6,093 research outputs found
Global existence of critical nonlinear wave equation with time dependent variable coefficients
In this paper, we establish global existence of smooth solutions for the
Cauchy problem of the critical nonlinear wave equation with time dependent
variable coefficients in three space dimensions
{equation}\partial_{tt}\phi-\partial_{x_i}\big(g^{ij}(t,x)\partial_{x_j}\phi\big)+\phi^5=0,
mathbb{R}_t \times \mathbb{R}_x^3,{equation} where is a
regular function valued in the spacetime of positive definite matrix
and its inverse matrix. Here and in the sequence, a
repeated sum on an index in lower and upper position is never indicated. In the
constant coefficients case, the result of global existence is due to Grillakis
\cite{Grillakis1}; and in the time-independent variable coefficients case, the
result of global existence and regularity is due to Ibrahim and Majdoub
\cite{Ibrahim}. The key point of our proofs is to show that the energy cannot
concentrate at any point. For that purpose, following Christodoulou and
Klainerman \cite{Chris}, we use a null frame associated to an optical function
to construct a geometric multiplier similar to the well-known Morawetz
multiplier. Then we use comparison theorem originated from Riemannian Geometry
to estimate the error terms. Finally, using Strichartz inequality due to
\cite{Smith} as Ibrahim and Majdoub \cite{Ibrahim}, we obtain global existence
Global Existence of the Critical Semilinear Wave Equations with Variable Coefficients Outside Obstacles
In this paper, we consider exterior problem of the critical semilinear wave
equation in three space dimensions with variable coefficients and prove global
existence of smooth solutions.
Similar to the constant coefficients case, we show that the energy cannot
concentrate at any point . For that purpose,
following Ibrahim and Majdoub \cite{Ibrahim}, we use a geometric multiplier
close to the well-known Morawetz multiplier used in the constant coefficients
case. Then we use comparison theorem from Riemannian Geometry to estimate the
error terms. Finally, using Strichartz inequality as in Smith and Sogge
\cite{Sogge}, we get the global existence
The zero inertia limit of Ericksen-Leslie's model for liquid crystals
In this paper we study the zero inertia limit that is from the hyperbolic to
parabolic Ericksen-Leslie's liquid crystal flow. By introducing an initial
layer and constructing an energy norm and energy dissipation functional
depending on the solutions of the limiting system, we derive a global in time
uniform energy bound to the remainder system under the small size of the
initial data.Comment: 56 pages; all coments wellcome
Learning Disentangled Representations for Timber and Pitch in Music Audio
Timbre and pitch are the two main perceptual properties of musical sounds.
Depending on the target applications, we sometimes prefer to focus on one of
them, while reducing the effect of the other. Researchers have managed to
hand-craft such timbre-invariant or pitch-invariant features using domain
knowledge and signal processing techniques, but it remains difficult to
disentangle them in the resulting feature representations. Drawing upon
state-of-the-art techniques in representation learning, we propose in this
paper two deep convolutional neural network models for learning disentangled
representation of musical timbre and pitch. Both models use encoders/decoders
and adversarial training to learn music representations, but the second model
additionally uses skip connections to deal with the pitch information. As music
is an art of time, the two models are supervised by frame-level instrument and
pitch labels using a new dataset collected from MuseScore. We compare the
result of the two disentangling models with a new evaluation protocol called
"timbre crossover", which leads to interesting applications in audio-domain
music editing. Via various objective evaluations, we show that the second model
can better change the instrumentation of a multi-instrument music piece without
much affecting the pitch structure. By disentangling timbre and pitch, we
envision that the model can contribute to generating more realistic music audio
as well
Multitask learning for frame-level instrument recognition
For many music analysis problems, we need to know the presence of instruments
for each time frame in a multi-instrument musical piece. However, such a
frame-level instrument recognition task remains difficult, mainly due to the
lack of labeled datasets. To address this issue, we present in this paper a
large-scale dataset that contains synthetic polyphonic music with frame-level
pitch and instrument labels. Moreover, we propose a simple yet novel network
architecture to jointly predict the pitch and instrument for each frame. With
this multitask learning method, the pitch information can be leveraged to
predict the instruments, and also the other way around. And, by using the
so-called pianoroll representation of music as the main target output of the
model, our model also predicts the instruments that play each individual note
event. We validate the effectiveness of the proposed method for framelevel
instrument recognition by comparing it with its singletask ablated versions and
three state-of-the-art methods. We also demonstrate the result of the proposed
method for multipitch streaming with real-world music. For reproducibility, we
will share the code to crawl the data and to implement the proposed model at:
https://github.com/biboamy/ instrument-streaming.Comment: This is a pre-print version of an ICASSP 2019 pape
Entropy dynamics of a dephasing model in a squeezed thermal bath
We study the entropy dynamics of a dephasing model, where a two-level system
(TLS) is coupled with a squeezed thermal bath via non-demolition interaction.
This model is exactly solvable, and the time dependent states of both the TLS
and its bath can be obtained exactly. Based on these states, we calculate the
entropy dynamics of both the TLS and the bath, and find that the dephasing rate
of the system relies on the squeezing phase of the bath. In zero temperature
and high temperature limits, we prove that both the system and bath entropy
increases monotonically. Moreover, we find that the dephasing rate of the
system relies on the squeezing phase of the bath, and this phase dependence
cannot be precisely derived from the Born-Markovian approximation which is
widely adopted in open quantum systems.Comment: 9.3 pages, 2 figure
On well-posedness of Ericksen-Leslie's parabolic-hyperbolic liquid crystal model in compressible flow
We study the Ericksen-Leslie's parabolic-hyperbolic liquid crystal model in
compressible flow. Inspired by our study for incompressible case
\cite{Jiang-Luo-arXiv-2017} and some techniques from compressible Navier-Stokes
equations, we prove the local-in-time existence of the classical solution to
the system with finite initial energy, under some constraints on the Leslie
coefficients which ensure the basic energy law is dissipative. Furthermore,
with an additional assumption on the coefficients which provides a damping
effect, and the smallness of the initial energy, the global classical solution
can be established.Comment: arXiv admin note: text overlap with arXiv:1709.0637
Hit Song Prediction for Pop Music by Siamese CNN with Ranking Loss
A model for hit song prediction can be used in the pop music industry to
identify emerging trends and potential artists or songs before they are
marketed to the public. While most previous work formulates hit song prediction
as a regression or classification problem, we present in this paper a
convolutional neural network (CNN) model that treats it as a ranking problem.
Specifically, we use a commercial dataset with daily play-counts to train a
multi-objective Siamese CNN model with Euclidean loss and pairwise ranking loss
to learn from audio the relative ranking relations among songs. Besides, we
devise a number of pair sampling methods according to some empirical
observation of the data. Our experiment shows that the proposed model with a
sampling method called A/B sampling leads to much higher accuracy in hit song
prediction than the baseline regression model. Moreover, we can further improve
the accuracy by using a neural attention mechanism to extract the highlights of
songs and by using a separate CNN model to offer high-level features of songs
Coupled Self-Organized Hydrodynamics and Navier-Stokes models: local well-posedness and the limit from the Self-Organized Kinetic-fluid models
A coupled system of self-organized hydrodynamics and Navier-Stokes equations
(SOH-NS), which models self-propelled particles in a viscous fluid, was
recently derived by Degond et al. \cite{DMVY-2017-arXiv}, starting from a
micro-macro particle system of Vicsek-Navier-Stokes model, through an
intermediate step of a self-organized kinetic-kinetic model by multiple
coarse-graining processes. We first transfer SOH-NS into a non-singular system
by stereographic projection, then prove the local in time well-posedness of
classical solutions by energy method. Furthermore, employing the Hilbert
expansion approach, we justify the hydrodynamic limit from the self-organized
kinetic-fluid model to macroscopic dynamics. This provides the first
analytically rigorous justification of the modeling and asymptotic analysis in
\cite{DMVY-2017-arXiv}.Comment: 42 pages. arXiv admin note: text overlap with arXiv:1706.05666 by
other author
Cultural evolution and personalization
In social sciences, there is currently no consensus on the mechanism for
cultural evolution. The evolution of first names of newborn babies offers a
remarkable example for the researches in the field. Here we perform statistical
analyses on over 100 years of data in the United States. We focus in particular
on how the frequency-rank distribution and inequality of baby names change over
time. We propose a stochastic model where name choice is determined by
personalized preference and social influence. Remarkably, variations on the
strength of personalized preference can account satisfactorily for the observed
empirical features. Therefore, we claim that personalization drives cultural
evolution, at least in the example of baby names
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