9,289 research outputs found
Holding Dissapearance in RTD-based Quantizers
Multiple-valued Logic (MVL) circuits are one of the most attractive
applications of the Monostable-to-Multistable transition Logic (MML), and they
are on the basis of advanced circuits for communications. The operation of such
quantizer has two steps : sampling and holding. Once the quantizer samples the
signal, it must maintain the sampled value even if the input changes. However,
holding property is not inherent to MML circuit topologies. This paper analyses
the case of an MML ternary inverter used as a quantizer, and determines the
relations that circuit representative parameters must verify to avoid this
malfunction.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Terrestrial Planet Formation Surrounding Close Binary Stars
Disk material has been observed around both components of some young close
binary star systems. It has been shown that if planets form at the right places
within such disks, they can remain dynamically stable for very long times.
Herein, we numerically simulate the late stages of terrestrial planet growth in
circumbinary disks around 'close' binary star systems with stellar separations
between 0.05 AU and 0.4 AU and binary eccentricities up to 0.8. In each
simulation, the sum of the masses of the two stars is 1 solar mass, and giant
planets are included. Our results are statistically compared to a set of planet
formation simulations in the Sun-Jupiter-Saturn system that begin with
essentially the same initial disk of protoplanets. The planetary systems formed
around binaries with apastron distances less than ~ 0.2 AU are very similar to
those around single stars, whereas those with larger maximum separations tend
to be sparcer, with fewer planets, especially interior to 1 AU. We also provide
formulae that can be used to scale results of planetary accretion simulations
to various systems with different total stellar mass, disk sizes, and
planetesimal masses and densities.Comment: 60 pages, 4 tables, and 11 low resolution eps figures. Article with
high resolution figures is available at
http://www-personal.umich.edu/~equintan/publications.html . Accepted for
publication in Icaru
Using Multi-Threshold Threshold Gates in RTD-based Logic Design. A Case Study
The basic building blocks for Resonant Tunnelling Diode (RTD) logic circuits
are Threshold Gates (TGs) instead of the conventional Boolean gates (AND, OR,
NAND, NOR) due to the fact that, when designing with RTDs, threshold gates can
be implemented as efficiently as conventional ones, but realize more complex
functions. Recently, RTD structures implementing Multi-Threshold Threshold
Gates (MTTGs) have been proposed which further increase the functionality of
the original TGs while maintaining their operating principle and allowing also
the implementation of nanopipelining at the gate level. This paper describes
the design of n-bit adders using these MTTGs. A comparison with a design based
on TGs is carried out showing advantages in terms of latency, device counts and
power consumption.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
The Butcher--Oemler effect at z~0.35: a change in perspective
The present paper focuses on the much debated Butcher-Oemler effect: the
increase with redshift of the fraction of blue galaxies in clusters.
Considering a representative cluster sample made of seven group/clusters at
z~0.35, we have measured the blue fraction from the cluster core to the cluster
outskirts and the field mainly using wide field CTIO images. This sample
represents a random selection of a volume complete x-ray selected cluster
sample, selected so that there is no physical connection with the studied
quantity (blue fraction), to minimize observational biases. In order to
statistically assess the significance of the Butcher-Oemler effect, we
introduce the tools of Bayesian inference. Furthermore, we modified the blue
fraction definition in order to take into account the reduced age of the
universe at higher redshifts, because we should no longer attempt to reject an
unphysical universe in which the age of the Universe does depend on redshift,
whereas the age of its content does not. We measured the blue fraction from the
cluster center to the field and we find that the cluster affects the properties
of the galaxies up to two virial radii at z~0.35. Data suggest that during the
last 3 Gyrs no evolution of the blue fraction, from the cluster core to the
field value, is seen beyond the one needed to account for the varying age with
redshift of the Universe and of its content. The agreement of the radial
profiles of the blue fraction at z=0 and z~0.35 implies that the pattern infall
did not change over the last 3 Gyr, or, at least, its variation has no
observational effect on the studied quantity.Comment: MNRAS, in pres
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
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