381,081 research outputs found
Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems
No full textSemiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy EF locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density ne and not inversely proportional to ne. While the magnetoresistance (MR) and Nernst coefficient vanish when EF locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when EF decreases below the BCP. Both of them are nonmonotonic functions of EF below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.National Natural Science Foundation of China [11274018]SCI(E)[email protected]
Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel
No full textA transmission electron microscopy study was conducted on nanoprecipitates formed in Ti microalloyed transformation-inducedplasticity-assisted steels, revealing the presence of Ti(N), Ti2CS and a novel type of ultra-fine Fe(C) precipitate. The matrix/precipitate orientation relationships, sizes and shapes were investigated in detail. The ultrafine, disc-shaped Fe(C) precipitates have sizes of 2–5 nm and possess a hexagonal close packed crystal structure with lattice parameters a = 5.73 ± 0.05A ? , c = 12.06 ± 0.05A ?. They are in a well-defined Pitsch–Schrader orientation relationship with the basal plane of the precipitate parallel to the [110] habit plane of the surrounding body-centred-cubic ferritic matrix. Detailed analysis of precipitate distribution, orientation relationship, lattice mismatch and inter-particle spacing suggests that these ultrafine precipitates contribute considerably to the strengthening of these steels.High Resolution Electron Microscopy (HREM)Kavli Institute of NanoscienceApplied Science
Structural tale of two novel (Cr,Mn)C carbides in steel
No full textChromium (Cr), Manganese (Mn), and Carbon (C) are well known alloying elements used in technologically important alloy steels and advanced high strength steels. It is known that binary CrCx and MnCx carbides can be formed in steels, but in this study we reveal for the first time that Cr and Mn were found combined in novel ternary cementite type (Cr,Mn)C carbides. Electron diffraction experiments showed that Cr, Mn, and C have formed two distinct carbide phases possessing orthorhombic and monoclinic crystal structures. Density functional theory (DFT) calculations were performed on these phases and excellent agreement was found between calculations and experiments on the lattice parameters and relative atomic positions. The calculations showed that the combination of Mn and Cr has resulted in a very high thermodynamic stability of the (Cr,Mn)C carbides, and that local structural relaxations are associated with carbon additions. Possible implications of these ternary carbides for novel applications in steel design and manufacturing are discussed.Quantum NanoscienceApplied Science
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structural and magnetic properties of NiCx and NiNx (x=0 to 1/3) solid solutions from first-principles calculations
No full textFirst-principles calculations have been performed for a variety of Ni3X (X = C, N) phases, as well as for NiXy (y = 0 to 1/3) solid solutions to clarify the persistent controversy regarding its magnetic state. The calculations show that the solid solution phases based on hexagonal-close-packed (hcp or ?-) Ni have relatively high stability for X concentrations greater than about 0.1 whereas the face-centered-cubic (fcc or ?-) Ni phases are favored for smaller X concentration. Hence, during carburization or nitridization of Ni, a phase transformation is to be expected. In spite of the close-packed nature of both hcp- and fcc-based solid solutions, X quenches the magnetization more effectively in fcc than in hcp-based solid solutions. These findings resolve many apparently contradictory experimental observations concerning C- and N-containing Ni alloys in the literature.QN/Quantum NanoscienceApplied Science
Soil organic matter recovery in semiarid grasslands: implications for the Conservation Reserve Program
No full textAlthough the effects of cultivation on soil organic matter and nutrient supply capacity are well understood, relatively little work has been done on the long-term recovery of soils from cultivation. We sampled soils from 12 locations within the Pawnee National Grasslands of northeastern Colorado, each having native fields and fields that were historically cultivated but abandoned 50 years ago. We also sampled fields that had been cultivated for at least 50 years at 5 of these locations. Our results demonstrated that soil organic matter, silt content, microbial biomass, potentially mineralizable N, and potentially respirable C were significantly lower on cultivated fields than on native fields. Both cultivated and abandoned fields also had significantly lower soil organic matter and silt contents than native fields. Abandoned fields, however, were not significantly different from native fields with respect to microbial biomass, potentially mineralizable N, or respirable C. In addition, we found that the characteristic small-scale heterogeneity of the shortgrass steppe associated with individuals of the dominant plant, Bouteloua gracilis, had recovered on abandoned fields. Soil beneath plant canopies had an average of 200 g/m2 more C than between-plant locations. We suggest that 50 years is an adequate time for recovery of active soil organic matter and nutrient availability, but recovery of total soil organic matter pools is a much slower process. Plant population dynamics may play an important role in the recovery of shortgrass steppe ecosystems from disturbance, such that establishment of perennial grasses determines the rate of organic matter recovery
Vanishing White Matter Disease Associated With Ptosis and Myoclonic Seizures
No full textA 5-year-old boy who presented with progressive ataxia, neuroregression, and worsening with febrile illnesses is described. He also had myoclonic jerks and ptosis. His elder sister had died of a similar illness. Serial magnetic resonance imaging of the brain demonstrated extensive abnormality of the cerebral white matter with rarefaction and cystic degeneration, suggestive of vanishing white matter disease. The patient was found to be compound heterozygous for 2 new mutations in the gene EIF2B5, confirming the diagnosis. © The Author(s) 2011
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Determination Of The Valence Band Offset Of A μ-c/c-si(100) Heterojunction Using Low Energy Yield Spectroscopy
No full textThe valence band offset developed in the heterostructure formed by depositing carbon on a Si(1OO) substrate was determined using a combination of low energy yield spectroscopy and x-ray photoemission spectroscopy. The spontaneous formation of an SiC layer between the crystalline silicon substrate and the carbon film was observed. Valence band offsets of 0.77 ± 0.08 eV at the SiC/c-Si interface and 1.55 ± 0.08 eV for the μC/SiC interface were found. Taking into account the band bending at the SiC layer after the microcrystalline graphite layer formation, the valence band offset between the silicon substrate and the carbon layer was evaluated to be 0.63 ± 0.08 eV, with the valence band edge of the carbon film being at higher energy than that of the silicon.114955961Mandel, T., Frischholz, M., Heibig, R., Birkle, S., Hammerschmidt, A., (1993) Appl. Surf. Sci., 65-66, p. 784Wang, W.N., Fox, N.A., Richardson, D., Lynch, G.M., Steeds, J.W., (1997) J. Appl. Phys., 81, p. 1505Amaratunga, G., Segal, D., Mckenzie, D.R., (1991) Appl. Phys. Lett., 59, p. 69Konofaos, N., Thomas, C.B., (1997) J. Appl. Phys., 81, p. 6238Margaritondo, G., Capasso, F., (1987) Heterojunctions Band Discontinuities-Physics Device Applications, , Amsterdam: North-HollandRobertson, J., (1987) J. Non-Ciyst. Sollte, 97 (98), p. 863Sebastiani, M., Digaspare, L., Capellini, G., Bittencourt, C., Evangelisti, F., (1995) Phys. Rev. Lett., 75, p. 3352Brown, T.M., Bittencourt, C., Sebastiani, M., Evangelisti, F., (1997) Phys. Rev. B, 55, p. 9904Kusmoki, I., Igari, Y., (1992) Appl. Surf. Sci., 59, p. 95Bittencourt, C., De Seta, M., Evangelisti, F., (1998) J Vac. Sci. Technol. B, 16, p. 1599Bittencourt, C., (1998) J. Phys.: Condera., , Matter submittedRobertson, J., (1991) Prog. Solid State Chem., 21, p. 199Robertson, J., O'Reilly, E.P., (1987) Phys. Rev. B, 35, p. 2946noteHarrison, W.A., (1985) J. Vac. Sci. Technol. B, 3, p. 1231Tersoff, J., (1984) Phys. Rev. B, 30, p. 4874Tersoff, J., (1986) Phys. Rev. Lett., 56, p. 2755List, R.S., Spicer, W.E., (1988) J. Vac. Sci. Technol. B, 6, p. 122
Carbon isotope and C/N ratios of suspended matter in rivers: An indicator of seasonal change in C4/C3 vegetation
No full text A combination of d 13C values with C/N ratios in suspended matter has been used to examine the seasonal relationshipbetween C4 and C3 vegetation along the Loess Plateau, NW China. The C isotopic composition of suspended organic matter in rivers, together with C/N ratios can differentiate between soil and plant material, and can be used to estimate the relative contributions of soil organic C and plant litter to the suspended matter. The relationship between C isotopic composition and C/N ratios indicates that the samples are a mixture of two end members: (1) modern soils with relatively constant d 13C values, low C content and low C/N ratios; (2) plant litter with varying d 13C values, high C content and high C/N ratios. The results reflect the seasonal distribution of C4/C3 vegetation within the area studied, as part of the Loess Plateau. The abundance of C4 grasses is about 20%for the current summer vegetation ecosystem in the eastern part of the Loess Plateau. Hence, the use of d 13C values and C/N ratios of suspended matter in rivers and modern soil may be useful for reflecting seasonal distribution of C4/C3 vegetation in catchments. This could be a useful tool for distinguishing between catchments for GIS studies, and long term planning for ecological management of catchment areas.</p
- …
