Statistical Journals

Publication year: 2012
Source: Computational Statistics & Data Analysis, Available online 4 February 2012

Min Wang, Xiaoqian Sun

We study the problems of hypothesis testing and point estimation for the correlation coefficient between the disturbances in the system of two seemingly unrelated regression equations. An objective Bayesian solution to each problem is proposed based on combined use of the invariant loss function and the objective prior distribution for the unknown model parameters. It is shown that this new solution possesses an invariance property under monotonic reparameterization of the quantity of interest. The performance of the proposed solution is examined through a simulation study. Furthermore, the solution is illustrated by an application to the real annual data for analyzing the investment model.

Publication year: 2012
Source: Computational Statistics & Data Analysis, Volume 56, Issue 4, 1 April 2012, Pages iii-v

[No author name available]

Publication year: 2012
Source: Computational Statistics & Data Analysis, Volume 56, Issue 4, 1 April 2012, Pages vi-vii

[No author name available]

Publication year: 2012
Source: International Journal of Thermal Sciences, Available online 31 January 2012

Mastaneh Hajipour, Asghar Molaei Dehkordi

In this article, mixed-convective heat transfer of nanofluids in a vertical channel partially filled with highly porous medium was studied. In the porous region, the Brinkman–Forchheimer extended Darcy model was used to describe the fluid flow pattern. Different viscous dissipation models were also applied to account for viscous heating. At the porous medium–fluid interface, interfacial coupling conditions for the fluid velocity and temperature were used to derive the analytical solution using a two-parameter perturbation method. The model used for the nanofluids incorporates the effects of Brownian motion and thermophoresis. With constant wall temperature, velocity and temperature profiles and expressions for the Nusselt number values were obtained for fully-developed fluid flow. In addition, a numerical analysis was conducted using finite-difference method to compare the obtained results. Finally, a parametric study was conducted to investigate the influences of various parameters on the fluid flow pattern and heat-transfer performance. The predicted results clearly indicate that the presence of nanoparticles in the base fluid enhances the heat-transfer process significantly.

Highlights► We present an analysis of mixed-convective heat transfer of nanofluids. ► Brinkman–Forchheimer extended Darcy model is used to describe fluid flow pattern. ► Different viscous dissipation models are applied to account for viscous heating. ► We present an analytical approximate solution using a perturbation method. ► Effects of Brownian motion and thermophoresis are included.

Summary Treatment-selection markers are biological molecules or patient characteristics associated with one’s response to treatment. They can be used to predict treatment effects for individual subjects and subsequently help deliver treatment to those most likely to benefit from it. Statistical tools are needed to evaluate a marker’s capacity to help with treatment selection. The commonly adopted criterion for a good treatment-selection marker has been the interaction between marker and treatment. While a strong interaction is important, it is, however, not sufficient for good marker performance. In this article, we develop novel measures for assessing a continuous treatment-selection marker, based on a potential outcomes framework. Under a set of assumptions, we derive the optimal decision rule based on the marker to classify individuals according to treatment benefit, and characterize the marker’s performance using the corresponding classification accuracy as well as the overall distribution of the classifier. We develop a constrained maximum-likelihood method for estimation and testing in a randomized trial setting. Simulation studies are conducted to demonstrate the performance of our methods. Finally, we illustrate the methods using an HIV vaccine trial where we explore the value of the level of preexisting immunity to adenovirus serotype 5 for predicting a vaccine-induced increase in the risk of HIV acquisition.

Publication year: 2012
Source: International Journal of Thermal Sciences, Available online 31 January 2012

M. Geri, M. Lorenzini, G.L. Morini

The operational behavior of silicon open channel DC electro-osmotic (EO) pumps is numerically investigated to highlight the role of the micro channel cross-sectional geometry and the influence of the electrical properties that characterize the fluid/wall interaction on the fluid-dynamic performances. The mathematical formulation is based on the classical theory for isothermal electro-osmotic flows but all the modeling assumptions have been deeply discussed, since they represent the limit to the application of the model itself. The equations that determine the electric potential and the local velocity field have been numerically solved using a specific in-house code. The model has been applied to micro and nano channels, manufactured by chemical etching on silicon wafers, that feature rectangular or trapezoidal cross-sections and a broad range of operating conditions has been examined. The interactions between the channel geometry and the fluid/wall electrical properties have been deeply analyzed and their role on the pumps performance is discussed in terms of macroscopic parameters, namely the volumetric flow rate and the pressure head. With the aim of giving a useful tool to designers, numerical results have been processed to develop two simple correlations that enable the computation of the characteristic curve of the EO pump. Their formulation directly stems from the comparison between results obtained using the model and analytical results for parallel plates and it puts in evidence the effect of the flow confinement due to a finite cross-section. Such correlations can be used for both rectangular and trapezoidal channels in the whole range of the operating conditions considered within this work.

Highlights► Performances depends on: non-dimensional zeta-potential and electrokinetic diameter. ► Geometry plays a role by: the aspect ratio and the cross-sectional area. ► Narrow cross-sections cannot always be approximated as two infinite parallel plates. ► Two correlations have been derived to draw characteristic curves of EOPs.

Publication year: 2012
Source: International Journal of Thermal Sciences, Available online 30 January 2012

Luben Cabezas-Gómez, Hélio Aparecido Navarro, José Maria Sáiz-Jabardo, Sergio de Morais Hanriot, Cristiana Brasil Maia

The present paper presents a theoretical analysis of a cross flow heat exchanger with a new flow arrangement comprehending several tube rows. The thermal performance of the proposed flow arrangement is compared with the thermal performance of a typical counter cross flow arrangement that is used in chemical, refrigeration, automotive and air conditioning industries. The thermal performance comparison has been performed in terms of the following parameters: heat exchanger effectiveness and efficiency, dimensionless entropy generation, entransy dissipation number, and dimensionless local temperature differences. It is also shown that the uniformity of the temperature difference field leads to a higher thermal performance of the heat exchanger. In the present case this is accomplished thorough a different organization of the in-tube fluid circuits in the heat exchanger. The relation between the recently introduced “entransy dissipation number” and the conventional thermal effectiveness has been obtained in terms of the “number of transfer units”. A case study has been solved to quantitatively to obtain the temperature difference distribution over two rows units involving the proposed arrangement and the counter cross flow one. It has been shown that the proposed arrangement presents better thermal performance regardless the comparison parameter.

Highlights► We thermally characterize a cross flow heat exchanger with new flow arrangement. ► We show that the proposed arrangement presents better thermal performance. ► It is shown that a more uniform TDF leads to higher thermal performance. ► We obtain a new relation between entransy dissipation and thermal effectiveness. ► The proposed arrangement can be used in design single-phase heat exchangers.