718 research outputs found
Sorption of Perfluorochemicals to Granular Activated Carbon in the Presence of Ultrasound
Perfluorochemicals (PFCs) are emerging pollutants of increasing public health and environmental concern due to their worldwide distribution, environmental persistence, and bioaccumulation potential. Activated carbon adsorption is an effective method to remove PFCs from water. Herein, we report on the sorption of four PFCs: perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorobutane sulfonate (PFBS), and perfluorobutanoate (PFBA), from deionized water (MQ) and landfill groundwater (GW) by granular activated carbon (GAC) in the absence and presence of 20 kHz ultrasound. In all cases, the adsorption kinetics were found to be well-represented by a pseudosecond-order model, with maximum monolayer sorption capacity and initial sorption rate values following the orders q_(e)^(PFOS) > q_(e)^(PFOA) > q_(e)^(PFBS) > q_(e)^(PFBA) and v_(0)^(PFOS) > v_(0)^(PFBS) > v_(0)^(PFOA) > v_(0)^(PFBA), respectively. The equilibrium adsorption was quantified by the BET multilayer absorption isotherm, and the monolayer sorption capacity increased with increasing PFC chain length: q_(m)^(PFOS) > q_(m)^(PFOA) > q_(m)^(PFBS) > q_(m)^(PFBA). The equilibrium PFC sorption constants, q_e and q_m, and the sorption kinetic constants, v_0 and k_2, were greater in Milli-Q water than in landfill groundwater with or without pretreatment, indicating competition for sorption sites by natural and cocontaminant groundwater organics. Ultrasonic irradiation significantly increased the PFC−GAC sorption kinetics, 250−900%, and slightly increased the extent of PFC equilibrium adsorption, 5−50%. The ultrasonic PFC−GAC sorption kinetics enhancement increased with increasing PFC chain length, suggesting ultrasound acts to increase the PFC diffusion rate into GAC nanopores
Infrared Eclipses of the Strongly Irradiated Planet WASP-33b, and Oscillations of its Host Star
We observe two secondary eclipses of the strongly irradiated transiting
planet WASP-33b in the Ks band, and one secondary eclipse each at 3.6- and 4.5
microns using Warm Spitzer. This planet orbits an A5V delta-Scuti star that is
known to exhibit low amplitude non-radial p-mode oscillations at about
0.1-percent semi-amplitude. We detect stellar oscillations in all of our
infrared eclipse data, and also in one night of observations at J-band out of
eclipse. The oscillation amplitude, in all infrared bands except Ks, is about
the same as in the optical. However, the stellar oscillations in Ks band have
about twice the amplitude as seen in the optical, possibly because the
Brackett-gamma line falls in this bandpass. We use our best-fit values for the
eclipse depth, as well as the 0.9 micron eclipse observed by Smith et al., to
explore possible states of the exoplanetary atmosphere, based on the method of
Madhusudhan and Seager. On this basis we find two possible states for the
atmospheric structure of WASP-33b. One possibility is a non-inverted
temperature structure in spite of the strong irradiance, but this model
requires an enhanced carbon abundance (C/O>1). The alternative model has solar
composition, but an inverted temperature structure. Spectroscopy of the planet
at secondary eclipse, using a spectral resolution that can resolve the water
vapor band structure, should be able to break the degeneracy between these very
different possible states of the exoplanetary atmosphere. However, both of
those model atmospheres absorb nearly all of the stellar irradiance with
minimal longitudinal re-distribution of energy, strengthening the hypothesis of
Cowan et al. that the most strongly irradiated planets circulate energy poorly.
Our measurement of the central phase of the eclipse yields e*cos(omega)=0.0003
+/-0.00013, which we regard as being consistent with a circular orbit.Comment: 23 pages, 9 figures, 3 tables, accepted for the Astrophysical Journa
Intra and Inter-PON ONU to ONU Virtual Private Networking using OFDMA in a Ring Topology
Abstract—In this paper, we propose a novel WDM-PON architecture to support efficient and bandwidth-scalable virtual private network (VPN) emulation over both inter-PON and intra- PON. The virtual ring link for the VPN communications among ONUs is realized by using additionally low-cost optical passive components and OFDMA technology. Moreover, the downstream traffic wavelength is reused for the upstream traffic signal by using re-modulation technology. We report on a successful transmission of 10.7 Gbps OOK upstream and 10.7 Gbps DPSK downstream, together with 1.25 Gbps 16-QAM OFDM VPN traffic, over 20 km no-zero dispersion shifted fiber (NZDSF). In this paper, we propose a novel WDM-PON architecture to support efficient and bandwidth-scalable virtual private network (VPN) emulation over both inter-PON and intra-PON. The virtual ring link for the VPN communications among ONUs is realized by using additionally low-cost optical passive components and OFDMA technology. Moreover, the downstream traffic wavelength is reused for the upstream traffic signal by using re-modulation technology. We report on a successful transmission of 10.7 Gbps OOK upstream and 10.7 Gbps DPSK downstream, together with 1.25 Gbps 16-QAM OFDM VPN traffic, over 20 km no-zero dispersion shifted fiber (NZDSF)
Dimethyl 2,6-dihydroxybenzene-1,4-dicarboxylate
The title compound, C10H10O6, was obtained from an esterification reaction of 2,6-dihydroxyterephthalic acid and methanol. In the molecular structure, all of the C atoms are nearly coplanar. The two hydroxy groups have C2 symmetry. Intramolecular O—H⋯O hydrogen bonds are observed. In the crystal, weak O—H⋯O interactions link the molecules
Ground-based detections of thermal emission from CoRoT-1b and WASP-12b
We report a new detection of the H-band thermal emission of CoRoT-1b and two
confirmation detections of the Ks-band thermal emission of WASP-12b at
secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth
of 0.145%\pm0.049% with a 3-{\sigma} percentile between 0.033% - 0.235%. This
depth is consistent with the previous conclusions that the planet has an
isother- mal region with inefficient heat transport from dayside to nightside,
and has a dayside thermal inversion layer at high altitude. The two Ks band
detections of WASP-12b show a joint eclipse depth of 0.299%\pm0.065%. This
result agrees with the measurement of Croll & collaborators, providing
independent confirmation of their measurement. The repeatability of the
WASP-12b measurements also validates our data analysis method. Our
measurements, in addition to a number of previous results made with other
telescopes, demonstrate that ground-based observations are becoming widely
available for characterization of atmospheres of hot Jupiters.Comment: 20 pages, including 8 figures and 1 table. Accepted for publication
in Ap
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