Ozone production in the upper troposphere and the influence of aircraft during SONEX: Approach of NO(x)-saturated conditions

During October/November 1997, simultaneous observations of NO, HO2 and other species were obtained as part of the SONEX campaign in the upper troposphere. We use these observations, over the North Atlantic (40-60°N), to derive ozone production rates, P(O3), and to examine the relationship between P(O3) and the concentrations of NO(x) (= NO + NO2) and HO(x) (= OH + peroxy) radicals. A positive correlation is found between P(O3) and NO(x) over the entire data set, which reflects the association of elevated HO(x) with elevated NO(x) injected by deep convection and lightning. By filtering out this association we find that for NO(x)>70 pptv, P(O3) is nearly independent of NO(x), showing the approach of NO(x)-saturated conditions. Predicted doubling of aircraft emissions in the future will result in less than doubling of the aircraft contribution to ozone over the North Atlantic in the fall. Greater sensitivity to aircraft emissions would be expected in the summer

Photochemistry of HOx in the upper troposphere at northern midlatitudes

The factors controlling the concentrations of HOx radicals (= OH + peroxy) in the upper troposphere (8-12 km) are examined using concurrent aircraft observations of OH, HO2, H2O2, CH3OOH, and CH2O made during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) at northern midlatitudes in the fall. These observations, complemented by concurrent measurements of O3, H2O, NO, peroxyacetyl nitrate (PAN), HNO3, CH4, CO, acetone, hydrocarbons, actinic fluxes, and aerosols, allow a highly constrained mass balance analysis of HOx and of the larger chemical family HOy (= HOx + 2 H2O2 + 2 CH3OOH + HNO2 + HNO4). Observations of OH and HO2 are successfully simulated to within 40% by a diel steady state model constrained with observed H2O2 and CH3OOH. The model captures 85% of the observed HOx variance, which is driven mainly by the concentrations of NOx (= NO + NO2) and by the strength of the HOx primary sources. Exceptions to the good agreement between modeled and observed HOx are at sunrise and sunset, where the model is too low by factors of 2-5, and inside cirrus clouds, where the model is too high by factors of 1.2-2. Heterogeneous conversion of NO2 to HONO on aerosols (γNO2=10-3) during the night followed by photolysis of HONO could explain part of the discrepancy at sunrise. Heterogeneous loss of HO2 on ice crystals (γice_HO2=0.025) could explain the discrepancy in cirrus. Primary sources of HOx from O(1D)+H2O and acetone photolysis were of comparable magnitude during SONEX. The dominant sinks of HOy were OH+HO2 (NOx<50 parts per trillion by volume (pptv)) and OH+HNO4 (NOx>50 pptv). Observed H2O2 concentrations are reproduced by model calculations to within 50% if one allows in the model for heterogeneous conversion of HO2 to H2O2 on aerosols (γHO2=0.2). Observed CH3OOH concentrations are underestimated by a factor of 2 on average. Observed CH2O concentrations were usually below the 50 pptv detection limit, consistent with model results; however, frequent occurrences of high values in the observations (up to 350 pptv) are not captured by the model. These high values are correlated with high CH3OH and with cirrus clouds. Heterogeneous oxidation of CH3OH to CH2O on aerosols or ice crystals might provide an explanation (γice_CH3OH∼0.01 would be needed). Copyright 2000 by the American Geophysical Union

OH and HO2 chemistry in the North Atlantic free troposphere

Interactions between atmospheric hydrogen oxides and aircraft nitrogen oxides determine the impact of aircraft exhaust on atmospheric chemistry. To study these interactions, the Subsonic Assessment: Ozone and Nitrogen Oxide Experiment (SONEX) assembled the most complete measurement complement to date for studying HO(x) (OH and HO2) chemistry in the free troposphere. Observed and modeled HO(x) agree on average to within experimental uncertainties (±40%). However, significant discrepancies occur as a function of NO and at solar zenith angles >70°. Some discrepancies appear to be removed by model adjustments to HO(x)-NO(x) chemistry, particularly by reducing HO2NO2 (PNA) and by including heterogeneous reactions on aerosols and cirrus clouds

Looking back at superfluid helium

A few years after the discovery of Bose Einstein condensation in several gases, it is interesting to look back at some properties of superfluid helium. After a short historical review, I comment shortly on boiling and evaporation, then on the role of rotons and vortices in the existence of a critical velocity in superfluid helium. I finally discuss the existence of a condensate in a liquid with strong interactions, and the pressure variation of its superfluid transition temperature.Comment: Conference "Bose Einstein Condensation", Institut henri Poincare, Paris, 29 march 200

Use of approximations of Hamilton-Jacobi-Bellman inequality for solving periodic optimization problems

We show that necessary and sufficient conditions of optimality in periodic optimization problems can be stated in terms of a solution of the corresponding HJB inequality, the latter being equivalent to a max-min type variational problem considered on the space of continuously differentiable functions. We approximate the latter with a maximin problem on a finite dimensional subspace of the space of continuously differentiable functions and show that a solution of this problem (existing under natural controllability conditions) can be used for construction of near optimal controls. We illustrate the construction with a numerical example.Comment: 29 pages, 2 figure

Spontaneous creation of Kibble-Zurek solitons in a Bose-Einstein condensate

When a system crosses a second-order phase transition on a finite timescale, spontaneous symmetry breaking can cause the development of domains with independent order parameters, which then grow and approach each other creating boundary defects. This is known as Kibble-Zurek mechanism. Originally introduced in cosmology, it applies both to classical and quantum phase transitions, in a wide variety of physical systems. Here we report on the spontaneous creation of solitons in Bose-Einstein condensates via the Kibble-Zurek mechanism. We measure the power-law dependence of defects number with the quench time, and provide a check of the Kibble-Zurek scaling with the sonic horizon. These results provide a promising test bed for the determination of critical exponents in Bose-Einstein condensates.Comment: 7 pages, 4 figure

Revisiting the anatomy of the left ventricle in the light of knowledge of its development

\ua9 2024 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.Despite centuries of investigation, certain aspects of left ventricular anatomy remain either controversial or uncertain. We make no claims to have resolved these issues, but our review, based on our current knowledge of development, hopefully identifies the issues requiring further investigation. When first formed, the left ventricle had only inlet and apical components. With the expansion of the atrioventricular canal, the developing ventricle cedes part of its inlet to the right ventricle whilst retaining the larger parts of the cushions dividing the atrioventricular canal. Further remodelling of the interventricular communication provides the ventricle with its outlet, with the aortic root being transferred to the left ventricle along with the newly formed myocardium supporting its leaflets. The definitive ventricle possesses inlet, apical and outlet parts. The inlet component is guarded by the mitral valve, with its leaflets, in the normal heart, supported by papillary muscles located infero-septally and supero-laterally. There is but a solitary zone of apposition between the leaflets, which we suggest are best described as being aortic and mural. The trabeculated component extends beyond the inlet to the apex and is confluent with the outlet part, which supports the aortic root. The leaflets of the aortic valve are supported in semilunar fashion within the root, with the ventricular cavity extending to the sinutubular junction. The myocardial-arterial junction, however, stops well short of the sinutubular junction, with myocardium found only at the bases of the sinuses, giving rise to the coronary arteries. We argue that the relationships between the various components should now be described using attitudinally appropriate terms rather than describing them as if the heart is removed from the body and positioned on its apex