3,293 research outputs found
Beta-decay properties of Si and P
The -decay properties of the neutron-deficient nuclei Si and
P have been investigated at the GANIL/LISE3 facility by means of
charged-particle and -ray spectroscopy. The decay schemes obtained and
the Gamow-Teller strength distributions are compared to shell-model
calculations based on the USD interaction. B(GT) values derived from the
absolute measurement of the -decay branching ratios give rise to a
quenching factor of the Gamow-Teller strength of 0.6. A precise half-life of
43.7 (6) ms was determined for P, the - (2)p decay mode of which
is described
Quantum phase space picture of Bose-Einstein Condensates in a double well: Proposals for creating macroscopic quantum superposition states and a study of quantum chaos
We present a quantum phase space model of Bose-Einstein condensate (BEC) in a
double well potential. In a two-mode Fock-state analysis we examine the
eigenvectors and eigenvalues and find that the energy correlation diagram
indicates a transition from a delocalized to a fragmented regime. Phase space
information is extracted from the stationary quantum states using the Husimi
distribution function. It is shown that the quantum states are localized on the
known classical phase space orbits of a nonrigid physical pendulum, and thus
the novel phase space characteristics of a nonrigid physical pendulum such as
the motions are seen to be a property of the exact quantum states. Low
lying states are harmonic oscillator like libration states while the higher
lying states are Schr\"odinger cat-like superpositions of two pendulum rotor
states. To study the dynamics in phase space, a comparison is made between a
displaced quantum wavepacket and the trajectories of a swarm of points in
classical phase space. For a driven double well, it is shown that the classical
chaotic dynamics is manifest in the dynamics of the quantum states pictured
using the Husimi distribution. Phase space analogy also suggests that a
phase displaced wavepacket put on the unstable fixed point on a separatrix will
bifurcate to create a superposition of two pendulum rotor states - a
Schr\"odinger cat state (number entangled state) for BEC. It is shown that the
choice of initial barrier height and ramping, following a phase
imprinting on the condensate, can be used to generate controlled entangled
number states with tunable extremity and sharpness.Comment: revised version, 13 pages, 13 figure
Evolution of an elliptical bubble in an accelerating extensional flow
Mathematical models that describe the dynamical behavior of a thin gas bubble embedded in a glass fiber during a fiber drawing process have been discussed and analyzed.
The starting point for the mathematical modeling was the equations presented in [1] for a glass fiber with a hole undergoing extensional flow. These equations were reconsidered here with the additional reduction that the hole, i.e. the gas bubble, was thin as compared to the radius of the fiber and of finite extent. The primary model considered was one in which the mass of the gas inside the bubble was fixed. This fixed-mass model involved equations for the axial velocity and fiber radius, and equations for the radius of the bubble and the gas pressure inside the bubble. The model equations assumed that the temperature of the furnace of the drawing tower was known.
The governing equations of the bubble are hyperbolic and predict that the bubble cannot extend beyond the limiting characteristics specified by the ends of the initial bubble shape. An analysis of pinch-off was performed, and it was found that pinch-off can occur, depending on the parameters of the model, due to surface tension when the bubble radius is small.
In order to determine the evolution of a bubble, a numerical method of solution was presented. The method was used to study the evolution of two different initial bubble shapes, one convex and the other non-convex. Both initial bubble shapes had fore-aft symmetry, and it was found that the bubbles stretched and elongated severely during the drawing process. For the convex shape, fore-aft symmetry was lost in the middle of the drawing process, but the symmetry was re-gained by the end of the drawing tower. A small amount of pinch-off was observed at each end for this case, so that the final bubble length was slightly shorter than its theoretical maximum length. For the non-convex initial shape, pinch-off occurred in the middle of the bubble resulting in two bubbles by the end of the fiber draw.
The two bubbles had different final pressures and did not have fore-aft symmetry.
An extension of the fixed-mass model was considered in which the gas in the bubble was allowed to diffuse into the surrounding glass. The governing equations for this leaky-mass model were developed and manipulated into a form suitable for a numerical treatment
Sub-monolayers of carbon on alpha-iron facets: an ab-initio study
Motivated by recent in situ studies of carbon nanotube growth from large
transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at
different carbon concentrations using ab initio methods. The studied (110),
(100) and (111) facets show qualitatively different behaviour when carbon
concentration changes. In particular, adsorbed carbon atoms repel each other on
the (110) facet, resulting in carbon dimer and graphitic material formation.
Carbon on the (100) facet forms stable structures at concentrations of about
0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a
frustration of the top layer iron atoms. The stability of the (111) facet is
weakly affected by the amount of adsorbed carbon and its stability increases
further with respect to the (100) facet with increasing carbon concentration.
The exchange of carbon atoms between the surface and sub-surface regions on the
(111) facet is easier than on the other facets and the formation of carbon
dimers is exothermic. These findings are in accordance with a recent in situ
experimental study where the existence of graphene decorated (111) facets is
related to increased carbon concentration
Spin picture of the one-dimensional Hubbard model: Two-fluid structure and phase dynamics
We propose a scheme for investigating the quantum dynamics of interacting
electron models by means of time-dependent variational principle and spin
coherent states of space lattice operators. We apply such a scheme to the
one-dimensional hubbard model, and solve the resulting equations in different
regimes. In particular, we find that at low densities the dynamics is mapped
into two coupled nonlinear Schroedinger equations, whereas near half-filling
the model is described by two coupled Josephson junction arrays. Focusing then
to the case in which only the phases of the spin variables are dynamically
active, we examine a number of different solutions corresponding to the
excitations of few macroscopic modes. Based on fixed point equation of the
simpler among them, we show that the standard one-band ground state phase space
is found.Comment: 10 pages, 1 figure, to appear on Phys. Rev.
Quantized Roentgen Effect in Bose-Einstein Condensates
A classical dielectric moving in a charged capacitor can create a magnetic
field (Roentgen effect). A quantum dielectric, however, will not produce a
magnetization, except at vortices. The magnetic field outside the quantum
dielectric appears as the field of quantized monopoles
Space Shuttle main engine powerhead structural modeling, stress and fatigue life analysis. Volume 1: Gasdynamic environment of the SSME HPFTP and HPOTP turbines
Gasdynamic analysis for the turbine blades and nozzle vanes, HPFTP turbine analysis, and HPOTP turbine analysis are provided
Pasts and pagan practices: moving beyond Stonehenge
Theorizing the past is not restricted to archaeology and interpretations of 'past' both influence and are themselves constituted within politicized understandings of self, community and in certain instances, spirituality. 'The past in the imagination of the present' is appropriated, variously, to give meaning to the present or to justify actions and interpret experiences. Summer solstice at Stonehenge, with an estimated 21,000 celebrants in 2005, is only the most publicized appropriation (by pagans and other adherents of alternative spirituality and partying) of a 'sacred site'; and conflicts and negotiations occurring throughout Britain are represented in popular and academic presentations of this 'icon of Britishness'. This paper presents work from the Sacred Sites, Contested Rites/Rights Project (http://www.sacredsites.org.uk) project, a collaboration of archaeology and anthropology informed by pagan and alternative approaches and standpoints investigating and theorizing discourse and practice of heritage management and pagan site users. Whether in negotiations around the Stonehenge solstice access or in dealing with numerous other sites, boundaries between groups or discourses are not clearly drawn - discursive communities merge and re-emerge. But clearly 'past' and 'site' are increasingly important within today's Britain, even as television archaeology increases its following, and pagan numbers continue to grow.</p
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