Nanocharacterization techniques for investigating the durability of wood coatings

Nanocharacterization techniques such as nanoindentation and atomic force microscopy were used to investigate the exterior durability of waterborne coatings improved with inorganic nanosized UV-absorbers. Nanocomposite coatings for exterior uses of wood were formulated with different type of nanoparticles and their performance was evaluated trough artificial aging. Nanoindentation in continuous stiffness mode was used to demonstrate the changes of hardness and Young’s modulus of the coatings after accelerated weathering. The degradation mechanism of the surface coatings was investigated with atomic force microscopy that has provided valuable information on the morphological and microstructural changes of the surface coatings with the artificial aging. Additionally, the glass transition temperature and optical appearance changes were reported. The results obtained have shown that the nanoindentation technique in conjunction with atomic force microscopy can be satisfactorily used for durability investigation and service life prediction of nanocomposite coatings for wood.     

Rare event simulation for a slotted time M/G/s model

This paper develops a rare-event simulation algorithm for a discrete-time version of the M/G/s loss system and a related Markov-modulated variant of the same loss model. The algorithm is shown to be efficient in the many-server asymptotic regime in which the number of servers and the arrival rate increase to infinity in fixed proportion. A key idea is to study the system as a measure-valued Markov chain and to steer the system to the rare event through a randomization of the time horizon over which the rare event is induced.     

Simultaneous analysis of plasma and CSF by NMR and hierarchical models fusion

Because cerebrospinal fluid (CSF) is the biofluid which interacts most closely with the central nervous system, it holds promise as a reporter of neurological disease, for example multiple sclerosis (MScl). To characterize the metabolomics profile of neuroinflammatory aspects of this disease we studied an animal model of MScl-experimental autoimmune/allergic encephalomyelitis (EAE). Because CSF also exchanges metabolites with blood via the blood-brain barrier, malfunctions occurring in the CNS may be reflected in the biochemical composition of blood plasma. The combination of blood plasma and CSF provides more complete information about the disease. Both biofluids can be studied by use of NMR spectroscopy. It is then necessary to perform combined analysis of the two different datasets. Mid-level data fusion was therefore applied to blood plasma and CSF datasets. First, relevant information was extracted from each biofluid dataset by use of linear support vector machine recursive feature elimination. The selected variables from each dataset were concatenated for joint analysis by partial least squares discriminant analysis (PLS-DA). The combined metabolomics information from plasma and CSF enables more efficient and reliable discrimination of the onset of EAE. Second, we introduced hierarchical models fusion, in which previously developed PLS-DA models are hierarchically combined. We show that this approach enables neuroinflamed rats (even on the day of onset) to be distinguished from either healthy or peripherally inflamed rats. Moreover, progression of EAE can be investigated because the model separates the onset and peak of the disease.     

Asymptotic expansions of defective renewal equations with applications to perturbed risk models and processor sharing queues

We consider asymptotic expansions for defective and excessive renewal equations that are close to being proper. These expansions are applied to the analysis of processor sharing queues and perturbed risk models, and yield approximations that can be useful in applications where moments are computable, but the distribution is not.     

Temporal and spatial assessment of normal cerebrospinal fluid dynamics with MR imaging

The purpose of this study was to measure normal cerebrospinal fluid (CSF) pulsations within the intracranial and upper cervical subarachnoid spaces and the ventricular system. Phase contrast cine MR sequences were performed in sagittal and axial planes on 13 volunteers with flow encoding in the craniocaudal direction. CSF pulsations displayed considerable variations in healthy subjects, depending both on measurements localization and subjects, with CSF peak velocities ranging from 0 to 7 cm/s. In the subarachnoid spaces, the highest velocities occurred in the anterior location and increased from the cerebellar pontine angle cisterns towards the lower cervical spaces. In the ventricular system, the highest velocities occurred through the aqueduct of Sylvius. CSF flow within the third ventricle seemed to reflect a circular motion. There was a caudal net CSF flow in the aqueduct whereas in the upper cervical spaces net CSF flow was caudal anteriorly and cranial laterally. Velocity profiles of CSF pulsations demonstrated arterial morphology. After the R wave, caudal systolic motion was first observed in the posterior subarachnoid spaces, soon after in the anterior subarachnoid spaces and later in the ventricular system. Considering the morphology of CSF pathways, three successively initiated phenomena may explain the temporal course of CSF motion: the systolic expansion of the main arteries at the base of the brain, the systolic expansion of the cerebrospinal axis and, finally, the systolic expansion of the choroid plexuses.     

Buffeting lift forces and local air–water flow aspects around a rigid cylinder

A new experimental programme is conducted in order to relate the characteristics of two-phase flow around a rigid cylinder with the resulting lift forces. The local characteristics of air–water flow measured in the vicinity of the cylinder provide a useful source of information about the effects of flow on the excitation mechanisms. In particular, a selection of relevant parameters has been identified which, with the help of a standard dimensional analysis, may explain the energetic contents of buffeting forces. Among the parameters effective in reducing the data are the flow regime, bubble frequency and gravity forces. In addition, in the range of bubbly regimes, the magnitude of the random forces is found to be related to the local fluctuations of void fraction. Finally, a new formulation is proposed to collapse the dimensionless spectra of the buffeting lift forces in a single characteristic curve. This analysis shows a marked improvement over the collapse of data in comparison with previous normalized models.     

Synthesis and reactivity of mixed alkynylalanes by direct triethylamine-catalyzed alumination of terminal alkynes

[reaction: see text] Terminal alumination of alkynes by DIBALH or trimethylaluminum can be performed in a simple manner in the presence of a small amount of triethylamine. This new Lewis-base-catalyzed process delivers mixed alkynyldialkylalanes of great interest, without the need of an initial deprotonation step with lithium or sodium derivatives followed by a transmetalation.     

Asymptotic behaviour for small mass in the two-dimensional parabolic-elliptic Keller-Segel model

The Keller-Segel system describes the collective motion of cells that are attracted by a chemical substance and are able to emit it. In its simplest form, it is a conservative drift-diffusion equation for the cell density coupled to an elliptic equation for the chemo-attractant concentration. This paper deals with the rate of convergence towards a unique stationary state in self-similar variables, which describes the intermediate asymptotics of the solutions in the original variables. Although it is known that solutions globally exist for any mass less 8π, a smaller mass condition is needed in our approach for proving an exponential rate of convergence in self-similar variables.