On the Matrix Inversion Approximation Based on Neumann Series in Massive MIMO Systems

Zero-Forcing (ZF) has been considered as one of the potential practical precoding and detection method for massive MIMO systems. One of the most important advantages of massive MIMO is the capability of supporting a large number of users in the same time-frequency resource, which requires much larger dimensions of matrix inversion for ZF than conventional multi-user MIMO systems. In this case, Neumann Series (NS) has been considered for the Matrix Inversion Approximation (MIA), because of its suitability for massive MIMO systems and its advantages in hardware implementation. The performance-complexity trade-off and the hardware implementation of NS-based MIA in massive MIMO systems have been discussed. In this paper, we analyze the effects of the ratio of the number of massive MIMO antennas to the number of users on the performance of NS-based MIA. In addition, we derive the approximation error estimation formulas for different practical numbers of terms of NS-based MIA. These results could offer useful guidelines for practical massive MIMO systems.Comment: accepted to conference; Proc. IEEE ICC 201

Association Between Intraoperative Steroid and Postoperative Mortality in Patients Undergoing Craniotomy for Brain Tumor

BACKGROUND: Despite the widespread use of intraoperative steroids in various neurological surgeries to reduce cerebral edema and other adverse symptoms, there is sparse evidence in the literature for the optimal and safe usage of intraoperative steroid administration in patients undergoing craniotomy for brain tumors. We aimed to investigate the effects of intraoperative steroid administration on postoperative 30-day mortality in patients undergoing craniotomy for brain tumors. METHODS: Adult patients who underwent craniotomy for brain tumors between January 2011 to January 2020 were included at West China Hospital, Sichuan University in this retrospective cohort study. Stratified analysis based on the type of brain tumor was conducted to explore the potential interaction. RESULTS: This study included 8,663 patients undergoing craniotomy for brain tumors. In patients with benign brain tumors, intraoperative administration of steroids was associated with a higher risk of postoperative 30-day mortality (adjusted OR 1.98, 95% CI 1.09-3.57). However, in patients with malignant brain tumors, no significant association was found between intraoperative steroid administration and postoperative 30-day mortality (adjusted OR 0.86, 95% CI 0.55-1.35). Additionally, administration of intraoperative steroids was not associated with acute kidney injury (adjusted OR 1.11, 95% CI 0.71-1.73), pneumonia (adjusted OR 0.89, 95% CI 0.74-1.07), surgical site infection (adjusted OR 0.78, 95% CI 0.50-1.22) within 30 days, and stress hyperglycemia (adjusted OR 1.05, 95% CI 0.81-1.38) within 24 h after craniotomy for brain tumor. CONCLUSION: In patients undergoing craniotomy for benign brain tumors, intraoperative steroids were associated with 30-day mortality, but this association was not significant in patients with malignant brain tumors

Paleomagnetism of the Upper Cretaceous Daijiaping Formation red beds in the Chaling Basin, Hunan Province, China

Objective Red beds are widely used in palaeomagnetic studies as they can carry stable natural remanence. Most previous studies on red beds have mainly focused on lacustrine-fluvial facies, with limited targeting the aeolian red beds. Consequently, the influence of aeolian deposition processes and sedimentary environments on remanence records remains poorly understood. Methods In this study, we conducted a palaeomagnetic investigation of the red beds from the Upper Cretaceous Daijiaping Formation in the Chaling Basin, Hunan Province, China, to compare the stability and reliability of remanence in aeolian and lacustrine-fluvial red beds. Results Rock magnetic results indicate that magnetite, maghemite and hematite are the dominant magnetic remanence carriers. Specimens were subjected to stepwise thermal demagnetization, and only 1/6 of the specimens yielded characteristic remanent magnetisations (ChRMs). Although the mean directions of ChRM in both aeolian(Ds=222.7°, Is=-43.3°, κ=5.9, α95=20.6°, n=11) and lacustrine-fluvial (Ds=204.6°, Is=-47.8°, κ=2.4, α95=23.1°, n=28) samples are statistically indistinguishable, the distribution of individual ChRM directions is scattered, as evidenced by the large α95 values. Thin section observation reveals that the aeolian samples are predominantly composed of fine grains, with some coarser grains and almost no interstitial fillings compared with the lacustrine-fluvial red beds. This makes them susceptible to physical disturbance and subsequent chemical alteration, which compromises the stability of their remanence records. Analysis of palaeomagnetic data of specimens from different positions of an aeolian foreset bed reveals that the reliability of remanence is significantly influenced by aeolian depositional processes in case the angle between the foreset bed and the bedding plane is larger than 20°. Statistical analysis of palaeomagnetic data previously published from the Cretaceous red beds in South China and these in this study suggests that the remanence records in the Cretaceous aeolian red beds in South China tend to be less stable and less reliable, compared with that of the coeval lacustrine-fluvial red beds. It is probably because of their loose structure and low hematite content, which hinders the acquisition of primary remanence and makes them susceptible to diagenetic alteration. Conclusion These findings provide valuable insights for studying the stability and reliability of remanence in aeolian red beds and their application in palaeomagnetic study

Structure identification and variable selection in geographically weighted regression models

<p>Geographically weighted regression (GWR) is an important tool for exploring spatial non-stationarity of a regression relationship, in which whether a regression coefficient really varies over space is especially important in drawing valid conclusions on the spatial variation characteristics of the regression relationship. This paper proposes a so-called GWGlasso method for structure identification and variable selection in GWR models. This method penalizes the loss function of the local-linear estimation of the GWR model by the coefficients and their partial derivatives in the way of the adaptive group lasso and can simultaneously identify spatially varying coefficients, nonzero constant coefficients and zero coefficients. Simulation experiments are further conducted to assess the performance of the proposed method and the Dublin voter turnout data set is analysed to demonstrate its application.</p

Effects of the Substitution of 20% Nd for La or Doping with 20% C on the Magnetic Properties and Magnetocaloric Effect in LaFe11.5Si1.5 Compound

The effects of element substitution and element doping on the magnetic properties and magnetocaloric effect of the LaFe11.5Si1.5 compound were investigated. The crystals of the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds all showed cubic NaZn13-type structures, but the lattice of the La0.8Nd0.2Fe11.5Si1.5 shrank and the lattice of the LaFe11.5Si1.5C0.2 expanded. All three compounds had the characteristic of first-order magnetic transition due to the obvious itinerant-electron metamagnetic (IEM) transition occurring above Curie temperature (TC). For the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds, the TC were approximately 194 K, 188 K, and 232 K, respectively. Meanwhile, the maximum magnetic entropy changes (−ΔSM) under a magnetic field change of 0–3 T were approximately 18.7 J/kg·K, 22.8 J/kg·K, and 16.4 J/kg·K, respectively. The TC was mainly affected by the lattice constant. Furthermore, the −ΔSM was mainly affected by the latent heat of the first-order magnetic transition