4,583 research outputs found
Tracking Vector Magnetograms with the Magnetic Induction Equation
The differential affine velocity estimator (DAVE) developed in Schuck (2006)
for estimating velocities from line-of-sight magnetograms is modified to
directly incorporate horizontal magnetic fields to produce a differential
affine velocity estimator for vector magnetograms (DAVE4VM). The DAVE4VM's
performance is demonstrated on the synthetic data from the anelastic
pseudospectral ANMHD simulations that were used in the recent comparison of
velocity inversion techniques by Welsch (2007). The DAVE4VM predicts roughly
95% of the helicity rate and 75% of the power transmitted through the
simulation slice. Inter-comparison between DAVE4VM and DAVE and further
analysis of the DAVE method demonstrates that line-of-sight tracking methods
capture the shearing motion of magnetic footpoints but are insensitive to flux
emergence -- the velocities determined from line-of-sight methods are more
consistent with horizontal plasma velocities than with flux transport
velocities. These results suggest that previous studies that rely on velocities
determined from line-of-sight methods such as the DAVE or local correlation
tracking may substantially misrepresent the total helicity rates and power
through the photosphere.Comment: 30 pages, 13 figure
PRODUCTIVITY AND THE ENACTMENT OF A MACRO CULTURE
This paper reports the puzzling results of a study which examined IT capital investment
and productivity at three of the largest IT user sites in the U.S. for the period 1970-1990: Social
Security Administration (SSA), Internal Revenue Service (IRS), and the Federal Bureau of
Investigation (FBI). Based on detailed IT investment, employment, and output data over twenty
years, we found that only one agency had achieved significant productivity benefits, a second
agency had modest results, and a third agency achieved no results whatever. These results
cannot be explained by traditional theories of productivity of how productivity is produced.
We argue that IT-induced productivity results not simply from strategic choice, nor the
operation of the invisible hand in the market place, nor simply from keen managers adjusting
their organizations to an "objective" environment. Instead we propose instead a new theory in
which productivity benefits derive from a larger macro-culture enacted by powerful institutions
in an organizational field. We extend this analysis to the larger economy and examine how this
new theory helps us understand recent claims that IT is finally having positive productivity
benefits at the sector level, and also helps us understand how the current fascination with reengineering
and downsizing may be a self-fulfilling prophecy.Information Systems Working Papers Serie
Managing the patient with osteogenesis imperfecta: a multidisciplinary approach
Osteogenesis imperfecta (OI) is a heterogeneous heritable connective tissue disorder characterized by low bone density. The type and severity of OI are variable. The primary manifestations are fractures, bone deformity, and bone pain, resulting in reduced mobility and function to complete everyday tasks. OI affects not only the physical but also the social and emotional well-being of children, young people, and their families. As such, medical, surgical, and allied health professionals' assessments all play a role in the management of these children. The multidisciplinary approach to the treatment of children and young people living with OI seeks to provide well-coordinated, comprehensive assessments, and interventions that place the child and family at the very center of their care. The coordinated efforts of a multidisciplinary team can support children with OI to fulfill their potential, maximizing function, independence, and well-being
Information Technology and Occupational Structure
A central tenet of much popular and scholarly
literature is that computers -and more broadly speaking
"information systems"- bring about significant change in
organizations. Some scholars focus on changes in
organizational structure- the division of labor and its
coordination through authority and power (Blau, 1976;
Danziger, et. d., 1982; Laudon, 1976; 1986; Keen 1981;
Kling and Iacono, 1984; Orlikowski and Robey, 1991;
Robey, 1981; Walton, 1989; Barley 1986; 1990) . Others
focus on IT induced changes in the design of work
(Zuboff, 1984; Bikson, et. al., 1985: Kraut, et. al., 1987;
Sproull and Kiesler, 199 1; Turner, 1984; Iacono and
Kling, 1987). Still others have argued that IT
significantly alters occupational structure in
organizations--the distribution of employment among
occupations and skill classes of workers (Braverman,
1984; Kling and Turner, 1987; Berndt, et. al., 1992;
Howell and W e , 1993; Cyert and Mowry, 1988; 1989).
In general, the impact of IT on occupational structure of
firms and organizations is a neglected area of empirical
research despite the fact that scholars have strong
opinions, and convincing theories, about such
occupational shifts.
In this paper we report the results of a twenty year
longitudinal study of occupational structure in three of the
largest and most intensive organizational users of IT in
the United States. For benchmarking purposes we also
examine occupational change at the aggregate society
level and in the federal government sector over a twenty
year period. The results of our research question the
claim that IT brings about significant change in
occupational structure. While the organizations we
examine did experience significant change in
occupational structure during periods of intense
computerization, these changes did not conform to
theoretical predictions and they were inconsistent from
one organization to another. We conc1ude that
organizational occupational structures are quite stable in
the face of massive IT change and claims that IT brings
about "revo1utionaryâ changes in organizational structure
have little empirical foundation even though there may be
isolated cases where such rapid and drastic changes do
occur.Information Systems Working Papers Serie
The Regularizing Capacity of Metabolic Networks
Despite their topological complexity almost all functional properties of
metabolic networks can be derived from steady-state dynamics. Indeed, many
theoretical investigations (like flux-balance analysis) rely on extracting
function from steady states. This leads to the interesting question, how
metabolic networks avoid complex dynamics and maintain a steady-state behavior.
Here, we expose metabolic network topologies to binary dynamics generated by
simple local rules. We find that the networks' response is highly specific:
Complex dynamics are systematically reduced on metabolic networks compared to
randomized networks with identical degree sequences. Already small topological
modifications substantially enhance the capacity of a network to host complex
dynamic behavior and thus reduce its regularizing potential. This exceptionally
pronounced regularization of dynamics encoded in the topology may explain, why
steady-state behavior is ubiquitous in metabolism.Comment: 6 pages, 4 figure
Speeding up gate operations through dissipation
It is commonly believed that decoherence is the main obstacle to quantum information processing. In contrast to this, we show how decoherence in the form of dissipation can improve the performance of certain quantum gates. As an example we consider the realisations of a controlled phase gate and a two-qubit SWAP operation with the help of a single laser pulse in atom-cavity systems. In the presence of spontaneous decay rates, the speed of the gates can be improved by a factor 2 without sacrificing high fidelity and robustness against parameter fluctuations. Even though this leads to finite gate failure rates, the scheme is comparable with other quantum computing proposals
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