Ageing and thermal stability studies on quasi-solid composite electrolytes for Grätzel-type solar cells

Loss of volatile components from two types of quasi-solid gel electrolytes to be used in Grätzel (or dye-sensitized, DSSC)-type alternative solar cells are checked time to time by thermogravimetry (TG) to follow the stability or changes of composites during storage at ambient. One of the gel samples, labeled as P2000 and based on UreaSil 2000, a 3D-cage precursor compound, has been found quite stable, while the related P230 sample based on UreaSil 230 seems to have a bit higher deviation in heterogeneity and some tendencies losing gradually from its volatile content, time to time. In addition, two online coupled evolved gas analytical tools (TG–EGA–FTIR and TG/DTA–EGA–MS) are applied to check the gel electrolytes for thermal vaporization, degradation, and decomposition processes as a function of temperature during dynamic heating in air. Initial minor elimination of ethyl acetate has been detected by both in situ coupled mass spectroscopy and FTIR spectroscopic gas cell. According to both evolved gas analytical systems, the other liquid ingredients, acetic acid (AcOH) and sulfolane are also released in the order of their volatility. Above 300 °C, an oxidative thermal degradation of UreaSil-type host matrices is indicated by the occurrence of, among others, formaldehyde or ammonia for electrolyte samples P2000 and P230, respectively. Evolution of various alkyl iodides with short chain length has only been detected by the mass spectroscopic evolved gas analysis method only.     

A low-Reynolds-number actuator driven by instability: rotating or oscillating

Nonlinear Dynamics - Due to an electro-hydrodynamic instability, a dielectric spherical particle immersed in a dielectric viscous solvent can exhibit steady rotation spontaneously (Quincke...     

Cosmic-ray neutron spectrometry by solid state detectors

Extensive data have been gathered since the early 1990s on the response of different detectors based on the registration of neutron-induced fission in bismuth, gold, tantalum by the spark replica counter and the thin film breakdown counter. These detectors make it possible to exploit the excellent characteristics of the fission reactions in bismuth, gold and tantalum for the measurements of high-energy neutrons.

Most of the investigations have been carried out at the quasi-monoenergetic neutron beam facility at The Svedberg Laboratory-TSL of the Uppsala University in cooperation with the Khlopin Radium Institute (KRI).

The responses of different fission detectors in the intermediate range of neutron energy (35–180 MeV) have been evaluated: a region where the predictive power of available nuclear reaction models and codes is not reliable yet. For neutron energy greater than 200 MeV, the fission-detector responses have been derived from the data of the proton fission cross-sections.

Finally, by using the ratio of the responses of these detectors, a simple and accurate way to evaluate the spectrum hardness can be obtained, thus providing a tool to obtain spectral information needed for neutron dosimetry without the need to know the entire spectrum.

The experimentally measured spectra obtained to-date have different shapes and they are also different from those calculated.

In this paper, a new approach will be reported to analyse the existing spectra by using response ratios of different detectors. Preliminary data have been already obtained for the high-energy neutron spectrum from the CERN concrete facility.     

Biaxial Load Effect on Crack Initiation for Orthotropic Materials

This paper is concerned with the study of the elastostatic fracture response of an orthotropic plate with an inclined crack and subjected at infinity to a biaxial uniform load. To this end an unconventional approach to the derivation of the complex variable expressions of the elastic fields is proposed. The above formulation has been used to solve the boundary value problem as superposition of Mode-I and Mode-II crack problems and it is shown that the near tip asymptotic expressions of stress and displacement fields are affected by non-singular terms originated by load biaxiality. The maximum circumferential tensile stress criterion is applied in order to investigate the effects of non-singular terms on the angle of crack extension.     

Crack energy density of a piezoelectric material under general electromechanical loading

Crack energy density is considered and used as a possible fracture parameter in piezoelectricity under arbitrary electromechanical remote loads. The closed-form solution of a crack in a piezoelectric infinite plate subjected to general static electromechanical loading is obtained through a method alternative to the more common Stroh’s formalism. This analytical method, which is based on the spectral theorem of linear algebra, involves a transformation of similarity induced by the fundamental matrix in order to express the equations governing the problem in terms of complex potentials. The application of the mechanical boundary condition of stress-free crack and of one of the three considered electric boundary conditions (impermeable, permeable or semipermeable) leads then to the formulation of a Hilbert problem whose solution yields the stress and displacement fields. The crack energy density factors for mixed mode are then calculated under different mechanical and electrical loadings, as well as under different electric boundary conditions. The non-singular terms of the stress expressions are retained as well. The definition of the minimum energy density fracture criterion, as proposed by Sih, is given, and the influence of load biaxiality and positive or negative applied electric field on the criterion results is analyzed. The prediction of the incipient branching angle as from the energy density approach is also compared to that arising from the maximum circumferential stress theory for a mixed mode loading condition. Numerical results and graphs are presented and discussed for a PZT-4 piezoelectric ceramic.