1,673 research outputs found
Vector magnetic field microscopy using nitrogen vacancy centers in diamond
The localized spin triplet ground state of a nitrogen vacancy (NV) center in
diamond can be used in atomic-scale detection of local magnetic fields. Here we
present a technique using these defects in diamond to image fields around
magnetic structures. We extract the local magnetic field vector by probing
resonant transitions of the four fixed tetrahedral NV orientations. In
combination with confocal microscopy techniques, we construct a 2-dimensional
image of the local magnetic field vectors. Measurements are done in external
fields less than 50 G and under ambient conditions.Comment: 9 pages, 3 figure
Spin Control of Drifting Electrons using Local Nuclear Polarization in Ferromagnet/Semiconductor Heterostructures
We demonstrate methods to locally control the spin rotation of moving
electrons in a GaAs channel. The Larmor frequency of optically-injected spins
is modulated when the spins are dragged through a region of spin-polarized
nuclei created at a MnAs/GaAs interface. The effective field created by the
nuclei is controlled either optically or electrically using the ferromagnetic
proximity polarization effect. Spin rotation is also tuned by controlling the
carrier traverse time through the polarized region. We demonstrate coherent
spin rotations exceeding 4 pi radians during transport.Comment: 15 pages, 4 figure
DEEP: a provenance-aware executable document system
The concept of executable documents is attracting growing interest from both academics and publishers since it is a promising technology for the dissemination of scientific results. Provenance is a kind of metadata that provides a rich description of the derivation history of data products starting from their original sources. It has been used in many different e-Science domains and has shown great potential in enabling reproducibility of scientific results. However, while both executable documents and provenance are aimed at enhancing the dissemination of scientific results, little has been done to explore the integration of both techniques. In this paper, we introduce the design and development of DEEP, an executable document environment that generates scientific results dynamically and interactively, and also records the provenance for these results in the document. In this system, provenance is exposed to users via an interface that provides them with an alternative way of navigating the executable document. In addition, we make use of the provenance to offer a document rollback facility to users and help to manage the system's dynamic resources
Measurements of Nanoscale Domain Wall Flexing in a Ferromagnetic Thin Film
We use the high spatial sensitivity of the anomalous Hall effect in the
ferromagnetic semiconductor Ga1-xMnxAs, combined with the magneto-optical Kerr
effect, to probe the nanoscale elastic flexing behavior of a single magnetic
domain wall in a ferromagnetic thin film. Our technique allows position
sensitive characterization of the pinning site density, which we estimate to be
around 10^14 cm^{-3}. Analysis of single site depinning events and their
temperature dependence yields estimates of pinning site forces (10 pN range) as
well as the thermal deactivation energy. Finally, our data hints at a much
higher intrinsic domain wall mobility for flexing than previously observed in
optically-probed micron scale measurements
Properties of the solvation force of a two-dimensional Ising strip in scaling regimes
We consider d=2 Ising strip with surface fields acting on boundary spins.
Using the properties of the transfer matrix spectrum we identify two
pseudotransition temperatures and show that they satisfy similar scaling
relations as expected for real transition temperatures in strips with d>2. The
solvation force between the boundaries of the strip is analysed as a function
of temperature, surface fields and the width of the strip. For large widths the
solvation force can be described by scaling functions in three different
regimes: in the vicinity of the critical wetting temperature of 2D
semi-infinite system, in the vicinity of the bulk critical temperature, and in
the regime of weak surface fields where the critical wetting temperature tends
towards the bulk critical temperature. The properties of the relevant scaling
functions are discussed
No classical limit of quantum decay for broad states
Though the classical treatment of spontaneous decay leads to an exponential
decay law, it is well known that this is an approximation of the quantum
mechanical result which is a non-exponential at very small and large times for
narrow states. The non exponential nature at large times is however hard to
establish from experiments. A method to recover the time evolution of unstable
states from a parametrization of the amplitude fitted to data is presented. We
apply the method to a realistic example of a very broad state, the sigma meson
and reveal that an exponential decay is not a valid approximation at any time
for this state. This example derived from experiment, shows the unique nature
of broad resonances
Uncovering hidden modes in RR Lyrae stars
The Kepler space telescope revealed new, unexpected phenomena in RR Lyrae
stars: period doubling and the possible presence of additional modes.
Identifying these modes is complicated because they blend in the rich features
of the Fourier-spectrum. Our hydrodynamic calculations uncovered that a
'hidden' mode, the 9th overtone is involved in the period doubling phenomenon.
The period of the overtone changes by up to 10 per cent compared to the linear
value, indicating a very significant nonlinear period shift caused by its
resonance with the fundamental mode. The observations also revealed weak peaks
that may correspond to the first or second overtones. These additional modes
are often coupled with period doubling. We investigated the possibilities and
occurrences of mutual resonances between the fundamental mode and multiple
overtones in our models. These theoretical findings can help interpreting the
origin and nature of the 'hidden' modes may be found in the high quality light
curves of space observatories.Comment: In proceedings of "20th Stellar Pulsation Conference Series: Impact
of new instrumentation & new insights in stellar pulsations", 5-9 September
2011, Granada, Spai
A note on the Cops & Robber game on graphs embedded in non-orientable surfaces
The Cops and Robber game is played on undirected finite graphs. A number of
cops and one robber are positioned on vertices and take turns in sliding along
edges. The cops win if they can catch the robber. The minimum number of cops
needed to win on a graph is called its cop number. It is known that the cop
number of a graph embedded on a surface of genus is at most ,
if is orientable (Schroeder 2004), and at most , otherwise
(Nowakowski & Schroeder 1997).
We improve the bounds for non-orientable surfaces by reduction to the
orientable case using covering spaces.
As corollaries, using Schroeder's results, we obtain the following: the
maximum cop number of graphs embeddable in the projective plane is 3; the cop
number of graphs embeddable in the Klein Bottle is at most 4, and an upper
bound is for all other .Comment: 5 pages, 1 figur
Constraints on R-parity violating couplings from LEP/SLD hadronic observables
We analyze the one loop corrections to hadronic Z decays in an R-parity
violating extension to the Minimal Supersymmetric Standard Model (MSSM).
Performing a global fit to all the hadronic observables at the Z-peak, we
obtain stringent constraints on the R-violating couplings constants lambda' and
lambda''. As a result of the strong constraints from the b asymmetry parameters
A_b and A_FB(b), we find that the couplings lambda'{i31}, lambda'{i32}, and
lambda''{321} are ruled out at the 1 sigma level, and that lambda'{i33} and
lambda''{33i} are ruled out at the 2 sigma level. We also obtain Bayesian
confidence limits for the R-violating couplings.Comment: 30 pages, 19 postscript figures, REVTeX, new section 8 on Bayesian
confidence limits adde
Constraints on the mass of the superlight gravitino from the muon anomaly
We reexamine the limits on the gravitino mass supplied by the muon anomaly in
the frame of supergravity models with a superlight gravitino and a superlight
scalar S and a superlight pseudoscalar P.Comment: 7 pages, REVTeX with 5 figures. Uses epsfi
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