Catalytic Enantioselective [4+2] Cycloadditions of Salicylaldehyde Acetals with Enol Ethers.

A readily accessible conjugate-base-stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde-derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2- and 4-positions. Stereochemically more complex products can be obtained from racemic enol ethers. Spirocyclic products are also accessible.

Freeform mirror array design for concentrating sunlight onto a CPV solar cell.

In a concentrating photovoltaic (CPV) system, realizing an illumination spot consistent with the photosensitive area of the CPV cell while maintaining high optical performances is a challenging but rewarding issue. For instance, uniform irradiance distribution not only reduces the risk of damage to CPV cells due to the local heat accumulation, but also improves photoelectric conversion efficiency; free chromatic aberration ensures that a wide solar spectrum can be regulated; a high concentration ratio helps reduce the usage of CPV cells, and so on. Here, we propose a method to design a freeform mirror array to concentrate sunlight and generate a square light pattern with uniform irradiance distribution on the photovoltaic cell. Each freeform mirror can produce a uniform illumination pattern on the CPV cell. We demonstrate the effectiveness of the proposed method with several design examples, and a series of factors affecting the optical performance is also analyzed.

Divergent Functionalization of Alkynes Enabled by Organic Photoredox Catalysis.

Direct functionalization of alkynes under oxidative conditions is challenging, as alkynes are usually recalcitrant towards typical oxidants. Herein, we communicate a strategy for the divergent functionalization of alkynes with photoexcited acridinium organic dyes, presumably via the formation of vinyl cation radicals as key intermediates. Based on the nature of the nucleophiles, different types of difunctionalized products were obtained in moderate to good yields. Addition of lithium Lewis acids resulted in a surprising reversal of diastereocontrol.

Design and parameter study of banana crown mechanical cutting device.

Banana mechanical crown cutting tool which is a critical component of banana crown cutting machine is designed and studied in this paper. Experiments were designed to optimize parameters of the cutting tool. Indexes are cut surface quality grade of banana crown, maximum cutting force and useful power consumption. For banana preservation, get high grade of cut surface quality is more significant than consume less energy. Results of experiments show that the optimum parameters are as follows: cutting speed is about 50-60 mm/s, number of cut sets are about 4-6, angle between thick cutter and axis of banana rachis is about 5°, width of thick cutter is about 8-14 mm, thickness of thick cutter is about 2-3 mm, edge angle of thick cutter is between 20° and 30°, width of thin cutter is about 10-14 mm and thickness of thin cutter is about 0.2-0.4mm. This study helps to make the completely mechanical postharvest treatments for banana postharvest treatments.

Freeform illumination optics design for extended LED sources through a localized surface control method.

Freeform illumination optics design with extended light sources to realize an accurate light control is very important, but still remains a challenging issue. Here, we propose a new method to design compact and efficient freeform lenses for extended sources. We employ a localized surface control strategy to directly modify the freeform surface to redistribute the light rays emitted from the extended LED source in a desired manner. By the combination of basic radiometry calculation and backward ray tracing, we obtain the irradiance distribution on the target plane and estimate the localized freeform surface to be modified. The optimization function with a Gaussian form is adopted to modify the localized surface. The smoothness of the freeform surface is taken into account in the optimization process to guarantee the processability of the freeform optics. We demonstrate the effectiveness of the proposed method with three design examples.

Compact freeform illumination optics design by deblurring the response of extended sources.

Freeform illumination design for extended sources is a very challenging but rewarding issue that can benefit a wide range of illumination systems. Here, we propose a method that can achieve compact and highly efficient illumination lenses by deconvolving the blur caused by the extent from light sources. We combine the illumination calculation with the mathematical model of spatially variant convolution and develop a direct computational scheme to calculate the blur kernel without approximations. Two design examples with high optical performances are presented to demonstrate the effectiveness of the proposed method.

Freeform illumination optics for 3D targets through a virtual irradiance transport.

Freeform illumination optics design for 3D target surfaces is a challenging and rewarding issue. The current researches on freeform illumination optics are mostly involved in planar targets, especially for the cases where the targets are perpendicular to the optical axis. Here, we propose a general method to design freeform optics for illuminating 3D target surfaces for zero-étendue sources. In this method, we employ a virtual observation plane which is perpendicular to the optical axis and transfer the irradiance on the 3D target surface to this virtual plane. By designing freeform optics to generate the transferred irradiance distribution, the prescribed irradiance distribution on the 3D target can be realized automatically. The influence of the freeform optics size is considered in the optics design process, which makes it possible to design illumination system for near-field configuration where the influence of the freeform optics size cannot be ignored. We demonstrate the robustness and elegance of the proposed method with three design examples.

Design of a high-throughput telescope based on scanning an off-axis three-mirror anastigmat system.

A high-throughput optical system possesses a large field of view (FOV) and high resolution. However, it is a major challenge to design such a telescope with these two conflicting specifications. In this paper, we propose a method to design a high-throughput telescope based on the classical off-axis three-mirror anastigmat (TMA) configuration by introducing a scanning mechanism. We derive the optimum initial design for the TMA system with no primary aberrations through characteristic ray tracing. During the design process, a real exit pupil is necessitated to accommodate the scanning mirror. By gradually increasing the system's FOV during the optimization procedure, we finally obtained a high-throughput telescope design with an F-number of 6, a FOV of 60∘×1.5∘, and a long focal length of 876 mm. In addition, a tolerance analysis is also conducted to demonstrate the instrumentation feasibility. We believe that this kind of large rectangle FOV telescope with high resolution has broad future applications in the optical remote sensing field.

Least-squares ray mapping method for freeform illumination optics design: erratum.

We provide corrections of the author list as well as Eq. (12) and (13) in our previous publication [Opt. Express28, 38113811 (2020)10.1364/OE.385254].

Variable-diameter beam-shaping system design with high zoom ratio containing aspheric optical components.

Recently, the optical design of refractive beam-shaping systems has been extensively studied, although such study remains focused on two optical surfaces. Designing a beam-shaping system with variable output beam sizes and prescribed irradiance profiles remains a challenging but rewarding task. Here, we present a design framework, including calculation of the initial system and optimization process, to achieve variable-diameter beam-shaping systems with high zoom ratios. We introduce the whole process of designing a compact 8× zoom system of superior optical performance by transforming a Gaussian beam into flat-top beams with different magnifications. We also present a design of a zoom beam-shaping system transforming a Gaussian beam into variable beams with inverse Gaussian distributions to demonstrate the robustness and efficiency of the proposed method.

Hemin-decreased cadmium uptake in pak choi (Brassica chinensis L.) seedlings is heme oxygenase-1 dependent and relies on its by-products ferrous iron and carbon monoxide.

Cadmium (Cd) is a major pollutant in farmland, which not only greatly restricts crop production, but also brings a serious threat to human health through entering the food chain. Our previous study showed that hemin treatment could reduce the accumulation of Cd in pak choi seedlings. However, the underlying mechanism remains unclear. In this study, we used non-invasive micro-test technology (NMT) to detect the real-time Cd2+ flux from pak choi roots and demonstrated that hemin treatment decreased Cd uptake rather than its translocation within plants. Moreover, through comparing the responses of different chemical treatments in pak choi seedlings and Arabidopsis wild-type and heme oxygenase-1 (HO-1) mutant, we provided evidence that hemin-decreased Cd uptake was HO-1 dependent. Furthermore, analyses of hemin degradation products suggested that the hemin-derived suppression of Cd uptake suppression was probably relying on its degradation by-products, ferrous iron (Fe2+) and carbon monoxide (CO), via repressing the expression of a Fe2+/Cd2+ transporter BcIRT1 in pak choi roots.

Modular Design of Chiral Conjugate-Base-Stabilized Carboxylic Acids: Catalytic Enantioselective [4 + 2] Cycloadditions of Acetals.

Readily available 1,2-amino alcohols provide the framework for a new generation of chiral carboxylic acid catalysts that rival the acidity of the widely used chiral phosphoric acid catalyst (S)-TRIP. Covalently linked thiourea sites stabilize the carboxylate conjugate bases of these catalysts via anion-binding, an interaction that is largely responsible for the low pKa values. The utility of the new catalysts is illustrated in the context of challenging [4 + 2] cycloadditions of salicylaldehyde-derived acetals with homoallylic and bishomoallylic alcohols, providing polycyclic chromanes in a highly enantioselective fashion.

Least-squares ray mapping method for freeform illumination optics design.

Computing a source-target map that yields integrable surface normal field is quite challenging for freeform illumination design. Here, we propose a least-squares ray mapping method to calculate a superior ray mapping by iteratively correcting an integrable map to approach the energy conservation and boundary condition. The process is implemented via solving three minimization problems. The first two problems can be figured out pointwise and the third can be converted to two decoupled Poisson equations with Robin boundary conditions. We demonstrate the robustness and high efficiency of the proposed method with several design examples.

Highly Acidic Conjugate-Base-Stabilized Carboxylic Acids Catalyze Enantioselective oxa-Pictet-Spengler Reactions with Ketals.

Acyclic ketone-derived oxocarbenium ions are involved as intermediates in numerous reactions that provide valuable products, however, they have thus far eluded efforts aimed at asymmetric catalysis. We report that a readily accessible chiral carboxylic acid catalyst exerts control over asymmetric cyclizations of acyclic ketone-derived trisubstituted oxocarbenium ions, thereby providing access to highly enantioenriched dihydropyran products containing a tetrasubstituted stereogenic center. The high acidity of the carboxylic acid catalyst, which exceeds that of the well-known chiral phosphoric acid catalyst TRIP, is largely derived from stabilization of the carboxylate conjugate base through intramolecular anion-binding to a thiourea site.

Globally optimal first-order design of zoom systems with fixed foci as well as high zoom ratio.

In this paper, we propose a systematic approach to automatically retrieve the first-order designs of three-component zoom systems with fixed spacing between focal points based on Particle Swarm Optimization (PSO) algorithm. In this method, equations are derived for the first-order design of a three-component zoom lens system in the framework of geometrical optics to decide its basic optical parameters. To realize the design, we construct the mathematical model of the special zoom system with two fixed foci based on Gaussian reduction. In the optimization phase, we introduce a new merit function as a performance metric to optimize the first-order design, considering maximum zoom ratio, total optical length and aberration term. The optimization is performed by iteratively improving a candidate solution under the specific merit function in the multi-dimensional parametric space. The proposed method is demonstrated through several examples, which cover almost all the common application scenarios. The results show that this method is a practical and powerful tool for automatically retrieving the optimal first-order design for complex optical systems.

Automatically retrieving an initial design of a double-sided telecentric zoom lens based on a particle swarm optimization.

In this paper, we propose an efficient and robust approach to retrieve an optimal first-order design of a double-sided telecentric zoom lens based on the particle swarm optimization (PSO) algorithm. In this method, the design problem is transformed to realize a zoom system with fixed positions of both the front focal point and the rear focal point during zooming. Equations are derived for the paraxial design of the basic parameters of a three-component zoom lens in the framework of geometrical optics. We implement the PSO algorithm in MATLAB to design some test cases to verify the feasibility. As the computational work is completed by the optimization algorithm, instead of the traditional trial-and-error method, our proposed method is efficient and low-threshold. By a simulation result, it is verified that the described method is stable and necessary in finding a proper initial configuration of a zoom lens with two fixed foci as well as a required zoom ratio. Furthermore, a compact initial design of a three-component 2X zoom system with two fixed foci is proposed. Based on the initial design data, a double-sided telecentric zoom system is developed. The result shows the great potential of our proposed method in retrieving proper initial designs of complex optical systems.

Double freeform surfaces design for beam shaping with non-planar wavefront using an integrable ray mapping method.

We propose a method to design double smooth freeform surfaces applied in beam shaping with a ray mapping method in the paper. We couple the calculation of ray mapping and the construction of freeform surfaces to approach the surface normal field integrability condition based on the symplectic flow mapping scheme. In this paper, the incident beam wavefront is not limited to be planar or spherical. Several challenging design examples are presented that include transforming a circular Gaussian beam to an unconventional beam with variously shaped contour, and transforming an elliptic beam to a convergent beam with complex irradiance distribution in non-paraxial regime. The results show the high efficiency and feasibility of the proposed method in designing freeform optics for beam shaping applications.

Hydrogen gas alleviates toxic effects of cadmium in Brassica campestris seedlings through up-regulation of the antioxidant capacities: Possible involvement of nitric oxide.

Hydrogen gas (H2) has been shown as an important factor in plant tolerance to abiotic stresses, but the underlying mechanisms remain unclear. In the present study, the effects of H2 and its interaction with nitric oxide (NO) on alleviating cadmium (Cd) stress in Brassica campestris seedlings were investigated. NO donor (SNP) or hydrogen-rich water (HRW) treatment showed a significant improvement in growth of Cd-stressed seedlings. Cd treatment upregulated both endogenous NO and H2 (36% and 66%, respectively), and the increase of H2 was prior to NO increase. When treated with NO scavenger (PTIO) or NO biosynthesis enzyme inhibitors (L-NAME and Gln), HRW-induced alleviation under Cd stress was prevented. Under Cd stress, HRW pretreatment significantly enhanced the NO accumulation, and together up-regulated the activity of NR (nitrate reductase) and expression of NR. HRW induced lower reactive oxygen species (ROS), higher AsA content, enhanced activity of POD (peroxidase) and SOD (superoxide dismutase) in seedling roots were inhibited by PTIO, L-NAME and Gln. Through proteomic analysis, the level of 29 proteins were changed in response to H2 and NO-induced amelioration of Cd stress. Nearly half of them were involved in oxidation-reduction processes (about 20%) or antioxidant enzymes (approximately 20%). These results strongly indicate that in Cd-stressed seedlings, pretreatment with HRW induces the accumulation of H2 (biosynthesized or permeated), which further stimulates the biosynthesis of NO through the NR pathway. Finally, H2 and NO together enhance the antioxidant capabilities of seedlings in response to Cd toxicity.

Increased antioxidative capacity and decreased cadmium uptake contribute to hemin-induced alleviation of cadmium toxicity in Chinese cabbage seedlings.

Hemin (ferroprotoporphyrin IX), a compound derivative of heme, has been shown to exert numerous beneficial physiological functions in the resistance of plant to various abiotic stresses. This work investigated the effects of hemin on ameliorating Cd toxicity in Chinese cabbage (Brassica chinensis L.). Our results showed that leaf chlorosis, growth inhibition, root morphology and photosynthetic activity were significantly improved by the addition of hemin in Cd-stressed plants. Meanwhile, Cd-induced oxidative damage was also alleviated by hemin, which was supported by the decreased level of malondialdehyde (MDA) in roots of the seedlings treated with hemin. In the same time, the activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the concentrations of ascorbic acid (AsA) and glutathione (GSH) were elevated by hemin, which contributed to the scavenging of Cd-elicited H2O2 and O2•－ within the roots of Chinese cabbage seedlings. Furthermore, compared with Cd stressed plants, Cd concentrations in both shoots and roots were markedly decreased by exogenous hemin. Hence, it can be speculated that hemin-mediated tolerance to Cd stress may be associated with the inhibition of Cd uptake in Chinese cabbage. This hypothesis was supported by the down-regulated expressions of transporter genes, including BcIRT1, BcIRT2, BcNramp1 and BcZIP2 caused by hemin addition in Chinese cabbage seedlings under Cd treatment. Taken together, these results suggested that hemin alleviated Cd toxicity probably through increasing antioxidative capacities and inhibiting Cd uptake of Chinese cabbage.

Design of a head-up display based on freeform reflective systems for automotive applications.

Automotive head-up display (HUD), a typical application in augmented reality (AR), has gained popularity in recent years. In this paper, we propose a novel design configuration of freeform off-axis three-mirror systems for automotive head-up display (HUD) application. In the configuration, the image source, the flat mirror, and the freeform mirror are allocated on the same horizontal level to guarantee a compact structure as well as to make the optical elements easy to be assembled. The whole design philosophy and procedure, including the analytic method to determine initial structure, structure constraints, and optimization strategy, are demonstrated in detail. Superior optical performance is achieved regardless of the pupil being located at any position inside a rectangular eye box.