An oxidized squalene derivative from Protium subserratum Engl. (Engl.) growing in Peru

Protium subserratum (Burseraceae) is a neotropical tree species that is comprised of several habitat-specific ecotypes having distinct defense chemical profiles. A previously unknown triterpene, 25,30-dicarboxy-26,27,28,29-tetraacetoxy-10,11,14,15-tetrahydrosqualene, was isolated from P. subserratum young leaf tissue of one ecotype growing in Peru. The structure of 1 was determined by spectroscopic study, including 1 and 2D nuclear magnetic resonance experiments.     

Toric Anti-self-dual 4-manifolds Via Complex Geometry

Using the twistor correspondence, this article gives a one-to-one correspondence between germs of toric anti-self-dual conformal classes and certain holomorphic data determined by the induced action on twistor space. Recovering the metric from the holomorphic data leads to the classical problem of prescribing the ?ech coboundary of 0-cochains on an elliptic curve covered by two annuli. The classes admitting Kähler representatives are described; each such class contains a circle of Kähler metrics. This gives new local examples of scalar flat Kähler surfaces and generalises work of Joyce [Duke. Math. J. 77(3), 519–552 (1995)] who considered the case where the distribution orthogonal to the torus action is integrable.     

A 2-Tyr-1-carboxylate Mononuclear Iron Center Forms the Active Site of a Paracoccus Dimethylformamidase

N,N-dimethyl formamide (DMF) is an extensively used organic solvent but is also a potent pollutant. Certain bacterial species from genera such as Paracoccus, Pseudomonas, and Alcaligenes have evolved to use DMF as a sole carbon and nitrogen source for growth via degradation by a dimethylformamidase (DMFase). We show that DMFase from Paracoccus sp. strain DMF is a halophilic and thermostable enzyme comprising a multimeric complex of the α₂β₂ or (α₂β₂)₂ type. One of the three domains of the large subunit and the small subunit are hitherto undescribed protein folds of unknown evolutionary origin. The active site consists of a mononuclear iron coordinated by two Tyr side-chain phenolates and one carboxylate from Glu. The Fe³⁺ ion in the active site catalyzes the hydrolytic cleavage of the amide bond in DMF. Kinetic characterization reveals that the enzyme shows cooperativity between subunits, and mutagenesis and structural data provide clues to the catalytic mechanism.     

投影光刻物镜倍率的公差分析与补偿

为满足严格的套刻需求,双远心结构的投影光刻物镜需要选择恰当的元件移动来进行倍率的补偿和调节。提出了一种简单而实用的方法来进行倍率的公差分析。该方法利用商业优化设计软件和有限差分算法计算了多项公差对物镜倍率的敏感程度,同时结合公差对系统波像差的敏感度选择最佳的倍率补偿元件。利用以上方法,对一台双远心、工作波长193nm以及数值孔径0.75的投影光刻物镜进行了倍率的公差分析和补偿器优选。结果显示,系统较好地实现了±50×10-6的倍率调节功能,而系统波像差劣化程度均方根值小于1.5nm。     

The euclidean bianchi group

The Bianchi Groups Γ_d are PSL₂(0_d) where 0_d is the ring of integers in the quadratic imaginary number field Q√-d with d a positive square-free rational integer. If d=1,2,3,7,11 0_d has a Euclidean algorithm and the corresponding groups are called the Euclidean Bianchi Groups. The group Γ₁ is the Picard Group has been studied independently. Here the subgroup structure of the remaining Euclidean Bianchi Groups is investigated. We show that they have a unique normal subgroup of index in if(n,6)=1 among other results. We also classify the abelian and nilpotent subgroups and discuss the structure of both congruence and non-congruence subgroups.     

Phase transformation and shape evolution of iron oxide nanocrystals synthesized in the ethylene glycol-water system

Iron oxide particles with various shapes,sizes and phase concentrations(including--Fe2O3 and Fe3O4) have been synthesized through a simple hydrothermal method in the ethylene glycol(EG)-water system.In the preparation conditions,ferric chloride(FeCl3.6H2O) was used as the iron source in the presence of sodium hydroxide(NaOH) without any surfactants.By adjusting the experimental parameters(EG/H2O ratio,base content,iron ions concentration,etc.),the shape,the size,the phase and the magnetic property of the pr...     

Fluorescence lidar for remote monitoring of plant

<正>The laser-induced fluorescence(LIF) characteristic of plant is directly linked to the photosynthesis.The LIF lidar for remote monitoring of plant has been suggested as one of the useful tools to identify plant species and determine its physiological status for a long time.So recently a LIF lidar for remote sensing of plant in Anhui Institute of Optics and Fine Mechanics is developed.It transmits laser beam at wavelength of 354.7 and 532 nm,and receives elastic echo and fluorescence echo at wavelength of 680 and 740 nm.Numerical simulations are carried out to determine achievable lidar performance including operation range.Validity of fluorescence signal is certified and then some results are presented.Comparison of the fluorescence characteristic among birch,conifer,and algae show that the fluorescence lidar is one of the potential tools to differentiate plant species.     

Seasonal Variation in Urocanic Acid Isomers in Human Skin

Abstract— Urocanic acid (UCA) is a major chromophore for UV in the skin and has been suggested to act as an initiator of UV-induced immunosuppression. It converts from the naturally occurring trans-isomer to the cis-isomer on UV exposure. Isomerization is dose dependent until the photostationary state is reached, and the seasonal variation in irradiance from the sun may lead to changes in the percentage of UCA present as cis -UCA throughout the year. Thirty young healthy subjects, skin types I-IV, were followed from early summer till spring. At each of six visits (June, July, August, October, December, March), pigmentation and the concentration of UCA isomers were measured at six body sites: forehead, upper chest, upper back, outer upper arm, inner upper arm and buttock. In exposed as well as unexposed regions a variation in pigmentation was found, peak values being recorded in August. Total UCA concentration was lower in July and August than in the rest of the year, irrespective of body site. In July, the percentage of cis -UCA was close to the maximal obtainable (50-60%) at all sites except the buttock. In the three winter months the percentage of cis-UCA was below 7% in all regions except for the forehead, where the mean cis -UCA was 18% in October and March. No consistent relationship was found between UCA isomers and pigmentation or skin type.     

用于空间的三反射镜光学系统设计

在三块反射镜系统的高斯公式基础上 ,就中间成一次实像的情况进行了系统的讨论 ,中间成一次实像可分为主镜成一次实像和主镜与次镜成一次实像两种 ,在对系统的几何参量进行分析的基础上 ,得出了这两种情况下的求解范围 ,并进行了实例设计 ,给出了对应的两个焦距为 4m、视场为 3°的设计结果。