Benthic communities in Spartina alterniflora and Phragmites australis dominated salt marshes

The benthic communities were investigated in Phragmites australis and Spartina altemiflora salt marshes, conducted in natural and mitigated salt marshes located in a highly urbanized area, the Hackensack Meadowlands, New Jersey. Benthic samples were taken with a 5-centimeter core at two habitats, the creek bank and the edge of the vegetation in the low marsh zone. Salinity levels and textural and structural sediment characteristics were also collected at each site. A recolonization experiment that utilized sediment from an undisturbed and uncontaminated salt marsh was conducted to determine if substrate is important in benthic colonization. The results suggest that there were differences in abundance, taxa richness, diversity, and composition in the benthic communities found among the different types of grasses as well as the mitigated and natural marshes. The Phragmites australis marsh had a more diverse benthic community than the natural and mitigated Spartina alterniflora marshes. The mitigated marshes had a greater abundance and lower diversity than the natural marshes. However, there were differences in salinity levels (oligohaline to polyhaline) between the mitigated and natural marshes that could result in different types of benthic communities. Substrate and contamination did not seem to be a factor in the recolonization of benthic communities. The principles of opportunism were responsible for shaping the benthic communities in the recolonization experiment. This study shows that Phragmites australis supports a healthy benthic community. The benthic community of the mitigated marsh did not resemble the natural marshes after 12-years of establishment

Acoustical Imaging and Holography Seventh International Symposium

I am going to report briefly on the Acoustical Imaging and Holography Conference that was concluded yesterday in Chicago. These conferences were started in 1967, and are concerned primarily with ultrasonics and visualization techniques as applied to medicine, nondestructive evaluation, sonar, seismic analysis and acoustic microscopy

Ultrasonic Thermometry for Recession Measurements in Ablative Materials

Recent developments in ultrasonic instrumentation & sensors, improved signal processing, and high speed data acquisition have rekindled interest in ultrasonic thermometry and made temperature localization feasible and economically attractive to a wider range of applications. Ultrasound-based temperature measurements offer several advantages: they are non-intrusive, have high temporal response, isolate the sensor from explosive or chemically harsh environments and do not adversely influence thermal transport. Ultrasonic thermometry techniques rely on precise measurements of ultrasonic time-of-flight (ToF) which forms the basis for many applications including measurements of flow, heat flux, temperature, ablation and strain. In this report, we characterize the ultrasonic propagation characteristics of several ablative materials. Properties relevant to ultrasonic thermometry include backscattering properties, attenuation coefficient, ultrasonic velocity, and velocity-temperature coefficient. We will present preliminary experiments directed at developing ultrasonic methods for simultaneous temperature and recession measurements on ablators. Various approaches to measuring recession, heat flux, and internal temperature profiles in ablators will be described

Flaw Detection and Characterization in Ceramics with the Scanning Laser Acoustic Microscope (SLAM)

The high resolving power coupled with the real time capability of the SLAM make it a useful technique for characterization of materials including ceramics. The elastic structure of·ceramics is often dependent upon the details of the fabrication process, e.g., sintering, hot pressing, amount of. binder, etc .. Accordingly, acoustic micrographs and acoustic interferograms which reveal characteristic sonic transmission patterns and sonic velocity variations, respectively, can be used to nondestructively evaluate ceramics to ensure material uniformity. In addition, the ability to nondestructively detect flaws and inclusions is important in fracture toughness studies and in the evaluation of finished components

High Resolutional Real Time Acoustic Microscopy

A commercially available scanning-laser-acoustic-microscope {SLAM) has been developed which provides new and unique analytical capabilities for materials science and non-destructive testing. By employing 100 MHz acoustic waves to create images, the elastic microstructure of complex materials is visualized directly. The acoustic micrographs which contain 2 x 104 image points, are displayed on a real time TV monitor. The sample remains accessible to the investigator during the procedure and stressing fixtures can be employed. Dynamic activities can be recorded either on movie film or video tape. There are two acoustic imaging modes which appear to be essential for flaw and defect characterization. The first mode displays the acoustic transmission level through the sample (normal mode) and the second mode displays fringes related to the acoustic phase (interference mode). The presence of a defect within a sample may be evidenced by a change in transmission level or a change in phase or both. The nature of the defect (e.g. high density inclusion or void) can be determined through the combined analysis of the interference and normal mode micrographs. The SLAM technique has been applied to a wide variety of materials including ceramics, metals, glasses, polymers, etc. Defect localization down to 25 μm has been achieved. Samples can be systematically searched, area by area, by simply repositioning the part on the stage of the microscope and observing the acoustic image on the TV monitor

Scanning Laser Acoustic Microscope Visualization of Solid Inclusions in Silicon Nitride

The Scanning Laser Acoustic Microscope (SLAM) operating at a frequency of 100 MHz is used to characterize solid inclusions in silicon nitride. Ten, seven millimeter thick discs, with 100 and 400 micron implanted inclusions are analyzed. We find that the images of a solid inclusion are characterized by a bright high transmission central zone, a well defined dark boundary and a characteristic diffraction ring pattern. These image features differentiate solid inclusions from pores and voids which may also be encountered in the samples. The images of the implanted flaws were generally found to be larger than anticipated. This can be understood in terms of the divergence of the sound due to diffraction and due to lens action of the curved boundary of the flaw. Our initial observations suggest that accurate estimates of defect size may be obtaiRable from a more complete analysis of SLAM micrographs

Differentiation of Various Flaw Types in Ceramics Using the Scanning Laser Acoustic Microscope

High frequency acoustic imaging represents a powerful technique for the nondestructive evaluation of optically opaque materials. In this report the Scanning Laser Acoustic Microscope (SLAM) is used to detect and characterize flaws in ceramics. SLAM micrographs showing typical examples of cracks, laminar flaws, porosity and solid inclusions. are presented. The various flaw types are easily differentiated on the basis of their characteristic acoustic signatures. The importance of an imaging approach to the nondestructive evaluation of ceramics is demonstrated

Acoustic Microscopy of Ceramics

The scanning laser acoustic microscope (SLAM) is applied to the problem of nondestructive testing of ceramic materials. The employment of a very high resolution ultrasonic imaging instrument provides capabilities which supplement ultrasonic pulse-echo testing. In addition, by means of showing a picture of the flaw, the SLAM technique provides its own capabilities which alleviate some of the limitations of other techniques. Flaws of various types are documented in this paper