Band dispersion and electronic lifetimes in crystalline organic semiconductors

The consequences of several microscopic interactions on the photoemission spectra of crystalline organic semiconductors are studied theoretically. It is argued that their relative roles can be disentangled by analyzing both their temperature and their momentum-energy dependence. Our analysis shows that the polaronic thermal band narrowing, which is the foundation of most theories of electrical transport in organic semiconductors, is inconsistent in the range of microscopic parameters appropriate for these materials. An alternative scenario is proposed to explain the experimental trends.     

A copula approach to test asymmetric information with applications to predictive modeling

In this article, we present a copula regression model for testing asymmetric information as well as for predictive modeling applications in automobile insurance market. We use the Frank copula to jointly model the type of coverage and the number of accidents, with the dependence parameter providing for evidence of the relationship between the choice of coverage and the frequency of accidents. This dependence therefore provides an indication of the presence (or absence) of asymmetric information. The type of coverage is in some sense ordered so that coverage with higher ordinals indicate the most comprehensive coverage. Henceforth, a positive relationship would indicate that more coverage is chosen by high risk policyholders, and vice versa. This presence of asymmetric information could be due to either adverse selection or moral hazard, a distinction often made in the economics or insurance literature, or both. We calibrated our copula model using a one-year cross-sectional observation of claims arising from a major automobile insurer in Singapore. Our estimation results indicate a significant positive coverage-risk relationship. However, when we correct for the bias resulting from possible underreporting of accidents, we find that the positive association vanishes. We further used our estimated model for other possible actuarial applications. In particular, we are able to demonstrate the effect of coverage choice on the incidence of accidents, and based on which, the pure premium is derived. In general, a positive margin is observed when compared with the gross premium available in our empirical database.     

Dynamic behavior of gear pumps: effect of variations in operational and design parameters

This work presents a wide number of results about the influence that variations in terms of operational and design parameters play on the dynamic behavior of external gear pumps. These results are obtained by using a non-linear lumped-parameter kineto-elastodynamic model developed and experimentally assessed with the aim of including all the important dynamic effects. On the one hand, the effects of variations in the operational parameters—namely output pressure, rotational speed and oil viscosity—are analysed; on the other hand, the effects of modifications of some design parameters are shown: clearances and relief groove dimension. The results in terms of gear eccentricity, pressure evolution, pressure forces, gear accelerations and variable forces exciting the pump casing enlighten the dynamic behavior of gear pumps and give useful indications for design improvements and vibration and noise reduction. As regards specifically gear accelerations as well as forces exciting the casing, they strongly increase with both output pressure and rotational speed, but variations in rotational speed in the operational range give lower effects. Conversely, the modifications of the clearances give negligible effects, while the relief groove dimension is very important: the larger the relief grooves are, the higher the gear accelerations and forces exciting the casing become.     

Photophysical properties of a series of electron-donating and -withdrawing platinum acetylide two-photon chromophores

To explore spectroscopic structure-property relationships in platinum acetylides, we synthesized a series of complexes having the molecular formula trans-bis(tributylphosphine)-bis(4-((9,9-diethyl-7-ethynyl-9H-fluoren-2-yl)ethynyl)-R)-platinum. The substituent, R = NH(2), OCH(3), N(phenyl)(2), t-butyl, CH(3), H, F, benzothiazole, CF(3), CN, and NO(2), was chosen for a systematic variation in electron-donating and -withdrawing properties as described by the Hammett parameter σ(p). UV/vis, fluorescence, and phosphorescence spectra, transient absorption spectra on the fs-ps time scale, and longer time scale flash photolysis on the ns time scale were collected. DFT and TDDFT calculations of the T(1) and S(1) energies were performed. The E(S) and E(T) values measured from linear spectra correlate well with the calculated results, giving evidence for the delocalized MLCT character of the S(1) state and confinement of the T(1) exciton on one ligand. The calculated T(1) state dipole moment ranges from 0.5 to 14 D, showing the polar, charge-transfer character of the T(1) state. The ultrafast absorption spectra have broad absorption bands from 575 to 675 nm and long wavelength contribution, which is shown from flash photolysis measurements to be from the T(1) state. The T(1) energy obtained from phosphorescence, the T(1)-T(n) transition energy obtained from flash photolysis measurements, and the triplet-state radiative rate constant are functions of the calculated spin density distribution on the ligand. The calculations show that the triplet exciton of chromophores with electron-withdrawing substituents is localized away from the central platinum atom, red-shifting the spectra and increasing the triplet-state lifetime. Electron-donating substituents have the opposite effect on the location of the triplet exciton, the spectra, and the triplet-state lifetime. The relation between the intersystem crossing rate constant and the S(1)-T(1) energy gap shows a Marcus relationship with a reorganization energy of 0.83 eV. The calculations show that intersystem crossing occurs by conversion from a nonpolar, delocalized S(1) state to a polar, charge-transfer T(1) state confined to one ligand, accompanied by conformation changes and charge transfer, supporting the experimental evidence for Marcus behavior.     

Fluorescence imaging assisted by surface modes on dielectric multilayers

The scaling behavior of criticality for spin-1 XXZ chains with uniaxial single-ion-type anisotropy is investigated by employing the infinite matrix product state representation with the infinite time evolving block decimation method. At criticality, the accuracy of the ground state of a system is limited by the truncation dimension χ of the local Hilbert space. We present four evidences for the scaling of the entanglement entropy, the largest eigenvalue of the Schmidt decomposition, the correlation length, and the connection between the actual correlation length ξ and the energy. The result shows that the finite scalings are governed by the central charge of the critical system. Also, it demonstrates that the infinite time evolving block decimation algorithm by the infinite matrix product state representation can be a quite accurate method to simulate the critical properties at criticality.     

Thermal degradation and flammability behavior of polypropylene/clay/carbon nanotube composite systems

This paper reports on the testing and development of a polypropylene (PP) nanocomposite systems with improved flame retardancy. The work utilizes the unique properties of sepiolite nanoclay (Sep) in combination with carbon nanotubes (CNTs) in order to develop an optimized ternary nanocomposite system. Thermogravimetric analysis (TGA) showed significant improvements to the residual char towards the later stages of the thermal ramp. The pyrolysis combustion flow calorimeter (PCFC) was employed to screen the various PP composites with respect to their potential flammability performance. The heat release capacity, which is an indicator of a materials fire hazard, did not show any reduction with the addition of nanofillers using the apparatus standard testing procedure. However, this changed by switching to a lower burn within the PCFC's furnace; this diverted oxygen to the pyrolysing sample. Using the results gained from TGA and the PCFC, the optimized ternary nanocomposite system (10 wt.% Sep + 2 wt.% CNT) was compounded on a larger scale and tested in the cone calorimeter. This showed a significant reduction of 82% in peak heat release rate in comparison to unfilled PP. Comparisons were also made between the testing of these samples in the PCFC and cone calorimeter. The main objectives were to develop a flame‐retardant PP nanocomposite ternary system as well as assessing the PCFC with traditional techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

Versatile and self-assembling urea-linked neosaccharides from sugar aminoalcohols

The increasing interest in urea compounds as self-assembling molecules, ion transporters and organocatalysts prompted several efforts towards synthetic urea-linked glycomimetics. In this frame we studied in details a novel two steps dimerization reaction of sugar vicinal aminoalcohol building blocks, opening a synthetic path to a series of urea-linked neosaccharides. Glucosamine neodisaccharide possessing an oxazolidinone–urea–oxazolidinone system could be transformed into both cyclic and higher linear neosaccharides. Furthermore, a series of six urea-linked glucosamine and galactosamine neodisaccharides was tested for self-assembling properties by measuring NMR spectra at different temperatures and concentrations as well as by gelation of several organic solvents.     

Hydration kinetics of tricalcium silicate by calorimetric methods

The kinetics of the cement hydration reaction is a relevant issue in the cement research field, particularly in the presence of additional inorganic and organic components that consistently increase the complexity of the cement paste. In the present study, the hydration reaction of pure tricalcium silicate has been monitored by different calorimetric approaches: the conventional Isothermal Conduction Calorimetry (IC) and a novel Differential Scanning Calorimetry (DSC) protocol. The measured hydration curves have been modeled by using the Boundary Nucleation and Growth Model (BNGM) to extract thermodynamic parameters of the early stages of the hydration reaction. IC and DSC methods provide similar results in terms of rate constants, linear growth, and nucleation rates even though the IC accesses the total evolved heat while DSC discloses the fraction of unreacted water. The validation of the DSC approach as a reliable analytical method to the study of cement hydration kinetic is of particular importance because it allows following very long hydration processes, such as those of pastes containing organic retarders or superplasticizers. The thermodynamic and kinetic parameters for the tricalcium silicate setting has been also evaluated and discussed as a function of the surface area of the powder.     

Subsurface Engineering Induced Fermi Level De-pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-O_v) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-O_v were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated O_v located at sub ∼2–5 nm region. Mott–Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm⁻² at 1.23 V vs. RHE were achieved on BiVO₄, Bi₂O₃, TiO₂ with outstanding stability for 72 h, outperforming most reported works under the identical conditions.     

Highly Efficient Decomposition of Perfluorocarbons for over 1000 Hours via Active Site Regeneration

Tetrafluoromethane (CF₄), the simplest perfluorocarbon (PFC), has the potential to exacerbate global warming. Catalytic hydrolysis is a viable method to degrade CF₄, but fluorine poisoning severely restricts both the catalytic performance and catalyst lifetime. In this study, Ga is introduced to effectively assists the defluorination of poisoned Al active sites, leading to highly efficient CF₄ decomposition at 600 °C with a catalytic lifetime exceeding 1,000 hours. ²⁷Al and ⁷¹Ga magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) showed that the introduced Ga exists as tetracoordinated Ga sites (Ga_IV), which readily dissociate water to form Ga−OH. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density function theory (DFT) calculations confirmed that Ga−OH assists the defluorination of poisoned Al active sites via a dehydration-like process. As a result, the Ga/Al₂O₃ catalyst achieved 100 % CF₄ decomposition keeping an ultra-long catalytic lifetime and outperforming reported results. This work proposes a new approach for efficient and long-term CF₄ decomposition by promoting the regeneration of active sites.