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Accumulating experimental studies have indicated the influence of lncRNAs on various critical biological processes as well as disease development and progression. Calculating lncRNA functional similarity is of high value in inferring lncRNA functions and identifying potential lncRNA-disease associations. However, little effort has been attempt to measure the functional similarity among lncRNAs on a large scale. In this study, we developed a Fuzzy Measure-based LNCRNA functional SIMilarity calculation model (FMLNCSIM) based on the assumption that functionally similar lncRNAs tend to be associated with similar diseases. The performance improvement of FMLNCSIM mainly comes from the combination of information content and the concept of fuzzy measure, which was applied to the directed acyclic graphs of disease MeSH descriptors. To evaluate the effectiveness of FMLNCSIM, we further combined it with the previously proposed model of Laplacian Regularized Least Squares for lncRNA-Disease Association (LRLSLDA). As a result, the integrated model, LRLSLDA-FMLNCSIM, achieve good performance in the frameworks of global LOOCV (AUCs of 0.8266 and 0.9338 based on LncRNADisease and MNDR database) and 5-fold cross validation (average AUCs of 0.7979 and 0.9237 based on LncRNADisease and MNDR database), which significantly improve the performance of previous classical models. It is anticipated that FMLNCSIM could be used for searching functionally similar lncRNAs and inferring lncRNA functions in the future researches., Competing Interests: The authors declare no conflict(s) of interest.

In order to better understand biatrial conduction, investigate various conduction pathways, and compare the differences between isotropic and anisotropic conductions in human atria, we present a simulation study of biatrial conduction with known/assumed conduction pathways using a recently developed human atrial model. In addition to known pathways: (1) Bachmann's bundle (BB), (2) limbus of fossa ovalis (LFO), and (3) coronary sinus (CS), we also hypothesize that there exist two fast conduction bundles that connect the crista terminalis (CT), LFO, and CS. Our simulation demonstrates that use of these fast conduction bundles results in a conduction pattern consistent with experimental data. The comparison of isotropic and anisotropoic conductions in the BB case showed that the atrial working muscles had small effect on conduction time and conduction speed, although the conductivities assigned in anisotropic conduction were two to four times higher than the isotropic conduction. In conclusion, we suggest that the hypothesized intercaval bundles play a significant role in the biatrial conduction and that myofiber orientation has larger effects on the conduction system than the atrial working muscles. This study presents readers with new insights into human atrial conduction.

Education equity has become a critical sustainable development goal worldwide, and it has aroused significant concern among educators. While virtual teaching communities have emerged as an approach to minimizing educational inequity through resource sharing and information exchange, the achievement of deep collaboration among individuals remains an area that requires further study. Metaverse, with its advanced behavior interaction capabilities, has shown the potential in promoting deep collaboration and communication among individuals. However, the pathway toward leveraging Metaverse for enhancing educational equity remains unclear. To address this gap, this study aims to review the concept and educational applications of Metaverse, as well as its evolution to pedagogical interactions within virtual teaching communities. This article, specifically, proposes the possibility of achieving educational equity by establishing a Metaverse-supported virtual community that leverages immersive environments for behavior interaction, employs diversified avatars for affective communication, and implements equitable mechanisms for knowledge creation. Overall, the present study underscores the importance of constructing a warmer virtual teaching community that promotes deep collaboration and equitable knowledge creation. By leveraging the capabilities of Metaverse, educators and learners can work together to create a more inclusive and equitable learning environment.

The novel centrifugal micro hydrodynamic axial-thrust bearing has been demonstrated to substantially mitigate the wear in hydrodynamic suspension micropumps. To further elevate the bearing performance, the flow mechanism is systematically analyzed via numerical simulations and experiments in this work. The effects of various properties of bearing on the performance are explored and explained. Results indicate that the load capacity augments with the growth of inlet-suction flow rate and with the reduction of rotational speed. Meanwhile, it initially decreases and then increases as fluid film thickness expands. Further, the bearing exhibits proper stiffness and adaptable anti-abrasion when thickness maintains 0.3 mm. This study provides a profound understanding of centrifugal micro hydrodynamic axial-Thrust bearing, and identifies its optimization measures. • The mechanism of bearing involves a combination of centrifugation and inlet-suction. • The effects of various properties of bearing on the performance are explored and explained. • The parameters are identified to optimize the bearing performance. • A novel measurement rig to assess the load capacity is proposed. • This bearing structure and its mechanism can also be extended to other mechanical devices. [ABSTRACT FROM AUTHOR]

Diesel flame lift-off and stabilization in the presence of laser-ignition were numerically investigated with the method of Eulerian stochastic fields. The aim was to scrutinise the interaction between the lifted diesel flame and an ignition kernel upstream of the lifted flame. The numerical simulation was carried out in a constant-volume combustion vessel withn-heptane as fuel. The process was studied previously in an experiment employing Diesel #2 as the fuel in the same combustion vessel. In the experiment a lifted flame was first established at a position downstream of the nozzle. An ignition kernel was then initiated using a high-energy pulse laser at a position upstream of the natural lift-off position of the diesel flame. The laser-ignition kernel was modelled using a high-temperature (∼2000 K) hot spot. In both experiment and simulations the upstream front of the ignition kernel was shown to remain around the initial laser ignition site for a substantially long period of time, while the downstream front of the ignition kernel propagates rapidly towards the natural lift-off position downstream of the laser ignition site. The lift-off position oscillated before the final stabilization at the natural lift-off position. The structures and the propagation speed of the reaction fronts in the laser-ignition kernel and the main flame were analysed. Two different stabilization mechanisms, the auto-ignition mechanism and the flame propagation mechanism, were identified for the naturally lifted flame and the laser-induced reaction front, respectively. A mechanism was proposed to explain the oscillation of the lift-off position. [ABSTRACT FROM PUBLISHER]

Computer vision models are currently making great strides in object detection with the rapid development of deep convolutional detectors. However, generating a large number of anchors is an indispensable step in the object detection models for locating targets, which inevitably leads to redundant detections and low computational efficiency. Detecting contours in an image is a fundamental cognitive ability in human vision system, which offers effective evidences for object detection. This paper proposes a novel and simple method by utilizing the distribution of line segments to facilitate the Non-Maximum Suppression (NMS) for the object detection models. Multiple differentiated metrics are designed for the overlap measure between bounding boxes. As a post-processing technique, the proposed segment-based NMS can be easily applied by various models. Furthermore, the proposed method is verified on multiple benchmarks and extensive experiments have been implemented to illustrate its effectiveness. [ABSTRACT FROM AUTHOR]

ABSTRACT A compact dual-frequency rectenna has been developed. The receiving antenna is based on a planar inverted F antenna for dual frequency operation. A voltage doubler is proposed to improve the output voltage and the robustness of the rectenna. The simulation and measurement results validate the performance of the rectenna. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:319-322, 2015 [ABSTRACT FROM AUTHOR]

The proposed algorithm aims to realize the division of arbitrary fractional frequency. The general frequency divider is comprised of the counter cascade ,and can realize the even frequency division easily, but it is difficult to realize odd frequency divider and fractional frequency divider. This paper proposes a design method of Arbitrary Fractional Frequency Divider (AFFD)based on FPGA circuit cores by an improved Bresenham line-drawing algorithm, which reduces the hardware resource and eases the implementation process. Bresenham line-drawing algorithm is introduced briefly in this paper outside its original applications. The circuit is designed with Verilog Hard Design Language(VHDL), and the program is proposed. The frequency divider is simulated in Quartus II and the divider is examined in FPGA-Based gear hobbling machine CNC system to control the step-servo motor, and the result is steady and reliable. This paper extends the investigation on the frequency division by the improved algorithm. The algorithm designs arbitrary Fractional Frequency Multiplier, and it is also examined by simulation and experiment. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on two-dimensional (2D) and three-dimensional (3D) direct numerical simulations (DNSs) of the auto-ignition process of a lean H2/air mixture with temperature stratification in a constant volume enclosure. Detailed chemistry and transport properties are taken into account in the simulations. The combined propagation of spontaneous ignition front and deflagration front is identified and the relation between the reaction front displacement speed and the temperature gradient is verified. The difference between 2D- and 3D-DNS is investigated by comparing the evolutions of global combustion parameters such as the averaged heat release rate, total reaction front area and the averaged displacement speed of the reaction front. The extra spatial dimension in 3D-DNS has been shown to cause a higher velocity strain rate to enhance the heat transfer process, which leads to a delayed but more rapid ignition of the mixture than the 2D-DNS cases. The 3D reaction front surfaces are examined based on the local mean and Gaussian curvatures. By introducing a cutoff Gaussian curvature two types of 3D surface elements, the small sphere fronts and the strong saddle fronts, are defined. The effect of these fronts on the combustion process is studied in terms of their contribution to the total reaction front area, fuel consumption rate and curvature-induced stretch. [Copyright &y& Elsevier]

An L-band spatial variable radial waveguide power combiner with broad bandwidth and high power capacity is proposed. By adopting several techniques simultaneously, including multi-section impedance matching probes, grounded disc, and axial slots, the performance of the power combiner is improved. The parameters of the combiner are calculated, simulated and tested. It has a measured operation bandwidth ranging from 1.2 GHz to 2 GHz with VSWRs less than 1.4 at all ports. The extra insertion losses between the input ports and output port are less than 0.3 dB and the isolation between the input ports is better than 15 dB. The power capacity can reach 600 W and the combining efficiency achieves 90 %. The results from calculation, simulation, and measurement reasonably agree with each other. [ABSTRACT FROM AUTHOR]

A multidimensional chemistry coordinate mapping (CCM) approach is presented for efficient integration of chemical kinetics in numerical simulations of turbulent reactive flows. In CCM the flow transport is integrated in the computational cells in physical space, whereas the integration chemical reactions are carried out in a phase space made up of a few principal variables. Each cell in the phase space corresponds to several computational cells in the physical space, resulting in a speedup of the numerical integration. In reactive flows with small hydrocarbon fuels two principal variables have been shown to be satisfactory to construct the phase space. The two principal variables are the temperature (T) and the specific element mass ratio of the H atom (J H). A third principal variable, σ=∇J H·∇J H, which is related to the dissipation rate of J H, is required to construct the phase space for combustion processes with an initially non-premixed mixture. For complex higher hydrocarbon fuels, e.g. n-heptane, care has to be taken in selecting the phase space in order to model the low-temperature chemistry and ignition process. In this article, a multidimensional CCM algorithm is described for a systematic selection of the principal variables. The method is evaluated by simulating a laminar partially remixed pre-vaporised n-heptane jet ignition process. The CCM approach is then extended to simulate n-heptane spray combustion by coupling the CCM and Reynolds averaged Navier–Stokes (RANS) code. It is shown that the computational time for the integration of chemical reactions can be reduced to only 3–7%, while the result from the CCM method is identical to that of direct integration of the chemistry in the computational cells. [ABSTRACT FROM PUBLISHER]

A pattern reconfigurable Yagi patch antenna is proposed. The antenna is composed of three triangular microstrip patches, i.e., one driven patch and two parasitic patches. By controlling switches, which are installed on the parasitic patches, the radiation pattern of the antenna can point to three different directions, covering an elevation range from -61° to +63° in the E-plane. The simulated and measured results are presented and they agree with each other in reasonable precision. [ABSTRACT FROM AUTHOR]

In the civilian and commercial ad hoc networks, mobile nodes belong to different authorities or individuals, aren't willing to consume their own resources to provide service for another. The selfish behaviors need to be stimulated to participate in the cooperation. We design a Negotiationbased Stimulating Cooperation model of Ad Hoe nodes (AHNSC) that adopts virtual currency as the main incentive mechanism for bargaining of services and resources. We propose the initial and reserve price models for buyer and seller according to the context of the negotiation. In addition, a motivation-oriented mechanism is used to evaluate a seller's initial price, which imitates human's behaviors and determines whether it responds to the buyer rather than accepts unconditionally negotiation invitations. Negotiation tactics influence actions that a node plans to perform and negotiation outcomes. We develop a hierarchical clusteringbased genetic model to generate offers by imitating opponents' behaviors and optimize the mutual benefits at each round. Simulation results demonstrate the AHNSC model has the superior performances in reducing energy consumption and traffic of network, achieving a balance between the mutual beneficial utility and the negotiation speed. [ABSTRACT FROM AUTHOR]

Due to the smaller size, smaller artificial surface, and higher efficiency, axial blood pumps have been widely applied in clinic in recent years. However, because of its high rotor speed, axial flow pump always has a high risk for hemolysis, which the red blood cells devastated by the shearing of tip clearance flow. We reported a novel design with the integrated blade-shroud structure that was expected to solve this problem by abolishing the radial clearance between blade and casing designed with the techniques of computational fluid dynamics (CFD). However, the numerical simulation result of the newly designed structure showed an unexpected backflow (where flow velocity is reverse of the main flow direction) at the blade tip. In order to eliminate this backflow, four flow passes were attempted, and the expansion angles (which reflect the radial amplification of the flow pass, on the meridional section, and should be defined as the angle between the center line of the flow pass and the axial direction) of the blades of the integrated rotor are 0°, 8°, 15°, and 20°, respectively. In the CFD result, it could be easily found as the expansion angles increased, the backflow was restrained gradually, and was eliminated at last. After numerous “cut and try” circles, the pump model was finally optimized. The numerical simulation of this model also showed a stable hydraulic characteristic. [ABSTRACT FROM AUTHOR]

This paper presents a new multi-step predictive controller based on neural networks and researches the adaptability of the predictive controller for a pneumatic position servo system which has some typical characteristics of non-linearity and time-varying. A diagonal recurrent neural network (DRNN) is used to predict the system output of the multi-step ahead directly. According to the intrinsic defects of a back-propagation (BP) algorithm that cannot update network weights incrementally, a new hybrid learning algorithm combining the temporal differences (TD) method with the BP algorithm to train the DRNN is put forward. A three-layer feedforward BP neural network is used as a non-linear rolling optimal controller to realize the optimization of control input of the next step according to a single-value predictive control algorithm to simplify computation. Simulation and experimental results indicate that the proposed predictive controller is suitable for real-time control of a pneumatic position servo system because of its characteristics of a simple algorithm, fast calculation of the control input and good tracking effects. [ABSTRACT FROM AUTHOR]

We present a simple design for a broadband tunable terahertz (THz) metamaterial absorber (MMA) consisting of a complementary cross-oval-shaped graphene (CCOSG) structure and dielectric substrate placed on a continuous metal film. Both numerical simulation and theoretical calculation results indicate that the absorbance is greater than 80% from 1.2 to 1.8 THz, and the corresponding relative bandwidth is up to 40%. Simulated electric field and power loss density distributions reveal that the broadband absorption mainly originates from the excitation of continuous surface plasmon resonance (SPR) on the CCOSG. In addition, the MMA is polarization-insensitive for both transverse-electric (TE) and transverse-magnetic (TM) modes due to the geometry rotational symmetry of the unit-cell structure. Furthermore, the broadband absorption properties of the designed MMA can be effectively tunable by varying the geometric parameters of the unit-cell and chemical potential of graphene. Our results may find promising applications in sensing, detecting, and optoelectronic-related devices. [ABSTRACT FROM AUTHOR]

We present a simple design of a dual-band plasmonic perfect absorber (PA) based on all-metal nanostructure for ultra-sensitive refractive index (RI) sensing applications in infrared region. The proposed PA is only consisted of an assembly of vertical-split-ring (VSR) structure array adhered on a continuous gold film. The numerical simulation results show that the designed PA can achieve absorbance of 99.1% and 98.8% with quality-factor (Q-factor) of 16.4 and 19.8 at 163.6 THz and 258.8 THz, respectively. The physical origin of the observed absorption is elucidated through distributions of magnetic field and power loss density at resonances. The designed PA served as a refractive index (RI) sensor can achieve sensitivity of 1518 and 959 nm/refractive index unit (RIU), respectively. The proposed dual-band PA could be a desirable candidate for applications in the RI sensing, notch filtering and the enhanced infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH 4 /air and H 2 /air flames at high Karlovitz numbers (Ka ∼ 1800) is carried out. It is found that the high intensity turbulence along with differential diffusion result in a much more rapid transport of H radicals from the reaction zone to the low temperature unburned mixtures (∼500 K) than that in laminar flamelets. The enhanced concentration of H radicals in the low temperature zone drastically increases the reaction rates of exothermic chain terminating reactions (e.g., H + O 2 +M = HO 2 + M in lean H 2 /air flames), which results in a significantly enhanced heat release rate at low temperatures. This effect is observed in both CH 4 /air and H 2 /air flames and locally, the heat release rate in the low temperature zone can exceed the peak heat release rate of a laminar flamelet. The effects of chemical kinetics and transport properties on the H 2 /air flame are investigated, from which it is concluded that the enhanced heat release rate in the low temperature zone is a convection–diffusion-reaction phenomenon, and to obtain it, detailed chemistry is essential and detailed transport is important. [ABSTRACT FROM AUTHOR]

The performance of the gas attenuator (GAT) with argon as the working medium for the high repetition frequency free electron laser facility (SHINE) is simulated and investigated by means of the finite element numerical simulation method, and the results of the temperature and normalized density distribution of the gas inside the active gas cell at steady state are obtained, demonstrating the density depression effect of the internal gas and the corresponding attenuation results. Under the assumption of equivalent continuous-wave (CW) power input, the gas pressures are obtained for photon intensity attenuation of 103 at different photon energy (0.4–7 keV) and repetition frequencies (1 kHz, 10 kHz, 100 kHz), and compared with the theoretical calculations. The results show that the density depression is gradually enhanced with the increase in the repetition frequency, and the nonlinear deviation of the simulation attenuation gas pressure relative to the theoretical value is also gradually increased. The thermal outflux on the wall of the active gas cell gradually decreases along the beam path, so the cooling system needs extra attention to the inlet region of the cell. According to the simulation results, at the highest operating repetition frequency of 100 kHz, the attenuation gas pressure varies from 0.0767 to 17 Torr, and the highest wall thermal outflux value reaches 52.1 W/m2. The study provides a useful reference for the performance prediction and subsequent optimization design of the gas attenuator. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations were carried out to identify the mode of ignition and ignition delay time of pulverized biomass particles in hot flue gas produced by a methane/air flame. In the experiments, it was observed that for most biomass residues the dominant combustion mode was the staged gas-phase ignition in the surrounding gas followed by surface ignition at the char surface. There were some exceptions to this general trend, e.g. wheat straw particles, which ignited at the surface of the particle under some temperature conditions. Moreover, temporally and spectrally resolved images of the single burning particles were obtained in the experiments and CH* chemiluminescence at different stages of biomass conversion was recorded. In this study, by means of a detailed numerical model for conversion of biomass particles and employing detailed gas chemistry mechanism, the ignition mode and ignition delay time of the particles are studied. The model is able to distinguish between different ignition modes of the particles in agreement with the experimental data. The underlying physics behind shifting ignition mode from homogeneous ignition to heterogeneous ignition for wheat straw are discussed. The ignition delay times for different biomass sources at different conditions are calculated and the results are in good agreement with the experimental data. Apart from the detailed model, CFD simulations are performed to assess the flow and combustion process (temperature, O 2 concentration and velocity difference between the ambient gas and the particle) around the particle. The CFD results show similar trends compared with the CH* chemiluminescence from the particle at different times during the devolatilization stage. [ABSTRACT FROM AUTHOR]

Abstract Dealing with high-dimensional dataset has always been an important problem and feature selection is one of useful tools. In this paper, we develop a new filter based supervised feature selection method by combining Trace Ratio Criterion of Linear Discriminant Analysis (TRC-LDA) and group sparsity regularization. The filter based supervised feature selection method is a classifier-independent method while the TRC-LDA criterion is a recently developed criterion for dimensionality reduction that can well preserve discriminative information of dataset. However, there are seldom methods by utilizing TRC-LDA criterion for feature selection. On the other hand, imposing the l2,0-norm to the projection matrix of TRC-LDA will force some rows in it to be zero while keep other rows nonzero making the index of nonzero rows to be the selected features, however, l 2,0 -nom minimizing problem is NP-hard and intractable. To solve the above problem, in this paper, we develop a new method, namely, Trace Ratio Criterion Discriminative Feature Selection (TRC-DFS), for feature selection. The proposed TRC-DFS has imposed l 2,1 -norm, i.e. an approximation of l 2,0 -norm, to the projection matrix W of TRC-LDA to achieve feature selection. As a result, the proposed TRC-DFS can both achieve feature selection as well as capture the discriminative structure of data. We also extend the proposed method with l 2, p -norm (0 < p < 1) regularization to grasp more sparse property and develop an iterative approach to calculate the optimal solution, which is rigorously proved to be converged. Extensive simulations based on several real-world datasets verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Lean premixed turbulent methane-air flames have been investigated using direct numerical simulations (DNS) for different Karlovitz numbers (Ka), ranging from 65 to 3350. The flames are imposed to a high intensity small-scale turbulent environment, corresponding to high Ka conditions, and the effect on the flame structure is investigated during the transition from initial laminar flame to highly distorted turbulent flame. The focus is on the internal structure of different sub-layers of these flames. The preheat layer, fuel consumption layer and oxidation layer are characterized by the distribution of formaldehyde, the fuel consumption rate and the CO consumption rate, respectively. Different measures that quantify sub-layer thickness for turbulent flames have been defined and analyzed. The flame brush is broadened with time while the local thickness (excluding large scale wrinkling) of all three layers initially show thinning due to the interaction of the flame with the turbulent flow field. As time passes, the local thickness of the preheat layer and fuel consumption layer are restored while the oxidation layer remains thinned due to suppression of CO consuming reactions. As Ka increases there is an increasing probability of finding thinned, large gradient regions in each of these sub-layers. The contribution to the evolution of flame thickness from normal strain rate, chemical reaction and normal and tangential diffusion is analyzed in terms of a gradient transport equation. The relative size of the terms changes as Ka increase and, in particular, the term due to chemical reactions loses its relative significance. The observed thinning of the local flame structure is attributed to the preferential alignment of the flame normal with the compressive strain rate eigenvectors. Such alignment provides a mechanism for the flame thinning, consistent with the behavior of non-reacting scalars. A preferred angle of about 20 degrees is observed between the flame normal and the compressive strain rate eigenvector. [ABSTRACT FROM AUTHOR]

The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed. [ABSTRACT FROM AUTHOR]

Transient mixing and ignition mechanisms in a simplified pre-chamber/main-chamber system are investigated using direct numerical simulation (DNS) with detailed chemical kinetics. Full ignition and flame propagation processes in the premixed methane/air mixtures are simulated. Ignition, the progress and topology of flame evolution, and the mean burning velocity in the main chamber are analyzed in detail. Four important phases in the ignition and flame propagation processes are identified based on the flame structure development in the main chamber, the pressure and velocity evolution at typical points in both the pre-chamber and main chamber. Results show that the intermediate species OH, CH 2 O, and HO 2 are critical for flame stabilization and propagation in the main chamber due to their high reactivity. This is sorted as the chemical effect that the pre-chamber jet acts on the main chamber. The high temperature jet also brings heat and unburned fuel into the main chamber, which are sorted as thermal and enrichment effect, respectively. The heat release rate is found to be approximately proportional to the product of CH 2 O and OH mass fractions, which could be regarded as a reliable and effective marker for the heat release rate of methane/air mixtures. It is found that the mean burning velocity in the main chamber can be elevated up to 30 times under the condition investigated. [ABSTRACT FROM AUTHOR]

Numerical simulation of biomass gasification in fluidized bed reactors faces several challenges including proper modeling of the physical and chemical processes involved in the gasification and numerical stiffness of the two-phase dense particle flow problem. In this paper, the multi-phase particle-in-cell (MP-PIC) model coupled with a recently developed distribution kernel method (DKM) and a new one-step pyrolysis model are employed to investigate biomass gasification in two lab-scale fluidized bed gasifiers (FBGs). The results are evaluated by comparing with the results from the Particle Centroid Method (PCM) and experimental measurements. The performance of DKM is shown to improve the robustness of the model and the new pyrolysis model is shown to improve the sensitivity of the yields of gasification products to operating temperature. The simulation results using the new pyrolysis model agree well with the experimental data under different gasification conditions. The model is shown to be able to capture the trend of gas products with respect to variations of steam/biomass ratio (SR) and operating temperature (T r). The mechanisms of the formation of gas products are analyzed based on the numerical results. By increasing the SR and T r , the production of H 2 and CO 2 is shown to increase while the production of CO and CH 4 to decrease. It is shown that varying the steam/biomass ratio in the range of 0.8 ∼ 2.0 has a minor effect on the pyrolysis process and heterogeneous reactions, while homogeneous reactions are significantly affected, leading to changes in the final composition of the gas products. Varying the gasifier temperature T r has on the other hand a crucial effect on the pyrolysis process and as such a significant impact on the gasification products and carbon conversion. • An empirical one-step model was developed for biomass pyrolysis. • Prediction of gasification products at varying operating temperatures was improved. • Impact of steam/biomass ratio on gasification products was identified. • A distribution kernel model is shown to resolve local particle over-loading problem. [ABSTRACT FROM AUTHOR]

Large Eddy Simulation (LES) was employed to investigate the fuel/oxidizer mixing process in an ethylene fueled scramjet combustor with a rearwall-expansion cavity. The numerical solver was first validated for an experimental flow, the DLR strut-based scramjet combustor case. Shock wave structures and wall-pressure distribution from the numerical simulations were compared with experimental data and the numerical results were shown in good agreement with the available experimental data. Effects of the injection location on the flow and mixing process were then studied. It was found that with a long injection distance upstream the cavity, the fuel is transported much further into the main flow and a smaller subsonic zone is formed inside the cavity. Conversely, with a short injection distance, the fuel is entrained more into the cavity and a larger subsonic zone is formed inside the cavity, which is favorable for ignition in the cavity. For the rearwall-expansion cavity, it is suggested that the optimized ignition location with a long upstream injection distance should be in the bottom wall in the middle part of the cavity, while the optimized ignition location with a short upstream injection distance should be in the bottom wall in the front side of the cavity. By employing a cavity direct injection on the rear wall, the fuel mass fraction inside the cavity and the local turbulent intensity will both be increased due to this fueling, and it will also enhance the mixing process which will also lead to increased mixing efficiency. For the rearwall-expansion cavity, the combined injection scheme is expected to be an optimized injection scheme. [ABSTRACT FROM AUTHOR]

A particle-based transported probability density function (PDF) method with a novel chemistry acceleration technique is developed in this work. The technique is based on the chemistry coordinate mapping (CCM) approach that was proposed in our previous works for accelerating direct numerical simulations (DNS) of partially premixed combustion. The method is first validated using Sandia flames D and F. It is shown that PDF-CCM results converge toward those obtained without CCM as phase-space resolution increases. PDF-CCM is then applied to simulate methane/air lifted jet flames in vitiated coflow reported in experiments by Cabra et al. (2005). It is shown that combustion is initiated in the form of auto-ignition in very fuel-lean gases where the gas velocity is low (the residence time is long) and the gas temperature is high (the ignition delay time is short). The ignition delay of the mixture below the liftoff position scales well with the liftoff height at different coflow temperature conditions. The combustion process above the liftoff height can develop into different modes depending on the coflow temperature. For high-temperature coflow, a premixed-burned combustion is formed above the liftoff height, which involves fuel-lean to fuel-rich burning modes; a triple-flame structure eventually is formed a few nozzle diameters above the liftoff position. For low-temperature coflow, the ignition delay and the liftoff height are sufficiently large to allow premixing between fuel and oxidizer before the onset of high-temperature combustion; in this case, a lean-to-stoichiometric premixed burn combustion is established downstream of the liftoff height, and no obvious triple-flame structure is formed at this condition. [ABSTRACT FROM AUTHOR]