scholarly journals Cavitation Nuclei Population and Event Rates

1998 ◽  
Vol 120 (4) ◽  
pp. 728-737 ◽  
Author(s):  
Zhenhuan Liu ◽  
Christopher E. Brennen
Keyword(s):  
Boundary Layer ◽  
Bubble Growth ◽  
Event Rate ◽  
Correct Order ◽  
Cavitation Inception ◽  
Order Of Magnitude ◽  
Cavitation Nuclei ◽  
The Individual ◽  
Event Rates ◽  
Oncoming Stream

To model the processes of cavitation inception, noise and damage, it is necessary to generate a model of the cavitation event rate which can then be coupled with the consequences of the individual events to produce a complete synthesis of the phenomenon. In this paper we describe recent efforts to connect the observed event rates to the measured distributions of cavitation nuclei in the oncoming stream. Comparisons are made between the observed event rates and event rates calculated from measured nuclei distributions using an algorithm which includes the dynamics of the nuclei motion and growth. Various complications are explored including the effect of the boundary layer, the relative motion between the nucleus and the liquid, the observable bubble size effect, and the effect of bubble growth on neighboring nuclei. All of these are seen to have important influences on the event rate, and therefore, on cavitation inception and other macroscopic consequences. We demonstrate that it is possible to predict the correct order of magnitude of the event rate when an attempt is made to model the important flow complications.

The Influence of Velocity and Scale on Cavitation Inception where Wall-Generated Gas Bubbles are the Sole Source of Cavitation Nuclei

1975 ◽  
Vol 17 (2) ◽  
pp. 45-51
Author(s):  
M. R. Baum
Keyword(s):  
Bubble Growth ◽  
Flow System ◽  
Scale Effects ◽  
Gas Bubbles ◽  
Sole Source ◽  
Gas Bubble ◽  
Cavitation Inception ◽  
Boundary Wall ◽  
Cavitation Nuclei ◽  
System Properties

It is established, using recently derived expressions relating the flow system properties to the size at which a gas bubble grown at a boundary wall will become detached, that the commonly observed variation in cavitation inception pressure with velocity in a given system can be simply attributed to variations in the size of bubble detached. However, it is concluded, from a comparison of predicted and experimental variations of inception pressure with scale of the system, that when considering scale effects the pressure necessary to promote gas-bubble growth must also be taken into account.

scholarly journals Measurements of Counter?Gradient Heat Flows in the Atmosphere

1956 ◽  
Vol 9 (1) ◽  
pp. 133 ◽  
Author(s):  
AF Bunker
Keyword(s):  
United States ◽  
Heat Flow ◽  
East Coast ◽  
Temperature Fluctuations ◽  
Temperature Gradients ◽  
Correct Order ◽  
Maximum Heat ◽  
Heat Flows ◽  
Order Of Magnitude ◽  
The Individual

Heat flows and temperature gradients were measured in a stable atmosphere heated by the water during a United States east coast to Bermuda aeroplane flight. The flux was computed from , where w' and T' are the vertical velocities and temperature deviations of the individual gusts. It is found that the heat flow is directed up the gradient as predicted by Priestley (1954). The expression for the maximum heat flow to be expected derived by Priestley in terms of the standard deviation of the temperature fluctuations and the temperature gradient gives the correct order of magnitude for the observed flow.

Planning the Size of Clinical Trials with Allowance for Patient Noncompliance

1990 ◽  
Vol 29 (03) ◽  
pp. 243-246 ◽  
Author(s):  
M. A. A. Moussa
Keyword(s):  
Clinical Trial ◽  
Clinical Trials ◽  
Sample Size ◽  
Event Rate ◽  
Survival Functions ◽  
Time Intervals ◽  
Patient Noncompliance ◽  
Event Rates ◽  
Larger Sample

AbstractVarious approaches are considered for adjustment of clinical trial size for patient noncompliance. Such approaches either model the effect of noncompliance through comparison of two survival distributions or two simple proportions. Models that allow for variation of noncompliance and event rates between time intervals are also considered. The approach that models the noncompliance adjustment on the basis of survival functions is conservative and hence requires larger sample size. The model to be selected for noncompliance adjustment depends upon available estimates of noncompliance and event rate patterns.

scholarly journals Statistical Uncertainty of DNS in Geometries without Homogeneous Directions

2021 ◽  
Vol 11 (4) ◽  
pp. 1399
Author(s):  
Jure Oder ◽  
Cédric Flageul ◽  
Iztok Tiselj
Keyword(s):  
Channel Flow ◽  
A Priori ◽  
Time Integration ◽  
Navier Stokes ◽  
Statistical Uncertainty ◽  
Time Step ◽  
Order Of Magnitude ◽  
Averaging Time ◽  
The Individual ◽  
Time Required

In this paper, we present uncertainties of statistical quantities of direct numerical simulations (DNS) with small numerical errors. The uncertainties are analysed for channel flow and a flow separation case in a confined backward facing step (BFS) geometry. The infinite channel flow case has two homogeneous directions and this is usually exploited to speed-up the convergence of the results. As we show, such a procedure reduces statistical uncertainties of the results by up to an order of magnitude. This effect is strongest in the near wall regions. In the case of flow over a confined BFS, there are no such directions and thus very long integration times are required. The individual statistical quantities converge with the square root of time integration so, in order to improve the uncertainty by a factor of two, the simulation has to be prolonged by a factor of four. We provide an estimator that can be used to evaluate a priori the DNS relative statistical uncertainties from results obtained with a Reynolds Averaged Navier Stokes simulation. In the DNS, the estimator can be used to predict the averaging time and with it the simulation time required to achieve a certain relative statistical uncertainty of results. For accurate evaluation of averages and their uncertainties, it is not required to use every time step of the DNS. We observe that statistical uncertainty of the results is uninfluenced by reducing the number of samples to the point where the period between two consecutive samples measured in Courant–Friedrichss–Levy (CFL) condition units is below one. Nevertheless, crossing this limit, the estimates of uncertainties start to exhibit significant growth.

‘Inactive’ motion and pressure fluctuations in turbulent boundary layers

1967 ◽  
Vol 30 (2) ◽  
pp. 241-258 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Outer Layer ◽  
Pressure Fluctuations ◽  
Turbulent Energy ◽  
Viscous Sublayer ◽  
Wave Number ◽  
Noticeable Effect ◽  
Frequency Spectra ◽  
Active Motion ◽  
Order Of Magnitude

Townsend's (1961) hypothesis that the turbulent motion in the inner region of a boundary layer consists of (i) an ‘active’ part which produces the shear stress τ and whose statistical properties are universal functions of τ and y, and (ii) an ‘inactive’ and effectively irrotational part determined by the turbulence in the outer layer, is supported in the present paper by measurements of frequency spectra in a strongly retarded boundary layer, in which the ‘inactive’ motion is particularly intense. The only noticeable effect of the inactive motion is an increased dissipation of kinetic energy into heat in the viscous sublayer, supplied by turbulent energy diffusion from the outer layer towards the surface. The required diffusion is of the right order of magnitude to explain the non-universal values of the triple products measured near the surface, which can therefore be reconciled with universality of the ‘active’ motion.Dimensional analysis shows that the contribution of the ‘active’ inner layer motion to the one-dimensional wave-number spectrum of the surface pressure fluctuations varies as τ2w/k1 up to a wave-number inversely proportional to the thickness of the viscous sublayer. This result is strongly supported by the recent measurements of Hodgson (1967), made with a much smaller ratio of microphone diameter to boundary-layer thickness than has been achieved previously. The disagreement of the result with most other measurements is attributed to inadequate transducer resolution in the other experiments.

scholarly journals Use of Composite Outcomes in Neonatal Trials: An Analysis of the Cochrane Reviews

Neonatology ◽  
2021 ◽  
pp. 1-5
Author(s):  
Nai Ming Lai ◽  
Amanda Qiao Ying Yap ◽  
Hwee Chin Ong ◽  
Sheng Xuan Wai ◽  
Julie Hsiao Hui Yeo ◽  
...  
Keyword(s):  
Event Rate ◽  
A Priori ◽  
Effect Sizes ◽  
Common Component ◽  
Randomized Controlled ◽  
Cochrane Reviews ◽  
Contrasting Effect ◽  
Composite Outcomes ◽  
Event Rates ◽  
The Relationship

<b><i>Introduction:</i></b> Composite outcomes are used to increase the power of a study by combining event rates. Many composite outcomes in adult clinical trials have components that differ substantially in patient importance, event rate, and effect size, making interpretation challenging. Little is known about the use of composite outcomes in neonatal randomized controlled trials (RCTs). <b><i>Methods:</i></b> We assessed the use of composite outcomes in neonatal RCTs included in Cochrane Neonatal reviews published till November 2017. Two authors reviewed the components of the composite outcomes to compare their patient importance and computed the ratios of effect sizes and event rates between the components, with an a priori threshold of 1.5, indicating a substantial difference. Descriptive statistics were presented. <b><i>Results:</i></b> We extracted 7,766 outcomes in 2,134 RCTs in 312 systematic reviews. Among them, 55 composite outcomes (0.7%) were identified in 46 RCTs. The vast majority (92.7%) of composite outcomes had 2 components, with death being the most common component (included 51 times [92.7%]). The components in nearly three-quarters of the composite outcomes (<i>n</i> = 40 [72.7%]) had different patient importance, while the effect sizes and event rates differed substantially between the components in 27 (49.1%) and 35 (63.6%) outcomes, respectively, with up to 43-fold difference in the event rates observed. <b><i>Conclusions:</i></b> The majority of composite outcomes in neonatal RCTs had different patient importance with contrasting effect sizes and event rates between the components. In patient communication, clinicians should highlight individual components, rather than the composites, with explanation on the relationship between the components, to avoid misleading impression on the effect of the intervention. Future trials should report the estimates of all individual components alongside the composite outcomes presented.

Trailing-edge stall

1970 ◽  
Vol 42 (3) ◽  
pp. 561-584 ◽  
Author(s):  
S. N. Brown ◽  
K. Stewartson
Keyword(s):  
Boundary Layer ◽  
Complete Solution ◽  
Leading Edge ◽  
Asymptotic Solutions ◽  
Angle Of Incidence ◽  
Trailing Edge ◽  
Boundary Layer Equations ◽  
Order Of Magnitude ◽  
Stall Angle ◽  
Fundamental Equations

A study is made of the laminar flow in the neighbourhood of the trailing edge of an aerofoil at incidence. The aerofoil is replaced by a flat plate on the assumption that leading-edge stall has not taken place. It is shown that the critical order of magnitude of the angle of incidence α* for the occurrence of separation on one side of the plate is$\alpha^{*} = O(R^{\frac{1}{16}})$, whereRis a representative Reynolds number, for incompressible flow, and α* =O(R−¼) for supersonic flow. The structure of the flow is determined by the incompressible boundary-layer equations but with unconventional boundary conditions. The complete solution of these fundamental equations requires a numerical investigation of considerable complexity which has not been undertaken. The only solutions available are asymptotic solutions valid at distances from the trailing edge that are large in terms of the scaled variable of orderR−⅜, and a linearized solution for the boundary layer over the plate which gives the antisymmetric properties of the aerofoil at incidence. The value of α* for which separation occurs is the trailing-edge stall angle and an estimate is obtained from the asymptotic solutions. The linearized solution yields an estimate for the viscous correction to the circulation determined by the Kutta condition.

scholarly journals Characteristics and Indications of Legal Abortion among the Pregnant Women in Lorestan Province of Iran during 2017–2019

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Zahra Fatemi ◽  
Soheila Akbari
Keyword(s):  
Event Rate ◽  
Cross Sectional Study ◽  
Legal Abortion ◽  
Descriptive Data ◽  
Cross Sectional ◽  
Maternal Characteristics ◽  
Regional Population ◽  
The Mean ◽  
Event Rates ◽  
The Brain

Background. Legal abortion is a challenge from the viewpoint of ethics and religion. The present study was conducted to investigate the frequency of fetal and maternal indications of legal abortion and also the maternal characteristics in Lorestan Province of Iran. Methods. As a descriptive cross-sectional study, all the cases with issued permits for legal abortion were selected by a census during 2017–2019. Descriptive data analysis was used to report the results. Event rates with Poisson 95% confidence intervals (CIs) were calculated based on the regional population. Results. A total of 305 cases were selected. The mean age of the mothers was 31.61 ± 7.48 years, and the mean of gestational age was 15.76 ± 2.80 weeks. Demographically, most cases were from Khorramabad city (101 cases) followed by Borujerd (51 cases) and Doroud (46 cases). The overall event rate was 1.732 per 10,000 individuals (95% CI: 1.543–1.938) of the general population of the region per 3 years. Fetal disturbance of the brain and spine was the most prevalent reason of abortion (24.92%, 95% CI: 19.63%–31.19%) followed by Down syndrome (19.34%, 95% CI: 14.73%–24.95), hydrops fetalis (12.79%, 95% CI: 9.09%–17.48%), and anencephaly (12.79%, 95% CI: 9.09%–17.48%). Conclusion. From each 10,000 individuals of the population, one to two cases of legal abortion were screened per 3 years. More than 90% of cases had fetal indication. In cities with lower event rates, we should plan for better screening.

scholarly journals An integrated microfluidic platform for quantifying drug permeation across biomimetic vesicle membranes

2019 ◽  
Author(s):  
Michael Schaich ◽  
Jehangir Cama ◽  
Kareem Al Nahas ◽  
Diana Sobota ◽  
Kevin Jahnke ◽  
...  
Keyword(s):  
Drug Transport ◽  
Membrane Composition ◽  
Drug Permeability ◽  
Bacterial Membranes ◽  
Drug Molecules ◽  
Total Analysis System ◽  
Transport Assay ◽  
Order Of Magnitude ◽  
Analysis System ◽  
The Individual

The low membrane permeability of candidate drug molecules is a major challenge in drug development and insufficient permeability is one reason for the failure of antibiotic treatment against bacteria. Quantifying drug transport across specific pathways in living systems is challenging since one typically lacks knowledge of the exact lipidome and proteome of the individual cells under investigation. Here, we quantify drug permeability across biomimetic liposome membranes, with comprehensive control over membrane composition. We integrate the microfluidic octanol-assisted liposome assembly platform with an optofluidic transport assay to create a complete microfluidic total analysis system for quantifying drug permeability. Our system enables us to form liposomes with charged lipids mimicking the negative charge of bacterial membranes at physiological salt and pH levels, which proved difficult with previous liposome formation techniques. Furthermore, the microfluidic technique yields an order of magnitude more liposomes per experiment than previous assays. We demonstrate the feasibility of the assay by determining the permeability coefficient of norfloxacin across biomimetic liposomes.

On the Control of Chaos in Extended Structures

1997 ◽  
Vol 119 (4) ◽  
pp. 551-556 ◽  
Author(s):  
C. Barratt
Keyword(s):  
Nearest Neighbor ◽  
Duffing Oscillator ◽  
Vertical Plane ◽  
Small Time ◽  
Time Dependent ◽  
External Forcing ◽  
Control Of Chaos ◽  
Chaotic Vibrations ◽  
Order Of Magnitude ◽  
The Individual

A mechanism is proposed for synchronizing the chaotic vibrations of an externally forced array of oscillators with nearest-neighbor viscoelastic coupling. The proposed mechanism involves the application of small time-dependent perturbations to the individual oscillators. The perturbations required to preserve the coherence are of the order of magnitude of any noise present. The mechanism works with any form of external forcing. A modification of the mechanism is used to control the forced chaotic vibrations of a single Duffing oscillator allowed to vibrate out of the vertical plane.

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