856 research outputs found
Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures
Controlling magnetic properties on the nm-scale is essential for basic
research in micro-magnetism and spin-dependent transport, as well as for
various applications such as magnetic recording, imaging and sensing. This has
been accomplished to a very high degree by means of layered heterostructures in
the vertical dimension. Here we present a complementary approach that allows
for a controlled tuning of the magnetic properties of Co/Pt heterostructures on
the lateral mesoscale. By means of in-situ post-processing of Pt- and Co-based
nano-stripes prepared by focused electron beam induced deposition (FEBID) we
are able to locally tune their coercive field and remanent magnetization.
Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic
behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850
Oe. We attribute the observed effects to the locally controlled formation of
the CoPt L1 phase, whose presence has been revealed by transmission
electron microscopy.Comment: Accepted for publication in Beilstein J. Nanotechno
Magnetooptical Study of Zeeman Effect in Mn modulation-doped InAs/InGaAs/InAlAs Quantum Well Structures
We report on a magneto-photoluminescence (PL) study of Mn modulation-doped
InAs/InGaAs/InAlAs quantum wells. Two PL lines corresponding to the radiative
recombination of photoelectrons with free and bound-on-Mn holes have been
observed. In the presence of a magnetic field applied in the Faraday geometry
both lines split into two circularly polarized components. While temperature
and magnetic field dependences of the splitting are well described by the
Brillouin function, providing an evidence for exchange interaction with spin
polarized manganese ions, the value of the splitting exceeds the expected value
of the giant Zeeman splitting by two orders of magnitude for a given Mn
density. Possible reasons of this striking observation are discussed
Central American Subduction System
Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, Heredia, Costa Rica, 18–22 June 2007 The driving force for great earthquakes and the cycling of water and climate-influencing volatiles (carbon dioxide, sulfur, halogens) across the convergent margin of Central America have been a focus of international efforts for over 8 years, as part of the MARGINS program of the U.S. National Science Foundation, the Collaborative Research Center (SFB 574) of the German Science Foundation, and the Central American science community. Over 120 scientists and students from 10 countries met in Costa Rica to synthesize this intense effort spanning from land to marine geological and geophysical studies
Opto-Electronic Characterization of Three Dimensional Topological Insulators
We demonstrate that the terahertz/infrared radiation induced photogalvanic
effect, which is sensitive to the surface symmetry and scattering details, can
be applied to study the high frequency conductivity of the surface states in
(Bi1-xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In
particular, measuring the polarization dependence of the photogalvanic current
and scanning with a micrometre sized beam spot across the sample, provides
access to (i) topographical inhomogeneity's in the electronic properties of the
surface states and (ii) the local domain orientation. An important advantage of
the proposed method is that it can be applied to study TIs at room temperature
and even in materials with a high electron density of bulk carriers.Comment: 6 pages, 4 figure
Resting-state fMRI activity predicts unsupervised learning and memory in an immersive virtual reality environment
In the real world, learning often proceeds in an unsupervised manner without explicit instructions or feedback. In this study, we employed an experimental paradigm in which subjects explored an immersive virtual reality environment on each of two days. On day 1, subjects implicitly learned the location of 39 objects in an unsupervised fashion. On day 2, the locations of some of the objects were changed, and object location recall performance was assessed and found to vary across subjects. As prior work had shown that functional magnetic resonance imaging (fMRI) measures of resting-state brain activity can predict various measures of brain performance across individuals, we examined whether resting-state fMRI measures could be used to predict object location recall performance. We found a significant correlation between performance and the variability of the resting-state fMRI signal in the basal ganglia, hippocampus, amygdala, thalamus, insula, and regions in the frontal and temporal lobes, regions important for spatial exploration, learning, memory, and decision making. In addition, performance was significantly correlated with resting-state fMRI connectivity between the left caudate and the right fusiform gyrus, lateral occipital complex, and superior temporal gyrus. Given the basal ganglia's role in exploration, these findings suggest that tighter integration of the brain systems responsible for exploration and visuospatial processing may be critical for learning in a complex environment
Generalized Hamiltonian structures for Ermakov systems
We construct Poisson structures for Ermakov systems, using the Ermakov
invariant as the Hamiltonian. Two classes of Poisson structures are obtained,
one of them degenerate, in which case we derive the Casimir functions. In some
situations, the existence of Casimir functions can give rise to superintegrable
Ermakov systems. Finally, we characterize the cases where linearization of the
equations of motion is possible
Epidermal Growth Factor–PEG Functionalized PAMAM-Pentaethylenehexamine Dendron for Targeted Gene Delivery Produced by Click Chemistry
Aim of this study was the site-specific conjugation of an epidermal growth factor (EGF)-polyethylene glycol (PEG) chain by click chemistry onto a poly(amido amine) (PAMAM) dendron, as a key step toward defined multifunctional carriers for targeted gene delivery. For this purpose, at first propargyl amine cored PAMAM dendrons with ester ends were synthesized. The chain terminal ester groups were then modified by oligoamines with different secondary amino densities. The oligoamine-modified PAMAM dendrons were well biocompatible, as demonstrated in cytotoxicity assays. Among the different oligoamine-modified dendrons, PAMAM-pentaethylenehexamine (PEHA) dendron polyplexes displayed the best gene transfer ability. Conjugation of PAMAM-PEHA dendron with PEG spacer was conducted via click reaction, which was performed before amidation with PEHA. The resultant PEG-PAMAM-PEHA copolymer was then coupled with EGF ligand. pDNA transfections in HuH-7 hepatocellular carcinoma cells showed a 10-fold higher efficiency with the polyplexes containing conjugated EGF as compared to the ligand-free ones, demonstrating the concept of ligand targeting. Overall gene transfer efficiencies, however, were moderate, suggesting that additional measures for overcoming subsequent intracellular bottlenecks in delivery have to be taken
- …