Ultrasonic scattering properties of three random media with implications for tissue characterization

Random media with different structural properties were used to simulate some of the differences in liver morphology that may occur with disease. First, a reference medium consisting of glass spheres in agar was studied to verify the accuracy and precision of the data obtained with our equipment and processing procedures. Then, studies were conducted on a pair of media comprised of graphite particles in gelatin, one of the pair with twice as many particles as the other. Finally, studies were carried out on a set of media composed of Sephadex particles in water. Three samples were employed, each with a different size of Sephadex. The average differential scattering cross section per unit volume sigma sd (v) of each media was obtained as a function of scattering angle v and frequency. The measured sigma sd were compared with predictions based on models of scattering from the media. The agreement between the measured and predicted sigma sd of the glass sphere medium was excellent. The graphite medium with twice the number of particles as the other was observed to scatter twice as much power as the other. The shape of the angular scattering pattern measured from each size of Sephadex followed the prediction reasonably well. The largest size exhibited marked variations in the shape of sigma sd as a function of frequency, while the absolute magnitude of sigma sd of the smallest size grade was extremely sensitive to frequency. Our results suggest that the dependence of sigma sd (v) on scatterer number density and size, both in absolute magnitude and shape, can provide reliable information which may be useful in the diagnosis of some diseases.     

The stability of FCC crystal Ni under uniaxial loading

Taking Ni as an example, the structural stability and theoretical strength of FCC crystals under uniaxial loading were investigated by combining the modified analytical embedded atom method (MAEAM) with modified Born stability criteria. The results revealed that, under sufficient compression, there existed a stress-free instable BCC phase and then a stress-free metastable BCT phase corresponding to local maximum and minimum internal energy, respectively. The stable region ranged for the theoretical strength from −5.143 eV/nm³ with a corresponding strain of −9.94% under compression to 10.396 eV/nm³ with a corresponding strain of 9.66% under tension.     

Ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with dipolar interactions

The ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with both short range exchange and long range dipolar interactions are calculated near the critical point using renormalization group theory. The dispersion and temperature dependences found differ logarithmically from classical theory and suggest new experiments. In the pure system a recent phenomenological calculation of the ultrasonic attenuation in the low frequency limit is confirmed.Project of the Sonderforschungsbereich Frankfurt/Darmstadt financed by special funds of the Deutsche Forschungsgemeinschaft     

Order parameters in heterogeneuos media under loading

Plastic deformation is treated as a nonequilibrium structural transformation characterized by order parameters. The latter determine the plastic part of the strain tensor. Nonlinear rate equations of the reaction-diffusion type with temperature and stress dependent coefficients are derived for the order parameters. The coefficients are calculated for the case where plastic deformation is described by a single order parameter. Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–7, June, 1999.     

Electronic properties of Z-shaped graphene nanoribbon under uniaxial strain

Based on tight-binding approximation and a generalized Green's function method, the effect of uniaxial strain on the electron transport properties of Z-shaped graphene nanoribbon (GNR) composed of an armchair GNR sandwiched between two semi-infinite metallic armchair GNR electrodes is numerically investigated. Our results show that the increase of uniaxial strain enhances the band gap and leads to a metal-to-semiconductor transition for Z-shaped GNR. Furthermore, in the Landauer–Büttiker formalism, the current–voltage characteristics, the noise power resulting from the current fluctuations and Fano factor of strained Z-shaped GNR are explored. It is found the threshold voltage for the current and the noise power increased so that with reinforcement of the uniaxial strain parameter strength, the noise power goes from the Poisson limit to sub-Poisson region at higher bias voltages.     

Transport properties of random media composed of core-shell spheres

With the energy-density coherent potential approximation method, a series of calculations concerning the contribution from the morphology and dispersion of random media composed of core-shell spheres on the transport properties of random media are conducted in terms of the scattering-cross-section efficiency factor, mean free path, velocity of electromagnetic energy, and diffusion coefficient. It is found that the core layer introduces more complicated resonant modes which lead to diverse possibilities to sharply decrease the transport of light within random media.     

Structural stability and theoretical strength of the single crystal Ag under uniaxial loading

The structural stability and theoretical strength of FCC crystal Ag under uniaxial loading have been investigated by combining MAEAM with Wang modified Born stability criteria. The results reveal that, under sufficient compression, there exists a stress-free BCC phase, which is unstable and slips spontaneously to a stress-free mBCT phase by consuming internal energy. The stable region ranges from −2.076 to 4.390 GPa in the theoretical strength or from −7.972% to 8.721% in the strain correspondingly. The calculated structural energy difference between the BCC and FCC phase is in good agreement with the experimental value.     

Reflectometry of absorbing uniaxial multilayer media

A novel reflection technique for index determination of isotropic or uniaxial absorbing multilayer on a lower refractive index substrate is presented. Above the angle of total reflection at the layer-substrate interface characteristic minima occur in the reflectivity which are suitable for high accuracy fitting of the layer parameters. The 4 × 4 transfer matrices of uniaxial multilayer are given for computer evaluation. Refraction index determination of a poled polymeric layer on an indium-tin-oxide coated glass is demonstrated. Advantages of the new method are outlined.     

The experimental research on response characteristics of coal samples under the uniaxial loading process

In order to study the response characteristics of infrasound in coal samples under the uniaxial loading process, coal samples were collected from GengCun mine. Coal rock stress loading device, acoustic emission tested system and infrasound tested system were used to test the infrasonic signal and acoustic emission signal under uniaxial loading process. The tested results were analyzed by the methods of wavelet filter, threshold denoise, time–frequency analysis and so on. The results showed that in the loading process, the change of the infrasonic wave displayed the characteristics of stage, and it could be divided into three stages: initial stage with a certain amount infrasound events, middle stage with few infrasound events, and late stage gradual decrease. It had a good consistency with changing characteristics of acoustic emission. At the same time, the frequency of infrasound was very low. It can propagate over a very long distance with little attenuation, and the characteristics of the infrasound before the destruction of the coal samples were obvious. A method of using the infrasound characteristics to predict the destruction of coal samples was proposed. This is of great significance to guide the prediction of geological hazards in coal mines.     

Magnets with random uniaxial anisotropy: Thermodynamic properties in the large-N limit

We show that the random-axis model lends itself to a systematic large-N calculation. The model shows different behavior below and above four dimensions. The equation of state is derived and discussed in terms of “Arrott” plots. Higher-order terms in the disorder, when summed, have a crucial effect on the susceptibility which is found to be finite below four dimensions (and above four dimensions for strong disorder). A spin-glass to paramagnetic phase transition is characterized by the vanishing of the Edwards-Anderson order parameter, which differs from zero in the spin-glass phase. A cusp in the specific-heat and susceptibility is seen across the transition. The cross-over exponent and other exponents of interest are calculated. Above four dimensions a third phase appears for weak disorder and low-temperature ferromagnetic in nature. The transverse and longitudinal susceptibilities are discussed. Whereas the ferromagnetic transition is characterized by mean-field exponents, the ferromagnetic to spin-glass exponents are equal to their counterparts in the non-random system in d ? 2 dimensions. This is shown to originate from an effective random field proportional to the EA order parameter. The flow equations in the large-N limit are also discussed.     

Magnets with random uniaxial anisotropy: Large-N effective potential and infrared properties

We study the magnetic properties of systems with random uniaxial anisotropy using a large-N effective potential approach for d = 4, 3.It is found that the random interactions induce a strong infrared behavior that prevents the existence of a ferromagnetic phase and massless transverse modes.The transverse susceptibility is finite for all values of the temperature and at d = 4 it has an esential singularity in the couplings. We argue that this is indicative of a mechanism of dynamical mass generation due to the infrared instabilities of the theory.For both d = 4, 3 there is a spin-glass low-temperature phase and a paramagnetic high-temperature phase, the susceptibility having a cusp across the transition.We prove that these phases are stable and that the transverse and longitudinal susceptibilities are equal.     

Light transmission properties in inhomogeneously‐disordered random media

Spatially inhomogeneous disorder exists widely in optical systems. We present a numerical study on the light transport properties and analysis of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist. The distribution of the total transmission is broadened and one most transmitted incident channel emerges.     

Background thermal noise correction methodology for average infrared radiation temperature of coal under uniaxial loading

This paper proposes a new background thermal noise correction (BTNC) Methodology for better utilization of average infrared radiation temperature (AIRT) as a precursor for rock fracturing and failure under uniaxial loading. The key innovative concept in the proposed Methodology is the introduction of control samples in the thermal infrared experimental setup. A strong linear correlation was observed between the background thermal noise (BTN) of the test samples and that of control samples, which was used to develop the AIRT-BTNC model. By utilizing the AIRT-BTNC model, the signal-to-noise ratio (SNR) of AIRT can be improved by two orders of magnitude from a mean value of 0.40–70.69. The variation in the AIRT after BTNC on the surface of the uniaxial loading coal samples can be categorized into two types instead of the three reported by previous researchers. The above achievements will be useful in monitoring and forecasting the natural and engineering hazards related to rock/coal structural failures during mining activities.     

Direct determination of diffusion properties of random media from speckle contrast

We present a simple scheme to determine the diffusion properties of a thin slab of strongly scattering material by measuring the speckle contrast resulting from the transmission of a femtosecond pulse with controlled bandwidth. In contrast with previous methods, our scheme does not require time measurements nor interferometry. It is well adapted to the characterization of samples for pulse shaping, nonlinear excitation through scattering media, and biological imaging.     

Diffraction of three-dimensional beams in uniaxial media

Within here we make an analysis of two and three-dimensional beams synthesized by extraordinary waves that propagate in uniaxial media. A relation between the geometric place of the first interference maxima and the energy flow direction is established. In addition, we determine that three-dimensional extraordinary symmetrical beams can be obtained from two two-dimensional ones that are not to be necessarily orthogonal.     

Radiation properties of a uniaxial chiral quadratic inhomogeneous slab under oblique incidence

In this paper, the focussing of the transmitted electromagnetic field through a quadric inhomogeneous slab of lossless uniaxial chiral medium is derived using transmission coefficient under oblique incidence. The inhomogeneity in the uniaxial chiral slab has been incorporated through permittivity parameter. Asymptotic ray theory provides valid field everywhere except at focal point where it gives infinite value. Singularity of the field at focal point is addressed using Maslov's method. The derived analytical field expressions at caustic or focal point of uniaxial quadratic inhomogeneous slab have been solved numerically using MATHEMATICA. The effects of chirality parameter, axial permittivity, transvers permittivity, angle of incidence on the refracted field are discussed and the effects of Brewster angle on the focussed field are also discussed. The results obtained using Maslov's method are compared with Huygens–Kirchhoff's integral which are in good agreement.     

Temporal properties of random lasers under ultrashort pulse excitation

Temporal properties of random lasing under ultrashort pulse excitation are investigated in a two-dimensional disordered medium. The pumping light is described individually and coupled into the rate equations. The Maxwell equations and rate equations are numerically solved by using the finite-difference time domain method. The time evolution of the emission pulse is studied with the variation of the surface-filling fraction, refractive index,and scatterer radius. Results show that the behavior of random lasing depends strongly on the sample parameters. Our work enriches the knowledge about random lasers in the ultrashort pulse pumping regime and offers some guidance for relevant experiments.