Precipitation of chromium containing phases in aluminide coated nickel-base superalloy single crystals

The precipitation of chromium-containing phases, in both the B2 type β-phase coating matrix (nominally NiAl) and the substrate of high-activity-pack-aluminized single crystals of a nickel-base superalloy, is considered in this paper. An ‘edge-on’ transmission electron microscopy (TEM) technique is employed to examine the precipitation of M23X6, σ, α-Cr and other phases after coating and diffusion treatment and subsequent post-coating treatment at 850 and 950 °C. Initial precipitation is dominated by the formation of M23X6 in both the coating and substrate, however, in the case of single-crystal substrates the formation of this carbon-rich phase is not sustained. M23X6 precipitation is superceded by the formation of coherent precipitates of the α-Cr phase which effectively retains the basis but removes the superlattice of the β-matrix. Extensive precipitation of α-Cr has the effect of changing the balance of chromium to molybdenum in solution in the β-phase and further precipitation is dominated by Σ-phase intermetallics and other Cr-Mo-containing phases.

Foveation time measure in Congenital Nystagmus through second order approximation of the slow phases

Congenital Nystagmus (CN) is an ocular-motor disorder characterised by involuntary, conjugated ocular oscillations, and its pathogenesis is still unknown. The pathology is de fined as "congenital" from the onset time of its arise which could be at birth or in the first months of life. Visual acuity in CN subjects is often diminished due to nystagmus continuous oscillations, mainly on the horizontal plane, which disturb image fixation on the retina. However, during short periods in which eye velocity slows down while the target image is placed onto the fovea (called foveation intervals) the image of a given target can still be stable, allowing a subject to reach a higher visual acuity. In CN subjects, visual acuity is usually assessed both using typical measurement techniques (e.g. Landolt C test) and with eye movement recording in different gaze positions. The offline study of eye movement recordings allows physicians to analyse nystagmus main features such as waveform shape, amplitude and frequency and to compute estimated visual acuity predictors. This analytical functions estimates the best corrected visual acuity using foveation time and foveation position variability, hence a reliable estimation of this two parameters is a fundamental factor in assessing visual acuity. This work aims to enhance the foveation time estimation in CN eye movement recording, computing a second order approximation of the slow phase components of nystag-mus oscillations. About 19 infraredoculographic eye-movement recordings from 10 CN subjects were acquired and the visual acuity assessed with an acuity predictor was compared to the one measured in primary position. Results suggest that visual acuity measurements based on foveation time estimation obtained from interpolated data are closer to value obtained during Landolt C tests. © 2010 IEEE.

Synthesis of M2AC (M = Ti, V, Cr, Nb, Zr, A = Al, Sn, S) (MAX) carbide phases and study of their physical behavior under extreme conditions

Materials known as Mn+1AXn phases, where n is 1, 2, or 3, and M represents an early transition metal, A an A-group element, and X is either Carbon and/or Nitrogen [1], are fast becoming technologically important materials due to the interesting combination of unique properties. However, a lot of important information about the high temperature and high pressure behavior of many of these compounds is still missing, which needs to be determined systematically. ^ In this dissertation the synthesis of M2AC (M = Ti, V, Cr, Nb, Zr) and A = (Al, Sn, S) compounds by arc melting, vacuum sintering and piston cylinder synthesis is presented along with the synthesis of Zr 2SC, which has been synthesized for first time in bulk form, by piston cylinder technique. The microstructural analysis by electron microscopy and phase analysis by x-ray diffraction is presented next. Finally, a critical analysis of the behavior of these compounds under the application of extreme pressure (as high as 50 GPa) and temperature (≈ 1000°C) is presented. ^ The high pressure studies, up to 50 GPa, showed that these compounds were structurally intact and their bulk moduli ranged from 140 to 190 GPa. The high temperature studies in the inert atmosphere showed that the M 2SnC compounds were unstable above 650°C and the expansion along the a-axis was higher than that along the c-axis, unlike the other phases. M2SC compounds on the other hand showed negligible difference in the thermal expansion along the two axes. The oxidation study revealed that Ti2AC (Al, S) compounds had highest resistance to oxidation while the M2SnC compounds had the least. Furthermore, from the oxidation study of these compounds, which were short time oxidation experiments, it was found that all of these compounds oxidized to their respective binary oxides. ^

Radiogenic neodymium, strontium and lead isotopes of authigenic and detrital sedimentary phases and stable oxygen and carbon isotopes of benthic foraminifera from gravity cores SO213-59-2 and SO213-60-1 (central South Pacific).

The South Pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the Atlantic Ocean, the Southern Ocean, and the Pacific Basin are exchanged. Here we reconstruct the deep water circulation of the central South Pacific for the last two glacial cycles (from 240,000 years ago to the Holocene) based on radiogenic neodymium (Nd) and lead (Pb) isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the East Pacific Rise. The records show small but consistent glacial/interglacial changes in all three isotopic systems with interglacial average values of -5.8 and 18.757 for epsilon Nd and 206Pb/204Pb, respectively, whereas glacial averages are -5.3 and 18.744. Comparison of this variability of Circumpolar Deep Water (CDW) to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of North Atlantic Deep Water to CDW during cold stages. The absolute values and amplitudes of the benthic delta13C variations are essentially indistinguishable from other records of the Southern Hemisphere and confirm that the low central South Pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies. In addition, the combined detrital Nd and strontium (87Sr/86Sr) isotope signatures imply that Australian and New Zealand dust has remained the principal contributor of lithogenic material to the central South Pacific.

Étude du diagramme de bifurcation d'un système prédateur-proie

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Physics of Hexagonal Limit-Periodic Phases: Thermodynamics, Formation and Vibrational Modes

Limit-periodic (LP) structures exhibit a type of nonperiodic order yet to be found in a natural material. A recent result in tiling theory, however, has shown that LP order can spontaneously emerge in a two-dimensional (2D) lattice model with nearest-and next-nearest-neighbor interactions. In this dissertation, we explore the question of what types of interactions can lead to a LP state and address the issue of whether the formation of a LP structure in experiments is possible. We study emergence of LP order in three-dimensional (3D) tiling models and bring the subject into the physical realm by investigating systems with realistic Hamiltonians and low energy LP states. Finally, we present studies of the vibrational modes of a simple LP ball and spring model whose results indicate that LP materials would exhibit novel physical properties.

A 2D lattice model defined on a triangular lattice with nearest- and next-nearest-neighbor interactions based on the Taylor-Socolar (TS) monotile is known to have a LP ground state. The system reaches that state during a slow quench through an infinite sequence of phase transitions. Surprisingly, even when the strength of the next-nearest-neighbor interactions is zero, in which case there is a large degenerate class of both crystalline and LP ground states, a slow quench yields the LP state. The first study in this dissertation introduces 3D models closely related to the 2D models that exhibit LP phases. The particular 3D models were designed such that next-nearest-neighbor interactions of the TS type are implemented using only nearest-neighbor interactions. For one of the 3D models, we show that the phase transitions are first order, with equilibrium structures that can be more complex than in the 2D case.

In the second study, we investigate systems with physical Hamiltonians based on one of the 2D tiling models with the goal of stimulating attempts to create a LP structure in experiments. We explore physically realizable particle designs while being mindful of particular features that may make the assembly of a LP structure in an experimental system difficult. Through Monte Carlo (MC) simulations, we have found that one particle design in particular is a promising template for a physical particle; a 2D system of identical disks with embedded dipoles is observed to undergo the series of phase transitions which leads to the LP state.

LP structures are well ordered but nonperiodic, and hence have nontrivial vibrational modes. In the third section of this dissertation, we study a ball and spring model with a LP pattern of spring stiffnesses and identify a set of extended modes with arbitrarily low participation ratios, a situation that appears to be unique to LP systems. The balls that oscillate with large amplitude in these modes live on periodic nets with arbitrarily large lattice constants. By studying periodic approximants to the LP structure, we present numerical evidence for the existence of such modes, and we give a heuristic explanation of their structure.

Étude du diagramme de bifurcation d'un système prédateur-proie

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Characterization of cation exchanger stationary phases applied for the separations of therapeutic monoclonal antibodies.

Cation exchange chromatography (CEX) is a well established strategy for the characterization of monoclonal antibodies (mAbs). The optimization of mobile phase conditions is well described in the literature, but there is a lack of information about CEX stationary phases for the analysis of therapeutic proteins. The aim of this study was to compare five state-of-the-art CEX stationary phases based on the retention, selectivity and resolving power achieved in pH- and salt-gradient modes, with various therapeutic mAbs and their variants. The Sepax Antibodix WCX-NP3, Thermo MAbPac SCX-10 RS, YMC BioPro SP-F, Waters Protein-Pak Hi Res SP and Agilent Bio mAb NP1.7 SS were considered in this study. In terms of retention, the YMC Bio Pro SP-F material was the less retentive one, while the Agilent Bio mAb NP1.7 SS provides the highest retention. Regarding the selectivity achieved between the main mAbs isoforms and their variants, the Thermo MabPac SCX column generally gave the highest selectivity. Finally, it was hard to rank columns in term of kinetic performance since their performance is strongly solute (mAb) and elution mode (pH or salt gradient) dependent. However, the highest resolution--in most cases--was observed on the strong cation exchanger YMC Bio Pro SP-F material.

Assessment of heavy metals' bonding with various sedimentary phases in Shefa-Rud river (Guilan Province)

In the present investigation, bulk and chemical partitioning of elements in the Shefa-Rud riverbed sediments are studied. Higher concentrations of elemental concentrations have been observed in estuarine zone when compared with riverine sediments (except for Al, Fe, Pb and Mn). Manganese is mobilized under anoxic conditions prevailing in the Caspian Sea. Lithogenous materials are greatly diluted in the estuarine zone by various pollutants present in the Caspian Sea. Organic metallic bonds are not significantly present in the area of study. Geological units of the area of study have resulted in the lower concentrations of elemental concentrations of riverbed sediments when compared with published values for mean crust and world sediments ones. Though, cluster analysis has clearly shown the importance of alumina-silicates in controlling the distribution of Fe and Mn in riverbed sediments but it could not depict controlling mechanism for other studied elements. Geochemical Index (Igeo) and Enrichment Factor (EF) values are indicative of a clean environment throughout the river course. These values are in a well agreement with results of chemical partitioning data. Quantification of EF values is not logically possible and therefore Igeo values can be used more effectively.

Effect of myrrh and thyme on Trichinella spiralis enteral and parenteral phases with inducible nitric oxide expression in mice

Trichinellosis is a serious disease with no satisfactory treatment. We aimed to assess the effect of myrrh ( Commiphora molmol ) and, for the first time, thyme ( Thymus vulgaris L.) against enteral and encysted (parenteral) phases of Trichinella spiralis in mice compared with albendazole, and detect their effect on inducible nitric oxide synthase (iNOS) expression. Oral administration of 500 mg/kg of myrrh and thyme led to adult reduction (90.9%, 79.4%), while 1,000 mg/kg led to larvae reduction (79.6%, 71.3%), respectively. Administration of 50 mg/kg of albendazole resulted in adult and larvae reduction (94.2%, 90.9%). Positive immunostaining of inflammatory cells infiltrating intestinal mucosa and submucosa of all treated groups was detected. Myrrh-treated mice showed the highest iNOS expression followed by albendazole, then thyme. On the other hand, both myrrh and thyme-treated groups showed stronger iNOS expression of inflammatory cells infiltrating and surrounding encapsulated T. spiralis larvae than albendazole treated group. In conclusion, myrrh and thyme extracts are highly effective against both phases of T. spiralis and showed strong iNOS expressions, especially myrrh which could be a promising alternative drug. This experiment provides a basis for further exploration of this plant by isolation and retesting the active principles of both extracts against different stages of T. spiralis.

Fitting phase type distribution to service process with sequential phases

The work of this thesis is concerned with fitting Hypo-exponential and Erlang phase type distributions for modeling real life processes with non-exponential service time. There exist situations where exponential distributions cannot explain the distribution of service time properly. This thesis presents the application of two traditional statistical estimation techniques to approximate the service distributions of processes with coefficient of variation less than one. It also presents an algorithm to fit Hypo-exponential distribution for complex situations which can’t be handled properly with traditional estimation techniques. The result shows the effect of variation of sample size and other parameters on the efficiency of the estimation techniques by comparing their respective outputs. Furthermore it checks how accurately the proposed algorithm approximates a given distribution.

Phases Dynamic Balancer

Most of the current domestic installations are single phase, with contracted power equal to or less than 15 kW and with a potential difference of 230 V. When consumption is expected to be higher you choose to use three different alternating currents with a difference voltage of 400 V between them, which are called phases. This enables the subdivision of the installation in different single-phase circuits, fed independently with the neutral installation. These couples have, in turn, a difference in voltage of 230 V. The neutral is common for all three phases so that, if the system is balanced, no current flows through it. The problem with these installations is that they are designed to work in an offset manner, using phase loads, and simultaneously an equal amount of energy consumed by the three phases of the network. Connection to each of the phases makes independent single-phase loads or disturbance of the operation of the original phase circuit and, consequently, the corresponding increases in consumption, heating of engines, etc.