8,851 research outputs found
Patterned Irradiation of YBa_2Cu_3O_(7-x) Thin Films
We present a new experiment on YBa_2Cu_3O_{7-x} (YBCO) thin films using
spatially resolved heavy ion irradiation. Structures consisting of a periodic
array of strong and weak pinning channels were created with the help of metal
masks. The channels formed an angle of +/-45 Deg with respect to the symmetry
axis of the photolithographically patterned structures. Investigations of the
anisotropic transport properties of these structures were performed. We found
striking resemblance to guided vortex motion as it was observed in YBCO single
crystals containing an array of unidirected twin boundaries. The use of two
additional test bridges allowed to determine in parallel the resistivities of
the irradiated and unirradiated parts as well as the respective current-voltage
characteristics. These measurements provided the input parameters for a
numerical simulation of the potential distribution of the Hall patterning. In
contrast to the unidirected twin boundaries in our experiment both strong and
weak pinning regions are spatially extended. The interfaces between
unirradiated and irradiated regions therefore form a Bose-glass contact. The
experimentally observed magnetic field dependence of the transverse voltage
vanishes faster than expected from the numerical simulation and we interpret
this as a hydrodynamical interaction between a Bose-glass phase and a vortex
liquid.Comment: 7 pages, 8 Eps figures included. Submitted to PR
Isotropic covariance functions on graphs and their edges
We develop parametric classes of covariance functions on linear networks and
their extension to graphs with Euclidean edges, i.e., graphs with edges viewed
as line segments or more general sets with a coordinate system allowing us to
consider points on the graph which are vertices or points on an edge. Our
covariance functions are defined on the vertices and edge points of these
graphs and are isotropic in the sense that they depend only on the geodesic
distance or on a new metric called the resistance metric (which extends the
classical resistance metric developed in electrical network theory on the
vertices of a graph to the continuum of edge points). We discuss the advantages
of using the resistance metric in comparison with the geodesic metric as well
as the restrictions these metrics impose on the investigated covariance
functions. In particular, many of the commonly used isotropic covariance
functions in the spatial statistics literature (the power exponential,
Mat{\'e}rn, generalized Cauchy, and Dagum classes) are shown to be valid with
respect to the resistance metric for any graph with Euclidean edges, whilst
they are only valid with respect to the geodesic metric in more special cases.Comment: 6 figures, 1 tabl
Content Delivery Latency of Caching Strategies for Information-Centric IoT
In-network caching is a central aspect of Information-Centric Networking
(ICN). It enables the rapid distribution of content across the network,
alleviating strain on content producers and reducing content delivery
latencies. ICN has emerged as a promising candidate for use in the Internet of
Things (IoT). However, IoT devices operate under severe constraints, most
notably limited memory. This means that nodes cannot indiscriminately cache all
content; instead, there is a need for a caching strategy that decides what
content to cache. Furthermore, many applications in the IoT space are
timesensitive; therefore, finding a caching strategy that minimises the latency
between content request and delivery is desirable. In this paper, we evaluate a
number of ICN caching strategies in regards to latency and hop count reduction
using IoT devices in a physical testbed. We find that the topology of the
network, and thus the routing algorithm used to generate forwarding
information, has a significant impact on the performance of a given caching
strategy. To the best of our knowledge, this is the first study that focuses on
latency effects in ICN-IoT caching while using real IoT hardware, and the first
to explicitly discuss the link between routing algorithm, network topology, and
caching effects.Comment: 10 pages, 9 figures, journal pape
Nested (inverse) binomial sums and new iterated integrals for massive Feynman diagrams
Nested sums containing binomial coefficients occur in the computation of
massive operator matrix elements. Their associated iterated integrals lead to
alphabets including radicals, for which we determined a suitable basis. We
discuss algorithms for converting between sum and integral representations,
mainly relying on the Mellin transform. To aid the conversion we worked out
dedicated rewrite rules, based on which also some general patterns emerging in
the process can be obtained.Comment: 13 pages LATEX, one style file, Proceedings of Loops and Legs in
Quantum Field Theory -- LL2014,27 April 2014 -- 02 May 2014 Weimar, German
Perpendicular transport properties of YBa_2Cu_3O_{7-\delta}/PrBa_2Cu_3O_{7-\delta} superlattices
The coupling between the superconducting planes of YBa2Cu3O{7-\delta}/
PrBa2Cu3O{7-\delta} superlattices has been measured by c-axis transport. We
show that only by changing the thickness of the superconducting
YBa2Cu3O{7-\delta} layers, it is possible to switch between quasi-particle and
Josephson tunneling. From our data we deduce a low temperature c-axis coherence
length of 0.27 nm.Comment: Presented at LT22, contains 2 pages and 2 figures. to appear in
Physica
Current dependence of grain boundary magnetoresistance in La_0.67Ca_0.33MnO_3 films
We prepared epitaxial ferromagnetic manganite films on bicrystal substrates
by pulsed laser ablation. Their low- and high-field magnetoresistance (MR) was
measured as a function of magnetic field, temperature and current. At low
temperatures hysteretic changes in resistivity up to 70% due to switching of
magnetic domains at the coercitive field are observed. The strongly non-ohmic
behavior of the current-voltage leads to a complete suppression of the MR
effect at high bias currents with the identical current dependence at low and
high magnetic fields. We discuss the data in view of tunneling and mesoscale
magnetic transport models and propose an explicit dependence of the spin
polarization on the applied current in the grain boundary region.Comment: 5 pages, to appear in J. Appl. Phy
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