2,578 research outputs found
The Logic of Uncertainty and Executive Discretion in Decision Making: The Dallas-Fort Worth Metroplex Ebola Response
This paper addresses an important question: what can a highly complex public health situation such as the Dallas-Fort Worth Ebola outbreak tell us about the use of discretion by executive level public administrators? The public administration literature is rich with evidence of street-level bureaucratic discretion, but has not explored executive level discretion decision making. The authors argue that in highly complex situations of uncertainty, such as in the case of the Dallas-Fort Worth regional Ebola emergency response, the executive use of discretion translates to decisions under the conditions of uncertainty. This article theorizes a logic of uncertainty when two important assumptions exist; the situation is absent a plan to guide decision making, and the decision makers lack any previous precedent with the situation. Results indicate that when survey respondents departed from their emergency management plan, and planned as the event folded, they were more likely to use executive discretion decision making
Mean-atom-trajectory model for the velocity autocorrelation function of monatomic liquids
We present a model for the motion of an average atom in a liquid or
supercooled liquid state and apply it to calculations of the velocity
autocorrelation function and diffusion coefficient . The model
trajectory consists of oscillations at a distribution of frequencies
characteristic of the normal modes of a single potential valley, interspersed
with position- and velocity-conserving transits to similar adjacent valleys.
The resulting predictions for and agree remarkably well with MD
simulations of Na at up to almost three times its melting temperature. Two
independent processes in the model relax velocity autocorrelations: (a)
dephasing due to the presence of many frequency components, which operates at
all temperatures but which produces no diffusion, and (b) the transit process,
which increases with increasing temperature and which produces diffusion.
Because the model provides a single-atom trajectory in real space and time,
including transits, it may be used to calculate all single-atom correlation
functions.Comment: LaTeX, 8 figs. This is an updated version of cond-mat/0002057 and
cond-mat/0002058 combined Minor changes made to coincide with published
versio
The nonmesonic weak decay of the hypertriton
The nonmesonic decay of the hypertriton is calculated based on a hypertriton
wavefunction and 3N scattering states, which are rigorous solutions of 3-body
Faddeev equations using realistic NN and hyperon-nucleon interactions. The
pion-exchange together with heavier meson exchanges for the transition is considered. The total nonmesonic decay rate is found to be 0.5%
of the free decay rate. Integrated as well as differential decay
rates are given. The p- and n- induced decays are discussed thoroughly and it
is shown that the corresponding total rates cannot be measured individually.Comment: 27 pages, 20 figures, revtex, submitted to Phys. Rev.
Time and Space Bounds for Reversible Simulation
We prove a general upper bound on the tradeoff between time and space that
suffices for the reversible simulation of irreversible computation. Previously,
only simulations using exponential time or quadratic space were known.
The tradeoff shows for the first time that we can simultaneously achieve
subexponential time and subquadratic space.
The boundary values are the exponential time with hardly any extra space
required by the Lange-McKenzie-Tapp method and the ()th power time with
square space required by the Bennett method. We also give the first general
lower bound on the extra storage space required by general reversible
simulation. This lower bound is optimal in that it is achieved by some
reversible simulations.Comment: 11 pages LaTeX, Proc ICALP 2001, Lecture Notes in Computer Science,
Vol xxx Springer-Verlag, Berlin, 200
Zero-Field Time-of-Flight Measurements of Electron Diffusion in P+-GaAs
Minority electron diffusivities in p+-GaAs-doped NA =~1.4×1018 and ~1019 cm-3 have been measured in zero-field conditions with an extension of the zero-field time-of-flight technique. Extension of the technique to make it applicable to heavily doped p+-GaAs is described and zero-field data are discussed. Unexpectedly, majority carrier drag effects are not evident in a comparison of this data with recently reported high-field data. Low zero-field mobility of electrons in p+-GaAs has important implications for high-speed devices such as heterojunction bipolar transistors
Instantaneous Normal Mode Analysis of Supercooled Water
We use the instantaneous normal mode approach to provide a description of the
local curvature of the potential energy surface of a model for water. We focus
on the region of the phase diagram in which the dynamics may be described by
the mode-coupling theory. We find, surprisingly, that the diffusion constant
depends mainly on the fraction of directions in configuration space connecting
different local minima, supporting the conjecture that the dynamics are
controlled by the geometric properties of configuration space. Furthermore, we
find an unexpected relation between the number of basins accessed in
equilibrium and the connectivity between them.Comment: 5 pages, 4 figure
Redistribution of Stars and Gas in the Star Formation Deserts of Barred Galaxies
Bars strongly influence the distribution of gas and stars within the central regions of their host galaxies. This is particularly pronounced in the star formation desert (SFD) which is defined as two symmetrical regions either side of the bar that show a deficit in young stars. Previous studies proposed that, if star formation is truncated because of the influence of the bar, then the age distribution of stars within the SFD could be used to determine the epoch of bar formation. To test this, we study the properties of SFDs in 6 galaxies from zoom-in cosmological re-simulations. Age maps reveal old regions on both sides of the bars, with a lack of stars younger than 10 Myr, confirming the SFD phenomenon. Local star formation is truncated in the SFDs because after the bar forms, gas in these regions is removed on 1 Gyr timescales. However, the overall age distribution of stars in the SFD does not show a sharp truncation after bar formation but rather a gradual downturn in comparison to that of the bar. This more subtle signature may still give information on bar formation epochs in observed galaxies, but the interpretation will be more difficult than originally hoped. The gradual drop in the SFD age distribution, instead of a truncation, is due to radial migration of stars born in the disk. The SFD is thus one of the only regions where an uncontaminated sample of stars only affected by radial migration can be studied
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