143 research outputs found
Functional renormalization group approach to zero-dimensional interacting systems
We apply the functional renormalization group method to the calculation of
dynamical properties of zero-dimensional interacting quantum systems. As case
studies we discuss the anharmonic oscillator and the single impurity Anderson
model. We truncate the hierarchy of flow equations such that the results are at
least correct up to second order perturbation theory in the coupling. For the
anharmonic oscillator energies and spectra obtained within two different
functional renormalization group schemes are compared to numerically exact
results, perturbation theory, and the mean field approximation. Even at large
coupling the results obtained using the functional renormalization group agree
quite well with the numerical exact solution. The better of the two schemes is
used to calculate spectra of the single impurity Anderson model, which then are
compared to the results of perturbation theory and the numerical
renormalization group. For small to intermediate couplings the functional
renormalization group gives results which are close to the ones obtained using
the very accurate numerical renormalization group method. In particulare the
low-energy scale (Kondo temperature) extracted from the functional
renormalization group results shows the expected behavior.Comment: 22 pages, 8 figures include
Density-matrix renormalisation group approach to quantum impurity problems
A dynamic density-matrix renormalisation group approach to the spectral
properties of quantum impurity problems is presented. The method is
demonstrated on the spectral density of the flat-band symmetric single-impurity
Anderson model. We show that this approach provides the impurity spectral
density for all frequencies and coupling strengths. In particular, Hubbard
satellites at high energy can be obtained with a good resolution. The main
difficulties are the necessary discretisation of the host band hybridised with
the impurity and the resolution of sharp spectral features such as the
Abrikosov-Suhl resonance.Comment: 16 pages, 6 figures, submitted to Journal of Physics: Condensed
Matte
Heart rate variability in response to pain stimulus in VLBW infants followed longitudinally during NICU stay.
The objective of this longitudinal study, conducted in a neonatal intensive care unit, was to characterize the response to pain of high-risk very low birth weight infants (\u3c1,500 g) from 23 to 38 weeks post-menstrual age (PMA) by measuring heart rate variability (HRV). Heart period data were recorded before, during, and after a heel lanced or wrist venipunctured blood draw for routine clinical evaluation. Pain response to the blood draw procedure and age-related changes of HRV in low-frequency and high-frequency bands were modeled with linear mixed-effects models. HRV in both bands decreased during pain, followed by a recovery to near-baseline levels. Venipuncture and mechanical ventilation were factors that attenuated the HRV response to pain. HRV at the baseline increased with post-menstrual age but the growth rate of high-frequency power was reduced in mechanically ventilated infants. There was some evidence that low-frequency HRV response to pain improved with advancing PMA
Performance of the X-Calibur Hard X-Ray Polarimetry Mission during its 2018/19 Long-Duration Balloon Flight
X-Calibur is a balloon-borne telescope that measures the polarization of
high-energy X-rays in the 15--50keV energy range. The instrument makes use of
the fact that X-rays scatter preferentially perpendicular to the polarization
direction. A beryllium scattering element surrounded by pixellated CZT
detectors is located at the focal point of the InFOC{\mu}S hard X-ray mirror.
The instrument was launched for a long-duration balloon (LDB) flight from
McMurdo (Antarctica) on December 29, 2018, and obtained the first constraints
of the hard X-ray polarization of an accretion-powered pulsar. Here, we
describe the characterization and calibration of the instrument on the ground
and its performance during the flight, as well as simulations of particle
backgrounds and a comparison to measured rates. The pointing system and
polarimeter achieved the excellent projected performance. The energy detection
threshold for the anticoincidence system was found to be higher than expected
and it exhibited unanticipated dead time. Both issues will be remedied for
future flights. Overall, the mission performance was nominal, and results will
inform the design of the follow-up mission XL-Calibur, which is scheduled to be
launched in summer 2022.Comment: 19 pages, 31 figures, submitted to Astropart. Phy
Modelling microbial fuel cells with suspended cells and added electron transfer mediator
Repetition Priming of Face Gender Judgments: An Instance Based Explanation.
Earlier studies of repetition priming using faces have been interpreted as indicating that such effects are confined to the processing of known faces. The experiment reported here employed 8 rather than the more usual 2 presentation trials and required subjects to make gender decisions ( is it a male or is it a female face?) to both familiar and unfamiliar faces. This allowed the currently favoured recognition unit theories of face processing to be compared with the Logan (1988) instance model. Equivalent repetition priming effects were observed for both familiar and unfamiliar faces and were well fitted by power functions. It is argued that the findings are consistent with the strong predictions made by Logan’s model and pose problems for recognition unit based theories
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