A mixed transform approach for efficient compression of medical images

A novel technique is presented to compress medical data employing two or more mutually nonorthogonal transforms. Both lossy and lossless compression implementations are considered. The signal is first resolved into subsignals such that each subsignal is compactly represented in a particular transform domain. An efficient lossy representation of the signal is achieved by superimposing the dominant coefficients corresponding to each subsignal. The residual error, which is the difference between the original signal and the reconstructed signal is properly formulated. Adaptive algorithms in conjunction with an optimization strategy are developed to minimize this error. Both two-dimensional (2-D) and three-dimensional (3-D) approaches for the technique are developed. It is shown that for a given number of retained coefficients, the discrete cosine transform (DCT)-Walsh mixed transform representation yields a more compact representation than using DCT or Walsh alone. This lossy technique is further extended for the lossless case. The coefficients are quantized and the signal is reconstructed. The resulting reconstructed signal samples are rounded to the nearest integer and the modified residual error is computed. This error is transmitted employing a lossless technique such as the Huffman coding. It is shown that for a given number of retained coefficients, the mixed transforms again produces the smaller rms-modified residual error. The first-order entropy of the error is also smaller for the mixed-transforms technique than for the DCT, thus resulting in smaller length Huffman codes.     

Atomic Layer Deposition of Nanostructured Materials for Energy and Environmental Applications

Atomic layer deposition (ALD) is a thin film technology that in the past two decades rapidly developed from a niche technology to an established method. It proved to be a key technology for the surface modification and the fabrication of complex nanostructured materials. In this Progress Report, after a short introduction to ALD and its chemistry, the versatility of the technique for the fabrication of novel functional materials will be discussed. Selected examples, focused on its use for the engineering of nanostructures targeting applications in energy conversion and storage, and on environmental issues, will be discussed. Finally, the challenges that ALD is now facing in terms of materials fabrication and processing will be also tackled.     

Electrodeposition of amorphous silicon in non-oxygenated organic solvent

We report on the synthesis of amorphous silicon using electrodeposition in two non-oxygenated organic solvents, acetonitril and dichloromethane, under controlled atmosphere. In both solvents, tetraethylammonium chloride has been used as a supporting electrolyte and silicon tetrachloride as a silicon precursor. The porosity and the morphology of the electrodeposited silicon layers have been studied as a function of depositing parameters (solvent, voltage, etc.). We will show the formation from dense to highly porous Si deposits as a function of solvent and experimental parameters. To increase the stability of the deposits before exposure to air, a heat treatment under hydrogen has been performed. The chemical and structural characterizations of the deposit by scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy show the formation of pure amorphous silicon.     

Multifidelity JPEG based compression of images using variablequantisation

In image processing applications, certain regions in an image may be of greater interest to the user. For these types of applications, a multifidelity region based variable quantisation scheme is proposed. The resulting subjective visual duality is considerably higher than for comparable compression ratios employing the standard JPEG implementation     

Adaptive vector quantisation of non-orthogonal representations for image compression

An efficient compression technique employing adaptive vector quantisation of multiple non-orthogonal transform domain representations of still images is developed. For each sub-image, the encoder selects a code from the domain that yields best representation. The performance improvement employing the proposed technique relative to existing single domain vector quantisation coding methods, for the same compression ratio, is obtained at the expense of increased computational complexity.     

Quartz crystal impedance response of nonhomogenous composite electrodes in contact with liquids

A new model of quartz-crystal impedance (QCI) of nonuniform layers composed of bumps of carbon particles (either porous or nonporous) and a polymeric binder layer has been proposed. The solid particles are modeled by semispherical and oblate semispheroid bumps embedded into the "sea" of a polymeric binder layer. On the basis of this model and elaborating on the principles of hydrodynamic spectroscopy of composite electrode materials, the geometric and porous structure parameters of nanoporous carbon and nonporous graphite composite electrodes in contact with liquids have been reliably determined. This work is believed to create a solid theoretical background for both advanced studies and optimized formulations of the composite electrodes suited to practical electrochemical devices and for the interpretation of the processes of ions and solvent insertion into nanoporous carbon electrodes uniquely probed by the QCI method (supercapacitive cells, desalination membranes).     

Stability properties of some RC active realisations

Some stability properties of a recently reported minimal-capacitor low-sensitivity RC active realisation of voltage transfer functions are investigated. It is shown that the realisation can attain a low-frequency unstable mode of operation. Five new circuits are derived from the original, using the theory of singular elements. Only two of these circuits are shown to be free from low-frequency unstable modes. The two new stable structures retain all the attractive features of the original realisation.     

Thermal and dyeing properties of acrylonitrile-glycidyl methacrylate copolymers

The copolymerization of acrylonitrile (AN) with glycidyl methacrylate (GMA) has been investigated in tetrahydrofuran (THF). The reactivity ratios were estimated and the thermal behaviour of the homo- as well as the copolymers, both in air, and under nitrogen atmosphere was investigated using differential thermal analysis (DTA) and thermogravimetry (TG) techniques. GMA was found to initiate the nitrile oligomerization reaction in the copolymers upon heating. The dyeing ability, as well as the colour fastness towards UV light have also been investigated. It was found that the copolymers showed better affinity towards basic dyes compared to homopolyacrylonitrile. This affinity increases with increasing the GMA content in the copolymer.