1,857 research outputs found
Quantitative determination of engine water ingestion
A nonintrusive optical technique is described for determination of liquid mass flux in a droplet laden airstream. The techniques were developed for quantitative determination of engine water ingestion resulting from heavy rain or wheel spray. Independent measurements of the liquid water content (LWC) of the droplet laden airstream and of the droplet velocities were made at the stimulated nacelle inlet plane for the liquid mass flux determination. The LWC was measured by illuminating and photographing the droplets contained within a thin slice of the flow field by means of a sheet of light from a pulsed laser. A fluorescent dye introduced in the water enchanced the droplet image definition. The droplet velocities were determined from double exposed photographs of the moving droplet field. The technique was initially applied to a steady spray generated in a wind tunnel. It was found that although the spray was initially steady, the aerodynamic breakup process was inherently unsteady. This resulted in a wide variation of the instantaneous LWC of the droplet laden airstream. The standard deviation of ten separate LWC measurements was 31% of the average. However, the liquid mass flux calculated from the average LWC and droplet velocities came within 10% of the known water ingestion rate
Career Concerns of Top Executives, Managerial Ownership and CEO Succession
We model the portfolio decisions by managers with career concerns in a context where ownership of the firm's stock can affect the outcome of promotion contests. In addition to their utility from wealth, such managers derive utility from the monetary and non-monetary benefits (prestige) of running a corporation. Our theory predicts that top managers competing for the CEO position will distort their investment decisions away from the optimum portfolio choice in the absence of career concerns. Thus, our model suggests that changing career opportunities can explain portfolio decisions by managers and that insider ownership can help explain the outcomes of promotion contests. Our main testable predictions are that higher ownership by insiders increases their chances of being appointed CEO; that lower ownership by inside managers makes outside CEO appointments more likely; and that a lower probability of CEO turnover (and thus reduced promotion opportunities) leads inside managers to reduce their ownership in the firm and/or to leave the company. Using data on managerial ownership surrounding CEO turnover events, we find evidence supporting the predictions of our model. Overall, our main insight is that insider ownership, the outcome of promotion contests, the choice between inside and outside CEO replacements, and executive departure decisions are all related. Nous développons un modèle de choix de portefeuille des gestionnaires dans un environnement où leurs chances d'être promu PDG sont liées à leur actionnariat dans l'entreprise. Puisque les gestionnaires valorisent leur nomination potentielle au rang de PDG, nous prédisons que leur choix de portefeuille sera biaisé par rapport au choix qu'ils auraient fait en l'absence d'anticipations carriéristes. Notre modèle prédit que des changements dans les chances d'être promu expliquent les choix de portefeuille des gestionnaires. En particulier, nous montrons empiriquement qu'un plus grand actionnariat augmente la chance d'être promu au rang de PDG, réduit la chance qu'un gestionnaire externe à l'entreprise soit nommé. De plus, une réduction dans la possibilité d'être promu réduit l'actionnariat des gestionnaires ou induit leur départ. Nous testons les hypothèses découlant du modèle en utilisant les changements dans l'actionnariat des gestionnaire lors de la démission du PDG. Les hypothèses importantes du modèle sont confirmées.managerial compensation, CEO succession, corporate tournament, portfolio allocation, rémunération des dirigeants, changement de PDG, tournoi corporatif, choix de portefeuille
Fault-tolerant control under controller-driven sampling using virtual actuator strategy
We present a new output feedback fault tolerant control strategy for
continuous-time linear systems. The strategy combines a digital nominal
controller under controller-driven (varying) sampling with virtual-actuator
(VA)-based controller reconfiguration to compensate for actuator faults. In the
proposed scheme, the controller controls both the plant and the sampling
period, and performs controller reconfiguration by engaging in the loop the VA
adapted to the diagnosed fault. The VA also operates under controller-driven
sampling. Two independent objectives are considered: (a) closed-loop stability
with setpoint tracking and (b) controller reconfiguration under faults. Our
main contribution is to extend an existing VA-based controller reconfiguration
strategy to systems under controller-driven sampling in such a way that if
objective (a) is possible under controller-driven sampling (without VA) and
objective (b) is possible under uniform sampling (without controller-driven
sampling), then closed-loop stability and setpoint tracking will be preserved
under both healthy and faulty operation for all possible sampling rate
evolutions that may be selected by the controller
Velocity dispersion estimates of APM galaxy clusters
We present 83 new galaxy radial velocities in the field of 18 APM clusters
with redshifts between 0.06 and 0.13. The clusters have Abell identifications
and the galaxies were selected within 0.75 hMpc in projection from their
centers. We derive new cluster velocity dispersions for 13 clusters using our
data and published radial velocities.
We analyze correlations between cluster velocity dispersions and cluster
richness counts as defined in Abell and APM catalogs. The correlations show a
statistically significant trend although with a large scatter suggesting that
richness is a poor estimator of cluster mass irrespectively of cluster
selection criteria and richness definition. We find systematically lower
velocity dispersions in the sample of Abell clusters that do not fulfill APM
cluster selection criteria suggesting artificially higher Abell richness counts
due to contamination by projection effects in this subsample.Comment: Accepted for publication in MNRA
Non-perturbative laser effects on the electrical properties of graphene nanoribbons
The use of Floquet theory combined with a realistic description of the
electronic structure of illuminated graphene and graphene nanoribbons is
developed to assess the emergence of non-adiabatic and non-perturbative effects
on the electronic properties. Here, we introduce an efficient computational
scheme and illustrate its use by applying it to graphene nanoribbons in the
presence of both linear and circular polarization. The interplay between
confinement due to the finite sample size and laser-induced transitions is
shown to lead to sharp features on the average conductance and density of
states. Particular emphasis is given to the emergence of the bulk limit
response.Comment: 14 pages, 8 figures, to appear in J. Phys.: Condens. Matter, special
issue on "Ultrafast and nonlinear optics in carbon nanomaterials
Laser-induced effects on the electronic features of graphene nanoribbons
We study the interplay between lateral confinement and photon-induced
processes on the electronic properties of illuminated graphene nanoribbons. We
find that by tuning the device setup (edges geometries, ribbon width and
polarization direction), a laser with frequency {\Omega} may either not affect
the electronic structure, or induce bandgaps or depletions at \hbar {\Omega}/2,
and/or at other energies not commensurate with half the photon energy. Similar
features are also observed in the dc conductance, suggesting the use of the
polarization direction to switch on and off the graphene device. Our results
could guide the design of novel types of optoelectronic nano-devices.Comment: 4 pages, 3 figure
Bounds and Invariant Sets for a Class of Switching Systems with Delayed-state-dependent Perturbations
We present a novel method to compute componentwise transient bounds, ultimate
bounds, and invariant regions for a class of switching continuous-time linear
systems with perturbation bounds that may depend nonlinearly on a delayed
state. The main advantage of the method is its componentwise nature, i.e. the
fact that it allows each component of the perturbation vector to have an
independent bound and that the bounds and sets obtained are also given
componentwise. This componentwise method does not employ a norm for bounding
either the perturbation or state vectors, avoids the need for scaling the
different state vector components in order to obtain useful results, and may
also reduce conservativeness in some cases. We give conditions for the derived
bounds to be of local or semi-global nature. In addition, we deal with the case
of perturbation bounds whose dependence on a delayed state is of affine form as
a particular case of nonlinear dependence for which the bounds derived are
shown to be globally valid. A sufficient condition for practical stability is
also provided. The present paper builds upon and extends to switching systems
with delayed-state-dependent perturbations previous results by the authors. In
this sense, the contribution is three-fold: the derivation of the
aforementioned extension; the elucidation of the precise relationship between
the class of switching linear systems to which the proposed method can be
applied and those that admit a common quadratic Lyapunov function (a question
that was left open in our previous work); and the derivation of a technique to
compute a common quadratic Lyapunov function for switching linear systems with
perturbations bounded componentwise by affine functions of the absolute value
of the state vector components.Comment: Submitted to Automatic
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