Search

The synergistic influence of microalgae on the two forms of organic waste biomasses, namely biomass wastes (BW) and its digested form (DBW), during co-pyrolysis was evaluated based on the thermal decomposition behaviour, gas yields, extent of thermal decomposition and reaction kinetics. The biomasses and their blends were co-pyrolysed at three different heating rates (10, 15 and 20 °C min−1) in a thermogravimetric analyzer coupled with a mass spectrometer. Initial assessment, based on TG-DTG data, revealed that the thermal degradation can be divided into three zones (50-150 °C, 150-550 °C and 550-800 °C) for all the biomasses and their blends. The thermogravimetric data was used to evaluate the kinetic triplet, which include apparent activation energy (Eα), pre-exponential factor (A) and reaction mechanism, f(α). Semi-quantitative method was used to quantify the gas species, H2, CO2 and CO were dominant species, implying the water gas reactions and oxidation reactions were predominant. The synergistic influence of microalgae was clearly evident in terms of reaction kinetics, as noted in the reduction in the apparent activation energy and increase in the total gas yields. The obtained kinetic triplet and thermodynamic parameters are expected to facilitate the design and optimization of co-pyrolysis of microalgae with other forms of organic wastes.

Solid–liquid interaction plays a key role in substrate wettability and spreading dynamics of liquid droplets. Yet, how the solid–liquid interaction controls wettability and the spreading process is...

Hypothesis The imbibition dynamics is controlled by energy dissipation mechanisms and influenced by asymmetric wettability in a nanochannel. We hypothesize that the imbibition dynamics can be described by a combined model of the Lucas–Washburn equation and the Cox-Voinov law considering velocity-dependent contact angles. Methods Molecular dynamics simulations are utilized to investigate the imbibition dynamics. A wide range of wetting conditions is achieved via adjusting the liquid–solid interaction parameters, and the spontaneous imbibition processes are quantified and compared. Findings The critical condition for the occurrence of spontaneous imbibition is analyzed from a surface energy perspective. The analyses of energy conversion and dissipation indicate that the viscous dissipation is dominant during spontaneous imbibition. The classical Lucas-Washburn equation is modified with the Cox–Voinov law considering the effect of the dynamic contact angle and an effective equilibrium contact angle. We show that the proposed theory well captures the imbibition dynamics embodied in the growth of imbibition length as well as the transient interface shape and velocity for both the symmetric and asymmetric wetting conditions. In nanochannels with asymmetric wettability, the imbibition length difference between the sidewalls and interface oscillations increases with wetting disparity. Our findings deepen the understanding of imbibition dynamics on the nanoscale, and provide a theoretical reference for relevant applications.

The synergistic influence of microalgae on the two forms of organic waste biomasses, namely biomass wastes (BW) and its digested form (DBW), during co-pyrolysis was evaluated based on the thermal decomposition behaviour, gas yields, extent of thermal decomposition and reaction kinetics. The biomasses and their blends were co-pyrolysed at three different heating rates (10, 15 and 20 ⁰C min-1) in a thermogravimetric analyzer coupled with a mass spectrometer. Initial assessment, based on TG-DTG data, revealed that the thermal degradation can be divided into three zones (50-150 ⁰C, 150-550 ⁰C and 550-800 ⁰C) for all the biomasses and their blends. The thermogravimetric data was used to evaluate the kinetic triplet, which include apparent activation energy (Eα), pre-exponential factor (A) and reaction mechanism, f(α). Semi-quantitative method was used to quantify the gas species, H2, CO2 and CO were dominant species, implying the water gas reactions and oxidation reactions were predominant. The synergistic influence of microalgae was clearly evident in terms of reaction kinetics, as noted in the reduction in the apparent activation energy and increase in the total gas yields. The obtained kinetic triplet and thermodynamic parameters are expected to facilitate the design and optimization of co-pyrolysis of microalgae with other forms of organic wastes.

Here, Tg-minimised bandwidth-allocated scheme is proposed for VPON supporting joint scheduling of multiple subsystems in metro-access optical network. To minimise guard time (Tg) in WDM-PON and TDM-PON, the Tg-transferred mechanism is introduced. To reduce the number of Tg in OFDM-PON, the subcarrier allocation algorithm based on the minimum number of Tg is proposed. To effectively utilise the network bandwidth resources, the bandwidth allocation based on matrix model is established. To increase the utilisation of wavelength, a dynamic-wavelength allocation mechanism is proposed. Finally, by the simulation, the effectiveness of Tg-minimised bandwidth-allocated scheme is demonstrated. Compared with other schemes, this scheme has at least 3% bandwidth utilisation improvement and lower average delay.

Direct communication among optical network units (ONUs) is very significant for next-generation optical networks. In this paper, a metro-access optical network architecture supporting intra-communication and inter-communication is proposed based on dual-fiber ring topology. By adopting two tunable fiber Bragg gratings and one arrayed waveguide grating in the remote node, direct peer-to-peer communication of ONUs can be achieved. By designing the architecture to provide inter-communication in two opposite transmission directions, not only the efficiency and flexibility of inter-communication can be guaranteed depending on the shortest transmission path, but also the inter-communication can be supported even if a dual-fiber fault occurs. By allocating three wavelengths to one ONU, not only the intra-communication and inter-communication for one ONU can be carried out simultaneously, but also the inter-communication for different ONUs can be realized simultaneously. By using a dual-fiber ring structure, both the scale and the reliability can be improved. Because the network capacity and scale are relatively large, the relative construction-and-maintenance cost of the network is low. The availability of the proposal can be verified via the performance analyses and the simulations.

Recently, the IEEE 802.3 Ethernet Working Group has been working to explore new solutions for the next-generation Ethernet passive optical network (NG-EPON). It’s desirable for NG-EPON to support the coexistence of multi-type users and multi-type services (MUMS) on a single access platform. Moreover, in the future, ONU may be equipped with multiple transceivers to break through bandwidth limit of a single wavelength and then achieve greater throughput per ONU. In this paper, a two-dimensional priority queue model is designed for buffer differentiation management. Then, a dynamic bandwidth allocation (DBA) algorithm including joint grant sizing and scheduling is presented to carry out differentiated bandwidth allocation among MUMS. By providing different aggregated data rates and setting scalable wavelength resource pools for different users and services, flexible ONU configurations are allowed. By using time-order filling (ToF) and wavelength-order filling (WoF) in combination to realize grant scheduling, the flexibility of multi-transceiver ONUs gets further exploited. Finally, the simulation demonstrates the effectiveness of the proposed algorithm. Not only each type of service/user can get reasonable network access capacity that matches its bandwidth requirements, but the overall network performance also gets improved compared with other DBAs for NG-EPON.

Adopting the pay-as-you-grow approach to upgrade passive optical network (PON) facilities by WDM technology insures the smoothness of the upgrade, and also results in the coexistence of wavelength-fixed/tunable optical network units (ONUs) in WDM/TDM PONs. Dynamic bandwidth allocation (DBA) is the key to support such coexistence of heterogeneous ONUs. Thus, DBA is also the key to support the smooth evolution of PONs. To more fairly coordinate the bandwidth allocation among the coexisting heterogeneous ONUs, a differentiated grant sizing (DGS) scheme is proposed. In DGS, not only the fairness between the wavelength-fixed/tunable ONUs but also the fairness between the lightly/heavily loaded ONUs is taken into account. To further carry out load balancing among wavelengths, a grant scheduling scheme is also proposed to cooperate with the grant sizing scheme. In the grant scheduling scheme, a measure of the ONUs’ flexibility is given, and then the least flexible job first rule (LFJF) is adopted for joint wavelength and time-slot assignment. Finally, to demonstrate the effectiveness of the proposed algorithm, a series of comparative analyses is conducted based on simulation experiments.

A passive optical network (PON) with multiple optical line terminals (OLTs) will play an important role in the optical access network. In this study, a novel dynamic bandwidth allocation (DBA) algorithm for the downstream channel in a multi-OLT PON is proposed. To take care of bandwidth demands of different users, weight factors are introduced. Based on different weight factors, a core framework of the algorithm is constructed. Moreover, by combining a decision criterion and a bandwidth surplus ratio, a mathematical model of release bandwidth is established. Furthermore, by uniting judgement conditions and overload amount, a mathematical model of allocation bandwidth is also built. By constructing two mathematical models, the order and amount of release and allocation bandwidth are effectively solved. Moreover, to describe accurately the power of bandwidth transfer, a new concept ‘bandwidth-transfer work’ is introduced. Based on the bandwidth-transfer work, a ranking model is created to maximise the efficiency of the DBA. Finally, the effectiveness of the DBA algorithm and ranking model is demonstrated by the simulation and analysis.

In this paper, a novel architecture of hybrid PON for smart grid is proposed by introducing a wavelength-routing module (WRM). By using conventional optical passive components, a WRM with M ports is designed. The symmetry and passivity of the WRM makes it be easily integrated and very cheap in practice. Via the WRM, two types of network based on different ONU-interconnected manner can realize online access. Depending on optical switches and interconnecting fibers, full-fiber-fault protection and dynamic bandwidth allocation are realized in these networks. With the help of amplitude modulation, DPSK modulation and RSOA technology, wavelength triple-reuse is achieved. By means of injecting signals into left and right branches in access ring simultaneously, the transmission delay is decreased. Finally, the performance analysis and simulation of the network verifies the feasibility of the proposed architecture.

Cement-based materials are widely utilized in infrastructure. The main product of hydrated products of cement-based materials is calcium silicate hydrate (C-S-H) gels that are considered as the binding phase of cement paste. C-S-H gels in Portland cement paste account for 60–70% of hydrated products by volume, which has profound influence on the mechanical properties and durability of cement-based materials. The preparation method of C-S-H gels has been well documented, but the quality of the prepared C-S-H affects experimental results; therefore, this review studies the preparation method of C-S-H under different conditions and materials. The progress related to C-S-H microstructure is explored from the theoretical and computational point of view. The fractality of C-S-H is discussed. An evaluation of the mechanical properties of C-S-H has also been included in this review. Finally, there is a discussion of the durability of C-S-H, with special reference to the carbonization and chloride/sulfate attacks.

With the emergence of new services such as high-definition video, cloud computing and virtual reality, the load's bandwidth prediction ability is necessary to support soaring services request bandwidth with diversified characteristics and requirements. In this paper, a novel bandwidth allocation algorithm based on differential bandwidth request prediction (BRP) models is proposed. This algorithm firstly combines linear prediction and nonlinear prediction. According to different characteristics of services, the linear prediction model and the Kalman-filter prediction model are used to predict request bandwidths of corresponding services. By the differential BRP models, the proposed algorithm can greatly better the accuracy of service's request bandwidth prediction and the efficiency of allocating bandwidth. The simulation results demonstrate that the proposed models and algorithm can reduce network's average delay, increase throughput and bandwidth utilization.

Molecular dynamics simulations are used to investigate the interactions between water molecules and C-S-H surfaces and transport properties of water confined in the nanopore. Firstly, a C-S-H model based on experimental results is constructed, then a nanopore induced by tensile loading is taken into account for the first time. Structural and dynamical properties of confined water and interactions between water solution and C-S-H surface are further investigated at the molecular level. Water molecules gathering in the vicinity of C-S-H surfaces perpendicular to Z direction present peculiar structural and dynamic characteristic: layer structure, high density, obvious orientation preference, and low diffusion coefficient. The silicate chains are connected with water molecules by the high-strength hydrogen bonds formed among water and non-bridge oxygen atoms (ONB), bridge oxygen atoms (OB) in silicate chains, while surface calcium ions sheets are prone to attract oxygen atoms in water molecules. The special structural and dynamic features are mainly determined by the interactions among water, silicate chains, and surface calcium ions sheets. Due to the lack of strong constraint from the C-S-H substrates and driven by water molecules in the nanopore, the surface calcium ions diffuse more rapidly than those constrained inside of the C-S-H gel and could diffuse into the nanopore full of water molecules.