1,464 research outputs found
Extreme Starlight Polarization in a Region with Highly Polarized Dust Emission
Galactic dust emission is polarized at unexpectedly high levels, as revealed
by Planck. The origin of the observed polarization fractions can
be identified by characterizing the properties of optical starlight
polarization in a region with maximally polarized dust emission. We measure the
R-band linear polarization of 22 stars in a region with a submillimeter
polarization fraction of . A subset of 6 stars is also measured in
the B, V and I bands to investigate the wavelength dependence of polarization.
We find that starlight is polarized at correspondingly high levels. Through
multiband polarimetry we find that the high polarization fractions are unlikely
to arise from unusual dust properties, such as enhanced grain alignment.
Instead, a favorable magnetic field geometry is the most likely explanation,
and is supported by observational probes of the magnetic field morphology. The
observed starlight polarization exceeds the classical upper limit of
%mag and is at least
as high as 13%mag that was inferred from a joint analysis of Planck
data, starlight polarization and reddening measurements. Thus, we confirm that
the intrinsic polarizing ability of dust grains at optical wavelengths has long
been underestimated.Comment: Accepted by A&AL, data to appear on CDS after publication. 6 page
Third Order Optical Nonlinearity of Colloidal Metal Nanoclusters Formed by MeV Ion Implantation
We report the results of characterization of nonlinear refractive index of the composite material produced by MeV Ag ion implantation of LiNbO(sub 3) crystal (z-cut). The material after implantation exhibited a linear optical absorption spectrum with the surface plasmon peak near 430 nm attributed to the colloidal silver nanoclusters. Heat treatment of the material at 500 deg C caused a shift of the absorption peak to 550 nm. The nonlinear refractive index of the sample after heat treatment was measured in the region of the absorption peak with the Z-scan technique using a tunable picosecond laser source (4.5 ps pulse width).The experimental data were compared against the reference sample made of MeV Cu implanted silica with the absorption peak in the same region. The nonlinear index of the Ag implanted LiNbO(sub 3) sample produced at five times less fluence is on average two times greater than that of the reference
The Lagrange and Markov spectra from the dynamical point of view
This text grew out of my lecture notes for a 4-hours minicourse delivered on
October 17 \& 19, 2016 during the research school "Applications of Ergodic
Theory in Number Theory" -- an activity related to the Jean-Molet Chair project
of Mariusz Lema\'nczyk and S\'ebastien Ferenczi -- realized at CIRM, Marseille,
France. The subject of this text is the same of my minicourse, namely, the
structure of the so-called Lagrange and Markov spectra (with an special
emphasis on a recent theorem of C. G. Moreira).Comment: 27 pages, 6 figures. Survey articl
A New Detection of Extragalactic Anomalous Microwave Emission in a Compact, Optically-Faint Region of NGC\,4725
We discuss the nature of a discrete, compact radio source (NGC 4725 B)
located 1.9 kpc from the nucleus in the nearby star-forming galaxy NGC
4725, which we believe to be a new detection of extragalactic Anomalous
Microwave Emission (AME). Based on detections at 3, 15, 22, 33, and 44 GHz, NGC
4725 B is a Jy radio source peaking at 33 GHz. While the source
is not identified in photometry, we detect counterparts in the
mid-infrared /IRAC bands (3.6, 4.5, 5.8, 8.0 m) that appear to be
associated with dust emission in the central region of NGC 4725. Consequently,
we conclude that NGC 4725 B is a new detection of AME, and very similar to a
recent detection of AME in an outer-disk star-forming region in NGC 6946. We
find that models of electric dipole emission from rapidly rotating ultra-small
grains are able to reproduce the radio spectrum for reasonable interstellar
medium conditions. Given the lack of an optical counterpart and the shape of
the radio spectrum, NGC 4725 B appears consistent with a nascent star-forming
region in which young ( Myr) massive stars are still highly
enshrouded by their natal cocoons of gas and dust with insufficient supernovae
occurring to produce a measurable amount of synchrotron emission.Comment: 10 pages, 4 figures, accepted for publication in Ap
Where's the Dust?: The Deepening Anomaly of Microwave Emission in NGC 4725 B
We present new Atacama Large Millimeter Array (ALMA) observations toward NGC 4725 B, a discrete, compact, optically faint region within the star-forming disk of the nearby galaxy NGC 4725 that exhibits strong anomalous microwave emission (AME). These new ALMA data include continuum observations centered at 92, 133, 203, and 221 GHz accompanied by spectral observations of the ¹²CO ( J = 2 → 1) line. NGC 4725 B is detected in the continuum at all frequencies, although the detection at 203 GHz is marginal. While molecular gas is not detected at the exact location of NGC 4725 B, there is molecular gas in the immediate vicinity (i.e., ≾100 pc) along with associated diffuse 8 μm emission. When combined with existing Very Large Array continuum data at 1.5, 3, 5.5, 9, 14, 22, 33, and 44 GHz, the spectrum is best fit by a combination of AME, synchrotron, and free–free emission that is free–free absorbed below ~6 GHz. Given the strength of the AME, there is surprisingly no indication of millimeter dust emission associated with NGC 4725 B on ≾6" spatial scales at the sensitivity of the ALMA interferometric data. Based on the properties of the nearest molecular gas complex and the inferred star formation rate, NGC 4725 B is consistent with being an extremely young (~3–5 Myr) massive (≾10⁵ M_⊙) cluster that is undergoing active cluster feedback. However, the lack of millimeter thermal dust emission is difficult to reconcile with a spinning dust origin of the 30 GHz emission. On the other hand, modeling NGC 4725 B as a new class of background radio galaxy is also unsatisfactory
Recent results from the canfranc dark matter search with germanium detectors
Two germanium detectors are currently operating in the Canfranc Underground
Laboratory at 2450 m.w.e looking for WIMP dark matter. One is a 2 kg 76Ge IGEX
detector (RG-2) which has an energy threshold of 4 keV and a low-energy
background rate of about 0.3 c/keV/kg/day. The other is a small (234 g) natural
abundance Ge detector (COSME), of low energy threshold (2.5 keV) and an energy
resolution of 0.4 keV at 10 keV which is looking for WIMPs and for solar
axions. The analysis of 73 kg-days of data taken by COSME in a search for solar
axions via their photon Primakoff conversion and Bragg scattering in the Ge
crystal yields a 95% C.L. limit for the axion-photon coupling g < 2.8 10^-9
GeV^-1. These data, analyzed for WIMP searches provide an exclusion plot for
WIMP-nucleon spin-independent interaction which improves previous plots in the
low mass region. On the other hand, the exclusion plot derived from the 60
kg-days of data from the RG-2 IGEX detector improves the exclusion limits
derived from other ionization (non thermal) germanium detector experiments in
the region of WIMP masses from 30 to 100 GeV recently singled out by the
reported DAMA annual modulation effect.Comment: 6 pages, talk given at IDM2000, York, September 200
Generational Differences in Faculty and Student Comfort With Technology Use.
BackgroundNavigating through online education courses continues to be a struggle for some nursing students. At the same time, integrating technology into online courses can be difficult for nursing faculty.PurposeThe purpose of this study was to assess faculty technology integration practices, student attitudes about technology use, and generational differences related to faculty and student technology use.MethodsA descriptive cross-sectional survey design was used to obtain data for this study.ResultsIntegration of technology into online courses and student attitudes about technology use were not significantly different by generation. Faculty and students from the Baby Boomer and Generation X reported less comfort using technology and higher levels of anxiety using technology than did individuals from Generation Y.ConclusionSignificant generational variations were not noted in relation to technology integration into courses and overall student attitudes about technology in this study, but differences were noted in relation to comfort with use of technology and anxiety when using technology. Student learning outcomes and satisfaction with learning may be influenced by the student's comfort using technology and faculty's confidence in integrating and using technology to provide online instruction
Real values of the W-function
Approximations for real values of W(x), where W is defined by solutions of W exp(W) = x, are presented. All of the approximations have maximum absolute (|W|>1) or relative (|W|<1) errors of O(10−4). With these approximations an efficient algorithm, consisting of a single iteration of a rapidly converging iteration scheme, gives estimates of W (x) accurate to at least 16 significant digits (15 digits if double precision is used). The Fortran code resulting from the algorithm is written to account for the different floating-point- number mantissa lengths on different computers, so that W (x) is computed to the floating-point precision available on the host machine
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