Limit Theorems for Estimating the Parameters of Differentiated Product Demand Systems

We provide an asymptotic distribution theory for a class of Generalized Method of Moments estimators that arise in the study of differentiated product markets when the number of observations is associated with the number of products within a given market. We allow for three sources of error: the sampling error in estimating market shares, the simulation error in approximating the shares predicted by the model, and the underlying model error. The limiting distribution of the parameter estgimator is normal provided the size of the consumer sample and the number of simulation draws grow at a large enough rate relative to the number of products. The required rates differ for two frequently used demand models, and a small Monte Carlo study shows that the difference in asymptotic properties of the two models are reflected in the models' small sample properties. The differences impact directly on the computational burden of the two models.Choice models, Method of Moments, Multinominal, Random Coefficients, Vertical Model

Simple Estimators for the Parameters of Discrete Dynamic Games (with Entry/Exit Examples)

This paper considers the problem of estimating the distribution of payoffs in a discrete dynamic game, focusing on models where the goal is to learn about the distribution of firms' entry and exit costs. The idea is to begin with non parametric first stage etimates of entry and continuation values obtained by computing sample averages of the realized continuation values of entrants who do enter and incumbents who do continue. Under certain assumptions these values are linear functions of the parameters of the problem, and hence are not computationally burdensome to use. Attention is given to the small sample problem of estimation error in the non parametric estimates and this leads to a preference for use of particularly simple estimates of continuation values and moments.

Simple Estimators for the Parameters of Discrete Dynamic Games (with Entry/Exit Samples)

This paper considers the problem of estimating the distribution of payoffs in a discrete dynamic game, focusing on models where the goal is to learn about the distribution of firms' entry and exit costs. The idea is to begin with non parametric first stage estimates of entry and continuation values obtained by computing sample averages of the realized continuation values of entrants who do enter and incumbents who do continue. Under certain assumptions these values are linear functions of the parameters of the problem, and hence are not computationally burdensome to use. Attention is given to the small sample problem of estimation error in the non parametric estimates and this leads to a preference for use of particularly simple estimates of continuation values and moments.

The Sixth Alumni Conference of the International Space University

These proceedings cover the sixth alumni conference of the International Space University, coordinated by the ISU U.S. Alumni Organization, which was held at Rice University in Houston, Texas, on July 11, 1997. The alumni conference gives graduates of the International Space University's interdisciplinary, international, and intercultural program a forum in which they may present and exchange technical ideas, and keep abreast of the wide variety of work in which the ever-growing body of alumni is engaged. The diversity that is characteristic of ISU is reflected in the subject matter of the papers published in this proceedings. This proceedings preserves the order of the alumni presentations given at the 1997 ISU Alumni Conference. As in previous years, a special effort was made to solicit papers with a strong connection to the two ISU 1997 Summer Session Program design projects: (1) Transfer of Technology, Spin-Offs, Spin-Ins; and (2) Strategies for the Exploration of Mars. Papers in the remaining ten sessions cover the departmental areas traditional to the ISU summer session program

Can we use digital life-log images to investigate active and sedentary travel behaviour? Results from a pilot study

<p>Abstract</p> <p>Background</p> <p>Active travel such as walking and cycling has potential to increase physical activity levels in sedentary individuals. Motorised car travel is a sedentary behaviour that contributes to carbon emissions. There have been recent calls for technology that will improve our ability to measure these travel behaviours, and in particular evaluate modes and volumes of active versus sedentary travel. The purpose of this pilot study is to investigate the potential efficacy of a new electronic measurement device, a wearable digital camera called SenseCam, in travel research.</p> <p>Methods</p> <p>Participants (n = 20) were required to wear the SenseCam device for one full day of travel. The device automatically records approximately 3,600 time-stamped, first-person point-of-view images per day, without any action required by the wearer. Participants also completed a self-report travel diary over the same period for comparison, and were interviewed afterwards to assess user burden and experience.</p> <p>Results</p> <p>There were a total of 105 confirmed journeys in this pilot. The new SenseCam device recorded more journeys than the travel diary (99 vs. 94). Although the two measures demonstrated an acceptable correlation for journey duration (r = 0.92, p < 0.001) self-reported journey duration was over-reported (mean difference 154 s per journey; 95% CI = 89 to 218 s; 95% limits of agreement = 154 ± 598 s (-444 to 752 s)). The device also provided visual data that was used for directed interviews about sources of error.</p> <p>Conclusions</p> <p>Direct observation of travel behaviour from time-stamped images shows considerable potential in the field of travel research. Journey duration derived from direct observation of travel behaviour from time-stamped images appears to suggest over-reporting of self-reported journey duration.</p

Shuttle Entry Imaging Using Infrared Thermography

During the Columbia Accident Investigation, imaging teams supporting debris shedding analysis were hampered by poor entry image quality and the general lack of information on optical signatures associated with a nominal Shuttle entry. After the accident, recommendations were made to NASA management to develop and maintain a state-of-the-art imagery database for Shuttle engineering performance assessments and to improve entry imaging capability to support anomaly and contingency analysis during a mission. As a result, the Space Shuttle Program sponsored an observation campaign to qualitatively characterize a nominal Shuttle entry over the widest possible Mach number range. The initial objectives focused on an assessment of capability to identify/resolve debris liberated from the Shuttle during entry, characterization of potential anomalous events associated with RCS jet firings and unusual phenomenon associated with the plasma trail. The aeroheating technical community viewed the Space Shuttle Program sponsored activity as an opportunity to influence the observation objectives and incrementally demonstrate key elements of a quantitative spatially resolved temperature measurement capability over a series of flights. One long-term desire of the Shuttle engineering community is to calibrate boundary layer transition prediction methodologies that are presently part of the Shuttle damage assessment process using flight data provided by a controlled Shuttle flight experiment. Quantitative global imaging may offer a complementary method of data collection to more traditional methods such as surface thermocouples. This paper reviews the process used by the engineering community to influence data collection methods and analysis of global infrared images of the Shuttle obtained during hypersonic entry. Emphasis is placed upon airborne imaging assets sponsored by the Shuttle program during Return to Flight. Visual and IR entry imagery were obtained with available airborne imaging platforms used within DoD along with agency assets developed and optimized for use during Shuttle ascent to demonstrate capability (i.e., tracking, acquisition of multispectral data, spatial resolution) and identify system limitations (i.e., radiance modeling, saturation) using state-of-the-art imaging instrumentation and communication systems. Global infrared intensity data have been transformed to temperature by comparison to Shuttle flight thermocouple data. Reasonable agreement is found between the flight thermography images and numerical prediction. A discussion of lessons learned and potential application to a potential Shuttle boundary layer transition flight test is presented

Deeper, Wider, Sharper: Next-Generation Ground-Based Gravitational-Wave Observations of Binary Black Holes

Next-generation observations will revolutionize our understanding of binary black holes and will detect new sources, such as intermediate-mass black holes. Primary science goals include: Discover binary black holes throughout the observable Universe; Reveal the fundamental properties of black holes; Uncover the seeds of supermassive black holes.Comment: 14 pages, 3 figures, White Paper Submitted to Astro2020 (2020 Astronomy and Astrophysics Decadal Survey) by GWIC 3G Science Case Team (GWIC: Gravitational Wave International Committee

STEM Initiatives: Stimulating Students to Improve Science and Mathematics Achievement

The article focuses on how concepts in science, technology education, and mathematics show powerful relationships when it comes to student learning. Learning theorists believe that, through designed learning environments (contexts) and learning with hands-on projects, new knowledge can not only be learned, but learned in such a way that the knowledge can be transferred for other applications. Scholars in the applied sciences (school science, technology, and mathematics) believe that these subjects have transfer among themselves and that engineering activities can establish the contexts to learn these subjects, plus aid in the transfer of knowledge. This collaborative movement is referred to as STEM — integrating instruction in science, technology education, engineering, and mathematics. For more information on the national standards, conduct a web search for National Science Education Standards (1996), Standards for Technological Literacy: Content for the Study of Technology (2000/2002), and Principles and Standards for School Mathematics, (2000)