135 research outputs found
Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes
We introduce the concept of computerized tomographic microscopy in magnetic
resonance imaging using the magnetic fields and field gradients from a
ferromagnetic probe. We investigate a configuration where a two-dimensional
sample is under the influence of a large static polarizing field, a small
perpendicular radio-frequency field, and a magnetic field from a ferromagnetic
sphere. We demonstrate that, despite the non-uniform and non-linear nature of
the fields from a microscopic magnetic sphere, the concepts of computerized
tomography can be applied to obtain proper image reconstruction from the
original spectral data by sequentially varying the relative sample-sphere
angular orientation. The analysis shows that the recent proposal for atomic
resolution magnetic resonance imaging of discrete periodic crystal lattice
planes using ferromagnetic probes can also be extended to two-dimensional
imaging of non-crystalline samples with resolution ranging from micrometer to
Angstrom scales.Comment: 9 pages, 11 figure
Energy-momentum balance in quantum dielectrics
We calculate the energy-momentum balance in quantum dielectrics such as
Bose-Einstein condensates. In agreement with the experiment [G. K. Campbell et
al. Phys. Rev. Lett. 94, 170403 (2005)] variations of the Minkowski momentum
are imprinted onto the phase, whereas the Abraham tensor drives the flow of the
dielectric. Our analysis indicates that the Abraham-Minkowski controversy has
its root in the Roentgen interaction of the electromagnetic field in dielectric
media
The Constitutive Relations and the Magnetoelectric Effect for Moving Media
In this paper the constitutive relations for moving media with homogeneous
and isotropic electric and magnetic properties are presented as the connections
between the generalized magnetization-polarization bivector and
the electromagnetic field F. Using the decompositions of F and ,
it is shown how the polarization vector P(x) and the magnetization vector M(x)
depend on E, B and two different velocity vectors, u - the bulk velocity vector
of the medium, and v - the velocity vector of the observers who measure E and B
fields. These constitutive relations with four-dimensional geometric
quantities, which correctly transform under the Lorentz transformations (LT),
are compared with Minkowski's constitutive relations with the 3-vectors and
several essential differences are pointed out. They are caused by the fact
that, contrary to the general opinion, the usual transformations of the
3-vectors , , , , etc. are
not the LT. The physical explanation is presented for the existence of the
magnetoelectric effect in moving media that essentially differs from the
traditional one.Comment: 18 pages, In Ref. [10] here, which corresponds to Ref. [18] in the
published paper in IJMPB, Z. Oziewicz's published paper is added. arXiv admin
note: text overlap with arXiv:1101.329
Casimir-Polder forces: A non-perturbative approach
Within the frame of macroscopic QED in linear, causal media, we study the
radiation force of Casimir-Polder type acting on an atom which is positioned
near dispersing and absorbing magnetodielectric bodies and initially prepared
in an arbitrary electronic state. It is shown that minimal and multipolar
coupling lead to essentially the same lowest-order perturbative result for the
force acting on an atom in an energy eigenstate. To go beyond perturbation
theory, the calculations are based on the exact center-of-mass equation of
motion. For a nondriven atom in the weak-coupling regime, the force as a
function of time is a superposition of force components that are related to the
electronic density-matrix elements at a chosen time. Even the force component
associated with the ground state is not derivable from a potential in the
ususal way, because of the position dependence of the atomic polarizability.
Further, when the atom is initially prepared in a coherent superposition of
energy eigenstates, then temporally oscillating force components are observed,
which are due to the interaction of the atom with both electric and magnetic
fields.Comment: 23 pages, 3 figures, additional misprints correcte
Quantized Roentgen Effect in Bose-Einstein Condensates
A classical dielectric moving in a charged capacitor can create a magnetic
field (Roentgen effect). A quantum dielectric, however, will not produce a
magnetization, except at vortices. The magnetic field outside the quantum
dielectric appears as the field of quantized monopoles
States insensitive to the Unruh effect in multi-level detectors
We give a general treatment of the spontaneous excitation rates and the
non-relativistic Lamb shift of constantly accelerated multi-level atoms as a
model for multi-level detectors. Using a covariant formulation of the dipole
coupling between the atom and the electromagnetic field we show that new
Raman-like transitions can be induced by the acceleration. Under certain
conditions these transitions can lead to stable ground and excited states which
are not affected by the non inertial motion. The magnitude of the Unruh effect
is not altered by multi-level effects. Both the spontaneous excitation rates
and the Lamb shift are not within the range of measurability.Comment: 9 Pages, late
Entropy-driven liquid-liquid separation in supercooled water
Twenty years ago Poole et al. (Nature 360, 324, 1992) suggested that the
anomalous properties of supercooled water may be caused by a critical point
that terminates a line of liquid-liquid separation of lower-density and
higher-density water. Here we present an explicit thermodynamic model based on
this hypothesis, which describes all available experimental data for
supercooled water with better quality and with fewer adjustable parameters than
any other model suggested so far. Liquid water at low temperatures is viewed as
an 'athermal solution' of two molecular structures with different entropies and
densities. Alternatively to popular models for water, in which the
liquid-liquid separation is driven by energy, the phase separation in the
athermal two-state water is driven by entropy upon increasing the pressure,
while the critical temperature is defined by the 'reaction' equilibrium
constant. In particular, the model predicts the location of density maxima at
the locus of a near-constant fraction (about 0.12) of the lower-density
structure.Comment: 7 pages, 6 figures. Version 2 contains an additional supplement with
tables for the mean-field equatio
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