327 research outputs found
Evaluation of Hybrid Membrane Bioreactor (MBR) For Palm Oil Mill Effluent (POME) Treatment
The pollution load of palm oil mill effluent (POME) is in the range of 50,000 mg COD/L. With more than 500 palm oil mills, Malaysia produces some 13.9 million tonnes of crude palm oil annually and generates around 35 x 106 m3 POME. Typically, raw POME is difficult to degrade because it contains significant amounts of oil (tryacylglycerols) and degradative products such as di-and monoacylglycerols and fatty acids. The fatty acids composition (C12 – C20) of each of this fraction are different from one another and contribute to the high value of pollution load in POME. Thus POME has to be treated, usually in a series of anaerobic and aerobic treatment steps, for the organic matter to be degraded before the effluent is allowed to be discharged into public waterways. The objective of this study was to observe the performance of a hybrid membrane bioreactor (MBR) for POME. The raw POME was introduced into sequencing processes of anaerobic, anoxic and aerobic in order to achieve biological nutrient removal and the membrane modules were submerged into the aerobic zone. The critical flux of MBR using the flux-step method based on transmembrane pressure (TMP) was conducted as well as flux and permeability studies for assessing fouling in a membrane bioreactor operating at constant flux. The reactor was operated at a mixed liquor suspended solid (MLSS) concentration of 4000 to 8000 mg/l. The removal efficiency of COD, SS, TN and TP achieved were 94%, 98%, 83% and 64% respectively. The hybrid MBR was found to be able to degrade POME significantly and high quality effluent could be reused for various other applications.Keywords
Miracles and complementarity in de Sitter space
In this paper we consider a scenario, consisting of a de Sitter phase
followed by a phase described by a scale factor , where
, which can be viewed as an inflationary toy model. It is argued that
this scenario naively could lead to an information paradox. We propose that the
phenomenon of Poincar\'{e} recurrences plays a crucial role in the resolution
of the paradox. We also comment on the relevance of these results to inflation
and the CMBR.Comment: 13 page
Critical scaling of the a.c. conductivity for a superconductor above Tc
We consider the effects of critical superconducting fluctuations on the
scaling of the linear a.c. conductivity, \sigma(\omega), of a bulk
superconductor slightly above Tc in zero applied magnetic field. The dynamic
renormalization- group method is applied to the relaxational time-dependent
Ginzburg-Landau model of superconductivity, with \sigma(\omega) calculated via
the Kubo formula to O(\epsilon^{2}) in the \epsilon = 4 - d expansion. The
critical dynamics are governed by the relaxational XY-model
renormalization-group fixed point. The scaling hypothesis \sigma(\omega) \sim
\xi^{2-d+z} S(\omega \xi^{z}) proposed by Fisher, Fisher and Huse is explicitly
verified, with the dynamic exponent z \approx 2.015, the value expected for the
d=3 relaxational XY-model. The universal scaling function S(y) is computed and
shown to deviate only slightly from its Gaussian form, calculated earlier. The
present theory is compared with experimental measurements of the a.c.
conductivity of YBCO near Tc, and the implications of this theory for such
experiments is discussed.Comment: 16 pages, submitted to Phys. Rev.
Two-hadron semi-inclusive production including subleading twist
We extend the analysis of two-hadron fragmentation functions to the
subleading twist, discussing also the issue of color gauge invariance. Our
results can be used anywhere two unpolarized hadrons are semi-inclusively
produced in the same fragmentation region, also at moderate values of the hard
scale Q. Here, we consider the example of polarized deep-inelastic production
of two hadrons and we give a complete list of cross sections and spin
asymmetries up to subleading twist. Among the results, we highlight the
possibility of extracting the transversity distribution with longitudinally
polarized targets and also the twist-3 distribution e(x), which is related to
the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae,
added text in Secs. III-V, added reference
Effects of columnar disorder on flux-lattice melting in high-temperature superconductors
The effect of columnar pins on the flux-lines melting transition in
high-temperature superconductors is studied using Path Integral Monte Carlo
simulations. We highlight the similarities and differences in the effects of
columnar disorder on the melting transition in YBaCuO
(YBCO) and the highly anisotropic BiSrCaCuO (BSCCO) at
magnetic fields such that the mean separation between flux-lines is smaller
than the penetration length. For pure systems, a first order transition from a
flux-line solid to a liquid phase is seen as the temperature is increased. When
adding columnar defects to the system, the transition temperature is not
affected in both materials as long as the strength of an individual columnar
defect (expressed as a flux-line defect interaction) is less than a certain
threshold for a given density of randomly distributed columnar pins. This
threshold strength is lower for YBCO than for BSCCO. For higher strengths the
transition line is shifted for both materials towards higher temperatures, and
the sharp jump in energy, characteristic of a first order transition, gives way
to a smoother and gradual rise of the energy, characteristic of a second order
transition. Also, when columnar defects are present, the vortex solid phase is
replaced by a pinned Bose glass phase and this is manifested by a marked
decrease in translational order and orientational order as measured by the
appropriate structure factors. For BSCCO, we report an unusual rise of the
translational order and the hexatic order just before the melting transition.
No such rise is observed in YBCO.Comment: 32 pages, 13 figures, revte
Anomalous dimensions and phase transitions in superconductors
The anomalous scaling in the Ginzburg-Landau model for the superconducting
phase transition is studied. It is argued that the negative sign of the
exponent is a consequence of a special singular behavior in momentum space. The
negative sign of comes from the divergence of the critical correlation
function at finite distances. This behavior implies the existence of a Lifshitz
point in the phase diagram. The anomalous scaling of the vector potential is
also discussed. It is shown that the anomalous dimension of the vector
potential has important consequences for the critical dynamics in
superconductors. The frequency-dependent conductivity is shown to obey the
scaling . The prediction is
obtained from existing Monte Carlo data.Comment: RevTex, 20 pages, no figures; small changes; version accepted in PR
Energy Transfer in Multi Field Inflation and Cosmological Perturbations
In cascade inflation and some other string inflation models, collisions of
mobile branes with other branes or orbifold planes occur and lead to
interesting cosmological signatures. The fundamental M/string-theory
description of these collisions is still lacking but it is clear that the
inflaton looses part of its energy to some form of brane matter, e.g. a
component of tensionless strings. In the absence of a fundamental description,
we assume a general barotropic fluid on the brane, which absorbs part of the
inflaton's energy. The fluid is modeled by a scalar with a suitable exponential
potential to arrive at a full-fledged field theory model. We study numerically
the impact of the energy transfer from the inflaton to the scalar on curvature
and isocurvature perturbations and demonstrate explicitly that the curvature
power spectrum gets modulated by oscillations which damp away toward smaller
scales. Even though, the contribution of isocurvature perturbations decays
toward the end of inflation, they induce curvature perturbations on scales that
exit the horizon before the collision. We consider cases where the scalar
behaves like radiation, matter or a web of cosmic strings and discuss the
differences in the resulting power spectra.Comment: v1: 25 pages, 7 figures; v2: references added;v3: typo corrected,
accepted for publication to JCA
Review and application of Artificial Neural Networks models in reliability analysis of steel structures
This paper presents a survey on the development and use of Artificial Neural Network (ANN) models in structural reliability analysis. The survey identifies the different types of ANNs, the methods of structural reliability assessment that are typically used, the techniques proposed for ANN training set improvement and also some applications of ANN approximations to structural design and optimization problems. ANN models are then used in the reliability analysis of a ship stiffened panel subjected to uniaxial compression loads induced by hull girder vertical bending moment, for which the collapse strength is obtained by means of nonlinear finite element analysis (FEA). The approaches adopted combine the use of adaptive ANN models to approximate directly the limit state function with Monte Carlo simulation (MCS), first order reliability methods (FORM) and MCS with importance sampling (IS), for reliability assessment. A comprehensive comparison of the predictions of the different reliability methods with ANN based LSFs and classical LSF evaluation linked to the FEA is provided
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
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