Duplex surface treatment of AISI 1045 steel via plasma nitriding of chromized layer

In this work AISI 1045 steel were duplex treated via plasma nitriding of chromized layer. Samples were pack chromized by using a powder mixture consisting of ferrochromium, ammonium chloride and alumina at 1273 K for 5 h. The samples were then plasma-nitrided for 5 h at 803 K and 823 K, in a gas mixture of 75%N₂ + 25%H₂. The treated specimens were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and Vickers micro-hardness test. The thickness of chromized layer before nitriding was about 8 μm and it was increased after plasma nitriding. According to XRD analysis, the chromized layer was composed of chromium and iron carbides. Plasma nitriding of chromized layer resulted in the formation of chromium and iron nitrides and carbides. The hardness of the duplex layers was significantly higher than the hardness of the base material or chromized layer. The main cause of the large improvement in surface hardness was due to the formation of Cr_xN and Fe_xN phases in the duplex treated layers. Increasing of nitriding temperature from 803 to 823 K enhanced the formation of CrN in the duplex treated layer and increased the thickness of the nitrided layer.     

Crystal structure of the zinc-dependent beta-lactamase from Bacillus cereus at 1.9 A resolution: binuclear active site with features of a mononuclear enzyme

The structure of the zinc-dependent beta-lactamase II from Bacillus cereus has been determined at 1.9 A resolution in a crystal form with two molecules in the asymmetric unit and 400 waters (space group P3121; Rcryst = 20.8%). The active site contains two zinc ions: Zn1 is tightly coordinated by His86, His88, and His149, while Zn2 is loosely coordinated by Asp90, Cys168, and His210. A water molecule (W1) lies between the two zinc ions but is significantly closer to Zn1 and at a distance of only 1.9 A is effectively a hydroxide moiety and a potential, preactivated nucleophile. In fact, Asp90 bridges W1 to Zn2, and its location is thus distinct from that of the bridging water molecules in the binuclear zinc peptidases or other binuclear zinc hydrolases. Modeling of penicillin, cephalosporin, and carbapenem binding shows that all are readily accommodated within the shallow active site cleft of the enzyme, and the Zn1-bound hydroxide is ideally located for nucleophilic attack at the beta-lactam carbonyl. This enzyme also functions with only one zinc ion present. The Zn1-Zn2 distances differ in the two independent molecules in the crystal (3.9 and 4.4 A), yet the Zn1-W1 distances are both 1.9 A, arguing against involvement of Zn2 in W1 activation. The role of Zn2 is unclear, but the B. cereus enzyme may be an evolutionary intermediate between the mono- and bizinc metallo-beta-lactamases. The broad specificity of this enzyme, together with the increasing prevalence of zinc-dependent metallo-beta-lactamases, poses a real clinical threat, and this structure provides a basis for understanding its mechanism and designing inhibitors.     

Scalable shared-memory multiprocessor architectures

Directory-based and bus-based cache coherence schemes are defined and described. Directory-based schemes can be classified as centralized or distributed. Both categories support local caches to improve processor performance and reduce traffic in the interconnection. Schemes using presence flags, B pointers, and linked lists are discussed. Bus-based systems provide uniform memory access to all processors. This memory organization allows a simpler programming model, making it easier to develop new parallel applications or to move existing applications from a uniprocessor to a parallel system. Two architectural variations of bus-based systems are described: multiple-bus and hierarchical architectures     

Analysis of ecdysteroid action in Malacosoma disstria cells: cloning selected regions of E75- and MHR3-like genes

IPRI-MD-66 (MD-66) cells respond to 20-hydroxyecdysone (20E, 4 x 10(-6) M) in the medium by producing cytoplasmic extensions, clumping and attaching themselves to the substrate. These morphological changes are at a maximum by 6 days post treatment. Degenerate oligonucleotides, designed on the basis of conserved amino acid sequences in the DNA and ligand binding regions of the members of the steroid hormone receptor superfamily, were used in RNA-PCR to isolate two cDNA fragments, Malacosoma disstria hormone receptor 2 (MdHR2) and Malacosoma disstria hormone receptor 3 (MdHR3) from the MD-66 cells. Comparison of deduced amino acid sequences of these cDNA fragments with the members of the steroid hormone receptor superfamily showed that MdHR2 is most closely related to E75 proteins of Manduca sexta, Galleria mellonella and Drosophila melanogaster. The MdHR3 is most closely related to Manduca hormone receptor 3 (MHR3), Galleria hormone receptor 3 (GHR3) and Drosophila hormone receptor 3 (DHR3) proteins. At a concentration of 4 x 10(-6) M, 20E induces the expression of MdHR2 and MdHR3 beginning at 3 h, reaching maximum levels in 12 h and declining in 24 h. MdHR2 binds to a 2.5 kb mRNA, whereas MdHR3 binds to a 4.5 kb mRNA. Based on sequence similarity, RNA size and ecdysone inducibility, we conclude that these cDNA fragments, cloned from MD-66 cells, are regions of E75- (MdHR2) and MHR3- (MdHR3) like genes.     

Effect of heat treatment on wear behavior of HVOF thermally sprayed WC-Co coatings

A WC-17Co coating was deposited onto ST37 mild steel substrate using HVOF spray technique and then heat treated at different temperatures in a vacuum chamber. The coatings were then evaluated in the as sprayed and heat treated conditions. Inspections by SEM and phase analysis by XRD indicated that some brittle eta (η) phases were produced at high temperature heat treatments. Generation of these phases increased the coating's hardness and decreased fracture toughness of the coating. Tribological properties were studied under dry condition by using pin on disc machine and diamond metal matrix composite disc as counterface. Wear test results showed that as sprayed deposit had the best wear resistance and its wear mechanism was sharp cutting abrasion. The weight loss in heat treated samples increased by increasing heat treatment temperature and the wear mechanisms gradually changed from cutting to gouging abrasion.     

Surface recording of His-Purkinje activity on an every-beat basis without digital averaging

Efforts to record evidence of electrical activity from the body surface originating in the His bundle or bundle branches have been reported since 1973. Almost exclusively, these techniques have required digital averaging of 50-100 sequential cardiac cycles. For immediate diagnostic, therapeutic and prognostic application, recording on an every-beat basis is highly desirable. This is especially important in instances of changing atrioventricular conduction, arrhythmias or less-than-constant RR intervals. Our object has been to develop a system for more nearly optimal noise reduction, to avoid the disadvantages of serial signal averaging, and to be able to record His-Purkinje activity in man on an every-beat basis. Using multiple parallel inputs wih linear amplification, additional logarithmic amplification, some bandpass filtering, and a logic circuit that ultimately examines and accepts or rejects a deflection as "true" signal, we can record, in most instances, on a beat-by-beat basis, this very valuable component of the cardiac electrical cycle.     

Corrosion behavior of severely plastic deformed magnesium based alloys: A review

The purpose of this paper is to provide an overview of the impact of the microstructural modifications via severe plastic deformation on the corrosion behavior of magnesium and its alloys, especially when they are considered to be biodegradable materials. Mechanical processing involved in grain refinement modifies textures and residual stresses of materials which have their own impacts on corrosion behavior as reported in a large number of studies. However, the existing literature on the influence of microstructure on corrosion resistance is often contradictory, which discloses a lack of knowledge in this area. In this article the effects and contributions of critical factors such as the grain size, texture, residual stress and second phase distribution, affected by severe plastic deformation, on the magne-sium corrosion behavior is reviewed in order to find a relation between the microstructure and corrosion resistance.     

An energy efficient stable clustering approach using fuzzy extended grey wolf optimization algorithm for WSNs

Wireless Networks - Wireless sensor network (WSN) is a cost-effective networking solution for information updating in the coverage radius or in the sensing region. To record a real-time event, a...