360 research outputs found
Quantum simulation of an extra dimension
We present a general strategy to simulate a D+1-dimensional quantum system
using a D-dimensional one. We analyze in detail a feasible implementation of
our scheme using optical lattice technology. The simplest non-trivial
realization of a fourth dimension corresponds to the creation of a bivolume
geometry. We also propose single- and many-particle experimental signatures to
detect the effects of the extra dimension.Comment: 5 pages, 3 figures, revtex style;v2 minor changes, references adde
High-resolution DCE-MRI of the pituitary gland using radial k-space acquisition with compressed sensing reconstruction
BACKGROUND AND PURPOSE: The pituitary gland is located outside of the blood-brain barrier. Dynamic T1 weighted contrast enhanced sequence is considered to be the gold standard to evaluate this region. However, it does not allow assessment of intrinsic permeability properties of the gland. Our aim was to demonstrate the utility of radial volumetric interpolated brain examination with the golden-angle radial sparse parallel technique to evaluate permeability characteristics of the individual components (anterior and posterior gland and the median eminence) of the pituitary gland and areas of differential enhancement and to optimize the study acquisition time.
MATERIALS AND METHODS: A retrospective study was performed in 52 patients (group 1, 25 patients with normal pituitary glands; and group 2, 27 patients with a known diagnosis of microadenoma). Radial volumetric interpolated brain examination sequences with goldenangle radial sparse parallel technique were evaluated with an ROI-based method to obtain signal-time curves and permeability measures of individual normal structures within the pituitary gland and areas of differential enhancement. Statistical analyses were performed to assess differences in the permeability parameters of these individual regions and optimize the study acquisition time.
RESULTS: Signal-time curves from the posterior pituitary gland and median eminence demonstrated a faster wash-in and time of
maximum enhancement with a lower peak of enhancement compared with the anterior pituitary gland (P .005). Time-optimization
analysis demonstrated that 120 seconds is ideal for dynamic pituitary gland evaluation. In the absence of a clinical history, differences in the signal-time curves allow easy distinction between a simple cyst and a microadenoma.
CONCLUSIONS: This retrospective study confirms the ability of the golden-angle radial sparse parallel technique to evaluate the
permeability characteristics of the pituitary gland and establishes 120 seconds as the ideal acquisition time for dynamic pituitary gland
imaging
Simulation of gauge transformations on systems of ultracold atoms
We show that gauge transformations can be simulated on systems of ultracold
atoms. We discuss observables that are invariant under these gauge
transformations and compute them using a tensor network ansatz that escapes the
phase problem. We determine that the Mott-insulator-to-superfluid critical
point is monotonically shifted as the induced magnetic flux increases. This
result is stable against the inclusion of a small amount of entanglement in the
variational ansatz.Comment: 14 pages, 6 figure
Topological Wilson-loop area law manifested using a superposition of loops
We introduce a new topological effect involving interference of two meson
loops, manifesting a path-independent topological area dependence. The effect
also draws a connection between quark confinement, Wilson-loops and topological
interference effects. Although this is only a gedanken experiment in the
context of particle physics, such an experiment may be realized and used as a
tool to test confinement effects and phase transitions in quantum simulation of
dynamic gauge theories.Comment: Superceding arXiv:1206.2021v1 [quant-ph
XANES and EXAFS study of the local order in nanocrystalline yttria-stabilized zirconia
The local order around Zr and Y atoms of nanocrystalline yttria-stabilized zirconia (YSZ) powders with
different grain sizes has been investigated by x-ray absorption spectroscopies. The samples were prepared by
means of mechanical alloying with or without subsequent sintering treatment and also by milling commercial
YSZ. Our study is motivated by the interest in the electrical properties of grain boundaries and the controversy about the level of disorder in the intergrain regions in nanocrystalline YSZ. The x-ray absorption near edge
structure (XANES) analysis indicates that the local order of all the sintered samples is independent of the grain
size. This is confirmed by the analysis of the extended x-ray absorption fine structure, which points out also that,
in contrast to that found in sintered samples, the local order around the cation in the samples milled without
further sintering treatment extends only to the first coordination shell. Finally, the results of ab initio Zr K-edge XANES calculations lead us to conclude that the observed changes of the shape of the white line are not related to a phase transformation but reflects the short-range order present in the as-milled samples
An Optical-Lattice-Based Quantum Simulator For Relativistic Field Theories and Topological Insulators
We present a proposal for a versatile cold-atom-based quantum simulator of
relativistic fermionic theories and topological insulators in arbitrary
dimensions. The setup consists of a spin-independent optical lattice that traps
a collection of hyperfine states of the same alkaline atom, to which the
different degrees of freedom of the field theory to be simulated are then
mapped. We show that the combination of bi-chromatic optical lattices with
Raman transitions can allow the engineering of a spin-dependent tunneling of
the atoms between neighboring lattice sites. These assisted-hopping processes
can be employed for the quantum simulation of various interesting models,
ranging from non-interacting relativistic fermionic theories to topological
insulators. We present a toolbox for the realization of different types of
relativistic lattice fermions, which can then be exploited to synthesize the
majority of phases in the periodic table of topological insulators.Comment: 24 pages, 6 figure
Ionic conductivity of nanocrystalline yttria-stabilized zirconia: grain boundary and size effects
We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity
Optical lattice quantum simulator for QED in strong external fields: spontaneous pair creation and the Sauter-Schwinger effect
Spontaneous creation of electron-positron pairs out of the vacuum due to a
strong electric field is a spectacular manifestation of the relativistic
energy-momentum relation for the Dirac fermions. This fundamental prediction of
Quantum Electrodynamics (QED) has not yet been confirmed experimentally as the
generation of a sufficiently strong electric field extending over a large
enough space-time volume still presents a challenge. Surprisingly, distant
areas of physics may help us to circumvent this difficulty. In condensed matter
and solid state physics (areas commonly considered as low energy physics), one
usually deals with quasi-particles instead of real electrons and positrons.
Since their mass gap can often be freely tuned, it is much easier to create
these light quasi-particles by an analogue of the Sauter-Schwinger effect. This
motivates our proposal of a quantum simulator in which excitations of
ultra-cold atoms moving in a bichromatic optical lattice represent particles
and antiparticles (holes) satisfying a discretized version of the Dirac
equation together with fermionic anti-commutation relations. Using the language
of second quantization, we are able to construct an analogue of the spontaneous
pair creation which can be realized in an (almost) table-top experiment.Comment: 21 pages, 10 figure
Rapamycin-Loaded Leukosomes Reverse Vascular Inflammation
Rationale: Through localized delivery of rapamycin via a biomimetic drug delivery system, it is possible to reduce vascular inflammation and thus the progression of vascular disease. Objective: Use..
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