3,339 research outputs found
Fidelity and visibility reduction in Majorana qubits by entanglement with environmental modes
We study the dynamics and readout of topological qubits encoded by
zero-energy Majorana bound states in a topological superconductor. We take into
account bosonic modes due to the electromagnetic environment which couple the
Majorana manifold to above-gap continuum quasi-particles. This coupling causes
the degenerate ground state of the topological superconductor to be dressed in
a polaron-like manner by quasi-particle states and bosons, and the system to
become gapless. Topological protection and hence full coherence is only
maintained if the qubit is operated and read out within the low-energy spectrum
of the dressed states. We discuss reduction of fidelity and/or visibility if
this condition is violated by a quantum-dot readout that couples to the bare
(undressed) Majorana modes. For a projective measurement of the bare Majorana
basis, we formulate a Bloch-Redfield approach that is valid for weak
Majorana-environment coupling and takes into account constraints imposed by
fermion-number-parity conservation. Within the Markovian approximation, our
results essentially confirm earlier theories of finite-temperature decoherence
based on Fermi's golden rule. However, the full non-Markovian dynamics reveals,
in addition, the fidelity reduction by a projective measurement. Using a
spinless nanowire model with -wave pairing, we provide quantitative results
characterizing these effects.Comment: 18 pages, 10 figure
Transition from spot to faculae domination -- An alternate explanation for the dearth of intermediate \textit{Kepler} rotation periods
The study of stellar activity cycles is crucial to understand the underlying
dynamo and how it causes activity signatures such as dark spots and bright
faculae. We study the appearance of activity signatures in contemporaneous
photometric and chromospheric time series. Lomb-Scargle periodograms are used
to search for cycle periods present in both time series. To emphasize the
signature of the activity cycle we account for rotation-induced scatter in both
data sets by fitting a quasi-periodic Gaussian process model to each observing
season. After subtracting the rotational variability, cycle amplitudes and the
phase difference between the two time series are obtained by fitting both time
series simultaneously using the same cycle period. We find cycle periods in 27
of the 30 stars in our sample. The phase difference between the two time series
reveals that the variability in fast rotating active stars is usually in
anti-phase, while the variability of slowly rotating inactive stars is in
phase. The photometric cycle amplitudes are on average six times larger for the
active stars. The phase and amplitude information demonstrates that active
stars are dominated by dark spots, whereas less active stars are dominated by
bright faculae. We find the transition from spot to faculae domination at the
Vaughan-Preston gap, and around a Rossby number equal to one. We conclude that
faculae are the dominant ingredient of stellar activity cycles at ages >2.55
Gyr. The data further suggest that the Vaughan-Preston gap can not explain the
previously detected dearth of Kepler rotation periods between 15-25 days.
Nevertheless, our results led us to propose an explanation for the rotation
period dearth to be due to the non-detection of periodicity caused by the
cancellation of dark spots and bright faculae at 800 Myr.Comment: 12+15 pages, 10+2 figures, accepted for publication in A&
Collisions of Slow Highly Charged Ions with Surfaces
Progress in the study of collisions of multiply charged ions with surfaces is
reviewed with the help of a few recent examples. They range from fundamental
quasi-one electron processes to highly complex ablation and material
modification processes. Open questions and possible future directions will be
discussed.Comment: 13 pages, 16 figures, review pape
Conditional co-occurrence probability acts like frequency in predicting fixation durations
The predictability of an upcoming word has been found to be a useful predictor in eye movement research, but is expensive to collect and subjective in nature. It would be desirable to have other predictors that are easier to collect and objective in nature if these predictors were capable of capturing the information stored in predictability. This paper contributes to this discussion by testing a possible predictor: conditional co-occurrence probability. This measure is a simple statistical representation of the relatedness of the current word to its context, based only on word co-occurrence patterns in data taken from the Internet. In the regression analyses, conditional co-occurrence probability acts like lexical frequency in predicting fixation durations, and its addition does not greatly improve the model fits. We conclude that readers do not seem to use the information contained within conditional co-occurrence probability during reading for meaning, and that similar simple measures of semantic relatedness are unlikely to be able to replace predictability as a predictor for fixation durations. Keywords: Co-occurrence probability, Cloze predictability, frequency, eye movement, fixation duration
A Retrospective Cost-Analysis Based on 44500 Insured Persons
Objectives The aim of this study was to compare the health care costs for
patients using additional homeopathic treatment (homeopathy group) with the
costs for those receiving usual care (control group). Methods Cost data
provided by a large German statutory health insurance company were
retrospectively analysed from the societal perspective (primary outcome) and
from the statutory health insurance perspective. Patients in both groups were
matched using a propensity score matching procedure based on socio-demographic
variables as well as costs, number of hospital stays and sick leave days in
the previous 12 months. Total cumulative costs over 18 months were compared
between the groups with an analysis of covariance (adjusted for baseline
costs) across diagnoses and for six specific diagnoses (depression, migraine,
allergic rhinitis, asthma, atopic dermatitis, and headache). Results Data from
44,550 patients (67.3% females) were available for analysis. From the societal
perspective, total costs after 18 months were higher in the homeopathy group
(adj. mean: EUR 7,207.72 [95% CI 7,001.14–7,414.29]) than in the control group
(EUR 5,857.56 [5,650.98–6,064.13]; p<0.0001) with the largest differences
between groups for productivity loss (homeopathy EUR 3,698.00
[3,586.48–3,809.53] vs. control EUR 3,092.84 [2,981.31–3,204.37]) and
outpatient care costs (homeopathy EUR 1,088.25 [1,073.90–1,102.59] vs. control
EUR 867.87 [853.52–882.21]). Group differences decreased over time. For all
diagnoses, costs were higher in the homeopathy group than in the control
group, although this difference was not always statistically significant.
Conclusion Compared with usual care, additional homeopathic treatment was
associated with significantly higher costs. These analyses did not confirm
previously observed cost savings resulting from the use of homeopathy in the
health care system
Long-term economic outcomes
Objectives: This study aimed to provide a long-term cost comparison of
patients using additional homeopathic treatment (homeopathy group) with
patients using usual care (control group) over an observation period of 33
months. Methods: Health claims data from a large statutory health insurance
company were analysed from both the societal perspective (primary outcome) and
from the statutory health insurance perspective (secondary outcome). To
compare costs between patient groups, homeopathy and control patients were
matched in a 1:1 ratio using propensity scores. Predictor variables for the
propensity scores included health care costs and both medical and demographic
variables. Health care costs were analysed using an analysis of covariance,
adjusted for baseline costs, between groups both across diagnoses and for
specific diagnoses over a period of 33 months. Specific diagnoses included
depression, migraine, allergic rhinitis, asthma, atopic dermatitis, and
headache. Results: Data from 21,939 patients in the homeopathy group (67.4%
females) and 21,861 patients in the control group (67.2% females) were
analysed. Health care costs over the 33 months were 12,414 EUR [95% CI
12,022–12,805] in the homeopathy group and 10,428 EUR [95% CI 10,036–10,820]
in the control group (p<0.0001). The largest cost differences were attributed
to productivity losses (homeopathy: EUR 6,289 [6,118–6,460]; control: EUR
5,498 [5,326–5,670], p<0.0001) and outpatient costs (homeopathy: EUR 1,794
[1,770–1,818]; control: EUR 1,438 [1,414–1,462], p<0.0001). Although the costs
of the two groups converged over time, cost differences remained over the full
33 months. For all diagnoses, homeopathy patients generated higher costs than
control patients. Conclusion: The analysis showed that even when following-up
over 33 months, there were still cost differences between groups, with higher
costs in the homeopathy group
The Sun is less active than other solar-like stars
Magnetic activity of the Sun and other stars causes their brightness to vary.
We investigate how typical the Sun's variability is compared to other
solar-like stars, i.e. those with near-solar effective temperatures and
rotation periods. By combining four years of photometric observations from the
Kepler space telescope with astrometric data from the Gaia spacecraft, we
measure photometric variabilities of 369 solar-like stars. Most of the
solar-like stars with well-determined rotation periods show higher variability
than the Sun and are therefore considerably more active. These stars appear
nearly identical to the Sun, except for their higher variability. Their
existence raises the question of whether the Sun can also experience epochs of
such high variability.Comment: Accepted for publication in Science. 3 (main) + 10 (supplementary)
figure
The Midpoint Rule as a Variational--Symplectic Integrator. I. Hamiltonian Systems
Numerical algorithms based on variational and symplectic integrators exhibit
special features that make them promising candidates for application to general
relativity and other constrained Hamiltonian systems. This paper lays part of
the foundation for such applications. The midpoint rule for Hamilton's
equations is examined from the perspectives of variational and symplectic
integrators. It is shown that the midpoint rule preserves the symplectic form,
conserves Noether charges, and exhibits excellent long--term energy behavior.
The energy behavior is explained by the result, shown here, that the midpoint
rule exactly conserves a phase space function that is close to the Hamiltonian.
The presentation includes several examples.Comment: 11 pages, 8 figures, REVTe
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