26,074 research outputs found
The 12CO/13CO ratio in AGB stars of different chemical type-Connection to the 12C/13C ratio and the evolution along the AGB
The aim of this paper is to investigate the evolution of the 12C/13C ratio
along the AGB through the circumstellar 12CO/13CO ratio. This is the first time
a sample including a significant number of M- and S-type stars is analysed
together with a carbon-star sample of equal size, making it possible to
investigate trends among the different types and establish evolutionary
effects. The circumstellar 12CO/13CO abundance ratios are estimated through a
detailed radiative transfer analysis of single-dish radio line emission
observations. First, the 12CO radiative transfer is solved, assuming an
abundance (dependent on the chemical type of the star), to give the physical
parameters of the gas, i.e. mass-loss rate, gas expansion velocity, and gas
temperature distribution. Then, the 13CO radiative transfer is solved using the
results of the 12CO model giving the 13CO abundance. Finally, the 12CO/13CO
abundance ratio is calculated. The circumstellar 12CO/13CO abundance ratio
differs between the three spectral types. This is consistent with what is
expected from stellar evolutionary models assuming that the spectral types
constitute an evolutionary sequence; however, this is the first time this has
been shown observationally for a relatively large sample covering all three
spectral types. The median value of the 13CO abundance in the inner
circumstellar envelope is 1.6x10^-5, 2.3x10^-5, and 3.0x10^-5 for the M-type,
S-type, and carbon stars of the sample, respectively, corresponding to
12CO/13CO abundance ratios of 13, 26, and 34, respectively. Interestingly, the
abundance ratio spread of the carbon stars is much larger than for the M- and
S-type stars, even when excluding J-type carbon stars, in line with what could
be expected from evolution on the AGB. We find no correlation between the
isotopologue ratio and the mass-loss rate, as would be expected if both
increase as the star evolves.Comment: 11 pages, 5 figures, accepted for publication in A&
Operator mixing in N=4 SYM: The Konishi anomaly revisited
In the context of the superconformal N=4 SYM theory the Konishi anomaly can
be viewed as the descendant of the Konishi multiplet in the 10 of
SU(4), carrying the anomalous dimension of the multiplet. Another descendant
with the same quantum numbers, but this time without anomalous
dimension, is obtained from the protected half-BPS operator (the
stress-tensor multiplet). Both and are renormalized mixtures
of the same two bare operators, one trilinear (coming from the superpotential),
the other bilinear (the so-called "quantum Konishi anomaly"). Only the operator
is allowed to appear in the right-hand side of the Konishi anomaly
equation, the protected one does not match the conformal properties of
the left-hand side. Thus, in a superconformal renormalization scheme the
separation into "classical" and "quantum" anomaly terms is not possible, and
the question whether the Konishi anomaly is one-loop exact is out of context.
The same treatment applies to the operators of the BMN family, for which no
analogy with the traditional axial anomaly exists. We illustrate our abstract
analysis of this mixing problem by an explicit calculation of the mixing matrix
at level g^4 ("two loops") in the supersymmetric dimensional reduction scheme.Comment: 28 pp LaTeX, 3 figure
The V-A sum rules and the Operator Product Expansion in complex q^2-plane from tau-decay data
The operator product expansion (OPE) for the difference of vector and axial
current correlators is analyzed for complex values of momentum q^2. The vector
and axial spectral functions, taken from hadronic tau-decay data, are treated
with the help of Borel, Gaussian and spectral moments sum rules. The range of
applicability, advantages and disadvantages of each type are discussed. The
general features of OPE are confirmed by the data. The vacuum expectation
values of dimension 6 and 8 operators are found to be O_6=-(6.8\pm 2.1)*10^{-3}
GeV^6, O_8=(7\pm 4)*10^{-3} GeV^8.Comment: 1 latex + 10 eps files, 14 page
Data generator for evaluating ETL process quality
Obtaining the right set of data for evaluating the fulfillment of different quality factors in the extract-transform-load (ETL) process design is rather challenging. First, the real data might be out of reach due to different privacy constraints, while manually providing a synthetic set of data is known as a labor-intensive task that needs to take various combinations of process parameters into account. More importantly, having a single dataset usually does not represent the evolution of data throughout the complete process lifespan, hence missing the plethora of possible test cases. To facilitate such demanding task, in this paper we propose an automatic data generator (i.e., Bijoux). Starting from a given ETL process model, Bijoux extracts the semantics of data transformations, analyzes the constraints they imply over input data, and automatically generates testing datasets. Bijoux is highly modular and configurable to enable end-users to generate datasets for a variety of interesting test scenarios (e.g., evaluating specific parts of an input ETL process design, with different input dataset sizes, different distributions of data, and different operation selectivities). We have developed a running prototype that implements the functionality of our data generation framework and here we report our experimental findings showing the effectiveness and scalability of our approach.Peer ReviewedPostprint (author's final draft
Four-level and two-qubit systems, sub-algebras, and unitary integration
Four-level systems in quantum optics, and for representing two qubits in
quantum computing, are difficult to solve for general time-dependent
Hamiltonians. A systematic procedure is presented which combines analytical
handling of the algebraic operator aspects with simple solutions of classical,
first-order differential equations. In particular, by exploiting and sub-algebras of the full SU(4)
dynamical group of the system, the non-trivial part of the final calculation is
reduced to a single Riccati (first order, quadratically nonlinear) equation,
itself simply solved. Examples are provided of two-qubit problems from the
recent literature, including implementation of two-qubit gates with Josephson
junctions.Comment: 1 gzip file with 1 tex and 9 eps figure files. Unpack with command:
gunzip RSU05.tar.g
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