Values Of Density Ratio Research Articles

Envelope solitary waves in two-negative ions with stationary dust grains

Using a multi-fluid model, we look at how modulated electrostatic dust-ion-acoustic wave packets move nonlinearly through a plasma made up of a three-ion fluid with Maxwellian electrons and stationary dust grains. A nonlinear Schrödinger (NLS) equation describes the electric potential envelope wave packet. The analysis reveals the existence of different types of localized modes, namely bright, dark, and grey solitons. We numerically analyse the coefficients of the NLS equation to identify stable or unstable regions for wave packet propagation. It is found that higher relative density ratios increase the group velocity of the wave packets. Stable pulses can become unstable when plasma parameters exceed certain relative density ratio values. Stable pulses can exist within a crucial window of the relative dust density ratio. Controlling the dust grain density ratio outside the zone can cause unstable wave packets or bright envelope solitons to propagate.

Landslide Occurrences under Diverse Landuse/cover in Lower Kosi Watershed, Central Himalaya

Abstract Present study was related to land degradation after landslide and risk analysis of Lower Kosi watershed in Central Himalaya using RS and GIS. The study was aimed to identifying the relation of land use with landslide activity in Himalayan terrain and landslide management. The landslide inventory map was prepared for the detailed study with the help of Google Earth Image and field verifications. Landslide had been sub-categorized into two categories; natural and road induced. The land use map was prepared from Google Earth image followed by toposheets. Statistical analysis of landslide frequency and density as well as frequency and density ratios were applied. The collected data was evaluated in combination with GIS. The relationship between land use categories and landslide occurrences was determined. The landslide frequency ratio (FR) and density ratio (DR) were analyzed. The FR and DR value of 1 is an average value. Hence, the value of ratio more than 1 signifies a strong relationship between landslides and the given factor while ratio values less than 1 registers a poor relationship. The FR and DR values were >1.0 in the areas of fallow land, barren/rocky land, agricultural land and open forest revealing a strong relation to landslide processes while the lesser values of FR and DR in ‘dense forest’ area determines the impact of sufficient vegetation cover on the least occurrence of landslides. This study may be applicable for new and existing land use planning projects as the adopted methodology provides rapid estimation of landslide vulnerability of the area.

Impact of the Purge Flow Density Ratio on the Rim Sealing Effectiveness in Hot Gas Ingestion Measurements

Abstract The rim seals of gas turbines are used to control the ingestion of hot mainstream gas into the wheel space between the rotor disk and the stationary casing. Sealing air, which is generally used to pressurize the cavity space, flows through the seal clearance and then mixes with the flow path in the annulus. Predicting the correct quantity of purge flow necessary to prevent excessive ingestion of hot gases while, at the same time, minimizing the penalties in terms of engine efficiency and stage aerodynamics represents a great challenge for the designers and a crucial point for the design of reliable engines. Such estimate is governed by unsteady phenomena, and computational fluid dynamics (CFD) approaches are still expensive and time consuming, especially if 3D domains and unsteady conditions have to be simulated. Fundamental test cases, replicating actual engines geometries, are still a valid approach to calibrate correlations or simplified models such as the so-called orifice model. However, most of the experimental studies deal with test rigs at room temperature and do not take into account the effect of the density ratio (DR) between purge and main flows. To fill this gap, the present article reports the impact of the density ratio on the rim sealing effectiveness by performing a nonintrusive diagnostic based on the pressure-sensitive paint (PSP) technique on both the stator side and the rotor side. The analysis was performed on a cold rotating cavity rig, developed for the study of hot gas ingestion, where two different values of density ratios were tested by using N2 (DR = 1) and CO2 (DR = 1.52) as purge flow. The data extracted from the PSP seal effectiveness maps allowed to calibrate the orifice model for the stator side and to fit the coefficients of the buffer ratio model for the rotor surface at different flow conditions where the externally induced ingress is the dominant mechanism for gas ingestion. The results highlighted the impact of the DR on the seal effectiveness and on the low-order models considered for the data analysis. In the end, it is shown that the obtained results can be used to scale experimental data, generally collected at DR close to one, toward more representative engine values where the difference between the density of purge and main flows cannot be neglected.

СТАТИСТИЧЕСКИЕ ХАРАКТЕРИСТИКИ СИСТЕМЫ ОТНОСИТЕЛЬНОЙ ПЕРЕДАЧИ ИНФОРМАЦИИ НА ОСНОВЕ ХАОТИЧЕСКИХ ИМПУЛЬСОВ В КАНАЛЕ С ГАУССОВСКИМ ШУМОМ

The purpose of this paper is to analyze the statistical characteristics of a differentially coherent communication scheme based on the use of chaotic pulses in the presence and absence of thermal noise for various distributions of chaotic signal instantaneous values. To achieve this goal, a numerical simulation for the performance of direct chaotic differentially coherent communication scheme is carried out in the work by a computer simulation. A numerical simulation was carried out, confirming the previously obtained analytical bit error probability estimates vs energy per bit to gaussian noise power spectral density ratio. The minimum energy per bit to gaussian noise power spectral density ratio values, which provide the given error probabilities, are obtained. It is shown that the proposed communication system works effectively at high values of processing gain(the behavior of the communication system was studied for various values of processing gain), and in the case of high values of processing gain, the results obtained do not depend on the choice of a specific discrete chaotic signal distribution.

Free vibration analysis of curved lattice sandwich beams

In this paper, the effects of initial curvature and lattice core shape on the bending vibration of sandwich beams are investigated. The three-dimensional (3D) sandwich beam is simulated by combining a two-dimensional (2D) cross-sectional analysis with a one-dimensional (1D) nonlinear beam analysis. The sandwich beam is composed of two identical isotropic faces covering a lattice core. Four different lattice core structures are used to take into account the effect of core unit cell shape on the dynamic properties of the sandwich beam. The nonlinear governing equations of the sandwich beam are Discretized using a time-space scheme. Numerical results show that the lattice unit cell shape affects both in-plane and out of plane stiffness values and hence changes the dynamic behavior of the beam. Furthermore, it is observed that by changing the density ratio of the beam, modes veer away from each other at a specific value of density ratio for specific unit cell types. Moreover, the initial curvature of the beam is shown to affect the dynamics of the beam especially lower modes. Finally, it is obtained that the dynamics of the beam is different when it is initially curved or curved due to an applied end follower moment.

Dictyocaulus viviparus bulk tank milk seropositivity is correlated with meteorological variables

Control of infections with Dictyocaulus viviparus is difficult due to its volatile epidemiology. In the absence of predictive models, ‘vigilance and treatment’ is today’s mainstay for control. In order to evaluate the potential of predictive model development to support a more preventative approach, this longitudinal study aimed at understanding the influence of weather factors on D. viviparus bulk tank milk antibody ELISA results. Bulk tank milk samples were analysed with a Major Sperm Protein-based ELISA (expressed as an optical density ratio) twice monthly on 717 Flemish dairy farms during the grazing season (April–October) in 2018. Meteorological data of the sampled farms were obtained at 1 km spatial scale using the ALARO-SURFEX climate model. A mixed effects model showed that the bulk tank milk optical density ratio was significantly associated with the month of sampling, evapotranspiration, temperature and its quadratic term, the number of hot days and the number of rainy days in the 7–8 weeks prior to sampling. There were significant farm effects involved. The model’s accuracy to predict bulk tank milk optical density ratio infection status was 80%, while optical density ratios were generally overestimated by 38%. Inclusion of the previous (2-week-old) optical density ratio values increased accuracy to 86% and reduced the mean square error. We conclude that meteorological parameters have a predictive value for bulk tank milk optical density ratio results, while further research should evaluate model improvements through the addition of herd management factors as well as confirm the predictive power through external validation in additional farms and years.

Predictors of thermal increase in magnetic resonance-guided focused ultrasound treatment for essential tremor: histogram analysis of skull density ratio values for 1024 elements.

Sufficient thermal increase capable of generating thermocoagulation is indispensable for an effective clinical outcome in patients undergoing magnetic resonance-guided focused ultrasound (MRgFUS). The skull density ratio (SDR) is one of the most dominant predictors of thermal increase prior to treatment. However, users currently rely only on the average SDR value (SDRmean) as a screening criterion, although some patients with low SDRmean values can achieve sufficient thermal increase. The present study aimed to examine the numerical distribution of SDR values across 1024 elements to identify more precise predictors of thermal increase during MRgFUS. The authors retrospectively analyzed the correlations between the skull parameters and the maximum temperature achieved during unilateral ventral intermediate nucleus thalamotomy with MRgFUS in a cohort of 55 patients. In addition, the numerical distribution of SDR values was quantified across 1024 elements by using the skewness, kurtosis, entropy, and uniformity of the SDR histogram. Next, the authors evaluated the correlation between the aforementioned indices and a peak temperature > 55°C by using univariate and multivariate logistic regression analyses. Receiver operating characteristic curve analysis was performed to compare the predictive ability of the indices. The diagnostic performance of significant factors was also assessed. The SDR skewness (SDRskewness) was identified as a significant predictor of thermal increase in the univariate and multivariate logistic regression analyses (p < 0.001, p = 0.013). Moreover, the receiver operating characteristic curve analysis indicated that the SDRskewness exhibited a better predictive ability than the SDRmean, with area under the curve values of 0.847 and 0.784, respectively. The SDRskewness is a more accurate predictor of thermal increase than the conventional SDRmean. The authors suggest setting the SDRskewness cutoff value to 0.68. SDRskewness may allow for the inclusion of treatable patients with essential tremor who would have been screened out based on the SDRmean exclusion criterion.

Coupled lattice Boltzmann-large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number.

A coupled lattice Boltzmann-large eddy simulation model is developed for modeling three-dimensional multiphase flows at large density ratios and high Reynolds numbers. In the framework of the lattice Boltzmann method, the model is proposed based on the standard Smagorinsky subgrid-scale approach, and a reconstructed multiple-relaxation-time collision operator is adopted. The conservative Allen-Cahn equation and Navier-Stokes equations are solved through the lattice Boltzmann discretization scheme for the interface tracking and velocity field evolution, respectively. Relevant benchmark cases are carried out to validate the performance of this model in simulating multiphase flows at a large density ratio and a high Reynolds number, including a stationary droplet, the process of spinodal decomposition, the Rayleigh-Taylor instability, the phenomenon of a droplet splashing on a thin liquid film, and the liquid jet breakup process. The maximum values of density ratio and Re number are 1000 and 10 240, respectively. The capability and reliability of the proposed model have been demonstrated by the good agreement between simulation results and the analytical solutions or the previously available results.

Influence of multi-ion on the dust grain surface potential of complex plasmas using non-Maxwellian approach

Dust grain surface potential in multi-ion plasmas having two negative ions within the context of kappa-distributed dusty plasma is studied analytically and numerically. The plasmas current equations Xe+-F--SF6- and Ar+-F--SF6- solved using the typical parameters of laboratory multi-ion plasmas and attained dust grain surface potential strongly depends on the plasma parameters for example kappa, density, and temperature ratios. The dust grain surface potential displays the non-monotonic behavior for values of the kappa, temperature ratio and for changed values of density ratios in the framework of both Xe+-F--SF6- and Ar+-F--SF6- plasmas. Additionally, the temperature ratio effect is minor on the dust grain surface potential. Our results show that considering the broad variety of Xe+-F--SF6- and Ar+-F--SF6- masses is of great importance and advantageous for the analyses of plasma physics, particularly the physics of multicomponent plasmas.

Non-isothermal mixing characteristics in the extreme near-field of a turbulent jet in hot crossflow

The nonreacting and reacting jet in crossflow (JICF) is an important flow configuration for effective mixing and combustion in practical applications. Many studies in the literature exist that examine the overall mixing characteristics of an isothermal, unconfined, nonreacting JICF. This experimental study examines the mixing characteristics in the very near field (s/d ≤ 3) of a nonreacting jet in a hot crossflow of combustion products (1500 K), a configuration relevant to gas turbine combustion. A range of jet-to-crossflow momentum flux ratios (5.2 ≤ J ≤ 24.2) and jet-to-crossflow density ratios (3.2 ≤ ρj/ρcf ≤ 7.8) was studied for a round jet with fully developed turbulent pipe flow and 4% mean turbulence intensity at the jet exit. Temperature measurements were made using planar laser Rayleigh scattering. Jet trajectory, jet centerline concentration decay based on adiabatic mixing assumption, Favre-averaged scalar dissipation, and scalar mixing time scales were determined as a function of the above-mentioned jet parameters. The observed center-plane mixing metrics indicated that better near field mixing was exhibited for lower values of the momentum flux ratio and larger values of density ratio in the extreme near field of the jet. As the momentum flux ratio was increased, windward and leeward mixing around the elongated potential core decreased, as indicated by the relative temperatures in these regions. The magnitude of scalar dissipation in the windward region decreased as the jet momentum flux increased, while the leeward dissipation region increased in size and magnitude as the momentum flux ratio increased. When the density ratio was decreased toward unity, both the windward and leeward dissipation regions reduced in size and magnitude.

Dynamics of settling‐driven convection beneath a sediment‐laden buoyant overflow: Implications for the length‐scale of deposition in lakes and the coastal ocean

AbstractA series of laboratory experiments was conducted in order to determine how settling‐driven convection influences the length‐scale over which the majority of particles settle beneath a buoyant sediment‐laden plume spreading over a denser saline layer. This system is analogous to sediment‐laden river water spreading into a lake or the coastal ocean. The key dimensionless parameter that controls the settling dynamics of such flows is the density ratio, defined as the ratio of density differences due to the added salt and sediment. For a buoyant plume, this ratio has to be greater than unity, so that the experiments in the current study were performed for density ratios between one and five. When density ratio was close to one, settling‐driven convection was vigorous and the length‐scale over which sedimentation occurred was very small. A strong secondary turbidity current was generated in this case. On the other hand, for larger values of density ratio, the predicted length‐scale over which a secondary plume was generated increased in proportion to the density ratio. A complete mathematical expression for this length‐scale was developed using recent theory that described the timescale over which settling‐driven convection evolved. The theoretically predicted propagation length‐scale showed very good quantitative agreement with laboratory experiments. The use of the dimensionless density ratio allows the expression to predict which sediment‐laden river plumes in lakes and the coastal ocean could quickly form secondary turbidity currents.

Generation of internal waves by flow past a flat plate in a two-layer fluid of finite depth

This paper is concerned with an analytical study on the internal wave generated by a flat plate that is submerged and located at the interface of a two-layer fluid. The flow pattern can be constructed as it applies near the stern of a wide blunt ship or submarine. The Fourier transform and Wiener–Hopf techniques are applied to analytically solve the linearized problem for the Froude number F < 1 and different values of density ratio ρ. The main objective of this research paper is to investigate the impact of the density ratio on the downstream waves, as well as to minimize or eliminate the waves past the stern completely. It is shown that for the flat plate the wave amplitude was not eliminated, but it decreased for a small Froude number F as the density ratio decreased.

Feasibility of ultrashort echo time images using full-wave acoustic and thermal modeling for transcranial MRI-guided focused ultrasound (tcMRgFUS) planning

Transcranial MRI-guided focused ultrasound (tcMRgFUS) is increasingly used to non-invasively treat a wide variety of neurological disorders including essential tremors, Parkinson’s disease, and neuropathic pain. Although this treatment is an MRI-guided procedure, the current pre-treatment screening and planning involve a CT of the head to obtain 3D skull images. These images are necessary for estimating the proportion of absorbed energy and the acoustic phase shift associated with the skull and determining the transmit energy of ultrasonic waves to create thermal lesions at a desired focal spot. Ultrashort echo time (UTE) MR sequences can capture signals from tissues such as bone which have a very short transverse relaxation time. In this manuscript, we assess the use of a UTE based sequence to image the calvarium and test the feasibility of obviating the need for CT based imaging during an MR-guided focused ultrasound therapy. We demonstrate that the segmentation of bone using UTE images leads to similar skull density ratio values as determined from CT with high correlation (r = 0.88; p < 0.0001). Furthermore, through treatment specific modeling we demonstrate that the thermal profiles and focal locations are in concordance with the actual treatment plan when using the UTE based skull intensity information suggesting the possibility of replacing the CT scans with UTE based skull imaging in all tcMRgFUS procedures, potentially eliminating unnecessary radiation exposure. Overall, the results indicate that UTE MR imaging may serve as an effective and accurate alternative to CT imaging for both screening and pre-treatment planning on patients undergoing the tcMRgFUS procedure.

OPTICAL DENSITY RATIO OF THE SUBRETINAL FLUID IN CHOROIDAL MELANOMA AND METASTASIS.

To investigate the optical density (OD) characteristics and clinical relevance of subretinal fluid in choroidal melanoma and choroidal metastasis. Medical records of patients with choroidal melanoma and choroidal metastasis who underwent optical coherence tomography examinations at diagnosis before any intervention and whose optical coherence tomography scans showed sufficient subretinal fluid for sampling were reviewed. The highest quality B-scan containing subretinal fluid was analyzed. Optical density measurements obtained using ImageJ and optical density ratios (ODRs) were calculated as subretinal fluid OD divided by vitreous OD. Patient details and diagnosis were masked during measurements. Nonparametric tests for independent samples were used to detect differences in ODR between groups. Of the 39 cases of choroidal tumors that met the inclusion criteria, 14 were diagnosed as metastases and 25 as malignant melanoma. There were no significant differences between the groups in age, optical coherence tomography acquisition and parameters of quality, and vitreous OD. Optical density ratio values were significantly lower in metastases cases (mean 0.68, SD ±0.18) than in melanoma cases (0.95 ± 0.33, P = 0.006). Receiver operating characteristic curve analysis yielded an optimal cutoff of ODR = 0.771 (sensitivity = 78.6%, specificity = 72.0%). Optical density ratio can serve as an additional test to differentiate between choroidal melanoma and choroidal metastases.

Test cases for comparison of two interfacial solvers

We present novel test cases to study the effect of density ratio on free and forced capillary oscillations at an interface separating two immiscible, inviscid fluids. Using these tests, results obtained from two in-house developed, Volume of Fluid (VoF) based codes for solving the incompressible Euler equations with surface tension, are reported. The first solver (FSS: free surface solver) ignores the dynamics of the lighter phase solving only for the denser phase, explicitly accounting for free surface boundary conditions using the approach presented in Malan et al. (2015). The second is an interfacial solver which implements the one-fluid algorithm (OFS: one fluid solver) for simulating two-phase flows. We present four test cases involving inviscid, free and parametrically forced, capillary oscillations on Cartesian and circular base states. Explicit closed form analytical solutions in the linearised limit are presented for each case. It is found that for small value of the nonlinearity parameter (ϵ or ϵaz < 0.1) and with density ratio (ρr) ranging from 50−103, the FSS shows excellent agreement with linearised analytical predictions. For lower values of density ratio approaching ∼ 10 and below, the FSS results display substantial disagreement with those obtained from the OFS as well as with analytical predictions. At large density ratios ( ∼ 103) (and larger values of ϵ or ϵaz), the FSS shows better accuracy over longer times, when compared to the OFS, partly due to less numerical dissipation. The analytical results presented here add to the repository of test cases in the two-phase CFD literature and are expected to be useful for validating numerical models for surface tension. The comparison of the OFS with the FSS also provides useful rule-of-thumb estimates for choosing between speed (FSS) and accuracy (OFS) in numerical computations of capillary, interfacial flows.

Analysis of Basic Features in Dynamic Network Models.

Time evolving Random Network Models are presented as a mathematical framework for modelling and analyzing the evolution of complex networks. This framework allows the analysis over time of several network characterizing features such as link density, clustering coefficient, degree distribution, as well as entropy-based complexity measures, providing new insight on the evolution of random networks. First, some simple dynamic network models, based only on edge density, are analyzed to serve as a baseline reference for assessing more complex models. Then, a model that depends on network structure with the aim of reflecting some characteristics of real networks is also analyzed. Such model shows a more sophisticated behavior with two different regimes, one of them leading to the generation of high clustering coefficient/link density ratio values when compared with the baseline values, as it happens in many real networks. Simulation examples are discussed to illustrate the behavior of the proposed models.

Direct numerical simulation and analytical modeling of electrically induced multiphase flow

In this study deformation of a falling drop which is surrounded by another liquid is modeled analytically and numerically. The drop is influenced by an external electric field which is applied uniformly on the side walls of the domain. An open-source volume-of-fluid solver, Gerris with dynamic adaptive grid refinement has been used for numerically modeling the three-dimensional deformation of a falling droplet. Analytical solutions of drop's deformation are presented in detail and then the outcomes are compared with numerical results. The numerical results are presented for various values of density ratios and electrical conductivity and permittivity. The comparison of the results shows a great agreement between the analytical solutions and the direct numerical simulation (DNS) results.

Characterization of forced response of density stratified reacting wake

The hydrodynamic stability of a reacting wake depends primarily on the density ratio [i.e., ratio of unburnt gas density (ρu) to burnt gas density (ρb)] of the flow across the wake. The variation of the density ratio from high to low value, keeping ρu/ρb>1, transitions dynamical characteristics of the reacting wake from a linearly globally stable (or convectively unstable) to a globally unstable mode. In this paper, we propose a framework to analyze the effect of harmonic forcing on the deterministic and synchronization characteristics of reacting wakes. Using the recurrence quantification analysis of the forced wake response, we show that the deterministic behaviour of the reacting wake increases as the amplitude of forcing is increased. Furthermore, for different density ratios, we found that the synchronization of the top and bottom branches of the wake with the forcing signal is dependent on whether the mean frequency of the natural oscillations of the wake (fn) is lesser or greater than the frequency of external forcing (ff). We notice that the response of both branches (top and bottom) of the reacting wake to the external forcing is asymmetric and symmetric for the low and high density ratios, respectively. Furthermore, we characterize the phase-locking behaviour between the top and bottom branches of the wake for different values of density ratios. We observe that an increase in the density ratio results in a gradual decrease in the relative phase angle between the top and bottom branches of the wake, which leads to a change in the vortex shedding pattern from a sinuous (anti-phase) to a varicose (in-phase) mode of the oscillations.

A parametric investigation of vane pressure side cutback film cooling by dual luminophor PSP

Because of its geometry, the vane trailing edge is one of the most difficult regions to be cooled. A trailing edge cutback cooling system is one of the most effective solution for cooling the trailing edge of high-pressure gas turbine nozzle vanes. In this study, a parametric analysis of the thermal performance of a nozzle vane cascade with a pressure side cooling system including two rows of cylindrical holes and a trailing edge cutback featuring 8 rectangular slots was carried out by using dual luminophor (binary) PSP technique. Coolant to mainstream mass flow rate (MFR), density ratio (DR), main flow Mach number (Ma2is) and turbulence intensity level (Tu1) and the state of the approaching boundary layer were the considered parameters. Binary PSP was able to measure the coolant concentration independently from temperature, thus allowing to compute the true adiabatic film cooling effectiveness in a complex environment. MFR was shown to have a strong impact on both holes and cutback performance. The thermal protection over the cutback region was promoted by high Ma2is and high DR values, while Tu1 and the boundary layer state only marginally affected the thermal behavior, especially at high MFR.

Investigation of a single droplet impact onto a liquid film with given horizontal velocity

The dynamics of a single droplet impact onto a liquid film is numerically studied in this work. A two-dimensional droplet is initially placed above a liquid film and falls freely under gravity together with a given horizontal velocity. To conduct numerical simulations, a hybrid method is adopted, in which the flow field is solved by using the lattice Boltzmann method and the interface is captured by solving the Cahn–Hilliard equation directly. At a fixed value of density ratio of droplet to ambient fluid (ρ∗), the effects of Bond number (Bo), Weber number (We) and dimensionless liquid film thickness (H∗) are systematically investigated. Based on the results achieved, it is found that the behavior of resultant splash structure after droplet impact is greatly affected by Bo, We and H∗. By increasing Bo and We, a higher right jet can be generated, but it has an opposite influence on the left jet. Moreover, there exists a critical value of H∗. When the thickness is lower than the critical value, the right jet height would increase with H∗, otherwise, it would decrease with H∗.