4,889 research outputs found
Initial State Radiation to Off-shell Pair Production in Annihilation
A study of the Standard Model reaction \e^+e^- \rightarrow (\Z^0\Z^0)
\rightarrow f_1\bar{f_1}f_2\bar{f_2} including the effects of the finite
~width and initial state radiative corrections is presented. All angular
phase space integrations are performed analytically. The remaining invariant
masses are integrated numerically. Semi-analytical and numerical results in the
energy range \RS=200\;GeV to are reported.Comment: 6 pages (LaTeX), 2 figures (not included, a uuencoded file containing
the LaTeX and all postscript files is available via anonymous ftp from
convex.ifh.de as /pub/preprint/desy94-105.uu), DESY 94-10
Detection of Ne VIII in the Low-Redshift Warm-Hot IGM
High resolution FUSE and STIS observations of the bright QSO HE 0226-4110
(zem = 0.495) reveal the presence of a multi-phase absorption line system at
zabs(O VI) = 0.20701 containing absorption from H I (Ly alpha to Ly theta), C
III, O III, O IV, O VI, N III, Ne VIII, Si III, S VI and possibly S V. Single
component fits to the Ne VIII and O VI absorption doublets yield logN(Ne VIII)
= 13.89+/-0.11 and logN(O VI) = 14.37+/-0.03. The Ne VIII and O VI doublets are
detected at 3.9 sigma and 16 sigma significance levels, respectively. This
represents the first detection of intergalactic Ne VIII, a diagnostic of gas
with temperature in the range from 5x10(5) to 1x10(6) K. The O VI and Ne VIII
are not likely created in a low density medium photoionized solely by the
extragalactic background at z = 0.2 since the required path length of ~11 Mpc
implies the Hubble flow absorption line broadening would be ~10 times greater
than the observed line widths. A collisional ionization origin is therefore
more likely. Assuming [Ne/H] and [O/H] = -0.5, the value N(Ne VIII)/N(O VI) =
0.33+/-0.10 is consistent with gas in collisional ionization equilibrium near
T=5.4x10(5) K with logN(H)= 19.9 and N(H)/N(H I) = 1.7x10(6). The observations
support the basic idea that a substantial fraction of the baryonic matter at
low redshift exists in hot very highly ionized gaseous structures.Comment: 32 pages text and 9 pages of figures. Accepted by the Astrophysical
Journa
Einfluss von HTC-Biokohle als Bodenverbesserer auf den Wachstums- und Entwicklungsverlauf bei Sojabohnen
The influence of biochar with an amount of 0 to 20 t/ha on growth, yield and ingredients on soybeans of different variants was compared. Differences between the variants until blooming could be found. Plants from the HTC variant have shown significantly longer stems than others. These differences diminished until the harvest. Due to extrem low precipitation values in spring and early summer, no rhizobia could be developed and nitrogen fixation for the soybean was impossible. The plants could only use nitrogen from the soil. As a result, plots prepared with mineral fertilizer have shown the significantly longest plants, highest mass of dry matter and highest yields. Further, HTC variants have shown the lowest values in oil- and sugar contents. The
highest value in sugar content was measured in the variant with mineral fertilizer, but did not differ significantly. This results show, that due to the lower amount of available
nitrogen in the year of application there can be a negative influence of biochar on the yield
The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars
A primary goal of the FUSE mission is to understand the origin of the O VI
ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along
sightlines to OB-type stars, these interstellar components are usually blended
with O VI stellar wind profiles, which frequently vary in shape. In order to
assess the effects of this time-dependent blending on measurements of the
interstellar O VI lines, we have undertaken a mini-survey of repeated
observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud.
These sparse time series, which consist of 2-3 observations separated by
intervals ranging from a few days to several months, show that wind variability
occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does
in other resonance lines. However, in the interstellar O VI 1032
region, the O VI 1038 wind varies only in 30% of the cases. By
examining cases exhibiting large amplitude variations, we conclude that
stellar-wind variability {\em generally} introduces negligible uncertainty for
single interstellar O VI components along Galactic lines of sight, but can
result in substantial errors in measurements of broader components or blends of
components like those typically observed toward stars in the Large Magellanic
Cloud. Due to possible contamination by discrete absorption components in the
stellar O VI line, stars with terminal velocities greater than or equal to the
doublet separation (1654 km/s) should be treated with care.Comment: Accepted for publication in the Astrophysical Journal Lette
Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields
In addition to producing loud gravitational waves (GW), the dynamics of a
binary black hole system could induce emission of electromagnetic (EM)
radiation by affecting the behavior of plasmas and electromagnetic fields in
their vicinity. We here study how the electromagnetic fields are affected by a
pair of orbiting black holes through the merger. In particular, we show how the
binary's dynamics induce a variability in possible electromagnetically induced
emissions as well as an enhancement of electromagnetic fields during the
late-merge and merger epochs. These time dependent features will likely leave
their imprint in processes generating detectable emissions and can be exploited
in the detection of electromagnetic counterparts of gravitational waves.Comment: 12 page
Spherically symmetric scalar field collapse in any dimension
We describe a formalism and numerical approach for studying spherically
symmetric scalar field collapse for arbitrary spacetime dimension d and
cosmological constant Lambda. The presciption uses a double null formalism, and
is based on field redefinitions first used to simplify the field equations in
generic two-dimensional dilaton gravity. The formalism is used to construct
code in which d and Lambda are input parameters. The code reproduces known
results in d = 4 and d = 6 with Lambda = 0. We present new results for d = 5
with zero and negative Lambda.Comment: 16 pages, 6 figures, typos corrected, presentational changes, PRD in
pres
Head-on collisions of boson stars
We study head-on collisions of boson stars in three dimensions. We consider
evolutions of two boson stars which may differ in their phase or have opposite
frequencies but are otherwise identical. Our studies show that these phase
differences result in different late time behavior and gravitational wave
output
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