Rate constants for the reaction of NO and HO2 with peroxy radicals formed from the reaction of OH, Cl or NO3 with alkenes, dienes and α,β-unsaturated carbonyls

Rate constants for the gas-phase reaction of NO and HO2 radicals with 33 peroxy radicals are presented. The peroxy radicals are derived from the addition of either OH, Cl, or NO3 radicals, followed by addition of O2, to a series of alkenes: tetrachloroethene, ethene, 2,3-dimethyl but-2-ene, butadiene, 2,3,4,5-tetramethyl hexa-2,4-diene, 1,1,2,3,4,4-hexachlorobutadiene, but-1-ene-3-one (methyl vinyl ketone) and 2,3-dimethylpen-2-ene-4-one. The rate constants were predicted using a correlation between the singly occupied molecular orbital (SOMO) energy of the peroxy radical and the logarithm of the rate constant for reaction with NO or HO2. A discussion of the accuracy of the method and the trends in the reactivity of the titled peroxy radicals is given. Peroxy radicals derived from halogenated alkenes have larger values of rate constants for reaction with NO relative to reaction with HO2, indicating that they are more likely to react with NO, rather than HO2, in the atmosphere. The reverse is true for peroxy radicals derived from alkylated alkenes

Stagnation–saddle points and flow patterns in Stokes flow between contra-rotating cylinders

The steady flow is considered of a Newtonian fluid, of viscosity mu, between contra-rotating cylinders with peripheral speeds U-1 and U-2 The two-dimensional velocity field is determined correct to O(H-0/2R)(1/2), where 2H(0) is the minimum separation of the cylinders and R an 'averaged' cylinder radius. For flooded/moderately starved inlets there are two stagnation-saddle points, located symmetrically about the nip, and separated by quasi-unidirectional flow. These stagnation-saddle points are shown to divide the gap in the ratio U-1 : U-2 and arise at \X\ = A where the semi-gap thickness is H(A) and the streamwise pressure gradient is given by dP/dX = mu(Ulf U-2)/H-2(A). Several additional results then follow. (i) The effect of non-dimensional flow rate, lambda: A(2) = 2RH(0)(3 lambda - 1) and so the stagnation-saddle points are absent for lambda 1/3. (ii) The effect of speed ratio, S = U-1/U-2: stagnation-saddle points are located on the boundary of recirculating flow and are coincident with its leading edge only for symmetric flows (S = i). The effect of unequal cylinder speeds is to introduce a displacement that increases to a maximum of O(RH0)(1/2) as S --> 0. Five distinct flow patterns are identified between the nip and the downstream meniscus. Three are asymmetric flows with a transfer jet conveying fluid across the recirculation region and arising due to unequal cylinder speeds, unequal cylinder radii, gravity or a combination of these. Two others exhibit no transfer jet and correspond to symmetric (S = 1) or asymmetric (S not equal 1) flow with two asymmetric effects in balance. Film splitting at the downstream stagnation-saddle point produces uniform films, attached to the cylinders, of thickness H-1 and H-2, where H-1/H-2 = S(S + 3)/3S + 1, provided the flux in the transfer jet is assumed to be negligible. (iii) The effect of capillary number, Ca: as Ca is increased the downstream meniscus advances towards the nip and the stagnation-saddle point either attaches itself to the meniscus or disappears via a saddle-node annihilation according to the flow topology. Theoretical predictions are supported by experimental data and finite element computations

Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers

The results of an experimental study into the oxidative degradation of proxies for atmospheric aerosol are presented. We demonstrate that the laser Raman tweezers method can be used successfully to obtain uptake coeffcients for gaseous oxidants on individual aqueous and organic droplets, whilst the size and composition of the droplets is simultaneously followed. A laser tweezers system was used to trap individual droplets containing an unsaturated organic compound in either an aqueous or organic ( alkane) solvent. The droplet was exposed to gas- phase ozone and the reaction kinetics and products followed using Raman spectroscopy. The reactions of three different organic compounds with ozone were studied: fumarate anions, benzoate anions and alpha pinene. The fumarate and benzoate anions in aqueous solution were used to represent components of humic- like substances, HULIS; a alpha- pinene in an alkane solvent was studied as a proxy for biogenic aerosol. The kinetic analysis shows that for these systems the diffusive transport and mass accommodation of ozone is relatively fast, and that liquid- phase di. ffusion and reaction are the rate determining steps. Uptake coe. ffcients, g, were found to be ( 1.1 +/- 0.7) x 10(-5), ( 1.5 +/- 0.7) x 10 (-5) and ( 3.0 - 7.5) x 10 (-3) for the reactions of ozone with the fumarate, benzoate and a- pinene containing droplets, respectively. Liquid- phase bimolecular rate coe. cients for reactions of dissolved ozone molecules with fumarate, benzoate and a- pinene were also obtained: k(fumarate) = ( 2.7 +/- 2) x 10 (5), k(benzoate) = ( 3.5 +/- 3) x 10 (5) and k(alpha-pinene) = ( 1-3) x 10(7) dm(3) mol (-1) s (- 1). The droplet size was found to remain stable over the course of the oxidation process for the HULIS- proxies and for the oxidation of a- pinene in pentadecane. The study of the alpha- pinene/ ozone system is the first using organic seed particles to show that the hygroscopicity of the particle does not increase dramatically over the course of the oxidation. No products were detected by Raman spectroscopy for the reaction of benzoate ions with ozone. One product peak, consistent with aqueous carbonate anions, was observed when following the oxidation of fumarate ions by ozone. Product peaks observed in the reaction of ozone with alpha- pinene suggest the formation of new species containing carbonyl groups

The surface density of Extremely Red Objects in high-z quasar fields

We report on a study of the surface density of Extremely Red Objects (EROs) in the fields of 13 radio-loud quasars at 1.8 < z < 3.0 covering a total area of 61.7 sqr arcmin. There is a large variation in the ERO surface density from field to field, and as many as 30--40 % of the fields have roughly 4--5 times more EROs than what is expected from a random distribution. The average surface density exceeds the value found in large random-field surveys by a factor of 2--3, a result which is significant at the >3 sigma level. Hence, it appears that the quasar lines of sight are biassed towards regions of high ERO density. This might be caused by clusters or groups of galaxies physically associated with the quasars. However, an equally likely possibility is that the observed ERO excess is part of overdensities in the ERO population along the line of sight to the quasars. In this case, the non-randomness of quasar fields with respect to EROs may be explained in terms of gravitational lensing.Comment: 6 pages, 2 figures, to appear in "Radio galaxies: past, present and future", eds. M. Jarvis et al., Leiden, November 200

Challenges and opportunities in abdominal aortic aneurysm research

AbstractAbdominal Aortic Aneurysms (AAAs) are associated with advanced age, male gender, cigarette smoking, atherosclerosis, hypertension, and genetic predisposition. Basic research studies have led to a better understanding of aneurysm disease over the past two decades. There has also been a growing appreciation that fundamental knowledge regarding the process of aneurysmal degeneration is still somewhat limted. Opportunities in research include: 1) the investigation of potential new mechanism-based pharmacologic interventions; 2) identify the genetic basis for an inherited predisposition; 3) develop and refine noninvasive approaches for the early detection; 4) examine potential novel surgical approaches and design new biomaterials; and 5) initiate and promote awareness programs for diagnosis and treatment of aortic aneurysms. The optimal approach to addressing these issues will require integrative, multidisciplinary research programs that involve basic scientists working in concert with vascular and cardiothoracic surgeons, as well as other clinical specialists with expertise in vascular disease

Geophysical exploration in the Lautertal at the Combat Maneuver Training Center, Hohenfels, Germany

Geophysical exploration was conducted in the Lautertal at the Combat Maneuver Training Center, Hohenfels, Germany, to determine the shallow geological framework of a typical dry valley in this karstic environment. The complementary methods of electromagnetic surveying, vertical electrical soundings, and seismic refraction profiling were successful in determining the depth and configuration of the bedrock surface, the character of the unconsolidated deposits resting on the bedrock surface, and the nature of the bedrock surface. Channels and other depressions in the bedrock surface are aligned with structurally induced fractures in the bedrock. The unconsolidated deposits consist of coarse alluvium and colluvium, which are confined to these channels and other depressions, and fine-grained loam and loess, which cover most of the Lautertal. Wide ranges in the electrical and elastic parameters of the bedrock surface are indicative of carbonate rock that is highly fractured and dissolved at some locations and competent at others. Most local groundwater recharge occurs in the uplands where the Middle Kimmeridge (Delta) Member of the Maim Formation (Jurassic) is widely exposed. These carbonate rocks are known to be susceptible to dissolution along the fractures and joints; thus, they offer meteoric waters ready access to the main shallow aquifers lower in the Malm Formation. These same rocks also form the bedrock surface below many of the dry valleys, but in the Lautertal, the infiltration of meteoric waters into the subsurface is generally impeded by the surficial layer of fine-grained loam and loess, which have low hydraulic conductivity. Further, the rocks of the Middle Kimmeridge Member appear to be closely associated with the localized occurrence of turbidity in such perennial streams as the Lauterach

Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe

Integrated, flexible, and rapid geophysical surveying

Aberdeen Proving Ground (APG), in the state of Maryland (Figure 1), is currently managing a comprehensive Installation Restoration Program involving more than 360 solid-waste managing units contained within 13 study areas. The Edgewood area and two landfills in the Aberdeen area appear on the National Priority List under the Comprehensive Environmental Response, Compensation, and Liability Act. Therefore, APG has entered into an interagency agreement with the US Environmental Protection Agency to address the listed areas. The West Branch of the Canal Creek area (Figure 1), located within the Edgewood area, is one of the areas that requires a Source Definition Study because there is an ongoing release of volatile organic compounds into the creek. A report prepared by EAI Corporation (1989) included a list of 29 potentially contaminated buildings in the Edgewood area. Sixteen of the buildings contain known contaminants, nine buildings contain unknown contaminants, and four of the buildings are potentially clean. The EAI report recommended that a sampling and monitoring program be established to verify contamination levels in and around each building. Thirteen of the potentially contaminated buildings are in the West Branch of the Canal Creek area and are potential sources of volatile organic compounds. Operations have ceased and the buildings have been abandoned, but processing equipment, sumps, drains, ventilation systems, and underground storage tanks remain. These appurtenances may contain liquid, solid, or vapor contaminants of unknown nature

Geophysics: Building E5481 decommissioning, Aberdeen Proving Ground

Building E5481 is one of ten potentially contaminated sites in the Canal Creek and Westwood areas of the Edgewood section of Aberdeen Proving Ground examined by a geophysical team from Argonne National Laboratory in April and May of 1992. Noninvasive geophysical surveys, including magnetics, electrical resistivity, and ground-penetrating radar, were conducted around the perimeter of the building to guide a sampling program prior to decommissioning and dismantling. The building is located on the northern margin of a landfill that was sited in a wetland. The large number of magnetic sources surrounding the building are believed to be contained in construction fill that had been used to raise the grade. The smaller anomalies, for the most part, are not imaged with ground radar or by electrical profiling. A conductive zone trending northwest to southeast across the site is spatially related to an old roadbed. Higher resistivity areas in the northeast and east are probably representive of background values. Three high-amplitude, positive, rectangular magnetic anomalies have unknown sources. The features do not have equivalent electrical signatures, nor are they seen with radar imaging

Duration of breastfeeding and risk of SIDS: an individual participant data meta-analysis

CONTEXT: Sudden infant death syndrome (SIDS) is a leading cause of postneonatal infant mortality. Our previous meta-analyses showed that any breastfeeding is protective against SIDS with exclusive breastfeeding conferring a stronger effect.The duration of breastfeeding required to confer a protective effect is unknown. OBJECTIVE: To assess the associations between breastfeeding duration and SIDS. DATA SOURCES: Individual-level data from 8 case-control studies. STUDY SELECTION: Case-control SIDS studies with breastfeeding data. DATA EXTRACTION: Breastfeeding variables, demographic factors, and other potential confounders were identified. Individual-study and pooled analyses were performed. RESULTS: A total of 2267 SIDS cases and 6837 control infants were included. In multivariable pooled analysis, breastfeeding for &#60;2 months was not protective (adjusted odds ratio [aOR]: 0.91, 95% confidence interval [CI]: 0.68–1.22). Any breastfeeding ≥2 months was protective, with greater protection seen with increased duration (2–4 months: aOR: 0.60, 95% CI: 0.44–0.82; 4–6 months: aOR: 0.40, 95% CI: 0.26–0.63; and &gt;6 months: aOR: 0.36, 95% CI: 0.22–0.61). Although exclusive breastfeeding for &#60;2 months was not protective (aOR: 0.82, 95% CI: 0.59–1.14), longer periods were protective (2–4 months: aOR: 0.61, 95% CI: 0.42–0.87; 4–6 months: aOR: 0.46, 95% CI: 0.29–0.74). LIMITATIONS: The variables collected in each study varied slightly, limiting our ability to include all studies in the analysis and control for all confounders. CONCLUSIONS: Breastfeeding duration of at least 2 months was associated with half the risk of SIDS. Breastfeeding does not need to be exclusive to confer this protection