We report on the effect of germanium (Ge) coatings on the thermal transport properties of silicon (Si) nanowires using nonequilibrium molecular dynamics simulations. Our results show that a simple ...deposition of a Ge shell of only 1 to 2 unit cells in thickness on a single crystalline Si nanowire can lead to a dramatic 75% decrease in thermal conductivity at room temperature compared to an uncoated Si nanowire. By analyzing the vibrational density states of phonons and the participation ratio of each specific mode, we demonstrate that the reduction in the thermal conductivity of Si/Ge core−shell nanowire stems from the depression and localization of long-wavelength phonon modes at the Si/Ge interface and of high frequency nonpropagating diffusive modes.
Following the discovery of high-entropy alloys, high-entropy oxides have gained considerable interest due to their unconventional structural characteristics and versatile functional properties for ...promising applications. Via synchrotron radial x-ray diffraction in a diamond anvil cell, the mechanical strength and deformation behavior of a typic high-entropy oxide (Mg,Co,Ni,Cu,Zn)O with a rock-salt structure under extreme compression has been investigated in situ. This compound in a polycrystalline state shows a large elastic anisotropy at the initial compression stage and then gradually becomes isotropic at around 21.4 GPa, similar with the behavior of MgO. Based on the lattice strain order conversion and texture evolution under compression, a dominant slip system transition from {100} to {110}<1–10> is proposed in this high-entropy oxide. This work deepens our understanding on the role of chemical disorder in the mechanical properties of entropy-stabilized oxides, which would be indispensable to the design of advanced structural ceramics with optimal strength-to-ductility ratio.
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Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and ...photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the thermal conductivity of bilayer graphene using equilibrium molecular dynamics simulations. It is revealed that, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, however, for the regularly bonded bilayer graphene structure the thermal conductivity possesses unexpectedly non-monotonic dependence on the interlayer bonding density. The results suggest that the thermal conductivity of bilayer graphene depends not only on the interlayer bonding density, but also on the detailed topological configuration of the interlayer bonding. The underlying mechanism for this abnormal phenomenon is identified by means of phonon spectral energy density, participation ratio and mode weight factor analysis. The large tunability of thermal conductivity of bilayer graphene through rational interlayer bonding arrangement paves the way to achieve other desired properties for potential nanoelectronics applications involving graphene layers.
Infrared PbS colloidal quantum dot (CQD)-based materials receive significant attention because of its unique properties. The PbS CQD ink that originates from ligand exchange of CQDs is highly ...potential for efficient and stable infrared CQD solar cells (CQDSCs) using low-temperature solution-phase processing. In this review, we present a comprehensive overview of CQD inks for the development of efficient infrared solar cells, which can effectively harvest the photons from the infrared wavelength region of the solar spectrum, including the importance of infrared absorbers for solar cells, the unique properties of CQDs, ligand-exchange determined CQD inks, and related photovoltaic performance of CQDSCs. Finally, we present a brief conclusion, and the possible challenges and opportunities of the CQD inks are discussed in-depth to further develop highly efficient and stable infrared solar cells.
Photon Absorption; Colloids; Optical Property; Optical Materials
Sparse MRI has been introduced to reduce the acquisition time and raw data size by undersampling the k-space data. However, the image quality, particularly the contrast to noise ratio (CNR), ...decreases with the undersampling rate. In this work, we proposed an interpolated Compressed Sensing (iCS) method to further enhance the imaging speed or reduce data size without significant sacrifice of image quality and CNR for multi-slice two-dimensional sparse MR imaging in humans. This method utilizes the k-space data of the neighboring slice in the multi-slice acquisition. The missing k-space data of a highly undersampled slice are estimated by using the raw data of its neighboring slice multiplied by a weighting function generated from low resolution full k-space reference images. In-vivo MR imaging in human feet has been used to investigate the feasibility and the performance of the proposed iCS method. The results show that by using the proposed iCS reconstruction method, the average image error can be reduced and the average CNR can be improved, compared with the conventional sparse MRI reconstruction at the same undersampling rate.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Semitransparent solar cells (SSCs) can open new photovoltaic applications in many areas. However, because of the fundamental trade-off between optical transparency and photovoltaic efficiency, it is ...of special importance to minimize additional optical losses such as from reflectance and parasitic absorption. In this work, a semitransparent colloidal quantum dot solar cell (SCQDSC) with high efficiency, transparency and stability is investigated using a coupled theoretical and experimental approach. Extensive numerical simulations and experimental investigations are performed for optimizing the device transparency and efficiency simultaneously. The results show that the transparency and efficiency are largely enhanced as a result of lowering the optical losses in the SCQDSC, and the device exhibits a high efficiency of 7.3% with an average visible transmittance of 20.4%. Importantly, the SCQDSC exhibits very good stability under long term continuous illumination and the unencapsulated SCQDSCs show no large degradation in performance during storage for 70 days under ambient conditions. These findings suggest that the SCQDSC has high potential for applications, such as for building integrated photovoltaics, automobiles or screens. Moreover, this work also provides practical and quantitative guidelines for further enhancing the SSC performance.
Liquid‐state ligand exchange provides an efficient approach to passivate a quantum dot (QD) surface with small binding species and achieve a QD ink toward scalable QD solar cell (QDSC) production. ...Herein, experimental studies and theoretical simulations are combined to establish the physical principles of QD surface properties induced charge carrier recombination and collection in QDSCs. Ammonium iodide (AI) is used to thoroughly replace the native oleic acid ligand on the PbS QD surface forming a concentrated QD ink, which has high stability of more than 30 d. The ink can be directly applied for the preparation of a thick QD solid film using a single deposition step method and the QD solid film shows better characteristics compared with that of the film prepared with the traditional PbX2 (X = I or Br) post‐treated QD ink. Infrared light‐absorbing QDSC devices are fabricated using the PbS‐AI QD ink and the devices give a higher photovoltaic performance compared with the devices fabricated with the traditional PbS‐PbX2 QD ink. The improved photovoltaic performance in PbS‐AI‐based QDSC is attributed to diminished charge carrier recombination induced by the sub‐bandgap traps in QDs. A theoretical simulation is carried out to atomically link the relationship of QDSC device function with the QD surface properties.
A stable quantum dot (QD) ink is reported by using ammonium iodide for the liquid‐state ligand exchange, and improved photovoltaic performance of QD solar cell is obtained by using the ink for the deposition of QD solid film. Experimental studies and theoretical calculations reveal that the enhanced photovoltaic performance is attributed to the improved passivation on the QD surface.
Crumb rubber (CR) manufactured from waste tires used in bitumen could improve bitumen performance and reduce environmental pollution. In this work, three different modification methods, pretreatment ...of the CR particles (microwave activation), warm mix additive (Sasobit), and trans-polyoctenamer (TOR) were used to improve the compatibility of CR with bitumen. Moreover, two other specimens, Sasobit and microwave activated and TOR and microwave activation were fabricated, and their performance was investigated. The softening point, elastic recovery, force ductility, rotational viscosity, temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) tests were measured to evaluate the physical and rheological properties of rubberized bitumen. The results showed that TOR improved the physical properties of rubberized bitumen significantly but had a negative effect on the viscosity. Sasobit decreased the viscosity of rubberized bitumen considerably and improved the physical properties of rubberized bitumen moderately. Microwave treatment on CR had a negative effect on the high temperature performance and elastic recoverability of rubberized bitumen, however, attributing to the degradation and devulcanization effect of microwave on CR, the viscosity of rubberized bitumen was improved. From the results of composite modification, the influence of TOR on the performance of rubberized bitumen was more obvious than that of the microwave activation treatment. Moreover, the influence of Sasobit on its performance was less than that of the microwave activation treatment.
The great majority of investigations of thermal transport in carbon nanotubes (CNTs) in the open literature focus on low heat fluxes, that is, in the regime of validity of the Fourier heat conduction ...law. In this paper, by performing nonequilibrium molecular dynamics simulations we investigated thermal transport in a single-walled CNT bridging two Si slabs under constant high heat flux. An anomalous wave-like kinetic energy profile was observed, and a previously unexplored, wave-dominated energy transport mechanism is identified for high heat fluxes in CNTs, originated from excited low frequency transverse acoustic waves. The transported energy, in terms of a one-dimensional low frequency mechanical wave, is quantified as a function of the total heat flux applied and is compared to the energy transported by traditional Fourier heat conduction. The results show that the low frequency wave actually overtakes traditional Fourier heat conduction and efficiently transports the energy at high heat flux. Our findings reveal an important new mechanism for high heat flux energy transport in low-dimensional nanostructures, such as one-dimensional (1-D) nanotubes and nanowires, which could be very relevant to high heat flux dissipation such as in micro/nanoelectronics applications.
Abstract
Since the outbreak of the novel coronavirus, the epidemic has received extensive attention all over the world. In this article, an evaluation system was established to analyze the epidemic ...prevention and control situation of some countries. And the ARIMA model was built to predict the epidemic situation in a short period of time. Then taking the United States as an example, the predicted values of the number of newly diagnosed cases, death rate, and cure rate in 10 days were obtained, which were then compared with the actual data. It is shown from the results that the ARIMA model can be used to predict the epidemic and provide a decision-making basis for the current world’s epidemic prevention and control.
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