640,796 research outputs found
Measurements Should Generate Value, Rather than Data,
Success factors for measurement programs as identified in the literature typically focus on the `internals' of the measurement program: incremental implementation, support from management, a well-planned metrics framework, and so on. However, for a measurement program to be successful within its larger organizational context, it has to generate value for the organization. This implies that attention should also be given to the proper mapping of some identifiable organizational problem onto the measurement program, as well as the translation back of measurement results to organizational actions. In this paper, we present a generic process model for measurement-based improvement, which does cover the latter issues as well. We describe a number of common uses for measurement programs in software organizations, from which we derive additional `external' success factors. In addition, we propose a number of activities that organizations can use to implement value-generating measurement programs
Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation
In this paper we consider the problem of tracking the state of a quantum
system via a continuous measurement. If the system Hamiltonian is known
precisely, this merely requires integrating the appropriate stochastic master
equation. However, even a small error in the assumed Hamiltonian can render
this approach useless. The natural answer to this problem is to include the
parameters of the Hamiltonian as part of the estimation problem, and the full
Bayesian solution to this task provides a state-estimate that is robust against
uncertainties. However, this approach requires considerable computational
overhead. Here we consider a single qubit in which the Hamiltonian contains a
single unknown parameter. We show that classical frequency estimation
techniques greatly reduce the computational overhead associated with Bayesian
estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page
Resolving the A_{FB}^b puzzle in an extra dimensional model with an extended gauge structure
It is notorious that, contrary to all other precision electroweak data, the
forward-backward asymmetry for b quarks measured in Z decays at LEP1
is nearly three standard deviations away from the predicted value in the
Standard Model; significant deviations also occur in measurements of the
asymmetry off the Z pole. We show that these discrepancies can be resolved in a
variant of the Randall-Sundrum extra-dimensional model in which the gauge
structure is extended to to allow for
relatively light Kaluza-Klein excitations of the gauge bosons. In this
scenario, the fermions are localized differently along the extra dimension, in
order to generate the fermion mass hierarchies, so that the electroweak
interactions for the heavy third generation fermions are naturally different
from the light fermion ones. We show that the mixing between the Z boson with
the Kaluza-Klein excitations allows to explain the anomaly without
affecting (and even improving) the agreement of the other precision
observables, including the partial decay width, with experimental
data. Some implications of this scenario for the ILC are summarized.Comment: 23 pages, 5 figure
The Role of Ejecta in the Small Crater Populations on the Mid-Sized Saturnian Satellites
We find evidence that crater ejecta play an important role in the small
crater populations on the Saturnian satellites, and more broadly, on cratered
surfaces throughout the Solar System. We measure crater populations in Cassini
images of Enceladus, Rhea, and Mimas, focusing on image data with scales less
than 500 m/pixel. We use recent updates to crater scaling laws and their
constants to estimate the amount of mass ejected in three different velocity
ranges: (i) greater than escape velocity, (ii) less than escape velocity and
faster than the minimum velocity required to make a secondary crater (v_min),
and (iii) velocities less than v_min. Although the vast majority of mass on
each satellite is ejected at speeds less than v_min, our calculations
demonstrate that the differences in mass available in the other two categories
should lead to observable differences in the small crater populations; the
predictions are borne out by the measurements we have made to date. Rhea,
Tethys, and Dione have sufficient surface gravities to retain ejecta moving
fast enough to make secondary crater populations. The smaller satellites, such
as Enceladus but especially Mimas, are expected to have little or no
traditional secondary populations because their escape velocities are near the
threshold velocity necessary to make a secondary crater. Our work clarifies why
the Galilean satellites have extensive secondary crater populations relative to
the Saturnian satellites. The presence, extent, and sizes of sesquinary craters
(craters formed by ejecta that escape into temporary orbits around Saturn
before re-impacting the surface) is not yet well understood. Finally, our work
provides further evidence for a "shallow" size-frequency distribution (slope
index of ~2 for a differential power-law) for comets a few km diameter and
smaller. [slightly abbreviated]Comment: Submitted to Icarus. 77 double-spaced pages, including 25 figures and
5 table
A Measurement of Small Scale Structure in the 2.2 < z < 4.2 Lyman-alpha Forest
The amplitude of fluctuations in the Ly-a forest on small spatial scales is
sensitive to the temperature of the IGM and its spatial fluctuations. The
temperature of the IGM and its spatial variations contain important information
about hydrogen and helium reionization. We present a new measurement of the
small-scale structure in the Ly-a forest from 40 high resolution, high
signal-to-noise, VLT spectra at z=2.2-4.2. We convolve each Ly-a forest
spectrum with a suitably chosen wavelet filter, which allows us to extract the
amount of small-scale structure in the forest as a function of position across
each spectrum. We compare these measurements with high resolution hydrodynamic
simulations of the Ly-a forest which track more than 2 billion particles. This
comparison suggests that the IGM temperature close to the cosmic mean density
(T_0) peaks near z=3.4, at which point it is greater than 20,000 K at 2-sigma
confidence. The temperature at lower redshift is consistent with the fall-off
expected from adiabatic cooling (), after the peak
temperature is reached near z=3.4. At z=4.2 our results favor a temperature of
T_0 = 15-20,000 K. However, owing mostly to uncertainties in the mean
transmitted flux at this redshift, a cooler IGM model with T_0 = 10,000 K is
only disfavored at the 2-sigma level here, although such cool IGM models are
strongly discrepant with the z ~ 3-3.4 measurement. We do not detect large
spatial fluctuations in the IGM temperature at any redshift covered by our data
set. The simplest interpretation of our measurements is that HeII reionization
completes sometime near z ~ 3.4, although statistical uncertainties are still
large [Abridged].Comment: Submitted to ApJ. Best printed in colo
Testing the Halo Model Against the SDSS Photometric Survey
We present halo model predictions for the expected angular clustering and
associated errors from the completed Sloan Digital Sky Survey (SDSS)
photometric galaxy sample. These results are used to constrain halo model
parameters under the assumption of a fixed LCDM cosmology using standard Fisher
matrix techniques. Given the ability of the five-color SDSS photometry to
separate galaxies into sub-populations by intrinsic color, we also use
extensions of the standard halo model formalism to calculate the expected
clustering of red and blue galaxy sub-populations as a further test of the
galaxy evolution included in the semi-analytic methods for populating dark
matter halos with galaxies. The extremely small sample variance and Poisson
errors from the completed SDSS survey should result in very impressive
constraints (~1-10%) on the halo model parameters for a simple
magnitude-limited sample and should provide an extremely useful check on the
behavior of current and future N-body simulations and semi-analytic techniques.
We also show that similar constraints are possible using a narrow selection
function, as would be possible using photometric redshifts, without making
linear assumptions regarding the evolution of the underlying power spectra. In
both cases, we explore the effects of uncertainty in the selection function on
the resulting constraints and the degeneracies between various combinations of
parameters.Comment: 16 pages, 17 figure
Correlated Resource Models of Internet End Hosts
Understanding and modelling resources of Internet end hosts is essential for
the design of desktop software and Internet-distributed applications. In this
paper we develop a correlated resource model of Internet end hosts based on
real trace data taken from the SETI@home project. This data covers a 5-year
period with statistics for 2.7 million hosts. The resource model is based on
statistical analysis of host computational power, memory, and storage as well
as how these resources change over time and the correlations between them. We
find that resources with few discrete values (core count, memory) are well
modeled by exponential laws governing the change of relative resource
quantities over time. Resources with a continuous range of values are well
modeled with either correlated normal distributions (processor speed for
integer operations and floating point operations) or log-normal distributions
(available disk space). We validate and show the utility of the models by
applying them to a resource allocation problem for Internet-distributed
applications, and demonstrate their value over other models. We also make our
trace data and tool for automatically generating realistic Internet end hosts
publicly available
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