流体力学半径对估算胶体微球聚集速率常数的影响

胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响.     

Reissert compound studies LXVI. Regioselective synthesis of pyridine reissert analogs

The reaction of ethyl chloroformate and pyridine with diethylaluminum cyanide as the cyanide source gave the Reissert analog, 1-ethoxycarbonyl-4-cyano-1,4-dihydropyridine and not the expected 1,2-dihydro regio isomer. Under the same conditions, 3-bromopyridine also directly gave the corresponding 1,4-dihydro Reissert analog. Reinvestigation of trimethylsilylcyanide, as the cyanide source, resulted in the observation that both regio isomers are formed and the ratio of these isomers are affected by both solvent polarity and by copper(I) iodide.     

Third order elastic constants of rubidium chloride

The third order elastic constants of RbCl, determined by measurements of the static stress dependence of ultrasonic waves, are found to be (in units of 10¹²$\text{dynes}\text{cm}{}^2$)

$\text{C}{}_{111}\text{= ?6.71 ± 0.1 C}{}_{123}\text{= 0.05 ± 0.07}$

$\text{C}{}_{112}\text{=?0.18 ± 0.04 C}{}_{144}\text{= 0.11 ± 0.02}$

$\text{C}{}_{166}\text{=?0.17 ± 0.01 C}{}_{456}\text{= 0.4 ± 0.01}$

. The calculation of third order constants using a rigid ion Born model is briefly discussed, and results are compared to the measurements. The comparison qualitatively supports the model, but no quantitative evaluation of the repulsive interaction is possible.     

Asymptotic sign-solvability, multiple objective linear programming, and the nonsubstitution theorem

In this paper we investigate the asymptotic stability of dynamic, multiple-objective linear programs. In particular, we show that a generalization of the optimal partition stabilizes for a large class of data functions. This result is based on a new theorem about asymptotic sign-solvable systems. The stability properties of the generalized optimal partition are used to address a dynamic version of the nonsubstitution theorem.All research was conducted at Trinity University and was supported by NSF Grant 0097366.     

Optimal treatments for photodynamic therapy

Medical applications in operations research have flourished over the last few decades, and one of the most prolific topics has been how to optimally design cancer treatments. The preponderance of this research has considered radiotherapy design, but several new procedures are emerging as alternatives to standard treatments. This paper addresses the developing treatment modality called photodynamic therapy (PDT), which uses the light-harvesting properties of a photosensitizer. The premise is that cells expire due to a toxic reaction caused by exposing a photosensitizer to a specific wavelength of light. The purpose of treatment design is to decide how to best treat the patient, meaning that cancerous tissues are damaged but that surrounding organs are not. This paper has two objectives. First, we develop a model that allows us to explore the design process. In particular, we develop a standard pharmacokinetic model to estimate the absorption and elimination of the photosensitizer. The biological model provides the data to cast the design process as a time dependent linear program. Second, we use the linear program to answer the question of whether or not PDT is a viable treatment for deep tissue cancers with the only drug currently approved in the USA. Our results indicate that even under optimal conditions, the treatments based on the currently approved drug are not capable of targeting tumors without destroying surrounding tissues. However, a treatment’s success significantly increases with the drug’s affinity for cancerous tissues. The authors are grateful for the comments of the editor and the referee on the original submission.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Electrophilic Substitution of 1,3-Dimethoxybenzene By Pentadienyltricarbonyliron Cations

Kinetics of reactions of several open-chain pentadienyltricarbonyliron cations with 1,3-dimethoxybenzene have been studied; the reactions are faster than those of the cyclohexadienyltricarbonyliron cation and a mechanism is proposed.     

Observation of trimuon events produced in neutrino and antineutrino interactions

We report two trimuon events producedin v interactions. Of these, one is of the charge type ?++, not previously reported. In an antineutrino exposure, one candidate of the charge type +?? has been observed. This type of event has also not been reported previously. The combined π → μ and K → μ background for the three events are calculated to be ～ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 × 10^?5.