다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

CuO nanostructures: Synthesis, characterization, growth mechanisms, fundamental properties, and applications

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Nanofluids—a simple product of the emerging world of nanotechnology—are suspensions of nanoparticles (nominally 1–100 nm in size) in conventional base fluids such as water, oils, or glycols. Nanofluids have seen enormous growth in popularity since they were proposed by Choi in 1995. In the year 2011 alone, there were nearly 700 research articles where the term nanofluid was used in the title, showing rapid growth from 2006 (175) and 2001 (10). The first decade of nanofluid research was primarily focused on measuring and modeling fundamental thermophysical properties of nanofluids (thermal conductivity, density, viscosity, heat transfer coefficient). Recent research, however, explores the performance of nanofluids in a wide variety of other applications. Analyzing the available body of research to date, this article presents recent trends and future possibilities for nanofluids research and suggests which applications will see the most significant improvement from employing nanofluids.

Small particles, big impacts: A review of the diverse applications of nanofluids

Introduction to Nanotechnology

Behaviour of ultrasonic attenuation in intermetallics

The ultrasonic attenuation in intermetallic praseodymium monochalcogenides are evaluated in the temperature interval 100–500 K along the crystallographic directions 〈100〉, 〈110〉, and 〈111〉 for longitudinal and shear waves. A comparison has been made with lanthanum monochalcogenides and other similar materials. Ultrasonic attenuation at different temperatures is mainly affected by the lattice thermal conductivity values of the materials at these temperatures. Thermoelastic loss is very small in comparison to the attenuation due to phonon-phonon interaction mechanism at higher temperatures.

Effect of thermal conductivity on ultrasonic attenuation in praseodymium monochalcogenides

The ultrasonic attenuation is evaluated at 300 K along [100], [110], and [111] directions for the characterization of bcc metal Ta The size of the metal is considered in nanorange Ultrasonic velocity, Gruneisen parameter and acoustic coupling constant that depend on second and third order elastic constants are calculated for determination of ultrasonic attenuation coefficient Second and third order elastic constants of the bcc metal Ta at nanoscale at 300 K are also calculated starting with only two basic parameters For the information about defects at nanoscale, the dislocation drag coefficients are calculated for the metal at different size along [100] orientation The ultrasonic attenuation increases with the size of material as the size variation of the thermal conductivity and the thermal relaxation time There is significant increase in the attenuation up to 150 nm

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Size Dependent Acoustical Properties of bcc Metal

Ultrasonic attenuation in dielectric crystals KCl, KBr and KI have been calculated in a wide temperature range. Starting from nearest neighbour distance and hardness parameter of the substance and using Born-Mayer type of potential, the attenuation due to phonon-viscosity loss is evaluated. The final values are compared with experimental results available in literature. A successful effort is made to conclude satisfactorily that ultrasonic attenuation is one of the fundamental property of the substance.

Raja Ram Yadav

Papers

Behaviour of ultrasonic attenuation in intermetallics

Effect of thermal conductivity on ultrasonic attenuation in praseodymium monochalcogenides

Size Dependent Acoustical Properties of bcc Metal

Ultrasonic Attenuation in Dielectric Crystals

Surfactant free synthesis of metal oxide (Co and Ni) nanoparticles and applications to heat propagation in nanofluids