Direct numerical simulation of a transitional temporal mixing layer laden with multicomponent-fuel evaporating drops using continuous thermodynamics

A model of a temporal three-dimensional mixing layer laden with fuel drops of a liquid containing a large number of species is derived. The fuel model is based on continuous thermodynamics, whereby the composition is statistically described through a distribution function parametrized on the species molar weight. The drop temperature is initially lower than that of the carrier gas, leading to drop heat up and evaporation. The model describing the changes in the multicomponent (MC) fuel drop composition and in the gas phase composition due to evaporation encompasses only two more conservation equations when compared with the equivalent single-component (SC) fuel formulation. Single drop results of a MC fuel having a sharply peaked distribution are shown to compare favorably with a validated SC-fuel drop simulation. Then, single drop comparisons are performed between results from MC fuel and a representative SC fuel used as a surrogate of the MC fuel. Further, two mixing layer simulations are conducted with a MC fuel and they are compared to representative SC-fuel simulations conducted elsewhere. Examination of the results shows that although the global layer characteristics are generally similar in the SC and MC situations, the MC layers display a higher momentum-thickness-based Reynolds number at transition. Vorticity analysis shows that the SC layers exhibit larger vortical activity than their MC counterpart. An examination of the drop organization at transition shows more structure and an increased drop-number density for MC simulations in regions of moderate and high strain. These results are primarily attributed to the slower evaporation of MC-fuel drops than of their SC counterpart. This slower evaporation is due to the lower volatility of the higher molar weight species, and also to condensation of already-evaporated species on drops that are transported in regions of different gas composition. The more volatile species released in the gas phase earlier during the drop lifetime reside in the lower stream while intermediary molar weight species, which egress after the drops are entrained in the mixing layer, reside in the mixing layer and form there a very heterogeneous mixture; the heavier species that evaporate later during the drop lifetime tend to reside in regions of high drop number density. This leads to a segregation of species in the gas phase based on the relative evaporation time from the drops. The ensemble-average drop temperature becomes eventually larger/smaller than the initial drop temperature in MC/SC simulations. Neither this species segregation nor the drop temperature variation with respect to the initial temperature or as a function of the mass loading can be captured by the SC-fuel simulations

Coherent population trapping with polarization modulation

Coherent population trapping (CPT) is extensively studied for future vapor cell clocks of high frequency stability. In the constructive polarization modulation CPT scheme, a bichromatic laser field with polarization and phase synchronously modulated is applied on an atomic medium. A high contrast CPT signal is observed in this so-called double-modulation configuration, due to the fact that the atomic population does not leak to the extreme Zeeman states, and that the two CPT dark states, which are produced successively by the alternate polarizations, add constructively. Here we experimentally investigate CPT signal dynamics first in the usual configuration, a single circular polarization. The double-modulation scheme is then addressed in both cases: one pulse Rabi interaction and two pulses Ramsey interaction. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We show that a simple sevenlevel model explains the experimental observations. The double-modulation scheme yields a high contrast similar to the one of other high contrast configurations like push-pull optical pumping or crossed linear polarization scheme, with a setup allowing a higher compactness. The constructive polarization modulation is attractive for atomic clock, atomic magnetometer and high precision spectroscopy applications.Comment: 13 pages, 15 figures. To be published in Journ. Appl. Phys.(2016

GROUND REACTION FORCES AND SPATIO-TEMPORAL VARIABLES DURING BAREFOOT AND SHOD RUNNING

INTRODUCTION The purpose of this study was to investigate the variations in step length, step frequency and ground reaction forces between barefoot and shod-foot running at three different velocities. Nine trained, male runners (age : 27.3 k 9 years ; height : 1.78 ? 0.07 m ; weight : 70 i 9 kg) were tested by using a Kistler force plate and by film analysis while running on a. 40m indoor runway. Ten trials, both barefoot and shod, at 3 different speeds (3.5, 4.5 and 5.5 m.sel) were analyzed with two-factor Anova tests with repeated measures with a significance level p r 0.05. The variables characterizing the vertical ground reaction forces (right foot) were defined following Nigg (1 986). RESULTS AND CONCLUSION All variables change significantly with Increasing speed. The increase of step length and step frequency support the findings in previous studies (Komi ef a/, 1987; Cavanagh and Kram, 1990). For the barefoot and shod-foot condition, there is a significant difference for all variables except for the amplitude of the Impact and active peak (Fzi and Fza). Considering the vertical ground reaction forces, more than one impact peak was seen during barefoot running. Although the amplitude of the impact peaks does not differ significantly, the maximal loading rate (Gzi = Fzilti) which is an important variable determining the impact load during heelstrike, is significantly larger in the barefoot condition. This supports the thesis that in barefoot running a maxmal deformation of the fatty heel tissue reduces its shock reduction capacity at heelstrike (De Clercq et a/, 1994). During push-off no important differences were found. A larger step frequency and a smaller step length for the barefoot condition were found. One possible explanation could be that the runners adapt a strategy to decrease the local stress underneath the heel (= pain sensation) in the barefoot condition. Taking smaller steps will change the touchdown conditions, with a larger plantar flexion of the bare foot as result. But further investigation of other kinematic variables of these nine persons will explain more clearly the differences found till now. REFERENCES Cavanagh, P.R. & Kram, R. (1990) in Cavanagh (Ed.) Biomechanics of distance running, Champaign, IL De Clercq, D. et al (1994). J. Biomechanics, 27(1 O), 121 3-1222. Komi, P.V. et al (1987). Int. J. Sports Med, 8, 196-202. Nigg, B.M. (1986). Biomechanics of running shoes, Champaign.IL

Intraguild predation between lady beetles and lacewings: outcomes and consequences vary with focal prey and arena of interaction

Citation: Noppe, Christophe, J. P. Michaud, and Patrick De Clercq. 2012. “Intraguild Predation Between Lady Beetles and Lacewings: Outcomes and Consequences Vary With Focal Prey and Arena of Interaction.” Annals of the Entomological Society of America 105 (4): 562–71. https://doi.org/10.1603/AN11165.We examined reciprocal intraguild predation (IGP) and cannibalism among various combinations of Coleomegilla maculata DeGeer and Chrysoperla carnea Stephens larvae as they developed feeding on greenbugs, Schizaphis graminum Rondani, on sorghum plants in microcosms. Pairs of C. maculata larvae suppressed aphids better than pairs of C. carnea larvae or heterospecific larval pairs and yielded the highest rate of plant survival. IGP by C. carnea larvae occurred mostly in the first instar, whereas C. maculata larvae were more aggressive in later instars. Although C. carnea was the superior intraguild predator, winning 62.7% of contests in microcosms, this value increased to 88.9% when the experiment was repeated in petri dishes without plant material, regardless of whether greenbugs or eggs of Ephestia kuehniella Zeller were offered as focal prey. Provision in petri dishes of the sessile, higher quality prey (Ephestia) as opposed to greenbugs, improved the survival of solitary larvae and delayed cannibalism and IGP until later developmental stages in both species. Larvae of C. maculata that cannibalized took longer to develop and weighed less at pupation, independent of the arena or prey offered. Although larvae of C. carnea did not pay a cost for cannibalism or IGP in microcosms, there were some negative developmental effects of IGP in petri dishes, particularly on the Ephestia diet. These results illustrate how the plant, as a substrate, can mediate the strength of IGP interactions and how the relative suitability of the focal prey can influence both the timing and consequences of cannibalism and IGP

Statistical Model of Multicomponent-Fuel Drop Evaporation for Many-Drop Flow Simulations

A statistical formulation is developed describing the composition in an evaporating multicomponent-fuel liquid drop and in the gas phase surrounding it. When a complementary discrete-component model is used, it is shown that, when drops are immersed in a carrier gas containing fuel vapor, condensation of species onto the drop results in the development of a minor peak in the liquid composition probability distribution function (PDF). This peak leads to a PDF shape that can be viewed as a combination of two gamma PDFs, which is determined by five parameters. A model is developed for calculating the parameters of the two combined gamma PDFs. Extensive tests of the model for both diesel and gasoline show that the PDF results replicate accurately the discrete model predictions. Most important, the mean and variance of the composition at the drop surface are in excellent agreement with the discrete model. Results from the model show that although the second peak is minor for the liquid PDF, its corresponding peak for the vapor distribution at the drop surface has a comparable magnitude to and sometimes exceeds that corresponding to the first peak. Four-parameter models are also exercised, and it is shown that they are unable to capture the physics of the problem

Welcome Home: Exploring Housing Options for Adults with Developmental Disabilities in Maine

This poster describes various housing options offering varying levels of supports for adults living with developmental disabilities in Maine. It also provides information for housing options in other states.https://digitalcommons.library.umaine.edu/ccids_posters/1036/thumbnail.jp