Photocontrolled Hierarchical Self‐Assembly of Anisotropic Micropatterns of Nanofibers onto Isotropic Surfaces

Hierarchical self‐assembly is achieved using a visible light triggered photoreaction. A pro‐gelator, α‐diketone‐2,3‐didecyloxyanthracene, is photoconverted into a low molecular weight gelator, 2,3‐didecyloxyanthracene (DDOA), that self‐assembles into nanofibers. Spatial confinement and patterns of these nanofibers onto a surface are achieved by localizing initial nucleation with a focused laser and photogenerate subsequent fiber growth with the laser or gentler wide‐field irradiation. Remarkably, collective growth of nanofibers results in anisotropic micropatterns with orientation factors (OF) reaching 79%, resulting in collective emission of linearly polarized light. The OF, distance of collective growth and fiber density, are controlled by the photoirradiation conditions and the balance of interactions between DDOA aggregates and the glass surface. An unprecedented juxtaposition of orthogonally oriented nanofiber patterns on an isotropic surface is achieved with individual control of the fibers' main direction. In perspective, this photochemical method can be extended to a large variety of self‐assembling molecules.     

Influence of pressure cycling on damage evolution in an unfilled EPDM exposed to high-pressure hydrogen

This study aims to reveal the internal damage evolution process in a transparent ethylene propylene diene rubber (EPDM) under high-pressure hydrogen cycles (9 and 15 MPa). Damage accumulation of EPDM was tracked from in-situ pictures during cycling. Several dedicated image processing routines allowed the discrimination of mechanisms (separated cavities, clusters and cracks) and sometimes the qualification of their morphology (size distribution, number, ratio of cavities reappearing at any cycle). Numerous small cavities were observed at any cycle, some of them being clustered under the highest pressure. Only part of them systematically appeared again. Some of these cavities inflated and “absorbed” small cavities around them when clustered. Finally, a few cracks were nucleated from some large cavities and grew, following a “stop and grow” process.     

Flagging incorrect nucleotide sequence reagents in biomedical papers: To what extent does the leading publication format impede automatic error detection?

Scientometrics - In an idealised vision of science the scientific literature is error-free. Errors reported during peer review are supposed to be corrected prior to publication, as further research...     

Molecular Semiconductors for Logic Operations: Dead-End or Bright Future?

The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm² V⁻¹ s⁻¹. However, it is also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them. The goal is to inspire chemists and materials scientists and to give them hope that the field of molecular semiconductors for logic operations is not engaged into a dead end. To the contrary, it offers plenty of research opportunities in materials chemistry.     

Effects of preprocessing of ultraviolet-induced fluorescence spectra in plant fingerprinting applications

Preprocessing is an important step in data analysis. Dealing with spectral data, normalization is mandatory in order to compare items collected under various conditions. This paper addresses normalization of frontface fluorescence spectroscopy data where spectra are affected by an unknown multiplicative effect. The usual methods for reducing multiplicative problems are reviewed and a more detailed analysis of the normalization by closure is provided based on data on the fluorescence of plants as a means for plant species fingerprinting. As normalization is essentially the reduction of information, some methods of carrying it out are likely to remove either meaningful or discriminant pieces of information. As a result, it is demonstrated that normalization by closure should be performed using spectral data in a range where the spectra contain no information relevant to the problem at hand. This applies provided that in this range the signal-to-noise ratio is high enough. When the noise level is too high, a compromise should be found between preserving useful information and limiting the amount of noise introduced by the normalization procedure. Even if this study were carried out using fluorescence spectra, the overall process is likely to be applied to other spectral data.     

System modelling of a lateral force microscope

To quantitatively analyse lateral force microscope measurements one needs to develop a model able to relate the photodiode signal to the force acting on the tip apex. In this paper we focus on the modelling of the interaction between the cantilever and the optical chain. The laser beam is discretized by a set of rays which propagates in the system. The analytical equation of a single ray's position on the optical sensor is presented as a function of the reflection's state on top of the cantilever. We use a finite element analysis on the cantilever to connect the optical model with the force acting on the tip apex. A first-order approximation of the constitutive equations are derived along with a definition of the system's crosstalk. Finally, the model is used to analytically simulate the 'wedge method' in the presence of crosstalk in 2D. The analysis shows how the torsion loop and torsion offset signals are affected by the crosstalk.     

Nonparaxial analysis of continuous self-imaging gratings in oblique illumination

Tolerance in angles of continuously self-imaging gratings (CSIGs) is explored. The degradation in angle of the shape of the point-spread function is theoretically investigated and illustrated by simulations and experiments. The formalism presented is inspired by the one used for classical lenses and can be easily generalized to diffraction gratings. It turns out that well-designed CSIGs could be used for scanning optical systems requiring a large field of view.     

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.