scholarly journals Turbulent pair dispersion as a ballistic cascade phenomenology

2015 ◽  
Vol 772 ◽  
pp. 678-704 ◽  
Author(s):  
Mickaël Bourgoin
Keyword(s):  
Diffusion Coefficient ◽  
Turbulent Flows ◽  
Relative Dispersion ◽  
Mean Square ◽  
Short Term ◽  
Third Order ◽  
Temporal Asymmetry ◽  
Diffusive Regime ◽  
The Mean

Since the pioneering work of Richardson in 1926, later refined by Batchelor and Obukhov in 1950, it is predicted that the rate of separation of pairs of fluid elements in turbulent flows with initial separation at inertial scales, grows ballistically first (Batchelor regime), before undergoing a transition towards a super-diffusive regime where the mean-square separation grows as $t^{3}$ (Richardson regime). Richardson empirically interpreted this super-diffusive regime in terms of a non-Fickian process with a scale-dependent diffusion coefficient (the celebrated Richardson’s ‘$4/3$rd’ law). However, the actual physical mechanism at the origin of such a scale dependent diffusion coefficient remains unclear. The present article proposes a simple physical phenomenology for the time evolution of the mean-square relative separation in turbulent flows, based on a scale-dependent ballistic scenario rather than a scale-dependent diffusive. It is shown that this phenomenology accurately retrieves most of the known features of relative dispersion for particles mean-square separation, among others: (i) it is quantitatively consistent with most recent numerical simulations and experiments for mean-square separation between particles (both for the short-term Batchelor regime and the long-term Richardson regime, and for all initial separations at inertial scales); (ii) it gives a simple physical explanation of the origin of the super-diffusive $t^{3}$ Richardson regime which naturally builds itself as an iterative process of elementary short-term scale-dependent ballistic steps; (iii) it shows that the Richardson constant is directly related to the Kolmogorov constant (and eventually to a ballistic persistence parameter); and (iv) in a further extension of the phenomenology, taking into account third-order corrections, it robustly describes the temporal asymmetry between forward and backward dispersion, with an explicit connection to the cascade of energy flux across scales. An important aspect of this phenomenology is that it simply and robustly connects long-term super-diffusive features to elementary short-term mechanisms, and at the same time it connects basic Lagrangian features of turbulent relative dispersion (both at short and long times) to basic Eulerian features of the turbulent field: second-order Eulerian statistics control the growth of separation (both at short and long times) while third-order Eulerian statistics control the temporal asymmetry of the dispersion process, which can then be directly identified as the signature of the energy cascade and associated to well-known exact results as the Karman–Howarth–Monin relation.

scholarly journals On the Theory of Electron Diffusion in Electrostatic Fields in Gases

1974 ◽  
Vol 27 (2) ◽  
pp. 195 ◽  
Author(s):  
HR Skullerud
Keyword(s):  
Diffusion Coefficient ◽  
Boltzmann Equation ◽  
Diffusion Equation ◽  
Diffusion Tensor ◽  
Lateral Diffusion ◽  
Mean Square ◽  
Electrostatic Fields ◽  
The Mean ◽  
Lateral Diffusion Coefficient

The motion of electrons in a gas in the presence of large electron density gradients has been studied theoretically, starting from the two-term expansion of the Boltzmann equation. The effects of material boundaries have not been considered. An electron swarm released as a b-function in space and with an equilibrium energy distribution is found initially to develop as a spheroid with dimensions determined by the lateral diffusion coefficient. It subsequently passes through a stage involving a slowly decaying pear-shaped deformation, before ultimately becoming an ellipsoid with dimensions determined by the longitudinal and lateral components of the diffusion tensor. Numerical values cited in the literature for the long-term deviations from the mean square widths predicted by the diffusion equation have been found to be in error by factors of 10 or more.

Elevations in Thyroid-Stimulating Hormone in Normal Subjects after Receiving Short-Term Lithium Carbonate

1988 ◽  
Vol 22 (3) ◽  
pp. 202-204 ◽  
Author(s):  
Merlin V. Nelson ◽  
Vickie Tutag-Lehr ◽  
R. Lee Evans
Keyword(s):  
Lithium Carbonate ◽  
Normal Subjects ◽  
Thyroid Stimulating Hormone ◽  
Short Term ◽  
The Mean ◽  
Early Rise ◽  
State Concentration ◽  
Male Subjects ◽  
Stimulating Hormone

Nine normal, healthy male subjects had significantly elevated thyroid-stimulating hormone (TSH) concentrations while receiving oral lithium carbonate for two weeks. The mean minimum lithium serum concentration was 0.765 mEq/L. The TSH concentrations after 15 days on lithium were significantly correlated to the TSH concentration at baseline. No correlation was found between mean minimum lithium steady-state concentration and TSH concentration after 15 days on lithium. Further research is necessary to determine if a high baseline TSH concentration or an early rise in TSH will predict those patients who will eventually develop hypothyroidism after long-term lithium therapy.

scholarly journals A SLR Pre-Processing Algorithm Based on Satellite Signature Effect

2021 ◽  
Vol 11 (19) ◽  
pp. 8880
Author(s):  
Bowen Guan ◽  
Cunbo Fan ◽  
Ning An ◽  
Ricardo Cesar Podesta ◽  
Dra Ana Pacheco ◽  
...  
Keyword(s):  
Mean Value ◽  
Observation Data ◽  
Short Term ◽  
Error Sources ◽  
Effect Model ◽  
The Mean ◽  
The Stability ◽  
First Time ◽  
Satellite Signature Effect

As one of the major error sources, satellite signature effect should be reduced or even erased from the distribution of the post-fit residuals to improve the ranging precision. A simulation of satellite signature effect removal process for normal point algorithm is conducted based on a revised model of satellite response, which fully considers the structural and distribution characteristics of retroreflectors. In order to eliminate both long-term and short-term satellite signature effect, a clipping method for SLR data processing is proposed by defining the clipping location as 5.6 mm away from the mean value of the long-term fit residuals to select effective returns for normal points. The results indicate that, compared to normal points algorithm, the RMS per NP of LAGEOS-1 observation data processed by the clipping method is reduced from 62.90 ± 9.9 mm to 56.07 ± 4.69 mm, and the stability of RMS is improved 53%. This study improves the satellite signature effect model and simulates the fluctuation of normal points caused by satellite signature effect for the first time. The new method based on the simulation of satellite signature effect has stronger robustness and applicability, which can further minimize the influence of satellite signature effect on the SLR production and significantly improve the data property.

scholarly journals Early and long-term complications following transanal pull through Soave technique in infants with Hirschsprung's diseaseric infants with Hirschsprung's disease

2019 ◽  
Author(s):  
Manoochehr Ghorbanpour ◽  
Mohammad Ali Seyfrabie ◽  
Babak Yousefi
Keyword(s):  
Intestinal Obstruction ◽  
Hirschsprung's Disease ◽  
Hirschsprung’S Disease ◽  
Statistical Tests ◽  
Case Series ◽  
P Value ◽  
Short Term ◽  
Case Series Study ◽  
The Mean

Objective. Patients undergoing Soave surgery for Hirschsprung's disease are at risk for some complications. The aim of this study was to investigate such short-term and long-term complications and evaluate the outcome of the operation in these patients. Methods. A case series study was carried out during the last 12 years, during 2007 to 2018 in Besat hospital of Hamadan. Data collection conducted using a checklist includes questions about demographic information, clinical features, and short-term and long-term complications, and consequences of post-operative surgery. The findings of the study were analyzed using SPSS software version 20 and appropriate statistical tests. P-value less than 0.05 was considered statistically significant. Results. A total of 55 children underwent Soave surgery during the last 12 years in Besat Hospital Hamadan, Iran. The mean age of the patients was 38±10 days during surgery, of which 56.4% were female. The mean hospital stay was 7.3 days. Also, the mean weight of children at birth was 2970±447 gr. Most of the patients were born as NVD (52.7%) and term (74.5%). The most common comorbidity was congenital heart disease. The most common short-term complication was intestinal obstruction in 14 patients (25.5%) and the most frequent long-term complication was intestinal obstruction and constipation (27.3% each cases). The mortality rate of patients in this study was 14.5% in total. Conclusions. One stage surgical procedure in Hirschsprung's disease is a safe and effective method, but care should be taken in choosing patients and patients should be monitored for possible complications, so that they can be considered and implemented for proper treatment.

Optical studies on the turbulent motion of solid particles in a pipe flow

1991 ◽  
Vol 231 ◽  
pp. 665-688 ◽  
Author(s):  
James B. Young ◽  
Thomas J. Hanratty
Keyword(s):  
Diffusion Coefficient ◽  
Particle Velocity ◽  
Turbulent Diffusion ◽  
Slip Velocity ◽  
Rate Of Change ◽  
Solid Particles ◽  
Mean Square ◽  
Turbulent Diffusion Coefficient ◽  
Fluid Turbulence ◽  
The Mean

An extension of an axial viewing optical technique (first used by Lee, Adrian & Hanratty) is described which allows the determination of the turbulence characteristics of solid particles being transported by water in a pipe. Measurements are presented of the mean radial velocity, the mean rate of change radial velocity, the mean-square of the radial and circumferential fluctuations, the Eulerian turbulent diffusion coefficient, and the Lagrangian turbulent diffusion coefficient. A particular focus is to explore the influence of slip velocity for particles which have small time constants. It is found that with increasing slip velocity the magnitude of the turbulent velocity fluctuations remains unchanged but that the turbulent diffusivity decreases. The measurements of the average rate of change of particle velocity are consistent with the notion that particles move from regions of high fluid turbulence to regions of low fluid turbulence. Measurements of the root-mean-square of the fluctuations of the rate of change of particle velocity allow an estimation of the average magnitude of the particle slip in a highly turbulent flow, which needs to be known to analyse the motion of particles not experiencing a Stokes drag.

The influence of mixtures of Stylosanthes spp. accessions on the occurrence of anthracnose caused by Colletotrichum gloeosporioides

1994 ◽  
Vol 45 (1) ◽  
pp. 203 ◽  
Author(s):  
RD Davis ◽  
S Chakraborty ◽  
DF Cameron ◽  
JAG Irwin ◽  
RM Boland
Keyword(s):  
Colletotrichum Gloeosporioides ◽  
Resistant Cultivar ◽  
Pure Stand ◽  
Northern Australia ◽  
Short Term ◽  
Mixed Stands ◽  
The Mean ◽  
Moderately Resistant ◽  
Long Term Studies

The effectiveness of using accession mixtures of Stylosanthes spp. to manage anthracnose (Colletotrichum gloeosporioides) in pastures in northern Australia was examined during three consecutive years. Two mixtures containing six accessions were compared with the components grown as pure stands. No significant differences in anthracnose incidence (proportion of infected plants/plot) were indicated between the two mixtures and the mean incidence of their respective components grown in pure swards. Areas under the disease progress curves for the accessions were not significantly different between pure and mixed stands of the cultivars other than Seca and Verano. Resistant cultivar Seca developed more disease in a mixture than in a pure stand, and moderately resistant Verano had less disease in a mixture than in a pure stand. In the short term, no apparent anthracnose control advantage is achieved in highly susceptible accessions of Stylosanthes spp. when they are included in mixtures with less susceptible accessions. Long term studies involving grazing animals are necessary to adequately evaluate control of this disease through the use of mixtures.

The Effects of Upstream Wall Roughness on Separated and Reattached Flows Over a Forward-Facing Step

2020 ◽  
Author(s):  
Sedem Kumahor ◽  
Xingjun Fang ◽  
William Ediger ◽  
Mark F. Tachie
Keyword(s):  
Correlation Coefficient ◽  
Turbulent Flows ◽  
Eddy Viscosity ◽  
Leading Edge ◽  
Step Height ◽  
Stream Velocity ◽  
Reynolds Stresses ◽  
Third Order ◽  
The Mean ◽  
Forward Facing Step

Abstract Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers developed over smooth and rough walls were investigated using time-resolved particle image velocimetry. Both smooth and fully rough upstream bottom wall conditions were examined and the resultant oncoming boundary layer thickness were 4.3 and 6.7 times the step height, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The mean velocities, Reynolds stresses analyzed in both Cartesian and curvilinear coordinate systems, eddy viscosity, correlation coefficient and third order moments are discussed. The results indicate that, due to the enhanced turbulence intensity and shear rate in the fully rough case, distinct elevated regions of vertical and shear Reynolds stresses are consistent upstream of the leading edge of the step while the magnitude of the Reynolds stresses are consistently higher than observed in the smooth case. The correlation coefficient, eddy viscosity and third order moments also show distinct elevated regions upstream of the leading edge of the step in the fully rough case. Above the step, distinct elevated regions of the Reynolds stresses, eddy viscosity and correlation coefficient are observed in both cases with the peak values at a vertical location corresponding to the maximum elevation of the mean separating streamline.

scholarly journals Mid-infrared evolution of η Carinae from 1968 to 2018

2019 ◽  
Vol 630 ◽  
pp. L6 ◽  
Author(s):  
A. Mehner ◽  
W.-J. de Wit ◽  
D. Asmus ◽  
P. W. Morris ◽  
C. Agliozzo ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Short Term ◽  
Dust Extinction ◽  
Bolometric Luminosity ◽  
Very Large Telescope ◽  
Optical Wavelengths ◽  
The Mean

η Car is one of the most luminous and massive stars in our Galaxy and is the brightest mid-IR source in the sky outside our solar system. Since the late 1990s, the central source has dramatically brightened at UV and optical wavelengths. This might be explained by a decrease in circumstellar dust extinction. We aim to establish the mid-IR flux evolution and further our understanding of the star’s UV and optical brightening. Mid-IR images from 8−20 μm were obtained in 2018 with VISIR at the Very Large Telescope. Archival data from 2003 and 2005 were retrieved from the ESO Science Archive Facility, and historical records were collected from publications. We present mid-IR images of η Car with the highest angular resolution to date at the corresponding wavelengths (≥0.22″). We reconstruct the mid-IR evolution of the spectral energy distribution of the spatially integrated Homunculus nebula from 1968 to 2018 and find no long-term changes. The bolometric luminosity of η Car has been stable over the past five decades. We do not observe a long-term decrease in the mid-IR flux densities that could be associated with the brightening at UV and optical wavelengths, but circumstellar dust must be declining in our line of sight alone. Short-term flux variations within about 25% of the mean levels could be present.

scholarly journals Supratentorial cavernous malformations adjacent to the corticospinal tract: surgical outcomes and predictive value of diffusion tensor imaging findings

2018 ◽  
Vol 128 (2) ◽  
pp. 541-552 ◽  
Author(s):  
Yuanxiang Lin ◽  
Fuxin Lin ◽  
Dezhi Kang ◽  
Yuming Jiao ◽  
Yong Cao ◽  
...  
Keyword(s):  
Surgical Outcomes ◽  
Predictive Value ◽  
Diffusion Tensor ◽  
Motor Deficits ◽  
Short Term ◽  
Cavernous Malformations ◽  
Scale Scores ◽  
The Mean ◽  
Deep Location

OBJECTIVEDiffusion tensor imaging (DTI) findings may facilitate clinical decision making in patients with supratentorial cavernous malformations adjacent to the corticospinal tract (CST-CMs). The objective of this study was to determine the predictive value of preoperative DTI findings for surgical outcomes in patients with CST-CMs.METHODSA prospectively maintained database of patients with CM referred to the authors' hospital between September 2012 and October 2015 was reviewed to identify all consecutive surgically treated patients with CST-CM. All patients had undergone sagittal T1-weighted anatomical imaging and DTI before surgery. Both DTI findings and clinical characteristics of the patients and lesions were analyzed with respect to surgery-related motor deficits. DTI findings included lesion-to-CST distance (LCD) and the alteration (i.e., deviation, interruption, or degeneration due to the CM) of CST on preoperative DTI images. Surgery-related motor deficits at 1 week and the last clinic visit (≥ 3 months) after surgery were defined as short-term and long-term deficits, respectively. Preoperative and final modified Rankin Scale scores were also analyzed to identify the surgical outcomes in these patients.RESULTSA total of 56 patients with 56 CST-CMs were included in this study. The mean LCD was 3.9 ± 3.2 mm, and alterations of the CST were detected in 20 (36.7%) patients. One week after surgery, 21 (37.5%) patients had short-term surgery-related motor deficits, but only 14 (25.0%) patients had long term deficits at the last clinical visit. The mean patient follow-up was 14.7 ± 10.1 months. The difference between preoperative and final modified Rankin Scale scores was not statistically significant (p = 0.490). Multivariate analysis showed that both short-term (p < 0.001) and long-term (p = 0.002) surgery-related motor deficits were significantly associated with LCD. Receiver operating characteristic (ROC) curve results were as follows: for short-term surgery-related motor deficits, the area under the ROC curve (AUC) was 0.860, and the cutoff point was LCD = 2.55 mm; for long-term deficits, the AUC was 0.894, and the cutoff point was LCD = 2.30 mm. Both univariate (p = 0.012) and multivariate (p = 0.049) analyses revealed that CST alteration on preoperative DTI was significantly correlated with short-term surgery-related motor deficits. On univariate analysis, deep location of the CST-CMs was significantly correlated with long-term motor deficits (p = 0.016). Deep location of the CST-CMs had a trend toward significance with long-term motor deficits on the multivariate analysis (p = 0.060).CONCLUSIONSTo facilitate clinical practice, the authors propose that 3.00 mm (2.55 to ∼3.00 mm) may be the safe LCD for surgery in patients with CST-CMs. A CST alteration on preoperative DTI and a deep location of the CST-CM may be risk factors for short- and long-term surgery-related motor deficits, respectively. A randomized controlled trial is needed to demonstrate the predictive value of preoperative DTI findings on surgical outcomes in patients with CST-CMs in future studies.

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