2,328 research outputs found
XMM-Newton, Chandra, and CGPS observations of the Supernova Remnants G85.4+0.7 and G85.9-0.6
We present an XMM-Newton detection of two low radio surface brightness SNRs,
G85.4+0.7 and G85.9-0.6, discovered with the Canadian Galactic Plane Survey
(CGPS). High-resolution XMM-Newton images revealing the morphology of the
diffuse emission, as well as discrete point sources, are presented and
correlated with radio and Chandra images. The new data also permit a
spectroscopic analysis of the diffuse emission regions, and a spectroscopic and
timing analysis of the point sources. Distances have been determined from HI
and CO data to be 3.5 +/- 1.0 kpc for SNR G85.4+0.7 and 4.8 +/- 1.6 kpc for SNR
G85.9-0.6. The SNR G85.4+0.7 is found to have a temperature of ~12-13 MK and a
0.5-2.5 keV luminosity of ~1-4 x 10^33 D(3.5)^2 erg/s (where D(3.5) is the
distance in units of 3.5 kpc), with an electron density n_e of
~0.07-0.16(fD(3.5))^-1/2 cm^-3 (where f is the volume filling factor), and a
shock age of ~9-49(fD(3.5))^1/2 kyr. The SNR G85.9-0.6 is found to have a
temperature of ~15-19 MK and a 0.5-2.5 keV luminosity of ~1-4 x 10^34 D(4.8)^2
erg/s (where D(4.8) is the distance in units of 4.8 kpc), with an electron
density n_e of ~0.04-0.10(fD(4.8))^-1/2 cm^-3 and a shock age of
~12-42(fD(4.8))^1/2 kyr. Based on the data presented here, none of the point
sources appears to be the neutron star associated with either SNR.Comment: 30 pages using emulateapj, 16 figures with quality reduced for
astro-ph only. The original version with high-resolution figures can be
downloaded from:
http://www.physics.umanitoba.ca/~samar/astro-ph/G85s-ms09102007.pdf To appear
in ApJ (Jan 20 2008 issue, v673, n1
The tunneling conductance between a superconducting STM tip and an out-of-equilibrium carbon nanotube
We calculate the current and differential conductance for the junction
between a superconducting (SC) STM tip and a Luttinger liquid (LL). For an
infinite single-channel LL, the SC coherence peaks are preserved in the
tunneling conductance for interactions weaker than a critical value, while for
strong interactions (g <0.38), they disappear and are replaced by cusp-like
features. For a finite-size wire in contact with non-interacting leads, we find
however that the peaks are restored even for extremely strong interactions. In
the presence of a source-drain voltage the peaks/cusps split, and the split is
equal to the voltage. At zero temperature, even very strong interactions do not
smear the two peaks into a broader one; this implies that the recent
experiments of Y.-F. Chen et. al. (Phys. Rev. Lett. 102, 036804 (2009)) do not
rule out the existence of strong interactions in carbon nanotubes.Comment: 8 pages, 3 figure
AC conductance and non-symmetrized noise at finite frequency in quantum wires and carbon nanotubes
We calculate the AC conductance and the finite-frequency non-symmetrized
noise in interacting quantum wires and single-wall carbon nanotubes in the
presence of an impurity. We observe a strong asymmetry in the frequency
spectrum of the non-symmetrized excess noise, even in the presence of the
metallic leads. We find that this asymmetry is proportional to the differential
excess AC conductance of the system, defined as the difference between the AC
differential conductances at finite and zero voltage, and thus disappears for a
linear system. In the quantum regime, for temperatures much smaller than the
frequency and the applied voltage, we find that the emission noise is exactly
equal to the impurity partition noise. For the case of a weak impurity we
expand our results for the AC conductance and the noise perturbatively. In
particular, if the impurity is located in the middle of the wire or at one of
the contacts, our calculations show that the noise exhibits oscillations with
respect to frequency, whose period is directly related to the value of the
interaction parameter
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
Dynamics of one-dimensional Bose liquids: Andreev-like reflection at Y-junctions and absence of the Aharonov-Bohm effect
We study one dimensional Bose liquids of interacting ultracold atoms in the
Y-shaped potential when each branch is filled with atoms. We find that the
excitation packet incident on a single Y-junction should experience a negative
density reflection analogous to the Andreev reflection at normal-superconductor
interfaces, although the present system does not contain fermions. In a ring
interferometer type configuration, we find that the transport is completely
insensitive to the (effective) flux contained in the ring, in contrast to the
Aharonov-Bohm effect of a single particle in the same geometry.Comment: 4 pages, 2 figures, final versio
Transport properties of single channel quantum wires with an impurity: Influence of finite length and temperature on average current and noise
The inhomogeneous Tomonaga Luttinger liquid model describing an interacting
quantum wire adiabatically coupled to non-interacting leads is analyzed in the
presence of a weak impurity within the wire. Due to strong electronic
correlations in the wire, the effects of impurity backscattering, finite bias,
finite temperature, and finite length lead to characteristic non-monotonic
parameter dependencies of the average current. We discuss oscillations of the
non-linear current voltage characteristics that arise due to reflections of
plasmon modes at the impurity and quasi Andreev reflections at the contacts,
and show how these oscillations are washed out by decoherence at finite
temperature. Furthermore, the finite frequency current noise is investigated in
detail. We find that the effective charge extracted in the shot noise regime in
the weak backscattering limit decisively depends on the noise frequency
relative to , where is the Fermi velocity, the
Tomonaga Luttinger interaction parameter, and the length of the wire. The
interplay of finite bias, finite temperature, and finite length yields rich
structure in the noise spectrum which crucially depends on the
electron-electron interaction. In particular, the excess noise, defined as the
change of the noise due to the applied voltage, can become negative and is
non-vanishing even for noise frequencies larger than the applied voltage, which
are signatures of correlation effects.Comment: 28 pages, 19 figures, published version with minor change
Local ethnic composition and natives' and immigrants' geographic mobility in France, 1982-1999
This article provides empirical results on patterns of native and immigrant geographic mobility in France. Using longitudinal data, we measure mobility from one French municipality (commune) to another over time and estimate the effect of the initial municipality’s ethnic composition on the probability of moving out. These data allow us to use panel techniques to correct for biases related to selection based on geographic and individual unobservables. Our findings tend to discredit the hypothesis of a “white flight” pattern in residential mobility dynamics in France. Some evidence does show ethnic avoidance mechanisms in natives’ relocating. We also find a strong negative and highly robust effect of co-ethnics’ presence on immigrants’ geographic mobility
Electron injection in a nanotube with leads: finite frequency noise-correlations and anomalous charges
The non-equilibrium transport properties of a carbon nanotube which is
connected to Fermi liquid leads, where electrons are injected in the bulk, are
computed. A previous work which considered an infinite nanotube showed that the
zero frequency noise correlations, measured at opposite ends of the nanotube,
could be used to extract the anomalous charges of the chiral excitations which
propagate in the nanotube. Here, the presence of the leads have the effect that
such-noise cross-correlations vanish at zero frequency. Nevertheless,
information concerning the anomalous charges can be recovered when considering
the spectral density of noise correlations at finite frequencies, which is
computed perturbatively in the tunneling amplitude. The spectrum of the noise
cross-correlations is shown to depend crucially on the ratio of the time of
flight of quasiparticles traveling in the nanotube to the ``voltage'' time
which defines the width of the quasiparticle wave-packets injected when an
electron tunnels. Potential applications toward the measurement of such
anomalous charges in non-chiral Luttinger liquids (nanotubes or semiconductor
quantum wires) are discussed.Comment: 11 pages, 5 figure
In vitro toxicity of nanoceria: effect of coating and stability in biofluids
Due to the increasing use of nanometric cerium oxide in applications,
concerns about the toxicity of these particles have been raised and have
resulted in a large number of investigations. We report here on the
interactions between 7 nm anionically charged cerium oxide particles and living
mammalian cells. By a modification of the particle coating including
low-molecular weight ligands and polymers, two generic behaviors are compared:
particles coated with citrate ions that precipitate in biofluids and particles
coated with poly(acrylic acid) that are stable and remain nanometric. We find
that nanoceria covered with both coating agents are taken up by mouse
fibroblasts and localized into membrane-bound compartments. However, flow
cytometry and electron microscopy reveal that as a result of their
precipitation, citrate-coated particles interact more strongly with cells. At
cerium concentration above 1 mM, only citrate-coated nanoceria (and not
particles coated with poly(acrylic acid)) display toxicity and moderate
genotoxicity. The results demonstrate that the control of the surface chemistry
of the particles and its ability to prevent aggregation can affect the toxicity
of nanomaterials.Comment: 33 pages 10 figures, accepted at Nanotoxicolog
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