8,308 research outputs found
Binary Mixtures of Particles with Different Diffusivities Demix
The influence of size differences, shape, mass and persistent motion on phase
separation in binary mixtures has been intensively studied. Here we focus on
the exclusive role of diffusivity differences in binary mixtures of equal-sized
particles. We find an effective attraction between the less diffusive
particles, which are essentially caged in the surrounding species with the
higher diffusion constant. This effect leads to phase separation for systems
above a critical size: A single close-packed cluster made up of the less
diffusive species emerges. Experiments for testing of our predictions are
outlined.Comment: 5 figures in main text, 8 figures in Supplemental Materia
Mungo and StMungo: tools for typechecking protocols in Java
We present two tools that support static typechecking of communica- tion protocols in Java. Mungo associates Java classes with typestate specifications, which are state machines defining permitted sequences of method calls. StMungo translates a communication protocol specified in the Scribble protocol description language into a typestate specification for each role in the protocol by following the message sequence. Role implementations can be typechecked by Mungo to ensure that they satisfy their protocols, and then compiled as usual with javac. We demonstrate the Scribble, StMungo and Mungo toolchain via a typechecked POP3 client that can communicate with a real-world POP3 server
Pearson Codes
The Pearson distance has been advocated for improving the error performance
of noisy channels with unknown gain and offset. The Pearson distance can only
fruitfully be used for sets of -ary codewords, called Pearson codes, that
satisfy specific properties. We will analyze constructions and properties of
optimal Pearson codes. We will compare the redundancy of optimal Pearson codes
with the redundancy of prior art -constrained codes, which consist of
-ary sequences in which pre-determined reference symbols appear at least
once. In particular, it will be shown that for the -constrained
codes are optimal Pearson codes, while for these codes are not
optimal.Comment: 17 pages. Minor revisions and corrections since previous version.
Author biographies added. To appear in IEEE Trans. Inform. Theor
Shuttle Ku-band and S-band communications implementation study
Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed
Human infants' learning of social structures: the case of dominance hierarchy
We tested 15-month-olds’ capacity to represent social-dominance hierarchies with more than two agents. Our results showed that infants found it harder to memorize dominance relations that were presented in an order that hindered the incremental formation of a single structure (Study 1). These results suggest that infants attempt to build structures incrementally, relation by relation, thereby simplifying the complex problem of recognizing a social structure. Infants also found circular dominance structures harder to process than linear dominance structures (Study 2). These expectations about the shape of structures may facilitate learning. Our results suggest that infants attempt to represent social structures composed of social relations. They indicate that human infants go beyond learning about individual social partners and their respective relations and form hypotheses about how social groups are organized
Combustion waves in a model with chain branching reaction and their stability
In this paper the travelling wave solutions in the adiabatic model with
two-step chain branching reaction mechanism are investigated both numerically
and analytically in the limit of equal diffusivity of reactant, radicals and
heat. The properties of these solutions and their stability are investigated in
detail. The behaviour of combustion waves are demonstrated to have similarities
with the properties of nonadiabatic one-step combustion waves in that there is
a residual amount of fuel left behind the travelling waves and the solutions
can exhibit extinction. The difference between the nonadiabatic one-step and
adiabatic two-step models is found in the behaviour of the combustion waves
near the extinction condition. It is shown that the flame velocity drops down
to zero and a standing combustion wave is formed as the extinction condition is
reached. Prospects of further work are also discussed.Comment: pages 32, figures 2
Asymptotic expansions of the Cotton-York tensor on slices of stationary spacetimes
We discuss expansions for the Cotton-York tensor near infinity for arbitrary
slices of stationary spacetimes. From these expansions it follows directly that
a necessary condition for the existence of conformally flat slices in
stationary solutions is the vanishing of a certain quantity of quadrupolar
nature (obstruction). The obstruction is nonzero for the Kerr solution. Thus,
the Kerr metric admits no conformally flat slices. An analysis of higher orders
in the expansions of the Cotton-York tensor for solutions such that the
obstruction vanishes suggests that the only stationary solution admitting
conformally flat slices are the Schwarzschild family of solutions.Comment: Revised version to appear in Class. Quantum Grav. with 13 pages.
Section 2 regarding multipolar expansions of stationary spacetimes largely
expanded. A Maple script demonstrating the calculations in the axially
symmetric case is available upon request from the autho
Baryon Current Matrix Elements in a Light-Front Framework
Current matrix elements and observables for electro- and photo-excitation of
baryons from the nucleon are studied in a light-front framework. Relativistic
effects are estimated by comparison to a nonrelativistic model, where we use
simple basis states to represent the baryon wavefunctions. Sizeable
relativistic effects are found for certain transitions, for example, to radial
excitations such as that conventionally used to describe to the Roper
resonance. A systematic study shows that the violation of rotational covariance
of the baryon transition matrix elements stemming from the use of one-body
currents is generally small.Comment: 32 pages, LaTeX, 10 postscript figures, uses epsf.sty; figures
uuencoded with uufiles (or available by request in .ps or hardcopy form
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