超声空化强度测量的研究进展

近几十年来,超声波已经广泛应用于生物学和医学领域,在医学领域中超声波可以作为信息载体用于探测人体的病变信息,并且可以用一定剂量的超声波作用于人体病变组织,并通过它对组织的作用达到一定的治疗目的。作为一种无创、非介入性外科技术,它的疗效和安全性越来越被人们所关注。超声波与人体组织的相互作用有三种,分别是机械机制,热学机制,和空化机制。对于机械机制和热机制人们比较熟悉,而对于空化机制则相对陌生。随着超声空化在医学中的应用越来越广泛,其安全性越来越受到人们的关心。要么是其强度迭不到治疗效果,要么是其强度过大损伤人体,因此其强度已成为人们关心的主要主题。本文主要介绍超声空化的主要探讨了几种测量方法及对超声空化有影响的几种参量,并对超声空化的发展进行了展望。     

Developments in ultrasound--non-medical

Ultrasound is defined as sound of a frequency that is too high for the human ear to detect—i.e. it is inaudible. Nevertheless this “silent sound” has a large range of applications in science, medicine and industry. The study of the effects of ultrasound on materials—known as sonochemistry—is one of the broadest and most exciting areas in current research. In this review some recent developments with major potential are identified from the fields environmental protection and materials processing.

Environmental protection can refer to methods of preventing pollution or to the removal of existing pollution. Here we will look at examples drawn from the latter in which ultrasound has been used for the purification of water (chemical and biological), the decontamination of the atmosphere and soil remediation i.e. the classic three domains of water, air and land.

In terms of materials processing two examples have been chosen, the treatment of sewage sludge and the control of crystallisation. In both of these cases it is predominantly the mechanical effects of acoustic cavitation, which produce the enhanced digestion, and dewatering of sludge and provide for the control in crystallisation processes.     

Lianas may be favoured by low rainfall: evidence from Ghana

We review the evidence in support of the hypotheses that (i) lianas are now increasing in tropical forests and (ii) lianas are more abundant in the drier tropical forests. There is good evidence to support both hypotheses, including a new analysis of data from Ghana. In this dataset, there is a linear increase in the percentage of species that are lianas, from 30% at a mean annual rainfall of 2,000 mm year⁻¹ to 43% at a mean annual rainfall of 1,000 mm year⁻¹. Both trends in lianas, one temporal, the other spatial, may be related to water availability, though parallel changes in canopy density (disturbance) may be contributory. It is also clear that most liana species in West Africa show restricted distribution along the rainfall gradient implying adaptation to different water availability. The reasons for the high sensitivity to rainfall may be that lianas have an especially effective water-transport system, with deep roots, large xylem vessels and a mechanism to avoid cavitation of water. As the climate of much of the tropics is becoming drier, we may expect increases in both liana abundance and their proportion in the flora over the future decades.     

Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2–4-mm diameter) collected at 20–30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance (g_s) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20–30 cm depth above –0.5 MPa in the old-growth Douglas-fir site and –1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about –2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g_s decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.     

Hybrid Cavitation/Constructed Wetland Reactors for Treatment of Chlorinated and Non‐Chlorinated Organics

Mitigation strategies can be implemented to decrease chlorinated and non‐chlorinated organic exposures to biota of aquatic receiving systems thereby reducing associated risks. In this work, we investigated the concept of coupling a physical/chemical reactor (i.e. a cavitation reactor) with a biological reactor (i.e. a constructed wetland) in an effort to efficiently transform PCE, TCE, and petroleum in freshwater into non‐toxic chemical forms or concentrations. Rates of TCE degradation due to cavitation ranged from 0.010 to 0.026 min^‐1 with corresponding half‐lives of 69 to 27 min. Compared to controls, degradation of petroleum in water by cavitation was not detected in these experiments. After treatment in anaerobic wetland reactors, TCE and PCE decreased by more than 99 % under two flow regimes (5‐d and 20‐d HRT). In reciprocating constructed wetland reactors receiving petroleum, mean COD, BOD₅, and total Zn decreased by 90.0, 88.8, and 86.8 %, respectively, in wetland outflows compared to the initial conditions (96‐h HRT). Percent survival (96‐h) of D. magna and P. promelas increased from zero percent in initial conditions to 80.1 (± 18.9) and 80.0 (± 21.4) %, respectively, after treatment in the constructed wetland reactors. The experimental results obtained in the laboratory‐scale set‐up and the theoretical model for the hybrid reactor concept will be used to obtain the intrinsic kinetic coefficients for the appropriate reactors. This kinetic information will be used to scale‐up the hybrid reactor model concept for the same level of pollutant removal.     

Maximum sustainable xylem sap tensions in Rhododendron and other species

The acoustic technique was used in conjunction with the pressure chamber to determine the tensions causing cavitation of xylem sap in leaves of five woody angiosperms (Acer pseudoplatanus L., Alnus glutinosa L. Gaertn., Eucalyptus globulus Labill., Fraxinus excelsior L. and Rhododendron ponticum L.) and three species of herbs (Lycopersicum esculentum Mill., Plantago major L. and Ricinus communis L.). The results showed leaves of most species to suffer considerably from cavitation at sap tensions of 1.6-3 MPa. Two of the herbs, Lycopersicum and Ricinus, cavitated extensively at sap tensions below 1 MPa. Additional evidence is presented that clicks, detected by acoustic amplification, are caused by cavitation of sap in the xylem conduits. A rapid method is suggested for the determination of sap tensions in cavitating leaves and which is suitable for surveys of the critical sap tension in a large number of species.     

Topoedaphic and morphological complexity of foliar damage and mortality within western juniper (Juniperus occidentalis var. occidentalis) woodlands following an extreme meteorological event

Aim An extreme early season freeze event in October 2002 resulted in significant foliar damage and/or mortality within western juniper woodlands. We identify the geographical patterns of tree damage based on morphological, topographical and edaphic parameters, and discuss the ecological implications of this event. Location Oregon, USA (44.0–44.2° N, 120.3–120.9° W). Methods We sampled trees on four matched pairs of disturbed and minimally disturbed study sites within the core area of tree damage. We collected information about age, morphology (height, basal area, level of foliar damage), and topographic position (elevation, slope, aspect) for each tree sampled using dendroecological and GPS/GIS procedures. We collected plot‐level data on tree density and degree of cover for shrubs and grasses. We used a series of Mann–Whitney, Kruskal–Wallis and Wilcoxon tests and graphical analyses to determine if significant differences exist in our collected variables both between matched pairs and within our disturbed sites. Results Topographically, we found that aspect was a critical element regulating damage, with trees in colder microenvironments (north‐westerly slopes) experiencing less damage because they were further along in the annual process of cold‐hardening. The majority of damaged trees were found in areas of higher density and more even age structure that are typical of recent juniper afforestation. Morphologically, we show that trees with greater basal areas and/or less stature were less likely to have foliar damage, consistent with winter cavitation. Main conclusions Our results show that the spatial pattern of damage was closely related to topography and tree morphology, parameters that, in turn, correspond closely to differences between the historical locales of western juniper and juniper woodlands that have emerged in a 100+ year period of rapid afforestation. This freeze event fits the criteria for a large, infrequent disturbance in that it was spatially complex and may act as an endogenous factor that can contribute to stand maintenance.     

Reduction in excess sludge production in a dairy wastewater treatment plant via nozzle-cavitation treatment: Case study of an on-farm wastewater treatment plant

Nozzle-cavitation treatment was used to reduce excess sludge production in a dairy wastewater treatment plant. During the 450-d pilot-scale membrane bioreactor (MBR) operation, when 300 l of the sludge mixed liquor (1/10 of the MBR volume) was disintegrated per day by the nozzle-cavitation treatment with the addition of sodium hydrate (final concentration: 0.01% W/W) and returned to the MBR, the amount of excess sludge produced was reduced by 80% compared with that when sludge was not disintegrated.     

Kidney damage in extracorporeal shock wave lithotripsy: a numerical approach for different shock profiles

In shock-wave lithotripsy—a medical procedure to fragment kidney stones—the patient is subjected to hypersonic waves focused at the kidney stone. Although this procedure is widely applied, the physics behind this medical treatment, in particular the question of how the injuries to the surrounding kidney tissue arise, is still under investigation. To contribute to the solution of this problem, two- and three-dimensional numerical simulations of a human kidney under shock-wave loading are presented. For this purpose a constitutive model of the bio-mechanical system kidney is introduced, which is able to map large visco-elastic deformations and, in particular, material damage. The specific phenomena of cavitation induced oscillating bubbles is modeled here as an evolution of spherical pores within the soft kidney tissue. By means of large scale finite element simulations, we study the shock-wave propagation into the kidney tissue, adapt unknown material parameters and analyze the resulting stress states. The simulations predict localized damage in the human kidney in the same regions as observed in animal experiments. Furthermore, the numerical results suggest that in first instance the pressure amplitude of the shock wave impulse (and not so much its exact time-pressure profile) is responsible for damaging the kidney tissue.     

植物管状细胞栓塞后的重新充注研究进展

在植物吸收水分以后 ,水分运输对于植物正常的生长发育是非常重要的。在干旱和冬季反复冻融循环以后 ,植物体内的管状细胞容易充满水蒸气和空气 ,形成腔隙和栓塞。腔隙和栓塞的形成对水分在植物体内的运输造成了很大的障碍 ,从而影响了植物的生长与发育。当植物重新获得水分时 ,已形成腔隙和栓塞的管状细胞的重新充注能使一部分管状细胞的输水功能得到恢复 ,从而保证了一些器官的生理功能的正常进行。近些年来 ,人们对植物管状细胞的重新充注涉及到的许多植物组织和生理过程进行深入的研究 ,并提出了各种机理。鉴于植物管状细胞形成栓塞后重新充注对植物水分运输的重要生理作用 ,本文对重新充注的许多机理进行了综合评述