Despite all the benefits of small cells in heterogeneous networks (HetNets) such as coverage improvement and spectral efficiency, they may cause additional interferences. Interference alignment (IA) ...by cell clustering is a possible candidate to manage HetNets interferences. Several picocells coexist within a microcell area while the nodes that cause interferences in a similar range of the desired signals are grouped in a cluster. IA removes the intra-cluster interferences, and the strong remaining interferences are estimated by interference detection. The simulation results show improvement in the symbol-error rate by the proposed scheme.
Summary
An innovative semiactive device, named the spindle adaptive tuned vibration absorber (SATVA), is proposed herein, having the potential of attenuating unfavorable vibrations of the host ...systems. The proposed device includes a preferably spindle‐shaped body of mass, whose mass moment of inertia can be altered simply by moving a pair of rotating supports. Therefore, the natural frequency of the device can be altered with a fairly low power consumption. A comprehensive analytical approach is employed in order to derive the governing equations of motion of the device, considering physical and practical issues. Through a numerical case study, it is demonstrated that the device is capable of reducing unfavorable vibrations of a rotating machinery during start‐up, while requiring considerably less amount of physical mass, compared with conventional absorbers. In addition, the spindle adaptive tuned vibration absorber has a quite rapid adaptation mechanism in comparison with other adaptive‐mass tuned vibration absorbers. Provided that its absolute acceleration during operation can be kept within reasonable limits to prevent slipping, this device is capable of finding different applications in various engineering disciplines.
Abstract
Water supply is a crucial concern for planners across all countries, especially in rural communities. This paper proposes a multidimensional approach to examining the effective criteria for ...water supply projects in rural areas of Iran. The study compares alternative methods of project implementation and employs three multi-criteria decision-making (MCDM) methods: analytical hierarchy process (AHP), Fuzzy-AHP, and technique for order preference by similarity to ideal solution (TOPSIS) to prioritize criteria, sub-criteria, and alternatives. The results indicate that, among the five options analyzed, diverting water from the river and constructing temporary storage dams are the highest priorities, while pipeline branching to the nearby city or village is given the lowest priority. The study reveals that environmental and economic criteria are more critical than social-security and technical-management criteria, while negative environmental impacts and the possibility of risk-taking by subversive agents are the most important among the 14 sub-criteria studied.
A wide-band, dual polarized printed antenna is designed and developed in this paper. The antenna is based upon an aperture stacked patch layout and incorporates a simple dual-layered feeding ...technique to achieve dual-polarized radiation. The printed antenna has a measured 10 dB return loss bandwidth of 52% and an isolation between the excitation ports of greater than 39 dB over this frequency range. The gain of the antenna is 7.4 dBi /spl plusmn/ 0.4 dB and the typical issues associated with incorporating an aperture excited solution are resolved by using a cross-shaped reflector patch to ensure the front-to-back ratio is greater than 20 dB.
AbstractA new method, optimal step-by-step tuning (OSST), is presented for the frequency adjustment of variable stiffness semiactive tuned mass dampers (SATMDs). In this method, the external ...excitation of the system fitted with a SATMD is divided into several time steps, and the response components are expressed as polynomial functions of the SATMD’s stiffness. An objective function is defined, the minimization of which leads to the desired SATMD’s stiffness in each time step. In order to assess the efficiency of the OSST method, a single-degree-of-freedom (SDOF) system equipped with an innovative SATMD under transient vibrations is considered. The system’s response is obtained and compared with the following cases: (1) unity tuning ratio (UTR) method, in which the frequency of the SATMD is equal to the excitation frequency, and (2) constant tuning ratio (CTR) method, in which the ratio of the SATMD frequency to excitation frequency is a constant value close to unity. The results reveal the superiority of the OSST method in transient response reduction in comparison with the UTR and CTR methods.
In this study an innovative mobile Tuned Mass Damper (TMD) system is proposed which enables the TMD device to move along the cable and optimize its position. A three dimensional model of an inclined ...cable with sag is created using OpenSees. A mobile TMD device incorporating a semi-active Magnetorheological (MR) damper is implemented. Nine different control strategies, including six fuzzy strategies as well as a continuous sky-hook, an on-off sky-hook, and a passive-on strategy, are employed for the purpose of vibration mitigation. A locating algorithm is also devised so as to optimize the TMD position. A specific load pattern containing a chirp signal is utilized with the purpose of performing the nonlinear time history analyses. The results investigate the efficiency of different control systems in a comparative manner. The effect of locating algorithm is also examined. The results claim that although the suggested control systems can effectively reduce the displacements of the cable, they are relatively incompetent to make a remarkable reduction in maximum and normed values of the cable tension. The output data certify the significant contribution of LA for promoting the performance of control systems. This algorithm especially influences the reduction of normed values of displacement. In general, the fuzzy control algorithms show a much higher performance compared with the passive-on and sky-hook counterparts.
In this study, through novel drift-based equations of motion in the frequency domain, optimum placement and characteristics of linear velocity-dependent dampers are investigated. In this study, the ...sum of the square of the absolute values of transfer matrix elements for interstory drifts is considered as the optimization index. Optimum placement and characteristics of dampers are simultaneously obtained by minimizing the optimization index through an incremental procedure. In each step of the procedure, a predefined value is considered as the damper characteristic. The optimum story for this increment is selected such that it leads to a minimum value for the optimization index. The procedure is repeated for the next increments until the optimization index meets its target value, which is obtained according to the desired damping ratio for the overall structure. In other words, the desired overall damping ratio is the input to the proposed procedure, and the optimal placement and characteristics of the dampers are its output. It is observed that the optimal placement of a velocitydependent damper depends on the damping coefficient of the added damper, frequency of the excitation, and distribution of the mass, stiffness, and inherent damping of the main structure.
The design is described of a planar dual-arm equiangular spiral antenna incorporated with chip resistors inside the substrate. The chip resistors were applied to this equiangular spiral antenna to ...achieve 9:1 impedance bandwidth (2 to 18 GHz) with an extremely low profile structure. The simulated and measured magnitude of the reflection coefficient ( S 11 ), gain, and measured radiation patterns are presented.
We calculate the scalar semileptonic kaon decay in finite volume at the momentum transfer tm=(mK−mπ)2, using chiral perturbation theory. At first we obtain the hadronic matrix element to be ...calculated in finite volume. We then evaluate the finite size effects for two volumes with L=1.83 fm and L=2.73 fm and find that the difference between the finite volume corrections of the two volumes are larger than the difference as quoted in Boyle et al. (Phys. Rev. Lett. 100:141601, 2008). It appears then that the pion masses used for the scalar form factor in ChPT are large which result in large finite volume corrections. If appropriate values for pion mass are used, we believe that the finite size effects estimated in this paper can be useful for lattice data to extrapolate at large lattice size.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
PDF
