22,661 research outputs found
Resonant purification of mixed states for closed and open quantum systems
Pure states are fundamental for the implementation of quantum technologies,
and several methods for the purification of the state of a quantum system S
have been developed in the past years. In this letter we present a new
approach, based on the interaction of S with an auxiliary system P, having a
wide range of applicability. Considering two-level systems S and P and assuming
a particular interaction between them, we prove that complete purifications can
be obtained under suitable conditions on the parameters characterizing P. Using
analytical and numerical tools, we show that the purification process exhibits
a resonant behavior in both the cases of system isolated from the external
environment or not.Comment: 4 pages, LaTe
The boson-fermion model: An exact diagonalization study
The main features of a generic boson-fermion scenario for electron pairing in
a many-body correlated fermionic system are: i) a cross-over from a poor metal
to an insulator and finally a superconductor as the temperature decreases, ii)
the build-up of a finite amplitude of local electron pairing below a certain
temperature , followed by the onset of long-range phase correlations among
electron pairs below a second characteristic temperature , iii) the
opening of a pseudogap in the DOS of the electrons below , rendering these
electrons poorer and poorer quasi-particles as the temperature decreases, with
the electron transport becoming ensured by electron pairs rather than by
individual electrons. A number of these features have been so far obtained on
the basis of different many-body techniques, all of which have their built-in
shortcomings in the intermediate coupling regime, which is of interest here. In
order to substantiate these features, we investigate them on the basis of an
exact diagonalization study on rings up to eight sites. Particular emphasis has
been put on the possibility of having persistent currents in mesoscopic rings
tracking the change-over from single- to two-particle transport as the
temperature decreases and the superconducting state is approached.Comment: 7 pages, 8 figures; to be published in Phys. Rev.
Chemical abundances and properties of the ionized gas in NGC 1705
We obtained [O III] narrow-band imaging and multi-slit MXU spectroscopy of
the blue compact dwarf (BCD) galaxy NGC 1705 with FORS2@VLT to derive chemical
abundances of PNe and H II regions and, more in general, to characterize the
properties of the ionized gas. The auroral [O III]\lambda4363 line was detected
in all but one of the eleven analyzed regions, allowing for a direct estimate
of their electron temperature. The only object for which the [O III]\lambda4363
line was not detected is a possible low-ionization PN, the only one detected in
our data. For all the other regions, we derived the abundances of Nitrogen,
Oxygen, Neon, Sulfur and Argon out to ~ 1 kpc from the galaxy center. We detect
for the first time in NGC 1705 a negative radial gradient in the oxygen
metallicity of -0.24 \pm 0.08 dex kpc^{-1}. The element abundances are all
consistent with values reported in the literature for other samples of dwarf
irregular and blue compact dwarf galaxies. However, the average (central)
oxygen abundance, 12 + log(O/H)=7.96 \pm 0.04, is ~0.26 dex lower than previous
literature estimates for NGC 1705 based on the [O III]\lambda4363 line. From
classical emission-line diagnostic diagrams, we exclude a major contribution
from shock excitation. On the other hand, the radial behavior of the emission
line ratios is consistent with the progressive dilution of radiation with
increasing distance from the center of NGC 1705. This suggests that the
strongest starburst located within the central 150 pc is responsible for
the ionization of the gas out to at least 1 kpc. The gradual dilution of
the radiation with increasing distance from the center reflects the gradual and
continuous transition from the highly ionized H II regions in the proximity of
the major starburst into the diffuse ionized gas.Comment: Accepted for publication on A
Environment induced incoherent controllability
We prove that the environment induced entanglement between two non
interacting, two-dimensional quantum systems S and P can be used to control the
dynamics of S by means of the initial state of P. Using a simple, exactly
solvable model, we show that both accessibility and controllability of S can be
achieved under suitable conditions on the interaction of S and P with the
environment.Comment: revtex4, 5 page
2D-3D registration of CT vertebra volume to fluoroscopy projection: A calibration model assessment (doi:10.1155/2010/806094)
This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1?mm for displacements parallel to the fluoroscopic plane, and of order of 10?mm for the orthogonal displacement.<br/
Control of magnetism in singlet-triplet superconducting heterostructures
We analyze the magnetization at the interface between singlet and triplet
superconductors and show that its direction and dependence on the phase
difference across the junction are strongly tied to the structure of the
triplet order parameter as well as to the pairing interactions. We consider
equal spin helical, opposite spin chiral, and mixed symmetry pairing on the
triplet side and show that the magnetization vanishes at only in the
first case, follows approximately a behavior for the second, and
shows higher harmonics for the last configuration. We trace the origin of the
magnetization to the magnetic structure of the Andreev bound states near the
interface, and provide a symmetry-based explanation of the results. Our
findings can be used to control the magnetization in superconducting
heterostructures and to test symmetries of spin-triplet superconductors.Comment: 5 pages, 3 figure
Effect of Ferric Sodium EDTA administration, in combination with vitamin C, folic acid, copper gluconate, zinc gluconate and selenomethionine, on cardiovascular risk evaluation: exploration of the HRV frequency domain
diseases. Using the Heart Rate Variability (HRV) analysis is possible to provide an evaluation of the safety and the
effectiveness of intervention.
Objective: To evaluate the efficacy and safety of Ferric Sodium EDTA in combination with vitamin C, folic acid, copper
gluconate, zinc gluconate and selenomethionine (Ferachel forte®) 2 tabs/day for 24 days in elderly patients with secondary
anaemia, by exploring the HRV frequency domain.
Methods: In 45 elderly patients with secondary anaemia and/or low-moderate kidney failure, laboratory values after
administration of Ferric Sodium EDTA, 2 tabs a day, in combination with vitamin C, folic acid, copper gluconate, zinc
gluconate and selenomethionine (Ferachel forte®) for 24 days (N=16 patients) or ferrous gluconate 63 mg/day added to
saline solution, administered using intravenous access during the hospitalization period of 15 ± 5 days (N=29 patients)
were evaluated. Also, ECG signals and bioelectrical impedance (BIA) were measured.
Results: Oral iron supplementation with Ferric Sodium EDTA, in combination with vitamin C, folic acid, copper gluconate,
zinc gluconate and selenomethionine (Ferachel forte®) confirmed to be effective and safe about the cardiovascular risk
in old patients. This study showed the real superiority of the oral administration about the cardiovascular risk in elderly
patients in comparison with intravenous administration of ferrous gluconate.
Conclusion: This study confirms that Ferric Sodium EDTA combination (Ferachel forte®) can be a valid alternative to ferrous
gluconate intravenous therapy (gold standard) in the treatment of secondary anaemia in elderly patients. In fact, during
the treatment, efficacy results have been maintained without statistically significant variations about cardiovascular risk,
evaluated by exploring the HRV frequency domain
PNe and H II regions in the starburst irregular galaxy NGC 4449 from LBT MODS data
We present deep 350010000 spectra of H II regions and planetary
nebulae (PNe) in the starburst irregular galaxy NGC 4449, acquired with the
Multi Object Double Spectrograph at the Large Binocular Telescope. Using the
"direct" method, we derived the abundance of He, N, O, Ne, Ar, and S in six H
II regions and in four PNe in NGC 4449. This is the first case of PNe studied
in a starburst irregular outside the Local Group. Our H II region and PN sample
extends over a galacto-centric distance range of 2 kpc and spans
0.2 dex in oxygen abundance, with average values of and for H II regions and PNe, respectively. PNe and H
II regions exhibit similar oxygen abundances in the galacto-centric distance
range of overlap, while PNe appear more than 1 dex enhanced in nitrogen
with respect to H II regions. The latter result is the natural consequence of N
being mostly synthesized in intermediate-mass stars and brought to the stellar
surface during dredge-up episodes. On the other hand, the similarity in O
abundance between H II regions and PNe suggests that NGC 4449' s interstellar
medium has been poorly enriched in elements since the progenitors of
the PNe were formed. Finally, our data reveal the presence of a negative oxygen
gradient for both H II regions and PNe, whilst nitrogen does not exhibit any
significant radial trend. We ascribe the (unexpected) nitrogen behaviour as due
to local N enrichment by the conspicuous Wolf-Rayet population in NGC 4449.Comment: Accepted for publication on Ap
Teleportation is necessary for faithful quantum state transfer through noisy channels of maximal rank
Quantum teleportation enables deterministic and faithful transmission of
quantum states, provided a maximally entangled state is pre-shared between
sender and receiver, and a one-way classical channel is available. Here, we
prove that these resources are not only sufficient, but also necessary, for
deterministically and faithfully sending quantum states through any fixed noisy
channel of maximal rank, when a single use of the cannel is admitted. In other
words, for this family of channels, there are no other protocols, based on
different (and possibly cheaper) sets of resources, capable of replacing
quantum teleportation.Comment: 4 pages, comments are welcom
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