5,697 research outputs found
Model development for the estimation of urban air temperature based on surface temperature and NDVI - a case study in Szeged
Predictive models for urban air temperature (Tair) were developed by using urban land surface temperature (LST) retrieved from Landsat-8 and MODIS data, NDVI retrieved from Landsat-8 data and Tair measured by 24 climatological stations in Szeged. The investigation focused on summer period (JuneâSeptember) during 2016â2019 in Szeged. The relationship between Tair and LST was analyzed by calculating Pearson correlation coefficient, root-mean-square error and mean-absolute error using the data of 2017â2019, then unary (LST) and binary (LST and NDVI) linear regression models were developed for estimating Tair. The data in 2016 were used to validate the accuracy of the models. Correlation analysis indicated that there were strong correlations during the nighttime and relatively weaker ones during the daytime. The errors between Tair and LSTMODIS-Night was the smallest, followed by LSTMODIS-Day and LSTLandsat-8 respectively. The validation results showed that all models could perform well, especially during nighttime with an error of less than 1.5â. However, the addition of NDVI into the linear regression models did not significantly improve the accuracy of the models, and even had a negative effect. Finally, the influencing factors and temporal and spatial variability of the correlation between Tair and LST were analyzed. LSTLandsat-8 had a larger original error with Tair, but the regression model based on Landsat-8 had a stronger ability to reduce errors
Sensitive VLBI Continuum and H I Absorption Observations of NGC 7674: First Scientific Observations with the Combined Array VLBA, VLA & Arecibo
We present phase-referenced VLBI observations of the radio continuum emission
from, and the H I 21 cm absorption toward, the Luminous Infrared Galaxy NGC
7674. The observations were carried out at 1380 MHz using the VLBA, the phased
VLA, and theArecibo radio telescope. These observations constitute the first
scientific use of the Arecibo telescope in a VLBI observation with the VLBA.
The high- and low-resolution radio continuum images reveal several new
continuum structures in the nuclear region of this galaxy. At ~100 mas
resolution, we distinguish six continuum structures extending over 1.4 arcsec,
with a total flux density of 138 mJy. Only three of these structures were known
previously. All these structures seem to be related to AGN activity. At the
full resolution of the array, we only detect two of the six continuum
structures. Both are composed of several compact components with brightness
temperatures on the order of K. While it is possible that one of these
compact structures could host an AGN, they could also be shock-like features
formed by the interaction of the jet with compact interstellar clouds in the
nuclear region of this galaxy. Complex H I absorption is detected with our VLBI
array at both high and low angular resolution. Assuming that the widest H I
feature is associated with a rotating H I disk or torus feeding a central AGN,
we estimate an enclosed dynamical mass of ~7 x 10^7 M_sun, comparable to the
value derived from the hidden broad H emission in this galaxy. The
narrower H I lines could represent clumpy neutral hydrogen structures in the H
I torus. The detection of H I absorption toward some of the continuum
components, and its absence toward others, suggest an inclined H I disk or
torus in the central region of NGC 7674.Comment: 37 pages, 11 figures. ApJ accepted. To appear in the Nov. 10, 2003
issue of ApJ. Please use the PDF version if the postscript doesn't show the
figure
On the Nature of Intrinsic Absorption in Reddened Seyfert 1 Galaxies
We discuss the origin of the ``dusty lukewarm absorber'', which we previously
identified in the reddened Seyfert 1 galaxies NGC 3227 and Akn 564. This
absorber is characterized by saturated UV absorption lines (C IV, N V) near the
systemic velocity of the host galaxy, and is likely responsible for reddening
both the continuum and the emission lines (including those from the narrow-line
region) from these Seyferts. From a large sample of Seyfert 1 galaxies, we find
that continuum reddening (as measured by UV color) tends to increase with
inclination of the host galaxy. Furthermore, reddened, inclined Seyfert
galaxies observed at moderate to high spectral resolution all show evidence for
dusty lukewarm absorbers. We suggest that these absorbers lie in the plane of
the host galaxy at distances > 100 pc from the nucleus, and are physically
distinct from the majority of intrinsic absorbers that are outflowing from the
nucleus.Comment: 14 pages, including 2 figures, accepted for publication in the
Astrophysical Journal (Letters
Detailed Radio Spectra of Selected Compact Sources in the Nucleus of M82
We have determined detailed radio spectra for 26 compact sources in the
starburst nucleus of M82, between 74 and 1.3 cm. Seventeen show low-frequency
turnovers. One other has a thermal emission spectrum, and we identify it as an
HII region. The low frequency turnovers are due to absorption by the
interstellar gas in M82. New information on the AGN candidate 44.01+595, shows
it to have a non-thermal falling powerlaw spectrum at the highest frequencies,
and that it is strongly absorbed below 2 GHz. We derive large magnetic fields
in the supernova remnants, of order 1-2 milliGauss, hence large pressures in
the sources suggest that the brightest ones are either expanding or are
strongly confined by a dense interstellar medium. From the largest source in
our sample, we derive a supernova rate of 0.016 SN/yr.Comment: 19 pages, 7 tables, 29 figures, LaTeX, requires AAS macros v. 4.0. To
appear in ApJ July 20, 199
The Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies
We use the difference (delta) between the position angles of the nuclear
radio emission and the host galaxy major axis to investigate the distribution
of the angle (beta) between the axes of the nuclear accretion disk and the host
galaxy disk in Seyfert galaxies. We provide a critical appraisal of the quality
of all measurements, and find that the data are limited by observational
uncertainties and biases, such as the well known deficiency of Seyfert galaxies
of high inclination. There is weak evidence that the distribution of delta for
Seyfert 2 galaxies may be different (at the 90% confidence level) from a
uniform distribution, while the Seyfert 1 delta distribution is not
significantly different from a uniform distribution or from the Seyfert 2 delta
distribution. The cause of the possible non-uniformity in the distribution of
delta for Seyfert 2 galaxies is discussed. Seyfert nuclei in late-type spiral
galaxies may favor large values of delta (at the ~96% confidence level), while
those in early-type galaxies show a more or less random distribution of delta.
This may imply that the nuclear accretion disk in non-interacting late-type
spirals tends to align with the stellar disk, while that in early-type galaxies
is more randomly oriented, perhaps as a result of accretion following a galaxy
merger.
We point out that biases in the distribution of inclination translate to
biased estimates of beta in the context of the unified scheme. When this effect
is taken into account, the distributions of beta for all Seyferts together, and
of Seyfert 1's and 2's separately, agree with the hypothesis that the radio
jets are randomly oriented with respect to the galaxy disk. The data are
consistent with the expectations of the unified scheme, but do not demand it.Comment: To appear in the Astrophysical Journal, Vol 516 #1, May 1, 1999.
Corrected figure placement within pape
The Seyfert-Starburst Connection in X-rays. II. Results and Implications
We present the results of X-ray imaging and spectroscopic analysis of a
sample of Seyfert 2 galaxies that contain starbursts, based on their optical
and UV characteristics. These composite galaxies exhibit extended, soft,
thermal X-ray emission, which we attribute to their starburst components.
Comparing their X-ray and far-infrared properties with ordinary Seyfert and
starburst galaxies, we identify the spectral characteristics of their various
intrinsic emission sources. The observed far-infrared emission of the composite
galaxies may be associated almost exclusively with star formation, rather than
the active nucleus. The ratio of the hard X-ray luminosity to the far-infrared
and [O III] 5007 luminosity distinguishes most of these composite galaxies from
``pure'' Seyfert 2 galaxies, while their total observed hard X-ray luminosity
distinguishes them from ``pure'' starbursts. The hard nuclear X-ray source is
generally heavily absorbed (N_H > 10^{23} cm^{-2}) in the composite galaxies.
Based on these results, we suggest that the interstellar medium of the nuclear
starburst is a significant source of absorption. The majority of the sample are
located in groups or are interacting with other galaxies, which may trigger the
starburst or allow rapid mass infall to the central black hole, or both. We
conclude that starbursts are energetically important in a significant fraction
of active galaxies, and starbursts and active galactic nuclei may be part of a
common evolutionary sequence.Comment: 16 pages including 8 figures and 5 tables; to appear in the ApJ, Mar.
10, 200
Electrohydrodynamic Jet Printing of 1D Photonic Crystals: Part IIâOptical Design and Reflectance Characteristics
Additive manufacturing systems that can arbitrarily deposit multiple materials into precise, 3D spaces spanning the microâ to nanoscale are enabling novel structures with useful thermal, electrical, and optical properties. In this companion paper set, electrohydrodynamic jet (eâjet) printing is investigated for its ability in depositing multimaterial, multilayer films with microscale spatial resolution and nanoscale thickness control, with a demonstration of this capability in creating 1D photonic crystals (1DPCs) with response near the visible regime. Transfer matrix simulations are used to evaluate different material classes for use in a printed 1DPC, and commercially available photopolymers with varying refractive indices (n = 1.35 to 1.70) are selected based on their relative high index contrast and fast curing times. Eâjet printing is then used to experimentally demonstrate pixelated 1DPCs with individual layer thicknesses between 80 and 200 nm, square pixels smaller than 40 ”m across, with surface roughness less than 20 nm. The reflectance characteristics of the printed 1DPCs are measured using spatially selective microspectroscopy and correlated to the transfer matrix simulations. These results are an important step toward enabling costâeffective, customâfabrication of advanced imaging devices or photonic crystal sensing platforms.Electrohydrodynamic jet printing is used to create patterned arrays of multimaterial photopolymer 1D photonic crystals. Patterns are demonstrated with inâplane dimensions below 40 ”m, layer thicknesses less than 100 nm, and surface root mean square roughness below 20 nm. This novel fabrication method can enable rapid, reconfigurable manufacturing of custom photonic sensing arrays.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163389/2/admt202000431-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163389/1/admt202000431.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163389/3/admt202000431_am.pd
- âŠ