Strainburst is one type of rockburst that generally occurs in deep tunnel. In this study, the strainburst behaviors of marble specimens were investigated under tunnel-excavation-induced stress ...condition, and two stress paths were designed, a commonly used stress path in true triaxial unloading rockburst tests and a new test path in which the intermediate principal stress was varied. During the tests, a high-speed camera was used to record the strainburst process, and an acoustic emission (AE) monitoring system was used to monitor the AE characteristics of failure. In these two stress paths, all the marble specimens exhibited strainbursts; however, when the intermediate principal stress was varied, the rockburst became more violent. The obtained results indicate that the intermediate principal stress has a significant effect on rockburst behavior of marble. Under a higher intermediate principal stress before the unloading, more elastic strain energy was accumulated in the specimen, and the cumulative AE energy was higher in the rockburst-induced failure, i.e., more elastic strain energy was released during the failure. Therefore, more violent failure was observed: more rock fragments with a higher mass and larger size were ejected outward.
Polymorphism (and its extended form – pseudopolymorphism) in solids is ubiquitous in mineralogy, crystallography, chemistry/biochemistry, materials science, and the pharmaceutical industries. Despite ...the difficulty of controlling (pseudo‐)polymorphism, the realization of specific (pseudo‐)polymorphic phases and associated boundary structures is an efficient route to enhance material performance for energy conversion and electromechanical applications. Here, this work applies the pseudopolymorphic phase (PP) concept to a thermoelectric copper sulfide, Cu2‐xS (x ≤ 0.25), via CuBr2 doping. A peak ZT value of 1.25 is obtained at 773 K in Cu1.8S + 3 wt% CuBr2, which is 2.3 times higher than that of a pristine Cu1.8S sample. Atomic‐resolution scanning transmission electron microscopy confirms the transformation of pristine Cu1.8S low digenite into PP‐engineered high digenite, as well as the formation of (semi‐)coherent interfaces between different PPs, which is expected to enhance phonon scattering. The results demonstrate that PP engineering is an effective approach for achieving improved thermoelectric performance in Cu‐S compounds. It is also expected to be useful in other materials.
A material consisting of the same substance can crystalize in different structural phases with (or without) identical composition, termed “(pseudo)polymorphic phases” (PPs). This work applies this PP concept to copper sulfides to improve thermoelectric performance. The resulting PPs maintain electron transport and enhance phonon scattering. A peak ZT value of 1.25 is obtained, which is 2.3 times higher than that of pristine copper sulfide.
A new numerical-based fragility relation for cast iron (CI) pipelines with lead-caulked joints subjected to seismic body-wave propagation is proposed in this article. Two-dimensional 1600-m-length ...finite element models for pipelines buried in sand are developed in OpenSees. Parametric analysis is performed to investigate the influence of various parameters on the damage estimates of the buried pipelines. Numerical analyses are conducted to estimate the repair rates (RR) for CI pipelines subjected to wave propagation. The predictive model for RR is thus developed based on the numerical results and the Gaussian Process Regression approach. The model developed employs four predictor variables, namely, the peak particle velocity and wave propagation velocity along axial direction, the maximum soil shear force per unit length, and the outer diameter of pipelines, exhibiting desirable performance in terms of predictive efficiency and generalization. The performance of the developed relation is compared to several existing fragility relations. The new fragility relation can be used to estimate RR for CI pipelines with lead-caulked joints with outer diameters ranging from 169 to 1554 mm subjected to seismic body-wave propagation.
•Bi2Te3 +1 wt% Ru bulk sample was prepared by hand milling and SPS using commercial Bi2Te3 ingot.•A ZT peak reaches 0.93 at 150 °C for Bi2Te3 +1 wt% Ru sample which is 45.3% higher than that of ...pristine.•Vickers hardness reaches 2.38 GPa for Bi2Te3 +1 wt% Ru sample which is the highest in Bi2Te3 system.
Recently, researchers have been exploring the optimization of the thermoelectric properties of composite materials. Composite technology with many successful cases of enhancement in thermoelectric properties have been confirming effectively to optimize thermoelectric materials. In this study, Ru nano-micro composite particles were successfully introduced in commercial bismuth telluride (Bi2Te3) as second phase to simultaneously optimize the thermoelectric and mechanical properties. In a Bi2Te3 sample containing 1 wt% Ru (+1 wt% Ru), the ZT peak was measured to be 0.93 (at 150 °C) and the maximum Vickers hardness was measured to be 2.38 GPa. These values exceeded the values of a pure sample by 45.3% and 36%, respectively. The average ZT of the +1 wt% Ru sample at 50–200 °C was 0.86, which is comparable with the Bi2Te3-xSex system. By varying the Ru content, the components, microstructure, thermoelectric and mechanical properties of Bi2Te3 were manipulated and their interdependence demonstrated. The extent to which the thermoelectric and mechanical properties of Bi2Te3 can be optimized, via Ru compositing and nano-Bi2Te3 producing, is related by the complex nano-micro composite structure. The superior thermoelectric properties of composite materials hold great the commercial value and may reduce the input of raw materials.
The decrease in lattice thermal conductivity is one of the most effective methods for enhancing thermoelectric properties. Achieving lattice thermal conductivity close to the theoretical limit is ...extremely difficult while maintaining an impressive power factor. By introducing ultrafine bismuth sulfide nanograins, strong phonon scattering was generated by associated multiscale lattice defects to further gain a low lattice thermal conductivity of 0.244 W/m/K approaching Clarke's limitation of 0.242 W/m/K. Simultaneously, the electrical conductivity was increased by S diffusion and suppression of the antisite defects, and a high power factor was maintained to produce an improved ZT peak of 1.2 at 473 K for the Bi2Te2.7Se0.3 + 1 wt% Bi2S3 #2 sample. This sample was used to fabricate a small device with a p-leg, and the direct conversion efficiency reached 4.39%. Inverse changes in hardness and Young's modulus in conjunction with Bi2S3 content are first reported in thermoelectric materials, which has potential assistance in synchronously improving their mechanical and thermoelectric properties.
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This study aimed to elucidate the role of microRNA-503 (miR-503) in pancreatic cancer (PC) progression and the underlying regulatory mechanisms. We acquired miR-503-3p and miR-503-5p expression data ...along with survival times of PC and normal samples from the UCSC Xena database. Using the t-test, we compared the expression of miR-503-3p and miR-503-5p between PC and normal samples, and evaluated their prognostic significance via Kaplan-Meier survival analysis. The expression of miR-503-5p in PC cells was detected by quantitative PCR. We subsequently overexpressed miR-503-5p in PC cells and examined cell viability, apoptosis, and migration through CCK8 assay, flow cytometry, and Transwell assay, respectively. Potential functional targets were identified using miRTarBase and validated by dual-luciferase reporter assay. Both miR-503-3p and miR-503-5p expression were found to be downregulated in PC; however, only miR-503-5p was linked to cancer prognosis based on public data. In vitro experiments demonstrated that overexpression of miR-503-5p substantially decreased cell viability, induced apoptosis, caused G0/G1 arrest, and inhibited cell migration. miR-503-5p was found to target cyclin E2 (CCNE2), and overexpression of CCNE2 could counteract the effects of miR-503-5p on PC cells. Conclusion: The downregulation of miR-503-5p enhances the progression of PC by targeting CCNE2. The detection of miR-503-5p expression may provide valuable insights for the prevention and prognostic evaluation of PC.
Stimulation-Based Control of Dynamic Brain Networks Muldoon, Sarah Feldt; Pasqualetti, Fabio; Gu, Shi ...
PLOS computational biology/PLoS computational biology,
09/2016, Volume:
12, Issue:
9
Journal Article
Peer reviewed
Open access
The ability to modulate brain states using targeted stimulation is increasingly being employed to treat neurological disorders and to enhance human performance. Despite the growing interest in brain ...stimulation as a form of neuromodulation, much remains unknown about the network-level impact of these focal perturbations. To study the system wide impact of regional stimulation, we employ a data-driven computational model of nonlinear brain dynamics to systematically explore the effects of targeted stimulation. Validating predictions from network control theory, we uncover the relationship between regional controllability and the focal versus global impact of stimulation, and we relate these findings to differences in the underlying network architecture. Finally, by mapping brain regions to cognitive systems, we observe that the default mode system imparts large global change despite being highly constrained by structural connectivity. This work forms an important step towards the development of personalized stimulation protocols for medical treatment or performance enhancement.
Artificial ground freezing (AGF) has been widely used as a temporary soil stabilization and waterproofing technique in geotechnical practices (e.g., tunnel construction). Many sources of uncertainty ...exist during AGF. Firstly, groundwater seepage flow can adversely affect the freezing efficacy. Secondly, freeze pipe inclination inevitably occurs during installation, which is likely to yield an unfrozen path and elevate construction risk. Thirdly, as a key soil parameter, the spatial variability in thermal conductivity can also affect the freezing process. In this work, a unit cell model of freeze pipes is established by a coupled thermo-hydraulic finite element method to examine the effects of these sources of uncertainty. The pipe inclination is considered in the unit cell model by prescribing various values of freeze pipe spacing. The thermal conductivity of soil solid is simulated as a three-dimensional lognormal random field to account for the spatial variability of soil. Results are tabulated to evaluate the additional freezing time required in the AGF system due to the existence of these uncertainties. The findings are capable of determining a reasonable range of freeze pipe spacings and the corresponding critical seepage velocity, and can offer practitioners a rule of thumb for estimating freeze pipe spacing.
In this study, a 34‐MW tubular hydro‐generator was selected as the study example. For the electromagnetic field–circuit coupling analysis model, the effects of the ideal DC voltage and current ...sources (i.e. two models of the rotor excitation power supply) on the no‐load voltage waveform quality and the damper winding loss calculation results were studied by considering the influence of the electromagnetic induction of the rotor excitation winding. The obtained results provide direct and effective theoretical support and technical reference for improving the accuracy and rationality of the calculation results of the electromagnetic performance parameters and the analysis, design, manufacturing and operating level of such generators.
For the electromagnetic field–circuit coupling analysis model of hydro‐generator, by considering the influence of the electromagnetic induction of the rotor excitation winding, the effects of the ideal DC current source and the ideal DC voltage source on the no‐load voltage waveform quality and the damper winding loss calculation results are examined. The obtained results can serve as effective theoretical support and technical reference that would improve the accuracy of the calculation results of the electromagnetic performance parameters. The findings will also improve the analysis, design, and manufacturing level of hydro‐generators.
Adult human cognition is supported by systems of brain regions, or modules, that are functionally coherent at rest and collectively activated by distinct task requirements. However, an understanding ...of how the formation of these modules supports evolving cognitive capabilities has not been delineated. Here, we quantify the formation of network modules in a sample of 780 youth (aged 8–22 y) who were studied as part of the Philadelphia Neurodevelopmental Cohort. We demonstrate that the brain’s functional network organization changes in youth through a process of modular evolution that is governed by the specific cognitive roles of each system, as defined by the balance of within- vs. between-module connectivity. Moreover, individual variability in these roles is correlated with cognitive performance. Collectively, these results suggest that dynamic maturation of network modules in youth may be a critical driver for the development of cognition.
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