2,714 research outputs found
The polarimetric multi-frequency radio sources properties
The polarization properties of extragalactic radio sources at frequencies
higher than 20 GHz are still poorly constrained. However, their
characterization would provide invaluable information about the physics of the
emission processes and is crucial to estimate their contamination as
foregrounds of the polarized cosmic microwave background (CMB) angular power
spectrum on scales < 30 arcmin. In this contribution, after summarizing the
state-of-the-art of polarimetric observations in the millimetric wavelength
bands, we present our observations of a complete sample of 53 sources with S >
200 mJy (at 20 GHz) carried out with the Australia Telescope Compact Array
between 5.5 and 38 GHz. The analysis clearly shows that polarization properties
cannot be simply inferred from total intensity ones, as the spectral behaviors
of the two signals are typically different
Average fractional polarization of extragalactic sources at Planck frequencies
Recent detailed simulations have shown that an insufficiently accurate
characterization of the contamination of unresolved polarized extragalactic
sources can seriously bias measurements of the primordial cosmic microwave
background (CMB) power spectrum if the tensor-to-scalar ratio as
predicted by models currently of special interest (e.g., Starobinsky's
and Higgs inflation). This has motivated a reanalysis of the median
polarization fraction of extragalactic sources (radio-loud AGNs and dusty
galaxies) using data from the \textit{Planck} polarization maps. Our approach,
exploiting the intensity distribution analysis, mitigates or overcomes the most
delicate aspects of earlier analyses based on stacking techniques. By means of
simulations, we have shown that the residual noise bias on the median
polarization fraction, , of extragalactic sources is
generally \simlt 0.1\%. For radio sources, we have found , with no significant dependence on either frequency or flux
density, in good agreement with the earlier estimate and with high-sensitivity
measurements in the frequency range 5--40\,GHz. No polarization signal is
detected in the case of dusty galaxies, implying 90\% confidence upper limits
of \Pi_{\rm dusty}\simlt 2.2\% at 353\,GHz and of \simlt 3.9\% at 217\,GHz.
The contamination of CMB polarization maps by unresolved point sources is
discussed.Comment: 10 pages, 3 figures, 7 tables; revised version. In press on Astronomy
and Astrophysic
Anisotropy and directional pinning in YBaCuO with BaZrO3 nanorods
Measurements of anisotropic transport properties (dc and high-frequency
regime) of driven vortex matter in YBaCuO with elongated
strong-pinning sites (c-axis aligned, self-assembled BaZrO nanorods) are
used to demonstrate that the effective-mass angular scaling takes place only in
intrinsic physical quantities (flux-flow resistivity), and not in
pinning-related Labusch parameter and critical currents. Comparison of the
dynamics at different time scales shows evidence for a transition of the vortex
matter toward a Mott phase, driven by the presence of nanorods. The strong
pinning in dc arises partially from a dynamic effect.Comment: 4 pages, 4 figures. Accepted for publication on Applied Physics
Letters. With respect to v1: changed title, slightly shortene
Multitasking associative networks
We introduce a bipartite, diluted and frustrated, network as a sparse
restricted Boltzman machine and we show its thermodynamical equivalence to an
associative working memory able to retrieve multiple patterns in parallel
without falling into spurious states typical of classical neural networks. We
focus on systems processing in parallel a finite (up to logarithmic growth in
the volume) amount of patterns, mirroring the low-level storage of standard
Amit-Gutfreund-Sompolinsky theory. Results obtained trough statistical
mechanics, signal-to-noise technique and Monte Carlo simulations are overall in
perfect agreement and carry interesting biological insights. Indeed, these
associative networks pave new perspectives in the understanding of multitasking
features expressed by complex systems, e.g. neural and immune networks.Comment: to appear on Phys.Rev.Let
INTERFACIAL PROPERTIES OF IONIC LIQUIDS:ELECTRIC PROPERTIES OF THIN FILMS AND INTERACTION WITH MODEL MEMBRANES AND LIVING CELLS
Room-Temperature Ionic Liquids (ILs) have attracted considerable interest in recent years. This interest is motivated by the physico-chemical properties of these systems, tunable modifying the chemical structure of ions. Generally, ILs show chemical and thermal stability, i.e. they do not easily decompose or react. Furthermore, these compounds remain liquid over an extended range of temperatures, in which they show also a remarkably low volatility. The low vapor pressure of ILs, promote them as good solvents for the growing field of the \u201dGreen Chemistry\u201d, in substitution of the volatile organic compounds. The fact that ILs are composed solely by ions, and can have a quite wide electrochemical window, make them very interesting as electrolytes. For these purposes, this PhD thesis is devoted to the investigation of ILs in contact with solid interfaces, primary targets of interaction. To deepen the analysis of electric properties at the solid interface, thin layers of ILs deposited on conductive substrates were investigated by means of AFM. The \u201dGreen\u201d character of these compounds was investigated studying their interaction with biomembrane models and external membranes of living cells, by means of AFM and electrochemical methods. Because of their ionic nature, ILs can be used as electrolytes in several devices aimed at conversion and storage of energy, such as electrochemical supercapacitors, Graetzel solar cells and batteries. In these devices a key role is played by the interface between the surface of the electrodes and the electrolyte; in particular, structural-morphological and electrical properties of the first few nanometers of IL interacting with the solid electrode surface are expected to have the strongest impact on device performance. AFM morphological analysis of small quantity of [C 4 MIM] [NTf 2 ] IL, deposited on various insulating surfaces revealed a population of nanodroplets and new structures. Remarkably, the solid surfaces induce the organization of the ionic liquid into regular, lamellar solid-like nanostructures presenting a high degree of vertical structural order and high mechanical resistance to normal compressive stresses. Nanomechanical investigation reveals that the structures resist to normal compressive loads up to 1.5 MPa; beyond that limit, indentation, in discrete steps, occurs. Furthermore, lamellar [C 4 MIM] [NTf 2 ] islands are not affected when scanned by a biased AFM tip under the influence of an electric field as intense as 10 8 V/m, while the liquid nano-and micro-droplets are easily swept away. These results confirm the solid-like character of the ordered lamellar nanostructures observed when thin films of [C 4 MIM] [NTf 2 ] are deposited on solid surfaces, and suggest that these films may possess an insulating, dielectric behavior, at odd with the case of the bulk ionic liquids. Nanoscale impedance measurements (capacitance vs. distance) and electrostatic force spectroscopy (electric force vs. distance) between a conductive AFM tip and the IL structures confirmed that values of the dielectric constant (\u3b5 r = 3-5) are significantly smaller than those measured in the bulk liquid (\u3b5 r = 9-15). These results support the picture of solid-like ordered domains where the ion mobility is significantly inhibited with respect to the bulk liquid phase. These findings also highlight the potentialities of scanning probe techniques for the quantitative investigation of the interfacial electrical properties of thin ionic liquid films, suggesting that ILs at electrified solid surfaces may possess unexpected electrical and structural properties, thus influencing the behavior of photo-electrochemical devices. The \u201dgreen\u201d character of ionic liquids (ILs) is dependent on their negligible vapor pressure but in contrast to their environmental behavior their intrinsic toxicity is not at present completely understood. Accordingly, although ILs will not evaporate which alleviates air pollution problems, a potential hazard of Ils to living organisms via aqueous media cannot be ruled out. A rigorous investigation on the interaction of ILs with biomaterials is required to provide information about their intrinsic toxicity. In order to test the
biocompatible character of ILs, as a first objective, the interaction of various ILs with biological membrane (biomembrane) models was studied using electrochemical methods. A series of imidazolium based ILs were investigated whose interactions highlighted the role of anion and lateral side chain of cation during the interaction with dioleoyl phosphatidylcholine (DOPC) monolayer. It was shown that the hydrophobic and lipophilic character of the IL cations is a primary factor responsible for this interaction. The modifications of the Hg supported monolayer caused by ILs were simultaneously monitored electrochemically in a well controlled manner using rapid cyclic voltammetry (RCV), alternating current voltammetry (ACV), and electrochemical impedance spectroscopy (EIS). Hg supported monolayers provide an accurate analysis of the behavior of ILs at the interface of a biomembrane leading to a comprehensive understanding of the interaction mechanisms involved. At the same time, these experiments show that the Hg-phospholipid model is an effective toxicity sensing technique as shown by the correlation between literature in vivo toxicity data and the data from this study. Cell membrane is the main target of ILs interaction, depending on the lipophilicity of hydrophobic lateral chain of cation. In order to test the biocompatible character of ILs, the interaction of various imidazolium-based ILs with supported DOPC phospholipid bilayers (as models of the cell membrane) and living MDA-MB-231 cells (@37 \u25e6C) was investigated. Atomic Force Microscopy (AFM) was used to carry on a combined topographic and mechanical analysis of supported DOPC bilayers as well as of living cells. During the analysis of DOPC bilayers we have observed modifications in breakthrough force and membrane elasticity related to the ingress of lateral chains of cations in the bilayer, demonstrating agreement with electrochemical results. The parallel nanomechanical analysis performed on living cells interacting with ILs at various concentrations showed modifications of elasticity (effective Young\u2019s modulus) and morphology of cells after exposure to ILs dispersed in their culture medium. The measurements confirmed the primary action of ILs on membrane and actin cytoskeleton, highlighting a subtoxic/toxic effect dependent on ILs concentration and chemical nature of cation. Our results may be helpful for filling existing gaps of knowledge about ionic liquids toxicity and their impact on living organisms. From these evidences, interaction of ILs with micro-organisms and single cells is an important step to assess the environmental sustainability of this novel and promising class of solvents and to attribute a \u201dgreen\u201d label to it.
Studying the interaction of ionic liquids, it has been recognized that the interface is a vital component. When the bulk symmetry of IL is broken by surfaces, the electrical properties are greatly affected, leading from a ion conductor to an insulator behavior. Also the interaction with biological entity is driven, in first instance, by surface interaction. Biomembrane models and cell membranes are affected by ILs that accumulate/penetrate the surface interface, leading to structural reorganization/damage of
external membrane
Glutathione increase by the n-butanoyl glutathione derivative (GSH-C4) inhibits viral replication and induces a predominant Th1 immune profile in old mice infected with influenza virus
During aging, glutathione (GSH) content declines and the immune system undergoes a
deficiency in the induction of Th1 response. Reduced secretion of Th1 cytokines, which is
associated with GSH depletion, could weaken the host defenses against viral infections.
We first evaluated the concentration of GSH and cysteine in organs of old mice; then, the
effect of the administration of the N-butanoyl GSH derivative (GSH-C4) on the response of
aged mice infected with influenza A PR8/H1N1 virus was studied through the determination
of GSH concentration in organs, lung viral titer, IgA and IgG1/IgG2a production and
Th1/Th2 cytokine profile.
Old mice had lower GSH than young mice in organs. Also the gene expression of
endoplasmic reticulum (ER) stress markers involved in GSH metabolism and folding of
proteins, i.e. Nrf2 and PDI, was reduced. Following infection, GSH content remained low
and neither infection nor GSH-C4 treatment affected Nrf2 expression. In contrast, PDI
expression was upregulated during infection and appeared counterbalanced by GSH-C4.
Moreover, the treatment with GSH-C4 increased GSH content in organs, reduced viral
replication and induced a predominant Th1 response.
In conclusion, GSH-C4 treatment could be used in the elderly to contrast influenza virus
infection by inducing immune response, in particular the Th1 profile
Identification of ä-Spectrin Domains Susceptible to Ubiquitination
Previously, we demonstrated that alpha-spectrin is a substrate for the ubiquitin system and that this conjugation is a dynamic process (Corsi, D., Galluzzi, L., Crinelli, R., and Magnani, M. (1995) J. Biol. Chem. 270, 8928-8935). In this study, we mapped the sites of ubiquitination on erythrocyte alpha-spectrin. A peptide map of digested alpha-spectrin, previously submitted to in vitro 125I-ubiquitin conjugation, revealed the presence of four distinct labeled bands with Mr 40,000, 36,000, 29,000, and 25,500. Western blotting experiments using antibodies against each alpha-spectrin domain revealed that only IgG anti-alphaIII domain recognized the 125I-labeled ubiquitin peptide of 29 kDa, whereas the IgG anti-alphaV domain recognized the Mr 40,000 125I-ubiquitin-labeled peptide. The other two labeled bands of Mr 36,000 and Mr 25,500 were identified as tetra and tri multiubiquitin chains. Ubiquitination of the alphaIII and alphaV domains was further confirmed by anti-alpha-spectrin domain immunoaffinity chromatography. Endoprotease Lys C-digested spectrin conjugated previously to 125I-ubiquitin was incubated with antibodies against each trypsin-resistant domain of alpha-spectrin. Gamma counting of the radiolabeled antigen-antibody complexes purified by protein A chromatography showed labeling in the IgG anti-alphaIII and anti-alphaV complexes alone. Domain alphaIII is not associated with any known function, whereas domain alphaV contains the nucleation site for the association of the alpha and beta chains. Ubiquitination of the latter domain suggests a role for ubiquitin in the modulation of the stability, deformability, and viscoelastic properties of the erythrocyte membrane
- …