10,696 research outputs found
Statistical switching kinetics in ferroelectrics
By assuming a more realistic nucleation and polarization reversal scenario we
build a new statistical switching model for ferroelectrics, which is different
from either the Kolmogorov-Avrami-Ishibashi (KAI) model or the
Nucleation-Limited-Switching (NLS) model. After incorporating a time-dependent
depolarization field this model gives a good description about the retardation
behavior in polycrystalline thin films at medium or low fields, which can not
be described by the traditional KAI model. This model predicts correctly n=1
for polycrystalline thin films at high Eappl or ceramic bulks in the ideal
case
Periodic and Localized Solutions of the Long Wave-Short Wave Resonance Interaction Equation
In this paper, we investigate the (2+1) dimensional long wave-short wave
resonance interaction (LSRI) equation and show that it possess the Painlev\'e
property. We then solve the LSRI equation using Painlev\'e truncation approach
through which we are able to construct solution in terms of three arbitrary
functions. Utilizing the arbitrary functions present in the solution, we have
generated a wide class of elliptic function periodic wave solutions and
exponentially localized solutions such as dromions, multidromions, instantons,
multi-instantons and bounded solitary wave solutions.Comment: 13 pages, 6 figure
Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers
We have investigated the size effect in lead zirconate titanate (PZT) thin
films with a range of manganese (Mn) doping concentrations. We found that the
size effect in the conventional Pt/PZT/Pt thin-film capacitors could be
systematically reduced and almost completely eliminated by increasing Mn doping
concentration. The interfacial layer at the electrode-film interface appears to
disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed
by the fits using the conventional in-series capacitor model. Our work
indicates that the size effect in ferroelectrics is extrinsic in nature,
supporting the work by Saad et al. Other implications of our results have also
been discussed. By comparing a variety of experimental studies in the
literature we propose a scenario that the dead layer between PZT (or barium
strontium titanate, BST) and metal electrodes such as Pt and Au might have a
defective pyrochlore/fluorite structure (possibly with a small portion of
ferroelectric perovskite phase).Comment: 21 pages, 6 figure
Phase Separation of Bismuth Ferrite into Magnetite under Voltage Stressing
Micro-Raman studies show that under ~700 kV/cm of d.c. voltage stressing for
a few seconds, thin-film bismuth ferrite BiFeO3 phase separates into magnetite
Fe3O4. No evidence is found spectroscopically of hemite alpha-Fe2O3, maghemite
gamma-Fe2O3, or of Bi2O3. This relates to the controversy regarding the
magnitude of magnetization in BiFeO3.Comment: 9 pages and 2 figure
Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface
We show that the accumulation of spin-polarized electrons at a forward-biased
Schottky tunnel barrier between Fe and n-GaAs can be detected electrically. The
spin accumulation leads to an additional voltage drop across the barrier that
is suppressed by a small transverse magnetic field, which depolarizes the spins
in the semiconductor. The dependence of the electrical accumulation signal on
magnetic field, bias current, and temperature is in good agreement with the
predictions of a drift-diffusion model for spin-polarized transport.Comment: Submitted to Phys. Rev. Let
Vortices, circumfluence, symmetry groups and Darboux transformations of the (2+1)-dimensional Euler equation
The Euler equation (EE) is one of the basic equations in many physical fields
such as fluids, plasmas, condensed matter, astrophysics, oceanic and
atmospheric dynamics. A symmetry group theorem of the (2+1)-dimensional EE is
obtained via a simple direct method which is thus utilized to find \em exact
analytical \rm vortex and circumfluence solutions. A weak Darboux
transformation theorem of the (2+1)-dimensional EE can be obtained for \em
arbitrary spectral parameter \rm from the general symmetry group theorem. \rm
Possible applications of the vortex and circumfluence solutions to tropical
cyclones, especially Hurricane Katrina 2005, are demonstrated.Comment: 25 pages, 9 figure
Coupled KdV equations derived from atmospherical dynamics
Some types of coupled Korteweg de-Vries (KdV) equations are derived from an
atmospheric dynamical system. In the derivation procedure, an unreasonable
-average trick (which is usually adopted in literature) is removed. The
derived models are classified via Painlev\'e test. Three types of
-function solutions and multiple soliton solutions of the models are
explicitly given by means of the exact solutions of the usual KdV equation. It
is also interesting that for a non-Painlev\'e integrable coupled KdV system
there may be multiple soliton solutions.Comment: 19 pages, 2 figure
Metoda za optimizaciju tehničkih parametara liofilizacije
Vacuum freeze-drying is a technique that makes a material dehydrate at low temperature and low pressure, and it has many merits. A control system is designed and developed based on a certain area freeze-drying machine. A test by the control system is done to optimize the freeze-drying technical parameters. According to the test results, by the method of quadratic orthogonal experiment, the key parameters, including duration, temperature and vacuum of freeze-drying, are analysed and optimized. The test proves the optimized parameters valid for certain vacuum freeze-drying machines and certain bacterins. Furthermore, the optimized parameters show that the vacuum freeze-drying method is useful for any area vacuum freeze-drying machine and any bacterin.Liofilizacija u vakuumu postupak je koji dehidrira materijal pri niskoj temperaturi i niskom tlaku, što ima mnogo prednosti. Kontrolni sustav dizajniran je i razvijen za određeni uređaj za liofilizaciju. Kako bi se optimizirali tehnički parametri liofilizacije, provedeno je ispitivanje od strane nadzornog sustava. Prema rezultatima, metodom kvadratnog ortogonalnog eksperimenta, analizirani su i optimizirani ključni parametri uključujući trajanje, temperaturu i razinu vakuuma liofilizacije. Ispitivanje dokazuje da optimizirani parametri vrijede za određene uređaje za liofilizaciju i određene bakterine. Dodatno, optimizirani parametri pokazuju da je liofilizacija upotrebljiva za bilo koji uređaj za liofilizaciju u vakuumu i bilo koji bakterin
Optical and electrical spin injection and spin transport in hybrid Fe/GaAs devices
We discuss methods for imaging the nonequilibrium spin polarization of
electrons in Fe/GaAs spin transport devices. Both optically- and
electrically-injected spin distributions are studied by scanning
magneto-optical Kerr rotation microscopy. Related methods are used to
demonstrate electrical spin detection of optically-injected spin polarized
currents. Dynamical properties of spin transport are inferred from studies
based on the Hanle effect, and the influence of strain on spin transport data
in these devices is discussed.Comment: 5 pages, 6 figs. ICPS-28 proceedings (July'06, Vienna) for J. Appl.
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