In situ growth of well-dispersed CdS nanocrystals in semiconducting polymers

A straight synthetic route to fabricate hybrid nanocomposite films of well-dispersed CdS nanocrystals (NCs) in poly[2-methoxy-5-(2''-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) is reported. A soluble cadmium complex [Cd(SBz)₂]₂·MI, obtained by incorporating a Lewis base (1-methylimidazole, MI) on the cadmium bis(benzyl)thiol, is used as starting reagent in an in situ thermolytic process. CdS NCs with spherical shape nucleate and grow well below 200°C in a relatively short time (30 min). Photoluminescence spectroscopy measurements performed on CdS/MEH-PPV nanocomposites show that CdS photoluminescence peaks are totally quenched inside MEH-PPV, if compared to CdS/PMMA nanocomposites, as expected due to overlapping of the polymer absorption and CdS emission spectra. The CdS NCs are well-dispersed in size and homogeneously distributed within MEH-PPV matrix as proved by transmission electron microscopy. Nanocomposites with different precursor/polymer weight ratios were prepared in the range from 1:4 to 4:1. Highly dense materials, without NCs clustering, were obtained for a weight/weight ratio of 2:3 between precursor and polymer, making these nanocomposites particularly suitable for optoelectronic and solar energy conversion applications.     

Serine Hydroxymethyltransferase from the Cold Adapted Microorganism Psychromonas ingrahamii: A Low Temperature Active Enzyme with Broad Substrate Specificity

Serine hydroxymethyltransferase from the psychrophilic microorganism Psychromonas ingrahamii was expressed in Escherichia coli and purified as a His-tag fusion protein. The enzyme was characterized with respect to its spectroscopic, catalytic, and thermodynamic properties. The properties of the psychrophilic enzyme have been contrasted with the characteristics of the homologous counterpart from E. coli, which has been structurally and functionally characterized in depth and with which it shares 75% sequence identity. Spectroscopic measures confirmed that the psychrophilic enzyme displays structural properties almost identical to those of the mesophilic counterpart. At variance, the P. ingrahamii enzyme showed decreased thermostability and high specific activity at low temperature, both of which are typical features of cold adapted enzymes. Furthermore, it was a more efficient biocatalyst compared to E. coli serine hydroxymethyltransferase (SHMT) particularly for side reactions. Many β-hydroxy-α-amino acids are SHMT substrates and represent important compounds in the synthesis of pharmaceuticals, agrochemicals and food additives. Thanks to these attractive properties, this enzyme could have a significant potential for biotechnological applications.     

The puzzling afterglow of GRB 050721: a rebrightening seen in the optical but not in the X-ray

We present here the analysis of the early and late multiwavelength afterglow emission, as observed by Swift a small robotic telescope and very large telescope (VLT). We compare early observations with late afterglow observations obtained with Swift and the VLT and we observe an intense rebrightening in the optical band at about 1 day after the burst, which is not present in the X-ray band. The lack of detection in X-ray of such a strong rebrightening at lower energies may be described with a variable external density profile. In such a scenario, the combined X-ray and optical observations allow us to derive that the matter density located at approximately 1017 cm from the burst is approximately a factor of 10 higher than in the inner region. This is the first time in which a rebrightening has been observed in the optical afterglow of a gamma-ray burst that is clearly absent in the X-ray afterglow.     

Production and characterization of pure and Cr<Superscript>3+</Superscript>-doped hydroxyapatite for biomedical applications as fluorescent probes

Pure and Cr³⁺-doped hydroxyapatite (HAP) were prepared via chemical precipitation route. The XRD measurements revealed that the typical HAP powder pattern was obtained. SEM analysis indicated that aggregates of nanoparticles were formed. EDX analysis indicates that the [Ca]/[P] concentration ratio was higher than the expected values but can be explained by the presence of carbonate groups as dopants. The optical absorption spectra of the doped samples presented absorption bands typical of Cr³⁺ occupying to different crystalline sites. From the position of the bands, it was possible to estimate the crystal field parameters for both sites of Cr³⁺ in the HAP matrix. The emission spectra of the Cr-doped samples were also investigated and typical transitions of the dopant ion, in trivalent state, were identified. The potential use of the Cr³⁺-HAP as fluorescent probes for medical applications was discussed.     

Modeling the performance of coated LPG tanks engulfed in fires

The improvement of passive fire protection of storage vessels is a key factor to enhance safety among the LPG distribution chain. A thermal and mechanical model based on finite elements simulations was developed to assess the behaviour of full size tanks used for LPG storage and transportation in fire engulfment scenarios. The model was validated by experimental results. A specific analysis of the performance of four different reference coating materials was then carried out, also defining specific key performance indicators (KPIs) to assess design safety margins in near-miss simulations. The results confirmed the wide influence of coating application on the expected vessel time to failure due to fire engulfment. A quite different performance of the alternative coating materials was evidenced. General correlations were developed among the vessel time to failure and the effective coating thickness in full engulfment scenarios, providing a preliminary assessment of the coating thickness required to prevent tank rupture for a given time lapse. The KPIs defined allowed the assessment of the available safety margins in the reference scenarios analyzed and of the robustness of thermal protection design.     

1923 Gleno Dam Break: Case Study and Numerical Modeling

On the morning of December 1, 1923, the Gleno Dam (located in the Central Italian Alps) suddenly collapsed a few days after the first complete reservoir filling. Nearly 4.5×106??m3 of water was released. The consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives. This failure is the only historical case of dam break caused by structural deficiencies that has occurred in Italy. As a result, it has deeply influenced the evolution of Italian regulations regarding dam design and hydraulic risk evaluation. However, in spite of its relevance, this event has never been characterized from a hydraulic standpoint. This paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the Gleno Dam break to set up a case study useful for validating dam-break models in mountain settings. Moreover, it presents the main results of one-dimensional (1D) modeling of the dam break wave propagation accomplished with a first-order finite volume numerical scheme recently proposed in the literature for field applications. The overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography. Finally, the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested.     

Inherent safety key performance indicators for hydrogen storage systems

The expected inherent safety performance of hydrogen storage technologies was investigated. Reference schemes were defined for alternative processes proposed for hydrogen storage, and several storage potentialities were considered. The expected safety performance of alternative process technologies was explored estimating key performance indicators based on consequence assessment and credit factors of possible loss of containment events. The results indicated that the potential hazard is always lower for the innovative technologies proposed for hydrogen storage, as metal or complex hydrides. This derived mainly from the application of the inherent safety principles of "substitution" and "moderation", since in these processes hydrogen is stored as a less hazardous hydride. However, the results also evidenced that in the perspective of an industrial implementation of these technologies, the reliability of the auxiliary equipment will be a critical issue to be addressed.