An Experimental Investigation into the Acoustic Characteristics of Fluid-filled Porous Structures—A Simplified Model of the Human Skull Cancellous Structure

In nature, shape and structure evolve from the struggle for better performance. Often, biological structures combine multiple beneficial properties, making research into mimicking them very complex. Presented here is a summary of observations from a series of experiments performed on a material that closely resembles the human skull bone’s cancellous structure under acoustic loads. Transmission loss through flat and curved open-cell polyurethane foam samples is observed using air and water as the two interstitial fluids. Reduction in strength and stiffness caused by porosity can be recovered partially by filling the interstitial pores with a fluid. The test findings demonstrate the influence of the interstitial fluid on the mechanical characteristics of a porous structure in a quantitative manner. It is also demonstrated that the transmission loss does not depend only on the mass per unit area of the structure as predicted by acoustic mass law. Current tests also demonstrate that the transmission loss is more sensitive to the interstitial fluid than the shape and support conditions of the structures. Test observations thus support the concepts of “moisture-sensitivity of biological design” and the “law of hierarchy in natural design”.     

Baseline studies of radon/thoron concentration levels in and around the Lambapur and Peddagattu areas in Nalgonda district, Andhra Pradesh, India

Studies conducted by Atomic Minerals Directorate of Exploration and Research (AMD) of Hyderabad, India had established the presence of higher concentrations of uranium in Lambapur and Peddagattu areas of Nalgonda district, AP, India and it was estimated that it could be a viable source for commercial extraction. The envisaged extraction process involves dispersion of radioactive particulate matter into atmosphere. Environmental radioactive studies in and around proposed mining areas at this point of time will be extremely useful for establishing base line data before a large scale uranium extraction process comes into existence. To this end, Solid State Nuclear Track Detectors were installed to evaluate indoor radon and thoron concentration levels in the dwellings of the area. The geometric means of radon and thoron concentration levels were found to be (7.1±0.2)×10¹ and (6.7±0.3)×10¹ Bq/m³, respectively. Simultaneously, natural background radiation measurements were also made and these levels are found to vary from 770 to 3995 μGy/y in the spatial distribution.     

Fluctuation study of pionisation in ultrarelativistic nucleus-nucleus interaction

The scaled factorial moments and the multifractal moments have been investigated in differentη-intervals to study the dynamical fluctuation of pions produced in 200 AGeV³²S-Ag/Br interaction. In order to investigate the detail characteristics of intermittency behaviour, theF-moments are extracted up to the eighth order of moments in differentM-intervals. The analysis indicates a non-thermal phase transition and different regime of particle production during the hadronisation process.     

High-energy gamma-rays accompanying the spontaneous fission of 252Cf

The γ-ray spectrum of ²⁵²Cf(sf) was measured in the Darmstadt-Heidelberg Crystal Ball spectrometer, with a double ionization chamber mounted inside to detect the fission fragments. The measurement was aimed at a better understanding of an unusual component found in the high-energy region between 3 and 8 MeV, with fragment mass splits near symmetry. This component was proved to be predominantly emitted by the heavier fragment, to reach its highest intensity at a fragment mass split of 132:120, and to have an almost isotropic angular distribution. Calculations with the statistical code CASCADE could reproduce the main features.     

Penetration of a magnetic field into a thin unclosed ellipsoidal sheath in the presence of a thick-walled conducting spherical sheath

The solution of the problem of magnetic field penetration into a conducting unclosed ellipsoidal sheath in the presence of a conducting thick-walled spherical sheath is reduced to the solution of the integral Fredholm equation of the second kind. The effect of the apex angle of the unclosed ellipsoidal sheath, geometric parameters of the screens, and electrophysical properties of the spherical sheath material on the field attenuation coefficient inside the ellipsoidal sheath is studied numerically.     

Nonrelativistic polarization operator of a photon in an external nonabelian field of magnetic type

The photon polarization operator is computed in the presence of a constant external chromomagnetic field in nonrelativistic approximation. The found branching points of the polarization operator are compared with the minimal energy necessary for creation of scalar colored particles. The absence of confinement for such quarks in the field under consideration is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 23–26, October, 1990.     

Exciton-related optical nonlinearities in semiconductors and semiconductor microcrystallites

We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1m slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm² range.     

The electrical resistivity of the reentrant spin glass alloys (Fe0.65Ni0.35)1−x Mn x in the temperature range 4 to 280 K

The specific electrical resistivityp(T) was measured for the reentrant spin glass system (Fe_0.65Ni_0.35)_1–x Mn _x (0x0.102) in the temperature range 4 KT280 K. We used our own phenomenological ansatz to explain the results obtained in order to provide the fitted parameters with physical meaning. The cause of the observed minimum in the measured curves can be given by a model of local magnetism.     

Surface diffusion of potassium on theW (112) plane

Dependent on temperature and coverage, numerous spectral density functionsW(f) of the field-emission flicker noise of potassium adsorbed on the tungsten (112) plane were determined. The analysis in terms of the Timm and van der Ziel model gives surface diffusion energies between 0.55 and 0.83 eV for (average) coverages from 0.3 to 1.0 and diffusion coefficients between 2×10^–10 and 3×10^–9 cm²/s at 400 K. The results are compared with those obtained previously for the tungsten (111) region. Some conclusions as to the mechanism of diffusion and the manifestation of phase transitions between commensurate and incommensurate adlayer structures are discussed.On leave from Wrocaw University