261 research outputs found
Compositional dependence of the giant magnoresistance in FexRh1-x thin films
In this article we report on the magnetic and transport properties of FexRh1-x thin films, prepared by evaporation in high vacuum, in the composition range 0.4
Tissue identification with micro-magnetic resonance imaging in a caprine spinal fusion model
Nonunion is a major complication of spinal
interbody fusion. Currently X-ray and computed tomography
(CT) are used for evaluating the spinal fusion process.
However, both imaging modalities have limitations in
judgment of the early stages of this fusion process, as they
only visualize mineralized bone. Magnetic resonance
imaging (MRI) could be of great value as it is able to discriminate
between different types of tissue. A feasibility
study was performed in nine animals from a goat spinal
fusion study, to evaluate the detection capacity of different
tissues with micro-MRI. In this study bioresorbable polylactic
acid cages were used. Six- and 12-months follow-up
specimens were scanned in a 6.3 T micro-MRI scanner.
After scanning, the specimens were processed for histology.
Different types of tissue as well as the degradable cage
material were identified in the fusion zone and designated as
regions of interest (ROIs). Subsequently, the location of
these ROIs was determined on the corresponding micro-
MRI image, and average signal intensities of every individual
ROI were measured. An excellent match was seen
between the histological sections and micro-MRI images.
The micro-MRI images showed quantifiable differences in
signal intensity between bone with adipose marrow, bone
with hematopoietic marrow, fibrocartilage, fibrous tissue,
and degradable implant material. In time the signal intensity
of bone with adipose marrow, bone with hematopoietic red
marrow, and of fibrous tissue remained relatively constant.
On the other hand, the signal intensity of the degradable
implant material and the fibrocartilage changed significantly
in time, indicating change of structure and
composition. In conclusion, in our model using bioresorbable
cages the MRI provides us with detailed information
about the early fusion process and may therefore, allow
early diagnosis of non-union
Contrast enhancement by differently sized paramagnetic MRI contrast agents in mice with two phenotypes of atherosclerotic plaque
Interest in the use of contrast-enhanced MRI to enable in vivo specific characterization of atherosclerotic plaques is increasing. In this study the intrinsic ability of three differently sized gadolinium-based contrast agents to permeate different mouse plaque phenotypes was evaluated with MRI. A tapered cast was implanted around the right carotid artery of apoE-/- mice to induce two different plaque phenotypes: a thin cap fibroatheroma (TCFA) and a non-TCFA lesion. Both plaques were allowed to develop over 6 and 9 weeks, leading to an intermediate and advanced lesion, respectively. Signal enhancement in the carotid artery wall, following intravenous injection of Gd-HP-DO3A as well as paramagnetic micelles and liposomes was evaluated. In vivo T1-weighted MRI plaque enhancement characteristics were complemented by fluorescence microscopy and correlated to lesion phenotype. The two smallest contrast agents, i.e. Gd-HP-DO3A and micelles, were found to enhance contrast in T1-weighted MR images of all investigated plaque phenotypes. Maximum contrast enhancement ranged between 53 and 70% at 6¿min after injection of Gd-HP-DO3A with highest enhancement and longest retention in the non-TCFA lesion. Twenty-four hours after injection of micelles maximum contrast enhancement ranged between 24 and 35% in all plaque phenotypes. Administration of the larger liposomes did not cause significant contrast enhancement in the atherosclerotic plaques. Confocal fluorescence microscopy confirmed the MRI-based differences in plaque permeation between micelles and liposomes. Plaque permeation of contrast agents was strongly dependent on size. Our results implicate that, when equipped with targeting ligands, liposomes are most suitable for the imaging of plaque-associated endothelial markers due to low background enhancement, whereas micelles, which accumulate extravascularly on a long timescale, are suited for imaging of less abundant markers inside plaques. Low molecular weight compounds may be employed for target-specific imaging of highly abundant extravascular plaque-associated target
ОБМЕН СООБЩЕНИЯМИ В МИКС-СЕТЯХ
Рассмотрена идея Д.Чаума организации анонимной микс-сети с пересылкой сообщений
через каскад миксов (передаточных узлов) и последовательным шифрованием всех
промежуточных результатов. Описаны задачи, решаемые миксами в ходе обеспечения
анонимности связи, обговариваются проблемы ее безопасности
The BCS-like gap in superconductor SmFeAsO_0.85F_0.15
Since the discovery of superconductivity in the cuprates two decades ago, it
has been firmly established that the CuO_2 plane is consequential for high T_C
superconductivity and a host of other very unusual properties. A new family of
superconductors with the general composition of LaFeAsO_(1-x)F_x has recently
been discovered but with the conspicuous lacking of the CuO_2 planes, thus
raising the tantalizing questions of the different pairing mechanisms in these
oxypnictide superconductors. Intimately related to pairing in a superconductor
are the superconducting gap, its value, structure, and temperature dependence.
Here we report the observation of a single gap in the superconductor
SmFeAsO_0.85F_0.15 with T_C = 42 K as measured by Andreev spectroscopy. The gap
value of 2Delta = 13.34+/-0.3 meV gives 2Delta/k_BT_C = 3.68, close to the BCS
prediction of 3.53. The gap decreases with temperature and vanishes at T_C in a
manner consistent with the Bardeen-Cooper-Schrieffer (BCS) prediction but
dramatically different from that of the pseudogap behavior in the cuprate
superconductors. Our results clearly indicate a nodeless gap order parameter,
which is nearly isotropic in size across different sections of the Fermi
surface, and are not compatible with models involving antiferromagnetic
fluctuations, strong correlations, t-J model, and the like, originally designed
for cuprates.Comment: 8 pages, 3 figure
Andreev Reflection in Ferromagnet/Superconductor/Ferromagnet Double Junction Systems
We present a theory of Andreev reflection in a
ferromagnet/superconductor/ferromagnet double junction system. The spin
polarized quasiparticles penetrate to the superconductor in the range of
penetration depth from the interface by the Andreev reflection. When the
thickness of the superconductor is comparable to or smaller than the
penetration depth, the spin polarized quasiparticles pass through the
superconductor and therefore the electric current depends on the relative
orientation of magnetizations of the ferromagnets. The dependences of the
magnetoresistance on the thickness of the superconductor, temperature, the
exchange field of the ferromagnets and the height of the interfacial barriers
are analyzed. Our theory explains recent experimental results well.Comment: 8 pages, 9 figures, submitted to Phys. Rev.
Transport spin polarisation in SrRuO3 measured through Point Contact Andreev reflection
We report a study in which Andreev reflection using a Nb point contact is
used to measure the transport spin polarisation of the 4d itinerant ferromagnet
SrRuO3. By performing the study in high quality thin films with residual
resistivities less than 7micro-ohm-cm, we ensure that the study is done in the
ballistic limit, a regime which is difficult to reach in oxide ferromagnets.
The degree of transport spin polarisation that we find is comparable to that of
the hole doped rare-earth manganites. We conclude that the large transport spin
polarisation results mainly from a difference in the Fermi velocities between
the majority and minority spin channels in this material.Comment: Text and 2 Figure
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