257 research outputs found
Some Discussions about the Error Functions on SO(3) and SE(3) for the Guidance of a UAV Using the Screw Algebra Theory
In this paper a new error function designed on 3-dimensional special Euclidean group SE(3) is proposed for the guidance of a UAV (Unmanned Aerial Vehicle). In the beginning, a detailed 6-DOF (Degree of Freedom) aircraft model is formulated including 12 nonlinear differential equations. Secondly the definitions of the adjoint representations are presented to establish the relationships of the Lie groups SO(3) and SE(3) and their Lie algebras so(3) and se(3). After that the general situation of the differential equations with matrices belonging to SO(3) and SE(3) is presented. According to these equations the features of the error function on SO(3) are discussed. Then an error function on SE(3) is devised which creates a new way of error functions constructing. In the simulation a trajectory tracking example is given with a target trajectory being a curve of elliptic cylinder helix. The result shows that a better tracking performance is obtained with the new devised error function
Peripheral blood T Regulatory cell counts may not predict transplant rejection
<p>Abstract</p> <p>Background</p> <p>Recent evidence shows that allograft survival rates show a positive correlation with the number of circulating T regulatory cells (Tregs). This study investigated both the number and the cytokine profiles exhibited by Foxp3<sup>+ </sup>Tregs in blood, spleen and lymph nodes of Lewis rat recipients of BN rat cardiac allografts after a single-dose of Rapamycin (RAPA).</p> <p>Results</p> <p>Rats were divided into three groups: control group (containing healthy control and acute rejection group), and recipients treated with a single dose of RAPA on either Day 1 (1D group)or Day 3 (3D group) post-transplant. We analyzed the number of Foxp3+Tregs and the expression of Foxp3 and cytokines in the peripheral blood and the peripheral lymphoid tissues. No difference was found in the numbers of circulating Foxp3+ Tregs between these three groups. RAPA administration significantly increased Foxp3 expression in peripheral lymphoid tissues after a single dose of RAPA on Day 3 post-transplant. Foxp3+Tregs inhibited the activity of effector T cells (T<sub>eff</sub>) via the secretion of TGF-β1.</p> <p>Conclusion</p> <p>The number of Tregs in the recipient's blood may not be a good predictor of transplant rejection. Foxp3+Tregs inhibit the activity of T<sub>eff </sub>cells mainly in the peripheral lymphoid tissues.</p
Multi-Granularity Archaeological Dating of Chinese Bronze Dings Based on a Knowledge-Guided Relation Graph
The archaeological dating of bronze dings has played a critical role in the
study of ancient Chinese history. Current archaeology depends on trained
experts to carry out bronze dating, which is time-consuming and
labor-intensive. For such dating, in this study, we propose a learning-based
approach to integrate advanced deep learning techniques and archaeological
knowledge. To achieve this, we first collect a large-scale image dataset of
bronze dings, which contains richer attribute information than other existing
fine-grained datasets. Second, we introduce a multihead classifier and a
knowledge-guided relation graph to mine the relationship between attributes and
the ding era. Third, we conduct comparison experiments with various existing
methods, the results of which show that our dating method achieves a
state-of-the-art performance. We hope that our data and applied networks will
enrich fine-grained classification research relevant to other interdisciplinary
areas of expertise. The dataset and source code used are included in our
supplementary materials, and will be open after submission owing to the
anonymity policy. Source codes and data are available at:
https://github.com/zhourixin/bronze-Ding.Comment: CVPR2023 accepte
Improving a Spectral Bin Microphysical Scheme Using TRMM Satellite Observations
Comparisons between cloud model simulations and observations are crucial in validating model performance and improving physical processes represented in the mod Tel.hese modeled physical processes are idealized representations and almost always have large rooms for improvements. In this study, we use data from two different sensors onboard TRMM (Tropical Rainfall Measurement Mission) satellite to improve the microphysical scheme in the Goddard Cumulus Ensemble (GCE) model. TRMM observed mature-stage squall lines during late spring, early summer in central US over a 9-year period are compiled and compared with a case simulation by GCE model. A unique aspect of the GCE model is that it has a state-of-the-art spectral bin microphysical scheme, which uses 33 different bins to represent particle size distribution of each of the seven hydrometeor species. A forward radiative transfer model calculates TRMM Precipitation Radar (PR) reflectivity and TRMM Microwave Imager (TMI) 85 GHz brightness temperatures from simulated particle size distributions. Comparisons between model outputs and observations reveal that the model overestimates sizes of snow/aggregates in the stratiform region of the squall line. After adjusting temperature-dependent collection coefficients among ice-phase particles, PR comparisons become good while TMI comparisons worsen. Further investigations show that the partitioning between graupel (a high-density form of aggregate), and snow (a low-density form of aggregate) needs to be adjusted in order to have good comparisons in both PR reflectivity and TMI brightness temperature. This study shows that long-term satellite observations, especially those with multiple sensors, can be very useful in constraining model microphysics. It is also the first study in validating and improving a sophisticated spectral bin microphysical scheme according to long-term satellite observations
A Moving Frame Trajectory Tracking Method of a Flying-Wing UAV Using the Differential Geometry
The problem of UAV trajectory tracking is a difficult issue for scholars and engineers, especially when the target curve is a complex curve in the three-dimensional space. In this paper, the coordinate frames during the tracking process are transformed to improve the tracking result. Firstly, the basic concepts of the moving frame are given. Secondly the transfer principles of various moving frames are formulated and the Bishop frame is selected as a final choice for its flexibility. Thirdly, the detailed dynamic equations of the moving frame tracking method are formulated. In simulation, a moving frame of an elliptic cylinder helix is formulated precisely. Then, the devised tracking method on the basis of the dynamic equations is tested in a complete flight control system with 6 DOF nonlinear equations of the UAV. The simulation result shows a satisfactory trajectory tracking performance so that the effectiveness and efficiency of the devised tracking method is proved
Bis[2-(1H-benzimidazol-2-yl)benzoato]copper(II) dihydrate
In the title compound, [Cu(C14H9N2O2)2]·2H2O, the Cu(II) ion lies on a centre of symmetry and is four-coordinated by two N atoms and two O atoms from two 2-(1H-benzimidazol-2-yl)benzoate ligands in a square-planar environment. The benzimidazol and benzyl rings form a dihedral angle of 42.8 (5)°. The molecule contains two H-bonded carboxyl O acceptors and two H-bonded N—H donors in the benzimidazol groups, which interact with two symmetry-related uncoordinated water molecules so that neighboring molecular units are linked by (O—H)water⋯Ocarboxyl hydrogen bonds with an R
2
4(8) graph-set motif, generating a helical chain in the a-axis direction. These chains are, in turn, interconnected by (N—H)benzimidazol⋯Owater hydrogen bonds, forming a three-dimensional supramolecular network
CharFormer: A Glyph Fusion based Attentive Framework for High-precision Character Image Denoising
Degraded images commonly exist in the general sources of character images,
leading to unsatisfactory character recognition results. Existing methods have
dedicated efforts to restoring degraded character images. However, the
denoising results obtained by these methods do not appear to improve character
recognition performance. This is mainly because current methods only focus on
pixel-level information and ignore critical features of a character, such as
its glyph, resulting in character-glyph damage during the denoising process. In
this paper, we introduce a novel generic framework based on glyph fusion and
attention mechanisms, i.e., CharFormer, for precisely recovering character
images without changing their inherent glyphs. Unlike existing frameworks,
CharFormer introduces a parallel target task for capturing additional
information and injecting it into the image denoising backbone, which will
maintain the consistency of character glyphs during character image denoising.
Moreover, we utilize attention-based networks for global-local feature
interaction, which will help to deal with blind denoising and enhance denoising
performance. We compare CharFormer with state-of-the-art methods on multiple
datasets. The experimental results show the superiority of CharFormer
quantitatively and qualitatively.Comment: Accepted by ACM MM 202
Erbium-ytterbium co-doped lithium niobate single-mode microdisk laser with an ultralow threshold of 1 uW
We demonstrate single-mode microdisk lasers in the telecom band with
ultra-low thresholds on erbium-ytterbium co-doped thin-film lithium niobate
(TFLN). The active microdisk were fabricated with high-Q factors by
photo-lithography assisted chemo-mechanical etching. Thanks to the
erbium-ytterbium co-doping providing high optical gain, the ultra-low loss
nanostructuring, and the excitation of high-Q coherent polygon modes which
suppresses multi-mode lasing and allows high spatial mode overlap factor
between pump and lasing modes, single-mode laser emission operating at 1530 nm
wavelength was observed with an ultra-low threshold, under 980-nm-band optical
pump. The threshold was measured as low as 1 uW, which is one order of
magnitude smaller than the best results previously reported in single-mode
active TFLN microlasers. And the conversion efficiency reaches 0.406%, which is
also the highest value reported in single-mode active TFLN microlasers.Comment: 5 pages,3 figure
Generation of Kerr soliton microcomb in a normally dispersed lithium niobate microdisk resonator by mode trimming
Anomalous microresonator dispersion is mandatory for Kerr soliton microcomb
formation, which depends critically on the geometry of the microresonator and
can hardly be tuned after the structure is made. To date, cavity-based
microcombs have only been generated with fundamental whispering gallery modes
(WGMs) of anomalous dispersion in microresonators. Moreover, microcomb
generation in highly Raman-active platforms such as lithium niobate (LN)
microresonators frequently suffers from stimulated Raman scattering and mode
crossing due to the existence of multiple families of high-order WGMs. Here, we
reveal a unique Kerr soliton microcomb generation mechanism through mode
trimming in a weakly perturbed LN microdisk resonator. Remarkably, the soliton
comb is generated with fundamental WGMs of normal dispersion and free from the
mode crossing and Raman scattering effects. A robust soliton with a spectrum
spanning from 1450 nm to 1620 nm at an on-chip pump power of 35 mW. Our
discovery offers a powerful solution to circumvent the stringent requirements
on high-precision dispersion engineering and termination of Raman excitation
for soliton generation in the high-Q microdisk.Comment: 16 pages,and 5 figure
Electro-optically tunable low phase-noise microwave synthesizer in an active lithium niobate microdisk
Photonic-based low-phase-noise microwave generation with real-time frequency
tuning is crucial for a broad spectrum of subjects, including next-generation
wireless communications, radar, metrology, and modern instrumentation. Here,
for the first time to the best of our knowledge, narrow-bandwidth
dual-wavelength microlasers are generated from nearly degenerate polygon modes
in a high-Q active lithium niobate microdisk. The high-Q polygon modes
formation with independently controllable resonant wavelengths and free
spectral ranges is enabled by the weak perturbation of the whispering gallery
microdisk resonators using a tapered fiber. The stable beating signal confirms
the low phase-noise achieved in the tunable laser. Owing to the high spatial
overlap factors between the two nearly degenerate lasing modes as well as that
between the two lasing modes and the pump mode, gain competition between the
two modes is suppressed, leading to stable dual-wavelength laser generation and
in turn the low noise microwave source. The measured microwave signal shows a
linewidth of ~6.87 kHz, a phase noise of ~-123 dBc/Hz, and an electro-optic
tuning efficiency of -1.66 MHz/V.Comment: 13 pages, 5 figure
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