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2006-06-27
|
Fe adatoms along Bi lines on H/Si(001): Patterning atomic magnetic chains
|
The stability, electronic and magnetic properties of Fe atoms adsorbed on the
self-assembled Bi-dimer lines nanostructure on the H/Si(001) surface are
addressed by spin-density functional calculations. Our results show that Fe
adatoms are much more stable on sites closer to the Bi nanolines being able to
form one-dimensional atomic arrays. The most stable structure occurs on a
missing dimer line aside the Bi dimers, which corresponds to an array with
distances between Fe adatoms of about 8 Ang. In this array the irons are
coupled antiferromagnetically with spin magnetic moment of about 1.5 Bohr
magnetons per Fe atom, whereas the coupling exchange interactions is found to
be of 14.4 meV. We also estimate a large magnetic anisotropy energy for the Fe
adatom of about 3 meV/atom. In addition, the electronic band structure of the
Fe array at the most stable structure shows a magnetic half-metal behavior.
|
0606707v2
|
2006-08-14
|
Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy
|
The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.
|
0608307v3
|
2006-09-15
|
Surfactant effects in monodisperse magnetite nanoparticles of controlled size
|
Monodisperse magnetite Fe3O4 nanoparticles of controlled size within 6 and 20
nm in diameter were synthesized by thermal decomposition of an iron organic
precursor in an organic medium. Particles were coated with oleic acid. For all
samples studied, saturation magnetization Ms reaches the expected value for
bulk magnetite, in contrast to results in small particle systems for which Ms
is usually much smaller due to surface spin disorder. The coercive field for
the 6 nm particles is also similar to that of bulk magnetite. Both results
suggest that the oleic acid molecules covalently bonded to the nanoparticle
surface yield a strong reduction in the surface spin disorder. However,
although the saturated state may be similar, the approach to saturation is
different and, in particular, the high-field differential susceptibility is one
order of magnitude larger than in bulk materials. The relevance of these
results in biomedical applications is discussed.
|
0609384v1
|
2006-10-18
|
A new type of temperature driven reorientation transition in magnetic thin films
|
We present a new type of temperature driven spin reorientation transition
(SRT) in thin films. It can occur when the lattice and the shape anisotropy
favor different easy directions of the magnetization. Due to different
temperature dependencies of the two contributions the effective anisotropy may
change its sign and thus the direction of the magnetization as a function of
temperature may change. Contrary to the well-known reorientation transition
caused by competing surface and bulk anisotropy contributions the reorientation
that we discuss is also found in film systems with a uniform lattice
anisotropy. The results of our theoretical model study may have experimental
relevance for film systems with positive lattice anisotropy, as e.g. thin iron
films grown on copper.
|
0610504v1
|
2006-11-09
|
New ultrasmall iron-oxide nanoparticles with high magnetisation as potential T1-MRI contrast agents for Molecular Imaging
|
Here we report on the synthesis of very small gamma-Fe2O3 nanoparticles (5
nm) presenting very narrow particle size distribution and exceptionally high
saturation magnetisation. The synthesis has been carried out in an organic
medium with subsequent transfer to an aqueous solution at physiological pH. The
structural and magnetic properties were kept unaltered after the solvent
exchange. NMR relaxometric measurements show the potential of these particles
as specific reporters for magnetic resonance molecular imaging.
|
0611243v1
|
2006-12-10
|
Substituting the main group element in cobalt - iron based Heusler alloys: Co$_2$FeAl$_{1-x}$Si$_x$
|
This work reports about electronic structure calculations for the Heusler
compound Co$_2$FeAl$_{1-x}$Si$_x$. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series Co$_2$FeAl$_{1-x}$Si$_x$ is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for $x=0.5$.
|
0612241v1
|
2006-12-23
|
Magnetic phase diagram of Ce2Fe17
|
Rare-earth-based permanent-magnet materials rich in iron have relatively low
ferromagnetic ordering temperatures. This is believed to be due to the presence
of antiferromagnetic exchange interactions, besides the ferromagnetic
interactions responsible for the magnetic order. The magnetic properties of
Ce2Fe17 are anomalous. Instead of ferromagnetic, it is antiferromagnetic, and
instead of one ordering temperature, it shows two, at the Neel temperature TN ~
208 K and at TT ~ 124 K. Ce2Fe17, doped by 0.5% Ta, also shows two ordering
temperatures, one to an antiferromagnetic phase, at TN ~ 214 K, and one to a
ferromagnetic phase, at T0 ~ 75 K. In order to clarify this behavior,
single-crystalline samples were prepared by solution growth, and characterized
by electron microscopy, single crystal x-ray diffraction, temperature-dependent
specific heat, and magnetic field and temperature-dependent electrical
resistivity and magnetization. From these measurements, magnetic H-T phase
diagrams were determined for both Ta-doped Ce2Fe17 and undoped Ce2Fe17. These
phase diagrams can be very well described in terms of a theory that gives
magnetic phase diagrams of systems with competing antiferro- and
ferromagnetism.
|
0612603v1
|
2007-01-02
|
Resonant soft x-ray magnetic scattering from the 4f and 3d electrons in DyFe(4)Al(8)
|
Soft x-ray resonant scattering has been used to examine the charge and
magnetic interactions in the cycloidal antiferromagnetic compound \dyfeal. By
tuning to the Dy $M_4$ and $M_5$ absorption edges and the Fe L(2) and L(3)
absorption edges we can directly observe the behavior of the Dy 4f and Fe 3d
electron shells. Magnetic satellites surrounding the (110) Bragg peak were
observed below 60 K. The diffraction peaks display a complex spectra at the Dy
M(5) edge, indicative of a split 4f electron band. This is in contrast to a
simple resonance observed at the Fe L(3) absorption edge, which probes the Fe
3d electron shell. Temperature dependant measurements detail the ordering of
the magnetic moments on both the iron and the dysprosium antiferromagnetic
cycloids. The ratio between the intensities of the Dy M(4) and M(5) remained
constant throughout the temperature range, in contrast to a previous study
conducted at the Dy L(2,3) edges. Our results demonstrate the ability of soft
x-ray diffraction to separate the individual magnetic components in complicated
multi-element magnetic structures.
|
0701034v1
|
2007-01-26
|
Use of Superparamagnetic Nanoparticle/Block Copolymer Electrostatic Complexes as Contrast Agents in Magnetic Resonance Imaging
|
During the past years we have investigated the complexation between
nanocolloids and oppositely charged polymers. The nanocolloids examined were
ionic surfactant micelles and inorganic oxide nanoparticles. For the polymers,
we used homopolyelectrolytes and block copolymers with linear and comb
architectures. In general, the attractive interactions between oppositely
charged species are strong and as such, the simple mixing of solutions
containing dispersed constituents yield to a precipitation, or to a phase
separation. We have developed means to control the electrostatically-driven
attractions and to preserve the stability of the mixed solution. With these
approaches, we designed novel core-shell nanostructures, e.g. as those obtained
with polymers and iron oxide superparamagnetic nanoparticles. In this
presentation, we show that electrostatic complexation can be used to tailor new
functionalized nanoparticles and we provide examples related to biomedical
applications in the domain of contrast agents for Magnetic Resonance Imaging.
|
0701663v1
|
2007-02-23
|
Spectral and Fermi surface properties from Wannier interpolation
|
We present an efficient first-principles approach for calculating Fermi
surface averages and spectral properties of solids, and use it to compute the
low-field Hall coefficient of several cubic metals and the magnetic circular
dichroism of iron. The first step is to perform a conventional first-principles
calculation and store the low-lying Bloch functions evaluated on a uniform grid
of k-points in the Brillouin zone. We then map those states onto a set of
maximally-localized Wannier functions, and evaluate the matrix elements of the
Hamiltonian and the other needed operators between the Wannier orbitals, thus
setting up an ``exact tight-binding model.'' In this compact representation the
k-space quantities are evaluated inexpensively using a generalized
Slater-Koster interpolation. Because of the strong localization of the Wannier
orbitals in real space, the smoothness and accuracy of the k-space
interpolation increases rapidly with the number of grid points originally used
to construct the Wannier functions. This allows k-space integrals to be
performed with ab-initio accuracy at low cost. In the Wannier representation,
band gradients, effective masses, and other k-derivatives needed for transport
and optical coefficients can be evaluated analytically, producing numerically
stable results even at band crossings and near weak avoided crossings.
|
0702554v1
|
2007-03-15
|
Theoretical introduction to express way of the complex determination of the thermophysical parameters of metals
|
A method to measure thermophysical characteristics (TPC) of conductive
materials is described. The method is based upon controlled bulk (e.g., Ohmic)
heating and measurement of the averaged over the volume of a sample temperature
and the temperature of the surface of a sample. To measure averaged over a
sample volume temperature a dilatometric technique could be used and surface
temperature could be measured by x-ray method. This allows one to avoid
distortion of the temperature field by the thermocouples and directly takes
into account heat losses from the surface of a sample. The treatment of the
experimental data should be based upon theoretical calculations presented in
this paper. The measured values of the averaged over the volume of a sample
temperature and a surface temperature allow for the calculation of TPC of the
material. The experimental data obtained on the iron-based materials prove the
high accuracy of the described approach [1-3].
|
0703392v2
|
1999-01-15
|
The Atmospheric Neutrino Flavor Ratio from a 3.9 Fiducial Kiloton-Year Exposure of Soudan 2
|
We report a measurement of the atmospheric neutrino flavor ratio, R, using a
sample of quasi-elastic neutrino interactions occurring in an iron medium. The
flavor ratio (tracks/showers) of atmospheric neutrinos in a 3.9 fiducial
kiloton-year exposure of Soudan 2 is 0.64 +- 0.11 (stat.) +- 0.06 (syst.) of
that expected. Important aspects of our main analysis have been checked by
carrying out two independent, alternative analyses; one is based upon automated
scanning, the other uses a multivariate approach for background subtraction.
Similar results are found by all three approaches.
|
9901024v1
|
1999-12-14
|
Longitudinal Hadronic Shower Development in a Combined Calorimeter
|
This work is devoted to the experimental study of the longitudinal hadronic
shower development in the ATLAS barrel combined prototype calorimeter
consisting of the lead-liquid argon electromagnetic part and the
iron-scintillator hadronic part. The results have been obtained on the basis of
the 1996 combined test beam data which have been taken on the H8 beam of the
CERN SPS, with the pion beams of 10, 20, 40, 50, 80, 100, 150 and 300 GeV/c.
The degree of description of generally accepted Bock parameterization of the
longitudinal shower development has been investigated. It is shown that this
parameterization does not give satisfactory description for this combined
calorimeter. Some modification of this parameterization, in which the e/h
ratios of the compartments of the combined calorimeter are used, is suggested
and compared with the experimental data. The agreement between such
parameterization and the experimental data is demonstrated.
|
9912028v1
|
2000-01-05
|
Search for Nucleon Decay with Final States l+ eta, nubar eta, and nubar pi+,0 Using Soudan 2
|
We have searched for nucleon decay into five two-body final states using a
4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter.
For proton decay into the fully visible final states mu+ eta and e+ eta, we
observe zero and one event, respectively, that satisfy our search criteria for
nucleon decay. The lifetime lower limits (tau/B) thus implied are 89 x 10^30
years and 81 x 10^30 years at 90% confidence level. For neutron decay into
nubar eta, we obtain the lifetime lower limit 71 x 10^30 years. Limits are also
reported for neutron decay into nubar pi0, and for proton decay into nubar pi+.
|
0001015v1
|
2000-01-13
|
Neutrino Oscillation Appearance Experiment using Nuclear Emulsion and Magnetized Iron
|
This report describes an apparatus that could be used to measure both the
identity and charge of an outgoing lepton in a charged current neutrino
interaction. This capability in a massive detector would allow the most
comprehensive set of neutrino oscillation physics measurements. By measuring
the six observable transitions between initial and final state neutrinos, one
would be able to measure all elements of the neutrino mixing matrix, as well as
search for CP violation, and matter effects. If the measured matrix is not
unitary, then one would also have an unambiguous determination of sterile
neutrinos. Emulsion is considered as the tracking medium, and different
techniques are discussed for the application of a magnetic field.
|
0001035v1
|
2000-04-06
|
Hadron Energy Reconstruction for the ATLAS Barrel Prototype Combined Calorimeter in the Framework of the Non-parametrical Method
|
Hadron energy reconstruction for the Atlas barrel prototype combined
calorimeter, consisting of the lead-liquid argon electromagnetic part and the
iron-scintillator hadronic part, in the framework of the non-parametrical
method has been fulfilled. This method uses only the known e/h ratios and the
electron calibration constants and does not require the determination of any
parameters by a minimization technique and can be used for the fast energy
reconstruction in the first level trigger. The obtained reconstruction of the
mean values of energies is within $\pm 1%$ and the fractional energy resolution
is $[(58\pm3)% \sqrt{GeV}/\sqrt{E}+(2.5\pm0.3)%]\oplus (1.7\pm0.2) GeV/E$. The
obtained value of the e/h ratio for electromagnetic compartment of the combined
calorimeter is $1.74\pm0.04$ and agrees with the prediction that $e/h > 1.7$
for this electromagnetic calorimeter. The results of the study of the
longitudinal hadronic shower development are presented. The data have been
taken in the H8 beam line of the CERN SPS using pions of 10 -- 300 GeV.
|
0004009v1
|
2001-04-02
|
Hadron Energy Reconstruction for the ATLAS Calorimetry in the Framework of the Non-parametrical Method
|
This paper discusses hadron energy reconstruction for the ATLAS barrel
prototype combined calorimeter (consisting of a lead-liquid argon
electromagnetic part and an iron-scintillator hadronic part) in the framework
of the non-parametrical method. The non-parametrical method utilizes only the
known $e/h$ ratios and the electron calibration constants and does not require
the determination of any parameters by a minimization technique. Thus, this
technique lends itself to an easy use in a first level trigger. The
reconstructed mean values of the hadron energies are within $\pm 1%$ of the
true values and the fractional energy resolution is $[(58\pm3)%
/\sqrt{E}+(2.5\pm0.3)%]\oplus (1.7\pm0.2)/E$. The value of the $e/h$ ratio
obtained for the electromagnetic compartment of the combined calorimeter is
$1.74\pm0.04$ and agrees with the prediction that $e/h > 1.7$ for this
electromagnetic calorimeter. Results of a study of the longitudinal hadronic
shower development are also presented. The data have been taken in the H8 beam
line of the CERN SPS using pions of energies from 10 to 300 GeV.
|
0104002v2
|
2001-04-11
|
New calibrations and time stability of the response of the INTERCAST CR-39
|
We present new calibrations of different production batches (from 1989 to
1999) of the INTERCAST CR-39, using the BNL-AGS 1 A GeV iron beam. The
comparison with previous results, obtained with the 158 A GeV lead beam from
the CERN-SPS shows that, while each production batch has a different
calibration curve (mainly due to minor differences in the production
conditions), the aging effect is negligible. We also tested the dependence of
the CR-39 response from the time elapsed between exposure and analysis (fading
effect). The fading effect, if present, is less than 10%. It may be compatible
with the experimental uncertainties on the bulk etching rate vB.
|
0104022v1
|
2001-05-22
|
Extraction of R=sigma_L/sigma_T from CCFR Neutrino and Antinetrino Differential Cross Sections
|
We report on the extraction of R=sigam_L/sigma_T from CCFR neutrino and
antineutrino-Iron differential cross sections. R as measured in neutrno
scattering is in agreement with $R$ as measured in muon and electron
scattering. All data on R for Q2 > 1 GeV2 are in agreement with a NNLO QCD
calculation which uses NNLO PDFs and includes target mass effects. We report on
the first measurements of R in the low x and Q2 < 1 GeV2 region (where an
anomalous large rise in R for nuclear targets has been observed by the HERMES
collaboration).
|
0105067v1
|
2002-11-07
|
Design and test results of the AMS RICH detector
|
The AMS-02 detector will operate for at least 3 years on the International
Space Station, measuring cosmic ray spectra at about 400 km above sea level
over a wide range of geomagnetic latitude.
The proximity focusing ring imaging \v{C}erenkov counter of AMS-02 will
measure the particle velocity $\beta$ with $\approx 0.1%$ uncertainty, making
possible to discriminate Beryllium isotopes up to about 15 GeV/nucl. In
addition its charge measurement will allow to study the elemental composition
of cosmic rays up to Iron. A prototype of the RICH detector was tested with
cosmic rays and on a ion beam accelerated by SPS, at CERN (October 2002).
|
0211018v1
|
2006-07-31
|
Machine-Related Backgrounds in the SiD Detector at ILC
|
With a multi-stage collimation system and magnetic iron spoilers in the
tunnel, the background particle fluxes on the ILC detector can be substantially
reduced. At the same time, beam-halo interactions with collimators and
protective masks in the beam delivery system create fluxes of muons and other
secondary particles which can still exceed the tolerable levels for some of the
ILC sub-detectors. Results of modeling of such backgrounds in comparison to
those from the e+ e- interactions are presented in this paper for the SiD
detector.
|
0608001v1
|
1992-11-19
|
Recent Work on Standard Solar Models
|
Recent results on standard solar models are reviewed. I shall summarize
briefly three of the themes that I stressed at the Neutrino '92 Conference: 1)
Different solar model codes give the same answers when the same input data are
used; 2) Improved calculations of standard solar models include helium
diffusion, the Livermore radiative opacity, the meteoritic iron abundance, and
a variety of other corrections; and 3) There are a few basic rules that should
be followed in using standard solar models. At the Neutrino '92 Conference, I
reviewed in more detail the recent work on standard solar models by Marc
Pinsonneault and myself. This work has by now appeared in print (Rev. Mod.
Phys. 64, 885, 1992, hereafter Paper I, and ApJ Letters, 69, 717, 1992, Paper
II). Therefore, there is no need for me to repeat the details here.
|
9211280v1
|
1997-09-09
|
Neutrino-photon reactions in astrophysics and cosmology
|
At energies above the threshold for $W$ production the process $\nu \gamma
\to l W^+$ is competive with $\nu \nu$ scattering at the same center of mass
energies. In a cosmological setting, absorption of ultra high energy neutrinos
by the microwave photon background is comparable to absorption by the neutrino
background. In passing through matter, the process $\nu \to l W^+$ will occur
in the coulomb field of nuclei. For iron, the interaction rate per nucleon is
roughly 20% of the charge current cross-section. The related process,
$\anti\nu_e e^- \to \gamma W^-$ dominates $\anti\nu_e e^-$ scattering for about
a decade in energy above the resonance for $W$ production.
|
9709290v1
|
1997-12-07
|
Off-shell Corrections and Moments of the Deep Inelastic Nuclear Structure Functions
|
We present an improved method for handling off-shell effects in deep
inelastic nuclear scattering. With a firm understanding of the effects of the
nuclear wave function, including these off-shell corrections as well as binding
and nucleon-nucleon correlations, we can begin to examine the role of QCD in
nuclei through an analysis of the moments of the nuclear structure function.
Our analysis is aimed at extracting the Q^2 dependence of the moments of the
nucleon structure function by using the recent high x world Iron data and by
properly removing nuclear effects from the perturbative contribution. In
addition, we compare quantitatively the behavior of the extracted moments with
a simple O(1/Q^2) phenomenological form and we determine the mass term for this
parametrization.
|
9712286v1
|
1998-05-07
|
Measurement of Atmospheric Neutrino Oscillations with a High-Density Detector
|
We propose an experiment to test the hypothesis that the reported anomaly on
atmospheric neutrino fluxes is due to nu_mu <-> nu_x oscillations. It will rely
both on a disappearance technique, exploiting the method of the dependence of
the event rate on L/E, which was recently shown to be effective for detection
of neutrino oscillation and measurement of the oscillation parameters, and on
an appearance technique, looking for an excess of muon-less events at high
energy produced by upward-going tau neutrinos. The detector will consist of
iron planes interleaved by limited streamer tubes. The total mass will be about
30 kt. The possibility of recuperating most of the instrumentation from
existing detectors allows to avoid R&D phases and to reduce construction time.
In four years of data taking, this experiment will be sensitive to oscillations
nu_mu <-> nu_x with Delta m^2 > 10^-4 eV^2 and a mixing near to maximal, and
answer the question whether nu_x is a sterile or a tau neutrino.
|
9805249v2
|
2000-12-13
|
CP-violation in 3- and 4-family at the Neutrino Factory
|
The leptonic CP-violating phase $\delta$ can be measured with a Neutrino
Factory with $2 \times 10^{20} $ useful muons per year, if the solar neutrino
problem is solved by the LMA-MSW solution, with $\Delta m_{12}^2 \ge 2 \times
10^{-5}$ eV$^2$ (in this analysis a 40 kT magnetized iron detector is
considered, taking into account its efficiencies and backgrounds). If LSND is
confirmed, CP-violating phenomena in four-family scenarios can be most easily
addressed with a small 1 kT detector at $L = \cal O$(10) km (no detailed
analysis of the detector efficiencies and backgrounds has been performed in
this case).
|
0012153v1
|
2000-12-27
|
Propagation of Muons and Taus at High Energies
|
The photonuclear contribution to charged lepton energy loss has been
re-evaluated taking into account HERA results on real and virtual photon
interactions with nucleons. With large $Q^2$ processes incorporated, the
average muon range in rock for muon energies of $10^9$ GeV is reduced by only
5% as compared with the standard treatment. We have calculated the tau energy
loss for energies up to $10^9$ GeV taking into consideration the decay of the
tau. A Monte Carlo evaluation of tau survival probability and range show that
at energies below $10^7-10^8$ GeV, depending on the material, only tau decays
are important. At higher energies the tau energy losses are significant,
reducing the survival probability of the tau. We show that the average range
for tau is shorter than its decay length and reduce to 17 km in water for an
incident tau energy of $10^9$ GeV, as compared with its decay length of 49 km
at that energy. In iron, the average tau range is 4.7 km for the same incident
energy.
|
0012350v1
|
2001-07-27
|
Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei
|
In this article we examine the hypothesis that the highest energy cosmic rays
are complex nuclei from extragalactic sources. Under reasonable physical
assumptions, we show that the nearby metally rich starburst galaxies (M82 and
NGC 253) can produce all the events observed above the ankle. This requires
diffusion of particles below $10^{20}$ eV in extragalactic magnetic fields $B
\approx 15$ nG. Above $10^{19}$ eV, the model predicts the presence of
significant fluxes of medium mass and heavy nuclei with small rate of change of
composition. Notwithstanding, the most salient feature of the
starburst-hypothesis is a slight anisotropy induced by iron debris just before
the spectrum-cutoff.
|
0107287v4
|
2002-06-04
|
The silver channel at the Neutrino Factory
|
We notice that looking for $\nu_e \to \nu_\tau$ at the same time as $\nu_e
\to \nu_\mu$ oscillations could significantly help to reduce the errors in the
leptonic CP-violating phase $\delta$ measurement. We show how the $\nu_e \to
\nu_\mu$ (``golden'') and $\nu_e \to \nu_\tau$ (``silver'') transitions
observed at an OPERA-like 2 Kton lead-emulsion detector at L = 732 Km, in
combination with the $\nu_e \to \nu_\mu$ transitions observed at a 40 Kton
magnetized iron detector with a baseline of L = 3000 Km, strongly reduce the
so-called $(\theta_{13}, \delta)$ ambiguity. We also show how a moderate
increase in the OPERA-like detector mass (4 Kton instead of 2 Kton) completely
eliminates the clone regions even for small values of $\theta_{13}$.
|
0206034v1
|
2002-07-12
|
Possible Studies of Parton Distribution Functions at JHF
|
We discuss possible studies of parton distribution functions (PDFs) in the
nucleon and nuclei at the Japan Hadron Facility (JHF). First, the PDFs could be
investigated by the 50 GeV primary proton facility. The distributions at medium
x are determined, for example, by Drell-Yan measurements. Second, there are
feasibility studies to propose a neutrino factory within the 50 GeV proton
ring. If such an intensive high-energy neutrino facility is built, neutrino
reactions should be able to provide valuable information on the PDFs, whereas
the current structure functions have been measured mainly for neutrino-iron
reactions.
|
0207151v1
|
2002-09-18
|
Modified Paschos-Wolfenstein relation and extraction of weak mixing angle sin^2 theta_W
|
The NuTeV collaboration reported anomalously large weak mixing angle sin^2
theta_W in comparison with the standard model prediction. Neutrino and
antineutrino charged- and neutral-current events are analyzed for extracting
sin^2 theta_W. Although the Paschos-Wolfenstein relation is not directly used
in the analysis, it plays an important role in the determination. Noting that
the target nucleus, iron, is not an isoscalar nucleus, we derive a
leading-order expression for a modified Paschos-Wolfenstein relation for
nuclei, which may have neutron excess. Then, using charge and baryon-number
conservations for nuclei, we discuss a nuclear correction in the sin^2 theta_W
determination. It is noteworthy that nuclear modifications are different
between valence up- and down-quark distributions. We show this difference
effect on the NuTeV sin^2 theta_W deviation.
|
0209200v2
|
2003-01-18
|
Charge Symmetry Violating Contributions to Neutrino Reactions
|
The NuTeV group has measured charged and neutral current reactions for
neutrinos on iron targets. Ratios of these cross sections provide an
independent measurement of the Weinberg angle. The NuTeV value for sin^2
theta_W is three standard deviations larger than the value measured in other
electroweak processes. By reviewing theoretical estimates of parton charge
symmetry violation (CSV), we study CSV contributions to the NuTeV measurement.
We conclude that charge symmetry violating effects should remove roughly 30% of
the discrepancy between the NuTeV result and other determinations of sin^2
theta_W.
|
0301147v3
|
2003-05-16
|
The synergy of the golden and silver channels at the Neutrino Factory
|
We deepen the study of the so-called ``silver channel'' $\nu_e \to \nu_\tau$
\cite{Donini:2002rm} and of its relevance to solve some of the ambiguities that
can arise in the simultaneous measurement of $(\theta_{13},\delta)$ at the
Neutrino Factory by presenting in full detail the characteristics of the
considered OPERA-like detector and the experimental treatment of the different
backgrounds and signals. Furthermore, we perform a detailed study of the
systematic errors associated both with the OPERA-like and the magnetized-iron
detectors and their effects on the sensitivity. Finally, we also apply a
refined statistical analysis of the simulated events based on the frequentist
approach.
|
0305185v1
|
2003-06-06
|
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star
|
We investigate the initial progenitor mass dependence of the early-phase
neutrino signal from supernovae taking neutrino oscillations into account. The
early-phase analysis has advantages in that it is not affected by the time
evolution of the density structure of the star due to shock propagation or
whether the remnant is a neutron star or a black hole. The initial mass affects
the evolution of the massive star and its presupernova structure, which is
important for two reasons when considering the neutrino signal. First, the
density profile of the mantle affects the dynamics of neutrino oscillation in
supernova. Second, the final iron core structure determines the features of the
neutrino burst, i.e., the luminosity and the average energy. We find that both
effects are rather small. This is desirable when we try to extract information
on neutrino parameters from future supernova-neutrino observations. Although
the uncertainty due to the progenitor mass is not small for intermediate
$\theta_{13}$ ($10^{-5} \lesssim \sin^{2}{2 \theta_{13}} \lesssim 10^{-3}$), we
can, nevertheless, determine the character of the mass hierarchy and whether
$\theta_{13}$ is very large or very small.
|
0306056v1
|
2003-07-08
|
Nuclear modification of structure functions in lepton scattering
|
We discuss nuclear structure functions in lepton scattering including
neutrino reactions. First, the determination of nuclear parton distribution
functions is explained by using the data of electron and muon deep inelastic
scattering and those of Drell-Yan processes. Second, NuTeV sin^2 theta_W
anomaly is discussed by focusing on nuclear corrections in the iron target.
Third, we show that the HERMES effect, which indicates nuclear modification of
the longitudinal-transverse structure function ratio, should exist at large x
with small Q^2 in spite of recent experimental denials at small x.
|
0307105v1
|
2004-10-19
|
Detecting matter effects in long baseline experiments
|
Experiments strongly suggest that the flavour mixing responsible for the
atmospheric neutrino anomaly is very close to being maximal. Thus, it is of
great theoretical as well as experimental importance to measure any possible
deviation from maximality. In this context, we reexamine the effects of matter
interactions in long baseline neutrino oscillation experiments. Contrary to
popular belief, the muon neutrino survival probability is shown to be quite
sensitive to matter effects. Moreover, for moderately long baselines, the
difference between the survival probilities for $\nu_\mu$ and $\bar\nu_\mu$ is
shown to be large and sensitive to the deviation of $|U_{\mu 3}|$ from
maximality. Performing a realistic analysis, we demonstrate that a muon-storage
ring $\nu$-source alongwith an iron calorimeter detector can measure such
deviations. (Contrary to recent claims, this is not so for the NuMI--{\sc
minos} experiment.) We also discuss the possible correlation in measuring
$U_{\mu 3}$ and $U_{e3}$ in such experiment.
|
0410266v1
|
2004-12-20
|
Nuclear modification difference between u_v and d_v distributions and its relation to NuTeV sin^2 theta_W anomaly
|
We investigate a possible nuclear correction to the NuTeV measurement of the
weak-mixing angle sin^2 theta_W. In particular, a nuclear modification
difference between u_v and d_v distributions contributes to the NuTeV
measurement with the iron target. First, the modification differenceis
determined by a chi^2 analysis so as to reproduce nuclear data on the structure
function F_2 and Drell-Yan processes. Then, taking the NuTeV kinematics into
account, we calculate a contribution to the sin^2 theta_W determination. In
addition, its uncertainty is estimated by the Hessian method. Although the
uncertainty becomes comparable to the NuTeV deviation, the effect is not large
enough to explain the whole NuTeV sin^2 theta_W anomaly at this stage. However,
it is difficult to determine such a nuclear modification difference, so that we
need further investigations on the difference and its effect on the NuTeV
anomaly.
|
0412284v2
|
2005-11-10
|
Perspectives for a neutrino program based on the upgrades of the CERN accelerator complex
|
In this paper, we discuss the possibilities offered to neutrino physics by
the upgrades of the CERN accelerator complex. Emphasis is on the physics reach
of a medium $\gamma$ (350-580) $\beta$-beam that fully exploits the
improvements in the CERN accelerator complex for the luminosity/energy upgrade
of the LHC. We show that, this design not only profits of the ongoing efforts
for the upgrades of the LHC, but also leverage out the existing infrastructures
of the LNGS underground laboratory. Furthermore, given the involved high
neutrino energies, above 1 GeV, a non-magnetized iron detector could
efficiently exploit the neutrino beam.
We show that the performance of this complex for what concerns the discovery
of the CP violation in the leptonic sector, in case $\theta_{13}$ is discovered
by Phase I experiments, is comparable with the current baseline design based on
a gigantic water Cherenkov at Frejus. Furthermore, this complex has also some
sensitivity to the neutrino mass hierarchy.
|
0511134v2
|
2006-09-25
|
Probing Lepton Number Violating Interactions with Beta-beams
|
We show that a detector placed near a beta-beam storage ring can probe lepton
number violating interactions, as predicted by supersymmetric theories with
R-parity non-conservation. In the presence of such interactions, nu_tau can be
produced during beta-decay leading to tau leptons through weak interactions.
Alternatively, electron neutrinos from beta-decay of radioactive ions can
produce tau leptons in a nearby detector through these interactions. The muons
from the decay of these tau leptons can be readily identified in a small iron
calorimeter detector and will signal violation of R-parity.
|
0609252v2
|
2006-10-16
|
The mass hierarchy with atmospheric neutrinos at INO
|
We study the neutrino mass hierarchy at the magnetized Iron CALorimeter
(ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino
events generated by the Monte Carlo event generator Nuance. We judicially
choose the observables so that the possible systematic uncertainties can be
reduced. The resolution as a function of both energy and zenith angle
simultaneously is obtained for neutrinos and anti-neutrinos separately from
thousand years un-oscillated atmospheric neutrino events at ICAL to migrate
number of events from neutrino energy and zenith angle bins to muon energy and
zenith angle bins. The resonance ranges in terms of directly measurable
quantities like muon energy and zenith angle are found using this resolution
function at different input values of $\theta_{13}$. Then, the marginalized
$\chi^2$s are studied for different input values of $\theta_{13}$ with its
resonance ranges taking input data in muon energy and zenith angle bins.
Finally, we find that the mass hierarchy can be explored up to a lower value of
$\theta_{13}\approx 5^\circ$ with confidence level $>$ 95% in this set up.
|
0610196v3
|
2006-10-25
|
Neutrino mass hierarchy and $θ_{13}$ with a magic baseline beta-beam experiment
|
We underscore the physics advantage of an experiment where neutrinos produced
in a beta-beam facility at CERN are observed in a large magnetized iron
calorimeter (ICAL) at the India-based Neutrino Observatory (INO). The CERN-INO
distance is close to the so-called "magic" baseline which helps evade some of
the parameter degeneracies and allows for a better measurement of the neutrino
mass hierarchy and $\theta_{13}$. We expound the possibility of using
radioactive $^8B$ and $^{8}Li$ as the source isotopes for the $\nue$ and
$\anue$ beta-beam, respectively, and show that very good sensitivity to both
the mass hierarchy and $\theta_{13}$ is possible with a boost $\gamma$ in the
250-500 ballpark.
|
0610333v2
|
2007-02-18
|
A GEANT-based study of atmospheric neutrino oscillation parameters at INO
|
We have studied the dependence of the allowed space of the atmospheric
neutrino oscillation parameters on the time of exposure for a magnetized Iron
CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We
have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating
events by the neutrino generator NUANCE and simulating the detector response by
GEANT. A chi-square analysis for the ratio of the up-going and down-going
neutrinos as a function of $L/E$ is performed and the allowed regions at 90%
and 99% CL are displayed. These results are found to be better than the current
experimental results of MINOS and Super-K. The possibilities of further
improvement have also been discussed.
|
0702180v3
|
2007-03-20
|
Neutrino hierarchy from CP-blind observables with high density magnetized detectors
|
High density magnetized detectors are well suited to exploit the outstanding
purity and intensities of novel neutrino sources like Neutrino Factories and
Beta Beams. They can also provide independent measurements of leptonic mixing
parameters through the observation of atmospheric muon-neutrinos. In this
paper, we discuss the combination of these observables from a multi-kton iron
detector and a high energy Beta Beam; in particular, we demonstrate that even
with moderate detector granularities the neutrino mass hierarchy can be
determined for $\theta_{13}$ values greater than 4$^\circ$.
|
0703209v3
|
1996-08-18
|
M-Theory (the Theory Formerly Known as Strings)
|
Superunification underwent a major paradigm shift in 1984 when
eleven-dimensional supergravity was knocked off its pedestal by ten-dimensional
superstrings. This last year has witnessed a new shift of equal proportions:
perturbative ten-dimensional superstrings have in their turn been superseded by
a new non-perturbative theory called {\it $M$-theory}, which describes
supermembranes and superfivebranes, which subsumes all five consistent string
theories and whose low energy limit is, ironically, eleven-dimensional
supergravity. In particular, six-dimensional string/string duality follows from
membrane/fivebrane duality by compactifying $M$-theory on $S^1/Z_2 \times K3$
(heterotic/heterotic duality) or $S^1 \times K3$ (Type $IIA$/heterotic duality)
or $S^1/Z_2 \times T^4$ (heterotic/Type $IIA$ duality) or $S^1 \times T^4$
(Type $IIA$/Type $IIA$ duality).
|
9608117v3
|
2002-10-03
|
Critical analyses of order parameter and phase transitions at high density in Gross-Neveu model
|
By critical analyses of the order parameter of symmetry breaking, we have
researched the phase transitions at high density in D=2 and D=3 Gross-Neveu
(GN) model and shown that the gap equation obeyed by the dynamical fermion mass
has the same effectivenesss as the effective potentials for such analyses of
all the second order and some special first order phase transitions. In the
meantime we also further ironed out a theoretical divergence and proven that in
D=3 GN model a first order phase transition does occur in the case of zero
temperature and finite chemical potential.
|
0210023v3
|
1999-10-18
|
A high-precision polarimeter
|
We have built a polarimeter in order to measure the electron beam
polarization in hall C at JLAB. Using a superconducting solenoid to drive the
pure-iron target foil into saturation, and a symmetrical setup to detect the
Moller electrons in coincidence, we achieve an accuracy of <1%. This sets a new
standard for Moller polarimeters.
|
9910013v1
|
2002-11-25
|
The Single-Particle Structure of Neutron-Rich Nuclei of Astrophysical Interest at the Ornl Hribf
|
The rapid nuetron-capture process (r process) produces roughly half of the
elements heavier than iron. The path and abundances produced are uncertain,
however, because of the lack of nuclear strucure information on important
neutron-rich nuclei. We are studying nuclei on or near the r-process path via
single-nucleon transfer reactions on neutron-rich radioactive beams at ORNL's
Holifield Radioactive Ion Beam Facility (HRIBF). Owing to the difficulties in
studying these reactions in inverse kinematics, a variety of experimental
approaches are being developed. We present the experimental methods and initial
results.
|
0211027v1
|
2003-07-11
|
Low-Q scaling, duality, and the EMC effect
|
High energy lepton scattering has been the primary tool for mapping out the
quark distributions of nucleons and nuclei. Data on the proton and deuteron
have shown that there is a fundamental connection between the low and high
energy regimes, referred to as quark-hadron duality. We present the results of
similar studies to more carefully examine scaling, duality, and in particular
the EMC effect in nuclei. We extract nuclear modifications to the structure
function in the resonance region, and for the first time demonstrate that
nuclear effects in the resonance region are identical to those measured in deep
inelastic scattering. With the improved precision of the data at large $x$, we
for the first time observe that the large-x crossover point appears to occur at
lower $x$ values in carbon than in iron or gold.
|
0307012v3
|
2005-11-28
|
Cosmogenic activation of Germanium and its reduction for low background experiments
|
Production of $^{60}$Co and $^{68}$Ge from stable isotopes of Germanium by
nuclear active component of cosmic rays is a principal background source for a
new generation of $^{76}$Ge double beta decay experiments like GERDA and
Majorana. The biggest amount of cosmogenic activity is expected to be produced
during transportation of either enriched material or already grown crystal.
In this letter properties and feasibility of a movable iron shield are
discussed. Activation reduction factor of about 10 is predicted by simulations
with SHIELD code for a simple cylindrical configuration. It is sufficient for
GERDA Phase II background requirements. Possibility of further increase of
reduction factor and physical limitations are considered. Importance of
activation reduction during Germanium purification and detector manufacturing
is emphasized.
|
0511049v1
|
2006-04-06
|
Level density of $^{56}$Fe and low-energy enhancement of $γ$-strength function
|
The $^{55}$Mn$(d,n)^{56}$Fe differential cross section is measured at $E_d=7$
MeV\@. The $^{56}$Fe level density obtained from neutron evaporation spectra is
compared to the level density extracted from the
$^{57}$Fe$(^3$He,$\alpha\gamma)^{56}$Fe reaction by the Oslo-type technique.
Good agreement is found between the level densities determined by the two
methods. With the level density function obtained from the neutron evaporation
spectra, the $^{56}$Fe $\gamma$-strength function is also determined from the
first-generation $\gamma$ matrix of the Oslo experiment. The good agreement
between the past and present results for the $\gamma$-strength function
supports the validity of both methods and is consistent with the low-energy
enhancement of the $\gamma$ strength below $\sim 4$ MeV first discovered by the
Oslo method in iron and molybdenum isotopes.
|
0604002v1
|
1996-01-30
|
Temperature Dependence of Pair Correlations in Nuclei in the Iron-Region
|
We use the shell model Monte Carlo approach to study thermal properties and
pair correlations in $^{54,56,58}$Fe and in $^{56}$Cr. The calculations are
performed with the modified Kuo-Brown interaction in the complete $1p0f$ model
space. We find generally that the proton-proton and neutron-neutron $J=0$
pairing correlations, which dominate the ground state properties of even-even
nuclei, vanish at temperatures around 1 MeV. This pairing phase transition is
accompanied by a rapid increase in the moment of inertia and a partial
unquenching of the M1 strength. We find that the M1 strength totally unquenches
at higher temperatures, related to the vanishing of isoscalar proton-neutron
correlations, which persist to higher temperatures than the pairing between
like nucleons. The Gamow-Teller strength is also correlated to the isoscalar
proton-neutron pairing and hence also unquenches at a temperature larger than
that of the pairing phase transition.
|
9601047v1
|
1997-11-21
|
Approximate Treatment of Lepton Distortion in Charged-Current Neutrino Scattering from Nuclei
|
The partial-wave expansion used to treat the distortion of scattered
electrons by the nuclear Coulomb field is simpler and considerably less
time-consuming when applied to the production of muons and electrons by low and
intermediate-energy neutrinos. For angle-integrated cross sections, however, a
modification of the "effective-momentum-transfer" approximation seems to work
so well that for muons the full distorted-wave treatment is usually
unnecessary, even at kinetic energies as low as an MeV and in nuclei as heavy
as lead. The method does not work as well for electron production at low
energies, but there a Fermi function usually proves adequate. Scattering of
electron-neutrinos from muon decay on iodine and of atmospheric neutrinos on
iron are discussed in light of these results.
|
9711045v1
|
1998-01-08
|
Electron capture on iron group nuclei
|
We present Gamow-Teller strength distributions from shell model Monte Carlo
studies of fp-shell nuclei that may play an important role in the pre-collapse
evolution of supernovae. We then use these strength distributions to calculate
the electron-capture cross sections and rates in the zero-momentum transfer
limit. We also discuss the thermal behavior of the cross sections. We find
large differences in these cross sections and rates when compared to the naive
single-particle estimates. These differences need to be taken into account for
improved modeling of the early stages of type II supernova evolution.
|
9801012v1
|
1998-03-11
|
Shell model calculation of the beta- and beta+ partial halflifes of 54Mn and other unique second forbidden beta decays
|
The nucleus 54Mn has been observed in cosmic rays. In astrophysical
environments it is fully stripped of its atomic electrons and its decay is
dominated by the beta- branch to the 54Fe ground state. Application of 54Mn
based chronometer to study the confinement of the iron group cosmic rays
requires knowledge of the corresponding halflife, but its measurement is
impossible at the present time. However, the branching ratio for the related
beta+ decay of 54Mn was determined recently. We use the shell model with only a
minimal truncation and calculate both beta+ and beta- decay rates of 54Mn. Good
agreement for the beta+ branch suggests that the calculated partial halflife of
the beta- decay, (4.94 \pm 0.06) x 10^5 years, should be reliable. However,
this halflife is noticeably shorter than the range 1-2 x 10^6 y indicated by
the fit based on the 54Mn abundance in cosmic rays. We also evaluate other
known unique second forbidden beta decays from the nuclear p and sd shells
(10Be, 22Na, and two decay branches of 26Al) and show that the shell model can
describe them with reasonable accuracy as well.
|
9803032v1
|
2000-03-08
|
Level Densities by Particle-Number Reprojection Monte Carlo Methods
|
A particle-number reprojection method is applied in the framework of the
shell model Monte Carlo approach to calculate level densities for a family of
nuclei using Monte Carlo sampling for a single nucleus. In particular we can
also calculate level densities of odd-even and odd-odd nuclei despite a new
sign problem introduced by the projection on an odd number of particles. The
method is applied to level densities in the iron region using the complete
$pf+g_{9/2}$-shell. The single-particle level density parameter $a$ and the
backshift parameter $\Delta$ are extracted by fitting the microscopically
calculated level densities to the backshifted Bethe formula. We find good
agreement with experimental level densities with no adjustable parameters in
the microscopic calculations. The parameter $a$ is found to vary smoothly with
mass and does not show odd-even effects. The calculated backshift parameter
$\Delta$ displays an odd-even staggering effect versus mass and is in better
agreement with the experimental data than are the empirical values.
|
0003015v1
|
2002-08-12
|
Liquid-Gas Phase Transition of Supernova Matter and Its Relation to Nucleosynthesis
|
We investigate the liquid-gas phase transition of dense matter in supernova
explosion by the relativistic mean field approach and fragment based
statistical model. The boiling temperature is found to be high (T_{boil} >= 0.7
MeV for rho_B >= 10^{-7} fm^{-3}), and adiabatic paths are shown to go across
the boundary of coexisting region even with high entropy. This suggests that
materials experienced phase transition can be ejected to outside. We calculated
fragment mass and isotope distribution around the boiling point. We found that
heavy elements at the iron, the first, second, and third peaks of r-process are
abundantly formed at rho_B = 10^{-7}, 10^{-5}, 10^{-3} and 10^{-2} fm^{-3},
respectively.
|
0208020v1
|
2002-11-08
|
Nuclear Reactions Important in Alpha-Rich Freezeouts
|
The alpha-rich freezeout from equilibrium occurs during the core-collapse
explosion of a massive star when the supernova shock wave passes through the
Si-rich shell of the star. The nuclei are heated to high temperature and broken
down into nucleons and alpha particles. These subsequently reassemble as the
material expands and cools, thereby producing new heavy nuclei, including a
number of important supernova observables. In this paper we introduce two
web-based applications. The first displays the results of a reaction-rate
sensitivity study of alpha-rich freezeout yields. The second allows the
interested reader to run paramaterized explosive silicon burning calculations
in which the user inputs his own parameters. These tools are intended to aid in
the identification of nuclear reaction rates important for experimental study.
We then analyze several iron-group isotopes (59Ni, 57Co, 56Co, and 55Fe) in
terms of their roles as observables and examine the reaction rates that are
important in their production.
|
0211022v1
|
2003-03-18
|
Nuclear level statistics: extending the shell model theory to higher temperatures
|
The Shell Model Monte Carlo (SMMC) approach has been applied to calculate
level densities and partition functions to temperatures up to ~ 1.5 - 2 MeV,
with the maximal temperature limited by the size of the configuration space.
Here we develop an extension of the theory that can be used to higher
temperatures, taking into account the large configuration space that is needed.
We first examine the configuration space limitation using an
independent-particle model that includes both bound states and the continuum.
The larger configuration space is then combined with the SMMC under the
assumption that the effects on the partition function are factorizable. The
method is demonstrated for nuclei in the iron region, extending the calculated
partition functions and level densities up to T ~ 4 MeV. We find that the
back-shifted Bethe formula has a much larger range of validity than was
suspected from previous theory. The present theory also shows more clearly the
effects of the pairing phase transition on the heat capacity.
|
0303040v1
|
2005-06-17
|
Charged Lepton Production from Iron Induced by Atmospheric Neutrinos
|
The charged current lepton production induced by neutrinos in $^{56}Fe$
nuclei has been studied. The calculations have been done for the quasielastic
as well as the inelastic reactions assuming $\Delta$ dominance and take into
account the effect of Pauli blocking, Fermi motion and the renormalization of
weak transition strengths in the nuclear medium. The quasielastic production
cross section for lepton production are found to be strongly reduced due to
nuclear effects while there is about 10% reduction in the inelastic cross
sections in the absence of the final state interactions of the pions. The
numerical results for the momentum and angular distributions of the leptons
averaged over the various atmospheric neutrino spectra at the Soudan and
Gransasso sites have been presented. The effect of nuclear model dependence and
the atmospheric flux dependence on the relative yield of ${\mu}$ to e has been
studied and discussed.
|
0506057v1
|
2005-08-13
|
The nuclear moment of inertia and spin distribution of nuclear levels
|
We introduce a simple model to calculate the nuclear moment of inertia at
finite temperature. This moment of inertia describes the spin distribution of
nuclear levels in the framework of the spin-cutoff model. Our model is based on
a deformed single-particle Hamiltonian with pairing interaction and takes into
account fluctuations in the pairing gap. We derive a formula for the moment of
inertia at finite temperature that generalizes the Belyaev formula for zero
temperature. We show that a number-parity projection explains the strong
odd-even effects observed in shell model Monte Carlo studies of the nuclear
moment of inertia in the iron region.
|
0508027v1
|
2000-08-18
|
An ECR hydrogen negative ion source at CEA/Saclay: preliminary results
|
The development of a high intensity negative ion source is part of a
considerably larger activity presently undergoing at CEA Saclay in the field of
high intensity linear accelerators. Preliminary studies toward the construction
of a 2.45 GHz ECR H- ion source have been performed for few months. This new
test bench takes advantage of our experience on the French high intensity
proton source SILHI. In the new source, the high-energy electrons created in
the ECR zone are trapped by a dipole magnetic filter. A rectangular 200 mm long
plasma chamber and an intermediate iron shield are used to minimize the
magnetic field in the extraction region. A second magnetic filter separates
electrons and negative ions in a 10 kV extraction system. To reduce the
electron/H- ratio, the plasma electrode is slightly polarized. The design
allows future evolutions such as cesium injection, higher energy extraction and
plasma diagnostics. The installation of the source is now in progress. The
first helium plasma has been produced for few weeks to verify the electron
separator behavior. The design, computations and the first results of the
source are presented.
|
0008143v1
|
2003-05-09
|
The particle-in-cell model for ab initio thermodynamics: implications for the elastic anisotropy of the Earth's inner core
|
We assess the quantitative accuracy of the particle-in-cell (PIC)
approximation used in recent ab initio predictions of the thermodynamic
properties of hexagonal-close-packed iron at the conditions of the Earth's
inner core. The assessment is made by comparing PIC predictions for a range of
thermodynamic properties with the results of more exact calculations that avoid
the PIC approximation. It is shown that PIC gives very accurate results for
some properties, but that it gives an incorrect treatment of anharmonic lattice
vibrations. In addition, our assessment does not support recent PIC-based
predictions that the hexagonal c/a ratio increases strongly with increasing
temperature, and we point out that this casts doubt on a proposed
re-interpretation of the elastic anisotropy of the inner core.
|
0305033v2
|
2004-11-19
|
New applications of Equinox code for real-time plasma equilibrium and profile reconstruction for tokamaks
|
Recent development of real-time equilibrium code Equinox [1] using a
fixed-point algorithm [2] allow major plasma magnetic parameters to be
identified in real-time, using rigorous analytical method. The code relies on
the boundary flux code providing flux values on the first wall of vacuum
vessel. By means of least-square minimization of differences between magnetic
field obtained from previous solution and the next measurements the code
identifies the source term of the non-linear Grad-Shafranov equation [3]. The
strict use of analytical equations together with a flexible algorithm offers an
opportunity to include new measurements into stable magnetic equilibrium code
and compare the results directly between several tokamaks while maintaining the
same physical model (i.e. no iron model is necessary inside the equilibrium
code). The successful implementation of this equilibrium code for JET and Tore
Supra have been already published [1], in this paper, we show the preliminary
results of predictive runs of the Equinox code using the ITER geometry.
|
0411181v1
|
2006-01-04
|
Simulation Studies of Delta-ray Backgrounds in a Compton-Scatter Transition Radiation Detector
|
In order to evaluate the response to cosmic-ray nuclei of a Compton-Scatter
Transition Radiation Detector in the proposed ACCESS space-based mission, a
hybrid Monte Carlo simulation using GEANT3 and an external transition radiation
(TR) generator routine was constructed. This simulation was employed to study
the effects of delta-ray production induced by high-energy nuclei and to
maximize the ratio of TR to delta-ray background. The results demonstrate the
ability of a Compton-Scatter Transition Radiation Detector to measure nuclei
from boron to iron up to Lorentz factors ~ 10^5 taking into account the steeply
falling power-law cosmic ray spectra.
|
0601020v1
|
2006-11-22
|
Efficient Degradation and Expression Prioritization with Small RNAs
|
We build a simple model for feedback systems involving small RNA (sRNA)
molecules based on the iron metabolism system in the bacterium E. coli, and
compare it with the corresponding system in H. pylori which uses purely
transcriptional regulation. This reveals several unique features of sRNA based
regulation that could be exploited by cells. Firstly, we show that sRNA
regulation can maintain a smaller turnover of target mRNAs than transcriptional
regulation, without sacrificing the speed of response to external shocks.
Secondly, we propose that a single sRNA can prioritize the usage of different
target mRNAs. This suggests that sRNA regulation would be more common in more
complex systems which need to co-regulate many mRNAs efficiently.
|
0611069v3
|
2007-04-06
|
Millimeter-Thick Single-Walled Carbon Nanotube Forests: Hidden Role of Catalyst Support
|
A parametric study of so-called "super growth" of single-walled carbon
nanotubes(SWNTs) was done by using combinatorial libraries of iron/aluminum
oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and
those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs.
Although nanotube forests grew under a wide range of reaction conditions such
as gas composition and temperature, the window for SWNT was narrow. Fe
catalysts rapidly grew nanotubes only when supported on aluminum oxide.
Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays
an essential role in enhancing the nanotube growth rates.
|
0704.0915v1
|
2007-04-11
|
Physical parameters of evolved stars in clusters and in the field from line-depth ratios
|
We present a high-resolution spectroscopic analysis of two samples of evolved
stars selected in the field and in the intermediate-age open cluster IC 4651,
for which detailed measurements of chemical composition were made in the last
few years. Applying the Gray's method based on ratios of line depths, we
determine the effective temperature and compare our results with previous ones
obtained by means of the curves of growth of iron lines. The knowledge of the
temperature enables us to estimate other fundamental stellar parameters, such
as color excess, age, and mass.
|
0704.1462v1
|
2007-04-13
|
Spectrum of cosmic rays, produced in supernova remnants
|
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to calculate CR spectra. The magnetic field in SNRs is
assumed to be significantly amplified by the efficiently accelerating nuclear
CR component. It is shown that the calculated CR spectra agree in a
satisfactory way with the existing measurements up to the energy $10^{17}$ eV.
The power law spectrum of protons extends up to the energy $3\times 10^{15}$ eV
with a subsequent exponential cutoff. It gives a natural explanation for the
observed knee in the Galactic CR spectrum. The maximum energy of the
accelerated nuclei is proportional to their charge number $Z$. Therefore the
break in the Galactic CR spectrum is the result of the contribution of
progressively heavier species in the overall CR spectrum so that at $10^{17}$
eV the CR spectrum is dominated by iron group nuclei. It is shown that this
component plus a suitably chosen extragalactic CR component can give a
consistent description for the entire Galactic CR spectrum.
|
0704.1715v1
|
2007-04-16
|
Single pion electro-- and neutrinoproduction on heavy targets
|
We present a calculation of single pion electroproduction cross sections on
heavy targets in the kinematic region of the Delta(1232) resonance. Final state
interactions of the pions are taken into account using the pion multiple
scattering model of Adler, Nussinov and Paschos (ANP model). For
electroproduction and neutral current reactions we obtain results for carbon,
oxygen, argon and iron targets and find a significant reduction of the
W-spectra for pi^0 as compared to the free nucleon case. On the other hand, the
charged pion spectra are only little affected by final state interactions.
Measurements of such cross sections with the CLAS detector at JLAB could help
to improve our understanding of pion rescattering effects and serve as
important/valuable input for calculations of single pion neutrinoproduction on
heavy targets relevant for current and future long baseline neutrino
experiments. Two ratios, in Eq. (3.8) and (3.10), will test important
properties of the model.
|
0704.1991v1
|
2007-04-17
|
Maximum Entropy for Gravitational Wave Data Analysis: Inferring the Physical Parameters of Core-Collapse Supernovae
|
The gravitational wave signal arising from the collapsing iron core of a Type
II supernova progenitor star carries with it the imprint of the progenitor's
mass, rotation rate, degree of differential rotation, and the bounce depth.
Here, we show how to infer the gravitational radiation waveform of a core
collapse event from noisy observations in a network of two or more LIGO-like
gravitational wave detectors and, from the recovered signal, constrain these
source properties. Using these techniques, predictions from recent core
collapse modeling efforts, and the LIGO performance during its S4 science run,
we also show that gravitational wave observations by LIGO might have been
sufficient to provide reasonable estimates of the progenitor mass, angular
momentum and differential angular momentum, and depth of the core at bounce,
for a rotating core collapse event at a distance of a few kpc.
|
0704.2157v2
|
2007-05-09
|
Quark-nova explosion inside a collapsar: application to Gamma Ray Bursts
|
If a quark-nova occurs inside a collapsar, the interaction between the
quark-nova ejecta (relativistic iron-rich chunks) and the collapsar envelope,
leads to features indicative of those observed in Gamma Ray Bursts. The
quark-nova ejecta collides with the stellar envelope creating an outward moving
cap
(Gamma ~ 1-10) above the polar funnel. Prompt gamma-ray burst emission from
internal shocks in relativistic jets (following accretion onto the quark star)
become visible after the cap becomes optically thin. Model features include:
(i) precursor activity (optical, X-ray, gamma-ray), (ii) prompt gamma-ray
emission, and (iii) afterglow emission. We discuss SN-less long duration GRBs,
short hard GRBs (including association and non-association with star forming
regions), dark GRBs, the energetic X-ray flares detected in Swift GRBs, and the
near-simultaneous optical and gamma-ray prompt emission observed in GRBs in the
context of our model.
|
0705.1240v3
|
2007-05-17
|
Applications of nanoparticles of gamma Fe2O3 for hyperthermia in E.coli by Nd:YAG laser
|
The paper explores the use of nanoparticles of gamma Fe2O3 for hyperthermia
treatment of living organisms by absorption of 1064 nm radiations from Nd:YAG
laser. Escherichia coli cells have been used as the model system for
demonstrating the effect wherein lysine is used as an interface between the
cell walls and the nanoparticles. Scanning Electron Microscopic observations
have, exclusively, proved that attachment of nanoparticles of iron oxide along
with lysine alone is responsible for absorption of above radiations. The
quantitative estimation has been provided by growth rate measurements and
protein assessment of the cells. The nanoparticles of gamma Fe2O3 were
synthesized by DC arc plasma assisted gas phase condensation.
|
0705.2523v1
|
2007-05-21
|
Room temperature spin polarized magnetic semiconductor
|
Alternating layers of granular Iron (Fe) and Titanium dioxide
(TiO$_{2-\delta}$) were deposited on (100) Lanthanum aluminate (LaAlO$_3$)
substrates in low oxygen chamber pressure using a controlled pulsed laser
ablation deposition technique. The total thickness of the film was about 200
nm. The films show ferromagnetic behavior for temperatures ranging from 4 to
$400 ^oK$. The layered film structure was characterized as p-type magnetic
semiconductor at $300 ^oK$ with a carrier density of the order of $10^{20}
/cm^3$. The undoped pure TiO$_{2-\delta}$ film was characterized as an n-type
magnetic semiconductor. The hole carriers were excited at the interface between
the granular Fe and TiO$_{2-\delta}$ layers similar to holes excited in the
metal/n-type semiconductor interface commonly observed in
Metal-Oxide-Semiconductor (MOS) devices. The holes at the interface were
polarized in an applied magnetic field raising the possibility that these
granular MOS structures can be utilized for practical spintronic device
applications.
|
0705.2993v1
|
2007-05-30
|
Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order
|
Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser
deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed
X-ray diffraction and cross-section transmission electron microscopy analysis
revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films
very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+
cation ordering along the [111] direction. The films contain no detectable
magnetic iron oxide impurities and have the correct cationic average
stoichiometry throughout their thickness. They however exhibit a slight
modulation in the Fe and Cr compositions forming complementary stripe patterns,
suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO
films exhibit good ferroelectric and piezoelectric properties, in addition to
magnetic properties at room temperature, as well as an unexpected
crystallographic orientation dependence of their room temperature magnetic
properties. Our results qualitatively confirm the predictions made using the
ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films
exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along
with the unpredicted existence of magnetic ordering at room temperature.
|
0705.4390v1
|
2007-06-04
|
Sum-rules for electron energy-loss near-edge spectra
|
We derive four sum-rule expressions for spectra measured in electron
energy-loss near edge structure experiments. These sum-rules permit the
determination spin and orbital magnetic moments, spin-orbit interaction and
number of states, analogously to the sum rules of x-ray magnetic circular
dichroism. The derivation of the sum-rules is based on dynamical electron
diffraction theory and the properties of the mixed dynamic form-factor. The
accuracy of the sum-rules is tested by a complete evaluation of the thickness
dependent electron energy-loss spectra for iron, cobalt, and nickel crystals.
We find that the sum-rules reproduce both spin and orbital moments with very
good accuracy. Our results provide a foundation for the use of the energy loss
magnetic chiral dichroism technique as a quantitative probe of element specific
magnetic properties.
|
0706.0402v2
|
2007-06-14
|
Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up
|
The concomitant overabundances of C, N and s-process elements are commonly
ascribed to the complex interplay of nucleosynthesis, mixing and mass loss
taking place in Asymptotic Giant Branch stars. At low metallicity, the
enhancement of C and/or N may be up to 1000 times larger than the original iron
content and significantly affects the stellar structure and its evolution. For
this reason, the interpretation of the already available and still growing
amount of data concerning C-rich metal-poor stars belonging to our Galaxy as
well as to dwarf spheroidal galaxies would require reliable AGB stellar models
for low and very low metallicities. In this paper we address the question of
calculation and use of appropriate opacity coefficients, which take into
account the C enhancement caused by the third dredge up. A possible N
enhancement, caused by the cool bottom process or by the engulfment of protons
into the convective zone generated by a thermal pulse and the subsequent huge
third dredge up, is also considered. Basing on up-to-date stellar models, we
illustrate the changes induced by the use of these opacity on the physical and
chemical properties expected for these stars.
|
0706.2100v1
|
2007-06-18
|
The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton
|
We present XMM observations of the black hole X-ray nova V404 Cygni in
quiescence. Its quiescent spectrum can be best fitted by a simple power-law
with slope 2. The spectra are consistent with that expected for the
advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in
luminosity compared to the previous observation of Chandra. We see variability
of a factor of 4 during the observation. We find no evidence for the presence
of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and
110 eV respectively. The limit on the fluorescent emission is improved by a
factor of 15 over the previous estimate, and the restriction on H-like/He-like
emission is lower than predicted from models by a factor of roughly 2.
|
0706.2652v1
|
2007-06-20
|
Optical spectroscopy of RU Cam, a pulsating carbon star
|
We analysed the high resolution spectra of a RU Cam, classified as W Vir type
star. The atmospheric parameters of RU Cam were estimated Teff=5250K and log
g=1.0. The hydrogen deficiency of RU Cam was not confirmed. The iron abundance,
[Fe/H]=-0.37, is close to the solar one. Abundances of most other elements are
also close to normal. We found considerable excesses of carbon and nitrogen:
[C/Fe]=+0.98, [N/Fe]=+0.60. The carbon to oxygen ratio is C/O$\ge$1. The carbon
isotopic abundance ratio is equal to C^12/C^13=4.5. For sodium a moderate
overabundance Na/Fe=+0.55 was obtained. For two moments of observations we
found close heliocentric velocity values, Vr=-21.7+/-0.8 and -23.1+/-1.0 km/s.
Both spectra contain a peculiar feature - an emission component of NaI doublet
which location agrees with the radial velocity from the bulk of metallic lines.
For our two observing moments we found no dependence of radial velocities on
the formation depth or on excitation energy for metallic lines.
|
0706.2969v1
|
2007-06-20
|
Neutrino-driven explosions twenty years after SN1987A
|
The neutrino-heating mechanism remains a viable possibility for the cause of
the explosion in a wide mass range of supernova progenitors. This is
demonstrated by recent two-dimensional hydrodynamic simulations with detailed,
energy-dependent neutrino transport. Neutrino-driven explosions were not only
found for stars in the range of 8-10 solar masses with ONeMg cores and in case
of the iron core collapse of a progenitor with 11 solar masses, but also for a
``typical'' progenitor model of 15 solar masses. For such more massive stars,
however, the explosion occurs significantly later than so far thought, and is
crucially supported by large-amplitude bipolar oscillations due to the
nonradial standing accretion shock instability (SASI), whose low (dipole and
quadrupole) modes can develop large growth rates in conditions where convective
instability is damped or even suppressed. The dominance of low-mode deformation
at the time of shock revival has been recognized as a possible explanation of
large pulsar kicks and of large-scale mixing phenomena observed in supernovae
like SN 1987A.
|
0706.3056v1
|
2007-07-18
|
Charge Order Superstructure with Integer Iron Valence in Fe2OBO3
|
Solution-grown single crystals of Fe2OBO3 were characterized by specific
heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific
heat at 340 K indicates the onset of charge order. Evidence for a doubling of
the unit cell at low temperature is presented. Combining structural refinement
of diffraction data and Mossbauer spectra, domains with diagonal charge order
are established. Bond-valence-sum analysis indicates integer valence states of
the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest
example of ionic charge order so far.
|
0707.2743v1
|
2007-07-27
|
Magnetic Field Generation in Planets and Satellites by Natural Nuclear Fission Reactors
|
One of the most fundamental problems in physics has been to understand the
nature of the mechanism that generates the geomagnetic field and the magnetic
fields of other planets and satellites. For decades, the dynamo mechanism,
thought to be responsible for generating the geomagnetic field and other
planetary magnetic fields, has been ascribed to convection in each planet's
iron-alloy core. Recently, I described the problems inherent in Earth-core
convection and proposed instead that the geomagnetic field is produced by a
dynamo mechanism involving convection, not in the fluid core, but in the
electrically conductive, fluid, fission-product sub-shell of a natural nuclear
fission reactor at the center of the Earth, called the georeactor. Here I set
forth in detail the commonality in the Solar System of the matter like that of
the inside of the Earth, which is my basis for generalizing the concept of
planetary magnetic field generation by natural planetocentric nuclear fission
reactors.
|
0707.4161v4
|
2007-08-01
|
Abundances on the Main Sequence of Omega Centauri
|
Abundance ratios of carbon, nitrogen and strontium relative to iron,
calculated using spectrum synthesis techniques, are given for a sample of main
sequence and turnoff stars that belong to the globular cluster omega Centauri.
The variations of carbon, nitrogen and/or strontium show several different
abundance patterns as a function of [Fe/H]. The source of the
enhancements/depletions in carbon, nitrogen and/or strontium may be enrichment
from asymptotic giant branch stars of low (1--3 solar masses) and intermediate
(3--8 solar masses) mass. Massive rotating stars which produce excess nitrogen
without carbon and oxygen overabundances may also play a role. These abundances
enable different contributors to be considered and incorporated into the
evolutionary picture of omega Cen.
|
0708.0096v1
|
2007-08-01
|
The 4th Concept Detector for the International Linear Collider
|
The 4th Concept detector presently being designed for the International
Linear Collider introduces several innovations in order to achieve the
necessary experimental goal of a detecter that is 2-to-10 times better than the
already excellent SLC and LEP detectors. We introduce a dual-readout
calorimeter system, a cluster counting drift chamber, and a second solenoid to
return the magnetic flux without iron. We discuss particle identification,
momentum and energy resolutions, and the machine-detector interface that
together offer the possibility of a very high-performance detector for
e^+e^-physics up to $\sqrt{s} = 1$ TeV.
|
0708.0142v2
|
2007-08-01
|
First-principles thermal equation of state and thermoelasticity for hcp Fe under high pressures
|
We investigate the equation of state and elastic properties of nonmagnetic
hcp iron at high pressures and high temperatures using the first principles
linear response linear-muffin-tin-orbital method in the generalized-gradient
approximation. We calculate the Helmholtz free energy as a function of volume,
temperature, and volume-constrained strain, including the electronic excitation
contributions from band structures and lattice vibrational contributions from
quasi-harmonic lattice dynamics. We perform detailed investigations on the
behavior of elastic moduli and equation of state properties as a function of
temperature and pressure, including the pressure-volume equation of state, bulk
modulus, the thermal expansion coefficient, the Gruneisen ratio, and the shock
Hugoniots. A detailed comparison has been made with available experimental
measurements and theoretical predictions.
|
0708.0183v1
|
2007-08-03
|
Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles
|
The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.
|
0708.0463v1
|
2007-08-06
|
Emission Lines in X-ray Spectra of Clusters of Galaxies
|
Emission lines in X-ray spectra of clusters of galaxies reveal the presence
of heavy elements in the diffuse hot plasma (the Intra Cluster Medium, or ICM)
in virial equilibrium in the dark matter potential well. The relatively simple
physical state of the ICM allows us to estimate, with good accuracy, its
thermodynamical properties and chemical abundances. These measures put strong
constraints on the interaction processes between the galaxies and the
surrounding medium, and have significant impact on models of galaxy formation
as well. This field is rapidly evolving thanks to the X-ray satellites Chandra
and XMM-Newton. Among the most relevant progresses in the last years, we
briefly discuss the nature of cool cores and the measure of the Iron abundance
in high redshift clusters. Future X-ray missions with bolometers promise to
provide a substantial step forward to a more comprehensive understanding of the
complex physics of the ICM.
|
0708.0674v1
|
2007-08-29
|
A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction
|
We present initial results of a 750 ks Chandra observation of the remnant of
Kepler's supernova of AD 1604. The strength and prominence of iron emission,
together with the absence of O-rich ejecta, demonstrate that Kepler resulted
from a thermonuclear supernova, even though evidence for circumstellar
interaction is also strong. We have analyzed spectra of over 100 small regions,
and find that they fall into three classes. (1) The vast majority show Fe L
emission between 0.7 and 1 keV and Si and S K alpha emission; we associate
these with shocked ejecta. A few of these are found at or beyond the mean blast
wave radius. (2) A very few regions show solar O/Fe abundance rations; these we
associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A
few regions are dominated by continuum, probably synchrotron radiation.
Finally, we find no central point source, with a limit about 100 times fainter
than the central object in Cas A. The evidence that the blast wave is
interacting with CSM may indicate a Ia explosion in a more massive progenitor.
|
0708.3858v1
|
2007-08-31
|
Stellar Models and Yields of Asymptotic Giant Branch Stars
|
We present stellar yields calculated from detailed models of low and
intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a
range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th
of the solar metallicity. Each model was evolved from the zero age main
sequence to near the end of the thermally-pulsing AGB phase, and through all
intermediate phases including the core He-flash for stars initially less
massive than 2.5Msun. For each mass and metallicity, we provide tables
containing structural details of the stellar models during the TP-AGB phase,
and tables of the stellar yields for 74 species from hydrogen through to
sulphur, and for a small number of iron-group nuclei. All tables are available
for download. Our results have many applications including use in population
synthesis studies and the chemical evolution of galaxies and stellar systems,
and for comparison to the composition of AGB and post-AGB stars and planetary
nebulae.
|
0708.4385v2
|
2007-09-03
|
X-ray reflection in accreting stellar-mass black hole systems
|
The X-ray spectra of accreting stellar-mass black hole systems exhibit
spectral features due to reflection, especially broad iron K alpha emission
lines. We investigate the reflection by the accretion disc that can be expected
in the high/soft state of such a system. First, we perform a self-consistent
calculation of the reflection that results from illumination of a hot, inner
portion of the disc with its atmosphere in hydrostatic equilibrium. Then we
present reflection spectra for a range of illumination strengths and disc
temperatures under the assumption of a constant-density atmosphere. Reflection
by a hot accretion disc differs in important ways from that of a much cooler
disc, such as that expected in an active galactic nucleus.
|
0709.0270v1
|
2007-09-21
|
Self-assembly of polymers or copolymers and ferrofluids leading to either 1-d, 2-d or 3-d aggregates decorated with magnetic nanoparticles
|
A novel type of hybrid colloids is presented, based on the association of
several polymeric systems and ferrofluids. On the one hand, we use inorganic
nanoparticles made of magnetic iron oxide prepared at the LI2C, which response
to a magnetic field of low intensity. On the other hand the organic part is
made either of long linear polyacrylamide chains or of mesoscopic structures
(vesicles and micelles) self-assembled from amphiphile
polybutadiene-b-poly(glutamic acid) di-block copolymers, which conformation is
pH-sensitive.
|
0709.3514v1
|
2007-09-25
|
The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation
|
Gravitationally redshifted absorption lines from highly ionized iron have
been previously identified in the burst spectra of the neutron star in EXO
0748-676. To repeat this detection we obtained a long, nearly 600 ks
observation of the source with XMM-Newton in 2003. The spectral features seen
in the burst spectra from the initial data are not reproduced in the burst
spectra from this new data. In this paper we present the spectra from the 2003
observations and discuss the sensitivity of the absorption structure to changes
in the photospheric conditions.
|
0709.4062v1
|
2007-10-10
|
The control of iron oxidation state during FeO and olivine crystal growth
|
Crystal growth experiments (micro-pulling down or Czochralski methods,
respectively) and DTA/TG measurements with Fe2+ containing olivines
(fayalite--forsterite solid solution) and with FeO (wustite) are performed. For
both substances the oxygen partial pressure p_O2 of the growth atmosphere had
to be adjusted within the stability region of Fe2+ for all temperatures ranging
from room temperature to the melting point. The formation of Fe3+ (Fe3O4,
Fe2O3) had to be avoided. The adjustment of p_O2 could be obtained by a mixture
of argon, carbon dioxide and carbon monoxide. Thermodynamic equilibrium
calculations show, that mixtures of an inert gas (e.g. argon) with another gas
or gas mixture that supplies oxygen at elevated temperature (e.g. CO2/CO) are
superior to the use of inert gases with constant oxygen admixture. The reason
is that the Ar/CO2/CO mixture adjusts its oxygen concentration with temperature
in a way similar to that needed for the stabilization of Fe2+.
|
0710.2050v1
|
2007-10-11
|
RXTE confirmation of the Intermediate Polar status of Swift J0732.5-1331
|
Aims. We intend to establish the X-ray properties of Swift J0732.5-1331 and
therefore confirm its status as an intermediate polar. Method. We analysed
36,240 s of X-ray data from RXTE. Frequency analysis was used to constrain
temporal variations and spectral analysis used to characterise the emission and
absorption properties. Results. The X-ray spin period is confirmed to be
512.4(3) s with a strong first harmonic. No modulation is detected at the
candidate orbital period of 5.6 h, but a coherent modulation is present at the
candidate 11.3 h period. The spectrum is consistent with a 37 keV
bremsstrahlung continuum with an iron line at 6.4 keV absorbed by an equivalent
hydrogen column density of around 10^22 atoms cm^-2. Conclusions. Swift
J0732-1331 is confirmed to be an intermediate polar.
|
0710.2248v1
|
2007-10-23
|
NGC3147: a "true" Seyfert 2 without the broad-line region
|
We report on simultaneous optical and X-ray observations of the Seyfert
galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in
the X-rays ($N_H<5\times10^{20}$ cm$^{-2}$). On the other hand, no broad lines
are present in the optical spectrum. The origin of this optical/X-rays
misclassification (with respect to the Unification Model) cannot be attributed
to variability, since the observations in the two bands are simultaneous.
Moreover, a Compton-thick nature of the object can be rejected on the basis of
the low equivalent width of the iron K$\alpha$ line ($\simeq130$ eV) and the
large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore
inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region
(BLR), making it the first "true" Seyfert 2.
|
0710.4226v1
|
2007-10-24
|
Magnetic tight-binding and the iron-chromium enthalpy anomaly
|
We describe a self consistent magnetic tight-binding theory based in an
expansion of the Hohenberg-Kohn density functional to second order, about a non
spin polarised reference density. We show how a first order expansion about a
density having a trial input magnetic moment leads to the Stoner--Slater rigid
band model. We employ a simple set of tight-binding parameters that accurately
describes electronic structure and energetics, and show these to be
transferable between first row transition metals and their alloys. We make a
number of calculations of the electronic structure of dilute Cr impurities in
Fe which we compare with results using the local spin density approximation.
The rigid band model provides a powerful means for interpreting complex
magnetic configurations in alloys; using this approach we are able to advance a
simple and readily understood explanation for the observed anomaly in the
enthalpy of mixing.
|
0710.4399v1
|
2007-10-25
|
Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
|
The bulk composition of an exoplanet is commonly inferred from its average
density. For small planets, however, the average density is not unique within
the range of compositions. Variations of a number of important planetary
parameters--which are difficult or impossible to constrain from measurements
alone--produce planets with the same average densities but widely varying bulk
compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the
mass of a solid planet causes the radius to increase 5-60% above its gas-free
value. A planet with a given mass and radius might have substantial water ice
content (a so-called ocean planet) or alternatively a large rocky-iron core and
some H and/or He. For example, a wide variety of compositions can explain the
observed radius of GJ 436b, although all models require some H/He. We conclude
that the identification of water worlds based on the mass-radius relationship
alone is impossible unless a significant gas layer can be ruled out by other
means.
|
0710.4941v1
|
2007-10-31
|
XMM-Newton Detection of a Compton-thick AGN in the 1-Jy ULIRG/LINER F04103-2838
|
We report on the detection of Fe Kalpha emission in F04103$-$2838, an
ultraluminous infrared galaxy (ULIRG; log[L$_{\rm IR}$/L$_\odot$] $\ge$ 12)
that is optically classified as a LINER. Previous {\it Chandra} observations
suggested the presence of both a starburst and an AGN in this source. A deeper
($\sim$20 ksec) {\it XMM-Newton} spectrum reveals an Fe Kalpha line at rest
frame energy $\sim$6.4 keV, consistent with cold neutral iron. The best-fit
spectral model indicates the Fe Kalpha line has an equivalent width of
$\sim$1.6 keV. The hard X-ray emission is dominated by a Compton-thick AGN with
intrinsic 0.2--10 keV luminosity $\sim10^{44}$ ergs s$^{-1}$, while the soft
X-ray emission is from $\sim$0.1 keV gas attributed to the starburst. The X-ray
spectrum of this source bears a striking resemblance to that of the archetypal
luminous infrared galaxy NGC 6240 despite differences in merger state and
infrared properties.
|
0711.0002v1
|
2007-11-01
|
Magnetic resonance in iron oxide nanoparticles: quantum features and effect of size
|
In order to better understand the transition from quantum to classical
behavior in spin system, electron magnetic resonance (EMR) is studied in
suspensions of superparamagnetic magnetite nanoparticles with an average
diameter of ~ 9 nm and analyzed in comparison with the results obtained in the
maghemite particles of smaller size (~ 5 nm). It is shown that both types of
particles demonstrate common EMR behavior, including special features such as
the temperature-dependent narrow spectral component and multiple-quantum
transitions. These features are common for small quantum systems and not
expected in classical case. The relative intensity of these signals rapidly
decreases with cooling or increase of particle size, marking gradual transition
to the classical FMR behavior.
|
0711.0168v1
|
2007-11-07
|
Ultrahigh energy cosmic rays as heavy nuclei from cluster accretion shocks
|
Large-scale accretion shocks around massive clusters of galaxies, generically
expected in hierarchical scenarios of cosmological structure formation, are
shown to be potential sources of the observed ultrahigh energy cosmic rays
(UHECRs) by accelerating a mixture of heavy nuclei including the iron group
elements. Current observations can be explained if the source composition at
injection for the heavier nuclei is somewhat enhanced from simple expectations
for the accreting gas. The proposed picture should be testable by current and
upcoming facilities in the near future through characteristic features in the
UHECR spectrum, composition and anisotropy. The associated X-ray and gamma-ray
signatures are also briefly discussed.
|
0711.1027v1
|
2007-11-12
|
Low temperature dephasing in irradiated metallic wires
|
We present phase coherence time measurements in quasi-one-dimensional Ag
wires implanted with Ag$^{+}$ ions with an energy of $100 keV$. The
measurements have been carried out in the temperature range from $100 mK$ up to
$10 K$; this has to be compared with the Kondo temperature of iron in silver,
i.e. $T_{K}^{Ag/Fe} \approx 4 K$, used in recent experiments on dephasing in
Kondo systems\cite{mallet_prl_06,birge_prl_06}. We show that the phase
coherence time is not affected by the implantation procedure, clearly proving
that ion implantation process by itself \emph{does not lead to any extra
dephasing} at low temperature.
|
0711.1810v2
|
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