5,455 research outputs found
Keck Spectroscopy of Faint 3 < z < 7 Lyman Break Galaxies: III. The Mean Ultraviolet Spectrum at z=4
We present and discuss the mean rest-frame ultraviolet spectrum for a sample
of 81 Lyman Break Galaxies (LBGs) selected to be B-band dropouts with a mean
redshift of z=3.9 and apparent magnitudes z_AB<26. Most of the individual
spectra are drawn from our ongoing survey in the GOODS fields with the Keck
DEIMOS spectrograph, and we have augmented our sample with published data taken
with FORS2 on the VLT. In general we find similar trends in the spectral
diagnostics to those found in the earlier, more extensive survey of LBGs at z=3
undertaken by Shapley et al (2003). Specifically, we find low-ionization
absorption lines which trace the presence of neutral outflowing gas are weaker
in galaxies with stronger Lyman-alpha emission, bluer UV spectral slopes, lower
stellar masses, lower UV luminosities and smaller half-light radii. This is
consistent with a physical picture whereby star formation drives outflows of
neutral gas which scatters Lyman-alpha and gives rise to strong low-ionization
absorption lines, while increasing the stellar mass, size, metallicity, and
dust content of galaxies. Typical galaxies are thus expected to have stronger
Lyman-alpha emission and weaker low-ionization absorption at earlier times
(higher redshifts). Indeed, our mean spectrum at z=4 shows somewhat weaker
low-ionization absorption lines than at z=3 and available data at higher
redshift indicates a rapid decrease in low-ionization absorption strength with
redshift. We argue that the reduced low-ionization absorption is likely caused
by a decrease in the covering fraction and/or velocity range of outflowing
neutral gas at earlier epochs. Our continuing survey will enable us to extend
these diagnostics more reliably to higher redshift and determine the
implications for the escape fraction of ionizing photons which governs the role
of early galaxies in cosmic reionization. [Abridged]Comment: 17 pages, 12 figures, submitted to ApJ. Comments welcom
Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six
As Lyman-alpha photons are scattered by neutral hydrogen, a change with
redshift in the Lyman-alpha equivalent width distribution of distant galaxies
offers a promising probe of the degree of ionization in the intergalactic
medium and hence when cosmic reionization ended. This simple test is
complicated by the fact that Lyman-alpha emission can also be affected by the
evolving astrophysical details of the host galaxies. In the first paper in this
series, we demonstrated both a luminosity and redshift dependent trend in the
fraction of Lyman-alpha emitters seen within color-selected Lyman-break
galaxies (LBGs) over the range 3<z<6; lower luminosity galaxies and those at
higher redshift show an increased likelihood of strong emission. Here we
present the results from much deeper 12.5 hour exposures with the Keck DEIMOS
spectrograph focused primarily on LBGs at z~6 which enable us to confirm the
redshift dependence of line emission more robustly and to higher redshift than
was hitherto possible. We find 54+/-11% of faint z~6 LBGs show strong (W_0>25
A) emission, an increase of 1.6x from a similar sample observed at z~4. With a
total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha
equivalent width distribution. Assuming continuity in these trends to the new
population of z~7 sources located with the Hubble WFC3/IR camera, we predict
that unless the neutral fraction rises in the intervening 200 Myr, the success
rate for spectroscopic confirmation using Lyman-alpha emission should be high.Comment: 6 pages, 3 figures, submitted to ApJ
Matching bias in syllogistic reasoning: Evidence for a dual-process account from response times and confidence ratings
We examined matching bias in syllogistic reasoning by analysing response times, confidence ratings, and individual differences. Robertsâ (2005) ânegations paradigmâ was used to generate conflict between the surface features of problems and the logical status of conclusions. The experiment replicated matching bias effects in conclusion evaluation (Stupple & Waterhouse, 2009), revealing increased processing times for matching/logic âconflict problemsâ. Results paralleled chronometric evidence from the belief bias paradigm indicating that logic/belief conflict problems take longer to process than non-conflict problems (Stupple, Ball, Evans, & Kamal-Smith, 2011). Individualsâ response times for conflict problems also showed patterns of association with the degree of overall normative responding. Acceptance rates, response times, metacognitive confidence judgements, and individual differences all converged in supporting dual-process theory. This is noteworthy because dual-process predictions about heuristic/analytic conflict in syllogistic reasoning generalised from the belief bias paradigm to a situation where matching features of conclusions, rather than beliefs, were set in opposition to logic
Marshall University Music Department Presents a BFA Junior Recital, Daniel Ellis, bass trombone
https://mds.marshall.edu/music_perf/1567/thumbnail.jp
Learning to Infer Graphics Programs from Hand-Drawn Images
We introduce a model that learns to convert simple hand drawings into
graphics programs written in a subset of \LaTeX. The model combines techniques
from deep learning and program synthesis. We learn a convolutional neural
network that proposes plausible drawing primitives that explain an image. These
drawing primitives are like a trace of the set of primitive commands issued by
a graphics program. We learn a model that uses program synthesis techniques to
recover a graphics program from that trace. These programs have constructs like
variable bindings, iterative loops, or simple kinds of conditionals. With a
graphics program in hand, we can correct errors made by the deep network,
measure similarity between drawings by use of similar high-level geometric
structures, and extrapolate drawings. Taken together these results are a step
towards agents that induce useful, human-readable programs from perceptual
input
Species diversity and community stability: cause or effect? a study using moorland spiders and other invertebrates
SUMMARY 1) Pitfall trapping was used to sample invertebrate communities on Monk's Moor, County Durham. 2) The effects of habitat and altitude upon communities of invertebrates, in particular spiders, were analysed using indices of alpha and beta diversity. The diversity indices were then compared to investigate any relationship between the diversity and stability o f the communities. 3) Spider diversity was significantly higher in heather moorland than in pasture. This was thought to reflect greater spatial heterogeneity within the heather moorland. No relationship was found between spider diversity and altitude. 4) A significant relationship was established between the invertebrate community and both habitat and altitude. However, it was limitations of the statistical technique, rather than biological effects that caused the significant relationship. 5) The lack of a marked effect of altitude upon diversity prevented detailed analysis of the diversity - stability hypothesis
Multimodal segmentation of lifelog data
A personal lifelog of visual and audio information can be very helpful as a human memory augmentation tool. The SenseCam, a passive wearable camera, used in conjunction with an iRiver MP3 audio recorder, will capture over 20,000 images and 100 hours of audio per week. If used constantly, very soon this would build up to a substantial collection of personal data. To gain real value from this collection it is important to automatically segment the data into meaningful units or activities. This paper investigates the optimal combination of data sources to segment personal data into such activities. 5 data sources were logged and processed to segment a collection of personal data, namely: image processing on captured SenseCam images; audio processing on captured iRiver audio data; and processing of the temperature, white light level, and accelerometer sensors onboard the SenseCam device. The results indicate that a combination of the image, light and accelerometer sensor data segments our collection of personal data better than a combination of all 5 data sources. The accelerometer sensor is good for detecting when the user moves to a new location, while the image and light sensors are good for detecting changes in wearer activity within the same location, as well as detecting when the wearer socially interacts with others
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