2,953 research outputs found
Geometry fluctuations in a two-dimensional quantum antiferromagnet
The paper considers the effects of random fluctuations of the local spin
connectivities (fluctuations of the geometry) on ground state properties of a
two-dimensional quantum antiferromagnet. We analyse the behavior of spins
described by the Heisenberg model as a function of what we call phason flip
disorder, following a terminology used for aperiodic systems. The calculations
were carried out both within linear spin wave theory and using quantum Monte
Carlo simulations. An "order by disorder" phenomenon is observed in this model,
wherein antiferromagnetism is found to be enhanced by phason disorder. The
value of the staggered order parameter increases with the number of defects,
accompanied by an increase in the ground state energy of the system.Comment: 5 pages, 7 figures. Shortened and corrected version (as accepted for
publication in Physical Review B
Random quantum channels I: graphical calculus and the Bell state phenomenon
This paper is the first of a series where we study quantum channels from the
random matrix point of view. We develop a graphical tool that allows us to
compute the expected moments of the output of a random quantum channel. As an
application, we study variations of random matrix models introduced by Hayden
\cite{hayden}, and show that their eigenvalues converge almost surely. In
particular we obtain for some models sharp improvements on the value of the
largest eigenvalue, and this is shown in a further work to have new
applications to minimal output entropy inequalities.Comment: Several typos were correcte
Semi-classical analysis of real atomic spectra beyond Gutzwiller's approximation
Real atomic systems, like the hydrogen atom in a magnetic field or the helium
atom, whose classical dynamics are chaotic, generally present both discrete and
continuous symmetries. In this letter, we explain how these properties must be
taken into account in order to obtain the proper (i.e. symmetry projected)
expansion of semiclassical expressions like the Gutzwiller trace
formula. In the case of the hydrogen atom in a magnetic field, we shed light on
the excellent agreement between present theory and exact quantum results.Comment: 4 pages, 1 figure, final versio
Comment on "Turbulent heat transport near critical points: Non-Boussinesq effects" (cond-mat/0601398)
In a recent preprint (cond-mat/0601398), D. Funfschilling and G. Ahlers
describe a new effect, that they interpret as non-Boussinesq, in a convection
cell working with ethane, near its critical point. They argue that such an
effect could have spoiled the Chavanne {\it et al.} (Phys. Rev. Lett. {\bf 79}
3648, 1997) results, and not the Niemela {\it et al.} (Nature, {\bf 404}, 837,
2000) ones, which would explain the differences between these two experiments.
We show that:-i)Restricting the Chavanne's data to situations as far from the
critical point than the Niemela's one, the same discrepancy remains.-ii)The
helium data of Chavanne show no indication of the effect observed by D.
Funfschilling and G. Ahlers.Comment: comment on cond-mat/060139
Slippage of water past superhydrophobic carbon nanotube forests in microchannels
We present in this letter an experimental characterization of liquid flow
slippage over superhydrophobic surfaces made of carbon nanotube forests,
incorporated in microchannels. We make use of a micro-PIV (Particule Image
Velocimetry) technique to achieve the submicrometric resolution on the flow
profile necessary for accurate measurement of the surface hydrodynamic
properties. We demonstrate boundary slippage on the Cassie superhydrophobic
state, associated with slip lengths of a few microns, while a vanishing slip
length is found in the Wenzel state, when the liquid impregnates the surface.
Varying the lateral roughness scale L of our carbon nanotube forest-based
superhydrophobic surfaces, we demonstrate that the slip length varies linearly
with L in line with theoretical predictions for slippage on patterned surfaces.Comment: under revie
Design and production of nanoparticles formulated from nano-emulsion templates-a review
A considerable number of nanoparticle formulation methods are based on nano-emulsion templates, which in turn are generated in various ways. It must therefore be taken into account that active principles and drugs encapsulated in nanoparticles can potentially be affected by these nano-emulsion formulation processes. Such potential differences may include drug sensitivity to temperature, high-shear devices, or even contact with organic solvents. Likewise, nano-emulsion formulation processes must be chosen in function of the selected therapeutic goals of the nano-carrier suspension and its administration route. This requires the nanoparticle formulation processes (and thus the nano-emulsion formation methods) to be more adapted to the nature of the encapsulated drugs, as well as to the chosen route of administration. Offering a comprehensive review, this paper proposes a link between nano-emulsion formulation methods and nanoparticle generation, while at the same time bearing in mind the above-mentioned parameters for active molecule encapsulation. The first part will deal with the nano-emulsion template through the different formulation methods, i.e. high energy methods on the one hand, and low-energy ones (essentially spontaneous emulsification and the phase inversion temperature (PIT) method) on the other. This will be followed by a review of the different families of nanoparticles (i.e. polymeric or lipid nanospheres and nanocapsules) highlighting the links (or potential links) between these nanoparticles and the different nano-emulsion formulation methods upon which they are based
Reverse micelles-loaded lipid nanocapsules for a sustained release of doxorubicin hydrochloride
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