Hierarchical-Absolute Reciprocity Calibration for Millimeter-wave Hybrid Beamforming Systems

In time-division duplexing (TDD) millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems, the reciprocity mismatch severely degrades the performance of the hybrid beamforming (HBF). In this work, to mitigate the detrimental effect of the reciprocity mismatch, we investigate reciprocity calibration for the mmWave-HBF system with a fully-connected phase shifter network. To reduce the overhead and computational complexity of reciprocity calibration, we first decouple digital radio frequency (RF) chains and analog RF chains with beamforming design. Then, the entire calibration problem of the HBF system is equivalently decomposed into two subproblems corresponding to the digital-chain calibration and analog-chain calibration. To solve the calibration problems efficiently, a closed-form solution to the digital-chain calibration problem is derived, while an iterative-alternating optimization algorithm for the analog-chain calibration problem is proposed. To measure the performance of the proposed algorithm, we derive the Cram\'er-Rao lower bound on the errors in estimating mismatch coefficients. The results reveal that the estimation errors of mismatch coefficients of digital and analog chains are uncorrelated, and that the mismatch coefficients of receive digital chains can be estimated perfectly. Simulation results are presented to validate the analytical results and to show the performance of the proposed calibration approach

Hierarchical-absolute reciprocity calibration for millimeter-wave hybrid beamforming systems

In time-division duplexing (TDD) millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems, the reciprocity mismatch severely degrades the performance of the hybrid beamforming (HBF). In this work, to mitigate the detrimental effect of the reciprocity mismatch, we investigate reciprocity calibration for the mmWave-HBF system with a fully-connected phase shifter network. To reduce the over-head and computational complexity of reciprocity calibration, we first decouple digital radio frequency (RF) chains and analog RF chains with beamforming design. Then, the entire calibration problem of the HBF system is equivalently decomposed into two subproblems corresponding to the digital-chain calibration and analog-chain calibration. To solve the calibration problems efficiently, a closed-form solution to the digital-chain calibration problem is derived, while an iterative-alternating optimization algorithm for the analog-chain calibration problem is proposed. To measure the performance of the proposed algorithm, we derive the Cramér-Rao lower bound on the errors in estimating mismatch coefficients. The results reveal that the estimation errors of mismatch coefficients of digital and analog chains are uncorrelated, and that the mismatch coefficients of receive digital chains can be estimated perfectly. Simulation results are presented to validate the analytical results and to show the performance of the proposed calibration approach

N-(4-hydroxyphenyl) retinamide inhibits migration of renal carcinoma cells and promotes autophagy via MAPK p38 pathway

Purpose: To investigate the effect of N-(4-hydroxyphenyl) retinamide (4HPR) on autophagy and migration of renal carcinoma cells.Methods: Renal cancer cell lines were treated with various concentrations of 4HPR. Proliferation of the cells was studied using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltrazolium bromide (MTT), while apoptosis and cell cycle arrest were determined by flow cytometry.Results: Treatment of RCCs with 30 μM 4HPR caused significant inhibition of viability. In 786-O and OS-RC-2 cell lines, 4HPR reduced colony formation by 39 and 43 %, respectively. In addition, 4HPR increased the percentage of 786-O cells in G1 phase from 58.79 ± 3.43 to 71.68 ± 4.47 % (p < 0.05). It also decreased the percentage of cells in the S-phase from 21.98 ± 2.78 to 09.17 ± 1.43 %, and enhanced the activation of p38 and JNK in 786-O cells at 48 h. Western blot assay showed that the activation of p38 and JNK by 4HPR was inhibited on pre-treatment with SB203580 (inhibitor of p38) and SP600125 (inhibitor of JNK), respectively. Reduction of 786-O cell viability by 4HPR treatment was also significantly inhibited by pre-treatment with sp203580 and sp600125 (p < 0.05). Furthermore, the inhibitors also reversed the effect of 4HPR on the expressions of Bax and Bcl-2 in 786-O cells.Conclusion: These results indicate that 4HPR inhibits the growth of renal cancer cells via activation of MAPK signalling pathway. Thus, 4HPR is a potential drug target for management of renal cancer.Keywords: Retinamide, Renal cancer, Autophagy, MAPK signalling, Cell proliferation, N-terminal kinas

Different male mate location behaviour of the Glanville fritillary butterfly in different landscapes in the Tianshan Mountains, northwestern China

In a previous study most males of the Glanville fritillary butterfly (Melitaea cinxia) were caught in valleys, whereas almost all females were distributed on slopes in the Tianshan Mountains, northwestern China. To help understand this phenomenon, male mate location behaviours were observed in different landscapes of the Tianshan Mountains. In valleys, males exhibited perching behaviour. On slopes, spatial distribution of males showed patrolling behaviour on meadows, but intermediate behaviour between perching and patrolling at forest edge. The temporal distribution of males also varied, being found on slopes from 7:00 to 18:00, but in valleys from 8:00 to 13:00 each day. Ambient temperatures were higher on slopes than those in valleys between 8:00 to 13:00. Males exhibited lower tolerance to high temperature than females, leading to the conclusion that valleys are more likely to be used by males as thermoregulation sites, rather than for mating

Impact and calibration of nonlinear reciprocity mismatch in massive MIMO systems

Time-division-duplexing massive multiple-input multiple-output (MIMO) systems estimate the channel state information (CSI) by leveraging the uplink-downlink channel reciprocity, which is no longer valid when the mismatch arises from the asymmetric uplink and downlink radio frequency (RF) chains. Existing works treat the reciprocity mismatch as constant for simplicity. However, the practical RF chain consists of nonlinear components, which leads to nonlinear reciprocity mismatch. In this work, we examine the impact and the calibration approach of the nonlinear reciprocity mismatch in massive MIMO systems. To evaluate the impact of the nonlinear mismatch, we first derive the closed-form expression of the ergodic achievable rate. Then, we analyze the performance loss caused by the nonlinear mismatch to show that the impact of the mismatch at the base station (BS) side is much larger than that at the user equipment side. Therefore, we propose a calibration method for the BS. During the calibration, polynomial function is applied to approximate the nonlinear mismatch factor, and over-the-air training is employed to estimate the polynomial coefficients. After that, the calibration coefficients are computed by maximizing the downlink achievable rate. Simulation results are presented to verify the analytical results and to show the performance of the proposed calibration approach

Secondary Fault Activity of the North Anatolian Fault near Avcilar, Southwest of Istanbul: Evidence from SAR Interferometry Observations

Strike-slip faults may be traced along thousands of kilometers, e.g., the San Andreas Fault (USA) or the North Anatolian Fault (Turkey). A closer look at such continental-scale strike faults reveals localized complexities in fault geometry, associated with fault segmentation, secondary faults and a change of related hazards. The North Anatolian Fault displays such complexities nearby the mega city Istanbul, which is a place where earthquake risks are high, but secondary processes are not well understood. In this paper, long-term persistent scatterer interferometry (PSI) analysis of synthetic aperture radar (SAR) data time series was used to precisely identify the surface deformation pattern associated with the faulting complexity at the prominent bend of the North Anatolian Fault near Istanbul city. We elaborate the relevance of local faulting activity and estimate the fault status (slip rate and locking depth) for the first time using satellite SAR interferometry (InSAR) technology. The studied NW-SE-oriented fault on land is subject to strike-slip movement at a mean slip rate of ~5.0 mm/year and a shallow locking depth of <1.0 km and thought to be directly interacting with the main fault branch, with important implications for tectonic coupling. Our results provide the first geodetic evidence on the segmentation of a major crustal fault with a structural complexity and associated multi-hazards near the inhabited regions of Istanbul, with similarities also to other major strike-slip faults that display changes in fault traces and mechanisms

Validation of a simple dynamic thermal performance characterization model based on the piston flow concept for flat-plate solar collectors

A simple dynamic characterization model of flat-plate solar collectors based on the piston flow concept is used both to identify the collector characteristic parameters and to predict the dynamic thermal performance. The heat transport time originally defined as (1 − e−1)−1τC by Amrizal et al. (2012) for the model turns out to be the collector static response time constant τC by analytical derivation. The nonlinear least squares method is applied to determine the characteristic parameters of a flat-plate solar air collector previously tested by the authors. Then the obtained parameters are used to predict the dynamic behavior of the collector outlet temperature. The model coefficients particularly c3 in the simple dynamic characterization model are examined by the collector dynamic prediction under variable meteorological conditions. Meanwhile, the prediction accuracy of the simple dynamic model based on the first-order difference method is compared to that of the numerical solution of the collector ordinary differential equation (ODE) model using the fourth-order Runge-Kutta method. The improved thermal inertia model (TIM) on the basis of closed-form solution presented by Deng et al. (2016a) is also considered. The results show that the prediction performance of the simple dynamic model is nearly as accurate as the ODE numerical solution and the TIM by Deng et al. (2016a) except some special conditions such as sharply changed solar irradiance and collector inlet temperature