4,326 research outputs found
Experimental search for anisotropic flux flow resistivity in the a-b plane of optimally doped epitaxial thin films of YBCO
Transport measurements along the node and anti-node directions in the a-b
plane of optimally doped and epitaxial thin films of YBCO are reported. Low
bias magnetoresistance measurements near and below T_c show that the flux flow
resistivity along the node and anti-node directions versus magnetic field are
indistinguishable. This result suggests that within the experimental error of
our measurements, no correspondence is found between the flux pinning
properties in YBCO and the d-wave nature of the order parameter.Comment: 5 figure
Conformative Filtering for Implicit Feedback Data
Implicit feedback is the simplest form of user feedback that can be used for
item recommendation. It is easy to collect and is domain independent. However,
there is a lack of negative examples. Previous work tackles this problem by
assuming that users are not interested or not as much interested in the
unconsumed items. Those assumptions are often severely violated since
non-consumption can be due to factors like unawareness or lack of resources.
Therefore, non-consumption by a user does not always mean disinterest or
irrelevance. In this paper, we propose a novel method called Conformative
Filtering (CoF) to address the issue. The motivating observation is that if
there is a large group of users who share the same taste and none of them have
consumed an item before, then it is likely that the item is not of interest to
the group. We perform multidimensional clustering on implicit feedback data
using hierarchical latent tree analysis (HLTA) to identify user `tastes' groups
and make recommendations for a user based on her memberships in the groups and
on the past behavior of the groups. Experiments on two real-world datasets from
different domains show that CoF has superior performance compared to several
common baselines
Phases of a two dimensional large N gauge theory on a torus
We consider two-dimensional large N gauge theory with D adjoint scalars on a
torus, which is obtained from a D+2 dimensional pure Yang-Mills theory on
T^{D+2} with D small radii. The two dimensional model has various phases
characterized by the holonomy of the gauge field around non-contractible cycles
of the 2-torus. We determine the phase boundaries and derive the order of the
phase transitions using a method, developed in an earlier work
(arxiv:0910.4526), which is nonperturbative in the 'tHooft coupling and uses a
1/D expansion. We embed our phase diagram in the more extensive phase structure
of the D+2 dimensional Yang-Mills theory and match with the picture of a
cascade of phase transitions found earlier in lattice calculations
(arxiv:0710.0098). We also propose a dual gravity system based on a
Scherk-Schwarz compactification of a D2 brane wrapped on a 3-torus and find a
phase structure which is similar to the phase diagram found in the gauge theory
calculation.Comment: 28 pages (+ 17 pages of appendix + 6 pages of ref.); 8 figures; (v2)
LaTeX Showkeys command deleted; (v3) refs and minor clarifications added;
emphasized the new proposal for applying holography to nonsupersymmetric
gauge theory; (v4) modified the arguments about holography; (v5) minor
corrections, version appeared in PR
Role of Interfaces in the Proximity Effect in Anisotropic Superconductors
We report measurements of the critical temperature of YBCO-Co doped YBCO
Superconductor-Normal bilayer films. Depending on the morphology of the S-N
interface, the coupling between S and N layers can be turned on to depress the
critical temperature of S by tens of degrees, or turned down so the layers
appear almost totally decoupled. This novel effect can be explained by the
mechanism of quasiparticle transmission into an anisotropic superconductor.Comment: 13 pages, 3 figure
Substantial near-infrared radiation-driven photosynthesis of chlorophyll f-containing cyanobacteria in a natural habitat
© Kühl et al. Far-red absorbing chlorophylls are constitutively present as chlorophyll (Chl) d in the cyanobacterium Acaryochloris marina, or dynamically expressed by synthesis of Chl f, red-shifted phycobiliproteins and minor amounts of Chl d via far-red light photoacclimation in a range of cyanobacteria, which enables them to use near-infrared-radiation (NIR) for oxygenic photosynthesis. While the biochemistry and molecular physiology of Chl f-containing cyanobacteria has been unraveled in culture studies, their ecological significance remains unexplored and no data on their in situ activity exist. With a novel combination of hyperspectral imaging, confocal laser scanning microscopy, and nanoparticle-based O2 imaging, we demonstrate substantial NIR-driven oxygenic photosynthesis by endolithic, Chl f-containing cyanobacteria within natural beachrock biofilms that are widespread on (sub)tropical coastlines. This indicates an important role of NIR-driven oxygenic photosynthesis in primary production of endolithic and other shaded habitats
Post- and peritraumatic stress in disaster survivors: An explorative study about the influence of individual and event characteristics across different types of disasters
Background:
Examination of existing research on posttraumatic adjustment after disasters suggests that survivors’ posttraumatic stress levels might be better understood by investigating the influence of the characteristics of the event experienced on how people thought and felt, during the event as well as afterwards.
Objective:
To compare survivors’ perceived post- and peritraumatic emotional and cognitive reactions across different types of disasters. Additionally, to investigate individual and event characteristics.
Design:
In a European multi-centre study, 102 survivors of different disasters terror attack, flood, fire and collapse of a building were interviewed about their responses during the event. Survivors’ perceived posttraumatic stress levels were assessed with the Impact of Event Scale-Revised (IES-R). Peritraumatic emotional stress and risk perception were rated retrospectively. Influences of individual characteristics, such as socio-demographic data, and event characteristics, such as time and exposure factors, on post- and peritraumatic outcomes were analyzed.
Results:
Levels of reported post- and peritraumatic outcomes differed significantly between types of disasters. Type of disaster was a significant predictor of all three outcome variables but the factors gender, education, time since event, injuries and fatalities were only significant for certain outcomes.
Conclusion:
Results support the hypothesis that there are differences in perceived post- and peritraumatic emotional and cognitive reactions after experiencing different types of disasters. However, it should be noted that these findings were not only explained by the type of disaster itself but also by individual and event characteristics. As the study followed an explorative approach, further research paths are discussed to better understand the relationships between variables
Magnetoresistance of Junctions made of Underdoped YBCO Separated by a Ga-doped YBCO Barrier
We report magnetoresistance measurements of ramp type
superconductor-normal-superconductor (SNS) junctions. The junctions consist of
underdoped (YBCO) electrodes separated by a barrier of
. We observe a large positive magnetoresistance,
linear in the field. We suggest that this unusual magnetoresistance originates
in the field dependence of the proximity effect. Our results indicate that in
underdoped YBCO/N/YBCO SNS structures, the proximity effect does not exhibit
the anomalously long range found in optimally doped YBCO structures. From our
data we obtain the diffusion coefficient and relaxation time of quasiparticles
in underdoped YBCO.Comment: 5 figures, accepted for publication in Physical Review
Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting Films
We report observations of spontaneous formation of magnetic flux lines during
a rapid quench of YBaCuO films through T. This
effect is predicted according to the Kibble-Zurek mechanism of creation of
topological defects of the order parameter during a symmetry-breaking phase
transition. Our previous experiment, at a quench rate of 20K/sec, gave null
results. In the present experiment, the quench rate was increased to
\TEXTsymbol{>} 10 K/sec. Within experimental resolution, the dependence
of the measured flux on the cooling rate is consistent with the prediction
Current density inhomogeneity throughout the thickness of superconducting films and its effect on their irreversible magnetic properties
We calculate the distribution of the current density in superconducting
films along the direction of an external field applied perpendicular to the
film plane. Our analysis reveals that in the presence of bulk pinning is
inhomogeneous on a length scale of order the inter vortex distance. This
inhomogeneity is significantly enhanced in the presence of surface pinning. We
introduce new critical state model, which takes into account the current
density variations throughout the film thickness, and show how these variations
give rise to the experimentally observed thickness dependence of and
magnetic relaxation rate.Comment: RevTex, 9 PS figures. To appear in Phys. Rev.
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