28 research outputs found
Directly from -flux to the family of three nonlocal -flux theories
In this article we consider T-dualization of the 3D closed bosonic string in
the weakly curved background - constant metric and Kalb-Ramond field with one
non-zero component, , where field strength is infinitesimal. We
use standard and generalized Buscher T-dualization procedure and make
T-dualization starting from coordinate , via and finally along
coordinate. All three theories are {\it nonlocal}, because variable ,
defined as line integral, appears as an argument of background fields. After
the first T-dualization we obtain commutative and associative theory, while
after we T-dualize along , we get, -Minkowski-like, noncommutative
and associative theory. At the end of this T-dualization chain we come to the
theory which is both noncommutative and nonassociative. The form of the final
T-dual action does not depend on the order of T-dualization while
noncommutativity and nonassociativity relations could be obtained from those in
the case by replacing .Comment: Section 4 (quantum aspect of the problem) is added, some other
explanations, clarifications and comments adde
Die Auswirkungen aus Evaluierung und Aktivierung auf die Speicherung affektiver Stimuli
Na uzorku od 45 ispitanika ispitani su efekti evaluacije i aktivacije
na neposredno i odgođeno slobodno dosjećanje, prepoznavanje
i inicijalnu fazu obrade afektivnih podražaja. Dobiveni rezultati
pokazuju da se i pri neposrednom i pri odgođenom dosjećanju
ispitanici više dosjećaju afektivnih podražaja niske aktivacije,
dok se podražaji visoke aktivacije bolje prepoznaju i izazivaju
više netočnih "DA" odgovora. Samo pri neposrednom dosjećanju
neugodni afektivni podražaji dosjećaju se bolje od ugodnih,
dok pri odgođenom dosjećanju nema razlike između ugodnih
i neugodnih afektivnih podražaja. Također, neugodni afektivni
podražaji bolje se prepoznaju, dok ugodni podražaji izazivaju
više netočnih "DA" odgovora. Općenito, rezultati ovoga istraživanja
pokazuju da evaluacija i aktivacija, samostalno i u interakciji,
imaju značajan utjecaj na pamćenje afektivnih podražaja. Utjecaj tih
dviju dimenzija na pamćenje afektivnih podražaja je različit, a također je
ovisan i o korištenom tipu testa
pamćenja. Navedeni su rezultati interpretirani u kontekstu postojećih
teorija o ulozi evaluacije i aktivacije pri pamćenju afektivnih
podražaja.On a sample of 45 examinees the authors have examined
the effects of evaluation and activation on immediate and
delayed free memory, recognition and the initial phase of
processing affective stimuli. The results obtained indicate that
both in immediate and delayed memory examinees
remember low activation affective stimuli more, while high
activation stimuli are better recognized and produce more
incorrect (yes) answers. Only in immediate memory are the unpleasant affective stimuli remembered better than the
pleasant ones, while in delayed memory there is no
difference between pleasant and unpleasant affective stimuli.
Also, the unpleasant affective stimuli are better recognized,
while the pleasant ones give rise to more incorrect (yes)
answers. In general, the results of this research show that
evaluation and activation both independently and in
interaction have a significant influence on the memory of
affective stimuli. The influence of these two dimensions on
remembering affective stimuli is diverse, and is also
dependent on the type of memory test used. The
aforementioned results have been interpreted in the context
of existing theories on the role of evaluation and activation in
remembering affective stimuli.In einer Gruppe von 45 Testpersonen wurden die
Auswirkungen von Evaluierung und Aktivierung auf die
unmittelbare sowie die zeitlich verzögerte, freie Abberufung,
Wiedererkennung und initiale Verarbeitung von im
Gedächtnis gespeicherten affektiven Stimuli untersucht. Die
Resultate zeigen, dass sowohl bei der unmittelbaren als auch
der zeitlich verzögerten Abberufung gespeicherter Stimuli die
Testpersonen sich überwiegend affektiver Stimuli von
niedrigem Aktivierungsgrad entsannen, während Stimuli
hohen Aktivierungsgrads besser erkannt werden und mehr
unkorrekte Ja-Antworten zur Folge haben. Nur im Falle des
unmittelbaren Entsinnens werden unangenehme affektive
Stimuli besser aus dem Gedächtnis abberufen als
angenehme, während es im Falle zeitlich verzögerten
Entsinnens keinen Unterschied zwischen angenehmen und
unangenehmen affektiven Stimuli gibt. Ebenso gilt, dass
unangenehme affektive Stimuli besser erkannt werden,
während angenehme Stimuli mehr unkorrekte Ja-Antworten
hervorrufen. Die Ergebnisse dieser Untersuchung zeigen
ganz allgemein, dass Evaluierung und Aktivierung ”jeweils,
aber auch in Interaktion” einen wesentlichen Einfluss auf die
Abberufung affektiver Stimuli aus dem Gedächtnis haben.
Der Einfluss dieser beiden Dimensionen auf die Speicherung
affektiver Stimuli ist jeweils unterschiedlich und außerdem
abhängig vom Typus des eingesetzten Memo-Tests. Die
Interpretation der angeführten Ergebnisse bewegt sich im
Kontext der bestehenden Theorien zur Rolle der Evaluierung
und Aktivierung bei der Abberufung affektiver Stimuli aus
dem Gedächtnis
The Rest-frame Optical Colors of 99,000 SDSS Galaxies
We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088
galaxies selected from Data Release 1. This narrow-band ~200 AA photometric
system (uz, vz, bz, yz), first designed for the determination of effective
temperature, metallicity and gravity of stars, measures the continuum spectral
slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies
form a remarkably narrow locus (~0.03 mag) in the resulting color-color
diagram. The Bruzual & Charlot population synthesis models suggest that the
position of a galaxy along this locus is controlled by a degenerate combination
of metallicity and age of the dominant stellar population. Galaxy distribution
along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr
old single stellar population. The position perpendicular to the locus is
independent of metallicity and age, and reflects the galaxy's dust content, as
implied by both the models and the statistics of IRAS detections. A comparison
of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized
by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight
correlation, although the two analyzed spectral ranges barely overlap. Overall,
the galaxy spectral energy distribution in the entire UV to near-IR range can
be described as a single-parameter family with an accuracy of 0.1 mag, or
better. This nearly one-dimensional distribution of galaxies in the
multi-dimensional space of measured parameters strongly supports the conclusion
of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy
spectra can be described by a small number of eigenspectra. Apparently, the
contributions of stellar populations that dominate the optical emission from
galaxies are combined in a simple and well-defined way.Comment: Accepted for publication in MNRAS; 19 pages, 28 color figure
Source Matching in the SDSS and RASS: Which Galaxies are Really X-ray Sources?
The current view of galaxy formation holds that all massive galaxies harbor a
massive black hole at their center, but that these black holes are not always
in an actively accreting phase. X-ray emission is often used to identify
accreting sources, but for galaxies that are not harboring quasars
(low-luminosity active galaxies), the X-ray flux may be weak, or obscured by
dust. To aid in the understanding of weakly accreting black holes in the local
universe, a large sample of galaxies with X-ray detections is needed. We
cross-match the ROSAT All Sky Survey (RASS) with galaxies from the Sloan
Digital Sky Survey Data Release 4 (SDSS DR4) to create such a sample. Because
of the high SDSS source density and large RASS positional errors, the
cross-matched catalog is highly contaminated by random associations. We
investigate the overlap of these surveys and provide a statistical test of the
validity of RASS-SDSS galaxy cross-matches. SDSS quasars provide a test of our
cross-match validation scheme, as they have a very high fraction of true RASS
matches. We find that the number of true matches between the SDSS main galaxy
sample and the RASS is highly dependent on the optical spectral classification
of the galaxy; essentially no star-forming galaxies are detected, while more
than 0.6% of narrow-line Seyferts are detected in the RASS. Also, galaxies with
ambiguous optical classification have a surprisingly high RASS detection
fraction. This allows us to further constrain the SEDs of low-luminosity active
galaxies. Our technique is quite general, and can be applied to any
cross-matching between surveys with well-understood positional errors.Comment: 10 pages, 10 figures, submitted to The Astronomical Journal on 19
June 200
The UV, Optical, and IR Properties of SDSS Sources Detected by GALEX
We discuss the UV, optical, and IR properties of the SDSS sources detected by
GALEX as part of its All-sky Imaging Survey Early Release Observations.
Virtually all of the GALEX sources in the overlap region are detected by SDSS.
GALEX sources represent ~2.5% of all SDSS sources within these fields and about
half are optically unresolved. Most unresolved GALEX/SDSS sources are bright
blue turn-off thick disk stars and are typically detected only in the GALEX
near-UV band. The remaining unresolved sources include low-redshift quasars,
white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically
unresolved sources detected in both GALEX bands.
Almost all the resolved SDSS sources detected by GALEX are fainter than the
SDSS 'main' spectroscopic limit. These sources have colors consistent with
those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX
bands. Measurements of their UV colors allow much more accurate and robust
estimates of star-formation history than are possible using only SDSS data.
Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly
selected from the GALEX data by requiring that they be brighter in the far-UV
than in the near-UV band. However, older starburst galaxies have UV colors
similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX
fluxes alone.
With the aid of 2MASS data, we construct and discuss median 10 band
UV-optical-IR spectral energy distributions for turn-off stars, hot white
dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out
the high degree of correlation between the UV color and the contribution of the
UV flux to the UV-optical-IR flux of galaxies detected by GALEX.Comment: 35 pages, 11 figures, 3 tables; to appear in the AJ. PS with better
figures available from http://www.astro.washington.edu/agueros/pub
A Huge Filamentary Structure at z=0.55 and Star Formation Histories of Galaxies at z<1
We report a definitive confirmation of a large-scale structure around the
super rich cluster CL0016+1609 at z=0.55. We made spectroscopic follow-up
observations with FOCAS on Subaru along the large filamentary structure
identified in our previous photometric studies. We have confirmed the physical
connection of the huge filament extending over 20 Mpc in the N-S direction, and
another filament extending from the main cluster to the East. Based on a simple
energy argument, we show that it is likely that most of the clumps are bound to
the main CL0016 cluster. This structure is surely one of the most prominent
confirmed structures ever identified in the distant Universe, which then serves
as an ideal laboratory to examine the environmental variation of galaxy
properties. We draw star formation histories of galaxies from the composite
spectra of red galaxies in field, group, and cluster environments. Combining
the results from our previous studies, we find that red galaxies in groups at
z~0.8 and red field galaxies at z~0.5 show strong Hd absorption lines for their
D4000 indices. These are the environments in which we observed the on-going
build-up of the colour-magnitude relation in our previous photometric analyses.
The strong Hd absorption lines imply that their star formation is truncated on
a relatively short time scale. We suggest that a galaxy-galaxy interaction is
the most likely physical driver of the truncation of star formation and thus
responsible for the build-up of the colour-magnitude relation since z~1.
(Abridged)Comment: 13 pages, 5 figures, accepted for publication in MNRA
Recommended from our members
The Ultraviolet, Optical, and Infrared Properties of Sloan Digital Sky Survey Sources Detected by GALEX
We discuss the ultraviolet, optical, and infrared properties of the Sloan Digital Sky Survey (SDSS) sources detected by the Galaxy Evolution Explorer (GALEX) as part of its All-sky Imaging Survey Early Release Observations. Virtually all (>99%) the GALEX sources in the overlap region are detected by SDSS; those without an SDSS counterpart within our 6'' search radius are mostly unflagged GALEX artifacts. GALEX sources represent ~2.5% of all SDSS sources within these fields, and about half are optically unresolved. Most unresolved GALEX-SDSS sources are bright (r < 18 mag), blue, turnoff, thick-disk stars and are typically detected only in the GALEX near-ultraviolet (NUV) band. The remaining unresolved sources include low-redshift quasars (z < 2.2), white dwarfs, and white dwarf–M dwarf pairs, and these dominate the optically unresolved sources detected in both GALEX bands. Almost all the resolved SDSS sources detected by GALEX are fainter than the SDSS main spectroscopic limit. (Conversely, of the SDSS galaxies in the main spectroscopic sample, about 40% are detected in at least one GALEX band.) These sources have colors consistent with those of blue (spiral) galaxies (u - r < 2.2), and most are detected in both GALEX bands. Measurements of their UV colors allow much more accurate and robust estimates of star formation history than are possible using only SDSS data. Indeed, galaxies with the most recent (lesssim20 Myr) star formation can be robustly selected from the GALEX data by requiring that they be brighter in the far-ultraviolet (FUV) than in the NUV band. However, older starburst galaxies have UV colors similar to those of active galactic nuclei and thus cannot be selected unambiguously on the basis of GALEX fluxes alone. Additional information, such as spatially resolved FUV emission, optical morphology, or X-ray and radio data, is needed before blue GALEX colors can be unambiguously interpreted as a sign of recent star formation. With the aid of Two Micron All Sky Survey data, we construct and discuss median 10-band UV through infrared spectral energy distributions for turnoff stars, hot white dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out the high degree of correlation between the UV color and the contribution of the UV flux to the UV through infrared flux of galaxies detected by GALEX; for example, this correlation can be used to predict the SDSS z-band measurement, using only two GALEX fluxes, with a scatter of only 0.7 mag
The census of nuclear activity of late-type galaxies in the Virgo cluster
The first spectroscopic census of AGNs associated to late-type galaxies in
the Virgo cluster is carried on by observing 213 out of a complete set of 237
galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are
classified as AGNs (including 21 transition objects, 47 LINERs and 9 Seyferts),
and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic
incompleteness at most 21 AGNs are missed in the survey, so that the fraction
would increase up to 41%. Using corollary Near-IR observations, that enable us
to estimate galaxies dynamical masses, it is found that AGNs are hosted
exclusively in massive galaxies, i.e. M_dyn\gsim 10^{10} solar masses. Their
frequency increases steeply with the dynamical mass from zero at
M_dyn\approx10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar
masses. These frequencies are consistent with the ones of low luminosity AGNs
found in the general field by the SDSS. Massive galaxies that harbor AGNs
commonly show conspicuous r-band star-like nuclear enhancements. Conversely
they often, but not necessarily contain massive bulges. Few well known AGNs
(e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no
bulge. The AGN fraction seems to be only marginally sensitive to galaxy
environment. We infer the black hole masses using the known scaling relations
of quiescent black holes. No black holes lighter than \msol are
found active in our sample.Comment: The paper contains 13 figures and 5 tables; accepted for publication
in MNRA
A new method to separate star forming from AGN galaxies at intermediate redshift: The submillijansky radio population in the VLA-COSMOS survey
We explore the properties of the submillijansky radio population at 20 cm by
applying a newly developed optical color-based method to separate star forming
(SF) from AGN galaxies at intermediate redshifts (z<1.3). Although optical
rest-frame colors are used, our separation method is shown to be efficient, and
not biased against dusty starburst galaxies. This classification method has
been calibrated and tested on a local radio selected optical sample. Given
accurate multi-band photometry and redshifts, it carries the potential to be
generally applicable to any galaxy sample where SF and AGN galaxies are the two
dominant populations.
In order to quantify the properties of the submillijansky radio population,
we have analyzed ~2,400 radio sources, detected at 20 cm in the VLA-COSMOS
survey. 90% of these have submillijansky flux densities. We classify the
objects into 1) star candidates, 2) quasi stellar objects, 3) AGN, 4) SF, and
5) high redshift (z>1.3) galaxies. We find, for the composition of the
submillijansky radio population, that SF galaxies are not the dominant
population at submillijansky flux levels, as previously often assumed, but that
they make up an approximately constant fraction of 30-40% in the flux density
range of ~50 microJy to 0.7 mJy. In summary, based on the entire VLA-COSMOS
radio population at 20 cm, we find that the radio population at these flux
densities is a mixture of roughly 30-40% of SF and 50-60% of AGN galaxies, with
a minor contribution (~10%) of QSOs.Comment: 26 pages, 26 figures; accepted for publication in ApJ