Lakes

Lakes have always held an aesthetic fascination for people; they figure prominently in both art and literature and have even been endowed with spiritual qualities. For example, the nineteenth century American writer Henry D. Thoreau (1854) considered a lake to be 'the landscape's most beautiful and expressive feature. It is the earth's eye; looking into which the beholder measures the depth of his own nature'. More prosaically, lakes are also of considerable geomorphological interest as dynamic landfonns originating in varied and often complex ways

What can 14 CO measurements tell us about OH?

The possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis

Resolving the black hole information paradox

The recent progress in string theory strongly suggests that formation and evaporation of black holes is a unitary process. This fact makes it imperative that we find a flaw in the semiclassical reasoning that implies a loss of information. We propose a new criterion that limits the domain of classical gravity: the hypersurfaces of a foliation cannot be stretched too much. This conjectured criterion may have important consequences for the early Universe.Comment: harvmac, 11 pages (1 figure) (This essay received an ``honorable mention'' in the Annual Essay Competition of the Gravity Research Foundation for the year 2000.

Stratigraphy and development of c. 17 000 year old Lake Maratoto, North Island, New Zealand, with some inferences about postglacial climatic change

The stratigraphy and geomorphology of Lake Maratoto and its surrounds were investigated as part of a programme of paleolimnological studies based on sediment cores from lakes in northern North Island. Changes in the lake and catchment were inferred from variations in sediment character, the correlation and timing being determined from distinctive tephra layers in the sediments and by radiocarbon dating. Nineteen new C-l4 dates, on gyttja or peat, are reported (old T½, years B.P,): 11 on tephras (Mamaku Ash 6830 ±90. Wk227; Rotoma Ash 8370 ± 90, Wk522; 8350 ± 100, Wk523; Opepe Tephra 9370 ± 210, Wk230; Mangamate Tephra 9700 ± 140, Wk23l; 10000 ± 120, Wk232; Waiohau Ash 12 200 ± 230, Wk233; 12500 ± 190, Wk234; 12450 ± 200, Wk5l5; 12300 ± 190,Wk516; RotoruaAsh 13450 ± 120, Wk511); 5 on the deposition of Hinuera Formation alluvium (16 300 ± 250, Wk239; 16 900 ± 470, Wk240; 17050 ± 200, Wk358; 16200 +360 -340, Wk509; 15 850 ± 130, Wk510); and 3 on basal peat of the Rukuhia bog (10 250 ± 90, Wk114; 15200 ± 130, Wk534; 10600 ± 90, Wk553). Lake Maratoto originated c. 17 000 years ago when a small valley was dammed by volcanogenic alluvium (Hinuera Formation). From c. 17 000 to c. 14 000 years ago the lake was about 2 m deep with clear water. Marginal peat first developed at c. 15000 years ago, reducing the area of the lake by about one-half by c. 13 000 years ago. Lake area then expanded, possibly because of marginal erosion and/or oxidation of the peat, to its maximum size at the present day. The adjacent Rukuhia peat bog grew rapidly from c. 11 000 years ago and is now 8 m thick immediately to the west of the lake. As a result of this growth, the lake became dystrophic and deepened (3.5 m at c. 7000 years ago, 6.4 m at c. 2000 years ago, and 7. 1 m today). The developmental history suggests that net precipitation increased at c. 15 000 years ago, increased further at c. 11 000 years ago, remaining high to c. 7000 years ago at least, but with a decline at or before c. 2000 years ago. There may have been a distinctly wetter or windier period from c. 10 000 to 9000 years ago. This interpretation is consistent with other reconstructions of postglacial climate in the Southern Hemisphere

Appendix B: Some morphometric parameters of named lakes with areas [greater than or equal to] 1.0 km2, and some smaller lakes, in New Zealand

Gaps indicate uncertainty or that accurate data are unavailable. Note that lakes with fluctuating levels e.g., those used for hydro-electric purposes, or near coasts have varying parameters. Table based mainly on Irwin (1975) with some data from Cunningham et al. (1953), Irwin (1972), Jolly & Brown (1975), Irwin & Pickrill (1983), Howard-Williams & Vincent 1984, Boswell et al. (1985), Livingstone et al. (1986), N.Z.O.I. Lake Chart series, N.Z. Topographical Map Series NZMS1 (1:63 360) and NZMS26O (1:50 000), and other sources

Introduction to the new usability

This paper introduces the motivation for and concept of the "new usability" and positions it against existing approaches to usability. It is argued that the contexts of emerging products and systems mean that traditional approaches to usability engineering and evaluation are likely to prove inappropriate to the needs of "digital consumers." The paper briefly reviews the contributions to this special issue in terms of their relation to the idea of the "new usability" and their individual approaches to dealing with contemporary usability issues. This helps provide a background to the "new usability" research agenda, and the paper ends by posing what are argued to be the central challenges facing the area and those which lie at the heart of the proposed research agenda

Oscillatory combustion in rockets Third semiannual report, Jun. 1 - Nov. 30, 1965

Rocket engine oscillatory combustion studie