Rotational Raman lidar for obtaining aerosol scattering coefficients

Two-channel lidar signals that are composed of total rotational scattering and elastic signals provide good information about aerosol scattering coefficients. We can calculate the aerosol backscattering coefficient and extinction coefficient directly, without making any assumption or calibration. Generally, a high-spectral-resolution lidar is used for aerosol monitoring, but we have designed a new low-spectral-resolution lidar system that contains both kinds of scattering information simultaneously, and we have retrieved the aerosol scattering coefficient. The results show that there is no need to assume any relation between aerosol backscattering and extinction or to consider any wavelength calibration to determine the aerosol scattering coefficient.     

Knot signature functions are independent

A Seifert matrix is a square integral matrix satisfying

To such a matrix and unit complex number there corresponds a signature,

Let denote the set of unit complex numbers with positive imaginary part. We show that is linearly independent, viewed as a set of functions on the set of all Seifert matrices.

If is metabolic, then unless is a root of the Alexander polynomial, . Let denote the set of all unit roots of all Alexander polynomials with positive imaginary part. We show that is linearly independent when viewed as a set of functions on the set of all metabolic Seifert matrices.

To each knot one can associate a Seifert matrix , and induces a knot invariant. Topological applications of our results include a proof that the set of functions is linearly independent on the set of all knots and that the set of two-sided averaged signature functions, , forms a linearly independent set of homomorphisms on the knot concordance group. Also, if is the root of some Alexander polynomial, then there is a slice knot whose signature function is nontrivial only at and . We demonstrate that the results extend to the higher-dimensional setting.

     

Group-velocity-matched cascaded quadratic nonlinearities of femtosecond pulses in periodically poled MgO:LiNbO3

Large nonlinear phase shifts were generated with femtosecond pulses at 1560 nm through cascaded quadratic interactions in periodically poled MgO-doped LiNbO3. The off-diagonal component of the nonlinear coefficient was utilized for simultaneous quasi phase matching and group-velocity matching. The effective nonlinear refractive index was varied from -2.9 x 10(-14) to +3.3 x 10(-14) cm2/W by tuning the phase-mismatch conditions.     

Synthesis of novel 2,6-disubstituted-3,4-dimethylidene tetrahydropyrans via Prins-type cyclization

Synthesis of novel substituted tetrahydropyrans with adjacent exo-methylene groups at the C3 and C4 positions via Prins-type cyclization has been described.     

Spontaneous formation of nanoparticle vesicles from homopolymer polyelectrolytes

Nanoparticle vesicles were spontaneously assembled from homopolymer polyamine polyelectrolytes and water-soluble, citrate-stabilized quantum dots. The further addition of silica nanoparticles to a solution of quantum dot vesicles generated stable micrometer-sized hollow spheres whose walls were formed of a thick, inner layer of close-packed quantum dots followed by an outer layer of silica. The method employed here to assemble both the nanoparticle vesicles and the hollow spheres is in direct contrast to previous syntheses that use either tailored block copolymers or oil-in-water emulsion templating. We propose that the formation of charge-stabilized hydrogen bonds between the positively charged amines of the homopolymer polyelectrolytes and the negatively charged citrate molecules stabilizing the quantum dots is responsible for the macroscopic phase separation in this completely aqueous system. The ease and processibility of the present approach gives promise for the production of a diverse array of materials ranging in applications from drug delivery to catalysis to micrometer-scale optical devices.     

Tunable stimulated-Brillouin-scattering resonator started by feedback provided by Bragg scattering from the dynamic grating within an active medium

We report a tunable stimulated-Brillouin-scattering resonator that does not require a starting mirror or a wavelength selector. The resonator is based on the Bragg scattering from the dynamic grating within the active medium itself. The laser dye (Rhodamine 6G dissolved in ethanol) was utilized as the active medium and was pumped by a frequency-doubled Nd:YAG laser. The quality factor (M(2)) of the output beam was 2.2. A single short pulse (<1 ns) with a pumping efficiency of ~4% was observed.     

基于遗传算法构建巴耳末公式

基于遗传算法构建了巴耳末公式．通过建立合适的拟合数学模型，用计算机对数学模型进行优化，使之尽可能反映氢原子实际谱线分布，并求出经验常量和拟合公式，最后分析了所得结果．     

Total Synthesis of Cyathin A3 and Cyathin B2

A stereoselective synthesis of cyathin A₃ and cyathin B₂ has been achieved by a Prins‐type reaction of a cycloalkenyl cyclopropanol. Particularly noteworthy is the use of a spirocyclobutanone moiety as a convenient scaffold for an efficient ring‐closing metathesis to stereoselectively construct a suitably functionalized seven‐membered ring (see scheme).

     

Understanding the junction degradation mechanism in CdS/CdTe solar cells using a Cd-deficient CdTe layer

It is known that CdTe solar cells are often degraded under solar illumination. But the degradation mechanism is not fully proved because it does not appear consistently. The junction degradation in CdS/CdTe solar cells was investigated using a CdTe layer with Cd deficient composition, where Cd vacancy concentration is high. It was found that the Cu atoms easily filled the Cd vacancies in CdTe and transport to junction area from Cu back contact. PL measurement and spectral quantum efficiency measurement showed that the incorporation of Cu atoms in CdS forms a defect energy level at 1.55 eV below the conduction band in CdS. As a result, the junction built-in potential is decreased and light penetration into CdTe absorber is shielded. For reliable and stable CdTe cells, the formation of Cd vacancy in CdTe should be avoided by careful control of CdTe.     

Fabrication of Nb2O5/C nanocomposites as a high performance anode for lithium ion battery

Nb₂O₅/C nanosheets are successfully prepared through a mixing process and followed by heating treatment.Such Nb₂O₅/C based electrode exhibits high rate performance and remarkable cycling ability, showing a high and stable specific capacity of ~380 mAh g^-1 at the current density of 50 mA g^-1(much higher than the theoretical capacity of Nb₂O₅).Further more,at a current density of 500 mA g^-1,the nanocomposites electrode still exhibits a specific capacity of above 150 mAh g^-1 after 100 cycles.These results suggest the Nb₂O₅/C nanocomposite is a high performance anode material for lithium-ion batteries.