Role of thermal conduction in the acceleration of the solar wind

The thermal and suprathermal processes involving solar wind electrons are discussed from a theoretical point of view. A model for the electron distribution function, f(e), based on the solutions of the Boltzmann equation in Krook's approximation is outlined: the angular and energy dependences of for various distances from the Sun between the coronal base and the Earth are presented with the express purpose of obtaining the radial profile of the heat flux generated by the suprathermals. The basic fluid-dynamical equations for the solar wind plasma as a whole along any given magnetic field line are solved. Results are in good agreement with observations. The predicted density and temperature profiles for positive ions exhibit the characteristics of recent measurements, both in the corona (above the coronal holes) and between 0.3 and 1 A.U. (the Helios region). It is concluded that the suprathermal electrons play an important role in the formation and the dynamics of the solar wind

The response function of modulated grid Faraday cup plasma instruments

Modulated grid Faraday cup plasma analyzers are a very useful tool for making in situ measurements of space plasmas. One of their great attributes is that their simplicity permits their angular response function to be calculated theoretically. An expression is derived for this response function by computing the trajectories of the charged particles inside the cup. The Voyager Plasma Science (PLS) experiment is used as a specific example. Two approximations to the rigorous response function useful for data analysis are discussed. The theoretical formulas were tested by multi-sensor analysis of solar wind data. The tests indicate that the formulas represent the true cup response function for all angles of incidence with a maximum error of only a few percent

The collapse of the local, Spitzer-Haerm formulation and a global-local generalization for heat flow in an inhomogeneous, fully ionized plasma

The breakdown of the classical (CBES) field aligned transport relations for electrons in an inhomogeneous, fully ionized plasma as a mathematical issue of radius of convergence is addressed, the finite Knudsen number conditions when CBES results are accurate is presented and a global-local (GL) way to describe the results of Coulomb physics moderated conduction that is more nearly appropriate for astrophysical plasmas are defined. This paper shows the relationship to and points of departure of the present work from the CBES approach. The CBES heat law in current use is shown to be an especially restrictive special case of the new, more general GL result. A preliminary evaluation of the dimensionless heat function, using analytic formulas, shows that the dimensionless heat function profiles versus density of the type necessary for a conduction supported high speed solar wind appear possible

Stellar winds driven by Alfven waves

Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds

A theory of local and global processes which affect solar wind electrons. 2: Experimental support

The microscopic characteristics of the Coulomb cross section show that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E kT sub c; the transthermals with kT sub c E 7 kT sub c and the extrathermals E 7 kT sub c. Data from three experimental groups on three different spacecraft in the interplanetary medium over a radial range are presented to support the five interrelations projected between solar wind electron properties and changes in the interplanetary medium: (1) subthermals respond primarily to local changes (compression and rarefactions) in stream dynamics; (2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; (3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; (4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and (5) the extrathermal differential 'temperature' should be nearly independent of radius within 1 AU

Statefull Processing of TCP/IP Flows

Rychlý vývoj počítačových sítí s sebou přináší potřebu tyto sítě zabezpečit proti stále pokročilejším útokům. Bezpečnostní systémy vyžadují pro svoji činnost pokročilou analýzu síťového provozu, která je prováděna na základě stavového zpracování toků. Zaměřením této bakalářské práce je návrh a simulace systému stavového zpracování toků. Navrhovaný systém využívá specializovaného hardware pro akceleraci zpracování síťového provozu vysokorychlostních páteřních linek. Specifickou vlastností systému je distribuce paměti toků mezi hardware a software. Vytvořený simulační model umožní otestování a optimalizaci systému stavového zpracování toků již ve fázi návrhu a tím usnadní případnou implementaci.The fast development of computer networks brings the necessity to protect those networks against more and more advanced attacks. The security systems require an advanced analysis for their operation which is carried out based on the stateful processing of flows. This Bachelor Thesis focuses on the proposal and simulation of the stateful flow processing system. The proposed system uses a specialized hardware for network operation processing acceleration of high-speed backbone lines. The specific feature of the system is the flow memory distribution between the hardware and software. The created simulation model will make it possible to test and optimize the stateful flow processing system already in the phase of proposal and thus the possible implementation will be facilitated.

Radiation of plasma waves by a conducting body moving through a magnetized plasma

A theory is presented describing energy loss due to radiation of plasma waves by a conducting body moving through a magnetized plasma, which makes it possible to estimate the total power radiated at all frequencies. Using energy conservation and a source current deduced by physical reasoning, numerical predictions were made for the power radiated. It was found that radiation is produced at all frequencies for which one of the plasma modes has zero phase velocity in some direction

Steps towards fully nonlinear simulations of arrays of OWSC

OWSCs in waves reflect, refract and radiate waves in different directions depending on geometrical,structural and dynamic properties of the flap. Array interaction describes the changes induced on theexcitation of flaps in an array compared to the excitation of a single flap.Renzi and Dias, 2013, Renzi et al., 2014, investigated array effects of OWSCs using a linearised semi-analytical and a linearised FEM method. However, research suggests that the applicability of linear meth-ods for the simulation of OWSCs is limited to very small flap angles (Crooks et al., 2014, Crooks et al., 2016).Linear inviscid assumptions seem to break down in typical operating conditions (Folley et al., 2004,Asmuth et al., 2014). It can therefore be assumed that the accuracy of linear methods in predicting the characteristic wave pat-tern around a flap and the interaction between multiple such devices is limited when applied to realisticoperating conditions with typical pitch motion amplitudes.Although RANS CFD tools have been shown to reproduce the motion of single flaps in waves within thelevels of experimental accuracy and can provide detailed data of all field variables like surface elevation,pressure or velocity (Schmitt and Els ¨asser, 2015a), the simulation of arrays of WECs remains an openchallenge. Due to numerical dissipation water waves simulated using volume of fluid methods tend todiminish in height and require careful spatial and temporal discretisation.The simulation of multiple moving bodies requires adaptation of the mesh and constitutes a considerablecomputational effort. As with physical test facilities numerical wave tanks require non-reflecting bound-ary conditions and wave makers