346 research outputs found
Edge Effect in Electronic and Transport Properties of 1D Fluorinated Graphene Materials
A systematic examination of the electronic and transport properties of 1D fluorine-saturated zigzag graphene nanoribbons (ZGNRs) is presented in this article. One publication (Withers et al., Nano Lett., 2011, 11, 3912–3916.) reported a controlled synthesis of fluorinated graphene via an electron beam, where the correlation between the conductivity of the resulting materials and the width of the fluorinated area is revealed. In order to understand the detailed transport mechanism, edge-fluorinated ZGNRs with different widths and fluorination degrees are investigated. Periodic density functional theory (DFT) is employed to determine their thermodynamic stabilities and electronic structures. The associated transport models of the selected structures are subsequently constructed. The combination of a non-equilibrium Green’s function (NEGF) and a standard Landauer equation is applied to investigate the global transport properties, such as the total current-bias voltage dependence. By projecting the corresponding lesser Green’s function on the atomic orbital basis and their spatial derivatives, the local current density maps of the selected systems are calculated. Our results suggest that specific fluorination patterns and fluorination degrees have significant impacts on conductivity. The conjugated π system is the dominate electron flux migration pathway, and the edge effect of the ZGNRs can be well observed in the local transport properties. In addition, with an asymmetric fluorination pattern, one can trigger spin-dependent transport properties, which shows its great potential for spintronics applications
Development of a novel energy efficient phase change emulsion for air conditioning systems
Buildings represent more than 40% of final global energy consumption, among which 50%-60% of energy consumption is attributed to Heating, Ventilation and Air Conditioning (HVAC) systems. The application of phase change material emulsions (PCMEs) in air conditioning systems is considered to be a potential way of saving energy because with their relatively higher energy storage capacity, they are able to reduce flow rate whilst delivering the same amount of cooling energy. PCMEs can also simultaneously act as cold energy storage to shift peak-load to off-peak time and improve coefficient of performance of systems. However, one of the main barriers affecting the application of PCME is the difficulty in maintaining stability in the emulsions without experiencing any temperature stratification during phase change process.
To this end, an innovative energy efficient phase change emulsion has been developed and evaluated. The emulsion (PCE-10) which consists of an organic PCM (RT10) and water has a phase change temperature range of 4-12°C with heat capacity of twice as much as that of water thus making it a good candidate for cooling applications. Particular attention was also paid to the selection of the surfactant blends of Tween60 and Brij52 since they are capable of minimizing the effect of sub-cooling as well as ensuring stability of the emulsion.
For the purpose of testing the performance of developed PCE-10 in fin-and-tube heat exchangers, series of theoretical and experimental studies have been carried out to understand the rheological behaviour and heat transfer characteristics of the developed PCE-10 in a fin-and-tube heat exchanger. Both experimental and theoretical results were fairly close and showed that the PCE-10 did enhance the overall heat transfer rate of the heat exchanger.
In order to evaluate the potential of the integrated system, whole building energy simulation was carried out with a building simulation code TRNSYS. It was found out that the required volumetric flow rate of PCE-10 was 50% less than that of water which is equivalent to 7% reduction in total energy consumption when providing the same amount of cooling power.
Despite its potential in cooling systems, the viscosity of the developed sample was found to be much higher than water which could contribute to high pressure drop in a pumping system. Its thermal conductivity was also found to be about 30% lower than the value for water which could influence heat transfer process. There is therefore the need to enhance these thermophysical properties in any future investigations
Development of a novel energy efficient phase change emulsion for air conditioning systems
Buildings represent more than 40% of final global energy consumption, among which 50%-60% of energy consumption is attributed to Heating, Ventilation and Air Conditioning (HVAC) systems. The application of phase change material emulsions (PCMEs) in air conditioning systems is considered to be a potential way of saving energy because with their relatively higher energy storage capacity, they are able to reduce flow rate whilst delivering the same amount of cooling energy. PCMEs can also simultaneously act as cold energy storage to shift peak-load to off-peak time and improve coefficient of performance of systems. However, one of the main barriers affecting the application of PCME is the difficulty in maintaining stability in the emulsions without experiencing any temperature stratification during phase change process.
To this end, an innovative energy efficient phase change emulsion has been developed and evaluated. The emulsion (PCE-10) which consists of an organic PCM (RT10) and water has a phase change temperature range of 4-12°C with heat capacity of twice as much as that of water thus making it a good candidate for cooling applications. Particular attention was also paid to the selection of the surfactant blends of Tween60 and Brij52 since they are capable of minimizing the effect of sub-cooling as well as ensuring stability of the emulsion.
For the purpose of testing the performance of developed PCE-10 in fin-and-tube heat exchangers, series of theoretical and experimental studies have been carried out to understand the rheological behaviour and heat transfer characteristics of the developed PCE-10 in a fin-and-tube heat exchanger. Both experimental and theoretical results were fairly close and showed that the PCE-10 did enhance the overall heat transfer rate of the heat exchanger.
In order to evaluate the potential of the integrated system, whole building energy simulation was carried out with a building simulation code TRNSYS. It was found out that the required volumetric flow rate of PCE-10 was 50% less than that of water which is equivalent to 7% reduction in total energy consumption when providing the same amount of cooling power.
Despite its potential in cooling systems, the viscosity of the developed sample was found to be much higher than water which could contribute to high pressure drop in a pumping system. Its thermal conductivity was also found to be about 30% lower than the value for water which could influence heat transfer process. There is therefore the need to enhance these thermophysical properties in any future investigations
The Design of Compass/BeiDou Navigation Satellite Terminal for Migrant Bird Research
A terminal of Compass Navigation Satellite System (CNSS), which can not only support BeiDou-1 and BeiDou-2 but also support Global Positioning System (GPS), is designed to research the activities of the migrant birds, with our novel design of a multiband antenna. By a high-density integration, this terminal is designed with a compact size and light weight. When the terminal is assembled to a whooper swan, its flying trace is recorded by the CNSS, which is in agreement with that of GPS. The flying route map based on the CNSS is useful to check the situation and habit of the migrant bird, which is important for animal protection and bird flu outbreak prediction
An Initial Study on the Intensifying Enterprises Information Management
The information management has become an important base of developing an enterprise’s eBusiness. Although our country has spent abundant manpower, material resources and financial support on enterprise information management, most of the information systems were not so good to meet our need and they didn’t bring the effect into play sufficiently. Based on the two large questionnaires, this paper has made an initial study and analysis on the status and actual questions of Chinese information management. And then this paper studies the current status of information management of some of the dominant enterprises in Sichuan Province. At last this paper presents some suggestions of intensifying enterprises information management
An Approach to the Production of Soluble Protein from a Fungal Gene Encoding an Aggregation-Prone Xylanase in Escherichia coli
The development of new procedures and protocols that allow researchers to obtain
recombinant proteins is of fundamental importance in the biotechnology field. A
strategy was explored to overcome inclusion-body formation observed when
expressing an aggregation-prone fungal xylanase in Escherichia
coli. pHsh is an expression plasmid that uses a synthetic
heat-shock (Hsh) promoter, in which gene expression is regulated by an
alternative sigma factor (σ32). A derivative of pHsh was
constructed by fusing a signal peptide to xynA2 gene to
facilitate export of the recombinant protein to the periplasm. The xylanase was
produced in a soluble form. Three factors were essential to achieving such
soluble expression of the xylanase: 1) the target gene was under the control of
the Hsh promoter, 2) the gene product was exported into the periplasm, and 3)
gene expression was induced by a temperature upshift. For the first time we
report the expression of periplasmic proteins under the control of an Hsh
promoter regulated by σ32. One unique feature of this approach
was that over 200 copies of the Hsh promoter in an E. coli cell
significantly increased the concentration of σ32. The growth
inhibition of the recombinant cells corresponded to an increase in the levels of
soluble periplasmic protein. Therefore, an alternative protocol was designed to
induce gene expression from pHsh-ex to obtain high levels of active soluble
enzymes
Development of a novel phase change material emulsion for cooling systems
In this paper, a novel phase change material emulsion (PCE-10) consisting of an organic PCM (RT10) and water has been developed. Its thermophysical properties such as heat of fusion, viscosity and sub-cooling temperature have been established. The chemical stability during both storage and discharge periods have also been evaluated. The results indicate low sub-cooling temperature and relatively long period of stability without any sign of segregation but the viscosity was found to be much higher than that of water.Further improvement and experimental studies into its flow characteristics are therefore being encouraged
Public perceptions towards MOOCs on social media: an alternative perspective to understand personal learning experiences of MOOCs
This study attempted to assess public perceptions of and interest in MOOCs by examining how
Weibo increases public discussion of MOOCs as well as by interpreting how individual learners
talk about their learning experiences. Over 4,000 microblog posts were collected and analysed
between 2013 and 2018. The findings showed that Weibo is used as a public service medium to
augment the publicity of the MOOC movement and increase the accessibility of MOOC portals.
The results also demonstrated that Weibo acts as a space for learners to share their personal
learning experiences, which reflect aspects of autonomous, self-regulated, interactive and
cooperative learning. By posting on Weibo, close peer connections and learning groups were
established to encourage MOOC learning. This study’s findings further the scholarly
understanding of how MOOCs are discussed on social media and address an important gap
around what is known in one of the largest and most under-researched sites of informal online learning
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Dynamic route choice model with departure time in combined trip
The dynamic route choice model with departure time was carried out in a multi-modal transportation network, in which the combined travel mode was considered. The multi-modal transportation network was built based on the super network theory and the expansion technique. The simultaneous departure time and the route choice preference were described in a Logit model from the view of path formulation, as well as analyzing the equilibrium conditions. A variational inequality model was proposed to be equivalent to the equilibrium condition and was solved by a direct algorithm based on a dynamic stochastic network loading method. The efficient of the model and the algorithm were validated by a numerical example. The results show that the proposed model can not only describe the route choice behavior in the multimodal transportation network, but also get the departure time, which comes closer to the reality and has good suitability
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