59,685 research outputs found
Nuclear Reactions Rates Governing the Nucleosynthesis of Ti44
Large excesses of Ca44 in certain presolar graphite and silicon carbide
grains give strong evidence for Ti44 production in supernovae. Furthermore,
recent detection of the Ti44 gamma-line from the Cas A SNR by CGRO/COMPTEL
shows that radioactive Ti44 is produced in supernovae. These make the Ti44
abundance an observable diagnostic of supernovae. Through use of a nuclear
reaction network, we have systematically varied reaction rates and groups of
reaction rates to experimentally identify those that govern Ti44 abundance in
core-collapse supernova nucleosynthesis. We survey the nuclear-rate dependence
by repeated calculations of the identical adiabatic expansion, with peak
temperature and density chosen to be 5.5xE9 K and 1E7 g/cc, respectively, to
approximate the conditions in detailed supernova models. We find that, for
equal total numbers of neutrons and protons (eta=0), Ti44 production is most
sensitive to the following reaction rates: Ti44(alpha,p)V47,
alpha(2alpha,gamma)C12, Ti44(alpha,gamma)Cr48, V45(p,gamma)Cr46. We tabulate
the most sensitive reactions in order of their importance to the Ti44
production near the standard values of currently accepted cross-sections, at
both reduced reaction rate (0.01X) and at increased reaction rate (100X)
relative to their standard values. Although most reactions retain their
importance for eta > 0, that of V45(p,gamma)Cr46 drops rapidly for eta >=
0.0004. Other reactions assume greater significance at greater neutron excess:
C12(alpha,gamma)O16, Ca40(alpha,gamma)Ti44, Al27(alpha,n)P30, Si30(alpha,n)S33.
Because many of these rates are unknown experimentally, our results suggest the
most important targets for future cross section measurements governing the
value of this observable abundance.Comment: 37 pages, LaTex, 17 figures, 8 table
Generation of GHZ and W states for stationary qubits in spin network via resonance scattering
We propose a simple scheme to establish entanglement among stationary qubits
based on the mechanism of resonance scattering between them and a
single-spin-flip wave packet in designed spin network. It is found that through
the natural dynamical evolution of an incident single-spin-flip wave packet in
a spin network and the subsequent measurement of the output single-spin-flip
wave packet,multipartite entangled states among n stationary qubits,
Greenberger-Horne-Zeilinger (GHZ) and W states can be generated.Comment: 8 pages, 6 figure
Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study
In order to gain insights into the origin of colossal magneto-resistance
(CMR) in manganese oxides, we performed a ^{139}La NMR study in the
double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie
temperature T_C=126 K, applying a magnetic field induces a long-range
ferromagnetic order that persists up to T=330 K. The critical field at which
the induced magnetic moment is saturated coincides with the field at which the
CMR effect reaches to a maximum. Our results therefore indicate that the CMR
observed above T_C in this compound is due to the field-induced ferromagnetism
that produces a metallic state via the double exchange interaction
TeV leptogenesis in Z-prime models and its collider probe
We show that the U(1)-prime models linked with the seesaw mechanism at TeV
scale can lead to a successful baryogenesis through soft leptogenesis with a
resonant behavior in the B parameter. Such a consideration constrains the
Z-prime mass to be larger than 2-3 TeV depending on the seesaw scale and the
spharelon rate. Together with multi-TeV Z-prime, large sneutrino-antisneutrino
mixing and CP violating phenomena required by TeV leptogenesis could be
searched for in future colliders by observing the distinct same-sign
dilepton--dichargino as well as dislepton--diHiggs signatures.Comment: 10 pages with 2 figure
Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons
The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons
was measured in the low-frequency range using a pick-up coil wound around the
sample. The asymmetric two-peak behavior of the field dependence of the
off-diagonal impedance was observed. The asymmetry is attributed to the
formation of a hard magnetic crystalline phase at the ribbon surface. The
experimental results are interpreted in terms of the surface impedance tensor.
It is assumed that the ribbon consists of an inner amorphous region and surface
crystalline layers. The coupling between the crystalline and amorphous phases
is described through an effective bias field. A qualitative agreement between
the calculated dependences and experimental data is demonstrated. The results
obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure
Observation of Heteronuclear Feshbach Resonances in a Bose-Fermi Mixture
Three magnetic-field induced heteronuclear Feshbach resonances were
identified in collisions between bosonic 87Rb and fermionic 40K atoms in their
absolute ground states. Strong inelastic loss from an optically trapped mixture
was observed at the resonance positions of 492, 512, and 543 +/- 2 G. The
magnetic-field locations of these resonances place a tight constraint on the
triplet and singlet cross-species scattering lengths, yielding -281 +/- 15 Bohr
and -54 +/- 12 Bohr, respectively. The width of the loss feature at 543 G is
3.7 +/- 1.5 G wide; this broad Feshbach resonance should enable experimental
control of the interspecies interactions.Comment: revtex4 + 5 EPS figure
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