Electron beam damage of chemisorbed surface species: A tunneling spectroscopy study

Electron beam damage is a problem for low-energy electron diffraction, Auger electron spectroscopy, and electron microscopy. We have used tunneling spectroscopy to study the damage caused by 30 keV incident electrons on chemisorbed monolayer films of hexanoic acid, 2,4-hexadienoic acid, and benzoic acid. Our results on monolayer films are compared to existing work on bulk samples. Damage cross sections are similar to bulk values; molecules with more delocalized electrons are more resistant to damage. In contrast to bulk results, however, we find little if any conjugation or cross linking after irradiation.     

On the microscopic basis of Newton's law of cooling and beyond

The microscopic basis of Newton's law of cooling and its modification when the difference in temperature between the system and the surroundings is very large is discussed. When the system of interest is interacting with a small bath, the effect of the dynamical evolution of the bath variables is important to find out its dynamical feedback on the system. As in the usual system-bath approach, however, the bath is finally considered to be in thermal equilibrium and thereby provides an effective generalization of the Born-Markov master equation. It is shown that the cooling at early time is faster than that predicted by Newton's law due to the dynamical feedback of the bath.     

Analysis of diffraction efficiency of a holographic coupler with respect to angular divergence

We present a method to optimize the Coupling efficiency between two fibers using a Holographic Coupler taking diffraction effect into account. For this we obtain expressions for field distributions at the end facet of a fiber. The results obtained by using the expression is found to be in good agreement with the finite element method in literature, the small deviation is attributed to the negligence of field in the cladding. We then use the Kogelnik theory to obtain useful formulae suitable for diffracted optical elements. The diffraction efficiency expressions are then used to predict the different parameters of Holograting so as to get maximum diffraction efficiency in a direction where the field distribution from the end facet is minimum thereby increasing the coupling efficiency.      

A Degenerate Birdcage with Integrated Tx/Rx Switches and Butler Matrix for the Human Limbs at 7 T

The theoretically known degeneracy condition of the band-pass birdcage coil has rarely been exploited in transmit coil designs. We have created an eight-channel degenerate birdcage for the human limbs at 7 T, with dedicated Tx/Rx switches and a Butler matrix. The coil can be split into two half cylinders, as required for its application to patients with limited mobility. The design of the coil, the Butler matrix, and Tx/Rx switches relied on a combination of analytical, circuital, and numerical simulations. The birdcage theory was extended to the degenerate case. The theoretical and practical aspects of the design and construction of the coil are presented. The performance of the coil was demonstrated by simulations, workbench, and scanner measurements. The fully assembled prototype presents good performance in terms of efficiency, B₁ homogeneity, and signal-to-noise ratio, despite the asymmetry introduced by the splittable design. The first in vivo images of the knee are also shown. A novel RF coil design consisting of an eight-channel splittable degenerate birdcage has been developed, and it is now available for 7 T MRI applications of the human lower limbs, including high-resolution imaging of the knee cartilages and of the patellar trabecular structure.     

Pseudo-supersymmetry and third order intertwining operator

It has been shown how one can obtain an intertwining operator of order (in terms of derivatives) higher than two, linking a non-Hermitian Hamiltonian to its Hermitian conjugate partner. Explicit third order realization of this intertwining operator is derived for complex Scarf potential.     

Dynamical symmetry breaking of lambda- and vee-type three-level systems on quantization of the field modes

We develop a scheme to construct the Hamiltonians of the lambda-, vee- and cascade-type three-level configurations using the generators of SU(3) group. It turns out that this approach provides a well-defined selection rule to give different Hamiltonians for each configuration. The lambda- and vee-type configurations are exactly solved with different initial conditions while taking the two-mode classical and quantized fields. For the classical field, it is shown that the Rabi oscillation of the lambda model is similar to that of the vee model and the dynamics of the vee model can be recovered from lambda model and vice versa simply by inversion. We then proceed to solve the quantized version of both models by introducing a novel Euler matrix formalism. It is shown that this dynamical symmetry exhibited in the Rabi oscillation of two configurations for the semiclassical models is completely destroyed on quantization of the field modes. The symmetry can be restored within the quantized models when both field modes are in the coherent states with large average photon number which is depicted through the collapse and revival of the Rabi oscillations.      

Infrared Spectroscopic and Thermal Studies of Gel Grown Spherulitic Crystals of Iron Tartrate

Growth of spherulitic crystals of iron tartrate by controlled diffusion in sodium metasilicate gels has been described. Infrared spectroscopic, thermogravimetric and elemental analysis have been conducted to characterize the crystals. The results are interpreted and explained.     

Spiked and screened oscillatorsV(r) =Ar 2 +B/r 2 +C/r 4 +D/r 6 +F/(1 +Gr)2 and their elementary bound states

We show that the complicated superpositionsV(r) of several important phenomenological forces may still lead to an elementary form of doublets of bound states under transparent algebraic constraints. Constructively, we show how (and when) the constrained couplings preserve compatibility with the physical regularity of wavefunctions.     

Electromagnetic field in two-dimensional locally flat space-time

It is shown that an infinite-dimensional symmetry is present in two-dimensional electromagnetic field theory. The generators of the ensuing Virasoro algebra are explicitly calculated both for periodic and antiperiodic fields.     

Sine-Gordon equation in curved space-time

We study the static solution of the sine-Gordon wave equation in a background geometry determined by a point mass in 1+1 dimension.