Tapered transmission line technique based graded matching layers for thickness mode piezoelectric transducers

Conventionally, in order to acoustically match thickness mode piezoelectric transducers to a low acoustic impedance load medium, multiple quarter wavelength (QW) matching layers are employed at the front face of the device. Typically a number of layers, 2-4 in number, are employed resulting in discrete impedance steps within the acoustic matching scheme. This can result in impedance matching with limited bandwidth characteristics. This paper investigates the application of tapered transmission line filter theory to implement a graded impedance profile, through the thickness of the matching layer scheme, to solve the impedance mismatch problem whilst accounting for enhanced transducer sensitivity and bandwidth

A pop-up float recovery system for coastal oceanographic tripods

The recovery package described here was used as the primary retrieval system to recover tripod instrument platforms from a depth of 90 meters. The device uses dual in-line burn wires, one of which is acoustically commanded from the surface ship. The other is set to release by back-up timer, ensuring recovery in the event of a poor acoustic command channel. The burn wire activates spring loaded cam latches which release the float package and pull a ~ inch Dacron line to the surface. The float package is recovered and the line is used to winch the tripod to the surface for recovery by the ship's crane. Major benefits of the system are reliability, low cost, light weight, and use of many off-the-shelf components. The float package provides 50 pounds of buoyancy and is fabricated using commercial fish trawl net floats. The retrieval line container is separate from the float assembly, and is fabricated from plastic storage containers. The line is coiled and restricted to prevent unpackaging due to waves or current action. The system described here is not appropriate in areas of high current or great depth due to drag and dead weight of the lift line.Funding was provided by the Office of Naval Research under contract No. N00014-89.J-1058

A Predictive Study of Seventh Graders’ Academic Achievement from Objective and Subjective Grade Six Ratings

The general purpose of this study was to discover the effectiveness of the elementary school ratings in predicting a student\u27s academic performance during his first year of high school (Grade 7)

Understanding the mechanism by which nitrilotriacetic acid interacts with precipitating barium sulfate

Morphology modifiers can act in many different ways on the precipitating phase. Inhibitors can alter the solution chemistry and thereby change the supersaturation, they may adsorb onto the surface and block growth and agglomeration, they may alter the ritical nucleus and affect nucleation or they may do a combination of these three. revious work showing that nitrilotriacetic acid (NTA) had a significant effect on barium sulfate precipitation has been expanded upon in order to determine the mechanism by which the observed morphology modification occurs. The absence of significant complexation to barium at the pH of the experiment suggests that NTA affects the critical nuclei of the precipitating barium sulfate. This results in the longer induction times observed using nephelometry, and adsorption onto growth features is probably the mechanism of interaction. Molecular modelling shows that NTA adsorption is favourable on terraces and that hydrogen bonding improves the ability of an additive to adsorb. A fundamental nderstanding of the mechanisms by which additives affect crystal growth is essential if new additives, with predictable effect, are to be designed a priori

Bio-Inspired Calix[4]arene Additives for Crystal Growth Modification of Inorganic Materials

Crystal growth of inorganic materials, calcium carbonate, barium sulfate and calcium oxalate, was studied in the presence of calix[4]arene additives functionalized with aspartic or glutamic acids at the lower rim. The additives were synthesized by reaction of the appropriate amino acid ester with 5,11,17,23-tetra-tert-butyl-25,-26,27,28-tetrakis(chlorocarbonylmethoxy)calix[4]arene, followed by controlled hydrolysis of the ester groups. Both additives inhibited the nucleation and growth of calcium carbonate but induced different changes in calcite morphology. The aspartic acid derivative was the more potent barium sulfate inhibitor at low concentrations, with comparable performance at higher levels. Both additives induced a polycrystalline barite precipitate. The aspartic acid functionalized calixarene also stabilized calcium oxalate dihydrate at low additive concentrations, whereas the glutamic acid derivative induced morphological changes in calcium oxalate monohydrate

Belief bias during reasoning among religious believers and skeptics

We provide evidence that religious skeptics, as compared to believers, are both more reflective and effective in logical reasoning tasks. While recent studies have reported a negative association between an analytic cognitive style and religiosity, they focused exclusively on accuracy, making it difficult to specify potential underlying cognitive mechanisms. The present study extends the previous research by assessing both performance and response times on quintessential logical reasoning problems (syllogisms). Those reporting more religious skepticism made fewer reasoning errors than did believers. This finding remained significant after controlling for general cognitive ability, time spent on the problems, and various demographic variables. Crucial for the purpose of exploring underlying mechanisms, response times indicated that skeptics also spent more time reasoning than did believers. This novel finding suggests a possible role of response slowing during analytic problem solving as a component of cognitive style that promotes overriding intuitive first impressions. Implications for using additional processing measures, such as response time, to investigate individual differences in cognitive style are discussed

Morphological Control of Ca3Al2(OH)12

The effect of a range of inorganic and organic crystal growth modifiers on the morphology of Ca3Al2(OH)12 has been studied. It has been found that some additives show a strong preference for a single crystal face forming polyhedral crystals whilst others are less selective, producing crystals with a less well defined morphology. In this way sulphite and dithionite preferentially interact with the {111} face producing octahedral crystals and nitrilotriacetic acid stabilises the {110} face forming rhombic dodecahedral crystals. Phosphate, however, leads to the formation of small needle-like crystals and the organic acids, N(CH2CO2H)2(CH2PO3H2), N(CH2CO2H)(CH2PO3H2)2, HN(CH2PO3H2)2, and H3CN(CH2PO3H2)2, produce near spherical crystals