The high-frequency backscattering angular response of gassy sediments: Model/data comparison from the Eel River Margin, California

A model for the high-frequency backscatter angular response of gassy sediments is proposed. For the interface backscatter contribution we adopted the model developed by Jackson et al. @J. Acoust. Soc. Am. 79, 1410–1422 ~1986!#, but added modifications to accommodate gas bubbles. The model parameters that are affected by gas content are the density ratio, the sound speed ratio, and the loss parameter. For the volume backscatter contribution we developed a model based on the presence and distribution of gas in the sediment. We treat the bubbles as individual discrete scatterers that sum to the total bubble contribution. This total bubble contribution is then added to the volume contribution of other scatters. The presence of gas affects both the interface and the volume contribution of the backscatter angular response in a complex way that is dependent on both grain size and water depth. The backscatter response of fine-grained gassy sediments is dominated by the volume contribution while that of coarser-grained gassy sediments is affected by both volume and interface contributions. In deep water the interface backscatter is only slightly affected by the presence of gas while the volume scattering is strongly affected. In shallow water the interface backscatter is severely reduced in the presence of gas while the volume backscatter is only slightly increased. Multibeam data acquired offshore northern California at 95 kHz provides raw measurements for the backscatter as a function of grazing angle. These raw backscatter measurements are then reduced to scattering strength for comparison with the results of the proposed model. The analysis of core samples at various locations provides local measurements of physical properties and gas content in the sediments that, when compared to the model, show general agreement

A study of Massachusetts elementary principals\u27 knowledge and attitudes toward their leadership role in building based change.

Principals are assuming more responsibility and are becoming accountable to a greater extent for the success of students. This has become particularly the case in Massachusetts since passage of the Education Reform Act of 1993 which expanded the principal\u27s role and powers at the building level. Knowledge of how change can be led in the elementary building is an essential skill for principals. The purpose of this research was to study Massachusetts elementary principal\u27s knowledge and attitudes regarding change in educational settings, adults\u27 response to change, leadership style, and building climate issues. This information was compared to research regarding how change is effectively led in schools. It was also studied in regard to several demographic indicators such as, gender, size of school and community, educational background, and years of experience. To gather this information, a random sample of elementary principals in Massachusetts was stratified by gender and size of community and then surveyed using an instrument composed of a five point Likert scale. The results indicated that elementary principals in Massachusetts describe their leadership style as primarily collaborative. The Directive model of leadership was rejected. Their knowledge and attitudes toward change in schools indicates a thorough understanding of change principles, adult learning styles and life cycle issues. They see little difference between working with men and women and differently experienced staff. They understand that the principal\u27s role in this process is essential and take much responsibility for the success of their schools. The skills of empowerment of staff, consensus building, participatory decision making, vision and goal setting and creating a professional and stimulating climate in their buildings are all valued. Male and female principals differed in regards to age, and experience with female principals being three years younger and having more teaching yet less administrative experience. There were few areas of differences in Leadership style between the genders. Women ranked coaching, modeling, and empowering staff higher than men. Men ranked consensus making, and managerial skills higher

A Chromosome Study of Chlorophytum Elatum

The spider plant, Chlorophytum elatum R. Br., a member of the family Liliaceae, is a native of South Africa. It has been propagated almost exclusively by vegetative means and it is now grown widely over the world as an ornamental plant. Many studies by other workers have revealed that with only two exceptions all species in the genus Chlorophytum have somatic chromosome numbers that are multiples of seven, ranging from 14 to 56 (c.f. Darlington and Wiley, 1955). Although the chromosome number of Chlorophytum elatum has ·been reported to be 2N = 28 (Sato, 1942; Baldwin and Speese, 1951) information regarding its karyotype is not complete and meiotic behavior is still lacking. Storey (1968), after studying the mitotic phenomenon in roottip cells, suggested that this species might be an autotetraploid with a basic number X = 7. However, he failed to study the meiotic chromosomes which would be essential in order to verify his assumption. The clone of Chlorophytum elatum, which has been maintained in the Botany Greenhouse, was noted to show some degree of sterility. Preliminary observations of the pollen indicated that about 25 percent of the grains were non-stainable and irregular in shape. This implied that either a change in chromosome number or an alteration of chromosome structure might occur in this particular clone such as was observed in other genera by Carnahan and Hill (1962); Dhaliwal, Pollard, and Lorz (1962); Doughty (1936); Honma (1968); Kreft (1968); Sutton (1937); Thomas (1960); Upcott and Lacour (1936); Upcott (1937); and Whitaker (1935). This study was undertaken to ascertain the karyotype of Chlorophytum elatum and to study the meiotic chromosome behavior. A karyotypic analysis supported by a study of the behavior of chromosomes during diakinesis and/or metaphase I was made to determine the ploidy of this clone. The study of the meiotic chromosome behavior at later stages of meiosis along with a karyotypic analysis was made to find an explanation for the clone\u27s sterility

Time-Resolved Detection of Individual Electrons in a Quantum Dot

We present measurements on a quantum dot and a nearby, capacitively coupled, quantum point contact used as a charge detector. With the dot being weakly coupled to only a single reservoir, the transfer of individual electrons onto and off the dot can be observed in real time in the current signal from the quantum point contact. From these time-dependent traces, the quantum mechanical coupling between dot and reservoir can be extracted quantitatively. A similar analysis allows the determination of the occupation probability of the dot states.Comment: 3 pages, 3 figure

Finite bias charge detection in a quantum dot

We present finite bias measurements on a quantum dot coupled capacitively to a quantum point contact used as a charge detector. The transconductance signal measured in the quantum point contact at finite dot bias shows structure which allows us to determine the time-averaged charge on the dot in the non-blockaded regime and to estimate the coupling of the dot to the leads.Comment: 6 pages, 4 figure

Thermally excited Trivelpiece–Gould modes as a pure electron plasma temperature diagnostic

Thermally excited plasma modes are observed in trapped, near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05<kT<5 eV. The modes are excited and damped by thermal fluctuations in both the plasma and the receiver electronics. The thermal emission spectra together with a plasma-antenna coupling coefficient calibration uniquely determine the plasma (and load) temperature. This calibration is obtained from the mode spectra themselves when the receiver-generated noise absorption is measurable; or from separate wave reflection/absorption measurements; or from kinetic theory. This nondestructive temperature diagnostic agrees well with standard diagnostics, and may be useful for expensive species such as antimatter

Thermally excited fluctuations as a pure electron plasma temperature diagnostic

Thermally excited charge fluctuations in pure electron plasma columns provide a diagnostic for the plasma temperature over a range of 0.05 0.2, so that Landau damping is dominant and well modeled by theory. The third method compares the total (frequency-integrated) number delta N of fluctuating image charges on the wall antenna to a simple thermodynamic calculation. This method works when lambda(D)/R-p > 0.2