2,933 research outputs found
An hourglass model for the flare of HST-1 in M87
To explain the multi-wavelength light curves (from radio to X-ray) of HST-1
in the M87 jet, we propose an hourglass model that is a modified two-zone
system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or
Laval nozzle-shaped layer connected by two revolving exponential surfaces
surrounding a fast spine, through which plasma blobs flow. Based on the
conservation of magnetic flux, the magnetic field changes along the axis of the
hourglass. We adopt the result of TG08---the high-energy emission from GeV to
TeV can be produced through inverse Compton by the two-zone system, and the
photons from radio to X-ray are mainly radiated by the fast inner zone system.
Here, we only discuss the light curves of the fast inner blob from radio to
X-ray. When a compressible blob travels down the axis of the first bulb in the
hourglass, because of magnetic flux conservation, its cross section experiences
an adiabatic compression process, which results in particle acceleration and
the brightening of HST-1. When the blob moves into the second bulb of the
hourglass, because of magnetic flux conservation, the dimming of the knot
occurs along with an adiabatic expansion of its cross section. A similar broken
exponential function could fit the TeV peaks in M87, which may imply a
correlation between the TeV flares of M87 and the light curves from radio to
X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1
verifies our prediction based on the model fit to the main peak of the VLA 15
GHz radio light curve.Comment: 14 pages, 2 figures, accepted for publication in A
Efficient-Adam: Communication-Efficient Distributed Adam
Distributed adaptive stochastic gradient methods have been widely used for
large-scale nonconvex optimization, such as training deep learning models.
However, their communication complexity on finding -stationary
points has rarely been analyzed in the nonconvex setting. In this work, we
present a novel communication-efficient distributed Adam in the
parameter-server model for stochastic nonconvex optimization, dubbed {\em
Efficient-Adam}. Specifically, we incorporate a two-way quantization scheme
into Efficient-Adam to reduce the communication cost between the workers and
server. Simultaneously, we adopt a two-way error feedback strategy to reduce
the biases caused by the two-way quantization on both the server and workers,
respectively. In addition, we establish the iteration complexity for the
proposed Efficient-Adam with a class of quantization operators, and further
characterize its communication complexity between the server and workers when
an -stationary point is achieved. Finally, we apply Efficient-Adam
to solve a toy stochastic convex optimization problem and train deep learning
models on real-world vision and language tasks. Extensive experiments together
with a theoretical guarantee justify the merits of Efficient Adam.Comment: IEEE Transactions on Signal Processin
A general study on the volume dependence of spectral weights in lattice field theory
It has been suggested that the volume dependence of the spectral weight could
be utilized to distinguish single and multi-particle states in Monte Carlo
simulations. In a recent study using a solvable model, the Lee model, we found
that this criteria is applicable only for stable particles and narrow
resonances, not for the broad resonances. In this paper, the same question is
addressed within the finite size formalism outlined by L\"uscher. Using a
quantum mechanical scattering model, the conclusion that was found in previous
Lee model study is recovered. Then, following similar arguments as in
L\"uscher's, it is argued that the result is valid for a general massive
quantum field theory under the same conditions as the L\"uscher's formulae.
Using the spectral weight function, a possibility of extracting resonance
parameters is also pointed out.Comment: 18 pages, no figure
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