32,650 research outputs found
Flying qualities criteria for superaugmented aircraft
An overview of Dryden superaugmented aircraft flying qualities research is presented. This includes F-8 digital fly by wire flight experiments, orbiter flying qualities, shuttle improvements, AFTI/F-16, flying qualities and control system alternatives, Vertical Motion Simulator Shuttle evaluation and Total in Flight Simulator pitch rate criteria
Loss-resistant unambiguous phase measurement
Entangled multi-photon states have the potential to provide improved
measurement accuracy, but are sensitive to photon loss. It is possible to
calculate ideal loss-resistant states that maximize the Fisher information, but
it is unclear how these could be experimentally generated. Here we propose a
set of states that can be obtained by processing the output from parametric
down-conversion. Although these states are not optimal, they provide
performance very close to that of optimal states for a range of parameters.
Moreover, we show how to use sequences of such states in order to obtain an
unambiguous phase measurement that beats the standard quantum limit. We
consider the optimization of parameters in order to minimize the final phase
variance, and find that the optimum parameters are different from those that
maximize the Fisher information.Comment: 8 pages, 7 figures, comments are welcom
Mergers, Station Entry, and Programming Variety in Radio Broadcasting
Free entry into markets with decreasing average costs and differentiated products can result in an inefficient number of firms and suboptimal product variety. Because new firms and products draw their customers in part from existing products, concentration can affect incentives to enter as well as how to position products. This paper examines how product variety in the radio industry is affected by changes in ownership structure. While it is in general difficult to measure the effect of concentration on other factors such as the number of products and the extent of product variety, the 1996 Telecommunications Act substantially relaxed local radio ownership restrictions, giving rise to a major and exogenous consolidation wave. Between 1993 and 1997 the average Herfindahl index in major US media markets increased by almost 65 percent. Using a panel data set on 243 U.S. radio broadcast markets in 1993 and 1997, we find that concentration reduces entry and increases product variety. Our results are consistent with spatial preemption. Jointly owned stations broadcasting from the same market are more likely than unrelated stations - and more likely than jointly owned stations in different markets - to broadcast in similar formats.
Public Radio in the United States: Does It Correct Market Failure or Cannibalize Commercial Stations?
Radio signals are pure public goods whose total value to society is the sum of their value to advertisers and listeners. Because broadcasters can capture only part of the value of their product as revenue, there is the potential for a classic problem of underprovision. Small markets have much less commercial program variety than larger markets, suggesting a possible underprovision problem. Public funding of radio broadcasting targets programming in three formats - news, classical music, and jazz - with at least some commercial competition. Whether public support corrects a market failure depends on whether the market would have provided similar services in the absence of public broadcasting. To examine this we ask whether public and commercial classical stations compete for listening share and revenue. We then directly examine whether public stations crowd out commercial stations. We find evidence consistent with the view that public broadcasting crowds out commercial programming in large markets, particularly in classical music and to a lesser extent in jazz. Although the majority of government subsidies to radio broadcasting are allocated to stations without commercial competition in their format (thereby possibly correcting inefficient market underprovision), roughly a quarter of subsidies support direct competition with existing commercial stations.
Identification in Differentiated Products Markets Using Market Level Data
We consider nonparametric identification in models of differentiated products markets, using only market level observables. On the demand side we consider a nonparametric random utility model nesting random coefficients discrete choice models widely used in applied work. We allow for product/market-specific unobservables, endogenous product characteristics (e.g., prices), and high-dimensional taste shocks with arbitrary correlation and heteroskedasticity. On the supply side we specify marginal costs nonparametrically, allow for unobserved firm heterogeneity, and nest a variety of equilibrium oligopoly models. We pursue two approaches to identification. One relies on instrumental variables conditions used previously to demonstrate identification in a nonparametric regression framework. With this approach we can show identification of the demand side without reference to a particular supply model. Adding the supply side allows identification of firms' marginal costs as well. Our second approach, more closely linked to classical identification arguments for supply and demand models, employs a change of variables approach. This leads to constructive identification results relying on exclusion and support conditions. Our results lead to a testable restriction that provides the first general formalization of Bresnahan's (1982) intuition for empirically discriminating between alternative models of oligopoly competition.
Flux String in Quantum Billiards with Two Particles
We examine the quantum motion of two particles interacting through a contact
force which are confined in a rectangular domain in two and three dimensions.
When there is a difference in the mass scale of two particles, adiabatic
separation of the fast and slow variables can be performed. Appearance of the
Berry phase and magnetic flux is pointed out. The system is reduced to a
one-particle Aharonov-Bohm billiard in two-dimensional case. In three
dimension, the problem effectively becomes the motion of a particle in the
presence of closed flux string in a box billiard.Comment: 10 pages, REVTeX file, 3 postscript figures, uuencode
Tracking Articulator Movements Using Orientation Measurements
This paper introduces a new method to track articulator movements, specifically jaw position and angle, using 5 degree of freedom (5 DOF) orientation data. The approach uses a quaternion rotation method to accomplish this jaw tracking during speech using a single senor on the mandibular incisor. Data were collected using the NDI Wave Speech Research System for one pilot subject with various speech tasks. The degree of jaw rotation from the proposed approach is compared with traditional geometric calculation. Results show that the quaternion based method is able to describe jaw angle trajectory and gives more accurate and smooth estimation of jaw kinematics
Vowel Production in Mandarin Accented English and American English: Kinematic and Acoustic Data from the Marquette University Mandarin Accented English Corpus
Few electromagnetic articulography (EMA) datasets are publicly available, and none have focused systematically on non-native accented speech. We introduce a kinematic-acoustic database of speech from 40 (gender and dialect balanced) participants producing upper-Midwestern American English (AE) L1 or Mandarin Accented English (MAE) L2 (Beijing or Shanghai dialect base). The Marquette University EMA-MAE corpus will be released publicly to help advance research in areas such as pronunciation modeling, acoustic-articulatory inversion, L1-L2 comparisons, pronunciation error detection, and accent modification training. EMA data were collected at a 400 Hz sampling rate with synchronous audio using the NDI Wave System. Articulatory sensors were placed on the midsagittal lips, lower incisors, and tongue blade and dorsum, as well as on the lip corner and lateral tongue body. Sensors provide five degree-of-freedom measurements including three-dimensional sensor position and two-dimensional orientation (pitch and roll). In the current work we analyze kinematic and acoustic variability between L1 and L2 vowels. We address the hypothesis that MAE is characterized by larger differences in the articulation of back vowels than front vowels and smaller vowel spaces compared to AE. The current results provide a seminal comparison of the kinematics and acoustics of vowel production between MAE and AE speakers
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