308 research outputs found
Thermally induced magnetic relaxation in square artificial spin ice
The properties of natural and artificial assemblies of interacting elements,
ranging from Quarks to Galaxies, are at the heart of Physics. The collective
response and dynamics of such assemblies are dictated by the intrinsic
dynamical properties of the building blocks, the nature of their interactions
and topological constraints. Here we report on the relaxation dynamics of the
magnetization of artificial assemblies of mesoscopic spins. In our model
nano-magnetic system - square artificial spin ice - we are able to control the
geometrical arrangement and interaction strength between the magnetically
interacting building blocks by means of nano-lithography. Using time resolved
magnetometry we show that the relaxation process can be described using the
Kohlrausch law and that the extracted temperature dependent relaxation times of
the assemblies follow the Vogel-Fulcher law. The results provide insight into
the relaxation dynamics of mesoscopic nano-magnetic model systems, with
adjustable energy and time scales, and demonstrates that these can serve as an
ideal playground for the studies of collective dynamics and relaxations.Comment: 15 pages, 5 figure
Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays
Extraordinary optical transmission is observed due to the excitation of
surface plasmon polaritons (SPPs) in 2-Dimensional hexagonal anti-dot patterns
of pure Ni thin films, grown on sapphire substrates. A strong enhancement of
the polar Kerr rotation is recorded at the surface plasmon related transmission
maximum. Angular resolved reflectivity measurements under an applied field,
reveal an enhancement and a shift of the normalized reflectivity difference
upon reversal of the magnetic saturation (transverse magneto-optical Kerr
effect-TMOKE). The change of the TMOKE signal clearly shows the magnetic field
modulation of the dispersion relation of SPPs launched in a 2D patterned
ferromagnetic Ni film
Magnetic order and energy-scale hierarchy in artificial spin ice
In order to explain and predict the properties of many physical systems, it
is essential to understand the interplay of different energy-scales. Here we
present investigations of the magnetic order in thermalised artificial spin ice
structures, with different activation energies of the interacting Ising-like
elements. We image the thermally equilibrated magnetic states of the
nano-structures using synchrotron-based magnetic microscopy. By comparing
results obtained from structures with one or two different activation energies,
we demonstrate a clear impact on the resulting magnetic order. The differences
are obtained by the analysis of the magnetic spin structure factors, in which
the role of the activation energies is manifested by distinct short-range
order. This demonstrates that artificial spin systems can serve as model
systems, allowing the definition of energy-scales by geometrical design and
providing the backdrop for understanding their interplay.Comment: 8 pages, 5 figures (+ supplementary 6 pages, 4 figures
A novel wheat variety with elevated content of amylose increases resistant starch formation and may beneficially influence glycaemia in healthy subjects
Previous studies indicate that elevated amylose content in products from rice, corn, and barley induce lower postprandial glycaemic responses and higher levels of resistant starch (RS). Consumption of slowly digestible carbohydrates and RS has been associated with health benefits such as decreased risk of diabetes and cardiovascular disease.To evaluate the postprandial glucose and insulin responses in vivo to bread products based on a novel wheat genotype with elevated amylose content (38%).Bread was baked from a unique wheat genotype with elevated amylose content, using baking conditions known to promote amylose retrogradation. Included test products were bread based on whole grain wheat with elevated amylose content (EAW), EAW with added lactic acid (EAW-la), and ordinary whole grain wheat bread (WGW). All test breads were baked at pumpernickel conditions (20 hours, 120°C). A conventionally baked white wheat bread (REF) was used as reference. Resistant starch (RS) content was measured in vitro and postprandial glucose and insulin responses were tested in 14 healthy subjects.The results showed a significantly higher RS content (on total starch basis) in breads based on EAW than in WGW (p<0.001). Lactic acid further increased RS (p<0.001) compared with both WGW and EAW. Breads baked with EAW induced lower postprandial glucose response than REF during the first 120 min (p<0.05), but there were no significant differences in insulin responses. Increased RS content per test portion was correlated to a reduced glycaemic index (GI) (r= − 0.571, p<0.001).This study indicates that wheat with elevated amylose content may be preferable to other wheat genotypes considering RS formation. Further research is needed to test the hypothesis that bread with elevated amylose content can improve postprandial glycaemic response
SN 2006oz: rise of a super-luminous supernova observed by the SDSS-II SN Survey
We study SN 2006oz, a newly-recognized member of the class of H-poor,
super-luminous supernovae. We present multi-color light curves from the SDSS-II
SN Survey, that cover the rise time, as well as an optical spectrum that shows
that the explosion occurred at z~0.376. We fitted black body functions to
estimate the temperature and radius evolution of the photosphere and used the
parametrized code SYNOW to model the spectrum. We constructed a bolometric
light curve and compared it with explosion models. The very early light curves
show a dip in the g- and r-bands and a possible initial cooling phase in the
u-band before rising to maximum light. The bolometric light curve shows a
precursor plateau with a duration of 6-10 days in the rest-frame. A lower limit
of M_u < -21.5 can be placed on the absolute peak luminosity of the SN, while
the rise time is constrained to be at least 29 days. During our observations,
the emitting sphere doubled its radius to 2x10^15 cm, while the temperature
remained hot at 15000 K. As for other similar SNe, the spectrum is best modeled
with elements including O II and Mg II, while we tentatively suggest that Fe
III might be present. We suggest that the precursor plateau might be related to
a recombination wave in a circumstellar medium (CSM) and discuss whether this
is a common property of all similar explosions. The subsequent rise can be
equally well described by input from a magnetar or by ejecta-CSM interaction,
but the models are not well constrained owing to the lack of post-maximum
observations, and CSM interaction has difficulties accounting for the precursor
plateau self-consistently. Radioactive decay is less likely to be the mechanism
that powers the luminosity. The host galaxy, detected in deep imaging with the
10 m GTC, is a moderately young and star-forming, but not a starburst, galaxy.
It has an absolute magnitude of M_g = -16.9.Comment: Contains minor changes (of editorial nature) with respect to v1 in
order to match the published version. The abstract has been modified to fit
the arXiv space requirements. 11 pages, 8 figures, 3 table
The importance of the weak: Interaction modifiers in artificial spin ices
The modification of geometry and interactions in two-dimensional magnetic
nanosystems has enabled a range of studies addressing the magnetic order,
collective low-energy dynamics, and emergent magnetic properties, in e.g.
artificial spin ice structures. The common denominator of all these
investigations is the use of Ising-like mesospins as building blocks, in the
form of elongated magnetic islands. Here we introduce a new approach: single
interaction modifiers, using slave-mesospins in the form of discs, within which
the mesospin is free to rotate in the disc plane. We show that by placing these
on the vertices of square artificial spin ice arrays and varying their
diameter, it is possible to tailor the strength and the ratio of the
interaction energies. We demonstrate the existence of degenerate ice-rule
obeying states in square artificial spin ice structures, enabling the
exploration of thermal dynamics in a spin liquid manifold. Furthermore, we even
observe the emergence of flux lattices on larger length-scales, when the energy
landscape of the vertices is reversed. The work highlights the potential of a
design strategy for two-dimensional magnetic nano-architectures, through which
mixed dimensionality of mesospins can be used to promote thermally emergent
mesoscale magnetic states.Comment: 17 pages, including methods, 4 figures. Supplementary information
contains 16 pages and 15 figure
Selective activation of oxidized PTP1B by the thioredoxin system modulates PDGF-ß receptor tyrosine kinase signaling
The inhibitory reversible oxidation of protein tyrosine phosphatases (PTPs) is an important regulatory mechanism in growth factor signaling. Studies on PTP oxidation have focused on pathways that increase or decrease reactive oxygen species levels and thereby affect PTP oxidation. The processes involved in reactivation of oxidized PTPs remain largely unknown. Here the role of the thioredoxin (Trx) system in reactivation of oxidized PTPs was analyzed using a combination of in vitro and cell-based assays. Cells lacking the major Trx reductase TrxR1 (Txnrd1-/-) displayed increased oxidation of PTP1B, whereas SHP2 oxidation was unchanged. Furthermore, in vivo-oxidized PTP1B was reduced by exogenously added Trx system components, whereas SHP2 oxidation remained unchanged. Trx1 reduced oxidized PTP1B in vitro but failed to reactivate oxidized SHP2. Interestingly, the alternative TrxR1 substrate TRP14 also reactivated oxidized PTP1B, but not SHP2. Txnrd1-depleted cells displayed increased phosphorylation of PDGF-ß receptor, and an enhanced mitogenic response, after PDGF-BB stimulation. The TrxR inhibitor auranofin also increased PDGF-ß receptor phosphorylation. This effect was not observed in cells specifically lacking PTP1B. Together these results demonstrate that the Trx system, including both Trx1 and TRP14, impacts differentially on the oxidation of individual PTPs, with a preference of PTP1B over SHP2 activation. The studies demonstrate a previously unrecognized pathway for selective redox-regulated control of receptor tyrosine kinase signaling
Why Are Male Social Relationships Complex in the Doubtful Sound Bottlenose Dolphin Population?
Copyright 2008 Elsevier B.V., All rights reserved.Peer reviewedPublisher PD
The properties of SN Ib/c locations
Aims: To gain better insight on the physics of stripped-envelope
core-collapse supernovae through studying their environments. Methods: We
obtained low-resolution optical spectroscopy with the New Technology Telescope
(+ EFOSC2) at the locations of 20 Type Ib/c supernovae. We measure the flux of
emission lines in the stellar-continuum-subtracted spectra from which local
metallicities are computed. For the supernova regions we estimate both the mean
stellar age, interpreting the stellar absorption with population synthesis
models, and the age of the youngest stellar populations using the H-alpha
equivalent width as an age indicator. These estimates are compared with the
lifetimes of single massive stars. Results: Based on our sample, we detect a
tentative indication that Type Ic supernovae might explode in environments that
are more metal-rich than those of Type Ib supernovae (average difference of
0.08 dex), but this is not a statistically significant result. The lower limits
placed on the ages of the supernova birthplaces are overall young, although
there are several cases where these appear older than what is expected for the
evolution of single stars more massive than 25-30 M_{sun}. This is only true,
however, assuming that the supernova progenitors were born during an
instantaneous (not continuous) episode of star formation. Conclusions: These
results do not conclusively favor any of the two evolutionary paths (single or
binary) leading to stripped supernovae. We do note a fraction of events for
which binary evolution is more likely, due to their associated age limits. The
fact, however, that the supernova environments contain areas of recent (< 15
Myr) star formation and that the environmental metallicities are, at least, not
against the single evolutionary scenario, suggest that this channel is also
broadly consistent with the observations.Comment: Matches published version (after proofs
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