730 research outputs found
Simulations of gamma-ray burst afterglows with a relativistic kinetic code
This paper introduces a kinetic code that simulates gamma-ray burst (GRB)
afterglow emission from the external forward shock and presents examples of
some of its applications. One interesting research topic discussed in the paper
is the high-energy radiation produced by Compton scattering of the prompt GRB
photons against the shock-accelerated electrons. The difference between the
forward shock emission in a wind-type and a constant-density medium is also
studied, and the emission due to Maxwellian electron injection is compared to
the case with pure power-law electrons. The code calculates the time-evolving
photon and electron distributions in the emission region by solving the
relativistic kinetic equations for each particle species. For the first time,
the full relativistic equations for synchrotron emission/absorption, Compton
scattering, and pair production/annihilation were applied to model the forward
shock emission. The synchrotron self-absorption thermalization mechanism, which
shapes the low-energy end of the electron distribution, was also included in
the electron equation. The simulation results indicate that inverse Compton
scattering of the prompt GRB photons can produce a luminous TeV emission
component, even when pair production in the emission region is taken into
account. This very high-energy radiation may be observable in low-redshift
GRBs. The test simulations also show that the low-energy end of a pure
power-law distribution of electrons can thermalize owing to synchrotron
self-absorption in a wind-type environment, but without an observable impact on
the radiation spectrum. Moreover, a flattening in the forward shock X-ray light
curve may be expected when the electron injection function is assumed to be
purely Maxwellian instead of a power law.Comment: 16 pages, 11 figures, accepted for publication in A&
Evolutionary multi-stage financial scenario tree generation
Multi-stage financial decision optimization under uncertainty depends on a
careful numerical approximation of the underlying stochastic process, which
describes the future returns of the selected assets or asset categories.
Various approaches towards an optimal generation of discrete-time,
discrete-state approximations (represented as scenario trees) have been
suggested in the literature. In this paper, a new evolutionary algorithm to
create scenario trees for multi-stage financial optimization models will be
presented. Numerical results and implementation details conclude the paper
Simulations of gamma-ray burst afterglows with a relativistic kinetic code
Aims. This paper introduces a kinetic code that simulates gamma-ray burst (GRB) afterglow emission from the external forward shock and presents examples of some of its applications. One interesting research topic discussed in the paper is the high-energy radiation produced by Compton scattering of the prompt GRB photons against the shock-accelerated electrons. The difference between the forward shock emission in a wind-type and a constant-density medium is also studied, and the emission due to Maxwellian electron injection is compared to the case with pure power-law electrons.
Methods. The code calculates the time-evolving photon and electron distributions in the emission region by solving the relativistic ki- netic equations for each particle species. For the first time, the full relativistic equations for synchrotron emission/absorption, Compton scattering, and pair production/annihilation were applied to model the forward shock emission. The synchrotron self-absorption ther- malization mechanism, which shapes the low-energy end of the electron distribution, was also included in the electron equation. Results. The simulation results indicate that inverse Compton scattering of the prompt GRB photons can produce a luminous TeV emission component, even when pair production in the emission region is taken into account. This very high-energy radiation may be observable in low-redshift GRBs. The test simulations also show that the low-energy end of a pure power-law distribution of electrons can thermalize owing to synchrotron self-absorption in a wind-type environment, but without an observable impact on the radiation spectrum. Moreover, a flattening in the forward shock X-ray light curve may be expected when the electron injection function is assumed to be purely Maxwellian instead of a power law. The flux during such a flattening is likely to be lower than the Swift/XRT sensitivity in the case of a constant-density external medium, but a wind environment may result in a higher flux during the shallow decay.
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The flux distribution of the three quark system in SU(3)
We study the abelian color-flux distribution of the three quark system in the
maximally abelian gauge on SU(3) lattices. The distribution of the color
electric field suggests , which might be interpreted through the dual
superconductor picture as the result of the vacuum pressure in the confined
phase. In order to clarify the flux structure, we investigate the color
electric field in the three quark system also in the monopole part and in the
photon part.Comment: 3pages, 5figures, Lattice2002(topology
Four-quark flux distribution and binding in lattice SU(2)
The full spatial distribution of the color fields of two and four static
quarks is measured in lattice SU(2) field theory at separations up to 1 fm at
beta=2.4. The four-quark case is equivalent to a qbar q qbar q system in SU(2)
and is relevant to meson-meson interactions. By subtracting two-body flux tubes
from the four-quark distribution we isolate the flux contribution connected
with the four-body binding energy. This contribution is further studied using a
model for the binding energies. Lattice sum rules for two and four quarks are
used to verify the results.Comment: 46 pages including 71 eps figures. 3D color figures are available at
www.physics.helsinki.fi/~ppennane/pics
Haitallisten vieraiden kala-, rapu- ja nisäkäslajien leviäminen, tietoisuuden lisääminen ja hallinta
Työssä kerättiin tietoa mm. hopearuutanan, mustatäplätokon, puronieriän, täpläravun, rapuruton, minkin, supikoiran, amerikanmajavan ja valkohäntäkauriin tilanteesta. Hopearuutanan ja mustatäplätokon levittäytymisestä ja populaatioista kerättiin laaja aineisto. Vieraiden nisäkäslajien haittavaikutusten laajuutta arvioitiin supikoiran ja minkin osalta. Arviointiin käytettiin RKTL:ssa koottuja aineistoja, kuten saalistietoja, peltokolmio- ja riistakolmioaineistoja sekä kala-atlastietoja. Osa tiedoista on koottu julkaistuista aineistoista, osa vielä julkaisemattomista tai valmisteilla olevista materiaaleista.
Vieraslajitietoisuuden lisäämiseksi ja uusien havaintojen keräämiseksi vieraslajeista tiedottamista on lisättävä sekä mediassa että kohdennetusti asiantuntijoille. Vieraslajit.fi -portaali tarjoaa hyvän kanavan tähän, mutta sen kehittämistä on edelleen syytä jatkaa. Vieraslajien levinneisyyden muutokset ja niiden elinympäristössään aiheuttamat muutokset saattavat olla nopeita. Esimerkiksi kalojen esiintymisen ja runsastumisen muutoksia olisi seurattava vuosittain. Erityistä huomiota tulisi kiinnittää leviämisvaiheen varhaisiin signaaleihin, kuten yksittäisiin havaintoihin uusista lajeista.
Mustatäplätokon ja hopearuutanan todettiin aiheuttavan haittaa alkuperäisille lajeille ja ekosysteemitason muutoksia. Haittojen minimoimiseksi olisi ryhdyttävä välittömiin toimenpiteisiin lajien sisävesiin leviämisen estämiseksi. Useimmiten vieraslajien leviämistä ei voida estää, mutta tietoisuuden lisäämisellä ja asettautumiseen vaikuttavilla säätelytoimenpiteillä kyetään hidastamaan muutoksia. Pääasiassa laivojen painolastivesien mukana leviävien merilajien asettautumismahdollisuuksiin on mahdollista puuttua painolastivesisopimuksella. Sisävesien järvialtailla ja virtavesissä on paikallisilla ratkaisuilla, riskinarvioinneilla ja päätöksillä helpommin saavutettavaa vaikuttavuutta vieraslajien hallinnassa verrattuna merialueisiin. Julkaisussa annetaan lajikohtaisia suosituksia ja ohjeita vieraslajien leviämisen estämiseksi ja torjumiseksi Suomessa.
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Liite 5. HAVINA-loppuraporttiin URN:NBN:fi-fe2014062529465</a
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