7,709 research outputs found
Activity of glucose oxidase functionalized onto magnetic nanoparticles
BACKGROUND: Magnetic nanoparticles have been significantly used for coupling with biomolecules, due to their unique properties. METHODS: Magnetic nanoparticles were synthesized by thermal co-precipitation of ferric and ferrous chloride using two different base solutions. Glucose oxidase was bound to the particles by direct attachment via carbodiimide activation or by thiophene acetylation of magnetic nanoparticles. Transmission electron microscopy was used to characterize the size and structure of the particles while the binding of glucose oxidase to the particles was confirmed using Fourier transform infrared spectroscopy. RESULTS: The direct binding of glucose oxidase via carbodiimide activity was found to be more effective, resulting in bound enzyme efficiencies between 94–100% while thiophene acetylation was 66–72% efficient. Kinetic and stability studies showed that the enzyme activity was more preserved upon binding onto the nanoparticles when subjected to thermal and various pH conditions. The overall activity of glucose oxidase was improved when bound to magnetic nanoparticles CONCLUSION: Binding of enzyme onto magnetic nanoparticles via carbodiimide activation is a very efficient method for developing bioconjugates for biological application
Non-Langevin behaviour of the uncompensated magnetisation in nanoparticles of artificial ferritin
The magnetic behaviour of nanoparticles of antiferromagnetic ferritin has
been investigated by 57Fe Mossbauer absorption spectroscopy and magnetisation
measurements, in the temperature range 2.5K-250K and with magnetic fields up to
7T. Samples containing nanoparticles with an average number of Fe atoms ranging
from 400 to 2500 were studied. The value of the anisotropy energy per unit
volume was determined and found to be in the range 3-6 10**5 ergs/cm3, which is
a value typical for ferric oxides. By comparing the results of the two
experimental methods at large field, we show that, contratry to what is
currently assumed, the uncompensated magnetisation of the feritin cores in the
superparamagnetic regime does not follow a Langevin law. For magnetic fields
below the spin-flop field, we propose an approximate law for the field and
temperature variation of the uncompensated magnetisation which has so far never
been applied in antiferromagnetic systems. This approach should more generally
hold for randomly oriented antiferro- magnetic nanoparticles systems with weak
uncompensated moments.Comment: 11 pages, 11 figure
Hysteresis and avalanches in the T=0 random-field Ising model with 2-spin-flip dynamics
We study the non-equilibrium behavior of the three-dimensional Gaussian
random-field Ising model at T=0 in the presence of a uniform external field
using a 2-spin-flip dynamics. The deterministic, history-dependent evolution of
the system is compared with the one obtained with the standard 1-spin-flip
dynamics used in previous studies of the model. The change in the dynamics
yields a significant suppression of coercivity, but the distribution of
avalanches (in number and size) stays remarkably similar, except for the
largest ones that are responsible for the jump in the saturation magnetization
curve at low disorder in the thermodynamic limit. By performing a finite-size
scaling study, we find strong evidence that the change in the dynamics does not
modify the universality class of the disorder-induced phase transition.Comment: 9 pages, 10 figure
Entanglement Cost of Nonlocal Measurements
For certain joint measurements on a pair of spatially separated particles, we
ask how much entanglement is needed to carry out the measurement exactly. For a
class of orthogonal measurements on two qubits with partially entangled
eigenstates, we present upper and lower bounds on the entanglement cost. The
upper bound is based on a recent result by D. Berry [Phys. Rev. A 75, 032349
(2007)]. The lower bound, based on the entanglement production capacity of the
measurement, implies that for almost all measurements in the class we consider,
the entanglement required to perform the measurement is strictly greater than
the average entanglement of its eigenstates. On the other hand, we show that
for any complete measurement in d x d dimensions that is invariant under all
local Pauli operations, the cost of the measurement is exactly equal to the
average entanglement of the states associated with the outcomes.Comment: 14 pages; new result in v4: cost of an arbitrary measurement
invariant under local Pauli operation
Magnetoresistance in Disordered Graphene: The Role of Pseudospin and Dimensionality Effects Unraveled
We report a theoretical low-field magnetotransport study unveiling the effect
of pseudospin in realistic models of weakly disordered graphene-based
materials. Using an efficient Kubo computational method, and simulating the
effect of charges trapped in the oxide, different magnetoconductance
fingerprints are numerically obtained in system sizes as large as 0.3
micronmeter squared, containing tens of millions of carbon atoms. In
two-dimensional graphene, a strong valley mixing is found to irreparably yield
a positive magnetoconductance (weak localization), whereas crossovers from
positive to a negative magnetoconductance (weak antilocalization) are obtained
by reducing disorder strength down to the ballistic limit. In sharp contrast,
graphene nanoribbons with lateral size as large as 10nm show no sign of weak
antilocalization, even for very small disorder strength. Our results
rationalize the emergence of a complex phase diagram of magnetoconductance
fingerprints, shedding some new light on the microscopical origin of pseudospin
effects.Comment: 8 pages, 5 figure
Theoretical limits on magnetic field strengths in low-mass stars
Observations have suggested that some low-mass stars have larger radii than
predicted by 1-D structure models. Some theoretical models have invoked very
strong interior magnetic fields (of order 1 MG or more) as a possible cause of
such large radii. Whether fields of that strength could in principle by
generated by dynamo action in these objects is unclear, and we do not address
the matter directly. Instead, we examine whether such fields could remain in
the interior of a low mass object for a significant time, and whether they
would have any other obvious signatures. First, we estimate timescales for the
loss of strong fields by magnetic buoyancy instabilities. We consider a range
of field strengths and simple morphologies, including both idealized flux tubes
and smooth layers of field. We confirm some of our analytical estimates using
thin flux tube magnetohydrodynamic (MHD) simulations of the rise of buoyant
fields in a fully-convective M-dwarf. Separately, we consider the Ohmic
dissipation of such fields. We find that dissipation provides a complementary
constraint to buoyancy: while small-scale, fibril fields might be regenerated
faster than they rise, the dissipative heating associated with such fields
would in some cases greatly exceed the luminosity of the star. We show how
these constraints combine to yield limits on the internal field strength and
morphology in low-mass stars. In particular, we find that for stars of 0.3
solar masses, no fields in flux tubes stronger than about 800 kG are
simultaneously consistent with both constraints.Comment: 19 pages, 10 figures, accepted to Ap
Effects of environmental factors on development of Pyrenopeziza brassicae (light leaf spot) apothecia on oilseed rape debris
Publication no. P-2001-0221-01R. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2001The development of Pyrenopeziza brassicae (light leaf spot) apothecia was studied on petiole debris from artificially infected oilseed rape leaves incubated at temperatures from 6 to 22 degreesC under different wetness regimes and in 16 h light/8 h dark or continuous darkness. There was no significant difference between light treatments in numbers of apothecia that developed. Mature apothecia developed at temperatures from 5 to 18 degreesC but not at 22 degreesC. The rate of apothecial development decreased as temperature decreased from 18 to 5 degreesC; mature apothecia were first observed after 5 days at 18 degreesC and after 15 days at 6 degreesC. Models were fitted to estimates of the time (days) for 50% of the maximum number of apothecia to develop (t(1); model 1, t(1) = 7.6 + 55.8(0.839)(T)) and the time for 50% of the maximum number of apothecia to decay (t(2); model 2, t(2) = 24.2 + 387(0.730)(T)) at temperatures (T) from 6 to 18 degreesC. An interruption in wetness of the petiole debris for 4 days after 4, 7, or 10 days of wetness delayed the time to observation of the first mature apothecia for approximate to4 days and decreased the number of apothecia produced (by comparison with continuous wetness). A relationship was found between water content of pod debris and electrical resistance measured by a debris-wetness sensor. The differences between values of tl predicted by model 1 and observed values of t(1) were 1 to 9 days. Model 2 did not predict t(2); apothecia decayed more quickly under natural conditions than predicted by model 2.Peer reviewe
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