Learning Rotation-Equivariant Features for Visual Correspondence

Extracting discriminative local features that are invariant to imaging variations is an integral part of establishing correspondences between images. In this work, we introduce a self-supervised learning framework to extract discriminative rotation-invariant descriptors using group-equivariant CNNs. Thanks to employing group-equivariant CNNs, our method effectively learns to obtain rotation-equivariant features and their orientations explicitly, without having to perform sophisticated data augmentations. The resultant features and their orientations are further processed by group aligning, a novel invariant mapping technique that shifts the group-equivariant features by their orientations along the group dimension. Our group aligning technique achieves rotation-invariance without any collapse of the group dimension and thus eschews loss of discriminability. The proposed method is trained end-to-end in a self-supervised manner, where we use an orientation alignment loss for the orientation estimation and a contrastive descriptor loss for robust local descriptors to geometric/photometric variations. Our method demonstrates state-of-the-art matching accuracy among existing rotation-invariant descriptors under varying rotation and also shows competitive results when transferred to the task of keypoint matching and camera pose estimation.Comment: Accepted to CVPR 2023, Project webpage at http://cvlab.postech.ac.kr/research/REL

Co-primary Spectrum Sharing for Inter-operator Device-to-Device Communication

The business potential of device-to-device (D2D) communication including public safety and vehicular communications will be realized only if direct communication between devices subscribed to different mobile operators (OPs) is supported. One possible way to implement inter-operator D2D communication may use the licensed spectrum of the OPs, i.e., OPs agree to share spectrum in a co-primary manner, and inter-operator D2D communication is allocated over spectral resources contributed from both parties. In this paper, we consider a spectrum sharing scenario where a number of OPs construct a spectrum pool dedicated to support inter-operator D2D communication. OPs negotiate in the form of a non-cooperative game about how much spectrum each OP contributes to the spectrum pool. OPs submit proposals to each other in parallel until a consensus is reached. When every OP has a concave utility function on the box-constrained region, we identify the conditions guaranteeing the existence of a unique equilibrium point. We show that the iterative algorithm based on the OP's best response might not converge to the equilibrium point due to myopically overreacting to the response of the other OPs, while the Jacobi-play strategy update algorithm can converge with an appropriate selection of update parameter. Using the Jacobi-play update algorithm, we illustrate that asymmetric OPs contribute an unequal amount of resources to the spectrum pool; However all participating OPs may experience significant performance gains compared to the scheme without spectrum sharing.Comment: Accepted to appear in IEEE Journal on Selected Areas in Communications (JSAC

Numerical Verification of Dielectric Contactor as Auxiliary Loads for Measuring the Multi-Port Network Parameter of Vertical Interconnection Array

For the accurate and reliable multi-port characterization of vertical interconnection array structures, this paper presents an indirect-contact probing method to obtain network parameters of Nport device-under-tests (DUTs) using an M-port (N > M) vector network analyzer (VNA) with a dielectric contactor. By utilizing the dielectric contactor as auxiliary loads for un-probed ports for vertical interconnections, multiple M-port sub-array network parameters can be correctly synthesized into the Nport network parameters through the renormalization processes. To verify the proposed method, four-port DUTs for packaging and microwave applications were characterized with two-port indirect-contact probing sub-array simulations including the dielectric contactor. Compared with two-port direct-contact probing simulations without the dielectric contactor, it was confirmed that the proposed method with the dielectric contactor provides improved accuracy in terms of the feature selective validation (FSV) method

Design of a High Performance Earth Imaging Microsatellite

Multispectral Earth Imaging Satellite (MEISAT) is SaTReCi’s 100 kg micro satellite which will be adequate to support a high resolution multispectral Earth imaging camera. MEISAT, whose development is currently in progress, is capable of achieving a ground resolution of 8.5 meters with a 47 km swath width and 400 km scan length from its intended orbit of 730 km. The low-cost satellite is also capable of storing 8 Gbits of image data which will be transmitted to ground at 10 Mbps with an X-band transmitter. This paper provides an overview of MEISAT mission operation concept. The mission requirements and the system specifications are also discussed. The paper then describes the overall system configuration. The design of the command and data handling system, the power system, the attitude control system, the RF system, and the payload system is presented

Privacy-Preserving Federated Model Predicting Bipolar Transition in Patients With Depression:Prediction Model Development Study

BACKGROUND: Mood disorder has emerged as a serious concern for public health; in particular, bipolar disorder has a less favorable prognosis than depression. Although prompt recognition of depression conversion to bipolar disorder is needed, early prediction is challenging due to overlapping symptoms. Recently, there have been attempts to develop a prediction model by using federated learning. Federated learning in medical fields is a method for training multi-institutional machine learning models without patient-level data sharing. OBJECTIVE: This study aims to develop and validate a federated, differentially private multi-institutional bipolar transition prediction model. METHODS: This retrospective study enrolled patients diagnosed with the first depressive episode at 5 tertiary hospitals in South Korea. We developed models for predicting bipolar transition by using data from 17,631 patients in 4 institutions. Further, we used data from 4541 patients for external validation from 1 institution. We created standardized pipelines to extract large-scale clinical features from the 4 institutions without any code modification. Moreover, we performed feature selection in a federated environment for computational efficiency and applied differential privacy to gradient updates. Finally, we compared the federated and the 4 local models developed with each hospital's data on internal and external validation data sets. RESULTS: In the internal data set, 279 out of 17,631 patients showed bipolar disorder transition. In the external data set, 39 out of 4541 patients showed bipolar disorder transition. The average performance of the federated model in the internal test (area under the curve [AUC] 0.726) and external validation (AUC 0.719) data sets was higher than that of the other locally developed models (AUC 0.642-0.707 and AUC 0.642-0.699, respectively). In the federated model, classifications were driven by several predictors such as the Charlson index (low scores were associated with bipolar transition, which may be due to younger age), severe depression, anxiolytics, young age, and visiting months (the bipolar transition was associated with seasonality, especially during the spring and summer months). CONCLUSIONS: We developed and validated a differentially private federated model by using distributed multi-institutional psychiatric data with standardized pipelines in a real-world environment. The federated model performed better than models using local data only.</p

Efficacy and Safety of Guardcel Nasal Packing After Endoscopic Sinus Surgery: A Prospective, Single-Blind, Randomized Controlled Study

Objectives Nasal packing after endoscopic sinus surgery is frequently used to control postoperative bleeding, enhance the wound healing process, and prevent lateralization of the middle turbinate, which causes insufficient ventilation. Many biodegradable materials have been developed to reduce pain and mucosal damage during packing removal. The purpose of this study was to compare the efficacy of Guardcel (Genewel Co.) middle meatal packing with a traditional nonabsorbable middle meatal packing, Merocel (Medtronic Xomed), on wound healing and patient satisfaction. Methods In this prospective, single-blind, randomized controlled study, we enrolled 32 consecutive patients (64 nostrils) undergoing bilateral endoscopic sinus surgery at Korea University Guro Hospital from February 2015 to August 2015. Guardcel and Merocel were inserted postoperatively into a randomly assigned side. Objective findings about bleeding, hemostasis, adhesion, and infection were evaluated with nasal endoscopy. Patients’ symptoms including pain and nasal obstruction were evaluated with a visual analog scale. Each evaluation was done at 2–3 days, 1 week, 2 weeks, and 4 weeks after surgery. Results At 2–3 days after endoscopic sinus surgery, the Guardcel side had a significantly less hemostasis time than the Merocel side (P=0.001). During this period, the pain during packing removal was significantly lower on the Guardcel-inserted side than the Merocel-inserted side (P=0.002). At two weeks after surgery, the adhesion score on the Guardcel side was significantly lower than that of the Merocel side (P=0.011). Other parameters during the study follow-up periods were not statistically significant. There were no severe adverse reactions. Conclusion Guardcel, a newly developed packing material, appeared to shorten the hemostasis time and reduce pain sensation at 2–3 days after surgery; it also prevented adhesion formation 2 weeks after surgery when compared with the control. Guardcel can be an effective and safe candidate to replace conventional packing materials after endoscopic sinus surgery

Functionalized Poly(3-hexylthiophene)s via Lithium–Bromine Exchange

Poly(3-hexylthiophene) (P3HT) is one of the most extensively investigated conjugated polymers and has been employed as the active material in many devices including field-effect transistors, organic photovoltaics and sensors. As a result, methods to further tune the properties of P3HT are desirable for specific applications. Herein, we report a facile postpolymerization modification strategy to functionalize the 4-position of commercially available P3HT in two simple steps–bromination of the 4-position of P3HT (Br–P3HT) followed by lithium−bromine exchange and quenching with an electrophile. We achieved near quantitative lithium–bromine exchange with Br–P3HT, which requires over 100 thienyl lithiates to be present on a single polymer chain. The lithiated-P3HT is readily combined with functional electrophiles, resulting in P3HT derivatives with ketones, secondary alcohols, trimethylsilyl (TMS) group, fluorine, or an azide at the 4-position. We demonstrated that the azide-modified P3HT could undergo Cu-catalyzed or Cu-free click chemistry, significantly expanding the complexity of the structures that can be appended to P3HT using this method.National Science Foundation (U.S.) (ECCS-0939514