395 research outputs found
Bifurcation and chaotic behaviors of 4-UPS-RPS high-speed parallel mechanism
In order to grasp the nonlinear characteristics of high-speed spatial parallel mechanism, the bifurcation and chaotic behaviors of 4-UPS-RPS mechanism are analyzed. Firstly, the nonlinear elastic dynamic model of the mechanism is established by using the Lagrange equation and the finite element method. Then the effects of parameters including driving angular velocity, the radius of motion trajectory, the material of driving limbs, the diameter of driving limbs, and the mass of moving platform, on the bifurcation and chaotic behaviors of high-speed spatial parallel mechanism are studied. The results show that the above parameters all have a certain influence on nonlinear characteristics of the 4-UPS-RPS high-speed spatial parallel mechanism. The research can provide important theoretical basis for the further research on the non-linear dynamics of spatial parallel mechanism
Long-term Orbital Period Variation of Hot Jupiters from Transiting Time Analysis using TESS Survey Data
Many hot Jupiters may experience orbital decays, which are manifested as
long-term transit timing variations. We have analyzed 7068 transits from the
Transiting Exoplanet Survey Satellite (TESS) for a sample of 326 hot Jupiters.
These new mid-transit time data allow us to update ephemerides for these
systems. By combining the new TESS transit timing data with archival data, we
search for possible long-term orbital period variations in these hot Jupiters
using a linear and a quadratic ephemeris model. We identified 26 candidates
that exhibit possible long-term orbital period variations, including 18
candidates with decreasing orbital periods and 8 candidates with increasing
orbital periods. Among them, 12 candidates have failed in our leave-one-out
cross-validation (LOOCV) test and thus should be considered as marginal
candidates. In addition to tidal interaction, alternative mechanisms such as
apsidal precession, R{\o}mer effect, and Applegate effect could also contribute
to the observed period variations. The ephemerides derived in this work are
useful for scheduling follow-up observations for these hot Jupiters in the
future. The Python code used to generate the ephemerides is made available
online.Comment: Accepted for publication in ApJ
Visual-Kinematics Graph Learning for Procedure-agnostic Instrument Tip Segmentation in Robotic Surgeries
Accurate segmentation of surgical instrument tip is an important task for
enabling downstream applications in robotic surgery, such as surgical skill
assessment, tool-tissue interaction and deformation modeling, as well as
surgical autonomy. However, this task is very challenging due to the small
sizes of surgical instrument tips, and significant variance of surgical scenes
across different procedures. Although much effort has been made on visual-based
methods, existing segmentation models still suffer from low robustness thus not
usable in practice. Fortunately, kinematics data from the robotic system can
provide reliable prior for instrument location, which is consistent regardless
of different surgery types. To make use of such multi-modal information, we
propose a novel visual-kinematics graph learning framework to accurately
segment the instrument tip given various surgical procedures. Specifically, a
graph learning framework is proposed to encode relational features of
instrument parts from both image and kinematics. Next, a cross-modal
contrastive loss is designed to incorporate robust geometric prior from
kinematics to image for tip segmentation. We have conducted experiments on a
private paired visual-kinematics dataset including multiple procedures, i.e.,
prostatectomy, total mesorectal excision, fundoplication and distal gastrectomy
on cadaver, and distal gastrectomy on porcine. The leave-one-procedure-out
cross validation demonstrated that our proposed multi-modal segmentation method
significantly outperformed current image-based state-of-the-art approaches,
exceeding averagely 11.2% on Dice.Comment: Accepted to IROS 202
CIP2A facilitates the G1/S cell cycle transition via B-Myb in human papillomavirus 16 oncoprotein E6-expressing cells
Infection with high-risk human papillomaviruses (HR-HPVs, including HPV-16, HPV-18, HPV-31) plays a central aetiologic role in the development of cervical carcinoma. The transforming properties of HR-HPVs mainly reside in viral oncoproteins E6 and E7. E6 protein degrades the tumour suppressor p53 and abrogates cell cycle checkpoints. Cancerous inhibitor of protein phosphatase 2A (CIP2A) is an oncoprotein that is involved in the carcinogenesis of many human malignancies. Our previous data showed that CIP2A was overexpressed in cervical cancer. However, the regulation of CIP2A by HPV-16E6 remains to be elucidated. In this study, we demonstrated that HPV-16E6 significantly up-regulated CIP2A mRNA and protein expression in a p53-degradation-dependent manner. Knockdown of CIP2A by siRNA inhibited viability and DNA synthesis and caused G1 cell cycle arrest of 16E6-expressing cells. Knockdown of CIP2A resulted in a significant reduction in the expression of cyclin-dependent kinase 1 (Cdk1) and Cdk2. Although CIP2A has been reported to stabilize c-Myc by inhibiting PP2A-mediated dephosphorylation of c-Myc, we have presented evidence that the regulation of Cdk1 and Cdk2 by CIP2A is dependent on transcription factor B-Myb rather than c-Myc. Taken together, our study reveals the role of CIP2A in abrogating the G1 checkpoint in HPV-16E6-expressing cells and helps in understanding the molecular basis of HPV-induced oncogenesis
High-performance cVEP-BCI under minimal calibration
The ultimate goal of brain-computer interfaces (BCIs) based on visual
modulation paradigms is to achieve high-speed performance without the burden of
extensive calibration. Code-modulated visual evoked potential-based BCIs
(cVEP-BCIs) modulated by broadband white noise (WN) offer various advantages,
including increased communication speed, expanded encoding target capabilities,
and enhanced coding flexibility. However, the complexity of the
spatial-temporal patterns under broadband stimuli necessitates extensive
calibration for effective target identification in cVEP-BCIs. Consequently, the
information transfer rate (ITR) of cVEP-BCI under limited calibration usually
stays around 100 bits per minute (bpm), significantly lagging behind
state-of-the-art steady-state visual evoked potential-based BCIs (SSVEP-BCIs),
which achieve rates above 200 bpm. To enhance the performance of cVEP-BCIs with
minimal calibration, we devised an efficient calibration stage involving a
brief single-target flickering, lasting less than a minute, to extract
generalizable spatial-temporal patterns. Leveraging the calibration data, we
developed two complementary methods to construct cVEP temporal patterns: the
linear modeling method based on the stimulus sequence and the transfer learning
techniques using cross-subject data. As a result, we achieved the highest ITR
of 250 bpm under a minute of calibration, which has been shown to be comparable
to the state-of-the-art SSVEP paradigms. In summary, our work significantly
improved the cVEP performance under few-shot learning, which is expected to
expand the practicality and usability of cVEP-BCIs.Comment: 35 pages, 5 figure
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