59,826 research outputs found
Poly(acrylic acid)-coated iron oxide nanoparticles : quantitative evaluation of the coating properties and applications for the removal of a pollutant dye
In this work, 6 to 12 nm iron oxide nanoparticles were synthesized and coated
with poly(acrylic acid) chains of molecular weight 2100 g/mol. Based on a
quantitative evaluation of the dispersions, the bare and coated particles were
thoroughly characterized. The number densities of polymers adsorbed at the
particle surface and of available chargeable groups were found to be 1.9 +/-
0.3 nm-2 and 26 +/- 4 nm-2, respectively. Occurring via a multi-site binding
mechanism, the electrostatic coupling leads to a solid and resilient anchoring
of the chains. To assess the efficacy of the particles for pollutant
remediation, the adsorption isotherm of methylene blue molecules, a model of
pollutant, was determined. The excellent agreement between the predicted and
measured amounts of adsorbed dyes suggests that most carboxylates participate
to the complexation and adsorption mechanisms. An adsorption of 830 mg/g was
obtained. This quantity compares well with the highest values available for
this dye.Comment: 14 pages 5 figures, accepted 06-Dec-2012; Journal of Colloid and
Interface Science (2013
Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance
We demonstrate control of the collapse and expansion of an 88Sr Bose-Einstein
condensate using an optical Feshbach resonance (OFR) near the 1S0-3P1
intercombination transition at 689 nm. Significant changes in dynamics are
caused by modifications of scattering length by up to +- ?10a_bg, where the
background scattering length of 88Sr is a_bg = -2a0 (1a0 = 0.053 nm). Changes
in scattering length are monitored through changes in the size of the
condensate after a time-of-flight measurement. Because the background
scattering length is close to zero, blue detuning of the OFR laser with respect
to a photoassociative resonance leads to increased interaction energy and a
faster condensate expansion, whereas red detuning triggers a collapse of the
condensate. The results are modeled with the time-dependent nonlinear
Gross-Pitaevskii equation.Comment: 5 pages, 3 figure
Strong eigenfunction correlations near the Anderson localization transition
We study overlap of two different eigenfunctions as compared with
self-overlap in the framework of an infinite-dimensional version of the
disordered tight-binding model. Despite a very sparse structure of the
eigenstates in the vicinity of Anderson transition their mutual overlap is
still found to be of the same order as self-overlap as long as energy
separation is smaller than a critical value. The latter fact explains
robustness of the Wigner-Dyson level statistics everywhere in the phase of
extended states. The same picture is expected to hold for usual d-dimensional
conductors, ensuring the form of the level repulsion at critical
point.Comment: 4 pages, RevTe
Rotational Symmetry Breaking in Sodium Doped Cuprates
For reasonable parameters a hole bound to a Na^{+} acceptor in
Ca_{2-x}Na_{x}CuO_{2}Cl_{2} has a doubly degenerate ground state whose
components can be represented as states with even (odd) reflection symmetry
around the x(y) -axes. The conductance pattern for one state is anisotropic as
the tip of a tunneling microscope scans above the Cu-O-Cu bonds along the
x(y)-axes. This anisotropy is pronounced at lower voltages but is reduced at
higher voltages. Qualitative agreement with recent experiments leads us to
propose this effect as an explanation of the broken local rotational symmetry.Comment: 10 pages, 4 figure
Microflow valve control system design
A design synthesis for a microflow control system is presented based on the interrogation of an analytical model, testing, and observation. The key issues relating to controlling a microflow using a variable geometry flow channel are explored through the implementation and testing of open and closed-loop control systems. The reliance of closed-loop systems on accurate flow measurement and the need for an open-loop strategy are covered. A valve and control system capable of accurately controlling flowrates between 0.09 and 400 ml/h and with a range of 900:1 is demonstrated
Efficient -separability criteria for mixed multipartite quantum states
We investigate classification and detection of entanglement of multipartite
quantum states in a very general setting, and obtain efficient -separability
criteria for mixed multipartite states in arbitrary dimensional quantum
systems. These criteria can be used to distinguish different classes of
multipartite inseparable states and can detect many important multipartite
entangled states such as GHZ states, W states, anti W states, and mixtures
thereof. They detect -nonseparable -partite quantum states which have
previously not been identified. Here . No optimization or
eigenvalue evaluation is needed, and our criteria can be evaluated by simple
computations involving components of the density matrix. Most importantly, they
can be implemented in today's experiments by using at most
local measurements.Comment: 6 pages, 4 figure
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