Climate and Vegetation of the Interior Lowlands of Southern Baffin Island : Long-term Stability at the Low Arctic Limit

The interior of southern Baffin Island between 64 N and 68 N latitude is a mainly lowland area over 50 000 km² in extent, containing two large lakes (Amadjuak and Nettilling) and numerous smaller lakes and ponds. This area is important as summer range for caribou and a variety of birds, and there is evidence for a human presence as early as 3000 B.P. Field studies between 1984 and 1988 and the operation of climatic autostations from 1987 to 1995 revealed a warm summer climate and cold winters. There is a locally rich and diverse vegetation, including Betula glandulosa and other species that are indicative of the low arctic bioclimatic zone and mark the present northern limit of that zone in the eastern Canadian Arctic. Air photos and Landsat imagery were used to map vegetation beyond the field areas, leading to an estimate of 46% of the land area in continuous vegetation (tundra) of some type and 15% with shrub and heath elements. Palynology of sediment cores taken from Nettilling Lake permitted extrapolation from present bioclimatic conditions to 4750 years B.P. Betula and therefore elements of a low arctic vegetation association appear to have been present in the area during most of that period, indicating a local bioclimatic system that has been relatively stable under regional variations of climate.La région intérieure du sud de la terre de Baffin située entre le 64° et le 68° de latit. N. est essentiellement une zone de basses-terres s'étendant sur plus de 50 000 km², qui renferme deux grands lacs (Amadjuak et Nettilling) et de nombreux petits lacs et étangs. Cette région est importante en tant que territoire estival du caribou et d'une diversité d'oiseaux, et on y a découvert des preuves attestant une présence humaine dès 3000 BP. Des études sur le terrain menées entre 1984 et 1988 et l'activité de stations climatologiques automatisées de 1987 à 1995 ont révélé un climat d'été tempéré et d'hiver froid. La végétation locale est riche et diversifiée et comprend Betula glandulosa ainsi que d'autres espèces typiques d'une zone bioclimatique du Bas-Arctique et marquant la limite septentrionale actuelle de cette zone dans l'Arctique canadien oriental. Des clichés aériens et des images du satellite Landsat ont servi à cartographier la végétation au-delà des zones d'étude sur le terrain, ce qui a amené à une estimation de 46 p. cent de la zone possédant un couvert végétal continu (toundra) d'une certaine sorte et 15 p. cent possédant des composants d'arbrisseaux et de bruyère. La palynologie de carottes de sédiments provenant du lac Nettilling a permis d'extrapoler les conditions bioclimatiques depuis la période actuelle jusqu'à 4750 ans BP. Il semble que Betula et par conséquent des composants d'une association végétale du Bas-Arctique ont été présents dans la région pendant la plus grande partie de cette période, ce qui révèle l'existence d'un système bioclimatique relativement stable à l'intérieur de variations climatiques régionales

A Quasi-Elastic Neutron Scattering Study of the Ammonium Ions in CsNH4-Y Zeolite

Quasi-elastic neutron scattering was used to study the reorientation mechanism for ammonium ions in Cs-exchanged zeolite Y. This sample contains ammonium ions preferentially located in the sodalite cages at site 1'. These ions reorient with 120 or 180 Deg jumps around fixed axes through the N atom. This corresponds to a bonding geometry in which the ammonium ion interacts via 3 or 2 H atoms with the lattice O atoms. Addnl., a reorientation around a fixed axis through 2 H atoms of the ammonium ion may occur. The ammonium ion then jumps between 2 equil. positions: one position involves a 2-fold bonding geometry and the other a 3-fold bonding geometry. At 300 K the effective time interval between 2 jumps is t = 1.2 +- 0.5 ps. Compared to zeolite Rho, the ammonium ions in the Cs-exchanged zeolite Y show a more restricted reorientational behavior, resulting in a larger elastic incoherent structure factor. [on SciFinder (R)

Tribocorrosion behavior of CoCrMo alloy for hip prosthesis as a function of loads: A comparison between two testing systems

Metal-on-metal (MOM) hip prosthesis bearings have enjoyed renewed popularity, but concerns remain with wear debris and metal ion release causing a negative response in the surrounding tissues. Further understanding into the wear and corrosion mechanisms occurring in MOM hips is therefore essential. The purpose of this study was to evaluate the tribocorrosion behavior, or interplay between corrosion and wear, of a low-carbon CoCrMo alloy as a function of loading. The tribocorrosion tests were performed using two tribometer configurations. In the first configuration, “System A”, a linearly reciprocating alumina ball slid against the flat metal immersed in a phosphate buffer solution (PBS). In the second configuration, “System B”, the flat end of a cylindrical metal pin was pressed against an alumina ball that oscillated rotationally, using bovine calf serum (BCS) as the lubricant and electrolyte. System B was custom-built to emulate in vivo conditions. The tribocorrosion tests were performed under potentiostatic conditions at −0.345 V, with a sliding duration of 1800 s and a frequency of 1 Hz. In System A the applied loads were 0.05, 0.5, and 1 N (138, 296 and 373 MPa, respectively) and in System B were 16, 32, and 64 N (474, 597, and 752 MPa, respectively). Electrochemical impedance spectroscopy (EIS) and polarization resistance were estimated. The total mass loss (Kwc) in the CoCrMo was determined. The mass loss due to wear (Kw) and that due to corrosion (Kc) were determined. The dominant wear regime for the CoCrMo alloy subjected to sliding changes from wear–corrosion to mechanical wear as the contact stress increases. An attempt was made to compare both system, in their tribochemical responses and formulate some insights in the total degradation processes. Our results also suggest that the proteins in the serum lubricant assist in the generation of a protective layer against corrosion during sliding. The study highlights the need of adequate methodology/guidelines to compare the results from different test systems and translating in solving the practical problems

4pi Models of CMEs and ICMEs

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major anifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-bound missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3-D ('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication in Solar Physics (SUN-360 topical issue

The Planetary Nebula Luminosity Function at the Dawn of Gaia

The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent extragalactic standard candle. In theory, the PNLF method should not work at all, since the luminosities of the brightest planetary nebulae (PNe) should be highly sensitive to the age of their host stellar population. Yet the method appears robust, as it consistently produces < 10% distances to galaxies of all Hubble types, from the earliest ellipticals to the latest-type spirals and irregulars. It is therefore uniquely suited for cross-checking the results of other techniques and finding small offsets between the Population I and Population II distance ladders. We review the calibration of the method and show that the zero points provided by Cepheids and the Tip of the Red Giant Branch are in excellent agreement. We then compare the results of the PNLF with those from Surface Brightness Fluctuation measurements, and show that, although both techniques agree in a relative sense, the latter method yields distances that are ~15% larger than those from the PNLF. We trace this discrepancy back to the calibration galaxies and argue that, due to a small systematic error associated with internal reddening, the true distance scale likely falls between the extremes of the two methods. We also demonstrate how PNLF measurements in the early-type galaxies that have hosted Type Ia supernovae can help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally, we discuss how the results from space missions such as Kepler and Gaia can help our understanding of the PNLF phenomenon and improve our knowledge of the physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", to appear in Astrophysics and Space Scienc

Experimental Study of the Shortest Reset Word of Random Automata

In this paper we describe an approach to finding the shortest reset word of a finite synchronizing automaton by using a SAT solver. We use this approach to perform an experimental study of the length of the shortest reset word of a finite synchronizing automaton. The largest automata we considered had 100 states. The results of the experiments allow us to formulate a hypothesis that the length of the shortest reset word of a random finite automaton with $n$ states and 2 input letters with high probability is sublinear with respect to $n$ and can be estimated as $1.95 n^{0.55}.

Study of Hadronic Five-Body Decays of Charmed Mesons Involving KS0K_S^0

We study the decay of $D^0$ and $D^+_s$ mesons into five-body final states including a $K_S^0$ and report the discovery of the decay mode $D_s^+\to K_S^0 K_S^0\pi^+\pi^+\pi^-$. The branching ratio for the new mode is {${\Gamma(D_s^+\to K_S^0K_S^0\pi^+\pi^-\pi^+)} \over {\Gamma(D_s^+\to K_S^0K^-\pi^+\pi^+)}$} = 0.102$\pm0.029\pm$0.029. We also determine the branching ratio of {${\Gamma(D^0\to K_S^0\pi^+\pi^+\pi^-\pi^-)} \over {\Gamma(D^0 \to K_S^0\pi^+\pi^-)}$} = 0.095$\pm0.005\pm$0.007 as well as an upper limit for {${\Gamma(D^0\to K_S^0K^-\pi^+\pi^+\pi^-)} \over {\Gamma(D^0\to K_S^0\pi^+\pi^+\pi^-\pi^-)}$} $<$ 0.054 (90% CL). An analysis of the resonant substructure for $D^0 \to K_S^0\pi^+\pi^+\pi^-\pi^-$ is also performed

Two-proton correlations from 158 AGeV Pb+Pb central collisions

The two-proton correlation function at midrapidity from Pb+Pb central collisions at 158 AGeV has been measured by the NA49 experiment. The results are compared to model predictions from static thermal Gaussian proton source distributions and transport models RQMD and VENUS. An effective proton source size is determined by minimizing CHI-square/ndf between the correlation functions of the data and those calculated for the Gaussian sources, yielding 3.85 +-0.15(stat.) +0.60-0.25(syst.) fm. Both the RQMD and the VENUS model are consistent with the data within the error in the correlation peak region.Comment: RevTeX style, 6 pages, 4 figures, 1 table. More discussion are added about the structure on the tail of the correlation function. The systematic error is revised. To appear in Phys. Lett.

Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.Comment: 6 pages, 2 figures, submitted to Phys. Lett.