Vertically stacked low-dimensional heterostructures are outstanding systems both for exploring fundamental physics and creating new devices. Due to nanometer-scale building blocks, atomic scale phenomena become for them of fundamental importance, including during device operation. These can be accessed in situ in aberration-corrected scanning transmission electron microscopy (STEM) experiments. Here, the dynamics of a graphene-MoS2 heterostructure are studied under Joule heating, where the graphene serves as a high temperature atomically thin and electron transparent “hot plate” for the MoS2. Structural dynamics and evolution of the system are shown at the atomic scale, demonstrating that at the highest temperatures (estimated to exceed 2000 K), the continuous 2D MoS2 transforms into separated 3D nanocrystals, initiated by sulfur vacancy creation and migration followed by formation of voids and clustering at their edges. The resulting nanocrystals exhibit predominantly hexagonal shapes with the 2H and hybrid (2H/3R, 3R/TZ) polytypes. The observed morphology of the crystals is further discussed during and after the transformation, as well as their different edge configurations and stability under electron irradiation. These observations of MoS2 at extreme temperatures provide insights into the operation of devices based on graphene/MoS2 heterostructures and ultimately may help device fabrication techniques to create MoS2-based nanostructures, for example, in hydrogen evolution reaction applications. 相似文献
Electrocaloric device structures have been developed as multilayer ceramics (MLCs) based on fundamental research carried out on PMN‐8PT bulk ceramics. Two different MLC structures were prepared with nine layers each and layer thicknesses of 86 μm and 39 μm. The influence of the device design on its properties has been characterized by microstructural, dielectric, ferroelectric, and direct electrocaloric measurement. For direct characterization two different methods, ie temperature reading (thermistor and thermocouple) and heat flow measurement (differential scanning calorimetry), were used. A comparison of results revealed a highly satisfactory agreement between the different methods. This study confirms that MLCs are promising candidates for implementation into energy‐efficient electrocaloric cooling systems providing large refrigerant volume and high electrocaloric effect. Due to their micron‐sized active layers, they allow for the application of high electric fields under low operation voltages. We measured a maximum electrocaloric temperature change of ΔT=2.67 K under application/withdrawal of an electric field of ΔE=16 kV mm?1, which corresponds to operation voltages below 1.5 kV. 相似文献
This paper deals with a multidimensional examination of the infrastructural, technical/technological, operational, economic, social, and environmental performances of high-speed rail (HSR) systems, including their overview, analysis of some real-life cases, and limited (analytical) modeling. The infrastructural performances reflect design and geometrical characteristics of the HSR lines and stations. The technical/technological performances relate to the characteristics of rolling stock, i.e., high-speed trains, and supportive facilities and equipment, i.e., the power supply, signaling, and traffic control and management system(s). The operational performances include the capacity and productivity of HSR lines and rolling stock, and quality of services. The economic performances refer to the HSR systems’ costs, revenues, and their relationship. The social performances relate to the impacts of HSR systems on the society such as congestion, noise, and safety, and their externalities, and the effects in terms of contribution to the local and global/country social-economic development. Finally, the environmental performances of the HSR systems reflect their energy consumption and related emissions of green house gases, land use, and corresponding externalities.
Global commercial air transportation has grown over the past two decades at a rather stable annual rate of 4.5–5% in the passenger and 6% in the cargo segment. Such developments have contributed to globalization of the economy and overall social welfare while at the same time increased impacts on the environment and society in terms of fuel consumption from non-renewable sources and related emissions of GHG (Green House Gases), land use, congestion, and local noise. In particular, further growth of emissions of GHG driven by growth of air transportation demand could contribute to global warming and consequent climate change. 相似文献
In this article, we report the electron beam-induced current (EBIC) measurements in a GaN Schottky diode performed in the
line-scan configuration. A theoretical model with an extended generation source was used to accurately extract some minority
carrier transport properties of the unintentionally doped n-GaN layer. The minority hole diffusion length is found to increase
from ∼0.35 μm near the junction to ∼1.74 μm at the bulk regions. This change is attributed to an increase of the carrier lifetime
caused by the polarization effects, which are preponderant in this component. For depth distances exceeding 0.65 μm, it is
shown that the measured current is produced by the reabsorption recombination radiation process. This corresponds to an absorption
coefficient of 0.178 μm−1, in good agreement with the optical absorption measurement. 相似文献
This paper describes the Mobile Fair Diary (MFD), which is designed to allow a housing fair customer to make a personalized
digital recording of his/her visit to a hectic fairground for later use. The MFD is a hybrid interface service comprising
of an application for a camera equipped smart phone and a website accessed by a PC. The smart phone application is used for
taking context-aware notes such as visual codes, photos, dictations and text. The notes are uploaded onto a website, where
they can be viewed with a PC in a contextually ordered view for browsing, organizing and sharing. The MFD was empirically
evaluated in a real-life environment of use with genuine end users by a large-scale field trial at a national housing fair.
The results testify to the very successful design of the MFD with high usefulness. 相似文献
Fuelwood moisture content is an important parameter for small and medium-sized heating plants. Optimal storage location and good fuelwood storage maintenance promotes drying efficiency and ensures good fuelwood quality. The effective drying period is limited to spring and summer. It is known that partial debarking of wood will enhance drying and improve fuelwood quality.The aim of the study was to test strip debarking as a mean to speed up the drying rate and to lower moisture and bark contents. The prerequisite was that debarking had to be integrated into the processing phase of a single grip harvester. The changes made in the harvester head had to be simple, easily installed and inexpensive.The mechanical objective was solved by drilling holes into the delimbing knives and placing bolts through the knives. In this manner the bolt head would strip bark off the stems when fed through the delimbing knives. The qualitative goal was to see if debarking improved drying rate and if harvesting season and species played a role.The data was collected on non-frozen and frozen pine wood in spring 2005 and in winter 2006, and on non-frozen birch in spring 2007. The debarking results of the non-frozen pine were 3-6% of the total surface area for the normal harvester head and 7-9% for the modified harvester head. The results for frozen pine were correspondingly 1% and 2-2.5%. The debarking results of non-frozen birch were 5-6% and 5-8%. Both studies of pine show that the bolts in delimbing knives doubled the amount of bark removed. There was no significant difference in birch.The delimbed Scots pine fuelwood storages reached 30% moisture content on fresh weight basis during the first drying season at landing. This result was obtained independently of the rate of debarking or the harvesting season. Seasoning over the second summer lowered the moisture content of pine fuelwood by another 5% units to 25%. Birch reached 20% during the first season. 相似文献