WISE Circumstellar Disks in the Young Sco-Cen Association

We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using the latest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 of which are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly. We infer that 41+-5% of Sco-Cen OB2 BAF stars to have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups. Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than A and F-type association members.Comment: 5 Pages, 3 figure, 4 tables. Complete table 1 included. Accepted to MNRAS Letter

Analysis on the hull girder ultimate strength of a bulk carrier using simplified method based on an incremental-iterative approach

The hull girder ultimate strength of a typical bulk carrier is analyzed using a simplified method based on an incremental-iterative approach. First, vertical bending moment is examined by seven different methods. The moment versus curvature curves and the values of the ultimate longitudinal moments at collapse states are determined for both hogging and sagging cases. Second, the ultimate strength under coupled vertical and horizontal bending moment is accounted. An interaction curve is obtained, which corresponds to the results of series of calculation for the ship hull subject to bending conditions with different angles of curvature. It is found that the interaction curve is asymmetrical because the hull cross section is not symmetrical with respect to the horizontal axis and the structural response of the elements under compression is different from that under tension due to nonlinearity caused by buckling. The angles of the resultant bending moment vector and that of the curvature vector are different in investigated cases. The interaction design equations proposed by other researches are also addressed to discuss the results presented by this study

Testing the gamma-ray burst variability/peak luminosity correlation on a Swift homogeneous sample

We test the gamma-ray burst correlation between temporal variability and peak luminosity of the $\gamma$-ray profile on a homogeneous sample of 36 Swift/BAT GRBs with firm redshift determination. This is the first time that this correlation can be tested on a homogeneous data sample. The correlation is confirmed, as long as the 6 GRBs with low luminosity (<5x10^{50} erg s^{-1} in the rest-frame 100-1000 keV energy band) are ignored. We confirm that the considerable scatter of the correlation already known is not due to the combination of data from different instruments with different energy bands, but it is intrinsic to the correlation itself. Thanks to the unprecedented sensitivity of Swift/BAT, the variability/peak luminosity correlation is tested on low-luminosity GRBs. Our results show that these GRBs are definite outliers.Comment: Accepted for Publication in MNRAS. 10 pages, 5 figures, 3 table

Polylactic acid-lauryl functionalized nanocellulose nanocomposites: Microstructural, thermo-mechanical and gas transport properties

Thermo-mechanical and gas transport properties of polylactic acid (PLA) matrix containing various amounts (from 1 to 20 wt%) of nanocellulose esterified with lauryl chains (LNC) were investigated on solvent cast film of about 50 micron. Scanning electron microscopy indicated that, up to a filler content of 6.5 wt%, LNC was well dispersed or formed small, sub-micrometric clusters. At higher filler contents, oval aggregates in the micrometric range were detected. The addition of LNC did not change the matrix glass transition temperature and melting temperature. Concurrently, as LNC content increased, both elastic and storage moduli at room temperature exhibited a sharp decrease up to 5 wt% of filler, and a lower reduction for LCN concentration of 10\u201320 wt.%. Nanocomposites with 3 and 5 wt% of LNC showed the highest strain at break and a large amount of plastic deformation due to a strong interfacial adhesion between the PLA and filler particles. For higher LNC fractions the presence of aggregates weakened the nanocomposite leading to lower values of maximum stress and strain at break. With the addition of LNC particles, gas barrier properties of the PLA film versus deuterium, nitrogen and carbon dioxide were improved up to a critical LNC concentration of 6.5 wt%, where the gas permeability of the nanocomposite resulted to be 70% lower than that of the PLA matrix. At higher filler contents, large LNC aggregates increased the gas permeability of the nanocomposites

Crystallization kinetics as a sensitive tool to detect degradation in poly(lactide)/poly(ε-caprolactone)/ PCL-co-PC copolymers blends

Poly(lactide)/poly(ε-caprolactone) blends (PLA/PCL) with composition 80/20 (w/w%) are immiscible but biodegradable and therefore often studied in the literature. We have prepared 80/20 PLA/PCL blends with and without poly(ε-caprolactone)-co-poly(carbonate) copolymers (block and random). The blends were prepared both by melt extrusion and by solution blending. The concentration of PCL-co-PC copolymers added to the blends was 2 wt%. Compression molded sheets and solvent cast films were evaluated by GPC (Gel Permeation Chromatography), TGA (Thermogravimetric Analysis), SEM (Scanning Electron Microscopy), PLOM (Polarized Light Optical Microscopy) and DSC (Differential Scanning Calorimetry). Copolymer addition causes a reduction of molecular weight in melt mixed blends. In particular, the random copolymer (PCL-ran-PC) causes the highest molecular weight reduction, since it has lower thermal stability, as shown by TGA. PLOM experiments show that these degraded PLA chains in melt-mixed blends can nucleate and grow faster than similar but undegraded PLA chains in solution-mixed blends. As a result, the PLA phase within melt mixed blends containing PCL-co-PC copolymers shows a higher tendency to crystallize during both isothermal and non-isothermal DSC experiments. Upon molecular weight reduction in melt mixed blends containing copolymers, PLA chains have a higher mobility resulting in faster diffusion towards the growing crystal front. Our results show crystallization kinetic measurements, performed by PLOM or DSC, are useful tools to qualitatively detect molecular weight changes produced by degradation of PLA chains, when the molecular weight reduction is not large enough to decrease Tm values

Are Swift gamma-ray bursts consistent with the Ghirlanda relation?

A few tight correlations linking several properties of gamma-ray bursts (GRBs), namely the spectral peak energy, the total radiated energy, and the afterglow break time, have been discovered with pre-Swift GRBs. They were used to constrain the cosmological parameters, together with type-Ia supernovae. However, the tightness of these correlations is a challenge to GRB models. We explore the effect of adding Swift bursts to the Ghirlanda and Liang-Zhang relations. Although they are both still valid, they become somewhat weakened mostly due to the presence of significant outliers, which otherwise are apparently normal GRBs so difficult to distinguish. The increased dispersion of the relations makes them less reliable for purposes of precision cosmology.Comment: Paper accepted for publication on A&A (7 pages, 2 figures). Small changes after comment

Nonlocal field correlations and dynamical Casimir-Polder forces between one excited- and two ground-state atoms

The problem of nonlocality in the dynamical three-body Casimir-Polder interaction between an initially excited and two ground-state atoms is considered. It is shown that the nonlocal spatial correlations of the field emitted by the excited atom during the initial part of its spontaneous decay may become manifest in the three-body interaction. The observability of this new phenomenon is discussed.Comment: 17 pages, 1 figure, sub. to Phys. Rev.