3,941 research outputs found
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
Perception of nonnative tonal contrasts by Mandarin-English and English-Mandarin sequential bilinguals
This study examined the role of acquisition order and crosslinguistic similarity in influencing transfer at the initial stage of perceptually acquiring a tonal third language (L3). Perception of tones in Yoruba and Thai was tested in adult sequential bilinguals representing three different first (L1) and second language (L2) backgrounds: L1 Mandarin-L2 English (MEBs), L1 English-L2 Mandarin (EMBs), and L1 English-L2 intonational/non-tonal (EIBs). MEBs outperformed EMBs and EIBs in discriminating L3 tonal contrasts in both languages, while EMBs showed a small advantage over EIBs on Yoruba. All groups showed better overall discrimination in Thai than Yoruba, but group differences were more robust in Yoruba. MEBs’ and EMBs’ poor discrimination of certain L3 contrasts was further reflected in the L3 tones being perceived as similar to the same Mandarin tone; however, EIBs, with no knowledge of Mandarin, showed many of the same similarity judgments. These findings thus suggest that L1 tonal experience has a particularly facilitative effect in L3 tone perception, but there is also a facilitative effect of L2 tonal experience. Further, crosslinguistic perceptual similarity between L1/L2 and L3 tones, as well as acoustic similarity between different L3 tones, play a significant role at this early stage of L3 tone acquisition.Published versio
The Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
Modern data empower observers to describe galaxies as the spatially and
biographically complex objects they are. We illustrate this through case
studies of four, systems based on deep, spatially resolved, 17-band
+ G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full
spectrum rest-UV/-optical continuum fitting, we characterize these galaxies'
observed kpc-scale structures and star formation rates (SFRs) and
reconstruct their history over the age of the universe. The sample's
diversity---passive to vigorously starforming; stellar masses to ---enables us to draw spatio-temporal inferences
relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass
progenitors). Specifically, we find signs that bulge mass-fractions () and
SF history shapes/spatial uniformity are linked, such that higher s
correlate with "inside-out growth" and central specific SFRs that peaked above
the global average for all starforming galaxies at that epoch. Conversely, the
system with the lowest had a flat, spatially uniform SFH with normal peak
activity. Both findings are consistent with models positing a feedback-driven
connection between bulge formation and the switch from rising to falling SFRs
("quenching"). While sample size forces this conclusion to remain tentative,
this work provides a proof-of-concept for future efforts to refine or refute
it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data
amenable to this and more sophisticated analyses. These samples---spanning
representative mass, redshift, SFR, and environmental regimes---will be ripe
for converting into thousands of sub-galactic-scale empirical windows on what
individual systems actually looked like in the past, ushering in a new dialog
between observation and theory.Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table
(appendix); Submitted to AAS Journals 1 October 201
Beyond Exploratory: A Tailored Framework for Assessing Rigor in Qualitative Health Services Research
Objective: To propose a framework for assessing the rigor of qualitative research that identifies and distinguishes between the diverse objectives of qualitative studies currently used in patient-centered outcomes and health services research (PCOR and HSR).
Study Design: Narrative review of published literature discussing qualitative guidelines and standards in peer-reviewed journals and national funding organizations that support PCOR and HSR.
Principal Findings: We identify and distinguish three objectives of current qualitative studies in PCOR and HSR: exploratory, descriptive, and comparative. For each objective, we propose methodological standards that can be used to assess and improve rigor across all study phases—from design to reporting. Similar to quantitative studies, we argue that standards for qualitative rigor differ, appropriately, for studies with different objectives and should be evaluated as such.
Conclusions: Distinguishing between different objectives of qualitative HSR improves the ability to appreciate variation in qualitative studies as well as appropriately evaluate the rigor and success of studies in meeting their own objectives. Researchers, funders, and journal editors should consider how adopting the criteria for assessing qualitative rigor outlined here may advance the rigor and potential impact of qualitative research in patient-centered outcomes and health services research
Small world effect in an epidemiological model
A model for the spread of an infection is analyzed for different population
structures. The interactions within the population are described by small world
networks, ranging from ordered lattices to random graphs. For the more ordered
systems, there is a fluctuating endemic state of low infection. At a finite
value of the disorder of the network, we find a transition to self-sustained
oscillations in the size of the infected subpopulation
Class of self-limiting growth models in the presence of nonlinear diffusion
The source term in a reaction-diffusion system, in general, does not involve
explicit time dependence. A class of self-limiting growth models dealing with
animal and tumor growth and bacterial population in a culture, on the other
hand are described by kinetics with explicit functions of time. We analyze a
reaction-diffusion system to study the propagation of spatial front for these
models.Comment: RevTex, 13 pages, 5 figures. To appear in Physical Review
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
Space construction system analysis. Part 2: Platform definition
The top level system requirements are summarized and the accompanying conceptual design for an engineering and technology verification platform (ETVP) system is presented. An encompassing statement of the system objectives which drive the system requirements is presented and the major mission and subsystem requirements are described with emphasis on the advanced communications technology mission payload. The platform design is defined and used as a reference configuration for an end to space construction analyses. The preferred construction methods and processes, the important interactions between the platform design and the construction system design and operation, and the technology development efforts required to support the design and space construction of the ETVP are outlined
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