scholarly journals Driven oscillations of a curved object under a laminar jet of water

2021 ◽  
Vol 5 ◽  
pp. 1
Author(s):  
Francis Pagaud ◽  
Léa Delance
Keyword(s):  
Theoretical Model ◽  
Empirical Model ◽  
Flat Surface ◽  
Laminar Jet ◽  
Dynamic Hysteresis ◽  
Direct Measurements ◽  
Spontaneous Oscillations

By putting a ball on a flat surface under a jet of water, one may observe spontaneous oscillations of the ball of well-defined amplitude and frequency. As a simpler conformation, the study of a cylinder shows that the mere effect of the jet is sufficient to observe an oscillation for a certain range of parameters such as the curvature of the object and the characteristics of the jet. An empirical model of the forces strengthened by direct measurements of the forces and torque allowed us to predict a theoretical period of 0.64 s when the experimental one was 0.80 s. Further, the origin of the oscillation was determined to be a dynamic hysteresis of the torque as it is deflected on one side of the can even when the jet hits its center. This phenomenon results in a gain of energy that counterbalances the losses by friction and leads to oscillations. Domain of oscillation is also shortly addressed while improvements of the theoretical model and other experiments are suggested as well.

Appointee vacancies in US executive branch agencies

2020 ◽  
pp. 1-24
Author(s):  
William G. Resh ◽  
Gary E. Hollibaugh ◽  
Patrick S. Roberts ◽  
Matthew M. Dull
Keyword(s):  
United States ◽  
Theoretical Model ◽  
Empirical Model ◽  
Separation Of Powers ◽  
Executive Branch ◽  
Principal Agent ◽  
High Status ◽  
Constitutional Design ◽  
Committee Chair ◽  
Institutional Politics

Abstract We analyse United States presidential appointee positions subject to Senate confirmation without a confirmed appointee in office. These “vacant” positions are byproducts of American constitutional design, shaped by the interplay of institutional politics. Using a novel dataset, we analyse appointee vacancies across executive branch departments and single-headed agencies from 1989 to 2013. We develop a theoretical model that uncovers the dynamics of vacancy onset and length. We then specify an empirical model and report results highlighting both position and principal–agent relations as critical to the politics of appointee vacancies. Conditional on high status positions reducing the frequency and duration of vacancies, we find important principal–agent considerations from a separation of powers perspective. Appointee positions in agencies ideologically divergent from the relevant Senate committee chair are vacant for less time than in ideologically proximal agencies. Importantly, this relationship strengthens as agency ideology diverges away from the chair and towards the chair’s party extreme.

scholarly journals Systemic Risk Modeling

2020 ◽  
Vol 20 (54) ◽  
Author(s):  
Raphael Espinoza ◽  
Miguel Segoviano ◽  
Ji Yan
Keyword(s):  
Theoretical Model ◽  
Empirical Model ◽  
Systemic Risk ◽  
Empirical Models ◽  
Equity Returns ◽  
Counterparty Risk ◽  
Risk Modeling ◽  
Cross Sectional ◽  
Fire Sales ◽  
Multivariate Density

We propose a framework to link empirical models of systemic risk to theoretical network/ general equilibrium models used to understand the channels of transmission of systemic risk. The theoretical model allows for systemic risk due to interbank counterparty risk, common asset exposures/fire sales, and a “Minsky" cycle of optimism. The empirical model uses stock market and CDS spreads data to estimate a multivariate density of equity returns and to compute the expected equity return for each bank, conditional on a bad macro-outcome. Theses “cross-sectional" moments are used to re-calibrate the theoretical model and estimate the importance of the Minsky cycle of optimism in driving systemic risk.

Running, breathing and visceral motion in the domestic rabbit (Oryctolagus cuniculus): testing visceral displacement hypotheses

1999 ◽  
Vol 202 (5) ◽  
pp. 563-577 ◽  
Author(s):  
R.S. Simons
Keyword(s):  
Theoretical Model ◽  
Phase Angle ◽  
Relative Motion ◽  
Relative Position ◽  
Oryctolagus Cuniculus ◽  
Mass Motion ◽  
Visceral Mass ◽  
Mechanics Model ◽  
Domestic Rabbit ◽  
Direct Measurements

The relative motion of the visceral mass may be important to ventilation during running. A visceral piston hypothesis predicts that, during galloping, cranial motion of the liver during expiration and caudal motion of the liver during inspiration may characterize efficient quadrupedal mammalian locomotion. Although a theoretical model based on vibration mechanics casts doubt on this prediction, only limited direct measurements of visceral mass motion during galloping have been reported. In the present study, mechanical interactions between running, breathing and liver oscillations in the domestic rabbit are recorded using synchronized videographic, cineradiographic and pneumotachographic techniques. The analysis focuses on the variation in locomotor-respiratory coupling (LRC) and on the relative position of the liver. Results from running rabbits show (1) variation in phase angle between the locomotor and respiratory periods that is inconsistent with the 1:1 LRC ratio that has been reported for other galloping mammals; (2) a tendency towards a 1:1 LRC ratio at higher speeds and stride frequencies; and (3) that the relative motion of the liver is caudal during expiration and cranial during inspiration, which is inconsistent with the visceral piston hypothesis. The data presented here are generally consistent with the theoretical vibration mechanics model for liver motion and with a pneumatic stabilization hypothesis that the lungs serve an important role in the stabilization of the thorax during locomotion.

Research on Material Removal Characteristics in Plane Lapping Method for Aspherical Surface Using Elastic Deformation

2011 ◽  
Vol 487 ◽  
pp. 293-297 ◽  
Author(s):  
Zhe Wu ◽  
Ju Long Yuan ◽  
Bing Hai Lv ◽  
Duc Nam Nguyen
Keyword(s):  
Theoretical Model ◽  
Elastic Deformation ◽  
Material Removal ◽  
Flat Surface ◽  
Plate Theory ◽  
Deformation Method ◽  
Aspherical Surface ◽  
Surface Machining

Plane lapping method using the elasticity of materials has many advantages comparing with current machining method for aspherical surface machining. Due to the deformation of the workpiece, the material removal characteristics of this method are different from the traditional lapping process of flat surface. In this paper, based on the Preston equation and plate theory, the theoretical model of the material remove rate is built in the case of proving experiment. Then the proving experiment of elastic deformation method is carried out, the recorded values fit well with theoretical ones, which shows that the theoretical model of material removal property is valid and the variation of MRR is related to the deformed profile of workpiece.

A New Method for Wax Precipitation Prediction of Waxy Oil Wells and Software Designing

2014 ◽  
Vol 568-570 ◽  
pp. 1437-1442
Author(s):  
Ren Yuan Sun ◽  
Cheng Xiang Wang ◽  
Ying Long Xuan ◽  
Qi Yong Xiong ◽  
Ai Xian Huang ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Empirical Model ◽  
Oil Production ◽  
Mechanism Analysis ◽  
Wax Precipitation ◽  
Waxy Oil ◽  
Precipitation Prediction ◽  
Production Wells ◽  
Water Cut ◽  
Productive Time

Wax precipitation of oil production wells seriously influence the oil production. In order to improve the level of wax removal, it is necessary to predict the depth, thickness and period of wax precipitation in the wellbore with oil production. On the basis of the mechanism analysis for wax precipitation in the wellbore, the theoretical model and empirical model were built up and programmed wax precipitation of oil production wells software and the results by the two models were compared. The sensitive factors which influence wax precipitation in the wellbore were analyzed. The results show that the two models can be used to predict the wax thickness, depth and precipitation cycle. The empirical model for wax precipitation profile prediction is more accurate than the theoretical model. The wax precipitation varies with the productive time and water cut.

scholarly journals Determining radium-226 concentration from radon-222 emanation in building materials: a theoretical model

2019 ◽  
Vol 7 (2A) ◽  
Author(s):  
Rafael Carvalho Barreto ◽  
Allan F. N. Perna ◽  
Danielle C. Narloch ◽  
Flavia Del Claro ◽  
Janine N. Correa ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Building Material ◽  
Nuclear Physics ◽  
Building Materials ◽  
Gamma Ray ◽  
Cement Mortar ◽  
One Dimension ◽  
Gamma Ray Spectrometry ◽  
Direct Measurements ◽  
Non Destructive

It was developed an improved theoretical model capable to estimate the radium concentration in building materials solely measuring the radon-222 concentration in a confined atmosphere.This non-destructive technique is not limited by the size of the samples, and it intrinsically includes back diffusion.The resulting equation provides the exact solution for the concentration of radon-222 as a function of time and distance in one dimension.The effective concentration of radium-226 is a fit parameter of this equation.In order to reduce its complexity, this equation was simplified considering two cases:low diffusion in the building material compared to the air, anda building material initially saturated with radon-222.These simplified versions of the exact one dimension solution were used to fit experimental data.Radon-222 concentration was continuously measured for twelve days with an AlphaGUARD detector, located at the Laboratory of Applied Nuclear Physics at Universidade Tecnologica Federal do Parana (UTFPR).This model was applied to two different materials: cement mortar and concrete, which results were respectively (15.7 +- 8.3) Bq/kg and (10.5 +- 2.4) Bq/kg for the radium-226 effective concentration.This estimation was confronted with the direct measurements of radium in the same materials (same sources) using gamma-ray spectrometry, fulfilled at Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), which results were respectively (13.81 +- 0.23) Bq/kg and (12.61 +- 0.22) Bq/kg.

The Circular Model of Victimization and Teamwork Within the Italian Anti-Violence Centers: A General Survey

2020 ◽  
Vol 58 (2) ◽  
pp. 153-172
Author(s):  
Marco Monzani
Keyword(s):  
Theoretical Model ◽  
Family Violence ◽  
International Society ◽  
Empirical Model ◽  
Explanatory Model ◽  
Necessary Condition ◽  
General Survey ◽  
Circular Model ◽  
Correct Understanding ◽  
First Moment

AbstractA correct understanding of the dynamics and mechanisms that make it possible for a woman to become a victim of intra-family violence allows the necessary measures to be taken so that she can escape from the situation of victimization. Emilio C. Viano, President of the International Society of Criminology, defines the victim of an abuse as “any subject injured or that has suffered wrongdoing on the part of others, who perceives herself to be a victim, who shares the experience with others looking for help, assistance and compensation, who is recognized as a victim and who presumably is being helped by public, private or collective agencies/structures”. Before the birth of Anti-Violence Centers it was believed that the awareness of being a victim was the necessary condition for a woman to ask for help. Experience has shown that, in reality, it is the request for help that allows her to begin a process of awareness together with the operators in the Anti-Violence Centers. This reflection has led to the creation of a theoretical model called “The Circular Model of Victimization”. The aim of the research, and which is presented here, was to verify whether the Italian Anti-Violence Centers recognize the Circular Model in the daily operational reality, and thus to ascertain whether this model can be considered a real empirical model, as well as a theoretical explanatory model. In conclusion, the revisited Circular Model of Victimization will be presented, in which it is assumed that the way out of the circuit of violence passes from a first moment of perception of victimization to arrive at a real awareness of the same.

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