Search results for "Spherical shell"
showing 10 items of 11 documents
Dynamic Modeling, Energy Analysis, and Path Planning of Spherical Robots on Uneven Terrains
2020
Spherical robots are generally comprised of a spherical shell and an internal actuation unit. These robots have a variety of applications ranging from search and rescue to agriculture. Although one of the main advantages of spherical robots is their capability to operate on uneven surfaces, energy analysis and path planning of such systems have been studied only for flat terrains. This work introduces a novel approach to evaluate the dynamic equations, energy consumption, and separation analysis of these robots rolling on uneven terrains. The presented dynamics modeling, separation analysis, and energy analysis allow us to implement path planning algorithms to find an optimal path. One of t…
Self-assembly of semiflexible polymers confined to thin spherical shells
2018
Confinement effects are critical for stiff macromolecules in biological cells, vesicles, and other systems in soft matter. For these molecules, the competition between the packing entropy and the enthalpic cost of bending is further shaped by strong confinement effects. Through coarse-grained molecular dynamics simulations, we explore the self-assembly of semiflexible polymers confined in thin spherical shells for various chain lengths, chain stiffnesses, and shell thicknesses. Here, we focus on the case where the contour and persistence length of the polymers are comparable to the radius of the confining cavity. The range of ordered structures is analyzed using several order parameters to …
Excited states in Ra217 populated in the α decay of Th221
2020
Fine structure in the α decay of Th90221, populating excited states in Ra88217, was studied using αγ-coincidence spectroscopy. Two α-decay branches from Th221 have been newly observed, with Eα(keV)[bα(%)]=7951(8)[0.14(3)] and 8247(3)[1.51(12)], together with three previously known branches. Also, two new states in Ra217 were identified at E = 177 and 227 keV. The ground-state configurations of the odd-A, N = 131 transitional isotones above Pb208 are interpreted from their α-decay fine structure systematics and considered in terms of predictions using spherical shell and reflection-asymmetric models.
Self-dressing and radiation reaction in classical electrodynamics
2002
A canonical approach to self-dressing in classical electrodynamics is presented. A slowly moving, rigid charge distribution is assumed to be completely deprived of the transverse electric E⊥ at an initial time t1' and the development of this component of the field is studied for t > t1' by solving the coupled charge-field Hamilton equations of motion. The theory is specialized to charge distributions of spherical symmetry, and in particular the point-charge, the spherical shell of charge and the spherical volume of charge are considered. As for the dynamics of the charge, the radiation-reaction force during self-dressing is obtained and it is shown to be substantially different at short tim…
Shell model and octupole states in148Gd from in-beam experiments
1990
Through (α, 4n) and (τ, 3n) reactions the high-spin states in the two-neutron nucleus148Gd were populated up toI π=21− at 7.2 MeV, including numerous states above the yrast line. The148Gd energy spectrum is interpreted in terms of the spherical shell model. Identification of the (νf 7/2 i 1 3/2)10− state gives the νi 13/2 single particle energy free of octupole admixtures as 2.1(1) MeV. Eight high-spin states between 1.2 and 3.7 MeV were identified as the couplings of the two valence-particles to the146Gd octupole phonon, and three above-lying levels are assigned as double-octupole excitations including a 12+ state which decays by anE3-E3 stretched cascade. All these octupole levels can be …
In-beam study of high-spin states in199,200,201Po and systematical features of Z=84 polonium isotopes
1985
Excited states in199,200,201Po were populated in the reactions12C+194Pt and12C+195Pt. The subsequentγ-radiation was studied using conventional in-beam spectroscopic methods. States with spins up to (29/2), 18 and ≧35/2ħ, respectively, were populated in the three nuclides. Three isomeric states with the following half-lives were observed in200Po:T1/2(8+)=90(15) ns,T1/2(11−)=120(20) ns andT1/2(12+)=267(4) ns. The structure of the excited states was interpreted within the framework of the spherical shell model. The three isomers are suggested to be two-quasiparticle states with configurationsπ(h22)8J, π(h9i13/2)11- and v(i1 3/2−2)12+. A self-consistent Hartree-Fock calculation was performed to…
Medium-spin levels in the N=83 nucleus147Gd
1983
Levels of theN=83 nucleus147Gd have been investigated by methods of in-beamγ-ray and conversion electron spectroscopy using the147Sm(3He, 3n) and144Sm(α, n) reactions. Sixteen new low- and medium-spin levels have been observed in147Gd. We have located six members of thevf7/2×3− particle-octupole septuplet and several neutron single-particle states in147Gd. The levels of147Gd are discussed on the basis of the spherical shell model.
Medium-spin levels and the character of the 20.4 ns isomer in 145Gd
1982
Abstract Levels of the N = 81 nucleus 145Gd have been investigated by in-beam γ-ray and conversion electron spectroscopy with the 144Sm(3He, 2n) reaction. Fourteen new low- and medium-spin states between 1.0 and 2.4 MeV excitation, the known yrast levels up to spin 21 2 + , five other high-spin non-yrast states and a new 20.4 ns 13 2 isomer at 2200.2 keV in 145Gd have been observed. The isomer decays via a fast 927.3 keV E3 transition with B(E3) = 48 ± 7 W.u. Another weaker decay branch is a mixed, strongly hindered E1 + M2 + E3 transition to the v h −1 11 2 state. We propose an octupole v f 7 2 j −2 × 3 − main configuration for the isomer, analogous to the 997 keV 13 2 + isomer in 147Gd. T…
Electrons on a spherical surface: Physical properties and hollow spherical clusters
2012
We discuss the physical properties of a noninteracting electron gas constrained to a spherical surface. In particular we consider its chemical potentials, its ionization potential, and its electric static polarizability. All these properties are discussed analytically as functions of the number $N$ of electrons. The trends obtained with increasing $N$ are compared with those of the corresponding properties experimentally measured or theoretically evaluated for quasispherical hollow atomic and molecular clusters. Most of the properties investigated display similar trends, characterized by a prominence of shell effects. This leads to the definition of a scale-invariant distribution of magic n…
Dynamic tuning of the director field in liquid crystal shells using block copolymers
2020
When an orientationally ordered system, like a nematic liquid crystal (LC), is confined on a self-closing spherical shell, topological constraints arise with intriguing consequences that depend critically on how the LC is aligned in the shell. We demonstrate reversible dynamic tuning of the alignment, and thereby the topology, of nematic LC shells stabilized by the nonionic amphiphilic block copolymer Pluronic F127. Deep in the nematic phase, the director (the average molecule orientation) is tangential to the interface, but upon approaching the temperature TNI of the nematic– isotropic transition, the director realigns to normal. We link this to a delicate interplay between an interfacial …