Fabrication of Porous Anodic Alumina (PAA) by High-Temperature Pulse-Anodization: Tuning the Optical Characteristics of PAA-Based DBR in the NIR-MIR Region

In this work, the influence of various electrochemical parameters on the production of porous anodic alumina (PAA)-based DBRs (distributed Bragg reflector) during high-temperature-pulse-anodization was studied. It was observed that lowering the temperature from 30 to 27 °C brings about radical changes in the optical performance of the DBRs. The multilayered PAA fabricated at 27 °C did not show optical characteristics typical for DBR. The DBR performance was further tuned at 30 °C. The current recovery (iamax) after application of subsequent UH pulses started to stabilize upon decreasing high (UH) and low (UL) voltage pulses, which was reflected in a smaller difference between initial and final thickness of alternating dH and dL segments (formed under UH and UL, respectively) and a better DBR performance. Shortening UH pulse duration resulted in a progressive shift of photonic stopbands (PSBs) towards the blue part of the spectrum while keeping intensive and symmetric PSBs in the NIR-MIR range. Despite the obvious improvement of the DBR performance by modulation of electrochemical parameters, the problem regarding full control over the homogeneous formation of dH+dL pairs remains. Solving this problem will certainly lead to the production of affordable and efficient PAA-based photonic crystals with tunable photonic properties in the NIR-MIR region.

LATERAL PERIODONTAL CYST– A CASE REPORT AND LITERATURE REVIEW

Background: Lateral periodontal cyst (LPC) is a rare example of a developmental odontogenic cyst. LPC may clinically be diagnosed as a radicular cyst, keratocyst, ameloblastoma, odontogenic fibroma, odontogenic myxoma or as other types of odontogenic cysts and tumours. Purpose: The aim is to present an unusual two clinical cases of LPC of the upper and lower jaw. Material and methods: We present two cases with histologically proved LPC. The X-ray revealed radiolucent well-defined, circular in shape homogeneous formation around the root of the affected tooth. Results: The treatment of choice was surgery- enucleation of cyst formation. The complete removal of the cysts was successfully performed. The result of the pathophysiological examination of both cases showed LPC. Since after the operation regular follow up was perform and till now there was not any signs of recurrence. Conclusion: LPC is a rare odontogenic cyst of developmental origin, which should be timely diagnosed and surgically removed.

Determining Pressure Recovery Time for Non-Steady-State Spherical Flow of Viscoplastic Oil in a Homogeneous Formation

The paper solves a non-steady-state hydrodynamic problem concerning a spherical flow of viscoplastic oil in a homogeneous formation. Pressure recovery in the formation occurs in two stages after well operation stops instantaneously. At the first stage the perturbation region appears at the well, expands and eventually reaches the external boundary, and keeps expanding during the second stage until steady-state pressure is reached in every formation region. We solved the differential equations for specific initial and boundary conditions, assuming pressure distribution laws over the formation and respective integral relations, and derived equations to determine pressure recovery time. At each stage pressure in the formation is a function of two variables, that is, a spatial coordinate and time. We assume that the first variable equals zero. We derived an expression for recovering the bottomhole pressure in the wellbore. We used the transient flow method to study the wells, plotted the pressure recovery curve (PRC) and determined formation parameters.

Radial Curvilinear Motion in a Free Flow of Compressible Viscoplastic Oil in a Homogeneous Formation

The paper presents a solution to a steady-state hydrodynamic problem dealing with one-dimensional free-surface radial flow of compressible viscoplastic oil in a horizontal homogeneous circular formation. A vertical producing oil well is located in the centre of the formation, penetrating the pay zone fully, with no well casing or perforation present. We used generalised Darcy's law and equations of state for a compressible fluid to determine mass flow rate of the compressible viscoelastic oil and derive equations for current density, oil flow rate, current pressure distribution in the drainage area, and current pressure gradient. The equations take into account oil compressibility and initial pressure gradient. We also determined the time it takes an oil particle to reach the well starting from the current radius vector and from the external boundary. This is the case when the oil deposit lies close to the earth surface. This depth range features no shale beds or interbedded formations. Since subsurface mining is possible with shallow oil deposits, both wells and tunnels may be used for production.

Influence of W Addition on Microstructure and Mechanical Properties of Al-12%Si Alloys

A widespread method exerting the influence on the homogeneous formation of the microstructure and enhancement of strength properties of Al-Si alloys is a modification by super- and nanodispersed particles of different chemical compositions. In spite of the significant advances in the studies of the influence of various modifying compositions on the structure and mechanical properties of casted silumins, the literature contains no data about the influence of nanodispersed W-powder on formation of the structural-phase state and mechanical properties of Al-Si alloys. The paper considers the influence of 0.01–0.5 mass % W nanopowder on the structural-phase state and mechanical properties of an Al-12%Si alloy. It has been established that 0.1 mass % of W is an optimal addition. It results in the uniform distribution of eutectic (α-Al + Si), a 1.5-time decrease in the size of the plates of eutectic Si, a change of the shape of coarse plates (coarse plate-like or acicular) into a fine fibrous one, and an enhancement of the mechanical properties by 16–20%.

Horizontal Bedding Shale Geostress Calculation Method

Background: Since the fragile anisotropy of shale, it is difficult to carry out laboratory experiments of geostress by shale cores. The existing geostress calculation model that is based on the homogeneous hypothesis also cannot meet the accuracy requirement. Therefore, it is necessary to establish the new geostress calculation model and test methods which are suitable for shale and provide the effective guidance for drilling and fracturing. Methods: Firstly, the triaxial stress experiments were carried out. It showed that the mechanical parameters had strong difference between parallel and vertical bedding direction. The characteristics of transversely isotropic were shown obviously. Then, the geostress calculation model which considers the mechanical parameters of anisotropy in different direction was established by the constitutive relation of transversely isotropic materials. Finally, it was assumed that there is no relative displacement between formations in the process of deposition and the late tectonic movement; the prediction method for the shale geostress was established by the adjacent homogeneous formation. The sensitivity factors and influence laws were analyzed for the horizontal bedding shale geostress. Results: The results showed that the shale geostress was controlled by the elastic parameters of its own and the adjacent beds’. Conclusion: The research can provide the theoretical basis and easy way for calculating the shale geosterss.