81 research outputs found
Spectroscopy of a fractional Josephson vortex molecule
In long Josephson junctions with multiple discontinuities of the Josephson
phase, fractional vortex molecules are spontaneously formed. At each
discontinuity point a fractional Josephson vortex carrying a magnetic flux
, Wb being the magnetic flux
quantum, is pinned. Each vortex has an oscillatory eigenmode with a frequency
that depends on and lies inside the plasma gap.
We experimentally investigate the dependence of the eigenfrequencies of a
two-vortex molecule on the distance between the vortices, on their topological
charge and on the bias current applied to the
Josephson junction. We find that with decreasing distance between vortices, a
splitting of the eigenfrequencies occurs, that corresponds to the emergence of
collective oscillatory modes of both vortices. We use a resonant microwave
spectroscopy technique and find good agreement between experimental results and
theoretical predictions.Comment: submitted to Phys. Rev.
Simultaneous observation of high order multiple quantum coherences at ultralow magnetic fields
We present a method for the simultaneous observation of heteronuclear
multi-quantum coherences (up to the 3rd order), which give an additional degree
of freedom for ultralow magnetic field (ULF) MR experiments, where the chemical
shift is negligible. The nonequilibrium spin state is generated by Signal
Amplification By Reversible Exchange (SABRE) and detected at ULF with
SQUID-based NMR. We compare the results obtained by the heteronuclei Correlated
SpectroscopY (COSY) with a Flip Angle FOurier Series (FAFOS) method. COSY
allows a quantitative analysis of homo- and heteronuclei quantum coherences
Spectroscopy of the fractional vortex eigenfrequency in a long Josephson 0-kappa junction
Fractional Josephson vortices carry a magnetic flux Phi, which is a fraction
of the magnetic flux quantum Phi_0 ~ 2.07x10^{-15} Wb. Their properties are
very different from the properties of the usual integer fluxons. In particular,
fractional vortices are pinned and have an oscillation eigenfrequency which is
expected to be within the Josephson plasma gap. Using microwave spectroscopy,
we investigate the dependence of the eigenfrequency of a fractional Josephson
vortex on its magnetic flux and on the bias current. The experimental
results are in good agreement with the theoretical predictions.Comment: submitted to PR
Thermal escape of fractional vortices in long Josephson junctions
We consider a fractional Josephson vortex in a long 0-kappa Josephson
junction. A uniformly applied bias current exerts a Lorentz force on the
vortex. If the bias current exceeds the critical current, an integer fluxon is
torn off the kappa-vortex and the junction switches to the voltage state.
In the presence of thermal fluctuations the escape process takes place with
finite probability already at subcritical values of the bias current.
We experimentally investigate the thermally induced escape of a fractional
vortex by high resolution measurements of the critical current as a function of
the topological charge kappa of the vortex and compare the results to numerical
simulations for finite junction lengths and to theoretical predictions for
infinite junction lengths. To study the effect caused by the junction geometry
we compare the vortex escape in annular and linear junctions.Comment: submitted to PR
Follow-Up Care for Breast and Colorectal Cancer Across the Globe: Survey Findings From 27 Countries
Purpose: The purpose of this study was to describe follow-up care for breast and colorectal cancer survivors in countries with varying levels of resources and highlight challenges regarding posttreatment survivorship care.
Methods: We surveyed one key stakeholder from each of 27 countries with expertise in survivorship care on questions including the components/structure of follow-up care, delivery of treatment summaries and survivorship care plans, and involvement of primary care in survivorship. Descriptive analyses were performed to characterize results across countries and variations between the WHO income categories (low, middle, high). We also performed a qualitative content analysis of narratives related to survivorship care challenges to identify major themes.
Results: Seven low- or /lower-middle-income countries (LIC/LMIC), seven upper-middle-income countries (UMIC), and 13 high-income countries (HICs) were included in this study. Results indicate that 44.4% of countries with a National Cancer Control Plan currently address survivorship care. Additional findings indicate that HICs use guidelines more often than those in LICs/LMICs and UMICs. There was great variation among countries regardless of income level. Common challenges include issues with workforce, communication and care coordination, distance/transportation issues, psychosocial support, and lack of focus on follow-up care.
Conclusion: This information can guide researchers, providers, and policy makers in efforts to improve the quality of survivorship care on a national and global basis. As the number of cancer survivors increases globally, countries will need to prioritize their long-term needs. Future efforts should focus on efforts to bridge oncology and primary care, building international partnerships, and implementation of guidelines
Challenges and opportunities of ultra-high and ultra-low fields
This presentation will focus on the possibility of (functional) brain imaging in humans at 9.4T such as rf coil design, methods to minimize B1 and B0 inhomogeneities and novel fast fMRI methods. The second part (by Kai Buckenmaier) will present our new low-field system, initial results and potential applications
Image acceleration with an 8-channel local B0 coil array compatible with parallel imaging in a 9.4T human MR scanner
A recent idea of spread spectrum MRI utilizes rapid modulations of localized magnetic fields to speed up image acquisitions. To push this concept further, we experimentally demonstrated 2D FLASH scans at 9.4T accelerated by 3-fold with modulation of a newly built 8-channel local B0 coil array, and 6-fold together with parallel imaging. Moreover, for FLASH and single shot spiral acquisitions, we designed and simulated another two modulation schemes for the B0 coil array to further investigate the advantages of independent control over each local coil for imaging acceleration
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