Irreversible helix rearrangement from Cis‐transoid to Cis‐cisoid in poly(p‐n‐hexyloxyphenylacetylene) induced by heat‐treatment in solid phase

Polymerization of p‐n‐hexyloxyphenylacetylene (pHPA) by using a [Rh(norbornadine)Cl]₂‐triethylamine catalyst was carried out at room temperature to afford stereoregular helical poly(p‐n‐hexyloxyphenylacetylene)s (PpHPAs). When ethanol and n‐hexane were used as polymerization solvents, a bright yellow PpHPAs, poly( Y ) with M_n = 8.5 × 10⁴ and its purple red polymer, poly( R ) with M_n = 5.3 × 10⁴ were obtained in 95% yields and 84% yields, respectively. Diffuse reflective UV–vis spectra of poly( Y ) and poly( R ) in solid phase showed different broad absorption peaks at 445 and 575 nm, respectively. X‐Ray diffraction patterns of poly( Y ) and poly( R ) showed typical columnar structures assignable to cis‐transoid and cis‐cisoid structures, respectively, which were also supported by molecule mechanics calculation. Poly( Y ) was irreversibly transformed to a reddish‐black polymer, poly( Y‐B ), which columnar diameter was nearly the same as that of poly( R ). Further, poly( Y ) showed an exothermic peak in the differential scanning calorimetry trace at 80 °C for 1 h in N₂ gas. Thus, these findings suggest a thermally irreversible rearrangement from an unstable cis‐transoid form, poly( Y ) with a stretched cis‐transoid helix to a stable cis‐cisoid form, poly( R ), with a contracted cis‐cisoid helix in the solid phase to give poly( Y → B ) with the cis‐cisoid form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A Stochastic Model for Transport of Particulate Matter in Air: An Asymptotic Analysis

A branching particle system with changes of size is considered as a model for transport of particulate matter in air. This type of model is motivated by problems arising in the context of air pollution. High-density fluctuation limits for the process recording the positions and sizes of the particles through time are presented. These results allow to compute approximate probabilities for the temporal and spatial concentrations of particles of given sizes (in particular the small-sized pollutant particles which pose a health hazard).     

The dynamics of asset lifetime under technological change

The variable lifetime of assets is analyzed in a serial replacement problem. Technological change impacts the maintenance cost and new asset cost. The optimal asset lifetime appears to be constant only when both costs decrease with the same rate. We identify cases when the technological change decreases or increases the optimal lifetime.     

Note on Signature Change and Colombeau Theory

Recent work alludes to various 'controversies' associated with signature change in general relativity and claims to resolve them. As we have argued previously, these are in fact disagreements about the (often unstated) assumptions underlying various possible approaches. We demonstrate that the issue has not been resolved and the choice between approaches remains open.     

全新世浙江的海岸变迁与海面变化

本文就指示浙江古岸线与古海面位置的主要标志作了评述;首次公布了8个~(14)C测年数据,并据此及其他有关资料再现了浙江全新世海面变化;最后着重讨论了全新世海岸线变迁,提出四个不同的发展阶段。     

Consistency of change point estimators for symmetrical stable distribution with parameters shift

Assume that the characteristic indexαof stable distribution satisfies 1<α<2,and that the distribution is symmetrical about its mean.We consider the change point estimators for stable distribution withαor scale parameterβshift.For the one case that mean is a known constant,ifαorβchanges,then density function will change too.To this end,we suppose the kernel estimation for a change point.For the other case that mean is an unknown constant,we suppose to apply empirical characteristic function to estimate the change-point location.In the two cases,we consider the consistency and strong convergence rate of estimators.Furthermore,we consider the mean shift case.If mean changes,then corresponding characteristic function will change too.To this end,we also apply empirical characteristic function to estimate change point.We obtain the similar convergence rate.Finally,we consider its application on the detection of mean shift in financial market.     

Synthesis and characterization of proton‐conducting copolyimides bearing pendant sulfonic acid groups

A series of sulfonated copolyimides (co‐SPIs) bearing pendant sulfonic acid groups were synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride (NTDA), bis(3‐sulfopropoxy) benzidines (BSPBs), and common nonsulfonated diamines via statistical or sequenced polycondensation reactions. Membranes were prepared by casting their m‐cresol solutions. The co‐SPI membrane had a microphase‐separated structure composed of hydrophilic and hydrophobic domains, but the connecting behavior of hydrophilic domains was different from that of the homo‐SPIs. The co‐SPI membranes displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. With water uptake values of 39–94 wt %, they showed dimensional changes in membrane thickness of about 0.11–0.58, which were much lower than those of homo‐SPIs. The proton conductivity σ values of co‐SPI membranes with ion exchange capacity values ranging from 1.95–2.32 meq/g increased sigmoidally with increasing relative humidity. They displayed σ values of 0.05–0.16 S/cm at 50 °C in liquid water. Increasing temperature up to 120 °C resulted in further increase in proton conductivity. The co‐SPI membranes showed relatively good conductivity stability during the aging treatment in water at 100 °C for 300 h. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1545–1553, 2005     

Laser induced optoacoustic spectroscopy of benzil: Evaluation of structural volume change upon photoisomerization

The cis-skew to trans-planar photoisomerization of benzil in the photoexcited state was studied by laser-induced optoacoustic spectroscopy (LIOAS) in a series of normal alkane solvents at room temperature. The structural volume change due to the photoisomerization process has been estimated and compared with the same calculated from the optimized skew and trans structures. The magnitude of the structural volume change is estimated to be 22.9 ± 1.2 mL/mol. This study reveals that an expansion in volume occurs during the photoinduced isomerization process. In non-polar alkane solvents, the estimated volume change has been argued to be free from electrostrictional contribution.     

Wind effects on noise propagation for complicated geographical and road configurations

Outdoor propagation from roads is influenced by wind, temperature and humidity. It is necessary to predict wind effects to simulate long-term environmental noise accurately. Noise levels have been measured in conjunction with wind speed and wind direction measurements. These noise levels showed noticeable daily changes. Excess attenuations of noise levels were found to depend on the vector wind (U_vec). By relating the vector wind and observed sound attenuations under all wind conditions, the influence of wind can be more accurately predicted for purposes of simulating noise propagation.