The elastic theory of a single DNA molecule

We study the elastic responses of double-(ds) and single-stranded (ss) DNA at external force fields. A double-strand-polymer elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity, cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that short-ranged base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairpin-coil transition in ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized by base pairing and base-pair stacking, into random coils. This phase transition is predicted to be of first order for stacking potential higher than some critical level, in accordance with experimental observations.     

正确的答案错误的解法

有些题目即使解法不正确,也可能得出正确的答案. 如果注意了答案对但解法错的情况,让学生判别其正误,那么对于物理概念的理解、物理规律的掌握、思维能力的提高都将起重要作用. 例l 重10N的均匀木棒AB长为L,B端放在地面上,A端用竖直的绳子吊起(图     

燃煤烟气中As、Se、Pb的形态分布及S、Cl元素对其形态分布的影响

基于化学热力学平衡分析方法，计算分析了燃煤烟气中重金属As、Se、Pb的形态分布规律，研究了S、Cl等元素对As、Se、Pb的形态分布规律的影响。结果表明，氧化性气氛下，As以As₂O₅、As₄O₆、AsO等氧化物的形式存在；Se主要以SeO₂形式存在；Pb在1000 K以下主要是固态PbSO₄，1200 K以上为气态PbO。还原性气氛下，As在较低温度时为固态As₂S₂，900-1400 K以As₂、AsS、AsN气体共存，2000 K以上全部转化为气态AsO。Se在1100 K以下主要以气态H₂Se存在，1100 K开始生成SeS和Se₂气体，1800 K时主要是气态Se和少量气态SeO；Pb在中低温时主要是PbS，1800 K以上气态Pb为主要存在形态。S在还原性气氛下增大了AsS（g）、PbS（g）、SeS（g）的比例，氧化性气氛下对As、Se、Pb形态分布基本无影响；Cl无论在氧化还是还原气氛下对As、Se影响均较小，但对Pb的形态分布影响较大。     

Dubrovin赋值斜群环

本文中对一个斜群环为Dubrovin赋值环给出了一系列等价刻画,并且刻画了一个Dubrovin赋值斜群环的所有素理想.     

Microwave-assisted Regioselective 1-O-Deacylation of Peracylated Glycopyranoses on Alumina

A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation.     

Nonlinear Boundary Layers of the Boltzmann Equation: I. Existence

 We study the half-space problem of the nonlinear Boltzmann equation, assigning the Dirichlet data for outgoing particles at the boundary and a Maxwellian as the far field. We will show that the solvability of the problem changes with the Mach number ℳ^∞ of the far Maxwellian. If ℳ^∞<−1, there exists a unique smooth solution connecting the Dirichlet data and the far Maxwellian for any Dirichlet data sufficiently close to the far Maxwellian. Otherwise, such a solution exists only for the Dirichlet data satisfying certain admissible conditions. The set of admissible Dirichlet data forms a smooth manifold of codimension 1 for the case −1<ℳ^∞<0, 4 for 0<ℳ^∞<1 and 5 for ℳ^∞>1, respectively. We also show that the same is true for the linearized problem at the far Maxwellian, and the manifold is, then, a hyperplane. The proof is essentially based on the macro-micro or hydrodynamics-kinetic decomposition of solutions combined with an artificial damping term and a spatially exponential decay weight. Received: 20 April 2002 / Accepted: 4 December 2002 Published online: 21 March 2003 Communicated by H.-T. Yau     

Urea method for the synthesis of hydrotalcites

Mg-Al, Zn-Al and Ni-Al hydrotalcite-like compounds with high crystallinity were synthesized by using the decomposing property of urea at high temperature. The crystallinity and the regularly of the samples were much preferable to those synthesized by other methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bush连续不可微函数的分形性质

本文对用递推关系确定的Bush连续不可微函数,找出了迭代函数系(IFS),从而得到它的级数表达式和所具有的自仿射分形的有关性质.最后还计算出函数图象的Hausdorff 维数的准确值.     

酸糖蛋白手性柱分离6种手性化合物

通过考察缓冲液种类、浓度及其pH值对对映体在手性柱上的保留和分离行为的影响,以及流动相中加入不同种类、不同浓度的不带电荷的有机溶剂乙腈、甲醇、正丙醇、异丙醇、流动相流速和柱温对对映体分离能力的影响,优化了含碳手性中心的碱性药物苯丙哌林、酸性化合物MT-A5及MT-酸和含硫手性中心的质子泵抑制剂奥美拉唑、泮托拉唑、雷贝拉唑对映体分离条件,最佳手性分离条件为:苯丙哌林,0.05 mol/L磷酸二氢铵缓冲液(pH 3.0)-乙腈(95∶5,V/V)为流动相,流速为0.7 mL/m in,柱温为20℃;MT-A5及MT-酸,流动相为0.01 mol/L醋酸铵缓冲液(pH 5.0)-乙腈(74∶26,V/V),流速为0.9 mL/m in,柱温为20℃;泮托拉唑,流动相为10 mmol/L醋酸铵缓冲液(pH 5.5)-乙腈(93∶7,V/V),流速为0.9 mL/m in;柱温为20℃;奥美拉唑和雷贝拉唑,流动相为0.01 mol/L醋酸铵缓冲液(pH 3.0)-乙腈(95∶5,V/V),流速为0.7 mL/m in,柱温为20℃。实现了应用高效液相色谱法在α1-酸糖蛋白手性柱上对上述化合物的对映体分离,并成功用于手性药物合成中的对映体过量百分率的测定。