1,059 research outputs found
Stabilization and control system power sensitivity study
Stabilization and control system sensitivity to power-off failure rate studied by simulated missions using block power switchin
Writing and Reading antiferromagnetic MnAu: N\'eel spin-orbit torques and large anisotropic magnetoresistance
Antiferromagnets are magnetically ordered materials which exhibit no net
moment and thus are insensitive to magnetic fields. Antiferromagnetic
spintronics aims to take advantage of this insensitivity for enhanced
stability, while at the same time active manipulation up to the natural THz
dynamic speeds of antiferromagnets is possible, thus combining exceptional
storage density and ultra-fast switching. However, the active manipulation and
read-out of the N\'eel vector (staggered moment) orientation is challenging.
Recent predictions have opened up a path based on a new spin-orbit torque,
which couples directly to the N\'eel order parameter. This N\'eel spin-orbit
torque was first experimentally demonstrated in a pioneering work using
semimetallic CuMnAs. Here we demonstrate for MnAu, a good conductor with a
high ordering temperature suitable for applications, reliable and reproducible
switching using current pulses and readout by magnetoresistance measurements.
The symmetry of the torques agrees with theoretical predictions and a large
read-out magnetoresistance effect of more than ~ is reproduced by
ab initio transport calculations.Comment: 5 pages, 4 figure
Conceptual mechanization studies for a horizon definition spacecraft electrical power subsystem
Solar cell-battery electrical power subsystem for horizon definition spacecraf
Late glacial palaeoclimate investigations at King Arthurâs Cave and Sun Hole Cave.
King Arthurâs Cave (Wye Valley) and Sun Hole Cave (Cheddar Gorge) currently provide the earliest dates for a human presence in the British Isles after the Last Glacial Maximum. The
earliest phase of activity at these sites has been dated to c. 15.2 to 14.6 thousand years cal. BP, which spans the onset of the Late Glacial Interstadial, a major global climate transition characterised by rapidly warming temperatures. Here we present stable isotope data from horse (Equus ferus) teeth found in the zooarchaeological assemblages at the sites. We also report two new radiocarbon dates on specimens from King Arthurâs Cave. The Equus tooth enamel provides a record of climatic conditions during the animalsâ tooth formation. Evidence
of human modification of the teeth (cut marks and fractures) chronologically tie these palaeoclimatic records to the earliest post-LGM archaeology at the two sites, thus informing on the climatic and environmental context under which human activity in these areas took place. Results indicate that people were present at the two sites during a period of climatic warming, with temperatures perhaps only marginally colder than present day conditions. However, suboptimal environmental conditions are suggested and may indicate changing
vegetation dynamics within the local landscape
Elastic behavior in Contact Dynamics of rigid particles
The systematic errors due to the practical implementation of the Contact
Dynamics method for simulation of dense granular media are examined. It is
shown that, using the usual iterative solver to simulate a chain of rigid
particles, effective elasticity and sound propagation with a finite velocity
occur. The characteristics of these phenomena are investigated analytically and
numerically in order to assess the limits of applicability of this simulation
method and to compare it with soft particle molecular dynamics.Comment: submitted to PRE, 7 pages, 6 figure
Entropy production and fluctuation theorems under feedback control: the molecular refrigerator model revisited
We revisit the model of a Brownian particle in a heat bath submitted to an
actively controlled force proportional to the velocity that leads to thermal
noise reduction (cold damping). We investigate the influence of the continuous
feedback on the fluctuations of the total entropy production and show that the
explicit expression of the detailed fluctuation theorem involves different
dynamics and observables in the forward and backward processes. As an
illustration, we study the analytically solvable case of a harmonic oscillator
and calculate the characteristic function of the entropy production in a
nonequilibrium steady state. We then determine the corresponding large
deviation function which results from an unusual interplay between 'boundary'
and 'bulk' contributions.Comment: 16 pages, 5 figures. References 9,10,13,14,15 added. A few changes in
the text. Accepted for publication in J. Stat. Mec
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
Terahertz electromagnetic radiation is extremely useful for numerous
applications such as imaging and spectroscopy. Therefore, it is highly
desirable to have an efficient table-top emitter covering the 1-to-30-THz
window whilst being driven by a low-cost, low-power femtosecond laser
oscillator. So far, all solid-state emitters solely exploit physics related to
the electron charge and deliver emission spectra with substantial gaps. Here,
we take advantage of the electron spin to realize a conceptually new terahertz
source which relies on tailored fundamental spintronic and photonic phenomena
in magnetic metal multilayers: ultrafast photo-induced spin currents, the
inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an
analytical model, such spintronic route offers unique possibilities for
systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer
generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel
source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals
in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and
cost.Comment: 18 pages, 10 figure
Radiative capture of protons by deuterons
The differential cross section for radiative capture of protons by deuterons
is calculated using different realistic NN interactions. We compare our results
with the available experimental data below . Excellent agreement
is found when taking into account meson exchange currents, dipole and
quadrupole contributions, and the full initial state interaction. There is only
a small difference between the magnitudes of the cross sections for the
different potentials considered. The angular distributions, however, are
practically potential independent.Comment: 4 pages (twocolumn), 4 postscript figures included, submitted for
publication, revised versio
Improved liquid chromatographic method for determination of carotenoids in carrot
Carotenoids are a large class of plant metabolites with a function of either essential nutrients or health promoting compounds for humans. Carrot root is a well-known and significant source of dietary carotenoids, mainly: α- and ÎČ-carotene, lutein and lycopene. These pigments are the main carotenoids separated and quantified routinely by HPLC analysis. However, little is known about minor carotenoids, carotenoid esters and the carotenoids present in leaves despite their potential interest in metabolic and physiological studies. Previous works used C-18 columns but these stationary phases provide a poor resolution of structurally similar compounds and geometrical isomers. In recent years, C-30 columns have been developed and successfully applied at the separation of carotenoids from various plant materials, the number of resolved carotenoids being significantly improved. Based on literature procedures, we have developed a HPLC-DAD method with a C-30 column, adapted to the quantification of carotenoid compounds from carrot roots and leaves. A simple and rapid extraction method was optimized for both these types of samples on a panel of 5 genotypes displaying distinct root colours (different carotenoid composition and contents). Carotenoids from roots were separated in 23 minutes while carotenoids and chlorophylls from leaves were separated in 42 minutes. Compounds were identified according to their retention time and UV-visible spectrum in comparison with authentic standards (analysed individually and in combination, in the same conditions), or with data from literature, when standards were unavailable. Results showed that carrot root exhibited a simple profile with only 1 to 3 main carotenoids whereas a more complex composition was noticed in leaves, containing both identified and unidentified carotenoids and chlorophylls. Moreover, the composition was quite conservative for leaves but depended on the genotype for roots
Probing Nucleon Strangeness with Neutrinos: Nuclear Model Dependences
The extraction of the nucleon's strangeness axial charge, Delta_s, from
inclusive, quasielastic neutral current neutrino cross sections is studied
within the framework of the plane-wave impulse approximation. We find that the
value of Delta_s can depend significantly on the choice of nuclear model used
in analyzing the quasielastic cross section. This model-dependence may be
reduced by one order of magnitude when Delta_s is extracted from the ratio of
total proton to neutron yields. We apply this analysis to the interpretation of
low-energy neutrino cross sections and arrive at a nuclear theory uncertainty
of plus/minus 0.03 on the value of Delta_s expected to be determined from the
ratio of proton and neutron yields measured by the LSND collaboration. This
error compares favorably with estimates of the SU(3)-breaking uncertainty in
the value of Delta_s extracted from inclusive, polarized deep-inelastic
structure function measurements. We also point out several general features of
the quasielastic neutral current neutrino cross section and compare them with
the analogous features in inclusive, quasielastic electron scattering.Comment: 40 pages (including 11 postscript figures), uses REVTeX and
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