A Born-WKBJ inversion method for acoustic reflection data

Density and bulk modulus variations in an acoustic earth are separately recoverable from standard reflection surveys by utilizing the amplitude-versus-offset information present in the observed wave fields. Both earth structure and a variable background velocity can be accounted for by combining the Born and WKBJ approximations, in a "before stack" migration with two output sections, one for density variations and the other for bulk modulus variations. For the inversion, the medium is considered to be composed of a known low-spatial frequency variation (the background) plus an unknown high-spatial frequency variation in bulk modulus and density (the reflectivity). The division between the background and the reflectivity depends upon the frequency content of the source. For constant background parameters, computations are done in the Fourier domain, where the first part of the algorithm includes a frequency shift identical to that in an F-K migration. The modulus and density variations are then determined by observing in a least-squares sense amplitude versus offset wavenumber. For a spatially variable background, WKBJ Green's operators that model the direct wave in a medium with a smoothly varying background are used. A downward continuation with these operators removes the effects of variable velocity from the problem, and, consequently, the remainder of the inversion essentially proceeds as if the background were constant. If the background is strictly depth dependent, the inversion can be expressed in closed form. The method neglects multiples and surface waves and it is restricted to precritical reflections. Density is distinguishable from bulk modulus only if a sufficient range of precritical incident angles is present in the data

Earth rotation and core topography

The NASA Geodynamics program has as one of its missions highly accurate monitoring of polar motion, including changes in length of day (LOD). These observations place fundamental constraints on processes occurring in the atmosphere, in the mantle, and in the core of the planet. Short-timescale (t less than or approx 1 yr) variations in LOD are mainly the result of interaction between the atmosphere and the solid earth, while variations in LOD on decade timescales result from the exchange of angular momentum between the mantle and the fluid core. One mechanism for this exchange of angular momentum is through topographic coupling between pressure variations associated with flow in the core interacting with topography at the core-mantel boundary (CMB). Work done under another NASA grant addressing the origin of long-wavelength geoid anomalies as well as evidence from seismology, resulted in several models of CMB topography. The purpose of work supported by NAG5-819 was to study further the problem of CMB topography, using geodesy, fluid mechanics, geomagnetics, and seismology. This is a final report

Integrando aprendizaje-servicio y tecnologías digitales: análisis de sus desafíos y promesas

Our intent is to frame the integration of service learning and digital technologies broadly in teaching and learning and to explore some of the complexities of the challenge and the promise, thereby setting up readers’ engagement with the questions and issues that follow in the papers of RIED.  We seek to provide perspectives that may contribute to subsequent implementation of pedagogical innovations and research that will improve practice and, in consequence, outcomes for all.  We begin by offering an overview of the what’s and why’s of service learning.  We then examine some of the how’s of service learning in the context of its integration with digital technologies.  Finally, we explore several issues that may shape new developments at the interface of these two pedagogical innovation.En este artículo pretendemos enmarcar la incorporación del aprendizaje-servicio y las tecnologías digitales en la enseñanza y el aprendizaje, a la vez que analizar la complejidad de algunos de sus desafíos y promesas. De esta forma, se compromete a los lectores con las preguntas y los problemas que se abordan en los artículos que componen este monográfico de RIED. Buscamos proporcionar perspectivas que puedan contribuir a la implementación de innovaciones e investigaciones pedagógicas que mejorarán la práctica y, en consecuencia, los resultados de aprendizaje. Comenzamos brindando una descripción general de lo qué es y el porqué del aprendizaje-servicio, para examinar, en una segunda parte, el cómo del aprendizaje-servicio en escenarios digitales. Finalmente, exploramos varios temas que pueden dar forma a nuevos desarrollos en el contexto de estas dos innovaciones pedagógicas

Automatic speech recognition research at NASA-Ames Research Center

A trainable acoustic pattern recognizer manufactured by Scope Electronics is presented. The voice command system VCS encodes speech by sampling 16 bandpass filters with center frequencies in the range from 200 to 5000 Hz. Variations in speaking rate are compensated for by a compression algorithm that subdivides each utterance into eight subintervals in such a way that the amount of spectral change within each subinterval is the same. The recorded filter values within each subinterval are then reduced to a 15-bit representation, giving a 120-bit encoding for each utterance. The VCS incorporates a simple recognition algorithm that utilizes five training samples of each word in a vocabulary of up to 24 words. The recognition rate of approximately 85 percent correct for untrained speakers and 94 percent correct for trained speakers was not considered adequate for flight systems use. Therefore, the built-in recognition algorithm was disabled, and the VCS was modified to transmit 120-bit encodings to an external computer for recognition

The Third Way: Prevention and Compensation of Work Injury in Victoria, Australia

This study originated because the leadership of the VWA and the responsible Minister wanted an assessment of the performance of the Victorian scheme within a larger perspective. They commissioned the W. E. Upjohn Institute for Employment Research, an endowed, not-forprofit research foundation in the United States, to assemble an appropriate team of workers' compensation experts to conduct such a study. The assignment was to carry out a thorough, independent review of the Victorian system of prevention and compensation for work injuries and to provide a set of informed judgments about the system and its performance

Partnerships in Service Learning and Civic Engagement

Developing campus-community partnerships is a core element of well-designed and effective civic engagement, including service learning and participatory action research. A structural model, SOFAR, is presented that differentiates campus into administrators, faculty, and students, and that differentiates community into organizational staff and residents (or clients, consumers, advocates). Partnerships are presented as being a subset of relationships between persons. The quality of these dyadic relationships is analyzed in terms of the degree to which the interactions possess closeness, equity, and integrity, and the degree to which the outcomes of those interactions are exploitive, transactional, or transformational. Implications are then offered for how this analysis can improve practice and research

Influence of Restaurant Reviews Upon Consumers

It is generally believed that restaurant reviews can influence consumers\u27 decisions in choosing a restaurant. A survey administered to a sample of 420 college faculty and staff members suggests that while most restaurant patrons may read reviews, they are not used as the sole selection criterion. Recommendations of friends, the restaurant\u27s current reputation, and perceived value may have greater influence upon the choice than does a re- view. The authors discuss the implications of both favorable and unfavorable reviews

Development of flashlamp-pumped Q-switched Ho:Tm:Cr:YAG lasers for mid-infrared LIDAR application

A flashlamp-pumped 2.1 micron Ho:Tm:Cr:YAG laser was studied for both normal mode and Q-switched operations under a wide variety of experimental conditions in order to optimize performance. Laser output energy, slope efficiency, threshold and pulselength were determined as a function of operating temperature, output mirror reflectivity, input electrical energy and Q-switch opening time. The measured normal-mode laser thresholds of a Ho(3+) (0.45 atomic percent):Tm(3+) (2.5 atomic percent):Cr(3+) (0.8 atomic percent):YAG crystal ranged form 26 to 50 J between 120 and 200 K with slope efficiencies up to 0.36 percent with a 60 percent reflective output mirror. Under Q-switched operation the slope efficiency was 90 percent of the normal-mode result. Development of solid state lasers with Ho(3+), Tm(3+) and/or Er(3+) doped crystals has been pursued by NASA for eye-dafe mid-infrared LIDAR (light detection and ranging) application. As a part of the project, the authors have been working on evaluating Ho(3+):Tm(3+):Cr(3+):YAG crystals for normal-mode and Q-switched 2.1 micron laser operations in order to determine an optimum Tm(3+) concentration under flashlamp pumping conditions. Lasing properties of the Ho(3+) in the mid-infrared region have been studied by many research groups since the early 1960's. However, the technology of those lasers is still premature for lidar application. In order to overcome the inefficiency related to narrow absorption bands of the Ho(3+), Tm(3+) and Er(3+), the erbium has been replaced by chromium. The improvement in flashlamp-pumped Ho(3+) laser efficiency has been demonstrated recently by several research groups by utilizing the broad absorption spectrum of Cr(3+) which covers the flashlamp's emission spectrum. Efficient energy transfer to the Tm(3+) and then the Ho(3+) occurs subsequently. It is known that high Tm(3+) concentration and low Ho(3+) concentration are preferred to achieve a quantum efficiency approaching two and to avoid large reabsorption losses. However, determination of the optimum Tm(3+) concentration required to ensure efficient energy transfer from Cr(3+) to Tm(3+) and from Tm(3+) to Ho(3+) has not been made in the Ho:Tm:CR:YAG crystal. The results obtained so far are given