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In cognitive radio (CR) systems, the spectrum efficiency (SE) of the secondary users (SUs) is always limited by the interference temperature constraint imposed on the primary users (PUs). Intelligent reflecting surface (IRS) has been recently proposed as a revolutionary technique which can help to enhance the SE of wireless communications. In this paper, we propose to employ an IRS to assist the SUs’ data transmission in the multiple-input multiple-output (MIMO) CR system. By jointly optimizing the transmit precoding (TPC) of the SU transmitter (ST) and the phase shifts of the IRS, we aim to maximize the achievable weighted sum rate (WSR) of SUs subject to the ST's total power, the PU's interference temperature and unit modulus constraints. To solve this complicated optimization problem in which the variables are coupled, the block coordinate descent (BCD) algorithm is introduced to alternately solve the subproblems. For each subproblem, the Lagrange dual or inner approximation method is adopted with a low complexity. Simulation results confirm the benefits of employing IRS in a MIMO CR system. The performance comparisons of the proposed algorithm with several other benchmarks are carried out by evaluating the impacts of various parameters on the WSR.

Summary Perovskite solar cells (PSCs) and organic photovoltaics (OPVs) have both undergone rapid development recently. The composition and molecular tunability of perovskite and organic semiconductors enable a large material pool with different band gaps and various physical characters, giving feasibility to construct perovskite/organic tandem solar cells (TSCs). Here, we developed a semi-empirical model, rationally selected the best available material combination, and successfully demonstrated the efficient and reproducible TSCs benefiting from their complementary band gaps and orthogonal processing solvents. Featuring with all-thermally evaporated low-loss interconnecting layers (ICLs), our 2-termimal (2T) monolithic perovskite/organic TSCs deliver high reproducibility with power conversion efficiency (PCE) narrowly distributed between 20% and 20.6% (certified as 19.54%). In addition to the promising efficiency, the UV sensitivity of OPVs is eliminated in the tandem structure, demonstrating its advantage on device stability. Those results unfold significant potentials of perovskite/organic tandem devices as reproducible and cost-effective structures to achieve high-performance TSCs.

Background: Plasma-based biomarkers would be potential biomarkers for early diagnosis of Alzheimer's disease (AD) because they are more available and cost-effective than cerebrospinal fluid (CSF) or neuroimaging. Therefore, we aimed to evaluate whether phosphorylated tau181 (p-tau181) in plasma could be an accurate AD predictor.Methods: Participants from the ADNI database included 185 cognitively unimpaired subjects with negative Aβ (CU–), 66 subjects with pre-clinical AD (CU with positive Aβ), 164 subjects with mild cognitive impairment with negative Aβ (MCI–), 254 subjects with prodromal AD (MCI with positive Aβ), and 98 subjects with dementia. Multiple linear regression models, linear mixed-effects models, and local regression were used to explore cross-sectional and longitudinal associations of plasma p-tau181 with cognition, neuroimaging, or CSF biomarkers adjusted for age, sex, education, and APOE genotype. Besides, Kaplan–Meier and adjusted Cox-regression model were performed to predict the risk of progression to dementia. Receiver operating characteristic analyses were performed to evaluate the predictive value of p-tau181.Results: Plasma p-tau181 level was highest in AD dementia, followed by prodromal AD and pre-clinical AD. In pre-clinical AD, plasma p-tau181 was negatively associated with hippocampal volume (β = −0.031, p-value = 0.017). In prodromal AD, plasma p-tau181 was associated with decreased global cognition, executive function, memory, language, and visuospatial functioning (β range −0.119 to −0.273, p-value < 0.05) and correlated with hippocampal volume (β = −0.028, p-value < 0.005) and white matter hyperintensity volume (WMH) volume (β = 0.02, p-value = 0.01). In AD dementia, increased plasma p-tau181 was associated with worse memory. In the whole group, baseline plasma p-tau181 was significantly associated with longitudinal increases in multiple neuropsychological test z-scores and correlated with AD-related CSF biomarkers and hippocampal volume (p-value < 0.05). Meanwhile, CU or MCI with high plasma p-tau181 carried a higher risk of progression to dementia. The area under the curve (AUC) of the adjusted model (age, sex, education, APOE genotype, and plasma p-tau181) was 0.78; that of additionally included CSF biomarkers was 0.84.Conclusions: Plasma p-tau181 level is related to multiple AD-associated cognitive domains and AD-related CSF biomarkers at the clinical stages of AD. Moreover, plasma p-tau181 level is related to the change rates of cognitive decline and hippocampal atrophy. Thus, this study confirms the utility of plasma p-tau181 as a non-invasive biomarker for early detection and prediction of AD.

It is a crucial step locating the maize plant or even its target location precisely during the intelligent agricultural equipment working in farmland. Therefore, the segmentation of plants from the background image is one of the important research contents of agricultural machine vision. Under the background of significant color difference, the current method can effectively complete maize canopy segmentation and plant location identification. However, under the background of no-significant color difference, there is no robust and high-precision method for maize canopy segmentation and plant location identification. In this study, it was found that the grayscale of maize canopy had gradient distribution trend along the radial direction. The Hue Saturation Value color space and Support Vector Machine method was used to segment 600 maize canopy images, then the polynomial regression method was used to find out the functional relationship between grayscale gradient and canopy diameter. The functional relationship gave identification results of canopy central region under different gray gradient distribution. The result provided a theoretical basis for accurate identification and rapid location of maize plant center at seedling stage, and provided accurate position coordinate and yaw information for field navigation of agricultural intelligent equipment such as plant protection UAV.

Background: Depression is common in Alzheimer's disease (AD) with an unclear neural mechanism. This study aimed to investigate the underlying cerebral perfusion associated with depression in AD and evaluate its clinical significance.Method: Twenty-one AD patients and 21 healthy controls (HCs) were enrolled in this study. The depressive symptom was defined according to the Hamilton Depression Rating Scale (HAMD). Nine patients were diagnosed as AD with depression symptoms (HAMD >7). Three-dimensional pseudocontinuous arterial spin labeling MR imaging was conducted to measure regional cerebral blood flow (CBF). Neuropsychological tests covered cognition and depressive scores. Between-group comparisons on clinical variables and regional CBFs, relationship between regional CBF and depressive score, and identification of AD patients with depression were performed using covariance analysis, linear regression, and receiver operating characteristic (ROC) analysis, respectively.Results: Compared with HCs, AD patients without depression exhibited lower gray matter CBF (p = 0.016); compared with AD patients without depression, AD patients with depression had higher CBF in the right supplementary motor area (39.23 vs. 47.91 ml/100 g/min, p = 0.017) and right supramarginal gyrus (35.54 vs. 43.85 ml/100 g/min, p = 0.034). CBF in the right supplementary motor area was correlated with depressive score (β = 0.46, p = 0.025). The combination of CBF in the right supplementary motor area and supramarginal gyrus and age could identify AD patients with depression from those without depression with a specificity of 100%, sensitivity of 66.67%, accuracy of 85.71%, and area under the curve of 0.87.Conclusions: Our findings suggested that hyperperfusion of the right supplementary motor area and right supramarginal gyrus were associated with depression syndrome in AD, which could provide a potential neuroimaging marker to evaluate the depression state in AD.

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (VOC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of VOC have been well-established in the binary system; however, the understanding of VOC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased VOC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable VOC. Our results provide a perspective for understanding the origin of VOC in NFA-based ternary OSCs.

In this study, a quaternary blending strategy was applied in the fabrication of organic photovoltaic devices and large-area modules. As a result, the ultimate quaternary organic solar cells (OSCs) deliver 16.71% efficiency for small-area devices and 13.25% for large-area ( 19.34 cm 2 ) modules (certified as 12.36%), which is one of the highest efficiencies for organic solar modules to date. Our results have proved the synergistic effects of multiple components in OSCs, providing an effective strategy for achieving high-performance organic photovoltaic devices and modules.

In this paper, a positioning system is designed based on the visible light communication (VLC) technology for the tracking of mobile target in the indoor environment. The practical received signal strength (RSS) can be measured for subsequent positioning algorithm by using the designed system. Based on the practical measurements, an empirical equation is proposed to estimate the target's distances relative to the referenced LEDs. Then, taking advantage of the relative distances, the location estimation can be obtained by the trilateration method. Furthermore, Kalman Filter is used for improving the positioning result computed by trilateration method. Finally, experimental results show that the average location errors by adopting the derived empirical formula and trilateration can reach to 3.4cm, and the accuracy of positioning can be promoted to 2.6cm by using Kalman Filter in a real wireless environment.

Orthogonal frequency division multiplexing (OFDM) communication systems have great advantages, such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, this paper investigates an efficient utilization of both diversity combining and higher-level modulation (adaptive modulation) with a repetition code on the frequency domain in the OFDM systems. The repetition coded OFDM systems can achieve an improvement of performance with such a simple structure as one pair of transmit/receive antennas. In this paper, we derive simple closed-form equations for bit error probability (BEP) and throughput, and then improvements of those performances in the proposed OFDM systems are verified by both theoretical analysis and Monte Carlo simulation., Article, IEICE TRANSACTIONS ON COMMUNICATIONS. E94B(1):194-202 (2011)

Since the early 1970s, decision support systems (DSS) have evolved significantly. In this paper, the design and implementation of MSMiner, a developing platform for DSS, is introduced. The system is constructed on a data warehouse and integrated with a number of data mining algorithms. It is well suited for on-line analytical processing (OLAP). The characteristics of MSMiner include the ability to support multiple data sources and data mining strategies, additional organizational flexibility in regard to data and mining strategies, and the powerful expansibility of data mining tasks.

With the need of localization based services increasing, many algorithms are proposed using distance between two points and path loss exponent of the environment. In this paper, we propose an algorithm using received signal strength, Doppler Effect and frequency diversity in vehicular networks. The algorithm can estimate the path loss exponent and distance dynamically in mobile communication environment. And the higher the relative speed of vehicles, the better performance of the propose technique. We evaluate the performance of the proposed algorithm in the simulation and discuss the corresponding results.

In this paper, a new indoor positioning algorithm is proposed for mobile objects based on track smoothing. Considering the effects of indoor environment and the individual anchor nodes, the algorithm is realized in two filtering phases to modify the UWB range measurements and the trilateration localization results by the Unscented Kalman Filter, which reduces the influence of the additive non-Gaussian noise. Furthermore, the filtered positioning results of a mobile object are smoothed by a proposed adaptive smoothing algorithm, and the accuracy has been significantly improved with the positioning RMSE less than 0.8m and the maximum error is about 1m.

A novel cooperative spectrum sensing approach is introduced based on a approximate model of the power spectral density (PSD) map in space and frequency domain. This scheme uses a model coefficients estimator based the theory of Variational Bayesian Inference. It reveals the unknown positions of transmitting CRs and the spectrum holes in authorized frequency bands, by capitalizing on the forms of sparsity in Cognitive Radio Networks.

We experimentally demonstrate a visible light communication (VLC) system using pulse amplitude modulation (PAM). A commercially available phosphorised white LED is used as the optical transmitter and a Si photodiode (PD) is used as the optical receiver. The experiment is mainly implemented in an indoor environment which is influenced by the sunlight and fluorescent lamp. In variant conditions, the experimental results using 4-PAM and 2-PAM (i.e. on-off-keying (OOK)) and the related analysis are reported.

The research of localization has become a more and more important topic with the popularity of ubiquitous mobile computing. In indoor environment, since the global positioning system (GPS) is disabled, many miniaturized wireless and sensing technologies have shown giant potential in positioning applications such as Inertial Navigation. In this context, this paper present a methodology to locate and track pedestrians accurately in indoor scenarios, the proposed method employs the extended Kalman filter (EKF) to integration Received Signal Strength Indication (RSSI) measurements with the Inertial Navigation technology. Aiming at the cumulative errors existed in Pedestrian Dead Reckoning (PDR) algorithm, this method uses RSSI information as measurement vector of EKF to correct the cumulative errors. Experimental results show that the proposed fusion method can present more reliable positioning estimations.

In this paper, voice transmission is considered in visible light communication (VLC) systems. A digital voice transmission system is designed and analyzed for better quality and capacity than conventional analog voice transmission system. Commercially available white LED is used as the light source in this system, and to fit for the property of it, multi-level pulse code modulation (MPCM) is chosen as the VLC modulation method. A set of system prototype is developed by mainly using the field-programmable gate array (FPGA). Testing results of the prototype show that the system is reasonable and stable.

In this paper, to improve the data transmission rate, visible light communication (VLC) system based on multi-level pulse code modulation (MPCM) is considered. This system uses different brightness level of the visible light signals to realize the multi-level modulation, thus a high data transmission rate, which is several times of that in 2-level modulation system, can be achieved. The overall design of the system is firstly considered. Then with 4-level modulation as an example, a set of system prototype is developed. Testing results of the prototype show that the system is reasonable and stable. Therefore, it is proved that applying the MPCM in VLC system is feasible and effective.

In this paper, an intercarrier interference (ICI) suppression method for frequency domain differential orthogonal frequency division multiplexing (OFDM) systems with multiple symbol differential detection (MSDD) in time-varying frequency-selective fading channels is proposed. The decision metric is derived by considering the statistical effects of ICI from all the subcarriers as well as considering the fading autocorrelations. Knowledges of transmitted signals from both inner and outer subcarriers of an MSDD observation interval can be used to estimate and mitigate the effects of ICI. The effectiveness of the proposed method is demonstrated by computer simulations.

In this paper, the diversity reception of differential space-time block coding (STBC) system using multiple-symbol differential detection (MSDD) method with multiple receive antennas is considered. Postdetection maximum ratio combining (MRC), postdetection equal-gain combining (EGC) and predetection selective combining (SC) are used as diversity combining techniques. Their performance is analyzed by computer simulations

How to get text information from this huge information space becomes a more important problem with the rapid growth of the Internet. A semantic indexing system GHUNT based on concept space is proposed to solve the problem. Some new technologies are integrated in GHUNT to obtain good performance. GHUNT is an all-sided solution for information retrieval on the Internet.