227 research outputs found
High precision measurement of the form factors of the semileptonic decays K± → π0l±ν (Kl3) in NA48/2
No full textThe data collected by NA48/2 in 2003-2004 allowed several precise measurements in the charged kaon decay sector. In this paper we present the results obtained using a sample of 2.5×106 K± → π0μ±ν (Kμ3) and 4.0×106 K × → π0l ±ν (Ke3) events, collected in 2004 using a minimal trigger configuration. This unbiassed sample of kaon decays allows a high precision measurement of the semileptonic form factors. © Copyright owned by the author(s)
Searches for lepton number violation and resonances in K± → πμμ decays
No full textThe NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003–2004. A new upper limit on the rate of the lepton number violating decay K±→π∓μ±μ± is reported: B(K±→π∓μ±μ±)<8.6×10−11 at 90% CL. Searches for two-body resonances X in K±→πμμ decays (such as heavy neutral leptons N4 and inflatons χ) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K±→μ±N4)B(N4→πμ) and B(K±→π±X)B(X→μ+μ−) for ranges of assumed resonance masses and lifetimes. The limits are in the (10−11,10−9) range for resonance lifetimes below 100 ps. © 2017 The Author(s
Transformational and Transactional Leadership Styles as They Predict Constructive Culture and Defensive Culture
No full textThe purpose of this study was to test a predictive model of several components of organizational and leadership Culture in a large sample of municipal employees using three sets of predictors: demographic/employment status of employees, measures of employees' judgments of their supervisor's transactional leadership styles, and measures of employees' judgments of their supervisor's transformational leadership style. To what extent does transformational and transactional leadership (both individually and as an interaction) predict Constructive Culture and Defensive Culture?
The research utilized two concepts: leadership theory (transformational and transactional leadership) and organizational culture (constructive culture and defensive culture) to analyze the relationship of organizational culture to leadership styles. The research significantly determined how much the relationship of transformational and transactional leadership predicts the criterion variables, constructive culture, and defensive culture, within an organization's culture.
First, descriptive and correlational analyses were performed to identify the zero order relationships among demographic variables, leadership styles, and organizational culture variables. Demographic variables included gender, age, level of education, race (Caucasian, or African-American), type of employee (supervisor or non-supervisor), and length of employment.
Next, the researcher factor (principal components with an orthogonal varimax rotation) analyzed the interrelationships among the items of each of the two instruments (Multifactor Leadership Questionnaire and the Organizational Culture Inventory Questionnaire). Three separate factor analysis studies were performed for the: (a) 12 OCI scales; (b) twenty transformational leadership items; and (c) 12 transactional leadership items. Factor analysis was used as a means of understanding the underlying structure of the data and determining whether "local factors" (that is, derived solely on the current sample of data) needed to be used instead of the structure suggested by the authors of the published scales. As reported above, the structure suggested by the test authors was deemed appropriate for the study.
Stage 3: Multiple Regressions: Next, to answer the hypotheses, the researcher utilized multiple regression equations.
Five significant findings were suggested from this research study:
1.Transformational Leadership factored scores were positively and significantly correlated with Constructive Culture factored scores and therefore Transformational Leadership added significant variance in predicting Constructive Culture.
2.Transactional Leadership factored scores were positively and significantly correlated with Defensive Culture factored scores and therefore Transactional Leadership added significant variance in predicting Defensive Culture.
3.Organizations have subcultures that display the personality of the individual departments or units.
4.The type of work performed or provided influences the type of leadership style.
5.The MLQ instrument was found to be a weak measurement of leadership.
Perhaps the most important finding was the weakness of the MLQ instrument. As a result, this research revealed the need to develop an instrument that represent a more reliable and valid measure of Transformational Leadership and Transactional Leadership behaviors. This research suggested that the measures could be improved.Ph. D
Kinetic algorithms for non-equilibrium gas dynamics
No full textNew upwind kinetic-difference schemes have been developed for flows with nonequilibrium thermodynamics and chemistry. These schemes are derived from the Boltzmann equation with the resulting Euler schemes developed as moments of the discretized Boltzmann scheme with a locally Maxwellian velocity distribution. Application of a directionally-split Courant-Isaacson-Rees (CIR) scheme at the Boltzmann level results in a flux-vector splitting scheme at the Euler level and is called Kinetic Flux-Vector Splitting (KFVS). Extension to flows with finite-rate chemistry and vibrational relaxation is accomplished utilizing non-equilibrium kinetic theory. Computational examples are presented comparing KFVS with the schemes of Van-Leer and Roe for quasi-one-dimensional flow through a supersonic diffuser, inviscid flow through two-dimensional inlet, 'viscous flow over a cone at zero angle-of-attack, and shock-induced combustion/detonation in a premixed hydrogen-air mixture. Calculations are also shown for the transonic flow over a bump in a channel and the transonic flow over an NACA 0012 airfoil. The results show that even though the KFVS scheme is a Riemann solver at the kinetic level, its behavior at the Euler level is more similar to the the existing flux-vector splitting algorithms than to the flux-difference splitting scheme of Roe.
A new approach toward the development of a genuinely multi-dimensional Riemann solver is also presented. The scheme is based on the same kinetic theory considerations used in the development of the KF VS scheme. The work has been motivated by the recent progress on multi-dimensional upwind schemes by the groups at the University of Michigan and the Von Karman Institute. These researchers have developed effective upwind schemes for the multi-dimensional linear advection equation using a cell-vertex fluctuation-splitting approach on unstructured grids of triangles or tetrahedra. They have made preliminary applications to the Euler equations using several wave decomposition models of the flux derivative. The issue of the appropriate wave model does not appear to be adequately resolved. The approach taken in the present work is to apply these new multi-dimensional upwind schemes for the scalar advection equation at the Boltzmann level. The resulting Euler schemes are obtained as moments of the fluctuations in the Maxwellian distribution function. The development is significantly more complicated than standard (dimensionally-split) kinetic schemes in that the Boltzmann discretization depends upon the direction of the molecular velocities which must be accounted for in the limits of integration in velocity space. The theoretical issues have been solved through analytic quadrature and Euler schemes have been developed. For this formulation it was not necessary to prescribe any explicit wave decomposition model. Encouraging preliminary results have been obtained for perfect gases on uniform Cartesian meshes with first-order spatial accuracy. Results are presented for a 29° shock reflection, a 45° shear discontinuity, and Mach 3 flow over a step.
Finally, methods for obtaining accurate gas-dynamic simulations in the continuum transition regime are considered. In particular, large departures from translational equilibrium are modeled using algorithms based on the Burnett equations instead of the Navier-Stokes equations. Here, the same continuum formulation of the governing equations is retained, but new constitutive relations based on higher-order Chapman-Enskog theory are introduced. Both a rotational relaxation model and a bulk-viscosity model have been considered for simulating rotational non-equilibrium. Results are presented for hypersonic normal shock calculations in argon and diatomic nitrogen and comparisons are made with Direct Simulation Monte Carlo (DSMC) results. The present work closely follows that of the group at Stanford, however, the use of upwind schemes and the bulk-viscosity model represent new contributions.Ph. D
High precision measurement of the form factors of the semileptonic decays K± → π0l±ν (Kl3) in NA48/2
No full textThe data collected by NA48/2 in 2003-2004 allowed several precise measurements in the charged kaon decay sector. In this paper we present the results obtained using a sample of 2.5×106 K± → π0μ±ν (Kμ3) and 4.0×106 K × → π0l ±ν (Ke3) events, collected in 2004 using a minimal trigger configuration. This unbiassed sample of kaon decays allows a high precision measurement of the semileptonic form factors. © Copyright owned by the author(s)
Study of Cross-flow Cooling Effects in a Stirling Engine Heat Exchanger
No full textabstract: While much effort in Stirling engine development is placed on making the high-temperature region of the Stirling engine warmer, this research explores methods to lower the temperature of the cold region by improving heat transfer in the cooler. This paper presents heat transfer coefficients obtained for a Stirling engine heat exchanger with oscillatory flow. The effects of oscillating frequency and input heat rate on the heat transfer coefficients are evaluated and details on the design and development of the heat exchanger test apparatus are also explained. Featured results include the relationship between overall heat transfer coefficients and oscillation frequency which increase from 21.5 to 46.1 Wm-2K-1 as the oscillation frequency increases from 6.0 to 19.3 Hz. A correlation for the Nusselt number on the inside of the heat exchange tubes in oscillatory flow is presented in a concise, dimensionless form in terms of the kinetic Reynolds number as a result of a statistical analysis. The test apparatus design is proven to be successful throughout its implementation due to the usefulness of data and clear trends observed. The author is not aware of any other publicly-available research on a Stirling engine cooler to the extent presented in this paper. Therefore, the present results are analyzed on a part-by-part basis and compared to segments of other research; however, strong correlations with data from other studies are not expected. The data presented in this paper are part of a continuing effort to better understand heat transfer properties in Stirling engines as well as other oscillating flow applications.Dissertation/ThesisM.S. Mechanical Engineering 201
Precision measurement of the ratio BR(K-S -> pi(+)pi(-)e(+)e(-))/BR(K-L -> pi(+)pi(-)pi(0)(D))
No full textThe decay mode was investigated using the data collected in 2002 by the NA48/1 collaboration. With about 23,k events and 59,k normalization decays, the branching ratio relative to the one was determined to be BR()/BR() = . This result was used to set the upper limit at CL on the presence, in the decay amplitude, of an E1 direct emission () term relative to the dominant inner bremsstrahlung () term. The CP-violating asymmetry in the sin,cos distribution of events, where is the angle between the and the decay planes in the kaon centre of mass, was found to be , consistent with zero. These results are in good agreement with a description of the decay amplitude dominated by the CP-even inner bremsstrahlung process
Test of lepton flavour universality in K+→ℓ+ν decays
No full textA precision test of lepton flavour universality has been performed by measuring the ratio RK of kaon leptonic decay rates K+→e+ν and K+→μ+νin a sample of 59813 reconstructed K+→ℓ+ν candidates with (8.71±0.24)% background contamination. The result RK=(2.487±0.013)×10-5 is in agreement with the Standard Model expectation. © 2011 Elsevier B.V
Measurement of the K-L -> e(+)e(-)e(+)e(-) decay rate
No full textThe decay rate of the long-lived neutral K meson into the e(+)e(-)e(+)e(-) final state has been measured with the NA48 detector at the CERN SPS. Using data collected in 1998 and 1999, a total of 200 events has been observed with negligible background. This observation corresponds to a branching ratio of Br(K-L -> e(+)e(-)e(+)e(-)) = (3.30 +/- 0.24(stat)+/- 0.23(syst)+/- 0-10(norm)) x 10(-8). (c) 2005 Elsevier B.V. All rights reserved
Measurement of K-e3(0) form factors
No full textThe semi-leptonic decay of the neutral K meson , was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector , scalar and tensor interactions were measured. The linear slope of the vector form factor and values for the ratios and were obtained. The values for and for are consistent with zero. Assuming only vector-axial vector couplings, and a good fit consistent with pure V-A couplings were obtained. Alternatively a fit to a dipole form factor yields a pole mass of MeV, consistent with the mass.The semileptonic decay of the neutral K meson, KL0→π±e∓ν ( Ke3 ), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f+(q2)) , scalar ( fS ) and tensor ( fT ) interactions were measured. The linear slope of the vector form factor λ+=0.0284±0.0007±0.0013 and values for the ratios |fS/f+(0)|=0.015−0.010+0.007±0.012 and |fT/f+(0)|=0.05−0.04+0.03±0.03 were obtained. The values for fS and fT are consistent with zero. Assuming only vector–axial-vector couplings, λ+=0.0288±0.0004±0.0011 and a good fit consistent with pure V–A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M=859±18 MeV , consistent with the K*(892) mass.The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor (f_T) interactions were measured. The linear slope of the vector form factor lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| = 0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03 were obtained. The values for f_S and f_T are consistent with zero. Assuming only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with the K^*(892) mass
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