11,747 research outputs found
YARARA: Significant improvement of RV precision through post-processing of spectral time-series
Aims: Even the most-precise radial-velocity instruments gather
high-resolution spectra that present systematic errors that a data reduction
pipeline cannot identify and correct for efficiently. In this paper, we aim at
improving the radial-velocity precision of HARPS measurements by cleaning
individual extracted spectra using the wealth of information contained in
spectra time-series.
Methods: We developed YARARA, a post-processing pipeline designed to clean
high-resolution spectra from instrumental systematics and atmospheric
contamination. Spectra are corrected for: tellurics, interference pattern,
detector stitching, ghosts and fiber B contaminations as well as more advanced
spectral line-by-line corrections. YARARA uses Principal Component Analysis on
spectra time-series with prior information to disentangle contaminations from
real Doppler shifts. We applied YARARA on three systems: HD10700, HD215152 and
HD10180 and compared our results to the HARPS standard Data Reduction Software
and the SERVAL post-processing pipeline.
Results: On HD10700, we obtain radial-velocity measurements that present a
rms smaller than 1 m/s over the 13 years of the HARPS observations, which is 20
and 10 % better than the HARPS Data Reduction Software and the SERVAL
post-processing pipeline, respectively. We also injected simulated planets on
the data of HD10700 and demonstrated that YARARA does not alter pure Doppler
shifted signals. On HD215152, we demonstrated that the 1-year signal visible in
the periodogram becomes marginal after processing with YARARA and that the
signals of the known planets become more significant. Finally, on HD10180, the
known six exoplanets are well recovered although different orbitals parameters
and planetary masses are provided by the new reduced spectra.Comment: 23 pages, 19 figure
Properties of 10 (18)-10 (19)eV EAS at far core distance
The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km
Akeno 20 km (2) air shower array (Akeno Branch)
As the first stage of the future huge array, the Akeno air shower array was expanded to about 20 sq. km. by adding 19 scintillation detectors of 2.25 sq m area outside the present 1 sq. km. Akeno array with a new data collection system. These detectors are spaced about 1km from each other and connected by two optical fiber cables. This array has been in partial operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984. 20 sq m muon stations are planned to be set with 2km separation and one of them is now under construction. The origin of the highest energy cosmic rays is studied
New Lower Bounds on the Self-Avoiding-Walk Connective Constant
We give an elementary new method for obtaining rigorous lower bounds on the
connective constant for self-avoiding walks on the hypercubic lattice .
The method is based on loop erasure and restoration, and does not require exact
enumeration data. Our bounds are best for high , and in fact agree with the
first four terms of the expansion for the connective constant. The bounds
are the best to date for dimensions , but do not produce good results
in two dimensions. For , respectively, our lower bound is within
2.4\%, 0.43\%, 0.12\%, 0.044\% of the value estimated by series extrapolation.Comment: 35 pages, 388480 bytes Postscript, NYU-TH-93/02/0
On Random Bubble Lattices
We study random bubble lattices which can be produced by processes such as
first order phase transitions, and derive characteristics that are important
for understanding the percolation of distinct varieties of bubbles. The results
are relevant to the formation of topological defects as they show that infinite
domain walls and strings will be produced during appropriate first order
transitions, and that the most suitable regular lattice to study defect
formation in three dimensions is a face centered cubic lattice. Another
application of our work is to the distribution of voids in the large-scale
structure of the universe. We argue that the present universe is more akin to a
system undergoing a first-order phase transition than to one that is
crystallizing, as is implicit in the Voronoi foam description. Based on the
picture of a bubbly universe, we predict a mean coordination number for the
voids of 13.4. The mean coordination number may also be used as a tool to
distinguish between different scenarios for structure formation.Comment: several modifications including new abstract, comparison with froth
models, asymptotics of coordination number distribution, further discussion
of biased defects, and relevance to large-scale structur
Scaling and Density of Lee-Yang Zeroes in the Four Dimensional Ising Model
The scaling behaviour of the edge of the Lee--Yang zeroes in the four
dimensional Ising model is analyzed. This model is believed to belong to the
same universality class as the model which plays a central role in
relativistic quantum field theory. While in the thermodynamic limit the scaling
of the Yang--Lee edge is not modified by multiplicative logarithmic
corrections, such corrections are manifest in the corresponding finite--size
formulae. The asymptotic form for the density of zeroes which recovers the
scaling behaviour of the susceptibility and the specific heat in the
thermodynamic limit is found to exhibit logarithmic corrections too. The
density of zeroes for a finite--size system is examined both analytically and
numerically.Comment: 17 pages (4 figures), LaTeX + POSTSCRIPT-file, preprint UNIGRAZ-UTP
20-11-9
Scaling of Self-Avoiding Walks in High Dimensions
We examine self-avoiding walks in dimensions 4 to 8 using high-precision
Monte-Carlo simulations up to length N=16384, providing the first such results
in dimensions on which we concentrate our analysis. We analyse the
scaling behaviour of the partition function and the statistics of
nearest-neighbour contacts, as well as the average geometric size of the walks,
and compare our results to -expansions and to excellent rigorous bounds
that exist. In particular, we obtain precise values for the connective
constants, , , ,
and give a revised estimate of . All of
these are by at least one order of magnitude more accurate than those
previously given (from other approaches in and all approaches in ).
Our results are consistent with most theoretical predictions, though in
we find clear evidence of anomalous -corrections for the scaling of
the geometric size of the walks, which we understand as a non-analytic
correction to scaling of the general form (not present in pure
Gaussian random walks).Comment: 14 pages, 2 figure
Beam Switching Cylindrical Array Antenna System for Communication
The beam switching cylindrical array, which is a unique system, has been designed and developed to cover 360° in azimuth plane by generating 16 beams with specified elevation coverage.In this design, the concept of fast aperture selection (4 x 4) in microseconds from the total cylindrical array has been realised successfully to meet the requirement of point-to-multipoint communication. The components of the array, viz., radiating elements, powder dividers, switches, etc., are designed in printed circuit type, and hence, objectives of lightweight and ease of reproducibility are achieved. The lightweight of the array makes it accessible for easy mounting at a specified height for achieving longer communication range. Finally, a low-loss radome is incorporated to protect the array from environmental conditions. The various parameters, viz., return loss, gain, and switched-beam radiation patterns were measured over a bandwidth of 300 MHz in L- band and typical measured results are presented in this paper
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