15,157 research outputs found
Modal analysis and nonlinear characterization of an airborne power ultrasonic transducer with rectangular plate radiator
Some industrial processes like particle agglomeration or food dehydration among others can be enhanced by the use of power ultrasonic technologies. These technologies are based on an airborne power ultrasonic transducer (APUT) constituted by a pre-stressed Langevin-type transducer, a mechanical amplifier and an extensive plate radiator. In order to produce the desired effects in industrial processing, the transducer has to vibrate in an extensional mode driving an extensive radiator in the desired flexural mode with high amplitude displacements. Due to the generation of these high amplitude displacements in the radiator surfaces, non-linear effects like frequency shifts, hysteresis or modal interactions, among others, may be produced in the transducer behavior. When any nonlinear effect appears, when applying power, the stability and efficiency of this ultrasonic technology decreases, and the transducer may be damaged depending on the excitation power level and the nature of the nonlinearity. In this paper, an APUT with flat rectangular radiator is presented, as the active part of an innovative system with stepped reflectors. The nonlinear behavior of the APUT has been characterized numerically and experimentally in case of the modal analysis and experimentally in the case of dynamic analysis. According to the results obtained after the experiments, no modal interactions are expected, nor do other nonlinear effects
Photocatalytic degradation and mineralization of diazinon in aqueous solution using nano-TiO2(Degussa, P25): kinetic and statistical analysis
Abstract: In this study, photocatalytic degradation of diazinon was investigated using nano-TiO2, Degussa P25, as a photocatalyst and the effects of some operational parameters such as aeration, pH, photocatalyst concentration, and the irradiation time were also examined. Dispersive liquid-liquid microextraction technique was used to extract and pre-concentration of residual diazinon from the liquid samples and all experiments were carried out by gas chromatography. Amount of degradation and mineralization were determined by gas chromatograph with flame ionization detector (GC/FID) and COD measurements, respectively. The optimum condition for degradation of diazinon has been obtained in the pH 6, [nano-TiO2] = 0.2 g/L, and [time] = 120 min. In the optimal condition the removal efficiency of diazinon and COD were 99.64 and 65%, respectively. The results have shown that the nano-TiO2, aeration and time of reaction have a positive effect on photocatalytic degradation of diazinon and COD removal. Statistical analysis showed that the maximum removal of diazinon and COD were due to UV irradiation (71%, 41%), exposure time (16%, 39%), aeration (7%, 4%), and increased concentration of nano-TiO2 (0.4%, 2%), respectively; and the kinetics of photodegradation were found to follow a first-order kinetic model and the constant rate, at optimal condition, was 0.038 (minâ1). © 2014 Balaban Desalination Publications. All rights reserved
Economic feasibility of second generation ethanol with and without indirect greenhouse gas reduction benefits : a simulation for Brazil
The aim of this study is to determine the economic feasibility of second generation ethanol from sugar cane, whereby traditional ethanol production is combined with the use of lignocellulosic biomass for ethanol production. By applying cost-benefit analysis, this study evaluated the viability of the second generation ethanol technology as an alternative to conventional sugarcaneto- ethanol, both in terms of processing technology, and of land use impacts. Furthermore, an attempt is made to analyze impacts on CO2 mitigation and land use in economic. The research results indicate that: i) from an economic point of view, the first generation plant is clearly preferable. With IRR of 18.7%, Minimum selling price of US 213.0 million, first generation ethanol production from sugar cane has a large economic advantage compared to the second generation plant (IRR of 13.5%, Minimum selling price of US 78.5 million). ii) from an environmental point of view, a second generation biofuel that makes use of lignocellulosic biomass plant is clearly preferable. The second generation plant uses 49.6% less land and avoids a CO2 debt average of 942,282 ton per year throughout the life of the project. iii) Productivity gains improve profitability (IRR) and reduce biofuel prices (Minimum selling prices). Increasing the yearlt Ethanol and sugar cane productivityâs growth rate from 0.5% to 4.0% leads to a range of IRR from 17.5% to 21.5%, and of price from 0.29 US/l for first generation plant, and from 13.2% to 14.2% and of price from 0.39 US/l for second generation plant. iv) Process improvement shows little economic impact but matters on environmental side because less land is needed. Up to 10% more land can be saved compared to least advanced technology. v) Energy conversion development can improve income of the plant, especially for the first generation plant. Each 5% improvement can lead to 0.6% change in IRR project, and a reduction of 1.1% in the Minimum selling price. vi) Equipment investment is the most sensitive parameter to alter biofuel prices and profitability. The conventional plant is more sensitive to equipment investment, land prices and trash costs in this order while second generation plant is sensitive to equipment investment and almost insensitive to land prices and trash costs changes. vii) Assuming an average payment of US 27.7 million). viii) Productivity gains reduce the repayment time of CO2 debt, with ethanol productivity having a stronger contribution. Besides, from a growth rate of ethanol and sugar cane productivity from 0.5% to 4.0% per year, the repayment time changes from 11.8 years to a range between 6.5 years and 5.5 years and 13 and 9.5, respectively. In conclusion, the appraisal model represents a useful tool for analyzing many issues related with the dilemmas involved in biofuel production
The Association of Compact Groups of Galaxies with Large-scale Structures
We use various samples of compact groups (CGs) to examine the types of
association CGs have with rich and poor clusters of galaxies at low (z~0.04)
and intermediate (z~0.1) redshifts. We find that ~10-20 % of CGs are associated
with rich clusters and a much larger fraction with poorer clusters or loose
groups. Considering the incompleteness of catalogs of poorer systems at
intermediate redshift, our result is consistent with all CGs at intermediate
redshift being associated with larger-scale systems. The richness of the
clusters associated with CGs significantly increases from z~0.04 to z~0.1,
while their Bautz-Morgan type changes from early to late type for the same
range in z. Neither trend is compatible with a selection effect in the cluster
catalogs used. We find earlier morphological types of galaxies to be more
frequent in CGs associated with larger-scale structures, compared to those in
CGs not associated to such structures. We consider this as new evidence that
CGs are part of the large-scale structure formation process and that they may
play an important role in the evolution of galaxies in these structures.Comment: 5 pages, no figures, Proc. ESO Workshop "Groups of galaxies in the
nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia,
eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verlag; very minor
revision of text on 15 Mar 2006, added one referenc
Exactly solvable model of superstring in Ramond-Ramond plane wave background
We describe in detail the solution of type IIB superstring theory in the
maximally supersymmetric plane-wave background with constant null Ramond-Ramond
5-form field strength. The corresponding light-cone Green-Schwarz action found
in hep-th/0112044 is quadratic in both bosonic and fermionic coordinates. We
find the spectrum of the light-cone Hamiltonian and the string representation
of the supersymmetry algebra. The superstring Hamiltonian has a
``harmonic-oscillator'' form in both the string-oscillator and the zero-mode
parts and thus has discrete spectrum in all 8 transverse directions. We analyze
the structure of the zero-mode sector of the theory, establishing the precise
correspondence between the lowest-lying ``massless'' string states and the type
IIB supergravity fluctuation modes in the plane-wave background. The zero-mode
spectrum has certain similarity to the supergravity spectrum in AdS_5 x S^5 of
which the plane-wave background is a special limit. We also compare the
plane-wave string spectrum with expected form of the light-cone gauge spectrum
of superstring in AdS_5 x S^5.Comment: 33 pages, latex. v4: minor sign corrections in (1.5) and (3.62), to
appear in PR
Asymmetries in Mars' Exosphere: Implications for X-ray and ENA Imaging
Observations and simulations show that Mars' atmosphere has large seasonal
variations. Total atmospheric density can have an order of magnitude
latitudinal variation at exobase heights. By numerical simulations we show that
these latitude variations in exobase parameters induce asymmetries in the
hydrogen exosphere that propagate to large distances from the planet. We show
that these asymmetries in the exosphere produce asymmetries in the fluxes of
energetic neutral atoms (ENAs) and soft X-rays produced by charge exchange
between the solar wind and exospheric hydrogen. This could be an explanation
for asymmetries that have been observed in ENA and X-ray fluxes at Mars.Comment: Submitted to Space Science Review. v2: Minor changes in text and
figure
Superparticle and superstring in AdS_3 x S^3 Ramond-Ramond background in light-cone gauge
We discuss superparticle and superstring dynamics in AdS_3 x S^3 supported by
R-R 3-form background using light-cone gauge approach. Starting with the
superalgebra psu(1,1|2) + psu(1,1|2) representing the basic symmetry of this
background we find the light-cone superparticle Hamiltonian. We determine the
harmonic decomposition of light-cone superfield describing fluctuations of type
IIB supergravity fields expanded near AdS_3 x S^3 background and compute the
corresponding Kaluza-Klein spectrum. We fix the fermionic and bosonic
light-cone gauges in the covariant Green-Schwarz AdS_3 x S^3 superstring action
and find the light-cone string Hamiltonian. We also obtain a realization of the
generators of psu(1,1|2) + psu(1,1|2) in terms of the superstring 2-d fields in
the light-cone gauge.Comment: 32 pages, late
Model fluid in a porous medium: results for a Bethe lattice
We consider a lattice gas with quenched impurities or `quenched-annealed
binary mixture' on the Bethe lattice. The quenched part represents a porous
matrix in which the (annealed) lattice gas resides. This model features the 3
main factors of fluids in random porous media: wetting, randomness and
confinement. The recursive character of the Bethe lattice enables an exact
treatment, whose key ingredient is an integral equation yielding the
one-particle effective field distribution. Our analysis shows that this
distribution consists of two essentially different parts. The first one is a
continuous spectrum and corresponds to the macroscopic volume accessible to the
fluid, the second is discrete and comes from finite closed cavities in the
porous medium. Those closed cavities are in equilibrium with the bulk fluid
within the grand canonical ensemble we use, but are inaccessible in real
experimental situations. Fortunately, we are able to isolate their
contributions. Separation of the discrete spectrum facilitates also the
numerical solution of the main equation. The numerical calculations show that
the continuous spectrum becomes more and more rough as the temperature
decreases, and this limits the accuracy of the solution at low temperatures.Comment: 13 pages, 12 figure
Anisotropic scattering and quantum magnetoresistivities of a periodically modulated 2D electron gas
We calculate the longitudinal conductivities of a two-dimensional
noninteracting electron gas in a uniform magnetic field and a lateral electric
or magnetic periodic modulation in one spatial direction, in the quantum
regime. We consider the effects of the electron-impurity scattering anisotropy
through the vertex corrections on the Kubo formula, which are calculated with
the Bethe-Salpeter equation, in the self-consistent Born approximation. We find
that due to the scattering anisotropy the band conductivity increases, and the
scattering conductivities decrease and become anisotropic. Our results are in
qualitative agreement with recent experiments.Comment: 19 pages, 8 figures, Revtex, to appear in Phys. Rev.
Accurate and robust image superresolution by neural processing of local image representations
Image superresolution involves the processing of an image sequence to generate a still image with higher resolution. Classical approaches, such as bayesian MAP methods, require iterative minimization procedures, with high computational costs. Recently, the authors proposed a method to tackle this problem, based on the use of a hybrid MLP-PNN architecture. In this paper, we present a novel superresolution method, based on an evolution of this concept, to incorporate the use of local image models. A neural processing stage receives as input the value of model coefficients on local windows. The data dimension-ality is firstly reduced by application of PCA. An MLP, trained on synthetic se-quences with various amounts of noise, estimates the high-resolution image data. The effect of varying the dimension of the network input space is exam-ined, showing a complex, structured behavior. Quantitative results are presented showing the accuracy and robustness of the proposed method
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