Strings in Horizons, Dissipation and a Possible Interpretation of the Hagedorn Temperature

We consider the entanglement of closed bosonic strings intersecting the event horizon of a Rindler spacetime and, by using some simplified (rather semiclassical) arguments and some elements of the string field theory, we show the existence of a critical temperature beyond which closed strings \emph{cannot be in thermal equilibrium}. The order of magnitude of this critical value coincides with the Hagedorn temperature, which suggests an interpretation consistent with the fact of having a partition function which is bad defined for temperatures higher than it. Possible implications of the present approach on the microscopical structure of stretched horizons are also pointed out.Comment: A detailed description of string boundary states in a Rindler horizon was added, and their relation with the stretched horizon microscopic structure was emphasized. References added. To appear in Eur. Phys. J.

Photochromic and Photluminescence Properties of N-substituted-4,4’-Bipyridinium based Complexes

Date du colloque : 10/2012International audienc

Photochromism and Solid State Photoluminescence of Bi and Pb Complexes and Coordination Polymers based on N-R-4,4’-bipyridinium entities (R= O-, CH3, CH2CN)

Date du colloque : 05/2013</p

Bipyridinium Ligands: Highly Luminescent Bismuth Complexes

International audienc

N-Methyl-4,4-bipyridinium and N-Methyl-N -oxide-4,4 -bipyridinium Bismuth Complexes - Photochromism and Photoluminescence in the Solid State

Three bismuth complexes based on N-methyl-4,4-bipyridinium (hMV(+)), (hMV)[Bi(hMV)Cl-5] (1), and N-methyl-N-oxide-4,4-bipyridinium (MVO+), [Bi(MVO)X-4(dmso)]center dot dmso [X = Cl (2), Br (3)], are reported. All three compounds show luminescence in the solid state with maxima at 545 nm (yellow for 1) and 560 nm (orange for 2 and 3) with quantum yields up to 10 %. Upon UV irradiation, 1 undergoes a color change from white to blue accompanied by a reduction of the photoluminescence intensity. The analysis of the crystal structure of the three complexes points to a photoinduced charge-transfer (PICT) process at the origin of the photochromism in 1

Adding Mandarin Peel Waste to a Biodegradable Polymeric Matrix: Reinforcement or Degradation Effect?

In the current context, the use of fillers derived from fruit and vegetable waste is a crucial approach to mitigate waste and promote sustainable resource use, thus contributing to product life cycle completion and the achievement of sustainability goals. This study focuses on incorporating an endemic waste hitherto considered irrelevant within a biodegradable matrix. The resulting biocomposites were carefully characterized mechanically, rheologically, and morphologically to identify the connections between processability, structure, and properties. The results show that the presence of the filler results in an increase in the stiffness of the material (up to 27% in elastic modulus) accompanied by a decrease in tensile strength (approximately 50%) and elongation at break, which is on average about 7% at the highest filler content. This behavior was attributed to poor interfacial adhesion and the influence of a degradation process caused by the presence of citric acid and/or impurities in the filler

Basalt/polypropylene composites: The effects of mechanical reprocessing on their morphological, thermal, rheological and mechanical behavior

Considering the increasing spread of basalt fibers on the market as bio-based alternative to glass and the massive use of polypropylene (PP) in the automotive sector, the end-of-life of PP/basalt composites through mechanical reprocessing was addressed. Their thermal, rheological and mechanical properties were investigated up to seven reprocessing cycles and the main relationship between their changes and composites fibers length reduction was disclosed. The composites displayed a parabolic increase in their melt volume rate for increasing reprocessing cycles and were characterized by an improved flowability compared to the neat matrix at the fifth cycle, i.e., 89.3 against 74.8 cm3/10min, due to the intimate contact between the fibers and the matrix which causes a stronger degradation in PP molecular weight. Concerning the mechanical response, the logarithmic decrease in stiffness and strength was not directly proportional to fibers length reduction due to a progressive better orientation of the fibers along the injection direction. Finally, the comparison of the mechanical results obtained with the data available for PP composites reinforced with vegetable fibers allowed to conclude that PP/basalt composites are competitive with this type of composites up to the fifth cycle, displaying a tensile modulus of 3.5 GPa and tensile strength of 38 MPa