External Direct Sum Invariant Subspace and Decomposition of Coupled Differential-Difference Equations

This article discusses the invariant subspaces that are restricted to be external direct sums. Some existence conditions are presented that facilitate finding such invariant subspaces. This problem is related to the decomposition of coupled differential-difference equations, leading to the possibility of lowering the dimensions of coupled differential-difference equations. As has been well documented, lowering the dimension of coupled differential-difference equations can drastically reduce the computational time needed in stability analysis when a complete quadratic Lyapunov-Krasovskii functional is used. Most known ad hoc methods of reducing the order are special cases of this formulation

Structured invariant subspace and decomposition of systems with time delays and uncertainties

This article discusses invariant subspaces of a matrix with a given partition structure. The existence of a nontrivial structured invariant subspace is equivalent to the possibility of decomposing the associated system with multiple feedback blocks such that the feedback operators are subject to a given constraint. The formulation is especially useful in the stability analysis of time-delay systems using the Lyapunov-Krasovskii functional approach where computational efficiency is essential in order to achieve accuracy for large scale systems. The set of all structured invariant subspaces are obtained (thus all possible decompositions are obtained as a result) for the coupled differential-difference equations associated with the differential-difference equations of retarded and neutral types, as well as systems with a time-varying delay. It was shown that the known ad hoc methods of reducing the dimensions of delay channels can be considered as special cases of decomposition where one subsystem has trivial dynamics. The reduction of computational cost is demonstrated by a numerical example. For the general case, a recursive procedure is developed to obtain the set of all structured invariant subspaces. Based on this procedure, a method is presented to obtain a nontrivial structured invariant subspace that considers computational efficiency and increased possibility of terminating in a finite number of steps

BIẾN ĐỘNG CỦA TRƯỜNG NHIỆT ĐỘ VÀ MỐI QUAN HỆ CỦA NÓ VỚI ENSO TRONG VÙNG BIỂN NINH THUẬN - BÌNH THUẬN

In this paper, our aim was to examine the role of ENSO in the recent climate variations. Analyzed results on temporal variability of thermal fields in period of 38 years (Jan. 1979-Aug. 2016) showed that Ninh Thuan - Binh Thuan waters were subjected to the significant impact of the ENSO phases (warming and cooling) as well as other processes related to seasonal, inter-seasonal, yearly and mutlti-yearly variations such as in the periods 1986-1989, 1996-2000 and 2009-2011. In order to clarify above issues, authors carried out the analysis of the temporal -spatial changes of temperature fields (include air temperature and sea surface temperature) in Ninh Thuan - Binh Thuan region. The temperature data were exploited from The National Centers for Environmental Prediction (NCEP) and Climate Forecast System Reanalysis (CFSR) in the form of hourly time-series products with spatial resolution of 0.3o (1979-2010) and 0.20o (2011-8/2016). The results showed that 2016 was quite similar to 1998 and 2010 when the coral bleaching occurred in the study area.Các kết quả phân tích trường nhiệt độ trong 38 năm (1/1979 - 8/2016) đã cho thấy vùng biển Ninh Thuận - Bình Thuận chịu sự tác động không nhỏ của các pha ENSO (ấm, lạnh) mà còn có liên quan đến các quá trình khác có chu kỳ mùa, liên mùa, năm, nhiều năm thể hiện tại các giai đoạn 1986-1989; 1996-2000 và 2009-2011. Để góp phần làm sáng tỏ vấn đề trên, chúng tôi đã tiến hành phân tích sự thay đổi nền nhiệt độ của nhiệt độ không khí, nhiệt độ nước bề mặt biển. Các số liệu nhiệt độ sử dụng trong nghiên cứu này được khai thác từ Hệ thống Dự đoán Khí hậu Phân tích lại (CFSR) theo bước thời gian 1 giờ với độ phân giải ngang 0,3° (1979-2010) và 0,2o (2011-8/2016) của Trung tâm Dự báo Môi trường Quốc gia Hoa Kỳ (NCEP). Kết quả phân tích cho thấy năm 2016 có nét khá tương đồng với năm 1998 và 2010, các năm được phát hiện đã xảy ra hiện tượng tẩy trắng san hô tại khu vực nghiên cứu

Awareness and preparedness of healthcare workers against the first wave of the COVID-19 pandemic: A cross-sectional survey across 57 countries.

BACKGROUND: Since the COVID-19 pandemic began, there have been concerns related to the preparedness of healthcare workers (HCWs). This study aimed to describe the level of awareness and preparedness of hospital HCWs at the time of the first wave. METHODS: This multinational, multicenter, cross-sectional survey was conducted among hospital HCWs from February to May 2020. We used a hierarchical logistic regression multivariate analysis to adjust the influence of variables based on awareness and preparedness. We then used association rule mining to identify relationships between HCW confidence in handling suspected COVID-19 patients and prior COVID-19 case-management training. RESULTS: We surveyed 24,653 HCWs from 371 hospitals across 57 countries and received 17,302 responses from 70.2% HCWs overall. The median COVID-19 preparedness score was 11.0 (interquartile range [IQR] = 6.0-14.0) and the median awareness score was 29.6 (IQR = 26.6-32.6). HCWs at COVID-19 designated facilities with previous outbreak experience, or HCWs who were trained for dealing with the SARS-CoV-2 outbreak, had significantly higher levels of preparedness and awareness (p<0.001). Association rule mining suggests that nurses and doctors who had a 'great-extent-of-confidence' in handling suspected COVID-19 patients had participated in COVID-19 training courses. Male participants (mean difference = 0.34; 95% CI = 0.22, 0.46; p<0.001) and nurses (mean difference = 0.67; 95% CI = 0.53, 0.81; p<0.001) had higher preparedness scores compared to women participants and doctors. INTERPRETATION: There was an unsurprising high level of awareness and preparedness among HCWs who participated in COVID-19 training courses. However, disparity existed along the lines of gender and type of HCW. It is unknown whether the difference in COVID-19 preparedness that we detected early in the pandemic may have translated into disproportionate SARS-CoV-2 burden of disease by gender or HCW type

Trajectory Control of Omnidirectional Robots Considering Actuator Dynamics

A high degree of maneuverability in omnidirectional mobile robots, which stems from their holonomic nature, has posed them as an attractive solution in a variety of applications. This paper studies the problem of trajectory control in omnidirectional robots based on practical observations. More specifically, the dynamics of the low-level motor drivers are explicitly incorporated during the development of a hierarchical controller. Lyapunov's stability theorem is then used to analytically derive the control law which could achieve seamless integration of different control structure hierarchies. The simulation results show the effectiveness of the proposed method compared to other commonly-used algorithms. Furthermore, the controller exhibits low sensitivity to model parameter variations despite its model-based nature, which would be a very beneficial feature in practical implementations as it would limit the need for extensive modeling and calibration. The experimental results tested on Omnidirectional Robot are presented to show the further study based on the proposed controller

ẢNH HƯỞNG CỦA NGUỒN CARBON VÀ MỘT SỐ ELICITOR LÊN KHẢ NĂNG SINH TRƯỞNG CỦA TẾ BÀO HUYỀN PHÙ ĐINH LĂNG (POLYSCIAS FRUTICOSA (L.) HARMS)

Polyscias fruticosa (L.) Harms is a valuable medicinal plant, widely used in folk medicine. In this study, the effects of carbon sources and elicitors (yeast extract, salicylic acid, and silver nitrate) on the growth of suspension cells were evaluated. The results indicated that the optimal medium for growth of the cells was liquid MS supplemented with 2 mg/L NAA, 0.5 mg/L Kinetin, and 3% sucrose, with fresh cell biomass reaching 7.50 g (0.40 g dry weight) after 16 days of culture. All elicitors used in this study inhibited the cell growth. These were necessary conditions for the accumulation of secondary substances in the suspension cell culture.Đinh lăng (Polyscias fruticosa (L.) Harms) là một loài cây thuốc có giá trị, được dân gian sử dụng rộng rãi làm thuốc tăng cường sức khỏe. Trong nghiên cứu này, ảnh hưởng của nguồn carbon và một số loại elicitor (dịch chiết nấm men, salicylic acid và AgNO3) lên khả năng sinh trưởng của tế bào huyền phù đinh lăng đã được khảo sát. Kết quả cho thấy môi trường MS (Murashige and Skoog) lỏng có bổ sung α-naphthaleneacetic acid (NAA) 2 mg/L, Kinetin 0,5 mg/L và sucrose 3% là tốt nhất cho khả năng sinh trưởng của tế bào đinh lăng; sinh khối tế bào tươi đạt 7,50 g (0,40 g khô) sau 16 ngày nuôi cấy. Tất cả các loại elicitor sử dụng trong nghiên cứu đều ức chế sự sinh trưởng của tế bào huyền phù; nồng độ elicitor càng cao sinh khối tế bào càng giảm. Đây là điều kiện cần thiết để tăng sự tích lũy các hợp chất thứ cấp trong nuôi cấy tế bào huyền phù

Peroxymonosulfate Activation on a Hybrid Material of Conjugated PVC and TiO2 Nanotubes for Enhancing Degradation of Rhodamine B under Visible Light

Visible-light-driven photocatalysis is a robust technology for amending the negative effect of pollutants on the environment with a minimum energy use. Herein, we describe a simple approach to producing such a photocatalyst by coupling conjugated polyvinyl chloride (cPVC) with the TiO2 nanotube (TNT) thermolysis method. By activating peroxymonosulfate (PMS) to make a cPVC/TNT/PMS system using visible light as the source, we obtain a significant enhancement in the photocatalytic performance. We show that PMS use at a concentration of 3 mM can fully degrade rhodamine B (RhB) solution at a remarkably high concentration (200 mg L-1) just in 120 min under visible light. The cPVC/TNT/PMS system also shows excellent stability in recycling tests for at least five times. Further, by confining the active species in photocatalytic reactions, we report a thorough understanding of the extent of involvement from those radicals. Our work presents a robust approach to make a high-performance, visible-light-driven photocatalyst, which can be potentially used in practice