High-temperature deformation processing maps for a NiTiCu shape memory alloy

The properties of widely used Ni-Ti-based shape memory alloys (SMAs) are highly sensitive to the underlying microstructure. Hence, controlling the evolution of microstructure during high-temperature deformation becomes important. In this article, the ``processing maps'' approach is utilized to identify the combination of temperature and strain rate for thermomechanical processing of a Ni(42)Ti(50)Cu(8) SMA. Uniaxial compression experiments were conducted in the temperature range of 800-1050 degrees C and at strain rate range of 10(-3) and 10(2) s(-1). Two-dimensional power dissipation efficiency and instability maps have been generated and various deformation mechanisms, which operate in different temperature and strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results show that the safe window for industrial processing of this alloy is in the range of 800-850 degrees C and at 0.1 s(-1), which leads to grain refinement and strain-free grains. Regions of the instability were identified, which result in strained microstructure, which in turn can affect the performance of the SMA.

Scalable processes for fabricating non-volatile memory devices using self-assembled 2D arrays of gold nanoparticles as charge storage nodes

We propose robust and scalable processes for the fabrication of floating gate devices using ordered arrays of 7 nm size gold nanoparticles as charge storage nodes. The proposed strategy can be readily adapted for fabricating next generation (sub-20 nm node) non-volatile memory devices.

Interference in Multiprocessor Systems with Localized Memory Access Probabilities

Past studies of memory interference in multiprocessor systems have generally assumed that the references of each processor are uniformly distributed among the memory modules. In this paper we develop a model with local referencing, which reflects more closely the behavior of real-life programs. This model is analyzed using Markov chain techniques and expressions are derived for the multiprocessor performance. New expressions are also obtained for the performance in the traditional uniform reference model and are compared with other expressions-available in the literature. Results of a simulation study are given to show the accuracy of the expressions for both models.

Variable Granularity Access Tracking Scheme for Improving the Performance of Software Transactional Memory

Software transactional memory (STM) has been proposed as a promising programming paradigm for shared memory multi-threaded programs as an alternative to conventional lock based synchronization primitives. Typical STM implementations employ a conflict detection scheme, which works with uniform access granularity, tracking shared data accesses either at word/cache line or at object level. It is well known that a single fixed access tracking granularity cannot meet the conflicting goals of reducing false conflicts without impacting concurrency adversely. A fine grained granularity while improving concurrency can have an adverse impact on performance due to lock aliasing, lock validation overheads, and additional cache pressure. On the other hand, a coarse grained granularity can impact performance due to reduced concurrency. Thus, in general, a fixed or uniform granularity access tracking (UGAT) scheme is application-unaware and rarely matches the access patterns of individual application or parts of an application, leading to sub-optimal performance for different parts of the application(s). In order to mitigate the disadvantages associated with UGAT scheme, we propose a Variable Granularity Access Tracking (VGAT) scheme in this paper. We propose a compiler based approach wherein the compiler uses inter-procedural whole program static analysis to select the access tracking granularity for different shared data structures of the application based on the application's data access pattern. We describe our prototype VGAT scheme, using TL2 as our STM implementation. Our experimental results reveal that VGAT-STM scheme can improve the application performance of STAMP benchmarks from 1.87% to up to 21.2%.

Stress Evolution With Temperature in Titanium-Rich NiTi Shape Memory Alloy Films

The effect of deposition temperature on residual stress evolution with temperature in Ti-rich NiTi films deposited on silicon substrates was studied. Ti-rich NiTi films were deposited on 3? Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 degrees C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 degrees C and the lowest for the film deposited and annealed at 300 degrees C. All the three films were found to be amorphous in the as-deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 degrees C) was similar for all three films although the spike in tensile stress, which occurs at similar to 330 degrees C, was significantly higher in the film deposited and annealed at 300 degrees C. All the films were also found to undergo partial crystallisation on heating up to 450 degrees C and this resulted in decrease in the stress values around 5560 degrees C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 degrees C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.

Electrical Breakdown of Gases Between Coaxial Cylindrical Electrodes in Crossed Electric and Magnetic Fields

Sparking potentials have been measured in nitrogen and dry air between coaxial cylindrical electrodes for values of n = R2/R1 = approximately 1 to 30 (R1 = inner electrode radius, R2 = outer electrode radius) in the presence of crossed uniform magnetic fields. The magnetic flux density was varied from 0 to 3000 Gauss. It has been shown that the minimum sparking potentials in the presence of the crossed magnetic field can be evaluated on the basis of the equivalent pressure concept when the secondary ionization coefficient does not vary appreciably with B/p (B = magnetic flux density, p = gas pressure). The values of secondary ionization coefficients �¿B in nitrogen in crossed fields calculated from measured values of sparking potentials and Townsend ionization coefficients taken from the literature, have been reported. The calculated values of collision frequencies in nitrogen from minimum sparking potentials in crossed fields are found to increase with increasing B/p at constant E/pe (pe = equivalent pressure). Studies on the similarity relationship in crossed fields has shown that the similarity theorem is obeyed in dry air for both polarities of the central electrode in crossed fields.

A Long Memory Process Based Parametric Modeling and Recognition of PD Signal

We address the problem of recognition and retrieval of relatively weak industrial signal such as Partial Discharges (PD) buried in excessive noise. The major bottleneck being the recognition and suppression of stochastic pulsive interference (PI) which has similar time-frequency characteristics as PD pulse. Therefore conventional frequency based DSP techniques are not useful in retrieving PD pulses. We employ statistical signal modeling based on combination of long-memory process and probabilistic principal component analysis (PPCA). An parametric analysis of the signal is exercised for extracting the features of desired pules. We incorporate a wavelet based bootstrap method for obtaining the noise training vectors from observed data. The procedure adopted in this work is completely different from the research work reported in the literature, which is generally based on deserved signal frequency and noise frequency.

First passage distributions for long memory processes

We study the distribution of first passage time for Levy type anomalous diffusion. A fractional Fokker-Planck equation framework is introduced.For the zero drift case, using fractional calculus an explicit analytic solution for the first passage time density function in terms of Fox or H-functions is given. The asymptotic behaviour of the density function is discussed. For the nonzero drift case, we obtain an expression for the Laplace transform of the first passage time density function, from which the mean first passage time and variance are derived.

Non-linear electrical response of chalcogenide glasses: Memory state phenomena

Investigations on the switching behaviour of arsenic-tellurium glasses with Ge or Al additives, yield interesting information about the dependence of switching on network rigidity, co-ordination of the constituents, glass transition & ambient temperature and glass forming ability.

Vertical uplift capacity of a group of two coaxial anchors in a general c-phi soil

The vertical uplift resistance of a group of two horizontal coaxial strip anchors, embedded in a general c-phi soil (where c is the unit cohesion and phi is the soil friction angle), has been determined by using the lower bound finite element limit analysis. The variation of uplift factors F-c and F-gamma, due to the components of soil cohesion and unit weight, respectively, with changes in depth (H)/width (B) has been established for different values of vertical spacing (S)/B. As compared to a single isolated anchor, the group of two anchors provides a significantly greater magnitude of F-c for phi <= 20 degrees and with H/B >= 3. The magnitude of F-c becomes almost maximum when S/B is kept closer to 0.5H/B. On the other hand, with the same H/B, as compared to a single anchor, hardly any increase in F-gamma occurs for a group of two anchors.

Vertical Uplift Resistance of a Group of Two Coaxial Anchors in Clay

The vertical uplift resistance for a group of two horizontal coaxial rigid strip anchors embedded in clay under undrained condition has been determined by using the upper bound theorem of limit analysis in combination with finite elements. An increase of undrained shear strength of soil mass with depth has been incorporated. The uplift factor F-c gamma has been computed. As compared to a single isolated anchor, a group of two anchors provides greater magnitude of the uplift resistance. For a given embedment ratio, the group of two anchors generates almost the maximum uplift resistance when the upper anchor is located midway between ground surface and the lower anchor. For a given embedment ratio, F-c gamma increases linearly with an increase in the normalized unit weight of soil mass up to a certain value before attaining a certain maximum magnitude; the maximum value of F-c gamma increases with an increase in embedment ratio. DOI: 10.1061/(ASCE)GT.19435606.0000599. (C) 2012 American Society of Civil Engineers.