Microfluidic thermal management of 2.5D and 3D microsystems

Both 2.5 dimensional (2.5D) and 3 dimensional (3D) stacked integrated chip (SIC) heterogeneous architectures are promising to go beyond Moore's law for compact, high-performance, energy-efficient microsystems. However, these systems face significant thermal management challenges due to the increased volumetric heat generation rates, and reduced surface area. In addition, highly spatially and temporally non-uniform heat generation occurs due to different functionalities of various heterogeneous chips. This dissertation focuses on thermal management challenges for both 2.5D and 3D-SICs, by utilizing micro-gap liquid cooling with enhanced non-uniform heterogeneous pin-fin structures. Single phase convection thermal performance of heterogeneous pin-fin enhanced micro-gap liquid cooling under non-uniform power map has been evaluated under steady state conditions. Heat transfer and pressure drop characteristics of dielectric coolants in cooling manifold with cooling enhanced structure and hergeneous pin-fins have been parametrically studied by full-scale computational fluid mechanics/heat transfer (CFD/HT) to achieve non-uniform cooling capacities for multi-chip test structures of 2.5D-SICs. Non-uniform heterogeneous pin-fin structures in cold plates have been numerically and systematically optimized using design of experiment method, coupling with full-scale CFD/HT simulations. A compact thermal model accounting for both spatially and temporally varying heat-flux distributions for inter-layer liquid cooling of 3D-SICs, with realistic leakage power simulation feature has also been developed as a thermal-electrical co-design tool for 3D-SICs. In addition to the active micro-gap liquid cooling thermal managements, this dissertation also investigates the passive micro-gap two-phase liquid cooling using a miniature-thermosyphon with dielectric coolant Novec 7200, for future 3D-SICs. Experimental characterizations, including heat transfer measurements, and bubble flow visualizations are performed under two phase conditions. Implementation of miniature-thermosyphon on 3D-SICs provides non-uniform in-plane as well as cross-plane cooling capacities, which can be used and further enhanced for 3D-SICs thermal management with heterogeneous chips.Ph.D

Terahertz nonlinear hall rectifiers based on spin-polarized topological electronic states in 1T-CoTe2

The zero-magnetic-field nonlinear Hall effect (NLHE) refers to the second-order transverse current induced by an applied alternating electric field; it indicates the topological properties of inversion-symmetry-breaking crystals. Despite several studies on the NLHE induced by the Berry-curvature dipole in Weyl semimetals, the direct current conversion by rectification is limited to very low driving frequencies and cryogenic temperatures. The nonlinear photoresponse generated by the NLHE at room temperature can be useful for numerous applications in communication, sensing, and photodetection across a high bandwidth. In this study, observations of the second-order NLHE in type-II Dirac semimetal CoTe2 under time-reversal symmetry are reported. This is determined by the disorder-induced extrinsic contribution on the broken-inversion-symmetry surface and room-temperature terahertz rectification without the need for semiconductor junctions or bias voltage. It is shown that remarkable photoresponsivity over 0.1 A W−1, a response time of approximately 710 ns, and a mean noise equivalent power of 1 pW Hz−1/2 can be achieved at room temperature. The results open a new pathway for low-energy photon harvesting via nonlinear rectification induced by the NLHE in strongly spin–orbit-coupled and inversion-symmetry-breaking systems, promising a considerable impact in the field of infrared/terahertz photonicsPID2019–109525RB-I00, CEX2018-000805-M, EU’s H2020 NFFA-Europe (n. 654360), and NFFA-Europe-Pilot (10100741

Implicit Active Contours Driven by Local and Global Image Fitting Energy for Image Segmentation and Target Localization

We propose a novel active contour model in a variational level set formulation for image segmentation and target localization. We combine a local image fitting term and a global image fitting term to drive the contour evolution. Our model can efficiently segment the images with intensity inhomogeneity with the contour starting anywhere in the image. In its numerical implementation, an efficient numerical schema is used to ensure sufficient numerical accuracy. We validated its effectiveness in numerous synthetic images and real images, and the promising experimental results show its advantages in terms of accuracy, efficiency, and robustness

Microstructures and hardness prediction of an ultrafine-grained Al-2024 alloy

High-pressure torsion (HPT) is a high efficiency processing method for fabricating bulk ultrafine-grained metallic materials. This work investigates microstructures and evaluates the corresponding strengthening components in the center of HPT disks, where effective shear strains are very low. An Al-4.63Cu-1.51Mg (wt. %) alloy was processed by HPT for 5 rotations. Non-equilibrium grain and sub-grain boundaries were observed using scanning transmission electron microscopy in the center area of HPT disks. Solute co-cluster segregation at grain boundaries was found by energy dispersive spectrometry. Quantitative analysis of X-ray diffraction patterns showed that the average microstrain, crystalline size, and dislocation density were (1.32 ± 0.07) × 10−3, 61.9 ± 1.4 nm, and (2.58 ± 0.07) × 1014 m−2, respectively. The ultra-high average hardness increment was predicted on multiple mechanisms due to ultra-high dislocation densities, grain refinement, and co-cluster–defect complexes

Sensitive and Specific Detection of Lumpy Skin Disease Virus in Cattle by CRISPR-Cas12a Fluorescent Assay Coupled with Recombinase Polymerase Amplification

Lumpy skin disease (LSD) is a severe and highly infectious pox disease of cattle caused by the lumpy skin disease virus (LSDV). To facilitate early control of LSD, this study aimed to develop a new rapid on-site LSDV detection method using an orf068 gene-based recombinase polymerase amplification assay (RPA) coupled with a CRISPR-Cas12a-based fluorescence assay (RPA-Cas12a-fluorescence assay). The results showed that the sensitivity of our RPA-Cas12a-fluorescence assay for detecting LSDV orf068 gene reached 5 copies/μL with plasmid as a template, and 102 TCID50/mL with viral genomic DNA as a template. No cross-reaction with other common bovine viruses was observed. Further, an on-site RPA-Cas12a-fluorescence assay of 40 clinical samples from cattle with or without LSD showed a diagnostic sensitivity of 96.3% (95% CI: 81.0–99.9%) and specificity of 92.31% (95% CI: 62.1–99.6%), which was close to those of the quantitative PCR assay. Therefore, our RPA-Cas12a-fluorescence assay has promising prospects in on-site rapid LSDV detection

Impacts of rural worker migration on ambient air quality and health in China: From the perspective of upgrading residential energy consumption

International audienc

Trade, R&D spending and financial development

This paper assesses the importance of financial development and R&D spending for exports using both a theoretical model and econometric testing. It is shown that financial development and R&D expenditures are positively related to exports and the balance of manufactured goods. The results suggest that countries that want to increase their exports should invest more in R&D activities and increase the priority of their financial reforms.

Spike mutations contributing to the altered entry preference of SARS-CoV-2 Omicron BA.1 and BA.2

SARS-CoV-2 B.1.1.529.1 (Omicron BA.1) emerged in November 2021 and quickly became the predominant circulating SARS-CoV-2 variant globally. Omicron BA.1 contains more than 30 mutations in the spike protein, which contribute to its altered virological features when compared to the ancestral SARS-CoV-2 or previous SARS-CoV-2 variants. Recent studies by us and others demonstrated that Omicron BA.1 is less dependent on transmembrane serine protease 2 (TMPRSS2), less efficient in spike cleavage, less fusogenic, and adopts an altered propensity to utilize the plasma membrane and endosomal pathways for virus entry. Ongoing studies suggest that these virological features of Omicron BA.1 are in part retained by the subsequent Omicron sublineages. However, the exact spike determinants that contribute to these altered features of Omicron remain incompletely understood. In this study, we investigated the spike determinants for the observed virological characteristics of Omicron. By screening for the individual changes on Omicron BA.1 and BA.2 spike, we identify that 69-70 deletion, E484A, and H655Y contribute to the reduced TMPRSS2 usage while 25-27 deletion, S375F, and T376A result in less efficient spike cleavage. Among the shared spike mutations of BA.1 and BA.2, S375F and H655Y reduce spike-mediated fusogenicity. Interestingly, the H655Y change consistently reduces serine protease usage while increases the use of endosomal proteases. In keeping with these findings, the H655Y substitution alone reduces plasma membrane entry and facilitates endosomal entry when compared to SARS-CoV-2 WT. Overall, our study identifies key changes in Omicron spike that contributes to our understanding on the virological determinant and pathogenicity of Omicron.</p