A realistic many-body approach to the EMC effect

The EMC effect in few nucleon systems and complex nuclei is calculated within a realistic many-body approach. The effect ofQ ²-rescaling is also investigated.Contributed paper to the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia, September 5–10, 1988.     

A correlated-basis-functions approach to realistic nuclear matter

The method of correlated basis functions is adapted to the nuclear-matter problem with two-nucleon potentials containing tensor as well as central components. Procedures are described for evaluating through three-body cluster order the energy expectation value with respect to a constrained trial ground-state wave function incorporating tensor and central correlations, and for calculating in two-body cluster approximation the second-order perturbation correction in a basis of likewise-correlated functions. Results for the 5100, 5200, Gammel-Christian-Thaler and Hamada-Johnston potentials are presented and dissected.     

A new approach to produce spread-out Bragg peak using the MINUIT fit

A new approach to obtain a spread-out Bragg peak (SOBP) using the MINUIT fit is presented. The SOBP has been adopted in proton therapy in order to irradiate a proton beam equally over the tumor along the beam direction. In principle, an SOBP can be easily obtained by using several Bragg peaks from different beam energies, since the position of the peak varies with the energy. However, this is not practical in real medical situations, because the beam energy is fixed by the accelerator. Thus, a modulation method has been employed to obtain an SOBP, where the position of Bragg peak is controlled by a modulator with varying thickness. In this study, we use the GEANT4 package to simulate a generic proton therapy apparatus. A modulator with thickness control is assumed in the proton therapy setup and a set of Bragg peaks is obtained from the GEANT4 simulation. Assuming that the position and the size of the tumor are known, we first determine which Bragg peaks should be used in the fit. Then a MINUIT fit is applied to calculate the weights of each Bragg peak in order to maximize the flatness of the SOBP while minimizing the dose in the normal tissue area, thus maximizing the dose in the tumor. The fit has turned out to be very robust and converges quickly. Since the MINUIT is a small size library and the proposed SOBP fit shows stable behavior, this method can be readily applied to the real therapy.     

Axiomatic foundations of nonrelativistic quantum mechanics: A realistic approach

A realistic axiomatic formulation of nonrelativistic quantum mechanics for a single microsystem with spin is presented, from which the most important theorems of the theory can be deduced. In comparison with previous formulations, the formal aspect has been improved by the use of certain mathematical theories, such as the theory of rigged spaces, and group theory. The standard formalism is naturally obtained from the latter, starting from a central primitive concept: the Galilei group.     

A multi-frequency EPR spectroscopy approach in the detection of boson peak excitations

The influence of boson peak (BP) excitations on low-temperature spin-lattice relaxation rate of a paramagnetic center embedded in a glassy matrix is investigated in the context of multi-frequency electron paramagnetic resonance (EPR) detection. In the theoretical analysis, the transition rate of spin one-half in the presence of a phonon field is calculated within the approximation of Fermi's golden rule. Several phonon densities of states are compared, among which one originating from a model of quasi-localized vibrations has been introduced into electron spin relaxation formalism for the first time. The respective frequency dependencies of spin-lattice relaxation rates are predicted which should lead to observable effects of BP modes if a multi-frequency study at very low temperatures is performed.     

A generalized approach to automated NMR peak list editing: application to reduced dimensionality triple resonance spectra

We present an algorithm and program called Pattern Picker that performs editing of raw peak lists derived from multidimensional NMR experiments with characteristic peak patterns. Pattern Picker detects groups of correlated peaks within peak lists from reduced dimensionality triple resonance (RD-TR) NMR spectra, with high fidelity and high yield. With typical quality RD-TR NMR data sets, Pattern Picker performs almost as well as human analysis, and is very robust in discriminating real peak sets from noise and other artifacts in unedited peak lists. The program uses a depth-first search algorithm with short-circuiting to efficiently explore a search tree representing every possible combination of peaks forming a group. The Pattern Picker program is particularly valuable for creating an automated peak picking/editing process. The Pattern Picker algorithm can be applied to a broad range of experiments with distinct peak patterns including RD, G-matrix Fourier transformation (GFT) NMR spectra, and experiments to measure scalar and residual dipolar coupling, thus promoting the use of experiments that are typically harder for a human to analyze. Since the complexity of peak patterns becomes a benefit rather than a drawback, Pattern Picker opens new opportunities in NMR experiment design.     

A realistic experiment to demonstrate macroscopic quantum coherence

According to quantum theory, microscopic objects exist in a superposition of distinct states until they are “observed”. Nobody knows whether such quantum coherence can actually exist in a macroscopic system. In the experiment described here, a superconducting quantum interference device is extremely well isolated from any interaction with internal or external modes, and a superposition state can be demonstrated even if it lasts for less than 1 ns. This is accomplished by using superconducting digital electronic circuitry as the experimental apparatus. If successful, it is the first step toward a future full-scale quantum computer fabricated using integrated circuit manufacturing techniques.     

Water peak suppression: time-frequency vs time-scale approach

Wavelets are the most popular time-scale analysis tool. A well-known application of wavelets in nuclear magnetic resonance spectroscopy is water peak extraction/suppression. However, spectroscopists are more familiar with frequency than scale. So, from a spectroscopist point of view, a time-scale analysis tool (i.e., wavelets) is not natural and a time-frequency approach would be much more satisfactory. We explain a time-frequency solution to this problem based on Gabor analysis. As the two formalisms are closely linked together we continuously emphasize their similarities and differences. In particular we show that, here, the Gabor method is as efficient as the wavelet approach, and we give some examples. Those remarks also apply to other NMR problems solved previously with the continuous wavelet transform, such as quantification or dynamical phase correction.     

The filtering approach to solvent peak suppression in MRS: a critical review

Suppressing the solvent peak is important in many applications of biomedical NMR spectroscopy in order to quantify the metabolites with a great accuracy. Among the postprocessing methods proposed in the literature, many deal with the concept of filtering. However, several proposals lack a theoretical perspective and some have not been explicitly applied to quantification problems. The present article is intended to bridge this gap: five methods are analyzed from a theoretical perspective. Subsequently the different methods are applied to the same set of data, and then the latter are quantified using the model fitting method AMARES. With our set, the scheme proposed by T. Sundin et al. (J. Magn. Reson. 139(2), 189-204 (1999)) proved to be the most reliable method.     

Electronic density of states of group-IV semiconductors: A cluster-Bethe lattice approach for realistic Hamiltonians

We have extended the cluster-Bethe lattice method to study realistic tight-binding Hamiltonians. The numerical solution of the transfer matrix in the Bethe lattice is very stable and requires about 50 steps of our iterative procedure to reach convergency. We apply this method to study the density of states of group-IV semiconductors (C, Si, Ge) using a five-parameter sp³ Hamiltonian, which takes into account all possible interactions between sp³ hybrids in nearest-neighbor atoms. Our results show clearly that the main features of the density of states are due to short-range order. Clusters of about 30 atoms reproduce very well the crystalline density of states. Based on our results we propose a model for the density of states in the gap region of an amorphous semiconductor.     

A realistic heat bath: theory and application to kink-antikink dynamics

We propose a new method of studying a real-time canonical evolution of field-theoretic systems with boundary coupling to a realistic heat bath. In the free-field case the method is equivalent to an infinite extension of the system beyond the boundary, while in the interacting case the extension of the system is done in linear approximation. We use this technique to study kink-antikink dynamics in φ⁴ field theory in 1+1 dimensions.     

Three-body monopole corrections to realistic interactions

It is shown that a very simple three-body monopole term can solve practically all the spectroscopic problems-in the p, sd, and pf shells-that were hitherto assumed to need drastic revisions of the realistic potentials.     

One-dimensional solar radiative transfer: Perturbation approach and its application to independent-pixel calculations for realistic cloud fields

The radiative transfer perturbation theory (RTPT), which has already been introduced in atmospheric radiative transfer several years ago, is applied to cloud related problems. The RTPT requires the solution of the radiative transfer equation in the forward and the adjoint mode. The basic principles of this technique are presented as well as its extensions to isotropic surface reflection and its conjunction with the Hermite interpolation. This set of methods is applied to different atmospheric conditions including realistic cloud scenes. The results are compared with the usual (forward) independent-pixel calculations with respect to errors of individual pixels and domain-averaged values. The RTPT turns out to be sufficiently accurate in the case the clouds’ internal vertical variations remain moderate. It is also shown that, depending on the specific radiative transfer problem, the RTPT can offer some advantages on computational speed. However, the limitations of the RTPT with regard to realistic clouds are addressed as well.     

A simple and realistic triton wave function

We propose a simple triton wave function that consists of a product of three correlation operators operating on a three-body spin-isospin state. This wave function is formally similar to that used in the recent variational theories of nuclear matter, the main difference being in the long-range behavior of the correlation operators. Variational calculations are carried out with the Reid potential, using this wave function in the so-called “symmetrized product” and “independent pair” forms. The triton energy and density distributions obtained with the symmetrized product wave function agree with those obtained in Faddeev and other variational calculations using harmonic oscillator states. The proposed wave function and calculational methods can be easily generalized to treat the four-nucleon α-particle.     

A realistic structural model of glassy iron

The Ichikawa model with k = 2.0 (the Bennett model) for iron was relaxed using Johnson's potential and the potential by Pak and Doyama. The relaxed models reproduce the experimental pair-distribution function and structure sensitive intensity and have high packing fractions.     

A local realistic explanation of EPR correlations

The reality of physical properties is divided into two types: relatively and absolutely real. Concerning the reality of spatial observables, it is proposed to drop the concept of an absolute reality of spatial observables. The resulting relative reality then isnot the observer-dependent reality of the standard interpretation of quantum mechanics, but rather the reference frame-dependent reality implied by the principle of relativity. Within the frame of this relative reality, it is then shown that a local explanation for the existence of EPR correlations can be found when two-valued discrete spatially directed observables (like the spin-1/2 components of electrons, or the polarization states of photons) are assumed. The new explanation is formally analogous to the standard explanation of classical correlations at a distance. Sufficient assumptions to obtain this result are the isotropy of space and the existence of two-valued discrete spatially directed observables. Thus, the possibility to find a both local and realistic explanation of correlations at a distance is extended to quantum variables violating Bell's inequality.     

A realistic three-dimensional calculation of the 3H binding energy

Recently developed three-dimensional Faddeev integral equations for the three-nucleon bound state with two-nucleon interactions have been solved in momentum space for the Bonn-B potential.     

A hamiltonian approach to the roper resonance

The breathing modes along with the spin-isospin zero modes of the ω-stabilized skyrmion are quantized using Dirac's method. The result is a hamiltonian for the nucleon, the δ-isobar and the Roper with explicit meson couplings. The linear pion coupling is used to evaluate the decay width of the Roper into πN.     

A fractional approach to the Fermi-Pasta-Ulam problem

This paper studies the Fermi-Pasta-Ulam problem having in mind the generalization provided by Fractional Calculus (FC). The study starts by addressing the classical formulation, based on the standard integer order differential calculus and evaluates the time and frequency responses. A first generalization to be investigated consists in the direct replacement of the springs by fractional elements of the dissipative type. It is observed that the responses settle rapidly and no relevant phenomena occur. A second approach consists of replacing the springs by a blend of energy extracting and energy inserting elements of symmetrical fractional order with amplitude modulated by quadratic terms. The numerical results reveal a response close to chaotic behaviour.