719 research outputs found
On almost randomizing channels with a short Kraus decomposition
For large d, we study quantum channels on C^d obtained by selecting randomly
N independent Kraus operators according to a probability measure mu on the
unitary group U(d). When mu is the Haar measure, we show that for
N>d/epsilon^2. For d=2^k (k qubits), this includes Kraus operators
obtained by tensoring k random Pauli matrices. The proof uses recent results on
empirical processes in Banach spaces.Comment: We added some background on geometry of Banach space
Ground state of the spin-1/2 Heisenberg antiferromagnet on an Archimedean 4-6-12 lattice
An investigation of the N\'eel Long Range Order (NLRO) in the ground state of
antiferromagnetic Heisenberg spin system on the two-dimensional, uniform,
bipartite lattice consisting of squares, hexagons and dodecagons is presented.
Basing on the analysis of the order parameter and the long-distance correlation
function the NLRO is shown to occur in this system. Exact diagonalization and
variational (Resonating Valence Bond) methods are applied.Comment: 4 pages, 6 figure
Specific Internalisation of Gold Nanoparticles into Engineered Porous Protein Cages via Affinity Binding
Porous protein cages are supramolecular protein self-assemblies presenting pores that allow the access of surrounding molecules and ions into their core in order to store and transport them in biological environments. Protein cages’ pores are attractive channels for the internalisation of inorganic nanoparticles and an alternative for the preparation of hybrid bioinspired nanoparticles. However, strategies based on nanoparticle transport through the pores are largely unexplored, due to the difficulty of tailoring nanoparticles that have diameters commensurate with the pores size and simultaneously displaying specific affinity to the cages’ core and low non-specific binding to the cages’ outer surface. We evaluated the specific internalisation of single small gold nanoparticles, 3.9 nm in diameter, into porous protein cages via affinity binding. The E2 protein cage derived from the Geobacillus stearothermophilus presents 12 pores, 6 nm in diameter, and an empty core of 13 nm in diameter. We engineered the E2 protein by site-directed mutagenesis with oligohistidine sequences exposing them into the cage’s core. Dynamic light scattering and electron microscopy analysis show that the structures of E2 protein cages mutated with bis- or penta-histidine sequences are well conserved. The surface of the gold nanoparticles was passivated with a self-assembled monolayer made of a mixture of short peptidols and thiolated alkane ethylene glycol ligands. Such monolayers are found to provide thin coatings preventing non-specific binding to proteins. Further functionalisation of the peptide coated gold nanoparticles with Ni2+ nitrilotriacetic moieties enabled the specific binding to oligohistidine tagged cages. The internalisation via affinity binding was evaluated by electron microscopy analysis. From the various mutations tested, only the penta-histidine mutated E2 protein cage showed repeatable and stable internalisation. The present work overcomes the limitations of currently available approaches and provides a new route to design tailored and well-controlled hybrid nanoparticles
Bubble-Mediated Gas Transfer and Gas Transfer Suppression of DMS and CO2
Direct dimethyl sulfide (DMS) flux measurements using eddy covariance have shown a suppression of gas transfer at medium to high wind speed. However, not all eddy covariance measurements show evidence of this suppression. Processes, such as wave-wind interaction and surfactants, have been postulated to cause this suppression. We measured DMS and carbon dioxide eddy covariance fluxes during the Asian summer monsoon in the western tropical Indian Ocean (July and August 2014). Both fluxes and their respective gas transfer velocities show signs of a gas transfer suppression above 10 m/s. Using a wind-wave interaction, we describe a flow separation process that could be responsible for a suppression of gas transfer. As a result we provide a Reynolds number-based parameterization, which states the likelihood of a gas transfer suppression for this cruise and previously published gas transfer data. Additionally, we compute the difference in the gas transfer velocities of DMS and CO2 to estimate the bubble-mediated gas transfer using a hybrid model with three whitecap parameterizations
Infrared Properties of Electron Doped Cuprates: Tracking Normal State Gaps and Quantum Critical Behavior in Pr(2-x)Ce(x)CuO(4)
We report the temperature dependence of the infrared-visible conductivity of
Pr(2-x)Ce(x)CuO(4) thin films. When varying the doping from a
non-superconducting film (x = 0.11) to a superconducting overdoped film (x =
0.17), we observe, up to optimal doping (x = 0.15), a partial gap opening. A
model combining a spin density wave gap and a frequency and temperature
dependent self energy reproduces our data reasonably well. The magnitude of
this gap extrapolates to zero for x ~ 0.17 indicating the coexistence of
magnetism and superconductivity in this material and the existence of a quantum
critical point at this Ce concentration.Comment: 5 pages 6 figures include
Quantum Gauge Equivalence in QED
We discuss gauge transformations in QED coupled to a charged spinor field,
and examine whether we can gauge-transform the entire formulation of the theory
from one gauge to another, so that not only the gauge and spinor fields, but
also the forms of the operator-valued Hamiltonians are transformed. The
discussion includes the covariant gauge, in which the gauge condition and
Gauss's law are not primary constraints on operator-valued quantities; it also
includes the Coulomb gauge, and the spatial axial gauge, in which the
constraints are imposed on operator-valued fields by applying the
Dirac-Bergmann procedure. We show how to transform the covariant, Coulomb and
spatial axial gauges to what we call
``common form,'' in which all particle excitation modes have identical
properties. We also show that, once that common form has been reached, QED in
different gauges has a common time-evolution operator that defines
time-translation for states that represent systems of electrons and photons.
By combining gauge transformations with changes of representation from
standard to common form, the entire apparatus of a gauge theory can be
transformed from one gauge to another.Comment: Contribution for a special issue of Foundations of Physics honoring
Fritz Rohrlich; edited by Larry P. Horwitz, Tel-Aviv University, and Alwyn
van der Merwe, University of Denver (Plenum Publishing, New York); 40 pages,
REVTEX, Preprint UCONN-93-3, 1 figure available upon request from author
Localized f-electron magnetism in the semimetal Ce3Bi4Au3
CeBiAu crystallizes in the same non-centrosymmetric cubic
structure as the prototypical Kondo insulator CeBiPt. Here we
report the physical properties of CeBiAu single crystals
using magnetization, thermodynamic, and electrical-transport measurements.
Magnetic-susceptibility and heat-capacity data reveal antiferromagnetic (AFM)
order below K. The magnetic entropy reaches ln2
slightly above , which suggests localized -moments in a doublet ground
state. Multiple field-induced magnetic transitions are observed at temperatures
below , which indicate a complex spin structure with competing
interactions. CeBiAu shows semimetallic behavior in
electrical resistivity measurements in contrast to the majority of reported
Cerium-based 343 compounds. Electrical-resistivity measurements under
hydrostatic pressure reveal a slight enhancement of under pressures up to
2.3 GPa, which supports a scenario wherein CeBiAu belongs to
the far left of the Doniach phase diagram dominated by
Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Using realistic many-body
simulations, we confirm the semi-metallic electronic structure of
CeBiAu and quantitatively reproduce its local moment behavior
in the paramagnetic state.Comment: 10 pages, 10 figure
Localized <i>f</i>-electron magnetism in the semimetal Ce<sub>3</sub>Bi<sub>4</sub>Au<sub>3</sub>
Ce3Bi4Au3 crystallizes in the same noncentrosymmetric cubic structure as the prototypical Kondo insulator Ce3Bi4Pt3. Here we report the physical properties of Ce3Bi4Au3 single crystals using magnetization, thermodynamic, and electrical-transport measurements. Magnetic-susceptibility and heat-capacity data reveal antiferromagnetic order below TN=3.2K. The magnetic entropy Smag reaches Rln2 slightly above TN, which suggests localized 4f moments in a doublet ground state. Multiple field-induced magnetic transitions are observed at temperatures below TN, which indicate a complex spin structure with competing interactions. Ce3Bi4Au3 shows semimetallic behavior in electrical resistivity in contrast to the majority of reported cerium-based 343 compounds which are semiconducting. Electrical-resistivity measurements under hydrostatic pressure reveal a slight enhancement of TN under pressures up to 2.3 GPa, which supports a scenario wherein Ce3Bi4Au3 belongs to the far left of the Doniach phase diagram dominated by Ruderman-Kittel-Kasuya-Yosida interactions. Using realistic many-body simulations, we confirm the semimetallic electronic structure of Ce3Bi4Au3 and quantitatively reproduce its local moment behavior in the paramagnetic state.</p
- …