Perturbation-Assisted PAPR Reduction for Large-Scale MIMO-OFDM Systems via ADMM

We consider the problem of peak-to-average power ratio (PAPR) reduction for orthogonal frequency-division multiplexing (OFDM) based large-scale multiple-input multipleoutput (MIMO) systems. A novel perturbation-assisted scheme is developed to reduce the PAPRs of the transmitted signals by exploiting the redundant degrees-of-freedom (DoFs) inherent in the large-scale antenna array. Specifically, we introduce artificial perturbation signals to the frequency-domain precoded signals, with the aim of reducing the PAPRs of their time-domain counterpart signals. Meanwhile, the additive perturbation signal associated with each tone is constrained to lie in the null-space of its associated channel matrix, such that it does not cause any multi-user inference or out-of-band radiations. Such a problem is formulated as a convex optimization problem, and an efficient algorithm is developed by resorting to the variable splitting and alterative direction method of multipliers (ADMM) techniques. Simulation results show that the proposed method has a fast convergence rate and achieves substantial PAPR reduction within only tens of iterations. In addition, unlike other precoding-based PAPR reduction methods, our proposed method which introduces perturbation signals to the precoded signals is independent of the precoding stage and thus could be more suitable for practical systems

Dynamic tomography of the spin-orbit coupling in nonlinear optics

Spin-orbit coupled (SOC) light fields with spatially inhomogeneous polarization have attracted increasing research interest within the optical community. In particular, owing to their spin-dependent phase and spatial structures, many nonlinear optical phenomena which we have been familiar with up to now are being re-examined, hence a revival of research in nonlinear optics. To fully investigate this topic, knowledge on how the topological structure of the light field evolves is necessary, but, as yet, there are few studies that address the structural evolution of the light field. Here, for the first time, we present a universal approach for theoretical tomographic treatment of the structural evolution of SOC light in nonlinear optics processes. Based on a Gedanken vector second harmonic generation, a fine-grained slice of evolving SOC light in a nonlinear interaction and the following diffraction propagation are studied theoretically and verified experimentally, and which at the same time reveal several interesting phenomena. The approach provides a useful tool for enhancing our capability to obtain a more nuanced understanding of vector nonlinear optics, and sets a foundation for further broad-based studies in nonlinear systems.Comment: 10 pages, 7 figure

An Efficient Bayesian PAPR Reduction Method for OFDM-Based Massive MIMO Systems

We consider the problem of peak-to-average power ratio (PAPR) reduction in orthogonal frequency-division multiplexing (OFDM) based massive multiple-input multiple-output (MIMO) downlink systems. Specifically, given a set of symbol vectors to be transmitted to K users, the problem is to find an OFDM-modulated signal that has a low PAPR and meanwhile enables multiuser interference (MUI) cancellation. Unlike previous works that tackled the problem using convex optimization, we take a Bayesian approach and develop an efficient PAPR reduction method by exploiting the redundant degrees-of-freedom of the transmit array. The sought-after signal is treated as a random vector with a hierarchical truncated Gaussian mixture prior, which has the potential to encourage a low PAPR signal with most of its samples concentrated on the boundaries. A variational expectation-maximization (EM) strategy is developed to obtain estimates of the hyperparameters associated with the prior model, along with the signal. In addition, the generalized approximate message passing (GAMP) is embedded into the variational EM framework, which results in a significant reduction in computational complexity of the proposed algorithm. Simulation results show our proposed algorithm achieves a substantial performance improvement over existing methods in terms of both the PAPR reduction and computational complexity

Feed-forward control for quantum state protection against decoherence

We propose a novel scheme of feed-forward control and its reversal for protecting quantum state against decoherence. Before the noise channel our pre-weak measurement and feed-forward are just to change the protected state into the state almost immune to the noise channel, and after the channel our reversed operations and post-weak measurements are just to restore the protected state. Unlike most previous state protection schemes, ours only concerns the noise channel and does not care about the protected state. We show that our scheme can effectively protect unknown states, nonorthogonal states and entangled states against amplitude damping noise. Our scheme has dramatic merits of protecting quantum states against heavy amplitude damping noise, and can perfectly protect some specific nonorthogonal states in an almost deterministic way, which might be found some applications in current quantum communication technology. And it is most important that our scheme is experimentally available with current technology

Direct Urca processes involving singlet proton superfluidity in neutron star cooling

A detailed description of the baryon direct Urca processes A: $n\rightarrow p+e+\bar{\nu}_{e}$, B: $\Lambda\rightarrow p+e+\bar{\nu}_{e}$, C: $\Xi^{-}\rightarrow\Lambda+e+\bar{\nu}_{e}$ related to the neutron star cooling is given in the relativistic mean field approximation.The contributions of the reactions B and C on the neutrino luminosity are calculated by means of the relativistic expressions of the neutrino energy losses.Our results show that the total neutrino luminosities of the reactions A, B, C within the mass range 1.603-2.067$M_{\odot}$ (1.515-1.840$M_{\odot}$ for TM1 model) for GM1 model are larger than the corresponding values for neutron stars in npe$\mu$ matter. Although the hyperon direct Urca processes B and C reduce the neutrino emissivity of the reaction A, it illustrates the reactions B and C still make the total neutrino luminosity enhancement in the above mentioned areas.Furthermore, when we only consider the $^{1}S_{0}$ proton superfluidity in neutron star cooling, we find that although the neutrino emissivity of the reactions A and B is suppressed with the appearance of $^{1}S_{0}$ proton superfluidity, the total contribution of the reactions A, B, C can still quicken a massive neutron star cooling.These results could be used to help prove appearing hyperons in PSR J1614-2230 and J0348+0432 from neutron star cooling perspective

Prognostics Estimations with Dynamic States

The health state assessment and remaining useful life (RUL) estimation play very important roles in prognostics and health management (PHM), owing to their abilities to reduce the maintenance and improve the safety of machines or equipment. However, they generally suffer from this problem of lacking prior knowledge to pre-define the exact failure thresholds for a machinery operating in a dynamic environment with a high level of uncertainty. In this case, dynamic thresholds depicted by the discrete states is a very attractive way to estimate the RUL of a dynamic machinery. Currently, there are only very few works considering the dynamic thresholds, and these studies adopted different algorithms to determine the discrete states and predict the continuous states separately, which largely increases the complexity of the learning process. In this paper, we propose a novel prognostics approach for RUL estimation of aero-engines with self-joint prediction of continuous and discrete states, wherein the prediction of continuous and discrete states are conducted simultaneously and dynamically within one learning framework

Construction of Chiral Metamaterial with U-Shaped Resonator Assembly

Chiral structure can be applied to construct metamaterial with negative refractive index (NRI). In an assembly of double-layered metallic U-shaped resonators with two resonant frequencies wH and wL, the effective induced electric and magnetic dipoles, which are contributed by the specific surface current distributions, are collinear at the same frequency. Consequently, for left circularly polarized light, NRI occurs at wH, whereas for right circularly polarized light it occurs at wL. Our design provides a new example to apply chiral structures to tune electromagnetic properties, and could be enlightening in exploring chiral metamaterials.Comment: 17pages 4 figures, submitted to PRB on Nov. 5th 200

Synchronous Observation on the Spontaneous Transformation of Liquid Metal under Free Falling Microgravity Situation

The unusually high surface tension of room temperature liquid metal is molding it as unique material for diverse newly emerging areas. However, unlike its practices on earth, such metal fluid would display very different behaviors when working in space where gravity disappears and surface property dominates the major physics. So far, few direct evidences are available to understand such effect which would impede further exploration of liquid metal use for space. Here to preliminarily probe into this intriguing issue, a low cost experimental strategy to simulate microgravity environment on earth was proposed through adopting bridges with high enough free falling distance as the test platform. Then using digital cameras amounted along x, y, z directions on outside wall of the transparent container with liquid metal and allied solution inside, synchronous observations on the transient flow and transformational activities of liquid metal were performed. Meanwhile, an unmanned aerial vehicle was adopted to record the whole free falling dynamics of the test capsule from the far end which can help justify subsequent experimental procedures. A series of typical fundamental phenomena were thus observed as: (a) A relatively large liquid metal object would spontaneously transform from its original planar pool state into a sphere and float in the container if initiating the free falling; (b) The liquid metal changes its three-dimensional shape due to dynamic microgravity strength due to free falling and rebound of the test capsule; and (c) A quick spatial transformation of liquid metal immersed in the solution can easily be induced via external electrical fields. The mechanisms of the surface tension driven liquid metal actuation in space were interpreted. All these findings indicated that microgravity effect should be fully treated in developing future generation liquid metal space technologies.Comment: 16 pages, 9 figure

Radial modal transitions of Laguerre-Gauss modes during parametric upconversion: towards the full-field selection rule of spatial modes

Optical orbital angular momentum transformation and corresponding azimuthal-mode selection rules have been studied exhaustively for various nonlinear optical interactions. However, nonlinear transformation of radial mode has not been systematically studied since the pioneering work [Phys. Rev. A 56, 4193, 1997]. In this paper, we theoretically study and experimentally verify the radial modal transitions of Laguerre-Gauss (LG) modes in parametric upconversion. Specifically, we provide a general solution that describes the sum-frequency generation (SFG) field excited by two arbitrary LG modes. Based on the solution, one can predict the full spatial complex amplitude of SFG fields upon propagation precisely and readily obtain the associated full-field selection rule including both azimuthal and radial modes. This work provides a theoretical basis for quantum and nonlinear optical research involving parametric upconversion of complex structured light, and paves the way for future work on full-field transformation of spatial modes in other nonlinear interactions.Comment: 10 pages, 6 figure

M\"{o}ssbauer Effect Probe of Local Jahn-Teller distortion in Fe-doped Colossal Magnetoresistive Manganites

Local structure of the Fe-doped La$_{1-x}$Ca$_{x}$MnO$_{3}$ (x=0.00-1.00) compounds has been investigated by means of M\"{o}ssbauer spectroscopy. $^{57}$Fe M\"{o}ssbauer spectra provide a direct evidence of Jahn-Teller distortion in these manganites. On the basis of M\"{o}ssbauer results, the Jahn-Teller coupling was estimated. It is noteworthy that Ca-concentration dependence of Jahn-Teller coupling strength is very consistent with the magnetic phase diagram. Our results reveal that M\"{o}ssbauer spectroscopy can not only detect the local structural distortion, but also provide a technique to investigate Jahn-Teller coupling of Fe-doped La$_{1-x}$Ca$_{x}$MnO$_{3}$ colossal magnetoresistive perovskites.Comment: 3 figures, will appear in Applied Physics Letter