56,826 research outputs found
Semiclassical approach to Bose-Einstein condensates in a triple well potential
We present a new approach for the analysis of Bose-Einstein condensates in a
few mode approximation. This method has already been used to successfully
analyze the vibrational modes in various molecular systems and offers a new
perspective on the dynamics in many particle bosonic systems. We discuss a
system consisting of a Bose-Einstein condensate in a triple well potential.
Such systems correspond to classical Hamiltonian systems with three degrees of
freedom. The semiclassical approach allows a simple visualization of the
eigenstates of the quantum system referring to the underlying classical
dynamics. From this classification we can read off the dynamical properties of
the eigenstates such as particle exchange between the wells and entanglement
without further calculations. In addition, this approach offers new insights
into the validity of the mean-field description of the many particle system by
the Gross-Pitaevskii equation, since we make use of exactly this correspondence
in our semiclassical analysis. We choose a three mode system in order to
visualize it easily and, moreover, to have a sufficiently interesting
structure, although the method can also be extended to higher dimensional
systems.Comment: 15 pages, 15 figure
Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper. Part 2: Partially Sealed Configuration
Experimental results from a partially sealed squeeze film damper (SFD) test rig, executing a circular centered orbit are presented and discussed. A serrated piston ring is installed at the damper exit. This device involves a new sealing concept which produces high damping values while allowing for oil flow to cool the damper. In the partially sealed damper, large cavitation regions are observed in the pressure fields at orbit radii epsilon equals 0.5 and epsilon equals 0.8. The cavitated pressure distributions and the corresponding force coefficients are compared with a cavitated bearing solution. The experimental results show the significance of fluid inertia and vapor cavitation in the operation of squeeze film dampers. Squeeze film Reynolds numbers tested reach up to Re equals 50, spanning the range of contemporary applications
Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper. Part 1: Fully Open Ended Configuration
Measurements of pressure distributions and force coefficients were carried out in two types of squeeze film dampers, executing a circular centered orbit, an open-ended configuration, and a partially sealed one, in order to investigate the effect of fluid inertia and cavitation on pressure distributions and force coefficients. Dynamic pressure measurements were carried out for two orbit radii, epsilon 0.5 and 0.8. It was found that the partially sealed configuration was less influenced by fluid inertia than the open ended configuration
Strong electron correlations in cobalt valence tautomers
We have examined cobalt based valence tautomer molecules such as
Co(SQ)(phen) using density functional theory (DFT) and variational
configuration interaction (VCI) approaches based upon a model Hamiltonian. Our
DFT results extend earlier work by finding a reduced total energy gap (order
0.6 eV) between high temperature and low temperature states when we fully relax
the coordinates (relative to experimental ones). Futhermore we demonstrate that
the charge transfer picture based upon formal valence arguments succeeds
qualitatively while failing quantitatively due to strong covalency between the
Co 3 orbitals and ligand orbitals. With the VCI approach, we argue that
the high temperature, high spin phase is strongly mixed valent, with about 30 %
admixture of Co(III) into the predominantly Co(II) ground state. We confirm
this mixed valence through a fit to the XANES spectra. Moreover, the strong
electron correlations of the mixed valent phase provide an energy lowering of
about 0.2-0.3 eV of the high temperature phase relative to the low temperature
one. Finally, we use the domain model to account for the extraordinarily large
entropy and enthalpy values associated with the transition.Comment: 10 pages, 4 figures, submitted to J. Chem. Phy
Recommended from our members
The Effect of Inkjet Ink Composition on Rheology And Jetting Behaviour
This work presents recent results on the way linear and non linear viscoelastic properties of the fluids affect the jetting
mechanism. Recent progress on quantitative characterising both high frequency linear (LVE) and non-linear (NLVE) viscoelasticity
of fluids allows fluids to be assessed for their jettability before using such materials in a DoD print head. In term of linear viscoelastic measurements, the Piezo Axial Vibrator (PAV) was used to probe the rheology of the fluids on a frequency range
between 10Hz and 10000Hz. A filament stretching apparatus, called the “Cambridge Trimaster”, was used in combination with
high speed cinematography, to characterize the fluids high speed stretching and break-up behaviour. The series of fluids investigated here consist in dilutions of mono disperse polystyrene with different molecular weight (110, 210, 306 and 488 kg/mol respectively) diluted in diethyl phthalate. The choice of polymer weights and concentrations were chosen to match both the
complex viscosity and the LVE. However, non linear rheological data experiments exhibit differences in the fluid relaxation time
and filament break-up mechanism. Ultra-high speed cinematography of DoD jetting events were correlated with filament break-up experiments and demonstrated that fluid rheology provides valuable information on the jetting quality of the fluids
Some GrĂĽss' Type Inequalities in 2-Inner Product Spaces and Applications for Determinantal Integral Inequalities
Some new GrĂĽss type inequalities in 2-inner product spaces are given. Using this framework, some determinantal integral inequalities for synchronous functions are also derived
Temperature- and magnetic-field-dependent resistivity of MgB2 sintered at high temperature and high pressure condition
We report the temperature- and magnetic-field-dependent resistivity of MgB2
sintered at high temperature and high pressure condition. The superconducting
transition width for the resistivity measurement was about 0.4 K, and the
low-field magnetization showed a sharp superconducting transition with a
transition width of about 1 K. The resistivity in the normal state roughly
followed T^2 behavior with smaller residual resistivity ratio (RRR) of 3 over
broad temperature region above 100 K rather than reported T^3 behavior with
larger RRR value of ~ 20 in the samples made at lower pressures. Also, the
resistivity did not change appreciably with the applied magnetic field, which
was different from previous report. These differences were discussed with the
microscopic and structural change due to the high-pressure sintering.Comment: 2 pages, 3 figures. Accepted by Physica
- …