7,859 research outputs found
Topological superconductivity in lead nanowires
Superconductors with an odd number of bands crossing the Fermi energy have
topologically protected Andreev states at interfaces, including Majorana states
in one dimensional geometries. Superconductivity, a low number of 1D channels,
large spin orbit coupling, and a sizeable Zeeman energy, are present in lead
nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in
magnetic fields higher than the Pb bulk critical field. A number of such
devices have been analyzed. In some of them, the dependence of the critical
current on magnetic field, and the Multiple Andreev Reflections observed at
finite voltages, are compatible with the existence of topological
superconductivity
Highly charged ions: optical clocks and applications in fundamental physics
Recent developments in frequency metrology and optical clocks have been based
on electronic transitions in atoms and singly charged ions as references. These
systems have enabled relative frequency uncertainties at a level of a few parts
in . This accomplishment not only allows for extremely accurate time
and frequency measurements, but also to probe our understanding of fundamental
physics, such as variation of fundamental constants, violation of the local
Lorentz invariance, and forces beyond the Standard Model of Physics. In
addition, novel clocks are driving the development of sophisticated technical
applications. Crucial for applications of clocks in fundamental physics are a
high sensitivity to effects beyond the Standard Model and Einstein's Theory of
Relativity and a small frequency uncertainty of the clock. Highly charged ions
offer both. They have been proposed as highly accurate clocks, since they
possess optical transitions which can be extremely narrow and less sensitive to
external perturbations compared to current atomic clock species. The selection
of highly charged ions in different charge states offers narrow transitions
that are among the most sensitive ones for a change in the fine-structure
constant and the electron-to-proton mass ratio, as well as other new physics
effects. Recent advances in trapping and sympathetic cooling of highly charged
ions will in the future enable high accuracy optical spectroscopy. Progress in
calculating the properties of selected highly charged ions has allowed the
evaluation of systematic shifts and the prediction of the sensitivity to the
"new physics" effects. This article reviews the current status of theory and
experiment in the field.Comment: 53 pages, 16 figures, submitted to RM
Introduction to the Symposium: Leveraging on Disruption: The Potential of Dispute System Design for Justice, Accountability, and Impact in Our Global Economy
X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters
Context: Weak flares are supposed to be an important heating agent of the
outer layers of stellar atmospheres. However, due to instrumental limitations,
only large X-ray flares have been studied in detail until now.
Aims: We used an XMM-Newton observation of the very active BY-Dra type binary
star CC Eri in order to investigate the properties of two flares that are
weaker than those typically studied in the literature.
Methods: We performed time-resolved spectroscopy of the data taken with the
EPIC-PN CCD camera. A multi-temperature model was used to fit the spectra. We
inferred the size of the flaring loops using the density-temperature diagram.
The loop scaling laws were applied for deriving physical parameters of the
flaring plasma. We also estimated the number of loops involved in the observed
flares.
Results: A large X-ray variability was found. Spectral analysis showed that
all the regions in the light curve, including the flare segments, are
well-described by a 3-T model with variable emission measures but,
surprisingly, with constant temperatures (values of 3, 10 and 22 MK). The
analysed flares lasted ~ 3.4 and 7.1 ks, with flux increases of factors
1.5-1.9. They occurred in arcades made of a few tens of similar coronal loops.
The size of the flaring loops is much smaller than the distance between the
stellar surfaces in the binary system, and even smaller than the radius of each
of the stars. The obtained results are consistent with the following ideas: (i)
the whole X-ray light curve of CC Eri could be the result of a superposition of
multiple low-energy flares, and (ii) stellar flares can be scaled-up versions
of solar flares.Comment: 14 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
The MIPSGAL View of Supernova Remnants in the Galactic Plane
We report the detection of Galactic supernova remnants (SNRs) in the mid-infrared (at 24 and 70 μm), in the coordinate ranges 10° < l < 65° and 285° < l < 350°, |b| < 1°, using MIPS aboard the Spitzer Space Telescope. We search for infrared counterparts to SNRs in Green's catalog and identify 39 out of 121, i.e., a detection rate of about 32%. Such a relatively low detection fraction is mainly due to confusion with nearby foreground/background sources and diffuse emission. The SNRs in our sample show a linear trend in [F_8/F_(24)] versus [F_(70)/F_(24)]. We compare their infrared fluxes with their corresponding radio flux at 1.4 GHz and find that most remnants have a ratio of 70 μm to 1.4 GHz which is similar to those found in previous studies of SNRs (with the exception of a few that have ratios closer to those of H II regions). Furthermore, we retrieve a slope close to unity when correlating infrared (24 and 70 μm) with 1.4 GHz emission. Our survey is more successful in detecting remnants with bright X-ray emission, which we find is well correlated with the 24 μm morphology. Moreover, by comparing the power emitted in the X-ray, infrared, and radio, we conclude that the energy released in the infrared is comparable to the cooling in the X-ray range
Single-shot implementation of dispersion-scan for the characterization of ultrashort laser pulses
We demonstrate a novel, single-shot ultrafast diagnostic, based on the
dispersion-scan (d-scan) technique. In this implementation, rather than
scanning wedges to vary the dispersion as in standard d-scan, the pulse to be
measured experiences a spatially varying amount of dispersion in a Littrow
prism. The resulting beam is then imaged into a second-harmonic generation
crystal and an imaging spectrometer is used to measure the two-dimensional
trace, which is analyzed using the d-scan retrieval algorithm. We compare the
single-shot implementation with the standard d-scan for the measurement of
sub-3.5-fs pulses from a hollow core fiber pulse compressor. We show that the
retrieval algorithm used to extract amplitude and phase of the pulse provides
comparable results, proving the validity of the new single-shot implementation
down to near single-cycle durations.Comment: 6 pages, 4 figure
Probing halo nucleus structure through intermediate energy elastic scattering
This work addresses the question of precisely what features of few body
models of halo nuclei are probed by elastic scattering on protons at high
centre-of-mass energies. Our treatment is based on a multiple scattering
expansion of the proton-projectile transition amplitude in a form which is well
adapted to the weakly bound cluster picture of halo nuclei. In the specific
case of Li scattering from protons at 800 MeV/u we show that because
core recoil effects are significant, scattering crosssections can not, in
general, be deduced from knowledge of the total matter density alone.
We advocate that the optical potential concept for the scattering of halo
nuclei on protons should be avoided and that the multiple scattering series for
the full transition amplitude should be used instead.Comment: 8 pages REVTeX, 1 eps figure, accepted for publication in Phys. Rev.
Adaptive Control Allocation in the Presence of Actuator Failures
In this paper, a novel adaptive control allocation framework is proposed. In the adaptive control allocation structure, cooperative actuators are grouped and treated as an equivalent control effector. A state feedback adaptive control signal is designed for the equivalent effector and allocated to the member actuators adaptively. Two adaptive control allocation algorithms are proposed, which guarantee closed-loop stability and asymptotic state tracking in the presence of uncertain loss of effectiveness and constant-magnitude actuator failures. The proposed algorithms can be shown to reduce the controller complexity with proper grouping of the actuators. The proposed adaptive control allocation schemes are applied to two linearized aircraft models, and the simulation results demonstrate the performance of the proposed algorithms
Investigating the effect of target of rapamycin kinase inhibition on the Chlamydomonas reinhardtii phosphoproteome: from known homologs to new targets
Recuperado de: https://www.biorxiv.org/content/10.1101/310102v1Target of rapamycin (TOR) kinase is a conserved regulator of cell growth whose activity is modulated in response to nutrients, energy and stress. Key proteins involved in the pathway are conserved in the model photosynthetic microalga Chlamydomonas reinhardtii, but the substrates of TOR kinase and downstream signaling network have not been elucidated. Our study provides a new resource for investigating the phosphorylation networks governed by the TOR kinase pathway in Chlamydomonas. We used quantitative phosphoproteomics to investigate the effects of inhibiting Chlamydomonas TOR kinase on dynamic protein phosphorylation. Wild-type and AZD-insensitive Chlamydomonas strains were treated with TOR-specific chemical inhibitors (rapamycin, AZD8055 and Torin1), after which differentially affected phosphosites were identified. Our quantitative phosphoproteomic dataset comprised 2547 unique phosphosites from 1432 different proteins. Inhibition of TOR kinase caused significant quantitative changes in phosphorylation at 258 phosphosites, from 219 unique phosphopeptides. Our results include Chlamydomonas homologs of TOR signaling-related proteins, including a site on RPS6 with a decrease in phosphorylation. Additionally, phosphosites on proteins involved in translation and carotenoid biosynthesis were identified. Follow-up experiments guided by these phosphoproteomic findings in lycopene beta/epsilon cyclase showed that carotenoid levels are affected by TORC1 inhibition and carotenoid production is under TOR control in algae.National Science Foundation CAREER MCB-155252
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