Scholar iON
Academic Synthesis
The body of research presented focuses on advanced methodologies and critiques within the fields of condensed matter physics, nuclear physics, and statistical physics. A key theme is the critical examination of methodological accuracy and applicability, such as the limitations of the equation of motion method in low-energy scales for quantum dots, and the critique of Raynal's ECIS formulation for failing to account for nonlocality effects in nucleon-nucleus elastic scattering. The research further explores statistical identities in spin glass models, emphasizing that observed identity violations in finite systems should vanish in the thermodynamic limit. Additionally, the measurement of isotopic yield distributions in fission fragments highlights the interplay between experimental data and theoretical models, demonstrating substantial agreement. These studies collectively underscore the necessity of rigorous methodological scrutiny and the integration of advanced theoretical models to enhance understanding and accuracy in complex physical systems.
The equation of motion method (EOM) is one of the approximations to calculate transport coefficients of interacting electron systems. The method is known to be useful to examine high-temperature properties. However, sometimes a naive application of the EOM fails to capture an important physics at low-energy scale, and it happens in recent preprints cond-mat/0309458 and cond-mat/0308413 which study a series of quantum dots. These preprints concluded that a unitarity-limit transport due to the Kondo resonance, which has been deduced from a Fermi-liquid behavior of the self-energy at T=0, $Ο=0$ [A.O., PRB {\bf 63}, 115305 (2001)], does not occur. We show that the EOM self-energy obtained with a finite cluster has accidentally a singular $1/Ο$ dependence around the Fermi energy, and it misleads one to the result incompatible with a Fermi-liquid ground state.
We comment on recent numerical experiments by G.Hed and E.Domany [cond-mat/0608535v2] on the quenched equilibrium state of the Edwards-Anderson spin glass model. The rigorous proof of overlap identities related to replica equivalence shows that the observed violations of those identities on finite size systems must vanish in the thermodynamic limit. See also the successive version cond-mat/0608535v4
A detailed investigation on the relative isotopic distributions has been carried out for the first time in case of even-even correlated fission fragments for the $^{235}$U($n_{th}$,$f$) fission reaction. High-statistics data were obtained in a prompt $Ξ³$ ray spectroscopy measurement during the EXILL campaign at ILL, Grenoble, France. The extensive off-line analysis of the coincidence data have been carried out using four different coincidence methods. Combining the results from 2-dimensional $Ξ³-Ξ³$ and 3-dimensional $Ξ³-Ξ³-Ξ³$ coincidence analysis, a comprehensive picture of the relative isotopic yield distributions of the even-even neutron-rich fission fragments has emerged. The experimentally observed results have been substantiated by the theoretical calculations based on a novel approach of isospin conservation, and a reasonable agreement has been obtained. The calculations following the semi-empirical GEF model have also been carried out. The results from the GEF model calculations are found to be in fair agreement with the experimental results.
Recently, we published a paper (Nucl. Phys. A 728 (2003) 65; see nucl-th/0306068) presenting a new calculational method for nucleon-nucleus elastic scattering at low energies. That method is particularly appropriate for analyses in the region of narrow resonances. The method is based upon the sturmian representation of the S-matrix, and allows inclusion of nonlocality effects due to Pauli principle. It also provides a systematic identification of narrow-resonance spectra and subthreshold bound states. A phenomenological test calculation for low-energy (below 4 MeV) neutrons on 12-C (including the first two excitations of the target) was presented to illustrate the validity of the approach. The model calculation received a violent criticism (see nucl-th/0312038) by the developer of a method (ECIS) which to date cannot handle nonlocality effects and cannot be used easily to identify all narrow resonances. We demonstrate that Raynal's opposition to our development is not well founded by the arguments he presents. Indeed the work we published shows, on rewording the title of nucl-th/0312038, that it is ``aberrant'' phenomenologically to analyze resonant low-energy nucleon-nucleus processes with coupled-channel methods without taking into account the nonlocalities due to the Pauli principle; problems typically encountered in the ECIS formulation.
This article continues our previous study of level dynamics in the [O(6)-U(5)]$\supset$O(5) transition of the interacting boson model [nucl-th/0504016] using the semiclassical theory of spectral fluctuations. We find classical monodromy, related to a singular bundle of orbits with infinite period at energy E=0, and bifurcations of numerous periodic orbits for E>0. The spectrum of allowed ratios of periods associated with beta- and gamma-vibrations exhibits an abrupt change around zero energy. These findings explain anomalous bunching of quantum states in the E$\approx$0 region, which is responsible for the redistribution of levels between O(6) and U(5) multiplets.
Recently, a longitudinal sum rule for the electric polarizability of nuclei was used to revise a relativistic correction in a dipole sum rule for the polarizability (nucl-th/9802011). This revision is shown to be wrong because of neglecting an asymptotic contribution in the underlying dispersion relation. The status and correct use of the longitudinal sum rule is clarified.
Purpose: To identify optimal classification methods for computed tomography (CT) radiomics-based preoperative prediction of clear cells renal cell carcinoma (ccRCC) grade. Methods and material: Seventy one ccRCC patients were included in the study. Three image preprocessing techniques (Laplacian of Gaussian, wavelet filter, and discretization of the intensity values) were applied on tumor volumes. In total, 2530 radiomics features (tumor shape and size, intensity statistics, and texture) were extracted from each segmented tumor volume. Univariate analysis was performed to assess the association of each feature with the histological condition. In the case of multivariate analysis, the following was implemented: three feature selection including the least absolute shrinkage and selection operator (LASSO), students t-test and minimum Redundancy Maximum Relevance (mRMR) algorithms. These selected features were then used to construct three classification models (SVM, random forest, and logistic regression) to discriminate the high from low-grade ccRCC at nephrectomy. Lastly, multivariate model performance was evaluated on the bootstrapped validation cohort using the area under receiver operating characteristic curve (AUC). Results: Univariate analysis demonstrated that among different image sets, 128 bin discretized images have statistically significant different (q-value < 0.05) texture parameters with a mean of AUC 0.74 (q-value < 0.05). The three ML-based classifier shows proficient discrimination of the high from low-grade ccRCC. The AUC was 0.78 in logistic regression, 0.62 in random forest, and 0.83 in SVM model, respectively. Conclusion: Radiomics features can be a useful and promising non-invasive method for preoperative evaluation of ccRCC Fuhrman grades. Key words: RCC, Radiomics, Machine Learning, Computed Tomography