687 research outputs found
A Backward Stable Algorithm for Computing the CS Decomposition via the Polar Decomposition
We introduce a backward stable algorithm for computing the CS decomposition
of a partitioned matrix with orthonormal columns, or a
rank-deficient partial isometry. The algorithm computes two polar
decompositions (which can be carried out in parallel) followed by an
eigendecomposition of a judiciously crafted Hermitian matrix. We
prove that the algorithm is backward stable whenever the aforementioned
decompositions are computed in a backward stable way. Since the polar
decomposition and the symmetric eigendecomposition are highly amenable to
parallelization, the algorithm inherits this feature. We illustrate this fact
by invoking recently developed algorithms for the polar decomposition and
symmetric eigendecomposition that leverage Zolotarev's best rational
approximations of the sign function. Numerical examples demonstrate that the
resulting algorithm for computing the CS decomposition enjoys excellent
numerical stability
Circularly polarized microwaves for magnetic resonance study in the GHz range: application to nitrogen-vacancy in diamonds
The ability to create time-dependent magnetic fields of controlled
polarization is essential for many experiments with magnetic resonance. We
describe a microstrip circuit that allows us to generate strong magnetic field
at microwave frequencies with arbitrary adjusted polarization. The circuit
performance is demonstrated by applying it to an optically detected magnetic
resonance and Rabi nutation experiments in nitrogen-vacancy color centers in
diamond. Thanks to high efficiency of the proposed microstrip circuit and
degree of circular polarization of 85% it is possible to address the specific
spin states of a diamond sample using a low power microwave generator.Comment: 4 pages, 7 figures, nitrogen-vacancy, microwave circular
polarization, spin-state addressin
Non-destructive Neutron Activation Analysis of Aluminium and Phosphorus in Bone Biopsies
Peer Reviewe
Coherent population oscillations with nitrogen-vacancy color centers in diamond
We present results of our research on two-field (two-frequency) microwave
spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields
are tuned to transitions between the spin sublevels of the NV- ensemble in the
3A2 ground state (one field has a fixed frequency while the second one is
scanned). Particular attention is focused on the case where two microwaves
fields drive the same transition between two NV- ground state sublevels (ms=0
-> ms=+1). In this case, the observed spectra exhibit a complex narrow
structure composed of three Lorentzian resonances positioned at the pump-field
frequency. The resonance widths and amplitudes depend on the lifetimes of the
levels involved in the transition. We attribute the spectra to coherent
population oscillations induced by the two nearly degenerate microwave fields,
which we have also observed in real time. The observations agree well with a
theoretical model and can be useful for investigation of the NV relaxation
mechanisms.Comment: 17 page
How do you know if you ran through a wall?
Stable topological defects of light (pseudo)scalar fields can contribute to
the Universe's dark energy and dark matter. Currently the combination of
gravitational and cosmological constraints provides the best limits on such a
possibility. We take an example of domain walls generated by an axion-like
field with a coupling to the spins of standard-model particles, and show that
if the galactic environment contains a network of such walls, terrestrial
experiments aimed at detection of wall-crossing events are realistic. In
particular, a geographically separated but time-synchronized network of
sensitive atomic magnetometers can detect a wall crossing and probe a range of
model parameters currently unconstrained by astrophysical observations and
gravitational experiments.Comment: 5 pages, 2 figure; to appear in the PR
Microwave saturation spectroscopy of nitrogen-vacancy ensembles in diamond
Negatively-charged nitrogen-vacancy (NV) centers in diamond have
generated much recent interest for their use in sensing. The sensitivity
improves when the NV ground-state microwave transitions are narrow, but these
transitions suffer from inhomogeneous broadening, especially in high-density NV
ensembles. To better understand and remove the sources of broadening, we
demonstrate room-temperature spectral "hole burning" of the NV ground-state
transitions. We find that hole burning removes the broadening caused by
magnetic fields from C nuclei and demonstrate that it can be used for
magnetic-field-insensitive thermometry.Comment: Main text: 5 pages, 4 figures. Supplement: 6 pages, 3 figure
Analysis and calibration of absorptive images of Bose-Einstein condensate at non-zero temperatures
We describe the method allowing quantitative interpretation of absorptive
images of mixtures of BEC and thermal atoms which reduces possible systematic
errors associated with evaluation of the contribution of each fraction. By
using known temperature dependence of the BEC fraction, the analysis allows
precise calibration of the fitting results. The developed method is verified in
two different measurements and compares well with theoretical calculations and
with measurements performed by another group.Comment: 17 pages, 8 figure
Urban food consumption and associated water resources: The example of Dutch cities
AbstractFull self-sufficiency in cities is a major concern. Cities import resources for food, water and energy security. They are however key to global sustainability, as they concentrate a rapidly increasing and urbanising population (or number of consumers). In this paper, we analysed the dependency of urban inhabitants on the resource water for food consumption, by means of Dutch cities. We found that in extremely urbanised municipalities like Amsterdam and Rotterdam, people eat more meat and cereals and less potatoes than in other Dutch municipalities. Their current water footprint (WF) related to food consumption is therefore higher (3245l/cap/day) than in strongly urbanised cities (3126l/cap/day). Dutch urban citizens who eat too many animal products, crop oils and sugar can reduce their WF (with 29 to 32%) by shifting to a healthier diet. Recommended less meat consumption has the largest impact on the total WF reduction. A shift to a pesco-vegetarian or vegetarian diet would require even less water resources, where the WF can be reduced by 36 to 39% and 40 to 42% respectively. Dutch cities such as Amsterdam have always scored very high in international sustainability rankings for cities, partly due to a long history in integrated (urban) water management in the Netherlands. We argue that such existing rankings only show a certain – undoubtedly very important – part of urban environmental sustainability. To communicate the full picture to citizens, stakeholders and policy makers, indicators on external resource usage need to be employed. The fact that external resource dependency can be altered through changing dietary behaviour should be communicated
Quality of wholemeal wheat bread enriched with green coffee beans
Scientific studies have revealed that bioactive components of coffee play a preventive role against various degenerative diseases. Green coffee, in particular, is characterized by its unique composition and properties. The objective of this work was to investigate the influence of green coffee (Coffea arabica) beans (GCB) addition on the quality and antioxidant properties (AA) of the wholemeal bread. For bread preparation, flour form GCB, and wholemeal wheat flour, type 2000 were used. Wholemeal wheat flour was replaced with GCB flour at 1 to 5% levels. Loaf volume, texture, color and sensory properties of bread were determined. Furthermore, total phenolic content and antioxidant activity were evaluated. The results showed that bread supplementation with GCB had little influence on the bread volume. The highest volume of bread was obtained with 3 and 4% of GCB flour. The texture properties of bread crumb (hardness, elasticity, cohesiveness and chewiness) were slightly changed as a result of the GCB addition. The lightness of bread crumb decreased with the GCB addition (average from 46.3 to 42.6). Besides, the addition of GCB significantly enriched wheat bread with hydrophilic phenolic compounds. The phenolic compounds were highly bioaccessible in vitro. Moreover, the GCB addition enhanced antiradical activity of bread
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