Non-Extensive Statistical Analysis of Acoustic Emissions: The Variability of Entropic Index q during Loading of Brittle Materials Until Fracture

Non-extensive statistical mechanics (NESM), introduced by Tsallis based on the principle of non-additive entropy, is a generalisation of the Boltzmann–Gibbs statistics. NESM has been shown to provide the necessary theoretical and analytical implementation for studying complex systems such as the fracture mechanisms and crack evolution processes that occur in mechanically loaded specimens of brittle materials. In the current work, acoustic emission (AE) data recorded when marble and cement mortar specimens were subjected to three distinct loading protocols until fracture, are discussed in the context of NESM. The NESM analysis showed that the cumulative distribution functions of the AE interevent times (i.e., the time interval between successive AE hits) follow a q-exponential function. For each examined specimen, the corresponding Tsallis entropic q-indices and the parameters β_q and τq were calculated. The entropic index q shows a systematic behaviour strongly related to the various stages of the implemented loading protocols for all the examined specimens. Results seem to support the idea of using the entropic index q as a potential pre-failure indicator for the impending catastrophic fracture of the mechanically loaded specimens.     

Effects of hydrostaticity on the structural stability of carbonates at lower mantle pressures: the case study of dolomite

We have conducted high pressure far-infrared absorbance and Raman spectroscopic investigations on a natural iron-free dolomite sample up to 40?GPa. Comparison between the present observations and literature results unraveled the effect of hydrostatic conditions on the high pressure dolomite polymorph adopted close to 40?GPa, i.e. the triclinic Dol-IIIc modification. In particular, non-hydrostatic conditions impose structural disorder at these pressures, whereas hydrostatic conditions allow the detection of an ordered Dol-IIIc vibrational response. Hence, hydrostatic conditions appear to be a key ingredient for modeling carbon subduction at lower mantle conditions. Our complementary first-principles calculations verified the far-infrared vibrational response of the ambient- and high pressure dolomite phases.     

Temperature-controlled release of catechol dye in thermosensitive phenylboronate-containing copolymers: A quantitative study

The reversible complex formation between two phenylboronic acid bearing copolymers and the catechol dye Alizarin Red S (ARS) was studied by dialysis experiments coupled with UV-visible spectroscopy. The first copolymer based on N-isopropylacrylamide (NIPAM) is thermosensitive, whereas the second one based on N,N-dimethylacrylamide (DMAM) is not. The investigation resulted in the quantitative determination of the host-guest binding constants at two different temperatures at pH 7.4 in phosphate buffer. Above the phase transition temperature Tp of the thermosensitive copolymer, the binding constant decreases by a factor of 6, twice more than in the case of the non-thermosensitive copolymer. This behaviour is related to the coil-to-globule transition of NIPAM-based copolymer, which above Tp expels the dye marker.     

Refractive,dispersive and thermo-optic properties of twelve organic solvents in the visible and near-infrared

We report on experimental measurements of the refractive index of twelve organic solvents at five different wavelengths (450, 532, 632.8, 964 and 1,551 nm) and a temperature of 300 K. Based on these new data visible to near-infrared dispersion relations are constructed. Group-velocity dispersion (GVD) is theoretically calculated. Zero- and negative-GVD situations are identified for two common solvents in near-infrared wavelengths. Via comparison with refractive index data available in bibliography, estimated values of thermo-optic coefficients are also presented.     

Antimicrobial Constituents from Machaerium Pers.: Inhibitory Activities and Synergism of Machaeriols and Machaeridiols against Methicillin-Resistant Staphylococcus aureus,Vancomycin-Resistant Enterococcus faecium,and Permeabilized Gram-Negative Pathogens

Two new epimeric bibenzylated monoterpenes machaerifurogerol (1a) and 5-epi-machaerifurogerol (1b), and four known isoflavonoids (+)-vestitol (2), 7-O-methylvestitol (3), (+)-medicarpin (4), and 3,8-dihydroxy-9-methoxypterocarpan (5) were isolated from Machaerium Pers. This plant was previously assigned as Machaerium multiflorum Spruce, from which machaeriols A-D (6–9) and machaeridiols A-C (10–12) were reported, and all were then re-isolated, except the minor compound 9, for a comprehensive antimicrobial activity evaluation. Structures of the isolated compounds were determined by full NMR and mass spectroscopic data. Among the isolated compounds, the mixture 10 + 11 was the most active with an MIC value of 1.25 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA) strains BAA 1696, −1708, −1717, −33591, and vancomycin-resistant Enterococcus faecium (VRE 700221) and E. faecalis (VRE 51299) and vancomycin-sensitive E. faecalis (VSE 29212). Compounds 6–8 and 10–12 were found to be more potent against MRSA 1708, and 6, 11, and 12 against VRE 700221, than the drug control ciprofloxacin and vancomycin. A combination study using an in vitro Checkerboard method was carried out for machaeriols (7 or 8) and machaeridiols (11 or 12), which exhibited a strong synergistic activity of 12 + 8 (MIC 0.156 and 0.625 µg/mL), with >32- and >8-fold reduction of MIC’s, compared to 12, against MRSA 1708 and −1717, respectively. In the presence of sub-inhibitory concentrations on polymyxin B nonapeptide (PMBN), compounds 10 + 11, 11, 12, and 8 showed activity in the range of 0.5–8 µg/mL for two strains of Acinetobacter baumannii, 2–16 µg/mL against Pseudomonas aeruginosa PAO1, and 2 µg/mL against Escherichia coli NCTC 12923, but were inactive (MIC > 64 µg/mL) against the two isolates of Klebsiella pneumoniae.     

Universal Padé approximants and their behaviour on the boundary

There are several kinds of universal Taylor series. In one such kind the universal approximation is required at every boundary point of the domain of definition \({\varOmega }\) of the universal function f. In another kind the universal approximation is not required at any point of \(\partial {\varOmega }\) but in this case the universal function f can be taken smooth on \(\overline{\varOmega }\) and, moreover, it can be approximated by its Taylor partial sums on every compact subset of \(\overline{\varOmega }\). Similar generic phenomena hold when the partial sums of the Taylor expansion of the universal function are replaced by some Padé approximants of it. In the present paper we show that in the case of Padé approximants, if \({\varOmega }\) is an open set and S, T are two subsets of \(\partial {\varOmega }\) that satisfy some conditions, then there exists a universal function \(f\in H({\varOmega })\) which is smooth on \({\varOmega }\cup S\) and has some Padé approximants that approximate f on each compact subset of \({\varOmega }\cup S\) and simultaneously obtain universal approximation on each compact subset of \((\mathbb {C}{\backslash }\overline{\varOmega })\cup T\). A sufficient condition for the above to happen is \(\overline{S}\cap \overline{T}=\emptyset \), while a necessary and sufficient condition is not known.     

Noncovalent Lone Pair⋅⋅⋅(No‐π!)‐Heteroarene Interactions: The Janus‐Faced Hydroxy Group

A comparative study using NMR spectroscopy and designed top‐pan molecular balances demonstrates that the noncovalent interaction of a hydroxy group with π‐deficient pyrazine and quinoxaline units involves a lone pair–heteroarene interaction which is much stronger and solvent independent when measured relative to the classical π‐facial hydrogen bond to a benzene ring. Alkyl fluorides also prefer the heteroarene rings over the benzene ring. The attractive interaction between a quinoxaline and a terminal alkyne is also stronger than the intramolecular hydrogen bond to an arene.     

Sorption and Diffusion of Propylene and Ethylene in Heterophasic Polypropylene Copolymers

Summary: Sorption experiments of ethylene and propylene in different polypropylene powder samples, both homopolymer and heterophasic copolymers with different rubber content, have been carried out in a high-pressure magnetic suspension balance at 10 bars pressure and 70 °C. The gross solubilities measured can be well correlated with the rubber content of the polymer samples. Solubility of ethylene and propylene in the rubber phase differ from solubility in the amorphous fraction of the homopolymer, especially the concentration ratio of propylene to ethylene differs significantly between rubber phase and amorphous fraction of the homopolymer. From the slope of monomer uptake, information on kinetics of mass-transfer can be gained. No significant differences were observed in terms of mass-transfer for ethylene and propylene. With increasing rubber content, effective diffusion coefficients increased slightly. By combined sorption studies with powder samples and compressed films, information about both effective diffusion coefficients and the effective length scale of diffusion could be gained. It could be shown, that the particle radius is not the characteristic length of diffusion in the studied powder samples. Mass transfer of nearly all samples could be described by a constant diffusion length of 120 to 130 µm, independently on particle size. This indicates that the effective scale of diffusion in polymer particles is in between microparticle and macroparticle scale used in classical particle modeling.     

A speculative transmission scheme for scheduling-latency reduction

Low latency is a critical requirement in some switching applications, specifically in parallel computer interconnection networks. The minimum latency in switches with centralized scheduling comprises two components, namely, the control-path latency and the data-path latency, which in a practical high-capacity, distributed switch implementation can be far greater than the cell duration. We introduce a speculative transmission scheme to significantly reduce the average control-path latency by allowing cells to proceed without waiting for a grant, under certain conditions. It operates in conjunction with any centralized matching algorithm to achieve a high maximum utilization and incorporates a reliable delivery mechanism to deal with failed speculations. The speculative transmission scheme is employed in a non-blocking N ×N R input-queued crossbar switch with R receivers per output. The control-path latency can be almost entirely eliminated for loads up to 50%. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)