Improving thermoelectric performance by constructing a SnTe/ZnO core-shell structure.

SnTe is becoming a new research focus as an intermediate temperature thermoelectric material for its environment-friendly property. Herein, the SnTe/ZnO core-shell structure prepared by a facile hydrothermal method is firstly constructed to enhance the thermoelectric performance. The characterization results demonstrate that ZnO nanosheets are coated on the surface of SnTe particles by in situ synthesis and converted into ZnO nano-dots by spark plasma sintering. The energy barriers built by the SnTe/ZnO core-shell structure improve the Seebeck coefficient effectively. Additionally, the increased density of interfaces induced by ZnO can effectively scatter low/medium frequency phonons, reducing the lattice thermal conductivity in the low/medium temperature region. Further, the point defects caused by Cu2Te-alloying strengthen the scattering of high frequency phonons. The lattice thermal conductivity reaches 0.48 W m-1 K-1, which is close to the amorphous limit of pristine SnTe. As a result, a peak ZT value of 0.94 is achieved at 823 K for SnTe(Cu2Te)0.06-1.5% ZnO, benefiting from the synergistic optimization of thermal and electrical properties. This provides a new idea for exploring an optimization strategy of thermoelectric performance.

Enhancing the thermoelectric properties of SnTe via introducing PbTe@C core-shell nanostructures.

SnTe is an emerging IV-VI metal chalcogenide, but its low Seebeck coefficient and high thermal conductivity mainly originating from the high hole concentration limit its thermoelectric performance. In this work, an amorphous carbon core-shell-coated PbTe nanostructure prepared by a "bottom-up" method is first incorporated into the Sn1-ySbyTe matrix to enhance the thermoelectric performance of SnTe. The square-like PbTe nanoparticles maintain their original cubic morphology and do not grow up obviously after the SPS process due to the coating of the C layer, bringing about the formation of nanopores locally, while Sb alloying induces Sb point defects and Sb-rich precipitates. All these unique hierarchical microstructures finally lead to an ultralow lattice thermal conductivity (∼0.48 W-1 m-1 K-1) approaching amorphous limits (∼0.40 W-1 m-1 K-1). In addition, the incorporation of PbTe@C core-shell nanostructures decreases the carrier mobility obviously with a slight loss in carrier concentration, resulting in the deterioration of electrical properties to a certain extent. As a result, a peak thermoelectric figure of merit (ZT) of 1.07 is achieved for Sn0.89Sb0.11Te-5%PbTe@C at 873 K, which is approximately 154.76% higher than that of pristine SnTe. This work provides a new strategy to enhance the thermoelectric performance of SnTe and also offers a new insight into other related thermoelectric systems.

Ultralow Lattice Thermal Conductivity in SnTe by Incorporating InSb.

Herein, a series of (Sn1.06Te)1-x-(InSb)x (x = 0, 0.025, 0.05, 0.075) samples are fabricated, and their thermoelectric performances are studied. The all-scale structure defects containing the atomic-scale In doping defects, the nanoscale Sb precipitates, and the mesoscale grain boundary scatter phonons collectively in a wide range of frequencies to give the ultralow lattice thermal conductivity. Concurrently, the incorporation of InSb decreases carrier concentration with marginal loss in carrier mobility, resulting in a little variation of electrical properties over a wide temperature range. The significantly decreased thermal conductivity and the preserved high power factor lead to a maximum ZT value of ∼0.84 at 823 K in the (Sn1.06Te)0.95(InSb)0.05 sample. This strategy of rapidly constructing all-scale structure defects could be applied to other thermoelectric systems to enhance thermoelectric performance.

Quality Appraisal of Guidelines on Cancer-Associated Thrombosis Using AGREE II Instrument and Analysis of Current Status of New Oral Anticoagulants.

Cancer-associated thrombosis (CAT) studies have increased in recent years and the quality of guidelines to guide the clinical practice of CAT prevention and treatment becomes crucial. The therapy status of new oral anticoagulants (NOACs) has been established in some thrombotic diseases, but the evidence for CAT remains unconvincing. The aim of this research is to evaluate the quality of CAT guidelines and discuss the role of NOAC in CAT. A search of articles was performed using PubMed/Medline, Chinese National Knowledge Infrastructure, and other authoritative websites. Search terms included guideline or guidance, consensuses, cancer, and thrombosis. Appraisal of Guidelines for Research & Evaluation II (AGREE II) tool was used to evaluate the qualities of the guidelines. A total of 19 guidelines were screened out and evaluated, of which 8 were recommended, 5 were recommended after revision, and 6 were not recommended. For prevention and treatment of CAT, low-molecular-weight heparin is the most recommended, followed by vitamin K antagonist, unfractionated heparin, fondaparinux, and aspirin. New oral anticoagulant is optional in some cases of CAT treatment. Based on AGREE II assessment tool, the quality of CAT guidelines is inconsistent. Attention should be drawn to the quality of CAT guidelines during clinical practice. The role of NOAC in the treatment of CAT is gradually established but requires more supporting evidence from future clinical trials.

Estimation for sparse vegetation information in desertification region based on Tiangong-1 hyperspectral image.

In order to estimate the sparse vegetation information accurately in desertification region, taking southeast of Sunite Right Banner, Inner Mongolia, as the test site and Tiangong-1 hyperspectral image as the main data, sparse vegetation coverage and biomass were retrieved based on normalized difference vegetation index (NDVI) and soil adjusted vegetation index (SAVI), combined with the field investigation data. Then the advantages and disadvantages between them were compared. Firstly, the correlation between vegetation indexes and vegetation coverage under different bands combination was analyzed, as well as the biomass. Secondly, the best bands combination was determined when the maximum correlation coefficient turned up between vegetation indexes (VI) and vegetation parameters. It showed that the maximum correlation coefficient between vegetation parameters and NDVI could reach as high as 0.7, while that of SAVI could nearly reach 0.8. The center wavelength of red band in the best bands combination for NDVI was 630nm, and that of the near infrared (NIR) band was 910 nm. Whereas, when the center wavelength was 620 and 920 nm respectively, they were the best combination for SAVI. Finally, the linear regression models were established to retrieve vegetation coverage and biomass based on Tiangong-1 VIs. R2 of all models was more than 0.5, while that of the model based on SAVI was higher than that based on NDVI, especially, the R2 of vegetation coverage retrieve model based on SAVI was as high as 0.59. By intersection validation, the standard errors RMSE based on SAVI models were lower than that of the model based on NDVI. The results showed that the abundant spectral information of Tiangong-1 hyperspectral image can reflect the actual vegetaion condition effectively, and SAVI can estimate the sparse vegetation information more accurately than NDVI in desertification region.

[Analysis of sensitive spectral bands for burning status detection using hyper-spectral images of Tiangong-01].

To obtain the sensitive spectral bands for detection of information on 4 kinds of burning status, i. e. flaming, smoldering, smoke, and fire scar, with satellite data, analysis was conducted to identify suitable satellite spectral bands for detection of information on these 4 kinds of burning status by using hyper-spectrum images of Tiangong-01 (TG-01) and employing a method combining statistics and spectral analysis. The results show that: in the hyper-spectral images of TG-01, the spectral bands differ obviously for detection of these 4 kinds of burning status; in all hyper-spectral short-wave infrared channels, the reflectance of flaming is higher than that of all other 3 kinds of burning status, and the reflectance of smoke is the lowest; the reflectance of smoke is higher than that of all other 3 kinds of burning status in the channels corresponding to hyper-spectral visible near-infrared and panchromatic sensors. For spectral band selection, more suitable spectral bands for flaming detection are 1 000.0-1 956.0 and 2 020.0-2 400.0 nm; the suitable spectral bands for identifying smoldering are 930.0-1 000.0 and 1 084.0-2 400.0 nm; the suitable spectral bands for smoke detection is in 400.0-920.0 nm; for fire scar detection, it is suitable to select bands with central wavelengths of 900.0-930.0 and 1 300.0-2 400.0 nm, and then to combine them to construct a detection model.

A nanocrystalline Sm-Co compound for high-temperature permanent magnets.

The inherently high magnetic anisotropy and nanoscale grain size in a Sm5Co19 compound result in an intrinsic coercivity far higher than those of known Sm-Co compounds prior to orientation treatment. The combination of ultrahigh intrinsic coercivity, high Curie temperature and low coercivity temperature coefficient of nanocrystalline Sm5Co19 as a single phase material shows it to be a very promising compound to develop outstanding high-temperature permanent magnets.

Crystal structure and magnetic properties of ultrafine nanocrystalline SmCo3 compound.

The single-phase ultrafine nanocrystalline SmCo(3) compound with a high coercivity of 33 kOe and a Curie temperature of 925 K was prepared using a simple and efficient method, which took advantages of the concurrent processes of nanocrystallization and densification during spark plasma sintering. The crystal structure of the nanocrystalline SmCo(3) compound was constructed. As compared with the conventional microcrystalline SmCo(3) compound, a large axial ratio c/a = 4.920 and an expansion of the unit cell volume of 2.97% were obtained in the lattice structure of the nanocrystalline SmCo(3). The relationship between the magnetic properties and the nanocrystalline structure was analyzed. A specific magnetic transition from the weak ferromagnetic to the strong ferromagnetic state was discovered in the nanocrystalline SmCo(3) compound, which was considered to be related to the large anisotropic strain in the crystal lattice.

Preparation and properties characterization of the single-phased Sm2Co17, nanocrystalline alloy.

A novel route for the preparation of the single-phased Sm2Co17 nanocrystalline bulk with ultrafine grain sizes was proposed. It was found that the nanocrystalline Sm20Co17 has a hexagonal crystal structure at the room temperature, which shows a different thermal stability from the conventional polycrystalline alloy. The intrinsic coercivity of the nanocrystalline Sm2Co17 with a hexagonal crystal structure was greatly increased as compared with the single-phased polycrystalline alloy with a rhombohedral structure. The microhardness and the elastic modulus of the nanocrystalline Sm2Co17 bulk were increased as high as 1.8 and 2.6 times, respectively, when compared with the polycrystalline parent alloy.

Preparation and characterization of dysprosium (Dy) ultrafine nanocrystalline structures.

By combining the inert-gas condensation with the SPS technology in an entirely closed system with the oxygen concentration below 0.5 ppm, the pure Dy bulk with the ultrafine nanocrystalline structure has been prepared. Thus a novel and efficient route of preparing nano rare-earth metals, as well as metallic nanomaterials that are highly reactive in the air, is proposed. The thermal, physical and mechanical properties of the prepared ultrafine nanocrystalline Dy bulk have been characterized and compared with those of the conventional raw polycrystalline bulk. It is found that in the nanocrystalline Dy bulk, the starting temperature of phase transformation from hexagonal to rhombohedral crystal structure is reduced by 70 degrees C in comparison with that of the raw polycrystalline bulk. The electrical resistivity of the ultrafine nanocrystalline bulk is slightly increased by a few percent as compared with that of the polycrystalline bulk, while the thermal conductivity is reduced by 28-35%. The microhardness and the elastic modulus of the ultrafine nanocrystalline Dy bulk are found to be remarkably improved as compared with those of the raw polycrystalline bulk, e.g., the microhardness and the elastic modulus are approximately 2.4 and 2.0 times as high as those of the raw polycrystalline bulk, respectively.

Preparation and characterization of rare-earth bulks with controllable nanostructures.

The preparation and characterization of pure rare-earth-metal bulks with controllable nanostructures are reported in this paper. A novel 'oxygen-free' in situ synthesis technique that combines inert-gas condensation with spark plasma sintering (SPS) technology is proposed. Taking into account the special mechanisms of SPS consolidation and the scale effects of nanoparticles, we introduced practical procedures for preparing rare-earth bulks of amorphous, mixed amorphous and nanocrystals, and nanocrystalline microstructures, respectively. Compared with the conventional polycrystalline bulk, these nanostructured bulks exhibit substantially improved physical and mechanical properties. This technique enables comprehensive studies on the microstructures and properties of a large variety of nanostructured metallic materials that are highly reactive in the air.

Incontinuous grain growth in cobalt nanocrystalline powders prepared by high-energy mechanical milling.

Cobalt nanocrystalline powders with the average grain size of about 17 nm were prepared by high-energy mechanical milling. Grain growth in highly pure and particle-containing nanocrystalline Co powders were investigated respectively by a series of annealing experiments at different temperatures. The characteristics of incontinuous grain growth were found in both the pure and the particle-containing nanocrystalline powders. It is proposed by the authors that the sharp increase in nanograin size in the transition between the low and high temperature regions is a result of enhanced grain growth promoted by the stored energy as a supplied driving force, based on which rapid grain growth occurs through a particular dominant mechanism of nanograin rotations in the pure nanocrystalline powders, and that through off-pinning of grain boundaries in the particle-containing nanocrystalline powders.