48,840 research outputs found
Portable, high intensity isotopic neutron source provides increased experimental accuracy
Small portable, high intensity isotopic neutron source combines twelve curium-americium beryllium sources. This high intensity of neutrons, with a flux which slowly decreases at a known rate, provides for increased experimental accuracy
A Litner Model of Payout and Managerial Rents
We develop a dynamic agency model where payout, investment and financing decisions are made by managers who attempt to maximize the rents they take from the firm, subject to a capital market constraint. Managers smooth payout in order to smooth their flow of rents. Total payout (dividends plus net repurchases) follows Lintner's (1956) target-adjustment model. Payout smooths out transitory shocks to current income and adjusts gradually to changes in permanent income. Smoothing is accomplished by borrowing or lending. Payout is not cut back to finance capital investment. Risk aversion causes managers to underinvest, but habit formation mitigates the degree of underinvestment.
A closed-form solution for noise contours
An analytical approach for generating noise contours that overcome the difficulties of existing programs is described. This approach is valid for arbitrarily complex paths and reveals the importance of various factors that influence contour shape and size. The calculations are simple enough to be implemented on a small, hand-held programmable calculator, and a program for the HP-67 calculator is illustrated. The method is fast, simple, and gives the area, the contour, and its extremities for arbitrary flight paths for both takeoffs and landings
Layering Transitions and Solvation Forces in an Asymmetrically Confined Fluid
We consider a simple fluid confined between two parallel walls (substrates),
separated by a distance L. The walls exert competing surface fields so that one
wall is attractive and may be completely wet by liquid (it is solvophilic)
while the other is solvophobic. Such asymmetric confinement is sometimes termed
a `Janus Interface'. The second wall is: (i) purely repulsive and therefore
completely dry (contact angle 180 degrees) or (ii) weakly attractive and
partially dry (the contact angle is typically in the range 160-170 degrees). At
low temperatures, but above the bulk triple point, we find using classical
density functional theory (DFT) that the fluid is highly structured in the
liquid part of the density profile. In case (i) a sequence of layering
transitions occurs: as L is increased at fixed chemical potential (mu) close to
bulk gas--liquid coexistence, new layers of liquid-like density develop
discontinuously. In contrast to confinement between identical walls, the
solvation force is repulsive for all wall separations and jumps discontinuously
at each layering transition and the excess grand potential exhibits many
metastable minima as a function of the adsorption. For a fixed temperature
T=0.56Tc, where Tc is the bulk critical temperature, we determine the
transition lines in the L, mu plane. In case (ii) we do not find layering
transitions and the solvation force oscillates about zero. We discuss how our
mean-field DFT results might be altered by including effects of fluctuations
and comment on how the phenomenology we have revealed might be relevant for
experimental and simulation studies of water confined between hydrophilic and
hydrophobic substrates, emphasizing it is important to distinguish between
cases (i) and (ii).Comment: 16 pages, 13 figure
Optimal guidance and control for investigating aircraft noise-impact reduction
A methodology for investigating the reduction of community noise impact is reported. This report is concerned with the development of two models to provide data: a guidance generator and an aircraft control generator suitable for various current and advanced types of aircraft. The guidance generator produces the commanded path information from inputs chosen by an operator from a graphic scope display of a land-use map of the terminal area. The guidance generator also produces smoothing at the junctions of straight-line paths.The aircraft control generator determines the optimal set of the available controls such that the aircraft will follow the commanded path. The solutions for the control functions are given and shown to be dependent on the class of aircraft to be considered, that is, whether the thrust vector is rotatable and whether the thrust vector affects the aerodynamic forces. For the class of aircraft possessing a rotatable thrust vector, the solution is redundant; this redundancy is removed by the additional condition that the noise inpact be minimized. Information from both the guidance generator and the aircraft control generator is used by the footprint program to construct the noise footprint
Equivalence of two mathematical forms for the bound angular momentum of the electromagnetic field
It is shown that the mathematical form, obtained in a recent paper, for the
angular momentum of the electromagnetic field in the vicinity of electric
charge is equivalent to another form obtained previously by Cohen-Tannoudji,
Dupont-Roc and Gilbert. In this version of the paper an improved derivation is
given.Comment: 4 pages pdf, simpler derivatio
The population of propellers in Saturn's A Ring
We present an extensive data set of ~150 localized features from Cassini
images of Saturn's Ring A, a third of which are demonstrated to be persistent
by their appearance in multiple images, and half of which are resolved well
enough to reveal a characteristic "propeller" shape. We interpret these
features as the signatures of small moonlets embedded within the ring, with
diameters between 40 and 500 meters. The lack of significant brightening at
high phase angle indicates that they are likely composed primarily of
macroscopic particles, rather than dust. With the exception of two features
found exterior to the Encke Gap, these objects are concentrated entirely within
three narrow (~1000 km) bands in the mid-A Ring that happen to be free from
local disturbances from strong density waves. However, other nearby regions are
similarly free of major disturbances but contain no propellers. It is unclear
whether these bands are due to specific events in which a parent body or bodies
broke up into the current moonlets, or whether a larger initial moonlet
population has been sculpted into bands by other ring processes.Comment: 31 pages, 10 figures; Accepted at A
Human factors analysis of workstation design: Earth Radiation Budget Satellite Mission Operations Room
A human factors analysis addressed three related yet distinct issues within the area of workstation design for the Earth Radiation Budget Satellite (ERBS) mission operation room (MOR). The first issue, physical layout of the MOR, received the most intensive effort. It involved the positioning of clusters of equipment within the physical dimensions of the ERBS MOR. The second issue for analysis was comprised of several environmental concerns, such as lighting, furniture, and heating and ventilation systems. The third issue was component arrangement, involving the physical arrangement of individual components within clusters of consoles, e.g., a communications panel
A simplex-like search method for bi-objective optimization
We describe a new algorithm for bi-objective optimization, similar to the Nelder Mead simplex
algorithm, widely used for single objective optimization. For diferentiable bi-objective functions on
a continuous search space, internal Pareto optima occur where the two gradient vectors point in
opposite directions. So such optima may be located by minimizing the cosine of the angle between
these vectors. This requires a complex rather than a simplex, so we term the technique the \cosine
seeking complex". An extra beneft of this approach is that a successful search identifes the direction
of the effcient curve of Pareto points, expediting further searches. Results are presented for some
standard test functions. The method presented is quite complicated and space considerations here
preclude complete details. We hope to publish a fuller description in another place
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