1,922 research outputs found
Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions
We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the
spin-transfer torque vector T in MgO-based magnetic tunnel junctions as a
function of the offset angle between the magnetic moments of the electrodes and
as a function of bias, V. We explain the conflicting conclusions of two
previous experiments by accounting for additional terms that contribute to the
ST-FMR signal at large |V|. Including the additional terms gives us improved
precision in the determination of T(V), allowing us to distinguish among
competing predictions. We determine that the in-plane component of has a weak
but non-zero dependence on bias, varying by 30-35% over the bias range where
the measurements are accurate, and that the perpendicular component can be
large enough to be technologically significant. We also make comparisons to
other experimental techniques that have been used to try to measure T(V).Comment: 30 pages, 8 figures. Expanded with additional data and discussion. In
press at PR
Genomic Structure of the Amphioxus Calcium Vector Protein
Calcium vector protein (CaVP) is an EF-hand Ca2+-binding protein, which is unique to the protochordate, amphioxus. CaVP is supposed to act as a Ca2+ signal transductor, but its exact function remains unknown. Not only its function but also its exact evolutionary relationship to other Ca2+-binding proteins is unclear. To investigate the evolution of CaVP, we have determined the complete sequences of CaVP cDNAs from two amphioxus species, Branchiostoma lanceolatum and B. floridae, whose open reading frame cDNA and amino acid sequences show 96.5 and 98.2% identity, respectively. We have also elucidated the structure of the gene of B. floridae Ca VP, which is made up of seven exons and six introns. The positions of four of the six introns (introns 1, 2, 3, and 5) are identical with those of calmodulin, troponin C, and the Spec protein of the sea urchin. These latter proteins belong to the so-called troponin C superfamily (TnC superfamily) and thus CaVP likely also belongs to this family. Intron 6 is positioned in the 3‘ noncoding region and is unique to CaVP, so it may represent a landmark of the CaVP lineage only. The position of intron 4 is not conserved in the genes of the TnC superfamily or CaVP, and seems to result from either intron sliding or the addition of an intron (randomly inserted into or close to domain HE) to the genes of the TnC superfamily during their evolutio
Measuring quantumness via anticommutators
We introduce a method to witness the quantumness of a system. The method
relies on the fact that the anticommutator of two classical states is always
positive. We show that there is always a nonpositive anticommutator due to any
two quantum states. We notice that interference depends on the trace of the
anticommutator of two states and it is therefore more natural to detect
quantumness by looking at anticommutators of states rather than their
commutators.Comment: 7 pages, 2 figure
Diversity of the Troponin C Genes during Chordate Evolution
To elucidate the diversity of troponin C (TnC) during chordate evolution, we determined the organization of TnCs from the amphioxus, the lamprey, and the frog. Like the ascidian, the amphioxus possesses a single gene of TnC, and the fundamental gene structure is identical with the ascidian TnC. However, because alternative splicing does not occur in amphioxus, the potential for generation of TnC isoforms through this event arises only in the ascidian lineage. From the frog Xenopus laevis, two distinct cDNAs encoding fTnC isoforms and a single s/cTnC cDNA were determined. The duplication of the fTnC gene may be a character of only Xenopus or closely related species. The lamprey possesses two cDNAs each encoding fTnC and s/cTnC. The lamprey is the earliest diverged species among vertebrates, and thus it is supposed that the presence of both fTnC and s/cTnC is universal among vertebrate species, and that the gene duplication might have occurred at a vertebrate ancestor after the protochordate/vertebrate divergence. The position of the 4th intron is 3.24/0 in protochordate TnC genes, but at 3.11/2 in vertebrate fTnCs and s/cTnCs. It is suggested that the 4th intron sliding might have occurred prior to the gene duplicatio
Origin of the spectral linewidth in non linear oscillators based on MgO tunnel junctions
We demonstrate the strong impact of the oscillator agility on the line
broadening by studying spin transfer induced microwave emission in MgO-based
tunnel junctions with current. The linewidth is almost not affected by
decreasing the temperature. At very low currents, a strong enhancement of the
linewidth at low temperature is attributed to an increase of the non linearity,
probably due to the field-like torque. Finally we evidence that the noise is
not dominated by thermal fluctuations but rather by the chaotization of the
magnetization system induced by the spin transfer torque.Comment: 12 pages, 3 figures, published in Phys. Rev. B 80, 060404 (2009
Composition profiling InAs quantum dots and wetting layers by atom probe tomography and cross-sectional scanning tunnelling microscopy
This study compares cross-sectional scanning tunnelling microscopy (XSTM) and
atom probe tomography (APT). We use epitaxially grown self-assembled InAs
quantum dots (QDs) in GaAs as an exemplary material with which to compare these
two nanostructural analysis techniques. We studied the composition of the
wetting layer and the QDs, and performed quantitative comparisons of the indium
concentration profiles measured by each method. We show that computational
models of the wetting layer and the QDs, based on experimental data, are
consistent with both analytical approaches. This establishes a link between the
two techniques and shows their complimentary behaviour, an advantage which we
exploit in order to highlight unique features of the examined QD material.Comment: Main article: 8 pages, 6 figures. Appendix: 3 pages, 5 figure
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