314 research outputs found
Stochastic model of hysteresis
The methods of the probability theory have been used in order to build up a
new model of hysteresis. It turns out that the reversal points of the control
parameter (e. g., the magnetic field) are Markov points which determine the
stochastic evolution of the process. It has been shown that the branches of the
hysteresis loop are converging to fixed limit curves when the number of cyclic
back-and-forth variations of the control parameter between two consecutive
reversal points is large enough. This convergence to limit curves gives a clear
explanation of the accommodation process. The accommodated minor loops show the
return-point memory property but this property is obviously absent in the case
of non-accommodated minor loops which are not congruent and generally not
closed. In contrast to the traditional Preisach model the reversal point
susceptibilities are non-zero finite values. The stochastic model can provide a
good approximation of the Raylaigh quadratic law when the external parameter
varies between two sufficiently small values.Comment: 13 pages, 14 figure
Entanglement entropy in quantum spin chains with broken reflection symmetry
We investigate the entanglement entropy of a block of L sites in quasifree
translation-invariant spin chains concentrating on the effect of reflection
symmetry breaking. The majorana two-point functions corresponding to the
Jordan-Wigner transformed fermionic modes are determined in the most general
case; from these it follows that reflection symmetry in the ground state can
only be broken if the model is quantum critical. The large L asymptotics of the
entropy is calculated analytically for general gauge-invariant models, which
has, until now, been done only for the reflection symmetric sector. Analytical
results are also derived for certain non-gauge-invariant models, e.g., for the
Ising model with Dzyaloshinskii-Moriya interaction. We also study numerically
finite chains of length N with a non-reflection-symmetric Hamiltonian and
report that the reflection symmetry of the entropy of the first L spins is
violated but the reflection-symmetric Calabrese-Cardy formula is recovered
asymptotically. Furthermore, for non-critical reflection-symmetry-breaking
Hamiltonians, we find an anomaly in the behavior of the "saturation entropy" as
we approach the critical line. The paper also provides a concise but extensive
review of the block entropy asymptotics in translation invariant quasifree spin
chains with an analysis of the nearest neighbor case and the enumeration of the
yet unsolved parts of the quasifree landscape.Comment: 12 pages and 4 figure
Caffeine content of conventional and non conventional foods on the Hungarian market
Caffeine content of 377 food samples obtained from the Hungarian market was measured by a validated HPLC technique. The highest caffeine levels were observed in different instant coffees (3954±2355 mg/100 g) and ground coffee beans (1634±389 mg/100 g). Significant amount of caffeine could be detected in energy drinks (119 mg in 100 ml at the highest end). The caffeine content of different coffee drinks varied between 40 and 203 mg/100 ml. Significant amount of caffeine could be measured in special instant coffees called 2in1 and 3in1 (120 mg per serving at the highest end), cacao powders (125 mg in 100 g), in chocolates (on average, 16.1 mg and 52.5 mg in 100 g milk and dark chocolate, respectively), breakfast cereals (between 5.7 and 15.8 mg per 100 g), and ice creams (1.7–24.8 mg in 100 g)
Higher lattices, discrete two-dimensional holonomy and topological phases in (3+1)D with higher gauge symmetry
Higher gauge theory is a higher order version of gauge theory that makes possible the definition of 2-dimensional holonomy along surfaces embedded in a manifold where a gauge 2-connection is present. In this paper, we study Hamiltonian models for discrete higher gauge theory on a lattice decomposition of a manifold. We show that a construction for higher lattice gauge theory is well-defined, including in particular a Hamiltonian for topological phases of matter in 3+1 dimensions. Our construction builds upon the Kitaev quantum double model, replacing the finite gauge connection with a finite gauge 2-group 2-connection. Our Hamiltonian higher lattice gauge theory model is defined on spatial manifolds of arbitrary dimension presented by slightly combinatorialized CW-decompositions (2-lattice decompositions), whose 1-cells and 2-cells carry discrete 1-dimensional and 2-dimensional holonomy data. We prove that the ground-state degeneracy of Hamiltonian higher lattice gauge theory is a topological invariant of manifolds, coinciding with the number of homotopy classes of maps from the manifold to the classifying space of the underlying gauge 2-group.
The operators of our Hamiltonian model are closely related to discrete 2-dimensional holonomy operators for discretized 2-connections on manifolds with a 2-lattice decomposition. We therefore address the definition of discrete 2-dimensional holonomy for surfaces embedded in 2-lattices. Several results concerning the well-definedness of discrete 2-dimensional holonomy, and its construction in a combinatorial and algebraic topological setting are presented
Application of Surface Roughness Data for the Evaluation of Depth Profile Measurements of Nanoscale Multilayers
A secondary neutral mass spectrometric (SNMS) depth profile study of electrodeposited Co/Cu multilayers was performed. Depth
profile measurements were performed both in the conventional way (i.e., starting the sputtering from the final deposit surface) and
in the reverse manner (i.e., detaching the multilayers from the substrate and starting the analysis from the substrate side, which was
very smooth as compared to the final deposit surface). The latter method could yield significantly larger intensity fluctuations in
the SNMS spectra. Surface roughness data were measured with atomic force microscopy (AFM) for multilayers with different
bilayer numbers but otherwise exhibiting the same layer structure as those used for the depth profiling. The experimental AFM
surface roughness evolution was used to calculate the result of the depth profile measurements quantitatively. An excellent
agreement was obtained between this calculation and the SNMS measurements. It was shown that the decrease in the intensity
fluctuations during the depth profile analysis stems mainly from the increase in surface roughness of the samples studied,
especially in the conventional sputtering mode. It was also concluded that the thickness fluctuation of the entire multilayer deposit
and that of each layer are strongly correlated
European studies: Taking stock and looking ahead
This essay is an attempt to generalize experiences of Central and Eastern European universities in the field of European Studies over the past 20 years. The paper follows the logic of business analysis in order to come up with proposals for future action
The effects of leaching from alkaline red mud on soil biota: modelling the conditions after the Hungarian red mud disaster
A soil column experiment was set up to investigate the effect of red mud from Ajka (Hungary) on a typical soil profile from the concerned area. The chemical changes caused by the leachate of the red mud and the effects of these changes on living organisms were assessed. Ecotoxicological tests with Vibrio fischeri, Sinapis alba and Folsomia candida were performed and the number of aerobic heterotrophic microorganisms was determined. The total, plant available, exchangeable and water soluble fractions of Na, Mo, Cu, and Cr increased in the soil mostly due to their leaching from the red mud layer and partly to the increase of the pH and DOC concentration. The chemical changes had significant effects on the test organisms only in the 0 – 30 cm soil layer except for F. candida that had a lower survival rate also in the 30 – 50 cm soil layer. There were no severe toxic effects detected on the test organisms. Furthermore in case of the aerobic heterotrophic cell number and S. alba germination a stimulating effect was revealed. However, the red mud itself was toxic, therefore the performed ecotoxicology tests have justified the removal of red mud from the soil surface after the disaster
dUTPase based switch controls transfer of virulence genes in order to preserve integrity of the transferred mobile genetic elements
dUTPases ubiquitously regulate cellular dUTP levels to preserve
genome integrity. Recently, several other cellular processes were
reported to be controlled by dUTPases including the horizontal
transfer of Staphylococcus aureus pathogenicity islands (SaPI).
SaPIs are mobil genetic elements that encode virulence enhancing
factors e.g. toxins. Here, phage dUTPases were proposed to
counteract the repressor protein (Stl) and promote SaPI excision
and transfer. A G protein-like mechanism was proposed which is
unexpected in light of the kinetic mechanism of dUTPase.
Here we investigate the molecular mechanism of SaPI transfer
regulation, using numerous dUTPase variants and a wide range
of in vitro methods (steady-state and transient kinetics, VIS and
fluorescence spectroscopy, EMSA, quartz crystal microbalance,
X-ray crystallography).
Our results unambiguously show that Stl inhibits the enzymatic
activity of dUTPase in the nM concentration range and
dUTP strongly inhibits the dUTPase: Stl complexation. These
results identify Stl as a highly potent dUTPase inhibitor protein
and disprove the G protein-like mechanism. Importantly, our
results clearly show that the dUTPase:dUTP complex is inaccessible
to the Stl repressor. Unlike in small GTPases, hydrolysis of
the substrate nucleoside triphosphate (dUTP in this case) is
required prior to the interaction with the partner (Stl repressor in
this case). We propose that dUTPase can efficiently interact with
Stl and induce SaPI excision only if the cellular dUTP level is low (i.e. when dUTPase resides mainly in the apo enzyme form)
while high dUTP levels would inhibit SaPI transfer. This mechanism
may serve the preservation of the integrity of the transferred
SaPI genes and links the well-known metabolic role of
dUTPases to their newly revealed regulatory function in spread
of virulence factors
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