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A Rare Case of Hip Pain Secondary to Pigmented Villonodular Synovitis
A 19-year-old Asian male presented to our emergency department with atraumatic right hip pain radiating to the right groin associated with pain on ambulation. Magnetic resonance imaging of the right hip with and without contrast revealed the diagnosis. Pigmented villonodular synovitis is a rare, monoarticular benign tumor originating from the synovium of the joint. The treatment is synovectomy of the pathological joint to prevent further disease progression
Dynamical Tides in Eccentric Binaries and Tidally-Excited Stellar Pulsations in KEPLER KOI-54
Recent observation of the tidally-excited stellar oscillations in the
main-sequence binary KOI-54 by the KEPLER satellite provides a unique
opportunity for studying dynamical tides in eccentric binary systems. We
develop a general theory of tidal excitation of oscillation modes of rotating
binary stars, and apply our theory to tidally excited gravity modes (g-modes)
in KOI-54. The strongest observed oscillations, which occur at 90 and 91 times
the orbital frequency, are likely due to prograde m=2 modes (relative to the
stellar spin axis) locked in resonance with the orbit. The remaining flux
oscillations with frequencies that are integer multiples of the orbital
frequency are likely due to nearly resonant m=0 g-modes; such axisymmetric
modes generate larger flux variations compared to the m=2 modes, assuming that
the spin inclination angle of the star is comparable to the orbital inclination
angle. We examine the process of resonance mode locking under the combined
effects of dynamical tides on the stellar spin and orbit and the intrinsic
stellar spindown. We show that KOI-54 can naturally evolve into a state in
which at least one m=2 mode is locked in resonance with the orbital frequency.
Our analysis provides an explanation for the fact that only oscillations with
frequencies less than 90-100 times the orbital frequency are observed. We have
also found evidence from the published KEPLER result that three-mode nonlinear
coupling occurs in the KOI-54 system. We suggest that such nonlinear mode
coupling may explain the observed oscillations that are not harmonics of the
orbital frequency.Comment: 15 pages, 5 figures, accepted by MNRA
Riesz bases of exponentials for multi-tiling measures
Let be a closed subgroup of and let be a Borel
probability measure admitting a Riesz basis of exponentials with frequency sets
in the dual group . We form a multi-tiling measure where is translationally equivalent to and
different and have essentially disjoint support. We obtain some
necessary and sufficient conditions for to admit a Riesz basis of
exponentials . As an application, the square boundary, after a rotation, is a
union of two fundamental domains of and can
be regarded as a multi-tiling measure. We show that, unfortunately, the square
boundary does not admit a Riesz basis of exponentials of the form as a union of
translate of discrete subgroups . This rules out a
natural candidate of potential Riesz basis for the square boundary.Comment: To appear in Sampling Theory, Signal Processing, and Data Analysi
The Response of Schwann Cells to Weak DC Electric Fields
Schwann cells are glial cells that serve the vital role of supporting neurons in the peripheral nervous system. While their primary function is to provide insulation (myelin) for axons, they also help regenerate injured axons by digesting severed axons and providing scaffolding to guide the regeneration process. This specific role of Schwann cells makes them highly important cellular targets following nerve injury. Although some efforts have been made to encourage Schwann cell migration after nerve damage, the use of electric fields to control cell responses remain unexplored; therefore, this experiment serves to characterize the behavior of Schwann cells to weak direct current (DC) electric fields. Rat Schwann cells were seeded onto IBIDI culture slides and exposed to varying DC electric field strengths of 0 to 500 mV/mm for up to 6 hours. Preliminary responses to alternating DC electric fields were also observed. Pictures of the cells in their culture slides were taken after 0, 3, and 6 hours with images analyzed using ImageJ. Results showed that Schwann cells changed their orientation perpendicular to the electric field after they were exposed to field strengths of 75 mV/mm or greater. When exposed to alternating DC electric fields, the cells are also changed their orientation perpendicularly, but only at field strengths of 500 mV/mm. Although the mechanism behind this change needs further research, this shift in morphology may provide a framework for directed control/acceleration of axon regeneration using electric fields
Mitigating Data Imbalance and Representation Degeneration in Multilingual Machine Translation
Despite advances in multilingual neural machine translation (MNMT), we argue
that there are still two major challenges in this area: data imbalance and
representation degeneration. The data imbalance problem refers to the imbalance
in the amount of parallel corpora for all language pairs, especially for
long-tail languages (i.e., very low-resource languages). The representation
degeneration problem refers to the problem of encoded tokens tending to appear
only in a small subspace of the full space available to the MNMT model. To
solve these two issues, we propose Bi-ACL, a framework that uses only
target-side monolingual data and a bilingual dictionary to improve the
performance of the MNMT model. We define two modules, named bidirectional
autoencoder and bidirectional contrastive learning, which we combine with an
online constrained beam search and a curriculum learning sampling strategy.
Extensive experiments show that our proposed method is more effective both in
long-tail languages and in high-resource languages. We also demonstrate that
our approach is capable of transferring knowledge between domains and languages
in zero-shot scenarios.Comment: Accepted to Findings of EMNLP 2023, add statistical significance
tests. code available at https://github.com/lavine-lmu/Bi-AC
Extending Multilingual Machine Translation through Imitation Learning
Despite the growing variety of languages supported by existing multilingual
neural machine translation (MNMT) models, most of the world's languages are
still being left behind. We aim to extend large-scale MNMT models to a new
language, allowing for translation between the newly added and all of the
already supported languages in a challenging scenario: using only a parallel
corpus between the new language and English. Previous approaches, such as
continued training on parallel data including the new language, suffer from
catastrophic forgetting (i.e., performance on other languages is reduced). Our
novel approach Imit-MNMT treats the task as an imitation learning process,
which mimicks the behavior of an expert, a technique widely used in the
computer vision area, but not well explored in NLP. More specifically, we
construct a pseudo multi-parallel corpus of the new and the original languages
by pivoting through English, and imitate the output distribution of the
original MNMT model. Extensive experiments show that our approach significantly
improves the translation performance between the new and the original
languages, without severe catastrophic forgetting. We also demonstrate that our
approach is capable of solving copy and off-target problems, which are two
common issues existence in current large-scale MNMT models
Improving both domain robustness and domain adaptability in machine translation
We address two problems of domain adaptation in neural machine translation.
First, we want to reach domain robustness, i.e., good quality of both domains
from the training data, and domains unseen in the training data. Second, we
want our systems to be adaptive, i.e., making it possible to finetune systems
with just hundreds of in-domain parallel sentences. In this paper, we introduce
a novel combination of two previous approaches, word adaptive modelling, which
addresses domain robustness, and meta-learning, which addresses domain
adaptability, and we present empirical results showing that our new combination
improves both of these properties
Atmospheres and Spectra of Strongly Magnetized Neutron Stars -- III. Partially Ionized Hydrogen Models
We construct partially ionized hydrogen atmosphere models for magnetized
neutron stars in radiative equilibrium with surface fields B=10^12-5 \times
10^14 G and effective temperatures T_eff \sim a few \times 10^5-10^6 K. These
models are based on the latest equation of state and opacity results for
magnetized, partially ionized hydrogen plasmas that take into account various
magnetic and dense medium effects. The atmospheres directly determine the
characteristics of thermal emission from isolated neutron stars. For the models
with B=10^12-10^13 G, the spectral features due to neutral atoms lie at extreme
UV and very soft X-ray energy bands and therefore are difficult to observe.
However, the continuum flux is also different from the fully ionized case,
especially at lower energies. For the superstrong field models (B\ga 10^14 G),
we show that the vacuum polarization effect not only suppresses the proton
cyclotron line as shown previously, but also suppresses spectral features due
to bound species; therefore spectral lines or features in thermal radiation are
more difficult to observe when the neutron star magnetic field is \ga 10^14 G.Comment: 12 pages, 10 figures; ApJ, accepted (v599: Dec 20, 2003
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