scholarly journals Direct observations of blob deformation during a substorm

2015 ◽  
Vol 33 (5) ◽  
pp. 525-530 ◽  
Author(s):  
T. Ishida ◽  
Y. Ogawa ◽  
A. Kadokura ◽  
K. Hosokawa ◽  
Y. Otsuka
Keyword(s):  
High Speed ◽  
Temporal Evolution ◽  
Dissociative Recombination ◽  
Helmholtz Instability ◽  
Plasma Parameters ◽  
Flow Shear ◽  
Expansion Phase ◽  
Incoherent Scatter ◽  
Direct Observations ◽  
Transportation Process

Abstract. Ionospheric blobs are localized plasma density enhancements, which are mainly produced by the transportation process of plasma. To understand the deformation process of a blob, observations of plasma parameters with good spatial–temporal resolution are desirable. Thus, we conducted the European Incoherent Scatter radar observations with high-speed meridional scans (60–80 s) during October and December 2013, and observed the temporal evolution of a blob during a substorm on 4 December 2013. This paper is the first report of direct observations of blob deformation during a substorm. The blob deformation arose from an enhanced plasma flow shear during the substorm expansion phase, and then the blob split into two smaller-scale blobs, whose scale sizes were more than ~100 km in latitude. Our analysis indicates that the Kelvin–Helmholtz instability and dissociative recombination could have deformed the blob structure.

Spatial–Temporal Evolution and Plasma Parameters’ Diagnosis of a Transverse Glow Discharge in Atmospheric Pressure Air

2019 ◽  
Vol 47 (2) ◽  
pp. 1330-1335
Author(s):  
Xuechen Li ◽  
Kaiyue Wu ◽  
Renjing Liu ◽  
Linwei Yang ◽  
Jinling Geng ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Atmospheric Pressure ◽  
Temporal Evolution ◽  
Plasma Parameters

scholarly journals MIDAS-W: a workstation-based incoherent scatter radar data acquisition system

2000 ◽  
Vol 18 (9) ◽  
pp. 1231-1241 ◽  
Author(s):  
J. M. Holt ◽  
P. J. Erickson ◽  
A. M. Gorczyca ◽  
T. Grydeland
Keyword(s):  
Data Processing ◽  
Data Acquisition ◽  
High Speed ◽  
Data Acquisition System ◽  
Acquisition System ◽  
Incoherent Scatter Radar ◽  
Raw Data ◽  
Incoherent Scatter ◽  
Scatter Radar ◽  
Instruments And Techniques

Abstract. The Millstone Hill Incoherent Scatter Data Acquisition System (MIDAS) is based on an abstract model of an incoherent scatter radar. This model is implemented in a hierarchical software system, which serves to isolate hardware and low-level software implementation details from higher levels of the system. Inherent in this is the idea that implementation details can easily be changed in response to technological advances. MIDAS is an evolutionary system, and the MIDAS hardware has, in fact, evolved while the basic software model has remained unchanged. From the earliest days of MIDAS, it was realized that some functions implemented in specialized hardware might eventually be implemented by software in a general-purpose computer. MIDAS-W is the realization of this concept. The core component of MIDAS-W is a Sun Microsystems UltraSparc 10 workstation equipped with an Ultrarad 1280 PCI bus analog to digital (A/D) converter board. In the current implementation, a 2.25 MHz intermediate frequency (IF) is bandpass sampled at 1 µs intervals and these samples are multicast over a high-speed Ethernet which serves as a raw data bus. A second workstation receives the samples, converts them to filtered, decimated, complex baseband samples and computes the lag-profile matrix of the decimated samples. Overall performance is approximately ten times better than the previous MIDAS system, which utilizes a custom digital filtering module and array processor based correlator. A major advantage of MIDAS-W is its flexibility. A portable, single-workstation data acquisition system can be implemented by moving the software receiver and correlator programs to the workstation with the A/D converter. When the data samples are multicast, additional data processing systems, for example for raw data recording, can be implemented simply by adding another workstation with suitable software to the high-speed network. Testing of new data processing software is also greatly simplified, because a workstation with the new software can be added to the network without impacting the production system. MIDAS-W has been operated in parallel with the existing MIDAS-1 system to verify that incoherent scatter measurements by the two systems agree. MIDAS-W has also been used in a high-bandwidth mode to collect data on the November, 1999, Leonid meteor shower.Key words: Electromagnetics (instruments and techniques; signal processing and adaptive antennas) – Ionosphere (instruments and techniques)

scholarly journals Drag Reduction by Microvortexes in Transverse Microgrooves

2014 ◽  
Vol 6 ◽  
pp. 734012 ◽  
Author(s):  
Bao Wang ◽  
Jiadao Wang ◽  
Gang Zhou ◽  
Darong Chen
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Bottom Layer ◽  
Experimental Results ◽  
Dynamics Simulation ◽  
Surface Drag ◽  
Flow Shear ◽  
Detailed Simulation ◽  
Flow Shear Stress ◽  
Microgrooved Surface

A transverse microgrooved surface was employed here to reduce the surface drag force by creating a slippage in bottom layer in turbulent boundary layer. A detailed simulation and experimental investigation on drag reduction by transverse microgrooves were given. The computational fluid dynamics simulation, using RNG k- ε turbulent model, showed that the vortexes were formed in the grooves and they were a main reason for the drag reduction. On the upside of the vortex, the revolving direction was consistent with the main flow, which decreased the flow shear stress by declining the velocity gradient. The experiments were carried out in a high-speed water tunnel with flow velocity varying from 17 to 19 m/s. The experimental results showed that the drag reduction was about 13%. Therefore, the computational and experimental results were cross-checked and consistent with each other to prove that the presented approach achieved effective drag reduction underwater.

Different Flame Patterns Linked With Swirling Injector Interactions in an Annular Combustor

2015 ◽  
Author(s):  
Daniel Durox ◽  
Kevin Prieur ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
High Speed ◽  
Light Emission ◽  
Burning Velocity ◽  
High Speed Imaging ◽  
Direct Observations ◽  
Annular Combustor ◽  
Expansion Angle ◽  
Combustion Region ◽  
Flame Region ◽  
Side Walls

It is known from cold flow experiments that linear arrays of injectors may feature different types of aerodynamic patterns (see for example ASME-GT2013-94280, ASME-GT2014-25094). There are however no indications on what can happen under hot fire conditions since most experiments have been carried out in the absence of reaction or in single injector configurations. It is now possible to investigate this issue by making use of a recently developed annular combustion chamber. This device designated as MICCA is equipped with multiple swirling injectors and its side walls are made of quartz providing full optical access to the flame region thus allowing detailed studies of the combustion region structure and dynamics. Experiments reported in this article rely on direct observations of the flame region through light emission imaging using two standard cameras and an intensified high speed CMOS camera. The data gathered indicate that interactions between successive injectors give rise to patterns of flames which exhibit an alternate geometry where one flame has a relatively low expansion angle while the next spreads sideways. This pattern is then repeated with a period which corresponds to twice the injector spacing. Such arrangements arise when the angle of the cup used as the end-piece of each injector exceeds a critical value. Effects of mass flow rate, equivalence ratio, and injector offset are also investigated. It is shown that the angle which defines the cup opening is the main control parameter. It is also found that when this angle exceeds a certain value and when the laminar burning velocity is fast enough, the flame pattern switches in an unsteady manner between two possible configurations. This unsteady behavior is characterized using high-speed imaging. It is finally shown that these alternating flame patterns lead to alternating heat release rate distributions and inhomogeneous heat transfer to the chamber walls featuring a helicoidal pattern.

scholarly journals Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

2009 ◽  
Vol 27 (7) ◽  
pp. 2623-2631 ◽  
Author(s):  
D. M. Wright ◽  
R. S. Dhillon ◽  
T. K. Yeoman ◽  
T. R. Robinson ◽  
E. C. Thomas ◽  
...  
Keyword(s):  
Hf Radar ◽  
High Latitudes ◽  
Plasma Parameters ◽  
Power Cycle ◽  
Incoherent Scatter ◽  
Radiated Power ◽  
Induced Field ◽  
High Latitude Ionosphere ◽  
Very High ◽  
Field Aligned Irregularities

Abstract. On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs). The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt) and collapse (Pc) of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR) failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

scholarly journals Analysis of Hypersonic Platform-Borne SAR Imaging: A Physical Perspective

2021 ◽  
Vol 13 (23) ◽  
pp. 4943
Author(s):  
Lihao Song ◽  
Bowen Bai ◽  
Xiaoping Li ◽  
Gezhao Niu ◽  
Yanming Liu ◽  
...  
Keyword(s):  
High Speed ◽  
Signal Propagation ◽  
High Plasma ◽  
Plasma Sheath ◽  
Plasma Parameters ◽  
Sar Images ◽  
Scatter Matrix ◽  
Imaging Quality ◽  
Imaging Results ◽  
Sar Imaging

The usage of a hypersonic platform for remote sensing application has promising prospects, especially for hypersonic platform-borne synthetic aperture radar (SAR) imaging. However, the high-speed of hypersonic platform will lead to extreme friction between the platform and air, which will cause the ionization of air. The ionized gas forms the plasma sheath wrapped around the hypersonic platform. The plasma sheath will severely affect the propagation of SAR signal and further affect the SAR imaging. Therefore, hypersonic platform-borne SAR imaging should be studied from a physical perspective. In this paper, hypersonic platform-borne SAR imaging under plasma sheath is analyzed. The SAR signal propagation in plasma sheath is computed using scatter matrix method. The proposed SAR signal model is verified by using a ground experiment system. Moreover, the effect of attenuation caused by plasma sheath on SAR imaging is studied under different SAR parameters and plasma sheath. The result shows that attenuation caused by plasma sheath will degrade the SAR imaging quality and even cause the point and area targets to be submerged into the noise. The real SAR images under plasma sheath also illustrate this phenomenon. Furthermore, by studying imaging results under different SAR and plasma parameters, it can be concluded that the severe degradation of SAR imaging quality appears at condition of high plasma sheath electron density and low SAR carrier frequency. The work in this paper will be beneficial for the study of hypersonic platform-borne SAR imaging and design of hypersonic SAR imaging systems in the future.

scholarly journals The Kelvin-Helmholtz Instability From the Perspective of Hybrid Simulations

2021 ◽  
Vol 8 ◽  
Author(s):  
P. A. Delamere ◽  
N. P. Barnes ◽  
X. Ma ◽  
J. R. Johnson
Keyword(s):  
Solar Wind ◽  
Surface Waves ◽  
Energy Transport ◽  
Helmholtz Instability ◽  
Flow Shear ◽  
Planetary Magnetospheres ◽  
Dayside Magnetopause ◽  
Hybrid Simulations

The flow shear-driven Kelvin-Helmholtz (KH) instability is ubiquitous in planetary magnetospheres. At Earth these surface waves are important along the dawn and dusk flanks of the magnetopause boundary while at Jupiter and Saturn the entire dayside magnetopause boundary can exhibit KH activity due to corotational flows in the magnetosphere. Kelvin-Helmholtz waves can be a major ingredient in the so-called viscous-like interaction with the solar wind. In this paper, we review the KH instability from the perspective of hybrid (kinetic ions, fluid electrons) simulations. Many of the simulations are based on parameters typically found at Saturn’s magnetopause boundary, but the results can be generally applied to any KH-unstable situation. The focus of the discussion is on the ion kinetic scale and implications for mass, momentum, and energy transport at the magnetopause boundary.

scholarly journals Chinese High-speed Railway: Efficiency Comparison and the Future

2019 ◽  
Vol 31 (6) ◽  
pp. 693-702 ◽  
Author(s):  
Weidong Li ◽  
Olli-Pekka Hilmola ◽  
Jianhong Wu
Keyword(s):  
High Speed ◽  
Diffusion Models ◽  
High Speed Railway ◽  
Expansion Phase ◽  
South Korean ◽  
Network Building ◽  
Network Investment ◽  
Dea Efficiency ◽  
Efficiency Comparison ◽  
Frontier Efficiency

High-speed railway (HSR) network building was initiated in China in the early 2000s, and full-scale construction began several years later as a larger use phase started in 2008. Thereafter, the expansion speed has been impressive. Network investment could be considered as a success, if evaluating the amount of high-speed railway usage already during the expansion phase. The diffusion models built in this research show that expansion in the network and growth of the passengers will continue at least until the following decade. The performance is evaluated in terms of DEA efficiency model. It is shown that efficiency started from very low levels, but it has been increasing together with the expansion of HSR network. Currently, the efficiency is near the level of the leading European High-speed (HS) countries (Germany and France). However, it is projected with linear model and by Bass diffusion models that the efficiency will reach Japanese and South Korean standards in the next decade. A somewhat larger network length with smaller relative growth of passengers, but with a higher growth of passenger-km seems to be able to reach even the frontier efficiency.

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