For several decades, thermoelectric advancements have largely relied on the reduction of lattice thermal conductivity (κL). According to the Boltzmann transport theory of phonons, κL mainly depends ...on the specific heat, the velocity, and the scattering of phonons. Intensifying the scattering rate of phonons is the focus for reducing the lattice thermal conductivity. Effective scattering sources include 0D point defects, 1D dislocations, and 2D interfaces, each of which has a particular range of frequencies where phonon scattering is most effective. Because acoustic phonons are generally the main contributors to κL due to their much higher velocities compared to optical phonons, many low‐κL thermoelectrics rely on crystal structure complexity leading to a small fraction of acoustic phonons and/or weak chemical bonds enabling an overall low phonon propagation velocity. While these thermal strategies are successful for advancing thermoelectrics, the principles used can be integrated with approaches such as band engineering to improve the electronic properties, which can promote this energy technology from niche applications into the mainstream.
Phonon transport is reviewed, considering its guiding principles, and including a summary of newly proven strategies and further considerations for κL‐minimization. Most of the strategies presented can effectively reduce the lattice thermal conductivity, which leads to a great increase in thermoelectric performance in many materials.
Taking Shenzhen stock as an example, this paper explores the opportunity for high returns in the stock market through the study of the price-to-earnings ratio, and finally determines the optimal ...stock market decision. By trying different numerical value on the price-to-earnings ratio and calculating the total return based on historical data, it is obtained that buying when the price-to-earnings ratio is lower than 156 and selling when it is higher than 224.5 can get the highest return. However, in the following general study of high-yield decisions, it is found that all decisions are concentrated in the rapid rise in stock prices caused by “reform cattle” in 2015 in China. Therefore, in order to study more general strategies, the scope and difference of price-to-earnings ratio are redrawn and two feasible decision-making methods are obtained: risk-averse decision-making and risk-preference decision-making. Both two decisions are suitable in a relatively stable stock market, and can earn almost the same profit theoretically, so investors can choose any of them based on their preferences.
Low-grade heat accounts for >50% of the total dissipated heat sources in industries. An efficient recovery of low-grade heat into useful electricity not only reduces the consumption of fossil-fuels ...but also releases the subsequential environmental-crisis. Thermoelectricity offers an ideal solution, yet low-temperature efficient materials have continuously been limited to Bi
Te
-alloys since the discovery in 1950s. Scarcity of tellurium and the strong property anisotropy cause high-cost in both raw-materials and synthesis/processing. Here we demonstrate cheap polycrystalline antimonides for even more efficient thermoelectric waste-heat recovery within 600 K than conventional tellurides. This is enabled by a design of Ni/Fe/Mg
SbBi and Ni/Sb/CdSb contacts for both a prevention of chemical diffusion and a low interfacial resistivity, realizing a record and stable module efficiency at a temperature difference of 270 K. In addition, the raw-material cost to the output power ratio in this work is reduced to be only 1/15 of that of conventional Bi
Te
-modules.
GeTe-based alloys have been intensively considered as p-type thermoelectrics for about 50 years, yet existing literature barely discussed the thermoelectric properties of pristine GeTe at high ...temperatures (300–800 K). This work first backs to a fundamental understanding on the thermoelectric transport properties inherent to p-type GeTe, based on more than 50 samples synthesized with expected carrier concentrations ranging from 1 × 1020 to 3 × 1021 cm–3. A thermoelectric figure of merit zT as high as ∼1.7 is found inherent to this compound when it is optimally doped with a Hall carrier concentration of 2.2 ± 10% × 1020 cm–3, offering a reference substance to expose the origins for the high zT in historical GeTe-based alloys. Guided by the above knowledge, further alloying Te with Se in samples with an optimal carrier concentration enables a reduction on the lattice thermal conductivity by ∼40% and eventually leads to a further enhancement on zT (up to 2.0) by ∼20%. This work demonstrates not only GeTe as an inherently high performance thermoelectric matrix compound but also its availability for further improvements by additional strategies.
Nature provides an almost limitless supply of sources that inspire scientists to develop new materials with novel applications and less of an environmental impact. Recently, much attention has been ...focused on preparing natural‐product‐derived carbon dots (NCDs), because natural products have several advantages. First, natural products are renewable and have good biocompatibility. Second, natural products contain heteroatoms, which facilitate the fabrication of heteroatom‐doped NCDs without the addition of an external heteroatom source. Finally, some natural products can be used to prepare NCDs in ways that are very green and simple relative to traditional methods for the preparation of carbon dots from man‐made carbon sources. NCDs have shown tremendous potential in many fields, including biosensing, bioimaging, optoelectronics, and photocatalysis. This Review addresses recent progress in the synthesis, properties, and applications of NCDs. The challenges and future direction of research on NCD‐based materials in this booming field are also discussed.
On the dot: In this Review, methods for the preparation of natural‐product‐derived carbon dots (NCDs) are summarized. Then, the physical and optical properties of the NCDs are outlined, and finally, several applications of NCDs are noted, including their use in sensors, bioimaging, and solar cells and their use as catalysts.
Optimization of carrier concentration plays an important role on maximizing thermoelectric performance. Existing efforts mainly focus on aliovalent doping, while intrinsic defects (e.g., vacancies) ...provide extra possibilities. Thermoelectric GeTe intrinsically forms in off-stoichiometric with Ge-vacancies and Ge-precipitates, leading to a hole concentration significantly higher than required. In this work, Sb2Te3 having a smaller cation-to-anion ratio, is used as a solvend to form solid solutions with GeTe for manipulating the vacancies. This is enabled by the fact that each substitution of 3 Ge2+ by only 2 Sb3+ creates 1 Ge vacancy, because of the overall 1:1 cation-to-anion ratio of crystallographic sites in the structure and by the charge neutrality. The increase in the overall Ge-vacancy concentration facilitates Ge-precipitates to be dissolved into the matrix for reducing the hole concentration. In a combination with known reduction in hole concentration by Pb/Ge-substitution, a full optimization on hole concentration is realized. In addition, the resultant high-concentration point defects including both vacancies and substitutions strongly scatter phonons and reduce the lattice thermal conductivity to the amorphous limit. These enable a significantly improved thermoelectric figure of merit at working temperatures of thermoelectric GeTe.
Liquid crystal elastomers (LCEs) with intrinsic anisotropic strains are reversible shape‐memory polymers of interest in sensor, actuator, and soft robotics applications. Rapid gelation of LCEs is ...required to fix molecular ordering within the elastomer network, which is essential for directed shape transformation. A highly efficient photo‐cross‐linking chemistry, based on two‐step oxygen‐mediated thiol–acrylate click reactions, allows for nearly instant gelation of the main‐chain LCE network upon exposure to UV light. Molecular orientation from the pre‐aligned liquid crystal oligomers can be faithfully transferred to the LCE films, allowing for preprogrammed shape morphing from two to three dimensions by origami‐ (folding‐only) and kirigami‐like (folding with cutting) mechanisms. The new LCE chemistry also enables widely tunable physical properties, including nematic‐to‐ isotropic phase‐transition temperatures (TN‐I), glassy transition temperatures (Tg), and mechanical strains, without disrupting the LC ordering.
Liquid crystal (LC) elastomers are generated by a thiol–acrylate click reaction mediated by ambient oxygen. Superfast gelation occurs upon photopolymerization of liquid crystalline diacrylate monomers and dithiol‐terminated oligomers, leading to instant locking of the molecular order of the liquid crystals and allowing for programmable shape transformation from two to three dimensions.
Objectives
Antiviral treatments for Bell palsy have been widely used, but there is no definite conclusion of which is the most effective antiviral drug. We conducted a systematic review of randomized ...controlled trials (RCTs) including network meta-analysis to investigate the comparative effectiveness of antiviral treatments for Bell palsy.
Data
RCTs comparing effectiveness between antiviral treatments and placebo were included. Risk of bias within and across studies was assessed with the Cochrane tool and the GRADE approach, respectively. Random-effects pairwise meta-analyses were conducted, followed by network meta-analysis.
Sources
Three electronic databases were searched from inception to May 18, 2020.
Study selection
11 trials and 3393 patients with four arms and eleven contrasts were included.
Results
Significant differences were observed between placebo and famciclovir with respect to overall recovery and no statistically significant differences were found from other comparisons. Treatment ranking based on the evidence network indicated that famciclovir shared the best results, followed by valacyclovir, acyclovir, and finally placebo. Adverse events of famciclovir were too rare and slight to be analyzed. Our confidence in pairwise comparisons was moderate to low, due to study limitations, inconsistency, and imprecision; our confidence in ranking was moderate, due to study limitations. Inconsistency is not deemed to exist by a loop-specific approach and node-splitting procedure. Results of exploring publication bias are satisfying.
Conclusions
According to pairwise and network comparisons, famciclovir could be better than placebo and the effectiveness of other antiviral treatments are similar. For clinical efficacy, famciclovir obtains the best recovery rate of facial function for Bell palsy. Acyclovir has the lowest rate of synkinesis, though, it is not adequately recommended and more superior trails are needed in the future.
Energy Performance Contracting, a type of contractual arrangements between clients and Energy Service Companies, is nowadays a key vehicle to implement energy efficiency measures in existing ...buildings. As well-designed contracts contribute to establishing partnerships between clients and Energy Service Companies and to promoting the Energy Performance Contracting's further development, this work was aimed to figure out the optimal solutions of the contract terms under two typical business models (the Shared Savings Model and the Guaranteed Savings Model). Based on game-theoretical methods, the non-cooperative scenario was considered at first because both the client and the Energy Service Companies are self-profit-oriented. However, the non-cooperative contracts are not so efficient as they cannot bring the maximal project profit. Thus, the cooperative game models where the maximal project profits were allocated between the contract parties were set up. The differences between the non-cooperative and the cooperative scenarios and the impacts of the parameters in the models were also discussed. The frameworks presented possible solutions for the contract-design problem under the Energy Performance Contracting and instructed the contract parties to conclude the most proper contracts.
Curcumin exerts a suppressive effect in tumor growth by acting as a modulator of multiple molecular targets. Circular RNA hsa_circ_0007580 (circ-PRKCA) accelerates the tumorigenesis of non-small cell ...lung cancer (NSCLC). However, whether curcumin can regulate circ-PRKCA to inhibit NSCLC progression is unclear.
Cell viability, colony formation, apoptosis, migration, and invasion were analyzed using Cell Counting Kit-8 (CCK-8), plate clone, flow cytometry, or transwell assay. Expression of circ-PRKCA, microRNA (miR)-384, and ITGB1 mRNA (integrin subunit beta 1) mRNA were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Curcumin repressed NSCLC growth through regulating circ-PRKCA expression was validated by xenograft assay. The targeting relationship between circ-PRKCA or ITGB1 and miR-384 was verified by dual-luciferase reporter assay. The level of ITGB1 protein was measured by western blotting.
Circ-PRKCA and ITGB1 expression were elevated in NSCLC tissues and cells, but miR-384 had an opposing tendency. After curcumin treatment, the expression tendency of circ-PRKCA, miR-384, and ITGB1 in NSCLC cells was overturned. Furthermore, curcumin impeded viability, colony formation, migration, invasion, and accelerated apoptosis of NSCLC cells, but these impacts were partially reversed by circ-PRKCA elevation, miR-384 downregulation, or ITGB1 overexpression. Also, the inhibitory effect of curcumin on xenograft tumor was further enhanced after circ-PRKCA knockdown. Notably, circ-PRKCA regulated ITGB1 expression through sponging miR-384 in curcumin-treated NSCLC cells.
Curcumin inhibited NSCLC growth through downregulating circ-PRKCA, which regulated ITGB1 expression by adsorbing miR-384. This study provided a new mechanism to understand how curcumin inhibited the progression of NSCLC.
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