5,052 research outputs found
The Fast Wandering of Slow Birds
I study a single "slow" bird moving with a flock of birds of a different, and
faster (or slower) species. I find that every "species" of flocker has a
characteristic speed , where is the mean speed of the
flock, such that, if the speed of the "slow" bird equals , it
will randomly wander transverse to the mean direction of flock motion far
faster than the other birds will: its mean-squared transverse displacement will
grow in with time like , in contrast to for the
other birds. In , the slow bird's mean squared transverse displacement
grows like , in contrast to for the other birds. If , the mean-squared displacement of the "slow" bird crosses over from
to scaling in , and from to scaling in
, at a time that scales according to .Comment: 10 pages; 5 pages of which did not appear in earlier versions, but
were added in response to referee's suggestion
Production of Jets at the Tevatron
Measurements of the inclusive jet cross section and the dijet angular
distribution using data from the Tevatron are presented. Comparisons to NLO QCD
show good agreement below 250 GeV, but CDF data show an excess at higher ET;
qualitative agreement is seen between the CDF and DO cross sections. Analysis
of the dijet angular distributions exclude quark compositeness below 2.1 TeV.Comment: 5 pages, 6 figure
A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks
I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find
new linear terms in the hydrodynamic equations which slightly modify the
anisotropy, but not the scaling, of the damping of sound modes. I also find
that the nonlinearities allowed {\it in equilibrium} do not stabilize long
ranged order in spatial dimensions ; in accord with the Mermin-Wagner
theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in
, as argued by earlier work. Some of these were missed by earlier work; it
is unclear whether or not they change the scaling exponents in .Comment: 6 pages, no figures. arXiv admin note: text overlap with
arXiv:0909.195
Shuttle Ku-band and S-band communications implementations study
The interfaces between the Ku-band system and the TDRSS, between the S-band system and the TDRSS, GSTDN and SGLS networks, and between the S-band payload communication equipment and the other Orbiter avionic equipment were investigated. The principal activities reported are: (1) performance analysis of the payload narrowband bent-pipe through the Ku-band communication system; (2) performance evaluation of the TDRSS user constraints placed on the S-band and Ku-band communication systems; (3) assessment of the shuttle-unique S-band TDRSS ground station false lock susceptibility; (4) development of procedure to make S-band antenna measurements during orbital flight; (5) development of procedure to make RFI measurements during orbital flight to assess the performance degradation to the TDRSS S-band communication link; and (6) analysis of the payload interface integration problem areas
Bounded analysis of constrained dynamical systems: a case study in nuclear arms control
We introduce a simple dynamical system that describes key features of a bilateral nuclear arms control regime. The evolution of each party's beliefs and declarations under the regime are represented, and the e ects of inspection processes are captured. Bounded analysis of this model allows us to explore { within a nite horizon { the consequences of changes to the rules of the arms control process and to the strategies of each party, bounded scope invariants for variables of interest, and dynamics for initial states containing strict uncertainty. Together these would potentially enable a decision support system to consider cases of interest irrespective of unknowns. We realize such abilities by building a Python package that draws on the capabilities of a Satis ability Modulo Theory (SMT) solver to explore particular scenarios and to optimize measures of interest { such as the belief of one nation in the statements made by another, or the timing of an unscheduled inspection such that it has maximum value. We show that these capabilities can in principle support the design or assessment of future bilateral arms control instruments by applying them to a set of representative and relevant test scenarios with realistic nite horizons
Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization
The observation of jets in a variety of hard-scattering processes has allowed
the quantitative study of perturbative quantum chromodynamics (PQCD) by
comparing detailed theoretical predictions with a wide range of experimental
data. This paper examines how some important, nonperturbative, facets of QCD
involving the internal dynamical structure of jets can be studied by measuring
the spin orientation of Lambda particles produced in these jets. The
measurement of the transverse polarization for an individual Lambda within a
QCD jet permits the definition of spin-directed asymmetries in local quantum
number densities in rapidity space (such as charge, strangeness and baryon
number densities) involving neighboring hadrons in the jet. These asymmetries
can only be generated by soft, nonperturbative dynamical mechanisms and such
measurements can provide insight not otherwise accessible into the color
rearrangement that occurs during the hadronization stage of the fragmentation
process.Comment: The replacement manuscript contains a new abstract, five pages of
additional material and a revised version of Fig.
Functional Subdomains within Human FFA
Cataloged from PDF version of article.The fusiform face area (FFA) is a well-studied human brain region that shows strong activation for faces. In functional MRI studies, FFA is often assumed to be a homogeneous collection of voxels with similar visual tuning. To test this assumption, we used natural movies and a quantitative voxelwise modeling and decoding framework to estimate category tuning profiles for individual voxels within FFA. We find that the responses in most FFA voxels are strongly enhanced by faces, as reported in previous studies. However, we also find that responses of individual voxels are selectively enhanced or suppressed by a wide variety of other categories and that these broader tuning profiles differ across FFA voxels. Cluster analysis of category tuning profiles across voxels reveals three spatially segregated functional subdomains within FFA. These subdomains differ primarily in their responses for nonface categories, such as animals, vehicles, and communication verbs. Furthermore, this segregation does not depend on the statistical threshold used to define FFA from responses to functional localizers. These results suggest that voxels within FFA represent more diverse information about object and action categories than generally assumed. © 2013 the authors
Probing jet properties via two particle correlation method
The formulae for calculating jet fragmentation momentum, , and conditional yield are discussed in
two particle correlation framework. Additional corrections are derived to
account for the limited detector acceptance and inefficiency, for cases when
the event mixing technique is used. The validity of our approach is confirmed
with Monte-carlo simulation.Comment: Proceeding for HotQuarks2004 conference. 11 pages, 8 figures,
corrected for typo
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