371 research outputs found
Astronomical Image Processing with Array Detectors
We address the question of astronomical image processing from data obtained
with array detectors. We define and analyze the cases of evenly, regularly, and
irregularly sampled maps for idealized (i.e., infinite) and realistic (i.e.,
finite) detectors. We concentrate on the effect of interpolation on the maps,
and the choice of the kernel used to accomplish this task. We show how the
normalization intrinsic to the interpolation process must be carefully
accounted for when dealing with irregularly sampled grids. We also analyze the
effect of missing or dead pixels in the array, and their consequences for the
Nyquist sampling criterion.Comment: 31 pages, 5 figures, accepted for publication in the PAS
Characterization of Turbulence from Submillimeter Dust Emission
In this paper we use our recent technique for estimating the turbulent
component of the magnetic field to derive the structure functions of the
unpolarized emission as well as that of the Stokes Q and U parameters of the
polarized emission. The solutions for the structure functions to 350-um SHARP
polarization data of OMC-1 allow the determination of the corresponding
turbulent correlation length scales. The estimated values for these length
scales are 9.4" +/- 0.1", 7.3" +/- 0.1", 12.6" +/- 0.2" (or 20.5 +/- 0.2, 16.0
+/- 0.2, and 27.5 +/- 0.4 mpc at 450 pc, the adopted distance for OMC-1) for
the Stokes Q and U parameters, and for the unpolarized emission N,
respectively. Our current results for Q and U are consistent with previous
results obtained through other methods, and may indicate presence of anisotropy
in magnetized turbulence. We infer a weak coupling between the dust component
responsible for the unpolarized emission N and the magnetic field B from the
significant difference between their turbulent correlation length scales.Comment: 14 pages, 3 figures; accepted for publication in the Ap
The Removal of Artificially Generated Polarization in SHARP Maps
We characterize the problem of artificial polarization for the Submillimeter
High Angular Resolution Polarimeter (SHARP) through the use of simulated data
and observations made at the Caltech Submillimeter Observatory (CSO). These
erroneous, artificial polarization signals are introduced into the data through
misalignments in the bolometer sub-arrays plus pointing drifts present during
the data-taking procedure. An algorithm is outlined here to address this
problem and correct for it, provided that one can measure the degree of the
sub-array misalignments and telescope pointing drifts. Tests involving
simulated sources of Gaussian intensity profile indicate that the level of
introduced artificial polarization is highly dependent upon the angular size of
the source. Despite this, the correction algorithm is effective at removing up
to 60% of the artificial polarization during these tests. The analysis of
Jupiter data taken in January 2006 and February 2007 indicates a mean
polarization of 1.44%+/-0.04% and 0.95%+/-0.09%, respectively. The application
of the correction algorithm yields mean reductions in the polarization of
approximately 0.15% and 0.03% for the 2006 and 2007 data sets, respectively.Comment: 19 pages, 7 figure
Le numérisme : un objet religieux contemporain?
Pour majoritĂ©, les Ă©tudes consacrĂ©es aux rapports numĂ©rique/religions peuvent ĂȘtre regroupĂ©es sous le vocable de « religion numĂ©rique » (Digital Religion). Sans y ĂȘtre complĂštement Ă©tranger, le phĂ©nomĂšne qui nous intĂ©resse ici semble dâun autre ordre. PlutĂŽt quâĂ de la « religion numĂ©risĂ©e », nous sommes face Ă ce que nous pourrions interprĂ©ter comme une quĂȘte de sens de type numĂ©rique. Quelques auteurs ont dĂ©jĂ entrepris de dĂ©crire cette religiositĂ© technologique, certains allant jusquâĂ prĂ©tendre quâelle servirait Ă lĂ©gitimer la croyance en « sociĂ©tĂ© nouvelle ». LâĂ©tude du numĂ©risme aurait donc pour fondement ce quâon prĂ©sente comme la sacralisation dâun ensemble de « valeurs numĂ©riques » dont le rĂ©seau internet serait Ă la fois lâoutil de diffusion et le principal objet symbolique. Pour peu que lâon reconnaisse que la religion Ă quelque chose Ă voir avec lâidĂ©e que se fait la sociĂ©tĂ© dâelle-mĂȘme, on peut se demander si la « rĂ©volution numĂ©rique », en engendrant un nouveau type de sociĂ©tĂ©, ne comprendrait pas une dimension spĂ©cifiquement religieuse
Dispersion of Magnetic Fields in Molecular Clouds. II.
We expand our study on the dispersion of polarization angles in molecular clouds. We show how the effect of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam inherent to dust continuum measurements can be incorporated in our analysis to correctly account for its effect on the measured angular dispersion and inferred turbulent to large-scale magnetic field strength ratio. We further show how to evaluate the turbulent magnetic field correlation scale from polarization data of sufficient spatial resolution and high enough spatial sampling rate. We apply our results to the molecular cloud OMC-1, where we find a turbulent correlation length of ÎŽ â 16 mpc, a turbulent to large-scale magnetic field strength ratio of approximately 0.5, and a plane-of-the-sky large-scale magnetic field strength of approximately 760 ÎŒG
Dispersion of Magnetic Fields in Molecular Clouds. IV - Analysis of Interferometry Data
We expand on the dispersion analysis of polarimetry maps toward applications to interferometry data. We show how the filtering of low spatial frequencies can be accounted for within the idealized Gaussian turbulence model, initially introduced for single-dish data analysis, to recover reliable estimates for correlation lengths of magnetized turbulence, as well as magnetic field strengths (plane-of-the-sky component) using the DavisâChandrasekharâFermi method. We apply our updated technique to TADPOL/CARMA data obtained on W3(OH), W3 Main, and DR21(OH). For W3(OH), our analysis yields a turbulence correlation length ÎŽ â 19 mpc, a ratio of turbulent-to-total magnetic energy â©BâȘ_^2_t/â©B^2âȘ â 0.58, and a magnetic field strength B_0 ~ 1.1 mG for W3 Main ÎŽ â 22mpc, â©B_t^2âȘ/â©B^2âȘ â 0.74, and B_0 ~ 0.7 mG while for DR21(OH) ÎŽ â 12 mpc, â©B_t^2âȘ/â©B^2âȘ â 0.70, and B_0 ~ 1.2 mG
Dispersion of Magnetic Fields in Molecular Clouds. III
We apply our technique on the dispersion of magnetic fields in molecular
clouds to high spatial resolution Submillimeter Array polarization data
obtained for Orion KL in OMC-1, IRAS 16293, and NGC 1333 IRAS 4A. We show how
one can take advantage of such high resolution data to characterize the
magnetized turbulence power spectrum in the inertial and dissipation ranges.
For Orion KL we determine that in the inertial range the spectrum can be
approximately fitted with a power law k^-(2.9\pm0.9) and we report a value of
9.9 mpc for {\lambda}_AD, the high spatial frequency cutoff presumably due to
turbulent ambipolar diffusion. For the same parameters we have \sim
k^-(1.4\pm0.4) and a tentative value of {\lambda}_AD \simeq 2.2 mpc for NGC
1333 IRAS 4A, and \sim k^-(1.8\pm0.3) with an upper limit of {\lambda}_AD < 1.8
mpc for IRAS 16293. We also discuss the application of the technique to
interferometry measurements and the effects of the inherent spatial filtering
process on the interpretation of the results.Comment: 25 pages, 9 figures; accepted for publication in The Astrophysical
Journa
Cortical and subcortical alterations associated with precision visuomotor behavior in individuals with autism spectrum disorder
In addition to core deficits in social-communication abilities and repetitive behaviors and interests, many 2 patients with autism spectrum disorder (ASD) experience developmental comorbidities, including 3 sensorimotor issues. Sensorimotor issues are common in ASD and associated with more severe clinical 4 symptoms. Importantly, sensorimotor behaviors are precisely quantifiable and highly translational, 5 offering promising targets for neurophysiological studies of ASD. We used functional MRI to identify 6 brain regions associated with sensorimotor behavior using a visually-guided precision gripping task in 7 individuals with ASD (N=20) and age-, IQ-, and handedness-matched controls (N=18). During 8 visuomotor behavior, individuals with ASD showed greater force variability than controls. BOLD signal 9 for multiple cortical and subcortical regions was associated with force variability, including motor and 10 premotor cortex, posterior parietal cortex, extrastriate cortex, putamen, and cerebellum. Activation in 11 right premotor cortex scaled with sensorimotor variability in controls, but not in ASD. Individuals with 12 ASD showed greater activation than controls in left putamen and left cerebellar lobule VIIb and activation 13 in these regions was associated with more severe clinically-rated symptoms of ASD. Together, these 14 results suggest that greater sensorimotor variability in ASD is associated with altered cortical-striatal 15 processes supporting action selection and cortical-cerebellar circuits involved in feedback-guided reactive 16 adjustments of motor output. Our findings also indicate that atypical organization of visuomotor cortical 17 circuits may result in heightened reliance on subcortical circuits typically dedicated to motor skill 18 acquisition. Overall, these results provide new evidence that sensorimotor alterations in ASD involve 19 aberrant cortical and subcortical organization that may contribute to key clinical issues in patients. 20
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New and noteworthy: This is the first known study to examine functional brain activation during 22 precision visuomotor behavior in autism spectrum disorder (ASD). We replicate previous findings of 23 elevated force variability in ASD and find these deficits are associated with atypical function of ventral 24 premotor cortex, putamen, and posterolateral cerebellum, indicating cortical-striatal processes supporting 25 action selection and cortical-cerebellar circuits involved in feedback-guided reactive adjustments of motor 26 output may be key targets for understanding the neurobiology of ASD.NICHD 055751NIMH R01 12743-01NCATS TL1 TR002368,Kansas Center for Autism Research and Training (K-CART) Research Investment Council Strategic Initiative Gran
Magnetic Fields and Infall Motions in NGC 1333 IRAS 4
We present single-dish 350 micron dust continuum polarimetry as well as HCN
and HCO+ J=4-3 rotational emission spectra obtained on NGC 1333 IRAS 4. The
polarimetry indicates a uniform field morphology over a 20" radius from the
peak continuum flux of IRAS 4A, in agreement with models of magnetically
supported cloud collapse. The field morphology around IRAS 4B appears to be
quite distinct however, with indications of depolarization observed towards the
peak flux of this source. Inverse P-Cygni profiles are observed in the HCN
J=4-3 line spectra towards IRAS 4A, providing a clear indication of infall gas
motions. Taken together, the evidence gathered here appears to support the
scenario that IRAS 4A is a cloud core in a critical state of support against
gravitational collapse.Comment: 23 pages, 6 figures, 2 table
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