Microstructure evolution and mechanical behavior of bulk copper obtained by consolidation of micro- and nanopowders using equal-channel angular extrusion

The consolidation of copper micro- and nanoparticles (325 mesh, 130 nm, and 100 nm) was performed using room-temperature equal-channel angular extrusion (ECAE). The effects of extrusion route, number of passes, and extrusion rate on consolidation performance were evaluated. The evolution of the microstructure and the mechanical behavior of the consolidates were investigated and related to the processing route. Possible deformation mechanisms are proposed and compared to those in ECAE-processed bulk Cu. A combined high ultimate tensile stress (470 MPa) and ductility (∼20 pct tensile fracture strain) with near-elasto-plastic behavior was observed in consolidated 325-mesh Cu powder. On the other hand, early plastic instability took place, leading to a continuous softening in flow stress of bulk ECAE-processed copper. Increases in both strength and ductility were evident with an increasing number of passes in the bulk samples, which appears to be inconsistent with grain-boundary-moderated deformation mechanisms for a microstructure with an average grain size of 300 to 500 nm. Instead, this increase is attributed to microstructural refinement and to dynamic recovery and bimodal grain-size distribution. Near-perfect elastoplasticity in consolidated 325-mesh Cu powder is explained by a combined effect of strain hardening accommodated by large grains in the bimodal structure and softening caused by recovery mechanisms. Compressive strengths as high as 760 MPa were achieved in consolidated 130-nm copper powder. Although premature failure occurred during tensile loading in 130-nm consolidated powder, the fracture strength was still about 730 MPa. The present study shows that ECAE consolidation of nanoparticles opens a new possibility for the study of mechanical behavior of bulk nanocrystalline (NC) materials, as well as offering a new class of bulk materials for practical engineering applications.     

Detwinning in NiTi alloys

This work focuses on the stress-induced transformation in solutionized and overaged single-crystal NiTi alloys. The potential role of detwinning on the recoverable strains was investigated both theoretically and also with temperature-cycling experiments. The detwinning is the growth of one variant within a martensite in expense of the other. It is shown that the experimental recoverable strains in tension (near 8.01 pct in the [123], 9.34 pct in the [111], and 7.8 pct in the [011] orientations) exceed the theoretical martensite (correspondent-variant pair (CVP) formation strains (6.49 pct in [123], 5.9 pct in [111], and 5.41 pct in [011]), lending further support that partial detwinning of martensite has occurred in both the solutionized and overaged specimens. In compression, the experimental recoverable strains are lower than the theoretical martensite (CVP) formation strain. In the compression cases, the detwinning strain contribution is calculated to be negligible in most orientations. The transformation strains observed in overaged NiTi are similar to the solutionalized NiTi, suggesting that incoherent precipitates do not restrict the detwinning of the martensite. For the [123] orientation, it is demonstrated that the thermal hysteresis is higher in solutionized NiTi compared to the overaged NiTi. The higher thermal hysteresis can be exploited in applications involving damping and shape stability, while the lower hysteresis is suited for actuators.     

Tumor-Cut: segmentation of brain tumors on contrast enhanced MR images for radiosurgery applications

In this paper, we present a fast and robust practical tool for segmentation of solid tumors with minimal user interaction to assist clinicians and researchers in radiosurgery planning and assessment of the response to the therapy. Particularly, a cellular automata (CA) based seeded tumor segmentation method on contrast enhanced T1 weighted magnetic resonance (MR) images, which standardizes the volume of interest (VOI) and seed selection, is proposed. First, we establish the connection of the CA-based segmentation to the graph-theoretic methods to show that the iterative CA framework solves the shortest path problem. In that regard, we modify the state transition function of the CA to calculate the exact shortest path solution. Furthermore, a sensitivity parameter is introduced to adapt to the heterogeneous tumor segmentation problem, and an implicit level set surface is evolved on a tumor probability map constructed from CA states to impose spatial smoothness. Sufficient information to initialize the algorithm is gathered from the user simply by a line drawn on the maximum diameter of the tumor, in line with the clinical practice. Furthermore, an algorithm based on CA is presented to differentiate necrotic and enhancing tumor tissue content, which gains importance for a detailed assessment of radiation therapy response. Validation studies on both clinical and synthetic brain tumor datasets demonstrate 80%-90% overlap performance of the proposed algorithm with an emphasis on less sensitivity to seed initialization, robustness with respect to different and heterogeneous tumor types, and its efficiency in terms of computation time.     

Economic analysis of standalone and grid connected hybrid energy systems

A pilot region was selected and cost analysis of using renewable energy sources with a hydrogen system for that region’s energy demand is introduced, in a techno-economic perspective, in this paper. The renewable energy potential for the region was evaluated by implementing energy cost analysis. The study also evaluates the feasibility of utilizing solar and wind energy with hydrogen as a storage unit to meet the electricity requirements of the pilot region as a standalone system and in conjunction with the conventional grid based electricity.In order to simulate the operation of the system and to calculate the technical and economic parameters, micropower optimization program Homer (NREL, US) was used in this study. Homer requires some input values, such as technological options, cost of components, and resource compliance; and then the program ranges the feasible system configurations according to the net present cost (system cost) by using these inputs.The pilot region in this study, where the renewable based energy will be used, is determined to be Electrics & Electronics Faculty, Istanbul Technical University.     

Characterization of O/W model system meat emulsions using shear creep and creep recovery tests based on mechanical simulation models and their correlation with texture profile analysis (TPA) parameters

The effects of different oil and temperature levels on the viscoelastic behavior of O/W model system meat emulsions were assessed using creep and creep recovery tests. The viscoelastic behavior of such emulsions was characterized using the Burgers model parameters. In addition, texture profile analysis (TPA) of cooked meat emulsions was carried out to find a possible relationship between the creep and creep recovery data and TPA parameters. The final percentage recovery of the emulsions remarkably increased with oil content, but decreased with temperature level. Significant correlations among the creep-recovery data and TPA parameters were observed, this enabling meat processor to predict TPA parameters by resorting to shorter and less material consuming creep and creep recovery tests.     

Estimated environmental loads of alpha-amylase from transgenic high-amylase maize

Environmental exposure of plants bioengineered to improve efficiencies of biofuel production is an important consideration for their adoption. High-amylase maize genetically engineered to produce thermostable alpha-amylase in seed endosperm is currently in development, and its successful adoption will entail >1000 km² of annual production in the USA. Environmental exposure of thermostable amylase will occur in production fields from preharvest and harvest dropped grain, with minor additional contributions from stover and root biomass. Mass loadings of thermostable alpha-amylase are projected to be 16 kg km⁻² and represent a potential source of increased alpha-amylase activity in receiving soils. An understanding of the degradation, persistence, accumulation, and activity of thermostable alpha-amylase introduced from transgenic high-amylase maize will be necessary in order to effectively manage transgenic crop systems intended or biofeedstock production.     

Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging

For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse echo operation, the average - 6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 mPa/pHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.