3,334 research outputs found
Exciton-exciton scattering: Composite boson versus elementary boson
This paper introduces a new quantum object, the ``coboson'', for composite
particles, like the excitons, which are made of two fermions. Although commonly
dealed with as elementary bosons, these composite bosons -- ``cobosons'' in
short -- differ from them due to their composite nature which makes the
handling of their many-body effects quite different from the existing
treatments valid for elementary bosons. Due to this composite nature, it is not
possible to correctly describe the interaction between cobosons as a potential
. Consequently, the standard Fermi golden rule, written in terms of ,
cannot be used to obtain the transition rates between exciton states. Through
an unconventional expression for this Fermi golden rule, which is here given in
terms of the Hamiltonian only, we here give a detailed calculation of the time
evolution of two excitons. We compare the results of this exact approach with
the ones obtained by using an effective bosonic exciton Hamiltonian. We show
that the relation between the inverse lifetime and the sum of transition rates
for elementary bosons differs from the one of composite bosons by a factor of
1/2, whatever the mapping from composite bosons to elementary bosons is. The
present paper thus constitutes a strong mathematical proof that, in spite of a
widely spread belief, we cannot forget the composite nature of these cobosons,
even in the extremely low density limit of just two excitons. This paper also
shows the (unexpected) cancellation, in the Born approximation, of the
two-exciton transition rate for a finite value of the momentum transfer
Single-crystal growth of underdoped Bi-2223
To investigate the origin of the enhanced Tc ({\approx} 110 K) of the
trilayer cuprate superconductor Bi2Sr2Ca2Cu3O10+{\delta} (Bi-2223), its
underdoped single crystals are a critical requirement. Here, we demonstrate the
first successful in-plane resistivity measurements of heavily underdoped
Bi-2223 (zero-resistivity temperatures {\approx} 20~35 K). Detailed crystal
growth methods, the annealing process, as well as X-ray diffraction (XRD) and
magnetic susceptibility measurement results are also reported.Comment: 4 pages, 4 figures, 27th International Symposium on
Superconductivity, ISS 2014, to appear in Physics Procedi
Low-Degree Partial Melting Experiments of CR and H Chondrite Compositions: Implications for Asteroidal Magmatism Recorded in GRA 06128 and GRA 06129 T
Studies of differentiated meteorites have revealed a diversity of differentiation processes on their parental asteroids; these differentiation mechanisms range from whole-scale melting to partial melting without the core formation [e.g., 1]. Recently discovered paired achondrites GRA 06128 and GRA 06129 (hereafter referred to as GRA) represent unique asteroidal magmatic processes. These meteorites are characterized by high abundances of sodic plagioclase and alkali-rich whole-rock compositions, implying that they could originate from a low-degree partial melt from a volatile-rich oxidized asteroid [e.g., 2, 3, 4]. These conditions are consistent with the high abundances of highly siderophile elements, suggesting that their parent asteroid did not segregate a metallic core [2]. In this study, we test the hypothesis that low-degree partial melts of chondritic precursors under oxidizing conditions can explain the whole-rock and mineral chemistry of GRA based on melting experiments of synthesized CR- and H-chondrite compositions
Study on the Prognosis of Tuberculous Meningitis Treated with Streptomycin in Children
この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました
Characteristics of Kiso Ultra-Violet Excess Galaxies
We examined the general characteristics of the Kiso Ultra-violet Excess
Galaxies (KUGs). We present for the first time the quantitative expressions for
the criteria of the KUGs; the boundary color separating the KUGs from the
non-KUGs is (B-V)_{T} = 0.74 and the KUG degrees of UV strength are found to
correlate with the mean (B-V)_{T} colors. We investigate the nature of the
KUGs, a sample of blue galaxy population, and show that (1) about a half of the
KUGs are spiral galaxies with Sb to Scd, (2) the KUGs are biased to late-type
galaxies and include early-type galaxies with young star populations, and (3)
the KUGs are preferably found among less luminous galaxies with log L(B) < 10.
The KUGs also contain the post-starburst galaxies, many of which are found
among the blue galaxy population at intermediate redshifts. The analysis of the
far-infrared data shows that a typical present-to-past star formation rate for
a KUG is 0.4.Comment: Revised version of astro-ph/9706088, accepted manuscript for AJ;
uuencoded gzip'ed tar'ed file containing 25 files; a manuscript (aasms4), 7
tables (aj_pt4), 17 PS figures; To be appeared in The Astronomical Journal,
Vol. 114, No. 5 (1997 November issue
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