74 research outputs found
Channel capacity conditions for stabilization of networked control systems
No full textNetworked control systems (NCSs) are the control mechanism with noisy communication channels in between, which are ubiquitous in modern computing and guided devices and systems. Stabilization plays the most respected and dominated role in NCSs. While there are lots of research work on single input systems, how to describe the quality of MIMO channels, how to design the controller and the transceiver jointly, and how to characterize fundamental performance limits in control setting with both MIMO plants and MIMO channels are open to study. In the first part, we will study those issues in context of additive white Gaussian channels. First of all, we will use the concept of channel capacity from classic information theory to quantify the channel, where a necessary condition and a sufficient one are derived, respectively. Generally, there exists a gap between these two due to the closed-loop characteristics of the NCSs. Then incremental mutual information has been introduced and defined, in term of which a necessary and sufficient condition has been given. Finally, how to design the optimal controller and the transceiver with the gap minimized is investigated. In the second part, the multiplicative noise channel has been studied. Firstly, we have researched the issues about how to use positive system techniques to analyze the system variances, how to design the control and communication scheme, and what conditions of stabilization are. Secondly, the results are further extended to a generalized stable plant with the transceiver as the only design freedom. Lastly, the poles and zeros together with their associated directions have been used to study the output feedback case.</p
When MIMO control meets MIMO communication: A majorization condition for networked stabilizability
No full textIn this paper, we initiate the study of networked stabilization via a MIMO communication scheme between the controller and the plant. Specifically, the communication system is modeled as a MIMO transceiver, which consists of three parts: an encoder, a MIMO channel, and a decoder. In the spirit of MIMO communication, the number of SISO subchannels in the transceiver is often greater than the number of data streams to be transmitted. Moreover, the subchannel capacities are assumed to be fixed a priori. In this case, the encoder/decoder pair gives an additional design freedom on top of the controller, leading to a stabilization problem via coding/control co-design. It turns out that how to take the best advantage of the coding mechanism is quite crucial. From a demand/supply perspective, the design of the coding mechanism boils down to reshaping the demands for communication resource from different control inputs to match the given supplies. We study the problem for the case of AWGN subchannels and fading subchannels, respectively. In both cases, we arrive at a unified necessary and sufficient condition on the capacities of the subchannels under which the coding/control codesign problem is solvable. The condition is given in terms of a majorization type relation. As we go along, systematic procedures are also put forward to carry out the coding/control co-design. A numerical example is presented to illustrate our results
Levels of serum sclerostin, FGF-23, and intact parathyroid hormone in postmenopausal women treated with calcitriol
No full textQun Cheng,1–3 Xiaoxing Wu,1,2 Yanping Du,1–3 Wei Hong,1–3 Wenjing Tang,1–3 Huilin Li,1–3 Minmin Chen,1–3 Songbai Zheng3 1Department of Osteoporosis and Bone Disease, Huadong Hospital Affiliated to Fudan University, Shanghai, China; 2Research Section of Geriatric Metabolic Bone Disease, Shanghai Geriatric Institute, Shanghai, China; 3National Clinical Research Center for Aging and Medicine, Fudan University, Shanghai, China Objective: This study aimed to determine the effect of calcitriol on serum concentrations of fibroblast growth factor-23 (FGF-23), sclerostin, intact parathyroid hormone (PTH), and handgrip strength in postmenopausal women with low bone mass.Methods: A randomized, double-blind controlled trial was carried out among 141 postmenopausal women with low bone mass. Participants were randomized into two groups: 75 participants received calcitriol 0.5 μg/day and 66 participants received a placebo for 12 weeks.Results: After 12-week calcitriol treatment, significant decreases in serum intact PTH (P=0.035) and sclerostin (P=0.039), as well as significant increases in serum creatinine (P=0.027), uric acid (P=0.032), 24-hour urinary calcium (P=0.0026), and left handgrip strength (P=0.03), were observed, compared to placebo group. Level of serum sclerostin was weakly but significantly positively correlated with serum PTH (r=0.277; P=0.01) and negatively correlated with 24-hour urinary calcium (r=−0.221; P=0.04) and left handgrip strength (r=−0.338; P=0.03) after calcitriol treatment. Multiple regression analysis demonstrated that decrease in serum sclerostin was associated with decrease in PTH serum level after calcitriol treatment (OR, 7.90; 95% CI, 2.28–27.42; P=0.002). However, no significant change in FGF-23 level was observed after calcitriol treatment.Conclusion: Calcitriol treatment yields a considerable decrease in serum sclerostin and significant increase of handgrip strength, and the change in serum sclerostin is regulated by serum PTH and by muscle strength. Keywords: calcitriol, FGF-23, fibroblast growth factor 23, handgrip, intact PTH, sclerostin 
Multiple ignitions and the stability of rotating detonation waves
No full textWe perform a numerical study on rotating detonation engines (RDE). The simulations demonstrate the feasibility of creating multiple detonation waves and examine their stabilization process. The computations are based on the three-dimensional Euler equations with reactive sources. The Arrhenius chemistry model is used to calculate the reaction rate of the pre-mixed stoichiometric hydrogen-air mixture. The simulations show the oscillation phenomenon characterized by the pressure-time traces and the stabilization process. Also, the results indicate the existence of one-, two-, and eight-wave propagation modes in the fully-developed detonation flow. The initial detonation waves dominate the flow throughout the stabilization process in the one- and two-wave modes. On the other hand, the eight-wave mode is the result of the generation of new detonation waves during the intermediate stage. The simulations are compared with the experimental studies to confirm the existence of the multi-wave modes discussed herein. In addition, it is found that the velocity of detonation waves decreases with the increase of the number of detonation waves, which is also reported in some experiments. (C) 2016 Elsevier Ltd. All rights reserved.National Nature Science Foundation of China [91441110]SCI(E)[email protected]; [email protected]
Feasible channel capacity region for MIMO stabilization via MIMO communication
No full textIn this paper, we study the stabilization of MIMO networked control systems over MIMO communication systems. Here the parallel additive white Gaussian noise subchannels in the MIMO transceiver are used to express the spatial freedom of communication. In addition, the number of subchannels in general can be greater than that of control inputs. The aim is to find the feasible capacity region rendering stabilization possible. We also wish to examine how to design the controller and transceiver jointly. A super-region and a sub-region for the feasible channel capacity region are obtained which are characterized in terms of two majorization relations, respectively. The results are demonstrated by numerical examples.</p
A majorization condition for MIMO stabilizability via MIMO transceivers with pure fading subchannels
No full textThis paper aims at characterizing a fundamental limitation on the information constraints required for multi-input networked stabilization. A MIMO communication system is deployed for information exchange between the controller and the plant. The communication system is modeled as a MIMO transceiver, which consists of three parts: an encoder, a MIMO channel consisting of parallel SISO subchannels, and a decoder. We focus on the pure fading subchannels in this paper while the case of pure AWGN subchannels has been discussed in our previous work. Inheriting the spirit of MIMO communication, the number of SISO subchannels in the transceiver is often greater than the number of control inputs to be transmitted. The subchannel capacities are assumed to be fixed a priori. With the encoder/decoder pair at hand, the controller designer gains an additional design freedom on top of the controller, leading to a stabilization problem via coding/control co-design. A necessary and sufficient condition is obtained for the solvability of this coding/control co-design problem given in terms of a majorization type relation. A numerical example is presented to illustrate our results.</p
MIMO control using MIMO communication: A Majorization condition for networked stabilizability
No full textIn this paper, we initiate the study of networked stabilization via a MIMO communication scheme between the controller and the plant. Specifically, the communication system is modeled as a MIMO transceiver, which consists of three parts: an encoder, a MIMO channel, and a decoder. In the spirit of MIMO communication, the number of SISO subchannels in the transceiver is often greater than the number of data streams to be transmitted. Moreover, the subchannel capacities are assumed to be fixed a priori. In this case, the encoder/decoder pair gives an additional design freedom on top of the controller, leading to a stabilization problem via coding/control co-design. The controller designer needs to design the encoder/decoder pair and the controller jointly so as to stabilize the system. We arrive at a necessary and sufficient condition on the subchannel capacities under which the coding/control co-design problem is solvable. Quite surprisingly, the condition is given in terms of a majorization type relation. As we go along, a systematic procedure is also put forward to perform the coding/control co-design. A numerical example is presented to illustrate our results.</p
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