Density Correction Research Articles

An SPH multi‐fluid model based on quasi buoyancy for interface stabilization up to high density ratios and realistic wave speed ratios

SummaryWe introduce a smoothed particle hydrodynamics (SPH) concept for the stabilization of the interface between 2 fluids. It is demonstrated that the change in the pressure gradient across the interface leads to a force imbalance. This force imbalance is attributed to the particle approximation implicit to SPH. To stabilize the interface, a pressure gradient correction is proposed. In this approach, the multi‐fluid pressure gradients are related to the (gravitational and fluid) accelerations. This leads to a quasi‐buoyancy correction for hydrostatic (stratified) flows, which is extended to nonhydrostatic flows. The result is a simple density correction that involves no parameters or coefficients. This correction is included as an extra term in the SPH momentum equation. The new concept for the stabilization of the interface is explored in 5 case studies and compared with other multi‐fluid models. The first case is the stagnant flow in a tank: The interface remains stable up to density ratios of 1:1000 (typical for water and air), in combination with artificial wave speed ratios up to 1:4. The second and third cases are the Rayleigh‐Taylor instability and the rising bubble, where a reasonable agreement between SPH and level‐set models is achieved. The fourth case is an air flow across a water surface up to density ratios of 1:100, artificial wave speed ratios of 1:4, and high air velocities. The fifth case is about the propagation of internal gravity waves up to density ratios of 1:100 and artificial wave speed ratios of 1:4. It is demonstrated that the quasi‐buoyancy model may be used to stabilize the interface between 2 fluids up to high density ratios, with real (low) viscosities and more realistic wave speed ratios than achieved by other weakly compressible SPH multi‐fluid models. Real wave speed ratios can be achieved as long as the fluid velocities are not very high. Although the wave speeds may be artificial in many cases, correct and realistic wave speed ratios are essential in the modelling of heat transfer between 2 fluids (eg, in engineering applications such as gas turbines).

Evaluation of a lower-powered analyzer and sampling system for eddy-covariance measurements of nitrous oxide fluxes

Abstract. Nitrous oxide (N2O) fluxes measured using the eddy-covariance method capture the spatial and temporal heterogeneity of N2O emissions. Most closed-path trace-gas analyzers for eddy-covariance measurements have large-volume, multi-pass absorption cells that necessitate high flow rates for ample frequency response, thus requiring high-power sample pumps. Other sampling system components, including rain caps, filters, dryers, and tubing, can also degrade system frequency response. This field trial tested the performance of a closed-path eddy-covariance system for N2O flux measurements with improvements to use less power while maintaining the frequency response. The new system consists of a thermoelectrically cooled tunable diode laser absorption spectrometer configured to measure both N2O and carbon dioxide (CO2). The system features a relatively small, single-pass sample cell (200 mL) that provides good frequency response with a lower-powered pump ( ∼ 250 W). A new filterless intake removes particulates from the sample air stream with no additional mixing volume that could degrade frequency response. A single-tube dryer removes water vapour from the sample to avoid the need for density or spectroscopic corrections, while maintaining frequency response. This eddy-covariance system was collocated with a previous tunable diode laser absorption spectrometer model to compare N2O and CO2 flux measurements for two full growing seasons (May 2015 to October 2016) in a fertilized cornfield in Southern Ontario, Canada. Both spectrometers were placed outdoors at the base of the sampling tower, demonstrating ruggedness for a range of environmental conditions (minimum to maximum daily temperature range: −26.1 to 31.6 °C). The new system rarely required maintenance. An in situ frequency-response test demonstrated that the cutoff frequency of the new system was better than the old system (3.5 Hz compared to 2.30 Hz) and similar to that of a closed-path CO2 eddy-covariance system (4.05 Hz), using shorter tubing and no dryer, that was also collocated at the site. Values of the N2O fluxes were similar between the two spectrometer systems (slope = 1.01, r2 = 0.96); CO2 fluxes as measured by the short-tubed eddy-covariance system and the two spectrometer systems correlated well (slope = 1.03, r2 = 0.998). The new lower-powered tunable diode laser absorption spectrometer configuration with the filterless intake and single-tube dryer showed promise for deployment in remote areas.

3-D Lagrangian-based investigations of the time-dependent cloud cavitating flows around a Clark-Y hydrofoil with special emphasis on shedding process analysis

In the present paper, the unsteady cavitating flow around a 3-D Clark-Y hydrofoil is numerically investigated with the filter-based density correction model (FBDCM), a turbulence model and the Zwart-Gerber-Belamri (ZGB) cavitation model. A reasonable agreement is obtained between the numerical and experimental results. To study the complex flow structures more straightforwardly, a 3-D Lagrangian technology is developed, which can provide the particle tracks and the 3-D Lagrangian coherent structures (LCSs). Combined with the traditional methods based on the Eulerian viewpoint, this technology is used to analyze the attached cavity evolution and the re-entrant jet behavior in detail. At stage I, the collapse of the previous shedding cavity and the growth of a new attached cavity, the significant influence of the collapse both on the suction and pressure sides are captured quite well by the 3-D LCSs, which is underestimated by the traditional methods like the iso-surface of Q-criteria. As a kind of special LCSs, the arching LCSs are observed in the wake, induced by the counter-rotating vortexes. At stage II, with the development of the re-entrant jet, the influence of the cavitation on the pressure side is still not negligible. And with this 3-D Lagrangian technology, the tracks of the re-entrant jet are visualized clearly, moving from the trailing edge to the leading edge. Finally, at stage III, the re-entrant jet collides with the mainstream and finally induces the shedding. The cavitation evolution and the re-entrant jet movement in the whole cycle are well visualized with the 3-D Lagrangian technology. Moreover, the comparison between the LCSs obtained with 2-D and 3-D Lagrangian technologies indicates the advantages of the latter. It is demonstrated that the 3-D Lagrangian technology is a promising tool in the investigation of complex cavitating flows.

The density–salinity relation of standard seawater

Abstract. The determination of salinity by means of electrical conductivity relies on stable salt proportions in the North Atlantic Ocean, because standard seawater, which is required for salinometer calibration, is produced from water of the North Atlantic. To verify the long-term stability of the standard seawater composition, it was proposed to perform measurements of the standard seawater density. Since the density is sensitive to all salt components, a density measurement can detect any change in the composition. A conversion of the density values to salinity can be performed by means of a density–salinity relation. To use such a relation with a target uncertainty in salinity comparable to that in salinity obtained from conductivity measurements, a density measurement with an uncertainty of 2 g m−3 is mandatory. We present a new density–salinity relation based on such accurate density measurements. The substitution measurement method used is described and density corrections for uniform isotopic and chemical compositions are reported. The comparison of densities calculated using the new relation with those calculated using the present reference equations of state TEOS-10 suggests that the density accuracy of TEOS-10 (as well as that of EOS-80) has been overestimated, as the accuracy of some of its underlying density measurements had been overestimated. The new density–salinity relation may be used to verify the stable composition of standard seawater by means of routine density measurements.

Density enhancement mechanism of upwind schemes for low Mach number flows

Many all-speed Roe schemes have been proposed to improve performance in terms of low speeds. Among them, the F-Roe and T-D-Roe schemes have been found to get incorrect density fluctuation in low Mach flows, which is expected to be with the square of Mach number. Asymptotic analysis presents the mechanism of how the density fluctuation problem relates to the incorrect order of terms in the energy equation $${{\tilde{\rho }} {\tilde{a}} {\tilde{U}}\varDelta U}$$ . It is known that changing the upwind scheme coefficients of the pressure-difference dissipation term $$D^P$$ and the velocity-difference dissipation term in the momentum equation $$D^{\rho U}$$ to the order of $$O(c^{-1})$$ and $$O(c^{0})$$ can improve the level of pressure and velocity accuracy at low speeds. This paper shows that corresponding changes in energy equation can also improve the density accuracy in low speeds. We apply this modification to a recently proposed scheme, TV-MAS, to get a new scheme, TV-MAS2. Unsteady Gresho vortex flow, double shear-layer flow, low Mach number flows over the inviscid cylinder, and NACA0012 airfoil show that energy equation modification in these schemes can obtain the expected square Ma scaling of density fluctuations, which is in good agreement with corresponding asymptotic analysis. Therefore, this density correction is expected to be widely implemented into all-speed compressible flow solvers.

Numerical analysis of the unsteady cavitation shedding flow around twisted hydrofoil based on hybrid filter model

Cavitation is a common phenomenon in components of fluid machinery and it may induce material damage and vibration. A more accurate and commercial turbulence model is required to predict cavitation. In this paper, we make a combination of filter-based model (FBM) and density correction method (DCM) to propose a new DCM FBM. Firstly, the new DCM FBM and the homogeneous cavitation model are validated by comparing the simulation result with the experiment of cavitation shedding flow around the Clark-y hydrofoil and the filter size is determined as well. Then, the cavitation pattern cycle and shedding vortex structure of the twist hydrofoil experimented by Delft University of Technology were predicted using the DCM FBM. The predicted 3-D cavitation structures and development cycle of twist hydrofoil as well as the collapsing features show a good qualitative agreement with the high speed photography results. Numerical results show that the improved turbulence model could predict the cloud cavity evolution well, including the cloud cavity generation, shedding and dissipation. It is found that the re-entrant jet induced by the by adverse pressure gradient is the main reason to generate the cloud cavity shedding. The secondary shedding is al-so observed which is result from the combination of the radially advancing re-entrant jet and side-entrant jet simulated by the DCM FBM turbulence method.

The influence of post-consumer car mats waste on selected concrete parameters

In recent years, a systematic increase of various types of wastes has been observed, including polymeric wastes that, to a large degree, are difficult to manage. The present paper deals with the problem of car mats wastes and the possibility of their application for producing concrete composites. The scope of the research involved designing and making concrete mixtures modified by waste rubber retrieved from rubber car mats. For the experiment the authors used: Portland cement CEM I 42,5R, sand, gravel aggregate of the 2-8 and 8-16 fractions, water, plasticizing and aerating admixture and car mats wastes fragmented into 0-2 mm and 2-8 mm. The authors made 4 series of concrete samples modified by wastes, for which the following factors have been assigned: compression strength after 7 and 28 days of maturing, absorptivity, frost resistance F100 of freezing and thawing and bulk density. In two samples’ composition (S1 and S2) the authors used 2-8 mm fraction rubber wastes as a substitute for 2-8 mm gravel in the amount of 5% and 7,5% of the cement bulk, making the density correction of 2-8 gravel. In contrast, in the remaining two samples S3 and S4 were modified by rubber wastes of the 0-8 mm fraction in the amount of 5% and 10%, respectively, of the cement bulk, subtracting a certain amount of the aggravate mixture at the same time. The research conducted for the series of the designed concrete samples, unfortunately did not confirm the thesis that rubber wastes retried from rubber car mats could be reused as the aggravate substitute.

An Overview of Thermal Mass Flowmeters Applicability in Oil and Gas Industry

Measuring and modeling flow has played a central role in predicting its behavior and its effects on the surroundings. Flow measurement is the basis of trade between producers, transporters, process plants, state and public marketers. To improve transactional operation, thermal flowmeters could provide direct mass flow measurement of gases and vapors over a wide range of process conditions without the need for density corrections based on pressure and temperature.The flow meters are classified according to the domain in which they are used and their operating principle. The goal of this work is to provide an overview of using thermal flow meter in hydrocarbons industries. The applicability of thermal flow meters is discussed by a simulation using one-dimensional mathematical model of thermal flow sensor.

Density and Shape Factor Terms in Stokes' Equation for Aerodynamic Behavior of Aerosols

Pharmaceutical aerosols are used to treat many pulmonary diseases. The use of low-density powders has proven useful to support efficient drug delivery. Measurements must account for the low-density, spherical particle features contributing to aerodynamic behavior. Ideally, the aerodynamic particle size distribution (APSD) is measured experimentally. Without formal measurement of APSD, calculations may be performed using surrogate measures such as bulk or tapped density and dynamic shape factor in Stokes' equation. However, the particles' low density must be established independently for this approach to be valid. In addition, where particles deviate from sphericity, the dynamic shape factor must be estimated from aerodynamic measurement not from geometric imaging of morphology. Finally, geometric sizing from particle images results in number distributions that exhibit smaller median sizes than mass distributions for the same polydisperse system. Simply applying density and shape factor corrections to geometric particle sizes does not convert number distributions to mass distributions. For log-normally distributed particle size distributions, Hatch-Choate equations, employing both median size and geometric standard deviation terms, may be used to convert number to mass distributions. Assigning small APSDs from calculations based on erroneous assumptions will result in serious interpretive flaws in subsequent in vitro and in vivo data.

Modeling of orthogonal cutting process of A2024-T351 with an improved SPH method

Modeling the cutting process is traditionally based on the finite element method (FEM). All element-based numerical methods, however, have difficulties in handling with extremely large deformation and material fragmentation that always occur in cutting processes. In contrast, mesh-free methods such as smoothed-particle hydrodynamics (SPH) have a lot of attractive features in solving extremely large deformation problems. This work introduces first an improved SPH method and then applies it to further develop a cutting model for A2024-T351 materials to predict cutting forces and chip morphology under different cutting conditions. The improvement to the traditional SPH is achieved through modifying schemes for approximating density (density correction) and kernel gradient (kernel gradient correction). The simulation results demonstrate the improved SPH is more stable and accurate compared with the traditional SPH that is implemented in the commercial code LS-DYNA® and element-based numerical methods in FEM models. Numerical tests show that the improved SPH cutting model better explains the shear-localized chip formation and correctly estimates the chip morphology as well as the cutting forces.

Pulmonary ventilation imaging in asthma and cystic fibrosis using oxygen-enhanced 3D radial ultrashort echo time MRI.

A previous study demonstrated the feasibility of using 3D radial ultrashort echo time (UTE) oxygen-enhanced MRI (UTE OE-MRI) for functional imaging of healthy human lungs. The repeatability of quantitative measures from UTE OE-MRI needs to be established prior to its application in clinical research. To evaluate repeatability of obstructive patterns in asthma and cystic fibrosis (CF) with UTE OE-MRI with isotropic spatial resolution and full chest coverage. Volunteer and patient repeatability. Eighteen human subjects (five asthma, six CF, and seven normal subjects). Respiratory-gated free-breathing 3D radial UTE (80 μs) sequence at 1.5T. Two 3D radial UTE volumes were acquired sequentially under normoxic and hyperoxic conditions. A subset of subjects underwent repeat acquisitions on either the same day or ≤15 days apart. Asthma and CF subjects also underwent spirometry. A workflow including deformable registration and retrospective lung density correction was used to compute 3D isotropic percent signal enhancement (PSE) maps. Median PSE (MPSE) and ventilation defect percent (VDP) of the lung were measured from the PSE map. The relations between MPSE, VDP, and spirometric measures were assessed using Spearman correlations. The test-retest repeatability was evaluated using Bland-Altman analysis and intraclass correlation coefficients (ICC). Ventilation measures in normal subjects (MPSE = 8.0%, VDP = 3.3%) were significantly different from those in asthma (MPSE = 6.0%, P = 0.042; VDP = 21.7%, P = 0.018) and CF group (MPSE = 4.5%, P = 0.0006; VDP = 27.2%, P = 0.002). MPSE correlated significantly with forced expiratory lung volume in 1 second percent predicted (ρ = 0.72, P = 0.017). The ICC of the test-retest VDP and MPSE were both ≥0.90. In all subject groups, an anterior/posterior gradient was observed with higher MPSE and lower VDP in the posterior compared to anterior regions (P ≤ 0.0021 for all comparisons). 3D radial UTE OE-MRI supports quantitative differentiation of diseased vs. healthy lungs using either whole lung VDP or MPSE with excellent test-retest repeatability. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:1287-1297.

Abstract ID: 41 Consequences of patient heterogeneities for intermediate-energy sources in post-implant assessment of prostate brachytherapy treatment plans

Purpose Recent studies have identified and proposed gamma emitting radionuclides (75Se, 169Yb, 153Gd) with intermediate energy (50 keV Materials and methods Post implant treatment plans were simulated with a Geant4-based Monte Carlo dose calculation engine, BrachySource, coupled to a column-generation based optimizer, for a prostate brachytherapy case. The patient was treated with a brachytherapy boost with a dose of 15 Gy in a single fraction. Simulations were performed using 60Co, 192Ir, 75Se, 169Yb, and 153Gd as the active cores of the source. The plans were independently approved by two radiation oncologists. Two MC calculation protocols were performed for each radionuclide: (1) dose calculations for which patient anatomy is modelled as unit density water and (2) dose calculations for which patient anatomy is modelled with accurate chemical composition of tissues and densities are obtained using the HU values from CT scan. Results With 90% of the planning target volume (PTV) receiving over 15 Gy, plans can reduce the PTV V150 to 19.8%, 18.0%, 18.5%, 13.7% and 11.6% for 60Co, 192Ir, 75Se, 169Yb, and 153Gd, respectively, without sacrificing the urethral D10, the bladder V75 and the rectum V75. In general, dose homogeneity within the PTV increased with decreasing average photon energy. The inclusion of tissue composition and density corrections resulted in a reduction of the PTV D90 (urethral D10) by 0.0% (0.0%), 0.8% (0.7%), 1.8% (1.6%), 3.0% (4.7%) and 4.5% (4.1%) for 60Co, 192Ir, 75Se, 169Yb, and 153Gd, respectively. Conclusion Intermediate-energy sources have the potential to increase dose homogeneity within the PTV while reducing hot spots in the urethra, bladder, and rectum. This work shows the importance of accurate MC-based treatment planning engine, which can account for tissue composition and heterogeneities, for the dosimetry of intermediate-energy sources.

The temperature effect on the methane and CO2 adsorption capacities of Illinois coal

The sorption capacity of coal is influenced by temperature, coal rank, mineral composition and moisture content. In the study, we experimentally measure the methane and carbon dioxide sorption capacity at various temperature for Illinois coal. A volumetric adsorption apparatus was employed to determine the excess gas adsorption capacity, and then the absolute adsorption capacity was estimated through the adsorbed gas phase density correction at each tested pressure. The adsorption isotherms were estimated for various temperatures from 283.15K to 343.15K. The experimental results indicated that both the methane and carbon dioxide adsorption capacities decrease linearly with an increase in temperature from 283.15K up to 323.15K, and the adsorption capacity reduction for CO2 is more significant than that for methane. When the temperature is equal to or greater than 323.15K, the adsorption capacities are independent of the temperature and remain constant for both gases. This means that there is a “critical temperature point” at which the influence of the temperature on the adsorption capacity vanishes, and the adsorption isotherms are very similar when the temperature is beyond the critical temperature point. The ratios of the CO2/CH4 absolute adsorption capacities vary from 2.62 and 3.80 with the tested pressures and temperatures.

Viscometric flow for a many-body dissipative particle dynamics (MDPD) fluid with Lees–Edwards boundary condition

Viscometric properties of polymer are explored by the many-body dissipative particle dynamics (MDPD) using Lees–Edwards boundary conditions. The equation of state for the MDPD system is modified by fitting the density correction to different values of the cut-off radius. Due to the many-body interactions in MDPD, the viscosity contributed from the conservative force increases considerably with increasing repulsive coefficient, density and cut-off radius, and cannot be ignored compared to the ‘standard’ DPD case. The influence of these parameters on the MDPD viscosity is investigated, and we propose an equation to predict the viscosity in MDPD model. Additionally, the dumbbell polymer suspension model is investigated in the MDPD fluid, and the relations concerning first normal stress difference and shear rate, the relaxation time and spring constant, are consistent to theoretical works. We conclude that the MDPD model can be used to investigate the dynamics of non-Newtonian droplets.

The bootstrap method to improve statistical analysis of dosimetric data for radiotherapy outcomes

Purpose: The purpose of this study is to validate a new technique in radiotherapy, the medical physicist needs to evaluate the dosimetric benefit and the risk of toxicity before integrating it in the clinical use. Methods: We validate a sound decision tool based on bootstrap method to help the radio oncologist and the medical physicist to usefully analyze the dosimetric data obtained from small-sized samples, with few patients. Statistical investigation principles are presented in the framework of a clinical example based on 36 patients with 6 different cancer sites treated with radiotherapy. For each patient, two treatment plans were generated. In plan 1, the dose was calculated using Modified Batho's (MB) density correction method integrated with pencil beam convolution (PBC) as type (a) algorithm. In plan 2, the dose was calculated using Anisotropic Analytical Algorithm (AAA) as type (b) algorithm. The delivered doses in monitor units (MUs) were compared using the two plans. Then, the bootstrap method was applied to the original data set to assess the dose differences and evaluate the impact of sample size on the 95% confidence interval (95%.CI). Shapiro-Wilks and Wilcoxon signed-rank tests were used to assess the normality of the data and determine the p-value. In addition, Spearman’s rank test was used to calculate the correlation coefficient between the doses calculated with both algorithms. Results: A significant difference was observed between AAA and MB for all tested radiation sites. Spearman’s test indicated a good correlation between the doses calculated with both methods. The bootstrap simulation with 1000 random samplings can be used for small populations with n = 10 and provides a true estimation. Conclusion: one must be cautious when implementing this method for radiotherapy: the data should be representative of the real variations of the cases and the cases should be as homogeneous as possible to avoid bias of over/under estimation of the results.

Comparison of low density and high density pedicle screw instrumentation in Lenke 1 adolescent idiopathic scoliosis

BackgroundThe correlation between implant density and deformity correction has not yet led to a precise conclusion in adolescent idiopathic scoliosis (AIS). The aim of this study was to evaluate the effects of low density (LD) and high density (HD) pedicle screw instrumentation in terms of the clinical, radiological and Scoliosis Research Society (SRS)-22 outcomes in Lenke 1 AIS.MethodsWe retrospectively reviewed 62 consecutive Lenke 1 AIS patients who underwent posterior spinal arthrodesis using all-pedicle screw instrumentation with a minimum follow-up of 24 months. The implant density was defined as the number of screws per spinal level fused. Patients were then divided into two groups according to the average implant density for the entire study. The LD group (n = 28) had fewer than 1.61 screws per level, while the HD group (n = 34) had more than 1.61 screws per level. The radiographs were analysed preoperatively, postoperatively and at final follow-up. The perioperative and SRS-22 outcomes were also assessed. Independent sample t tests were used between the two groups.ResultsComparisons between the two groups showed no significant differences in the correction of the main thoracic curve and thoracic kyphosis, blood transfusion, hospital stay, and SRS-22 scores. Compared with the HD group, there was a decreased operating time (278.4 vs. 331.0 min, p = 0.004) and decreased blood loss (823.6 vs. 1010.9 ml, p = 0.048), pedicle screws needed (15.1 vs. 19.6, p < 0.001), and implant costs ($10,191.0 vs. $13,577.3, p = 0.003) in the LD group.ConclusionsBoth low density and high density pedicle screw instrumentation achieved satisfactory deformity correction in Lenke 1 AIS patients. However, the operating time and blood loss were reduced, and the implant costs were decreased with the use of low screw density constructs.

Bouguer Density Analysis using Nettleton Method at Banten NPP Site

BOUGUER DENSITY ANALYSIS USING NETTLETON METHOD AT BANTEN NPP SITE. Sub-surface information become crucial in determining a feasible NPP site that safe from external hazards. Gravity survey which result as density information, is essential to understand the sub-surface structure. Nevertheless, overcorrected or under corrected will lead to a false interpretation. Therefore, density correction in term of near-surface average density or Bouguer density is necessary to be calculated. The objective of this paper is to estimate and analyze Bouguer density using Nettleton method at Banten NPP Site. Methodology used in this paper is Nettleton method that applied in three different slices (A-B, A-C and A-D) with density assumption range between 1700 and 3300 kg/m3. Nettleton method is based on minimum correlation between gravity anomaly and topography to determine density correction. The result shows that slice A-B which covers rough topography difference, Nettleton method failed. While using the other two slices, Nettleton method yield with a different density value, 2700 kg/m3 for A-C and 2300 kg/m3 for A-D. A-C provides the lowest correlation value which represents the Upper Banten tuff and Gede Mt. volcanic rocks in accordance with Quartenary rocks exist in the studied area.

Effect of flexibility and implant density on curve correction in adolescent idiopathic scoliosis

Type of study: Retrospective study Objectives: To evaluate correlation between flexibility, implant density on curve correction in adolescent idiopathic scoliosis Materials and methods: We retrospectively reviewed all consecutive patients of adolescent idiopathic scoliosis who underwent single stage posterior-only correction and instrumented spinal fusion at a single centre between 2013 and 2015 performed by single surgeon. All cases of adolescent idiopathic scoliosis treated with all pedicle screw instrumentation were included. A total of 30 patients were studied, which included 20 females and 10 males. Correlation between implant density, flexibility and curve correction was investigated with pearson correlation coefficient. Results: Average flexibility was 41.86%. Average implant density for rigid curves was 54.49%, flexible curves was 58%. Average curve correction for rigid curve was 60.22%, flexible curves79.56%.The correlation coefficient for curve correction and implant density was 0.096 for flexible curves, 0.075 for rigid curves, both were statistically not significant. The correlation coefficient for flexibility and curve correction was 0.578 for flexible curves and 0.506 for rigid curves which was statistically significant for rigid curves. Conclusion: There was minimal positive correlation correlation between implant density and curve correctability in both flexible and rigid curves not statistically significant. There is positive correlation between flexixibility & curve correctability in both flexible and rigid curves which is significant in rigid curves.

Evaluation of Density Corrections to Methane Fluxes Measured by Open-Path Eddy Covariance over Contrasting Landscapes

Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide $$(\hbox {CO}_{2})$$ fluxes, but less attention has been paid to evaluating these corrections for methane $$(\hbox {CH}_{4})$$ fluxes. We measured $$\hbox {CH}_{4}$$ fluxes with open-path sensors over a suite of sites with contrasting $$\hbox {CH}_{4}$$ emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3–10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency $$\hbox {CH}_{4}$$ fluctuations led to large differences in observed $$\hbox {CH}_{4}$$ flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting $$\hbox {CH}_{4}$$ cospectra for comparable ecosystems. These results give us confidence in $$\hbox {CH}_{4}$$ fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.

Agreement between gamma passing rates using computed tomography in radiotherapy and secondary cancer risk prediction from more advanced dose calculated models.

During the past decades, in radiotherapy, the dose distributions were calculated using density correction methods with pencil beam as type 'a' algorithm. The objectives of this study are to assess and evaluate the impact of dose distribution shift on the predicted secondary cancer risk (SCR), using modern advanced dose calculation algorithms, point kernel, as type 'b', which consider change in lateral electrons transport. Clinical examples of pediatric cranio-spinal irradiation patients were evaluated. For each case, two radiotherapy treatment plans with were generated using the same prescribed dose to the target resulting in different number of monitor units (MUs) per field. The dose distributions were calculated, respectively, using both algorithms types. A gamma index (γ) analysis was used to compare dose distribution in the lung. The organ equivalent dose (OED) has been calculated with three different models, the linear, the linear-exponential and the plateau dose response curves. The excess absolute risk ratio (EAR) was also evaluated as (EAR = OED type 'b' / OED type 'a'). The γ analysis results indicated an acceptable dose distribution agreement of 95% with 3%/3 mm. Although, the γ-maps displayed dose displacement >1 mm around the healthy lungs. Compared to type 'a', the OED values from type 'b' dose distributions' were about 8% to 16% higher, leading to an EAR ratio >1, ranged from 1.08 to 1.13 depending on SCR models. The shift of dose calculation in radiotherapy, according to the algorithm, can significantly influence the SCR prediction and the plan optimization, since OEDs are calculated from DVH for a specific treatment. The agreement between dose distribution and SCR prediction depends on dose response models and epidemiological data. In addition, the γ passing rates of 3%/3 mm does not translate the difference, up to 15%, in the predictions of SCR resulting from alternative algorithms. Considering that modern algorithms are more accurate, showing more precisely the dose distributions, but that the prediction of absolute SCR is still very imprecise, only the EAR ratio could be used to rank radiotherapy plans.