469,416 research outputs found
Vortex states in patterned exchange biased NiO/Ni samples
We investigated the magnetization reversal of arrays of exchange biased
NiO/Ni squares with superconducting quantum interference device magnetometry
and micromagnetic simulations. The edges of the squares were 0.5, 1.5, and 3.0
m long. The NiO/Ni structures exhibit vortexlike hysteresis loops and
micromagnetic calculations show that this feature is due to several vortices
nucleating in the islands. Furthermore, for the arrays with squares of 1.5
m edge length, the sign of the exchange bias field changes, as compared to
the same continuous NiO/Ni layer. We attribute the vortex nucleation and the
change of the exchange bias field to the interplay between shape and
unidirectional anisotropy.Comment: 6 pages, 7 figure
Interplay between field-induced and frustration-induced quantum criticalities in the frustrated two-leg Heisenberg ladder
The antiferromagnetic Heisenberg two-leg ladder in the presence of
frustration and an external magnetic field is a system that is characterized by
two sorts of quantum criticalities, not only one. One criticality is the
consequence of intrinsic frustration, and the other one is a result of the
external magnetic field. So the behaviour of each of them in the presence of
the other deserves to be studied. Using the Jordan-Wigner transformation in
dimensions higher than one and bond-mean-field theory we examine the interplay
between the field-induced and frustration-induced quantum criticalities in this
system. The present work could constitute a prototype for those systems showing
multiple, perhaps sometimes competing, quantum criticalities. We calculate
several physical quantities like the magnetization and spin susceptibility as
functions of field and temperature.Comment: 9 pages, 8 figures, submitted to the Canadian Journal of Physic
Consistent estimates of (56)Ni yields for type Ia supernovae
We present (56)Ni mass estimates for seventeen well-observed type Ia
supernovae determined by two independent methods. Estimates of the (56)Ni mass
for each type Ia supernova are determined from (1) modeling of the late-time
nebular spectrum and (2) through the combination of the peak bolometric
luminosity with Arnett's rule. The attractiveness of this approach is that the
comparison of estimated (56)Ni masses circumvents errors associated with the
uncertainty in the adopted values of reddening and distance. We demonstrate
that these two methods provide consistent estimates of the amount of (56)Ni
synthesized. We also find a strong correlation between the derived (56)Ni mass
and the absolute B-band magnitude (M(B)). Spectral synthesis can be used as a
diagnostic to study the explosion mechanism. By obtaining more nebular spectra
the Nif--M(B) correlation can be calibrated and can be used to investigate any
potential systematic effects this relationship may have on the determination of
cosmological parameters, and provide a new way to estimate extra-galactic
distances of nearby type Ia supernovae.Comment: Accepted for publication in A&A, constructive comments welcome
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution
On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8
and detected by Fermi. Using medium and high resolution ground-based optical
spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we
describe the behavior of the high-velocity profile evolution for this nova
during its first three months. The peak of the X-ray emission occurred at about
day 40 with a broad maximum and decline after day 50. The main changes in the
optical spectrum began at around that time. The He II 4686A line first appeared
between days 7 and 14 and initially displayed a broad, symmetric profile that
is characteristic of all species before day 60. Low-excitation lines remained
comparatively narrow, with v(rad,max) of order 200-400 km/s. They were
systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and
He II, all of which showed a sequence of profile changes going from symmetric
to a blue wing similar to that of the low ionization species but with a red
wing extended to as high as 600 km/s . The Na I D doublet developed a broad
component with similar velocity width to the other low-ionization species. The
O VI Raman features were not detected. We interpret these variations as
aspherical expansion of the ejecta within the Mira wind. The blue side is from
the shock penetrating into the wind while the red wing is from the low-density
periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n}
with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)Comment: Accepted for publication, A&A (submitted: 9 Oct 2010; accepted: 1 Dec
2010) in press; based on data obtained with Swift, Nordic Optical Telescope,
Ondrejov Observatory. Corrected typo, Fermi?LAT detection was at energies
above 100 MeV (with thanks to C. C. Cheung
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Fe-Ni Sulphides within a CM1 clast in Tagish Lake
The composition, abundance and mineral associations of Fe-Ni sulphides within a CM1 clast in Tagish Lake are described, and compared with Fe-Ni sulphides in the carbonate-rich and carbonate-poor lithology of Tagish Lake, as well as Fe-Ni sulphides from CI and CM chondrites
Isospin diffusion in semi-peripheral + collisions at intermediate energies (II): Dynamical simulations
We study isospin effects in semi-peripheral collisions above the Fermi energy
by considering the symmetric + and the asymmetric reactions
+ over the incident energy range 52-74 A MeV. A
microscopic transport model with two different parameterizations of the
symmetry energy term is used to investigate the isotopic content of
pre-equilibrium emission and the N/Z diffusion process. Simulations are also
compared to experimental data obtained with the INDRA array and bring
information on the degree of isospin equilibration observed in Ni + Au
collisions. A better overall agreement between data and simulations is obtained
when using a symmetry term which linearly increases with nuclear density
Effects of Chronic Waterborne Nickle Exposure on Two Successive Generations of \u3cem\u3eDaphnia Magna\u3c/em\u3e
In a 21-d chronic toxicity test in which an F0 generation of Daphnia magna were exposed to waterborne Ni, the noobservable-effect concentration (for survival, reproduction, and growth) was 42 μg Ni L-1, or 58% of the measured 21-d median lethal concentration (LC50) of 71.9 μg Ni L-1 (95% confidence interval, 56.5–95.0). Chronic exposure to 85 μg Ni L-1 caused marked decreases in survival, reproduction, and growth in F0 animals. In the F1 generation (daphnids born of mothers from the chronically exposed F0 generation), animals chronically exposed to 42 μg Ni L-1 for 11 d weighed significantly less (20%) than controls, indicating increased sensitivity of F1 animals. Additionally, in this successive generation, significant decreases in whole-body levels of metabolites occurred following exposure to both 42 μg Ni L-1 (decreased glycogen and adenosine triphosphate [ATP]) and 21 μg Ni L-1 (decreased ATP). No significant changes were observed in whole-body total lipid, total protein, and lactate levels at any concentration. Whereas F1 neonates with mothers that were exposed to 21 μg Ni L-1 showed increased resistance to acute Ni challenge, as measured by a significant (83%) increase in the acute (48-h) LC50, F1 neonates with mothers that were exposed to 42 μg Ni L-1 were no more tolerant of acute Ni challenge than control animals were. Nickel accumulations in F1 animals chronically exposed to 21 and 42 μg Ni L-1 were 11- and 18-fold, respectively, above control counterparts. The data presented suggest that chronic Ni exposure to two successive generations of D. magna lowered the overall energy state in the second generation. Whereas the quantity of neonates produced was not affected, the quality was; thus, environmentally meaningful criteria for regulating waterborne Ni concentrations in freshwater require consideration of possible multigenerational effects
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