2,278 research outputs found
The Virgo High-Resolution CO Survey. II. Rotation Curves and Dynamical Mass Distributions
Based on a high-resolution CO survey of Virgo spirals with the Nobeyama
Millimeter-wave Array, we determined the dynamical centers using velocity
fields, and derived position-velocity diagrams (PVDs) along the major axes of
the galaxies across their dynamical centers. We applied a new iteration method
to derive rotation curves (RCs), which reproduce the observed PVDs. The
obtained high-accuracy RCs generally show steep rise in the central 100 to 200
pc regions, followed by flat rotation in the disk. We applied a deconvolution
method to calculate the surface-mass density (SMD) using the RCs based on two
extreme assumptions that the mass distribution is either spherical or thin-disk
shaped. Both assumptions give nearly identical results, agreeing with each
other within a factor of two at any radii. The SMD distributions revealed
central massive cores with peak SMD of 10^4 - 10^5 Msun pc^-2 and total mass
within 200 pc radius of the order of about 10^9 Msun Correlation analysis among
the derived parameters show that the central CO-line intensity is positively
correlated with the central SMD, which suggests that the deeper is the
gravitational potential, the higher is the molecular gas concentration in the
nuclei regardless morphological types.Comment: PASJ 2003 in press, Latex 12 pages, 6 figures (Bigger gif/ps figures
available at http://www.ioa.s.u-tokyo.ac.jp/radio/virgo2
Resonant Two-Magnon Raman Scattering and Photoexcited States in Two-Dimensional Mott Insulators
We investigate the resonant two-magnon Raman scattering in two-dimensional
(2D) Mott insulators by using a half-filled 2D Hubbard model in the strong
coupling limit. By performing numerical diagonalization calculations for small
clusters, we find that the Raman intensity is enhanced when the incoming photon
energy is not near the optical absorption edge but well above it, being
consistent with experimental data. The absence of resonance near the gap edge
is associated with the presence of background spins, while photoexcited states
for resonance are found to be characterized by the charge degree of freedom.
The resonance mechanism is different from those proposed previously.Comment: REVTeX4, 4 pages, 3 figures, to be published in Phys. Rev. Let
Effect of Gravity on the Macro-Segregation of Larger Steel Ingots
Upon the problem involved in the study of solidification and segregation of larger steel ingots numerous papers have hitherto been published. Nevertheless their nature
is still vague from both the scientific and practical
points of view.
Previous studies have been devoted to the measurement of specific physical values of molten steel, the detailed observation of the sections of solidified ingots, simulat-ion experiments using different materials, experiments on the formation and change of non-metallic inclusions, etc. Isn't there any room for re-examination in these methods of study? Even if these items could be clarified in details, it would not give rise to a satisfactory solut-ion for the phenomenon of ''differential freezing" and to the reduction of segregation and other accompanied defects.
We feel much necessity of thorough studies on the solidi-fication and segregation of large steel ingots, before we rush into the epoch of large scale vacuum casting of steel ingots
Transformation Characteristics of Large Steel Forgings
Inspite of voluminous papers hitherto published on the heat treatment of large steel forgings,it would not he exaggerated to say that the transformation characteri-stics of them are not fully known yet. The cause is attributed , to our best knowledge, to those factors as inner local properties of original ingots , effects of forging and accompanied soaking, liberation and trans-mission of latent heat of transformation , Hydrogen retained at the deep portions, thermal and transformat-
ion stresses etc.
which refuse analogy with the results obtained by
means of small specimens
A Contribution to the Service Failure of Large Chilled Iron Rolls due to Fatigue
A case of service rupture of chilled iron roll due to fatigue is presented with condition of rupture, invest-igation of the cause, and remedial result through remo-delling.
As a result of this, it is suggested that service strength of chilled iron rolls should be considered
through fatigue, and that standard size is not necessar-ily of sufficient strength from this point of view ; a remark for the prevention of service failures in existent mills, and to which reference is desired to make in bui-lding new mill
Temperature and Dimensionality Dependences of Optical Absorption Spectra in Mott Insulators
We investigate the temperature dependence of optical absorption spectra of
one-dimensional (1D) and two-dimensional (2D) Mott insulators by using an
effective model in the strong-coupling limit of a half-filed Hubbard model. In
the numerically exact diagonalization calculations on finite-size clusters, we
find that in 1D the energy position of the absorption edge is almost
independent of temperature, while in 2D the edge position shifts to lower
energy with increasing temperature. The different temperature dependence
between 1D and 2D is attributed to the difference of the coupling of the charge
and spin degrees of freedom. The implications of the results on experiments are
discussed in terms of the dimensionality dependence.Comment: 5 pages, 4 figure
Theoretical study of angle-resolved two-photon photoemission in two-dimensional insulating cuprates
We propose angle-resolved two-photon photoemission spectroscopy (AR-2PPES) as
a technique to detect the location of the bottom of the upper Hubbard band
(UHB) in two-dimensional insulating cuprates. The AR-2PPES spectra are
numerically calculated for small Hubbard clusters. When the pump photon excites
an electron from the lower Hubbard band, the bottom of the UHB is less clear,
but when an electron in the nonbonding oxygen band is excited, the bottom of
the UHB can be identified clearly, accompanied with additional spectra
originated from the spin-wave excitation at half filling.Comment: 5 pages, 4 figure
Investigation of the thermal expansion and heat capacity of the CaCu3Ti4O12 ceramics
The thermal expansion of the CaCu3Ti4O12 ceramics has been measured over a wide temperature
range 120–1200 K. The high quality of the samples under study has been confirmed by good agreement of
the results of measurements of the heat capacity in the range 2–300 K and in the vicinity of the phase transition of magnetic nature at 25 K with the data for the single crystal. No anomalies in the thermal expansion
that can be associated with the phase transition at 726–732 K assumed by other investigators have been found.
The influence exerted on the thermal expansion by the heat treatment of the sample in a helium atmosphere
and in air has been investigated
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