Topological doping and the stability of stripe phases

We analyze the properties of a general Ginzburg-Landau free energy with competing order parameters, long-range interactions, and global constraints (e.g., a fixed value of a total ``charge'') to address the physics of stripe phases in underdoped high-Tc and related materials. For a local free energy limited to quadratic terms of the gradient expansion, only uniform or phase-separated configurations are thermodynamically stable. ``Stripe'' or other non-uniform phases can be stabilized by long-range forces, but can only have non-topological (in-phase) domain walls where the components of the antiferromagnetic order parameter never change sign, and the periods of charge and spin density waves coincide. The antiphase domain walls observed experimentally require physics on an intermediate lengthscale, and they are absent from a model that involves only long-distance physics. Dense stripe phases can be stable even in the absence of long-range forces, but domain walls always attract at large distances, i.e., there is a ubiquitous tendency to phase separation at small doping. The implications for the phase diagram of underdoped cuprates are discussed.Comment: 18 two-column pages, 2 figures, revtex+eps

The Influence of the Nocturnal Boundary Layer on Secondary Trace Species in the Atmosphere at Dorset, Ontario

The impact of the nocturnal boundary layer (NBL) on the concentrations of O3, H2O2, PAN and CH2O has been studied for two 4-day periods, one in the summer of 1989 and the other in the spring of 1990. Where the presence of the nocturnal layer is clear, O3, PAN and CH2O concentrations decrease rapidly and these species appear to be deposited to the surface. Break-up of the inversion in the morning returns concentrations to levels typical of the previous day. H2O2 is removed much faster than the other species and it is replenished much more slowly. This appears to be due to the H2O2 dissolving in water droplets resulting from the rapid cooling of the air. There is evidence for a morning maximum in PAN, likely due to the combination of high concentrations being brought downwards during the break-up of the NBL followed by thermal decomposition

Relationships between PAN, PPN, O3 and NOx at Urban and Rural sites in Ontario

PAN concentrations were determined during the summer of 1989 and the winter of 1990 at three sites in Ontario representing urban (Toronto), suburban downwind (Stouffville) and rural (Dorset) locations. PAN concentrations were found to reach levels of ≈ 4 ppb in Toronto under conditions of stagnant southerly air flow. Observed PAN concentrations were compared with concurrent measurements of PPN and O3. PPN concentrations were found to be, on average, between 8 and 11% of those of PAN, with slightly higher PPN/PAN ratios found for air masses that were relatively anthropogenic-pollution impacted. For the Dorset site, however, the dependence on air-mass origin was small. The slopes of regressions of ozone vs PAN were found to increase substantially from urban to rural air masses, with typical O3/PAN ratios for a mid-range ozone concentration of 50 ppb being 50, 110 and 330, for Toronto, Stouffville and Dorset, respectively. Analysis of the data for Toronto and Stouffville under varying meteorological conditions indicates significant potential for oxidant production in the absence of transport of pollutants from other sources

The Southern Ontario Oxidant Study (SONTOS): Overview and Case Studies for 1992

The southern Ontario oxidant study (SONTOS) is one of the scientific responses to the problem of ozone exceedences in the Windsor/Quebec City corridor, the strip extending from Windsor in the extreme southwest of Ontario, along the north shores of Lake Erie and Lake Ontario and down the St Lawrence valley. This corridor includes the two major metropolitan areas of Toronto and Montreal and experiences more exceedences of the Canadian ozone guideline per year than any other part of the country. The overall objective of SONTOS is to elucidate the factors which lead to these high levels. The study design is based on intensive measurements made at a site to the NNW of Toronto, with supplementary measurements at other sites and on board an aircraft. This paper, and the seven which follow, describe and interpret the measurements made in the summer of 1992. Although this summer was noteworthy for generally very low ozone concentrations, a number of interesting observations have been made which have a bearing on the oxidant phenomenon in southern Ontario. In particular, this paper describes two specific events. In one, which occurred on 6 August 1992, the intensive measurement site experienced the impact of a polluted air mass, which had apparently travelled to the site from Toronto, by way of Lake Ontario. This case has been contrasted with an event in the last week of August, in which large-scale, organised southwesterly flow led to the conditions which more typically give rise to widespread ozone episodes in the province. Events similar to the 6 August episode occurred on several occasions during the study period, and underline the very important role of the Great Lakes in ozone transport and delivery in southern Ontario

Atmospheric Concentrations and Temporal Variations of C1-C3 Carbonyl Compounds at Two Rural Sites in Central Ontario

Measurements of formaldehyde, acetaldehyde, acetone and propionaldehyde concentrations were made at two rural sites in central Ontario. One site (at Egbert, Ont.) is located ≈60 km northwest of Toronto, while the other site (at Dorset, Ont.) is ≈150 km northeast of the Egbert site. Measurements were made using a modified version of a derivatization technique in which sample air is pumped through Teflon tubes packed with silica gel that is coated with 2,4-dinitrophenylhydrazine (DNPH). The product hydrazones were separated and quantified using HPLC. Quantitative determinations of formaldehyde, acetaldehyde and acetone were made for 49 and 47 samples at the Dorset and Egbert sites, respectively, between 25 July and 30 August 1988. The average concentrations determined at the Dorset site for formaldehyde, acetaldehyde, and acetone were 1.6, 0.46 and 1.8 ppb, respectively, and for the Egbert site the corresponding averages were 1.8, 0.57 and 1.6 ppb. A set of 10 samples from the Egbert site were analysed for propionaldehyde yielding an average concentration of 0.03 ppb. The formaldehyde measurements were compared with measurements made at the same time using Tunable Diode Laser Absorption Spectroscopy. The observed concentrations reported here are compared with previously reported measurements of these species and interpreted in terms of atmospheric variables (e.g. meteorology, concentrations of precursor hydrocarbons) influencing their concentrations