992 research outputs found
Can antiferromagnetism and superconductivity coexist in the high-field paramagnetic superconductor Nd(O,F)FeAs?
We present measurements of the temperature and field dependencies of the
magnetization M(T,H) of Nd(O0.89F0.11)FeAs at fields up to 33T, which show that
superconductivity with the critical temperature Tc ~ 51K cannot coexist with
antiferromagnetic ordering. Although M(T,H) at 55 < T < 140K exhibits a clear
Curie-Weiss temperature dependence corresponding to the Neel temperature TN ~
11-12K, the behavior of M(T,H) below Tc is only consistent with either
paramagnetism of weakly interacting magnetic moments or a spin glass state. We
suggest that the anomalous magnetic behavior of an unusual high-field
paramagnetic superconductor Nd(O1-xFx)FeAs is mostly determined by the magnetic
Nd ions.Comment: 4 pages, 4 figure
Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field
We report on the microwave surface resistance of two polycrystalline Mg11B2
samples; one consists of pristine material, the other has been irradiated at
very high neutron fluence. It has already been reported that in the strongly
irradiated sample the two gaps merge into a single value. The mw surface
resistance has been measured in the linear regime as a function of the
temperature and the DC magnetic field, at increasing and decreasing fields. The
results obtained in the strongly irradiated sample are quite well justified in
the framework of a generalized Coffey and Clem model, in which we take into
account the field distribution inside the sample due to the critical state. The
results obtained in the pristine sample show several anomalies, especially at
low temperatures, which cannot be justified in the framework of standard models
for the fluxon dynamics. Only at temperatures near Tc and for magnetic fields
greater than 0.5Hc2(T) the experimental data can quantitatively be accounted
for by the Coffey and Clem model, provided that the upper-critical-field
anisotropy is taken into due account.Comment: RevTeX, 13 pages with 10 eps figures, in press on EPJ
Effectiveness of omalizumab in a patient with severe asthma and atopic dermatitis
The anti-IgE antibody omalizumab is currently indicated in severe asthma not controlled by standard drug therapy. Recently, new indications for omalizumab were suggested, which include atopic dermatitis (AD), a skin disorder characterized by elevated levels of IgE. We report the case of a 39-year old woman with severe asthma and severe AD, both resistant to conventional drug treatment. The patient had a IgE level of 1304 kU/L, which exceeded the recommended maximum level for treating asthma with omalizumab (stated in 700 Ku/L) but was far lower than previously reported in cases of AD treated with anti-IgE. The treatment consisted of a dose of omalizumab 375 mg every two weeks, and induced a rapid improvement of asthma, with no need of other drugs after three months, along with a progressive decline of severity of AD, which after five months was completely cured. These findings suggest the usefulness of omalizumab in patients with concomitant severe asthma and AD, also considering the pharmaco-economic balance obtained by withdrawing the multiple drugs used to treat both diseases
Enhanced flux pinning in neutron irradiated MgB2
We study the effect of neutron irradiation on the critical current density Jc
of isotopically pure polycrystalline Mg11B2 samples. For fluences in the range
1017-1018 cm-2, Jc is enhanced and its dependence on magnetic field is
significantly improved: we demonstrate that, in this regime, point-like pinning
centers are effectively introduced in the system proportionally to the neutron
fluence. Instead, for larger fluences, a strong suppression of the critical
temperature accompanied by a decrease of both the upper critical field Bc2 and
Jc is found.Comment: 13 pages, 3 igure
Neutron Irradiation of Mg11B2 : From the Enhancement to the Suppression of Superconducting Properties
In this letter we present the effect of neutron irradiation up to fluences of
3.9 1019 n/cm2 on the superconducting properties of MgB2. In order to obtain a
disorder structure homogeneously distributed, the experiment was carried out on
bulk samples prepared with the 11B isotope. Up to fluences of 1018 n/cm2 the
critical temperature is slightly diminished (36 K) and the superconducting
properties are significantly improved; the upper critical field is increased
from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K.
For larger neutron fluences the critical temperature is suppressed down to 12 K
and the superconducting properties come out strongly degraded.Comment: 13 pages, 4 figures. Submitted to Appl.Phys.Let
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