40,890 research outputs found
Microscopic observations of X-ray and gamma-ray induced decomposition of ammonium perchlorate crystals
The X-ray and gamma-ray induced decomposition of ammonium perchlorate was studied by optical, transmission, and scanning electron microscopy. This material is a commonly used oxidizer in solid propellents which could be employed in deep-space probes, and where they will be subjected to a variety of radiations for as long as ten years. In some respects the radiation-induced damage closely resembles the effects produced by thermal decomposition, but in other respects the results differ markedly. Similar radiation and thermal effects include the following: (1) irregular or ill-defined circular etch pits are formed in both cases; (2) approximately the same size pits are produced; (3) the pit density is similar; (4) the c face is considerably more reactive than the m face; and (5) most importantly, many of the etch pits are aligned in crystallographic directions which are the same for thermal or radiolytic decomposition. Thus, dislocations play an important role in the radiolytic decomposition process
Different steady states for spin currents in noncollinear multilayers
We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.Comment: 8 pages, no figure. Accepted for publication in Journal of Physics:
Condensed Matte
Simultaneous electric and magnetic field induced nonvolatile memory
We investigate the electric field induced resistive switching effect and
magnetic field induced fraction enlargement on a polycrystalline sample of a
colossal magnetoresistive compound displaying intrinsic phase coexistence. Our
data show that the electric effect (presumably related to the presence of
inhomogeinities) is present in a broad temperature range(300 to 20 K), being
observable even in a mostly homogeneous ferromagnetic state. In the temperature
range in which low magnetic field determines the phase coexistence fraction,
both effects, though related to different mechanisms, are found to determine
multilevel nonvolatile memory capabilities simultaneously.Comment: Submited to AP
The electrical current effect in phase separated La5/8-yPryCa3/8MnO3: Charge order melting vs. Joule heating
We have studied the effect of electric field on transport properties of the
prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our
results show that the suggested image in which the charge ordered state is
melted by the appliance of an electric current and/or voltage has to be
revised. We were able to explain the observed resistivity drop in terms of an
artifact related to Joule heating and the particular hysteresis that the system
under study display, common to many other phase separated manganites.Comment: 2 figures. Accepted in J. Appl. Phy
Magnetoresistive memory in phase separated LaCaMnO
We have studied a non volatile memory effect in the mixed valent compound
LaCaMnO induced by magnetic field (H). In a previous work
[R.S. Freitas et al., Phys. Rev. B 65 (2002) 104403], it has been shown that
the response of this system upon application of H strongly depends on the
temperature range, related to three well differentiated regimes of phase
separation occurring below 220 K. In this work we compare memory capabilities
of the compound, determined following two different experimental procedures for
applying H, namely zero field cooling and field cooling the sample. These
results are analyzed and discussed within the scenario of phase separation.Comment: 4 pages, 2 figure
Correlation between magnetic and transport properties of phase separated LaCaMnO
The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
LaCaMnO is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.Comment: 3 pages, 3 figures, presented at the Fifth LAW-MMM, to appear in
Physica B, Minor change
Microscopic theory of Cooper pair beam splitters based on carbon nanotubes
We analyze microscopically a Cooper pair splitting device in which a central
superconducting lead is connected to two weakly coupled normal leads through a
carbon nanotube. We determine the splitting efficiency at resonance in terms of
geometrical and material parameters, including the effect of spin-orbit
scattering. While the efficiency in the linear regime is limited to 50% and
decay exponentially as a function of the width of the superconducting region we
show that it can rise up to in the non-linear regime for certain
regions of the stability diagram.Comment: 5 pages, 5 figure
Implementation of elastic-plastic structural analysis into NASTRAN
Elastic-plastic analytic capabilities were incorporated into the NASTRAN program. The present implementation includes a general rigid format and additional bulk data cards as well as to two new modules. The modules are specialized to include only perfect plasticity of the CTRMEN and CROD elements but can easily be expanded to include other plasticity theories and elements. The practical problem of an elastic-plastic analysis of a ship's bracket connection is demonstrated and compared to an equivalent analysis using Grumman's PLANS program. The present work demonstrates the feasibility of incorporating general elastic-plastic capabilities into NASTRAN
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