This chapter analyzes the performance of directional collision avoidance schemes, in which antenna systems are used to direct the transmission and reception of control and data packets in channel access protocols based on four-way handshakes to try to avoid collisions. The first analytical model to consider directional reception and the possible difference in gain between omni-directional and d...

To increase the payload capacity of the hidden secret information and to provide an imperceptible stegoimage for human vision, an enhanced steganographic method using multidirectional block based pixel-value differencing is proposed in this paper.To enhance the hiding payload capacity in image an steganographic method based on three-pixel block differences by Lin and Hseuh referring to only one...

This paper presents a new compression technique and image watermarking algorithm based on Contourlet Transform (CT). For image compression, an energy based quantization is used. Scalar quantization is explored for image watermarking. Double filter bank structure is used in CT. The Laplacian Pyramid (LP) is used to capture the point discontinuities, and then followed by a Directional Filter Bank...

the efficiency and robustness of reliability methods are two important factors in first order reliability method (form). the conjugate choice control (ccc) and directional chaos control method (dcc) were developed to improve the robustness and efficiency of form formula using the stability transformation method. in this paper, the ccc and dcc methods are applied for reliability analysis of a co...

directional felling of trees plays a key role in reducing of damages to forest residual trees and can also facilitate skidding. the aim of this study was presents a practical linear model for estimation of tree falling direction error in an uneven-aged mixed stand in northern forests of iran. to conduct the study a number of 95 trees of four species fagus orientalis lipsky, carpinus betulus l.,...

in recent years, different damage indexes have been introduced in engineering literature. the most prominent one among other counterparts is the 1985 park and ang's damage index (dipa), which demonstrates well calibration against experimental results. hence, it has traditionally had broad application in the field of structural engineering. commonly, in dipa relevant parameters are assessed...

bankruptcy in the same amount of time and history is very rampant and therefore the vision of the future can be prevented. using data envelopment analysis (dea) and malmquist index can precise evaluating of the performances of many different kinds of decision making units (dmu) such as hospitals, universities, business firms, etc. in this paper, we will modify directional distance formulation o...

in this article, we suggested a novel design of polarization splitter based on coupler waveguide on inp substrate at 1.55mm wavelength. photonic crystal structure is consisted of two dimensional (2d) air holes embedded in inp/ingaasp material with an effective refractive index of 3.2634 which is arranged in a hexagonal lattice. the photonic band gap (pbg) of this structure is determined using t...

The use of directional antennae in ad-hoc networks has received growing attention in recent years. However, most directional MAC protocols assume interchangeable directional and omni-directional modes of operation. Such operation reduces the spatial gain and introduces the asymmetry in gain problem. In this paper, we propose a directional-to-directional (DtD) MAC protocol for ad-hoc networks th...