9,300 research outputs found
Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect
By using a highly sensitive homemade AC magnetic susceptibility technique,
the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals
with giant screw dislocations (having the structure of the Archimedean spirals)
exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height
c=1.2nm (the last parameter is responsible for creation of extended weak-link
structure around the giant defects). The magnetic field applied parallel to the
surface enters winding around the weak-link regions of the screw in the form of
the so-called spiral Josephson fluxons characterized by the temperature
dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon
structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw
dislocations) and manifests itself as a pronounced low-field peak in the
dependence of the susceptibility on magnetic field (applied normally to the
surface) in the form resembling the high-field (Abrikosov) fishtail effect.Comment: see also http://www.jetpletters.ac.ru/ps/1886/article_28701.shtm
Exact solutions for supersymmetric stationary black hole composites
Four dimensional N=2 supergravity has regular, stationary, asymptotically
flat BPS solutions with intrinsic angular momentum, describing bound states of
separate extremal black holes with mutually nonlocal charges. Though the
existence and some properties of these solutions were established some time
ago, fully explicit analytic solutions were lacking thus far. In this note, we
fill this gap. We show in general that explicit solutions can be constructed
whenever an explicit formula is known in the theory at hand for the
Bekenstein-Hawking entropy of a single black hole as a function of its charges,
and illustrate this with some simple examples. We also give an example of
moduli-dependent black hole entropy.Comment: 13 pages, 1 figur
Manifestation of finite temperature size effects in nanogranular magnetic graphite
In addition to the double phase transition (with the Curie temperatures
T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the
magnetization is observed in the bulk magnetic graphite (with an average
granular size of L=10nm), which is attributed to manifestation of the size
effects below the quantum temperature. The best fits of the high-temperature
data (using the mean-field Curie-Weiss and Bloch expressions) produced
reasonable estimates for the model parameters, such as defects mediated
effective spin exchange energy J=12meV (which defines the intragranular Curie
temperature T_C) and proximity mediated interactions between neighboring grains
(through potential barriers created by thin layers of non-magnetic graphite)
with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie
temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and
characteristic length, respectively
Goodness of fit comparisons among five bayesian models in genome-wide association of tick resistance in brazilian Hereford and Braford beef cattle.
This study aimed to compare five models fitness and top effect SNPs obtained with three different Bayesian GWAS methods applied to cattle tick resistance in Braford and Hereford
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