approximation of static fluctuations, analytical relations of anticommutator Green’s functions and energy spectra of С36 fullerene and La@C36 endohedral fullerene with the D6h symmetry groups are obtained. Using the group theory methods, a classification of the energy states is performed and the allowed transitions in the energy spectra of the С36 and La@C36 molecules are determined.

Thermal Transport of Viscoelastic Fluids Within Rotating Couette Flows

The remarkable ability of viscoelastic fluids to augment local and global surface heat transfer characteristics is demonstrated by new experimental results, which are provided for a rotating Couette flow (RCF) environment (also referred to as von Karman swirling flow) with convective heat transfer. Included are Nusselt number variations, flow visualization results, and spectral analysis of flow static temperature fluctuations. Augmented surface Nusselt numbers are measured for sucrose-based, viscoelastic solutions with polyacrylamide (as they are subject to different magnitudes of flow strain), relative to Newtonian flows and relative to fluids with zero shear rate. The resulting Nusselt number enhancements are related to the experimental conditions that are believed to be associated with the onset and development of elastic instabilities. Resulting comparisons show that the Weissenberg number is the parameter that best correlates and characterizes Nusselt number augmentations, which are strongly correlated with pronounced redistributions of fluorescein FWT red tracer dye fronts, obtained from flow visualizations. As such, the present investigation provides new insight into thermal transport of viscoelastic fluids, and new experimental data that illustrate the utility of different analytic and numerical models for predicting experimental conditions associated with significant Nusselt number augmentations.

Spatial assessment of termites interaction with groundwater potential conditioning parameters in Keffi, Nigeria

Termite mounds are traditionally presumed to be good indicators of groundwater in places they inhabit but this hypothesis is yet to be scientifically substantiated. To confirm this assertion, it is expected that termite mounds would have strong correlations with groundwater conditioning parameters (GCPs). In this study, termite mounds distribution covering an area of about 156 km2 were mapped and their structural characteristics documented with the aim of examining their relationships with twelve (12) chosen GCPs. Other specific objectives were to identify specific mound types with affinity to groundwater and to produce a groundwater potential map of the study area. To achieve this, 12 GCPs including geology, drainage density, lineament density, lineament intersection density, land use/land cover, topographic wetness index (TWI), normalized difference vegetation index (NDVI), slope, elevation, plan curvature, static water level and groundwater level fluctuation were extracted from relevant sources. Frequency ratio (FR) and Spearman’s rank correlation were used to find relationships and direction of such relationships. The result revealed a consistent agreement between FR and Spearman’s rank correlation that tall (≥1.8 m) and Cathedral designed mounds are good indicators of groundwater. Further, the groundwater potential map produced from the Random Forest (RF) model via Correlation-based Feature Selection (CFS) using best-first algorithm depicted an erratic nature of groundwater distribution in the study area. This was then classified using natural break into very-high, high, moderate, low and very low potential classes and area under curve (AUC) of the receiver operating characteristics (ROC) showed an 86.5% validity of the model. About 75% of mapped termite mounds fell within the very-high to moderate potential classes thereby suggesting that although tall and cathedral mounds in particular showed good correlations with a number of GCPs, high mound density in a locality is also an indication of good groundwater potential.

Growth responses of eight wetland species to water level fluctuation with different ranges and frequencies.

Fluctuation range and frequency are two important components of water level fluctuation, but their effects on wetland plants have not been evaluated separately. We subjected eight wetland species to a control treatment with static water level and fluctuation treatments with different ranges or frequencies to examine their effects on plant growth. Acorus calamus, Butomus umbellatus and Iris wilsonii showed high survival rates in all treatments with various fluctuation ranges and frequencies. Their survival rates were higher at the medium fluctuation frequency than at the low and high frequencies, suggesting beneficial effects of the medium frequency. In the experiment comparing the fluctuation ranges, A. calamus and I. wilsonii could maintain the capacity for asexual propagation and accumulate higher biomass compared with the control plants, while biomass of the other six species dramatically decreased. In the experiment comparing fluctuation frequency, species with relatively high survival rates (≥ 50%) maintained or increased the capacity of asexual propagation, and A. calamus and I. wilsonii allocated relatively more biomass to roots, which may enhance plant growth and survival. In contrast, these species did not show increased biomass allocation to shoots in response to both fluctuation range and frequency, presumably because shoots are prone to mechanical damage caused by streaming floodwater. Taken together, biomass accumulation in roots rather than in shoots and the ability to asexually propagate are important for the survival of these species during water fluctuation.

A microscopic study of spin-polarized 6Li atoms in highly elongated traps using the static fluctuation approximation (SFA)

The thermodynamic properties of spin-polarized 6Li atoms in highly elongated traps are studied within the Static Fluctuation Approximation. The chemical potential μ, energy per particle U/N, specific heat capacity CV/N, and the effective magnetic field h are determined as a function of temperature and potential strength (magnetic field B). We used the contact potential as the two-body interaction potential. For a repulsive interaction μ and U increase parabolically with B, while for an attractive interaction both increase monotonically with B until saturation at B larger than the resonance field. The effect of the two-body interaction on CV appears at temperatures comparable with the Fermi temperature. μ and U/N of the system were studied of different channels; It is found that these quantities are channel dependent, and the behavior of h at low temperature depends on the potential strength. Our results are consistent with that obtained by the mean-field Bogoliubov–de Gennes method.

Perpendicular diffusion of magnetic field lines in double curl Beltrami magnetic fields

The transport of magnetic field lines is investigated numerically by considering a static magnetic fluctuation with a uniform background field in which the fluctuating part is obtained as a particular solution of the double curl equation and is non force-free in nature. It is found that the transport of magnetic field lines is anomalous, in fact, subdiffusion for lower fluctuation level, δB∕B0, relative to the mean field. The situation corresponds to weak chaos and closed magnetic surfaces in the phase space. Stochasticity increases by increasing the fluctuation level. Higher fluctuation levels with δB∕B0>1 lead to global stochasticity and almost normal diffusion. These results for transport characteristics are supported by analyzing the kurtosis of the displacement distribution of the chaotic field lines. A mixed phase space leads to non-Gaussian structure of the displacement probability distribution for the chaotic trajectories, whereas a wholly chaotic phase space supports nearly Gaussian distribution.

Optical Absorption Spectrum of Metal–Nitride Complexes of С80 Fullerene as Strongly Correlated Systems

Within the framework of Hubbard’s model using an approximation of static fluctuations, the energy spectrum of the π-electron subsystem of an icosahedral C80 fullerene isomer is obtained. Based on the energy spectrum, an optical absorption spectrum of metal-nitride complexes M3N@C80 (M = Gd, Tm, Dy) is simulated. It is quite consistent with the respective experimental spectrum.

Theoretical study of electronic properties of gold fullerenes Au16–Au20

A theoretical study of gold fullerenes Au16–Au20 as strongly correlated electron systems is carried out within the framework of the Hubbard model in the approximation of static fluctuations. The Fourier transforms of anticommutator Green’s functions for electrons at different fullerene sites of gold atoms are obtained and energy spectra are constructed. The density of electron states, the graphical depiction of the equation for the chemical potential, thermodynamic averages characterizing electron transitions among adjacent sites and the description of the probabilities of detecting two electrons with oppositely oriented spin projections on a single site within nanosystems are presented and analyzed. The considered gold fullerenes are demonstrated to possess semiconductor properties.

Solar PV Grid Power Flow Analysis

As the unconstrained integration of distributed photovoltaic (PV) power into a power grid will cause changes in the power flow of the distribution network, voltage deviation, voltage fluctuation, and so on, system operators focus on how to determine and improve the integration capacity of PV power rationally. By giving full consideration to the static security index constraints and voltage fluctuation, this paper proposes a maximum integration capacity optimization model of the PV power, according to different power factors for the PV power. Moreover, the proposed research analyzes the large-scale PV grid access capacity, PV access point, and multi-PV power plant output, by probability density distribution, sensitivity analysis, standard deviation analysis, and over-limit probability analysis. Furthermore, this paper establishes accessible capacity maximization problems from the Institute of Electrical and Electronics Engineers (IEEE) standard node system and power system analysis theory for PV power sources with constraints of voltage fluctuations. A MATLAB R2017B simulator is used for the performance analysis and evaluation of the proposed work. Through the simulation of the IEEE 33-node system, the integration capacity range of the PV power is analyzed, and the maximum integration capacity of the PV power at each node is calculated, providing a rational decision-making scheme for the planning of integrating the distributed PV power into a small-scale power grid. The results indicate that the fluctuations and limit violation probabilities of the power system voltage and load flow increase with the addition of the PV capacity. Moreover, the power loss and PV penetration level are influenced by grid-connected spots, and the impact of PV on the load flow is directional.

A microscopic study of spin-polarized asymmetric hot nuclear matter within the static fluctuation approximation (SFA)

In this work, the thermodynamic properties of spin-polarized asymmetric hot nuclear matter are studied within the Static Fluctuation Approximation (SFA). Specifically, the energy per unit volume, pressure, entropy per unit volume, and specific heat capacity are determined as functions of density up to 0.6 fm−3, and temperature up to 80 MeV. Also, the effects of the asymmetry and spin-polarization parameters on these quantities are explored. The main input in the formalism is the Urbana V14 nucleon–nucleon potential. It is found that these parameters have significant effects on the thermodynamic properties at high densities or low temperatures where quantum features become pronounced. As expected, the entropy results show that the system is more ordered when polarized or for large values of the asymmetry parameter. The quadratic dependence of the energy on the asymmetry and spin-polarization parameters is confirmed at different densities and temperatures. The results are compared to those obtained with different approaches, such as the lowest-order constrained variational method, the conventional variational method, and the relativistic mean-field approximation. It is found that the present results are consistent with those.

Influence of Deformation on the Energy and Optical Absorption Spectra of Fullerene C20 within the Hubbard Model

Abstract—Anticommutator Green’s functions and energy spectra of fullerene C20 with the Ih, D5d, and D3d symmetry groups have been obtained in an analytical form within the Hubbard model and static fluctuation approximation. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of fullerene C20 with the Ih, D5d, and D3d symmetry groups have been determined. It is also shown how the energy levels of fullerene C20 with the Ih symmetry group are split with the symmetry reduction.

LED Mini Lidar for Atmospheric Application.

The creation of a compact and easy-to-use atmospheric lidar has been the aim of researchers for a long time. Micro Pulse Lidars (MPL) and commercialized ceilometers were designed for such purposes. Laser Diodes (LD) and Diode-Pumped Solid State (DPSS) Laser technology has evolved, making lidar system more compact; however, their vulnerability to static electricity and fluctuation of electrical power prevented the growth of atmospheric lidar technology as a system suited to all kinds of users. In this study, a mini lidar with a Light Emitting Diode (LED)-based light source was designed and developed. As LED lamp modules do not need a heat sink or fan, they are resilient and can emit light for long periods with constant intensity. They also offer ease of handling for non-professionals. On the other hand, a LED lamp module has a large divergence, when compared to laser beams. A prototype LED mini lidar was thus developed, with focus on transmitting power optimization and optical design. This low-cost lidar system is not only compact, but also offers near-range measurement applications. It visualizes rapid activities of small air cells in a close range (surface atmosphere), and can verify and predict the condition of the surface atmosphere. This paper summarizes the principle, design, practical use and applications of the LED mini-lidar.

Electronic properties of gold nanotubes (5, 3) and (5, 0) in the Hubbard model in the static fluctuation approximation

A theoretical analysis of the electronic properties of single-walled gold nanotubes with chiralities (5, 3) and (5, 0) with the growth of nanotubes is presented. The results of the study of single-walled gold nanotubes with chiralities (5, 3) and (5, 0) were compared with the results obtained by X.P. Yang and J.M. Dong. The Hubbard model with a certain selection of model parameters allows us to explain the data obtained using the electron density functional theory. According to our results, only the semiconductor–metal transition occurs with the growth of gold nanotubes, and there are no semiconductor–metal–semiconductor–metal “oscillations”, which were indicated in the following work: X.P. Yang and J.M. Dong, Phys. Rev. B 71, 233403 (2005).

Влияние деформации на энергетический спектр и спектр оптического поглощения фуллерена C-=SUB=-20-=/SUB=- в модели Хаббарда

Abstract —Anticommutator Green’s functions and energy spectra of fullerene C_20 with the I _ h , D _5 d , and D _3 d symmetry groups have been obtained in an analytical form within the Hubbard model and static fluctuation approximation. The energy states have been classified using the methods of group theory, and the allowed transitions in the energy spectra of fullerene C_20 with the I _ h , D _5 d , and D _3 d symmetry groups have been determined. It is also shown how the energy levels of fullerene C_20 with the I _ h symmetry group are split with the symmetry reduction.

Characterization of Flow Interactions in a One-Stage Shrouded Axial Turbine

The aim of this paper is to characterize the steady and unsteady flow interactions through a one-stage high-pressure (hp) shrouded axial turbine with a tip cavity. The vane and blade passages were reduced based on the scaling technique, and the domains of compromise were identified and used in the flow computations. The flow structures are mainly in the form of vanes’ wakes and vortices inducing circumferential distortions and interacting with the rotor blades. Fast Fourier transform (FFT) of the static pressure fluctuations recorded at the selected points and lines through the turbine stage revealed high unsteadiness characterized by a space-time periodic behavior, and described by the double Fourier decomposition. The vane-rotor interactions (VRI) appeared in the form of a potential flow field about the blades extending both upstream and downstream and correlated with the rotational speed. The other sources of unsteadiness are induced in the rotor blades by the vanes’ wakes and referred to as the wake interaction, in addition to the secondary flows and vortices in endwall regions.