521 research outputs found
Variability of the soft X-ray excess in IRAS 13224-3809
We study the soft excess variability of the narrow line Seyfert 1 galaxy IRAS
13224-3809. We considered all five archival XMM-Newton observations, and we
applied the 'flux-flux plot' (FFP) method. We found that the flux-flux plots
were highly affected by the choice of the light curves' time bin size, most
probably because of the fast and large amplitude variations, and the intrinsic
non-linear flux--flux relations in this source. Therefore, we recommend that
the smallest bin-size should be used in such cases. Hence, We constructed FFPs
in 11 energy bands below 1.7 keV, and we considered the 1.7-3 keV band, as
being representative of the primary emission. The FFPs are reasonably well
fitted by a 'power-law plus a constant' model. We detected significant positive
constants in three out of five observations. The best-fit slopes are flatter
than unity at energies below keV, where the soft excess is
strongest. This suggests the presence of intrinsic spectral variability. A
power-law-like primary component, which is variable in flux and spectral slope
(as ) and a soft-excess component, which varies
with the primary continuum (as ),
can broadly explain the FFPs. In fact, this can create positive `constants',
even when a stable spectral component does not exist. Nevertheless, the
possibility of a stable, soft--band constant component cannot be ruled out, but
its contribution to the observed 0.2-1 keV band flux should be less than %. The model constants in the FFPs were consistent with zero in one
observation, and negative at energies below 1 keV in another. It is hard to
explain these results in the context of any spectral variability scenario, but
they may signify the presence of a variable, warm absorber in the source.Comment: Accepted for publication in A&A, 10 pages, 7 figure
Geant4 Predictions of Energy Spectra in Typical Space Radiation Environment
Accurate knowledge of energy spectra inside spacecraft is important for protecting astronauts as well as sensitive electronics from the harmful effects of space radiation. Such knowledge allows one to confidently map the radiation environment inside the vehicle. The purpose of this talk is to present preliminary calculations for energy spectra inside a spherical shell shielding and behind a slab in typical space radiation environment using the 3D Monte-Carlo transport code Geant4. We have simulated proton and iron isotropic sources and beams impinging on Aluminum and Gallium arsenide (GaAs) targets at energies of 0.2, 0.6, 1, and 10 GeV/u. If time permits, other radiation sources and beams (_, C, O) and targets (C, Si, Ge, water) will be presented. The results are compared to ground-based measurements where available
Black Holes and Flop Transitions in M-Theory on Calabi-Yau Threefolds
We present fivedimensional extreme black hole solutions of M-theory
compactified on Calabi-Yau threefolds and study these solutions in the context
of flop transitions in the extended Kahler cone. In particular we consider a
specific model and present black hole solutions, breaking half of N=2
supersymmetry, in two regions of the extended Kahler cone, which are connected
by a flop transition. The conditions necessary to match both solutions at the
flop transition are analysed. Finally we also discuss the conditions to obtain
massless black holes at the flop transition.Comment: 19 pp, LaTe
The Effect of Interlanguage and Arabic Verb System on Producing Present Perfect by EFL Learners
The acquisition of foreign language goes through many processes. One of these processes, which attempts to frame the impact of native language on foreign language, is Interlanguage. This study investigated the effect of Interlanguage and Arabic Verb System on producing Present Perfect by EFL learners. The participants of the study were Lebanese University undergraduates who had been studying EFL for 14 years. The erroneous, absence or unconventional USAge of the present perfect motivated the researcher to inspect the reasons behind this production. The instrument of the study is four topics, addressing the present perfect temporal notion,was presented to the learners who chose two of them, and wrote a paragraph on each. The studied samples, which consisted of 100 paragraphs, belonged to 50 participants. Following quantitative and descriptive approach, the samples were collected, corrected, and data were analyzed using tables to demonstrate the percentages of proper USAge of the present perfect and the verb forms that replaced it mistakenly. The results revealed that interlanguage is the reason behind the learnersrsquo wrong production of the present perfect form, as they produced their own systematic linguistic system, which mixed between their native Arabic language verb system and their English tenses in replacing erroneously the present perfect
The Nature of the UV/X-Ray Absorber in PG 2302+029
We present Chandra X-ray observations of the radio-quiet QSO PG 2302+029.
This quasar has a rare system of ultra-high velocity (-56,000 km/s) UV
absorption lines that form in an outflow from the active nucleus (Jannuzi et
al. 2003). The Chandra data indicate that soft X-ray absorption is also
present. We perform a joint UV and X-ray analysis, using photoionization
calculations, to detemine the nature of the absorbing gas. The UV and X-ray
datasets were not obtained simultaneously. Nonetheless, our analysis suggests
that the X-ray absorption occurs at high velocities in the same general region
as the UV absorber. There are not enough constraints to rule out multi-zone
models. In fact, the distinct broad and narrow UV line profiles clearly
indicate that multiple zones are present. Our preferred estimates of the
ionization and total column density in the X-ray absorber (log U=1.6,
N_H=10^22.4 cm^-2) over predict the O VI 1032, 1038 absorption unless the X-ray
absorber is also outflowing at ~56,000 km/s, but they over predict the Ne VIII
770, 780 absorption at all velocities. If we assume that the X-ray absorbing
gas is outflowing at the same velocity of the UV-absorbing wind and that the
wind is radiatively accelerated, then the outflow must be launched at a radius
of < 10^15 cm from the central continuum source. The smallness of this radius
casts doubts on the assumption of radiative acceleration.Comment: Accepted for Publication in Ap
Supersymmetry of Black Strings in D=5 Gauged Supergravities
Supersymmetry of five dimensional string solutions is examined in the context
of gauged D=5, N=2 supergravity coupled to abelian vector multiplets. We find
magnetic black strings preserving one quarter of supersymmetry and approaching
the half-supersymmetric product space AdS_3\times H^2 near the event horizon.
The solutions thus exhibit the phenomenon of supersymmetry enhancement near the
horizon, like in the cases of ungauged supergravity theories, where the near
horizon limit is fully supersymmetric. Finally, product space compactifications
are studied in detail, and it is shown that only for negative curvature
(hyperbolic) internal spaces, some amount of supersymmetry can be preserved.
Among other solutions, we find that the extremal rotating BTZ black hole
tensored by H^2 preserves one quarter of supersymmetry.Comment: 19 pages, LaTeX, no figures, published versio
Sputtering of Lunar Regolith by Solar Wind Protons and Heavy Ions, and General Aspects of Potential Sputtering
New simulation results for the sputtering of lunar soil surface by solar-wind protons and heavy ions will be presented. Previous simulation results showed that the sputtering process has significant effects and plays an important role in changing the surface chemical composition, setting the erosion rate and the sputtering process timescale. In this new work and in light of recent data, we briefly present some theoretical models which have been developed to describe the sputtering process and compare their results with recent calculation to investigate and differentiate the roles and the contributions of potential (or electrodynamic) sputtering from the standard (or kinetic) sputtering
Toward Forecasting Volcanic Eruptions using Seismic Noise
During inter-eruption periods, magma pressurization yields subtle changes of
the elastic properties of volcanic edifices. We use the reproducibility
properties of the ambient seismic noise recorded on the Piton de la Fournaise
volcano to measure relative seismic velocity variations of less than 0.1 % with
a temporal resolution of one day. Our results show that five studied volcanic
eruptions were preceded by clearly detectable seismic velocity decreases within
the zone of magma injection. These precursors reflect the edifice dilatation
induced by magma pressurization and can be useful indicators to improve the
forecasting of volcanic eruptions.Comment: Supplementary information:
http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguier_SI.pdf Supplementary
video:
http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguierMovieVolcano.av
Anti-de Sitter/CFT Correspondence in Three-Dimensional Supergravity
Anti-de Sitter supergravity models are considered in three dimensions.
Precise asymptotic conditions involving a chiral projection are given on the
Rarita-Schwinger fields. Together with the known boundary conditions on the
bosonic fields, these ensure that the asymptotic symmetry algebra is the
superconformal algebra. The classical central charge is computed and found to
be equal to the one of pure gravity. It is also indicated that the asymptotic
degrees of freedom are described by 2D "induced supergravity" and that the
boundary conditions "transmute" the non-vanishing components of the WZW
supercurrent into the supercharges.Comment: Additional remarks in the extended case, added references, and small
misprints corrected. To appear in Phys. Rev. D. Latex, 19 pages, no figure
Does lidocaine gel produce an effective analgesia prior to copper IUD insertion? Randomized clinical trial
Background: IUD is a small contraceptive device, often containing either copper or levonorgestrel, which is inserted into the uterus. Objective of present study was to determine if lidocaine gel prior to intrauterine device (IUD) insertion decreases pain with the insertion procedure among multiparous women choosing the copper T380A-IUD.Methods: It is a randomized double-blind controlled trial carried out at Assiut Women's Health Hospital, Assiut, Egypt. Parous women eligible for Copper IUD insertion attended the Family Planning Clinic were recruited and randomized in a 1:1 ratio to lidocaine gel or placebo. Two ml of the study medications were topically placed on the cervix 3 minutes before IUD insertion. The primary outcome was the difference in pain scores using a 10-cm Visual Analogue Scale (VAS) during IUD insertion. We considered a 1.5 cm difference in VAS scores between study groups as clinically significant.Results: One hundred women consented to participate and randomized either to group I:Â lidocaine group or group II: placebo group. Both groups were homogenous in baseline socio-demographic data. There was significant difference in mean pain scores for IUD placement between women who received lidocaine gel and placebo at two steps of insertion (at vulsellum application and at uterine sounding) while the rest of steps show no statistical significant difference (p=0.000). There were no statistical significant differences between both group as regard the ease of insertion, the duration of insertion and the satisfaction score after the procedure (p>0.05).Conclusions: This study depicts that the use of lidocaine gel prior to copper IUD insertion in multiparous women could partially reduce the pain during tenaculum placement and uterine sounding
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