856 research outputs found
Joint UAV Placement and IRS Phase Shift Optimization in Downlink Networks
This study investigates the integration of an intelligent reflecting surface
(IRS) into an unmanned aerial vehicle (UAV) platform to utilize the advantages
of these leading technologies for sixth-generation communications, e.g.,
improved spectral and energy efficiency, extended network coverage, and
flexible deployment. In particular, we investigate a downlink IRS-UAV system,
wherein single-antenna ground users (UEs) are served by a multi-antenna base
station (BS). To assist the communication between UEs and the BS, an IRS
mounted on a UAV is deployed, in which the direct links are obstructed owing to
the complex urban channel characteristics. The beamforming at the BS, phase
shift at the IRS, and the 3D placement of the UAV are jointly optimized to
maximize the sum rate. Because the optimization variables, particularly the
beamforming and IRS phase shift, are highly coupled with each other, the
optimization problem is naturally non-convex. To effectively solve the
formulated problem, we propose an iterative algorithm that employs block
coordinate descent and inner approximation methods. Numerical results
demonstrate the effectiveness of our proposed approach for a UAV-mounted IRS
system on the sum rate performance over the state-of-the-art technology using
the terrestrial counterpart
POLLUTION OF GROUNDWATER BY LEACHATE FROM DONG THANH LANDFILL DISPOSAL SITE
Joint Research on Environmental Science and Technology for the Eart
A note on dissipative particle dynamics (DPD) modelling of simple fluids
In this paper, we show that a Dissipative Particle Dynamics (DPD) model of a viscous Newtonian fluid may actually produce a linear viscoelastic fluid. We demonstrate that a single set of DPD particles can be used to model a linear viscoelastic fluid with its physical parameters, namely the dynamical viscosity and the relaxation time in its memory kernel, determined from the DPD system at equilibrium. The emphasis of this study is placed on (i) the estimation of the linear viscoelastic effect from the standard parameter choice; and (ii) the investigation of the dependence of the DPD transport properties on the length and time scales, which are introduced from the physical phenomenon under examination. Transverse-current auto-correlation functions (TCAF) in Fourier space are employed to study the effects of the length scale, while analytic expressions of the shear stress in a simple small amplitude oscillatory shear flow are utilised to study the effects of the time scale. A direct mechanism for imposing the particle diffusion time and fluid viscosity in the hydrodynamic limit on the DPD system is also proposed
Free vibration analysis of laminated composite plates based on FSDT using one-dimensional IRBFN method
This paper presents a new effective radial basis function (RBF) collocation technique for the free vibration
analysis of laminated composite plates using the first order shear deformation theory (FSDT). The plates, which can be rectangular or non-rectangular, are simply discretised by means of Cartesian grids. Instead of using conventional differentiated RBF networks, one-dimensional integrated RBF networks (1D-IRBFN) are employed on grid lines to approximate the field variables. A number of examples concerning various thickness-to-span ratios, material properties and boundary conditions are considered. Results obtained are compared with the exact solutions and numerical results by other techniques in the literature to
investigate the performance of the proposed method
Conditional expectation with regularization for missing data imputation
Missing data frequently occurs in datasets across various domains, such as
medicine, sports, and finance. In many cases, to enable proper and reliable
analyses of such data, the missing values are often imputed, and it is
necessary that the method used has a low root mean square error (RMSE) between
the imputed and the true values. In addition, for some critical applications,
it is also often a requirement that the imputation method is scalable and the
logic behind the imputation is explainable, which is especially difficult for
complex methods that are, for example, based on deep learning. Based on these
considerations, we propose a new algorithm named "conditional
Distribution-based Imputation of Missing Values with Regularization" (DIMV).
DIMV operates by determining the conditional distribution of a feature that has
missing entries, using the information from the fully observed features as a
basis. As will be illustrated via experiments in the paper, DIMV (i) gives a
low RMSE for the imputed values compared to state-of-the-art methods; (ii) fast
and scalable; (iii) is explainable as coefficients in a regression model,
allowing reliable and trustable analysis, makes it a suitable choice for
critical domains where understanding is important such as in medical fields,
finance, etc; (iv) can provide an approximated confidence region for the
missing values in a given sample; (v) suitable for both small and large scale
data; (vi) in many scenarios, does not require a huge number of parameters as
deep learning approaches; (vii) handle multicollinearity in imputation
effectively; and (viii) is robust to the normally distributed assumption that
its theoretical grounds rely on
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