411 research outputs found
Damped Lyman alpha Absorbing Galaxies At Low Redshifts z<1 From Hierarchical Galaxy Formation Models
We investigate Damped Ly-alpha absorbing galaxies (DLA galaxies) at low
redshifts z<1 in the hierarchical structure formation scenario to clarify the
nature of DLA galaxies because observational data of such galaxies mainly at
low redshifts are currently available. We find that our model well reproduces
distributions of fundamental properties of DLA galaxies such as luminosities,
column densities, impact parameters obtained by optical and near-infrared
imagings. Our results suggest that DLA systems primarily consist of low
luminosity galaxies with small impact parameters (typical radius about 3 kpc,
surface brightness from 22 to 27 mag arcsec^{-2}) similar to low surface
brightness (LSB) galaxies. In addition, we investigate selection biases arising
from the faintness and from the masking effect which prevents us from
identifying a DLA galaxy hidden or contaminated by a point spread function of a
background quasar. We find that the latter affects the distributions of DLA
properties more seriously rather than the former, and that the observational
data are well reproduced only when taking into account the masking effect. The
missing rate of DLA galaxies by the masking effect attains 60-90 % in the
sample at redshift 0<z<1 when an angular size limit is as small as 1 arcsec.
Furthermore we find a tight correlation between HI mass and cross section of
DLA galaxies, and also find that HI-rich galaxies with M(HI) \sim 10^{9} M_sun
dominate DLA systems. These features are entirely consistent with those from
the Arecibo Dual-Beam Survey which is a blind 21 cm survey. Finally we discuss
star formation rates, and find that they are typically about 10^{-2} M_sun
yr^{-1} as low as those in LSB galaxies.Comment: 21 pages, 13 figures, Accepted for publication in Astrophsical
Journa
Evolution of Multiphase Hot Interstellar Medium in Elliptical Galaxies
We present the results of a variety of simulations concerning the evolution
of multiphase (inhomogeneous) hot interstellar medium (ISM) in elliptical
galaxies. We assume the gases ejected from stars do not mix globally with the
circumferential gas. The ejected gas components evolve separately according to
their birth time, position, and origin. We consider cases where supernova
remnants (SNRs) mix with local ISM. The components with high metal abundance
and/or high density cool and drop out of the hot ISM gas faster than the other
components because of their high metal abundance and/or density. This makes the
average metal abundance of the hot ISM low. Furthermore, since the metal
abundance of mass-loss gas decreases with radius, gas inflow from outer region
makes the average metal abundance of the hot ISM smaller than that of mass-loss
gas in the inner region. As gas ejection rate of stellar system decreases, mass
fraction of mass-loss gas ejected at outer region increases in a galaxy. If the
mixing of SNRs is ineffective, our model predicts that observed [Si/Fe] and
[Mg/Fe] should decrease towards the galactic center because of strong iron
emission by SNRs. In the outer region, where the cooling of time of the ISM is
long, the selective cooling is ineffective and most of gas components remain
hot. Thus, the metal abundance of the ISM in this region directly reflects that
of the gas ejected from stars. Our model shows that supernovae are not
effective heating sources in the inner region of elliptical galaxies, because
most of the energy released by them radiates. Therefore, cooling flow is
established even if the supernova rate is high. Mixing of SNRs with ambient ISM
makes the energy transfer between supernova explosion and ambient ISM more
effective.Comment: 21 pages (AASTeX), 14 figures, accepted for publication in The
Astrophysical Journa
Chemical Enrichment in Damped Lyman Alpha Systems From Hierarchical Galaxy Formation Models
We investigate chemical enrichment in Damped Lyman alpha (DLA) systems in the
hierarchical structure formation scenario using a semi-analytic model of galaxy
formation. The model developed by Nagashima, Totani, Gouda and Yoshii takes
into account various selection effects on high-redshift galaxies and can show
fundamental observational properties of galaxies, such as luminosity functions
and number-magnitude/redshift relations. DLA systems offer the possibilities of
measuring metal abundance more accurately than faint galaxies. For example,
recent measurements of zinc abundance can provide good evidence for
understanding the processes of metal pollution and star formation in DLA
systems because zinc is virtually unaffected by dust depletion. Here we focus
on this advantage for observation in order to explore the metallicity evolution
in DLA systems at high redshifts. We can consistently show the metallicity
evolution for reasonable models which also reproduce fundamental properties of
local galaxy population. This result suggests that the chemical evolution of
DLA systems can be consistently reconciled with the observational features of
typical galaxies. We also investigate other properties of DLA systems (column
density distribution and mass density of cold gas), and find that star
formation in massive galaxies should be more active than that in low-mass ones.
This is consistent with the results by Nagashima et al. and Cole et al. in
which the star formation timescale is set by reproducing cold gas mass fraction
in local spiral galaxies. Finally we discuss host galaxies associated with DLA
systems. We conclude that they primarily consist of sub-L* and/or dwarf
galaxies from the observations.Comment: 16 pages, 11 figures, Accepted for publication in Astrophsical
Journa
Análise do mercado de serviços de regulação de frequência secundária e terciária no sistema eléctrico português
Dissertação para obtenção do grau de Mestre em Engenharia Electrotécnica Ramo EnergiaOs operadores das redes de transporte (ORT) enfrentam desafios cada vez maiores e mais imprevisíveis. A forte penetração de energias renováveis e a liberalização do mercado de energia eléctrica dão origem a uma maior volatilidade na produção de energia eléctrica e a desencontros entre produção e consumo, passíveis de acontecer no decorrer da operação do sistema eléctrico. Os serviços de sistema são um complemento aos mercados de energia eléctrica e caracterizam-se como sendo uma segurança necessária ao bom funcionamento do sistema pois é através destes que é feito o equilíbrio entre geração e consumo em tempo real e assim feita a regulação de frequência da rede eléctrica.
Com o presente trabalho pretende-se fazer uma análise aprofundada do que são os serviços de sistema para regulação de frequência, nomeadamente sobre a regulação secundária e a regulação terciária bem como abordar a regulamentação que as fundamenta. Será também aprofundado o funcionamento do mercado de serviços de sistema para regulação de frequência em Portugal e oencadeamento cronológico deste com o mercado diário e com as diversas sessões intradiárias do Mercado Ibérico de Electricidade (MIBEL). Serão ainda referidos diversos serviços de sistema noutros países europeus em comparação com Portugal.
Para apoio a esta análise desenvolveu-se uma ferramenta em Matlab®que permita visualizar sob a
forma de gráficos as ofertas dos agentes de mercado participantes através das suas unidades físicas (grupos geradores), o custo marginal dessas mesmas centrais e ainda visualizar o preço de fecho de mercado na respectiva hora.
Os resultados obtidos apontam para uma dependência do perfil de licitação relativamente à tecnologia da central. Foram ainda analisadas as correlações entre centrais e a dependência do preço das ofertas e da banda contratada relativamente à existência de meses mais ou menos chuvosos, ou seja com maior ou menos índice de produtibilidade hidroeléctrica (IPH). Denota-se ainda uma elevada participação das centrais hídricas neste mercado de banda secundária.Abstract: The transmission system operators (TSO) face increasing and more unpredictable challenges. The high penetration of renewable energy and the liberalization of the electricity market rises the volatility in electricity generation and bigger differences between production and consumption, in the course of the electrical system operation. Ancillary services are a complement to electricity markets and are characterized as a necessary service that allows a proper and reliable functioning of the system as it is the mechanism that allows the TSO to balance generation and consumption in real time operation and control the frequency of the system.
The present work aims to make a thorough analysis of what are the ancillary services for frequency regulation, particularly on secondary regulation and tertiary regulation and to address the laws that allow to develop the frequency regulation in Portugal. It will also be studied the operation of the ancillary services market for frequency regulation in Portugal and the chronological connection with the daily market and the various intraday market sessions of Iberian Electricity Market (MIBEL). Itwill be studied also various ancillary services in other European countries compared to Portugal.
To support this data analysis a Matlab® tool was developed allowing the user to view in the graphical form the offers of market players participating with their physical units (power plants), the marginal cost of these same power plants and the market clearing price, all for the same selected period of time.
The results show a dependence of the bidding profile relative to the power plant technology. It will be also studied the correlations between different power plants and the price variation of the market due to the variation of the hydroelectric capability factor (HCF) variation. It is also relevant the high share of hydro power plants participating in the ancillary services market for secondary frequency control
HI Observations of the Ca II absorbing galaxies Mrk 1456 and SDSS J211701.26-002633.7
In an effort to study Damped Lyman Alpha galaxies at low redshift, we have
been using the Sloan Digital Sky Survey to identify galaxies projected onto QSO
sightlines and to characterize their optical properties. For low redshift
galaxies, the HI 21cm emission line can be used as an alternate tool for
identifying possible DLA galaxies, since HI emitting galaxies typically exhibit
HI columns that are larger than the classical DLA limit. Here we report on
follow-up HI 21 cm emission line observations of two DLA candidates that are
both low-redshift spiral galaxies, Mrk 1456 and SDSS J211701.26-002633.7. The
observations were made using the Green Bank and Arecibo Telescopes,
respectively. Analysis of their HI properties reveal the galaxies to be about
one and two M_HI* galaxies, respectively, and to have average HI mass,
gas-richness, and gas mass fraction for their morphological types. We consider
Mrk 1456 and SDSS J211701.26-002633.7 to be candidate DLA systems based upon
the strength of the CaII absorption lines they cause in their QSO's spectra,
and impact parameters to the QSO that are smaller than the stellar disk.
Compared to the small numbers of other HI-detected DLA and candidate DLA
galaxies, Mrk 1456 and SDSS J211701.26-002633.7 have high HI masses. When
compared with the expected properties of low-z DLAs from an HI-detected sample
of galaxies, Mrk 1456 and SDSS J211701.26-002633.7 fall within the ranges for
impact parameter and B-band absolute magnitude; and the HI mass distribution
for the HI-detected DLAs agrees with that of the expected HI mass distribution
for low-z DLAs. Our observations support galaxy-evolution models in which high
mass galaxies make up an increasing contribution to the DLA cross-section at
lower redshifts. [abridged]Comment: 12 pages, 5 figures, 5 tables; to be published in The Astronomical
Journa
Hypoxia induces expression and activation of AMPK in rat dental pulp cells
博士(歯学)・第1721号(甲第1004号)・平成20年3月31日http://jdr.iadrjournals.org/cgi/content/full/86/9/90
Multifaceted anti-amyloidogenic and pro-amyloidogenic effects of C-reactive protein and serum amyloid P component in vitro
C-reactive protein (CRP) and serum amyloid P component (SAP), two major classical pentraxins in humans, are soluble pattern recognition molecules that regulate the innate immune system, but their chaperone activities remain poorly understood. Here, we examined their effects on the amyloid fibril formation from Alzheimer’s amyloid β (Aβ) (1-40) and on that from D76N β2-microglobulin (β2-m) which is related to hereditary systemic amyloidosis. CRP and SAP dose-dependently and substoichiometrically inhibited both Aβ(1-40) and D76N β2-m fibril formation in a Ca2+-independent manner. CRP and SAP interacted with fresh and aggregated Aβ(1-40) and D76N β2-m on the fibril-forming pathway. Interestingly, in the presence of Ca2+, SAP first inhibited, then significantly accelerated D76N β2-m fibril formation. Electron microscopically, the surface of the D76N β2-m fibril was coated with pentameric SAP. These data suggest that SAP first exhibits anti-amyloidogenic activity possibly via A face, followed by pro-amyloidogenic activity via B face, proposing a model that the pro- and anti-amyloidogenic activities of SAP are not mutually exclusive, but reflect two sides of the same coin, i.e., the B and A faces, respectively. Finally, SAP inhibits the heat-induced amorphous aggregation of human glutathione S-transferase. A possible role of pentraxins to maintain extracellular proteostasis is discussed
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