达标污水离岸排海末端处置技术研究综述

达标污水离岸排海处置具有低成本、高处理率等优点,是国内外沿海港口和临港工业园区进行污水处置的重要选择。介绍了国内外达标污水离岸排海末端处置技术的发展情况,分析了排污口位置选划、扩散器射流参数及水力结构优化等研究技术上存在的问题。认为排污口位置选划应在水动力、污染物扩散、泥沙冲淤及工程经济因素分析的基础上,还需要重点考虑污水排放对区域生态要素长期的影响;排海末端扩散器射流参数及水力结构优化也尤为关键,不仅直接影响稀释扩散效果,而且涉及到主管、上升管、喷口等多个可控因子,可以采用建立物理模型、数值模型及量纲分析等方法,合理优化扩散器的结构参数和扩散器的型式,对提高达标污水离岸处置的效果具有重要意义。     

Frontal impingement of nanojets: formation,disintegration and mixing of nano liquid sheets

We investigate nano liquid sheets formed by frontal impingement of two cylindrical nanojets using the molecular dynamics method. The results show that only with a high enough velocity can a stable liquid sheet be formed because of the strong surface tension effect in nanoscale. In relatively low jet velocity range, the relationship between the intact sheet radius and the jet velocity takes on the power function form with the power being ? 0.502. This relationship is explained by considering the thermal fluctuation effect, thus confirming the dominating role of the thermal fluctuation effect in the disintegration process. The influence of the jet velocity on the time-domain evolution of mixing of the system and the spatial mixing distribution of the liquid sheet are also investigated. Our results suggest that nanojets do not coalesce at the impingement point, the mixing occurs mainly through diffusion. And there is recoil that happens at the stagnation plane.     

Molecular dynamics simulation of formation and control of nanodroplets in piezoelectric nanoejection systems

In this paper, the formation of nanodroplets in piezoelectric nanoejection processes is investigated by non-equilibrium molecular dynamics simulation. By compressing liquid propane molecules with various specific pushing periods of oscillation, the phenomena of liquid thread breakup and droplet formation are simulated. The simulation results revealed that various features aid the piezoelectric nanoejection system. Two breakup shapes including double-cone and long tail structures were found in this process. To analyse the ejection process in detail, 2D contour plots and thermal properties for various pushing periods are shown and discussed in this paper. The results show that the sizes of nanodroplets are linear depending on the pushing periods. The findings show a new control factor and mechanism for nanodroplet formation through piezoelectric nanoejection processes.     

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.     

Flow and oxygen transfer in a plunging water jet system using inclined short nozzles and performance characteristics of its system in aerobic treatment of wastewater

For the plunging water jet system using inclined short nozzles, the flow characteristics such as the bubble penetration depth and the gas entrainment rate, which changed depending on the jet velocity, the nozzle diameter, the jet length, and the jet angle were first evaluated in an air-water system. A comparable investigation between our results and those of existing studies used the long nozzles on those characteristics revealed that both the bubble penetration depth and the gas entrainment rate differed depending on the nozzle length; that is, the nozzle-length-to-diameter ratio L(N)/D(N) and that of these characteristics the gas entrainment rate affected considerably by its magnitude and tended to be high when the nozzle of a large L(N)/D(N) ratio was used. It was also confirmed from the oxygen transfer experiments that the transfer efficiency at low jet velocities in the present water jet system was not inferior to the ones of other types of existing aeration systems; that is, the utilization of this jet aeration system to a high rate reactor for wastewater treatment or fermentation was sufficiently possible. The applicability of the plunging jet aeration method to microbial processes was then examined. As a typical example of microbial processes to be tested, the continuous treatment of an organic wastewater using activated sludge microorganisms was carried out, and the performance and related problem when this type of aeration system was applied to such a microbial process were investigated. Experimental results showed that, when viewed from the removal ability of dissolved organic matters, the plunging jet aeration system was capable of treating a wastewater of considerable high loading without the rate of oxygen transfer becoming the biooxydation-rate-limiting factor. Special attention was necessary for the choice of the liquid pump to be employed, however, due to the increased amount of fine suspended solids in the treated water caused by the shearing action between sludge flocks and pump blades.     

Molecular dynamics simulation of thread break-up and formation of droplets in nanoejection system

This study investigated nanojet processes by a non-equilibrium molecular dynamics simulation. The phenomena of liquid thread break-up and droplet formation were simulated by compressing liquid propane molecules with various compressing velocities. Properties' distributions show that, at the nanoscale, density and pressure were neither uniform nor continuous during the ejection process. Shear heating phenomena were found in the contact area of the nozzle channel. A linear relationship between the length of liquid threads and the compressing velocity was also found in this study. The results from different trials using various compressing velocities show that higher compressing velocities in nanojet processes result in longer liquid thread lengths and liquid molecules with higher energy levels. Therefore, the ejection process is more unstable, resulting in an increase in the number of evaporating molecules and satellite droplets. Results that illustrate various features are presented to aid in the comprehension of the nanojet processes.     

Analysis of energy and friction coefficient fluctuations of a Lennard-Jones liquid coupled to the Nosé–Hoover thermostat

Thermal fluctuations of a many-body system coupled to a Nosé–Hoover thermostat depend on the strength of the coupling parameter τ*. A wrong choice may bring non-ergodic features and non-canonical fluctuations. Here, we analyse by means of molecular dynamics simulations both the energy fluctuations and the spectrum of the friction coefficient ζ^* of an extended Lennard-Jones system in a wide range of τ* at liquid density. Three ranges of τ* are identified – small, intermediate and large, plus their transitions. For τ* values in the intermediate range, ζ^* shows chaotic behaviour, and the particle system requires reasonable computing time for its thermalisation. As a result, the extended system is ergodic and energy fluctuations are canonical and stable in time. On the contrary, small and large ranges of τ* reveal clear evidence of periodicity in the thermostat variable, for instance by propagating the initial temperature condition. For these two ranges, the extended system shows non-ergodic features and energy fluctuations are non-canonical. For large τ*, micro-canonical fluctuations are occasionally obtained. For small to intermediate and intermediate to large ranges of τ*, the thermostat variable exhibits beat waves and is thus unable to reach equilibrium no matter how extended in time the simulations are. Here, we compare our results with previous work and explain the differences.     

Diagnostics of jet structures formed in the plasma corona during the irradiation of porous targets by intense laser pulses

Jet structures formed during laser irradiation of porous targets with an average density of ?? = 1?30 mg/cm³ were studied experimentally by using the diagnostic complex of the Mishen facility. To study complicated plasma structures, the experimental data were processed using specially elaborated mathematical methods. The probability of the emergence of jet plasma structures in plane open-pore triacetate cellulose targets was studied as a function of the parameter ??d, where ?? is the average mass density and d is the target thickness. Analysis of the experimental results and their comparison with the existing data on the jet structures formed during laser irradiation of solid-density targets allowed the authors to reveal the characteristic features and mechanisms of the development of large-scale plasma jets.     

Lessons from seashells: silica mineralization via protein templating

Silica, the most abundant compound in the earth's crust, is also widespread in biological systems. Silica has many functions, including support and protection in single-celled organisms and in higher plants and animals alike. Despite this widespread occurrence and importance of function, little is known about biosilica and the mechanisms that produce controlled microscopic and macroscopic silica structures with nanoscale precision, exceeding present synthetic technological approaches. Here we highlight recent progress in identifying proteins, genes and the various environmental factors responsible for the controlled synthesis of silica by marine organisms. Examples of biomimetic approaches to biosilica formation using model peptides to control the formation of structures through manipulation of the processing environment are discussed.     

Orderly formation of the double ring structures for plastid and mitochondrial division in the unicellular red alga Cyanidioschyzon merolae

The formation of the plastid-dividing ring (PD ring) and mitochondrion-dividing ring (MD ring) was studied in a highly synchronous culture of the unicellular red alga Cyanidioschyzon merolae. The timing and the order of formation of the MD and PD rings were determined by observing organelles around the onset of their division, using transmission electron microscopy. In  C. merolae, there is one chloroplast and one mitochondrion per cell, and the shape of the chloroplast changes sequentially from acorn-like, to round, to trapezoidal, to peanut-shaped, in that order, during the early stage of chloroplast division. None of the cells with acorn-shaped or round chloroplasts contained organelles with PD rings or MD rings, while all of the cells with peanut-shaped chloroplasts contained organelles with both PD rings and MD rings. In cells with peanut-shaped chloroplasts, the PD and MD rings were double ring structures, with an outer ring located on the cytoplasmic face of the outer membrane of the organelle, and an inner ring located in the matrix beneath the inner membrane. These results suggested that the double ring structures of the PD ring and the MD ring form when chloroplasts are trapezoidal in shape. Detailed three-dimensional observation of cells with trapezoidal chloroplasts revealed the following steps in the formation of the double ring structures of the PD and MD rings: (i) the inner ring of the PD ring forms first, followed by the outer ring; (ii) then the MD ring forms and becomes visible; (iii) when the double ring structures of the two rings have formed, the microbody then moves from its remote location to the plane of division of the mitochondrion and contraction of the PD and MD rings commences. These steps were also confirmed by computer-aided three-dimensional reconstruction of the images from serial thin sections. This study reveals the order of formation of the double ring structures of the PD and MD rings, and the behavior of the microbody around the onset of division of plastids and mitochondria. The results also provide the first evidence that the inner PD ring is not a tension element formed by the contractile pressure but a definite structure, independent of the outer ring. Received: 31 March 1998 / Accepted: 14 May 1998     

The Gō model revisited: Native structure and the geometric coupling between local and long-range contacts

Monte Carlo simulations show that long-range interactions play a major role in determining the folding rates of 48-mer three-dimensional lattice polymers modeled by the Gō potential. For three target structures with different native geometries we found a sharp increase in the folding time when the relative contribution of the long-range interactions to the native state's energy is decreased from approximately 50% towards zero. However, the dispersion of the simulated folding times is strongly dependent on native geometry and Gō polymers folding to one of the target structures exhibits folding times spanning three orders of magnitude. We have also found that, depending on the target geometry, a strong geometric coupling may exist between local and long-range contacts, which means that, when this coupling exists, the formation of long-range contacts is forced by the previous formation of local contacts. The absence of a strong geometric coupling results in a kinetics that is more sensitive to the interaction energy parameters; in this case, the formation of local contacts is not capable of promoting the establishment of long-range ones when the latter are strongly penalized energetically and this results in longer folding times.     

Ad hoc continuum-atomistic thermostat for modeling heat flow in molecular dynamics simulations

An ad hoc thermostating procedure that couples a molecular dynamics (MD) simulation and a numerical solution to the continuum heat flow equation is presented. The method allows experimental thermal transport properties to be modeled without explicitly including electronic degrees of freedom in a MD simulation. The method is demonstrated using two examples, heat flow from a constant temperature silver surface into a single crystal bulk, and a tip sliding along a silver surface. For the former it is shown that frictional forces based on the Hoover thermostat applied locally to grid regions of the simulation are needed for effective feedback between the atomistic and continuum equations. For fast tip sliding the thermostat results in less surface heating, and higher frictional and normal forces compared to the same simulation without the thermostat.     

Local overall volumetric gas-liquid mass transfer coefficients in gas-liquid-solid reversed flow jet loop bioreactor with a non-Newtonian fluid

The local overall volumetric gas-liquid mass transfer coefficients at the specified point in a gas-liquid-solid three-phase reversed flow jet loop bioreactor (JLB) with a non-Newtonian fluid was experimentally investigated by a transient gassing-in method. The effects of liquid jet flow rate, gas jet flow rate, particle density, particle diameter, solids loading, nozzle diameter and CMC concentration on the local overall volumetric gas-liquid mass transfer coefficient (K(L)a) profiles were discussed. It was observed that local overall K(L)a profiles in the three-phase reversed flow JLB with non-Newtonian fluid increased with the increase of gas jet flow rate, liquid jet flow rate, particle density and particle diameter, but decreased with the increase of the nozzle diameter and CMC concentration. The presence of solids at a low concentration increased the local overall K(L)a profiles, and the optimum of solids loading for a maximum profile of the local overall K(L)a was found to be 0.18x10(-3)m(3) corresponding to a solids volume fraction, varepsilon(S)=2.8%.     

Helical structures in complex plasma I: Noncollective interaction

The conditions for the formation and stability of helical quasi-crystals in a complex plasma containing dust grains of equal size are investigated. A study is made of both the confinement of such helical structures in a direction transverse to the cylinder axis by means of an external parabolic potential well and the possibility of their self-confinement. Computer simulations of the helical dust structures were carried for two cases: for a structure of infinite length along the symmetry axis (or a closed structure in toroidal geometry) and for a structure of finite length. The dust grains were assumed to interact through a potential that is a superposition of the non-Debye nonlinear screened potential and the nonscreened noncollective attractive potential (the Lesage effect). Molecular dynamics simulations showed that, in the presence of dissipation, any initial random distribution of the dust grains interacting through such a potential in cylindrical geometry evolves to an equilibrium helical structure. When the external control parameter was varied smoothly, the pitch angle of the helix was observed to bifurcate (i.e., to undergo sharp jumps). The structure of the helix was also observed to bifurcate when the external parameter was varied: a helix changed into two interwoven helices, which then changed into three interwoven helices, etc. The smaller the confinement parameter (and, accordingly, the larger the radius of the helical structures) and the stronger the attractive forces between the grains, the larger the number of bifurcations. The results of analytical calculations of the parameters of the equilibrium structures and of their energies are in complete agreement with numerical results. It is also shown that noncollective attraction between dust grains makes it probable that helical structures will exists when the external confinement parameter is zero or even when it is negative. Bifurcations in such systems may provide the possibility of creating new types of memory elements.     

A model investigation of the velocity and pressure spectra in vascular murmurs

A physical model consisting of an axisymmetrical jet in a rigid plexiglass pipe was used to study the flow and pressure fluctuations downstream from an aortic stenosis. The fluctuating velocity components, u and v, at several locations in the steady liquid jet were measured using a laser Doppler anemometer system. Simultaneous wall pressure fluctuations were monitored by an array of nine miniature pressure transducers wall mounted in the axial direction. This paper presents the detailed measurements of mean velocity profiles, turbulent intensity distributions and RMS pressure fluctuations. The energy spectra obtained for the pressure fluctuations and the u and v velocity components are compared. Contrary to earlier works, we found that the differences between peak frequencies of the pressure spectra and the characteristic frequencies of the velocity spectra vary with positions downstream from the nozzle. These differences are discussed in light of pseudosound generation by the eddy structures in the stenotic flow field.     

Molecular dynamics study of the thermal conductivity of nanoscale argon films

Non-equilibrium molecular dynamics (MD) simulations were used to study the thermal conductivity of thin argon films. The MD simulations show that the argon film's thermal conductivity is affected by the thickness up to thickness of about 100 nm, which agrees with theoretical estimates. The results show that the MD method is very effective for modeling nanoscale thermal conduction. Besides pure argon films, the effect of vacancies on the argon film's thermal conductivity was also studied. The vacancies greatly reduce the thermal conductivity as a function of the vacancy concentration but not as a function of the vacancy distribution when the film's temperature is constant.     

Self-Organization in Living Cells: Networks of Protein Machines and Nonequilibrium Soft Matter

Microscopic self-organization phenomena inside a living cell should not represent merely a reduced copy of self-organization in macroscopic systems. A cell is populated by active protein machines that communicate via small molecules diffusing through the cytoplasm. Mutual synchronization of machine cycles can spontaneously develop in such networks – an effect which is similar to coherent laser generation. On the other hand, an interplay between reactions, diffusion and phase transitions in biological soft matter may lead to the formation of stationary or traveling nonequilibrium nanoscale structures.     

MD Simulation of Colloidal Particle Transportation in a Fiber Matrix

Surface glycocalyx, as a barrier to material exchange between circulating blood and body tissues, can be treated as a periodic square array of cylindrical fibers. Previous study treated the glycocalyx as porous media and simulated by continuum theory. However, it has recently been found that a relatively hexagonal fibre-matrix structure may be responsible for the ultrafiltration properties of microvascular walls. The fibre-matrix is an underlaying three-dimensional meshwork with a fibre diameter of 10$\sim$12 nm and characteristic spacing of about 20 nm. The porous medium model does not consider the particle size, when the particle size is comparable to the fibre spacing, the porous medium assumption may not be appropriate to study the permeable characteristics of nanosize particle in such fibre-matrix structure. \newline Molecular dynamics (MD) simulation is a powerful method to simulate the fluid flow at the molecular level, it has been applied successfully in many fields including hydrodynamics and demonstrated surprising results at nanoscale which is different from their macroscopic counterparts. In this study we use MD to investigate the permeable characteristics of nano-particle in a quasi-periodic ultra-structure of the endothelial glycocalyx. As the first attempt, fibre-matrix is simplified as a two dimensional periodic system in which the colloidal particles, fluid solvent, fibers are all treated as atomic systems, and the study is focused on the effect of particle size on particle motion in fiber matrix.     

Analysis of the formation of ordered dust-grain structures in a thermal plasma

The possibility is studied of the formation of ordered dust-grain structures in a low-temperature thermal plasma consisting of electrons, ions, and micron-sized charged dust grains. The range of the required values of the coupling parameter Γ defining the degree to which the plasma is nonideal is calculated using the results of diagnostic measurements carried out in a plasma consisting of combustion products of propane in air with grains of different materials. The results obtained show that the most favorable conditions for the formation of strongly correlated grain structures (for both positively and negatively charged grains) take place at the maximum grain number density and a plasma temperature close to the minimum flame temperature (∼1600 K). In this case, the optimum grain radii lie in the range 4–10 μm and the maximum value of the parameter Γ is less than 200. Since the calculated values of Γ give an upper estimate, liquidlike ordered structures are most likely to form in a thermal plasma. Based on the results of the analysis, it is stated that an increase in the parameter Γ and, accordingly, the formation of plasma-crystal structures in a thermal plasma can only occur for positively charged grains. __________ Translated from Fizika Plazmy, Vol. 26, No. 7, 2000, pp. 626–632. Original Russian Text Copyright ? 2000 by Samarian, Vaulina, Nefedov, Petrov.