1,853 research outputs found
Fractional charge in the noise of Luttinger liquid systems
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between shot noise and backscattering current crucially depends on
the noise frequency relative to the ballistic frequency v_F/gL, where v_F is
the Fermi velocity, g the Luttinger liquid interaction parameter, and L the
length of the wire. In contrast to chiral Luttinger liquids, the noise is not
only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections of
plasmons at the contacts, so that the frequency dependence of the noise needs
to be analyzed to extract the fractional charge e*=e g of the bulk excitations.
We show that the frequencies needed to see interaction effects in the Fano
factor are within experimental reach.Comment: 9 pages, 4 figures, conference proceedings of Fluctuations and Noise
2005, Austin, Texa
Appearance of fractional charge in the noise of non-chiral Luttinger liquids
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between noise and backscattered current crucially depends on the
noise frequency relative to the ballistic frequency , where
is the Fermi velocity, the Luttinger liquid interaction parameter,
and the length of the wire. In contrast to chiral Luttinger liquids the
noise is not only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections at
the contacts, so that the frequency dependence of the noise needs to be
analyzed to extract the fractional charge of the bulk excitations.Comment: 4 pages, 2 figures, final version, to appear in PR
The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles
Engineered inorganic nanoparticles are essential components in the
development of nanotechnologies. For applications in nanomedicine, particles
need to be functionalized to ensure a good dispersibility in biological fluids.
In many cases however, functionalization is not sufficient : the particles
become either coated by a corona of serum proteins or precipitate out of the
solvent. In the present paper, we show that by changing the coating of iron
oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small
carboxylated polymers (poly(acrylic acid)), the colloidal stability of the
dispersion is improved and the adsorption/internalization of iron towards
living mammalian cells is profoundly affected. Citrate-coated particles are
shown to destabilize in all fetal-calf-serum based physiological conditions
tested, whereas the polymer coated particles exhibit an outstanding
dispersibility as well as a structure devoid of protein corona. The
interactions between nanoparticles and human lymphoblastoid cells are
investigated by transmission electron microscopy and flow cytometry. Two types
of nanoparticle/cell interactions are underlined. Iron oxides are found either
adsorbed on the cellular membranes, or internalized into membrane-bound
endocytosis compartments. For the precipitating citrate-coated particles, the
kinetics of interactions reveal a massive and rapid adsorption of iron oxide on
the cell surfaces. The quantification of the partition between adsorbed and
internalized iron was performed from the cytometry data. The results highlight
the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.Comment: 21 pages, 11 figures, accepted at Biomaterials (2011
Using Chandra to Unveil the High-Energy Properties of the High-Magnetic Field Radio Pulsar J1119-6127
(shortened) PSR J1119-6127 is a high magnetic field (B=4.1E13 Gauss), young
(<=1,700 year-old), and slow (P=408 ms) radio pulsar associated with the
supernova remnant (SNR) G292.2-0.5. In 2003, Chandra allowed the detection of
the X-ray counterpart of the radio pulsar, and provided the first evidence for
a compact pulsar wind nebula (PWN). We here present new Chandra observations
which allowed for the first time an imaging and spectroscopic study of the
pulsar and PWN independently of each other. The PWN is only evident in the hard
band and consists of jet-like structures extending to at least 7" from the
pulsar, with the southern `jet' being longer than the northern `jet'. The
spectrum of the PWN is described by a power law with a photon index~1.1 for the
compact PWN and ~1.4 for the southern long jet (at a fixed column density of
1.8E22/cm2), and a total luminosity of 4E32 ergs/s (0.5-7 keV), at a distance
of 8.4 kpc. The pulsar's spectrum is clearly softer than the PWN's spectrum. We
rule out a single blackbody model for the pulsar, and present the first
evidence of non-thermal (presumably magnetospheric) emission that dominates
above ~3keV. A two-component model consisting of a power law component (with
photon index ~1.5--2.0) plus a thermal component provides the best fit. The
thermal component can be fit by either a blackbody model with a temperature
kT~0.21 keV, or a neutron star atmospheric model with a temperature kT~0.14
keV. The efficiency of the pulsar in converting its rotational power, Edot,
into non-thermal X-ray emission from the pulsar and PWN is ~5E-4, comparable to
other rotation-powered pulsars with a similar Edot. We discuss our results in
the context of the X-ray manifestation of high-magnetic field radio pulsars in
comparison with rotation-powered pulsars and magnetars.Comment: 26 pages including 3 tables and 7 figures. Accepted for publication
in Ap
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