Estimation and Application of 2-D Scattering Matrices for Sparse Array Imaging of Impact Damage in Composite Panels

Reliable detection of hidden damage in composites is important for failure prevention in the aerospace industry since these materials are being more frequently used in high stress applications. Structural health monitoring (SHM) via guided wave sensors mounted on or embedded within a composite structure can help detect and localize damage in real-time while also reducing overall maintenance costs. One approach to guided wave SHM is sparse array imaging via the minimum variance algorithm, and it has been shown in prior work that incorporating estimated scattering from expected defects can improve the quality of damage localization and characterization [1]. For this study, impacts were applied to induce delaminations within a composite panel. Wavefield data were recorded on a circle centered at the damage location from multiple incident directions before and after the impacts. Baseline subtraction [2] is used to estimate scattering patterns for each incident direction, and these patterns are combined and interpolated to form a full 2-D scattering matrix. This matrix is then incorporated into the minimum variance imaging algorithm, and imaging efficacy is evaluated for both these impacts and impact damage in other similar composite plates. Results are compared to images generated using simpler scattering assumptions

Regenerative fuel cell energy storage system for a low earth orbit space station

A study was conducted to define characteristics of a Regenerative Fuel Cell System (RFCS) for low earth orbit Space Station missions. The RFCS's were defined and characterized based on both an alkaline electrolyte fuel cell integrated with an alkaline electrolyte water electrolyzer and an alkaline electrolyte fuel cell integrated with an acid solid polymer electrolyte (SPE) water electrolyzer. The study defined the operating characteristics of the systems including system weight, volume, and efficiency. A maintenance philosophy was defined and the implications of system reliability requirements and modularization were determined. Finally, an Engineering Model System was defined and a program to develop and demonstrate the EMS and pacing technology items that should be developed in parallel with the EMS were identified. The specific weight of an optimized RFCS operating at 140 F was defined as a function of system efficiency for a range of module sizes. An EMS operating at a nominal temperature of 180 F and capable of delivery of 10 kW at an overall efficiency of 55.4 percent is described. A program to develop the EMS is described including a technology development effort for pacing technology items

Ultrasonic Wavefield Imaging: Research Tool or Emerging NDE Method?

Ultrasonic wavefield imaging refers to acquiring full waveform data over a region of interest for waves generated by a stationary source. Although various implementations of wavefield imaging have existed for many years, the widespread availability of laser Doppler vibrometers that can acquire signals in the high kHz and low MHz range has resulted in a rapid expansion of fundamental research utilizing full wavefield data. In addition, inspection methods based upon wavefield imaging have been proposed for standalone NDE with most of these methods coming from the SHM community and based upon guided waves. If transducers are already embedded in or mounted on the structure as part of an SHM system, then a wavefield-based inspection can potentially take place with very little required disassembly. A frequently-proposed paradigm for wavefield NDE is its application as a follow-up inspection method using embedded SHM transducers as guided wave sources if the in situ SHM system generates an alarm. This presentation considers the broad role of wavefield imaging in ultrasonic NDE, both as a research tool and as an emerging NDE method. Examples of current research will be presented based upon both guided and bulk wavefield imaging in metals and composites, drawing primarily from the author’s work. Progress towards wavefield NDE will be discussed in the context of such issues as defect detection and characterization capabilities, required scan times, equipment cost, and operator training; recent research efforts will be highlighted that can potentially enable wavefield NDE

Migrations and Diasporas. German Writers in Mexican Exile. Egon Erwin Kisch’s and Anna Seghers’ Promotion of Cross-Cultural Understanding

The journalist and popular travel writer, Egon Erwin Kisch, and the well-known novelist and short story writer Anna Seghers were among the many left wing and communist intellectuals for whom Mexico was a haven during the Hitler years. Kisch traveled extensively in Mexico, immersed himself in its history and culture and interpreted Mexico for the other German exiles. On her return from exile Seghers became an important mediator in the GDR of Mexican and South American culture and a strong voice for crosscultural understandin

The Role of Literature in Promoting a Multicultural Society: The Austrian Case

This essay examines the efforts of Austrian writers to make their fellow citizens more tolerant of recent immigrant groups. Postmodern discourses on identity, diversity and cultural difference have shaped debates in Austria about multiculturalism and have encouraged Austrian writers to challenge concepts of national identity and cultural homogeneity and to insist that multicultural and marginalized voices be heard. Like their counterparts in other countries, they encourage the celebration of difference. In their literary works as well as in political essays both in print and on the world wide web they play a leading role in speaking out against anti-foreigner sentiments and intolerance and they present models of a multicultural and multiethnic Austria in which not only Austria's historical minorities such as Jews, Roma and other groups from the former Austro-Hungarian Empire, but also more recently arrived immigrants and refugees can live together and mutually enrich each other's cultures and lives

Deterministic Source Inversion for Wave Propagation Problems in Nondestructive Testing

A source of acoustic or elastic waves is of considerable interest for many nondestructive testing methods. During acoustic emission, waves are generated by transient deformation processes in materials or by externally applied excitations. During ultrasonic testing, transducers of several possible types are used to generate waves. Source inversion refers to the process of determining characteristics of the source of waves from measurements of the resulting wave motion