1,129 research outputs found
The large-scale magnetic field of a thin accretion disk with outflows
The large-scale magnetic field threading an accretion disk plays an important
role in launching jets/outflows. The field may probably be advected inwards by
the plasma in the accretion disk from the ambient environment (interstellar
medium or a companion star). It has been suggested that the external field can
be efficiently dragged inwards in a thin disk with magnetic outflows. We
construct a self-consistent global disk-outflow model, in which the large-scale
field is formed by the advection of the external field in the disk. The
outflows are accelerated by this field co-rotating with the disk, which carry
away most angular momentum of the disk and make its structure significantly
different from the conventional viscous disk structure. We find that the
magnetic field strength in the inner region of the disk can be several orders
of magnitude higher than the external field strength for a geometrically thin
disk with , if the ratio of the gas to magnetic pressure
at the outer edge of the disk. The outflow
velocity shows layer-like structure, i.e., it decreases with radius where it is
launched. The outflow can be accelerated up to c from the inner
region of the disk, and the mass loss rate in the outflows is
of the mass accretion rate at the outer radius of the disk, which may account
for the fast outflows observed in some active galactic nuclei (AGNs).Comment: Accepted for publication in Ap
Modelling exchange rate volatility with random level shifts
Recent literature has shown that the volatility of exchange rate returns displays long memory features. It has also been shown that if a short memory process is contaminated by level shifts, the estimate of the long memory parameter tends to be upward biased. In this article, we directly estimate a random level shift model to the logarithm of the absolute returns of five exchange rates series, in order to assess whether random level shifts (RLSs) can explain this long memory property. Our results show that there are few level shifts for the five series, but once they are taken into account the long memory property of the series disappears. We also provide out-of-sample forecasting comparisons, which show that, in most cases, the RLS model outperforms popular models in forecasting volatility. We further support our results using a variety of robustness checks
Bilevel Scheduled Sampling for Dialogue Generation
Exposure bias poses a common challenge in numerous natural language
processing tasks, particularly in the dialog generation. In response to this
issue, researchers have devised various techniques, among which scheduled
sampling has proven to be an effective method for mitigating exposure bias.
However, the existing state-of-the-art scheduled sampling methods solely
consider the current sampling words' quality for threshold truncation sampling,
which overlooks the importance of sentence-level information and the method of
threshold truncation warrants further discussion. In this paper, we propose a
bilevel scheduled sampling model that takes the sentence-level information into
account and incorporates it with word-level quality. To enhance sampling
diversity and improve the model's adaptability, we propose a smooth function
that maps the combined result of sentence-level and word-level information to
an appropriate range, and employ probabilistic sampling based on the mapped
values instead of threshold truncation. Experiments conducted on the
DailyDialog and PersonaChat datasets demonstrate the effectiveness of our
proposed methods, which significantly alleviate the exposure bias problem and
outperform state-of-the-art scheduled sampling methods.Comment: 13 pages, 4 figures, Natural Language Processing and Chinese
Computing(NLPCC 2023) accepte
Tracial states on groupoid -algebras and essential freeness
Let be a locally compact Hausdorff \'{e}tale groupoid. We call
a tracial state on a general groupoid -algebra
canonical if , where is the canonical
conditional expectation. In this paper, we consider so-called fixed point
traces on , and prove that is essentially free
if and only if any tracial state on is canonical and any
fixed point trace is extendable to .
As applications, we obtain the following: 1) a group action is essentially
free if every tracial state on the reduced crossed product is canonical and
every isotropy group is amenable; 2) if the groupoid is second
countable, amenable and essentially free then every (not necessarily faithful)
tracial state on the reduced groupoid -algebra is quasidiagonal
Three-dimensional solutions for the geostrophic flow in the Earth's core
In his seminal work, Taylor (1963) argued that the geophysically relevant
limit for dynamo action within the outer core is one of negligibly small
inertia and viscosity in the magnetohydrodynamic equations. Within this limit,
he showed the existence of a necessary condition, now well known as Taylor's
constraint, which requires that the cylindrically-averaged Lorentz torque must
everywhere vanish; magnetic fields that satisfy this condition are termed
Taylor states. Taylor further showed that the requirement of this constraint
being continuously satisfied through time prescribes the evolution of the
geostrophic flow, the cylindrically-averaged azimuthal flow. We show that
Taylor's original prescription for the geostrophic flow, as satisfying a given
second order ordinary differential equation, is only valid for a small subset
of Taylor states. An incomplete treatment of the boundary conditions renders
his equation generally incorrect. Here, by taking proper account of the
boundaries, we describe a generalisation of Taylor's method that enables
correct evaluation of the instantaneous geostrophic flow for any 3D Taylor
state. We present the first full-sphere examples of geostrophic flows driven by
non-axisymmetric Taylor states. Although in axisymmetry the geostrophic flow
admits a mild logarithmic singularity on the rotation axis, in the fully 3D
case we show that this is absent and indeed the geostrophic flow appears to be
everywhere regular.Comment: 29 Pages, 8 figure
Real-time Data Flow Control for CBM-TOF Super Module Quality Evaluation
Super module assembled with MRPC detectors is the component unit of TOF (Time
of Flight) system for the Compressed Baryonic Matter (CBM) experiment. Quality
of super modules needs to be evaluated before it is applied in CBM-TOF. Time
signals exported from super module are digitalized at TDC (Time to Digital
Converter) station. Data rate is up to 6 Gbps at each TDC station, which brings
a tremendous pressure for data transmission in real time. In this paper, a
real-time data flow control method is designed. In this control method, data
flow is divided into 3 types: scientific data flow, status data flow and
control data flow. In scientific data flow, data of each TDC station is divided
into 4 sub-flows, and then is read out by a parallel and hierarchical network,
which consists of multiple readout mother boards and daughter boards groups. In
status data flow, status data is aggregated into a specific readout mother
board. Then it is uploaded to DAQ via readout daughter board. In control data
flow, control data is downloaded to all circuit modules in the opposite
direction of status data flow. Preliminary test result indicated data of STS
was correctly transmitted to DAQ with no error and three type data flows were
control orderly in real time. This data flow control method can meet the
quality evaluation requirement of supper module in CBM-TOF
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