10,432 research outputs found
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
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
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
Src family kinases as therapeutic targets in advanced solid tumors. What we have learned so far
Src is the prototypal member of Src Family tyrosine Kinases (SFKs), a large non-receptor kinase class that controls multiple signaling pathways in animal cells. SFKs activation is necessary for the mitogenic signal from many growth factors, but also for the acquisition of migratory and invasive phenotype. Indeed, oncogenic activation of SFKs has been demonstrated to play an important role in solid cancers; promoting tumor growth and formation of distant metastases. Several drugs targeting SFKs have been developed and tested in preclinical models and many of them have successfully reached clinical use in hematologic cancers. Although in solid tumors SFKs inhibitors have consistently confirmed their ability in blocking cancer cell progression in several experimental models; their utilization in clinical trials has unveiled unexpected complications against an effective utilization in patients. In this review, we summarize basic molecular mechanisms involving SFKs in cancer spreading and metastasization; and discuss preclinical and clinical data highlighting the main challenges for their future application as therapeutic targets in solid cancer progression
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