908 research outputs found
Seeding supermassive black holes with a nonvortical dark-matter subcomponent
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Critical sets of the total variance of state detect all SLOCC entanglement classes
We present a general algorithm for finding all classes of pure multiparticle
states equivalent under Stochastic Local Operations and Classsical
Communication (SLOCC). We parametrize all SLOCC classes by the critical sets of
the total variance function. Our method works for arbitrary systems of
distinguishable and indistinguishable particles. We also discuss the Morse
indices of critical points which have the interpretation of the number of
independent non-local perturbations increasing the variance and hence
entanglement of a state. We illustrate our method by two examples.Comment: 4 page
Cavitation Effects on the Stability of a Submerged Journal Bearing
A computational procedure for the mechanism of shear between the liquid sublayer and air cavity in the cavitation zone of a submerged journal bearing is presented here. Using the mass conservation principle, Elrod's universal equation is modified to take into consideration the shear of the air cavity in the cavitation region. Results of steady state and transient response for the submerged journal bearing using the present approach are compared with the universal equation based on the striated flow in the cavitation region. At steady state, the angular extent of cavitation region predicted by the present approach is higher than that predicted by Elrod's model and the limit cycle journal transient response using the present approach predicts higher eccentricity
ratios
Unbalance Response Prediction for Accelerating Rotors With Load-Dependent Nonlinear Bearing Stiffness
Rolling-element bearing forces vary nonlinearly with bearing deflection. Thus an accurate rotordynamic analysis requires that bearing forces corresponding to the actual bearing deflection be utilized. Previous papers have explored the transient effect of suddenly applied imbalance and the steady-state unbalance response, using bearing forces calculated by the rolling-element bearing analysis code COBRA-AHS. The present work considers the acceleration of a rotor through one or more critical speeds. The rotordynamic analysis showed that for rapid acceleration rates the maximum response amplitude may be considerably less than predicted by steady-state analysis. Above the critical speed, transient vibration at the rotor natural frequency occurs, similar to that predicted for a Jeffcott rotor with constant-stiffness bearings. A moderate amount of damping will markedly reduce the vibration amplitude, but this damping is not inherent in ball bearings
Solving Bethe-Salpeter equation in Minkowski space
We develop a new method of solving Bethe-Salpeter (BS) equation in Minkowski
space. It is based on projecting the BS equation on the light-front (LF) plane
and on the Nakanishi integral representation of the BS amplitude. This method
is valid for any kernel given by the irreducible Feynman graphs. For massless
ladder exchange, our approach reproduces analytically the Wick-Cutkosky
equation. For massive ladder exchange, the numerical results coincide with the
ones obtained by Wick rotation.Comment: 10 pages, 4 figure
Entanglement of four qubit systems: a geometric atlas with polynomial compass I (the finite world)
We investigate the geometry of the four qubit systems by means of algebraic
geometry and invariant theory, which allows us to interpret certain entangled
states as algebraic varieties. More precisely we describe the nullcone, i.e.,
the set of states annihilated by all invariant polynomials, and also the so
called third secant variety, which can be interpreted as the generalization of
GHZ-states for more than three qubits. All our geometric descriptions go along
with algorithms which allow us to identify any given state in the nullcone or
in the third secant variety as a point of one of the 47 varieties described in
the paper. These 47 varieties correspond to 47 non-equivalent entanglement
patterns, which reduce to 15 different classes if we allow permutations of the
qubits.Comment: 48 pages, 7 tables, 13 figures, references and remarks added (v2
Antireflective photonic structure for coherent nonlinear spectroscopy of single magnetic quantum dots
This work presents epitaxial growth and optical spectroscopy of CdTe quantum
dots (QDs) in (Cd,Zn,Mg)Te barriers placed on the top of (Cd,Zn,Mg)Te
distributed Bragg reflector. The formed photonic mode in our half-cavity
structure permits to enhance the local excitation intensity and extraction
efficiency of the QD photoluminescence, while suppressing the reflectance
within the spectral range covering the QD transitions. This allows to perform
coherent, nonlinear, resonant spectroscopy of individual QDs. The coherence
dynamics of a charged exciton is measured via four-wave mixing, with the
estimated dephasing time ps. The same structure contains
QDs doped with single Mn ions, as detected in photoluminescence spectra.
Our work therefore paves the way toward investigating and controlling an
exciton coherence coupled, via ,- exchange interaction, with an
individual spin of a magnetic dopant.Comment: 6 pages, 5 figure
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