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We have created a spatially homogeneous polariton condensate in thermal equilibrium, up to very high condensate fraction. Under these conditions, we have measured the coherence as a function of momentum and determined the total coherent fraction of this boson system from very low density up to density well above the condensation transition. These measurements reveal a consistent power law for the coherent fraction as a function of the total density over nearly three orders of its magnitude. The same power law is seen in numerical simulations solving the two-dimensional Gross-Pitaevskii equation for the equilibrium coherence. 

As the importance of non-tailpipe particles (NTP) over tailpipe emissions from urban traffic has been increasing, there is a need to evaluate NTP contributions to ambient particulate matter (PM) using representative source profiles. The Brake and Tire Wear Study conducted in Los Angeles, California in the winter of 2020 collected 64 PM2.5 and 64 PM10 samples from 32 pairs of downwind-upwind measurements at two near-road locations (I-5 in Anaheim and I-710 in Long Beach). These samples were characterized for inorganic and organic markers and, along with locally-developed brake wear, tire wear, and road dust source profiles, subject to source apportionment using the effective-variance chemical mass balance (EV-CMB) model. Model results highlighted the dominance of resuspended dust in both PM2.5 (23–33%) and PM10 (32–53%). Brake and tire wear contributed more to PM2.5 than tailpipe exhausts (diesel + gasoline) for I-5 (29–30% vs. 19–21%) while they were comparable for I-710 (15–17% vs. 15–19%). For PM10, the brake and tire wear contributions were 2–3 times the exhaust contributions. Different fleet compositions on and near I-5 and I-710 appeared to influence the relative importance of NTP and exhaust sources. The downwind-upwind differences in source contributions were often insignificant, consistent with small and/or nearly equal impacts of adjacent highway traffic emissions on the downwind and upwind sites. The utility of sole markers, such as barium and zinc, to predict brake and tire wear abundances in ambient PM is evaluated. 

An instrumental trifecta now exists for aerosol separation and classification by aerodynamic diameter (Dae), mobility diameter (Dm) and mass (m) utilizing an aerodynamic aerosol classifier (AAC), differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM), respectively. In principle, any combination of two measurements yields the third. These quantities also allow for the derivation of the particle effective density (ρeff) and dynamic shape factor (χ). Measured and/or derived deviations between tandem measurements are dependent upon the configuration but are generally less than 10 %. Notably, non-physical values of χ (< 1) and ρeff (> bulk) were determined by the AAC-APM. Harmonization of the results requires the use of χ in the determination of m and Dm from the AAC-DMA and AAC-APM requiring either a priori assumptions or determination from another method. Further errors can arise from assuming instead of measuring physical conditions – e.g. temperature and pressure affect the gas viscosity, mean free path and the Cunningham slip correction factor therefore impacting Dm, Dae – but are expected to have a smaller impact than χ. Utilizing this triplet of instrumentation in combination allows for quantitative determination of χ and the particle density (ρp). If the bulk density is known or assumed, then the packing density can be determined. The χ and ρp were determined to be 1.10 ± 0.03 and (1.00 ± 0.02) g cm-3, respectively, for a water stabilized black carbon mimic that resembles aged (collapsed) soot in the atmosphere. Assuming ρbulk = 1.8 g cm 3, a packing density of 0.55 ± 0.02 is obtained. 

The emerging field of superconductor (SC) spintronics has attracted intensive attentions recently. Many fantastic spin dependent properties in SC have been discovered, including the observation of large magnetoresistance, long spin lifetimes and the giant spin Hall effect in SC, as well as spin supercurrent in Josephson junctions, etc. Regarding the spin dynamic in SC films, few studies has been reported yet. Here, we report the investigation of the spin dynamics in an s-wave superconducting NbN film via spin pumping from an adjacent insulating ferromagnet GdN layer. A profound coherence peak of the Gilbert damping is observed slightly below the superconducting critical temperature of the NbN layer, which is consistent with recent theoretical studies. Our results further indicate that spin pumping could be a powerful tool for investigating the spin dynamics in 2D crystalline superconductors. 

Abstract. Changes in aerosol chemical mixtures modify cloud condensation nuclei (CCN)activity. Previous studies have developed CCN models and validated changesin external and internal mixing state with ambient field data. Here, wedevelop an experimental method to test and validate the CCN activation ofknown aerosol chemical composition with multicomponent mixtures and varyingmixing states. CCN activation curves consisting of one or more activationpoints are presented. Specifically, simplified two-component systems ofvarying hygroscopicity were generated under internal, external, andtransitional mixing conditions. κ-Köhler theory predictions werecalculated for different organic and inorganic mixtures and compared toexperimentally derived kappa values and respective mixing states. This workemploys novel experimental methods to provide information on the shifts inCCN activation data due to external to internal particle mixing fromcontrolled laboratory sources. Results show that activation curvesconsisting of single and double activation points are consistent withinternal and external mixtures, respectively. In addition, the height of theplateau at the activation points is reflective of the externally mixedconcentration in the mixture. The presence of a plateau indicates that CCNactivation curves consisting of multiple inflection points are externallymixed aerosols of varying water-uptake properties. The plateau disappearswhen mixing is promoted in the flow tube. At the end of the flow tubeexperiment, the aerosols are internally mixed and the CCN activated fractiondata can be fit with a single-sigmoid curve. The technique to mimicexternally to internally mixed aerosol is applied to non-hygroscopiccarbonaceous aerosol with organic and inorganic components. To ourknowledge, this work is the first to show controlled CCN activation of mixednon-hygroscopic soot with hygroscopic material as the aerosol populationtransitions from externally to internally mixed states in laboratoryconditions. Results confirm that CCN activation analysis methods used hereand in ambient data sets are robust and may be used to infer the mixingstate of complex aerosol compositions of unknown origin.