565 research outputs found
Theoretical studies of spin-dependent electrical transport through carbon nanotbes
Spin-dependent coherent quantum transport through carbon nanotubes (CNT) is
studied theoretically within a tight-binding model and the Green's function
partitioning technique. End-contacted metal/nanotube/metal systems are modelled
and next studied in the magnetic context, i.e. either with ferromagnetic
electrodes or at external magnetic fields. The former case shows that quite a
substantial giant magnetoresistance (GMR) effect occurs () for
disorder-free CNTs. Anderson-disorder averaged GMR, in turn, is positive and
reduced down to several percent in the vicinity of the charge neutrality point.
At parallel magnetic fields, characteristic Aharonov-Bohm-type oscillations are
revealed with pronounced features due to a combined effect of:
length-to-perimeter ratio, unintentional electrode-induced doping, Zeeman
splitting, and energy-level broadening. In particular, a CNT is predicted to
lose its ability to serve as a magneto-electrical switch when its length and
perimeter become comparable. In case of perpendicular geometry, there are
conductance oscillations approaching asymptotically the upper theoretical limit
to the conductance, . Moreover in the ballistic transport regime,
initially the conductance increases only slightly with the magnetic field or
remains nearly constant because spin up- and spin down-contributions to the
total magnetoresistance partially compensate each other.Comment: 15 pages, 6 figures (to apppear in Semicond. Sci. Technol.
Reversal of Nonlocal Vortex Motion in the Regime of Strong Nonequilibrium
We investigate nonlocal vortex motion in weakly pinning a-NbGe
nanostructures, which is driven by a transport current I and remotely detected
as a nonlocal voltage Vnl. At high I, the measured Vnl exhibits dramatic sign
reversals that at low and high temperatures T occur for opposite polarities of
I. The sign of Vnl becomes independent of that of the drive current at large
abs(I). These unusual effects can be nearly quantitatively explained by a novel
enhancement of magnetization, arising from a nonequilibrium distribution of
quasiparticles at high T, and a Nernst-like effect resulting from local
electron heating at low T
Nonlocal vs local vortex dynamics in the transversal flux transformer effect
In this follow-up to our recent Letter [F. Otto et al., Phys. Rev. Lett. 104,
027005 (2010)], we present a more detailed account of the superconducting
transversal flux transformer effect (TFTE) in amorphous (a-)NbGe nanostructures
in the regime of strong nonequilibrium in local vortex motion. Emphasis is put
on the relation between the TFTE and local vortex dynamics, as the former turns
out to be a reliable tool for determining the microscopic mechanisms behind the
latter. By this method, a progression from electron heating at low temperatures
T to the Larkin-Ovchinnikov effect close to the transition temperature Tc is
traced over a range 0.26 < T/Tc < 0.95. This is represented by a number of
relevant parameters such as the vortex transport entropy related to the
Nernst-like effect at low T, and a nonequilibrium magnetization enhancement
close to Tc. At intermediate T, the Larkin-Ovchinnikov effect is at high
currents modified by electron heating, which is clearly observed only in the
TFTE
SURGICAL CONDITIONS OF THE ABDOMEN VIEWED ON A NATIVE ABDOMINAL RADIOGRAPH IN AN UPRIGHT POSITION
The paper presents surgical conditions of the abdomen viewed on a native abdominal radiograph in an upright position: atresia anus, the Chilaiditi syndrome, ileus, pneumo-peritoneum, calcified pancreas. Conclusion: A native radiograph of the abdomen in an upright position is a dominant examination method in diagnostics of an acute abdomen, intestinal obstruction and perforation and other pathological conditions of the abdomen
Magnetophoresis of Flexible DNA-based Dumbbell Structures
Controlled movement and manipulation of magnetic micro and nanostructures
using magnetic forces can give rise to important applications in biomedecine,
diagnostics and immunology. We report controlled magnetophoresis and
stretching, in aqueous solution, of a DNA-based dumbbell structure containing
magnetic and diamagnetic microspheres. The velocity and stretching of the
dumbbell were experimentally measured and correlated with a theoretical model
based on the forces acting on individual magnetic beads or the entire dumbbell
structures. The results show that precise and predictable manipulation of
dumbbell structures is achievable and can potentially be applied to
immunomagnetic cell separators.Comment: 4 pages, 3 figures, preprint, to be published in AP
Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy
The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too
Monoaminergic Neuropathology in Alzheimer's disease
Acknowledgments This work was supported by The Croatian Science Foundation grant. no. IP-2014-09-9730 (āTau protein hyperphosphorylation, aggregation, and trans-synaptic transfer in Alzheimerās disease: cerebrospinal fluid analysis and assessment of potential neuroprotective compoundsā) and European Cooperation in Science and Technology (COST) Action CM1103 (āStucture-based drug design for diagnosis and treatment of neurological diseases: dissecting and modulating complex function in the monoaminergic systems of the brainā). PRH is supported in part by NIH grant P50 AG005138.Peer reviewedPostprin
Predictive value of cerebrospinal fluid visinin-like protein-1 levels for Alzheimer's disease early detection and differential diagnosis in patients with mild cognitive impairment
Visinin-like protein 1 (VILIP-1) recently emerged as a potential biomarker of Alzheimer's disease (AD). This neuronal calcium sensor protein previously used as a marker of acute ischemic stroke is elevated in the cerebrospinal fluid (CSF) of AD patients. The goal of this study was to assess CSF VILIP-1 potential in early AD diagnosis and in differentiating mild cognitive impairment (MCI) patients with and without risk of AD. Additionally, we tested VILIP-1 ability to differentiate AD from other primary causes of dementia, and predict the progression of AD-related cognitive decline. VILIP-1 levels were compared with five CSF AD biomarkers (t-tau, AĪ²1-42, p-tau181, p-tau199, and p-tau231). VILIP-1 successfully differentiated two MCI patient groups characterized by absence or presence of pathological levels of these CSF biomarkers, except for t-tau. VILIP-1/AĪ²(1-42) and VILIP-1/p-tau181 ratios also differentiated MCI patients with pathological CSF biomarker levels. However, there was no difference in VILIP-1 levels between AD and MCI patients. VILIP-1/AĪ²(1-42) and VILIP-1/p-tau231 ratios reached high sensitivities (above 70%) and very high specificities (above 85%) in differentiating AD patients from HC. Additionally, VILIP-1 differentiated AD from patients with Lewy body disease with 77.1% sensitivity and 100% specificity. VILIP-1 potential as a prognostic biomarker of cognitive decline in AD was also proved since VILIP-1/t-tau, VILIP-1/p-tau181, and VILIP-1/p-tau231 ratios correlated with MMSE scores. These data indicate that VILIP-1 alone or in combination with other AD CSF biomarkers represent a valuable marker for the early diagnosis of AD, recognition of MCI patients at higher risk to develop dementia, and in differentiating AD from LBD
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