Unique opportunity to harness polarization in GaN to override the conventional power electronics figure-of-merits

Owing to the large breakdown electric field, wide bandgap semiconductors such as SiC, GaN, Ga2O3 and diamond based power devices are the focus for next generation power switching applications. The unipolar trade-off relationship between the area specific-on resistance and breakdown voltage is often employed to compare the performance limitation among various materials. The GaN material system has a unique advantage due to its prominent spontaneous and piezoelectric polarization effects in GaN, AlN, InN, AlxInyGaN alloys and flexibility in inserting appropriate heterojunctions thus dramatically broaden the device design space.Comment: Invited paper, to appear in IEEE Device Research Conference (DRC), June 201

DyCAPS: Asynchronous Dynamic-committee Proactive Secret Sharing

Dynamic-committee proactive secret sharing (DPSS) enables the refresh of secret shares and the alternation of shareholders without changing the secret. Such a proactivization functionality makes DPSS a promising technology for long-term key management and committee governance. In non-asynchronous networks, CHURP (CCS ’19) and COBRA (S&P ’22) have achieved best-case square and cubic communication cost, respectively, w.r.t. the number of shareholders. However, the overhead of asynchronous DPSS remains high. This gap hinders asynchronous protocols from evolving to the dynamic setting, such as BFT systems and threshold cryptography services. In this paper, we fill this gap and propose DyCAPS, an efficient asynchronous DPSS protocol with a cubic communication cost. DyCAPS supports the transfer of both low- and high-threshold secret shares among dynamic committees with the same communication and computation complexity. Experimental results show that proactivization between two disjoint committees of 4 (resp., 64) members takes 1.3 (resp., 51) seconds. Moreover, DyCAPS is designed to be compatible with asynchronous BFT protocols without increasing the asymptotic communication cost. Given a payload of 5–10 MB per node, DyCAPS achieves member change in Dumbo2 (CCS ’20) at around 10% temporary throughput degradation, with the committee size varying from 4 to 22

Association Between Pre-operative BUN and Post-operative 30-Day Mortality in Patients Undergoing Craniotomy for Tumors: Data From the ACS NSQIP Database

ObjectiveThere is limited evidence to clarify the specific relationship between pre-operative blood urea nitrogen (BUN) and post-operative 30-day mortality in patients undergoing craniotomy for tumors. Therefore, we aimed to investigate this relationship in detail.MethodsElectronic medical records of 18,642 patients undergoing craniotomy for tumors in the ACS NSQIP from 2012 to 2015 were subjected to secondary retrospective analysis. The principal exposure was pre-operative BUN. Outcome measures were post-operative 30-day mortality. We used binary logistic regression modeling to evaluate the association between them and conducted a generalized additive model and smooth curve fitting (penalized spline method) to explore the potential relationship and its explicit curve shape. We also conducted sensitivity analyses to ensure the robustness of the results and performed subgroup analyses.ResultsA total of 16,876 patients were included in this analysis. Of these, 47.48% of patients were men. The post-operative 30-day mortality of the included cases was 2.49% (420/16,876), and the mean BUN was 16.874 ± 6.648 mg/dl. After adjusting covariates, the results showed that pre-operative BUN was positively associated with post-operative 30-day mortality (OR = 1.020, 95% CI: 1.004, 1.036). There was also a non-linear relationship between BUN and post-operative 30-day mortality, and the inflection point of the BUN was 9.804. For patients with BUN < 9.804 mg/dl, a 1 unit decrease in BUN was related to a 16.8% increase in the risk of post-operative 30-day mortality (OR = 0.832, 95% CI: 0.737, 0.941); for patients with BUN > 9.804 mg/dl, a 1 unit increase in BUN was related to a 2.8% increase in the risk of post-operative 30-day mortality (OR = 1.028, 95% CI: 1.011, 1.045). The sensitivity analysis proved that the results were robust. The subgroup analysis revealed that all listed subgroups did not affect the relationship between pre-operative BUN and post-operative 30-day mortality (P > 0.05).ConclusionOur study demonstrated that pre-operative BUN (mg/dl) has specific linear and non-linear relationships with post-operative 30-day mortality in patients over 18 years of age who underwent craniotomy for tumors. Proper pre-operative management of BUN and maintenance of BUN near the inflection point (9.804 mg/dl) could reduce the risk of post-operative 30-day mortality in these cases

Breakdown Walkout in Polarization-Doped Vertical GaN Diodes

We demonstrate the avalanche capability and the existence of breakdown walkout in GaN-on-GaN vertical devices with polarization doping. By means of combined electrical and optical characterization, we demonstrate the following original results: 1) vertical p-n junctions with polarization doping have avalanche capability; 2) stress in avalanche regime induces an increase in breakdown voltage, referred to as breakdown walkout; 3) this process is fully-recoverable, thus being related to a trapping mechanism; 4) temperature-dependent measurements of the breakdown walkout identify $\text{C}_{N}$ defects responsible for this process; and 5) capacitance deep level transient spectroscopy (C-DLTS) and deep level optical spectroscopy (DLOS) confirm the presence of residual carbon in the devices under test. A possible model to explain the avalanche walkout is then proposed