1,383 research outputs found
EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing
The tight inter-band correlation and the lag-wavelength relation among
UV/optical continua of active galactic nuclei have been firmly established.
They are usually understood within the widespread reprocessing scenario,
however, the implied inter-band lags are generally too small. Furthermore, it
is challenged by new evidences, such as the X-ray reprocessing yields too much
high frequency UV/optical variations as well as it fails to reproduce the
observed timescale-dependent color variations among {\it Swift} lightcurves of
NGC 5548. In a different manner, we demonstrate that an upgraded inhomogeneous
accretion disk model, whose local {\it independent} temperature fluctuations
are subject to a speculated {\it common} large-scale temperature fluctuation,
can intrinsically generate the tight inter-band correlation and lag across
UV/optical, and be in nice agreement with several observational properties of
NGC 5548, including the timescale-dependent color variation. The emergent lag
is a result of the {\it differential regression capability} of local
temperature fluctuations when responding to the large-scale fluctuation. An
average speed of propagations as large as of the speed of light
may be required by this common fluctuation. Several potential physical
mechanisms for such propagations are discussed. Our interesting
phenomenological scenario may shed new light on comprehending the UV/optical
continuum variations of active galactic nuclei.Comment: 18 pages, 8 figures. ApJ accepted. Further comments are very welcome
Millimeter Spectral Line Mapping Observations Toward Four Massive Star Forming HII Regions
We present spectral line mapping observations toward four massive
star-forming regions (Cepheus A, DR21S, S76E and G34.26+0.15), with the IRAM 30
meter telescope at 2 mm and 3 mm bands. Totally 396 spectral lines from 51
molecules, one helium recombination line, ten hydrogen recombination lines, and
16 unidentified lines were detected in these four sources. An emission line of
nitrosyl cyanide (ONCN, 14-13) was detected in G34.26+0.15,
as first detection in massive star-forming regions. We found that the
-CH and NHD show enhancement in shocked regions as
suggested by evidences of SiO and/or SO emission. Column density and rotational
temperature of CHCN were estimated with the rotational diagram method for
all four sources. Isotope abundance ratios of C/C were derived
using HCN and its C isotopologue, which were around 40 in all four
massive star-forming regions and slightly lower than the local interstellar
value (65). N/N and O/O abundance ratios in
these sources were also derived using double isotopic method, which were
slightly lower than that in local interstellar medium. Except for Cep A,
S/S ratio in the other three targets were derived, which were
similar to that in the local interstellar medium. The column density ratios of
N(DCN)/N(HCN) and N(DCO)/N(HCO) in these sources were more than two
orders of magnitude higher than the elemental [D]/[H] ratio, which is
1.510. Our results show the later stage sources, G34.26+0.15 in
particular, present more molecular species than earlier stage ones. Evidence of
shock activity is seen in all stages studied.Comment: 32 pages, 11 figures, 8 tables, accepted for publication in MNRA
MimicPlay: Long-Horizon Imitation Learning by Watching Human Play
Imitation learning from human demonstrations is a promising paradigm for
teaching robots manipulation skills in the real world. However, learning
complex long-horizon tasks often requires an unattainable amount of
demonstrations. To reduce the high data requirement, we resort to human play
data - video sequences of people freely interacting with the environment using
their hands. Even with different morphologies, we hypothesize that human play
data contain rich and salient information about physical interactions that can
readily facilitate robot policy learning. Motivated by this, we introduce a
hierarchical learning framework named MimicPlay that learns latent plans from
human play data to guide low-level visuomotor control trained on a small number
of teleoperated demonstrations. With systematic evaluations of 14 long-horizon
manipulation tasks in the real world, we show that MimicPlay outperforms
state-of-the-art imitation learning methods in task success rate,
generalization ability, and robustness to disturbances. Code and videos are
available at https://mimic-play.github.ioComment: 7th Conference on Robot Learning (CoRL 2023 oral presentation
An intrinsic link between long-term UV/optical variations and X-ray loudness in quasars
Observations have shown that UV/optical variation amplitude of quasars depend
on several physi- cal parameters including luminosity, Eddington ratio, and
likely also black hole mass. Identifying new factors which correlate with the
variation is essential to probe the underlying physical processes. Combining
~ten years long quasar light curves from SDSS stripe 82 and X-ray data from
Stripe 82X, we build a sample of X-ray detected quasars to investigate the
relation between UV/optical variation amplitude () and X-ray
loudness. We find that quasars with more intense X-ray radiation (com- pared to
bolometric luminosity) are more variable in UV/optical. Such correlation
remains highly significant after excluding the effect of other parameters
including luminosity, black hole mass, Ed- dington ratio, redshift, rest-frame
wavelength (i.e., through partial correlation analyses). We further find the
intrinsic link between X-ray loudness and UV/optical variation is gradually
more prominent on longer timescales (up to 10 years in the observed frame), but
tends to disappear at timescales < 100 days. This suggests a slow and long-term
underlying physical process. The X-ray reprocessing paradigm, in which
UV/optical variation is produced by a variable central X-ray emission
illuminating the accretion disk, is thus disfavored. The discovery points to an
interesting scheme that both the X-ray corona heating and UV/optical variation
is quasars are closely associated with magnetic disc turbulence, and the
innermost disc turbulence (where corona heating occurs) correlates with the
slow turbulence at larger radii (where UV/optical emission is produced).Comment: 9 pages, 4 figures, 1 table, accepted by Ap
3-{[Bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzaldehyde
In the title compound, C21H21N3O2, the pyridine rings and the benzene ring lie in a propeller arrangement around the central tertiary amine N atom. The dihedral angles formed by the benzene ring with the pyridine rings are 61.0 (3) and 49.6 (3)°, while the dihedral angle between the pyridine rings is 69.7 (3)°. The molecular conformation is stabilized by intramolecular bifurcated O—H⋯N hydrogen bonds. In the crystal, inversion dimers are formed via pairs of C—H⋯N hydrogen bonds
VIMA: General Robot Manipulation with Multimodal Prompts
Prompt-based learning has emerged as a successful paradigm in natural
language processing, where a single general-purpose language model can be
instructed to perform any task specified by input prompts. Yet task
specification in robotics comes in various forms, such as imitating one-shot
demonstrations, following language instructions, and reaching visual goals.
They are often considered different tasks and tackled by specialized models. We
show that a wide spectrum of robot manipulation tasks can be expressed with
multimodal prompts, interleaving textual and visual tokens. Accordingly, we
develop a new simulation benchmark that consists of thousands of
procedurally-generated tabletop tasks with multimodal prompts, 600K+ expert
trajectories for imitation learning, and a four-level evaluation protocol for
systematic generalization. We design a transformer-based robot agent, VIMA,
that processes these prompts and outputs motor actions autoregressively. VIMA
features a recipe that achieves strong model scalability and data efficiency.
It outperforms alternative designs in the hardest zero-shot generalization
setting by up to task success rate given the same training data.
With less training data, VIMA still performs better than
the best competing variant. Code and video demos are available at
https://vimalabs.github.io/Comment: ICML 2023 Camera-ready version. Project website:
https://vimalabs.github.io
New Clues to Jet Launching: The inner disks in radio loud quasars may be more stable
Jet launching in radio loud (RL) quasars is one of the fundamental problems
in astrophysics. Exploring the differences in the inner accretion disk
properties between RL and radio quiet (RQ) quasars might yield helpful clues to
this puzzle. We previously discovered that the shorter term UV/optical
variations of quasars are bluer than the longer term ones, i.e., the so-called
timescale-dependent color variation. This is consistent with the scheme that
the faster variations come from the inner and hotter disk regions, thus
providing a useful tool to map the accretion disk which is otherwise
unresolvable. In this work we compare the UV/optical variations of RL quasars
in SDSS Stripe 82 to those of several RQ samples, including those matched in
redshift-luminosity-black hole mass and/or color-magnitude. We find that while
both RL and RQ populations appear bluer when they brighten, RL quasars
potentially show a weaker/flatter dependence on timescale in their color
variation. We further find that while both RL and RQ populations on average
show similar variation amplitudes at long timescales, fast variations of RL
sources appear weaker/smaller (at timescales of ~ 25 -- 300 days in the
observer's frame), and the difference is more prominent in the g-band than in
the r-band. Inhomogeneous disk simulations can qualitatively reproduce these
observed differences if the inner accretion disk of RL quasars fluctuates less
based on simple toy models. Though the implications are likely model dependent,
the discovery points to an interesting diagram that magnetic fields in RL
quasars may be prospectively stronger and play a key role in both jet launching
and the stabilization of the inner accretion disk.Comment: Accepted by Science China: Physics, Mechanics & Astronomy; Figures 4,
14, and 15 are the main result
LL3DA: Visual Interactive Instruction Tuning for Omni-3D Understanding, Reasoning, and Planning
Recent advances in Large Multimodal Models (LMM) have made it possible for
various applications in human-machine interactions. However, developing LMMs
that can comprehend, reason, and plan in complex and diverse 3D environments
remains a challenging topic, especially considering the demand for
understanding permutation-invariant point cloud 3D representations of the 3D
scene. Existing works seek help from multi-view images, and project 2D features
to 3D space as 3D scene representations. This, however, leads to huge
computational overhead and performance degradation. In this paper, we present
LL3DA, a Large Language 3D Assistant that takes point cloud as direct input and
respond to both textual-instructions and visual-prompts. This help LMMs better
comprehend human interactions and further help to remove the ambiguities in
cluttered 3D scenes. Experiments show that LL3DA achieves remarkable results,
and surpasses various 3D vision-language models on both 3D Dense Captioning and
3D Question Answering.Comment: Project Page: https://ll3da.github.io
- …