Mineral Bridges Versus the Mechanical Properties of Nacre

通过对天然珍珠母材料有机基质界面的微结构及其力学性能的研究,简要地分析了珍珠母有机界面的弹性模量以及裂纹阻力与其微结构的联系,由此说明在珍珠母所表现出来的优异力学性能中微结构所起的重要作用。

Mineral Bridges of Nacre and Its Effects

Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the micro architecture that is traditionally described as a "brick and mortar" arrangement. In this paper, a new microstructure, referred to as mineral bridge in the biomineralization, is directly observed in the organic matrix layers (mortar) of nacre. This is an indication that the organic matrix layer of nacre should be treated as a three-dimensional interface and the micro architecture of nacre ought to be considered as a "brick-bridge-mortar" structure rather than the traditional one. Experiments and analyses show that the mineral bridges not only improve the mechanical properties of the organic matrix layers but also play an important role in the pattern of the crack extension in nacre.

Thermocapillary Flows In Liquid Bridges Of Molten Tin With Small Aspect Ratios

Numerical simulations were conducted to study thermocapillary flows in short half-zone liquid bridges of molten tin with Prandtl number Pr = 0.009, under ramped temperature difference. The spatio-temporal structures in the thermocapillary flows in short half-zone liquid bridges with aspect ratios As = 0.6, 0.8, and 1.0 were investigated. The first critical Marangoni numbers were compared with those predicted by linear stability analyses (LSA). The second critical Marangoni numbers for As = 0.6 and 0.8 were found to be larger than that for As = 1.0. The time evolutions of the thermocapillary flows exhibited unusual features such as a change in the azimuthal wave number during the three-dimensional stationary (non-oscillating) flow regime, a change in the oscillation mode during the three-dimensional oscillatory flow regime, and the decreasing and then increasing of amplitudes in a single oscillation mode. The effects of the ramping rate of the temperature difference on the flow modes and critical conditions were studied as well. In this paper, the experimental observability of the critical conditions was also discussed. (C) 2008 Elsevier Inc. All rights reserved.

A Linear Stability Analysis Of Large-Prandtl-Number Thermocapillary Liquid Bridges

A linear stability analysis is applied to determine the onset of oscillatory thermocapillary convection in cylindrical liquid bridges of large Prandtl numbers (4 <= Pr <= 50). We focus on the relationships between the critical Reynolds number Re-c, the azimuthal wave number m, the aspect ratio F and the Prandtl number Pr. A detailed Re-c-Pr stability diagram is given for liquid bridges with various Gamma. In the region of Pr > 1, which has been less studied previously and where Re, has been usually believed to decrease with the increase of Pr, we found Re-c exhibits an early increase for liquid bridges with Gamma around one. From the computed surface temperature gradient, it is concluded that the boundary layers developed at both solid ends of liquid bridges strengthen the stability of basic axisymmetric thermocapillary convection at large Prandtl number, and that the stability property of the basic flow is determined by the "effective" part of liquid bridge. (c) 2008 Published by Elsevier Ltd on behalf of COSPAR.

Hydrothermal Instability Of Thermocapillary Convection In Large-Prandtl-Number Liquid Bridges Under Microgravity

Linear stability analysis was performed to study the mechanism of transition of thermocapillary convection in liquid bridges with liquid volume ratios ranging from 0.4 to 1.2, aspect ratio of 0.75 and Prandtl number of 100. 2-D governing equations were solved to obtain the steady axi-symmetric basic flow and temperature distributions. 3-D perturbation equations were discretized at the collocation grid points using the Chebyshev-collocation method. Eigenvalues and eigenfunctions were obtained by using the Q-R. method. The predicted critical Marangoni numbers and critical frequencies were compared with data from space experiments. The disturbance of the temperature distribution on the free surface causes the onset of oscillatory convection. It is shown that the origin of instability is related to the hydrothermal origin for convections in large-Prandtl-number liquid bridges. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Proper orthogonal decomposition of oscillatory Marangoni flow in half-zone liquid bridges of low-Pr fluids

Proper orthogonal decomposition (POD) using method of snapshots was performed on three different types of oscillatory Marangoni flows in half-zone liquid bridges of low-Pr fluid (Pr = 0.01). For each oscillation type, a series of characteristic modes (eigenfunctions) have been extracted from the velocity and temperature disturbances, and the POD provided spatial structures of the eigenfunctions, their oscillation frequencies, amplitudes, and phase shifts between them. The present analyses revealed the common features of the characteristic modes for different oscillation modes: four major velocity eigenfunctions captured more than 99% of the velocity fluctuation energy form two pairs, one of which is the most energetic. Different from the velocity disturbance, one of the major temperature eigenfunctions makes the dominant contribution to the temperature fluctuation energy. On the other hand, within the most energetic velocity eigenfuction pair, the two eigenfunctions have similar spatial structures and were tightly coupled to oscillate with the same frequency, and it was determined that the spatial structures and phase shifts of the eigenfunctions produced the different oscillatory disturbances. The interaction of other major modes only enriches the secondary spatio-temporal structures of the oscillatory disturbances. Moreover, the present analyses imply that the oscillatory disturbance, which is hydrodynamic in nature, primarily originates from the interior of the liquid bridge. (C) 2007 Elsevier B.V. All rights reserved.

A Continuation Method Applied to the Study of Thermocapillary Instabilities in Liquid Bridges

A continuation method is applied to investigate the linear stability of the steady, axisymmetric thermocapillary flows in liquid bridges. The method is based upon an appropriate extended system of perturbation equations depending on the nature of transition of the basic flow. The dependence of the critical Reynolds number and corresponding azimuthal wavenumber on serval parameters is presented for both cylindrical and non-cylindrical liquid bridges.

Fabrication of nanoscale metallic air-bridges by introducing a SiO2 sacrificial layer

A new method to fabricate nanoscale metallic air-bridges has been investigated. The pillar patterns of the air-bridge were defined on a SiO2, sacrificial layer by electron-beam lithography combined with inductively coupled plasma etching. Thereafter, the span (suspended part between the pillars) patterns were defined with a second electron-beam exposure on a PMMA/PMMA-MAA resist system. The fabrication process was completed by subsequent metal electron-beam evaporation, lift-off in acetone, and removal of the sacrificial layer in a buffered hydrofluoric (HF) solution. Air-bridges with two different geometries (line-shaped and cross-shaped) were studied in detail. The narrowest width of the air-bridges was around 200 nm, and the typical length of the air-bridges was 2-5 mu m. The advantages of our method are the simplicity of carrying out electron-beam exposure with good reproducibility and the capability of more accurate control of the pillar sizes and shapes of the air-bridge. (C) 2007 Elsevier Ltd. All rights reserved.

Fabrication of metallic air bridges using multiple-dose electron beam lithography

The techniques of fabricating metallic air bridges using different resists in a one-step electron beam lithography are presented. The exposure process employed a single-layer polymethyl methacrylate (PMMA) or photoresists with either different doses in the span and feet areas or with varying acceleration voltage of the electron beam. The process using photoresists with different doses has produced air bridges more stable than what the PMMA method using various acceleration voltages would achieve. Using this method, air bridges up to 12 mu m long have been fabricated. The length and height of these metallic air bridges vary with the photoresist thickness. (c) 2006 American Institute of Physics.

A wide-band front-end for terrestrial and cable receptions

In this paper, a wide-band low noise amplifier, two mixers and a VCO with its buffers implemented in 50GHz 0.35 mu m SiGe BiCMOS technology for dual-conversion digital TV tuner front-end is presented. The LNA and up-converting mixer utilizes current injection technology to achieve high linearity. Without using inductors, the LNA achieves 0.1-1GHz wide bandwidth and 18.8-dB gain with less than 1.4-dB gain variation. The noise figure of the LNA is less than 5dB and its 1dB compression point is -2 dBm. The IIP3 of two mixers is 25-dBm. The measurement results show that the VCO has -127.27-dBc/Hz phase noise at 1-MHz offset and a linear gain of 32.4-MHz/V between 990-MHz and 1.14-GHz. The whole chip consume 253mW power with 5-V supply.

The wideband high-linearity mixers for cable television tuner application

The wideband high-linearity mixers for a double conversion cable TV tuner is presented. The up-conversion mixer converts the input signal from 100MHz to 1000 MHz to the intermediate frequency (IF) of I GHz above. And the down-conversion mixer converts the frequency back. The degeneration resistors are used to Improve the linearity. The tuner is implemented in a 0.35 mu m SiGe technology. Input power at 1dB compression point can reach +14.23dBm. The lowest noise figure is 17.5dB. The two mixers consume 103mW under a supply voltage of 5 V.

A high-gain high-linearity wide-band low noise amplifier for terrestrial and cable receptions

This paper presents the design of a wide-band low-noise amplifier (LNA) implemented in a 0.35 mu m SiGe BiCMOS technology for cable (DVB-C) and terrestrial (DVB-T) tuner applications. The LNA utilizes current injection to achieve high linearity. Without using inductors, the LNA achieves 0.1-1GHz wide bandwidth and 18.8-dB gain with less than 1.4-dB gain variation. The noise figure(NF) of the wideband LNA is 5dB, its 1-dB compression point is -2dBm and IIP3 is 8dBm. The LNA dissipates 120mW power with a 5-V supply.

A Wide-Band Low Noise Amplifier for Terrestrial and Cable Receptions

We present the design of a wide-band low-noise amplifier （LNA） implemented in 0.35μm SiGe BiCMOS technology for cable and terrestrial tuner applications. The LNA utilizes current injection to achieve high linearity. Without using inductors, the LNA achieves 0.1 ～ 1GHz wide bandwidth and 18. 8dB gain with less than 1.4dB of gain variation. The noise figure of the wideband LNA is 5dB, and its 1dB compression point is - 2dBm and IIP3 is 8dBm. The LNA dissipates 120mW of power with a 5V supply.

A Wide-Band High-Linearity Down-Conversion Mixer for Cable Receptions

We analyze a wide-band,high-linearity down-conversion mixer for cable receptions that is implemented in 0. 35μm SiGe BiCMOS technology. The bandwidth of the RF （radio frequency） input covers the range from 1 to 1.8GHz. The measured input power at the - 1dB compression point of the mixer reaches ＋ 14.23dBm. The highest voltage conversion gain is 8. 31dB, while the lowest noise figure is 19.4dB. The power consumed is 54mW with a 5V supply. The test result of the down-conversion mixer is outlined.

Effect of volume ratio on thermocapillary flow in liquid bridges of high-Prandtl-number fluids

In present study, the transition of thermocapillary convection from the axisymmetric stationary flow to oscillatory flow in liquid bridges of 5cst silicon oil (aspect ratio 1.0 and 1.6) is investigated in microgravity conditions by the linear instability analysis. The corresponding marginal instability boundary is closely related to the gas/liquid configuration of the liquid bridge noted as volume ratio. With the increasing volume ratio, the marginal instability boundary consists of the increasing branch and the decreasing branch. A gap region exists between the branches where the critical Marangoni number of the corresponding axisymmetric stationary flow increases drastically. Particularly, a unique axisymmetric oscillatory flow (the critical azimuthal wave number is m=0) in the gap region is reported for the liquid bridge of aspect ratio 1.6. Moreover, the energy transfer between the basic state and the disturbance fields of the thermocapillary convection is analyzed at the corresponding critical Marangoni number, which reveals different major sources of the energy transfer for the development of the disturbances in regimes of the increasing branch, the gap region and the decreasing branch, respectively.