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Selection of failure criteria for estimation of safe mud weights in a tight gas sand reservoir
No full textIn an undisturbed state, a stress field present in the earth consists of virgin stress in the rock. A change in this stress occurs due to drilling the borehole and disturbing the original stress by either introducing drilling fluids or by getting reservoir flow in the borehole. This change in stress leads to a classical problem of well bore instability. To resolve wellbore instability, evaluation of rock mechanical properties and in-situ stresses is essential. The output of this study is evaluation of safe mud weights which is critical to safe drilling. If the mud weight used for drilling is higher than those predicted by the failure criteria, the mud percolates into the formation, causing tensile failure (fracture stress) which induces fluid losses. Conversely, the lower mud weight results in shear failure (collapse stress) of rock leading to borehole breakout and collapse of wellbore. Three types of failure criteria i.e. Mohr-Coulomb, Mogi-Coulomb and Modified Lade are considered in this study. The stress around the wellbore is obtained using Kirsch equation. The input parameters required for estimating the safe mud weights from these failure criteria are rock mechanical properties, friction angle and cohesion which are estimated from well log data. The rock mechanical properties like Poisson's ratio and Uniaxial Compressive Strength are computed using sonic derived compressional and shear velocities. Internal friction angle is obtained using gamma ray log and is validated with core data before it is used in further analysis. The failure criteria have been applied to two wells located in a field in Gulf of Oman. The analyses show that the Mohr-Coulomb overestimates the mud weight while the Modified Lade criterion underestimates it. The result for a tight gas sand reservoir suggests that the Mogi-Coulomb predicts better mud weight values that are in agreement to those measured values chosen for drilling
Investigation of Superparamagnetism in Microwave and Conventional Processed Mn0.5Zn0.5Fe2O4 Nanoparticles
No full textNanoparticles of spinel cubic Mn0.5Zn0.5Fe2O4 are first prepared by the coprecipitation method and then subjected to conventional solid-state sintering and microwave processing techniques. Particle sizes are estimated by field emission scanning electron microscopy (FESEM) to be in the nanometer (5-13 nm) range. Transmission electron microscopy (TEM) also supports the FESEM data. The magnetization measurement by vibration sample magnetometry of the conventionally sintered sample shows a paramagnetic nature at room temperature, a superparamagnetic behaviour at low temperature, and a ferromagnetic nature at even lower temperature. The blocking temperature is estimated to be nearly 110 K. Microwave-processed samples show a superparamagnetic nature even at room temperature. The Fe3+ cations are found at both the sites confirmed by X-ray photoelectron spectroscopy (XPS), are prepared by microwave processing, and have better magnetic properties as compared to the conventionally sintered particles
Output Tracking of Nonminimum-Phase Systems via Reduced-Order Sliding-Mode Design
No full textIn this paper, a method to design the reduced-order sliding-mode control is proposed for the robust output tracking of an arbitrary signal for nonminimum-phase systems. The main contributions in this paper include the design of the reduced-order switching function that ensures the asymptotic tracking of an arbitrary reference signal during sliding motion, the design of the reduced-order sliding-mode controller that enforces the sliding motion in finite time, and the computation of bounds on stable and virtually stable zero dynamics that is required for the output tracking. To show the effectiveness of the proposed design method, results of implementation on the experimental setup of an inverted pendulum system are also presented here
Effect of initial texture on deformation-induced grain growth in pulsed electrodeposited microcrystalline copper
No full textOwing to the presence of large fraction of grain boundaries, deformation-induced grain growth is commonly observed in fine-grained electrodeposited metals. Here we demonstrate that microcrystalline copper (d similar to 1-10 mu m) with different textures produced by electrodeposition exhibit significant deformation-induced grain growth in tension by coalescence along with twin boundary migration and detwinning. Oriented growth with the formation of a cube texture was noted in the deformed samples. There was an increased fraction of twin boundaries with large angular deviation from Brandon's criterion during deformation
Wigner distributions for gluons
No full textWe investigate the gluon Wigner distributions for unpolarized, longitudinally polarized and transversely polarized target state. Instead of a nucleon, we take the target state to be a quark dressed with a gluon at one loop and investigate the gluon Wigner distributions at leading twist. Better numerical convergence is obtained compared to an earlier study, that removes the regulator dependence of the results. We present a first calculation of the Wigner distribution for the transversely polarized target and linearly polarized gluon. We study the spin densities in momentum and impact parameter space. We also investigate the quark and gluon helicity and orbital angular momentum distributions at small-x
An On-Chip Trainable and the Clock-Less Spiking Neural Network With 1R Memristive Synapses
No full textSpiking neural networks (SNNs) are being explored in an attempt to mimic brain's capability to learn and recognize at low power. Crossbar architecture with highly scalable resistive RAM or RRAM array serving as synaptic weights and neuronal drivers in the periphery is an attractive option for the SNN. Recognition (akin to "reading" the synaptic weight) requires small amplitude bias applied across the RRAM to minimize conductance change. Learning (akin to "writing" or updating the synaptic weight) requires large amplitude bias pulses to produce a conductance change. The contradictory bias amplitude requirement to perform reading and writing simultaneously and asynchronously, akin to biology, is a major challenge. Solutions suggested in the literature rely on time-division-multiplexing of read and write operations based on clocks, or approximations ignoring the reading when coincidental with writing. In this paper, we overcome this challenge and present a clock-less approach wherein reading and writing are performed in different frequency domains. This enables learning and recognition simultaneously on an SNN. We validate our scheme in SPICE circuit simulator by translating a two-layered feed-forward Iris classifying SNN to demonstrate software-equivalent performance. The system performance is not adversely affected by a voltage dependence of conductance in realistic RRAMs, despite departing from linearity. Overall, our approach enables direct implementation of biological SNN algorithms in hardware
Modeling of gate bias controlled NO2 response of the PCDTBT based organic field effect transistor
No full textOrganic field effect transistors consisting of Poly [N-9'-heptadecanyl-2, 7-carbazole-alt-5, 5-(4', 7'-di-2-thienyl- 2', 1', 3'-benzothiadiazole] (PCDTBT) as active layer have been fabricated for detection of gases. The device exhibited highly selective response towards parts-per-million level of NO2 gas. For these devices response towards NO2 decreases with increasing gate bias due to the existing high density of free charges. A model has been developed to explain this variation of response with gate bias using transfer characteristics of the device (in air). This model enables to determine the density of holes released in PCDTBT layer on interaction with NO2 gas. (C) 2018 Published by Elsevier B.V
Rheology of dense granular flows in two dimensions: Comparison of fully two-dimensional flows to unidirectional shear flow
No full textWe consider the rheology of steady two-dimensional granular flows, in different geometries, using discrete element method-based simulations of soft spheres. The flow classification parameter (psi), which defines the local flow type (ranging from pure rotation to simple shear to pure extension), varies spatially, to a significant extent, in the flows. We find that the material behaves as a generalized Newtonian fluid. The mu-I scaling proposed by Jop et al. [Nature (London) 441, 727 (2006)] is found to be valid in both two-dimensional and unidirectional flows, as observed in previous studies; however, the data for each flow geometry fall on a different curve. The results for the two-dimensional silo flow indicate that the viscosity does not depend directly on the flow type parameter, psi. We find that the scaling based on "granular fluidity" [Zhang and Kamrin, Phys. Rev. Lett. 118, 058001 (2017)] gives good collapse of the data to a single curve for all the geometries. The data for the variation of the solid faction with inertial number show a reasonable collapse for the different geometries
Abnormal Addition of NHC to a Conjugate Acid of CAAC: Formation of N-Alkyl-Substituted CAAC
No full textThe addition reactions of N-heterocyclic carbenes (NHCs) are mostly known to occur through the carbenic centre (C2), which leads to a "normal" adduct. Herein, we report the abnormal addition of NHCDip 1 (1,3-(2,6-iPr(2)C(6)H(3))-imidazole-2-ylidene) to a conjugate acid of cyclic (alkyl)(amino)carbene 2 (CAAC(iPr)=1-iPr-3,3,5,5-Me-4-pyrrolinium triflate). Mechanistic study revealed that this reaction proceeded through the in situ formation of 1,3-(2,6-iPr(2)C(6)H(3))-imidazolium cation 4 and N-iPr-substituted CAAC 5 followed by the oxidative addition of compound 5 across the C4-H bond (alias backbone C-H) of compound 4. The in situ formation of compound 5 was also proven by the oxidative addition of it to the N-H group of iPrNH(2). DFT calculations also supported the mechanistic findings. A different methodology for the in situ generation of compound 5 by using TMPLi is also described
Effect of Reinforced Cutouts and Ply-Orientations on Buckling Behavior of Composite Panels Subjected to Non-Uniform Edge Loads
No full textBuckling loads of laminated panels calculated by analytical approaches are usually based on the assumptions that the panels are subjected to uniform in-plane edge loads without cutouts, despite of the fact that real structural components are subjected to various kinds of non-uniform in-plane edge loads along with different sized cutouts. The main objective of this paper is to study the effects of reinforced/unreinforced circular cutouts and non-uniform in-plane edge loads on the buckling behavior of composite panels with different ply-orientations by the finite element technique. Furthermore, it addresses the effects of different boundary conditions and thickness of panels. To carry out the analyses, a nine-noded heterosis plate element and a compatible three-noded beam element are developed, including the effect of shear deformation and rotary inertia for both the plate and the stiffeners. In structural modeling, the plate and the stiffener elements are treated separately, with their displacement compatibility maintained using transformation matrices. It has been illustrated in this study that presence of larger-sized reinforced cutouts predominantly increases the buckling strength of the panel as compared to those with smaller sized cutouts