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Light quality and intensity can have a significant impact on plant health and crop productivity. Chlorophylls and carotenoids are classes of plant pigments that are responsible for harvesting light energy and protecting plants from the damaging effects of intense light. Our understanding of the role played by plant pigments in light sensitivity has been aided by light-sensitive mutants that change colors upon exposure to light of variable intensity. In this study, we conducted transcriptomic, metabolomic, and hormone analyses on a novel yellowing mutant of pepper (yl1) to shed light on the molecular mechanism that regulates the transition from green to yellow leaves in this mutant upon exposure to high-intensity light. Our results revealed greater accumulation of the carotenoid precursor phytoene and the carotenoids phytofluene, antheraxanthin, and zeaxanthin in yl1 compared with wild-type plants under high light intensity. A transcriptomic analysis confirmed that enzymes involved in zeaxanthin and antheraxanthin biosynthesis were upregulated in yl1 upon exposure to high-intensity light. We also identified a single bHLH transcription factor, bHLH71-like, that was differentially expressed and positively correlated with light intensity in yl1. Silencing of bHLH71-like in pepper plants suppressed the yellowing phenotype and led to reduced accumulation of zeaxanthin and antheraxanthin. We propose that the yellow phenotype of yl1 induced by high light intensity could be caused by an increase in yellow carotenoid pigments, concurrent with a decrease in chlorophyll accumulation. Our results also suggest that bHLH71-like functions as a positive regulator of carotenoid biosynthesis in pepper.

The critical need to enhance the quality of indoor air leads to the improvement of catalyst activity for the removal of formaldehyde. Sepiolite can be utilized in catalytic reactions for its unique structure, composition and high surface area. The adhesion between sepiolite fibers and the blocked microporous channel (by impurities) demands the activation of natural sepiolite through acid treatment. This treatment successfully produces acid-modified sepiolite Pt-supported samples. The impacts of different acid concentrations, Pt loading content and calcination temperature on catalytic activity for formaldehyde (HCHO) oxidation are studied. The catalytic activity of HCHO is characterized and evaluated by techniques including specific surface area, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy and transmission electron microscopy. The results show the maximum specific area of sepiolite at the optimized 0.06 M acid concentration. Among all the prepared samples, the 0.02Pt/Sep catalyst calcined at 500 °C exhibits the highest catalytic activity for the oxidation of HCHO.

Capsicum annuum is also known as chili which is one of the most important vegetable crops grown in the world. Breeding new varieties with heterosis could improve the quality of pepper, increase yield, growth potential, disease resistance, adaptability, and seed viability. To investigate the heterosis among three cross combinations of different parents, the mRNA-miRNA integrated analysis was performed. A total number of 22,659,009 to 36,423,818 clean data were generated from mRNA-seq with 81 libraries, and the unique mapped reads were from 35,495,567 (86.81%) to 46,466,622 (88.95%). The plant-hormone signal transduction pathway (40 genes) was detected with a higher DEG number. The SAUR32L, GID1, PYR1, EIN2. ERF1, PR1, JAR1-like, IAA from this pathway play a key role in plant development. From the miRNA-seq, the number of clean reads was ranging from 12,132,221 to 25,632,680. A total of 220 miRNAs were predicted in this study, and all of them were identified as novel miRNA. The top three candidate KEGG pathways of miRNA were ribosome signaling pathway (13 miRNAs), spliceosome pathway (13 miRNAs), and plant hormone signal transduction pathways (10 miRNAs). With the mRNA and miRNA integrated analysis, we found some key genes were regulated by some miRNAs. Among them, the scarecrow-like 6 protein can be up or down regulated by mir8, mir120, mir184, mir_214, mir125, and mir130. The function of Della protein was regulated by mir24, mir74, mir94, mir139, and mir190. This study contributes to understanding how heterosis regulates the traits, such as crop production, fruit weight, and fruit length.

Long non-coding RNAs (lncRNAs) participate in many biological processes and play extremely important regulatory roles in animals and plants. However, little is known about lncRNAs and their functions in cytoplasmic male sterility (CMS) during the developmental process of floral buds in pepper. In the present study, we systematically identified lncRNAs in the pepper CMS line (9704A) and maintainer line (9704B) using high-throughput sequencing and bioinformatic analyses. A total of 10,655 putative lncRNAs were identified during the developmental process of floral buds, and 262, 298 and 905 differentially expressed lncRNAs (DELs) were obtained in three stages, respectively. Moreover, 1137 unique DELs were identified between 9704A and 9704B, and their cis and trans target protein-coding genes were predicted. We used Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses to decipher the potential functions of DELs. The cell and cellular process GO terms were significantly enriched, and KEGG pathway analysis showed enrichments in the pathways for starch and sucrose metabolism genes, pentose and glucuronate interconversions, all of which were highly associated with pollen development. Besides, a regulatory network about the lncRNAs and the protein-coding genes involved in the formation of CMS was constructed. Our findings laid a foundation for further studies on the function of lncRNAs in pollen development and provided valuable insights into the regulatory mechanism underlying CMS.

Dwarfing is the development trend of pepper breeding. It is of great practical and scientific value to generate new dwarf germplasms, and identify new genes or alleles conferring dwarf traits in pepper. In our previous study, a weakly BR-insensitive dwarf mutant, E29, was obtained by EMS mutagenesis of the pepper inbred line 6421. It can be used as a good parent material for breeding new dwarf varieties. Here, we found that this dwarf phenotype was controlled by a single recessive gene. Whole-genome resequencing, dCAPs analysis, and VIGs validation revealed that this mutation was caused by a nonsynonymous single-nucleotide mutation (C to T) in CaBRI1. An enzyme activity assay, transcriptome sequencing, and BL content determination further revealed that an amino-acid change (Pro1157Ser) in the serine/threonine protein kinase and catalytic (S_TKc) domain of CaBRI1 impaired its kinase activity and caused the transcript levels of two important genes (CaDWF4 and CaROT3) participating in BR biosynthesis to increase dramatically in the E29 mutant, accompanied by significantly increased accumulation of brassinolide (BL). Therefore, we concluded that the novel single-base mutation in CaBRI1 conferred the dwarf phenotype and resulted in brassinosteroid (BR) accumulation in pepper. This study provides a new allelic variant of the height-regulating gene CaBRI1 that has theoretical and practical values for the breeding of the plants suitable for the facility cultivation and mechanized harvesting of pepper varieties.

This paper presents the electrical and thermal modeling of an Integrated Drive Unit (IDU) in a production electric SUV (GAC Aion LX). The IDU consists of a permanent magnet synchronous motor (PMSM), an inverter and a transmission gear box, and is cooled by circulating coolant through inverter and PMSM. Three IDU motor models were developed: Lumped Parameter Model, Saturated PMSM Model, and Efficiency-Map Model. Heat generation of the motor components, obtained from electromagnetic FEA simulation, was used as input to a transient Lumped Parameter Thermal Network (LPTN) model of the IDU. The IDU models were developed using MATLAB/ Simulink/ Simscape. The performance and inner temperature field of the IDU can be predicted real-time at various drive conditions, crucial for IDU design optimization and real-time temperature prediction.

Limited knowledge is available for phosphorylation modifications in pepper (Capsicum annuum L.), especially in pepper fruit development. In this study, we conducted the first comprehensive phosphoproteomic analysis of pepper fruit at four development stage by Tandem Mass Tag proteomic approaches. A total of 2639 unique phosphopeptides spanning 1566 proteins with 4150 nonredundant sites of phosphorylation were identified, among which 2327 peptides in 1413 proteins were accurately quantified at four different stages. Mature Green (MG) to breaker stage showed the largest number of differentially expressed phosphoproteins and the number of downregulated phosphoproteins was significantly higher than that of upregulated after MG stage. Twenty seven phosphorylation motifs, including 22 pSer motifs and five pThr motifs and 85 kinase including 28 serine/threonine kinases, 14 receptor protein kinases, six mitogen-activated protein kinases, seven calcium-dependent protein kinases, two casein kinases, and some other kinases were quantified. Then the dynamic changes of phosphorylated proteins in ethylene and abscisic acid signaling transduction pathways during fruit development were analyzed. Our results provide a cascade of phosphoproteins and a regulatory network of phosphorylation signals, which help to further understand the mechanism of phosphorylation in pepper fruit development.

Long non-coding RNAs (lncRNAs) have been shown to play critical regulatory roles in diverse biological processes in plants. However, the presence of lncRNAs and their potential functions in hot pepper are still unknown. Using strand-specific RNA-sequencing, a total of 2505 putative lncRNAs were identified in the fruits of hot pepper. The lncRNAs were transcribed from all pepper chromosomes and 95.37% of them originated from intergenic regions. And 1066 lncRNAs were differentially expressed among the four samples during pepper fruit development. Many potential protein-coding (PC) genes targeted by lncRNAs with cis or trans-acting were also identified. Six of them and their target genes were further validated by quantitative RT-PCR. Some of these target genes were involved in plant hormone signal transduction, cell wall formation and carotenoid biosynthesis, indicating the roles of lncRNAs in the regulation of fruit development and quality. This study identified a large number of lncRNAs in hot pepper, thereby providing some insights into the fruit development of hot pepper.

This paper presents thermal modeling of a lithiumion battery pack to be used in a Plug-in Hybrid Electrical Vehicle (PHEV). The battery pack consists of eight modules (totally 96 prismatic cells) cooled by circulating 50/50 ethylene glycol-water mixture in a cold plate. Three cases, e.g., (a) battery heating up from -30 ˚C environment, (b) high-speed ramping in pure electrical driving mode, and (c) NEDC cycle in pure electrical driving mode, were modeled using a 1D simulation software. To study the internal temperature variation inside modules, each battery module was further decomposed into three nodes in the height direction, showing 5-8 ˚C temperature variation. We also conducted CFD to study the fluid flow and heat transfer in the cold plates, and the results are in great agreement with theoretical predictions. The work provides deep insight of thermal physics and can greatly help thermal design of the battery pack.

To understand the mechanism of the color formation of pepper fruit, integrative analysis of the metabolome and transcriptome profiles was performed in pepper varieties with 4 different fruit colors. A total of 188 flavonoids were identified, and most of the anthocyanins, flavonols and flavones showed markedly higher abundances in purple variety than in other varieties, which was linked to the high expression of flavonoid synthesis and regulatory genes. Using weighted gene co-expression network analyses, modules related to flavonoid synthesis and candidate genes that regulate flavonoid synthesis and transport were identified. Furthermore, the analysis of 12 carotenoids showed that the content of xanthophylls at 50 days after anthesis was significantly different between the four pepper varieties, which was resulted from the differential expressions of genes downstream of the carotenoid pathway. Our results provide new insights into the understanding of the synthesis and accumulation of flavonoids and carotenoids in pepper fruit.

This paper presents the thermal modeling and measurement of an electric traction motor used in a production electric vehicle, i.e., GAC’s 2017 pure electric SUV GE3. The motor is a high-efficiency permanent magnet (PM) synchronous motor which is actively cooled by circulating coolant through a water jacket. The motor’s electromagnetic loss (i.e., internal heat generation) in the stator and rotor was modeled and measured at typical conditions, which was used as input to the thermal simulations. To achieve accurate modeling results, the axial thermal conductivity of the motor’s stator/rotor lamination stack was measured to be ~3.5 W/m-K using special equipment. Theoretic heat transfer analysis, CFD numerical simulation, and lumped parameter thermal network (LPTN) method were conducted to model the heat transfer of the traction motor. Measurement of the rotor temperature using slip ring and infrared (IR) thermography validifies the CFD and lumped parameter thermal network (LPTN) modeling results.

WRKY proteins are a large group of plant transcription factors that are involved in various biological processes, including biotic and abiotic stress responses, hormone response, plant development, and metabolism. WRKY proteins have been identified in several plants, but only a few have been identified in Capsicum annuum. Here, we identified a total of 62 WRKY genes in the latest pepper genome. These genes were classified into three groups (Groups 1-3) based on the structural features of their proteins. The structures of the encoded proteins, evolution, and expression under normal growth conditions were analyzed and 35 putative miRNA target sites were predicted in 20 CaWRKY genes. Moreover, the response to cold or CMV treatments of selected WRKY genes were examined to validate the roles under stresses. And alternative splicing (AS) events of some CaWRKYs were also identified under CMV infection. Promoter analysis confirmed that CaWRKY genes are involved in growth, development, and biotic or abiotic stress responses in hot pepper. The comprehensive analysis provides fundamental information for better understanding of the signaling pathways involved in the WRKY-mediated regulation of developmental processes, as well as biotic and abiotic stress responses.

MicroRNAs (miRNAs) are non-coding small RNAs which play an important regulatory role in various biological processes. Previous studies have reported that miRNAs are involved in fruit development in model plants. However, the miRNAs related to fruit development and quality in hot pepper (Capsicum annuum L.) remains unknown. In this study, small RNA populations from different fruit ripening stages and different varieties were compared using next-generation sequencing technology. Totally, 59 known miRNAs and 310 novel miRNAs were identified from four libraries using miRDeep2 software. For these novel miRNAs, 656 targets were predicted and 402 of them were annotated. GO analysis and KEGG pathways suggested that some of the predicted miRNAs targeted genes involved in starch sucrose metabolism and amino sugar as well as nucleotide sugar metabolism. Quantitative RT-PCR validated the contrasting expression patterns between several miRNAs and their target genes. These results will provide an important foundation for future studies on the regulation of miRNAs involved in fruit development and quality.

This paper presents a microfluidic device that can passively reduce fluctuations in an upstream fluid flow and generate a largely steady flow in a microfluidic system. The device features a series of compliant membranes that form deformable walls of a microchannel. For an incoming pulsatile flow, passive vibrations of the membranes allow the fluid to be accumulated for an overflow and discharged for an underflow, resulting in drastically reduced fluctuations in flow rate and pressure. A lumped-parameter model is developed to simulate the device characteristics, in which the coupling of membrane vibrations and fluid flow in individual channel sections associated with a single membrane is first represented by squeeze-film theory and inertia-free structural dynamics. The entire device is next represented as a system by connecting individual channel sections in series. The model is numerically solved, and the results agree with experiments. The theoretical and experimental results both show that a five-membrane device can stabilize a pulsating flow by a factor of about 20. These results also reveal that smaller average flow rate, smaller fluctuation, and higher fluctuation frequency lead to more effective flow stabilization. With these characteristics, the flow stabilizer can be used to obtain steady flow in microfluidic systems.

We present a MEMS sensor aiming to enable continuous monitoring of glucose levels in diabetes patients. The device features a magnetically-driven vibrating microcantilever, which is situated in a microchamber and separated from the environment by a semi-permeable membrane. Glucose sensing is based on affinity binding principles using a solution of dextran concanavalin-A (Con A) as the sensing fluid. The glucose concentration is determined by detecting viscosity changes induced by the binding of glucose to Con A through the measurement of the cantilever's vibration parameters. The device is capable of measuring physiologically relevant glucose concentrations from 0 to 25 mM with a resolution better than 0.025 mM and a phase sensitivity better than 0.4° mM−1. The response of the sensor to glucose concentration changes has a time constant down to 4.27 min, and can be further improved with optimized device designs.

PurposeThe goal of this review paper is to provide information on several commonly used thermography techniques in semiconductor and micro‐device industry and research today.Design/methodology/approachThe temperature imaging or mapping techniques include thin coating methods such as liquid crystal thermography and fluorescence microthermography, contact mechanical methods such as scanning thermal microscopy, and optical techniques such as infrared microscopy and thermoreflectance. Their principles, characteristics and applications are discussed.FindingsThermal issues play an important part in optimizing the performance and reliability of high‐frequency and high‐packing density electronic circuits. To improve the performance and reliability of microelectronic devices and also to validate thermal models, accurate knowledge of local temperatures and thermal properties is required.Originality/valueThe paper provides readers, especially technical engineers in industry, a general knowledge of several commonly used thermography techniques in the semiconductor and micro‐device industries.

This paper presents a self-adaptive microfluidic variable resistor that accomplishes passive control of liquid flows by exploiting the large compliance of elastomeric polymers such as polydimethylsiloxane. The device features a compliant microstructure embedded in a microchannel that consists of a flexible thin flap and a stiff stopper located in close proximity. The shape and size of the gap between the flap and stopper vary with the applied pressure, resulting in small resistance with respect to forward flow and large resistance with respect to reverse flow. The variable flow resistor shows an interesting diode behavior because its flow resistance is drastically different for different directions of applied pressures and is self-adaptive in the sense that its flow resistance varies with reverse pressure in such a way that the resulting flow rate remains a constant. That is, the flow resistor can be used as a check valve and, more importantly, a passive flow regulator. Prototype devices have demonstrated regulation of nearly constant water flow rates from 0.21 to 1.2 ml/min, with variations less than 3%, under driving pressures that vary significantly from 100 to over 200 kPa. Three-dimensional fluid-structure interaction simulations have been performed to investigate the interactions between the fluid flow and flap deflection. The simulation results agree with the experimental data and provide insight into the device characteristics. Based on its single-layer planar configuration, passive operation over a large pressure range, and use of a flexible and inexpensive polymer, this self-adaptive variable flow resistor is well suited to flow control in lab-on-a-chip systems

This paper presents a novel latchable phase-change microvalve that can potentially be used for flow gating in portable lab-on-a-chip systems where minimal energy consumption is desired. The microvalve innovatively exploits paraffin wax of low melting point, whose solid–liquid phase changes allow the closing and opening of fluid flow through deformable microchannel ceiling. The latchable phase-change actuation scheme can be used in an active valve to shut off and open fluid flow. Valve switching is initiated by melting of paraffin through heating, with an additional pneumatic pressure used for valve switching from open to closed state. Energy consumption is only required during the valve switching. After paraffin solidifies the switched state is subsequently maintained passively without further consumption of energy. The microvalve can be fabricated from PDMS through the multilayer soft lithography technique. Testing results demonstrate that the valve has response times of 60 s for closing and 100 s for opening; when closed, the valve can passively withstand a pressure up to 35 kPa without significant leakage. The relatively slow time response of the proof-of-concept device can be readily improved by integrating on-chip heaters, while the latchability of the microvalve can be improved by optimizing the wax chamber and membrane design. Compared to existing latchable phase-change valves, the thin compliant channel ceiling of the valve separates the fluid channel from the wax chamber. Therefore, the microvalve is free of potential contamination of the fluid by the paraffin wax. In addition, the improved sealing offered by the compliant membrane makes the valve robust and flexible in operation, allowing large ranges of initiation pressure generated from various actuation schemes.

This paper presents three types of microfabricated planar check valves that exploit the large compliance of elastomeric polymers such as polydimethylsiloxane (PDMS). The micro-check valves consist of a thin compliant flap and a rigid stopper embedded in close proximity in a microchannel. The flap is perpendicular to the flow and lies near the stopper, forming a restricted fluid path inside the channel. The shape and size of the gap between the flap and stopper vary with the applied pressure, resulting in large flow resistance for forward flow and small resistance for reverse flow. The microfabricated valves have either two- or three-dimensional arrangement of valving elements. In particular, a interesting normally closed check valve was designed and fabricated using a special technique, in which the flap and stopper are, as fabricated, in intimate contact and form a zero-gap between them. Testing results show that the check valves can achieve a diodicity up to 105. The check valves can be fabricated using the standard replica molding technique from PDMS, and thus are highly amenable to integration with other PDMS-based microfluidic systems. The planar check valves can potentially used in lab-on-a-chip systems due to its high diodicity, planar configuration and use of inexpensive polymeric materials.

This paper presents lumped-parameter simulation of dynamic characteristics of peristaltic micropumps. The pump consists of three pumping cells connected in series, each of which is equipped with a compliant diaphragm that is electrostatically actuated in a peristaltic sequence to mobilize the fluid. Diaphragm motion in each pumping cell is first represented by an effective spring subjected to hydrodynamic and electrostatic forces. These cell representations are then used to construct a system-level model for the entire pump, which accounts for both cell- and pump-level interactions of fluid flow and diaphragm vibration. As the model is based on first principles, it can be evaluated directly from the device's geometry, material properties and operating parameters without using any experimentally identified parameters. Applied to an existing pump, the model correctly predicts trends observed in experiments. The model is then used to perform a systematic analysis of the impact of geometry, materials and pump loading on device performance, demonstrating its utility as an efficient tool for peristaltic micropump design.

This paper proposes non-fragile compliant humidity nanosensors that can be fabricated inexpensively on various types of nanoporous polymer membranes such as polycarbonate, cellulose acetate, and nylon membranes. The nanosensor contains a pair of interdigitated electrodes deposited on the nanoporous polymer membranes. The resistance and/or capacitance between these electrodes vary at different humidity levels with a very high sensitivity due to the water adsorption (capillary condensation) inside the nanopores. The proposed sensors are low-cost in both material and fabrication. Due to its compliance, the sensors can be suitable for certain applications such as in situ water leakage detection on roofs, where people can walk on top of them. Testing results demonstrated that the sensor changes resistance within large range of relative humidity (RH) values (40–100% RH) with very high sensitivity. Design A and B sensors exhibit high sensitivities, 2.5 and 1.3 GΩ/% RH, respectively, to relative humidity changes but are not linear in response till 55% RH is reached (R2 ∼ 0.7391 for design A, R2 ∼ 0.8824 for design B). For the design C sensors, sensitivity is around 20 GΩ/% RH and the response is highly linear (R2 ∼ 0.96) for 40–100% relative humidity range. These results showed the feasibility of the proposed compliant and low-cost nanopore polymer membrane based humidity nanosensors which could be used for in situ water leakage and humidity level detection on three-dimensional and complex surfaces such as roofs and airplane bodies in the near future.

This paper presents the design and simulation of a novel flexure structure to potentially support a thermal energy storage (TES) salt vessel that is mounted on a solar dish Stirling Engine. During operation, the TES vessel expands significantly due to the elevated salt temperature leading to large deformation (thus high thermal stress) and large temperature change on the flexures. The flexure design consists of two sets of stacked flexures (∼100 mm in distance), each having eight stacked L-shaped flexures symmetrically distributed around the salt vessel. The axial and circumferential section of each flexure allows the radial and axial vessel expansion respectively. The stacking concept is expected to provide sufficient lateral rigidity (to avoid sag under gravity) while still allows the desired axial flexibility. Super Alloy Inconel 625 is selected as the flexure material due to its desired properties at elevated temperatures. A simplified model and a system model (including flexures, dummy engine, and salt vessel) of the design were analyzed using Finite Element Analysis (FEA). Analysis shows that the design meets the stress, deformation, and fatigues requirements. Test will be conducted to verify the simulation results. The flexure design is compact, simple, and low-cost to fabricate, and the concept can potentially be used for other applications that involve support of structures with large thermal expansion.Copyright © 2010 by ASME

This paper presents the analytical solution of the heat conduction across a corrugated thermal interface material with rectangular straight fin arrangement. Domain decomposition and eigenfunction expansion method were used to study the thermal diffusion in such geometry for the first time. The temperature field solved from the analytical method agrees well with FEM simulation. The total heat transfer rate across the corrugated interface and thermal boundary resistance were derived analytically also. Results have shown that the effective thermal resistance across the interface can be significantly reduced with the corrugated TIM geometry. The analytical solution in the paper can provide insight into geometry effect on the heat transfer enhancement, and is a very useful complement to experimental work and numerical simulation in designing high-performance corrugated thermal interface.Copyright © 2007 by ASME

This paper presents a novel phase-change actuator that can be potentially used for microvalves in lab-on-a-chip systems where minimal energy consumption is required. The actuator exploits a low melting-point paraffin wax, whose solid-liquid phase changes allow the closing and opening of fluid flow through deformable microchannels. Flow switching is initiated by melting of paraffin using integrated heaters, with an additional pneumatic pressure used for flow switching from open to closed state. After paraffin solidifies the switched flow state is subsequently maintained without further energy consumption. The actuator can be fabricated from PDMS through the multilayer soft lithography technique. Experiments demonstrate that the actuators can switch the flow state within 4-8 seconds, which can be further sped up with improved heater designs.

This paper presents fluid-structure interaction (FSI) simulation of a microfluidic diode, which features a thin flexible flap and a rigid stopper embedded closely inside a microchannel. The thin flap deforms under different applied pressure, leading to a small flow resistance for forward flow and a large flow resistance for reverse flow. Three-dimensional simulations of structure deflection and CFD were interactively carried out to calculate the flap deformation and flow filed using ANSYS® Multi-field™ solver. In the simulations nonlinear hyperelastic material property was used for the thin flap, and the pressure drop across device inlet and outlet was applied in small increments to solve the nonlinear continuum mechanics problems. The simulated flap deflections under both forward and reverse flow show nonlinear relation between deflection and pressure, consistent with experimental data. The simulated flow rates under various pressures also agree well with the measurement results, within 15% error for forward flow and 17% for reverse flow. The simulations can be used as guidelines for optimal design of the microfluidic diode.Copyright © 2006 by ASME

This paper presents a simple and novel device to stabilize a fluctuating fluid flow in microfluidic systems. The device consists of a microchannel and several compliant membranes in series on one or more walls of the channel. Vibrations of the compliant membranes are used to remove fluctuations in an incoming flow, resulting in nearly constant outlet flow rates and inlet pressures. A lumped-parameter model was developed to simulate the device operation. Testing of prototype devices demonstrates that the device is able to stabilize a pulsating flow by a flow rate stabilization ratio up to 20.

This paper presents a novel latchable phase-change actuator that can potentially be used for flow valving and gating in portable lab-on-a-chip systems, where minimal energy consumption is required. The actuator exploits a low melting-point paraffin wax, whose solid-liquid phase changes allow the closing and opening of fluid flow through deformable microchannels. Flow switching is initiated by melting of paraffin, with an additional pneumatic pressure required for flow switching from open to closed state. After paraffin solidifies the switched state is subsequently maintained passively without further consumption of energy. The actuator can be fabricated from PDMS through the multilayer soft lithography technique. Testing results demonstrate that the actuator has a response time about 60-100 sec for flow switching, and can passively hold a microvalve closed under pressures up to 35 kPa.Copyright © 2005 by ASME

This paper presents three types of planar check valves that uniquely exploit the large compliance of simple PDMS structures. The micro check valves consist of a thin compliant flap and a rigid stopper embedded in a microchannel. The flap is perpendicular to the flow and lies near the stopper, forming a restricted fluid path inside the channel. In particular, a novel “zero flap-stopper gap” valve design was proposed and fabricated using a special technique, in which the flap and stopper are in contact naturally forming a normally-closed device with high diodicity. Testing results show that the check valves can achieve a diodicity up to 105. The check valves can be fabricated using the standard replica molding technique from PDMS, and thus are highly amenable to integration with other PDMS-based microfluidic systems.Copyright © 2005 by ASME

This paper presents a microfluidic control device that regulates nearly constant flow rates under variable driving pressures. This flow regulator is fabricated from PDMS and exploits the large compliance of PDMS to achieve passive flow regulation without consuming power or requiring active control circuitry. The device features a compliant flap and a rigid block that form a flow constriction in a microchannel within which they are embedded. Under driving pressure variations, the flow constriction is narrowed due to flap deflections, and flow rate changes that would result from the pressure variations are canceled by constriction narrowing effects. As a result, a nearly constant flow rate can be maintained, as will be demonstrated with prototype devices that regulate water flow rates from 0.15 to 1.2 ml/min under driving pressures varying from 100 to 200 kPa.

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min(-1) and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (microTAS).

This paper proposes non-fragile compliant humidity sensors that can be fabricated inexpensively on various types of nano-porous polymer membranes such as polycarbonate, cellulose acetate, and nylon membranes. The sensor contains a pair of interdigitated electrodes deposited on the nano-porous polymer membranes. The resistance and/or capacitance between these electrodes vary at different humidity levels with a very high sensitivity due to the water adsorption (capillary condensation) inside the nano-pores. The proposed sensors are low-cost in both material and fabrication. Due to its compliance, the sensors can be suitable for certain applications such as in-situ water leakage detection on roofs, where people can walk on top of them. Testing results demonstrated that the sensor changes resistance within large range of humidity values. For most sensors, the resistance changes from 0.1 GΩ to 2000 GΩ when the relative humidity changes from 39% to 100% at room temperature. It takes about 4–8 minutes for the resistance to reach steady state when the sensor was taken from 100% to 39% relative humidity at the room temperature.

This paper presents two types of novel micro check valves that are based on PDMS. The valves consist of a thin flap and a flow restriction block inside a microchannel. The flap is perpendicular to the flow and lies near the block, which forms a restricted fluid path inside the channel. The valves are fabricated entirely from PDMS through replica molding techniques and can be readily integrated in PDMS-based complex microfluidic systems. Testing results show that for a reverse flow, the 2D valve has a saturated leakage rate at higher pressures, leading to an interesting “fluid diode” phenomenon, while the 3D valve has zero leakage at higher pressures.Copyright © 2003 by ASME