Wideband Beamforming for STAR-RIS-assisted THz Communications with Three-Side Beam Split

In this paper, we consider the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-assisted THz communications with three-side beam split. Except for the beam split at the base station (BS), we analyze the double-side beam split at the STAR-RIS for the first time. To relieve the double-side beam split effect, we propose a time delayer (TD)-based fully-connected structure at the STAR-RIS. As a further advance, a low-hardware complexity and low-power consumption sub-connected structure is developed, where multiple STAR-RIS elements share one TD. Meanwhile, considering the practical scenario, we investigate a multi-STAR-RIS and multi-user communication system, and a sum rate maximization problem is formulated by jointly optimizing the hybrid analog/digital beamforming, time delays at the BS as well as the double-layer phase-shift coefficients, time delays and amplitude coefficients at the STAR-RISs. Based on this, we first allocate users for each STAR-RIS, and then derive the analog beamforming, time delays at the BS, and the double-layer phase-shift coefficients, time delays at each STAR-RIS. Next, we develop an alternative optimization algorithm to calculate the digital beamforming at the BS and amplitude coefficients at the STAR-RISs. Finally, the numerical results verify the effectiveness of the proposed schemes

Beamforming Design for the Distributed RISs-aided THz Communications with Double-Layer True Time Delays

In this paper, we investigate the reconfigurable intelligent surface (RIS)-aided terahertz (THz) communication system with the sparse radio frequency chains antenna structure at the base station (BS). To overcome the beam split of the BS, different from the conventional single-layer true-time-delay (TTD) scheme, we propose a double-layer TTD scheme that can effectively reduce the number of large-range delay devices, which involve additional insertion loss and amplification circuitry. Next, we analyze the system performance under the proposed double-layer TTD scheme. To relieve the beam split of the RIS, we consider multiple distributed RISs to replace an ultra-large size RIS. Based on this, we formulate an achievable rate maximization problem for the distributed RISs-aided THz communications via jointly optimizing the hybrid analog/digital beamforming, time delays of the double-layer TTD network and reflection coefficients of RISs. Considering the practical hardware limitation, the finite-resolution phase shift, time delay and reflection phase are constrained. To solve the formulated problem, we first design an analog beamforming scheme including optimizing phase shift and time delay based on the RISs' locations. Then, an alternatively optimization algorithm is proposed to obtain the digital beamforming and reflection coefficients based on the minimum mean square error and coordinate update techniques. Finally, simulation results show the effectiveness of the proposed scheme

Beamforming Analysis and Design for Wideband THz Reconfigurable Intelligent Surface Communications

Reconfigurable intelligent surface (RIS)-aided terahertz (THz) communications have been regarded as a promising candidate for future 6G networks because of its ultra-wide bandwidth and ultra-low power consumption. However, there exists the beam split problem, especially when the base station (BS) or RIS owns the large-scale antennas, which may lead to serious array gain loss. Therefore, in this paper, we investigate the beam split and beamforming design problems in the THz RIS communications. Specifically, we first analyze the beam split effect caused by different RIS sizes, shapes and deployments. On this basis, we apply the fully connected time delayer phase shifter hybrid beamforming architecture at the BS and deploy distributed RISs to cooperatively mitigate the beam split effect. We aim to maximize the achievable sum rate by jointly optimizing the hybrid analog/digital beamforming, time delays at the BS and reflection coefficients at the RISs. To solve the formulated problem, we first design the analog beamforming and time delays based on different RISs physical directions, and then it is transformed into an optimization problem by jointly optimizing the digital beamforming and reflection coefficients. Next, we propose an alternatively iterative optimization algorithm to deal with it. Specifically, for given the reflection coefficients, we propose an iterative algorithm based on the minimum mean square error technique to obtain the digital beamforming. After, we apply LDR and MCQT methods to transform the original problem to a QCQP, which can be solved by ADMM technique to obtain the reflection coefficients. Finally, the digital beamforming and reflection coefficients are obtained via repeating the above processes until convergence. Simulation results verify that the proposed scheme can effectively alleviate the beam split effect and improve the system capacity

Antiviral biflavonoids from Radix Wikstroemiae (Liaogewanggen)

<p>Abstract</p> <p>Background</p> <p><it>Radix Wikstroemiae </it>is a common Chinese herbal medicine. The ethyl acetate fraction of the ethanolic extract of <it>W. indica </it>possesses potent <it>in vitro </it>antiviral activity against respiratory syncytial virus (RSV). This study aims to identify the antiviral components of the active fraction.</p> <p>Methods</p> <p>The active fraction of the <it>Radix Wikstroemiae </it>extract was isolated with chromatographic methods such as silica gel, Sephadex LH-20 and semi-preparative high performance liquid chromatography (HPLC) columns. The structures of the isolated compounds were determined based on spectroscopic analyses. The <it>in vitro </it>antiviral activity of the compounds against RSV was tested with the cytopathic effect (CPE) reduction assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method.</p> <p>Results</p> <p>Four biflavonoids, namely neochamaejasmin B, genkwanol B, genkwanol C and stelleranol, were isolated and characterized. Genkwanol B, genkwanol C and stelleranol, which are stereo isomers of spirobiflavonoids, showed potent anti-RSV activity whereas neochamaejasmin B did not.</p> <p>Conclusion</p> <p>Neochamaejasmin B, genkwanol B, genkwanol C and stelleranol were isolated from <it>Radix Wikstroemiae </it>and the complete absolute configurations of five chiral carbons in stelleranol were substantiated for the first time. Furthermore, the anti-RSV activity of genkwanol B, genkwanol C and stelleranol was reported for the first time.</p

A high-stability single pumped L-band superfluorescent fiber source for the fiber optic gyroscope

In this paper, a simple single-backward configuration with a section of un-pump fiber is presented to achieve a stable L-band superfluorescent fiber source (SFS). The effects of the structural parameters on the output characteristics of the L-band SFS in terms of output spectrum, mean wavelength, and linewidth are theoretically examined. By selecting suitable structure parameters, an L-band SFS with mean wavelength insensitive to pump power is achieved under a pump power of 190mW, corresponding to a mean wavelength of 1583.20nm, an output power of 47mW, and a spectral linewidth of 49.6nm. The proposed L-band SFS design shows its tremendous advantages as simple structure and good performances that make it be useful in WDM system, fiber optic gyroscopes and fiber sensor systems applications

A hybrid solar energy generation system using photovoltaic and thermoelectrics

With an increasing demand on energy conservation, there is a fast growing interest in the area of renewable energy so as to reduce the amounts of fossil fuels burned and to reduce global warming. Renewable energy makes it more environmentally friendly and also reduces the cost of electricity. Due to the limited resources and land available, one of the most promising forms of renewable energy is solar energy, given that Singapore is situated near the equatorial sun-belt that has approximately 12 hours of sunlight in a day. The student will investigate the amount of solar energy that could be generated by the photovoltaic cells. Depending on the composite materials used in manufactured photovoltaic cells, it would result in a difference to the cells’ efficiency and cost. The student will be using a super-capacitor bank for the experiment to obtain the amount of energy harvested from the sunlight to the PV cells. The student will also investigate on the thermoelectric device which could convert heat into electricity. Thermoelectric device can operate in two different modes: as a thermoelectric generator (TEG) or a cooler (TEC). In the experiment, the student will only focus on the power generation and the amount of energy stored in the capacitor. The efficiency of the device is relatively low compared to the photovoltaic cells. Thus, photovoltaic cells are often used as they have a higher efficiency as compared to thermoelectric devices.Bachelor of Engineerin

A survey of health information techology development in public hospitals Guangzhou between 2008-2010

Objective: In order to evaluate the current situation of health information technology (HIT) in Guangzhou, to assess the different status of HIT between different classifications of public hospitals, and find out the influencing factors, to identify the core barriers affecting the development of HIT, I conducted a comprehensive survey, to analyze the framework of HIT from various aspects. Through this study, we would accurately grasp the development level of HIT in Guangzhou, and provide basic information for guideline making in the future. Methods: This is a cross-sectional & descriptive study design. I was responsible for organizing the survey, and monitoring the project cycle and work on a regular basis. I designed the questionnaire based on “The questionnaire of the development situation of national health information technology in 2009 in China”. Cluster sampling method was used, 415 public hospitals (based on the health statistics in Guangzhou in 2009) were selected for the analysis. I sent the questionnaires to all these public hospitals, and collected and entered the data with my colleague Miss LIU. I analyzed the data and wrote up the report solely by myself. At the other side, in order to evaluate the acceptance of HIT among different stakeholders, an interview was conducted by two interviewers among 20 public hospitals (using systematic sampling method, every 10th public hospital was selected). What’s more, in order to explore the characteristics of the development status of HIT in Guangzhou, diverse approaches like descriptive statistics, linear regression, t-test, and chi-square were used for the analysis. Outcome measures: Basic information of public hospitals includes the classifications of the public hospitals; the usage status of basic infrastructure, including the utilization rates of a variety of hardware, system software, new technologies and standards; the application situation of information system, including the utilization rates of a variety of information systems, such as HIS, LIS, PACS, EHR and RHIS; the status of input of funding. In addition, the information includes the core barriers affecting the development of HIT and the acceptance of HIT. Results: 205 of the public hospitals participated in this study, and the total response rate was 49.4%. Data showed that 91% of the public hospitals adopted at least one standard; 36.3% of them had established the Main Patient Index (MPI); 34.8%, 29.4.0%, 31.5% and 37.8% of the public hospitals implemented the Inpatient Doctor Workstation System, Inpatient Nurse Workstation System, Electronic Medical Records (EMR) and Laboratory Information System (LIS), respectively. Only12.1% of the public hospitals had participated in the development of region health information system (RHIS). Besides, “high speed Ethernet”, “bar code technology” and “data safety technology” were the top three information technologies in public hospitals, and the utilization rates were 91.2%, 44.1% and 29.4% respectively. In addition, the top three main barriers were “lack of funding”, “human resources which is not enough” and “on the part of device makers or software developers their lack of abilities to provide products and services”, these three accounted for 84.8%, 56.9% and 47.1% respectively. Data showed that the total investments were 235 million RMB, 270 million RMB and 320 million RMB in 2008, 2009 and 2010, respectively. On average, the accumulative total investments had doubled digit growth in the past 3 years. [1, 2] Conclusion: In general, data displayed that public hospitals in Guangzhou had made significant progress in HIT development in the past few years, which has greatly contributed to hospital management and the delivery of healthcare services. In recent years, there were increasing investments, more and more public hospitals began to implement HIT, a large number of new technologies were used (such RFID, cloud computing), and certain core information systems, liking HIS, LIS, PACS, EMR and RHIS were implemented. At the other side, the development direction of HIT had shifted from hospital management stage to clinical information stage. Although the process of health information in Guangzhou was rapidly developing in the past few years, however, there still have many barriers and shortages in it, for instance, shortage of IT professional and lack of funding are still the main factors that affects the development of HIT; the overall utilization level of basic infrastructure is still not satisfied; the development of information systems is unbalanced, meanwhile the breadth and depth of the information systems are not well enough.published_or_final_versionPublic HealthMasterMaster of Public Healt