Substitution Matrices of Residue Triplets Derived from Protein Blocks.

In protein sequence alignment, residue similarity is usually evaluated by substitution matrix, which scores all possible exchanges of one amino acid with another. Several matrices are widely used in sequence alignment, including PAM matrices derived from homologous sequence and BLOSUM matrices derived from aligned segments of BLOCKS. However, most matrices have not addressed the high-order residue-residue interactions that are vital to the bioproperties of protein.With consideration for the inherent correlation in residue triplet, we present a new scoring scheme for sequence alignment. Protein sequence is treated as overlapping and successive 3-residue segments. Two edge residues of a triplet are clustered into hydrophobic or polar categories, respectively. Protein sequence is then rewritten into triplet sequence with 2 · 20 · 2 = 80 alphabets. Using a traditional approach, we construct a new scoring scheme named TLESUMhp (TripLEt SUbstitution Matrices with hydropobic and polar information) for pairwise substitution of triplets, which characterizes the similarity of residue triplets. The applications of this matrix led to marked improvements in multiple sequence alignment and in searching structurally alike residue segments. The reason for the occurrence of the ‘‘twilight zone,’’ i.e., structure explosion of lowidentity sequences, is also discussed.

Combined study of gamma p ->eta p and pi(-)p ->eta n in a chiral constituent quark approach

Within a chiral constituent quark model approach, η-meson production on the proton via electromagnetic and hadron probes is studied. With few parameters, the differential cross section and polarized beam asymmetry for γp → ηp and differential cross section for π − p → ηn processes are calculated and successfully compared with the data in the center-of-mass energy range from threshold up to 2 GeV. The five known resonances S11(1535), S11(1650), P13(1720),D13(1520), and F15(1680) are found to be dominant in the reaction mechanisms in both channels. Possible roles played by new resonances are also investigated; and in the photoproduction channel, significant contribution from S11 and D15 resonances, with masses around 1715 and 2090 MeV, respectively, are deduced. For the so-called missing resonances, no evidence is found within the investigated reactions. The helicity amplitudes and decay widths of N ∗ → πN, ηN are also presented and found to be consistent with the Particle Data Group values.

eta-production on the proton via electromagnetic and hadronic probes

The reactions pi(-)p -> eta n and gamma p -> eta p are investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region The meson-baryon channels included are pi N, pi Delta, sigma N, and rho N The direct eta-photoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU(6)circle times O(3) symmetry In the models search, the following known nucleon resonances are embodied S-11(1535), S-11(1650), P-11(1440), P-11(1710), P-13(1720), D-13(1520), D-13(1700), D-15(1675), and F-15(1680). Data for the pi(-)p -> eta n reaction from threshold up to a total center-of-mass energy of W approximate to 2 GeV are satisfactorily reproduced For the photoproduction channel: two additional higher mass known resonances, P-13(1900) and F-15(2000), are also considered However, reproducing the data for gamma p -> eta p requires, within our approach, two new nucleon resonances, for which we extract, mass and width

Study of nucleon resonances in a chiral quark model via eta productions

In this report we investigate eta-meson productions oil the proton via electromagnetic and hadron probes in a chiral quark model approach. The observables, such as, differential cross section and beam asymmetry for the two productions are calculated and compared with the experiment. The five known resonances S-11(1535) S-11(1650); P-13(1720) D-13(1520), and F-15(1680) are found to be dominant in the reaction mech-anisms in both channels. Significant, contribution from a new S-11 resonances are deduced. For the so-called "missing resonances", no evidence is found within the investigated reactions. The partial wave amplitudes for pi(-)p -> eta n are also presented.

eta photoproduction on the proton in a chiral constituent quark approach via a one-gluon-exchange model

A formalism based on a chiral quark model (chi QM) approach complemented with a one-gluon-exchange model, to take into account the breakdown of the SU(6)circle times O(3) symmetry, is presented. The configuration mixing of wave functions for nucleon and resonances are derived. With few adjustable parameters, differential cross-section and polarized-beam asymmetry for the gamma p -> eta p process are calculated and successfully compared with the data in the center-of-mass energy range from threshold to 2 GeV. The known resonances S-11(1535), S-11(1650), P-13(1720), D-13(1520), and F-15(1680), as well as two new S-11 and D-15 resonances, are found to be dominant in the reaction mechanism. Moreover, connections among the scattering amplitudes of the chi QM approach and the helicity amplitudes, as well as decay widths of resonances, are established. Possible contributions from the so-called missing resonances are investigated and found to be negligible.

快重离子在聚苯乙烯中的辐照效应研究

本工作用兰州重离子加速器提供的2.1GeV的Kr离子分别在空气和真空条件下辐照了多层堆叠的聚苯乙烯薄膜样品，辐照剂量在5 * 10~(10)到3 * 10~(12)ions/cm~2之间，辐照温度在室温附近。辐照后对样品分别进行了傅立叶变换红外光谱和紫外可见光谱的测量，由此研究了快重离子辐照聚苯乙烯产生的物理和化学改性。实验结果表明，聚苯乙烯经Kr离子辐照后发生了降解，包括苯环在内的大部分官能团遭到破坏，相应特征峰的吸光度随辐照剂量和能损的增加而减小。与此同时，辐照还在1650-1750cm~(-1)之间和3300cm~(-1)处产生了新的吸收峰，其分别对应于C=O双键的分子振动和C≡C-H的C-H伸缩振动，表明辐照在聚苯乙烯中产生了炔基。实验发现产生炔基需要离子有足够高的电子能损值，在聚苯乙烯中该能损阈值约为1.0keV/nm。在材料经辐照发生降解的同时，样品的光吸收边界逐渐红移，并伴有透光率的下降。详细的测量显示，在紫外可见区材料吸光度的增加随剂量近似呈线性关系，随能损呈约二次方的指数关系。通过对2.1GeV的Kr离子和1.4GeV的Ar离子辐照结果的比较还发现，快重离子辐照产生的物理化学改性不仅与离子的能损有关，还与离子的速度有关。在同一能损条件下，速度越小，产生的效应就越大。文中用径向能量沉积密度和有效化学反应半径对上述结果进行分析讨论。

CO_2浓度升高对两种沈阳城市森林树种光合特性的影响

利用开顶式气室,研究了CO2浓度升高条件下城市森林主要树种油松(Pinus tabulaefomis)和银杏(Ginkgo biloba)主要光合特性的变化。结果表明,整个生长季,CO2浓度升高(700μmol.mol-1)条件下2树种叶片的净光合速率、可溶性糖、淀粉和可溶性蛋白含量均接近或高于相应对照(自然CO2浓度)值,但不同树种增加的幅度不同;而2树种的叶绿素含量和Chla/Chlb值对CO2浓度升高反应不一,表现为CO2浓度升高条件下油松的叶绿素含量较对照值高,Chla/Chlb值降低,银杏的叶绿素含量为前期升高,后期降低,Chla/Chlb值变化与之正好相反,说明城市森林组成树种对CO2浓度升高的响应具有复杂性。CO2浓度升高条件下,两树种均未发生光合适应现象。

黄土高原地区土壤可蚀性及其应用研究

通过回顾已有的成果 ,分析评价了我国土壤可蚀性研究的进展及存在的问题 ,提出我国土壤可蚀性研究中的标准小区定义。运用野外观测资料 ,研究计算了黄土高原地区土壤可蚀性指标值。结果表明 ,陕北和晋西北一带黄土可蚀性 K值变化于 0 .3～ 0 .7之间 ,并且有以陕西子洲、绥德一带为最大 ,以此为中心 ,向南、向北和向东都减少的变化趋势。