Interfacial friction of ethanol–water mixtures in graphene pores

The interfacial friction of fluid within nanoscale pores is important to nanofluidic devices and processes. Herein, molecular dynamics simulations have been used to study the interfacial flow resistance of ethanol–water mixtures confined within graphene-based nanochannels. The friction coefficients of the mixtures were investigated by considering the effects of slit pore width and mixture composition. The simulated results show that the flow friction coefficient is sensitive to the graphene slit pore size for ethanol-containing solution systems. In particular, the mixture composition has a significant impact on the friction coefficients for the mixture in 7–10 Å nanoslits, while the composition dependence of friction coefficients becomes weak at larger pore widths. In addition, qualitative theoretical analysis has been carried out to reveal the molecular origin of mixture friction behavior. The ethanol–wall interaction accounts for the major role on the mixture friction coefficients. The changing behavior of mixture friction coefficient is caused by the joint effects from the interfacial ethanol density and the potential energy barrier felt by ethanol molecules.     

Activity of the integrated on-line trypsin microreactor and nanoelectrospray emitter in acetonitrile–water co-solvent mixtures

The on-line trypsin microreactor and nanoelectrospray emitter for peptide mass mapping was demonstrated to be functional under aqueous conditions, but it is well known that electrospray ionization works more efficiently with organic co-solvents. Here, an activity assay was developed to determine the activity of this integrated device with acetonitrile as a co-solvent. Trypsin was immobilized onto fused silica capillaries pulled to fine tips as integrated microreactors coupled as nanoelectrospray ionization emitters. The model substrate N _α-benzoyl-l-arginine ethyl ester (2.5–20 μM) and an internal standard (N _α-Z-l-arginine (Z-Arg)) were dissolved in acetonitrile/water at various ratios and infused through the immobilized trypsin microreactor. The trypsin digestion product N _α-benzoyl-l-arginine (B-Arg) was detected by nanoelectrospray ionization coupled to an ion trap mass spectrometer, and its abundance compared to Z-Arg for quantification. The activity of immobilized trypsin in the microreactor was determined by measuring the ratio of the peak intensities of the hydrolysis product B-Arg to Z-Arg internal standard (three replicates). Kinetic parameters determined from Lineweaver–Burk analysis indicate an enhancement of trypsin activity upon immobilization and the addition of increasing ratios of acetonitrile up to 80 %, where K _m is 0.14 mM and V _max = 1.2 μM/s. Much lower immobilized trypsin activities were noted at 100 % ammonium acetate or 100 % acetonitrile than when the two solvents were mixed. The results clearly indicate that immobilized trypsin retains high biocatalytic activity in 20–80 % acetonitrile and is highly compatible with nanoelectrospray ionization mass spectrometry.     

Thermocapillary and thermosolutal Marangoni convection of ethanol and ethanol–water mixtures in a microfluidic device

We have investigated Marangoni convection at an evaporating meniscus of pure ethanol and of ethanol–water mixtures. The experiments were performed in a microfluidic device consisting of \(100\,{\upmu \text{m}}\) wide channels of quadratic cross section and a cylindric reservoir of the same height. Tracer particles were added to determine the velocity field using particle image velocimetry. In the case of pure ethanol, thermocapillary convection rolls similar to those reported in the literature were observed. The velocity of the flow can be controlled by local laser heating, confirming the thermocapillary nature of the process. Ethanol–water mixtures show distinctly different patterns when compared to pure ethanol: the flow velocity of the symmetric vortices is significantly increased and almost insensitive to heating on the symmetry line. By heating near the contact line of the meniscus, the symmetric two-roll state can be reversibly switched into an asymmetric one-roll state with the flow at the interface pointing in the direction of the temperature gradient. A consistent interpretation is obtained based on the assumption that solutocapillary instead of thermocapillary forces is the main driving mechanism in the case of the mixtures.     

Gas–liquid dynamics at low Reynolds numbers in pillared rectangular micro channels

Most heterogeneously catalyzed gas–liquid reactions in micro channels are chemically/kinetically limited because of the high gas–liquid and liquid–solid mass transfer rates that can be achieved. This motivates the design of systems with a larger surface area, which can be expected to offer higher reaction rates per unit volume of reactor. This increase in surface area can be realized by using structured micro channels. In this work, rectangular micro channels containing round pillars of 3 μm in diameter and 50 μm in height are studied. The flow regimes, gas hold-up, and pressure drop are determined for pillar pitches of 7, 12, 17, and 27 μm. Flow maps are presented and compared with flow maps of rectangular and round micro channels without pillars. The Armand correlation predicts the gas hold-up in the pillared micro channel within 3% error. Three models are derived which give the single-phase and the two-phase pressure drop as a function of the gas and liquid superficial velocities and the pillar pitches. For a pillar pitch of 27 μm, the Darcy-Brinkman equation predicts the single-phase pressure drop within 2% error. For pillar pitches of 7, 12, and 17 μm, the Blake-Kozeny equation predicts the single-phase pressure drop within 20%. The two-phase pressure drop model predicts the experimental data within 30% error for channels containing pillars with a pitch of 17 μm, whereas the Lockhart–Martinelli correlation is proven to be non-applicable for the system used in this work. The open structure and the higher production rate per unit of reactor volume make the pillared micro channel an efficient system for performing heterogeneously catalyzed gas–liquid reactions.     

A novel approach for estimating heat transfer coefficients of ethylene glycol–water mixtures

Ethylene glycol–water mixtures (EGWM) are vital for cooling engines in automotive industry. Scarce information is available in the literature for estimating the heat transfer coefficients (HTC) of EGWM using knowledge-based estimation techniques such as adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural networks (ANN) which offer nonlinear input–output mapping. In this paper, the supervised learning methods of ANFIS and ANN are exploited for estimating the experimentally determined HTC. This original research fulfills the preceding modeling efforts on thermal properties of EGWM and HTC applications in the literature. An experimental test setup is designed to compute HTC of mixture over a small circular aluminum heater surface, 9.5 mm in diameter, placed at the bottom 40-mm-wide wall of a rectangular channel 3 mm × 40 mm in cross section. Measurement data are utilized as the train and test data sets of the estimation process. Prediction results have shown that ANFIS provide more accurate and reliable approximations compared to ANN. ANFIS present correlation factor of 98.81 %, whereas ANN estimate 87.83 % accuracy for test samples.     

Sensing viscosity and density of glycerol–water mixtures utilizing a suspended plate MEMS resonator

A sensor suitable for online monitoring of viscosity and density of glycerol–water mixtures is presented. The device is based on Lorentz force excitation and features an integrated piezoresistive readout. The core sensing element is a rectangular vibrating plate suspended by four beam springs. Two of the plate-carrying springs comprise piezoresistors. With two additional resistors on the silicon rim they form a half Wheatstone-bridge. Through the conductive layer of the beam springs a sinusoidal excitation current is driven. In the field of a permanent magnet, the Lorentz force excites plate vibrations resulting in a bridge unbalance. We recorded both the frequency response of the amplitude and the phase of the bridge output. By evaluating the properties of the resonant system, it is possible to extract the glycerol percentage and, hence, the viscosity and the mass density of the mixtures.     

Decoherent dynamics of quantum correlations in qubit–qutrit systems

We study the dynamics of quantum correlations of qubit–qutrit systems under various decoherent channels. It is shown that the multi-local and local decoherent channels bring different influences for the dynamics of quantum correlations measured by negativity, quantum discord and geometric discord, which depend on the initial state parameters and the properties of the decoherent channels. We put emphasis on the phenomena such as entanglement sudden death, sudden transition between classical and quantum decoherence and stable quantum discord and geometric discord.     

Conserved water mediated H-bonding dynamics of Ser117 and Thr119 residues in human transthyretin–thyroxin complexation: Inhibitor modeling study through docking and molecular dynamics simulation

Transthyretin (TTR) is a protein whose aggregation and deposition causes amyloid diseases in human beings. Amyloid fibril formation is prevented by binding of thyroxin (T4) or its analogs to TTR. The MD simulation study of several solvated X-ray structures of apo and holo TTR has indicated the role of a conserved water molecule and its interaction with T4 binding residues Ser117 and Thr119. Geometrical and electronic consequences of those interactions have been exploited to design a series of thyroxin analogs (Mod1–4) by modifying 5′ or 3′ or both the iodine atoms of thyroxin. Binding energy of the designed ligands has been calculated by docking the molecules in tetrameric structure of the protein. Theoretically investigated pharmacological parameters along with the binding energy data indicate the potentiality of 3′,5′-diacetyl-3,5-dichloro-l-thyronine (Mod4) to act as a better inhibitor for TTR-related amyloid diseases.     

MD simulation of a NaCl solution in equimolar methanol–water mixture

Molecular dynamics simulations of the equimolar methanol–water mixture and NaCl solution in this binary solvent at room temperature have been performed. The solvent molecules have been described using three-site flexible models. The structural properties of the binary solvent and NaCl solution confirm the tendencies previously observed. Both ions are preferentially solvated by the methanol molecules, but this phenomenon vanishes gradually with increasing methanol concentration.     

Nafion-film-based micro–nanofluidic device for concurrent DNA preconcentration and separation in free solution

This paper presents a Nafion-film-based micro–nanofluidic device for concurrent DNA preconcentration and separation. The principle of the device is based on the combination of (a) ion concentration polarization phenomenon at the junction of the microchannel and the nanochannels in the Nafion film to form opposing electrophoretic and electroosmotic forces acting on the DNAs and (b) end-labeled-free solution electrophoresis to harness the charge-to-mass ratio for molecular differentiation. The experiments successfully demonstrated concurrent preconcentration and separation of DNA mixture in free solution within 240 s, yielding concentration ratios up to 1,150× and separation resolution of 1.85. The effect of applied electric field on the concentration and separation performance was also investigated. The device can be used as a key sample preparation element in conjunction with micro- or nano-fluidic sensors for microTAS functionality.     

Asymptotic convergence of constrained primal–dual dynamics

This paper studies the asymptotic convergence properties of the primal–dual dynamics designed for solving constrained concave optimization problems using classical notions from stability analysis. We motivate the need for this study by providing an example that rules out the possibility of employing the invariance principle for hybrid automata to study asymptotic convergence. We understand the solutions of the primal–dual dynamics in the Caratheodory sense and characterize their existence, uniqueness, and continuity with respect to the initial condition. We use the invariance principle for discontinuous Caratheodory systems to establish that the primal–dual optimizers are globally asymptotically stable under the primal–dual dynamics and that each solution of the dynamics converges to an optimizer.     

Impact of control on agitation–sedation dynamics

Agitation in the critically ill damages patient health and increases length of stay and healthcare costs. The control model presented captures the essential dynamics of the agitation–sedation system, and is statistically validated using recorded infusion data for 37 patients. Derivative focused control is seen to provide an essentially bolus-driven management approach, which is shown to be an effective means of managing agitation, given consistent agitation measurement. Improved agitation management using feedback of patient agitation reduces the modelled mean and peak agitation levels 68.4% and 52.9% on average, respectively, illustrating the effectiveness of simple control in this non-linear system.     

Comparative study of liquid–liquid extraction in miniaturized channels over other conventional extraction methods

We demonstrate the complexion of extracting an aromatic organic compound in microchannel system over other conventional methods like batch extraction, microwave assisted extraction and ultrasonic assisted extraction. Extraction studies were carried out for phenol, an aromatic organic compound from dodecane into distilled water. The extraction process is studied for a varying extraction time, microwave energy, percent ultrasonic power and micro channel diameter. Batch extraction is carried out at 25, 50, 100 and 200 rpm, microwave assisted extraction is carried out at 119, 231, 385, 539 and 700 W, ultrasonic assisted extraction is conducted in a 130 W ultrasonicator at a frequency of 20 kHz and amplitude of 10, 20, 30, 40 and 50 % for a varying extraction time of 1, 2, 4, 8, 16 and 32 min. While, the microsystem based extraction was carried out in a circular T junction microchannel. Among the various flow types in a microchannel, slug flow is intensified for its better hydrodynamic and mass transfer properties. Microchannel having diameter 600, 800, 1,000, 1,200 µm is used and compared for better extraction percentage. Experimental results manifested that 600 µm showed better extraction percentage. When comparing the extraction percentage of phenol acquired in microchannel system with other convention methods we observed the following ladder: slug based extraction > ultrasonic assisted extraction > microwave assisted extraction > batch extraction. Also, the microsystem based extraction needed just half of the operation time required by other conventional methods for achieving maximum extraction percentage. This subsequently causes effective usage of chemicals, thereby reducing chemical wastage. And, high efficient extraction can be obtained at very less time.     

Mathematical modeling in the geoinformation problem of the dynamics of geomigration under space–time nonlocality

A mathematical model is set up to analyze the dynamics of locally time- and space-nonequilibrium migration–consolidation processes in a porous earth saturated with salt solutions under mass transfer. The corresponding nonlinear boundary-value problem is stated, an algorithm of its approximate solution is presented, and the results of the numerical implementation of the algorithm are given.     

Landsat-satellite-based analysis of spatial–temporal dynamics and drivers of CyanoHABs in the plateau Lake Dianchi

ABSTRACT

Dianchi Lake, located in southwest China’s Yungui plateau, is facing severe eutrophication and frequent outbreaks of harmful cyanobacteria blooms (CyanoHABs). It is of great significance to monitor the occurrence and development of CyanoHABs in Dianchi Lake over a long period and analyse the main influences. Based on Landsat Thematic Mapper/Enhanced Thematic Mapper Plus/Operational Land Imager 1986–2016 data, we derived the distribution of the CyanoHABs in Dianchi Lake, and analysed spatial–temporal dynamics of the CyanoHABs by correlation with nutrition, meteorological, and humanities data. The results showed that the first outbreak of CyanoHABs in Dianchi Lake occurred in 1987, which is likely to be influenced by a rapid increase of nutrients in the lake, while the weather conditions also have some impact on the CyanoHABs occurrence. After 1990, the frequency of CyanoHABs is relatively high in the water near Longmen village, Fubao Bay, Hui Bay, and the lake inlet of the Panlong River to the north of Waihai in Dianchi Lake from June to November every year. Moreover, the CyanoHABs increased year by year until 2000. This is closely related to population growth and economic development. Furthermore, a large amount of precipitation and small wind speeds can also promote the occurrence of CyanoHABs. After 2000, the frequency of CyanoHABs decreased, as the large-scale management of water pollution in Dianchi Lake achieved certain effects. The area and frequency of CyanoHABs from 2011 to 2014 are the smallest in the last 20 years, which may be related to the large-scale planting of Eichhornia crassipes in the north of Dianchi Lake.     

Molecular dynamics–continuum hybrid simulation for condensation of gas flow in a microchannel

A molecular dynamics-continuum coupling method combining fluid flow and heat transfer is developed to study the condensation process of gas flow in a microchannel. The computational domain is decomposed into particle (P), continuum (C) and overlap (O) regions with solving approaches of molecular dynamics simulation, finite volume method and the developed coupling method, respectively. Continuities of momentum and energy in O region are ensured by constraint dynamics and the Langevin method. The validity of the developed method is confirmed by a good agreement between hybrid results and analytical solutions from two cases including the unsteady dynamical and thermal problems. For the condensation process of gas flow, the hybrid transient velocity and temperature fields indicate that the process does not progress smoothly but wavily with noticeable fluctuation, leading to oscillation in temperature field and recirculation flow in velocity field. Analysis based on heat and mass transfer is carried out in P region, and the Kapitza resistance and the thermal conductivity in liquid are obtained with the satisfying agreement with experimental data, which shows the availability of the developed model for the investigation on the thermal boundary resistance. The good performance had demonstrated that the developed coupling method and computational model are available to provide a multiscale overview in dynamical and thermal problems including phase-transition from nanoscale to microscale, which will show significantly potential in micro fluidics and thermal engineering.     

Response of NDVI dynamics to precipitation in the Beijing–Tianjin sandstorm source region

This article analysed the spatio-temporal changes in vegetation cover in the Beijing–Tianjin sandstorm source region in China and related these changes to vegetation types based on the Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data set from 1982 to 2006. The annual maximum NDVI and peak time were identified. The different periods (1–12 months) of accumulated precipitation before the peak time were then calculated at the grid scale for each year. On this basis, the NDVI–rainfall relationship and the temporal responses in this area were studied by calculating the correlation coefficient between the annual maximum NDVI and different periods (1–12 months) of accumulated precipitation before the occurrence of the annual maximum NDVI for each pixel. The results show an upward trend in regional vegetation, a significant recovery efficiency for grassland, and the evident degradation of cropland. Peak plant growth is significantly related to precipitation and is strongly positively correlated with precipitation in the previous period (1 month) regardless of vegetation type. The regions showing the strongest correlations between peak plant growth and 1 month cumulative rainfall are the western desert grassland, grassland to forest in the transitional hill regions, the mountains of Yanshan, and the Greater Hinggan Mountains.     

Feedback control of Hodgkin–Huxley nerve cell dynamics

Nerve cells communicate by generation and transmission of short electrical pulses (action potentials). A cascaded feedback control scheme consisting of an optimal controller (model predictive control, MPC) and a state feedback controller to control the time-courses of the biophysical state variables underlying action potential generation was developed and evaluated in simulations. The control scheme was shown to provide new means for action potential generation, suppression of oscillations and blockage of action potential transmission. These new theoretical developments could represent a starting point for the design of new closed-loop electrical stimulation systems for patients suffering from different nerve system dysfunctions.     

Fabrication of SU-8 photoresist micro–nanofluidic chips by thermal imprinting and thermal bonding

Micro–nanofluidic chips have been widely applied in biological and medical fields. In this paper, a simple and low-cost fabrication method for micro–nano fluidic chips is proposed. The nano-channels are fabricated by thermal nano-imprinting on an SU-8 photoresist layer followed by thermal bonding with a second SU-8 photoresist layer. The micro-channels are produced on the second layer by UV exposure and then thermal bonded by a third layer of SU-8 photoresist. The final micro–nano fluidic chip consists of micro-channels (width of 200.0 ± 0.1 μm and, depth of 8.0 ± 0.1 μm) connected by nano-channels (width of 533 ± 6 nm and, depth of 372 ± 6 nm), which has great potential in molecular filtering and detection.