Showing papers on "Shell (structure) published in 1999"

Analysis of cracks in solids

Abstract: Introduction: Modelling of solids with cracks - Elements of convex analysis Approximation methods Problems with singular boundaries. Cracks in plates and shells: Viscoelastic contact problem for a plate A plate under creep conditions A plate with vertical and horizontal displacements Contact problem for a plate having a crack Cracks of minimal opening in plates Solving methods for plates with cracks Contact problem for a shell with a crack Signorini problem for cracks in shells Simplified nonpenetration conditions in contact problems Solving methods for the simplified models. Cracks in complicated plates: Plate with a crack under the creep condition Contact of two plates one of which has a crack Thermoelastic plates with cracks Cracks of minimal opening in thermoelastic plates Inclined cracks in plates Friction problem for plates with cracks. Variation of cracks in solids: Variation of a crack length A plate with a crack A crack moving to the external boundary A case of a shallow shell A crack near the boundary Asymptotics of the energy functional for the Poisson equation Asymptotics of the energy functional for the Lam? equations Three-dimensional case Extreme crack shapes in a shallow shell. Cracks in elastoplastic bodies: Elastoplastic problems for the Hencky model Elastoplastic problems for the Prandtl-Reuss model Elastoplastic problems for plates with cracks The Prandtl-Reuss elastoplastic plates Contact elastoplastic problem for the curvilinear Kirchhoff rod Contact elastoplastic problem for the curvilinear Timoshenko rod Viscoelastoplastic curvilinear Timoshenko rod Curvilinear rod under creep conditions Conclusion.

Convective instability in Europa's floating ice shell

Abstract: Models of the tidally heated, floating ice shell proposed for the jovian satellite Europa generally find shell thicknesses less than 30 km. Past parameterized convection models indicated that such shells are stable against convective overturn, which otherwise ostensibly leads to freezing of the ocean underneath. Here I apply the temperature-dependent viscosity convection scaling developed by Solomatov and coworkers to the Europan ice shell. The temperature-dependent properties of ice are linearized about 260 K, as any convective interior should be close to this temperature, with the colder ice forming an essentially passive, stagnant lid. Ice shells ≳ 10 km thick are found to be unstable to convection at their base for melting-point viscosities of 1013 Pa-s (as linearized by tidal stresses), if the ice deforms by superplastic creep, but such low viscosities require small grain sizes (<1 mm). This requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain-rate scaled to Europa. Regardless, convection at the base of the ice shell, if initiated, may not freeze the ocean. Because of tidal heating, a stagnant-lid regime ice shell is much more dissipative than a conductive shell of the same thickness. Such a shell should thin, not thicken, and the potential exists for further thermal instabilities and runaways.

Observation of shell structure in sodium nanowires

Abstract: The fact that the rare gas atoms at the end of each row in the periodic table of the elements are exceptionally stable is explained by the closed-shell configuration of their electronic structure. In general, the quantum states of a system of particles in a finite spacial domain form a set of discrete energy eigenvalues, which are usually grouped into bunches of degenerate or close-lying levels, called shells [1]. For fermions this gives rise to a local minimum in the total energy of the system when all states of a given shell are occupied. Shell effects have previously been observed for protons and neutrons in nuclei and for clusters of metal atoms [2], [3], [4]. Here, we report the first observation of a shell effect in an open system, a metal nanowire. When recording the statistical distribution of conductance values observed while pulling off the contact between two bulk sodium metal electrodes, the histogram shows oscillations up to contacts larger than 100 atoms in cross section. The period follows the law expected for the electronic shell-closing effect similar to that determining the “magic numbers” in metal clusters [3], [4]

A study of 13C hyperfine structure in the EPR of nickel-nitrogen-containing centres in diamond and correlation with their optical properties

Abstract: Electron paramagnetic resonance (EPR) and optical spectroscopy have been used to determine the structure and electronic state of nickel-nitrogen centres in natural diamonds and in synthetic diamonds enriched in 13C. The latter were grown in an Fe-Ni-C solvent/catalyst system at 1750 K, under stabilizing pressure, by the temperature gradient method and afterwards treated at high temperature and pressure. The parameters and directions of the 13C hyperfine structure (HFS) tensors for the NE1 centre were found to confirm the previously proposed model for this defect, with a nickel ion at the centre of a double semivacancy as the basic structural unit. In this unit the nickel atom has six atoms in its coordination shell. The NE1 centre has C2h symmetry, and the two equivalent nitrogen atoms in the coordination shell lie in the symmetry plane. New data on the HFS of 14N and 13C for the NE5 centre, also with C2h symmetry, indicated the same structural unit, but the two equivalent nitrogen atoms (and two equivalent carbon atoms) lie out of the symmetry plane and are related to one another by reflection in it. A new paramagnetic centre was found, labelled NE8, also with C2h symmetry, with four equivalent nitrogen atoms in the coordination shell all lying out of the symmetry plane. This centre is responsible for the 793.6 nm vibronic system in absorption and luminescence spectra. The new data have allowed a reinterpretation of the HFS tensors for the NE2 centre, which has C1 symmetry, suggesting that it has the same structure as NE1 but with one additional nitrogen atom in the coordination shell. The electronic states of these nickel-containing centres are discussed using the approach of Ludwig and Woodbury to transition metal ions in covalent crystals.

Thermally insulated container

Abstract: A container has a base, peripheral walls and a lid. Each of the base, peripheral walls and lid includes an interior wall spaced from an exterior wall, with vacuum panel in between. The sides of the vacuum panels are covered by compressible insulation fill, minimizing thermal flow along the vacuum panels despite any manufacturing tolerance differences in the width of the vacuum panels as compared to the distance between the interior wall and the exterior wall. The interior wall of the body of the container is provided by a liner formed of a single, deep drawn sheet of material. The exterior wall is similarly formed as a deep drawn shell. The inner liner and the outer shell are welded together with a bead to encase the vacuum panels in a water-tight manner, with the liner, the shell the bead all formed of the same material.

Relativistic Hartree+Bogoliubov description of the deformed N = 28 region

Abstract: Ground-state properties of neutron-rich N≈28 nuclei are described in the framework of relativistic Hartree plus Bogoliubov (RH+B) theory. The model uses the NL3 effective interaction in the mean-field Lagrangian, and describes pairing correlations by the pairing part of the finite range Gogny interaction D1S. Two-neutron separation energies and ground-state quadrupole deformations that result from fully self-consistent RH+B solutions are compared with available experimental data. The model predicts a strong suppression of the spherical N=28 shell gap for neutron-rich nuclei: the 1f7/2 fp core breaking results in deformed ground states. Shape coexistence is expected for neutron-rich Si, S, and Ar isotopes.

Observation of shell structure in sodium nanowires

Abstract: The quantum states of a system of particles in a finite spatial domain in general consist of a set of discrete energy eigenvalues; these are usually grouped into bunches of degenerate or close-lying levels, called shells. In fermionic systems, this gives rise to a local minimum in the total energy when all the states of a given shell are occupied. In particular, the closed-shell electronic configuration of the noble gases produces their exceptional stability. Shell effects have previously been observed for protons and neutrons in nuclei and for clusters of metal atoms. Here we report the observation of shell effects in an open system - a sodium metal nanowire connecting two bulk sodium metal electrodes, which are progressively pulled apart. We measure oscillations in the statistical distribution of conductance values, for contact cross-sections containing up to a hundred atoms or more. The period follows the law expected from shell-closure effects, similar to the abundance peaks at `magic numbers' of atoms in metal clusters.

Resealable pushable container closure and cover therefor

Abstract: A container closure is disclosed which includes a shell attachable to a container around a container opening thereof. The shell has a shell opening in fluid communication with the container opening when the shell is attached to the container. A tip is received on the shell movable between a closed position sealing the shell opening and an open position. A cover is releasably attached to the shell in a manner indicative of the tip being positioned in the closed position when the cover is attached to the shell. Both the shell and the cover may be provided with tamper-evident bands. The present invention is particularly well adapted to be formed as a push-pull container closure for sports bottles and the like.

Local atomic arrangements in polytetrahedral materials

Abstract: The paper presents a topological classification of the first-coordination-shell shapes for atoms in solids. The classification includes the coordination shells with up to 13 atoms in a shell. Application of the scheme to the classification of disclination junction configurations and interstitial hole shapes is discussed.

Three dimensional laminate beam structure

Abstract: A three-dimensional laminate beam (10) is formed by inserting a preformed foam core (18) insert within a hydra-formed metal section (12) having curved three-dimensional geometry. A reinforcing polymer (20) is pumped in and around the foam core insert so as to be adjacent the inside wall of the shell. The polymer bonds to the inside wall of the shell upon the polymer being cured.

Pipe repair clamp

Abstract: A clamp for repairing a damaged pipe member. Shell members are matingly engaged around the damaged pipe member. Segmented inserts are received in a complementary annular channel formed in an inside face of the shell members to form a ring assembly supporting annular seals between the ring assembly and the damaged pipe member. A shell-sealing annular channel is formed between the ring assembly and the shell members to receive a liquid sealant to form an annular seal between the ring assembly and the shell members. A longitudinal channel is formed in longitudinal faces of the shell member to form longitudinal seals in the shell assembly when a ring assembly is disposed at either end of the shell members. The ring assemblies support seals against the damaged pipe member, including a pipe-sealing annular channel formed between each ring and the damaged pipe member between inner and outer annular seals for receiving a liquid sealant. The pipe-sealing annular channels, the shell-sealing annular channels and the longitudinal channels are in fluid communication to facilitate filling with the liquid sealant.

Protective device for impact management

Abstract: A protective device comprising a shell and a liner. The shell includes an interior surface. The liner is associated with the interior surface of the shell. The liner includes a member for enabling control displacement of the preselected regions of the liner upon various degrees of impact of the protective device. The control displacement member comprises a first member and a second member. Each of the first and second members having a top surface, a bottom surface and a different impact absorbing characteristic. The top surface of at least one of the first and second members is associated with the interior surface of the shell. At least a portion of the bottom surface of the first member extends further from the interior surface of the shell and the bottom surface of the second member.

The volume transition in thermosensitive core–shell latex particles containing charged groups

Abstract: An investigation of the volume transition in thermosensitive core–shell particles by dynamic light scattering (DLS) is presented. The core of the particles consists of polystyrene (diameter 118 nm), whereas the thermosensitive shell is composed of a network of poly (N-isopropylacrylamide) containing 2 mol% acrylic acid counits. The hydrodynamic radius of these particles as determined by DLS decreases in a continuous manner when raising the temperature. It is shown that the volume transition in the core–shell microgels remains continuous for a wide range of ionic strengths and pH values. This behavior is opposite to that of macrogels of the same chemical composition, which undergo a discontinuous volume transition. The present investigation therefore demonstrates that affixing the network to solid colloidal particles profoundly alters the volume transition of thermosensitive networks. The reason is that shrinking can take place only along the radial direction of the particles. The solid core thus exerts a strong spatial constraint onto the network, which leads to the observed behavior.

Core-shell particles and preparation and use thereof

Abstract: Disclosed are core-shell particles, whose core and shell materials are capable of forming a two-phase system, the shell material being filmable, the core being essentially form-stable under shell-filming conditions and being only very minimally swellable by the shell material, if at all, the cores having a monodisperse size distribution, and there being a difference between the refractive indices of the core material and of the shell material of at least 0.001. Also disclosed are the preparation of the core-shell particles and their use for preparing effect colorants.

Fuel tank assembly

Abstract: A fuel tank assembly for a vehicle includes a tank shell having a first half shell and a second half shell. The fuel tank assembly also includes a plurality of column supports disposed between and attached to the first half shell and the second half shell. The fuel tank assembly further includes a cradle baffle disposed between the first half shell and the second half shell and attached to the column supports. The cradle baffle has at least one compliant joint disposed between a pair of the column supports to allow the cradle baffle to distort when a force is applied to the tank shell.

Feedback stabilization of resistive shell modes in a reversed field pinch

Abstract: A reactor relevant reversed field pinch (RFP) must be capable of operating successfully when surrounded by a close-fitting resistive shell whose L/R time is much shorter than the pulse length. Resonant modes are largely unaffected by the shell resistivity, provided that the plasma rotation is maintained against the breaking effect of nonaxisymmetric eddy currents induced in the shell. This may require an auxiliary momentum source, such as a neutral beam injector. Nonresonant modes are largely unaffected by plasma rotation, and are expected to manifest themselves as nonrotating resistive shell modes growing on the L/R time of the shell. A general RFP equilibrium is subject to many simultaneously unstable resistive shell modes; the only viable control mechanism for such modes in a RFP reactor is active feedback. It is demonstrated than an N-fold toroidally symmetric arrangement of feedback coils, combined with a strictly linear feedback algorithm, is capable of simultaneously stabilizing all intrinsically u...