房地产市场泡沫评价研究综述

分析了房地产泡沫形成的原因,描述了房地产泡沫的检测方法,全面回顾了房地产预警指标和模型。通过对房地产泡沫的成因、检测、预警等方面的梳理,总结出该领域的研究成果,为房地产市场研究和管理提供参考。     

Estimating adult Chinook salmon exposure to dissolved gas supersaturation downstream of hydroelectric dams using telemetry and hydrodynamic models

Gas bubble disease (GBD) has been recognized as a potential problem for fishes in the Columbia River basin. GBD results from exposure to gas supersaturated water created by discharge over dam spillways. Spill creates a downstream plume of water with high total dissolved gas supersaturation (TDGS) that may be positioned along either shore or mid‐channel, depending on dam operations. We obtained spatial data on fish migration paths and migration depths for adult spring and summer Chinook salmon, Oncorhynchus tshawytscha, during 2000. Migration paths were compared to output from a two‐dimensional (2‐dimensional) hydrodynamic and dissolved gas model to estimate the potential for GBD expression and to test for behavioural avoidance of the high TDGS plume. We observed salmon swam sufficiently deep in the water column to receive complete hydrostatic compensation 95.9% of the time spent in the Bonneville Dam tailrace and 88.1% of the time in the Ice Harbor Dam tailrace. The majority of depth uncompensated exposure occurred at TDGS levels >115%. Adult Chinook salmon tended to migrate near the shoreline and they tended to remain in relatively deep water. Adults moved into the high dissolved‐gas plume as often as they moved out of it downstream of Bonneville Dam, providing no evidence that adults moved laterally to avoid areas with elevated dissolved gas levels. When water depths decreased due to reduced river discharge, adults tended to migrate in the deeper navigation channel downstream from Ice Harbor Dam. The strong influence of dam operations on the position of the high‐TDGS plume and shoreline‐orientation behaviours of adults suggest that exposure of adult salmonids to high‐TDGS conditions may be minimized using operational conditions that direct the spilled water mid‐channel. Our approach illustrates the potential for combined field and modelling efforts to estimate the fine‐scale environmental conditions encountered by fishes in natural and regulated rivers. Published in 2007 by John Wiley & Sons, Ltd.     

Effect of scale‐up on wall shear rates in circulating bubble columns

Effective wall shear rates were investigated experimentally in an external loop circulating bubble column made from transparent acrylic resin. The riser (D_R) and downcomer (D_D) diameters were 0.19 m and 0.14 m, respectively. The column working volume (V_R) was 170 dm³, with a scale‐up factor (A_D/A_R) of 0.54, and a dispersion height (H_D) of 2.25 m. Polymer solutions of xanthan gum and carboxymethyl cellulose were used to simulate non‐Newtonian behavior of biological systems. Effective wall shear rates for the non‐Newtonian solutions were found by analogy with Newtonian glycerol solutions, employing downcomer liquid velocity as the measurable and comparable parameter. The experimental shear rate results were found to fit between those of the literature data. A new single correlation taking into account all the relevant data in the literature and the results of this work is proposed. The new correlation is an improvement over the other correlations because it includes two important design constants: scale‐up factor and dispersion height. Copyright © 2005 Society of Chemical Industry     

Bubble behavior during boiling of subcooled binary mixtures on very thin wires

Experimental investigations were conducted to explore the characteristics of subcooled nucleate boiling of binary mixtures composed of water and ethanol on very thin wires, and an emphasis was addressed to observe bubble movement and bubble jet flow. The experiments exhibited many different bubble jet flows, such as continuous, discontinuous, diverged, bifurcate jet flows, and small bubble spraying, corresponding to different vapor bubble sizes and bubble‐moving modes such as bubble initial momentum and bubble‐generating frequency. The bubble movement within the jet flow also was analyzed. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 105–111, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20142     

Physically sorbed collectors in froth flotation and their activity. Part I

It is demonstrated that the basic factor, identifying the capability to form a flotation complex, is the availability of a reagent sorbed physically on a particle surface and promoting the thinning-down of water interlayer between a mineral particle and a bubble at final stages of their approach. The numerical evaluation of the effect of physically sorbed collector on variations in the velocity of water discharge from an interlayer, partitioning a mineral particle and a gas bubble at the moment of their meeting is given. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 118–125, November–December, 2008.     

A statistical approach of heat transfer coefficient analysis in the slurry bubble column

Heat transfer plays an important role in slurry bubble column reactors (SBCRs). Design of heat transfer equipments for SBCRs is a limiting step in sizing and scale up of them. In order to study the convection heat transfer coefficient (CHTC) in industrial SBCRs, a proper column was designed and manufactured in pilot scale with a special convection heat transfer coefficient measurement probe (CHTC MP). In this study, influence of effective parameters such as solid fraction, superficial gas velocity, radial and vertical position of the column was investigated on CHTC. The design of experiments was performed using a full factorial method including 3¹ × 2² × 9¹ = 108 experiments, to determine the main effects, binary and ternary interactions of variables. Study of the curvature functionality of CHTC versus gas velocity and effect of flow regime transition from homogeneous to heterogeneous flow was the other goal of this work. A statistical model including the main variables and their significant binary and ternary interactions was explained for CHTC with a good fitness with experimental data. Interactions of four effective parameters including solid fraction, superficial gas velocity, radial and vertical position of the column was studied for the first time in the SBCRs. A dimensionless correlation for local Stanton number was developed as a function of Pr, Re, Fr, non-dimensional radial position and non-dimensional distance from the sparger. Considering local positions in the correlation is a novel work and this correlation has good agreement with experimental data.     

Influence of structured packing on gas holdup in a three-phase bubble column

In this work, the influence of structured packing on gas holdup in gas-liquid-solid dispersions has been studied. The experiments were carried out in an empty column and in column containing structured packing operating under identical conditions. Glass beads and silicon carbide particles were used as the solid material and the volumetric fraction of solids was varied from 0% to around 10%. The liquid viscosity was strongly modified using water, CMC solution and glycerol. The experimental results obtained with both columns were compared with previous results obtained in two-phase bubble columns. The influence of structured packing on the total gas holdup for different superficial gas velocities was found to be similar with and without suspended solids. Therefore, the results obtained in this work were analysed on the basis of correlations derived earlier for gas-liquid dispersions. Excepting the results obtained with glycerol, these correlations can predict the gas holdup of three-phase bubble columns with reasonable accuracy.     

孔口出流气泡运动特性数值模拟

为了研究连续供气条件下,气泡运动特性与孔口进气速度、孔口直径的关系,对孔口出流气泡在静水中上升运动过程进行了研究,采用OpenFoam开源程序计算得到的静水中气泡上升运动模拟结果与试验结果吻合较好。通过改变孔口进气速度、孔口直径,分析了气泡的脱离时间和脱离直径,对比了初始球型气泡与孔口出流气泡的上升运动差异,提出可将相对速度B用于描述初始气泡终速度与孔口进气速度的关系,并采用不同无量纲参数对气泡运动相对速度进行了预测。结果表明:We数及Re数对气泡运动相对速度B的预测效果较好,气泡初始状态对气泡运动轨迹影响较大。研究成果进一步丰富了气泡运动相关领域的成果,为下一步精细刻画气泡复杂运动开创了思路。     

Method of mass production of monodisperse microbubbles aided by intense pressure gradients

Here we present a method for producing noncoalescing monodisperse microbubbles in an efficient, massive and controlled way. Since our prototype is easily scalable, it can be straightforwardly adapted to satisfy the specific gas injection demands required by the different applications where it can be used, like bioreactors or water treatment or purification plants. The main feature of the bubbling device described here consists of injecting the gas at the leading edge of a wing in relative motion with respect to a liquid. The reasons for this particular design relies on the smallness of the drag coefficient of streamlined bodies and also on the fact that the strongest favorable pressure gradients and the minimum values of the liquid pressures are located at the leading edge of the airfoils composing the wing.     

Smart Bubble Sort: A Novel and Dynamic Variant of Bubble Sort Algorithm

In the present era, a very huge volume of data is being stored in online and offline databases. Enterprise houses, research, medical as well as healthcare organizations, and academic institutions store data in databases and their subsequent retrievals are performed for further processing. Finding the required data from a given database within the minimum possible time is one of the key factors in achieving the best possible performance of any computer-based application. If the data is already sorted, finding or searching is comparatively faster. In real-life scenarios, the data collected from different sources may not be in sorted order. Sorting algorithms are required to arrange the data in some order in the least possible time. In this paper, I propose an intelligent approach towards designing a smart variant of the bubble sort algorithm. I call it Smart Bubble sort that exhibits dynamic footprint: The capability of adapting itself from the average-case to the best-case scenario. It is an in-place sorting algorithm and its best-case time complexity is Ω(n). It is linear and better than bubble sort, selection sort, and merge sort. In average-case and worst-case analyses, the complexity estimates are based on its static footprint analyses. Its complexity in worst-case is O(n²) and in average-case is Θ(n²). Smart Bubble sort is capable of adapting itself to the best-case scenario from the average-case scenario at any subsequent stages due to its dynamic and intelligent nature. The Smart Bubble sort outperforms bubble sort, selection sort, and merge sort in the best-case scenario whereas it outperforms bubble sort in the average-case scenario.