Effect of Ti and Ta on the oxidation of a complex superalloy

The oxidation behaviors of a series of directionally solidified Ni-base superalloys were studied at 1000 and 1100°C. These alloys are based on a composition of Ni-4.2Co-4.8Cr-12.8Al-1.6W3.1Mo-1.0Re (at.%), with additions of Ta and Ti. Both Ta and Ti partition to alloy phases in a manner similar to Al. With addition of 1 at. % of Ta, the oxidation resistance is improved significantly, while 1 at. % of Ti appears to have no effect. Raising the concentration of Ta and Ti to 3 at. % degrades the oxidation resistance, the degradation is especially severe with 3 at. % of Ta. At only 1 at. % of Ta and Ti, both alloys establish a protective layer of Al₂O₃. The loss of the oxidation resistance at 3 at. % addition of Ta and Ti is related to the formation of complex oxides which are less protective. Detailed analysis of the oxide phases are conducted using a combination of X-ray diffraction and SEM. Characterizations of the oxidation behaviors are made under isothermal and cyclic conditions. The discrepancies between data obtained under both conditions were noted.     

Detection of nanosecond-scale, high power THz pulses with a field effect transistor

We demonstrate detection and resolution of high power, 34 ns free electron laser pulses using a rectifying field effect transistor. The detector remains linear up to an input power of 11 ± 0.5 W at a pulse energy of 20 ± 1 μJ at 240 GHz. We compare its performance to a protected Schottky diode, finding a shorter intrinsic time constant. The damage threshold is estimated to be a few 100 W. The detector is, therefore, well-suited for characterizing high power THz pulses. We further demonstrate that the same detector can be used to detect low power continuous-wave THz signals with a post detection limited noise floor of 3.1 μW/√Hz. Such ultrafast, high power detectors are important tools for high power and high energy THz facilities such as free electron lasers.     

Terahertz ionization of highly charged quantum posts in a perforated electron gas

"Quantum posts" are roughly cylindrical semiconductor nanostructures that are embedded in an energetically shallower "matrix" quantum well of comparable thickness. We report measurements of voltage-controlled charging and terahertz absorption of 30 nm thick InGaAs quantum wells and posts. Under flat-band (zero-electric field) conditions, the quantum posts each contain approximately six electrons, and an additional ~2.4 × 10(11) cm(-2) electrons populate the quantum well matrix. In this regime, absorption spectra show peaks at 3.5 and 4.8 THz (14 and 19 meV) whose relative amplitude depends strongly on temperature. These peaks are assigned to intersubband transitions of electrons in the quantum well matrix. A third, broader feature has a temperature-independent amplitude and is assigned to an absorption involving quantum posts. Eight-band k·p calculations incorporating the effects of strain and Coulomb repulsion predict that the electrons in the posts strongly repel the electrons in the quantum well matrix, "perforating" the electron gas. The strongest calculated transition, which has a frequency close to the center of the quantum post related absorption at 5 THz (20 meV), is an ionizing transition from a filled state to a quasi-bound state that can easily scatter to empty states in the quantum well matrix.     

Modelling Uncertainty in Flood Studies

Estimates of average annual damage (AAD) are a key central component of the hydrologic, hydraulic, and economic information developed in the evaluation of flood damage reduction plans. AAD or the expected value of annual damage, in dollars or other monetary units, is a probability-weighted average of the economic losses associated with the full range of possible flood magnitudes. Economic benefits are assessed as the reduction in AAD which would result from implementation of a particular plan. Traditional methodologies for performing hydrologic, hydraulic, and economic studies and estimating AAD have recently been expanded to explicitly incorporate analysis of the uncertainties inherent in the data collection and modelling effort. This paper presents a strategy for modelling uncertainties in the estimation of AAD for ungauged urban floodplains.     

Oxidation and antioxidants in fat and oil processing

The roles of oxidation and antioxidants in the various major processing steps in producing edible fats and oils are reviewed, including the basic nature of the oxidation problem, the function of phenolic antioxidants in overcoming it, and a listing of antioxidants currently available. In addition, some important considerations in achieving best results with antioxidants, whether added during processing or to the finished fat or oil, are emphasized.     

Influence of forest machine function on operator exposure to whole-body vibration in a cut-to-length timber harvester

The influence of machine function (tree felling and processing, and machine movement over the terrain) on operator exposure to whole-body vibration in a cut-to-length (CTL) timber harvester was evaluated. Vibrations were measured on the seat and the cabin chassis in three orthogonal (x, y, z) axes for the tree felling and processing, and during motion on a test track. It was found that the level of vibration transmitted to the operator during felling and processing was mainly affected by the tree size (diameter). For tree diameter at breast height (dbh) range of 0.25-0.35 m that was investigated, the vertical (z-axis) vibration component during processing increased by up to 300%, and increased by 50% during felling. However, the associated vibration levels were not sufficient to pose any serious health risks to the operator for an exposure limit of 8 h. Vibration at the operator seat and cabin chassis was predominant in the lateral (y-axis) and vertical (z-axis) respectively, during vehicle motion over the standard test track. Vibration peaks of approximately 0.20 and 0.17 ms(-2) occurred at 5 and 3.2 Hz respectively.     

Neural network based expectation learning in perception control: learning and control with unreliable sensory system

In this article, we investigate the viability of our proposed neural network-based extension of the perception control concept introduced by Randløv and Alstrøm. In their work, each of the expectation elements is linearly acquired such that the expectation gives only the dominant information of the recent past. This handicap could become a serious problem when the perception process is applied to real physical systems. Such an approach has no capability to sense the trend or the dynamics in the information. Here, we introduce an extension of the perception control process by using a radial basis function feedforward neural network to learn the trend and the dynamics in the information queue. Through our simulations, we show that our neural network-based method is better than the conventional method.This work was presented, in part, at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

To CG or to HDG: A Comparative Study

Hybridization through the border of the elements (hybrid unknowns) combined with a Schur complement procedure (often called static condensation in the context of continuous Galerkin linear elasticity computations) has in various forms been advocated in the mathematical and engineering literature as a means of accomplishing domain decomposition, of obtaining increased accuracy and convergence results, and of algorithm optimization. Recent work on the hybridization of mixed methods, and in particular of the discontinuous Galerkin (DG) method, holds the promise of capitalizing on the three aforementioned properties; in particular, of generating a numerical scheme that is discontinuous in both the primary and flux variables, is locally conservative, and is computationally competitive with traditional continuous Galerkin (CG) approaches. In this paper we present both implementation and optimization strategies for the Hybridizable Discontinuous Galerkin (HDG) method applied to two dimensional elliptic operators. We implement our HDG approach within a spectral/hp element framework so that comparisons can be done between HDG and the traditional CG approach.     

Role of Moisture in Maillard Browning Reaction Rate in Intermediate Moisture Foods: Comparing Solvent Phase and Matrix Properties

ABSTRACT: In intermediate-moisture foods, a mechanism describing how moisture affects chemical reaction rate is unknown. Previously, research showed glycol addition to model systems allowed high rates of nonenzymatic browning below the monolayer moisture value and an a_w of 0.2. These works were replicated, focusing on a mechanism of either plasticization or reactant dissolution. T_g curves showed plasticization increased with added glycerol and sorbitol. The maximum rate of nonenzymatic browning with glycerol occurred at an a_w= 0.25 and was 1.5 times higher than the control (a_w= 0.65). Sorbitol showed rates similar to the control. Plasticization and aw were poor predictors of reaction rate. Dissolution of glucose in glycerol explained the effect.