摘要 :
This paper presents a framework for onboard trajectory planning and guidance for a large class of autonomously
guided parafoils. The problem is for the parafoil to reach a given location at a specified altitude with a specified fi...
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This paper presents a framework for onboard trajectory planning and guidance for a large class of autonomously
guided parafoils. The problem is for the parafoil to reach a given location at a specified altitude with a specified final
heading. Through appropriate change of the independent variable, the trajectory planning problem is converted
from a three-dimensional free-final-time problem to a two-dimensional fixed-final-time problem. Using the wellknown
Dubins path synthesis and known parafoil performance parameters, a concept of altitude margin is developed
as a quantitative measure of the available maneuvering energy for use in trajectory planning.Ahybrid strategy using
two methods to generate kinematically feasible fixed-time trajectories is presented, each targeting a different range
of initial values of the altitude margin. The trajectory can be replanned onboard in every guidance cycle, making
the guidance effectively closed-loop, or replanned whenever the actual deviation of the actual condition from the
reference trajectory exceeds a threshold. The proposed planning and guidance algorithm applies to a large class of
parafoil canopies and payloads, which encompasses wide variations in the lift-to-drag ratio, wing loading, and
maximum turn rate. The guidance logic has the potential of requiring little or no tuning to accommodate variations in
canopy performance. Monte Carlo simulations are conducted to evaluate the effectiveness of the algorithm with
dispersions in canopy performance, loading, wind profile errors, navigation uncertainty, using lateral control only,
and using both longitudinal and lateral control.
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摘要 :
A series of 2′,7′-diarylspiro(cyclopropane-1,9′-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-viole...
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A series of 2′,7′-diarylspiro(cyclopropane-1,9′-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet to blue photolumines-cence (PL) (λ_(max)~(PL) = 353-419 nm) with excellent PL quantum efficiencies (Φ_(PL)= 83-100%) in solution and show high thermal stabilities (T_d = 267-474℃). The variation of the optical properties of these molecules in the solid state depends on the different stacking modes of these compounds containing different substituents, which are revealed by Crystallographic analysis. CH···π hydrogen bonds instead of interm'olecular π-π interactions act as the driving force between adjacent fluorenes, even though a very small dialkyl group (cyclopropane) is introduced at the C-9 position of fluorene. The crosslike molecular stacking efficiently reduces the energy transfer between the herring-like aggregates and therefore results in the absence of a "green-light" emission tail. In order to determine the cause of the "green-light" emission tails, the fluorescence spectra of the films annealed in N_2 or in air are recorded. Broad green-light emission tails were observed for the films annealed in air, which might be caused by fluorenone defects generated during processing or during the course of the photophysical analysis by reaction with residual oxygen.
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摘要 :
A series of 2',7'-diarylspiro(cyclopropane-1,9'-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet t...
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A series of 2',7'-diarylspiro(cyclopropane-1,9'-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet to blue photolumines-cence (PL) (λ_(max)~(PL) = 353-419 nm) with excellent PL quantum efficiencies (Φ_(PL)= 83-100%) in solution and show high thermal stabilities (T_d = 267-474 ℃). The variation of the optical properties of these molecules in the solid state depends on the different stacking modes of these compounds containing different substituents, which are revealed by crystallographic analysis. CH…π hydrogen bonds instead of intermolecular π-π interactions act as the driving force between adjacent fluorenes, even though a very small dialkyl group (cyclopropane) is introduced at the C-9 position of fluorene. The crosslike molecular stacking efficiently reduces the energy transfer between the herring-like aggregates and therefore results in the absence of a "green-light" emission tail. In order to determine the cause of the "green-light" emission tails, the fluorescence spectra of the films annealed in N_2 or in air are recorded. Broad green-light emission tails were observed for the films annealed in air, which might be caused by fluorenone defects generated during processing or during the course of the photophysical analysis by reaction with residual oxygen.
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摘要 :
A five-gene cluster cvhABCDE was identified from Streptomyces hygroscopicus 10–22. As the first gene of this cluster, cvhA encoded a putative sensor histidine kinase with a predicted sensor domain consisting of two trans-membrane...
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A five-gene cluster cvhABCDE was identified from Streptomyces hygroscopicus 10–22. As the first gene of this cluster, cvhA encoded a putative sensor histidine kinase with a predicted sensor domain consisting of two trans-membrane segments at the N-terminus and a conserved HATPase_c domain at the C-terminus. The C-terminus polypeptide of CvhA expressed in Escherichia coli was purified and shown to be autophosphorylated with [γ-32P]ATP in vitro. The phosphoryl group was acid-labile and basic-stable, which supported histidine as the phosphorylation residue. No obvious difference of mycelia development was observed between the null mutant of cvhA generated by targeted gene replacement and the wild-type parental strain 10–22 grown on solid soya flour medium with 2%–8% glucose or sucrose, but the cvhA mutant could form much more abundant aerial mycelia and spores than the wild-type strain on solid soya flour medium supplemented with 6%–8% mannitol, 6%–8% sorbitol, 4%–6% mannose, or 4%–6% fructose. This pheno-type was complemented by the cloned wild-type cvhA gene, and no difference was observed for growth curves of the cvhA mutant and the wild strain in liquid minimal medium with the tested sugars at a concentration of 4%, 6% and 8%. We thus propose that CvhA is likely a sensor histidine kinase and negatively regulates the morphological differentiation in a sugar-dependent manner in S. hygroscopicus 10–22.
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摘要 :
Novel fluorene-based compounds, TCPC-6 and TCPC-4, with rigid central spirobifluorene cores and peripheral carbazole groups are synthesized using the Suzuki coupling reaction. The optical, electrochemical, and thermal properties o...
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Novel fluorene-based compounds, TCPC-6 and TCPC-4, with rigid central spirobifluorene cores and peripheral carbazole groups are synthesized using the Suzuki coupling reaction. The optical, electrochemical, and thermal properties of these compounds are characterized. The compounds show strong deep-blue emission both in solution and as thin films. Both TCPC-6 and TCPC-4 exhibit amorphous morphologies in the solid state with high glass transition temperatures (T_g) of 108 and 143 ℃, respectively. Atomic force microscopy (AFM) measurements indicate that high-quality amorphous films of these novel compounds can be prepared by spin-coating. The oxidation potentials of TCPC-6 and TCPC-4 are significant lower than that of model compounds without peripheral carbazole groups, which suggests that these compounds have relatively high highest occupied molecular orbital (HOMO) energy levels and better hole-injection capabilities. Light-emitting devices fabricated by spin-coating films of these molecules exhibit deep-blue emission with Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of (0.16, 0.05); the devices fabricated using spin-coated TCPC-6 and TCPC-4 layers exhibit high luminance efficiencies of 1.35 and 0.90 cd A~(-1) (with external quantum efficiencies of 3.72 and 2.47 %), respectively.
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摘要 :
Starting from the key intermediate 5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazole-2-thiol (4) or the oxadiazole analogue (5), the title compounds 9 and 10 are synthesized by a two-step process. Thioetherification reaction of 4 or 5 ...
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Starting from the key intermediate 5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazole-2-thiol (4) or the oxadiazole analogue (5), the title compounds 9 and 10 are synthesized by a two-step process. Thioetherification reaction of 4 or 5 with an organic halide catalyzed by indium or indium tribromide first affords appropriate sulfide 7 or 8, which is then converted into title compounds 9 or 10 by hydrogen peroxide oxidation catalyzed by ammonium molybdate in ionic liquid [bmim]PF_6. The structures are unequivocally confirmed by spectroscopic (IR, ~1H and ~(13)C NMR) data and elemental analyses. The structures of 8d and 10q are further established by X-ray crystallographic diffraction analysis. The compounds have been shown to be fungicidally active. Title compounds 10i and 10j can inhibit mycelia growth by approximately 50% (EC_(50)) at 2.9-93.3 μg/mL in vitro against 10 kinds of fungi.
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A series of highly fluorescent, pyrene-modified oligo(2,7-fluorene ethynylene)s were synthesized and fully characterized. Different emissions were observed between pyrene-end-capped and pyrene-centered oligo(2,7-fluorene ethynylen...
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A series of highly fluorescent, pyrene-modified oligo(2,7-fluorene ethynylene)s were synthesized and fully characterized. Different emissions were observed between pyrene-end-capped and pyrene-centered oligo(2,7-fluorene ethynylene)s. Moreover, these oligomers were applied to fabricate organic light-emitting diodes (OLEDs), and bright blue or green electroluminescence (EL) with good device performances was achieved in multilayer OLEDs. These pyrene-modified oligo(2,7-fluorene ethynylene)s could be used as optoelectronics materials or models to investigate fluorescent structure-property relationship of fluorene derivatives.
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Two fluorescent molecules with an alkynylanthracene core and pyrene end-cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enha...
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Two fluorescent molecules with an alkynylanthracene core and pyrene end-cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enhance the hole-transport ability of the molecule and to reduce intermolecular interactions. Both compounds exhibit high thermal stabilities and narrow energy bandgaps. Single-layer polymer light-emitting diodes (PLEDs) based on poly(9,9-dioctylfluorone) (PFO) doped with the synthesized compounds exhibit excellent performance. A PLED with 0.2 % of dopant 7 had a high luminance efficiency of 10.7±0.3 cd A~(-1) as well as a brightness of 1400 cdm~(-2) at a current density of 13 mA cm~(-2), and a low turn on voltage (3.1 V) at a brightness of 10 cd m~(-2). A maximum brightness of 20 500 ± 1400 cd m~(-2) at 7 V was also measured. The high efficiency of the device's performance is attributed to the good electron and hole trapping ability of the dopants, which possess suitable energy levels as compared to those of PFO.
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摘要 :
An in-line one-fiber approach to realize simultaneous measurement of salinity and temperature is proposed. The sensor system, which consists of multiplexed polymer-coated fiber Bragg gratings, showed that the polyimide-coated grat...
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An in-line one-fiber approach to realize simultaneous measurement of salinity and temperature is proposed. The sensor system, which consists of multiplexed polymer-coated fiber Bragg gratings, showed that the polyimide-coated grating responds to variation
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摘要 :
6-Fluoro-4-quinazolinol is prepared by the cyclization reaction of 2-amino-5-fluorobenzoic acid and formamide. The resulting thiol obtained by treatment of hydroxyl group with phosphorus (V) sulfide is converted under phase transf...
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6-Fluoro-4-quinazolinol is prepared by the cyclization reaction of 2-amino-5-fluorobenzoic acid and formamide. The resulting thiol obtained by treatment of hydroxyl group with phosphorus (V) sulfide is converted under phase transfer condition to 4-substituted 4-alkylthio-6-fluoroquinazoline derivatives by reaction with halide. The structures of the compounds are confirmed by elemental analysis, IR, and ~1H NMR. Title compounds 3a, 3g, and 3h are found to possess good antifungal activities. Using the mycelial growth rate method in the laboratory, the mechanism of action of 3g against Fusarium oxysporum in vitro is studied. The results indicate that 3a, 3g, and 3h have high inhibitory effect on the growth of most of the fungi with EC_(50) values ranging from 8.3 to 64.2 μg/mL. After treating F. oxysporum with compound 3g at 100 μg/mL, only 6.5% of its spore bourgeoned. The permeability of the cell membrane increases along with the malformation of the hypha and condensation of its endosome. After treatment with compound 3g at 100 μg/mL within 12 h, the mycelial reducing sugar, d-G1cNAc, content and chitinase activity decline, but the soluble protein content shows no obvious change.
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