High Velocity Impact Performance of a Dual Layer Thermal Protection System for the Mars Sample Return Earth Entry Vehicle

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VAR(MA), What is it Good For? More Bad News for Reduced-form Estimation and Inference

It is common practice to use reduced-form vector autoregression (VAR) models, or more generally vector autoregressive moving average (VARMA) models, to characterize the dynamics in observed data and to identify innovations to the macroeconomy in some economically meaningful way. We demonstrate that neither approach|VAR or VARMA|are suitable reduced form guides to \reality", if reality were induced by some underlying structural DSGE model. We conduct such a thought experiment across a wide class of DSGE structures that imply particular VARMA data generating processes (DGPs). We find that with the typical small samples for macroeconomic data, the MA component of the fitted VARMA models is close to being non-identified. This in turn leads to an order reduction when identifying the lag structures of the VARMA models. As a result, VARMA models barely show any advantage over VARs using realistic sample sizes. However, the VAR remains a truly misspecified approximation. The VAR's performance deteriorates, in contrast to the VARMA's, as we enlarge the sample size generated from the true DGPs

Investigating Ancient Maya Agricultural Adaptation Through Ground Penetrating Radar (GPR) Analysis of Karst Terrain, Northern Yucatán, Mexico

Landscape adaptation on the Northern Yucatán Peninsula, Mexico, is particularly difficult, as soils are thin and the terrain is devoid of any surface water other than the occasional sinkhole (cenote) that connects directly to the groundwater system. Despite this, ancient Maya cities, including Xuenkal, emerged and thrived, likely because of their proximity to natural sinkholes. In the case of Xuenkal, these sinkholes, known locally as rejolladas, have bases above the local water table and, as such, do not provide direct access to the underlying water, but they provide closer access. Recognizing that the presence of rejolladas was likely important to the ancient Maya the purpose of this study is to characterize the rejolladas in terms of their subsurface characteristics, specifically bedrock configuration and soil. Ground penetrating radar analysis, as well as the results of a test pit excavation, confirm the presence of deep soils in the rejollada bases. It seems that the smaller deeper rejolladas have the thickest soils and sediment. The ancient city of Xuenkal is constructed amidst a particularly dense cluster of rejolladas which may have contributed to its location. Rejolladas, containing significantly thicker soils than the surrounding karst surface, and the ability to sustain dense healthy vegetation would have been particularly desirable for the Maya to capitalize on

Exposure to violence and PTSD symptoms among Somali women

Posttraumatic stress disorder (PTSD) symptoms, exposure to traumatic stressors, and health care utilization were examined in 84 women attending a primary health care clinic in Mogadishu, Somalia. The Somalia-Posttraumatic Diagnostic Scale was used in this active warzone to measure symptoms. Nearly all women reported high levels of confrontations with violence; half described being exposed to a potentially traumatizing event. Nearly one third had significant PTSD symptoms. Compared to those who did not, women who reported exposure to a traumatic stressor reported more confrontations with violence (7.1 vs. 3.3; p < . 001), health complaints (3.8 vs. 2.9; p = .03), and nearly 3 times as much (p = .03) health service utilization. A potentially traumatizing event was found to be a simplified proxy for assessing mental health distress in women attending a primary health care facility in highly insecure, unpredictable, resource-limited settings

Recent developments in monolithic integration of InGaAsP/InP optoelectronic devices

Monolithically integrated optoelectronic circuits combine optical devices such as light sources (injection lasers and light emitting diodes) and optical detectors with solid-state semiconductor devices such as field effect transistors, bipolar transistors, and others on a single semiconductor crystal. Here we review some of the integrated circuits that have been realized and discuss the laser structures suited for integration with emphasis on the InGaAsP/InP material system. Some results of high frequency modulation and performance of integrated devices are discussed

Pile Setup in Cohesive Soil. II: Analytical Quantifications and Design Recommendations

: This paper establishes a methodology to quantify pile setup by using recent field test data that was presented in a companion paper for steel H-piles driven in cohesive soils. Existing methods found in literature for the same purpose either require restrikes of piles onsite or are developed for a specific soil type and seldom use easily quantifiable soil properties, despite their significant influence on pile setup. Following a critical evaluation of the existing methods, a new approach for estimating pile setup was developed using dynamic measurements and analyses in combination with measured soil properties, such as the horizontal coefficient of consolidation, undrained shear strength, and the standard penetration test N value. Using pile setup information available in the literature, the proposed approach has shown that it provides good estimates for the setup of steel H-piles, as well as for other types and sizes of driven piles

Developing and applying a user-centered model for the design and implementation of information visualization tools

The objective of this paper is to show how approaches for user-centered information visualization design and development are being applied in the context of healthcare where users are not familiar with information visualization techniques. We base our design methods on user-centered frameworks in which 'prototyping' plays an important role in the process. We modify existing approaches to involve prototyping at an early stage of the process as the problem domain is assessed. We believe this to be essential, as it increases users' awareness of what information visualization techniques can offer them and that it enables users to participate more effectively in later stages of the design and development process. This also acts as a stimulus for engagement. The problem domain analysis stage of a pilot study using this approach is presented, in which techniques are being collaboratively developed with domain users from a healthcare institution. Our results suggest that this approach has engaged users, who are subsequently able to apply generic information visualization concepts to their domains and as a result are better equipped to take part in the subsequent collaborative design and development process

The Impact of the Costs of Subscription on Measured IPO Returns: The Case of Asia

Asian initial public offerings (IPOs) require investors to pay subscription funds up-front upon submission of applications, and these funds are locked-up for one to three weeks without interest. Hence, the IPO process entails an explicit financing cost (opportunity cost) whether investors borrow funds or use their own funds to apply for IPO shares. The IPO subscription costs are not trivial, especially in a high interest rate environment or when an IPO is highly oversubscribed. These costs should be considered in any comparison of IPO returns across countries

Quantum Hall induced currents and the magnetoresistance of a quantum point contact

We report an investigation of quantum Hall induced currents by simultaneous measurements of their magnetic moment and their effect on the conductance of a quantum point contact (QPC). Features in the magnetic moment and QPC resistance are correlated at Landau-level filling factors nu=1, 2 and 4, which demonstrates the common origin of the effects. Temperature and non-linear sweep rate dependences are observed to be similar for the two effects. Furthermore, features in the noise of the induced currents, caused by breakdown of the quantum Hall effect, are observed to have clear correlations between the two measurements. In contrast, there is a distinct difference in the way that the induced currents decay with time when the sweeping field halts at integer filling factor. We attribute this difference to the fact that, while both effects are sensitive to the magnitude of the induced current, the QPC resistance is also sensitive to the proximity of the current to the QPC split-gate. Although it is clearly demonstrated that induced currents affect the electrostatics of a QPC, the reverse effect, the QPC influencing the induced current, was not observed