A fractal model for heat transfer of nanofluids by convection in a pool

Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.     

On Debye temperature anomaly observed in Ge-Se-Ag glasses

Anomalous values of Debye temperature have been obtained from recoil free factor measurements Ge-Se-Ag glasses recently [B. Arcondo, M.A. Urena, A. Piarristeguy, A. Pradel, M. Fontana, Physica B 389 (2007) 77]. In the present paper we show that this anomaly may arise due to the presence of anharmonic potential at the high spin ferrous site. We use q Lamb Mossbauer factor and anharmonic Lamb Mossbauer factor to study this anharmonicity.     

A Simple Systematical Law of E2＋ Values for Heavy Nuclei in the NpNn Scheme and the Evolution of the Z=64 Shell Gap

A systematics of excitation energy of the first 2^＋ state E2＋ in even-even heavy nuclei （A ≥ 120） is studied in the NpNn scheme. It is found that a simple exponential function describes the dependence of E2＋ values on NpNn values very well. In addition, the Z = 64 shell gap is reexamined by investigating the systematics of the 52 ≤ Z ≤66 region. It is found that the Z = 64 shell gap is largest at N = 82 and becomes smMler with either increasing or decreasing of neutron numbers. The effects of this shell gap become negligible for counting the valence proton numbers when N ≥ 92 or N ≤ 72.     

Vibro-acoustography imaging of permanent prostate brachytherapy seeds in an excised human prostate - Preliminary results and technical feasibility

Objective:

The objective in this work is to investigate the feasibility of using a new imaging tool called vibro-acoustography (VA) as a means of permanent prostate brachytherapy (PPB) seed localization to facilitate post-implant dosimetry (PID).

Methods and materials:

Twelve OncoSeed (standard) and eleven EchoSeed (echogenic) dummy seeds were implanted in a human cadaver prostate. Seventeen seeds remained after radical retropubic prostatectomy. VA imaging was conducted on the prostate that was cast in a gel phantom and placed in a tank of degassed water. 2-D magnitude and phase VA image slices were obtained at different depths within the prostate showing location and orientation of the seeds.

Results:

VA demonstrates that twelve of seventeen (71%) seeds implanted were visible in the VA image, and the remainder were obscured by intra-prostatic calcifications. Moreover, it is shown here that VA is capable of imaging and locating PPB seeds within the prostate independent of seed orientation, and the resulting images are speckle free.

Conclusion:

The results presented in this research show that VA allows seed detection within a human prostate regardless of their orientation, as well as imaging intra-prostatic calcifications.     

Sensitivity of Josephson junctions to high-pass filtered noise of black-body radiation

The influence of the nonwhite noise on the Josephson junction is considered by using the averaging principle. It is shown that in contrast to the case of white noise there is a non-zero critical current, but it has high sensitivity to the noise power. The dependence of noise power on the critical current can be used for the detection of cold black-body radiation.     

The vibration and rotation of piezoelectric particles in high frequency electric fields observed by a thermoacoustic method

We have observed, by a thermoacoustic method, the acoustic resonance vibration of small (diameter 115 m) piezoelectric particles in high frequency (15 MHz) electric fields. The frequency dependence of the thermoacoustic signal gives direct information about the size distribution of the particles.In very strong rf electric fields we also observed a rotation of the vibrating particles by large angles — as originally suggested by Melcher and Shiren [3] — orienting the initially random rf dipoles parallel to the rf electric fields.The observed strong forces acting on vibrating piezoelectric particles in rf fields can probably be used as a new method of selectively extracting particles of a given size from a broad distribution of very small particles.     

The effective thermal conductivity of porous media based on statistical self-similarity

A fractal model is presented based on the thermal-electrical analogy technique and statistical self-similarity of fractal saturated porous media. A dimensionless effective thermal conductivity of saturated fractal porous media is studied by the relationship between the dimensionless effective thermal conductivity and the geometrical parameters of porous media with no empirical constant. Through this study, it is shown that the dimensionless effective thermal conductivity decreases with the increase of porosity (?) and pore area fractal dimension (Df) when ks/kg>1. The opposite trends is observed when ks/kg<1. In addition, the dimensionless effective thermal conductivity decreases with increasing tortuous fractal dimension (Dt). The model predictions are compared with existing experimental data and the results show that they are in good agreement with existing experimental data.     

Water Surface Wave in a Trough with Periodical Topographical Bottom under Vertical Vibration

We investigate the water surface waves in a vertically vibrated long rectangular trough with several identical Plexiglas rectangles lined periodically on the bottom. The band structure is computed theoretically by the method of transfer matrix. Some interesting phenomena, such as the localized wave, especially the solitary-like wave inside the band gap . are observed in the experiments.     

The influence of the micro-topology on the phononic band gaps in 2D porous phononic crystals

The phononic band structures of two-dimensional metal porous phononic crystals consisting of different lattices (the lattice structures transformed from square to triangle), and pores of various shapes (circle, square, and triangle) and sizes are studied numerically by using Finite Difference Time Domain (FDTD) scheme. It is found that for x-y mode waves, the absolute phononic band gaps (PBGs) rely more on the pore shapes. For triangular pores, the PBG is opening in the whole process of the lattice transformation, and for circular ones, the PBG is closed after a certain lattice structure. No PBG forms in the crystals with square pores. The PBG can be varied by adjusting the size of the pores. But a critical porosity exists for the opening of the PBG.     

Diffusion and correlation in a coherent representation

Using a Fock-space formalism for the Master equation and introducing the density operator we present an unified method to derive kinetic equations for hopping processes with and without exclusion on a lattice. The corresponding Liouvillians are written in terms of Fermi or Bose operators, respectively. Although the Liouvillians are different the averaged particle numbers obey the same diffusion equation. Differences appear in the correlation functions only. The Master equation can be transformed into a differential equation in a coherent state representation. Using the algebraic properties of Grassmann numbers we are able to find the exact statonary solution for diffusion with exclusion. The conductivity can be derived in the bosonic and the fermionic case. The results are in accordance with those obtained with different other methods.     

Ultrasonic resonator with electrical discharge cell for ozone generation

The effect of ultrasound waves in an ultrasonic resonator cell on ozone generation by a hollow needle to plate electrical discharge enhanced by the airflow through the needle is experimentally investigated. It was found that the application of ultrasound waves increases ozone generation for discharge when the needle is negatively biased, and has no effect on ozone generation for the discharge when the needle is biased positively. We try to explain the influence of ultrasound on the discharge mechanisms.     

The photodetector of Ge nanocrystals/Si for 1.55 μm operation deposited by pulsed laser deposition

The photodetector properties of a Ge nanocrystals detector fabricated by pulsed laser deposition and in situ rapid thermal annealing treatment at 600 °C have been studied. Strong optical absorption and photocurrent response of the detector are measured in the wavelength range 1.3-1.55 μm. The detector possesses a low dark current of 61.4 nA and a photocurrent responsivity of 56 mA/W at the reverse bias 5 V. The external quantum efficiency at 1.55 μm is estimated to be 15%. The stop wavelength of absorption spectra extends to 1.65 μm. It indicates that these kind of Ge nanocrystals devices can be used as a 1.3-1.55 μm near infrared detector.     

Dielectric relaxation measurements on nonlinear side-chain polymers

Dynamic dielectric relaxation measurements in the frequency range from 0.001 Hz to 5 kHz have been performed on an amorphous nonlinear optical side-chain polymer, containing the active molecule 4-dimethylamino-4-nitrostilbene as pendant group. The results yielded the relaxation times of the group in the temperature region from 20° below to 40° above the glass-transition temperature of the polymer. The temperature dependence could be described well by the Williams-Landel-Ferry (WLF) equation. It is shown that the relaxation times have a distribution, which could be fit to the form of Cole and Cole with a parameter =0.55. Consequently a substantial part of the active molecules will not be aligned when the polymer is subjected to a poling procedure.     

Electronic structure of dimerized spinel ZnV2O4

Electronic structure calculations were performed for ZnV₂O₄, a material close to a metal-insulator transition. Structural optimization leads to the formation of V-V dimers along the off-plane chains. A strong spin-lattice coupling is expected close to the transition to itinerancy. No orbital ordering is observed in such a structure, and the experimentally found magnetic structure is naturally explained.     

Determination of90Sr in environmental samples with resonance ionization spectroscopy in collinear geometry

A new, fast technique for trace analysis of the radioactive isotopes⁸⁹Sr and⁹⁰Sr in environmental samples has been developed. Conventional mass separation is combined with resonance ionization spectroscopy in collinear geometry, which provides high selectivity and sensitivity. In addition, a chemical separation procedure for sample preparation has been developed. The described technique was used to determine the⁹⁰Sr content in 870 m³ air samples collected near Munich during and shortly after the Chernobyl reactor accident in April 1986. The content of⁹⁰Sr was measured to be 1.4 mBq per m³, corresponding to 1.6 × 10⁹ atoms of⁹⁰Sr per sample. This value is in good agreement with the results of radiochemical measurements.This publication comprises part of the Dissertations of J. Stenner and K. Zimmer     

On the low-temperature thermal properties and low-energy Fermi excitations in CeNiSn

The thermal expansion of a single crystal of the intermetallic compound CeNiSn has been measured at low temperatures 0.3 K<T<12 K and in a magnetic field up to 8 T. A large anisotropy of the linear expansion is observed which is strongly influenced by the magnetic field. These data are interpreted within the theory explaining the origin of the quasigap in the heavy fermion spectrum of CeNiSn by the interplay between the heavy fermions and low-energy excitations in non-cubic Kondo lattices.     

On the momentum of mechanical plane waves

Momentum of a mechanical, harmonic plane wave is derived and explained as a relativistic effect arising from the presence of tension in moving elements of the medium. Neglect of the relativistic corrections leads to the paradox, which is formulated and explained. Explicit results for momentum density resulting from tension for transverse and longitudinal waves are discussed. The idea of experiments for quantitative measurements of the momentum density is presented.     

Series Solution for Unsteady Boundary-Layer Flows Due to Impulsively Stretching Plate

The third-order nonlinear partial differential equation modelling the unsteady boundary-layer flows caused by an impulsively stretching fiat plate is solved by using the Adomian decomposition method （ADM）. The ADM yields analytic solution in the form of a rapidly convergent infinite series with easily computable terms. The series solution using the ADM for the unsteady flows is presented for the first time.     

Interplay of exciton or electron transfer and relaxation

A trick permitting to apply generalized master equation (GME) theory together with canonical transformation but quantities of interest (single-particle density matrix) remaining untransformed is applied to the time-convolutionless GME approach for carriers interacting with phonons by a local linear coupling. In contrast with time convolution theories (Mori, time-convolution GME), it is found that the second-order perturbational approach in the above coupling is already able to yield a loss of coherence of carrier propagation with increasing time as well as a proper asymptotic state at any temperature. Moreover, dependence on the degree of the initial polaron cloud formation is shown, as expected but again in contrast with the above theories, to disappear explicitly after a short period of the polaron cloud reconstruction from equations determining the time development of the single-particle density matrix. A prediction on the Weber effect and charge-carrier generation process in narrow band materials is given. Correspondence with a recent generalization of the Haken-Strobl-Reineker model is found.     

A Brillouin study of the temperature-dependence of the acoustic modes across the insulator-metal transitions in V2O3 and Cr-doped V2O3

Brillouin scattering studies have been carried out on high-quality single crystals of undoped and 0.9% Cr-doped V₂O₃. The observed modes in both the samples at ∼12 and ∼60 GHz are associated with the surface Rayleigh wave (SRW) and bulk acoustic wave (BAW), respectively. In the undoped sample, the mode frequencies of the SRW and BAW modes decrease as the temperature is lowered from room temperature to the insulator-metal transition temperature (T_IM=T_N=∼130 K). Below the transition, the modes show hardening. In the doped sample, the SRW mode shows a similar temperature-dependence as the undoped one, but the BAW mode shows hardening from room temperature down to the lowest temperature (50 K). This is the first measurement of the sound velocity below T_IM in the V₂O₃ system. The softening of the SRW frequency from 330 K to T_IM can be qualitatively understood on the basis of the temperature-dependence of C₄₄, which, in turn, is related to the orbital fluctuations in the paramagnetic metallic phase. The hardening of the mode frequencies below T_IM suggests that C₄₄ must increase in the antiferromagnetic insulating phase, possibly due to the orbital ordering.