Cumulant functions in optical coherence theory

Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders greater than some numberN ₀ vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would need to introduce cumulant tensors.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Arginine-based molecular transporters: the synthesis and chemical evaluation of releasable taxol-transporter conjugates

[structure: see text] A flexible and efficient procedure has been developed for the conjugation of taxol to various arginine-based molecular transporters via the taxol C2' O-chloroacetyl derivative. The resultant taxol-transporter conjugates are highly water soluble and release free taxol with half-lives of minutes to hours depending on the pH and the linker structure.     

An efficient, scalable synthesis of the molecular transporter octaarginine via a segment doubling strategy

[reaction: see text]. Short oligomers of arginine function as remarkably efficient molecular transporters of drugs and probe molecules into cells and tissue. Currently, these compounds are prepared on resin through a unidirectional solid-phase synthesis. To extend the utility of these compounds for therapeutic and research applications, a scalable solution-phase synthesis of Arg8 (1) has been developed on the basis of a segment doubling strategy that proceeds in 13 steps and 28% overall yield from 4, including a novel one-step perdeprotection-perguanidinylation reaction.     

铌酸锶钡薄膜的微结构与电光性能的研究

本文叙述了使用溶胶凝胶法在MgO(0 0 1)的衬底上制备铌酸锶钡薄膜的过程 ,膜层厚度可达 5 μm。通过X射线衍射、摇摆曲线、扫描、拉曼散射光谱等方法研究了薄膜的微结构性能 ,实验发现 ,铌酸锶钡薄膜具有了较好的 (0 0 1)方向的优先取向性能 ,并且随着薄膜厚度的增加 ,其晶体取向性也会随之不断改进。熔石英的透明衬底上生长的SBN薄膜具有较大的电致双折射效应 ,其有效电光系数能够高达 6 6 2× 10 -11m/V。     

A concise,selective synthesis of the polyketide spacer domain of a potent bryostatin analogue

[reaction: see text] A concise, asymmetric synthesis of the polyketide spacer domain portion (C1-C13) of a highly potent bryostatin analogue was developed. The route utilizes asymmetric hydrogenation methodology to install the C3, C5, and C11 stereocenters, while a substrate directed syn reduction sets the C9 stereocenter. The spacer domain 1 is obtained in 10 steps with a 25% overall yield and is readily incorporated into the synthesis of 2.