Miracle-dz/UniFAR-FTUs huggingface dataset:
Deriving plasma densities in tenuous plasma regions, with the spacecraft potential under active control

Variations of the floating potential on spacecraft are often used to derive plasma densities, complementing the plasma instrument measurements. All spacecraft of the Cluster mission are equipped with Active Spacecraft POtential Control (ASPOC) instruments that control the spacecraft potential. Although the ASPOC operation increases the accuracy of electric field and plasma measurements, it prevents a direct use of the spacecraft potential variations to derive plasma densities. In this work we develop a new reconstruction method of uncontrolled spacecraft potential from controlled spacecraft potential data and a derived photoelectron curve, using multispacecraft observations. We assume that the same curve governs the plasma environment for the spacecraft with ASPOC on and off. The current work focuses on reconstructions in the magnetotail region. The period that was more extensively studied was the one from August to October 2003, when the spacecraft were close to each other, while results from the periods of August–October 2001, 2002, and 2004, when the Cluster spacecraft had their apogee in the magnetotail region, are also presented. In this way, we investigate how the photoelectron curve varies at different time intervals and also how the reconstruction results are modified when the distance between the spacecraft is increasing. Finally, by using the reconstructed results, we proceed by estimating the plasma densities and we discuss the uncertainties of such estimations. While, on average, spacecraft potential measurements are successfully reconstructed, plasma and solar activity variations on short timescales seem to affect the reconstructions, requiring in some cases more detailed analysis in order to achieve results with higher accuracy. Moreover, there are some limitations while deriving results in very tenuous plasma regions due to increased uncertainties in some of the scientific measurements used there. The results and the methods developed for this work can be applied for any other current and future mission with instruments that control the spacecraft potential, such as the recently launched Magnetospheric Multiscale Mission.
The control of the magnetosphere by power line radiation

Evidence is presented that radiated power line harmonics leak into high-altitude regions of the magnetosphere with sufficient intensity to control the starting frequencies of chorus emissions. OGO-3 data from three passes show that the starting frequencies of all measurable chorus emissions were within a few hertz of power line harmonics. It is also found that emissions detected over Western Europe were controlled by harmonics of 50 Hz; over the eastern United States and Canada by 60 Hz; and along the Alaska-New Zealand meridian by harmonics of both 50 and 60 Hz. These results indicate that man-made VLF noise plays an important role in the generation of chorus, one of the commonly observed forms of wave activity in the outer magnetosphere.
Effects of a low‐level precursor and frontal stability on cyclogenesis during FASTEX IOP17

The Fronts and Atlantic Storm‐Track EXperiment (FASTEX) has provided comprehensive data to document the life‐cycle of secondary frontal cyclones over the North Atlantic, and to improve the understanding of cyclogenesis mechanisms. This study analyses the processes leading to the triggering of a particularly well‐sampled frontal cyclone that developed on the trailing cold front of a mature primary cyclone during FASTEX Intensive Observation Period 17 (IOP17) between 16 and 20 February 1997.
Opportunities for Improving Consumer Research through Latent Variable Structural Equation Modeling

This article discusses several advantages of latent variable structural equation modeling (LVSEM), and the potential it has for solving some fundamental problems hindering research in the field. The advantages highlighted include the ability to control for measurement error; an enhanced ability to test the effects of experimental manipulations; the ability to test complex theoretical structures; the ability to link micro and macro perspectives; and more powerful ways to assess measure reliability and validity. My hope is to sensitize researchers to some of the key limitations of currently used alternative methodologies, and demonstrate how LVSEM can help to improve theory testing and development in our discipline.
Vector Autoregressions and Causality

A limit theory for Wald tests of Granger causality in levels vector autoregressions (VAR's) and error correction models (ECM's) is developed, which allows for stochastic trends and cointegration. Earlier work is extended to the general case, thereby characterizing when these Wald tests are asymptotically valid as 'x'(superscript 2) criteria. Our results for inference from unrestricted levels VAR are not encouraging: the limit theory often involves nuisance parameters and nonstandard distributions, a situation offering no satisfactory statistical basis for these tests. Granger causality tests in ECM's also suffer from nuisance parameter dependencies asymptotically and in some cases nonstandard limit theory. Both these results are somewhat surprising in light of earlier research. Copyright 1993 by The Econometric Society.
Extremal and additive processes generated by Pareto distributed random vectors

Pareto distributions are most popular for modeling heavy tailed data. Here, we obtain weak limits of a sequence of extremal and a sequence of additive processes constructed by a series of Bernoulli point processes with bivariate Pareto space components. For the limiting processes we derive the one dimensional distributions in explicit forms. Some of the main properties of these distributions are also proved.
Low-speed streaks in drag-reduced turbulent flow

The effect of a surfactant drag-reducing additive (530 ppm Habon G solution) on the structure of wall turbulence, both in a flume and in pipe flow, was investigated experimentally. Real-time infrared thermography was used for flow visualization and measurements of the spanwise spacing between the thermal streaks. The experiments were carried out over a broad range of friction velocities, i.e., up*=0.51–3.27 cm/s. With wall shear velocities 1.54⩽up*⩽3.27 cm/s drag reduction of 82%–85% was achieved in a tube flow, well below the predictions of the Virk maximum drag reduction asymptote proposed for high polymers. The results of spanwise streak spacing indicate that wall shear velocity may be an appropriate parameter for describing nondimensional streak spacing behavior in drag reducing flows. A hypothesis, based on the average spanwise streak spacing λ+, can be applied to describe the mean velocity profiles of Habon G solutions. The ratio (λp+−100)/100 was applied to describe mean velocity profiles with 530 .
Numerical Study on Crack Dilatancy Part 2: Applications

Discrete cracks have been modeled with interface elements in which the tractions are related to the relative displacements of the crack sides. Three stages in the cracking process can be distinguished: (1) The linear‐elastic state; (2) the development state in which a tension‐softening model is used; and (3) the open‐crack state, for which five different crack‐dilatancy models have been implemented. The predictions of these crack‐dilatancy models have been compared mutually as well as with available experimental data. The discrete‐crack elements have subsequently been used in an analysis of an experiment on crack dilatancy. Again, the results for the various crack‐dilatancy models are compared. Finally, a nonlinear analysis of a moderately deep shear‐critical beam is presented including aggregate‐interlock effects.
Equatorial Long Waves in Geostationary Satellite Observations and in a Multichannel Sea Surface Temperature Analysis

Geostationary satellite observations of a zonally oriented sea surface temperature front in the eastern equatorial Pacific were made between 1975 and 1981. Long waves appeared along the front mainly during the summer and fall, except during 1976, the year of an El Nino. The waves have averaged periods of 25 days and wavelengths of 1000 km. At the end of 1981, the long waves also were detected in a new sea surface temperature analysis based on multichannel infrared measurements from a polar-orbiting satellite. This quantitative analysis may improve the ability to resolve low-frequency equatorial wave motions from satellite observations.
Almost every number has a continuum of beta-expansions

1. D. Austin, A geometric proof of the Lebesgue differentiation theorem, Proc. Amer. Math. Soc. 16 (1965) 220-221. 2. R. P. Boas, A Primer of Real Functions, 3rd ed., Mathematical Association of America, Washington, D.C., 1981. 3. C. Goffman, Real Functions, Holt, Rinehart and Winston, New York, 1961. 4. H. Lebesgue, Legons sur l'intdgration et la recherche des fonctions primitives, Paris, 1904; 2nd ed., Gauthier-Villars, Paris, 1928. 5. E Riesz, Sur l'existence de la ddriv6e des fonctions monotones et sur quelques problbmes qui s'y rattachent, Acta Litt. Sci. Szeged 5 (1932) 208-221. 6. H. L. Royden, Real Analysis, 3rd ed., Macmillan, New York, 1988. 7. L. A. Rubel, Differentiability of monotonic functions, Colloq. Math. 10 (1963) 277-279. 8. B. S. Thomson, Real Functions, Lecture Notes in Mathematics, no. 1170, Springer-Verlag, Berlin, 1985.
Effects of slowly varying depth and current on the evolution of a Stokes wavepacket

We consider the effects of slowly varying depth and current on the evolution of a packet of Stokes waves. The lengthscale of one-dimensional depth variation is assumed to be much greater than that of the wave envelope, and the direction of the current is perpendicular to the depth contours. By the method of multiple scales, the wave envelope is found to satisfy a cubic Schrödinger equation with slowly varying coefficients The criterion of spatial instability to small sidebands is extended. Numerical integration shows that the nonlinear evolution of a wavepacket is directly related to the instability parameter, which depends strongly on the current and depth variation. The heuristic hypothesis of Djordjevic & Redekopp on the soliton evolution over a slope in the absence of current is assessed.
A unified approach to a class of slow dynamos

Abstract Dynamo action in a highly conducting fluid with small magnetic diffusivity η is particularly sensitive to the topology of the flow. The sites of rapid magnetic field regeneration, when they occur, appear to be located at the stagnation points or in regions where the particle paths are chaotic. Elsewhere only slow dynamo action is to be expected. Two such examples are the nearly axially symmetric dynamo of Braginsky and the generalisation to smooth velocity fields of the Ponomarenko dynamo. Here a method of solution is developed, which applies to both these examples and is applicable to other situations, where magnetic field lines are close to either closed or spatially periodic contours. Particular attention is given to field generation in the neighbourhood of resonant surfaces where growth rates may be intermediate between the slow diffusive and fast convective time scales. The method is applied to the case of the two-dimensional ABC-flows, where it is shown that such intermediate dynamo action .
TOWARDS A RAPIDLY ROTATING LIQUID SODIUM DYNAMO EXPERIMENT

The main characteristics of the Earth's dynamo are reviewed. The combined actions of Coriolis and Lorentz forces lead to the so-called \magnetostrophic" regime. We derive an estimate of the power needed to sustain the magnetic eld in this regime. We show that an experiment with liquid sodium can be designed to operate in the magnetostrophic regime. Such an experiment would bring most valuable information on the mechanisms of planetary dynamos. In order to prepare this large-scale experiment and explore the magnetostrophic balance, a smaller scale liquid sodium set-up has been designed and is being built. It consists of a rapidly rotating spherical shell lled with liquid sodium, in which motions are set by spinning at a dierent rotation rate an inner core permeated by a strong magnetic eld. We discuss the processes that can be explored with this new device. 1. The magnetic elds in the solar system. Most planets of the solar system have or have had an internal magnetic eld. Recent satellite missions have revealed that Mars probably had a magnetic eld in its early history (1), while two moons of Jupiter, Io and Ganymede (2), show evidence for present magnetic activity. Explaining the origin and behaviour of planetary magnetic elds is a fascinating challenge. As a starting point, one may attempt to build a model of the geodynamo since the Earth's magnetic eld is, by far, the best documented. 2. The Earth's magnetic eld. The characteristics of the magnetic eld of the Earth are known over a wide range of time scales. In historical times, observa- tory records permit to monitor the secular variation of magnetic structures, with typical drift velocities of 0.1 mm/s. Sudden variations of the internal magnetic eld, aecting the entire core surface, have also been discovered in these records, the so-called \jerks", while the total intensity of the eld displays large fluctua- tions and has dropped by more than 30% in the past 2000 years, as recorded in archaeological artefacts.The most striking property of the Earth's magnetic eld, as seen at present, but also in the paleomagnetic records over several hundred of million years, is that it is dominated by a dipole component, whose axis is aligned with the axis of rotation of the Earth. Just as fascinating is the evidence that this dipole has changed polarity many times over the Earth's history, the last inversion having taken place only 780,000 years ago (3). Models of the geodynamo aim at explaining this rich set of behaviours, starting with the dominant dipole character of the eld. 3. The mechanism. Since the pioneer work of Larmor, Bullard and Elsasser, it is widely accepted that the Earth's magnetic eld is created by self-induction in its core. In an electrically conducting liquid, fluid motions in a magnetic eld produce electrical currents, which in turn feed the magnetic eld. When the induc- tion of the magnetic eld overcomes its diusion (i.e., for a large enough magnetic
Magnetically controlled circumstellar plasma in the helium-weak stars

We report the discovery of variable C  line profiles in the magnetic helium-weak stars HD 142301, HD 142990, and HD 144334, all of which are members of the Sco-Cen association, and the hot helium-weak star HD 175362. These stars display behavior that is similar to HD 5737 and HD 79158, two helium-weak stars for which magnetically confined plasma has previously been reported. The present study thus extends the C  survey to all of the stars for which strong radio emission has been detected. No C  absorption has been detected for two other Sco-Cen chemically peculiar stars, HD 144844 and 146001, nor has it been detected from archival spectra of HD 28843, HD 49333, or HD 124224. The reported detections are the first helium-weak stars that do not belong to thesn subclass that have been found to display such UV line profile variations. It appears that the restriction of this phenomenon to the extreme helium-weak subgroup was a selection effect and that the occurrence of magnetically trapped corotating plasma is more widespread among the upper main sequence magnetic spectrum variables. We show model calculations for the C  variability that clarify the plasmaspheric structure. Supporting Hα observations show no evidence of line profile variability for HD 142301 and HD 144334, while HD 142990 appears to have extremely weak emission at certain phases, and the profile of HD 124224 shows some changing asymmetry.
The Influence of the Downstream State on Extratropical Transition: Hurricane Earl (1998) Case Study

Abstract The multitude of tropical–extratropical interactions that occur during an extratropical transition (ET) complicate the prediction and diagnosis of these extreme events. This study focuses on the analysis of a double ET and reintensification event that took place between 5 and 7 September 1998. Ex-Hurricanes Earl and Danielle reintensified rapidly over the western and eastern North Atlantic, respectively. A set of simulations designed to test the sensitivity of Earl's ET to features in the downstream state was run using a set of idealizations for a numerical model's initial and boundary conditions downstream of ex-Hurricane Earl. Dynamic tropopause analyses and the “PV thinking” paradigm applied under the Eady model highlight important developmental and structural differences between the tests. In fact, two distinct solution modes are diagnosed both in the control and in the sensitivity tests. Earl's ET proceeds according to a “baroclinic mode” of redevelopment, whereas Danielle displays distinct .
Convective Momentum Transport Observed during the TOGA COARE IOP. Part II: Case Studies

Abstract Convective momentum transport (CMT) associated with the Madden–Julian oscillation (MJO), tropical waves, squall and nonsquall mesoscale convective systems (MCSs), and the diurnal cycle is studied by examining the momentum budget residual X = (X, Y) deduced from the objectively analyzed in situ observations during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intensive observing period (IOP; November 1992–February 1993). Using wavelet transform, time evolution of signals of these disturbances in the time series of |X| and ITBB (an index for deep convection), averaged over the intensive flux array (IFA), is analyzed. Signals of disturbances with periods ≥1 day in |X| generally evolve in phase with those in ITBB. During the convective phase of MJO, signals in both |X| and ITBB with shorter periods are also enhanced. Frequency distribution of IFA-mean E = −v · X in the troposphere is examined. The mean E is positive, that is, kinetic energy (K) transfe.
Model Search With TETRAD II and LISREL

This article is a comment on the paper by Spirtes, Scheines, and Glymour. The problem of equivalent models is discussed. The conclusion of the authors that the automatic model modification procedure in LISREL performs poorly may be due to the fact that all equivalent models are not counted as correct models. Our own experiment based on their model 8 demonstrates that the automatic model modification procedure in LISREL indeed performs very well when all equivalent models are counted as correct. Contrary to what the authors claim, the modification index in LISREL can be used to detect equivalent models and give useful insight into the problem of model modification.
On the energy transport in internal transport barriers of RFP plasmas

Single helical axis (SHAx) states obtained in high current reversed field pinch (RFP) plasmas feature an internal transport barrier delimiting the hot helical core region. The electron temperature jump across this region, and the related temperature gradient, display a clear relationship with the normalized amplitude of the secondary MHD modes. A transport analysis performed with the ASTRA code, taking into account the helical geometry, yields values of the thermal conductivity in the barrier region as low as 5 m2 s−1. The thermal conductivity is also related to the secondary mode amplitude. Since such amplitude is reduced when plasma current is increased, it is expected that higher current plasmas will display even steeper thermal gradients and hotter helical cores.
Genetic algorithm and calculus of variations-based trajectory optimization technique

A genetic algorithm is used cooperatively with the Davidon‐Fletcher‐Powell penalty function method and the calculus of variations to optimize low-thrust, Mars-to-Earth trajectories for the Mars Sample Return Mission. The return trajectory is chosen thrust-coast-thrust a priori, has a fixed time of flight, and is subject to initial and final position and velocity equality constraints. The global search properties of the genetic algorithm combine with the local search capabilities of the calculus of variations to produce solutions that are superior to those generated with the calculus of variations alone, and these solutions are obtained more quickly and require less user interaction than previously possible. The genetic algorithm is not hampered by ill-behaved gradients and is relatively insensitive to problems with a small radius of convergence, allowing it to optimize trajectories for which solutions had not yet been obtained. The use of the calculus of variations within the genetic algorithm optimization routine increased the precision of the final solutions to levels uncommon for a genetic algorithm.
Direct probe of excitonic and continuum transitions in the photocurrent spectroscopy of individual carbon nanotube p-n diodes

The authors show that a carbon nanotube p-n diode is a very sensitive probe of optical transitions in individual single-walled carbon nanotubes. In the photocurrent spectra, an alternating sequence of resonant peaks from dissociation of excitons and exciton-phonon bound states, for the lowest and higher electronic subbands, is observed. At an intermediate energy, the onset of continuum is observed that allows measurement of exciton binding energies. Both the binding energy and the onset of continuum follow the inverse diameter relation as expected from general theory of optical transitions in nanotubes.
Magnetic design optimization and objective function approximation

This paper addresses the problem of optimizing a device by using an interpolation of the objective function. Optimization by means of stochastic methods can explore the objective function and give reliable indications on its global extrema, but the number of function calls can be unacceptably large when numerically evaluated functions are used. An optimization procedure applied not directly on the objective function but on its interpolation can significantly reduce the cost of the optimization. An efficient coupling between interpolation technique and optimization method is needed both to explore features of the optimization algorithm and to exploit advantages of the interpolation. This paper analyzes the performance of a multiquadric interpolation procedure on analytical functions and on finite-element evaluations.
A sphere in a uniformly rotating or shearing flow

It is known that, in a linear shear flow, fluid inertia causes a particle to spin more slowly than the surrounding fluid. The present experiments performed with a sphere with fixed centre, but free to rotate in a fluid undergoing solid-body rotation around a horizontal axis indicate that the spin rate of the sphere can be larger than that of the flow when the sphere is sufficiently far from the axis. Numerical simulations at Reynolds number 5≤Re≤200 confirm this observation. To gain a better understanding of the phenomenon, the rotating flow is decomposed into two shear flows along orthogonal directions. It is found numerically that the cross-stream shear has a much stronger effect on the particle spin rate than the streamwise shear. The region of low stress at the back of the sphere is affected by the shear component of the incident flow. While for the streamwise case the shift is minor, it is significant for cross-stream shear. The results are interpreted on the basis of the effect of the shear flow components on the quasi-toroidal vortex attached in the sphere's near wake. The contributions of streamwise and cross-stream shear to the particle spin can be linearly superposed for Re=20 and 50.