1,768 research outputs found
Phenol degradation using 20, 300 and 520 kHz ultrasonic reactors with hydrogen peroxide, ozone and zero valent metals
The extent of phenol degradation by the advanced oxidation process in the presence of zero valent iron (ZVI) and zero valent copper (ZVC) was studied using 20, 300 and 520 kHz ultrasonic (US) reactors. Quantification of hydrogen peroxide has also been performed with an aim of investigating the efficacy of different sonochemical reactors for hydroxyl radical production. It has been observed that the 300 kHz sonochemical reactor has the maximum efficacy for hydroxyl radical production. Phenol degradation studies clearly indicate that degradation of phenol is intensified in the presence of the catalyst and hydrogen peroxide, which can be attributed to enhanced production of hydroxyl radicals in the system. Experimental data shows that with ZVI, when the reaction was subjected to 300 kHz, complete phenol removal and 37% TOC mineralization was achieved within 25 min, whereas, in the case of 20 kHz US treatment no phenol was detected after 45 min and 39% TOC mineralization was observed. This novel study also investigated the use of zero valent copper (ZVC) and results showed that with 20, 300 and 520 kHz ultrasonic rectors, phenol removal was 10–98%, however, the maximum TOC mineralization achieved was only 26%. A comparative study between hydrogen peroxide and ozone as a suitable oxidant for Fenton-like reactions in conjunction with zero valent catalysts showed that an integrated approach of US/Air/ZVC/H2O2 system works better than US/ZVC/O3 (the ZOO process)
MULTILATERAL GOVERNANCE OF FISHERIES: MANAGEMENT AND COOPERATION IN THE WESTERN AND CENTRAL PACIFIC TUNA FISHERIES
The tuna resources of the Western and Central Pacific are the world's largest and most valuable fisheries of their type and are of significant economic importance to the Pacific island countries through whose waters they migrate. Two major concerns exist with the current governance of this fishery. First, Pacific island countries receive only a small share of the resource rents from the tuna fisheries. Second, the current management structure of the fisheries will not ensure the long-term sustainability of the resources. This paper derives a model to show that the sustainability of the resource can be improved when a single policymaker acts as Stackelberg leader and sets a tax, or an equivalent quantity instrument, to maximize rents from the resource. A practical institutional mechanism is presented that mimics the model's rent maximization outcome and that offers substantial benefits to both Pacific island countries and distant water fishing nations.Resource /Energy Economics and Policy,
Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates
For a new sample of 8 weak-line-quasars (WLQs) we report a sensitive search
in 20 intranight monitoring sessions, for blazar-like optical flux variations
on hour-like and longer time scale (day/month/yearlike). The sample consists
exclusively of the WLQs that are not radioloud and have either been
classified as `radio-weak probable BL Lac candidates' and/or are known to have
exhibited at least one episode of large, blazarlike optical variability.
Whereas only a hint of intranight variability is seen for two of these WLQs,
J104833.5620305.0(z = 0.219) and J133219.6622715.9 (z = 3.15),
statistically significant internight variability at a few per cent level is
detected for three of the sources, including the radio-intermediate WLQ
J133219.6622715.9 (z = 3.15) and the well known bonafide radioquiet
WLQs J121221.5534128.0 (z = 3.10) and WLQ J153259.9003944.1 (z = 4.62).
In the restframe, this variability is intra-day and in the farUV band. On
the time scale of a decade, we find for three of the WLQs large brightness
changes, amounting to 1.6550.009, 0.1630.010 and 0.1440.018 mag,
for J104833.5620305.0, J123743.1630144.9 and J232428.4144324.4,
respectively. Whereas the latter two are confirmed radio-quiet WLQs, the
extragalactic nature of J104833.5620305.0 remains to be well established,
thanks to the absence of any feature(s) in its available optical spectra. The
present study forms a part of our ongoing campaign of intranight optical
monitoring of radio quiet weak-line quasars, in order to improve the
understanding of this enigmatic class of Active Galactic Nuclei and to look
among them for a possible tiny, elusive population of radio-quiet BL Lacs.Comment: Accepted to MNRAS. 12 pages, 1 figure, 4 Tabl
Intensification of oxidation capacity using chloroalkanes as additives in hydrodynamic and acoustic cavitation reactors
The effect of the presence and absence of the chloroalkanes, dichloromethane (CH2Cl2), chloroform (CHCl3) and carbon tetrachloride (CCl4) on the extent of oxidation of aqueous I- to I3- has been investigated in (a) a liquid whistle reactor (LWR) generating hydrodynamic cavitation and (b) an ultrasonic probe, which produces acoustic cavitation. The aim has been to examine the intensification achieved in the extent of oxidation due to the generation of additional free radicals/oxidants in the reactor as a result of the presence of chloroalkanes. It has been observed that the extent of increase in the oxidation reaction is strongly dependent on the applied pressure in the case of the LWR. Also, higher volumes of the chloroalkanes favour the intensification and the order of effectiveness is CCl4> CHCl3 > CH2Cl2. However, the results with the ultrasonic probe suggest that an optimum concentration of CH2Cl2 or CHCl3 exists beyond which there is little increase in the extent of observed intensification. For CCl4, however, no such optimum concentration was observed and the extent of increase in the rates of oxidation reaction rose with the amount of CCl4 added. Stage wise addition of the chloroalkanes was found to give marginally better results in the case of the ultrasonic probe as compared to bulk addition at the start of the run. Although CCl4 is the most effective, its toxicity and carcinogenicity may mean that CH2Cl2 and CHCl3 offer a safer viable alternative and the present work should be useful in establishing the amount of chloroalkanes required for obtaining a suitable degree of intensification
Probing the variation of the fine-structure constant using QSO absorption lines
Search for the time variation of the fundamental constants is motivated by various unification theories. Here we present constraints on the variation of the fine-structure constant α≡2/ ħc) obtained using UVES/VLT samples of QSO absorption systems. We find < Δα/α >w = (-0.06 ± 0.06) × 10-5 using 23 Mg II systems and the many-multiplet (MM) method. Well selected 15 Si IV systems provide < Δα/α >w = (0.15 ± 0.43) ×10-5. Absence of detectable variation in α is also confirmed by our new very high resolution (R ~ 100,000) observation of zabs = 1.1508 toward HE 0515-4414 using HARPS on the ESO 3.6m telescope
Stability of Coalescence Hidden variable Fractal Interpolation Surfaces
In the present paper, the stability of Coalescence Hidden variable Fractal
Interpolation Surfaces(CHFIS) is established. The estimates on error in
approximation of the data generating function by CHFIS are found when there is
a perturbation in independent, dependent and hidden variables. It is proved
that any small perturbation in any of the variables of generalized
interpolation data results in only small perturbation of CHFIS. Our results are
likely to be useful in investigations of texture of surfaces arising from the
simulation of surfaces of rocks, sea surfaces, clouds and similar natural
objects wherein the generating function depends on more than one variable
Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars
Most of the successful physical theories rely on the constancy of few
fundamental quantities (such as the speed of light, , the fine-structure
constant, \alpha, the proton to electron mass ratio, \mu, etc), and
constraining the possible time variations of these fundamental quantities is an
important step toward a complete physical theory. Time variation of \alpha can
be accurately probed using absorption lines seen in the spectra of distant
quasars. Here, we present the results of a detailed many-multiplet analysis
performed on a new sample of Mg II systems observed in high quality quasar
spectra obtained using the Very Large Telescope. The weighted mean value of the
variation in \alpha derived from our analysis over the redshift range 0.4<z<2.3
is \Delta\alpha/\alpha = (-0.06+/-0.06) x 10^{-5}. The median redshift of our
sample (z=1.55) corresponds to a look-back time of 9.7 Gyr in the most favored
cosmological model today. This gives a 3\sigma limit, -2.5 x 10^{-16} yr^-1
<(\Delta\alpha/\alpha\Delta t) <+1.2x10^{-16} yr^-1, for the time variation of
\alpha, that forms the strongest constraint obtained based on high redshift
quasar absorption line systems.Comment: uses revtex, 4 pages 3 figures. Accepted for publication in Physical
Review Letter
Probing the variation of fundamental constants using QSO absorption lines
Absorption lines seen in the spectra of distant QSOs allow us to probe the space and time evolution of various fundamental constants. Here, we summarize results on the variation of α obtained by our group and others using UVES/VLT. Most upper limits reside in the range 0.5-1.5×10-5 at the 3σ level over a redshift range of approximately 0:5 ≤ z ≤ 2:5. In addition, we also briefly report on preliminary results based on the analysis of 21-cm absorbers detected with Giant Meterwave Radio Telescope(GMRT) that lead to Δx=x = (0:0 ± 1:5) × 10-6 at z=1.3. Discussions on future improvement are also presented
Antisymmetric-Tensor and Electromagnetic effects in an alpha'-non-perturbative Four-Dimensional String Cosmology
Starting from an exact (in the Regge slope alpha') functional method for a
bosonic stringy sigma-model, we investigate four-dimensional cosmological
string solutions in graviton, dilaton and antisymmetric tensor backgrounds,
compatible with world-sheet conformal invariance, and valid beyond perturbative
expansions in powers of alpha'. The antisymmetric tensor field, playing the
role of an axion in the four-dimensional target space time, leads to spatial
anisotropies of the emergent Robertson-Walker expanding Universe, and, upon
coupling the system to the electromagnetic field, it results in non-trivial
optical activity. Some estimates of the corresponding effects are made and
their relevance to current cosmology is briefly discussed
Probing the time-variation of the fine-structure constant: Results based on Si IV doublets from a UVES sample
We report a new constraint on the variation of the fine-structure constant
based on the analysis of 15 Si IV doublets selected from a ESO-UVES sample. We
find \Delta\alpha/\alpha = (+0.15+/-0.43) x 10^-5 over a redshift range of
1.59< z < 2.92 which is consistent with no variation in \alpha. This result
represents a factor of three improvement on the constraint on
\Delta\alpha/\alpha based on Si IV doublets compared to the published results
in the literature. The alkali doublet method used here avoids the implicit
assumptions used in the many-multiplet method that chemical and ionization
inhomogeneities are negligible and isotopic abundances are close to the
terrestrial value.Comment: 12 Pages, 7 figures. Accepted for publication in A&A. In addition to
minor corrections an appendix is added in this revised versio
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