The asymptotic stage of longitudinal turbulent dispersion within a tube

1977 ◽  
Vol 80 (2) ◽  
pp. 293-303 ◽  
Author(s):  
R. Dewey ◽  
Paul J. Sullivan
Keyword(s):  
Turbulent Flows ◽  
Friction Velocity ◽  
Turbulent Dispersion ◽  
Time Interval ◽  
Longitudinal Diffusion ◽  
A Value ◽  
Discharge Velocity ◽  
Concentration Curves ◽  
Temporal Growth Rate ◽  
Short Times

This paper describes an experimental investigation of the conditions for which the asymptotic description of longitudinal dispersion given by Taylor (1954) would apply. At non-dimensional times following the release of a dye pulse that are significantly larger than those previously investigated, the integrated concentration curves were observed to be skewed. At relatively short times from release the concentration curves appear to be well described by the models presented by Sullivan (1971) and by Chatwin (1973). Some features of the asymptotic behaviour, namely the translation of the modal value of the integrated concentration curve at the discharge velocity and the constant temporal growth rate of the variance, are observed at the longest times following release. On the basis of these observations it is estimated that a non-dimensional time interval oftu*/d=O(105/R*), whereR*=u*d/v,u*is the friction velocity,vthe kinematic viscosity anddthe tube diameter, is required for the Taylor result to become applicable. Thus application of Taylor's theory is significantly restricted in turbulent flows, especially those with irregular boundaries and those that are not stationary. There the variations in the flow must be small with respect to an equivalent ‘development time’ if a value of the ‘local’ longitudinal diffusion coefficient is to have meaning.

scholarly journals Definition and estimation of an actual reproduction number describing past infectious disease transmission: application to HIV epidemics among homosexual men in Denmark, Norway and Sweden

2004 ◽  
Vol 132 (6) ◽  
pp. 1139-1149 ◽  
Author(s):  
E. J. AMUNDSEN ◽  
H. STIGUM ◽  
J.-A. RØTTINGEN ◽  
O. O. AALEN
Keyword(s):  
Infectious Disease ◽  
Disease Transmission ◽  
Reproduction Number ◽  
Infectious Period ◽  
Secondary Case ◽  
Time Interval ◽  
Homosexual Men ◽  
Infectious Disease Transmission ◽  
A Value ◽  
The Common

Prevalence and incidence measures are the common way to describe epidemics. The reproduction number supplies information on the potential for growth or decline of an epidemic. We define an actual reproduction number for infectious disease transmission that has taken place. An estimator is suggested, based on the number of new infections observed in a given time-interval, the number of those infected at the start of the interval, and the length of the infectious period. That estimator is applied to HIV among men having sex with other men over the period, 1977–1995, in Scandinavia. The actual reproduction number was estimated with acceptable certainty from the period, 1981–1982, yielding a value of 15 secondary cases. A value of less than one secondary case was assessed for the period, 1988–1995, in Denmark and Sweden. The actual reproduction number gives us some additional understanding of the dynamics of epidemics, compared with prevalence and incidence curves.

scholarly journals On the modeling of droplet transport, dispersion and evaporation in turbulent flows

2005 ◽  
Vol 122 (3) ◽  
pp. 42-55
Author(s):  
Jorge BARATA
Keyword(s):  
Turbulent Flows ◽  
Gas Turbines ◽  
Numerical Study ◽  
Droplet Diameter ◽  
Turbulent Transport ◽  
Three Dimensional ◽  
Turbulent Dispersion ◽  
Droplet Transport ◽  
New Formulation ◽  
Evaporation Models

The present paper presents a numerical study on evaporating droplets injected through a turbulent cross-stream. Several models have been used with more or less success to describe similar phenomena, but much of the reported work deals only with sprays in stagnant surroundings. The ultimate goal of this study is to develop an Eulerian/Lagragian approach to account for turbulent transport, dispersion, evaporation and coupling between both processes in practical spray injection systems, which usually include air flows in the combustion chamber like swirl, tumble and squish in I.C. engines or crossflow in gas turbines. In this work a method developed to study isothermal turbulent dispersion is extended to the case of an array of evaporating droplets through a crossflow, and the performance of two different evaporation models widely used is investigated. The convection terms were evaluated using the hybrid or the higher order QUICK scheme. The dispersed phase was treated using a Lagrangian reference frame. The differences between the two evaporation models and its applicability to the present flow are analysed in detail. During the preheating period of the Chen and Pereira [1] model the droplets are transported far away from the injector by the crossflow, while with the Sommerfeld [2] formulation for evaporation the droplet has a continuous variation of the diameter. This result has profound implications on the results because the subsequent heat transfer and turbulent dispersion is extremely affected by the size of the particles (or droplets). As a consequence, droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the evaporation model used. So, a new formulation that takes into account also the transport of the evaporating droplets needs to be developed if practical injection systems are to be simulated. Also, in order to better evaluate and to improve the vaporization models more detailed measurements of three-dimensional configurations are required.

scholarly journals PREDIKSI PELUANG KEMATIAN DAN KELAHIRAN MURNI PENDUDUK KABUPATEN MERAUKE MENGGUNAKAN METODE BIRTH AND DEATH PROCESS

2021 ◽  
Vol 15 (1) ◽  
pp. 095-102
Author(s):  
Minuk Riyana ◽  
Marius Agustinus Welliken K.
Keyword(s):  
Population Data ◽  
The Elderly ◽  
Death Process ◽  
Initial Time ◽  
Time Interval ◽  
Birth And Death Process ◽  
Female Sex ◽  
A Value ◽  
Calculation Results ◽  
Process Method

This study aims to estimate the probability of birth and death purely based on gender and population data of Merauke City. The chance of birth and death will be used to estimate the life table of the elderly in a population of the City of Merauke. The method used in this research is the birth and process method. The Birth and death process method which is a Poisson distribution is used to predict the chances of birth and death at time t. If the birth and death process fulfills the linearity requirements, then the processes are called the Yule-Furry process. This research discusses the stochastic process of pure birth-death with two sexes in the Yule-Furry Process. From the data on the population of Merauke district which is divided based on the sex of men and women using the pure birth and death model, the calculation results show that the probability value at the time interval 0 ≤ t <1 hour, at the initial time t = 0, the chance of individual birth at female sex is stationary at a value of 0.1762, while the chance of individual death for female sex is stationary at a value of 0.00154. The odds of birth and death in male individuals are stationary at a value of 0.305034 and 0, 059487.

scholarly journals Dependency of particle size distribution at dust emission on friction velocity and atmospheric boundary-layer stability

2020 ◽  
Vol 20 (21) ◽  
pp. 12939-12953
Author(s):  
Yaping Shao ◽  
Jie Zhang ◽  
Masahide Ishizuka ◽  
Masao Mikami ◽  
John Leys ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Size ◽  
Probability Distribution ◽  
Particle Size Distribution ◽  
Atmospheric Boundary Layer ◽  
Size Distribution ◽  
Turbulent Flows ◽  
Friction Velocity ◽  
Surface Shear Stress ◽  
Surface Shear

Abstract. Particle size distribution of dust at emission (dust PSD) is an essential quantity to estimate in dust studies. It has been recognized in earlier research that dust PSD is dependent on soil properties (e.g. whether soil is sand or clay) and friction velocity, u∗, which is a surrogate for surface shear stress and a descriptor for saltation-bombardment intensity. This recognition has been challenged in some recent papers, causing a debate on whether dust PSD is “invariant” and the search for its justification. In this paper, we analyse the dust PSD measured in the Japan Australian Dust Experiment and show that dust PSD is dependent on u∗ and on atmospheric boundary-layer (ABL) stability. By simple theoretical and numerical analysis, we explain the two reasons for the latter dependency, which are both related to enhanced saltation bombardment in convective turbulent flows. First, u∗ is stochastic and its probability distribution profoundly influences the magnitude of the mean saltation flux due to the non-linear relationship between saltation flux and u∗. Second, in unstable conditions, turbulence is usually stronger, which leads to higher saltation-bombardment intensity. This study confirms that dust PSD depends on u∗ and, more precisely, on the probability distribution of u∗, which in turn is dependent on ABL stability; consequently, dust PSD is also dependent on ABL. We also show that the dependency of dust PSD on u∗ and ABL stability is made complicated by soil surface conditions. In general, our analysis reinforces the basic conceptual understanding that dust PSD depends on saltation bombardment and inter-particle cohesion.

Drag reduction in turbulent flows along a cylinder by streamwise-travelling waves of circumferential wall velocity

2019 ◽  
Vol 862 ◽  
pp. 75-98 ◽  
Author(s):  
Ming-Xiang Zhao ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Energy Saving ◽  
Turbulent Flows ◽  
Friction Velocity ◽  
Oscillation Amplitude ◽  
Reduction Rate ◽  
Net Energy ◽  
Centrifugal Instability ◽  
Increase Rate

Drag reduction at the external surface of a cylinder in turbulent flows along the axial direction by circumferential wall motion is studied by direct numerical simulations. The circumferential wall oscillation can lead to drag reduction due to the formation of a Stokes layer, but it may also result in centrifugal instability, which can enhance turbulence and increase drag. In the present work, the Reynolds number based on the reference friction velocity and the nominal thickness of the boundary layer is 272. A map describing the relationship between the drag-reduction rate and the control parameters, namely, the angular frequency $\unicode[STIX]{x1D714}^{+}=\unicode[STIX]{x1D714}\unicode[STIX]{x1D708}/u_{\unicode[STIX]{x1D70F}0}^{2}$ and the streamwise wavenumber $k_{x}^{+}=k_{x}\unicode[STIX]{x1D708}/u_{\unicode[STIX]{x1D70F}0}$, is obtained at the oscillation amplitude of ${A^{+}=A/u}_{\unicode[STIX]{x1D70F}0}=16$, where $u_{\unicode[STIX]{x1D70F}0}$ is the friction velocity of the uncontrolled flow and $\unicode[STIX]{x1D708}$ is the kinematic viscosity of the fluid. The maximum drag-reduction rate and the maximum drag-increase rate are both approximately 48 %, which are respectively attained at $(\unicode[STIX]{x1D714}^{+},k_{x}^{+})=$ (0.0126, 0.0148) and (0.0246, 0.0018). The drag-reduction rate can be scaled well with the help of the effective thickness of the Stokes layer. The drag increase is observed in a narrow triangular region in the frequency–wavenumber plane. The vortices induced by the centrifugal instability become the primary coherent structure in the near-wall region, and they are closely correlated with the high skin friction. In these drag-increase cases, the effective control frequency or wavenumber is crucial in scaling the drag-increase rate. As the wall curvature normalised by the boundary layer thickness becomes larger, the drag-increase region in the $(\unicode[STIX]{x1D714}^{+},k_{x}^{+})$ plane as well as the maximum drag-increase rate also become larger. Net energy saving with a considerable drag-reduction rate is possible when reducing the oscillation amplitude. At $A^{+}=4$, a net energy saving of 18 % can be achieved with a drag-reduction rate of 25 % if only the power dissipation due to viscous stress is taken into account in an ideal actuation system.

An Efficient Method for Frequent Itemset Mining on Temporal Data

2019 ◽  
pp. 558-568
Author(s):  
Fathima Sherin T K ◽  
Anish Kumar B.
Keyword(s):  
Data Mining ◽  
Computation Time ◽  
Frequent Itemsets ◽  
Frequent Itemset ◽  
Frequent Itemset Mining ◽  
Edge Density ◽  
Time Interval ◽  
Related Data ◽  
Itemset Mining ◽  
A Value

Frequent itemset mining (FIM) is a data mining idea with extracting frequent itemset from a database. Finding frequent itemsets in existing methods accept that datasets are static or steady and enlisted guidelines are pertinent all through the total dataset. In any case, this isn't the situation when information is temporal which contains time-related data that changes data mining results. Patterns may occur during all or at specific interims, to limit time interims, frequent itemset mining with time cube is proposed to manage time arranges in the mining technique. This is how patterns are perceived that happen occasionally, in a period interim, or both. Thus, this paper mostly centres around developing up a productive calculation to mine frequent itemsets and their related time interval from a value-based database by expanding from the earlier calculation dependent on support and density as another edge. Density is proposed to deal with the overestimated timespan issue and to ensure the authenticity of the patterns found. As an extension from the current framework, here the density rate and minimum threshold is dynamically generated which is user determined parameter previously. Likewise, an analysis concerning time is made between dataset with partitioning and without apportioning the dataset, which shows computation time is less on account of partitioning technique.

scholarly journals Error growth and dynamical vectors during southern hemisphere blocking

2004 ◽  
Vol 11 (1) ◽  
pp. 99-118 ◽  
Author(s):  
M. Wei ◽  
J. S. Frederiksen
Keyword(s):  
Southern Hemisphere ◽  
Normal Modes ◽  
Time Interval ◽  
Random Perturbations ◽  
Time Intervals ◽  
Amplification Factors ◽  
Fast Growing ◽  
A Value ◽  
The Mean ◽  
Basic States

Abstract. The structural organization of initially random perturbations or "errors" evolving in a barotropic tangent linear model with time-dependent basic states taken from observations, is examined for cases of block development, maturation and decay in the Southern Hemisphere atmosphere during April, November and December 1989. We determine statistical results relating the structures of evolved errors to singular vectors (SVs), Lyapunov vectors (LVs) and finite-time normal modes (FTNMs). The statistics of 100 evolved error fields are studied for six day periods or longer and compared with the growth and structures of leading fast growing SVs, LVs and FTNMs. The SVs are studied in the kinetic energy (KE), enstrophy (EN) and streamfunction (SF) norms, while all FTNMs and the first LV are norm independent. The mean of the largest pattern correlations between the 100 error fields and dynamical vectors, taken over the five fastest growing SVs, in any of the three norms, or over the five fastest growing FTNMs, increases with increasing time interval to a value close to 0.6 after six days. Corresponding pattern correlations with the five fastest growing LVs are slightly lower. The leading dynamical vectors (SVs 1, FTNM1 or LV 1) generally, but not always, give the largest pattern correlations with the error fields. It is found that viscosity slightly increases the average correlations between the evolved errors and LV 1 and evolved SVs 1. Mean pattern correlations with fast growing dynamical vectors increase further for time intervals longer than six days. The properties of the dynamical vectors during Southern Hemisphere blocking are briefly outlined. After a few days integration, the structures of the leading evolved SVs in the KE, EN and SF norms, are in general quite similar and also similar to some of the dominant FTNMs that are norm independent. For optimization times of six days or less, the evolved SVs and FTNMs are, in general, different from the dominant LVs on the same day. Nevertheless, amplification factors of the first FTNMs and first LVs are very similar, and also similar to, but slightly larger than, the mean amplification factor of 100 initially random perturbations in the SF norm, while the amplification factors in the SF norm of KE SVs 1 and SF SV 1 are much higher. For longer optimization times, the first SVs and the first FTNM increasingly turn towards the leading LV with convergence achieved within a month.

Sur l'existence d'une longueur élémentaire et d'un intervalle de temps élémentaire. II

1979 ◽  
Vol 57 (10) ◽  
pp. 1681-1685 ◽  
Author(s):  
Robert Lacroix
Keyword(s):  
Energy Band ◽  
Free Particle ◽  
Complete Agreement ◽  
Tunnel Effect ◽  
Time Interval ◽  
A Value

Giving a value for the elementary time interval t0 is the main purpose of this paper. For this, an analysis of the formula for the energy of a free particle is given, formula which has been found in our first paper on that subject. The value 4.4 × 10−24 s for t0 is in complete agreement with the results of our analysis. An energy band between 75 and 100 MeV is predicted as to be inaccessible for all particles at rest. The solution of the tunnel effect is given in the framework of our theory.

scholarly journals Myoplasmic calcium transients monitored with purpurate indicator dyes injected into intact frog skeletal muscle fibers.

1991 ◽  
Vol 97 (2) ◽  
pp. 245-270 ◽  
Author(s):  
M Konishi ◽  
S M Baylor
Keyword(s):  
Muscle Fibers ◽  
Diffusion Constant ◽  
Bound State ◽  
Longitudinal Diffusion ◽  
Single Action ◽  
A Value ◽  
Single Twitch ◽  
Indicator Dyes ◽  
Peak Value

Intact single twitch fibers from frog muscle were studied on an optical bench apparatus after microinjection with tetramethylmurexide (TMX) or purpurate-3,3' diacetic acid (PDAA), two compounds from the purpurate family of absorbance Ca2+ indicators previously used in cut muscle fibers (Maylie, J., M. Irving, N. L. Sizto, G. Boyarsky, and W. K. Chandler. 1987. J. Gen. Physiol. 89:145-176; Hirota, A., W. K. Chandler, P. L. Southwick, and A. S. Waggoner. 1989. J. Gen. Physiol. 94:597-631.) The apparent longitudinal diffusion constant of PDAA (mol wt 380) in myoplasm was 0.99 (+/- 0.04, SEM) x 10(-6) cm2 s-1 (16-17 degrees C), a value which suggests that 24-43% of the PDAA molecules were bound to myoplasmic constituents of large molecular weight. The corresponding values for TMX (mol wt 322) were 0.98 (+/- 0.05) x 10(-6) cm2 s-1 and 44-50%, respectively. Muscle membranes (surface and/or transverse-tubular) appear to be permeable to TMX and, to a lesser extent, to PDAA, since the total amount of indicator contained within a fiber decreased with time after injection. The average time constants for disappearance of indicator were 46 (+/- 7, SEM) min for TMX and 338 (+/- 82) min for PDAA. The fraction of indicator in the Ca2(+)-bound state in resting fibers was significantly different from zero for TMX (0.070 +/- 0.008) but not for PDAA (0.026 +/- 0.009). In in vitro calibrations PDAA but not TMX appeared to react with Ca2+ with 1:1 stoichiometry. In agreement with Hirota et al. (Hirota, A., W. K. Chandler, P. L. Southwick, and A. S. Waggoner. 1989. J. Gen. Physiol. 94:597-631), we conclude that PDAA is probably a more reliable myoplasmic Ca2+ indicator than TMX. In fibers that contained PDAA and were stimulated by a single action potential, the calibrated peak value of the myoplasmic free [Ca2+] transient (delta[Ca2+]) averaged 9.4 (+/- 0.6) microM, a value about fivefold larger than that calibrated with antipyrylazo III under otherwise identical conditions (Baylor, S. M., and S. Hollingworth. 1988. J. Physiol. 403:151-192). The fivefold difference is similar to that previously reported in cut fibers with antipyrylazo III and PDAA. Since in both intact and cut fibers the percentage of PDAA bound to myoplasmic constituents is considerably smaller than that found for antipyrylazo III, the PDAA calibration of delta[Ca2+] is likely to be more accurate. Interestingly, in intact fibers the peak value of delta[Ca2+] calibrated with either PDAA or antipyrylazo III is about half that calibrated in cut fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

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