546 research outputs found
Anisotropic optical properties of Fe/GaAs(001) nanolayers from first principles
We investigate the anisotropy of the optical properties of thin Fe films on
GaAs(001) from first-principles calculations. Both intrinsic and
magnetization-induced anisotropy are covered by studying the system in the
presence of spin-orbit coupling and external magnetic fields. We use the
linearized augmented plane wave method, as implemented in the WIEN2k density
functional theory code, to show that the symmetric anisotropy of the
spin-orbit coupling fields at the Fe/GaAs(001) interface manifests itself in
the corresponding anisotropy of the optical conductivity and the polar
magneto-optical Kerr effect. While their magnetization-induced anisotropy is
negligible, the intrinsic anisotropy of the optical properties is significant
and reflects the underlying symmetry of the Fe/GaAs(001) interface.
This suggests that the effects of anisotropic spin-orbit coupling fields in
experimentally relevant Fe/GaAs(001) slabs can be studied by purely optical
means.Comment: 8 pages, 11 figure
Optical conductivity of hydrogenated graphene from first principles
We investigate the effect of hydrogen coverage on the optical conductivity of
single-side hydrogenated graphene from first principles calculations. To
account for different degrees of uniform hydrogen coverage we calculate the
complex optical conductivity for graphene supercells of various sizes, each
containing a single additional hydrogen atom. We use the linearized augmented
plane wave (LAPW) method, as implemented in the WIEN2k density functional
theory code, to show that the hydrogen coverage strongly influences the complex
optical conductivity and thus the optical properties, such as absorption, of
hydrogenated graphene. We find that the optical conductivity of graphene in the
infrared, visible, and ultraviolet range has different characteristic features
depending on the degree of hydrogen coverage. This opens up new possibilities
to tailor the optical properties of graphene by reversible hydrogenation, and
to determine the hydrogen coverage of hydrogenated graphene samples in the
experiment by contact-free optical absorption measurements.Comment: 8 pages, 7 figure
Rezension von: Lav Subaric und Franz Daxecker: Christoph Scheiners Sol ellipticus. Veröffentlichung der Universität Innsbruck, 226, Innsbruck, 1998
SCoT: a Python toolbox for EEG source connectivity
Analysis of brain connectivity has become an important research tool in neuroscience. Connectivity can be estimated between cortical sources reconstructed from the electroencephalogram (EEG). Such analysis often relies on trial averaging to obtain reliable results. However, some applications such as brain-computer interfaces (BCIs) require single-trial estimation methods. In this paper, we present SCoT—a source connectivity toolbox for Python. This toolbox implements routines for blind source decomposition and connectivity estimation with the MVARICA approach. Additionally, a novel extension called CSPVARICA is available for labeled data. SCoT estimates connectivity from various spectral measures relying on vector autoregressive (VAR) models. Optionally, these VAR models can be regularized to facilitate ill posed applications such as single-trial fitting. We demonstrate basic usage of SCoT on motor imagery (MI) data. Furthermore, we show simulation results of utilizing SCoT for feature extraction in a BCI application. These results indicate that CSPVARICA and correct regularization can significantly improve MI classification. While SCoT was mainly designed for application in BCIs, it contains useful tools for other areas of neuroscience. SCoT is a software package that (1) brings combined source decomposition and connectivtiy estimation to the open Python platform, and (2) offers tools for single-trial connectivity estimation. The source code is released under the MIT license and is available online at github.com/SCoT-dev/SCoT
Hydrophobic lung surfactant proteins B and C remain associated with surface film during dynamic cyclic area changes
AbstractThe biophysical activity of lung surfactant depends, to a large extent, on the presence of the hydrophobic surfactant proteins B (SP-B) and C (SP-C). The role of these proteins in lipid adsorption and lipid squeeze-out under dynamic conditions simulating breathing is not yet clear. Therefore, the aim of this study was to investigate the interaction of spread hydrophobic surfactant proteins with phospholipids in a captive-bubble surfactometer during rapid cyclic area changes (6 cycles/min). We found that SP-B and SP-C facilitated the rapid transport of lipids into the air–water interface in a concentration-dependent manner (threshold concentration ≥0.05:0.5 mol% SP-B/SP-C). Successive rapid cyclic area changes did not affect the concentration-dependent lipid adsorption process, suggesting that SP-B and SP-C remained associated with the surface film
Spin-orbit coupling in fluorinated graphene
We report on theoretical investigations of the spin-orbit coupling effects in
fluorinated graphene. First-principles density functional calculations are
performed for the dense and dilute adatom coverage limits. The dense limit is
represented by the single-side semifluorinated graphene, which is a metal with
spin-orbit splittings of about 10 meV. To simulate the effects of a single
adatom, we also calculate the electronic structure of a
supercell, with one fluorine atom in the top position. Since this dilute limit
is useful to study spin transport and spin relaxation, we also introduce a
realistic effective hopping Hamiltonian, based on symmetry considerations,
which describes the supercell bands around the Fermi level. We provide the
Hamiltonian parameters which are best fits to the first-principles data. We
demonstrate that, unlike for the case of hydrogen adatoms, fluorine's own
spin-orbit coupling is the principal cause of the giant induced local
spin-orbit coupling in graphene. The hybridization induced transfer of
spin-orbit coupling from graphene's bonds, important for hydrogenated
graphene, contributes much less. Furthermore, the magnitude of the induced
spin-orbit coupling due to fluorine adatoms is about times more than
that of pristine graphene, and 10 times more than that of hydrogenated
graphene. Also unlike hydrogen, the fluorine adatom is not a narrow resonant
scatterer at the Dirac point. The resonant peak in the density of states of
fluorinated graphene in the dilute limit lies 260 meV below the Dirac point.
The peak is rather broad, about 300 meV, making the fluorine adatom only a
weakly resonant scatterer.Comment: 11 pages, 14 figure
In Pursuit of an Easy to Use Brain Computer Interface for Domestic Use in a Population with Brain Injury
This paper presents original research investigating a sensor based, ambient assisted smart home platform, within the framework of a brain computer interface (BackHome). This multimodal system integrates home-based sensors, mobile monitoring, with communication tools, web browsing, smart home control and cognitive rehabilitation. The target population are people living at home with acquired brain injury. This research engaged with the target population and those without brain injury, who provided a control for system testing. Aligned with our ethical governance a strong user centric ethos was foundational to participant engagement. Participant experience included three individual sessions to complete a pre-set protocol with supervision. Evaluation methodology included observations, time logging, completion of protocol and usability questionnaires. Results confirmed the average accuracy score for the people without brain injury was 82.6% (±4.7), performing best with the cognitive rehabilitation. Target end users recorded an average accuracy score of 76% (±11.5) with the speller logging the highest accuracy score. Additional outcomes included the need to refine the aesthetic appearance, as well as improving the reliability and responsiveness of the BCI. The findings outline the importance of engaging with end users to design and develop marketable BCI products for use in a domestic environment.
DOI: 10.17762/ijritcc2321-8169.150610
Towards a versatile and multidimensional framework to analyse regional governance
Regional governance has received growing attention, not only from researchers, but also from politicians and practitioners of regional development. The understanding and usage of the concept, however, are highly heterogeneous: sometimes regional governance is described or explained in terms of its characteristics, processes and impacts, while at other times, it is framed as a tool for regional development. This article develops a definition and framework for a systematic assessment of various regional governance forms. For this purpose, it draws on material from a three-round Delphi survey among practitioners and researchers who are experts of regional governance. On this basis, a consolidated definition of regional governance is proposed as ‘the vertical and horizontal coordination of regional transformation processes beyond administrative boundaries by state and non-state actors’. Furthermore, the framework identifies five dimensions of regional governance: (a) participation, (b) bindingness, (c) formalisation, (d) regional autonomy and (e) power relations. These dimensions are disaggregated into a total of 21 indicators to systematically describe and analyse different regional governance forms., Regional governance has received growing attention, not only from researchers, but also from politicians and practitioners of regional development. The understanding and usage of the concept, however, are highly heterogeneous: sometimes regional governance is described or explained in terms of its characteristics, processes and impacts, while at other times, it is framed as a tool for regional development. This article develops a definition and framework for a systematic assessment of various regional governance forms. For this purpose, it draws on material from a three-round Delphi survey among practitioners and researchers who are experts of regional governance. On this basis, a consolidated definition of regional governance is proposed as ‘the vertical and horizontal coordination of regional transformation processes beyond administrative boundaries by state and non-state actors’. Furthermore, the framework identifies five dimensions of regional governance: (a) participation, (b) bindingness, (c) formalisation, (d) regional autonomy and (e) power relations. These dimensions are disaggregated into a total of 21 indicators to systematically describe and analyse different regional governance forms
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