5,769 research outputs found
Constraining the Variation in Fine-Structure Constant Using SDSS DR8 QSO Spectra
We report a robust constrain on the possible variation of fine-structure
constant, alpha = e^2/(hbar*c), obtained using O III 4959,5007, nebular
emission lines from QSOs. We find Delta-alpha/alpha=-(2.1 +/- 1.6) x 10^(-5)
based on a well selected sample of 2347 QSOs from Sloan Digital Sky Survey Data
Release 8 with 0.02 < z < 0.74. Our result is consistent with a non-varying
alpha at a level of 2 x 10^(-5) over approximately 7 Gyr. This is the largest
sample of extragalactic objects yet used to constrain the variation of alpha.
While this constraint is not as stringent as those determined using
many-multiplet method it is free from various systematic effects. A factor of ~
4 improvement in Delta-alpha/alpha achieved here compared to the previous study
(Bahcall et al. 2004) is just consistent with what is expected based on a
factor of 14 times bigger sample used here. This suggests that errors are
mainly dominated by the statistical uncertainty. We also find the ratio of
transition probabilities corresponding to the O III 5007 A and 4959 A lines to
be 2.933+/-0.002, in good agreement with the National Institute of Standards
and Technology measurements.Comment: 5 pages, 3 figures; Accepted for publication in MNRAS Lette
Removal of benzotriazole by Photo-Fenton like process using nano zero-valent iron: Response surface methodology with a Box-Behnken design
In this paper, the removal of benzotriazole (BTA) was investigated by a Photo-Fenton process using nano zero valent iron (NZVI) and optimization by response surface methodology based on Box-Behnken method. Effect of operating parameters affecting removal efficiency such as H2O2, NZVI, and BTA concentrations as well as pH was studied. All the experiments were performed in the presence of ultraviolet radiation. Predicted levels and BTA removal were found to be in good agreement with the experimental levels (R2 = 0. 9500). The optimal parameters were determined at 60 min reaction time, 15 mg L-1 BTA, 0.10 g L-1 NZVI, and 1.5 mmol L-1 H2O2 for Photo-Fenton-like reaction. NZVI was characterized using X-ray diffraction (XRD), transmission electron microscope (TEM) images, and scanning electron microscope (SEM) analysis
Heterogeneous oxidation of sulfacetamide in aquatic environment using ultrasonic and nano-fenton: Kinetics intermediates and bioassay test
In present study, degradation of sulfacetamide from a synthetic wastewater by sonofenton process using zero valent iron nanoparticles was investigated. The synthesized iron nanoparticles were characterized using transmission electron microscopy (TEM), UV-visible and X-ray diffraction pattern (XRD). The effect of various parameters, such as pH, nZVI dose, H2 O2 concentration and contact time was studied with batch experiments. The removal efficiency of sulfacetamide by US/nZVI/H2 Of process was about 91 for reaction time of 60 min, but less than 27 of chemical oxygen demand (COD) was removed. Kinetics studies showed that the degradation of sulfacetamide fitted well to the pseudo-second-order model. Using the LC/MS device, five intermediate from degradation of sulfacetamide were detected. The toxicity test, using micro toxicity study also showed that the effluent from the sono-Fenton reactor has a lower toxicity than sulfacetamide antibacterial. © 2019 Desalination Publications. All rights reserved
Identification of mono-and few- layer graphene: Raman study
International audienceIn this theoretical work, the Raman spectra were analyzed by considering the origin of the G peak, its shape, position and relative intensity as a function of the number of graphene layers. By using the spectral moment's method, the Raman spectra of mono, bi and few-layers of graphene are calculated and a good agreement was found with group theory concerning the number of the Raman-active modes and the Raman measurements. Our results provide a Raman analysis to evaluate the number of layers in multilayer graphene
Inactivation of Fecal coliforms during solar and photocatalytic disinfection by zinc oxide (ZnO) nanoparticles in compound parabolic concentrators (CPCs)
Water samples of 0, 50, and 100 nephelometric turbidity units (NTU) spiked with fecal coliforms (107 CFU/ml) were exposed to natural sunshine in 1l quartz glass tubes fitted with rectors' compound parabolic concentrators CPCS at two forms CPC1 (whit nanoparticle zinc oxide) and CPC2(without nanoparticle zinc oxide). The samples were characterized using the X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). On clear days, the complete inactivation times (more than 7-log unit reduction in bacterial population) in the systems with CPC1, and CPC2 were 15, and 30 min, respectively. The maximum temperatures obtained in the water samples were 80°C for CPC1, and 82°C for CPC2. The use of CPC1 with hydroxyl radicals (OH·) production significantly improved the efficiency of the old CPCS technique, since these systems (CPC1-2) shortened the exposure times to solar radiation and also minimized the negative effects of turbidity and also regrowth was zero in the disinfected samples. Due to two simultaneous effects of high temperatures and UV, regrowth in most ways of solar disinfection was not seen in these examples. Overall, this technology has been proved to be a good enhancement method to inactivate microorganisms under real conditions and represents a good alternative technique to drinking water treatment. © 2019, Islamic Azad University
An investigation of the line of sight towards QSO PKS 0237-233
We present a detailed analysis of absorption systems along the line of sight
towards QSO PKS 0237-233 using a high resolution spectrum of signal-to-noise
ratio (SNR) ~ 60-80 obtained with the Ultraviolet and Visual Echelle
Spectrograph mounted on the Very Large Telescope. This line of sight is known
to show a remarkable overdensity of CIV systems that has been interpreted as
revealing the presence of a supercluster of galaxies. A detailed analysis of
each of these absorption systems is presented. In particular, for the z_abs =
1.6359 (with two components of logN(HI) = 18.45, 19.05) and z_abs = 1.6720
(logN(H I) = 19.78) sub-Damped Ly-alpha systems (sub-DLAs), we measure accurate
abundances (resp. [O/H] = -1.63(0.07) and [Zn/H] = - 0.57(0.05) relative to
solar). While the depletion of refractory elements onto dust grains in both
sub-DLAs is not noteworthy, photoionization models show that ionization effects
are important in a part of the absorbing gas of the sub-DLA at z_abs = 1.6359
(HI is 95 percent ionized) and in part of the gas of the sub-DLA at z_abs =
1.6359. The CIV clustering properties along the line of sight is studied in
order to investigate the nature of the observed overdensity. We conclude that
despite the unusually high number of CIV systems detected along the line of
sight, there is no compelling evidence for the presence of a single unusual
overdensity and that the situation is consistent with chance coincidence.Comment: Accepted for publication in MNRAS. 23 pages, 16 figures, 12 table
Sharp Response Microstrip LPF using Folded Stepped Impedance Open Stubs
A novel microstrip lowpass filter with high selectivity and wide stopband is proposed that comprises two lateral folded open stubs and a central mirrored semi-circle ended suppressing cell. The proposed filter has cut-off frequency of 2.28 GHz and is very compact. The stopband width with attenuation level more than -20 dB is equal to 5.47 fc and the transition band is only 0.14 GHz. This filter is designed, fabricated and measured and the simulated and measured results are in good agreemen
Thermally isolated Luttinger liquids with noisy Hamiltonians
We study the dynamics of a quantum-coherent thermally isolated Luttinger
liquid with noisy Luttinger parameter. To characterize the fluctuations of the
absorbed energy in generic noise-driven systems, we first identify two types of
energy moments, which can help tease apart the effects of classical
(sample-to-sample) and quantum sources of fluctuations. One type of moment
captures the total fluctuations due to both sources, while the other one
captures the effect of the classical source only. We then demonstrate that in
the Luttinger liquid case, the two types of moments agree in the thermodynamic
limit, indicating that the classical source dominates. In contrast to
equilibrium thermodynamics, in this driven system the relative fluctuations of
energy do not decay with the system size. Additionally, we study the deviations
of equal-time correlation functions from their ground-state value, and find a
simple scaling behavior.Comment: 11 pages, 2 figure
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