Scientific Publications 2010
2010. "The cloud condensation nuclei and ice nuclei effects on tropical anvil characteristics and water vapor of the tropical tropopause layer." Environmental Research Letters 5(4):Article No. 044005. doi:10.1088/1748-9326/5/4/044005 Abstract Cloud anvils from deep convective clouds are of great importance to the radiative energy budget and the aerosol impact on them is the least understood. Few studies examined the effects of both cloud condensation nuclei (CCN) and ice nuclei (IN) on anvil properties and water vapor content (WVC) in the Tropical Tropopause Layer (TTL). Using a 3-dimensional cloud-resolving model with size-resolved cloud microphysics, we focus on the CCN and IN effects on cloud anvil properties and WVC in the TTL. We find that cloud microphysical changes induced by CCN/IN play a very important role in determining cloud anvil area and WVC in the TTL, whether convection is enhanced or suppressed. Also, CCN effects on anvil microphysical properties, anvil size and lifetime are much more evident relative to IN. IN has little effect on convection, but can increase ice number and mass concentrations significantly under humid conditions. CCN in the PBL is found to have greater effects on convective strength and mid-tropospheric CCN has negligible effects on convection and cloud properties. Convective transport may only moisten the main convective outflow region but the cloud anvil size determines the WVC in the TTL domain. This study shows an important role of CCN in the lower-troposphere in modifying convection, the upper-level cloud properties. It also shows the effects of IN and the PBL CCN on the upper-level clouds depends on the humidity, resolving some contradictory results in past studies. 2
2010. "Tropical anvil characteristics and water vapor of the tropical tropopause layer: Impact of heterogeneous and homogeneous freezing parameterizations ." Journal of Geophysical Research. D. (Atmospheres) 115:D12201. doi:10.1029/2009JD012696 Abstract Abstract Two isolated deep convective clouds (DCCs) that developed in clean-humid and polluted-dry air masses, observed during the TWP-ICE and ACTIVE campaigns, are simulated using a 3-dimensional cloud-resolving model with size-resolved aerosol and cloud microphysics. We examine the impacts of different homogeneous and immersion freezing parameterizations on the anvil characteristics and the water vapor content (WVC) in the Tropical Tropopause Layer (TTL) for the two DCCs that developed in contrasting environments. The modeled cloud properties such as liquid/ice water path and precipitation generally agree with the available radar and satellite retrievals and in situ aircraft measurements. We find that anvil size and anvil microphysical properties such as ice number concentration and ice effective radius (rei) are much more sensitive to the homogeneous freezing parameterization (HomFP) under the polluted-dry condition, while the strength of anvil convection is more sensitive to HomFP under the clean-humid condition. Specifically, the cloud anvil with the Koop et al. (2000) (KOOP) relative humidity dependent scheme has up to 2 and 4 times lower ice number than those with other schemes (temperature dependent) for the clean humid and polluted-dry cases, respectively. Consequently, the rei is increased in both cases, with a larger increase in the polluted-dry case. As a result, extinction coefficient of cloud anvils is reduced by over 25% for the polluted-dry case. Anvil size and evolution are also much affected by HomFPs in the polluted-dry case. Higher immersion-freezing rates leads to a stronger convective cloud, with higher precipitation and ice water path under both humid and dry conditions. As a result, homogeneous freezing rates are enhanced by over 20%. Also, the higher immersion-freezing rate results in stronger convection in cloud anvils, much larger anvil size (up to 3 times) and longer lifetime. The moistening effect of deep convection on the WVC in the TTL is very significant with a increase of more than 2 times. Homogeneous freezing parameterizations do not significantly change the WVC in the TTL, but higher immersion freezing rate leads to an increase in TTL WVC by enhancing convection.
2010. "Effect of Produced HCl during the Catalysis on Micro- and Mesoporous MOFs." Crystal Growth & Design 10(9):4118-4122. doi:10.1021/cg100796e Abstract This communication reports the influence of alkylation reaction byproducts, particularly HCl, on MOF-5 with unusual structural transformation to starting precursor and yet maintaining the great catalytic activity in terms of high conversion and selectivity towards the less bulky para-oriented products.
2010. "Synthesis, characterization, and application of metal organic framework nanostructures." Langmuir 26(24):18591–18594. doi:10.1021/la103590t Abstract Nano sized (square and cube) prussian blue analogues were synthesized using PVP, AOT and Chitosan as stabilizers at room temperature
2010. "Hydrogen-bond acidic functionalized carbon nanotubes (CNTs) with covalently-bound hexafluoroisopropanol groups." Carbon 48(7):2085-2088. doi:10.1016/j.carbon.2010.02.019 Abstract Fluorinated hydrogen-bond acidic groups are directly attached to the backbone of single walled carbon nanotubes (SWCNTs) without the introduction of intermediate electron donating surface groups. Hexafluoroalcohol functional groups are exceptionally strong hydrogen bond acids, and are added to the nanotube surface using the aryl diazonium approach to create hydrogen-bond acidic carbon nanotube (CNT) surfaces. These groups can promote strong hydrogen-bonding interactions with matrix materials in composites or with molecular species to be concentrated and sensed. In the latter case, this newly developed material is expected to find useful application in chemical sensors and in CNT-based preconcentrator devices for the detection of pesticides, chemical warfare agents and explosives.
2010. "Effect of Cr2O3 on the O-18 Tracer Incorporation in SOFC Materials." Solid State Ionics 181(13-14):640-645. doi:10.1016/j.ssi.2010.03.007 Abstract To gain insight into the Cr poisoning mechanism at the cathode side of solid oxide fuel cells (SOFCs) with stainless steel interconnects, we conducted an investigation of the impact of Cr2O3 overlayers on oxygen diffusion in various SOFC electrolyte and cathode materials. High density Gd0.10Ce0.90O2 (GDC), Y0.15Zr0.85O2 (YSZ) and La0.6Sr0.4Co0.2Fe0.8O2 (LSCF) sintered pellets were covered with 3 to 30 nm Cr - overlayers that were subsequently oxidized, forming Cr2O3. Standard 18O tracer diffusion experiments at 800°C were performed and TOFSIMS profiling revealed a Cr2O3 thickness-dependent oxygen uptake process. The oxygen ion diffusion coefficients were found to be unaffected by the Cr2O3 overlayers, which is predictable since they are a bulk property. The extracted surface exchange coefficients however varied with Cr2O3 overlayer thickness. Solid state reaction measurements of Cr2O3 with the three materials of interest, and electronic structure considerations concerning the surface exchange, led to the conclusion that the observed oxygen uptake hindrance for LSCF and the slight increase of the surface exchange coefficient for YSZ can be attributed to the electronic properties of Cr2O3. The rate limitation of the oxygen incorporation into the materials is therefore strongly dependent on the surface electronic properties. A critical thickness of Cr2O3 was determined where the transition from decreased cathode-performance to a Cr2O3-property-governed regime occurs.