1,617 research outputs found
Magnetic properties of GaMnAs single layers and GaInMnAs superlattices investigated at low temperature and high magnetic field
Magnetotransport properties of GaMnAs single layers and InGaMnAs/InGaAs
superlattice structures were investigated at temperatures from 4 K to 300 K and
magnetic fields up to 23 T to study the influence of carriers confinement
through different structures. Both single layers and superlattice structures
show paramagnetic-to-ferromagnetic phase transition. In GaMnAs/InGaAs
superlattice beside the Curie temperature (Tc ~ 40 K), a new phase transition
is observed close to 13 K.Comment: 8 pages, 5 figures, Proceedings of the XXXII International School on
the Physics of Semiconducting Compounds, Jaszowiec 2003, Polan
Programming multiple protein patterns on a single DNA nanostructure
The ability to create assemblies of proteins with spacing on the nanometer scale has important implications for proteomics, biodetection, and self-assembly. Structural DNA nanotechnology has led to the creation of a variety of nanostructures which should be capable of serving as an addressable template for the creation of complex molecular assemblies. The goal of such systems is to be able to position proteins or other components in distinct
patterns with precise spacing. These systems take advantage of the well-defined structure and spacing of DNA and use these properties to act as a template for secondary components in a bottom-up approach toward self-assembly. Previous work in this area has primarily focused on the use of chemical or structural modifications of the DNA template in order to attach or recruit proteins or nanoparticles. We have recently shown that a single polyamide-biotin conjugate is capable of binding to a DX array made from two tiles without any modification of the target DNA
Initial Populations of Black Holes in Star Clusters
Using an updated population synthesis code we study the formation and
evolution of black holes (BHs) in young star clusters following a massive
starburst. This study continues and improves on the initial work described by
Belczynski, Sadowski & Rasio (2004). In our new calculations we account for the
possible ejections of BHs and their progenitors from clusters because of natal
kicks imparted by supernovae and recoil following binary disruptions. The
results indicate that the properties of both retained BHs in clusters and
ejected BHs (forming a field population) depend sensitively on the depth of the
cluster potential. In particular, most BHs ejected from binaries are also
ejected from clusters with central escape speeds Vesc < 100 km/s. Conversely,
most BHs remaining in binaries are retained by clusters with Vesc > 50 km/s.
BHs from single star evolution are also affected significantly: about half of
the BHs originating from primordial single stars are ejected from clusters with
Vesc < 50 km/s. Our results lay a foundation for theoretical studies of the
formation of BH X-ray binaries in and around star clusters, including possible
ultra-luminous sources, as well as merging BH--BH binaries detectable with
future gravitational-wave observatories.Comment: 35 pages, 8 tables, 17 figures; resubmitted to ApJ (revised version
Magnetodielectric effect and optic soft mode behaviour in quantum paraelectric EuTiO3 ceramics
Infrared reflectivity and time-domain terahertz transmission spectra of
EuTiO3 ceramics revealed a polar optic phonon at 6 - 300K, whose softening is
fully responsible for the recently observed quantum paraelectric behaviour.
Even if our EuTiO3 ceramics show lower permittivity than the single crystal due
to a reduced density and/or small amount of secondary pyrochlore Eu2Ti2O7
phase, we confirmed the magnetic field dependence of the permittivity, also
slightly smaller than in single crystal. Attempt to reveal the soft phonon
dependence at 1.8K on the magnetic field up to 13T remained below the accuracy
of our infrared reflectivity experiment
Large-scale environments of binary AGB stars probed by Herschel. II: Two companions interacting with the wind of pi1 Gruis
Context. The Mass loss of Evolved StarS (MESS) sample observed with PACS on
board the Herschel Space Observatory revealed that several asymptotic giant
branch (AGB) stars are surrounded by an asymmetric circumstellar envelope (CSE)
whose morphology is most likely caused by the interaction with a stellar
companion. The evolution of AGB stars in binary systems plays a crucial role in
understanding the formation of asymmetries in planetary nebul{\ae} (PNe), but
at present, only a handful of cases are known where the interaction of a
companion with the stellar AGB wind is observed.
Aims. We probe the environment of the very evolved AGB star Gruis on
large and small scales to identify the triggers of the observed asymmetries.
Methods. Observations made with Herschel/PACS at 70 m and 160 m
picture the large-scale environment of Gru. The close surroundings of
the star are probed by interferometric observations from the VLTI/AMBER
archive. An analysis of the proper motion data of Hipparcos and Tycho-2
together with the Hipparcos Intermediate Astrometric Data help identify the
possible cause for the observed asymmetry.
Results. The Herschel/PACS images of Gru show an elliptical CSE whose
properties agree with those derived from a CO map published in the literature.
In addition, an arc east of the star is visible at a distance of
from the primary. This arc is most likely part of an
Archimedean spiral caused by an already known G0V companion that is orbiting
the primary at a projected distance of 460 au with a period of more than 6200
yr. However, the presence of the elliptical CSE, proper motion variations, and
geometric modelling of the VLTI/AMBER observations point towards a third
component in the system, with an orbital period shorter than 10 yr, orbiting
much closer to the primary than the G0V star.Comment: 13 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Termination dependent topological surface states of the natural superlattice phase BiSe
We describe the topological surface states of BiSe, a compound in the
infinitely adaptive Bi-BiSe natural superlattice phase series,
determined by a combination of experimental and theoretical methods. Two
observable cleavage surfaces, terminating at Bi or Se, are characterized by
angle resolved photoelectron spectroscopy and scanning tunneling microscopy,
and modeled by ab-initio density functional theory calculations. Topological
surface states are observed on both surfaces, but with markedly different
dispersions and Kramers point energies. BiSe therefore represents the
only known compound with different topological states on differently terminated
surfaces.Comment: 5 figures references added Published in PRB:
http://link.aps.org/doi/10.1103/PhysRevB.88.08110
The mechanism of caesium intercalation of graphene
Properties of many layered materials, including copper- and iron-based
superconductors, topological insulators, graphite and epitaxial graphene can be
manipulated by inclusion of different atomic and molecular species between the
layers via a process known as intercalation. For example, intercalation in
graphite can lead to superconductivity and is crucial in the working cycle of
modern batteries and supercapacitors. Intercalation involves complex diffusion
processes along and across the layers, but the microscopic mechanisms and
dynamics of these processes are not well understood. Here we report on a novel
mechanism for intercalation and entrapment of alkali-atoms under epitaxial
graphene. We find that the intercalation is adjusted by the van der Waals
interaction, with the dynamics governed by defects anchored to graphene
wrinkles. Our findings are relevant for the future design and application of
graphene-based nano-structures. Similar mechanisms can also play a role for
intercalation of layered materials.Comment: 8 pages, 7 figures in published form, supplementary information
availabl
Small and large polarons in nickelates, manganites, and cuprates
By comparing the optical conductivities of La_{1.67}Sr_{0.33}NiO_{4} (LSNO),
Sr_{1.5}La_{0.5}MnO_4 (SLMO), Nd_2CuO_{4-y} (NCO), and
Nd_{1.96}Ce_{0.04}CuO_{4} (NCCO), we have identified a peculiar behavior of
polarons in this cuprate family. While in LSNO and SLMO small polarons localize
into ordered structures below a transition temperature, in those cuprates the
polarons appear to be large, and at low T their binding energy decreases. This
reflects into an increase of the polaron radius, which may trigger coherent
transport.Comment: File latex, 15 p. incl. 4 Figs. epsf, to appear on the Journal of
Superconductivity - Proc. "Stripes 1996" - Roma Dec 199
Addressing single molecules on DNA nanostructures
The synthesis of devices and materials from molecular components is a major goal of nanotechnology. Although many such molecular components have been demonstrated previously,1–3 the ability to combine these components into designed architectures containing significant complexity remains a challenge. By using the hybridization properties of DNA and Watson–Crick base pairing, it has been possible to create well-defined DNA architectures of increasing complexity.4 The structure of an assembled DNA complex is directly and uniquely determined by the sequence of the DNA bases, which can be designed and manipulated. These methods provide a versatile and programmable way to control the structure and architecture of DNA nanostructures
Addressing single molecules on DNA nanostructures
The synthesis of devices and materials from molecular components is a major goal of nanotechnology. Although many such molecular components have been demonstrated previously,1–3 the ability to combine these components into designed architectures containing significant complexity remains a challenge. By using the hybridization properties of DNA and Watson–Crick base pairing, it has been possible to create well-defined DNA architectures of increasing complexity.4 The structure of an assembled DNA complex is directly and uniquely determined by the sequence of the DNA bases, which can be designed and manipulated. These methods provide a versatile and programmable way to control the structure and architecture of DNA nanostructures
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