358 research outputs found
A Comprehensive View of Circumstellar Disks in Chamaeleon I: Infrared Excess, Accretion Signatures and Binarity
We present a comprehensive study of disks around 81 young low-mass stars and
brown dwarfs in the nearby ~2-Myr-old Chamaeleon I star-forming region. We use
mid-infrared photometry from the Spitzer Space Telescope, supplemented by
findings from ground-based high-resolution optical spectroscopy and adaptive
optics imaging. We derive disk fractions of 52 (+/-6) % and 58 (+6/-7) % based
on 8-micron and 24-micron colour excesses, respectively, consistent with those
reported for other clusters of similar age. Within the uncertainties, the disk
frequency in our sample of K3-M8 objects in Cha I does not depend on stellar
mass. Diskless and disk-bearing objects have similar spatial distributions.
There are no obvious transition disks in our sample, implying a rapid timescale
for the inner disk clearing process; however, we find two objects with weak
excess at 3-8 microns and substantial excess at 24 microns, which may indicate
grain growth and dust settling in the inner disk. For a sub-sample of 35
objects with high-resolution spectra, we investigate the connection between
accretion signatures and dusty disks: in the vast majority of cases (29/35) the
two are well correlated, suggesting that, on average, the timescale for gas
dissipation is similar to that for clearing the inner dust disk. The exceptions
are six objects for which dust disks appear to persist even though accretion
has ceased or dropped below measurable levels. Adaptive optics images of 65 of
our targets reveal that 17 have companions at (projected) separations of 10-80
AU. Of the five <20 AU binaries, four lack infrared excess, possibly indicating
that a close companion leads to faster disk dispersal. The closest binary with
excess is separated by ~20 AU, which sets an upper limit of ~8 AU for the outer
disk radius. (abridged)Comment: accepted for publication in the Astrophysical Journa
Room temperature ammonia gas sensor based on p-type-like V2O5 nanosheets towards food spoilage monitoring
Gas sensors play an important role in many areas of human life, including the monitoring of production processes, occupational safety, food quality assessment, and air pollution monitoring. Therefore, the need for gas sensors to monitor hazardous gases, such as ammonia, at low operating temperatures has become increasingly important in many fields. Sensitivity, selectivity, low cost, Citation: Van Duy, L.; Nguyet, T.T.; Le, D.T.T.; Van Duy, N.; Nguyen, H.; Biasioli, F.; Tonezzer, M.; Di Natale, C.; Hoa, N.D. Room Temperature AmmoniaGasSensor Based on p-Type-like V2O5 Nanosheets towards Food Spoilage Monitoring. Nanomaterials 2023, 13, 146. https:// doi.org/10.3390/nano13010146 Academic Editors: Sergei Kulinich and Li Hai Received: 17 November 2022 Revised: 23 December 2022 Accepted: 24 December 2022 Published: 28 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). and ease of production are crucial characteristics for creating a capillary network of sensors for the protection of the environment and human health. However, developing gas sensors that are not only efficient but also small and inexpensive and therefore integrable into everyday life is a difficult challenge. In this paper, we report on a resistive sensor for ammonia detection based on thin V2O5 nanosheets operating at room temperature. The small thickness and porosity of the V2O5 nanosheets give the sensors good performance for sensing ammonia at room temperature (RT), with a relative change of resistance of 9.4% to 5 ppm ammonia (NH3) and an estimated detection limit of 0.4 ppm. The sensor is selective with respect to the seven interferents tested; it is repeatable and stable over the long term (four months). Although V2O5 is generally an n-type semiconductor, in this case the nanosheets show a p-type semiconductor behavior, and thus a possible sensing mechanism is proposed. The device’s performance, along with its size, low cost, and low power consumption, makes it a good candidate for monitoring freshness and spoilage along the food supply chai
User-Centric Beam Selection and Precoding Design for Coordinated Multiple-Satellite Systems
This paper introduces a joint optimization framework for user-centric beam
selection and linear precoding (LP) design in a coordinated multiple-satellite
(CoMSat) system, employing a Digital-Fourier-Transform-based (DFT) beamforming
(BF) technique. Regarding serving users at their target SINRs and minimizing
the total transmit power, the scheme aims to efficiently determine satellites
for users to associate with and activate the best cluster of beams together
with optimizing LP for every satellite-to-user transmission. These technical
objectives are first framed as a complex mixed-integer programming (MIP)
challenge. To tackle this, we reformulate it into a joint cluster association
and LP design problem. Then, by theoretically analyzing the duality
relationship between downlink and uplink transmissions, we develop an efficient
iterative method to identify the optimal solution. Additionally, a simpler
duality approach for rapid beam selection and LP design is presented for
comparison purposes. Simulation results underscore the effectiveness of our
proposed schemes across various settings
TextANIMAR: Text-based 3D Animal Fine-Grained Retrieval
3D object retrieval is an important yet challenging task, which has drawn
more and more attention in recent years. While existing approaches have made
strides in addressing this issue, they are often limited to restricted settings
such as image and sketch queries, which are often unfriendly interactions for
common users. In order to overcome these limitations, this paper presents a
novel SHREC challenge track focusing on text-based fine-grained retrieval of 3D
animal models. Unlike previous SHREC challenge tracks, the proposed task is
considerably more challenging, requiring participants to develop innovative
approaches to tackle the problem of text-based retrieval. Despite the increased
difficulty, we believe that this task has the potential to drive useful
applications in practice and facilitate more intuitive interactions with 3D
objects. Five groups participated in our competition, submitting a total of 114
runs. While the results obtained in our competition are satisfactory, we note
that the challenges presented by this task are far from being fully solved. As
such, we provide insights into potential areas for future research and
improvements. We believe that we can help push the boundaries of 3D object
retrieval and facilitate more user-friendly interactions via vision-language
technologies.Comment: arXiv admin note: text overlap with arXiv:2304.0573
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