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Li Y.J.,Harvard University | Li Y.J.,University of Macau | Liu P.,Harvard University | Gong Z.,Harvard University | And 6 more authors.
Environmental Science and Technology | Year: 2015

The reactivity of secondary organic material (SOM) of variable viscosity, ranging from nonliquid to liquid physical states, was studied. The SOM, produced in aerosol form from terpenoid and aromatic precursor species, was reacted with ammonia at variable relative humidity (RH). The ammonium-to-organic mass ratio (MMNH4 +/MOrg) increased monotonically from <5% RH to a limiting value at a threshold RH, implicating a transition from particle reactivity limited by diffusion at low RH to one limited by other factors at higher RH. For the studied size distributions and reaction times, the transition corresponded to a diffusivity above 10-17.5 ± 0.5 m2 s-1. The threshold RH values for the transition were <5% RH for isoprene-derived SOM, 35-45% RH for SOM derived from α-pinene, toluene, m-xylene, and 1,3,5-trimethylbenzene, and >90% for β-caryophyllene-derived SOM. The transition RH for reactivity differed in all cases from the transition RH of a nonliquid to a liquid state. For instance, for α-pinene-derived SOM the transition for chemical reactivity of 35-45% RH can be compared to the nonliquid to liquid transition of 65-90% RH. These differences imply that chemical transport models of atmospheric chemistry should not use the SOM liquid to nonliquid phase transition as one-to-one surrogates of SOM reactivity. © 2015 American Chemical Society. Source


Laulagnet B.,National Institute of Applied science of Lyon
18th International Congress on Sound and Vibration 2011, ICSV 2011 | Year: 2011

Instabilities generated by friction are responsible for many noises in real life, such as squealing, squeak or juddering. The challenge to model this strongly non-linear acoustic radiation problem depends on the possibility to predict the interacting contact forces with accuracy, since they entirely govern the sound radiation and the way this sound is perceived as, squeak, squeal or juddering. A first approach to tackle this problem consists in linearising it and to calculate a solution around a sliding equilibrium. The main advantage is the simplicity of this approach which consists in calculating the perturbed solution which will exhibit, if the system is unstable, complex solutions. We only have the possibility to detect instabilities, but we are in the impossibility to describe what appends during the instability and for example separating juddering from squealing. A second approach consists in finding the entire solution solving the problem in time. This second approach is used here, in the case of two interacting beams; one is pushed on the other at rest, by external constant forces or driven at constant velocity. The equations of movement of the two beams are solved explicitly in time. A Coulomb friction law is introduced in the equations of the contact point taking into account all the possible status: separated, sliding or sticking. Solutions for the contact force, contact point trajectories and acceleration contact point are calculated at each instant of time for durations of one or two seconds, allowing acoustic radiation simulations. We show how different events appear depending on the beam relative angle, friction coefficient, and how instability occurs leading to limit cycles appearance. Source


Zhang Y.,Harvard University | Sanchez M.S.,Harvard University | Sanchez M.S.,University of Sao Paulo | Douet C.,Harvard University | And 14 more authors.
Atmospheric Chemistry and Physics | Year: 2015

The change in shape of atmospherically relevant organic particles is used to estimate the viscosity of the particle material without the need for removal from aerosol suspension. The dynamic shape factors χ of particles produced by α-pinene ozonolysis in a flow tube reactor, under conditions of particle coagulation, were measured while altering the relative humidity (RH) downstream of the flow tube. As relative humidity was increased, the results showed that χ could change from 1.27 to 1.02, corresponding to a transition from aspherical to nearly spherical shapes. The shape change could occur at elevated RH because the organic material had decreased viscosity and was therefore able to flow to form spherical shapes, as favored by the minimization of surface area. Numerical modeling was used to estimate the particle viscosity associated with this flow. Based on particle diameter and RH exposure time, the viscosity dropped from 10(8.7±2.0) to 10(7.0±2.0) Pa s (two sigma) for an increase in RH from < 5 to 58 % at 293 K. These results imply that the equilibration of the chemical composition of the particle phase with the gas phase can shift from hours at mid-range RH to days at low RH. © Author(s) 2015. Source


Lakhian V.,McMaster University | Bocquet F.,National Institute of Applied science of Lyon | Brocilo D.,Exponent, Inc. | Harvel G.D.,McMaster University | And 7 more authors.
IEEE Transactions on Industry Applications | Year: 2010

The discharge characteristics of a ring-type flow-stabilized pulsed corona discharge radical shower system (RCDRS) were investigated. An RCDRS with six hollow electrodes was studied. A low dc voltage charging of an ignition coil-type power supply was used to generate a pulse high voltage. Experiments were conducted for an applied charging dc voltage from 5 V to 18 V, a pulse repetition rate from 50 Hz to 200 Hz, and an injected air flow rate from 2.5 to 4.6 L/min per hollow electrode. The discharge characteristics were measured using current and voltage probes, and the morphology of the discharge was observed using a CCD camera. The pulsed waveforms of current, voltage, and power (secondary side output) were studied in terms of the input power (primary side), as well as the current and voltage, with the observed optical images for optimization. The results show that the maximum discharge current, voltage, and power increase with increasing primary side dc voltage or power. The pulse repetition rate affected the maximum discharge characteristics in terms of the primary side dc voltage, while the air flow rate did not. The maximum volume averaged plasma density is on the order of 1011ions/cm3 for the 10-cm diameter and 5-cm-long flow channel volume. © 2010 IEEE. Source

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