1,078 research outputs found
Balanced truncation and singular perturbation approximation model order reduction for stochastically controlled linear systems
When solving linear stochastic differential equations numerically, usually a high order spatial discretisation is used. Balanced truncation (BT) and singular perturbation approximation (SPA) are well-known projection techniques in the deterministic framework which reduce the order of a control system and hence reduce computational complexity. This work considers both methods when the control is replaced by a noise term. We provide theoretical tools such as stochastic concepts for reachability and observability, which are necessary for balancing related model order reduction of linear stochastic differential equations with additive L'evy noise. Moreover, we derive error bounds for both BT and SPA and provide numerical results for a specific example which support the theory
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Balanced truncation and singular perturbation approximation model order reduction for stochastically controlled linear systems
When solving linear stochastic differential equations numerically,
usually a high order spatial discretisation is used. Balanced truncation (BT)
and singular perturbation approximation (SPA) are well-known projection
techniques in the deterministic framework which reduce the order of a control
system and hence reduce computational complexity. This work considers both
methods when the control is replaced by a noise term. We provide theoretical
tools such as stochastic concepts for reachability and observability, which
are necessary for balancing related model order reduction of linear
stochastic differential equations with additive Lévy noise. Moreover, we
derive error bounds for both BT and SPA and provide numerical results for a
specific example which support the theory
Energy dissipation in graphene field-effect transistors
We measure the temperature distribution in a biased single-layer graphene
transistor using Raman scattering microscopy of the 2D-phonon band. Peak
operating temperatures of 1050 K are reached in the middle of the graphene
sheet at 210 KW cm^(-2) of dissipated electric power. The metallic contacts act
as heat sinks, but not in a dominant fashion. To explain the observed
temperature profile and heating rate, we have to include heat-flow from the
graphene to the gate oxide underneath, especially at elevated temperatures,
where the graphene thermal conductivity is lowered due to umklapp scattering.
Velocity saturation due to phonons with about 50 meV energy is inferred from
the measured charge density via shifts in the Raman G-phonon band, suggesting
that remote scattering (through field coupling) by substrate polar surface
phonons increases the energy transfer to the substrate and at the same time
limits the high-bias electronic conduction of graphene.Comment: The pdf-file contains the main manuscript (19 pages, 3 figures) and
the supplement (5 pages, 4 figures
Detaching from the negative by reappraisal: the role of right superior frontal gyrus (BA9/32)
The ability to reappraise the emotional impact of events is related to long-term mental health. Self-focused reappraisal (REAPPself), i.e., reducing the personal relevance of the negative events, has been previously associated with neural activity in regions near right medial prefrontal cortex, but rarely investigated among brain-damaged individuals. Thus, we aimed to examine the REAPPself ability of brain-damaged patients and healthy controls considering structural atrophies and gray matter intensities, respectively. Twenty patients with well-defined cortex lesions due to an acquired circumscribed tumor or cyst and 23 healthy controls performed a REAPPself task, in which they had to either observe negative stimuli or decrease emotional responding by REAPPself. Next, they rated the impact of negative arousal and valence. REAPPself ability scores were calculated by subtracting the negative picture ratings after applying REAPPself from the ratings of the observing condition. The scores of the patients were included in a voxel-based lesion-symptom mapping (VLSM) analysis to identify deficit related areas (ROI). Then, a ROI group-wise comparison was performed. Additionally, a whole-brain voxel-based-morphometry (VBM) analysis was run, in which healthy participant's REAPPself ability scores were correlated with gray matter intensities. Results showed that (1) regions in the right superior frontal gyrus (SFG), comprising the right dorsolateral prefrontal cortex (BA9) and the right dorsal anterior cingulate cortex (BA32), were associated with patient's impaired down-regulation of arousal, (2) a lesion in the depicted ROI occasioned significant REAPPself impairments, (3) REAPPself ability of controls was linked with increased gray matter intensities in the ROI regions. Our findings show for the first time that the neural integrity and the structural volume of right SFG regions (BA9/32) might be indispensable for REAPPself. Implications for neurofeedback research are discussed.Fil: Falquez, Rosalux. University of Heidelberg; AlemaniaFil: Couto, Juan Blas Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Neurociencia Cognitiva. Fundación Favaloro. Instituto de Neurociencia Cognitiva; ArgentinaFil: Ibáñez Barassi, Agustín Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Neurociencia Cognitiva. Fundación Favaloro. Instituto de Neurociencia Cognitiva; ArgentinaFil: Freitag, Martin T.. German Cancer Research Center; AlemaniaFil: Berger, Moritz. German Cancer Research Center; AlemaniaFil: Arens, Elisabeth A.. University of Heidelberg; AlemaniaFil: Lang, Simone. University of Heidelberg; AlemaniaFil: Barnow, Sven. University of Heidelberg; Alemani
Autistic Traits and Autism Spectrum Disorders: The Clinical Validity of Two Measures Presuming a Continuum of Social Communication Skills
Research indicates that autism is the extreme end of a continuously distributed trait. The Social Responsiveness Scale (SRS) and the Social and Communication Disorders Checklist (SCDC) aim to assess autistic traits. The objective of this study was to compare their clinical validity. The SRS showed sensitivities of .74 to .80 and specificities of .69 to 1.00 for autism. Sensitivities were .85 to .90 and specificities .28 to.82 for the SCDC. Correlations with the ADI-R, ADOS and SCQ were higher for the SRS than for the SCDC. The SCDC seems superior to the SRS to screen for unspecific social and communicative deficits including autism. The SRS appears more suitable than the SCDC in clinical settings and for specific autism screening
Minimum Conductivity and Evidence for Phase Transitions in Ultra-clean Bilayer Graphene
Bilayer graphene (BLG) at the charge neutrality point (CNP) is strongly
susceptible to electronic interactions, and expected to undergo a phase
transition into a state with spontaneous broken symmetries. By systematically
investigating a large number of singly- and doubly-gated bilayer graphene (BLG)
devices, we show that an insulating state appears only in devices with high
mobility and low extrinsic doping. This insulating state has an associated
transition temperature Tc~5K and an energy gap of ~3 meV, thus strongly
suggesting a gapped broken symmetry state that is destroyed by very weak
disorder. The transition to the intrinsic broken symmetry state can be tuned by
disorder, out-of-plane electric field, or carrier density
High-power single-frequency operation, at 1064nm and 1061.4nm of a Nd:YAG ring laser end-pumped by a beam-shaped diode bar
A Nd:YAG laser having a ring configuration, with Faraday rotator to provide unidirectional operation has been end-pumped by a single 20 W diode bar equipped with a beam-shaper. A single-frequency TEMoo output of 5.4 W is achieved at 1064 nm. Using a thin intracavity etalon for wavelength selection, a single-frequency output of 4.2 W is obtained on the 1061.4 nm transition
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