Why Our Hand is not the Whole Deck: Embrace, Acceptance, or Use of Limitations

I investigate with examples limitations that mathematicians accept in research: aesthetic, scientific, and practical, in particular, on what bases such choices are made. Discussion is partly in terms of the ideal agents that Philip Kitcher and Brian Rotman used to analyse mathematical writing

The Breeding Distribution and Current Population Status of the Ivory Gull in Canada

Aerial surveys were conducted in the eastern Canadian High Arctic from 1982 to 1985 to determine the distribution and size of breeding populations of the ivory gull (Pagophila eburnea). The known Canadian population is confined to Ellesmere, Devon, Seymour, Baffin and Perley islands. Two major concentrations of ivory gull colonies exist, one among the granitic nunataks of southeastern Ellesmere Island and the other on the sedimentary plateaus of the Brodeur Peninsula of Baffin Island. The size of breeding groups varies greatly from 4 to over 300 adult gulls. Breeding colonies are typified by their inland, remote and desolate locations and virtual absence of other animal species. We suggest that there is a single Canadian population of ivory gulls whose adult cohort contains over 2400 birds. The small number of leg band recoveries and retrapping of banded birds indicates that individuals can live at least 15 years. One-year-old ivory gulls were not seen at the colonies or on adjacent waters, and their location during summer remains unknown.Key words: ivory gull, Pagophila eburnea, arctic breeding populations, nunataks, polynyas On a effectué des relevés aériens dans la partie est de l'Extrême-Arctique canadien de 1982 à 1985 pour établir la distribution et la taille des populations de mouettes blanches (Pagophila eburnea) qui se reproduisent. La population canadienne que l'on connaît habite seulement les îles Ellesmere, Devon, Seymour, Baffin et Perley. Il y a deux endroits importants où se concentrent les colonies de mouettes blanches, l'une parmi les nunataks granitiques du sud-est de l'île Ellesmere, et l'autre sur les plateaux sédimentaires de la presqu'île Brodeur dans l'île Baffin. La taille des groupes qui se reproduisent varie grandement, allant de 4 à plus de 300 oiseaux adultes. Les colonies d'animaux qui se reproduisent sont caractérisées par leur aire de nidification isolée, loin à l'intérieur des terres, et par l'absence virtuelle d'autres espèces animales. Notre opinion est qu'il existe une seule population canadienne de mouettes blanches, dont l'ensemble des adultes compte plus de 2400 oiseaux. Le petit nombre de bagues récupérées et d'oiseaux bagués avoisinantes, et l'endroit où elles se tiennent reste inconnu. Mots clés : mouette blanche, Pagophila eburnea, populations qui se reproduisent dans l'Arctique, nunataks, polynie

Confinement and the Pion Nucleon Sigma Term

Gribov's theory of confinement offers a simple explanaton of the value of the pion nucleon sigma term. There is no need to invoke a large strange quark component in the nucleon.Comment: 4 pages, Cavendish HEP 93/

Structural investigation into the threading intercalation of a chiral dinuclear ruthenium(II) polypyridyl complex through a B-DNA oligonucleotide

Herein we report the separation of the three stereoisomers of the DNA light-switch compound [{Ru(bpy)2}2(tpphz)]4+ (tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine) by column chromatography and the characterization of each stereoisomer by X-ray crystallography. The interaction of these compounds with a DNA octanucleotide d(GCATATCG).d(CGATATGC) has been studied using NMR techniques. Selective deuteration of the bipyridyl rings was needed to provide sufficient spectral resolution to characterize structures. NMR-derived structures for these complexes show a threading intercalation binding mode with slow and chirality-dependent rates. This represents the first solution structure of an intercalated bis-ruthenium ligand. Intriguingly, we find that the binding site selectivity is dependent on the nature of the stereoisomer employed, with Λ RuII centers showing a better intercalation fit

Finescale topographical correlates of behavioural investment in offspring by female grey seals, Halichoerus grypus

Grey seals breed colonially on substrates ranging from ice to rocky or sandy beaches. Clear differences in seal behaviour patterns exist among such broad classes of breeding habitat. However, finer scale topographical variation is likely to influence individual behaviour with consequences for pupping success. We examined topographical influences on the behaviour of breeding female grey seals by quantifying topography at a subseal size resolution. Using submetre resolution digital terrain models of two sites within a rocky breeding colony, we compared site topography in relation to observed differences in female behaviour at these sites. Females at both sites preferred breeding close to water (standing pools or sea) and frequently commuted between their pups and water. Topographical models indicated that one site was more costly for seals in terms of their locations and movements within the site. This was due to a lack of low-elevation land adjacent to the main access points from the sea and the reduced availability of pools. Females at this site showed reduced pup attendance and an increase in energetically costly behaviours, whilst females at the lower-cost site spent more time interacting with their pups and resting. These topographically induced behavioural differences are likely to affect the quantity and quality of pup provisioning by mothers and influence individual pupping site selection. Less costly sites are likely to be colonized preferentially and by larger, older and more dominant females, potentially generating finescale spatial heterogeneity in female quality within the breeding colony

Non-alcoholic fatty liver disease: relationship with cardiovascular risk markers and clinical endpoints

Non-alcoholic fatty liver disease (NAFLD) is a common diagnosis and is increasing in prevalence worldwide. NAFLD is usually asymptomatic at presentation; progression of the disease is unpredictable, leading to the development of a variety of techniques for screening, diagnosis and risk stratification. Clinical methods in current use include serum biomarker panels, hepatic ultrasound, magnetic resonance imaging, and liver biopsy. NAFLD is strongly associated with the metabolic syndrome, and the most common cause of death for people with the condition is cardiovascular disease. Whether NAFLD is an independent cardiovascular risk factor needs exploration. NAFLD has been associated with surrogate markers of cardiovascular disease such as carotid intima-media thickness, the presence of carotid plaque, brachial artery vasodilatory responsiveness and CT coronary artery calcification score. There is no effective medical treatment for NAFLD and evidence is lacking regarding the efficacy of interventions in mitigating cardiovascular risk. Health care professionals managing patients with NAFLD should tackle the issue with early identification of risk factors and aggressive modification. Current management strategies therefore comprise lifestyle change,with close attention to known cardiovascular risk factors

Time-varying phase noise and channel estimation in MIMO systems

Performance of high speed communication systems is negatively affected by oscillator phase noise (PN). In this paper joint estimation of channel gains and Wiener PN in multi-input multi-output (MIMO) systems is analyzed. The signal model for the estimation problem is outlined in detail. In order to reduce overhead, a low complexity data-aided least-squares (LS) estimator for jointly obtaining the channel gains and PN parameters is derived. In order to track PN processes over a frame, a new decision-directed extended Kalman filter (EKF) is proposed. Numerical results show that the proposed LS and EKF based PN estimator performances are close to the CRLB and simulation results indicate that by employing the proposed estimators the bit-error rate (BER) performance of a MIMO system can be significantly improved in the presence of PN

Black Ring Deconstruction

We present a sample microstate for a black ring in four and five dimensional language. The microstate consists of a black string microstate with an additional D6-brane. We show that with an appropriate choice of parameters the piece involving the black string microstate falls down a long AdS throat, whose M-theory lift is AdS_3 X S^2. We wrap a spinning dipole M2-brane on the S^2 in the probe approximation. In IIA, this corresponds to a dielectric D2-brane carrying only D0-charge. We conjecture this is the first approximation to a cloud of D0-branes blowing up due to their non-abelian degrees of freedom and the Myers effect.Comment: 10 pages, 2 figure

Polarization of the top quark as a probe of its chromomagnetic and chromoelectric couplings in single-top production at the Large Hadron Collider

We study the sensitivity of the Large Hadron Collider, LHC, to top quark chromomagnetic, CMDM, and chromoelectric, CEDM, dipole moments and Wtb effective couplings in singletop production in association with a W, boson, followed by semileptonic decay of the top. We calculate the top polarization and the effects of these anomalous couplings on it at two centre-ofmass, cm, energies, TeV and, TeV. As a measure of top polarization, we look at decay-lepton angular distributions in the laboratory frame, without requiring reconstruction of the rest frame of the top, and study the effect of the anomalous couplings on these distributions. We construct certain asymmetries to study the sensitivity of these distributions to top-quark couplings. TheWt single-top production mode helps to isolate the anomalous ttg and Wtb couplings, in contrast to top-pair production and other single-top production modes, where other new-physics effects can also contribute. We determine individual limits on the dominant couplings, viz., the real part of the CMDM Rer, the imaginary part of the CEDM Imr, and the real part of the tensorWtb coupling Ref, R, which may be obtained by utilizing these asymmetries at the LHC. We also obtain simultaneous limits on pairs of these couplings taking two couplings to be non-zero at a time.Saurabh D. Rindani, Pankaj Sharma, Anthony W. Thoma