scholarly journals Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays

2004 ◽  
Vol 22 (4) ◽  
pp. 1115-1132 ◽  
Author(s):  
T. Grydeland ◽  
E. M. Blixt ◽  
U. P. Løvhaug ◽  
T. Hagfors ◽  
C. La Hoz ◽  
...  
Keyword(s):  
Video Camera ◽  
Initial Study ◽  
Video Data ◽  
Marginal Stability ◽  
Time Variability ◽  
Clear Correlation ◽  
Radio Science ◽  
Auroral Activity ◽  
Ionosphere Plasma ◽  
Ion Acoustic

Abstract. Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at mid- and high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations is whether or not simultaneously observed up- and down-shifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging. The EISCAT Svalbard Radar has two antennas in the same radar system, which can be used as an interferometer when pointed parallel. In observations from 17 January 2002, between 06:46:10 and 06:46:30 UT, we used this possibility, in combination with direct sampling of the received signals, to yield measurements of "naturally enhanced ion-acoustic echoes" with sufficiently high resolution to resolve such averaging, if any. For the first time, radar interferometry has been employed to estimate the sizes of coherent structures. The observations were coordinated with an image intensified video camera with a narrow field of view. Together, this forms the initial study on the causal relationships between enhanced echoes and fine structure in the auroral activity on sub-kilometer, sub-second scales. The results confirm that the enhanced echoes originate from very localised regions (~300m perpendicular to the magnetic field at 500km altitude) with varying range distribution, and with high time variability (≈200ms). The corresponding increase in scattering cross section, up to 50dB above incoherent scattering, eliminates theoretical explanations based on marginal stability. The simultaneously observed up- and down-shifted enhanced shoulders, when caused by sufficiently narrow structures to be detected by the interferometer technique, originate predominantly from the same volume. These results have significant impact on theories attempting to explain the enhancements, in particular it is found that the ion-electron two-stream mechanism favoured by many authors is an unlikely candidate to explain the observations. The video data has helped establish a clear correlation between the enhanced echoes and auroral activity, on sub-second time scales, showing a threshold connection between the auroral intensity and the triggering of the radar enhancements. It appears that the up- and down-shifted enhanced echoes correlate with fine auroral structures in different ways. Key words. Ionosphere (auroral ionosphere; plasma waves and instabilities) – Radio science (interferometry)

scholarly journals Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P+N Junction Rectifiers

1997 ◽  
Vol 483 ◽  
Author(s):  
P. G. Neudeck ◽  
W. Huang ◽  
M. Dudley
Keyword(s):  
Video Camera ◽  
Initial Study ◽  
Hollow Core ◽  
Power Devices ◽  
Screw Dislocations ◽  
Burgers Vector ◽  
X Ray ◽  
Current Voltage ◽  
The Impact ◽  
Sic Wafer

AbstractIt is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = Ic with no hollow core) in densities on the order of thousands per cm2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p+n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p+n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

Mixed bottom-friction–Kelvin–Helmholtz destabilization of source-driven abyssal overflows in the ocean

2009 ◽  
Vol 626 ◽  
pp. 33-66 ◽  
Author(s):  
GORDON E. SWATERS
Keyword(s):  
Water Column ◽  
Thermohaline Circulation ◽  
Unstable Mode ◽  
Stability Boundary ◽  
Phase Speed ◽  
Bottom Friction ◽  
Marginal Stability ◽  
Time Variability ◽  
Gravitational Acceleration ◽  
Overlying Water

Source-driven ocean currents that flow over topographic sills are important initiation sites for the abyssal component of the thermohaline circulation. These overflows exhibit vigorous space and time variability over many scales as they progress from a predominately gravity-driven downslope flow to a geostrophic along-slope current. Observations show that in the immediate vicinity of a sill, grounded abyssal ocean overflows can possess current speeds greater than the local long internal gravity wave speed with bottom friction and downslope gravitational acceleration dominating the flow evolution. It is shown that these dynamics lead to the mixed frictionally induced and Kelvin–Helmholtz instability of grounded abyssal overflows. Within the overflow, the linearized instabilities correspond to bottom-intensified baroclinic roll waves, and in the overlying water column amplifying internal gravity waves are generated. The stability characteristics are described as functions of the bottom drag coefficient and slope, Froude, bulk Richardson and Reynolds numbers associated with the overflow and the fractional thickness of the abyssal current compared to the mean depth of the overlying water column. The marginal stability boundary and the boundary separating the parameter regimes in which the most unstable mode has a finite or infinite wavenumber are determined. When it exists, the high-wavenumber cutoff is obtained. Conditions for the possible development of an ultraviolet catastrophe are determined. In the infinite-Reynolds-number limit, an exact solution is obtained which fully includes the effects of mean depth variations in the overlying water column associated with a sloping bottom. For parameter values characteristic of the Denmark Strait overflow, the most unstable mode has a wavelength of about 19 km, a geostationary period of about 14 hours, an e-folding amplification time of about 2 hours and a downslope phase speed of about 74 cm s−1.

scholarly journals EYE-C: Eye-Contact Robust Detection and Analysis during Unconstrained Child-Therapist Interactions in the Clinical Setting of Autism Spectrum Disorders

2021 ◽  
Vol 11 (12) ◽  
pp. 1555
Author(s):  
Gianpaolo Alvari ◽  
Luca Coviello ◽  
Cesare Furlanello
Keyword(s):  
Clinical Sample ◽  
Eye Contact ◽  
Video Camera ◽  
Autism Spectrum ◽  
Individual Characteristics ◽  
Video Data ◽  
Contact Dynamics ◽  
Treatment Programs ◽  
Robust Detection ◽  
High Level

The high level of heterogeneity in Autism Spectrum Disorder (ASD) and the lack of systematic measurements complicate predicting outcomes of early intervention and the identification of better-tailored treatment programs. Computational phenotyping may assist therapists in monitoring child behavior through quantitative measures and personalizing the intervention based on individual characteristics; still, real-world behavioral analysis is an ongoing challenge. For this purpose, we designed EYE-C, a system based on OpenPose and Gaze360 for fine-grained analysis of eye-contact episodes in unconstrained therapist-child interactions via a single video camera. The model was validated on video data varying in resolution and setting, achieving promising performance. We further tested EYE-C on a clinical sample of 62 preschoolers with ASD for spectrum stratification based on eye-contact features and age. By unsupervised clustering, three distinct sub-groups were identified, differentiated by eye-contact dynamics and a specific clinical phenotype. Overall, this study highlights the potential of Artificial Intelligence in categorizing atypical behavior and providing translational solutions that might assist clinical practice.

scholarly journals Application of Shore-Based Video and Unmanned Aerial Vehicles (Drones): Complementary Tools for Beach Studies

2020 ◽  
Vol 12 (3) ◽  
pp. 394 ◽  
Author(s):  
Donatus Bapentire Angnuureng ◽  
Philip-Neri Jayson-Quashigah ◽  
Rafael Almar ◽  
Thomas Christian Stieglitz ◽  
Edward Jamal Anthony ◽  
...  
Keyword(s):  
Low Cost ◽  
Video Camera ◽  
Video Data ◽  
Camera System ◽  
Camera Systems ◽  
Camera View ◽  
Aerial Vehicle ◽  
One Year ◽  
Video Camera System ◽  
Good Agreement

Video camera systems have been used over nearly three decades to monitor coastal dynamics. They facilitate a high-frequency analysis of spatiotemporal shoreline mobility. Video camera usage to measure beach intertidal profile evolution has not been standardized globally and the capacity to obtain accurate results requires authentication using various techniques. Applications are mostly site specific due to differences in installation. The present study examines the accuracy of intertidal topographic data derived from a video camera system compared to data acquired with unmanned aerial vehicle (UAV, or drone) surveys of a reflective beach. Using one year of 15-min video data and one year of monthly UAV observations, the intertidal profile shows a good agreement. Underestimations of intertidal profile elevations by the camera-based method are possibly linked to the camera view angle, rectification and gaps in data. The resolution of the video-derived intertidal topographic profiles confirmed, however, the suitability of the method in providing beach mobility surveys matching those required for a quantitative analysis of nearshore changes. Beach slopes were found to vary between 0.1 and 0.7, with a steep slope in May to July 2018 and a gentle slope in December 2018. Large but short-scale beach variations occurred between August 2018 and October 2018 and corresponded to relatively high wave events. In one year, this dynamic beach lost 7 m. At this rate, and as also observed at other beaches nearby, important coastal facilities and infrastructure will be prone to erosion. The data suggest that a low-cost shore-based camera, particularly when used in a network along the coast, can produce profile data for effective coastal management in West Africa and elsewhere.

scholarly journals Determination of areal surface-feature coverage in the Beaufort Sea using aircraft video data

1997 ◽  
Vol 25 ◽  
pp. 434-438 ◽  
Author(s):  
Mark A. Tschudi ◽  
Judith A. Curry ◽  
James A. Maslanik
Keyword(s):  
Sea Ice ◽  
Open Water ◽  
Video Camera ◽  
Surface Feature ◽  
Video Data ◽  
Surface Energy Budget ◽  
The Arctic ◽  
Areal Coverage ◽  
Melt Ponds

The surface-energy budget of the Arctic Ocean depends on the distribution of various sea-ice features that form by both mechanical and thermodynamic processes. Melt ponds, new ice and open water greatly affect the determination of surface albedo. However, even basic measurements of some surface-feature characteristics, such as areal extent of melt ponds, remain rare.A method has been developed to assess the areal coverage of melt ponds, new ice and open water using video data from the Beaufort and Arctic Storms Experiment (BASE). A downward-looking video camera mounted on the underside of a Hercules C-130 aircraft provided clear images of the surface. Images acquired over multi-year ice on 21 September 1994 were analyzed using a spectral technique to determine the areal coverage of melt ponds, new ice and open water. Statistics from this analysis were then compared to previous field studies and to the Schramm and others (in press) sea-ice model.

Braking Response Times for 100 Drivers in the Avoidance of an Unexpected Obstacle as Measured in a Driving Simulator

1996 ◽  
Vol 40 (18) ◽  
pp. 900-904 ◽  
Author(s):  
Nancy L. Broen ◽  
Dean P. Chiang
Keyword(s):  
Standard Deviation ◽  
Response Time ◽  
Driving Simulator ◽  
Response Times ◽  
Video Camera ◽  
Video Data ◽  
Location Information ◽  
Accelerator Pedal ◽  
Shoe Size ◽  
Dynamic Research

This study examined the effect of brake and accelerator pedal configuration on braking response time to an unexpected obstacle. One hundred subjects drove in the Dynamic Research, Inc, (DRI) Interactive Driving Simulator through a simulated neighborhood 21 times, each time with a different pedal configuration. Each subject was presented with an unexpected obstacle only one time, for one of three previously selected pedal configurations, to which he or she was instructed to brake as quickly as possible. Foot movements were recorded with a video camera mounted above the pedals. Data were analyzed manually, using time and course location information superimposed on the video data. Response times were analyzed using ANOVA to determine effects of pedal configuration and various driver factors. Response times ranged from 0.81 sec to 2.44 sec with a mean of 1.33 sec and a standard deviation of 0.27 sec. There was no significant effect of pedal configuration on response time. Driver age was significant, with increased age corresponding to increased response time. Car normally driven, gender, driver height, and shoe size had no significant effect.

Finite-Amplitude Baroclinic Instability of Time-Varying Abyssal Currents

2006 ◽  
Vol 36 (1) ◽  
pp. 122-139 ◽  
Author(s):  
Seung-Ji Ha ◽  
Gordon E. Swaters
Keyword(s):  
Baroclinic Instability ◽  
Soliton Solutions ◽  
Zonal Flow ◽  
Finite Amplitude ◽  
Marginal Stability ◽  
Time Variability ◽  
Time Varying ◽  
Weakly Nonlinear ◽  
Abyssal Current ◽  
The Stability

Abstract The weakly nonlinear baroclinic instability characteristics of time-varying grounded abyssal flow on sloping topography with dissipation are described. Specifically, the finite-amplitude evolution of marginally unstable or stable abyssal flow both at and removed from the point of marginal stability (i.e., the minimum shear required for instability) is determined. The equations governing the evolution of time-varying dissipative abyssal flow not at the point of marginal stability are identical to those previously obtained for the Phillips model for zonal flow on a β plane. The stability problem at the point of marginally stability is fully nonlinear at leading order. A wave packet model is introduced to examine the role of dissipation and time variability in the background abyssal current. This model is a generalization of one introduced for the baroclinic instability of zonal flow on a β plane. A spectral decomposition and truncation leads, in the absence of time variability in the background flow and dissipation, to the sine–Gordon solitary wave equation that has grounded abyssal soliton solutions. The modulation characteristics of the soliton are determined when the underlying abyssal current is marginally stable or unstable and possesses time variability and/or dissipation. The theory is illustrated with examples.

scholarly journals Low frequency waves in plasmas with spatially varying electron temperature

2000 ◽  
Vol 18 (12) ◽  
pp. 1613-1622 ◽  
Author(s):  
P. Guio ◽  
S. Børve ◽  
H. L. Pécseli ◽  
J. Trulsen
Keyword(s):  
Numerical Simulation ◽  
Electron Temperature ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Plasma Temperature ◽  
Electrostatic Waves ◽  
Radio Science ◽  
Particle In Cell ◽  
Ionosphere Plasma ◽  
Low Frequency Waves

Abstract. Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2½-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (ω ≪ Ωci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (ω ≫ Ωci) will on the other hand have a spatially more uniform intensity distribution.Key words: Ionosphere (plasma temperature and density) · Radio science (waves in plasma) · Space plasma physics (numerical simulation studies)

scholarly journals Statement of the Problem of Complete Set of UAV Group on the Basis of Models of Granular Calculations and Fuzzy Logic

2021 ◽  
pp. 25-38
Author(s):  
Vyacheslav Korolyov ◽  
Maksim Ogurtsov ◽  
Alexander Khodzinsky
Keyword(s):  
Fuzzy Logic ◽  
Aerial Photography ◽  
Situational Awareness ◽  
Video Camera ◽  
Video Data ◽  
Aerial Photographs ◽  
Navigation Data ◽  
Heterogeneous Groups ◽  
Big Data Technologies

Introduction. The increase in the number of heterogeneous groups of UAVs that jointly perform aerial photography missions generates a large amount of poorly structured information: videos, photos, telemetry records, navigation data. To build intelligent databases from unstructured information sources from UAV groups, granular computational approaches are proposed. These approaches are the basis for the application of Big Data technologies and artificial intelligence to increase situational awareness or commercial value of knowledge gained from the data flow from UAV groups. The purpose of the article. Develop new models for assessing the quality of video data from UAVs, approaches to equipping heterogeneous groups of UAVs and indicators for assessing its tactical and technical characteristics as a team. Results. The success of UAV group mission planning is based on the forecast of quantitative and qualitative indicators of the received video data. For this purpose, a model for forecasting the quality of the obtained aerial photographs based on the data on the speed, height of the UAV and the angle of the video camera is proposed. The model is based on the development of the theory of fuzzy sets of the first and second types. An example of the implementation of the model in the system of computer mathematics MatLab 2020b is given. Based on the analysis of a number of works on UAV classification and the proposed model of image quality, the method of equipment for the UAV group and the choice of UAV types are built, as well as the content of the combinatorial optimization problem based on the classic backpack problem. An example of calculations of tactical and technical characteristics for the Ukrainian UAV "Spectator" of Meridian ltd. is given. Conclusions. A new model for assessing the quality of aerial photography images based on fuzzy logic has been developed. The method of staffing UAV groups is proposed. Keywords: Fuzzy logic, granular calculations, UAV equipment, heterogeneous groups, computer simulation.

scholarly journals Artwork as Practical Social Action: An Ethnomethodological Study and the New Sociology of Art.

2021 ◽  
Author(s):  
Maximilon Baddeley
Keyword(s):  
Social Action ◽  
Social Order ◽  
Functional Significance ◽  
Ad Hoc ◽  
Video Camera ◽  
Video Data ◽  
Social Phenomena ◽  
Sociology Of Art ◽  
Observable Actions ◽  
Written Descriptions

<p>Few studies in the sociology of art observe artists in their work. Of the few, little investigate the phenomenon of social order, and when they do, they research artists at a distance. Hence, there is room to contribute studies and descriptions of the observable actions artists conduct when they find themselves in the midst of doing their work; that work is argued here as a sociological accomplishment, topic of interest, and evidence of the actual and not imagined practical management of social reality. An emergent literature, the new Sociology of Art, has started to pay close attention toward observing artists’ situated and sequential actions as they occur naturally and in real time. Yet neglected in these often overly conceptual studies are detailed descriptions of artists finding ad hoc solutions to their practical workplace problems. In my motivation to observe artists in their work, I ask how artworks are organised in and as practical social action. With video camera in hand and in aid by the sociological attitudes of ethnomethodology and its research praxis, I aim to explicate social phenomena of order, specifically observable within sites consisting of a street corner, an artist’s studio, an urban café, and river terrain. This thesis presents data first collected and then taken from the large video data corpus to form four single-cases. I recognise in this thesis the effort evident within ethnomethodology’s recent scholarship to acknowledge Aron Gurwitsch’s gestalt concept functional significance as partially influencing Harold Garfinkel’s study of endogenous order. I saw functional significance as an opportunity to explore, rather experimentally, how one artistic action relates to another, and how that interdependence was locally managed by the artists themselves during their artistic processes. This thesis contributes written descriptions of artistic action as social action, findings from which the new Sociology of Art may benefit.</p>

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