Polynomial-time perfect matchings in dense hypergraphs

Let $H$ be a $k$-graph on $n$ vertices, with minimum codegree at least $n/k + cn$ for some fixed $c > 0$. In this paper we construct a polynomial-time algorithm which finds either a perfect matching in $H$ or a certificate that none exists. This essentially solves a problem of Karpi\'nski, Ruci\'nski and Szyma\'nska; Szyma\'nska previously showed that this problem is NP-hard for a minimum codegree of $n/k - cn$. Our algorithm relies on a theoretical result of independent interest, in which we characterise any such hypergraph with no perfect matching using a family of lattice-based constructions.Comment: 64 pages. Update includes minor revisions. To appear in Advances in Mathematic

A survey for cool white dwarfs and the age of the galactic disc

The use of white dwarf cooling times is now established as one of the most important methods of determining the age of our Galaxy. Estimates of the age of the Galactic Disk from the study of cool white dwarf samples have remained at approximately 9 Gyr since the technique was first applied over a decade ago, in contrast to globular clusters ages and cosmological timescales, which have been the subject of much revision and debate. Much of the white dwarf work has of necessity relied on all -sky photographic proper motion surveys to provide sufficiently large numbers of white dwarfs in conjunction with quantifiable survey limits, unfortunately resulting in demonstrably incomplete samples.This thesis describes a survey specifically undertaken to obtain a sample of cool white dwarfs directly from original Schmidt plate material. Concerns regarding the subjectivity of `eye -blinked' proper motion measures are avoided by using digitised data obtained using the COSMOS and SuperCOSMOS microdensitometers. The observational material is restricted to a single 6° field in which an exceptionally large database of over 300 Schmidt plates exists. As a brief aside, the issue of stacking digitised plate data is examined. In particular, recommendations for the correct weighting algorithm and bad pixel rejection algorithm to adopt are made, following detailed experimentation with a variety of techniques. The plate stacking technique is used for the white dwarf survey material to extend the photometric survey limits, while the optimum proper motion limit to adopt is investigated in detail, with the principal concern being elimination of contaminants while retaining as many genuine proper motion objects as possible. Application of the reduced proper motion population discrimination technique to the resultant proper motion catalogue results in a final sample comprising 56 white dwarf candidates. Follow up spectroscopic observations show the survey has been successful in identifying cool white dwarfs, gives no indication of contamination in the white dwarf sample by other stellar types, and also provides two further cool white dwarfs to include in the sample which were marginally excluded by the reduced proper motion survey criteria.Comparison of photographic colours with model predictions allow effective temperatures and bolometric luminosities to be estimated for the sample members. The luminosity function constructed from the sample members is in good agreement with previous work, although the slightly higher space density found for the coolest white dwarfs leads to a modest increase in the age estimate for the Galactic Disc when the luminosity function is compared to theoretical models. The Disc age is found to be 10±1/3 Gyr.Recurring themes in this work are the related questions of sample completeness and sample contamination. These have been addressed in several ways, notably via number counts, the V /Vmax completeness test and sample distributions on the reduced proper motion diagram. The results of these analyses may be summarised by stating that the sample is consistent with being drawn from a complete sample, shows no statistical evidence of incompleteness, and is unlikely to be contaminated by non -degenerates. Probably the most serious source of error here is the omission of very cool white dwarfs due to the conservative reduced proper motion survey criteria adopted. This concern, along with other considerations regarding the atmospheric constituents of the sample members, imply that a 9 Gyr Disc age may be regarded as a quite robust lower limit from this work

Mind almost divine

© Cambridge University Press 2003. Reprinted with permission

Dataset associated with "A First-Order Approximation of Floodplain Soil Organic Carbon Stocks in a River Network: the South Platte River, Colorado, USA"

This data includes floodplain extent, raw floodplain data (elevation, stream order association), floodplain widths, and lake and reservoir information for the South Platte river basin.We use the hydrogeomorphic floodplain tool GFPLAIN to delineate the extent of 100-year floodplains in the South Platte River watershed of Colorado, USA. We distinguish elevation bands for the steppe, montane, subalpine, and alpine zones. We also differentiate bead (floodplain width/channel width > 5) and string (floodplain width/channel width < 5) reaches within the montane and subalpine zones. Drawing on prior, field-based measurements of organic carbon stock in downed, dead wood and soil in these floodplain types, we estimate total floodplain organic carbon storage, which includes organic carbon storage in lake and reservoir sediments in the watershed. Soil constitutes the greatest reservoir of floodplain carbon. The total estimated area of floodplain is 2916 km2, which is 4.3% of the total watershed area of the South Platte River. Our preferred estimate is 42.7 Tg C storage (likely range of 39.1-42.7 Tg). This equates to 11.1% of a previously estimated overall carbon stock (above and belowground biomass and soil organic carbon) in the entire watershed of 384 Tg C. Floodplains are thus disproportionately important, relative to their surface area, in storing organic carbon in this semiarid watershed. Field measurements of floodplain soil organic carbon storage from across the globe indicate that this finding is not unique to this watershed and this has implications for prioritizing floodplain management and restoration as a means of enhancing carbon sequestration

Incorporating Environmental Impacts in the Measurement of Agricultural Productivity Growth

Agricultural production is known to have environmental impacts, both adverse and beneficial, and it is desirable to incorporate at least some of these impacts in an environmentally sensitive productivity index. In this paper, we construct indicators of water contamination from the use of agricultural chemicals. These environmental indicators are merged with data on marketed outputs and purchased inputs to form a state-by-year panel of relative levels of outputs and inputs, including environmental impacts. We do not have prices for these undesirable by products, since they are not marketed. Consequently, we calculate a series of Malmquist productivity indexes, which do not require price information. Our benchmark scenario is a conventional Malmquist productivity index based on marketed outputs and purchased inputs only. Our comparison scenarios consist of environmentally sensitive Malmquist productivity indexes that include indicators of risk to human health and to aquatic life from chronic exposure to pesticides. In addition, we derive a set of virtual prices of the undesirable by-products that can be used to calculate an environmentally sensitive Fisher index of productivity change.environmental impacts, productivity growth, Environmental Economics and Policy,

Modeling of Instrument Landing System (ILS) localizer signal on runway 25L at Los Angeles International Airport

A joint NASA/FAA flight test has been made to record instrument landing system (ILS) localizer receiver signals for use in mathematically modeling the ILS localizer for future simulation studies and airplane flight tracking tasks. The flight test was conducted on a portion of the ILS localizer installed on runway 25L at the Los Angeles International Airport. The tests covered the range from 10 to 32 n.mi. from the localizer antenna. Precision radar tracking information was compared with the recorded localizer deviation data. Data analysis showed that the ILS signal centerline was offset to the left of runway centerline by 0.071 degrees and that no significant bends existed on the localizer beam. Suggested simulation models for the ILS localizer are formed from a statistical analysis

Effective treatment with a tetrandrine/chloroquine combination for chloroquine-resistant falciparum malaria in Aotus monkeys

Background In vitro evidence indicates that tetrandrine (TT) can potentiate the action of chloroquine 40-fold against choloquine-resistant Plasmodium falciparum. The key question emanating from that study is “would tetrandine and chloroquine be highly effective in a live Aotus monkey model with chloroquine-resistant parasites”. This study was designed to closely mimic the pharmacological/anti-malarial activity in man. Methods The Vietnam Smith/RE strain of P. falciparum, which is chloroquine-resistant was used in this study. Previous experimental procedures were followed. Panamanian owl monkeys (Aotus) were inoculated with 5×106 erythrocytes parasitized with the CQ-resistant strain of P. falciparum. Oral drug treatment was with CQ (20 mg/kg) and/or tetrandrine at 15 mg/Kg, 30 mg/Kg or 60 mg/Kg or 25 mg/Kg depending on experimental conditions. Results and Discussion Parasitaemia was cleared rapidly with CQ and TT while CQ treatment alone was ineffective. Recrudescence of malaria occurred after seven days post-infection. However, four animals were treated orally with TT and CQ parasites were cleared. It is likely that monkeys were cured via a combination of both drug and host immune responses. A single Aotus monkey infected with P. falciparum and untreated with drugs, died. No side effects were observed with these drug treatments. Conclusions This combination of chloroquine and tetrandrine forms the basis of a new attack on chloroquine-resistant malaria - one based upon inhibition of the basis of chloroquine resistance, the multiple drug resistance pump. Previous studies demonstrated that the parasite MDR pump was found on parasite membranes using 3H azidopine photoaffinity labelling. Since MDR-based choloroquine resistance is induced by chloroquine, the basis of the action of tetrandrine is the following: 1) tetrandrine inhibits the MDR pump by stimulating MDR ATPase which limits the energy of the pump by depletion of parasite ATP, 2) tetrandrine blocks the genetic factor which controls the induction of the pump. Therefore, it appears that the parasite cannot outsmart these mechanisms and produce a new mode of resistance. Only time will tell if this is correct

Calculational model for condensation of water vapor during an underground nuclear detonation

An empirally derived mathematical model was developed to calculate the pressure and temperature history during condensation of water vapor in an underground-nuclear-explosion cavity. The condensation process is non-isothermal. Use has been made of the Clapeyron-Clausius equation as a basis for development of the model. Analytic fits to the vapor pressure and the latent heat of vaporization for saturated-water vapor, together with an estimated value for the heat-transfer coefficient, have been used to describe the phenomena. The calculated pressure-history during condensation has been determined to be exponential, with a time constant somewhat less than that observed during the cooling of the superheated steam from the explosion. The behavior of the calculated condensation-pressure compares well with the observed-pressure record (until just prior to cavity collapse) for a particular nuclear-detonation event for which data is available. (auth

Constraining Large Scale Structure Theories with the Cosmic Background Radiation

We review the relevant 10+ parameters associated with inflation and matter content; the relation between LSS and primary and secondary CMB anisotropy probes; COBE constraints on energy injection; current anisotropy band-powers which strongly support the gravitational instability theory and suggest the universe could not have reionized too early. We use Bayesian analysis methods to determine what current CMB and CMB+LSS data imply for inflation-based Gaussian fluctuations in tilted $\Lambda$CDM, $\Lambda$hCDM and oCDM model sequences with age 11-15 Gyr, consisting of mixtures of baryons, cold (and possibly hot) dark matter, vacuum energy, and curvature energy in open cosmologies. For example, we find the slope of the initial spectrum is within about 5% of the (preferred) scale invariant form when just the CMB data is used, and for $\Lambda$CDM when LSS data is combined with CMB; with both, a nonzero value of $\Omega_\Lambda$ is strongly preferred ($\approx 2/3$ for a 13 Gyr sequence, similar to the value from SNIa). The $o$CDM sequence prefers $\Omega_{tot}<1$, but is overall much less likely than the flat $\Omega_\Lambda \ne 0$ sequence with CMB+LSS. We also review the rosy forecasts of angular power spectra and parameter estimates from future balloon and satellite experiments when foreground and systematic effects are ignored.Comment: 20 pages, LaTeX, 5 figures, 2 tables, uses rspublic.sty To appear in Philosophical Transactions of the Royal Society of London A, 1998. "Discussion Meeting on Large Scale Structure in the Universe," Royal Society, London, March 1998. Text and colour figures also available at ftp://ftp.cita.utoronto.ca/bond/roysoc9