179 research outputs found
Possible superconductivity in brain
The unprecedented power of the brain suggests that it may process information
quantum-mechanically. Since quantum processing is already achieved in
superconducting quantum computers, it may imply that superconductivity is the
basis of quantum computation in brain too. Superconductivity could also be
responsible for long-term memory. Following these ideas, the paper reviews the
progress in the search for superconductors with high critical temperature and
tries to answer the question about the superconductivity in brain. It focuses
on recent electrical measurements of brain slices, in which graphene was used
as a room-temperature quantum mediator, and argues that these measurements
could be interpreted as providing evidence of superconductivity in the neural
network of mammalian brains. The estimated critical temperature of
superconducting network in brain is rather high: 2063 plus-minus 114 K. A
similar critical temperature was predicted in the Little's model for
one-dimensional organic chains linked to certain molecular complexes. A
reasonable suggestion is that superconductivity develops in microtubules inside
the neurons of brain.Comment: Preprint of a review paper, 10 pages, 13 figures, Journal of
Superconductivity and Novel Magnetism, ISSN: 1557-1939, accepted, in
productio
Visualization of Spin Polarized States in Biologically-Produced Ensembles of Ferromagnetic Palladium Nanoparticles
We report visualization of spin polarized states in macroscopic ensembles of biologically-produced
ferromagnetic palladium nanoparticles using the Faraday effect-based technique of magneto-optical
imaging. The ferromagnetic palladium only exists in the form of nanoparticles. Large quantities of
palladium nanoparticles may be synthesized via biomineralization from a Pd2+ solution. The ferromagnetic
Pd nanoparticles are formed in the periplasmic space of bacteria during the hydrogen-assisted reduction of
Pd2+ ions by hydrogenases. The ferromagnetism in Pd comes from itinerant electrons. A high Curie
temperature of ferromagnetic palladium, about 200 degrees centigrade above room temperature, would
allow for a range of room-temperature magnetic applications. The processes of the isolation of electron
spins in separate nanoparticles, spin hopping, spin transport and spin correlations may even form a basis
of quantum computing. So far, measurements of the magnetic properties of Pd nanoparticles (PdNP) have
been limited by integral techniques such as SQUID magnetometry, magnetic circular dihroism and muon
spin rotation spectroscopy ( SR). In the present study, ferromagnetic Pd nanoparticles are characterized
using the technique of magneto-optical imaging. This allows visualization of the spin polarization by the
variations in the intensity of polarized light. To perform measurements at relatively low magnetic fields, a
spin injection from a colossal magnetoresistive material has been used.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3533
Observation of the Curie Transition in Palladium Bionanomaterial Using Muon Spin Rotation Spectroscopy
Palladium bionanomaterial was manufactured using the sulfate-reducing bacterium, Desulfovibrio
desulfuricans, to reduce soluble Pd(II) ions to cell-bound Pd(0). The material was examined using a
Superconducting Quantum Interference Device (SQUID) to observe bulk magnetisation over the
temperature range 10 – 300 K and by Muon Spin Rotation (μSR), which is a probe of the local magnetic
environment inside the sample, over the temperature range 200 – 700 K. Results from SQUID were used
to model the temperature dependence of ferromagnetic and paramagnetic components of the bulk
magnetisation and, by extrapolation, to predict the Curie transition temperature. Results from μSR
confirmed the accuracy of the prediction to within 20 K. The Curie transition, which started at 528 K, was
shown to be spread over a wide ( 100 K) range. This was attributed to dependence of the transition on
particle size and the range of particle sizes in the population. A competing contribution to the overall
magnetisation was observed due to partial thermal decomposition of the organic component of the
material.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3533
Ray optics in flux avalanche propagation in superconducting films
Experimental evidence of wave properties of dendritic flux avalanches in
superconducting films is reported. Using magneto-optical imaging the
propagation of dendrites across boundaries between a bare NbN film and areas
coated by a Cu-layer was visualized, and it was found that the propagation is
refracted in full quantitative agreement with Snell's law. For the studied film
of 170 nm thickness and a 0.9 mkm thick metal layer, the refractive index was
close to n=1.4. The origin of the refraction is believed to be caused by the
dendrites propagating as an electromagnetic shock wave, similar to damped modes
considered previously for normal metals. The analogy is justified by the large
dissipation during the avalanches raising the local temperature significantly.
Additional time-resolved measurements of voltage pulses generated by segments
of the dendrites traversing an electrode confirm the consistency of the adapted
physical picture.Comment: 4 pages, 4 figure
Stray-fields-based magnetoresistance mechanism in Ni80Fe20-Nb-Ni80Fe20 trilayers
We report on the transport and magnetic properties of hybrid trilayers and
bilayers that consist of low spin-polarized Ni80Fe20 exhibiting in-plane but no
uniaxial anisotropy and low-Tc Nb. We reveal a magnetoresistance effect that is
pronounced. In our trilayers the magnetoresistance exhibits an increase of two
orders of magnitude when the superconducting state is reached: from the
conventional normal-state values 0.6 % it goes up to 1000 % for temperatures
below Tc. In contrast, in the bilayers the effect is only minor since from 3%
in the normal state increases only to 70 % for temperatures below Tc.
Magnetization data of both the longitudinal and transverse magnetic components
are presented. Most importantly, we present data not only for the normal state
of Nb but also in its superconducting state. Strikingly, these data show that
below its Tc SC the Nb interlayer under the influence of the outer Ni80Fe20
layers attains a magnetization component transverse to the external field. By
comparing the transport and magnetization data we propose a candidate mechanism
that could motivate the pronounced magnetoresistance effect observed in the
trilayers. Adequate magnetostatic coupling of the outer Ni80Fe20 layers is
motivated by stray fields that emerge naturally in their whole surface due to
the multidomain magnetic structure that they attain near coercivity. Atomic
force microscopy is employed in order to examine the possibility that such
magnetostatic coupling could be promoted by interface roughness. Referring to
the bilayers, although out-of-plane rotation of the magnetization of the single
Ni80Fe20 layer is still observed, in these structures magnetostatic coupling
does not occur due to the absence of a second Ni80Fe20 one so that the observed
magnetoresistance peaks are only modest.Comment: 9 pages, 7 figure
Use of Desulfovibrio and Escherichia coli Pd-nanocatalysts in reduction of Cr(VI) and hydrogenolytic dehalogenation of polychlorinated biphenyls and used transformer oil
BACKGROUND Desulfovibrio spp. biofabricate metallic nanoparticles (e.g. ‘Bio-Pd’) which catalyse the reduction of Cr(VI) to Cr(III) and dehalogenate polychlorinated biphenyls (PCBs). Desulfovibrio spp. are anaerobic and produce H2S, a potent catalyst poison, whereas Escherichia coli can be pre-grown aerobically to high density, has well defined molecular tools, and also makes catalytically-active ‘Bio-Pd’. The first aim was to compare ‘Bio-Pd’ catalysts made by Desulfovibrio spp. and E. coli using suspended and immobilised catalysts. The second aim was to evaluate the potential for Bio-Pd-mediated dehalogenation of PCBs in used transformer oils, which preclude recovery and re-use.\ud
RESULTS Catalysis via Bio-PdD. desulfuricans and Bio-PdE. coli was compared at a mass loading of Pd:biomass of 1:3 via reduction of Cr(VI) in aqueous solution (immobilised catalyst) and hydrogenolytic release of Cl- from PCBs and used transformer oil (catalyst suspensions). In both cases Bio-PdD. desulfuricans outperformed Bio-Pd E. coli by ~3.5-fold, attributable to a ~3.5-fold difference in their Pd-nanoparticle surface areas determined by magnetic measurements (Bio-PdD. desulfuricans) and by chemisorption analysis (Bio-PdE. coli). Small Pd particles were confirmed on D. desulfuricans and fewer, larger ones on E. coli via electron microscopy. Bio-PdD. desulfuricans-mediated chloride release from used transformer oil (5.6 0.8 g mL-1 ) was comparable to that observed using several PCB reference materials. \ud
CONCLUSIONS At a loading of 1:3 Pd: biomass Bio-PdD. desulfuricans is 3.5-fold more active than Bio-PdE. coli, attributable to the relative catalyst surface areas reflected in the smaller nanoparticle sizes of the former. This study also shows the potential of Bio-PdD. desulfuricans to remediate used transformer oil
Scaling Behavior of Quasi-One-Dimensional Vortex Avalanches in Superconducting Films
Scaling behaviour of dynamically driven vortex avalanches in superconducting
YBaCuO films deposited on tilted crystalline
substrates has been observed using quantitative magneto-optical imaging. Two
films with different tilt angles are characterized by the probability
distributions of avalanche size in terms of the number of moving vortices. It
is found in both samples that these distributions follow power-laws over up to
three decades, and have exponents ranging between 1.0 and 1.4. The
distributions also show clear finite-size scaling, when the system size is
defined by the depth of the flux penetration front -- a signature of
self-organized criticality. A scaling relation between the avalanche size
exponent and the fractal dimension, previously derived theoretically from
conservation of the number of magnetic vortices in the stationary state and
shown in numerical simulations, is here shown to be satisfied also
experimentally.Comment: 7 pages, 5 figure
Characterization of Palladium Nanoparticles Produced by Healthy and Microwave-Injured Cells of Desulfovibrio desulfuricans and Escherichia coli
Numerous studies have focused on the bacterial synthesis of palladium nanoparticles
(bio-Pd NPs), via uptake of Pd (II) ions and their enzymatically-mediated reduction to Pd (0).
Cells of Desulfovibrio desulfuricans (obligate anaerobe) and Escherichia coli (facultative anaerobe,
grown anaerobically) were exposed to low-dose radiofrequency (RF) radiation(microwave (MW)
energy) and the biosynthesized Pd NPs were compared. Resting cells were exposed to microwave
energy before Pd (II)-challenge. MW-injured Pd (II)-treated cells (and non MW-treated controls)
were contacted with H2 to promote Pd(II) reduction. By using scanning transmission electron
microscopy (STEM) associated with a high-angle annular dark field (HAADF) detector and energy
dispersive X-ray (EDX) spectrometry, the respective Pd NPs were compared with respect to their mean
sizes, size distribution, location, composition, and structure. Differences were observed following
MWinjury prior to Pd(II) exposure versus uninjured controls. With D. desulfuricans the bio-Pd NPs
formed post-injury showed two NP populations with different sizes and morphologies. The first,
mainly periplasmically-located, showed polycrystalline Pd nano-branches with different crystal
orientations and sizes ranging between 20 and 30 nm. The second NPpopulation, mainly located
intracellularly, comprised single crystals with sizes between 1 and 5 nm. Bio-Pd NPs were produced
mainly intracellularly by injured cells of E. coli and comprised single crystals with a size distribution
between 1 and 3 nm. The polydispersity index was reduced in the bio-Pd made by injured cells of
E. coli and D. desulfuricans to 32% and 39%, respectively, of the values of uninjured controls, indicating
an increase in NP homogeneity of 30–40% as a result of the prior MWinjury. The observations are
discussed with respect to the different locations of Pd(II)-reducing hydrogenases in the two organisms
and with respect to potential implications for the catalytic activity of the produced NPs following
injury-associated altered NP patterning.The study was supported by NERC (grant NE/L014076/1) to LEM
Nonlocal electrodynamics of normal and superconducting films
Electrically conducting films in a time-varying transverse applied magnetic field are considered. Their behavior is strongly influenced by the self-field of the induced currents, making the electrodynamics nonlocal, and consequently difficult to analyze both numerically and analytically. We present a formalism which allows many phenomena related to superconducting and Ohmic films to be modeled and analyzed. The formalism is based on the Maxwell equations and a material current-voltage characteristics, linear for normal metals and nonlinear for superconductors, plus a careful account of the boundary conditions. For Ohmic films, we consider the response to a delta function source-field turned on instantly. As one of few problems in nonlocal electrodynamics, this has an analytical solution, which we obtain in both Fourier and real space. Next, the dynamical behavior of a square superconductor film during ramping up of the field, and subsequently returning to zero, is treated numerically. Then, this remanent state is used as initial condition for triggering thermomagnetic avalanches. The avalanches tend to invade the central part where the density of trapped flux is largest, forming dendritic patterns in excellent agreement with magneto-optical images. Detailed profiles of current and flux density are presented and discussed. Finally, the formalism is extended to multiply connected samples, and numerical results for a patterned superconducting film, a ring with a square lattice of antidots, are presented and discusse
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