12,475 research outputs found
Concatenated Multilevel Coded Modulation Schemes for Digital Satellite Broadcasting
The error performance of bandwith-efficient concatenated multilevel coded modulation (MCM) schemes for digital satellite broadcasting is analyzed. Nonstandard partitioning, multistage decoding, and outer Reed-Solomon (RS) codes are employed to provided unequal error protection capabilities
Binary Multilevel Convolutional Codes with Unequal Error Protection Capabilities
Binary multilevel convolutional codes (CCs) with unequal error protection (UEP) capabilities are studied. These codes belong to the class of generalized concatenated (GC) codes. Binary CCs are used as outer codes. Binary linear block codes of short length, and selected subcodes in their two-way subcode partition chain, are used as inner codes. Multistage decodings are presented that use Viterbi decoders operating on trellises with similar structure to that of the constituent binary CCs. Simulation results of example binary two-level CC\u27s are also reported
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Laser Sintering of Stainless Steel using Resin Powder
We tried laser sintering of 316L stainless steel powder using resin powder. The laser
sintering conditions such as laser power, scan speed and scan pitch with a YAG laser, and the
influence of additional resin powder on the density and the tensile properties of the sintered alloy
were investigated experimentally. The tensile specimen was laser-sintered with a YAG laser, and
then debound and sintered in a vacuum furnace. The tensile specimen was successfully fabricated.
The relative density and the tensile strength varied with the additional resin powder, and the
optimum weight percentage of additional resin powder was around 4%.The relative density of the
sintered alloy was approximately 85%, and the tensile strength and elongation of the sintered
alloy were more than 280 MPa and 15% respectively.Mechanical Engineerin
Pairs of Bubbles in Planetary Nebulae and Clusters of Galaxies
I point to an interesting similarity in the morphology and some
non-dimensional quantities between pairs of X-ray-deficient bubbles in clusters
of galaxies and pairs of optical-deficient bubbles in planetary nebulae (PNs).
This similarity leads me to postulate a similar formation mechanism. This
postulate is used to strengthen models for PN shaping by jets (or collimated
fast winds: CFW). The presence of dense material in the equatorial plane
observed in the two classes of bubbles constrains the jets and CFW activity in
PNs to occur while the AGB star still blows its dense wind, or very shortly
after. I argue that only a stellar companion can account for such jets and CFW.Comment: PASP, in pres
JVN observations of H2O masers around the evolved star IRAS 22480+6002
We report on the H2O maser distributions around IRAS 22480+6002 (=IRC+60370)
observed with the Japanese VLBI Network (JVN) at three epochs spanning 2
months. This object was identified as a K-type supergiant in 1970s, which was
unusual as a stellar maser source. The spectrum of H2O masers consists of 5
peaks separated roughly equally by a few km/s each. The H2O masers were
spatially resolved into more than 15 features, which spread about 50 mas along
the east--west direction. However, no correlation was found between the proper
motion vectors and their spatial distributions; the velocity field of the
envelope seems random. A statistical parallax method applied to the observed
proper-motion data set gives a distance of 1.0+-0.4 kpc for this object, that
is considerably smaller than previously thought. The distance indicates that
this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and
optical characteristics quite similar to those of the population II post-AGB
stars such as RV Tau variables.Comment: 7 pages, 5 figures, PASJ 60, No. 1 (2008 Feb. 25 issue) in press.
High res. figures available at ftp://ftp.nro.nao.ac.jp/nroreport/no657.pdf.g
Generalized Landau-Pollak Uncertainty Relation
The Landau-Pollak uncertainty relation treats a pair of rank one projection
valued measures and imposes a restriction on their probability distributions.
It gives a nontrivial bound for summation of their maximum values. We give a
generalization of this bound (weak version of the Landau-Pollak uncertainty
relation). Our generalization covers a pair of positive operator valued
measures. A nontrivial but slightly weak inequality that can treat an arbitrary
number of positive operator valued measures is also presented.Comment: Simplified the proofs. To be published in Phys.Rev.
Entropic Inequalities for a Class of Quantum Secret Sharing States
It is well-known that von Neumann entropy is nonmonotonic unlike Shannon
entropy (which is monotonically nondecreasing). Consequently, it is difficult
to relate the entropies of the subsystems of a given quantum state. In this
paper, we show that if we consider quantum secret sharing states arising from a
class of monotone span programs, then we can partially recover the monotonicity
of entropy for the so-called unauthorized sets. Furthermore, we can show for
these quantum states the entropy of the authorized sets is monotonically
nonincreasing.Comment: LaTex, 5 page
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