22,321 research outputs found
An optimal gap theorem
By solving the Cauchy problem for the Hodge-Laplace heat equation for
-closed, positive -forms, we prove an optimal gap theorem for
K\"ahler manifolds with nonnegative bisectional curvature which asserts that
the manifold is flat if the average of the scalar curvature over balls of
radius centered at any fixed point is a function of .
Furthermore via a relative monotonicity estimate we obtain a stronger
statement, namely a `positive mass' type result, asserting that if is
not flat, then for any
Relativistic Effects on the Appearance of a Clothed Black Hole
For an accretion disk around a black hole, the strong relativistic effects
affect every aspect of the radiation from the disk, including its spectrum,
light-curve, and image. This work investigates in detail how the images of a
thin disk around a black hole will be distorted, and what the observer will see
from different viewing angles and in different energy bands.Comment: 4 pages, 5 figures. Based on the poster presented at the Sixth
Pacific Rim Conference on Stellar Astrophysics (Xi'an, China, July 11-17,
2002). Color versions of figures are given separatel
Three-dimensional turbopump flowfield analysis
A program was conducted to develop a flow prediction method applicable to rocket turbopumps. The complex nature of a flowfield in turbopumps is described and examples of flowfields are discussed to illustrate that physics based models and analytical calculation procedures based on computational fluid dynamics (CFD) are needed to develop reliable design procedures for turbopumps. A CFD code developed at NASA ARC was used as the base code. The turbulence model and boundary conditions in the base code were modified, respectively, to: (1) compute transitional flows and account for extra rates of strain, e.g., rotation; and (2) compute surface heat transfer coefficients and allow computation through multistage turbomachines. Benchmark quality data from two and three-dimensional cascades were used to verify the code. The predictive capabilities of the present CFD code were demonstrated by computing the flow through a radial impeller and a multistage axial flow turbine. Results of the program indicate that the present code operated in a two-dimensional mode is a cost effective alternative to full three-dimensional calculations, and that it permits realistic predictions of unsteady loadings and losses for multistage machines
Physical and magnetic properties of Ba(FeRu)As single crystals
Single crystals of Ba(FeRu)As, , have been grown
and characterized by structural, magnetic and transport measurements. These
measurements show that the structural/magnetic phase transition found in pure
BaFeAs at 134 K is suppressed monotonically by Ru doping, but, unlike
doping with TM=Co, Ni, Cu, Rh or Pd, the coupled transition seen in the parent
compound does not detectably split into two separate ones. Superconductivity is
stabilized at low temperatures for and continues through the highest
doping levels we report. The superconducting region is dome like, with maximum
T ( K) found around . A phase diagram of temperature
versus doping, based on electrical transport and magnetization measurements,
has been constructed and compared to those of the
Ba(FeTM)As (TM=Co, Ni, Rh, Pd) series as well as to the
temperature-pressure phase diagram for pure BaFeAs. Suppression of the
structural/magnetic phase transition as well as the appearance of
superconductivity is much more gradual in Ru doping, as compared to Co, Ni, Rh
and Pd doping, and appears to have more in common with BaFeAs tuned
with pressure; by plotting and as a function of changes in unit
cell dimensions, we find that changed in the ratio, rather than changes
in , or V, unify the and phase diagrams for BaFeAs
and Ba(FeRu)As respectively.Comment: 16 pages, 10 figure
Knot Floer homology detects fibred knots
Ozsv\'ath and Szab\'o conjectured that knot Floer homology detects fibred
knots in . We will prove this conjecture for null-homologous knots in
arbitrary closed 3--manifolds. Namely, if is a knot in a closed 3--manifold
, is irreducible, and is monic, then is fibred.
The proof relies on previous works due to Gabai, Ozsv\'ath--Szab\'o, Ghiggini
and the author. A corollary is that if a knot in admits a lens space
surgery, then the knot is fibred.Comment: version 4: incorporates referee's suggestions, to appear in
Inventiones Mathematica
Aktivitas Antimalaria Ekstrak Metanol Daun Murbei (Morus Alba) Pada Mencit Terinfeksi Plasmodium Berghei
Malaria adalah penyakit infeksi yang disebabkan oleh parasit Plasmodium. Masalah yang muncul dalam pengendalian malaria saat ini adalah resistensi parasit terhadap obat antimalaria yang tersedia. Eksplorasi tanaman obat merupakan salah satu strategi penting dalam penemuan obat antimalaria. Morus alba dari suku Moraceae, telah digunakan dalam sistem pengobatan tradisional Indonesia untuk obat demam dan malaria. Tujuan dari penelitian ini adalah untuk mengevaluasi aktivitas antimalaria ekstrak metanol daun M. alba secara in vivo terhadap mencit yang terinfeksi Plasmodium berghei. Uji aktivitas antimalaria dilakukan dengan metode Peter\u27s Test. Artesunat digunakan sebagai obat standar dan ekstrak diberikan secara oral sekali sehari pada mencit yang terinfeksi P. berghei selama 4 hari. Persentase parasitemia diamati selama tujuh hari dengan membuat hapusan darah yang diwarnai dengan Giemsa. Data dianalisis menggunakan ANOVA satu arah, Tukey dan probit. Hasil dari penelitian ini menunjukkan bahwa ekstrak metanol daun M. alba memiliki aktivitas antimalaria terhadap mencit terinfeksi P. berghei dengan nilai ED50 dari 12,86 mg/kgBB
Local Magnetic Inhomogeneities in Lightly Doped BaFeAs
We report As NMR measurements in BaFeAs doped with Ni. Like
Co, Ni doping suppresses the antiferromagnetic and structural phase transitions
and gives rise to superconductivity for sufficiently large Ni doping. The spin
lattice relaxation rate diverges at , with a critical exponent consistent
with 3D ordering of local moments. In the ordered state the spectra quickly
broaden inhomogeneously with doping. We extract the average size of the ordered
moment as a function of doping, and show that a model in which the order
remains commensurate but with local amplitude variations in the vicinity of the
dopant fully explains our observations.Comment: 4 pages, 4 figure
Decoupling of the superconducting and magnetic (structural) phase transitions in electron-doped BaFe2As2
Study and comparison of over 30 examples of electron doped BaFe2As2 for
transition metal (TM) = Co, Ni, Cu, and (Co/Cu mixtures) have lead to an
understanding that the suppression of the structural/antiferromagnetic phase
transition to low enough temperature in these compounds is a necessary
condition for superconductivity, but not a sufficient one. Whereas the
structural/antiferromagnetic transitions are suppressed by the number of TM
dopant ions (or changes in the c-axis) the superconducting dome exists over a
limited range of values of the number of electrons added by doping (or values
of the {a/c} ratio). By choosing which combination of dopants are used we can
change the relative positions of the upper phase lines and the superconducting
dome, even to the extreme limit of suppressing the upper structural and
magnetic phase transitions without the stabilization of low temperature
superconducting dome
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