Relationship between the recovery factor and the viscous dissipation in a confined, impinging, circular jet of high-Prandtl number liquid

The radial distribution of the recovery factor for a confined impinging jet of high-Prandtl number liquid is investigated by numerical approach with emphasis on its physical mechanism. The recovery factor is determined by the viscous dissipation and Prandtl number. Unlike the case of the gas jet impingement, the recovery factor in the region close to the stagnation point can be much larger than unity, while the recovery factor at the stagnation point approaches zero. The dependence of the recovery factor on the nozzle exit velocity profile, the jet Reynolds number, and the nozzle-to-plate spacing is examined.     

Experimental Study of the Productive Bed Filtration Mode Changed by an Unsteady Action on the Host Rock Blocks

A laboratory study including physical modeling of filtration processes in porous beds with similarity criteria satisfied is performed. It is demonstrated that weak dynamic actions on stressed host rock blocks can initiate repacking of the system of blocks, leading to an increase in pressure in the productive bed and in oil recovery. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 131–138, January–February, 2006.     

Synthesis of voiced sounds using low-dimensional models of the vocal cords and time-varying subglottal pressure

The vocal cords play an important role on voice production. Air coming from the lungs is forced through the narrow space between the two vocal cords that are set in motion in a frequency that is governed by the tension of the attached muscles. The motion of the vocal cords changes the type of flow, that comes from the lungs, to pulses of air, and as the flow passes through the oral and nasal cavities, it is amplified and further modified until it is radiated from the mouth. This complex process can be modeled by a system of integral-differential equations. This paper considers two mechanical models previously used for explaining the dynamics of the vocal cords. It shows that the level of naturalness of the sound generated by these models is rather poor, and it proposes temporal variations of the parameters of the models to increase such level. Examples of synthetic vowels and diphthongs are given to assess the models. In general, the results show that, although the system of voice production is complex, we can achieve satisfactory results with relatively simple low-dimensional models, by suitable temporal variations of the aerodynamic parameters.     

Signal enhancement of a novel multi-address coding lidar backscatters based on a combined technique of demodulation and wavelet de-noising

Multi-address coding (MAC) lidar is a novel lidar system recently developed by our laboratory. By applying a new combined technique of multi-address encoding, multiplexing and decoding, range resolution is effectively improved. In data processing, a signal enhancement method involving laser signal demodulation and wavelet de-noising in the downlink is proposed to improve the signal to noise ratio (SNR) of raw signal and the capability of remote application. In this paper, the working mechanism of MAC lidar is introduced and the implementation of encoding and decoding is also illustrated. We focus on the signal enhancement method and provide the mathematical model and analysis of an algorithm on the basis of the combined method of demodulation and wavelet de-noising. The experimental results and analysis demonstrate that the signal enhancement approach improves the SNR of raw data. Overall, compared with conventional lidar system, MAC lidar achieves a higher resolution and better de-noising performance in long-range detection.     

Sensitive pseudobienzyme electrocatalytic DNA biosensor for mercury(II) ion by using the autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification

Herein, a novel sensitive pseudobienzyme electrocatalytic DNA biosensor was proposed for mercury ion (Hg²⁺) detection by using autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification. Thiol functionalized capture DNA was firstly immobilized on a nano-Au modified glass carbon electrode (GCE). In presence of Hg²⁺, the specific coordination between Hg²⁺ and T could result in the assembly of primer DNA on the electrode, which successfully triggered the HCR to form the hemin/G-quadruplex DNAzyme nanowires with substantial redox probe thionine (Thi). In the electrolyte of PBS containing NADH, the hemin/G-quadruplex nanowires firstly acted as an NADH oxidase to assist the concomitant formation of H₂O₂ in the presence of dissolved O₂. Then, with the redox probe Thi as electron mediator, the hemin/G-quadruplex nanowires acted as an HRP-mimicking DNAzyme that quickly bioelectrocatalyzed the reduction of produced H₂O₂, which finally led to a dramatically amplified electrochemical signal. This method has demonstrated a high sensitivity of Hg²⁺ detection with the dynamic concentration range spanning from 1.0 ng L⁻¹ to 10 mg L⁻¹ Hg²⁺ and a detection limit of 0.5 ng L⁻¹ (2.5 pM) at the 3S_blank level, and it also demonstrated excellent selectivity against other interferential metal ions.     

Influence of organoclay dispersed state of poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate)/organoclay nanocomposites on their characteristics

This work prepared poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG)/organoclay nanocomposites via a melt intercalation process and investigated the influences of organoclay aspect ratio and organoclay content on the dispersed state, mechanical, thermal, gas barrier, and heat recovery properties of PETG/organoclay nanocomposites. X‐ray diffraction (XRD) and transmission electron microscopic analyses showed that the organoclay dispersed in the polymer matrix with intercalation in the nanometer scale range. Differential scanning calorimetry (DSC) analysis demonstrated that all of the obtained nanocomposites were amorphous, indicating that the addition of organoclay did not affect the amorphous nature of PETG. The gas barrier properties of the nanocomposites improved with organoclay content and the properties were also affected by the organoclay aspect ratio. Water vapor and oxygen transmission rates (OTRs) of PETG/organoclay nanocomposites containing 3 phr Cloisite 15A, and 3 phr modified polymer grade Na‐montmorillonites (MPGN) were the lowest among the samples tested, and were 41.7 and 44.3%, respectively, of those of neat PETG. Similar organoclay content‐ and aspect ratio‐related effects were observed in the mechanical and heat recovery properties of the tested nanocomposites. Copyright © 2010 John Wiley & Sons, Ltd.     

基于特殊路径的局内车辆路径问题混合策略研究

针对运输途中遇到的某一或一系列无法预知的堵塞事件对决策者路径选择策略的影响,考虑堵塞只发生在一条特殊路径上且可恢复的情况,采用局内竞争分析的思想,建立了局内车辆路径问题的数学模型,对车辆到达堵塞点时堵塞恢复时间未知这一情形下的路径选择问题,提出了两种混合策略,给出了相应的竞争比,并对其竞争性能进行了理论分析。     

A cycle for validating a learning progression illustrated with an example from the concept of function

A learning progression, or learning trajectory, describes the evolution of student thinking from early conceptions to the target understanding within a particular domain. As a complex theory of development, it requires conceptual and empirical support. In earlier work, we proposed a cycle for the validation of a learning progression with four steps: 1) Theory Development, 2) Examination of Empirical Recovery, 3) Comparison to Competing Models, and 4) Evaluation of Instructional Efficacy. A group of experts met to discuss the application of learning sciences to the design, use, and validation of classroom assessment. Learning progressions, learning trajectories, and how they can support classroom assessment were the main focuses. Revisions to the cycle were suggested. We describe the adapted cycle and illustrate how the first third of it has been applied towards the validation of a learning progression for the concept of function.