scholarly journals Distributed Multistatic Sky-Wave Over-The-Horizon Radar Based on the Doppler Frequency for Marine Target Positioning

Electronics ◽  
2021 ◽  
Vol 10 (12) ◽  
pp. 1472
Author(s):  
Fangyu Ren ◽  
Huotao Gao ◽  
Lijuan Yang
Keyword(s):  
Measurement Error ◽  
Weighted Least Squares ◽  
Doppler Frequency ◽  
Frequency Measurement ◽  
Difficult Problem ◽  
Radar System ◽  
Height Measurement ◽  
Safety Issues ◽  
Rectangular Coordinates ◽  
Set Up

Maritime safety issues have aroused great attention, and it has become a difficult problem to use the sky-wave over-the-horizon radar system to locate foreign targets or perform emergency rescue quickly and timely. In this paper, a distributed multi-point sky-wave over-the-horizon radar system is used to locate marine targets. A positioning algorithm based on the Doppler frequency is proposed, namely, the two-step weighted least squares (2WLS) method. This algorithm first converts the WGS-48 geodetic coordinates of the transceiver station to spatial rectangular coordinates; then, introduces intermediate variables to convert the nonlinear optimization problem into a linear problem. In the 2WLS method, four mobile transmitters and four mobile receivers are set up, and the Doppler frequency is calculated by transmitting and receiving signals at regular intervals; it is proven that the 2WLS algorithm has always maintained a better positioning accuracy than the WLS algorithm as the error continues to increase with a certain ionospheric height measurement error and the Doppler frequency measurement error. This paper provides an effective method for the sky-wave over-the-horizon radar to locate maritime targets.

Enhancement of Radar Imagery by Maximum Entropy Processing

1977 ◽  
Vol 21 (3) ◽  
pp. 241-243 ◽  
Author(s):  
Clanton E. Mancill
Keyword(s):  
Maximum Entropy ◽  
Signal To Noise Ratio ◽  
Super Resolution ◽  
Doppler Frequency ◽  
Frequency Measurement ◽  
Entropy Method ◽  
Frequency Resolution ◽  
Sampled Data ◽  
Maximum Entropy Spectrum ◽  
Using Data

The maximum entropy spectrum (MES), a sampled data power spectrum estimator, is applied to the enhancement of imagery obtained by synthetic array radar (SAR) imaging systems. MES offers better frequency resolution than conventional Fourier transform methods for certain signal classes. Since azimuth ground resolution in SAR systems is obtained by doppler frequency measurement of the radar return, the method is capable of enhancing the resolution of SAR maps. The principal signal requirement is adequate signal-to-noise ratio. The maximum entropy method has been tested using data obtained by the Hughes FLAMR radar system. The super-resolution capabilities of the method are demonstrated using FLAMR images of corner reflector arrays.

Microstructured Reactors for Gas Phase Reactions

2008 ◽  
Author(s):  
Steffen Schirrmeister
Keyword(s):  
Gas Phase ◽  
Flow Distribution ◽  
Pilot Scale ◽  
Gas Phase Reactions ◽  
Process Technology ◽  
Safety Issues ◽  
Catalyst Coating ◽  
Coating Flow ◽  
Set Up ◽  
Micro Technology

Pilot-scale micro-process technology for heterogeneously catalyzed gas phase reactions is generally highly demanding towards the methods of catalyst coating, flow distribution, reactor manufacturing and assembly, safety issues and other factors. Yet, first cost analysis have shown that economical processes can be developed using micro-technology. For this matter, it is necessary to improve and simplify the laboratory set-up, meaning that the stacked architectures at the meter-scale must be brought down to the micron-scale. This in return calls for specific methods of catalyst coating and a particularly precise assembly of the operation unit.

A New Airborne Passive DF Method only Based on Frequency Difference

2011 ◽  
Vol 219-220 ◽  
pp. 846-850
Author(s):  
Tao Yu
Keyword(s):  
Direction Cosine ◽  
Doppler Frequency ◽  
Frequency Measurement ◽  
Frequency Difference ◽  
Baseline Length ◽  
Direct Proportion ◽  
Unknown Parameters ◽  
Flight Direction ◽  
Phase Interference ◽  
Circular Functions

If three antenna units are divided into two set and two baselines are placed at right angles to each other in flight plain, in which the direction of one baseline is parallel to the actual flight direction of air vehicle, the sine and cosine function of target bearing respectively in two baseline directions can be simultaneously obtained according to the analysis principle of the direction cosine change rate. The angulations’ formula only based on Doppler frequency difference can be derived after eliminating the unknown parameters including angular velocity and wavelength by the specific value of two circular functions. The analog calculation shows that the relative error is in direct proportion to the baseline length provided that the incident wave is parallel in derivation. But the error analysis depicts that the measurement accuracy is in direct proportion to the baseline length. Moreover, the measurement error relies on mainly the accuracy of frequency measurement. Furthermore, the derived formula has irregularity in airborne axis direction. However, since the new method is not associated with wavelength, this new DF only based on Doppler frequency difference will be more adapted to passive sounding as compared with phase interference method.

scholarly journals 4D Flow MRI Pressure Estimation Using Velocity Measurement-Error-Based Weighted Least-Squares

2020 ◽  
Vol 39 (5) ◽  
pp. 1668-1680 ◽  
Author(s):  
Jiacheng Zhang ◽  
Melissa C. Brindise ◽  
Sean Rothenberger ◽  
Susanne Schnell ◽  
Michael Markl ◽  
...  
Keyword(s):  
Measurement Error ◽  
Least Squares ◽  
Velocity Measurement ◽  
Weighted Least Squares ◽  
4D Flow Mri ◽  
4D Flow ◽  
Flow Mri ◽  
Pressure Estimation

scholarly journals Can the Planck Length Be Found Independent of Big G?

2017 ◽  
Vol 9 (6) ◽  
pp. 58 ◽  
Author(s):  
Espen Gaarder Haug
Keyword(s):  
Measurement Error ◽  
Particle Accelerators ◽  
Relative Measurement ◽  
Planck Length ◽  
Relative Measurement Error ◽  
Set Up

In this paper we show how it is possible to measure the Planck length through a series of different methods. One of these measurements is totally independent of big G, but moving from the theoretical realm to the empirical realm would require particle accelerators far more powerful than the ones that we have today. However, a Cavendish-style experiment can also be performed to find the Planck length with no knowledge of the value of big G. Furthermore, the Cavendish style set-up gives half of the relative measurement error in the Planck length compared to the measurement error in big G.

scholarly journals Detection of a Semi-Rough Target in Turbulent Atmosphere by an Electromagnetic Gaussian Schell-Model Beam

2019 ◽  
Vol 9 (14) ◽  
pp. 2790
Author(s):  
Xiaofei Li ◽  
Yuefeng Zhao ◽  
Xianlong Liu ◽  
Yangjian Cai
Keyword(s):  
Inverse Problem ◽  
Atmospheric Turbulence ◽  
Turbulent Atmosphere ◽  
Incident Beam ◽  
Radar System ◽  
Equivalent Model ◽  
Laser Radar ◽  
Beam Radius ◽  
Tensor Method ◽  
Set Up

The interaction of an electromagnetic Gaussian Schell-model beam with a semi-rough target located in atmospheric turbulence was studied by means of a tensor method, and the corresponding inverse problem was analyzed. The equivalent model was set up on the basis of a bistatic laser radar system and a rough target located in a turbulent atmosphere. Through mathematical deduction, we obtained detailed information about the parameters of the semi-rough target by measuring the beam radius, coherence radius of the incident beam and the polarization properties of the returned beam.

Numerical simulation of dispersion and distribution behaviors of hydrogen leakage in the garage with a crossbeam

SIMULATION ◽  
2019 ◽  
Vol 95 (12) ◽  
pp. 1229-1238 ◽  
Author(s):  
Yunhao Li ◽  
Juncheng Jiang ◽  
Yuan Yu ◽  
Qingwu Zhang
Keyword(s):  
Mole Fraction ◽  
Natural Ventilation ◽  
Stokes Equations ◽  
Ventilation System ◽  
Three Dimensional ◽  
Dynamics Simulation ◽  
Navier Stokes ◽  
Explosion Hazard ◽  
Safety Issues ◽  
Set Up

A three-dimensional computational fluid dynamics simulation model resolved by the unsteady Reynolds-Averaged Navier–Stokes equations was developed to predict hydrogen dispersion in an indoor environment. The effect of the height of the crossbeam (Hc) on hydrogen dispersion and distribution behaviors in a four-car garage was numerically investigated under fully confined and natural ventilation conditions. For the fully confined condition, the garage was almost completely filled with a flammable hydrogen cloud at t=600 s. In addition, the volumetric ratio of the flammable region, thickness of the hydrogen stratification, and hydrogen mole fraction all increased as Hc increased. When two symmetric ventilation openings were set up, the volumetric ratio of the flammable region decreased by 50% at t=600 s. Moreover, Hc had evident influence on the vertical distribution of hydrogen mole fraction. In addition, there existed little explosion hazard under the height of 1.6 m. The results show that Hc was a non-negligible factor for the safety design of hydrogen in the garage and Hc=0.12 m was the optimal height of the crossbeam. Furthermore, the ventilation system in the present study cannot completely eliminate the risk of hydrogen explosion. The present risk assessment results can be useful to analyze safety issues in automotive applications of hydrogen.

scholarly journals Comparing the Air Abrasion Cutting Efficacy of Dentine Using a Fluoride-Containing Bioactive Glass versus an Alumina Abrasive: AnIn VitroStudy

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Melissa H. X. Tan ◽  
Robert G. Hill ◽  
Paul Anderson
Keyword(s):  
Bioactive Glass ◽  
Health And Safety ◽  
Air Abrasion ◽  
X Ray ◽  
Safety Issues ◽  
Outflow Rate ◽  
Caries Removal ◽  
Cutting Efficacy ◽  
Set Up ◽  
Removal Technique

Air abrasion as a caries removal technique is less aggressive than conventional techniques and is compatible for use with adhesive restorative materials. Alumina, while being currently the most common abrasive used for cutting, has controversial health and safety issues and no remineralisation properties. The alternative, a bioactive glass, 45S5, has the advantage of promoting hard tissue remineralisation. However, 45S5 is slow as a cutting abrasive and lacks fluoride in its formulation. The aim of this study was to compare the cutting efficacy of dentine using a customised fluoride-containing bioactive glass Na0SR (38–80 μm) versus the conventional alumina abrasive (29 μm) in an air abrasion set-up. Fluoride was incorporated into Na0SR to enhance its remineralisation properties while strontium was included to increase its radiopacity. Powder outflow rate was recorded prior to the cutting tests. Principal air abrasion cutting tests were carried out on pristine ivory dentine. The abrasion depths were quantified and compared using X-ray microtomography. Na0SR was found to create deeper cavities than alumina (p<0.05) despite its lower powder outflow rate and predictably reduced hardness. The sharper edges of the Na0SR glass particles might improve the cutting efficiency. In conclusion, Na0SR was more efficacious than alumina for air abrasion cutting of dentine.

scholarly journals Incentive Decision on Safety Investment of Supply Chain of Agricultural Products in “Agricultural Super-Docking”

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Weiqin Tang ◽  
Weimin Tang ◽  
Changsheng Jiang ◽  
Shan Lu
Keyword(s):  
Decision Making ◽  
Supply Chain ◽  
Agricultural Products ◽  
Practical Case ◽  
Safety Issues ◽  
Distributed Decision Making ◽  
Set Up ◽  
Safety Investment ◽  
Decision Making Model ◽  
Distributed Decision

Since the “agriculture super-docking” mode was introduced in China in 2007, remarkable success has been made in reducing the transaction cost and improving the quality safety of agricultural products. However, the quality safety issues of agricultural products still occur frequently because both specialized farmers’ cooperatives and supermarkets have insufficient safety investment. In order to study the necessity, goal, and incentive decision schemes of safety investment in “agriculture super-docking” supply chain, three kinds of models, which include noncooperatives distributed decision-making model, centralized decision-making model, and incentive coordination models led by cooperatives and supermarkets, are, respectively, set up in this paper. Conclusions are drawn as follows: when making the uncooperative decentralized decision, both cooperatives and supermarkets have the moral risks to decrease the safety investment, but appropriate measures can achieve the coordination of the supply chain; when achieving the coordination of supply chain, the two contacts under the guidance of cooperatives and supermarkets are the same, and the schemes of distributing profits are also the same. Moreover, a practical case is given to improve the effectiveness and feasibility of the incentive decision schemes.

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