COVID-19 is Not All Bad News: Negative and Surprisingly Positive Reports from College STEM Students and Implications for STEM Instruction

The negative educational consequences of COVID-19 are well documented. Much less investigated have been any potential positive outcomes of the pandemic. We surveyed 392 students at one college querying why they continue studying STEM or leave the STEM disciplines and about the effects of COVID-19 on their education. STEM students may have been especially impacted by pandemic-imposed remote instruction given STEM’s reliance on hands-on laboratory experiences. Because the literature indicates that people of color and those from lower socioeconomic groups were more negatively affected by COVID-19, we hypothesized that students from these groups would report greater adverse educational consequences of the pandemic; however, this was not borne out by our findings. Across demographic groups, students reported negative impacts of COVID-19, although in a few areas we found that more traditionally “privileged” groups complained of more negative outcomes than traditionally “marginalized” students did. Most novel and dramatic in our results were the positive outcomes of the “lockdown” reported by students in the areas of enhanced resilience, improved social relationships, greater opportunities, academic improvement, and better mental health. We conclude with recommendations for addressing the negative outcomes of COVID-19 and remote instruction, and for taking advantage of the unexpected positive effects

High-voltage vertical Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e power rectifiers operational at high temperatures up to 600 K

This work presents the temperature-dependent forward conduction and reverse blocking characteristics of a high-voltage vertical Ga2O3 power rectifier from 300 K to 600 K. Vertical β-Ga2O3 Schottky barrier diodes (SBDs) were fabricated with a bevel-field-plated edge termination, where a beveled sidewall was implemented in both the mesa and the field plate oxide. The Schottky barrier height was found to increase from 1.2 eV to 1.3 eV as the temperature increases from 300 K to 600 K, indicating the existence of barrier height inhomogeneity. The net donor concentration in the drift region shows little dependence on the temperature. The reverse leakage current up to 500 V was found to be limited by both the thermionic-field electron injection at the Schottky contact and the electron hopping via the defect states in the depletion region. At 300-500 K, the leakage is first limited by the electron injection at low voltages and then by the hopping in depleted Ga2O3 at high voltages. At temperatures above 500 K, the thermionic field emission limits the device leakage over the entire voltage range up to 500 V. Compared to the state-of-the-art SiC and GaN SBDs when blocking a similar voltage, our vertical Ga2O3 SBDs are capable of operating at significantly higher temperatures and show a smaller leakage current increase with temperature. This shows the great potential of Ga2O3 SBDs for high-temperature and high-voltage power applications

TCAD-Machine learning framework for device variation and operating temperature analysis with experimental demonstration

This work, for the first time, experimentally demonstrates a TCAD-Machine Learning (TCAD-ML) framework to assist the analysis of device-to-device variation and operating (ambient) temperature without the need of physical quantities extraction. The ML algorithm used in this work is the Principal Component Analysis (PCA) followed by third order polynomial regression. After calibrated to limited \u27expensive\u27 experimental data, \u27low cost\u27 TCAD simulation is used to generate a large amount of device data to train the ML model. The ML was then used to identify the root cause of device variation and operating temperature from any given experimental current-voltage (I-V) characteristics. We applied this framework to study the ultra-wide-bandgap gallium oxide (Ga2O3) Schottky barrier diode (SBD), an emerging device technology that holds great promise for temperature sensing, RF, and power applications in harsh environments. After calibration, over 150,000 electrothermal TCAD simulations are performed with random variation of physical parameters (anode effective work function, drift layer doping, and drift layer thickness) and operating temperature. An ML model is trained using these TCAD data and we found 1,000-10,000 TCAD data can train an accurate machine. We show that without physical quantities extraction, performing PCA is essential for the TCAD trained ML model to be applicable to analyze experimental characteristics. The physical parameters and temperatures predicted by the ML model show good agreement with experimental analysis. Our TCAD-ML framework shows great promise to accelerate the development of new device technologies with a significantly more efficient process of material and device experimentation

Surface modification of interconnected porous scaffolds

Surface properties of scaffolds play an important role in cell adhesion and growth. Biodegradable poly(Α-hydroxy acids) have been widely used as scaffolding materials for tissue engineering; however, the lack of functional groups is a limitation. In this work, gelatin was successfully immobilized onto the surface of poly(Α-hydroxy acids) films and porous scaffolds by a new entrapment process. The surface composition and properties were examined using attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectra (XPS), and contact angle measurements. Control over the amount of entrapped gelatin was achieved by varying the solvent composition, the duration of soaking, the concentration of gelatin in solution, and chemical crosslinking. The amount of entrapped gelatin increased with the ratio of dioxane/water in the solvent mixture used. Chemical crosslinking after physical entrapment considerably increased the amount of retained gelatin on the surface of poly(Α-hydroxy acids). Osteoblasts were cultured on these films and scaffolds. The surface modification significantly improved cell attachment and proliferation. Cell numbers on the surface-modified films and scaffolds were significantly higher than those on controls 4 h and 1 day after cell seeding. The osteoblasts showed higher proliferation on surface-modified scaffolds than on the control during 4 weeks of in vitro cultivation. More collagen fibers and other cell secretions were deposited on the surface-modified scaffolds than on the control scaffolds. This novel surface treatment strategy provides a convenient and universal way to modify the surface properties of three-dimensional scaffolds and thus promote cell adhesion and proliferation for tissue engineering. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48704/1/30367_ftp.pd

Modulation of inflammation by anti-TNF α mAb-dendrimer nanoparticles loaded in tyramine-modified gellan gum hydrogels in a cartilage-on-a-chip model

Rheumatoid arthritis (RA) is an autoimmune and chronic inflammatory disease characterized by joint inflammation. Since the inflammatory condition plays an important role in the disease process, it is important to develop and test new therapeutic approaches that specifically target and treat joint inflammation. In this study, a human 3D inflammatory cartilage-on-a-chip model was established to test the therapeutic efficacy of anti-TNFα mAb-CS/PAMAM dendrimer NPs loaded-Tyramine-Gellan Gum in the treatment of inflammation. The results showed that the proposed therapeutic approach applied to the human monocyte cell line (THP-1) and human chondrogenic primary cells (hCH) cell-based inflammation system revealed an anti-inflammatory capacity that increased over 14 days. It was also possible to observe that Coll type II was highly expressed by inflamed hCH upon the culture with anti-TNF α mAb-CS/PAMAM dendrimer NPs, indicating that the hCH cells were able maintain their biological function. The developed preclinical model allowed us to provide more robust data on the potential therapeutic effect of anti-TNF α mAb-CS/PAMAM dendrimer NPs loaded-Ty-GG hydrogel in a physiologically relevant model.The authors thank the financial support under the Norte2020 project (NORTE-08-5369-FSE000044). M. R. C. acknowledges TERM RES Hub Ref. Norte-01-0145-FEDER-02219015 working contract. D. C. F. acknowledges Portuguese Foundation for Science and Technology (FCT) for his phD scholarship (PD/ BD/143081/2018) and F. R. M. for her contract under the Transitional Rule DL 57/2016 (CTTI-57/18-I3BS(5)). C. M. A., D. C. V. and S. C. K. thank the support of FCT (PTDC/BTM-ORG/ 28070/2017). D. C. V acknowledges the CEEC individual contract (CEECIND/00352/2017). S. C. K wishes to record the financial support from EU Framework Programme for Research and Innovation H2020 on FoReCaST under grant agreement no. 668983 and BREAST-IT FCT-Portugal project (PTDC/BTM-ORG/ 28168/2017). The FCT distinction attributed to J. M. O. under the Investigator FCT program (number IF/01285/2015) is also greatly acknowledge

Biological effects of rinsing morsellised bone grafts before and after impaction

Rinsing bone grafts before or both before and after impaction might have different effects on the incorporation of the graft. Rinsing again after impaction might negatively influence bone induction if growth factors released by impaction are washed away. We studied if transforming growth factor-βs (TGF-βs) and bone morphogenetic proteins (BMPs) are released from the mineralised matrix by impaction and if these released growth factors induce osteogenic differentiation in human mesenchymal stem cells (hMSCs). Rinsed morsellised bone allografts were impacted in a cylinder and the escaping fluid was collected. The fluid was analysed for the presence of TGF-βs and BMPs, and the osteoinductive capacity was tested on hMSCs. Abundant TGF-β was present in the fluid. No BMPs could be detected. Osteogenic differentiation of hMSCs was inhibited by the fluid. Results from our study leave us only able to speculate whether rinsing grafts again after impaction has a beneficial effect on the incorporation process or not

Surface modification of electrospun polycaprolactone nanofiber meshes by plasma treatment to enhance biological performance

A critical aspect in the development of biomaterials is the optimization of their surface properties to achieve an adequate cell response. In the present work, electrospun polycaprolactone nanofiber meshes (NFMs) are treated by radio-frequency (RF) plasma using different gases (Ar or O2), power (20 or 30 W), and exposure time (5 or 10 min). Morphological and roughness analysis show topographical changes on the plasma-treated NFMs. X-ray photoelectron spectroscopy (XPS) results indicate an increment of the oxygen-containing groups, mainly –OH and –C––O, at the plasma-treated surfaces. Accordingly, the glycerol contact angle results demonstrate a decrease in the hydrophobicity of plasma-treated meshes, particularly in the O2-treated ones. Three model cell lines (fibroblasts, chondrocytes, and osteoblasts) are used to study the effect of plasma treatments over the morphology, cell adhesion, and proliferation. A plasma treatment with O2 and one with Ar are found to be the most successful for all the studied cell types. The influence of hydrophilicity and roughness of those NFMs on their biological performance is discussed. Despite the often claimed morphological similarity of NFMs to natural extracellular matrixes, their surface properties contribute substantially to the cellular performance and therefore those should be optimized.This work was partially supported by the European Integrated Project GENOSTEM (LSH-STREP-CT-2003-503161) and the European Network of Excellence EXPERTISSUES (NMP3-CT2004-500283). The Portuguese Foundation for Science and Technology for the project Naturally Nano (POCI/EME/589821 2004) and the Ph.D. grant of A. Martins (SFRH/BD/24382/2005) is also acknowledged

Micro-CT studies on 3-D bioactive glass-ceramic scaffolds for bone regeneration

The aim of this study was the preparation and characterization of bioactive glass-ceramic scaffolds for bone tissue engineering. For this purpose, a glass belonging to the system SiO2-P2O5-CaO-MgO-Na2O-K2O (CEL2) was used. The sponge-replication method was adopted to prepare the scaffolds; specifically, a polymeric skeleton was impregnated with a slurry containing CEL2 powder, polyvinyl alcohol (PVA) as a binding agent and distilled water. The impregnated sponge was then thermally treated to remove the polymeric phase and to sinter the inorganic one. The obtained scaffolds possessed an open and interconnected porosity, analogous to cancellous bone texture, and with a mechanical strength above 2 MPa. Moreover, the scaffolds underwent partial bioresorption due to ion-leaching phe- nomena. This feature was investigated by X-ray computed microcomputed tomography (micro-CT). Micro-CT is a three-dimensional (3- D) radiographic imaging technique, able to achieve a spatial resolution close to 1 lm3. The use of synchrotron radiation allows the selected photon energy to be tuned to optimize the contrast among the different phases in the investigated samples. The 3-D scaffolds were soaked in a simulated body fluid (SBF) to study the formation of hydroxyapatite microcrystals on the scaffold struts and on the internal pore walls. The 3-D scaffolds were also soaked in a buffer solution (Tris-HCl) for different times to assess the scaffold bioresorp- tion according to the ISO standard. A gradual resorption of the pores walls was observed during the soakings both in SBF and in Tris- HC