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.

Durability of biodegradable polymers for the conservation of cultural heritage

The use of polymers for conservation of cultural heritage is related to the possibility to slow down or stop natural deterioration which, in many cases, corresponds to stopping the entrance of liquid water and to favor spontaneous water vapor removal. Unfortunately, hydrophobicity is generally favored by surface roughness and thus competitive with transparency. It is therefore important to find an optimal balance hydrophobicity, transparency and durability (especially to photooxidation). However, polymers typically used for applications in this field come from non-renewable resources and are not biodegradable. In this work, the mechanical, structural, and optical properties of PLA, PBAT, and a PBAT/PLA blends, as well as surface properties and water vapor permeability, were investigated before and after exposure to UV irradiation, in order to evaluate their durability and suitability for conservation of cultural heritage

The surface accessibility of α-bungarotoxin monitored by a novel paramagnetic probe

The surface accessibility of {alpha}-bungarotoxin has been investigated by using Gd2L7, a newly designed paramagnetic NMR probe. Signal attenuations induced by Gd2L7 on {alpha}-bungarotoxin C{alpha}H peaks of 1H-13C HSQC spectra have been analyzed and compared with the ones previously obtained in the presence of GdDTPA-BMA. In spite of the different molecular size and shape, for the two probes a common pathway of approach to the {alpha}-bungarotoxin surface can be observed with an equally enhanced access of both GdDTPA-BMA and Gd2L7 towards the protein surface side where the binding site is located. Molecular dynamics simulations suggest that protein backbone flexibility and surface hydration contribute to the observed preferential approach of both gadolinium complexes specifically to the part of the {alpha}-bungarotoxin surface which is involved in the interaction with its physiological target, the nicotinic acetylcholine receptor

Recyclability of a bio-based biocomposite under different reprocessing conditions

The present paper studies the effect of reprocessing, on both dry and wet reprocessing conditions, on the rheological and mechanical properties of a biocomposite made of a bio-based, biodegradable polymer with 40 wt% wood flour. The results show that the viscosity of the matrix decreases as the number of extrusions increases, with the greatest reduction for samples processed under wet conditions. The same behavior was observed for the biocomposite, but since the viscosity of the biocomposite is much higher than that of the matrix, this causes a greater reduction of molecular weight. Mechanical results show that properties such as tensile strength and elongation decrease as the number of extrusions increases for the matrix. In terms of maximum variations, the tensile strength experiences a decrease of approximately 18%, while the elongation at break shows a more significant reduction of about 40%. Conversely, the biocomposite shows an increase in tensile strength (about 30%) and elongation at break (about 90%) after the first extrusion and then a slight decrease, but with values of tensile strength and elongation higher than those of the virgin biocomposite

Mirror symmetry breaking as a problem in dynamical critical phenomena

The critical properties of the Frank model of spontaneous chiral synthesis are discussed by applying results from the field theoretic renormalization group (RG). The long time and long wavelength features of this microscopic reaction scheme belong to the same universality class as multi-colored directed percolation processes. Thus, the following RG fixed points (FP) govern the critical dynamics of the Frank model for d<4: one unstable FP that corresponds to complete decoupling between the two enantiomers, a saddle-point that corresponds to symmetric interspecies coupling, and two stable FPs that individually correspond to unidirectional couplings between the two chiral molecules. These latter two FPs are associated with the breakdown of mirror or chiral symmetry. In this simplified model of molecular synthesis, homochirality is a natural consequence of the intrinsic reaction noise in the critical regime, which corresponds to extremely dilute chemical systems.Comment: 9 pages, 3 figure

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

IR ion spectroscopy in a combined approach with MS/MS and IM-MS to discriminate epimeric anthocyanin glycosides (cyanidin 3-O-glucoside and -galactoside)

Anthocyanins are widespread in plants and flowers, being responsible for their different colouring. Two representative members of this family have been selected, cyanidin 3-O-β-glucopyranoside and 3-O-β-galactopyranoside, and probed by mass spectrometry based methods, testing their performance in discriminating between the two epimers. The native anthocyanins, delivered into the gas phase by electrospray ionization, display a comparable drift time in ion mobility mass spectrometry (IM-MS) and a common fragment, corresponding to loss of the sugar moiety, in their collision induced dissociation (CID) pattern. However, the IR multiple photon dissociation (IRMPD) spectra in the fingerprint range show a feature particularly evident in the case of the glucoside. This signature is used to identify the presence of cyanidin 3-O-β-glucopyranoside in a natural extract of pomegranate. In an effort to increase any differentiation between the two epimers, aluminum complexes were prepared and sampled for elemental composition by FT-ICR-MS. CID experiments now display an extensive fragmentation pattern, showing few product ions peculiar to each species. More noteworthy is the IRMPD behavior in the OH stretching range showing significant differences in the spectra of the two epimers. DFT calculations allow to interpret the observed distinct bands due to a varied network of hydrogen bonding and relative conformer stability