Background Major unresolved questions regarding vertebrate limb development concern how the numbers of skeletal elements along the proximodistal (P-D) and anteroposterior (A-P) axes are determined and how the shape of a growing limb affects skeletal element formation. There is currently no generally accepted model for these patterning processes, but recent work on cartilage development (chondrogenesis) indicates that precartilage tissue self-organizes into nodular patterns by cell-molecular circuitry with local auto-activating and lateral inhibitory (LALI) properties. This process is played out in the developing limb in the context of a gradient of fibroblast growth factor (FGF) emanating from the apical ectodermal ridge (AER). Results We have simulated the behavior of the core chondrogenic mechanism of the developing limb in the presence of an FGF gradient using a novel computational environment that permits simulation of LALI systems in domains of varying shape and size. The model predicts the normal proximodistal pattern of skeletogenesis as well as distal truncations resulting from AER removal. Modifications of the model's parameters corresponding to plausible effects of Hox proteins and formins, and of the reshaping of the model limb, bud yielded simulated phenotypes resembling mutational and experimental variants of the limb. Hypothetical developmental scenarios reproduce skeletal morphologies with features of fossil limbs. Conclusions The limb chondrogenic regulatory system operating in the presence of a gradient has an inherent, robust propensity to form limb-like skeletal structures. The bare bones framework can accommodate ancillary gene regulatory networks controlling limb bud shaping and establishment of Hox expression domains. This mechanism accounts for major features of the normal limb pattern and, under variant geometries and different parameter values, those of experimentally manipulated, genetically aberrant and evolutionary early forms, with no requirement for an independent system of positional information.
A numerical simulation of two-dimensional compressible Navier-Stokes equations using a high-order weighted essentially nonoscillatory finite difference shock capturing scheme is carried out in this paper, to study the effect of shock waves on the development of Rayleigh-Taylor instability. Shocks with different Mach numbers are introduced ahead or behind the Rayleigh-Taylor interface, and their effect on the transition to instability is demonstrated and compared. It is observed that shock waves can speed up the transition to instability for the Rayleigh-Taylor interface significantly. Stronger shocks are more effective in this speed-up process.
The interaction between a shock wave and two counter-rotating vortices is simulated systematically through solving the two-dimensional, unsteady, compressible Navier–Stokes equations using a fifth order weighted essentially nonoscillatory finite difference scheme. The main purpose of this study is to reveal the mechanism of sound generation in the interaction between a shock wave and two counter-rotating vortices. It is found that there are two regimes of sound generation in this interaction. The first regime corresponds to the shock interaction with two isolated vortices, in which the sound wave generated by the interaction between the shock wave and two counter-rotating vortices equals to the linear combination of the sound waves generated by the interactions between the same shock wave and each vortex. The second regime corresponds to the shock interaction with a coupled vortex pair, in which the sound wave comes from two processes. One is the vortex coupling, and the second is the interaction between the shock wave and the coupled vortex pair.
Abstract In this paper, an enclosed membrane‐photobioreactor was designed to remove CO 2 using Chlorella vulgaris . The performances of four reactors, which included the presented novel bioreactor, a draft tube airlift photobioreactor, a bubble column and a membrane contactor, were compared. The effects of the gas flow rate, light intensity, quality of the inner light source, and the characteristics of membrane module on CO 2 fixation were investigated. The results showed that the rate of CO 2 fixation in the membrane‐photobioreactor was 0.95–5.40 times higher than that in the other three conventional reactors under the optimal operating conditions
Localisation is an essential and important part in wireless sensor networks (WSNs). Many applications require location information. So far, there are less researchers studying on mobile sensor networks (MSNs) than static sensor networks (SSNs). However, MSNs are required in more and more areas such that the number of anchor nodes can be reduced and the location accuracy can be improved. In this paper, we firstly propose a range-free Voronoi-based Monte Carlo localisation algorithm (VMCL) for MSNs. We improve the localisation accuracy by making better use of the information that a sensor node gathers. Then, we propose an optimal region selection strategy of Voronoi diagram based on VMCL, called ORSS-VMCL, to increase the efficiency and accuracy for VMCL by adapting the size of Voronoi area during the filtering process. Simulation results show that the accuracy of these two algorithms, especially ORSS-VMCL, outperforms traditional MCL.
The weighted essentially non-oscillatory (WENO) schemes are a popular class of high order accurate numerical methods for solving hyperbolic partial differential equations (PDEs). The computational cost of such schemes increases significantly when the spatial dimensions of the PDEs are high, due to large number of spatial grid points and nonlinearity of high order accuracy WENO schemes. How to achieve fast computations by WENO methods for high spatial dimension PDEs is a challenging and important question. Recently, sparse-grid has become a major approximation tool for high dimensional problems. The open question is how to design WENO computations on sparse grids such that comparable high order accuracy of WENO schemes in smooth regions and essentially non-oscillatory stability in non-smooth regions of the solutions can still be achieved as that for computations on regular single grids? In this paper, we combine the third order finite difference WENO method with sparse-grid combination technique and solve high spatial dimension hyperbolic equations on sparse grids. WENO interpolation is proposed for the prolongation part in sparse grid combination techniques to deal with discontinuous solutions of hyperbolic equations. Numerical examples are presented to show that significant computational times are saved while both high order accuracy and stability of the WENO scheme are maintained for simulations on sparse grids.
Abstract The oil layers in Dagang Banqiao Oilfield are deeply buried, have many layers, and have large differences in water absorption between layers. The existing bridge-type concentric injection technology to control water distribution requires well test trucks and personnel to arrive at the well site to perform cable hoisting and instrument operations. Obtaining the injection parameters is short-term, and long-term monitoring cannot be achieved. During the operation, problems such as instrument obstruction and jamming often occur, resulting in a low operation success rate and difficulty in meeting the needs of the oil field for injection, control and water distribution. To solve the above problems, remote monitoring and remote control intelligent injection technology were proposed. This technology consists of a host computer client, a data center server, a monitoring remote control and a digital water distributor. The connection between the client and the data center server relies on the internal network of the oil field, and the remote wireless communication between the data center server and the monitoring remote control is carried out through VPDN. The monitoring remote control is installed on the injection wellhead water injection pipeline and consists of a pressure gauge, flow meter, chip, electronic control valve, communication module, etc. The digital water distributor integrates modules such as batteries, motors, chips, pressure sensors, and adjustable water nozzles, one for each water injection layer. Wave code wireless communication is used between the monitoring remote control and the digital water distributor. Wave code wireless communication uses injected water as the carrier. By changing the opening of the ground electronic control valve or the water nozzle of the digital water distributor in a short time, it establishes the water injection pressure fluctuation signal in the oil pipe. After coding and decoding processing, it realizes monitoring of remote control and digital water distribution. Two-way communication between controllers, that is, the monitoring remote controller sends control instructions to the digital water distributor, the monitoring remote controller receives instructions or the digital water distributor executes control instructions, and sends the collected dispensing parameter data to the monitoring remote controller. Up to now, 36 wells have been applied on site, with a success rate of 100%, maximum well depth: 3827m, maximum oil layer temperature: 120°, and maximum validity period: 1482 days. This technology is not affected by well site environment, weather changes, time and other factors, and has significant advantages such as high measurement and adjustment efficiency, high measurement and adjustment success rate, and low management cost. The dispensing parameters can be monitored remotely from the PC client in the office for a long time, and the digital water distributor can be remotely controlled to inject water or inspect the seal according to the water distribution requirements. This technology is simple and convenient to operate, and can provide experience and reference for the development of layered water injection in domestic and foreign oil fields.
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