Numerical approximation of the solution of Koiter's model for an elliptic membrane shell subjected to an obstacle via the penalty method

This paper is devoted to the analysis of a numerical scheme based on the Finite Element Method for approximating the solution of Koiter's model for a linearly elastic elliptic membrane shell subjected to remaining confined in a prescribed half-space. First, we show that the solution of the obstacle problem under consideration is uniquely determined and satisfies a set of variational inequalities which are governed by a fourth order elliptic operator, and which are posed over a non-empty, closed, and convex subset of a suitable space. Second, we show that the solution of the obstacle problem under consideration can be approximated by means of the penalty method. Third, we show that the solution of the corresponding penalised problem is more regular up to the boundary. Fourth, we write down the mixed variational formulation corresponding to the penalised problem under consideration, and we show that the solution of the mixed variational formulation is more regular up to the boundary as well. In view of this result concerning the augmentation of the regularity of the solution of the mixed penalised problem, we are able to approximate the solution of the one such problem by means of a Finite Element scheme. Finally, we present numerical experiments corroborating the validity of the mathematical results we obtained

Cellulose-starch hybrid films plasticized by aqueous ZnCl2 solution

Starch and cellulose are two typical natural polymers from plants that have similar chemical structures. The blending of these two biopolymers for materials development is an interesting topic, although how their molecular interactions could influence the conformation and properties of the resultant materials has not been studied extensively. Herein, the rheological properties of cellulose/starch/ZnCl2 solutions were studied, and the structures and properties of cellulose-starch hybrid films were characterized. The rheological study shows that compared with starch (containing mostly amylose), cellulose contributed more to the solution’s viscosity and has a stronger shear-thinning behavior. A comparison between the experimental and calculated zero-shear-rate viscosities indicates that compact complexes (interfacial interactions) formed between cellulose and starch with ≤50 wt % cellulose content, whereas a loose structure (phase separation) existed with ≥70 wt % cellulose content. For starch-rich hybrid films prepared by compression molding, less than 7 wt % of cellulose was found to improve the mechanical properties despite the reduced crystallinity of the starch; for cellulose-rich hybrid films, a higher content of starch reduced the material properties, although the chemical interactions were not apparently influenced. It is concluded that the mechanical properties of biopolymer films were mainly affected by the structural conformation, as indicated by the rheological results. View Full-Tex

Lasing- Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer

Microlasers are emerging tools for biomedical applications. In particular, whispering- gallery- mode (WGM) microlasers are promising candidates for sensing at the biointerface owing to their high quality- factor and potential in molecular assays, and intracellular and extracellular detection. However, lasing particles with sensing functionality remain challenging since the overlap between the WGM optical mode and external gain medium is much lower compared to internal gain inside the cavity. To overcome this problem, the concept of Förster resonant energy transfer (FRET) is exploited on WGM droplet microlaser by separating donor and acceptor molecules at the cavity- surface interface. It is first discovered that the interfacial FRET laser not only originates from conventional FRET but utilizes coherent radiative energy transfer (CRET) to excite acceptor molecules by inducing light- harvesting effect near the cavity interface. Simulations and experiments have revealed that the absorption spectrum of individual analyte plays a crucial role in interfacial FRET laser. Distinct lasing spectra can therefore distinguish molecules of different absorption properties upon binding. Finally, detection of small fluorescent molecules and photosynthetic protein is performed. The results presented here not only demonstrate the wide- ranging potential of microlaser external cavity implementation in molecular sensing applications, but also provide comprehensive insights into cavity energy transfer in laser physics.A novel concept is proposed to achieve active lasing- encoded biosensors by taking advantage of light- harvesting effect at the cavity interface, where interfacial molecular lasers based on cavity resonant energy transfer are demonstrated. This work marks a critical step of realizing whispering- gallery- mode (WGM) laser probes for biosensing, opening a new avenue in laser- based molecular sensing.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154969/1/adom201901596-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154969/2/adom201901596_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154969/3/adom201901596.pd

Energy-resolved Photoconductivity Mapping in a Monolayer-bilayer WSe2 Lateral Heterostructure

Vertical and lateral heterostructures of van der Waals materials provide tremendous flexibility for band structure engineering. Since electronic bands are sensitively affected by defects, strain, and interlayer coupling, the edge and heterojunction of these two-dimensional (2D) systems may exhibit novel physical properties, which can be fully revealed only by spatially resolved probes. Here, we report the spatial mapping of photoconductivity in a monolayer-bilayer WSe2 lateral heterostructure under multiple excitation lasers. As the photon energy increases, the light-induced conductivity detected by microwave impedance microscopy first appears along the hetero-interface and bilayer edge, then along the monolayer edge, inside the bilayer area, and finally in the interior of the monolayer region. The sequential emergence of mobile carriers in different sections of the sample is consistent with the theoretical calculation of local energy gaps. Quantitative analysis of the microscopy and transport data also reveals the linear dependence of photoconductivity on the laser intensity and the influence of interlayer coupling on carrier recombination. Combining theoretical modeling, atomic scale imaging, mesoscale impedance microscopy, and device-level characterization, our work suggests an exciting perspective to control the intrinsic band-gap variation in 2D heterostructures down to the few-nanometer regime.Comment: 18 pages, 5 figures; Nano Lett., Just Accepted Manuscrip

Elucidating Piezoelectricity and Strain in Monolayer MoS2 at the Nanoscale Using Kelvin Probe Force Microscopy

Strain engineering modifies the optical and electronic properties of atomically thin transition metal dichalcogenides. Highly inhomogeneous strain distributions in twodimensional materials can be easily realized, enabling control of properties on the nanoscale; however, methods for probing strain on the nanoscale remain challenging. In this work, we characterize inhomogeneously strained monolayer MoS2 via Kelvin probe force microscopy and electrostatic gating, isolating the contributions of strain from other electrostatic effects and enabling the measurement of all components of the two-dimensional strain tensor on length scales less than 100 nm. The combination of these methods is used to calculate the spatial distribution of the electrostatic potential resulting from piezoelectricity, presenting a powerful way to characterize inhomogeneous strain and piezoelectricity that can be extended toward a variety of 2D materials.This research was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement Nos. DMR-1720595 and DMR-2308817. This work was performed in part at the University of Texas Microelectronics Research Center, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (Grant ECCS-2025227), and using the facilities and instrumentation supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement Nos. DMR-1720595 and DMR-2308817 and NSF Major Research Instrumentation (MRI) program DMR- 2019130. E.B. acknowledges support from the National Science Foundation under grant DMR-2308817 (X.P.) and the Robert A. Welch Foundation under grant F-2092- 20220331 (F.Y.G.).Center for Dynamics and Control of Material

Simultaneous extraction and purification of alkaloids from Sophora flavescens Ait. by microwave-assisted aqueous two-phase extraction with ethanol/ammonia sulfate system

A rapid and effective method of integrating extraction and purification for alkaloids from Sophora flavescens Ait. was developed by microwave-assisted aqueous two-phase extraction (MAATPE) based on the high efficiency of microwave-assisted extraction (MAE) and the demixing effect of aqueous two-phase extraction (ATPE). The aqueous two-phase system (ATPS), ethanol/ammonia sulfate was chosen from seven combinations of ethanol/salt systems, and its extraction properties were investigated in detail. Key factors, namely, the compositions of ATPS, solvent-to-materials ratio, and the extraction temperature were selected for optimization of the experimental conditions using response surface methodology (RSM) on the basis of the results of the single-factor experiment. The final optimized conditions were, the compositions of ATPS: ethanol 28% (w/w) and (NH4)2SO4 18% (w/w), solvent-to-material ratio 60:1, temperature 90 C, extraction time 5 min, and microwave power 780 W. MAATPE was superior to MAE, the latter using a single solvent, not only in extraction yield but also in impurity content. Moreover, compared with the combination of MAE and ATPE in the two-step mode, MAATP demonstrated fewer impurities, a better yield (63.78 ± 0.45 mg/g) and a higher recovery (92.09 ± 0.14%) in the extraction and purification of alkaloids. A continuous multiphase-extraction model of MAATPE was proposed to explicate the extraction mechanism. MAATPE revealed that the interaction between microwave and ATPS cannot only cause plant cell rupture but also accelerate demixing, improving mass-transfer from solid–liquid extraction to liquid– liquid purification. MAATPE simplified procedures also contributed to the lower loss occurrence, better extraction efficiency, and reduced impurity to target constituents.The Science and Technology Project of Guangzhou (No. 2008Z1-E301) and Faculty Development fund Project of Guangdong Pharmaceutical University (No. 52104109

Coexistence of Cu(ii) and Cu(i) in Cu ion-doped zeolitic imidazolate frameworks (ZIF-8) for the dehydrogenative coupling of silanes with alcohols.

Recently, metal-ion-doped zeolitic imidazolate frameworks have gained considerable attention for their structure tailorability and potential catalytic applications. Herein, Cu ion-doped ZIF-8 nanocrystals were successfully prepared by the mechanical grinding of Cu(NO3)2, ZnO and 2-methylimidazole (HMeIM) using ethanol as an additive. In contrast to the general view that only Cu(ii) is present in Cu-doped ZIF-8, we found the coexistence of Cu(ii) and Cu(i) in this material, which was supported by XPS and X-ray induced Auger electron spectroscopy (XAES) characterizations. Moreover, ethanol might have acted as a reducer to induce the reduction of Cu(ii) during synthesis. Due to the mixed valency of Cu ions, the Cu ion-doped ZIF-8 nanocrystals showed excellent catalytic performance in the dehydrogenative coupling of silanes with alcohols

Contact-hardening behavior of calcium silicate hydrate powders

Calciumsilicate hydrate (C-S-H) synthesized by a hydrothermal process fromlime and siliceous materials was oven-dried and compressed into compacts. The microstructure and compaction properties of the resulting powderswere characterized. The results showthat the powders containing an amorphous structure become hardened compacts immediately after compression. Compacts with high strength but a relatively lower bulk density were produced. Amorphous C-S-H plays a key role in the bonding formation during powder compaction. According to the Heckel plots, particle rearrangement and plastic deformation were involved in the compaction of C-S-H powders. Point contact between C-S-H particles due to particle rearrangement dominates at a low compression pressure (i.e., < 20MPa). Van derWaals forces and hydrogen bonding are the main bonding types. Plastic deformation occurs at a higher compression pressure (i.e., > 60MPa), which results in surface contact. Consequently, a solid bridge forms, and the strength of compacts increases rapidly. These findings provide novel insight into the utilization of materials containing amorphous calcium silicate hydrate

Structural disorganization and chain aggregation of high-amylose starch in different chloride salt solutions

As high-amylose starch (HAS) has a higher content of linearly structured chains than other types of starch, it is more scientifically interesting to realize enhanced properties or new functions for food and materials applications. However, the full dissolution of the compact granule structure of HAS is challenging under moderate conditions, which limits its applications. Here, we have revealed that the granule structure of HAS can be easily destructed by certain concentrations of acidic ZnCl2, neutral MgCl2, and alkaline CaCl2 solutions (43, 34, and 31 wt %, respectively) at a moderate temperature (under 50 °C). The ZnCl2 and CaCl2 solutions resulted in complete dissolution of HAS granules, whereas small amounts of HAS granule remnants still existed in the MgCl2 solution. The regenerated starch from the CaCl2 solution was completely amorphous, that from the ZnCl2 solution only presented a weak peak at 17°, and that from the MgCl2 solution contained V-type crystallites. No new reflections were found on the FTIR spectra indicating that all these three chloride solutions can be considered as a nonderivatizing solvent for starch. In all the three cases, nanoparticles were formed in the regenerated starch, which could be due to the aggregation of starch chains or their complexation with the metal cation. In addition, their water absorption ratio was 1.5 to 3 times that of the control (treated in water)

The occurrence of early atrial fibrillation after cardiac valve operation and the establishment of a nomogram model

BackgroundPostoperative atrial fibrillation (POAF) is a common complication after cardiac surgery, which is associated with age and massive bleeding. However, whether thyroid hormone (TH) level can affect POAF remains controversial.AimTo investigate the occurrence and risk factors of POAF, in particular, the preoperative TH level of patients was introduced into this study as a variable for analysis, and a column graph prediction model of POAF was constructed.MethodsPatients who underwent valve surgery in Fujian Cardiac Medical Center from January 2019 to May 2022 were retrospectively analyzed and divided into POAF group and NO-POAF group. Baseline characteristics and relevant clinical data were collected from the two groups of patients. Independent risk factors for POAF were screened using univariate analysis and binary logistic regression analysis, and a column line graph prediction model was established based on the regression analysis results, and the diagnostic efficacy and calibration of the model were evaluated using the Receiver Operating Characteristic Curve (ROC) and calibration curve.ResultsA total of 2,340 patients underwent valve surgery, excluding 1,751 patients, a total of 589 patients were included, including 89 patients in POAF group and 500 patients in NO-POAF group. The total incidence of POAF was 15.1%. The results of the Logistics regression analysis showed that gender, age, leukocytes and TSH were risk factors of POAF. The area under the ROC curve of the nomogram prediction model for POAF was 0.747 (95% CI: 0.688–0.806, P < 0.001), with a sensitivity of 74.2% and specificity of 68%. Hosmer-Lemeshow test showed χ2 = 11.141, P = 0.194 > 0.05, the calibration curve was well fitted.ConclusionThe results of this study show that gender, age, leukocyte and TSH are risk factors of POAF, and the nomogram prediction model has a good prediction effect. Due to the limited sample size and included population, more studies are needed to validate this result