Thermal processes in semimoment asymmetric hydrodynamics and the method of characteristics

A resolving system of equations of the asymmetric theory of viscous fluid media with account for the propagation of thermal processes in it is derived under the condition of equality of the rotation of the local trihedron to the mean rotation of the field of permutation, and the equation of propagation of characteristics is obtained. Translated from Inzhenemo-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 387–389, March–April, 2000.     

Construction of hierarchical three-dimensional interspersed flower-like nickel hydroxide for asymmetric supercapacitors

Low-cost and easily obtainable electrode materials are crucial for the application of supercapacitors.Nickel hydroxides have recently attracted intensive attention owning to their high theoretical specific capacitance,high redox activity,low cost,and eco-friendliness.In this study,novel three-dimensional (3D) interspersed flower-like nickel hydroxide was assembled under mild conditions.When ammonia was used as the precipitant and inhibitor and CTAB was used as an exfoliation agent,the obtained exfoliated ultrathin Ni(OH)2 nanosheets were assembled into 3D interspersed flower-like nickel hydroxide.In this novel 3D structure,the ultrathin Ni(OH)2 nanosheets not only provided a large contact area with the electrolyte,reducing the polarization of the electrochemical reaction and providing more active sites,but also reduced the concentration polarization in the electrode solution interface.Consequently,the utilization efficiency of the active material was improved,yielding a high capacitance.The electrochemical performance was improved via promoting the electrical conductivity by mixing the as-synthesized Ni(OH)2 with carbon tubes (N-4-CNT electrode),yielding excellent specific capacitances of 2,225.1 F·g-1 at 0.5 A·g-1 in a three-electrode system and 722.0 F·g-1 at 0.2 A·g-1 in a two-electrode system.The N-4-CNT//active carbon (AC) device exhibited long-term cycling performance (capacitance-retention ratio of 111.4％ after 10,000 cycles at 5 A·g-1) and a high specific capacitance of 180.5 F·g-1 with a high energy density of 33.5 W·h·kg-1 and a power density of 2,251.6 W·kg-1.     

Cellulose nanofiber/nanodiamond composite films: Thermal conductivity enhancement achieved by a tuned nanostructure

Thermally conductive and electrically insulating composite materials are required for thermal management in advanced electronic industry. The present work aimed at creating a composite film of cellulose nanofiber (CNF) and nanodiamond (ND) with superior thermal conductivity. The thermal conductivity of the prepared nanocomposite film was ～2.7?Wm^?1?K^?1, which corresponds to triple of usual CNF/ND composites with similar composition. The distinct thermal conductivity is attributed to a unique nanostructure we made out in the nanocomposite film. The nanostructure can be characterized by CNF fibrils which are densely covered with ND particles.     

Thermal state of coated solids in asymmetric cyclic heat exchange with ambient media

An analytical solution with improved convergence at the external boundary of the problem of transient heat conduction in a solid—coating system that is cyclically washed by media with different temperatures is given. The solids in question are a plate, a cylinder, and a sphere. It is suggested that the duration of adjacent half-periods, the laws of change in the temperatures of the media in each, and the heat-transfer coefficients may not be the same. Kazan Branch of the Moscow Power Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 1, pp. 123–128, January, 1996.     

Thermal transport in three-dimensional foam architectures of few-layer graphene and ultrathin graphite

At a very low solid concentration of 0.45 ± 0.09 vol %, the room-temperature thermal conductivity (κ(GF)) of freestanding graphene-based foams (GF), comprised of few-layer graphene (FLG) and ultrathin graphite (UG) synthesized through the use of methane chemical vapor deposition on reticulated nickel foams, was increased from 0.26 to 1.7 W m(-1) K(-1) after the etchant for the sacrificial nickel support was changed from an aggressive hydrochloric acid solution to a slow ammonium persulfate etchant. In addition, κ(GF) showed a quadratic dependence on temperature between 11 and 75 K and peaked at about 150 K, where the solid thermal conductivity (κ(G)) of the FLG and UG constituents reached about 1600 W m(-1) K(-1), revealing the benefit of eliminating internal contact thermal resistance in the continuous GF structure.     

Optical rectification effect in nanocarbon films

When a nanocarbon film obtained by plasmachemical deposition is fixed between two parallel electrodes and exposed to the pulsed radiation of a Q-switched neodymium laser, a pulsed electric voltage appears between the electrodes, with the pulse shape repeating the laser pulse envelope. It is shown that the amplitude and polarity of the pulsed voltage strongly depend on the angle of incidence and polarization of laser beam and on the spatial orientation of a carbon film with electrodes relative to the laser beam. The observed phenomenon exhibits all features characteristic of the optical rectification effect. For the optimum spatial orientation of a film, the factor of conversion of the laser pulse power into electric voltage amounted to 500 mV/MW, which is many times greater than the values observed in the case of optical rectification in well-known dielectric nonlinear optical crystals.     

三目视觉图像的极线校正方法

提出了解决垂直双基线三目(左、右、顶)极线校正的两步法.第一步摄像机旋转变换,按照特定的规则将各摄像机的对应坐标轴绕其光心旋转至互相平行,使得各像平面共面且与焦平面平行.第二步顶摄像机的平移变换,使三个摄像机光心构成空间等腰直角三角形.为此,提出一种等效处理方法.采用一面平面靶标,采集旋转变换前的三目图像,然后施以旋转变换,分析变换后三目图像所提供的特征对应点对的坐标,确定出顶图像变换至理想视图需要偏移的主点坐标,该过程等效于顶摄像机位置的平移.实验表明,该方法简便有效.     

Vortex-induced rectification in type II superconductors

We report a large rectification effect in superconducting films in a parallel magnetic field. This rectification effect is manifested in two features in current-voltage characteristics: The critical current, I_c,is found to differ by as much as 40% for negative and positive currents, and beyond I_c,the magnitude of the voltage is different for positive and negative currents, ¦V(+I)¦ ¦V(–I)¦.Furthermore, the critical current difference ¦I_c+¦ – ¦I_c–¦shows complicated behavior, changing sign as temperature and magnetic field are varied. We discuss a model based on the Bean-Livingston surface barrier and inhomogeneous bulk pinning that accounts for all observed behavior.     

Self-assembled one-dimensional nanostructure arrays

A range of proposed devices relies on the electronic, optical or magnetic properties of one-dimensional (1D) chains of nanoparticles. Here, well-controlled 1D arrays have been formed by templating a spherical-morphology block copolymer within a narrow groove. Significantly, the domains are distorted into ellipses with aspect ratio and major axis orientation controlled by the groove width. This technique gives unprecedented control over the period, particle size, aspect ratio, and orientation of nanoparticles in 1D arrays, making it valuable for creating self-assembled masks for the fabrication of novel devices.     

Alkaline hydrothermal kinetics in titanate nanostructure formation

In this study, the mechanism of precursor dissolution and the influence of kinetics of dissolution on titanate nanotube formation were investigated. This comparative study explored the dissolution kinetics for the case of commercial titania powders, one composed of predominantly anatase (>95%) and the other rutile phase (>93%). These nanoparticle precursors were hydrothermally reacted in 9 mol L⁻¹ NaOH at 160 °C over a range of reaction times of between 2 and 32 h. The high surface area nanotube-form product was confirmed using X-ray diffraction, FT-Raman spectroscopy, and transmission electron microscopy. The concentration of nanotubes produced from the different precursors was established using Rietveld analysis with internal and external corundum standardization to calibrate the absolute concentrations of the samples. Interpretation of the dissolution process of the precursor materials indicated that the dissolution of anatase proceeds via a zero-order kinetic process, whereas rutile dissolution is through a second-order process. The TiO₂ nanostructure formation process and mechanism of TiO₂ precursor dissolution was confirmed by non-invasive dynamic light scattering measurements. Significant observations are that nanotube formation occurred over a broad range of hydrothermal treatment conditions and was strongly influenced by the order of precursor dissolution.     

Image rectification for stereoscopic visualization

This paper proposes an approach to rectifying two images of the same scene captured by cameras at general positions so that the results form a stereo pair that satisfies the constraints of the stereoscopic visualization platforms. This is unlike conventional image rectification research that primarily focuses on making stereo matching easier but pays little attention to 3D viewing. The novel derivation of the rectification algorithm also has an intuitive physical meaning that is not available from conventional approaches. Practical issues related to wide-baseline rectification and operation range of the proposed method are analyzed. Both simulated and real data experiments are used to assess the performance of the proposed algorithm.     

胫骨羟基磷灰石片平行纳米结构

扫描电镜观察显示胫骨是一种由羟基磷灰石和胶原蛋白组成的生物陶瓷复合材料,其增强相羟基磷灰石平行于骨的表面以层状的形式排列.观察也显示这些羟基磷灰石层又是由许多长而薄的羟基磷灰石片所组成,这些羟基磷灰石片也平行排列,且其厚度具有纳米的尺度.基于在胫骨中观察到的羟基磷灰石片平行纳米结构,建立模型,研究了其最大拔出能.结果表明羟基磷灰石片长而薄的形状以及平行排列方式增加了其最大拔出能,进而提高了骨的断裂韧性.     

蛤蜊贝壳霰石片纤维交错纳米结构

扫描电镜观察表明蛤蜊贝壳是由无机霰石层和有机胶原蛋白组成的一种生物陶瓷复合材料.无机霰石层由平行于贝壳表面的长而薄的霰石片所组成.观察也发现每一霰石片又是由更细小的霰石片纤维所组成,霰石片纤维的厚度具有纳米的尺度.不同霰石层中的霰石片纤维具有不同的取向,构成一种交错纳米结构.在实验观察基础上,研究了在交错纳米结构中的霰石片纤维的最大拔出力,并与在0°结构中的霰石片纤维的最大拔出力进行了比较.结果显示在交错纳米结构中的霰石片纤维的最大拔出力明显大于在0°结构中的霰石片纤维的最大拔出力,霰石片纤维的交错纳米结构使得贝壳具有高的断裂韧性.     

Bifurcation-based acoustic switching and rectification

Switches and rectification devices are fundamental components used for controlling the flow of energy in numerous applications. Thermal and acoustic rectifiers have been proposed for use in biomedical ultrasound applications, thermal computers, energy- saving and -harvesting materials, and direction-dependent insulating materials. In all these systems the transition between transmission states is smooth with increasing signal amplitudes. This limits their effectiveness as switching and logic devices, and reduces their sensitivity to external conditions as sensors. Here we overcome these limitations by demonstrating a new mechanism for tunable rectification that uses bifurcations and chaos. This mechanism has a sharp transition between states, which can lead to phononic switching and sensing. We present an experimental demonstration of this mechanism, applied in a mechanical energy rectifier operating at variable sonic frequencies. The rectifier is a granular crystal, composed of a statically compressed one-dimensional array of particles in contact, containing a light mass defect near a boundary. As a result of the defect, vibrations at selected frequencies cause bifurcations and a subsequent jump to quasiperiodic and chaotic states with broadband frequency content. We use this combination of frequency filtering and asymmetrically excited bifurcations to obtain rectification ratios greater than 10(4). We envisage this mechanism to enable the design of advanced photonic, thermal and acoustic materials and devices.     

Theoretical study of molecular rectification in porphyrin dimer

Carrying out theoretical calculations using the density functional method for nonequilibrium electron transport, we investigated the electric conductibility of a porphyrin dimer coupled to gold electrodes by thiolate bonds. A porphyrin with four electron-donating amino groups in the dimer is connected to a porphyrin with four electron-withdrawing cyano groups by a dimethylene bridge. The calculations demonstrated that this dimer allows more flow of electrons from the first porphyrin (donor) to the second porphyrin (acceptor) than in the opposite direction. This means that the porphyrin dimer has favorable rectifier characteristics that are accounted for by the mechanism of not Aviram and Ratner [Chem. Phys. Lett. 29 (1974) 277] but of Stokbro, et al. [J. Am. Chem. Soc. 125 (2003) 3674].     

Current rectification with poly-l-lysine-coated quartz nanopipettes

Ion current rectification with quartz nanopipette electrodes was investigated through the control of the surface charge. The presence and absence of a positively charged poly-l-lysine (PLL) coating resulted in the rectified current with opposite polarity. The results agreed with the theories developed for current-rectifying conical nanopores, suggesting the similar underlying mechanism among asymmetric nanostructure in general. This surface condition dependence can be used as the fundamental principle of multi-purpose real-time in vivo biosensors.