Active Reconfigurable Intelligent Surface Aided Wireless Communications

Reconfigurable Intelligent Surface (RIS) is a promising solution to reconfigure the wireless environment in a controllable way. To compensate for the double-fading attenuation in the RIS-aided link, a large number of passive reflecting elements (REs) are conventionally deployed at the RIS, resulting in large surface size and considerable circuit power consumption. In this paper, we propose a new type of RIS, called active RIS, where each RE is assisted by active loads (negative resistance), that reflect and amplify the incident signal instead of only reflecting it with the adjustable phase shift as in the case of a passive RIS. Therefore, for a given power budget at the RIS, a strengthened RIS-aided link can be achieved by increasing the number of active REs as well as amplifying the incident signal. We consider the use of an active RIS to a single input multiple output (SIMO) system. {However, it would unintentionally amplify the RIS-correlated noise, and thus the proposed system has to balance the conflict between the received signal power maximization and the RIS-correlated noise minimization at the receiver. To achieve this goal, it has to optimize the reflecting coefficient matrix at the RIS and the receive beamforming at the receiver.} An alternating optimization algorithm is proposed to solve the problem. Specifically, the receive beamforming is obtained with a closed-form solution based on linear minimum-mean-square-error (MMSE) criterion, while the reflecting coefficient matrix is obtained by solving a series of sequential convex approximation (SCA) problems. Simulation results show that the proposed active RIS-aided system could achieve better performance over the conventional passive RIS-aided system with the same power budget

Ring Chromosome 7 Presenting with Intrauterine Growth Restriction and Multiple Anomalies

SummaryObjectiveRing chromosome 7 is a very rare chromosomal anomaly that may have a grave prognosis. Nevertheless, the clinical features associated with ring chromosome 7 are highly variable. Here, we report a case with ring chromosome 7 and the perinatal findings.Case ReportA 32-year-old, gravida 1, para 0, woman was referred to our hospital because of intrauterine growth restriction (IUGR) and oligohydramnios at 35 weeks of gestation. Prenatal ultrasound revealed a severe IUGR fetus presenting with multicystic kidney, hydronephrosis and oligohydramnios. At parturition, the birth weight of this male infant was 1,720 g, and a battery of anomalies were also noted, including imperforate anus, hypospadia, micropenis, right cryptorchidism, severe IUGR, multiple nevi on the forehead, shoulder and left thigh, brain atrophy, right multicystic kidney, and left mild hydronephrosis. Cytogenetic study from cord blood revealed a ring chromosome 7.ConclusionRing chromosome 7 is extremely rare and our case might be the 15th and youngest case in the medical literature. Our case had multicystic kidney and imperforate anus, which have not been reported previously. Prenatal diagnosis of ring chromosome 7 is very difficult. When fetuses present with severe IUGR, oligohydramnios and multicystic kidney, chromosomal aberrations should be kept in mind, and perinatal cytogenetic workup is warranted

Modulation Design and Optimization for RIS-Assisted Symbiotic Radios

In reconfigurable intelligent surface (RIS)-assisted symbiotic radio (SR), the RIS acts as a secondary transmitter by modulating its information bits over the incident primary signal and simultaneously assists the primary transmission, then a cooperative receiver is used to jointly decode the primary and secondary signals. Most existing works of SR focus on using RIS to enhance the reflecting link while ignoring the ambiguity problem for the joint detection caused by the multiplication relationship of the primary and secondary signals. Particularly, in case of a blocked direct link, joint detection will suffer from severe performance loss due to the ambiguity, when using the conventional on-off keying and binary phase shift keying modulation schemes for RIS. To address this issue, we propose a novel modulation scheme for RIS-assisted SR that divides the phase-shift matrix into two components: the symbol-invariant and symbol-varying components, which are used to assist the primary transmission and carry the secondary signal, respectively. To design these two components, we focus on the detection of the composite signal formed by the primary and secondary signals, through which a problem of minimizing the bit error rate (BER) of the composite signal is formulated to improve both the BER performance of the primary and secondary ones. By solving the problem, we derive the closed-form solution of the optimal symbol-invariant and symbol-varying components, which is related to the channel strength ratio of the direct link to the reflecting link. Moreover, theoretical BER performance is analyzed. Finally, simulation results show the superiority of the proposed modulation scheme over its conventional counterpart.Comment: 16 pages,15 figure

Existence theorems for a crystal surface model involving the p-Laplace operator

The manufacturing of crystal films lies at the heart of modern nanotechnology. How to accurately predict the motion of a crystal surface is of fundamental importance. Many continuum models have been developed for this purpose, including a number of PDE models, which are often obtained as the continuum limit of a family of kinetic Monte Carlo models of crystal surface relaxation that includes both the solid-on-solid and discrete Gaussian models. In this paper we offer an analytical perspective into some of these models. To be specific, we study the existence of a weak solution to the boundary value problem for the equation - \Delta e^{-\mbox{div}\left(|\nabla u|^{p-2}\nabla u\right)}+au=f, where $p>1, a>0$ are given numbers and $f$ is a given function. This problem is derived from a crystal surface model proposed by J.L.~Marzuola and J.~Weare (2013 Physical Review, E 88, 032403). The mathematical challenge is due to the fact that the principal term in our equation is an exponential function of a p-Laplacian. Existence of a suitably-defined weak solution is established under the assumptions that $p\in(1,2], \ N\leq 4$, and $f\in W^{1,p}$. Our investigations reveal that the key to our existence assertion is how to control the set where -\mbox{div}\left(|\nabla u|^{p-2}\nabla u\right) is $\pm\infty$

Effects of orthographic consistency and homophone density on Chinese spoken word recognition

Studies of alphabetic language have shown that orthographic knowledge influences phonological processing during spoken word recognition. This study utilized the Event-Related Potentials (ERPs) to differentiate two types of phonology-to-orthography (P-to-O) mapping consistencies in Chinese, namely homophone density and orthographic consistency. The ERP data revealed an orthographic consistency effect in the frontal-centrally distributed N400, and a homophone density effect in central-posteriorly distributed late positive component (LPC). Further source analyses using the standardized low-resolution electromagnetic tomography (sLORETA) demonstrated that the orthographic effect was not only localized in the frontal and temporal-parietal regions for phonological processing, but also in the posterior visual cortex for orthographic processing, while the homophone density effect was found in middle temporal gyrus for lexical-semantic selection, and in the temporal-occipital junction for orthographic processing. These results suggest that orthographic information not only shapes the nature of phonological representations, but may also be activated during on-line spoken word recognition

The feedback consistency effect in Chinese character recognition:evidence from a psycholinguistic norm

Researchers have demonstrated the importance of phonology in literacy acquisition and in visual word recognition. For example, the spelling-to-sound consistency effect has been observed in visual word recognition tasks, in which the naming responses are faster and more accurate for words with the same letters that also have the same pronunciation (e.g. -ean is always pronounced /in/, as in lean, dean, and bean). In addition, some studies have reported a much less intuitive feedback consistency effect when a rime can be spelled in different ways (e.g. /ip/ in heap and deep) in lexical decision tasks. Such findings suggest that, with activation flowing back and forth between orthographic and phonological units during word processing, any inconsistency in the mappings between orthography and phonology should weaken the stability of the feedback loop, and, thus, should delay recognition. However, several studies have failed to show reliable feedback consistency in printed word recognition. One possible reason for this is that the feedback consistency is naturally confounded with many other variables, such as orthographic neighborhood or bigram frequency, as these variables are difficult to tease apart. Furthermore, there are challenges in designing factorial experiments that perfectly balance lexical stimuli on all factors besides feedback consistency. This study aims to examine the feedback consistency effect in reading Chinese characters by using a normative data of 3,423 Chinese phonograms. We collected the lexical decision time from 180 college students. A linear mixed model analysis was used to examine the feedback consistency effect by taking into account additional properties that may be confounded with feedback consistency, including character frequency, number of strokes, phonetic combinability, semantic combinability, semantic ambiguity, phonetic consistency, noun-to-verb ratios, and morphological boundedness. Some typical effects were observed, such as the more frequent and familiar a character, the faster one can decide it is a real character. More importantly, the linear mixed model analysis revealed a significant feedback consistency effect while controlling for other factors, which indicated that the pronunciation of phonograms might accommodate the organization of Chinese orthographic representation. Our study disentangled the feedback consistency from the many other factors, and supports the view that phonological activation would reverberate to orthographic representation in visual word recognition