Orbital debris and meteoroid population as estimated from LDEF impact data

Examination of LDEF's various surfaces shows numerous craters and holes due to hypervelocity impacts of meteoroids and man-made orbital debris. In this paper, the crater numbers as reported by Humes have been analyzed in an effort to understand the orbital debris and natural meteoroid environment in LEO. To determine the fraction of man-made to natural impacts, the side to top ratio of impacts and results of the Chemistry of Micrometeoroids Experiment are used. For craters in the 100 micron to 500 micron size range, about 25 percent to 30 percent of the impacts on the forward-facing surfaces and about 10 percent of the impacts on the trailing surfaces were estimated due to man-made orbital debris. A technique has been developed to convert crater numbers to particle fluxes, taking the fact into account that the distributions of impact velocity and incidence angle vary over the different surfaces of LDEF, as well as the ratio of the surface area flux to the cross-sectional area flux. Applying this technique, Humes' data concerning craters with limiting lip diameters of 100 micron, 200 micron and 500 micron have been converted into orbital debris and meteoroid fluxes ranging from about 20 micron to 200 micron particle diameter. The results exhibit good agreement with orbital debris model and meteoroid model. The converted meteoroid flux is slightly larger than Grun's model (by 40 to 70 percent). The converted orbital debris flux is slightly lower than Kessler's model for particle diameter smaller than about 30 micron and slightly larger than the model for particle diameter larger than about 40 micron. Taking also into account the IDE data point at about 0.8 micron particle diameter, it suggests to change the slope log (flux) versus log (diameter) of orbital debris flux in the 1 micron to 100 micron particle diameter range from 2.5 to 1.9

Aircraft Ground Taxiing Deduction and Conflict Early Warning Method Based on Control Command Information

Aircraft taxiing conflict is a threat to the safety of airport operations, mainly due to the human error in control command infor-mation. In order to solve the problem, The aircraft taxiing deduction and conflict early warning method based on control order information is proposed. This method does not need additional equipment and operating costs, and is completely based on his-torical data and control command information. When the aircraft taxiing command is given, the future route information will be deduced, and the probability of conflict with other taxiing aircraft will be calculated to achieve conflict detection and early warning of different levels. The method is validated by the aircraft taxi data from real airports. The results show that the method can effectively predict the aircraft taxiing process, and can provide early warning of possible conflicts. Due to the advantages of low cost and high accuracy, this method has the potential to be applied to airport operation decision support system

The immunoregulation effect of tumor microenvironment in pancreatic ductal adenocarcinoma

Pancreatic cancer has the seventh highest death rate of all cancers. The absence of any serious symptoms, coupled with a lack of early prognostic and diagnostic markers, makes the disease untreatable in most cases. This leads to a delay in diagnosis and the disease progresses so there is no cure. Only about 20% of cases are diagnosed early. Surgical removal is the preferred treatment for cancer, but chemotherapy is standard for advanced cancer, although patients can eventually develop drug resistance and serious side effects. Chemoresistance is multifactorial because of the interaction among pancreatic cancer cells, cancer stem cells, and the tumor microenvironment (TME). Nevertheless, more pancreatic cancer patients will benefit from precision treatment and targeted drugs. This review focuses on the immune-related components of TME and the interactions between tumor cells and TME during the development and progression of pancreatic cancer, including immunosuppression, tumor dormancy and escape. Finally, we discussed a variety of immune components-oriented immunotargeting drugs in TME from a clinical perspective

ELECTRICAL CONTACTS COUPLING EFFECT ON SINGLE-WALLED CARBON NANOTUBE ELECTRON RESONATOR

Abstract. We have studied the electrical contacts coupling effect on a left lead/central singlewalled carbon nanotubes(SWNTs)/right lead system by using the tight binding Green function approach. It is showed that at strong coupling strength between electrical contact and central SWNT, the system behaves as Fabry-Perot electron resonator, which can show distinct quantum conductance oscillations and complicate background as the Fermi energy is driven far from the charge neutrality energy point by the applied gate-voltage V g , the shape of conductance background is dependent on the contacts coupling strength and the chirality of SWNT. For very weak contacts coupling strength, the system presents well defined resonant peaks, which is the limit of the quantum conductance oscillations

Stability of the Stochastic Reaction-Diffusion Neural Network with Time-Varying Delays and p-Laplacian

The main aim of this paper is to discuss moment exponential stability for a stochastic reaction-diffusion neural network with time-varying delays and p-Laplacian. Using the Itô formula, a delay differential inequality and the characteristics of the neural network, the algebraic conditions for the moment exponential stability of the nonconstant equilibrium solution are derived. An example is also given for illustration

Self-Attention Based Sequential Recommendation With Graph Convolutional Networks

Learning embeddings representations of users and items lies at the core of modern recommender systems. Existing methods based on Graph Convolutional Network (GCN) and sequential recommendation typically obtain a user’s or an item’s embedding by mapping from pre-existing features into better embeddings for users and items, such as ID and attributes. GCN integrates the user-item interaction as the bipartite graph structure into the embedding process, which can better represent sparse data, but cannot capture users’ long-term interests. Sequential recommendation seek to capture the “context” of users’ activities based on their historical actions, but requires dense data to support it. The goal of our work is to combine the advantages of GCN and sequential recommendation models by proposing a novel Self-Attention based Sequential recommendation with Graph Convolutional Networks (SASGCN). It uses multiple lightweight GCN layers to capture high-order connectivity between users and items, and by introducing ratings as auxiliary information into the user-item interaction matrix, it provides richer information. By incorporating self-attention based methods, the proposed model capture long-term semantics through relatively few actions. Extensive experiments on three benchmark datasets show that our model outperforms various state-of-the-art models consistently

GPU-accelerated transient lattice Boltzmann simulation of bubble column reactors

Design parameters for Bubble Column Reactors such as backmixing and light/dark cycles of microalgae cells are pertinent to transient flow dynamics and mesoscale coherent structures. Transient simulation is therefore of practical significance. Traditional CFD solvers are generally implemented on multi-core CPU workstations, which is time-consuming and difficult to meet the requirement of industry applications. We developed a GPU-accelerated transient LBM simulation of gas-liquid flow, achieving 5000 times acceleration in comparison with the CFD simulation. A notable feature of this method, which allows a tunable and smaller dimensionless relaxation time, is the remarkable decrease of required mesh number in LBM simulation by several orders of magnitude. The solver is validated against experimental data, resolving two mechanisms of mesoscale structure, i.e., vortex rotation and radial migration, in the intensification of macromixing. The computation acceleration and resolution of mesoscale structures demonstrate the potential of this approach for fast simulation of industrial applications. (C) 2019 Elsevier Ltd. All rights reserved

Lattice Boltzmann simulation of drop splitting in a fractal tree-like microchannel

Fractal tree-like microchannel is advantageous to faster emulsification and droplet production in microchannels. Although computer simulation is becoming a powerful tool for design and optimization, precise treatment of a large number of walls in fractal tree-like microchannel is troublesome. The numer-ical roughness caused by traditional bounce-back boundary condition may accumulate and generate large errors in flow pattern recognization. In this paper, an approach integrating Immersed Boundary Method (IBM), Phase-Field Model (PFM) and Lattice Boltzmann Method (LBM) is developed, aiming to accurately simulate droplet splitting in fractal tree-like microchannel system involving surfactants and wetting boundary walls. Then the operating conditions including capillary number, flow rate ratio and wetting boundary conditions were optimized. We found that the capillary number in 0.02 ti 0.05 and flow rate ratio in 1/3.6 - 1/9 can accelerate emulsification. Hydrophobic-lipophilic walls generate a slug-like water drop of bullet shape and thin oil film between the drop and walls, facilitating drop move-ment in microchannel. The effects of surfactant, Marangoni stress and interfacial tension force on droplet splitting were investigated. The contact walls at the corner and forks resist the surfactant migration, and therefore enrich surfactant at the upstream end of drop interface, leading to uneven distribution of inter-facial tension. The breaking interfaces and the interfaces contacting with wall or fork are subjected to opposite reaction of Marangoni stress and tend to be thinner and finally deform or break. (c) 2021 Elsevier Ltd. All rights reserved

THE STUDY OF EMBEDDED INTELLIGENT VEHICLE NAVIGATION SYSTEM*

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, CaliforniaThe intelligent vehicle navigation system is the multifunctional and complex integrate system that involved in auto positioning technology, geography information system and digital map database, computer technology, multimedia and wireless communication technology. In this paper, the autonomous navigation system based on the embedded hardware and embedded software platform is proposed. The system has advantages of low cost, low power consumption, multifunction and high stability and reliability.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

Design of double-notch UWB filter with upper stopband characteristics based on ACPW-DGS.

In this manuscript, a compact (size only 9.8mm*9.8mm) Ultra Wide Band (UWB) bandpass filter with a new structure is proposed, which can be used in the UWB wireless communication band authorized by the FCC. The top plane is composed of a pair of back-to-back microstrip lines, and the ground plane structure is based on an asymmetric coplanar waveguide-defect ground structure (ACPW-DGS). UWB is formed by the vertical electromagnetic coupling of the top plane and the ground plane. On this basis, split ring resonator (SRR) and C type resonator (CTR) are utilized to place double notch bands. A novel third order nested C-type resonator (TONCTR) is obtained by performing CTR, which can further optimize the upper stopband while ensuring double notch bands. The filter can be used for filtering within the UWB system, and it can also avoid the amateur radio band (9.2 -10.3GHz) and the X-band satellite link band (9.6-12.3GHz) on UWB communication systems. Finally, the measured results from the fabricated prototype are basically consistent with the simulation results