2,337 research outputs found
Complex Lagrangian embeddings of moduli spaces of vector bundles
By means of a Fourier-Mukai transform we embed moduli spaces of stable
bundles on an algebraic curve C as isotropic subvarieties of moduli spaces of
mu-stable bundles on the Jacobian variety J(C). When g(C)=2 this provides new
examples of special Lagrangian submanifolds.Comment: 9 pages, no figures, to appear in Diff. Geom. App
F-Theory, T-Duality on K3 Surfaces and N=2 Supersymmetric Gauge Theories in Four Dimensions
We construct T-duality on K3 surfaces. The T-duality exchanges a 4-brane R-R
charge and a 0-brane R-R charge. We study the action of the T-duality on the
moduli space of 0-branes located at points of K3 and 4-branes wrapping it. We
apply the construction to F-theory compactified on a Calabi-Yau 4-fold and
study the duality of N=2 SU(N_c) gauge theories in four dimensions. We discuss
the generalization to the N=1 duality scenario.Comment: 13 pages, late
DiffuSeq: Sequence to Sequence Text Generation with Diffusion Models
Recently, diffusion models have emerged as a new paradigm for generative
models. Despite the success in domains using continuous signals such as vision
and audio, adapting diffusion models to natural language is under-explored due
to the discrete nature of texts, especially for conditional generation. We
tackle this challenge by proposing DiffuSeq: a diffusion model designed for
sequence-to-sequence (Seq2Seq) text generation tasks. Upon extensive evaluation
over a wide range of Seq2Seq tasks, we find DiffuSeq achieving comparable or
even better performance than six established baselines, including a
state-of-the-art model that is based on pre-trained language models. Apart from
quality, an intriguing property of DiffuSeq is its high diversity during
generation, which is desired in many Seq2Seq tasks. We further include a
theoretical analysis revealing the connection between DiffuSeq and
autoregressive/non-autoregressive models. Bringing together theoretical
analysis and empirical evidence, we demonstrate the great potential of
diffusion models in complex conditional language generation tasks. Code is
available at \url{https://github.com/Shark-NLP/DiffuSeq}Comment: ICLR 2023 camera read
Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi
Radio, infrared, and optical observations of the 2006 eruption of the
symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion
produced non-spherical ejecta. Some of this ejected material was in the form of
bipolar jets to the east and west of the central source. Here we describe Xray
observations taken with the Chandra X-ray Observatory one and a half years
after the beginning of the outburst that reveal narrow, extended structure with
a position angle of approximately 300 degrees (east of north). Although the
orientation of the extended feature in the X-ray image is consistent with the
readout direction of the CCD detector, extensive testing suggests that the
feature is not an artifact. Assuming it is not an instrumental effect, the
extended X-ray structure shows hot plasma stretching more than 1,900 AU from
the central binary (taking a distance of 1.6 kpc). The X-ray emission is
elongated in the northwest direction - in line with the extended infrared
emission and some minor features in the published radio image. It is less
consistent with the orientation of the radio jets and the main bipolar optical
structure. Most of the photons in the extended X-ray structure have energies of
less than 0.8 keV. If the extended X-ray feature was produced when the nova
explosion occurred, then its 1".2 length as of 2007 August implies that it
expanded at an average rate of more than 2 mas/d, which corresponds to a flow
speed of greater than 6,000 km/s (d/1.6 kpc) in the plane of the sky. This
expansion rate is similar to the earliest measured expansion rates for the
radio jets.Comment: accepted in Ap
RNA interference of gonadotropin-inhibitory hormone gene induces arousal in songbirds.
Gonadotropin-inhibitory hormone (GnIH) was originally identified in quail as a hypothalamic neuropeptide inhibitor of pituitary gonadotropin synthesis and release. However, GnIH neuronal fibers do not only terminate in the median eminence to control anterior pituitary function but also extend widely in the brain, suggesting it has multiple roles in the regulation of behavior. To identify the role of GnIH neurons in the regulation of behavior, we investigated the effect of RNA interference (RNAi) of the GnIH gene on the behavior of white-crowned sparrows, a highly social songbird species. Administration of small interfering RNA against GnIH precursor mRNA into the third ventricle of male and female birds reduced resting time, spontaneous production of complex vocalizations, and stimulated brief agonistic vocalizations. GnIH RNAi further enhanced song production of short duration in male birds when they were challenged by playbacks of novel male songs. These behaviors resembled those of breeding birds during territorial defense. The overall results suggest that GnIH gene silencing induces arousal. In addition, the activities of male and female birds were negatively correlated with GnIH mRNA expression in the paraventricular nucleus. Density of GnIH neuronal fibers in the ventral tegmental area was decreased by GnIH RNAi treatment in female birds, and the number of gonadotropin-releasing hormone neurons that received close appositions of GnIH neuronal fiber terminals was negatively correlated with the activity of male birds. In summary, GnIH may decrease arousal level resulting in the inhibition of specific motivated behavior such as in reproductive contexts
L-Eval: Instituting Standardized Evaluation for Long Context Language Models
Recently, there has been growing interest in extending the context length of
instruction-following models in order to effectively process single-turn long
input (e.g. summarizing a paper) and conversations with more extensive
histories. While proprietary models such as GPT-4 and Claude have demonstrated
considerable advancements in handling tens of thousands of tokens of context,
open-sourced models are still in the early stages of experimentation. It also
remains unclear whether developing these long context models can offer
substantial gains on practical downstream tasks over retrieval-based methods or
models simply trained on chunked contexts. To address this challenge, we
propose to institute standardized evaluation for long context language models.
Concretely, we develop L-Eval which contains 411 long documents and over 2,000
query-response pairs manually annotated and checked by the authors encompassing
areas such as law, finance, school lectures, lengthy conversations, news,
long-form novels, and meetings. L-Eval also adopts diverse evaluation methods
and instruction styles, enabling a more reliable assessment of Long Context
Language Models (LCLMs). Our findings indicate that while open-source models
typically lag behind their commercial counterparts, they still exhibit
impressive performance. LLaMA2 achieves the best results (win 45\% vs
turbo-16k) on open-ended tasks with only 4k context length and ChatGLM2
achieves the best results on closed-ended tasks with 8k input tokens. We
release our new evaluation suite, code, and all generation results including
predictions from all open-sourced LCLMs, GPT4-32k, Cluade-100k at
{\url{https://github.com/OpenLMLab/LEval}}
A Luminous Be+White Dwarf Supersoft Source in the Wing of the SMC: MAXI J0158-744
We present a multi-wavelength analysis of the very fast X-ray transient MAXI
J0158-744, which was detected by MAXI/GSC on 2011 November 11. The subsequent
exponential decline of the X-ray flux was followed with Swift observations, all
of which revealed spectra with low temperatures (~100eV) indicating that MAXI
J0158-744 is a new Supersoft Source (SSS). The Swift X-ray spectra near maximum
show features around 0.8 keV that we interpret as possible absorption from
OVIII, and emission from O, Fe, and Ne lines. We obtained SAAO and ESO optical
spectra of the counterpart early in the outburst and several weeks later. The
early spectrum is dominated by strong Balmer and HeI emission, together with
weaker HeII emission. The later spectrum reveals absorption features that
indicate a B1/2IIIe spectral type, and all spectral features are at velocities
consistent with the Small Magellanic Cloud. At this distance, it is a luminous
SSS (>10^37 erg/s) but whose brief peak luminosity of >10^39 erg/s in the 2-4
keV band makes it the brightest SSS yet seen at "hard" X-rays. We propose that
MAXI J0158-744 is a Be-WD binary, and the first example to possibly enter ULX
territory. The brief hard X-ray flash could possibly be a result of the
interaction of the ejected nova shell with the B star wind in which the white
dwarf (WD) is embedded. This makes MAXI J0158-744 only the third Be/WD system
in the Magellanic Clouds, but it is by far the most luminous. The properties of
MAXI J0158-744 give weight to previous suggestions that SSS in nearby galaxies
are associated with early-type stellar systems.Comment: 15 pages, 8 figures; ApJ accepte
Sub-mm observations and modelling of Vega type stars
We present new sub-mm observations and modelling of Vega excess stars, using
realistic dust grain models. For resolved disks, we find that different objects
require very different dust grain properties in order to simultaneously fit the
image data and SED. Fomalhaut and Vega require solid dust grains, whilst HR4796
and HD141569 can only be fitted using porous grains. The older stars tend to
have less porous grains than younger stars, which may indicate that collisions
have compacted the dust grains. Eps Eri appears to be deficient in small dust
grains compared to our best fitting model. This may be due to factors which
affect the size distribution of grains close to the radiation pressure blowout
limit. Alternatively, this discrepancy may be due to some external influence on
the disk (e.g. a planet). When the model is applied to unresolved targets, an
estimate of the disk size can be made. However, the large diversity in dust
composition for the resolved disks means that we cannot make a reliable
assumption as to the composition of the grains in an unresolved disk, and there
is corresponding uncertainty in the disk size. In addition, the poor fit for
Eps Eri shows that the model cannot always account for the SED even if the disk
size is known. These two factors mean that it may not be possible to determine
a disk's size without actually resolving it.Comment: 15 pages, 15 figures, accepted by MNRAS. Revised Eps Eri modelling to
show larger range of minimum size cutoffs with porous grains, Figure
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