Al based ultra-fine eutectic with high room temperature plasticity and elevated temperature strength

Developments of aluminum alloys that can retain strength at and above 250 degrees C present a significant challenge. In this paper we report an ultrafine scale Al-Fe-Ni eutectic alloy with less than 3.5 aa transition metals that exhibits room temperature ultimate tensile strength of similar to 400 MPa with a tensile ductility of 6-8%. The yield stress under compression at 300 degrees C was found to be 150 MPa. We attribute it to the refinement of the microstructure that is achieved by suction casting in copper mold. The characterization using scanning and transmission electron microscopy (SEM and TEM) reveals an unique composite structure that contains the Al-Al3Ni rod eutectic with spacing of similar to 90 nm enveloped by a lamellar eutectic of Al-Al9FeNi (similar to 140 nm). Observation of subsurface deformation under Vickers indentation using bonded interface technique reveals the presence of extensive shear banding during deformation that is responsible for the origin of ductility. The dislocation configuration in Al-Al3Ni eutectic colony indicates accommodation of plasticity in alpha-Al with dislocation accumulation at the alpha-Al/Al3Ni interface boundaries. In contrast the dislocation activities in the intermetallic lamellae are limited and contain set of planner dislocations across the plates. We present a detailed analysis of the fracture surface to rationalize the origin of the high strength and ductility in this class of potentially promising cast alloy. (C) 2015 Elsevier B.V. All rights reserved.

Cross-section fluctuations in open microwave billiards and quantum graphs: The counting-of-maxima method revisited

The fluctuations exhibited by the cross sections generated in a compound-nucleus reaction or, more generally, in a quantum-chaotic scattering process, when varying the excitation energy or another external parameter, are characterized by the width Gamma(corr) of the cross-section correlation function. Brink and Stephen Phys. Lett. 5, 77 (1963)] proposed a method for its determination by simply counting the number of maxima featured by the cross sections as a function of the parameter under consideration. They stated that the product of the average number of maxima per unit energy range and Gamma(corr) is constant in the Ercison region of strongly overlapping resonances. We use the analogy between the scattering formalism for compound-nucleus reactions and for microwave resonators to test this method experimentally with unprecedented accuracy using large data sets and propose an analytical description for the regions of isolated and overlapping resonances.

Low-Order Harmonic Suppression for Open-End Winding IM With Dodecagonal Space Vector Using a Single DC-Link Supply

This paper proposes a technique to suppress low-order harmonics for an open-end winding induction motor drive for a full modulation range. One side of the machine is connected to a main inverter with a dc power supply, whereas the other inverter is connected to a capacitor from the other side. Harmonic suppression (with complete elimination of fifth- and seventh-order harmonics) is achieved by realizing dodecagonal space vectors using a combined pulsewidth modulation (PWM) control for the two inverters. The floating capacitor voltage is inherently controlled during the PWM operation. The proposed PWM technique is shown to be valid for the entire modulation range, including overmodulation and six-step mode of operation of the main inverter. Experimental results have been presented to validate the proposed technique.

Processing of EEG Signals for Study of Coupling in Brain Regions for Eyes Open and Eyes Closed Conditions

This paper deals with processing the EEG signals obtained from 16 spatially arranged electrodes to measure coupling or synchrony between the frontal, parietal, occipital and temporal lobes of the cerebrum under the eyes open and eyes closed conditions. This synchrony was measured using magnitude squared coherence, Short Time Fourier Transform and wavelet based coherences. We found a pattern in the time-frequency coherence as we moved from the nasion to the inion of the subject's head. The coherence pattern obtained from the wavelet approach was found to be far more capable of picking up peaks in coherence with respect to frequency when compared to the regular Fourier based coherence. We detected high synchrony between frontal polar electrodes that is missing in coherence plots between other electrode pairs. The study has potential applications in healthcare.

An Open-End winding IM drive with Multilevel 12-sided Polygonal Vectors with Symmetric Triangles

Multilevel inverters with hexagonal voltage space vector structures have improved performance of induction motor drives compared to that of the two level inverters. Further reduction in the torque ripple on the motor shaft is possible by using multilevel dodecagonal (12-sided polygon) voltage space vector structures. The advantages of dodecagonal voltage space vector based PWM techniques are the complete elimination of fifth and seventh harmonics in phase voltages for the full modulation range and the extension of linear modulation range. This paper proposes an inverter circuit topology capable of generating multilevel dodecagonal voltage space vectors with symmetric triangles, by cascading two asymmetric three level inverters with isolated H-Bridges. This is made possible by proper selection of DC link voltages and the selection of resultant switching states for the inverters. In this paper, a simple PWM timing calculation method is proposed. Experimental results have also been presented in this paper to validate the proposed concept.

Study of a four-level system in vee plus ladder configuration

We present the results of a theoretical study of a four-level atomic system in vee + ladder configuration using a density matrix analysis. The absorption and dispersion profiles are derived for a weak probe field and for varying strengths of the two strong control fields. For specificity, we choose energy levels of Rb-87, and present results for both stationary atoms and moving atoms in room temperature vapor. An electromagnetically induced absorption (EIA) peak with negative dispersion is observed at zero probe de-tuning when the control fields have equal strengths, which switches to electromagnetically induced transparency (ET) with positive dispersion (due to splitting of the EIA peak) when the control fields are unequal. There is significant linewidth narrowing in thermal vapor. (C) 2015 Elsevier B.V. All rights reserved.

Mass spectrometry based characterization of Hb Beckman variant in a falsely elevated HbA(1c) sample

Glycated hemoglobin (HbA(1c)) is a `gold standard' biomarker for assessing the glycemic index of an individual. HbA(1c) is formed due to nonenzymatic glycosylation at N-terminal valine residue of the P-globin chain. Cation exchange based high performance liquid chromatography (CE HPLC) is mostly used to quantify HbA(1c), in blood sample. A few genetic variants of hemoglobin and post-translationally modified variants of hemoglobin interfere with CE HPLC-based quantification,. resulting in its false positive estimation. Using mass spectrometry, we analyzed a blood sample with abnormally high HbA(1c) (52.1%) in the CE HPLC method. The observed HbA(1c) did not corroborate the blood glucose level of the patient. A mass spectrometry based bottom up proteomics approach, intact globin chain mass analysis, and chemical modification of the proteolytic peptides identified the presence of Hb Beckman, a genetic variant of hemoglobin, in the experimental sample. A similar surface area to charge ratio between HbA(1c) and Hb Beckman might have resulted in the coelution of the variant with HbA(1c) in CE HPLC. Therefore, in the screening of diabetes mellitus through the estimation of HbA(1c), it is important to look for genetic variants of hemoglobin in samples that show abnormally high glycemic index, and HbA(1c) must be estimated using an alternative method. (C) 2015 Elsevier Inc. All rights reserved.

Performance evaluation of a two-stage silica gel plus water adsorption based cooling-cum-desalination system

The first objective of this paper is to show that a single-stage adsorption based cooling-cum-desalination system cannot be used if air cooled heat rejection is used under tropical conditions. This objective is achieved by operating a silica gel + water adsorption chiller first in a single-stage mode and then in a 2-stage mode with 2 beds/stage in each case. The second objective is to improve upon the simulation results obtained earlier by way of empirically describing the thermal wave phenomena during switching of operation of beds between adsorption and desorption and vice versa. Performance indicators, namely, cooling capacity, coefficient of performance and desalinated water output are extracted for various evaporator pressures and half cycle times. The improved simulation model is found to interpret experimental results more closely than the earlier one. Reasons for decline in performance indicators between theoretical and actual scenarios are appraised. (C) 2015 Elsevier Ltd and IIR. All rights reserved.

Recognition of open vocabulary, online handwritten pages in Tamil script

In this work, we describe a system, which recognises open vocabulary, isolated, online handwritten Tamil words and extend it to recognize a paragraph of writing. We explain in detail each step involved in the process: segmentation, preprocessing, feature extraction, classification and bigram-based post-processing. On our database of 45,000 handwritten words obtained through tablet PC, we have obtained symbol level accuracy of 78.5% and 85.3% without and with the usage of post-processing using symbol level language models, respectively. Word level accuracies for the same are 40.1% and 59.6%. A line and word level segmentation strategy is proposed, which gives promising results of 100% line segmentation and 98.1% word segmentation accuracies on our initial trials of 40 handwritten paragraphs. The two modules have been combined to obtain a full-fledged page recognition system for online handwritten Tamil data. To the knowledge of the authors, this is the first ever attempt on recognition of open vocabulary, online handwritten paragraphs in any Indian language.

Instrumentation and control of a two-stage 4-bed silica gel plus water adsorption cooling cum desalination system

This paper presents the instrumentation and control architecture for a laboratory based two-stage 4-bed silica gel + water adsorption system. The system consists of primarily two fluids: refrigerant (water vapour) and heat transfer fluid (water) flowing through various components. Heat input to the system is simulated using multiple heaters and ambient air is used as the heat sink. The laboratory setup incorporates a real time National Instruments (NI) controller to control several digital and analog valves, heaters, pumps and fans along with simultaneous data acquisition from various flow, pressure and temperature sensors. The paper also presents in detail the various automated and manual tasks required for successful operation of the system. Finally the system pressure and temperature dynamics are reported and its performance evaluated for various cycle times. (C) 2015 Elsevier Ltd. All rights reserved.

PLUTO plus : Near-Complete Modeling of Affine Transformations for Parallelism and Locality

Affine transformations have proven to be very powerful for loop restructuring due to their ability to model a very wide range of transformations. A single multi-dimensional affine function can represent a long and complex sequence of simpler transformations. Existing affine transformation frameworks like the Pluto algorithm, that include a cost function for modern multicore architectures where coarse-grained parallelism and locality are crucial, consider only a sub-space of transformations to avoid a combinatorial explosion in finding the transformations. The ensuing practical tradeoffs lead to the exclusion of certain useful transformations, in particular, transformation compositions involving loop reversals and loop skewing by negative factors. In this paper, we propose an approach to address this limitation by modeling a much larger space of affine transformations in conjunction with the Pluto algorithm's cost function. We perform an experimental evaluation of both, the effect on compilation time, and performance of generated codes. The evaluation shows that our new framework, Pluto+, provides no degradation in performance in any of the Polybench benchmarks. For Lattice Boltzmann Method (LBM) codes with periodic boundary conditions, it provides a mean speedup of 1.33x over Pluto. We also show that Pluto+ does not increase compile times significantly. Experimental results on Polybench show that Pluto+ increases overall polyhedral source-to-source optimization time only by 15%. In cases where it improves execution time significantly, it increased polyhedral optimization time only by 2.04x.

Effect of semi-solid heat treatment on elevated temperature plasticity of 304L stainless steel

The present work explores the potential of semi-solid heat treatment technique by elucidating its effect on the plastic behavior of 304L SS in hot working domain. To accomplish this objective, hot isothermal compression tests on 304L SS specimens with semi-solid heat treatment and conventional annealing heat treatment have been carried out within a temperature range of 1273-1473 K and strain rates ranging from 0.01 to 1 s(-1). The dynamic flow behavior of this steel in its conventional heat-treated condition and semi-solid heat-treated condition has been characterized in terms of strain hardening, temperature softening, strain rate hardening, and dynamic flow softening. Extensive microstructural investigation has been carried out to corroborate the results obtained from the analysis of flow behavior. Detailed analysis of the results demonstrates that semi-solid heat treatment moderates work hardening, strain rate hardening, and temperature sensitivity of 304L SS, which is favorable for hot deformation. The post-deformation hardness values of semi-solid heat-treated steel and conventionally heat-treated steel were found to remain similar despite the pre-deformation heat treatment conditions. The results obtained demonstrate the potential of semi-solid heat treatment as a pre-deformation heat treatment step to effectively reduce the strength of the material to facilitate easier deformation without affecting the post-deformation properties of the steel.

Small-Signal Stability Analysis of an Open-Loop Induction Motor Drive Including the Effect of Inverter Deadtime

This paper demonstrates light-load instability in a 100-kW open-loop induction motor drive on account of inverter deadtime. An improved small-signal model of an inverter-fed induction motor is proposed. This improved model is derived by linearizing the nonlinear dynamic equations of the motor, which include the inverter deadtime effect. Stability analysis is carried out on the 100-kW415-V three-phase induction motor considering no load. The analysis brings out the region of instability of this motor drive on the voltage versus frequency (V-f) plane. This region of light-load instability is found to expand with increase in inverter deadtime. Subharmonic oscillations of significant amplitude are observed in the steady-state simulated and measured current waveforms, at numerous operating points in the unstable region predicted, confirming the validity of the stability analysis. Furthermore, simulation and experimental results demonstrate that the proposed model is more accurate than an existing small-signal model in predicting the region of instability.

Full current statistics for a disordered open exclusion process

We consider the nonabelian sandpile model defined on directed trees by Ayyer et al. (2015 Commun. Math. Phys. 335 1065). and restrict it to the special case of a one-dimensional lattice of n sites which has open boundaries and disordered hopping rates. We focus on the joint distribution of the integrated currents across each bond simultaneously, and calculate its cumulant generating function exactly. Surprisingly, the process conditioned on seeing specified currents across each bond turns out to be a renormalised version of the same process. We also remark on a duality property of the large deviation function. Lastly, all eigenvalues and both Perron eigenvectors of the tilted generator are determined.

Modelling and analysis of an open-loop induction motor drive incorporating the effect of inverter dead-time

The objective of this paper is to study the influence of inverter dead-time on steady as well as dynamic operation of an open-loop induction motor drive fed from a voltage source inverter (VSI). Towards this goal, this paper presents a systematic derivation of a dynamic model for an inverter-fed induction motor, incorporating the effect of inverter dead-time, in the synchronously revolving dq reference frame. Simulation results based on this dynamic model bring out the impact of inverter dead-time on both the transient response and steady-state operation of the motor drive. For the purpose of steady-state analysis, the dynamic model of the motor drive is used to derive a steady-state model, which is found to be non-linear. The steady-state model shows that the impact of dead-time can be seen as an additional resistance in the stator circuit, whose value depends on the stator current. Towards precise evaluation of this dead-time equivalent resistance, an analytical expression is proposed for the same in terms of inverter dead-time, switching frequency, modulation index and load impedance. The notion of dead-time equivalent resistance is shown to simplify the solution of the non-linear steady-state model. The analytically evaluated steady-state solutions are validated through numerical simulations and experiments.