4,947 research outputs found
The effect of consumer ratings and attentional allocation on product valuations
Online marketplaces allow consumers to leave reviews about the products they purchase, which are visible to potential customers and competitors. While the impact of reviews on valuations of worth and purchasing decisions has been intensively studied, little is known about how the reviews themselves are attended to, and the relation between attention and valuations. In three studies we use eye-tracking methodologies to investigate attention in subjective monetary valuations of consumer goods. We find that, when evaluating consumer goods, individuals’ attention to ratings are related to their frequencies, attention to positive or negative information is related to subjective valuations, and that perspective (owner vs. non-owner) influences the type of information attended to. These findings extend previous research regarding the valuations of risky prospects as implemented in abstract monetary gambles and suggest that similar cognitive processes might underlie both types of tasks
New measurements of the cosmic infrared background fluctuations in deep Spitzer/IRAC survey data and their cosmological implications
We extend previous measurements of cosmic infrared background (CIB)
fluctuations to ~ 1 deg using new data from the Spitzer Extended Deep Survey.
Two fields, with depths of ~12 hr/pixel over 3 epochs, are analyzed at 3.6 and
4.5 mic. Maps of the fields were assembled using a self-calibration method
uniquely suitable for probing faint diffuse backgrounds. Resolved sources were
removed from the maps to a magnitude limit of AB mag ~ 25, as indicated by the
level of the remaining shot noise. The maps were then Fourier-transformed and
their power spectra were evaluated. Instrumental noise was estimated from the
time-differenced data, and subtracting this isolates the spatial fluctuations
of the actual sky. The power spectra of the source-subtracted fields remain
identical (within the observational uncertainties) for the three epochs
indicating that zodiacal light contributes negligibly to the fluctuations.
Comparing to 8 mic power spectra shows that Galactic cirrus cannot account for
the fluctuations. The signal appears isotropically distributed on the sky as
required for an extragalactic origin. The CIB fluctuations continue to diverge
to > 10 times those of known galaxy populations on angular scales out to < 1
deg. The low shot noise levels remaining in the diffuse maps indicate that the
large scale fluctuations arise from the spatial clustering of faint sources
well below the confusion noise. The spatial spectrum of these fluctuations is
in reasonable agreement with an origin in populations clustered according to
the standard cosmological model (LCDM) at epochs coinciding with the first
stars era.Comment: ApJ, to be publishe
Pan-European grading scales: lessons from national systems and the ECTS
This article assesses the impact of the Bologna Process on the grading schemes of EU member countries. In light of some problems regarding the implementation of the European Credit Transfer system (ECTS), the author proposes further reforms and offers some elements of a unified grading system for European higher education. The author explores the variation among Europe’s grading systems and the resulting lessons learned are shared here. Lastly, this article also argues that principles of justice and fairness, deemed central to academic freedom, are best upheld by the use of a unified grading system at national and European levels
S-CANDELS: The Spitzer-Cosmic Assembly Near-Infrared Deep Extragalactic Survey. Survey Design, Photometry, and Deep IRAC Source Counts
The Spitzer-Cosmic Assembly Deep Near-Infrared Extragalactic Legacy Survey
(S-CANDELS; PI G. Fazio) is a Cycle 8 Exploration Program designed to detect
galaxies at very high redshifts (z > 5). To mitigate the effects of cosmic
variance and also to take advantage of deep coextensive coverage in multiple
bands by the Hubble Space Telescope Multi-Cycle Treasury Program CANDELS,
S-CANDELS was carried out within five widely separated extragalactic fields:
the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS,
the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon
the existing coverage of these fields from the Spitzer Extended Deep Survey
(SEDS) by increasing the integration time from 12 hours to a total of 50 hours
but within a smaller area, 0.16 square degrees. The additional depth
significantly increases the survey completeness at faint magnitudes. This paper
describes the S-CANDELS survey design, processing, and publicly-available data
products. We present IRAC dual-band 3.6+4.5 micron catalogs reaching to a depth
of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by
S-CANDELS are consistent with models based on known galaxy populations. The
increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a
significant additional contribution from discrete sources to the diffuse Cosmic
Infrared Background (CIB). Thus it remains true that only roughly half of the
estimated CIB flux from COBE/DIRBE is resolved.Comment: 23 pages, 19 figures, accepted by ApJ
High-precision Photometric Redshifts from Spitzer/IRAC: Extreme [3.6]-[4.5] Colors Identify Galaxies in the Redshift Range z~6.6-6.9
One of the most challenging aspects of studying galaxies in the z>~7 universe
is the infrequent confirmation of their redshifts through spectroscopy, a
phenomenon thought to occur from the increasing opacity of the intergalactic
medium to Lya photons at z>6.5. The resulting redshift uncertainties inhibit
the efficient search for [C II] in z~7 galaxies with sub-mm instruments such as
ALMA, given their limited scan speed for faint lines. One means by which to
improve the precision of the inferred redshifts is to exploit the potential
impact of strong nebular emission lines on the colors of z~4-8 galaxies as
observed by Spitzer/IRAC. At z~6.8, galaxies exhibit IRAC colors as blue as
[3.6]-[4.5] ~-1, likely due to the contribution of [O III]+Hb to the 3.6 mum
flux combined with the absence of line contamination in the 4.5 mum band. In
this paper we explore the use of extremely blue [3.6]-[4.5] colors to identify
galaxies in the narrow redshift window z~6.6-6.9. When combined with an
I-dropout criterion, we demonstrate that we can plausibly select a relatively
clean sample of z~6.8 galaxies. Through a systematic application of this
selection technique to our catalogs from all five CANDELS fields, we identify
20 probable z~6.6-6.9 galaxies. We estimate that our criteria select the ~50%
strongest line emitters at z~6.8 and from the IRAC colors we estimate a typical
[O III]+Hb rest-frame equivalent width of 1085A for this sample. The small
redshift uncertainties on our sample make it particularly well suited for
follow-up studies with facilities such as ALMA.Comment: In submission to the Astrophysical Journal, updated in response to
the referee report, 13 pages, 11 figures, 1 tabl
Rotational Doppler Effect in Magnetic Resonance
We compute the shift in the frequency of the spin resonance in a solid that
rotates in the field of a circularly polarized electromagnetic wave. Electron
spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are
considered. We show that contrary to the case of the rotating LC circuit, the
shift in the frequency of the spin resonance has strong dependence on the
symmetry of the receiver. The shift due to rotation occurs only when rotational
symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape
of the body, or by magnetocrystalline anisotropy. General expressions for the
resonance frequency and power absorption are derived and implications for
experiment are discussed.Comment: 8 pages, 4 figure
Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns
We present the first detection from the Spitzer Space Telescope of 4.5 micron
variability from Sgr A*, the emitting source associated with the Milky Way's
central black hole. The >23 hour continuous light curve was obtained with the
IRAC instrument in 2013 December. The result characterizes the variability of
Sgr A* prior to the closest approach of the G2 object, a putative infalling gas
cloud that orbits close to Sgr A*. The high stellar density at the location of
Sgr A* produces a background of ~250 mJy at 4.5 microns in each pixel with a
large pixel-to-pixel gradient, but the light curve for the highly variable Sgr
A* source was successfully measured by modeling and removing the variations due
to pointing wobble. The observed flux densities range from the noise level of
~0.7 mJy rms in a 6.4-s measurement to ~10 mJy. Emission was seen above the
noise level ~34% of the time. The light curve characteristics, including the
flux density distribution and structure function, are consistent with those
previously derived at shorter infrared wavelengths. We see no evidence in the
light curve for activity attributable to the G2 interaction at the observing
epoch, ~100 days before the expected G2 periapsis passage. The IRAC light curve
is more than a factor of two longer than any previous infrared observation,
improving constraints on the timescale of the break in the power spectral
distribution of Sgr A* flux densities. The data favor the longer of the two
previously published values for the timescale.Comment: 13 pages, 10 figures, 2 tables, accepted for publication in the Ap
The Off-nuclear Starbursts In NGC 4038/4039 (The Antennae Galaxies)
Imaging of the Antennae galaxies (NGC 4038/4039) with the Infrared Array
Camera (IRAC) aboard the Spitzer Space Telescope reveals large concentrations
of star forming activity away from both nuclei of the two merging galaxies.
These images confirm earlier findings based on ISO data with lower angular
resolution. The short wavelength emission shows numerous compact sources
identified as stellar clusters. At the longer wavelengths, bright, more
amorphous and filamentary features correlate well with the known distributions
of denser gas, warm dust, and HII regions. There are also fainter, more diffuse
components at all wavelengths that permeate the entire region and extend into
the two tidal tails. Non-stellar dust emission dominates the 5.8 and 8.0 micron
images, accounting for as much as 79% of the light at 5.8 micron and 95% at 8
micron, averaged over the entire galaxy. Assuming that the non-stellar emission
traces star formation, the IRAC data provide a view into the total underlying
star forming activities unaffected by obscuration. Using the flux ratio of
non-stellar to stellar emission as a guide, we map the local star formation
rate in the Antennae and compare that to similar measurements in both normal
and infrared-luminous galaxies. This rate in the active regions is found to be
as high as those seen in starburst and some ultra-luminous infrared galaxies on
``per unit mass'' basis. The two galactic centers actually have lower star
forming rates than the off-nuclear regions despite the presence of abundant
dense gas and dust, suggesting that the latter is a necessary but not
sufficient condition for on-going star formation.Comment: 13 pages, 3 figures, to appear in the ApJ Supplement, September 2004
(Spitzer Special Issue
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