152,693 research outputs found
Solar surface rotation: N-S asymmetry and recent speed-up
Context. The relation between solar surface rotation and sunspot activity
still remains open. Sunspot activity has dramatically reduced in solar cycle 24
and several solar activity indices and flux measurements experienced
unprecedentedly low levels during the last solar minimum.
Aims. We aim to reveal the momentary variation of solar surface rotation,
especially during the recent years of reducing solar activity. Methods. We used
a dynamic, differentially rotating reference system to determine the best-fit
annual values of the differential rotation parameters of active longitudes of
solar X-ray flares and sunspots in 1977-2012.
Results. The evolution of rotation of solar active longitudes obtained with
X-ray flares and with sunspots is very similar. Both hemispheres speed up since
the late 1990s, with the southern hemisphere rotating slightly faster than the
north. Earlier, in 1980s, rotation in the northern hemisphere was considerably
faster, but experienced a major decrease in the early 1990s. On the other hand,
little change was found in the southern rotation during these decades. This led
to a positive asymmetry in north-south rotation rate in the early part of the
time interval studied.
Conclusions. The rotation of both hemispheres has been speeding up at roughly
the same rate since late 1990s, with the southern hemisphere rotating slightly
faster than the north. This period coincides with the start of dramatic
weakening of solar activity, as observed in sunspots and several other solar,
interplanetary and geomagnetic parameters.Comment: Astron. Astrophys. Lett. (accepted
A Conservative Discontinuous Galerkin Scheme With O(N-2) Operations In Computing Boltzmann Collision Weight Matrix
In the present work, we propose a deterministic numerical solver for the homogeneous Boltzmann equation based on Discontinuous Galerkin (DG) methods. The weak form of the collision operator is approximated by a quadratic form in linear algebra setting. We employ the property of >shifting symmetry> in the weight matrix to reduce the computing complexity from theoretical O(N-3) down to O(N-2), with N the total number of freedom for d-dimensional velocity space. In addition, the sparsity is also explored to further reduce the storage complexity. To apply lower order polynomials and resolve loss of conserved quantities, we invoke the conservation routine at every time step to enforce the conservation of desired moments (mass, momentum and/or energy), with only linear complexity. Due to the locality of the DG schemes, the whole computing process is well parallelized using hybrid OpetiMP and MPI. The current work only considers integrable angular cross-sections under elastic and/or inelastic interaction laws. Numerical results on 2-D and 3-D problems are shown.Mathematic
Distributed Deep Learning for Question Answering
This paper is an empirical study of the distributed deep learning for
question answering subtasks: answer selection and question classification.
Comparison studies of SGD, MSGD, ADADELTA, ADAGRAD, ADAM/ADAMAX, RMSPROP,
DOWNPOUR and EASGD/EAMSGD algorithms have been presented. Experimental results
show that the distributed framework based on the message passing interface can
accelerate the convergence speed at a sublinear scale. This paper demonstrates
the importance of distributed training. For example, with 48 workers, a 24x
speedup is achievable for the answer selection task and running time is
decreased from 138.2 hours to 5.81 hours, which will increase the productivity
significantly.Comment: This paper will appear in the Proceeding of The 25th ACM
International Conference on Information and Knowledge Management (CIKM 2016),
Indianapolis, US
Characteristics of Bose-Einstein condensation in an optical lattice
We discuss several possible experimental signatures of the Bose-Einstein
condensation (BEC) transition for an ultracold Bose gas in an inhomogeneous
optical lattice. Based on the commonly used time-of-flight imaging technique,
we show that the momentum-space density profile in the first Brillouin zone,
supplemented by the visibility of interference patterns, provides valuable
information about the system. In particular, by crossing the BEC transition
temperature, the appearance of a clear bimodal structure sets a qualitative and
universal signature of this phase transition. Furthermore, the momentum
distribution can also be applied to extract the condensate fraction, which may
serve as a promising thermometer in such a system.Comment: 12 pages, 13 figures; Revised version with new figures; Phys. Rev. A
77, 043626 (2008
Accuracy Assessment on Drone Measured Heights at Different Height Levels
The advancement in unmanned aerial system (UAS) technology has made it possible to attain an aerial unit, commonly known as a drone, at an affordable price with increasing precision and accuracy in positioning and photographing. While aerial photography is the most common use of a drone, many of the models available in the market are also capable of measuring height, the height of the drone above ground, or the altitude above the mean sea level. On board a drone, a barometer is used to control the flight height by detecting the atmospheric pressure change; while a GPS receiver is mainly used to determine the horizontal position of the drone. While both barometer and GPS are capable of measuring height, they are based on different algorithms. Our study goal was to assess the accuracy of height measurement by a drone, with different landing procedures and GPS settings
Dark viscous fluid described by a unified equation of state in cosmology
We generalize the CDM model by introducing a unified EOS to describe
the Universe contents modeled as dark viscous fluid, motivated by the fact that
a single constant equation of state (EOS) () reproduces the
CDM model exactly. This EOS describes the perfect fluid term, the
dissipative effect, and the cosmological constant in a unique framework and the
Friedmann equations can be analytically solved. Especially, we find a relation
between the EOS parameter and the renormalizable condition of a scalar field.
We develop a completely numerical method to perform a minimization to
constrain the parameters in a cosmological model directly from the Friedmann
equations, and employ the SNe data with the parameter measured
from the SDSS data to constrain our model. The result indicates that the
dissipative effect is rather small in the late-time Universe.Comment: 4 pages, 2 figures. v2: new materials added. v3: matches the version
to appear in IJMP
Large-Alphabet Time-Frequency Entangled Quantum Key Distribution by means of Time-to-Frequency Conversion
We introduce a novel time-frequency quantum key distribution (TFQKD) scheme
based on photon pairs entangled in these two conjugate degrees of freedom. The
scheme uses spectral detection and phase modulation to enable measurements in
the temporal basis by means of time-to-frequency conversion. This allows
large-alphabet encoding to be implemented with realistic components. A general
security analysis for TFQKD with binned measurements reveals a close connection
with finite-dimensional QKD protocols and enables analysis of the effects of
dark counts on the secure key size.Comment: 14 pages, 3 figures, submitte
Two-parameter quantum general linear supergroups
The universal R-matrix of two-parameter quantum general linear supergroups is
computed explicitly based on the RTT realization of
Faddeev--Reshetikhin--Takhtajan.Comment: v1: 14 pages. v2: published version, 9 pages, title changed and the
section on central extension remove
Nonlinear screening and ballistic transport in a graphene p-n junction
We study the charge density distribution, the electric field profile, and the
resistance of an electrostatically created lateral p-n junction in graphene. We
show that the electric field at the interface of the electron and hole regions
is strongly enhanced due to limited screening capacity of Dirac quasiparticles.
Accordingly, the junction resistance is lower than estimated in previous
literature.Comment: 4 pages, 2 figures. (v1) Original version (v2) Introduction largely
rewritten, minor typos fixed throughou
Status and future directions of anti-metastatic cancer nanomedicines for the inhibition of cathepsin L
Angiogenesis, tissue invasion and metastasis in the tumour microenvironment are all critical hallmarks of cancer. Upregulation of cathepsin L plays an important role in angiogenesis and metastasis through its ability to degrade the extracellular matrix, facilitating tissue remodeling and tumour cell invasion. Thus, cathepsin L is a potential therapeutic target for anticancer nanomedicine, with its inhibition emerging as an innovative and potentially promising therapeutic intervention for the development of anti-invasion and anti-metastatic enzyme therapies. Nanotechnology-based platforms have been extensively tested in the anti-cancer nanomedicine field with effective anti-tumour efficacy. These nanodrugs can suppress tumour cell proliferation, thereby reducing tumour growth. Recently, nanomedicinal approaches have also emerged as effective anti-metastatic strategies, including the use of graphene oxide and gold nanoparticles. With a focus on recent advances in developing nanotechnology to inhibit cathepsin L, this review provides an in-depth examination of this stimulating field in the context of tumour microenvironments. Innovative anti-metastatic agents may lead to new options for the treatment of cancers
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