4,105 research outputs found

    The atomistic structure and energy of nascent dislocation loops

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    An harmonic lattice theory is used, in conjunction with Mura's theory of eigendistorsions, to study the structure and energetics of nascent dislocation loops in face-centred-cubic (FCC) crystals. An analytical expression for the activation energies of such loops is derived. The results obtained herein indicate that thermal activation of small dislocation loops is possible at high stress levels such as those found in the vicinity of a crack tip. The implications of these results in understanding phenomena such as the brittle-ductile transition are discussed

    An Analysis of the Quasicontinuum Method

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    The aim of this paper is to present a streamlined and fully three-dimensional version of the quasicontinuum (QC) theory of Tadmor et al. and to analyze its accuracy and convergence characteristics. Specifically, we assess the effect of the summation rules on accuracy; we determine the rate of convergence of the method in the presence of strong singularities, such as point loads; and we assess the effect of the refinement tolerance, which controls the rate at which new nodes are inserted in the model, on the development of dislocation microstructures.Comment: 30 pages, 16 figures. To appear in Jornal of the Mechanics and Physics of Solid

    Molecular and Clinical Features of Heterogeneous Vancomycin Intermediate Staphylococcus aureus in Tertiary Care Hospitals of South India

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    Objectives: This study aimed to detect heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) among methicillin resistant S. aureus (MRSA) isolated from healthcare-associated infections and identify staphylococcal cassette chromosome mec (SCCmec) types. Methods: Isolation and identification of MRSA were done using standard bacteriological methods. Antimicrobial susceptibility testing was done using Kirby-Bauer disc diffusion and macrolide-lincosamide-streptogramin B (MLSB) phenotypes identified using D test. The minimum inhibitory concentration (MIC) of vancomycin was determined using agar dilution. hVISA were confirmed by modified population analysis profile-area under the curve (PAP-AUC) test. SCCmec types and Panton-Valentine leukocidin (pvl) were detected using multiplex PCR. Results: Out of 220 MRSA stains, 14 (6.4%) were hVISA. None of the MRSA isolate was vancomycin intermediate or resistant. All hVISA were susceptible to linezolid and teicoplanin. Macrolide-streptogramin B (MSB) phenotype was present in 42.9% hVISA. 92.9% hVISA strains had vancomycin MIC in the range 1-2 µg/mL. Majority of hVISA and vancomycin susceptible MRSA were isolated from skin and soft tissue infections. SCCmec III and IV were present in 50% and 35.7% hVISA respectively. 14.3% hVISA harboured SCCmec V. Conclusion: The rate of hVISA among MRSA was 6.4%. MRSA strains should be tested for hVISA before starting vancomycin treatment. None of the isolates was vancomycin intermediate or resistant. All the hVISA strains were susceptible to linezolid and teicoplanin. The majority of hVISA were isolated from skin and soft tissue infections. The majority hVISA harboured SCCmec III and IV. Keywords: MRSA; Hospital infection; Molecular typing; Vancomyci

    Possible ferro-spin nematic order in NiGa2S4

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    We explore the possibility that the spin-1 triangular lattice magnet NiGa2 S4 may have a ferro-nematic ground state with no frozen magnetic moment but a uniform quadrupole moment. Such a state may be stabilized by biquadratic spin interactions. We describe the physical properties of this state and suggest experiments to help verify this proposal. We also contrast this state with a `non-collinear' nematic state proposed earlier by Tsunetsugu and Arikawa for NiGa2S4

    Non recurrent laryngeal nerve with right aberrant subclavian artery in recurrent case of papillary carcinoma of thyroid: an interesting clinical entity.

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    Background/objectives: A nonrecurrent laryngeal nerve is a rare anatomical variant and a routine preoperative imaging studies are not indicated. NRLN is related with absence of the brachiocephalic trunk and aberrant (mainly retroesophageal) course of theright subclavian artery which is evident on contrast enhanced CT scan of the chest.Case report: The patient presented with a swelling in the neck for 4 months which is slowly increasing in size. Patient gives history of a surgery done in the neck with an old midlinesuprasternal scar which was done 40 years earlier.laryngoscopic mirror examinartion was normal with moving vocal cords. Rest of the oral and oropharyngeal examination along with completeblood picture and biochemical investigations were normal. The patient was not a known diabetic or hypertensive.Conclusion: Accurate knowledge of frequent variations of the nerve along with the non recurrent variant reduces the risk of intraoperative injury. A nonrecurrent laryngealnerve(NRLN) is a rare anatomical variant and a routine preoperative imaging studies are not indicated. NRLN is related with absence of the brachiocephalic trunk and aberrant(mainly retroesophageal) course of the right subclavian artery which is evident on contrast enhanced CT scan of the chest.

    Surface pressure measurements at two tips of a model helicopter rotor in hover

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    Surface pressures were measured near the tip of a hovering single-bladed model helicopter rotor with two tip shapes. The rotor had a constant-chord, untwisted blade with a square, flat tip which could be modified to a body-of-revolution tip. Pressure measurements were made on the blade surface along the chordwise direction at six radial stations outboard of the 94 percent blade radius. Data for each blade tip configuration were taken at blade collective pitch angles of 0, 6.18 and 11.4 degrees at a Reynolds number of 736,000 and a Mach number of 0.25 both based on tip speed. Chordwise pressure distributions and constant surface pressure contours are presented and discussed

    Freezing characteristics of tropical fishes 2. Tilapia (Tilapia mosambica)

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    Tilapia from fresh water and brackish water-sources behaved differently during iced and frozen storage. The former showed an ice storage shelf life of about 13 days while the latter showed signs of spoilage beyond 10 days. In their respective freezing characteristics, the samples from the two sources exhibited far more significant variations. The fresh water type iced for 13 days preserved well for over 24 weeks when frozen and kept at a temperature of -18° C, while the brackish water variety held in ice for 10 days and subsequently frozen gave a shelf life of only 8 weeks under similar conditions

    Quasicontinuum Models of Interfacial Structure and Deformation

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    Microscopic models of the interaction between grain boundaries (GBs) and both dislocations and cracks are of importance in understanding the role of microstructure in altering the mechanical properties of a material. A recently developed mixed atomistic and continuum method is extended to examine the interaction between GBs, dislocations and cracks. These calculations elucidate plausible microscopic mechanisms for these defect interactions and allow for the quantitative evaluation of critical parameters such as the stress to nucleate a dislocation at a step on a GB and the force needed to induce GB migration.Comment: RevTex, 4 pages, 4 figure
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