Substrate Contact Research Articles

Computational fluid dynamics simulations of silicon μ-structure formation during excimer laser modification of silicon-nanoparticle layers

The laser modification of silicon-nanoparticle layers with a nanosecond pulsed excimer laser leads to the self-organized formation of crystalline, μ-cone-shaped silicon structures with good electronic properties, which have allowed the demonstration of their potential for printed flexible electronics. With the current nanosecond laser process, silicon exhibits only short melting times, resulting in a method-defined substrate contact angle, instead of this parameter being defined by the substrate surface energy as expected for equilibrium conditions. This substrate material-independent non-equilibrium contact angle of the silicon melt was experimentally determined in this study to be Θ = 68 ± 10°. To gain deeper insight into the process of the sequential melting and the formation of the silicon μ-cone structures during laser modification, a two-dimensional computational fluid dynamics simulation was performed in COMSOL Multiphysics® solving the Navier–Stokes equation for incompressible fluids. The simulation uses an effective medium approach by applying the conservative level set method to describe the porous silicon-nanoparticle layer. Its sequential melting during the pulsed laser modification is modeled using a newly developed simulation methodology, which uses a time- and depth-dependent dynamic viscosity of the molten silicon. The simulation was carried out for different laser energy densities and verified using scanning electron microscopy images of corresponding laser-modified samples. The simulation results agree well with the experiment and were subsequently used to optimize the laser process.

Numerical study of thermocapillary migration of a droplet on an oleophilic track

The thermocapillary migration dynamics of a droplet with a non-circular footprint on an oleophilic track is studied numerically. Three-dimensional simulations showed that reducing the width of the oleophilic track improves the droplet migration velocity only upto a specific track width when compared to the change in velocity of a droplet with circular footprint. Further decrease in track width is seen to depreciate the enhancement in migration velocity. The spread length of the droplet on the oleophilic track is also observed to have a similar variation with track width. The two trends are related because the temperature difference in the droplet, which scales with spread length, determines the driving force governing the migration velocity characteristics. Further, a parametric study is performed to assess the migration behaviour on oleophilic tracks with change in substrate temperature gradient, droplet volume and contact angles within and outside the track. The influence of change in these parameters on the variation in enhancement in spread length and corresponding track width is also investigated. The study identified trends in the minimum track width that may be used to improve migration characteristics, as well as the order of enhancement that can be noticed with changes in each parameter.

Generation of Hybrid Lead Halide CH3NH3PbI3-xClx Perovskite Crystals via Convective Self-Assembly

In this study, we have employed a film deposition technique based on convective forces acting at the triple air–solution–substrate contact line to tune the rate of solvent evaporation and, thus, to exert control over the morphology of the resulting mixed lead halide perovskite CH3NH3PbI3-xClx films. By varying the speed of film deposition while processing at two different temperatures, perovskite crystals of various shapes and dimensions were generated upon the crystallization of the initial perovskite precursor ink. More precisely, longer than half a millimeter 3D needle-like perovskite crystals exhibiting sharp edges co-existing with large cross-like 3D perovskite crystals could only be obtained upon the slow deposition of films at a low sample processing temperature of 17 °C, i.e., under conditions of low solvent evaporation rate. On the contrary, the utilization of higher film deposition speeds and/or processing temperatures led to smaller 3D needle-like or quasi-2D rectangular perovskite crystals that often appeared interconnected and coalesced. Moreover, as it was revealed by the photoluminescence measurements, the emission intensity of perovskite crystals was larger and dominated by a shorter wavelength peak, as compared to the uncrystallized material that emitted much less light, but at a longer wavelength.

Ion-Selective Electrodes With Sensing Membranes Covalently Attached to Both the Inert Polymer Substrate and Conductive Carbon Contact.

The use of solid-contact ion-selective electrodes (ISEs) is of interest to many clinical, environmental, and industrial applications. However, upon extended exposure to samples and under thermal and mechanical stress, adhesion between these membranes and underlying substrates often weakens gradually. Eventually, this results in the formation of a water layer at the interface to the underlying electron conductor and in delamination of the membrane from the electrode body, both major limitations to long-term monitoring. To prevent these problems without increasing the complexity of design with a mechanical attachment, we use photo-induced graft polymerization to simultaneously attach ionophore-doped crosslinked poly(decyl methacrylate) sensing membranes covalently both to a high surface area carbon as ion-to-electron transducer and to inert polymeric electrode body materials (i.e., polypropylene and poly(ethylene-co-tetrafluoroethylene)). The sensors provide high reproducibility (standard deviation of E0 of 0.2 mV), long-term stability (potential drift 7 μV h-1 over 260 h), and resistance to sterilization in an autoclave (121 °C, 2.0 atm for 30 min). For this work, a covalently attached H+ selective ionophore was used to prepare pH sensors with advantages over conventional pH glass electrodes, but similar use of other ionophores makes this approach suitable to the fabrication of ISEs for a variety of analytes.

Ion‐Selective Electrodes With Sensing Membranes Covalently Attached to Both the Inert Polymer Substrate and Conductive Carbon Contact

AbstractThe use of solid‐contact ion‐selective electrodes (ISEs) is of interest to many clinical, environmental, and industrial applications. However, upon extended exposure to samples and under thermal and mechanical stress, adhesion between these membranes and underlying substrates often weakens gradually. Eventually, this results in the formation of a water layer at the interface to the underlying electron conductor and in delamination of the membrane from the electrode body, both major limitations to long‐term monitoring. To prevent these problems without increasing the complexity of design with a mechanical attachment, we use photo‐induced graft polymerization to simultaneously attach ionophore‐doped crosslinked poly(decyl methacrylate) sensing membranes covalently both to a high surface area carbon as ion‐to‐electron transducer and to inert polymeric electrode body materials (i.e., polypropylene and poly(ethylene‐co‐tetrafluoroethylene)). The sensors provide high reproducibility (standard deviation of E0 of 0.2 mV), long‐term stability (potential drift 7 μV h−1 over 260 h), and resistance to sterilization in an autoclave (121 °C, 2.0 atm for 30 min). For this work, a covalently attached H+ selective ionophore was used to prepare pH sensors with advantages over conventional pH glass electrodes, but similar use of other ionophores makes this approach suitable to the fabrication of ISEs for a variety of analytes.

The dispersion of Trichosporon fermentans was controlled by optimizing the shear environment in the reactor to improve the cell sedimentation and separation performance

The morphology of pseudomycelium in Trichosporon fermentans is not conducive to the accumulation of lipids and the recovery of yeast cells by sedimentation. In this study, the computational fluid dynamics method was used to study the effects of shear force on the flow field distribution and on the dimorphism transition and dispersion of yeast cells in a 5 L stirred bioreactor, and to explore the sedimentation performance of yeast cells in different forms. It was shown that under the condition of moderate shear force, such as 3.45 Pa corresponding to a stirring speed of 300 rpm as selected in this experiment, most of the yeast cells in the fermentation broth were spherical or short rod-shaped, and there were almost no pseudohyphal yeasts, which contributed to the good sedimentation performance of the yeast cells. The results showed that the appropriate shear force could effectively inhibit the transformation of yeast cells into pseudohyphae, retain a large number of cells in a single cell shape, enhance cell dispersion and facilitate cell contact, absorption and utilization of organic substrates, as well as increase the lipid accumulation in yeast cells. By controlling the shear force, after 40 h of treatment of RSOW using Trichosporon fermentans, the chemical oxygen demand and oil content removal were approximately 95.81% and 88.09%, respectively, which indicate a significant improvement compared with those before optimizing the shear environment. Therefore, based on shear control of the cell morphology to improve yeast cell dispersion and sedimentation performance, the oily wastewater treatment method established in this study can be used to guide the process design of fermented Trichosporon fermentans for the treatment of RSOW and the resource recycling of yeasts.

Experimental study of water management and performance of titanium fibre felts as versatile gas diffusions layers for PEMFCs

This work compares titanium fibre felts and conventional carbon gas diffusion layers (GDLs), varying in thickness, as cathode GDLs for polymer electrolyte membrane fuel cells (PEMFCs) in terms of i) overall performance, ii) mass transport properties, and iii) water management. The study presents a comprehensive approach to understanding GDL properties which affect performance. Titanium fibre felts exhibit improved performance across thicknesses and operating conditions, and both GDL types exhibit optimised performance at a thickness of 400 μm. Greater porosity and pore size of titanium fibre felts contribute to greater air permeability than carbon GDLs. Ohmic resistance for titanium fibre felts remains low across thicknesses, indicating good electrical conductivity of the titanium substrate and good interfacial contact with the catalyst layer. In contrast, ohmic resistance for carbon GDLs is higher and sensitive to thickness. Finally, flooding resistance is optimised at 400 μm for both GDL types, consistent with the observed performance.

On adiabatic shear instability in impacts of micron-scale Al-6061 particles with sapphire and Al-6061 substrates

Impact mechanics of micron-scale, Al-6061 particles on sapphire and Al-6061 substrates were investigated experimentally and through simulations. Particle impact experiments were carried out by using the laser induced projectile impact test (LIPIT) and the coefficient of restitution was evaluated for impact velocities in the range of 50–950 m/s. Bonding was observed only in Al-on-Al impacts with impact velocities over 810 m/s. A continuum model of the impacts was implemented by using commercially available finite element software. The bilinear Johnson–Cook model was implemented to model the material flow effects in the ultra-high strain rate (UHSR) regime. A cohesive zone model was used for the bonding along the particle–substrate contact interface. Heat generation due to plasticity and friction, and material damage were also included in the simulations. A quantitative measure of adiabatic shear instability (ASI) was implemented into the modeling framework to search for material points that experience drop of strength during loading. A small volume of the material internal to the particle was found to experience ASI in Al-on-sapphire impacts, but this was not observed in Al-on-Al impacts. However, if the flow rule is switched to one that neglects the effects of the UHSR-regime, ASI can be predicted in regions of the particle where the finite element mesh deforms excessively. It is recommended that any study searching for ASI in high-velocity impact simulations should assess the mesh distortion carefully and use a flow rule that includes UHSR effects.

PO-03-101 PEAK FREQUENCY INITIAL US AND EUROPEAN EXPERIENCE: A NOVEL MEASURE TO DISTINGUISH NEAR-FIELD FROM FAR-FIELD EGM COMPONENTS

Discrimination between near-field (NF) vs. far-field (FF) components in electrograms (EGMs) is mostly based upon intuitive perception of local EGM sharpness. As high-density mapping catheter use has expanded, the difficulty of discerning sub-components across many EGMs in realtime has increased. To date no mapping system had employed a means to quantify this distinction. A novel detection algorithm was designed to identify sharpness of NF EGM components by annotating the highest Peak Frequency (PF) of a signal. To provide insight into first clinical use cases of NF annotation algorithm and PF data. Acute procedure data were prospectively collected from 32 operators at 16 institutions in the US and Europe. All cases were performed on EnSite X system with EnSite OT Near Field software (Abbott). PF information was used as an adjunct to activation or voltage maps via an emphasis layer or as a standalone map (Figure). Choice of mapping tools and technique was at physician discretion. Analysis included ablation cases (n=175) with the following indications: AF (60.6% [54.7% PAF, 45.3%, PsAF; 34.9% redo]), SVT (20.6%), and VT/PVC (18.9%). The NF algorithm was the roving detection option of choice for automated point collection in most cases (96.2% of AF cases, 91.7% SVT, 69.7% VT/PVC). Alternative detections were Last Deflection in VT cases (33%) and First Deflection in PVC cases (29%). When NF was used, correctness of EGM annotation was noted as highly accurate in 93.5% of cases. Standalone PF maps were used as a diagnostic tool in 48 (27.4%) Depth of Activation Insights cases. Bounding values for map display were variable based on use-case to highlight various electrophysiologic phenomena (Table). In an AF use case, PF was used for gap identification (n=6); values were applied at 225±28 Hz, consistent with previously published value of 240Hz (Merino, et al. EHRA 2022). Alternatively in VT/PVC cases, low PF far-field zones were highlighted to assess activation at depth in tissue; mean values were 198±10 Hz. Peak frequency mapping helps distinguish near field from far-field electrograms. PF mapping can be used as (1) a standalone mapping technique to accurately identify near field components and (2) PF mapping can be used as an adjunctive technique to complement activation and voltage maps. PF mapping appears to assist in substrate differentiation, pathway localization, and contact assessment. Further research is warranted on optimal settings for various tissue types and rhythms.Tabled 1Table. Standalone PF mapsValues in HzValues in HzUsed InUsed InUsed InIntention of Map UseColor Range HighColor Range LownAFSVTVT/PVCCritical Isthmus Identification424 +/- 70222 +/- 445YesYesYesDepth of Activation Insights490 +/- 300198 +/- 3010YesYesFF LAA vs NF PV EGM475 +/- 268220 +/- 256YesPV Gap Identification400 +/- 257225 +/- 286YesSlow Pathway Modification231 +/- 4345 +/- 7911YesOther**10YesYesYes Open table in a new tab

Coalescence dynamics of droplets collision on substrates with different contact angles

Droplet collision coalescence is widely encountered in the petroleum industry, chemical industry, and agricultural applications. In this study, the dynamic behavior of the coalescence process of a free-falling droplet impacting a sessile droplet on substrates with different wettabilities is investigated via high-speed photography. The influences of the substrate contact angle (α) and the Weber number (We) of the droplet collision were analyzed. Based on the experiments, the process of droplet collision coalescence was divided into four stages: coalescence, spreading, retraction, and oscillation. The maximum spreading diameters, maximum jet heights, spreading velocities, and retraction velocities of droplets with different values of the substrate contact angle and We were obtained. The dynamic mechanism of different collision coalescence stages was revealed by the interconversion of inertial forces, surface tension, and wall adhesion forces. The relationship between the dimensionless spreading coefficient and the dimensionless time was established for different values of the collision We and contact angle α based on the experimental results. The effects of We and α on the coalescence process of the droplets were obtained by analysis of the energy conversion.

Molecular dynamics study of graphene-coated reinforced tribomechanical properties: Hard versus soft substrates

As a two-dimensional material, graphene film is a good solid lubricant candidate for improving the tribomechanical performance of micro-and nano-electromechanical systems. Graphene has a significant impact on protecting the top layer of a substrate from wear and reducing friction. However, the frictional behavior has been found to vary when coating graphene onto different substrates. In the present study, using molecular dynamics (MD) simulations, graphene was deposited as a monolayer coating on the substrate sliding against the diamond tip, which revealed not only significant improvement in tribological behavior by reducing both friction and contact deformation volume, but also notably demonstrated the difference between hard and soft substrate coating with graphene. Under 58.5nN loading, the optimal antifriction effect of graphene coating on Au substrate was 94.2%, with a higher friction indicating a greater indentation depth and greater contact deformation. The contact deformation volume can be used as a standard to measure the surface friction of graphene. Unlike hard Si substrates, monolayer graphene coatings are prone to rupture at 200 nN loads. At low loads, the single graphene coating has the best anti-friction effect on the soft gold substrate, and at higher loads, the graphene on the hard silicon substrate is not prone to rupture, providing continuous and stable lubrication. The study also revealed a tunable toughening mechanism of graphene layers. The mechanism entails a reduction in the volume of substrate contact deformation with the progressive addition of graphene layers. This finding has the potential to enhance the tribological performance of the graphene-coated substrate.

No evidence for regeneration of pectines in the scorpion Euscorpius italicus (Herbst, 1800)

AbstractAlthough scorpions have comparatively low regenerative potential, legs and pedipalps are able to regenerate some structures in an often incomplete manner. The most intriguing scorpion appendages are the ventrally located pectines. These organs are equipped with numerous sensilla that scan the substrate for mechanosensory‐ and chemosensory cues. Due to their ventral position and frequent substrate contact, pectines are vulnerable to traumatic injuries. Pecten malformations have been hypothesized to be the result of incomplete regeneration. To investigate their regeneration capabilities, the pectines of postembryonic stages of Euscorpius italicus (Herbst, 1800) were amputated before the second moult at three different positions. Data on intermoult periods and the number of pectinal teeth were gathered for approximately 2.5 years. The regeneration process on exuviae of up to six moulting events was documented by photographs and confocal laser‐scanning microscopy. Regardless of the amputation site, no evidence for regenerative capabilities of pectines in E. italicus could be reported. Thus, incomplete regenerations mentioned in the literature are likely the result of simple wound healing. Depending on habitat complexity, substrate contact time of the pectines seem to differ, which might be interpreted as a trade‐off between highest sensory input and the avoidance of traumatic injury of the pectines.

Effect of Substrate Roughness and Contact Scale on the Tribological Performance of MoS2 Coatings

This present study aimed to clarify the effect of contact scale and surface topography of substrates with different roughnesses on the actual contact area, tangential stiffness, and tangential deformation of the substrate at micro- and macro-scales via finite element method (FEM) simulations, as well as the final tribological performances of MoS2 coatings by experiments. The MoS2 coatings were deposited on stainless steel (SS) substrates with different roughnesses, and the settings in the simulation models were based on the roughness of the SS substrates. The predicted tribological behavior of the simulation results was confirmed by the morphological and compositional analysis of the wear track using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), 3D profilometer, and Raman spectroscopy. The results showed that the substrate with a surface roughness of Ra 600 nm (R600), coated by MoS2 nanosheets, exhibited excellent tribological properties at both micro- and macro-scales. At the micro-scale, the lubrication lifetime of R600 was as long as 930 cycles, while the substrates with surface roughnesses of Ra 60 nm (R60) and Ra 6 nm (R6) had a lubrication lifetime of 290 cycles and 47 cycles, respectively. At the macro-scale, the lifetime of the substrate R600 was 9509 cycles, which was nearly six times longer than the 1616 cycles of substrate R60. For the rough surface of substrate, the surface grooves could not only effectively preserve the lubricant but also continuously release them, ensuring that the lubricants with low shear strength were always present in the contact interface. It was further verified that the high surface roughness of the substrate reduced friction and wear by reducing the actual contact area and enhancing the tangential stiffness of asperities, thereby prolonging the lubrication lifetime. The wear mechanisms were discussed in terms of the morphology and chemical composition of the wear tracks.

Nonlinear Modeling of Contact Stress Distribution in Thin Plate Substrates Subjected to Aspect Ratio.

The foundation substrate's basal contact stresses are typically thought to have a linear distribution, although the actual form is nonlinear. Basal contact stress in thin plates is experimentally measured using a thin film pressure distribution system. This study examines the nonlinear distribution law of basal contact stresses in thin plates with various aspect ratios under concentrated loading, and it establishes a model for the distribution of contact stresses in thin plates using an exponential function that accounts for aspect ratio coefficients. The outcomes demonstrate that the thin plate's aspect ratio significantly affects how the substrate contact stress is distributed during concentrated loading. The contact stresses in the thin plate's base exhibit significant nonlinearity when the aspect ratio of the test thin plate is greater than 6~8. The aspect ratio coefficient-added exponential function model can better optimize the strength and stiffness calculations of the base substrate and more accurately describe the actual distribution of contact stresses in the base of the thin plate compared to linear and parabolic functions. The correctness of the exponential function model is confirmed by the film pressure distribution measurement system that directly measures the contact stress at the base of the thin plate, providing a more accurate nonlinear load input for the calculation of the internal force of the base thin plate.

Contact Area and Deformation of Escherichia coli Cells Adhered on a Cationic Surface.

When bacteria adhere to surfaces, the chemical and mechanical character of the cell-substrate interface guides cell function and the development of microcolonies and biofilms. Alternately on bactericidal surfaces, intimate contact is critical to biofilm prevention. The direct study of the buried cell-substrate interfaces at the heart of these behaviors is hindered by the small bacterial cell size and inaccessibility of the contact region. Here, we present a total internal reflectance fluorescence depletion approach to measure the size of the cell-substrate contact region and quantify the gap separation and curvature near the contact zone, providing an assessment of the shapes of the near-surface undersides of adhered bacterial cells. Resolution of the gap height is about 10%, down to a few nanometers at contact. Using 1 and 2 μm silica spheres as calibration standards we report that, for flagella-free Escherichia coli (E. coli) adhering on a cationic poly-l-lysine layer, the cell-surface contact and apparent cell deformation vary with adsorbed cell configuration. Most cells adhere by their ends, achieving small contact areas of 0.15 μm2, corresponding to about 1-2% of the cell's surface. The altered Gaussian curvatures of end-adhered cells suggest the flattening of the envelope within the small contact region. When cells adhere by their sides, the contact area is larger, in the range 0.3-1.1 μm2 and comprising up to ∼12% of the cell's total surface. A region of sharper curvature, greater than that of the cells' original spherocylindrical shape, borders the flat contact region in cases of side-on or end-on cell adhesion, suggesting envelope stress. From the measured curvatures, precise stress distributions over the cell surface could be calculated in future studies that incorporate knowledge of envelope moduli. Overall the small contact areas of end-adhered cells may be a limiting factor for antimicrobial surfaces that kill on contact rather than releasing bactericide.

Unspecific peroxygenases immobilized on Pd-loaded three-dimensional ordered macroporous (3DOM) titania photocatalyst for photo-enzyme integrated catalysis

The selective oxyfunctionalization of C-H and CC bonds is highly important and catalyzed by unspecific peroxygenases (UPOs) which suffer from inactivation by hydrogen peroxide (H2O2). Herein, photo-enzyme integrated catalysts were constructed by immobilizing AaeUPO as cross-linked enzyme aggregates (CLEAs) in Pd-loaded three-dimensional ordered macroporous titania (3DOM TiO2) with in situ photocatalytic H2O2 production. The prepared AaeUPO@3DOM TiO2-Pd obtained higher catalytic efficiency compared with CLEAs-AaeUPO. The conversion of ethylbenzene to (R)-1-phenethyl alcohol was significantly improved, reaching 99 % compared with free enzyme (38 %) and CLEAs-AaeUPO (49 %), with ee value of > 99 %. AaeUPO@3DOM TiO2-Pd exhibited good stability and reusability attributed to the protection of macropores and in situ H2O2 production. By using the designed 3DOM platform for photocatalysis and enzyme immobilization, the in situ photocatalytic generation of H2O2 was highly efficient, and the monodisperse CLEAs-AaeUPO in the macropores facilitated the contact of substrate and enzyme, thus obtaining excellent photo-enzyme coupled catalysis.

Effects of Numerical Schemes of Contact Angle on Simulating Condensation Heat Transfer in a Subcooled Microcavity by Pseudopotential Lattice Boltzmann Model

Various numerical schemes of contact angle are widely used in pseudopotential lattice Boltzmann model to simulate substrate contact angle in condensation. In this study, effects of numerical schemes of contact angle on condensation nucleation and heat transfer simulation are clarified for the first time. The three numerical schemes are pseudopotential-based contact angle scheme, pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate with weighted average density of surrounding fluid nodes, and the geometric formulation scheme. It is found that the subcooling condition destabilizes algorithm of pseudopotential-based contact angle scheme. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the algorithm becomes stable. The subcooling condition also decreases the simulated contact angle magnitude compared with that under an isothermal condition. The fluid density variation near a microcavity wall simulated by pseudopotential-based contact angle scheme plays the role of the condensation nucleus and triggers “condensation nucleation”. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the simulated fluid density distribution near the wall is uniform so that no condensation nucleus appears in the microcavity. Thus, “condensation nucleation” cannot occur spontaneously in the microcavity unless a thin liquid film is initialized as a nucleus in the microcavity. The heat flux at the microcavity wall is unphysical during the “condensation nucleation” process, but it becomes reasonable with a liquid film formed in the microcavity. As a whole, it is recommended to use pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate or use the geometric formulation scheme to simulate condensation under subcooling conditions. This study provides guidelines for choosing the desirable numerical schemes of contact angle in condensation simulation by pseudopotential lattice Boltzmann model so that more efficient strategies for condensation heat transfer enhancement can be obtained from numerical simulations.

Study on Adhesion Force of Graphene under Cylinder–Plane Contact

There are many cylinder–plane contacts in microaccelerators, microgyroscopes, and RF switches. Adhesion is one of the main factors affecting the manufacture and use of these micro–nano devices, but its research is insufficient. Graphene is expected to be used in these fields due to its excellent electrical and mechanical properties. Therefore, it is significant to research the adhesion force of graphene under cylinder–plane. Firstly, the meniscus formation process was introduced using the variable-water-contact-angle method. Secondly, the adhesion force of the graphene surface was measured with a cylindrical atomic-force-microscope probe. Finally, the contact area was considered as a number of nanoscale cylinders in contact with the plane, and the adhesion force of the cylinder–plane model was obtained. The results showed that there was a maximum adhesion force at a relative humidity of 65%. The adhesion force was evidently not time-dependent when the relative humidity was below 45%, because the meniscus cannot be formed on the graphene surface at low relative humidity. While the graphene contact surface formed a meniscus for higher relative humidity, and the adhesion force-versus-time curves first increased and then decreased to stability. Moreover, the relationship between adhesion force and substrate contact angle, roughness, relative humidity, and dwell time was established, and the number of cylinders was determined. The error between the modified theoretical model and the experimental values was only 6%.

Site-directed mutagenesis improves the practical application of L-glutamic acid decarboxylase in Escherichia coli.

γ-Aminobutyric acid (GABA) is a kind of non-proteinogenic amino acid which is highly soluble in water and widely used in the food and pharmaceutical industries. Enzymatic conversion is an efficient method to produce GABA, whereby glutamic acid decarboxylase (GAD) is the key enzyme that catalyzes the process. The activity of wild-type GAD is usually limited by temperature, pH or biotin concentration, and hence directional modification is applied to improve its catalytic properties and practical application. GABA was produced using whole cell transformation of the recombinant strains Escherichia coli BL21(DE3)-Gad B, E. coli BL21(DE3)-Gad B-T62S and E. coli BL21(DE3)-Gad B-Q309A. The corresponding GABA concentrations in the fermentation broth were 219.09, 238.42, and 276.66g/L, and the transformation rates were 78.02%, 85.04%, and 98.58%, respectively. The results showed that Gad B-T62S and Gad B-Q309A are two effective mutation sites. These findings may contribute to ideas for constructing potent recombinant strains for GABA production. Practical Application : Enzymatic properties of the GAD from Escherichia coli and GAD site-specific mutants were examined by analyzing their conserved sequences, substrate contacts, contact between GAD amino acid residues and mutation energy (ΔΔG) of the GAD mutants. The enzyme activity and stability of Gad B-T62S and Gad B-Q309A mutants were improved compared to Gad B. The kinetic parameters Km and Vmax of Gad B, Gad B-T62S, and Gad B-Q309A mutants were 11.3 ± 2.1mM and 32.1 ± 2.4U/mg, 7.3 ± 2.5mM and 76.1 ± 3.1U/mg, and 7.2 ± 3.8mM and 87.3±1.1U/mg, respectively. GABA was produced using whole cell transformation of the recombinant strains E. coli BL21(DE3)-Gad B, E. coli BL21(DE3)-Gad B-T62S, and E. coli BL21(DE3)-Gad B-Q309A. The corresponding GABA concentrations in the fermentation broth were 219.09, 238.42, and 276.66g/L, and the transformation rates were 78.02%, 85.04%, and 98.58%, respectively.

Preference of black soldier fly larvae for feed substrate previously colonised by conspecific larvae

AbstractThe black soldier fly Hermetia illucens Linnaeus (Diptera: Stratiomyidae; BSF) is gaining interest as an alternative protein ingredient for livestock feed. Larval aggregation behaviour occurs commonly in larvae of various dipteran species. However, the cues initiating aggregation behaviour and its occurrence in subsequent larval instars are still unknown in BSF larvae. Here, we focus on understanding the attraction of larvae to cues left behind in the substrate by conspecific larvae. We developed a dual‐choice test in the dark and examined the preference behaviour of different instars with the use of video recordings. Larval choices were identified based on first substrate contact, cumulative number of substrate contacts, entry of the substrate and number of larvae present in a substrate over time. Our results demonstrate that BSF larvae discriminated between similar substrates with or without cues released by conspecifics, with a strong preference for previously colonised substrates. Our results also showed a difference in behaviour between head‐capsule classes. Substrate contacts occurred more frequently in larvae from a lower head‐capsule class and the number of larvae present in a substrate over time differed between the head‐capsule classes 0.71–0.80 mm and 0.91–1.00 mm. Demonstrating arrestment in response to chemical cues from conspecifics is the first step of understanding aggregation behaviour of BSF larvae and offers opportunities to identify the chemical cues involved.