114 research outputs found
Recommended from our members
Radial evolution of sunward strahl electrons in the inner heliosphere
The heliospheric magnetic field (HMF) exhibits local inversions, in which the field apparently “bends back” upon itself. Candidate mechanisms to produce these inversions include various configurations of upstream interchange reconnection; either in the heliosphere, or in the corona where the solar wind is formed. Explaining the source of these inversions, and how they evolve in time and space, is thus an important step towards explaining the origins of the solar wind. Inverted heliospheric magnetic field lines can be identified by the anomalous sunward (i.e. inward) streaming of the typically anti-sunward propagating, field aligned (or anti-aligned), beam of electrons known as the “strahl”. We test if the pitch angle distribution (PAD) properties of sunward-propagating strahl are different from those of outward strahl.We perform a statistical study of strahl observed by the Helios spacecraft, over heliocentric distances spanning ≈ 0.3 – 1 AU. We find that sunward strahl PADs are broader and less intense than their outward directed counterparts; particularly at distances 0.3 – 0.75 AU. This is consistent with sunward strahl being subject to additional, path-length dependent, scattering in comparison to outward strahl.We conclude that the longer and more variable path from the Sun to the spacecraft, along inverted magnetic field, leads to this additional scattering. The results also suggest that the relative importance of scattering along this additional path length drops off with heliocentric distance. These results can be explained by a relatively simple, constant-rate, scattering process
The Optimization Design of Logistic Processes of a Selected Company
Import 11/07/2012Předmětem bakalářské práce "Návrh optimalizace logistických procesů vybraného podniku" je analyzovat situaci vybraného podniku se zaměřením na zakázkovou logistiku a pomocí logistických technologií a metod posoudit jeho efektivitu. Součástí této práce je i vyhodnocení efektivity výrobních zařízení a jejich následná optimalizace pomocí automatizace výrobních procesů.The subject of this bachelor´s work named "The optimization design of logistic processes of selected company" is to analyze the situation of the selected company focusing on custom logistics and logistics using technologies and methods to assess it is effectiveness. Part of this work is the evaluation of the effectiveness of production facilities and their subsequent optimization through automation of production processes.152 - Katedra podnikohospodářskádobř
Competitiveness Analysis of the Selected Company
Import 05/08/2014Diplomové práce se zaměřuje na analýzu konkurenceschopnosti vybraného podniku. Cílem je analyzovat současnou situaci firmy Patok, a.s. pomocí rozboru vnějšího a vnitřního prostředí podniku. Na základě provedených analýz jsou identifikovány problémové oblasti a zároveň navrženy způsoby, které by mohly vést ke zvýšení konkurenceschopnosti podniku.The master´s thesis focuses on the analysis of the competitiveness of the chosen company. The aim is to analyze the current situation of the company Patok by analyzing the external and internal environment of the company. Based on the analyses, some problem areas are identified and the ways that could lead to increased competitiveness are suggested.152 - Katedra podnikohospodářskávelmi dobř
Radial Evolution of Sunward Strahl Electrons in the Inner Heliosphere
The heliospheric magnetic field (HMF) exhibits local inversions, in which the field apparently “bends back” upon itself. Candidate mechanisms to produce these inversions include various configurations of upstream interchange reconnection; either in the heliosphere, or in the corona where the solar wind is formed. Explaining the source of these inversions, and how they evolve in time and space, is thus an important step towards explaining the origins of the solar wind. Inverted heliospheric magnetic field lines can be identified by the anomalous sunward (i.e. inward) streaming of the typically anti-sunward propagating, field-aligned (or anti-aligned), beam of electrons known as the “strahl”. We test if the pitch angle distribution (PAD) properties of sunward-propagating strahl are different from those of outward strahl. We perform a statistical study of strahl observed by the Helios spacecraft, over heliocentric distances spanning ≈0.3 – 1 AU. We find that sunward strahl PADs are broader and less intense than their outward directed counterparts; particularly at distances 0.3 – 0.75 AU. This is consistent with sunward strahl being subject to additional, path-length dependent, scattering in comparison to outward strahl. We conclude that the longer and more variable path from the Sun to the spacecraft, along inverted magnetic field, leads to this additional scattering. The results also suggest that the relative importance of scattering along this additional path length drops off with heliocentric distance. These results can be explained by a relatively simple, constant-rate, scattering process
The oblique firehose instability in a bi-kappa magnetized plasma
In this work, we derive a dispersion equation that describes the excitation
of the oblique (or Alfv\'en) firehose instability in a plasma that contains
both electron and ion species modelled by bi-kappa velocity distribution
functions. The equation is obtained with the assumptions of low-frequency waves
and moderate to large values of the parallel (respective to the ambient
magnetic field) plasma beta parameter, but it is valid for any direction of
propagation and for any value of the particle gyroradius (or Larmor radius).
Considering values for the physical parameters typical to those found in the
solar wind, some solutions of the dispersion equation, corresponding to the
unstable mode, are presented. In order to implement the dispersion solver,
several new mathematical properties of the special functions occurring in a
kappa plasma are derived and included. The results presented here suggest that
the superthermal characteristic of the distribution functions leads to
reductions to both the maximum growth rate of the instability and of the
spectral range of its occurrence
Electromagnetic waves and electron anisotropies downstream of supercritical interplanetary shocks
We present waveform observations of electromagnetic lower hybrid and whistler
waves with f_ci << f < f_ce downstream of four supercritical interplanetary
(IP) shocks using the Wind search coil magnetometer. The whistler waves were
observed to have a weak positive correlation between \partialB and normalized
heat flux magnitude and an inverse correlation with T_eh/T_ec. All were
observed simultaneous with electron distributions satisfying the whistler heat
flux instability threshold and most with T_{perp,h}/T_{para,h} > 1.01. Thus,
the whistler mode waves appear to be driven by a heat flux instability and
cause perpendicular heating of the halo electrons. The lower hybrid waves show
a much weaker correlation between \partialB and normalized heat flux magnitude
and are often observed near magnetic field gradients. A third type of event
shows fluctuations consistent with a mixture of both lower hybrid and whistler
mode waves. These results suggest that whistler waves may indeed be regulating
the electron heat flux and the halo temperature anisotropy, which is important
for theories and simulations of electron distribution evolution from the sun to
the earth.Comment: 20 pages, 3 PDF figures, submitted to Journal of Geophysical Researc
Electron-Driven Instabilities in the Solar Wind
The electrons are an essential particle species in the solar wind. They often exhibit non-equilibrium features in their velocity distribution function. These include temperature anisotropies, tails (kurtosis), and reflectional asymmetries (skewness), which contribute a significant heat flux to the solar wind. If these non-equilibrium features are sufficiently strong, they drive kinetic micro-instabilities. We develop a semi-graphical framework based on the equations of quasi-linear theory to describe electron-driven instabilities in the solar wind. We apply our framework to resonant instabilities driven by temperature anisotropies. These include the electron whistler anisotropy instability and the propagating electron firehose instability. We then describe resonant instabilities driven by reflectional asymmetries in the electron distribution function. These include the electron/ion-acoustic, kinetic Alfvén heat-flux, Langmuir, electron-beam, electron/ion-cyclotron, electron/electron-acoustic, whistler heat-flux, oblique fast-magnetosonic/whistler, lower-hybrid fan, and electron-deficit whistler instability. We briefly comment on non-resonant instabilities driven by electron temperature anisotropies such as the mirror-mode and the non-propagating firehose instability. We conclude our review with a list of open research topics in the field of electron-driven instabilities in the solar wind
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Space plasma physics science opportunities for the lunar orbital platform - Gateway
The Lunar Orbital Platform - Gateway (LOP - Gateway, or simply Gateway) is a crewed platform that will be assembled and operated in the vicinity of the Moon by NASA and international partner organizations, including ESA, starting from the mid-2020s. It will offer new opportunities for fundamental and applied scientific research. The Moon is a unique location to study the deep space plasma environment. Moreover, the lunar surface and the surface-bounded exosphere are interacting with this environment, constituting a complex multi-scale interacting system. This paper examines the opportunities provided by externally mounted payloads on the Gateway in the field of space plasma physics, heliophysics and space weather, and also examines the impact of the space environment on an inhabited platform in the vicinity of the Moon. It then presents the conceptual design of a model payload, required to perform these space plasma measurements and observations. It results that the Gateway is very well-suited for space plasma physics research. It allows a series of scientific objectives with a multi-disciplinary dimension to be addressed
- …