Virtual References Research Articles

Current coordinated distribution and voltage optimization control for multi-VSGs system considering nonlinear and negative sequence loads

In a microgrid system where multiple virtual synchronous generators (VSGs) are interconnected through high impedance cables, the total output negative sequence and harmonic current of multiple VSGs cannot be coordinated based on the capacity of each power conversion system (PCS). In addition, there is significant distortion in the voltage at the point of common coupling (PCC). Because the impedance amplitude and impedance angle of the cable change with the harmonic frequency, the resistive virtual impedance reshaping method and fixed impedance angle virtual impedance reshaping method used in the current research cannot solve the harmonic current distribution problem. To solve the above problems, a multi-frequency points VSG impedance reshaping control strategy is proposed in this paper, which can adjust the resistive and inductive output impedance of each harmonic frequency independently. The strategy is based on the harmonic separation algorithm of LPF with Feedforward Compensation (FCLPF) and the voltage controller of Vector Proportional Integral (VPI) in fundamental dq rotation coordinate system, which effectively improve the flexibility and accuracy of harmonic impedance reshaping. Among them, FCLPF harmonic separation algorithm has the characteristics of target frequency bandpass and non-target frequency notch, and can eliminate the coupling interference of each harmonic virtual impedance when accumulating virtual impedance voltage references at various frequency points. The closed-loop transfer function of the multi-parallel VPI voltage controller has the characteristics of unit gain and zero phase shift at each harmonic frequency point, which means the static response error of virtual impedance voltage command can be almost completely eliminated. Under the proposed control strategy, the fundamental positive power can be allocated according to the droop coefficient, the fundamental negative current and harmonic current can be allocated according to the sum of the reshaped virtual impedance and the actual line impedance. Reshaping virtual impedance at each harmonic frequency to negative value can also compensate the harmonic voltage drop on the high impedance cable and improve the voltage quality at the PCC.

Perceived awareness and usefulness of artificial intelligence technology for efficient library operations in university libraries in Kwara State, Nigeria

The integration of artificial intelligence technology in academic libraries has immensely elevated the image of their operations and services to users. This study investigates the perceived awareness and usefulness of artificial intelligence technology for library operations in Kwara State academic libraries. Descriptive survey design was adopted for this study and the population consisted of 108 librarians and paraprofessionals in all university libraries in Kwara State which are University of Ilorin, Kwara State university Malete, Al Hikmah University, Ojaja , University, Eyenkorin, Landmark University, Omu Aran, and Ahmad Pategi University, Patigi. A total enumeration technique was employed and questionnaire was used to collect data from the respondents. Data collected wewre analysed with frequency counts and simple percentages. Findings revealed that AI Robots, AI chatbots, face recognition technology, virtual references, Humanoids, Dynamed and AI expert systems are the AI technologies the respondents were highly aware of. The respondents perceived the usefulness of AI technologies for efficient library operations such as AI chatbots can be useful for reference services, AI can used for cataloguing and classification of library materials, AI drone surveillance can be used for library security, AI expert search tools for information search, AI can be useful for automating library routines. The findings also revealed the challenges of artificial intelligence technology integration to library operations to includes potential loss of job, high risk of maintenance, inadequate internet service provision, technical problems, epileptic electricity or power supply, and Inadequate ICT facilities for AI technologies. This study concluded that the librarians in university libraries in Kwara State are aware of AI technology and perceived the usefulness of its integration to library operations. It also recommends that AI technologies such as robots, chatbots, and expert systems should be integrated to libraries in other to provide top-notch services to their users.

Health Information From Web Search Engines and Virtual Assistants About Pre-Exposure Prophylaxis for HIV Prevention in Adolescents and Young Adults: Content Analysis.

Adolescents and young adults are disproportionately affected by HIV, suggesting that HIV prevention methods such as pre-exposure prophylaxis (PrEP) should focus on this group as a priority. As digital natives, youth likely turn to internet resources regarding health topics they may not feel comfortable discussing with their medical providers. To optimize informed decision-making by adolescents and young adults most impacted by HIV, the information from internet searches should be educational, accurate, and readable. The aims of this study were to compare the accuracy of web-based PrEP information found using web search engines and virtual assistants, and to assess the readability of the resulting information. Adolescent HIV prevention clinical experts developed a list of 23 prevention-related questions that were posed to search engines (Ask.com, Bing, Google, and Yahoo) and virtual assistants (Amazon Alexa, Microsoft Cortana, Google Assistant, and Apple Siri). The first three results from search engines and virtual assistant web references, as well as virtual assistant verbal responses, were recorded and coded using a six-tier scale to assess the quality of information produced. The results were also entered in a web-based tool determining readability using the Flesch-Kincaid Grade Level scale. Google web search engine and Google Assistant more frequently produced PrEP information of higher quality than the other search engines and virtual assistants with scores ranging from 3.4 to 3.7 and 2.8 to 3.3, respectively. Additionally, the resulting information generally was presented in language at a seventh and 10th grade reading level according to the Flesch-Kincaid Grade Level scale. Adolescents and young adults are large consumers of technology and may experience discomfort discussing their sexual health with providers. It is important that efforts are made to ensure the information they receive about HIV prevention methods, and PrEP in particular, is comprehensive, comprehensible, and widely available.

Effect of angulation on the 3D trueness of conventional and digital implant impressions for multi-unit restorations.

The study aimed to determine the influence of implant angulation on the trueness of multi-unit implant impressions taken through different techniques and strategies. As reference models, three partially edentulous mandibular models (Model 1: No angulation; Model 2: No angulation for #33, 15-degree distal angulation for #35 and #37; Model 3: No angulation for #33, 25-degree distal angulation for #35 and #37) were created by modifying the angulations of implant analogues. Using a lab scanner, these reference models were scanned. The obtained data were preserved and utilized as virtual references. Three intraoral scanning (IOS) strategies: IOS-Omnicam, ISO-Quadrant, and IOS-Consecutive, as well as two traaditional techniques: splinted open tray (OT) and closed tray (CT), were used to create impressions from each reference model. The best-fit alignment approach was used to sequentially superimpose the reference and test scan data. Computations and statistical analysis of angular (AD), linear (LD), and 3D deviations (RMS) were performed. Model type, impression technique, as well as interaction factor, all demonstrated a significant influence on AD and LD values for all implant locations (P < .05). The Model 1 and SOT techniques displayed the lowest mean AD and LD values across all implant locations. When considering interaction factors, CT-Model 3 and SOT-Model 1 exhibited the highest and lowest mean AD and LD values, respectively. Model type, impression technique, and interaction factor all revealed significant effects on RMS values (P ≤ .001). CT-Model 3 and SOT-Model 1 presented the highest and lowest mean RMS values, respectively. Splinted-OT and IOS-Omnicam are recommended for multi-unit implant impressions to enhance trueness, potentially benefiting subsequent manufacturing stages.

Reference Modulation for High-Quality Scan Images of 2-D Laser Scanner Systems

For laser scanner systems, the most critical issue for high-quality images is the linearity of the slow axis. The laser scanner systems have various disturbances and uncertainties, such as manufacturing tolerances, structure vibrations, and parameter uncertainties. Further, there are vertical and horizontal resonance modes that hinder controller design. In this letter, we propose a reference modulation technique to enhance the vertical angle linearity of the slow axis for two-dimensional laser scanner systems. First, the laser scanner system is mathematically modeled in the state-space form. Then, the reference modulation is designed to boost the loop gain over the desired frequency range. The reference modulation can guarantee high-quality scan images by redesigning the desired reference based on the output feedback. The current tracking controller was then implemented with virtual references for the states. We investigated its tracking performance via sensitivity function analysis against the disturbances. Experiments were performed to evaluate the effectiveness of the proposed method using four different laser scanners. We confirmed that the proposed method achieved up to 48% improvement in the angle tracking error from the experimental results.

Source decomposition and reduced-order modeling of an installed F404-GE-103 engine using the optimized-location virtual reference method

Principal component analysis-related methods (i.e., proper orthogonal decomposition or partial field decomposition) are used widely in aeroacoustic applications for source characterization and reduced-order modeling. A previous paper [A. T. Wall et al., J. Acoust. Soc. Am. 144, 1356 (2018)] developed a coherence-based, virtual-reference method for performing physically meaningful PFD known as the optimized-location virtual references (OLVR) method. This paper performs a source decomposition using the OLVR method on acoustical holography data from an installed GE F404 engine. The OLVR-derived partial fields are compared with far-field radiation characteristics and partial equivalent sources are fitted to analytical wavepackets. Characteristics of this reduced-order model are discussed as a function of frequency and engine condition. [Work supported ONR Grant No. N00014-21-1-2069.]

Backstepping Controller Design of Maglev System for Air-gap Position Control

Since the magnetic levitation system is nonlinear, linearization of the system is required to use linear control method in nonlinear system, and the stability and control performance cannot be guaranteed. To solve this problem, a nonlinear control system should be designed. In this paper, backstepping control (BSC) is proposed for position control in maglev systems. For the design of BSC, three Lyapunov functions are defined, and a virtual reference is obtained based on the Lyapunov stability theorem. Based on the virtual velocity and current references, the control input is designed to guarantee the stability of the control system. The proposed control system is implemented using MATLAB/Simulink, and tracking and disturbance performance analyses are performed. As a result, using state feedback control the performance of the proposed control system is verified through comparison with conventional control system.

The prospect of virtual references: focused on reference questions and the automation of virtual references

The prospect of virtual references: focused on reference questions and the automation of virtual references

STRATEGI PR INDONESIA DALAM MEMBANGUN CORPORATE REPUTATION MELALUI EVENT JAMBORE PR INDONESIA (JAMPIRO)

In establishing an excellent corporation's reputation, PR Indonesia, an Indonesian public relations magazine company, holds an award event every year, the Jambore PR Indonesia. This jamboree event is for all Indonesian public relations figures, both public relations who work for the government and private companies. However, during Covid-19, this event's euphoria could not be felt entirely even though PR Indonesia had tried to establish its reputation by innovating the event virtually online. Therefore, this study aimed to explore PR Indonesia's strategy in establishing corporate reputation from a virtual event, Jambore PR Indonesia (JAMPIRO), by using corporate reputation theory, event theory, and virtual event. The qualitative method was applied to this research. Interpretative research paradigm and cases study approach were also used. The data collections were obtained by using observation, interview and documentation. The research results showed that PR Indonesia had several strategies to build corporate reputation. They conducted city tours, researched public relations’ issues, and discussed with public relations specialists to find new ideas and used PR's Icon as brand reputation. Those corporate reputation strategies created the JAMPIRO event, which was promoted in offline and online media. Looking for event references, keeping participants' trust, and holding JAMPIRO events in various cities were also the other strategies. Hence, during the Covid-19 pandemic, PR Indonesia invented many innovations by creating virtual events to maintain its reputation. The maneuverings were to run online promotions, find virtual event references, create innovative events, determine the virtual event's criteria and hold the low-cost event.

The Ukrainian medical libraries network digital services development strategy

The relevance of the study. The digital revolution has had a significant effect on the functioning of libraries. Successful operation in the digital environment requires the improvement of the competitiveness of library services provided: libraries must be able to rethink their role, justify the value of their services for their own customers. Due to the increasing level of the Internet use among scientists, medical professionals, students, patients, community, medical libraries web-presence is of crucial importance. Websites serve as a digital gateway for library services and resources.&#x0D; The aim of the article is to study and present the current state of Ukrainian medical libraries service and to propose the digital services development strategy.&#x0D; The methodology. A content analysis was conducted over 21 Ukrainian and 5 foreign medical library websites. All data were collected within a month. Research data are presented in the form of tables and figures and analyzed using a simple method of percentages.&#x0D; The results. The findings show that many researched Ukrainian medical libraries are yet to exploit the full potential of the digital technologies in library service. The most common services: online public access catalog, virtual references services, identification UDC index, repository, electronic document delivery service (EDDS). Less than half (43%) of medical library sites in Ukraine are adapted to mobile devices. The most popular social media among medical libraries in Ukraine: Facebook (57%), Instagram (33%) and YouTube (29%). Over the last 5 years, libraries have become more active in offering web-based services and resources: plagiarism testing services, repositories, EDDS, virtual references services, identification UDC index. The main strategic objectives of the digital services development for medical libraries in Ukraine should be: increasing the web and social media presence, introducing mobile technologies, improving communication between the library and users, developing services to support research lifecycle, interdisciplinary partnership, support for information literacy of biomedical professionals and medical literacy of the community, developing competences of the medical librarians, corporate cooperation of the Ukrainian medical libraries system.&#x0D; The scientific topicality. The current state of Ukrainian medical libraries digital service was analyzed and compared with the state of five years ago and foreign academic medical libraries. Digital services development strategy was proposed.&#x0D; The practical significance. The study can be very interesting and important for medical librarians for upgrading, creation and support of relevant medical library services.

Partial-field decomposition analysis of full-scale supersonic jet noise using optimized-location virtual references.

Supersonic jet noise reduction efforts benefit from targeted source feature extraction and high-resolution acoustic imaging. Another useful tool for feature extraction is partial field decomposition of sources into independent contributors. Since such decomposition processes are nonunique, care must be taken in the physical interpretation of decomposed partially coherent aeroacoustic fields. The optimized-location virtual reference method (OLVR) is a partial field decomposition designed to extract physically meaningful source and field information through the strategic placement of virtual references within a reconstructed field. The OLVR method is applied here to obtain spatially distinct and ordered partial sources at multiple frequencies of a full-scale, high-performance supersonic jet engine operating at 100% engine power. Partial sources are shown to mimic behaviors of the total source distributions including monotonic growth and decay. Because of finite spatial coherence, multiple partial sources are used to reproduce far-field radiation away from the main lobe, and the number of required sources increases with increasing frequency. An analytical multiwavepacket model is fitted to the partial sources to demonstrate how OLVR partial fields can be leveraged to produce reduced-order models.

The diversity of lexicographic references

Based on the author’s detailed analysis of the archive of completed references, the specific classification of lexicographic references is introduced. The virtual lexicographical references are the result of joint efforts of bibliographers and lexicographers. This type of reference holds a specific place in bibliographic reference user service. Polyfunctionality and specific diversity make information specific features of this type of references. The focus is made on the subtypes of the lexicographic references; the examples are provided. Potential lexicographical and bibliographic services are suggested for the libraries’ virtual environment to support user self-education and self-service and intensive use of lexicographic information. The article is complemented by the table to present the classification of lexicographic virtual references.

Adaptive Reference Model Predictive Control With Improved Performance for Voltage-Source Inverters

Power converters under the model predictive control (MPC) inherently suffer from nonignorable steady-state residuals in its control outputs when it exists a mismatch in the parameters between the actual system in control and the system’s model adopted in the control. In this brief, an adaptive reference MPC (ARMPC) is proposed in response to this issue. Unlike those conventional derivatives of MPC, the ARMPC is designed to track the so-called virtual references instead of the actual references. The virtual references are generated by a flexibly modeled virtual multiple input multiple output system. Consequently, additional tuning is not required for different operating conditions. ARMPC has been applied to a single-phase full-bridge voltage-source inverter with both resistive and resistive-inductive loads. It is experimentally verified that the proposed ARMPC can significantly attenuate the steady-state offsets in the environment of model mismatch (which is an inherent problem of MPC without significantly sacrifice transient performance). Also, a demonstration that ARMPC renders a consistent attenuation of steady-state errors than the conventional MPC with integrator is provided. More importantly, ARMPC shows better transient performance than the MPC with integrator for some cases.

Development of a patient-specific atrial phantom model for planning and training of inter-atrial interventions.

Several authors have presented cardiac phantoms to mimic the particularities of the heart, making it suitable for medical training and surgical planning. Although the initial models were mainly focused on the ventricles, personalized phantoms of the atria were recently presented. However, such models are typically rigid, the atrial wall is not realistic and they are not compatible with ultrasound (US), being sub-optimal for planning/training of several interventions. In this work, we propose a strategy to construct a patient-specific atrial model. Specifically, the target anatomy is generated using a computed tomography (CT) dataset and then constructed using a mold-cast approach. An accurate representation of the inter-atrial wall (IAS) was ensured during the model generation, allowing its application for IAS interventions. Two phantoms were constructed using different flexible materials (silicone and polyvinyl alcohol cryogel, PVA-C), which were then compared to assess their appropriateness for US acquisition and for the generation of complex anatomies. Two experiments were set up to validate the proposed methodology. First, the accuracy of the manufacturing approach was assessed through the comparison between a post-production CT and the virtual references. The results proved that the silicone-based model was more accurate than the PVA-C-based one, with an error of 1.68±0.79, 1.36±0.94, 1.45±0.77mm for the left (LA) and right atria (RA) and IAS, respectively. Second, an US acquisition of each model was performed and the obtained images quantitatively and qualitatively assessed. Both models showed a similar performance in terms of visual evaluation, with an easy detection of the LA, RA, and the IAS. Furthermore, a moderate accuracy was obtained between the atrial surfaces extracted from the US and the ideal reference, and again a superior performance of the silicone-based model against the PVA-C phantom was observed. The proposed strategy proved to be accurate and feasible for the correct generation of complex personalized atrial models.

El espacio turístico, entre el enclave y el derrame: estudio en dos barrios de Buenos Aires

Este trabajo problematiza la idea de “espacio turístico” al proponer entenderlo no como un dato cartográfico sino -partiendo de una mirada antropológica- como producto de las prácticas que se realizan en él. Para ello tomamos dos barrios de la ciudad de Buenos Aires como estudios de caso: La Boca y Palermo, diferentes en su historia, paisaje y composición demográfica, pero igualados por su interés turístico. La metodología desarrollada incluyó estrategias etnográficas, análisis de prensa y referentes virtuales. A partir del trabajo de campo se observó cómo los discursos y prácticas sobre estos barrios modelan espacios turísticos diferentes, tanto en términos de la propuesta como del uso y sentidos otorgados por parte de los turistas.

3D machining allowance analysis method for the large thin-walled aerospace component

The structural distortion problem of large thin-walled aerospace components has roused much concern on more agile, digitized and cost-efficient precision manufacturing techniques, in particular, designing suitable machining plans according to the real shape of workpieces. To improve the machining accuracy of large thin-walled aerospace components, a methodology of three-dimensional machining allowance modeling and analysis is proposed in this paper. Firstly, the fundamental principles of 3D models matching and alignment between the casting blank and the design part are presented. And by datum transformation from virtual design references to real-world references on casting blanks which are accessible more easily, measuring, positioning and machining the casting blank will be more convenient to realize. Furthermore, the technical character of a large thin-walled aerospace component is considered and a technical framework for 3D machining allowance analysis is given. Finally, the proposed methodology is validated by an experimental study using a typical large thin-walled aerospace component of a hypersonic vehicle. Improvements in accuracy and efficiency performance are realized in comparison with traditional methods.

Coordinated tracking for multiple nonholonomic vehicles on SE(2)

This paper addresses the problem of consensus and formation control for nonholonomic multivehicle systems. The problem is formulated using the definition of the convex combination on SE(2) which simultaneously preserves the nonholonomic constraint in its left-invariant kinematics. The formation tracking follows by asymptotically tracking of the virtual references precisely defined based on the convex combination of the states of the neighboring vehicles. The methodology is applied to a group of seven unicycle-type vehicles connected with each other through a directed acyclic graph. The conditions on which nonholonomic vehicles can be in a coordination are developed by the notion of the nonholonomic adjoint orbit. For trajectory tracking, we develop the error dynamics in polar terms which provides a suitable setting for designing a simple and efficient control law. Finally, a backstepping technique is used to shift the kinematic control to the dynamic system. The theoretical results are supported by numerical simulation of the trajectory tracking as well as the formation tracking.

3D Air-Touch User Interface With High Touch Accuracy on Stereoscopic Displays

To interact with stereoscopic images through 3D air-touch technology, the depth information for a touched 3D virtual object and the fingertip position should be aligned accurately. However, the fused 3D position is affected when the virtual object is blocked by the fingertip. Additionally, the 3D image with a large disparity decreases 3D touch accuracy. In order to improve the touch accuracy, virtual references and 3D image feedback were introduced respectively, and the touch accuracy was more than 90% based on a human interaction experiment.

Digital human modeling and its applications: Review and future prospects.

The digital human modeling combines information technology with bioscience, applied to analog study from DNA molecule and protein to cell and tissue, as well as organ. It has been widely implemented in various fields such as aviation, national defense, film and television, sports and medical treatment. This paper sorts relative research achievements and progress in recent years and summarizes issues and challenges of research work. The purpose of this paper is to provide references for the development of Digital Human Modeling. Basing on the development plans proposed by Federation of American Scientists (FAS) and current theories, we sorted academic achievements and relative references since the beginning of the digital human concept until 2014 into four aspects, which were named as Visible Human, Virtual Physical Human, Virtual Physiological Human, and Intelligent Virtual Human. We collected information of data acquisition, data analysis and dataset establishment for Visible Human. We outlined the Virtual Physical Human references in four physical categories, including radiation, ultrasonic, electrics, and mechanics. For Virtual Physiological Human, relative researches related to the physiological and biochemical changes of human body were categorized in four aspects as gene molecules, cells, and organs. Relative researches of Virtual Brain Human were mainly concentrated on virtual human brain and virtual human control. According to the differences in investigations and applications requirements of Digital Human in all aspects, we classified, analyzed and concluded extensive preference data. The overall plan of Digital Human, as well as technical routes, work plans, present states, goals, results and application value in each stage of research was summarized. We discussed the technical issues existing in each aspect of Digital Human, along with the urgent key technologies including data collection, data processing, and modeling. Analyzing the core technologies and the general technical schemes in the field of Digital Human, this paper summarizes the technical solutions, research results and technical problems of major researchers. The future prospects of Digital Human are reviewed.

Page Replacement for Write References in NAND Flash Based Virtual Memory Systems

Contemporary embedded systems often use NAND flash memory instead of hard disks as their swap space of virtual memory. Since the read/write characteristics of NAND flash memory are very different from those of hard disks, an efficient page replacement algorithm is needed for this environment. Our analysis shows that temporal locality is dominant in virtual memory references but that is not the case for write references, when the read and write references are monitored separately. Based on this observation, we present a new page replacement algorithm that uses different strategies for read and write operations in predicting the re-reference likelihood of pages. For read operations, only temporal locality is used; but for write operations, both write frequency and temporal locality are used. The algorithm logically partitions the memory space into read and write areas to keep track of their reference patterns precisely, and then dynamically adjusts their size based on their reference patterns and I/O costs. Without requiring any external parameter to tune, the proposed algorithm outperforms CLOCK, CAR, and CFLRU by 20%–66%. It also supports optimized implementations for virtual memory systems.