3,191 research outputs found
Aqueous alteration on main belt primitive asteroids: results from visible spectroscopy
This work focuses on the study of the aqueous alteration process which acted
in the main belt and produced hydrated minerals on the altered asteroids. The
aqueous alteration is particularly important for unraveling the processes
occurring during the earliest times of the Solar System history, as it can give
information both on the asteroids thermal evolution and on the localization of
water sources in the asteroid belt. We present new spectral observations in the
visible region of 80 asteroids belonging to the primitive classes C, G, F, B
and P. We combine the present observations with the visible spectra of
asteroids available in the literature for a total of 600 primitive main belt
asteroids. Our analysis shows that the aqueous alteration sequence starts from
the P-type objects, practically unaltered, and increases through the F, B, C,
and G asteroids. Around 50% of the observed C-type asteroids show absorption
features in the vis. range due to hydrated silicates, implying that more than
70% of them will have a 3 m absorption band and thus hydrated minerals on
their surfaces. The process dominates in primitive asteroids located between
2.3 and 3.1 AU, that is at smaller heliocentric distances than previously
suggested. The aqueous alteration process dominates in the 50--240 km sized
primitive asteroids, while it is less effective for bodies smaller than 50 km.
No correlation is found between the aqueous alteration process and the
asteroids albedo or orbital elements. Comparing the 0.7 m band
parameters of hydrated silicates and CM2 carbonaceous chondrites, we see that
the band center of meteorites is at longer wavelengths than that of asteroids.
This difference on center positions may be attributed to different minerals
abundances, and to the fact that CM2 available on Earth might not be
representative of the whole aqueous altered asteroids population.Comment: Icarus, accepted for publication on 28 January 2014 Manuscript pages:
38; Figures: 13 ; Tables:
Determining the alpha dynamo parameter in incompressible homogeneous magnetohydrodynamic turbulence
Alpha, an important parameter in dynamo theory, is proportional to either the kinetic, current, magnetic, or velocity helicity of the fluctuating magnetic field and fluctuating velocity field. The particular helicity to which alpha is proportional depends on the assumptions used in deriving the first order smoothed equations that describe the alpha effect. In two cases, when alpha is proportional to either the magnetic helicity or velocity helicity, alpha is determined experimentally from two point measurements of the fluctuating fields in incompressible, homogeneous turbulence having arbitrary symmetry. For the other two possibilities, alpha is determined if the turbulence is isotropic
Short and Intermediate Term Outcomes of the Convergent Procedure: Initial Experience in a Tertiary Referral Center
PURPOSE:
The Convergent procedure is a hybrid, multidisciplinary treatment for symptomatic atrial fibrillation (AF) consisting of minimally invasive surgical epicardial ablation and percutaneous/catheter endocardial ablation. We investigated outcomes following introduction of the Convergent procedure at our institution.
METHODS:
Retrospective study examining single-center outcomes. Demographic, procedural, and post-procedural variables were collected with follow-up data obtained at 3, 6, and 12 months.
RESULTS:
In all, 36 patients with paroxysmal (11%) or persistent/long-standing persistent (89%) AF underwent the Convergent procedure. 36% also underwent concomitant left atrial appendage (LAA) exclusion by thoracoscopic placement of an epicardial clip. Mean age 60.6 ± 8.0 years with mean arrhythmia burden of 3.9 ± 2.7 years. All patients had failed prior attempts at medical management, 81% had failed prior cardioversion, and 17% had failed prior catheter ablation. Convergent was performed successfully in all patients with no peri-procedural deaths or major complications. At 3 and 12 months, 77.8% and 77.3% of patients, respectively, were free from symptomatic arrhythmia. 65.8% were off anti-arrhythmic medication at 12 months.
CONCLUSIONS:
The Convergent procedure is safe and has good short- and intermediate-term clinical success rates. This unique hybrid approach combines strengths of surgical and catheter ablation and should be part of any comprehensive AF treatment program
Andreev Level Qubit
We investigate the dynamics of a two-level Andreev bound state system in a
transmissive quantum point contact embedded in an rf-SQUID. Coherent coupling
of the Andreev levels to the circulating supercurrent allows manipulation and
read out of the level states. The two-level Hamiltonian for the Andreev levels
is derived, and the effect of interaction with the quantum fluctuations of the
induced flux is studied. We also consider an inductive coupling of qubits, and
discuss the relevant SQUID parameters for qubit operation and read out.Comment: 4 pages, 1 figur
Realization of the purely spatial Einstein-Podolsky-Rosen paradox in full-field images of spontaneous parametric down conversion
We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely
spatial quantum correlations in the near and far fields of spontaneous
parametric down-conversion generated in a type-2 beta barium borate crystal.
Full-field imaging is performed in the photon-counting regime with an
electron-multiplying CCD camera. The data are used without any postselection,
and we obtain a violation of Heisenberg inequalities with inferred quantities
taking into account all the biphoton pairs in both the near and far fields by
integration on the entire two-dimensional transverse planes. This ensures a
rigorous demonstration of the EPR paradox in its original position momentum
form
Spectral variability on primitive asteroids of the Themis and Beagle families: space weathering effects or parent body heterogeneity?
Themis is an old and statistically robust asteroid family populating the
outer main belt, and resulting from a catastrophic collision that took place
2.51.0 Gyr ago. Within the old Themis family a young sub-family, Beagle,
formed less than 10 Myr ago, has been identified. We present the results of a
spectroscopic survey in the visible and near infrared range of 22 Themis and 8
Beagle families members. The Themis members investigated exhibit a wide range
of spectral behaviors, while the younger Beagle family members look spectrally
bluer with a smaller spectral slope variability. The best meteorite spectral
analogues found for both Themis and Beagle families members are carbonaceous
chondrites having experienced different degrees of aqueous alteration,
prevalently CM2 but also CV3 and CI, and some of them are chondrite samples
being unusual or heated. We extended the spectral analysis including the data
available in the literature on Themis and Beagle families members, and we
looked for correlations between spectral behavior and physical parameters using
the albedo and size values derived from the WISE data. The analysis of this
larger sample confirm the spectral diversity within the Themis family and that
Beagle members tend to be bluer and to have an higher albedo. The differences
between the two family may be partially explained by space weathering
processes, which act on these primitive surfaces in a similar way than on
S-type asteroids, i.e. producing reddening and darkening. However we see
several Themis members having albedos and spectral slopes similar to the young
Beagle members. Alternative scenarios are proposed including heterogeneity in
the parent body having a compositional gradient with depth, and/or the survival
of projectile fragments having a different composition than the parent body.Comment: Manuscript pages: 40; Figures: 15 ; Tables: 4 Icarus (2016),in pres
Josephson junction qubit network with current-controlled interaction
We design and evaluate a scalable charge qubit chain network with
controllable current-current coupling of neighbouring qubit loops via local
dc-current gates. The network allows construction of general N-qubit gates. The
proposed design is in line with current main stream experiments.Comment: 4 pages, 4 figure
Trends in Basic Sciences Education in Dental Schools, 1999–2016
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153754/1/jddjde017008.pd
Two-step Emergence of the Magnetic Flux Sheet from the Solar Convection Zone
We perform two-dimensional MHD simulations on the solar flux emergence. We
set the initial magnetic flux sheet at z=-20,000 km in the convection zone. The
flux sheet rises through the convective layer due to the Parker instability,
however, decelerates beneath the photosphere because the plasma on the flux
sheet piles up owing to the convectively stable photosphere above. Meanwhile,
the flux sheet becomes locally unstable to the Parker instability within the
photosphere, and the further evolution to the corona occurs (two-step emergence
model). We carry out a parameter survey to investigate the condition for this
two-step model. We find that magnetic fluxes which form active regions are
likely to have undergone the two-step emergence. The condition for the two-step
emergence is 10^21 - 10^22 Mx with 10^4 G at z=-20,000 km in the convection
zone.Comment: 41 pages, 15 figures, 1 table, Accepted for publication in Ap
The Status of Ethics Teaching and Learning in U.S. Dental Schools
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153779/1/jddj0022033720117510tb05174x.pd
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