1,860 research outputs found
Spin-dependent electronic hybridization in a rope of carbon nanotubes
We demonstrate single electron addition to different strands of a carbon
nanotube rope. Anticrossings of anomalous conductance peaks occur in quantum
transport measurements through the parallel quantum dots forming on the
individual strands. We determine the magnitude and the sign of the
hybridization as well as the Coulomb interaction between the carbon nanotube
quantum dots, finding that the bonding states dominate the transport. In a
magnetic field the hybridization is shown to be selectively suppressed due to
spin effects.Comment: 4 pages, 4 figure
Impact of tunnel barrier strength on magnetoresistance in carbon nanotubes
We investigate magnetoresistance in spin valves involving CoPd-contacted
carbon nanotubes. Both temperature and bias voltage dependence clearly indicate
tunneling magnetoresistance as the origin. We show that this effect is
significantly affected by the tunnel barrier strength, which appears to be one
reason for the variation between devices previously detected in similar
structures. Modeling the data by means of the scattering matrix approach, we
find a non-trivial dependence of the magnetoresistance on the barrier strength.
Furthermore, analysis of the spin precession observed in a nonlocal Hanle
measurement yields a spin lifetime of ns, a value comparable
with those found in silicon- or graphene-based spin valve devices.Comment: 10 pages, 5 figures, 1 tabl
Spin-Transfer Torque Induced Vortex Dynamics in Fe/Ag/Fe Nanopillars
We report experimental and analytical work on spin-transfer torque induced
vortex dynamics in metallic nanopillars with in-plane magnetized layers. We
study nanopillars with a diameter of 150 nm, containing two Fe layers with a
thickness of 15 nm and 30 nm respectively, separated by a 6 nm Ag spacer. The
sample geometry is such that it allows for the formation of magnetic vortices
in the Fe disks. As confirmed by micromagnetic simulations, we are able to
prepare states where one magnetic layer is homogeneously magnetized while the
other contains a vortex. We experimentally show that in this configuration
spin-transfer torque can excite vortex dynamics and analyze their dependence on
a magnetic field applied in the sample plane. The center of gyration is
continuously dislocated from the disk center, and the potential changes its
shape with field strength. The latter is reflected in the field dependence of
the excitation frequency. In the second part we propose a novel mechanism for
the excitation of the gyrotropic mode in nanopillars with a perfectly
homogeneously magnetized in-plane polarizing layer. We analytically show that
in this configuration the vortex can absorb energy from the spin-polarized
electric current if the angular spin-transfer efficiency function is
asymmetric. This effect is supported by micromagnetic simulations.Comment: The article has been sent to J. Phys. D. Submitted on August 9, 2010.
(7 pages and 4 figures.
Methode zur Analyse der Tropfenpositionierung im Inkjet-Druck
Inkjet-Druckmaschinen befinden sich auf dem Weg zu mehr Produktivität und Zuverlässigkeit. Da der Produktionsdruck zunehmend personalisiert wird und die Chargen kleiner werden, steigt die Nachfrage nach dem Digitaldruck mit seiner erhöhten Flexibilität. Zwei verbleibende Nachteile sind die geringere Produktionsgeschwindigkeit und Druckqualität. Die Inkjet-Technologie bringt derzeit noch viele Schwächen und Herausforderungen mit sich, wie z. B. die im Vergleich zum konventionellen Druck erhöhte Neigung zu sichtbaren Fehlern im Druckergebnis.
In dieser Arbeit wird eine Methodik vorgestellt, die mit einem kamerabasierten Inspektionssystem und einem Simulationsmodell der Bilderfassung die Analyse der Tropfenpositionierung in Produktionsdruckmaschinen ermöglicht. Die Untersuchungen zeigen, wie im laufenden Druckbetrieb bei minimaler Makulatur eine vollständige Überprüfung aller Druckdüsen erfolgt. Die Herangehensweise lässt sich auf die Überprüfung von bedarfsgesteuert aufgetragener, transparenter Grundierung übertragen. Darüber hinaus wird eine Methode für Kompensationen und Korrekturen unter Berücksichtigung der Messdaten, die in der Produktionsdruckmaschine erfasst werden, abgeleitet. Durch die Kombination von Bildauswertung, zielgerichteten Testmustern und einem Regressionsmodell können gegenüber dem Stand der Technik und der Wissenschaft schnellere und erfolgversprechendere Maßnahmen erfolgen, die zu weniger Druckprodukten mit minderer Druckqualität führen. Experimente zur vorgestellten Methodik zeigen die Grenzen der Kompensationsgeschwindigkeit sowie die Fähigkeit und Qualität des Ansatzes, mit Druckfehlern umzugehen. Als Resultat der Korrekturmaßnahmen wird die Druckqualität auf einem konstant hohen Niveau gehalten und die Verfügbarkeit der Druckmaschine steigt
Ultrafast dynamics of a magnetic antivortex - Micromagnetic simulations
The antivortex is a fundamental magnetization structure which is the
topological counterpart of the well-known magnetic vortex. We study here the
ultrafast dynamic behavior of an isolated antivortex in a patterned Permalloy
thin-film element. Using micromagnetic simulations we predict that the
antivortex response to an ultrashort external field pulse is characterized by
the production of a new antivortex as well as of a temporary vortex, followed
by an annihilation process. These processes are complementary to the recently
reported response of a vortex and, like for the vortex, lead to the reversal of
the orientation of the antivortex core region. In addition to its fundamental
interest, this dynamic magnetization process could be used for the generation
and propagation of spin waves for novel logical circuits.Comment: 4 pages, 4 figures. To be published in Physical Review B (R
Eigenvarieties and invariant norms: Towards p-adic Langlands for U(n)
We give a proof of the Breuil-Schneider conjecture in a large number of
cases, which complement the indecomposable case, which we dealt with earlier in
[Sor]. In some sense, only the Steinberg representation lies at the
intersection of the two approaches. In this paper, we view the conjecture from
a broader global perspective. If is any definite unitary group, which
is an inner form of \GL(n) over \K, we point out how the eigenvariety
\X(K^p) parametrizes a global -adic Langlands correspondence between
certain -dimensional -adic semisimple representations of
\Gal(\bar{\Q}|\K) (or what amounts to the same, pseudo-representations) and
certain Banach-Hecke modules with an admissible unitary action of
U(F\otimes \Q_p), when splits. We express the locally regular-algebraic
vectors of in terms of the Breuil-Schneider representation of
. Upon completion, this produces a candidate for the -adic local
Langlands correspondence in this context. As an application, we give a weak
form of local-global compatibility in the crystalline case, showing that the
Banach space representations of Schneider-Teitelbaum [ScTe] fit
the picture as predicted. There is a compatible global mod (semisimple)
Langlands correspondence parametrized by \X(K^p). We introduce a natural
notion of refined Serre weights, and link them to the existence of crystalline
lifts of prescribed Hodge type and Frobenius eigenvalues. At the end, we give a
rough candidate for a local mod correspondence, formulate a local-global
compatibility conjecture, and explain how it implies the conjectural Ihara
lemma in [CHT].Comment: Comments and suggestions are very welcom
Human Skin Permeation Enhancement Using PLGA Nanoparticles Is Mediated by Local pH Changes
The steady improvement and optimization of transdermal permeation is a constant and
challenging pharmaceutical task. In this study the influence of poly(lactide-co-glycolide) (PLGA)
nanoparticles on the dermal permeation of the anti-inflammatory drug flufenamic acid (FFA) was
investigated. For this aim, different vehicles under non-buffered and buffered conditions and different
skin models (human heat separated epidermis and reconstructed human epidermis equivalents)
were tested. Permeation experiments were performed using static Franz diffusion cells under infinite
dosing conditions. Already the presence of drug-free nanoparticles increased drug permeation
across the skin. Drug permeation was even enhanced when applying drug-loaded nanoparticles. In
contrast, buffered vehicles with different pH values (pH 5.4–7.4) revealed the influence of the pH
on the permeation of FFA. The change of the surrounding pH of the biodegradable nanoparticulate
system was demonstrated and visualized using pH-sensitive fluorescent probes. While a potential
contribution of hair follicles could be ruled out, our data suggest that the enhanced permeation of
FFA through human skin in the presence of PLGA nanoparticles is mediated by a locally decreased
pH during hydrolytic degradation of this polymer. This hypothesis is supported by the observation
that skin permeation of the weak base caffeine was not affected
Taking the Perfect Selfie: Investigating the Impact of Perspective on the Perception of Higher Cognitive Variables
Taking selfies is now becoming a standard human habit. However, as a social phenomenon, research is still in the fledgling stage and the scientific framework is sparse. Selfies allow us to share social information with others in a compact format. Furthermore, we are able to control important photographic and compositional aspects, such as perspective, which have a strong impact on the assessment of a face (e.g., demonstrated by the height-weight illusion, effects of gaze direction, faceism-index). In Study 1, we focused on the impact of perspective (left/right hemiface, above/below vs. frontal presentation) on higher cognitive variables and let 172 participants rate the perceived attractiveness, helpfulness, sympathy, dominance, distinctiveness, and intelligence, plus important information on health issues (e.g., body weight), on the basis of 14 3D faces. We could show that lateral snapshots yielded higher ratings for attractiveness compared to the classical frontal view. However, this effect was more pronounced for left hemifaces and especially female faces. Compared to the frontal condition, 30° right hemifaces were rated as more helpful, but only for female faces while faces viewed from above were perceived as significant less helpful. Direct comparison between left vs. right hemifaces revealed no effect. Relating to sympathy, we only found a significant effect for 30° right male hemifaces, but only in comparison to the frontal condition. Furthermore, female 30° right hemifaces were perceived as more intelligent. Relating to body weight, we replicated the so-called “height-weight illusion.” Other variables remained unaffected. In Study 2, we investigated the impact of a typical selfie-style condition by presenting the respective faces from a lateral (left/right) and tilted (lower/higher) vantage point. Most importantly, depending on what persons wish to express with a selfie, a systematic change of perspective can strongly optimize their message; e.g., increasing their attractiveness by shooting from above left, and in contrast, decreasing their expressed helpfulness by shooting from below. We could further extent past findings relating to the height-weight illusion and showed that an additional rotation of the camera positively affected the perception of body weight (lower body weight). We discuss potential explanations for perspective-related effects, especially gender-related ones
Towards a Continuous Manufacturing Process of Protein-Loaded Polymeric Nanoparticle Powders
To develop a scalable and efficient process suitable for the continuous manufacturing of poly(lactic-co-glycolic acid) (PLGA) nanoparticles containing ovalbumin as the model protein. PLGA nanoparticles were prepared using a double emulsification spray-drying method. Emulsions were prepared using a focused ultrasound transducer equipped with a flow cell. Either poly(vinyl alcohol) (PVA) or poloxamer 407 (P-407) was used as a stabilizer. Aliquots of the emulsions were blended with different matrix excipients and spray dried, and the yield and size of the resuspended nanoparticles was determined and compared against solvent displacement. Nanoparticle sizes of spray-dried PLGA/PVA emulsions were independent of the matrix excipient and comparable with sizes from the solvent displacement method. The yield of the resuspended nanoparticles was highest for emulsions containing trehalose and leucine (79%). Spray drying of PLGA/P-407 emulsions led to agglomerated nanoparticles independent of the matrix excipient. PLGA/P-407 nanoparticles pre-formed by solvent displacement could be spray dried with limited agglomeration when PVA was added as an additional stabilizer. A comparably high and economically interesting nanoparticle yield could be achieved with a process suitable for continuous manufacturing. Further studies are needed to understand the robustness of a continuous process at commercial scale
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