Coherent microscopy by laser optical feedback imaging (LOFI) technique

The application of the non-conventional imaging technique LOFI (laser optical feedback imaging) to coherent microscopy is presented. This simple and efficient technique using frequency-shifted optical feedback needs the sample to be scanned in order to obtain an image. The effects on magnitude and phase signals such as vignetting and field curvature occasioned by the scanning with galvanometric mirrors are discussed. A simple monitoring method based on phase images is proposed to find the optimal position of the scanner. Finally, some experimental results illustrating this technique are presented.     

Natural and persistent superhydrophilicity of SiO2/TiO2 and TiO2/SiO2 bi-layer films

Sol-gel SiO₂/TiO₂ and TiO₂/SiO₂ bi-layer films have been deposited from a polymeric SiO₂ solution and either a polymeric TiO₂ mother solution (MS) or a derived TiO₂ crystalline suspension (CS). The chemical and structural properties of MS and CS bi-layer films heat-treated at 500 °C have been investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscospy. Water contact angle measurements show that MS SiO₂/TiO₂ and CS TiO₂/SiO₂ bi-layer films exhibit a natural superhydrophilicity, but cannot maintain a zero contact angle for a long time over film aging. In contrast, CS SiO₂/TiO₂ bi-layer films exhibit a natural, persistent, and regenerable superhydrophilicity without the need of UV light. Superhydrophilic properties of bi-layer films are discussed with respect to the nature of the TiO₂ single-layer component and arrangement of the bi-layer structure, i.e. TiO₂ underlayer or overlayer.     

XPS investigations of the proton exchange membrane fuel cell active layers aging: Characterization of the mitigating role of an anodic CO contamination on cathode degradation

This paper presents new results from XPS quantitative characterizations of cathode catalyst layers aged in a PEMFC with an anode operated under pure hydrogen and air and with 5 ppm CO contaminated hydrogen. Both oxygen rich and oxygen poor zones of the cathode catalyst layer were analyzed in order to show up heterogeneous degradation linked with gas distribution. The detailed chemical XPS analysis of the aged samples demonstrates in particular that in our operating conditions, the catalyst layer aging is mainly attributed to the oxidation of the carbon catalyst-support. A loss of the Nafion^® ionomer in the cathode is also highlighted by XPS. Furthermore, the characterization of the cathodic catalyst layer chemical composition when CO is introduced in the anode side shows that the catalyst layer degradation is lower. These results are in agreement with the experimental-modeling work by Franco et al. [1] demonstrating that anodic CO contamination decreases the reverse proton pumping effect between the cathode and the anode and enhances the PEMFC durability.     

The wetting of carbon by aluminium and aluminium alloys

The contact angle made by molten aluminium with vitreous carbon was measured by the sessile drop method in vacuum at temperatures up to 1100° C. The effect on wetting behaviour of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation. The investigation involved the variation of certain parameters affecting the stability of the oxide film, e.g. the temperature, additions of Ti, Si, Cr, Be, Ca and Li to aluminium and the time held at a certain temperature. The state of the molten aluminium surface under various experimental conditions was determined indirectly by surface tension measurements.     

Wettability of Metallic Oxides—Application to Stainless Stell Acid-Base Properties

The Brönsted acid-base properties of oxides of metallic systems are investigated by contact angle measurements of water droplets for different pH. Theoretical analysis based on the electrical and chemical variations of the solid/liquid interfacial tension allows to understand the experimental results observed on model oxide surfaces as SiO₂ and Al₂O₃. Similar wetting measurements are performed on the passive films of a model Fe-Cr-Si alloy and 304 stainless steel. Significant correlations are observed between the contact angle-pH curve and the oxide composition of the passive films deduced from XPS analysis.     

Influence of additions on the structure of rapidly solidified Ni2Al3 alloys

Raney nickel catalysts are prepared from Ni−Al alloys. In order to test the influence of the microstructure of the precursor alloys, we prepared homogenized and microcrystallized (NiM)₂Al₃ alloys with M=Cr, Cu, Fe, Ti, Zr, Ta. Microcrystallized alloys are prepared by meltspinning. Observations were made by scanning and transmission electron microscopies. The as-melted ribbons exhibit a flower dendritic shape with NiAl as a core. An intermediate zone is observed which corresponds to small axial domains according to the peritectic formation of Ni₂Al₃ (hexagonal structure) from NiAl (b c c). Petals of the flowers are made of domains of Ni₂Al₃ almost monocrystalline. The size of the domains depends essentially on the cooling rate and on the nature of the dopant.     

Continuous Mobile User Authentication Using a Hybrid CNN-Bi-LSTM Approach

Internet of Things (IoT) devices incorporate a large amount of data in several fields, including those of medicine, business, and engineering. User authentication is paramount in the IoT era to assure connected devices’ security. However, traditional authentication methods and conventional biometrics-based authentication approaches such as face recognition, fingerprints, and password are vulnerable to various attacks, including smudge attacks, heat attacks, and shoulder surfing attacks. Behavioral biometrics is introduced by the powerful sensing capabilities of IoT devices such as smart wearables and smartphones, enabling continuous authentication. Artificial Intelligence (AI)-based approaches introduce a bright future in refining large amounts of homogeneous biometric data to provide innovative user authentication solutions. This paper presents a new continuous passive authentication approach capable of learning the signatures of IoT users utilizing smartphone sensors such as a gyroscope, magnetometer, and accelerometer to recognize users by their physical activities. This approach integrates the convolutional neural network (CNN) and recurrent neural network (RNN) models to learn signatures of human activities from different users. A series of experiments are conducted using the MotionSense dataset to validate the effectiveness of the proposed method. Our technique offers a competitive verification accuracy equal to 98.4%. We compared the proposed method with several conventional machine learning and CNN models and found that our proposed model achieves higher identification accuracy than the recently developed verification systems. The high accuracy achieved by the proposed method proves its effectiveness in recognizing IoT users passively through their physical activity patterns.     

Natural superhydrophilicity of sol–gel derived SiO2–TiO2 composite films

Sol–gel SiO₂–TiO₂ mixed films have been deposited from a polymeric SiO₂ solution and either a polymeric TiO₂ mother solution (MS) or a derived TiO₂ crystalline suspension (CS). The chemical and structural compositions of MS and CS mixed films heat-treated at 110 or 500 °C have been investigated by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Water contact angle measurements show that TiO₂ rich MS films exhibit photo-induced superhydrophilicity, but cannot maintain a zero contact angle in the absence of UV light. In contrast, CS mixed films exhibit a natural and persistent superhydrophilicity for a large range of compositions. Superhydrophilic properties are analyzed in terms of enhanced acidity at the SiO₂–TiO₂ interfaces and discussed with respect to the chemical and structural composition of MS and CS films.     

Metallurgical structure and alkali leaching of the Al/Al3Ni eutectic

Raney-Nickel catalysts were prepared by aluminium leaching out of aluminium-rich binary Al-Ni alloys. In order to understand the behaviour of NiAl₃ during alkali leaching, different metallurgical structures of the Al/Al₃Ni eutectic were prepared as precursor alloys. This eutectic showed a fibrous morphology with Al₃Ni fibres embedded in an aluminium matrix. After alkali leaching, transmission electron microscopy observations showed that the fibrous microstructure was retained. The fibres were formed with small nickel crystallites. During the early stages of leaching, a reaction front was observed which remained parallel to the Al/Al₃Ni interface.