A simplified approach for the generation of projection data for cone beam geometry

To test a developed reconstruction algorithm for cone beam geometry, whether it is transmission or emission tomography, one needs projection data. Generally, mathematical phantoms are generated in three dimensions and the projection for all rotation angles is calculated. For non-symmetric objects, the process is cumbersome and computation intensive. This paper describes a simple methodology for the generation of projection data for cone beam geometry for both transmission and emission tomographies by knowing the object’s attenuation and/or source spatial distribution details as input. The object details such as internal geometrical distribution are nowhere involved in the projection data calculation. This simple approach uses the pixilated object matrix values in terms of the matrix indices and spatial geometrical coordinates. The projection data of some typical phantoms (generated using this approach) are reconstructed using standard FDK algorithm and Novikov’s inversion formula. Correlation between the original and reconstructed images has been calculated to compare the image quality.     

A variational approach to estimate incompressible fluid flows

A variational approach is used to recover fluid motion governed by Stokes and Navier–Stokes equations. Unlike previous approaches where optical flow method is used to track rigid body motion, this new framework aims at investigating incompressible flows using optical flow techniques. We formulate a minimization problem and determine conditions under which unique solution exists. Numerical results using finite element method not only support theoretical results but also show that Stokes flow forced by a potential are recovered almost exactly.     

NEW APPROXIMATE PHASE FUNCTIONS FOR SCATTERING OF UNPOLARIZED LIGHT BY DIELECTRIC PARTICLES

We present two new phase functions, one for particles small compared to the wavelength of the scattering radiation and the other for particles large compared to the wavelength of the scattering radiation. These phase functions have been validated for the case of Mie scatterers. For small particles, the results of the new phase function are found to be identical with the Mie results. For large particles, comparison with the Mie results show that the phase function presented here is an extremely good approximation to the Mie phase function. We believe that these phase functions can be expediently used in problems relating to solutions of the radiative transfer equations.     

Why Large Hadron Collider?

I discuss LHC physics in the historical perspective of the progress in particle physics. After a recap of the Standard Model (SM) of particle physics, I discuss the high energy colliders leading up to LHC and their role in the discovery of these SM particles. Then I discuss the two main physics issues of LHC, i.e. Higgs mechanism and supersymmetry. I briefly touch upon Higgs and SUSY searches at LHC along with their cosmological implications.     

PHOTOCHEMISTRY OF BENZOTHIAZOLE MODELS OF PHEOMELANIN

Abstract— The photochemistry of several 4-hydroxy- and 4-methoxybenzothiazoles has been investigated by laser flash photolysis. In aqueous solutions of pH3–12, the 4-hydroxybenzothiazole chromophore undergoes monophotonic photoionization to afford e^-_aq with quantum yields on the order of 0.06; no evidence for triplet species was obtained. The spectra and stability of the resultant free radicals were determined using pulse radiolysis. In contrast, triplet transients with life-times on the order of 8 mUs are readily observable upon irradiation of the 4-methoxybenzothiazole analog. Triplet sensitization experiments with the water-soluble carotenoid crocetin were employed to obtain the triplet extinction coefficients and subsequently the triplet quantum yields. The significance of these differences in photochemical behavior is discussed in relationship to the photochemistry and photobiology of the epidermal melanin pigment pheomelanin.     

ITINERANT MAGNETISM IN ULTRATHIN METALLIC FILMS

This paper addresses the question: “How do we define a two-dimensional itinerant magnet?” Results are presented indicating a cross-over from three-dimensional (3D) to two-dimensional (2D) behavior at a finite-size film thickness. It is argued that quantization of the electronic states in ultrathin metallic films dictate this behavior. Data from a broad range of epitaxial ferromagnetic films grown on different metallic substrates suggest a cross-over into just two classes of 2D behavior, viz 2D Ising model in the presence of uniaxial surface anisotropy and finite-size lattice 2D XY model behavior in films in which the preferred direction of magnetization lies in-plane. In this ultrathin film 2D limit, the Curie temperature falls rapidly to zero as the thickness approaches a single monolayer due to the sudden onset of disordered microdomains.     

Two-soliton and three-soliton interactions of electron acoustic waves in quantum plasma

The overtaking collision between electron acoustic multisolitons in an unmagnetized quantum plasma consisting of ions, and both hot and cold electrons has been investigated. The Hirota bilinear method is employed to study phase shifts and trajectories during the overtaking collision of multisolitons. It is observed that phase shifts are significantly affected by the quantum parameter H. The phase shifts are proportional to B^1/3 (dispersion coefficient) and are functions of their respective amplitudes. It is also seen that the soliton structure occurs only if H < 2.