30,685 research outputs found
Control jet placement on spacecraft
For efficient operation and configuration design of multijet spacecraft control systems methods of linear programming are used to select combinations of individual jet-burn times which produce the desired impulses. Minimum-fuel and fuel-time solutions are found
Endogenous Product Choice : A Progress Report
Empirical models of differentiated product demand are widely used by both academics and practitioners. While these methods treat carefully the potential endogeneity of price, until recently they have assumed the number and characteristics of the products o.ered by firms are exogenous. This paper presents a progress report on an ongoing research agenda to address this issue. First, it summarizes how the appropriate choice of âorthogonalâ instruments can yield consistent estimates of own and cross-price elasticities in the presence of endogenous product characteristics. Second, it summarizes how to measure âquality markupsâ and the welfare consequences of endogenous product quality in U.S. cable television markets. Related papers and extensions to consider multiple product characteristics and dynamics are also discussed.
Optical integral field spectroscopy of the extended line emission around six radio-loud quasars
We present integral field spectroscopy of a small sample of radio-loud
quasars at intermediate redshift (0.26<z<0.60), most of which are associated
with large radio sources. All have oxygen line emission extended over tens of
kiloparcsecs, and these nebulae display a diverse range in both morphology and
kinematic behaviour. Two quasars show 'plumes' of extended line emission, two
show a clumpy structure and a further one shows a smooth distribution. There is
no clear pattern with regard to the distribution of the ionized gas in relation
to the radio source axis; the extended emission-line regions are found both
parallel and perpendicular - and also totally unrelated to - the radio axis.
The velocity structure of the ionized gas ranges from essentially static to
apparent smooth rotation, and in two cases, show a clear association with the
radio source. Given the disparity in properties, the nebulae all show a
surprisingly similar ionization state, as measured by the extended lines of
[OII] and [OIII]. Assuming the gas is ionized by at least the nearby quasar
nucleus, we use the emission line ratios to infer a pressure in the ionized
gas; in all cases we find it to be at high pressure, suggesting confinement by
an external (probably intracluster) medium.Comment: 14 pages, 18 figures, 10 of which are presented separately; accepted
for publication in MNRA
Monopoly quality degradation and regulation in cable television
Using an empirical framework based on the Mussa-Rosen model of monopoly quality choice, we calculate the degree of quality degradation in cable television markets and the impact of regulation on those choices. We find lower bounds of quality degradation ranging from 11 to 45 percent of offered service qualities. Furthermore, cable operators in markets with local regulatory oversight offer significantly higher quality, less degradation, and greater quality per dollar, despite higher prices
The Supreme Court, Due Process and State Income Taxation of Trusts
What are the constitutional limits on a state\u27s power to tax a trust with no connection to the state, other than the accident that a potential beneficiary lives there? The Supreme Court of the United States will take up this question this term in the context of North Carolina Department of Revenue v. Kimberley Rice Kaestner 1992 Family Trust. The case involves North Carolina\u27s income taxation of a trust with a contingent beneficiary, meaning someone who is eligible, but not certain, to receive a distribution or benefit from the trust, who resides in that state. Part I of this Article explains the background of Kaestner Trust and frames the constitutional questions that will be before the Court at oral arguments on April 16, 2019. Part II examines how and why due process applies in the state income taxation context, with a particular emphasis on how familiar concepts of general and specific jurisdiction apply uneasily to donative trusts. Part III articulates the reasons that the Court should hold that a state has no constitutional authority to impose a tax on trust income where the trust\u27s only connection with the forum state is the residence of a contingent beneficiary. Kaestner Trust is the most important due process case involving trusts that the Court has decided in over sixty years; it bears directly on the fundamental meaning of due process
Extended X-ray emission around four 3C quasars at 0.55<z<0.75 observed with Chandra
We report on the detection of a soft spatially-extended component of X-ray
emission around four intermediate-redshift 3C quasars observed with Chandra:
3C254, 3C263, 3C275.1 and 3C281. The bolometric luminosity of this emission
ranges over 0.3-1.6 times 10^{44}erg/s, and extends to lengthscales of over 350
kpc at the redshift of the quasar. The X-rays are most likely thermal emission
from the intracluster medium of a cluster of galaxies around each quasar, which
provides the working surface for the powerful radio lobes. Some X-ray emission
is also seen to be associated with the radio plasma.Comment: 8 pages, 4 panelled figures, MNRAS in pres
A deep Chandra observation of the cluster environment of the z=1.786 radio galaxy 3C294
We report the results from a 200 ks Chandra observation of the z=1.786 radio
galaxy 3C294 and its cluster environment, increasing by tenfold our earlier
observation. The diffuse emission, extending about 100 kpc around the nucleus,
has a roughly hourglass shape in the N-S direction with surprisingly sharp
edges to the N and S. The spectrum of the diffuse emission is well fitted by
either a thermal model of temperature 3.5 keV and abundance <0.9 solar
(2-sigma), or a power-law with photon index 2.3. If the emission is due to hot
gas then the sharp edges mean that it is probably not in hydrostatic
equilibrium. Much of the emission is plausibly due to inverse Compton
scattering of the Cosmic Microwave Background (CMB) by nonthermal electrons
produced earlier by the radio source. The required relativistic electrons would
be of much lower energy and older than those responsible for the present radio
lobes. This could account for the lack of detailed spatial correspondence
between the X-rays and the radio emission, the axis of which is at a position
angle of about 45 deg. Hot gas would still be required to confine the
relativistic plasma; the situation could parallel that of the radio bubbles
seen as holes in nearby clusters, except that in 3C294 the bubbles are bright
in X-rays owing to the extreme power in the source and the sixty fold increase
in the energy density of the CMB. The X-ray spectrum of the radio nucleus is
hard, showing a reflection spectrum and iron line. The source is therefore an
obscured radio-loud quasar.Comment: In press (MNRAS), 10 pages, 12 figures (2 colour
Space shuttle post-entry and landing analysis. Volume 2: Appendices
Four candidate navigation systems for the space shuttle orbiter approach and landing phase are evaluated in detail. These include three conventional navaid systems and a single-station one-way Doppler system. In each case, a Kalman filter is assumed to be mechanized in the onboard computer, blending the navaid data with IMU and altimeter data. Filter state dimensions ranging from 6 to 24 are involved in the candidate systems. Comprehensive truth models with state dimensions ranging from 63 to 82 are formulated and used to generate detailed error budgets and sensitivity curves illustrating the effect of variations in the size of individual error sources on touchdown accuracy. The projected overall performance of each system is shown in the form of time histories of position and velocity error components
- âŠ