On the existence and exponential attractivity of a unique positive almost periodic solution to an impulsive hematopoiesis model with delays

In this paper, a generalized model of hematopoiesis with delays and impulses is considered. By employing the contraction mapping principle and a novel type of impulsive delay inequality, we prove the existence of a unique positive almost periodic solution of the model. It is also proved that, under the proposed conditions in this paper, the unique positive almost periodic solution is globally exponentially attractive. A numerical example is given to illustrate the effectiveness of the obtained results.Comment: Accepted for publication in AM

Retail business in an emerging economy: The case of Vietnam

In the recent decades, emerging economies have developed rapidly attracting foreign direct investment and advanced services, especially in the retail business sector. This research paper aims to point out the trend of retail business in a Southeast Asian emerging country, Vietnam. Retail business in Vietnam is more attractive due to its young population occupying 65% of the national population who maintain optimistic shopping behaviors. Since 2008, the negative impact of the global financial crisis and Vietnam’s economic instability have affected the Vietnam’s retail market negatively. It seems that potential retail market is on the decrease when the attractive index of the retail market was number one in 2008, number sixth in 2009 and number fourteen in 2010 in the world. This research assesses whether an emerging economy like Vietnam would continue to be an attractive destination for international retail market and what deterred big retailers from investing in Vietnamese market? Furthermore, are local retail businesses ready for competition? If so, what is the current trend in a rapidly changing and risky environment as Vietnamese economy is experiencing at the moment. This research employs integrated statistical comparison and analysis. Demand and supply model in retail business is employed to identify the trend of retail business in Vietnam. Furthermore, this paper proposes strategies for retail business development in Vietnam in order to refocus the role of government to support the development of retail business. Our assessment suggests that Vietnamese businesses which utilize modern business concepts have grown swiftly while local businesses that follow traditional retail channel are under increased pressure for change due to market competition. The urban market remains attractive to domestic and foreign investors while the rural market is largely unexplored. Consequently, a combination between modern and traditional concepts could be utilized to promote and exploit full potentials of Vietnam’s retail business. This adaptation, which requires businesses to shift from traditional concepts into modern concepts, demands drastic change in business modeling such as size, structure and business practices. The research also provides policy suggestions including improvement of facility development, refining local supply chain, and simplifying procedural logistics for businesses to help them smoother this transition

Robust probabilistic-constrained optimization for IRS-aided MISO communication systems

Taking into account imperfect channel state information, this letter formulates and solves a joint active/passive beamforming optimization problem in multiple-input single-output systems with the support of an intelligent reflecting surface. In particular, we introduce an optimization problem to minimize the total transmit power subject to maintaining the users' signal-to-interference-plus-noise-ratio coverage probability above a predefined target. Due to the presence of probabilistic constraints, the proposed optimization problem is non-convex. To circumvent this issue, we first recast the proposed problem in a convex form by adopting the Bernstein-type inequality, and we then introduce a converging alternating optimization approach to iteratively find the active/passive beamforming vectors. In particular, the transformed robust optimization problem can be effectively solved by using standard interior-point methods. Numerical results demonstrate the effectiveness of jointly optimizing the active/passive beamforming vectors

Permanence and positive bounded solutions of Kolmogorov predator-prey system

Our main purpose is to present some criteria for the perma- nence and existence of a positive bounded solution of Kolmogorov predator-prey system. Under certain conditions, it is shown that the system is per- manent and there exists a solution which is de_ned on the whole R and whose components are bounded from above and from below by positive constants

A successive optimization approach to pilot design for multi-cell massive MIMO systems

In this letter, we introduce a novel pilot design approach that minimizes the total mean square errors of the minimum mean square error estimators of all base stations (BSs) subject to the transmit power constraints of individual users in the network, while tackling the pilot contamination in multicell Massive MIMO systems. First, we decompose the original non-convex problem into distributed optimization sub-problems at individual BSs, where each BS can optimize its own pilot signals given the knowledge of pilot signals from the remaining BSs. We then introduce a successive optimization approach to transform each optimization sub-problem into a linear matrix inequality (LMI) form, which is convex and can be solved by available optimization packages. Simulation results confirm the fast convergence of the proposed approach and prevails a benchmark scheme in terms of providing higher accuracy

VIBRATION ANALYSIS OF CROSS-PLY LAMINATED COMPOSITE DOUBLY CURVED SHALLOW SHELL PANELS WITH STIFFENERS

In this paper, the analytical solution for the cross-ply laminated composite double curved shell panels with stiffeners is presented. Based on the smeared stiffeners technique and the first shear deformation theory (FSDT), the motion equations are derived by applying the Hamilton’s principle. The Navier’s solution for the simply supported boundary condition for all edges is presented. The numerical results are verified with the known results in the literature. The effects of the number of stiffeners, dimensions of stiffeners, and lamination scheme of cross-ply laminated composite doubly curved shell panels on the natural fundamental frequencies are investigated

FREE VIBRATION ANALYSIS OF LAMINATED STIFFENED CYLINDRICAL PANELS USING FINITE ELEMENT METHOD

A study on the free vibration analysis of stiffened laminated composite cylindrical shell is described in this paper. The eight-noded isoparametric degenerated shell element is developed to model both shell panel and stiffeners by using the degenerated solid concept based on Reissner-Mindlin assumptions which taking to account the shear deformation and rotatory effect. Numerical results are presented and comparison is made with the published results from the literature and the good agreement is found. Parametric studies considering different geometrical variables of shell and stiffeners have also been carried out

Global attractivity of positive periodic solution of a delayed Nicholson model with nonlinear density-dependent mortality term

This paper is concerned with the existence, uniqueness and global attractivity of positive periodic solution of a delayed Nicholson’s blowflies model with nonlinear density-dependent mortality rate. By some comparison techniques via differential inequalities, we first establish sufficient conditions for the global uniform permanence and dissipativity of the model. We then utilize an extended version of the Lyapunov functional method to show the existence and global attractivity of a unique positive periodic solution of the underlying model. An application to the model with constant coefficients is also presented. Two numerical examples with simulations are given to illustrate the efficacy of the obtained results