Inference in Experiments with Matched Pairs and Imperfect Compliance

This paper studies inference for the local average treatment effect in randomized controlled trials with imperfect compliance where treatment status is determined according to "matched pairs." By "matched pairs," we mean that units are sampled i.i.d. from the population of interest, paired according to observed, baseline covariates and finally, within each pair, one unit is selected at random for treatment. Under weak assumptions governing the quality of the pairings, we first derive the limiting behavior of the usual Wald (i.e., two-stage least squares) estimator of the local average treatment effect. We show further that the conventional heteroskedasticity-robust estimator of its limiting variance is generally conservative in that its limit in probability is (typically strictly) larger than the limiting variance. We therefore provide an alternative estimator of the limiting variance that is consistent for the desired quantity. Finally, we consider the use of additional observed, baseline covariates not used in pairing units to increase the precision with which we can estimate the local average treatment effect. To this end, we derive the limiting behavior of a two-stage least squares estimator of the local average treatment effect which includes both the additional covariates in addition to pair fixed effects, and show that the limiting variance is always less than or equal to that of the Wald estimator. To complete our analysis, we provide a consistent estimator of this limiting variance. A simulation study confirms the practical relevance of our theoretical results. We use our results to revisit a prominent experiment studying the effect of macroinsurance on microenterprise in Egypt

Tensor-Based Target Parameter Estimation Algorithm for FDA-MIMO Radar with Array Gain-Phase Error

As a new radar system, FDA-MIMO radar has recently developed rapidly, as it has broad prospects in angle-range estimation. Unfortunately, the performance of existing algorithms for FDA-MIMO radar is greatly degrading or even failing under the condition of array gain-phase error. This paper proposes an innovative solution to the joint angle and range estimation of FDA-MIMO radar under the condition of array gain-phase error and an estimation algorithm is developed. Moreover, the corresponding Cramér-Rao bound (CRB) is derived to evaluate the algorithm. The parallel factor (PARAFAC) decomposition technique can be utilized to calculate transmitter and receiver direction matrices. Taking advantage of receiver direction matrix, the angle estimation can be obtained. The range estimation can be estimated by transmitter direction matrix and angle estimation. To eliminate the error accumulation effect of array gain-phase error, the gain error and phase error are obtained separately. In this algorithm, the impact of gain-phase error on parameter estimation is removed and so is the error accumulation effect. Therefore, the proposed algorithm can provide excellent performance of angle-range and gain-phase error estimation. Numerical experiments prove the validity and advantages of the proposed method

Effects of high-temperature curing on hydration and microstructure of alkali-activated typical steel slag cementitious material

Hydration process, products, microstructure, and compressive strength of steel slag in alkaline environments at room and high temperature were investigated. Results show that high-temperature curing significantly promotes the early hydration, causing more products. The promoting effect of temperature becomes more apparent with higher activator content. The cumulative heat apparently increases by approximately twice at 6% alkali content. Increasing temperature has no effect on the types of products and hydration of inactive components. The products remain as Ca(OH)2 and C-(A)-S-H, but Ca/Si and Al/Si ratios significantly increase from 1.42 to 2.41 and from 0.14 to 0.21, respectively. High-temperature curing makes matrix denser, resulting in a substantial increase in the early strength. However, promoting effect on the strength diminishes over time. The growth rates of 28 d strength are only −1% and 4% at different alkali content. Moreover, alkali-activated steel slag material has great potential in the field of low-carbon cementitious materials

An FMCW MIMO Radar-Vision Fusion Algorithm for Target Classification and Localization

In order to solve the problems of slow real-time and poor detection of small targets that still exist in multi-sensor information fusion technology, a frequency-modulated continuous wave (FMCW) multiple-input multiple-output (MIMO) radar-vision fusion algorithm for target classification and localization is proposed in this paper. Firstly, the signal model of FMCW MIMO radar is established. Then, the target localization is performed using a forward-backward spatial smoothing (SS) based linear prediction-orthogonal propagator method (LP-OPM) to obtain information about the radar target. Next, the YOLOv7 and the visual ranging algorithms are used to identify and localize the target to get information about the camera target. In addition, a Kalman-weighted fusion algorithm is used to fuse the data from the two sensor targets for output. Finally, the performance of the method is proved to be superior by the experimental results

Tensor-Based Angle Estimation Approach for Strictly Noncircular Sources with Unknown Mutual Coupling in Bistatic MIMO Radar

In the paper, the estimation of joint direction-of-departure (DOD) and direction-of-arrival (DOA) for strictly noncircular targets in multiple-input multiple-output (MIMO) radar with unknown mutual coupling is considered, and a tensor-based angle estimation method is proposed. In the proposed method, making use of the banded symmetric Toeplitz structure of the mutual coupling matrix, the influence of the unknown mutual coupling is removed in the tensor domain. Then, a special enhancement tensor is formulated to capture both the noncircularity and inherent multidimensional structure of strictly noncircular signals. After that, the higher-order singular value decomposition (HOSVD) technology is applied for estimating the tensor-based signal subspace. Finally, the direction-of-departure (DOD) and direction-of-arrival (DOA) estimation is obtained by utilizing the rotational invariance technique. Due to the use of both noncircularity and multidimensional structure of the detected signal, the algorithm in this paper has better angle estimation performance than other subspace-based algorithms. The experiment results verify that the method proposed has better angle estimation performance

Effects of iron oxide nanoparticles on polyvinyl alcohol: Interfacial layer and bulk nanocomposites thin film

Iron oxide (α-phase) nanoparticles with coercivity larger than 300 Oe have been fabricated at a mild temperature by an environmentally benign method. The economic sodium chloride has been found to effectively serve as a solid spacer to disperse the iron precursor and to prevent the nanoparticles from agglomeration. Higher ratios of sodium chloride to iron nitrate result in smaller nanoparticles (19 nm for 20:1 and 14 nm for 50:1). The presence of polyvinyl alcohol (PVA) limits the particle growth (15 nm for 20:1 and 13 nm for 50:1) and favors nanoparticle dispersion in polymer matrices. Obvious physicochemical property changes have been observed with PVA attached to the nanoparticle surface. With PVA attached to the nanoparticle surface, the nanoparticles are found not only to increase the PVA cross-linking with an increase in melting temperature but also to enhance the thermal stability of the PVA. The nanoparticles are observed to be uniformly dispersed in the polymer matrix. Scanning electron microscopy (SEM) microstructure also shows an intermediate phase with a strong interaction between the nanoparticles and the polymer matrices, arising from the hydrogen bonding between the PVA and hydroxyl groups on the nanoparticle surface. The addition of nanoparticles favors the cross-linkage of the bulk PVA matrices, resulting in a higher melting temperature, and an enhanced thermal stability of the polymer matrix. © Springer Science+Business Media B.V. 2009

UV-Triggered Self-Healing of a Single Robust SiO₂ Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings

UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO₂ microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO₂ precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO₂ microcapsule via a combined interfacial/in situ polymerization. The single SiO₂ microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO₂ microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO₂ microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen