We first review the shell evolution in exotic nuclei driven by nuclear forces. We then demonstrate that the underlying mechanism played by the balance of the tensor and central components in the ...effective nucleon-nucleon interaction is crucial when describing shape coexistence. This effect will be referred to as type II shell evolution, while the shell evolution passing through a series of isotopes or isotones is denoted as type I. We describe type II shell evolution in some detail for the case of the 68Ni nucleus as an example. We present how the fission dynamics can be related to enhanced deformation triggered by type II shell evolution, at its initial stage. It is suggested that the island of stability may be related to the suppression of this mechanism.
A long-standing crucial question with atomic nuclei is whether or not α clustering occurs there. An α particle (helium-4 nucleus) comprises two protons and two neutrons, and may be the building block ...of some nuclei. This is a very beautiful and fascinating idea, and is indeed plausible because the α particle is particularly stable with a large binding energy. However, direct experimental evidence has never been provided. Here, we show whether and how α(-like) objects emerge in atomic nuclei, by means of state-of-the-art quantum many-body simulations formulated from first principles, utilizing supercomputers including K/Fugaku. The obtained physical quantities exhibit agreement with experimental data. The appearance and variation of the α clustering are shown by utilizing density profiles for the nuclei beryllium-8, -10 and carbon-12. With additional insight by statistical learning, an unexpected crossover picture is presented for the Hoyle state, a critical gateway to the birth of life.
The underlying structure of low-lying collective bands of atomic nuclei is discussed from a novel perspective on the interplay between single-particle and collective degrees of freedom, by utilizing ...state-of-the-art configuration interaction calculations on heavy nuclei. Besides the multipole components of the nucleon-nucleon interaction that drive collective modes forming those bands, the monopole component is shown to control the resistance against such modes. The calculated structure of ^{154}Sm corresponds to the coexistence between prolate and triaxial shapes, while that of ^{166}Er exhibits a deformed shape with a strong triaxial instability. Both findings differ from traditional views based on β/γ vibrations. The formation of collective bands is shown to be facilitated from a self-organization mechanism.
We explore two-particle transfer reactions as a crucial probe of the occurrence of shape coexistence in shape phase transitions. The (t,p) reactions to the ground state and to excited 0+ states are ...calculated for the isotope chain of even-even Zirconium isotopes starting from stable nuclei up to beyond current experimental limits. Two-particle spectroscopic factors derived from Monte Carlo Shell Model calculations are used, together with the sequential description of the two-particle transfer reaction mechanism. The calculation shows a clear signature for a shape phase transition between 98Zr and 100Zr, which displays coexistence of a deformed ground state with an excited spherical 0+ state. Furthermore, we show that there is a qualitative difference with respect to the case of a normal shape phase transition that can be discriminated with two-neutron transfer reactions.
This study investigates group navigation with the aid of strong interaction between two kinds of agents: A shepherd drives a sheep group with a large population to a given goal position. Even though ...numerous studies have been performed on the realization of shepherd-like navigation, they are based on the condition that all sheep positions are given. This study examines the navigation of a sheep group using a local-camera-based approach, i.e. a shepherd perceives sheep using the shepherd's vision. Before testing local-camera-based navigation, we design a shepherd controller referred to as a farthest-agent targeting controller, in which the shepherd selects the sheep farthest from the goal. We demonstrate the validity of the proposed controller using statistical analysis and comparison with previous conventional controllers. After examining the effectiveness of this controller, we show that the controller works appropriately even if the shepherd cannot know all sheep positions. In addition, we show the robustness of the proposed controller for the positional errors of the sheep flock or for agent-lost cases to apply it to real-world situations.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The atomic masses of ^{55}Sc, ^{56,58}Ti, and ^{56-59}V have been determined using the high-precision multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN's ...Radioactive Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system, which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For ^{56,58}Ti and ^{56-59}V, the mass uncertainties have been reduced down to the order of 10 keV, shedding new light on the N=34 shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species ^{58}Ti and ^{59}V. With the new precision achieved, we reveal the nonexistence of the N=34 empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap above the occupied νp_{3/2} orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell model calculations including the νd_{5/2} and νg_{9/2} orbits and compare the results with conventional shell model calculations, which exclude the νg_{9/2} and the νd_{5/2} orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at N=34.
Twenty-four calves were cloned from six somatic cell types of female and male adult, newborn and fetal cows. The clones were derived from female cumulus (n = 3), oviduct (n = 2) and uterine (n = 2) ...cells, female and male skin cells (n = 10), and male ear (n = 5) and liver (n = 2) cells. On the basis of the number of cloned embryos transferred (n = 172) to surrogate cows, the overall rate of success was 14%, but based on the number of surrogate mothers that became pregnant (n = 50), the success rate was 48%. Cell nuclei from uterus, ear and liver cells, which have not been tested previously, developed into newborn calves after nuclear transfer into enucleated oocytes. To date, seven female and six male calves have survived: six of the females were from adult cells (cumulus (n = 3), oviduct (n = 2) and skin (n = 1) cells) and one was from newborn skin cells, whereas the male calves were derived from adult ear cells (n = 3), newborn liver and skin cells (n = 2), and fetal cells (n = 1). Clones derived from adult cells frequently aborted in the later stages of pregnancy and calves developing to term showed a higher number of abnormalities than did those derived from newborn or fetal cells. The telomeric DNA lengths in the ear cells of three male calves cloned from the ear cells of a bull aged 10 years were similar to those of the original bull. However, the telomeric DNA lengths from the white blood cells of the clones, although similar to those in an age-matched control, were shorter than those of the original bull, which indicates that telomeric shortening varies among tissues.
Nuclear charge radii of 62−80Zn have been determined using collinear laser spectroscopy of bunched ion beams at CERN-ISOLDE. The subtle variations of observed charge radii, both within one isotope ...and along the full range of neutron numbers, are found to be well described in terms of the proton excitations across the Z=28 shell gap, as predicted by large-scale shell model calculations. It comprehensively explains the changes in isomer-to-ground state mean square charge radii of 69−79Zn, the inversion of the odd-even staggering around N=40 and the odd-even staggering systematics of the Zn charge radii. With two protons above Z=28, the observed charge radii of the Zn isotopic chain show a cumulative effect of different aspects of nuclear structure including single particle structure, shell closure, correlations and deformations near the proposed doubly magic nuclei, 68Ni and 78Ni.
Purpose The purpose of this study was to assess the diagnostic value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for lymph node (LN) metastasis of ...colorectal cancer. Methods FDG-PET/CT was used to preoperatively evaluate 88 patients with colorectal cancer. In this study, LN sites were divided into proximal and distant according to their distance from the primary tumor. The FDG-PET/CT images were evaluated by three criteria; nodal diameter, abnormal uptake and maximum standardized uptake value (SUV). We compared the diagnostic ability of these methods for LN metastasis at proximal and distant sites. Results The mean SUV of the malignant LNs was significantly higher than that of the benign LNs. The sensitivity, specificity and accuracy of diagnosis by abnormal uptake were 28.6, 92.9 and 75.0%, those by nodal diameter using cutoff value of 10 mm were 30.6, 95.3 and 74.4% and those by SUV using cutoff value of 1.5 were 53.1, 90.6 and 80.1%, respectively. The sensitivity, specificity and accuracy of diagnosis based on optimal SUV were 51.2, 85.1 and 69.3% in the proximal site and 62.5, 92.5 and 89.7%, respectively, in the distant site. Conclusions FDG-PET/CT is useful for preoperative diagnosis of distant LN metastases of colorectal cancers.
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