Academic literature on the topic 'Flow afterglow'

The role of magnetic fields in the GRB flow is still controversial. The afterglow emission, particularly the early phases, may provide a probe into the magnetization of the outflow. Using ultrahigh resolution relativistic MHD simulations, the interaction between radially expanding magnetized ejecta with the interstellar medium is studied. We explore the effect of the magnetic field strength of the ejecta on the afterglow structure, particularly regarding the presence and strength of a reverse shock. We compute synthetic afterglow light curves to quantify the effect of the magnetization of the flow on observed radiation.

The reaction kinetics in argon flowing afterglow (post-discharge) with the air addition was studied by optical emission spectroscopy. The optical emission spectra were measured along the~post-discharge flow tube. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows to calculate the time dependencies of particle concentrations.

ABSTRACT We develop a model for the radio afterglow of the giant flare of SGR 1806-20 arising due to the interaction of magnetically dominated cloud, an analogue of Solar Coronal Mass Ejections (CMEs), with the interstellar medium (ISM). The CME is modelled as a spheromak-like configuration. The CME is first advected with the magnetar’s wind and later interacts with the ISM, creating a strong forward shock and complicated backwards exhaust flow. Using 3D magnetohydrodynamic simulations, we study various relative configurations of the magnetic field of the CME with respect to the ISM’s magnetic field. We show that the dynamics of the forward shock mostly follows the Sedov–Taylor blastwave, while the internal structure of the shocked medium is considerably modified by the back flow, creating a multiple shock configuration. We calculate synthetic synchrotron emissivity maps and light curves using two assumptions: (i) magnetic field compression; (ii) amplification of the magnetic field at the shock. We find that models with magnetic field amplification account better for the observed radio emission.

Metallic iron and iron oxide particles were produced by injecting ferrocene into the afterglow region of a low pressure, low power, plasma generated using a microwave power source. This was done as part of an effort to explore the feasibility of using flow type microwave plasmas for the production of metal nanoparticles. It was found that two parameters had the largest impact on the particles: injection point and plasma composition. Analysis done using Mössbauer effect spectroscopy, transmission electron microscopy, and x-ray diffraction indicated that low yields of small particles (ca. 10 nm) resulted from injection into the afterglow region. Much higher yields of large particles (ca. 50 nm) formed if the ferrocene was injected through the coupler. In hydrogen plasmas the particles that were produced were metallic iron, whereas in oxygen and argon plasmas the particles were iron oxide. In all cases significant amounts of graphitic carbon formed around the metal particles.

The work presented herein revolves around the design, installation, testing, and use of a new flowing afterglow-selected ion flow drift tube (FA-SIFDT) at the University of Canterbury. This is the latest in the series of FA and SIFT apparatus that have been installed at Canterbury. The second chapter contains a detailed description of the new instrument. Also present is a description of the characterisation of the new FA-SIFT in particular a comparison of two different types of venturi inlet, viz. an annulus and a hole type injector. The performance of both of these types of venturi inlet with respect to pumping efficiency, signal transmission, dissociation of weakly bound cluster ions, and the isomerisation of ions during injection. Despite the greater mechanical complexity of the annulus injector it is concluded that the annulus injector is slightly superior to the hole type injector, predominantly when the injection of ions needs to be at low energy. Next a new application of the SIFT, namely its use in the real time detection, identification and quantification of trace components in gas samples, is presented. This technique has only recently been developed by overseas researchers and its use at Canterbury has been facilitated by the new FA-SIFDT. The technique has been applied to several systems: the analysis of the changes in the largest trace components of human breath (ammonia, acetone, isoprene) during exercise; the monitoring of breath concentrations of organic solvents following exposure; and the headspace analysis of the gases emitted by soil following fertilisation with an artificial urine solution. The reactions of H3+, N2H+, and H3O+ with thirteen different hydrocarbons have been investigated. The rate coefficients and product distributions of these reactions were investigated in order to obtain a better understanding of exothermic proton transfer reactions. The H3+ was generated in two different manners in an effort to get accurate data about the products of proton transfer from ground state H3 . As expected, in most cases where the proton transfer was exothermic a rate coefficient just less than the collision rate was observed. The reactions became more dissociative as more energy was placed into the collision complex with the channels that predominated usually being between 100 and 200 kJ mol-1 exothermic. The proton affinity of cyanogen (C2N2) has been investigated using the FA-SIFDT. The new value has been determined using the equilibrium method with reference to the C2N2/C2H2 and CH3Cl/C2N2 cycles. The new value is 651±2 kJ mol-1 some 24 kJ mol-1 less than the previously tabulated value. The reactions of methylated cyanogen were also investigated with the intention of determining the methyl cation affinity of cyanogen. Instead it has been determined that the CH3+.C2N2 adduct is strongly bonded, a characteristic that has previously been observed for alkyl ion-cyanide functionality type adducts. Two classes of reaction relevant to the lower cosmic ray-induced ionosphere of Saturn's largest moon Titan have been investigated. The first class is the bimolecular reactions of the N3+ and N4+ ion species with a range of hydrocarbons likely to be present in Titan's atmosphere. These ionic species will be formed deep into Titan's atmosphere by the termolecular association of N+ and N2+ (the primary ions formed in Titan's atmosphere) with nitrogen. The association reactions of some of the terminal ions in Titan's atmosphere, viz. H3O+, HCNH+ and c-C3H3+, with methane, ethylene and acetylene in the presence of both helium and nitrogen bath gases. The termolecular reaction rate coefficients are greatly enhanced in the presence of a nitrogen carrier gas. Preliminary results of an investigation into the structure of the HCNH+.C2H4 and HCNH+.C2H2 adducts is also presented. The termolecular association of the CH2CHCN+ and CH2CHCNH+ ions derived from acrylonitrile with neutral acrylonitrile have been investigated over a wide range of pressure in both the SIFT and an ion cyclotron resonance (ICR) mass spectrometer. This has enabled the pressure dependence of these two reaction to be experimentally investigated and theoretically modelled. In the non-protonated case (CH2CHCN+) there is a competition between termolecular association and bimolecular reaction to give CH2CHCNH+. The reaction is observed to pressure saturate without a complete conversion to termolecular kinetics, an assumption made by the commonly used single-well model for association. A different, double-well, association mechanism is proposed for this reaction and modelled theoretically giving an acceptable fit. The CH2CHCNH+/CH2CHCN system shows only termolecular kinetics and is well modelled by a single-well model. Work begun by earlier researchers at Canterbury on the reactions of ionic species with neutral carbon atoms has been continued. However an effective method for forming neutral carbon atoms has still not been found. The ultraviolet photolysis of carbon suboxide (C3O2) was hoped to solve this problem, however the wavelength of photolysis used was too long to get any significant C atom production. A vacuum UV flash system may be required.

I. Etude de la preparation des etats excites de no dans un dispositif de post-decharge en ecoulement a partir de n::(2) excite (prepare par transfert d'excitation a partir d'atomes ar metastables dans une decharge basse pression) et de o (obtenu par dissociation de o::(2) dans une decharge de he). Observation d'une emission intense des bandes gamma de no, qui implique un etat a courte duree de vie (b) de n::(2) et le premier etat metastable de o. Ii. Analyse des processus d'extinction et de transfert d'excitation a partir d'etats a courte duree de vie de ti (crees dans un dispositif a cathode creuse) lors de collisions avec des gaz rares (ar, ne, he) et des molecules (n::(2),h::(2)). Ces experiences permettent l'etude de cinetiques de reactions elementaires au sein d'un plasma basse pression ensemence de vapeurs metalliques, a l'aide du dispositif de post-decharge en ecoulement