7,012 research outputs found
Telescoping columns
An extendable column is described which consists of several axially elongated rigid structural sections nested within one another. Each section includes a number of rotatably attached screws running along its length. The next inner section includes threaded lugs oriented to threadingly engage the screws. The column is extended or retracted upon rotation of the screws. The screws of each section are selectively rotated by a motor and an engagement mechanism
Founding family firms, CEO incentive pay, and dual agency problems
This paper contributes to the literature on agency theory by examining relations between family involvement and CEO compensation. Using a panel of 362 small U.S. listed firms, we analyze how founding families influence firm performance through option portfolio price sensitivity. Consistent with the dual agency framework, we find that family firms have lower CEO incentive pay, which is further reduced by higher executive ownership. Interestingly, such incentive pay offsets the positive impact that families have on firm valuation. Collectively, our results show that, compared with nonfamily firms, lower incentive pay adopted by family firms due to lower agency costs mitigates the direct effect of family involvement on firm performance. Once accounting for CEO incentive pay, we do not observe performance differences between family and nonfamily firms
Reconnection Studies Under Different Types of Turbulence Driving
We study a model of fast magnetic reconnection in the presence of weak
turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional
direct numerical simulations. The model has been already successfully tested in
Kowal et al. (2009) confirming the dependencies of the reconnection speed
on the turbulence injection power and the injection scale
expressed by a constraint
and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in
order to drive turbulence, we injected velocity fluctuations in Fourier space
with frequencies concentrated around , as described in
Alvelius (1999). In this paper we extend our previous studies by comparing fast
magnetic reconnection under different mechanisms of turbulence injection by
introducing a new way of turbulence driving. The new method injects velocity or
magnetic eddies with a specified amplitude and scale in random locations
directly in real space. We provide exact relations between the eddy parameters
and turbulent power and injection scale. We performed simulations with new
forcing in order to study turbulent power and injection scale dependencies. The
results show no discrepancy between models with two different methods of
turbulence driving exposing the same scalings in both cases. This is in
agreement with the Lazarian and Vishniac (1999) predictions. In addition, we
performed a series of models with varying viscosity . Although Lazarian
and Vishniac (1999) do not provide any prediction for this dependence, we
report a weak relation between the reconnection speed with viscosity,
.Comment: 19 pages, 9 figures. arXiv admin note: text overlap with
arXiv:0903.205
Numerical Studies of Weakly Stochastic Magnetic Reconnection
We study the effects of turbulence on magnetic reconnection using
three-dimensional numerical simulations. This is the first attempt to test a
model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999),
which assumes the presence of weak, small-scale magnetic field structure near
the current sheet. This affects the rate of reconnection by reducing the
transverse scale for reconnection flows and by allowing many independent flux
reconnection events to occur simultaneously. We performed a number of
simulations to test the dependencies of the reconnection speed, defined as the
ratio of the inflow velocity to the Alfven speed, on the turbulence power, the
injection scale and resistivity. Our results show that turbulence significantly
affects the topology of magnetic field near the diffusion region and increases
the thickness of the outflow region. We confirm the predictions of the Lazarian
& Vishniac model. In particular, we report the growth of the reconnection speed
proportional to ~ V^2, where V is the amplitude of velocity at the injection
scale. It depends on the injection scale l as ~ (l/L)^(2/3), where L is the
size of the system, which is somewhat faster but still roughly consistent with
the theoretical expectations. We also show that for 3D reconnection the Ohmic
resistivity is important in the local reconnection events only, and the global
reconnection rate in the presence of turbulence does not depend on it.Comment: 8 pages, 8 figure
NGC 4654: polarized radio continuum emission as a diagnostic tool for a galaxy--cluster interaction
A recent comparison between deep VLA HI observations and dynamical models of
the Virgo cluster spiral galaxy NGC 4654 has shown that only a model involving
a combination of a tidal interaction and ram pressure can reproduce the data.
Deep radio polarization studies, together with detailed MHD modeling, can
independently verify those conclusions, that are based on HI observations and
dynamical models. We performed deep polarized radio-continuum observations of
the Virgo cluster spiral galaxy NGC 4654 with the Effelsberg 100m telescope at
8.35 GHz and the VLA at 4.85 GHz. Detailed 3D MHD simulations were made to
determine the large-scale magnetic field and the emission distribution of the
polarized radio continuum in the model, during the galaxy evolution within the
cluster environment. This direct comparison between the observed and simulated
polarized radio continuum emission corroborates the earlier results, that the
galaxy had a recent rapid close encounter with NGC 4639 and is undergoing weak
ram pressure by the intracluster medium. This combination of deep radio
polarization studies and detailed MHD modeling thus gives us unique insight
into the interactions of a galaxy with its cluster environment. It represents a
diagnostic tool that is complementary to deep HI observations.Comment: Corrected galaxy name in captions of figures (1 & 2
Lessons Learned from Development of a Software Tool to Support Academic Advising
We detail some lessons learned while designing and testing a
decision-theoretic advising support tool for undergraduates at a large state
university. Between 2009 and 2011 we conducted two surveys of over 500 students
in multiple majors and colleges. These surveys asked students detailed
questions about their preferences concerning course selection, advising, and
career paths. We present data from this study which may be helpful for faculty
and staff who advise undergraduate students. We find that advising support
software tools can augment the student-advisor relationship, particularly in
terms of course planning, but cannot and should not replace in-person advising.Comment: 5 Figures, revised version including more figures and
cross-referencin
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