Shell Model Research Articles

Characterization of the gravitational wave spectrum from sound waves within the sound shell model

Characterization of the gravitational wave spectrum from sound waves within the sound shell model

STUDYING INELASTIC TRANSVERSE ELECTRON SCATTERING FORM FACTORS OF THE ISOSCALAR TRANSITIONS IN 10B NUCLEUS

The inelastic transverse electron scattering form factors are studied for the fourisoscalar transitions for the states of 10B nucleus. These states are specifiedby J T  =1+0 (0.718 MeV), 1 0 2 (2.154 MeV), 2+0 (3.587 MeV) and 3 0 2 (4.774MeV). These form factors are analyzed in the framework of the harmonic oscillatorshell model.The transverse form factors have been calculated in the framework of the multinucleonconfiguration mixing shell model using the two-body interaction of Cohenand Kurath (C-K) to generate the 1p-shell wave function. The core polarization (CP)effects are included in the calculations through effective g-factors. A higherconfiguration effect outside the 1p-shell model space enhances the form factors forq-values and reasonably reproduces the data. The value of the size parameter (b) ischosen to reproduce the root mean square charge radius. The present results arecompared with available experimental data and with that of other models.PACS:21.60-n,21.60 Cs, 25.30Dh,27.20 th

Exponencial stability of the energy in Naghdi shell model with localized internal dissipation and internal exact controllability

In this work we study the exponential stability of the energy associated with a Naghdi's shell model with localized internal dissipation. Using several tools from Riemannian Geometry we show the well possedness of the model, via semigroup theory, and obtain observability inequalities which allows us to prove the exponential decay of the total energy. As a consequence then we use Russell Principle to obtain exact controllability.

Vibration of black phosphorus nanotubes via orthotropic cylindrical shell model

Black phosphorus nanotubes (BPNTs) may have good properties and potential applications. Determining the vibration property of BPNTs is essential for gaining insight into the mechanical behaviour of BPNTs and designing optimized nanodevices. In this paper, the mechanical behaviour and vibration property of BPNTs are studied via orthotropic cylindrical shell model and molecular dynamics (MD) simulation. The vibration frequencies of two chiral BPNTs are analysed systematically. According to the results of MD calculations, it is revealed that the natural frequencies of two BPNTs with approximately equal sizes are unequal at each order, and that the natural frequencies of armchair BPNTs are higher than those of zigzag BPNTs. In addition, an armchair BPNTs with a stable structure is considered as the object of research, and the vibration frequencies of BPNTs of different sizes are analysed. When comparing the MD results, it is found that both the isotropic cylindrical shell model and orthotropic cylindrical shell model can better predict the thermal vibration of the lower order modes of the longer BPNTs better. However, for the vibration of shorter and thinner BPNTs, the prediction of the orthotropic cylindrical shell model is obviously superior to the isotropic shell model, thereby further proving the validity of the shell model that considers orthotropic for BPNTs.

Intermittency as a Consequence of a Stationarity Constraint on the Energy Flux.

In his seminal work on turbulence, Kolmogorov made use of the stationary hypothesis to determine the power density spectrum of the velocity field in turbulent flows. However, to our knowledge, the constraints that stationary processes impose on the fluctuations of the energy flux have never been used in the context of turbulence. Here, we recall that the power density spectra of the fluctuations of the injected power, the dissipated power, and the energy flux have to converge to a common value at vanishing frequency. Hence, we show that the intermittent Gledzer-Ohkitani-Yamada (GOY) shell model fulfills these constraints. We argue that they can be related to intermittency. Indeed, we find that the constraint on the fluctuations of the energy flux implies a relation between the scaling exponents that characterize intermittency, which is verified by the GOY shell model and in agreement with the She-Leveque formula. It also fixes the intermittency parameter of the log-normal model at a realistic value. The relevance of these results for real turbulence is drawn in the concluding remarks.

Toward a new approach for the pygmy dipole resonance in even–even nuclei. Application to isotopes 144,148,150,152,154Sm

A many-body Hamiltonian consisting of a spherical shell model mean-field term, a pairing interaction for alike nucleons and a dipole–dipole interaction, with the dipole operator involving a cubic term in the radial coordinate, was studied within a quasiparticle random-phase approximation and applied numerically to five even–even isotopes of Sm. The resulting wavefunctions were further used to calculate the B(E1) values, which at their turn were employed to calculate the photoabsorption cross section, integrated moments of the cross section and energy weighted sum rule (EWSR). The calculated cross section and its integrated moments were compared with the available data, and a good agreement was observed. Two regions were distinguished: one corresponding to the pygmy dipole resonance (PDR) (1–10 MeV) and the other to the giant dipole resonance (GDR) (10–20 MeV), which were studied separately. The peaks belonging to each of the two ranges were analyzed in detail. The PDR states were located around the neutron separation energy and were mainly formed by the collective isoscalar and neutron collective states. The PDR states describe oscillations of the neutron excess against protons from the isospin-saturated core. The character of the states from the GDR region, isoscalar or isovector, is also pointed out. The PDR states carry only 0.8%–2.7% of the total EWSR and 0.4%–5.9% of the total E1 strength. The dependence of the dipole strength on nuclear deformation is evidenced. A comment on the cross section splitting into two branches for deformed isotopes is included. The r-cubic term and nuclear deformation have opposite effects on the dipole strength. In addition, it diminishes the effect of nonconservation of the center of mass momentum. The famous Thomas–Reiche–Kuhn sum rule formula is generalized to the case of the Schiff dipole momentum. The new sum rule is well satisfied. The projected spherical single-particle basis used in our formalism allows for a unified description of spherical transitional and deformed isotopes.

On mechanics of piezocomposite shell structures

This study presents an original and novel investigation into the mechanics of piezo-flexo-magneto-elastic nanocomposite doubly-curved shells (PFMDCSs) and the ability to detect the lower and higher levels of electro-magnetic fields. In this context, by utilizing the first-order shear deformation shell model, stresses and strains are acquired. By imposing Hamilton's principle and the von Kármán approach, the governing equations have been obtained. The intelligent shell model consists of size-dependent influences, viz., strain gradients. This will take place via Mindlin's strain gradient elasticity theory and the subsequent re-establishing of the mathematical framework by incorporating this concept. The strain gradient results in a flexoelectric/flexomagnetic effect. The converse effect of the magnetic field on the basis of a close circuit has been assumed. The developed bending equations have been transferred into the algebraic ones by substituting an analytical technique based on homogeneous immovable simple support for the four edges. The problem has been solved according to the Newton-Raphson iteration scheme, and transverse deflections have been computed. For researching the rightness and precision of the shell models together with the solution process, a comparison is prepared by the finite element method (FEM) results for simplified shells, and a good correlation has been observed. At last, by examining several factors governing the problem, the conditions under which the magnetic effects can be noticeable and dominant in doubly-curved shells have been sought. This study could serve as a benchmark reference for piezoceramic-DCSs, as the presented governing equations are original. The most interesting outcome of this research is that the electro-magnetic response of intelligent structures can be entirely geometry-dependent.

Large rotation isogeometric shell model for alternating stiff/soft curved laminates including warping and interlayer thickness change

The mechanics of laminates made up of elastic alternating stiff/soft layers is dominated by bending and membrane actions in the stiff layers, while transverse shear deformations concentrate in the soft interlayers producing significant zigzag warping effects. Additionally, curved geometry and large deformations can induce an interlayer thickness strain affecting the overall response of the laminate. This work presents a rotation-free Total Lagrangian large deformation curved shell model to accurately capture such a structural response. Each stiff layer is modeled as a Kirchhoff–Love shell. Without additional DOFs, each soft interlayer is modeled as a solid-shell by expressing, in finite kinematics, the displacement of top and bottom interfaces as a function of the mid-surface displacement of the upper and lower stiff layers it couples. The model is characterized by a sparse stiffness matrix compared to high-order theories and requires a small number of DOFs (3 per stiff layer) to reproduce the 3D solution. A NURBS discretization meets the high continuity of the weak form with a patch-wise reduced quadrature to avoid locking and enhance efficiency. All thickness integrals are pre-computed just once.

Investigation of the effect of model structure type on the thermal performance of phase change materials through molecular dynamics simulation

Using molecular dynamics (MD) simulation, the thermal efficacy of phase change materials (PCMs) in solar energy applications and solar thermal energy storage was evaluated. In order to achieve this objective, an investigation was conducted into the structure's temperature (Temp), velocity, and density profiles, heat flux, thermal conductivity, charge and discharge time, and thermal stability. Three models of tube, shell, and shell-tube were adopted to scrutinize the atomic behavior and thermal performance (TP) of PCMs. The results show that the maximum density of the tube model, shell model, and shell-tube model was 0.042, 0.036, and 0.033 atom/A3, respectively. Other numerical results showed that the maximum velocity for the three structures of tube model, shell model, and shell-tube model under the initial Temp of 300 K was 0.0066 Å/fs, 0.0059 Å/fs, and 0.0054 Å/fs, respectively. The structure in the tube model manifested more optimal atomic behavior compared to other models. The TP of simulated structures revealed that the heat flux of the samples reached 5.69, 4.85, and 4.15 W/m2, respectively. Finally, the thermal conductivity of the structures approached 1.35, 1.32, and 1.31 W/m.K, respectively. The results suggested that the tube model had the most thermal stability and showed the optimal thermal behavior in the simulation. The findings of this study, particularly the optimal atomic behavior and thermal stability of the tube model, can be useful in designing and optimizing PCMs for solar energy applications. In general, this research had the potential to significantly advance the field of solar energy system efficiency and cost-effectiveness.

Nonlocal-Strain-Gradient-Based Anisotropic Elastic Shell Model for Vibrational Analysis of Single-Walled Carbon Nanotubes

In this study, a new anisotropic elastic shell model with a nonlocal strain gradient is developed to investigate the vibrations of simply supported single-walled carbon nanotubes (SWCNTs). The Sanders–Koiter shell theory is used to obtain strain–displacement relationships. Eringen’s nonlocal elasticity and Mindlin’s strain gradient theories are adopted to derive the constitutive equations, where the anisotropic elasticity constants are expressed via Chang’s molecular mechanics model. An analytical method is used to solve the equations of motion and to obtain the natural frequencies of SWCNTs. First, the anisotropic elastic shell model without size effects is validated through comparison with the results of molecular dynamics simulations reported in the literature. Then, the effects of the nonlocal and material parameters on the natural frequencies of SWCNTs with different geometries and wavenumbers are analyzed. From the numerical simulations, it is confirmed that the natural frequencies decrease as the nonlocal parameter increases, while they increase as the material parameter increases. As new results, the reduction in natural frequencies with increasing SWCNT radius and the increase in natural frequencies with increasing wavenumber are both amplified as the material parameter increases, while they are both attenuated as the nonlocal parameter increases.

Coexistence of low-K oblate and high-K prolate g9/2 proton-hole bands in 115Sb

A positive parity sequence of ΔI=2γ transitions has been identified above Iπ=9/2+ state (Ex=2019 keV) in 115Sb through in-beam γ ray spectroscopic technique. Rotational features of this sequence are found similar to a low-K decoupled band. Observation of this newly identified low-K decoupled band, along with the earlier reported strongly coupled high-K band in this nucleus, provides the first experimental evidence for prolate-oblate shape coexistence associated with g9/2 proton-hole configuration around Z=50 shell closure. Experimental results are reproduced reasonably well in the frameworks of the projected shell model and the total Routhian surface calculations.

Indispensability of cross-shell contributions in neutron resonance spacing

Spin- and parity-dependent nuclear level densities (NLDs) are obtained for a configuration interaction shell model using a numerically efficient spectral distribution method. The calculations are performed for 24Na and 25,26,27Mg nuclei using full sd-pf model space that incorporates the cross-shell excitations from the sd to the pf-shell. The obtained NLDs are then employed to determine the s-wave neutron resonance spacing (D0), which is one of the crucial inputs for the predictions of astrophysical reaction rates. Although the considered nuclei are not neutron-rich, the contributions from cross-shell excitations to the pf-shell are indispensable for explaining the experimental data for D0, which otherwise are significantly overestimated.

Multidimensional typologies of faulty medical device events: analysis, risk characterisation, and stakeholder mapping

ABSTRACT This study uses the publicly available International Medical Devices Database in three-phase research to present empirically grounded multi-dimensional typologies of events involving faulty medical devices. In the first phase, considering three major categorical data, i.e. event actions, event types, and countries, and, by employing descriptive analysis, we identify that perhaps ‘Field safety notice’ is the most dominant event type under which 66 event actions exist. In the second phase, employing the two-step clustering analysis technique, we identify that four distinct clusters exist. Finally, in the last phase, employing the focus group-driven content analysis approach using event reason description in conjunction with the SHELL (software-hardware-equipment-liveware) model, we classify the top 10 event actions. We also identify corresponding risk levels considering the top 10 sources of device problems. Further, the focus group employing the interest-influence framework in conjunction with pertinent self-addressed questions ascertained that the greatest number of top 10 event actions lies at the quadrant wherein the major stakeholder has a high degree of interest and influence in mitigating those medical events. Our study bridges the extant research gap about the lack of comprehensive, data-driven, and evidence-based themes around medical device events, the associated risk characteristics, and stakeholder mapping.

Spontaneous Stochasticity Amplifies Even Thermal Noise to the Largest Scales of Turbulence in a Few Eddy Turnover Times.

How predictable are turbulent flows? Here, we use theoretical estimates and shell model simulations to argue that Eulerian spontaneous stochasticity, a manifestation of the nonuniqueness of the solutions to the Euler equation that is conjectured to occur in Navier-Stokes turbulence at high Reynolds numbers, leads to universal statistics at finite times, not just at infinite time as for standard chaos. These universal statistics are predictable, even though individual flow realizations are not. Any small-scale noise vanishing slowly enough with increasing Reynolds number can trigger spontaneous stochasticity, and here we show that thermal noise alone, in the absence of any larger disturbances, would suffice. If confirmed for Navier-Stokes turbulence, our findings would imply that intrinsic stochasticity of turbulent fluid motions at all scales can be triggered even by unavoidable molecular noise, with implications for modeling in engineering, climate, astrophysics, and cosmology.

Nonlinear vibrations analysis of two-directional functionally graded porous cylindrical shells resting on elastic substrates in a thermal environment based on Donnell nonlinear shell theory

The primary objective of this study is to investigate the nonlinear free vibrational characteristics of temperature-dependent two-directional functionally graded porous (TDFGP) cylindrical shells resting on elastic substrates in a thermal environment. To accomplish this, the thermomechanical equations are derived based on the Donnell nonlinear shell theory framework in conjunction with the von Kármán assumption. Two-directional functionally graded porous cylindrical shell models have mechanical properties that can change smoothly and continuously across the length and thickness of the shell. Additionally, it is assumed that the internal porosities in the matrix materials can be dispersed into two independent patterns, either even or uneven porosity distribution. The nonlinearity in free vibration assessed via the nonlinear-to-linear frequency ratio concerning the central deflection amplitude can be gained employing the Galerkin discretization approach and modified Poincare–Lindstedt (P-L) method. The accuracy and effectiveness of the present analytical model are indicated through comparison with existing solutions. Finally, some comprehensive parametric investigations are carried out to gain insight into the impacts of several factors on the nonlinear free vibration characteristics of structures under different conditions. The results of this article demonstrate that parameters such as gradient indices, volume fraction, distribution pattern of porosity, geometric parameters, and ambient temperature rise significantly influence the structure’s nonlinear frequency and free vibration response.

COMPARATIVE STUDY BETWEEN SHELL AND SOLID FINITE ELEMENT MODELS FOR STEEL JOINTS CHARACTERIZATION

AbstractSolid and shell finite element models (FEM) are two commonly used possibilities to analyse the structural behaviour of steel joints. The choice between solid and shell models often comes down to a balance between computational resources and the level of detail required for the study. In this paper, a set of welded beam‐column joints with hot‐rolled open sections is studied using both modelling techniques. The joints' behaviour is assessed in terms of resistance and initial stiffness. An improved shell FEM is proposed. The results indicate that for the studied dataset, both techniques return comparable results. Hence, the use of shell FEM seems to be a possible alternative to solid FEM and can be efficiently used for the joint characterization.

Odd elastic stability of cylindrical shells

Biologically active shells typically exhibit complex mechanical behaviors, with their morphogenesis involving rich symmetry breaking events and non-conservative biological forces. In this article, an accurate buckling solution model of active cylindrical shells is established based on the odd elasticity theory. The tension buckling, non-reciprocal torsional buckling and stress-free active buckling of odd elastic cylindrical shells are reported, which are an anomalous instability caused by odd elastic effects. The result shows that the anomalous buckling of cylindrical shells can only occur in the form of chiral deformation, because the energy required for instability can be obtained based on the odd elastic effects.

STUDY MAGNETIC ELECTRON SCATTERING FORM FACTOR OF 24Mg ISOTOPE

The magnetic form factor of 24Mg isotope under inelastic electron scattering was subjected to computational scrutiny via the utilization of the Oxbash code. The endeavor involved elucidating energy levels intrinsic to this nucleus through the application of the shell model, wherein the model space encompassed zbm, psd, spsdpf, and sd configurations. In the context of the sd model, the investigation harnessed two pioneering USD-type Hamiltonians, denoted as USDC and USDI, in conjunction with tailored amendments to these interaction potentials, referred to as USDCm and USDIm. This study culminated in comprehensively juxtaposing all computational outputs with empirical data sources, including information extracted from the National Nuclear Data Center (NNDC) repository. Significantly, this systematic examination underscored a notable congruence between the derived computational outcomes and the empirical observations. This alignment became conspicuously pronounced subsequent to judicious adjustments made to the g-factors, specifying values of = 1.060 and = -0.060. The profound unity between the findings of this study and experimental data manifests as compelling evidence, substantiating the efficacy and precision of the employed interaction models. It implies a reliable capacity of these models in the precise computation of magnetic form factors M1, M2, and M3

New beam-based models for fire-induced buckling analysis of class 4 steel columns

Steel cross-sections with thin walls are vulnerable to fire-induced buckling instability, which reduces their load-bearing capacity. Eurocode 3 design provisions have been found inadequate, leading to alternative methods such as effective design strategies and advanced structural models built mostly with shell FE, which can be complex. For Class 4 steel beam-columns subjected to fire conditions, beam-type modelling to predict the Flexural-Torsional Buckling (FTB) strength has been proposed as an alternative approach, but it has not yielded satisfactory results for large compressive load eccentricities. This paper presents two new low computational cost modelling strategies based on Timoshenko's beam FE to address this issue: the Single beam-column Model (SbcM) and the Cruciform beam-column Model (CbcM). The first consists of a single line of beam FE, while the second uses a grid of beam FE for more flexibility. Both strategies effectively simulate the FTB behaviour in Class 4 steel beam-column during a fire, offering quicker computations compared to shell models. Still, the single-line model is favoured for its simplicity, making it more efficient in analysing complex fire engineering problems.

PROBING THE NUCLEAR STRUCTURE OF EXOTIC 33Mg ISOTOPE

Research on the nuclear structure of exotic isotopes, such as 33Mg, is an exciting and cuttingedge field of nuclear physics. Exotic isotopes are typically those that are far from the stable region of the nuclear chart and often exhibit unique properties that can help us better understand the fundamental forces and structure of atomic nuclei. In this paper the largescale shell model calculations are performed within the model spaces SDPFMU, to study the positive- and negative-parity energy levels and electromagnetic transitions in the exotic 33Mg isotope. Core-polarization effects on reduced transition probability are introduced through first order perturbation theory, which allows for higher energy configurations through excitations of nucleons from core orbits to that outside model space up to . The corepolarization effects have been improved the agreement of B(E2) with their corresponding experimental data, and have ignorable effect on B(M1)