Dynamic behavior of an aggregate material at simultaneous high pressure and strain rate: SHPB triaxial tests

Low velocity impacts on energetic materials induce plastic deformations and sliding friction which can lead to ignition. If some ignition criteria have been proposed, the remaining difficulty is to characterize the mechanical behavior of the material when submitted to the corresponding solicitations (high pressure and high strain rate). Thus, a technique based on the Split Hopkinson Pressure Bars system is proposed to carry out a triaxial compression test. A cylindrical specimen is placed into a confining ring and is compressed by the system of bars. The ring prevents the radial extension of the specimen and creates a lateral confining pressure. The material and dimensions chosen for the ring maintain a constant radial pressure during the test. Some tests were carried out on an inert aggregate material and proved the validity of this experimental device. The experimental data processing shows the influence of both the pressure and the strain rate. The shear stresses, which contribute to thermal dissipation and then to the ignition threshold, increase according to the pressure.     

Friction studies of tough pitch copper using a hollow punch-torque method

A hollow punch-torque method was used to measure friction between tough pitch copper and three different lubricants. The tests indicated that the coefficient μ is not a function of the applied pressure, while the friction factorm is. Both μ andm depend only slightly on the degree of prior deformation. The range of pressure investigated was that encountered in drawing operations and is below that for lubricated sliding surfaces where sublayer plastic flow occurs.     

Dielectric Structure with Periodic Strips for Increasing Radiation Power of Photoconductive Antennas: Theoretical Analysis

Low terahertz (THz) radiation power and low efficiency are the well-known drawbacks of photoconductive antennas (PCAs). To increase THz-radiation power of PCAs, a dielectric structure with periodic low-temperature-grown GaAs strips is proposed. Transmitted power of the proposed structure is obtained from a theoretical model, and further confirmed by finite element simulations. Results show that the structure is capable to transmit into the substrate 90 % of the power of transverse magnetic wave with wavelength as wide as from 0.7 to 1.0 μm. Favorability of this property gets amplified when power transmission in a wide range of frequency bandwidth is desired, e.g., for optical pulse with short duration time incident to PCA, which generates carriers in the semiconductor that create THz emission. Furthermore, the proposed dielectric structure with periodic strips, the whole structure placed in between electrodes of PCA is considered, and analyzed by the existing photoconductive antenna equivalent circuit model, to see how power radiation changes. Interestingly, THz-radiation power enhancements of 70 and 20 % are evinced for, respectively, 20 and 150 mW incident optical powers as instances, as compared to PCA without strips in the gap area.     

Simulation of SiGe:C HBTs using neural network and adaptive neuro-fuzzy inference system for RF applications

In this article, the small-signal equivalent circuit model of SiGe:C heterojunction bipolar transistors (HBTs) has directly been extracted from S-parameter data. Moreover, in this article, we present a new modelling approach using ANFIS (adaptive neuro-fuzzy inference system), which in general has a high degree of accuracy, simplicity and novelty (independent approach). Then measured and model-calculated data show an excellent agreement with less than 1.68?×?10^?5% discrepancy in the frequency range of higher than 300 GHz over a wide range of bias points in ANFIS. The results show ANFIS model is better than ANN (artificial neural network) for redeveloping the model and increasing the input parameters.     

A Novel 2.5–3.1 GHz Wide-Band Low-Noise Amplifier in 0.18 \upmu \hbox {m} CMOS

Aiming for the simultaneous realization of constant gain, accurate input and output impedance matching and minimum noise figure (NF) over a wide frequency range, the circuit topology and detailed design of wide broadband low noise amplifier (LNA) are presented in this paper. A novel 2.5–3.1 GHz wide-band LNA with unique characteristics has been presented. Its design and layout are done by TSMC 0.18  \(\upmu \hbox {m}\) technology. Common gate stage has been used to improve input matching. In order to enhance output matching and reduce the noise as well, a buffer stage is utilized. Mid-stages which tend to improve the gain and reverse isolation are exploited. The proposed LNA achieves a power gain of 15.9 dB, a NF of 3.5 dB with an input return loss less than \(-\) 11.6, output return loss of \(-\) 19.2 to \(-\) 19 and reverse isolation of \(-\) 38 dB. The LNA consumes 54.6 mW under a supply voltage of 2 V while having some acceptable characteristics.     

Seismic geomorphology and stratigraphic trap analyses of the Lower Cretaceous siliciclastic reservoir in the Kopeh Dagh-Amu Darya Basin

Lower Cretaceous Shurijeh–Shatlyk Formations host some of the main reservoirs in the Kopeh Dagh-Amu Darya Basin.Exploration in this area so far has focused on the development of structural traps, but recognition of stratigraphic traps in this area is of increasing importance. Integration of 3D seismic data with borehole data from thirteen wells and five outcrop sections was used to identify potential reservoir intervals and survey the hydrocarbon trap types in the East Kopeh Dagh Foldbelt(NE Iran). Analyses of horizontal slices indicated that the lower Shurijeh was deposited in a braided fluvial system.Generally, three types of channel were identified in the lower Shurijeh Formation: type 1, which is low-sinuosity channels interpreted to be filled with non-reservoir fine-grained facies; type 2, which is a moderately sinuous sand-filled channel with good prospectively; and type 3, which is narrow, high sinuosity channel filled with fine-grained sediments. Results indicate that upper Shurijeh–Shatlyk Formations were deposited in fluvial to delta and shallow marine environments. The identified delta forms the second reservoir zone in the Khangiran Field. Study of the stratigraphic aspects of the Shurijeh succession indicates that both lower and upper Shurijeh reservoirs are stratigraphic reservoir traps that improved during folding.     

Visible light emission from silicon: a quantum effect in highlyporous materials

The authors discuss progress in the control of the luminescent properties of porous silicon and in the understanding of the basic mechanisms which govern the light emission. The main features of porous silicon formation and properties are briefly recalled. The photoluminescence characteristics are reported. It is shown that anodic oxidation of porous silicon is a technique which provides photoluminescent layers with good mechanical properties and enhanced emission efficiency. A model accounting for the quite long measured carrier lifetimes is outlined. The electroluminescence which appears during the anodic oxidation of porous silicon in pure water was studied