Comments on, `Improved multilevel quantization for detection ofnarrowband signals' by C.W. Helstrom

It is shown that optimum quantization levels may be obtained by using C.W. Helstrom's approach of the above named work (see ibid., vol.AES-24, p.141-147, Mar. 1988) but maximizing exact detection probabilities instead of approximations to it if the moment generating function of the test statistic can be expressed in rational form. Adaptive levels may be obtained for the quantizers by cell averaging, leading to constant false alarm rate (CFAR) detectors     

Surface effects on the free vibration behavior of postbuckled circular higher-order shear deformable nanoplates including geometrical nonlinearity

This investigation deals with the free vibration characteristics of circular higher-order shear deformable nanoplates around the postbuckling configuration incorporating surface effects. Using the Gurtin–Murdoch elasticity theory, a size-dependent higher-order shear deformable plate model is developed which takes account all surface effects including surface elasticity, surface stress and surface density. Geometrical nonlinearity is considered based on the von Karman type nonlinear strain–displacement relationships. Also, in order to satisfy the balance conditions between bulk and surfaces of nanoplate, it is assumed that the normal stress is distributed cubically through the thickness of nanoplate. Hamilton?s principle is utilized to derive non-classical governing differential equations of motion and related boundary conditions. Afterwards, an efficient numerical methodology based on a generalized differential quadrature (GDQ) method is employed to solve numerically the problem so as to discretize the governing partial differential equations along various edge supports using Chebyshev–Gauss–Lobatto grid points and pseudo arc-length continuation technique. A comparison between the results of present non-classical model and those of the classical plate theory is conducted. It is demonstrated that in contrast to the prebuckling domain, for a specified value of axial load in the postbuckling domain, increasing the plate thickness leads to higher frequencies.     

Multiwavelength astronomy using ESIS

We present results on multi-frequency astronomy obtained using the European Space Information System, ESIS. ESIS is an ESA service designed to access, manipulate and combine archival data from a number of remote archives in the fields of Astronomy and Space Physics. The examples presented here include plots of radio-to-X-ray energy distribution of Active Galactic Nuclei, spectrograms of IUE/UV data, direct comparison of images from different experiments and overlay of catalogue sources on image data. The ESIS project is currently reaching the end of its pilot phase. Its services will be available to the general astronomical community in 1993.