Matching characteristics of the physically short linear impedance transformer

In contrast to the conventional quarter-wavelength transformer for matching two transmission lines of different characteristic impedance, it has been found that the length can be significantly shortened by using two stratified line sections in cascade. The frequency response of this short-length transformer (SLT) is investigated and it is shown that asymmetry and a reduction in matching bandwidth is the price to be paid for a shorter length. A comparison has also been made with the short-step transformer of Matthaei, which also provides a reduction in length

On the Selectivity of a Resistance Capacitance Network

A resistance, capacitance network, used in circuits for generation (Wien bridge oscillator) and measurement (Wien bridge) of low frequencies, has been analysed for the maximum selectivity condition by defining a design parameter n. It has been shown that a lower value of n gives (i) a more selective response and as such, a purer waveform in the oscillator circuit and a sharper null point in the Wien bridge circuit and (ii) a more favourable condition of operation of the active device in the oscillator circuit. The effect of cascading such networks on the selectivity of the resultant transfer characteristic has been discussed.The effect of interchanging the series and the shunt arms of the network has been considered. It has been shown that if n is high, the resulting network has a characteristic similar to that of a Wien bridge and is superior to the latter in some respects

Compact analogue neural network: a new paradigm for neural based combinatorial optimisation

The authors present a new approach to neural based optimisation, to be termed as the compact analogue neural network (CANN), which requires substantially fewer neurons and interconnection weights as compared to the Hopfield net. They demonstrate that the graph colouring problem can be solved by using the CANN, with only O(N) neurons and O(N2) interconnections, where N is the number of nodes. In contrast, a Hopfield net would require N2 neurons and O(N4) interconnection weights. A novel scheme for realising the CANN in hardware form is discussed, in which each neuron consists of a modified phase locked loop (PLL), whose output frequency represents the colour of the relevant node in a graph. Interactions between coupled neurons cause the PLLs to equilibrate to frequencies corresponding to a valid colouring. Computer simulations and experimental results using hardware bear out the efficacy of the approach

Bioactive composites for bone tissue engineering

One of the major challenges of bone tissue engineering is the production of a suitable scaffold material. In this review the current composite materials options available are considered covering both the methods of both production and assessing the scaffolds. A range of production routes have been investigated ranging from the use of porogens to produce the porosity through to controlled deposition methods. The testing regimes have included mechanical testing of the materials produced through to in vivo testing of the scaffolds. While the ideal scaffold material has not yet been produced, progress is being made

On digital differentiators, Hilbert transformers, and half-band low-pass filters

Interrelationships between the digital differentiator (DD), the digital Hilbert transformer (DHT), and the half-band low-pass (½-LPF) are brought out. A number of important properties confirming the close proximity of these filters are highlighted. Theoretical results are substantiated by transforming minimax relative error DDs to equiripple DHTs and equiripple ½-LPFs. Relations connecting their impulse responses and their frequency responses are brought out. The precise frequencies of ripple extrema and the magnitudes of their peaks are shown to be simple related to the corresponding values for the minimax relative error differentiators

Polymeric ionic liquid nanoparticle emulsions as a corrosion inhibitor in anticorrosion coatings

In this contribution, we report the facile preparation of cross-linked polymerizable ionic liquid (PIL)-based nanoparticles via thiol–ene photopolymerization in a miniemulsion. The synthesized PIL nanoparticles with a diameter of about 200 nm were fully characterized with regard to their chemical structures, morphologies, and properties using different techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. To gain an in-depth understanding of the physical and morphological structures of the PIL nanoparticles in an emulsion, small-angle neutron scattering and ultra-small-angle neutron scattering were used. Neutron scattering studies revealed valuable information regarding the formation of cylindrical ionic micelles in the spherical nanoparticles, which is a unique property of this system. Furthermore, the PIL nanoparticle emulsion was utilized as an inhibitor in a self-assembled nanophase particle (SNAP) coating. The corrosion protection ability of the resultant coating was examined using potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the PIL nanoparticle emulsion in the SNAP coating acts as an inhibitor of corrosion and is promising for fabricating advanced coatings with improved barrier function and corrosion protection.Mona Taghavikish, Surya Subianto, Naba Kumar Dutta, Liliana de Campo, Jitendra P. Mata, Christine Rehm, and Namita Roy Choudhur

One-loop flavor changing electromagnetic transitions

We discuss the effect of the external fermion masses in the flavor-changing radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion at the one-loop level, and point out an often overlooked crucial difference in the sign of a charge factor between transitions of the down type $s\to d\gamma$ and the up type $c\to u\gamma$. We give formulas for the $F\to f\gamma$ effective vertex in various approximations and the exact formula for $t\to c\gamma$ and $\tau \to \mu \gamma$.Comment: LaTeX 16 pages + 4 postscript figures. Misprints corrected, some Comments adde

Omega meson as a chronometer and thermometer in hot-dense hadronic matter

Changes in the properties of the vector mesons in hot and dense hadronic matter, as produced in heavy ion collisions, lead to the intriguing possibility of the opening of the decay channel \omega \ra \rho \pi, for the omega meson, which is impossible in free space. This along with the channel \omega \pi \ra \pi \pi would result in a decrease in its effective life-time enabling it to decay within the hot zone and act as a chronometer in contradiction to the commonly held opinion and would have implications vis a vis determination of the size of the region through pion interferometry. A new peak and a radically altered shape of the low invariant mass dilepton spectra appears due to different shift in the masses of $\rho$ and $\omega$ mesons. The Walecka model is used for the underlying calculation for the sake of illustration.Comment: To appear in Phys. ReV.

New Supersymmetric Contributions to t−>cVt->cV

We calculate the electroweak-like one-loop supersymmetric contributions to the rare and flavor-violating decay of the top quark into a charm quark and a gauge boson: $t->c V$, with $V=\gamma,Z,g$. We consider loops of both charginos and down-like squarks (where we identify and correct an error in the literature) and neutralinos and up-like squarks (which have not been calculated before). We also account for left-right and generational squark mixing. Our numerical results indicate that supersymmetric contributions to $t->cV$ can be upto 5 orders of magnitude larger than their Standard Model counterparts. However, they still fall short of the sensitivity expected at the next-generation top-quark factories.Comment: 13 pages, LaTex, 1 figure included. Final version to appear in Physical Review D. Chargino contribution dealt with in greater detail. Minor revisions in tex

Unstable particles in matter at a finite temperature: the rho and omega mesons

Unstable particles (such as the vector mesons) have an important role to play in low mass dilepton production resulting from heavy ion collisions and this has been a subject of several investigations. Yet subtleties, such as the implications of the generalization of the Breit-Wigner formula for nonzero temperature and density, e.g. the question of collisional broadening, the role of Bose enhancement, etc., the possibility of the kinematic opening (or closing) of decay channels due to environmental effects, the problem of double counting through resonant and direct contributions, are often given insufficient emphasis. The present study attempts to point out these features using the rho and omega mesons as illustrative examples. The difference between the two versions of the Vector Meson Dominance Model in the present context is also presented. Effects of non-zero temperature and density, through vector meson masses and decay widths, on dilepton spectra are studied, for concreteness within the framework of a Walecka-type model, though most of the basic issues highlighted apply to other scenarios as well.Comment: text and figures modifie