Electro-Osmotic Flow and Mixing in Heterogeneous Microchannels

Analytical and numerical studies of secondary electro-osmotic flow EOF and its mixing in microchannels with heterogeneous zeta potentials are carried out in the present work. The secondary EOFs are analyzed by solving the Stokes equation with heterogeneous slip velocity boundary conditions. The analytical results obtained are compared with the direct numerical simulation of the Navier-Stokes equations. The secondary EOFs could transport scalar in larger areas and increase the scalar gradients, which significantly improve the mixing rate of scalars. It is shown that the heterogeneous zeta potentials could generate complex flow patterns and be used to enhance scalar mixing.

A simple method to simulate shrinkage-induced cracking in cement-based composites by lattice-type modeling

A new numerical procedure is proposed to investigate cracking behaviors induced by mismatch between the matrix phase and aggregates due to matrix shrinkage in cement-based composites. This kind of failure processes is simplified in this investigation as a purely spontaneous mechanical problem, therefore, one main difficulty during simulating the phenomenon lies that no explicit external load serves as the drive to propel development of this physical process. As a result, it is different from classical mechanical problems and seems hard to be solved by using directly the classical finite element method (FEM), a typical kind of "load -> medium -> response" procedures. As a solution, the actual mismatch deformation field is decomposed into two virtual fields, both of which can be obtained by the classical FEM. Then the actual response is obtained by adding together the two virtual displacement fields based on the principle of superposition. Then, critical elements are detected successively by the event-by-event technique. The micro-structure of composites is implemented by employing the generalized beam (GB) lattice model. Numerical examples are given to show the effectiveness of the method, and detailed discussions are conducted on influences of material properties.

Shrinkage of Gobiocypris rarus, Procypris rabaudi, and Sinilabeo rendahli preserved in formalin

Length measurements of preserved fishes are necessary in many types of fish surveys because logistics often do not allow for fish measurement immediately after catch. If the fixative causes significant shrinkage, then the preserved lengths cannot be directly used to indicate accurate live lengths. The objective of this study was to determine how preservation in formalin affects standard length of Gobiocypris rarus larvae (24-day-old and newly hatched), larval Procypris rabaudi (4-day-old), and larval Sinilabeo rendahli (12-day-old). Fishes were measured (to nearest 0.01 mm) and individually fixed in the appropriate formalin solution (2.5% or 5.0% formalin), then re-measured at 0.5, 1, 3, 7, 14, 30, 45 and 75 days after preservation to follow the time course of shrinkage. Most of the shrinkage occurred within the first half day after preservation. The 5.0% formalin caused a higher relative shrinkage rate than did the 2.5% solution; however, the difference was not statistically significant. In G. rarus, initial shrinkage of newly hatched larvae was higher than that of 24-day-old larvae.

Nanocavity shrinkage and preferential amorphization during irradiation in silicon

We model the recent experimental results and demonstrate that the internal shrinkage of nanocavities in silicon is intrinsically associated with preferential amorphization as induced by self-ion irradiation. The results reveal novel thermodynamic nonequilibrium properties of such an open-volume nanostructure in condensed matter and also of covalently bound amorphous materials both at nanosize scale and during ultrafast interaction with energetic beam.

Nanoinstabilities as revealed by shrinkage of nanocavities in silicon during irradiation

While the thermodynamic nonequilibrium properties of nanoparticles are being extensively studied, the thermodynamic nonequilibrium properties of their counterpart: nanocavities, however, are less noticed. Here, we systematically review and comprehensively model the recently published results on the newly-found thermodynamic nonequilibriurn properties of nanocavities in covalently bound materials during energetic beam irradiation. We also review and model the thermodynamic nonequilibrium properties of nanoparticles. The review and modelling not only demonstrates the novel nonequilibriurn properties of such an open-volume nanostructure during external excitation but also gives a deep insight into the nonequilibrium thermodynamics of amorphous structures and the difference in the behaviours of defects in crystalline and in amorphous silicon. Especially, the review and modelling leads to two new concepts:anti-symmetry relation between a nanoparticle and a nanocavity；energetic beam induced-soft mode and lattice instability in condensed matter；which reveals that structure of a condensed matter would be unstable not only at nanosize scale but also at a nanotime scale in general. It is also reveals that such nanoinstabilities would be more pronounced in an amorphous structure than in a crystalline structure.

Shrinkage of nanocavities in silicon during electron beam irradiation

An internal shrinkage of nanocavity in silicon was in situ observed under irradiation of energetic electron on electron transmission microscopy. Because there is no addition of any external materials to cavity site, a predicted nanosize effect on the shrinkage was observed. At the same time, because there is no ion cascade effect as encountered in the previous ion irradiation-induced nanocavity shrinkage experiment, the electron irradiation-induced instability of nanocavity also provides a further more convincing evidence to demonstrate the predicted irradiation-induced athermal activation effect. (c) 2006 American Institute of Physics.

An Electro-osmotic Fuel Pump for Dircet Methanol Fuel Cells

This work reports on the design and performance evaluation of a miniature direct methanol fuel cell(DMFC)integrated with an electro_osmotic(EO)pump for methanol delivery.Electro-osmotic pumps require minimal parasitic power while boasting no moving parts and simple fuel cell integration.Here ,aneletro-osmotic pump is realized from a commercially available porous glass frit.We characterize a custom-fabricated DMFC with a free convection cathode and coupled to an extennal electro-osmotic pump operated at applied potentials of 4.0,7.0,and 10V.Maximum gross power density of our free convection DMFC(operated at 50°)is 55 mW/cm2 using 4.0 mol/L concentration methanol solution supplied by the EO pump.Experimental results show that electro-osmotic pumps can deliver 2.0,4.0 and 8.0mol/L methanol/water mixtures to DMFCs while utilizing ~5.0% of the fuel cell power.Furthermore ,we discuss pertinent design considerations when using electro-osmotic pumps with DMFCs and areas of further study.

THE COMPOUND EYE AS AN INDICATOR OF AGE AND SHRINKAGE IN ANTARCTIC KRILL

Laboratory studies have shown that Antarctic krill (Euphausia superba) shrink if maintained in conditions of low food availability. Recent studies have also demonstrated that E. superba individuals may be shrinking in the field during winter. If krill shrink during the winter, conclusions reached by length-frequency analysis may be unreliable because smaller animals may not necessarily be younger animals. In this study, the correlation between the body-length and the crystalline cone number of the compound eye was examined. Samples collected in the late summer show an apparent linear relationship between crystalline cone number and body-length. From a laboratory population, it appears that when krill shrink the crystalline cone number remains relatively unchanged. If crystalline cone number is little affected by shrinking, then the crystalline cone number may be a more reliable indicator of age than body-length alone. The ratio of crystalline cone number to body-length offers a method for detecting the effect of shrinking in natural populations of krill. On the basis of the crystalline cone number count, it appears from a field collection in early spring that E. superba do shrink during winter.

Quantifying Cell Binding Kinetics Mediated By Surface-Bound Blood Type B Antigen To Immobilized Antibodies

Cell adhesion is crucial to many biological processes, such as inflammatory responses, tumor metastasis and thrombosis formation. Recently a commercial surface plasmon resonance (SPR)-based BIAcore biosensor has been extended to determine cell binding mediated by surface-bound biomolecular interactions. How such cell binding is quantitatively governed by kinetic rates and regulating factors, however, has been poorly understood. Here we developed a novel assay to determine the binding kinetics of surface-bound biomolecular interactions using a commercial BIAcore 3000 biosensor. Human red blood cells (RBCs) presenting blood group B antigen and CM5 chip bearing immobilized anti-B monoclonal antibody (mAb) were used to obtain the time courses of response unit, or sensorgrams, when flowing RBCs over the chip surface. A cellular kinetic model was proposed to correlate the sensorgrams with kinetic rates. Impacts of regulating factors, such as cell concentration, flow duration and rate, antibody-presenting level, as well as pH value and osmotic pressure of suspending medium were tested systematically, which imparted the confidence that the approach can be applied to kinetic measurements of cell adhesion mediated by surface-bound biomolecular interactions. These results provided a new insight into quantifying cell binding using a commercial SPR-based BIAcore biosensor.

Case Study: Influence Of Morphological Changes On Flooding In Jingjiang River

The middle reach of the Yangtze River, customarily called the Jingjiang River, together with its diversion channels and Dongting Lake, form a large complicated drainage system. In the last five decades, significant geomorphological changes have occurred in the drainage system, including the shrinkage of diversion channels, contraction of Dongting Lake, changes in the rating curve at the Luoshan station, and cutoffs of the lower Jingjiang River. These changes are believed to be the cause of the occurrence of abnormal floods in the Jingjiang River. Qualitative analyses suggest that the first three factors aggravate the flood situation in the lower Jingjiang River, while the last factor seems beneficial for flood prevention. To quantitatively evaluate these conclusions, a finite-volume numerical model was constructed. A series of numerical simulations were carried out to test the individual and combined effects of the aforementioned four factors, and these simulations showed that high flood stages in the Jingjiang River clearly are related to the geomorphological changes.