Cooling and heating of the fluid in the cylindrical volume

Experimental studies of the non-stationary heat exchange in the system «environment I – body II» have been carried out. It is established that in the body II, which consists of the fluid and thin-walled metal envelope, the characteristic features of the regular thermal mode occur, i.e., cooling (heating) rate of the body II- m = const; heat transfer coefficient between the water (environment I) and body II is practically stable α1 = const; uneven temperatures distribution coefficient in the body II ψ = const. This new notion of the heat transfer regularities in the body II is planned to apply for further development of the experimental-calculation method for the forecasting of the heat exchange intensity in the compound fluid media with limited information regarding thermophysical and rheological properties.

Thermoelectric precession in turbulent magnetoconvection

We present laboratory measurements of the interaction between thermoelectric currents and turbulent magnetoconvection. In a cylindrical volume of liquid gallium heated from below and cooled from above and subject to a vertical magnetic field, it is found that the large-scale circulation (LSC) can undergo a slow axial precession. Our experiments demonstrate that this LSC precession occurs only when electrically conducting boundary conditions are employed, and that the precession direction reverses when the axial magnetic field direction is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC magnetoprecession model hinges on thermoelectric current loops at the top and bottom boundaries, which create Lorentz forces that generate horizontal torques on the overturning large-scale circulatory flow. The thermoelectric torques in our model act to drive a precessional motion of the LSC. This model yields precession frequency predictions that are in good agreement with the experimental observations. We postulate that thermoelectric effects in convective flows, long argued to be relevant in liquid metal heat transfer and mixing processes, may also have applications in planetary interior magnetohydrodynamics.

Improvement of the Point Spread Function by Collimators’ New Configuration in Nuclear Medicine

Objective: The collimators in which the various geometrical configurations have been suggested to optimize the sensitivity and resolution have a key role in acquiring the qualified images in nuclear medicine towards a better recognition of some diseases. Methods: In this study, a new configuration as a geometrical combination of the conical, cylindrical and spherical (CCS) volumes for parallel hole collimators which is assessed by using the volumetric-parametric method has been introduced to improve point spread function (PSF) being the collimators response on the radioactive point source. It has been simulated by the MCNPX code at the various energies values of the point source along with the traditional collimator in which included the cylindrical volume only. Results: The PSF will transmogrify from a delta function to a distribution which can correlate with a Gaussian distribution, while the scattered gamma rays were increased. The simulation results have indicated that the PSF in the CCS configuration is narrower than that of the cylindrical one at all the energies, leading the improvement of the resolution. Also, the theoretical results are agreement with the simulated ones. The more the energy value of the source, the more broaden the PSF will be due the more penetration strength. The narrower the PSF, the better the qualified image will be. Conclusion: This method may be employed to determine the accurate attenuation coefficient of absorbers as well.

The effect of calibration factors and recovery coefficients on 177Lu SPECT activity quantification accuracy: a Monte Carlo study

Background Different gamma camera calibration factor (CF) geometries have been proposed to convert SPECT data into units of activity concentration. However, no consensus has been reached on a standardised geometry. The CF is dependent on the selected geometry and is further affected by partial volume effects. This study investigated the effect of two CF geometries and their corresponding recovery coefficients (RCs) on the quantification accuracy of 177Lu SPECT images using Monte Carlo simulations. Methods The CF geometries investigated were (i) a radioactive-sphere surrounded by non-radioactive water (sphere-CF) and (ii) a cylindrical phantom uniformly filled with radioactive water (cylinder-CF). Recovery coefficients were obtained using the sphere-CF and cylinder-CF, yielding the sphere-RC and cylinder-RC values, respectively, for partial volume correction (PVC). The quantification accuracy was evaluated using four different-sized spheres (15.6–65.4 ml) and a kidney model with known activity concentrations inside a cylindrical, torso and patient phantom. Images were reconstructed with the 3D OS-EM algorithm incorporating attenuation, scatter and detector-response corrections. Segmentation was performed using the physical size and a small cylindrical volume inside the cylinder for the sphere-CF and cylinder-CF, respectively. Results The sphere quantification error (without PVC) was better for the sphere-CF (≤ − 5.54%) compared to the cylinder-CF (≤ − 20.90%), attributed to the similar geometry of the quantified and CF spheres. Partial volume correction yielded comparable results for the sphere-CF-RC (≤ 3.47%) and cylinder-CF-RC (≤ 3.53%). The accuracy of the kidney quantification was poorer (≤ 22.34%) for the sphere-CF without PVC compared to the cylinder-CF (≤ 2.44%). With PVC, the kidney quantification results improved and compared well for the sphere-CF-RC (≤ 3.50%) and the cylinder-CF-RC (≤ 3.45%). Conclusion The study demonstrated that upon careful selection of CF-RC combinations, comparable quantification errors (≤ 3.53%) were obtained between the sphere-CF-RC and cylinder-CF-RC, when all corrections were applied.

The Effect of Calibration Factors and Recovery Coefficients on 177Lu SPECT Activity Quantification Accuracy: A Monte Carlo Study

Background: Different gamma camera calibration factor (CF) geometries have been proposed to convert SPECT data into units of activity concentration. However, no consensus has been reached on a standardized geometry. The CF is dependent on the selected geometry and affected by partial volume effects. This study investigated the effect of two CF geometries and their corresponding recovery coefficients (RCs) on the quantification accuracy of 177Lu SPECT images using Monte Carlo simulations.Methods: The CF geometries investigated were (i) a radioactive-sphere surrounded by non-radioactive water (sphere-CF) and (ii) a cylindrical phantom uniformly filled with radioactive water, (cylinder-CF). Recovery coefficients were obtained using the sphere-CF and cylinder-CF, yielding the sphere-RC and cylinder-RC values, respectively, for partial volume correction (PVC). The quantification accuracy was evaluated using four different sized spheres (15.6 ml – 65.4 ml) and a kidney model with known activity concentrations inside a cylindrical, torso and patient phantom. Images were reconstructed with the OS-EM algorithm incorporating attenuation, scatter and detector-response corrections. Segmentation was performed using the physical size and a small cylindrical volume inside the cylinder for the sphere-CF and cylinder-CF, respectively.Results: The sphere quantification error (without PVC) was better for the sphere-CF (≤ -5.54%) compared to the cylinder-CF (≤ -20.90%), attributed to the similar geometry of the quantified and CF spheres. Partial volume correction yielded comparable results for the sphere-CF (≤ 3.47%) and cylinder-CF (≤ 3.53%). The accuracy of the kidney quantification was poorer (≤ 22.34%) for the sphere-CF without PVC compared to the cylinder-CF (≤ 2.44%). With PVC, the kidney quantification results improved and compared well for the sphere-CF (≤ 3.50%) and the cylinder-CF (≤ 3.45%).Conclusion: The study demonstrated that upon careful selection of CF-RC combinations, comparable quantification errors (≤ 3.53%) were obtained between the sphere-CF and cylinder-CF, when all corrections were applied.

Linking the spatiotemporal variation of litterfall to standing vegetation biomass in Brazilian savannas

Aims Litterfall at a global scale is affected by climate, edaphic features and vegetation structure, with litter production increasing from grasslands to forests following the rise in standing biomass. However, at landscape scales, the same relationship between litter production and vegetation structure has rarely been studied and comparisons of litterfall patterns between adjacent, structurally distinct communities are lacking. Here, we use a standardized methodology to describe the structural differences among four savanna physiognomies and analyze their relationship with changes in litterfall across the Cerrado. Methods We evaluated the woody vegetation structure and composition in 48 sites, equally distributed across four physiognomies and monitored the monthly litter production from April 2014 to March 2015. Important Findings Results showed that the density, basal area, cylindrical volume and aboveground biomass of woody vegetation differ among physiognomies, increasing consistently from cerrado ralo, cerrado típico, cerrado denso and cerradão. Indeed, we found a strong and positive relationship between aboveground biomass and annual litter production, with litter yield increasing from 0.9 to 8.4 Mg ha−1 across different physiognomies, following the increment in vegetation structure. Monthly production was seasonal and similar among vegetation types, increasing during the dry season. Leaves comprised the dominant fraction (approx. 85%) and litterfall seasonality primarily resulted from the concentration of leaf shedding during dry months. However, the temporal pattern of litterfall throughout the year showed a gradual reduction in the seasonality from open to closed vegetation types, likely following the decrease of deciduous species abundance in the plant community. Our results showed that changes in vegetation structure may affect spatial and temporal litterfall patterns in different physiognomies, which co-occur across the Cerrado landscape, with potential implications for the overall functioning of this ecosystem. Moreover, these findings highlight the use of standardized methods as essential to correctly compare litterfall patterns among different environments.

Капиллярная неустойчивость цилиндрической струи феррожидкости, находящейся в однородном продольном магнитном поле

In this article a ferrofluid jet located inside a solenoid is considered. The jet is modeled by a cylindrical volume of incompressible inviscid fluid moving at a constant velocity parallel to the axis of the cylinder. The axes of the jet and the solenoid coincide. The variation of the strength of the magnetic field generated by the solenoid is allowed from very small to experimentally achievable maximal values. We investigate the influence of the magnetic forces on the growth rate and the wavelength of the most rapidly growing perturbations of the jet surface shape.