85 research outputs found
Effects of crystal morphology on the hot-carrier dynamics in mixed-cation hybrid lead halide perovskites
Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the per-ovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved spectroscopies in discriminating the transient response due to the different morphology of the crystals embedded in the layers of the same sample can be applied in the general characterization of materials to be used in solar cell devices and large area modules, providing further and valuable information for the optimization and enhancement of stability and efficiency in the power conversion of new perovskite-based devices
Emissions and topographic effects on column CO2 (XCO2) variations, with a focus on the Southern California Megacity
Within the California South Coast Air Basin (SoCAB), XCO2 varies significantly due to atmospheric dynamics and the nonuniform distribution of sources. XCO2 measurements within the basin have seasonal variation compared to the âbackgroundâ due primarily to dynamics, or the origins of air masses coming into the basin. We observe basinâbackground differences that are in close agreement for three observing systems: Total Carbon Column Observing Network (TCCON) 2.3 ± 1.2 ppm, Orbiting Carbon Observatoryâ2 (OCOâ2) 2.4 ± 1.5 ppm, and Greenhouse gases Observing Satellite 2.4 ± 1.6 ppm (errors are 1Ï). We further observe persistent significant differences (âŒ0.9 ppm) in XCO2 between two TCCON sites located only 9 km apart within the SoCAB. We estimate that 20% (±1Ï confidence interval (CI): 0%, 58%) of the variance is explained by a difference in elevation using a full physics and emissions model and 36% (±1Ï CI: 10%, 101%) using a simple, fixed mixed layer model. This effect arises in the presence of a sharp gradient in any species (here we focus on CO2) between the mixed layer (ML) and free troposphere. Column differences between nearby locations arise when the change in elevation is greater than the change in ML height. This affects the fraction of atmosphere that is in the ML above each site. We show that such topographic effects produce significant variation in XCO2 across the SoCAB as well.Plain Language SummaryCities persistently have elevated carbon dioxide (CO2) levels as compared to surrounding regions. Within a city CO2 levels can also vary significantly at different locations for reasons such as more CO2 being emitted in some parts than others. Elevated column CO2 levels in the South Coast Air Basin (SoCAB) are in agreement for three observation systems (two satellite and one groundâbased) systems and vary with regional wind patterns throughout the year. In Pasadena, California, within the SoCAB, a significant fraction (about 25%) of variation in the columnâaveraged CO2 can be explained by differences in surface altitude. This is important to understand so that all variations in column CO2 within an urban region are not mistakenly interpreted as being from CO2 surface fluxes.Key PointsIn the SoCAB, 20â36% of spatial variance in XCO2 is explained by topography on scales âČ10 kmIn Pasadena, XCO2 is enhanced by 2.3 ± 1.2 (1Ï) ppm above background levels, at 1300 (UTC 8) with seasonal variationThe SoCAB XCO2 enhancement is in agreement for 3 different observation sets (TCCON, GOSAT, and OCOâ2)Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137737/1/jgrd53887.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137737/2/jgrd53887_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137737/3/jgrd53887-sup-0001-supinfo.pd
Rapid interferon independent expression of IFITM3 following T cell activation protects cells from influenza virus infection
<div><p>Interferon-induced transmembrane protein 3 (IFITM3) is a potent antiviral protein that enhances cellular resistance to a variety of pathogens, including influenza virus. Classically defined as an interferon-stimulated gene, expression of IFITM3 on cells is rapidly up-regulated in response to type I and II interferon. Here we found that IFITM3 is rapidly up-regulated by T cells following their activation and this occurred independently of type I and II interferon and the interferon regulatory factors 3 and 7. Up-regulation of IFITM3 on effector T cells protected these cells from virus infection and imparted a survival advantage at sites of virus infection. Our results show that IFITM3 expression on effector T cells is crucial for these cells to mediate their effector function and highlights an interferon independent pathway for the induction of IFITM3 which, if targeted, could be an effective approach to harness the activity of IFITM3 for infection prevention.</p></div
Insights into 2-Chloropyrimidine fragmentation through a thermochemical analysis of the ionic fragments
In the present work we have studied the photoinduced ion chemistry of the 2Cl-pyrimidine
molecule in the energy region 9â14 eV. The theoretical gas phase enthalpies of formation of the main
fragments calculated using the G3B3 and G2 ab initio methods are compared to the
experimental values, derived by the measured appearance energy of the fragments. This
approach provides new insights into both the geometric structure of the ionic fragments
and the basic mechanisms governing the molecular fragmentation
Excited state dynamics of Znâsalophen complexes
Znâsalophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UVâVis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (ZnâSal) and the effect of the interaction between ZnâSal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared ZnâSal ethanol solution, a longer relaxation constant, in comparison to ZnâSal, was measured, indicative of the interaction between ZnâSal and ADP. After a few days, the ZnâSalâADP solution displayed the same static and dynamic behavior of a solution containing only the Sal ligand, demonstrating that the coordination of the ADP anion to Zn(II)leads to the demetallation of the Sal ligand. Fluorescence measurements also revealed an enhanced fluorescence at 375 nm following the addition of ADP to the solution, caused by the presence of 2,3-diamino naphthalene that is formed by demetallation and partial decomposition of the Sal ligand. The efficient fluorescence of this species at 375 nm could be selectively detected and used as a probe for the detection of ADP in solution
Insights into 2-Chloropyrimidine fragmentation through a thermochemical analysis of the ionic fragments
In the present work we have studied the photoinduced ion chemistry of the 2Cl-pyrimidine
molecule in the energy region 9â14 eV. The theoretical gas phase enthalpies of formation of the main
fragments calculated using the G3B3 and G2 ab initio methods are compared to the
experimental values, derived by the measured appearance energy of the fragments. This
approach provides new insights into both the geometric structure of the ionic fragments
and the basic mechanisms governing the molecular fragmentation
Time-dependent optical response of three-dimensional Au nanoparticle arrays formed on silica nanowires
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Silver Nanoparticles Functionalized by Fluorescein Isothiocyanate or Rhodamine B Isothiocyanate: Fluorescent and Plasmonic Materials
This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent molecules, in particular with xanthene-based dyes, i.e., fluorescein isothiocyanate (FITC, λmax = 485 nm) and rhodamine B isothiocyanate (RITC, λmax = 555 nm). An in-depth characterization of the particleâdye systems, i.e., AgNPsâRITC and AgNPsâFITC, is presented to evaluate their chemical structure and optical properties due to the interaction between their plasmonic and absorption properties. UVâVis spectroscopy and the dynamic light scattering (DLS) measurements confirmed the nanosize of the AgNPsâRITC and AgNPsâFITC. Synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) was used to study the chemical surface functionalization by structural characterization, confirming/examining the isothiocyanateâmetal interaction. For AgNPsâRITC, in which the plasmonic and fluorescence peak are not superimposed, the transient dynamics of the dye fluorescence were also studied. Transient absorption measurements showed that by exciting the AgNPsâRITC sample at a wavelength corresponding to the AgNP plasmon resonance, it was possible to preferentially excite the RITC dye molecules attached to the surface of the NPs with respect to the free dye molecules in the solution. These results demonstrate how, by combining plasmonics and fluorescence, these AgNPs can be used as promising systems in biosensing and imaging applications
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