91 research outputs found
Auger Spectra and Different Ionic Charges Following 3s, 3p and 3d Sub-Shells Photoionization of Kr Atoms
The decay of inner-shell vacancy in an atom through radiative and
non-radiative transitions leads to final charged ions. The de-excitation decay
of 3s, 3p and 3d vacancies in Kr atoms are calculated using Monte-Carlo
simulation method. The vacancy cascade pathway resulted from the de-excitation
decay of deep core hole in 3s subshell in Kr atoms is discussed. The generation
of spectator vacancies during the vacancy cascade development gives rise to
Auger satellite spectra. The last transitions of the de-excitation decay of 3s,
3p and 3d holes lead to specific charged ions. Dirac-Fock-Slater wave functions
are adapted to calculate radiative and non-radiative transition probabilities.
The intensity of Kr^{4+} ions are high for 3s hole state, whereas Kr^{3+} and
Kr^{2+} ions have highest intensities for 3p and 3d hole states, respectively.
The present results of ion charge state distributions agree well with the
experimental data.Comment: Published in SIGMA (Symmetry, Integrability and Geometry: Methods and
Applications) at http://www.emis.de/journals/SIGMA
Compton Dragged Gamma--Ray Bursts associated with Supernovae
It is proposed that the gamma-ray photons that characterize the prompt
emission of Gamma-Ray Bursts are produced through the Compton drag process,
caused by the interaction of a relativistic fireball with a very dense soft
photon bath. If gamma-ray bursts are indeed associated with Supernovae, then
the exploding star can provide enough soft photons for radiative drag to be
effective. This model accounts for the basic properties of gamma-ray bursts,
i.e. the overall energetics, the peak frequency of the spectrum and the fast
variability, with an efficiency which can exceed 50%. In this scenario there is
no need for particle acceleration in relativistic collisionless shocks.
Furthermore, though Poynting flux may be important in accelerating the outflow,
no magnetic field is required in the gamma-ray production. The drag also
naturally limits the relativistic expansion of the fireball to Gamma < 10^4.Comment: Minor changes, accepted for publication in ApJ Letters, 18/11/199
Neon Lights Up a Controversy: the Solar Ne/O Abundance
The standard solar model was so reliable that it could predict the existence
of the massive neutrino. Helioseismology measurements were so precise that they
could determine the depth of the convection zone. This agreement between theory
and observation was the envy of all astrophysics -- until recently when
sophisticated three-dimensional hydrodynamic calculations of the solar
atmosphere reduced the metal content by a factor of almost two. Antia & Basu
(2005) suggested that a higher value of the solar neon abundance, Ne/O = 0.52,
would resolve this controversy. Drake & Testa (2005) presented strong evidence
in favor of this idea from a sample of 21 Chandra stars with enhanced values of
the neon abundance, Ne/O = 0.41. In this paper, we have analyzed solar active
region spectra from the archive of the Flat Crystal Spectrometer on Solar
Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra
from the pioneering days of X-ray astronomy in the 1960s. These data seem
consistent with the standard neon-to-oxygen abundance value, Ne/O = 0.15
(Grevesse & Sauval 1998). If these results prove to be correct, than the
enhanced-neon hypothesis will not resolve the current controversy.Comment: submitted to ApJ Letter
Variability in GRBs - A Clue
We show that external shocks cannot produce a variable GRB, unless they are
produced by an extremely narrow jets (angular opening of < ~10^{-4}) or if only
a small fraction of the shell emits the radiation and the process is very
inefficient. Internal shocks can produce the observed complex temporal
structure provided that the source itself is variable. In this case, the
observed temporal structure reflects the activity of the ``inner engine'' that
drives the bursts. This sets direct constraints on it.Comment: 15 page latex file with 5 PS figure. Complete uuencoded compressed PS
file is available at ftp://shemesh.fiz.huji.ac.il or at
http://shemesh.fiz.huji.ac.il/papers/SaP_aclue.u
Coronal Emission Measures and Abundances for Moderately Active K Dwarfs Observed by Chandra
We have used Chandra to resolve the nearby 70 Oph (K0 V+K5 V) and 36 Oph (K1
V+K1 V) binary systems for the first time in X-rays. The LETG/HRC-S spectra of
all four of these stars are presented and compared with an archival LETG
spectrum of another moderately active K dwarf, Epsilon Eri. Coronal densities
are estimated from O VII line ratios and emission measure distributions are
computed for all five of these stars. We see no substantial differences in
coronal density or temperature among these stars, which is not surprising
considering that they are all early K dwarfs with similar activity levels.
However, we do see significant differences in coronal abundance patterns.
Coronal abundance anomalies are generally associated with the first ionization
potential (FIP) of the elements. On the Sun, low-FIP elements are enhanced in
the corona relative to high-FIP elements, the so-called "FIP effect." Different
levels of FIP effect are seen for our stellar sample, ranging from 70 Oph A,
which shows a prominent solar-like FIP effect, to 70 Oph B, which has no FIP
bias at all or possibly even a weak inverse FIP effect. The strong abundance
difference exhibited by the two 70 Oph stars is unexpected considering how
similar these stars are in all other respects (spectral type, age, rotation
period, X-ray flux). It will be difficult for any theoretical explanation for
the FIP effect to explain how two stars so similar in all other respects can
have coronae with different degrees of FIP bias. Finally, for the stars in our
sample exhibiting a FIP effect, a curious difference from the solar version of
the phenomenon is that the data seem to be more consistent with the high-FIP
elements being depleted in the corona rather than a with a low-FIP enhancementComment: 35 pages, 8 figures, AASTEX v5.0 plus EPSF extensions in mkfig.sty;
accepted by Ap
The energy spectrum observed by the AGASA experiment and the spatial distribution of the sources of ultra-high energy cosmic rays
Seven and a half years of continuous monitoring of giant air showers
triggered by ultra high-energy cosmic rays have been recently summarized by the
AGASA collaboration. The resulting energy spectrum indicates clearly that the
cosmic ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK)
cut-off at eV. Furthermore, despite the small number
statistics involved, some structure in the spectrum may be emerging. Using
numerical simulations, it is demonstrated in the present work that these
features are consistent with a spatial distribution of sources that follows the
distribution of luminous matter in the local Universe. Therefore, from this
point of view, there is no need for a second high-energy component of cosmic
rays dominating the spectrum beyond the GZK cut-off.Comment: 14 pages, 4 figures, Astrophys. J. Letters (submitted
Combinatorial strategies based on CRAd-IL24 and CRAd-ING4 virotherapy with anti-angiogenesis treatment for ovarian cancer
BACKGROUND: A major hurdle incurrent to the human clinical application of conditionally replicative adenovirus (CRAd)-based virotherapy agents is their limited therapeutic efficacy. In this study we evaluated whether arming our previously reported Ad5/3Δ24 CRAd vector containing a 24-base pair deletion in the E1A conserved region 2, which allows selective replication within Rb-p16-deficient tumor cells, to express therapeutic genes could improve oncolytic virus potency in ovarian cancer cells. We choose to assess the therapeutic benefits achieved by virus-mediated expression of interleukin 24 (IL-24), a cytokine-like protein of the IL-10 family, and the inhibitor of growth 4 (ING4) tumor suppressor protein. RESULTS: The generated CRAd-IL24 and CRAd-ING4 vectors were tested in ovarian cancer cell lines in vitro to compare their replication, yield, and cytotoxic effects with control CRAd Ad5/3∆24 lacking the therapeutic gene. These studies showed that CRAd-IL24 infection resulted in significantly increased yield of infectious particles, which translated to a marked enhancement of virus-induced cytotoxic effects as compared to CRAd-ING4 and non-armed CRAd. Testing CRAd-IL24 and CRAd-ING4 vectors combined together did not revealed synergistic effects exceeding oncolytic potency of single CRAD-IL24 vector. Both CRAds were also tested along with anti-VEGF monoclonal antibody Avastin and showed no significant augmentation of viral cytolysis by anti-angiogenesis treatment in vitro. CONCLUSIONS: Our studies validated that arming with these key immunomodulatory genes was not deleterious to virus-mediated oncolysis. These findings thus, warrant further preclinical studies of CRAd-IL24 tumoricidal efficacy in murine ovarian cancer models to establish its potential utility for the virotherapy of primary and advanced neoplastic diseases
Can Fireball or Firecone Models Explain Gamma Ray Bursts?
The observed afterglows of gamma ray bursts, in particular that of GRB 970228
six months later, seem to rule out relativistic fireballs and relativistic
firecones driven by merger or accretion induced collapse of compact stellar
objects in galaxies as the origin of GRBs. GRBs can be produced by superluminal
jets from such events.Comment: A short summary of the main properties of GRBs which are produced by
relativistic jets from merger/AIC of compact stellar objects is included.
Additional references to very recent publication
Relativity at Action or Gamma-Ray Bursts
Gamma ray Bursts (GRBs) - short bursts of few hundred keV -rays -
have fascinated astronomers since their accidental discovery in the sixties.
GRBs were ignored by most relativists who did not expect that they are
associated with any relativistic phenomenon. The recent observations of the
BATSE detector on the Compton GRO satellite have revolutionized our ideas on
these bursts and the picture that emerges shows that GRBs are the most
relativistic objects discovered so far.Comment: 7 pages, 4th prize in this years gravity essay competition to appear
in General Relativity and Gravitation. Complete PS file is available at
ftp://shemesh.fiz.huji.ac.il or at
http://shemesh.fiz.huji.ac.il/papers/essay96.u
COSMOLOGICAL GAMMA RAY BURSTS AND THE HIGHEST ENERGY COSMIC RAYS
We discuss a scenario in which the highest energy cosmic rays (CR's) and
cosmological -ray bursts (GRB's) have a common origin. This scenario is
consistent with the observed CR flux above , provided that
each burst produces similar energies in -rays and in CR's above
. Protons may be accelerated by Fermi's mechanism to energies
in a dissipative, ultra-relativistic wind, with
luminosity and Lorentz factor high enough to produce a GRB. For a homogeneous
GRB distribution, this scenario predicts an isotropic, time-independent CR
flux.Comment: Phys. Rev. Lett. in press (Received: March 22, 1995; Accepted: May
17, 1995
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