Multi-plectoneme phase of double-stranded DNA under torsion

We use the worm-like chain model to study supercoiling of DNA under tension and torque. The model reproduces experimental data for a much broader range of forces, salt concentrations and contour lengths than previous approaches. Our theory shows, for the first time, how the behavior of the system is controlled by a multi-plectoneme phase in a wide range of parameters. This phase does not only affect turn-extension curves but also leads to a non-constant torque in the plectonemic phase. Shortcomings from previous models and inconsistencies between experimental data are resolved in our theory without the need of adjustable parameters.Comment: 4 pages, 6 figures, submitted, 2 typo's corrected, one reference adde

Photoexcitation dynamics in polyacetylene probed by transient photoinduced resonant Raman scattering

Journal ArticleWe have measured photoexcitation dynamics in the picosecond time domain in fully trans and partially isomerized (CH)X and (CD)X films with different cis/trans content ratios, using the technique of transient photoinduced resonant Raman scattering. Following the distinctively different decay kinetics of cis and trans resonantly enhanced vibrations, we observed an intersystem crossing of photoexcitations from cis to trans segments which is dominated by a diffusion process in the cis segments, with a time constant between 24 and 215 ps depending on the cis/trans ratio

Transient spectroscopy of Frenkel and charge transfer excitons in α-sexithienyl films

Journal ArticlePhotoexcitations dynamics are investigated in a-sexithienyl nanocrystalline films using transient photomodulation in a spectral range from 0.4 to 2.5 eV and time domain from 200 fs to 50 ms. We identify intrachain and interchain excitations. The former are even parity excitons with ultrafast dynamics, whereas the latter are long-lived charge transfer excitons generated within 300 fs, which separate into uncorrelated polaron pairs in the submicrosecond time domain

Direct observation of the ultrafast electron transfer process in a polymer/fullerene blend

Photoinduced electron transfer in organic molecules is an extensively investigated topic both because of fundamental interest in the photophysics and for applications to artificial photosynthesis. Highly efficient ultrafast electron transfer from photoexcited conjugated polymers to C60 has been reported, the back transfer is heavily hindered, thus providing an intrinsic stabilization mechanism of the photogenerated charges. Although an upper limit for the forward electron transfer time of 1 ps has been reported, its detailed time resolution is still missing and is highly needed to shed light on the photophysics of the charge transfer mechanism. We perform ultrafast experiments on conjugated polymer/C60 blends with sub-10-fs time resolution. We are able to time resolve for the first time the charge transfer process, obtaining a forward electron transfer time constant τct≈45 fs

Assessing the Economic Value of a Regional Air Quality Plan

When developing an air quality plan, environmental authorities usually devise a number of individual actions, constituted by the application of both technical (end-of-pipe) and energy efficiency measures. They may range from the incentives to buy less polluting vehicles, to the enforcement of stricter rules on domestic heating. The assessment of the economic effectiveness for the society as a whole of the individual measures and of the overall plan requires a flexible support system able to quickly perform air quality impact evaluations on the specific area. One such system is RIAT+, a software package developed and tested during a series of European research projects, which has been used to evaluate costs and benefits of the Lombardy Region Air Quality Plan (PRIA), constituted by about 90 different actions to be implemented within 2020. The adoption of each measure means a certain change in the emission, which is distributed over the regional territory in different way, depending on the type of measure. A shift of the car fleet to a different EURO class, for instance, means an emission reduction only on the road network, while a reduced use of electricity may imply a lower emission of power plants at specific sites. To evaluate the effects of these emission changes, RIAT+ adopts a surrogate model approach, namely using a neural network calibrated on few results of a full chemical transport model. It is thus possible to rapidly evaluate the improvements in the population exposure and health and the consequent reduction of external costs. The final economic assessment is obtained by comparing the sum of energy savings and external cost reductions with the implementation costs of the corresponding measures

Direct observation of the ultrafast electron transfer process in a polymer/fullerene blend

Photoinduced electron transfer in organic molecules is a topic of fundamental interest in photophysics and for applications to artificial photosynthesis. The detailed time resolution of this process is needed to shed light on the charge transfer mechanism. We perform ultrafast experiments on conjugated polymer/C60 blends with sub-10-fs time resolution. We are able to time resolve for the first time the charge transfer process, obtaining a time constant ≈45 fs