4,573 research outputs found
Exciting polaritons with quantum light
We discuss the excitation of polaritons---strongly-coupled states of light
and matter---by quantum light, instead of the usual laser or thermal
excitation. As one illustration of the new horizons thus opened, we introduce
Mollow spectroscopy, a theoretical concept for a spectroscopic technique that
consists in scanning the output of resonance fluorescence onto an optical
target, from which weak nonlinearities can be read with high precision even in
strongly dissipative environments.Comment: 5 pages, 3 figure
Strength distribution of solar magnetic fields in photospheric quiet Sun regions
The magnetic topology of the solar photosphere in its quietest regions is
hidden by the difficulties to disentangle magnetic flux through the resolution
element from the field strength of unresolved structures. The observation of
spectral lines with strong coupling with hyperfine structure, like the observed
MnI line at 553.7 nm, allows such differentiation.
The main aim is to analyse the distribution of field strengths in the network
and intranetwork of the solar photosphere through inversion of the MnI line at
553.7 nm.
An inversion code for the magnetic field using the Principal Component
Analysis (PCA) has been developed. Statistical tests are run on the code to
validate it. The code has to draw information from the small-amplitude spectral
feature oppearing in the core of the Stokes V profile of the observed line for
field strengths below a certain threshold, coinciding with lower limit of the
Paschen-Back effect in the fine structure of the involved atomic levels.
The inversion of the observed profiles, using the circular polarization (V)
and the intensity (I), shows the presence of magnetic fields strengths in a
range from 0 to 2 kG, with predominant weak strength values. Mixed regions with
mean strength field values of 1130 and 435 Gauss are found associated with the
network and intranetwork respectively.
The MnI line at 553 nm probes the field strength distribution in the quiet
sun and shows the predominance of weak, hectoGauss fields in the intranetwork,
and strong, kiloGauss fields in the network. It also shows that both network
and intranetwork are to be understood at our present spatial resolutions as
field distributions of which we hint the mean properties.Comment: 10 pages, 6 figure
Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution
We present deep echelle spectrophotometry of the brightest emission-line
knots of the star-forming galaxies He 2-10, Mkn 1271, NGC 3125, NGC 5408, POX
4, SDSS J1253-0312, Tol 1457-262, Tol 1924-416 and the HII region Hubble V in
the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with
the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the
3100-10420 {\AA} range. We determine electron densities and temperatures of the
ionized gas from several emission-line intensity ratios for all the objects. We
derive the ionic abundances of C and/or O from faint pure
recombination lines (RLs) in several of the objects, permitting to derive their
C/H and C/O ratios. We have explored the chemical evolution at low
metallicities analysing the C/O vs. O/H, C/O vs. N/O and C/N vs. O/H relations
for Galactic and extragalactic HII regions and comparing with results for halo
stars and DLAs. We find that HII regions in star-forming dwarf galaxies occupy
a different locus in the C/O vs. O/H diagram than those belonging to the inner
discs of spiral galaxies, indicating their different chemical evolution
histories, and that the bulk of C in the most metal-poor extragalactic HII
regions should have the same origin than in halo stars. The comparison between
the C/O ratios in HII regions and in stars of the Galactic thick and thin discs
seems to give arguments to support the merging scenario for the origin of the
Galactic thick disc. Finally, we find an apparent coupling between C and N
enrichment at the usual metallicities determined for HII regions and that this
coupling breaks in very low-metallicity objects.Comment: 27 pages, 12 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Psychological elements explaining the consumer's adoption and use of a website recommendation system: A theoretical framework proposal
The purpose of this paper is to understand, with an emphasis on the psychological perspective of the research problem, the consumer's adoption and use of a certain web site recommendation system as well as the main psychological outcomes involved. The approach takes the form of theoretical modelling. Findings: A conceptual model is proposed and discussed. A total of 20 research propositions are theoretically analyzed and justified. Research limitations/implications: The theoretical discussion developed here is not empirically validated. This represents an opportunity for future research. Practical implications: The ideas extracted from the discussion of the conceptual model should be a help for recommendation systems designers and web site managers, so that they may be more aware, when working with such systems, of the psychological process consumers undergo when interacting with them. In this regard, numerous practical reflections and suggestions are presented
From Coulomb blockade to the Kondo regime in a Rashba dot
We investigate the electronic transport in a quantum wire with localized
Rashba interaction. The Rashba field forms quasi-bound states which couple to
the continuum states with an opposite spin direction. The presence of this
Rashba dot causes Fano-like antiresonances and dips in the wire's linear
conductance. The Fano lineshape arises from the interference between the direct
transmission channel along the wire and the hopping through the Rashba dot. Due
to the confinement, we predict the observation of large charging energies in
the local Rashba region which lead to Coulomb-blockade effects in the transport
properties of the wire. Importantly, the Kondo regime can be achieved with a
proper tuning of the Rashba interaction, giving rise to an oscillating linear
conductance for a fixed occupation of the Rashba dot.Comment: 6 pages, 3 figures; presentation improved, discussions extended.
Published versio
II Zwicky 23 and Family
II Zwicky 23 (UGC 3179) is a luminous, nearby compact narrow emission line
starburst galaxy with blue optical colors and strong emission lines. We present
a photometric and morphological study of II Zw 23 and its interacting
companions using data obtained with the WIYN 3.5-m telescope in Kitt Peak,
Arizona. II Zwicky 23 has a highly disturbed outer structure with long trails
of debris that may be feeding tidal dwarfs. Its central regions appear disky, a
structure that is consistent with the overall rotation pattern observed in the
H-alpha velocity field measured from Densepak observations obtained with WIYN.
We discuss the structure of II Zwicky 23 and its set of companions and possible
scenarios of debris formation in this system.Comment: 5 pages, 2 figures. To appear in the proceedings of ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Burissova (Springer
Kondo effect in spin-orbit mesoscopic interferometers
We consider a flux-threaded Aharonov-Bohm ring with an embedded quantum dot
coupled to two normal leads. The local Rashba spin-orbit interaction acting on
the dot electrons leads to a spin-dependent phase factor in addition to the
Aharonov-Bohm phase caused by the external flux. Using the numerical
renormalization group method, we find a splitting of the Kondo resonance at the
Fermi level which can be compensated by an external magnetic field. To fully
understand the nature of this compensation effect, we perform a scaling
analysis and derive an expression for the effective magnetic field. The
analysis is based on a tight-binding model which leads to an effective Anderson
model with a spin-dependent density of states for the transformed lead states.
We find that the effective field originates from the combined effect of Rashba
interaction and magnetic flux and that it contains important corrections due to
electron-electron interactions. We show that the compensating field is an
oscillatory function of both the spin-orbit and the Aharonov-Bohm phases.
Moreover, the effective field never vanishes due to the particle-hole symmetry
breaking independently of the gate voltage.Comment: 9 pages, 5 figure
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