Toughness in synthetic and biological multilayered systems

Toughness in hard biological tissues is associated with fibrous or lamellar structures that deflect or stop growing cracks. In some cases, such as nacreous shell, protein interlayers absorb much of the crack energy. In other tissues, such as tooth enamel, the toughness derives from the mineral microstructure, and the small amount of residual protein apparently has little effect. There have been a number of efforts to make tough synthetic materials using layered structures. In this work, freeform fabrication has been used to make layered structures with a view to introducing similar toughness into brittle materials. Results are presented for epoxy-glass composites with glass fabric interlayers, porous alumina back-filled with aluminium metal, and layered glass-ceramic/silver materials.     

An apparatus for characterization and control of isolated muscle.

An apparatus for characterization and control of muscle tissue is presented. The apparatus is capable of providing generalized mechanical boundary conditions to muscle tissue, as well as implementing real-time feedback control via electrical stimulation. The system is intended to serve as an experimental platform for implementing a wide variety of muscle control and identification studies that will serve as fundamental investigations of muscle mechanics, energetics, functional electrical stimulation, and fatigue. In one illustration of the capabilities of the apparatus, pilot experimental results of muscle workloops against a finite-admittance passive load are presented, illustrating how richer boundary conditions may reveal interesting muscle behavior.     

Searchable words on the Web

In designing data structures for text databases, it is valuable to know how many different words are likely to be encountered in a particular collection. For example, vocabulary accumulation is central to index construction for text database systems; it is useful to be able to estimate the space requirements and performance characteristics of the main-memory data structures used for this task. However, it is not clear how many distinct words will be found in a text collection or whether new words will continue to appear after inspecting large volumes of data. We propose practical definitions of a word and investigate new word occurrences under these models in a large text collection. We inspected around two billion word occurrences in 45 GB of World Wide Web documents and found just over 9.74 million different words in 5.5 million documents; overall, 1 word in 200 was new. We observe that new words continue to occur, even in very large datasets, and that choosing stricter definitions of what constitutes a word has only limited impact on the number of new words found.     

INCLUDING SOFT INFORMATION IN EISs

Although much of executive decision making is based on soft information—opinions, predictions, news, and even rumors—executive information systems (EISs) have only recently begun to augment factual data with such information. A study of current use of soft information in EISs yields 15 propositions designed to help EIS developers determine what kinds of soft information are most valuable and how best to capture and deliver this information.     

Salmonid Spawning Runs and Estimated Ova Production in Normandale Creek of Lake Erie

The Normandale Creek study area (2,531 m²)provides spawning and nursery grounds for lake-run coho salmon (Oncorhynchus kisutch), rainbow trout (Salmo gairdneri), and brown trout (Salmo trutta), In 1973–74, 59 adult salmonids (58% rainbow trout, 39% coho salmon, and 3% brown trout) ascended the stream between 31 October and 12 May. Upstream movements were significantly related to peak stream discharge (r = 0.21) and highly significantly related to discharge occurring on the day following the peak freshet (r = 0.34). Despite a highly significant correlation (r = 0.29) between flow and water temperature, the latter factor is not significantly related with upstream movement of adult fish. Coho salmon spawned at water temperatures of 1 to 10° C between 2 November and 19 December, rainbow trout at 1 to 15° C between 9 November and 14 May, and brown trout at 7° C between 4 and 5 November. Of 86 nests constructed, 60% were disturbed by re-use or sand deposition. From a calculated deposition of 90,403 ova, it is estimated that some 22% survived to emergence.     

Low-Frequency Piezoelectric Energy Conversion for an Intrathoracic Artificial Heart

The present paper is concerned with an evaluation of a piezoelectric energy conversion system in which two columns of piezoelectric ceramic disks are excited axially by means of thin metallic shims stacked alternately with the disks. Mechanical energy output is extracted through the expansion and contraction of the Columns. The treatment is based upon the equivalent circuit approach first suggested by Mason. A lever system is used in making the mechanical impedance transformation between the very high force and small displacement of the piezoelectric columns and the low force and relatively large displacement required for an artificial heart. The role of mass loading in improving the power capability and efficiency of the energy converter is clearly indicated. It is concluded that the theoretical energy output per unit mass of material per cycle and the efficiency of conversion are such as to justify a continued developmental effort.     

Solvent Decontamination of PCB Electrical Equipment

Polychlorinated biphenyls (PCB's) which are used as dielectric fluids in transformers and capacitors, are toxic relatively inert materials which are persistent and widespread in the environment and biomagnified in the food chain. Disposal of contaminated electrical equipment requires removal of the majority of PCB's. Various solvent cleaning techniques have been investigated for decontamination of intact transformers and shredded capacitors. The PCB content of transformers which originally contained 180-270 kg PCB was reduced by 99.72-99.96 percent. The relatively small amount of retained PCB resides primarily in the interstices and absorbent material of the core and coil assembly. Shredded power factor correction capacitors were decontaminated using trichlorethylene in a multistage concurrent batch extraction process. The PCB content was reduced by 99.9 percent, leaving a residual PCB content of 0.01 kg per capacitor.     

Comparison of SeaWiFS measurements of the Moon with the U.S. Geological Survey lunar model

The Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) has made monthly observations of the Moon since 1997. Using 66 monthly measurements, the SeaWiFS calibration team has developed a correction for the instrument's on-orbit response changes. Concurrently, a lunar irradiance model has been developed by the U.S. Geological Survey (USGS) from extensive Earth-based observations of the Moon. The lunar irradiances measured by SeaWiFS are compared with the USGS model. The comparison shows essentially identical response histories for SeaWiFS, with differences from the model of less than 0.05% per thousand days in the long-term trends. From the SeaWiFS experience we have learned that it is important to view the entire lunar image at a constant phase angle from measurement to measurement and to understand, as best as possible, the size of each lunar image. However, a constant phase angle is not required for using the USGS model. With a long-term satellite lunar data set it is possible to determine instrument changes at a quality level approximating that from the USGS lunar model. However, early in a mission, when the dependence on factors such as phase and libration cannot be adequately determined from satellite measurements alone, the USGS model is critical to an understanding of trends in instruments that use the Moon for calibration. This is the case for SeaWiFS.