Search

Recently the shape-restricted inference has gained popularity in statistical and econometric literature in order to relax the linear or quadratic covariate effect in regression analyses. The typical shape-restricted covariate effect includes monotonic increasing, decreasing, convexity or concavity. In this paper, we introduce the shape-restricted inference to the celebrated Cox regression model (SR-Cox), in which the covariate response is modeled as shape-restricted additive functions. The SR-Cox regression approximates the shape-restricted functions using a spline basis expansion with data driven choice of knots. The underlying minimization of negative log-likelihood function is formulated as a convex optimization problem, which is solved with an active-set optimization algorithm. The highlight of this algorithm is that it eliminates the superfluous knots automatically. When covariate effects include combinations of convex or concave terms with unknown forms and linear terms, the most interesting finding is that SR-Cox produces accurate linear covariate effect estimates which are comparable to the maximum partial likelihood estimates if indeed the forms are known. We conclude that concave or convex SR-Cox models could significantly improve nonlinear covariate response recovery and model goodness of fit., Updated with new latex template, 33 pages

Nowadays, there is great interest in the use of microfluidic paper-based analytical devices (μPADs) for low-cost diagnostics. In most cases, the test equipment is needed. Here we report a new type of device-independent detection method based on timer-paper-based analytical devices, which can be tested by smartphone, and its application for cholesterol detection. The Quick Response code was designed as the timer component of this device. Wax printing method was employed to print the pattern on filter paper. The color and enzyme reagents have been immobilized in the hydrophilic channel to complete the colorimetric detection for cholesterol. Under laminar flow conditions of the cellulose network, the liquid volume of detection zone has been quantified by monitoring the fluid residence time on different area of the timer-paper-based devices. The precise monitoring of detection time can promote the accuracy of colorimetric detection. This is very important for the quantitative detection of paper-based analytical devices. One significant outcome of this report is that simple and accurate timer can be used for detection process self-clocking. The factors of total detection time have been investigated. The linear range of the calibration curve was 3.0 ~ 6.0 mmol L−1, with correlation coefficient of 0.9956. With the characteristic of easy to use, low cost and accurate monitoring of detection time, this kind of timer-paper-based devices can be applied to cholesterol or other substances rapid detection.

A closed-form time domain analytic solution for UWB impulse signal reflected from a finitely conducting half space is proposed in this paper. This approach requires first evaluating the impulse response of the half space and then convolving it with the specified incident UWB impulsive field. Approximations to the Fresnel reflection coefficients, which take into account the frequency range from 3.1 to 10.6 GHz, are made, thereby permitting an analytical time domain expression for both vertically and horizontally polarized UWB impulsive reflected field. The numerical analysis illustrates that the analytic solution is suitable for dry concrete, wood, glass, etc., which are envisioned as common building construction materials for indoor environment.

A simulation of UWB impulse signals propagation within an indoor non-line-of-sight (NLOS) environment is addressed in this paper. The transmitter and the receiver are placed in two rooms respectively with a concrete wall blocking the line-of-sight (LOS) propagation path. The radiation pattern and the polarization pattern of transmitting/receiving antenna are modelled. The corresponding transient electromagnetic field transmitting through as well as reflected from the wall, the floor, the ceiling, the objects, etc. are calculated in time domain. The simulation results provide the space-time distribution of received pulsed field, which give more intrinsically interpretations for the mechanics of UWB impulse signals propagation in indoor NLOS environment.