15,370 research outputs found
The entanglement dynamics of interacting qubits embedded in a spin environment with Dzyaloshinsky-Moriya term
We investigate the entanglement dynamics of two interacting qubits in a spin
environment, which is described by an XY model with Dzyaloshinsky-Moriya (DM)
interaction. The competing effects of environmental noise and interqubit
coupling on entanglement generation for various system parameters are studied.
We find that the entanglement generation is suppressed remarkably in
weak-coupling region at quantum critical point (QCP). However, the suppression
of the entanglement generation at QCP can be compensated both by increasing the
DM interaction and by decreasing the anisotropy of the spin chain. Beyond the
weak-coupling region, there exist resonance peaks of concurrence when the
system-bath coupling equals to external magnetic field. We attribute the
presence of resonance peaks to the flat band of the self-Hamiltonian. These
peaks are highly sensitive to anisotropy parameter and DM interaction.Comment: 8 pages, 9 figure
Evolution of black-hole intermediate-mass X-ray binaries: the influence of a circumbinary disc
Justham, Rappaport & Podsiadlowski (2006) recently suggested that black-hole
low-mass X-ray binaries (BHLMXBs) with short orbital periods may have evolved
from black-hole intermediate-mass X-ray binaries (BHIMXBs). In their model the
secondaries in BHIMXBs are assumed to possess anomalously high magnetic fields,
so that magnetic braking can lead to substantial loss of angular momentum. In
this paper we propose an alternative mechanism for orbital angular momentum
loss in BHIMXBs. We assume that a small fraction of the transferred
mass from the donor star form a circumbinary disc surrounding the binary
system. The tidal torques exerted by the disc can effectively drain orbital
angular momentum from the binary. We have numerically calculated the
evolutionary sequences of BHIMXBs, to examine the influence of the circumbinary
disc on the binary evolution. Our results indicate when \delta\la 0.01-0.1
(depending on the initial orbital periods), the circumbinary disc can cause
secular orbital shrinking, leading to the formation of compact
BHLMXBs, otherwise the orbits always expand during the evolution. This
scenario also suggests the possible existence of luminous, persistent BHLMXBs,
but it suffers the same problem as in Justham, Rappaport & Podsiadlowski (2006)
that, the predicted effective temperatures of the donor stars are significantly
higher than those of the observed donor stars in BHLMXBs.Comment: 7 pages, 5 figures, accepted for publication in MNRA
The progenitors of Type Ia supernovae with long delay times
The nature of the progenitors of Type Ia supernovae (SNe Ia) is still
unclear. In this paper, by considering the effect of the instability of
accretion disk on the evolution of white dwarf (WD) binaries, we performed
binary evolution calculations for about 2400 close WD binaries, in which a
carbon--oxygen WD accretes material from a main-sequence star or a slightly
evolved subgiant star (WD + MS channel), or a red-giant star (WD + RG channel)
to increase its mass to the Chandrasekhar (Ch) mass limit. According to these
calculations, we mapped out the initial parameters for SNe Ia in the orbital
period--secondary mass () plane for various WD
masses for these two channels, respectively. We confirm that WDs in the WD + MS
channel with a mass as low as can accrete efficiently and reach
the Ch limit, while the lowest WD mass for the WD + RG channel is . We have implemented these results in a binary population synthesis
study to obtain the SN Ia birthrates and the evolution of SN Ia birthrates with
time for both a constant star formation rate and a single starburst. We find
that the Galactic SN Ia birthrate from the WD + MS channel is according to our standard model, which is higher than
previous results. However, similar to previous studies, the birthrate from the
WD + RG channel is still low (). We also
find that about one third of SNe Ia from the WD + MS channel and all SNe Ia
from the WD + RG channel can contribute to the old populations (\ga1 Gyr) of
SN Ia progenitors.Comment: 11 pages, 9 figures, 1 table, accepted for publication in MNRA
MuseGAN: Multi-track Sequential Generative Adversarial Networks for Symbolic Music Generation and Accompaniment
Generating music has a few notable differences from generating images and
videos. First, music is an art of time, necessitating a temporal model. Second,
music is usually composed of multiple instruments/tracks with their own
temporal dynamics, but collectively they unfold over time interdependently.
Lastly, musical notes are often grouped into chords, arpeggios or melodies in
polyphonic music, and thereby introducing a chronological ordering of notes is
not naturally suitable. In this paper, we propose three models for symbolic
multi-track music generation under the framework of generative adversarial
networks (GANs). The three models, which differ in the underlying assumptions
and accordingly the network architectures, are referred to as the jamming
model, the composer model and the hybrid model. We trained the proposed models
on a dataset of over one hundred thousand bars of rock music and applied them
to generate piano-rolls of five tracks: bass, drums, guitar, piano and strings.
A few intra-track and inter-track objective metrics are also proposed to
evaluate the generative results, in addition to a subjective user study. We
show that our models can generate coherent music of four bars right from
scratch (i.e. without human inputs). We also extend our models to human-AI
cooperative music generation: given a specific track composed by human, we can
generate four additional tracks to accompany it. All code, the dataset and the
rendered audio samples are available at https://salu133445.github.io/musegan/ .Comment: to appear at AAAI 201
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