Gas-Aerosol Model For Mechanism Analysis: Kinetic Prediction Of Gas- And Aqueous-Phase Chemistry Of Atmospheric Aerosols

Atmospheric aerosols are a major contributor to the total energy balance of the Earth's atmosphere. The exact effect of these aerosols on global climate is not well understood, due to poorly-characterized compositional variation that takes place over a given aerosol's lifetime. Organic aerosol (OA) species are of particular interest, forming through a myriad of gas- and aerosol-phase mechanisms and contributing to aerosol light absorbance, cloud formation properties, and overall particle lifetime. As different organic species will affect physical properties in different ways, proper prediction of these compounds forming in the aerosol phase is necessary to estimate the net physical properties of aerosols, and subsequently their effects on overall global climate. Several previous models exist that attempt to predict organic components of aqueous-phase mass in aerosols, with varying degrees of scope of chemistry and range of applicability. Many of such simulations emphasize OA formation via oxidation of gas-phase organic species that results in low-volatility compounds that subsequently partition into aerosols. Other models focus on aqueous-phase processing of semi-volatile and non-volatile water-soluble organic compounds (WSOC's) under cloud water conditions. However, aqueous reactions that occur in atmospheric, deliquesced salt aerosols have recently also been found to be potentially important additional pathway for the creation of additional aerosol-phase organic mass, contributing different products due to the significantly higher inorganic concentrations present under these conditions. It is desirable to incorporate these reactions into analogous predictive simulations, allowing for the chemistry taking place in small, deliquesced salt atmospheric aerosols to be more accurately represented. In this work, we discuss a new photochemical box model known as GAMMA, the Gas-Aerosol Model for Mechanism Analysis. GAMMA couples gas-phase organic chemistry with highly detailed aqueous-phase chemistry, yielding speciated predictions for dozens of secondary organic aqueous aerosol-phase compounds under various atmospheric and laboratory initial conditions. From these studies, we find that isoprene-derived epoxides (IEPOX) and their substitution products are predicted to dominate aqueous-phase organic aerosol mass in conditions with low NOx in the atmosphere, representative of rural environments. The contribution of these epoxide species is expected to be high under acidic conditions, though our findings still estimate significant contribution to aqueous-phase organic mass under higher pH or under cloudwater conditions, when acidity is expected to be lower. Under high-NOx conditions typical of urban environments, glyoxal is seen to form the majority of evolved aqueous organic species, with organic acids comprising the bulk of the difference. We then implement a series of physical property modules, designed to predict changes in aerosol absorbance and surface tension due to bulk concentrations of evolved OA species. Preliminary results from these modules indicate that bulk solution effects of aqueous-phase carbonyl-containing volatile organic compounds (CVOCs) and organic acids are insufficient to significantly affect net aerosol surface tension under any condition tested, implying that observed deviations from pure inorganic aerosol surface tension will arise from surface-aerosol partitioning rather than bulk compositional effects. Light absorption of aqueous aerosols is seen to be driven by dark glyoxal chemistry in deliquesced salt aerosols and organic acids in cloud droplets, though additional information about the absorbance properties of IEPOX and its derivatives is required to accurately predict the net absorbance of aerosols where these species dominate OA mass. The predictions as described by GAMMA are comparable to field observations, and give further credence to the significance of epoxide formation as a source of aqueous-phase organic aerosol mass. These results also suggest the relative importance of specific organic compounds in the aqueous phase of both deliquesced salt aerosols and cloud droplets in the atmosphere, which gives direction to the study of compounds whose impact on aerosol physical properties will matter the most. In turn, new kinetic and physical information can be directly applied into the groundwork laid here, allowing GAMMA to provide a continuously better understanding of the effect of organic material on aqueous aerosols and their implicit effect on the environment

simpleGAMMA – a reduced model of secondary organic aerosol formation in the aqueous aerosol phase (aaSOA)

There is increasing evidence that the uptake and aqueous processing of water-soluble volatile organic compounds (VOCs) by wet aerosols or cloud droplets is an important source of secondary organic aerosol (SOA). We recently developed GAMMA (Gas–Aerosol Model for Mechanism Analysis), a zero-dimensional kinetic model that couples gas-phase and detailed aqueous-phase atmospheric chemistry for speciated prediction of SOA and organosulfate formation in cloudwater or aqueous aerosols. Results from GAMMA simulations of SOA formation in aerosol water (McNeill et al., 2012) indicate that it is dominated by two pathways: isoprene epoxydiol (IEPOX) uptake followed by ring-opening chemistry (under low-NOx conditions) and glyoxal uptake. This suggested that it is possible to model the majority of aqueous aerosol phase SOA mass using a highly simplified reaction scheme. We have therefore developed a reduced version of GAMMA, simpleGAMMA. Close agreement in predicted aaSOA mass is observed between simpleGAMMA and GAMMA under all conditions tested (between pH 1–4 and RH 40–80%) after 12 h of simulation. simpleGAMMA is computationally efficient and suitable for coupling with larger-scale atmospheric chemistry models

Alkoxido, Amido, and Imido Derivatives of Titanium(IV) Tetratolylporphyrin

Treatment of (TTP)TiCl2 (1) [TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion] with excess NaOR (R = Ph, Me, t-Bu) affords the bis(alkoxide) derivatives (TTP)Ti(OR)2 [R = Ph (2), Me (3), t-Bu (4)] in moderate yield. The corresponding amido derivative (TTP)Ti(NPh2)2(5) is prepared in an analogous fashion employing LiNPh2. The disubstituted complexes 2, 3, and 5 react cleanly with (TTP)TiCl2 to afford the ligand exchange products (TTP)Ti(OR)Cl [R = Ph (6), Me (7)] and (TTP)Ti(NPh2)Cl (8), respectively. The monosubstituted complexes 6−8are also obtained by treatment of 1 with 1 equiv of the appropriate NaOR or LiNPh2 reagent. Treatment of 5 with excess phenol produces the bis(phenoxide) derivative 2 and 2 equiv of HNPh2. The imido derivatives (TTP)TiNR [R = t-Bu (9), Ph (10), C6H4-p-Me (11)] are prepared by the treatment of 1 with excess LiNHR. The t-Bu derivative (9) is also obtained by reaction of 1 with excess H2N-t-Bu at elevated temperatures. The phenyl imido complex (10) may be produced by the reaction of 0.5 equiv of PhNNPh with (TTP)Ti(η2-EtC⋮CEt) in refluxing toluene. Finally, (TTP)TiNTMS (12) is obtained by oxidation of (TTP)Ti(η2-EtC⋮CEt) with N3TMS

Layered Micro-Wall Structures from the Gas Phase

The use of3-D LCVD with volumetric rate feedback was investigated in the fabrication ofmicromechanical wall structures. These were constructed by recursive laser scanning and resulted in layered wall composed ofrecursive line deposition. Experiments were designed to uncover the relationship between scan rate, volumetric deposition rate, pressure and laser powerfor pyrolytic graphite from an ethylene precursor. Results point to a conduction dominated heat transfer which greatly limits the volumetric deposition rate at the wall. This also results in a highly unstable deposition process, since volumetric deposition increases by orders ofmagnitude as soon as rod growth is initiated. An unexpected results ofthis work is the ability to grow rods at an angle to the laser axis, with good control ofthe linear growth rate. This is achieved by adaptive laser scanning during rod growth.Mechanical Engineerin

Ventricular assist device implantation in the elderly

BACKGROUND: Dramatic advances in ventricular assist device (VAD) design and patient management have made mechanical circulatory support an attractive therapeutic option for the growing pool of elderly heart failure patients. METHODS: A literature review of all relevant studies was performed. No time or language restrictions were imposed, and references of the selected studies were checked for additional relevant citations. RESULTS: In concordance with the universal trend in mechanical circulatory support, continuous flow devices appear to have particular benefits in the elderly. In addition, the literature suggests that early intervention before the development of cardiogenic shock, important in all patients, is particularly paramount in older patients. CONCLUSIONS: The ongoing refinement of patient selection, surgical technique, and post-operative care will continue to improve surgical outcomes, and absolute age may become a less pivotal criterion for mechanical circulatory support. However, clear guidelines for the use of mechanical circulatory support in the elderly remain undefined

Inorganic salts interact with organic di-acids in sub-micron particles to form material with low hygroscopicity and volatility.

Volatility and hygroscopicity are two key properties of organic aerosol components, and both are strongly related to chemical identity. Here we show that inorganic-organic component interactions typically not considered in atmospheric models may strongly affect aerosol volatility and hygroscopicity. In particular, bi-dentate binding of di-carboxylic acids (DCA) to soluble inorganic ions can lead to very strongly bound metal-organic complexes with largely undetermined hygroscopicity and volatility. These reactions profoundly impact particle hygroscopicity, transforming hygroscopic components into irreversibly non-hygroscopic material. While the hygroscopicities of pure salts, DCA, and DCA salts are known, the hygroscopicity of internal mixtures of hygroscopic salts and DCA, as they are typically found in the atmosphere, has not been fully characterized. We have studied the volatility of pure, dry organic salt particles and the hygroscopicity of internal mixtures of oxalic acid (OxA, the dominant DCA in the atmosphere) and a number of salts, both mono- and di-valent. The formation of very low volatility organic salts was confirmed, with minimal evaporation of oxalate salt particles below 75 C. Dramatic increases in the CCN activation diameter for particles with divalent salts (e.g. CaCl2) and relatively small particle mass fractions of OxA indicate that standard volume additivity rules for hygroscopicity do not apply. Thus small organic compounds with high O : C are capable of forming low volatility and very low hygroscopicity particles. Given current knowledge of the formation mechanisms of OxA and M-Ox salts, surface enrichment of insoluble M-Ox salts is expected. The resulting formation of an insoluble coating of metal-oxalate salts can explain low particle hygroscopicities. The formation of particles with a hard coating could offer an alternative explanation for observations of glass-like particles with very low viscosity

Replication of Known Dental Characteristics in Porcine Skin: Emerging Technologies for the Imaging Specialist

This study demonstrates that it is sometimes possible to replicate patterns of human teeth in pig skin and determine scientifically that a given injury pattern (bite mark) correlates with the dentitions of a very small proportion of a population dataset, e.g., 5 percent or even 1 percent. The authors recommend building on the template of this research with a sufficiently large database of samples that reflects the diverse world population. They also envision the development of a sophisticated imaging software application that enables forensic examiners to insert parameters for measurement, as well as additional methods of applying force to produce bite marks for research. The authors further advise that this project is applied science for injury pattern analysis and is only foundational research that should not be cited in testimony and judicial procedures. It supplements but does not contradict current guidelines of the American Board of Forensic Odontology regarding bite mark analysis and comparisons. A much larger population database must be developed. The project’s methodology is described in detail, accompanied by 11 tables and 41 figures

Cell-cell communication enhances the capacity of cell ensembles to sense shallow gradients during morphogenesis

Collective cell responses to exogenous cues depend on cell-cell interactions. In principle, these can result in enhanced sensitivity to weak and noisy stimuli. However, this has not yet been shown experimentally, and, little is known about how multicellular signal processing modulates single cell sensitivity to extracellular signaling inputs, including those guiding complex changes in the tissue form and function. Here we explored if cell-cell communication can enhance the ability of cell ensembles to sense and respond to weak gradients of chemotactic cues. Using a combination of experiments with mammary epithelial cells and mathematical modeling, we find that multicellular sensing enables detection of and response to shallow Epidermal Growth Factor (EGF) gradients that are undetectable by single cells. However, the advantage of this type of gradient sensing is limited by the noisiness of the signaling relay, necessary to integrate spatially distributed ligand concentration information. We calculate the fundamental sensory limits imposed by this communication noise and combine them with the experimental data to estimate the effective size of multicellular sensory groups involved in gradient sensing. Functional experiments strongly implicated intercellular communication through gap junctions and calcium release from intracellular stores as mediators of collective gradient sensing. The resulting integrative analysis provides a framework for understanding the advantages and limitations of sensory information processing by relays of chemically coupled cells.Comment: paper + supporting information, total 35 pages, 15 figure