510 research outputs found
Stability w.r.t. Disturbances for the Global Attractor of Multi-Valued Semiflow Generated by Nonlinear Wave Equation
The paper investigates the issue of stability with respect to external disturbances for the global attractor of the wave equation under conditions that do not ensure the uniqueness of the solution to the initial problem. Under general conditions for nonlinear terms, it is proved that the global attractor of the undisturbed problem is locally stable in the sense of ISS and has the AG property with respect to disturbances
Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content
Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs
structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and
Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content,
are studied. In these structures DL is separated from QW by GaAs spacer with
the thickness ds = 2-5 nm. All structures possess a dielectric character of
conductivity and demonstrate a maximum in the resistance temperature dependence
Rxx(T) at the temperature {\approx} 46K which is usually associated with the
Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is
found that the Hall effect concentration of holes pH in QW does not decrease
below TC as one ordinary expects in similar systems. On the contrary, the
dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer
thickness, then increases at low temperatures more strongly than ds is smaller
and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are
interpreted in the terms of magnetic proximity effect of DL on QW, leading to
induce spin polarization of the holes in QW. Strong structural and magnetic
disorder in DL and QW, leading to the phase segregation in them is taken into
consideration. The high pH value is explained as a result of compensation of
the positive sign normal Hall effect component by the negative sign anomalous
Hall effect component.Comment: 19 pages, 6 figure
Synthesis and structural features of Fe3O4, γ-Fe2O3 and CoxFe2−xO4 materials for local low-frequency magnetic hyperthermia of cancer tumors
Discriminating Z' from anomalous trilinear gauge coupling signatures in e+e- \to W+W- at ILC with polarized beams
New heavy neutral gauge bosons Z' are predicted by many models of physics
beyond the Standard Model. It is quite possible that Z's are heavy enough to
lie beyond the discovery reach of the CERN Large Hadron Collider LHC, in which
case only indirect signatures of Z' exchanges may emerge at future colliders,
through deviations of the measured cross sections from the Standard Model
predictions. We discuss in this context the foreseeable sensitivity to Z's of
W^\pm-pair production cross sections at the e^+e^- International Linear
Collider (ILC), especially as regards the potential of distinguishing
observable effects of the Z' from analogous ones due to competitor models with
anomalous trilinear gauge couplings (AGC) that can lead to the same or similar
new physics experimental signatures at the ILC. The sensitivity of the ILC for
probing the Z-Z' mixing and its capability to distinguish these two new physics
scenarios is substantially enhanced when the polarization of the initial beams
and the produced W^\pm bosons are considered. A model independent analysis of
the Z' effects in the process e^+e^- \to W^+W^- allows to differentiate the
full class of vector Z' models from those with anomalous trilinear gauge
couplings, with one notable exception: the sequential SM (SSM)-like models can
in this process not be distinguished from anomalous gauge couplings. Results of
model dependent analysis of a specific Z' are expressed in terms of discovery
and identification reaches on the Z-Z' mixing angle and the Z' mass.Comment: 33 pages; v2: version to appear in EPJ
Identification of extra neutral gauge bosons at the International Linear Collider
Heavy neutral gauge bosons, Z's, are predicted by many theoretical schemes of
physics beyond the Standard Model, and intensive searches for their signatures
will be performed at present and future high energy colliders. It is quite
possible that Z's are heavy enough to lie beyond the discovery reach expected
at the CERN Large Hadron Collider LHC, in which case only indirect signatures
of Z' exchanges may occur at future colliders, through deviations of the
measured cross sections from the Standard Model predictions. We here discuss in
this context the foreseeable sensitivity to Z's of fermion-pair production
cross sections at an e^+e^- linear collider, especially as regards the
potential of distinguishing different Z' models once such deviations are
observed. Specifically, we assess the discovery and identification reaches on
Z' gauge bosons pertinent to the E_6, LR, ALR and SSM classes of models, that
should be attained at the planned International Linear Collider (ILC). With the
high experimental accuracies expected at the ILC, the discovery and the
identification reaches on the Z' models under consideration could be increased
substantially. In particular, the identification among the different models
could be achieved for values of Z' masses in the discovery (but beyond the
identification) reach of the LHC. An important role in enhancing such reaches
is played by the electron (and possibly the positron) longitudinally polarized
beams. Also, although the purely leptonic processes are experimentally cleaner,
the measurements of c- and b-quark pair production cross sections are found to
carry important, and complementary, information on these searches.Comment: 21 page
Justification of the coupled-mode approximation for a nonlinear elliptic problem with a periodic potential
Coupled-mode systems are used in physical literature to simplify the
nonlinear Maxwell and Gross-Pitaevskii equations with a small periodic
potential and to approximate localized solutions called gap solitons by
analytical expressions involving hyperbolic functions. We justify the use of
the one-dimensional stationary coupled-mode system for a relevant elliptic
problem by employing the method of Lyapunov--Schmidt reductions in Fourier
space. In particular, existence of periodic/anti-periodic and decaying
solutions is proved and the error terms are controlled in suitable norms. The
use of multi-dimensional stationary coupled-mode systems is justified for
analysis of bifurcations of periodic/anti-periodic solutions in a small
multi-dimensional periodic potential.Comment: 18 pages, no figure
The running of the electromagnetic coupling alpha in small-angle Bhabha scattering
A method to determine the running of alpha from a measurement of small-angle
Bhabha scattering is proposed and worked out. The method is suited to high
statistics experiments at e+e- colliders, which are equipped with luminometers
in the appropriate angular region. A new simulation code predicting small-angle
Bhabha scattering is also presentedComment: 15 pages, 3 Postscript figure
Signals of additional Z boson in e+e-\to W+W^- at the ILC with polarized beams
We consider the possibility of fingerprinting the presence of heavy
additional Z' bosons that arise naturally in extensions of the standard model
such as E_6 models and left-right symmetric models, through their mixing with
the standard model Z boson. By considering a class of observables including
total cross sections, energy distributions and angular distributions of decay
leptons we find significant deviation from the standard model predictions for
these quantities with right-handed electrons and left-handed positrons at
\sqrt{s}=800 GeV. The deviations being less pronounced at smaller centre of
mass energies as the models are already tightly constrained. Our work suggests
that the ILC should have a strong beam polarization physics program
particularly with these configurations. On the other hand, a forward backward
asymmetry and lepton fraction in the backward direction are more sensitive to
new physics with realistic polarization due to interesting interplay with the
neutrino t- channel diagram. This process complements the study of fermion pair
production processes that have been considered for discrimination between these
models.Comment: 23 pages, 9 figures, uses plain latex; substantially improved
discussion, references added, version accepted for publication in JHE
Oxygen-deficient perovskite-related (Nd0.4Sr0.6)2Ni0.8M0.2O4-δ as oxygen electrode materials for SOFC/SOEC
Perovskite-related Ln2NiO4+δ (Ln = La, Pr, Nd) nickelates with layered Ruddlesden-Popper combine redox
stability with noticeable oxygen stoichiometry changes, yielding enhanced mixed transport and
electrocatalytic properties. These unique features are promising for applications as oxygen electrodes with
good electrochemical performance in reversible SOFC/SOEC (solid oxide fuel/electrolysis cell) systems.
To date, most efforts were focused on oxygen-hyperstoichiometric Ln2NiO4+δ-based phases, whereas
nickelates with oxygen-deficient lattice remain poorly explored. Recent studies demonstrated that the
highest electrical conductivity in (Ln2-xSrx)2NiO4±δ series at elevated temperatures is observed for the
compositions containing ~ 60 at.% of strontium in A sublattice [1,2]. The present work was focused on the
characterization of (Nd0.4Sr0.6)2Ni0.8M0.2O4-δ (M = Ni, Co, Fe) nickelates for the possible use as materials
for reversible oxygen electrodes.
The ceramic materials were prepared by Pechini method with repeated annealings at 650-1200°C and
sintered at 1250-1300°C for 5 h under oxygen atmosphere. Variable-temperature XRD studies confirmed
that all studied compositions retain tetragonal K2NiF4-type structure in the temperature range 25-900°C.
The results of thermogravimetric analysis showed that the prepared nickelates has oxygen-deficient lattice
under oxidizing conditions at temperatures above 700°C. Partial substitution of nickel by cobalt or iron
results in a decrease of p-type electronic conductivity and the concentration of oxygen vacancies in the
lattice (Fig.1), but also suppresses dimensional changes associated with microcracking effects (due to
anisotropic thermal expansion of tetragonal lattice). Electrochemical performance of porous
(Nd0.4Sr0.6)2Ni0.8M0.2O4-δ electrodes in contact with Ce0.9Gd0.1O2-δ solid electrolyte was evaluated at 600-
800°C employing electrochemical impedance spectroscopy and steady-state polarization (anodic and
cathodic) measurements.publishe
Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells
We report results of investigations of structural and transport properties of
GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn
layer, separated from the QW by a 3 nm thick spacer. The structure has hole
mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher
than in known ferromagnetic two-dimensional structures. The analysis of the
electro-physical properties of these systems is based on detailed study of
their structure by means of high-resolution X-ray diffractometry and
glancing-incidence reflection, which allow us to restore the depth profiles of
structural characteristics of the QWs and thin Mn containing layers. These
investigations show absence of Mn atoms inside the QWs. The quality of the
structures was also characterized by photoluminescence spectra from the QWs.
Transport properties reveal features inherent to ferromagnetic systems: a
specific maximum in the temperature dependence of the resistance and the
anomalous Hall effect (AHE) observed in samples with both "metallic" and
activated types of conductivity up to ~100 K. AHE is most pronounced in the
temperature range where the resistance maximum is observed, and decreases with
decreasing temperature. The results are discussed in terms of interaction of
2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations
related to random distribution of Mn atoms. The AHE values are compared with
calculations taking into account its "intrinsic" mechanism in ferromagnetic
systems.Comment: 15 pages, 9 figure
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