1,049 research outputs found
On the importance of nonlinear modeling in computer performance prediction
Computers are nonlinear dynamical systems that exhibit complex and sometimes
even chaotic behavior. The models used in the computer systems community,
however, are linear. This paper is an exploration of that disconnect: when
linear models are adequate for predicting computer performance and when they
are not. Specifically, we build linear and nonlinear models of the processor
load of an Intel i7-based computer as it executes a range of different
programs. We then use those models to predict the processor loads forward in
time and compare those forecasts to the true continuations of the time seriesComment: Appeared in "Proceedings of the 12th International Symposium on
Intelligent Data Analysis
Teams in Small Organizations: Conceptual, Methodological, and Practical Considerations
Research on teams and teamwork has flourished in the last few decades. Much of what we know about teams and teamwork comes from research using short-term student teams in the lab, teams in larger organizations, and, more recently, teams in rather unique and extreme environments. The context in which teams operate influences team composition, processes, and effectiveness. Small organizations are an understudied and often overlooked context that presents a rich opportunity to augment our understanding of teams and team dynamics. In this paper, we discuss how teams and multi-team systems in small organizations may differ from those found in larger organizations. Many of these differences present both methodological and practical challenges to studying team composition and processes in small complex organizational settings. We advocate for applying and accepting new and less widely used methodological approaches to advance our understanding of the science of teams and teamwork in such contexts
Spatial Evidence for Transition Radiation in a Solar Radio Burst
Microturbulence, i.e. enhanced fluctuations of plasma density, electric and
magnetic fields, is of great interest in astrophysical plasmas, but occurs on
spatial scales far too small to resolve by remote sensing, e.g., at ~ 1-100 cm
in the solar corona. This paper reports spatially resolved observations that
offer strong support for the presence in solar flares of a suspected radio
emission mechanism, resonant transition radiation, which is tightly coupled to
the level of microturbulence and provides direct diagnostics of the existence
and level of fluctuations on decimeter spatial scales. Although the level of
the microturbulence derived from the radio data is not particularly high,
/n^2 ~ 10^{-5}$, it is large enough to affect the charged particle
diffusion and give rise to effective stochastic acceleration. This finding has
exceptionally broad astrophysical implications since modern sophisticated
numerical models predict generation of much stronger turbulence in relativistic
objects, e.g., in gamma-ray burst sources.Comment: 13 pages, 4 figures, ApJL accepte
Auditory reafferences: The influence of real-time feedback on movement control
© 2015 Kennel, Streese, Pizzera, Justen, Hohmann and Raab. Auditory reafferences are real-time auditory products created by a person's own movements. Whereas the interdependency of action and perception is generally well studied, the auditory feedback channel and the influence of perceptual processes during movement execution remain largely unconsidered. We argue that movements have a rhythmic character that is closely connected to sound, making it possible to manipulate auditory reafferences online to understand their role in motor control. We examined if step sounds, occurring as a by-product of running, have an influence on the performance of a complex movement task. Twenty participants completed a hurdling task in three auditory feedback conditions: a control condition with normal auditory feedback, a white noise condition in which sound was masked, and a delayed auditory feedback condition. Overall time and kinematic data were collected. Results show that delayed auditory feedback led to a significantly slower overall time and changed kinematic parameters. Our findings complement previous investigations in a natural movement situation with non-artificial auditory cues. Our results support the existing theoretical understanding of action-perception coupling and hold potential for applied work, where naturally occurring movement sounds can be implemented in the motor learning processes
Good Catch! Using Interdisciplinary Teams and Team Reflexivity to Improve Patient Safety
Interdisciplinary teams play an important role implementing innovations that facilitate the quality and safety of patient care. This article examined the role of reflexivity in team innovation implementation and its association with an objective patient safety outcome, inpatient fall rates (a fall is an unintended downward displacement of a patient’s body to the ground or other object). In this study, we implemented, supported, and evaluated interdisciplinary teams intended to decrease fall risk in 16 small rural hospitals. These hospitals were part of a collaborative that sought to increase knowledge and facilitate reflexivity about fall event reporting and fall risk reduction structures and processes. We assessed team reflexivity at the start and at the end of the 2-year intervention and innovation implementation at the end of the intervention. The 16 hospitals reported objective fall event data and patient days throughout the project, which we used to calculate comparative rates for assisted, unassisted, and injurious falls. The results suggest that teams benefited from the intervention, increasing reflexivity from the start of the project to the end, which was related to innovation implementation and decreases in fall rates. Theoretical and practical applications of the results are discussed
Group and Organizational Safety Norms Set the Stage for Good Post-Fall Huddles
We explored group and organizational safety norms as antecedents to meeting leader behaviors and achievement of desired outcomes in a special after-action review case—a post-fall huddle. A longitudinal survey design was used to investigate the relationship between organizational/group safety norms, huddle leader behavior, and huddle meeting effectiveness. The sample included health care workers in critical access hospitals (N = 206) who completed a baseline safety norm assessment and an assessment of post-fall huddle experiences 3 to 6 months later. Findings indicate that organizational and group safety norms relate to perceived huddle meeting effectiveness through appropriate huddle leader behavior in a partial mediated framework. In contrast to previous research showing after-action reviews predicting group and organizational safety norms, the longitudinal study presented here suggests that group and organizational safety norms set the stage for the enactment of post-fall huddles in an effective manner
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
Analytic solution for nonlinear shock acceleration in the Bohm limit
The selfconsistent steady state solution for a strong shock, significantly
modified by accelerated particles is obtained on the level of a kinetic
description, assuming Bohm-type diffusion. The original problem that is
commonly formulated in terms of the diffusion-convection equation for the
distribution function of energetic particles, coupled with the thermal plasma
through the momentum flux continuity equation, is reduced to a nonlinear
integral equation in one variable. Its solution provides selfconsistently both
the particle spectrum and the structure of the hydrodynamic flow. A critical
system parameter governing the acceleration process is found to be , where , with a suitably
normalized injection rate , the Mach number M >> 1, and the cut-off
momentum . We particularly focus on an efficient solution, in which
almost all the energy of the flow is converted into a few energetic particles.
It was found that (i) for this efficient solution (or, equivalently, for
multiple solutions) to exist, the parameter
must exceed a critical value ( is the injection
momentum), (ii) the total shock compression ratio r increases with M and
saturates at a level that scales as $ r \propto \Lambda_1 (iii) the downstream
power-law spectrum has the universal index q=3.5 over a broad momentum range.
(iv) completely smooth shock transitions do not appear in the steady state
kinetic description.Comment: 39 pages, 3 PostScript figures, uses aasms4.sty, to appear in Aug.
20, 1997 issue ApJ, vol. 48
The plerion nebula in IC 443: the XMM-Newton view
\xmm ~observations of the X-ray feature 1SAX J0617.1+2221 in the IC443
supernova remnant are reported.We resolve the structure of the nebula into a
compact core with a hard spectrum of photon index in the 2--10 keV energy range. The nebula also has an
extended (\sim 8\arcmin \times 5\arcmin) X-ray halo, much larger than the
radio emission extension. The photon index softens, following a linear scaling
with distance from the centroid, similar to other known X-ray plerions. The
index range is compatible with synchrotron burn-off models. All the
observational evidence points toward a confirmation of the plerionic nature of
the nebula, as recently suggested by a \ch observation, but with
characteristics more similar to "non Crab-like" plerions. We discuss the
implications on the synchrotron nebula magnetic field if the MeV
emission reported by {\it CGRO EGRET} is produced by the synchrotron emission.
We also constrain the thermal emission of the central object, arguing that the
surface temperature should be around 0.1 keV, although other possible fits
cannot be excluded on the base of the \xmm dataComment: 6 pages, 5 figures, accepted for publication in A&A. Color PDF file
ftp://astro.estec.esa.nl/pub/sciproj/fbocchin_h2804.pdf. Color PS file
http://www.astropa.unipa.it/biblioteca/OAPA_preprints/h2804.ps.g
Nonlinear dynamics of giant resonances in atomic nuclei
The dynamics of monopole giant resonances in nuclei is analyzed in the
time-dependent relativistic mean-field model. The phase spaces of isoscalar and
isovector collective oscillations are reconstructed from the time-series of
dynamical variables that characterize the proton and neutron density
distributions. The analysis of the resulting recurrence plots and correlation
dimensions indicate regular motion for the isoscalar mode, and chaotic dynamics
for the isovector oscillations. Information-theoretic functionals identify and
quantify the nonlinear dynamics of giant resonances in quantum systems that
have spatial as well as temporal structure.Comment: 24 pages, RevTeX, 15 PS figures, submitted Phys. Rev.
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