Modeling of secondary organic aerosol yields from laboratory chamber data

Laboratory chamber data serve as the basis for constraining models of secondary organic aerosol (SOA) formation. Current models fall into three categories: empirical two-product (Odum), product-specific, and volatility basis set. The product-specific and volatility basis set models are applied here to represent laboratory data on the ozonolysis of α-pinene under dry, dark, and low-NOx conditions in the presence of ammonium sulfate seed aerosol. Using five major identified products, the model is fit to the chamber data. From the optimal fitting, SOA oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios are modeled. The discrepancy between measured H/C ratios and those based on the oxidation products used in the model fitting suggests the potential importance of particle-phase reactions. Data fitting is also carried out using the volatility basis set, wherein oxidation products are parsed into volatility bins. The product-specific model is most likely hindered by lack of explicit inclusion of particle-phase accretion compounds. While prospects for identification of the majority of SOA products for major volatile organic compounds (VOCs) classes remain promising, for the near future empirical product or volatility basis set models remain the approaches of choice

Energetic Components of Cooperative Protein Folding

A new lattice protein model with a four-helix bundle ground state is analyzed by a parameter-space Monte Carlo histogram technique to evaluate the effects of an extensive variety of model potentials on folding thermodynamics. Cooperative helical formation and contact energies based on a 5-letter alphabet are found to be insufficient to satisfy calorimetric and other experimental criteria for two-state folding. Such proteinlike behaviors are predicted, however, by models with polypeptide-like local conformational restrictions and environment-dependent hydrogen bonding-like interactions.Comment: 11 pages, 4 postscripts figures, Phys. Rev. Lett. (in press

Supercritical multicomponent solvent coal extraction

The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal

Role of aldehyde chemistry and NO_x concentrations in secondary organic aerosol formation

Aldehydes are an important class of products from atmospheric oxidation of hydrocarbons. Isoprene (2-methyl-1,3-butadiene), the most abundantly emitted atmospheric non-methane hydrocarbon, produces a significant amount of secondary organic aerosol (SOA) via methacrolein (a C_4-unsaturated aldehyde) under urban high-NO_x conditions. Previously, we have identified peroxy methacryloyl nitrate (MPAN) as the important intermediate to isoprene and methacrolein SOA in this NO_x regime. Here we show that as a result of this chemistry, NO_2 enhances SOA formation from methacrolein and two other α, β-unsaturated aldehydes, specifically acrolein and crotonaldehyde, a NO_x effect on SOA formation previously unrecognized. Oligoesters of dihydroxycarboxylic acids and hydroxynitrooxycarboxylic acids are observed to increase with increasing NO_2/NO ratio, and previous characterizations are confirmed by both online and offline high-resolution mass spectrometry techniques. Molecular structure also determines the amount of SOA formation, as the SOA mass yields are the highest for aldehydes that are α, β-unsaturated and contain an additional methyl group on the α-carbon. Aerosol formation from 2-methyl-3-buten-2-ol (MBO232) is insignificant, even under high-NO_2 conditions, as PAN (peroxy acyl nitrate, RC(O)OONO_2) formation is structurally unfavorable. At atmospherically relevant NO_2/NO ratios (3–8), the SOA yields from isoprene high-NO_x photooxidation are 3 times greater than previously measured at lower NO_2/NO ratios. At sufficiently high NO_2 concentrations, in systems of α, β-unsaturated aldehydes, SOA formation from subsequent oxidation of products from acyl peroxyl radicals+NO_2 can exceed that from RO_2+HO_2 reactions under the same inorganic seed conditions, making RO_2+NO_2 an important channel for SOA formation

Non-radial oscillations of anisotropic neutron stars in the Cowling approximation

One of the most common assumptions in the study of neutron star models and their oscillations is that the pressure is isotopic, however there are arguments that this may not be correct. Thus in the present paper we make a first step towards studying the nonradial oscillations of neutron stars with an anisotropic pressure. We adopt the so-called Cowling approximation where the spacetime metric is kept fixed and the oscillation spectrum for the first few fluid modes is obtained. The effect of the anisotropy on the frequencies is apparent, although with the present results it might be hard to distinguish it from the changes in the frequencies caused by different equations of state.Comment: 17 pages, 8 figures; title changed, comments adde

Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs)

Current atmospheric models do not include secondary organic aerosol (SOA) production from gas-phase reactions of polycyclic aromatic hydrocarbons (PAHs). Recent studies have shown that primary emissions undergo oxidation in the gas phase, leading to SOA formation. This opens the possibility that low-volatility gas-phase precursors are a potentially large source of SOA. In this work, SOA formation from gas-phase photooxidation of naphthalene, 1-methylnaphthalene (1-MN), 2-methylnaphthalene (2- MN), and 1,2-dimethylnaphthalene (1,2-DMN) is studied in the Caltech dual 28-m^3 chambers. Under high-NO_x conditions and aerosol mass loadings between 10 and 40μgm^(−3), the SOA yields (mass of SOA per mass of hydrocarbon reacted) ranged from 0.19 to 0.30 for naphthalene, 0.19 to 0.39 for 1-MN, 0.26 to 0.45 for 2-MN, and constant at 0.31 for 1,2-DMN. Under low-NO_x conditions, the SOA yields were measured to be 0.73, 0.68, and 0.58, for naphthalene, 1- MN, and 2-MN, respectively. The SOA was observed to be semivolatile under high-NO_x conditions and essentially nonvolatile under low-NO_x conditions, owing to the higher fraction of ring-retaining products formed under low-NO_x conditions. When applying these measured yields to estimate SOA formation from primary emissions of diesel engines and wood burning, PAHs are estimated to yield 3–5 times more SOA than light aromatic compounds over photooxidation timescales of less than 12 h. PAHs can also account for up to 54% of the total SOA from oxidation of diesel emissions, representing a potentially large source of urban SOA

Energy landscapes, supergraphs, and "folding funnels" in spin systems

Dynamical connectivity graphs, which describe dynamical transition rates between local energy minima of a system, can be displayed against the background of a disconnectivity graph which represents the energy landscape of the system. The resulting supergraph describes both dynamics and statics of the system in a unified coarse-grained sense. We give examples of the supergraphs for several two dimensional spin and protein-related systems. We demonstrate that disordered ferromagnets have supergraphs akin to those of model proteins whereas spin glasses behave like random sequences of aminoacids which fold badly.Comment: REVTeX, 9 pages, two-column, 13 EPS figures include

Constraining New Forces in the Casimir Regime Using the Isoelectronic Technique

We report the first isoelectronic differential force measurements between a Au-coated probe and two Au-coated films, made out of Au and Ge. These measurements, performed at submicron separations using soft microelectromechanical torsional oscillators, eliminate the need for a detailed understanding of the probe-film Casimir interaction. The observed differential signal is directly converted into limits on the parameters $\alpha$ and $\lambda$ which characterize Yukawa-like deviations from Newtonian gravity. We find \alpha \lsim 10^{12} for $\lambda \sim 200$ nm, an improvement of $\sim$ 10 over previous limits.Comment: 10 pages, 4 figure

A Model Behind the Standard Model

In spite of its many successes, the Standard Model makes many empirical assumptions in the Higgs and fermion sectors for which a deeper theoretical basis is sought. Starting from the usual gauge symmetry $u(1) \times su(2) \times su(3)$ plus the 3 assumptions: (A) scalar fields as vielbeins in internal symmetry space \cite{framevec}, (B) the ``confinement picture'' of symmetry breaking \cite{tHooft,Banovici}, (C) generations as ``dual'' to colour \cite{genmixdsm}, we are led to a scheme which offers: (I) a geometrical significance to scalar fields, (II) a theoretical criterion on what scalar fields are to be introduced, (III) a partial explanation of why $su(2)$ appears broken while $su(3)$ confines, (IV) baryon-lepton number (B - L) conservation, (V) the standard electroweak structure, (VI) a 3-valued generation index for leptons and quarks, and (VII) a dynamical system with all the essential features of an earlier phenomenological model \cite{genmixdsm} which gave a good description of the known mass and mixing patterns of quarks and leptons including neutrino oscillations. There are other implications the consistency of which with experiment, however, has not yet been systematically explored. A possible outcome is a whole new branch of particle spectroscopy from $su(2)$ confinement, potentially as rich in details as that of hadrons from colour confinement, which will be accessible to experiment at high energy.Comment: 66 pages, added new material on phenomenology, and some new reference