4,971 research outputs found
Refracting profiles and generalized holodiagrams
The recently developed concept of refracting profiles and that of refraction
holodiagrams are combined so that the classical Abramson holodiagrams can be
generalized taking into account a wider class of wave fronts and refraction at
an interface, whenever regions of caustics are avoided. These holodiagrams are
obtained as envelopes of specific families of Cartesian Ovals with an
appropriate parametrization. Classical and reflecting holodiagrams are
particular cases of this class. Several of the properties of the classical
holodiagrams are shared by their richer generalized versionsComment: 12 pages, 7 figure
OFT ascent/descent ancillary data requirements document
Requirements are presented for the ascent/descent (A/D) navigation and attitude-dependent ancillary data products to be generated for the space shuttle orbiter in support of orbital flight test requirements, MPAD guidance and navigation performance assessment, and the mission evaluation team. It was intended that this document serve as the sole requirements control instrument between MPB/MPAD and the A/D ancillary data users. The requirements are primarily functional in nature, but some detail level requirements are also included
Regression of ranked responses when raw responses are censored
We discuss semiparametric regression when only the ranks of responses are
observed. The model is , where is the unobserved response, is a monotone
increasing function, is a known vector of covariates,
is an unknown -vector of interest, and
is an error term independent of . We observe
, where is the ordinal
rank function. We explore a novel estimator under Gaussian assumptions. We
discuss the literature, apply the method to an Alzheimer's disease biomarker,
conduct simulation studies, and prove consistency and asymptotic normality.Comment: 33 pages, 6 figure
Long transients and cluster size in globally coupled maps
We analyze the asymptotic states in the partially ordered phase of a system
of globally coupled logistic maps. We confirm that, regardless of initial
conditions, these states consist of a few clusters, and they properly belong in
the ordered phase of these systems. The transient times necessary to reach the
asymptotic states can be very long, especially very near the transition line
separating the ordered and the coherent phases. We find that, where two
clusters form, the distribution of their sizes corresponds to windows of
regular or narrow-band chaotic behavior in the bifurcation diagram of a system
of two degrees of freedom that describes the motion of two clusters, where the
size of one cluster acts as a bifurcation parameter.Comment: To appear in Europhysics Letter
Space use by foragers consuming renewable resources
We study a simple model of a forager as a walk that modifies a relaxing
substrate. Within it simplicity, this provides an insight on a number of
relevant and non-intuitive facts. Even without memory of the good places to
feed and no explicit cost of moving, we observe the emergence of a finite home
range. We characterize the walks and the use of resources in several
statistical ways, involving the behavior of the average used fraction of the
system, the length of the cycles followed by the walkers, and the frequency of
visits to plants. Preliminary results on population effects are explored by
means of a system of two non directly interacting animals. Properties of the
overlap of home ranges show the existence of a set of parameters that provides
the best utilization of the shared resource
A simplex-like search method for bi-objective optimization
We describe a new algorithm for bi-objective optimization, similar to the Nelder Mead simplex
algorithm, widely used for single objective optimization. For diferentiable bi-objective functions on
a continuous search space, internal Pareto optima occur where the two gradient vectors point in
opposite directions. So such optima may be located by minimizing the cosine of the angle between
these vectors. This requires a complex rather than a simplex, so we term the technique the \cosine
seeking complex". An extra beneft of this approach is that a successful search identifes the direction
of the effcient curve of Pareto points, expediting further searches. Results are presented for some
standard test functions. The method presented is quite complicated and space considerations here
preclude complete details. We hope to publish a fuller description in another place
Spatio-temporal patterns in the Hantavirus infection
We present a model of the infection of Hantavirus in deer mouse, Peromyscus
maniculatus, based on biological observations of the system in the North
American Southwest. The results of the analysis shed light on relevant
observations of the biological system, such as the sporadical disappearance of
the infection, and the existence of foci or ``refugia'' that perform as
reservoirs of the virus when environmental conditions are less than optimal.Comment: 6 pages, 5 inlined figures, RevTeX 4 forma
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