Absolute calibration of photostimulable image plate detectors used as (0.5-20 MeV) high-energy proton detectors

In this paper, the absolute calibration of photostimulable image plates (IPs) used as proton detectors is presented. The calibration is performed in a wide range of proton energies (0.5-20 MeV) by exposing simultaneously the IP and calibrated detectors (radiochromic films and solid state detector CR39) to a source of broadband laser-accelerated protons, which are spectrally resolved. The final result is a calibration curve that enables retrieving the proton number from the IP signal.     

Color effects of uniform colloidal particles of different morphologies packed into films

The experimentally determined chromaticities and reflectance spectra of films consisting of uniform ellipsoidal or spherical colloidal hematite particles are compared with calculated values and are found to be in good agreement. The theoretical treatment of the light-scattering problem involves the Mie theory for the spheres and the T-matrix method for the ellipsoids. The reflectance spectra for the pigment films are calculated through the use of the Kubelka-Munk analysis.     

Algorithm for the determination of intrinsic optical constants of metal films: application to aluminum

Optical and electron-energy-loss data for evaporated-aluminum films have been critically analyzed and used in an iterative, self-consistent algorithm that represents a combination of the Kramers-Kronig analysis and the semiquantum-model application. The novel values of the intrinsic optical functions of aluminum have been determined in a wide spectral range from 200 μm (6.2 meV) to 0.12 nm (10 keV). These functions are in accordance with recent calculations by Lee and Chang [Phys. Rev. B 49, 2362 (1994)], with dc conductivity measurements, and are in good agreement with both peak positions and line widths obtained from electron-energy-loss experiments. The results are examined for internal consistency by inertial and f-sum rules.     

The influence of adding pitch to resin as a matrix precursor on properties of carbon-carbon composites

Carbon-carbon composites were prepared with commercially available carbonized and graphitized fibres, with a mixture of pitch and phenolic resin as a binder and pitch as an impregnant. The contents of pitch in mixtures were: 0, 10, 20 and 30 wt %. The influence of pitch content in the mixture and fibre type on mass loss, shrinkage and mechanical properties of the composites was examined. With an increase of pitch content mass loss and shrinkage increased, while mechanical properties decreased. After three densification cycles, flexural strength increased with increasing pitch content in the binder, especially for composites with graphitized fibres.     

The influence of temperature and grain size on substructure evolution in stainless steel 316L

The flow stress of polycrystals is controlled by the processes occurring in the grain interior as well as in the mantle, i.e. at the grain boundary and its immediate vicinity. The early stages of evolution of dislocation substructure in these two regions with strain in 316L stainless steel polycrystals have been studied at 293 K, 673 K and 1123 K representing the low temperature thermal, the intermediate temperature athermal and the high temperature thermal regimes respectively. Specimens with grain sizes of 4 and 12 m were employed to determine the effect of grain size.Transmission electron microscopy studies on deformed specimens show the different roles of grain boundary and grain interior in different temperature regimes. In the low temperature regime grain boundaries act as obstacles to moving dislocations and as such high density of dislocation is found in the grain boundary vicinity. In the intermediate temperature regime the dislocations which are easily spread into the grain interior rearrange to form cell walls. In the high temperature regime grain boundaries transform to the equilibrium state and do not contain any grain boundary dislocations, and the distribution of dislocations within grains is homogeneous at all strains. Significantly higher values of dislocation densities in the vicinity as well as in the grain interior were found in the finer grain size material in the whole strain region employed.     

Evolutionary design of neural network architectures: a review of three decades of research

We present a comprehensive review of the evolutionary design of neural network architectures. This work is motivated by the fact that the success of an Artificial Neural Network (ANN) highly depends on its architecture and among many approaches Evolutionary Computation, which is a set of global-search methods inspired by biological evolution has been proved to be an efficient approach for optimizing neural network structures. Initial attempts for automating architecture design by applying evolutionary approaches start in the late 1980s and have attracted significant interest until today. In this context, we examined the historical progress and analyzed all relevant scientific papers with a special emphasis on how evolutionary computation techniques were adopted and various encoding strategies proposed. We summarized key aspects of methodology, discussed common challenges, and investigated the works in chronological order by dividing the entire timeframe into three periods. The first period covers early works focusing on the optimization of simple ANN architectures with a variety of solutions proposed on chromosome representation. In the second period, the rise of more powerful methods and hybrid approaches were surveyed. In parallel with the recent advances, the last period covers the Deep Learning Era, in which research direction is shifted towards configuring advanced models of deep neural networks. Finally, we propose open problems for future research in the field of neural architecture search and provide insights for fully automated machine learning. Our aim is to provide a complete reference of works in this subject and guide researchers towards promising directions.

     

Selective Al-Ti reactivity in laser-processed Al/Ti multilayers

Multilayers consisting of five (Al/Ti) bilayers were deposited on (100) silicon wafers. On top was deposited the Ti layer, aimed at preventing Al from diffusing to the surface upon laser treatment. The total thickness of the thin-film structure was 200?nm. Laser irradiations with Nd:YAG picoseconds laser pulses in the defocused regime were performed in air. Laser beam energy was 4?mJ and laser spot diameter on the sample surface was 3?mm (fluence 0.057?J?cm^?2). The samples were treated with different numbers of laser pulses. Structural characterizations were performed by different analytical methods and nano-hardness was also measured. Laser processing induced layer intermixing, formation of titanium aluminides, oxidation of the surface titanium layer and enhanced surface roughness. Aluminum appears at the sample surface only for the highest density of laser irradiation. Laser processing induces increment of nano-hardness by approximately 20% and decrease of residual Young’s modulus for a few percentages from the starting value of the untreated samples. These results can be interesting toward achieving structures with a selective extent of Al-Ti reactivity in this multilayered system, within the development of biocompatible materials.     

Cross-property connections for copper–graphite composites

Copper–graphite composite materials in the range of 0–10 vol% of carbon phase were prepared from the mixture of copper and graphite powders by hot isostatic pressing. The microstructure, mechanical (tensile strength, elongation to fracture) and physical (electrical and thermal conductivity) properties of composite samples were investigated, and the cross-property connections were calculated. It was shown that electrical and thermal conductivity cross-property (Lorenz number) is almost constant and increases only slightly (no more than 10 % increase was observed). This implies that in the investigated composition range the Lorenz number of a copper–graphite composite system behaves according to Franz–Wiedemann law for pure metals at constant temperature. On the contrary, the conductivity to tensile strength cross-property connections showed significant linear increase (over 200 % in the investigated composition range) for both electrical conductivity and thermal conductivity of composite materials. The cross-property connections of conductivity to the elongation to fracture exhibit a nonlinear dependence on the volume fraction of graphite.