1,966 research outputs found
Digital Signal Processing
Contains reports on three research projects.U. S. Navy Office of Naval Research (Contract N00014-67-A-0204-0064)National Science Foundation (Grant GK-31353
Perceived mental effort correlates with changes in tonic arousal during attentional tasks
<p>Abstract</p> <p>Background</p> <p>It has been suggested that perceived mental effort reflects changes in arousal during tasks of attention. Such changes in arousal may be tonic or phasic, and may be mediated by the locus-coeruleus norepinephrine (LC-NE) system. We hypothesized that perceived mental effort during attentional tasks would correlate with tonic changes in cortical arousal, as assessed by relative electroencephalogram (EEG) band power and theta/beta ratio, and not with phasic changes in cortical arousal, assessed by P300 amplitude and latency.</p> <p>Methods</p> <p>Forty-six healthy individuals completed tasks that engage the anterior and posterior attention networks (continuous performance task, go/no-go task, and cued target detection task). During completion of the three attentional tasks a continuous record of tonic and phasic arousal was taken. Cortical measures of arousal included frequency band power, theta/beta ratios over frontal and parietal cortices, and P300 amplitude and latency over parietal cortices. Peripheral measures of arousal included skin conductance responses, heart rate and heart rate variance. Participants reported their perceived mental effort during each of the three attentional tasks.</p> <p>Results</p> <p>First, changes in arousal were seen from rest to completion of the three attentional tasks and between the attentional tasks. Changes seen between the attentional tasks being related to the task design and the attentional network activated. Second, perceived mental effort increased when demands of the task increased and correlated with left parietal beta band power during the three tasks of attention. Third, increased mental effort during the go/no-go task and the cued target detection task was inversely related to theta/beta ratios.</p> <p>Conclusion</p> <p>These results indicate that perceived mental effort reflects tonic rather than phasic changes in arousal during tasks of attention. We suggest that perceived mental effort may reflect in part tonic activity of the LC-NE system in healthy individuals.</p
Heavy Dark Matter Through the Higgs Portal
Motivated by Higgs Portal and Hidden Valley models, heavy particle dark
matter that communicates with the supersymmetric Standard Model via pure Higgs
sector interactions is considered. We show that a thermal relic abundance
consistent with the measured density of dark matter is possible for masses up
to \sim 30\tev. For dark matter masses above \sim 1\tev, non-perturbative
Sommerfeld corrections to the annihilation rate are large, and have the
potential to greatly affect indirect detection signals. For large dark matter
masses, the Higgs-dark-matter-sector couplings are large and we show how such
models may be given a UV completion within the context of so-called "Fat-Higgs"
models. Higgs Portal dark matter provides an example of an attractive
alternative to conventional MSSM neutralino dark matter that may evade
discovery at the LHC, while still being within the reach of current and
upcoming indirect detection experiments.Comment: LaTex, 21 pages, 9 figures. Discussion improved, comments and
references adde
Deep Big Simple Neural Nets Excel on Handwritten Digit Recognition
Good old on-line back-propagation for plain multi-layer perceptrons yields a
very low 0.35% error rate on the famous MNIST handwritten digits benchmark. All
we need to achieve this best result so far are many hidden layers, many neurons
per layer, numerous deformed training images, and graphics cards to greatly
speed up learning.Comment: 14 pages, 2 figures, 4 listing
Changes with Age in the Moisture Content of Human Skin
A technique to measure the dynamic mechanical properties of human skin in vivo is described. The technique measures the propagation and attenuation of shear waves in skin tissue over a range of frequencies (8–1016 Hz). Results show that both the propagation velocity and attenuation of shear waves in skin are highly dependent upon the water content of the stratum corneum. The technique was used to measure the dynamic mechanical properties of the skin on the back of the left hand for a group of 16 men ranging in age from 24–63 years. The results suggest that aged skin has a lower water content than the skin of younger men
Heavy dark matter through the Higgs portal
Abstract Motivated by Higgs Portal and Hidden Valley models, heavy particle dark matter that communicates with the supersymmetric Standard Model via pure Higgs sector interactions is considered. We show that a thermal relic abundance consistent with the measured density of dark matter is possible for masses up to ∼ 30 TeV. For dark matter masses above ∼ 1 TeV, non-perturbative Sommerfeld corrections to the annihilation rate are large, and have the potential to greatly affect indirect detection signals. For large dark matter masses, the Higgs-dark matter sector couplings are large and we show how such models may be given a UV completion within the context of so-called "Fat-Higgs" models. Higgs Portal dark matter provides an example of an attractive alternative to conventional MSSM neutralino dark matter that may evade discovery at the LHC, while still being within the reach of current and upcoming indirect detection experiments
UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3
We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.Comment: Accepted A
Agmatidine, a modified cytidine in the anticodon of archaeal tRNA\u3csup\u3eIle\u3c/sup\u3e, base pairs with adenosine but not with guanosine
Modification of the cytidine in the first anticodon position of the AUA decoding tRNAIle (tRNAIle 2 ) of bacteria and archaea is essential for this tRNA to read the isoleucine codon AUA and to differentiate between AUA and the methionine codon AUG. To identify the modified cytidine in archaea, we have purified this tRNA species from Haloarcula marismortui, established its codon reading properties, used liquid chromatography–mass spectrometry (LC-MS) to map RNase A and T1 digestion products onto the tRNA, and used LC-MS/MS to sequence the oligonucleotides in RNase A digests. These analyses revealed that the modification of cytidine in the anticodon of tRNAIle 2 adds 112 mass units to its molecular mass and makes the glycosidic bond unusually labile during mass spectral analyses. Accurate mass LC-MS and LC-MS/MS analysis of total nucleoside digests of the tRNAIle 2 demonstrated the absence in the modified cytidine of the C2-oxo group and its replacement by agmatine (decarboxy-arginine) through a secondary amine linkage. We propose the name agmatidine, abbreviation C+, for this modified cytidine. Agmatidine is also present in Methanococcus maripaludis tRNAIle 2 and in Sulfolobus solfataricus total tRNA, indicating its probable occurrence in the AUA decoding tRNAIle of euryarchaea and crenarchaea. The identification of agmatidine shows that bacteria and archaea have developed very similar strategies for reading the isoleucine codon AUA while discriminating against the methionine codon AUG
Homophily and Contagion Are Generically Confounded in Observational Social Network Studies
We consider processes on social networks that can potentially involve three
factors: homophily, or the formation of social ties due to matching individual
traits; social contagion, also known as social influence; and the causal effect
of an individual's covariates on their behavior or other measurable responses.
We show that, generically, all of these are confounded with each other.
Distinguishing them from one another requires strong assumptions on the
parametrization of the social process or on the adequacy of the covariates used
(or both). In particular we demonstrate, with simple examples, that asymmetries
in regression coefficients cannot identify causal effects, and that very simple
models of imitation (a form of social contagion) can produce substantial
correlations between an individual's enduring traits and their choices, even
when there is no intrinsic affinity between them. We also suggest some possible
constructive responses to these results.Comment: 27 pages, 9 figures. V2: Revised in response to referees. V3: Ditt
Recommended from our members
SIMULANT DEVELOPMENT FOR SAVANNAH RIVER SITE HIGH LEVEL WASTE
The Defense Waste Processing Facility (DWPF) at the Savannah River Site vitrifies High Level Waste (HLW) for repository internment. The process consists of three major steps: waste pretreatment, vitrification, and canister decontamination/sealing. The HLW consists of insoluble metal hydroxides (primarily iron, aluminum, magnesium, manganese, and uranium) and soluble sodium salts (carbonate, hydroxide, nitrite, nitrate, and sulfate). The HLW is processed in large batches through DWPF; DWPF has recently completed processing Sludge Batch 3 (SB3) and is currently processing Sludge Batch 4 (SB4). The composition of metal species in SB4 is shown in Table 1 as a function of the ratio of a metal to iron. Simulants remove radioactive species and renormalize the remaining species. Supernate composition is shown in Table 2
- …