28 research outputs found
Dimerization effect on HF elimination from the photoionized fluorophenols
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Previous issue date: 2019-06-21A time of flight mass spectrometry study for multi-photon ionization dissociation of monomers and dimers of 2- and 3-fluorophenols (2FP and 3FP) by a pulsed UV laser light of wavelength 266 nm will be presented. For these molecules, HF elimination from the excited and ionic states is a vital reaction channel. Our measurements reveal that the reaction does not occur from the monomer of 3FP, but it does occur with a measurable yield from the monomer cation of 2FP. On the other hand, upon formation of hydrogen bonded dimers, this reaction is triggered in the cation of 3FP, but for 2FP dimer cation the reaction is so facile that no intact dimer cation survives and only the HF eliminated dimer ion shows up in the mass spectrum. Electronic structure theory predicts that in the D state of 2FP dimer cation, HF elimination is exothermic, but the process encounters a large barrier, 2.75 eV. However, in S state of the dimer the reaction is predicted to be barrierless. Thus, we propose that for this dimer, HF elimination takes place in the intermediate S state, and the remaining fragment that has relatively lower ionization energy is ionized effectively by an overall two-photon (1+1) process. For the reaction to occur from 3FP dimer cation, a rearrangement of the dimer geometry and formation of an intermediate adduct has been suggested, and it is argued that the latter could be produced by nucleophilic attack of the neutral moiety at the ortho site of the cationic counterpart, and the whole process requires 3-photon (2+1) absorption
Why do mosquitoes use two modes of drinking? An analytical test of a blockage clearing hypothesis
No full textMosquitoes drink using a pair of in-line muscular pumps in the head that draw liquid food through a long drinking channel termed as proboscis. Experimental investigations of mosquito drinking using synchrotron x-ray indicate two modes of drinking, a predominantly occurring continuous mode in which the anterior cibarial and posterior pharyngeal pumps expand cyclically at a constant phase difference and an isolated burst mode in which the pharyngeal pump expansion is several orders of magnitude larger than in the continuous mode. The objective of this thesis is to explain the mechanics and functional implication of this two-pump dual mode drinking of a mosquito. A reduced order mathematical model suggests that the primary role of the pharyngeal pump is in the burst mode. Since the precise geometry of the pump during drinking is yet not known, the drinking mechanism is modeled using different pump geometries based on morphological constraints in the animal. The model shows the continuous mode as being more effective in terms of energy expenditure, while the burst mode creates a large pressure difference across the proboscis which might be used to clear an obstruction in the channel or prime the channel. The hypothesis regarding the ability of a mosquito to self-clear an obstruction is analyzed by modeling the presence of an air bubble inside the system. The model indicates that air bubbles maybe able to stop flow during continuous mode drinking, and these same bubbles can be cleared by switching temporarily to burst mode drinking.Master of Scienc
Petrophysical study of the Glorieta-Clearfork dolomite in the Monahans Field, Ward County, Texas
No full textCalculation of a reservoir's water saturation using the Archie equation requires the values for cementation exponent (m) and saturation exponent (n). Determination of these two parameters, particularly in carbonate reservoirs, is often difficult. Recently a new method (CAPE) for estimating m and n has been proposed by Maute et al. (1992). In the CAPE (Core Archie Parameter Estimation) method, m and n are determined by minimizing the error between laboratory derived water saturation (Sw (core)) and water saturation calculated by the Archie equation (Sw(Archie)). Because core data are often unavailable, the author substituted dielectric water saturation (Sxo(dielectric)) for core-derived water saturation to determine m and n, and applied the technique to the Glorieta-Clearfork dolomites in the Monahans field, Ward County, Texas.
The Permian (Leonardian) Glorieta-Clearfork dolomites in the Monahans field represents an upward-shoaling carbonate platform sequence. The predominant rock type is dolostone and the major mineral constituents are dolomite and anhydrite. Petrographic analysis reveals mainly intercrystalline/intergranular pore geometry with minor vuggy/moldic porosity.
In this study the author applied three techniques: (1) non-linear, (2) linear, and (3) m-porosity transform to determine m and n values that minimize the error (errorfunction) between Sxo (dielectric) and Sxo (Archie). Two mporosity transforms were established, but the transform that represented the majority of the data (85%) was used to derive m values. Using data from the Glorieta-Clearfork dolomite in the Monahans field, the non-linear method resulted in the minimum error between Sxo (dielectric) and Sxo (Archie).
The m and n values determined by the non-linear and linear methods probably do not represent physical rock characteristics but are only values that minimize the error functions. In contrast, m and n values determined by the mporosity transform method should represent physical attributes of reservoirs such as pore geometry or wettability.
In order to further reduce the error between Sxo (dielectric) and Sxo (Archie), m and n were approximated by mathematical functions (polynomial and Fourier series) to model the vertical variation of m and n in the reservoir (variable m and n method). This variable m and n method based on a Fourier series resulted in the greatest errorreduction when compared to the non-linear method.
After determining m and n values that result in the minimum error between Sxo (dielectric) and Sxo (Archie), these values can then be used to calculate the water saturation in the uninvaded zone (Sw)
Numerical Simulation to Characterize Homogeneity of Air-Fuel Mixture for Premixed Combustion in Gas Turbine Combustor
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Importance of Body Stance in Fog Droplet Collection by the Namib Desert Beetle
No full textThe fog-basking behavior of the Onymacris unguicularis, a beetle species living in the coastal regions of the Namibian desert, has recently caught the attention of the engineering community, as suggesting a viable biomimetic approach to address the problem of harvesting water in arid regions of the globe. Previous research has focused on observation and analysis of the beetle’s elytron properties and how these affect fog-collection rates. The head stance taken by the Onymacris unguicularis when fog basking is well documented. However, how this stance affects droplet collection has not been studied up to now. The present paper addresses this problem from a computational fluid dynamics perspective, where three-dimensional numerical simulations are used to characterize the fog flow properties around a simplified geometry mimicking the beetle’s body. The simulations employ two-way coupling between the gas flow and the dispersed fog phase to account for feedback effects of fog droplets on the carrier fluid (air), and assume that droplets are captured after hitting the elytron surface. The study considers several combinations of free-stream velocity and droplet volume fraction. The analysis reveals that there is a range of head-stance angles, corresponding to an inclination of the beetle between 35 deg and 45 deg with respect to the horizon, that maximizes water collection on the beetle’s back, in qualitative agreement with observations in nature and laboratory experiments. A rationale is proposed to explain this phenomenon, finding that the specific head stance corresponds to the maximum residence time of fluid particles above the beetle’s elytron surface. This, in turn, designates the maximum likelihood for water droplets to be captured in the boundary layer developing over the beetle and subsequently hit the surface where they get captured. The results reveal the importance of the fluid flow pattern around the beetle’s body in addition to the microphysical properties of the elytron when reliable predictions of the water droplet collection efficiency are sought
Effect of a Confined Outer Air Stream on Instability of an Annular Liquid Sheet Exposed to Gas Flow
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