830 research outputs found
Coexistence of Single and Double-Quantum Vortex Lines
We discuss the configurations in which singly and doubly quantized vortex
lines may coexist in a rotating superfluid. General principles of energy
minimization lead to the conclusion that in equilibrium the two vortex species
segregate within a cylindrical vortex cluster in two coaxial domains where the
singly quantized lines are in the outer annular region. This is confirmed with
simulation calculations on discrete vortex lines. Experimentally the
coexistence can be studied in rotating superfluid He-A. With cw NMR
techniques we find the radial distribution of the two vortex species to depend
on how the cluster is prepared: (i) By cooling through in rotation,
coexistence in the minimum energy configuration is confirmed. (ii) A glassy
agglomerate is formed if one starts with an equilibrium cluster of
single-quantum vortex lines and adds to it sequentially double-quantum lines,
by increasing the rotation velocity in the superfluid state. This proves that
the energy barriers, which separate different cluster configurations, are too
high for metastabilities to anneal.Comment: 12 pages, 11 figures; Changed content, 15 pages, 14 figure
A comparative histological study of the osteoderms in the lizards Heloderma suspectum (Squamata: Helodermatidae) and Varanus komodoensis (Squamata: Varanidae)
This is the peer reviewed version of the following article: Kirby, A, Vickaryous, M, Boyde, A, et al. A comparative histological study of the osteoderms in the lizards Heloderma suspectum (Squamata: Helodermatidae) and Varanus komodoensis (Squamata: Varanidae). J Anat. 2020; 00: 1â 9. https://doi.org/10.1111/taja.13156 which has been published in final form at https://doi.org/10.1111/taja.13156
Kaon-Nucleon Scattering Amplitudes and Z-Enhancements from Quark Born Diagrams
We derive closed form kaon-nucleon scattering amplitudes using the ``quark
Born diagram" formalism, which describes the scattering as a single interaction
(here the OGE spin-spin term) followed by quark line rearrangement. The low
energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with
experiment given conventional quark model parameters. For Gev
however the I=1 elastic phase shift is larger than predicted by Gaussian
wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent
low energy KN potentials for S-wave scattering are also derived. Finally we
consider OGE forces in the related channels K, KN and K,
and determine which have attractive interactions and might therefore exhibit
strong threshold enhancements or ``Z-molecule" meson-baryon bound states.
We find that the minimum-spin, minimum-isospin channels and two additional
K channels are most conducive to the formation of bound states.
Related interesting topics for future experimental and theoretical studies of
KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte
Unusual magnetic relaxation behavior in La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3
We have carried out a systematic magnetic relaxation study, measured after
applying and switching off a 5 T magnetic field to polycrystalline samples of
La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3. The long time logarithmic relaxation rate
(LTLRR), decreased from 10 K to 150 K and increased from 150 K to 195 K in
La0.5Ca0.5MnO3. This change in behavior was found to be related to the complete
suppression of the antiferromagnetic phase above 150 K and in the presence of a
5 T magnetic field. At 195 K, the magnetization first decreased, and after a
few minutes increased slowly as a function of time. Moreover, between 200 K and
245 K, the magnetization increased throughout the measured time span. The
change in the slope of the curves, from negative to positive at about 200 K was
found to be related to the suppression of antiferromagnetic fluctuations in
small magnetic fields. A similar temperature dependence of the LTLRR was found
for the Nd0.5Sr0.5MnO3 sample. However, the temperature where the LTLRR reached
the minimum in Nd0.5Sr0.5MnO3 was lower than that of La0.5Ca0.5MnO3. This
result agrees with the stronger ferromagnetic interactions that exist in
Nd0.5Sr0.5MnO3 in comparison to La0.5Ca0.5MnO3. The above measurements
suggested that the general temperature dependence of the LTLRR and the
underlying physics were mainly independent of the particular charge ordering
system considered. All relaxation curves could be fitted using a logarithmic
law at long times. This slow relaxation was attributed to the coexistence of
ferromagnetic and antiferromagnetic interactions between Mn ions, which
produced a distribution of energy barriers.Comment: Accepted to PRB as a regular article, 10 figures, Scheduled Issue: 01
June 200
A high stability semiconductor laser system for a Sr-based optical lattice clock
We describe a frequency stabilized diode laser at 698 nm used for high
resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the
laser stabilization we use state-of-the-art symmetrically suspended optical
cavities optimized for very low thermal noise at room temperature. Two-stage
frequency stabilization to high finesse optical cavities results in measured
laser frequency noise about a factor of three above the cavity thermal noise
between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote
spectroscopy on the 88Sr clock transition by transferring the laser output over
a phase-noise-compensated 200 m-long fiber link between two separated
laboratories. Our dedicated fiber link ensures a transfer of the optical
carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration
time, which could enable the observation of the strontium clock transition with
an atomic Q of 10^{14}. Furthermore, with an eye towards the development of
transportable optical clocks, we investigate how the complete laser system
(laser+optics+cavity) can be influenced by environmental disturbances in terms
of both short- and long-term frequency stability.Comment: 9 pages, 9 figures, submitted to Appl. Phys.
Intravital FRAP imaging using an E-cadherin-GFP mouse reveals disease- and drug-dependent dynamic regulation of cell-cell junctions in live tissue
E-cadherin-mediated cell-cell junctions play a prominent role in maintaining the epithelial architecture. The disruption or deregulation of these adhesions in cancer can lead to the collapse of tumor epithelia that precedes invasion and subsequent metastasis. Here we generated an E-cadherin-GFP mouse that enables intravital photobleaching and
quantification of E-cadherin mobility in live tissue without affecting normal biology. We demonstrate the broad applications of this mouse by examining
E-cadherin regulation in multiple tissues, including mammary, brain, liver, and kidney tissue, while specifically monitoring E-cadherin mobility during
disease progression in the pancreas. We assess E-cadherin stability in native pancreatic tissue upon genetic manipulation involving Kras and p53
or in response to anti-invasive drug treatment and gain insights into the dynamic remodeling of E-cadherin during in situ cancer progression. FRAP in the E-cadherin-GFP mouse, therefore, promises to be a valuable tool to fundamentally expand our understanding of E-cadherin-mediated events in native microenvironments
Light curves and radio structure for the September 1999 transient event in XTE J1819-254 (=SAX J1819.3-2325 = V4641 Sagittarii)
Response of Wheat Fungal Diseases to Elevated Atmospheric CO2 Level
Infection with fungal pathogens on wheat varieties with different levels of resistance was
tested at ambient (NC, 390 ppm) and elevated (EC, 750 ppm) atmospheric CO2 levels in the
phytotron. EC was found to affect many aspects of the plant-pathogen interaction. Infection
with most fungal diseases was usually found to be promoted by elevated CO2 level in susceptible
varieties. Powdery mildew, leaf rust and stem rust produced more severe symptoms on
plants of susceptible varieties, while resistant varieties were not infected even at EC. The penetration
of Fusarium head blight (FHB) into the spike was delayed by EC in Mv Mambo, while
it was unaffected in Mv Regiment and stimulated in Mv Emma. EC increased the propagation
of FHB in Mv Mambo and Mv Emma. Enhanced resistance to the spread of Fusarium within
the plant was only found in Mv Regiment, which has good resistance to penetration but poor
resistance to the spread of FHB at NC. FHB infection was more severe at EC in two varieties,
while the plants of Mv Regiment, which has the best field resistance at NC, did not exhibit a
higher infection level at EC.
The above results suggest that breeding for new resistant varieties will remain a useful
means of preventing more severe infection in a future with higher atmospheric CO2 levels
Ripples in a pond: Do social work students need to learn about terrorism?
In the face of heightened awareness of terrorism, however it is defined, the challenges for social work are legion. Social work roles may include working with the military to ensure the well-being of service-men and women and their families when bereaved or injured, as well as being prepared to support the public within the emergency context of an overt act of terrorism. This paper reviews some of the literature concerning how social work responds to confl ict and terrorism before reporting a smallscale qualitative study examining the views of social work students, on a qualifying programme in the UK, of terrorism and the need for knowledge and understanding as part of their education
Level models of continuing professional development evaluation: a grounded review and critique
Continuing professional development (CPD) evaluation in education has been heavily influenced by âlevel modelsâ, deriving from the work of Kirkpatrick and Guskey in particular, which attempt to trace the processes through which CPD interventions achieve outcomes. This paper considers the strengths and limitations of such models, and in particular the degree to which they are able to do justice to the complexity of CPD and its effects. After placing level models within the broader context of debates about CPD evaluation, the paper reports our experience of developing such models heuristically for our own evaluation practice. It then draws on positivist, realist and constructivist traditions to consider some more fundamental ontological and epistemological questions to which they give rise. The paper concludes that level models can be used in a number of ways and with differing emphases, and that choices made about their use will need to reflect both theoretical choices and practical considerations
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