scholarly journals Plasma convection at high latitudes using the EISCAT VHF and ESR incoherent scatter radars

2000 ◽  
Vol 18 (9) ◽  
pp. 1088-1096 ◽  
Author(s):  
J. M. Holt ◽  
A. P. van Eyken
Keyword(s):  
Three Dimensional ◽  
Data Sets ◽  
Plasma Convection ◽  
Vhf Radar ◽  
Common Assumption ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
The Common ◽  
Convection Patterns

Abstract. The recent availability of substantial data sets taken by the EISCAT Svalbard Radar allows several important tests to be made on the determination of convection patterns from incoherent scatter radar results. During one 30-h period, the Svalbard Radar made 15 min scans combining local field aligned observations with two, low elevation positions selected to intersect the two beams of the Common Programme Four experiment being simultaneously conducted by the EISCAT VHF radar at Tromsø. The common volume results from the two radars are compared. The plasma convection velocities determined independently by the two radars are shown to agree very closely and the combined three-dimensional velocity data used to test the common assumption of negligible field-aligned flow in this regime.Key words: Ionosphere (auroral ionosphere; polar ionosphere) - Magnetospheric physics (plasma convection)

scholarly journals SuperDARN convection and Sondrestrom plasma drift

2001 ◽  
Vol 19 (7) ◽  
pp. 749-759 ◽  
Author(s):  
L. Xu ◽  
A. V. Koustov ◽  
J. Thayer ◽  
M. A. McCready
Keyword(s):  
Reasonable Agreement ◽  
Temporal Variations ◽  
Line Of Sight ◽  
Data Sets ◽  
Plasma Convection ◽  
Map Comparison ◽  
Incoherent Scatter ◽  
Plasma Drift ◽  
End Products ◽  
Strong Disagreement

Abstract. Plasma convection measurements by the Goose Bay and Stokkseyri SuperDARN radar pair and the Sondrestrom incoherent scatter radar are compared in three different ways, by looking at the line-of-sight (l-o-s) velocities, by comparing the SuperDARN vectors and corresponding Sondrestrom l-o-s velocities and by comparing the end products of the instruments, the convection maps. All three comparisons show overall reasonable agreement of the convection measurements though the data spread is significant and for some points a strong disagreement is obvious. The convection map comparison shows a tendency for the SuperDARN velocities to be often less than the Sondrestrom drifts for strong flows (velocities > 1000 m/s) and larger for weak flows (velocities < 500 m/s). On average, both effects do not exceed 35%. Data indicate that inconsistencies between the two data sets occur largely at times of fast temporal variations of the plasma drift and for strongly irregular flow ac-cording to the SuperDARN convection maps. These facts indicate that the observed discrepancies are in many cases a result of the different spatial and temporal resolutions of the instruments.Key words. Ionosphere (ionospheric irregularities; plasma convection; polar ionosphere)

scholarly journals Enhanced incoherent scatter plasma lines

1996 ◽  
Vol 14 (12) ◽  
pp. 1462-1472 ◽  
Author(s):  
H. Nilsson ◽  
S. Kirkwood ◽  
J. Lilensten ◽  
M. Galand
Keyword(s):  
High Plasma ◽  
Collision Term ◽  
Vhf Radar ◽  
Detailed Model ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Plasma Line ◽  
E Region ◽  
Radar Measurements

Abstract. Detailed model calculations of auroral secondary and photoelectron distributions for varying conditions have been used to calculate the theoretical enhancement of incoherent scatter plasma lines. These calculations are compared with EISCAT UHF radar measurements of enhanced plasma lines from both the E and F regions, and published EISCAT VHF radar measurements. The agreement between the calculated and observed plasma line enhancements is good. The enhancement from the superthermal distribution can explain even the very strong enhancements observed in the auroral E region during aurora, as previously shown by Kirkwood et al. The model calculations are used to predict the range of conditions when enhanced plasma lines will be seen with the existing high-latitude incoherent scatter radars, including the new EISCAT Svalbard radar. It is found that the detailed structure, i.e. the gradients in the suprathermal distribution, are most important for the plasma line enhancement. The level of superthermal flux affects the enhancement only in the region of low phase energy where the number of thermal electrons is comparable to the number of suprathermal electrons and in the region of high phase energy where the suprathermal fluxes fall to such low levels that their effect becomes small compared to the collision term. To facilitate the use of the predictions for the different radars, the expected signal- to-noise ratios (SNRs) for typical plasma line enhancements have been calculated. It is found that the high-frequency radars (Søndre Strømfjord, EISCAT UHF) should observe the highest SNR, but only for rather high plasma frequencies. The VHF radars (EISCAT VHF and Svalbard) will detect enhanced plasma lines over a wider range of frequencies, but with lower SNR.

scholarly journals ADAPTIVE ALGORITHM FOR DETERMINING THE PARAMETERS OF AN INACCESSIBLE POINT OF AN OBJECT

2021 ◽  
pp. 58-70
Author(s):  
Aleksandr Brailov ◽  
Vitaliy Panchenko
Keyword(s):  
Adaptive Algorithm ◽  
Minimum Distance ◽  
Three Dimensional ◽  
Geometrical Model ◽  
Multiple Variables ◽  
The Common ◽  
Relative Errors ◽  
The Given ◽  
Real Experimental Data

In the present research the optimizing approach to the determination of the parameters of an inaccessible point of an object is developed. The common issues are revealed and essential steps of their resolution are identified. The essence of the problem is an objective contradiction between a requirement for the location of points A and B of the centers of the sighting tubes of optical devices in the same horizontal plane P1 and the lack of a real possibility to perform such to achieve this an identical one-level arrangement without error. The aim of the study is to develop strategies for determining the position of an inaccessible point of an object in the minimum domain between intersecting sighting rays as well as an adaptive algorithm for determining the values of the parameters of an inaccessible point under the given absolute and relative errors. To achieve this aim, the following problems are formulated and solved in the paper: 1. Develop strategies for determining the position of the inaccessible point of the object in the minimum domain between the intersecting sighting rays. 2. Develop an adaptive algorithm for determining the values of the parameters of an inaccessible point based on the specified absolute and relative errors. In the proposed optimizing approach, the three-dimensional geometrical model with crossed directional rays for the determination of coordinates of the inaccessible point of an object is developed. It is discussed that points С and C', coordinated of which to be determined, locates in domain [CDM, CEM], [C'D'M, C'E'M] of the minimum distance ρmin between crossed directional rays. The optimizing problem of the determination of coordinates of an inaccessible point of an object in space is reduced to a problem of the determination of the minimum distance between two crossed directional rays. It’s known from the theory of function of multiple variables that function ρ = f (tC'D', tC'E') reaches its extremum ρmin when its partial derivatives by each variable are equal to zero. Three strategies for selecting the position of the inaccessible point C (xC, yC, zC) in the found minimum region [CDM, CEM] are proposed. The required point C' (xC', yC', zC') can be located, for example, in the middle of the minimum segment [C'D'M, C'E'M]. The essence of the adaptive algorithm is in optimizing the variation of the initial values of data α, α', β, γ, γ', AB, at which the absolute and relative errors of the coordinates of the inaccessible point satisfy the error values set by the customer (0.0001-1.2%) The proposed approach is verified using real experimental data.

Radar studies of high-latitude ionospheric flows

1989 ◽  
Vol 328 (1598) ◽  
pp. 107-118 ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Flow Pattern ◽  
Electric Fields ◽  
Strong Interactions ◽  
Plasma Convection ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Coupling Processes

Strong interactions occur between the solar wind and the Earth’s magnetic field which result in the convection of ionospheric plasma over the polar cap regions. This generally forms a two-cell pattern with westward and eastward flows in the pre- and post-midnight sectors respectively. The flow pattern is sensitive to the flux of the solar wind and the direction of the interplanetary magnetic field. Observations of the flow pattern are thus of considerable value in the interpretation of the magnetosphere-ionosphere coupling processes and in identifying the influence of the solar wind on the Earth’s environment. The plasma convection can be observed by ground-based coherent and incoherent scatter radars and the flow vectors determined. Measurements for a range of flow conditions are presented. These are interpreted in terms of the interactions of the solar wind with the magnetosphere and the resulting electric fields which drive the plasma flows in the ionosphere.

scholarly journals Determination of crystallographic intensities from sparse data

IUCrJ ◽  
2015 ◽  
Vol 2 (1) ◽  
pp. 29-34 ◽  
Author(s):  
Kartik Ayyer ◽  
Hugh T. Philipp ◽  
Mark W. Tate ◽  
Jennifer L. Wierman ◽  
Veit Elser ◽  
...  
Keyword(s):  
Diffraction Data ◽  
Crystal Size ◽  
Three Dimensional ◽  
Sparse Data ◽  
Data Sets ◽  
X Rays ◽  
Diffraction Intensity ◽  
X Ray ◽  
Proof Of Principle

X-ray serial microcrystallography involves the collection and merging of frames of diffraction data from randomly oriented protein microcrystals. The number of diffracted X-rays in each frame is limited by radiation damage, and this number decreases with crystal size. The data in the frame are said to be sparse if too few X-rays are collected to determine the orientation of the microcrystal. It is commonly assumed that sparse crystal diffraction frames cannot be merged, thereby setting a lower limit to the size of microcrystals that may be merged with a given source fluence. TheEMCalgorithm [Loh & Elser (2009),Phys. Rev. E,80, 026705] has previously been applied to reconstruct structures from sparse noncrystalline data of objects with unknown orientations [Philippet al.(2012),Opt. Express,20, 13129–13137; Ayyeret al.(2014),Opt. Express,22, 2403–2413]. Here, it is shown that sparse data which cannot be oriented on a per-frame basis can be used effectively as crystallographic data. As a proof-of-principle, reconstruction of the three-dimensional diffraction intensity using sparse data frames from a 1.35 kDa molecule crystal is demonstrated. The results suggest that serial microcrystallography is, in principle, not limited by the fluence of the X-ray source, and collection of complete data sets should be feasible at, for instance, storage-ring X-ray sources.

Three-Dimensional Electron Microscopy of Individual Biological Objects

1976 ◽  
Vol 31 (6) ◽  
pp. 645-655 ◽  
Author(s):  
W. Hoppe ◽  
H. J. Schramm ◽  
M. Sturm ◽  
N. Hunsmann ◽  
J. Gaßmann
Keyword(s):  
Electron Microscopy ◽  
Three Dimensional ◽  
Image Point ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Biological Objects ◽  
Dimensional Reconstruction ◽  
The Common ◽  
Measuring Scheme

In this paper methods and results of three-dimensional electron microscopy of individual molecules will be presented. Part I describes the general experimental and theoretical methods (microgoniometer, measuring scheme, two-dimensional and three-dimensional reconstruction, determination of the common origin of the projections). Special attention will be given to the image point shapes under different reconstruction conditions

A new method for determination of magnetization direction

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. L69-L73 ◽  
Author(s):  
Neal Dannemiller ◽  
Yaoguo Li
Keyword(s):  
Large Deviation ◽  
Three Dimensional ◽  
Vertical Gradient ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Data Sets ◽  
Magnetization Direction ◽  
Total Magnetization ◽  
Total Gradient

The characterization and interpretation of magnetic anomalies rely upon knowledge of the total magnetization direction. Magnetization is usually assumed to consist solely, or primarily, of induced magnetization. The presence of strong remanent magnetization can alter the direction significantly and consequently adversely affect the interpretation, leading to erroneous sizes or shapes of causative bodies. Therefore, it is imperative to have some understanding of the total magnetization direction. We propose a method based upon the correlation between two quantities in magnetic data interpretation: the vertical gradient and the total gradient of the reduced-to-pole (RTP) field. This method is tested on both synthetic and field data sets. The results show that the method is effective in a variety of situations, including those with two-dimensional and three-dimensional dipping bodies and a field example that has a large deviation between the inducing field direction and the total magnetization direction.

Mathematics as a Means to Culture and Discipline

1914 ◽  
Vol 6 (3) ◽  
pp. 135-157
Author(s):  
A. Duncan Yocum
Keyword(s):  
Mental Training ◽  
Specific Instruction ◽  
Common Assumption ◽  
The Common

Perhaps the strongest obstacle to the determination of the disciplinary value of mathematics has been the common assumption that its disciplinary value is not open to question. While the new psychology long since shattered the theory of formal discipline in the sense of the training of generally useful mental faculties, the mass of thinkers still look upon mathematics and the languages as formal disciplines,—as pre-eminently adapted to a mental training that results as a matter of course and is carried over without specific instruction into every field of experience.

scholarly journals Methods for merging data sets in electron cryo-microscopy

2019 ◽  
Vol 75 (9) ◽  
pp. 782-791 ◽  
Author(s):  
Max E. Wilkinson ◽  
Ananthanarayanan Kumar ◽  
Ana Casañal
Keyword(s):  
Three Dimensional ◽  
Scaling Factor ◽  
Biological Macromolecules ◽  
Data Sets ◽  
Independent Data ◽  
Pixel Size ◽  
Combine Data ◽  
Data Merging ◽  
Recent Developments

Recent developments have resulted in electron cryo-microscopy (cryo-EM) becoming a useful tool for the structure determination of biological macromolecules. For samples containing inherent flexibility, heterogeneity or preferred orientation, the collection of extensive cryo-EM data using several conditions and microscopes is often required. In such a scenario, merging cryo-EM data sets is advantageous because it allows improved three-dimensional reconstructions to be obtained. Since data sets are not always collected with the same pixel size, merging data can be challenging. Here, two methods to combine cryo-EM data are described. Both involve the calculation of a rescaling factor from independent data sets. The effects of errors in the scaling factor on the results of data merging are also estimated. The methods described here provide a guideline for cryo-EM users who wish to combine data sets from the same type of microscope and detector.

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