173,201 research outputs found
Assessment criteria for 2D shape transformations in animation
The assessment of 2D shape transformations (or morphing) for animation is a difficult task because it is a multi-dimensional problem. Existing morphing techniques pay most attention to shape information interactive control and mathematical simplicity. This paper shows that it is not enough to use shape information alone, and we should consider other factors such as structure, dynamics, timing, etc. The paper also shows that an overall objective assessment of morphing is impossible because factors such as timing are related to subjective judgement, yet local objective assessment criteria, e.g. based on shape, are available. We propose using “area preservation” as the shape criterion for the 2D case as an acceptable approximation to “volume preservation” in reality, and use it to establish cases in which a number of existing techniques give clearly incorrect results. The possibility of deriving objective assessment criteria for dynamics simulations and timing under certain conditions is discussed
Sudden Death of Entanglement of Two Jaynes-Cummings Atoms
We investigate entanglement dynamics of two isolated atoms, each in its own
Jaynes-Cummings cavity. We show analytically that initial entanglement has an
interesting subsequent time evolution, including the so-called sudden death
effect.Comment: 3 pages, 3 figure
The Accretion and Cooling of Preheated Gas in Dark Matter Halos
(abridged) We use a one-dimensional hydrodynamical code to investigate the
effects of preheating on gas accretion and cooling in cold dark matter halos.
In the absence of radiative cooling, preheating reduces the amount of gas that
can be accreted into a halo, and the accreted gas fraction is determined by the
ratio of the initial specific entropy of the gas to the virial entropy of the
halo. In the presence of radiative cooling, preheating affects the gas fraction
that can cool in two different ways. For small halos with masses <10^12Msun,
preheating suppresses gas accretion, but most of the accreted gas can cool. For
more massive halos, preheating not only reduces the amount of accreted gas, but
also reduces the cooling efficiency. For both small and massive halos, gas
cooling is delayed by preheating and in an inside-out fashion if the halo gas
is assumed to be a single-phase medium. However, cooling can occur over a wider
range of redshifts and radii, if we assume a multi-phase medium. As examples,
two specific preheating cases are investigated. In the first case, the
preheating entropy is assumed to be proportional to the virial entropy of the
halo, as expected from AGN feedback. Such preheating effectively suppresses
radiative cooling in halos with M>10^13Msun. We suggest that this may be the
reason why the stellar mass function of galaxies breaks sharply at the massive
end. Such preheating also helps create the hot diffused halos within which the
"radio mode" feedback of AGNs can act effectively. In the second case, we
assume the intergalactic medium is warm. Here the total amount of gas that can
cool in a halo scales with halo mass as ~M^2, as would be required to match the
observed stellar- and HI-mass functions in the current CDM model at the small
mass end.Comment: 14 pages, 13 figures, submitted to MNRA
Phonon decoherence of quantum entanglement: Robust and fragile states
We study the robustness and fragility of entanglement of open quantum systems
in some exactly solvable models in which the decoherence is caused by a pure
dephasing process. In particular, for the toy models presented in this paper,
we identify two different time scales, one is responsible for local dephasing,
while the other is for entanglement decay. For a class of fragile entangled
states defined in this paper, we find that the entanglement of two qubits, as
measured by concurrence, decays faster asymptotically than the quantum
dephasing of an individual qubit.Comment: 11 pages, revtex, no figure
Coherent State Control of Non-Interacting Quantum Entanglement
We exploit a novel approximation scheme to obtain a new and compact formula
for the parameters underlying coherent-state control of the evolution of a pair
of entangled two-level systems. It is appropriate for long times and for
relatively strong external quantum control via coherent state irradiation. We
take account of both discrete-state and continuous-variable degrees of freedom.
The formula predicts the relative heights of entanglement revivals and their
timing and duration.Comment: Published in PRA, 10 pages, 7 figure
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