Cylindrical Sheath Research Articles

A multi-layer nanocased model to explain the U-shaped evolution of shale gas permeability at constant confining pressure

Understanding the evolution of shale permeability is critical in efficiently recovering gas from shale reservoirs. Two representative profiles of permeability evolution are typically experimentally observed under constant confining pressure and incremented gas pressure – “U-shape” with increasing gas pressure but sometimes absent the second upright limb of the “U” at high gas pressures. Current models fail to address these two different profiles, potentially leading to inappropriate explanation of experiment observations or inaccurate predictions of gas production. In order to determine the mechanistic reason, a multi-layer nanocased model, in which transmissive nanotubes are embedded within a cylindrical sheath of matrix, is proposed. In the model, permeability evolution is defined as a function of the evolving nanotube radius within a total matrix radius. The ensemble structure governs the transition from local deformation of the nanotube wall to the global deformation of the matrix sheath, particularly as sorbing/swelling gas gradually permeates the sheath wall. The finite element method is employed to calculate permeability evolution from an initial equilibrium state to final equilibrium. We develop a series of permeability evolution curves that match various experimental profiles. Contrasting observed permeability responses are attributed to the competition between nanotube strain and matrix global strain. The former term enlarges the nanotube radius while the latter term swells the matrix declining the permeability value. Therefore, when the matrix global strain dominates at late time, permeability decreases. Conversely, a permeability recovery stage is barely observed in the late stage because in most cases global swelling dominates the permeability evolution and an extended observational period is necessary before this swelling appears. This is also the reason why the observed final permeability ratio is rarely greater than unity. A small nanotube radius or a large adsorption strain favors a significant decrease in permeability. When the nanotubes are located within the inorganic matrix, the permeability profile conforms to poro-elastic theory and the decreasing permeability stage is barely apparent or absent. The proposed model thus provides insight into the controls on permeability evolution in shales and the controlling impact of shale matrix properties by considering the inhomogeneities of the shale matrix.

Development of method for calculation of pre-strained steel cylindrical sheaths in view of the winding angle, pitch and thickness

This paper sets out the findings of an investigation on the development of a method for calculating aboveground pre-strained cylindrical sheaths, in view of design parameters: the winding angle, pitch and thickness on a concrete base, as a result of which a new expression was obtained. The analysis of the obtained expression showed that the winding thickness variation from 4 mm to 6 mm at the angle of helix of 90º, the value of the strained state parameter (k) varies from 1.3 % to 4.64 %, similar increases in the value of k were obtained with an increase in thickness and at angles of helix of 60º and 75º, where the value of k increased by 0.94–3.82 % and 1.12–4.56 %, respectively. The findings also showed that as the winding thickness increases, the value of k increases independently at different winding angles and pitches. A similar analysis was performed with a variation in the pitch, but with respect to the winding thickness and angle, where the value of k also varies in terms of the winding pitch ranging from 2.61 % to 18.59 % depending on the specific case, and the analysis of the angle of helix showed a variation in the value of k ranging from 0.37 % to 5.24 %. The findings of the variant analysis showed the practicality of the expression obtained, which affords ground for obtaining the required value of the strained state parameter for a particular specific case without carrying out lengthy calculations, which may explicitly supplement the investigations formerly pursued in this course.

Amarillis Pompei: The Napatan Cylindrical Sheaths. A Catalogue and Analysis of Precious Objects from the Royal Cemetery of Nuri

Amarillis Pompei: The Napatan Cylindrical Sheaths. A Catalogue and Analysis of Precious Objects from the Royal Cemetery of Nuri

Plasma-Surface Interactions Within Helicon Plasma Sources

Helicon plasma sources do not require electrodes or grids directly immersed in the plasma, and also present an axial magnetic field confining the plasma discharge. These factors are believed to provide them with long operational lifetimes because of the reduced potential for surface etching. The physics of helicon waves, cylindrical magnetized plasmas, sheaths, and plasma-surface interactions are discussed in the context of this claim. Practical implementation aspects are also reviewed, along with relevant experimental results. It is shown that understanding the distribution of ion density within the source, the presence of induced potentials in its surfaces, and the physics of low-energy sputtering reactions is essential to properly model erosion phenomena within helicons, and consequently predict their performance in practical applications.

Breakup of a liquid column jet in a surrounding gas flowing through a coaxial cylindrical sheath

Breakup of a liquid column jet in a surrounding gas flowing through a coaxial cylindrical sheath

Influence of secondary electron emission on plasma-surface interactions in the low earth orbit environment

The low earth orbit plasma experienced by exposed interconnect-dielectric junctions commonly found on spacecraft solar panel surfaces was modeled using a fully kinetic particle-in-cell (PIC) simulation of both ambient ions and electrons. From time-accurate simulations we observed that the plasma sheath had a formation time somewhere between the ion and electron time scales of 17 μs and 30 ps, respectively and electron and ion velocity distribution functions were observed to be highly non-Maxwellian. Comparison of the electron plasma sheath thickness with analytic cylindrical sheath models gave reasonable agreement if the embedded biased interconnect voltage was sufficiently high to cause the dielectric surface to act as a free electron flowing medium. Finally, it was found from the fully kinetic PIC simulations that the fundamental mechanism behind parasitic current is closely related to electron avalanche and the fraction of SEE emitted from different avalanche levels as well as the current collected at the interconnect could be modeled by a power law series for avalanche levels greater than two.

Chapter 3 Thrusts, extensional faults and fold patterns of the major units

Abstract This chapter is concerned with the main faults and folds within the Southeastern Oman Mountains based on available literature. The main, best and most widely exposed thrusts are those related to the SW-directed late Cretaceous obduction of the allochthonous nappes onto the Arabian platform and margin. These thrusts are related to obduction of rocks, which had formed hundreds of kilometres offshore Oman. The thrusts were active from the Cenomanian to the Campanian. Obduction-related thrusts and folds are spectacularly exposed within the rocks of the Arabian platform in the eastern part of the Saih Hatat Dome, including large-scale recumbent cylindrical folds and sheath folds. At least six fold sets can be studied in the Southeastern Oman Mountains. At least two of them had formed prior to obduction and are exposed in the Pre-Permian formations of the Jabal Akhdar Dome. At least three fold sets formed in the course of obduction, while at least one fold set is postobductional in age. Besides the compressional structures, the Oman Mountains expose major post-obductional extensional faults, mostly at the margins of the Jabal Akhdar and Saih Hatat domes. The throw of these faults amounts to a few to several kilometres. Finally, this chapter provides an overview of the enigmatic Batinah Mélange which consists of slivers of Hawasina rocks, resting (unusually) structurally above the Semail Ophiolite.

Instabilities of a liquid column jet in a surrounding gas flowing through a coaxial cylindrical sheath

In this paper, instabilities and breakup phenomena of a viscous liquid column jet in an inviscid stationary surrounding gas are analytically investigated, when the jet flows through a coaxial cylindrical sheath. Under a long wave approximation, axisymmetric non-linear evolution equations of the jet and surrounding gas are derived and numerically solved under a spatially periodic boundary condition. Validity and limitation of the approximation are examined in the linear regime in comparison with exact three-dimensional instabilities. It is shown in the non-linear analysis that there exist three types of breakup modes: the Rayleigh mode in which the surface tension instability is dominant and the breakup is caused by pinching, the first wind-induced mode in which blobs connected by threads are produced by increased aerodynamic instability and the second wind-induced mode in which the jet surface deforms to be spiked like a cusp without pinching and droplets are to be produced from a tip of the cusp. The existing regions of these modes are examined in the parameter space of the Weber number and the sheath radius for different Reynolds numbers and density ratios.

Retrofitting Steel Moment Frames by Using the Cable Bracing

In this paper, the behavior of retrofitted steel moment frames with bracing has been investigated. Braces include double-channel cross brace, cross braces with cable and brace with two cables passed through a cylindrical steel sheath at the location of the cables. Nonlinear analysis of frames has been carried out under cyclic loading with increasing amplitudes. Comparison of numerical analysis results with laboratory data shows the accuracy of finite element models. By determining the hysteresis and plasticity behavior of the frames, advantages and disadvantages of each of the retrofitting methods have been examined. The results have shown the use of double channels and cables to retrofit the frame increases the initial hardness and final load of the frame considerably compared to the moment frames and reduces its ductility. In frame with sheathed cable brace, the initial hardness was the same with the moment frames and the frame has been shown to have ductile behavior.

Inferring plasma parameters from the sheath characteristics of a dc biased hairpin probe

In this paper, the cylindrical sheath around a hairpin resonator probe has been varied by applying a dc potential to the hairpin to infer different plasma parameters in an argon and oxygen discharge. As the sheath width increases due to negative bias, the resonance frequency of the hairpin correspondingly shifts toward a lower value. An analytical model based on fluid approximation has been developed to estimate the sheath width variation as a function of the applied voltage on the probe. The analytical result is then compared with the well-known capacitance model that assumes a conjugate dielectric region around the hairpin consisting of a pair of cylindrical sheaths and the plasma. Using this method, a wide range of plasma parameters, including the electron temperature plasma potential and electronegativity parameter , have been obtained in an electronegative oxygen discharge. The advantage of this method over the conventional floating hairpin resonator probe has been qualitatively discussed.

Retrofitting steel moment frames by using the cable bracing

In this paper, the behavior of retrofitted steel moment frames with bracing has been investigated. Braces include double-channel cross brace, cross braces with cable and brace with two cables passed through a cylindrical steel sheath at the location of the cables. Nonlinear analysis of frames has been carried out under cyclic loading with increasing amplitudes. Comparison of numerical analysis results with laboratory data shows the accuracy of finite element models. By determining the hysteresis and plasticity behavior of the frames, advantages and disadvantages of each of the retrofitting methods have been examined. The results have shown the use of double channels and cables to retrofit the frame increases the initial hardness and final load of the frame considerably compared to the moment frames and reduces its ductility. In frame with sheathed cable brace, the initial hardness was the same with the moment frames and the frame has been shown to have ductile behavior.

Comparative multi-scale analysis of filamentous microfossils from the c. 850 Ma Bitter Springs Group and filaments from the c. 3460 Ma Apex chert

Filamentous microfossils belonging to Cephalophytarion from the 850 Ma Bitter Springs Group have previously been used as key analogues in support of a biological interpretation for filamentous objects from the 3460 Ma Apex chert. Here we provide a new perspective on this interpretation by combining Raman data with correlative electron microscopy data from both Cephalophytarion and Apex specimens. We show that, when analysed at high spatial resolution, the Apex filaments bear no morphological resemblance to the younger Bitter Springs microfossils. Cephalophytarion filaments are shown to be cylindrical, comprising chains of box-like cells of approximately constant dimensions with lateral kerogenous walls and transverse kerogenous septa. They exhibit taphonomic shrinkage and folding, possess fine cylindrical sheaths and are permineralized by sub-micrometric quartz grains. They fulfil all established biogenicity criteria for trichomic microfossils. In contrast, Apex filaments do not possess lateral cell walls, are not cylindrical in nature, and vary considerably in diameter along their length. Their kerogenous carbon does not have a cell-like distribution and their chemistry is consistent with an origin as exfoliated phyllosilicate grains. This work demonstrates the importance of high-resolution data when interpreting the microstructure, and origins, of putative Precambrian microfossils.

Role of sheath dynamics in multiple double layer formations in expanding RF plasma

Potential double layers are observed to form as nested cylindrical sheaths that energize charge particles in the absence of any externally applied magnetic field. These visibly glowing nested cylindrical sheaths are named as “Fire Tube” in the present work. Sheaths, in unmagnetized collisionless plasmas, have been observed to be functional in generating energetic charge particles. Two characteristically different plasma sources are compared in terms of the dependence of potential and density profiles on the plasma sheath formations near the source boundary. The sheath structures, complex fire tube formation, and space charge formations demarcate the two sources in terms of complex structure formations and motion of the charge particles. We present here the characteristic study of high pressure collisional boundary sheath formations through systematic experiments carried out during the transition from unmagnetized to magnetized charge particles, in the case of two different plasma sources designed. The cylindrical ambient plasma sheaths are observed to energize the charge particles, in the absence of any external magnetic field. The fire tube formations essentially represent a non-neutral region located radially away from the plasma source boundary, connecting the ion sheath with the electron sheath. The probe diagnostic results suggest a significant role of energetic electrons in the formation of multiple double layer structures in the present operational regime. Generation of nonthermal electrons during the formation of MDL in radio frequency capacitive discharges is subjected to interactions of the plasma with the electrodes as well as the confining wall material.

Nits and pseudonits in Indian children: A dermoscopic perspective

Background: Hair casts or pseudonits are tubular accretions that are movable encircling the hair shafts of the scalp. It is commonly confused as head lice or pediculosis capitis, which is a common concern in pediatric age group. Hair casts are common in psoriasis, seborrheic dermatitis, and pityriasis amiantacea. This misdiagnosis is a reason of patient and physician anxiety. We attempted to evaluate significance of trichoscopy in differentiating nits and pseudonits and therefore a better treatment plan. Aims and Objective: To evaluate trichoscopic patterns in nits and pseudonits. Methodology: The study was conducted in a tertiary hospital. Ethical clearance and consent from patients were obtained. DermLite 3 with ×10 magnification was employed for trichoscopy. Tiny concretions on the hair shafts were examined with trichoscopy. Patterns were analyzed. Results: Totally, 25 patients were included in the study with 7 boys and 18 girls. The mean age was 9 years. Trichoscopy demonstrated cylindrical white sheaths (2–7 mm) encircling the hair shafts in 15 patients (60%). Forty percent of the patients showed pyriform-shaped translucent and yellowish structures (0.8 mm) attached to hair shafts. Based on the trichoscopy patterns, diagnosis of pseudonits and nits was made in former and latter groups, respectively. Conclusion: Trichoscopy plays an important role in differentiation of nits and pseudonits. Since nits are contagious, correct diagnosis is of utmost importance for better management. Thus, trichoscopy is a reliable diagnostic procedure in daily practice of dermatologists.

Morphological-molecular characterization and phylogenetic relationships of a new Trichuris species (Nematoda: Trichuridae) parasitic on Holochilus chacarius (Cricetidae: Sigmodontinae) from the Chaco ecoregion (Argentina)

A new Trichuris species isolated from Holochilus chacarius (Cricetidae: Sigmodontinae) from the Chaco ecoregion in Argentina is described based on morphological characteristics and mitochondrial (cox1, cob) and nuclear (ITS2) markers. The new species is distinguished from 27 species of Trichuris from North and South American rodents based on morphological and biometrical features, such as the absence of a spicular tube, presence of a cylindrical spicular sheath, non-protrusive vulva, length of spicule, and proximal and distal cloacal tube. In addition, the results based on three molecular markers of the new species and three Trichuris species previously analysed from sigmodontine rodents: Trichuris pardinasi, Trichuris navonae and Trichuris bainae confirmed that the specimens here studied belong to a different species. Molecular data are further used to discuss the phylogenetic relationships among the Trichuris species of rodents from Argentina. The combined analysis of mitochondrial genes (cox1 and cob) revealed four clades corresponding with four different species of Trichuris. T. navonae (Akodontini rodents) and T. massoiai n. sp. as a sister group related to T. bainae (Oryzomyini rodents) and separated of T. pardinasi (Phyllotini rodents).

Technology of Producing the Contact Connections of Superconductor Metal-Sheathed Cable

Abstract The technology of producing the current contact connections on the superconductor cable edges is presented. This lead cable is used as one of the major elements of the magnetic system in thermonuclear reactor construction, actuality for modern world energy. The technology is realized by the radial draft of metal thin-walled tube on the conductor’s package. The filling of various profiles by round section wire is optimized. Geometrical characteristics of the dangerous crosssection (as a broken ring) of thin-walled tube injured by the sector cut-out are accounted. The comparative strength calculation of the solid and injured tubes at a longitudinal compression and lateral bending is acted. The radial draft mechanism of cylindrical thin-walled sheath with the wire packing is designed. The necessity to use the nonlinear theory for the sheaths calculate is set. The resilient co-operation of wires as the parallel located cylinders with the contact stripes of rectangular form is considered.

New Approach for Airflow Measurement Using Thermal Resistance Simulation

<p>This paper presents a new model-based approach to detect and compensate errors of positive temperature coefficient (PTC) sensors used for airflow measurement. From modeling and simulation, it can be shown that the thermal resistance of the sensor at self-heating mode was influenced by air flow magnitude. The sensor of type EPCOS-AG B59010 in a steel case, length 20 mm, diameter 2 mm was characterised over the flow rate range between 0 and 6 m/s and modeled to determine coupling thermal resistance interaction R<sub>th</sub> between the medium surrounding and sensor’s structure. Soiling caused by dust transported with the air on the sensor surface changing in the thermal resistance has observed and simulated in an experiment using a cylindrical sheath of PTFE – <em>Polytetrafluorethylen</em> with known heat conductivity λ<sub>S</sub> = 0.24 W/Km and diameter D. Parameters of model were then calibrated by evaluating current-voltage I(U)-characteristic at air velocity of v = 0m/s, and recalibration is then also used to correct the model parameters for v ¹ 0m/s. Result shows the soiling has exceeded critical thickness at D/d = 9 wherein the thermal resistance tends to be constant meaning cleaning sensor surface or replacing are needed.</p>

New Approach for Airflow Measurement Using Thermal Resistance Simulation

<p>This paper presents a new model-based approach to detect and compensate errors of positive temperature coefficient (PTC) sensors used for airflow measurement. From modeling and simulation, it can be shown that the thermal resistance of the sensor at self-heating mode was influenced by air flow magnitude. The sensor of type EPCOS-AG B59010 in a steel case, length 20 mm, diameter 2 mm was characterised over the flow rate range between 0 and 6 m/s and modeled to determine coupling thermal resistance interaction R<sub>th</sub> between the medium surrounding and sensor’s structure. Soiling caused by dust transported with the air on the sensor surface changing in the thermal resistance has observed and simulated in an experiment using a cylindrical sheath of PTFE – <em>Polytetrafluorethylen</em> with known heat conductivity λ<sub>S</sub> = 0.24 W/Km and diameter D. Parameters of model were then calibrated by evaluating current-voltage I(U)-characteristic at air velocity of v = 0m/s, and recalibration is then also used to correct the model parameters for v ¹ 0m/s. Result shows the soiling has exceeded critical thickness at D/d = 9 wherein the thermal resistance tends to be constant meaning cleaning sensor surface or replacing are needed.</p>

A new species of Trichuris Roederer, 1761 (Nematoda: Trichuridae) from Heteromys gaumeri Allen & Chapman (Rodentia: Heteromyidae) in Yucatan, Mexico.

In Mexico, four species of Trichuris Roederer, 1761 have been recorded in wild rodents belonging to the family Heteromyidae. In the present paper, we describe a new species based on specimens collected from Heteromys gaumeri Allen & Chapman (Heteromyidae: Heteromyinae) in the tropical forests of the Yucatan Peninsula, Mexico. Trichuris silviae n. sp. can be differentiated from the congeners described in North and South American rodents by morphological and morphometric features, such as the possession of a wide spicular tube, a thicker proximal cloacal tube, a shorter distal cloacal tube and a cylindrical spicular sheath. This is the first description of a Trichuris spp. from heteromyid rodents in Mexico and the fourth in North America. Despite the broad distribution of Heteromys spp., few cases of Trichuris infection have been reported. Further studies are necessary to verify if the new species is present in other heteromyid rodents in order to increase our knowledge about its geographical and host distribution.

Study of heat conduction through a self-heated composite cylinder by Laplace transfer functions

A study of heat conduction through a composite cylinder showing large differences in scale is presented. The system consists of a thin electrically conductive sensing layer, subjected to Joule self-heating and placed in thermal contact with an inner core and an outer concentric cylindrical sheath. The formalism of Laplace transfer functions is used to relate the operating temperature of the sensing layer to the unknown outermost temperature, to the Joule self-heating and to the thermal contact resistances. Analytical expressions for the overheating temperatures are deduced from these transfer functions. Digital filters are derived from the Laplace transfer functions by using Padé approximants and a bilinear transformation. The real-time direct and inverse heat conduction problems are solved without resorting to Laplace inversion, but rather by using the recursion relations associated with the Padé digital filters. This method allows one to easily solve the problems of heat conduction through a self-heated composite cylinder, even in the nonlinear case of a temperature dependent source term. This approach could be applied to optimize and accurately describe the operation of commonly used wire-wound resistance temperature detectors.