Analytic solutions to compartmental models of the HIV/AIDS epidemic

For many years compartmental models have provided useful insightsinto the spread of epidemics. Such models are usually fairlyeasy to set up, but even the simpler models have the disadvantagethat they are intractable to analytic solution. In this paperwe examine models of the HIV/AIDS epidemic, and show that theequations may be linearized in a piecewise manner over time,thus allowing analytic solutions to be obtained. Indicationsof the usefulness of this approach are provided. In particular,an analytic solution gives insight into the mechanism of theepidemic, together with a clearer picture of the sensitivityof results to changes in parameter values. Further, the processesof parameter estimation and the methodology of back-calculationalso benefit from the provision of functional forms for thestate variables.     

QUALITATIVE STUDIES OF THE LOW TEMPERATURE PHOTOCHEMISTRY OF RHODOPSIN AND RELATED PIGMENTS

Abstract— Rhodopsin, the isomeric pigments formed from 9- cis - and 9, 13- dicis -retinal, and the synthetic pigments formed from 9- cis - and 11- cis -14-methylretinal were irradiated with 490 nm light at -196C. Absorption spectral changes indicate that a distinguishable bathorhodopsin type intermediate may be formed for each pigment. The bathorhodopsin intermediates of the 9- cis pigments have band maxima hypsochromically shifted by4–5 nm compared to their corresponding rhodopsins. The bathorhodopsin type intermediate formed upon irradiation of 9, 13- dicis -rhodopsin has an absorption that maximizes 6 nm shorter than that of rhodopsin. Band maxima of the bathorhodopsin intermediates of the 14-methylrhodopsins are bathochromatically shifted ca. 8 nm compared to their corresponding rhodopsins.     

利用高能锂束激光荧光法测量托卡马克中的角向磁场

本文介绍了利用高能锂束激光荧光法测量托卡马克中角向磁场的原理、实验装置和主要技术,同时也介绍了该方法的局限性。     

SOLVENT INFLUENCES ON THE SINGLET QUENCHING OF CHLOROPHYLL a BY 2, 5-DIMETHYL-p-BENZOQUINONE

Abstract— The quenching of chlorophyll a excited singlet states by 2.5-dimethyl- p -benzoquinone has been investigated in solvents of varying viscosity and polarity. The observed singlet lifetimes showed little variation in several hydrocarbon solvents. Stern-Volmer constant K depends on the viscosity of the solvent, although cyclic and straight-chain hydrocarbons behave somewhat differently. The decrease of the K values with increase of viscosity suggests that the quenching mechanism is at least partly dynamic, although there is evidence for static quenching as well. The influence of solvent polarity on the K values was found to be insignificant, which is consistent with a very short-lived ion pair intermediate formed by electron-transfer quenching.     

Photoelectron spectroscopy of atomic oxygen using the Elettra synchrotron source

Atomic oxygen has been studied using angle resolved photoelectron spectroscopy (PES) and constant-ionic-state (CIS) measurements using radiation from the Elettra synchrotron as the photon source. Relative partial photoionization cross-sections and angular distributions for the O⁺(⁴S) ← O(³P) and O⁺(²D) ← O(³P) ionizations have been measured as a function of photon energy from threshold (13.6 eV) to 19.0 eV. Comparison of the results obtained with recent experimental work performed at lower resolution reveals a number of differences and comparison with results of recent calculations shows the need for the inclusion of coupling intermediate between the j-j and L-S limits in future calculations of photoionization cross-sections and angular distributions. This work has demonstrated the feasibility of and results to be expected from angle resolved PES and CIS measurements on reactive intermediates at Elettra, a third-generation synchrotron source, and further studies on small molecular radicals are proposed.     

几种硅-硅链高聚物的合成和性质

采用具有不同取代基的二氯硅烷,在金属钠作用下共缩合的方法,合成了几种硅-硅链共聚物。这些共聚物分子量高,既能溶于一般的有机溶剂,也可在较低的温度下熔融,模压或浇铸成膜,或抽成纤维。在紫外光辐照下,高聚物的薄膜或纤维发生降解或交联反应。     

DELAYED-LIGHT STUDIES ON PHOTOSYNTHETIC ENERGY CONVERSION-III. EFFECT OF 3-(3,4-DICHLOROPHENYL)-1,1 -DIMETHYL UREA ON THE MILLISECOND EMISSION FROM CHLOROPLASTS PERFORMING PHOTOREDUCTION OF FERRICYANIDE*

Abstract— How does a plant convert electronic excitation of chlorophyll into stable chemical potential? The time scales of fluorescence (10^--⁹ sec) and steady-state enzymatic turnover (10–² sec) indicate that energy storage must be involved. Millisecond delayed singlet emission from chlorophyll allows measurement of metastable energy storage at Photoreaction II. Activation of noncyclic electron transport results in more rapid decay and in increase of emission at 10^--³ sec, both effects being inhibited by the poison DCMU. These results can be explained by at least three different models of the reaction center: the oxidized chlorophyll model, the chlorophyll triplet model, and the two-quantum electron-hole model.