Magnetic behaviour of spin-mixed iron(III) porphyrins

Detailed average magnetic susceptibility (295-4.2 K) and average magnetisation (20-2 K, 50-10 kOe) are reported for two novel spin-mixed iron(III) porphyrins, namely Fe(TPP)ClO4 and Fe(OEP)ClO4. The results confirm an S = 3/2 ground state substantially spin-mixed with a low-lying S = 5/2 state, but do not agree in detail with the crystal-field model of Maltempo.     

The effect of hair on auditory localization cues

Previous empirical and analytical investigations into human sound localization have illustrated that the head-related transfer function (HRTF) and interaural cues are affected by the acoustic material properties of the head. This study utilizes a recent analytical treatment of the sphere scattering problem (which accounts for a hemispherically divided surface boundary) to investigate the contribution of hair to the auditory cues below 5 kHz. The hair is modeled using a locally reactive equivalent impedance parameter, and cue changes are discussed for several cases of measured hair impedance. The hair is shown to produce asymmetric perturbations to the HRTF and the interaural time and level differences. The changes in the azimuth plane are explicated via analytical examination of the surface pressure variations with source angle. Experimental HRTFs obtained using a sphere with and without a hemispherical covering of synthetic hair show a good agreement with analytical results. Additional experimental and analytical investigations illustrate that the relative contribution of the hair remains robust, regardless of the placement of the pinnas, or inclusion of a cylindrical neck.     

Hybrid active and passive control of fan noise

This paper deals with the global reduction of axial flow fan noise in ducts in a building using a hybrid passive-active noise control method. The effectiveness of using an infra-red device as a reference signal source is also investigated. It is shown that using such a hybrid noise control system over an axial-flow fan reduces the overall sound pressure level by 5 dB(A) in the surrounding environment and global control of the blade passing frequency can also be achieved. This paper also shows that using an infra-red device as a reference signal source produces marginally better control as compared with using a microphone reference sensor. Moreover, long term stability is guaranteed and the possibility of acoustic feedback is eliminated.     

The effect of impedance on interaural azimuth cues derived from a spherical head model

Recent implementations of binaural synthesis have combined high-frequency pinna diffraction data with low-frequency acoustic models of the head and torso. This combination ensures that the salient cues required for directional localization in the horizontal plane are consistent with psychophysical expectations, regardless of the accuracy or match of the high-frequency cues, or the fidelity of experimental low-frequency information. This paper investigates the effect of a nonrigid boundary condition on the surface pressure and the resulting interaural cues used for horizontal localization. These are derived from an analytical single sphere diffraction model assuming a locally reacting and uniformly distributed impedance boundary condition. Decreasing the magnitude of a purely resistive surface impedance results in an overall decrease in the sphere surface pressure level, particularly in the posterior region. This produces nontrivial increases in both the interaural level and time difference, especially for sound source directions near the interaural axis. When the surface impedance contains a reactive component the interaural cues exhibit further changes. The basic impedance characteristics of human hair and their incorporation into the sphere diffraction model are also discussed.     

An experimental study of the acoustic impedance characteristics of human hair

Previous analytical and empirical studies of the human auditory system have shown that the cues used for localization are modified by the inclusion of nonrigid scattering surfaces (clothing, hair etc). This paper presents an investigation into the acoustic impedance properties of human hair. The legitimacy of a locally reactive surface assumption is investigated, and an appropriate boundary condition is formulated to account for the physiological composition of a human head with hair. This utilizes an equivalent impedance parameter to allow the scattering boundary to be defined at a reference plane coincident with the inner rigid surface of the head. Experimental examination of a representative synthetic hair material at oblique incidence is used to show that a locally reactive surface assumption is legitimate. Additional experimental analysis of a simple scattering problem illustrates that the equivalent impedance must be used in favor of the traditional surface impedance to yield physically correct pressure magnitudes. The equivalent acoustic impedance properties of a representative range of human hair samples are discussed, including trends with sample thickness, fiber diameter, bulk density, and mass.     

Acoustic scattering by a sphere with a hemispherically split boundary condition

A general analytical model is developed for the scattering of sound by a sphere with a nonuniform impedance boundary condition that is divided into two uniformly distributed hemispheres. In addition to the overall solution for the time harmonic pressure, the analytical result gives insight into the modal contributions and coupling for different cases of source incidence and boundary impedance. Modal cross coupling is shown to exist between incoming and scattered wave modes of equi-order and nonequal degree when the degrees are opposite in parity (odd-even or even-odd coupling). This cross coupling is strongest between modes of adjacent degree, and decreases as the degrees become dissimilar. The overall magnitude of the cross coupling is dependent on the extent of the impedance mismatch between the two surface hemispheres. Simulation and discussion are given for several specific cases of source incidence and impedance (each hemisphere is given a different constant impedance value). These results are consistent with expectations from the scattering of sound by a sphere with a uniformly distributed surface boundary. The broad scattering characteristics of the hemispherically divided sphere are shown to be analogous to connecting the appropriate sectors from the corresponding uniformly distributed spheres.     

An example of an iron (III) porphyrin with spin mixed ground state

The paper reports synthesis and physical characterisation of a new iron(III) porphyrin which shows unusual features of quantum mechanically mixed ground state in its magnetic properties. Magnetic susceptibility (300−3·6 K) and M?ssbauer spectroscopy (300−77 K) studies of the compound are described and discussed with reference to some bacterial ferricytochromeC' exhibiting similar spin-mixed ground state.