1,545 research outputs found
Spin wave propagation and spin polarized electron transport in single crystal iron films
The technique of propagating spin wave spectroscopy is applied to a 20 nm
thick Fe/MgO (001) film. The magnetic parameters extracted from the position of
the resonance peaks are very close to those tabulated for bulk iron. From the
propagating waveforms, a group velocity of 4 km/s and an attenuation length of
about 6 micrometers are extracted for 1.6 micrometers-wavelength spin-wave at
18 GHz. From the measured current-induced spin-wave Doppler shift, we also
extract a surprisingly high degree of spin-polarization of the current of 83%.
This set of results makes single-crystalline iron a promising candidate for
building devices utilizing high frequency spin-waves and spin-polarized
currents.Comment: 5 figures, submitted to Phys. Rev.
Independence of hyperlogarithms over function fields via algebraic combinatorics
We obtain a necessary and sufficient condition for the linear independence of
solutions of differential equations for hyperlogarithms. The key fact is that
the multiplier (i.e. the factor in the differential equation ) has
only singularities of first order (Fuchsian-type equations) and this implies
that they freely span a space which contains no primitive. We give direct
applications where we extend the property of linear independence to the largest
known ring of coefficients
Steroid substrate-induced epimerase mechanism in the active site of the human 11β-hydroxysteroid dehydrogenase type 1
Cytochrome P4507B1 7[alpha]-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5[alpha]-androstane-3[beta],17[beta]-diol (Adiol). 11[beta]-Hydroxysteroid dehydrogenase type 1 (11[beta]-HSD1) interconverts 7[alpha]- and 7[beta]- forms. Whether the inter-conversion proceeds through oxido-reductive steps or epimerase activity is investigated. Experiments using ^3^H-labeled 7[beta]-hydroxy-DHEA, 7[beta]-hydroxy-EpiA and 7[beta]-hydroxy-Adiol show the ^3^H-label to accumulate in 7-oxo-DHEA trap but neither in 7-oxo-EpiA nor 7-oxo-Adiol traps. Computed models of 7-oxygenated steroids dock in the active site of 11[beta]-HSD1 either in a flipped or turned form relative to cortisone and cortisol. 7-Oxo-steroid reduction in 7[alpha]- or 7[beta]-hydroxylated derivatives results from either turned or flipped forms. 11[beta]-HSD1 incubation in H~2~^18^O medium with each 7-hydroxysteroid did not incorporate ^18^O in 7-hydroxylated derivatives of EpiA and Adiol independently of the cofactor used. Thus oxido-reductive steps apply for the interconversion of 7[alpha]- and 7[beta]-hydroxy-DHEA through 7-oxo-DHEA. Epimerisation may proceed on the 7-hydroxylated derivatives of EpiA and Adiol through a mechanism involving the cofactor and Ser170
PAGAI: a path sensitive static analyzer
We describe the design and the implementation of PAGAI, a new static analyzer
working over the LLVM compiler infrastructure, which computes inductive
invariants on the numerical variables of the analyzed program. PAGAI implements
various state-of-the-art algorithms combining abstract interpretation and
decision procedures (SMT-solving), focusing on distinction of paths inside the
control flow graph while avoiding systematic exponential enumerations. It is
parametric in the abstract domain in use, the iteration algorithm, and the
decision procedure. We compared the time and precision of various combinations
of analysis algorithms and abstract domains, with extensive experiments both on
personal benchmarks and widely available GNU programs.Comment: Tools for Automatic Program AnalysiS (TAPAS 2012), Deauville : France
(2012
Unidirectional spin-wave channeling along magnetic domain walls of Bloch type
From the pioneering work of Winter [Phys. Rev. 124, 452 (1961)], a magnetic
domain wall of Bloch type is known to host a special wall-bound spin-wave mode,
which corresponds to spin-waves being channeled along the magnetic texture.
Using micromagnetic simulations, we investigate spin-waves travelling inside
Bloch walls formed in thin magnetic media with perpendicular-to-plane magnetic
anisotropy and we show that their propagation is actually strongly
nonreciprocal, as a result of dynamic dipolar interactions. We investigate
spin-wave non-reciprocity effects in single Bloch walls, which allows us to
clearly pinpoint their origin, as well as in arrays of parallel walls in stripe
domain configurations. For such arrays, a complex domain-wall-bound spin-wave
band structure develops, some aspects of which can be understood qualitatively
from the single-wall picture by considering that a wall array consists of a
sequence of up/down and down/up walls with opposite non-reciprocities.
Circumstances are identified in which the non-reciprocity is so extreme that
spin-wave propagation inside individual walls becomes unidirectional.Comment: 7 pages, 5 figure
Enantioselective and Regiodivergent Copper-Catalyzed Electrophilic Arylation of Allylic Amides with Diaryliodonium Salts.
A catalytic enantioselective and regiodivergent arylation of alkenes is described. Chiral copper(II)bisoxazoline complexes catalyze the addition of diaryliodonium salts to allylic amides in excellent ee. Moreover, the arylation can be controlled by the electronic nature of the diaryliodonium salt enabling the preparation of nonracemic diaryloxazines or β,β'-diaryl enamides.We are grateful to EPSRC, GSK and the University of Cambridge
(E.C., H.P.J.M. & M.T.) and the ERC and EPSRC for fellowships
(M.J.G.). Mass spectrometry data were acquired at the EPSRC UK
National Mass Spectrometry Facility at Swansea University.This is the final version of the article. It first appeared from ACS via http://dx.doi.org/10.1021/jacs.5b0393
Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgOFeMgO films
Broadband ferromagnetic resonance is measured in single crystalline Fe films
of varying thickness sandwiched between MgO layers. An exhaustive magnetic
characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first
perpendicular standing spin wave modes as a function of applied magnetic field
and film thickness. Additional measurements of non-reciprocal spin wave
propagation allow us to separate each of the two interface contributions to the
total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom
interfaces, a difference ascribed to different oxidation states
Clustering, host halos and environment of z2 galaxies as a function of their physical properties
Using a sample of 25683 star-forming and 2821 passive galaxies at ,
selected in the COSMOS field following the BzK color criterion, we study the
hosting halo mass and environment of galaxies as a function of their physical
properties. Spitzer and Herschel provide accurate SFR estimates for starburst
galaxies. We measure the auto- and cross-correlation functions of various
galaxy sub-samples and infer the properties of their hosting halos using both
an HOD model and the linear bias at large scale. We find that passive and
star-forming galaxies obey a similarly rising relation between the halo and
stellar mass. The mean host halo mass of star forming galaxies increases with
the star formation rate between 30 and 200 M.yr, but flattens
for higher values, except if we select only main-sequence galaxies. This
reflects the expected transition from a regime of secular co-evolution of the
halos and the galaxies to a regime of episodic starburst. We find similar large
scale biases for main-sequence, passive, and starburst galaxies at equal
stellar mass, suggesting that these populations live in halos of the same mass.
We detect an excess of clustering on small scales for passive galaxies and
showed, by measuring the large-scale bias of close pairs, that this excess is
caused by a small fraction () of passive galaxies being hosted by
massive halos ( M) as satellites. Finally,
extrapolating the growth of halos hosting the z2 population, we show that
M M galaxies at z2 will evolve, on average,
into massive (M M), field galaxies in the local
Universe and M M galaxies at z=2 into local,
massive, group galaxies. The most massive main-sequence galaxies and close
pairs of massive, passive galaxies end up in today's clusters.Comment: 18 pages, 16 figures, Accepted by A&
Probing Spin Wave Diffraction Patterns of Curved Antennas
We report on the dependence of curvilinear shaped coplanar waveguides on the
near-field diffraction patterns of spin waves propagating in perpendicularly
magnetized thin films. Implementing the propagating spin waves spectroscopy
techniques on either concentrically or eccentrically shaped antennas, we show
how the link budget is directly affected by the spin wave interference, in good
agreement with near-field diffraction simulations. This work demonstrates the
feasibility to inductively probe a magnon interference pattern with a
resolution down to 1m, and provides a methodology for shaping spin
wave beams from an antenna design. This methodology is successfully implemented
in the case study of a spin wave Young's interference experiment
The Herschel view of the dominant mode of galaxy growth from z=4 to the present day
We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS-North, GOODS-South, UDS and COSMOS obtained within the GOODS-Herschel and CANDELS-Herschel key programs. The picture provided by 10497 individual far-infrared detections is supplemented by the stacking analysis of a mass-complete sample of 62361 star-forming galaxies from the CANDELS-HST H band-selected catalogs and from two deep ground-based Ks band-selected catalogs in the GOODS-North and the COSMOS-wide fields, in order to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called "scatter stacking" that may be easily generalized to other experiments. We demonstrate that galaxies of all masses from z=4 to 0 follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the logSFR-logM* relation with evidence for a flattening of the main sequence at high masses (log(M*/Msun) > 10.5) that becomes less prominent with increasing redshift and almost vanishes by z~2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies. Within the main sequence, we measure a non varying SFR dispersion of 0.3 dex. The specific SFR (sSFR=SFR/M*) of star-forming galaxies is found to continuously increase from z=0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and show that more than 2/3 of present-day stars must have formed in a regime dominated by the main sequence mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 Gyr
- …