4,256 research outputs found
Thermodynamical Properties of Hall Systems
We study quantum Hall effect within the framework of a newly proposed
approach, which captures the principal results of some proposals. This can be
established by considering a system of particles living on the non-commutative
plane in the presence of an electromagnetic field and quantum statistical
mechanically investigate its basic features. Solving the eigenvalue equation,
we analytically derive the energy levels and the corresponding wavefunctions.
These will be used, at low temperature and weak electric field, to determine
the thermodynamical potential \Omega^{nc} and related physical quantities.
Varying \Omega^{nc} with respect to the non-commutativity parameter \theta, we
define a new function that can be interpreted as a \Omega^{nc} density.
Evaluating the particle number, we show that the Hall conductivity of the
system is \theta-dependent. This allows us to make contact with quantum Hall
effect by offering different interpretations. We study the high temperature
regime and discuss the magnetism of the system. We finally show that at
\theta=2l_B^2, the system is sharing some common features with the Laughlin
theory.Comment: 20 pages, misprints correcte
Posterior Reversible Encephalopathy Syndrome in a Child with Steroid Sensitive Nephrotic Syndrome
Introduction: Posterior reversible encephalopathy syndrome (PRES) was described in adults more than children. It was reported in cases of nephrotic syndrome which were mainly on immunosuppressant medicationsor had severe hypertension.Case report: We report the case of a 9-years old girl who presented with nephrotic syndrome and moderate hypertension. Nine days after the initiation of steroid therapy she developed disturbed level of consciousnessand generalized tonic clonic seizures. Her blood pressure was 145/90 mm Hg and she had normal serum creatinine and electrolytes levels. She was treated with furosemide and convulsions were controlled. After regainingconsciousness, the patient complained of loss of vision. Fundal  examination was normal. Magnetic resonant  imaging, axial FLAIR images and diffusion weighted imaging showed hyper-intensity signal in the parieto-occipital areas. Magnetic resonant arteriography and spectroscopy excluded ischemic insults and neoplastic process. She regained full consciousness and normal vision and was discharged from the ICU four days later. PRES was diagnosed based on the typical pattern of brainimaging and the reversibility of symptoms. .Conclusion: Nephrotic syndrome in children should be considered a risk factor for developing PRES even without the use of immunosuppressant agents or high doses of steroids
Magnetization reversal and spin dynamics exchange in biased F/AF bilayers probed with complex permeability spectra
The spin dynamics of the ferromagnetic pinned layer of
ferro-antiferromagnetic coupled NiFe/MnNi bilayers is investigated in a broad
frequency range (30 MHz-6 GHz). A phenomenological model based on the
Landau-Lifshitz equation for the complex permeability of the F/AF bilayer is
proposed. The experimental results are compared to theoretical predictions. We
show that the resonance frequencies, measured during the magnetization, are
likewise hysteretic.Comment: 4 pages, 4 figure
Spin dynamics in exchange-biased F/AF bilayers
The spin dynamics of the ferromagnetic pinned layer of
ferro-antiferromagnetic coupled NiFe/MnNi bilayers is investigated in a broad
frequency range (30 MHz-6 GHz). A phenomenological model based on the
Landau-Lifshitz equation for the complex permeability of the F/AF bilayer is
proposed. The experimental results are compared to theoretical predictions.Comment: 12 pages, 3 figures, 1 tabl
Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles
A temperature dependent coherent magnetization reversal model is proposed for
size-distributed assemblies of ferromagnetic nanoparticles and
ferromagnetic-antiferromagnetic core-shell nanoparticles. The nanoparticles are
assumed to be of uniaxial anisotropy and all aligned along their easy axis. The
thermal dependence is included by considering thermal fluctuations, implemented
via the N\'eel-Arrhenius theory. Thermal and angular dependence of
magnetization reversal loops, coercive field and exchange-bias field are
obtained, showing that F-AF size-distributed exchange-coupled nanoparticles
exhibit temperature-dependent asymmetric magnetization reversal. Also,
non-monotonic evolutions of He and Hc with T are demonstrated. The angular
dependence of Hc with T exhibits a complex behavior, with the presence of an
apex, whose position and amplitude are strongly T dependent. The angular
dependence of He with T exhibits complex behaviors, which depends on the AF
anisotropy and exchange coupling. The resulting angular behavior demonstrates
the key role of the size distribution and temperature in the magnetic response
of nanoparticles.Comment: Revised arguments in Introduction and last sectio
Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers
We report temperature dependencies of material properties such as dielectric anisotropy, birefringence, splay (Kââ), twist (Kââ), and bend (Kââ) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behavior to that of a corresponding monomer MCT5. DTC5C9 forms a twist-bend nematic (Ntb) at temperatures below the N phase. Anisotropic properties of MCT5 are typical of the rod-like mesogens. In particular, birefringence increases as the temperature is reduced, following the classic behavior, described by Haller. The elastic constants also follow the standard behavior, with their ratios being practically temperature-independent. In contrast, DTC5C9 shows a dramatic departure from the standard case. Birefringence changes non-monotonously with temperature, decreasing on approaching the N-Ntb phase transition. Kââ decreases strongly to 0.4 pN near the N - Ntb transition, although remains finite. The ratios of the elastic constants in DTC5C9 show a strong temperature dependence that can be associated with the bend-induced changes in the orientational distribution function. The measured elastic properties are consistent with the tendency of the dimeric molecules to adopt bent configurations that give rise to the Ntb phase
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