286 research outputs found
Localization of Gravity on Brane Embedded in and
We address the localization of gravity on the Friedmann-Robertson-Walker type
brane embedded in either or bulk space,and derive two
definite limits between which the value of the bulk cosmological constant has
to lie in order to localize the graviton on the brane.The lower limit implies
that the brane should be either or 4d Minkowski in the
bulk.The positive upper limit indicates that the gravity can be trapped also on
curved brane in the bulk space.Some implications to recent
cosmological scenarios are also discussed.Comment: 18 pages, 3 figures, Latex fil
Insights on the Sun birth environment in the context of star-cluster formation in hub-filament systems
Cylindrical molecular filaments are observed to be the main sites of Sun-like
star formation, while massive stars form in dense hubs, at the junction of
multiple filaments. The role of hub-filament configurations has not been
discussed yet in relation to the birth environment of the solar system and to
infer the origin of isotopic ratios of Short-Lived Radionuclides (SLR, such as
Al) of Calcium-Aluminum-rich Inclusions (CAIs) observed in meteorites.
In this work, we present simple analytical estimates of the impact of stellar
feedback on the young solar system forming along a filament of a hub-filament
system. We find that the host filament can shield the young solar system from
the stellar feedback, both during the formation and evolution of stars (stellar
outflow, wind, and radiation) and at the end of their life (supernovae). We
show that the young solar system formed along a dense filament can be enriched
with supernova ejecta (e.g., Al) during the formation timescale of CAIs.
We also propose that the streamers recently observed around protostars may be
channeling the SLR-rich material onto the young solar system. We conclude that
considering hub-filament configurations as the birth environment of the Sun is
important when deriving theoretical models explaining the observed properties
of the solar system.Comment: Accepted for publication in The Astrophysical Journal Letter
Effective action and brane running
We address the renormalized effective action for a Randall-Sundrum brane
running in 5d bulk space. The running behavior of the brane action is obtained
by shifting the brane-position without changing the background and the
fluctuations. After an appropriate renormalization, we obtain an effective, low
energy braneworld action, in which the effective 4d Planck mass is independent
of the running-position. We address some implications of this effective action.Comment: 15 pages, no figur
Rappemonads are haptophyte phytoplankton
20年以上謎だった生物の正体が判明 --光合成生物進化解明のカギに--. 京都大学プレスリリース. 2021-03-29.Rapidly accumulating genetic data from environmental sequencing approaches have revealed an extraordinary level of unsuspected diversity within marine phytoplankton, which is responsible for around 50% of global net primary production.However, the phenotypic identity of many of the organisms distinguished by environmental DNA sequences remains unclear. The rappemonads represent a plastid-bearing protistan lineage that to date has only been identified by environmental plastid 16S rRNA sequences.The phenotypic identity of this group, which does not confidently cluster in any known algal clades in 16S rRNA phylogenetic reconstructions, has remained unknown since the first report of environmental sequences over two decades ago. We show that rappemonads are closely related to a haptophyte microalga, Pavlomulina ranunculiformis gen. nov. et sp. nov., and belong to a new haptophyte class, the Rappephyceae. Organellar phylogenomic analyses provide strong evidence for the inclusion of this lineage within the Haptophyta as a sister group to the Prymnesiophyceae. Members of this new class have a cosmopolitan distribution in coastal and oceanic regions. The relative read abundance of Rappephyceae in a large environmental barcoding dataset was comparable to, or greater than, those of major haptophyte species, such as the bloom-forming Gephyrocapsa huxleyi and Prymnesium parvum, and this result indicates that they likely have a significant impact as primary producers. Detailed characterization of Pavlomulina allowed for reconstruction of the ancient evolutionary history of the Haptophyta, a group that is one of the most important components of extant marine phytoplankton communities
Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions
South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer-monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric CO2 changes at Earth-orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising CO2 levels is fully consistent with dynamics of the past 0.9 million years
Origin of Small Cosmological Constant in Brane-World
We address the relation among the parameters of accelerating brane-universe
embedded in five dimensional bulk space. It is pointed out that the tiny
cosmological constant of our world can be obtained as quantum corrections
around a given brane-solution in the bulk theory or in the field theory on the
boundary from the holographic viewpoint.Some implications to the cosmology and
constarints on the parameters are also given.Comment: 11 pages, no figur
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
Work-related allergy in medical doctors: atopy, exposure to domestic animals, eczema induced by common chemicals and membership of the surgical profession as potential risk factors
Purpose To investigate the risk factors associated with
work-related allergy-like symptoms in medical doctors.
Methods Self-administered questionnaire survey and CAP
test were conducted among medical school students in the
4th grade of their 6-year medical course in 1993–1996 and
1999–2001. Follow-up questionnaires were sent in 2004 to
the graduates. These questionnaires enquired into personal
and family history of allergic diseases, lifestyle, history of
allergy-like symptoms including work-relatedness and
occupational history as medical doctors. Relationships
between allergy-like symptoms and relevant factors were
evaluated by multivariate logistic regression analysis.
Results Of 261 respondents at the follow-up survey, 139
(53.3%) and 54 (20.7%) had a history of any allergy-like
symptoms and any work-related allergy-like symptoms,
respectively. Female gender and family history of allergic
diseases were signiWcantly associated with any allergy-like
symptoms. Personal history of allergic disease, exposure
to domestic animals, eczema caused by rubber gloves,
metallic accessories, or cosmetics during schooling days,
and membership of the surgical profession were signiW-
cant risk factors for work-related allergy-like symptoms.
On the contrary, to work-related allergy-like symptoms,
gender, age, and smoking status were not signiWcantly
related, and consumption of prepared foods was inversely
related.
Conclusions Personal history of atopy and eczema
induced by common goods and the history of keeping
domestic animals may be predictors of work-related
allergy-like symptoms in doctors. After graduation from
medical school, physicians start with exposure to various
allergens and irritants at work, which relate to work-related
allergy-like symptoms, especially for surgeons
Automatic recognition of schwa variants in spontaneous Hungarian speech
This paper analyzes the nature of the process involved in optional vowel reduction in Hungarian, and the acoustic structure of schwa variants in spontaneous speech. The study focuses on the acoustic patterns of both the basic realizations of Hungarian vowels and their realizations as neutral vowels (schwas), as well as on the design, implementation, and evaluation of a set of algorithms for the recognition of both types of realizations from the speech waveform. The authors address the question whether schwas form a unified group of vowels or they show some dependence on the originally intended articulation of the vowel they stand for. The acoustic study uses a database consisting of over 4,000 utterances extracted from continuous speech, and recorded from 19 speakers. The authors propose methods for the recognition of neutral vowels depending on the various vowels they replace in spontaneous speech. Mel-Frequency Cepstral Coefficients are calculated and used for the training of Hidden Markov Models. The recognition system was trained on 2,500 utterances and then tested on 1,500 utterances. The results show that a neutral vowel can be detected in 72% of all occurrences. Stressed and unstressed syllables can be distinguished in 92% of all cases. Neutralized vowels do not form a unified group of phoneme realizations. The pronunciation of schwa heavily depends on the original articulation configuration of the intended vowel
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