Synchrotron Radiation from Electrons with a Pitch-angle Distribution

In most astrophysical processes involving synchrotron radiation, the pitch-angle distribution of the electrons is assumed to be isotropic. However, if electrons are accelerated anisotropically, e.g., in a relativistic shock wave with an ordered magnetic field or in magnetic reconnection regions, the electron pitch angles might be anisotropic. In this Letter, we study synchrotron radiation from electrons with a pitch-angle distribution with respect to a large-scale uniform magnetic field. Assuming that the pitch-angle distribution is normal with a scatter of σ p and that the viewing direction is where the pitch-angle direction peaks, we find that for electrons with a Lorentz factor γ, the observed flux satisfies F ν ∝ ν 2/3 for ν ν cr (ν cr is the critical frequency of synchrotron), if σ p 1/γ is satisfied. On the other hand, if σ p 1/γ, the spectrum below ν cr is a broken power law with a break frequency , e.g., for ν ν br and for . Thus, the ultimate synchrotron line of death is F ν ∝ ν 2/3. We discuss the application of this theory to blazars and gamma-ray bursts

A Refined Holographic QCD Model and QCD Phase Structure

We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic gauge function and a dilaton potential. A family of analytic solutions is obtained by the potential reconstruction method. We then study its holographic dual QCD model. The kinetic gauge function can be fixed by requesting the linear Regge spectrum of mesons. We calculate the free energy to obtain the phase diagram of the holographic QCD model.Comment: 21 pages, 17 figures. arXiv admin note: substantial text overlap with arXiv:1301.038

Confinement-Deconfinment Phase Transition for Heavy Quarks

We study confinement-deconfinement phase transition for heavy quarks in a bottom-up holographic QCD model. We consider a black hole background in an Einstein-Maxwell-scalar system and add probe open strings to the background. Combining the various configurations of the open strings and the phase structure of the black hole background itself, we obtain the confinement-deconfinement phase diagram for heavy quarks in the holographic QCD model.Comment: 23 pages, 14 figures, published in JHEP. arXiv admin note: text overlap with arXiv:1301.038

Dispersion Measure Variation of Repeating Fast Radio Burst Sources

The repeating fast radio burst (FRB) 121102 was recently localized in a dwarf galaxy at a cosmological distance. The dispersion measure (DM) derived for each burst from FRB 121102 so far has not shown significant evolution, even though an apparent increase was recently seen with newly detected VLA bursts. It is expected that more repeating FRB sources may be detected in the future. In this work, we investigate a list of possible astrophysical processes that might cause DM variation of a particular FRB source. The processes include (1) the cosmological scale effects such as Hubble expansion and large-scale structure fluctuations; (2) the FRB local effects such as gas density fluctuation, expansion of a supernova remnant, a pulsar wind nebula, and an HII region; and (3) the propagation effect due to plasma lensing. We find that the DM variations contributed by the large-scale structure are extremely small, and any observable DM variation is likely caused by the plasma local to the FRB source. Besides mechanisms that produce decreasing DM with time, we suggest that an FRB source in an expanding supernova remnant around a nearly neutral ambient medium during the deceleration (Sedov-Taylor and snowplow) phases or in a growing HII region can introduce DM increasing. Some effects (e.g. an FRB source moving in an HII region or plasma lensing) can give either positive or negative DM variations. Future observations of DM variations of FRB 121102 and other repeating FRB sources can bring important clues for the physical origin of these sources.Comment: 12 pages. Accepted for publication in Ap

An Ecocritical Exploration into Yvonne Vera's Butterfly Burning and The Stone Virgins

Yvonne Vera, one of the most outstanding novelists in Zimbabwe retells the agonies that women experienced in a male–dominated society and presents us with the most chaotic moment in Zimbabwe‘s history. She daringly confronts the taboo topic in Zimbabwe – the 1980 genocide. Her poetic writing style has gained her international readership and literary critiques. By employing ecological literary critique, also known as ecocriticism, my thesis explores into the discursive landscape in Vera‘s two award–wining novels: Butterfly Burning (1997) and The Stone Virgins (2002) and illustrate how the landscapes in her novels reveal the culturally, socially and politically sensitive issues, such as feminism and colonialism and nationalism. A qualitative literary research into her novels reveals that the discursive landscapes in her novels are socially, historically and politically conducted. Intertextual analysis shows how ecofeminist dualism is manifested in her novels. Dualistic connections such as woman/nature, man/culture, and wilderness/city are found to be abundant in Vera‘s novels. The spatial difference between the white citiness and the black wilderness has its colonial and nationalist implications. The nationalist authenticity is attached to the trees and the roots buried underground. An ecocritical study in African literature provides us with some critical considerations over our anthropocentric notions on human culture. A dialogue between human culture and the natural world may not only inspire us to review the current ecological crisis in our planet from a humanistic perspective, but also reveals ecological interconnections between humankind and our social–culturally constructed surroundings.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Power Partial Isometry Index and Ascent of a Finite Matrix

We give a complete characterization of nonnegative integers $j$ and $k$ and a positive integer $n$ for which there is an $n$-by-$n$ matrix with its power partial isometry index equal to $j$ and its ascent equal to $k$. Recall that the power partial isometry index $p(A)$ of a matrix $A$ is the supremum, possibly infinity, of nonnegative integers $j$ such that $I, A, A^2, \ldots, A^j$ are all partial isometries while the ascent $a(A)$ of $A$ is the smallest integer $k\ge 0$ for which $\ker A^k$ equals $\ker A^{k+1}$. It was known before that, for any matrix $A$, either $p(A)\le\min\{a(A), n-1\}$ or $p(A)=\infty$. In this paper, we prove more precisely that there is an $n$-by-$n$ matrix $A$ such that $p(A)=j$ and $a(A)=k$ if and only if one of the following conditions holds: (a) $j=k\le n-1$, (b) $j\le k-1$ and $j+k\le n-1$, and (c) $j\le k-2$ and $j+k=n$. This answers a question we asked in a previous paper.Comment: 11 page