Underpinning and benchmarking multi-scale models with micro- and nanoscale experiments

Predictive models of materials behavior depend on: accurate databases of constitutive material properties, identification of underlying deformation mechanisms, and the availability of experimentally measured benchmarks with which to compare. Micro- and nano-scale experiments can be used to facilitate collection of salient mechanical properties of individual phases at appropriate temperatures, chemistries and microstructural states. Coupling with TEM observations allows one to identify underlying deformation mechanisms and to imbibe models with the requisite fundamental physics and materials science. Simulations must be benchmarked with experiments, conducted at scale with relevant material volumes and identifiable microstructures. This presentation will outline efforts to characterize the constitutive behavior of materials, to identify deformation mechanisms, and to benchmark crystal plasticity simulations at appropriate length scales. Micro-scale experiments designed and conducted to complement crystal plasticity modeling of two different microstructural variants of Ni-base superalloys, polycrystalline Rene 88 and directionally solidified GTE 444, will be presented. If size-scale effect can be avoided, constitutive (single-crystalline) data may be obtained with micro-tensile tests at various orientations and temperatures. Moreover, preparing and testing specimens with reduced volumes and a finite number of grains allows for direct comparison with crystal plasticity simulations of stress-strain behavior as well as strain localization. With regard to the latter, digital image correlation (DIC) of spatially resolved surface displacements produces strain maps that provide a much more rigorous benchmark for crystal plasticity predictions than stress-strain curves. Using directionally solidified specimens allows for 2.5D microstructures (grains that extend through the thickness of the specimen) and greatly simplifies such comparisons. Moving beyond uniaxial tension, micro-bending resonance fatigue experiments provide an opportunity to measure the number of cycles, location, and microstructural features associated with slip, intragranular crack formation, and eventual transgranular crack growth. These experimental measures can in turn be used to inform and benchmark multi-scale fatigue simulations. Similarly, strain-controlled fracture experiments involving 2.5D unidirectional polymer matrix composites (PMC) have been developed and are being used to identify the microstructural features and fracture paths that govern delamination and fracture. The availability of orientation mapping techniques (EBSD, PACOM, TKD) now allows for nano-scale characterization of underlying deformation mechanisms and their relation to crystallographic microstructures and surrounding neighborhoods. Studies investigating the role of grain growth, twinning and dislocation plasticity will be presented. Special attention will be placed on attempts to measure intragranular strains that can be related to the accumulation of geometrically necessary dislocations (GNDs) and compared with crystal plasticity simulations. Support for these projects has been provided through the AFOSR and AFRL funded Center of Excellence on Integrated Materials Modeling and the DOE office of Basic Energy Sciences

Triple Band Textile Array Antenna with Enhanced Gain and Low SAR for Off Body Communication Applications

A triple band wearable microstrip patch antenna array has been designed and analyzed in this work. The designed antenna can be operated in ISM, LAES and X-Band with moderate average gain of 4.2 dB. The antenna gain has been improved by constructing array structure of 1X2 and 1X4 with good impedance feeding by quarter wave transformer. The proposed array antennas are providing moderate gain of 5.7 dB (1X2) and 8.3 dB (1X4) with efficiency more than 90% in the operating bands. The antenna model and the array has been constructed on wearable substrate with conductive textile as radiating element in the design for off body wearable communication applications. SAR analysis also providing acceptable values below 1.6 w/kg at triple operating bands with body placement experimentation. &nbsp

Clinical Profile and Outcome of Conservatively Managed Emphysematous Pyelonephritis

Emphysematous pyelonephritis (EPN) is a severe, necrotizing renal parenchymal infection characterized by production of intraparenchymal gas. EPN predominantly affects female diabetics and immunocompromised patients. In a three-year period 2008–2011, a total of 8 patients were admitted to our hospital. All of them were diabetics, and both males and females were equally affected. These patients showed vague symptoms at admission and frequently presented with fever, loin pain, dysuria, and pyuria necessitating urgent medical attention. EPN required radiological diagnosis. CT scan revealed bilateral EPN with urinary obstruction and hydronephrosis in 50% of patients. Escherichia coli was found to be the causative organism in all the patients. Treatment comprised of resuscitation, normalization of serum electrolytes and blood sugars, administration of parenteral antibiotics, and relieving ureteric obstruction if present. All the patients improved with conservative management without any mortality

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Our Letter reported high-resolution transmission electron microscopy on commercial quality boron showing that ∼2=3 of the grains exhibit smooth microstructure, leading to an x-ray diffraction pattern of well-known beta boron [1]. The other 1=3 grains exhibit a uniform zigzag pattern that extends across the entire grain and exhibits a very regular twinlike symmetry on every other lattice plane. This second phase gives diffraction patterns that are different from beta

New Ground-State Crystal Structure of Elemental Boron

Elemental boron exhibits many polymorphs in nature based mostly on an icosahedral shell motif, involving stabilization of 13 strong multicenter intraicosahedral bonds. It is commonly accepted that the most thermodynamic stable structure of elemental boron at atmospheric pressure is the β rhombohedral boron (β−B). Surprisingly, using high-resolution transmission electron microscopy, we found that pure boron powder contains grains of two different types, the previously identified β−B containing a number of randomly spaced twins and what appears to be a fully transformed twinlike structure. This fully transformed structure, denoted here as τ−B, is based on the Cmcm orthorhombic space group. Quantum mechanics predicts that the newly identified τ−B structure is 13.8  meV/B more stable than β−B. The τ−B structure allows 6% more charge transfer from B_(57) units to nearby B_(12) units, making the net charge 6% closer to the ideal expected from Wade’s rules. Thus, we predict the τ−B structure to be the ground state structure for elemental boron at atmospheric pressure

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Coplanar Wave Guide Fed Dual Band Notched MIMO Antenna

A coplanar wave guide fed of semicircle monopole antenna is designed in this work to overcome polarization diversity mimo technique is implemented in this paper. The proposed antenna is designed to notch a particular band of frequencies in UWB range. The designed model is notching the first band from 2 to 5 GHz & the second band from 7 to 11 GHz. The proposed antenna has been fabricated on FR4 substrate with di electric constant 4.4 & tested for its reliability on ZNB20 vector network analyzer. The operating bands will come under WLAN, KU band, satellite communication applications. A peak realized gain of 4.3 dB with radiation efficiency 90% is attained at the operating bands of the designed antenna. At notch band significant gain reduction is observed from the current design. The antenna is showing omnidirectional radiation pattern in the pass band & disturbed radiation pattern in the notch band. Antenna is fabricated with dimensions of 40x68x1.6 mm & simulation works are carried with finite element method based HFSS tool

Nucleation of amorphous shear bands at nanotwins in boron suboxide

The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B_6O) with twin boundaries along the {0111} planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B_6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B_6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B_6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics