Enhancement Of Recombination Research Articles

Coexpressing the Signal Peptide of Vip3A and the Trigger Factor of Bacillus thuringiensis Enhances the Production Yield and Solubility of eGFP in Escherichia coli.

Many fusion tags have been developed to improve the expression of recombinant proteins. Besides the translocation of cargo proteins, the signal peptides (SPs) of some secretory proteins, such as the ssTorA and Iasp, have been used as an inclusion body tag (IB-tag) or the recombinant expression enhancer in the cytosol of E. coli. In this study, the approach to utilize the SP of Vip3A (Vasp) from Bacillus thuringiensis (Bt) as a fusion tag was investigated. The results showed that either the Vasp or its predicted N- (VN), H- (VH), and C-regions (VC), as well as their combinations (VNH, VNC, and VHC), were able to significantly enhance the production yield of eGFP. However, the hydrophobic region of the Vasp (VH and/or VC) made more than half of the eGFP molecules aggregated (VeGFP, VHeGFP, VCeGFP, VNHeGFP, VNCeGFP, and VHCeGFP). Interestingly, the addition of the Bt trigger factor (BtTF) led to the neutralization of the negative impact and solubilization of the fusion proteins. Therefore, the coexpression of Vasp or its derivates with the chaperone BtTF could be a novel dual-enhancement system for the production yield and solubility of recombinant proteins. Notably, EcTF was unable to impact the solubility of Vasp or its derivates guided proteins, suggesting its different specificities on the recognition or interaction. Additionally, this study also suggested that the translocation of Vip3 in the host cell would be regulated by the BtTF-involved model.

Euchromatin factors HULC and Set1C affect heterochromatin organization and mating-type switching in fission yeast Schizosaccharomyces pombe.

Mating-type (P or M) of fission yeast Schizosaccharomyces pombe is determined by the transcriptionally active mat1 cassette and is switched by gene conversion using a donor, either mat2 or mat3, located in an adjacent heterochromatin region (mating-type switching; MTS). In the switching process, heterochromatic donors of genetic information are selected based on the P or M cell type and on the action of two recombination enhancers, SRE2 promoting the use of mat2-P and SRE3 promoting the use of mat3-M, leading to replacement of the content of the expressed mat1 cassette. Recently, we found that the histone H3K4 methyltransferase complex Set1C participates in donor selection, raising the question of how a complex best known for its effects in euchromatin controls recombination in heterochromatin. Here, we report that the histone H2BK119 ubiquitin ligase complex HULC functions with Set1C in MTS, as mutants in the shf1, brl1, brl2 and rad6 genes showed defects similar to Set1C mutants and belonged to the same epistasis group as set1Δ. Moreover, using H3K4R and H2BK119R histone mutants and a Set1-Y897A catalytic mutant, we found that ubiquitylation of histone H2BK119 by HULC and methylation of histone H3K4 by Set1C are functionally coupled in MTS. Cell-type biases in MTS in these mutants suggested that HULC and Set1C inhibit the use of the SRE3 recombination enhancer in M cells, thus favoring SRE2 and mat2-P. Consistent with this, imbalanced switching in the mutants was traced to compromised association of the directionality factor Swi6 with the recombination enhancers in M cells. Based on their known effects at other chromosomal locations, we speculate that HULC and Set1C control nucleosome mobility and strand invasion near the SRE elements. In addition, we uncovered distinct effects of HULC and Set1C on histone H3K9 methylation and gene silencing, consistent with additional functions in the heterochromatic domain.

Physical and technological analysis of the AlGaN-based UVC-LED: an extended discussion focused on cubic phase as an alternative for surface disinfection.

Crisis in coronavirus times requires understanding the effects on society and establishing efficient mechanisms to prevent infections. The disinfection of personal protection equipment by UVC light remains a key opportunity area. Therefore, this letter presents the main drawbacks and challenges on the fabrication of deep ultraviolet LEDs based on III-nitrides, such as the substrate selection, dislocation reduction, the increase of external quantum efficiency, enhancement of the radiative recombination in the active region, the complications to reach high Al content in AlGaN-based UVC LED avoiding the reduction of the p-doping, replacing the p-GaN contact layer by p-AlGaN without hindering the deposition of ohmic contacts. Furthermore, the cubic phase is suggested as a promising candidate for AlGaN UVC-LEDs applications as is discussed in this work.

RecBCD enzyme and Chi recombination hotspots as determinants of self vs. non-self: Myths and mechanisms.

Bacteria face a challenge when DNA enters their cells by transformation, mating, or phage infection. Should they treat this DNA as an invasive foreigner and destroy it, or consider it one of their own and potentially benefit from incorporating new genes or alleles to gain useful functions? It is frequently stated that the short nucleotide sequence Chi (5' GCTGGTGG 3'), a hotspot of homologous genetic recombination recognized by Escherichia coli's RecBCD helicase-nuclease, allows E. coli to distinguish its DNA (self) from any other DNA (non-self) and to destroy non-self DNA, and that Chi is "over-represented" in the E. coli genome. We show here that these latter statements (dogmas) are not supported by available evidence. We note Chi's wide-spread occurrence and activity in distantly related bacterial species and phages. We illustrate multiple, highly non-random features of the genomes of E. coli and coliphage P1 that account for Chi's high frequency and genomic position, leading us to propose that P1 selects for Chi's enhancement of recombination, whereas E. coli selects for the preferred codons in Chi. We discuss other, previously described mechanisms for self vs. non-self determination involving RecBCD and for RecBCD's destruction of DNA that cannot recombine, whether foreign or domestic, with or without Chi.

Coercivity Enhancement of Hydrogenation Disproportionation Desorption Recombination Nd-Fe-B Powders by Grain Boundary Diffusion Process Using Tb70cu15al15 Alloy

Coercivity Enhancement of Hydrogenation Disproportionation Desorption Recombination Nd-Fe-B Powders by Grain Boundary Diffusion Process Using Tb70cu15al15 Alloy

Compositionally graded AlGaN hole source layer for deep-ultraviolet nanowire light-emitting diode without electron blocking layer

The electron blocking layer (EBL) plays a vital role in blocking the electron overflow from an active region in the AlGaN-based deep-ultraviolet light-emitting diode (DUV-LED). Besides the blocking of electron overflow, EBL reduces hole injection toward the active region. In this work, we proposed a DUV nanowire (NW) LED structure without EBL by replacing it with a compositionally continuous graded hole source layer (HSL). Our proposed graded HSL without EBL provides a better electron blocking effect and enhanced hole injection efficiency. As a result, optical power is improved by 48% and series resistance is reduced by 50% with 4.8 V threshold voltage. Moreover, graded HSL without EBL offer reduced electric field within the active region, which leads to a significant increment in radiative recombination rate and enhancement of spontaneous emission by 34% at 254 nm wavelength, as a result, 52% maximum internal quantum efficiency with 24% efficiency drop is reported.

Optimized performances in InGaN/GaN quantum-well membrane based vertical optoelectronics by the Piezo-phototronic effect

In this work, by conducting selective electrochemical (EC) etching of the sapphire based nitrides epitaxial film, freestanding InGaN/GaN quantum-wells (QWs) membrane was firstly and specifically prepared. InGaN/GaN QWs based device with vertical geometry were then fabricated using the membranes, which can work either as a light-emitting diode (LED) or as a photodetector (PD). The emission intensity and polarization characteristics of vertical devices are optimized by introducing the Piezo-phototronic effect under external straining. Under a tensile strain of 2.04%, the relative electroluminescence (EL) intensity of the LED is increased by 183%, which is ascribed to the enhancement of carriers recombination arisen from the external-strain-induced Piezo-phototronic effect. And the polarization ratio of the emission light is increased or decreased by 135% and 56% under the tensile or compressive strain of 2.04%. For the PD working mode, the polarization ratio of photoresponse current is increased by 107% under the condition of 2.04% tensile strain, while it is reduced by 81% under compressive strain. The modulated polarization characteristics in the vertical devices were attributed to the adjustment in anisotropic optoelectronic properties of InGaN/GaN QWs. This work provides a novel method to fabricate vertical nitride optoelectronics and also presents a unique strategy to their optoelectronic performances.

Bicistronic design as recombinant expression enhancer: characteristics, applications, and structural optimization.

The bicistronic design (BCD) is characterized by a short fore-cistron sequence and a second Shine-Dalgarno (SD2) sequence upstream of the target gene. The outstanding performance of this expression cassette in promoting recombinant protein production has attracted attention. Recently, the application of the BCD has been further extended to gene expression control, protein translation monitoring, and membrane protein production. In this review, we summarize the characteristics, molecular mechanisms, applications, and structural optimization of the BCD expression cassette. We also specifically discuss the challenges that the BCD system still faces. This is the first review of the BCD expression strategy, and it is believed that an in-depth understanding of the BCD will help researchers to better utilize and develop it. KEY POINTS: • Summary of the characteristics and molecular mechanisms of the BCD system. • Review of the actual applications of the BCD expression cassette. • Summary of the structural optimization of the BCD system.

Three-body recombination near the d -wave resonance in ultracold Rb85−Rb87 mixtures

In this study, we investigate the three-body recombination (TBR) rates on both sides of the interspecies $d$-wave Feshbach resonance in the $^{85}\mathrm{Rb}$ -$^{87}\mathrm{Rb}\ensuremath{-}^{87}\mathrm{Rb}$ system using the $R$-matrix propagation method in the hyperspherical coordinate frame. Our calculations are based on the Lennard-Jones model potential for the Rb-Rb interaction. Two different mechanisms of recombination-rate enhancement for positive and negative $^{85}\mathrm{Rb}$ -$^{87}\mathrm{Rb} d$-wave scattering lengths are analyzed. On the positive-scattering-length side, recombination-rate enhancement occurs due to the existence of three-body shape resonance, while on the negative-scattering-length side, the coupling between the lowest entrance channel and the highest recombination channel is crucial to the appearance of the enhancement. In addition, our study shows that the intraspecies interaction has a significant role in determining the emergence of recombination-rate enhancements. Compared to the case in which the three pairwise interactions are in $d$-wave resonance, when the $^{87}\mathrm{Rb}\ensuremath{-}^{87}\mathrm{Rb}$ interaction is near the $d$-wave resonance, the values of the interspecies scattering length that produce the recombination enhancement shift. In particular, when the $^{87}\mathrm{Rb}\ensuremath{-}^{87}\mathrm{Rb}$ interaction is away from the $d$-wave resonance, the enhancement disappears on the side with negative interspecies scattering length.

Tandem Organic Solar Cells with 18.7% Efficiency Enabled by Suppressing the Charge Recombination in Front Sub‐Cell

AbstractThe maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub‐cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub‐cell in such TOSCs can be reduced by increasing the proportion of a non‐fullerene acceptor in the active layer. The non‐fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub‐cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub‐cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine‐turning of the composition in the front sub‐cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained.

Emergent Midgap Excitons in Large‐Size Freestanding 2D Strongly Correlated Perovskite Oxide Films

Abstract2D materials exhibit strong excitonic effects due to low dimensionality and enhanced Coulomb interactions, resulting in fascinating many‐particle phenomena like excitons. Though perovskite is a classical type of material hosting abundant correlated electronic phases, freestanding 2D perovskite oxides are not easy to fabricate and yet to be extensively studied. Here the realization of large size (1 × 1 cm2) freestanding perovskite SrTiO3 films, which show unexpected excitonic photoluminescence (PL) spectra and carrier dynamics, is reported. Two pronounced broad PL peaks emerge in 2D freestanding SrTiO3 films at 2.34–2.4 and 1.8–1.9 eV, of which the 2.34–2.4 eV emission originates from self‐trapped excitons localized within TiO6 octahedra, and the 1.8–1.9 eV peak from Ti vacancies. The time‐resolved PL shows a remarkable enhancement of nonradiative Auger recombination through three‐particle process, in which electron–hole excitons transfer their kinetic energy to other free electrons or holes. The results demonstrate unique excitonic properties in 2D perovskite SrTiO3 films and unravel their potential for high‐performance optoelectronic devices.

Effects of All-Organic Interlayer Surface Modifiers on the Efficiency and Stability of Perovskite Solar Cells.

Surface imperfections created during fabrication of halide perovskite (HP) films could induce formation of various defect sites that affect device performance and stability. In this work, all-organic surface modifiers consisting of alkylammonium cations and alkanoate anions are introduced on top of the HP layer to passivate interfacial vacancies and improve moisture tolerance. Passivation using alkylammonium alkanoate does not induce formation of low-dimensional perovskites species. Instead, the organic species only passivate the perovskite's surface and grain boundaries, which results in enhanced hydrophobic character of the HP films. In terms of photovoltaic application, passivation with alkylammonium alkanoate allows significant reduction in recombination losses and enhancement of open-circuit voltage. Alongside unchanged short-circuit current density, power conversion efficiencies of more than 18.5 % can be obtained from the treated sample. Furthermore, the unencapsulated device retains 85 % of its initial PCE upon treatment, whereas the standard 3D perovskite device loses 50 % of its original PCE when both are subjected to ambient environment over 1500 h.

Influence of light illumination on the potential-induced degradation of n-type interdigitated back-contact crystalline Si photovoltaic modules

We investigate the potential-induced degradation (PID) of n-type interdigitated back-contact (IBC) crystalline Si (c-Si) photovoltaic (PV) modules under a negative bias stress and the influence of light illumination on the PID. IBC PV modules show PID characterized by a reduction in the short-circuit current density (J sc) and open-circuit voltage (V oc) under negative bias stress, while no fill factor (FF) reduction is observed. The degradation may originate from the introduction of sodium (Na) into c-Si and the resulting enhancement of carrier recombination on the surfaces of the IBC cells. Light illumination of 1 sun during the negative bias PID test results in less severe reductions of J sc and V oc. A reduction in the electric field on the surface Si nitride (SiN x ) film, due to carrier generation in the SiN x and the resulting increase in its conductivity, is a possible explanation for the mitigation of the Na-related PID.

Enhanced room-temperature electroluminescence from a germanium waveguide on a silicon-on-insulator diode with a silicon nitride stressor.

Germanium (Ge) is an attractive material for monolithic light sources on a silicon chip. Introduction of tensile strain using a silicon nitride (SiNx) stressor is a promising means for Ge-based light sources due to the enhancement of direct band gap recombination. We propose a device structure that enables current injection from a silicon-on-insulator (SOI) diode to a Ge waveguide with a SiNx stressor formed by a simple fabrication process. Direct-band-gap electroluminescence and direct-band-gap shrinkage due to the applied SiNx stressor was confirmed. Intensity of electroluminescence from the Ge waveguide with the SiNx stressor was about three times higher than that corresponding to the device without the SiNx stressor.

Photoinduced Enhancement of Photoluminescence of Colloidal II-VI Nanocrystals in Polymer Matrices.

The environment strongly affects both the fundamental physical properties of semiconductor nanocrystals (NCs) and their functionality. Embedding NCs in polymer matrices is an efficient way to create a desirable NC environment needed for tailoring the NC properties and protecting NCs from adverse environmental factors. Luminescent NCs in optically transparent polymers have been investigated due to their perspective applications in photonics and bio-imaging. Here, we report on the manifestations of photo-induced enhancement of photoluminescence (PL) of aqueous colloidal NCs embedded in water-soluble polymers. Based on the comparison of results obtained on bare and core/shell NCs, NCs of different compounds (CdSe, CdTe, ZnO) as well as different embedding polymers, we conclude on the most probable mechanism of the photoenhancement for these sorts of systems. Contrary to photoenhancement observed earlier as a result of surface photocorrosion, we do not observe any change in peak position and width of the excitonic PL. Therefore, we suggest that the saturation of trap states by accumulated photo-excited charges plays a key role in the observed enhancement of the radiative recombination. This suggestion is supported by the unique temperature dependence of the trap PL band as well as by power-dependent PL measurement.

A “Turn-on” fluorescence perovskite sensor based on MAPbBr3/mesoporous TiO2 for NH3 and amine vapor detections

Recently, lead halide perovskites have attracted great interest in toxic gas detection, but as gas sensor, it is still a challenge to achieve their high-performance. Here, we propose a novel “turn-on” fluorescence NH3/amine vapor sensor by depositing the CH3NH3PbBr3 (MAPbBr3) on the mesoporous TiO2 (mp-TiO2) layer. The fluorescence intensity of the sensor increases rapidly within seconds upon exposure to NH3 gas (72 % at 5 ppm and 988 % at 100 ppm, respectively) with excellent reversibility, high gas selectivity, humidity insensitivity, and regeneration. Moreover, the sensor can be further used for detecting various amine vapors, including methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, and decylamine. We presumed the “turn-on” fluorescence sensing mechanism is that the trace NH3 or amine molecules could decrease the surface trap defects and facilitate the formation of passivation layer. It will impede the electron-injection into mp-TiO2, which induces the radiative electron-hole recombination and fluorescence enhancement. This research demonstrates that it is feasible to design a “turn-on” fluorescence gas sensor based on the mp-TiO2-based perovskite.

Enhanced stability and photovoltaic performance of planar perovskite solar cells through anilinium thiobenzoate interfacial engineering

Organic-inorganic halide perovskite absorbers remain top contenders for current photovoltaic technologies owing to their ability to attain high efficiency at relatively low cost. However, commercialization of perovskite solar cells remains difficult due to their poor long-term stability. Such instability is commonly attributed to the ease in defect formation within the polycrystalline absorber film as well as at the surfaces between the layers, acting as recombination centers, reducing the overall performance of the device. Introduction of suitable interfacial layers has proven effective in defect passivation, allowing enhanced device stability and improving photovoltaic performance. In this study, a novel anilinium thiobenzoate (ATB) interlayer is deposited between the perovskite/hole transport layer (HTL) interface. Since ATB contains functional groups such as sulfur and ammonium, favourable coordination with under-coordinated lead ions on the perovskite film allows significant reduction in recombination losses and enhancement of open-circuit voltage from 1.05 to 1.11 V. Apart from the paramount efficiency of 19.33%, the 10 mg/mL ATB passivated device also shows exceptional long-term stability whereby 92% of initial efficiency is retained despite storage in ambient conditions for 150 days. Hence, results from this study highlights the importance of device passivation in attaining superior device performance and long-term stability.

Influence of emitter position of silicon heterojunction photovoltaic solar cell modules on their potential-induced degradation behaviors

Potential-induced degradation (PID)-test results of modules fabricated from the rear- and front-emitter silicon heterojunction (SHJ) solar cells were compared to clarify the influence of the emitter position of SHJ photovoltaic (PV) cell modules on their PID behaviors. The PID tests were performed by applying a bias of −2000 V to the shorted interconnector ribbons from the front surface of the cover glass, at 85 °C. In the initial stage, both modules showed the same degradation characterized by a reduction in the short-circuit current density (Jsc). After the first-stage degradation, the rear-emitter SHJ PV modules exhibited subsequent degradation characterized by a significant reduction in the Jsc and open-circuit voltage (Voc), due to the enhancement of the minority-carrier recombination in the front surface region of the n-type crystalline silicon base. The front-emitter SHJ PV modules, on the other hand, showed a reduction in the fill factor (FF), in addition to moderate reductions in Jsc and Voc. The FF reduction of the front-emitter SHJ PV modules is considered to be caused by the enhancement of the recombination in the front surface region of the n-type crystalline-silicon base as the region corresponds to the pn junction interface of the front-emitter configuration. The moderate reductions in both Jsc and Voc may be due to further progression of the first-stage degradation. These findings are essential for understanding the mechanism of PID in SHJ PV cell modules.

InGaN blue light emitting micro-diodes with current path defined by tunnel junction.

We have fabricated tunnel-junction InGaN micro-LEDs using plasma-assisted molecular beam epitaxy technology, with top-down processing on GaN substrates. Devices have diameters between 5 µm and 100 µm. All of the devices emit light at 450 nm at a driving current density of about 10Acm-2. We demonstrate that within micro-LEDs ranging in size from 100 µm down to 5 µm, the properties of these devices, both electrical and optical, are fully scalable. That means we can reproduce all electro-optical characteristics using a single set of parameters. Most notably, we do not observe any enhancement of non-radiative recombination for the smallest devices. We assign this result to a modification of the fabrication process, i.e., replacement of deep dry etching by a tunnel junction for the current confinement. These devices show excellent thermal stability of their light emission characteristics, enabling operation at current densities up to 1kAcm-2.

A high-performance soybean meal-based plywood adhesive prepared via an ultrasonic process and using significantly lower amounts of chemical additives

The development of a formaldehyde-free, high-performance soybean meal (SM)-based adhesive for manufacturing cleaner wood-based panels is important for minimizing environmental pollution and promoting sustainability. However, the addition of chemical agents for this purpose negatively impacts the environment. Drawing from molecular recombination enhancement theory, a simple physical ultrasonic treatment was used to pretreat the SM to break its particles down and reduce the protein molecular weight. A bio-derived crosslinker was mixed into the SM to recombine the soy protein and prepare a clean, high-performance, bio-based adhesive requiring significantly lower amounts of chemical agents. After 20 min of ultrasonic treatment, the SM particle size was reduced by up to 48.8%, the quaternary structure of the soybean protein was destroyed, and the protein molecular weight decreased, exposing more active groups on the protein surface and resulting in an adhesive system that was both more stable and had a higher reactivity. Moreover, when adding only 4% crosslinker and zero denaturing agent, the ultrasonic treatment process increased the adhesive residual rate by 15.78%, decreased the moisture absorption rate by 25.26%, and improved the wet shear strength of the resultant plywood by 368.2% (to 1.03 MPa), meeting the requirements of the GB/T 9846.3–2004 standard for interior-use plywood. The loading of chemical agents was reduced by up to 650% in comparison to that used in other SM-based adhesive formulations reported in the literature. Thus, using a clean ultrasonic pretreatment process on the SM enabled the preparation of a high-performance, stable, and clean SM-based adhesive, thereby providing a promising option for the implementation of a bio-based product in industrial applications.