Restricted dynamics of molecular hydrogen confined in activated carbon nanopores

Quasi-elastic neutron scattering was used for characterization of dynamics of molecular hydrogen confined in narrow nanopores of two activated carbon materials: a carbon derived from polyfurfuryl alcohol and an ultramicroporous carbon. Fast, but incomplete ortho–para conversion was observed at 10 K, suggesting that scattering originates from the fraction of unconverted ortho isomer which is rotation-hindered because of confinement in nanopores. Hydrogen molecules entrapped in narrow nanopores (<7 Å) were immobile below 22–25 K. Mobility increased rapidly with temperature above this threshold, which is higher than the melting point of bulk hydrogen (13.9 K). Diffusion obeyed fixed-jump length mechanism, indistinguishable between 2D and 3D processes. Thermal activation of diffusion was characterized between ～22 and 37 K, and structure-dependent differences were found between the two carbons. Activation energy of diffusion was higher than that of bulk solid hydrogen. Classical notions of liquid and solid do not longer apply for H₂ confined in narrow nanopores.     

Multiscale computation of fretting wear at the blade/disk interface

Dovetail joints between fan blades and the disk of turbine engines are subjected to fretting. The objective of this research is to realize wear prediction by computational methods. The goal is obviously the estimation of wear kinetics, but also to obtain worn surfaces, and permit the manufacturer to realize complementary design analyses with worn surfaces. A wear law developed for titanium alloy and based on the friction dissipated energy is used. A computational method based on a three scale analysis is presented. The originality consists of coupling a semi-analytical (SA) contact solver with the FE method for the structural behavior, allowing a fine discretization of the contact zone. Contact computations are fast enough to realize cyclic wear computations. Results for the blade/disk system are exhibited.     

High-efficiency volume holograms recording on acrylamide and N,N′methylene-bis-acrylamide photopolymer with pulsed laser

In order to achieve a better understanding of the mechanisms of hologram formation and higher diffraction efficiencies in volume gratings stored in acrylamide based photopolymers, a crosslinker (N,N′methylene-bis-acrylamide) has been incorporated in the photopolymer to record holograms by pulsed laser exposure. The presence of this component increases the polymerization rate and refractive index modulation. The recording was performed using a holographic copying process. The original was a grating of 1000?lines/mm processed using silver halide sensitized gelatin. First, the effect of the pulse fluence was investigated. When the pulse fluence was optimized, the results obtained using the new composition of material were compared with those using the composition without a crosslinker. Using a pulsed laser at 532?nm the photopolymer without crosslinker presented diffraction efficiencies slightly less than 60%. On the other hand, when the crosslinker was introduced in the photopolymer composition, the diffraction efficiencies achieved were higher than 85%. The non-linearity of the material's response was also studied comparing the energetic sensitivity, diffraction efficiencies and index modulation of gratings recorded with pulsed and continuous laser exposure. This study was performed fitting the angular scan of each grating using Kogelnik's theory.     

On-site non-destructive measurement of termite activity using the spectral kurtosis and the discrete wavelet transform

In this paper we present the operation results of a portable computer-based measurement equipment, conceived to perform non-destructive testing of suspected termite infestations. Its signal processing nucleus is the spectral kurtosis (SK), whose pattern allows the targeting of alarms and activity signals. Data have been also de-noised using the discrete wavelet transform (DWT) in order to study its potential complementarity to SK. The DWT keeps the successive approximations of the termite emissions, supposed more non-Gaussian (less noisy) and with less entropy than the detail coefficients. For a given mother wavelet, the maximum acceptable level in the wavelet decomposition tree, which preserves the insects’ emissions features, depends on the comparative evolution of the approximations vs. details’ entropies, and the value of the global SK associated to the approximation of the separated signals. The paper explains the detection criterion by showing different types of real-life recordings (alarms, activity, and background).     

Evolution of the properties of a poly(l‐lactic acid) scaffold with double porosity during in vitro degradation in a phosphate‐buffered saline solution

A poly(l ‐lactic acid) scaffold prepared by a combination of freeze‐extraction and porogen‐leaching methods was submitted to static degradation in a phosphate‐buffered saline solution at pH 7.4 and 37°C for up to 12 months. After 6 months of degradation, the scaffold maintained its integrity, although noticeable changes in its permeability and pore size were recorded. After 12 months, scanning electron microscopy pictures showed that most of the trabeculae were broken, and the sample disaggregated under minimum loading. Neither weight loss nor crystallinity changes in the first heating calorimetric scan were observed during the degradation experiment. However, after 12 months, a rise in the crystallinity from 13 to 38% and a drop in the glass‐transition temperature from 58 to 54°C were measured in the second heating scan. The onset of thermal degradation moved from 300 to 210°C after 12 months. Although the elastic modulus suffered only a very slight reduction with degradation time, the aggregate modulus decreased 44% after 6 months. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40956.     

Artificial neural networks in neutron dosimetry

An artificial neural network (ANN) has been designed to obtain neutron doses using only the count rates of a Bonner spheres spectrometer (BSS). Ambient, personal and effective neutron doses were included. One hundred and eighty-one neutron spectra were utilised to calculate the Bonner count rates and the neutron doses. The spectra were transformed from lethargy to energy distribution and were re-binned to 31 energy groups using the MCNP 4C code. Re-binned spectra, UTA4 response matrix and fluence-to-dose coefficients were used to calculate the count rates in the BSS and the doses. Count rates were used as input and the respective doses were used as output during neural network training. Training and testing were carried out in the MATLAB environment. The impact of uncertainties in BSS count rates upon the dose quantities calculated with the ANN was investigated by modifying by +/-5% the BSS count rates used in the training set. The use of ANNs in neutron dosimetry is an alternative procedure that overcomes the drawbacks associated with this ill-conditioned problem.     

Performance analysis of multiplexed medical data transmission for mobile emergency care over the UMTS channel

In this paper, a third-generation universal mobile telecommunications system (UMTS) solution for the delivery of biomedical information from an ambulance to a hospital is presented. The joint transmission of voice, real-time video, electrocardiogram signals, and medical scans in a realistic cellular multiuser simulation environment is considered, taking into account the advantages and particularities of UMTS technology for such transmission. The accomplishment of quality of service constraints for different services is investigated and quantitative results are provided in order to demonstrate the feasibility of using UMTS technology for emergency care services on high-speed moving ambulance vehicles.     

GRASP and path relinking for the max–min diversity problem

The max–min diversity problem (MMDP) consists in selecting a subset of elements from a given set in such a way that the diversity among the selected elements is maximized. The problem is NP-hard and can be formulated as an integer linear program. Since the 1980s, several solution methods for this problem have been developed and applied to a variety of fields, particularly in the social and biological sciences. We propose a heuristic method—based on the GRASP and path relinking methodologies—for finding approximate solutions to this optimization problem. We explore different ways to hybridize GRASP and path relinking, including the recently proposed variant known as GRASP with evolutionary path relinking. Empirical results indicate that the proposed hybrid implementations compare favorably to previous metaheuristics, such as tabu search and simulated annealing.     

Analysis and modelling of broadcast services for TDMA wireless ad hoc networks

MAC protocols designed to provide QoS in wireless ad hoc networks need to be able to reserve and control resources efficiently. To this purpose, TDMA-based networks often lie in a frame subdivision that consists of a broadcast control phase and an information phase. In the control phase, each active terminal broadcasts signalling information required to handle the access to the data resources. Analysis and modelling of the broadcast service is carried out, which allows an efficient frame dimensioning in this scenario     

Dry reforming of methane over LaNi1−yByO3±δ (B = Mg,Co) perovskites used as catalyst precursor

Perovskites LaNiO₃, LaNi_1−xMg_xO_3−δ and LaNi_1−xCo_xO_3−δ were synthesized by auto combustion method. TPR analysis reveled that Mg or Co substituted perovskites were more difficult to reduce. The perovskites were evaluated as catalyst precursors in the dry reforming of methane. Catalysts obtained by reduction of LaNiO₃ and LaNi_1−xMg_xO_3−δ perovskite had the highest catalytic activity for CO₂ reforming of CH₄ at 700 °C using drastic reaction conditions (10 mg of catalyst, a mixture of CH₄/CO₂ without dilution gas). Methane and carbon dioxide conversions were 57% and 67%, respectively, with a H₂/CO ratio equal to 0.47.The presence of cobalt leads to a decrease of the catalytic activity. This decreasing of activity may be attributed to the Co–Ni alloy formation. Computational calculations revealed that Ni atom cleaves the C–H atom while Co is not able to activate the CH₄ molecule. The interaction energy of CH₄ with the Ni and CO atom was 18 kcal/mol and 0.7 kcal/mol, respectively.The catalysts were characterized by TPR, TEM and in situ XRD.