Novel coexistence of superconductivity with two distinct magnetic orders

The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.     

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.     

Selection of mandrel wrap mode filters for optical fiber loss measurements

A selection criterion for mode filters based on far-field patterns is developed. The criterion is used to select a mandrel wrap filter for 50 μm core diameter, 125 μm outside diameter fibers with δ=1.1%. When cut-back loss measurements were made using the mandrel wrap chosen in this way, loss scaled with length to within ± 0.05 dB/km in three 2-km fibers.     

Some new methods for preparing 2,3- and 3,4-diaminopyridines

New methods of preparing 2,3-diaminopyridine ( 13 ) from 2-chloro-3-nitropyridine ( 11 ) and 3,4-diaminopy-ridine ( 8 ) from 4-ethoxy-3-nitropyridine hydrochloride ( 5 ) have been explored and evaluated.     

Neural networks for prediction of acoustical properties of polyurethane foams

This paper presents a study of neural networks for prediction of acoustical properties of polyurethane foams. The proposed neural network model of the foam uses easily measured parameters such as frequency, airflow resistivity and density to predict multiple acoustical properties including the sound absorption coefficient and the surface impedance. Such a model is quite robust in the sense that it can be used to develop models for many different classes of materials with different sets of input and output parameters. The current neural network model of the foam is empirical and provides a useful complement to the existing analytical and numerical approaches.     

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.     

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.