Monocrystalline high-saturation magnetization ferrites for video recording head application: III. CoII doped MnZn ferrites with large FeII contents

It is shown that substitution of Co^II into Fe^II-rich MnZn ferrites makes it possible to enlarge the Fe^II content permissible for combined write/read video recording heads. This results in an increase of the saturation magnetization M_s, which is important when high-coercivity magnetic tapes are used. A properly chosen Co^II content compensates the magnetocrystalline anisotropy of the ferrites in such a way that the temperature of the maximum in the magnetic permeability μ′ versus temperature curve, caused by anisotropy compensation by Fe^II, is lowered to the level at which a recording head operates. We report on monocrystalline ferrites with suitable Co^II-Fe^II concentration combinations, showing M_s values of up to 0.660 T and a maximum in μ′(T) at 40°C of 600–700 at 4.5 MHz. We show that with Co^II substitutions, the enlargement of the Fe^II content does not give rise to larger magnetic disaccommodation effects. The present paper is the third in a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: I. Zn ferrous ferrites

Monocrystalline Zn ferrous ferrites Zn_xFe_3-xO₄, with x ? 0.4, are considered as candidate materials for video recording heads, to be used for writing on magnetic tapes of high coercivity. The saturation magnetization of these ferrites can be as high as 0.7 T at 20°C. We show that because of the small dimensions of modern video recording heads, the relatively high electrical conductivity of the Zn ferrous ferrites is not an obstacle to their use at video frequencies. Measurements are reported of magnetic and electrical parameters relevant to recording head application. It is shown that some of the magnetic parameters can be influenced positively by Co^II additions. The present paper is the first of a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Dichromated gelatin for volume holographic recording with high sensitivity. Part II

A method is described to raise the sensitivity of dichromated gelatin layers by hardening them before exposure, with compounds binding not the carboxyl but the amino groups of the gelatin molecules. The experiments showed a tenfold increase in the light sensitivity of the layers.     

An acoustic head simulator for hearing protector evaluation. II: Measurements in steady-state and impulse noise environments

The attenuation characteristics of hearing protection devices (HPDs) were measured using a modular acoustic head simulator. The effect in changes in the head configuration was assessed in a steady-state diffuse sound field. The use of artificial circumaural skin had a relatively small influence on the insertion loss of earmuffs (max. 6-7 dB at low frequencies). This contrasts to the very large effects found for the artificial intraaural skin on the insertion loss of earplugs (in excess of 40 dB at low frequencies for some devices). Results were also compared with real-ear attenuation at threshold (REAT) data (ANSI S3.19-1974). In general, there is good agreement between the two methods, especially for earmuffs. Design improvements are proposed for earplugs. The result of an exploratory study aimed at measuring the complex (amplitude and phase) insertion loss of HPDs using an impulse noise source are also reported.     

基于平面声全息的全空间场变换:Ⅱ.水下大面积平面发射声基阵的近场声全息实验

研制了一套多通道水声声全息测量系统,解决了多通道系统的校准及弱散射水听器接收线阵的设计等问题。在非消声水池内,利用该系统对水下大面积平面发射声基阵进行了近场声全息实验,给出了声基阵表面的声强分布、声基阵各阵元及全阵的辐射声功率、基阵远场空间指向性图和指向性参数等。实验结果证明脉冲法和分区扫描数据合成的测量方法是可行的,实验系统的设计与实施方法可用于更大规模的声全息系统。     

Non-equilibrium thermodynamics of interfacial systems: II. Boundary conditions for fluids with spin

The theory of non-equilibrium thermodynamics is applied to a system of two immiscible fluids whose molecules possess internal angular momentum (spin) which are separated by an interface. The conservation laws and the Gibbs relation are used to derive the entropy production at the interface. The resulting linear laws relating the fluxes and forces represent boundary conditions on the hydrodynamic equations for the bulk phases. A limiting case is considered and boundary conditions derived by previous authors are obtained.     

Holographic nanocomposites for recording polymer-nanoparticle periodic structures: II. Mechanism of formation of polymer-nanoparticle bulk periodic structure and effect of parameters of forming field on structure efficiency

We studied polymerizable nanocomposites for obtaining polymer-nanoparticle periodic structures by a holographic method. A general approach to choosing components of composites is developed that ensures a maximal contrast and high efficiency of structures for different types of nanoparticles. We found that the optimal monomeric component of a nanocomposite is a combination of single- and multifunctional monomers with substantially different reactivities. In this case, the low-reactivity monomer should posses a low viscosity, be a good solvent for nanoparticles, and have a low thermodynamic affinity to the polymer network formed upon the polymerization of the high-reactivity monomer. We developed a holographic composition based on known commercially produced monomers that ensures the formation of highly efficient periodic structures for nanoparticles of different types. We described the holographic properties of obtained nanocomposites, as well as parameters of bulk gratings recorded in them.     

A model for the enzyme activity in systems with large composition fluctuations. An application to the unusual kinetics of phospholipase A2

A non-equilibrium thermodynamics based model is proposed in order to describe the role of large concentration fluctuations of enzymes, reactants and products in modulating the macroscopic time evolution of chemical kinetics. The encounter probabilities between reactants and enzyme depend on their local concentration. Fluctuations modify the bimolecular encounter probability. Since, in turn, the amplitude of fluctuations depends itself on the instantaneous composition of the reacting mixture, the time-varying chemical composition acts as a positive feedback mechanism for the reactive fluid mixture near the critical temperature for phase separation. The model is applied to rationalize the unusual features of phospholipase kinetics, an enzyme which catalyzes the hydrolisis of membrane forming phospholipids, yielding products which are still soluble in the lipid matrix. A typical feature of the enzyme reaction is the long induction time prior to a ”burst” of activity. This effect is well reproduced by the theory, together with the dependence of the induction time on the exogeneous addition of products or other liposoluble substances, the effects of enzyme and substrate concentration, and the temperature dependence of the enzyme activation. All these properties emerge as a consequence of the coupling between enconter probability and time-varying bilayer heterogeneity. A good qualitative agreement between theoretical results and the available experimental results has been generally found. Received: 25 June 1996 / Revised: 17 April 1997 / Accepted: 26 November 1997     

A highly stable holographic medium based on CaF<Subscript>2</Subscript>:Na crystals with colloidal color centers: II. Mechanisms of hologram recording and erasure

The mechanisms of formation and erasure of holographic gratings recorded in calcium fluoride crystals with a low sodium content have been considered. It is found that in the case of recording by UV radiation, an effective holographic grating is formed due to the spatial modulation of the colloidal centers arising under the action of the radiation at temperatures about 200°C. The decisive role of photoinduced diffusion of anion vacancies in this modulation is demonstrated.     

Simulation of viscous flows with undulatory boundaries: Part II. Coupling with other solvers for two-fluid computations

We extend the direct numerical simulation (DNS) capability developed in [D. Yang, L. Shen, Simulation of viscous flows with undulatory boundaries: Part I. Basic solver, J. Comput. Phys. (submitted for publication) ] to the simulation of two-fluid interaction with deformable interface. Two approaches are used to couple the DNS of one fluid with the simulation of another fluid. In the first, the DNS is coupled with a potential-flow based wave solver that uses a high-order spectral (HOS) method. This coupled method is applied to simulate the interaction of turbulent wind with surface waves, including single wave train and broadband wavefield. Validation with previous theoretical and experimental studies shows the accuracy and efficiency of this coupled DNS-HOS method for capturing the essential physics of wind–wave interaction. In the second approach, both of the fluids are simulated by the DNS and are coupled by an efficient iterative scheme, in which the continuity of velocity and the balance of stress are enforced at the interface. The performance of this coupled DNS–DNS method is demonstrated and validated by several test cases including: interfacial wave between two viscous fluids, water surface wave over highly viscous mud flow with interfacial wave, and interaction of two-phase vortex pairs with a deformable interface. Comparison with existing theoretical and numerical results confirms the accuracy of this coupled DNS–DNS method. Finally, this method is applied to study the interaction of air and water turbulence. The nonlinear development of interfacial wave by the excitation of the air and water turbulence, and the wave effect on the instantaneous and statistical characteristics of the turbulence are elucidated.     

A continuum model of a solid with a free surface: II. Considerations of application of the model to particle-surface interaction theory

Considerations of application of a continuum model of a solid with a free surface to particle-surface interaction theory are presented. The work is based on the recent normal-mode analysis of such a model by the author. It is shown that the model has some important unrealistic properties which do not occur in discrete-lattice models, and it is concluded that considerable care is needed in interpreting some of the predictions of the model, particularly with regard to the importance of normal modes of the non-bulk type, for example surface modes.     

Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. II: Articulation index predictions

Articulation index (AI) theory was used to evaluate stop-consonant recognition of normal-hearing listeners and listeners with high-frequency hearing loss. From results reported in a companion article [Dubno et al., J. Acoust. Soc. Am. 85, 347-354 (1989)], a transfer function relating the AI to stop-consonant recognition was established, and a frequency importance function was determined for the nine stop-consonant-vowel syllables used as test stimuli. The calculations included the rms and peak levels of the speech that had been measured in 1/3 octave bands; the internal noise was estimated from the thresholds for each subject. The AI model was then used to predict performance for the hearing-impaired listeners. A majority of the AI predictions for the hearing-impaired subjects fell within +/- 2 standard deviations of the normal-hearing listeners' results. However, as observed in previous data, the AI tended to overestimate performance of the hearing-impaired listeners. The accuracy of the predictions decreased with the magnitude of high-frequency hearing loss. Thus, with the exception of performance for listeners with severe high-frequency hearing loss, the results suggest that poorer speech recognition among hearing-impaired listeners results from reduced audibility within critical spectral regions of the speech stimuli.     

Finite-aperture effects for Fourier transform systems with convergent illumination. Part II: 3-D system analysis

One of the most important optical signal processing operations is the optical Fourier transform (OFT). Of the arrangements for implementation of the OFT, perhaps the most flexible is that for the scaled optical Fourier transform (SOFT), as it allows control over the scale of the output Fourier transform distribution. By means of an analysis in cylindrical coordinates, we examine some of the practical limits introduced by the use of a thin lens of finite aperture in the implementation of the SOFT. Using simple rules of thumb that are based on an examination of the phase and magnitude deviations from the ideal (infinite-lens) diameter case, we define a volume inside the geometric shadow, which we refer to as a sub-geometric shadow. We then show that inside this sub-geometric shadow errors introduced by diffraction can be quantified.     

Group structure analysis for classical lattice systems with constraints: II. Zeroes of the partition function and unicity of states

The Asano-Ruelle method is used to discuss the zeroes of the partition function of arbitrary lattice systems with constraints. The group structure associated with these systems yields necessary and sufficient conditions to build up the partition function by Asano contractions. For a large class of systems with constraints, uniqueness of the symmetric equilibrium state, as well as analyticity properties of the free energy and the correlation functions, is established at sufficiently low temperature. Explicit analyticity domains are obtained for several models with constraints. Some properties of power sets are derived.     

Bethe-ansatz solution of a model for a mixed valent impurity with two magnetic configurations: II. Numerical solution of the thermodynamic equations

A mixed valence impurity with two magnetic configurations of total angular momentumJ ₂ andJ ₁=J ₂+1/2, respectively, coupled by conduction electrons with total angular momentum 1/2 via a hybridization matrix element is considered. The thermodynamic Bethe-ansatz equations derived previously are solved numerically for various values ofJ ₂. Thef-level occupation, the entropy, the magnetic susceptibility and the specific heat are obtained as a function of temperature for variousf-level positions. The magnetic field dependence is also discussed in the limit of integer valence (exchange model).Supported by the CONICET, Argentina     

Possible ionic systems for the development of a pulsed laser on the basis of ion-ion recombination: II. Recombination with oxygen, sulfur, selenium, and tellurium negative ions

Pairs of positive and negative ions, which can be used for the creation of a pulsed ion-ion recombination laser, are considered. Pairs for recombination with negative ions in which the electron affinity is lower than in halogens are analyzed. Such a choice ensures a significant increase in the number of working atoms and allows the consideration of new ways to obtain the inversion in the process of ion-ion recombination.