Sound cancellation by the use of secondary multipoles: experiments

Theory related to global, free-field cancellation of a primary monopole field by the use of a displaced, secondary multipole was presented previously: a corresponding experimental investigation is presented here. The construction of multipole source components to octopole order is described, as are procedures for determining their source strengths. Dipoles, longitudinal quadrupoles, and longitudinal octopoles that conformed closely to their theoretical models were constructed using arrays of unbaffled loudspeakers. Two methods of calculating the multipole strengths required to cancel a primary monopole field were implemented in an open-loop manner: a "direct" approach based on a multipole expansion of the primary field, and a least-squares procedure based on fitting the secondary field to the primary field either along a circle enclosing a secondary source, or along a segment of that circle. Cancellation measurements were made on a 1-m-radius circle centered on the secondary source: the primary-to-secondary source separation was approximately 0.2 wavelengths. It was found both that a secondary multipole could provide far greater cancellation than a monopole placed at the same distance from the primary source and that the least-squares approach resulted in greater far-field cancellation than did the direct approach.     

An acoustic study of soils that model seabed sediments containing gas bubbles

The acoustic response of gassy seabed sediment is unique. It is a dispersive and extraordinarily attenuative natural material at frequencies which cause gas bubble resonance. It conceals the structure of the seabed from seismic profiling and it dampens acoustic signals that, for example, trigger acoustic mines. In the past, theoretical studies have formulated the probable cause of this response and crude experimental work has partially corroborated theory. This study measures compressional wave velocity and attenuation in a laboratory soil simulating natural gassy soil, and it investigates the structural properties that cause the unique acoustic response. It was confirmed that below the frequencies which cause resonance the soil behaves as a compressible material (containing gas), and above as a relatively incompressible material (containing no gas). Over the frequency range producing bubble resonance it is suggested that the soil should be modeled as a biphasic material of gas and a relatively incompressible saturated soil matrix (particles and fluid). Velocities for gassy soil were found to be as low as 220 m/s at frequencies below resonance and 1500 m/s above resonance; attenuations were found to be as high as 60 dB/cm for moderately gassy soil and as low as 1 dB/cm for soil with almost no gas.     

Stochastic PAC models for vacancy motions with trapping and detrapping

In order to explain PAC data for tetragonal zirconia at temperatures between 900 and 1300oC, we have developed a four-state stochastic model. The model simulates vacancies which trap and detrap at a PAC probe nucleus. While trapped, the vacancies hop around the probe in equivalent sites. The four states in this Winkler–Gerdau stochastic theory are three trapped states with equivalent electric field gradients (EFGs) of different orientations and a detrapped state with a weaker EFG whose axis of symmetry is oriented along the diagonal between the three trapped EFGs. There are three hopping rates in this model: w, the rate a trapped vacancy hops around the probe, w_D, the detrapping rate, and w_t, the trapping rate. We report results of calculations for values of these hopping rates implied by our tetragonal zirconia data, and we report heuristic fitting functions which summarize the computer results and can be used to fit data efficiently for a wide range of parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Eine Analyse von betr?chtliche Mengen Indigrot enthaltendem Indigo

Ohne Zusammenfassung     

High-frequency nanostructured magnetic materials for integrated inductors

Electroplating is compatible with the deposition of relatively thick layers i.e. several μm to 10s- of μm. However eddy current losses mean that thick layers will have an inferior frequency response. We have used a low content phosphorous bath together with pulse reverse plating to generate Co-rich and Co-deficient multi-nanolayers of CoP having improved saturation magnetisation and a better frequency response. The plating parameters have been optimised in order to produce a material with low loss, and a high permeability of around 700 retained up to 103 MHz for a sample with a thickness of 1.7 μm and a resistivity of 136 μΩ cm.     

Surface-enhanced vibrational investigation of adsorbed analgesics

Adsorption properties of acetylsalicylic acid (AA), ibuprofen and acetaminophen deposited from volatile solvents with varying protic/aprotic properties on vacuum-evaporated silver films were characterized using surface-enhanced infrared absorption (SEIRA) and surface-enhanced Raman spectroscopy (SERS). SERS preferentially enhances monolayer Raman shifts, while SEIRA can enhance the infrared absorbance of the monolayer and multilayers. To our best knowledge, this is the first reported study of these molecules using a combination of SERS/SEIRA. SERS revealed that AA and ibuprofen adsorbed ionically in monolayers, independent of the deposition solvents used in the process. SEIRA experiments showed that AA multilayers condensed molecularly using a deposition solvent with polar bonds. However, when an alkane deposition solvent with non-polar bonds such as n-heptane was used, AA adsorbed as acetylsalicylate ions in the first few multilayers, while ibuprofen always adsorbed as the free acid in the multilayer. These ionization trends depend upon the affinity of AA and ibuprofen for the underlying silver film. TPD experiments on silver powders further demonstrated that ibuprofen affinity for silver was less than AA. Furthermore, SEIRA indicated that acetaminophen adsorbed as multilayers of metastable polymorphs using protic or polar aprotic deposition solvents. Protic deposition solvents gave higher quality SERS spectra of an acetaminophen monolayer in comparison to polar aprotic deposition solvents. Such studies could find significant applications in biochemical and nanotechnology processes such as drug delivery, catalysis, and tissue engineering and will contribute to the understanding of the impact and fate of analgesics released into the environment.     

Copper-catalyzed hydroamination of propargyl imidates

Propargyl imidates derived from aromatic and aliphatic nitriles cyclize at room temperature in high yields when treated with a catalytic amount of copper (I) iodide. This 5-exo-dig process affords dihydrooxazoles which do not aromatize under the reaction conditions, and which are isolated without chromatography. Investigations of the reaction scope, subsequent functionalization of the reaction products, and preliminary mechanistic data are presented.     

Deep swirling flow down a plughole with air entrainment

Experiments have been carried out to determine the water depth required to entrain a given amount of air with a given circulating water flow discharging through a vertical pipe set in the flat bottom of a vessel. The circulation angle, , between the radial direction and the velocity vector far from discharge pipe was set at 0°, 10°, 30° or 60°.

It is shown that results are not dependent upon the diameter of the offtake pipe, if that is sufficiently small, and results are then expressed either as a dimensionless water depth vs a dimensionless ratio of the flow rates of the two phases or as a dimensionless flow rate of one phase vs the dimensionless flow rate of the other phase. An approximate theory describes trends in the data and is mostly in good quantitative agreement.

The results are used to examine the work of others on the entrainment of air or steam by water flowing along the bottom of a horizontal pipe into a small bottom offtake and the similar entrainment of water by air or steam flowing into a small top offtake. These systems occur in certain PWR loss of coolant accidents.     

Spin liquid state in the S = 1/2 triangular lattice Ba3CuSb2O9

The synthesis and characterization of Ba3CuSb2O9, which has a layered array of Cu2+ spins in a triangular lattice, are reported. The magnetic susceptibility and neutron scattering experiments of this material show no magnetic ordering down to 0.2 K with a θ(CW) = -55 K. The magnetic specific heat reveals a T-linear dependence with a γ = 43.4 mJ K(-2) mol(-1) below 1.4 K. These observations suggest that Ba3CuSb2O9 is a new quantum spin liquid candidate with a S = 1/2 triangular lattice.     

Enhanced reactivity of nanoscale iron particles through a vacuum annealing process

A reactivity study was undertaken to compare and assess the rate of dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by annealed and non-annealed nanoscale iron particles. The current study aims to resolve the uncertainties in recently published work studying the effect of the annealing process on the reduction capability of nanoscale Fe particles. Comparison of the normalized rate constants (m²/h/L) obtained for dechlorination reactions of trichloroethene (TCE) and cis-1,2-dichloroethene (cis-1,2-DCE) indicated that annealing nanoscale Fe particles increases their reactivity ~30-fold. An electron transfer reaction mechanism for both types of nanoscale particles was found to be responsible for CAH dechlorination, rather than a reduction reaction by activated H₂ on the particle surface (i.e., hydrogenation, hydrogenolysis). Surface analysis of the particulate material using X-ray diffraction (XRD) and transmission electron microscopy (TEM) together with surface area measurement by Brunauer, Emmett, Teller (BET) indicate that the vacuum annealing process decreases the surface area and increases crystallinity. BET surface area analysis recorded a decrease in nanoscale Fe particle surface area from 19.0 to 4.8 m²/g and crystallite dimensions inside the particle increased from 8.7 to 18.2 nm as a result of annealing.