Lattice Instabilities and Phase Transformations in Fe from Atomistic Simulations

The stability of the body- and face-centered cubic lattices corresponding to the α and γ phases of Fe, respectively, as well as the transformation of one phase to the other were investigated by atomistic simulations. Two interatomic potentials were used: the embedded atom method (EAM) potential of Meyer and Entel and the bond order potential (BOP) developed by Müller et al. The suitability of the potentials for investigating structural transformations in Fe was verified using nonequilibrium free energy calculations and molecular dynamics simulations. The results showed that the EAM potential is capable of describing the bcc → fcc and fcc → bcc transformations whereas no transformation was observed for the computationally more expensive BOP potential with the simulation set up used.     

Addressing self-similarity in optical switching networks by means of ant colony optimization

In this work, we propose the use of an Ant Colony Optimization (ACO) algorithm to mitigate packet loss in an optical packet switching network that carries self-similar traffic, which is known to have a great impact in the buffer performance in terms of loss probability as exemplified in this work. By adaptively routing the packets and balancing the network load, we demonstrate by some simulations the effectiveness of this approach when compared with a shortest-path routing scheme, achieving a performance that is comparable to the Poisson traffic scenario in some cases. The proposed algorithm can be used as a viable alternative to traffic shaping techniques.     

High temperature flexural strength and fracture toughness of AlN with Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic

The effects of temperature on the fast fracture behavior of aluminum nitride with 5 wt% Y₂O₃ ceramic were investigated. Four-point flexural strength and fracture toughness were measured in air at several temperatures (30–1,300 °C). The flexural strength gradually decreased with the increase of temperature up to 1,000 °C due to the change in the fracture mode from transgranular to intergranular, and then became almost constant up to 1,300 °C. Two main flaw types as fracture origin were identified: small surface flaw and large pores. The volume fraction of the large pores was only 0.01%; however, they limited the strength on about 50% of the specimens. The fracture toughness decreased slightly up to 800 °C controlled by the elastic modulus change, and then decreased significantly at 1,000 °C due to the decrease in the grain-boundary toughness. Above 1,000 °C, the fracture toughness increased significantly, and at 1,300 °C, its value was close to that measured at room temperature.     

Exploring heuristic and optimum branching algorithms for image phylogeny

Currently, multimedia objects can be easily created, stored, (re)-transmitted, and edited for good or bad. In this sense, there has been an increasing interest in finding the structure of temporal evolution within a set of documents and how documents are related to one another overtime. This process, also known in the literature as Multimedia Phylogeny, aims at finding the phylogeny tree(s) that best explains the creation process of a set of near-duplicate documents (e.g., images/videos) and their ancestry relationships. Solutions to this problem have direct applications in forensics, security, copyright enforcement, news tracking services and other areas. In this paper, we explore one heuristic and one optimum branching algorithm for reconstructing the evolutionary tree associated with a set of image documents. This can be useful for aiding experts to track the source of child pornography image broadcasting or the chain of image distribution in time, for instance. We compare the algorithms with the state-of-the-art solution considering 350,000 test cases and discuss advantages and disadvantages of each one in a real scenario.     

Adaptive edge-preserving image denoising using wavelet transforms

Image denoising is a relevant issue found in diverse image processing and computer vision problems. It is a challenge to preserve important features, such as edges, corners and other sharp structures, during the denoising process. Wavelet transforms have been widely used for image denoising since they provide a suitable basis for separating noisy signal from the image signal. This paper describes a novel image denoising method based on wavelet transforms to preserve edges. The decomposition is performed by dividing the image into a set of blocks and transforming the data into the wavelet domain. An adaptive thresholding scheme based on edge strength is used to effectively reduce noise while preserving important features of the original image. Experimental results, compared to other approaches, demonstrate that the proposed method is suitable for different classes of images contaminated by Gaussian noise.     

The Cerro Prieto IV (Mexico) geothermal reservoir: Pre-exploitation thermodynamic conditions and main processes related to exploitation (2000–2005)

The Cerro Prieto IV (CP IV) reservoir, located in the northeastern part of the Cerro Prieto (Mexico) geothermal field, was studied in order to define its pre-exploitation conditions and initial (2000–2005) response to exploitation. Bottomhole thermodynamic conditions were estimated by modeling heat and fluid flows using the WELLSIM program and well production data. Produced fluid chemical and isotopic data were also analyzed to investigate characteristic patterns of behavior over time, which were then compared against simulation results to obtain a conceptual model of the CP IV reservoir. According to the proposed model, two zones in the reservoir – separated by Fault H and producing fluids of different characteristics – were identified under pre-exploitation conditions. Wells in the area to the east-southeast (south block) produce very high-enthalpy fluids (≥2000 kJ/kg), with very low chloride (≤7000 mg/kg) and high CO₂ (>6‰ molar) and δD (<−94‰). In contrast, wells toward the west-northwest (north block) show moderate-enthalpy fluids (1400–1800 kJ/kg), with high chloride (∼12,000 mg/kg) and relatively low CO₂ (<6‰ molar) and δD (<−94‰). Dilution caused by cooler water entry, boiling due to steam gain, both occurring in the north block, and steam condensation in the south block were identified as the three main reservoir processes associated with exploitation. Also, it was found that the dynamics of the CP IV reservoir is controlled by the Fault H system.     

Short communication: The first report of Cyberlindnera rhodanensis associated with clinical bovine mastitis

An acute case of clinical mastitis in a Holstein cow from second lactation is reported here. A milk sample from the affected quarter was cultured on 5% bovine blood agar and incubated at 37°C for 72 h. After 24 h of incubation, numerous colonies of yeast were observed: the Candida characteristic was not detected by CHROMagar Candida (Difco, Franklin Lakes, NJ). The DNA extraction of the isolate was performed, and DNA was subjected to amplification and sequencing of the D1/D2 region of the large subunit rRNA gene. The sequences were aligned using Mega 7.0 and used for searching GenBank by BLASTn (Basic Local Alignment Search Tool for nucleotides), revealing 98% of identity with Cyberlindnera rhodanensis. To date, this is the first report of this yeast associated with clinical bovine mastitis.     

Overall kinetics and morphology of the products of austenite decomposition in a Fe-0.46 Pct C-5.2 Pct Cr alloy transformed isothermally above the bay

The overall transformation kinetics of austenite isothermal decomposition above the bay of the time-temperature-transformation (TTT) curve and the eutectoid morphology of the resulting products have been studied in a Fe-0.46 pct C-5.2 pct Cr alloy. Classical lamellar pearlite was formed at high temperatures while complex ferrite plus carbide morphologies, sometimes described as spiky pearlite, arborescent structures, or nonclassical decompositions products of austenite in Fe-Cr-C alloys, formed at low temperatures. While X-ray diffraction of extracted carbides and selected area diffraction-transmission electron microscopy (TEM) showed evidence for a mixture of M₃C and M₇C₃ carbides, thermodynamic calculations results obtained only M₇C₃ as the equilibrium carbide at the temperatures studied. A tentative explanation for the arborescent morphology is presented, based on the hypothesis of the existence of a drag force or free energy dissipation term that is locally relaxed by the partition of Cr into the carbides at the reaction front, consequently removing Cr from the interface. This article is based on a presentation made in the “Hillert Symposium on Thermodynamics & Kinetics of Migrating Interfaces in Steels and Other Complex Alloys,” December 2–3, 2004, organized by The Royal Institute of Technology in Stockholm, Sweden.