scholarly journals Assessment of Relevant Physical Phenomena Controlling Thermal Performance of Nanofluids

2006 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Experimental Data ◽  
Systematic Approach ◽  
Large Degree ◽  
Upper Bounds ◽  
Upper And Lower Bounds ◽  
Theoretical Studies ◽  
Lower And Upper Bounds ◽  
Physical Phenomena ◽  
Experimental And Theoretical Studies

This paper provides an overview of the important physical phenomena necessary for the determination of effective thermal conductivity of nanofluids. Through an investigation, a large degree of randomness and scatter has been observed in the experimental data published in the open literature. Given the inconsistency in the data, it is impossible to develop a comprehensive physical-based model that can predict all the trends. This also points out the need for a systematic approach in both experimental and theoretical studies. Upper and lower bounds are developed for steady-state conduction in stationary nanofluids. Comparisons between these bounds and the experimental data indicate that all the data (except for carbon nanotube data) lie between the lower and upper bounds.

scholarly journals Experimental and theoretical studies of the behaviour of slow electrons in air. II. Ionospheric and other applications

1949 ◽  
Vol 196 (1046) ◽  
pp. 427-435 ◽  
Keyword(s):  
Experimental Data ◽  
Free Electron ◽  
Laboratory Data ◽  
Wave Interaction ◽  
Theoretical Studies ◽  
Radio Waves ◽  
Electronic Motion ◽  
Slow Electrons ◽  
Experimental And Theoretical Studies

The significance, for ionospheric and other studies, of the experimental data given in part I is considered. It is shown how the data obtained from rocket soundings may be combined with the measurements of wave interaction in the ionosphere and the laboratory data given in part I, to estimate the height at which wave interaction occurs and the collisional frequency at that height. The following topics are also discussed: the theory of electronic motion in direct and alternating fields; the power communicated to a free electron in a gas by an alternating field; and the interaction of radio waves in the ionosphere.

Formation of solitons in transitional boundary layers: theory and experiment

1993 ◽  
Vol 251 ◽  
pp. 273-297 ◽  
Author(s):  
Y. S. Kachanov ◽  
O. S. Ryzhov ◽  
F. T. Smith
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Asymptotic Theory ◽  
Subsequent Development ◽  
Boundary Layer Transition ◽  
Theoretical Studies ◽  
Layer Transition ◽  
Experimental And Theoretical Studies ◽  
Theory And Experiment ◽  
Good Agreement

This work brings together experimental and theoretical studies of nonlinear stages aimed at the K-regime in boundary-layer transition, and some combined theoretical and experimental results are discussed. It is shown that the initial stages in the formation of so-called spikes, observed in many experiments, may be described very well by the asymptotic theory. These flashes-spikes are shown to be (in certain regimes) possible solitons of the boundary layer and governed by the integral-differential Benjamin-Ono equation. Properties of the spike-solitons, obtained both theoretically and experimentally in the quasi-planar stages of their development, are presented. Features of the disturbance behaviour connected with the subsequent development of three-dimensionality are also discussed, as are the effects of viscosity and shorter lengthscales. The main conclusion of the work concerns the hypothesis of the possible soliton nature of the flashes-spikes (within limits), which seems reliably corroborated by the good agreement found between the theory and the experimental data.

scholarly journals Determination of the time scale of photoemission from the measurement of spin polarization

2018 ◽  
Vol 5 (6) ◽  
Author(s):  
Mauro Fanciulli ◽  
Hugo Dil
Keyword(s):  
Experimental Data ◽  
Time Delay ◽  
Matrix Element ◽  
Spin Polarization ◽  
Time Delays ◽  
Upper And Lower Bounds ◽  
Recent Experimental Data ◽  
The Matrix ◽  
Phase Term

The Eisenbud-Wigner-Smith (EWS) time delay of photoemission depends on the phase term of the matrix element describing the transition. Because of an interference process between partial channels, the photoelectrons acquire a spin polarization which is also related to the phase term. The analytical model for estimating the time delay by measuring the spin polarization is reviewed in this manuscript. In particular, the distinction between scattering EWS and interfering EWS time delay will be introduced, providing an insight in the chronoscopy of photoemission. The method is applied to the recent experimental data for Cu(111) presented in M. Fanciulli et al., PRL 118, 067402 (2017), allowing to give better upper and lower bounds and estimates for the EWS time delays.

scholarly journals Predicting the unpredictable: how dynamic COVID-19 policies and restrictions challenge model forecasts

2021 ◽  
Author(s):  
Farah Houdroge ◽  
Anna Palmer ◽  
Dominic Delport ◽  
Tom Walsh ◽  
Sherrie Kelly ◽  
...  
Keyword(s):  
Upper Bounds ◽  
Actual Data ◽  
Upper And Lower Bounds ◽  
Baseline Scenario ◽  
Policy Changes ◽  
Lower And Upper Bounds ◽  
Model Accuracy ◽  
Agent Based ◽  
Future Policy ◽  
Post Hoc

Abstract Introduction To retrospectively assess the accuracy of a mathematical modelling study that projected the rate of COVID-19 diagnoses for 72 locations worldwide in 2021, and to identify predictors of model accuracy. Methods Between June and August 2020, an agent-based model was used to project rates of COVID-19 infection incidence and cases diagnosed as positive from 15 September to 31 October 2020 for 72 geographic settings. Five scenarios were modelled: a baseline scenario where no future changes were made to existing restrictions, and four scenarios representing small or moderate changes in restrictions at two intervals. Post hoc, upper and lower bounds for number of diagnosed Covid-19 cases were compared with actual data collected during the prediction window. A regression analysis with 17 covariates was performed to determine correlates of accurate projections. Results The actual data fell within the lower and upper bounds in 27 settings and out of bounds in 45 settings. The only statistically significant predictor of actual data within the predicted bounds was correct assumptions about future policy changes (OR = 15.04; 95%CI 2.20-208.70; p=0.016). Conclusions For this study, the accuracy of COVID-19 model projections was dependent on whether assumptions about future policies are correct. Frequent changes in restrictions implemented by governments, which the modelling team was not always able to predict, in part explains why the majority of model projections were inaccurate compared with actual outcomes and supports revision of projections when policies are changed as well as the importance of policy experts collaborating on modelling projects.

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