73 research outputs found
Efficient room-temperature light-emitters based on partly amorphised Ge quantum dots in crystalline Si
Semiconductor light emitters compatible with standard Si integration
technology (SIT) are of particular interest for overcoming limitations in the
operating speed of microelectronic devices 1-3. Light sources based on group-IV
elements would be SIT compatible but suffer from the poor optoelectronic
properties of bulk Si and Ge. Here, we demonstrate that epitaxially grown Ge
quantum dots (QDs) in a fully coherent Si matrix show extraordinary optical
properties if partially amorphised by Ge-ion bombardment (GIB). The GIB-QDs
exhibit a quasi-direct-band gap and show, in contrast to conventional SiGe
nanostructures, almost no thermal quenching of the photoluminescence (PL) up to
room-temperature (RT). Microdisk resonators with embedded GIB-QDs exhibit
threshold-behaviour and super-linear increase of the integrated PL-intensity
(IPL) with increasing excitation power Pexc which indicates light amplification
by stimulated emission in a fully SIT-compatible group-IV nano-system
Centrosymmetric PbTe/CdTe quantum dots coherently embedded by epitaxial precipitation
A concept for the fabrication of highly symmetric quantum dots that are
coherently embedded in a single crystalline matrix is demonstrated. In this
approach, the formation of the quantum dots is induced by a transformation of
an epitaxial 2D quantum well into an array of isolated precipitates with
dimensions of about 25 nm. The formation process is driven by the immiscibility
of the constituent materials resulting from their different lattice structures.
The investigated PbTe/CdTe heterosystem combines two different cubic lattices
with almost identical lattice constants. Therefore, the precipitated quantum
dots are almost strain free and near thermodynamic equilibrium they exhibit the
shape of small-rhombo-cubo-octahedrons. The PbTe/CdTe quantum dots, grown on
GaAs substrates, display intense room temperature luminescence at wavelength
around 3.2 micrometer, which makes them auspicious for applications in
mid-infrared photonic devices.Comment: 12 pages, 3 figure
Out-of-Plane Magnetic Anisotropy in Ordered Ensembles of FeN Nanocrystals Embedded in GaN
Phase-separated semiconductors containing magnetic nanostructures are
relevant systems for the realization of high-density recording media. Here, the
controlled strain engineering of GaFeN layers with FeN embedded
nanocrystals (NCs) \textit{via} AlGaN buffers with different Al
concentration \% is presented. Through the addition of Al
to the buffer, the formation of predominantly prolate-shaped
-FeN NCs takes place. Already at an Al concentration
\,\,5\% the structural properties---phase, shape,
orientation---as well as the spatial distribution of the embedded NCs are
modified in comparison to those grown on a GaN buffer. Although the magnetic
easy axis of the cubic '-GaFeN nanocrystals in the layer on
the buffer lies in-plane, the easy axis of the
-FeN NCs in all samples with AlGaN buffers
coincides with the growth direction, leading to a sizeable
out-of-plane magnetic anisotropy and opening wide perspectives for
perpendicular recording based on nitride-based magnetic nanocrystals.Comment: 29 pages, 10 figures, submitte
Modulation of Human Time Processing by Subthalamic Deep Brain Stimulation
Timing in the range of seconds referred to as interval timing is crucial for cognitive operations and conscious time processing. According to recent models of interval timing basal ganglia (BG) oscillatory loops are involved in time interval recognition. ParkinsoĆs disease (PD) is a typical disease of the basal ganglia that shows distortions in interval timing. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a powerful treatment of PD which modulates motor and cognitive functions depending on stimulation frequency by affecting subcortical-cortical oscillatory loops. Thus, for the understanding of BG-involvement in interval timing it is of interest whether STN-DBS can modulate timing in a frequency dependent manner by interference with oscillatory time recognition processes. We examined production and reproduction of 5 and 15 second intervals and millisecond timing in a double blind, randomised, within-subject repeated-measures design of 12 PD-patients applying no, 10-Hz- and â„130-Hz-STN-DBS compared to healthy controls. We found under(re-)production of the 15-second interval and a significant enhancement of this under(re-)production by 10-Hz-stimulation compared to no stimulation, â„130-Hz-STN-DBS and controls. Milliseconds timing was not affected. We provide first evidence for a frequency-specific modulatory effect of STN-DBS on interval timing. Our results corroborate the involvement of BG in general and of the STN in particular in the cognitive representation of time intervals in the range of multiple seconds
The comorbidity profiles and medication issues of patients with multiple system atrophy: a systematic cross-sectional analysis
Background
Multiple system atrophy (MSA) is a complex and fatal neurodegenerative movement disorder. Understanding the comorbidities and drug therapy is crucial for MSA patientsâ safety and management.
Objectives
To investigate the pattern of comorbidities and aspects of drug therapy in MSA patients.
Methods
Cross-sectional data of MSA patients according to Gilman et al. (2008) diagnostic criteria and control patients without neurodegenerative diseases (non-ND) were collected from German, multicenter cohorts. The prevalence of comorbidities according to WHO ICD-10 classification and drugs administered according to WHO ATC system were analyzed. Potential drug-drug interactions were identified using AiDKlinikÂź.
Results
The analysis included 254 MSA and 363 age- and sex-matched non-ND control patients. MSA patients exhibited a significantly higher burden of comorbidities, in particular diseases of the genitourinary system. Also, more medications were prescribed MSA patients, resulting in a higher prevalence of polypharmacy. Importantly, the risk of potential drug-drug interactions, including severe interactions and contraindicated combinations, was elevated in MSA patients. When comparing MSA-P and MSA-C subtypes, MSA-P patients suffered more frequently from diseases of the genitourinary system and diseases of the musculoskeletal system and connective tissue.
Conclusions
MSA patients face a substantial burden of comorbidities, notably in the genitourinary system. This, coupled with increased polypharmacy and potential drug interactions, highlights the complexity of managing MSA patients. Clinicians should carefully consider these factors when devising treatment strategies for MSA patients
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