20,687 research outputs found
Star Formation Rate from Dust Infrared Emission
We examine what types of galaxies the conversion formula from dust infrared
(IR) luminosity into the star formation rate (SFR) derived by
Kennicutt (1998) is applicable to. The ratio of the observed IR luminosity,
, to the intrinsic bolometric luminosity of the newly (\la 10
Myr) formed stars,
, of a galaxy can be determined by a mean dust opacity in the
interstellar medium and the activity of the current star formation. We find
that these parameters area being is very large, and many nearby normal and active star-forming
galaxies really fall in this area. It results from offsetting two effects of a
small dust opacity and a large cirrus contribution of normal galaxies relative
to starburst galaxies on the conversion of the stellar emission into the dust
IR emission. In conclusion, the SFR determined from the IR luminosity under the
assumption of like Kennicutt (1998) is reliable within
a factor of 2 for all galaxies except for dust rich but quiescent galaxies and
extremely dust poor galaxies.Comment: Accepted by ApJL: 6 pages (emulateapj5), 2 figures (one is an extra
figure not appeared in ApJL
Toward an understanding of short distance repulsions among baryons in QCD -- NBS wave functions and operator product expansion --
We report on our recent attempts to determine the short distance behaviors of
general 2-baryon and 3-baryon forces, which are defined from the
Nambu-Bethe-Salpeter(NBS) wave function, by using the operator product
expansion and a renormalization group analysis in QCD. We have found that the
repulsion at short distance increases as the number of valence quarks increases
or when the number of different flavors involved decreases. This global
tendency suggests a Pauli suppression principle among quark fields at work.Comment: 14 pages, add two exmples in sect.3.4, a version accepted for
Progress of Theoretical Physic
Minimization of the vibration energy of thin-plate structure
An optimization method is proposed to reduce the vibration of thin plate structures. The method is based on a finite element shell analysis, a modal analysis, and a structural optimization method. In the finite element analysis, a triangular shell element with 18 dof is used. In the optimization, the overall vibration energy of the structure is adopted as the objective function, and it is minimized at the given exciting frequency by varying the thickness of the elements. The technique of modal analysis is used to derive the sensitivity of the vibration energy with respect to the design variables. The sensitivity is represented by the sensitivities of both eigenvalues and eigenvectors. The optimum value is computed by the gradient projection method and a unidimensional search procedure under the constraint condition of constant weight. A computer code, based on the proposed method, is developed and is applied to design problems using a beam and a plate as test cases. It is confirmed that the vibration energy is reduced at the given exciting frequency. For the beam excited by a frequency slightly less than the fundamental natural frequency, the optimized shape is close to the beam of uniform strength
Mobilizing agro-biodiversity and social networks to cope with adverse effects of climate and social changes: experiences from Kitui, Kenya
Poster presented at 13th Congress of the International Society of Ethnobiology. Montpellier (France), 20-25 May 201
Optimum design of a gearbox for low vibration
A computer program was developed for designing a low vibration gearbox. The code is based on a finite element shell analysis, a modal analysis, and a structural optimization method. In the finite element analysis, a triangular shell element with 18 degrees-of-freedom is used. In the optimization method, the overall vibration energy of the gearbox is used as the objective function and is minimized at the exciting frequency by varying the finite element thickness. Modal analysis is used to derive the sensitivity of the vibration energy with respect to the design variable. The sensitivity is representative of both eigenvalues and eigenvectors. The optimum value is computed by the gradient projection method and a unidimensional search procedure under the constraint condition of constant weight. The computer code is applied to a design problem derived from an experimental gearbox in use at the NASA Lewis Research Center. The top plate and two side plates of the gearbox are redesigned and the contribution of each surface to the total vibration is determined. Results show that optimization of the top plate alone is effective in reducing total gearbox vibration
Two-Fluid MHD Simulations of Converging HI Flows in the Interstellar Medium. I: Methodology and Basic Results
We develop an unconditionally stable numerical method for solving the
coupling between two fluids (frictional forces/heatings, ionization, and
recombination), and investigate the dynamical condensation process of thermally
unstable gas that is provided by the shock waves in a weakly ionized and
magnetized interstellar medium by using two-dimensional two-fluid
magnetohydrodynamical simulations. If we neglect the effect of magnetic field,
it is known that condensation driven by thermal instability can generate high
density clouds whose physical condition corresponds to molecular clouds
(precursor of molecular clouds). In this paper, we study the effect of magnetic
field on the evolution of supersonic converging HI flows and focus on the case
in which the orientation of magnetic field to converging flows is orthogonal.
We show that the magnetic pressure gradient parallel to the flows prevents the
formation of high density and high column density clouds, but instead generates
fragmented, filamentary HI clouds. With this restricted geometry, magnetic
field drastically diminishes the opportunity of fast molecular cloud formation
directly from the warm neutral medium, in contrast to the case without magnetic
field.Comment: ApJ accepte
Tunnel magnetoresistance and interfacial electronic state
We study the relation between tunnel magnetoresistance (TMR) and interfacial
electronic states modified by magnetic impurities introduced at the interface
of the ferromagnetic tunnel junctions, by making use of the periodic Anderson
model and the linear response theory. It is indicated that the TMR ratio is
strongly reduced depending on the position of the -levels of impurities,
based on reduction in the spin-dependent -electron tunneling in the majority
spin state. The results are compared with experimental results for Cr-dusted
ferromagnetic tunnel junctions, and also with results for metallic multilayers
for which similar reduction in giant magnetoresistance has been reported.Comment: 5 pages, 4 figures, 2 column revtex4 format, ICMFS 2002 (Kyoto
Decoupling of the -scalar mass in softly broken supersymmetry
It has been shown recently that the introduction of an unphysical
-scalar mass is necessary for the proper renormalization
of softly broken supersymmetric theories by dimensional reduction (\drbar).
In these theories, both the two-loop -functions of the scalar masses and
their one-loop finite corrections depend on . We find, however,
that the dependence on can be completely removed by slightly
modifying the \drbar renormalization scheme. We also show that previous \drbar
calculations of one-loop corrections in supersymmetry which ignored the
contribution correspond to using this modified scheme.Comment: 7 pages, LTH-336, NUB-3094-94TH, KEK-TH-40
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