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In order to predict and optimize the contour laser transmission welding (LTW) process, it is important to understand how the laser energy behaves during transmission through the transparent part. In this study, transmission measurements were made on unreinforced and glass-fiber-reinforced amorphous and semi-crystalline thermoplastics at different thicknesses. Using the ratio of transmitted power to laser power, apparent absorption coefficients and apparent reflections were calculated. The results indicate that there is a linear relationship between the glass fiber volume fraction and the apparent absorption coefficient of reinforced polymers; similar effects were also observed for crystallinity. A simple model was developed to estimate apparent absorption coefficient of reinforced polymers as a function of composition. The apparent reflection increased with crystallinity due to increased back scattering. However, for glass-fiber-reinforced polymers, the apparent reflection displayed a more complex behavior. [ABSTRACT FROM AUTHOR]

Metabolism is comprised of networks of chemical transformations, organized into integrated biochemical pathways that are the basis of cellular operation, and function to sustain life. Metabolism, and thus life, is not static. The rate of metabolites transitioning through biochemical pathways (i.e., flux) determines cellular phenotypes, and is constantly changing in response to genetic or environmental perturbations. Each change evokes a response in metabolic pathway flow, and the quantification of fluxes under varied conditions helps to elucidate major and minor routes, and regulatory aspects of metabolism. To measure fluxes requires experimental methods that assess the movements and transformations of metabolites without creating artifacts. Isotopic labeling fills this role and is a long-standing experimental approach to identify pathways and quantify their metabolic relevance in different tissues or under different conditions. The application of labeling techniques to plant science is however far from reaching it potential. In light of advances in genetics and molecular biology that provide a means to alter metabolism, and given recent improvements in instrumentation, computational tools and available isotopes, the use of isotopic labeling to probe metabolism is becoming more and more powerful. We review the principal analytical methods for isotopic labeling with a focus on seminal studies of pathways and fluxes in lipid metabolism and carbon partitioning through central metabolism. Central carbon metabolic steps are directly linked to lipid production by serving to generate the precursors for fatty acid biosynthesis and lipid assembly. Additionally some of the ideas for labeling techniques that may be most applicable for lipid metabolism in the future were originally developed to investigate other aspects of central metabolism. We conclude by describing recent advances that will play an important future role in quantifying flux and metabolic operation in plant tissues. [ABSTRACT FROM AUTHOR]

Highlights: [•] Recent research has identified new intricacies in assembly of seed oils. [•] Oil synthesis involves multiple subcellular compartments requiring lipid trafficking. [•] Phosphatidylcholine is both a central intermediate and a carrier of acyl chains. [•] Different plants utilize alternative pathways to produce diverse oil structures. [•] Major questions and unknowns are highlighted for future oilseed research. [Copyright &y& Elsevier]

Abstract: Laser light reflection during the laser transmission welding (LTW) of thermoplastics has the potential to overheat and/or cause unintentional welding of adjacent features of the part being welded. For this reason, and in order to assess how much light is being absorbed by the transparent part (after measurement of the light transmitted through the transparent part), it is important to be able to quantify the magnitude and distribution of reflected light. The magnitude and distribution of the reflected light depends on the total laser input power as well as its distribution, the laser incidence angle (angle between the normal to the transparent part surface and the laser beam), the laser light polarization as well as the surface and optical properties of the transparent part. A novel technique based on thermal imaging of the reflected light was previously developed by the authors. It is used in this study to characterize the magnitude and distribution of reflected light from thermoplastics as a function of thickness (1–3.1mm), laser incidence angle (20–40°) and surface roughness (0.04–1.04μm). Results from reflection tests on nearly polished nylon 6 (surface roughness between 0.04 and 0.05μm) have shown that, for the various thicknesses tested (1–3.1mm), the total reflection was larger than the specular top surface reflection predicted via the Fresnel relation. From these observations, it is conjectured that, in addition to top surface reflection, the bulk and/or bottom surface also contribute to the total reflection. The results also showed that reflection decreased slightly with increasing thickness. As expected, for the p-polarized light used in this study, the reflection decreased with increasing angle of incidence for the range of angles studied. It was also found that when the surface roughness was close to zero and when it was close to the wavelength of the input laser beam (i.e. 940nm), the reflectance values were close and reached a minimum between these two roughness values. [Copyright &y& Elsevier]

Abstract: Characterization of laser light reflection during the laser transmission welding (LTW) 3 [3] Abbreviations: LTW—laser transmission welding, CB—carbon black, IR—infrared, NPFD—normalized power flux distribution of thermoplastics is especially important for applications in which non-zero laser incidence angles are used. At higher laser incidence angles, reflection increases and has the potential to burn surrounding features of the part to be welded. This study presents and validates a technique for laser reflection measurement. Reflected energy is absorbed by a black plastic plate (containing carbon black, which is the absorber of the reflected energy). The surface temperature of the plate is measured by an infrared (IR) camera. The distribution of reflected power required to generate this temperature profile is estimated using a simple heat transfer model. The technique was validated by irradiating the black plate by the laser directly, while observing the time-varying temperature distribution of the plate by the IR camera. In this case, good agreement was observed between the estimated total power and the actual laser input power. Good agreement also existed between the estimated power distribution and that determined experimentally via a knife edge based beam profiling technique. The thermal imaging technique was subsequently used to measure the magnitude and distribution of laser light reflection from unreinforced nylon 6. [Copyright &y& Elsevier]

In expanding pea leaves, over 95% of fatty acids (FA) synthesized in the plastid are exported for assembly of eukaryotic glycerolipids. It is often assumed that the major products of plastid FA synthesis (18:1 and 16:0) are first incorporated into 16:0/18:1 and 18:1/18:1 molecular species of phosphatidic acid (PA), which are then converted to phosphatidylcholine (PC), the major eukaryotic phospholipid and site of acyl desaturation. However, by labeling lipids of pea leaves with [14C]acetate, [14C]glycerol, and [14C]carbon dioxide, we demonstrate that acyl editing is an integral component of eukaryotic glycerolipid synthesis. First, no precursor-product relationship between PA and PC [14C]acyl chains was observed at very early time points. Second, analysis of PC molecular species at these early time points showed that >90% of newly synthesized [14C] 18:1 and [14C] 16:0 acyl groups were incorporated into PC alongside a previously synthesized unlabeled acyl group (18:2, 18:3, or 16:0). And third, [14C]glycerol labeling produced PC molecular species highly enriched with 18:2, 18:3, and 16:0 FA, and not 18:1, the major product of plastid fatty acid synthesis. In conclusion, we propose that most newly synthesized acyl groups are not immediately utilized for PA synthesis, but instead are incorporated directly into PC through an acyl editing mechanism that operates at both sn-1 and sn-2 positions. Additionally, the acyl groups removed by acyl editing are largely used for the net synthesis of PC through glycerol 3-phosphate acylation. [ABSTRACT FROM AUTHOR]

Meltdown is the term used to describe the collapse of two thermoplastic parts during welding. It is a critical process parameter in the laser-transmission welding of thermoplastics. This study examines the effect of quasi-simultaneous (QS) laser transmission welding (LTW) processing parameters including input power ( P ), number of passes ( N ), scan speed ( V ), total scan length (L S ) and weld pressure on the meltdown behavior of polycarbonate (PC) and polypropylene (PP), using a T-shaped test assembly. The total meltdown is shown to depend linearly on the total line energy ( LE T ) defined as the product of P and N divided by V. Increasing L S increases the critical LE T for meltdown to begin. A simple model is presented that captures the main elements of meltdown in this thermoplastic welding process. [ABSTRACT FROM AUTHOR]

The chemical and physical properties of vegetable oils are largely dictated by the ratios of 4–6 common fatty acids contained within each oil. However, examples of plant species that accumulate from trace amounts to >90% of certain unusual fatty acids in seed triacylglycerols have been reported. Many of the general enzymatic reactions that drive both common and unusual fatty acid biosynthesis and accumulation in stored lipids are known, but which isozymes have evolved to specifically fill this role and how they coordinate in vivo is still poorly understood. Cotton (Gossypium sp.) is the very rare example of a commodity oilseed that produces biologically relevant amounts of unusual fatty acids in its seeds and other organs. In this case, unusual cyclopropyl fatty acids (named after the cyclopropane and cyclopropene moieties within the fatty acids) are found in membrane and storage glycerolipids (e.g. seed oils). Such fatty acids are useful in the synthesis of lubricants, coatings, and other types of valuable industrial feedstocks. To characterize the role of cotton acyltransferases in cyclopropyl fatty acid accumulation for bioengineering applications, we cloned and characterized type-1 and type-2 diacylglycerol acyltransferases from cotton and compared their biochemical properties to that of litchi (Litchi chinensis), another cyclopropyl fatty acid-producing plant. The results presented from transgenic microbes and plants indicate both cotton DGAT1 and DGAT2 isozymes efficiently utilize cyclopropyl fatty acid-containing substrates, which helps to alleviate biosynthetic bottlenecks and enhances total cyclopropyl fatty acid accumulation in the seed oil. • Cotton contains two DGAT1 genes and ten DGAT2 orthologs. • Metabolic bottlenecks typically limit CPFA production in transgenic seeds. • Cotton and litchi DGATs alleviate the bottleneck and enhance CPFA accumulation in transgenic yeast and plants. [ABSTRACT FROM AUTHOR]

It is important to understand how laser energy scatters within the transparent component in order to predict and optimize the laser transmission welding process. This paper examines the influence of part thickness, glass fiber and crystallinity levels on the distribution of laser light after transmission through amorphous polycarbonate (PC) and semi-crystalline polymers such as polyamide 6 (PA6), polypropylene (PP), and polyethylene (PE). An experimental technique based on laser-scanned lines of progressively increasing power was used to assess the transmitted energy distribution. This distribution was characterized using a two-parameter model that captures scattered and un-scattered components of the laser beam. The results clearly show how the scattering is increased by increasing the numbers of interactions between laser light and phase boundaries either by increasing the particle concentration (i.e., glass fiber level and crystallinity) or increasing part thickness. [ABSTRACT FROM AUTHOR]

Recycled polyamide 6 (PA6) from post-industrial waste fibers (PIW) and post-consumer carpet waste (PCW) are characterized in this study. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) indicate the presence of polypropylene (PP) in PCW. Furthermore, measured ash content of PCW is ca. 6 wt.%, while PIW has only 0.5 wt.% inorganic content. X-ray fluorescence (XRF) and X-ray diffraction (XRD) show that inorganic contaminants of PCW and PIW are calcium carbonate (CaCO 3 ) and titanium dioxide (TiO 2 ), respectively. Due to higher inorganic filler content, PCW exhibits higher melt viscosity and higher storage modulus than that of PIW. PIW has 20% higher tensile strength than that of PCW. However, a drastic 70% drop is observed in vibration weld strength of PCW, which is attributed to its PP contamination. The negative effect of PP on the weld strength of recycled PA6 is also confirmed by measuring the mechanical properties of model compounds. [ABSTRACT FROM AUTHOR]

Acetyl-CoA carboxylase (ACCase) catalyzes the first committed step in the de novo synthesis of fatty acids. The multisubunit ACCase in the chloroplast is activated by a shift to pH 8 upon light adaptation and is inhibited by a shift to pH 7 upon dark adaptation. Here, titrations with the purified ACCase biotin attachment domain-containing (BADC) and biotin carboxyl carrier protein (BCCP) subunits from Arabidopsis indicated that they can competently and independently bind biotin carboxylase (BC) but differ in responses to pH changes representing those in the plastid stroma during light or dark conditions. At pH 7 in phosphate buffer, BADC1 and BADC2 gain an advantage over BCCP1 and BCCP2 in affinity for BC. At pH 8 in KCl solution, however, BCCP1 and BCCP2 had more than 10- fold higher affinity for BC than did BADC1. The pH-modulated shifts in BC preferences for BCCP and BADC partners suggest they contribute to light-dependent regulation of heteromeric ACCase. Using NMR spectroscopy, we found evidence for increased intrinsic disorder of the BADC and BCCP subunits at pH 7. We propose that this intrinsic disorder potentially promotes fast association with BC through a "fly-casting mechanism." We hypothesize that the pH effects on the BADC and BCCP subunits attenuate ACCase activity by night and enhance it by day. Consistent with this hypothesis, Arabidopsis badc1 badc3 mutant lines grown in a light–dark cycle synthesized more fatty acids in their seeds. In summary, our findings provide evidence that the BADC and BCCP subunits function as pH sensors required for light-dependent switching of heteromeric ACCase activity. [ABSTRACT FROM AUTHOR]

Abstract: Culturing microalgae heterotrophically for producing lipid-based biofuels such as biodiesel and renewable hydrocarbons has attracted increasing attention due to the advantages of fast growth and high lipid yield under this growth mode without being subjected to light limitation. High cell density in the culture broth is desirable for reducing downstream processing costs. Oleaginous microalga Chlorella sorokiniana was investigated for high cell density culture with glucose as the carbon source. Best growth performance was obtained first with batch culture at pH 7.0 when ammonium was the nitrogen source. Then, two-stage fed-batch fermentation was conducted under the optimal conditions. The algal biomass grew linearly in the first stage with a productivity of 24.2gL−1 d−1, and the lipid content increased from 14.5% to 38.7% in the second stage. This fermentation strategy resulted in algal biomass and lipid concentrations of 103.8gL−1 and 40.2gL−1 respectively. Analysis of lipid and fatty acid profiles showed C. sorokiniana accumulated a large amount of neutral lipids (92.9% of total lipids), triacylglycerols (82.8% of neutral lipids), and high contents of palmitic, oleic and linoleic acids, which are ideal form of lipid for making biodiesel. These results suggest that heterotrophic culture of C. sorokiniana holds great potential for lipid-based biofuel production. [Copyright &y& Elsevier]