Kernel Development Research Articles

A comparison study between different kernel functions in the least square support vector regression model for penicillin fermentation process

Soft sensors are becoming increasingly important in our world today as tools for inferring difficult-to-measure process variables to achieve good operational performance and economic benefits. Recent advancement in machine learning provides an opportunity to integrate machine learning models for soft sensing applications, such as Least Square Support Vector Regression (LSSVR) which copes well with nonlinear process data. However, the LSSVR model usually uses the radial basis function (RBF) kernel function for prediction, which has demonstrated its usefulness in numerous applications. Thus, this study extends the use of non-conventional kernel functions in the LSSVR model with a comparative study against widely used partial least square (PLS) and principal component regression (PCR) models, measured with root mean square error (RMSE), mean absolute error (MAE) and error of approximation (Ea) as the performance benchmark. Based on the empirical result from the case study of the penicillin fermentation process, the Ea of the multiquadric kernel (MQ) is lowered by 63.44% as compared to the RBF kernel for the prediction of penicillin concentration. Hence, the MQ kernel LSSVR has outperformed the RBF kernel LSSVR. The study serves as empirical evidence of LSSVR performance as a machine learning model in soft sensing applications and as reference material for further development of non-conventional kernels in LSSVR-based models because many other functions can be used as well in the hope to increase the prediction accuracy.

Hydrodynamic effects of shock interactions on initial flame kernel development of close dual-point laser induced sparks

Flame kernel formations of close dual-point laser induced sparks were investigated experimentally, focusing on the hydrodynamic effects induced by an interaction of shock waves produced by the laser induced sparks. Dual sparks were produced near the center of the combustion chamber by splitting of a ray emitted by a 532 nm Nd:YAG laser. Methane/air mixtures were ignited under a quiescent condition in a constant volume chamber with detailed measurements of the ignition energy and the pressure history. The minimum ignition energy was derived as an ignition energy having an ignitability of 50% using the logistic regression method. The flame kernel initiation process was also observed by Schlieren photography using a high-speed video camera. The offset of laser induced sparks were adjusted by tuning angles of mirrors and lenses. The ignition performance of single- and close dual-point laser breakdown induced sparks was investigated in detail in terms of the minimum ignition energy and the combustion induction time. Time resolved Schlieren photographs indicated that two hump shaped kernels grew rapidly during the initial stage in the vicinity of the plane of symmetry defined by the laser sparks under certain conditions. Their formation was due to the hydrodynamic effects induced by Mach shock waves, which resulted from interactions of the dual shock waves. The minimum ignition energy of the close dual-point laser induced sparks near the lean limit at 1.0 MPa was much lower than that of single-point laser induced sparks, although it was greater than that of the single ones at 0.1 MPa. The combustion induction time, which was defined as the time corresponding to the maximum pressure increase rate, was shortened for close dual-point laser induced sparks, especially for lean mixtures at high pressure. Robust flame kernels were formed by close dual-point laser induced sparks with Mach shock wave formation, and improved ignition performance for lean mixtures at high pressure was observed.

Spark discharge energy effect on in-cylinder characteristics performance of rapid compression and expansion machine with spark ignition direct injection strategy

A spark ignition strategy in compression ignition has been considered to achieve high performance of gasoline direct injection engines. The spark ignition energy depends on the discharge current and the spark discharge duration. However, the respective roles of both on the rapid compression and expansion machine (RCEM) running with spark ignition and gasoline direct injection in-cylinder pressure have not been fully investigated. Both experiments and simulations were carried out in this study to investigate the spark discharge energy’s effect on in-cylinder characteristics performance. Three spark ignition strategy ranging from 50 mA up to 200 mA is applied to enhance the ignition discharge energy according to six selected cases of ignition timing variation (0.7 ms, 1.0 ms, 2.0 ms, 3.0 ms, 4.0 ms, and 5.0 ms). The results show the total released energy at the simultaneous ignition strategy was the largest (around 190 mJ/s), followed in order by the pair ignition strategy and individual ignition strategy. The highest turbulent kinetic energy of gasoline RCEM with spark ignition strategy is 1.43 m2/s2 (an increase 27.96 % from RCEM fueled with diesel). When the start of injection (SOI) of direct injection gasoline was set the same as the SOI of direct injection diesel at 10 oCA BTDC resulted in the thermal efficiency of gasoline RCEM with spark application slightly increased when spark time duration is prolonged at the average of 15.96 %. Finally, the establishment of a compression ignition engine combined with spark energy discharge might contribute to faster plasma formation, as well as expose the kernel development to a wider range of spark duration.

Conservation Study of Imprinted Genes in Maize Triparental Heterozygotic Kernels

Genomic imprinting is a classic epigenetic phenomenon related to the uniparental expression of genes. Imprinting variability exists in seeds and can contribute to observed parent-of-origin effects on seed development. Here, we conducted allelic expression of the embryo and endosperm from four crosses at 11 days after pollination (DAP). First, the F1 progeny of B73(♀) × Mo17(♂) and the inducer line CAU5 were used as parents to obtain reciprocal crosses of BM-C/C-BM. Additionally, the F1 progeny of Mo17(♀) × B73(♂) and CAU5 were used as parents to obtain reciprocal crosses of MB-C/C-MB. In total, 192 and 181 imprinted genes were identified in the BM-C/C-BM and MB-C/C-MB crosses, respectively. Then, by comparing the allelic expression of these imprinted genes in the reciprocal crosses of B73 and CAU5 (BC/CB), fifty-one Mo17-added non-conserved genes were identified as exhibiting imprinting variability. Fifty-one B73-added non-conserved genes were also identified by comparing the allelic expression of imprinted genes identified in BM-C/C-BM, MB-C/C-MB and MC/CM crosses. Specific Gene Ontology (GO) terms were not enriched in B73-added/Mo17-added non-conserved genes. Interestingly, the imprinting status of these genes was less conserved across other species. The cis-element distribution, tissue expression and subcellular location were similar between the B73-added/Mo17-added conserved and B73-added/Mo17-added non-conserved imprinted genes. Finally, genotypic and phenotypic analysis of one non-conserved gene showed that the mutation and overexpression of this gene may affect embryo and kernel size, which indicates that these non-conserved genes may also play an important role in kernel development. The findings of this study will be helpful for elucidating the imprinting mechanism of genes involved in maize kernel development.

Effect of coil charge duration on combustion variability and flame morphology in a GDI engine working in lean burn conditions

Spark ignition (SI) and subsequent flame front development exert a significant influence on cyclic variability of internal combustion engines (ICEs). The increasing exploitation of lean air-fuel mixtures in SI engines to lower fuel consumption and CO2 emissions is driving the scientific community towards the search for innovative combustion strategies. Moreover, although lean combustion has been widely investigated and an important number of studies is already present in literature, the high cyclic variability typical of this combustion process still represents a major hinder to its exploitation. This study aims to investigate the effects of increasing ignition energy on combustion characteristics of lean mixtures. Tests were performed on an optically accessible gasoline direct injection (GDI) engine that allowed to investigate the correlation between the thermodynamic results and spark arc-flame morphology. Engine speed was fixed at 2000 rpm, a relative air fuel ratio (AFRrel) of about 1.3 was selected and ignition timing was set at 12 crank angle degrees (CAD) bTDC. Coil charge duration was swept from 10 to 40 CAD. Two intake pressure levels were investigated, the first corresponding to wide open throttle under naturally aspirated operating mode, the second with an intake pressure of 1.2 bar, thus corresponding to a boosted operating condition. Two dedicated scripts built using NI Vision were employed for image processing, allowing the evaluation of temporal and spatial evolution of the early stages of combustion. Arc elongation and flame front contour were used as correlation parameters that characterize flame kernel inception and development. The results confirm that, as expected, the increase of the coil charge duration tends to reduce cyclic variability in terms of engine output. The optical investigations revealed that for both examined cases the standard deviation related to the wrinkling effect on flame edge at CA5 decreased as the coil charge duration increased.

Large-Eddy Simulation Analysis of Flow and Combustion in a Pre-Chamber Ignited Gasoline Engine

ABSTRACT Multi-cycle large eddy simulations were conducted to resolve the turbulent flow field spatially and temporally in a pre-chamber ignited gasoline engine. The numerical models were validated by comparing with both the passive and active pre-chamber experimental data. Correlation analysis results of the two pressure peaks during combustion inside the pre-chamber showed that the combustion inside the pre-chamber directly influences the timing and strength of the turbulent jets, which would ignite the mixture inside the main chamber. Then, the flow field evolution and fuel/air mixture formation inside both the main chamber and pre-chamber during intake and compression strokes were investigated numerically. Results of the passive pre-chamber showed that mixture distribution near the orifices during the compression stroke affects the averaged lambda of the gas inside the pre-chamber. By using the orifices with a tilted orientation, the fuel inside the pre-chamber could be stratified. When the mixture near electrodes is rich, the development of ignition kernel and the consequent flame propagation would benefit. In the case of active pre-chamber, although the lambda distribution patterns of mixture before the spark plug ignition are similar between different cycles, the magnitude of velocity would affect the early flame propagation inside the pre-chamber.

Analysis of key biological pathways for sugar accumulation during kernel development in different genotypes of sweet corn

Analysis of key biological pathways for sugar accumulation during kernel development in different genotypes of sweet corn

Regional prediction of Fusarium head blight occurrence in wheat with remote sensing based Susceptible-Exposed-Infectious-Removed model

• Fusarium head blight (FHB) is a major fungal disease affecting wheat production. • Regional disease prediction using mechanistic models is difficult. • A remote sensing based model for regional prediction of FHB in wheat is proposed. • Optimized soil adjusted vegetation index (OSAVI) was used for model initialization. • Susceptible-Exposed-Infectious-Removed (SEIR) model was calibrated and verified. Fusarium head blight (FHB) is one of the major fungal diseases affecting wheat production worldwide, influencing kernel development and producing poisonous mycotoxins. Mechanistic models have been extensively used for plant disease simulation; however, regional disease prediction using these models is difficult because they simplify the heterogeneous plant growth conditions. Herein, we present a remote sensing based Susceptible-Exposed-Infectious-Removed (SEIR) model for regional prediction of FHB occurrence in wheat. Plant properties that are key to the development of FHB are extracted from remote sensing data or data products to initialize or drive the model. Fractional vegetation cover products, time-series curves from satellite images, and vegetation indices were used to indicate plant density, phenology, and vegetation vigor. We applied our model to a plain region in China that suffers greatly from FHB annually. The SEIR model was parameterized by incorporating remote sensing data products, and then calibrated and verified for regional FHB prediction. The model was trained and evaluated by comparing the results of its prediction of FHB incidence to field observations during the susceptible period for wheat; satisfactory results were observed with a correlation coefficient of 0.804, root mean-square error of 0.131, classification accuracy of 0.860, and missed detection rate of 0.035 when the model was initialized with the Optimized Soil Adjusted Vegetation Index (OSAVI). The disease progress curves furnished by our model display an S-shape—a characteristic of polycyclic diseases—which matches the wheat FHB epidemiology. These results indicate that our remote sensing-based SEIR model is promising for the regional prediction of FHB occurrence in wheat.

The Integration of Metabolomics and Transcriptomics Provides New Insights for the Identification of Genes Key to Auxin Synthesis at Different Growth Stages of Maize.

As a staple food crop, maize is widely cultivated worldwide. Sex differentiation and kernel development are regulated by auxin, but the mechanism regulating its synthesis remains unclear. This study explored the influence of the growth stage of maize on the secondary metabolite accumulation and gene expression associated with auxin synthesis. Transcriptomics and metabonomics were used to investigate the changes in secondary metabolite accumulation and gene expression in maize leaves at the jointing, tasseling, and pollen-release stages of plant growth. In total, 1221 differentially accumulated metabolites (DAMs) and 4843 differentially expressed genes (DEGs) were screened. KEGG pathway enrichment analyses of the DEGs and DAMs revealed that plant hormone signal transduction, tryptophan metabolism, and phenylpropanoid biosynthesis were highly enriched. We summarized the key genes and regulatory effects of the tryptophan-dependent auxin biosynthesis pathways, giving new insights into this type of biosynthesis. Potential MSTRG.11063 and MSTRG.35270 and MSTRG.21978 genes in auxin synthesis pathways were obtained. A weighted gene co-expression network analysis identified five candidate genes, namely TSB (Zm00001d046676 and Zm00001d049610), IGS (Zm00001d020008), AUX2 (Zm00001d006283), TAR (Zm00001d039691), and YUC (Zm00001d025005 and Zm00001d008255), which were important in the biosynthesis of both tryptophan and auxin. This study provides new insights for understanding the regulatory mechanism of auxin synthesis in maize.

Study of Flame Kernel Development at High EGR and High Flow Speed Using Conventional Spark Igniter and Non-Thermal Plasma Under Gasoline Engine Relevant Conditions

ABSTRACT As a novel ignition approach, nanosecond repetitively pulsed discharge (NRPD)-based non-thermal plasma offers significant benefits such as low energy consumption, and lean operating conditions. However, there is no investigation conducted on the early flame kernel formation and development induced by non-thermal plasma. Therefore, in this paper, experiments of conventional spark and non-thermal plasma ignition systems in constant volume combustion chamber (CVCC) are conducted under gasoline engine relevant conditions: wide initial ambient pressures (6.5, 8.3, 11.3 bar), a range of equivalence ratios (0.7–1.0), EGR rates (10−25%), and cross flow speeds (0–30 m/s). The discharge energy of non-thermal plasma is of around 210 mJ, while a single spark event can generate energy from 65 mJ to 83 mJ depending on ambient conditions. A consecutive spark strategy is adopted to guarantee comparable total input energy to non-thermal plasma. The ignition delay and combustion phase obtained from the chamber pressure history are calculated. In the meanwhile, flame kernel radius, flame propagation rate, and flame front length ratio via schlieren images are quantified and analyzed. Results showed that the flame initiated by non-thermal plasma can maintain a robust flame kernel and propagates fast. Under high-speed cross flow and high EGR rate conditions, non-thermal plasma can maintain a robust flame kernel at early stage supporting the initial flame kernel to survive and improve its ignition probability. Considering the effects of the EGR ratio and high-speed cross flow on flame kernel development, non-thermal plasma ignition can efficiently enhance the flame propagation and ignition probability. It is also concluded that non-thermal plasma can successfully ignite under lean (equivalence ratio between 0.7–1.0), high-diluted mixture (25% EGR), and high-speed cross flow of 30 m/s within the range of current study.

Genetic and molecular analysis of starch physicochemical properties and its relationship with endosperm modification in quality protein maize

Quality protein maize (QPM) was created converting the soft opaque-2 endosperm into a vitreous phenotype, but the mechanisms involved in this modification are not completely understood. Recombinant inbred lines (RILs) derived from K0326Y QPM and W64Ao2 were used to identify quantitative trait loci (QTL) associated with starch physicochemical properties. RILs contrasting in vitreousness were also used to evaluate the expression of starch biosynthesis genes. Mapping identified 5-6 QTLs for each trait that explained 66 % of the phenotypic variation. Three QTLs on bins 4.05, 5.04, and 9.03 were found close to the starch biosynthesis genes Brittle-2 (Bt2), Amylose extender-1 (Ae1), and Waxy-1 (Wx1), respectively. The expression of Wx1 was three-fold greater in K0326Y QPM than W64Ao2 and eight-fold higher in vitreous than opaque RILs, which corresponded with the greater accumulation of granule bound starch synthase I (GBSSI) and the higher amylose content observed in the vitreous lines. The increased synthesis of amylose may result in starch granules with more amorphous regions that favor their compaction. These results suggest that endosperm modification in QPM is associated with the synthesis of starch containing more amylose during kernel development, which may facilitate the packing of the starch granules resulting in the vitreous phenotype.

The Italian Research on the Molecular Characterization of Maize Kernel Development.

The study of the genetic control of maize seed development and seed-related pathways has been one of the most important themes approached by the Italian scientific community. Maize has always attracted the interest of the Italian community of agricultural genetics since its beginning, as some of its founders based their research projects on and developed their “schools” by adopting maize as a reference species. Some of them spent periods in the United States, where maize was already becoming a model system, to receive their training. In this manuscript we illustrate the research work carried out in Italy by different groups that studied maize kernels and underline their contributions in elucidating fundamental aspects of caryopsis development through the characterization of maize mutants. Since the 1980s, most of the research projects aimed at the comprehension of the genetic control of seed development and the regulation of storage products’ biosyntheses and accumulation, and have been based on forward genetics approaches. We also document that for some decades, Italian groups, mainly based in Northern Italy, have contributed to improve the knowledge of maize genomics, and were both fundamental for further international studies focused on the correct differentiation and patterning of maize kernel compartments and strongly contributed to recent advances in maize research.

Ignition kernel development in a reactive flow for nanosecond-pulsed high-frequency and DC arc discharges

The development of energy efficient combustion systems is a critical technical objective in the engine and power generation industries. This pursuit often prompts using conditions at the limits of capability, dictating the need to expand the envelope of robust and reliable operation. Nanosecond-pulsed high-frequency discharges (NPHFD) have proven to be effective in extending ignition limits in both quiescent and flowing environments. However, limited research has been conducted comparing the kernel growth behavior in a flowing environment of a train of discrete nanosecond discharges to that of a conventional DC arc discharge. Therefore, this work focused on comparing these two types of discharges by matching the total energy deposited, total deposition time, and average power. For each system, three average power conditions (100, 180, and 400 W) were tested, each including five total discharge times (0.05, 0.15, 0.25, 0.50, and 1.00 ms) at two inter-electrode gap distances of 1 and 2 mm. The 1 mm gap distance results showed that the NPHFD system produced larger ignition kernel areas than the conventional system at the highest average power (therefore, highest pulsation frequency) setting. At all other average power conditions, the NPHFD system produced equivalent or smaller ignition kernels than the conventional system due to a lack of pulse-to-pulse coupling. At the 2 mm inter-electrode gap distance, the NPHFD ignition system produced larger kernels at all conditions except at the lowest average power and discharge duration setting. At the highest average power and longest discharge duration setting, the NPHFD kernel was nearly twice as large in area as the kernel produced by the conventional system at 5 ms after discharge. The larger kernel area created by the NPHFD system at the larger gap distance, higher average power, and longer total discharge duration conditions could be explained by the high level of pulse-to-pulse coupling and discharge-induced jetting behavior. The jetting behavior was a function of electrode polarity and mainly extended the reactive region of the kernel in the spanwise direction.

Genome-wide identification of B3 superfamily in pecan (Carya illinoensis): In silico and experimental analyses

The B3 superfamily comprises a class of transcription factors containing B3 functional domains that play crucial roles in plant growth and development. However, the identification and analysis of the B3 superfamily have not been reported in pecans. In this study, 75 B3 superfamily members were identified and divided into four families, namely ARF (31), RAV (10), LAV (8), and REM (26). The gene structure, conserved motifs and domain analysis indicated that each family was highly similar. The Ka/Ks results indicated that the CiB3s underwent purifying selection. Several growth- and development-related cis-elements, such as Box 4, GATA-motif, and G-Box, were found in the promoter of the B3 transcription factor. The results obtained from the transcriptomic analysis of different kernel development stages and different tissues of pecan and qRT-PCR, indicated that several transcription factors, particularly CiABI3, CiFUS3, and CiLEC2, were involved in regulating kernel development. In particular, the expression of CiFUS3 changed significantly between S3 and S5. Additionally, CiFUS3 is localized in the nucleus and has no self-transcriptional activity. A yeast one-hybrid experiment showed that CiFUS3 could bind to the RY-motif related to seed development. Overall, our study provides a reference for the role of CiFUS3 in oil synthesis and the functional study of B3 genes in pecan.

Combining xenia, male sterility, and synchronous pollination to improve maize grain yield and market value

Xenia (pollination of florets with genetically unrelated pollen), male sterility (removal of fertile pollen), and synchronous pollination (application of pollen when all silks are present) are well-documented processes that influence kernel formation and development in maize. There also have been numerous reports in which xenia and male sterility were combined in an attempt to increase kernel number, kernel weight, and/or grain yield. We present an analysis of published literature exploring impacts of xenia resulting from cross-pollination, male sterility, and synchronous pollination applied individually or in combination. Although synchronous pollination has had the most consistent and positive impact on seed formation, to our knowledge there are no reports combining all three effectors together. Recently developed technology to collect, preserve, and apply large volumes of maize pollen has provided the opportunity to evaluate the cumulative and potentially synergistic effects of synchronous pollination, xenia, and male sterility applied together on maize hybrids. We present the results of a field trial combining all three effectors in maize; this approach increased kernels per ear, kernel oil concentration, and grain yield per hectare. The results suggest synchronous pollination is essential to enable the greatest number of kernels to develop successfully. Male sterility supports kernel formation by providing greater assimilate supply per kernel, and xenia increases sink strength to attract the additional assimilates. The positive response and economic return when these effectors are applied in combination provides a novel opportunity for grain producers to manage kernel formation and composition proactively using pollen to deliver the trait of choice.

Laser-induced ignition of methane-air mixtures by a four-beam, pulse-burst mode passively Q-switched Nd:YAG/Cr4+:YAG laser

In this work we report on the characteristics of laser ignition of CH4-air mixtures, using multi-point (up to four points) ignition with single-pulse beams as well as with trains of two pulses. A compact Nd:YAG/Cr4+:YAG laser with four beams, each beam being operated in single-pulse or burst mode (with up to five pulses), each pulse with an energy of 3.8 mJ and 0.9 ns duration was employed in the experiments. A combustion chamber with spherical geometry was used to ignite CH4-air mixtures with various values of the air–fuel equivalence ratio, λ and at different initial pressures of the fuel mixtures. Analysis of pressure curves indicates that using multiple ignition points leads to an acceleration of the flame speed in the early kernel development phase. It has been observed that for an initial pressure of 1 bar in the combustion chamber, ignition at a point with two laser pulses decreases the duration of combustion by about 7 % compared to ignition at a point with a single laser pulse. For ignition in four points with one or two pulses, the combustion is 10 % and 20 % faster, respectively. The combustion efficiency is also analyzed, and we report that a multi-point laser ignition source leads to a slight increase in the efficiency of burning the fuel near the lean limit. The ignition limits, for both lean and rich CH4-air mixtures, have also been determined for initial pressures in the combustion chamber of up to 9 bars and each ignition method, and a discussion of these is presented.

Environmental Factors Influence the Seed Phenotypic Variation of Sapindus mukorossi Gaertn. and Sapindus delavayi (Franch.) Radlk. in China

Abstract The phenotypes of Sapindus are significantly influenced by environmental factors, but the responses of oil-related seed phenotypes to environmental factors are still unclear. We sampled 115 seed accessions of Sapindus mukorossi Gaertn. and 33 of Sapindus delavayi (Franch.) Radlk. from fifty-six distinct locations in China to explore the effects of environmental factors on the seed phenotypes. Pearson’s correlation analysis showed that 100-seed kernel weight (SKW), 100-seed shell weight (SSW), and seed kernel content (SKC) were the phenotypes most sensitive to the environmental influence (significantly associated with at least ten environmental factors). Redundancy analysis explained 26.13% of the variance and revealed that longitude was negatively correlated with SKW and SKC but was positively correlated with SSW, whereas elevation had the opposite effect. Monthly sunshine hours was negatively correlated with 100-seed weight and SSW. Additionally, the Mantel test showed that the seed phenotypic variations in Sapindus mukorossi and Sapindus delavayi were significantly affected by environmental factors differently. SKW and SKC of Sapindus delavayi were more sensitive to the influence of key environmental factors and therefore had more potential for oil development. It is recommended to cultivate Sapindus delavayi at lower longitudes to facilitate seed kernel development and promote oil yield.

Effects of differential diffusion on hydrogen flame kernel development under engine conditions

The early flame kernel development in spark ignition engines is crucial for engine performance. For non-unity-Lewis-number mixtures, it can be significantly influenced by differential diffusion due to the large curvature of the small kernel. Differential diffusion can lead to thermodiffusive instabilities for lean hydrogen/air flames, which are enhanced for high pressures but diminish for increasing temperatures. In this study, direct numerical simulations of lean hydrogen flame kernels under engine conditions have been performed to investigate how differential diffusion affects their growth with an effective Lewis number far smaller than unity and if thermodiffusive instabilities appear under realistic engine conditions with elevated in-cylinder pressure and high unburned temperature. It is found that turbulence triggers the instabilities for flame kernel sizes far smaller than the critical radius of the onset of cellular instabilities for laminar flames. The strong thermodiffusive instabilities significantly facilitate the flame kernel growth. The normalized fuel consumption rate is increased by a factor of up to four, due to an enhanced propagation speed. This is remarkable as it was found in earlier studies that for laminar flames the effects of instabilities become much weaker under these conditions. Thermodiffusive instabilities also lead to large variations of the local fuel/air equivalence ratio resulting in temperatures up to 500 K above the adiabatic temperature, which impacts NOx formation. In addition, thermodiffusive instabilities alter the mechanisms of flame surface area formation. The production and destruction of the surface area by flame propagation are significantly increased. A transition phase can be identified during the formation of the negative curvature regions from the initial spherical kernel.

Integrated microRNA and transcriptome profiling reveals the regulatory network of embryo abortion in jujube.

Hybridization is an important approach to the production of new varieties with exceptional traits. Although the kernel rate of wild jujube (Ziziphus jujuba Mill. var. spinosa Hu.) is generally high, that of cultivated jujube (Z. jujuba Mill.) is low, greatly hampering the jujube breeding process. However, the mechanism by which this trait changed during jujube domestication remains unclear. Here, we explored the potential regulatory network that governs jujube embryo abortion using correlation analysis of population traits, artificial pollination, sugar content measurements and multi-omics analysis. The results showed that embryo abortion was an important reason for the low kernel rate of cultivated jujube, and kernel rate was negatively correlated with edible rate. Twenty-one days after pollination was a critical period for embryo abortion. At this time, the sugar content of cultivated 'Junzao' kernels decreased significantly compared with that of the pulp, but sugar content remained relatively stable in kernels of wild 'Suanzao'. A total of 1142 differentially expressed genes targeted by 93 microRNAs (miRNAs) were identified by transcriptome, miRNA and degradome sequencing, and may be involved in the regulation of embryo abortion during kernel development. Among them, DELLA protein, TCP14 and bHLH93 transcription factors have been shown to participate in the regulation of embryonic development. Our findings suggest that carbohydrate flow between different tissues of cultivated jujube exhibits a bias toward the pulp at 21days after pollination, thereby restricting the process of kernel development. This information enhances our understanding of the embryo abortion process and reveals miRNA-target gene pairs that may be useful for molecular-assisted breeding.

A Combined Numerical and Experimental Investigation of Cycle-to-Cycle Variations in an Optically Accessible Spark-Ignition Engine

A combined numerical and experimental investigation is carried out to analyze the cycle-to-cycle variations (CCV) in an optically accessible spark-ignition engine with port fuel injection. A stable and an unstable operating condition is considered. Well-established turbulence, combustion, and ignition models are employed in the large-eddy simulations (LES). High-speed measurements of the velocity field via particle image velocimetry and flame imaging in the tumble plane are conducted in the experiments. A detailed comparison between LES and experiments is carried out, including the in-cylinder pressure, the flow fields, the spatial flame distribution, and the fields conditioned on fast and slow cycles. Good agreement is achieved for the variables considering all cycles; yet, some discrepancies are observed for the conditionally averaged quantities. A systematic quantitative correlation analysis between the selected influencing variables and the CCV is presented, in which the influencing variables are extracted from different length scales (r = 3 mm, 12 mm, and 43 mm) and the CCV are distinguished between the early flame kernel development and later flame propagation. Even though the most relevant influencing parameters are different for the two operating conditions, the location of the coherent vortex structure is found to be important for the CCV of both cases.