1,987 research outputs found
Identification of Si-vacancy related room temperature qubits in 4H silicon carbide
Identification of microscopic configuration of point defects acting as
quantum bits is a key step in the advance of quantum information processing and
sensing. Among the numerous candidates, silicon vacancy related centers in
silicon carbide (SiC) have shown remarkable properties owing to their
particular spin-3/2 ground and excited states. Although, these centers were
observed decades ago, still two competing models, the isolated negatively
charged silicon vacancy and the complex of negatively charged silicon vacancy
and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are
argued as an origin. By means of high precision first principles calculations
and high resolution electron spin resonance measurements, we here unambiguously
identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively
charged silicon vacancies. Moreover, we identify the Si-vacancy qubit
configurations that provide room temperature optical readout.Comment: 3 figure
ADAQ: Automatic workflows for magneto-optical properties of point defects in semiconductors
Automatic Defect Analysis and Qualification (ADAQ) is a collection of
automatic workflows developed for high-throughput simulations of
magneto-optical properties of point defect in semiconductors. These workflows
handle the vast number of defects by automating the processes to relax the unit
cell of the host material, construct supercells, create point defect clusters,
and execute calculations in both the electronic ground and excited states. The
main outputs are the magneto-optical properties which include zero-phonon
lines, zero-field splitting, and hyperfine coupling parameters. In addition,
the formation energies are calculated. We demonstrate the capability of ADAQ by
performing a complete characterization of the silicon vacancy in silicon
carbide in the polytype 4H (4H-SiC).Comment: Typo corrected in eq. 3, references adde
How entrepreneurs deal with ethical challenges : an application of the Business Ethics Synergy Star Technique
Entrepreneurs typically live with the ever present threat of business failure arising from limited financial resources and aggressive competition in the marketplace. Under these circumstances, conflicting priorities arise and the entrepreneur is thus faced with certain dilemmas. In seeking to resolve these, entrepreneurs must often rely on their own judgment to determine ‘‘what is right’’. There is thus a need for a technique to assist them decide on a course of action when no precedent or obvious solution exists. This research paper examines how entrepreneurs experience and deal with these dilemmas. The research is based on interviews with seven entrepreneurs in established service-oriented ventures, which gave rise to 26 dilemmas. These dilemmas were analyzed by making use of the Synergy Star technique, which is introduced here as a tool that is useful in defining any dilemma, isolating the ethical component, and resolving the dilemma in a way that is congruent with the entrepreneur’s personal world-view
Zinc absorption in adult humans: the effect of protein sources added to liquid test meals
The influence of different protein sources on Zn absorption was evaluated in healthy adults by radioisotopic labelling of single meals, followed by whole-body retention measurements 14 d after intake. Semi-synthetic liquid diets were used for the evaluation of different animal-protein sources and dephytinized soyabean-protein isolate ( ··01 g phytic acid/kg). Zn absorption was measured in the same subjects from identical test meals containing no added protein. No statistically significant differences were found in the Zn absorption from test meals containing bovine whey, casein or egg albumen when compared with test meals without added protein. Bovine serum albumin (BSA) and soyabean-protein isolate (< ··01 g phytic acid/kg) significantly reduced the mean absorption of Zn from 45-49% (no added protein) to 38·0 (SD 10·9) (BSA, P < ··05) and 33·9 (SD 12·6)% (soyabean-protein isolate < ··01 g phytic acid/kg, P < ··01). These results demonstrate that Zn absorption is inhibited by certain protein sources, such as BSA and dephytinized soyabean-protein isolate, while other proteins have little or no effec
Predicting occupant head displacements in evasive maneuvers; tuning and comparison of a rotational based and a translational based neck muscle controller
Objective: Real-life car crashes are often preceded by an evasive maneuver, which can alter the occupant posture and muscle state. To simulate the occupant response in such maneuvers, human body models (HBMs) with active muscles have been developed. The aim of this study was to implement an omni-directional rotational head-neck muscle controller in the SAFER HBM and compare the bio-fidelity of the HBM with a rotational controller to the HBM with a translational controller, in simulations of evasive maneuvers.Methods: The rotational controller was developed using an axis-angle representation of head rotations, with x, y, and z components in the axis. Muscle load sharing was based on rotational direction in the simulation and muscle activity recorded in three volunteer experiments in these directions. The gains of the rotational and translational controller were tuned to minimize differences between translational and rotational head displacements of the HBM and volunteers in braking and lane change maneuvers using multi-objective optimizations. Bio-fidelity of the model with tuned controllers was evaluated objectively using CORrelation and Analysis (CORA).Results: The results indicated comparable performance for both controllers after tuning, with somewhat higher bio-fidelity for rotational kinematics with the translational controller. After tuning, good or excellent bio-fidelity was indicated for both controllers in the loading direction (forward in braking, and lateral in lane change), with CORA scores of 0.86-0.99 and 0.93-0.98 for the rotational and translational controllers, respectively. For rotational displacements, and translational displacements in the other directions, bio-fidelity ranged from poor to excellent, with slightly higher average CORA scores for the HBM with the translational controller in both braking and lane changing. Time-averaged muscle activity was within one standard deviation of time-averaged muscle activity from volunteers.Conclusion: Overall, the results show that when tuned, both the translational and rotational controllers can be used to predict the occupant response to an evasive maneuver, allowing for the inclusion of evasive maneuvers prior to a crash in evaluation of vehicle safety. The rotational controller shows potential in controlling omni-directional head displacements, but the translational controller outperformed the rotational controller. Thus, for now, the recommendation is to use the translational controller with tuned gains
Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs
We present results of 6 years of observations, reduced and analyzed with the
same tools in a systematic way. We report completely new data for 15 objects,
for 5 objects we present a new analysis of previously published results plus
additional data and for 9 objects we present a new analysis of data already
published. Lightcurves, possible rotation periods and photometric amplitudes
are reported for all of them. The photometric variability is smaller than
previously thought: the mean amplitude of our sample is 0.1mag and only around
15% of our sample has a larger variability than 0.15mag. The smaller
variability than previously thought seems to be a bias of previous
observations. We find a very weak trend of faster spinning objects towards
smaller sizes, which appears to be consistent with the fact that the smaller
objects are more collisionally evolved, but could also be a specific feature of
the Centaurs, the smallest objects in our sample. We also find that the smaller
the objects, the larger their amplitude, which is also consistent with the idea
that small objects are more collisionally evolved and thus more deformed.
Average rotation rates from our work are 7.5h for the whole sample, 7.6h for
the TNOs alone and 7.3h for the Centaurs. All of them appear to be somewhat
faster than what one can derive from a compilation of the scientific literature
and our own results. Maxwellian fits to the rotation rate distribution give
mean values of 7.5h (for the whole sample) and 7.3h (for the TNOs only).
Assuming hydrostatic equilibrium we can determine densities from our sample
under the additional assumption that the lightcurves are dominated by shape
effects, which is likely not realistic. The resulting average density is
0.92g/cm^3 which is not far from the density constraint that one can derive
from the apparent spin barrier that we observe.Comment: Accepted for publication in A&
Selection rules in the excitation of the divacancy and the nitrogen-vacancy pair in 4H- and 6H-SiC
In this study, we address the selection rules with respect to the
polarization of the optical excitation of two colour centres in 4H-SiC and
6H-SiC with potential for applications in quantum technology, the divacancy and
the nitrogen-vacancy pair. We show that the photoluminescence (PL) of the axial
configurations of higher symmetry (C3v) than the basal ones (C1h) can be
cancelled using any excitation (resonant or non-resonant) with polarization
parallel to the crystal axis (EL||c). The polarization selection rules are
determined using group-theoretical analysis and simple physical arguments
showing that phonon-assisted absorption with EL||c is prohibited despite being
formally allowed by group theory. A comparison with the selection rules for the
silicon vacancy, another defect with C3v symmetry, is also carried out. Using
the selection rules, we demonstrate selective excitation of only one basal
divacancy configuration in 4H-SiC, the P3 line and discuss the higher contrast
and increased Debye-Waller factor in the selectively excited spectrum
Divergent effects of liraglutide, exendin-4, and sitagliptin on beta-cell mass and indicators of pancreatitis in a mouse model of hyperglycaemia
AIMS:Glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP4) inhibitors improve glucose tolerance by still incompletely understood mechanisms. Each class of antihyperglycemic drugs has also been proposed to increase pancreatitis risk. Here, we compare systematically the effects of two widely-used GLP-1 analogues, liraglutide and exendin-4, and the DPP4 inhibitor, sitagliptin, in the mouse. METHODS:C57BL6 mice were maintained for 131 days on a normal diet (ND) or a diet comprising 60% fat (HFD) before measurements of fasting blood glucose and insulin, and intraperitoneal glucose tolerance. Beta- and alpha- cell volume, and Reg3b immunoreactivity, were measured by immunohistochemical analysis of pancreatic slices. RESULTS:Whereas liraglutide (200 µg/kg) and exendin-4 (10 µg/kg) treatment reduced body weight and/or improved glucose tolerance, sitagliptin (10 mg/kg) was without effect on either parameter. Liraglutide caused a sharp reduction in beta-cell mass in both ND and HFD mice, whereas exendin-4 exerted no effect. By contrast, sitagliptin unmasked an action of high fat diet to increase beta-cell mass. Reg3B positive area was augmented by all three agents in normal chow-fed mice, whilst sitagliptin and exendin-4, but not liraglutide, affected this parameter in HFD animals. Correspondingly sitagliptin, but not the GLP-1 analogues, increased circulating amylase levels in ND and HFD mice. CONCLUSIONS:Liraglutide improves glucose tolerance in the mouse whilst exerting relatively modest effects on pancreatitis risk. Conversely, exendin-4 and sitagliptin, at doses which exert, respectively, minor or no effects on metabolic parameters, lead to signs of pancreatitis
Photometry of cometary nuclei: Rotation rates, colours and a comparison with Kuiper Belt Objects
We present time-series data on Jupiter Family Comets (JFCs) 17P/Holmes,
47P/Ashbrook-Jackson and 137P/Shoemaker-Levy 2. In addition we also present
results from `snap-shot' observations of comets 43P/Wolf-Harrington,
44P/Reinmuth 2, 103P/Hartley 2 and 104P/Kowal 2 taken during the same run. The
comets were at heliocentric distances of between 3 and 7 AU at this time. We
present measurements of size and activity levels for the snap-shot targets. The
time-series data allow us to constrain rotation periods and shapes, and thus
bulk densities. We also measure colour indices (V-R) and (R-I) and reliable
radii for these comets. We compare all of our findings to date with similar
results for other comets and Kuiper Belt Objects (KBOs). We find that the
rotational properties of nuclei and KBOs are very similar, that there is
evidence for a cut-off in bulk densities at ~ 0.6 g cm^{-3} in both
populations, and the colours of the two populations show similar correlations.
For JFCs there is no observational evidence for the optical colours being
dependant on either position in the orbit or on orbital parameters.Comment: 15 pages, 19 figures, accepted for publication in MNRA
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