1,721,348 research outputs found
Numerical computation for parallel plate thermoacoustic heat exchangers in standing wave oscillatory flow
Full text linkA simplified computational method for studying the heat transfer characteristics of parallel plate thermoacoustic heat exchangers is presented. The model integrates the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. Details of the time-averaged temperature and heat flux density distributions within a representative domain of the heat exchangers
and adjoining stack are given. The effect of operation conditions and geometrical parameters on the heat exchanger performance is investigated and main conclusions relevant for HX design are drawn as far as fin length, fin spacing, blockage ratio, gas and secondary fluid-side heat transfer coefficients are concerned. Most relevant is that
the fin length and spacing affect in conjunction the heat exchanger behaviour and have to be simultaneously optimized to minimize thermal losses localized at the HX-stack
junctions. Model predictions fit experimental data found in literature within 36% and 49% respectively at moderate and high acoustic Reynolds numbers
I tumori delle palpebre. Contributo allo studio statistico degli epiteliomi baso e spinocellulare.
No full textInterazione di legame idrogeno tra Glyphosate e un acido umico purificato rilevata con spettrofotometria infrarosso
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Modification of Infrared Spectra of the Herbicide Glyphosate induced by pH variation
No full textAn infrared spectroscopy study was conducted on the herbicide Glyphosate (Roundup) at increasing pH. The IR bands followed the dissociation of the Glyphosate acidic groups at the different pHs. In particular the IR bands at about 1180 and 1090 cm‐1 were attributed to the P‐O stretching of the P‐OH and P‐O groups of the phosphono radical, respectively. In fact, the band at around 1180 cm‐1 appeared progressively reduced with increasing pH, whereas the absorption at about 1090 cm‐1 was concomitantly enhanced. This attribution had not been clearly indicated up to now in the literature, where the IR bands at about 1180 and 1090 cm‐1 were instead generally attributed to the asymmetric and symmetric stretchings of the P‐O bond of all three possible forms of the phosphono radical (‐PO3H2, ‐PO3H‐and ‐PO3 2‐). An increasing broadth of the bands was related to the enhanced number of possible intermolecular hydrogen bonds when the Glyphosate acidic functions were increasingly dissociated at higher pH
An infrared spectroscopy approach to the study of teh interaction of the herbicide Glyphosate
No full textSolid state nuclear magnetic resonance spectroscopy as a tool to characterize natural organic matter and soil samples. The basic principles
No full textBasic principles of solid state nuclear magnetic resonance spectroscopy (SS-NMR) are presented here. This paper is not pretending to provide an exhaustive treatment of the basics of SS-NMR.
However, it will give an overview of the main applications in the characterization of environmental systems and will describe the problems related to the acquisition of quantitative solid state NMR spectra
Hydrogen-bonding interactions between the herbicide Glyphosate and water-soluble humic substances
No full textIn this study, infrared spectroscopy (IR) was used to investigate the mechanism of interaction between the widely used herbicide Glyphosate [N-(phosphonomethyl) glycine] and a water-soluble humic acid (HA) obtained from a purified Leonardite Aliquots of the purified humic solution were set to pH 4, 5, and 6, and added with Glyphosate volumes corresponding to increasing percentages of total acidity of the water soluble HA The IR spectra of the HA-Glyphosate complexes showed two bands at 1,168 and 1,090 cm−1 for the stretchings of the P=O and P—O bonds, respectively, as they appear in the spectrum of Glyphosate alone where the phosphono group is involved in hydrogen bondings occurring in Glyphosate dimers Conversely, when the complex solutions were brought back to the starting pH levels (4, 5, and 6), the two IR bands of the phosphono group were shifted to higher frequencies (1,195 and 1,134 cm−1, respectively), suggesting that the P—O bonds were no longer involved in hydrogen bondings This behaviour supports the occurrence of hydrogen bondings in the Glyphosate-HA complex In fact, the IR band shift in the herbicide-HA complex indicates that, because the Glyphosate molecules are distributed along the humic macromolecule, they are too far apart to form the Glyphosate dimers again when the initial conditions are restored The hydrogen-bonding interaction between HA and Glyphosate evidenced in this study may well be responsible for the transport of Glyphosate in lower soil depths through the adsorption of Glyphosate on water soluble humic substance
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